Ore Hill - Summer 2006 Site Work

Ore Hill site map.

 

Ore Hill site plan. Click plan for enlarged image.

Overall plans called for the excavation of 21,400 cubic yards of mine tailings (tailings area) and waste rock (waste rock area), treatment of this material with a phosphate-based method to greatly reduce metals dissolving out of the material in the future (treatment area), and the placement of the treated material in an on-site repository (repository area). (See photo galleries of these areas from links at right. You can also view a pre-work topographic map or a post-2006 work topographic map of the area.)

Timeline

February 2006: The contract for the 2006 CERCLA Removal Action was awarded to ECI Northeast.

April 9: Removal action-specific water quality monitoring started at 16 locations; continued, with some added locations, until suspended by weather in January 2007. Monitoring was done through a partnership between the Center for the Environment at Plymouth State University and the White Mountain National Forest.

Mid-May 2006: Actual on-site work started with clearing of the excavation area and the repository site, and construction of temporary roads on site, including the 500' haul road from the excavation and treatment area to the repository.

June 7: Phosphate-based chemical treatment of the excavated tailings and waste rock materials started with 100-cubic-yard pilot tests on Wednesday June 7, 2006.

Once treated, materials were hauled to the repository area and stockpiled while testing was completed. Once the material passed the treatment test, it was placed at the repository.

Materials were tested to meet stringent standards established for the treated tailings and waste rock; the test is called the “Multiple Extraction Procedure” or “MEP” test. The MEP test was initially designed by the Environmental Protection Agency to simulate whether municipal landfills would leach or release metals over long periods (100-1000 years) of acid rain exposure. A sample is subjected to simulated acid rain events over a ten day period, so each test takes about two weeks to conduct. The Ore Hill contract required an MEP test for every 500-cubic-yards of treated material. Passing the MEP test gives the Forest Service and the State confidence that the treated materials should not release significant hazardous metals for hundreds of years.

On June 15, the contractor began moving the secondary tailings pile on east edge of site to form the main treatment pad in excavation area. Subsequent surveying indicated that 3,032 cubic yards had been removed from the secondary tailings pile.

By June 20, the waste rock pile was being excavated and treated; by the end of the day Friday June 23, a total of 2,900 cubic yards had been processed and stockpiled at the repository area.

By July 7, an estimated 5,000 cubic yards had been treated and stockpiled in 500-cubic-yard piles at the repository area. By July 10, the approximate volume excavated, treated, and stockpiled was 6,000 cubic yards. By July 14, an estimated 9,000 cubic yards had been treated and stockpiled. Note that the in-place volume of the material expanded by approximately 20% due to excavation and treatment, so the volume of material stockpiled was approximately 120% of the volume of material that had been excavated.

On July 18, excavation in the waste rock area was completed. Subsequent surveying indicated that 8,452 cubic yards had been removed from the waste rock area.

On July 19, to assure effective treatment, the dosage of chemical used to treat the tailings was increased. Ongoing testing had indicated a slightly different mix of chemical was needed to meet treatment standards for the tailings. The treatment chemical is a commercially available product marketed under the name Enviroblend .

By July 25, it had become apparent that more material than planned was being excavated and treated from the tailings area. Bedrock in the lower portion of the excavation area was deeper, and so tailings deposits were thicker, than concluded from previous site investigation work. Previous estimates had been 4-6 feet of tailings, and up to 15 feet of tailings were encountered.

As of August 1, an estimated 24,500 cubic yards (uncompacted) had been moved to the repository area, and approximately 1/4 to 1/3 of the excavation area had not been addressed. Some samples of fine-grained tailings material being excavated taken at this time contained lead at 26,000-29,000 parts per million (or ppm), and zinc at 9,100 to 32,000 ppm. 10,000 ppm equals 1 percent, so these samples had a combined 3.5 to 6% lead and zinc.

On August 8, excavation work was stopped as the project funds were projected to have been exhausted due to the additional volume of excavation. Fortunately, assurance of further funds from the Department of Agriculture was received, and excavation and treatment work resumed on August 9.

By August 11, all excavation on site, aside from road and treatment pad areas, was completed, and excavation, treatment, and hauling of the treatment pad area had started.

As of Thursday, August 28, excavation of the tailings area and treatment pad was complete, leaving 900 cubic yards of material in the haul road across the site to be excavated, treated, and taken to the repository. Work was stopped and equipment was moved off-site awaiting results of testing for all treated materials.

On September 25, work resumed and equipment was brought back to the site. All treated piles passed the treatment performance tests and were ready for placement and compaction in the repository.

By October 2, fill (capping material) was being hauled and placed on top of compacted treated material in the repository. The final surveyed volume of tailings and waste rock excavated, treated, and hauled to the repository was 35,992 cubic yards.

By October 13, fill on the repository had been spread, tracked in, and rolled. Began hauling loam to repository for top layer of repository cap.

By October 20, thirteen check dams sites were laid out in the tailings excavation area. Initial plans had called for removal of all soil and mine waste material down to solid bedrock, with spray treatment of minor residual areas where material could not be excavated, but this proved impractical. Two to four inches of residual material were left on bedrock in the majority of the excavation area, and the contract was changed to spray treat the entire excavation area to minimize future dissolution of hazardous metals out of the residual material. The contract was also changed to add check dams in the excavated area to slow surface water flow across excavation and reduce erosion. Loam was spread on the repository in preparation for seeding/mulching.

October 23: Heavy rains over the weekend caused considerable damage to the repository cap. Loam and select fill were washed down burying the silt fence in some areas. Part of the road to the repository washed out.

By October 27, repairs to the repository cap and road had been completed, and liquid slurry spray treatment of the excavated areas with phosphate mix (Enviroblend 80/20) was started.

On Monday October 30, treatment in excavation area with phosphate slurry continued. The repository cap held up well during heavy weekend rains. Hydroseeding and mulching with an anti-erosion product (Flexterra Flexible Growth Medium) followed the phosphate spray treatment.

October 31: First post-excavation water quality monitoring data for pH and metals in surface water downstream of the site showed improvement (monitoring status). Data from samples collected in November, December, and January appear to confirm improving water quality. pH downstream of site averaged about 4.1-4.2 from April to mid-October; four pH readings from October 31 to early January averaged about 6.2. Monitoring will resume in Spring, 2007.

By November 2, spray treatment with phosphate slurry was completed, samples were collected for treatment confirmation analysis, and hydroseeding and application of Flexterra of the repository and excavated area was initially completed. A native wildflower and winter rye seed mix was applied to the repository, and a different seed mix was applied to the excavation area. The phosphate-based spray treatment raised the pH of the treated material, so a seed mix tolerant of higher pH was used on the excavation areas. The seed and Flexterra mix was sprayed on by a truck-mounted nozzle, and was dyed blue to aide the site workers in seeing where it is applied; the blue quickly faded when the material was exposed to sunlight.

On November 3, results from spray treatment analysis indicated that four areas required re-treatment.

By November 15, the removal action was completed except for some minor debris removal which occurred in December.



Highlights