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r BIOSYSTEMS MANAGEMENT HEALTH INTERNATIONAL 360 OYSTER POINT BLVD.,SUITE 11C�EMAO ,CA 94080•(415)589-7171 September 1, 1988 Mr. David Carls San Joaquin Local Health District 1601 E. Hazelton Stockton, CA 95205 RE: New locations for monitoring wells at Stockton Scavenger trucking facility. Dear David: The following is pursuant to our phone conversation of August 31, 1988 regarding the modification of the groundwater monitoring plan at the Stockton Scavenger trucking facility in Stockton, CA. The changes have been made as a result of review by your department and the Central Valley Regional Water Quality Control Board (CVRWQCB) . The locations of the three groundwater monitoring wells will be as shown in the attached figure. These locations have been chosen for their ability to calculate a gradient for groundwater flow at the site and also to best determine the existence of contamination. In addition, the material to be used for well casing has been changed from 2-inch diameter, schedule 40, Poly Vinyl Chloride (PVC) to 2-inch diameter stainless steel for two of the wells. This change has been made due to the new locations of the wells which has placed them in areas where groundwater contamination is suspected. PVC casing has a tendency to become pliant and eventually falter in the presence of organic pollutants. The perforations in the well casings will be . 010 inch and will extend to a depth of 15 ft. below groundwater or until a 5 foot clay aquitard is encountered. In addition, the screened interval will extend to a minimum of 10 feet above the water table to account for seasonal var- iations in water table elevation. A five foot sanitary bentonite seal will be placed above the filter pack with the remaining annular space filled with a cement bentonite slurry. (1)