Introduction
IT Corporation (IT) prepared this Feasibility Study (FS) Report for Operable Unit V (OU V) at Brookhaven National Laboratory (BNL) site under BNL Contract Number 710617. The FS Report was prepared in accordance with the tasks outlined in the OU V Remedial Investigation/Feasibility Study Work Plan (IT, 1994); guidelines, criteria, and considerations set forth in the National Contingency Plan (NCP); and the U.S. Environmental Protection Agency (USEPA) guidance document Guidance for Conducting Remedial Investigations and Feasibility Studies Under CERCLA (USEPA, 1988).
The purpose of the OU V FS Report is to document the basis and procedures used in identifying, developing, screening and evaluating remedial alternatives and removal actions which will address contamination at OU V. The report provides the Department of Energy (DOE)/BNL, USEPA, and New York State of Environmental Conservation (NYSDEC) with sufficient data to select a feasible and cost-effective remedial alternative that will protect human health and the environment.
BNL has an active Pollution Prevention/Waste Minimization Program to minimize environmental impacts associated with operations conducted at BNL. By implementing a source reduction program, contribution of contaminants to the BNL sanitary sewer and ultimately the Peconic River are being minimized. Between 1993 and 1997, BNL cut its hazardous waste output by more than half (54 percent) and significantly reduced other types of waste. In 1998, BNL reduced hazardous waste output by 72 percent. The STP was upgraded from primary to tertiary treatment in 1998. The upgrade is expected to reduce the impact of the treated effluent on the Peconic Estuary by further reducing existing contaminant concentrations. Additional upgrades are scheduled for fiscal year 1999. Pending improvements include the replacement of an additional 9,000 linear feet of piping, construction of an aerobic digester and improvements to the sewage treatment plant's sand filtration system.
Summary of the Remedial Investigation
The BNL OU V Remedial Investigation (RI) Report characterized the physical conditions, the nature and extent of contaminant migration, and the potential current and future risks to human health and the environment for OU V. The areas of concern (AOCs) evaluated in the OU V RI included:
The field investigation consisted of two phases; the Phase I investigation was conducted from January 1995 through March 1995 and the Phase II investigation was conducted from June 1995 through October 1995. Subsequently, additional investigations focused on addressing ecological risk assessment issues or further characterization of the nature and extent of contamination were performed in 1996 and 1997. These included a toxicity testing study, an acid volatile sulfide/simultaneously extracted metals (AVS/SEM) study, and fish tissue bioaccumulation studies.
Sampling and analysis activities conducted during the Phase I and Phase II investigations consisted of geophysical surveys, radiological surveys, sludge/aqueous sampling, Geoprobe soil sampling, monitoring well borings, Geoprobe groundwater sampling, monitoring well groundwater sampling, surface water sampling, sediment sampling, and a site-wide biological investigation. The toxicity testing study included collection of sediment samples for benthic toxicity testing and chemical analysis. The AVS/SEM study involved collection of sediment samples for analysis of AVS and SEM only. Sampling and analysis activities for the two fish tissue bioaccumulation studies involved the collection of fish from both on-site and off-site locations as well as surface water and sediment samples, and analyses for metals, pesticides, PCBs, and radionuclides. Additionally, sediment samples were collected at an off-site location where previously elevated levels of contaminants were detected in order to better characterize the area.
Subsequent to the Final RI Report, a preliminary investigation was conducted in which several sediment samples were collected and analyzed for plutonium, uranium, and other previously unmeasured radionuclides. A further investigation of on and off-site Peconic River sediments and soils was conducted from March 1999 to May 1999 in order to accurately determine the presence or absence of these radionuclides and to assess the potential risk to human health. The results of this additional investigation are described in the Plutonium Contamination Characterization and Radiological Dose and Risk Assessment Report (IT, 1999), and show that plutonium and other radionuclides exist at levels that present no significant human health or ecological risk.
