The overall objectives of environmental monitoring at the Hanford Site are to demonstrate compliance with applicable federal, state, and local regulations; confirm adherence to DOE environmental protection policies; and support environmental management decisions.
Environmental monitoring of the site consists of 1) effluent monitoring, 2) environmental surveillance, and 3) groundwater and vadose zone monitoring.
Effluent monitoring includes facility effluent monitoring (monitoring effluents at the point of release to the environment) and near-facility environmental monitoring (monitoring the environment near operating facilities).
Liquid and gaseous effluents that may contain radioactive and hazardous constituents are continually monitored at the Hanford Site. Facility operators monitor effluents mainly through analyzing samples collected near points of release into the environment. Effluent monitoring data are evaluated to determine their degree of compliance with applicable federal, state, and local regulations and permits.
Measuring devices are used to quantify most facility effluent flows, with a smaller number of flows calculated using process information. Liquid and gaseous effluents with a potential to contain radioactivity at prescribed threshold levels are monitored for gross alpha and gross beta activity and, as warranted, specific gamma-emitting radionuclides. Nonradioactive hazardous constituents are also monitored, as applicable.
Radioactive effluents from many onsite facilities are approaching levels practically indistinguishable from the naturally occurring radioactivity present everywhere. This decrease translates to a very small offsite radiation dose attributable to site activities. The new site mission of environmental restoration rather than nuclear materials production is largely responsible for this trend. Consistent with these conditions of diminishing releases, totals of radionuclides in effluents released at the site in 1997 were not significantly different from totals in 1996.
The near-facility environmental monitoring program is designed to protect the environment adjacent to facilities. Specifically, this program monitors new and existing sites, processes, and facilities for potential impacts and releases; fugitive emissions and diffuse sources from contaminated areas; and surplus facilities before decontamination or decommissioning. Air, surface water and springs, surface contamination, soil and vegetation, external radiation, and investigative sampling (which can include wildlife) are sampled. Some parameters typically monitored are pH, radionuclide concentrations, radiation exposure levels, and concentrations of selected hazardous chemicals. Samples are collected from known or expected effluent pathways. These pathways are generally downwind of potential or actual airborne releases and downgradient of liquid discharges.
Near-Facility Air Monitoring. Radioactivity in air was sampled by a network of continuously operating samplers at 62 locations near nuclear facilities. Air samplers were primarily located within approximately 470 meters (1,500 feet) of sites and/or facilities having the potential for, or history of, environmental releases, with an emphasis on the prevailing downwind directions. Of the radionuclide analyses performed, strontium-90, cesium-137, plutonium-239,240, and uranium were consistently detected in the 100-K, 100-N, and 200 Areas. Cobalt-60 was consistently detected in the 100-N Area. Air concentrations for these radionuclides were elevated near facilities compared to the concentrations measured offsite by Pacific Northwest National Laboratory.
Surface-Water Disposal Units and 100-N Springs Monitoring. Samples collected from surface-water disposal units (ponds, ditches) included water, sediment, and aquatic vegetation. Only water samples were taken at 100-N shoreline springs. Radiological analyses of water samples from surface-water disposal units included strontium-90, plutonium-238, plutonium-239,240, uranium, tritium, and gamma-emitting radionuclides. Radiological analyses of sediment and aquatic vegetation samples were performed for strontium-90, plutonium-239,240, uranium, and gamma-emitting radionuclides. Nonradiological analyses were performed for pH, temperature, and nitrates (Figure 11).
Figure 11. Thousands of environmental samples are analyzed annually.
Radiological analytical results for liquid samples from surface-water disposal units located in the 200 Areas were less than the DOE-derived concentration guides and, in most cases, were equal to or less than the analytical detection limits. Although some elevated levels were seen in both aquatic vegetation and sediment, in all cases, the radiological analytical results were much less than the standards used for radiological control.
The results for pH were well within the 2.0 to 12.5 pH standard for liquid effluent discharges based on the discharge limits listed in the Resource Conservation and Recovery Act. The analytical results for nitrates were all less than the 45-milligram per liter EPA drinking water standard for public water supplies.
Groundwater springs along the 100-N Area shoreline are sampled annually to verify the reported radionuclide releases to the Columbia River from past N Reactor operations.
Near-Facility Radiological Surveys. In 1997, there were approximately 3,990 hectares (9,859 acres) of posted outdoor contamination areas and 614 hectares (1,517 acres) of posted underground radioactive materials areas, not including active facilities, at the Hanford Site. These areas were typically associated with burial grounds, covered ditches, cribs, and tank farms. The posted contamination areas vary in size between years because of an ongoing effort to clean, stabilize, and remediate areas of known contamination. New areas of contamination are also being identified. In 1997, it was estimated that the external dose rate at 80% of the identified outdoor contamination areas was less than 1 millirem per hour measured at 1 meter (3.28 feet), though direct dose rate readings from isolated radioactive specks (a diameter less than 0.64 centimeter [0.25 inch]) could have been considerably higher. Contamination levels of this magnitude did not significantly add to dose rates for the public or Hanford Site workers in 1997.
