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L. Knobel, L. Davis - U.S. Geological Survey
R. Mitchell - S. M. Stoller Corporation
T. Wood - Battelle Energy Alliance
M. Roddy , L. Nelson - CWI
One potential pathway for exposure from contaminants released at the Idaho National Laboratory (INL) Site is through the water pathway (surface water, drinking water, and groundwater). The Management and Operating contractor monitors groundwater, as well as liquid effluents, drinking water, and storm water runoff at the INL Site to comply with applicable laws and regulations, U.S. Department of Energy orders, and Wastewater Land Application Permit requirements. The Naval Reactors Facility conducts its own groundwater, effluent, and drinking water monitoring. The U.S. Geological Survey (USGS) INL Project Office performs groundwater monitoring, analyses, and studies of the Eastern Snake River Plain Aquifer (ESRPA) under and adjacent to the INL Site. The Environmental Surveillance, Education and Research program contractor monitors drinking water and surface water at offsite locations.
Historic waste disposal practices have produced localized areas of chemical and radiochemical contamination in the ESRPA beneath the INL Site. These contaminated areas are monitored by the above-mentioned organizations and other various organizations.
Results from a number of special studies conducted by the USGS describing the hydrologic and geochemical properties of the aquifer were published during 2005. Several purgeable organic compounds continue to be found in monitoring wells, including drinking water wells at the INL Site. Concentrations of organic compounds meansured by the USGS were below the U.S. Environmental Protection Agency (EPA) maximum contaminant levels and state of Idaho groundwater primary and secondary constituent standards for these constituents.
Groundwater surveillance monitoring required in area specific Records of Decisions under the Comprehensive Environmental Response, Compensation, and Liability Act was performed in 2005. Contaminant concentrations were within expected or historical concentrations. At Test Area North, a 24-month test was initiated to evaluate the effectiveness of the New Pump and Treat Facility in remediation of a portion of the plume of trichloroethylene. Chromium was above the Maximum Contaminant Level (MCL) in two wells at the Reactor Technology Complex. At Idaho Nuclear Technology and Engineering Center, four constituents exceeded their MCLs but concentrations continue to decline over time. Monitoring at the Central Facilities Area landfills detected nitrate and chromium levels above their respective MCLs. At the Radioactive Waste Management Complex, only carbon tetrachloride is reported near and sometimes in excess of the MCL in sampling conducted by the INL contractor.
Semiannual drinking water samples were collected from 14 locations off the INL Site. One sample from Idaho Falls had measurable gross alpha activity. Eight samples had measurable tritium, and 19 samples had detectable gross beta activity. None of the samples exceeded the EPA MCL for these constituents.
A total of 12 offsite surface water samples were collected from five locations along the Snake River. Most of the samples had measurable gross beta activity attributed to natural radioactivity from geologic materials, while only two samples had measurable tritium. Neither of these constituents was above regulatory limits. Detectable gross alpha activity was not found in any sample.
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This chapter presents results from both radiological and nonradiological surveillance sampling and Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) sampling of groundwater and surface water samples taken at both onsite and offsite locations. Reported results from sampling conducted by the Idaho Cleanup Project (ICP) contractor; the U.S. Geological Survey (USGS); and the Environmental Surveillance, Education and Research (ESER) contractor are presented here. Results are compared to the state of Idaho groundwater primary and secondary constituent standards (PCS) of Idaho Administrative Procedures Act (IDAPA) 58.01.11 and the U.S. Environmental Protection Agency (EPA) health-based maximum contaminant levels (MCL) for drinking water and/or the U.S. Department of Energy (DOE) Derived Concentration Guide for ingestion of water.
Sections 6.1 and 6.2 present discussions of the hydrogeology of the INL Site and hydrogeologic data management, respectively. Section 6.3 describes aquifer studies related to the INL Site and ESRPA. Radiological and nonradiological monitoring of groundwater at the INL Site are discussed in Sections 6.4 and 6.5, respectively. Section 6.6 outlines the CERCLA groundwater activities performed in 2005. Section 6.7 describes offsite drinking and surface water monitoring.
