Summary

Urbanization is the changing of land use from forest or agricultural uses to suburban and urban areas. This conversion is proceeding in the United States at an unprecedented pace, and the majority of the country’s population now lives in suburban and urban areas. The creation of impervious surfaces that accompanies urbanization profoundly affects how water moves both above and below ground during and following storm events, the quality of that stormwater, and the ultimate condition of nearby rivers, lakes, and estuaries.

The National Pollutant Discharge Elimination System (NPDES) program under the Clean Water Act (CWA) is the primary federal vehicle to regulate the quality of the nation’s waterbodies. This program was initially developed to reduce pollutants from industrial process wastewater and municipal sewage discharges. These point sources were known to be responsible for poor, often drastically degraded conditions in receiving waterbodies. They were easily regulated because they emanated from identifiable locations, such as pipe outfalls. To address the role of stormwater in causing or contributing to water quality impairments, in 1987 Congress wrote Section 402(p) of the CWA, bringing stormwater control into the NPDES program, and in 1990 the U.S. Environmental Protection Agency (EPA) issued the Phase I Stormwater Rules. These rules require NPDES permits for operators of municipal separate storm sewer systems (MS4s) serving populations over 100,000 and for runoff associated with industry, including construction sites five acres and larger. In 1999 EPA issued the Phase II Stormwater Rule to expand the requirements to small MS4s and construction sites between one and five acres in size.

With the addition of these regulated entities, the overall NPDES program has grown by almost an order of magnitude. EPA estimates that the total number of permittees under the stormwater program at any time exceeds half a million. For comparison, there are fewer than 100,000 non-stormwater (meaning wastewater) permittees covered by the NPDES program. To manage the large number of permittees, the stormwater program relies heavily on the use of general permits to control industrial, construction, and Phase II MS4 discharges. These are usually statewide, one-size-fits-all permits in which general provisions are stipulated.

To comply with the CWA regulations, industrial and construction permittees must create and implement a stormwater pollution prevention plan, and MS4 permittees must implement a stormwater management plan. These plans document the stormwater control measures (SCMs) (sometimes known as best management practices or BMPs) that will be used to prevent stormwater emanating from these sources from degrading nearby waterbodies. These SCMs range from structural methods such as detention ponds and bioswales to non-structural methods such as designing new development to reduce the percentage of impervious surfaces.

A number of problems with the stormwater program as it is currently implemented have been recognized. First, there is limited information available on



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Summary Urbanization is the changing of land use from forest or agricultural uses to suburban and urban areas. This conversion is proceeding in the United States at an unprecedented pace, and the majority of the country’s population now lives in suburban and urban areas. The creation of impervious surfaces that accom- panies urbanization profoundly affects how water moves both above and below ground during and following storm events, the quality of that stormwater, and the ultimate condition of nearby rivers, lakes, and estuaries. The National Pollutant Discharge Elimination System (NPDES) program under the Clean Water Act (CWA) is the primary federal vehicle to regulate the quality of the nation’s waterbodies. This program was initially developed to reduce pollutants from industrial process wastewater and municipal sewage dis- charges. These point sources were known to be responsible for poor, often dras- tically degraded conditions in receiving waterbodies. They were easily regu- lated because they emanated from identifiable locations, such as pipe outfalls. To address the role of stormwater in causing or contributing to water quality impairments, in 1987 Congress wrote Section 402(p) of the CWA, bringing stormwater control into the NPDES program, and in 1990 the U.S. Environ- mental Protection Agency (EPA) issued the Phase I Stormwater Rules. These rules require NPDES permits for operators of municipal separate storm sewer systems (MS4s) serving populations over 100,000 and for runoff associated with industry, including construction sites five acres and larger. In 1999 EPA issued the Phase II Stormwater Rule to expand the requirements to small MS4s and construction sites between one and five acres in size. With the addition of these regulated entities, the overall NPDES program has grown by almost an order of magnitude. EPA estimates that the total num- ber of permittees under the stormwater program at any time exceeds half a mil- lion. For comparison, there are fewer than 100,000 non-stormwater (meaning wastewater) permittees covered by the NPDES program. To manage the large number of permittees, the stormwater program relies heavily on the use of gen- eral permits to control industrial, construction, and Phase II MS4 discharges. These are usually statewide, one-size-fits-all permits in which general provisions are stipulated. To comply with the CWA regulations, industrial and construction permit- tees must create and implement a stormwater pollution prevention plan, and MS4 permittees must implement a stormwater management plan. These plans document the stormwater control measures (SCMs) (sometimes known as best management practices or BMPs) that will be used to prevent stormwater ema- nating from these sources from degrading nearby waterbodies. These SCMs range from structural methods such as detention ponds and bioswales to non- structural methods such as designing new development to reduce the percentage of impervious surfaces. A number of problems with the stormwater program as it is currently im- plemented have been recognized. First, there is limited information available on 1

