February 9, 2006

Santa Clara Valley Water District officials OK purchase of aerator
to reduce mercury contamination at Almaden Lake Park

Noiseless, solar-powered equipment to cost $50,000

By Sheila Sanchez
Staff Writer

The Santa Clara Valley Water District board of directors unanimously approved Tuesday purchasing a pond aerator to reduce the production of methyl mercury in Almaden Lake Park.

Water officials are trying to comply with recently adopted total-maximum-daily-loads for mercury in creeks and lakes impacted by mining waste, which require reduction of methyl mercury concentrations in water to reduce the concentration of the mineral in fish tissues.

According to water district officials, methyl mercury in the Guadalupe River Watershed is primarily produced in the district’s reservoirs and in shallow Lake Almaden.

The solar-powered aerator is said to be the most economical and efficient way to introduce oxygen into Lake Almaden.

The aerator will circulate water vertically in the lake, increasing the rate of oxygen transfer from the air-water surface interface to the bottom, where methyl mercury is produced, which in turn will improve fish and wildlife populations, particularly threatened, rare and endangered avian, amphibian and mammalian species at risk from mercury contamination in their diet.

The aerator will be operated continuously year-round and will be monitored to evaluate its performance.

The aerator is just one of several methods to reduce methyl mercury in water such as removing mercury-containing bottom sediment, prevention of mercury-containing sediment from entering the reservoirs and lake and capping of the bottom sediments with clean sediment of other material.

But removal or capping of bottom sediment at Lake Almaden is impractical, they say, until existing mercury-containing sediment entering from upstream is controlled. The condition can’t be implemented for at least three years due to the need to complete planning, environmental documentation, design and construction.

Water district officials said the aerator, which will cost $50,000, is expected to produce immediate reductions in methyl mercury production and can be continued in the interim until long-term solutions become practical. It will be installed in April.

Last year, water district officials learned from a mercury study in the Guadalupe River Watershed that the introduction of oxygen to reservoirs and impoundments could reduce methyl mercury production.

“It’s not a water quality issue, but it is a problem because it’s (mercury) is picked up by the plants and the animals that feed on the plant. We have fish that have high levels of mercury,” said Santa Clara Water District Director Larry Wilson. “If we can aerate the water in that thermocline (water temperature profile) it stops the methylation (the process that makes mercury bio available).”

Wilson said the mercury condition has existed in the watershed since 1935.

“It has not created any health problem with people in the community or people who recreate there,” he said. “It’s a problem that exists in the ecosystem and if we can improve the condition for fishery and the animals that live in the area then we will.”

The project is being conducted jointly with Santa Clara County officials and will include interpretive signs for display at several locations in the park prior to the system’s installation.

The district owns the lake and leases it to the city for recreational use. The aerator will not interfere with any of the recreational uses at the lake, and will likely improve fishing for catch and release, and reduce seasonal odors associated with algal blooms, said Water District Senior Engineer Dave Drewry.

Jim Fiedler, head of the Santa Clara Valley Water District Watershed branch, said the mercury in the lake is an accumulation of sediment and mercury that comes from “the legacy of the mines.”

“The problem with the mercury is the methylation,” Fiedler said. “It’s a natural occurrence, but certain conditions in the lake foster and contribute to the methylation process because of not enough oxygen in the water.”

Fiedler said the experiment would test to see if the aerator would help oxygenate the water and reduce the amount of mercury that gets methylated. “It’s an experiment. We haven’t tried it before. We’re being proactive to do things to improve water quality.”

For more information on the project visit www.valleywater.org or call (408) 265-2600.