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i� Advanced �- GeoEnvironmental, Inc . ; rtt Northcrn C alillwnia 28 October 1997 AGE-NC Project No. 95-0103 Mr. Russell Chapin CHAPIN BROTHERS INC. 1203 North Carlton Avenue Stockton- California 95203 Subject: Soil '%7apor Extraction/Air-Sparging Operation - Status Update CHAPIN BROTHERS INC. 1766 Monte Diablo Avenue, Stockton, California Dear Mr. Chapin: In accordance with your request, we are providing the following update concen-iing the operation of the SVE unit and the remediation effectiveness at the subject site: SITE CONDITIONS • Between the time of preparation of the Problem .4ssessinent Reports (PAR) and Final Remediation Plan (FRP) and initiation of the recommended and approved remediation system at the site, the elevation of ground water increased dramatically. The rise of ground water elevation has reduced the volume of the vadose zone, thereby changing the projected soil vapor removal effectiveness and duration. During feasibility testing, sand, silt and clay units were exposed to wells with screened portions in the vadose zone. Under the current regime of elevated ground water levels, silt and clay units are primarily exposed to the screened portions of the vadose zone. The loss of the more permeable sand units from the vadose zone, and thereby from the SVE network, has increased the resistance of the hydrocarbon vapor to movement out of the soils. • Due to the increased ground water elevation, the major portion of the hydrocarbon impacted soil at the site is currently in the saturated zone, increasing the volume of impacted soil requiring stripping of hydrocarbons by in-situ air sparging (IAS); and increasing the effort and time for the overall removal of hydrocarbons from the submerged impacted soils. 1803 West March Lane, Suite A. Stockton, California 95207 Telephone (209)956-0264 FAX (209)956-0700