The Next Step for the Stormwater Program
Improvement in the water quality of the nation’s receiving waters appears to have stalled; municipal permits require stormwater managers to meet ever-more-stringent requirements that are expensive and offer unknown environmental benefits. The solution? A roadmap for stormwater quality improvement that features volume control, source control, and regulatory changes.
Nationally, outfall monitoring data indicate that constituent concentrations in stormwater discharges are in excess of water-quality objectives/criteria in many cases. However, water-quality objectives/criteria apply in the receiving water, and an elevated constituent concentration at the outfall does not necessarily equate to an exceedance in the receiving water. A regulatory “exceedance” has not been defined for stormwater discharges. The courts are beginning to fill this definition void. (See United States Court of Appeals for the Ninth Circuit, NRDC et al. v. County of Los Angeles et al., No. 10-56017, March 10, 2011.) Permittees and stakeholders want to protect beneficial uses in the nation’s receiving waters and want to achieve this goal in the most effective, efficient, and timely manner possible. The adaptive program approach used to date needs to be improved through a comprehensive framework that includes a defined pathway to achieve standards, with a set of proven tools, both technical and financial, for stormwater permittees to use. The framework defined here includes familiar actions—prioritization, measurability, and periodic review and modification—and is based on four program areas: volume control, source control, program effectiveness assessment, and regulatory modification.
Controlling stormwater runoff volume makes good sense. Hydromodification impacts have been shown to adversely affect the habitat in natural stream systems, and a reduction in runoff volume equates to a reduction in constituent loading and potentially an increase in groundwater recharge. Stormwater volume control appears to be the number one issue in the current EPA rulemaking process.
Stormwater runoff volume can be controlled with the use of low-impact development (LID) principles. Novotny et al. (2010) note in Water Centric Sustainable Communities: Planning, Retrofitting, and Building the Next Urban Environment that LID principles are resilient and promote true sustainable principles by using and reusing water locally within the watershed. LID mechanisms are resistant to widespread failure because they are a distributed approach—one failed location does not bring down the entire system.
LID management measures should be sized to replicate the pre-project hydrologic condition. For greenfields, this means the predevelopment condition; for brownfields, this means the existing urbanized condition. Existing infrastructure generally does not lend itself readily to retrofit with LID, and a reduction in volume to predevelopment conditions in many cases is not technically or economically feasible. Imposing a predevelopment volume control standard on the built environment would be costly, with a poor return on investment. A balanced approach recognizes the value of existing infrastructure and incorporates measures that use existing infrastructure assets.
For example, permeable friction course overlays have been shown to dramatically improve water quality on arterial highways and freeways (Barrett et al. 2006), along with safety and other benefits. The overlay is compatible with existing infrastructure and drainage systems and is easily retrofit at a modest cost. Engineered flow dispersion may be an effective retrofit under prescribed conditions. Batch detention using active outlet control (Middleton et al. 2007) is also easily retrofit in existing flood control infrastructure and provides very good performance for a modest capital and operations and maintenance (O&M) cost. Green roofs may be suitable for some existing structures, and the use of permeable pavements can also be incorporated into rehabilitation projects.
Setting a goal of predevelopment hydrology in existing urban areas is not a high environmental priority. Urban channels that have been significantly altered for alignment, grade, flow, and sediment transport have adjusted to the new conditions; restoring stream hydrology within the watershed requires a large capital
investment but will not restore the functions and values of the predevelopment stream. The primary problem is that the stream alignment is confined in urban areas, and the floodplain no longer exists. Streams in nature meander, tending toward minimum work; a straight section more than 20 times the channel width is rare. In such cases, stream restoration projects should focus on accommodating the new channel conditions and providing benefits (restored aesthetics and habitat value) at a fraction of the cost of mitigating watershed hydrology to predevelopment conditions. Resources for environmental restoration must be prioritized and applied for maximum benefit, since under any scenario large capital outlays will be required, and public support will only be maintained if the benefit of restoration projects is apparent.