The USGS INL Project Office performs groundwater monitoring, analyses, and studies of the ESRPA under and adjacent to the INL Site. This is done through an extensive network of strategically placed monitoring wells on the INL Site (Figure 6-1 and Figure 6-2) and at locations throughout the Eastern Snake River Plain (ESRP). Chapter 3, Section 3.1, summarizes the USGS routine groundwater surveillance program. In 2005, USGS personnel collected and analyzed over 1200 samples for radionuclides and inorganic constituents including trace elements and approximately 35 samples for purgeable organic compounds.
As detailed in Chapter 3, CERCLA activities at the INL Site are divided into ten Waste Area Groups (WAGs) (Figure 3-3). Each WAG addresses groundwater for its particular contaminant(s). WAG 10 has been designated as the site-wide WAG and addresses the combined impact of the individual contaminant plumes. As individual Records of Decision (RODs) are approved for each WAG, many of the groundwater monitoring activities are turned over to the Long-Term Stewardship program as an effort to consolidate monitoring activities.
The ESER contractor monitors offsite drinking and surface water. There were 30 drinking water and 12 surface water samples analyzed in 2005.
Table 6-1 presents the various groundwater and surface water monitoring activities performed on and around the INL Site.
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The INL Site occupies 2300 km2 (890 mi2 ) at the northwest edge of the ESRP, with the site boundaries coinciding with the Mud Lake sub-basin and the Big Lost Trough. The ESRPA owes its existence and abundance to a unique sequence of tectonic, volcanic, and sedimentologic processes associated with the migration of the North American tectonic plate southwestward across the Yellowstone hotspot, or mantle plume (Geslin et al. 1999). The basalt lava flows that host the aquifer and comprise the overlying vadose zone are very porous and permeable due to emplacement processes and fracturing during cooling. Rubble zones between lava flows and cooling fractures allow very rapid flow of water in the saturated zone, rapid infiltration of water and contaminants, and deep penetration of air into the vadose zone. Alluvial, eolian, and lacustrine sediments interbedded within the basalt sequence are generally fine-grained, commonly serving as aquitards below the water table, and affecting infiltration and contaminant transport in the vadose zone (Smith 2004).
The subsiding ESRP and the high elevations of the surrounding recharge areas comprise a large drainage basin that receives enormous amounts of precipitation and feeds high-quality groundwater into the aquifer. Northeast–southwest directed extension of the ESRP produces significant anisotropy to the hydraulic conductivity of the rocks (Smith 2004).
The Big Lost Trough receives sediment primarily from Basin and Range fluvial systems of the Big Lost River, Little Lost River, and Birch Creek. The Big Lost trough contains a >200 m thick (650 ft) succession of lacustrine, fluvial, eolian, and playa sediments, recording high-frequency Quaternary climatic fluctuations interbedded with basalt flows. Alternating deposition of clay-rich lacustrine sediments and sandy fluvial and eolian sediments in the central part of the basin was in response to the interaction of fluvial and eolian systems with Pleistocene Lake Terreton, which also, in part, is responsible for the modern day Mud Lake.
Numerous studies suggest the hydraulic gradient of the ESRPA is to the south/southwest (Figure 6-3) with velocities ranging from 1.5 to 6.1 m/day (5-20 ft/day). This is much faster than most studied aquifers and is attributed to the ESRP architecture and porous media.
Groundwater is removed from the ESRPA through pumping and as spring flows along the Snake River in the area between Twin Falls and Hagerman. Because of the high flow velocities, travel time from the INL Site to the Snake River through the ESRPA varies from 50 to 100 years.
Beyond the regional controls on flow in the ESRPA, the hydrogeology of the INL Site is controlled locally by surface water flows in the Big Lost River. Periods of high flow in the river have been shown to create temporary shifts in the local flow direction from northeast-southwest to north-south. The effect of these local changes has been to spread contamination related to INL Site operations over a larger area than would be expected. Other impacts of INL Site operations to the subsurface hydrogeology have been the formation of numerous perched water zones beneath waste ponds as a result of the seepage of pond water into the soils and the introduction of contaminants both directly (through injection) and indirectly (through vertical movement of water beneath ponds) to the ESRPA.
