jericho aquatic discharge assessment presented by: bruce ott, senior environmental scientist, amec...

Jericho Aquatic Discharge Assessment

Presented by: Bruce Ott,

Senior Environmental Scientist,

AMEC Earth & Environmental

Water Quality Assessment

• Based on supplement work by:– SRK

• contaminant loading• water balance• regional and LSA climate analyses• discharge concentration estimates

– Greisman/Dunbar• Lake C3 and Carat Lake dilution modelling

• Used CCME Guidelines as No Chronic Effects Level

CCME Guidelines

• Copper – 0.002 mg/L

• Cadmium – 0.000017 mg/L

• Nickel – 0.025 – 0.150 mg/L

• Chromium (Cr6+) – 0.001 – 0.0015 mg/L

• Molybdenum – 0.073 mg/L (BC 1 mg/L)

• Ammonia (unionized) – approx. 2 mg/L

• Nitrate – 15 mg/L (proposed)

Water Quality Assessment Assumptions - Operations

• One discharge point for all Jericho water:

• Water is discharged from the PKCA polishing pond into Stream C3.

• The sewage treatment plant discharges to the PKCA.

• All mine water is routed to the PKCA prior to discharge.

• All uncontaminated water is routed through ditches and the Stream C1 diversion.

Scenarios Examined

Out of the range of scenarios that could be examined, the following were chosen as they represent the variation that could be encountered during operations:

– extreme low flows; maximum contaminants

– extreme low flows; average contaminants

– average flows; maximum contaminants

– average flows; average contaminants

Water Quality AssessmentOperations

Scenario 1: Extreme Low Flows and Probable Maximum PK Discharge Concentrations:

Results indicate:•No Health Canada guidelines are exceeded at the water intake. •Some potential for chronic effects from the substances listed for the most sensitive freshwater organisms.

Continued…

Mitigation during extreme low flows:– cessation of discharge– spray irrigation– addition of phosphate into the PKCA to reduce

ammonia and metal concentrations (enhanced degradation)

Water Quality AssessmentOperations

Scenario 2: Extremely low flows and average PK discharge concentrations

• Protection of aquatic life guidelines predicted to be met within 100 m of mouth of Stream C3

• No mitigation required

Water Quality AssessmentOperations

Scenario 3: Average Flows and Maximum PK Discharge Concentrations

• Only cadmium exceeds protection of aquatic life guidelines within 100 m of the mouth of Stream C3

• Mitigation: – treatment to tie up metals in the PKCA, e.g. add PO4

– Spray irrigation

Scenario 4: Average Flows and Average PK Discharge Concentrations

• Cadmium exceedance (0.00002 vs 0.000017 mg/L)

Water Quality Assessment Assumptions - Closure

• The PKCA will be reclaimed to land on closure and any water flowing from Stream C3 will be essentially uncontaminated.

• Water from the mine area after closure discharges to the open pit. After approximately 20 years the pit will overflow through a prepared channel to sediment pond A.

• No active water treatment

Water Quality AssessmentClosure

• ammonia completely oxidized prior to release• metals may still be present above CCME• exfiltration from Pond A if water meets health and

protection of aquatic life guidelines• discharge through a diffuser in Carat Lake if not to

provide 36:1 dilution within 7 m• diffusion of chronic not acutely toxic water

Assessment is Conservative

•CCME guidelines were used to indicate no chronic effects

•Dilution model uses conservative assumptions

•Sequestering of metals in the aquatic environment

Summary

• Under average conditions discharges during mining will not be chronically toxic

• Options are available to mitigate if required

• Closure treatment can be handled passively if the open pit is allowed to fill naturally