6 100-NR This chapter presents information for the 100-NR groundwater interest area, which encompasses the 100-NR-2 OU and the surrounding area, adjacent to the Columbia River (Figure 1-2). This chapter includes an overview; a discussion of CERCLA, RCRA, and AEA groundwater activities; and a summary of 2016 groundwater monitoring results.

6.1 Overview Among the Hanford Site plutonium-production reactors, the design of N Reactor (operational from 1964 to 1986) was unique because it was a dual-purpose reactor that produced plutonium for defense purposes and steam for commercial electrical power generation. Soil and groundwater contamination in 100-NR is primarily associated with waste from the reactor and associated processes. About 92 percent of the waste sites in 100-NR have been remediated under a CERCLA interim action ROD or classified as not requiring remediation. Additional details about the history of the area and waste sites are provided in Section 1.3 of DOE/RL-2012-15, Remedial Investigation/Feasibility Study for the 100-NR-1 and 100-NR-2 Operable Units.

Strontium-90 is the primary groundwater contaminant in 100-NR. Other contaminants include nitrate, TPH-D, chromium (total), Cr(VI), tritium, and sulfate. Strontium-90 and TPH-D are being remediated under a CERCLA interim action ROD (EPA/ROD/R10-99/112, Interim Remedial Action of Record of Decision for the 100-NR-1 and 100-NR-2 Operable Units). An apatite permeable reactive barrier (PRB) was installed between 2006 and 2011 to enhance attenuation of the strontium-90 in groundwater moving toward the Columbia River. TPH-D free product is being removed from groundwater in one well (199-N-18), and a bioventing system began full-scale operations in 2012 to remediate TPH-D in the deep vadose zone. Groundwater is also monitored at four TSD units to meet requirements of RCRA and WAC 173-303 (Section 6.8).

Groundwater across most of 100-NR generally flows northwest toward the Columbia River (Figure 6-1). Groundwater flow continued to be influenced in 2016 by groundwater injection wells for the KX P&T remediation system located in the southwest portion of 100-NR. Table 6-1 summarizes information on the 100-NR groundwater contaminants, Figure 6-2 shows wells and aquifer tubes sampled in 2016, and Figure 6-3 illustrates calculated plume areas for primary contaminants.

The vadose zone in 100-NR is up to 23 m (76 ft) thick and is composed of gravels and sands of the Hanford formation and Ringold unit E (Figure 6-4). The unconfined aquifer is 6.5 to 14 m (21 to 46 ft) thick and primarily located within Ringold unit E. When the Columbia River stage is high, the water table can rise into the Hanford formation in wells near the shoreline. The RUM forms the base of the unconfined aquifer.

Reference: NAVD88, North American Vertical Datum of 1988.

Figure 6-1. 100-NR Water Table, March 2016

Table 6-1. 100-NR at a Glance N Reactor operations: 1964 to 1986

2016 Groundwater Monitoring

Contaminant Water Quality

Standard Maximum Concentration Plume Areaa

(km2) Shorelineb (m)

Strontium-90 8 pCi/L 12,600 pCi/L (199-N-67) 0.63 675

Nitrate 45 mg/L 443 mg/L (199-N-67) 0.59 63

Diesel (as total petroleum hydrocarbons)

0.5 mg/L 17.2 mg/L (199-N-18) 0.02 48

Hexavalent chromium 48 µg/L/10 µg/L 117/110 µg/Lc

(RUM 199-N-80) Not

calculatedd 0

Tritium 20,000 pCi/L 373,000 pCi/L (aquifer tube C7934)

—e —e

Remediation

Waste sites: 92 percent completef Groundwater (interim action): 1995 to present Final record of decision anticipated in 2020.

a. Estimated area at a concentration greater than the water quality standard in the upper part of the unconfined aquifer. b. Length of shoreline intersected by plume above listed water quality standard. c. Total chromium (filtered) and hexavalent chromium values are listed. d. 100-NR Cr(VI) contamination is limited to a single well monitoring a water-bearing unit of the RUM. Cr(VI) in the unconfined aquifer in 100-NR originated from 100-K Area sources and is tallied with 100-KR plumes. e. Not calculated; isolated location with tritium greater than 20,000 pCi/L. f. Sites with status of final closed, interim closed, no action, not accepted, or rejected, as of December 31, 2016. RUM = Ringold upper mud unit

Figure 6-2. 100-NR Sampling Locations, 2016

Figure 6-3. 100-NR Plume Areas

Figure 6-4. 100-NR Geology

6.2 Strontium-90 The primary source of the 100-NR strontium-90 was liquid waste disposed to the 116-N-1 Crib and Trench and the 116-N-3 Crib and Trench. Concentrations vary with fluctuating water levels and installation of the PRB along the shoreline, but the size and shape of the strontium-90 plume (Figure 6-5) changes very little from year to year because of the low mobility of strontium-90. The strontium-90 plume extends from beneath the 116-N-1 and 116-N-3 waste sites to the Columbia River at concentrations exceeding the DWS (8 pCi/L). The portion of the plume with concentrations exceeding 800 pCi/L is found beneath the head end of the 116-N-3 Crib and beneath and downgradient of the 116-N-1 Trench. The plume with concentrations between 8 and 80 pCi/L is peripheral to the highest concentration area in a distribution consistent with historical radial flow away from the 116-N-1 and 116-N-3 Cribs and Trenches when the liquid waste disposal sites were receiving effluent, and elongated toward the Columbia River.

The highest concentration of strontium-90 in 100-NR groundwater in 2016 was 12,600 pCi/L at well 199-N-67 downgradient of the 116-N-1 Trench. This is slightly down from 13,600 pCi/L in 2015 at the same well.

Because strontium-90 has low mobility in groundwater, most of the contamination is limited to the upper portion of the aquifer. The seasonally low water table elevation in this area ranges from 116.8 to 117.8 m (383.2 to 386.5 ft). Strontium-90 was measured at 83.9 pCi/L in 2015 at well 199-N-182, which monitors the lower portion of the unconfined aquifer near the 116-N-1 Crib. The top of the well screen is at 114.8 m (376.6 ft), which is 2 to 3 m (6 to 10 ft) below the low water table. In contrast, strontium-90 was below the MDA in 2015 in well 199-N-69, with a screen top elevation of 113.2 m (371.4 ft). This difference implies that strontium-90 concentrations above 150 pCi/L are not deeper than 3 m (10 ft) below the PRZ.

Water levels in the unconfined aquifer were significantly higher beneath the 116-N-1 and 116-N-3 waste sites during 100-N operations. As the water level declined, strontium-90 remained sorbed to sediment in the lower vadose zone. As a result, when the water table rises beneath these former waste sites, strontium-90 from the vadose zone may be remobilized, increasing the concentrations in groundwater. This is illustrated in Figures 6-6 and 6-7 for wells 199-N-81 and 199-N-67, respectively, which show that strontium-90 concentration generally increase when the water level is elevated and decrease when it is lower. Strontium-90 concentrations declined in well 199-N-81 (Figure 6-6) between the late 1990s and 2010. Strontium-90 concentrations in well 199-N-67 show no obvious long-term decline (Figure 6-7). The positive variation of concentration with water level is more pronounced at well 199-N-67 near the 116-N-1 waste site, which received a much larger mass of strontium-90 than the 116-N-3 waste site and presumably has more residual strontium-90 in the lower vadose zone.

Strontium-90 concentrations in several wells within the downriver untreated portion of the apatite barrier exceeded 800 pCi/L in 2016 (Figure 6-5). This localized high-concentration area has been interpreted to extend upgradient toward the 116-N-1 source based on concentrations above 800 pCi/L at wells 199-N-75 and 199-N-105A. Strontium-90 concentrations at the apatite PRB are discussed in Section 6.7.2. Strontium-90 concentrations in aquifer tubes are consistent with the concentrations in near-shore monitoring wells.

Figure 6-5. 100-NR Strontium-90 Plume, 2016

Figure 6-6. 100-NR Strontium-90 Data for Well 199-N-81, Downgradient of the 116-N-3 Crib and Trench

Figure 6-7. 100-NR Strontium-90 Data for Well 199-N-67, Downgradient of the 116-N-1 Crib and Trench

The only strontium-90 detections outside the main strontium-90 groundwater plume are at aquifer tube cluster C7934/C7935/C7936, located upriver from the main plume (Figure 6-5). The tops of the aquifer tube screens are located 4.4 m (14.4 ft), 5.7 m (18.8 ft), and 8.9 m (29.2 ft) bgs at C7934, C7935, and C7936, respectively. Strontium-90 concentrations are higher in the shallow aquifer tubes (C7934 and C7935) than in the deep aquifer tube (C7936) (Figure 6-8). These aquifer tubes are near the engineered fill around the 1908-N outfall, which suggests that outfall construction created a preferential pathway for migration of contaminated groundwater to the river (Section 4.2 of SGW-49370, Columbia River Pore Water Sampling in 100-N Area, December 2010). Leaks from the FSB and associated facilities and pipelines between the N Reactor and the river are likely sources of the elevated strontium-90 concentrations at the aquifer tube cluster.

