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Problem Assessrnerlt Report USA Petroleum Station No. b5, Lodi, California December 5, 1989 - AGS 87050-3 blooms,under closely monitored conditions, cause lite reduction of adsorbed and dissolved Phases of subsurface hydrocarbon contamination, particularly in the vadose zone. Further reduction of contaminan#s occur in the saturated zone by using groundwater extraction and treatment to control file environmental conditions and to reduce the dissolved phase of contaminants. Each site must be evaluated prior to the implementation of all insitu bioreclamation program. The local hydrogeology, contaminant concentrations, aril soil microbiology are incorporated into fire construction of an in situ bioreactor. The main components of this method of treatment include (1) recoverywells to maintain hydraulic control and a closed operatin-- system; (2) an aboveground water treatment system to remove volatile components from the recovered water; (3) an infiltration system to return the cleaned ground water, augmented with oxygen and the necessary nutrients, into the contaminated zones.and(4)a closely supervised monitoring program to verify contaminant reduction and healthy bacterial growth. The time necessary to obtain satisfactory clean-up levels is generally shorter using in situ . bioremediation than with groundwater recovery and treatment; however, the costs associated with this method are generally higher during the first year of operation. Additional assessment of the aquifer characteristics, such as pump tests and the existing lire bacterial populations is required prior to selecting this remediation alf.ernativc. x � Carbon or tion Carbon adsorption is based on the natural tendency of a gas or liquid to be -attracted to and ! held at the surface of a solid. Activated carbon particles are characterized by very large T ratios of surface area to volume. Carbon adsorption is quite effective at removing organic compounds from water streams. i - F Activated carbon requires replacement or regeneration after. it is fully charged with additional hydrocart!ons. The frequency of the replacement will depend on organic loading, contaminated liquid flow rates, and the desired effluent objectives. The spent carbon must be disposers of at a Class I waste disposal site or regenerated. The cost associated with treatment solely by carbon adsorption will be evaluated but is often found to be prohibitive € : when compared to other equally effective methods. Direct Disch_ch_aree After hydrocarbon-contaminated water is removed from the subsurface, direct) to an a ce, �t can be released ; Y approved discharge site. The limiting factors of this metftod of disposal ace requirements,for-flow rates-and-contaminant-discharge-concentrations unposed by the 2 'GOPOS-Astems --