Gone are the days when a land development project is designed with massive underground drainage systems that simply dump site water into pipes which flow directly into the public storm drain systems and waterways. Environmentally sensitive regulations now require virtually zero increase in site runoff after development of a project. This creates a new quandary for developers, engineers, and design consultants on how to handle the change in flow rate leaving a site.

In 1972, because of growing public awareness of the effects of water pollution, the Federal government passed what is known today as the Clean Water Act. These regulations, as well as the many amendments, place controls on the discharge of pollutants that enter the waters of the United States. In 1990, the Environmental Protection Agency (EPA) required urban areas to issue and manage a special permit application process for regulating stormwater flows into natural water bodies. This permit is called a National Pollutant Discharge Elimination System permit (NPDES).

The initial regulations and NPDES (Phase I) permits require urban areas over 100,000 in population to develop and implement a Stormwater Management (SWM) program identifying specific activities to eliminate or control stormwater pollution.

Stormwater pollution, in the case of urban developments, includes rain that runs off roofs, streets, parking lots, and other paved, impervious surfaces. This water picks up contaminants along its way to the nearest storm drain system and off into the waterways. This urban stormwater can contain oil, grease, bacteria, trace metals, solvents, excess nutrients and chemical residue. The goal is to maximize on-site filtration of the runoff prior to it exiting the site and/or slow the runoff flow to encourage it to be absorbed back into the ground.

Developers and design consultants now ensure that their proposed projects are designed to reduce urban runoff pollution and achieve compliance with local regulations. There are many design alternatives available to help accomplish this. They involve the use of bioswales, the design of onsite detention and/or retention ponds, the use of permeable pavement, and the specifying of drainage products with filtration systems.

Until recently, onsite stormwater runoff was typically channeled directly into some form of underground piping system that flowed into streets or roadways and into the storm drain system. The preferred method today, however, is to have this drainage empty into long, open channels landscaped with dense cover of grasses or plants, called bioswales.

This green approach to design provides a relatively simple solution to a complex problem. The runoff is collected in these vegetated drainage ways and sent downstream as contaminants and pollutants are trapped by stems and leaves. The contaminants then settle into the landscape and decompose back into the soil. Bioswales are a self-maintaining system that can be incorporated into any residential, commercial, or industrial project.

They are an economical environmentally-friendly solution for onsite treatment of potential pollutants.

Detention pond design has also become an integral part of environmentally sensitive stormwater management on sites where there is adequate space to accommodate them. Stormwater detention ponds are intended to slow the peak flow of drainage to the waterways while encouraging the settling of sediment and contaminants back into the landscape. Ideally, bioswales are utilized as drainage is channeled through to the area designated for the detention pond.

More often now, detention ponds can be visually and functionally integrated into the landscape of a project so that their existence is barely noticeable. Detention ponds can be integrated into playgrounds, greenbelts, parks, playing fields, or other useable areas thereby filling an environmental need while providing desirable open space.


Today’s Reality - Roadways
As we clear land, construct buildings and houses, and pave roads and parking lots, we change the area available for falling rain to soak back into the ground gradually. Because traditional road surfaces are impervious to water, drainage systems must be designed to carry the increased flow.

Permeable pavement systems, which are becoming increasingly accepted and understood, allow natural, gradual filtration as water seeps through the roadway surface and back into the earth. They can also be more cost effective by eliminating the need for expensive storm drainage systems. There are many options for permeable pavement materials: porous asphalt, porous concrete, plastic grid systems and block pavers.

Porous asphalt uses essentially the same mixing and application equipment as for impervious asphalt except that the formula for the paving material changes. Small stones are typically left out of the aggregate and less tar is used. After construction, it appears no different than conventional blacktop yet allows water to pass below.

Porous concrete is similar to conventional concrete in installation and equipment used. Larger pea gravel and lower water to cement ratios achieve a pebbled, open surface accomplishing a pervious surface.

Plastic grid systems can be placed in roadway areas and are sometimes made of recycled materials. Some are designed to be filled with gravel and others are filled with some sort of sand/soil/aggregate mix that allows grass to be planted on the surface. This is often used in areas that must support vehicular traffic but where a more natural appearance is preferred.

Traditional-looking block pavers can also be used to give the aesthetic appeal of brick or stone while providing permeability. They are specially designed with channels to funnel water between each block into a subsurface of sand and gravel for gradual soil filtration. These are useful in areas where a more traditional, formal appearance is desired.

The opportunities for the use of permeable pavement in land development projects is only limited by one’s imagination. Perhaps the biggest adjustment needed for additional use of porous asphalt or concrete is from the design engineers and the construction professionals that need to eliminate one very important practice that has been taught as an essential component to road design - compaction. Placing a porous top layer over a compacted base and sub-base eliminates the benefits of a permeable surface.

Technological Advances Provide Solutions
The onset of new stormwater regulations has spurred the development of numerous new products on the market to facilitate compliance. True to the spirit of the American dream, many entrepreneurs have found a way to capitalize on the now popular “green design” by designing products that fill particular environmental needs. Many companies have now introduced drains that either filter contaminants before they enter a pipe or allow water to stay on the surface longer for increased time in bioswales.

Kristar Enterprises (www.kristar.com), with their Flogard® and Swalegard® line, is one of many companies that make filters that capture sediment, debris, and trash prior to entering a pipe inlet. The filters are made to fit most industry standard drainage inlets.

A relative newcomer to the market, Mitered Drain, Inc. (www.mitereddrain.com) has introduced a line of drains that have proved to be very popular with environmentally-sensitive designers. Their Mitered Drain™ comes in six pipe sizes and is a grate that is mounted on a section of pipe at a 3:1 slope. These drains are made to conform to the contour of the bioswale or detention pond. They can be used for both inlets and outlets in these structures.

Many other companies produce numerous different types and styles of permeable pavement—Invisible Structures, Inc., Presto Products, RK Manufacturing, and Wescon Pavers just to name a few. Many companies also offer products to help in the design and installation of detention ponds.


Summary
Although the Clean Water Act has been around since 1972, it has taken over three decades to see its original intentions become implemented. The trend for more earth-friendly designs can only multiply as new technology and innovations become available. It makes the land development industry ever more exciting as every new project brings with it the challenge of not only being profitable but being good for the long term health of our environment. A design professional is best able to direct you to the optimum alternative for your particular project.
Innovations in stormwater management have allowed developers, design engineers, and landscape architects to meet government regulations, utilize environmental solutions with a decreased environmental impact, and implement these technological advances without a premium or prohibitive outlay of capital. SLDT