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5. CONCLUSIONS AND RECOMMENDATIONS

The answers to the main study questions are as follows:

1. Are metals entering the Moira River system?

Water

Yes, but water concentrations have declined. Recent mean annual arsenic and nickel concentrations do not exceed the PWQO at any of the stations downstream of the Deloro Mine Site, although some exceedances occur seasonally during low-flow. Recent mean annual cobalt, copper and lead concentrations do not exceed the PWQO downstream of Moira Lake. Radioactive substances (e.g., uranium or radium-226) are not elevated in water at any location in the Moira River system.

Sediments

Yes, a substantial increase in the concentration of metals in sediment occurs downstream of the Deloro Mine Site, followed by an additional increase downstream of the confluence with Young's Creek. The highest concentrations observed in this study occurred in the Young's Creek sediment sample for most metals of concern. The sediments in Young's Creek are currently being held back behind a series of beaver dams. Metal concentrations in sediment within the Moira River gradually decline after the confluence with Young's Creek, with the most substantial drop occurring after the Moira Lake outlet. Concentrations remain elevated above reference values all the way to the farthest downstream station (Corbyville), except for lead and uranium.

Provincial sediment quality guidelines (Severe Effect Levels) for arsenic and nickel are exceeded at the stations from Highway 7 through to Moira Lake, and also at some stations in Stoco Lake. Copper concentrations are above the SEL in Young's Creek, Bend Bay and Moira Lake. Lead concentrations vary throughout the Moira River system and the reference systems; therefore, lead concentrations appear to be related to local geology rather than to the Deloro Mine Site. Cobalt concentrations exceed site-specific Screening Level Concentrations (SLC) in Young's Creek and from Highway 7 through to the outlet of Moira Lake. Silver concentrations exceed the SLC from downstream of Young's Creek through to the mid-basin station of Moira Lake. Uranium concentrations are significantly above reference concentrations in Young's Creek only; however, the radioactivity from the amount of uranium present is indistinguishable from reference levels. Other radionuclides are not a concern at any location in the Moira River system.

Sentinel Fish Species

Yes, metal concentrations in whole body white sucker samples are significantly higher than reference locations in the Moira River system, particularly at Bend Bay and Moira Lake. There are no differences in metal concentrations between smaller white sucker (< 30 cm length) and larger white sucker (> 30 cm length).

Arsenic, silver and nickel are the only metals that have significantly higher concentrations in longnose dace at the site downstream of the Deloro Mine Site compared to the two upstream sites. Arsenic is the most elevated relative to the reference data .

Sport Fish Species

Based on the findings of MOE (1999), metals of concern in fillets of sport fish species from the Moira River system are at concentrations below those that could require restrictions of fish consumption. This is supported by CanTox (1999), who reported that levels of arsenic in fish considered in the Deloro Village risk assessment study were consistent with those observed elsewhere in Ontario.

2. Is there a measurable biological response in aquatic invertebrates and fish?

Overall, there are some changes in the benthic community structure of lakes in the Moira River system that are consistent with the effects of metal concentrations, but these changes are quite subtle. Total abundance is not affected by metal concentrations in the exposed lakes, and species richness is only reduced in Moira Lake (although the pattern of richness in Moira Lake did not correspond with metal concentrations). Lake sediments are not toxic to Hyalella azteca or Chironomus riparius in laboratory toxicity tests. However, the abundance and percentage of metal-sensitive invertebrates is significantly reduced in both exposed lakes and in Bend Bay to both reference lakes. In addition, the among-lake variation in abundance of a number of; individual taxa is consistent with their relative metal-sensitivities.

The variation in total abundance within the Moira River appears to be related to habitat attributes rather than sediment metal concentrations. Total abundance varies moderately, but without a noticeable trend from upstream of the Deloro Mine Site to downstream. There is a significant positive relationship between sediment metal concentrations and species richness, which is contrary to expectations. This may be because the metals are largely in the more unavailable forms, such as the residual, oxides or organic/sulphide fractions. The toxicity test results did not show a consistent relationship between effects on growth or survival of Hyalella azteca or Chironomus riparius and metal concentrations.