Three documented unplanned releases (UPR-100-N-3, UPR-100-N-7, and UPR-100-N-12) may be the sources of the strontium-90 contamination at aquifer tube cluster C7934/C7935/C7936. Collectively, more than 4.22 million L (1.11 million gal) of radioactive liquid effluent was released to the soil between the reactor and river. The UPR-100-N-7 waste site is the largest of the radioactive liquid effluent spills. The spill occurred in April 1985 from a radioactive drain return pipe between the 109-N Building and 1909-N valve pit. Approximately 1,910,000 L (504,000 gal) of effluent water was released from a rupture in the 25.4 cm (10 in.) radioactive drain-return line containing mixed fission products. The UPR-100-N-3 waste site was an unplanned release of radioactively contaminated FSB water discovered north of the FSB in 1978. The leak reported as UPR-100-N-12 occurred in 1979 at the same location. An estimated 1,363,000 L (360,000 gal) and 946,000 L (250,000 gal) of storage basin water were released to the soil during 1978 and 1979, respectively. The estimated strontium-90 inventory released from UPR-100-N-3 was 0.8 Ci (DOE/RL-95-111, Corrective Measures Study for the 100-NR-1 and 100-NR-2 Operable Units). Based on the estimated release volume and inventory, the release concentration would calculate to be 586,000 pCi/L.

Six new wells were drilled in 2016 to provide additional monitoring to help assess nature and extent of COCs at 100-N (Table 6-2; Figure 6-9). Three of the new wells (199-N-371, 199-N-372, and 199-N-374) were installed to evaluate the source of the strontium-90 contamination detected at the aquifer tube cluster C7934/C7935/C7936. Vertical soil samples were collected during drilling. Soil samples collected during drilling showed contamination at the water table, which supports the conceptual model that the source of contamination is from unplanned releases from the FSB and associated facilities and pipelines. Strontium-90 contamination was detected at 1.29 pCi/g at the water table at well 199-N-374. Groundwater samples at the water table had strontium-90 concentration of 18.4 pCi/L at well 199-N-374. Soil and groundwater samples collected in the 199-N-371 and 199-N-372 boreholes were nondetect and below the 8 pCi/L DWS for strontium-90, respectively. The low strontium-90 concentrations at well 199-N-374 and nondetect at the 199-N-371 and 199-N-372 boreholes indicate a narrow contamination plume from the unplanned release sites to aquifer tube cluster C7934/7935/7936 as depicted in Figure 6-5.

The highest strontium-90 concentrations detected in a shoreline seep in 2016 was 51.9 pCi/L in 100-N SPRING 89-1. This seep is located near well 199-N-123 in the main strontium-90 plume (Figure 6-5).

Figure 6-8. 100-NR Strontium-90 Data for Aquifer Tubes C7934, C7935, and C7936

Table 6-2. Wells Installed in 100-NR in 2016

Well Name Well ID

Well Purpose

Construction Depth

(m bgs)

Construction Depth (ft bgs)

Drilled Depth

(m bgs)

Drilled Depth (ft bgs)

Acceptance Date

199-N-371 C9400 Monitoring 28.9 94.8 29.3 96.0 8/1/2016

199-N-372 C9401 Monitoring 31.7 104.0 32.1 105.4 8/1/2016

199-N-373 C9402 Monitoring 27.5 90.4 30.9 101.3 8/3/2016

199-N-374 C9403 Monitoring 30.5 100.0 31.1 101.9 8/2/2016

199-N-376 C9425 Monitoring 32.9 108.0 33.3 109.4 9/8/2016

199-N-377 C9429 Monitoring 28.7 94.1 33.3 109.3 9/8/2016

Figure 6-9. New 100-NR-2 OU Monitoring Well Locations Installed in 2016

6.3 Tritium Tritium concentrations remained elevated above the 20,000 pCi/L DWS in 2016 at aquifer tube cluster C7934/C7935/C7936 (Figure 6-10). Concentrations in 2016 were lower than peaks in 2015 (Figure 6-11). The tritium concentration trends did not fluctuate with river stage, suggesting that a pulse of tritium was moving through this area. Tritium sources are likely the same as discussed for strontium-90 in Section 6.2. Based on the high mobility of tritium, the increases in concentration are more likely a result of excavation during the implementation of interim remedial actions and the addition of dust-suppression water at waste sites between the reactor and the river. As discussed in Section 6.2, three new wells (199-N-371, 199-N-372, and 199-N-374) were installed to evaluate the source of contamination detected at the aquifer tube cluster C7934/C7935/C7936.

Soil samples were collected from the three wells to characterize the vertical and lateral extent of tritium Soil samples collected during drilling showed contamination at the water table, which supports the conceptual model that the source of contamination is from unplanned releases from the FSB and associated facilities and pipelines. Tritium contamination was detected at 49.7 pCi/g at the water table at well 199-N-374, and groundwater samples at the water table had tritium concentration of 267,000 pCi/L. Soil and groundwater samples collected in the 199-N-371 and 199-N-372 boreholes were nondetect and below the 20,000 pCi/L DWS for tritium, respectively. The detected tritium at well 199-N-374 and nondetect at the 199-N-371 and 199-N-372 boreholes indicate a narrow contamination plume from the unplanned release sites to the aquifer tube cluster C7934/7935/7936 as depicted in Figure 6-10.

The only other monitoring well in 100-NR with tritium concentrations above the DWS in recent years was 199-N-186 in the 116-N-1 Crib, with a concentration of 20,800 pCi/L in 2015, declining to 12,300 pCi/L in 2016. The well was drilled through the 116-N-1 Crib in 2011, and concentration trend has been declining since 2013.

Two shoreline seeps (100-N SPRING 8-13 and 89-1) were sampled for tritium in 2016. Concentrations were 4,000 pCi/L and 1,470 pCi/L, respectively.

6.4 Nitrate Nitrate exceeds 45 mg/L in groundwater beneath the 116-N-1 and 116-N-3 waste sites and the N Reactor area to the southwest (Figure 6-12). The 116-N-1 and 116-N-3 waste sites appear to be the primary source of nitrate based on the persistent plume beneath them. The highest concentration in 2016 was 443 mg/L in well 199-N-67, downgradient of the 116-N-1 Crib.

Nitrate concentrations were relatively low in groundwater during 116-N-1 and 116-N-3 liquid waste disposal operations (Figures 6-13 and 6-14). The nitrate concentrations have been increasing since discharges to the waste sites were terminated. Nitrate was not documented as a significant direct waste disposed to the waste sites during their operation, but compounds that could break down into nitrates were used during operations and the effluents were disposed (namely ammonium hydroxide, hydrazine, and to a much lesser extent, morpholine [DOE/RL-2012-15]). These compounds were used as corrosion inhibitors for the N Reactor cooling water system. It is theorized the nitrate plume resulted from bacterial nitrification of ammonium flushed to groundwater by the large-volume discharges to the waste sites. The increasing nitrate trends since the end of liquid waste disposal are postulated to be from sorption of nitrate into groundwater from the rewetted and saturated sediments rather than from vadose zone drainage. This is supported by comparing trend charts of wells 199-N-2 and 199-N-28 to upgradient well 199-N-74 for various metals and anions.

Figure 6-10. 100-NR Tritium Plume, 2016

Figure 6-11. 100-NR Tritium Data for Aquifer Tubes C7934, C7935, and C7936

Figure 6-12. 100-NR Nitrate Plume, 2016

Figure 6-13. 100-NR Nitrate Data for Wells 199-N-2 and 199-N-67

Figure 6-14. 100-NR Nitrate Data for Well 199-N-32

Figures 6-15 through 6-17 show comparisons of chloride, magnesium, and strontium trends. The trends show low concentrations of the metals and anions at wells 199-N-2 and 199-N-28 before 2000, which is attributed to the large discharge volumes from past operational discharges. Upgradient well 199-N-74 was also affected by the mounding of the water table from historic discharges, but concentrations were not as suppressed as in the downgradient wells. The trends show that concentrations in the downgradient wells recovered to match upgradient concentrations after the water table mound dissipated. Figures 6-18 and 6-19 show nitrate chloride, magnesium, and strontium have similar concentration trends at wells 199-N-2 and 199-N-28, respectively. This suggests that the higher nitrate concentration in the downgradient wells is from nitrate formed by nitrification of ammonium in the saturated sediments beneath and downgradient of the waste sites rather than vadose zone source migration to groundwater beneath the waste sites, because nitrate is not trending up faster than other constituents shown in Figures 6-18 and 6-19.

