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9110 Thornton Road, Stockton, California September 2, 1994 .i The Southland Corporation Page 2 Soil Contamination From February 1987 through January 1991, a sod vapor extraction system was In operation at the site During operation, a 100-cubie4eet-per-minute (cfm) blower was in use On January 13, 1994, a vapor extraction test was conducted using a 1 5-horsepower (hp) blower During the test the maximum measured flow rate was 83 cfm The test blower produced Induced vacuum of 0 1 inch of water column at 100 feet from the test well The linear regression graph on Figure 10 of the Addendum to Closure Report indicates that there was pressure (vacuum) gradient to at least 100 feet from the vapor extraction well The slope of the line on the graph represents pressure gradient which induces vapor flow The calculated radius of capture of 100 feet given in the report is a conservative estimate based on data collected during a short term test and based on laws of physics Sod samples collected from confirmation sod borings drilled on January 12, 1993, did not contain petroleum hydrocarbons at concentrations above detection limits Analysis of vapors collected during the January 1994 soil vapor extraction test did not contain benzene The maximum concentration of TPH-G detected in the sod vapors was 74 micrograms per liter and the hysirocarbon extraction rate during_ a k�nef tey st was a pproximately_U5 lbs q4y Typically, however, hydrocarbon concentrations drop rapidly with time when vapor extraction is initiated after a prolonged time of no vapor extraction, and the concentrations reach low asymptotic levels within a few hours or a few days The data indicate that low concentrations of petroleum hydrocarbons exist locally in the vadoze zone, but the results of sod analyses indicate that detectable levels of adsorbed hydrocarbons are not present In the sod Summary Sod vapor extraction was used to remediate the site from February 1987 through January 1991 The remediation system was turned off because hydrocarbon concentrations from the sod vapor extraction system had reached low asymptotic levels It is the opinion of Southland that the concentrations of remaining petroleum hydrocarbons in the soil are not sufficient to impact the groundwater Furthermore, groundwater sampling indicates that while low concentrations of petroleum hydrocarbons are present in groundwater, the random minor occurrences in one well do not constitute a measurable plume, do not demonstrate migration, and are not a threat to public health now and will not be a threat to public health in the future The Southland Corporation does not concur with the San Joaquin County's opinion as stated in the July 12, 1994 letter and wishes to appeal this matter to the Central Valley Regional Water Quality Control Board (CRWQCB-CVR) A copy of this letter will be submitted to the CRWQCB-CVR as a basis for beginning a formal technical appeal to that agency ❑❑� GROUNDWATER ❑❑❑ TECHNOLOGY