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October 13, 1992 BP Oil Facility No. 11191, Stockton;California Working To-Restore Nature If ground water is encountered above 45 feet below grade,:ground water monitoring wells MW-1 through MW-4 will be constructed in the four soil borings. Each well will be constructed of two- inch diameter,schedule 40 PVC casing with.flush treads and 0.020-inch-slot well screen. The Well screen for each of the monitoring wells will be installed approximately five feet above and ten feet below the current water table to.permit entry of separate-phase hydrocarbons, if present, and to allow for fluctuations.in the ground water elevation. A'sand filter will be placed around the well screen to a height of two feet above the top.of-the.screen: Each well will be completed with.a bentonite seal and cement grout (containing 2 to 3 percent bentonite powder) to grade. Each.wellhead will be protected by a locking cap and a traffic-rated street box with a water-tight bolted lid. A typical ground water monitoring well construction diagram-is presented as Plate 3. WELL DEVELOPMENT I SURVEYING I GROUND WATER MONITORING ' RESNA will wait a-minimum of.24.hours before.developing monitoring wells to allow the grout '.to harden. Each monitoring well will then be developed using.a surge block and pump to remove fine-grained sediments from the well and filter-pack. Well development will continue until the discharge water is clear of silt and sand.-'Clay-size.sediments derived from the screened portion of the formation-cannot be eliminated.by well development. Water from the development process will be placed Department of Transportation 17E drums and left at the site pending appropriate disposal. . After the water level has,been allowed to stabilize, the well will be checked for separate-phase hydrocarbons; if present, the apparent thickness will be measured using an interface probe. The thickness of any separate-phase hydrocarbons detected in the well will be recorded. The top-of-casing (TOC) and horizontal position of each- well,will be surveyed relative to an established'or assumed benchmark by a.licensed land surveyor. The survey data will be used together with depth to water measurements,taken from the TOC in the well to the nearest 0.01 foot with an electric water-level indicator to evaluate the relative elevation of the groundwater surface-in.each well, the slope-of the ground water surface across the site, and the local ground water flow direction. WELL-PURGING I WATER SAMPLING I ANALYSIS If separate-phase hydrocarbons.are not present in a well, the well will be.purged of three to.five ..well casing volumes, and a sample:will be collected forlaboratory analyses... Measurements of temperature,pH, and conductivity will be taken to assure that representative formation water,is present in the well prior to'sampling. The water level will be 'allowed.to recover to at least 80 percent of static conditions, and samples will'be collected with clean .disposable bailers. The water. will be"transferred slowly from the bailer to laboratory-cleaned sample containers- for laboratory analyses. -Chain of Custody Records.will be initiated in the field by the geologist, updated throughout handling of,the samples, and sent along with the samples to the analytical laboratory. . Copies of Chain-of Custody.Records'will be.included in our report. Water.ourged from the wells will be directed:,to the Department of Transportation 17E drums: RESNA will contact a contractor selected by BP to remove development and purge water. 7050.01wP 3