The Goldstrike is one of six major gold mines that are dewatering aquifers along the Humboldt River, where at least four big gold mines are planned. Six smaller gold and silver mines have also tapped groundwater in the basin site of the largest gold mining boom in the United States (HCN, 10/2/94).
As miners dig deeper into the ground, pumps draw the water table down into a funnel shape, forming a dry area known as a "cone of depression." In theory, pumping drains a limited and predictable area. In practice, dewatering can dry up hundreds of square miles of land and suck water from neighboring aquifers.
Mining companies say the aquifers will recover once the pumping stops. The open pit mines will fill with water, creating more than a dozen new lakes in the sage-covered hills and valleys that drain toward the Humboldt River. Meanwhile, miners say, workers are monitoring the effects of dewatering, compensating other water users for any losses, and making up for any damage to springs and streams by creating new wetlands with the pumped water.
The Sierra Club's Nevada field representative, Elyssa Rosen, however, says no one can accurately forecast the long-term consequences of the current gold boom because neither the mining companies nor the Bureau of Land Management, which permitted the mines, has studied the cumulative impact of this unprecedented dewatering.
Mining companies have pledged funding for a major study of dewatering by the U.S. Geological Survey, but that study will take at least two years to complete. In the meantime, the only thing approaching a comprehensive study of dewatering in the Humboldt Basin was commissioned by the Sierra Club.
It asked University of Nevada hydrologist Tom Myers to review all mine pumping permits at the state engineer's office. Myers concluded that by the time all the current mines in the area shut down after a projected life of some 30 years, they will have created a groundwater deficit of around 1 million acre-feet.
Myers says that although flows in the river might increase while the pumps are bringing water to the surface, dewatering is creating a deficit that may siphon off as much as two-thirds of the Humboldt's annual flow when pumping stops.
"The important thing to point out is that there is 1 million acre-feet to refill," he says, "and the annual flow at Winnemucca is only 150,000 acre-feet." Myers emphasizes that his estimate is conservative and does not include major mine expansions. He concludes that not enough is known about the groundwater hydrology of the basin to allow dewatering on such a scale.
Nevada's top water official, state engineer Mike Turnipseed, disagrees. He says mining companies have a good understanding of the hydrology of the Humboldt Basin and update their models of dewatering impacts four times a year. The state considers dewatering a temporary problem that will naturally be solved in the future.
Miners also downplay the problem. They say the mines are using the best available technology to monitor dewatering impacts. Barrick manager John McDonough says his company closely monitors groundwater levels near dewatering sites and complies fully with state and federal regulations. "In our case," McDonough says, "the fact that we have regular review meetings with the state engineer, the BLM, and the U.S. Fish and Wildlife Service leads to the best solutions possible."
Groundwater models, however, often prove inaccurate. Barrick, for instance, first estimated that dewatering at the Goldstrike mine would require pumping 28,000 gallons a minute. Within two years, the mine was pumping more than twice that amount.
For the mining companies and the BLM, mitigation is the solution. The BLM's mitigation plan for the expansion of Newmont's Gold Quarry mine, for instance, is as thick as the mine's environmental impact statement and provides for the preservation of nearly 2,000 acres of wetlands and riparian areas, some natural, others artificial. Under the plan, some springs and streams within the mine's cone of depression will depend on wells drilled nearby, while others will go dry. Wetlands will be created for the springs and streams that will be lost, the plan states. However, these wetlands will go dry after pumps are shut off.
Dean Rhoads, a state senator and rancher from Elko County, says that ranchers and farmers stand to lose big if dewatering is not carefully regulated. Rhoads says he is alarmed by the rate at which gold mines are buying up agricultural land so that they can dewater the aquifers and "dry up the fields for 40 years." Rhoads worries that water rights bought from ranchers as compensation for dewatering will eventually be sold to metropolitan areas like Reno when the pumps are shut off.
So far, however, growing concerns about dewatering have not deterred gold miners' expansion plans. Newmont, for example, will soon be pumping up to 50,000 gallons of water a minute at its Gold Quarry mine. And Santa Fe Pacific's Lone Tree Mine plans to expand pumping to 70,000 gallons a minute and lower the water table over 800 square miles.
Tom Myers' report, The Hydrologic Effects of Open Pit Gold Mining in the Humboldt River Drainage, is available for $3 from the Sierra Club, P.O. Box 8096, Reno, NV 89507-8096.
* Ernie Thompson,
HCN Great Basin intern