Stormwater Runoff Quality Management:
Are Real Water Quality Problems Being Addressed by
Current Structural BMP's?
G. Fred Lee, Ph.D., P.E, D.E.E. and Anne Jones-Lee, Ph.D.
G. Fred Lee & Associates
El Macero, California
Public works directors for many cities and counties, and stormwater runoff quality management agencies are involved in developing programs designed to implement "best management practices" (BMP's) for the control of chemical contaminants in stormwater runoff from urban areas. Numerous articles have been recently published in Public Works and other publications devoted to how a particular city, stormwater quality management entity, consulting firm, and/or regulatory agency is developing structural BMP's, such as detention basins, grassy swales, infiltration systems, etc., for stormwater quality management. While not frequently discussed, such BMP's are constructed at considerable public or private expense.
The current activities in stormwater quality management have evolved from the US EPA's National Urban Runoff Program (NURP) established in the 1970's, and an extension of that program established in 1990 to implement the stormwater-related provisions of the 1987 amendments to the Clean Water Act. Those provisions required the development of an NPDES permit system for urban stormwater discharges from cities with populations greater than 100,000, as well as from selected industries and new developments. The US EPA's current program requires that stormwater "pollution" be controlled to the "maximum extent practicable" ("MEP"). However, what is meant by the word, "pollution," or by the concept of pollution control to the "maximum extent practicable" has not been defined by the US Congress, the US EPA, state pollution control agencies, or local stormwater control agencies. This paper discusses issues of assessing the real pollution, i.e., designated beneficial use impairment in receiving waters, that stormwater runoff causes. Without a clear understanding of the pollution caused by stormwater runoff it is obviously not possible to develop technically valid, cost-effective control programs that control pollution to the "maximum extent practicable."
Large amounts of public and private funds are now being allocated for construction of structural BMP's ostensibly to protect water quality and, for existing discharges, to enhance water quality. However, it is the authors' experience that with few exceptions, a number of significant, inappropriate assumptions are made in the assessment of potential water quality/beneficial use impacts, and the selection and development of BMP's for stormwater runoff quality management. It is commonly taken for granted that the contaminants in existing urban stormwater runoff are having significant adverse impacts on the quality of the waters receiving those discharges. It is also taken for granted that a particular structural BMP will be effective in controlling the chemical contaminants in a stormwater runoff that are alleged to be detrimental to receiving water water quality. However, as discussed herein, there are few documented cases in which urban stormwater-associated chemical contaminants, not derived from illegal connections or illicit dumping, are having a significant adverse impact on the designated beneficial uses of the receiving waters for the discharges. Furthermore, many of the off-the-shelf structural BMP's that are used today have limited efficacy in controlling those portions of chemical contaminants in urban stormwater runoff that have a potential to adversely impact the water quality of the receiving waters for the runoff.
Public works directors and others responsible for the development and implementation of urban stormwater management programs have little reason to doubt that chemical contaminants in urban stormwater discharges are causing highly significant water quality problems in receiving waters. They frequently receive information from federal and state agencies claiming that urban stormwater-associated chemical contaminants are responsible for major water quality problems in the US. Based on its National Water Quality Inventory report to Congress, the US EPA (1992) stated,
"Based in part on national assessments conducted by the US Environmental Protection Agency (EPA) it is now recognized that nonpoint sources and certain diffuse point sources (e.g., stormwater discharges) are responsible for between one-third and two-thirds of existing and threatened impairments of the nation's waters (US EPA, 1991)."
In its "National Water Quality Inventory 1992 Report to Congress," the US EPA (1994) indicated that urban stormwater runoff ranks second in importance as the source of water quality impairment for US lakes and estuaries, and third as the source of water quality impairment of US rivers. As discussed below, however, examination of the basis upon which that conclusion was drawn shows it to be inappropriate for assessing the water quality impacts of stormwater runoff-associated contaminants.
Water quality management in the US is based on protection and/or enhancement of the designated beneficial uses of waterbodies. Stormwater discharges are generally a subject of concern because of the high concentrations of a variety of chemical contaminants that have the potential to be toxic or otherwise adverse to aquatic life in the receiving waters. The typical discussion of stormwater quality "impacts," such as that which evolved from the results of the US EPA's NURP as reported by Pitt and Field (1990) and more recently by the ASCE and WEF (1992) in their manual entitled, "Design and Construction of Urban Stormwater Management Systems," focuses on the presentation of concentrations of a laundry list of chemical contaminants found in stormwater runoff. This can be illustrated by Table 1, a portion of a table presented in the ASCE and WEF (1992) manual (which had been developed from the US EPA (1983) NURP results). While as shown in Table 1, the ASCE and WEF entitled their table, "Water Quality Characteristics of Runoff from Residential and Commercial Areas," that label is inappropriate. The table would have more properly been titled, "Average Concentrations of Selected Chemical Characteristics of Runoff from Residential and Commercial Areas." As discussed below, there is no way to reliably judge the water quality characteristics of urban stormwater runoff based on a laundry list of chemical concentrations found in the runoff, such as presented in Table 1. Trying to judge water quality impacts from such information is analogous to trying to judge the characteristics of clothes based on a laundry list from some unknown person, or on the "average" list received by a laundry. While the laundry list presents an inventory of the number of shirts, pants, ties, etc. in the laundry, it provides no information on the fit, stylishness, color-coordination, suitability for an occasion, etc. of the clothing for a person.
