The ongoing environmental cleanup of an old mine is costing too much to maintain, and those responsible are seeking a way to cut costs.
Mining brought the masses to the Mother Lode, but it was often an environmentally unfriendly process and water quality paid the price in the 1930s and ’60s, when a dam near Campo Seco was breeched and the polluted water from the Penn Mine leaked into the Mokelumne River.
The mine was in operation from the 1860s to the 1950s to retrieve copper and zinc ore. After property owners abandoned the project , the East Bay Municipal Utilities District acquired the land and the responsibility of dealing with the highly acidic waste rock.
Poisoned water from the mine tailings used to kill fish in in the Mokelumne River and Camanche Reservoir and vegetation along the hillside above.
“They (the previous owners) were ordered to clean up by the regulators (the California Water Resources Control Board), but they never did it. They were completely nonresponsive,” said Derrick Lee, an environmental and health specialist with EBMUD. “They deposited a lot of waste and it was washing down into the river, causing fish losses.”
To fix this problem, the EBMUD paid $16.5 million to clean up the area in the late 1990s. The strategy was to bury the contaminated waste rock in a landfill wrapped in a plastic “geo-membrane” and bury it under a hill. Since then, rainwater has been absorbed into the hill. After being exposed to the waste rock, the water becomes toxic and builds up at the bottom of the landfill in a basin. It must be removed before it spills out of the enclosure.
“They have sumps to collect the leachate (contaminated water) and ways of removing it” from underground, said Robert Busby, supervisor of mines program at the California Water Resources Control Board.
The landfill was supposed to be the final measure taken to safely house the toxic waste, but with the growing amount of toxic water collecting below the landfill, new action needs to be taken.
“The leachate volumes spike immediately after rainfall events indicating a significant source of surface water into the landfill,” read a resolution passed by the water control board. “Leachate buildup on the landfill liner system is a threat to underlying groundwater quality and leachate is periodically removed from the landfill sump, however, no groundwater impacts have been detected in the monitoring wells to date.”
The issues arose when more leachate than expected dripped through the landfill, causing engineers to believe that the plastic “geo-membrane” that enveloped the 350,000 cubic yards of waste rock had been breached.
“There is some of the water around the edge of the landfill,” Busby said. “The top cover did not seal with the bottom so some of the rain runoff was infiltrating with the waste. There are some gaps in the cover.”
Shaw Environmental was contracted to remove the collected wastewater from beneath the landfill, but the leaking membrane caused it to make more trips than expected. Keeping the water levels down was costing Shaw and EBMUD more money than expected. The decision was made to reseal the geo-membrane surrounding the landfill.
“There is not too much of a danger of contaminated water,” Busby said.
The work to reseal the mine started Aug. 26, and is expected to be completed within 10 weeks, according to EBMUD Spokeswopman Andrea Pook. The job will cost about $1.2 million – to be split between EBMUD, the California Water Resources Control Board and Shaw Environmental.
“The first company (EBMUD hired) designed and constructed the landfill and they went bankrupt and the work was acquired by another entity who also went bankrupt,” Pook said. “So this is the third company that’s taking its share of the responsibility.”
“When you think about the legacy idea on a micro scale, the contracting party ends up working on something those two companies before it had done,” she continued. “We as a society are here trying to correct mistakes of (miners) that came before us. There were a lot of mistakes made back on those days and there were environmental costs that we’re paying for now.”
Shaw Environmental will be paid to uncover the landfill, rewrap and seal the geo-membrane, cover the landfill back up and carve drainage ditches atop the landfill to minimize the amount of water that could potentially enter the landfill.
“Once you have it sealed off, it’s like a tomb,” Busby said.