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2 URBAN STORMWATER MANAGEMENT IN THE UNITED STATES the effectiveness and longevity of many SCMs, thereby contributing to uncer- tainty in their performance. Second, the requirements for monitoring vary de- pending on the regulating entity and the type of activity. For example, a subset of industrial facilities must conduct “benchmark monitoring” and the results often exceed the values established by EPA or the states, but it is unclear whether these exceedances provide useful indicators of potential water quality problems. Finally, state and local stormwater programs are plagued by a lack of resources to review stormwater pollution prevention plans and conduct regular compliance inspections. For all these reasons, the stormwater program has suf- fered from poor accountability and uncertain effectiveness at improving the quality of the nation’s waters. In light of these challenges, EPA requested the advice of the National Re- search Council’s Water Science and Technology Board on the federal stormwa- ter program, considering all entities regulated under the program (i.e., munici- pal, industrial, and construction). The following statement of task guided the work of the committee: (1) Clarify the mechanisms by which pollutants in stormwater discharges affect ambient water quality criteria and define the elements of a “protocol” to link pollutants in stormwater discharges to ambient water quality criteria. (2) Consider how useful monitoring is for both determining the potential of a discharge to contribute to a water quality standards violation and for determin- ing the adequacy of stormwater pollution prevention plans. What specific pa- rameters should be monitored and when and where? What effluent limits and benchmarks are needed to ensure that the discharge does not cause or contribute to a water quality standards violation? (3) Assess and evaluate the relationship between different levels of storm- water pollution prevention plan implementation and in-stream water quality, considering a broad suite of SCMs. (4) Make recommendations for how to best stipulate provisions in storm- water permits to ensure that discharges will not cause or contribute to ex- ceedances of water quality standards. This should be done in the context of general permits. As a part of this task, the committee will consider currently available information on permit and program compliance. (5) Assess the design of the stormwater permitting program implemented under the CWA. Chapter 2 of this report presents the regulatory history of stormwater con- trol in the United States, focusing on relevant portions of the CWA and the fed- eral and state regulations that have been created to implement the Act. Chapter 3 reviews the scientific aspects of stormwater, including sources of pollutants in stormwater, how stormwater moves across the land surface, and its impacts on receiving waters. Chapter 4 evaluates the current industrial and MS4 monitoring requirements, and it considers the multitude of models available for linking stormwater discharges to ambient water quality. Chapter 5 considers the vast

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SUMMARY 3 suite of both structural and nonstructural measures designed to control stormwa- ter and reduce its pollutant loading to waterbodies. In Chapter 6, the limitations and possibilities associated with a new regulatory approach are explored, as are those of a more traditional but enhanced scheme. This new approach, which rests on the broad foundation of correlative studies demonstrating the effects of urbanization on aquatic ecosystems, would reduce the impact of stormwater on receiving waters beyond any efforts currently in widespread practice. THE CHALLENGE OF REGULATING STORMWATER Although stormwater has been long recognized as contributing to water quality impairment, the creation of federal regulations to deal with stormwater quality has occurred only in the last 20 years. Because this longstanding envi- ronmental problem is being addressed so late in the development and manage- ment of urban areas, the laws that mandate better stormwater control are gener- ally incomplete and are often in conflict with state and local rules that have pri- marily stressed the flood control aspects of stormwater management (i.e., mov- ing water away from structures and cities as fast as possible). Many prior inves- tigators have observed that stormwater discharges would ideally be regulated through direct controls on land use, strict limits on both the quantity and quality of stormwater runoff into surface waters, and rigorous monitoring of adjacent waterbodies to ensure that they are not degraded by stormwater discharges. Fu- ture land-use development would be controlled to minimize stormwater dis- charges, and impervious cover and volumetric restrictions would serve as prox- ies for stormwater loading from many of these developments. Products that contribute pollutants through stormwater—like de-icing materials, fertilizers, and vehicular exhaust—would be regulated at a national level to ensure that the most environmentally benign materials are used. Presently, however, the regulation of stormwater is hampered by its associa- tion with a statute that focuses primarily on specific pollutants and ignores the volume of discharges. Also, most stormwater discharges are regulated on an individualized basis without accounting for the cumulative contributions from multiple sources in the same watershed. Perhaps most problematic is that the requirements governing stormwater dischargers leave a great deal of discretion to the dischargers themselves in developing stormwater pollution prevention plans and self-monitoring to ensure compliance. These problems are exacer- bated by the fact that the dual responsibilities of land-use planning and stormwa- ter management within local governments are frequently decoupled. EPA’s current approach to regulating stormwater is unlikely to pro- duce an accurate or complete picture of the extent of the problem, nor is it likely to adequately control stormwater’s contribution to waterbody im- pairment. The lack of rigorous end-of-pipe monitoring, coupled with EPA’s failure to use flow or alternative measures for regulating stormwater, make it

