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R. Wells - CH2M-WG Idaho
M. Roddy, L. Nelson - CH2M-WG Idaho
L. Knobel, L. Davis - U.S. Geological Survey
M. Case - S. M. Stoller Corporation
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.
Section 6.1 summarizes the monitoring programs. Sections 6.2 and 6.3 present discussions of the hydrogeology of the INL Site and hydrogeologic data management, respectively. Section 6.4 describes aquifer studies related to the INL Site and ESRPA. Radiological and nonradiological monitoring of groundwater at the INL Site are discussed in Sections 6.5 and 6.6, respectively. Section 6.7 outlines the CERCLA groundwater activities performed in 2006. Section 6.8 describes offsite drinking and surface water monitoring.
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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 2006, 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 2006.
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 2,300 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
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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.
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 2006, 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 tritium, strontium-90 (+Sr) 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 had 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) 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 (7.2 ± 0.3) x 103 pCi/L in 2005 to (6.3 ± 0.6) x 103 pCi/L in 2006; the tritium concentration in Well 77 south of INTEC was not received from the analytical laboratory in time for inclusion in this annual report.
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 2006. 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. However, the annual average concentration in Well 65 at RTC in 2006 was undetectable. Concentrations in Well 77 south of INTEC were not received from the analytical laboratory in time for inclusion for this report.
The trend of 90Sr over the past ten years (1996-2005) 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 2006. 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). Thirteen 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 eleven of
these purgeable organic compounds. Annual average concentrations of these
compounds in this well remained essentially unchanged from those observed in
2004; however, the 2006 average concentration for trichloroethene (3.33 μg/L)
was slightly above the average concentration of 2005 (2.97 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.
Groundwater monitoring is performed at WAG 1 to measure the progress of the remedial action at Test Area North (TAN). The groundwater plume at TAN has been divided into three zones to facilitate remediation. The monitoring program and the results are summarized by zone in the following paragraphs.
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 2006 included periodic whey injections, groundwater sampling and analysis, well maintenance, and minor construction activities. Groundwater samples were collected monthly from 12 sampling locations and quarterly from 6 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-372).
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 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. During 2006, the concentration of contaminants in the medial zone remained below the re-start threshold and the NPTF remained on standby throughout the year. The NPTF will resume operations no later than March 1, 2007 (ICP 2005).
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 2006 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 2006 indicates that the natural attenuation mechanisms, as defined in the MNA Remedial Action Work Plan for the radionuclides tritium, Cesium-137 (137Cs), 90Sr, and 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-383).
Groundwater samples were collected from seven aquifer wells for WAG-2 during calendar year 2006. 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 2006. TRA-08 was not sampled in March 2006 and USGS-065 was not sampled in October 2006. Aquifer samples were analyzed for chromium (filtered and unfiltered), 90Sr, gamma-emitting radionuclides, gross alpha, gross beta and tritium. The data for the March 2006 sampling event can be found in the Fiscal Year 2006 Annual Report for WAG 2 (DOE-ID 2007a) and the data for the October 2006 sampling event will be in the Fiscal Year 2007 annual report for WAG 2 (not yet published). The data for the March 2006 and October 2006 sampling events are summarized in Table 6-3. Chromium and 90Sr were detected above their respective MCLs in one well each.
Chromium concentrations in well TRA-07 were greater than the 100 μg/L MCL in both 2006 sampling events, with a maximum filtered concentration of 133 μg/L (Figure 6-9). Previously, USGS-065 had been above the chromium MCL but chromium concentrations were below the MCL for the one time that the well was sampled in 2006. 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.
Strontium-90 occurred at a concentration of 13.4 pCi/L and above its MCL of 8 pCi/L in the October 2006 sample from TRA-08. This well was not sampled in March 2006 because the pump was not working. Strontium-90 has only been detected in TRA-07 once before in October 2005. This occurrence of 90Sr in this well is uncertain since aquifer wells located between this well and RTC do not have 90Sr.
During 2006, groundwater samples were collected from a total of 22 Snake River Plain Aquifer (SRPA) monitoring wells, plus six aquifer wells sampled for the Idaho CERCLA Disposal Facility (ICDF) monitoring program (Figure 6-10). Groundwater samples were analyzed for a suite of radionuclides and inorganic constituents that included 90Sr, 99Tc, 129I, nitrate, tritium, plutonium isotopes, uranium isotopes, and mercury.
For each of the primary constituents of concern (COC), Table 6-4 summarizes the maximum COC concentration observed during 2006 in the SRPA groundwater at INTEC, along with the number of MCL exceedances. Highlights of the 2006 monitoring results are presented below.
