Pump and Treat and In Situ Bioremediation
- Groundwater is extracted using 5 wells (3 of which are no longer in service), at an average total pumping rate of 16 gpm
- NAPLs are separated from the extracted groundwater, and the groundwater is then routed to 2 fixed-film bioreactors in series
- Nutrients (nitrogen and phosphorus) are added prior to bioreactors and oxygen is added within the bioreactors
- Treated water is reinjected through 2 gravity injection systems (9 wells total)
- ROD Date: 12/30/88
|EPA Point of Contact:|
Jim Harris, RPM
U.S. EPA Region 8
301 S. Park Drive
P.O. Box 10096
Helena, MT 59626
(406) 441-1150 ext. 260
|State Point of Contact:|
Neil Marsh Montana
DEQ Remediation Division
Semivolatiles - halogenated (PCP); and PAHs
- Maximum concentrations detected during 1986 RI/FS were PCP (3,200 mcg/L), acenaphthene (100 mcg/L), acenaphthylene (200 mcg/L), benzo(a)anthracene(1 mcg/L), and naphthalene (500 mcg/L)
Improper storage and disposal of wood preserving products
Type/Quantity of Media Treated:
- 15.1 million gallons treated as of December 1996
- DNAPL and LNAPL observed in several monitoring wells on site
- Groundwater is found at 10-20 ft bgs
- Extraction wells are located in 1 aquifer, which is influenced by a nearby surface water and production wells
- Hydraulic conductivity ranges from 100 to 1,000 ft/day
Purpose/Significance of Application:
Combination of pump and treat and in situ bioremediation at site with LNAPL, DNAPL, and dissolved-phase contaminants.
Regulatory Requirements/Cleanup Goals:
- Remedial goals, developed based on a risk assessment and updated MCLs, were established for non-carcinogenic PAHs: naphthalene (1,460 mcg/L), acenaphthene (2,100 mcg/L), fluorene (1,460 mcg/L), anthracene (11,000 mcg/L), pyrene (1,100 mcg/L), and fluoranthene (1,460 mcg/L); carcinogenic PAHs: benzo(a)anthracene (0.1 mcg/L), chrysene (0.2 mcg/L), benzo(b)fluoranthene (0.2 mcg/L), benzo(a)pyrene (0.2 mcg/L), dibenzo(a,h)anthracene (0.3 mcg/L), and indeno(1,2,3-cd)pyrene (0.4 mcg/L); arsenic (50 mcg/L); benzene (5 mcg/L); and PCP (1 mcg/L).
- The goal of the source area extraction system is to remove oil-contaminated groundwater and NAPL from the area of the waste pit and remove as much NAPL as possible.
- The goal of the in situ bioremediation and pump and treat system is to reduce PAH and PCP concentrations in the upper aquifer to levels below remedial goals.
- As of December 1996, concentrations in many parts of the plume had declined to either remedial goals or detection limits. However, there are areas of groundwater contamination in which levels of PAHs and PCP remain near original levels.
- DO levels have been measured as an indication of the extent of influence on the intermediate injection system and as an indicator for PAH and PCP in the groundwater.
- The source area treatment system had removed 37,570 pounds of PAHs from the groundwater from 192 to 1996.
Estimated costs for treatment through 1996 were $5,628,600 ($3,010,000 in capital and $2,618,600 in O&M), which correspond to $374 per 1,000 gallons of groundwater extracted and $150 per pound of contaminant removed. These costs do not account for the volume of groundwater treated or the mass removed through in situ bioremediation. No estimates have been made for these two items.
The Libby Montana site has been used as a lumber mill and wood-treating facility since 1946. From 1946 to 1969, the site used various compounds, including creosote and PCP, in their wood-treating operations. The mill was operated by the St. Regis Company until 1985 when it was purchased by Champion International. In 1979, homeowners detected a creosote odor in their well water. EPA monitoring in 1981 confirmed groundwater contamination from the Libby site. The site was placed on the NPL in September 1983 and a ROD was signed in December 1988.
The remedial strategy at this site was to address the source area by removing NAPL and to stimulate bioremediation in the down-gradient upper aquifer plume. The three components to the aquifer remedial system are a source area extraction system, intermediate injection system, and boundary injection system. As of December 1996, concentrations in many parts of the plume had declined to either remedial goals or detection limits. However, there are areas of groundwater contamination in which levels of PAHs and PCP remain near original levels. The site operators believe that no additional modifications could be made to improve the system's performance or to reduce the time required to remediate the intermediate injection area.