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4 URBAN STORMWATER MANAGEMENT IN THE UNITED STATES difficult for EPA to develop enforceable requirements for stormwater discharg- ers. Instead, the stormwater permits leave a great deal of discretion to the regu- lated community to set their own standards and to self-monitor. Current statis- tics on the states’ implementation of the stormwater program, discharger com- pliance with stormwater requirements, and the ability of states and EPA to in- corporate stormwater permits with Total Maximum Daily Loads are uniformly discouraging. Radical changes to the current regulatory program (see Chapter 6) appear necessary to provide meaningful regulation of stormwater dischargers in the future. Flow and related parameters like impervious cover should be consid- ered for use as proxies for stormwater pollutant loading. These analogs for the traditional focus on the “discharge” of “pollutants” have great potential as a federal stormwater management tool because they provide specific and measur- able targets, while at the same time they focus regulators on water degradation resulting from the increased volume as well as increased pollutant loadings in stormwater runoff. Without these more easily measured parameters for evaluat- ing the contribution of various stormwater sources, regulators will continue to struggle with enormously expensive and potentially technically impossible at- tempts to determine the pollutant loading from individual dischargers or will rely too heavily on unaudited and largely ineffective self-reporting, self- policing, and paperwork enforcement. EPA should engage in much more vigilant regulatory oversight in the national licensing of products that contribute significantly to stormwater pollution. De-icing chemicals, materials used in brake linings, motor fuels, asphalt sealants, fertilizers, and a variety of other products should be examined for their potential contamination of stormwater. Currently, EPA does not appar- ently utilize its existing licensing authority to regulate these products in a way that minimizes their contribution to stormwater contamination. States can also enact restrictions on or tax the application of pesticides or other particularly toxic products. Even local efforts could ultimately help motivate broader scale, federal restrictions on particular products. The federal government should provide more financial support to state and local efforts to regulate stormwater. State and local governments do not have adequate financial support to implement the stormwater program in a rig- orous way. At the very least, Congress should provide states with financial sup- port for engaging in more meaningful regulation of stormwater discharges. EPA should also reassess its allocation of funds within the NPDES program. The agency has traditionally directed funds to focus on the reissuance of NPDES wastewater permits, while the present need is to advance the NPDES stormwater program because NPDES stormwater permittees outnumber wastewater permit- tees more than five fold, and the contribution of diffuse sources of pollution to degradation of the nation’s waterbodies continues to increase.

