Feb. 1, 2017 10:00

Stormwater: A Crash Course in NPDES Requirements

Stormwater
BY MELISSA HIGGINS Photos courtesy: Charlotte-Mecklenburg Storm Water Services

Paperwork is as much a part of construction as bulldozers and blueprints.

Permission to build has to be given, various building permits need to be pulled, safety parameters need to be met…the list goes on.

If you’re taking on a project that’s guaranteed to move around a lot of dirt, then one permit you’ll need to apply for is the National Pollutant Discharge Elimination System (NPDES) permit. For those of you who haven’t undertaken a project large enough to warrant a NPDES permit, or for those who want a little refresher, here’s a quick lesson on all that this permit entails.

“The NPDES permit is really the A to Z on how to protect the environment on a construction site,” says Heather Davis, a stormwater inspector for Charlotte-Mecklenburg Storm Water Services in Charlotte, North Carolina. Introduced by the Clean Water Act of 1972, an NPDES permit ensures that a project does not exceed the acceptable limit of a pollutant or pollutant parameter for the intended area of construction, in order to avoid contaminating natural bodies of water.

In pre-construction meetings, the project manager is given guidelines on acceptable pollution limits for the area. After guidelines are given, it’s up to the manager to come up with a plan as to how to stay within the pollution limits. They then present the details in a Stormwater Pollution Protection Plan (SWPPP).

SWPPPs usually include descriptions of the project and its major phases, the responsibilities of contractors and subcontractors, and what measures will be taken to control stormwater runoff. If any changes occur, then it can be updated as construction goes on. While it seems like just another hurdle in a long marathon of bureaucracy, an SWPPP is essential to the wellbeing of the surrounding area.

Its importance comes from the fact that construction sites are one of the prime sources of loose sediment, as well as chemicals and oils that can seep down into the soil. If there’s any rain, the subsequent runoff will carry both sediment and pollutants down to the natural water supply.

“Urban stormwater is the biggest threat to urban waterways,” says Marcia Willhite, a certified stormwater inspector from Springfield, Illinois. “And in an area that has a lot of construction going on, the sediment that can run off from unprotected sites can just choke out or fill up the urban streams.”

Davis adds, “Sediment is very detrimental to aquatic life and wildlife. It also transfers other pollutants to the streams that go to the drinking supply. The more polluted it is, the more harmful it is to us and the more difficult it is to treat in a water treatment plant.”

To avoid carelessness, the National Water Agency has stormwater management inspectors go out and make sure that everything is in line with EPA standards. The inspector examines the area, making sure everything’s in top shape.

“I start by going around the perimeter, checking the perimeter silt fence, making sure it’s intact and does not need repairs,” says Davis about her usual inspection routine. “And I look at the diversion ditches and the sediment basins; I also look at areas of soil that need to be stabilized, making sure they’re not exceeding their seven to 14 days [of exposure].”

If there hasn’t been enough done to prevent runoff pollution, a verbal warning will be given, along with one to three days to fix it. If several verbal warnings are ignored, then a notice of violation is given. If the notice is ignored, a violation is issued, along with a hefty fine. In Davis’ district, for example, a violation can cost $10,000.

Avoidance of a fine, however, shouldn’t be the only reason why a site should follow EPA standards. Adequate stormwater management is necessary for the safety of the project, the workers and, certainly, the future of the surrounding community and environment. Exposed soil means more chances for erosion. The more the soil erodes, the more sediment can be washed into waterways. And, in the worst-case scenario, the area may become prone to flooding and landslides.

In order to prevent a future catastrophe, precautions must be made to avoid any future damage. This is especially true in any sort of community area, where people living outside the worksite are also at risk from unsafe practices.

So how do you meet these stormwater management standards? The answer is BMPs. BMP stands for Best Management Practices, primarily in the area of stormwater and soil-erosion control. They come in two forms: structural and nonstructural.

Non-structural BMPs are actions taken to prevent pollution in the first place. This boils down to maintaining good housekeeping onsite. Keeping equipment and building materials properly stored and covered reduces potential contaminates, like oil and cement, from reaching sewage drains.

A project leader should also talk to employees about the importance of maintaining EPA standards, in order to make sure that protocol is followed. Creating a spill prevention and response plan will also ensure minimum pollution even if an accidental spill occurs. And definitely, make sure you’re not dragging any dirt offsite.

“A frequent thing that inspectors see is inadequate protection of the exit of the construction site, so that vehicles are tracking soil out onto the street. That’s a pretty common practice,” says Willhite. “You want to make sure that your exit has gravel or something that’s going to allow the sediment to drop off the truck as it’s rolling off the site.”