Table 1: "Water Quality Characteristics of Runoff from
Residential and Commercial Areas1"
Average Residential or Commercial Site Concentration
NO2 + NO3 (as N)
1from ASCE and WEF (1992); US EPA (1983)
While the NURP data presented in Table 1 provide information on the average concentrations of a few chemicals found in urban stormwater runoff, it provides no reliable information on the potential significance of those characteristics to water quality in general or for a particular urban stormwater runoff situation. Chemical contaminants exist in a wide variety of chemical forms, only some of which are available to adversely affect water quality/beneficial uses. For example, copper occurs in urban stormwater and highway runoff at elevated concentrations relative to US EPA water quality criteria and state water quality standards for fresh and marine waters. These forms include several soluble forms of copper, such as the uncomplexed copper ion, a variety of inorganic complexes with hydroxyl and carbonate species, a variety of organic complexes with natural and anthropogenic organics and many different particulate forms, such as copper metal, copper precipitates and copper sorbed on various types of particles (suspended solids and colloids). Several studies have shown that a very small part of the total copper present in urban stormwater runoff is toxic-available to potentially adversely affect aquatic life. Only the copper aquo ion, some of the hydroxyl complexes and some of the weak organic complexes are toxic. All of the strong complexes, both soluble and particulate, and all forms of particulate copper are non-toxic. The chemical analytical methods available however do not distinguish among the toxic and non-toxic forms of the soluble copper species.
The determination of contaminant availability cannot be made based on the total concentration of the chemical, especially in a matrix such as urban stormwater runoff. In order for a chemical contaminant to adversely affect an aquatic life-related designated beneficial use, it must adversely impact the numbers, types, and/or characteristics such as wholesomeness of fish and other aquatic life in the receiving water to a sufficient extent to concern the public and cause it to spend funds to control it. To evaluate the water quality impact of stormwater runoff, therefore, it is necessary to develop a site-specific understanding of the aquatic chemistry and aquatic toxicology of the chemical contaminants present in the stormwater runoff, in the particular waters receiving the runoff. This would include the acquisition of site-specific information on the physical, chemical, aquatic life, and beneficial use characteristics of the receiving waters in order to determine whether the chemicals in the particular urban stormwater runoff are having a significant adverse impact on the designated beneficial uses of the waters receiving the runoff.
Obviously, there is need to develop appropriate management approaches to alleviate real water quality problems - beneficial use impairments - caused by chemical contaminants in urban stormwater runoff. This means the effective control of those contaminant forms in stormwater runoff that are adversely impacting the designated beneficial uses of the waters receiving the stormwater runoff discharges. Not only does this involve the reliable assessment of impacts of chemical contaminants present, but it also requires that the management approach target and effectively control the available forms of those contaminants sufficiently to improve the designated beneficial uses of the receiving water without unnecessary expenditures for control of unavailable forms. A critical review of the physical and chemical characteristics of urban stormwater runoff and the aqueous environmental chemistry of the contaminants (i.e., how the chemical contaminants in urban stormwater runoff could potentially adversely impact receiving water quality) shows that it would be rare that conventional structural BMP's of the type being developed today, such as detention basins, grassy swales, and infiltration systems, would be appropriate to address those real water quality problems caused by urban stormwater runoff-associated contaminants. That notwithstanding, some environmental groups and regulatory agencies are advocating control programs for chemical contaminants in urban stormwater runoff that require large expenditures of public funds for the construction of structural BMP's based solely on the fact that the runoff contains elevated concentrations of chemicals and/or that the contaminants in the runoff persist in the waters receiving the runoff by accumulating in the receiving water sediments.
Assessing Water Quality Impacts of Stormwater Runoff
The impact that a chemical contaminant has on aquatic life-related designated beneficial uses of a waterbody depends on the concentrations of available forms of the chemical contaminant in the receiving water, and the duration of organism exposure to particular concentrations of available contaminant forms. The former is controlled by the nature of the chemical contaminants and the types and rates of their chemical reaction/transformation in the receiving water, and the influence of the latter depends on the types and sensitivity of the aquatic organisms of concern in the particular waterbody. These factors are all described by the aqueous environmental chemistry (aquatic chemistry) and aquatic toxicology of the particular situation. In order to evaluate the impact of urban stormwater runoff-associated chemical contaminants on receiving water quality/designated beneficial uses, it is necessary to reliably evaluate the aquatic chemistry and the associated aquatic toxicology of chemical contaminants in urban stormwater runoff as they may impact the designated beneficial uses of waters receiving such runoff.
