Suggested Effluent Quality Criteria for the Snap Lake Diamond Mine - PowerPoint PPT Presentation

Suggested Effluent Quality Criteria for the Snap Lake Diamond Mine Don Hart, Ph.D.; Ian Collins, P. Eng. EcoMetrix Incorporated 13 December, 2011

Introduction • Water and Effluent Quality Management Policy (MVLWB, 2011) for setting water quality objectives (WQOs) and effluent quality criteria (EQCs) for licensees. • EQCs should be set to ensure that water quality objectives will be met at a defined location. • EcoMetrix retained by MVLWB as an independent reviewer to suggest WQOs for Snap Lake and corresponding EQCs for Snap Lake Diamond Mine

Chemical Parameters • We were requested to address: • a) Parameters that have EQCs in the existing license (TSS, ammonia, nitrite, Al, As, Cd, Cr, Cu, Ni, Pb, Zn) • b) Parameters not in existing license that may need EQCs because they have or may exceed objectives for the lake in future (Fl, Cl, Mn) • c) Parameters not in existing license that are increasing in the lake (Ba, B, Sr)

Methodology • WQOs – generally used CCME guidelines (if available) – used alternate values in two cases (nitrate, Fl) based on review of toxicity literature. • No CCME values for Cl, TDS, Mn, Ba, Sr – used literature values or guidelines from other agencies to define protective levels. • EQCs for effluent calculated using a mass and water balance model for the lake such that, if EQCs are met by 2014, then WQOs will be met in Snap Lake by end of operations. • Flow through WTP assumed to increase over time as projected by Golder (2011b) Figure 6.2.

Other Assumptions • Baseline lake water quality at median values for 1998-2001(from Golder 2011c, Table 5.1) • Lake water balance from Golder 2011b, Figure 2. • About 70% of lake volume available for mixing. • Uncontrolled runoff and WMP water quality from Golder 2011c, Tables 8.1 and 8.3 • WTP effluent quality before 2014 at average values reported for Nov.2008-Oct.2010. • No contaminant losses from lake water by partitioning to air or sediment, or by biodegradation.

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Model Calibration • Initial runs with WTP effluent concentrations constant to end of mine life (2022); i.e. no shift to EQC. • Predicted TDS in lake agrees with 2010 measured maximum (2010 AEMP report, Golder 2011a); peak falls between upper and lower bound forecasts from Golder’s more complex model (Golder 2011b). • Predicted Cl, Fl, Sr in lake also agree with 2010 measured maximum values. • Model overpredicts ammonia and nitrite by 2-3 times because important loss processes are ignored.

Predicted TDS in Snap Lake 500 450 Total Dissolved Solids Concentration (mg/L) 400 350 300 250 200 150 100 50 0 2000 2005 2010 2015 2020 2025 2030 2035 2040 2045 2050 Year Predicted TDS Concentrations Water Quality Objective Measured 2010 Maximum Concentration

Predicted Ammonia in Snap Lake 2.5 Total Ammonia Concentration as N (mg/L) 2 1.5 1 0.5 0 2000 2005 2010 2015 2020 2025 2030 2035 2040 2045 2050 Year Predicted Ammonia Concentrations Water Quality Objective Measured 2010 Maximum Concentration

Results – Suggested WQOs Chemical WQO * CCME Parameter mg/L mg/L Basis of Selected WQO TSS 5 5 CCME (clear flow) Ammonia-N 1.47 1.47 CCME (17.9 o C, pH 7.5) Nitrite-N 0.06 0.06 CCME Nitrate-N 3.61 2.94 HC5 from EC 2011 draft Al 0.1 0.1 CCME (pH > 6.5) As 0.005 0.005 CCME Cd 3.30E-05 3.30E-05 CCME (H=100 mg/L) Cr 0.0089 0.0089 CCME (Cr III) Cu 0.0024 0.0024 CCME (H=100 mg/L) Ni 0.096 0.096 CCME (H=100 mg/L) Pb 0.0032 0.0032 CCME (H=100 mg/L) Zn 0.03 0.03 CCME pH 6.5-9 6.5-9 CCME F 0.4 0.12 BCMOE value Mn 1 - BCMOE (H=100 mg/L) Cl 213 - HC5 from EC 2001 Ba 1 - BC MOE working value B 1.5 1.5 CCME Sr 0.5 - GM of two lowest CVs TDS 350 - license value (protective) * Suggest WQO as a whole-lake average (there is little difference from NF to FF) WQOs for nitrate-N and F depart from CCME

Results – Suggested EQCs Effluent Derived Chemical WQO CCME Mean EQC * Parameter mg/L mg/L mg/L mg/L Note TSS 5 5 4.04 7 Ammonia-N 1.47 1.47 2.66 1.75 Nitrite-N 0.06 0.06 0.19 0.06 1 Nitrate-N 3.61 2.94 9.06 3.83 Al 0.1 0.1 0.0548 0.1 As 0.005 0.005 0.0005 0.007 Cd 3.30E-05 3.30E-05 4.70E-05 4.20E-05 2 Cr 0.0089 0.0089 0.0013 0.013 Cu 0.0024 0.0024 0.001 0.0033 Ni 0.096 0.096 0.01 0.14 Pb 0.0032 0.0032 0.00025 0.0048 Zn 0.03 0.03 0.00262 0.04 pH 6.5-9 6.5-9 7.55 6.3-10.4 F 0.4 0.12 0.42 0.5 3 Mn 1 - 0.0454 1.5 Cl 213 - 256.9 278 4 Ba 1 - 0.0306 1.5 B 1.5 - 0.1041 2.3 Sr 0.5 - 1.6 0.5 TDS 350 - 566.3 428 * Suggested EQC is a monthly average (based on model with constant effluent quality) Parameters expected or likely to exceed WQO in Snap Lake EQC well above effluent range; lower performance-based value is feasible 1 Derived EQC for nitrite is too low since conversion to nitrate is ignored; correction to modelled peak suggests that EQC could be 0.2 mg/L 2 Cd generally non-detect in both lake water and effluent 3 F expected to exceed CCME guideline but not WQO 4 Cl expected to exceed WQO in Golder's upper bound scenario

Summary- Treatment Options • Parameters expected or likely to exceed WQOs in Snap Lake, without improved treatment, are: ammonia-N, nitrate-N, chloride, TDS and strontium. • These chemicals exist mainly in dissolved form. • Ammonia and nitrate treatment options (air-stripping, biological) not efficient at low temperature (< 10 o C); BAT in the N.W.T. is source control (INAC,2002). • Major ions and TDS – two viable technologies (reverse osmosis, evaporation) (Golder, 2008); RO would also remove ammonia and nitrate. Expensive.