The second of three articles addressing urban stormwater runoff
The state of California is recognized as being among the leaders in the United States in developing consensus approaches for implementing the federal and state stormwater runoff quality management regulations. This leadership role evolved out of the State Water Resources Control Board (SWRCB) working with a number of stormwater quality management entities to develop a cooperative approach toward stormwater quality evaluation and management-an action promoted through the state's Stormwater Quality Task Force.
This task force consists of members of the SWRCB along with regional water quality control boards which regulate urban stormwater runoff within the state, municipal stormwater dischargers, representatives of various industrial and trade associations, environmental groups, consultants, academia, the California Highway Department, and various county highway departments and others interested in the urban stormwater issue. Participation in task force activities is open to anyone who is interested. The task force is organized through the California chapters of the American Public Works Association.
The group assisted the SWRCB in developing early NPDES permits for urban stormwater dischargers with populations above 100,000, developed a best management practices guidance manual, which was active in formulating a consensus approach for reauthorization of the urban stormwater runoff quality management sections of the Clean Water Act, and assisted in the development of state regulations and implementation guidance for urban and industrial runoff monitoring and management practices. Through the leadership of the task force, California is recognized as being one to two years ahead of many other states in implementing the necessary programs. The cooperative consensus approach developed in California is becoming a pattern for similar programs in other states.
A review of the associated technical issues led the task force to conclude quite early in its deliberations that urban stormwater runoff effects must be evaluated and managed in a different way than has been employed for other point source discharges, such as municipal and industrial effluents. Initially, this was motivated by the finding that conventional treatment methods used for municipal and industrial wastewater discharges could not be applied to urban stormwater runoff because of the very high costs of treatment to achieve current water quality standards at the edge of the mixing zone in the receiving waters.
Technically Valid Approaches
Coincident with gaining an understanding of the very high costs associated with trying to follow the conventional wastewater management practices used to comply with ambient water quality standards, the task force members came to the realization that attempting to manage chemical constituents in urban stormwater runoff similarly would result in massive over-regulation of the chemical constituents in the runoff. This in turn would result in large-scale waste of public and private funds for treating this runoff to meet the quality standards. It has been known since the mid-1960s that many of the chemical constituents in urban stormwater runoff, as well as in the runoff from rural areas, were present in non-toxic, non-available forms. Therefore, as discussed in the first article in this series, excursions outside a water quality standard based on total concentrations of chemical constituents at the edge of a mixing zone for the stormwater runoff, while causing an administrative out-of-limit quality situation in the ambient receiving waters, does not necessarily cause a real designated-use impairment of these waters.
Further, the short-term episodic nature of most urban stormwater runoff events means that the conventional standards used to regulate municipal and industrial wastewater discharges based on their acute and chronic toxicity to aquatic life would over-regulate the toxic-available forms of chemical constituents in typical urban runoff. This is because the exposure time of aquatic organisms in the receiving waters for the stormwater runoff is considerably shorter than the period which the water quality standards were designed to address. While the USEPA's water quality criteria have, since the mid-1980s, utilized a one-hour maximum and four-day average concentration for implementing requirements to control acute and chronic toxicity to aquatic life, it is well known that for essentially all chemical constituents these periods are grossly exaggerated in terms of protecting the designated beneficial uses of waterbodies from aquatic organisms of potential concern at the edge of a point or non-point source discharge mixing zone.
Basically, it is virtually impossible for aquatic organisms in the receiving waters' watercolumn to receive an acute or chronic duration of exposure at the edge of the mixing zone. The USEPA recently acknowledged this problem and is changing the exposure period against which the water quality criteria, and the state standards based on them, are implemented. The agency also is in the process of changing the allowed frequency of violations. Today, a violation of a water quality standard by any amount for more than once in three years represents a violation of the NPDES permit and is subject to regulatory action. This definition is well known to be extremely overprotective since substantial violations of many water quality standards can occur on a routine basis without significantly adversely affecting the designated beneficial use of the waterbodies.