Soil and Vegetation Sampling from Operational Areas. Soil and vegetation samples were collected for radiological analysis on or adjacent to waste disposal units and from locations downwind and near or within the boundaries of the operating facilities. Samples were collected to detect potential migration and deposition of contaminants in facility effluents. Special samples were also taken where physical or biological transport problems were identified.
Movement of contaminants can occur as a result of resuspension from radioactively contaminated surface areas, absorption of radionuclides by the roots of vegetation growing on or near underground and surface-water disposal units, or by waste site intrusion by animals. Soil and vegetation sample concentrations for some radionuclides were elevated near facilities when compared to concentrations measured off the site. The concentrations show a large degree of variance; in general, samples collected on or adjacent to waste disposal facilities had significantly higher concentrations than those collected farther away. The number of sampling locations at the 100-N Area was reduced by approximately 50% in 1997.
Near-Facility External Radiation. External radiation fields were measured near facilities and waste handling, storage, and disposal sites to measure, assess, and control the impacts of operations.
Four new thermoluminescent dosimeter monitoring sites were established in the 100-B,C Area during late 1997 to evaluate environmental restoration activities at the 116-B-11 Water Retention Basin and the 116-C-1 Liquid Waste Disposal Trench. The 1997 average reading for these locations was comparable to offsite background levels.
Five thermoluminescent dosimeter locations were established in the 100-D,DR Area during late 1996 to evaluate environmental restoration activities at the 116-D-7 and 116-DR-9 Water Retention Basins. The 1997 readings were comparable to offsite background levels.
This is the fifth year that thermoluminescent dosimeters were placed in the 100-K Area, surrounding the 105-K East and 105-K West Fuel Storage Basins and adjacent reactor buildings. Three of the dosimeters have consistently shown elevated readings as a result of their proximity to radioactive waste storage areas or stored radioactive rail equipment.
A hand-held micro-rem meter (to measure low-level radiation exposure) was used to survey points along the 100-N Area shoreline springs (Figure 12). The radiation rates measured continued to decline in 1997, reflecting discontinued discharges to the 1301-N Liquid Waste Disposal Facility and the continuing decay of its radionuclide inventory.
Figure 12. Radiation survey measurements are conducted along the 100-N Area shore-line. This figure compares results from 1988 and 1997.
The 1997 thermoluminescent dosimeter results indicate that direct radiation levels are highest near facilities that had contained or received liquid effluent from N Reactor. These facilities primarily include the 1301-N and 1325-N Liquid Waste Disposal Facilities. Exposure levels at these facilities in 1997 were approximately 17% lower than levels measured in 1996.
The highest dose rates in the 200/600 Areas were measured near waste handling facilities such as tank farms. The highest dose rate was measured at the A Tank Farm complex (200-East Area). The average annual dose rate measured in 1997 was 110 millirem per year, approximately 8% lower than the dose rate measured in 1996.
Two thermoluminescent dosimeter locations were established at the Environmental Restoration Disposal Facility during late 1996 to evaluate disposal activities in progress. Readings in 1997 were comparable to offsite background levels.
The highest dose rates in the 300 Area were measured near installations such as the 340 Waste Handling Facility. The average annual dose rate measured in the 300 Area in 1997 was 110 millirem per year, a decrease of 8% compared to the average measured in 1996. The average annual dose rate at the 300 Area Treated Effluent Disposal Facility in 1997 was 82 millirem per year, a decrease of 4% compared to the average dose rate measured in 1996.
The average annual dose rate measured in the 400 Area in 1997 was 86 millirem per year, an increase of 3% compared to the average dose rate measured in 1996.
Investigative Sampling. To confirm the absence or presence of radioactive or hazardous contaminants, investigative sampling was conducted in the operations areas near facilities such as storage and disposal sites for at least one of the following reasons:
Environmental surveillance at the Hanford Site includes sampling environmental media on and off the Hanford Site for potential chemical and radiological contaminants originating from site operations. The media sampled in 1997 included air, surface water and sediment, drinking water, food and farm products, fish and wildlife, soil and vegetation, and external radiation.
The primary pathways for movement of radioactive materials and chemicals from the site to the public are the atmosphere and surface water. Figure 13 illustrates these potential routes and exposure pathways to humans.
Figure 13. The primary pathways for movement of radioactive materials and chemicals from the site to the public are the atmosphere and surface water.