The nitrate plume in southern 100-NR has decreased in size because of the impact of treated water entering the aquifer through nearby 100-K injection wells. Concentrations have declined in wells 199-N-72 and 199-N-165 near the 120-N-1 waste site (Figure 6-20).

Nitrate concentrations near the 120-N-1 waste site were very low when it was in use but began to increase in the mid-1990s (Figure 6-20). Only low levels of nitrate (1 mg/L) were detected in the 120-N-1 effluent (Section 2.4.4 of DOE/RL-96-39, 100-NR-1 Treatment, Storage, and Disposal Units Corrective Measures Study/Closure Plan). These factors suggest that 120-N-1 was not the source of the nitrate plume in the southwest region of 100-NR. The probable source of the nitrate in these wells and this portion of the nitrate plume southwest of the reactor was from several septic systems located just upgradient and west of the pond location. Large capacity sanitary sewage systems are an acknowledged source of nitrate that can adversely affect groundwater quality.

Two new wells (199-N-373 and 199-N-376 shown in Figure 6-9) were drilled in 2016 to assess the nature and extent of nitrate in the southwest plume area near N Reactor. The maximum nitrate concentrations in the 199-N-373 and 199-N-376 soil samples were 8.81 mg/kg and 5.62 mg/kg, respectively, which are less than the Hanford Site background concentration of 52 mg/kg (DOE/RL-92-24, Hanford Site Background: Part 1, Soil Background for Nonradioactive Analytes). Groundwater concentrations at well 199-N-373 were below the DWS, indicating the extent of the nitrate plume to the southwest of the N Reactor. The maximum groundwater concentration was 88.5 mg/L. No documented releases are noted in the location of well 199-N-373, which supports the conceptual model that the source of southwest nitrate plume are septic systems.

Nitrate concentrations are anomalously low in wells in the area of the TPH-D groundwater plume. The low concentrations are caused by the chemical reduction of nitrate during biodegradation of the TPH-D contamination. Low dissolved oxygen levels, lower pH, detectable nitrite, and elevated iron and manganese indicate the presence of reducing conditions in this part of the aquifer.

Nitrate concentrations are highest in the upper part of the unconfined aquifer. Concentrations in deep wells 199-N-69, 199-N-70, and 199-N-182 are lower than in shallow wells with little variation in concentration over time. Well 199-N-182 was the only deep well sampled in 2016 for nitrate. The nitrate concentration was 48.7 mg/L.

In 2016, nitrate concentrations in 100-NR exceeded 45 mg/L in aquifer tube C6132, with a maximum concentration of 62 mg/L in August. Nitrate concentrations in seeps 100-N SPRING 8-13 and 89-1 were less than 25 mg/L.

Figure 6-15. 100-NR Chloride Trend Comparison for 199-N-2 and 199-N-28 to Upgradient Well 199-N-74

Figure 6-16. 100-NR Magnesium Trend Comparison for 199-N-2 and 199-N-28 to Upgradient Well 199-N-74

Figure 6-17. 100-NR Strontium Trend Comparison for 199-N-2 and 199-N-28 to Upgradient Well 199-N-74

Figure 6-18. 100-NR Nitrate to Chloride, Magnesium, and Strontium Trend Comparison for Well 199-N-2

Figure 6-19. 100-NR Nitrate to Chloride, Magnesium, and Strontium Trend Comparison for Well 199-N-28

Figure 6-20. 100-NR Nitrate Data for Wells 199-N-59, 100-N-72, and 199-N-165

6.5 Total Petroleum Hydrocarbons – Diesel The primary source of the TPH-D groundwater contamination is a 1966 diesel fuel spill (UPR-100-N-17). A small, relatively narrow groundwater plume extends downgradient from the spill to the river (Figure 6-21). The two highest concentrations in 2016 were detected in wells 199-N-18 and 199-N-172. Concentrations were 17,200 µg/L and 16,600 µg/L, respectively. In 2016, the maximum concentration detected in aquifer tubes was 371 µg/L in C6135. The concentration of TPH-D in shoreline seep 100-N SPRING 89-1 was less than detection in 2016. TPH concentrations have generally been decreasing from 2012 through 2016. The decrease is attributed primarily to in situ bioremediation (i.e., bioventing). For details regarding operation of the system, see UPR-100-N-17 (WCH-600, Annual Operations and Monitoring Report for UPR-100-N-17: November 2012 – February 2014; DOE/RL-2016-34, Annual Operations and Monitoring Report for UPR-100-N-17: March 2015-February 2016).

In situ bioventing introduces oxygen to promote aerobic biodegradation of the TPH-D in the deep vadose zone to carbon dioxide and water. The data from the bioventing pilot test (2010–2011) were used to support design of a full-scale bioventing system, which began to operate at UPR-100-N-17 in December 2012 using two vadose zone injection wells (199-N-167 and 199-N-172) and two vadose zone gas monitoring wells (199-N-169 and 199-N-171). Groundwater monitored is described in Appendix H of DOE/RL-2005-93, Remedial Design Report/Remedial Action Work Plan for the 100-N Area.

Some natural biodegradation of diesel occurs in groundwater, as shown by the anomalously low nitrate groundwater concentrations in this area (discussed in Section 6.4).

Figure 6-21. 100-NR TPH-D Plume, 2016

Removal of free product from well 199-N-18 continued in 2016 in accordance with the interim action ROD (EPA/ROD/R10-99/112). Diesel is removed using a polymer “smart sponge” that selectively absorbs petroleum products from the surface of the water in the well. About every 2 months, two sponges are lowered into well 199-N-18 and left to soak up the diesel. The sponges are weighed prior to placement and again after removal. The weight difference is the amount of diesel removed from the well. In 2016, 950 g of diesel were removed from 199-N-18 (Table 6-3). Removal of diesel from well 199-N-18 will continue in 2017.

Table 6-3. 100-NR Remedy Summary Permeable Reactive Barrier (2006 to 2016)

Well Name

Number of

Baseline Samples

Number of Baseline

Nondetects

Strontium-90 Concentration (pCi/L) Percent Reduction in Strontium-90

(Baseline Maximum to

2016c)

Minimum Detected Baseline

Maximum Baseline

Spring 2016a

Fall 2016b

Upriver Apatite PRB

April 2010 June 2016

Sept. 2016 Spring Fall

199-N-96A 56 8 1.54d 37.9d 1.0 7.2 97 81 199-N-347 1 1 7e 7e 5.0 4.6 29 34 199-N-348 1 0 1,800 1,800 57.8 93.2 97 95 199-N-349 2 0 220 230 61.6 118 73 49

Central (Original) Apatite PRB

(See footnote f) (See footnote g) June 2016

Sept. 2016 Spring Fall

199-N-122 10 0 657 4,630 585 1,580 87 66 199-N-146 4 0 318 985 177 286 82 71 199-N-147 3 0 522 1,842 244 226 87 88 199-N-123 6 0 689 1,180 133 119 89 90

Downriver Apatite PRB

July 2010 June 2016

Sept. 2016 Spring Fall

199-N-350 1 0 240 240 73 83 70 65 199-N-351 1 0 350 350 221 555 37 0 199-N-352 1 0 580 580 165 1,200 72 0 199-N-353 1 0 83 83 3.3 74 96 11

Total Petroleum Hydrocarbons (2003-2016) Product removal (top of aquifer) 950 g removed from well 199-N-18 in 2016; 15,044.5 g over lifetime

Bioventing (vadose zone) Introduces oxygen via 2 vadose zone injection wells to promote aerobic biodegradation of the TPH. Tested 2010-2011; full-scale December 2012 to present.

