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October 13, 1992 Working To Restore Nature <br /> BP Oil Facility No. 11193, Stockton, California <br /> If ground water is encountered above 45 feet below grade,ground water monitoring wells MW-1 <br /> k through MW-4 will be constructed in the four soil borings. Each well will be.constructed of two- <br /> inch diameter,schedule 40 PVC casing with flush treads.and 0.020-inch-slot well screen. The <br /> well screen for each of the monitoring wells will be installed approximately five feet above and <br /> ten feet.below the current water table to permit entry of separate-phase hydrocarbons, if present, <br /> and to allow for fluctuations in ground water elevation. A sand filter will be placed around <br /> the well screen to a height of two feet above the top of the screen. Each well will be completed <br /> with a bentonite seal and cement grout (containing 2 to 3 percent bentonite powder) to grade. <br /> Each wellhead will be protected by a locking cap and a traffic-rated street box with a water-tight <br /> bolted lid. A typical ground water monitoring well construction diagram is presented as Plate 3. <br />{ WELL DEVELOPMENT/SURVEYING/GROUND WATER MONITORING <br /> RESNA will wait a minimum of 24 hours beforedeveloping.monitoring wells to.allow the grout <br /> 1 to harden. Each monitoring well will then be developed using a surge block and pump to remove <br /> fine-grained sediments from the well and filter:pack. Well development will continue,until the <br /> discharge water is.clear of silt:and sand. Clay-size sediments derived from.the screened:portion <br /> of the.formation cannot be eliminated;by well development: Water from the development <br /> process will be placed Department of.Transportation 17E drums and left at the site pending <br /> appropriate disposal. After the water level has been allowed-to-stabilize, the well win be <br /> checked for separate-phase hydrocarbons; if;present; the apparent thickness will be measured <br /> using an interface probe. The thickness of any separate-phase hydrocarbons detected in the well <br /> t <br /> will be recorded. <br /> The top-of-casing (TOC) and horizontal position of each well will be surveyed relative to an <br /> established or assumed benchmark by a licensed land surveyor. The survey data will be used <br /> together with depth to water measurements taken from the TOC in the well to the nearest 0.01 <br /> foot with an electric'water-level indicator to evaluate the relative elevation of the groundwater <br /> j surface in each well, the slope of the ground water surface across the site,and the local ground <br />] water flow direction. <br /> WELL PURGING/WATER SAMPLING/ANALYSIS <br /> If separate-phase hydrocarbons are not present in a well,the.well will be purged of three to five <br /> well casing volumes, and a sample will be collected for laboratory analyses. Measurements of <br /> temperature;-pH, and conductivity will be taken to-assure that repcesentatrve formation water is <br /> present in't_he well prior to sampling. The water level will be allowed to recover to at least SO <br /> percent of static conditions, and samples will be collected-with clean disposable bailers. The <br /> Water'will.be transferred slowly from the bailer to laboratory-'cleaned sample containers for <br /> laboratory'analyses. Chain of Custody.Records will be. initiated in the field by the geologist, <br /> updated throughout handling of-the samples, and sent along With the samples to the analytical <br /> laboratory. . Copies of Chain of.Custody Records will:be included in our report. Water purged <br /> t <br /> from rthe'wells will be directed to the Department of Transportation 17E drums. RESNA will <br /> contact a contractor selected by BP to remove development and purge water. <br /> t <br /> `r <br /> 1 <br /> 17051.01w 3 <br /> I <br /> I ' <br />