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4.2.2 Grab-Groundwater Sampling <br /> Grab-groundwater samples will be collected by using a sonic drill rig to advance a hydropunch <br /> groundwater sampler(or equivalent closed-screen groundwater sampling apparatus)through the <br /> outer drill casing. At boring Location 1,grab-groundwater samples will be collected over a <br /> 3-foot interval every 10 feet from approximately 100 ft bgs to the top of the Corcoran Clay. At <br /> each boring,the results from the previous borings will be used to guide the decision making for <br /> sample collection. The number and depths of grab-groundwater samples at each boring may be <br /> adjusted to target the depths and geologic layers where sulfolane was detected in previous <br /> borings. <br /> Hydropunch or closed screen samplers are protected, sealed sampling devices consisting of a <br /> polyvinyl chloride(PVC)screen housed within a protective sheath with an expendable drive <br /> point, driverod(s), and drive head attached. The assembly will be initially driven with the outer <br /> casing in place. Rubber O-rings will be used to keep the device water-tight, eliminating the threat <br /> of formation fluids entering the screen before deployment and assuring sample integrity. Once <br /> the desired depth is reached, the outer casing will be retracted to expose the screen to formation <br /> water. The samples are anticipated to be collected over a 3-foot screen interval. After a sample is <br /> obtained,the expendable drive point will be left in place and the sampling assembly will be <br /> removed. The sampler will be driven past the end of the drill casing to eliminate the possibility <br /> of the material inside the casing effecting the hydropunch sampling results. Due to the <br /> hydropunch screen being exposed after the tool has been placed at the target depth, susceptibility <br /> of the screen to clogging is reduced. <br /> Groundwater samples will be collected directly from the sampling apparatus using a new, <br /> disposable bailer or polyethylene tubing fitted with a check valve and placed into laboratory <br /> supplied sample containers.All groundwater samples will be stored in an iced cooler, packaged <br /> under standard chain-of-custody protocols and shipped to a California certified analytical <br /> laboratory for analysis. Sulfolane samples will be run on a 24-hour turn-around time and all other <br /> analysis will be run on a standard 10-day turn-around time. Sample containers will be labeled <br /> with a unique sample identifier, date,time, requested analyses, preservation method, and <br /> samplers' initials. Grab-groundwater samples will be analyzed for the following constituents <br /> using one or more of the following methods: <br /> • Sulfolane by Agriculture& Priority Pollutants Laboratories(APPL) Standard Operating <br /> Procedure (SOP) Sulfolane; <br /> • Sulfate and Nitrate by United States Environmental Protection Agency (EPA) method <br /> 300.0; <br /> • Ammonia as N by EPA method 350.1; and <br /> • Iron and Manganese by EPA method 200.7. <br /> 4.2.3 Monitoring Well Installation <br /> A monitoring well may be installed in each of the borings based on the stratigraphy and grab- <br /> groundwater sulfolane results. A monitoring will be installed if sulfolane is detected at a location <br /> or depth interval that is not monitored by the existing wells. If a monitoring well is installed in <br /> Site Characterization Work Plan 7 June 22,2018 <br />