Contents Chapter 6 Acronyms

W. K. Jago, R. S. Loffman, and C. A. Motley

ABSTRACT

Most residents in the Oak Ridge area do not rely on groundwater for potable supplies, although suitable water is available. Local groundwater provides some domestic, municipal, farm, irrigation, and industrial uses, however, and must be viewed as both a potential pathway for exposure to hazardous wastes and as a means for contaminant transport. Statutes codified into regulations by the EPA specifically target the protection of groundwater from contamination by hazardous wastes. The regulations guide groundwater monitoring at the DOE plants in Oak Ridge. Monitoring programs established on the ORR assess groundwater contamination and transport on and off the reservation and are intended to comply with established regulatory requirements.

7.1 INTRODUCTION

The groundwater monitoring programs at the ORR gather information to determine the effects of DOE operations on groundwater quality in compliance with all applicable requirements.

The location and movement of groundwater must be determined to identify the extent of contamination in groundwater and to predict the possible fate of contaminants. To make this determination, an understanding is required of how groundwater moves in general and how that movement will be influenced by the geological setting.

7.1.1 Geological Setting

Two geologic units on the ORR, designated as the Knox Group and the Maynardville Limestone of the Conasauga Group, both consisting of dolostone and limestone, constitute the Knox Aquifer. A combination of fractures and solution conduits in this aquifer control flow over substantial areas, and relatively large quantities of water may move relatively long distances. Active groundwater flow can occur at substantial depths in the Knox Aquifer [300 to 400 ft (91.5 to 122 m)]. The Knox Aquifer is the primary source of groundwater to many streams (base-flow), and most large springs on the ORR discharge from the Knox Aquifer. Yields of some wells penetrating larger solution conduits are reported to exceed 1000 gal/min (3784 L/min).

The remaining geologic units on the ORR (the Rome Formation, the Conasauga Group below the Maynardville Limestone, and the Chickamauga Group) constitute the ORR Aquitards, which consist mainly of siltstone, shale, sandstone, and thinly bedded limestone of low to very low permeability. Nearly all groundwater flow in the aquitards occurs through fractures. The typical yield of a well in the aquitards is less than 1 gal/min (3.8 L/min), and the base flows of streams draining areas underlain by the aquitards are poorly sustained because of such flow rates.

7.1.2 Hydrogeological Setting

Water infiltrates by percolating downward through the pore spaces between sediment grains and also through fractures in bedrock. The smaller the pore spaces or fractures, the slower the flow of water through the subsurface. The physical property that describes the ease with which water may move through the pore spaces and fractures in a given material is called permeability, and it is largely determined by the volume and size of these features and how well they are connected.

As water infiltrates the earth, it travels down through the unsaturated zone, where the pore spaces and fractures are partly filled with water and partly filled with air. Water moving down through the unsaturated zone will eventually reach the saturated zone, where the pore spaces and fractures are completely filled with water. The boundary between the unsaturated and the saturated zones is known as the water table, which generally follows, in subtle form, the contour of the surface topography. Springs, swamps, and beds of streams and rivers are the outcrops of the water table, where groundwater is discharged to the surface.

Because the earth's permeability varies greatly, groundwater flowing through subsurface strata does not travel at a constant rate or without impediment. Strata that transmit water easily (such as those composed primarily of sand) are called aquifers, and strata that restrict water movement (such as clay layers) are called aquitards. An aquifer with an aquitard lying above and beneath it is termed a confined aquifer. Groundwater moves through aquifers toward natural exits, or discharge points, to reappear at the surface.

The direction of groundwater flow through an aquifer system is determined by the permeability of the strata containing the aquifer and by the hydraulic gradient, which is a measure of the difference in hydraulic head over a specified distance. Differences in hydraulic head comprise the driving force for groundwater movement through the saturated zone. The hydraulic head at any given point in an aquifer is a function of the energy associated with the water's elevation above sea level and the pressures exerted on it by surrounding water. Because hydraulic head is not solely a function of elevation, downgradient is not necessarily synonymous with downhill. The downgradient direction will have a horizontal and vertical component, just as a household drain moves wastewater both horizontally and vertically, seeking the lowest point of exit. Aquitards deflect groundwater movement just as drain pipe walls control the direction of wastewater movement. In an aquifer constrained by aquitards such as horizontal clay layers, the downgradient direction tends to be more horizontal than vertical.

Groundwater on the ORR occurs both in the unsaturated zone as transient, shallow subsurface stormflow and within the saturated zone. An unsaturated zone of variable thickness separates the stormflow zone and water table. Adjacent to surface water features or in valley floors, the water table is found at shallow depths and the unsaturated zone is thin. Along the ridge tops or near other high topographic areas, the unsaturated zone is thick, and the water table often lies at considerable depth [15 to 50 m (50 to 175 ft)]. In low-lying areas where the water table occurs near the surface, the stormflow zone and saturated zone are indistinguishable.

Several distinct flow intervals occur within the water table aquifer: the uppermost water table interval; the intermediate interval; the deep interval; and the aquiclude, which is defined by a transition to saline water (Fig. 7.1). The divisions within the saturated zone grade into one another vertically and are not separated by distinct boundaries but reflect an overall decrease in the rate of groundwater flow with depth. Within the ORR aquitards, the greatest groundwater flow rates occur in the stormflow zone and the smallest within the deep zone. Water does not flow in the aquiclude. In the Knox Aquifer, the greatest groundwater flow is in the water table and intermediate intervals [depths to approximately 300 ft (91.5 m)].

As denoted earlier, two broad hydrologic units are identified on the ORR: the Knox Aquifer and the ORR Aquitards, which consist of less permeable geologic units. Figure 7.2 is a generalized map showing surface distribution of the Knox Aquifer and the ORR Aquitards. Many waste areas on the ORR are located in areas underlain by the ORR Aquitards.

7.1.2.2 Unsaturated Zone Hydrology

The rate at which groundwater is transmitted through the stormflow zone is attributed to large pores (root channels, worm bores, and relict fractures). Stormflow is primarily a transport mechanism in undisturbed or vegetated areas, where it intersects shallow waste sources. Most buried wastes are below the stormflow zone; however, in some trenches a commonly observed condition known as ``bathtubbing'' can occur, in which the excavation fills with water and may overflow into the stormflow zone. All stormflow ultimately discharges to streams on the ORR.

7.1.2.3 Saturated Zone Hydrology

As in the stormflow zone, the bulk of groundwater in the saturated zone resides within the pore spaces of the rock matrix. The rock matrix typically forms blocks that are bounded by fractures. Contaminants in the fractures typically occur in higher concentrations than in the matrix; thus, the contaminants tend to move (diffuse) into the matrix. This process, termed diffusive exchange, between water in matrix pores and water in adjacent fractures reduces the overall contaminant migration rates relative to groundwater flow velocities. For example, the leading edge of a geochemically nonreactive contaminant mass such as tritium may migrate along fractures at a typical rate of 3 ft/day (1 m/day); however, the center of mass of a contaminant plume typically migrates at a rate less than 0.2 ft/day (0.66 m/day).

In the aquitards, chemical characteristics of groundwater change from mixed-cation-HCO₃ water type at shallow depth to a Na-HCO₃ water type at deeper levels. This transition, not marked by a distinct change in rock properties, serves as a useful marker and can be used to distinguish the more active water table and intermediate groundwater intervals from the sluggish flow of the deep interval. There is evidence of similar change with depth in the chemical characteristics of water in the Knox Aquifer. Although the mechanism responsible for this change in water types is not quantified, it most likely is related to the amount of time the water is in contact with a specific type of rock.

Most groundwater flow in the saturated zone occurs within the water table interval. Most flow is through weathered, permeable fractures and matrix rock and within solution conduits in the Knox Aquifer. The range of seasonal fluctuations in depth to the water table and in rates of groundwater flow varies significantly across the reservation. In areas underlain by the Knox Aquifer, seasonal fluctuations in water levels average 5.3 m (17 ft), and mean discharge from the active groundwater zone is typically 85 gal/min (322 L/min) per square mile. In the aquitards of BCV, Melton Valley, East Fork Valley, and Bethel Valley, seasonal fluctuations in water levels average 5 ft (1.5 m) and typical mean discharge is 26 gal/min (98 L/min) per square mile.

In the intermediate interval, groundwater flow paths are a product of fracture density and orientation. In this interval, groundwater movement occurs primarily in permeable fractures that are poorly connected. In the Knox Aquifer a few cavity systems and fractures control groundwater movement in this zone, but in the aquitards the bulk of flow is through fractures along which permeability may be increased by weathering.

The deep interval of the saturated zone is delineated by a change to a Na-HCO₃ water type. Hydrologically active fractures in the deep interval are significantly fewer in number and shorter in length than in the other intervals, and the spacing is greater. Wells finished in the deep interval of the ORR aquitards typically yield less than 0.3 gal/min (1.1 L/min) and thus are barely adequate for water supply.

In the aquitards, saline water characterized by total dissolved solids ranging up to 2.75 � 10⁵ mg/L and chlorides generally in excess of 5 � 10⁴ mg/L (ranging up to 1.63 � 10⁵ mg/L) lies beneath the deep interval of the groundwater zone, delineating an aquiclude. Chemically, this water resembles brines typical of major sedimentary basins, but its origin is not known. The chemistry suggests extremely long residence times (i.e., very low flow rates) and little or no mixing with shallow groundwater.

The aquiclude has been encountered at depths of 125 and 244 m (400 and 800 ft) in Melton and Bethel valleys, respectively (near ORNL), and it is believed to approach 305 m (1000 ft) in portions of BCV (near the Y-12 Plant) underlain by aquitard formations. Depth to the aquiclude in areas of the Knox Aquifer is not known but is believed to be greater than 366 m (1200 ft); depth to the aquiclude has not been established in the vicinity of the K-25 Site.

