Environmental Associates
Know Your Environment
Urban Stormwater: A Hidden Problem
Cities struggle with the surprisingly high cost of rain.
by Roland Wall, August 2001
- Introduction
- What comes down …
- As pure as rainwater?
- Best Management Practices
- Conclusion
- References
Impervious surfaces on the horizon? All over America, more and more land is being covered with pavement and buildings, blocking stormwater from reaching the ground.
Introduction
We often think of rainwater as being "pure" and "natural". Standing in a spring shower, or watching rivulets bubble into a stream after a storm, it seems certain that we are looking at "clean" water.
It may come as a surprise, then, that rainwater—in the form of urban runoff—is considered a major source of water pollution. Some researchers suggest that stormwater runoff in the U.S. may be responsible for up to 15% of river and lake water impairment, and over 25% of problems with estuaries. [1] Science is learning that a raindrop, passing through the atmosphere, across the landscape and into open water, is by no means "pure."
Because it's long term ramifications can be quite subtle (and even short term effects are difficult to determine) stormwater is unlikely to get the public attention or activism of other more visible environmental issues. Yet, managing the quality and effects of stormwater has become a key environmental issue of the 21st Century. There are several factors influencing this.
Stormwater, as a diffuse, non-point source, is found everywhere, so problems related to it cut across all sectors of society and the economy. Increases in the levels of storm runoff and water contamination are intimately linked to growth in population and development, meaning that the concerns will expand over time. And stormwater problems involve millions of actions by millions of people, making management and control particularly difficult.
In this issue we will be looking at how stormwater may threaten environmental quality, and at some of the steps being taken to lessen that threat. Though managing stormwater runoff to control floods is an ancient practice (understood by civilizations as early as the Egyptians), the variety of contaminants now found in stormwater gives the issue new urgency. The ever growing number of people affected by runoff makes understanding it an important part of environmental awareness.
What comes down…
As we've noted before (see KYE 4/01) rainfall is part of the predictable hydrological cycle. In settings with minimal development—forests or meadows for example—rainwater is absorbed by the soil and ultimately enters the surface water (lakes and streams) or percolates into deeper soils to become part of the groundwater. When the infiltration capacity and rate of inflow of the soil is exceeded—i.e. when no more water can be absorbed—additional rainfall pools on the surface and follows the local contours of the land, usually ending up in a natural stream channel.
Flooding is the term commonly used to indicate excess overland flow. It is a perfectly natural phenomena and occurs regularly in areas with or without human development. In nature, however, flood events tend to follow predictable patterns. This is because larger storms occur less frequently than smaller ones and, for the most part, landscape features have developed in conjunction with the natural rhythms of infiltration and flow.
That changes when human development enters the picture. One of the key features of development of human construction is covering pieces of land with structures that block rain flow. These so-called "impervious surfaces" can range from driveway to a superhighway, from the roof of a tool shed to the roof of a sports complex.
Accordingto the Natural Resources Defense Council (NRDC), [2] impervious surfaces come in three categories: "rooftop imperviousness from buildings and other structures; transport imperviousness from roadways, parking lots, and other transportation-related facilities; and impaired pervious surfaces, also known as urban soils, which are natural surfaces that become compacted or otherwise altered and less pervious through human action."
All of these, however, have one thing in common: almost every location now covered by an impervious surface was once a site where rainwater could reach the soil. By blocking the infiltration of water, these surfaces also effectively channel and redirect it.
With the natural patterns of runoff changed, we begin to see just how much stormwater was being absorbed by the soil. An inch of rain, for example, falling on a fifty acre parking lot might translate into over a million gallons of water that has to end up somewhere.
In many cases that "somewhere" is into a storm drain and out—in a high volume pulse—to a stream or waterway. The City of Santa Monica, California, for example, has over 2000 catch basins and 64 storm drain lines running to 5 outfalls that empty directly into the Santa Monica Bay and the Pacific Ocean. In Chesapeake, Virginia, 275 miles of piping and 1300 hundred miles of ditches and channels run—untreated—directly to the Elizabeth River and ultimately to the Chesapeake Bay.
Though runoff is a natural phenomena, studies indicate that only 10% of the rain falling on a natural landscape is typically converted to surface flow. The remainder infiltrates the soil, enters groundwater or returns to the atmosphere. On impervious surfaces this changes drastically. The runoff from that 50 acre parking lot may be as much as would be produced by 800 acres of meadowland.