Restoring natural water balance, optimizing the use of water resources locally, and protecting water quality are all important goals. The approach and emphasis on each will depend on the configuration of existing infrastructure, and on how the most benefit can be obtained the most efficiently. Continuous improvement on a prioritized basis that maximizes the effectiveness of available resources must be the foundation of any strategy.
Volume reduction through LID implementation has exceptional applicability on the urbanizing fringe. Matching predevelopment hydrology should be required, as should maintaining predevelopment bed material load in receiving channels. Continuous simulation tools, such as the Western Washington Hydrology Model, make the design and analysis for matching the predevelopment hydrology a relatively simple process. Predevelopment bed material load can be maintained by avoiding stream courses onsite and developing in upland areas that do not contribute bed material. Active and
passive recreation areas may be better placed adjacent to streams, since a setback will be required to allow streams to meander without threatening structures.
The number of chemical compounds used in society continues to expand, and the impact that these compounds have on surface water resources is, in most cases, poorly understood.
Daughton (2004) noted that, as of March 2004, nearly 23 million organic and inorganic substances had been indexed by the American Chemical Society’s Chemical Abstracts Service. Roughly seven million of those substances are available commercially. Not all of these compounds have an active pathway to the environment, nor would they be harmful if they did. However, when the number of commercially available substances is contrasted with the number of compounds sampled in a typical municipal stormwater program (about 150 at best), it is clear that there is a significant potential for surface water pollution of unknown origin. Viewed strictly from a human health perspective, about 120 diseases have been linked to pollution, with still others deemed to be potentially linked (Lean 2004); research is ongoing.
The implementation of total maximum daily loads (TMDLs)—the sum of the loads of a single pollutant from all contributing point and nonpoint sources that is allowed to be discharged to a water body under the Clean Water Act (CWA)—is consuming the permitting process. Many National Pollutant Discharge Elimination System (NPDES) permits now include load allocations for specific constituents in stormwater runoff. Some programs, such as the one operated by the Wisconsin Department of Natural Resources, have begun placing numeric limits on selected stormwater constituents. Unfortunately, the sophistication of many stormwater pollution control measures has failed to keep pace with these increased regulatory demands. Several studies have been completed of typical municipal discharges showing that water-quality standards cannot be achieved through the implementation of even the most comprehensive current source-control and stormwater treatment program. The current system results in the diversion of substantial resources to litigation regarding TMDLs and violations of receiving water standards, and does not promote innovation through assessment, prevention, and treatment. Compliance with TMDLs on a constituent-by-constituent basis is rapidly beginning to dominate municipal and institutional stormwater program budgets and resources—at the expense of efficiency.
The current problem facing most NPDES permittees is the few viable methods available to achieve water-quality standards in existing urban areas. Source-control options have been explored only modestly within current legislative boundaries, and treatment controls have consistently been shown to provide a basic level of performance. Implementation of LID and volume reduction is an important step in maintaining water quality, but alone will not meet the goals of the CWA. The fundamental problem lies in the wide variety of potential pollutants, both particulate and dissolved; the variability of the quality of runoff; and the high runoff volume. The variable nature of surface water runoff means engineered solutions quickly prove to be few and costly.
The author has reviewed characterization data from several municipal stormwater programs in northern and southern California to generally assess stormwater runoff discharge compliance in comparison to receiving water standards. Table 1 provides an overview of the constituents that were found to potentially exceed the receiving water objectives in stormwater discharges on a widespread basis.
It is clear from the number of potential constituents that can cause surface water pollution and the results of current constituent monitoring programs that chemical-based analysis programs (mass emissions monitoring) are inefficient and ineffective.
There are steps that can be taken to achieve water-quality standards and address the potential impairments to receiving waters that are of most interest to the public: toxicity, bioaccumulation, dissolved oxygen depletion, eutrophication, sanitary quality, sedimentation, litter, and oil and grease. Volume reduction—combined with a more aggressive form of source control, the second element of the roadmap—can achieve water-quality standards in receiving waters in many cases.
