U.S. flag

An official website of the United States government

Dot gov

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

HTTPS

Secure .gov websites use HTTPS
A lock () or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Des Moines TCE Southern Pond Area Removal

 
Site Contact:
Tim Curry
OSC

(curry.timothy@epa.gov)

Site Location:
200 SW 16th St.
Des Moines, IA 50309
epaosc.org/DesMoinesTCESouthernPondAreaRemoval

The site is near the south west corner of the central downtown business district of Des Moines on the east side of a bend in the Raccoon River. In all, the site encompasses more than 200 acres of which the southern pond surface water feature makes up approximately 5 to 10 acres. Former business/manufacturing at the site have included a variety of operations including steel wheel manufacturing, chemical herbicide distribution, and pesticide formulation/distribution processes. Hazardous substances known to have been released at the site include the following: TCE, 1,2-dichloroethene (DCE), and vinyl chloride (found in groundwater); residual pesticides, dioxins, polychlorinated biphenyls (PCBs), and metals (found in shallow soils); and pesticides, dioxins, and PCBs within building construction materials. The site was listed on the NPL in September 1983.

EPA sampling in June 2016 and May 2018 detected aldrin, dieldrin, chlordane, p,p’-Dichlorodiphenyldichloroethane, p,p’-Dichlorodiphenyldichloroethene and p,p’-Dichlorodiphenyltrichloroethane in sediments and nearby soils above ecological screening values.  The zoning in the area has been changed to permit commercial and mixed-use residential redevelopment.  It is anticipated the site itself will be redeveloped for a use that significantly broadens the potential receptor population. The change in ownership and property use prompted the collection and analyses of samples of the south pond sediments for a re-evaluation of human health and environmental threats. 

Analytical results from sediment samples collected at ten locations in the pond and its outflow feature found elevated levels of the following contaminants aldrin, dieldrin, chlordane, 4,4-DDD, 4,4-DDT, 4,4-DDE. Analytical results from surface water samples collected in the SPA found elevated levels of dieldrin. These results establish that releases of hazardous substances as defined by section 101(14) of CERCLA have occurred and have migrated to the SPA. The releases to the SPA are uncontrolled and may migrate further by sediment transport to the drainage ditch leading to the river during flooding events. 

 

Removal Action Completion

Prior to pond removal a leak of the public drinking water was discovered.  Investigation lead to identifying a leak in the City of Des Moines main supply line.  This leak was causing a flow of 50 gallons per minute to the pond from through the on-site subsurface drainage system.  The removal was put on hold until repairs to the main water supply line could be completed.  Pond sediment removal and disposal progressed in three phases.  The first phase was to pump down the water level in the pond.  This was accomplished after review and approval of the discharge plan from the responsible state authority.  Due to the low solubility of the contaminants the concentrations were very low in the pond water.  The state reviewed the operational plan and permitted discharge of pond waters to the drainage way from the site.  The discharge operation included filtering to prevent any contaminated solids to be released with the pond water.  Once the pond was pumped down the on-site outlets from the subsurface drainage to the pond were hydro-flushed and the material collected for additional solids settlement and disposal.  The next phase was to remove embankment and pond bottom sediments in three segments starting with the upper segments ending with the segment at the closest to the pond dewatering operations.  Backfilling the excavated areas with a foot of clean fill was completed in each segment prior to moving to the next segment to ensure no potential for residual contaminants to migrate.  Once all segments had been backfilled the pond dewatering operations ceased and natural precipitation accumulation refilled the pond.  Due to the heavy truck traffic on the asphalt contaminant cap near the pond those areas that had accumulated significant integrity damage were resurfaced with three inches of new asphalt.