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Report Seeond phue Subsurface tnvestiption <br /> City of Stocison,Benne*IsWW,Stwhton, CA <br /> May 20, 1992 <br /> W06MAD <br /> groundwater zone has been impacted even further eastward and at higher levels than the lower <br /> strata (DWR, 1967). <br /> Information obtained from the USGS' database included construction details, water elevations, <br /> and chemical data of water wells in the vicinity of the subject site based on the topographical <br /> township and range coordinates of 1 North and 6 East. Fifty-two wells were found in the USGS <br /> database search. Completed well depths ranged from 12 to 652 feet below grade. Screened <br /> intervals ranged from 10 to 12 feet below grade in the shallowest well and from 233 to 314 feet <br /> below grade in the deepest well. Depth to water measurements were conducted between 1953 <br /> and 1975 and levels ranged from 6 to 120 feet below land surface datum. Samples were <br /> collected between 1969 and 1979 from seven of the wells in the area and were submitted for <br /> chemical analysis. The sample data shows total dissolved solids (IDS) levels as high as 1,770 <br /> !` mg/I and chlorides as high as 1000 mg/l. Three of the seven wells exceed the 500 ppm <br /> secondary MCL for chlorides. The secondary drinking water standards for iron and manganese <br /> are also exceeded routinely. The chemical analyses are presented in Appendix B, Table B-1 and <br /> the data is included in Appendix B. <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/t) and <br /> chloride levels are as high as 1,959 mg/l. The analytical data is presented in Table B-2. <br /> Appendix B includes the section referenced herein from the SJCFCD report. <br /> R040992-SAY 5 <br />