7.1.3 Groundwater Flow

Topographic relief on the ORR is such that most active subsurface groundwater flow occurs at shallow depths. U.S. Geological Survey modeling (Tucci 1992 ) suggests that 95% of all groundwater flow occurs in the upper 15 to 30 m (50 to 100 ft) of the saturated zone in the aquitards. As a result, flow paths in the active-flow zones (particularly in the aquitards) are relatively short, and nearly all groundwater discharges to local surface water drainages on the ORR. Conversely, in the Knox Aquifer, it is believed that solution conduit flow paths may be considerably longer, perhaps as much as 1.6 km (2 miles) long in the along-strike direction. No evidence at this time substantiates the existence of any deep, regional flow off the ORR or between basins within the ORR in either the Knox Aquifer or the aquitards. Data collected in CY 1994 and 1995, however, has demonstrated that groundwater flow and contaminant transport occur off of the ORR in the intermediate interval of the Knox Aquifer, near the east end of the Y-12 Plant.

Migration rates of contaminants transported in groundwater are strongly influenced by natural chemical and physical processes in the subsurface (including diffusion and adsorption). Peak concentrations of solutes, including contaminants such as tritium moving from a waste area, for instance, can be delayed for several to many decades in the aquitards, even along flow paths as short as a few hundred feet. The processes that naturally retard contaminant migration and store contaminants in the subsurface are less effective in the Knox Aquifer than in the aquitards because of rapid flow along solution features allowing minimal time for diffusion to occur.

7.1.4 Groundwater Monitoring Considerations

7.1.5 Off-Site Spring and Residential Well Monitoring

7.1.6 Groundwater Monitoring Program on the ORR

Thus, the groundwater surveillance monitoring program for the ORR, while disposal site- and facility-specific, contains a number of common components that are interrelated and coordinated to allow both time- and cost-effective project management.

7.2 GROUNDWATER MONITORING AT THE Y-12 PLANT

7.2.1 Background and Regulatory Setting

• monitoring to comply with requirements of RCRA interim status assessment and detection monitoring,
• compliance with RCRA postclosure monitoring requirements,
• monitoring to support CERCLA RI/FS efforts and records of decision,
• compliance with TDEC solid waste management (SWM) regulations,
• monitoring to support DOE Order 5400.1 requirements (exit pathway and surveillance monitoring),
• compliance with regulatory monitoring requirements for petroleum USTs, and
• monitoring to support best management practices.

Through incorporation of these multiple considerations, the comprehensive monitoring program at the Y-12 Plant addresses multiple regulatory considerations and technical objectives. It eliminates redundancy between different regulatory programs and ensures consistent data collection and evaluation.

More than 200 sites have been identified at the Y-12 Plant that represent known or potential sources of contamination to the environment as a result of past waste management practices. These sites are being addressed either by the ER Program under exclusively CERCLA programs or a combination of CERCLA and RCRA regulations. The ER Program and Y-12 Plant management share responsibilities for sites regulated under dual CERCLA and RCRA drivers.

A number of the inactive waste management sites were grouped in 1992 into OUs under CERCLA as part of an FFA negotiated between EPA, TDEC, and DOE. Two types of OUs were identified: (1) source OUs consisting of sites or groups of sites that were known sources of contamination to the environment and (2) integrator OUs consisting of media, such as groundwater, soils, and surface water, that had been impacted by the source OUs. RI/FS activities were initiated for these OUs; however, as these activities progressed, it became evident that administrative separation of source and integrator OUs was not a technically feasible approach to ER because contamination from numerous source OUs had mingled and integrator OUs had been impacted significantly by multiple source OUs. As a result, distinction of the nature and extent of contamination, risk, and evaluation of remedial actions for individual source OUs was not practicable. An agreement was reached among regulatory agencies and DOE in 1994 to proceed with an integrated RI/FS strategy. In the integrated strategy, former source OUs and integrator OUs are addressed concurrently in a characterization area (CA) defined by physical limits, such as watershed boundaries and/or groundwater flow regimes (Fig. 7.4). Specific sites or locations of high risk or concern within the CA are targeted for focused, rapid remedial actions, while a general remedial strategy and/or administrative controls for the CA progresses. Individual focused actions are designated as OUs and documented under separate RODs.

Two CAs incorporating 27 known source units have been established for the Y-12 Plant, the UEFPC CA and the Bear Creek Valley (BCV) CA.

In addition, four individual source OUs remain on Chestnut Ridge, where available data indicate that contamination from each unit is distinct and separable. The remaining sites have been grouped into Y-12 Plant study areas that constitute lower-priority units that will be investigated under CERCLA as preliminary assessment/site investigations (PA/SIs). New OUs or additions to existing CAs will be made if the degree of contamination determined by the PA/SI warrants further study under an RI/FS.

Postclosure maintenance, monitoring, and reporting requirements of RCRA also apply to seven inactive CERCLA-regulated units that meet the definition of RCRA hazardous waste TSD facilitates. These units include the S-3 Site, portions of the Bear Creek Burial Grounds, Oil Landfarm, New Hope Pond, Chestnut Ridge Security Pits, Chestnut Ridge Sediment Disposal Basin, and Kerr Hollow Quarry. Postclosure requirements will be outlined in RCRA postclosure permits currently being issued by TDEC. These requirements will be integrated with CERCLA programs. Corrective actions addressing contaminant releases will be deferred to the CERCLA RI/FS process.

Additional primary regulatory drivers for groundwater monitoring at the Y-12 Plant are the TDEC regulations governing nonhazardous solid waste disposal facilities (SWDFs) and TDEC regulations governing petroleum USTs. Two facilities (Centralized Sanitary Landfill II and Industrial Landfill IV) have been subject to groundwater monitoring under the SWDF regulations since the late 1980s. Construction of three additional landfill facilities was completed between 1993 and 1994 (Industrial Landfill V, Construction/Demolition Landfill VI, and Construction/Demolition Landfill VII). Baseline groundwater monitoring has been completed for all SWDFs, and all of the sites are now under a semiannual detection monitoring program. Groundwater monitoring to support the petroleum UST program at the Y-12 Plant has progressed past the assessment phase into the corrective action phase, which requires only limited monitoring.

Specific regulatory requirements do not address all groundwater monitoring concerns at the Y-12 Plant. Selected areas where contamination is most likely to migrate to potential exposure points off of the ORR are monitored as part of DOE Order 5400.1 exit-pathway monitoring. Also, monitoring is performed as part of DOE 5400.1 surveillance monitoring in general areas not specifically regulated and not representing specific exit pathways off of the reservation, such as a large part of the industrialized portion of the Y-12 Plant. Surveillance monitoring is conducted to monitor contaminant plume boundaries and to trend contaminant concentrations specifically to augment regulatory and exit-pathway monitoring programs. Best management practice monitoring is conducted at a number of selected sites or locations either at the request of internal organizations, the TDEC/DOE Oversight Division, or in lieu of regulatory required monitoring at active facilities.

7.2.2 Hydrogeologic Setting and Summary of Groundwater Quality

In general, groundwater flow in the water table interval follows topography. Shallow groundwater flow in the Bear Creek and East Fork regimes is divergent from a topographic and groundwater table divide located near the western end of the Y-12 Plant. Shallow groundwater flow directions east and west of the divide are predominantly easterly and westerly, respectively. This divide defines the boundary between the Bear Creek and Chestnut Ridge regimes. In addition, flow converges toward the primary surface streams from Pine Ridge to the north and Chestnut Ridge to the south of the Y-12 Plant. In the Chestnut Ridge regime, a groundwater table divide exists that approximately coincides with the crest of the ridge. Shallow groundwater flow, therefore, tends to be toward either flank of the ridge, with discharge primarily to surface streams and springs located in Bethel Valley to the south and BCV to the north.

In BCV, groundwater in the intermediate and deep intervals moves predominantly through fractures in the ORR aquitards, converging toward and moving through fractures and solution conduits in the Maynardville Limestone. Karst development in the Maynardville Limestone has a significant impact on groundwater flow paths in the water table and intermediate intervals. In general, groundwater flow parallels geologic strike. Groundwater flow rates in BCV vary widely; they are very slow within the deep interval of the ORR aquitards but can be quite rapid within solution conduits in the Maynardville Limestone. The rate of groundwater flow perpendicular to geologic strike from the ORR aquitards to the Maynardville Limestone has not been well established. Several investigations are currently under way or planned to attempt to identify how quickly groundwater beneath waste sites over the ORR aquitards moves to the Maynardville Limestone. Recent data obtained as part of hydrologic studies in the Bear Creek regime suggest that strike-parallel transport of some contaminants can occur within the ORR aquitards for significant distances. Continuous elevated levels of nitrate within the ORR aquitards are now known to extend west from the S-3 Site for a distance of about 3000 ft, approximately twice the previous estimates. VOCs at source units in the ORR aquitards, however, tend to remain close to source areas because they tend to adsorb to the bedrock matrix, diffuse into pore spaces within the matrix, and degrade prior to migrating to exit pathways, where rapid transport for long distances can occur.

Groundwater flow in the Chestnut Ridge regime is almost exclusively through fractures and solution conduits in the Knox Group. Discharge points for intermediate and deep flow are not well known. Groundwater is currently presumed to flow primarily toward BCV to the north and Bethel Valley to the south. Groundwater from intermediate and deep zones may discharge at certain spring locations along the flanks of Chestnut Ridge. Along the crest of the ridge, water table elevations decrease from west to east, implying an overall easterly trend in groundwater flow.

