EPA ID# IDD081830994
EPA Region 10
Caribou County
Soda Springs

2nd Congressional District

Other Names:
Last Update: September, 2007

Hide details for Site DescriptionSite Description

The operating area of the Monsanto Chemical Company (Soda Springs Plant) encompasses 540 acres and processes locally mined phosphate ore to produce elemental phosphorus. Surrounding the operating area are approximately 260 acres of buffer properties. All 800 acres (540 acres in the operating area and 260 acres in the buffer properties) have institutional controls in place to prevent future land-use that could result in exposure to hazardous constituents. The elemental phosphorous plant consists of over a dozen administrative and processing buildings plus ore piles, slag piles, by-product materials, surface impoundments and a waste landfill. The site, formerly agricultural land, was purchased by Monsanto in 1952. Ore is stockpiled on-site prior to being processed for introduction into electric arc furnaces along with coke and silica. All process waters, with the exception of non-contact cooling water, are held and treated on site and then reused. The non-contact cooling water is discharged from the site to Soda Creek, which is used in agricultural irrigation. Land use in the vicinity of the Monsanto facility is primarily industrial and agricultural. The plant is staffed with about 400 employees, and 3,300 residents live within 3 miles of the site. Most residents' water is supplied by the City of Soda Springs from springs unaffected by the plant. The closest surface water is Soda Creek, located approximately 2,000 feet west of the facility. Some nearby residents depend on domestic wells, but none are known to be in use for drinking water downgradient of the site.

EPA completed the first five-year review for the Monsanto Chemical Company (Soda Springs Plant) on September 30th, 2003. Below is the protectiveness statement included in the five-year review report:

"The remedy at the Monsanto Chemical Co. (Soda Springs Plant) currently protects human health and the environment because all known groundwater and soil exposure pathways have been restricted through institutional controls or other means. However, in order for the remedy to be protective in the long-term, the following actions need to be taken: 1) the Lewis well and property needs to be evaluated for institutional controls; 2) Monsanto needs to submit a plan for upgrading their wind dispersal program and for evaluating in the short term those localized areas where increased 226Ra soil concentrations have been observed; and, 3) the U.S. Environmental Protection Agency (EPA) needs to reevaluate during the next five-year review whether the monitored natural attenuation remedy underneath the operating area is proceeding as intended in the decision documents."

Site Responsibility: This site is being addressed through federal and potentially responsible parties' actions.

NPL Listing HistoryDates
Proposed Date:05/05/1989
Removed Date:
Withdrawal Date:
Final Date:08/30/1990
Deleted Date:

Hide details for Threats and ContaminantsThreats and Contaminants

Media Affected: Groundwater
Groundwater underlying the site and the surrounding vicinity is contaminated with cadmium, selenium, nitrate, and fluoride. A health threat may exist for individuals who use or come into direct contact with contaminated groundwater. Studies to date have confirmed that Soda Springs drinking water supplies are uncontaminated and have not been affected by the Monsanto site.

Soil - Soil in both the operating area and in the buffer properties have been conaminated with 226Ra. Some of the buffer properties were selected primarily to restrict use of contaminated groundwater, and some of the buffer properties were selected primarily to control exposure to 226Ra-contaminated soils. Some of the samples collected during the recent five-year review show that 226Ra concentrations have increased in some locations. Based on this finding, EPA will request that Monsanto reevaluate and/or redesign their procedures for managing on-site stock piles, which are subject to wind dispersal if not properly controlled.

Hide details for Cleanup ProgressCleanup Progress

In 1991, Monsanto agreed to an administrative order with EPA to perform the necessary Remedial Investigation Feasibility Study (RI/FS) and to pay EPA’s oversight costs. The RI/FS was completed in the Summer of 1996. Process wastes, previously stored in unlined ponds or impoundments, have been pinpointed as sources of contamination to the local groundwater. Groundwater underlying the site and the surrounding vicinity is contaminated with cadmium, selenium, fluoride and nitrate. Studies to date have confirmed that Soda Springs drinking water supplies are uncontaminated and have not been affected by the site. Contaminated groundwater is not currently used for drinking. Without treatment, the groundwater is expected to recover through natural attenuation within 25-30 years. Treatment would be expensive and would likely only marginally improve the recovery time.

During the recent five-year review, EPA learned that natural attenuation of cadmium underneath the operating area my be proceeding at a much slower rate than anticipated five years ago. Further, as already mentioned above, EPA has observed increased 226Ra concentrations surrounding the site. Despite these findings, EPA has concluded in the five-year review report that the remedy at Monsanto remains protective, but will need to be reevaluated both in the the short term (226Ra concentrations) and in the long term (groundwater natural atenuation during next five-year review). If conditions change, additional remedial action will be considered.

Monsanto has completed all construction activities related to implementation of the ROD issued in 1997, and thereby obtained Construction Completion status in 2000. Ongoing monitoring to demonstrate complaince with remedial action objectives in the ROD will continue indefinitely.

The first Five-Year Review was completed in June 2003. The next Five-Year Review is due September 30, 2008. Groundwater monitoring and offsite soil sampling are continuing at the site.

Hide details for Regional ContactsRegional Contacts

PHONE NUMBER:206-553-1849
PHONE NUMBER:208-378-5761
Information pertaining to this site is housed at the following location(s):
Soda Springs Public Library (Administrative Record)
149 South Main Street
Soda Springs, ID 83276

EPA Region 10 Superfund Records Center (Administrative Record)
1200 Sixth Avenue, ECL-076
Seattle, WA 98101