San Benito County Water District San Benito County Water District

San Benito County 

Water District 

Annual Groundwater Report 

for Water Year 2008 

December 15, 2008 

Todd Engineers 

Emeryville, California 

with 

Gus Yates, Consulting Hydrologist 

Berkeley, , California

SAN BENITO COUNTY WATER DISTRICT 

ANNUAL GROUNDWATER REPORT 

FOR 

WATER YEAR 2008 

DECEMBER 2008 

PREPARED FOR 

SAN BENITO COUNTY 

WATER DISTRICT 

PREPARED BY 

TODD ENGINEERS 

2490 MARINER SQUARE LOOP, STE. 215 

ALAMEDA, CA 94501 

PHONE: 510/747-6920 

FAX: 510/747-6921 

www.toddengineers.com

TABLE OF CONTENTS 

EXECUTIVE SUMMARY ................................................................................. ES-1 

INTRODUCTION ..................................................................................................... 1 

OVERVIEW OF WATER SUPPLY SYSTEM ...............................................1 

HYDROLOGIC CONDITIONS IN WATER YEAR 2008 .............................7 

WATER MANAGEMENT ACTIVITIES ............................................................... 8 

WATER RESOURCES PLANNING ...............................................................8 

RECOMMENDATION FOR 2009 ANNUAL REPORT ..............................11 

REPLENISHMENT OF GROUNDWATER .................................................12 

DISTRIBUTION OF CVP WATER ..............................................................16 

WATER BANKING .......................................................................................17 

WATER SUPPLY SOURCES AND USE ............................................................. 18 

WATER SUPPLY SOURCES .......................................................................18 

WATER USE ..................................................................................................18 

GROUNDWATER LEVELS AND TRENDS ....................................................... 26 

GROUNDWATER LEVELS .........................................................................26 

CHANGE IN GROUNDWATER LEVELS ..................................................27 

WATER BALANCE ................................................................................................ 34 

INFLOWS .......................................................................................................34 

OUTFLOWS ...................................................................................................35 

CHANGE IN STORAGE ...............................................................................36 

WATER BALANCE CONCLUSIONS .........................................................36 

REVENUES AND CHARGES ............................................................................... 42 

DISTRICT REVENUES ................................................................................42 

DISTRICT CHARGES ...................................................................................42 

CONDITIONS EXPECTED FOR WATER YEAR 2009 .................................... 44 

RECOMMENDATIONS ........................................................................................ 46 

GROUNDWATER PRODUCTION AND REPLENISHMENT ...................46 

CVP IMPORTS ..............................................................................................47 

GROUNDWATER INFRASTRUCTURE .....................................................47 

GROUNDWATER MONITORING ..............................................................47 

GROUNDWATER CHARGES .....................................................................47 

CONSIDERATIONS FOR FUTURE STUDIES ...........................................48 

CONSIDERATIONS FOR FUTURE ANNUAL REPORTS ........................48 

REFERENCES ........................................................................................................ 49 

Annual Groundwater Report for Water Year 2008 December 2008 

San Benito County Water District

LIST OF TABLES 

Table 1. Managed Percolation of CVP Water and Wastewater During Water Years 1994-2008 ...................... 15 

Table 2. CVP Entitlements, Allocations, and 2008 Deliveries ........................................................................... 17 

Table 3. Water Use in Water Year 2008 (af) ...................................................................................................... 18 

Table 4. Comparison of Water Use in Water Years 2007 and 2008 ................................................................... 19 

Table 5. Change in Storage during Water Year 2008 for Zone 6 ....................................................................... 32 

Table 6. Water Balance for Water Year 2006 ..................................................................................................... 37 



Table 9. Charges for Zone 6 Water Users, March 2008 - February 2009........................................................... 43 

LIST OF FIGURES 

Figure 1. Groundwater Basins in San Benito County ........................................................................................... 2 

Figure 2. Subbasin Locations ................................................................................................................................ 4 

Figure 3. Zone 6 Boundary ................................................................................................................................... 6 

Figure 4. Monthly Precipitation in Water Year 2008 ........................................................................................... 7 

Figure 5. Percolation Areas of Local Surface Water and CVP Water ................................................................ 13 

Figure 6. Reservoir Releases for Percolation ...................................................................................................... 14 

Figure 7. Managed Percolation 1994-2008 ......................................................................................................... 15 

Figure 8. Water Use in Zone 6 by User Category ............................................................................................... 21 

Figure 9. Total Water use by Water Type (GW and CVP) ................................................................................. 22 

Figure 10. Total Subbasin Water Use by Water Type ........................................................................................ 23 

Figure 11. CVP and Groundwater Supply by Use .............................................................................................. 24 

Figure 12. Water Supply Contribution of Groundwater and CVP ..................................................................... 25 

Figure 13. Groundwater Elevations October 2007 ............................................................................................. 28 

Figure 14. Profiles of Historical Groundwater Levels ........................................................................................ 29 

Figure 15. Depth to Water October 2007 ............................................................................................................ 30 

Figure 16. Groundwater Elevation Change from October 2006 to October 2007 .............................................. 31 

Figure 17. Hydrographs of Key Wells (inset map of well locations) ................................................................. 33 

Figure 18. Summary of the Zone 6 Water Budgets (2005-2008) ....................................................................... 40 

Figure 19. Change in Storage (1978 – 2008) ...................................................................................................... 41 

APPENDICES 

A – Reporting Requirements and Previous Annual Reports 

B – Climate Data 

C – Streamflow Data and Groundwater Elevation Data 

D – Managed Percolation 

E – Water Balance Methodology 

F – Charges, Revenues, and Expenditures 

G – List of Acronyms 



EXECUTIVE SUMMARY 

This Annual Groundwater Report for San Benito County Water District (District) describes 

groundwater conditions in the San Benito County portion of the Gilroy-Hollister basin. It 

documents water supply sources and use, groundwater levels and storage, and District 

management activities for water year 2008. Recommendations are provided with regard to 

amounts of water import, groundwater replenishment, and groundwater pumping for water year 

2009. This report also assesses and summarizes the water balance of the groundwater basin. 

Rainfall amounts in water year 2008 were below average, marking the second consecutive year 

of below-average rainfall. CVP allocations were reduced to 40 and 75 percent of the contracted 

amount for agriculture and M&I respectively. This reduction was a direct result of the May 

2007 Federal Court decision on Delta smelt. The continued effects of the Court decision are 

discussed in more detail in the subsequent section on conditions expected for 2009. 

Total water supply decreased by 23 percent basin-wide. The reduction in CVP allocation 

resulted in a decrease in its use in all subbasins, with a total decrease of 47 percent in Zone 6. 

Groundwater pumping did not increase to fill the demand, remaining at levels similar to 2007. 

This lack of increase in groundwater pumping is most likely due to several factors including 

the loss of big contracts for lettuce growers in San Benito County, fallowing of fields, change 

in crop selections to less water-intensive crops (e.g., onions and garlic), and a lack of 

groundwater infrastructure to provide increased supply. Because these factors may only affect 

groundwater production in the short-term, an increase in groundwater pumping is expected in 

2009 if CVP allocations are reduced. 

Because groundwater pumping did not increase, groundwater levels have remained the same or 

in some parts of the basin increased slightly. Levels are still close to historical highs in all 

subbasins expect the Bolsa. No subbasin is currently in overdraft. 

Water year 2008 continued to reveal the stabilization or reversal of some previously identified 

trends as a result of reduced CVP imports and below-average rainfall; these include the 

following: 

• Total Zone 6 water use in 2008 decreased compared to 2007. Prior to 2007, total water 

use had showed a steady decline from year to year. 

• In 2008, groundwater pumping was much larger than the total CVP imports, as shown 

on Figure ES-1, reflecting the reduced CVP allocations. Over the previous four years, 

CVP imports were greater than groundwater. 


San Benito County Water District 

ES-1

Figure ES 1. 

Volumes of CVP Imports and 

Groundwater Pumping (1993-2008) 

Water year 2008 saw the continued active involvement of the District in water resource 

management projects, including regional projects as well as local cooperative efforts. Several 

projects were completed and approved by the District in water year 2008 including: a surface 

drainage study in San Juan, the Hollister Area Urban Water and Wastewater Master Plan, and 

the Hollister Urban Area Urban Water Management Plan (UWMP). Local studies include 

continued evaluation of the hydrogeology of Hollister Valley, and a series of hydrogeologic 

studies. The District is also working on projects with various local agencies—including the 

County, City of Hollister, and Sunnyslope CWD—that are focused on water and wastewater 

issues. 

In 2008, the basin water balance was updated for water years 2006, 2007, and 2008. The same 

methodology used in previous Annual Reports was adopted, and further documented as an 

Appendix to this Annual Report. The water balance provides a quantitative view of the state of 

the basin, providing estimates for the specific inflows and outflows of the basin or subbasins. 

While many of the values presented in the table are estimates, the relative magnitude of each 

water balance element helps illustrate the mechanisms at work in the basin. This detailed 

understanding of the groundwater system can serve as a basis to compare changes in the basin 

over time and provide valuable tools for groundwater basin management. The end goal of the 

water balance is to estimate inflows and outflows to each subbasin and then compare these to 

calculate a groundwater change in storage. In addition to comparing the estimated total inflows 

and outflows, changes in storage by subbasin are estimated independently using water level 

changes and aquifer storavity values. The water balance is prepared for each water year and for 

each subbasin. 

In general, groundwater outflows in Zone 6 remained fairly constant while inflows varied 

based on the hydrologic condition of the basin. The District should continue to manage 

groundwater levels (and therefore groundwater storage) by augmenting the inflows when water 

is available through managed percolation or other methods. Active management of the 

groundwater basin can help ensure that water supply is available when needed. 

Recently, the District revised its methodology for determining groundwater charges. Based on 

this method, a 2009 groundwater charge of $2.50 per af is recommended for agricultural use in 



ES-2

Zone 6 and a groundwater charge of $22.50 per af is recommended for M&I use in Zone 6. 

While the revised method is justifiable and reasonable, it is recommended that the District 

consider a longer term rate plan with a broader justification for groundwater charges. The 

District also renegotiated its contract with the U.S. Bureau of Reclamation for CVP water 

deliveries, changing the way existing capital costs are repaid. 

Water supply for 2009 will depend on factors including rainfall, local surface water storage, 

groundwater storage, and CVP operations and storage. Next year, water supply also will be 

impacted by court decisions on the Delta smelt, longfin smelt, and salmonoids. Given the 

uncertainty of CVP imports, the available water supply for 2009 is expected to be similar to 

2008, with significantly reduced CVP allocations. While groundwater pumping did not 

significantly increase in 2008, the factors limiting groundwater pumping are short term and 

pumping may be expected to increase in 2009 to compensate for the lack of CVP imports. 

Total water demand is expected to increase to the levels observed in 2008. 

Historically, the District conducted extensive percolation operations that ultimately reversed 

overdraft and then accumulated a substantial water supply reserve. District management of 

groundwater storage in conjunction with surface water is currently being refined to avoid 

excessively high or low water levels both on a temporal and geographic basis. In 2009, storage 

in Hernandez Reservoir may be replenished and percolation of available local water supplies 

should be focused on areas exhibiting declines in response to drought and increased pumping. 

The Annual Reports have regularly provided brief summaries of specific District groundwater 

basin management activities. However, these summaries have not been scoped to provide a 

comprehensive and integrated overview of existing groundwater basin management. Given the 

uncertainty of CVP supplies, it is recommended that the 2009 Annual Report include an 

expanded discussion of the overall state of the groundwater basin, planned development, and 

current and planned management activities. These will be examined within the context of the 

overarching water resource management planning documents—namely the groundwater 

management plan and integrated regional water management plan—with the intent of 

coordinating groundwater management planning and actions to address future issues. 



ES-3

INTRODUCTION 

This Annual Groundwater Report for San Benito County Water District (District) describes 

current groundwater conditions in the District and two zones of benefit: Zone 3 and Zone 6. It 

documents water supply sources and use, groundwater levels and storage, and District 

management activities from November 2007 through October 2008. In addition, this report 

presents an analysis of the basin water balance for water years 2006 through 2008. The water 

balance method used in this report and past annual reports is also summarized as an appendix. 

Recommendations are provided with regard to water year 2009 water imports, groundwater 

replenishment, groundwater pumping, and groundwater charges. This report focuses on the 

southern portion of the Gilroy-Hollister Valley groundwater basin, which underlies the broad 

valley that extends from San Benito County into southern Santa Clara County. This valley 

includes the City of Hollister, City of San Juan Bautista, unincorporated residential areas, and 

expansive areas of irrigated agriculture. 

This Annual Report has been prepared at the request of the District to meet its information 

needs and to fulfill statutory reporting requirements that specify the minimum content of the 

report should the District choose to prepare one. These requirements are presented in 

Appendix A. The District, at its discretion, has also directed that specific annual reports 

include focused discussion of selected topics. Appendix A tabulates the special topics featured 

in previous annual reports. 

Throughout this report, water volumes and change in storage are shown to the nearest acre-foot 

(af). As a result, large numbers may appear to be accurate to four or five digits, which is not the 

case. These values are accurate to one to three significant digits (depending on the 

measurement). All digits are retained in the text to preserve correct column totals in tables, and 

to maintain as much accuracy as possible during subsequent calculations based on the 

information presented in this report. 

Acknowledgments. This report was prepared by Iris Priestaf, PhD, Maureen Reilly, P.E., and 

Chad Taylor, P.G. of Todd Engineers; and Gus Yates, P.G. CHG, Consulting Hydrologist. We 

appreciate the assistance of San Benito County Water District staff, particularly Jeff Cattaneo 

and Dale Rosskamp. 

OVERVIEW OF WATER SUPPLY SYSTEM 

Three sources provide water supply for the municipal, rural, and agricultural land uses in San 

Benito County. These are local groundwater pumped from wells, local surface water stored in 

and released from the District-owned and operated Hernandez and Paicines reservoirs, and 

water purchased and imported from the Central Valley Project (CVP) by the District. 

Local Groundwater. The District has jurisdiction throughout San Benito County (Figure 1), 

which includes at least portions of twelve groundwater basins defined by the California 

Department of Water Resources (DWR). 


San Benito County Water District 1

SANTA CRUZ 

SANTA CLARA 

Legend 

DWR Groundwater Basins 

County Outline 

3-3 

3-2 

San Juan 

Bautista 

San Justo 

Reservoir 

Hollister 

Paicines 

Reservoir 

3-22 

Tres 

Pinos 

3-23 

3-25 

3-24 

MERCED 

FRESNO 

5-23 

3-28 

3-29 

MONTEREY 

3-30 

5-71 

Hernandez 

Reservoir 

3-31 

N 

DWR Groundwater Basins 

3-2 Pajaro Valley 3-24 Quien Sabe Valley 

3-3 Gilroy Hollister Valley 3-25 Tres Pinos Valley 

3-3.02 Bolsa Area 3-28 San Benito River Valley 

3-3.03 Hollister Area 3-29 Dry Lake Valley 

3-3.04 San Juan Bautista Area 3-30 Bitter Water Valley 

3-22 Santa Ana Valley 3-31 Hernandez Valley 

3-23 Upper Santa Ana Valley 5-23 Panoche Valley 

5-71 Vallecitos Valley 

December 2008 


Alameda, California 

Figure 1 

Groundwater Basins in 

San Benito County

These are listed on Figure 1 with the respective DWR basin numbers. With the exception of 

the Bitter Water Valley (which drains generally south to the Salinas River Valley) and the 

Panoche and Vallecitos valleys (which drain to the east toward Tulare Lake), the groundwater 

basins drain northward as part of the San Benito River and Pajaro River systems. This report 

focuses on the southern part of the Gilroy-Hollister Valley groundwater basin. 

Figure 2 shows groundwater basin boundaries in the northern portion of San Benito County. 

The three DWR-defined subbasins include the Bolsa, Hollister, and San Juan Bautista Areas. 

Figure 2 also shows the boundaries of eight subbasins that were originally delineated in 1996 

for the District annual reports: Bolsa, Bolsa Southeast (SE), Pacheco, Hollister East, Tres 

Pinos, Hollister West, and San Juan subbasins, and the Llagas subbasin in Santa Clara County. 

These subbasin boundaries are based on a combination of infrastructure (CVP subsystems), 

political boundaries (Zone 6), and geologic structures (faults). This definition of subbasins is 

maintained in this report, supporting consistent analysis and reporting of groundwater 

conditions. 

Local Surface Water. Figure 1 also shows the locations of the two reservoirs owned and 

operated by the District. Hernandez Reservoir (capacity 17,200 af) is located on the upper San 

Benito River in southern San Benito County. Paicines Reservoir (capacity 2,870 af) is an 

offstream reservoir between the San Benito River and Tres Pinos Creek. It is filled by water 

diverted from the San Benito River, with some of the diversions consisting of natural runoff 

and some consisting of water released from Hernandez Reservoir. Water stored in the two 

reservoirs is released for percolation in Tres Pinos Creek and the San Benito River to augment 

groundwater recharge during the dry season. 

Central Valley Project. The District also purchases Central Valley Project (CVP) water from 

the U. S. Bureau of Reclamation (USBR). The District has a 40-year contract (extending to 

2027) for a maximum of 8,250 af/yr of municipal and industrial (M&I) water and 35,550 af/yr 

of agricultural water. The District negotiated the renewal of this contract in May 2007. As part 

of this renewal, a separate repayment plan for existing capital costs was agreed upon, such that 

capital costs are not included in the cost per acre-foot of purchase water. San Justo Reservoir 

(see Figure 1) is used exclusively to store and regulate imported CVP water and has an 

operating capacity of 7,000 af. 

The imported water is delivered to agricultural, municipal, and industrial customers in the 

Pacheco, Bolsa Southeast, San Juan, Hollister East, Hollister West, and Tres Pinos subbasins 

through 12 subsystems containing approximately 120 miles of pressurized pipeline laterals. 

Since 2003, a portion of the M&I water has been treated at the Lessalt water treatment plant, 

which allows direct use of CVP water for municipal supply purposes by Sunnyslope County 

Water District (Sunnyslope CWD) and the City of Hollister. 



Pacheco Valley 

Llagas 

Pajaro River 

Bolsa 

Bolsa 

Pacheco 

Hollister 

Bolsa 

SE 

Hollister East 

San Benito River 

San Juan Bautista 


Hollister 

West 

Hollister 

Santa Ana Creek 


Bautista 

Legend 

SBCWD subbasin boundary 

DWR subbasins boundary 

Major roads 

Streams 

N 

County boundary 

Major Community/City 

0 

10,000 

Scale in Feet 

Tres Pinos 

Tres Pinos Creek 

December 2008 



Tres Pinos 

Figure 2 

Subbasin Locations

A total of 1,322 af of water was treated and used during 2008. CVP water has also been 

released historically to augment groundwater recharge along several local creeks and the San 

Benito River. This practice has diminished in recent years with the widespread recovery of 

groundwater levels throughout the basin. 

Zones of Benefit. In order to obtain funds to support its various water management activities, 

the District has formed three zones of benefit: 

• Zone 1 encompasses the entire county and provides the funding base for specific 

District administrative expenses. 

• Zone 3 generally covers the San Benito River Valley (from the Highway 25 bridge 

south of Paicines to San Juan Bautista) and the Tres Pinos Creek Valley from 

Paicines to the San Benito River. Zone 3 provides the funding base for operation of 

Hernandez and Paicines reservoirs (see Figure 1) and related groundwater recharge 

and management activities. 

• Zone 6 includes most of the Gilroy-Hollister Valley groundwater basin in San Benito 

County (see Figure 3) and provides the funding base for importation and distribution 

of CVP water and related groundwater management activities. 



Hollister 


Legend 

Zone 6 Boundary 

Generalized Calaveras fault 

Highways 

Secondary roads 

Major Streams 


N 

0 

12,000 

Scale in Feet 

December 2008 



Tres Pinos 

Figure 3 

Zone 6 

Boundary

HYDROLOGIC CONDITIONS IN WATER YEAR 2008 

Figure 4 provides a comparison of average monthly rainfall with monthly rainfall in water year 

2008 from the San Benito weather station at the District headquarters in Hollister. The overall 

total rainfall of 9.07 inches in water year 2008 was considerably less than average (13 inches) 

and similar to the precipitation in water year 2007. As shown, many months were unusually 

dry. Climate data and streamflow data for the local area can be found in Appendices B and C, 

respectively. 

Figure 4. Monthly Precipitation in Water Year 2008 

9.07 Inches 

Total 



WATER MANAGEMENT ACTIVITIES 

The District continued its participation in water management activities including water 

resources planning, augmentation of groundwater resources, and distribution of CVP water. No 

water banking occurred in 2008, although this remains a potential water management tool. The 

District also maintains a comprehensive monitoring program, including regular measurement of 

groundwater pumping, water quality, annual evaluation of groundwater storage change, and 

regular update of the basin water balance. These activities are addressed in subsequent sections 

of this report. 

WATER RESOURCES PLANNING 

In 2008, the District continued its active involvement in water resource management projects, 

programs and planning efforts that address water supply, water quality, wastewater 

management, and hydrogeology. This section provides an update on 2008 activities, including 

efforts sponsored and led by the District; cooperative programs with the County, local cities, 

and the Water Resources Association (WRA), respectively; and regional planning efforts with 

Santa Clara Valley Water District (SCVWD). 

