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♦ t. r y <br /> I� A dnve-over steel vault, with an 8-inch-diameter steel cover plate, will be placed over the <br /> top of the well for protection from vehicular traffic The vault will be set in a 2-foot- <br /> square concrete pad sloped away from the well to prevent surface infiltration The wells <br /> will be secured with a water-tight locking cap for protection from storm-water infiltration, <br /> and tampering <br /> B.5 ORGANIC VAPOR SCREENING OF SOIL SAMPLES <br /> The soil samples that are collected for screening purposes will be allowed to equilibrate <br /> for approximately 30 minutes A field reading will then be taken using a HNU PID <br /> Based on the PID readings, samples will be selected for laboratory analyses <br /> B.6 WATER LEVEL MEASUREMENTS <br /> Water levels in the Site wells will be measured using an oil-water interface probe The <br /> instrument has a dual-tone signal that identifies the type of fluid encountered (free-phase <br /> petroleum hydrocarbons or water) This allows each well to be checked for a measurable <br /> thickness of free product each time the water level is measured <br /> B.7 GROUNDWATER SAMPLING METHODS <br /> B 7 1 WELL PURGING METHODS <br /> After installation, the new monitoring well will be left undisturbed for at least 48 hours to <br /> allow the grout to set Before sampling, the wells will be purged with an electric <br /> submersible pump to allow fresh formation water to enter the well The volume of water <br /> to be purged will be assumed adequate if <br /> Three well volumes are purged, and the parameters pH, conductivity, and temperature <br /> have stabilized (pH to 0 1 pH unit, conductivity to 10 percent of previous reading, <br /> temperature to 0 5 degree C), <br /> • Five well volumes are purged, or <br /> The well is purged dry <br /> Purge water will be collected into 55-gallon drums and stored on-Site until the laboratory <br /> analytical results are received The contaminant concentrations in the groundwater <br /> samples will determine the appropriate method of disposal <br /> B 7 2 SAMPLING METHODS <br /> Wells will be sampled in an order based on the anticipated degree of petroleum <br /> hydrocarbon concentration Wells with the lowest suspected concentrations will be <br /> sampled first to lessen the potential for cross-contamination The three criteria used to <br /> rank the order of sampling are <br /> I <br /> I SII I! II i�l i{ f <br /> EI i E <br /> l; !EfI EI <br /> I h <br /> I I I <br /> I Ir { II I I I ; I I I I I fl li I <br /> II li li {1 I {'It 1 i { <br />