G. Fred Lee, PhD, PE, DEE and Anne Jones-Lee, PhD
G. Fred Lee & Associates
El Macero, CA
Ph: 530-753-9630
Fx: 530-753-9956
[email protected]

Extended Abstract

The federal Clean Water Act prohibits NPDES-permitted wastewater discharges from causing ambient water quality standard violations in the receiving waters for the discharge. This approach is being used to regulate point source discharges of domestic and industrial wastewaters. In 1990, the US EPA implemented a national urban area and highway stormwater runoff water quality management program which requires that pollution of the receiving waters by stormwater runoff from permitted areas be controlled to the maximum extent practicable (MEP) using best management practices (BMPs). Urban areas above a certain population (phase 1 100,000) and highway stormwater runoff management entities are issued NPDES permits for these discharges. Urban area and highway stormwater discharges must, under current regulatory requirements, also meet the traditional point source discharge Clean Water Act requirements of not causing exceedances of water quality standards in the receiving waters for the discharge.

The nature of urban area and highway stormwater runoff at times having high flows for short periods of time and then extended periods of time with no flow would require the construction of large treatment works to treat urban area and highway stormwater runoff to the same degree as is being used for traditional point source discharges of domestic and industrial wastewaters, i.e. no more than one exceedance of a water quality standard in the receiving waters for the discharge for more than once in three years. This would cause urban dwellers regulated under the NPDES stormwater permit to have to spend between $1 to $2 per person per day in perpetuity to achieve this degree of constituent control in highway and urban area stormwater runoff.

While it has been possible to require that traditional point source discharges of wastewaters achieve this degree of treatment, i.e. no exceedance of a water quality standard in the receiving waters at the edge of a mixing zone, if allowed, more than once in three years, it is recognized that that approach often leads to unnecessary expenditures for wastewater effluent constituent control. The application of traditional point source discharge requirements to urban area and highway stormwater runoff would lead to an even more over-protective situation due to the short-term, episodic nature of stormwater runoff and the fact that many of the constituents of potential concern in stormwater runoff from urban areas and highways are in particulate, non-toxic, non-available forms.

The US EPA, in an attempt to address this situation, has determined that while NPDES permitted urban area and highway stormwater runoff must conform to Clean Water Act requirements of not causing exceedances of water quality standards in the receiving waters for the runoff, such exceedances do not represent a violation of the NPDES permit. The situation has therefore evolved to one of using US EPA water quality criteria and state standards based on these criteria as goals for implementation of BMPs to control "pollution" to the MEP. This paper addresses the appropriateness of using US EPA water quality criteria as goals for urban area and highway stormwater runoff water quality management and presents an alternative more cost effective approach for regulating urban area and highway stormwater runoff that focuses on controlling real water quality use impairments in the receiving waters for the runoff.

One of the most significant fundamental problems with the current urban area and highway stormwater quality impact evaluation and management programs is a proper assessment of the pollution caused by such runoff-associated constituents. Far too often, a chemical constituent, such as a heavy metal, that has been found at some location in some waterbody at some time to be adverse to aquatic life in that waterbody and therefore be a pollutant that impairs use of that waterbody, there is an assumption made that all discharges of that constituent heavy metal at all locations at all times that cause an exceedance of a water quality standard at the point where the stormwater enters a waterbody causes pollution of the waterbody. Under these conditions, chemical constituents, irrespective of their chemical forms and duration of exposure, are considered to be pollutants. Obviously, such an approach is technically invalid and can result in massive waste of public and private funds in developing treatment works for chemical constituents in urban area and highway stormwater runoff that are not adverse to the designated beneficial uses of the receiving waters for the runoff.

In situations where there is a large surplus of funds available for managing environmental problems and there are no other significant social problems which need funding, it may be acceptable to conclude that as part of "pollution" prevention it is appropriate to control heavy metals and other constituents in urban area and highway stormwater runoff so that the receiving waters for such runoff do not have exceedances of water quality standards for regulated chemicals more than once in three years at the point where the stormwater runoff enters the receiving waters. However, today where there are significant societal problems for which there is need for funds and there are limited funds available for water pollution control, it is important to focus the funds available on managing real, significant water quality use impairments of the receiving waters for the stormwater runoff.

A critical review of how US EPA water quality criteria were developed relative to the characteristics of urban area and highway stormwater runoff-associated constituents shows that, in general, significant exceedances of water quality standards based on US EPA water quality criteria can occur in urban area and highway stormwater runoff without adversely impacting the designated beneficial uses the receiving waters for the runoff. This situation arises from two characteristics of US EPA criteria. The first of these is the aquatic chemistry of the constituents used in the toxicity testing used to establish the criteria for potentially toxic chemicals. Urban area and highway stormwater runoff-associated constituents are largely in particulate forms and have been, in general, demonstrated repeatedly since the 1960s to be non-toxic and non-available to be adverse to aquatic life through potential toxicity or to public health through bioaccumulation in aquatic organism tissue used as food.