Groundwater Ambient Monitoring and Assessment (GAMA). In August 2008 water 

quality sampling in the basin was begun as part of the GAMA program. The GAMA program is 

the joint effort of the United States Geological Survey (USGS), the California Water Boards 

(SWRCB/RWQCB), Department of Water Resources (DWR), Department of Public Health 

(DPH), and Lawrence Livermore National Laboratory. The USGS California Water Science 

Center is the project lead for the Priority Basin Project. The program’s main focus is to help 

better understand and identify risks to groundwater resources through water quality sampling 

and analysis. With the voluntary cooperation of local water agencies and well owners, USGS is 

testing water in California groundwater basins over a 10-year period. Groundwater will be 

sampled to characterize its constituents and identify trends in ground-water quality. The results 

of these tests will provide information for water agencies to address a variety of issues ranging 

in scale from local water supply to statewide resource management. A wrap up meeting is 

planned for late 2009 to present general findings. 

Occurrence and Management of High Groundwater. In 2006, the District conducted an 

evaluation of high groundwater conditions in the northern portion of the Hollister Valley (GEI, 

January 2006). The evaluation defined factors potentially contributing to high groundwater 

including percolation of irrigation water, recharge from creeks, and local reduction of pumping. 

The evaluation provides options for managing high groundwater including measures to control 

artesian flow, tile drains to manage shallow and perched groundwater, and installation of 

production wells to control regional groundwater levels. The evaluation also recommended 

additional monitoring wells and a survey along Pacheco Creek. In June 2007, the District 

authorized installation of eight monitoring wells located mostly along Pacheco Creek with one 

near the airport. Installation of the monitoring wells and the surveying have been postponed 

due to budget considerations. 



Hydrogeologic Assessments. In 2007, the District authorized hydrogeologic assessments of 

the San Juan, Hollister West, and Tres Pinos groundwater subbasins and the southern portions 

of the Hollister East groundwater subbasin. These assessments are intended to synthesize and 

expand previous focused groundwater investigations and groundwater-related water resource 

planning efforts. The assessments will address key issues including surface water-groundwater 

interactions, local high groundwater conditions, effects on groundwater levels and quality of 

recharge operations, and sources of local quality problems (e.g., high salinity, boron, arsenic). 

The draft hydrogeologic assessment for these subbasins was submitted to the District for 

review and comment in 2008. A separate report on the hydrogeologic conditions of the 

Hollister East subbasin will be submitted to the District in late 2008. Field reports are expected 

to be complete by February 2009. 

San Juan Basin Surface Drainage Option Study. Agricultural lands in the San Juan Valley 

have long been subject to flooding. In 2007, the District authorized Advanced Hydro 

Engineers to assess the technical design issues and potential routing of a new storm drainage 

channel. This channel would extend from Highway 156 near Lucy Brown Lane to a detention 

basin and outfall near the San Benito River. The assessment also includes review of drainagerelated 

portions of a CalTrans environmental impact report on the Highway 156 widening 

project. This study was completed in early 2008. 

Water Softener Rebate Program. In May 2007, the District, on behalf of the Water 

Resources Association (WRA), and San Clara Valley Water District (SCVWD) initiated a 

Water Softener Rebate Program, based on the award of a Water Use Efficiency Grant as part of 

the 2004 Proposition 50 grant program. The $300,000 grant is being applied, along with 

$152,780 from WRA and $152,780 from SCVWD, to provision of rebates to customers who 

agree to abandon and/or replace their pre-1999 inefficient water softener system with a newer, 

more efficient means of water softening. The program provides a range of rebates between 

$150 and $300. 

The program has a goal of 1,000 water softener replacements by the time of grant completion 

in December 2009. Initial participation in the program lagged expectations; as of November 

2008, 176 water rebates have been issued. In response, the WRA modified the program to 

encompass all of Zone 6, provide rebates for demolishing old water softeners, and increase 

community outreach. Outreach efforts have included bill inserts and flyers at farmer’s markets 

that educate the public on the effect of salt on the groundwater basin and the effective use of 

softeners. A user survey is currently underway to collect data on user’s perception of water 

softeners. Results of the survey, slated for completion in January 2009, will help improve 

outreach efforts. 

The community outreach is already stimulating new interest. In addition, it is possible that the 

program may be extended past December 2009. 

Hollister Area Urban Water and Wastewater Master Plan. The Revised Draft Hollister 

Urban Area Water and Wastewater Master Plan, completed in February 2007, is intended to 

integrate water supply, wastewater treatment and wastewater disposal into a single document 

(HDR, 2007). The plan systematically evaluates a range of water supply and wastewater 



disposal alternatives against a set of criteria. The Final Plan was approved by the City of 

Hollister, the District, and Sunnyslope in November 2008. 

The recommended water supply alternative includes the treatment of local groundwater to meet 

water quality objectives. The preferred alternative involves demineralization of groundwater 

from existing municipal supply wells and installation of new three new wells in the Hollister 

Urban Area. 

The preferred wastewater alternative consisted of near-term disposal of recycled wastewater at 

specific sites planted with turf or pasture varieties that tolerate relatively high irrigation 

salinity. Currently, two interim locations have been selected for the City of Hollister’s 

wastewater, an area near the airport and a city park. Sunnyslope plans to use treated wastewater 

on a golf course in its service area. According to the Plan, in the longer term—after 

demineralization of the municipal groundwater supply is implemented—the decreased salinity 

of recycled water would allow it to be used on a wider variety of crops throughout nearby 

agricultural areas. 

Regional Recycled Water Project. When the City of Hollister implements demineralization of 

the municipal water supply, high-quality recycled water will be available for general irrigation 

use. Previous studies have generally assumed that recycled water would replace CVP water in 

the San Juan Valley. The new project will evaluate one or more alternative regions for recycled 

water use outside the San Juan Valley. This project is co-managed by the District and the City. 

Recycled water was addressed on a conceptual level in the wastewater master plan and in 

preliminary reports. A more detailed analysis of the recycled water project is now underway 

and results are expected late 2009. 

City of Hollister Long-Term Wastewater Management Program. The City of Hollister’s 

Long-Term Wastewater Management Program (HydroScience Engineers, 2005) identified 

near-term and long-term strategies for treatment and disposal of municipal wastewater. The 

environmental impact report (EIR) was finalized in October 2006, except for issues related to 

impacts at sites selected for near-term irrigation with recycled water. To evaluate those 

impacts, a supplemental EIR (SEIR) has been in progress through water year 2007. The 

number of near-term sites was increased to five, and nine alternatives involving various 

configurations and combinations of those sites have been evaluated for water level and salinity 

impacts using the regional groundwater model. An additional region for long-term use of 

recycled water for irrigation was also evaluated. The SEIR was accepted by the City of 

Hollister, the District, and the County in 2008. 

Sunnyslope County Water District Long-Term Wastewater Management Plan. The 

primary issue addressed in the Long-Term Wastewater Management Plan is whether to invest 

in substantial improvements to Sunnyslope CWD’s own wastewater treatment and disposal 

facilities or to discontinue operating those facilities and convey wastewater to the City of 

Hollister’s plant for treatment and disposal. During water year 2008, Sunnyslope CWD decided 

to invest in improvements to its own wastewater treatment and disposal facilities. Planning for 

these improvements is in process. Sunnyslope CWD is also planning to implement salinity 



eduction measures at the wells it operates, by blending, demineralization, or softening of the 

water before pumping it into the distribution system. 

Hollister Urban Area Urban Water Management Plan (UWMP). In June 2005, Sunnyslope 

County Water Agency, along with the City of Hollister and the District, began preparing a joint 

Urban Water Management Plan (UWMP). The UWMP is a central document to long term 

water supply planning for the region. The UWMP includes detailed information on the current 

and future water demand and supply as well as best management practices for water 

conservation. The UWMP was approved by the City of Hollister and Sunnyslope in spring 

2008. The UWMP is slated to be approved by the District and the County in November 2008. 

RECOMMENDATION FOR 2009 ANNUAL REPORT 

Water year 2008 was marked by substantial progress on water management, particularly urban 

water and wastewater issues. Specifically, the Hollister Area Water and Wastewater Master 

Plan and the City of Hollister Long-Term Wastewater Management Program were approved in 

late 2008, Sunnyslope County Water District decided in 2008 to pursue its own wastewater 

management plan, and the UWMP was approved. These documents provide important direction 

for resolution of linked water and wastewater issues in the existing urban portion of the basin. 

In the meantime, the cutbacks in CVP allocations and prospects for continuing drought are 

likely to result in increased basin-wide groundwater pumping. This will occur over the near 

term, including the unknown duration of the drought and the time period needed to resolve 

Sacramento-San Joaquin Delta issues and to increase the certainty of CVP deliveries. Despite 

the recent economic downturn, the near term also is likely to reveal significant development in 

the basin (e.g., El Rancho San Benito) with as-yet undefined but important implications for the 

groundwater basin. Recognizing the pending increase in reliance on groundwater basin-wide, 

additional focus should be placed on enhanced management of groundwater storage (pumping 

and replenishment) to minimize high groundwater problems, help avoid adverse groundwater 

level drawdown while satisfying water demand and progressing toward improved groundwater 

quality. Some of the new projects and programs to meet these goals already have been defined 

and evaluated in previous studies and planning documents, but others likely remain to be 

identified. 

The Annual Reports have regularly provided brief summaries of specific District groundwater 

basin management activities, including the subbasin hydrogeologic assessments and 

drainage/high groundwater studies. However, these summaries have not been scoped to provide 

a comprehensive and integrated overview of existing groundwater basin management in light 

of pending changes. Given the immediacy of these changes, it is recommended that the 2009 

Annual Report included an expanded discussion and evaluation of the overall state of the 

groundwater basin (using existing reports), planned development, and current and planned 

management activities. These will be examined within the context of the overarching water 

resource management planning documents—namely the groundwater management plan and 

integrated regional water management plan—with the intent of coordinating groundwater 

management planning and actions to address future issues. 



REPLENISHMENT OF GROUNDWATER 

The District operates Hernandez and Paicines reservoirs in the San Benito River watershed to 

store runoff and release it during the dry season to replenish groundwater. In addition, the 

District has percolated imported CVP water as part of its management activities. Wastewater 

also is recharged to groundwater from municipal and industrial wastewater treatment plants. 

Figure 5 highlights the stream channels and sites that have been used for percolation of local 

surface water and CVP water, and also shows the locations of wastewater treatment plants. 

Appendix D provides information for water year 2008 on the operation of Hernandez and 

Paicines reservoirs, storage of CVP water in San Justo Reservoir, releases of CVP water for 

percolation along stream channels, and percolation of municipal wastewater. 

Recharge of Local Surface Water. Local surface water from Hernandez and Paicines 

reservoirs is percolated along the San Benito River and Tres Pinos Creek. Historically, releases 

have been managed to limit flows to the San Benito River channel above Lucy Brown Lane in 

San Juan Valley with the intent of maximizing percolation in the basin. Since 1998, releases of 

local surface water have been limited to percolation upstream of the Cienega Bridge near 

Hollister. In Water Year 2008, percolation was further reduced to a negligible volume. This 

minimizes or eliminates potential impacts on local high-groundwater conditions and avoids 

competition for storage capacity with percolation from City of Hollister wastewater percolation 

ponds. 

As shown in Table D-1 of Appendix D, 2008 inflows to Hernandez Reservoir were only 

10,662 af, but contributed to an increase in storage relative to 2007. Over 45 percent of inflows 

occurred during the wet month of January. No reservoir spills occurred. However, 7,646 af 

were released for downstream percolation. Reservoir releases ranged from 423 af per month in 

January and February to 2,814 af in August. Releases generally are greatest in August and 

September as storage is reduced to ensure adequate capacity for flood control before the rainy 

season. Over water year 2008, Hernandez Reservoir storage increased from 590 af to 2,693. 

The reduced storage at the beginning of the water year reflects the intentional releases in water 

year 2007 for maintenance purposes. 

The District operates Paicines Reservoir to provide off-stream storage of San Benito River 

water diverted for percolation in the Tres Pinos Creek channel. Paicines storage began the 

water year at 625 af, increased to 1,652 af, and then decreased to 300 af at the end of the water 

year, with 495 af released to Tres Pinos Creek for percolation, approximately 40 percent of 

water year 2007’s releases. 

Figure 6 shows the annual releases of local surface water for percolation from Hernandez and 

Paicines reservoirs from 1996 through 2008. Releases from Hernandez have ranged between 

3,500 af/yr and 26,300 af/yr, generally reflecting variations in inflow. The 2008 Hernandez 

release of 7,646 af amounted to 65 percent of the average over this period, reflecting dry 

conditions; precipitation was 70 percent of normal. 



Tequisquita Slough 

Pajaro River 

Pacheco Creek 

Arroyo De 

Las Viboras 

Arroyo Dos Picachos 


San Benito River 


Bautista 

WWTP 


Hollister 

DWTP 

IWTP 

Hollister 

Legend 

Streams 

Percolation area of CVP water and/or 

local surface water 

Wastewater treatment plant (WWTP) 

Subbasin Boundary 

City Boundary 


0 

N 

Scale in Feet 

10,000 

Sunnyslope 

Ridgemark WWTP 

Cielo Vista WWTP 

Tres Pino Creek 

December 2008 



Tres Pinos WWTP 

Tres Pinos 

Figure 5 

Location of 

Percolation Areas and 

Wastewater Treatment 

Plants

30,000 

25,000 

Hernandez 

Paicines 

Reservoir Releases (AFY) 

20,000 

15,000 

10,000 

5,000 

0 

1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 

2007 

2008 

Water Year 

December 2008 



Figure 6 

Reservoir Releases 

for Percolation

Table 1. Annual Percolation of San Felipe Water during Water Years 1994-2008 (acre-feet) 

Water 

Year 

Arroyo de las Viboras 

Pacheco 

Creek Road Creek 1 Creek 2 


Fallon 

Road 

Jarvis 

Lane 


John 

Smith Maranatha 

Creek Road Road 

Airline 

Highway 

Ridgemark 

Tres 

Pinos 

Creek 

San 

Benito 

River 

Total 

Waste 


1994 

1995 

1996 

1997 

1998 

1999 

2000 

2001 

2002 

2003 

2004 

2005 

2006 

2007 

2008 

232 

444 

0 

0 

0 

0 

1 

0 

0 

0 

0 

0 

0 

0 

0 

136 

238 

494 

447 

132 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

515 

770 

989 

601 

109 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

2 

832 

1,981 

403 

0 

6 

0 

2 

0 

0 

0 

0 

0 

0 

0 

0 

67 

77 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

550 

654 

235 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

209 

622 

708 

200 

0 

4 

3 

0 

1 

5 

52 

0 

6.8 

0 

0 

0 

73 

531 

17 

65 

256 

236 

161 

78 

119 

83 

0 

155.7 

0 

0 

0 

0 

197 

353 

0 

48 

21 

17 

2 

9 

0 

0 

0 

0 

0 

0 

0 

134 

286 

158 

141 

240 

186 

143 

172 

0 

0 

0 

0 

0 

0 

0 

25 

29 

74 

10 

12 

1 

0 

0 

0 

0 

0 

0 

0 

85 

809 

21 

1,477 

518 

452 

285 

703 

426 

163 

1 

0 

0.8 

88.3 

0 

158 

2,734 

6,097 

5,619 

1,084 

413 

938 

1,041 

470 

605 

882 

527 

450.5 

215.9 

6.1 

1,885 

6,345 

10,330 

11,087 

2,543 

1,322 

1,740 

2,110 

1,122 

1,074 

1,018 

527 

613.8 

304.2 

6.1 

2,590 

2,735 

3,273 

3,400 

3,557 

4,448 

3,789 

3,338 

3,952 

3,744 

3,635 

3,490 

3,279 

3,107 

2,977 

16,000 

14,000 

Surface Water Percolation 

12,000 

Wastewater Percolation 

Stream Percolation (AF) 

10,000 

8,000 

6,000 

4,000 

2,000 

0 

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 

2007 

2008 


December 2008 



Table 1 and Figure 7 

Managed Percolation 

1994-2008

Recharge of CVP Water. As shown in Figure 5, CVP water has historically been percolated 

along the San Benito River, Tres Pinos Creek, Santa Ana Creek, Arroyo Dos Picachos, Arroyo 

de las Viboras, Pacheco Creek and other percolation sites. 

Table 1 and Figure 7 summarize the annual percolation of CVP water from water year 1994 

through 2008, while monthly data for 2008 are provided in Appendix D. CVP percolation 

peaked in 1997 and was reduced subsequently in response to the successful recovery of the 

groundwater basin from overdraft. Releases of CVP water have been discontinued to Pacheco 

Creek, Arroyo Dos Picachos and Arroyo de las Viboras since the 1990s and discontinued from 

the Airline Highway and Ridgemark sites in recent years. In water year 2008, CVP releases for 

percolation were limited to 6 af along the San Benito River and Tres Pinos Creek. 

Wastewater Percolation. Figure 5 shows the locations of municipal wastewater treatment 

plants (WWTPs), including the Tres Pinos, Cielo Vista, and San Juan Bautista WWTPs, two 

sites operated by Sunnyslope County Water District near Ridgemark, and the City of Hollister 

domestic and industrial plants (DWTP and IWTP, respectively). 1 

The San Juan Bautista plant discharges to a small tributary of San Juan Creek that tends to gain 

rather than lose water from seepage. Accordingly, little or none of the 177 af of the San Juan 

Bautista plant effluent discharged during 2008 replenishes groundwater. The remaining 

wastewater treatment plants dispose of their wastewater effluent by percolation into the ground. 

Of these, the package wastewater treatment plant at the Cielo Vista residential development is 

the smallest, percolating less than 25 afy (Yates, 2005) to a leach field. 

Table 1 documents the annual amounts of wastewater percolation (see far right column) for the 

Hollister, Sunnyslope, and Tres Pinos facilities. The City of Hollister DWTP and IWTP 

represent the major portion, amounting to 1,580 af and 1,257 af in 2008, respectively. Figure 7 

provides a graphic comparison of wastewater percolation to the CVP percolation discussed 

previously. While CVP percolation has been reduced substantially in recent years in response 

to groundwater level recovery, wastewater percolation has remained relatively steady, although 

declining gradually in recent years. The decline is the result of both residential and industrial 

water conservation measures (Wittry, 2007). 

DISTRIBUTION OF CVP WATER 

CVP water is distributed by the District to agricultural and M&I customers in Zone 6. In water 

year 2008, water allocations to Zone 6 were significantly reduced. Table 2 shows the contract 

entitlements, recent average allocations (USBR, May 11, 2006) and 2008 deliveries for CVP 

water in Zone 6. Actual CVP deliveries have differed from the contracted amount, depending 

on hydrologic conditions. Allocations were decreased to 40 percent of the contracted amount 

for agriculture and 75 percent for M&I. This reduction is a direct result of the May 2007 

Federal Court decision on Delta smelt. The continued effects of the Court decision are 

discussed in more detail in the subsequent section on conditions expected for 2009. 

1 Another plant for the Rancho Larios development near San Juan Bautista discharges tertiary-treated 

effluent to a sprayfield located outside the basin. That discharge is not considered in this report. 



In water year 2008, 10,514 af were delivered to agricultural customers and 2,232 af were 

delivered to M&I and domestic customers. Distribution to M&I customers occurs primarily 

through the Lessalt water treatment plant, which provides treated water directly to the City of 

Hollister and Sunnyslope CWD water supply systems. M&I water is also distributed for 

irrigation use at the Ridgemark and San Juan Oaks golf courses. Domestic users include the 

Stonegate subdivision, which treats CVP water at a small water treatment plant. 

The use of CVP water for direct M&I use is limited by the available treatment capacity of the 

Lessalt treatment plant, which has a design capacity of 3 million gallons per day (MGD) or 

approximately 3,360 af/yr. In 2008, Lessalt produced 1,323 af for municipal supply, amounting 

to 39 percent of the design capacity. Other M&I uses of CVP water include urban irrigation 

(golf courses) and potable supply for the Stonegate community. The District was previously 

held to a minimum payment of M&I CVP water; this was reduced to 1 af in the renegotiated 

contract that became effective May 2008. The current alternative use for CVP water is 

groundwater replenishment, which is limited by allocation and the available storage capacity of 

the groundwater basin. 

Table 2. CVP Entitlements, Allocations, and 2008 Deliveries 

Contract 

Entitlement 

(af) 

Recent Average 

Allocation 

Actual 

2008 CVP 

Delivery 

(af) 

Percent of 

Contract 

Amount 

Used in 2008 

Current Total 

Usage 

(CVP & GW) 

(af) 

(%) (af) 

Agriculture 35,550 40% 14,220 10,514 30% 25,310 

M&I* 8,250 75% 3,320 2,232 27% 10,225 

TOTAL 43,800 46% 20,408 12,745 29% 35,535 

*2008 M&I allocation based on 75 percent of historical use per the Bureau’s M&I Shortage Policy. 

WATER BANKING 

Due to the reduced CVP allocation, the District procured additional water supplies through 

water transfers. In water year 2008, a total of 1,204 af of imported water was delivered through 

other programs. The volumes and sources of these transfers are below: 

• 170 af, Merced Irrigation District 

• 984 af, Yuba Water Transfer Program and the 2008 Pooled Water Transfer Program 

• 50 af, Del Puerto Water District 



WATER SUPPLY SOURCES AND USE 

WATER SUPPLY SOURCES 

The water needs of Zone 6 are satisfied by two types of water: imported CVP water and locally 

pumped groundwater. A third water source, local surface water, is managed to recharge the 

groundwater basin. 

