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1 <br /> Preliminary Subsurface Investigation <br /> City of Stockton, former Western Pacific Railroad Property,Stockton, CA <br /> May 27, 1992 <br /> W0601 AD <br /> A more recent groundwater quality investigation (1990) was obtained from the SJCFCD. The <br /> City of Stockton is divided into three different regions for the purpose of evaluating groundwater <br /> ' quality: Stockton North, South, and Central. The subject site is located on the border of the <br /> Central and South areas. Samples collected from five wells in the Stockton South area indicated <br /> ' that water quality has declined due to increases in both chlorides and TDS. The SJCFD data <br /> is similar to the USGS sample results. Very high TDS levels occur (up to 6120 mg/P) and <br /> chloride levels are as high as 1,959 mg/P. The analytical data is presented in Table D-2. <br /> Appendix D includes the section referenced herein from the SJCFCD report. <br /> Additionally, the computer search of environmental records identified two wells in the township <br /> ' and range coordinates of 1 North and 6 East listed on the State of California's Well Investigation <br /> Program (WIP or A131803) database (Appendix D). Both wells belong to the California Water <br /> Service in Stockton. The well identification numbers are 01N/06E-11KO1M and O1N/06E- <br /> 11P03M, and contain 1.70 ppb bromoform and 0.90 ppb bromodichloromethane, 4.1 ppb <br /> ' chloroform, 0.70 ppb dibromochloromethane, and 4.7 ppb total trihalomethanes (THMS), <br /> respectively (Appendix B). <br /> The Stockton area has long been recognized as having water quality problems. Deeper wells <br /> routinely exceed the secondary drinking water standards for chloride, iron, manganese, and <br /> TDS. Shallower wells have even poorer quality water due to the additional affects of infiltrating <br /> surface water (DWR, 1967). <br /> Several sources have been identified for the observed poor water quality. These include connate <br /> ' water contained within fine grained Deltaic sediments, tidal action through the Delta, and <br /> improperly sealed gas wells that tap deeper saline water zones. Thirty four abandoned gas wells <br /> were identified by DWR (1967) but it is believed many more exist. <br /> R041392.SAV 6 <br />