Strontium-90, 99Tc, and nitrate exceeded their respective drinking water MCLs in one or more of the aquifer monitoring wells at or near INTEC, with 90Sr exceeding its MCL by the greatest margin. Strontium-90 concentrations remain above the MCL (8 pCi/L) at nine of the 22 monitoring wells sampled in 2006, and 90Sr concentrations remained nearly constant (within ±2 sigma) in nine out of 14 monitoring wells that were sampled in both 2005 and 2006. Six of 22 wells showed 90Sr declines during this period, and only one well located southeast of INTEC showed a slight increase (USGS-67).
Technetium-99 was detected above the MCL (900 pCi/L) in two wells within INTEC, but concentrations were below the MCL at all other locations. As in the past, the highest 99Tc level was at the ICPP MON A 230 monitoring well (2150 pCi/L) located north of the INTEC tank farm. Technetium-99 concentrations declined between 2005 and 2006 at seven of the wells, and 99Tc levels at nine of the 16 aquifer wells sampled overlapped the results from the previous year. USGS-67 was the only well that showed an increase in 99Tc from 2005 to 2006.
Iodine-129 concentrations at all aquifer well locations were less than the MCL,
with the highest concentration reported at well USGS-67 (0.65 pCi/L). This is
the same well that has shown rising concentrations of 99Tc over the
past several years. The 129I results for 15 out of 16 aquifer wells
were similar to the results from the previous year. One well showed a decline in
129I during this interval (USGS-47), and none of the aquifer wells
showed increases in 129I.
Tritium concentrations have been below the MCL in all aquifer wells sampled during 2003–2006. The highest tritium concentration in groundwater during 2006 was at well MW-18-4 (8930 pCi/L) located near the former Waste Calcining Facility. The tritium results for 12 of the 16 wells were similar between 2005 and 2006. One well showed a tritium increase during this period (USGS-42), and three wells showed declines in tritium. Examination of longer-term trends indicates that tritium concentrations in groundwater have continued to decline during the period from 2000 through 2006.
Plutonium-238 was detected in a single SRPA groundwater sample from well USGS-112 (1.33 pCi/L). Similarly, 239/240Pu was detected only at well USGS-112 (1.42 pCi/L), as was 241Am (0.333 pCi/L). The gross alpha MCL that applies to Pu isotopes is 15 pCi/L. In addition, 241Pu (beta emitter) was detected in the groundwater sample from MW-18-4 (5.7 pCi/L). The derived MCL for 241Pu is 300 pCi/L. Neptunium-237 was not detected in any of the groundwater samples collected during 2006.
Uranium-238 was detected in SRPA groundwater at all sampling locations; however, with the exception of well USGS-112 located midway between INTEC and CFA, the reported concentrations of 238U are generally consistent with background concentrations reported for total uranium in SRPA groundwater elsewhere (Knobel, Orr, and Cecil 1992). Uranium-233/234 was also detected in all samples at concentrations similar to SRPA groundwater elsewhere, and 234U/238U ratios were similar to background 234U/238U ratios for the eastern SRPA. Uranium-235 was not detected in any of the WAG 3, Group 5 aquifer monitoring wells but was reportedly detected in several ICDF aquifer monitoring wells at concentrations ranging from 0.1 to 0.168 pCi/L.
Mercury was detected at a single location in SRPA groundwater (ICPP-2020; 0.065 µg/L). This value is below the mercury MCL of 2 µg/L.
Nitrate was detected in all of the wells sampled during 2006, but the only aquifer well that exceeded the MCL for nitrate-nitrogen of 10 mg/L was well ICPP-2021 (16.4 mg/L as N) located southeast of the tank farm.
The 2006 groundwater contour map is similar in shape to the maps prepared for 2003–2005. Groundwater levels declined during 2000-2005 as a result of drought during this time period. However, as a result of above-normal precipitation during 2005 and 2006 and corresponding periods of flow of the Big Lost River (BLR) during those 2 years, the aquifer well hydrographs show a slight rise in groundwater levels during 2006.
Groundwater monitoring for the CFA landfills consisted of sampling eight wells for volatile organic compounds, metals, and anions in October 2006 in accordance with the Field Sampling Plan (INEL 2006). The locations of the CFA monitoring wells are shown on Figure 6-11. Because of falling water levels in the aquifer, 4 wells, LF2-08, LF2-09, LF2-11 and LF3-10, had insufficient water for sampling. In addition, Well CFA-1932 south of CFA Landfill I was not sampled because of a malfunctioning pump. Wells were sampled for metals (filtered and unfiltered), VOCs, and anions (nitrate, chloride, fluoride and sulfate). Analytes detected in groundwater are compared to regulatory levels in Table 6-5. A complete listing of the groundwater sampling results is contained in RPT-362.
