EXECUTIVE SUMMARY

The Dome Mine (Ontario) study is one of four field evaluations carried out in 1997 under the Aquatic Effects Technology Evaluation (AETE) Program, a joint government-industry program to evaluate the cost-effectiveness of technologies for the assessment of mining related impacts in the aquatic environment. The other three mines studied were Myra Falls (British Columbia), Mattabi (Ontario) and Heath Steele (New Brunswick). Results of all four studies are summarized and evaluated in a separate summary report.

The Placer-Dome Dome Mine is large open pit and underground mine located west of Timmins, Ontario. The mine began operations in 1910, and is one of the oldest and largest gold mines in Canada. Effluent from the mine is discharged from a tailings pond after treatment for cyanide using a combination of natural degradation and the Inco SO2/air process. Effluent is discharged seasonally during the ice-free season to take advantage of natural cyanide degradation. The lnco treatment system was brought on-line for the first time in 1997. Mine effluent is discharged to the South Porcupine River, a relatively small, low-gradient watercourse. Approximately 3 km downstream of the effluent discharge, the South Porcupine joins the North Porcupine, and flows into Porcupine Lake.

A number of older mine workings and wastes occur in the South Porcupine watershed upstream of the Dome discharge, and may represent sources of contaminants through runoff and seepage.

The objectives of the 1997 field program were to test 13 hypotheses formulated under four guiding questions:

1. are contaminants getting into the system (and to what degree and in which compartments)?
2. are contaminants bioavailable?
3. is there a measurable (biological) response? and
4. are contaminants causing the responses?

The hypotheses are more specific questions about the ability or relative ability of different monitoring tools to answer these four general questions about mine effect. The evaluation of tools included: sediment monitoring (sediment toxicity tests); fish monitoring (tissue metallothionein and metal analyses, and population/community indicators), and; integration of tools (relationships between exposure and biological responses and use of effluent sublethal toxicity).

Of the 13 hypotheses, 11 were tested at Dome as outlined in Table 1. 1. The two hypotheses not tested at Dome were H5 (fish catch-per-unit-effort) and H6 (fish community). These hypotheses were deleted because of natural habitat and fish community differences among areas.

The sediment quality triad was used as an additional means of evaluating the linkages between sediment toxicity, sediment chemistry and benthic community response (H10 and H11) in the South and North Porcupine Rivers. The triad provides a more holistic means of evaluating the tools.

Study Design

The study design at Dome was based on both lake and river sampling for fish, and river sampling for benthos, sediment chemistry and sediment toxicity. River sampling followed a nearfield-farfield-reference design, with the nearfield in the South Porcupine River after mixing with the effluent, the farfield in the Porcupine River downstream of the South Porcupine-North Porcupine confluence, and the reference area in the South Porcupine River upstream of the effluent source. The farfield area for fish in the river was relocated immediately upstream of the North Porcupine confluence owing to a lack of sentinel species downstream. Lake sampling was carried out for one fish species only in Porcupine Lake (exposure area) and McDonald’s Lake (reference area).

Sampling Program

The Dome Mine field survey was completed in late September-early October 1997, and included:

• river water sampling at three nearfield stations, three farfield stations and six reference stations for determination of dissolved (filtered) and total metal concentrations, cyanide and other parameters; and lake water sampling at four locations each in Porcupine Lake and McDonald’s Lake. Effluent had not been discharged from Dome since 12 August 1997; thus, water quality conditions at the time of the survey were unlikely to reflect any direct effluent impact;
• surficial sediment sampling in the river at the seven nearfield stations, seven farfield stations and seven reference stations using a petite Ponar. Samples were analyzed for “total” metal concentrations, partial metal concentrations (i.e., the Fe and Mn oxide-bound fraction) and concentrations of acid volatile sulphide (AVS) and simultaneously extracted metals (SEM);
• surficial sediment sampling at the above 21 stations for benthic macroinvertebrate community analysis and for sediment toxicity testing (Hyalella azteca – survival and growth, Chironomus riparius – survival and growth, Tubifex tubifex – survival and growth);
• sampling of yellow perch in McDonald’s Lake and Porcupine Lake for analysis of growth, liver weight, gonad weight and fecundity (approximately 20 males and 20 females per lake). Fish were captured mainly by seine in Porcupine Lake and gill net in McDonald’s Lake. A subset of 12 fish per lake was analyzed for metallothionein (MT) and metals in muscle (metals only), liver, gill and kidney;
• sampling of pearl dace (20 males, 20 females per site area) from nearfield, farfield and reference river areas for analysis of growth, liver weight, gonad weight and fecundity. Fish were captured mainly in baited minnow traps. Nine pearl dace samples per site were analyzed for MT and metals in viscera. An additional nine pearl dace samples were captured from a second reference area (beaver pond in the South Porcupine River) for MT and metal analysis;
• sampling of caged young-of-the-year yellow perch, captured from a nearby unimpacted lake, after ten days of exposure at each of the two lake areas and three river areas. These fish were analyzed as three-fish composites for visceral MT and metals; and
• testing of chronic effluent toxicity, based on three sampling events. The first event was collected under conditions of treatment using the Inco process, the second was collected without Inco treatment (natural degradation only) and the third was collected under non-discharge conditions in October from the effluent storage pond.

