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... Geological Audit Services, Inc. �ONE" 1803 W. March Lane, Suite A •Stockton, CA 95207• (209) 956-0264• FAX(V944 .1 PROPOSED MITIGATION OF HYDROCARBON CONTAMINATIOAX :+ j ^1 AT ARCO MINI MART 4511 Pacific Avenue CNWRCNt,4E TAi MEALTri Stockton, California PERM17ISERViCES EXECUTIVE SUMMARY On February 19, 1991, unleaded gasoline was discovered pooling on the concrete pad between the center and northerly pump islands of this service station at 4511 Pacific Avenue. FALCON ENERGY, a Stockton Environmental Services firm, was contacted for assessment. FALCON excavated a trench in the area of the leak and subsequently located a hole in a coupling in one of the fuel lines. After repairing the damaged line, FALCON collected two soil samples for laboratory analysis. Both samples were contaminated, indicating that an unknown quantity of gasoline had leaked into the ground directly under the damaged pipe. FALCON has retained GEOLOGICAL AUDIT SERVICES to assess the extent of contamination and devise a remediation plan. Three soil borings will be drilled around the leak area and soil samples will be taken to determine the depth and extent of the contamination. Soil samples will be analyzed by a state-certified environmental testing laboratory. After sampling, the borings will be plugged and capped and the area will be repaved. One of the borings may be converted to an extraction well for later use in extracting gasoline vapors from the soil. If the volume of contaminated soil is fairly small and does not extend more than 30 feet in depth, the soil will be excavated and stored on site for three to four weeks while samples are collected and analyzed. The soil will then be transported to a suitable landfill facility. If the volume of soil exceeds the storage capacity of the site or the depth of contamination exceeds 30 feet, a vacuum--extraction system will be utilized to remediate the site. This system uses a catalytic-converter-equipped internal combustion engine to volatilize the gasoline and burn the hydrocarbon vapors. Fresh air is enters the ground through an array of injection wells, and an engine-driven blower is used to withdraw vapor-laden air from the soil through one or more extraction wells. The vapor is piped into the engine, passes through a filter to the carburetor, and is burned. A computer controls the fuel-air mixture. The catalytic converter oxidizes the hydrocarbons and carbon monoxide and reduces nitrogen oxides. Several such systems are currently in use or in trial programs in San Joaquin County and elsewhere. The extraction program commonly operates for six to twelve months. Environmental Services•Hydrogeology•Geotechnical Services