The short-term, episodic nature of urban area and highway stormwater runoff relative to the duration of time used in the toxicity tests or a period of time necessary to achieve significant bioaccumulation of the constituents of concern is short compared to the time necessary to be adverse aquatic life. While the US EPA water quality criteria and state standards based on these criteria have one-hour exposure criterion values, it is understood that these one-hour exposure concentrations, i.e. acute criterion, do not properly represent the real exposures that can occur without adverse impacts of most constituents to aquatic life without adverse impact on the organism. Therefore, exceedance of a water quality criterion at the point where stormwater runoff from urban areas and highways occurs should not be interpreted to mean that this exceedance represents a potentially significant impairment of the designated beneficial uses of the receiving waters for the runoff.

For potentially toxic chemicals, in order for this exceedance to be of significance to the public who must ultimately pay for controlling constituents in urban area and highway stormwater runoff, it must significantly alter the numbers, types and characteristics of desirable forms of aquatic life. For potentially toxic chemicals, this means that the stormwater runoff should be toxic at the point of discharge and the toxicity should persist for a sufficient period of time and over a sufficient area to be significantly adverse to aquatic life within this area and that these adverse impacts are manifested in terms of reduced numbers of aquatic organisms of concern to the public.

For chemicals of concern because of potential bioaccumulation, such as mercury in urban area and highway stormwater runoff, the concentrations of mercury in such runoff either alone or in combination with mercury in a bioaccumulatable form already in the receiving waters should result in excessive bioaccumulation of mercury in edible organism tissue that causes or could cause a human health advisory to be issued for the use of the organisms as food. Eventually as wildlife based critical tissue concentration criteria are established, consideration of the bioaccumulatable impacts of constituents on wildlife should be included in evaluating whether whole organism tissue residues are potentially adverse to wildlife.

One of the most significant problems associated with the use of exceedances of water quality criteria/standards to judge potential water quality problems from urban area and highway stormwater runoff is that only a limited number of the chemical constituents present in urban area and highway stormwater runoff are regulated, i.e. for which there are water quality criteria. There is growing evidence that the primary constituents of concern in urban area and highway stormwater runoff are unregulated chemicals for which there are no criteria, such as the organophosphorus pesticides as well as other pesticides and fungicides.

It therefore may be concluded that using US EPA water quality criteria as goals for regulating regulated chemical constituents in urban area and highway stormwater runoff can readily lead to technically invalid approaches and focus control programs on inert constituents of limited water quality significance, while at the same time fail to identify important constituents in urban area and highway stormwater runoff that are adverse to the beneficial uses of a waterbody receiving such runoff.

Alternative Goals for Stormwater Management

An alternative approach for developing a more technically valid, cost-effective management of real water quality problems associated with urban area and highway stormwater runoff involves examination of the receiving waters for adverse impacts in what is called an "evaluation monitoring" program. Rather than measuring a suite of heavy metals that are of concern because of their potential toxicity to aquatic life at the edge of the payment for urban area and highway stormwater runoff as it enters a particular waterbody, the evaluation monitoring approach measures toxicity using sensitive species and standard toxicity tests. These toxicity assessment involves the use of the same kinds of tests that have been used to establish the water quality criteria and therefore the organisms are responding to the same kinds of impacts as are protected by the criteria.

The evaluation monitoring approach focuses on toxicity and considers such issues as the fate, areal extent and persistence of toxicity within the receiving waters to determine whether toxicity in a stormwater discharge occurs in the receiving waters to a sufficient degree to be potentially adverse to aquatic life in the waterbody. Toxicity due to the unregulated chemicals such as the organophosphorus pesticides used in urban areas that is present in urban area stormwater runoff is also assessed in the evaluation monitoring program.

Evaluation monitoring considers not only toxicity, but also addresses bioaccumulation through direct measurement of excessive tissue residue of organisms in the region. If excessive concentrations of chlorinated hydrocarbons or mercury, i.e. those chemicals for which there are critical human health tissue residues, are found, then the source of the constituents specifically responsible for the available forms that are bioaccumulating to excessive levels is determined through forensic studies within the waterbody and watershed.

Evaluation monitoring is implemented as a watershed based regulatory agency, discharger, environmental group and public stakeholder implemented program that focuses on finding significant water quality use impairments in the receiving waters for the stormwater runoff that warrant the public's expenditure of funds for pollutant control using site specific BMPs to the MEP. In addition to considering toxicity and bioaccumulation, all other use impairments such as excessive fertilization, sanitary quality problems associated with contact recreation, impairment of domestic water supply raw water quality, excessive siltation, turbidity, aesthetic quality, oil and grease accumulation and litter, etc. are evaluated with respect to their significance in causing use impairments of a particular waterbody.

