Transcript Britannia Mines Environmental Impact Study of Treated

Britannia
Mine:
Environmental
Impact Study
of Treated
Effluent
Discharge
Lee Nikl
Background/Context:
• Recent changes to effluent permitting
procedures have increased the requirements
for dischargers to study potential
environmental effects of their discharge
• Dischargers are required to complete an
Environmental Impact Study (also called a
Technical Assessment) and demonstrate to
WLAP that the environment will not be
impaired.
What is it about effluents that
causes harm to the environment?
• Toxic substances
contained in the effluent
can act on aquatic
organisms to result in
adverse effects.
• Studying these toxic
substances allows us to
make responsible decisions
regarding effluent
discharges.
What do we need to know to predict
environmental effects of an effluent?
• Source: Identify contaminants of
potential concern (COPC).
• Pathway: Identify pathway between
the source and the receptors in the
environment.
• Receptors: Identify the organisms
that will be potentially exposed to the
effluent constituents
• Exposure Assessment: Identify the
exposure of organisms to the COPC.
• Effects Assessment: Identify the
likelihood that adverse effects will
take place.
Britannia Mine: Effluent EIS Approach
• The effluent treatment system is not yet
constructed and there is no treated effluent.
• The purpose of the EIS is to make informed
effluent permitting decisions before the
discharge takes place.
• This precautionary approach prevents
environmentally disruptive discharges at the
outset.
Britannia Mine: Effluent EIS Approach
• Source: The source of effluent is the High Density
Sludge treatment system
– COPCs identified are copper, zinc, cadmium
• Pathway: Conveyance through outfall pipe to Howe
Sound. EIS assessed discharge via existing (26m)
outfall and new (50m) outfall.
• Receptors: Fish, zooplankton, etc. Productivity greatest
in the photic zone which is ~10-15m in Howe Sound (20m
used)
Britannia Mine: Effluent EIS Approach
• Exposure Assessment:
– Predicted effluent chemistry was based on lab
analysis of actual tests on the effluent.
– Predicted concentrations in the environment were
derived from US EPA computer simulation model of
effluent dispersion.
– Various scenarios were examined to encompass
fluctuations due to seasonality and climate.
Britannia Mine: Effluent EIS Approach
• Exposure Assessment:
– The minimum requirements of WLAP are to identify
the concentration of contaminants at the edge of the
Initial Dilution Zone (IDZ), a 100m radius cylinder of
water surrounding the outfall terminus.
– WLAP can require additional requirements to suit
specific circumstances.
– EIS conducted here also examined exposure within the
IDZ, specifically, at the boundary of the photic zone
and also at the “end-of-pipe” (federal requirements)
Britannia Mine: Effluent EIS Approach
• Exposure Assessment:
– The scenarios modeled (simplified version presented
here – full version in report) were as follows:
Case
Flow
(m3/hr)
d.Cu
(ppm)
d.Zn
(ppm)
TSS
(ppm)
Average Flow
585
.02
.03
10
Design Flow
1050
.02
.03
10
Permit Flow
1050
.1
.2
30
High Flow
1400
.1
.2
30
Britannia Mine: Effluent EIS Approach
• Effects Assessment:
– The most simple and conservative means of assessing
effects is to compare predicted concentrations to
ambient criteria
– Comparison of predicted environmental
concentrations were compared to criteria in Tier 1 of
this assessment.
Metal Speciation
• The toxicity of a metal is related
to its bioavailability.
• Various factors in the environment
control bioavailability.
• Ambient criteria are based on the
most bioavailable form and do not
provide a realistic assessment of
effect.
Britannia Mine: Effluent EIS Approach
• Effects Assessment:
– In Tier 2 of assessment, the bioavailability of metals
was assessed.
– Computerized chemical speciation modeling was
undertaken using predicted concentrations and
background water chemistry.
– This approach provides more realistic information
from which to predict potential effects.
Effluent EIS: Findings
• Tier 1
Assessment:
(end of pipe)
– Treated
effluent was
submitted for
toxicity
testing.