It has been known for more than 20 years that while the total concentrations of certain chemicals in urban stormwater runoff may be high, the elevated concentrations of contaminants do not necessarily adversely impact real water quality. Figure 1 illustrates fundamental reactions of aqueous environmental chemistry, i.e., key reactions that chemical contaminants can undergo in aquatic systems. Each of the chemical reactions represented in that figure can result in the conversion of toxic/available forms of contaminants into non-toxic, unavailable forms of the contaminant that would be included in the determination of the total concentration of the contaminant. One of the reactions of particular note in the consideration of urban stormwater runoff-associated contaminants is the tendency for many of the contaminants of potential concern in urban stormwater runoff to be associated with particulates. Contaminants associated with particulate matter tend to be unavailable/non-toxic to aquatic life. Thus, while urban stormwater runoff can have high total concentrations of a wide variety of contaminants such as copper and other heavy metals, such contaminants are typically present in urban stormwater runoff as non-toxic, unavailable particulate forms; in such forms, they do not adversely impact the designated beneficial uses of the waters receiving the stormwater runoff. This point is especially noteworthy with regard to urban stormwater runoff contaminant management programs because many of the BMP's focus on removal of particulates and their associated contaminants.
Aquatic toxicology goes hand-in-hand with aquatic chemistry in assessing the impact of chemical contaminants on aquatic life. It describes the response that an organism may have to exposure to contaminant forms, and describes the availability of the chemical contaminants present to organisms. It also describes the conditions of organism exposure to available contaminant forms that elicit adverse responses in aquatic organisms that, in this context, significantly influence the designated beneficial uses of the water. These conditions include among others, the duration of organism exposure, the frequency of exposure, the stage/age of the organism exposed, and the sensitivity of the organism type. Each of those conditions affects or modifies the impact that available forms of a given chemical contaminant has on organisms and hence on aquatic life-related beneficial uses.
One of the elements of aquatic toxicology that is key in the consideration of the impact of urban stormwater runoff-associated contaminants on beneficial uses is the duration of organism exposure. Figure 2 illustrates a generic relationship among the conditions of concentration of available forms, duration of exposure, and potential impact, that is typical of potentially toxic contaminants. The stippled area in the figure represents the combinations of concentration of available forms and duration of organism exposure to that concentration of available forms, that could elicit an adverse impact on an aquatic organism.
The concentration of available forms of the contaminant to which organisms can be exposed for a lifetime without adverse impact (the horizontal delimiting line in Figure 2) is often selected as the water quality criterion or standard value. As illustrated by Figure 2, the presence of available forms of contaminants in concentrations well-above the US EPA water quality criteria and state water quality standards do not adversely impact beneficial uses of a waterbody as long as the duration of exposure is sufficiently short. The shorter the duration of exposure, generally the higher the concentration of available forms of the contaminant to which the organism can be exposed without adverse impact. Very high concentrations of toxic-available forms of contaminants can be present for short periods of time without adversely affecting aquatic life. This is of particular import in the consideration of potential impacts of urban stormwater runoff since such runoff tends to be episodic in nature; receiving-water organisms receive short-duration exposures to the associated chemical contaminants. Furthermore, in many situations, stormwater runoff undergoes rapid dilution in the receiving waters which diminishes the concentrations of contaminants to which organisms are exposed.
Therefore, owing to the aqueous environmental chemistry and toxicology of chemical contaminants, the forms in which many of the chemicals exist in urban stormwater discharges are non-toxic and unavailable to adversely affect aquatic life. Due to the episodic nature of such discharges and the attendant dilution and short durations of organism exposure even available forms of contaminants in urban stormwater runoff thus tend to have little or no impact on receiving water water quality/beneficial uses.
The US EPA's National Water Quality Inventory ranked urban stormwater runoff as the second/third-highest cause of water quality problems in the US. That ranking, however, was an artifact of the methodology employed in the Inventory and does not properly reflect the water quality significance of that source. In conducting the National Water Quality Inventory, the US EPA required states to consider violations of chemical specific water quality standards as tantamount to water quality impairment. As was shown in Table 1, urban stormwater runoff commonly contains a variety of chemical contaminants which, in total concentrations, often exceed US EPA water quality criteria and state water quality standards. This, in turn, causes the receiving waters at the point of stormwater runoff discharge during the discharge event to have concentrations of chemical contaminants above state numeric water quality standards. Since the US EPA arbitrarily adopted a requirement that the state numeric chemical water quality standards cannot be exceeded for more than one hour once in three years, there are many violations of state water quality standards associated with urban stormwater runoff-derived chemical contaminants.
