Monday, April 30, 2007

Why the Emphasis on Runoff When We Know that Sewage is the Sound's Biggest Pollutant?

Two more newspapers got around today to writing about the Long Island Sound survey, which came out last Wednesday (here and here). And there’s an editorial in the Hartford Courant that emphasizes the part of the survey that showed that most people don’t realize that stormwater and runoff pollute the Sound and that some of the runoff comes from their own properties.

Controlling runoff and reducing the amount of pollution is runoff is sort of important, but I’m surprised at the emphasis it has gotten, both in the survey and in the news accounts of the survey.
By far the biggest source of pollution in Long Island Sound is treated sewage. It is the source of the vast majority of the nitrogen that triggers the low levels of dissolved oxygen that make much of the western end of the Sound uninhabitable for marine life in late summer.

The second biggest source of nitrogen is air pollution. Nitrogen emitted from car tailpipes and power plants falls into the Sound and adds to the nitrogen from sewage plants.

And of the important sources of nitrogen, the smallest and the most difficult to control is runoff from streets and driveways and septic systems in the Sound’s watershed. Not only is it hard to control, it’s hard to measure. It’s been a while since I’ve asked, but the last time I did I was told that less than 10 percent of the nitrogen that damages the Sound comes from runoff.

So to me it’s not that huge of a deal if people don’t realize that runoff contributes to the Sound’s problems and if, because they don’t realize that, they don’t do the few small things that may or may not reduce the tiny amount of pollution they are personally responsible for.

Far more troubling to me is that most people don’t know that treated sewage and sewage plants are the biggest polluters of Long Island Sound (the survey is here). Presumably they also don’t realize that upgrading sewage plants is the single best thing we as a society can do for the Sound. And that perhaps explains why Connecticut for years was allowed to get away with ignoring its responsibility to upgrade sewage plants by failing to put money in its Clean Water Fund.

Convincing people not to wash their cars in the driveways is important, I suppose, but it’s a drop in the bucket compared to sewage plants. We really should keep our priorities straight.



Anonymous Bob said...

I think the inordinate concern in the Sound Survey with polluted runoff to the Sound, as opposed to the discharge of nitrogen in treated wastewater from sewage treatment plants, is due to confusion of the general with the specific. Polluted runoff is a principle source of surface water pollution nationwide. But as you say, the principle source of organic nitrogen-the pollutant identified by the LISS as the primary threat to the Sound-is nitrogen in the effluent from sewage treatment plants and also from acid rain. (A technical nuance:stormwater that finds its way into wastewater treatment plants through inflow and infiltration does carry about 1 mg/L of the total nitrogen the plant is responsible for limiting under the TMDL. This is significant because the treatment plants must reduce nitrogen down to between 6 to 4 mg/L.)

Between now and 2014, publicly owned wastewater treatment plants in the Long Island Sound watershed located in Connecticut, NYC, Long Island and Westchester, are required to complete the removal of 58.5% of the nitrogen contained in the treatment plant effluent. It would be very helpful if those concerned with long term health of the Sound kept that fact in mind.

11:47 AM  
Blogger Sam said...

I can buy the premis that municipal wastewater treatment plants are a major source of nitrogen, but I think it is more complex that making a broad statement. Overland stormwater can also contain organics, phosphate, fecal coliform, inorganic nitrogen, and suspended particulate that can and does significantly contribute of water degradation. Sure, it might be in the 15-25% range but every reduction counts, right? I don't thing anybody has studies the LIS for non-point pollution as well as has been done in the Chesepeake.

Now what does blue-green algae do? If can fix inorganic nitrogen and turn it into organic nitrogen. You mentioned vehicle air pollution as being a major contributor to nitrogen loading in LIS but that is mainly nirtic oxide (NO) and nitrogen dioxide (NO2), two inorganic compounds. However, when these gases react with sulphate and ammonium, some is precipitated into ammonium nitrate and ammonium sulfate - which we know as being key ingredients for fertilizer.

I'd be careful about making claims about Acif Rain because powerplants that burn coal and oil released tons of sulfur into the environment, some is which converted to sulfur trioxide, sulfur dioxide, and sulfur acid mist (H2SO4). What isn't reacted into aerosol can indeed end up as sulfuric acid, although I doubt that is a huge player in LIS eutrophication, given the buffering effect of seawater and rapid water exchange.

But let's talk overland stormwater pollution one day when we have most of those old municipal wasterwater treatment plants brought up to "best available practices." It's a fascinating subject and at the end of the day, when you've fixed 75% of the point source problem with the treatment plants, non-point sources could be a huge topic of debate. /Sam

5:40 PM  

Post a Comment

<< Home

eXTReMe Tracker