Receiving Water Quality Monitoring for Assessment of
Storm Water Runoff Impacts, A Case Study

Scott M. Taylor ¹
Member, ASCE

Traditional storm water monitoring programs fail to provide a link between the sampled parameters and pollution in the receiving water because it is necessary to try to extrapolate from the concentrations of a constituent in the runoff to a water quality impairment in the receiving water. A receiving water quality monitoring program termed 'evaluation monitoring' was developed to directly assess whether there is a real water quality impairment in the receiving water due to a constituent rather than assuming a problem is present through proxy chemical sampling. The implementation of evaluation monitoring discussed in this case study focuses on toxicity in San Diego Creek and Upper Newport Bay in Southern California as an identified priority for the receiving water. The program ultimately includes identifying the cause of toxicity, determining the cause (constituent(s)), and developing a cost-effective control program. This type of approach allows for prioritization of water quality programs to focus on the most acute problems rather than expending resources ineffectively, enabling measurable gains in receiving water quality at a more rapid pace. The program has been in operation for one year and toxicity in the receiving waters has been partially identified. Much of the toxicity present is due to unregulated or inadequately regulated organophosphate or carbamate pesticides.

The evaluation monitoring approach is a receiving water monitoring program designed to investigate impairments to the beneficial uses of a receiving water, determine the constituents responsible for such impairments, and ultimately develop a cost-effective Best Management Practice (BMP) to address the impairment. The program is a stakeholder driven process wherein decision-makers within the watershed prioritize the investigation to address the most acute problems first thereby effectively prioritizing the expenditure of storm water quality resources. The basic elements of the evaluation monitoring program are as follows:

The program is currently being applied to San Diego Creek and Upper Newport Bay in Orange County, California. The program has received funding from a 205j Planning grant and a 319h implementation grant. The evaluation monitoring approach was designed to consider the following types of impairment:

The above represents the scope of a comprehensive implementation of the program, for the subject case, a more narrowly focused program was implemented.

Existing water quality data for the receiving waters was reviewed in order to assess current conditions and prioritize the program implementation. Information available for each of the potential impairments listed was reviewed.

Previous studies conducted on San Diego Creek showed that aquatic life toxicity was measured in the Creek. Chemical analysis of the receiving water (for the Creek and the Bay) has shown that concentrations of some heavy metals with the potential to create aquatic life toxicity, in that average concentrations exceed US EPA water quality criteria. Aquatic life toxicity was judged to be a priority for the receiving waters for investigation.

The State Water Resources Control Board (SWRCB) Toxic Substances Monitoring Data was reviewed for fish tissue concentrations of chlorinated hydrocarbon pesticides, PCBs and heavy metals. The data indicated that chlordane, DDT, dieldrin, PCBs and mercury have all been present in the Creek fish tissue at concentrations representing a potential human health threat to anyone consuming the fish. This area was also judged to be a priority for investigation.

Recent SWRCB and US EPA Bay Protection and Toxics Cleanup Program studies have shown that the sediments of the Bay are, at some locations toxic to some forms of aquatic life. The cause of the toxicity has not been identified, and the significance of this toxicity relative to the beneficial uses of the Bay is not known. This are was judged to be a secondary priority for investigation.

The Bay is experiencing excessive fertilization due to the input of aquatic plant nutrients (nitrogen and phosphorus compounds). Excessive fertilization is significantly impairing the beneficial uses of the Bay through attached algal growth. This impairment is currently under review by the Regional Water Quality Control Board (RWQCB) which, in partnership with the US EPA, is promulgating a nutrient Total Maximum Daily Load (TMDL) standard. Consequently, this area was given a low priority for investigation.

After a review of available data, it did not appear that there are significant dissolved oxygen depletion problems in the Bay. This area was given a low priority for investigation.

Litter is a significant cause of water quality deterioration and beneficial use impairment of the Bay; this was documented through direct observation and review of available records. The local County storm water program initiated a litter control program (including the deployment of trash booms) to address this issue. This area was given a low priority for investigation.

A review of available data indicated that no oil and grease accumulation problems had been identified in the Creek or the Bay. This area was given a low priority for investigation.

There were determined to be potentially significant sanitary quality problems associated with contact recreation and shellfish harvesting in the Bay. Studies are necessary to better understand the current sources of human and animal fecal pathogenic indicator organisms such as total and fecal coliforms, fecal streptococci as well as pathogens such as Cryptosporiduim to determine if it is possible to improve Bay water quality. This are was given a moderate priority for investigation.