There are effects on benthic invertebrate abundance and species richness in Young's Creek. The sediments are toxic to Hyalella azteca and Chironomus riparius in laboratory toxicity tests.

There are no obvious adverse effects on white sucker characteristics in Moira Lake. The only observed difference is that female white sucker are older in Moira Lake. All other characteristics in white sucker from Moira Lake are intermediate between Round Lake and Consecon Lake.

Despite the exposure (and uptake) of the metals of concern, whole-organism characteristics of longnose dace do not reflect the increase in metal concentrations. It is possible that concentrations are not high enough to cause individual or population level changes in resident fishes. Alternatively, longnose dace may not be sensitive to increased metal concentrations.

3. Are the metals in the system causing the biological response observed in invertebrates and fish?

The weight of evidence from the benthic invertebrate community data suggests a weak relationship between metals and the presence of some sensitive invertebrate species in lakes within the Moira River system. The weight of evidence from the sentinel fish species data suggests that there is no readily apparent cause-effect relationship between metal concentrations and the whole-organism and population responses measured.

4. Do the metal concentrations present in water and sediment of the Moira River system pose a risk to human health?

Cadmium, chromium, cobalt, lead, and nickel do not represent a potential health risk in any study area and further assessment of the potential health risks posed by these metals is not required. Arsenic in Study Areas C and D is not expected to lead to significantly elevated exposures compared to the TOR, and further assessment of the potential health risks posed by this substance in these areas is not warranted.

The reminder issued by the MOE and the Hastings and Prince Edward Counties Health Unit to residents of Study Areas A and B (from the Deloro Mine Site to the outlet of Moira Lake) advising them not to drink the water was, and continues to be, appropriate. The reminder is not only appropriate because of concerns about arsenic, but also because of the risk of exposure to pathogens in untreated water. If residents drink untreated water from the river or lake, they would have greater estimated levels of exposure to arsenic than the TOR under the conservative conditions assumed in this assessment. Where water is not used for drinking, arsenic is not a concern for residents and cottagers on Moira Lake.

The section of the river above Moira Lake (Study Area A) is not well suited for in-water recreational activities and has only a limited number of residences. However, recreational use of this section of the river system may be an important exposure pathway, at least for some individuals. The amount of exposure through this pathway, both in absolute terms and relative to total arsenic exposure, requires further study. [This further study has since been conducted. The results show that exposure to the range of concentrations of arsenic detected in sediment in Study Area A will not result in adverse health effects after short-term or long-term exposure of area residents and other users of the river. Therefore, no specific risk management measures are required with respect to exposure to sediments in Study Area A.].

Metals of concern in fish fillets from the Moira River system are at concentrations below those that could require restrictions of fish consumption. However a fish consumption restriction for Moira and Stoco Lakes is in effect because of mercury; a substance not related to the Deloro Mine Site. Consumption restrictions based on mercury are widespread throughout Ontario's lakes and rivers, including the reference lakes considered for this Study.

5. What amount of clean up would be necessary at the Deloro site to meet Provincial Water Quality Objectives in the Moira River and to reduce sediment concentrations to below concentrations associated with biological effects?

The predictive model showed that total arsenic and cobalt loading from the Deloro Mine Site and surrounding area would have to be essentially eliminated for downstream water quality to meet PWQOs. For arsenic, the interim PWQO of 5 µg/L would not be met at Highway 7 during average summer low flows even with 99% reduction. However, arsenic concentrations would be less than 5 µg/L year-round in Moira Lake and farther downstream.

Cobalt concentrations are projected to exceed the PWQO downstream of the Deloro Mine Site to East Moira Lake for the 30-year period of the model, even with 95% reduction of loadings from the Deloro Mine site and surrounding area. If total cobalt loading rates from the Deloro Mine Site and surrounding area were reduced by 95%, cobalt concentrations downstream of East Moira Lake are projected to drop below the PWQO following the addition of dilution water by the Black and Skootamatta Rivers.

Total nickel loading rates to the Moira River would have to be reduced by 75% for downstream nickel concentrations to be equivalent to, or less than, the PWQO of 25 µg/L year round.