The significance of each pathway was determined from measurements and calculations that estimated the amount of radioactive material or chemical transported along each pathway and by comparing the concentrations or potential doses to environmental and public health protection standards or guides. Pathways were also evaluated based on prior studies and observations of radionuclide and chemical movement through the environment and food chains. Calculations based on effluent data showed the expected concentrations off the Hanford Site to be low for all Hanford-produced radionuclides and chemicals and to be frequently below the level that could be detected by monitoring technology. To ensure that radiological and chemical analyses of samples were sufficiently sensitive, minimum detectable concentrations of key radionuclides and chemicals were established at levels well below applicable health standards.
Radioactive materials in air were sampled continuously at 39 onsite locations, at the site perimeter, and in nearby and distant communities. Nine of these locations were community-operated environmental surveillance stations that were managed and operated by local school teachers (Figure 14). At all locations, particulates were filtered from the air and analyzed for radionuclides. Air was sampled and analyzed for selected gaseous radionuclides at key locations. Several radionuclides released at the site are also found worldwide from two other sources: naturally occurring radionuclides and radioactive fallout from historical nuclear activities not associated with Hanford. The potential influence of emissions from site activities on local radionuclide concentrations was evaluated by comparing differences between concentrations measured at distant locations within the region and concentrations measured at the site perimeter.
Figure 14. Teachers participate in environmental surveillance activities at nine local community-operated environmental surveillance stations.
For 1997, no differences were observed between the annual average gross alpha and beta air concentrations measured at the site perimeter and those measured at distant community locations. Quarterly composite samples were analyzed for numerous specific gamma-emitting radionuclides; however, no radionuclides of Hanford origin were detected consistently.
Tritium concentrations for 1997 were slightly lower at the site perimeter compared to the distant station.
Iodine-129 concentrations were statistically elevated at the site perimeter compared to distant locations, indicating a measurable Hanford source (Figure 15); however, the average concentration at the site perimeter was only 0.000001% of the DOE-derived concentration guide of 70 picocuries (70 x 10-12 curies) per cubic meter. The DOE-derived concentration guide is the air concentration that would result in a radiation dose equal to the DOE public dose limit (100 millirems per year).
Figure 15. Concentrations of Iodine-129 are measured in air. This figure shows concentrations from 1992 through 1997. Concentration units are in attocuries (10-18 curies) per cubic meter.
Strontium-90 was detected in 1 of the 9 onsite air samples, with the maximum concentration at 0.001% of the DOE-derived concentration guide of 9 picocuries per cubic meter. Strontium-90 was not detected at any of the perimeter or distant locations.
Plutonium-239,240 concentrations were significantly elevated for air samples collected at the site perimeter compared to distant locations, indicating a Hanford influence. The average concentration at the perimeter locations was less than 0.002% of the DOE-derived concentration guide of 0.02 picocuries per cubic meter. The maximum onsite plutonium-239,240 concentration was 0.02% of the DOE-derived concentration guide of 0.02 picocuries per cubic meter.
Uranium isotopic concentrations (uranium-234, uranium-235, and uranium-238) were similar on the site, at the perimeter, and at distant locations for 1997. The annual average uranium concentration at the site perimeter was 0.03% of the 0.1-picocurie per cubic meter DOE-derived concentration guide.
No samples were collected in 1997 to test for chemical contaminants in air.
The Columbia River was one of the primary environmental exposure pathways to the public during 1997 as a result of past operations at the Hanford Site. Radiological and chemical contaminants entered the river along the Hanford Reach primarily through seepage of contaminated groundwater. Water samples were collected from the river at various locations throughout the year to determine that contaminant concentrations were in compliance with applicable standards.
Although radionuclides associated with Hanford operations continued to be identified routinely in Columbia River water during the year (Figure 16), concentrations remained extremely low at all locations and were well below standards. The concentrations of tritium, iodine-129, and uranium were significantly higher (5% significance level) at the Richland Pumphouse (downstream from the site) than at Priest Rapids Dam (upstream from the site), indicating contribution along the Hanford Reach (Figure 17).
Figure 16. Water samples are routinely collected from the Columbia River.
Figure 17. Annual average tritium concentrations are determined in Columbia River water upstream and downstream of the site. This figure shows concentrations from 1992 through 1997.(AWQS = ambient water quality standard)
Transect sampling in 1997 revealed elevated tritium concentrations along the Benton County shoreline near the 100-N Area, Old Hanford Townsite, 300 Area, and Richland Pumphouse. Total uranium concentrations were elevated along the shorelines of both Benton and Franklin counties near the 300 Area and Richland Pumphouse. The highest total uranium concentration was measured near the Franklin County shoreline of the Richland Pumphouse and likely resulted from groundwater seepage and irrigation return canals on the east shore of the river.
Several metals and anions were detected in transect samples collected upstream and downstream of the Hanford Site. Nitrate concentrations were elevated along the Benton County shoreline at the Old Hanford Townsite and 300 Area. Nitrate, sulfate, and chloride were elevated along the Franklin County shoreline for the 300 Area and Richland Pumphouse transects.
