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DNR should crack down on mercury, environmental group says

Environmentalists want the Wiscon-sin Department of Natural Resources to get tougher with La Crosse on mercury discharges from its wastewater treatment plant into the Mississippi River.

"We think the DNR is being too easy on the city, and they should require the city to have discharge that is less than the limits for humans and wildlife," said Pat Wilson, chairman of the Coulee Region Group of the Sierra Club.

The Mississippi River has a fish consumption advisory, and the city is adding to that with discharges of mercury higher than the limits, he said.

On the Sierra Club's behalf, an attorney with Midwest Environmental Advocates Inc. of Madison has asked the DNR to modify the La Crosse treatment plant permit to require more immediate monitoring of mercury discharges.

The river where the city discharges does not meet water quality standards for mercury, Midwest Environmental said in a July 28 letter to the DNR. The human threshold is 1.5 parts per trillion, and the wildlife limit 1.3 ppt.

According to the city's data, the amount of mercury in the city's discharge was 3.2 ppt April 5, the last testing time in the report cited by Midwest Environmental Advocates. The amount has ranged from one to more than four parts per trillion over the past five years.

But DNR and city wastewater plant officials say the water in the Mississippi where the plant is discharging already has higher amounts of mercury than the discharge, in great part from pollutants in the air, which enter the river in rain water and runoff.

The mercury in the Mississippi here ranges from 1.5 to 8 ppt, said John Sullivan, Mississippi River water quality specialist for the DNR. That is less than inland waters, he said.

The amount of mercury at La Crosse is not unusual for a large river, said Tom Mugan, a wastewater engineer for the DNR in Madison.

The city has started a plan to decrease the amount of mercury going into the city's wastewater, said Greg Paul, wastewater treatment plant superintendent. That includes working with dentists to install filters on their water before it goes down the drains, he said.

Mugan said about half of the mercury in wastewater comes from dental offices, which use mercury in fillings. Though he did not know the cost of outfitting the plant to decrease mercury in the discharge, Paul said DNR has taken the preventive approach because installing a treatment process in the plant would be more expensive than local taxpayers would be willing to support.

Treatment plants are designed to remove solids and bacteria, not pollutants such as mercury, said Mugan.

But he said the DNR wants wastewater treatment plants to decrease mercury, not only in the direct discharge, but because the plants spread solids as fertilizer, which can be sources of mercury into the atmosphere.

Environmentalists also want DNR to make the city to test its discharges for 30 consecutive days instead of 12 times over 24 months.

Wisconsin law requires DNR to impose a mercury discharge limit when the average discharge concentration for 30 consecutive days exceeds the limits for humans and wildlife. If the city never is required to monitor for 30 consecutive days, Wilson said, DNR will never impose the limits.

Citing the city's data from the past five years, Wilson said the DNR already has enough data to show improvements are necessary.

But Paul and Mugan say that periodic monitoring over 24 months is better because it gives an average.

In addition, Mugan said forcing treatment plants to monitor daily would be very expensive.

Joan Kent can be reached at (608) 791-8221 or jkent@lacrossetribune.com.

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