SITE INFORMATION AND CORRESPONDENCE FILE 2

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a.. � envirOS(.) October 8, 1997 . 1 Ms. Mary Meays San Joaquin County Public Health Services P.O. Box 388 Stockton,California 95201-0388 RE: Shell Service Station 2575 Country Club Blvd. Stockton, California WIC 204-7525-3505 Dear Ms. Meays: This letter is prepared in response to San Joaquin County Public Health Services (SJCPHS) correspondence dated September 15, 1997. Cone Penetrometer Proposed Depths and Sampling Methodology Three cone penetrometer(CPT) borings have been proposed in Enviros' September 9, 1997 Revised Site Assessment Work Plan to evaluate lithology prior to installation of deeper ground water zone monitoring wells. The location of each CPT boring will be the same as the location of the proposed deep monitoring wells. The attached Extended Site Map legend has been updated to indicate this (Plate 2). Soil samples will not be collected during the drilling of the CPT borings. The CPT equipment interprets the lithology of the boring through measuring physical qualities of the soil it is penetrating. Although soil sampling is possible with CPT, it is a lengthy process involving a separate boring for each sample interval. Soil samples will be collected during the drilling of the deep wells with the hollow-stem auger drilling rig. The depth of the on-site CPT borings will be determined by the lithology encountered. The goal of each CPT boring is to determine where the deeper ground water zone occurs. The deep monitoring wells, which will be drilled at a later date, will be screened in the deeper ground water zone identified in the CPT borings. The proposed off-site CPT boring location has been moved slightly from the location shown on the September 9, 1997 work plan. Enviros met with the owners of the property at 2452 Country Club Boulevard(the Boardman's)to discuss placing the CPT boring and the deep monitoring well on their property -off of the common driveway. The Boardman's agreed to allow the CPT boring and deep monitoring well to be placed on their property in the driveway or in the grass adjacent to the driveway. This location has also been updated on the Extended Site Map (Plate 2). The proposed depth of this off-site CPT boring will be extended to 130 feet below grade to evaluate the lithology that the domestic wells may be constructed in. This boring will also be used to determine the depth at which the deep monitoring well screened interval should be placed. Envlles. ho, 270 Perkins Street Sonoma, California Tel 7071935-4850 P.O.Box 259 95476-0259 Fax 707/935-6649