Using source control to address storm water runoff pollution
My 7-year-old son absolutely loves mustard, so there are many opportunities for his clothes to get covered in it. Mustard can be a hard stain to remove, which is why my wife and I have told our son, “It’s easier to avoid the stain than remove it.” Put another way by Benjamin Franklin, “An ounce of prevention is worth a pound of cure.” This same ethic can apply to storm water runoff pollution.
According to the American Chemical Society, nearly 31 million organic and inorganic substances exist, 14 million of which are commercially available. Further, a 2013 Government Accountability Office report notes the current total number of chemicals contained in the EPA Toxic Substances Control Act (TSCA) database is 84,000, 22,000 of which were added between 1982 and 2012.
Between 1970 and 1995, the volume of synthetic organic chemicals used tripled from 50 million to 150 million tons, according to a 2002 Environmental Law Institute study. We live in an environment that is awash in millions of chemicals from a number of sources—lawn fertilizers, dish soap, aerosol sprays—and in many instances, we have limited knowledge about how these chemicals interact with the environment or with each other. Once these chemicals are in the environment, they often are transported via storm water runoff to lakes, streams and groundwater basins where they can be difficult to remove with standard treatment.
Urban runoff often contains a complex mixture of chemicals and delivers these substances in varied concentrations. Treating these chemicals with end-of-pipe practices is challenging, is costly and can have limited success. This is the paradigm under which storm water management systems and programs operate. The concept of green infrastructure in storm water management, which promotes the use of infiltration and capture of runoff through natural processes, is a step forward in its management. It addresses the driver of storm water runoff: volume of water. While green infrastructure treats water for some particulates, these practices alone cannot be the answer. The chemicals in the environment still exist, and rather than being transported downstream, they now may make their way to groundwater resources.
As with many complex problems faced by society, the solution is multi-pronged. We should promote green infrastructure and end-of-pipe treatment, and also support source control of chemicals. Of these three approaches, source control historically has received the least amount of attention.
Examples of Source Control
There are countless sources that impact our waters, some which are pervasive across a large region and others that tend to remain focused in a limited area. Additionally, some water quality issues are impacted by multiple sources that can be linked to a single type of pollutant.
The “Freshwater Salinity Syndrome”: The United States Geological Survey (USGS) collected data that highlights a disturbing trend: More than 1/3 of drainage areas in the U.S. are experiencing increases in salinity and 90% are experiencing changes in alkalinity. The problem is so widespread that researchers with the National Academy of Sciences are referring to this as the “freshwater salinity syndrome.” Three families of sources have been identified: anthropogenic inputs (road salts, sewage, irrigation runoff), acidic erosion of natural geologic materials and the decay of anthropogenic materials (concrete, lime). Of these sources, road salt often is the greatest culprit. Of course, salt is highly soluble, requiring treatment such as distillation or reverse osmosis to remove from water.
The use of road salt stretches from the Dakotas in the Midwest to Maine in New England and south to Missouri and Virginia. These are the same areas experiencing profound increases in and impacts from salinity. A study of the Delaware River shows sodium levels have increased 450% over the last 70 years near drinking water supply areas. Salinity increases impact public health and can affect those with hypertension or who are dependent upon kidney dialysis. More acidic water also can lead to pipe corrosion, which was the main culprit for the recent Flint, Mich., water crisis. It also affects ecosystems. In Milwaukee, there is a correlation between salinity levels and a populous type of water flea. While a seemingly minor impact, that condition can significantly impact aquatic insects and have adverse impacts on aquatic species.
To reduce these impacts, some state departments of transportation (DOTs) and municipal transportation departments have started using beet juice, cheese or pickle brine, or treated organic wastes instead of salt. Other options include road pretreatment, and some DOTs claim optimizing salt application provides the best overall benefit.
Phosphorus and PAHs in Minnesota: State legislation can limit or eliminate the use of specific products or chemicals within the state. Minnesota has two state-wide source control initiatives that address phosphorus and polycyclic aromatic hydrocarbons (PAHs) in coal-tar sealants.
The Minnesota Phosphorus Lawn Fertilizer Law regulates unnecessary phosphorus use to reduce runoff of nutrient phosphorus to rivers, lakes and wetlands. Similar laws exist in New Jersey, Connecticut, Maryland and the District of Columbia; they often restrict fertilizer application as well as the composition of commercial-grade fertilizer. The Minnesota law prohibits phosphorus lawn fertilizer unless new turf is being established or a soil test shows the need for it. The law also requires fertilizer of any type to be cleaned up immediately if spread or spilled on a paved surface. Restricting phosphorus fertilizer use is an effective and cheap solution.
The Minnesota Legislature also banned coal tar-based sealants commonly associated asphalt driveways, parking lots and recreational trails. While asphalt-based sealants are relatively benign, coal-tar sealants, which contain high concentrations of PAHs, are considered to be carcinogenic. PAHs in coal tar-based sealants are released through volatilization into the air and as dust as the sealant wears. Storm water ponds are especially susceptible to accumulating PAHs. A study by the Minnesota Pollution Control Agency (MPCA) found 67% of total PAHs of 15 metro-area storm water ponds were from coal tar-based sealants.
More than 14,000 facilities in the state are reported to have storm water pond and wetland facilities, and the MPCA estimated the cost of addressing them to be between $1 and $5 billion.
The traditional focus of addressing storm water pollution has been treatment similar to a wastewater facility—discharge the water downstream and treat it before releasing it to the environment. This type of approach may be reasonable for pollutants that can be removed through these processes, such as sediment; however, the use of downstream treatment for pollutants that are soluble becomes costlier and less practical. Individually tracking existing pollutants to entirely remove them from the environment becomes an exercise in futility. Screening chemicals for surface water pollution prior to commercial release is one option. Environmental historian Joel Tarr captures this dynamic in his book The Search for the Ultimate Sink. He notes that pollution of interest has existed in a variety of contexts—air pollution, nuclear waste, hazardous materials—and the pollution has shifted because of the regulatory framework. The way to truly provide a path to elimination of pollution is to remove it from the environment at its source.
Examples above show efforts to identify problems and sources in water quality with the hope of stopping pollutants from entering the environment in the first place. These examples show that opportunities to improve water quality are not limited to treatment facilities, but are realized through sound policy and legislative actions as well.