Technically Valid Water Quality Standards for Stormwater Runoff
The California Stormwater Quality Task Force has adopted the position that urban stormwater runoff discharge requirements should not be based on meeting current water quality standards at the edge of a mixing zone. The task force, in connection with its work on reauthorization of the Clean Water Act, joined with other groups in calling for the USEPA to develop technically valid water quality criteria and state standards that could be used to control real water quality problems associated with urban stormwater runoff. In the latest proposed revisions of the Clean Water Act's stormwater quality management section, a consensus among various interested agencies and entities called for a ten-year moratorium in the application of water quality standards to urban stormwater runoff.
During the moratorium, the USEPA would be provided with $10 million per year, for a total of $100 million, to conduct research which would lead to development of an appropriate stormwater quality criteria, an an approach that could be used by the states to implement these criteria in the NPDES permit system governing stormwater runoff. These criteria would be designed to protect designated beneficial uses of receiving waters from impairment by chemical constituents in urban stormwater runoff without significant unnecessary expenditures for chemical constituent control in this runoff.
These criteria would need to be consistent with wet weather standards, such that during the period of a runoff event, the concentrations of chemical constituents in the runoff would be allowed to exceed current ambient water quality standards near the point of discharge period. This technically valid approach should be followed in developing regulatory approaches for controlling real water quality problems associated with urban stormwater runoff.
Also, these could be wet weather standards where, during the period of a runoff event, the concentrations of chemical constituents in the runoff would be allowed to exceed current ambient water quality standards near the point of discharge, provided that over-the-limit excursions do not cause significant impairment of the designated beneficial uses of the waterbody. This is a technically appropriate approach that should be followed in developing regulatory means for controlling real water quality problems associated with urban runoff.
Industrial Stormwater Runoff
While there is widespread agreement that the current ambient water quality standards should not be applied to urban stormwater runoff, the USEPA and the states are applying these standards to industrial stormwater runoff at the edge of the property. This is not technically appropriate and results in over-regulation of the associated chemicals contained in the runoff. Similarly, significant over-regulation of stormwater discharges for industrial sites covered by the USEPA's multi-sector permit is occurring. The Agency's proposed idea of using benchmark values based on water quality criteria and its National Urban Runoff Program (NURP) studies also is technically invalid, and will result in significant over-regulation of many industrial stormwater discharges, and wasted funds devoted to inappropriate monitoring activities.
Concentrations of chemicals in runoff from industrial properties can exceed various NURP values, as well as USEPA water quality criteria/standards, by considerable amounts, and still not be adverse to the beneficial uses of the waterbodies which the runoff enters. A significantly different approach needs to be developed at the federal and state levels to protect surface and groundwater quality associated with industrial stormwater runoff that will protect the designated beneficial uses of receiving waterbodies without wasting funds on ineffective or inappropriate control programs.
Water Quality Significance of Chemical Compounds in Sediments
Referring again to the previous article in this series (April WEM), we discussed the potential significance of particulate matter in stormwater runoff on receiving water quality. There are two principal areas of concern. One is the particulates themselves, irrespective of their chemical characteristics. The other is the chemicals of concern associated with the sediments as precipitates and attached to the particle surfaces. Chemical compounds associated with particulates are typically non-toxic and non-available and, therefore, should not be regulated in terms of the receiving waters' quality standards. These standards are applicable to the water column. They do not consider the potential effects of contained chemical constituents on suspended sediments in stormwater runoff that become part of the deposited (bedded) sediments.
It is well known that while most chemicals in sediments are detoxified, i.e. non-toxic, non-available, there are situations where the detoxification capacity of the sediment is exceeded, with the result that chemical constituents in aquatic sediments can be toxic or otherwise available to adversely affect the designated beneficial uses of the waterbody in which the sediments are located. While there may be a desire to regulate in terms of the chemicals associated with deposited sediments through water quality criteria and standards, such an approach is not appropriate and fails to recognize the aquatic chemistry and toxicology of sediment-associated contaminants.
Two principal water quality concerns are associated with chemicals in sediments. One is the potential for toxicity effects on benthic and epibenthic organisms within or upon the sediments. The second is the potential for some sediment-borne chemicals to accumulate to excessive levels in benthic and epibenthic organisms that can serve as food for higher trophic-level organisms, such as other aquatic life, man and terrestrial wildlife. The accumulation of chlorinated hydrocarbon pesticides, PCBs and mercury in fish flesh, causing the fish to be considered unsuitable for use as human food, is an example of this type of problem.
