ARCHIVED REPORTS_XR0007731 - Laserfiche WebLink

Home Browse Search

5` a+ ti • activities resulted in the loss of wells MMI, MW3, VWl and VW2 which were located in close proximity to the former and new tank clusters In December 1994 and June 1995, Thnfty conducted a comprehensive subsurface investigation that included installation of four groundwater monitoring wells, six vapor wells, and three soil borings at the site Also, as part of site reconstruction, several underground Ines were installed from select groundwater and vapor wells to a proposed treatment compound area located in the southeastern corner of the site These lines were intended as vapor extraction and groundwater recovery lines for use in a remediation program Details from investigations performed prior to site reconstruction are presented in Thnfty's Site Assessment Report dated January 17, 1992 The most recent investigative results are presented in Thrifty's Site Assessment report dated July 24, 1995 The analytical results from soil sampling are summarized in Table 1 Analytical results from the most recent groundwater sampling are presented in Table 2 Based on the drilling logs, sediments beneath the site consist mostly of silty clay and clayey silt, with interbedded minor layers of silty sand, from the surface to approximately 65 to 70 feet bgs At this depth a sand layer occurs which is approximately 5 to 10 feet thick and contains various • fractions of silt and clay Underlying the sand layer at approximately 75 feet, the section is characterized by the silty clay/clayey silt sediments typical of the upper section to at least 90 feet bgs Figures 3A and 3B are geologic cross sections which show the generalized lithologic relationships The drilling logs contain descriptions of the sediments encountered and are presented in Appendix A Since 1988 when the first wells were installed at the site, the depth of groundwater has fluctuated substantially During dnthng in 1988, the depth to groundwater was measured to be approximately 50 feet below grade In November 1992, groundwater was encountered at about 80 feet below grade, indicating a significant drop in the groundwater elevation had occurred Because of this decrease in the water table elevation, none of the original wells (MW1-MW3) contained groundwater and only wells MW3R, MW4, MW5 and MW6 were available for groundwater monitoring In 1993, the depth to groundwater fluctuated slightly with a depth to water of about 70 feet generally observed In 1994, the Page 2