Table 6-3. 100-NR Remedy Summary Permeable Reactive Barrier (2006 to 2016)

Well Name

Number of

Baseline Samples

Number of Baseline

Nondetects

Strontium-90 Concentration (pCi/L) Percent Reduction in Strontium-90

(Baseline Maximum to

2016c)

Minimum Detected Baseline

Maximum Baseline

Spring 2016a

Fall 2016b

Prior Remedy (1994-2006)

P&T for strontium-90 1.8 Ci removed by P&T 1995-2006. Facility demolished in 2016.

a. Spring 2016 samples were collected from June 19 through July 5. b. Fall 2016 samples were collected from September 16 through September 26. c. The percent reduction in strontium-90 concentration is calculated as: ([baseline value] – [2015 value])/[baseline value]) × 100. d. Between 1995 and 2011, the maximum baseline was measured on December 6, 1995; the minimum detected baseline was measured on June 13, 2006, and June 22, 2007. e. Strontium-90 is a beta emitter. Gross beta concentrations are approximately two times the strontium-90 concentrations. The strontium-90 concentration was 1.1 (U) pCi/L. The gross beta concentration, 14 pCi/L, was divided by 2 to approximate the strontium-90 concentration of 7 pCi/L. f. From Table 8.1 in PNNL-17429, Interim Report: 100-NR-2 Apatite Treatability Test: Low-Concentration Calcium-Citrate-Phosphate Solution Injection for In Situ Strontium-90 Immobilization. g. From Table 4.1 in PNNL-19572, 100-NR-2 Apatite Treatability Test: High Concentration Calcium-Citrate-Phosphate Solution Injection for In Situ Strontium-90 Immobilization Final Report.

Grab samples of groundwater were collected from well 199-N-18 in 2016 to determine if TPH concentrations have decreased in the well from free product removal by the sponges. The maximum concentration in 2016 was 17,200 µg/L, which is lower than when the well was last sampled in 2011 (48,000 µg/L). The decrease may be a combination of remediation of deep vadose zone diesel and free product removal with the sponges.

In 2016, a new well (199-N-377 in Figure 6-9) was installed to evaluate the extent of TPH contamination. TPH contamination was observed in the soil from 5.5 m (18 ft) bgs to the top of the Ringold Formation (13.7 m [45 ft] bgs). The maximum detected soil concentration was 2,880 mg/kg at 5.5 to 6.4 m (18 to 21 ft) bgs. TPH concentrations were near or below detection in soil samples collected below the Hanford/Ringold contact. Groundwater samples were nondetect.

6.6 Chromium Sodium dichromate was used in N Reactor operations from 1964 to 1972 and in lesser amounts than other 100 Area reactors because of the design of the cooling system and the use of corrosion-resistant metals (e.g., zircaloy) in the fuel and facility (Section 1.3.2 of DOE/RL-2012-15). Although chromium was present in the effluent discharged to the 116-N-1 waste site, it was never detected in samples of the effluent (Section 3.1.1.4 of DOE/RL-90-22, RCRA Facility Investigation/Corrective Measures Study Work Plan for the 100-NR-1 Operable Unit, Hanford Site, Richland, Washington). Cr(VI) is mobile in solution and, while chromium was being delivered to the 116-N-1 waste site, discharge rates and effluent temperatures were high. Liquid discharges to 116-N-1 continued for another 10 years after the use of sodium dichromate had ceased. Because of these factors, the mobile portion of chromium was thoroughly flushed from the vadose zone and into the unconfined aquifer. Because a groundwater mound was present, the diluted effluent spread radially, with some portion reaching the Columbia River by the end of the N Reactor operational period (Section 4.8.1.4 of DOE/RL-2012-15).

In 2016, Cr(VI) (including filtered chromium) was detected at levels above the ambient water quality criterion (10 µg/L) in unconfined wells in eastern and southern 100-N. Cr(VI) was less than the MTCA (WAC 173-340) Method B cleanup level of 48 µg/L except for well 199-N-74, upgradient of the 116-N-3 Crib. The source of most of the Cr(VI) contamination in 100-NR is likely the 116-K-2 Trench, where a portion of the 100-KR Cr(VI) plume has migrated northward into 100-NR (Section 5.2; Figure 5-6).

The only well in 100-NR with dissolved chromium concentrations above the DWS (100 µg/L) in 2016 was 199-N-80 (located downgradient from the 116-N-1 Trench and screened in a thin, confined, water-bearing zone in the upper portion of the RUM). The filtered chromium concentration was 117 µg/L, which is slightly lower than previous results (Figure 6-22). The maximum Cr(VI) concentration was 110 µg/L, indicating that the dissolved chromium is primarily Cr(VI). This water-bearing zone has not been identified in surrounding wells and boreholes and is not believed to be laterally continuous (Section 4.4.3 of DOE/RL-2012-15).

The chromium detected in well 199-N-80 is likely the result of high-volume past disposal of chromium-bearing liquid waste into the nearby 116-N-1 waste site that was driven into this relatively shallow, confined interval when the water table in the unconfined aquifer was high. Today the contamination remains trapped and relatively stagnant in the locally confined interval (Section 4.8.1.4 of DOE/RL-2012-15). Well maintenance activities in 2001 confirmed that stainless-steel well screen corrosion was occurring, which could also release chromium into the water in this well.

Cr(VI) concentrations were near or below detection limits in 100-NR aquifer tube and seep samples in 2016. All were below the 10 µg/L ambient water quality criterion.

6.7 CERCLA Remediation and Monitoring In 2016, CERCLA activities in 100-NR included routine groundwater monitoring, continued interim remedial actions for strontium-90 and TPH-D contamination, revision to the 100-NR-2 RD/RAWP SAP (DOE/RL-2001-27, Remedial Design/Remedial Action Work Plan for the 100-NR-2 Operable Unit, Appendix A), and continued comment resolution process for Draft A of the RI/FS report (DOE/RL-2012-15).

CERCLA sampling is conducted primarily in September, with selected wells also monitored in March. Table A-8 of Appendix A lists the wells and constituents monitored.

6.7.1 CERCLA Decision Documents and Plans Routine groundwater monitoring is described in the RD/RAWP (DOE/RL-2001-27), which presents the approach for implementing the interim remedial actions for the 100-NR-2 OU, as specified in the interim action ROD (EPA/ROD/R10-99/112). The RD/RAWP includes the activities necessary to install and maintain an apatite PRB for the 100-NR-2 OU, as specified in the interim action ROD, as amended (EPA, 2010, U.S. Department of Energy 100-NR-1 and NR-2 Operable Units Hanford Site – 100 Area Benton County, Washington Amended Record of Decision, Decision Summary and Responsiveness Summary). Appendix A of the RD/RAWP is the SAP for interim remedial actions and routine groundwater monitoring.

DOE submitted Draft A of the RI/FS report (DOE/RL-2012-15) to Ecology, the lead regulatory agency for the 100-NR-1 and 100-NR-2 OUs, in June 2013 for review. The comment resolution process continued through 2016 for the draft RI/FS. The RI/FS report will be used to support future cleanup decisions specified in a proposed plan and ROD.

Figure 6-22. 100-NR Filtered Chromium Data for Well 199-N-80

6.7.2 Apatite Barrier The CERCLA interim action ROD (EPA/ROD/R10-99/112; amended by EPA, 2010) identifies the remedial action applicable for strontium-90 in groundwater in 100-NR-2. When the ROD was issued in 1995, the interim action for strontium-90 in groundwater was P&T. The 100-NR-2 groundwater P&T system operated from 1995 until 2006. The system removed approximately 1.8 Ci of strontium-90 from the aquifer, which was less than what decayed during the same period. Because strontium-90 binds strongly to the sediment, the P&T system was not effective in the cleanup of strontium-90 from the aquifer.

One of the requirements of the interim action ROD was to evaluate alternative technologies for groundwater cleanup. Therefore, in 2006, Ecology, EPA, and DOE approved placing the P&T system in cold-standby status and constructing a PRB. A 90 m (300 ft) long apatite PRB was completed as a treatability test in accordance with DOE/RL-2005-96, Strontium-90 Treatability Test Plan for 100-NR-2 Groundwater Operable Unit. Based on the treatability test results (PNNL-17429, Interim Report: 100-NR-2 Apatite Treatability Test: Low-Concentration Calcium-Citrate-Phosphate Solution Injections for In Situ Strontium-90 Immobilization; PNNL-SA-70033, 100-NR-2 Apatite Treatability Test FY09 Status: High Concentration Calcium-Citrate-Phosphate Solution Injection for In Situ Strontium-90 Immobilization, Interim Report), the apatite technology showed promise as a remediation option. As a result, the interim action ROD was amended in 2010 to allow expansion of the apatite barrier and permanent decommissioning of the 100-NR-2 P&T system (see Section 6.7.3). It is expected that the apatite PRB will provide a 90 percent reduction in strontium-90 flux to the river (as measured by a 90 percent reduction in strontium-90 concentrations in the PRB monitoring wells).

