DECIDING WHEN TO INTERVENE

Modified from the report:

McCorquodale, J. A., Tomczak, M. and G. D. Haffner. 1998. Overview of Findings - Summary and Recommendations - A component report of the Application of Computer Modeling and Biomonitoring in Decision Making for the St. Clair River Area of Concern. Great Lakes Institute for Environmental Research, Windsor, Ontario.

Introduction

The International Joint Commission has identified the St. Clair River as an Area of Concern within the Great Lakes Basin. Based on recent and historical data collected by the Ontario Ministry of the Environment, Environment Canada, and the Industrial sector (including the Lambton Industrial Society), a study area of approximately 75,000 m² (7.3 hectares) was selected for more intensive study and analysis. This area, referred to as the Study Area #1, is located on the Canadian side of the St. Clair River just south of the City of Sarnia.

The contaminants in Study Area #1 are primarily due to historical point source loads, all of which have been significantly reduced in the past 10 years, although a detectable load of HCB still enters the River through the Cole Drain. Loads used in this report reflect measurements taken in 1995 as reported by Kauss (1996). Remedial measures undertaken by Dow Chemical Canada Inc. in 1997 are expected to reduce the loads emitted via the Cole Drain to the St. Clair River. In anticipation of these load reductions, this report evaluates the impact of Cole Drain at 1995 and projected 1997 (no load) levels. However, persistent toxic substances (including HCB and mercury) that have already accumulated in bottom sediment pose a hazard to the aquatic environment and its users (Persaud et al. 1993) and may, in part, be responsible for 5 out of 9 of the St. Clair River use impairments as defined by the Great Lakes Water Quality Agreement (MOEE 1995). In addition, the contaminated sediment creates a risk of being transported (over time or by accidental release) to the downstream lakes, where as dispersed contaminants, it will be virtually impossible to clean up (IJC 1997).

Component studies

To assist in the decision-making process in the St. Clair River Area of Concern, six complementary studies were undertaken:

• Biomonitoring/biotoxicity analyses;
• Resolution of spatial extent of sediment contamination;
• Sediment resuspension and deposition studies;
• 3-D hydrodynamic and mass transport model;
• WASP5/IPX in-place pollutant fate and transport model; and
• Construction of GIS for the St. Clair River Area of Concern.

Summary of findings

The following is a summary of the findings of this study:

• Cytotoxicity and enzyme induction studies showed that the sediment in the Study Area #1 could be hazardous to benthic organisms;
• The total area of contaminated sediment under study, of 75,000 m² (approximately 7.3 hectares), was estimated to contain 400 kg of HCB and likely similar quantities of other chemicals including Hg and HCBD;
• Based on a triad-like, weighted, numerical score including chemistry, biodiversity, and acute and chronic toxicity (i.e., the Total Sediment Quality Score or TSQS), 20% or 4,500 m³ of the total volume of sediment (approximately 23,000 m³) in the Study Area #1 is highly contaminated and requires remediation;
• Up to 40% of the 4,500 m³ of the highly contaminated sediment could be gravel or other hard substrate that would not require treatment;
• Ship effects account for a significant amount of resuspension of fine sediment;
• The water column concentrations of HCB at the Study Area #1, as inferred from the clam tissue analysis, was less than 2-3 ng/L, which is consistent with the IPX model's predictions and field measurements;
• The estimated HCB export from the Study Area #1 for present conditions is 15 g/d;
• If the do-nothing option is taken, there will be a 25% decrease in this flux of HCB by the year 2010;
• The half-life of contaminants in the Study Area #1 is approximately 20 years;
• Implementation of capping or dredging of the 4,500 m³ of most contaminated sediment (respective area of approximately 1.6 hectares) would reduce the flux of HCB from the site by 90% by the year 2010;
• Environmental dredging will introduce a short-term increase in the flux of chemicals from the site; based on the analysis of the 1995 environmental dredging at this site, it would appear that approximately 1% of the dredged sediment could be lost to the River. Based on a 90 day dredging period, this could introduce up to four times the present HCB flux from the site during the time of the dredging. It is expected that capping can be carried out with only a fraction of this loss.

Conclusions and recommendations

Both the modeling and biological components of this study concluded that toxicological stress in the St. Clair River was confined to the sediment. This conclusion is supported by other independent studies on invertebrate communities that indicate that chemicals bound to sediment are the primary source of exposure in the St. Clair River ecosystem.

It is not known which specific contaminants are the cause of the stress due to the complex mixture of the chemicals in the sediment, but there is good coherence between the levels of HCB and toxicological stress measured in the in vitro assays. Although such a coherence is not a proof that HCB is the primary cause of the toxicological stress, it does support the use of HCB as a model contaminant. HCB, even if not the direct cause of toxicity, definitely shares common physical/chemical properties with the chemical(s) inducing the observed stress (e.g., persistent, hydrophobic, AHH inducer and potentially bioaccumulative). Thus predictions of the model, which are based on the physical/chemical properties of HCB, will accurately reflect the behavior of the chemical(s) of concern.