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Over time, hydrogeologic data at the INL Site has been collected by a number of organizations, including the USGS, the ICP contractor, and other site contractors. One of the functions of the INL Site Hydrogeologic Data Repository (HDR) is to maintain and make the data generated by these varied groups available to users and researchers. The HDR was established as a central location for the storage and retrieval of hydrologic and geologic information at the INL Site. The HDR is used to maintain reports, data files, maps, historic records, subcontractor reports, engineering design files, letter reports, subsurface information, and other data in many formats. This information is related to the hydrology and geology of the INL Site, the ESRP, and the ESRPA. The HDR is also used to maintain the INL Site Comprehensive Well Inventory, with records of well construction, modification, abandonment, and logging. The HDR also maintains databases of historic and current water analysis, water levels, and special studies. Information from the HDR is available by request. A web site is being constructed that will allow open access to much of this information.
The INL Site Sample and Analysis Management (SAM) Program was established to provide consolidated environmental sampling activities and analytical data management. The SAM provides a single point of contact for obtaining analytical laboratory services and managing cradle-to-grave analytical data records. The SAM develops statement(s) of work, procedures, and guidance documents to establish and maintain analytical and validation contracts. The consolidated approach is based on the need for Site-wide reporting compliance, comprehensive technical analyses, and increased consistency in the manner in which analytical data are managed at the INL Site. The SAM also participates in monitoring laboratory performance and annual onsite laboratory audits to ensure quality and compliance. The USGS utilizes the National Water Quality Laboratory and the Radiological and Environmental Sciences Laboratory.
The ESRPA serves as the primary source for drinking water and crop irrigation in the Upper Snake River Basin. A description of the hydrogeology of the INL Site and the movement of water in the ESRPA is given in Section 6.2. Further information may be found in numerous publications of the USGS. Copies of these publications can be requested from the USGS INL Project Office by calling 208-526‑2438. During 2005, personnel of the USGS INL Project Office published eight documents covering hydrogeologic conditions at the INL Site, on the ESRP, and in other areas of interest around the world. The abstracts to each of these reports are presented in Appendix C.
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Historic waste disposal practices have produced localized areas of radiochemical contamination in the ESRPA beneath the INL Site. The Idaho Nuclear Technology and Engineering Center (INTEC) facility used direct injection as a disposal method up to 1984. This wastewater contained high concentrations of both tritium and strontium-90 (90Sr) and iodine-129 (129I). Injection at the INTEC was discontinued in 1984 and the injection well sealed in 1990. When direct injection ceased, wastewater from INTEC was directed to a pair of shallow percolation ponds, where the water infiltrates into the subsurface. Disposal of low- and intermediate-level radioactive waste solutions to the percolation ponds ceased in 1993 with the installation of the Liquid Effluent Treatment and Disposal Facility. The old percolation ponds were taken out of service to be clean closed, and the new INTEC percolation ponds went into operation in August 2002. The Reactor Technology Complex (RTC), formerly known as the Test Reactor Area, also has a disposal well but primarily discharged contaminated wastewater to a shallow percolation pond. The RTC pond was replaced in 1993 by a flexible plastic (hypalon) lined evaporative pond, which stopped the input of tritium to groundwater.
The average combined rate of tritium wastewater disposal at the RTC and INTEC was highest between 1952 to 1983 (910 Ci/year), decreased during 1984 to 1991 (280 Ci/year), and continued to decrease during 1992 to 1995 (107 Ci/year). From 1952 to 1998, the INL Site disposed about 93 Ci of 90Sr at RTC and about 57 Ci at INTEC. Wastewater containing 90Sr was never directly discharged to the ESRPA at RTC; however, at INTEC a portion of the 90Sr was injected directly to the ESRPA. From 1996 to 1998, the INL Site disposed about 0.03 Ci of 90Sr to the INTEC infiltration ponds (Bartholomay et al. 2000).
Presently, only 90Sr continues to be detected by the ICP contractor and the USGS at levels above the PCS value in some surveillance wells between INTEC and Central Facilities Area (CFA). Other radionuclides (i.e., gross alpha) have been detected above their PCS values in wells monitored by individual WAGs.
Tritium – Because tritium is equivalent in chemical behavior to hydrogen, a key component of water, it has formed the largest plume of any of the radiochemical pollutants at the INL Site. The configuration and extent of the tritium contamination area, based on the most recent published data (2001), are shown in Figure 6-4 (Davis 2006). The area of contamination within the 0.5 pCi/L contour line decreased from about 103 km2 (40 mi2) in 1991 to about 52 km2 (approximately 20 mi2) in 1998 (Bartholomay et al. 2000).
