CLEARLAKE OAKS >> A study by the U.S. Environmental Protection Agency (EPA) to limit the ongoing mercury contamination of Clear Lake is yielding “pleasing” results as it nears completion, but conclusive data to determine the ultimate success of the project won”t be available until the end of the two-year study in early 2015.
The study, which is part of the EPA”s remedial investigation of the Sulphur Bank Mercury Mine Superfund Site, has included the construction of two test covers, or caps, made of layers of sand and gravel at the bottom of Clear Lake and near the shores of Clearlake Oaks.
Following the construction of the caps in early 2013 and with the goal of preventing mercury from migrating from the sediment and into the water, the EPA has been monitoring the physical, biological and chemical perimeters of the elements surrounding the caps every six months. Two more sample collections are necessary to evaluate the effectiveness of the caps, with the next collection taking place in October, according to EPA Environmental Engineer and Superfund Project Manager Gary Riley.
The caps are roughly 120-square-feet in size and are a pilot run to assess their effectiveness. Although the method has been successfully implemented in other bodies of water, the unique characteristics of different lakes and rivers require the test phase to ensure their effectiveness for Clear Lake”s conditions, Riley said.
Despite high afternoon winds and cloudy water, the construction of the caps went smoothly, Riley said.
“It”s relatively difficult to place a nice, even layer of sand on the bottom of a lake,” Riley said. “It was very pleasing to see how well the test areas were covered and we were happy to learn the tops of the caps were smooth and met our thickness criteria for the entire cap.”
Since construction, the sand and gravel layers are settling as a unit evenly, rather than with peaks and valleys, and there are no gaps in the patches to be seen, according to Riley.
If determined to be successful, the EPA will “be scaling up from these patches and determine how much of the elevated mercury near the mine needs to be placed under caps,” Riley said. “Potentially, tens of acres will need to be covered depending on the risk assessment.”
Riley said the future costs to build the full-scale caps “is very sensitive to the amount of area that will need to be covered.”
A settlement between various federal agencies, the Elem Tribal Colony and the Bradley Mining Company, the last operator of the mine, resulted in nearly $7 million of federal funds in 2012 to partially reimburse the EPA for cleanup costs. At the time of the settlement, the EPA estimated past and future costs could add up to roughly $80 million; the state will be responsible for 10 percent of the capital costs of the cleanup and for the cost of long-term operations and maintenance of the completed cleanup, while the EPA will be responsible for the remaining costs associated with the cleanup, EPA Public Affairs Specialist Suzanne Skadowski stated.
The California Department of Fish and Game discovered mercury in Clear Lake fish by accident after testing DDT pesticide levels in fish in 1976. The EPA maintains fish consumption guidelines for specific types of fish on its website, which can be viewed at www.oehha.ca.gov/fish/so_cal/fclearlake.html.
However, monitoring by University of California, Davis from 1992 to 1999 and by the EPA from 2005, 2007 and later have not shown a significant trend up or down in total mercury concentrations in sediment in Clear Lake, Skadowski stated.
The Sulphur Bank Mercury Mine site was intermittently mined for sulfur and mercury ore between 1865 and 1957 and includes the Elem Tribal Colony, located directly adjacent to the mine. One of the largest producers of mercury in California, the mining activities resulted in approximately 150 acres of mine tailings and waste rock and a flooded open pit mine called the Herman Impoundment on the property, as well as mine tailings that extend onto the Clearlake Oaks arm of Clear Lake along 1,300 feet of shoreline, according to the EPA.
“U.S. Geological Survey studies of sediment core samples show that mercury in sediments increased from the early part of the 20th century,” Skadowski said. “This corresponds with the period of time when the Sulphur Bank Mercury Mine was developed into an open pit mine and waste rock began to be pushed into Clear Lake.”
The EPA has worked on various projects to remove mine waste containing mercury and arsenic and control the further contamination of Clear Lake since 1992; contaminated mine wastes have been removed from residential areas at the Elem Tribal Colony, surface water diversions have been constructed and three wells that were not properly abandoned at the mine site were closed.
“There is a lot of work that”s been done and a lot of work is still to come,” Riley said.
