Stormwater Management Best Practices

Weathering the Storms

Early last year, the Environmental Protection Agency (EPA) issued new regulations for “operators of construction activity” that involves more than one acre. Since 1992, contractors working on these type of projects have been required to monitor and control any storm water leaving the construction site. These requirements are outlined in the project’s Construction General Permit (CGP) and a Stormwater Pollution Prevention Plan (SWPPP).

Along with this increase of concern with discharges during construction, many municipalities and regulatory agencies have begun to adopt regulations that require all new building sites to devise an ongoing post-construction plan that prevents stormwater discharge once construction is completed. This policy is designed to help mitigate the costs of expanding storm collection systems and treatment costs, while helping to regenerate water levels in the soil and ground waters.

The regulations focusing on zero stormwater discharge include hefty fines if contractors and property owners fail to adhere to these plans. The failure to comply with the stormwater permit requirements constitutes a violation of the Clean Water Act and may subject the violator to potential fines of $2,500.00 to $25,000.00 per day or more.

The best way to avoid exposure to discharge issues with local inspectors and potential fines starts with review of how to contain stormwater in the land development stage, and developing a SWPPP that includes the most current stormwater mitigation tools during construction. Site managers need to take the long view on containment and purchase supplies and equipment that are durable and will perform well in all types of weather, including a rare 100-year-rain event.

Starting with a plan

Site developers are using simple yet comprehensive design approaches to help develop a master plan that can lead to zero stormwater discharge. One example of these programs is the Green Infrastructure Flexible Model (GIFMod) developed by the EPA. The program is an open-source framework for modeling urban stormwater and agricultural green infrastructure (GIs) practices.

Users can build conceptual models of green infrastructure practices to predict hydraulic and water quality performance under given weather scenarios. GIFMod also allows site managers to interpret field results with the industry’s most current scientific data to help plan a thorough approach to control water movement, minimize erosion and reduce potential discharges.

GI practice refers to a decentralized network of site-specific stormwater management techniques implemented to reduce the volume of stormwater runoff entering the sewer or the receiving stream and potentially improving the overall water quality.

Some examples of techniques that lead to zero stormwater discharge include: Cisterns/Rain Barrels, Bioretention, Vegetated (“Green”) Roofs, Infiltration Practices (Basins, Trenches, Dry Wells), Pervious Pavement with Infiltration, and Vegetated Swales.

Four areas for best practices

These long-term practices are most effective when included in the project’s SWPPP.  From the project’s beginning, site managers focus on the four most important best practices during construction, which can lead to an effective long-term goal. Many of these practices can be incorporated in the grading and construction plan.

Preventing erosion

Erosion control measures are the first line of defense in a SWPPP. By incorporating the four basic principles of erosion control in a SWPPP, site managers can effectively keep soils in place and reduce exposure to unplanned and costly events.

  • The first, and most basic principal is to limit the amount of bare soil surfaces at any one time. The more bare soils that are exposed on a construction site, the greater the chance of soil movement. It’s important to include any temporary stockpiles of topsoil or bedding material as a part of the erosion control plan.
  • Sediment control measures are the second principal of erosion control. These practices are designed to capture onsite erosion near its source. Contractors should position sediment control devices close to the areas where the covering vegetation has been removed. This positioning can reduce buildup of soils following a rain event, reducing maintenance.

  • The third principal of erosion control is to install an effective runoff and drainage control system. Directing rain and melting snow into rock lined channels, drains, and ponds is essential to preventing erosion. These practices can minimize storm water contact to areas of bare soils.
  • The fourth and perhaps most important principal is to develop a strong erosion maintenance procedure. Controlling erosion can be more of an art than a science. It’s important to inspect the site after each significant rain event. Site managers can determine what practices are effective, and determine where enhancements must be made. That way you will know what is working and what needs to be enhanced.

