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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.
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.
Pahute Mesa at the Nevada Test Site contains about 8.0E+07 curies of radioactivity caused by underground nuclear testing. The Underground Test Area Subproject has entered Phase II of data acquisition, analysis, and modeling to determine the risk to receptors from radioactivity in the groundwater, establish a groundwater monitoring network, and provide regulatory closure. Evaluation of radionuclide contamination at Pahute Mesa is particularly difficult due to the complex stratigraphy and structure caused by multiple calderas in the Southwestern Nevada Volcanic Field and overprinting of Basin and Range faulting. Included in overall Phase II goals is the need to reduce the uncertainty and improve confidence in modeling results. New characterization efforts are underway, and results from the first year of a three-year well drilling plan are presented.