The original 90 m (300 ft) long apatite PRB was created from 2006 through 2008 by injecting apatite-forming solutions into 16 wells (PNNL-19572, 100-NR-2 Apatite Treatability Test: High-Concentration Calcium-Citrate-Phosphate Solution Injection for In Situ Strontium-90 Immobilization Final Report). The expanded PRB well network was installed between late 2009 and early 2010, extending the well network upriver and downriver for a total length of 760 m (2,500 ft) (Figure 6-23). In September 2011, two segments of the extended well network (one upriver and one downriver of the original barrier) were injected with apatite-forming solution, extending the PRB to 300 m (1,000 ft) (SGW-56970, Performance Report for the 2011 Apatite Permeable Reactive Barrier Extension for the 100-NR-2 Operable Unit). This expansion was in accordance with the design optimization study (DOE/RL-2010-29, Design Optimization Study for Apatite Permeable Reactive Barrier Extension for the 100-NR-2 Operable Unit), which had seven objectives for evaluating barrier implementation and effectiveness. Data from the injections and subsequent performance monitoring are used to evaluate these objectives in SGW-56970.

6.7.2.1 Apatite Permeable Reactive Barrier Technology The apatite PRB is formed by injecting a calcium-citrate-phosphate solution into the aquifer through a network of vertical wells (i.e., the barrier well network). After the solution is injected, biodegradation of the citrate releases the calcium, which results in formation of apatite (a calcium phosphate mineral [Ca10(PO4)6(F, Cl, OH)2]). Strontium ions (including strontium-90) in groundwater substitute for calcium ions in the apatite via cation exchange and eventually become trapped as part of the mineral matrix during apatite crystallization (Section 1.3 of PNNL-16891, Hanford 100-N Area Apatite Emplacement: Laboratory Results of Ca-Citrate-PO4 Solution Injection and Sr-90 Immobilization in 100-N Sediments). The strontium-90 in groundwater is sequestered within the apatite PRB as contaminant-laden groundwater flows through the barrier (Figure 6-23). Based on data collected from batch laboratory tests, the calculated average incorporation rate for the PRB design apatite content of 0.96 mg apatite/g of sediment is 2 to 200 times greater than the estimated strontium flux through the barrier (PNNL-23367, Hanford Apatite Treatability Test Report Errata: Apatite Mass Loading Calculation). At the design apatite content, strontium and strontium-90 would be incorporated into apatite more rapidly than the average groundwater flow rate and most high-flow events. The sequestered strontium-90 continues to decay in place within the barrier.

6.7.2.2 Apatite Permeable Reactive Barrier Performance Monitoring Performance monitoring at the apatite barrier was conducted twice in 2016. Groundwater samples were collected from performance monitoring wells and aquifer tubes during June during high river stage and during low river stage in September. Table 6-3 compares 2016 data to baseline conditions. Semiannual performance monitoring (high and low river stages) will continue for the apatite PRB in 2017.

Performance monitoring wells for the central (original) segment of the barrier show an overall reduction in strontium-90 concentrations following the apatite injections in 2008 (Figure 6-24). During injections, a temporary spike in strontium-90 occurred because the high ionic strength apatite solution temporarily mobilized cations and anions. The high concentration at monitoring well 199-N-123 in 2011 was associated with the temporary spike during injections for the barrier extension upriver of the original barrier segment.

Figure 6-23. 100-NR Apatite Barrier

Figure 6-24. 100-NR Strontium-90 Data for Performance Monitoring Wells

along the Central Segment of the Apatite PRB

In 2016, strontium-90 concentrations remained considerably lower in the wells monitored along the central segment of the barrier than before the injections began in 2006. The 2016 data indicate that strontium-90 concentrations in groundwater have been reduced by about 90 percent in two of the four performance monitoring wells (Table 6-3). The percent reduction in strontium-90 concentrations ranged from 82 percent (199-N-146) to 89 percent (199-N-123) in spring 2016 and 66 percent (199-N-122) to 90 percent (199-N-123) in fall 2016. Strontium-90 concentrations have been trending upward at 199-N-122.

In the performance monitoring wells along the upriver barrier extension (Figure 6-23), the percent reduction in strontium-90 concentrations in September 2016 (5 years following the injections) ranged from 29 percent (199-N-347) to 98 percent (199-N-96A). The relatively low percent reduction in 199-N-347 reflects comparison to the low baseline concentration; both the baseline and the 2016 concentrations were below the DWS (8 pCi/L). Strontium-90 concentrations at 199-N-349 have trended upward since the initial reduction following the 2011 injections. The reduction from baseline strontium-90 concentrations in that well were 73 percent and 49 percent in spring and fall 2016 samples, respectively.

In the performance monitoring wells along the downriver barrier extension (Figure 6-23), well 199-N-353 showed a strontium-90 reduction of 96 percent from pre-injection concentrations in spring 2016. In the fall, the reduction was only 11 percent; 73.7 pCi/L compared to less than DWS in previous years following injection. Continued monitoring will verify if concentrations are returning to pre-injection concentrations or if this is an out-of-trend result. Strontium-90 concentrations at 199-N-350 have trended upward since the initial reduction following the 2011 injections. The reduction from baseline strontium-90 concentrations in well 199-N-350 were 70 percent and 65 percent in spring and fall 2016 samples, respectively. Strontium-90 increased significantly in wells 199-N-351 and 199-N-352 in 2015 and have remained high in 2016 with concentrations exceeding pre-injection concentrations in the fall 2016 samples (Table 6-3).

A strontium-90 reduction of 90 percent occurred in only one of the four downriver barrier segment monitoring wells in spring 2016 and none in the fall. Ongoing monitoring will determine the continued effectiveness of the apatite barrier and support decisions regarding future apatite treatments and need for reinjection.

6.7.3 Demolition of the 100-NR-2 Pump and Treat System EPA, 2010 and DOE/RL-2001-27 require the complete decommissioning, demolition, and removal of the 100-NR-2 P&T system. These documents required removing the residual ion-exchange media and disposing this material at the Environmental Restoration Disposal Facility (ERDF), dismantling all noncontact treatment system hardware and salvaging reusable components, and cutting the high-density polyethylene conveyance piping into short lengths for transportation and disposal at ERDF. Continued use and reconfiguration of the existing wells for monitoring purposes was also a part of the decommissioning plan.

The 100-NR-2 P&T system was demolished, excavated, and removed between August 24 and November 15, 2016. Surface and subsurface features associated with the system, including permanent and temporary structures, concrete slab, vaults and culverts beneath roads, and three 100-NR-2 P&T signs, were removed from the site and disposed at ERDF. Approximately 308 m3 (10,875 ft3) of concrete, soil, piping, conduit, and miscellaneous debris and equipment, weighing 430,913 kg (475 tons), was removed and disposed at ERDF. Excavated areas were backfilled and contoured to match the surrounding terrain. A revegetation and site contouring plan will be prepared in consultation with the Tribal nations in accordance with MSA requirements to complete environmental restoration.

The only components of the P&T system remaining are the former extraction wells and injection wells. Extraction wells were converted to support groundwater monitoring prior to the start of demolition, and piping was removed from injection wells in January 2017. 6.7.4 Petroleum Hydrocarbons The CERCLA interim action ROD (EPA/ROD/R10-99/112) identifies the remedial action applicable to TPH-D in groundwater. The removal of the TPH-D is discussed in Section 6.5 and summarized in Table 6-3.

6.8 RCRA Monitoring This section describes the monitoring results for the following four RCRA WMAs in 100-NR: 116-N-1 Crib and Trench, 116-N-3 Crib and Trench, 120-N-1 Percolation Pond, and 120-N-2 Surface Impoundment (Figure 6-1). Groundwater is monitored at these facilities to meet the requirements of RCRA and WAC 173-303 for dangerous waste constituents. DOE/RL-2016-66 presents results of RCRA monitoring on the Hanford Site in 2016. That information is repeated in this section for completeness. Groundwater data for these facilities are available in the HEIS database and in the data files accompanying this online report version. Appendix B includes well and constituent lists, flow rates, and statistical tables for the four RCRA units in 100-NR.