The primary concerns associated with the OU V study area are the presence of elevated concentrations of metals, PCBs and DDD in the on-site Peconic River sediments. A detailed analysis of alternatives was conducted for the sediments. Other areas where contaminants were found at generally low levels, but above screening levels include metals and low levels of radionuclides in the surface soils found in the Sand Filter Beds and Sand Filter Berms/Adjacent Areas, and volatile organic compounds (VOCs) in the groundwater on-site and off-site. Tritium was also found at levels below the maximum contaminant levels (MCLs) in groundwater. Due to the limited nature of contamination in these areas, a detailed analysis of alternatives was not required. The natural attenuation remedy for the VOCs in groundwater was deemed appropriate because the VOC contaminants exist at such low levels as to render active remediation inefficient. The elevated metals concentrations and low levels of radionuclides in the sand filter beds and sand filter berms will be addressed as part of the SPDES closure activities; however, hot spot removal actions for the sand filter beds and berms are discussed in this report. The relatively low levels of VOCs that were found in groundwater will be monitored to evaluate the effectiveness of natural attenuation as part of each of the remedial alternatives. Tritium in groundwater will also be monitored and incorporated into the CERCLA review process to ensure that levels remain below the MCL. The Imhoff Tank removal action, the proposed hot spot removal for the sand filter beds/berms, and the monitoring of the low levels of VOCs and tritium in the groundwater are discussed in Chapter 2.0.
Summary of Imhoff Tank Removal Action
IT Corporation was contracted by Brookhaven National Laboratory to remove sludge from the Imhoff Tank and to dewater the Imhoff tank sludge for purposes of volume reduction. Between September 25 and October 6, 1995, the Imhoff Tank sludge was removed from the tank by using a vacuum truck and the sludge was temporarily stored in above ground tanks until further treatment could be performed. It was determined through analytical testing that the sludge could be disposed of as low level radioactive waste.
Approximately 10,000 pounds (4,500 kilograms) of absorbent material were added to the 64,000 gallons (240,000 liters) of sludge. The mixture was thoroughly mixed to ensure optimum water absorption. The final waste was then placed into 1 cubic yard, poly-mesh Super-Sacs, which were lined with PVC bags. A small amount of absorbent material was added to each Super-Sac (bottom and top) to account for condensation resulting in changing atmospheric/weather conditions. A paint filter test sample was performed at the site during filling of each Super-Sac to ensure final waste form requirements were met. Dewatering activities were completed on February 11, 1996. Transportation of these Super-Sacs to Envirocare was accomplished in September 1996.
The Imhoff Tank concrete structure was demolished in March 1997 and backfilled with concrete and clean fill from the OU III recharge basin construction. A concrete cap structure was installed and backfilling was completed in April 1997. All concrete debris, including the grit chamber, remained entombed in the remaining capped Imhoff vessels.
Summary of Proposed Hot Spot Removal at the Sand Filter Beds and Berms
Soils within the sand filter beds and adjacent to the sand filter berms were found to contain relatively high levels of mercury, silver, chromium, and lead, and also radionuclides. The results of the risk assessment indicated that potential exposure to soils in these areas are within acceptable ranges established by the USEPA for current and future exposure populations. The RI sampling results did not indicate that contaminants are migrating from soil to groundwater.
Although the concentrations of inorganics in the filter beds and berms do not pose an adverse risk to human health, a hot spot removal action has been proposed to remove levels of mercury and cesium-137 contamination present within the surface and subsurface soils of the beds and berms. The proposed hot spot removal action goes beyond that which is required to protect human health, but will reduce the potential for migration of mercury to groundwater and to the Peconic River, and will also reduce further the contribution of cesium to the already acceptable soil radiological risk to human health. Selected hot spot contamination removal within the sand filter beds will be addressed as part of future operational maintenance and upgrade projects for the beds.
Four hot spot removal scenarios have been proposed for the STP sand filter beds and berms and are discussed in Appendix F of this report. Appendix F describes the four hot spot removal action scenarios, and provides a brief screening of these scenarios and a recommendation for scenario selection based on the screening evaluation. The following four cleanup scenarios and respective cleanup levels for mercury and cesium-137 have been chosen for evaluation:
Based on the results of the screening evaluation, Scenario 2 was recommended as the selected removal scenario for either the beds or the berms because it is cost-effective, reasonably implementable and achieves the desired reduction of mercury and cesium-137 levels.
Summary of Groundwater Monitoring Action
On-site and off-site groundwater near the southeastern boundary was found to contain low concentrations of VOCs that exceeded the Federal MCLs and NYSDEC groundwater quality standards. The elevated concentrations of VOCs are believed to originate from discontinued practices that may have resulted in an inadvertent historical release of solvents to the STP. Investigations of soil and groundwater at the STP indicate that there are no continuing sources for VOC contamination. A residential area, which has utilized private wells for drinking water, is located southeast of the OU V study area. The potential for further migration of the contaminants with the groundwater into this residential area is a concern. As part of a good neighbor initiative, DOE has undertaken actions to ensure that the health of the residential area located downgradient of OU V is adequately protected via supplying public hookups. Also, as part of the CERCLA process, continued monitoring of VOCs in groundwater until MCLs are reached through natural attenuation (approximately 30 years) and continued monitoring of tritium to ensure that levels remain below MCLs will be performed and is incorporated into each remedial alternative.
