2015 Groundwater Monitoring and Inspection Report Gnome-Coach, New Mexico, Site
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Summary (3 min read)
- A Completion Report was prepared, and the State of New Mexico is currently proceeding with a conditional certificate of completion for the surface.
- This report summarizes groundwater monitoring and site investigation activities that were conducted at the site during the fiscal year 2012.
- No additional underground nuclear detonations occurred at the site; however, in 1963, the U.S. Geological Survey conducted a groundwater tracer test using four dissolved radionuclides—tritium, iodine-131, strontium-90, and cesium-137—as tracers (Beetem and Angelo 1964).
2.1 Summary of Reclamation and Remediation Activities
- Surface and subsurface contamination resulted from the underground nuclear testing, post-test drilling, and a groundwater tracer test performed at the site.
- A Completion Report, prepared in accordance with the Voluntary Remediation Program, recommended no further corrective actions, no use restrictions for the surface at the site, and the eventual goal of clean closure (DOE/NNSA 2005).
- The well logging was conducted to obtain borehole deviation data from wells USGS-1 and USGS-4, natural gamma data from wells USGS-4 and USGS-8, and down-hole video logs from wells USGS-4 and USGS-8.
- At the site, about 200 ft of Permian-age anhydrites, mudstones, and dolomites separate the Culebra Dolomite from younger overlying formations.
- The analytical results obtained from the annual sampling were validated in accordance with the Environmental Procedures Catalog (LMS/PRO/S04325), “Standard Practice for Validation of Laboratory Data.”.
4.1 Site Inspection Results
- The inspection included evaluating roads and monitoring well heads and inspecting the monument at SGZ for any signs of damage, natural deterioration from weather, or vandalism.
- All roads, well heads, and the monument were in good condition at the time of the inspection.
- Installation of the water access tubes established new measuring points on the top of casing for measuring depth to groundwater in the wells.
- The impact had damaged the well head and caused the water access tube and transducer to drop to the bottom of the well.
4.2 Hydraulic Head Monitoring and Results
- Transducer data in well USGS-1 were also not downloaded in September because the well had been damaged and the transducer was no longer accessible at the well head.
- The specific gravity of water in Culebra screened wells is about 1.0025.
- The manual water levels collected in January 2011 and 2012 support this determination and were used to convert the transducer data to elevations.
4.3 Groundwater Sampling and Results
- The sample from well USGS-1 was collected as a grab sample because the pump was operating to replace water in the nearby stock tank at the time of the sampling.
- Prior to 2008, EPA had conducted the sampling and, until the 2012 sampling event, had also analyzed the samples.
- For interpretation purposes, relatively high concentrations (i.e., concentrations significantly higher than detection limits associated with subsequent sampling) should be considered detections.
- The increases in tritium concentrations in samples collected from well LRL-7 (Chart 1) and cesium-137 concentrations in samples collected from wells USGS-8 and LRL-7 (Chart 4 and Chart 6) after the 2007 sampling event are attributed to changes in the sampling method.
4.4 Seismic Data Acquisition and Results
- A seismic survey was conducted at the Gnome-Coach site from February 23 to March 10, 2011.
- The well head has been repaired, but the water access tube with transducer currently remains in the well.
- Environmental Monitoring Report for the Nevada Test Site and Other Test Areas used for Underground Nuclear Detonations, NERC-LV-539-23, May.
- The Gnome-Coach site is located in the northwest portion of the Delaware Basin, southeastern New Mexico .
- The Permo-Triassic Dewey Lake siltstone, shale, and sandstone unit and the Rustler sandstone, silt, and dolomite unit lie in the upper 1,000 ft, unconformably below the Gatuna Formation, and above the Gnome blast depth.
- Reflections from them provide a regional framework for structural and stratigraphic controls for the Delaware Basin and can also be used to confirm that seismic energy has propagated through the target zone.
- Figure 2. Simplified cross section through 4 wells.
- The authors acquired a check-shot or vertical seismic profile (VSP) survey in well USGS-4 .
- Measurements at a 1.6 ft (0.5 m) interval to a depth of 450 ft were acquired using a sledgehammer seismic source, and measurements at greater depths were acquired using the minivib seismic source used for profile acquisition (see below).
- The first arrival results show that an average seismic velocity to a depth of 450 ft is 2,150 m/s .
- These measurements show an average seismic velocity of 2,706 m/s. Both natural gamma and seismic velocity measurements are consistent with the overlying member of the Rustler Formation, and no identifiable geophysical signature is apparent from USGS-4 at this member boundary.
- The authors acquired all seismic data with a 16 ft (5 m) source and receiver spacing along existing roads within the Gnome-Coach site .
- Figure 5. Seismic image and elevation profile for Line 1.
- The projected position for the SGZ well is near station 1125, while USGS‐1 projects to the west end of the profile.
- A prominent reflector at about the 2,200 ft depth likely represents the top of the high-velocity, anhydrite-dominated Castile Formation , while shallower reflectors contain significant topography and tie to lithologic contacts observed in nearby boreholes.
- Sources were not acquired between stations 2220 and 2250 due to a designated exclusion zone.
- Seismic reflection results from the Gnome-Coach site show stratigraphy in the upper few thousand feet of depth.
- Lithologic logs for the USGS‐2 and USGS‐4 wells are placed along the profile.
- Sources were not acquired north of station 7320 due to road termination.
- Reflectivity in the Salado, Rustler, Dewey Lake, and Gatuna Formations is highly variable both laterally and vertically .
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"2015 Groundwater Monitoring and Ins..." refers background in this paper
...The groundwater in the Culebra is of poor quality because of high concentrations of dissolved solids (Mercer 1983); despite the poor water quality, it is a source of water for ranchers who maintain livestock throughout the area....
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Q1. What are the contributions in this paper?
In this paper, the authors interpret the top of the Castile Formation to range from 1,900 to 2,400 ft below land surface.