2012 Groundwater Monitoring and Inspection Report Gnome-Coach, New Mexico, Site

Gnome-Coach was the site of a 3-kiloton underground nuclear test conducted in 1961. Surface and subsurface contamination resulted from the underground nuclear testing, post-test drilling, and a groundwater tracer test performed at the site. Surface reclamation and remediation began after the underground testing. A Completion Report was prepared, and the State of New Mexico is currently proceeding with a conditional certificate of completion for the surface. Subsurface corrective action activities began in 1972 and have generally consisted of annual sampling and monitoring of wells near the site. In 2008, the annual site inspections were refined to include hydraulic head monitoring and collection of samples from groundwater monitoring wells onsite using the low-flow sampling method. These activities were conducted during this monitoring period on January 18, 2012. Analytical results from this sampling event indicate that concentrations of tritium, strontium-90, and cesium-137 were generally consistent with concentrations from historical sampling events. The exceptions are the decreases in concentrations of strontium-90 in samples from wells USGS-4 and USGS-8, which were more than 2.5 times lower than last year's results. Well USGS-1 provides water for livestock belonging to area ranchers, and a dedicated submersible pump cycles on and off to maintain a constant volume in a nearby water tank. Water levels in wells USGS-4 and USGS-8 respond to the on/off cycling of the water supply pumping from well USGS-1. Well LRL-7 was not sampled in January, and water levels were still increasing when the transducer data were downloaded in September. A seismic reflection survey was also conducted this year. The survey acquired approximately 13.9 miles of seismic reflection data along 7 profiles on and near the site. These activities were conducted from February 23 through March 10, 2012. The site roads, monitoring well heads, and the monument at surface ground zero were in good condition at the time of the site inspection. However, it was reported in September 2012 that the USGS-1 well head had been damaged by a water truck in April 2012