The results of this rapid surface flow and storm pulse are well understood. Table 1 compares the immediate effects of landscape impermeability (e.g.. increased runoff volume) with the larger scale results such as flooding and habitat destruction. All of the immediate effects are due to changes in previous conditions.
While it is true that natural conditions can fluctuate just as much as those influenced by humans, in most cases natural changes develop more slowly, or natural systems return to their previous state more quickly. Since the time frame of most impervious surfaces is indefinite, (how often do you see parking lots made back into meadows?), the natural systems will have to make long term adjustments to their presence.
Increases in the volume of runoff, and increases in the volume and duration of the peak flow period (the largest volume of water during the storm) are, for obvious reasons, related. The more water that isn't getting absorbed by the soil, the more that will have to make its way into the waterways. Not only does this result in excess flooding and erosion, but a strong storm pulse can "scour" the stream bed, removing sediment and destroying habitat. Changes in the shape of a stream are one of the key factors that will degrade the diversity of the wildlife present in it.
| Impacts | |||||
|---|---|---|---|---|---|
| Increase in Volume of Overland Flow | Increase in Volume and Duration of Peak Flow | Decrease Base Flow / Increased Stream Temperature | Changes in Sediment Load | ||
| Outcomes | Flooding |  |
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| Habitat Loss | |
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| Erosion | |
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| Channel Widening | |
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| Stream Bed Changes | |
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| Source: National Resources Defense Council | |||||
"Baseflow," also called "dry weather" flow, is the groundwater that slowly enters and sustains a stream during non-rainy periods. With an increase in impervious surfaces, less water is able to infiltrate into the groundwater, making less water available during dry periods to recharge the stream.
Moreover, because baseflow water is cooler than surface water (a result of being underground) the increase in impervious surfaces will indirectly result in an increase temperature in natural stream systems. This can in turn have a number of adverse effects on the stream's ecological system, most notably a change in the level of dissolved oxygen and a decline in fish species.
While not all flooding is simply the result of impervious surfaces, there is no question that development, including such surfaces, has resulted in flooding becoming the most costly form of natural disaster in the United States. Between 1989 and 1999 just over 45 billion dollars in losses were sustained during floods, and more importantly, almost 1000 people lost their lives.
Yet, as great as the need to manage flood waters, contamination of stormwater may be a more critical issue. In recent years, it has moved stormwater management to the forefront of environmental challenges.
As pure as rainwater?
It is important to realize that stormwater runoff, particularly in urban areas, is not moving across pristine surfaces. Rather, as the NRDC points out, it travels "across rooftops, roads, parking lots, baseball diamonds, construction sites, golf courses, lawns, and other surfaces in our cities and suburbs."
Each of these surfaces has its own complement of natural and human produced substances that can carried into streams either as particles or solutions. From 1977 to 1983 the U.S. government conducted an extensive survey of stormwater pollutants from a total of 2300 storms in 28 major metropolitan areas. The resulting report [3] —known as the National Urban Runoff Program (NURP)—gave a sobering look at a little suspected problem and formed the basis for subsequent governmental action.
Among the substances the NURP study examined were nutrients, like phosphorous and nitrogen, and heavy metals like copper and lead. Subsequent studies have suggested that some of the NURP figures were over- or understated—not surprising, considering that sampling techniques have improved in the past twenty years. However, there is no question that all of these pollutants can still be found in varying amounts in stormwater runoff.
Research results also support concerns over the presence of contaminants in stormwater. One study [4] indicated that exposure to concentrations of some runoff as low as 10% can have detrimental effects on fish larvae. The same study indicated that the toxicity of stormwater is directly proportional to the level of urban development of in a watershed. Other studies [5] have shown that water samples collected in stormwater retention ponds have toxin levels that are considered dangerous to wildlife. Fish in such ponds have been found to have significant concentrations of heavy metals.
Recent studies by NASA [6] indicate that the danger of contaminants to waterways is directly related to the percentage of land covered by impervious surfaces. According the Goddard Spaceflight Center's EOS Project Science Office "when 10 percent to 15 percent of an area is covered by impervious surfaces, the increased sediment and chemical pollutants in runoff have a measurable effect on water quality." Between 15 and 25 percent is associated with reduced levels of oxygen available to stream life. And, with greater than 25 percent of an area covered "many types [of organisms] in streams die from concentrated runoff and sediments."