Historical monitoring efforts have shown that groundwater quality at the Y-12 Plant has been affected by four types of contaminants: nitrate, VOCs, metals, and radionuclides. Of these, nitrate and VOCs are the most widespread, although data obtained since 1988 suggest that the extent of some radionuclides may also be significant, particularly in the Bear Creek regime. Trace metals, the least extensive groundwater contaminants, generally occur in a small area of low-pH groundwater at the west end of the Y-12 Plant, in the vicinity of the S-3 Site. Data obtained as a result of previous monitoring efforts show that contaminant plumes from multiple source units have mixed with one another and that contaminants (other than nitrate) are no longer easily associated with a single source.

7.2.3 1995 Well Installation and Plugging and Abandonment Activities

The Y-12 Plant GWPP conducts well plugging and abandonment activities as part of an overall program to maintain the Y-12 Plant monitoring well network. Wells that are damaged beyond rehabilitation, interfere with planned construction activities, or for which no useful data can be obtained, are selected for plugging and abandonment. In 1995, 55 wells were plugged and abandoned. A majority of these wells were located in the extreme western portion of the Bear Creek regime. The wells were plugged and abandoned because of poor condition, historical lack of security or identity, or no identifiable future use.

7.2.4 1995 Monitoring Programs

Figure 7.6 shows the locations of ORR perimeter monitoring stations as specified in the EMP.

Detailed data reporting for monitoring activities conducted by the Y-12 Plant GWPP is contained within the 1995 annual groundwater quality reports for each hydrogeologic regime (Energy Systems 1996a , 1996b , and 1996c ). Details of small-scale monitoring efforts performed by organizations other than the Y-12 Plant GWPP specifically for CERCLA OUs are published in RI reports.

7.2.5 Y-12 Plant Groundwater Quality

Discussion of Monitoring Results

Plume Delineation

Nitrate

The extent of the nitrate plume is essentially defined in the unconsolidated zone and the shallow bedrock zone. In both zones, the nitrate plume extends about 2500 ft (762.5 m) eastward from the S-3 Site to just downgradient of the S-2 Site. Nitrate has traveled farthest in groundwater in the Maynardville Limestone.

Trace Metals

Volatile Organic Compounds

Concentrations of VOCs in most of the East Fork regime have remained relatively constant since 1988 (Fig. 7.9 ). Some monitoring locations (e.g., GW-220 and GW-733) on the eastern end of the regime, east of New Hope Pond, have shown increasing VOC concentrations, indicative of an easterly movement of part of the plume (Fig. 7.10). Data show that VOCs are the most extensive laterally in the shallow groundwater; however, data indicate that once contaminants migrate into the Maynardville Limestone, they tend to concentrate at depths between 100 and 500 ft. The highest VOC concentrations appear to be between 200 and 500 ft, as exemplified by vertical carbon tetrachloride distribution at the east end of the Y-12 Plant (Fig. 7.11).

The 1995 monitoring results generally confirm findings from the previous 4 years of monitoring. A continuous dissolved VOC plume in groundwater in the bedrock zone extends eastward from the S-3 Site over the entire length of the regime (Fig. 7.12). Additionally, the 1995 data confirm previous results identifying the Waste Coolant Processing Facility area as a VOCs source area. Pockets of VOCs also are present in groundwater at the Building 9754 and 9754-2 fuel facilities and upgradient of New Hope Pond. Data from the East Fork regime surveillance monitoring network show that a major source area also lies within process areas in the central portion of the plant.

Chloroethene compounds (perchloroethene, trichloroethene, dichloroethene, and vinyl chloride) tend to dominate the VOC plume composition in the western and central portions of the Y-12 Plant. However, perchloroethene and isomers of dichloroethene are almost ubiquitous throughout the extent of the VOC plume, indicating many source areas. Chloromethane compounds (carbon tetrachloride, chloroform, and methylene chloride) are the predominant VOCs in the eastern and southeastern portions of the plant.

Radionuclides

Groundwater with gross alpha activity greater than 15 pCi/L occurs in scattered areas throughout the East Fork regime (Fig. 7.13). Historical data collected about 5 years ago show that gross alpha activity exceeding the MCL for drinking water (annual average activity level of 15 pCi/L) is most extensive in groundwater in the unconsolidated zone in the western portion of the Y-12 Plant. Surveillance data collected from several wells in the western portion of the Y-12 Plant during 1995 show that gross alpha (and gross beta) activity levels remained elevated well above the MCL (wells GW-108, GW-109, GW-274, GW-275, and GW-782). Previous monitoring results have also suggested an area of elevated gross alpha activity west of New Hope Pond. Monitoring results during 1995 confirmed that gross alpha activity remains elevated above MCLs in the southeastern portions of the Y-12 Plant (wells GW-154, GW-222, and GW-605). Sporadic gross alpha activity was also observed in several shallow wells scattered across the East Fork regime, notably in exit pathway well GW-169 in Union Valley (Fig. 7.13). Erratic data distribution, coupled with high turbidity and total suspended solids content in samples from most of the wells, indicates that these sporadic values are false positives.

Elevated gross beta activity in groundwater in the East Fork regime shows a pattern similar to that observed for gross alpha activity (Fig. 7.14). In general, gross beta activity consistently exceeds the annual average MCL of 50 pCi/L in groundwater in the western portion of the regime, with the primary source being the S-3 Site. Monitoring data collected in 1995 showed annual average gross beta activity greater than the MCL near the Salvage Yard and Rust Garage (wells GW-108, GW-109, GW-274, and GW-275). Also, consistent with historical patterns, elevated gross beta was observed in an area immediately west of New Hope Pond within the Maynardville Limestone. Elevated sporadic gross beta activity observed in 1994 in off-site exit-pathway wells GW-169 and GW-170, located in Union Valley, was not observed during 1995.

Exit-Pathway and Perimeter Monitoring

Chemical water quality data from exit-pathway wells monitored in 1993 provided the first strong indication that VOCs are being transported off the ORR through the Maynardville Limestone at depths of approximately 100 to 300 ft (30.5 to 91.5 m). Sporadic occurrences of common chlorinated solvents, carbon tetrachloride and tetrachloroethene, above DWSs were confirmed at a depth of 160 ft (49 m) in both on-site and off-site wells (wells GW-170 and GW-733, Figs. 7.11 and 7.12). Well GW-170 is located approximately 1500 ft (458 m) east of the eastern ORR boundary. This off-site well also contained chloroform and trichloroethene, although below the MCLs for these two compounds. Two additional wells at the same location as Well GW-170 have also been sampled quarterly since 1990. Well GW-169 is approximately 40 ft (12.2 m) deep. Only trace levels of VOCs continue to be observed in this well; one sample for trichloroethene was slightly above the MCL in 1991. Carbon tetrachloride and chloroform have not been present above detection levels in this shallow well. Well GW-232 is approximately 400 ft (122 m) deep. No VOCs have been detected in this well. Carbon tetrachloride has also been detected at low levels in spring station SCR 7.1SP, located east of Well GW-170. Several VOCs were also observed at low levels in a spring located along South Illinois Avenue (SCR 7.8SP). Low levels of 1,2-dichloroethene have also been detected at Well GW-230, located east of South Illinois Avenue, which may or may not be connected to Y-12 Plant operations.

The concentration trend for carbon tetrachloride, the primary contaminant of concern, in both wells GW-170 and GW-733 is illustrated in Fig. 7.10. An areal distribution of VOCs is shown in Fig. 7.12. The data to date indicate that VOC transport is occurring at depth within the Maynardville Limestone and is restricted to that formation. A vertical profile of VOC contamination was obtained from a multiport monitoring well (GW-722), near the eastern boundary of the ORR (Fig. 7.6). The data show that the highest VOC concentrations occurred at depths between 200 and 500 ft (61 and 152.5 m) below ground surface (Fig. 7.11 ). VOC concentrations are highest at these depths because most dilution and mixing with rainwater occurs in the shallow portions of the Maynardville Limestone. VOCs have not been observed in exit-pathway wells drilled to a variety of depths in the ORR aquitards north of Well GW-733. Conversely, VOCs have not been observed at concentrations exceeding MCLs in several wells located south of Well GW-733 in the Knox Aquifer.

VOC data were obtained for the first time in 1994 from two sampling points near Lake Reality: a dewatering sump (LRS, Fig. 7.7) located just east of the site and groundwater seeps north of the site within the emergency overflow spillway (LRSPW, Fig. 7.7). These samples contained VOCs (in particular carbon tetrachloride), indicating that groundwater may be moving preferentially through permeable fill zones beneath a concrete-lined diversion channel for UEFPC . The sump was originally installed in 1990 to prevent the bottom liner for Lake Reality from floating as a result of upward hydrostatic pressure. The sump was intermittently active during 1992 and 1993, and was deactivated in mid-1994 because of concerns that it was inducing shallow groundwater flow to the north. The sump had to be reactivated in CY 1995. Monitoring of the groundwater seepage in the overflow spillway continued in 1995 to determine whether any trends in VOC levels resulted from deactivation of the sump. Results indicate that VOC levels did increase during periods of sump operation. In addition, VOC levels in well GW-220 (Fig. 7.12 ) located south of the sump have increased over time and the sump is documented as having a significant [approximate radius of 1000 ft (305 m)] zone of influence on groundwater table levels. Therefore, sump operation has been kept to minimal levels with monitoring of discharge when operation is required.

7.2.5.2 Union Valley Focus Study

An interim study, described in the 1994 ASER, was completed in the fall of 1994. Monitoring of wells and selected springs and surface water stations continued during 1995. Based on the results of the interim study, immediate actions to remediate or intercept groundwater were deemed unwarranted. An interim proposed plan defining administrative controls and public notification has been drafted and submitted to regulatory agencies for review and comment. Additional investigations and any long-term remedial actions in this area will be addressed in conjunction with DOE, TDEC, EPA, and the public as the RI/FS for the UEFPC CA progresses.