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SUMMARY 5 EFFECTS OF URBANIZATION ON WATERSHEDS Urbanization causes change to natural systems that tends to occur in the fol- lowing sequence. First, land use and land cover are altered as vegetation and topsoil are removed to make way for agriculture, or subsequently buildings, roads, and other urban infrastructure. These changes, and the introduction of a constructed drainage network, alter the hydrology of the local area, such that receiving waters in the affected watershed experience radically different flow regimes than prior to urbanization. Nearly all of the associated problems result from one underlying cause: loss of the water-retaining and evapotranspirating functions of the soil and vegetation in the urban landscape. In an undeveloped area, rainfall typically infiltrates into the ground surface or is evapotranspirated by vegetation. In the urban landscape, these processes of evapotranspiration and water retention in the soil are diminished, such that stormwater flows rapidly across the land surface and arrives at the stream channel in short, concentrated bursts of high discharge. This transformation of the hydrologic regime is a whole- sale reorganization of the processes of runoff generation, and it occurs throughout the developed landscape. When combined with the introduction of pollutant sources that accompany urbanization (such as lawns, motor vehicles, domesti- cated animals, and industries), these changes in hydrology have led to water quality and habitat degradation in virtually all urban streams. The current state of the science has documented the characteristics of storm- water runoff, including its quantity and quality from many different land covers, as well as the characteristics of dry weather runoff. In addition, many correla- tive studies show how parameters co-vary in important but complex and poorly understood ways (e.g., changes in macroinvertebrate or fish communities asso- ciated with watershed road density or the percentage of impervious cover). Nonetheless, efforts to create mechanistic links between population growth, land-use change, hydrologic alteration, geomorphic adjustments, chemical con- tamination in stormwater, disrupted energy flows and biotic interactions, and changes in ecological communities are still in development. Despite this as- sessment, there are a number of overarching truths that remain poorly integrated into stormwater management decision-making, although they have been robustly characterized for more than a decade and have a strong scientific basis that reaches even farther back through the history of published investigations. There is a direct relationship between land cover and the biological condition of downstream receiving waters. The possibility for the highest levels of aquatic biological condition exists only with very light urban transfor- mation of the landscape. Conversely, the lowest levels of biological condition are inevitable with extensive urban transformation of the landscape, commonly seen after conversion of about one-third to one-half of a contributing watershed into impervious area. Although not every degraded waterbody is a product of intense urban development, all highly urban watersheds produce severely de- graded receiving waters.

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6 URBAN STORMWATER MANAGEMENT IN THE UNITED STATES The protection of aquatic life in urban streams requires an approach that incorporates all stressors. Urban Stream Syndrome reflects a multitude of effects caused by altered hydrology in urban streams, altered habitat, and pol- luted runoff. Focusing on only one of these factors is not an effective manage- ment strategy. For example, even without noticeably elevated pollutant concen- trations in receiving waters, alterations in their hydrologic regimes are associ- ated with impaired biological condition. More comprehensive biological moni- toring of waterbodies will be critical to better understanding the cumulative im- pacts of urbanization on stream condition. The full distribution and sequence of flows (i.e., the flow regime) should be taken into consideration when assessing the impacts of stormwater on streams. Permanently increased stormwater volume is only one aspect of an urban-altered storm hydrograph. It contributes to high in-stream velocities, which in turn increase streambank erosion and accompanying sediment pollu- tion of surface water. Other hydrologic changes, however, include changes in the sequence and frequency of high flows, the rate of rise and fall of the hydro- graph, and the season of the year in which high flows can occur. These all can affect both the physical and biological conditions of streams, lakes, and wet- lands. Thus, effective hydrologic mitigation for urban development cannot just aim to reduce post-development peak flows to predevelopment peak flows. Roads and parking lots can be the most significant type of land cover with respect to stormwater. They constitute as much as 70 percent of total impervious cover in ultra-urban landscapes, and as much as 80 percent of the directly connected impervious cover. Roads tend to capture and export more stormwater pollutants than other land covers in these highly impervious areas, especially in regions of the country having mostly small rainfall events. As rain- fall amounts become larger, pervious areas in most residential land uses become more significant sources of runoff, sediment, nutrients, and landscaping chemi- cals. In all cases, directly connected impervious surfaces (roads, parking lots, and roofs that are directly connected to the drainage system) produce the first runoff observed at a storm-drain inlet and outfall because their travel times are the quickest. MONITORING AND MODELING The stormwater monitoring requirements under the EPA Stormwater Pro- gram are variable and generally sparse, which has led to considerable skepticism about their usefulness. This report considers the amount and value of the data collected over the years by municipalities (which are substantial on a nationwide basis) and by industries, and it makes suggestions for improvement. The MS4 and particularly the industrial stormwater monitoring programs suffer from a paucity of data, from inconsistent sampling techniques, and from requirements