Arsenic and nickel concentrations in surface sediments immediately downstream of Deloro are projected to remain above guideline levels for the 30-year period of the model, regardless of the levels of clean up completed on site. Following a 95% reduction in total cobalt loading from the Deloro Mine Site and surrounding area, cobalt concentrations in surface sediments in the Moira River between Young's Creek and Moira Lake would fall below the SLC of 296 µg/g within 20 years. In the other model segments downstream of Moira Lake, sediment cobalt levels are either currently below the SLC or projected to drop below the SLC within 5 years.

The relative metal loading from Young's Creek is small compared to loading from the Deloro Mine Site. Therefore, the most benefit will be gained by focussing on the cleanup of the Deloro Mine Site. However, a significant quantity of sediment is present in Young's Creek, currently contained behind a series of beaver dams. The potential exists for a failure of these dams, as illustrated by a partial failure in June 2000. Therefore, a sudden release of sediments into the Moira River is possible. The magnitude will depend upon the extent of the beaver dam failures and flow in Young's Creek.

It should be emphasized that meeting PWQOs and Severe Effect Level or Lowest Effect Level Guidelines for sediments after cleanup does not appear to be necessary to prevent effects on aquatic biota, because current conditions do not appear to be causing significant effects.

Overall Goal and Conclusions

The overall goal of the study was to assess the extent and significance of metals concentrations and predict the environmental response to cleanup activities that will in the future be conducted at the Deloro Mine Site. The three components of this study have shown the following:

1. The study confirmed the presence of elevated levels of arsenic, cobalt, copper, lead, nickel and silver in sediments and water of the Moira River system. Uranium is elevated in sediments in Young's Creek; however, the radioactivity from the amount of uranium present is the same as reference levels. Other radionuclides are not a concern at any location in the Moira River system.
2. Water quality has improved significantly over the past 35 years, in response to the cessation of processing activities and the ministry's cleanup activities at the mine site. Since the mid 1980s, arsenic, copper and nickel exceed the PWQO only at times of low river flow in the section of the river between the Deloro Mine Site and Bend Bay. For cobalt and lead, the PWQO is exceeded during low flow between the Deloro Mine Site and the outlet of Moira Lake.
3. Elevated concentrations of metals are present in sediments extending from below the Deloro Mine Site to downstream of Stoco Lake. The highest concentrations of metals are found in sediments in Young's Creek and in the deep basins of Bend Bay, Moira Lake and Stoco Lake.
4. Provincial Sediment Quality Guidelines (PSQG) are exceeded in the river system and for arsenic and nickel, these exceedances extend from the Deloro Mine Site through Moira and Stoco Lakes and further downstream.
5. Despite the exceedances of PWQOs during low flow and exceedances of PSQGs, no obvious adverse effects were observed in benthic invertebrates and fish populations in the Moira River, Moira Lake or Stoco Lake. Effects were observed on invertebrate abundance and species diversity in Young's Creek.
6. Cadmium, chromium, cobalt, lead and nickel do not represent a potential health risk to residents of the Moira River watershed and further assessment of the potential health risks posed by these metals is not required.
7. Exposure to arsenic in the Moira River downstream of Moira Lake is not expected to be greater than that of the Typical Ontario Resident (TOR), and further assessment of the potential health risks posed by this substance in these downstream areas is not warranted.
8. The reminder issued by the MOE and the Hastings and Prince Edward Counties Health Unit to residents of Study Areas A and B (from the Deloro Mine Site to the outlet of Moira Lake) advising them not to drink untreated surface water was, and continues to be, appropriate. The reminder is not only appropriate because of concerns about arsenic, but also because of the risk of exposure to pathogens in untreated water. If residents drink untreated water from the river or lake, they would have greater estimated levels of exposure to arsenic than the TOR under the conservative conditions assumed in this assessment. Where water is not used for drinking, arsenic is not a concern for residents and cottagers on Moira Lake.
9. Exposure to sediments in Study Area A during recreational use (wading or swimming) was identified as a potentially important exposure pathway. Further study was recommended. [This further study has since been conducted. The results show that exposure to the range of concentrations of arsenic detected in sediment in Study Area A will not result in adverse health effects after short-term or long-term exposure of area residents and other users of the river. Therefore, no specific risk management measures are required with respect to exposure to sediments in Study Area A.]
10. The concentrations of the metals of concern in fish fillets are below the levels that would require restrictions of fish consumption. However a fish consumption restriction for Moira and Stoco Lakes is in effect because of mercury; a substance not related to the Deloro Mine Site. Consumption restrictions based on mercury are widespread throughout Ontario's lakes and rivers, including the reference lakes considered for this Study.
11. The water quality data suggest that there may be an additional, so far undefined source, of some metals to the Moira River, somewhere between the Deloro Mine Site and immediately below the confluence with Young's Creek.
12. The results of the predictive modelling indicated that the loading of arsenic and cobalt to the Moira River from the Deloro Mine Site would have to be essentially eliminated for downstream water quality to meet PWQOs. For arsenic, the interim PWQO of 5 micrograms per litre would not be met at Highway 7 during low flows even after 99% reduction; however it would be met year-round in Moira Lake and further downstream. The PWQO for cobalt would only be met below Moira Lake. Mean annual concentrations of nickel currently meet the PWQO; after cleanup, the PWQO would be met year round.
13. Sediment quality downstream from the Deloro Mine Site in the Moira River will continue to improve over the long term. However metal concentrations in sediment in the Moira River system down to and including Stoco Lake will remain above PSQGs for many years to come, independent of cleanup actions at the Deloro Mine Site.
14. The amount of metals reaching the Moira River from Young's Creek is relatively small compared to the amount from the Deloro Mine Site. However, the presence of a significant quantity of sediments retained behind a series of beaver dams is a concern. Should these dams fail, a significant quantity of sediments could be released to the Moira River.

