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MEMORANDUM i ' �QAL'IFORNIA REGIONAL WA`fER QUALITY CONTROL BOARD•CENTRAL VALLEY REGION 3443 Routier Road, Suite A Phone: (916) 361-5600 Sacramento, CA 95827-3098 ATSS Phone: 8-495-5600 TO: GORDON L. BOGGS FROM: ELIZABETH A. THAYER UGT Program Coordinator Associate Engineer / DATE: 30 March 1992 SIGNATURE: �4 SUBJECT: REVIEW OF FINAL REMEDIAL ACTION WORK PLAN, 16 SOUTH CHEROKEE LANE, LODI, SAN JOAQUIN COUNTY I have reviewed the "Final Remedial Action Work Plan" (FRP) , dated 2 January 1992, prepared by Geological Audit Services, Inc. (GAS) for Geweke. The proposed remedial actions consist of soil vapor extraction, incineration of the extracted vapors, ground water extraction and carbon filtration, and reinjection of the treated ground water. However, the FRP was incomplete. The attached figure shows existing monitoring wells and the extraction well . My comments follow: 1 . Figures showing the extent of soil and ground water contamination were not provided. 2. On page 5 of the FRP, in a discussion of the soil vapor extraction system, GAS stated that when the vapor recovery system achieves 500 ppm as hexane, confirmatory soil samples will be collected. This value is not a soil cleanup limit used by the Central Valley Regional Board. When non-detectable levels of contamination have been achieved by a vapor extraction system, the vapor extraction system is to be pulsed or surged to determine if soil contamination remains. If contamination is not detected, then confirmatory soil borings are then drilled and soil samples collected for laboratory analysis. The extraction system must also be pulsed or surged if the extracted vapor concentrations have reached a plateau. Additional soil remediation techniques may be necessary if soil contamination levels cannot be reduced by pulsing. 3. The vapor extraction wells proposed in the FRP will be screened from 4 feet to 70 feet. In the vicinity of MW-4, where soil contamination is extensive, long screen lengths may be appropriate due to the sandy soil at the site. Long screen lengths provide a larger volume of soil to which a vacuum must be applied which means a more powerful vacuum must be applied to the extraction well . In addition, long screen lengths may extend through varying lithologies creating a short circuit effect where vapors move more easily through the more porous soils, such as sands and gravels, and bypass finer soils, such as clays and silts. In the soil above the ground water zone, hydrocarbons will be more concentrated in clays and silts than in sands and gravels, therefore, when the clays and silts are bypassed, contaminants may be left behind. 4. The proposed soil vapor extraction system is limited to the vicinity of MW-4. However, wells MW-1, -3, and -5, previously contained significant ground water contamination but are now dry. The proposed