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SUMMARY 7 that are difficult to relate to the compliance of individual dischargers. For these reasons, conclusions about stormwater management are usually made with in- complete information. Stormwater management would benefit most substan- tially from a well-balanced monitoring program that encompasses chemical, biological, and physical parameters from outfalls to receiving waters. Many processes connect sources of pollution to an effect observed in a downstream receiving water—processes that can be represented in watershed models, which are the key to linking stormwater dischargers to impaired receiv- ing waters. The report explores the current capability of models to make such links, including simple models and more involved mechanistic models. At the present time, stormwater modeling has not evolved enough to consistently say whether a particular discharger can be linked to a specific waterbody impair- ment. Some quantitative predictions can be made, particularly those that are based on well-supported causal relationships of a variable that responds to changes in a relatively simple driver (e.g., modeling how a runoff hydrograph or pollutant loading change in response to increased impervious land cover). How- ever, in almost all cases, the uncertainty in the modeling and the data (including its general unavailability), the scale of the problems, and the presence of multi- ple stressors in a watershed make it difficult to assign to any given source a spe- cific contribution to water quality impairment. Because of a 10-year effort to collect and analyze monitoring data from MS4s nationwide, the quality of stormwater from urbanized areas is well characterized. These results come from many thousands of storm events, sys- tematically compiled and widely accessible; they form a robust dataset of utility to theoreticians and practitioners alike. These data make it possible to accu- rately estimate stormwater pollutant concentrations from various land uses. Ad- ditional data are available from other stormwater permit holders that were not originally included in the database and from ongoing projects, and these should be acquired to augment the database and improve its value in stormwater man- agement decision-making. Industry should monitor the quality of stormwater discharges from certain critical industrial sectors in a more sophisticated manner, so that permitting authorities can better establish benchmarks and technology- based effluent guidelines. Many of the benchmark monitoring requirements and effluent guidelines for certain industrial subsectors are based on inaccurate and old information. Furthermore, there has been no nationwide compilation and analysis of industrial benchmark data, as has occurred for MS4 monitoring data, to better understand typical stormwater concentrations of pollutants from various industries. Continuous, flow-weighted sampling methods should replace the tradi- tional collection of stormwater data using grab samples. Data obtained from too few grab samples are highly variable, particularly for industrial monitoring

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8 URBAN STORMWATER MANAGEMENT IN THE UNITED STATES programs, and subject to greater uncertainly because of experimenter error and poor data-collection practices. In order to use stormwater data for decision mak- ing in a scientifically defensible fashion, grab sampling should be abandoned as a credible stormwater sampling approach for virtually all applications. It should be replaced by more accurate and frequent continuous sampling methods that are flow weighted. Flow-weighted composite monitoring should continue for the duration of the rain event. Emerging sensor systems that provide high tem- poral resolution and real-time estimates for specific pollutants should be further investigated, with the aim of providing lower costs and more extensive monitor- ing systems to sample both streamflow and constituent loads. Watershed models are useful tools for predicting downstream impacts from urbanization and designing mitigation to reduce those impacts, but they are incomplete in scope and do not offer definitive causal links between polluted discharges and downstream degradation. Every model simulates only a subset of the multiple interconnections between physical, chemical, and biological processes found in any watershed, and they all use a grossly simpli- fied representation of the true spatial and temporal variability of a watershed. To speak of a “comprehensive watershed model” is thus an oxymoron, because the science of stormwater is not sufficiently far advanced to determine causality between all sources, resulting stressors, and their physical, chemical, and bio- logical responses. Thus, it is not yet possible to create a protocol that mechanis- tically links stormwater dischargers to the quality of receiving waters. The util- ity of models with more modest goals, however, can still be high—as long as the questions being addressed by the model are in fact relevant and important to the functioning of the watershed to which that model is being applied, and sufficient data are available to calibrate the model for the processes included therein. STORMWATER MANAGEMENT APPROACHES A fundamental component of EPA’s stormwater program is the creation of stormwater pollution prevention plans that document the SCMs that will be used to prevent the permittee’s stormwater discharges from degrading local water- bodies. Thus, a consideration of these measures—their effectiveness in meeting different goals, their cost, and how they are coordinated with one another—is central to any evaluation of the stormwater program. The statement of task asks for an evaluation of the relationship between different levels of stormwater pol- lution prevention plan implementation and in-stream water quality. Although the state of knowledge has yet to reveal the mechanistic links that would allow for a full assessment of that relationship, enough is known to design systems of SCMs, on a site-scale or local watershed scale, that can substantially reduce the effects of urbanization. The characteristics, applicability, goals, effectiveness, and cost of nearly 20 different broad categories of SCMs to treat the quality and quantity of stormwa-

