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In this investigation, various information sources from the Nevada Test Site (NTS), national laboratories and the Desert Research Institute were utilized to verify the existence of approximately 250 existing wells or boreholes at the NTS. Of these wells, 40 were determined to be located within one kilometer of underground nuclear tests conducted near (within 25 m) or below the water table. These 40 existing wells were then investigated in detail to determine their drilling and construction history, lithology and hydrologic units penetrated, and current conditions. These findings are presented for each well, as well as recommendations as to whether individual wells should be plugged and abandoned or could possibly be recompleted as groundwater quality monitoring locations. Two of the 40 wells, UE-20e and UE-2a, contain lost drilling strings and do not penetrate aquifers. These two wells should be plugged and abandoned and removed from the NTS well inventory. Three other wells, TestWell No. 1, TestWell No. 5, and TestWell No. 6, are reported stemmed with sand to the surface. These three wells did not penetrate the water table and would require substantial deepening to be recompleted as groundwater monitoring locations. If not recompleted, these wells should also be plugged and abandoned and removed from the NTS well inventory. Eleven of the 34 wells, Test Well No. 7, RNM No. 1, RNM No. 2, RNM No. 2S, U-3cn No. 5, UE-20n No. 1, UE-7ns, UE-5n, UE-4t, UE-3e No. 3 and U-15k Test Hole, penetrate aquifers and do not require recompletion to produce groundwater monitoring locations. These wells are either constructed such that recompletion is not needed or not possible. Several of the 11 wells may require the removal of tubing and the placement or replacement of pump equipment. All five of the wells require wellhead rehabilitation to ensure they are not contaminated by surface water or other materials.
An evaluation of groundwater monitoring at non-Nevada Test Site underground nuclear test sites raised questions about the potential for radionuclide migration from the Faultless event and how to best monitor for such migration. With its long standing interest in the Faultless area and background in Nevada hydrogeology, the Desert Research Institute conducted a field investigation in FY92 to address the following issues: The status of chimney infilling (which determines the potential for migration); the best level(s) from which to collect samples from the nearby monitoring wells, HTH-1 and HTH-2; the status of hydraulic heads in the monitoring well area following records of sustained elevated post-shot heads. The field investigation was conducted from July 27 to 31 and August 4 to 7, 1992. Temperature and electrical conductivity logging were performed in HTH-1, HTH-2, and UC-1-P-2SR. Water samples were collected from HTH-1 and HTH-2. Lawrence Livermore National Laboratory (LLNL) also collected samples during the July trip, including samples from UC-1-P-2SR. This report presents the data gathered during these field excursions and some preliminary conclusions. Full interpretation of the data in light of the issues listed above is planned for FY93.
A total of 15 water-supply wells are currently being used at the Nevada Test Site (NTS). The purpose of this report is to bring together the information gleaned from investigations of these water-supply wells. This report should serve as a reference on well construction and completion, static water levels, lithologic and hydrologic characteristics of aquifers penetrated, and general water quality of water-supply wells at the NTS. Possible sources for contamination of the water-supply wells are also evaluated. Existing wells and underground nuclear tests conducted near (within 25 meters (m)) or below the water table within 2 kilometers (km) of a water-supply were located and their hydrogeologic relationship to the water-supply well determined.
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Existing Well UE-10j was deepened and recompleted for the U.S. Department of Energy, Nevada Operations Office in support of the Nevada Environmental Restoration Project at the Nevada Test Site, Nye County, Nevada. The well was originally drilled to a total depth of 725.4 meters in 1965 for use as a hydrologic test hole in the northern portion of Yucca Flat in Area 8 of the Nevada Test Site. The well is located up-gradient of the Yucca Flat underground test area and penetrates deep into the Paleozoic rocks that form the lower carbonate aquifer of the NTS and surrounding areas. The original 24.4-centimeter-diameter borehole was drilled to a depth of 725.4 meters and left uncompleted. Water-level measurements were made periodically by the U.S. Geological Survey, but access to the water table was lost between 1979 and 1981 due to hole sloughing. In 1993, the hole was opened to 44.5 centimeters and cased off to a depth of 670.0 meters. The hole diameter was then decreased to 31.1 centimeters for drilling to a total depth of 796.4 meters. The depth to water in the open borehole was measured at 658.7 meters on March 18, 1993.
Monitoring for the migration of contaminants in groundwater or for the proper design of nuclear test emplacement holes at the Nevada Test Site (NTS) requires proper placement and completion of monitoring wells. This is only possible if the hydrogeologic system is understood in a regional and local context, necessitating data from existing wells and boreholes. Though the NTS Groundwater Characterization Project will be drilling wells, their great expense limits the number of new wells. However, there are many existing boreholes and wells on the NTS which have not been completely evaluated hydrologically. Some of these are incorporated in the Long Term Hydrologic Monitoring Program (LTHMP) of the US Environmental Protection Agency (EPA), others are related to the testing programs. In all cases, additional site investigation in necessary to properly interpret the hydrogeologic data from these wells. Monitoring wells on the NTS are poorly characterized with regard to aquifers penetrated, vertical hydraulic gradients, and vertical variations in water quality. One of the goals of the well validation program was to gain a thorough understanding of the parameters needed to interpret the source and fate potential hazardous and radioactive substances that may be detected in these wells in the future. One of the most critical parameters for monitoring is the knowledge of what aquifer or geologic unit is being sampled when a water sample is collected. Pumped water samples are weighted most heavily to the water quality of the most productive (highest transmissivity) aquifer penetrated by the well.
This plan describes actions to improve the utility and credibility of the Nevada Test Site (NTS) interim groundwater monitoring program. The two principal actions are: (1) well maintenance/rehabilitation activities and (2) the deployment of dedicated low-cost and reliable jack-pumps for groundwater sampling from deep monitoring wells. The scope of this proposal is to perform these actions on some number of nine selected wells (Figure 1) to evaluate whether these actions are achievable, practical, cost effective, and result in improved groundwater data quality.