With the exception of nitrate, sulfate, and chloride, which had slightly higher average quarterly concentrations at the Richland Pumphouse, no consistent differences were found between average quarterly metal and anion contaminant concentrations in the Vernita Bridge and Richland Pumphouse transect samples. All metal and anion concentrations in Columbia River water collected in 1997 were less than Washington State ambient surface-water quality criteria levels for acute and chronic toxicity. Arsenic concentrations exceeded EPA standards; however, similar concentrations were measured for transect samples collected at Vernita Bridge (background location) and Richland Pumphouse.
In 1997, samples of Columbia River surface sediments were collected from permanently flooded monitoring sites above McNary Dam (downstream of the site), above Priest Rapids Dam (upstream of the site), and along the Hanford Reach. Strontium-90 was the only radionuclide to exhibit consistently higher median concentrations at McNary Dam compared to the other location. Sediment samples were also collected from four periodically inundated shoreline springs along the Hanford shoreline. The concentrations of radionuclides in sediment collected from riverbank springs were similar at all locations and were comparable to river sediment collected behind Priest Rapids Dam.
Similar concentrations of most metals were found in Columbia River sediment samples. The highest maximum and median concentrations of chromium were found in riverbank springs sediment. River sediment was also analyzed for simultaneously extracted metals and acid volatile sulfide (SEM/AVS). The SEM/AVS ratios are typically a better indicator of sediment toxicity than traditional total metals concentrations. When the amount of sulfide exceeds the amount of the metals (SEM/AVS ratio is below 1), the metal concentration in the sediment porewater will be low because of the limited solubility of the metal sulfides. SEM/AVS ratios were below 1.0 for all metals, except for zinc, which was above 1.0 for some samples.
Water samples were collected from six Columbia River shoreline spring areas in 1997. All radiological contaminant concentrations measured in riverbank spring water in 1997 were less than the DOE-derived concentration guides, except for strontium-90 at the 100-N Area where one spring was nearly 10 times the standard. The tritium concentration at the Old Hanford Townsite riverbank spring (Figure 18) exceeded the Washington State ambient surface-water quality criteria level and was close to the criteria for springs at the 100-B and 100-N Areas. There are currently no ambient surface-water quality criteria levels directly applicable to uranium. However, total uranium exceeded the site-specific proposed EPA drinking water standard in the 300 Area riverbank spring. All other radionuclides were below the Washington State ambient surface-water quality criteria levels.
Figure 18. Concentrations (average ±2 total propagated analytical uncertainty) of constituents of interest are measured in riverbank spring water near the Old Hanford Townsite. This figure shows concentrations from 1992 through 1997. As a result of figure scale, some uncertainties (error bars) are concealed by the point symbol.
Nonradiological contaminants measured in riverbank springs located on the Hanford shoreline in 1997 were below the Washington State ambient surface-water acute toxicity levels, except for chromium at the 100-D and 100-H Area springs. The Washington State ambient surface-water chronic toxicity levels for chromium and lead were exceeded at some locations. Riverbank spring sampling protocols do not lend themselves to a direct comparison of most metal concentrations measured in riverbank springs to ambient surface-water acute and chronic toxicity levels. The standards are used instead as a point of reference. Nitrate concentrations were the highest at the 100-F Area, but all locations were below the EPA drinking water standard.
Water was collected from three onsite ponds located near operational areas in 1997. Although the ponds were not accessible to the public and did not constitute a direct offsite environmental impact during 1997, they were accessible to migratory waterfowl and other animals. As a result, a potential biological pathway existed for the removal and dispersal of onsite pond contaminants. With the exception of uranium-234 and uranium-238 in water samples from West Lake, radionuclide concentrations in the onsite pond water were below the DOE-derived concentration guides. The median gross beta and uranium concentrations in West Lake exceeded the ambient surface-water quality criteria levels. Concentrations of most radionuclides in water collected from all three ponds during 1997 were similar to those observed during past years.
Irrigation water from the Riverview canal near Pasco was sampled three times in 1997 to determine radionuclide concentrations. Radionuclide concentrations in offsite irrigation water were below the DOE-derived concentration guides and ambient surface-water quality criteria levels and were similar to those observed in Columbia River water.
Surveillance of Hanford Site drinking water was conducted to verify the quality of water supplied by site drinking water systems and to comply with regulatory requirements. Radiological monitoring was performed by Pacific Northwest National Laboratory and DE&S Hanford, Inc.; nonradiological monitoring was conducted by DynCorp Tri-Cities Services, Inc. Nonradiological results are reported directly to the Washington State Department of Health and are not discussed here.
