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Farmington Groundwater Recharge Program STC Work Plan—Hammer Site <br /> 2.2. Field Data Collection #1 —Site Characterization <br /> The objective of the site characterization stage is to choose an optimal location and assess the <br /> feasibility of a short term (6-week) pilot recharge test. Table 1 lists the specific activities to be <br /> performed during the first site characterization stage. The following subsections describe these <br /> activities in detail. Borehole geology, grain size analysis, and falling head tests will be used to <br /> select locations with the highest percolation rates. An initial assessment of infiltration rates will <br /> be determined from borehole falling head tests. Borehole geology and grain size analysis data <br /> will be used to estimate percolation rates and calculate the flow rate and volume of water <br /> necessary for the pilot recharge test. Based on this information, a specific pilot recharge test <br /> technique will be specified for the site. The following is a list of activities conducted during the <br /> first site characterization stage. <br /> 2.2.1. Borehole Drilling and Lithologic Logging <br /> Ten boreholes will be drilled to a maximum depth of 15 feet at equal spacing to gain a general <br /> understanding of the site subsurface soils. Locations for falling head tests and the monitoring <br /> well location will be determined based on visual inspection of soil lithology encountered during <br /> borehole drilling. Borehole drilling will be performed using a hollow stem auger (HSA). An <br /> onsite field geologist under the direct supervision of a California Registered Geologist will <br /> describe the samples on a lithologic log (Appendix A) in accordance with the Unified Soil <br /> Classification System (USCS) (American Society for Testing and Materials (ASTM) D 2487 and <br /> 2488). Upon completion of lithologic logging, each borehole will be backfilled and abandoned in <br /> accordance with state and local regulations. <br /> 2.2.2. Grain Size Analysis <br /> After careful review of the borehole lithologic log, field observations, and identifying the most <br /> coarse and fine layers at each borehole, the on-site geologist will determine locations that most <br /> accurately represent the subsurface conditions at the site. Grain size analyses will be conducted <br /> on two samples from each of 7 representative boreholes and hydraulic conductivity will be <br /> estimated using the Kozeny-Carmen equation (Bear, 1972). Samples will be chosen from the <br /> most coarse and fine zones encountered during drilling and identified by the on-site geologist. In <br /> addition to these 14 samples, 5 wells will be selected for grain size analysis at the surface. <br /> Methods followed will be in accordance with USCS (ASTM D 2487 and 2488). <br /> 2.2.3. Borehole Falling Head Tests <br /> Preliminary estimates of soil infiltration rates and recharge potential will be determined from <br /> borehole falling head tests. A total of 3 borehole falling head tests will be conducted at pre- <br /> existing borehole locations. These locations will be selected based on borehole geology <br /> observations and are meant to represent the range of subsurface conditions present. Borehole <br /> falling head test methodology will be for tests above the water table (Bureau of Reclamation, <br /> 1974). This method involves the addition of water into the empty auger casing and maintaining <br /> the height of the water column at a constant level. Volume of water added to the system and <br /> water level within the auger casing is recorded continuously to calculate an infiltration rate. <br /> MWH 2-5 July 2004 <br />