What Effect Would Stopping the Flow Have on Ironman?

Posted on August 10, 2012 by Philip Orton

Westchester County officials say that repairs on a broken pipe are almost complete and they hope to stop discharging sewage into the Hudson River by Friday afternoon.  So, what effect would shutting it down have on pathogen concentrations near George Washington Bridge (GWB) and the Ironman triathalon swim tomorrow morning?

Here, back-to-back, are forecast maps for Saturday morning with (top) the same sewage pathogen simulation summarized in my last post, and (bottom) a simulation where the spill ends today at 1pm.  It looks like a factor of 5 reduction at GWB, roughly … which would help.

Sewage pathogen concentrations in surface waters Saturday morning for a continual spill (maximum from 6-9AM at each location), relative to a value of 1.0 Thursday afternoon in the region offshore of Tarrytown, NY.

Sewage pathogen concentrations in surface waters Saturday morning for a spill that stops at mid-day Friday (maximum from 6-9AM at each location).

However, as mentioned in the prior post, we do not have hard data to know what “relative concentration” exactly means for human health.  Governments tend to keep the actual spill data close to their chest, due to financial liabilities (they can be sued for spilling).

One clear conclusion is that stopping the flow today can help reduce the threat tomorrow.  This is because the pathogens die off and disperse rapidly, with a typical removal time scale of 1-2 days.  Combined sewer overflows that occur during rainfall events cause high pathogen concentrations for 1-2 days, though Riverkeeper has shown that rainfall isn’t a simple predictor.

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8 Responses to What Effect Would Stopping the Flow Have on Ironman?

  1. Johna Till Johnson says:
    August 10, 2012 at 1:37 pm

    Hey Philip:

    Thanks for this!

    I am planning to do some paddling tomorrow in the Buttermilk Channel, near Governor’s Island. Assuming the spillage stops as planned at 1 PM, any thoughts/insight on what pathogen concentrations look like down there?

    I’ve been advised that we’ll have a solid tidal, er, “flush” in between so we should be okay….but I’m just wondering about the “pig in the python” progression of pathogens down the Hudson….

    Any insight?

    • Philip Orton says:
      August 10, 2012 at 1:43 pm

      It’s likely to be safe, as the distance (and dilution) is large. But you should take caution (as always, frankly!) to keep from getting water in your mouth.

      The worst-case above of the spill continuing indefinitely leads to a “0.01 relative concentration” at Governor’s Island, so a 99% reduction from the values up in the Tappan Zee region. But until we get funding to really be experts on this topic and work with the sewage observers (NYC-DEP, Riverkeeper, etc) then we aren’t going to have the level of knowledge to translate our model results into actual pathogen concentration guidance. So just be cautious!

  2. writererikbaard says:
    August 10, 2012 at 2:03 pm

    You remarked that “… [P]athogens die off and disperse rapidly, with a typical removal time scale of 1-2 days.” Is that regardless of concentration? In other words, do bacteria cease reproduction when exposed and die en mass in a linear fashion so that a site registering at 150 MPN for enterococcus faecalis will clear at the same rate as if it had a 1500 MPN or 15000 MPN? Or is there a curve to this line of declination, owing to reproduction and the matting/gelling protection of bacterial slimes?

    I was schooled in the “three days” flash flood rule at the Downtown Boathouse and have largely stayed with it, especially for children’s programs. Improvement and refinement, however, is always welcome.

    Erik Baard

  3. Johna Till Johnson says:
    August 10, 2012 at 3:40 pm

    Thanks, Philip. I’ll try to drink less than a quart or two… And maybe wash it down afterwards with ethanol, for safety’s sake. 🙂

    Seriously, thanks!

  4. writererikbaard says:
    August 10, 2012 at 4:23 pm

    Thanks again, Phil! I’m taking shots in the dark regarding my slime hunch (see resistance factor study here: http://www.ncbi.nlm.nih.gov/pubmed/19578303) but might that behavior in larger populations work against dispersion? Also, sand (with its protection and greater surface area) in eddying coves might prolong that life span. Just maybe.

  5. Jen says:
    August 11, 2012 at 8:53 am

    They were never going to not have the triathlon, despte the sewage and the rains yesterday and all night…

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