The ways in which pollutants can enter stormwater are as numerous as they are varied. Gasoline spills reaching stormwater—even the few drops that land on the parking lot when fueling a car—can total up to thousands of gallons a year in urban areas, introducing into runoff both gasoline and additives, such as benzene and ethanol. As we saw last year (KYE 7/00), methyl tertiary-butyl ether (MTBE), an additive designed to combat air pollution, can enter water supplies through just such spills. Even in minuscule amounts, pollutants can add odors and tastes to water that leads to public outcry.
Construction is a major contributor to contaminants in stormwater runoff. Because the construction process often removes natural vegetation and alters the topography of a piece of land, runoff may be amplified as much as it would be on pavement. Construction also characteristically disrupts soil and adds dust, sediment and other particulate matter to the watershed. A variety of chemicals are used in construction processes and these too can enter the surface water through runoff.
It should be noted however, that even after construction is completed, residential development remains one of the most significant contributors to runoff contamination. Research shows that the level of toxins in residential runoff can be just as damaging to aquatic life as runoff from industrial and commercial settings. Examples of residential practices that contribute to runoff contamination include lawn fertilizing, automobile oil changes, car washing, or leaching from improperly disposed grass clippings. Most of these practices, when conducted by individual citizens, are only now starting to be regulated.
The NRDC notes that the "EPA ranks urban runoff and storm-sewer discharges as the second most prevalent source of water quality impairment in our nation's estuaries, and the fourth most prevalent source of impairment of our lakes." The New Jersey Department of Environmental Protection [7] puts it more plainly: "Undisputedly, the main threat to our water quality today is stormwater/nonpoint pollution."
As a result of these observations, in 1987 the US Congress amended the Clean Water Act (CWA), to require municipalities and other stormwater sources to take responsibility for the pollutants generated by their runoff. However, despite the best efforts of Congress to address the stormwater issue, progress has been slow.
As the Congressional Research Office [8] observes "the issue of how to regulate stormwater discharges had a lengthy history of regulatory proposal, delays and legal challenges, and court decisions." In fact, according to a chronology collected by the NRDC, most of the major enforcement moves by the EPA on this matter have been the results of court orders following citizen lawsuits.
The National Pollution Discharge Elimination System (NPDES) is the program designed to oversee and regulate discharges from "point-source" polluters under the CWA. With the 1987 amendments to the CWA, municipal stormwater discharges are considered to be a point source. Under the CWA, all dischargers of point source pollutants—including municipal stormwater—are required to have a permit from the NPDES.
Interpreting stormwater as a point source contaminant, however, has aroused significant criticism from many of those who are required to follow the regulations. The National Association of Flood and Stormwater Management Agencies (NAFSMA) , representing many of the affected municipalities, believes [9] "Rainwater falling on cities and flowing through the local storm drainage system and eventually into streams, rivers, and lakes is a non-point pollution problem that differs fundamentally from point sources of discharge."
The NAFSMA insists that "it is not logical to apply the same water quality standards to municipal stormwater as are applied to point sources." In this view, the requirements of the Clean Water Act are being distorted to address an entirely different class of problem. They believe that "the Clean Water Act should be amended to properly define municipal stormwater water into a specific stormwater program that is neither point source nor non-point source."
Recognizing the complexity of the problem, the legislation provides extended time for implementation, calling for a phased process that requires larger sources of runoff to take steps sooner. Starting in 1992, as the result of a court ruling, the EPA issued regulations requiring municipalities with a population greater than 100,000 to have a permit issued under Phase I of the NPDES. To obtain these permits, municipalities had to take specific steps, including passing and enforcing local ordinances, that would reduce stormwater pollution.
Many municipalities however balk at the costs which compliance with the regulations will require. Moreover, although a 1995 consent decree required the EPA issue regulations to commence Phase II of the law affecting smaller municipalities, there continues to be delays and objections to the plan.
The National Association of Counties (NACo) has pointed out [10] in comments on the pending Phase II regulations, that the average Phase I compliance plan cost municipalities $600,000. Phase II they suggest, will cost far more, to small cities and groups far less able to pay.