WATER USE 

Water use in Zone 6 is divided into two main user categories: agriculture use and municipal 

and industrial (M&I). M&I use includes the Sunnyslope CWD and the City of Hollister 

municipal systems and Stonegate, a small rural water system, and other domestic users. Water 

use by subbasin, user category, and water type for 2008 is shown in Table 3. 

Table 3. Water Use in Water Year 2008 (af) 

CVP Water 

Groundwater 

Domestic, 

Municipal, & 

Domestic, 

Municipal, & 

Subbasin Agriculture Industrial Agricultural Industrial 

Bolsa South East 333 0 2,001 13 

Hollister East 5,372 1,420 2,639 1,323 

Hollister West 366 33 1,143 3,232 

Pacheco 1,517 51 1,703 197 

San Juan 2,837 322 6,744 1,053 

Tres Pinos 88 405 567 2,176 

TOTAL 10,514 2,232 14,796 7,993 

Water Use in 2008. Overall, water usage in 2008 was significantly lower than in previous 

years. Table 4 shows total water use in 2008 was 35,535 af as compared to 46,424 af in 2007, a 

decrease of 23 percent. Changes in total water uses by user category were most pronounced in 

the CVP water usage. CVP water use decreased in all subbasins, a total of 47 percent in Zone 6 

mainly due to the reduced allocation. The decrease in CVP water use ranged from 28 percent in 

Hollister West to 59 percent in Pacheco. While CVP water use decreased to levels similar to 

the late 1990’s, groundwater water use did not increase to fill the demand. With the exception 

of Pacheco subbasin, total subbasin groundwater use remained about the same or decreased 

slightly. Only Pacheco subbasin showed a significant increase in groundwater use, almost 

doubling. 

Total water use decreased a total of 23 percent basin-wide. This decrease is most likely due to 

several factors including the loss of big contracts for lettuce growers in San Benito County, 

fallowing of fields, changes in crop selections to less water intensive crops (e.g. onions and 

garlic), and lack of groundwater infrastructure to provide increased supply. The temporary 

lack of groundwater infrastructure may have the most significant impact on current and future 



water use. As many users have relied solely on CVP imports, groundwater wells have not been 

maintained as a major water source. In order to switch to groundwater use, many growers may 

need to rehabilitate wells and pumps. As a result of this effort, groundwater use may increase 

significantly to meet the gap in water supply. If CVP imports remain low, groundwater use 

could increase substantially in water year 2009 (Rosskamp, 2008). 

Table 4. Comparison of Water Use in Water Years 2007 and 2008 

Total CVP Groundwater Total Water Supply 

% 

% 

Change 2007 2008 Change 2007 2008 

% 

Change 

2007 2008 

Bolsa 

South East 572 333 -42% 2,005 2,014 0% 2,577 2,347 -9% 

Hollister 

East 11,914 6,792 -43% 3,867 3,962 2% 15,781 10,754 -32% 

Hollister 

West 552 399 -28% 5,118 4,375 -15% 5,670 4,774 -16% 

Pacheco 3,832 1,568 -59% 1,034 1,900 84% 4,866 3,468 -29% 

San Juan 6,160 3,160 -49% 7,658 7,796 2% 13,818 10,956 -21% 

Tres Pinos 804 493 -39% 2,908 2,743 -6% 3,712 3,236 -13% 

TOTAL 23,834 12,745 -47% 22,590 22,789 1% 46,424 35,535 -23% 

Water Use Trends. As discussed above, total water use and the relative contribution of the 

two major sources in Zone 6 for water year 2008 decreased significantly relative to past years. 

However, the relative water use of agriculture and M&I has remained similar to last year. 

Figure 8 shows the total use by M&I and agriculture. Agricultural water use represented 71 

percent of total use, unchanged from water year 2007. This percent of total use has decreased 

consistently from 88 percent of the total water use in the early 1990’s. 

Figure 9 shows the volume of CVP water and groundwater used from 1993 to 2008. Since 

1993, the amount of groundwater pumped has slowly decreased as the amount of CVP water 

has increased. However, this trend did not hold true in 2007 or 2008 when total groundwater 

use increased and has remained steady. If the CVP allocations remain at the same level for 

water year 2009, groundwater is expected to increase significantly. As CVP water use has 

decreased across all subbasins, the future increase in groundwater is also expected to occur in 

all subbasins. Figure 10 reveals that the same trends of CVP and groundwater use are seen in 

the individual subbasins as the entire Zone 6. CVP water use was decreased in every subbasin. 

Pacheco subbasin is the only subbasin to show a significant increase in groundwater, such that 

groundwater use was greater than CVP imports. This could be to the result of better water 

quality and/or the state of groundwater infrastructure in the basin; wells were maintained and 

ready to increase supply. 

Figure 11 shows the type of uses for both CVP and groundwater. In addition to agricultural 

and M&I uses, some CVP water is used to replenish groundwater and some is lost to 



evaporation and seepage from San Justo Reservoir (see Appendix D). Both agricultural and 

M&I uses of CVP water have increased over the past 15 years but were greatly reduced in 

water year 2008 because of allocation reductions. Relative to groundwater, the better quality of 

CVP water and pressurized delivery provide tangible benefits to agricultural customers. In 

addition, completion of the Lessalt water treatment plant in 2003 has allowed direct use of CVP 

water for City of Hollister and Sunnyslope CWD supply. Figure 11 also shows stabilization in 

groundwater use after decreases over the past eight years; however, this is expected to change 

in 2009. 

Figure 12 shows the total supply contribution of groundwater and CVP imports. The 

previously observed steady trend of additional CVP water use has slowed and in the short term 

has reversed. For the past few years, use of groundwater and CVP water has been nearly equal. 

As shown in the upper graph, groundwater use in water year 2008 was almost double CVP 

water use. The lower graph illustrates how groundwater use and CVP use had equalized over 

time but was changed significantly due to the allocation reductions. 



60,000 

50,000 

Agriculture 

M & I 

40,000 

Water Use (AF) 

30,000 

20,000 

10,000 

0 

1988 1989 1990 1991 1992 1993 19941995 1996 1997 1998 1999 2000 2001 2002 2003 20042005 2006 

* 

2007 Values Corrected From Previous Annual Report 


December 2008 Figure 8 



2007 2008 

Water Use in Zone 6 

by User Category 

1988-2008

60,000 

Groundwater 


50,000 

40,000 


30,000 

20,000 

10,000 

0 

19931994 1995 1996 1997 1998 1999 2000 2001 2002 20032004 2005 2006 2007 2008 


December 2008 

* 

2007 Values Corrected From Previous Annual Report 



Figure 9 

Total Water Use by 

Water Type

Bolsa SE 

Pacheco 

12,000 

10,000 

Groundwater 

CVP water 

12,000 

10,000 

Groundwater 

CVP water 


8,000 

6,000 


8,000 

6,000 

4,000 

4,000 

2,000 

0 

1993 

1994 

1995 

1996 

1997 

1998 

1999 

2000 

2001 


2002 

Hollister West 

2003 

2004 

2005 

2006 

2007 

2008 

2,000 

0 

1993 

1994 

1995 

1996 

1997 

1998 

1999 

2000 

2001 



2002 

2003 

2004 

2005 

2006 

2007 

2008 

12,000 

10,000 

Groundwater 

CVP water 

12,000 

10,000 

Groundwater 

CVP water 


8,000 

6,000 


8,000 

6,000 

4,000 

4,000 

2,000 

0 

1993 

1994 

1995 

1996 

1997 

1998 

1999 

2000 

2001 


2002 

2003 

2004 

2005 

2006 

2007 

2008 

2,000 

0 

1993 

1994 

1995 

1996 

1997 

1998 

1999 

2000 

2001 


2002 

2003 

2004 

2005 

2006 

2007 

2008 

* 2007 Values Corrected From Previous Annual Report 

San Juan Valley 

Tres Pinos 

12,000 

10,000 

Groundwater 

CVP water 

12,000 

10,000 

Groundwater 

CVP water 


8,000 

6,000 


8,000 

6,000 

4,000 

4,000 

2,000 

0 

1993 

1994 

1995 

1996 

1997 

1998 

1999 

2000 

2001 


2002 

2003 

2004 

2005 

2006 

2007 

2008 

2,000 

0 

1993 

1994 

1995 

1996 

1997 

1998 

1999 

2000 

2001 


2002 

2003 

2004 

2005 

2006 

2007 

2008 




Subbasin Water Use 

by Water Type 

1993-2008 

Water Year

50,000 


Annual Water Use (AF) 

45,000 

40,000 

35,000 

30,000 

25,000 

20,000 

Percolation 

Percolation 

Agriculture 

Agriculture 

M & I 

M & I 

Seepage & Evaporation 

Seepage & Evaporation 

15,000 

1,000 

5,000 

0 

1988 1989 1990 1991 1992 1993 1994 1995 1996 19971998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 


50,000 

Groundwater 

45,000 

Agriculture 

40,000 

M & I I 

35,000 

30,000 

25,000 

20,000 

15,000 

10,000 

5,000 

0 


December 2008 

* 2007 Values Corrected From Previous Annual Report 

Annual Water Use (AF) 

1988 1989 1990 1991 1992 1993 1994 1995 1996 19971998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 



Figure 11 

Annual Total of CVP 

and Groundwater 

by Use

40,000 

35,000 

Groundwater 

CVP 

Total Water Use by Source (AFY) 

30,000 

25,000 

20,000 

15,000 

10,000 

5,000 

0 

1993 19941995 1996 1997 1998 1999 2000 2001 2002 2003 20042005 2006 2007 2008 


80% 

70% 

Percent CVP 

Percent Groundwater 

60% 

Percent of Total Water Supply 

50% 

40% 

30% 

20% 

10% 

0% 

1993 19941995 1996 1997 1998 1999 2000 2001 2002 2003 20042005 2006 2007 2008 


December 2008 



Figure 12 

Groundwater and 

CVP Imported Water 

Use over Time

GROUNDWATER LEVELS AND TRENDS 

GROUNDWATER LEVELS 

Groundwater levels in over 100 wells are monitored on a quarterly cycle by the District. Figure 

13 shows contoured groundwater elevations from the October 2008 monitoring event. The 

groundwater elevation contours shown on Figure 13 were created using the methodology 

developed in 2007, which differs from previous years in order to more accurately account for 

the effects of the Calaveras Fault on water levels. This was accomplished by separately 

contouring the wells on the east and west sides of the fault. The contoured October 2007 

groundwater elevations are presented in Appendix C as Figure C-3. Groundwater elevations 

are highest in the Tres Pinos area to the southeast (400 feet above mean sea level and higher) 

and lowest in the Bolsa to the northwest, where a pumping depression results in elevations as 

low as 80 feet above mean sea level (msl). More groundwater level data are presented in 

Appendix C, including maps showing monitoring locations and groundwater elevation 

contours for October 2007, and a table of groundwater level data from October 2007 through 

October 2008. 

Figure 14 shows water elevations for 2008 and 2007 along three profiles crossing the basin. 

These profiles show not only the recent groundwater elevations, but also the range of historical 

water levels depicted with shading on the profiles. Water elevations in most subbasins are close 

to the historical high of 1913; however, Profile B shows that water levels in the Bolsa area are 

closer to the middle of the historical range of groundwater elevations. The Bolsa subbasin does 

not receive CVP imports and still relies on groundwater for all water needs. The general 

contour patterns and groundwater flow directions did not change significantly from October 

2007, but water levels were slightly higher at the end of 2008 because of reduced groundwater 

pumping. This indicates that the basin is not threatened by overdraft in the near future. 

Several areas are experiencing problems from high groundwater levels. Figure 15 shows the 

contours of measured depth to groundwater. The eastern part of the San Juan subbasin, the 

Pacheco subbasin, and the northern part of the Hollister East subbasin are areas with 

particularly high water levels; in some places the groundwater is within five feet of the ground 

surface or flowing wells are present. Areas where wells were noted to be flowing are indicated 

on both Figure 13 and Figure 15. 

Near the streams and San Benito River, such high water levels decrease the amount of potential 

percolation because of insufficient groundwater storage capacity to receive it (rejected 

recharge). As a consequence, the effectiveness of managed percolation is reduced. 

Furthermore, additional managed percolation may exacerbate the problems of high 

groundwater, including interference with the effective operation of septic systems and poor 

drainage of agricultural land. Certain crops, including orchards with deep root zones, are 

adversely affected by groundwater levels approaching or in the root zone (e.g., about four to 

7.9 feet for walnuts; UC Davis, 2000 and UN Food and Agriculture Organization, 2006). In the 

northern portion of Hollister East and the central part of San Juan, high water levels may begin 



to damage the local walnut groves and apple orchards, respectively. High water levels can also 

cause a threat to water quality as the water table is closer to the ground surface and more 

susceptible to contamination. 

Note that two areas of low groundwater elevations surround major pumping centers: the 

southern portion of Hollister East where the City of Hollister and Sunnyslope CWD have wells 

and the southern part of the Bolsa where intensive agricultural pumping occurs. 

CHANGE IN GROUNDWATER LEVELS 

Figure 16 documents the change in water levels from October 2007 to October 2008. In order 

to compute the change in water elevations, the difference between the October 2008 and the 

October 2007 maps was calculated and contoured. The accuracy of this map was checked by 

examining water level changes in individual wells that were monitored in both October 2008 

and October 2007. 

Overall, water levels rose slightly during water year 2008. The largest change occurred near the 

southern edge of the Hollister East subbasin where October 2008 water levels were as much as 

80 feet higher than in October 2007. This area has historically experienced large year-to-year 

fluctuations in water levels, presumably reflecting variable pumping at nearby wells. 

Additionally, there was a small decrease of water levels near the City of Hollister (around 10 

feet). 

Groundwater elevation changes from year to year can be used to determine the change in 

storage, which is the net volume of water added or removed from the basin over the water year. 

The change in storage was calculated by using the change in water levels (ft) and multiplying 

by the total area (ft 2 ) to determine the total volume change. This volume change is then 

multiplied by the average storativity of the subbasin (shown in the table below) to represent the 

amount of water that a given volume of aquifer will produce. The storativity values for each 

subbasin were derived from a numerical model of the basin developed by Yates and Zhang 

(2000). 

Table 5 shows the calculated change in storage for each subbasin in Zone 6. The total change 

for Zone 6 was an increase of 2,807 af. The greatest change occurred in the Bolsa Southeast 

subbasin where 2,483 af more water was stored at the end of water year 2008 compared to 

water year 2007. Outside Zone 6, groundwater storage in the Bolsa subbasin increased by 1,796 

af. 



120 

140 

220 

240 

100 

160 

260 

280 

180 

200 

300 

120 

100 

320 

80 

340 

120 

140 

100 

140 

360 

380 


Bautista 

200 

160 

220 

180 

240 

300 

220 

260 

280 

200 

240 

180 

280 

260 

Hollister 

400 

Legend 

Monitored well, 2008 

Flowing artesian well, 2008 

20-foot groundwater elevation contour 

Approximate area of flowing well 

Generalized Calaveras Fault 

N 

Highways 


Major streams 

San Justo reservoir 

0 

12,000 

Scale in Feet 

240 

260 

280 

December 2008 

400 

420 



Tres Pinos 

480 

Figure 13 

Groundwater 

Elevations 

October 2008

Elevation (feet NGVD 1929) 

500 

450 

400 

350 

300 

250 

200 

150 

100 

50 

B 

Bolsa Pacheco Hollister East 

Shore 

Road 

S 

R 

Calaveras 

Fault 

Ground Surface 

0 

0 10,000 20,000 30,000 40,000 50,000 

Distance along Line of Profile (feet) 

San Felipe 

Road 

Fairview 

Road 

B' 

Fallon 

Road 

Range of 

historical 

water 

levels 

60,000 


500 

450 

400 

350 

300 

250 

200 

150 

100 

50 

A 

Range of 

historical 

water 

levels 

County 

Line 

Pacheco Hollister East Tres Pinos 

Orchard 

Road 

Fallon 

Road 

0 

0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 

McCloskey 

Road 


Sunnyslope 

Road 


Airline 

Highway 

A' 

Southside 

Road 

80,000 


500 

450 

400 

350 

300 

250 

200 

150 

100 

50 

Highway 

101 

C 

San Juan Hollister West Hollister East 

Bixby 

Road 

Mitchell 

Road 


Calaveras 

Fault 

Fairview 

Road 

C' 

Range of 

historical 

water 

levels 

C 

B 


A 

Hollister 

C’ 

B’ 

0 

0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 

Ground 

Surface 

Water year 

2007 


Legend 


2008 

Range of Historical 

Water Levels 

80,000 

December 2008 



A’ 

Tres Pinos 

Figure 14 

Profiles of 

Historical Groundwater 

Levels

80 

80 

40 

20 

0 

Legend 

20-foot depth to groundwater contours 

Approximate area of flowing wells 

Generalized Calaveras fault 

Highways 


Major Streams 

N 

0 

12,000 

Scale in Feet 

20 

40 

20 

20 

60 

60 

80 

120 

100 

80 

60 

20 

120 

80 

100 

0 

60 

60 

20 

40 

20 

December 2008 



100 

180 

120 

140 

140 

160 

120 

100 

80 

60 

20 

100 

80 

60 

40 

120 

140 

120 

140 

80 

40 

20 

40 

60 

40 

Figure 15 

Depth to Water 

October 2008 

20 

40

10 

10 

-20 

0 

-10 

0 

20 

-10 

10 

20 

0 

0 

0 

0 

0 

-10 

-10 

10 

-20 

0 

-10 

0 


0 

Hollister 

10 

0 

0 

0 

10 

0 

30 

50 

70 

Legend 

10-foot groundwater elevation change contour 


Major streams 

N 

Groundwater Elevation Change 

High: 50 

0 

Low: -50 

Scale in Feet 

12,000 

10 

0 




Tres Pinos 

Groundwater 

Elevation Change 

From October 2007 

to October 2008

Table 5. Change in Storage during Water Year 2008 for Zone 6 

Subbasin 

Area 

(acres) 

Average Change in 

Groundwater Height 

(feet) 

Average 

Subbasin 

Storativity 

San Juan 11,708 0.30 0.05 174 

Hollister West 6,059 3.33 0.05 1,009 

Tres Pinos 4,735 -0.67 0.05 -158 

Pacheco 7,290 -1.36 0.03 -298 

Hollister East 15,367 -0.87 0.03 -403 

Bolsa SE 2,690 11.54 0.08 2,483 

TOTAL ZONE 6 2,807 

Change in 

Storage (af) 

In recent years, the volume of managed percolation has been decreased in response to high 

water levels. The recent annual quantities of managed percolation are very small in comparison 

to the peak volumes from the late 1990s. Because managed recharge has been greatly reduced, 

storage fluctuations caused by pumping and other sources of recharge can be seen more clearly. 

When groundwater levels are high, upward fluctuations in storage are limited because excess 

groundwater tends to leak into streams rather than accumulate in storage. Conversely, when 

groundwater levels decline, groundwater discharge into streams is affected almost immediately. 

Figure 17 illustrates long term changes in groundwater levels in the basin. Water elevations in 

key wells from each subbasin for each monitoring event were averaged to produce 

representative hydrographs for each subbasin. These key wells are shown on the map in Figure 

17. It should be noted that these subbasin hydrographs represent average conditions in each 

subbasin and illustrate long term trends, but do not show localized variations in water levels. 

Over the past five years, water levels have remained fairly constant in most subbasins. This 

includes an interruption in the long-term rising trends seen from 1994 to 2006 in the Hollister 

East and Bolsa Southeast (SE) subbasins, where average water levels remained fairly stable 

between 2007 and 2008. The increasing trend was related to reduced groundwater pumping and 

increased CVP delivery for both agricultural and M&I uses. Water levels in all subbasins show 

a seasonal variation with the lowest water levels occurring in the fall and the highest in the 

spring. The Bolsa subbasin shows the most variation: 20 to 50 feet of elevation change between 

seasons. 

Water levels continue to remain generally near their historic highs in most parts of the basin. 

Based on these water levels and the stable management of the basin, there was no overdraft in 

2008 and overdraft is unlikely to occur in 2009. 



400 

350 




Tres Pinos 

Bolsa 

Bolsa SE 

Pacheco 


300 

GW Elevation (ft msl) 

250 

200 

150 

Bolsa 

Pacheco 


100 

50 


0 

1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 

250 



GW Elevation (ft msl) 

200 

150 

100 

Tres Pinos 

50 

0 

1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 

December 2008 



Figure 17 

Hydrographs of 

Key Wells

WATER BALANCE 

Annual reports prepared prior to 2006 included annual water balances to illustrate the state of 

the groundwater basin. Because water balances often do not change significantly from year to 

year, the District decided to include a special section on the groundwater balance in the Annual 

Report every three years. The water balances were prepared for the past three water years 

(2006, 2007, and 2008), employing a similar methodology as past annual reports for 

consistency. Detailed information about the methodologies used to estimate each water balance 

element is presented in Appendix E. 

The water balance provides a quantitative view of the state of the basin, providing estimates for 

the specific inflows and outflows of the basin or subbasins. While many of the values presented 

in the table are estimates, the relative magnitude of each water balance element helps illustrate 

the mechanisms at work in the basin. This detailed understanding of the groundwater system 

can serve as a basis to compare changes in the basin over time and provide valuable tools for 

groundwater basin management. The basic concept of the water balance is to show the 

difference between inflows and outflows and estimated change in storage. In addition to 

computing the net difference between the estimated total inflows and outflows, change in 

storage is estimated independently based on water level changes and aquifer storativity values. 

