Review of Technical Documents Submitted as Part of BHP Billitons - - PowerPoint PPT Presentation

Review of Technical Documents Submitted as Part of BHP Billiton’s Water Licence Renewal Application

Don Hart, Ph.D.; Ian Collins, P. Eng. EcoMetrix Incorporated

12-13 February, 2013

Scope

• Water quality modeling – methods, assumptions,

uncertainties, predictions vs monitoring data

• Derivation of site-specific water quality objectives

(SSWQOs) – methods, assumptions, uncertainties

• Parameters of Interest deemed not of potential

concern (predicted < 75% of SSWQO) (Mo, SO4, V)

• Parameters of Potential Concern (predicted > 75% of

SSWQO) but no EQC (K, Cl)

• Parameters of Potential Concern (predicted > 75% of

WQO) but no EQC (Al, Cd, Cu, Se)

Water Quality Model (Rescan)

Cell A DIKE E DIKE D Reclaim Water DIKE C DIKE B

Watershed Watershed Watershed

1616

• 30

Leslie Lake

Cell E Cell D Cell C Cell B Beartooth

Watershed

Process Plant

Underground Water

Koala Panda Natural Runoff Pumped Flows Seepage Processed Kimberlite

Waste Water Site Runoff

Water Quality Model

• Load Balance Model – Cells A-E, Beartooth Pit

submodel – geochemical predictions for pit wall input

• Downstream Model – Leslie, Moose, Nema, Slipper
• Modeled as a series of well-mixed stirred tanks
• Cell D modelled with two layers
• Nutrient degradation in Load Balance Model only
• Water balance calibrated to measured flows
• Flows from underground workings assumed constant
• Planned future flows out of Beartooth Pit
• Water quality based on measured concentrations for

PPD, natural runoff, sump water, underground water

Review of Water Modeling

• Modeling methods and assumptions are reasonable,

uncertainties not large enough to alter conclusions.

• Predictions agree well with measured lake water

quality, usually either accurate or conservative

• Ammonia, barium slightly under-predicted in the

Koala watershed lakes

• Iron under-predicted in Nema and Slipper lakes, but

will not approach WQO

• These small under-predictions are unlikely to alter

conclusions about chemicals of potential concern

Derivation of SSWQOs

• Based on Species Sensitivity Distributions (SSD)
• Followed CCME (2007) methods (5th percentile, HC5)
• Used “resident” species, and “surrogate” species
• Used “acceptable” studies based on quality review
• Chronic “no-effect” concentration for each species
• SSWQO is HC5, or hardness adjusted HC5
• Hardness adjustment for SO4, Cl, nitrate-N
• No hardness relationship for K, Mo, V
• Overall, the SSWQO methodology is appropriate
• Assumption- species used represent the community

Example- SSD for Mo (Rescan)

(x-1.917)

Proportion of Taxa Affected

1.0 0.8 0.6 0.4 0.2

Normal Model 95% Confidence Limits Fish Invertebrate Alga/Plant

y = ½ {1 + erf [

(0.383 2) ]}

HC

5 = 19 mg/L

Lemna minor Lymnaea stagnalis Brachionus calyciflorus Chironomus riparius Daphnia magna Pimephales promelas Ceriodaphnia dubia Chlorella regularis Oncorhynchus mykiss

0.0

Pseudokirchneriella subcapitata

1 10 100 1,000 10,000

Total Molybdenum (mg/L)

Key Uncertainties in SSWQOs

• Chloride – SSWQO adopted from Elphick (2011)
• Hardness relationship for C.dubia assumed for other

sensitive species (all daphnids in Elphick’s SSD)

• Clams may be more sensitive? they drive the lower

HC5 of 120 mg/L from CCME (2011)

• Nitrate – SSWQO is an HC5, hardness adjusted
• Hardness relationship, a pooled slope from 4 taxa,

assumed representative for other sensitive species (lake trout?). New data - trout is hardness protected.

• Sulphate – SSWQO is an HC5, hardness adjusted
• Hardness relationship for C. dubia assumed for other

sensitive species (trout?). New data - trout protected

Parameters of Interest Deemed not of Potential Concern

• Sulphate- SSWQO is 566 mg/L at hardness 160
• max predicted 133 mg/L Leslie, 137 mg/L Moose
• only 24% of SSWQO (not 75%)
• Molybdenum- SSWQO is 19 mg/L
• max predicted 0.168 mg/L Moose Lake
• < 1% of SSWQO (not 75%)
• Vanadium- SSWQO is 0.03 mg/L
• max predicted 0.0062 mg/L Leslie Lake
• only 21% of SSWQO (not 75%)

Parameters of Potential Concern (Predicted > 75% of SSWQO) but no EQC due to “low risk”

• Chloride - SSWQO is 388 mg/L at hardness 160
• max predicted 392 mg/L Moose, 383 mg/L Leslie
• 101% and 99% of SSWQO
• Potassium- SSWQO is 41 mg/L
• max predicted is 42 mg/L Moose, 41 mg/L Leslie
• 103% and 100% of SSWQO

Opinion – predicted to reach SSWQO implies a low level of effect on a few sensitive species; EQC links to SSWQO but allows closer scrutiny than annual AEMP; an EQC would be reasonable.

Parameters of Potential Concern (Predicted > 75% of WQO) but no EQC due to “low risk”

• Aluminum- WQO is 0.1 mg/L for pH >6.5 (CCREM)
• max predicted 0.15 mg/L Leslie Lake
• Chapman memo suggests low or negligible risk at

this level, due to particulate form or DOC or hardness, particularly in the pH 6-8 range

• Rescan memo indicates 87% dissolved in Leslie
• Further work needed to show no effects at 0.15mg/L
• Cadmium- WQO is too low, under revision.
• max predicted 0.3 ug/L in Leslie, hardness 350
• meets EPA WQC. Wait for CCME revision.

Parameters of Potential Concern (Predicted > 75% of WQO) but no EQC due to “low risk”

• Copper - WQO is as low as 2 ug/L at low hardness

(CCREM) but Cu is mainly due to natural runoff

• max predicted 2.5 ug/L Nema, but below WQO
• predicted 2 ug/L Slipper, equal WQO (low hardness)
• No benefit of EQC since mine does not control Cu
• Selenium- WQO is 1 ug/L, but tissue better indicator
• max predicted 1.2 ug/L in Leslie, RW flesh now 4.4

mg/kg dw (BHPB response to IEMA, Jan 2013, p12)

• EPA draft 7.9 mg/kg dw , BC MOE 1 mg/kg ww
• an EQC permits close scrutiny of effluent, not tissue

Thank you.

• Questions?