The groundwater data indicated that nitrate and thallium were the only analytes detected above a U.S. Environmental Protection Agency maximum contaminant level. Nitrate was detected above its maximum contaminant level (MCL) of 10 mg/L in Wells CFA MON A 002 (20.2 mg/L N) and CFA MON A 003 (11 mg/L N). Except for the recent spike in CFA-MON-A-003, nitrate concentrations in CFA MON-A-002 and 003 have remained relatively steady since monitoring began in 1995. Thallium was detected above its MCL in four wells, but its occurrence may be an artifact of the analytical method because of the high detection limit (5 μg/L) for the analytical method used. The analytical method for thallium will be changed to a method with a lower detection limit for the 2007 sampling event for WAG 4.
Iron, aluminum, and manganese occurred above secondary maximum contaminant levels (SMCLs). Iron was detected above its SMCL of 300 µg/L in unfiltered samples from four wells, and aluminum was detected above its SMCL of 200 µg/L in two unfiltered samples. The occurrence of both iron and the aluminum above their respective SMCLs is likely the result of suspended particulates since filtered samples were well below the SMCLs. Manganese exceeded its SMCL in one well, but the cause or source of the manganese is uncertain.
The 2006 water-level data for the CFA landfill wells suggest that water levels may be stabilizing. 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 2006 was completed in November 2006 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). The three wells, PBF-MON-A-001, SPERT-I, and PBF-MON-A-003, were sampled for volatile organic compounds. The locations of the WAG 5 wells are shown on Figure 6-12. The number of wells sampled for WAG 5 was reduced from nine to three because the analytical results for metals in 2005 were below maximum contaminant levels, secondary maximum contaminant levels, or action levels. Consequently, the sampling of Waste Area Group 5 wells for metals was discontinued after the late 2005 sampling event and the number of wells sampled reduced to three, as agreed upon in the first five-year review.
In 2006, no target analyte was detected; consequently, no analyte exceeded a maximum contaminant level. The complete listing of analytical results for 2006 can be found in RPT-382.
More than 4000 analyses were performed on samples collected from 15 RWMC aquifer monitoring wells in FY 2006. The location of aquifer monitoring wells sampled at the RWMC are shown on Figure 6-13. Reportable contaminants detected above reporting thresholds in FY 2006 include carbon tetrachloride, trichloroethylene, tritium, and uranium isotopes (RPT-339).
Carbon tetrachloride and trichloroethylene concentrations in seven wells consistently exceeded background reporting limits in FY 2006, and carbon tetrachloride exceeded the MCL in two of the wells. Since 2002, carbon tetrachloride concentrations at Well M7S have been above the MCL and are steadily increasing. Trichloroethylene concentrations are also increasing in Well M7S. Other wells in the vicinity of M7S (i.e., M3S, M15S, and USGS RWMC Production) also exhibit increasing concentrations of carbon tetrachloride and trichloroethylene. Increasing VOC concentrations in aquifer wells north northeast of the SDA are likely the result of migration from the SDA. While concentrations of carbon tetrachloride and trichloroethylene are increasing at locations north of the SDA, they are decreasing in wells south of the SDA (i.e., A11A31, OW2 USGS-88, and USGS-120).
Slightly elevated concentrations of tritium were detected in wells north-northeast of the SDA (M3S, M7S, M14S, M16S); however, concentrations are substantially below the drinking water MCL. Elevated concentrations have been measured in these wells since about 1975 and have not decreased as expected from effects of dilution, dispersion, and radioactive decay, suggesting a source of tritium is continually replenishing the area. Recent studies conducted by WAG 10 indicate that tritium found in RWMC wells north-northeast of the SDA are likely associated with plumes originating at INTEC and RTC (DOE-ID 2007a).
Uranium concentrations at three monitoring locations (M7S, M14S, OW2) slightly exceeded background reporting thresholds in FY 2006. Detections above background thresholds at M7S and M14S are rare; however, detections at OW2 often exceed background limits by a small amount. Slightly elevated uranium levels at OW2 are expected because of the well location and construction.
Detections of relevant analytes with concentrations above reporting thresholds are summarized in Table 6-6.
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 reported concentrations of analytes that were detected in at least one sample are summarized in Table 6-7a and Table 6-7b.
Groundwater sampling was conducted in accordance with the Groundwater Monitoring and Field Sampling Plan (DOE-ID 2006). Eighteen wells and two multi-level Westbay wells with five sampling intervals in each were sampled for volatile organic compounds (contact laboratory program target analyte list), metals (filtered), anions (including alkalinity), and radionuclides (129I, tritium, 99Tc, gross alpha, gross beta, and 90Sr) during June and July 2006. The locations of the wells are shown in Figure 6-15. The results are summarized on Table 6-8 and briefly described below. The complete listing of results can be found in the WAG 10 RI/FS Annual Report (DOE-ID, 2007b).
No contaminant exceeded an MCL in a well along the southern boundary of the INL Site or downgradient of the Site in the FY 2006 groundwater monitoring.
