Lower Pilarcitos Creek Groundwater Basin Study - Coastside ...

More documents

Recommendations

Info

The cost of water treated at the Nunes WTP is less expensive during the winter months since the water supply is entirely from Pilarcitos Lake and the upper Pilarcitos Creek wells. These sources do not have the associated energy costs, due to pumping across Sweeny Ridge from the Crystal Springs Reservoir to the Nunes WTP. In the future, as water consumption increases and/or a smaller than 3:1 blending ratio is needed to maintain acceptable water quality, then the unit costs of the Lower Pilarcitos Creek groundwater supply will be reduced. Comparatively, the Lower Pilarcitos Creek groundwater appear to cost about the same as the current surface water purchase and treatment costs. These costs may fluctuate from year to year based upon the length of time that the aquifer will sustain a reasonable pumping rate and may vary by as much as a third, either more or less, than the $1.721 estimated unit cost. 61
Conclusions This study indicates that a Lower Pilarcitos Creek groundwater project is technically and economically feasible. The following key conclusions have been developed: • The perennial or safe yield is 1,300 AFY and is defined here by the amount of groundwater that can be pumped without inducing significant adverse impacts, primarily saltwater intrusion from the ocean. This perennial yield value amounts to 60 percent of the estimated 2,200 AFY of total inflow to the groundwater basin, reflecting the unlikelihood that all of the basin inflow can be safely captured without incurring adverse impacts. • The estimated total annual perennial yield of 1,300 AFY takes into account long-term pumping. Relatively recent increases in pumping from the Balboa wellfield (140 AFY) should be included in the 1,300 AFY. The remainder (1,160 AFY) is sufficient for the potential Lower Pilarcitos wellfield and additional development by CCWD. • The estimated total yield of the five wells of the proposed Lower Pilarcitos wellfield ranges between 129 and 259 MGY for drought and normal years. For costing purposes, an average value of 194 MGY (595 AFY) is assumed. Pumping rates are limited by groundwater level changes, particularly in the dry season. • Estimated construction, operations and maintenance cost for the proposed Lower Pilarcitos Creek groundwater project are comparable to the current costs of surface water purchase and treatment. • Groundwater in the marine terrace aquifer is confined and not in direct hydraulic connection with Pilarcitos Creek; accordingly, pumping of the proposed wells would not deplete creek flows. • Should CCWD decide to proceed with evaluation of the proposed Lower Pilarcitos Creek wellfield, the recommended next step is installation and testing of a pilot production well. In addition, stream flow monitoring is recommended. 62
Page 1 and 2:
Coastside County Water District Hal
Page 3 and 4:
LIST OF FIGURES Figure 1 Figure 2 F
Page 5 and 6:
Executive Summary This report summa
Page 7 and 8:
criteria to a monthly evaluation of
Page 9 and 10:
top of well screens. Pumping at hig
Page 11 and 12:
1997 (Nelson, 1997 and 1998). This
Page 13 and 14:
Figure 4 illustrates the areal dist
Page 15 and 16:
• Urban: urban, urban residential
Page 17 and 18:
should be noted that Geoconsultants
Page 19 and 20: slopes. In addition, the Pilarcitos
Page 21 and 22: The bedrock has been affected by fo
Page 23 and 24: Cross section A-A’ (Figure 16) wa
Page 25 and 26: Lower Pilarcitos Creek Test Well An
Page 27 and 28: well construction. The drilling flu
Page 29 and 30: drawdown is defined as the distance
Page 31 and 32: Because drilling depths are shallow
Page 33 and 34: Marine Terrace Hydraulic Properties
Page 35 and 36: 1993. Review of these maps indicate
Page 37 and 38: (1.000 g/cm 3 ), allowing the fresh
Page 39 and 40: Watershed Water Balance Two water b
Page 41 and 42: ET can be expressed in terms of per
Page 43 and 44: groundwater inflow to the Lower Pil
Page 45 and 46: This is a simplified accounting of
Page 47 and 48: 3,000 homes exist within the basin.
Page 49 and 50: (Geoconsultants, June 1987 and Augu
Page 51 and 52: To estimate consumption of this wat
Page 53 and 54: echarge is one of the largest singl
Page 55 and 56: 1987 land use conditions to 822 AFY
Page 57 and 58: An example was provided involving p
Page 59 and 60: Water Quality Groundwater quality i
Page 61 and 62: colloidal form. Accordingly, the al
Page 63 and 64: Economic Feasibility This section a
Page 65 and 66: Overall, groundwater is characteriz
Page 67 and 68: The overall capacity of the five we
Page 69: Maintenance costs are estimated to
Page 73 and 74: Earth Sciences Associates, February
Page 75: Todd, David K., 1980, Groundwater H
show all

Lower Pilarcitos Creek Groundwater Basin Study - Coastside ...

Create successful ePaper yourself

Delete template?

Save as template?