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2007 Grassy Valley Supplemental Hydrogeologic Field Program <br />Introduction <br />Supplemental field work was conducted in Grassy Valley north of the Cresson Project <br />during two sessions late July through mid-August, 2007. The field program was <br />designed to enhance the understanding of Grassy Valley hydrogeology and generate <br />additional data to build the Grassy Valley water balance. A total of eight piezometers, 3 <br />alluvial wells, and 2 bedrock wells were installed in the course of the field program. <br />Drilling, Logging, and Construction Details <br />A summary of piezometer and well construction is provided in Table B 1. Construction <br />details are provided on the borehole logs (Figure B-2). <br />All wells and piezometers were drilled by direct rotary using a DR-12 Foremost Rig, and <br />geologic logging was conducted in the field by WMC staff. Logs include information on <br />• lithology <br />• color <br />• evidence of oxidation or fracture surfaces <br />• zones where rates of penetration changed significantly <br />• well construction details <br />• water strikes and flow rates. <br />Logs also include water levels collected during construction and at recently completed <br />wells. Field notes are available in the borehole logs (Figure B-2). <br />Wells and piezometers were constructed using 2-inch PVC and 20-slot PVC screens. <br />Gravel packs were composed of 6/9 sand, and backfill and seals were made using <br />bentonite chips. Surface completions are 8-inch steel casing. <br />Phase I <br />Phase I of the field program took place July 20`h through 25`h, 2007. During Phase I, <br />WMC staff investigated potential shallow flow paths along the alluvium/bedrock <br />interface under the proposed area of the East Cresson Overburden Storage Area <br />(ECOSA). A total of eight piezometers were constructed during this phase; piezometers <br />were distributed across the proposed ECOSA footprint in order to investigate the entire <br />area. Wells were screened across the alluvium-shallow bedrock interface. Well locations <br />are illustrated on Figure B-1, construction overviews are provided in Table 131, and <br />drilling and construction logs are provided in Figure B-2. <br />0