William D. Dugat III, managing partner of a Texas environmental law firm is explicit in criticizing the move: "Phase II, as proposed, imposes significant administrative and regulatory burdens on local governments in Texas without any funding and with no regard for actual water quality impacts." [11] Writing that the EPA lacks jurisdiction for imposing such requirements on local governments, Dugat also argues that the regulations are flawed in that they base requirements on population rather than local water quality criteria.
Others writers, however, citing the NURP report and other studies, would counter that the level of contaminant in urban runoff is remarkably similar from one metropolitan area to the next, and that it is the level of land use and development, usually linked to population, that determines the amount of contamination typically found. Given that urban non-point pollution derives from a diffuse range of causes, proponents of the regulations argue that population numbers are the only viable way to approximate impacts on the waterways.
Though the 1987 Amendments to the CWA required Phase II compliance by 1993, delays in setting regulations have pushed that date back to March, 2003. Legislation, supported by the NACo, was proposed in this Congressional session that would make some modifications in the specific requirements of the regulations. Thus far that bill remains in committee.
Best Management Practices
Despite the concerns over cost and the opposition to the regulations by some groups, a number of cities have begun to take steps to comply with the anticipated permit requirement. These requirements direct the operators of small municipal stormwater sewers (MS4's)—as Phase I did for larger municipal systems—to reduce pollutants to the Maximum Extent Possible (MEP), to protect water quality and to follow the Clean Water Act.
Given that stormwater is ubiquitous, and given that the pollutants in stormwater are so varied as to make regulation of individual polluters impossible, what are the alternatives available to municipalities to deal with this problem? Put another way, regulations can't stop the rain, and they can't stop the runoff; what then can they do to stop the flow of pollutants?
Actually, there are a variety of steps communities and individuals can take to decrease contaminants in stormwater runoff. The NRDC has done a study of various methods and found many that can be effective depending on the location and the characteristics of the surrounding landscape. These are often referred to as "Best Management Practices" (BMP's) a term originally coined to describe agricultural methods that reduce erosion. (It should be noted that runoff from agricultural land also presents major problems for waterways, but we are not discussing it here as the remedies and regulations are usually separate from the urban runoff issue.)
The selection and implementation of BMP's is key to how municipalities manage their runoff. The NPDES program, in granting permits, it is designed to promote municipalities using a "toolbox" of BMP's, drawing on a mix of both structural and nonstructural practices designed to address the specific needs of the locale. And while some of these may be costly "structural" BMP's, like stormwater basins or retention tanks, others, the so-called "nonstructural" BMP's may be simple and relatively inexpensive.
In order for the operator of an MS4 to qualify for a permit under Phase II, they must implement a stormwater management program that includes each of six "minimum control measures." These are: public education and outreach, public participation and involvement, detection of illicit discharge, controlling runoff from construction sites and from developed areas following construction, and a category of activities known as "pollution prevention and good housekeeping."
Some of these steps, like controlling runoff from development, are self evident. Others may be less apparent.
For example, few people think of street sweeping as a way of lessening water pollution. Ultimately, though, everything on the streets ends up in the gutter, and just as inevitably, everything in the gutter gets washed into storm drains. And usually, what goes in those drains ends up in waterways. This includes both contaminants and so-called "floatables," i.e. litter that gathers and clogs storm drains. Practices as simple as street cleaning, properly disposing of leaves and grass clippings, and recycling household chemicals can have a limited but tangible effect on the quality of stormwater runoff.
Public education is an important nonstructural BMP and is a specific requirement for communities receiving the NPDES permit. In San Mateo County, California, for example, the Storm Water Pollution Prevention Program (STOPP) coordinates activities that range from stenciling storm drains with warnings not to dump to producing fact sheets that instruct homeowners in techniques for lessening the dumping of contaminants.
"Illicit"discharges are a major part of the stormwater problem. An EPA study in Sacramento found that almost half of the water in the storm drains was not directly attributable to rainfall. In theory, storm sewers are not designed to handle any discharges other than stormwater. (Hence the motto of STOPP: "Only rain in the storm drain.")
The NPDES rules include requirements that each municipality have an ordinance in place to prohibit illicit discharges and that it map its storm sewers in order to identify unauthorized hook ups. They are then directed to have a plan for enforcement and public education.
