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Stantec 2010 TIDEWATER STOCKTON WORK PLAN In an effort to avoid shallow utilities, borings will be hand cleared to greater than eight feet bgs using a hand auger or air wand and vacuum tank prior to drilling. The GWE wells will be advanced using a Hollow Stem Auger (HSA) rig to a target depth of approximately 18.5 feet bgs using 12 inch augers. Soil logging and PID measurements will be completed at approximately five foot intervals. The GWE wells will be located in an area previously excavated and backfilled at the UOU, and therefore, soil samples will not be collected for laboratory analysis. The GWET wells will be completed to approximately 18 feet bgs with four inch diameter Schedule 40 PVC and 7 feet of 0.020 slotted casing will be installed from 18 feet bgs (and/or 2.5 feet below the base of the collection trench) to 11 feet bgs (and/or to 0.5 feet below the top of the two inch drain rock previously installed during backfill of remedial excavations in this area). The well annulus will be backfilled from 18.5 feet bgs to 16 feet bgs with #2/12 sand, from 16 feet bgs to 9.5 feet bgs with 3/4-inch pea gravel, and from 9.5 feet bgs to 4.5 feet bgs with hydrated bentonite chips. A concrete plug will be installed from 4.5 feet bgs to ground surface (including vault). The GWE wells will be completed to grade in 12-inch diameter traffic rated vaults with 6-inch thick concrete skirts in a manner consistent with regulatory requirements including surveying. 1> z Following completion, the GWE wells will be developed. Development will be accomplished by R3=4•s•J alternately surging each well with a vented surge block and bailer. Final purging will be ,�_ o , performed with a submersible pump and pH, temperature, and conductivity will be measured at regular intervals during purging. Development will be considered completed after physical- chemical parameter trends stabilize over three consecutive measurements (<0.05 variability in pH, 3% variability in conductivity, and 10% variability in temperature), or until the wells are purged dry. 3.3.2 Task 2 — Recovery Well Aquifer Test—High Vacuum Extraction 3.3.2.1 High Vacuum Extraction Configuration Two-phase extraction (TPE) systems utilize a single vacuum pump to extract both groundwater and soil vapor through a small diameter entrainment tube or pipe (stinger) inserted into an extraction well below the water surface. An existing TPE system will be employed to extract groundwater from the GWE wells concurrently. The planned test equipment configuration will consist of: • Vapor treatment system (thermal oxidizer or as conditions permit); • 20-horse power(hp) blower capable of approximately 500 cubic feet per minute flow and 12 in-Hg applied vacuum and a 10 hp blower and capable of approximately 250 cubic feet per minute flow and 12 in-Hg applied vacuum; • Vapor/water extraction manifolds; • Air/water separator tanks; 3.11