The water balance is prepared for each water year and for each subbasin. The results of the 

subbasin water balances are shown in Tables 6 through 8 and a summary of the 2006, 2007, 

and 2008 Zone 6 water balances is shown on Figure 18. Figure 18 also shows the water 

balance for 2005, the most recent wet year, for comparative purposes. 

INFLOWS 

There are six major sources of inflow to the subbasins in Zone 6 and surrounding areas. These 

include natural stream percolation, percolation of reservoir releases, percolation of CVP water, 

deep percolation (from rainfall and/or irrigation), percolation of reclaimed water, and 

subsurface groundwater inflow. Many of the basin inflows are controlled by hydrologic 

conditions. Natural stream percolation and deep percolation from rainfall are directly related to 

the volume and distribution of rainfall. Inflow to reservoirs is controlled by stream flow and 

releases are partly a function of current inflow and storage. Because they are related to rainfall, 

these three inflows are generally higher in wet years and lower in dry years. While water year 

2006 had average rainfall, both 2007 and 2008 were dry. 

Natural stream percolation occurs in every subbasin except the Bolsa Southeast subbasin and is 

most significant in subbasins with larger streams, Pacheco, Hollister West and San Juan. 

Stream percolation can vary considerably from year to year depending on rainfall and 

groundwater levels. For example, stream percolation in Zone 6 was an order of magnitude less 

in water year 2007 (a dry year) than in water year 2005(the most recent wet year): 1,241 af 

to11,540 af respectively (see Figure 18). In addition, relatively high groundwater levels in 

2007 and 2008 may have also contributed to “rejected recharge” or the decrease in percolation 

due to insufficient subsurface storage capacity. 



Reservoir releases from Hernandez and Paicines Reservoir flow to Zone 6 via the San Benito 

River. The river percolation in the Tres Pinos, Hollister West, and San Juan subbasins from 

natural flow and from reservoir releases are estimated separately. Natural percolation is greater 

in wet year than in dry years. In 2007, additional reservoir releases occurred to allow 

maintenance activities at the reservoirs. These releases resulted in more flow and stream 

percolation in the San Benito River than would be otherwise expected. In 2008, releases were 

reduced. 

In previous years, the active percolation of imported CVP water by discharging it to local 

streams was an important tool for managing groundwater levels in many of the Zone 6 

subbasins. In recent years, much less percolation of CVP imports has occurred because of 

rising groundwater levels and decreased CVP allocations. The percolation that does occur is 

limited to the Hollister West and Tres Pinos subbasins. 

Deep percolation from the root zone to the water table is estimated separately for rainfall 

percolation and irrigation percolation. Rainfall percolation varies significantly on an annual 

basis, while irrigation percolation remains relatively steady. Rainfall deep percolation is 

dependent on the volume of rainfall, temporal and areal distribution of rainfall, crop type/land 

cover, and soil type. More percolation from rainfall can occur if rainfall occurs in a short period 

of time when soils are already at field capacity, than if rainfall is evenly distributed over the 

season and subject to continual evapotranspiration. While 2005 was a wet year and water year 

2008 was a dry year, the volume of rainfall percolation was similar (see Figure 18), because of 

the large amount of rainfall that occurred in a short period of time in January 2008. Also as the 

volume of deep percolation accounts for the area of land, subbasins with the largest areas tend 

to have the largest amount of deep percolation (e.g. San Juan and Bolsa). Since land use and 

soil type do not change significantly from year to year, the relative volume of deep percolation 

(the portion of the total volume from an individual subbasin) also does not change significantly. 

Percolation of reclaimed water from wastewater disposal ponds occurs in three subbasins 

(Hollister West, Tres Pinos, and San Juan) at facilities operated by the City of Hollister, 

Sunnyslope, and Tres Pinos County Water District. Over the past four years, reclaimed water 

percolation has remained the same or has decreased slightly because of residential and 

industrial water conservation measures (Wittry, 2007). 

Groundwater can also flow between adjacent subbasins. While there is a large amount of 

uncertainty in calculating the subsurface flow, water level gradients were used to help quantify 

the volume of flow. As groundwater flow directions and levels have not changed significantly 

over the past few years, estimated groundwater inflow and outflow also have not changed 

significantly. Groundwater inflow may also include some component of baseflow in streams, 

which is difficult to accurately quantify. This component has not been specifically estimated 

and may be refined in future water balance calculations. 

OUTFLOWS 

The major outflows from the subbasins in Zone 6 and surrounding areas are groundwater 

pumping (agricultural and M&I plus domestic) and subsurface outflow (see Figure 18). 



Agricultural groundwater pumping is measured directly in Zone 6 and is estimated for the 

surrounding areas based on the soil moisture balance and crop water demands. The amount of 

agricultural pumping is dependent on the volume of CVP imports and the amount and 

distribution of rainfall, as growers in the area often rely on both groundwater and CVP imports 

for water supply. 

Agricultural groundwater pumping increased slightly. From 12,056 af in 2005 to 14,796 af in 

2008. Subbasins with the largest areal extent also have the largest amount of agricultural 

pumping (e.g., San Juan and the Bolsa). The relative amount of agricultural pumping per 

subbasin remains the same year to year. 

Domestic, municipal, and industrial pumping remained about the same during water years 2005 

through 2008. Municipal pumping is largely concentrated in the Hollister West, Hollister East, 

and Tres Pinos subbasins. 

Groundwater subsurface outflow was calculated along with subsurface inflow. As with 

subsurface inflow, volumes did not change significantly over time. Groundwater outflow may 

include baseflow in streams, which difficult to accurately quantify. This component has not 

been specifically estimated and may be refined in future water balance calculations. 

CHANGE IN STORAGE 

The water balance tables (Tables 6 through 8) include two estimates of storage change; the 

difference between inflows and outflows and the previously decribed estimate based on 

changes in measured water levels. In general, during wet and average years, the basin shows a 

net increase in groundwater storage and during dry years the basin shows a net decrease in the 

change in storage. These changes are also estimated on the subbasin level. The magnitude of 

the change in storage in the recent years has been smaller than those observed in previous 

years, as shown in Figure 19. The increased reliance on CVP imports has stabilized 

groundwater pumping in the basin. However, as a result of recent CVP allocation reductions, 

groundwater storage may once again vary widely as groundwater becomes a major water 

supply source. 

WATER BALANCE CONCLUSIONS 

As illustrated on Figure 18, groundwater outflows in Zone 6 have remained fairly constant in 

recent years while inflows have varied in response to annual hydrologic conditions. The district 

should continue to manage groundwater levels (and therefore groundwater storage) by 

augmenting inflows when water is available through managed percolation or other methods. 

Active management of the groundwater basin can help ensure that water supply is available 

when needed. 



Table 6. Water Balance for Water Year 2006 

Bolsa 

Southeast 

Hollister 

West 

Hollister 

East 

Zone 6 

Subtotal Bolsa Paicines 

Tres Pinos 

Creek 

Valley 

Pacheco 


Tres Pinos 

Inflows 

Stream percolation 

Natural streamflow* 1,659 0 1,410 1,134 2,681 378 7,263 500 238 2,521 10,522 

Reservoir releases 0 0 587 1,222 0 407 2,217 0 0 0 2,217 

CVP Percolation 0 0 0 451 0 1 452 0 0 0 452 

Deep percolation through soils 

Rainfall+ 1,763 699 5,499 1,396 2,859 842 13,059 3,853 451 110 17,472 

Irrigation 447 252 1,262 194 953 100 3,207 623 102 32 3,964 

Reclaimed water percolation 0 0 2,402 606 0 249 3,257 0 0 0 3,257 

Groundwater inflow 4,000 3,750 500 2,750 1,250 4,000 16,250 6,000 500 500 23,250 

Total 7,869 4,700 11,660 7,753 7,743 5,978 45,704 10,976 1,290 3,162 61,133 

Outflows 

Wells 

Agricultural 1,029 1,856 5,822 1,422 1,263 842 12,234 6,234 1,016 316 19,800 

Domestic and M &I 180 8 919 3,211 1,292 1,645 7,255 0 0 49 7,304 

Groundwater outflow 4,250 2,000 2,000 3,750 1,500 2,750 16,250 5,250 500 500 22,500 

Total 5,458 3,864 8,741 8,383 4,055 5,238 35,739 11,484 1,516 865 49,603 

Storage change 

Inflows - outflows 2,411 837 2,919 (630) 3,688 741 9,965 (508) (225) 2,298 11,530 

Water level change 410 245 442 770 1,539 409 3,815 1,195 0 0 5,010 

*Rejected recharge was assumed to be 50 % for Pacheco; natural percolation in San Juan subbasin was also decreased by 50 percent to represent rejected recharge. 

+Deep percolation from rainfall was decreased by 20 percent to account for additional runoff and rejected recharge during wet times. 

Grand 

Total


Bolsa 

Southeast 

Hollister 

West 

Hollister 

East 

Zone 6 


Tres Pinos 

Creek 

Valley 

Pacheco 


Tres Pinos 

Inflows 


Natural streamflow* 799 0 25 73 319 24 1,241 500 34 2,673 4,448 

Reservoir releases 0 0 767 2,297 0 766 3,830 0 0 0 3,830 



Rainfall 378 179 1,166 287 402 66 2,478 759 96 17 3,350 

Irrigation 457 257 1,218 214 1,069 95 3,311 709 116 35 4,170 



Total 6,135 3,436 5,781 6,701 3,040 4,197 29,290 7,968 746 3,224 41,228 

Outflows 

Wells 

Agricultural 810 1,998 6,562 1,662 2,366 849 14,247 7,086 1,156 350 22,839 

Domestic and M &I 224 7 1,096 3,456 1,501 2,013 8,297 0 0 46 8,343 

Groundwater outflow 4,250 2,000 500 2,750 1,500 1,250 12,250 1,500 500 500 14,750 

Total 5,284 4,005 8,158 7,868 5,367 4,112 34,794 8,586 1,656 896 45,932 


Inflows - outflows 851 (569) (2,377) (1,168) (2,327) 85 (5,504) (618) (910) 2,328 (4,703) 

Water level change (958) (1,466) (2,530) (400) (2,909) (220) (8,482) (862) 0 0 (9,344) 

* No rejected recharge removed. 

Grand 

Total


Bolsa 

Southeast 

Hollister 

West 

Hollister 

East 

Zone 6 


Tres Pinos 

Creek 

Valley 

Pacheco 


Tres Pinos 

Inflows 


Natural streamflow* 1,131 0 496 275 726 92 2,719 500 146 2,669 6,035 

Reservoir releases 0 0 412 564 0 188 1,164 0 0 0 1,164 



Rainfall 1,111 556 4,414 898 2,150 594 9,723 2,928 224 41 12,916 

Irrigation 322 233 958 151 801 66 2,531 789 126 37 3,483 



Total 7,314 4,790 8,739 5,522 4,678 4,597 35,639 11,217 996 3,247 51,099 

Outflows 

Wells 

Agricultural 1,703 2,001 6,744 1,143 2,639 567 14,796 7,889 1,255 372 24,313 

Domestic and M &I 197 13 1,053 3,232 1,323 2,130 7,947 0 0 47 7,993 

Groundwater outflow 5,500 1,250 250 3,500 1,500 2,500 14,500 1,250 500 500 16,750 

Total 7,400 3,264 8,046 7,875 5,462 5,197 37,243 9,139 1,755 919 49,056 


Inflows - outflows (85) 1,525 693 (2,353) (784) (600) (1,604) 2,078 (759) 2,328 2,043 

Water level change (298) 2,483 174 1,009 (403) (158) 2,807 1,796 0 0 4,603 

* No rejected recharge removed. 

Grand 

Total

60,000 

Water Balance Element Contribution (AFY) 

40,000 

20,000 

0 

Inflows 

Groundwater Inflow 

Reclaimed Wastewater 

Deep Perc - Irrigation 

Deep Perc - Rainfall 

Percolation of Reservoir releases 

Percolation of CVP releases 

Percolation of Natural streamflow 

Outflows 

Pumping - Agricultural 

Pumping - Domestic and M&I 

Groundwater Outflow 

(-20,000) 

(-40,000) 

2005 2006 2007 2008 


December 2008 



Figure 18 

Summary of Zone 6 

Water Balances 

2005 - 2008

40,000 

Water Balance Element Contribution (AFY) 

30,000 

20,000 

10,000 

0 

-10,000 

-20,000 

-30,000 

1975 1980 1985 1990 1995 2000 2005 2010 


December 2008 



Figure 19 

Change in Storage 

1978 - 2008

REVENUES AND CHARGES 

DISTRICT REVENUES 

The District derives its revenue from two primary sources: charges levied on landowners and 

water users, and income from property taxes. Income from charges on water users is classified 

as operating revenue and varies with the amount of water sold. Non-operating revenue is not a 

function of the volume of water sales or purchases, and consists primarily of property taxes, 

interest, standby and availability charges, and grants. Within each of these two categories, the 

accounting is further subdivided by zone of benefit. Zone 3 relates to the operation of 

Hernandez and Paicines reservoirs, and Zone 6 relates to the importation and distribution of 

CVP water. The Zone 6 budget is by far the larger of the two, and revenues during fiscal year 

2008 totaled $12.0 million. Approximately 21 percent of that amount was operating revenue 

from sales of CVP water and 53 percent was from property taxes. The remaining 26 percent 

came from interest, grants and other sources. 

DISTRICT CHARGES 

Some of the revenue received by the District stems from charges that are set by the District and 

adjusted annually in March. These include a standby and availability charge, water service 

charges for CVP water, power charges, and groundwater charges. The power charge reflects 

the energy cost of pumping CVP water to each subsystem of the distribution network, with 

higher charges for high-elevation subsystems. The current charges are shown in Table 9 and 

historical charges are tabulated in Appendix F, Table F-1. Charges for CVP water users were 

increased slightly from 2007. 

The standby and availability charge is a uniform per-acre charge assessed on all parcels that 

presently have access to CVP water (an active or idle turnout from the distribution system). 

The charge has remained at $6 per acre for over 10 years, which is the maximum charge 

allowed under the District’s formation act. 

Water service charges vary by type of user, reflecting the user categories established by the 

U.S. Bureau of Reclamation (USBR) for all CVP contractors. The water service charges consist 

of USBR fixed and variable costs that are assigned differently to agricultural users and M&I 

users, as itemized in Appendix F, Table F-2. In March 2007, the District’s contract with 

USBR was renegotiated to remove existing capital costs from the unit purchase cost of water. 

A separate repayment plan was established for existing capital cost. 



The groundwater rate basis reflects the cost of purchasing CVP water for percolation along 

local creeks and rivers and power charges associated with percolation. The per-acre-foot charge 

is determined by dividing these costs by the amount of anticipated percolation based on 

historical practice. In addition, District costs associated with groundwater monitoring and 

management are divided by the volume of groundwater usage. The groundwater charges are 

shown in Appendix F, Table F-3. The groundwater charge for 2009 is recommended to 

increase to $2.50/af and $22.50/af, for agriculture and M&I respectively. 

Table 9. Charges for Zone 6 Water Users, March 2008 - February 2009 

Agricultural 

Non--Full Full Municipal 

Charge Unit Cost Cost (1) 

& 

Industrial 

Standby and 

Availability dollars/acre $6.00 $6.00 $6.00 

Groundwater dollars/acre-foot $1.50 $1.50 $21.50 

CVP (Blue Valve) 

Water charge (2) dollars/acre-foot $100.00 $220.00 $170.00 

Power charge 

Subsystem 2 dollars/acre-foot $17.25 $17.25 $17.25 

Subsystem 6H dollars/acre-foot $19.40 $19.40 $19.40 

Subsystem 9H dollars/acre-foot $62.75 $62.75 $62.75 

Subsystem 9L dollars/acre-foot $32.60 $32.60 $32.60 

All other 

subsystems dollars/acre-foot $14.85 $14.85 $14.85 

Full-cost rates for agricultural users apply to landholders who have exceeded the respective nonfull-cost 

entitlement. There are two full-cost rates: 

1. Section 202(3) - the lower full-cost rate, which applies to qualified recipients leasing in excess of their 

960-acre entitlement, limited recipients that received USBR irrigation water on or before October 1, 

1981, and extended recordable contracts. There are currently no Zone 6 full-cost users under this section. 

2. Section 205(a)(3) - the higher full-cost rate, which applies to prior law recipients leasing in excess of 

their applicable nonfull-cost entitlement, and limited recipients that did not receive USBR irrigation 

water on or before October 1, 1981 See Section 202(3) or 205(a)(3) of RRA Rules and Regulations for 

further nonfull-cost definitions. 

For parcels 10 acres or smaller in size the water charge is $31.00 bi-monthly for all use categories. Bimonthly 

charges include annual minimum quantity (Agricultural at 2 acre-feet per year and M&I at 1 

acre-foot per year), with water use above the annual minimum charged at applicable Agricultural or Non- 

Agricultural water rate. 



CONDITIONS EXPECTED FOR WATER YEAR 2009 

Water supply for 2009 will depend on factors including rainfall, local surface water storage, 

groundwater storage, and CVP operations and storage. Next year, water supply will continue to 

be impacted by recent court decisions on the Delta smelt, Longfin smelt, and salmonoids. 

In May 2007, the U.S. District Court in Fresno ruled that the existing 2005 biological opinion 

for Delta smelt (issued by the U.S. Fish and Wildlife Service) was not in compliance with the 

Endangered Species Act. The biological opinion guides pumping operations for the CVP (and 

State Water Project) in the Delta with the intent of doing no harm to the endangered Delta 

smelt. In August of 2007, the Court also ordered interim actions to protect the smelt. For 2008 

allocations were 40 percent for agriculture and 75 percent of historical use based on the 

Bureau’s M&I shortage policy. 

While there is still considerable uncertainty about the percentage of allocation that is expected 

to be delivered in 2009, some reduction from 2008 may be anticipated. The amount of Delta 

pumping (and degree of water supply reductions) will depend not only on rainfall and storage 

in CVP reservoirs, but also on the amount and direction of San Joaquin River flows in the Delta 

and the abundance and distribution of Delta smelt as they occur next spring. 

The San Luis & Delta Mendota Water Authority have already forecasted a low CVP allocation 

based on relatively low storage in Northern California CVP reservoirs. As of November 6, 

2008, storage in major Northern California CVP reservoirs (Trinity, Shasta, and Folsom) was 

27 percent of capacity and 48 percent of the 15-year average. While long-range weather 

forecasts are not particularly reliable, the climate predictions indicate a weak La Niña condition 

in the Pacific Ocean, which is expected to continue into early 2009 (DWR 2009 California 

Winter Outlook Workshop, November 21, 2008). In response, much of California is expected 

to be drier than normal, although precipitation may be higher than normal in Northern 

California, where key CVP reservoirs are located. 

In 2008, the reduction in CVP imports did not result in an increase in groundwater pumping to 

meet the total water demand as expected. Instead total water demand decreased by 25 percent. 

The decrease could be attributed to several factors including the lack of groundwater 

infrastructure to meet demand, changes in crops and agricultural water use, and the fallowing 

of fields. These factors suggest that the decrease is short term and that groundwater pumping 

will increase significantly in 2009 to compensate for the lack of CVP imports. 

Total water demand in 2009 is expected to increase to the levels observed in 2007. Assuming 

CVP import allocations are decreased to similar levels as water year 2008, groundwater 

pumping in 2009 is expected to increase by about 8,300 af and 2,700 af for agricultural use and 

M&I use respectively. The expected total groundwater pumping (33,800 af) is still significantly 

lower than the historic high of 41,617 af (1991). 



Storage in local surface water reservoirs is generally higher than last year. Storage in 

Hernandez Reservoir was increased to 2,693 af by the end of water year 2008, up from the low 

of 590 af at the end of 2007 that was the result of maintenance activities. However, this is only 

16 percent of the reservoir’s capacity. Storage in Paicines Reservoir (capacity 2,870 af) was 

300 af, reduced from 800 af at the same time last year. This represents 10 percent of capacity. 

San Justo Reservoir stored 7,691 af as of September 2008, essentially the same as in September 

2007. In addition, since groundwater levels increased slightly from October 2007, groundwater 

levels and storage as of October 2008 were near historical highs over much of the basin. 

The reduction in CVP water availability following the U.S. District Court decision regarding 

Delta smelt protection is likely to decrease the average annual importation of CVP water by the 

District. Furthermore, municipal groundwater pumping is expected to increase as the City of 

Hollister implements a plan to meet future increases in water demand with demineralized 

groundwater. Both of these actions will tend to shift the groundwater balance in a negative 

direction, but it is not clear that the extent of the shift will create problems in the short term. 

The shift will be partially offset by increased recharge from stream percolation and decreased 

groundwater discharge to streams and agricultural drains. Current groundwater storage is 

sufficient to accommodate several successive dry years with negative water budgets, and the 

capacity for groundwater recovery in subsequent wet years is sufficient to balance moderate 

increases in groundwater pumping without causing long-term overdraft. 



RECOMMENDATIONS 

This annual report is required under Section 70-7.6 of the State Water Code to include 

recommendations regarding groundwater production, groundwater replenishment, CVP 

imports, and water charges in water year 2009. 

In 2009, the District continues to face an uncertain imported water supply as the ramifications 

of the May 2007 Court decision on Delta smelt and the July 2008 Court decision on the Delta 

salmonoids are materialized over the upcoming months. While CVP allocations are expected to 

remain similar to those observed in water year 2008, groundwater use is expected to increase as 

groundwater infrastructure is put in place to meet growing demand and users adjust their 

cropping and irrigation practices to rely more heavily on groundwater. However, in past years 

the District has accumulated substantial reserves in the groundwater basin that can now be 

relied upon for water supply. 