Illicit does not necessarily mean illegal. In many cases the discharge is due to lack of information. Private activities like car washing and radiator flushing are not commonly thought of as criminal behaviors. Jacksonville FL, for example—recognizing that dumping in storm drains is often due to lack of awareness rather than criminal intent—elicits aid from churches, schools and community groups to make people aware of the problem.
In other cases, however, the illicit use of storm sewers may represent efforts to avoid environmental laws. In such cases law enforcement becomes a tool preventing stormwater contamination. Effectively carrying out such enforcement, however, remains a significant challenge in implementing stormwater policy.
Although some small utilities do not have the power to enact legislation, most jurisdictions now have laws to control introducing waste into storm sewers. Shreveport LA, and Huntsville AL, for example, both have specific city ordinances with permit systems and penalties for discharging contaminants into storm drains.
But, while there is no question that quick and low-cost steps can be taken to address stormwater pollution, other larger scale actions will be required for municipalities to comply with the NPDES requirements. These costlier, structural BMP's often involve collecting, redirecting or treating the urban runoff. As such, they may involve significant capital investment on the part of responsible parties. In some cases these costs may be paid by the developers making changes to the watershed, but larger systems often require public funds. In any case it is the responsibility of the local government to design ordinances and enforcement mechanisms to ensure that these BMP's are utilized.
Many of these structural BMP's go to the heart of the runoff problem—i.e. the role of impervious surfaces in blocking storm water from returning to the soil. In general the EPA recommends three methods for offsetting impervious surfaces—storage, infiltration and vegetative practices. The first two involve collecting and storing the water, allowing it to slowly infiltrate into an area of soil or releasing it slowly into the waterway. The third—vegetative BMP's—refers to using plants and grasses to remove pollutants.
One of more common practices for decreasing flood pulses and minimizing contaminants is the use of one or more permanent storage ponds to detain the water, allow time for sediment and pollutants to settle out, and then release it to a natural waterway or wetlands. This practice has proven very effective in flood control and is showing considerable promise for the removal of toxins.
Storage ponds have become a common feature in the developed landscape. Chesapeake VA, for example, a city of 200,000 reports over 140 such ponds in its 350 square mile area, while Portland OR manages 365 in just 130 square miles. While the exact number of storm management ponds nationwide is unknown, it would almost certainly be in the tens of thousands.
Some municipalities are attempting to use stormwater ponds as landscape amenities, placing them in parks or designing them to serve as natural habitat. Designers have suggested that the ponds offer multiple use options, serving social and natural goals while also controlling stormwater.
The use of ponds, however, is not without controversy. Because these are utilitarian structures, they are often seen as marring the landscape while displacing natural ecosystems. Since they are placed in highly populated areas, there are safety concerns with having open water in proximity of children, and there are recurrent nuisance issues like mosquitoes and algal blooms.
Most recently, concerns have arisen [12] that the sediment collected in the pond, containing heavy metals and other runoff may be hazardous to the wildlife and people in their immediate proximity. Studies of the ponds recommend extreme care be taken in their design and that there be an on-going program of monitoring and maintenance, including removal of sediment.
Because of the strong public works orientation of stormwater management, there is a tendency to seek engineering solutions to stormwater problems. Others, such as the NRDC, however, maintain that the central features of stormwater runoff lie in the patterns of land use and development in the urbanizing of the nation. In this view, land use planning, watershed planning, and political entities may play a more crucial role than specific structures and machinery.
According to the NRDC, "the most important category of stormwater strategies focuses on land use and development. It encompasses a wide range of measures, from regional planning to the use of site-specific structural and nonstructural measures." In this view problems can best be handled by prevention, i.e. by not creating the excess runoff in the first place. "One of the best strategies a municipality can employ is to minimize the aggregate amount of new impervious surfaces."
For many cities, however, limiting impervious surfaces is often seen as limiting economic growth. Only in recent years has coping with stormwater contamination been given a significant role in planning. Moreover, planning for preventative step cannot be easily carried out in areas already urbanized. "These measures...apply more in developing and suburban areas than in ultra-urban areas that are already built up." In those areas that are "largely covered by impervious surfaces, municipalities will need to rely more on the other elements of a stormwater program or on stormwater treatment measures."
