As rain lands on rooftops, lawns, farms, and pavement it picks up whatever debris and pollutants may reside there and runs off into lakes or rivers. This contaminated rain and stormwater is referred to in the scientific community as non-point source water pollution, meaning that it is pollution which can not be attributed to a single source. It is more commonly known as stormwater runoff. We call it HYDROFILTH, a literal mixture of hydrology and human waste in all its forms, from street trash to fertilizer.
HYDROFILTH is made up of things we just don’t want in our water…pathogens, heavy metals, pesticides, salts, oil and common litter. It is a source of E. coli, fecal coliform, strepococci and other pathogens in the Grand River.
Studies of storm sewer outflows have revealed concentrations of heavy metals such as dissolved copper and zinc at levels exceeding acute and chronic toxicity criteria. All of the 13 metals on the EPA’s priority pollutant list have been detected in runoff samples in communities similar to Grand Rapids. Copper, zinc, and lead were detected in 91% of samples. Barium, mercury, arsenic, beryllium, nickel, cadmium and strontium have also been found.
Pesticides, herbicides and toxins such as PAHs and PCBs are frequently found in urban runoff specifically. Fecal coliform bacteria counts for urban runoff are 20 to 40 times higher than federally recommended health standards for swimming. Wisconsin DNR estimates (there is no comparable local data) that more than 95% of storm sewer discharges sampled in their state contained PAH levels that violate human cancer criteria for benzo-a-pyrene and benzo-ghi-peryline (common products of incomplete combustion). More than 60% of samples violated human cancer criteria for chrysene, phenanthrene, and pyrene.
And seemingly harmless materials such as leaves and grass clippings also play a role in degrading water quality. Among other issues, these pollutants remove oxygen from the water during decomposition, leading to a condition in the water known as hypoxia.
Stormwater runoff creates significant issues in the hydraulics of local rivers and streams. Stormwater discharge tends to be much warmer than the natural waters in rivers and streams, which are usually fed through groundwater sources. These temperature spikes put local coldwater fisheries, generally considered to be among the best in the world, at great risk.
Sedimentation and erosion are also a concern: Banks and nearby vegetation are damaged or washed away. Dirt and debris cover up stream bottoms and the life that would naturally thrive there.
And there are worries for local groundwater supplies. Stormwater runoff is by definition water that reaches local waterways through unnatural means, often never reaching the water table. This could mean more water in lakes and rivers, less in the ground.