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i WORKPLAN LATHROP PROPERTY WALLACE.KUHL&ASSOCIATES.INC. WKA No. 1184.02 October 30, 1990 Page 2 Proposed Scope of Work The scope of our work for the property will include the excavation of soils in the area indicated by our borings to be contaminated, as shown on Plate 1. The excavation will extend laterally until the point of zero contamination is reached or until excavation is limited by the property boundaries; the excavation will extend vertically until ground water is encountered. The southerly extent of the excavation will be no closer than eight feet to the northerly edge of Thomsen Road. Soils will be screened in the field using an organic vapor analyzer (OVA) and samples will be obtained of the sidewalls and bottom of the final excavation and of the stockpiled soils for laboratory testing. The resulting excavation will be backfilled with clean soil upon approval by the County. Excavated soils will be stored on 10-mil polyethylene and covered until remediation/disposal options are evaluated. Subsequent to excavation and backfilling procedures, we propose a preliminary ground water investigation to determine if the ground water beneath the site has been contaminated by petroleum hydrocarbons and to establish the local hydraulic gradient beneath the property. Three ground water monitoring wells will be installed on the property at the locations shown on Plate 1. Our preliminary estimate of the local ground water gradient is southerly to southeasterly, based on the "Spring 1990 Lines of Equal Elevation of Water in Wells map"prepared by the San Joaquin County Flood Control and Water Conservation District. Soil samples will be collected during drilling of the wells at minimum five-foot vertical intervals. Ground water is expected to be encountered at a depth of 10 to 15 feet below grade. The ground water monitoring wells will extend a minimum of ten feet below the first encounter of ground water (see Plate 2 for well construction diagram). After installation, the wells will be developed, sampled and surveyed to mean sea level for determination of the gradient. Well completion details and development and sampling procedures are appended. Ground water purged during well development and sampling will be stored in sealed 55-gallon drums until laboratory tests have been completed. We then will make provisions for the appropriate disposal of any contaminated ground water. Contaminated soil encountered during drilling will be placed with the stockpiled soil from the excavation. The materials encountered during drilling will be logged by an experienced field geologist and all work will be performed under the direct supervision of a registered geologist. Subsurface soil samples will be obtained in accordance with EPA and San Joaquin County protocol. After the field investigation has been completed and we have evaluated the laboratory data, a report will be prepared which will include: • a site plan showing locations of monitoring wells • logs of monitoring wells