Portions of thisDrilling problems included hole deviation and hole instability that prevented the timely completion of this borehole. Drilling methods used include rotary tri-cone and rotary hammer drilling with conventional and reverse circulation using aidwater, aidfoam (Davis mix), and bentonite mud.Geologic cuttings and geophysical logs were obtained from the well. The rocks penetrated by the ER-12-1 drillhole are a complex assemblage of Silurian, Devonian, and Mississippian sedimentary rocks that are bounded by numerous faults that show substantial stratigraphic offset.The final 7.3 m (24 ft) of this hole penetrated an unusual intrusive rock of Cretaceous age. The geology of this borehole was substantially different from that expected, with the Tongue Wash Fault encountered at a much shallower depth, paleozoic rocks shuffled out of stratigraphic sequence, and the presence of an altered biotite-rich microporphyritic igneous rock at the bottom of the borehole.Conodont CAI analyses and rock pyrolysis analyses indicate that the carbonate rocks in ER-12-1, as well as the intervening sheets of Eleana siltstone, have been thermally overprinted following movement on the faults that separate them. The probable source of heat for this thermal disturbance is the microporphyritic intrusion encountered at the bottom of the hole, and its age establishes that the major fault activity must have occurred prior to 102.3+0.5 Ma (middle Cretaceous).Geophysical logs run in the saturated and unsaturated sections of the borehole were invaluable for interpretation of stratigraphy and structure. Problems encountered during logging were lack of service tables for stacked logs, lack of calibration tables for the ER-12-1 hole size, and lack of written procedures for running these logs in the field. Hydrologic investigations consisted of water level monitoring, flow logging, aquifer tests, and drill-stem tests. The results indicate that the static composite fluid level in well ER-12-1 was 469 m ( 1540 ft) below land surface. Drill-stem tests and flow logs determined that the lower two intervals in the well are underpressured relative to the upper zones by approximately 396 m (1 300 ft). Aquifer tests, drill-stem tests, and flow logs determined that the transmissivity of the well ranged from 7.5 x m2/s, with the most transmissive zone being 518 to 555 m (1700 to 1820 ft) below land surface followed by the 9 14 to 963 m (3000 to 3 160 ft). The pressure differential between these zones allowed for substantial crossflow to occur while the well was open.to 4 x Two types of geochemical samples were acquired from this well. Water quality samples taken during drilling and testing indicated very few problems associated with the well. Those identified consisted of elevated quantities of volatile and semivolatile organics (sample 10006) and metals (sample 10007) associated with the drilling process. Geochemical characterization samples were taken only from the uppermost zone, 518 to 555 m (1700 to 1820 ft). The results from this sample vii indica...

In 2006, a drilling campaign was conducted at the Project Shoal Area (PSA) to provide information for model validation, emplace long-term monitoring wells, and develop baseline geochemistry for long term hydrologic monitoring. Water levels were monitored in the vicinity of the drilling, in the existing wells HC-1 and HC-6, as well as in the newly drilled wells, MV-1, MV-2 and MV-3 and their associated piezometers. Periodic water level measurements were also made in existing wells HC-2, HC-3, HC-4, HC-5 and HC-7.A lithium bromide chemical tracer was added to drilling fluids during the installation of the monitoring and validation (MV) wells and piezometers. The zones of interest were the fractured, jointed and faulted horizons within a granitic body. These horizons generally have moderate hydraulic conductivities. As a result, the wells and their shallower piezometers required strenuous purging and development to remove introduced drilling fluids as evidenced by bromide concentrations.After airlift and surging well development procedures, the wells were pumped continuously until the bromide concentration was less then 1 milligram per liter (mg/L).Water quality samples were collected after the well development was completed. Tritium scans were preformed before other analyses to ensure the absence of high levels of radioactivity. Tritium levels were less than 2,000 pico-curies per liter. Samples were also analyzed for carbon-14 and iodine-129, stable isotopes of oxygen and hydrogen, as well as major cations and anions. Aquifer tests were performed in each MV well after the bromide concentration fell below acceptable levels. Water level data from the aquifer tests were used to compute aquifer hydraulic conductivity and transmissivity. ACKNOWLEDGMENTS

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Water Well 5C Water Well 5B Water Well u E-5~ Water Well A r m y #1 Water Well UE-16d Water Well J-12 Water Well J-13 Water Well 8 Water Well #4 Water Well #MA Water Well C Water Well C-1 Water Well 2 Water Well U-20 Water Well UE-19c 129 Proximity to Underground Nuclear Tests and Existing Wells No underground tests or existing wells are located within 2 km of Water Well Army #l. Water We11 UE-16d Location Water Well UE-16d is located west of Yucca Flat on the western flank of Syncline Ridge (Figure 5). Land surface elevation at the well site is 1427.7 m MSL. Water Well UE-16d is located on the eastern edge of the Alkali Flat-Furnace Creek Ranch subbasin groundwater flow system. Potentiometric data (Winograd and Thordarson, 1975) indicate the general direction of groundwater flow in the area of Water Well UE-16d to be from northwest to southeast (Figure 3). Cons truc tion/Completion Water Well UE-16d (Figure 16) was drilled in 1977 to a total depth of 914.4 m. During construction, 17.8-cm-diameter casing was set in the well to a depth of 645.9 m. The annular space between this casing and the wellbore was cemented to from 574.5 to 645.9 m. Below this casing, a 15.9-cm-diameter hole was drilled to total depth. Air foam was used to circulate cuttings from the hole from 253 to 742.5 m; mud was used from 742.5 m to total depth. st1313 w ZMM Water Well U-20 Location Water Well U-20 is located on Pahute Mesa in the Alkali Flat-Furnace Creek Ranch subbasin (Figure 5). Potentiometric data (Winograd and Thordarson, 1975) indicated the general direction of groundwater flow in the area of Water Well U-20 to be from the northeast to the southwest (Figure 3). Land surface elevation at the well site is 197 1.4 m MSL. Construction/Completion Water Well U-20 (Figure 37) was drilled in 1982 to a total depth of 996.1 m. A 55.9-cm-diameter borehole was drilled to 8 18.1 m, followed by a 44.4-cm-diameter borehole to total depth. The well was completed with 34-cm-diameter casing (slotted from 692.2 to 925.1 m) set to a depth of 975 m. This casing was not cemented within the well. Hydro geolo gy Fluid level within the well is reported at 620.3 m below land surface. NTS Site Maintenance Department records (unpublished) indicate a specific capacity of 7.4 m3/day/m of drawdown at a discharge rate of 1526 m3/day. Water production from Water Well U-20 originates primarily from fractured rhyolite lava flows of the Tuffs and Rhyolites of Area 20 stratigraphic unit penetrated by the wellbore (Figure 40). Water quality data (Chapman and Lyles, 1993) from Water Well U-20 indicate a Na+K+HC03 type water typical of volcanic aquifers (Figure 38). Proximitv to Underground Nuclear Tests and Existing Wells Eight underground nuclear tests (U-20ac7 U-20a7 U-20b7 U-20n, U-20bf, U-20bd7 U-20ay, and U-2Oai) have been conducted near (within 25 m) or below the water table, and two wells (UE-20n#l and UE-20bh#l) are located within 2 km of Water Well U-20 (Figure 39). All of these tests and wells, except U-20bd, are located downgradient or along near equal pot...

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