The consideration of a violation of a water quality standard as equivalent to water quality "impairment" disregards the aquatic chemistry and aquatic toxicology of the stormwater-associated chemical contaminants. The exceedence of the water quality standard is an "administrative exceedence;" it does not necessarily, and often does not, represent an impairment of the aquatic life-related designated beneficial uses of the water, i.e., cause a significant diminution of the numbers, types, and characteristics of aquatic life in receiving waters. Judging the need for "management" based on administrative exceedances of numeric standards of the type being used today can be expected to result in the unwise expenditure of funds for the development of chemical contaminant control programs that effect little or no improvement in the designated beneficial uses of waterbodies.
In the past, the cost-effectiveness of contaminant control was rarely considered in developing water pollution control programs. The Clean Water Act made limited provision for the consideration of the cost-effectiveness of control programs for chemical contaminants. This has resulted in the US EPA's developing water quality criteria based on worst-case or near-worst-case assumptions about the impacts of chemical contaminants on aquatic life, and developing implementation approaches that grossly overestimate the impact of chemical contaminants on the designated beneficial uses of waterbodies. Until recently, the aquatic chemistry of chemical contaminants was largely ignored in the establishment and implementation of the criteria; all forms of a contaminant were assumed to be toxic/available. Further, as noted above, the criteria were developed and implemented assuming long-term or critical lifestage (chronic) exposure conditions; they do not consider the short-term, episodic nature of stormwater discharges.
Those in some parts of the US EPA maintain that it is the responsibility of the states in their implementation of the water quality criteria into state standards/enforceable limits, to consider issues of cost-effectiveness in evaluating the need and approaches for contaminant control. However, many states have taken a bureaucratically expedient but technically vacant approach, even under the direction of the US EPA, of simply adopting US EPA water quality criteria as the state's water quality standards, without giving appropriate consideration to the grossly over-protective nature of the application of those criteria/standards to many point- and especially non-point-source discharge/runoff situations.
Therefore, because of the criteria states were required to use in identifying water quality impairment in the National Water Quality Inventory, it is not surprising that they would report to the US EPA that urban stormwater runoff-associated chemical contaminants are a major cause of water quality impairment. However, it is the authors' experience that it will be rare that the chemical contaminants present in typical urban and commercial runoff that are frequently cited as causing impaired water quality will, in fact, impair the designated beneficial uses of the receiving waters for the stormwater runoff.
Another aspect of the US EPA National Water Quality Inventory that is of concern in assessing the impacts of urban stormwater runoff-associated chemical contaminants is its focus on the accumulation in receiving water sediments of contaminants from urban stormwater discharges. To that end, the US EPA is asking states to report sediments with elevated concentrations of chemical contaminants as part of the inventory assessment. It has been well-understood since the 1960's that there is no relationship between the total concentration of chemical contaminants in sediments and the impact of those chemical contaminants on water quality. However, there are still those in federal and state agencies and others who attempt to use the concentrations of selected contaminants in sediments as a basis for judging the impacts of those sediments on water quality. Because of the inherent technical deficiencies in that approach its use can lead to inappropriate assessments of the water quality significance of particulate forms of chemical contaminants as well as strong soluble complexes. This is of concern in urban stormwater runoff since many of the chemical contaminants in urban stormwater runoff are in particulate forms or are associated with particulate matter. Further, substantial parts of the "dissolved" metals in urban stormwater runoff are in colloidal forms or exist as metal complexes.
Because some contaminants in urban stormwater runoff accumulate in receiving water sediment, it has been suggested that such accumulations represent impairment of beneficial uses of receiving waters and that structural BMP's such as detention basins should be required to trap particulates in stormwater runoff. These arguments are without technical foundation. Such assessments cannot be made based on the total composition of stormwater runoff or receiving water sediments. Techniques such as benthic organism bioassays and fish tissue analysis for bioaccumulation of chemicals, have been available for about 20 years to more reliably assess whether chemical contaminants in sediments are potentially adverse to the aquatic-life-related beneficial uses of waterbodies. These techniques should be used to assess whether the discharge of particulate forms of contaminants in urban stormwater runoff that accumulate in sediments is causing significant water quality impacts in the receiving waters.
Example of Stormwater Runoff Regulatory Chaos
One of the better-documented cases of inappropriate classification of a waterbody as "impaired," due in part to urban stormwater contaminant discharges, is San Francisco Bay. The concentrations of total copper in the waters of San Francisco Bay, like many other estuarine bays near large urban centers, exceed the US EPA water quality criterion of 2.9 g/L for more than the one hour once in three years allowed; the total copper concentrations in San Francisco Bay waters are typically 10 to sometimes 15 g/L. Because of that finding, according to current US EPA policy, the San Francisco Bay Regional Water Quality Control Board had to list San Francisco Bay as an "impaired-use" waterbody. That listing, in turn, required that a wasteload allocation and a total maximum daily load (TMDL) for copper be developed for all external sources of copper to the Bay, including urban stormwater runoff, because of the potential toxicity of copper to aquatic life in the watercolumn. The stormwater management agencies that discharge to the Bay are now trying to develop programs to control copper in urban stormwater runoff to meet their TMDL's. However, toxicity studies on San Francisco Bay waters have repeatedly shown that those waters are not toxic to aquatic life. This means that the exceedance of the water quality criterion/standard for copper in San Francisco Bay is an "administrative exceedance" and is not causing impairment of the designated beneficial uses of the Bay waters.