The Creek and Bay waters contain excessive sediment due to erosion from within the watershed. The sediment accumulation effects navigation and alters the aquatic plant habitat, allowing macrophytes to encroach into open waters. The sedimentation issue in the Creek and Bay have been extensively studied, and the RWQCB has implemented a sediment TMDL. This area was given a low priority for investigation.

The Creek and the Bay are excepted from a designation as a municipal water supply, consequently this area of study was not pursued.

Meetings were held with potentially interested parties and stakeholders in the Upper Newport Bay (San Diego Creek) watershed. The agencies contacted included:

The objective of these contacts was to develop a greater understanding of the water quality issues in the subject watershed and to gain support for a watershed-based water quality evaluation and management approach. Input from the stakeholders was solicited relative to priorities for investigation and the sharing of data.

Once the literature review was completed, and subsequent to discussions with the technical stakeholders, the most immediate objective of the program was determined to be aquatic life toxicity, and whether aquatic life toxicity was present in the Creek and Bay waters during storm water runoff events. Two storm events were sampled in the 1996/1997 season. Laboratory analysis was performed by the University of California Davis Toxicology Lab.

Each of the sampled storm events had 8 to 10 toxic units of aquatic life toxicity to Ceriodaphnia, a zooplanketer that is representative of organisms as larval fish food. The toxic units mean that the sampled runoff needed to be diluted to about eight-fold to achieve a nontoxic water over a 7-day period of Ceriodaphnia exposure. There was not toxicity to fathead minnow larvae or algae. A sample of Creek water was also taken under dry weather base flow conditions. There was no toxicity to Ceriodaphniaor to fathead minnow larvae in the base flow sample.

A chemical (PBO) was added during the toxicity test that specifically interacts with organophosphate pesticides to cause them to be nontoxic. This approach, in conjunction with chemical measurements using two different analytical approaches showed that a substantial part of the toxicity present in the storm water runoff was apparently due to diazinon and chlorpyrifos for the first storm and methomyl in addition to diazinon and chlorpyrifos for the second storm. Diazinon and chlorpyrifos are organophosphate pesticides that are primarily used for structural pest control. Methomyl is a carbamate insecticide that is primarily used for agriculture.

Concentrations of carbaryl, malathion, pendimethalin and simazine were also found in the second storm water runoff sample. The concentrations of these pesticides/herbicides were less than what would be expected to cause toxicity to aquatic life.

From the characteristics of the toxicity, it is concluded that most of the toxicity in the Creek and potentially the Bay is due to inadequately regulated organophosphate or carbamate pesticides. There are currently no water quality criteria for diazinon or methomyl. The US EPA has developed a water quality criterion for chlorpyrifos.

Subsequent phases of the evaluation monitoring project will conduct additional sampling to determine the significance of the toxicity found in the runoff waters to both the Creek and the Bay. These pulses of toxicity last a few hours to a few days and their relationship to beneficial uses of the waterbody is unknown. This is an important issue since the organophosphate pesticides are not particularly toxic to fish and are also not equally toxic to all forms of zooplankton. The fundamental issue is whether the toxicity of a short duration to certain zooplankters in the bay is of significance to fish an other aquatic life of concern to the public who wish to use the resources of the bay.

Further studies will be conducted to better understand the magnitude, frequency and persistence of the organophosphate pesticide toxicity. The focus of the toxicity impact evaluation will be on the bay waters unless it can be shown that the toxicity is of sufficient magnitude, duration and frequency to be adverse to zooplankton and the fish populations in the tributaries to the Bay. Ceriodaphnia is not likely to be an important zooplankter in the Creek because of the Creek's high ambient salinity; however, there could be other zooplankton in the Creek as well as benthic organisms that are affected by the toxicity.

Finally, only about 50% of the toxicity present in the two storms sampled was identified. It will be important to focus future toxicity investigation evaluations (TIEs) of Ceriodaphnia toxicity to determine whether part of the toxicity that is found is due to some other constituent such as chromium VI. Additional sampling will occur over the 1997/1998 storm season.

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¹ Associate, Robert Bein, William Frost & Associates, 14725 Alton Parkway, Irvine CA 92618