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SUMMARY 9 ter runoff are discussed in Chapter 5, organized as they might be applied from the rooftop to the stream. SCMs, when designed, constructed, and maintained correctly, have demonstrated the ability to reduce runoff volume and peak flows and to remove pollutants. A multitude of case studies illustrates the use of SCMs in specific settings and demonstrates that a particular SCM can have a measurable positive effect on water quality or a biological metric. However, the implementation of SCMs at the watershed scale has been too inconsistent and too recent to be able to definitively link their performance to the prolonged sus- tainment—at the watershed level—of receiving water quality, in-stream habitat, or stream geomorphology. Individual controls on stormwater discharges are inadequate as the sole solution to stormwater in urban watersheds. SCM implementation needs to be designed as a system, integrating structural and nonstructural SCMs and in- corporating watershed goals, site characteristics, development land use, con- struction erosion and sedimentation controls, aesthetics, monitoring, and main- tenance. Stormwater cannot be adequately managed on a piecemeal basis due to the complexity of both the hydrologic and pollutant processes and their effect on habitat and stream quality. Past practices of designing detention basins on a site-by-site basis have been ineffective at protecting water quality in receiving waters and only partially effective in meeting flood control requirements. Nonstructural SCMs such as product substitution, better site design, downspout disconnection, conservation of natural areas, and watershed and land-use planning can dramatically reduce the volume of runoff and pollut- ant load from a new development. Such SCMs should be considered first be- fore structural practices. For example, lead concentrations in stormwater have been reduced by at least a factor of 4 after the removal of lead from gasoline. Not creating impervious surfaces or removing a contaminant from the runoff stream simplifies and reduces the reliance on structural SCMs. SCMs that harvest, infiltrate, and evapotranspirate stormwater are critical to reducing the volume and pollutant loading of small storms. Ur- ban municipal separate stormwater conveyance systems have been designed for flood control to protect life and property from extreme rainfall events, but they have generally failed to address the more frequent rain events (<2.5 cm) that are key to recharge and baseflow in most areas. These small storms may only gen- erate runoff from paved areas and transport the “first flush” of contaminants. SCMs designed to remove this class of storms from surface runoff (runoff- volume-reduction SCMs—rainwater harvesting, vegetated, and subsurface) can also help address larger watershed flooding issues. Performance characteristics are starting to be established for most structural and some nonstructural SCMs, but additional research is needed on the relevant hydrologic and water quality processes within SCMs across

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10 URBAN STORMWATER MANAGEMENT IN THE UNITED STATES different climates and soil conditions. Typical data such as long-term load reduction efficiencies and pollutant effluent concentrations can be found in the International Stormwater BMP Database. However, understanding the proc- esses involved in each SCM is in its infancy, making modeling of these SCMs difficult. Seasonal differences, the time between storms, and other factors all affect pollutant loadings emanating from SCMs. Research is needed that moves away from the use of percent removal and toward better simulation of SCM per- formance. Research is particularly important for nonstructural SCMs, which in many cases are more effective, have longer life spans, and require less mainte- nance than structural SCMs. EPA should be a leader in SCM research, both directly by improving its internal modeling efforts and by funding state efforts to monitor and report back on the success of SCMs in the field. The retrofitting of urban areas presents both unique opportunities and challenges. Promoting growth in these areas is desirable because it takes pres- sure off the suburban fringes, thereby preventing sprawl, and it minimizes the creation of new impervious surfaces. However, it is more complex than Greenfields development because of the need to upgrade existing infrastructure, the limited availability and affordability of land, and the complications caused by rezoning. These sites may be contaminated, requiring cleanup before rede- velopment can occur. Both innovative zoning and development incentives, along with the careful selection SCMs, are needed to achieve fair and effective storm-water management in these areas. For example, incentive or performance zoning could be used to allow for greater densities on a site, freeing other por- tions of the site for SCMs. Publicly owned, consolidated SCMs should be strongly considered as there may be insufficient land to have small, on-site sys- tems. The performance and maintenance of the former can be overseen more effectively by a local government entity. The types of SCMs that are used in consolidated facilities—particularly detention basins, wet/dry ponds, and stormwater wetlands—perform multiple functions, such as prevention of streambank erosion, flood control, and large-scale habitat provision. INNOVATIVE STORMWATER MANAGEMENT AND REGULATORY PERMITTING There are numerous innovative regulatory strategies that could be used to improve the EPA’s stormwater program. The course of action most likely to check and reverse degradation of the nation’s aquatic resources would be to base all stormwater and other wastewater discharge permits on watershed boundaries instead of political boundaries. Watershed-based permitting is the regulated allowance of discharges of water and wastes borne by those discharges to waters of the United States, with due consideration of: (1) the implications of those discharges for preservation or improvement of prevailing ecological con- ditions in the watershed’s aquatic systems, (2) cooperation among political ju-

