Scientific Investigations Report 2008–5089
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2008–5089
The USGS maintains ground-water monitoring networks at the INL to characterize the occurrence, movement, and quality of water, and to delineate waste-constituent plumes in the Snake River Plain aquifer and perched-water zones. Periodic water-level and water-quality data are obtained from these networks. Data from these monitoring networks are on file at the USGS INL Project Office and are available on the USGS National Water Information System (NWIS) Web site at http://waterdata.usgs.gov/id/nwis/nwis.
The USGS aquifer water-level monitoring network was designed to determine hydraulic-gradient changes that affect the rate and direction of ground-water and waste-constituent movement in the Snake River Plain aquifer, to identify sources of recharge to the aquifer, and to measure the effects of recharge. Water levels were monitored in 173 aquifer wells during 2002–05. Water levels were measured annually in 25 wells, semiannually in 51 wells, quarterly in 62 wells, monthly in 24 wells, and continuously recorded in 4 wells. Figures 2 and 3 show the location of aquifer wells and the frequency of water-level measurements as of December 2005.
The USGS perched water-level monitoring network was designed to estimate the extent of perched ground water and the volume of perched water in storage. Water levels in 36 wells (fig. 4) were monitored during 2002–05. At the RTC, the network included 22 wells to monitor deep perched ground-water levels and 9 wells to monitor shallow perched ground-water levels. Shallow perched ground water is considered water perched in surficial sediment deposits, and deep perched ground water is water perched at greater depth. Perching mechanisms are attributed to contrasting hydraulic properties between sedimentary interbeds and basalts or between low-permeability basalt-flow interiors and overlying fractured basalt. At the INTEC, the network included three wells to monitor deep perched ground-water levels around the original INTEC percolation ponds and one well to monitor the water-level changes in deep perched ground water beneath the INTEC. Perched ground water at the RWMC was monitored in one well. Well locations and frequency of water-level measurements as of December 2005 are shown in figure 4.
The radiochemical and chemical character of ground water and perched ground water in the Snake River Plain aquifer was determined from analyses of water samples collected as part of a comprehensive sampling program to identify contaminant concentrations and define patterns of waste migration in the aquifer and perched zones. Water samples from surface-water sites at or near the INL and from wells in perched ground-water zones were analyzed to document the chemical quality of water that recharges the aquifer. Water samples were collected from wells that penetrate the aquifer to various depths and with differing well completions and were analyzed to identify trends in water quality. Numerous water samples were collected from ground-water and perched ground-water wells near areas of detailed study, such as the RTC, INTEC, RWMC, TAN, and CFA. Water samples from the Naval Reactors Facility (NRF) were collected and analyzed as part of a separate study and results are presented in series of separate reports (most recently, Bartholomay and others, 2001a, 2001b).
The type, frequency, and depth of ground-water sampling generally depend on the information needed in a specific area. Water samples were routinely collected and analyzed for concentrations of tritium, strontium-90, cobalt-60, cesium-137, plutonium-238, plutonium-239, -240 (undivided), americium-241, gross alpha- and beta-particle radioactivity, chromium, sodium, chloride, sulfate, nitrate, volatile organic compounds, and measurements of specific conductance, pH, and temperature. Additionally, as part of the INL ground-water monitoring program adopted in 1994 (Sehlke and Bickford, 1993), samples from several wells also were analyzed for fluoride, an extensive suite of trace elements, and total organic carbon. Water samples were analyzed for the radiochemical constituents at the Radiological and Environmental Sciences Laboratory (RESL) at the INL and for chemical constituents at the USGS National Water Quality Laboratory (NWQL) in Lakewood, Colo. The location of wells in the aquifer water-quality monitoring network as of December 2005, and the frequency of sample collection are shown in figures 5 and 6, and in table 2. Well locations in the USGS water-quality monitoring network for perched ground water beneath INL facilities during 2002–05 and the frequency of sample collection are shown in figure 7 and table 3. A sample schedule that lists the constituents analyzed at each site is given in a report by Bartholomay and others (2003, attachment 1).
Methods used to sample and analyze for selected constituents generally follow the guidelines established by the USGS (Goerlitz and Brown, 1972; Stevens and others, 1975; Wood, 1976; Claassen, 1982; Wershaw and others, 1987; Fishman and Friedman, 1989; Faires, 1993; Fishman, 1993; and Wilde and others, 1998). Water samples were collected according to a quality-assurance plan for water-quality activities conducted by personnel at the USGS INL Project Office. The plan was finalized in June 1989, revised in March 1992, in 1996 (Mann, 1996), and in 2003 (Bartholomay and others, 2003) and is available for inspection at the USGS INL Project Office. Water samples collected for dissolved constituent analysis are filtered through a 0.45-micron membrane filter. About 10 percent of samples collected generally are for quality assurance. Quality-assurance samples collected by the USGS INL Project Office include equipment blanks, splits, and replicates. Comparative studies to determine agreement between analytical results for individual water‑sample pairs by laboratories involved in the INL Project Office quality-assurance program were summarized by Wegner (1989), and Williams (1996, 1997). Additional quality-assurance studies by personnel at the INL Project Office included:
U.S. Department of the Interior | U.S. Geological Survey
URL: http://pubs.usgs.gov/sir/2008/5089
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