Unless the regulatory agencies adopted a different approach, more than a billion dollars will be spent controlling copper in urban stormwater runoff to San Francisco Bay in an effort to try to eliminate the exceedances of the water quality objective (standard) for copper in Bay waters. This is being done despite the fact that even if all copper discharges to the Bay were eliminated, the stirring of the Bay sediments into the watercolumn during storms will still result in exceedances of the water quality objective for copper, and despite the fact that toxicity testing has shown no toxicity problems in the Bay waters caused by copper as well as other contaminants.
In the mid-1980's, the US EPA did develop an approach for modifying its water quality criteria to give consideration to site-specific water chemistry. However, that "Water Effects Ratio" adjustment approach does not consider the most important aspects of copper chemistry of concern to point- and non-point-source dischargers, namely the relationship between the chemical forms of contaminants such as copper added to the Bay and the forms of the contaminant used in the Water Effects Ratio testing. Following US EPA guidance, the San Francisco Bay Regional Water Quality Control Board conducted a Water Effects Ratio evaluation and was able to raise the copper water quality objective for San Francisco Bay waters from 2.9 to 4.9 g/L. That adjustment was obviously inadequate since Bay waters that contained copper in concentrations at least twice that of the adjusted objective showed no toxicity when evaluated using the same type/stage organism that had originally been used to establish the objective.
Unfortunately the US EPA's recently released "Interim Guidance on Determination and Use of Water-Effect Ratios for Metals" (US EPA, 1994) still does not address the most significant and fundamental problem in the use of the Water Effects Ratio approach for assessing the impacts of stormwater runoff, i.e., the toxicity of specific forms of chemical contaminants in urban stormwater runoff relative to those used to determine the Water Effects Ratio. A regulatory approach needs to be developed to more appropriately consider how chemical contaminants in urban stormwater runoff, and for that matter in many other sources, impact designated beneficial use of waterbodies. Without such an approach, massive amounts of public and private funds will be wasted in the construction of BMP's for urban stormwater runoff-associated contaminants that will effect little or no improvement in the designated beneficial uses of waters receiving those discharges.
As part of working with the US Congress in the reauthorization of the Clean Water Act, the state of California Stormwater Quality Task Force has proposed reauthorization language that would require the US EPA to develop "wet-weather" water quality criteria that could be used by states to regulate chemical contaminants in urban and rural stormwater runoff. Those criteria/standards would be developed to more appropriately consider the aquatic chemistry and aquatic toxicology of urban stormwater runoff-associated chemical contaminants than the current US EPA criteria and state water quality standards. Whatever the mechanism, it is clear that a more appropriate regulatory approach for assessing the water quality significance of stormwater runoff-associated contaminants is needed in the near future to avoid the waste of large amounts of public and private funds in the large-scale construction of structural BMP's that will not effect improvement in designated beneficial uses of receiving waters.
Selection of Structural BMP's
Typically, the structural BMP for a particular situation is selected from a list of BMP's that have been used or have been proposed for use for a number of years, such as detention basins, grassy swales, and infiltration systems. Such BMP's have been developed and used over the years largely for addressing hydraulic concerns, with limited regard for their efficacy in controlling chemical contaminants in stormwater runoff that may adversely impact beneficial uses of the receiving water. A critical review of the nature of the structural "BMP's" adopted for use for controlling urban stormwater runoff-associated contaminants shows that many of them will effect little or no improvement in the designated beneficial uses of the waters receiving existing stormwater discharges.
In order for a structural "BMP" to be cost-effective for managing real water quality problems caused by urban stormwater runoff-associated chemical contaminants, it must in fact control those forms of the chemical contaminant of concern that are adversely impacting the designated beneficial uses of the receiving waters. Further, the degree of improvement in beneficial uses of the receiving water that would accrue from the placement of such a "BMP" should be able to be determined.
One of the most common BMP's for urban stormwater runoff is the detention basin in which stormwater runoff, especially that which occurs during low to moderate flows, is detained for a period of time to allow particulates, and their associated contaminants, to settle. However, as noted above, the particulate forms of chemical contaminants that are removed in detention basins are typically non-toxic; their accumulation in receiving water sediments also rarely causes water quality problems. Where there is a potential problem with toxic chemicals in urban stormwater drainage, it is likely to be caused by dissolved fractions which would not be removed in a stormwater detention basin.
