Book Description

Well ER-EC-14 was drilled for the U.S. Department of Energy, National Nuclear Security Administration Nevada Site Office in support of the Nevada Environmental Management Operations Underground Test Area (UGTA) Activity at the Nevada National Security Site (NNSS; formerly Nevada Test Site), Nye County, Nevada. The well was drilled in September and October 2012, as part of the Central and Western Pahute Mesa Corrective Action Unit Phase II drilling program. The primary purpose of the well was to provide detailed hydrogeologic information for the Fortymile Canyon composite hydrostratigraphic unit in the Timber Mountain moat area, within the Timber Mountain caldera complex, that will help address uncertainties within the Pahute Mesa-Oasis Valley hydrostratigraphic framework model. The main 55.9-centimeter (cm) hole was drilled to a total depth of 325.5 meters (m) and cased with 40.6-cm casing to 308.1 m. The hole diameter was then decreased to 37.5 cm, and drilling continued to a total depth of 724.8 m. The completion casing string, set to the depth of 690.9 m, consists of 16.8-cm stainless-steel casing hanging from 19.4-cm carbon-steel casing. The stainless-steel casing has two slotted intervals open to the Rainier Mesa Tuff. Two piezometer strings were installed in Well ER-EC-14. Both piezometer strings, each with one slotted interval, consist of 6.0-cm carbon-steel tubing at the surface, then cross over to 7.3-cm stainless-steel tubing just above the water table. The shallow piezometer string was landed at 507.8 m, and the deep piezometer string was landed at 688.6 m. Both piezometer strings are set to monitor groundwater within moderately to densely welded Rainier Mesa Tuff. Data collected during and shortly after hole construction include composite drill cuttings samples collected every 3.0 m, various geophysical logs, water quality (including tritium and other radionuclides) measurements, and water level measurements. The well penetrated 15.2 m of alluvium and 709.6 m of Tertiary volcanic rocks. The stratigraphy and general lithology were not as expected due to the position of Well ER-EC-14 relative to the buried caldera margins of the Timber Mountain caldera complex. The well is located inside the Rainier Mesa caldera, but outside the younger Ammonia Tanks caldera. On November 5, 2012, a preliminary fluid level in the shallow piezometer string was measured at the depth of 311.8 m. This water level depth was taken before installation of the bridge plug (to be placed within the main completion casing to separate the two slotted zones). Well development, hydrologic testing, and sampling, will be conducted at a later date. No tritium above levels detectable by field methods were encountered in this hole. All Fluid Management Plan (FMP) requirements for Well ER-EC-14 were met. Analysis of monitoring samples and FMP confirmatory samples indicated that fluids generated during drilling at Well ER-EC-14 met the FMP criteria for discharge to an unlined sump or designated infiltration area. All sanitary and hydrocarbon waste generated was properly handled and disposed of.