While ensuring that trucks are going over the gravel would be considered a non-structural BMP, putting down that gravel would qualify as a structural BMP. Structural BMPs are installations used to stop or divert polluted water and sediment from reaching natural water bodies, such as silt fences, drains and sediment basins.

In the past, gray infrastructure methods like pipes, drains and constructed basins were used to divert stormwater from sites. While these are still available and used in some projects, a more efficient option would be to use proprietary BMPs.

A proprietary BMP, also called a manufactured BMP, works like a combination of a drain and a filtering system. Water flows into it, and via filtering chambers, vortex separation and absorptive materials, it captures sediment, metals, and other pollutants before releasing the cleaned water to a sewage system. Since they look like inconspicuous manhole covers, they can be left in after construction is completed to continue cleaning any stormwater runoff.

However, more and more contractors are favoring Low-Impact Development (LID) methods. Not only are these greener alternatives, but they are almost always cheaper than gray infrastructure.

The goal of LID is to make sure as little water as possible leaves the site. The most efficient way to do this is to use the natural landscape to control and manage stormwater, rather than constructing pipes and basins.

For example, a manager may set aside a patch of natural vegetation in an area where stormwater runoff is directed; this is called a bioswale. The water then infiltrates into the soil, which absorbs the sediment and other materials. While there may be some runoff that escapes the site, it will be a significantly lower amount. After being filtered by the soil, it’s also much cleaner than uninterrupted runoff.

Similarly, a sediment pond may be temporarily established near the work site. As with a bioswale, sediment and other debris in the water will sink down into the soil. So, whatever water is pumped out at the end of construction is now clean enough for the natural water bodies. A sand-filter basin works in the same way, with sand filtering out the pollutants before the water is pumped out.

There are also LID-compliant BMPs that can be installed on construction sites. Silt fences, a geotextile fence that keeps disturbed soil from escaping the site, are the most common. These require constant upkeep, and both Davis and Willhite agree that improperly maintained silt fences are one of the most common violations they run across in inspections.

Another LID installation is stormwater planters. These BMPs work like bioswales, except that they have installed greenery rather than untouched native land. Some, called infiltration planters, have open bottoms in order to allow stormwater to filter through and then gradually infiltrate the soil below. There are also flow-through planters. These look the same as infiltration planters, but have a

permeable liner, a layer of gravel, and an overflow pipe to divert stormwater in order to avoid flooding.

Heather Davis adds that, while structural BMPs are more typically used in construction, nonstructural ones shouldn’t be discounted. “I’d say they are equally important,” she said. “If there’s a big hydraulic spill that gets right into a creek, a response plan is going to be more important than a sediment pond.”

When completing your SWPPP, be sure to mention any and all structural and non-structural BMPs you’ve used. Both are essential to creating a competent plan to prevent stormwater runoff and keep your site EPA-compliant. Don’t be stingy with them, either.

“Two BMPs are always better than one,” says Brooke Cotta, an inspector with Mabbett & Associates, Inc, in Bedford, Massachusetts. “You want to have at least two BMPs that work together in various areas around the site.”

However, your SWPPP shouldn’t stop with the end of construction. The EPA also requires that the overseer install permanent BMPs for use when the constructed site is operational. But even without the requirement, the future needs to be considered. Flooding is a huge problem in urban areas, since sewer systems are often old and not equipped for wide areas of impermeable surfaces. BMPs can reduce flooding in the same way that they stop erosion: by diverting rainwater to places it can be absorbed.

“A public area sees a lot of use, so the permanent BMPs would protect the site in the long term, rather than just during the construction,” adds Cotta. “And that way, it’s protected in and out.”

As mentioned earlier, some BMPs set up during construction can be left as-is. Drains and proprietary BMPs are virtually unnoticeable. Bioswales and stormwater planters add a touch of greenery to a property while serving the same purpose of absorbing water.

Other options can be added specifically for use after the completion of a project. Pervious pavement has been gaining more traction recently. This pavement is structurally able to be walked or driven on, but there are small openings between the bricks to catch rainwater and direct it into the soil. Rain gardens, too, make for excellent displays, and they also allow water to be collected and reused, possibly for irrigating the landscape.

There are a wealth of BMPs available for construction sites. Knowing which ones will work best for your project not only can assure that you get your NPDES permit, but can also ensure the safety of your workers, the surrounding community, and the environment for years to come.

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