Since the mid-1970s the USEPA and the US Army Corps of Engineers have been regulating contaminated sediments associated with navigational dredging of US waterways. Based on the results of the Corps' Dredged Materials Research Program in the 1970s, where it was found that concentrations of chemicals in sediments were not reliable indicators of water quality, the Agency and the Corps developed biological effects-based contaminated sediment evaluation criteria. Rather than trying to estimate sediment toxicity based on chemical characteristics (an unreliable method), direct measurements with toxicity tests are used.
Assessing the potential for bioaccumulation of sediment-bound chemical compounds in higher trophic level organisms requires measurement of actual accumulations that occur in the tissues of desirable organisms in the waterbody of concern. There is no reliable approach available today to predict, based on sediment concentrations, whether a particular constituent, such as mercury, will bioaccumulate in aquatic organisms that may be a source of food for man to a sufficient degree to be potentially harmful if consumed.
To determine if there is a need to control the chemical constituents of runoff sediments, it is necessary to conduct site-specific investigations of how the bedded sediment contaminants are affecting the designated beneficial uses of the associated waterbody. There is no reliable way at this time, and none is foreseen in the near future, to predict, based on concentrations of sediment-associated constituents in stormwater runoff, the potential effects these compounds would have on the receiving water's quality when the suspended sediment of concern becomes part of the bedded sediments.
Santa Monica Bay Restoration Project
Recently, the Santa Monica Bay, California, Restoration Project has adopted a restoration plan that calls for the expenditure of $42 million over a five year period for the development of structural best management practices (BMPs) for the control of selected chemical constituents. Examples are several heavy metals in urban stormwater runoff in the Santa Monica Bay watershed. Review of the technical basis for development of this restoration plan shows that it was based on the finding that since urban stormwater runoff typically has elevated concentrations of heavy metals (e.g. copper, zinc, cadmium, nickel, lead, chromium, silver), and that some of these accumulate in Santa Monica Bay sediments to concentrations that exceed the arbitrarily established Long and Morgan ER-M values. This component of the Bay restoration plan focuses on the presence of chemicals in the area's stormwater runoff and in Bay sediments at elevated concentrations, irrespective of whether these concentrations are adverse to the designated beneficial uses.
The Long and Morgan ER-M co-occurence-based values are considered by many to be unreliable indicators for establishing the toxicity of heavy metals and other constituents of aquatic sediments. The ER-M values are based on total concentrations. It has been known for over 25 years that there is no relationship between the total concentration of a chemical constituent in sediments and that constituent's effect on aquatic life toxicity, or its availability for bioaccumlation in the tissue of higher trophic level aquatic organisms.
Managers of the Santa Monica Bay Restoration Project assumed that since heavy metals in some wastewater sources were toxic to aquatic life, the heavy metals in urban stormwater runoff from streets and highways in the local watershed also had to be significantly toxic to aquatic life if they were present in the Bay's sediments. Even though the project team, the Water Resources Control Board and the USEPA's Region IX staff were made aware of the unreliability of the test method used to establish the need to control certain heavy metals, these agencies choose to ignore the large amount of information in the aquatic chemistry and aquatic toxicology literature that shows that ER-M values should not be used as a basis for establishing regulatory programs. The ER-M values are easy to use, but they are not technically appropriate for this situation.
The development of the expensive Santa Monica Bay Restoration Project's Plan of Action to establish chemical contaminant control using structural BMPs without first finding a real stormwater runoff quality problem is becoming recognized as an example of how sediment data should not be used to evaluate the potential effect of contained heavy metals. Obviously before a waterbody restoration plan is developed, a real water quality/use impairment should be determined by site-specific studies, in this case of the Santa Monica Bay area.
If the issue of concern is heavy metal toxicity in aquatic sediments, then measurements of toxicity should be made. If the sediments are in fact toxic, then TIE studies should be conducted to determine if the source is chemical contamination in the stormwater runoff before any large expenditure of public funds is committed. Further, before structural BMPs are adopted in a Bay restoration plan based on contamination control, identification of specific causes of sediment toxicity should be accomplished. Subsequently, source control of the offending constituents should be implemented. If it is then established that source control is not sufficient to avoid impairment of the designated beneficial uses of Santa Monica Bay waters, treatment of the stormwater runoff can be adopted as an appropriate method for restoring the Bay.