The area of elevated concentrations near CFA likely represents water originating at INTEC some years earlier when larger amounts of tritium were disposed. This is further supported by the fact that there are no known sources of tritium contamination to groundwater at CFA.
Two monitoring wells downgradient of RTC (Well 65) and INTEC (Well 77) (see Figure 6-2) have continually shown the highest tritium concentrations in the aquifer over time. For this reason, these two wells are considered representative of maximum concentration trends in the rest of the aquifer. The average tritium concentration in Well 65 near RTC decreased from (8.3 ± 0.6) x 103 pCi/L in 2004 to (7.2 ± 0.3) x 103 pCi/L in 2005; the tritium concentration in Well 77 south of INTEC also showed a decrease, from (12.9 ± 1.2) x 103 pCi/L in 2004 to (11.5 ± 0.6) x 103 pCi/L in 2005.
The Idaho groundwater PCS value for tritium (20,000 pCi/L) is the same as the EPA MCL for tritium in drinking water. The values in both Well 65 and Well 77 dropped below this limit in 1997 as a result of radioactive decay (tritium has a half-life of 12.3 years), a cessation of tritium disposal, advective dispersion, and dilution within the ESRPA (See Figure 6-5).
Strontium-90 – The configuration and extent of 90Sr in groundwater, based on the latest published USGS data, are shown in Figure 6-6 (Davis 2006). The contamination originates from INTEC as a remnant of the earlier injection of wastewater. No 90Sr in groundwater was detected in the vicinity of RTC during 2005. All 90Sr at RTC was disposed to infiltration ponds in contrast to the direct injection that occurred at the INTEC. At RTC, 90Sr is retained in surficial sedimentary deposits, interbeds, and in the perched groundwater zones. The area of the 90Sr contamination from INTEC is approximately the same as it was in 1991.
Mean concentrations of 90Sr in INL Site monitoring wells have remained at about the same concentrations since 1989. The annual average concentration in Well 65 at RTC was about the same in 2004 (1.0 ± 2.0 pCi/L) as in 2005 (1.0 ± 0.6 pCi/L). Concentrations in Well 77 south of INTEC decreased from 1.8 ± 0.4 pCi/L in 2004 to 0.6 ± 0.9 pCi/L in 2005. The PCS and MCL for 90Sr in drinking water is 8 pCi/L.
The trend of 90Sr over the past ten years in Wells 65 and 77 is shown in Figure 6-7. No clear trends are seen in the data with one (Well 65) increasing and the other (Well 77) decreasing; moreover, the statistical fit is weak. The increases seen prior to the last few years were thought to be due, in part, to a lack of recharge from the Big Lost River that would act to dilute the 90Sr. Other reasons may also include an increase in the disposal of other chemicals into the INTEC percolation ponds that may have changed the affinity of 90Sr on soil and rock surfaces, causing it to become more mobile (Bartholomay et al. 2000).
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Sampling for purgeable (volatile) organic compounds in groundwater was conducted by the USGS at the INL Site during 2005. Water samples from an onsite production well and five groundwater monitoring wells were collected and submitted to the USGS National Water Quality Laboratory in Lakewood, Colorado, for analysis of 28 purgeable organic compounds. USGS reports describe the methods used to collect the water samples and ensure sampling and analytical quality (Mann 1996, Bartholomay et al. 2003). Eleven purgeable organic compounds were detected at concentrations above the laboratory reporting level of 0.2 or 0.1 μg/L in at least one well on the INL Site (Table 6-2). None of the measured constituents were above their respective PCS.
The RWMC production well contained detectable concentrations of nine of these purgeable organic compounds. Annual average concentrations of these compounds in this well remained essentially unchanged from those observed in 2004; however, the 2005 average concentration for trichloroethene (2.97 μg/L) was slightly above the average concentration of 2004 (2.66 μg/L).
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CERCLA activities at the INL Site are divided into WAGs that roughly correspond the major facilities at the site plus the site-wide WAG 10. The locations of the various WAGs are found on Figure 6-8. The following sub-sections provide an overview of groundwater sampling results.More detailed discussions of the CERCLA groundwater sampling can be found in the WAG specific monitoring reports within the CERCLA Administrative Record at http://ar.inel.gov . WAG 8 is managed by the Naval Reactors Facility and is not discussed in this report.
