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.
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.