Municipalities can rely on ordinances enacted by the local city or county to help them meet the requirements set forth in their NPDES permits, but municipal NPDES permits cannot dictate what is introduced into the
environment. Surface water pollution remains largely unregulated at the source level. Consumer education and enforcement are difficult tasks for municipalities that may not have the manpower or the right to enter and inspect property, and only limited influence to modify personal behavior. Municipal programs are left with treatment controls, including LID, as a primary tool for municipal separate storm sewer system (MS4) permit compliance.
If current municipal permitting strategies are taken to their apparent logical conclusion—requiring the retrofit of treatment controls in existing urbanized areas while maintaining current source-control implementation strategies—there will still remain a substantial gap between stormwater effluent quality and receiving water standards. The situation is analogous to control of water quality from a construction site where only sediment controls (such as sediment basins and silt fences) may be used. Without true source controls, municipal programs will be limited in the level of runoff receiving water quality that they can achieve.
To progress to the next level in urban runoff water quality, a new source-control program, true source control, must be implemented. Regulatory agencies must exercise more authority to control manufacturer activity based on the findings of municipal receiving water monitoring programs.
Specific tools that are needed at the municipal level include
- Greater focus on receiving water monitoring for beneficial use impairments, and less focus on mass emission monitoring
- The ability of the permitting authority, through current processes, to establish local ordinances to ban the sale and use of consumer products that are shown to be contributing to the exceedance of receiving water standards
The specific tool that the regulatory community must develop and implement is the ability of the permitting authority to restrict or otherwise control consumer, commercial, and agricultural application or use of products that are shown to be contributing to the exceedance of a receiving water standard.
The factors affecting water quality are numerous and cross all jurisdictional, regulatory, social, and economic boundaries. Government must therefore play a larger role for surface water quality efforts to be successful. EPA in 2003 noted that the application of a pesticide to waters of the United States, if consistent with the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), did not constitute a discharge of a pollutant under the CWA. Yet the presence of such a compound will violate receiving water standards for toxicity. The US Geological Survey has found widespread toxicity from pesticides in receiving waters nationally.
EPA has responsibility under Section 5 of the Toxic Substances Control Act (TSCA) to evaluate new commercial substances for threats to human health or the environment, but products are evaluated only at the point of use. It does not appear that this assessment is conducted in sufficient detail to evaluate or prohibit impacts regulated under the CWA. The agency is charged with weighing the “risks versus the social and economic benefits” of a substance to determine if it should be approved for use. The possibility of pollution occurring from “approved” compounds is anticipated by the CWA in section 403(a), which directs EPA to set water-quality criteria for pollutants. But the promulgation of standards under section 403(a) can be an exceptionally slow process. For example, in 2003 EPA published a draft criteria document for nonylphenol, but it does not appear to have made any progress since. Nonylphenol has been known for some time to cause surface water quality problems. A regulatory process that sets water-quality criteria after a compound is in use and only after it has been found to impact beneficial uses of receiving waters cannot possibly keep pace with the realities of chemical production and use.
The application of true source control means the approach to regulation through the requirements placed on manufacturers prior to approval of a compound for commercial use must change. Basic evaluations of water-quality impacts of new substances should be required of the manufacturer using established protocols. Methods of controlling the substance in the environment—and the costs to do so—could be predetermined so that a more informed cost-benefit analysis can be completed. Moreover, cross-media contamination is rarely examined; it is appropriate to regulate air and water quality together, setting standards that are protective of both resources and
recognizing their interdependence.
Program Effectiveness Assessment
Phase I of NPDES is entering its fourth generation of permits, and permit requirements continue to ratchet down without the benefit of a comprehensive effectiveness assessment. New permit requirements tend to be layered on top of the previous iteration, diluting the effort that may be applied to the most effective programs.
NPDES permits are, at best, locked in a five-year assessment cycle, which in many cases is not adequate to assess the performance of pollution prevention programs and best management practices. Although the NPDES program is adaptive in nature, there is no mechanism to eliminate less-effective programs in favor of more beneficial approaches; rather the stormwater program continues to grow in size and complexity but with a diminishing return on investment.
