Determining the Salinity of Groundwater for Regulatory Purposes in Alberta

Transcription

1 Determining the Salinity of Groundwater for Regulatory Purposes in Alberta Brent Welsh, P.Eng. District Hydrogeologist Alberta Environment and Water Operations, Northern Region Banff, Alberta April 12, 2012

2 Outline Background Regulatory Issue Methods for Determining Salinity (TDS) Case Studies Cause of Discrepancies between Methods Policy Direction Key Information Acknowledgements

3 Background (up to 1996) Prior to 1996: Groundwater was licensed regardless of salinity 1995: Definition of saline groundwater introduced Groundwater that has total dissolved solids (TDS) exceeding 4000 mg/l Exemption from licensing requirement for saline groundwater: Under Schedule 3 of Water (Ministerial) Regulation 1996: Alberta Environment and Water (AEW) stopped issuing and renewing licences for saline groundwater 149 Licences were cancelled (AEW query, 2010) throughout Alberta

4 Background (2006-Present) Water Conservation and Allocation Policy for Oilfield Injection (2006) Key Objective: Non-saline Water Conservation Minimizing use of non-saline water where reasonable and feasible alternatives exist Outcome Achieved Since 2006: Increased Saline Aquifer Exploration Increased Saline Water Use Especially at thermal in situ oil sands projects in Athabasca and Cold Lake Oil Sands Areas

5 Deep Saline Aquifer Drilling and Sampling Programs Oil rig drilling water well Blow-out preventer Reported cost: > $1 M / well Tanking saline water at surface

6 Regulatory Issue Method for determining TDS not specified by AEW Petroleum laboratories calculate TDS by summing major ions Environmental laboratories calculate TDS by summing major ions with gravimetric factor for HCO 3 Results can be significantly different for water from same well

7 Methods for Determining TDS Measured or Gravimetric Filtering, evaporating sample to dryness at 180 C, weighing residue Calculation TDS = major cations + major anions Same as above, but sub 0.6 x Alkalinity (mg/l CaCO 3 ) for HCO 3 + CO 3 Specific Gravity Approximate TDS based on specific gravity Conductivity Surrogate or Meter TDS = EC x conversion factor

8 Case Study 1: 1999 Licence not renewed 1999: Cardium Formation water source well assessed as saline based on of major ions calculation 2009: Energy Resources Conservation Board (ERCB) requests retesting of well Results indicate well is non-saline based on gravimetric method Discrepancy in classification due to method Discrepancies could be 2000 mg/l TDS high (i.e., well calculated as 6000 mg/l TDS could be 4000 mg/l if measured, thereby requiring regulation under Water Act)

9 Calculations from Case Study 1 Lab ID Na (mg/l) K (mg/l) Ca (mg/l) Mg (mg/l) Fe (mg/l) Cl (mg/l) HCO 3 (mg/l) SO 4 (mg/l) CO 3 (mg/l) T-Alkalinity (as mg/l CaCO 3 ) WG38620C (1999) (2009) < <4 5 <2 < < Used Σ Major Ions Method (incl. HCO 3 ): TDS = 4759 mg/l 2009 Used Σ Major Ions with 0.6 Alkalinity for HCO 3 + CO 3 : TDS = Na + K + Ca + Mg + Cl + SO x Alk = 3209 mg/l TDS = Σ Major Ions = 4656 mg/l No significant changes in Water Quality identified from Used Gravimetric Method (Dried at 180 o C): TDS = 3260 mg/l

10 Case Study 2: 2009 Referral to AEW Lower Grand Rapids Formation Operator Inquires with AEW to see if they need a Licence Σ Major Ions: TDS = 4987 mg/l Ion balance acceptable No mud contamination 3 Well Volumes were purged prior to sampling No Licence required? WRONG Major Ions with HCO 3 : TDS = 3939 mg/l Licence required

11 Case Study 2 Same well re-sampled during pump test 0.6 Alkalinity Method used: TDS = 3860 mg/l Ion Balance = 0.98 Conclusion: Confirmation of Licensing requirement SIDE NOTE: Using Major Ions, you get: TDS = mg/l

12 Why are there Method Discrepancies? Main cause of discrepancies is HCO 3 Some methods produce similar results Gravimetric method dehydrates HCO 3 and off-gases CO 2 and H 2 O HCO 3 - unstable at 100 C 2HCO 3 - = CO H 2 O (g) + CO 2 (g) i.e., 2 mol of HCO 3 yields 1 mol CO 3 left on pan 0.6 Alkalinity method accounts for HCO 3 in equivalent CaCO 3 The calculation by summation varies significantly Method accounts for full HCO 3 ion concentration Variations can be high enough to re-classify groundwater from saline to non-saline

13 Method for Determining TDS Policy: Groundwater Information Letter 1/2010 Clarification of the Method Used to Calculate Total Dissolved Solids for Regulatory Purposes in Alberta Purpose: Standardize the way TDS is measured for Regulatory Purposes AEW ERCB» Water Act Licensing Selected Method for TDS:» Base of Groundwater Protection» Deep well disposal assessments, etc. Standard Methods for the Examination of Water and Wastewater

14 Key Information for Labs Method to be used: Standard Methods for the Examination of Water and Wastewater, 1998 (as amended) TDS Gravimetric Method is 2540C (180 C) TDS Calculation using 0.6 Alkalinity is 1030E This is a correctness check that is part of 2540C CAUTION: Total Solids Method is 2540B not same as 2540C Alkalinity Titration Method is 2320B

15 Key Information for Exploration Hydrogeologists Petroleum Lab Data without Alkalinity can still be useful USGS (Hem, 1989) suggests: X mg/l HCO 3 x = Y mg/l CO 3 Use Y instead of X for Major Ions method This method produces results similar to Method 2540C When is a review of TDS data required? Lab results should be checked if: Major Ions or different gravimetric method used for TDS i.e., heated to 110 C instead of 180 C Water with TDS calculated > 6500 mg/l will be saline

16 Areas to Double Check for Compliance Purposes TDS = 4000 to 6500 mg/l i.e., borderline saline or brackish water High HCO 3 concentrations Deep groundwater resources Grande Prairie Area Cardium Formation Athabasca Oil Sands Area Grand Rapids Formation Clearwater Formation Old Water Source Wells ( 1996)

17 Acknowledgments AEW Groundwater Policy Developed by Petri Nieminen, P.Chem. Refined by Bob Chandler, Ph.D. AEW Operations Northern Region: Glenn Winner, Patrick Murray, Catherine Evans Southern Region: Jeff Gutsell, Claude Eckert ERCB Elena Zimmerman

18 Questions? TDS Measurement Method 2540C Desiccators Oven at 180 ± 2 C Scale Filtering Photos courtesy of Maxxam Analytics, Edmonton