2010 San Dimas System UWMP - Golden State Water Company

6.1.2 CIC’s Water Supply ReliabilityAccording to the CIC’s 2010 UWMP, the reliability of CIC’s various sources (surface waterdiversion and groundwater) is primarily dependent upon the management of the Main Basin. IfCIC’s annual groundwater right in the Main Basin is exceeded, CIC relies on the availability ofsupplemental imported water used to replace the annual extraction in excess of the annual right.CIC states that in most instances, including during drought years, water stored in the SanGabriel Reservoir and Morris Reservoir is available for surface diversion (CIC, 2011). For thesereasons, it is assumed CIC’s relatively small water supply to GSWC is 100 percent reliable.6.1.3 Groundwater Supply ReliabilityGSWC’s San Dimas System has a total share of 1.73984 percent of the total annual OSY of theMain San Gabriel Basin. Under the Main San Gabriel Basin Judgment the Watermaster isresponsible for managing the groundwater levels at the Baldwin Park Key Well. The Judgmentstates that the Watermaster shall not spread replenishment water when the groundwater level atthe Key Well exceeds 250 feet msl. The Judgment also states that the Watermaster shallspread replacement water necessary to maintain the water level elevation above 200 feet msl.During the period of management under the Judgment, significant drought events haveoccurred from 1969 to 1977, 1983 to 1991, and 1998 to 2004. In each drought cycle the MainSan Gabriel Basin was managed to maintain groundwater levels. Based on historicmanagement practices, all pumpers from the Main San Gabriel Basin are expected to haveadequate supply over the next 25 years under single year and multiple year drought periods(TVMWD, 2011). The TVMWD’s UWMP provides basin-wide details concerning the reliability ofthe Main San Gabriel Basin.GSWC and other water producers participate with the responsible agency, TVMWD, to ensurethat the OSY is available to the pumpers in the Main San Gabriel Basin. The TVMWD has acyclic storage agreement with Metropolitan and the Main Basin Watermaster. Cyclic storageaccounts have been used to increase storage in the basin since 1975. Metropolitan pre-deliversreplenishment water to the Basin and later sells the stored water to the water districts at areduced rate. Metropolitan can store up to 40,000 ac-ft of water for the TVMWD. Currently,Metropolitan has 11,200 ac-ft of water in storage for TVMWD (Main San Gabriel BasinWatermaster 2010).The Main San Gabriel Groundwater Basin’s pumping and reliability is subject to the OSYestablished each fiscal year by the Watermaster and the availability of replenishment water.Long-term cyclic storage provides a mechanism that allows the responsible agency to establisha buffer during droughts and periods of reduced OSY by allowing for storage recharge watersduring times of available import supplies. Recharge in the basin occurs from percolation ofprecipitation, return flow of applied water, some septic system discharges, and stream flow.Recharge through streams and spreading basins is generated from runoff from surroundingmountains and imported water from the State Water Project and the Colorado River. TheTVMWD also continues to evaluate alternatives to augment Metropolitan’s imported supply,such as implementation of recycled water programs.There are pending amendments to the Judgment that would enhance groundwater reliability inthe basin. The Watermaster has determined that its 1973 Judgment may require changes toreflect the current conditions and allow the Watermaster more flexibility in securing necessarysupplemental supplies. The Watermaster expects proposed changes to be finalized andsubmitted to the Los Angeles Superior Court for approval after FY 2010-11 (Watermaster 2010).Page 6-4Final Report, 2010 Urban Water Management Plan – San DimasGolden State Water Companyg:\adminasst\jobs\2010\1070001.00_gswc-uwmp\09-reports\9.09-reports\2011-08\grp2b\gswc_sandimas_2010_uwmp-final.doc