Hot Spot Zone (Trichloroethene [TCE] concentrations exceeding 20,000 µg/L) – In situ bioremediation (ISB) is used in the hot spot to promote bacterial growth by supplying essential nutrients to bacteria that occur naturally in the aquifer and are able to break down contaminants. An amendment (such as whey) is injected into well TSF-05 or other wells in the immediate vicinity. Amendment injections increase the rate at which the microbes break down the organic compounds into harmless compounds by supplying needed nutrients. The amendment supply is distributed, as needed, and the treatment system operates year-round.
In general, activities performed during 2005 included periodic whey injections, groundwater sampling and analysis, well maintenance, and minor construction activities. Groundwater samples were collected monthly from 18 sampling locations in the treatment cell to track the progress of ISB. Results of groundwater monitoring indicated that the ISB remedy continues to be effective at reducing the concentration of volatile organic compounds (VOCs) in the hot spot zone (RPT-192).
Medial Zone (TCE concentrations between 1000 and 20,000 µg/L) – Pump-and-treat is used in the medial zone. This process involves extraction of contaminated groundwater, treatment through air strippers, and reinjection of treated groundwater into the aquifer. Air stripping is a process that brings clean air into close contact with contaminated liquid, allowing the VOCs to pass from the liquid into the air.
On March 1, 2005, the New Pump and Treat Facility (NPTF) was placed into standby mode to conduct a 24-month medial zone rebound test. The purpose of this test is to evaluate the effectiveness of the NPTF in remediating the medial zone of the plume. A performance monitoring strategy has been implemented to assess the degree of rebound in trichloroethene (TCE) concentrations while the NPTF is in standby mode. The test will be dynamic in the sense that data analysis and interpretation following each sampling event will be used to determine if the NPTF needs to be re-started to treat TCE concentrations that have reached a pre-determined restart concentration criteria before the end of the 24-month test. Based on modeling, the rebound test will not have an adverse effect on the on-going remedial action. The NPTF will resume operations no later than March 1, 2007 (ICP 2005a).
Distal Zone (TCE concentrations between 5 and 1000 µg/L) – Monitored natural attenuation (MNA) is the treatment for the distal zone of the plume. MNA is the sum of the physical, chemical, and biological processes that act without human intervention to reduce the mass, toxicity, mobility, volume, or concentration of contaminants in groundwater. Engineering and administrative controls are in place to protect current and future users from health risks associated with groundwater contamination. During the early part of the restoration time frame, the contaminant plume may continue to increase slowly in size until the natural attenuation process overtakes it.
The primary MNA activities performed during 2005 were groundwater sampling and data analysis. Groundwater samples were collected for VOCs and/or radiological parameters from 60 sampling locations using 18 monitoring wells. Several of these locations were equipped with FLUTeTM systems and were sampled at multiple discrete depths below land surface. TCE concentration data and other data related to TCE degradation indicate that MNA will meet the remedial action objectives for the distal zone of the plume. Radionuclide groundwater monitoring in 2005 indicates that the natural attenuation mechanisms, as defined in the MNA Remedial Action Work Plan for the radionuclides tritium, Cesium-137 (137Cs), 90Sr, Uranium-234 (234U), continue to be functional within the contaminant plume (DOE-ID 2003a). Future groundwater monitoring, as outlined in the MNA Operations, Monitoring, and Maintenance Plan, will be sufficient to track the progress of the MNA remedy for radionuclides at Test Area North Operable Unit (OU) 1-07B (RPT-199).
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Groundwater samples were collected from seven aquifer wells for WAG-2 during calendar year 2005. The locations of the wells are shown on Figure 6-9, except for Highway 3 well (a public access potable water well), which is shown on the figure for WAG 10 sampling locations. Six of the wells were sampled in both March and October of 2005, while Middle-1823 was only sampled in October 2005. Aquifer samples were analyzed for chromium (filtered and unfiltered), 90Sr, gamma-emitting radionuclides and tritium. The data for the March 2005 sampling event can be found in the Fiscal Year 2005 Annual Report for WAG 2 (ICP 2005b) and the data for the October 2005 sampling will be in the Fiscal Year 2006 annual report for WAG 2 (not yet published). The data for the March 2005 and October 2005 sampling events are summarized in Table 6-3. Chromium was the only constituent detected above its MCL. Chromium concentrations in wells TRA-07 and USGS-065 were greater than the 100 µg/L MCL in at least one sampling event, with a maximum filtered concentration of 136 µg/L in TRA-07 (Figure 6-9). Except for the Highway-3 well, chromium concentrations were above background at all other aquifer wells sampled in WAG 2. Chromium concentrations are declining in both USGS-065 and TRA-07. \
Groundwater samples (aquifer) were collected from 22 wells under CERCLA at WAG 3 in April 2005 (DOE-ID 2006a). Groundwater samples were analyzed for tritium, 90Sr, 129I, uranium isotopes, plutonium isotopes, Americium-241 (241Am), mercury, gamma-emitting radionuclides, Neptunium-237 (237Np), Technetium-99 (99Tc), and gross alpha/beta activities. The sampling results are summarized in Table 6-4.
