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• • • 139 South Center, Stockton, California April 27, 1993 Chevron U.S.A. Products Company Page 2 spoon sampler lined with 2-inch-diameter by 6-inch-long brass sample tubes. Each soil sample will be screened for volatile organic compounds (V.O.C.) utilizing a photolonization detector (P.I.D). The soil samples will be logged using the Unified Soil Classification System by a Groundwater Technology field geologist, working under the supervision of a California registered geologist. One sample from every sampling interval will be sealed with aluminum foil, capped, taped, labeled, and placed on ice in an insulated container. All soil generated through drilling will be placed in Department of Transportation (DOT)-approved steel drums and stored on the Chevron site pending characterization and disposal. Groundwater Technology will select an appropriate number of soil samples from the soil boring utilizing the previously noted field screening techniques. Each sample will be analyzed by a State-certified laboratory for benzene, toluene, ethylbenzene and total xylenes (BTEX), and total petroleum hydrocarbons-as-gasoline (TPH-G) by EPA-approved methods 5030/8020/8015. Groundwater Technology personnel will install a groundwater monitoring well within the soil boring (MW-6). The well will be constructed of 2-inch diameter, schedule 40 PVC casing with flush threads and 0.020-inch-slot well screen. The well screen for the monitoring well will be installed approximately ten feet above and fifteen feet below the current water table to permit entry of separate-phase hydrocarbons (SP), if present. A sand filter will be placed around the well screen to a height of two feet above the top of the screen. The well will be completed with a bentonite seal and lean cement grout to grade. The wellhead will be protected by a locking cap and a traffic-rated street box with a water-tight bolted lid. TASK 3: WELL DEVELOPMENT / SURVEYING / GROUNDWATER MONITORING The monitoring well will be developed to remove fine-grained sediments from the well and filter pack. Water from the development process will be removed from the site in a DOT-approved purge water trailer and transported for recycling to the Chevron refinery in Richmond, California. In the days following the development procedure, the water table will be monitored to determine static levels and the thickness of any SP, if present. The water table levels will be measured using an ORS Environmental Equipment INTERFACE PROBETM Well Monitoring System, consisting of a dual optical sensor and electrical conductivity probe, that distinguishes between water and petroleum products. Top of casing (TOC) and horizontal position of the well will be surveyed relative to an established or assumed benchmark. The survey data will be used together with depth to water measurements to determine water table elevation in the monitoring well and the local groundwater flow direction. TASK 4: WELL PURGING / WATER SAMPLING / ANALYSIS Subsequent to groundwater monitoring, three to five well casing volumes will be removed from the well prior to sampling. Measurements of temperature, pH, and conductivity will be taken to assure that representative formation water is present in the well prior to sampling. Groundwater Technology Personnel will collect groundwater samples from the newly installed monitoring well. Each water sample will be analyzed for BTEX, and TPH-G, using previously mentioned EPA-approved methodologies. TASK 5: REPORT PREPARATION Groundwater Technology will prepare an assessment report summarizing the data collected. The report will include descriptions of all methodologies, laboratory results and suitable graphics. _ _ C GROUNDWATER TECHNOLOGY