GROUNDWATER PRODUCTION AND REPLENISHMENT 

Groundwater levels increased slightly over the past year and groundwater storage in most 

subbasins is near historic highs. Groundwater storage is adequate to meet water demands in 

2009 and years thereafter. As a matter of perspective, groundwater pumping over the four 

drought years of 1988 through 1991 averaged 34,456 afy, similar to the amount estimated for 

2009. These pumping rates resulted—as expected—in temporary groundwater level declines 

(see Figure 17). The recommended amount of groundwater production for 2009 is the 

amount—in conjunction with available CVP water—that meets agricultural, M&I, and 

domestic water demands, assuming efficient water management practices. 

Historically, the District conducted extensive percolation operations that ultimately reversed 

overdraft and then accumulated a substantial water supply reserve. District management of 

groundwater storage in conjunction with surface water is currently being refined to avoid 

excessively high or low water levels both on a temporal and geographic basis. In 2009, storage 

in Hernandez Reservoir should be replenished and percolation of available local water supplies 

should be focused on areas exhibiting declines in response to drought and increased pumping. 

In the longer term, the District should consider the ramifications for groundwater management 

of increasingly unreliable CVP supply. While overall groundwater storage is substantial, 

increasing use of groundwater is likely to result in localized declines. Such potential problems 

can be minimized with groundwater management planning that addresses the distribution of 

groundwater pumping relative to areas of historical high groundwater and to areas of historical 

and existing percolation activities. The percolation capabilities of the latter areas (including 

District access, permeable surficial sediments, and flat channel area for water spreading) may 

need protection in light of intensifying and potentially competing land uses. 



CVP IMPORTS 

For 2009, it is recommended that—insofar as reduced allocations allow—the District should 

continue providing CVP water requested by agricultural customers up to the base allocation 

and to apply restrictive measures only to additional amounts. Under the Court decisions 

mentioned above, the overall availability of CVP water for percolation is likely to be limited in 

2009. However, the ramifications of the Court ruling may vary from month to month, providing 

temporary opportunities that should be evaluated in the context of managing local groundwater 

levels. 

GROUNDWATER INFRASTRUCTURE 

Given the current predictions for CVP delivery in 2009 and beyond, it is likely that use of 

groundwater will be increased to meet the water demands of most of the water users in the 

basin. A key component of a transition to large scale groundwater use is rehabilitation and 

maintenance of wells and pumping equipment. This report should serve as an additional alert 

to existing CVP customers that delivery may continue to be reduced and that individual 

groundwater users may wish to take stock of their groundwater infrastructure, which could 

make this transition smoother. 

GROUNDWATER MONITORING 

The network of wells used for monitoring groundwater levels has developed a gap in the 

western San Juan Valley due to the destruction or capping of several wells that were formerly 

in the network. To enhance the existing network, the District should consider adding several 

wells in that area that can be added to the monitoring network. It is also recommended the 

District continue to monitor all available wells in the monitoring network quarterly to identify 

seasonal changes. 

GROUNDWATER CHARGES 

In 2006, the District revised its methodology for determining groundwater charges. This new 

methodology is straightforward, reasonable and justifiable. Based on this method, the 2009 

groundwater charge of $2.50 is recommended for agricultural use in Zone 6 and a groundwater 

charge of $22.50 is recommended for M&I use in Zone 6. 

While the revised method is justifiable and reasonable, it is recommended that the District 

consider a longer term rate plan with a broader justification for groundwater charges. This plan 

may be predicated on completion of a comprehensive financial plan and rate review. It also 

could include consideration of funding CVP percolation activities when needed from a reserve 

fund, modifying groundwater charges to encourage groundwater use in specified locales (for 

example, with high groundwater problems), and use of water transfers to minimize payment for 

unused District CVP M&I allocation. 



CONSIDERATIONS FOR FUTURE STUDIES 

Model Update and Documentation – A numerical model was developed for the District by 

Gus Yates to simulate regional groundwater flow. The numerical model is a powerful tool that 

allows simulation of management scenarios, prediction of future impacts to the basin, and 

quantitative assessment of the basin water balance. The model-simulated water balance and the 

analytical water balance methods presented in the annual report should be compared to identify 

inconsistencies and focus on reducing the uncertainty of both the analytical and numerical 

methods. The model should be updated to reflect the hydrologic conditions in recent years and 

tested to ensure that the conceptual and numerical model are still reasonable. Documentation of 

the model should be prepared for the District so the model objective and limitations are 

understood. 

Surface Water/Groundwater Interaction – Stream percolation, both natural and managed, 

has been a critical component of groundwater basin management. As water users in the basin 

transition from CVP imports to increased groundwater use, managed percolation will once 

again be a tool to help manage groundwater levels. An updated literature review, assessment of 

available data, and new field studies can refine the methodology used to estimate surface water 

contributions to the groundwater system and to better understand the groundwater-surface 

water interaction. This analysis would assist the District in increasing the efficiency of 

managed percolation, which could be beneficial in light of decreased CVP deliveries. 

Pending Developments – Several large developments have been proposed in the basin beyond 

existing urban limits and could significantly increase total water demand in some areas. While 

the Urban Water Management Plan (UWMP) documents future water demand for the Hollister 

Urban Area, there is no planning vehicle that examines future water demand of the entire basin. 

Water Supply Assessments (WSA) prepared for these projects, the Hollister Urban Area 

UWMP, and other water demand estimates should be reviewed by the District and incorporated 

in a comprehensive analysis of future basin-wide water demand. 

CONSIDERATIONS FOR FUTURE ANNUAL REPORTS 

For each of the past three water years, a special topic has been identified for further 

consideration. Recent topics have included: a detailed look at water rates in water year 2006, an 

update of water quality in water year 2007, and an update of the water balance in water year 

2008. It is recommended that the water quality analysis and the water balance continue to be 

updated every three years. The next water quality update and water balance update would be 

performed in water year 2010 and 2011, respectively. It is recommended that the 2009 Annual 

Report include a comprehensive review and evaluation of the current groundwater basin 

management activities. 



REFERENCES 

Allen, R.G., L.S. Pereira, D. Taes and M. Smith. 1999. Crop evapotranspiration. Irrigation and 

Drainage Paper No. 56, United Nations Food and Agriculture Organization, Rome, Italy. 

Blaney, H.F., P.R. Nixon, G.P. Lawless and E.J. Wiedman. 1963. Utilization of the waters of 

the Santa Ynez River basin for agriculture in southern Santa Barbara County, California. U.S. 

Dept. of Agriculture, Agricultural Research Service. 

Blaney, H.F., P.R. Nixon, G.P. Lawless and E.J. Wiedman. 1963. Utilization of the waters of 

the Santa Ynez River basin for agriculture in southern Santa Barbara County, California. U.S. 

Dept. of Agriculture, Agricultural Research Service. 

Bookman-Edmonston/GEI, Occurrence and Management of High Groundwater, Report to San 

Benito County Water District, 2006. 

California Department of Water Resources, Vegetative Water Use in California, Bulletin. 113- 

3, 1975, Published. 1979. 

Department of Water Resources, 2009 Winter Outlook Workshop, Webcast, November 21, 

2008. 

Draft report prepared for San Benito County Water District, January 16, 2006. 

Dunne, T. and L.B. Leopold. 1978. Water in Environmental Planning. W.H. Freeman and 

Company, San Francisco, CA. 

GEI Bookman-Edmonston, Occurrence and Management of High Groundwater, North Area, 

HDR, Hollister Urban Area Water and Wastewater Master Plan¸ Draft report prepared for San 

Benito County Water District, February 2007 

Hydroscience Engineers, City of Hollister Long-Term Wastewater Management Program for the 

DWTP and IWTP, December 2005. Accessed November 27, 2006 at 

http://www.hollister.ca.gov/Site/html/gov/office/engr_wwtp.asp 

RMC, Pajaro River Watershed Groundwater Desalination Feasibility Study, Draft Report, 

September 5, 2007. 

RMC, Sunnyslope County Water District Long-Term Wastewater Management Plan, Executive 

Summary, January 2006. 

Rosskamp, Dale, San Benito County Water District, Personal Communication, November 6, 

2008. 



San Benito County Water District, Pajaro Valley Water Management Agency, and Santa Clara 

Valley Water District, Pajaro River Watershed Integrated Regional Water Management Plan – 

Executive Summary, May 2007. 

San Luis & Delta Mendota Water Authority (SLDMWA), September Project Operations 

Update, Memorandum from Tom Boardman, Water Resources Engineer, to Dan Nelson, 

Executive Director, September 5, 2007. 

San Luis & Delta-Mendota Water Authority (SLDMWA), Central Valley Project Operations 

Status And Forecast Report For Week Ending 11-14-08, November 14, 2008, 

http://www.sldmwa.org/pdf_documents/sldmwareport11-14-08.pdf 

San Luis & Delta-Mendota Water Authority (SLDMWA), Central Valley Project Operations 

Status And Forecast Report For Week Ending 11-14-08, November 14, 2008, 

http://www.sldmwa.org/pdf_documents/Reclamation%20Water%20Allocation%20June%202% 

202008.pdf 

Smith, Richard, U.C. Cooperative Extension, Personal Communication to Gus Yates, 2001. 

State Water Resources Control Board, GAMA - Groundwater Ambient Monitoring & 

Assessment Program, http://www.swrcb.ca.gov/gama/, Last Accessed November 21,2008. 

Todd Engineers, Annual Groundwater Report for Water Year 2006, Prepared for San Benito 

County Water District, December 18, 2006. 

Todd Engineers, Annual Groundwater Report for Water Year 2007, Prepared for San Benito 

County Water District, December 10, 2007. 

Todd Engineers, Development of a Water Quality Monitoring Program, Prepared for San 

Benito County Water District, June 2004. 

U.S. Geological Survey, GAMA - Groundwater Ambient Monitoring & Assessment Program , 

http://ca.water.usgs.gov/gama/, Last Accessed November 21,2008. 

U.S. Geological Survey, National Water Information System (NWIS), Last accessed: 

November 2008. 

United Nations Food and Agriculture Organization, FAO Irrigation and Drainage Paper No. 56, 

Crop Evapotranspiration, February 2006. 

United States Bureau of Reclamation, Reclamation Updates the Central Valley Project Water 

Supply Allocation, June 2, 2008, 

http://www.sldmwa.org/pdf_documents/Reclamation%20Water%20Allocation%20June%202%2 

02008.pdf 

University of California, Davis, Orchard Facts, April 2000, Accessed December 11, 2006 at 

http://fruitsandnuts.ucdavis.edu/newsletters/glenn4-00.pdf. 



Wittry, Steve, City of Hollister, Personal communication, November 30, 2007. 

Yates, G. and C-M Zhang. 2001. Groundwater flow and solute transport models for the San 

Benito County portion of the Gilroy-Hollister groundwater basin. May 11. Davis, CA, and 

Denver, CO. Prepared for San Benito County Water District and San Benito County Planning 

Department, Hollister, CA. 

Yates, Gus, Personal Communication, November 2008. 

Yates, Gus. Annual Groundwater Report for Water Year 2005, Prepared for San Benito County 

Water District, December 19, 2005 



Appendix A 

Reporting Requirements and Previous Annual Reports 

The San Benito County Water District Act (1953) is codified in California Water Code 

Appendix 70. Section 70-7.6 authorizes the District Board of Directors to require the District to 

prepare an annual groundwater report; this report addresses groundwater conditions of the 

District and its zones of benefit for the water year, October 1 of the preceding year through 

September 30 of the current year. The Board has consistently ordered preparation of annual 

reports, with the requirements specified by Section 70-7.6: 

• An estimate of the annual overdraft for the current water year and for the ensuing 

water year 

• Information for the consideration of the Board in its determination of the annual 

overdraft and accumulated overdraft as of September 30 of the current year 

• A report as to the total production of water from the groundwater supplies of the 

District and its zones as of September 30 of the current year 

• Information for the consideration of the Board in its determination of the estimated 

amount of agricultural water and the estimated amount of water other than agricultural 

water to be withdrawn from the groundwater supplies of the District and its zones 

• The amount of water the District is obligated to purchase during the ensuing water 

year 

• A recommendation as to the quantity of water needed for surface delivery and for 

replenishment of the groundwater supplies of the District and its zones during the 

ensuing water year 

• A recommendation as to whether or not a groundwater charge should be levied in any 

zone(s) of the District in the ensuing water year and if so, a rate per acre-foot for all 

water other than agricultural water for such zone(s) 

• Any other information the Board requires. 

The full text of Appendix 70, Section 70-7.6 through 7.8 is enclosed at the end of this 

appendix. 

Each water year a special topic is identified for further consideration. These topics have 

included water quality, salt loading, shallow wells, and others. Additional analyses and 

documentation provided in previous annual reports are summarized in the following table. 



Table A-1. Special Discussions in Previous Annual Reports 

Annual Report 

Additional Analyses and Reporting 


1996 Inclusion of Paicines and Tres Pinos sub-basins and sub-basin water budgets 

1997 Seasonal water use, irrigation water duties, long-term water quality trends 

1998 Irrigation water duties, contamination sites, management plan summary 

1999 Wastewater dischargers, management strategies for sub-basin water budgets 

2000 Methodology to calculate water supply benefits of Zone 3 and 6 operations 

2001 Preliminary salt balance 

2002 Investigation of individual salt loading sources 

2003 Documentation of nitrate in supply wells, drains, monitor wells, San Juan Ck. 

2004 Documentation of depth to groundwater in shallow wells 

2005 Tabulation of waste discharger permit conditions and recent water quality 

monitoring results 

2006 Rate study 

2007 Water quality update 

2008 Water budget update 



App. 70- 7.6 

70- 7.6. Groundwater; investigation and report: recommendations San Benito County 

Sec. 7.6. the board by resolution require the district to annually prepare an investigation and 

report on groundwater conditions of the district and the zones thereof, for the period from 

October 1 of the preceding calendar year through September 30 of the current year and on 

activities of the district for protection and augmentation of the water supplies of the district and 

the zones thereof. The investigation and report shall include all of the following information: 

(a) Information for the consideration of the board in its determination of the annual overdraft. 

(b) Information for the consideration of the board in its determination of the accumulated 

overdraft as of September 30 of the current calendar year. 

(c) A report as to the total production of water from the groundwater supplies of the district and 

the zones thereof as of September 30 of the current calendar year. 

(d) An estimate of the annual overdraft for the current water year and for the ensuing water 

year. 

(e) Information for the consideration of the board in its determination of the estimated amount 

of agricultural water and the estimated amount of water other than agricultural water to be 

withdrawn from the groundwater supplies of the district and the zones thereof for the ensuing 

water year. 

(f) The amount of water the district is obligated to purchase during the ensuing water year. 

(g) A recommendation as to the quantity of water needed for surface delivery and for 

replenishment of the groundwater supplies of the district and the zones thereof the ensuing 

water year. 

(h) A recommendation as to whether or not a groundwater charge should be levied in any zone 

or zones of the district during the ensuing year. 

(i) If any groundwater charge is recommended, a proposal of a rate per acre-foot for 

agricultural water and a rate per acre-foot for all water other than agricultural water for such 

zone or zones. 

(j) Any other information the board requires. 

(Added by Stats. 1965,c. 1798,p.4167, 7. Amended by Stats.1967,c.934, 5, eff. July27,1967; 

Stats. 1983, c. 402, 1; Stats. 1998, c. 219 (A.B.2135), 1.) 

70-7.7. Receipt of report; notice of hearing; contents; hearing 

Sec. 7.7. (a) On the third Monday in December of each year, the groundwater report shall be 

delivered to the clerk of the board in writing. The clerk shall publish, pursuant to Section 6061 of 



the Government Code, a notice of the receipt of the report and of a public hearing to be held on 

the second Monday of January of the following year in a newspaper of general circulation 

printed and published within the district, at least 10 days prior to the date at which the public 

hearing regarding the groundwater report shall be held. The notice shall include, but is not 

limited to, an invitation to all operators of water producing facilities within the district to call at 

the offices of the district to examine the groundwater report. 

(b) The board shall hold, on the second Monday of January of each year, a public hearing, at 

which time any operator of a water-producing facility within the district, or any person interested 

in the condition of the groundwater supplies or the surface water supplies of the district, may in 

person, or by representative, appear and submit evidence concerning the groundwater conditions 

and the surface water supplies of the district. Appearances also may be made supporting or 

protesting the written groundwater report, including, but not limited to, the engineer's 

recommended groundwater charge. 

(Added by Stats. 1965, c. 1798, p. 4167, 8. Amended by Stats. 1983, c. 02,2; Stats. 1998, c. 219 

(A.B.2135,2.) 

70-7.8. Determination of groundwater charge; establishment of rates; zones; maximum 

charge; clerical errors 

Sec. 7.8. (a) Prior to the end of the water year in which a hearing is held pursuant to subdivision 

(b) of Section 7.7, the board shall hold a public hearing, noticed pursuant to Section 6061 of the 

government Code, to determine if a groundwater charge should be levied, it shall levy, assess, 

and affix such a charge or charges against all persons operating groundwater- producing 

facilities within the zone or zones during the ensuing water year. The charge shall be computed 

at fixed and uniform rate per acre-foot for agricultural water, and at a fixed and uniform rate per 

acre-foot for all water other than agricultural water. Different rates may be established in 

different zones. However, in each zone, the rate for agricultural water shall be fixed and uniform 

and the rate for water other than agricultural water shall be fixed and uniform. The rate for 

agricultural water shall not exceed one-third of the rate for all water other than agricultural 

water. 

(b) The groundwater charge in any year shall not exceed the costs reasonably borne by the 

district in the period of the charge in providing the water supply service authorized by this act in 

the district or a zone or zones thereof. 

(c) Any groundwater charge levied pursuant to this section shall be in addition to any general tax 

or assessment levied within the district or any zone or zones thereof. 

(d) Clerical errors occurring or appearing in the name of any person or in the description of the 

water-producing facility where the production of water there from is other wise properly 

charged, or in the making or extension of any charge upon the records which do not affect the 

substantial rights of the assessee or assesses, shall not invalidate the groundwater charge. 

(Added by Stats. 1965, c. 1798, p. 4168, 9. Amended by Stats. 1983, c. 402, 3; Stats.1983, c. 402, 3; 

Stats. 1998, c. 219 (A.B.2135), 3.) 



Appendix B 

Local Climate Data 



35 

30 

25 

Precipitation (in) 

20 

15 

Average = 13.03” 

10 

5 

0 

1875 1885 1895 1905 1915 1925 1935 1945 1955 1965 1975 1985 1995 2005 


December 2008 



Figure B-1 

Annual Precipitation 

Hollister 

1875-2007

Table B-1a. Monthly Precipitation at the SBCWD CIMIS Station (inches) 


Year 

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP TOTAL 

1995 3.26 5.35 1.96 15.2 3.16 5.7 1.84 0.56 0.43 0.02 0 0 37.5 

1996 0.12 0.01 2.21 4.38 4.52 1.56 1.33 1.32 0 0.01 0 0 15.5 

1997 0.96 3.16 4.26 6.84 0.21 0.09 0.19 0.02 0.1 0 0 0.03 15.9 

1998 0.16 3.78 2.59 4.94 9.06 2.7 2.31 2.4 0.09 0.02 0 0.08 28.1 

1999 0.54 1.93 0.79 2.54 2.49 1.52 0.67 0.06 0.07 0 0 0 10.6 

2000 0.14 0.98 0.11 4.05 4.53 0.68 0.4 0.45 0.1 0 0 0.02 11.5 

2001 3.54 0.8 0.23 2.86 2.77 0.62 2.2 0.01 0.01 0.03 0.02 0 13.1 

2002 0.7 11.48 11.93 0.66 1.15 1.57 0.37 0.28 0 0 0 0 28.1 

2003 0 1.67 5.04 0.77 1.41 1.06 3.05 0.06 0 0 0.06 0 13.1 

2004 0.2 0.6 5.25 1.31 4.21 0.59 0.27 0.08 0.01 0 0 0.01 12.5 

2005 1.95 0.54 3.46 2.49 2.89 3.42 0.83 0.64 0.43 0 0 0.04 16.7 

2006 0.07 0.27 3.08 1.49 1.01 4.96 1.73 0.39 0.01 0 0.02 0.01 13.0 

2007 0.2 0.73 1.69 0.57 2.22 0.29 0.55 0.02 0 0.02 0 0.43 6.7 

2008 0.71 0.67 0.92 4.56 2.06 0.09 0.06 0 0 0 0 0 9.1 

AVG 0.9 2.3 3.1 3.8 3.0 1.8 1.1 0.4 0.1 0.0 0.0 0.0 16.5 

*2007 monthly data were revised from WY2007 Annual Report to include data from the San Benito station, not the San Juan station as originally reported. 