Essentially, the model predicts that sediment-bound chemicals will be transported downstream and will accumulate in the wetlands of the Walpole Delta. This accumulation is evident in the data presented in that the sediment in Chenal Ecarte was exceeded in toxicological stress only by those being considered for remediation (i.e., Study Area #1). It is beyond the scope of this project to predict the effects of this accumulation of chemicals in the Delta, but previous studies have confirmed the exposure of fish (Hebert and Haffner 1991) and wildlife (Hebert and Haffner 1990) populations of the Delta to HCB and related chemicals (pentachlorobenzene, octachlorostyrene). Furthermore, Hudson and Ciborowski (1996) observed considerably elevated levels of deformities in midge fly larvae (Chironomus, Phaenopsectra) at the same site used in this study.

The following recommendations are based on the model predictions that currently 15 g/d of HCB are being exported from the site of concern, and that this loading will only decrease by 25% by the year 2010 if no remedial actions are implemented. Such an option will not directly affect drinking water quality in the system, but disturbance of the contaminated site by shipping, accidents, and rare events can cause a significant pulse of chemicals to be brought up into the water column. Most chemicals will be deposited in the Delta and a significant quantity will become incorporated into the food chain of the wetlands.

Within the Study Area # 1, the geo-statistically interpolated TSQS values produced three zones of impairment: highest, moderate, and lowest. Based on the results of the component studies, with respect to the Study Area # 1, the following management options are recommended:

1. The principle of virtual elimination should be applied to discharge of toxic chemicals from the Cole Drain.
2. The highest impaired areas should be capped or dredged using the technology demonstrated by Dow Chemical in the 1996 environmental dredging.

The recommended actions will have the following benefits:

• These actions would essentially meet all of the short and long-term sediment, water, and biota "yardsticks" of the Remedial Action Plan (RAP) and would represent a major step towards removing this site as an Area of Concern. Contaminated sediment directly or indirectly contributes to 5 of 9 beneficial use impairments (MOEE 1995).
• This remediation would yield economic and social benefits such as public confidence in their water supply and development opportunities.
• These actions should accelerate the recovery of the Delta, so that fish advisories for the St. Clair System can eventually be lifted or relaxed. In the absence of remedial work, contaminants such as mercury and HCB will continue to be exported from the site and could be biologically available in the Delta region for the foreseeable future.
• These actions would lower the risk of a serious accidental resuspension of a large amount of chemicals as a result of such events as the propeller wash from an errant ship, a ship going aground, or an extreme natural event such as a large ice jam or anchor ice condition.
• These actions would further strengthen goodwill between the chemical industries at Sarnia and the downriver communities.
• In addition, this site could become the model for other RAPs to follow (particularly on the Connecting Channels). For example, if the Trenton Channel in the Detroit River RAP was remediated to the level recommended in this report, a major environmental hazard in the Great Lakes would be eliminated with significant benefits to the Western Basin of Lake Erie. By the same token, if the St. Clair River is not remediated, it could be used as precedence for inaction in other seriously contaminated sites.

References

Hebert, C. and G. D. Haffner. 1991. "Habitat Partitioning and Contaminant Exposure in Cyprinids." Canadian Journal of Fisheries and Aquatic Science. 45:261-266.

Hebert, C. and G. D. Haffner. 1990. "Organochlorine Contaminants in Duck Populations of Walpole Island." Journal of Great Lakes Research. 16(1):21-26.

Hudson and Ciborowski. 1996. "Spatial and Taxonomic Variation in Incidence of Mouthpart Deformities in Midge Larvae (Dipterea:Chironimadae:Chironomini)." Canadian Journal of Fisheries and Aquatic Science. 53:297-304.

IJC (International Joint Commission). 1997. Overcoming Obstacles to Sediment Remediation in the Great Lakes Basin. White Paper by the Sediment Priority Action Committee, Great Lakes Water Quality Board, International Joint Commission. Windsor, Ontario.

Kauss, B. P. 1996. Cole Drain (Sarnia) Contaminant Concentration and Loadings. Draft Report. Environmental Monitoring and Reporting Branch, Ontario Ministry of Environment. Etobicoke, Ontario.

McCorquodale, J. A., Tomczak, M. and G. D. Haffner. 1998. Overview of Findings - Summary and Recommendations - A component report of the Application of Computer Modeling and Biomonitoring in Decision Making for the St. Clair River Area of Concern. Great Lakes Institute for Environmental Research, Windsor, Ontario.

MOEE (Ministry of Environment and Energy). 1995. The St. Clair River Area of Concern, Water Use Goals, Remedial Measures, and Implementation Strategy - Stage II Remedial Action Plan. Sarnia, Ontario.

Persaud, D., Jaagumagi, R. and A. Hayton. 1993. Guidelines for the Protection and Management of Aquatic Sediment in Ontario. Water Resources Branch, Ontario Ministry of Environment and Energy. Toronto, Ontario.