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Addendum To The Problem Assessment Report 2 Ranch Market 23564 Santa Fe Road Riverbank California DeCLmher 18 2000 feet and 30 feet deep have been prepared and are presented in Table 1, Option I SECOR does not recommend this remedial approach Option 2 Passive Biodegradation Passive biodegradation does not address migration of dissolved MtBE or the gasoline adsorbed to soil in the vadose zone The cost estimate presented in Table I assumes 20 years of quarterly groundwater monitonng and sampling SECOR does not recommend this remedial approach Option 3 In-situ Biologic and/or Chemical Treatment In-situ bioremediation or chemical treatment was eliminated because it would not be effective in the destruction of hydrocarbons in the vadose zone In-situ destruction of hydrocarbons in the groundwater may be used to supplement operation of the SVE/AS system Methods of in-situ treatment include 1) Injection of nutrients and cultured bacteria to stimulate biologic activity, and 2) Injection of chemical oxidizers such as peroxide or ozone to directly destroy hydrocarbons and to stimulate biologic activity by increasing the dissolved oxygen concentrations The cost estimate assumes a total of 10 injection events will be performed and a total of 15 years of groundwater monitoring and sampling will be needed before closure is granted Since this option does not address vadoes contamination, SECOR does not recommend this remedial approach Option 4 Soil Vapor Extraction combined with Air Sparging Based on results of the SVE test, operation of a SVE system will effectively remove the gasoline . adsorbed to soil within the vadose zone Operation of the air sparging may strip dissolved gasoline from the groundwater The air sparging will also increase the dissolved oxygen concentration in the groundwater and stimulate the in-situ destruction of gasoline by aerobic bacterial activity Based on the fourth quarter groundwater monitoring and sampling data, it appears the air sparging may have resulted in lateral transport of dissolved gasoline range hydrocarbons to the perimeter wells (Attachment 1, Table 2) Given the groundwater sample data, initial air sparging rates must be very low to avoid the lateral transport of dissolved gasoline range hydrocarbons The costs associated with installation and operation of an SVE/AS system for 3 years has been included in Table 1 Using an SVE radius of influence of 40 feet, a total of 10 soil vapor extraction wells are proposed to remove the hydrocarbons from the vadose zone and to capture the air injected into the air sparging wells Assuming a 30-foot radius of influence for the air sparging wells, a total of 7 air sparge wells are proposed to either remove or stimulate in-situ biologic destruction of the petroleum hydrocarbons in the saturated zone The assumed 3 year run time is conservative and may actually be less than two years Due to the apparent lateral transport of dissolved gasoline compounds during the air sparge test, SECOR does not recommend using aggressive air sparging combined with SVE at the site Option 5 Soil Vapor Extraction combined with Ozone Sparging Based on results of the SVE test, operation of a SVE system will effectively remove the gasoline adsorbed to soil within the vadose zone The ozone sparging will chemically destroy the File Ranch Market)PAR-Cost Est i doc