Unfortunately, a rigorous program effectiveness assessment is usually deferred in favor of reporting of implementation activities and the collection of mass emissions monitoring data. Adaptive programs require high-quality feedback to be successful. The quality of the feedback mechanisms will absolutely dictate the rate of improvement in the program being managed. There is very little information available to critically assess the effectiveness of municipal stormwater programs. The California Stormwater Quality Association has published a handbook, Municipal Stormwater Program Effectiveness Assessment Guidance, and is currently working on the second generation of this document to be available in early 2012.
More resources must be invested in effectiveness assessment for the municipal stormwater program to be successful. Simply stated, there are few resources being directed to inform the adaptive improvement process. Characterization monitoring, by far the focus of most programs, provides little actionable information to fourth-round Phase I programs or Phase II programs that can benefit from their experience.
The fourth and final part of the roadmap for stormwater runoff is implementation guidance, legislation, or rulemaking developed specifically for wet-weather events. Ultimately, receiving water standards and discharge standards for wet weather will be possible. The recent EPA memo (November 2010) regarding establishing TMDL wasteload allocations in NPDES permits could accelerate the rate at which numeric effluent limits become part of the landscape for stormwater NPDES permits. There is continuous pressure to establish numeric limits, with the expectation that compliance will improve. The variability of environmental factors and constituent concentrations in stormwater, and the vast number of chemicals in stormwater and potential pathways for contamination of runoff, will not allow a treatment-based solution.
Water-quality criteria for aquatic life and human health protection are needed, but the first priority is to solve known problems in stormwater in an effective and affordable manner. For many water-quality problems, such as sanitary quality, a solution will require all four elements of the roadmap.
The current water-quality criteria and regulations were established for an NPDES program intended to address continuous wastewater discharges, and are not appropriate for episodic and highly variable stormwater discharges. As shown in Table 1, stormwater exceeds numeric objectives for some constituents at the end of pipe, but in most cases there does not appear to be corresponding environmental harm. Resources used addressing administrative exceedances of inapplicable standards offer no public benefit. If all numerical exceedances of water-quality standards are given the same level of importance, the problems causing water pollution matter no more than those that do not.
It is impractical for EPA to develop water-quality standards for the potential millions of chemicals and compounds that may come in contact with stormwater. But it is not unreasonable to require manufacturers to develop this information prior to bringing a product to market, or to develop it when a product is reregistered. Studies must address the fate of the chemical or compound over its complete lifecycle, not just at the point of initial use. And guidelines for the use of the chemical must be developed to ensure that there are not pathways to the nations receiving waters that would exceed safe limits.
There is a critical need to develop a regulatory program for municipal stormwater discharges in the existing point-source program—specifically, the future development of the water-quality criteria for stormwater discharges. The development of these standards must not precede the availability of effective tools that are affordable by society to meet them. The most urgent need will be for effective and affordable tools for the built environment.
Sources of surface water pollution are diverse and dispersed and have a variable threat. Regulation at the point of greatest control (at the point of use of a potential pollutant) is the most viable and economic approach for stormwater quality improvement. There are far too few resources being invested in source identification and elimination for stormwater—true source control. Effectiveness assessment of municipal programs is deferred in favor of more prescriptive permits, with permit programs added to existing programs rather than meaningful approaches refined and less-effective ones eliminated. Fundamentally, the quality of feedback loops will determine the rate of improvement in stormwater programs. Behavior change will also be a critical component in the rate of progress. The number chemicals of concern and contamination pathways is simply too great in the environment to rely on treatment technology as the primary solution to the problem.
It is apparent that business as usual will not achieve our goal of compliance with the CWA and is neither affordable nor sustainable. In the end, there is more risk in continuing to pursue our current approach than in developing a new and comprehensive compliance plan to achieve beneficial uses in receiving waters. A balanced problem-based approach is needed that incorporates volume control, true constituent source control, improved effectiveness assessment, and a new regulatory approach for stormwater compliance with water-quality objectives.
Scott Taylor, P.E., D.WRE, FASCE, is a senior vice president with RBF Consulting in Irvine, CA.
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