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Site Name:  HANFORD 100-AREA (USDOE)
Address:  100 AREA 
City & State:  BENTON COUNTY  WA  99352
County:  BENTON
EPA ID:  WA3890090076
EPA Region:  10
NPL Status:  Currently on the Final NPL
ROD Type:  Amendment
ROD ID:  EPA/541/R-00/122
ROD Date:  10/24/1999
Operable Unit(s):  02
Abstract:  The Hanford Site was established during World War II as part of the "Manhattan Project" to produce plutonium for nuclear weapons. Hanford Site operations began in 1943, with USDOE facilities located throughout the Site and the City of Richland. Certain portions of the Site are known to have cultural significance and may be eligible for listing in the National Register of Historical Places.

In 1988, the Hanford Site was scored using EPA's Hazard Ranking System. As a result of the scoring, the Hanford Site was added to the National Priorities List (NPL) in November 1989 as four sites (the 100 Area, the 200 Area, the 300 Area, and the 1100 Area). Each of these areas was further divided into operable units. The 100 Area NPL site consists of the following operable units for contaminated sources such as soils, structures, debris, and burial grounds: 100-BC-1, 100-BC-2, 100-KR-1, 100-KR-2, 100-NR-1, 100-DR-1, 100-DR-2, 100-HR-1, 100-HR-2, 100-FR-1, 100-FR-2,100-IU-1, 100-IU-2, 100-IU-3, 100-IU-4 and 100-IU-5; for contaminated groundwater: 100-BC-5, 100-KR-4, 100-NR-2, 100-HR-3, and 100-FR-3.

In anticipation of the NPL listing, the Department of Energy (DOE), EPA, and the Washington State Department of Ecology (Ecology) entered into a Federal Facility Agreement and Consent Order in May 1989 known as the Tri-Party Agreement. This agreement established a procedural framework and schedule for developing, implementing, and monitoring remedial response actions at Hanford. The agreement also addressed Resource Conservation and Recovery Act (RCRA) compliance and permitting.

In 1992, the Hanford Future Site working Group evaluated four future land use options for the site and recommended cleanup of sources and contaminated groundwater flow into the Columbia River as an "immediate priority." This recommendation was a key consideration in the selection of high priority liquid radioactive disposal sites for interim remedial actions. The recommendations also expressed a desire for ultimately achieving "unrestricted use" for the air, surface, subsurface, and groundwater, with the exception of the B Reactor as a museum option. That option would place the reactor itself in a "restricted" status.

The Final River Conservation Study and the Environmental Impact Statement for the Hanford Reach of the Columbia River (National Park Service 1994) proposed that the Hanford Reach of the Columbia River and approximately 102,000 acres of adjacent lands be designated as a National Wild and Scenic River and a National Wildlife Refuge, respectively.

On September 27, 1995, the Interim Record of Decision was signed for this site.

DOE performed a 100 area wide phase 1 and 2 Feasibility Study (FS) and operable unit specific Limited Field Investigations for the 100-BC-1, 100-DR-1 and 100-HR-1 operable units. A 100 area-wide Phase 3 Source Waste Site FS and 100 Area operable unit specific Focused FS also were conducted to evaluate specific waste site remedial action goals, objectives and technologies.

The Riverland Rail Yard (100-IU-1 OU) supported Hanford construction and operations activities from 1943 until 1954, while decontamination of radioactive rail cars continued until 1956. Included in this site are a 2,4-D pesticide container site, a rail yard maintenance facility, and two former military installations with associated demolition debris.

In June 1993 an Action Memorandum, signed by the Tri-Parties, the USDOE agreed to perform an expedited response action for the cleanup of the Riverland Rail Yard Maintenance Facility and pesticide container sites, and closure of an empty munitions cache hole. Diesel contaminated concrete and soil from the rail yard and pesticide sites were removed from the site for bioremediation. The remaining contaminants in the soil were at levels which were below Model Toxics Control Act (MTCA) residential standards. Radioactive decontamination of the facility occurred around 1963, after which the maintenance facilities were dismantled and sold. Follow-up radiological surveys were performed in 1977, 1978, and 1993, revealing only natural background levels.

This area was acquired for use as a military buffer zone against potential hostile attacks on the 100 Area reactors. Several Anti-Aircraft Artillery Batteries and three Nike Missile Sites were located on the Wahluke Slope. These sites were decommissioned in 1960-1961, and demolished in 1974.

During 1989 and 1990, an investigation of the Wahluke Slope was performed to asses potential health, safety, and environmental concerns raised by Ecology and the public. Based on the investigation, three of the Wahluke Slope sites; the H-06-L Nike missile launch site, H-06-C Nike missile control site, and the 2,4-D pesticide disposal site, were identified and included as part of the 100-IU-3 OU. During the investigation of this OU, 36 additional sites were identified. Soil contamination in these areas resulted from historic use of petroleum products and pesticides by the military.