Groundwater monitoring results for 2005 confirm previous observations that the concentrations of most radionuclides in groundwater continue to decline over time. During 2005, 90Sr, 99Tc, 129I, and nitrate exceeded their respective drinking water MCLs in one or more of the monitoring wells at or near INTEC, with 90Sr exceeding its MCL by the greatest margin. The 90Sr concentrations remain above the MCL (8 pCi/L) at 9 of the 22 monitoring wells sampled in 2005, but 90Sr levels have declined at most locations during 2001–2005.
Strontium-90 concentrations are above the MCL (8 pCi/L) at ten monitoring wells sampled in 2005 for 90Sr (Figure 6-10). However 90Sr levels have declined at most locations from the concentrations that were observed in 2001 and 2003. Although 90Sr was above its maximum contaminant level of 8 pCi/L in several wells near INTEC, it was below its maximum contaminant level in the downgradient direction in a well at the CFA landfills (Figure 6-10).
In 2005, only one well exceeded the 129I MCL of 1 pCi/L (USGS-47; 1.23 pCi/L). During the previous two years (2003 and 2004), none of the INTEC aquifer wells exceeded the 129I MCL. Since 2001, it appears that 129I concentrations have increased slightly in several wells, but trends are inconclusive. Tritium concentrations have been below the MCL in all wells sampled during 2003–2005 and continue to decline in trend.
Technetium-99 was detected above the MCL (900 pCi/L) in two wells, ICPP-MON-A-230 and ICPP-2021, within INTEC, but concentrations were below the MCL at all other locations. The occurrence of elevated 99Tc in groundwater is believed to be the result of past leaks from underground pipelines and valve boxes at the INTEC tank farm.
Cesium-137 was present in a groundwater sample (10.9 pCi/L) from a monitoring well near the former injection well, but the concentration was far below the MCL of 200 pCi/L.
Plutonium-239/240 was reported in groundwater samples from the USGS-42 (0.045J pCi/L) and USGS‑67 (0.0428J pCi/L) wells. These concentrations were below the MCL (15 pCi/L). Plutonium-241 was detected in just one well (USGS-48; 20.6 pCi/L). This concentration was below the derived MCL (300 pCi/L). Americium-241 was not detected in any of the samples, and 237Np was only detected in a single well at a concentration close to the detection limit. Neither 237Np nor 241Am was detected in any of the groundwater samples collected during 2005.
Uranium‑238 was detected in groundwater at all sampling locations; however, with the possible exception of the ICPP-MON-A-230 well, the reported concentrations of 238U are generally consistent with background concentrations reported for total uranium in the ESRPA elsewhere. Uranium-233/234 was also detected in all samples at concentrations similar to the ESRPA elsewhere, and 234U/238U ratios were similar to background 234U/238U ratios for the ESRPA. Uranium-235 was detected in groundwater from 8 of the 22 wells, but concentrations were similar in upgradient and downgradient wells.
Dissolved mercury was detected at a single location in the groundwater sample from the USGS‑47 well (0.077 µg/L), which is below the MCL of 2 µg/L. The detection of mercury in groundwater samples from USGS-47 is consistent with the presence of mercury in the service waste previously discharged to the former injection well located about 750 ft upgradient of this well.
Nitrate was detected in all of the wells sampled during 2005. The highest concentrations were reported at the ICPP-2021 new aquifer well (13.2 mg/L as N), ICPP-MON-A-230 (7.7 mg/L), and MW‑18-4 (7.3 mg/L). All of these wells are located relatively close to the tank farm, and all show groundwater quality impacts attributed to past tank farm liquid waste releases. The nitrate-nitrogen at ICPP-2021 slightly exceeds the MCL for nitrate-nitrogen of 10 mg/L (as N).
