Radiological Results for River Water

Levels of radionuclides monitored in Columbia River water were extremely low throughout the year. Radionuclides consistently detected in river water collected from monitoring stations during 1994 at concentrations greater than their 2 sigma total propagated analytical uncertainty included iodine-129, plutonium-239,240, strontium-90, tritium, uranium-234, and -238. The concentrations of all other measured radionuclides were less than their respective 2 total propagated analytical uncertainties in over 75% of samples collected. Iodine-129, plutonium-239,240, strontium-90, and tritium exist in worldwide fallout, as well as in effluents from Hanford facilities. Tritium and uranium occur naturally in the environment in addition to being present in Hanford effluents.

Total alpha and total beta measurements are useful indicators of the general radiological quality of the river and provide an early indication of changes in the levels of radioactive contamination because results are obtained quickly. Figures 5.3.2 and 5.3.3 illustrate the average annual total alpha and total beta concentrations, respectively, at Priest Rapids Dam and the Richland Pumphouse during the past 6 years. The 1994 average total alpha and total beta concentrations were similar to those observed during recent years. Monthly total alpha concentrations measured at the Richland Pumphouse in 1994 were not significantly different (paired sample comparison and t-test of differences, 5% significance level) from those measured at Priest Rapids Dam. Monthly total beta concentrations, however, were significantly lower at the Richland Pumphouse. The 1994 total alpha and beta concentrations in Columbia River water at Priest Rapids Dam and the Richland Pumphouse were less than 10% of the applicable Drinking Water Standards of 15 and 50 pCi/L, respectively.

Figure 5.3.4

compares the average annual tritium concentrations at Priest Rapids Dam and the Richland Pumphouse from 1989 through 1994. The general decline in tritium concentrations in river water noted during the late 1980s remains evident at both locations. Statistical analysis (paired sample comparison, t-test of differences, 5% significance level) indicated that monthly tritium concentrations in river water at the Richland Pumphouse were significantly higher than those at Priest Rapids Dam. Onsite sources of tritium entering the river include ground-water seepage and direct discharge from outfalls located in the 100 Area (see Section 3.1, "Facility Effluent Monitoring," and Section 5.8, "Ground-Water Protection and Monitoring Program"). Tritium concentrations measured at the Richland Pumphouse, while representative of the Columbia River source of City of Richland drinking water, tend to overestimate the average concentrations of tritium in the river at this location (Dirkes 1993). This bias is attributable to the contaminated 200 Area ground-water plume entering the river along the portion of shoreline extending from the old Hanford Townsite to below the 300 Area, which is relatively close to the Richland sample intake. This plume is not completely mixed within the river at the Richland Pumphouse. Sampling along a cross section at the Richland Pumphouse during 1994 confirmed the existence of a concentration gradient in the river under certain flow conditions and is discussed in subsequent sections of this report. The extent to which samples taken from the Richland Pumphouse overestimate the average tritium concentrations in the Columbia River at this location is highly variable and appears to be related to the flow rate of the river just before and during sample collection. All tritium concentrations were less than 1% of the state of Washington and EPA Drinking Water Standard of 20,000 pCi/L.

The annual average strontium-90 concentrations at Priest Rapids Dam and the Richland Pumphouse during 1994 was at both locations. Figure 5.3.5

shows the average annual strontium-90 concentrations at these locations from 1989 through 1994. Concentrations observed in 1994 were similar to those seen in recent years. The differences between monthly strontium-90 concentrations at Priest Rapids Dam and the Richland Pumphouse observed in 1994 were not significant (paired sample comparison, t-test of differences, 5% significance level). The primary source of strontium-90 entering the Columbia River and attributable to Hanford has been the 100-N Area liquid waste disposal facilities, which are known to discharge to the river via ground water. Average strontium-90 concentrations in Columbia River water collected from Priest Rapids Dam and the Richland Pumphouse during 1994 remained less than 2% of the State of Washington and EPA Drinking Water Standard of 8 pCi/L.

Average annual total uranium concentrations (i.e., the sum of uranium-234, -235, and -238 concentrations) at the Richland Pumphouse and Priest Rapids Dam for 1989 through 1994 are shown in Figure 5.3.6.

Total uranium concentrations observed in 1994 were similar to those observed during recent years. The larger 2 standard error of the mean associated with 1994 results was attributed to an unusually low concentration found in the December sample of each location. Although there is no direct discharge of uranium to the river, uranium is present in the ground water beneath the 300 Area as a result of past Hanford operations (see Section 5.8, "Ground-Water Protection and Monitoring Program") and has been detected at elevated levels in riverbank springs in this area (see Riverbank Springs subsection). Naturally occurring uranium is also known to enter the river across from Hanford via seepage from extensive irrigation east of the river and via irrigation canal outfalls (Dirkes 1990). Though monthly total uranium concentrations measured at the Richland Pumphouse in 1994 were slightly higher than those measured at Priest Rapids Dam, the differences were not statistically significant (paired sample comparison, t-test of differences, 5% significance level). There is currently no Drinking Water Standard directly applicable to uranium. However, total uranium concentrations in the river during 1994 were well below the proposed EPA Drinking Water Standard of (30 pCi/L).