The primary radiological analytes detected in the boundary, guard, and distal wells included gross alpha, gross beta, and tritium (Table 6-8). These analytes were below their respective maximum contaminant levels (MCLs). The concentrations of gross alpha, and gross beta in the WAG 10 wells were similar to background, based on background values from Knobel, Orr, and Cecil (1992). Tritium was detected in two wells, USGS-104 and USGS-106, and both of these wells have a history of tritium detections. Over the past 20 years, both wells exhibit a downward trend in tritium concentration. The tritium concentrations in these wells currently are less than 1,100 pCi/L and considerably less than the MCL of 20,000 pCi/L (Table 6-8).
In the Westbay wells, tritium, gross alpha and gross beta were also the primary radiological analytes detected. Gross alpha and gross beta were at background concentrations. Tritium was detected in four intervals, 748 ft, 834 ft, 1048 ft and 1148 ft bgs, from MIDDLE-2051 in 2006 at concentrations less than 600 pCi/L. Strontium-90 was detected in 2006 in the two deepest intervals from MIDDLE-2050A, but the reported 90Sr concentrations were below the MDA. The occurrence of 90Sr in these samples below its MDA is questionable.
Three volatile organic compounds-toluene, carbon tetrachloride, and chloromethane-were detected at concentrations well below their respective MCLs. Toluene was detected in samples from two wells at concentrations of 2.9 µg/L (USGS-108) and 4.8 µg/L (USGS-105). Toluene was also detected in packer samples from USGS-108 (627 ft, 0.25 µg/L) and USGS-105 (769 ft, 2 µg/L). All the toluene detections were below the MCL for toluene of 1000 µg/L. The source of the toluene is uncertain, but the lack of other hydrocarbons at the locations with the toluene detections is not consistent with fuel migration. Toluene is a common laboratory contaminant and that source cannot be ruled out. Carbon tetrachloride was detected at 0.15 µg/L in USGS-109, located directly south of the RWMC on the INL boundary. The carbon tetrachloride concentration in USGS-109 is an estimated value or J flagged and is close to the method detection limit. A carbon tetrachloride plume originates at the RWMC and this carbon tetrachloride detection could represent migration from the RWMC. Chloromethane was detected in the deepest sample from MIDDLE-2051, but the concentration was near the detection limit.
In the Westbay wells, only manganese was above its secondary MCL of 50 µg/L in one sample. The elevated manganese concentration of 424 µg/L occurred in the deepest sample from MIDDLE-2051. However, this elevated manganese detection is not consistent with the previous sample from this depth in 2005. The inconsistent manganese detections above the secondary MCL make the occurrence suspect and are not traceable back to any known source at INL.
Although not above its secondary MCL, zinc concentrations in the groundwater samples from USGS 011, USGS-086, USGS-100, USGS-103, USGS-104, USGS 106, USGS-108, USGS-109, and the Highway 3 well were elevated. The elevated zinc concentrations in these groundwater monitoring wells are probably the result of corroding galvanized discharge/riser pipe used in their construction. Elevated zinc concentrations in groundwater have been correlated to galvanized riser pipes for other wells at the INL Site (INEEL 2003; ICP 2004).
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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 2006, the ESER contractor collected 30 drinking water samples from 14 offsite locations.
Gross alpha activity was detected in one sample from Howe in May. The measured concentration of 1.58 pCi/L was below the EPA MCL of 15 pCi/L. Gross alpha activity was also detected in two samples from Atomic City and Howe in November. The concentrations, 1.81 pCi/L and 1.03 pCi/L, respectively, were also below the EPA MCL.
As in years past, measurable gross beta activity was present in most offsite drinking water samples (26 of the 30 samples). Detectable concentrations ranged from 1.51 pCi/L to 7.83 pCi/L (Table 6-9). 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 two drinking water samples during November 2006, at Mud Lake and Shoshone (Table 6-9). The maximum level, 92.60 pCi/L, is significantly below the EPA MCL of 20,000 pCi/L for tritium in water.
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 2006, the ESER contractor collected 13 surface water samples from six offsite locations, including the Big Lost River in May. The Big Lost River is usually dry when surface water samples are collected.
Gross alpha activity was detected in two surface water samples during 2006, below the EPA MCL of 15 pCi/L. Gross beta activity was detected in all surface water samples collected in 2006, ranging in concentrations from 1.64 pCi/L to 8.82 pCi/L. These results are well below the EPA MCL of 50 pCi/L. Gross alpha and beta concentrations that were measured 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.
Tritium was detected in two offsite surface water samples collected in
November 2006. The sample collected at Mud Lake had a concentration of 92.0
pCi/L. The sample collected in Shoshone had a concentration of 92.6 pCi/L (Table 6-10). These concentrations were well below the PCS and EPA MCL of 20,000
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