Test
Result
Rainbow trout acute
lethality
Not acutely lethal
Amphipod survival
Not acutely lethal
Chinook salmon acute
lethality
Not acutely lethal
Topsmelt 7d survival
Not acutely lethal
Topsmelt 7d growth
No significant inhibition
Algal 72-h growth inhibition No significant inhibition
Echinoid fertilization
No significant inhibition
Effluent EIS: Findings
• Tier 1 Assessment: HQ’s @ edge of IDZ
(26m outfall)
26m Outfall - Total Metals
8
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
Hazard Quotient
Hazard Quotient
26m Outfall Depth - Dissolved metals
7
6
5
4
3
2
1
0
d.Cu d.Zn d.Cd d.Cu d.Zn d.Cd d.Cu d.Zn d.Cd d.Cu d.Zn d.Cd
Average
Design
Permit
Case
High
t.Cu t.Zn t.Cd t.Cu t.Zn t.Cd t.Cu t.Zn t.Cd t.Cu t.Zn t.Cd
Average
Design
Permit
Case
High
Effluent EIS: Findings
• Tier 1 Assessment: HQ’s @ edge of IDZ
(50m outfall)
50m Outfall depth - Total metals
50m Outfall Depth - Dissolved metals
1
Hazard Quotient
Hazard Quotient
1.2
0.8
0.6
0.4
0.2
0
d.Cu d.Zn d.Cd d.Cu d.Zn d.Cd d.Cu d.Zn d.Cd d.Cu d.Zn d.Cd
Average
Design
Permit
Case
High
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
t.Cu t.Zn t.Cd t.Cu t.Zn t.Cd t.Cu t.Zn t.Cd t.Cu t.Zn t.Cd
Average
Design
Permit
Case
High
Effluent EIS: Findings
• Tier 1
Assessment:
Dissolved Copper Concentration
5
4
Concentration
(µg/L)
Dilution with
distance from
50m outfall
terminus
3
2
1
0
0
100
200
300
400
Distance from Terminus (m)
Case 1
Case 2
Permit Scenario
Case 4
500
Effluent EIS: Findings
• Tier 1 Assessment: Photic Zone
– HQs are elevated (d.Cu = 8.8; d.Cd = 17;
d.Zn = 3.6) at the bottom of the photic zone
(20m) using the 26m outfall depth
– With a 50m outfall, effluent plume trapping
depths range from 16.2 to 26.1m, depending
on the flow scenario – interaction with the
photic zone is not significant if effluent is
discharged at 50m.
Effluent EIS: Findings
• Tier 1 Assessment: Summary
– Using the 50m deep outfall, WQC were met for
dissolved copper at the edge of the IDZ under all
cases modeled. Interaction with the photic zone is
minimal
– Using the 26m deep outfall, WQC for dissolved
copper are exceeded for the permit flow and high
flow cases.
– Total copper is predicted to exceed WQC for all
flow scenarios and outfalls modeled.
Effluent EIS: Findings
• Tier 2 Assessment (bioavailability):
Metal
Speciation Modeling Results
Copper
•Majority of copper bound by organic (65-81%) and inorganic (18-35%)
ligands.
•Less than 0.2% present in the highly bioavailable forms (Cu+2, the most
bioavailable form comprised less than 0.01%).
Zinc
•Majority of zinc exists as non-bioavailable inorganic (81-89%) and organic
(5-13%) complexes.
•Approximately 5% of the zinc exists as Zn2+.
Cadmium
•Majority of cadmium exists as organic complexes (64-94%) and inorganic
complexes (5-13%).
•Approximately 0.3 to 0.6% of the cadmium exists as Cd2+.
Effluent EIS: Findings
• Tier 2 Assessment (bioavailability):
– If the 50m outfall is used for discharge, exceedences
of ambient criteria will be infrequent and, when they
occur, small in magnitude
– These minor exceedences are not biologically relevant,
however, given the small proportion of metal that will
be in a bioavailable form
Uncertainty Analysis
• The EIS is a predictive exercise.
Assumptions were necessary and
direct measurements not possible.
• An analysis of the uncertainties was
undertaken to identify the
significance and consequence, if any,
to the predictions of effect.
Uncertainty Analysis
• Uncertainties were either not
significant or, if there was doubt,
this was identified as a need for
subsequent effluent monitoring.
• Deferral to monitoring was deemed
acceptable only if there is a means to
enact further control over the
effluent.
Conclusion
• Discharge via the existing
26m outfall is not
recommended.
• Discharge via the 50m outfall
is not expected to result in
adverse environmental
effects.