Ore Hill - Site Monitoring

Update: September 2008

Improving water quality in Ore Hill Brook is a long-term goal of the Ore Hill Mine reclamation project. The White Mountain National Forest is partnering with the Plymouth State University (PSU) Center for the Environment to monitor water quality changes related to work at the site, including the major work done in 2006.

Specifically, we are monitoring surface water quality at the mine excavation area and downstream in Ore Hill Brook, and surface water and shallow ground water at the new repository at the site. Samples are being collected at about 30 locations on site and up to about a mile downstream (note that maps do not show all the sample locations). The samples are analyzed for more than 30 parameters, including standard field measurements, about 20 metals, and several anions such as chloride, sulfate, and phosphate. Prior to the major Removal Action in 2006, acidic seeps at the mine had very low pH levels and concentrations of several metals (aluminum, cadmium, copper, lead, and zinc) that far exceeded New Hampshire surface water quality criteria (see the Ore Hill Environment page, “Ore Hill area surface waters” data table). Downstream waters were toxic to aquatic life for at least a mile.

As expected, post-work data show significant improvements in surface water leaving the mine site compared to pre-work data. pH has generally increased to near the background level, and dissolved metals have decreased significantly. Zinc, lead, and copper are the metals of greatest concern in surface water, and while we are seeing approximately 80% reductions compared to pre-work levels, our goal is 95% or more reduction in these metals from the site. If 95% metal reductions at the mine site can be achieved, water quality further downstream could meet water quality standards. Data related to the repository do not appear to show negative impacts to date. Further work to improve surface water quality is being evaluated. Monitoring will continue at the site for at least the next several years.

pH is in standard units, and metals data are in parts per million or "ppm" (ppm also equates to milligrams/liter or mg/L).


Data in this graph in blue and red are from the “OHMT” data point just downstream of the tailings excavation area. This data point captures all the surface water coming off of the former tailings and waste rock areas, and data from samples taken further downstream have lower metals concentrations both before and after the Removal Action, and similar reductions in metals concentrations.

  • Blue data are an average of three samples taken prior to the Removal Action (in April 2006). 
  • Red data are the average of seven samples taken from the same point, after the Removal Action (from the end of October, 2006 to May 2007).
  • Yellow data are the average of more than 20 samples taken from Ore Hill Brook just above the input from the Site (upstream of data point OHMT”) from October 2006 to May 2007.

Note that the pH in surface water “before” the Removal Action (blue data) at the “OHMT” monitoring location was approximately 4.2; “after” the Removal Action (red data), the pH at this location has averaged approximately 6.2. Background pH (yellow data) in the surface water also averaged approximately 6.2.

Aluminum in surface water “before” the Removal Action (blue data) averaged 2.21 ppm, and has averaged 0.16 ppm (red data) since the end of October 2006. Aluminum in the background surface water (yellow data) averaged 0.07 ppm.

Copper in surface water “before” the Removal Action (blue data) averaged 0.23 ppm, and has averaged 0.06 ppm (red data) since the end of October 2006. Copper in the background surface water (yellow data - not seen on this scale) was approximately 0.00 ppm.

Lead in surface water “before” the Removal Action (blue data) averaged 0.35 ppm, and has averaged 0.08 ppm (red data) since the end of October 2006. Lead in the background surface water (yellow data - not seen on this scale) was approximately 0.00 ppm.

Zinc in surface water “before” the Removal Action (blue data) averaged 8.11 ppm, and has averaged 1.98 ppm (red data) since the end of October 2006. Zinc in the background surface water (yellow data - not seen on this scale) was approximately 0.03 ppm.

Surface water and ground water data from the area around the repository are insufficient to draw any firm conclusions at this time, but tentatively do not appear to indicate degradation due the placement of the treated tailings and waste rock in the repository.

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.

After the 2006 Removal Action

In 2007, in addition to continuing ongoing water quality monitoring, 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 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 early 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.