7.2.5.3 Bear Creek Hydrogeologic Regime

Discussion of Monitoring Results

Plume Delineation

Contaminant plume boundaries are essentially defined in the bedrock formations that directly underlie many waste disposal areas in the Bear Creek regime, particularly the Nolichucky Shale. The elongated shape of the contaminant plumes in the Bear Creek regime is the result of preferential transport of the contaminants parallel to strike in both the Knox Aquifer and the ORR aquitards. A review of historical data suggests that, in general, contaminant concentrations in the Bear Creek regime, within the ORR aquitards, have remained relatively constant since 1986. Certain contaminants at specific sites, however, have shown non-steady-state concentration patterns, as detailed in the 1992 ORR environmental report (Energy Systems 1993b ). The same trends have been observed in exit-pathway wells located in the Bear Creek regime (Fig. 7.17), with slight increases or decreases observed for selected contaminants.

Nitrate

Data obtained during 1995 indicate that nitrate concentrations exceed the 10 mg/L MCL in an area that extends west from the S-3 Site for several thousand feet down BCV (Fig. 7.8). Nitrate concentrations greater than 100 mg/L extend about 3000 ft (915 m) west of the S-3 Site. During 1995, the highest nitrate concentrations continued to be seen adjacent to the S-3 Site in groundwater in the unconsolidated zone and at shallow depths [less than 100 ft (30.5 m) below the ground surface] in the Nolichucky Shale.

The horizontal extent of the nitrate plume is essentially defined in groundwater in the upper part of the aquifer [less than 200 ft (61 m) below the ground surface]. Data obtained from exit-pathway monitoring wells installed during 1991 and 1992 suggest that the nitrate plume in groundwater within bedrock in the Maynardville Limestone extends about 12,000 ft (3,660 m) west along BCV, which is consistent with CY  1993 and CY 1994 data.

Vertical plume boundaries are not so well defined. Typically, nitrate concentrations exceed the MCL in groundwater in the upper 300 ft (91.5 m) of the Maynardville Limestone. Below this depth nitrate concentrations exceed 10 mg/L in an area immediately down-dip (south) of the S-3 Site. Data obtained since 1986 suggest that the nitrate plume extends more than 600 ft (183 m) below the ground surface within the ORR aquitards at the S-3 Site.

Trace Metals

Based on the 1995 data, barium was consistently reported (\math{>}50% of samples) for samples from Well GW-537 and wells at the S-3 Site. Cadmium was consistently detected above its maximum contaminant level samples from well GW-042 (a background well in the Bear Creek Burial Grounds) and well GW-276 at the S-3 Site waste management area (Fig. 7.15).

Other trace metal contaminants in the Bear Creek regime are beryllium, boron, cobalt, copper, nickel, strontium, and uranium. Concentrations of these metals have commonly exceeded background levels in groundwater near the S-3 Site, Bear Creek Burial Grounds, and Oil Landfarm waste management areas. Selected stream and spring locations and exit-pathway study wells also have exhibited total uranium and strontium concentrations above background values.

Volatile Organic Compounds

Groundwater in the unconsolidated zone that contains detectable levels of VOCs occurs primarily within about 1000 ft (305 m) of the source areas. The highest VOC concentrations (greater than 10,000 mg/L) in the unconsolidated zone occur at the Bear Creek Burial Grounds waste management area.

The extent of the dissolved VOC plumes is slightly greater in the underlying bedrock. Although the plumes generally do not extend more than 1000 ft from the source areas in groundwater in the low-permeability formations that underlie many waste sites, significant transport of the VOCs has occurred in the Maynardville Limestone.

Data obtained from exit-pathway monitoring locations show that in the vicinity of the water table, an apparently continuous dissolved VOC plume extends for about 12,000 ft (3,660 m) westward from the S-3 Site to just west of the Bear Creek Burial Grounds waste management area. The highest levels of VOCs in the Bear Creek regime occur in bedrock, just south of the Bear Creek Burial Grounds Waste Management Area. Historical levels have been as high as 7000 mg/L in groundwater near the source area. Typical VOC levels in the exit pathway (Maynardville Limestone) range from about 160 �g/L in the eastern part of the regime (well GW-725, Fig. 7.12) to less than detectable levels in the western part of the regime.

Radionuclides

Evaluations of the extent of these radionuclides in groundwater in the Bear Creek regime during 1995 were based primarily on measurements of gross alpha activity and gross beta activity. If the annual average gross alpha activity in groundwater samples from a well exceeded 15 pCi/L (the MCL for gross alpha activity), then one or more of the alpha-emitting radionuclides were assumed to be present in the groundwater monitored by the well. A similar rationale was used for annual average gross beta activity that exceeded 50 pCi/L.

As shown in Fig. 7.13, groundwater with elevated levels of gross alpha activity occurs in the water table interval in the vicinity of the S-3 Site, the Bear Creek Burial Grounds, and the Oil Landfarm waste management areas. In the bedrock interval, gross alpha activity exceeds 15 pCi/L in groundwater in the Nolichucky Shale near the S-3 Site, the southern sides of the Bear Creek Burial Grounds, and east of the Oil Landfarm waste management areas. Data obtained from exit-pathway monitoring stations show that gross alpha activity in groundwater in the Maynardville Limestone exceeds the maximum contamination level for 10,000 ft (3,050 m) west of the S-3 Site. Elevated gross alpha activities were observed in four exit-pathway spring and stream monitoring locations (NT-01, SS-1, SS-4, and SS-5; Fig. 7.13).

The distribution of gross beta radioactivity in groundwater in the unconsolidated zone is similar to that of gross alpha radioactivity (Fig. 7.14). During 1995 gross beta activity exceeded 50 pCi/L within the water table interval in the Maynardville Limestone from south of the S-3 Site to the Oil Landfarm waste management area. Within the intermediate bedrock interval in the Maynardville Limestone, the elevated gross beta activity extends as far west as does gross alpha activity, just to the west of the Bear Creek Burial Grounds waste management area. Elevated gross beta activity was observed in two springs and one stream monitoring station (NT-01, SS-1, and SS-4; Fig. 7.14) that also exhibited elevated gross alpha activity.

Exit-Pathway and Perimeter Monitoring

Exit-pathway study activities in 1995 consisted of continued monitoring at four well transects (pickets). The 1992 ORR environmental report and (Shevenell et al. 1992 ) contain detailed information about the construction of these pickets and the rationale for their construction. Other related investigations initiated as part of exit-pathway studies have included evaluation of the geologic characteristics of the Maynardville Limestone, geochemical characterization of groundwater types in BCV, analysis of controlling variables for development of preferred groundwater flow paths, and cross-borehole testing. Studies are ongoing of the transport of contaminants adsorbed to colloidal particles and of contaminant transport in relation to rainfall events within the Maynardville Limestone.

Groundwater quality data obtained during 1995 from the exit-pathway monitoring wells confirmed previous data that contaminated groundwater does not seem to occur much beyond the western side of the Bear Creek Burial Grounds waste management area.

Surface water and spring samples collected during CY 1995 (Fig. 7.16) indicate that spring discharges and water in upper reaches of Bear Creek contain many of the compounds found in the groundwater; however, the concentrations in the creek and spring discharges decrease rapidly with distance downstream of the waste disposal sites. This assessment is consistent with data from previous years. CY 1995 data indicate an improvement in water quality in the lower reaches of Bear Creek over past years.

For example, in CY 1995, nitrate concentrations in Bear Creek exceeded 100 mg/L during 1995 from NT-01 west of the S-3 Site to BCK 11.97 (Fig. 7.16). Nitrate levels at BCK 9.40 averaged about 4.9 mg/L. Nitrate concentrations at BCK 4.55 (NPDES Outfall 304), at the junction of Bear Creek Road and Highway 95, averaged 1.35 mg/L, down from 2.7 mg/L in CY 1994. The average nitrate concentration in surface water samples collected from the farthest downstream point (BCK 0.63), which is located just upstream of the confluence of Bear Creek and EFPC, was 1.25 mg/L, down from 2.5 mg/L in CY 1994 (background is about 0.2 mg/L). Average nitrate concentrations in spring discharges decreased from an average of 25.5 mg/L at SS-1 to 4.3 mg/L at SS-5.

Low concentrations of VOCs (\math{<}10 �g/L) were detected in surface-water samples and spring discharge samples collected from the upper and middle reaches of Bear Creek (at NT-1 and BCK 9.40). Compounds detected in samples from the creek were trichloroethene, 1,2-dichloroethene, and tetrachloroethene. Spring discharges at SS-1 and SS-4 also contained trace amounts of VOCs. Each of these compounds is a primary component of the VOC plumes in groundwater in the regime.

Based on the 1995 data, uranium is again the most common trace metal contaminant in Bear Creek. Concentrations of uranium exceeded background levels throughout reaches of the creek upstream of BCK 9.40. Moreover, uranium concentrations in the creek slightly exceeded background levels at the farthest downstream sampling point (BCK 0.63). Uranium concentrations in spring effluents exceed background levels as far west as the SS-5 location.

Annual average gross alpha activity in 1994 mirrored the results of previous years. Gross alpha was above 15 pCi/L only at BCK 11.97 and BCK 9.40 along Bear Creek. Spring discharges west as far as SS-5 had annual average gross alpha above 15 pCi/L. Gross beta activity exceeded 50 pCi/L at BCK 11.97 and NT-01. Annual average gross beta exceeded 50 pCi/L at SS-1 and SS-4.

7.2.5.4 Chestnut Ridge Hydrogeologic Regime

Four categories of sites are located within the Chestnut Ridge regime: (1) RCRA interim-status units, (2) RCRA 3004(u) SWMUs and solid waste disposal units, (3) TDEC-permitted solid waste disposal facilities, and (4) CERCLA OUs. The Chestnut Ridge Security Pits is the only documented source of groundwater contamination in the regime. No integrating CA has been established for the regime because contamination from the Security Pits is distinct and is not mingled with plumes from other sources. Groundwater media will be addressed as part of the RI/FS for each source. Table 7.4 summarizes the regulatory status and operational history of waste management units in the regime. Detailed discussions of these sites have been included in previous annual site environmental reports.

