Impervious Cover TMDLs

This morning, I sat in on a public meeting where representatives from EPA Region 1 and the Maine Department of Environmental Protection answered questions about Maine DEP’s statewide impervious cover TMDL.  “Statewide impervious cover TMDL” may sound like a mouthful, even by environmental law standards, but when you unpack the terms and look at what DEP and EPA are trying to do, it’s pretty intriguing.

For decades now (as wonderfully chronicled here), TMDLs have been the neglected step-child of the Clean Water Act.  Getting TMDLs drafted, let alone turning them into a meaningful set of pollution controls, has been a challenge.  The difficulties have been particularly acute for streams impaired by urban stormwater runoff, which, unfortunately, means just about every stream in urban or suburban America.  Those streams generally are impaired by wide variety of stressors, only some of which would meet the Clean Water Act’s definition of “pollutant,” which makes them poor candidates for the pollutant-by-pollutant mass budgeting that Clean Water Act section 303 seems to require.

To address those problems, Maine (with the blessing of EPA Region 1) is trying something different.  Its first innovation (also pursued in Connecticut and, in slightly different form, in Vermont) was to prepare TMDLs for impervious cover (meaning roads, roofs, parking lots, and other surfaces that prevent rainwater from infiltrating into the ground) rather than for individual pollutants.  Scientifically, that makes good sense.  Impervious cover either causes or at least correlates with most of the stressors that degrade urban streams, and one of the best ways to protect urban watersheds is to limit the construction of new impervious cover and to treat stormwater running off existing impervious surfaces.  Maine’s second innovation was to try preparing an impervious cover TMDL for twenty-nine streams at once (in a more urbanized state, that number could be much higher).  Again, this makes sense; similar dynamics affect urban watersheds across the state, and there are obvious efficiencies in treating similar problems in a single document.

But, as today’s meeting revealed, there are also challenges.  A statewide impervious cover TMDL may address some of the standard problems with creating TMDLs, but it doesn’t resolve all the problems with protecting urban watersheds.  We still tend to develop our communities in ways inimical to protecting water quality.  And by the time we realize we our waterways are impaired, and we begin preparing TMDLs, the potential fixes aren’t at all cheap.  A better approach to writing TMDLs doesn’t make those problems go away.  It may help people understand them, but it also places them in a spotlight.  That can make municipal governments, which expect that they will eventually bear primary responsibility for addressing the problem, a little uncomfortable, and the discomfort was readily apparent at today’s meeting.  The great future challenge for urban water quality, then, is to find ways to help local governments address those challenges, or, better yet, to find effective regulatory approaches that help us develop in ways that stop water quality impairment before it starts.

-Dave Owen