Rain brings life to the land. Every living thing needs water to survive and thrive. However, what happens when the land itself pollutes that water?
This problem, also known as storm water runoff, can cause many issues. From polluted water supplies to erosion, runoff is hazardous and damaging.
Construction sites can exacerbate these problems. These locations feature dangerous chemicals, including petrochemicals, fertilizer and other pollutants. Plus, unfinished areas can create erosion hazards as runoff channels through incomplete lots.
Because of this, construction sites should follow storm water runoff management programs. These help ensure the proper containment and collection of site-based runoff —and that helps avoid pollution, destruction and other hazards.
There are many management practices for construction site storm water runoff, so not every plan will be identical. Often, runoff management focuses on local factors, such as ordinances and legislation. With that in mind, here are some of the best practices for construction site runoff management.
What is Storm Water Runoff?
Storm water runoff is more than just rain water. Rain water runoff is any rain that has only touched a roof. Storm water runoff has flowed over hard surfaces, such as asphalt or cement. These hard surfaces contain solid debris and hazardous chemicals. These pollutants then wash into the environment whenever it rains.
Storm water runoff needs specialized means of reclamation and recycling. The high levels of pollutants make it impossible to filter. As such, runoff must go through several treatment stages before it can flow back into public water spaces.
Because it collects surface pollutants, storm water runoff is dangerous and destructive. Therefore, containing runoff is an essential aspect of an area’s pollution control plans. Reclamation is often the desired goal. Through collection, treatment, and redistribution, storm water runoff can become clean again.
Standard methods of reclaiming storm water runoff include:
- Natural land filtration: Also known as rain gardens, these use native flora and specialized filtration to remove pollutants and debris from runoff.
- Combined sewer systems: Storm water runoff combines with wastewater before treatment at a recovery facility.
- Site-based containment: Used at specific locations with high surface pollution levels, like construction sites. This method combines ground filters, advanced construction technology, and best management practices to contain storm water runoff.
In areas of high surface impermeability, runoff containment plans are essential in keeping dangerous pollutants from causing damage, illness and even death.
Storm Water Runoff Causes Destruction & Pollution
As storm water runs over surfaces, it picks up debris, from dirt to discarded medical trash. Eventually, all that contaminated water will flow into something. This can be holding ponds, sewer systems or even natural waterways.
Even standing runoff water will absorb into the ground. In areas with poor filtration, this can cause stagnant ponds of wastewater.
Urban areas make storm water runoff issues even worse. Cities feature more impervious surfaces like roads and parking lots. This leads to urban runoff eventually flowing into water supplies.
Consequently, storm water runoff pollutes the land and natural waterways in the surrounding area. Sometimes, these pollutants travel miles downriver, leading to widespread ecological impacts.
Besides collected pollutants, storm water runoff can also overwhelm existing sewage systems. This can cause raw sewage to enter the water supply. Again, the impervious surfaces of urban areas make this worse. This added sewage pollution has many adverse effects on aquatic and human life.
As water will find the path of least resistance, it can eventually erode the land. An excess of impervious surfaces leads to channeled paths through which runoff flows. This can undermine building and road foundations, thus causing dangerous damage. It can also lead to overwhelmed holding ponds, which can cause flooding or dam erosion.
All in all, there are no positive qualities to storm water runoff. Indeed, when coupled with the pollutants and other hazards of a construction site, the problems can compound.
Managing Construction Site Runoff
Construction sites have a high potential for runoff pollution. Therefore, they must follow extra runoff prevention methods. The National Pollution Discharge Elimination System (NPDES) is one such program. It is a permit system that construction sites must follow. Through this program, regulations ensure that construction site pollutants stay out of water supplies.
These permits help construction sites keep a close eye on their runoff. Failure to do so can result in inspector visits, violations, and even fines.
As such, there are many means of runoff management used by construction sites all over the country. These management styles fall into two distinct categories: structural and non-structural storm water management.
