Pump and Treat
o Five extraction wells located along the downgradient edge of the landfill with a total design flow rate of 600 to 800 gallons per minute (gpm).
o Treatment system included aeration, clarification, and the addition of sodium hydroxide and polymer for iron removal.
o Air stripping used to remove volatile organic compounds (VOCs).
o Treated water was discharged to the river, and the clarifier sludge was dewatered and disposed in a landfill.
o During its 7.5 years of operation, more than 2 billion gallons of groundwater were extracted and treated.
Monitored Natural Attenuation
o After the P&T system was shut down, MNA was evaluated to address low levels of contamination.
o The monitoring network comprises of 26 monitoring points, including 6 air injection wells, 5 piezometers, 13 monitoring wells, and 2 residential wells.
o Analytes include VOCs; metals; benzene, toluene, ethylbenzene, xylenes (BTEX); naphthalene; and natural attenuation parameters such as oxidation-reduction potential, dissolved oxygen, pH, temperature, and specific conductance.
o Baseline monitoring of natural attenuation was performed in October 2001. The second and third monitoring events occurred in December 2002 and April 2003.
In Situ Bioventing
o Consisted of injecting air into the area of petroleum nonaqueous phase liquid (NAPL) contamination to stimulate naturally-occurring aerobic microbes and to promote biodegradation of the organic compounds.
o Area of NAPL contamination targeted was 2.5 acres downgradient of the landfill.
o 3- to 5-foot NAPL layer was estimated to be at a depth of 8 to 12 feet below ground surface (bgs).
o System consisted of 29 vertical air injection wells (each 2 inches in diameter, installed on 40- to 50-foot centers, and screened within the NAPL layer). The wells were connected by a header piping network to a single aeration well blower and operated between 270 and 320 standard cubic feet per minute (scfm).
CERCLA Remedial Action
-- ROD Date: August 14, 1990
-- ESD Dates: September 29, 2000; November 13, 2001
-- Five-Year Reviews: 1998, 2003
U.S. Environmental Protection Agency Contact:
U.S. Environmental Protection Agency Region 5
77 W. Jackson Blvd
Chicago, IL 60604
Phone: (312) 353-8983
Fax: (312) 353-8426
Wisconsin Department of Natural Resources
P.O. Box 4001
Eau Claire, WI 54702
Phone: (715) 839-3824
Fax: (715) 839-6076
EPA Support Contractor:
135 South 84th St, Suite 325
Milwaukee, WI 53214
Phone: (414) 272-2426
Fax: (414) 272-4408
Web Site: www.ch2m.com
State Support Contractor:
4500 Park Glen Road, Suite 210
St. Louis Park, MN 55416
Phone: (952) 924-0117
VOCs, SVOCs, and metals
-- VOCs (groundwater)- TCE; 1,1-DCA (800 µg/L maximum); 1,1,1-TCA (8 µg/L maximum); 1,1-DCE; 1,2-DCE (27 µg/L maximum); and BTEX.
-- SVOCs (soil) - petroleum hydrocarbon solvents, primarily naphtha, at levels as high as 550 mg/kg
-- Metals (groundwater) - barium, arsenic, iron, manganese, and lead
Disposal of municipal and chemical wastes in a landfill
Type/Quantity of Media Treated:
-- 10 to 70 feet below ground surface (bgs); 2.17 billion gallons of groundwater treated
-- 11 to 15 feet bgs (quantity of soil treated was not reported)
Purpose/Significance of Application:
Full-scale remediation of VOCs, SVOCs, and metals in groundwater and soil using P&T, in situ bioventing, and MNA.
Regulatory Requirements/Cleanup Goals:
-- Estimated cleanup goal was 80 to 95 percent reduction of the organic contaminant mass in the soil (ROD did not establish chemical-specific soil cleanup goals).
-- In 2000, cleanup goals for groundwater were revised to the current state goals in an explanation of significant differences (ESD).
-- The P&T system operated at an average extraction rate of 563 gpm.
