Pump and Treat of Contaminated Groundwater at the Des Moines TCE Superfund Site, OU 1, Des Moines, Iowa

Site Name:

Des Moines TCE Superfund Site

Location:

Des Moines, Iowa

Period of
Operation:

Status: Ongoing
Report covers: 12/87 - 10/96

Cleanup
Type:

Full-scale cleanup (interim results)

Vendor:

Tonka Equipment Company

Technology:
Pump and Treat
- Groundwater is extracted using 7 wells, located on site, at an average total pumping rate of 1,041 gpm
- Extracted groundwater is treated with air stripping and discharged to a surface water under a NPDES permit

Cleanup Authority:
CERCLA Remedial
- ROD Date: 7/21/86

Point of Contact:
Mary Peterson, RPM
U.S. EPA Region 7
726 Minnesota Avenue
Kansas City, KS 66101
(913) 551-7882
Additional Point of Contact:
None

Contaminants:
Chlorinated solvents
- Maximum concentrations detected during 1985 RI included TCE (8,467 mcg/L), 1,2-DCE (2,000 mcg/L), and vinyl chloride (95 mcg/L)

Waste Source:
Land application of waste sludges, including use of waste sludges on road surfaces for dust control

Type/Quantity of Media Treated:
Groundwater
- 4,900 million gallons treated as of December 1996 - DNAPL suspected in groundwater at this site
- Groundwater is found at 10-25 ft bgs
- Extraction wells are located in 1 aquifer, which is influenced by a nearby surface water
- Hydraulic conductivity reported as 535 ft/day

Purpose/Significance of Application:
Met goals for off-site plume within two years of operation; nearly five billion gallons treated.

Regulatory Requirements/Cleanup Goals:
- The cleanup goal for this site is to reduce the TCE concentration in groundwater on the west side of the Raccoon River to 5 mcg/L or less for four consecutive months. At this time, on-site goals have not been specified.
- As a secondary goal, the remedial system is designed to create an inward gradient toward the site to contain and treat the on-site plume.

Results:
- The pump and treat system met the cleanup goal for TCE within two years of system operation, and an inward hydraulic gradient appears to have been achieved within the first month of operation that encompasses the entire contaminant plume. Pumping continued after that time to maintain containment and provide for potential reductions in contaminant concentrations in on-site wells. However, on-site wells continue to show concentrations of TCE at greater than 5 mcg/L.
- By February 1997, the pump and treat system had removed nearly 30,000 pounds of contaminants from the groundwater.

Cost Factors:
Estimated costs for pump and treat were $2,596,000 ($1,587,000 in capital and $1,009,000 in O&M), which correspond to $0.53 per 1,000 gallons of groundwater extracted and $80 per pound of contaminant removed.

Description:
An iron foundry operated on this property from approximately 1910 until Dico Corporation purchased the property in the early 1940s. Dico manufactured metal wheels and brakes at the site from 1961 through 1993. In September 1976, testing by the DMWW and EPA detected TCE in the city's north gallery groundwater infiltration system, which served as a source of drinking water for the city. Investigations by EPA suggested that solvent sludges used on road and parking lot surfaces could be the cause of the subsurface contamination. The site was placed on the NPL in September 1983 and a ROD was signed in July 1986.

The groundwater extraction system consists of seven wells installed in the plume east of the Raccoon River on the Dico property to a depth of 40 ft. These wells were designed for full containment and partial aquifer restoration (to achieve off-site groundwater goals). Extracted groundwater is treated using an air stripper and discharged under a NPDES permit. The pump and treat system met the off-site cleanup goal for TCE within two years of system operation, and plume containment appears to have been achieved.