USDOE prepared an engineering evaluation and cost analysis, North Slope (Wahluke Slope) Expedited Response Action Cleanup Plan in 1993, regarding cleanup options applicable to the Wahluke Slope sites. The Tri-Parties signed an Action Memorandum in 1994, requiring removal of hazardous substances and proper abandonment of water wells. During 1994, a CERCLA expedited response action was performed to remove any hazardous substances that remained in the 39 sites on the Wahluke Slope. Soil contaminated with the pesticide DDT and its associated breakdown products was disposed of at a hazardous waste landfill in Arlington, OR. Petroleum contaminated soil (PCS) was transported to a PCS treatment facility in Pasco, WA, for bioremediation. Several 55-gallon drums of miscellaneous and hazardous substances were sent to appropriate handling facilities. Non-hazardous trash, debris, and concrete were either returned to their excavations or recycled. The remaining contaminants in the 100-IU-3 OU were measured at levels below MTCA residential cleanup standards. Water wells were decommissioned in accordance with WAC 173-160 regulations (Minimum Standards for Construction and Maintenance of Wells) to eliminate this potential contamination path to groundwater, and to prevent interconnection of aquifers. No groundwater contamination has been associated with the 100-IU-3 OU.

Little historical documentation of the site is available. The landfill was used during the years of reactor operation for disposal of crushed, empty Sodium Dichromate barrels.

In 1992, Ecology and EPA recommended an expedited response action be performed at the Sodium Dichromate Barrel Landfill, after which USDOE prepared an engineering evaluation and cost analysis regarding remediation alternatives applicable to this unit. The Tri-Parties signed an Action Memorandum in 1993, requiring full excavation and removal of all buried materials from the landfill.

Excavation, removal, and disposal activities took place between March and July, 1993. Approximately 5,000 crushed drums were removed from the site, along with minor amounts of asbestos-containing materials, two 5-gallon roofing tar cans, and a small amount of used oil and grease. Soil sampling results indicated levels below MTCA residential cleanup standards were achieved.

The White Bluffs Pickling Acid Cribs Site is the only site identified in the 100-IU-5 Operable Unit. This area was the location of construction activities from about 1943 - 1959. Little historical information is known about this site. It is believed that the cribs received waste streams from a pipe fabrication facility operating sometime between 1943 and 1959.

In EPA and Ecology recommended that USDOE perform an expedited response action for this site. Characterization activities indicated contaminants of concern were at levels below MTCA residential cleanup standards. No investigation of ground water was completed for this unit due to its close proximity to other 100 Area operable units. No radioactive contamination has been associated with this unit.

OU2: (100-HR-3 and 100-KR-4)(EPA/ROD/R1O-96/134)
Prior to starting the "Limited Field Investigation" in 1992 in the 100-KR-4 and 100-HR-3 Operable Units, groundwater monitoring consisted of periodic sampling under DOE Order 5400.1. A limited record exists for groundwater conditions during the reactor operating years. Riverbank seepage monitoring was completed in 1984 and 1988 as part of the Sitewide Environmental Surveillance program.

At the 100-K Area, groundwater sampling was associated with operations at the 100-K East and 100-K West fuel storage basins. Some post-1959 data from several wells are available to describe conditions downgradient of the 116-K-2 trench used for liquid effluent disposal that included chromium.

For the 100-D/DR reactor area, (100-HR-3 Operable Unit), historical data describing conditions during reactor operations are limited to several wells that were constructed in 1960. Quarterly sampling was started in 1991 under the RCRA/Operational program for monitoring liquid effluent discharge to 100-D Ponds. An infiltration experiment was conducted in 1967 that created a groundwater mound in the vicinity of the coolant water retention basins. The results may provide an analog for the un-monitored conditions that prevailed during reactor operating years.

A similar database exists for the 100-H Area (100-HR-3 Operable Unit). Monitoring of the 183-H Solar Evaporation Basins facility occurred between 1973 and 1985, when monitoring was substantially increased under the RCRA/Operational program. A comprehensive database exists to describe the contaminant plume, which includes chromium, associated with the 183-H facility for years after 1985.

The technical information baseline for the RI/FS associated with each operable unit was augmented substantially in 1992 with the installation of new monitoring wells and subsequent quarterly sampling as part of the limited field investigation. A comprehensive riverbank seepage sampling project was completed in late 1991, which helped relate contamination along the shoreline to groundwater contamination underlying the reactor areas. RI/FS characterization activities that followed the four quarters of sampling conducted during the limited field investigation consist of semiannual well sampling, annual riverbank seepage sampling and periodic Columbia River substrate sampling. Water table elevations were measured at periodic intervals to show the seasonal ranges in flow direction and gradients.

