An independent scientific report produced by the Center for Science in Public Participation for United Tribes of Bristol Bay documents contamination at reclaimed Pebble prospect drill sites.
The report concludes that there may be long-term reclamation and maintenance issues at the copper, gold and molybdenum prospect near the headwaters of the Bristol Bay watershed. The report also notes that the Alaska Department of Natural Resources currently requires no reclamation plan and has exempted the Pebble Limited Partnership from reclamation bond.
While there is no widespread contamination, there are localized areas with elevated copper and other elements in soil and water, the report said. “About 10 percent of the sites inspected had fine-grained, oxidized drill cuttings around the casing or leading in a trail away from the casing. If these are flushing periodically, this suggests that either the holes were not cemented, or the cement has failed.”
Environmental geochemist Kendra Zamzow, who wrote the report with CSP2 president Dave Chambers, said her concerns included dead vegetation around settling ponds and wells that had been duct-taped, zip locked and sprayed with foam, but still had water slowly emerging from them. “They are supposed to, if they are not using them, cut them off below ground level after the hole has been completely cemented and grouted to be sure no water comes up,” she said.
The latest DNR field monitoring report, written in July and amended on Nov. 3, said that the mine operator had identified and addressed maintenance and repair issues on site consistent with industry best management practices.
According to state inspectors, 141 sites were inspected and 107 boreholes were observed to be in stable condition with no evidence of water or other instability, and that nine sites needed further investigation, but none posed a significant environmental or compliance risk.
The complete DNR report is online at http://dnr.alaska.gov/mlw/mining/largemine/pebble/field-reports/A166118_20160726_TripReport_FINAL.pdf