During 1997, radionuclide concentrations in site drinking water were similar to those observed in recent years and were in compliance with Washington State Department of Health and EPA annual average drinking water standards.
The Hanford Site is situated in a large agricultural area that produces a wide variety of food products and alfalfa (Figure 19). Milk, vegetables, fruit, and wine were collected from areas around the site and were analyzed for cobalt-60, strontium-90, iodine-129, cesium-137, and tritium.
Figure 19. Food and farm products are sampled in agricultural areas surrounding the Hanford Site.
Most farm products sampled did not contain measurable concentrations of cobalt-60 or cesium-137. Iodine-129 was measured in milk at concentrations that appeared to be slightly elevated in downwind locations. Concentrations of iodine-129 in milk collected at downwind locations have decreased in the past 5 years, approaching the concentrations observed in milk collected at the upwind location. Strontium-90 was present in milk in equivalent concentrations at upwind and downwind locations. Tritium concentrations in wine were equivalent to background levels in surface water and do not indicate any upwind or downwind influence from Hanford. Strontium-90 concentrations in alfalfa have previously been slightly elevated in samples irrigated with Columbia River water withdrawn downstream of the Site. In 1997, this effect was not as apparent. Strontium-90 concentrations in alfalfa samples analyzed in 1997 are low and close to background levels. Measurable levels of man-made radioactivity were not detected in vegetable and fruit samples collected in 1997.
Analyses of fish and wildlife samples in 1997 indicated that some species had accumulated radionuclides at concentrations greater than background levels. Sculpin were collected near the 100-N Area springs as part of a special study with the Washington State Department of Health. Sculpin were sampled because they have a small home range, and their exposure in the 100-N Area springs is more constant than that of more mobile fish that are routinely sampled.
Concentrations of strontium-90 in sculpin collected in the vicinity of the 100-N Area springs were significantly higher than in a control group of sculpin collected upstream. Sculpin are not consumed by humans, but they have value as a biomonitoring species. Concentrations of strontium-90 in Columbia River whitefish collected near the 100-N Area in 1997 were considerably lower than in sculpin. Unlike sculpin, whitefish may be consumed by people.
Geese were also collected from around the 100-N to 100-D Area and at the Old Hanford Townsite. Concentrations of cesium-137 were at the limit of detection (0.02 picocuries per gram) in muscle. Strontium-90 concentrations in goose bone were lower than observed in 1995 and were within or below the range of strontium-90 in background samples of other wildlife species collected over the past decade. Collectively, the concentrations of radionuclides measured in fish and geese samples indicate accumulations of small amounts of specific radionuclides that possibly originated either from historic fallout or Hanford Site activities.
Special surveillance studies were also conducted in conjunction with the Washington State Department of Health to establish trace metal concentrations in aquatic organisms from the 100-N Area springs. Metals data were collected from bass, caddis fly larvae and adults, carp, clams, sculpin, and sucker. These samples provided additional data to assess the potential distribution and possible impacts of metals in the Columbia River ecosystem.
Soil and vegetation samples were collected for special surveillance activities in association with cleanup activities in the 300 Area operable units. Samples were collected around the cleanup area to the north of the 300 Area and at five locations in Franklin County across the Columbia River and east of the 300 Area. Neither soil nor vegetation samples indicated any transport of contaminated dust off the site.
Special samples were also collected from fruit trees growing on the site. Three apricot trees (leaf samples only) and a quince tree (leaves and fruit) were sampled. Two apricot trees were sampled from an abandoned orchard northeast of the 100-D Area. These samples had approximately 600 picocuries of tritium per liter of water distilled from the leaves. Concentrations of strontium-90 in all tree leaf samples were within levels associated with background concentrations in vegetation samples routinely monitored in undeveloped areas of the Hanford Site. These samples were also analyzed for metals. Observed concentrations of metals fell within the range of concentrations associated with natural background levels.
Metal concentrations were also determined for reed canary grass and milfoil collected from the 100-N Area springs and an upriver control station near the Vernita Bridge. Metal concentrations were within the range of natural concentrations.
Using thermoluminescent dosimeters, radiological dose rates were measured at both onsite and offsite locations during 1997. Radioactive substances contributing to the measured dose rates were of either natural or man-made origin. The dose rates did not change significantly from the dose rates measured in previous years.
The 1997 annual average background dose rate measured in communities distant from the Hanford Site was 67 ± 1 millirem per year; in 1996, the average background was 71 ± 1. The 1997 annual average perimeter dose rate was 89 ± 10 millirem per year; in 1996, the average measured dose rate was 88 ± 10 millirem per year.
All onsite thermoluminescent dosimeters averaged 85 ± 5 millirem per year, which compares favorably with the average of 86 ± 5 millirem per year measured in 1996. Columbia River shoreline dosimeters had a 1997 average of 90 ± 6 millirem per year; in 1996, the average was 89 ± 7 millirem per year. The average dose rate along the 100-N Area shoreline (121 ± 22 millirem per year) was approximately 50% higher than the typical shoreline dose rate (85 ± 3 millirem per year) (Figure 20).