Table B-1b. Reference Evaporation at the SBCWD CIMIS Station (inches) 


Year 

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP TOTAL 

1995 3.54 1.55 0.96 1.25 1.72 2.82 4.09 4.72 6.33 7.17 6.71 5.02 45.9 

1996 3.88 2.24 1.22 1.48 1.88 3.67 5.1 6.06 6.73 7.39 6.68 4.71 51.0 

1997 3.84 1.84 1.37 1.38 2.48 4.27 5.84 7.51 7.13 7.18 6.71 5.67 55.2 

1998 3.85 1.84 1.52 1.29 1.38 2.82 4.26 4.53 5.27 6.91 6.83 4.72 45.2 

1999 3.51 1.73 1.52 1.54 1.84 3.01 4.72 5.8 6.66 6.92 5.91 4.67 47.8 

2000 4 1.98 1.89 1.22 1.62 3.69 5.14 6.04 6.73 6.74 6.19 4.74 50.0 

2001 2.91 1.71 1.47 1.47 1.81 3.07 3.9 6.15 6.54 6.02 6.23 4.75 46.0 

2002 3.51 1.91 1.24 1.53 2.26 3.66 4.21 6.37 7.05 7.24 6.14 5.39 50.5 

2003 3.57 1.94 1.25 1.56 1.8 3.87 3.79 6 6.47 7.29 6.15 5.07 48.8 

2004 4.11 1.73 1.24 1.32 1.72 3.98 5.19 6.38 6.71 6.63 5.98 5.32 50.3 

2005 3.08 1.69 1.44 1.3 1.69 2.95 4.38 5.74 6.36 6.86 6.13 4.55 46.2 

2006 3.59 2 1.19 1.43 2.18 2.43 3 5.49 6.41 7.02 5.6 4.38 44.7 

2007 3.28 1.69 1.37 1.77 1.77 4.11 4.76 6.29 6.89 6.79 6.46 4.65 49.8 

2008 3.48 2.21 1.44 1.25 2.03 3.76 5.17 5.97 6.88 6.74 6.31 5 50.2 

AVG 3.6 1.8 1.4 1.4 1.9 3.4 4.5 5.9 6.6 6.9 6.3 4.9 48.6 

*2007 monthly data were revised from WY2007 Annual Report to include data from the San Benito station, not the San Juan station as originally reported. 

B-1. Monthy ET and Precip 

Todd Engineers 11/26/2008

Appendix C 

Local Streamflow and Groundwater Levels 



4E 5E 6E 

Surface Water Monitoring Locations 

11S 12 S 13S 

1 

1. Tres Pinos Cr - Southside Road Bridge (West) 

2. San Benito River - KT Road bridge 

3. San Benito River - Hospital Road 

4. San Benito River - Cienega Road 

5. San Benito River - Nash Road 

6. San Benito River - Old Highway 156 

7. San Benito River - near Mitchell Road 

8. San Benito River - near Flint Road 

9. San Benito River - upstream of Bixby Road 

10. San Benito River - Y Road 

11. San Juan Creek - - Highway 156 

12. San Juan Creek - Anzar Road 

13. San Juan Creek - 2000 ft downstream of Highway101 

14. Pacheco Creek - Walnut Avenue 

15. Pacheco Creek - Highway 156 

16. Pacheco Creek - Lovers Lane 

17. Arroyo de las Viboras - Hawkins Ranch driveway 

18. Arroyo de las Viboras - Fairview Road 

19. Arroyo Dos Picachos - Fallon Road 

20. Arroyo Dos Picachos - Aquistapace Road 

21. Santa Ana Creek - Fairview Road 

22. Santa Ana Creek - Fallon Road 

23. Tequisquita Sough - San Felipe Road 

24. Millers Canal - 2000 ft downstream of San Felipe Lake 

25. Arroyo Dos Picachos - Lone Tree Road 

26. Pajaro River - above Millers Canal 

27. Pajaro River - Highway 25 

28. Pajaro River - below Carnadaro Creek 

29. Carnadero Creek - above Pajaro River 

30. Tres Pinos Creek - Bolado Park 

December 2008 



Legend 

County boundary 

SBCWD subbasin 

Monitoring well 

Surface water monitoring location 

Township Range line 

0 10,000 

N 

Figure C-1 

Monitoring Locations 

Scale in Feet

9 

8 

13 

6 

1 

2 

7 

4 

Legend 

USGS Gage Station 

10 

Active 

Inactive 

Subbasin boundary 

0 

N 

30,000 

3 

11 

Scale in Feet 

Table C-1 USGS Gages 

12 5 

December 2008 



Table C-1 and Figure C-2 

USGS Stream Gage 

Locations

140 

140 

220 

120 

200 

220 

80 

240 

160 

260 

120 

120 

180 

280 

300 

320 

120 

140 

100 

100 

120 

340 

360 

380 

160 

180 

180 

200 

420 

200 

220 

Legend 

Monitored wells 

Flowing artesian wells 

20-foot groundwater elevation contours 

Approximate area of flowing wells N 


Highways 

0 

12,000 


Major streams 

Scale in Feet 

240 

260 

280 

300 

400 

December 2008 

420 



440 

Figure C-3 

Groundwater 

Elevations 

October 2007

Table C-2. Miscellaneous Streamflow Measurements during Water Year 2008 

Flow (cfs) 

Streamflow Measurement Site 

10/11/2007 2/5/2008 5/6/2008 7/8/2008 10/1/2008 

1 Tres Pinos Cr - Southside Road Bridge (~) dry 32.64 dry dry dry 

2 San Benito River - KT Road Bridge 0.78 108.90 3.31 dry dry 

3 San Benito River - Hospital Road dry 120.00 1.36 dry dry 

4 San Benito River - Cienega Road dry 

5 San Benito River - Nash Road dry 

6 San Benito River - old Highway 156 dry est120.2 dry dry dry 

7 San Benito River - near Flint Road dry 63.92 dry 

8 San Benito River - near Mitchell Road dry 

9 San Benito River - upstream of Bixby Road dry 

10 San Benito River - Y Road dry est144.4 0.77 est 45gpm pooled 

11 San Juan Creek - San Juan-Hollister Road dry 

12 San Juan Creek - Highway 156 pooled 2.29 0.46 0.75 pooled 

13 San Juan Creek - Anzar Road est 0.3 11.98 1.58 1.25 pooled 

14 San Juan Creek - 2000 ft downstream of HWY 101 pooled 

15 Pacheco Creek - Walnut Avenue dry 33.82 dry dry dry 

16 Pacheco Creek - Highway 156 dry 23.17 0.09 dry dry 

17 Pacheco Creek - Lovers Lane 0.73 est 20 0.90 0.23 pooled 

18 Arroyo de las Viboras - Hawkins Ranch driveway dry 2.59 dry dry 

19 Arroyo de las Viboras - Fairview Road dry Dry dry dry 

26 Arroyo Dos Picachos - Lone Tree Road dry 1.20 dry 

20 Arroyo Dos Picachos - Fallon Road dry 4.97 dry dry 

21 Arroyo Dos Picachos - Aquistapace Road pooled 2.94 pooled pooled 5gpm 

22 Santa Ana Creek - Fairview Road dry dry 

23 Santa Ana Creek - Fallon Road pooled 16gpm pooled pooled dry 

24 Tequisquita Slough - San Felipe Road pooled 2.50 pooled pooled pooled 

25 Millers Canal - 2000 ft downstream of San Felipe Lake 2.99 est59.375 3.76 0.21 pooled 

27 Pajaro River - above Millers Canal 4.20 

28 Pajaro River - Highway 25 13.02 

29 Pajaro River - below Carnadero Cr 23.31 

30 Carnadero Cr - above Pajaro River 8.05 

Notes: 

See Figure 3 for numbered site locations 

~ = streamflow estimated visually or by relatively inaccurate methods (e.g., width x depth x estimated centerline surface velocity) 

Some sites were measured on the day before or after the indicated date. 

However, most sites along any individual creek or river were measured on the same day. 

Todd Engineers 

11/26/2008

Table C-3. Groundwater Elevations October 2007 through October 2008 

Depth to Top of 

Screens 

(feet) 


Elevation 

(feet MSL) 

Groundwater Elevations (feet MSL) 

Well Number 

Well Depth 

(feet) 

Subbasin 

Index 

Well 

Oct 07 Jan 08 Apr 08 Jul 08 Oct 08 

Pacheco 

11-5-26N2 232 95 198 P * 166.82 167.90 168.82 166.16 165.64 

11-5-26R3 225 65 208 P * 183.81 184.00 185.64 182.88 181.68 

11-5-35C1 180 198 P * 174.94 175.40 176.58 174.71 173.82 

11-5-35G1 230 206 P * 182.98 183.10 185.12 183.52 184.55 

11-5-35Q3 203 P * 178.88 181.30 180.61 171.05 168.81 

11-5-36C1 98 223 P * 192.86 196.60 198.11 194.05 193.64 

11-5-36M1 223 P * 184.82 157.30 186.88 183.82 184.55 

11-6-31M2 188 155 284 P * 218.85 222.20 221.07 215.55 210.58 

12-5-01G2 300 215 P 186.87 185.20 185.39 183.55 182.15 

12-5-02H5 128 42 210 P 191.55 192.20 191.49 190.57 188.60 

12-5-02L2 170 202 P 197.92 198.10 197.99 196.05 195.88 

12-5-03B1 128 100 182 P * 182.00 182.00 182.00 182.00 182.00 

12-6-06K1 260 16 260 P 260.00 260.00 260.00 260.00 260.00 

12-6-06L4 235 50 248 P 226.78 226.54 225.70 224.15 224.20 

Pacheco Creek 

11-5-12E1 103 52 277 PC * 224.03 221.70 222.82 226.62 224.69 

11-5-13D1 125 258 PC * 223.01 221.62 222.48 223.51 221.05 

11-5-23R2 118 43 230 PC * 202.86 203.60 205.17 203.69 202.68 

11-5-24C1 134 244 PC * 228.60 229.20 227.62 226.85 

11-5-24C2 165 70 249 PC * 218.15 219.60 221.64 219.57 217.77 

11-5-24L1 70 234 PC * 202.06 204.20 206.11 204.92 205.44 

11-5-25G1 225 243 PC * 198.59 200.20 203.04 197.37 95.64 

Bolsa 

11-4-25H2 631 216 148 B * 94.39 117.20 117.98 114.66 111.72 

11-4-26B1 642 149 143 B * 125.58 134.10 133.52 132.89 130.88 

11-4-34A1 100 142 B * 128.88 135.19 139.24 139.51 135.89 

11-5-20N1 300 150 B * 103.72 122.11 116.27 113.42 112.57 

11-5-21E2 220 100 155 B 155.00 155.00 155.00 155.00 155.00 

11-5-27P2 331 67 185 B 169.81 159.80 160.88 157.27 156.86 

11-5-28B1 198 125 168 B 168.00 168.00 168.00 168.00 168.00 

11-5-28P4 140 80 165 B 165.00 165.00 165.00 165.00 165.00 

11-5-31F1 515 312 159 B * 60.70 103.60 98.18 95.72 94.82 

11-5-33B1 125 169 B 169.00 169.00 169.00 169.00 169.00 

12-5-05G1 500 150 175 B 109.52 128.40 127.52 125.64 125.45 

12-5-05M1 175 B 66.11 98.62 98.11 95.67 94.59 

12-5-06L1 177 B * 82.64 107.40 105.54 101.58 100.68 

12-5-07P1 750 360 204 B 72.02 

12-5-17D1 950 314 217 B 73.75 88.54 86.66 80.75 77.67 

Bolsa South East 

12-5-09M1 240 105 207 BSE * 129.68 140.07 140.51 138.52 137.57 

12-5-21Q1 500 260 BSE * 150.05 156.04 155.31 153.05 151.46 

12-5-22N1 372 250 265 BSE * 88.46 118.86 


12-4-17L20 140 SJ 111.77 111.54 109.86 106.86 104.19 

12-4-18J1 150 SJ 118.87 131.26 126.74 124.84 123.71 

12-4-20C3 155 SJ 118.86 124.51 123.11 122.89 120.77 

12-4-21M1 250 170 SJ * 141.79 145.39 135.62 129.86 129.47 

12-4-26G1 876 240 210 SJ * 171.87 176.81 173.59 172.86 171.51 

12-4-34H1 387 120 199 SJ * 161.86 183.88 181.11 180.55 179.77 

12-4-35A1 325 110 216 SJ 185.70 190.64 188.82 187.82 186.45 

12-4-36D2 219 SJ 189.88 195.87 192.26 191.57 188.87 

12-4-36N1 556 153 214 SJ * 176.61 195.82 190.86 188.71 186.42 

12-5-30H1 240 250 SJ 207.64 212.86 208.88 204.84 203.82 

12-5-30R1 199 87 240 SJ 212.04 216.81 214.62 213.67 214.07 

12-5-31H1 248 SJ 207.87 209.36 207.86 206.58 207.88 

13-4-01K1 209 223 SJ 212.88 214.88 213.64 211.88 209.88 

13-4-03H1 312 168 207 SJ 181.75 189.89 186.16 185.90 184.15 

13-4-04A3 195 48 210 SJ 186.88 193.19 191.82 190.67 188.64 

13-4-1K1 223 SJ 214.88 213.64 211.88 209.88 

Golf course (SJ Oaks) 353 SJ 333.97 335.16 334.38 333.67 334.58 

San Justo (TELEDYNE) 323 SJ 290.12 293.84 290.07 288.84 286.46 

San Justo 3 (BRIGANTINO) 384 SJ 312.84 294.00 304.44 302.88 


12-5-27E1 175 270 HW * 207.16 209.19 

12-5-28J1 220 276 HW * 218.35 219.88 224.38 218.11 216.80 

12-5-28L1 425 275 HW * 216.36 220.62 221.71 214.87 213.14 

12-5-28N1 408 168 254 HW 228.46 226.58 228.65 224.24 220.81 

12-5-33E2 121 81 266 HW * 223.07 223.60 224.61 218.72 219.22 

C-3 - 2008 GWE Summary 


Table C-3. Groundwater Elevations October 2007 through October 2008 

Depth to Top of 

Screens 

(feet) 


Elevation 

(feet MSL) 

Groundwater Elevations (feet MSL) 

Well Number 

Well Depth 

(feet) 

Subbasin 

Index 

Well 

Oct 07 Jan 08 Apr 08 Jul 08 Oct 08 

12-5-34P1 195 153 294 HW * 228.57 229.60 230.35 227.63 225.54 

12-5-35N2 612 288 305 HW * 234.36 233.14 234.66 231.35 230.11 

13-5-03H1 189 121 302 HW 244.66 245.83 247.17 244.68 243.36 

13-5-03L1 126 303 HW * 232.92 238.90 239.11 237.07 236.68 

13-5-04G1 320 100 281 HW 225.09 

13-5-10B1 305 HW * 232.88 233.24 234.27 231.54 230.15 

13-5-10L1 252 52 312 HW 243.58 244.81 246.69 243.67 242.29 

13-5-11E1 309 HW 288.61 288.39 289.42 284.69 284.88 

San Justo 4 (INDART) 318 HW 277.02 278.37 277.20 275.64 272.69 

San Justo 6 (ROSE) 338 HW 247.44 247.88 246.05 244.86 242.37 

San Justo 5 (INDART WINDMILL) 320 HW 280.84 


12-5-09K1 195 88 200 HE * 185.13 186.40 185.64 182.57 183.47 

12-5-12R1 350 150 237 HE * 

12-5-14N1 229 HE * 190.51 189.90 190.63 188.69 186.62 

12-5-22C1 237 102 236 HE 188.81 198.30 197.46 196.77 190.04 

12-5-22J2 355 120 250 HE * 203.55 202.70 203.11 201.51 200.07 

12-5-23A20 862 178 239 HE * 186.53 184.30 183.04 182.68 181.92 

12-5-24N1 300 182 270 HE * 186.74 187.30 189.11 185.84 183.69 

12-5-36B20 500 430 315 HE 199.41 199.30 201.97 197.58 196.20 

12-6-07P1 147 266 HE 235.40 

12-6-18G1 198 70 303 HE 268.61 265.48 268.96 264.86 263.58 

12-6-19E5 160 116 279 HE * 233.92 234.40 233.97 231.61 230.61 

12-6-19N1 300 HE * 234.75 234.20 235.17 231.88 234.20 

12-6-30E1 375 HE 352.90 353.60 354.33 351.59 351.69 

13-6-06E1 471 443 460 HE 344.57 354.60 355.11 352.62 352.04 

13-6-07D2 500 HE 332.50 332.50 333.40 330.35 335.40 

Tres Pinos 

13-5-11Q1 178 61 324 TP 285.5555 286.8787 287.62 285.44 284.8888 

13-5-12D4 360 TP 198.50 101.00 261.00 229.00 

13-5-12K1 440 TP 316.00 319.00 325.00 320.00 309.00 

13-5-12N20 352 301 332 TP * 319.16 319.40 319.59 316.82 315.90 

13-5-13F1 134 30 348 TP * 331.85 332.19 333.88 330.88 331.16 

13-5-13H1 252 112 400 TP * 334.02 335.64 336.31 333.22 333.11 

13-5-13J2 180 375 TP * 343.64 345.19 345.92 343.58 342.15 

13-5-13Q1 185 44 360 TP * 333.58 334.40 336.35 333.45 332.68 

13-5-14C1 365 TP 289.04 296.30 297.73 295.37 294.27 

13-6-19J1 340 128 450 TP 431.26 433.41 434.69 431.77 430.20 

13-6-19K1 211 422 TP * 368.15 369.40 370.11 367.09 366.77 

13-6-20K1 440 TP 427.05 429.20 428.66 427.88 426.90 

LEMOS (Ridgemark) 522 TP 353.31 356.44 353.64 350.15 347.88 

POSEY (Ridgemark) 521 TP 352.26 349.54 345.67 343.41 

Tres Pinos Creek Valley and Pacines 

BERTUCCIO 4 753 TPCV 720.87 706.47 715.59 712.86 

DONATI 2 696 TPCV 650.18 657.77 651.04 649.55 648.88 

HARDWICK 3 755 TPCV 

P. Bertuccio #4 753 TPCV 714.94 

RON COKE 1 708 TPCV 675.69 679.39 

San Justo 5 (WINDMILL) 320 TPCV 281.06 

WILDLIFE CENTER 5 766 TPCV 729.81 733.66 722.08 727.87 

DONATI 6 694 Paicines 645.06 650.81 649.59 644.17 645.07 

OAK HILL RANCH 1 745 Paicines 673.77 681.86 680.02 674.14 679.63 

RFP Vineyard 3 (FRANCHIONI) 705 Paicines 666.85 669.66 675.21 

RIDGEMARK 5 668 Paicines 649.60 650.69 649.57 

RIDGEMARK 7 692 Paicines 641.15 644.31 642.53 640.68 

SCHIELDS 2 737 Paicines 

SCHIELDS 4 (vineyard) 682 Paicines 645.87 649.67 646.00 

Llagas (SCVWD) 

11S04E02D008 229 L 141.85 154.77 136.20 

11S04E02N001 175 L 139.04 151.80 124.25 

11S04E03J002 196 L 132.45 149.51 145.10 118.14 112.1 

11S04E08K002 178 L 140.84 149.72 148.51 

11S04E10D004 170 L 134.56 151.21 153.06 122.67 124.34 

11S04E15J002 144 L 131.58 143.35 126.54 

11S04E17N004 180 L 137.77 146.89 151.25 

11S04E21P003 155 L 132.53 141.14 126.83 

11S04E21P004 155 L 

11S04E22N001 150 L 128.42 137.28 123.99 

11S04E32R002 140 L 123.33 130.36 121.25 

C-3 - 2008 GWE Summary 


Appendix D 

Managed Percolation Data 



Table D-1. Reservoir Water Budgets for Water Year 2008 (acre-feet) 

Hernandez Paicines San Justo 

Inflows 

Rainfall 275 n.a. 174 

San Benito River 10,387 2,029 n.a. 

Hernandez-Paicines transfer n.a. 0 n.a. 

San Felipe Project n.a. n.a. 3,663 

Total Inflows 10,662 2,029 3,837 

Outflows 

Hernandez spills 0 n.a. n.a. 

Hernandez-Paicines transfer 0 n.a. n.a. 

Tres Pinos Creek percolation releases n.a. 495 n.a. 

San Benito River percolation releases 7,646 0 n.a. 

San Felipe Project n.a. n.a. 2,747 

Evaporation and seepage 1,215 1,638 1,203 

Total Outflows 8,861 2,133 3,950 

Storage Change 

Reservoir capacity 17,200 2,870 11,000 

Maximum storage 9,497 1,652 7,816 

Minimum storage 550 300 6,698 

Net water year storage change 2,103 -500 265 

Unaccounted for Water 302 -396 378 

* The total operating capacity was reduced to 7,000 af in 2006. The previous total capacity was 11,000 af. 

D-1 Reservoir Water Budget 


Table D-2. Releases of CVP Water for Percolation in Local Streams and the San Benito River during Water Year 2008 (acre-feet) 

Arroyo de las Viboras 



John Tres San 

Pacheco Fallon Jarvis Smith Maranatha Airline Ridge- Pinos Benito 

Creek Road Creek 1 Creek 2 Road Lane Creek Road Road Highway mark Creek River Total 

Oct. 0 0 0 0 0 0 0 0 0 0 0 0 2 2 

Nov. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 

Dec. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 

Jan. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 

Feb. 0 0 0 0 0 0 0 0 0 0 0 0 4.1 4 

March 0 0 0 0 0 0 0 0 0 0 0 0 0 0 

April 0 0 0 0 0 0 0 0 0 0 0 0 0 0 

May 0 0 0 0 0 0 0 0 0 0 0 0 0 0 

June 0 0 0 0 0 0 0 0 0 0 0 0 0 0 

July 0 0 0 0 0 0 0 0 0 0 0 0 0 0 

Aug. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 

Sept. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 

Total 0 0 0 0 0 0 0 0 0 0 0 0 6 6 

D-2 2008 stream perc 


Table D-3. Percolation of Municipal Wastewater during Water Year 2008 

Effluent 

Pond Area Discharge Evaporation Percolation 

(acres) (acre-feet) (acre-feet) (acre-feet) 

Hollister -- domestic 92.9 1,927 347 1,580 

Hollister -- industrial 39.0 1,403 146 1,257 

Ridgemark Estates I & II 7.2 156 17 139 

Tres Pinos 1.8 26 7 19 

Total 140 3,486 510 2,977 

Notes: 

n.a. = not applicable. Average annual evaporation = 56 inches (DWR Bulletin 73-79) 

Assumes 80% of total pond area in use at any time (Rose, pers. comm.). Hollister pond areas are from Dickson and Kenneth D. Schmidt and Associates (1999) and include 

treatment ponds in addition to percolation ponds at the domestic wastewater treatment plant. 