Discussion of Monitoring Results

In late 1994, a detailed review of groundwater results from Kerr Hollow Quarry was conducted in response to the identification of total strontium and total uranium levels in three wells at the site that were consistently elevated above background concentrations (GW-142, GW-145, and GW-146; Fig. 7.18). The data review indicated that no elevated gross alpha or gross beta was associated with the elevated metals values. Isotopic uranium and strontium analyses also were conducted, with the results showing no elevated activity. Hence, the elevated metals concentrations may reflect natural geochemical variations in groundwater at the site or possibly the impacts of waste disposal operations. In addition to the metals evaluation, VOC occurrences were examined. The evaluation demonstrated that low levels of tetrachloroethene and carbon tetrachloride were sporadically observed in wells GW-142 and GW-144. The occurrences of these compounds were first detected in 1990. The frequency of occurrence increased during 1991 and 1992 and then began to decrease in 1993. The only detectable VOC in 1994 was carbon tetrachloride in one sample from well GW-144 in the second calendar quarter. The occurrences of these VOCs appears to correlate with underwater debris removal and shredding corrective actions at the quarry, which were conducted between August 1990 and October 1993. However, VOCs continued to be observed during CY 1995; therefore, a trend is not well established.

Plume Delineation

There are two distinct VOCs in groundwater at the security pits. In the western portion of the site, the VOC plume is characterized by high concentrations of 1,1,1-trichloroethane. Tetrachloroethene is a principal component of the VOC plume in the eastern portion of the site. The distinct difference in the composition of the plume is probably related to differences in the types of wastes disposed of in the eastern and western trench areas.

Nitrate

Trace Metals

Volatile Organic Compounds

Radionuclides

Exit-Pathway and Perimeter Monitoring

A dye-tracer study was initiated and completed in 1992 (SAIC 1993 ), primarily to confirm results of an initial study conducted in 1990 (Geraghty and Miller, Inc. 1990 ). The 1992 study used the same dye injection well near the Chestnut Ridge Security Pits and many of the same monitoring points as did the 1990 study. The primary differences included an expanded monitoring network and the use of two fluorescent dyes to verify dye detection.

Results of the second tracer-dye study showed no conclusive occurrences of dyes at the monitoring points and did not corroborate data for detection points in the first study. The 1992 study also showed that the injection well was inappropriate because dye-uptake rates by the formation were inadequate. It is likely that the dye-uptake rates are inadequate because the source well is not screened in a flow conduit interconnected to the rest of the system. A formal comparison report has been completed that examines results of both studies to provide recommendations for improvements for future dye-tracer studies in this regime. Future dye-tracer studies are possible. The TDEC DOE Oversight Division has conducted a small-scale tracer study east of the Sediment Disposal Basin, although the results have not yet been published.

Monitoring of one large spring located south of Industrial Landfill V and Construction/Demolition Landfill VII was conducted in 1994 as a best management practice. One other spring location (SCR 2.2SP; Fig. 7.18) was sampled in 1995, also as a best management practice in conjunction with the TDEC DOE Oversight Division.

7.2.5.5 Special Studies

An investigation into contaminant transport via colloidal particles was initiated in 1993. The study focuses on major ions and metals because these constituent types are the most likely to adsorb onto colloids being transported within the active flow system. The study includes about 30 wells located within the ORR aquitards, Maynardville Limestone, and Knox Group within the Bear Creek and Chestnut Ridge regimes. A wide range of geologic units and depths was selected to examine how colloidal transport of contaminants is related to these variables. Very slow pumping rates are used to sample groundwater. Various sizes of filters are used to filter the samples to obtain aliquots for analysis. The various aliquots are analyzed to determine what size range of colloidal particles adsorb and transport contaminants. All of the subject wells have been sampled to date, and results are being finalized. In addition, the study was amended in 1994 to include sampling of selected wells in conjunction with storm events. The data obtained will provide insight regarding how constituents may be mobilized in the shallow karst system as a result of high-precipitation events. All field efforts are anticipated to be complete by June 1996, with a final due in October 1996.

A short-term study was begun and completed in 1995 to delineate the extent and thickness of anthropogenic fill material emplaced throughout the Y-12 Plant during various periods of construction. These fill zones are thought to play a major role in the movement of contaminants and groundwater flow patterns in the water table interval beneath the Y-12 Plant. Large volumes of topographic data, engineering data, soil-boring logs, and monitoring-well installation logs have been generated throughout the operational history of the Y-12 Plant. These data were compiled, screened for completeness and accuracy, and reduced into tabular formats denoting thickness, extent, and general composition of anthropogenic fill material. These reduced data were used to generate a fill isopach (thickness) map that also delineates the known extent of anthropogenic fill for the entire Y-12 Plant (Sutton and Field 1995 ). As a follow-on study to begin in 1996, major underground utilities will be examined to investigate their potential impacts on contaminant distribution and shallow groundwater flow patterns in the Y-12 Plant area. These data are important for identification of potential exit pathways for contaminants, for determining whether existing and planned monitoring activities are adequate, and for helping to identify potential remediation points for source areas.

7.3 GROUNDWATER MONITORING AT THE OAK RIDGE NATIONAL LABORATORY

7.3.1 Background

At ORNL, 20 WAGs were identified by the RCRA Facility Assessment (RFA) conducted in 1987. Thirteen of these have been identified as potential sources of groundwater contamination. Additionally, there are a few areas where potential remedial action sites are located outside the major WAGs. These individual sites have been considered separately (instead of expanding the area of the WAG). Water quality monitoring wells have been established around the perimeters of the WAGs determined to have a potential for release of contaminants. Figure 7.19 shows the location of each of the 20 WAGs.

For discussion purposes the WAGs are grouped by the valley in which they are located; i.e., Bethel Valley WAG s include 1, 3, and 17; Melton Valley WAGs include 2, 4, 5, 6, 7, 8, and 9; and WAG 11 (the White Wing Scrapyard).

The ORNL exit pathway program is discussed in this section. The ORNL program monitors groundwater at four general locations that are thought to be likely exit pathways for groundwater affected by activities at ORNL (Fig. 7.20).

7.3.2 Bethel Valley

Most of the WAG 1 sites were used to collect and to store LLW in tanks, ponds, and waste treatment facilities, but some also include landfills and contaminated sites resulting from spills and leaks occurring over the last 50 years. Because of the nature of cleanup and repair, it is not possible to determine which spill or leak sites still represent potential sources of release. Most of the SWMUs are related to ORNL's waste management operations. Recent ER activities within WAG 1 include several CERCLA actions associated with sources of contamination; e.g., Surface Impoundments OU, a treatability study associated with the Gunite and Associated Tank OU, and two removal actions [Corehole 8 and the decontamination and decommissioning (D&D) of the Waste Evaporator Facility (Building 3506)].

7.3.2.2 WAG 3

SWSA 3 and the Closed Scrap Metal Area are inactive landfills known to contain radioactive solid wastes and surplus materials generated at ORNL from 1946 to 1979. Burial of solid waste ceased at this site in 1951; however, the site continued to be used as an above-ground scrap metal storage area until 1979. Sometime during the period from 1946 to 1949, radioactive solid wastes removed from SWSA 2 were buried at this site. In 1979, most of the scrap metal stored above ground at SWSA 3 was either transferred to other storage areas or buried on site in a triangular-shaped disposal area immediately south of SWSA 3.

Records of the composition of radioactive solid waste buried in SWSA 3 were destroyed in a fire in 1961. Sketches and drawings of the site indicate that alpha and beta-gamma wastes were segregated and buried in separate areas or trenches. Chemical wastes were probably also buried in SWSA 3 because there are no records of disposal elsewhere. Although the information is sketchy, the larger scrap metal equipment (such as tanks and drums) stored on the surface at this site was also probably contaminated. Because only a portion of this material is now buried in the Closed Scrap Metal Area, it is not possible to estimate the amount of contamination that exists in this SWMU.

The Contractors' Landfill was opened in 1975 and is now closed. It was used to dispose of various uncontaminated construction materials. No contaminated waste or asbestos was allowed to be buried at the site. ORNL disposal procedures require that only non-RCRA, nonradioactive solid wastes were to be buried in the Contractors' Landfill.

7.3.2.3 WAG 17

7.3.3 Melton Valley

In addition to natural drainage, WOC has received treated and untreated effluents and reactor cooling water from ORNL activities since 1943. Controlled releases include those from the NRWTF, the sewage treatment plant, and a variety of process waste holdup ponds throughout the ORNL main plant area (WAG 1). It also receives groundwater discharge and surface drainage from WAGs 1, 4, 5, 6, 7, 8, and 9.

There is little doubt that WAG 2 represents a source of continuing contaminant release (radionuclides and/or chemical contaminants) to the Clinch River. Although it is known that WAG 2 receives groundwater contamination from other WAGs, the extent to which WAG 2 may be contributing to groundwater contamination has yet to be determined. Recent ER activities include continued monitoring and support of the WAG 5 seeps removal action.

7.3.3.2 WAG 4

SWSA 4 was opened for routine burial of solid radioactive wastes in 1951. From 1955 to 1963, Oak Ridge was designated by the Atomic Energy Commission as the Southern Regional Burial Ground; as such, SWSA 4 received a wide variety of poorly characterized solid wastes (including radioactive waste) from about 50 sources. These wastes consisted of paper, clothing, equipment, filters, animal carcasses, and related laboratory wastes. About 50% of the waste was received from sources outside of Oak Ridge facilities. Wastes were placed in trenches, shallow auger holes, and in piles on the ground for covering at a later date.

