Laserfiche WebLink
4 2.0 Background <br /> Two underground storage tanks (USTs) have been the focus of soil and groundwater <br /> investigations conducted at the Site, beginning in 1985 A detailed history of investigations <br /> and planning are discussed in the report titled "Evaluation of Hydrocarbon Mobility" <br /> 1 (Dames & Moore, 1995a) <br /> The former UST locations are identified on Figure 2 The former diesel UST located <br /> adjacent to DMW-4 had a reported capacity of 10,000 gallons The former waste oil tank <br /> located adjacent to DMW-5 had a reported capacity of 500 gallons <br /> The USTs were removed in 1988 (Dames & Moore, 1988) A survey of groundwater wells <br /> in the vicinity was conducted as part of the 1988 report, and results are summarized in <br /> Appendix B Soil excavation was conducted in 1990 (Dames & Moore, 1990) Excavations <br /> were completed to 26 feet below grade at the former diesel tank, and 22 feet below grade <br /> at the location of the former waste oil tank Remedial activities are summarized in the Site <br /> Remediation Report (Dames & Moore, 19926) <br /> An assessment of contaminant mobility (Dames & Moore, 1994a) concluded that there was <br /> no significant risk to impact groundwater at the Site, and recommended a 5-year monitoring <br /> program, followed by closure Remediation options were assessed in 1994 (Dames & <br /> Moore, 1994b) An additional evaluation of hydrocarbon mobility was prepared by Dames <br /> & Moore in 1995, and concluded that the residual TPH-D in soil was relatively immobile <br /> and did not represent a threat to groundwater (Dames & Moore, 1995a), assuming that the <br />' groundwater remained at levels observed in 1990-1994 (60 to 70 feet bgs) <br /> A 5-year groundwater sampling and water level monitoring program was initiated in <br /> September 1996 (Dames & Moore, 1996) The most recent sampling event was conducted <br /> in July 1998 (Dames & Moore, 1998b) Although TPH-D has not been detected, the <br /> groundwater level has risen from a maximum depth of approximately 68 feet below grade <br /> in 1991, to the July 1998 level of approximately 38 feet below grade Given the rising <br /> groundwater levels throughout the Stockton area, PHS-EHD requested installation of <br /> addition wells screened across the groundwater surface The initial results of work <br /> conducted by Dames & Moore on behalf of AFPC in response to PHS/EHD requirements <br /> are presented in this document <br /> • <br /> DAMES&MOORE 2 R\sac)044misc19902_03 doc <br />