Mixing Zones: Why we shouldn’t have them

Mixing zones present a great visual example of how discharges directly impact the look, feel, and biological integrity of rivers. Many fisherman, fishing guides, and recreational boaters in the Upper Potomac who have come in contact with Westernport, Maryland’s wastewater treatment plant’s mixing zone have concerns over the impact it has on their use and enjoyment of the river.

Mixing zones are discharge zones where pollution is legally allowed to enter directly into the river at concentrations higher than normally allowed. However, questions remain over the effects these zones have on local ecosystems and recreation.

According to the EPA, “Mixing Zones are allocated impact zones where water quality criteria can be exceeded as long as acutely toxic conditions are prevented.”

However, the unescapable fact is that these are zones of concentrated pollution which can span the width of as much as a one third of the river—pollution that flows all the way downstream and irreversibly changes the river.

At the UPRC plant the mixing zone acts as a final step in the water treatment process as it is diluted within the body of the river. Residential fish in the area of the underwater discharge are assaulted with orange-brown stained discharge of bubbling water with an average temperature of 100 degrees. Mind you, the images don’t lie– this discharge is occurring in one of the premier cold-water trout fisheries of the East Coast of the United. Fishermen travel hundreds of miles to fish this legendary tail-water fishery. Before this discharge zone the river is aqua blue-green, clear and cold, but downstream of the discharge the river remains tainted a murky brown color and it is unacceptably warmed. It is our professional opinion that the warm water reduces the viability of this trout fishery by tens of miles by causing the water to remain above the trout’s threshold survival temperature.

After years of foot dragging, Maryland Department of the Environment (MDE) finally renewed the discharge permit and made some incremental improvements to the discharge. However, recent observations reveal the exact same issues remain.

As use and recreation continue to be damaged, we are pushing for better regulations or the total elimination of mixing zones in order to maintain the biological, chemical, and physical integrity of the Upper Potomac River.