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Construction of mercury control test covers to begin near Sulphur Bank Superfund site.

The EPA will soon begin constructing two test covers at sites in Clear Lake in an effort to stop or reduce mercury from a nearby Superfund site from getting into the lake.

The work will take place near the Sulphur Bank Mercury Mine site in Clearlake Oaks, California.

The EPA said the Sulphur Bank Mercury Mine initially was mined for sulphur from 1856 to 1871, mined intermittently for mercury ore from 1873 to 1905, with open pit mining taking place there from 1915 to 1957. The mine was listed as a Superfund site in 1990.

The agency said approximately 150 acres of tailings, waste rock and a flooded open pit mine--called the Herman Impoundment--are located on the mine property. The mine tailings extend into the Oaks Arm of Clear Lake along 1,300 feet of shoreline.

EPA Site Manager Gary Riley said the agency plans to install two test covers, or caps, composed of sand and gravel, and each measuring 100 by 120 feet, over two sites with high mercury concentrations offshore of the mine site.

The EPA has found mercury both in the sediments on the bottom of the lake as well as in the lake's food web, which led to an advisory to limit fish consumption due to mercury levels found in fish. The field mobilization on the project began in earnest just after the start of the year, with the barges and watercraft needed brought in last week, Riley said.

Lake County Public Works Director Scott De Leon said the county wasn't involved in designing the project, which it was notified of on Dec. 31.

In preparation for the equipment going into the lake, all of the barges--De Leon estimated there were about a dozen of them--went through an inspection for the possibility of invasive mussels on Jan. 8.

The equipment to be used included floating turbidity curtains that will be placed at both sites where the caps are to be placed, De Leon said. Both curtains are about 100 to 120 feet long. He estimated the work will be taking place in about 18 feet of water.

He said the two test covers will be placed in areas with different conditions. One will be in an area of some of the highest mercury concentration, with the other area having a moderate mercury level. He said one cap will be in shallow water, and one in a deeper area of the lake.

EPA wants to see if the covers will perform as they expect. Riley said capping and covering are ways to deal with contaminated sediments in harbors, lakes and rivers.

The test caps include 8 inches of sand placed on the bottom of the lake, which then will be covered with 8 inches of gravel, which Riley called an armoring layer. He pointed out that the Oaks Arm of the lake is long, and gets a lot of wind and waves, so they will be monitoring the caps for their integrity.

Over the next two years the EPA will monitor the sites and decide what steps to take next. The information to be gathered from monitoring the site will help the EPA decide on the most effective method for handling the site. If the covers are effective, Riley said they could end up placing a larger cover over the entire area. There are a variety of ways to monitor the caps, Riley said.

Right after inspection there are surveys to make sure the installations were carried out properly, he explained.

They will then collect sediment from the tops of the caps as well as from under the covers using a custom made device, Riley said.

Source: Lake County News
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Publication:Hazardous Waste Superfund Alert
Date:Jan 31, 2013
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