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lindbls (Civil/Environme)
29 Feb 08 16:19
Is it practical to remove bacteria from stormwater runoff, given the following conditions:
The runoff is from a proposed 7-lot, rural residential development;
The site soils are primarily clay, with a very high groundwater table (i.e., no infiltration);
The runoff drains to a county ditch, which leads directly to salt water.
Stormwater carries a variety of pollutants.
Water quality sampling by the State Dept of Health has identified the immediate area as at risk to shellfish harvesting, due to this bacteria;
The County is responsible for ensuring there is no further degradation of the saltwater.
Typical stormwater treatment techniques (biofilters, wet ponds, even Stormfilters, etc.)do not directly address bacteria removal.
So, short of the developer installing a small wastewater treatment plant, is there any way to effectively treat this runoff?
字串6
cvg (Civil/Environme)
29 Feb 08 17:22
why does the county assume that your tiny residential development will generate any significant increase in that bacteria? If you provide full stormwater retention with infiltration, you can probably show that you will reduce the amount of bacteria. What is currently causing this bacteria?
lindbls (Civil/Environme)
29 Feb 08 17:56
The county (my employer) is concerned that any further loading of bacteria will be a degradation of the salt water. I'm checking now to see if the DOH letter cited a likely source of the bacteria.
And, unfortunately, infiltration is not an option (high groundwater and tight soil).
cvg (Civil/Environme)
29 Feb 08 18:39
If there is any significant existing development - industrial, commercial or agricultural - upstream (or downstream) of the 7 acres site, then that is likely generating the pollution. Residential developments are not known for causing large amounts of runoff with bacteria (unless the development includes acreages or horse property). So I am not sure how treating the runoff from this proposed site will help. Also, are you sure there aren't some non point source polluters draining to the county ditch, downstream of the 7 acres? 字串6
To answer the initial question, probably not practical.
a) it would be very costly
b) probably be ineffective in reducing the bacteria
c) the site that is generating the bacteria should be responsible for cleaning it up...
tsgrue (Civil/Environme)
1 Mar 08 19:16
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Multiple studies have documented that residential developments can (and usually do) produce significant amounts of fecal coliform and other bacteria. This shuts down shellfish harvesting (and the livelihoods of the shellfishermen) as the shellfish are unsafe to eat from such exposure. Every "little" impact adds to the total. I suggest infiltration to the maximum amount practical (understanding your comments about the site limitations) and maximizing runoff detention exposure to sunlight. You might consider a brackish treatment marsh. There are lots of documents available to guide you on this. I suggest starting with the Center for Watershed Protection (www.cwp.org) and your state's Sea Grant program (www.seagrant.noaa.gov). 字串3
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tsgrue: site engineering, stormwater
management, landscape design, ecosystem
rehabilitation, mathematical simulation
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