Data Overview

Water Quality

Concentrations of Cu, Co and Ni were consistently greater at nearfield and farfield stations and in Porcupine Lake than in the reference areas, with total Cu consistently exceeding the Canadian Water Quality Guideline (CWQG). This could reflect the presence of residual effluent in the slow-flowing river, or secondary impact from mine-related metals in river sediments. Copper and cobalt concentrations appeared to respond to Dome Mine, while nickel was affected both by Dome and by the North Porcupine River. Arsenic concentrations were elevated above the CWQG at one of the reference areas, apparently reflecting an impact of historic mine waste. Other parameters, including nitrate, sulphate, hardness and total dissolved solids, were also greater in exposure areas than reference areas.

Total and dissolved metal concentrations showed similar spatial patterns. For copper and arsenic, the dissolved fraction represented the majority of the total metal concentration present in the water.

Sediment Chemistry

Sediments in the South Porcupine River system were predominantly silt and clay, with relatively low organic carbon contents.

Total metal concentrations in sediment were greatest in the nearfield and lowest in the reference area for Cu and Ni. Sediment arsenic concentrations were greatest in some of the reference sediment samples, although As levels were more variable in reference sediments than elsewhere. Other metals showed variable spatial patterns that did not appear related to Dome. Concentrations of Cu, Ni and As exceeded their Canadian Interim Sediment Quality Assessment Values (PEL values) at most (Cu, Ni) or all (As) stations.

Partial metal concentrations showed generally similar spatial patterns to those observed for total metals for As, Ni and Cu. The partial metal fractions represented about half of the total metals for As and Ni but only about 1% for copper.

The SEM/AVS ratio in sediments was consistently low (≤0.5), suggesting that sediments should be generally not be toxic to benthic organisms.

Sediment Toxicity

Sediments showed possible mine-related toxicity only in the case of Hyalella survival, although significant mortality was seen relative to laboratory controls in both Hyalella and Chironomus. No mine-related sublethal effects were observed.

Benthic Macroinvertebrates

The benthic macroinvertebrate community showed apparent responses in terms of reduced total densities, numbers of taxa and numbers of indicator taxa in the nearfield. The numbers of Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa and relative abundance of chironomids also separated exposed from reference areas. Impacts in the farfield, however, were generally not evident.

Fish

The most common fish species in the river were brook stickleback, pearl dace, northern redbelly dace and fathead minnow. However, pearl dace could not be captured downstream of the North Porcupine River confluence; accordingly, pearl dace were collected in the South Porcupine River at the nearfield area and approximately 1.5 km downstream, just upstream of the North Porcupine confluence. Pearl dace size, liver weight, gonad weight and fecundity were greatest in exposed fish and lowest in the reference fish. When adjusted for body weight, however, gonad weight and fecundity were lower in exposed dace than in reference dace.

Fish communities in McDonald’s Lake and Porcupine Lake differed, with rock bass dominating McDonald’s Lake but absent in Porcupine Lake catches. Yellow perch were captured in both lakes, but were difficult to capture in the reference. Yellow perch growth, fecundity, liver weight and gonad weight were similar in exposed and reference fish. However, when adjusted for body weight, exposed perch had lower gonad weights.

Visceral metal levels in pearl dace showed an apparent mine-related effect for Cu, Ag and Se. No visceral metallothionein (MT) response was apparent in dace.

Tissue metal levels in yellow perch varied substantially between lakes and among species. Greater tissue metal concentrations were observed in nearfield perch for liver, kidney and muscle, although the opposite trend was observed in gill (higher metals in reference fish). Tissue MT results were generally inconsistent with a mine-related effect, with greater MT in reference fish gill and kidney, but slightly greater MT in exposed fish liver.

Caged juvenile perch showed no responses in terms of visceral MT or metal concentration. In most cases, metal concentrations decreased and MT concentrations increased in caged fish over the exposure period, indicating that caging of fish may itself affect results.

Effluent Toxicity

Dome effluent was relatively toxic to test species, and produced lethality to Ceriodaphnia (all samples) and fathead minnow (two samples). The June sample was the least toxic and the October sample the most toxic. Ceriodaphnia and Lemna were the most sensitive species (chronic IC25 values <15 % effluent) and fathead minnow was least sensitive.

Hypothesis Testing

Hypothesis testing results are summarized in Table 5.2. Results of testing indicate that some contaminants (metals) are bioavailable, that some biological responses occurred and that contaminants may have caused some of the responses.

Technology Evaluation Some of the tools evaluated at Dome demonstrated a mine effect while others did not (Table 6.2). Monitoring tools that were effective included most water and sediment chemistry tools (except SEM and AVS), benthic community tools, some of the fish health tools (when adjusted for body weight) and some of the fish tissue metal tools. Tools showing no mine-related effect included MT, fish population/community tools (due to confounding habitat effects) and sediment toxicity as measured by Chironomus and Tubifex. The ineffectiveness of some monitoring tools may in part be attributed to the fact that effluent had not been discharged for several weeks before the survey, and the other confounding factors (habitat, other contaminant sources) were present.

Of related tools that were effective (e.g., total and dissolved metals in water), difference in effectiveness were relatively small as summarized in Table 6.3. Cost is therefore an important deciding factor in determining cost-effectiveness of these tools, as presented for all four mines studied in 1997 in a separate document “Summary and Cost-Effectiveness Evaluation of Aquatic Effects Monitoring Technologies Applied in the 1997 AETE Field Evaluation Program”.