The 303d List: A Primer

October 19, 2009
I was asked recently by our board to prepare a discussion on the processes in various states for developing the EPA’s 303(d) list of impaired waters. In attempting to do that, I discovered that I do not, in fact, understand the process, and I had to educate myself as to what the process is. I figured that a lot of you might also be confused, or not even know what the 303(d) list is (I didn’t), so I wanted to give you the same information I had.

Section 303(d) of the Clean Water Act orders states to prepare lists of streams that are, in the terms of the act, “impaired.” What that means is that the stream cannot be used for any of a particular set of designated uses, which can vary from state to state. The designated uses for Kentucky can be found here (pp. 592-604). Now, if you tried to read that and went cross-eyed, don’t worry (so did I, the first time). Kentucky has three designated uses for bodies of water: aquatic life habitat, secondary recreation, and domestic supply. They’re just what they sound like: places for water critters to live, places for people to do stuff that’s not drinking, and drinking water (technically, I believe “potable water,” but drinking is good enough). Every body of water is rated on these three uses as “not supporting,” “partially supporting,” and “supporting.” The Kentucky Division of Water (the organization responsible for developing the list) is not clear on how many data samples (water samples) from a given stretch of water to be able to make a determination as to its quality, but they do provide standards for determining when a stretch of river is supporting, partially supporting, or not supporting a given use. Here’s what you need to know:

    Sampling is done quarterly (every three months) in some places, every month in others.
    Kentucky Division of Water (KDOW) tests for the following:

    1. Dissolved oxygen (fish breathe oxygen through their gills, so a certain amount of dissolved oxygen is necessary).
    2. Un-ionized ammonia (I’m not sure why they test for this as opposed to anything else, but do you want ammonia in your water?)
    3. Temperature and pH (some types of water life can only live in very narrow temperature ranges, or only if the water is very close to neutral [pH is a scale that measures “acidity or basicity;” while these are two different things, for those who don’t know, at the extreme ends of the pH scale, the question is basically “how long will it take this solution to dissolve human flesh?” and the answer is “not long”])
    4. The following heavy metals are also tested: mercury, cadmium, copper, iron, lead, and zinc.
    5. Finally, the state tests for fecal coliform (poo, or more accurately, bacteria that live in poo).

    A stream is listed as “partially supporting” aquatic wildlife habitat use if it exceeds the standards for any of the non-heavy metal indicators in between 11-25% of the samples collected. It is listed as “not supporting” that use if those indicators are exceeded more than 25% of the time. With heavy metals, impairment is indicated if the standard is exceeded more than 10% of the time, with partial support indicated if it’s exceeded more than once, but less than 10% of the time. (All of these are over three years.) Fecal coliform is generally used for human use standards.

    What does all that mean? Basically, KDOW is going to have at least 12 and in some cases 36 samples when they evaluate a given stretch of river. That may not seem like much, but if KDOW knows about all the “point sources,” or places where pollution enters the river, then they can divide the river by point-source sites, and an entire stretch from point source to point source need only be sampled once. This could be a few hundred feet, or several miles. So they sample once a quarter or possibly once a month, and once they have three years of samples, then they can evaluate it. I should note for you that the aquatic wildlife habitat is the least demanding of the three standards (we want cleaner water for human use than for animal use), so if it doesn’t meet that standard it certainly won’t meet the other two.

    If they find that the water is either partially supporting or not supporting its designated use, then it has to be listed on the 303(d) list. (I bet you were wondering if we were ever coming back to that.) At that point, the state has to compute a Total Maximum Daily Load (TMDL) for that stretch of river. For every pollutant that the state finds, a TMDL must be calculated. A TMDL is the amount of the pollutant that is permitted to pass through that stretch of river per day. Basically, it is my understanding that a TMDL is the maximum amount of that pollutant that is permitted, as measured by sampling, multiplied by the amount of samples that flow through the river per day. That TMDL is then allocated to point sources along the stretch of river (these are called “Wasteload Allocations” or WLAs) and to non-point sources (which is any source that can’t be specifically identified with a single polluter; think roads, parking lots, and other large sources of “public” pollution; these allocations are called “Load Allocations” or LAs). Any point source that exceeds its WLA can be fined, and non-point sources that exceed their LAs are eligible for EPA grants to help correct the issue.

    Once a TMDL has been calculated and implemented (meaning that the levels of pollutants have dropped to TMDL levels), then the state can ask EPA for permission to “de-list” a stream, which just means it drops off the 303(d) list. And that is how the list is supposed to work. But it may not always work that way.

    It has been alleged that the state is not adding streams to the 303(d) list that need to be added. We’re not sure how that would work, since the standards seem pretty clear, but we’re not taking any chances. What we intend to do is ask the state for, basically, all of its data on water quality in Letcher County. Then we’ll crowd-source it.

    That’s where you come in. The way crowd-sourcing works is you get a whole bunch of people, and a whole bunch of data, and have each person look at a little bit of data (just a little bit, I promise!). Then you compile each person’s summary of what they looked at, and try and piece together a story from all that data. So if you want to get involved, contact Headwaters at,, or 606-634-8669 and talk to us about how to get involved in The Great Letcher Water Crowd-Source!

    Posted by Reid


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