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SUMMARY 11 risdictions sharing a watershed, and (3) coordinated regulation and management of all discharges having the potential to modify the hydrology and water quality of the watershed’s receiving waters. Responsibility and authority for implementation of watershed-based permits would be centralized with a municipal lead permittee working in partnership with other municipalities in the watershed as co-permittees. Permitting authori- ties (designated states or, otherwise, EPA) would adopt a minimum goal in every watershed to avoid any further loss or degradation of designated beneficial uses in the watershed’s component waterbodies and additional goals in some cases aimed at recovering lost beneficial uses. Permittees, with support by the states or EPA, would then move to comprehensive impact source analysis as a foundation for targeting solutions. The most effective solutions are expected to lie in isolating, to the extent possible, receiving waterbodies from exposure to those impact sources. In particular, low-impact design methods, termed Aquatic Resources Conservation Design in this report, should be employed to the fullest extent feasible and backed by conventional SCMs when necessary. The approach gives municipal co-permittees more responsibility, with commensurately greater authority and funding, to manage all of the sources dis- charging, directly or through municipally owned conveyances, to the waterbod- ies comprising the watershed. This report also outlines a new monitoring pro- gram structured to assess progress toward meeting objectives and the overlying goals, diagnosing reasons for any lack of progress, and determining compliance by dischargers. The proposal further includes market-based trading of credits among dischargers to achieve overall compliance in the most efficient manner and adaptive management to determine additional actions if monitoring demon- strates failure to achieve objectives. As a first step to taking the proposed program nationwide, a pilot program is recommended that will allow EPA to work through some of the more predict- able impediments to watershed-based permitting, such as the inevitable limits of an urban municipality’s authority within a larger watershed. Short of adopting watershed-based permitting, other smaller-scale changes to the EPA stormwater program are possible. These recommendations do not preclude watershed-based permitting at some future date, and indeed they lay the groundwork in the near term for an eventual shift to watershed-based permit- ting. Integration of the three permitting types is necessary, such that con- struction and industrial sites come under the jurisdiction of their associated municipalities. Federal and state NPDES permitting authorities do not pres- ently have, and can never reasonably expect to have, sufficient personnel to in- spect and enforce stormwater regulations on more than 100,000 discrete point source facilities discharging stormwater. A better structure would be one where the NPDES permitting authority empowers the MS4 permittees to act as the first tier of entities exercising control on stormwater discharges to the MS4 to protect

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12 URBAN STORMWATER MANAGEMENT IN THE UNITED STATES water quality. The National Pretreatment Program, EPA’s successful treatment program for municipal and industrial wastewater sources, could serve as a model for integration. To improve the industrial, construction, and MS4 permitting programs in their current configuration, EPA should (1) issue guidance for MS4, indus- trial, and construction permittees on what constitutes a design storm for water quality purposes; (2) issue guidance for MS4 permittees on methods to identify high-risk industrial facilities for program prioritization such as inspections; (3) support the compilation and collection of quality industrial stormwater effluent data and SCM effluent quality data in a national database; and (4) develop nu- merical expressions of the MS4 standard of “maximum extent practicable.” Each of these issues is discussed in greater detail in Chapter 6. *** Watershed-based permitting will require additional resources and regulatory program support. Such an approach shifts more attention to ambient outcomes as well as expanded permitting coverage. Additional resources for program implementation could come from shifting existing programmatic resources. For example, some state permitting resources may be shifted away from existing point source programs toward stormwater permitting. Strategic planning and prioritization could shift the distribution of federal and state grant and loan pro- grams to encourage and support more watershed-based stormwater permitting programs. However, securing new levels of public funds will likely be required. All levels of government must recognize that additional resources may be re- quired from citizens and businesses (in the form of taxes, fees, etc.) in order to operate a more comprehensive and effective stormwater permitting program.