EPA ID# IDD081830994
EPA Region 10
Caribou County
Soda Springs

2nd Congressional District

Other Names:
Last Update: September, 2007

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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.

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