-- By May 2001, concentrations for organic contaminants (except benzene and trimethylbenzene) had decreased to below cleanup goals, based on results for samples collected from 14 wells located on- and off-site. Arsenic, barium, iron, and manganese continued to be detected in groundwater at concentrations above the cleanup goals.
-- As of October and November 2001, elevated concentrations of organic contaminants were present, primarily in one well. Trimethylbenzenes were present in two wells, with concentrations as high as 670 µg/L.
-- As of November 2001, arsenic, barium, and manganese were present in several monitoring wells at levels as high as 14.9, 997 µg/L, and 3,780 µg/L, respectively.
In Situ Bioventing
-- The system operated with an air injection rate of 270 to 320 scfm and targeted 3 separate areas of the site (Areas A, B, and C).
-- In situ bioventing resulted in aerobic soil conditions, as evidenced by a steady increase in oxygen concentrations at the site, to levels as high as 21 percent. Carbon dioxide concentrations decreased from an average of 10 percent to less than 1 percent, and average methane concentrations decreased from 1.4 to 0.1 percent.
-- The average hydrocarbon degradation rate was estimated to be 1 milligram per kilogram per day (mg/kg/day) in Areas A and B and 0.5 mg/kg/day in Area C.
-- The total mass of hydrocarbons removed was estimated to be 7,780 kilograms (kg) from Area A; 11,000 kg from Area B and 1,247 kg from Area C.
-- The results of the December 2002 and April 2003 sampling events showed that the oxidation-reduction potential (ORP) ranged from 87 to 190 millivolts (mV), indicating that reductive dechlorination may be occurring. Concentrations of dissolved oxygen ranged from 0.23 to 7.07 milligrams per liter (mg/L), indicating aerobic conditions in the groundwater.
-- As of April 2003, two organic contaminants, trimethlybenzenes and methylene chloride, remained at concentrations above their respective cleanup goals. In addition, two inorganic compounds, iron and manganese remain at concentrations above their respective cleanup goals.
-- Monitoring for natural attenuation continues at the site.
-- Operation and maintenance (O&M) costs for the P&T system before the system was shut down (for 1998 through 2001) were about $200,000 per year including groundwater extraction, wastewater treatment plant O&M, sampling and monitoring, monitoring well maintenance, and reporting. After system shutdown, O&M costs were about $60,000 per year for 2002 and 2003.
The Onalaska Municipal Landfill Superfund Site is located in Onalaska, Wisconsin and was originally used as a sand and gravel quarry from the early to mid-1960s. In the mid-1960s, the Town of Onalaska began using the site as a landfill for both municipal and chemical wastes. Landfill operations stopped in September 1980, and the landfill was capped in June 1982. Subsequent investigations found elevated levels of VOCs and metals in a groundwater plume that extended at least 800 feet from the southwestern edge of the landfill and discharged to nearby wetlands and the adjacent Black River. The aquifer beneath the landfill served as the primary source of drinking water for the residents in the area. In addition, soils above the groundwater table and adjacent to the southwestern edge of the landfill were contaminated with petroleum solvents.
The site was placed on the National Priorities List in September 1984 and remedial investigations were conducted in 1988 and 1989. A record of decision (ROD) was signed in August 1990, which specified a P&T system for groundwater and in situ bioventing for soils. The P&T system operated from June 1994 through November 2001 and was designed to remove VOCs and metals. In situ bioventing operated from May 1994 to February 1997. In 1998, as part of the first 5-year review, EPA concluded that bioventing was no longer affecting biodegradation, and the system was shut down. Based on confirmation of oxygen levels in soil gas, EPA determined that the bioremediation cleanup phase was completed. An ESD was issued in November 2001 that allowed for the temporary shutdown of the P&T system to evaluate the effectiveness of MNA, based on the long-term groundwater monitoring that was being conducted at the site. Monitoring of natural attenuation at the site is ongoing.
Operation and maintenance (O&M) costs for the P&T system before the system was shut down (for 1998 through 2001) were about $200,000 per year including groundwater extraction, wastewater treatment plant O&M, sampling and monitoring, monitoring well maintenance, and reporting. After system shutdown, O&M costs were about $60,000 per year for 2002 and 2003.