Basically, US EPA water quality criteria and state standards based on these criteria are used in the evaluation monitoring approach as guides to potential water quality problems for the regulated chemicals. If an exceedance of a water quality criterion/standard is found, then the water body is examined to determine whether the potential problem associated with that exceedance is in fact occurring due to the constituent causing the exceedance. For example, the concentration of copper in urban area and highway stormwater runoff is typically above US EPA water quality criterion for protection of aquatic life from toxic effects. However, the criterion value is based on essentially 100% available/toxic forms of copper where the organisms were exposed for extended periods of time. It is being found repeatedly that the copper in urban area and highway stormwater runoff is in a non-toxic, non-available form and that the duration of exposure to the concentration above the criterion value is normally short compared to the exposure necessary to be toxic to aquatic life if the copper in the stormwater runoff were in a toxic form. Therefore the copper in the urban area and highway stormwater runoff is a chemical constituent but not a pollutant since it does not cause toxicity in the receiving waters for the stormwater runoff. A violation of Clean Water Act water quality requirements by the exceedance of the copper criterion/standard in urban area and highway stormwater runoff does not cause pollution and therefore there should be no need to develop a BMP to control the copper input to the waterbody.

There is widespread recognition today that the traditional stormwater runoff water quality "monitoring" is ineffective in providing information on what, if any, real water quality problems exist in the receiving waters for the stormwater runoff. Regulatory agencies and stormwater dischargers are shifting their monitoring efforts away from end-of-the-pipe, edge-of-the-pavement monitoring of a suite of chemicals to evaluation of the water quality impacts associated with stormwater runoff associated constituents in the receiving waters. Recently there have been a number of attempts by the US EPA and others to develop environmental "indicators" that can be used to assess water quality impacts of urban area and highway stormwater runoff associated constituents. Caution must be exercised in using this approach since many of the so called indicators proposed by the US EPA for assessing stormwater quality impacts are not real indicators of water quality problems - use impairments. It is essential in any reliable stormwater runoff water quality impact assessment focus on use impairments as opposed to using a water quality "indicator" such as an exceedance of a water quality standard that is in some ill-defined way related to water quality issues of concern to the public. The public does not care how much copper is in the water, they are concerned if the copper impairs the use of the water for various purposes. The coupling between the concentration of copper as normally measured and water quality impacts is poorly understood.

The evaluation monitoring approach shifts the emphasis from chemical constituents that could, in some situations cause water quality problems, to water finding quality problems associated with urban area and highway stormwater runoff, determining their cause and through forensic studies, the source of the constituents responsible for the problem - use impairment. Rather than using inappropriate water quality criteria/standards as goals for BMP development, which often diverts attention away from real water quality issues of concern to the pubic, the "evaluation monitoring" approach uses the control of significant water quality use impairments as the goal for BMP development. While this approach is different than the traditional chemical constituent approach that the US EPA adopted in the early 1980s, it recognizes what was well known then and is well known today that aquatic chemistry, aquatic toxicology, and hydrodynamics/mixing all play important roles in determining whether a chemical constituent in a particular discharge or runoff waters impairs the beneficial uses of the waterbody receiving the runoff.

The evaluation monitoring approach also quickly points out the inappropriateness of traditional "BMPs" that have been used for urban area and highway stormwater runoff "water quality" management such as detention basins, filters, etc. to remove particulate forms of constituents such as inert heavy metals and focuses BMP development on source control for those forms of the constituent that are, in fact, causing real use impairments in the receiving waters for the stormwater runoff. The traditional BMPs were not developed based on a finding that they control real water quality problems in the receiving waters for the stormwater runoff. They were developed based primarily on hydraulic considerations which ignored what has been known since the 1970s in the fields of aquatic chemistry, aquatic toxicology and water quality about how chemical constituents impact aquatic organisms and other beneficial uses of water bodies. Expensive structural BMPs should only be used where it is appropriately demonstrated that they will in fact be effective in controlling a real significant water quality use impairment in the receiving waters for the runoff and appropriate consideration of MEP has been given. The current approach of throwing a detention basin or a filter at a stormwater runoff situation because it is listed in a BMP manual and has been used in the past at some locations will soon be terminated in favor of finding real water quality problems in the receiving waters for the runoff, determining their cause and developing site specific BMPs for their control to the MEP.

Because of the confusion that exists today in the role that water quality criteria/standards play in regulating urban area and highway stormwater runoff water quality impacts, there is an urgent need to revise the Clean Water Act to allow stormwater dischargers and regulatory agencies to focus the water pollution control programs on the goal of defining and solving water quality problems - use impairments and abandon the misguided goal of achieving water quality standards in the receiving waters for the stormwater runoff. Additional information on this topic area is available from the authors' Web site: http://members.aol.com/gfredlee/gfl.htm

Reference as:"Lee, G. F. and Jones-Lee, A., "Extended Abstract: The Appropriateness of Using US EPA Water Quality Criteria as Goals for Urban Area and Highway Stormwater Runoff Water Quality Management," Presented annual national SETAC meeting, San Francisco, California, November (1997)"