6.8.1 116-N-1 Crib and Trench The 1301-N TSD unit, also known as the 116-N-1 waste site (Figure 6-25), was an unlined crib and trench used for disposal of liquid effluent from the 1960s through 1985. The effluent contained small quantities of dangerous waste and large volumes of radioactive waste. During remediation, the waste site was excavated from 4.6 to 6.1 m (15 to 20 ft) to remove shallow vadose zone sediment (where most of the radionuclide contamination resided). The waste site was backfilled with clean soil and revegetated with native shrubs and grasses. The waste site is undergoing RCRA closure and is classified as interim closed under CERCLA (Section 1.3.2.6 of DOE/RL-2012-15). Two characterization wells were drilled as part of the 100-NR-1 and 100-NR-2 RIs (DOE/RL-2012-15) to assess protection of groundwater beneath the remediated waste site. The soil characterization data indicated no remaining RCRA dangerous waste constituents above groundwater protection values.

The 1301-N unit is included in the Hanford RCRA Permit, which states that groundwater monitoring during the RCRA closure period will follow the requirements of BHI-00725, 100-N Pilot Project: Proposed Consolidated Groundwater Monitoring Program, and a supplemental plan (WHC-SD-EN-AP-038, Groundwater Monitoring Plan for the 1301-N, 1324-N/NA, and 1325-N Sites).

Two upgradient wells and three downgradient wells are used for RCRA monitoring (Table B-1). The water table in the 100-N Area fluctuates in response to river stage, but it is not declining overall. The 1301-N monitoring wells are expected to produce representative samples in the future, and no changes to the monitoring network were made in 2016.

The water table in March 2016 sloped to the north and northwest (Figure 6-25). Trend surface analysis of the water level data showed a hydraulic gradient with a magnitude of 9.04 × 10-4 m/m. Estimates of the groundwater flow rate ranged from 0.02 to 0.33 m/day (0.06 to 1.1 ft/day) (Table B-2).

Upgradient and downgradient wells are scheduled for sampling twice each year for RCRA contamination indicator parameters (pH, specific conductance, TOC, and TOX) and turbidity, and once each year for groundwater quality and supporting parameters (chloride, iron, manganese, sodium, sulfate, and alkalinity). Well sampling was as scheduled in 2016 with no critical mean exceedances (Table B-3).

Reference: NAVD88, North American Vertical Datum of 1988.

Figure 6-25. RCRA 1301-N (116-N-1) Monitoring Well Locations

6.8.2 116-N-3 Crib and Trench The 1325-N TSD unit, also known as the 116-N-3 waste site (Figure 6-26), was an unlined crib and trench used to dispose liquid effluent from 1983 through 1991. The N Reactor was on cold standby beginning in 1987, but effluent was generated and disposed at a reduced rate until 1991. The effluent contained small quantities of dangerous waste and a large volume of radioactive waste. The waste site was excavated to 1.5 m (5 ft) below the engineered structure to remove vadose zone material (which contained the highest concentrations of radionuclides), backfilled with clean soil, and revegetated with native shrubs and grasses. The waste site is undergoing RCRA closure and is classified as interim closed under CERCLA (Section 1.3.2.6 of DOE/RL-2012-15). One characterization well was drilled as part of the 100-NR-1 and 100-NR-2 RIs (DOE/RL-2012-15) to assess protection of groundwater beneath the remediated waste site. The soil characterization data indicated no remaining RCRA dangerous waste constituents above groundwater protection values.

The 1325-N unit is included in the Hanford RCRA Permit, which states that groundwater monitoring during the RCRA closure period will follow the requirements of BHI-00725 and WHC-SD-EN-AP-038.

Upgradient well 199-N-74 and downgradient wells 199-N-32, 199-N-41, and 199-N-81 monitor the site (Table B-7). Well 199-N-28 is monitored for supporting information. It previously reflected potential impacts from treated groundwater injected into a nearby well during operation of the 100-N Area P&T. Data from 199-N-28 are not evaluated statistically. The water table in the 100-N Area fluctuates in response to river stage, but it is not declining overall. Monitoring wells are expected to produce representative samples in the future, and no changes to the monitoring network were made in 2016.

Groundwater flows to the north beneath the 1325-N site (Figure 6-26), turns to the northwest, and discharges to the Columbia River. The hydraulic gradient in March 2016 was 9.35 × 10-4 m/m, with the groundwater flow rate estimated from 0.02 to 0.35 m/day (0.06 to 1.1 ft/day) (Table B-8).

All five wells in the RCRA network were sampled twice for RCRA contamination indicator parameters (pH, specific conductance, TOC, and TOX) and turbidity and once (in September) for groundwater quality and supporting parameters (chloride, iron, manganese, sodium, sulfate, and alkalinity) in 2016 (Table B-9). Iron exceeded the secondary DWS in samples from 199-N-32 and 199-N-41, and the presence of nickel, chromium, and manganese indicates that these metals are corrosion products from the carbon steel screens and casing.

TOX concentration in samples collected on September 9, 2016 at downgradient well 199-N-81 exceeded the critical mean of 10.73 µg/L. TASL analyzed the samples and results averaged 13.65 µg/L (highest reported value of the replicates was 16 µg/L), which is below the TASL LOQ for the third quarter of 2016 (25.7 µg/L). The third quarter LOQ was not available for comparison when the downgradient results were received, so verification samples were collected on November 11, 2016; the results did not confirm an exceedance.

Average specific conductance values in downgradient wells 199-N-41 and 199-N-81 exceeded the critical mean of 470 µS/cm (Table B-9) in 2016. Specific conductance measurements at well 199-N-32 were below the critical mean in 2016 samples but have exceeded it in the past. This is a continuation of previous exceedances from 1999 to 2015. The assessment report for the original 1999 exceedance (at well 199-N-41) concluded that it was from past discharges of nonregulated contaminants (sulfate and sodium) to 1324-N/NA (00-GWVZ-054, “Results of Assessment at the 1325-N Facility”). Another source of sulfate is from past discharges to waste site 100-N-58, which received similar effluents from 1977 to 1982, and is in the same location as 1324-N/NA. Sulfate and specific conductance trends (Figures 6-27 through 6-29) continue to show that the high specific conductance source is sulfate.

Reference: NAVD88, North American Vertical Datum of 1988.

Figure 6-26. RCRA 1325-N (116-N-3) Monitoring Well Locations

Figure 6-27. Specific Conductance and Sulfate in Well 199-N-32

Figure 6-28. Specific Conductance and Sulfate in Well 199-N-41

Figure 6-29. Specific Conductance and Sulfate in Well 199-N-81

The 1324-N/NA site is not currently upgradient of the 1325-N facility but during its use from 1977 to 1990, it created a recharge mound that may have pushed sulfate-laden water inland. Effluent discharges to 1325-N during operations (1985 to 1989) also resulted in water table mounding that contributed to cross gradient migration of the sulfate plume inland and upgradient of 1325-N. Figure 6-30 shows hydrographs for select 1324-N/NA and 1325-N monitoring wells, with elevations at 1324-N/NA (wells 199-N-59, 199-N-72, and 199-N-73) higher than at 1325-N, except during periods of high discharge to 1325-N.

High sulfate was not observed in groundwater beneath 1325-N during the operational period because mounding kept it from migrating to 1325-N monitoring wells. Discharges to the 1325-N Crib and 1324-NA percolation pond terminated in 1991 and 1990, respectively. After discharges to 1325-N ceased, the water table began to decline; sulfate that had been pushed upgradient of 1325-N began to flow toward 1325-N. Specific conductance and sulfate trends for 1324-N/NA downgradient monitoring well 199-N-165 continue to show decreasing concentrations (Section 6.8.3), while concentrations at the 1325-N monitoring wells are increasing.

These data support the conclusion of the 1999 assessment report (00-GWVZ-054) that the high specific conductance at 1325-N is attributed to the nonregulated sulfate discharged to 1324-N/NA, and the site remains in detection monitoring.

Figure 6-30. Water Levels in 1324-N/NA and 1325-N Monitoring Wells

6.8.3 120-N-1 Percolation Pond and 120-N-2 Surface Impoundment The 1324-N and 1324-NA facilities, also known as the 120-N-2 and 120-N-1 waste sites (Figure 6-31), were TSD units used to treat and dispose of corrosive, nonradioactive waste from 1977 to 1990. Both units have been remediated and backfilled. The remediation consisted of removal and disposal of the site structures, including a liner system, a small sampling shed, fencing, and other miscellaneous debris. The waste sites are undergoing RCRA closure, and they are classified as interim closed under CERCLA (Section 1.3.2.6 of DOE/RL-2012-15).

