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California egional Water Quality Control Board <br /> Central Valley Region <br /> (� Steven T. Butler, Chair <br /> Winston H.Hickox "�� Gray Davis <br /> Secretaryfor Sacramento Main Office Governor <br /> Environmental Internet Address: http://www.swrcb.ca.gov/—rwgcb5 <br /> Protection 3443 Routier Road,Suite A,Sacramento,California 95827-3003 <br /> Phone(916)255-3000•FAX(916)25340 l 5' ;%', P M 2 38 <br /> 18 August 1999 <br /> Mr. William Little <br /> Advanced GeoEnvironmental, Inc. <br /> 4005 North Wilson Way <br /> Stockton, CA. 95205 <br /> VOLPI FARM: REVIEW OF WORK PLAN, 14210 WEST STATE ROUTE FOUR, STOCKTON (San <br /> Joaquin County) <br /> Staff has reviewed the work plan for ground water monitoring well installation and interim soil <br /> remediation, prepared by Advanced GeoEnvironmental for work at Volpi Farm. Work proposed <br /> includes excavating impacted soil, installing six groundwater monitoring wells, and collecting <br /> groundwater quarterly groundwater samples for one year. Analyses proposed are: total petroleum <br /> hydrocarbons as gasoline by Method 8015M, benzene, toluene, ethylbenzene, and xylenes (BTEX) by <br /> Method 8020, and fuel oxygenates by Method 8260. <br /> Overall this proposal is acceptable, subject to the following comments. The comments are based on <br /> review of the work plan and on telephone conversations with staff of Advanced GeoEnvironmental. <br /> Detailed comments are found in the attached memo. <br /> 1. Groundwater conditions and site conceptual model: Adequate hydrogeologic information on this site <br /> is lacking. As discussed in the attached memo, staff understands that the site is characterized by <br /> approximately 5 feet of peaty soil overlying silty clay that extends to at least 8 feet below grade. <br /> Groundwater apparently occurs under semi-confined conditions, rising in excavations from a depth of 8 <br /> feet below surface to 5 feet below surface. Tidal conditions and seasonal changes in groundwater depth <br /> and gradient may exist. The relationship of an irrigation ditch on the south side of the site to <br /> groundwater is unknown. <br /> 2. Need To Achieve Full Characterization Of Extent Of Soil Impacts:. If feasible,the entire lateral and <br /> vertical extent of contamination should be determined and impacted soil removed. Sidewalls and base <br /> of the excavation should be field screened and adequately sampled and analyzed for all constituents of <br /> concern (COCs). In situ remedial actions may be required if significant contamination is left in place. <br /> Further, clean fill materials placed in a contaminated pit may in future be considered contaminated waste <br /> materials themselves. Field activity logs should document the basis of the decision to cease excavation. <br /> 3. Monitoring Well Construction and Installation: Six monitoring wells constructed of two-inch i.d. <br /> Schedule 40 PVC are proposed, with five-foot screens extending from about 10 to 15 feet below surface. <br /> This construction appears reasonable based on the site model, although such a screen placement is likely <br /> to miss any floating product that may be present or be mobilized by fluctuating water levels. If cross- <br /> California Environmental Protection Agency <br /> Ot Recycled Paper <br />