Storm drains serve their main purpose by effectively removing rainwater to help prevent floods after major storms. They give water a place to go. However, what’s often forgotten is the amount of chemicals, dirt, and debris that runoff water collects and carries with it. Runoff water can even pick up other urban contaminants such as trash and metals that are harmful to our local environments.
Sweeping is a best practice for managing storm water. The more you sweep, the more pollution is removed. This cost-effective means of removing debris is a classic pollution prevention technique that allows you to remove pollutants before they ever enter storm water.
According to the EPA, “Over 166 dead zones have been documented nationwide, affecting water bodies like the Chesapeake Bay and the Gulf of Mexico. The Gulf of Mexico dead zone is the largest in the United States, measured to be 5,840 square miles in 2013.”
While street sweeping is much more cost effective than other methods of capturing nutrients once they’ve been released, it’s not an inexpensive process. According to a 2011 report from the University of Florida and the Florida Stormwater Association, it costs about $165 per pound to recover nitrogen using street sweepers.
Nitrogen and other nutrients are considered the most damaging pollutant and most surface waters across the U.S. While necessary for life, nutrients can also fuel the growth of algae in marine environments. Too much algae clouds the water, blocking sunlight from seagrasses that provide critical habitat for valuable fish and shellfish. Then when the algae die, they absorb oxygen that other creatures need to survive.
Nutrient pollution occurs when there is an excess of nitrogen and phosphorus
50 out of 50 states are impacted by nutrient pollution.
States have identified about 15,000 waterbodies in the United States with nutrient-related problems.
Reported drinking water violations for nitrates have nearly doubled in the last decade.
Metal particles are a common part of the roadside debris that comes from vehicles and trash. These metals are detrimental to water life and other animals and even create air pollution by bonding to larger pieces. Larger metal pieces and other objects like rocks can also cause damage to cars, mostly by scraping the finish or hitting the underside.
Street sweeping effectiveness is determined by several factors including the type of street sweeper, particle size distribution, land use, tree cover, timing and frequency of sweeping, and whether there is a curb and gutter and parking restrictions.
Effectiveness is generally defined as the efficiency of the sweeper. Efficiency can be represented in a few ways, which tends to vary across studies. Most commonly, the efficiency is represented as the portion of particles/pollutants/debris removed by the sweeper on a mass basis. Note that this measure of efficiency is different from an evaluation of the changes in runoff water quality as a result of sweeping.
Street sweeping is an often overlooked yet very important part of keeping our roads, waterways and air clean, but this nearly silent service has great impact.