In Situ Bioremediation at the Hanford 200 West Area Site, Richland, Washington

Site Name:

Hanford Site

Location:

Richland, Washington

Period of
Operation:

January 1995 to March 1996

Cleanup
Type:

Field demonstration

Technology:
In Situ Bioremediation
- One injection/extraction well pair (dual multi-screened wells) used to recirculate groundwater; two monitoring wells located between recirculation wells; a nutrient injection system; and a groundwater sampling system
- Groundwater was extracted and filtered, nutrients were added, and reinjected
- Nutrients consisted of acetate and nitrate pulses added at 24 hr intervals; the nitrate pulses were skewed 10 hrs from the acetate pulses
- An Accelerated Bioremediation Design Tool (ABDT) was used to determine pulse requirements
- Two separate tests were performed - one in the upper aquifer zone and one in the lower aquifer zone

Cleanup Authority:
Not identified

Technical Contact:
Rod Skeen
Principal Investigator
Pacific Northwest National Laboratory
(509) 375-2265

Management Contact:
Jim Wright
DOE EM-50
Subsurface Contaminants Focus Area Manager
(803) 725-5608
Licensing Information:
John Sealock
Technology Transfer
PNNL
(509) 375-3635

Contaminants:
Chlorinated solvents
- Concentrations in groundwater at the demonstration site were approximately 2 mg/L for carbon tetrachloride (CCl4) and about 250 mg/L for nitrate
- Estimated 600,000 kg of CCl4 in soil and groundwater at demonstration site

Waste Source:
Chemical processing operations

Type/Quantity of Media Treated:
Groundwater
- The unsaturated zone is 75 m thick and uncontaminated
- Upper aquifer zone occurs at 75 - 78 m bgs; lower aquifer zone occurs at 87 - 92 m bgs; zones separated by low permeability unit and do not interact with each other significantly

Purpose/Significance of Application:
In situ bioremediation of chlorinated solvents and nitrate, including use of a computer-based tool to aid in system design and operating strategies

Regulatory Requirements/Cleanup Goals:
Not identified

Results:
- Approximately 2 kg of CCl4 were biodegraded during the upper and lower zone tests, with less than 2% conversion to chloroform
- CCl4 biodegradation rate - 0.8 mg/g-biomass/day in upper zone and 0.9 mg/g/day in lower zone
- The concentration of CCl4 in the upper zone was reduced from approximately 2.0 to 1.2 mg/L after 100 days
- The upper zone test produced more than 20 kg of bacteria and the lower zone more than 10 kg (dry weight)
- Contaminant destruction was effective without plugging of the injection well
- The ABDT was used to design and operate an effective in situ bioremediation system for the demonstration

Cost Factors:
- An analysis of projected costs showed that the costs for in situ bioremediation were $5.80/m3, compared to $13.30/m3 for the baseline technology of air sparging/GAC; the treatment time was estimated as 1.9 yrs for ISB and 4.5 yrs for AS/GAC
- In situ bioremediation is cost-effective where plumes or portions of plumes are small enough for volumetric treatment (100 m diameter range), in aquifers where contaminant plumes exhibit non-equilibrium contaminant partitioning, and in source area plumes with significant contaminant sorption

Description:
The Hanford Site's mission has been to support national defense efforts through the production of nuclear materials. From 1944 to 1989, as part of the plutonium recovery processes, a variety of wastes including solvents, metals, and radionuclides were released to the soil and groundwater. Soil and groundwater at the 200 West Site Area at Hanford, located approximately 250 ft north of the sanitary tile field and 750 ft west of the 221-T plant, is contaminated with an estimated 600,000 kg of CCl4. The 200 West Site Area was selected for a field-scale demonstration of in situ bioremediation. The demonstration included two separate tests, which were conducted in distinct, unconnected aquifer zones at the test site.

A recirculating well in situ bioremediation system was demonstrated at the 200 West Site Area, which showed reductions in the mass and concentration of CCl4 in the two aquifer zones. Lessons learned from the field demonstration included that effective ISB system design and operational process control requires an ABDT or similar process simulator, and that use of an ABDT allows quick corrective action (such as changes in the amount/duration of nutrient pulse or the pulse period) to maintain rapid contaminant destruction during these changes. In addition, ISB was found to yield significant economic and efficiency gains over conventional baseline technologies for remediation of groundwater contaminated with VOCs and nitrates, and to be potentially effective for treating plumes caused by dissolution of non-aqueous phase liquids.