The control of lead in urban and highway stormwater runoff through the use of detention basins (sediment traps) is an example of an inappropriate approach for the control of stormwater runoff associated contaminants. The lead present in urban and highway stormwater runoff is typically in particulate forms and is non-toxic to aquatic life in the receiving water's watercolumn and for that matter in sediments. While some of the particulate lead in stormwater runoff can be trapped in detention basins, sediment traps, etc., much of the finely divided particulate lead and the dissolved lead pass through such systems with little or no removal. Therefore, the use of detention basins and sediment traps for control of lead in urban and highway stormwater runoff is a waste of public and private funds since it will accomplish little, if anything, in the way of improving the designated beneficial uses of the receiving waters for the lead-containing stormwater runoff.
For a situation in which there is concern about the lead present in a particular stormwater runoff discharge, the authors recommend that before any efforts be made to develop a BMP to control lead that a real water quality problem associated with lead be found. If such a problem is found that cannot be controlled by controlling the source of lead that is specifically responsible for the problem, then the BMP for this situation is one in which stormwater treatment would have to be practiced to specifically remove those forms of lead that are responsible for the real water quality problem in the receiving waters caused by lead. That BMP could involve a variety of very costly treatment approaches that would remove the fraction of the dissolved lead that is causing the water quality problem. Such approaches as co-precipitation with iron or alum, ion exchange, reverse osmosis or other technologies would likely have to be used to control lead under those conditions. The cost of collecting, storing and treating the large volumes of stormwater that can occur over a short period of time will be very great compared to the cost of implementing the current structural BMP's. However while the current structural BMP's will largely be cosmetic and ineffective in controlling real water quality problems caused by lead in stormwater runoff, the stormwater treatment BMP would address real water quality problems caused by lead and control them.
The sediment that accumulates in detention basins and sediment traps must be periodically removed. The presence of lead in such sediments can cause these sediments to be considered a hazardous waste and thereby have to be managed as such at a considerably greater expense than the typical approaches that have been used in the past of disposal of a domestic sanitary landfill. Lead accumulated in the sediment traps and detention basins could become a much greater problem in the future if the US EPA changes the allowable TCLP extractable lead to conform to the recent changes in the drinking water standard for lead adopted by the Agency. Many of the stormwater detention basin and sediment trap sediments that now just pass the TCLP test and therefore are classified as a non-hazardous waste could be classified as a hazardous waste if the TCLP allowable lead limit is adjusted downward. This could increase the cost of disposal of sediment accumulated in a structural BMP by a factor of 10 or more. Such increased costs are a waste of public funds since they are arising out of an inappropriate approach for BMP selection to control a non-water quality problem associated with urban and highway stormwater runoff.
Similar problems exist with many other structural BMP's that are typically used today. Those structures were not developed to solve real water quality problems, and have been adopted for use for water quality control based on misconceptions of how chemical contaminants in urban stormwater runoff impact water quality. Unfortunately, in large part because various professional organizations have compiled lists of BMP's, they have now gained the appearance of credibility and reliability far-beyond their real capabilities for addressing real water quality problems arising from chemical contaminants in urban stormwater runoff.
Jones-Lee and Lee (1994) reviewed the approach that they feel stormwater quality managers should follow in developing control programs for chemical contaminants in urban stormwater. The first step should be the determination of whether or not there is a real water quality problem caused by the current stormwater discharges. As discussed above, the fact that a numeric water quality criterion or standard for a particular chemical(s) is exceeded does not evidence a water quality problem. Furthermore, simply finding toxicity in tests of urban stormwater runoff should not be interpreted to mean that there is an impairment of the designated beneficial uses of the receiving waters due to the presence of toxic chemicals in the stormwater runoff. The toxicity tests that are used for domestic and industrial wastewater discharges tend to overestimate the toxicity that will occur in the receiving waters for those discharges. This overestimation is magnified for urban stormwater discharge evaluation because of the short-term, episodic nature of stormwater discharges.
For example, toxicity tests on urban stormwater runoff from many areas are revealing toxicity. Study after study has shown that that toxicity is not due to heavy metals that may be present in the stormwater runoff in elevated concentrations. Rather, the toxicity in the tests appears to be caused by pesticides, such as diazinon, that are used in or around homes. It is important, however, to not jump to the conclusion that the fact that diazinon in stormwater runoff causes toxicity in laboratory tests means that there will be significant toxicity to aquatic life in the waters receiving that runoff. The duration of organism exposure typically used in laboratory toxicity tests typically greatly exceeds the exposure that aquatic organisms can receive in the receiving waters for stormwater discharges. The definition of a real water quality problem requires the conduct of field studies similar to those described by Lee and Jones (1991), in an aquatic-life hazard assessment framework, to determine if toxicity measured in urban stormwater runoff causes toxicity in the receiving waters that impairs the designated beneficial uses of those waters.
Once a real water quality problem (beneficial use impairment) has been identified and reliably traced to urban stormwater runoff as the cause, the sources of available forms of the chemical contaminants responsible for the problem should be determined. Again, the focus should not be on total contaminant concentrations, but rather on the available forms and their respective specific sources. With this type of information it may be possible to control the specific source that yields the contaminant(s) that is adversely impacting the beneficial uses of the waterbody, at the source and thereby eliminate the need to institute control programs for the entire stormwater runoff stream.