Figure 20. Average dose rates (±2 standard error of the mean) are calculated annually. This figure compares rates from 1992 through 1997.
Radiological and chemical constituents in groundwater at the Hanford Site were monitored to characterize physical and chemical trends in the flow system, establish groundwater quality baselines, assess groundwater remediation, and identify new or existing groundwater problems. Groundwater also was monitored to verify compliance with applicable environmental laws and regulations and to fulfill commitments made in official DOE documents.
Samples were collected from over 700 wells to determine the distribution of radiological and chemical constituents in Hanford Site groundwater. In addition, hydrogeologic characterization and modeling of the groundwater flow system were used to assess the monitoring network and to evaluate potential impacts of groundwater contaminants (Figure 21).
Figure 21. Scientists study groundwater flow patterns under Hanford using many years of monitoring data.
Vadose zone monitoring was conducted to characterize radioactive and hazardous waste in the soil column from past intentional liquid waste disposals, accidental spills, and leachate from solid waste burial grounds. Subsurface source characterization and vadose zone monitoring, using spectral gamma logging and soil-gas monitoring, were conducted during 1997 in the vicinity of single-shell tanks and selected liquid waste disposal sites.
The Hanford Groundwater Monitoring Project incorporates sitewide groundwater monitoring mandated by DOE orders with near-field groundwater monitoring conducted to ensure that operations in and around specific waste disposal facilities comply with applicable regulations. Groundwater monitoring was required by the Resource Conservation and Recovery Act at 25 waste treatment, storage, and disposal units.
To assess the quality of groundwater, sample concentrations were compared with EPA drinking water standards and DOE-derived concentration guides. Radiological constituents detected at levels greater than their respective EPA drinking water standards in one or more onsite wells included strontium-90, technetium-99, iodine-129, cesium-137, plutonium, tritium, uranium, gross alpha, and gross beta. Strontium-90, tritium, and uranium were detected at concentrations greater than their respective DOE-derived concentration guides.
Extensive tritium plumes extend from the 200-East and 200-West Areas into the 600 Area (Figure 22). The plume from the 200-East Area extends east and southeast, discharging to the Columbia River. This plume has impacted tritium concentrations in the 300 Area at levels of more than one-half the EPA drinking water standard. The spread of this plume farther south than the 300 Area is restricted by the groundwater flow away from the Yakima River and the recharge basins associated with the north Richland well field. Groundwater with tritium at levels above the EPA drinking water standard also discharges to the Columbia River at the 100-N Area. A small but high-concentration tritium plume near the 100-K East Reactor also may discharge to the river. Tritium levels greater than the EPA drinking water standard were also found in the 100-B,C, 100-D, and 400 Areas.
Figure 22. Extensive tritium plumes extend from the 200-East and 200-West Areas into the 600 Area. This figure shows the distribution of tritium in the unconfined aquifer, 1997.
Iodine-129 was detected at levels greater than the EPA drinking water standard in the 200-East Area and in an extensive part of the 600 Area to the east and southeast of the 200-East Area. The iodine-129 contamination extends as far east as the Columbia River but at concentrations less than the EPA drinking water standard. The iodine-129 and tritium plumes share common sources. Iodine-129 at levels greater than the EPA drinking water standard also extends into the 600 Area to the northwest of the 200-East Area, into the 600 Area in the southern part of the 200-West Area and to the northeast in the northcentral part of the 200-West Area.
Technetium-99 concentrations greater than the EPA drinking water standard were found in the northwestern part of the 200-East Area and adjacent 600 Area. Technetium-99 was also detected at levels greater than the EPA drinking water standard in the 100-H and 200-West Areas and adjacent 600 Area. In the upper basalt-confined aquifer, technetium-99 concentrations were found above the EPA drinking water standard in one well in the northern part of the 200-East Area. Greater than 180,923,000 liters (47,800,000 gallons) of groundwater have been treated and greater than 40 grams (1.4 ounces) of technetium-99 have been removed from groundwater since a pump-and-treat system began operating in the 200-West Area in 1994. Assessment studies indicate that Waste Management Areas B-BX-BY, SX, T, and TX-TY (where the tank farms are located) are sources of technetium-99 contamination in groundwater.
Uranium was detected at levels greater than the EPA drinking water standard in groundwater in the 100-F, 100-H, 200, 300, and 600 Areas. Wells near U Plant in the 200-West Area showed concentrations greater than the DOE-derived concentration guide. A pump-and-treat system has removed 125 pounds of uranium from groundwater in the 200-West Area since 1994. Groundwater with uranium concentrations greater than the EPA drinking water standard is discharging to the Columbia River from the 300 Area.