From 1954 to 1975, LLLW was transported from storage tanks at the main ORNL complex to waste pits and trenches in Melton Valley (WAG 7), and later to the hydrofracture disposal sites, through underground transfer lines. The Pilot Pit Area (Area 7811) was constructed for use in pilot-scale radioactive waste disposal studies from 1955 to 1959; three large concrete cylinders containing experimental equipment remain embedded in the ground. A removal action was initiated at WAG 4 during 1995 to grout, in place, sources of ⁹⁰Sr contamination emanating from selected trenches located within the WAG. A control building and asphalt pad have been used for storage through the years.

7.3.3.3 WAG 5

SWSA 5 South was used to dispose of solid LLW generated at ORNL from 1959 to 1973. From 1959 to 1963 the burial ground served as the Southeastern Regional Burial Ground for the Atomic Energy Commission. At the time SWSA 5 burial operations were initiated, about 10 acres of the site was set aside for the retrievable storage of TRU wastes.

The WAG 5 boundary includes the Old and New Hydrofracture Facilities. Because Melton Branch flows between the old and new hydrofracture facilities, the new hydrofracture facility has a separate boundary.

The WAG 5 RI field activities were completed and the RI report was written in 1995. A CERCLA removal action was initiated in 1994 to remove ⁹⁰Sr from Seeps C and D located along the southern boundary of WAG 5.

7.3.3.4 WAG 6

WAG 6 was among the first to be investigated at ORNL by the ER Program. WAG 6 is an interim-status RCRA unit because of past disposal of RCRA-regulated hazardous waste. Environmental monitoring is carried out under CERCLA and RCRA. A proposed CERCLA remedial action, which involved capping WAG 6, was abandoned after a public meeting in which members of the community objected to the high cost of capping.

In 1995 ORNL submitted a revision to the 1988 RCRA Closure Plan which proposed an integration of RCRA closure and CERCLA remedial action requirements. As of this writing, ORNL has not received a response from the TDEC.

7.3.3.5 WAG 7

7.3.3.6 WAGs 8 and 9

Radioactive wastes from these facilities are collected in on-site LLLW tanks and periodically pumped to the main plant area (WAG 1) for storage and treatment. The waste includes demineralizer backwash, regeneration effluents, decontamination fluids, experimental coolant, and drainage from the compartmental areas of filter pits.

WAG 9 is located in Melton Valley about 1 km (0.6 miles) southeast of the ORNL main plant area and adjacent to WAG 8. WAG 9 is composed of eight SWMUs: including the Homogeneous Reactor Experiment pond, which was used from 1958 to 1961 to hold contaminated condensate and shield water from the reactor, and LLLW collection and storage tanks, which were used from 1957 to 1986.

Because of the small number of groundwater monitoring wells in WAG 8 and WAG 9, they are sampled together. The analytical results for the two WAGs are also reported together.

7.3.3.7 WAG 10

Hydrofracture Experiment Site 1 is located within the boundary of WAG 7 (south of Lagoon Road) and was the site of the first experimental injection of grout (October 1959) as a testing program for observing the fracture pattern created in the shale and for identifying potential operating problems. Injected waste was water tagged with ¹³⁷Cs and ¹⁴¹Ce. Grout consisted of diatomaceous earth and cement.

Hydrofracture Experiment Site 2 is located about 0.8 km (0.5 mile) south of the 7500 (experimental reactor) area (WAG 8). The second hydrofracture experiment was designed to duplicate, in scale, an actual disposal operation; however, radioactive tracers were used instead of actual waste. Cement, bentonite, and water tagged with ¹³⁷Cs were used in formulating the grout.

The OHF is located about 1.6 km (1.0 mile) southwest of the main ORNL complex near the southwest corner of WAG 5. The facility, commissioned in 1963, disposed of liquid radioactive waste in impermeable shale formations by hydrofracture methods, at depths of 800 to 1000 ft. Wastes used in the disposal operations included concentrated LLLW from the Gunite tanks in WAG 2, ⁹⁰Sr, ¹³⁷Cs, ²⁴⁴Cm, TRU, and other, unidentified radionuclides.

The New Hydrofracture Facility is located 900 ft southwest of the OHF on the south side of Melton Branch. The facility was constructed to replace the OHF. Wastes used in the injections were concentrated LLLW and sludge removed from the Gunite tanks, ⁹⁰Sr, ¹³⁷Cs, ²⁴⁴Cm, TRU, and other nuclides. Plans to plug and abandon several deep injection wells at WAG 10 were made in 1995.

7.3.3.8 White Wing Scrap Yard (WAG 11)

The White Wing Scrap Yard was used for aboveground storage of contaminated material from ORNL, the K-25 Site, and the Y-12 Plant. The material stored at the site by ORNL consisted largely of contaminated steel tanks; trucks; earth-moving equipment; assorted large pieces of steel, stainless steel, and aluminum; and reactor cell vessels removed during cleanup of Building 3019. An interim record of decision was agreed to by the TDEC, EPA, and DOE requiring surface debris to be removed from the site. This work was completed in 1994.

The area began receiving material (primarily metal, glass, concrete, and trash with alpha, beta, and gamma contamination) in the early 1950s. Information regarding possible hazardous waste contamination has not been found. The precise dates of material storage are uncertain, as is the time when the area was closed to further storage. In 1966, efforts were begun to clean up the area by disposing of contaminated materials in ORNL's SWSA  5 and by the sale of uncontaminated material to an outside contractor for scrap. Cleanup continued at least into 1970, and removal of contaminated soil began in the same year. Some scrap metal, concrete, and other trash are still located in the area. Numerous radioactive areas, steel drums, and PCB-contaminated soil were identified during surface radiological investigations conducted during 1989 and 1990 at WAG 11. The amount of material or contaminated soil remaining in the area is not known.

7.3.4 1995 Groundwater Quality Well Installation, Development, and Sampling Activities

A summary of the groundwater surveillance program is presented in Table 7.6. RCRA assessment data for WAG 6 were submitted to TDEC in March 1995. As part of the WAG 6 RCRA/CERCLA integrated monitoring approach, RCRA assessment groundwater monitoring continued during 1995 under the auspices of the Environmental Monitoring Plan (EMP) for WAG 6 at ORNL, a CERCLA driver monitoring plan, agreed to in principle by DOE, EPA , and TDEC in June 1994. Baseline groundwater monitoring under the EMP was initiated in October 1994 and ended in September 1995. All 24 RCRA groundwater monitoring wells were sampled with the following recency: eight quarterly and 16 semiannually. Routine groundwater monitoring conducted under the EMP was initiated in October 1995. A subset of 12 RCRA groundwater monitoring wells will be sampled on a semi-annual basis under the routine monitoring scenario. The 12 downgradient wells involved in routine monitoring are 835, 837, 841, 842, 843, 844, 4315, 4316, and 4317. The remaining wells are located upgradient of the hazardous waste disposal area. These wells include 846, 857, and 858. Under baseline and routine monitoring selected VOCs and radionuclides will be sampled for. The remaining WAGs are currently monitored to comply with DOE orders 5400.1 and 5400.5, which do not specify sampling schedules. ORNL samples groundwater quality wells at the remaining WAGs on a rotational basis.

The plant perimeter surveillance program, as stipulated in the EMP, was initiated in 1993. A summary of the program is presented in Table 7.7.

7.3.5 ORNL Groundwater Quality

Eighteen of the 20 wells identified by the EMP represent ORNL's exit pathway and are also part of the WAG perimeter monitoring program (WAG s 2, 3, 6, 11, and 17). As such, 1995 result data from sampling conducted under the WAG perimeter program are used for the monitoring plan program. The other two wells (of the 20) were not sampled in 1995 because a decision is pending regarding installation of dedicated pumps in them. The four surface water locations (Bear Creek, Raccoon Creek, Bearden Creek, and WOC at WOD) were sampled in September 1995. The results of the plant perimeter monitoring program are discussed as part of the OU discussions.

Groundwater quality is regulated under RCRA by referring to the SDWA standards. The standards are applied when a site undergoes RCRA permitting. None of the ORNL WAGs are under RCRA permits at this time; therefore, no permit standards exist with which to compare sampling results. In an effort to provide a basis for evaluation of analytical results and for assessment of groundwater quality at ORNL WAGs, federal DWSs and Tennessee water quality criteria for domestic water supplies are used as reference values in the following discussions. When no federal or state standard has been established for a radionuclide, then 4% of the DOE DCG has been used. Although DWSs are used, it is unrealistic to assume that members of the public are going to drink groundwater from ORNL WAGs. There are no groundwater wells furnishing drinking water to personnel at ORNL.

7.3.6 Bethel Valley

The gross beta activity at the wells of concern is attributable mainly to total radioactive strontium and its daughters. Gross alpha activity at WAG 1 ranged from below detection to 4.3 pCi/L; beta activity ranged from below detection to 270 pCi/L (the DWS is 50 pCi/L); and total radioactive strontium ranged from below detection to 140 pCi/L (the DWS is 8 pCi/L). All of these much lower than values which have been observed in the past; however, two of the wells which have traditionally had high levels of radioactivity were not sampled this year.

VOCs were detected in some of the wells; however, most of these were also detected in the laboratory blanks. One well had vinyl chloride detected above DWSs and this well has had similar vinyl chloride concentrations in the past.

Fluoride at one well was detected above DWSs; this is the third time fluoride has exceeded the DWS. No well values for metals exceeded DWSs.

7.3.6.2 WAG 3

Strontium has been detected historically in wells along the entire northern perimeter of the site. Values exceeding the primary DWS for total radioactive strontium and gross beta activity have consistently been observed at four wells in every sampling event. The gross beta signatures are mainly attributable to total radioactive strontium. The data for the wells along the eastern and northeastern boundaries show evidence of radioactive contamination, including ³H and gross alpha activity. The data for the northwest boundary show the presence of ³H.

