Ore Hill Site Work Under CERCLA, Including CERCLA Removal Action
(Note:The various reports below are contained in the Site Administrative Record, available for public review at the Pemigewasset Ranger District Office, Campton, NH.)
Work under the Forest Service's CERCLA authority began at the Ore Hill site with a “Preliminary Assessment,” or “P. A.,” conducted by White Mountain National Forest Hydrologist Joan Carlson in 2000. A “Site Inspection,” or “S. I.,” was conducted under contract in 2000 and 2001. A “Potentially Responsible Party Search,” or “PRP Search,” was also conducted in 2001 to attempt to locate any parties, such as past owners or operating companies, which could be held liable for the site: no such entities were located. Low-flow and high-flow water sampling was conducted, and the results presented in a “Site Characterization” report in 2002. This report contains the most site data assembled in any single document. Topographic surveying was also conducted, and a Forest Service CERCLA “On-Scene Coordinator” or “O. S. C.” was designated (Tim Buxton).
A draft final “Engineering Evaluation/Cost Analysis,” or “EE/CA,” was completed under contract in 2002, and was revised in 2003. The EE/CA looked at various alternatives to address the site, including:
- Remove tailings and waste rock material to a landfill
- Remove tailings and waste rock material for mineral reprocessing
- Excavate waste rock and place on tailings pile to reduce footprint of material, upgrade drainage around tailings, cut-off subsurface inflow to tailings, recap tailings
- Excavate waste rock and tailings, and place in new on-site repository, with or without chemical treatment to stabilize the metals in the material
The EE/CA recommended the alternative to excavate tailings and waste rock and haul to on-site repository area for treatment and disposal. The EE/CA also documented the State and federal “Applicable or Relevant and Appropriate Regulations,” or “ARARs,” that the Forest Service followed to the extent practicable during the removal action.
The EE/CA did not evaluate specific treatment options to reduce metals dissolution and outflow from the tailings and waste rock once in the repository, and did not evaluate potential on-site repository locations.
To address issues remaining following the EE/CA, a “Treatability Study” was completed under contract in 2004, and determined that treatment with Portland cement, or with various proprietary phosphate-based treatments, could significantly reduce the metals leaching from the tailings and waste rock materials when placed in the repository. Site work to locate and survey a favorable repository location, and needed cultural resources work, was also conducted following the EE/CA.
Later in 2004, the OSC completed an EE/CA Addendum to further evaluate the Portland cement and phosphate-based treatments. Although both approaches could be projected to offer very substantial reductions in metal concentrations in any water passing through the treated materials for a reasonable length of time (~50 years), the phosphate approach appeared to offer this level of reduction of leachate metals for a much longer term (~100-1000 years), with lower upfront construction cost, and lower long-term maintenance costs. The EE/CA Addendum recommended that proprietary phosphate treatment be used.
Subsequent to the EE/CA Addendum, a contract was let for construction design, with the intent to implement a CERCLA Removal Action in the summer of 2005. Work on the construction design and construction bid package was not completed in time to award the contract and complete the work in 2005, however. Further, bid protests also delayed award of the construction contract.
Major CERCLA Removal Action construction occurred during the 2006 field season.
Excavation of the tailings and waste rock from where they were continuously exposed to water seepage creating acid mine drainage, and placement of the material in the repository, was expected to reduce metals movement from the materials by an estimated 90%. Treatment of the tailings and waste rock with a phosphate approach was expected to reduce metals in waters passing through the reposited material by additional 95% for the long term (100+years), so an overall reduction of dissolved metals leaving the site of more than 95% was expected from the Removal Action. Monitoring data indicate that dissolved metals of concern have been reduced by approximately 80% as a result of the 2006 work.
In 2007, Plymouth State University (PSU) conducted a study for the Forest Service on the acid mine drainage from the adit (tunnel) that had been excavated in 2006, and other on-site surface waters. The report for this study is included in the 2007 Ore Hill Site monitoring report by Plymouth State University, issued in draft form in April, 2008, and accessible from a link on the monitoring page. The study was intended to learn whether the approximately one gallon per minute of adit drainage was the major remaining source of dissolved metals within the excavation area, and to supply data for a supplemental Engineering Evaluation/Cost Analysis (EE/CA). The data collected by PSU indicated that although the acidic water seeping from the adit contains high concentrations of aluminum, cadmium, copper, lead, and zinc compared to background water or State water quality criteria, water quality in this small drainage improves considerably before the flow from the adit reaches the “pit” area in the middle of the excavation. The study also indicated that other surface water within the excavation area is mildly contaminated with hazardous metals. Neither the acid mine drainage at the adit seep, nor the mildly impacted surface water within the excavation area, meet state water quality criteria.
The supplemental EE/CA evaluated several technologies to treat the acidic mine water draining from the adit as well as other mildly impacted surface water within the 2006 excavation area. As a result of the PSU study, the supplemental EE/CA focused on options for treating a larger volume of less contaminated water rather than a very small volume of highly contaminated surface water. Both the PSU study and the supplemental EE/CA are contained in the Site Administrative Record file.
The supplemental EE/CA and was completed in May, 2008. The report recommends a sulfate reducing bioreactor be constructed downstream of the adit seep in the pit area, near the center of the 2006 tailings excavation area, to treat the water and remove high levels of hazardous metals such as cadmium, copper, lead, and zinc. The report also recommends installing an open limestone channel to increase alkalinity of the water upstream of the bioreactor to the adit seep, building a settling pond, and constructing wetlands downstream of the bioreactor to further improve water quality.
The Forest Service installed a small-scale bioreactor as a treatability study/pilot project in August, 2008, to provide further data.
The Forest Service is making the EE/CA report public, and is seeking public comments on the recommendations in the EE/CA, now or during a formal 30-day comment period to be announced in the near future.