This again, however, raises questions of enforcement and finances. For small municipalities, the costs of such programs may be quite daunting. Also, unlike many EPA programs, there has been no money set aside for grants to help localities defray the costs of the regulations.
Faced with uncertain expenses for items ranging from drain stenciling to pond inspections, groups like the NACo and the NAFSWM have expressed deep reservations about the implementation of the Phase II regulations. The politics of the question has become more polarized as some critics consider the stormwater regulation to be an "unfunded mandate," i.e. a directive from the federal government that lacks money to support it. Opposing unfunded mandates has become a major cause, independent of the specifics of stormwater pollution.
On the other hand, environmental groups, faced with understandable concerns over delays and possible effects on water quality, stand ready to again pursue litigation that would compel the EPA to enforce these provisions.
Conclusion
Unlike many environmental issues, which seem to pit government bodies against the private sector, the stormwater controversy is being contested squarely within the public sector. Industrial sites have generally shown greater willingness to retain and manage stormwater. Although the regulations would be felt at all levels of society, the crux of the issue lies with the intergovernmental dispute over local government being induced to take actions for which it feels it does not have sufficient resources.
Scientific evidence, however, supports the argument that non-point source pollution—of which urban runoff is a major component—is having a decidedly detrimental effect on surface water quality. Many would suggest that further delay in action will lead to a variety of environmental impacts, including habitat loss and toxic accumulations.
Perhaps the most intractable aspect of the contamination of urban runoff, is that the "blame" can only be placed on society as a whole. Lacking the "point" of a point source polluter to curtail, the answer to the urban runoff problem must come from widescale adjustments in the habits and practices of millions of individuals and communities. This will be no small task, regardless of the Best Management Practices employed and regardless of the regulations ultimately issued.
References
- US EPA, 1998. The Quality of Our Nation's Waters. A Summary of the National Water Quality Inventory:1998 Report to Congress. US Environmental Protection Agency, Publication EPA841-S-00-001. [go back]
- Lehner, P., G. Clark, D. Cameron and A. Frank, 1999 Stormwater Strategies: Community Responses to Runoff Pollution. Natural Resources Defense Council: Wash. DC. [go back]
- US EPA, 1983. Results of the Nationwide Urban Runoff Program: Volume1 - Final Report. National Technical Information Service Publication No. 83-185552. [go back]
- Skinner, L., A. de Peyster and K. Schiff. (1999) Developmental Effects of Urban Storm Water in Medaka (Oryzias latipes) and Inland Silverside (Menidia beryllina). Arch. Environ. Contam. Toxicology, v. 37, p. 227-235 [go back]
- Campbell, K.R .1994. Concentrations of heavy metals associated with urban runoff in fish living in stormwater treatment ponds. Archives of Environmental Contamination and Toxicology Vol. 27, no. 3, pp. 352-356. [go back]
- NASA, Press Release, 2001. "New Satellite Maps Provide Planners Improved Urban Sprawl Insight." Goddard Space Flight Center, Release 01-101, May 30, 2001. [go back]
- NJ DEP, 1999. Phase II - Stormwater Permitting Program: Improving Water Quality and the Quality of Life. NJ Department of Env. Protection, Division of Water Quality, Bureau of Nonpoint Pollution Control. [go back]
- Copeland, C. 1998. Stormwater Permits: Status of EPA's Regulatory Program.Congressional Research Service, Report for Congress, Wash. DC. [go back]
- NAFSMA. 2000. NAFSMA Position on Municipal Stormwater System Issues For the Clean Water Act Reauthorization. National Association of Flood and Stormwater Management Agencies. On-line: nafsma.org/ [go back]
- Pelletier, J. 1997. Clouds gather over stormwater regulations. County News On-Line, Vol. 29, No. 2. [go back]
- Dugat, B. 1999. "Phase II" Of The EPA'S Stormwater Regulations: An Analysis Of The Impact On Local Governments In Texas. Presented April 8, 1999 at the Local Government Seminar. Bickerstaff, Heath, Smiley, Pollan, Kever & McDaniel, L.L.P. [go back]
- Bishop, C.A. , J. Struger, L. Dunn, D. Forder and S. Kok. (1999) Stormwater detention ponds of Southern Ontario: Are they a risk to wildlife? Great Lakes Fact Sheet. Downsview, ONT: Canadian Wildlife Service, Environment Canada. [go back]