During heavy rainfall, the runoff that is not absorbed into the ground washes pollutants such as oil, grease, pesticides, bacteria, salts, animal waste, trash, heavy metals, etc. into storm drains. In fact, the Environmental Protection Agency (EPA) estimates 77 of 127 key pollutants have been detected in urban storm runoff. What can you do to help minimize the water contamination caused by your home? Plant a biorentention rain garden!
The EPA reports:
The most recent National Water Quality Inventory reports that runoff from urban areas is the leading source of impairments to surveyed estuaries and the third largest source of water quality impairments to surveyed lakes…The porous and varied terrain of natural landscapes like forests, wetlands, and grasslands trap rainwater and snowmelt and allow it to slowly filter into the ground. Runoff tends to reach receiving waters gradually. In contrast, nonporous urban landscapes like roads, bridges, parking lots, and buildings don’t let runoff slowly percolate into the ground…Urbanization also increases the variety and amount of pollutants transported to receiving waters. Sediment from development and new construction; oil, grease, and toxic chemicals from automobiles; nutrients and pesticides from turf management and gardening; viruses and bacteria from failing septic systems; road salts; and heavy metals are examples of pollutants generated in urban areas. Sediments and solids constitute the largest volume of pollutant loads to receiving waters in urban areas.
When runoff containing pollutants enters storm drains, it flows into nearby water ways without any sort of treatment where it degrades local watersheds. As a result, fish and wildlife are harmed, as well recreational areas become unsafe from the increase in contaminants. The solution is to stop the excess water before it enter storm drains.
Urban residents can do their part to minimize the impact of urban runoff through the use of plants. The Union for Concerned Scientists recommends planting a rain garden for this purpose:
We can all help minimize the problem of storm water runoff by planting rain gardens-6- to 12-inch-deep depressions filled with native plants. Rain gardens can capture hundreds of gallons of rainwater, filtering out up to 90 percent of pollutants while allowing the water to drain deep enough into the soil to help recharge groundwater supplies.
To maximize effectiveness, the rain garden’s size should be 20% of the square footage of your home’s roof. The bottom of the rain garden should feature an underdrain, like a piece of perforated pipe, that flows toward the existing storm drain and is covered with gravel. The middle layer should contain the planting medium of 50% sand, 20% compost, and 30% soil, which should then be covered with mulch to help remove metals from urban runoff. Finally, it is best to use native plants in your rain garden, because they establish deeper roots and are better suited to your local climate.
If every urban home planted a rain garden, water pollution would be minimized from storm runoff. It is a simple, environmentally friendly way to combat a problem that is killing aquatic life. This is a serious problem, as the EPA describes, “Native fish and other aquatic life cannot survive in urban streams severely impacted by urban runoff.”