The San Juan Bautista plant is not included because the unnamed tributary of San Juan Creek that receives its effluent usually gains flow along the affected reach and is on the 

southwest side of the San Andreas Fault. These conditions prevent the effluent from recharging the San Juan Subbasin. 

Flow data are accurate to a maximum of two significant digits. All digits are shown to avoid rounding small numbers to zero and to preserve correct column totals. 

D-3 Percolation of Wastewater 


Appendix E 

Water Balance Methodology 


San Benito County Water District E-1

WATER BALANCE METHODOLOGY 

As part of the 2008 Annual report, water balances for 2006, 2007, and 2008 were prepared. A 

water balance provides a quantitative view of the state of the basin, providing estimates for the 

specific inflows and outflows of the basin as a whole and by subbasin. While many of the 

values presented in the table are estimates, the relative magnitude of each water balance 

element helps illustrate the mechanisms at work in the basin. This detailed understanding of the 

groundwater system can serve as a basis to compare changes in the basin over time and provide 

valuable tools for groundwater basin management. The end goal of the water balance is to 

estimate inflows and outflows to each subbasin and then compare these to calculate a water 

balance change in storage. In addition to comparing the estimated total inflows and outflows, 

changes in storage by subbasin are estimated independently using water level changes and 

aquifer storavity values. 

The water balance is prepared for each water year and for each subbasin. The results of the 

water balances are shown in Tables 6 through 8 in the report. For each element, the methods 

of estimation used in past annual reports (water years 2005 and earlier) were repeated to allow 

for direct comparison. While these methods have been documented in previous annual reports, 

they are summarized here to provide complete documentation. Several areas of the water 

balance analysis could be updated with additional data; these have been noted for future 

consideration. 

INFLOWS 

There are six major sources of inflow to the subbasins in Zone 6 and surrounding areas. These 

include natural stream percolation, Hernandez/Paicines releases, percolation of CVP water, 

deep percolation (from rainfall and/or irrigation), percolation of reclaimed water, and 

subsurface groundwater inflow. 

Stream Percolation 

Natural stream percolation accounts for the volume of flow that recharges the groundwater 

system from natural flow in rivers and creeks in the area. The basic concept of estimating 

percolation is to determine the natural flow in the waterway, the distance that the waterway 

transverses a subbasin, and an estimated rate of percolation based on flow and length. Because 

many of the streams in the area are not continuously gauged, flow loss rates are based on 

occasional field measurements and extrapolation of data from reference streams. These 

estimated values are shown in Table E-1. Percolation rates, also shown in Table E-1, were 

derived from synoptic surveys completed in the late 1990’s (Yates, 2008). In addition, local 

high water levels have resulted in a reduction of the amount of percolation occurring from 

natural streams, contributing to the uncertainty of the percolation estimate. This “rejected 

recharge” is difficult to determine and may vary by waterway over time. 



Table E-1. Estimated parameters for stream percolation. 

Annual 

Precipitation 

Length Maximum 

Name 

Watershed 

Area (ac) (in) Calibration+ Subbasin 

of Perc 

(mi) 

Perc Rate 

(cfs/mi) 

Pacheco Creek 145.0 18 1 Pacheco 2 5.34 

Arroyo de las 

Viboras 22.1 22 1 Pacheco 2.28 6.29 

Arroyo Dos 

Picachos 16.2 20 1 Hollister East 1.31 1.02 

Santa Ana 

Creek 36.5 19 1 Hollister East 7.58 6 

Hollister West, Tres 

Bird Creek*+ 15.0 18 0.15 

Pinos 

-- -- 

Pescadero 

Hollister West, Tres 

Creek*+ 38.3 18 0.15 

Pinos 

-- -- 

Tres Pinos 

-- -- 

Creek* 

1 Tres Pinos 

-- -- 

San Benito -- -- 

San Juan, Hollister -- -- 

River* 

1 West, Tres Pinos 

*Percolation along these streams is calculated using a combination of USGS gage data and Hernandez/Paicines 

release information 

+Pescadero and Bird Creek flows were reduced by a calibration factor to remain consistent with observed flows 

Daily flows in ungaged streams are estimated from gaged flows in four reference streams 

outside the basin. These streams are listed in Table E-2. For each of these streams, a daily unit 

flow was determined by normalizing stream flow by watershed area and annual average 

precipitation. The unit flows of the four streams were averaged to determine a reference unit 

flow per day that could be applied to streams within the basin. The unit flow was multiplied by 

each stream’s watershed area and annual average precipitation, Table E-1, to develop a daily 

estimate of flow. The maximum portion of estimated daily flow that could result in recharge 

was determined by multiplying the length of the percolation reach in the subbasin by the 

maximum percolation rate in cfs per mile. 



Table E-2. Reference streams used to estimate daily flow on ungaged streams. 

Annual 

Precip 

(in) 

Name 

Watershed 

Area (ac) 

USGS 

Station ID Location Lat Long 

Gabilan 

Creek 36.7 18 11152600 Salinas, CA 36.755792 -121.610501 

San Joaquin 

Cantua Creek 46.4 11 11253310 Valley 36.402174 -120.43349 

Los Gatos 

Coalinga, 

Creek 95.8 16 11224500 CA 36.2146772 -120.470712 

Corralitos 

Creek 27.8 35 11159200 

Watsonville, 

CA 36.9393968 -121.770507 

The portion of percolation that occurs in Tres Pinos Creek Valley is determined through a 

water budget based on estimated values for deep percolation of rainfall and irrigation, pumping, 

change in storage, and subsurface outflow. The percolation amount is estimated as the volume 

needed to balance inflow, outflows, and change in storage. 

Percolation on the San Benito River can be estimated using two available USGS gages and 

available percolation rate data from synoptic surveys. However, flow in the river at these gages 

consists of a combination of natural sources and reservoir releases. In order to estimate the 

contribution of each source on the streamflow percolation, a more detailed analysis is required 

and described in the Reservoir Releases section below. 

Because of recent high groundwater levels, the percolation rate and the length of the stream 

recharging groundwater have decreased. Thus not all of the percolation calculated by the above 

method actually percolates to the groundwater aquifer. In past annual reports, this rejected 

recharge was roughly estimated between 0 and 50 percent. For percolation along the San 

Benito River, 50 percent of estimated percolation was considered to be rejected. For Pacheco 

Creek, percolation estimates for water year 2006 were also decreased by 50 percent. However, 

Pacheco creek recharge in water years 2007 and 2008 were not decreased as the estimated 

streamflow was low and subsurface storage was considered sufficient for the total to percolate. 

For consistency, the same percent of rejected recharge was used in this report; approximately 

50 percent of recharge is rejected for streams in the Pacheco subbasin and 50 percent for flows 

along the San Benito River. 

The uncertainty of the natural percolation estimate can be reduced by updating the percolation 

rates and variables to reflect current groundwater conditions. Synoptic surveys of local streams, 

along with additional monitoring or additional continuous gages, can measure many of these 

variables in the field. In addition, streamflow data for one reference stream, Cantua Creek, was 

not available for water year 2008. It is not clear if this site is still monitored by the USGS. If no 

longer monitored, a new reference stream will need to be identified for future application of 

this method. 



Reservoir Releases 

San Benito River and Tres Pinos Creek flows are augmented by releases from the upstream 

Hernandez and Paicines Reservoirs. The flow from natural sources (e.g., rainfall) and from 

reservoir releases must be apportioned to determine the contribution of flow by source. For the 

San Benito River, the USGS has continuous gages at two locations, Willow Creek School and 

Old Highway 156. Since reservoir releases from Hernandez and flow at Willow Creek School 

are both observed, the contribution of the releases to the total flow can be determined by 

assuming any flow up to the volume of the release is from a reservoir release. The remaining 

flow can be considered the natural flow component. This simple analysis sometimes leads to a 

more variable natural flow than expected under the current conceptual model. To smooth the 

estimated flow during the spring and summer months, flow is estimated using a recession 

analysis. The recession is applied beginning just after the last significant rainfall runoff peak in 

spring and is represented by: 

Q(t) = Qo K t 

in which Q(t) is the flow t days after the start of the recession, Qo is the flow the day before the 

recession, K is the recession constant, and exponent t is elapsed time in days. The rate of 

recession, K, is a calibrated value of 0.964 based on historical regressions when Hernandez 

releases were not occurring. The estimated recession flows also make it possible to continue 

the curve separation into summer, when Hernandez releases exceed the natural flow but when it 

is almost certain that a natural flow component is present. This approach and the above 

constant rate have been used in past annual reports to partition total flow at Willow Creek 

School into natural and released components (Yates 2008). The recession is only an 

approximation of natural flow at Willow Creek School and varies based on the disturbution of 

Hernandez releases. The method used to determine the portion of natural flow from reservoir 

releases should further be refined in summer months. 

The general area along the San Benito River where the percolation occurs and the volume can 

be determined by examining the stream flow loss between the two San Benito River gages 

(Willow Creek and Highway 156). The difference between these gages is calculated, taking 

into account additional flow from Pescadero and Bird Creeks (estimated by the reference 

stream method discussed above). 

Total percolation is the total flow loss between the two gages after correcting for tributary 

inflows. Percolation is assumed to first be satisfied by natural flow. If the percolation is greater 

than the natural flow, the remainder is made up from the Hernandez released flow. Flow past 

the Highway 156 gage is assumed to percolate at a maximum rate of 8 cfs based on synoptic 

surveys performed in the late 1990’s (Yates, 2008). 

Both natural flow and Hernandez releases are apportioned to each subbasin by the same 

method. Percolation that occurs upstream of the Highway 156 bridge is considered to recharge 

Paicines Valley, Tres Pinos, Hollister West, or San Juan subbasins. Percolation that occurs 

downstream of the Highway 156 gage is considered to recharge only the San Juan subbasin. 

The portion of percolation that occurs in Paicines Valley is determined through a water budget 



ased on estimated values for deep percolation of rainfall and irrigation, pumping, change in 

storage, and subsurface outflow. The percolation amount is estimated as the volume needed to 

balance inflow, outflows, and change in storage. The remaining percolation upstream of the 

Highway 156 gage is reduced by rejected recharge and divided among the three other 

subbasins. For water years 2006-2008, the assumed percolation proportions were the same as 

for water year 2005: an estimated 50 percent of recharge is rejected, 10 percent recharges Tres 

Pinos, 30 percent recharges Hollister West, and 10 percent (and any percolation downstream of 

the Highway 156 gage) recharges San Juan subbasin. 

Managed CVP Percolation 

In the past, the District has used surplus CVP imported water to recharge the groundwater 

basin. Water was released to streams and allowed to percolate. In recent years, this practice has 

been greatly reduced but still occurs on limited scales. The volume and location of these 

managed percolation activities are directly measured. For the water balance, any CVP water 

reported to percolate in the San Benito River occurred in the Hollister West basin and any 

percolation activity along Tres Pinos Creek occurred in the Tres Pinos subbasin. 

Deep Percolation 

Deep percolation refers to the portion of water applied to the basin (either through precipitation 

or irrigation) that percolates through the soil to the groundwater aquifer. A soil moisture budget 

was prepared to examine the portion of the daily volume of precipitation and irrigation that 

percolates to the aquifer. A soil moisture budget takes several factors into account including 

daily precipitation, amount and efficiency of applied irrigation, soil moisture storage, seasonal 

evapotranspiration of overlying land cover and crops, and potential runoff. The basic concept 

of a soil moisture budget is that deep percolation is expected to occur only when the maximum 

moisture-holding capacity of the soil is reached. The budget calculations update soil moisture 

storage and deep percolation on a daily time step for each zone. 

As in previous years, one-dimensional recharge rates were calculated for 27 combinations of 

crop type/land cover and soil type using appropriate values for the soil moisture budget 

variables. Table E-3 (located at the end of the section) shows the variables by zone along with 

global variables used in all zones. The global variables are assumptions that apply to all soil 

zones including irrigation efficiency, the fraction of soil moisture when irrigation is applied, 

and the fraction of soil moisture when AET depletion occurs. These are discussed in more 

detail below. The daily soil moisture capacity can be expressed as: 

Soil Moisture Storage = Precipitation– Runoff –ET demands + Irrigation + Previous Day’s Soil 

Moisture Storage 

If the calculated soil moisture storage is greater than the maximum, then deep percolation 

occurs: 

Deep Percolation = Soil Moisture Capacity – Maximum Soil Moisture Capacity 



Each of the variables and how they are estimated are discussed below: 

Precipitation – Daily rainfall (in inches) is downloaded from the California Irrigation 

Management Information System (CIMIS) for the San Benito station located at the District’s 

offices (Station # 126). 

Runoff – The amount of rainfall that results in runoff is estimated using a linear equation. The 

slope and intercept of the runoff equation varies by soil type and were obtained through model 

calibration (Yates, 2008). The variables used in the runoff equation for each zone are shown in 

Table E-3. 

ET Demands – The evapotranspiration needs of an area vary over time and based on crop 

type/land cover. The measured daily reference evapotranspiration (ETo) was downloaded from 

CIMIS for the San Benito station. Monthly ET crop coefficients (Kco) for each crop type were 

adapted from several sources. Table E-4 (located at the end of the section) shows the crop 

coefficients and their sources. The coefficient (Kco) and the reference ET (ETo) are multiplied 

along with an Etc factor to determine the potential ET of the land cover. Potential ET refers to 

the amount of water a plant or type of land cover could consume given sufficient water at all 

times. Actual ET is limited by the amount of water available from precipitation and soil 

moisture. During the winter months, rainfall often exceeds potential ET, so the plant’s water 

needs are fully satisfied and actual ET is equal to potential ET. Actual ET is also controlled by 

the global variable, AET depression. This variable limits the amount of water that can be used 

to satisfy the ET needs of the overlying land cover, as a fraction of the maximum soil moisture 

capacity. 

Irrigation – Some of the soil moisture zones represent crop types that are often irrigated. The 

irrigation water combines with the natural precipitation and contributes to soil moisture storage 

and deep percolation. The rate of applied irrigation is determined based on the potential ET of 

the crop and an irrigation efficiency of 90 percent. The irrigation efficiency indicates that the 

ET demands of the crop consume 90 percent of the water applied, and that the remaining 10 

percent infiltrates and becomes soil moisture or deep percolation. Irrigation is not expected to 

occur when soils are saturated. The global variable, soil moisture irrigation threshold, is the 

fraction of maximum soil moisture storage when irrigation occurs. If the soil moisture is greater 

than the threshold, no irrigation occurs. 

Soil Moisture Capacity - The maximum soil moisture capacity is the total amount of water 

that can be stored in the root zone of a specific soil with a given land cover. Any additional 

water results in deep percolation to the aquifer. Maximum soil moisture capacity is derived 

from the available capacity of a soil (the moisture range between field capacity and permanent 

wilting point, in inches per inch) and the rooting depth of the land cover/crop. The rooting 

depths were compiled from a variety of sources including Blaney and others (1963) for native 

vegetation, United Nations FAO Irrigation and Drainage Paper No. 56 for crops (2006), and 

Dunne and Leopold (1978) for bare soils. The available water capacity was based on Natural 

Resources Conservation Service hydrologic soil groups. The ending soil moisture for each soil 

moisture zone of the analysis performed for previous water years was used as the initial soil 

moisture balance for water years 2006 through 2008. 



As in previous water years, Zone 6 was divided into 15 recharge zones by area, shown on 

Figure E-1. Each recharge zone is made up of one or more soil moisture zone. While each 

recharge zone contains only one soil type, it consists of one or more crop/land covers. The 

resulting deep percolation of the recharge zone is based on a weighted average of the soil 

moisture zones. The proportions of various crop/soil combinations in a recharge zone can vary 

seasonally to reflect growing seasons. For example, recharge zone 4 is comprised of four soil 

moisture zone, native vegetation, fallow land, irrigated truck crops, and deciduous orchard. In 

the summer months, 40 percent of the zone is covered by irrigated truck crops. This decreases 

to 10 percent in the winter months when the previously irrigated land is not cultivated. In 

addition, two recharge zones (zones 12 and 13) incorporate large areas of impervious urban 

land. In order to reflect the decreased ET demands and deep percolation of runoff from 

impervious surfaces, a fraction of the rainfall on the impervious portion is assumed to go 

directly to deep percolation. Table E-5 (located at the end of the section) shows the proportions 

of crop/soil combinations in each recharge zone. Deep percolation can be further analyzed by 

subbasin based on the percent of subbasin area in each recharge zone, shown in Table E-5. 

For the purposes of the water balance, deep percolation from natural and irrigation sources are 

reported separately. Because irrigation water use is measured directly in Zone 6, irrigation 

percolation can be estimated as 10 percent of the applied water (total irrigation water multiplied 

by 1 – the irrigation efficiency). The remaining deep percolation calculated by the above 

method is considered natural percolation. For areas outside of Zone 6, irrigation percolation is 

considered to equal total percolation for irrigated areas. The deep percolation from rainfall and 

irrigation by subbasin is shown in Tables 6 through 8. 

The soil moisture balance could be further improved with additional data and testing. Based on 

previous sensitivity analyses of the large number of variables used in the analysis, some are 

known to strongly influence the calculated deep percolation. In areas of natural vegetation, root 

depth is a particularly influential variable and is one for which reliable, spatially averaged data 

are difficult to obtain. The parameters used to calculate rainfall runoff also have a large effect, 

and runoff data from relatively flat, purely agricultural watersheds are also difficult to find. 

Runoff parameters are also highly influenced by tillage practices and cover crops. Runoff 

parameters may underestimate runoff during wet times, thus overestimating the total 

percolation. In 2006, deep percolation estimates were reduced by 20 percent to refine the 

overall water budget balance. The “bathtub” conceptual model of the root zone also ignores the 

slow but sustained deep percolation that occurs under drier unsaturated conditions. In addition, 

changes in crop and land cover may have changed the percolation distribution of the basin. 

Recent land use maps and irrigation practices should be used to update the composition and 

areas of the recharge zones. Each of these aspects of the soil moisture budget could potentially 

be improved through additional data, model refinement and testing. 



Reclaimed Water Percolation 

Several municipalities have wastewater treatment plants (WWTPs) within the basin, including 

the Tres Pinos, Cielo Vista, and San Juan Bautista WWTPs, two sites operated by Sunnyslope 

County Water District near Ridgemark, and the City of Hollister domestic and industrial plants 

(DWTP and IWTP, respectively). Tres Pinos, Sunnyslope and the City of Hollister have 

percolation ponds where treated wastewater is allowed to percolate to the groundwater aquifer. 

The total volume percolated is reported by facility in Appendix D for Water Years 2006 

through 2008. The percolation from each facility is assigned to one or more subbasins. The 

distribution of reclaimed water percolation is shown in Table E-6. The proportions of recharge 

percolating each subbasin are estimated and may be further refined with additional study. 

Subsurface Inflow 

Table E-6. Percent of WW percolating in each subbasin 

San 

Juan 

Hollister 

West 

Tres 

Pinos 

Hollister -- domestic 100 

Hollister -- industrial 50 50 

Ridgemark Estates I & II 100 

Tres Pinos 100 

Subsurface inflows and outflows of individual subbasins can be estimated using Darcy’s Law. 

Darcy’s Law can be expressed by: 

Q = K * A * dh/dL 

Where Q represents the volume of flow, K represents the hydraulic conductivity of the local 

aquifer, A is the cross-sectional area of flow, and dh/dL is the gradient of water levels (change 

in head over the change in distance). While many of the variables are estimates, Darcy’s Law 

allows a reasonable estimate of the direction and magnitude of flow. Each subbasin is directly 

adjacent to one or more other subbasins and has the potential for both inflow and outflow. For 

each point of contact between subbasins, the basic variables (hydraulic conductivity and crosssectional 

area) were estimated, as shown in Table E-7 (located at the end of the section). The 

gradient of flow changes on seasonal basis and can be estimated from the groundwater level 

contours presented in each annual report. To simplify the analysis, only water levels from 

October were used to calculate the gradient. In addition, to seasonal and spatial variation of the 

water levels boundary conditions can also be controlled by surface water bodies. For example, 

the outflow from the Bolsa subbasin is generally considered to contribute to baseflow of the 

Pajaro River. These surface water groundwater interactions are not taken into account in this 

simple analysis and could be used to better refine the methodology. Because this method results 

in only a rough estimate of inflow and outflow, flows were rounded to the nearest 250 af. 



OUTFLOWS 

The major outflows from the subbasins in Zone 6 and surrounding areas are groundwater 

pumping (agricultural and M&I plus domestic) and subsurface outflow. 

