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southeast, towards the Stanislaus River The site specific groundwater gradient is in <br /> contrast to the westward regional gradient Uncertainty exists regarding the lateral <br /> distribution of hydrocarbons impacting groundwater in light of the current groundwater <br /> gradient, and suggests offsite contamination or seasonal variations in gradient <br /> direction <br /> The extent of soil and groundwater contamination deems that remedial measures are <br /> necessary In-situ soil vapor extraction, in concert with air sparging techniques, is the <br /> recommended remedial alternative for the site conditions and chemical constituents at <br /> this location <br /> 20 BACKGROUND <br /> This section provides a discussion on the site location and historical background <br /> 21 Facility Descnption <br /> The site, Thiemann's Service, is located at 106 West Second Street, in the City of <br /> Ripon, San Joaquin County, California as shown on Exhibit 1 The property is shown <br /> in detail on Exhibit 2 The property houses one building currently used for office and <br /> service garage Formerly located at the site were two dispenser islands, two (2) 5,000 <br /> gallon leaded gasoline underground storage tanks and one (1) 10,000 gallon leaded <br /> gasoline underground storage tank <br /> • <br /> 22 Project History <br /> On March 26, 1991, SEMCO removed three (3) underground storage tanks from the <br /> subject site The tanks consisted of two (2) 5,000-gallon leaded gasoline (Tanks 1 & <br /> 2), and one (1) 10,000-gallon leaded gasoline (Tank 3) Soil samples were collected <br /> from beneath the removed tanks on both the east and west ends The samples <br /> collected were analyzed for Total Petroleum Hydrocarbons as gasoline (TPHg), <br /> Volatile Aromatics (BTEX), Total Lead, and ethylenedibromide (EDB) The results of <br /> the laboratory analyses are summarized in Table 1 <br /> 3 of 17 <br />