There are no current or planned future uses of on-site groundwater in the OU V study area. Although future residential use of the BNL site is considered highly unlikely, potable use of on-site groundwater by a hypothetical future on-site resident was evaluated during the risk assessment. Based on the potential exposure pathways identified in the risk assessment, no on-site risks to human health have been indicated. The only complete exposure pathway for groundwater under the current use scenario is the dermal contact with, ingestion of, and/or inhalation of contaminated groundwater that has migrated off-site. Potential receptors for off-site groundwater include a residential adult and a residential child. Because off-site groundwater was used as a source of drinking water at OU V before the hookups were provided in 1997, concentrations of trichloroethene (TCE) exceeding the MCL of 5 µg/L was a potential concern.
Groundwater modeling was conducted to predict the concentrations of TCE downgradient of the OU V study area over the next 30 years (from 1996) in the Upper Glacial and Magothy aquifers. Groundwater modeling suggests that the TCE plume may migrate (within the deep portion of the Upper Glacial aquifer) below 11 residential areas given that most residential wells are relatively shallow. However, residential wells could be impacted by the off-site migration of TCE exceeding the MCL if they were installed into the deep portions of the Upper Glacial aquifer. Due to the uncertainty of the completed depths of many of the wells, DOE is conducting the following actions to protect the health of residents located downgradient of OU V from potential future exposure to TCE that might result due to groundwater migration:
Long-term groundwater monitoring activities will be performed as part of the CERCLA process and therefore the costs associated with these activities will be incorporated into the OU V remedial alternatives. The groundwater monitoring program will be incorporated into the CERCLA five-year review process. As part of this review, the semi-annual monitoring results for each 5-year period will be evaluated for trend analysis to examine if the objective of the remedy are being achieved.
Identification and Evaluation of Remedial Alternatives for Sediment
In order to provide adequate protection of human health and the environment, remedial action objectives (RAOs) and general response actions (GRAs) were identified for the Peconic River sediments that were found to contain elevated levels of metals. The RAOs were developed based on an evaluation of applicable or relevant and appropriate requirements (ARARs) and the results of the human health and ecological risk assessments. The RAOs for sediment are to prevent the exposure of aquatic communities to contaminants at concentrations that are deemed to be toxic to aquatic life, prevent bioaccumulation of toxic contaminants to protect potential consumers, and protect the ecosystem of the Peconic River. Sediment toxicity studies were conducted to determine what concentrations of metals, if any, are toxic to the aquatic community found in the Peconic River. Concentrations of mercury, silver, and copper were determined at which toxic effects could be expected. These were deemed the toxicity-based cleanup goals. Fish bioaccumulation studies determined that a risk to wildlife exists from feeding on fish which have bioaccumulated contaminants (mercury, PCBs, DDD). NYSDEC sediment screening levels based on protection of wildlife from bioaccumulation in the food chain are applicable for the Peconic River sediments for PCBs and DDD. These were deemed the bioaccumulation based cleanup goals. The concentrations in sediment of cesium-137, plutonium and other radionuclides were found at levels that do not warrant separate cleanup goals. GRAs were identified based on the toxicity and bioaccumulation based sediment cleanup goals. For each GRA, technology types and process options were identified and screened with respect to implementability.
The technology types and process options that passed the initial screening were assembled into five remedial alternatives: Alternative 1 (No Action), Alternative 2 (Excavation/Drying Beds/Off-site Disposal), Alternative 3 (Limited Excavation/Sediment Dispersion Control/Drying Beds/Off-site Disposal), Alternative 4 (Excavation/Drying Beds/Beneficial Reuse) and Alternative 5 (Excavation/Phytoremediation/Off-site Disposal). A brief description of each of these alternatives is provided below:
Each of these alternatives were evaluated against the following seven criteria (1) overall protection of human health and the environment, (2) compliance with ARARs, (3) long-term effectiveness and permanence, (4) reduction of toxicity, mobility and volume, (5) short-term effectiveness, (6) implementability, and (7) cost. CERCLA requires the evaluation of alternatives against nine evaluation criteria; however, the "State Acceptance" and "Community Acceptance" criteria will not be evaluated until comments from the regulatory agencies as well as the public have been received on the FS Report. To the maximum extent practical, CERCLA requires that remedial action alternatives must (1) be protective of human health and the environment, (2) attain ARARs, (3) be cost effective, (4) utilize permanent solutions and alternative treatment technologies, and (5) reduce toxicity, mobility, or volume. Once each of the alternatives was individually evaluated against the seven criteria, a comparative analysis of alternatives was conducted. A brief summary of the comparative analysis of alternatives is provided below.