The strontium-90 plume in the 100-N Area, which contains concentrations greater than the DOE-derived concentration guide, discharges to the Columbia River. Localized areas in the 100-K and 200-East Areas and near the former Gable Mountain Pond in the 600 Area also contain strontium-90 at levels greater than the derived concentration guide. Strontium-90 was detected at levels greater than the EPA drinking water standard in the 100, 200, and the 600 Areas. Removal of strontium-90 from groundwater in the 100-N Area by a pump-and-treat system continues.
Cesium-137 was detected above the EPA drinking water standard in a localized area associated with a former injection well (a well for injecting water or other fluid into the groundwater) in the 200-East Area. Plutonium was also detected in this localized area but at concentrations less than the 100-millirem per year dose equivalent guideline.
Cobalt-60 was detected in the 200-East Area and adjacent 600 Area but at concentrations less than the EPA drinking water standard.
Several nonradioactive chemicals regulated by the EPA and Washington State also were present in Hanford Site groundwater. These were carbon tetrachloride, chloroform, chromium, cyanide, fluoride, nitrate, cis-1,2-dichloroethylene, and trichloroethylene. Of these chemicals, nitrate, chromium, and carbon tetrachloride are the most widely distributed constituents in Hanford Site groundwater.
Nitrate concentrations exceeded the EPA drinking water standard in all areas, except the 100-B,C and 400 Areas. The nitrate plumes in the 100 Areas discharge to the Columbia River. A nitrate plume emanating from the 200-East Area extends east and southeast in the same area as the tritium plume. Nitrate from sources in the northwestern part of the 200-East Area is present in the adjacent 600 Area at levels greater than the EPA drinking water standard. Nitrate levels greater than the EPA drinking water standard occur in two areas of the 200-West Area and adjoining 600 Area. A pump-and-treat system in the 200-West Area removed 2,240 kilograms (4,938 pounds) of nitrate from groundwater in 1997.
Chromium was detected above the EPA drinking water standard in the 100-D, 100-H, and 100-K Areas and in localized sites in the 200-East, 200-West, and 600 Areas. Pump-and-treat systems began operating in the 100-D, 100-H, and 100-K Areas in 1997 to remove chromium from groundwater.
An extensive plume of carbon tetrachloride at levels greater than the EPA drinking water standard occurs in groundwater in the 200-West Area and adjoining 600 Area. As of 1997, greater than 117,713,500 liters (31,100,000 gallons) of groundwater have been treated by two pump-and-treat systems operating in the 200-West Area, resulting in the removal of approximately 870 kilograms (1,918 pounds) of carbon tetrachloride.
Levels of trichloroethylene and chloroform have been known to consistently occur above the EPA drinking water standard from year to year in the 200-West Area. However, the distribution of these levels for 1997 could not be defined because of sample interference from high levels of carbon tetrachloride. Trichloroethylene was found at levels greater than the EPA drinking water standard in the 100-F Area and the nearby 600 Area. Trichloroethylene was also detected at levels above the EPA drinking water standard in the 100-K and 300 Areas and near the former Horn Rapids Landfill in the southern part of the Hanford Site.
Cis-1,2-dichloroethylene concentrations were above the EPA drinking water standard in one well in the 300 Area. Cyanide was detected in groundwater in the 200-East Area but at levels below the EPA drinking water standard. Fluoride was detected at the same level as the EPA drinking water standard in one well in the 200-West Area.
The vadose zone baseline characterization project involves spectral gamma-ray geophysical logging of approximately 800 existing boreholes surrounding the single-shell tank farms. This project creates a database of information and provides interpretations and three-dimensional visualizations (computer-generated illustrations) of subsurface contamination. The geophysical logging method is used to determine the concentration of gamma-emitting radionuclides in the subsurface environment. These data are then used to outline regions of major subsurface contamination and identify where to focus the effort of a more comprehensive vadose zone characterization program.
During 1997, 211 additional boreholes, surrounding 42 tanks, were logged. Interpretations were made on a tank-farmwide (Figure 23) basis for four tank farms, and visualizations were prepared for the contamination at those farms.
Figure 23. Workers monitor the status of Hanford waste tanks every day.
Radioactive and hazardous waste in the soil column from past intentional liquid waste disposals, accidental spills, and leachate from solid waste burial grounds are potential sources of current and future groundwater contamination. Subsurface source characterization and vadose zone monitoring, using spectral gamma-ray logging and soil-gas monitoring, were conducted during 1997. The efforts focused primarily on vadose zone soil contamination associated with past liquid disposals to cribs, trenches, drain fields, and reverse wells at Waste Management Area B-BX-BY, Plutonium Finishing Plant liquid waste disposal sites, and Nonradioactive Dangerous Waste Landfill (part of the Central Landfill). The objectives of vadose zone borehole monitoring are to document contamination location and to determine moisture and radionuclide movement in the soil column. Borehole spectral gamma-ray logging is an in situ (in place) measurement of subsurface gamma-emitting radionuclides obtained through cased monitoring wells. By periodically recording detector response at various depths, changes over time can be documented.