Recommendations

1. The drinking water reminder to residents and cottagers in the Moira River watershed extending from the Deloro Mine Site to the outlet of Moira Lake not to use the river system as a source of drinking water should be continued.
2. The current monitoring programs for water quality and river flows conducted on behalf of or by the MOE should be continued.
3. Further assessment of the possible exposure of residents in Study Area A (Deloro Mine Site to the inlet of Moira Lake) to arsenic in sediments during recreational activities, is recommended. This assessment, an Updated PQRA, has since been conducted, the results of which have shown that further assessment of the potential health risks associated with arsenic in sediments in Study Area A is not warranted. The Updated PQRA reflects the conditions at the time of sediment sampling (August 2000). Should conditions change due to a major flood event, or in the event of a significant accidental release of sediments from Young's Creek, follow up sediment sampling would be recommended to confirm that exposure to sediments in Study Area A continues to represent no significant incremental health risk. In addition, sediment sampling following completion of the final cleanup program for the Deloro Mine Site, including Young's Creek, would also be appropriate.
4. An assessment of a possible source or sources of metals along the section of the Moira River between the Deloro Mine Site and immediately below the confluence with Young's Creek should be conducted. This assessment should include a review of mass loadings using the most recent water quality data.
5. As a precautionary measure, the public should be advised to avoid recreational activities in Young's Creek south of Highway 7 until such time as further characterization of sediment and water quality in this area has been completed. This characterization should also include an assessement of baseline biological conditions in Young's Creek including both aquatic and terrestrial resource components.
6. Subject to the results developed from the above recommendation, options to eliminate the likelihood of a release of sediments to the Moira River from Young's Creek should be evaluated and incorporated into the final cleanup plan for the Deloro Mine Site.
7. Development of the final cleanup plan for the Deloro Mine Site does not need to include consideration of effects in the downstream aquatic environment because benthic invertebrates and fish populations do not show adverse effects from the presence of metals in the Moira River system.
8. Development of the final cleanup plan for the Deloro Mine Site should include consideration of downstream water quality to reduce potential human health concerns associated with the presence of arsenic.

6. CLOSURE

We trust the above meets your present requirements. If you have any questions or require additional details, please contact the undersigned.

GOLDER ASSOCIATES LTD.

John Petrie, M.Sc.
Principal, Senior Hydrogeologist
Project Manager

Stella Swanson, Ph.D., P.Biol.
Associate
Senior Aquatic Biologist

GLOBALTOX INTERNATIONAL CONSULTANTS INC.

Ronald Brecher, Ph.D., C.Chem, DABT
Principal