Pump and Treat of Contaminated Groundwater at the Twin Cities Army Ammunition Plant, New Brighton, Minnesota

Site Name:

Twin Cities Army Ammunition Plant


New Brighton, Minnesota

Period of

Status: Ongoing Report covers - 10/87 to 9/92


Full-scale cleanup (interim results)


Not Available

Groundwater Extraction followed by Air Stripping - 12 boundary recovery wells and 5 source area recovery wells - Air stripping plant designed to treat 2,900 gal/min; 4 towers - 2 : 7 feet diameter and 2 : 8 feet diameter; all 36 feet tall with propylene packing - Treated water discharged to a sand and gravel pit, or, alternately to an elevated tank - Designed for an operating life of 30 years

Cleanup Authority:
CERCLA - ROD Date: 10/88

SIC Code:
9711 (National Security)
Point of Contact:Remedial Project Manager Twin Cities Army Ammunition Plant New Brighton, MN

Chlorinated Aliphatics - Contaminants of greatest concern in the groundwater are: 1,1-DCE, 1,1- DCA, 1,2-DCE, chloroform, 1,1,1-TCA, TCE, and PCE - TCE is the most prevalent VOC on site, with concentrations greater than 10,000 ppb in groundwater

Waste Source:
Other: Variety of Waste Disposal Practices, including Discharges to Sewer, Dumping, and Burning

Type/Quantity of Media Treated:
Groundwater - Over 1.4 billion gallons of water pumped from 10/91 to 9/92 - Complex hydrogeology and heterogeneities in a multilayer aquifer system - Fractured bedrock and discontinuous sand, clay, and till layers - Hydraulic conductivity 0.001 to 137 ft/day; transmissivity 3,160 to 28,724 ft2/day

Purpose/Significance of Application:
Pump and treat of large-volume of groundwater contaminated with VOCs.

Regulatory Requirements/Cleanup Goals:
- Several RODs apply to overall TCAAP remedial program, including a ROD for groundwater remediation - Target cleanup criteria focus on residual levels of contamination in groundwater and containment of existing plume - Target cleanup levels in groundwater include: TCE - 5 ppb; PCE - 6.9 ppb; 1,2-DCE - 70 ppb; and 1,1,1-TCA - 200 ppb

- Boundary Groundwater Recovery System (BGRS) recovered an average of 23 pounds of VOCs per day - TCAAP Groundwater Recovery System (TGRS) recovered 19,510 pounds of VOCs in one year of operation - Historical total of 92,700 pounds of VOCs recovered in 6 years of operation (BGRS and TGRS) - Plume containment successful at site - VOC plumes changed little after several years of treatment; estimate of remediation time increased to achieve a concentration of 17 ppb TCE in 50 to 70 years

Cost Factors:
- Capital costs - $8,034,454 (including construction of treatment plant, wells, force main and pump houses, startup, engineering, and project management) - Annual operating costs - $588,599 (including power, labor, maintenance, laboratory charges, and replacement of tower packing) - Total Life Cycle Costing estimated as $0.30 per 1,000 gallons of water treated - Total cost of operation and maintenance calculated as $0.12 per 1,000 gallons of water treated

The Twin Cities Army Ammunition Plant, established in 1941, has been used for the production and storage of munitions. The site includes 7 major production buildings and over 300 auxiliary buildings. A series of hydrogeological investigations beginning in 1981 revealed elevated levels of VOCs in groundwater; 14 separate source areas have been identified at the site. Trichloroethene (TCE) has been measured at concentrations over 10,000 ppb in the groundwater. Target groundwater cleanup levels were established for four constituents - TCE, PCE, 1,2-DCE, and 1,1,1-TCA.

Groundwater extraction followed by air stripping has been used at this site since October 1987 to treat contaminated groundwater. The groundwater extraction system includes 12 boundary recovery wells and 5 source area recovery wells. Extracted groundwater is treated using four 36-feet tall air stripping towers. An estimated 92,700 pounds of VOCs have been recovered in 6 years of system operation. Although plume containment has been successful at the site, the plumes have changed little after several years of treatment.

An estimate of the time required for remediation has been revised from 30 years to 50 to 70 years, based on a review of data collected to date. Capital costs for this application were $8,034,454, and annual operating costs are $588,599.