Gross beta results generally mirrored the results for 90Sr and 99Tc. Gross alpha activity in groundwater samples were all below the MCL.
Depth-specific groundwater samples were collected, using a packer-isolation method, from monitoring wells USGS-041, USGS-044, USGS-046, USGS-047, USGS-048, USGS-52 and USGS-059 to investigate variations in groundwater quality with depth in the aquifer. The results generally show that concentrations of the principal radionuclides decrease with depth below the water table, with the highest concentrations of 90Sr, 99Tc, 129I, and tritium observed at the USGS-47 well, which is located approximately 229 m (750 ft) downgradient of the former injection well. None of the packer samples exceeded the 5 pCi/L 129I action level established in the Explanation of Significant Differences (DOE-ID 2004a), and none of the packer samples collected below the HI sedimentary interbed exceeded the 1 pCi/L 129I MCL.
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Groundwater monitoring for the CFA landfills consisted of sampling nine wells for volatile organic compounds, metals, and anions in October 2005. Because of falling water levels in the aquifer, only nine of the thirteen wells WAG 4 wells had sufficient water for sampling. Groundwater samples were not collected from LF2-08, LF2-09, LF2-11 and LF3-10. The locations of the CFA monitoring wells are shown on Figure 6-11. Analytes detected in groundwater are compared to regulatory levels in Table 6-5. A full description of the groundwater sampling and results is contained in (RPT-196).
Nitrate and chromium are the only constituents found to exceed their groundwater MCLs during the 2005 CFA landfill monitoring effort. Nitrate exceeded its MCL in two wells, CFA-MON-A-002 and CFA-MON-A-003. Although nitrate concentrations increased in CFA-MON-A-003 in the 2005 sampling event, nitrate concentrations in CFA‑MON‑A‑002 and ‑003 had been relatively consistent since monitoring started in 1995. The occurrence of chromium above its MCL in LF3-09 could be due to suspended soil or rock particles in the unfiltered sample.
Groundwater gradients and groundwater flow directions are consistent with previous years and indicate that elevated nitrate concentrations in CFA-MON-A-002 and -003 should not affect the CFA production wells.
Groundwater monitoring for WAG 5 in 2005 was completed in November–December 2005 in accordance with the WAG 5 ROD (DOE-ID 2000), the Groundwater Monitoring Plan (DOE‑ID 2004b) and recommendations from the first 5-year review (DOE-ID 2005). Eight of nine wells were sampled with only well ARA-MON-A-002 not being sampled due to malfunctioning equipment. The locations of the WAG 5 wells are shown on Figure 6-12. Three wells were sampled for volatile organic compounds and eight wells were sampled for select metals. Specific metals requested included arsenic, barium, cadmium, chromium, lead, mercury, selenium, silver and zinc. The results are summarized below and on Table 6-6. The complete listing of results can be found in RPT-220. Overall, most analyte concentrations appear to be consistent with historical results and do not indicate the influence of contaminants from the surface of the Auxiliary Reactor Area (ARA) or Critical Infrastructure Test Range Complex (CITRC) areas.
All constituents analyzed from the groundwater samples collected during the November–December 2005 sampling event were below MCLs. Lead concentrations, which had been above the action level for lead in several wells in the past, were all below the action level in November–December 2005. The 2005 sampling event represents the fourth consecutive year that the lead concentrations have not exceeded the action level. Replacement of galvanized pipe with stainless steel pipe appears to have removed the source of the lead.
Fifteen aquifer-monitoring wells were sampled semiannually under operable unit (OU) 7‑13/14 and analyzed for a variety of radionuclide, inorganic, and organic contaminants (RPT-171). In addition to the wells monitored by OU 7‑13/14, the USGS routinely samples eight wells in the vicinity of the RWMC. The location of the aquifer monitoring wells sampled at the RWMC are shown on Figure 6-13.
In the aquifer near the RWMC, carbon tetrachloride was the only analyte consistently detected at concentrations near and occasionally exceeding the primary drinking water MCL in Fiscal Year 2005 (Table 6-7). Trichloroethene was also detected, but it occurred at concentrations less than its MCL. Tritium was consistently detected in the aquifer north of the RWMC; however, concentrations are substantially below the drinking water MCL. The source of the small, isolated tritium plume in the aquifer at the RWMC has been identified as being from upgradient facilities, primarily INTEC, and not from the SDA.