It’s also a good idea to always keep a few extra erosion-control supplies to make adjustments if necessary. These supplies can include mats, mulches, and blankets.

Better perimeter controls

Perimeter controls should be planned as a system, taking the entire site into consideration. Perimeter controls are most commonly installed prior to any land disturbing activity. They are required to be installed in locations down gradient of the construction activity.

The SWPPP must account for many factors in designing the temporary erosion prevention and sediment control BMPs.

Site managers can choose from a number of perimeter sediment control devices. All these devices are designed to intercept runoff and contain associated soils and sediment, while allowing water to pass through. It is important to select durable devices that can provide less expensive long-term solutions.

Silt fences are the most recognized method of perimeter control. However, other types of perimeter controls exist that can be equally, or even more effective, depending on the construction site circumstances. Commonly used sediment control devices include: ditch checks, rock logs, compost berms, biorolls, and geotextile wrapped jersey barriers.

Enhancing Inlet Controls

Site managers must provide inlet protection to eliminate sediment discharge on any newly developed areas, immediately after the storm sewer inlets are installed. When considering installation, these devices should only be used in locations where sediment can be removed without entering the stormwater sewers. It is also important to check the area behind the barrier to ensure any temporary ponding from the barriers will not create a safety hazard or cause property damage.

Inlet protection devices can be high-maintenance devices, so it is important to focus on up-gradient soil stabilization, perimeter protection, and other erosion control practices to minimize the amount of sediment in stormwater flowing to inlets.

Performance of all types of inlet protection depends on proper installation and use of materials. Inlet protection devices can be fabricated from clean aggregate, filter fabric, or other materials, or an appropriate device can be selected from the many commercial products available for construction site stormwater management. Common inlet protection devices include: compost and fiber logs, inlet frame filters, silt fence enclosures, pop-up head risers, geotextile wraps, filter bag inserts, and drop inlet baskets.

Road surface protection

A key part of any SWPPP is the containment of soil and mud on the construction site. This means all equipment leaving the site must be free of debris. Rock pads and other sediment tracking practices knock sediment off tires before it is tracked onto paved surfaces. When left untreated, trucks and cars can track sediment onto adjoining roadways creating safety hazards and contribute significantly to sediment pollution.

There are three common designs to clean tires: rock/stone pad (vehicle tracking pad), shaker racks, and wheel washer/wash racks.  For most projects tires cleaning areas should be positioned so that all cleaning water and residue is directed toward a stabilized swale or ditch which empties into a treatment area. This treatment area can include a sediment trap (a curved section of silt fence). Site managers should also consider adding a pipe, culvert, or water bar to prevent surface water and runoff from flowing across the entrance.

Rock/stone pads remove material through a physical scraping action between the tread and rock. Additionally, vehicle tracking pads can be installed to provide a barrier that keeps truck wheels from coming in contact with wet, sticky underlying soils. Rock used for the pad should be coarse aggregate of sufficient size to remove mud from vehicles. The rock pad should be underlain with nonwoven geotextile fabric, to prevent subsidence and migration of mud from underlying soil.

Shaker racks (also called exit grids, rumble strips, rumble racks, or rumble plates) remove material from vehicle tires through a bouncing, shaking action. These are appropriate when the rock pad alone is not sufficient to remove sediment from tires. Where used, shaker racks must be long enough and create enough rumble or shake to dislodge mud, soil, and rock. They can be fabricated from concrete or metal.

When the action of tires moving over the rock pad isn’t adequate to remove sediment, site managers may consider adding a wash rack. These systems often use pressure-sprayed water to remove mud, soil, and rock.

With a thorough team approach, from design through construction, engineers, site managers, and contractors can help ensure that their construction sites will be non-emitting stormwater areas.

The EPA has some great tools and info on Stormwater Management and SWPPPs

(including a comprehensive “How-To” PDF)

https://www.epa.gov/npdes/developing-stormwater-pollution-prevention-plan-swppp

 

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