Khayyam Mine Engineering Evaluation/Cost Analysis
US Forest Service
Tongass National Forest, Alaska
Hart Crowser conducted an Engineering Evaluation/Cost Analysis (EE/CA) that included a CERCLA site investigation and risk assessment for cleanup alternatives and estimated costs to remediate waste rock, impacted surface water and sediment, and mine drainage for abandoned copper mine workings in the Tongass National Forest. The remote nature of the site added additional complexity, including the need to camp and use a helicopter to access the site and for logistical support.
Our work included collecting data to support a streamlined human health and ecological risk assessment, and complete an EE/CA to determine the extent of a potential removal action. Previous Preliminary Assessment/Site Inspection (PA/SI) soil sampling results indicated that metal concentrations exceeded state ecological risk-based concentrations. However, the benefits of a removal action would be mixed at best, since the former mine is located in a pristine area with significant ecological value. In order to develop a second line of evidence on potential aquatic impacts, Hart Crowser accomplished surveys of benthic macroinvertebrates over two seasons in both Omar Creek and adjacent reference watersheds.
Hart Crowser developed three primary alternatives for cleanup of the mine waste rock and impacted stream sediments, and compared these with a No Action alternative using CERCLA evaluation criteria. As part of the engineering evaluation, Hart Crowser estimated costs for sediment and waste rock removal actions, including permanent disposal in one or more on-site repositories and compared this to the cost for transport to a licensed Subtitle D landfill. Hart Crowser’s evaluation included the impacts of constructing an access road to accomplish the remediation as well as the effects of construction disturbance on the watershed.
INNOVATIVE TECHNOLOGY AND COST-SAVING MEASURES
We used the Rapid Bioassessment Protocol developed by EPA for control in sampling benthic invertebrates, to enable comparison of biologic conditions in impacted areas and reference reaches that were not impacted by the release of contaminants. Biologic sampling provides a useful second line of evidence in evaluation of hazardous substances that provides a more detailed understanding of the potential impacts of contamination compared to relying solely on contaminant concentrations in surface water and/or contaminant concentrations in stream sediments. The same techniques are applicable to other contaminated sites and are especially relevant where the potential adverse impacts of remediation (e.g., construction of access roads, filling wetlands, opening borrow sites, and landfill siting) would impact high-value wilderness or areas used for subsistence hunting and fishing.