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Record of Decision System (RODS)

HANFORD 100-AREA (USDOE)

Abstract

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:  Record of Decision
ROD ID:  EPA/ROD/R10-96/134
ROD Date:  03/26/1996
Operable Unit(s):  02
 
Media:  groundwater
 
Contaminant:  Chromium, sulfide, bis(2-ethyl hexyl)phthalate, lead, iron, zinc
 
Abstract:  Please note that the text in this document summarizes the Record of Decision for the purposes of facilitating searching and retrieving key text on the ROD. It is not the officially approved abstract drafted by the EPA Regional offices. Once EPA Headquarters receives the official abstract, this text will be replaced.

The Hanford 100-Area site is a 560-square mile Federal facility located in southeastern Washington along the Columbia River. 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.

The 100-Area encompasses approximately 26 square miles bordering the south shore of the Columbia River. It is the site of nine retired plutonium production reactors. The groundwater impacted by operations associated with those nine reactors has been divided into five operable units. Two of five groundwater operable units are addressed here.

Pre-1943 land use at Hanford was primarily grazing and agriculture with some traditional use by Native Americans. Historically, groundwater use included domestic consumption, as well as other needs for the small agricultural communities, and by Native Americans. Currently groundwater is not used but is monitored to assess contaminant conditions. Existing land use in the 100-Area includes facilities support, waste management, and undeveloped land. Facilities support activities include operations such as water treatment and maintenance of the reactor buildings. The waste management land use designation results from former uncontrolled disposal activities in areas now known as past-practice waste sites located throughout the 100 Area. Lastly, there are undeveloped lands located throughout the 100 Area that comprise approximately 90 percent of the land area.

During the years of reactor operations at the operable units being addressed, large volumes of reactor coolant water containing chromium and radionuclides were discharged to retention basins for ultimate disposal in the Columbia River through outfall pipelines. Liquid wastes, containing significant quantities of chromium from reactor operations, were also discharged to the soil column at cribs, trenches, and french drains. Contaminant plumes in groundwater resulted from these former waste disposal practices.

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 site. 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.
 
Remedy:  The selected remedy is an interim action that involves removing hexavalent chromium from groundwater that discharges into the Columbia River. To intercept the chromium plumes, groundwater will be pumped from approximately 30 wells located along and inland from the river shoreline. The water will then be treated using an ion exchange treatment technology to remove chromium. The treated effluent will then be returned to the aquifer using injection wells located upgradient of the existing chromium plumes. The interim action includes monitoring of the groundwater near the river and the effluent from the treatment system to determine system performance in meeting the remedial action objectives for protection of the Columbia River. The interim action also involves institutional controls to protect human health from groundwater contaminants.
 
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