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Record of Decision System (RODS)

PERHAM ARSENIC SITE

Abstract

Site Name:  PERHAM ARSENIC SITE
Address:  SOUTH CO RD 8 
City & State:  PERHAM  MN  56573
County:  OTTER TAIL
 
EPA ID:  MND980609572
EPA Region:  05
 
NPL Status:  Currently on the Final NPL
 
ROD Type:  Record of Decision
ROD ID:  EPA/ROD/R05-94/247
ROD Date:  03/31/1994
Operable Unit(s):  01
 
Media:  groundwater
 
Contaminant:  Arsenic
 
Abstract:  Please note that the text in this document summarizes the Record of Decision for the purposes of facilitating searching and retrieving key text on the ROD. It is not the officially approved abstract drafted by the EPA Regional offices. Once EPA Headquarters receives the official abstract, this text will be replaced.

The Perham Arsenic Burial site is located in Perham, Minnesota. Adjacent properties are zoned for community and recreational purposes. Potable water is supplied to the City of Perham by a municipal well system. A total of four municipal wells are used to supply the residential and commercial demands. Two wells are located in the southern section of the city, approximately one-half mile west of the site. The other two wells are approximately one-half to three-quarter miles north of the site. The site is currently inactive.
During the grasshopper infestation of the 1930s and 1940s, the US Department of Agriculture distributed lead arsenate for use as grasshopper bait to several counties in the state of Minnesota. In order to form bait, technical grade lead arsenate was mixed with sawdust and molasses. The bait was dispersed around farm fields to prevent crop loss. The East Otter Tail County Fairgrounds in Perham, Minnesota was a mixing station for the bait. In 1947, lead arsenate and unused grasshopper bait were buried in a shallow pit in the southwest corner of the fairgrounds. It is reported that between 200 and 2,500 pounds of grasshopper bait containing over 50 pounds of technical grade lead arsenate is thought to have been buried in the pit in burlap bags, wood or other decomposable material.

The following chronologically summarizes the history of the subject site:

In 1971, the Hammers Construction Company (HCC) purchased the land from the city and erected an office and a construction warehouse adjacent to the pit. In 1972, a 31-foot deep, 1. 25-inch I.D. galvanized steel well was installed for HCC. In June, 11 employees became sick due to drinking water from the well. Two employees suffered permanent effects. In July, water samples were collected for arsenic analysis from Hammer's well and seven private wells within 120 to 1000 feet of the Hammers' building, and three municipal wells within one-half mile of the subject site. The maximum arsenic concentration found was in Hammers' well at 11,800 parts per billion (ppb). The well was capped. In August, the Minnesota Department of Agriculture collected soil samples at the site. Analytical results detected arsenic concentrations up to 12,600 ppb. In October, the Minnesota Department of Agriculture collected additional soil samples at the site to further define the extent of buried arsenic. In 1980, EPA began soil sampling and monitoring well installations. Investigation discovered arsenic-contaminated ground water to have extended 600 feet downgradient east of the source. Elevated levels of soil contamination were found in a 15 by 40 foot area north of HCC's property and well. In 1982, the burial pit was capped with a clay cover to reduce the amount of rainwater infiltration. In 1984, the Minnesota Pollution Control Agency (MPCA) completed the first Remedial Investigation/Feasibility Study (RI/FS) for the site and the following remedial action was proposed and implemented in 1985: 1) Excavation of approximately 200 cubic yards of arsenic wastes and contaminated soils containing greater than 500 parts per million, with subsequent disposal at an approved hazardous waste disposal facility. 2) Backfilling the excavated pit with clean fill material. 3) Reestablishment of the clay cap and impermeable membrane to minimize leaching of any residual arsenic. 4) Continuation of ground-water monitoring until levels of arsenic in the monitoring wells fell below the federal drinking water maximum contaminant level of 50 micrograms per liter. After completion of this initial remedial action ground water was expected to attenuate. Ground-water monitoring has continued on a semi-annual basis to the present. In 1989, the Agency for Toxic Substances and Disease Registry, US Public Health Service recommended a post-remedial sampling of the ground water to define the extent of the arsenic plume. Because arsenic concentrations in ground water did not significantly decrease, as assumed at the time of the 1985 remedial action, EPA developed a RI/FS Work Plan to define the extent of the arsenic plume, and determine whether residual soil contamination remained. In 1992 through 1993, EPA conducted a two phase Remedial Investigation of the site, which included the installation of 25 monitoring wells and 12 soil borings.

This ROD addresses 0perating Unit 1, arsenic-contaminated ground water at the site. The RI/FS conducted in 1992/1993 was designed to determine the present extent and movement of arsenic contamination in the ground water and whether residual levels of arsenic contamination were present in the soil. The 1992/1993 RI/FS concluded that arsenic is present in the ground water at concentrations ranging from below the detection limit, of 2 parts per billion (ppb), to 1260 ppb within a 600 by 400 foot plume. The vertical extent of contamination is approximately 85 feet below grade.

The remedy status for the media addressed in this ROD are as follows: Groundwater 1 is Final Action. The media associated with this site has a volume of 20,400,000 Acres. The state concurs with the selected remedy.
 
Remedy:  The selected remedial action includes implementing institutional controls, in the form of a deed restriction, to restrict ground water use at the site; removing arsenic-contaminated ground water above the clean up level of 50 ppb using a continuous-backwash filtration unit; treating ground water, on site, by activated alumina adsorption units. Disposing of the used alumina filter media and filtered solids; discharging treated effluent to the aquifer through an on-site infiltration gallery; and providing municipal water to a resident. The overall Present Worth costs are $2,548,776. The annual O&M costs are $217,805 (Year 1 to 6).
 
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