MFC samples five wells (four monitoring and one production) (Figure 6-14) twice a year for selected radionuclides, metals, total organic carbon, total organic halogens, and other water quality parameters as required under the WAG 9 ROD (ANL-W, 1998). The analytical results for 2005 are summarized in Table 6-8.
The groundwater sampling for WAG 10 consisted of sampling 27 wells in June-July, 2005. The wells were sampled for volatile organic compounds (target analyte list), metals (filtered), anions (including alkalinity), and radionuclides (129I, tritium, 99Tc, gross alpha, gross beta, gamma-emitting radionuclides, uranium-isotopes, and 90Sr). The locations of the wells are shown in Figure 6-15. The results are summarized on Table 6-9 and briefly described below. The complete results can be found in the WAG 10 RI/FS Annual Report (DOE-ID, 2006b).
Detected VOCs include toluene and acetone. Toluene was detected in seven
wells at concentrations ranging from 0.18 to 18 µg/L. Toluene detections are
notably beneath the MCL of 1000 µg/L.
Lead and antimony were reported above their respective MCLs in the duplicate sample from USGS-027, but both metals were considerably below their respective MCLs in the original sample from this well. All other metals were below there respective MCLs. Nitrate continues to be elevated in USGS-004 relative to other WAG 10 wells and probably represents off-site agricultural influences upgradient of the INL Site. Off-site influence was also indicated by elevated specific conductivity values for USGS-004 and USGS-027.
Tritium, gross alpha, gross beta, uranium isotopes were the primary radiological analytes detected. Gross alpha, gross beta, and uranium isotopes were at background concentrations. Tritium was detected in two wells south of CFA at concentrations less than 1000 pCi/L or well below the MCL of 20,000 pCi/L.
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As part of the offsite monitoring performed by the ESER contractor, radiological analyses are performed on drinking water samples taken at offsite locations. In 2005, the ESER contractor collected 30 drinking water samples from 14 offsite locations.
Gross alpha activity was detected in one sample from Idaho Falls in May. The measured concentration of 7.84 ± 1.45 pCi/L was below the EPA MCL of 15 pCi/L.
As in years past, measurable gross beta activity was present in most offsite drinking water samples (19 of the 30 samples). Detectable concentrations ranged from 2.62 ± 0.86 pCi/L to 13.50 ± 1.15 pCi/L (Table 6-10). The upper value of this range is appreciably below the EPA screening level for drinking water of 50 pCi/L. Concentrations in this range are normal and cannot be differentiated from the natural decay products of thorium and uranium that dissolve into water as the water passes through the basalt terrain of the Snake River Plain.
Tritium was measured in eight drinking water samples during 2005, ranging from 78.6 ± 25.1 pCi/L at Idaho Falls in May to 223.0 ± 31.4, also at Idaho Falls, in November (Table 6-11). The maximum level is still significantly below the EPA MCL of 20,000 pCi/L for tritium in water. These levels can be explained by natural variability.
As part of the offsite monitoring performed by the ESER contractor, radiological analyses are performed on surface water samples taken at offsite locations. Locations outside of the INL Site boundary are sampled twice a year for gross alpha, gross beta, and tritium. In 2005, the ESER contractor collected 12 surface water samples from five offsite locations.
Gross alpha activity was not detected in any surface water samples during 2005.
Tritium was detected in two offsite surface water samples during 2005. The November surface water sample collected at Idaho Falls had a concentration of 231.0 ± 31.0 pCi/L and the November duplicate sample collected in the Hagerman area had a concentration of 384.0 ± 32.9 pCi/L (Table 6-11). These concentrations were well below the PCS and EPA MCL of 20,000 pCi/L.
Gross beta activity was measured in 11 of the 12 offsite surface water samples. Detectable concentrations ranged from 3.22 ± 0.90 pCi/L to 7.09 ± 0.96 pCi/L at Hagerman and Bliss, respectively. The maximum concentration is below the EPA screening level for gross beta in drinking water of 50 pCi/L. Concentrations in this range are consistent with those measured in the past and cannot be differentiated from natural decay products of thorium and uranium that dissolve into water as the water passes through the surrounding basalts of the Snake River Plain.
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