Gross alpha activity at WAG 3 ranged from not being detected to 12 pCi/L (the DWS is 15 pCi/L); beta activity ranged from not being detected to 1500 pCi/L (the DWS is 50 pCi/L); and total radioactive strontium ranged from not being detected to 970 pCi/L (the DWS is 8 pCi/L). Tritium ranged from not being detected to 19,000 pCi/L (the DWS is 20,000 pCi/L).

In a few of the downgradient wells, VOCs were detected. Trichloroethene has consistently been detected above DWSs in every sampling event at one well located in the northeast part of the WAG.

7.3.6.3 WAG 17

The data for the wells along the southeastern and southwestern boundaries show evidence of VOCs. The contamination has consistently been located primarily in one well. The pollutants include trichloroethene, 1,2-dichloroethene, vinyl chloride, tetrachloroethene, 1,1-dichloroethene, and benzene.

7.3.6.4 Exit Pathway

7.3.7 Melton Valley

For example, four of the WAG 2 wells that exhibited high levels of ³H are located south of and downgradient of WAGs 5, 6, and 8. All of the WAG  2 wells show evidence of radioactivity, including gross alpha and gross beta activity and ³H. Gross beta activity above primary DWSs was detected at one well on the west side of WAG 7 and at one well south of WAG  6. The elevated levels of ³H and total radioactive strontium in the perimeter wells at WOD are believed to be the result of surface-water underflow at the dam, not groundwater contamination. Gross alpha activity at WAG 2 ranged from not being detected to 12 pCi/L (the DWS is 15 pCi/L); beta activity ranged from not being detected to 780 pCi/L (the DWS is 50 pCi/L); and total radioactive strontium ranged from not being detected to 320 pCi/L (the DWS is 8 pCi/L). Tritium ranged from not being detected to 350,000 pCi/L (the DWS is 20,000 pCi/L).

Chromium and nickel were detected above DWS at a well south of WAG 6. The nickel result was only slightly above DWS and has not been above a standard since 1992. Chromium has been above DWS the past 3 sampling events, and this year it is two and one half times the historical maximum.

7.3.7.2 WAG 4

VOCs continue to be detected in wells on the eastern boundary. Two wells have consistently had VOC concentrations above DWSs.

7.3.7.3 WAG 5

Total radioactive strontium appears to be the major beta emitter found in WAG 5 groundwater. It is found mainly in one well on the southern perimeter. Alpha activity above DWSs has historically been consistently observed in one well on the northwestern boundary of the WAG. This well was pumped dry in 1994 and in 1995 it was sampled and gross alpha was slightly less than DWS.

Gross alpha activity at WAG 5 ranged from not being detected to 14 pCi/L (the DWS is 15 pCi/L); beta activity ranged from not being detected to 1800 pCi/L (the DWS is 50 pCi/L); and total radioactive strontium ranged from not being detected to 840 pCi/L (the DWS is 8 pCi/L).

VOCs were detected in the wells along the southern and western boundaries, including vinyl chloride, 1,2-dichloroethene, acetone, carbon disulfide, benzene, and trichloroethene. Several wells have consistently exceeded DWSs for these contaminants.

No upgradient wells exceeded DWSs for radioactivity or volatile organics.

7.3.7.4 WAG 6

Elevated levels of ³H are found in wells along the eastern perimeter. Gross alpha activity at WAG 6 ranged from not being detected to 21 pCi/L (the DWS is 15 pCi/L); and total radioactive strontium ranged from not being detected to 54 pCi/L (the DWS is 8 pCi/L). Tritium ranged from not being detected to 3.5 � 10⁶ pCi/L (the DWS is 20,000 pCi/L).

7.3.7.5 WAG 7

Gross alpha activity was detected at one well in excess of primary DWSs. Isotopic identification shows this activity to be attributed to ²⁴¹Am, ²³⁸Pu, ²³⁹Pu, ²²⁸Th, ²³⁰Th, ²³⁴U, ²³⁵U, and ²³⁸U. Gross alpha activity ranged from not being detected to 210 pCi/L.

Gross beta activity was detected at levels in excess of primary DWSs at four wells, and ³H was detected at each of these wells, also above DWSs. Gross beta activity ranged from not being detected to 6200 pCi/L; total radioactive strontium ranged from not being detected to 4.6 pCi/L; and ³H ranged from not being detected to 380,000 pCi/L.

Three wells have consistently had nitrate detected at levels that exceed primary DWSs. One well had fluoride above DWS, consistent with historical values. Minimal VOC contamination has been detected in the WAG 7 wells.

7.3.7.6 WAGs 8 and 9

All of the perimeter wells show evidence of radioactivity. The data indicate that the gross beta activity is attributable to total radioactive strontium. The two wells on the northwestern perimeter exceeded DWSs: one well with respect to ³H contamination and the other with respect to gross beta activity and total radioactive strontium contamination. Gross alpha activity ranged from not being detected to 4.6 pCi/L (the DWS is 15 pCi/L); beta activity ranged from not being detected to 3800 pCi/L (the DWS is 50 pCi/L); and total radioactive strontium ranged from not being detected to 1300 pCi/L (the DWS is 8 pCi/L). Tritium ranged from not being detected to 59,000 pCi/L (the DWS is 20,000 pCi/L). Total radioactive strontium and gross beta activity levels exceeded the DWSs at the two WAG 9 wells.

VOCs were detected at downgradient wells, all below DWSs. One well has historically shown trichloroethene above DWSs; this year it did not. None of the data for the upgradient wells show evidence of VOCs.

7.3.7.7 Exit Pathway

7.3.7.8 White Wing Scrapyard (WAG 11)

Two wells had trichloroethene detected above DWSs, which is consistent with historical data for these two wells. No other VOCs were detected in those wells.

7.3.7.9 Exit Pathway

7.3.8 Well Plugging and Abandonment at ORNL

7.3.8.1 Wells Plugged During 1995

7.3.8.2 Methods Used

Splitting and abandoning the well casing in place also minimizes the generation of waste that would be created if other methods were used. Special tools were developed to split the casings of different sizes and material. A down-hole camera was used during development of the splitting tools to evaluate their effectiveness.

Detailed procedures have been developed and documented regarding the use of specific grout materials in different well environments. These procedures were tested and evaluated during the 1993 plugging and abandonment activities.

7.4 GROUNDWATER MONITORING AT THE K-25 SITE

7.4.1 Background and Hydrogeologic Setting

The K-25 Site Groundwater Program is a component in the ORR ER strategy described in the ORR Site Management Plan for the ER Program (DOE 1995 ). The cleanup strategy described in the site management plan has been developed to accelerate the transition of areas of concern from characterization to remediation by making decisions at the watershed scale based on recommended land use. The watershed is a surface drainage basin that includes an area of concern or group of areas of concern to be investigated and/or remediated. This approach allows for systematic monitoring and evaluation of contaminant sources and migration through the use of integrated surface water and groundwater monitoring.

Only one watershed has been designated at the K-25 Site. In this report, WAG boundaries defined to correspond with perceived hydrogeologic boundaries are used for reporting the results of groundwater monitoring. The WAG designations and associated areas of concern are described in the following section.

Unlike the other ORR facilities, where many source areas are located in relatively undeveloped areas of the reservation, most of the source areas at the K-25 Site are located within the highly industrialized areas of the site. The surface topography has been altered considerably as a result of site construction. Large areas have been excavated or filled to yield the present low-relief landscape. As much as 60 ft (18.3 m) of materials have been excavated locally, and equal amounts of fill have been placed in adjacent low areas. Where they extend below the water table, the filled areas may represent primary pathways for contaminant migration. A number of sinkholes identified in historical photographs are not visible on the surface today. Many have been filled during construction, and buildings (such as K-33) have been erected directly above them.

The storm drain network discharges to Mitchell Branch, the K-1007-P1 pond, the K-901A Holding Pond, or directly to Poplar Creek and the Clinch River. Storm drain video surveys show water flowing both in and out of the storm drain system, suggesting that the storm drains may serve as groundwater sinks or as sources. In addition, at least ten buildings have basements with sumps below the seasonal low water table. Water that accumulates in the sumps is discharged to the sanitary sewer or CNF system, storm drains, or, in rare occasions, to the ground. All of these systems have been active since the construction in the 1940s.

Bedrock underlying the K-25 Site can be broadly categorized as carbonate (Knox and Chickamauga groups) or clastic (Rome formation and possibly the Conasauga group). The carbonates underlie most of the main plant area, including the K-27/29 Peninsula K-1070-A Burial Ground, the K-25 Building, and the K-1004 laboratory area. The eastern portion of the site, including the K-1070-C/D Burial Ground and much of the Mitchell Branch area, is underlain by clastics of the Rome formation and possibly the Conasauga group. The structural geology of the K-25 Site is perhaps the most complicated on the ORR. It includes ``map-scale'' folds and faults and ``outcrop-scale'' fractures, folds, and faults. Complex faulting, fracturing, and folding in the clastic bedrock precludes definition of simple bedding geometry. Therefore, groundwater flow paths cannot be predicted in this area of the site.

Cavities have been encountered in 39% of all subsurface penetrations at the K-25 Site. Cavity heights are typically greater in the Knox group carbonates. Recent drilling activities in the vicinity of the K-1070-A Burial Ground have encountered cavernous bedrock with cavities up to 22 ft (6.7 m) in height; however, based on camera and sonar surveys, the lateral extent of these cavities appears limited. Although large cavities have been reported in some locations in the Chickamauga bedrock, typical cavity heights are generally less than 5 ft (1.5 m).

