ARCHIVED REPORTS_SEPARATE PHASE HYDROCARBON INVESTIGATION UNOCAL EXTRACTION WELL PILOT STUDY 2011

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• Hollow Stem Auger (HSA) Drilling/Well Installation Borehole Advancement Pre-cleaned hollow stem augers (typically 8 to 10 inches in diameter) are advanced using a drill rig. Upon completion of drilling, if no well is to be constructed, the augers are retracted, and the borehole is filled with neat cement grout, mixed at a ratio of 6 gallons of water per 94 pounds of Portland cement, through a tremmie pipe, and pumped to displace standing water in the borehole. In areas where the borehole penetrates asphalt or concrete, the borehole is capped with an equivalent thickness of asphalt or concrete patch to match finish grade. During the drilling process, the encountered soil characteristics (i.e. moisture content, consistency or density, odor, color, and plasticity), drilling difficulty, and soil type as a function of depth are described on boring logs. The soil cuttings are classified in accordance with the USCS. Groundwater Monitoring/Extraction Well Installation and Development Groundwater monitoring and extraction wells are constructed by inserting or tremmieing well materials through the annulus of the hollow stem auger. The wells are constructed with a screen interval determined from the encountered soil stratigraphy, to maintain a proper-seal at the surface (minimum three feet), and to avoid penetrating aquitards. Groundwater wells are installed in accordance with the conditions of the well construction permit issued by the regulatory agency exercising jurisdiction over the project site. The well screen generally consists of schedule 40 polyvinyl chloride (PVC) casing with 0.01 to 0.02 factory slots. As a general rule, 0.01 inch slots are used in fine-grained silts and clays and 0.02 inch slots are used in coarse-grained materials. The screen is then filter packed with #2/12 or#3 sand, or equivalent, for the 0.01 and 0.02 inch slots, respectively. Once the borehole has been drilled to the desired depth, bentonite (to backfill an aquitard) is tremmied to the bottom of the boring and hydrated. The well screen and blank well casing are then inserted through the annulus of the hollow stem augers. The well screen is sand packed by tremmieing the appropriate filter sand through the annulus between the casing and augers while slowly retracting the augers. During this operation, the depth of the sand pack in the auger is continuously sounded so that the sand remains in the auger annulus during auger retraction to avoid short-circuiting the well. The sand pack is tremmied to approximately two feet above the screen, at which time pre-development surging is performed to consolidate the sand pack. Additional sand is added as necessary to help ensure that the sand pack extends a minimum of two feet above top of screen. Following construction of the sand pack, a two foot thick bentonite seal is tremmied over the sand and hydrated in place. The remainder of the borehole is backfilled with Portland neat cement grout (or the equivalent), mixed at ratio of 6 gallons of water per 94 pounds of neat cement. The well head is then capped with a locking cap and secured with a lock to protect the well from surface water intrusion and vandalism. The well head is further protected from damage with traffic a rated well box in paved areas or locking steel riser in undeveloped areas. The protective boxes or risers are set in concrete. The details of well construction are recorded on well construction logs. 31