As a result of the discharge of groundwater from the operable units into the river, chromium, a metal that is toxic to aquatic organisms in low concentrations, poses a risk to aquatic organisms in the Columbia River adjacent to the 100-D/DR, 100-H and 100-K Areas. The most toxic form of chromium, hexavalent chromium, readily dissolves in water and, therefore, moves freely with groundwater. Hexavalent chromium has been detected in groundwater and in the groundwater/river interface where groundwater upwells into the river. Once discharged to the river, it is easily assimilated by aquatic organisms, some of which are adversely affected. Trivalent chromium is less soluble and less toxic, and is not easily transported by groundwater. Most chromium in groundwater at the Hanford Site is hexavalent chromium, because of the original sources and prevailing geochemical conditions.

In August 1994, a pilot-scale treatability test began at the 100-D/DR Area, to assess the effectiveness of an iron exchange treatment system to remove hexavalent chromium from groundwater. Through July 1995, this pump-and-treat system had extracted more than 4 million gallons (15 million liters) of groundwater and had removed more than 38 pounds (17 kilograms) of chromium. This system is successful in removing chromium from extracted groundwater at 100-D/DR, and indicates that an ion exchange treatment system can be a successful groundwater treatment technology for chromium in the 100 Area.

The DOE, Washington State Department of Ecology and EPA developed a Community Relations Plan in April 1990 that was designed to promote public awareness of investigations and public involvement in the decision-making process. The plan summarizes the known concerns based on community interviews. Several public meetings have been held and numerous fact sheets have been distributed in an effort to keep the public informed about Hanford cleanup issues. The Plan was updated in 1993 to enhance public involvement and is currently undergoing an additional update.

The Focused Feasibility Study Document and Proposed Plans were made available to the public in both the Administrative Record and several libraries. These documents underwent a 45 day public comment period from September 11, 1995 to October 25, 1995. Notice of this comment period was published in four State and Local papers on September 10 and 11, 1995. Separate mailings went to about 4, 700 "interested in Hanford" citizens. A meeting was held on October 18, 1995 that discussed the proposed actions relative to other Hanford groundwater and Columbia River issues.

The selected interim remedy is chosen in accordance with CERCLA, as amended by SARA, and to the extent practicable, the National Contingency Plan (NCP). The decision for these operable units is based on the Administrative Record.

The interim action is expected to provide adequate protection of human health and ecological receptors in the Columbia River and will continue until implementation of the final remedy for the 100-HR-3 and 100-KR-4 groundwater operable units, or until such time that the DOE demonstrates to the State and the EPA that no further interim action is required. This interim action is expected to become part of the final remedial action.

Because this is an interim action ROD, review of these operable units and the remedy will be ongoing as the Tri-Parties continue to develop and implement final remedial alternatives for the operable units and the 100 Area NPL site. Because this remedy will result in hazardous substances remaining on-site above health-based levels, a review will be conducted within five years after commencement of remedial action to ensure that the remedy continues to provide adequate protection of human health and the environment.

The Proposed Plan for 100-IU-1, 100-IU-3, 100-IU-4 and 100-IU-5 was made available to the public in both the Administrative Record and in Information Repositories on June 26, 1995. The public comment period was held from June 26, 1995 - August 9, 1995.
Remedy:  The In Situ Redox Manipulation (ISRM) technology used during the treatability tests has been selected as the remedy for treatment of the newly discovered chromium plume in the southwest portion of the 100-D Area. Other innovative treatment technologies will continue to be evaluated for final cleanup of this Operable Unit (OU). The use of ISRM technology will not affect ongoing operations of the 100-D and 100-H Area pump and treat systems. The ISRM technology involves creating a permeable subsurface treatment zone to reduce mobile chromium in groundwater to an insoluble form. This is accomplished through the injection of sodium dithonite into the aquifer through a series of wells. Several days after the injection of the sodium dithionite, unreacted reagent and reaction products are removed from the aquifer by extracting groundwater from the injection wells. The sodium dithionite reduces ferric iron to ferrous iron within the aquifer sediments, producing a reducing-type environment. Under these conditions, hexavalent chromium is not toxic or mobile. In this way, hexavalent chromium-contaminated groundwater flowing through the treatment zone will be treated to the less-toxic trivalent form. During this process, dissolved oxygen levels are also reduced. Treatability studies at the site indicate that the groundwater is reoxygenated to 75% to 95% of the original levels before discharging to the Columbia River. Recuperation of oxygen levels is further enhanced by dynamic mixing in the river bottom. In addition, a brief exceedance of the secondary water standard for sulfate is anticipated as a result of chemical injection; however, groundwater is expected to meet the sulfate standard following withdrawal of the chemicals, which occurs within a few days of injection. ISRM implementation and performance monitoring, including contingencies, will be described in the Remedial Design Report/Remedial Action Work Plan. Institutional Controls will continue during the interim remedial action period that will limit human access to the groundwater.

Estimated Capital Cost: $3,920,000
Estimated Annual O&M Costs: $50,000
Estimated Present Worth Costs: Not provided
Total O&M Costs: Not provided
Net Present Value (5 year) - $4,136,000
(10 year) - $4,330,000
(20 years) - $4,612,000
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