Atlantic Richfield Company
Butte, Montana

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Technical Impracticability Zone

What you should know

The TI Zone was established because removal of waste material within these areas and restoration of groundwater beneath had been determined by EPA to be technically impracticable and not cost effective.

The 2006 BPSOU ROD established a technically impracticable zone (TI Zone) for a portion of the ground water in the BPSOU. The TI Zone was established because removal of waste material within these areas and restoration of groundwater beneath had been determined by EPA to be technically impracticable and not cost effective. Resulting groundwater from this zone will be captured and treated to performance standards for surface water prior to its discharge to Silver Bow Creek. The Selected Remedy also requires that the contaminated plumes be prevented from migrating outside the established TI zone.

The Technical Impracticability (TI) Zone and the Controlled Ground Water Boundary Area (CGWBA) are shown in the map below. In the TI Zone ground water is not required to meet ARARs; however, surface water is required to meet ARAR standards throughout the site. This means contaminated BPSOU ground water must be prevented from discharging to Blacktail Creek and Silver Bow Creek in quantities or concentrations that cause exceedances of surface water ARARs.

For further information, visit our Reports and Publications page to download related documents.