Pumping 

Groundwater pumping in Zone 6 is metered and read three times per water year in early spring, 

summer, and early fall. Groundwater meters are categorized as agriculture use, domestic use, or 

municipal use. Monthly data for municipal wells are also received directly from the City of 

Hollister, Sunnyslope, the City of San Juan Bautista, and Tres Pinos Water District. For areas 

outside of Zone 6 (Bolsa, Pacheco, Tres Pinos Creek Valley), agricultural pumping is estimated 

using the soil moisture budget. The irrigation needs of the subbasins are based on land use, 

crop evapotranspiration coefficient, and irrigation efficiency. Domestic and municipal use in 

the Bolsa, and Pacheco subbasins are assumed negligible. Municipal wells of Tres Pinos Water 

District are located within the Tres Pinos Creek Valley and represent the total domestic and 

municipal water use for that area. 

Groundwater Outflow 

Subsurface outflow is determined by the same method as groundwater inflow, using Darcy’s 

law with available water level data. Table E-7 shows the variables used in the analysis. 

CHANGE IN STORAGE 

The change in groundwater storage can be estimated two ways. The first is simply: 

Inflows- Outflows = Change in Storage 

The second method, described in detail in the groundwater levels section of the report, involves 

analysis of the change in water levels and the regional storavitiy values. 

CONCLUSION 

The water balance analysis provides independent estimation of each element with consistent 

methodology, and thereby provides a useful check on the current basin conceptualization. The 

water balance can be used to help illustrate and document changes in groundwater basin 

conditions, and can pinpoint changes in groundwater use, hydrologic conditions, or 

groundwater management. The water balance should continue to be updated regularly. In 

addition, estimation of selected water balance elements can be improved with further data and 

analysis as described in the previous section. 



Legend 

Zones 

Subbasin 

December 2008 



Figure E-1 

Recharge 

Zones

Table E-3a. Properties of Soil Moisture Zone 1-13 

Zone Number 1 2 3 4 5 6 7 8 9 10 11 12 13 

crop Native Native Native Native Native Bare Bare Bare Bare Pasture Pasture Pasture Non-irrig. 

soil I II III IV V I II III IV II III IV III 

Root depth (inches) 48 48 30 30 18 12 12 12 12 36 36 36 30 

Available water capacity (in/in) 0.08 0.19 0.18 0.15 0.13 0.08 0.19 0.18 0.15 0.19 0.18 0.15 0.18 

Max. soil moisture storage (in.) 3.84 9.12 5.40 4.50 2.34 0.96 2.28 2.16 1.80 6.84 6.48 5.40 5.40 

Runoff equation slope (in/in) 0.72 0.8 0.85 0.9 0.85 0.75 0.8 0.85 0.95 0.8 0.85 0.95 0.85 

Runoff equation intercept (in.) 0.48 0.36 0.32 0.3 0.32 0.48 0.36 0.32 0.2 0.36 0.32 0.2 0.32 

Irrigation switch (1=yes, 0=no) 0 0 0 0 0 0 0 0 0 1 1 1 0 

Initial soil moisture storage (in.)* 0.01 0.50 0.06 0.02 0.00 0.05 0.60 0.53 0.31 6.48 4.87 3.67 0.12 

Etc factor (decimal) 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 

* Ending Soil Moisture of Previous Annual Reports Water Balance 

Table E-3b. Properties of Soil Moisture Zone 14-27 

Zone Number 14 15 16 17 18 19 20 21 22 23 24 25 26 27 

crop Non-irrig. Irrig. Irrig. Irrig. Truck Truck Truck Truck Orchard Orchard Orchard Turf Turf Pasture 

soil IV II III IV I II III IV I II III II IV IV 

Root depth (inches) 30 30 30 30 24 24 24 24 72 72 72 12 12 36 

Available water capacity (in/in) 0.15 0.19 0.18 0.15 0.08 0.19 0.18 0.15 0.08 0.19 0.18 0.19 0.15 0.15 

Max. soil moisture storage (in.) 450 4.50 5.70 570 5.40 540 4.50 450 1.92 192 4.56 456 4.32 432 3.60 360 5.76 576 13.68 12.96 2.28 228 1.80 180 5.40 540 

Runoff equation slope (in/in) 0.9 0.8 0.85 0.9 0.75 0.8 0.85 0.95 0.75 0.8 0.85 0.8 0.95 0.95 

Runoff equation intercept (in.) 0.2 0.36 0.32 0.2 0.48 0.36 0.32 0.2 0.48 0.36 0.32 0.36 0.2 0.2 

Irrigation switch (1=yes, 0=no) 0 1 1 1 1 1 1 1 1 1 1 1 1 1 

Initial soil moisture storage (in.)* 0.04 5.32 4.23 3.16 1.44 3.79 2.47 2.84 3.15 9.69 8.24 1.15 1.72 3.10 

Etc factor (decimal) 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 1 1 1.3 

* Ending Soil Moisture of Previous Annual Reports Water Balance 

Table E-3c. Properties of Soil Moisture Zones 

Global Variables 

Irrigation efficiency (%) 0.9 

Soil moisture irrigation threshold (fraction 

of max. moisture) 0.5 

AET depression from soil moisture 

depletion begins at this threshold (fraction 

of max. moisture) 0.9

Table E-4. Crop Coefficients Used in Soil Moisture Budget 

Grain/field 

Non- 

Month Native Bare Pasture Irrigation Truck Orchard Turf 

Jan 1.00 0.28 1.00 0.94 0.80 0.73 1.00 

Feb 1.00 0.24 1.00 1.05 0.69 0.59 1.00 

Mar 1.00 0.21 1.00 1.06 0.77 0.66 1.00 

Apr 0.98 0.15 0.98 0.65 0.88 0.80 1.00 

May 0.96 0.16 0.96 0.42 0.99 0.91 1.00 

Jun 0.94 0.20 0.94 0.61 1.06 0.98 1.00 

Jul 0.92 0.10 0.92 1.21 0.92 1.04 1.00 

Aug 0.94 0.12 0.94 1.08 0.83 0.99 1.00 

Sep 0.96 0.09 0.96 0.65 0.86 1.02 1.00 

Oct 0.98 0.12 0.98 0.12 0.81 1.00 1.00 

Nov 1.00 0.19 1.00 0.19 0.72 0.96 1.00 

Dec 1.00 0.30 1.00 0.40 0.52 0.74 1.00 

Source: Blaney et al. Blaney et al. Blaney et al. Bulletin 113-3 Richard Smith Richard Smith Ref ET

Table E-5. Description of Area, Soil, and Land Cover of Recharge Zones. 

Recharge zone 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 

Area of zone (acres) 3,477 6,112 22,269 587 4,213 2,113 8,765 8,487 1,872 3,241 1,287 5,347 4,451 9,787 1,022 

Soil group I II V I III III IV IV IV III III II III II II 

Vegetation types (%) 

Native vegetation 60 10 100 10 10 100 10 10 10 10 25 30 10 20 

Fallow/bare 40 40-10 40-10 40-10 50-10 40-10 50-10 50-10 

Pasture/turf/alfalfa 40 20 30 

Irrigated grain/field 20 20 

Nonirrigated 

grain/field 20 90 100 

Truck 10-40 10-40 10-40 20-60 10-40 20-60 20-60 

Deciduous orchard 40 40 40 20 30 80 

Impervious 35 10

Table E-7. Approximate Groundwater Inflow and Outflow Darcy Calculations 

Assumed 

Boundary Identifier Length Saturated 

Thickness 

Assumed 

Boundary 

Area 

2 

INFLOW 

K 

(ft/day) 

2006 

Slope 

(ft/ft) 

2006 Flow Across 2007 2007 Flow Across 2008 2008 Flow Across 

2006 Totals (AF) 2007 Totals (AF) 2008 Totals (AF) 

Boundary Slope Boundary Slope Boundary 

(ft3/day) (AF/yr) (ft/ft) (ft3/day) (AF/yr) (ft/ft) (ft3/day) (AF/yr) Inflow Outflow Inflow Outflow Inflow Outflow 

Hollister East Tres Pinos Creek Valley -- 3,853 -- 3,082 -- 3,596 

In to Hollister East - East Boundary (1) 16,142 280 4,519,722 1.5 0.0100 67,796 568 0.0100 67,796 568 0.0120 81,355 682 Tres Pinos 3,853 2,621 3,082 3,058 3,596 2,621 

In to Hollister East - East Boundary (2) 15,526 200 3,105,230 0.8 0.0100 24,842 208 0.0100 24,842 208 0.0050 12,421 104 Hollister West 2,678 3,883 3,112 2,848 2,652 3,883 

In to Hollister East - East Boundary (3) 5,032 140 704,530 8.0 0.0100 56,362 472 0.0100 56,362 472 0.0050 28,181 236 Hollister East 1,249 1,619 1,249 1,619 1,022 1,619 

Total in to Hollister East 149,000 1,249 149,000 1,249 121,957 1,022 Pacheco 4,086 4,167 4,497497 4,167 4,703 5,556556 

Hollister West Bolsa South East 3,883 1,985 2,848 1,985 3,883 1,323 

In to Hollister West from outside basin 18,977 240 4,554,575 0.1 0.0150 6,832 57 0.0140 6,376 53 0.0080 3,644 31 Bolsa 6,152 5,358 6,152 1,339 6,879 1,206 

In to Hollister West from Tres Pinos 8,021 500 4,010,601 26.0 0.0030 312,827 2,621 0.0035 364,965 3,058 0.0030 312,827 2,621 San Juan 236 21 264 21 283 37 

Total in to Hollister West 319,659 2,678 371,341 3,112 316,471 2,652 Total 22,137 23,507 21,203 18,120 23,017 19,841 

Pacheco 

In to Pacheco from outside basin (1) 11,344 200 2,268,782 20.0 0.0060 272,254 2,281 0.0070 317,629 2,661 0.0075 340,317 2,852 

In to Pacheco from outside basin (2) 9,844 250 2,460,923 1.5 0.0060 22,148 186 0.0070 25,840 217 0.0075 27,685 232 

In to Pacheco from Hollister East across northeast Boundary 7,973 500 3,986,603 0.8 0.0000 0 0 0.0000 0 0 0.0000 0 0 

In to Pacheco from Hollister East across northwest Boundary 21,469 500 10,734,258 12.0 0.0015 193,217 1,619 0.0015 193,217 1,619 0.0015 193,217 1,619 

Total in to Pacheco 487,619 4,086 536,686 4,497 561,219 4,703 


In To San Juan across northern southeast boundary (outside basin) 9,143 250 2,285,774 0.1 0.0125 2,857 24 0.0140 3,200 27 0.0150 3,429 29 

In To San Juan across southern southeast boundary (outside basin) 20,207 100 2,020,657 1.0 0.0125 25,258 212 0.0140 28,289 237 0.0150 30,310 254 

Ttli Total in to San Juan 28,115 236 31,489 264 33,739 283 

Tres Pinos 

In To Tres Pinos from TPCV 7,663 500 3,831,650 8.0 0.0150 459,798 3,853 0.0120 367,838 3,082 0.0140 429,145 3,596 

Bolsa 

In to Bolsa from Pacheco (NE Boundary) 7,037 700 4,926,240 20.0 0.0030 295,574 2,477 0.0030 295,574 2,477 0.0040 394,099 3,302 

In to Bolsa from Pacheco (SW Boundary) 9,604 700 6,722,894 10.0 0.0030 201,687 1,690 0.0030 201,687 1,690 0.0040 268,916 2,253 

In to Bolsa from Bolsa SE 17,949 550 9,871,760 4.0 0.0060 236,922 1,985 0.0060 236,922 1,985 0.0040 157,948 1,323 

Total in to Bolsa 734,183 6,152 734,183 6,152 820,963 6,879 

Bolsa SE 

In to Bolsa SE from Hollister West 8,828 700 6,179,446 5.0 0.0150 463,458 3,883 0.0110 339,870 2,848 0.0150 463,458 3,883 

OUTFLOW 

Bolsa 

Out of Bolsa 32,623 700 22,836,309 7.0 0.0040 639,417 5,358 0.0010 159,854 1,339 0.0009 143,869 1,206 


Out of San Juan 12,613 500 6,306,702 0.1 0.0040 2,523 21 0.0040 2,523 21 0.0070 4,415 37

Appendix F 

Charges, Revenues and Expenditures 



Table F-1. Historical and Current San Benito County Water District Water Charges 

CVP (Blue Valve) Water Rates (dollars/af) 

Standby & 

Availability 

Water Charge 

Power Charge 

Groundwater Charge (dollars/af) 

Charge 

Municipal 

Distribution Subsystem 

Municipal 

Year (dollars/acre) Agricultural & Industrial 2 6H 9H 9L Others Agricultural & Industrial 

1987 $8.00 $34.00 n.c. $5.00 (2) $25.00 (2) 

1988 $2.00 $34.00 n.c. $5.00 (2) $25.00 (2) 

1989 $2.00 $34.00 $90.00 $0.00 $0.00 

1990 $4.00 $34.00 $90.00 $6.25 $22.00 

1991 $4.00 $38.00 $113.00 $6.25 $22.00 

1992 $4.00 $45.00 $120.00 $2.00 $10.00 

1993 $4.50 $45.00 $120.00 $1.00 $15.00 (3) 

$55.00 (1) $146.00 (1) $1.00 $5.00 

1994 $4.50 $77.61 $168.92 $1.00 $5.00 

1995 $4.50 $77.61 $168.92 $1.00 $15.75 First 100 af 

$36.70 Next 500 af 

$54.60 Over 600 af 

1996 $6.00 $75.00 $150.00 $1.50 $33.00 

1997 $6.00 $75.00 $157.00 $1.50 $33.00 

1998 $6.00 $75.00 $155.00 $1.50 $33.00 

1999 $6.00 $75.00 $155.00 $1.50 $33.00 

2000 $6.00 $75.00 $155.00 $1.50 $11.50 

2001 $6.00 $75.00 $155.00 $1.50 $25.00 

2002 $6.00 $75.00 $150.00 $40.00 $50.00 $30.00 $15.00 (4) $1.50 $25.00 

2003 $6.00 $75.00 $150.00 $19.00 $35.00 $46.80 $22.70 $9.40 $1.50 $20.00 

2004 $6.00 $75.00 $150.00 $24.30 $46.75 $53.70 $25.05 $15.25 $1.50 $10.00 

2005 $6.00 $80.00 $150.00 $26.15 $49.40 $66.90 $35.00 $17.10 $1.50 $21.50 

2006 $6.00 $85.00 $160.00 $23.60 $36.05 $65.75 $34.70 $18.40 $1.50 $21.50 

2007 $6.00 $85.00 $160.00 $23.60 $36.05 $65.75 $34.70 $18.40 $1.50 $21.50 

2008 $6.00 $100.00 $170.00 $17.25 $19.25 $62.75 $32.60 $14.85 $1.50 $21.50 

Notes: 

af = acre-feet. 

n.c. = no classification. 

All rates effective March 1 through following February. 

(1) Revised August 1993. 

(2) Never implemented. 

(3) Amended, but never implemented. 

(4) First implemented in 2002 

F-1 Historical SB Charges Todd Engineers 12/7/2008

Table F-2. U.S. Bureau of Reclamation Charges per Acre-Foot for CVP Water, 1996-2008 

User Category and 

Cost Item 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 

Irrigation (1) 

Cost of service (2) $65.63 $69.57 $61.58 $60.30 $64.24 $69.50 $68.71 $72.20 $74.52 $77.10 $91.13 $93.53 $28.12 (6)(7) 

Restoration fund (3) $6.53 $6.70 $6.88 $6.98 $7.10 $7.28 $7.54 $7.69 $7.82 $7.93 $8.24 $8.58 $8.79 

SLDMWA (4) n.a. n.a. $5.00 $2.73 $6.43 $2.65 $6.61 $5.46 $6.61 $7.99 $9.31 $9.99 $10.95 

Total $72.16 $76.27 $73.46 $70.01 $77.77 $79.43 $82.86 $85.35 $88.95 $93.02 $108.68 $112.10 $47.86 

Contract rate (5) $27.46 $27.46 $27.46 $27.46 $27.46 $27.46 $24.30 $24.30 $24.30 $24.30 $30.93 $30.93 $30.93 

Municipal & Industrial 

Cost of service (2) $127.40 $143.27 $130.88 $127.91 $129.59 $129.40 $130.32 $129.07 $134.86 $132.01 $214.41 $215.32 $33.34 -7 

Restoration fund (3) $13.06 $13.39 $13.76 $13.96 $14.20 $14.56 $15.08 $15.38 $15.64 $15.87 $16.49 $17.15 $17.57 

SLDMWA (4) n.a. n.a. $5.00 $2.73 $6.43 $4.15 $6.61 $5.46 $6.61 $7.99 $9.31 $9.99 $10.95 

Total $140.46 $156.66 $149.64 $144.60 $150.22 $148.11 $152.01 $149.91 $157.11 $155.87 $240.21 $242.46 $61.68 

Contract rate (5) $85.86 $85.86 $85.86 $85.86 $85.86 $85.86 $79.13 $79.13 $79.13 $79.13 $77.12 $80.08 $33.34 

Notes: 

(1) The irrigation rates shown here are for non-full cost users, which include almost all agricultural users in Zone 6 

(2) Cost-of-service for agricultural and municipal and industrial users includes a capital repayment rate and an operation and maintenanc 

(O&M) rate. For municipal and industrial customers, cost-of-service also includes a deficit charge, which includes interest on unpai 

O&M and interest on capital and on unpaid deficit. Cost-of-service rates apply March 1 through the end of the following February 

(3) Restoration fund charges apply October 1 through September 30 

(4) Beginning in 1998, the San Luis-Delta Mendota Water Authority instituted this charge to "self-fund" costs associated with maintainin 

the Delta-Mendota Canal and certain other facilities, which were formerly funded directly by the Bureau of Reclamation. SLDMWA issues 

preliminary rates in October for the upcoming contract year (March-February). These rates are used for rate-setting purposes; actual 

rates may vary. 

(5) The contract rate is shown for comparison. It is the minimum rate CVP contractors are allowed to pay. To the extent that the contract rate 

does not cover interest plus actual operation and maintenance costs, a contractor deficit is accumulated that is charged interest at the 

current-year treasury borrowing rate. 

F-2 USBR Charges Todd Engineers 12/7/2008

Table F-3. 2006/2007 Recommended Groundwater Revenue Requirement/Charges 

REVENUE REQUIREMENTS 

Rate 

Component 

($/AF) 

Quantity 1 

Rates 2 

(af) Amount Ag M & I 

(per A/F) (per A/F) 

Source of Supply 

Ag Source of Supply Costs 7.36 12,449 91,666 $ 7.36 

M&I Source of Supply Costs 22.31 7,687 171,528 $ 22.31 

Percolation Costs 

Ag CVP Water Rate 3 123.89 180 22,300 $ 1.79 

M&I CVP Water Rate 3 198.23 250 49,558 $ 6.45 

Ag Power Charge for Percolation 17.49 180 3,148 $ 0.25 

M&I Power Charge for Percolation 17.49 250 4,373 $ 0.57 

TOTAL $ 9.40 $ 21.50 

Current Groundwater Charge 4 (per acre foot) $ 1.50 $ 21.50 

RECOMMENDED CHARGES (per acre foot) $ 2.50 $ 22.50 

1 Assumed Volumes 

Percolation (based on average of past 3 years) 

Ag volume 

180 

M&I volume 

250 

Groundwater Usuage (based on average of past 3 years) 

Ag usage 

12,449 

M&I usage 

7,687 

2 Rates=Revenue Requirement/projected usage 

3 CVP water rate basis for 2008-2009 water year 

4 Groundwater charge adopted by San Benito County Water District Board 

of Directors in Feburary 2006, effective March 2007 

Note: Section 70-7.8 (a) of the District Act states that the agricultural rate shall not exceed one-third of 

the rates for all water other than agricultural water. 

Tables08.xls F-3 Recommended Charges

Appendix G 

List of Acronyms 



LIST OF ACRONYMS 

af ....................................................................................................................................................................... acre-foot 

af/yr ..................................................................................................................................................... acre-foot per year 

CDHS ........................................................................................................... California Department of Health Services 

cfs .................................................................................................................................................. cubic feet per second 

CIMIS ....................................................................................... California Irrigation Management Information System 

COC ............................................................................................................................................. constituent of concern 

CVP ............................................................................................................................................. Central Valley Project 

District or SBCWD .................................................................................................... San Benito County Water District 

DWR ........................................................................................................... California Department of Water Resources 

DWTP .................................................................................................................... domestic wastewater treatment plant 

EIR ..................................................................................................................................... environmental impact report 

ET ...................................................................................................................................................... evapotranspiration 

ft ................................................................................................................................................................................. feet 

gpd .......................................................................................................................................................... gallons per day 

IRWMP .................................................................................................... Integrated Regional Water Management Plan 

IWTP .................................................................................................................... industrial wastewater treatment plant 

MGD ........................................................................................................................................... million gallons per day 

mg/l ................................................................................................................................................... milligrams per liter 

M&I .......................................................................................................................................... municipal and industrial 

PVWMA ...................................................................................................... Pajaro Valley Water Management Agency 

USBR .................................................................................................................................. U.S. Bureau of Reclamation 

RWQCB ............................................................................................................ Regional Water Quality Control Board 

SCVWD ..................................................................................................................... Santa Clara Valley Water District 

SEIR ............................................................................................................ supplemental environmental impact report 

SLDMWA ................................................................................................ San Luis & Delta-Mendota Water Authority 

Sunnyslope CWD ..................................................................................................... Sunnyslope County Water District 

TDS ................................................................................................................................................ total dissolved solids 

WRA ............................................................................................. Water Resources Association of San Benito County

San Benito County Water District San Benito County Water District

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