Alternatives 2, 3, 4, and 5 were generally found to be comparable with respect to the seven evaluation criteria. Each of these alternatives involves the excavation of contaminated sediment, which will eliminate the potential for the aquatic community to be exposed to contaminants. Excavation of the sediment, however, will result in the disturbance of the benthic community and the wetlands. Alternative 3 has a lesser impact on the wetlands than Alternatives 2, 4, and 5 because it leaves unexcavated the depositional wetland area of higher ecological value located east of the firebreak. Alternative 1, the no action alternative, leaves the contaminants in place which could continue to affect the aquatic community, though no ecosystem disturbance would take place due to remedial activities. The mobility of contaminated sediments is anticipated to be reduced over time due to the natural deposition of clean sediments over the existing contaminated sediments; however, natural deposition is estimated to be a slow process in this part of the Peconic River and it would take a long time to develop a protective barrier.
Since there are no promulgated standards for the remediation of sediment, each of the alternatives complies with chemical-specific ARARs. The action-specific and location-specific requirements associated with Alternatives 2, 3, 4, and 5 will require coordination with regulatory personnel. There are no action-specific nor location-specific ARARs for Alternative 1. Alternatives 2, 3, 4, and 5 are comparable with respect to long-term effectiveness and permanence, but each of these alternatives is rated higher than Alternative 1 with respect to this evaluation criterion. The long-term effectiveness and permanence of Alternative 3 is less than that of Alternatives 2, 4, and 5 because the contaminated sediments within the wetland area of higher ecological value remain unexcavated.
Under Alternatives 2, 3, 4, and 5 the contaminated sediment will be removed from the Peconic River, which limits the potential for exposure to stream sediments and reduces the volume, toxicity and mobility of contaminated material in the stream. However, once the sediments are excavated, the treatment of the sediment in Alternatives 2, 3 and 4 will not reduce the toxicity or mobility of the contaminants in the excavated sediment because treatment is limited to dewatering. Only Alternative 5 uses treatment to reduce the toxicity, mobility, or volume of the contaminants within the excavated sediments, although the effectiveness of phytoremediation in reducing the contaminant concentrations to the cleanup objectives is uncertain.
Alternative 1 is rated higher than Alternatives 2, 3, 4, and 5 with respect to short-term effectiveness, since no remedial activities will be conducted that have the potential to impact worker health and safety and the surrounding community.
Alternative 1 is the easiest alternative to implement from a technical and administrative standpoint. Alternatives 2, 3, 4, and 5 are similarly implementable, although phytoremediation as part of Alternative 5 is an evolving treatment technology with a relatively high level of technical uncertainty associated with its implementability and suitability. Alternative 4 calls for the beneficial reuse of the residual sediment. The feasibility of implementing Alternative 4 depends on the determination of a future beneficial use for the sediment. The future beneficial use for the sediments will consider the contaminants present within the sediments.
Alternative 1 does not involve any remedial action or the disturbance of the wetlands; thus, this alternative is the lowest cost option. Alternative 1 is the only option that will not result in the disturbance of the wetlands and forest. Of the remaining alternatives, Alternative 4 is the lowest in cost, but is comparable in cost to Alternative 3. Under Alternatives 2 and 3, the residual waste will be disposed at an off-site landfill and for Alternative 4 the residual waste will be beneficially reused either on-site or off-site. The costs for transport and disposal under Alternatives 2 and 3 could potentially increase by one order of magnitude if a DOE rad-added exemption cannot be obtained for the sediments in which case the sediments would have to be disposed at a low level rad facility. Although the costs for beneficially reusing the residual waste on-site would be less than off-site disposal costs, the potential uses for the material may be somewhat limited given the contaminants present and will require further investigation. Alternative 5 is the most expensive of the five alternatives, but is the only alternative that meets the USEPA's statutory preference for treatment as a principal component. However, if ex-situ phytoremediation fails to reach the cleanup objectives, the sediments would have to be disposed as a waste which would represent a significant additional cost for Alternative 5. If Alternative 5 could be implemented in-situ rather than ex-situ, the total remedial costs could be significantly reduced. However, to date, there have been no studies evaluating wetland plants for the in-situ removal of metals, PCBs, and DDD from sediments. The viability of in-situ phytoremediation cannot be evaluated unless focused treatability studies and field tests are conducted to identify appropriate wetland species which would bioaccumulate contaminants in the upper structures of the plant and could, therefore, be harvested.