If it is not possible to control the contaminant(s) responsible for the water quality problem at the source, a Best Management Practice should be developed for the specific pollutant(s). Such a BMP will likely be quite different from those on the laundry lists of BMP's that are typically presented as being available to control "water pollution" arising from stormwater runoff-associated contaminants. The development of an appropriate BMP requires thorough familiarity with aquatic chemistry, aquatic toxicology, and the behavior of various forms of chemical contaminants in various treatment processes in order to ensure that the BMP is designed and operated to cost-effectively and sufficiently remove the specific forms of the contaminants of concern, and to provide for proper disposal of residues generated during the treatment.
Public Works Directors' Dilemma
At several locations in the US, "environmental" groups are using stormwater runoff as a subject integral to their social engineering missions. "Stormwater quality" appears to be used as a vehicle for achieving control of growth, development, modes of transportation (especially decreased use of the automobile), etc. in an area. By filing lawsuits against a city, state highway agency or other entity responsible for stormwater quality management for alleged stormwater quality NPDES violations, environmental groups have the potential to gain considerable power over a city, etc. and especially its department of public works or other entity that is responsible for stormwater quality in an area. The public works director who suggests to the city council or county board of supervisors that it vigorously oppose the lawsuit soon becomes branded as anti-environment. Few city councils or county boards of supervisors want to be branded as anti-environment. However, capitulating to obviously inappropriate regulatory approaches or to ill-founded lawsuits that inappropriately claim that a city's stormwater runoff-associated chemical contaminants are adversely impacting water quality, is strongly contrary to the best interests of the public in the use of funds available for water quality management for the control of chemical contaminants to effect improvements in designated beneficial uses of waters.
While the broad mission of such environmental groups may be worthy, the attempt to claim that stormwater runoff-associated chemical contaminants are having a significant adverse impact on receiving water quality - designated beneficial uses of a waterbody - when the technical evidence considering the aquatic chemistry and aquatic toxicology is strongly contrary to that position is at best counterproductive. The social engineering of society's ills of inadequately regulated growth, over-dependence on individual auto use, etc. should be addressed through other channels rather than indirectly through maneuvering city or county public works directors to capitulate to an inappropriate settlement of lawsuit that results in expenditure of large amounts of public and private funds addressing the control of contaminants that are not having an adverse impact on designated beneficial uses of a waterbody.
In the early to mid-1970's, at the height of the E-Day movement when the Clean Water Act was developed, the issue of cost-effectiveness of "pollution control" efforts was largely ignored; it has largely been ignored, also, in the various subsequent amendments of the Clean Water Act. Today, however, the public expects that its public officials and their staffs will use the funds made available for water pollution control to address real water quality problems in a technically valid, cost-effective manner. Some states such as California have enacted regulations that require an evaluation of the cost-effectiveness of, and other economic issues associated with, implementing new water pollution control programs. Furthermore, the voters have made it clear that they are not willing to provide unlimited funds to throw at social problems.
California's Porter Cologne Act requires that consideration be given to economic issues in the adoption of regulations for water quality management. However, in 1991 the State Water Resources Control Board adopted water quality objectives (standards) without properly evaluating the economic issues associated with the implementation of those regulations, Plans, and objectives. Several years ago several cities and an industry filed suit against the California Water Resources Control Board because of their concern about the overly protective nature of the water quality objectives adopted in 1991. A California court recently determined that the State Water Resources Control Board did not follow appropriate administrative procedures in developing those objectives. This situation has very important implications for developing technically valid cost-effective approaches for managing stormwater runoff associated contaminants.
The public should be entitled to have their elected representatives, councils, and boards, as well as the public agencies, such as department of public works, stormwater quality management agencies, etc., critically evaluate the cost-effectiveness of a proposed stormwater contaminant control program prior to its implementation. The days when unjustified "water pollution control programs" are implemented to get the regulators and environmentalists "off their backs" are coming to an end. The public is entitled to know, before funds are expended on a structural BMP developed in the name of controlling chemical contaminants in stormwater runoff, what specific improvements in the designated beneficial uses of the receiving waters will accrue as a result of the proposed expenditures. If none can be identified, then the expenditures for "contaminant control" facilities should not be made.
If a community wants to adopt an exceptionally protective approach for the environment in an effort to provide protection against unexpected impacts of unknown stormwater runoff-associated chemical contaminants, then funds should be spent to try to find a real water quality problem caused by the current stormwater runoff, rather than to spend money rather blindly on structural BMP's (e.g., detention basins, wetlands, grassy swales, etc.) that have little likelihood of addressing such problems were they to exist.
