esaa | environmental services association of alberta ......determining the salinity of groundwater...
TRANSCRIPT
-
Determining the Salinity of
Groundwater for Regulatory
Purposes in Alberta
Banff, Alberta
April 12, 2012
Brent Welsh, P.Eng. District Hydrogeologist
Alberta Environment and Water
Operations, Northern Region
-
Outline
• Background
• Regulatory Issue
• Methods for Determining Salinity (TDS)
• Case Studies
• Cause of Discrepancies between Methods
• Policy Direction
• Key Information
• Acknowledgements
-
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
-
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
-
Deep Saline Aquifer Drilling and
Sampling Programs
Reported cost: > $1 M / well
Oil rig drilling water well Blow-out preventer
Tanking saline water at surface
-
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 HCO3
• Results can be
significantly different for
water from same well
-
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 CaCO3) for HCO3 + CO3
• Specific Gravity
– Approximate TDS based on specific gravity
• Conductivity Surrogate or Meter
– TDS = EC x conversion factor
-
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 re-
testing 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)
-
Calculations from Case Study 1
• 1999 Used Σ Major Ions Method (incl. HCO3):
– TDS = 4759 mg/L
• 2009 Used Σ Major Ions with 0.6 Alkalinity for HCO3 + CO3:
– TDS = Na + K + Ca + Mg + Cl + SO4 + 0.6 x Alk = 3209 mg/L
– TDS = Σ Major Ions = 4656 mg/L
– No significant changes in Water Quality identified from 1999 - 2009
• 2009 Used Gravimetric Method (Dried at 180 oC):
– TDS = 3260 mg/L
Lab ID Na
(mg/L)
K
(mg/L)
Ca
(mg/L)
Mg
(mg/L)
Fe
(mg/L)
Cl
(mg/L)
HCO3 (mg/L)
SO4 (mg/L)
CO3 (mg/L)
T-Alkalinity
(as mg/L CaCO3)
WG38620C
(1999)
1480 3.7 6.1 1.9
-
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 0.4917 HCO3:
– TDS = 3939 mg/L
– Licence required
-
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 = 4711.8 mg/L
-
Why are there Method Discrepancies?
• Main cause of discrepancies is HCO3
• Some methods produce similar results
– Gravimetric method dehydrates HCO3 and off-gases CO2 and H2O
• HCO3- unstable at 100 °C
• 2HCO3- = CO3-2 + H2O(g) + CO2(g)
• i.e., 2 mol of HCO3 yields 1 mol CO3 left on pan
– 0.6 Alkalinity method accounts for HCO3 in equivalent CaCO3
• The calculation by summation varies significantly
– Method accounts for full HCO3 ion concentration
• Variations can be high enough to re-classify groundwater from saline to non-saline
-
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
http://environment.gov.ab.ca/info/library/8547.pdf
• Purpose:
– Standardize the way TDS is measured for Regulatory Purposes
• AEW
» Water Act Licensing
• ERCB
» Base of Groundwater Protection
» Deep well disposal assessments, etc.
• Selected Method for TDS:
– Standard Methods for the Examination of Water and Wastewater
http://environment.gov.ab.ca/info/library/8547.pdf
-
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
-
Key Information for Exploration
Hydrogeologists
• Petroleum Lab Data without Alkalinity can still be useful
– USGS (Hem, 1989) suggests:
• X mg/L HCO3 x 0.4917 = Y mg/L CO3
• 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 TDScalculated > 6500 mg/L will be saline
-
Areas to Double Check for Compliance
Purposes
• TDS = 4000 to 6500 mg/L
– i.e., “borderline” saline or brackish
water
• High HCO3 concentrations
• Deep groundwater resources
– Grande Prairie Area
• Cardium Formation
– Athabasca Oil Sands Area
• Grand Rapids Formation
• Clearwater Formation
• Old Water Source Wells (≤ 1996)
-
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
-
Questions?
TDS Measurement Method 2540C
Oven at
180 ± 2 °C Desiccators
Scale Filtering
Photos courtesy of Maxxam Analytics, Edmonton