The #1 Source of Pollution in Our Watershed

The 7 million or so gallons of sewage that spilled from wastewater treatment plants into a couple of the Chesapeake Bay's tributaries two weeks ago turned my head in a new direction. It redirected me on my capstone project for the Watershed Stewards Academy to focus on humanure in my neighborhood. Septic tanks are the current locus of the problem. Particularly problematic are failed septic systems in which sewage resurfaces and then gets washed by storm runoff into surface water.

The environmental impact of failed septic systems can be estimated using a figure from Purdue University stating that one failed system will discharge 76,650 gallons of sewage to the surface in one year. Extending that to an estimate of the number of homes in the critical area of the Chesapeake Ranch Estates, and applying a factor of 10%, which is the EPA's estimate of the proportion of septic system failures, and the annual amount of sewage flowing overland from this 1,000 foot wide zone stretching about 1 mile along the Chesapeake Bay comes to 3.8 million gallons. It could be double or triple that, depending on the actual failure rate, which has be estimated at over 30% in some states. Project that kind of problem all along the coastline of the bay and its tributaries and the wastewater treatment plants end up smelling like a rose.

Maryland's laws pertaining to poop aren't all that stringent. Farmers are allowed to dump manure on their fields. Homeowners are allowed to spread it on their lawns. If the fertilizer limits on nitrogen are applied to manure (phosphorus is actually the more limiting element), you could legally put 40 pounds of horse manure on a 1,000 sq. ft. lawn in a single application. Not that anyone would, but you could instead apply 20 pounds of humanure to the same lawn and remain under the nitrogen limits. A failed septic system used by a family of four would expel roughly 700 pounds of excrement (assuming toilets outside the home are used 50% of the time) to the land. That amounts to over 35 times the nitrogen limit for lawn fertilization (humanure contains 5% - 7% N). And that's just the poo! There is also a lot of urine and other nasty liquids in the mix with a whole lot more nitrogen.

It is hard to say whether the nutrient-laden runoff or the 100 or so pathogens in the sewage are a greater problem. Research published in 2015 from leading experts in the field of water sustainability shows that pathogens from septic systems make it into surface water much more than what authorities had believed. The pathogens are pretty scary, but to fish and other marine life, nutrient overload can quickly become deadly.

Keep in mind that all septic systems, working or not, tend to pollute the environment. The total amount of nitrogen loading to the Chesapeake Bay watershed from septic systems in Calvert County exceeds that from every other category,
Photo by Jim Barter
which includes agriculture, urban runoff, forests, and wastewater treatment plants. On average, the amount of nitrogen entering the watershed from a septic system is 19 pounds per year, based on calculations using figures from the Calvert County Watershed Implementation Plan. That is equivalent to dumping lawn fertilizer for over twenty 1,000 sq. ft. applications straight into the bay.  Every house.  Every year. The pathogens (including certain bacteria, viruses, protozoa, and other parasites)  in the effluent from working septic systems also make it into groundwater to one degree or another. In areas where septic systems are greatly concentrated, such as the Chesapeake Ranch Estates, both pollutant types will make the surrounding waters inhospitable to man or beast.

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