Groundwater occurs in both the unconsolidated zone and bedrock, primarily as a single water table aquifer. Perched water may be of local significance. With few exceptions, the water table occurs in the overburden above bedrock across the site, with saturated overburden thickness ranging up to 70 ft (21.4 m). Because bedrock is exposed along the bottom of the Clinch River and Poplar Creek, the unconsolidated-zone flow paths are truncated at these boundaries. Surveys indicate that groundwater flows radially from higher elevations toward the bounding surface water features; however, the sumps and drains that lie below the seasonal low water table affect the configuration of the water table surface and thus affect the contaminant flow paths.

Groundwater flow in the unconsolidated zones is expected to be in the direction of the mapped hydraulic gradients. In the carbonate bedrock, groundwater flow is expected to be controlled by hydraulic gradients and geologic strike. In the Rome Formation groundwater flow directions cannot be predicted with any certainty. Recent studies have shown that hydraulic gradients are steepest (and consequently, overall flux is greatest) during the wet season and low pool stage periods. Much of the site is paved or otherwise covered, reducing direct recharge by groundwater; however, leaking underground utilities and storm drains are likely to recharge the groundwater substantially.

No perennial springs have been identified along Poplar Creek or the Clinch River. Wet-season springs located along the exposed low pool stage shores of Poplar Creek and the Clinch River do not appear consistently from year to year. It is unlikely that the karst features were active before the impoundment of the Clinch River. It is believed that since that time, however, the dramatic increase in base-level heads has resulted in a ``backed-up'' karst flow system. Consequently, the presence of karst features at the K-25 Site does not seem to indicate conduit-dominated groundwater flow.

7.4.2 Waste Area Groupings

7.4.2.1 South Main Plant Area

7.4.2.2 North Main Plant Area

7.4.2.3 K-25 and K-1064 Area

7.4.2.4 K-33 and K-31 Area

7.4.2.5 K-27 and K-29 Area

7.4.2.6 K-901 Area

7.4.2.7 Duct Island Area

7.4.2.8 Powerhouse Area

7.4.3 1995 Well Installation and Plugging and Abandonment Activities

No wells were plugged or abandoned during 1995 at the K-25 Site. A detailed evaluation of existing wells to identify candidates for plugging and abandonment will likely be conducted at some time in the future. Wells no longer required for monitoring or wells whose construction or annular seal integrity are in doubt will be designated at that time for plugging and abandonment.

7.4.4 1995 Groundwater Monitoring Program

7.4.5 Postremediation Monitoring

7.4.6 Exit-Pathway Monitoring

7.4.7 1995 Groundwater Monitoring Results

7.4.7.1 South Main Plant Area

Metals in groundwater that exceeded either a primary or secondary DWS include aluminum, chromium, iron, manganese, nickel, and thallium. The DWS for chromium was exceeded at one well during one sampling event. Nickel exceeded the DWS at three wells with a maximum reported concentration of 0.626 mg/L. Thallium exceeded the DWS at two wells during 1995 with a maximum concentration of 0.005 mg/L.

Gross alpha activity was not detected in any of the 15 monitoring wells during 1995. Gross beta activity did not exceed the reference level of 50 pCi/L.

7.4.7.2 North Main Plant Area

The DWS for gross alpha was exceeded in one bedrock well and three unconsolidated-zone wells. Gross alpha activity ranged from 22.2 to 43.2 pCi/L (limits of error ranged from 5.1 to 8.7 pCi/L). Uranium appears to be the primary alpha-emitting isotope present in groundwater in these four wells. Two of the wells are located along Mitchell Branch, one is near the K-1420 Building, and the fourth in the Blair Road Quarry.

Gross beta exceeded the reference value at seven wells within the north main plant area. Activity ranged from 86.1 to 528 pCi/L (limits of error ranged from 7.3 to 35 pCi/L). The wells are located in the vicinity of the former K-1407-B and C ponds and the K-1070-C/D classified burial ground.

Metals detected at concentrations above a primary DWS included antimony, arsenic, barium, cadmium, nickel, and thallium. The DWSs for antimony, arsenic, cadmium, and nickel were each exceeded in one well. The DWS for barium was exceeded in two wells. The DWS for thallium was exceeded in six wells; however, this occurred only during the spring sampling event. The DWS for thallium was exceeded at one well during the fall sampling event. The secondary DWSs for aluminum, iron, and manganese were exceeded in numerous wells in this area. In addition, DWSs for chloride, nitrate, and sulfate were exceeded at one well each.

Semivolatile organic chemicals are present in some of the wells in the vicinity of the K-1414 garage. This area is the only location within the K-25 Site where semivolatile organic chemicals that are not common laboratory contaminants have been consistently detected in groundwater samples.

7.4.7.3 K-25 and K-1064 Area

Gross alpha activity at levels exceeding the DWS was reported for four bedrock wells. The gross alpha activities ranged from 15.4 to 32.1 pCi/L (limits of error ranged from 5.3 to 8.2 pCi/L). Based on the limit of error, two of the four wells may not exceed the DWS of 15 pCi/L. Gross beta activity exceeding the reference level of 50 pCi/L was reported for one bedrock well during one sampling event. Gross beta activity was 60.1 pCi/L (limit of error of 6.3 pCi/L) in well BRW-3 during the spring of 1995.

The primary DWSs for arsenic and lead were exceeded at one well each, but this exceedence occurred during only one of the two sampling events. Aluminum, iron, and manganese exceeded secondary DWSs at four wells. Fluoride and sulfate also exceeded DWSs at one well.

7.4.7.4 K-33 and K-31 Area

Reported metals concentrations exceeding DWSs included aluminum, chromium, iron, manganese, nickel, and thallium. The primary DWS for chromium was exceeded at two bedrock wells, for nickel at one bedrock well and three unconsolidated-zone wells, and for thallium at one unconsolidated zone well.

Gross alpha activity and gross beta activity were detected in some monitoring wells; however, none of the reported activities exceeded a DWS.

7.4.7.5 K-27 and K-29 Area

Chromium concentrations in excess of the primary DWS were reported for three unconsolidated-zone wells. Chromium concentrations ranged from 0.112 to 0.741 mg/L. The DWS for nickel was exceeded at one unconsolidated-zone well and for thallium at four unconsolidated-zone wells and one bedrock well. Aluminum, iron, and manganese exceeded secondary DWSs at several wells. Fluoride exceeded its DWS at one well.

Gross beta activity was detected at many of the wells in this area; however, neither the gross beta activities nor the gross alpha activities reported for any of the wells exceeded its DWS.

7.4.7.6 K-901 Area

Nine VOCs were detected at concentrations exceeding their respective DWSs: 1,1,1-trichloroethane, 1,1,2-trichloroethane, 1,1-dichloroethene, benzene, carbon tetrachloride, chloroform, methylene chloride, tetrachloroethene, and trichloroethene. Trichloroethene is the predominant VOC; the DWS was exceeded in 20 monitoring wells. Reported concentrations of trichloroethene ranged from 7 to 3600 �g/L in both unconsolidated-zone wells and bedrock wells. Two VOCs, 1,1,1-trichloroethane and 1,1-dichloroethene, were detected at concentrations in excess of 1000 �g/L. Benzene, chloroform, and methylene chloride were detected above their DWSs in one well apiece. Generally, the wells in the K-901 area that exhibited contamination from VOCs are located near the K-1070-A burial ground.

Gross beta activity exceeded the reference value of 50 pCi/L in nine wells (six bedrock wells and three unconsolidated zone wells). The reported gross beta activities ranged from 59 pCi/L (limit of error of 5.6 pCi/L) to 6,770 pCi/L (limit of error of 340 pCi/L). Gross alpha activity exceeded the DWS at one bedrock well with a reported activity of 19.2 pCi/L (limit of error of 4.2 pCi/L).

Nickel, lead, and thallium were the only metals exceeding a primary DWS in this area. Nickel and thallium exceeded the DWS at one well each. Lead exceeded the DWS at two wells. Aluminum, iron, and manganese exceeded their respective secondary DWSs at several wells.

7.4.7.7 Duct Island Area

Aluminum, iron, and manganese are the metals that exceeded a DWS. Low concentrations of several VOCs and semivolatile organic compounds were detected; however, only trichloroethene exceeded a DWS. A concentration of 16 �g/L of trichloroethene was reported for one well during the fall sampling event.

Beta activity was detected in most of the wells. The maximum reported activity of 20.2 pCi/L is well below the reference value of 50 pCi/L. Gross alpha activity was not detected at any wells.

7.4.7.8 Powerhouse Area

The DWS for nickel was exceeded in one well; the concentration was reported as 0.154 mg/L. The DWS for thallium was exceeded in four wells; concentrations ranged from 0.007 to 0.021 mg/L. Secondary DWSs were exceeded for sulfate, aluminum, iron, and manganese in several wells.

Low concentrations of several VOCs were reported for some wells; however, no VOCs were detected at concentrations above a DWS.

7.4.7.9 K-25 Site Springs

Aluminum, iron, and manganese exceeded DWSs at most of the spring locations. No other metals exceeded a DWS at any of the springs. Two VOCs, tetrachloroethene and trichloroethene, were detected at concentrations exceeding DWSs at one spring within the plant site. This spring is located downgradient of the K-1070-C/D classified burial ground.

7.4.8 1995 K-25 Site Exit-Pathway Monitoring Results

Gross alpha activity exceeded the DWS of 15 pCi/L at one monitoring well location; however, taking into account the limit of error, this result may or may not be above the DWS. The reported activity was 17 pCi/L (limit of error of 7.1 pCi/L). This well is located near the K-1007-P1 pond in the southern portion of the K-25 Site. This exceedence was reported for the spring sampling event but was not repeated during the fall sampling event. None of the gross beta activity results for the exit-pathway wells exceeded the reference level of 50 pCi/L.

Contents Chapter 8