Sixteen wells were successfully surveyed from the ground surface to the water table. Four of the 16 gamma-ray logs obtained in Waste Management Area B-BX-BY suggest that gamma-emitting radionuclides may have redistributed in sediments surrounding these four boreholes in the last 10 years.
Movement of small amounts of cobalt-60 at one 200-East Area well was inferred in a small zone between 33 and 35 meters (109 and 114 feet), but the movement is interpreted to be horizontal (away from the borehole) not vertical (toward the water table). Recent logging of another 200-East Area well showed very minor changes in cobalt-60 at 37 and 42 meters (122 and 138 feet). The cobalt appears to have moved deeper down the profile. The amount of cobalt-60 migration is small at both locations and is not a significant risk.
Uranium from Hanford operations was identified in two 200-East Area wells at orders of magnitude higher than natural background concentrations. The uranium moved deeper in the last 10 years and, currently, is just above the water table. Groundwater at these wells has been showing rising uranium concentrations for the last 5 years. Uranium in deep sediments between 70.7 and 75.9 meters (232 and 249 feet) appeared in the September 1997 log at one of the 200-East Area wells. Uranium in the sediments at another well increased by a factor of 5 (from 200 to 1,000 picocuries per gram) in a deep zone between 67.1 and 73.2 meters (220 and 240 feet). The peak activity and whole plume seem to have migrated 1.2 to 6.1 meters (3.9 to 20 feet) deeper into the profile. The significance of the uranium migration at these two locations, which are separated by approximately 100 meters (328 feet), is under investigation. The source of the uranium may not be common for these two wells. Single-shell tank BX-102 is a likely source of the uranium in one of the wells.
Soil vapor extraction is being used to remove the carbon tetrachloride source from the vadose zone as part of the 200-West Area carbon tetrachloride expedited response action being conducted by Bechtel Hanford, Inc. The extraction systems are estimated to have removed 6% of the residual mass at the 216-Z-1A/216-Z-18 Well Fields and 21% of the residual mass at the 216-Z-9 Well Field. The location of the remaining carbon tetrachloride sources in the various strata is a result of its initial accumulation in the finer grained, lower permeability sediment and the relative inability of the extraction system to induce airflow through this lower permeability zone to effectively remove soil vapor.
Carbon tetrachloride concentrations measured in soil vapor near the water table increased relatively slowly after a pump was shut down and remained relatively constant during restart in July 1997. These relatively slow changes suggest that the volatilization of dissolved carbon tetrachloride from groundwater into the unsaturated zone, and/or the downward migration of carbon tetrachloride from the lower permeability zone toward the groundwater, was occurring slowly.
Groundwater monitoring below the carbon tetrachloride disposal units suggests there is a continuing groundwater source that produces somewhat uniform carbon tetrachloride concentrations with depth in the aquifer. A dense nonaqueous-phase liquid that has drained from the vadose zone into the aquifer and is slowly dissolving could produce such a pattern. The continuing presence of relatively high dissolved carbon tetrachloride concentrations in groundwater in the immediate vicinity of the 216-Z-9 Trench, 35 years after termination of disposal operations, suggests that a dense nonaqueous liquid phase of carbon tetrachloride is slowly dissolving within the aquifer.
Although this liquid phase may be slowly draining from the vadose zone to groundwater, the soil vapor concentrations monitored deep within the vadose zone suggest that extraction remediation may have removed much of the vadose zone source and that the continuing groundwater source is now within the aquifer. Carbon tetrachloride concentrations in the soil vapor and underlying groundwater do not appear to be in equilibrium, and the expected direction of carbon tetrachloride migration is from the groundwater to the vadose zone.
The Nonradioactive Dangerous Waste Landfill is a Resource Conservation and Recovery Act land disposal unit located approximately 5.6 kilometers (3.5 miles) southeast of the 200-East Area. The landfill was used to dispose of nonradioactive dangerous waste and asbestos waste from 1975 to 1985. A soil vapor survey was conducted at the landfill during 1997 to assess the vertical extent of volatile organic compound contamination and the potential impacts to groundwater and to resample selected shallow vapor probes for changes in contaminant distribution that may indicate contaminant movement.
Six volatile organic compounds were detected during the 1997 survey. Of these compounds, 1,1,1-trichloroethane was the most widespread. Carbon tetrachloride and chloroform were also detected beneath the chemical trenches.
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Document Number: PNNL-11795-SUM
Document
Date: September 1998
Posted: November 1998
