Orange County Basin - Metropolitan Water District of Southern ...

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Chapter IV – Groundwater Basin Reports Orange County Basins SOUTHWEST ELEVATION (FEET MEAN SEA LEVEL) 200 -200 -400 -600 -800 -1000 -1200 -1400 -1600 -1800 -2000 -2200 -2400 -2600 -2800 -3000 A PACIFIC OCEAN 0 Figure 10-2 Hydrogeologic Cross Section of the Orange County Basin HUNTINGTON BEACH Talbert Barrier NEWPORT-INGLEWOOD FAULT ZONE FOUNTAIN VALLEY SANTA ANA EXPLANATION SILTS, CLAYS BURRIS PIT PERCOLATION BASIN SANDS, GRAVELS COLORED WATER CONSOLIDATED, NON-WATERBEARING FORMATIONS WATER TABLE OCWD AQUIFER RECHARGE AREA ANAHEIM CONROCK AND WARNER PERCOLATION BASINS NORTHEAST FINAL IV-10-4 September 2007 SEA WATER A A' A' SANTA ANA RIVER The Upper aquifer system, which averages approximately 200 feet in thickness, consists of alluvial sediments and includes the Talbert aquifer and recent alluvium. The total storage of this aquifer system is estimated to be approximately five million AF (OCWD, 2004). However, only about five percent of the total basin production comes from this aquifer because of lower production rates and poorer water quality than the underlying aquifers. The Principal aquifer system averages approximately 1,000 feet in thickness and is the primary source of production in the Orange County Basin. The principal aquifers are located approximately 200 to 1,200 feet below ground surface (fbgs). This aquifer is correlative with portions of the Lakewood Formation and the San Pedro Formation of the Central and West Coast Basins in Los Angeles County. Orange County Water District (OCWD) estimates the total storage in this aquifer system is approximately 32.9 million AF (OCWD, 2004). Deeper aquifers below the principal aquifer system comprise the Lower aquifer system (DWR, 2004), with a thickness of about 300 to 1,000 feet. Few wells produce from this aquifer because of the increased depth and the potential presence of colored water. The total estimated volume of fresh groundwater capable of being stored in the Orange County Basin when it is completely full is estimated to be approximately 66 MAF by OCWD (2004). Based upon review of historical data, OCWD has established basin water contour levels, which represent a full basin. Volume in storage indicates how much storage space is available for use (defined as accumulated overdraft) within the Orange County Basin. OCWD estimates that between 400,000 and 500,000 AF of the total basin storage is actually usable (OCWD, 2004) in terms of emptying and filling operations. If groundwater levels are allowed to drop below the
Chapter IV – Groundwater Basin Reports Orange County Basin lower limit (i.e. >400,000 AF of accumulated overdraft) there is an increased potential for seawater intrusion, increased potential for colored water upwelling, and increased potential for subsidence. However, the basin can be operated on a short-term emergency basis with an accumulated overdraft up to approximately 500,000 AF without causing irreversible seawater intrusion or land subsidence (OCWD, 2004 and 2006). If groundwater levels are allowed to rise to near-full conditions, outflow to the Central Basin can increase, local near-surface groundwater levels may occur, and there would be a decreased potential for capturing large amounts of recharge if it were to become available. Historical data are shown in Figure 10-3. As shown in Figure 10-3, the accumulated overdraft increased more than 100,000 AF between 2000 and 2004 to more than 400,000 AF as a result of a six-year drought on the Santa Ana River. Due to recent heavy rains and basin management activities, as of June 2006, the accumulated overdraft or available storage space was 135,000 AF. Of this amount, 100,000 AF is kept in reserve for capture of stormwater runoff during a potentially wet year and 35,000 AF would be available for other storage purposes. It is also important to note that storage varies substantially from year to year in the Orange County Basin. Available Storage Space (AF) 0 100,000 200,000 300,000 400,000 500,000 600,000 Figure 10-3 Historical Available Storage Space in Orange County Basin 1986 1985 1988 1987 Source: OCWD 2004, 2005 Lower limit (500,000 AF) of accumulated overdraft 1990 1989 1992 1991 1994 1993 1996 1995 Fiscal Year Safe Yield/Long-Term Balance of Recharge and Discharge 1998 1997 2000 1999 2002 2001 2004 2003 Recharge to the Orange County Basin is primarily by direct percolation of Santa Ana River water through highly permeable sands and gravels within the forebay areas. Recharge also occurs as a result of injection through wells at the Talbert and Alamitos seawater barriers, use of imported water for groundwater replenishment, wastewater reclamation and other water conservation practices. The natural yield of the Orange County Basin, which includes infiltrated precipitation, irrigation, and other native incidental recharge, has been estimated to be FINAL IV-10-5 September 2007 2005
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Page 7 and 8: GROUNDWATER MANAGEMENT Chapter IV -
Page 9 and 10: BPP (%) 85% 80% 75% 70% 65% 60% Cha
Page 11 and 12: Category Non-Irrigation Wells (larg
Page 17 and 18: Water Level (feet MSL) 200 150 100
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Page 25 and 26: In-lieu Storage (AFY) 90,000 80,000

Orange County Basin - Metropolitan Water District of Southern ...

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