As the names suggest, these systems differ through design and deployment. Structural solutions involve creating or placing objects that can divert, slow and filter polluted runoff. Some common structural management programs include:
- Point-based management: Designed to capture drainage before it enters the water supply. This can include infiltration basins, cisterns and even specially constructed wetlands to slow and clean runoff.
- Linear management: Meant to slow and filter runoff. These are long trenches that collect water. Common iterations include subterranean sand filters and infiltration trenches.
- Area management: Focuses on increasing permeability through the site. Porous pavement and green, soil-covered roofs stop runoff by absorbing it as soon as it lands.
Alternatively, non-structural programs focus on the cause of runoff, specifically, a high amount of non-permeable surfaces. Thus, non-structural programs are often in place before construction breaks ground. Examples of non-structural runoff management include:
- Conservation areas: A conservation status protects an area from most forms of pollution, and often under penalty of heavy fines. Conservation statuses can help protect waterways and natural habitats.
- Watershed planning: By examining the entire watershed of an area, all involved can create a system of management that monitors the watershed from start to finish.
- Ordinances: Ordinances ensure polluting agents, like construction sites, follow runoff rules. While they don’t stop or prevent runoff, they can lead to severe penalties if broken.
Construction sites must adhere to any non-structural programs in place. Still, site-based structures and other programs can help avoid contamination issues.
Best Management Practices for Construction Sites
The best runoff management plans will use any combination of programs to keep runoff contained. Every site will need individual planning, but several practices can have a great impact on runoff containment.
According to the EPA, most runoff management programs have minimum requirements. These can include measuring sediment levels, planned inspections, and adherence to local laws.
To achieve these, construction sites use several methods of runoff management based on the site and project at hand. These five practices focus on runoff reduction and pollution containment. While there are countless other methods, these can have a high impact when used correctly.
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Surface Sand Filters:
Surface sand filters are beds of sand strategically placed to arrest, collect and filter runoff. The water absorbs through the sand, leaving behind up to 80% of solid pollution. This makes surface sand filters excellent first points of contact for runoff water.
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Vegetated Filter Strips:
Vegetated filter strips are areas of natural foliage (such as grasses and trees) next to existing waterways, ponds or lakes. These buffers act as natural barriers and filter the runoff water. While this method doesn’t keep runoff at the source, it ensures local water sources stay safe, should site containment fail.
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Porous Pavement:
Like sand filters, porous pavement absorbs runoff into the ground through specific areas. Materials such as interlocking plastic pavers and permeable asphalt filter the runoff before flowing into water supplies.
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Diverting Slopes:
Sometimes, the simple option works. Creating graded slopes at specific areas of a construction site can divert and manage runoff. Coupled with other filters and barriers, diverting slopes can help keep runoff contained and manageable.
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Phased Construction:
Construction sites can also use non-structural methods to regulate their runoff. Breaking a construction project into phases allows pollutants to remain more controlled. By limiting construction to smaller areas at a time, the site is compact and better managed.
Ensuring Site Control
No management plan can work without constant monitoring of the runoff. Failure to do so can lead to contamination of the local area by site runoff, or worse, pollution issues.
The EPA suggests monitoring the continual concentration of pollutants discharged from a site. This allows site managers to keep the volumes and loads of pollutants within safe ranges, and, if possible, reduced over the life of the project.
By using a runoff management practice, site managers can keep a close eye on the runoff of a site during each rainfall.
Final Thoughts
Storm water runoff is a dangerous contributor to water pollution. In fact, as the amount of impervious surfaces increases, so does the chance and severity of storm water runoff. When combined with pollution-creating factors, this runoff can become catastrophic.
This highlights the importance of runoff management practices. Construction sites can reduce or end the harmful runoff they produce with thoughtful planning. Construction sites can manage their runoff through active structures, passive filtration, and community-based mandates, thus keeping waterways safe.