The 1324-N/NA units are included in the Hanford RCRA Permit, which states that groundwater monitoring during the RCRA closure period will follow the requirements of BHI-00725 and WHC-SD-EN-AP-038. The units are monitored as a single WMA due to their proximity and similar waste types.

Upgradient well 199-N-71 and downgradient wells 199-N-72, 199-N-73, 199-N-77, and 199-N-165 monitor the sites (Table B-4). The 199-N-77 well screen is at the base of the unconfined aquifer, and statistical data comparisons are not performed on this well. No changes to the monitoring network were made in 2016.

Reference: NAVD88, North American Vertical Datum of 1988.

Figure 6-31. RCRA 1324-N and 1324-NA (120-N-1 and 120-N-2) Monitoring Well Locations

The 100-KR-4 OU injection wells, located south and west of the 1324-N/NA site, have raised the water table and continued to affect groundwater flow in 2016. Water table contours based on March 2016 data for the 100-N Area (Figure 6-31) and the surrounding region indicate flow to the north-northeast. Trend surface analysis of March 2016 data from the 1324-N/NA monitoring well network indicated that the local water table also sloped to the northeast. The hydraulic gradient was estimated to be 8.9 × 10-4 m/m in March 2016, with flow rates from 0.02 to 0.33 m/day (0.06 to 1.1 ft/day) (Table B-5). The direction of flow has varied from northeast to north-northwest over the past 3 years.

All five monitoring wells were sampled as planned during 2016 (Table B-6): semiannually for RCRA contamination indicator parameters (pH, specific conductance, TOC, and TOX) and turbidity, and annually for groundwater quality and supporting parameters (chloride, iron, manganese, sodium, sulfate, and alkalinity).

The pH measurement at upgradient monitoring well 199-N-71 on September 13, 2016 was below the lower critical range of 7.67 to 8.54. Verification samples taken in November showed that the pH measurement was within the pH measurement critical range.

Specific conductance results continued to be above the critical mean in downgradient wells 199-N-72, 199-N-73, and 199-N-165. A previous groundwater quality assessment indicated that the high specific conductance is caused by the nonregulated constituents sulfate and sodium (WHC-SD-EN-EV-003, Results of Groundwater Quality Assessment Monitoring at the 1301-N and 1324-N/NA Facilities). Sulfate and specific conductance trends continue to indicate that the source of high specific conductance is sulfate (Figures 6-32 through 6-34). These data indicate that the conclusion in the 1992 assessment report (WHC-SD-EN-EV-003) remains valid, and the site remains in detection monitoring.

The 100-N-58 waste site is a secondary source of sulfate to groundwater at 1324-N/NA. The 100-N-58 south setting pond is a past-practice waste site that received the same effluent disposed to the 1324-NA percolation pond from 1977 to 1983. The 100-N-58 site was co-located with the 1324-N/NA sites and was closed out after completing interim remedial actions for the sites. Groundwater monitoring at 1324-N/NA began about 10 years after effluent disposal began at the settling pond. Figure 6-35 illustrates the operational piping at 1324-N/NA and 100-N-58 and the locations of groundwater monitoring wells. No sulfate data are available to evaluate groundwater impacts from the date of initial discharge to the soil column beginning in 1977. Sulfate groundwater data are available for 1987 to present.

Figure 6-36 shows sulfate trends in 1324-N/NA groundwater monitoring wells. Sulfate concentrations were generally decreasing near waste site 100-N-58 from a 1990 maximum of about 1,800 mg/L in well 199-N-59. This initial maximum concentration in well 199-N-59 is a major indicator of the dominant influence of sulfate on groundwater from waste site 100-N-58. High sulfate concentrations were also detected in well 199-N-73, which is located at the boundary of waste site 100-N-58.

Figure 6-32. Specific Conductance and Sulfate in Well 199-N-72

Figure 6-33. Specific Conductance and Sulfate in Well 199-N-73

Figure 6-34. Specific Conductance and Sulfate in Well 199-N-165

Figure 6-35. 1324-N/NA and 100-N-58 Operational Piping and Groundwater Monitoring Network

Figure 6-36. Sulfate Concentrations in the 1324-N/NA Groundwater Monitoring Network

Higher concentrations of sulfate historically detected in the groundwater wells (199-N-59 and 199-N-73) suggest that the 100-N-58 waste site was the most significant source of sulfate of the three settling percolation ponds. The maximum concentration observed near the 100-N-58 waste site in groundwater (well 199-N-59) was about four times greater than concentrations observed in other wells. Elevated sulfate concentrations were also observed at well 199-N-73 near the 100-N-58 site boundary until about 2011. Injection of treated groundwater from the 100-K P&T systems into wells located south and west of the 1324-N/NA site shifted groundwater flow around 1324-N/NA to the north-northeast (Figure 6-31). After 2011, sulfate concentrations in wells 199-N-72 and 199-N-77 were the highest of all wells, which likely reflects sulfate migration in groundwater from 100-N-58 towards the two wells as a result of the change in groundwater flow direction. This regional flow change is also observed in higher sulfate concentration groundwater flowing farther north into the groundwater monitoring well network at 1325-N. Sulfate concentrations were below cleanup levels in soil samples collected from borehole 199-N-89 drilled in 1992 to characterize contamination beneath the 1324-N settling pond.

6.9 Atomic Energy Act Monitoring AEA groundwater monitoring was conducted at 62 groundwater wells and aquifer tubes in the 100-NR groundwater interest area in accordance with DOE/RL-2015-56. The primary AEA constituents for 100-NR are strontium-90, nitrate, and tritium. Wells were sampled in accordance with SAP requirements in 2016 (Table C-6 in Appendix C). Minor exceptions to planned monitoring occurred because of maintenance issues and scheduling constraints. Appendix C lists the sampling frequencies, types of laboratory analyses, and sample status for 2016 AEA monitoring of the 100-NR groundwater wells.

Concentrations of radionuclides in groundwater samples from 125 wells and aquifer tubes were used to estimate the cumulative TED and to compare the cumulative beta/photon emitters, alpha emitters, and uranium mass to DWSs, as described in Section 1.2.4. The DWSs for cumulative alpha emitters and uranium mass were not exceeded. The estimated TED exceeded the 100 mrem/yr standard at 14 groundwater wells in 100-NR (Table 6-4). The cumulative drinking water dose from beta/photon emitters exceeded the 4 mrem/yr standard at 69 locations in this interest area. Some of these locations are adjacent to the Columbia River, which is the primary potential pathway for offsite exposure to Hanford Site contaminated groundwater. Members of the public are protected from exposure to groundwater through the implementation of institutional controls that restrict access to groundwater and through remedial action measures to control the migration of contaminated groundwater to exposure points.

Table 6-4. Cumulative Total Effective Doses and Groundwater Concentrations that Exceeded Standards at Groundwater Monitoring Locations in 100-NR in 2016

Monitoring Location/Well Name

Cumulative TED ≥100 mrem/yr

Cumulative Drinking Water Dose (Beta/Photon) ≥4 mrem/yr

Minimum Maximum Minimum Maximum

199-N-103A

546.41 546.41

199-N-104A

146.53 146.53

199-N-105A 107.81 107.81 592.06 592.06

199-N-106A 183.21 183.21 1006.84 1006.84

199-N-122 143.82 143.82 292.50 790.72

199-N-123

59.96 66.50

199-N-136

7.15 7.15

199-N-14 123.27 124.24 676.79 681.98

199-N-146

88.50 143.18

199-N-147

113.07 122.00

199-N-159

84.50 84.50

199-N-173

10.45 12.03

199-N-183

45.26 45.26

199-N-184

107.71 107.71

199-N-186

98.96 98.96

199-N-187 918.74 918.74 5052.12 5052.12

199-N-188 162.32 162.32 891.11 891.11

199-N-19

8.32 8.32

199-N-2

132.36 132.36

199-N-27

64.51 64.51

199-N-28

17.11 17.11

Table 6-4. Cumulative Total Effective Doses and Groundwater Concentrations that Exceeded Standards at Groundwater Monitoring Locations in 100-NR in 2016