It is strongly recommended that any structural BMP that is developed include as part of the cost of construction and operation of the facility sufficient funds to properly monitor its efficacy in effecting an improvement in the designated beneficial use of the receiving waters. Such a monitoring program is significantly different from the monitoring programs that are typically used for stormwater runoff today. As discussed by Lee and Jones-Lee (1994b), the typical stormwater monitoring program conducted today consists largely of determining total concentrations of a few contaminants upgradient and downgradient from the structural BMP. Such monitoring of chemical concentrations has little or nothing to do with true water quality monitoring. Through properly developed monitoring programs it will be possible to gain information that can help to provide guidance to the use of this particular type of BMP at other locations. It will also provide guidance on how the particular type of BMP may be modified to improve its efficacy in addressing real water quality problems.
While it is recognized by many that current US EPA criteria and state water quality standards should not be used to regulate stormwater runoff-associated contaminants, a disturbing trend is developing of using those criteria and standards for judging the efficacy of stormwater structural BMP's. As discussed by Jones-Lee and Lee (1994), that approach is technically invalid and should not be followed. The only way to reliably judge the efficacy of a BMP is to determine how well it effects an improvement in the designated beneficial uses of the waters receiving the stormwater discharge. While this approach costs somewhat more than the typical public works director is used to spending on water pollution control monitoring programs, in the long-term appropriate field studies to define their efficacy will be highly cost-effective in developing BMP's that will cost-effectively control significant adverse impacts of chemical contaminants in urban stormwater runoff.
The technical foundation for the US EPA's and states' stormwater quality management programs has significant deficiencies which, if not addressed in the near-term, will lead to massive waste of public and private funds in constructing structural BMP's that will effect little improvement in the designated beneficial uses of the waters receiving stormwater runoff. In many situations such facilities will not be needed to protect the designated beneficial uses of the waterbody, or will not be cost-effective in removing those components of the urban stormwater runoff that are having a significant adverse impact on the designated beneficial uses of a waterbody. It is essential that public works directors and other concerned with developing and implementing urban stormwater quality management programs work closely with the state and federal agencies in formulating more technically valid approaches for evaluating the water quality significance of chemical contaminants in urban stormwater runoff. Where real water quality problems are found to be caused by stormwater-associated contaminants, they should work toward developing management approaches to address these problems without significant unnecessary expenditures of public and private funds for unjustified chemical contaminant control.
ASCE and WEF, Design and Construction of Urban Stormwater Management Systems, American Society of Civil Engineers and Water Environment Federation, ASCE Manuals and Reports of Engineering Practice No. 77, New York City, NY and Alexandria, VA (1992).
Jones-Lee, A., and Lee, G. F., "Achieving Adequate BMP's for Stormwater Quality Management," Proceedings of the 1994 National Conference on Environmental Engineering, "Critical Issues in Water and Wastewater Treatment," American Society of Civil Engineers, New York, NY, pp. 524-531, July (1994).
Lee, G. F., and Jones, R. A., "Suggested Approach for Assessing Water Quality Impacts of Urban Stormwater Drainage," IN: Symposium Proceedings on Urban Hydrology, American Water Resources Association Symposium, November 1990, AWRA Technical Publication Series TPS-91-4, AWRA, Bethesda, MD, pp.139-151 (1991).
Lee, G. F., and Jones-Lee, A., "Water Quality Impacts of Stormwater-Associated Contaminants: Focus on Real Problems - Condensed Version," Proc. First International IWQA Specialized Conference on Diffuse Pollution: Sources, Prevention, Impact and Abatement, Chicago, IL, pp. 231-240, September (1993).
Lee, G. F., and Jones-Lee, A., "Urban Stormwater Runoff Water Quality and Associated Sediment Quality Issues: An Overview," Report for American Public Works Association/State Water Resources Control Board Stormwater Quality Task Force, Sacramento, CA, March (1994a).
Lee, G. F., and Jones-Lee, A., "Stormwater Quality Monitoring: Correcting Current Deficiencies," Accepted for publication, Proceedings of the American Society of Civil Engineers and Engineering Foundation Conference, "Urban Stormwater Permitting and Related Monitoring," ASCE, New York, NY (1994b).
Pitt, R. E. and Field, R., "Hazardous and Toxic Wastes Associated with Urban Stormwater Runoff," Proc. of the Sixteenth Annual RREL Hazardous Waste Research Symposium, US EPA Office of Research and Development, EPA/600/9-90 037, pp. 274-289 (1990).
US Environmental Protection Agency, "Results of the Nationwide Urban Runoff Program (NURP)," Water Planning Division, Washington, DC (1983).
US EPA, "National Water Quality Inventory 1992 Report to Congress," US Environmental Protection Agency, Office of Water (4503F), EPA 841 F-94-002, Washington, DC, April (1994).
Reference as:"Lee, G. F., and Jones-Lee, A., 'Stormwater Runoff Management: Are Real Water Quality Problems Being Addressed by Current Structural Best Management Practices?,' Part 1 Public Works, 125:53-57,70-72 (1994). Part Two, 126:54-56 (1995)."