One major culprit when it comes to eco-disruptive practices is the site development of large parking lots. Thousands and thousands of existing paved lots are contoured and sealed to direct rainwater over the surface of the lot until it flows into drainage ditches or detention ponds. The problem is that along the way the rainwater picks up pollutants from these surfaces that can be transported to lakes and streams. In addition, there are issues of erosion caused by the increased volume and concentration of flowing water as well as thermal pollution to receiving waters as the rainwater is warmed by these surfaces.
The positive side to this specific environmental threat is that there are a variety of solutions that can minimize it, and they don’t require drastic measures or lifestyle changes. These are some of the techniques that civil engineers at SSOE employ to control and treat storm water while allowing it to enter the ground water table more naturally. They are among the EPA’s Best Management Practices or BMP’s for controlling storm water runoff to reduce sediments and pollutants from being transported to our lakes and rivers.
Which technique is most appropriate for a given situation depends on factors such as site characteristics, site specific soil conditions, and local climate. For example, before recommending certain infiltration methods, the engineers may need to determine existing water table conditions and how quickly storm water drains into the soil by boring down into it, taking samples and analyzing their composition and porosity.
Although many green initiatives are driven by governmental standards, local building and planning departments are not always aware of the options that are available for eco-friendly site development. Thanks to the widely publicized trend toward sustainable design, most entities are open to these solutions once they understand how they work.
Of course the most eco-friendly site plan won’t even get to the approval stage unless the owner/developer sees its practical or economic value. It’s the job of the architects and engineers with strong expertise in this arena to lay out the benefits in terms of both initial cost and maintenance costs. For example, SSOE’s project team illustrated to one developer how eliminating some detention ponds — which range from 10% -13% of total area on large retail projects – by using sustainable site design could save initial costs by reducing the amount of land needed for the project and also on maintenance costs by reducing the area requiring seasonal mowing. Reducing storm water detention or retention ponds can also be a useful strategy in increasing the usable land on an existing site and reducing site excavation costs on a new site.
SSOE is finding that our experience and knowledge of sustainable infrastructure design is as valuable to our clients’ bottom line as it is to the environment.
1. Use of permeable pavement systems rather than sealed surface material. This allows much of the rainwater to infiltrate directly into the underlying soil, reducing the amount of run-off. This technique also creates an opportunity to capture naturally filtered water in underground pipe systems and use it for irrigation.
2. Incorporating bioswales into the site plan. These specially engineered drainage swales are typically designed to receive surface runoff from parking lots. They can filter and aid in the reduction of Phosphorus and Nitrogen pollutants from the water. This is accomplished through the use of selected plant materials and engineered filter sand media before the water discharges to surface waters.
3. Directing storm water to landscaped areas. Storm water is directed to low, shallow “swales” with grass and landscaping. The water travels only a short distance before it is absorbed by the plants and soil and naturally filtered. Rain gardens are smaller versions of this concept. Water from rooftops is channeled through downspouts to gardens located away from the building foundation.
4. Creating infiltration trenches. These trenches are excavated into a layer of soil that can accept water and are then lined with a membrane that filters out clogging sediment and filled with gravel to allow water to seep back into the soil.
5. Utilizing “reclaimed” water. Creating swales where water can be collected in a cistern and using that un-treated water for irrigation. This reduces the amount of potable water needed from municipal water sources.
6. Developing strips of grass and plantings throughout a paved area. The water flows to these buffer strips and is filtered and partially absorbed into the soil. A secondary advantage of the strips is that they can improve the visual appeal of the site by creating landscaped areas that relieve the expanse of pavement.
7. Using grass “paving”. This technique uses egg-crate shaped pavers made of concrete or recycled plastic and placed on top of an engineered gravel base. The openings in the paver are filled with soil and planted so grass grows up through them. These areas are suitable for light traffic – fire lanes for example or event parking areas. As with many of the other solutions, this allows the storm water to be absorbed into the ground rather than collected directly into the storm system and reduces the thermal “heat island” affects of other pavement systems.
8. Constructing wetlands. Providing water a place to be naturally treated before entering a lake or stream also provides a place for wildlife. On large sites or regional developments that need to control large quantities of storm water, a wetland can be one of several areas where water can collect naturally with many environmental benefits.