Figure 5.3.7

presents the average annual iodine-129 concentrations (aCi/L units) for Priest Rapids Dam and the Richland Pumphouse for 1989 through 1994. The average concentration of iodine-129 in Columbia River water was extremely low during 1994 (less than one-tenth of 1% of the Drinking Water Standard of 1 pCi/L [1,000,000 aCi/L]) and similar to levels observed during recent years. The onsite source of iodine-129 to the Columbia River in 1994 was the discharge of contaminated ground water along the portion of shoreline extending from the old Hanford Townsite to below the 300 Area. The iodine-129 plume originated in the 200 Area from past waste disposal practices. Unlike past findings, average concentrations of iodine-129 measured at the Priest Rapids Dam () and the Richland Pumphouse ) in 1994 were not statistically significant (paired sample comparison and t-test of differences, 5% significance level). The lack of significance is attributable to third quarter results for which the iodine-129 concentration was higher at Priest Rapids Dam than at the Richland Pumphouse. The unusually high concentration observed at Priest Rapids Dam is reflected in the 2 standard error of the mean (Figure 5.3.7).

During 1994, average plutonium-239,240 concentrations at Priest Rapids Dam and the Richland Pumphouse were and , respectively. No Washington State or EPA Drinking Water Standard currently exists for plutonium-239 or plutonium-240; however, if the Derived Concentration Guides (Appendix C, Table C.6.), which are based on a 100-mrem dose standard, are converted to a 4-mrem dose equivalent used to develop the Drinking Water Standards, 1.2 pCi/L (1,200,000 aCi/L) would be the relevant guideline for both plutonium-239 and plutonium-240. Concentrations of plutonium-239,240 at Priest Rapids Dam were not statistically different from those observed at the Richland Pumphouse during 1994 (paired sample comparison, t-test of differences, 5% significance level).

Radiological results of samples collected along cross sections of the Columbia River established at the Vernita Bridge, 100-N Area, 100-F Area, old Hanford Townsite, 300 Area, and the Richland Pumphouse during 1994 are presented in Appendix A, Table A.4 and in Bisping (1995). Constituents that were consistently detected (in greater than 50% of river transect samples) at concentrations greater than their associated 2 total propagated analytical uncertainty included strontium-90, tritium, uranium-234, and -238. All measured radionuclide concentrations were less than applicable Washington State and federal Drinking Water Standards.

Mean strontium-90 and tritium concentrations measured along cross sections of the Columbia River during 1994 are depicted in Figures 5.3.8 and 5.3.9, respectively. The reported result is plotted for those transects that were sampled only once in 1994. The transects are displayed such that the observer's view is downstream. Vernita Bridge is the most upstream transect. Stations 1 and 10 are located along the Benton County and Franklin County shorelines, respectively.

Strontium-90 levels in 1994 transect samples (Figure 5.3.8) were elevated along the 100-N Area shoreline. This observation concurred with recent Hanford ground-water reports (Dresel et al. 1994) indicating that the highest shoreline concentrations of strontium-90 existed in the 100-N Area. With the exception of the 100-N Area transect, strontium-90 concentrations were fairly uniform across the width of the river. The mean concentration of strontium-90 found during cross-sectional sampling at the Richland Pumphouse was similar to that obtained from the routine single-intake automatic composite sampler used at that location.

The highest tritium concentrations observed in 1994 river transect water (Figure 5.3.9) were detected along the shoreline of the old Hanford Townsite where ground water containing tritium concentrations in excess of the Drinking Water Standard of 20,000 pCi/L is known to discharge to the river (Dresel et al. 1994). Elevated levels of tritium were also evident near the Hanford shoreline at the 100-N Area, 300 Area, and Richland Pumphouse transect locations. The presence of a tritium concentration gradient in the Columbia River at the Richland Pumphouse supports previous conclusions made by Backman (1962) and Dirkes (1993) that contaminants in the 200 Area ground-water plume entering the river at and upstream of the 300 Area are not completely mixed at the Richland Pumphouse. The mean concentration of tritium measured along the cross section established at the Richland Pumphouse was less than that measured using the single-intake sampler located near the western shoreline of the river.

Total uranium concentrations in 1994 were elevated along both the Benton and Franklin County shorelines of the 300 Area and Richland Pumphouse transects. The highest total uranium concentration was measured near the Franklin County shoreline of the 300 Area transect and likely resulted from irrigation returns. The mean concentration of total uranium across the Richland Pumphouse transect was similar to that obtained from the routine single-intake automatic composite sampler used at that location.

Figure 5.3.8

Figure 5.3.9

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