Monitoring Location/Well Name

Cumulative TED ≥100 mrem/yr

Cumulative Drinking Water Dose (Beta/Photon) ≥4 mrem/yr

Minimum Maximum Minimum Maximum

199-N-3

366.40 384.92

199-N-332

253.00 253.00

199-N-34

21.10 21.10

199-N-348

28.90 47.03

199-N-349

30.80 59.48

199-N-350

36.40 41.82

199-N-351

110.50 279.09

199-N-352 109.38 109.38 82.50 601.09

199-N-353

37.97 37.97

199-N-354

5.51 5.51

199-N-355 119.62 119.62 383.00 657.02

199-N-356

118.50 366.46

199-N-357 112.78 237.87 620.00 1306.87

199-N-358

267.50 501.20

199-N-359

156.00 163.99

199-N-360 104.01 104.01 157.50 571.40

199-N-361

15.88 153.50

199-N-362

205.50 245.25

199-N-363

270.28 287.50

199-N-364

132.50 283.29

199-N-365

58.50 156.32

199-N-366

31.65 146.49

199-N-367

9.70 9.70

199-N-374

6.41 62.60

199-N-377

7.05 18.28

199-N-46 108.19 108.19 595.00 595.00

199-N-67 1055.67 1145.92 5801.98 6300.00

199-N-75 195.11 278.11 1071.94 1527.19

Table 6-4. Cumulative Total Effective Doses and Groundwater Concentrations that Exceeded Standards at Groundwater Monitoring Locations in 100-NR in 2016

Monitoring Location/Well Name

Cumulative TED ≥100 mrem/yr

Cumulative Drinking Water Dose (Beta/Photon) ≥4 mrem/yr

Minimum Maximum Minimum Maximum

199-N-76

79.92 152.91

199-N-81

248.02 248.02

199-N-96A

4.04 4.04

APT1

235.50 240.00

APT5

73.50 108.00

C6132

4.37 8.65

C6317

4.05 4.05

C6320

6.37 6.37

C6324

5.10 7.00

C7881

15.25 21.00

C7934

79.08 251.60

C7935

96.70 220.00

C7936

32.25 78.90

C9587 75.5 96.5

C9588 19.8 27.75

C9589 20.7 21.4

C9590 20.25 22.45

N116mArray-11A

237.00 369.50

N116mArray-2A

9.15 9.25

N116mArray-3A

56.00 72.00

N116mArray-4A

78.50 100.00

N116mArray-6A

57.50 77.50

N116mArray-9A

94.00 127.50

NVP2-116.0 140.94 188.19 775.00 1035.00

Source: ECF-HANFORD-17-0022, Calculation of Radiological Dose based on Calendar Year 2016 Atomic Energy Act Groundwater Monitoring at Hanford. Notes: No wells in 100-NR had cumulative alpha activity ≥15 pCi/L or cumulative uranium mass ≥30 µg/L. Blank cells indicate no exceedances.

Contents 6 100-NR ............................................................................................................................................. 6-1

6.1 Overview ................................................................................................................................ 6-1 6.2 Strontium-90 ........................................................................................................................... 6-6 6.3 Tritium .................................................................................................................................. 6-12 6.4 Nitrate ................................................................................................................................... 6-12 6.5 Total Petroleum Hydrocarbons – Diesel .............................................................................. 6-22 6.6 Chromium ............................................................................................................................. 6-25 6.7 CERCLA Remediation and Monitoring ............................................................................... 6-26

6.7.1 CERCLA Decision Documents and Plans ............................................................. 6-26 6.7.2 Apatite Barrier ....................................................................................................... 6-27 6.7.3 Demolition of the 100-NR-2 Pump and Treat System .......................................... 6-31 6.7.4 Petroleum Hydrocarbons ....................................................................................... 6-32

6.8 RCRA Monitoring ................................................................................................................ 6-32 6.8.1 116-N-1 Crib and Trench ....................................................................................... 6-32 6.8.2 116-N-3 Crib and Trench ....................................................................................... 6-34 6.8.3 120-N-1 Percolation Pond and 120-N-2 Surface Impoundment ............................ 6-38

6.9 Atomic Energy Act Monitoring ........................................................................................... 6-43

Figures

Figure 6-1. 100-NR Water Table, March 2016 ...................................................................................... 6-2 Figure 6-2. 100-NR Sampling Locations, 2016 ..................................................................................... 6-4 Figure 6-3. 100-NR Plume Areas ........................................................................................................... 6-5 Figure 6-4. 100-NR Geology .................................................................................................................. 6-5 Figure 6-5. 100-NR Strontium-90 Plume, 2016 ..................................................................................... 6-7 Figure 6-6. 100-NR Strontium-90 Data for Well 199-N-81, Downgradient of the 116-N-3 Crib

and Trench ........................................................................................................................... 6-8 Figure 6-7. 100-NR Strontium-90 Data for Well 199-N-67, Downgradient of the 116-N-1 Crib

and Trench ........................................................................................................................... 6-8 Figure 6-8. 100-NR Strontium-90 Data for Aquifer Tubes C7934, C7935, and C7936 ...................... 6-10 Figure 6-9. New 100-NR-2 OU Monitoring Well Locations Installed in 2016 ................................... 6-11 Figure 6-10. 100-NR Tritium Plume, 2016 ............................................................................................ 6-13 Figure 6-11. 100-NR Tritium Data for Aquifer Tubes C7934, C7935, and C7936 ............................... 6-14 Figure 6-12. 100-NR Nitrate Plume, 2016 ............................................................................................. 6-15 Figure 6-13. 100-NR Nitrate Data for Wells 199-N-2 and 199-N-67 .................................................... 6-16 Figure 6-14. 100-NR Nitrate Data for Well 199-N-32 ........................................................................... 6-16 Figure 6-15. 100-NR Chloride Trend Comparison for 199-N-2 and 199-N-28 to Upgradient Well

199-N-74 ............................................................................................................................ 6-18

Figure 6-16. 100-NR Magnesium Trend Comparison for 199-N-2 and 199-N-28 to Upgradient Well 199-N-74 ................................................................................................................... 6-18

Figure 6-17. 100-NR Strontium Trend Comparison for 199-N-2 and 199-N-28 to Upgradient Well 199-N-74 ................................................................................................................... 6-19

Figure 6-18. 100-NR Nitrate to Chloride, Magnesium, and Strontium Trend Comparison for Well 199-N-2 ..................................................................................................................... 6-20

Figure 6-19. 200-NR Nitrate to Chloride, Magnesium, and Strontium Trend Comparison for Well 199-N-28 ................................................................................................................... 6-21

Figure 6-20. 100-NR Nitrate Data for Wells 199-N-59, 100-N-72, and 199-N-165 .............................. 6-22 Figure 6-21. 100-NR TPH-D Plume, 2016............................................................................................. 6-23 Figure 6-22. 100-NR Chromium Data for Well 199-N-80 ..................................................................... 6-27 Figure 6-23. 100-NR Apatite Barrier ..................................................................................................... 6-29 Figure 6-24. 100-NR Strontium-90 Data for Performance Monitoring Wells along the Central

Segment of the Apatite PRB .............................................................................................. 6-30 Figure 6-25. RCRA 1301-N (116-N-1) Monitoring Well Locations ..................................................... 6-33 Figure 6-26. RCRA 1325-N (116-N-3) Monitoring Well Locations ..................................................... 6-35 Figure 6-27. Specific Conductance and Sulfate in Well 199-N-32 ........................................................ 6-36 Figure 6-28. Specific Conductance and Sulfate in Well 199-N-41 ........................................................ 6-36 Figure 6-29. Specific Conductance and Sulfate in Well 199-N-81 ........................................................ 6-37 Figure 6-30. Water Levels in 1324-N/NA and 1325-N Monitoring Wells ............................................ 6-38 Figure 6-31. RCRA 1324-N and 1324-NA (120-N-1 and 120-N-2) Monitoring Well Locations ......... 6-39 Figure 6-32. Specific Conductance and Sulfate in Well 199-N-72 ........................................................ 6-41 Figure 6-33. Specific Conductance and Sulfate in Well 199-N-73 ........................................................ 6-41 Figure 6-34. Specific Conductance and Sulfate in Well 199-N-165 ...................................................... 6-42 Figure 6-35. 1324-N/NA and 100-N-58 Operational Piping and Groundwater Monitoring

Network ............................................................................................................................. 6-42 Figure 6-36. Sulfate Concentrations in the 1324-N/NA Groundwater Monitoring Network ................. 6-43

Tables

Table 6-1. 100-NR at a Glance ............................................................................................................. 6-3 Table 6-2. Wells Installed in 100-NR in 2016 .................................................................................... 6-10 Table 6-3. 100-NR Remedy Summary ................................................................................................ 6-24 Table 6-4. Cumulative Total Effective Doses and Groundwater Concentrations that Exceeded

Standards at Groundwater Monitoring Locations in 100-NR in 2016 ............................... 6-44