ARCHIVED REPORTS XR0012563 - Laserfiche WebLink

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-d'"_ ._ `=T x sfi Ms. Diane Hinsoa March 6, 1990 Page 2 August 1, 1989 HY ngeoloecAssra'sineni Work Plan was submitted!o San Joaquin county c,)ntaining a description of proposed monitoring well installation. September 6, 1989 :oil Maaagentenr Plan for Taint Replacement was submitted to San Joaquin County describing soil sampling and disposal of soils generated from old and new tank excavations. November 14, 1989 Four underground storage tanks were excavated and removed from the site. Soil samples were collected from the former tank, new tank, and waste oil tank ex:avations. Soii samples were also collected from former product line trench locations. December 11 and 12, 1989 Five soil borings were advanced to 40 feet below grade and completed as monitoring wells MW-1,NIW-2, MW-3, MWA, and MW-6. E January 10, 1990 Two soil borings were advanced to 40 feet below grade and completed as monitoring welts MW-5 and MW-7. Approximately 10 gallons of free petroleum product were removed from MW-2. January 26, 1940 Approximately 10 gallons of free petroleum product were removed from monitoring well MW-2 and 1 gallon of product was removed from MW-7. January 30, 1990 A Tank Closure Report was submitted to San Joaquin County summarizing soil sampling activities during the tank replacement. Januo;y 31, 1990 Site visits were made by Delta to remove product from monitoring well February 9 and 13, 19% MW-2 and MW-7. January and A manifold piping system was installed to convey compressed air,ground February 1990 water,and soil vapor vacuum to existing monitoring wells(MW-2,MW-3, MIW-i,MW-5,and MW-7)for future remediation,if required. piping was installed in conjunction with station reconstruction. Soil Horines and hionitorine Wells During the months of December 1989 and January 1990 Delta advanced a total of sever, soil borings to a depth of 40 feet below grade and completed each boring as a ground water monitoring well (MW-1 through MW-7). Monitoring well locations are illustrated in Figure 2. The methods used to drill and sample the soil borings are described in Enclosure A. Soil boring logs containing detailed descriptions of soil conditions are included in Enclosure B. Information gathered from the soil borings advanced by Delta indicate the soils underlying the site from the surface to 25 feet below grade consist predominately of sandy and clayey silt. A silty sand unit was encountered between approximately 25 and 35 feet below grade. Interbedded sand units were encountered between approximately 30 and 40 feet below grade. A gravel backfill was present to a r depth of 14 feet below grade in the vicinity of boring MW-2,where the former gasoline storage tants were Iocated. Soil cross-sections have been prepared to illustrate the inferred subsurface relationships.