Preliminary assessment approach for groundwater sustainability – case study: the Abbotsford-Sumas aquifer

Jo-Ann Aldridge, Cecilia Wong, Gwyn Graham

In the proceedings of: GeoMontréal 2013: 66th Canadian Geotechnical Conference; 11th joint with IAH-CNC

Session: Groundwater Management II

ABSTRACT: In 2006, the federal government tasked the Council of Canadian Academies (CCA) to determine what is needed to achieve sustainable management of Canada™s groundwater resources, from a science perspective. The CCA identified 5 groundwater sustainability goals and emphasized the need for a decision-support framework in addition to regular reporting on the state of groundwater resources in Canada and progress toward sustainable development. In response, the Canadian Council of Ministers of the Environment (CCME) Water Management Committee™s Groundwater Subcommittee initiated a preliminary study which identified a framework approach for evaluating the 5 CCA goals using the Driving Force-Pressure-State-Impact-Response (DPSIR) framework previously applied by the United Nations Educational, Scientific and Cultural Organization (UNESCO, 2007). This preliminary approach proposed twelve groundwater sustainability indicators for reporting against the 5 CCA goals. The CCME Groundwater Subcommittee also recommended piloting this preliminary assessment approach to a) determine the applicability of the DPSIR model and recommended indicators at a range of scales and issues; and b) identify the need for revisions and refinement of the approach. Environment Canada applied this preliminary assessment approach and proposed indicators to assess sustainability of the Abbotsford-Sumas Aquifer (ASA). Four other pilot projects have been completed at aquifers across Canada. Sustainability of the ASA was evaluated against the five CCA goals using indicators previously identified in reports by UNESCO (2007), Steinman (2007) and Gordon (2011), and several novel indicators proposed by Environment Canada. Indicators were also aligned with DPSIR components. Overall, each DPSIR component was characterized; however, each goal was not assessed for all DPSIR components. The CCA goal to protect groundwater quality from contamination was evaluated using three indicators: extent of groundwater contamination, aquifer vulnerability class and number of contaminated sites.: Using data from monitoring wells and homeowner wells as part of an extensive survey conducted jointly by Environment Canada, BC Ministry of Environment (BC MOE), Fraser Health Authority and University College of the Fraser Valley (Environment Canada, 2006), approximately fifty percent (50%) of the areal extent of the aquifer was found to exceed the Canadian Drinking Water Quality Criteria for nitrate (>10 mg/L nitrate as nitrogen). Aquifer vulnerability mapping (AVI) completed by the BC Ministry of Environment (BC MOE 2006) shows that 52% of the aquifer is classified as extremely high in vulnerability. This AVI is based on the thickness of each sedimentary unit above the uppermost aquifer, and estimated hydraulic conductivity of each of these layers. A search of BC MOE™s site database in 2012 identified 73 sites under investigation or remediation for contamination. An additional 12 contaminated sites were identified on the federal inventory of contaminated sites. Our resulting weight of evidence assessment concluded that current use and management of the ASA and /or the land use above could be currently considered unsustainable due to poor groundwater quality. Reliance on alternate water supply options has increased due to concerns over groundwater quality. The CCA Goal to protect groundwater supplies from depletion was assessed using estimates for renewable groundwater, usage, and measured changes to the water table. Renewable groundwater resources were estimated from precipitation data and estimates for recharge and stream losses together with BC statistics population data for the local communities. The resulting estimate is 392 m3/capita/yr. This estimate shows substantial aquifer surplus when compared with the National Water and Waste Water Benchmarking Initiative average for unmetered systems in BC of 160 m3/c/yr. Groundwater abstraction was estimated using data from municipalities, irrigation estimates from BC Agriculture and, to estimate private well use: well data from BC MOE coupled with water supply networks information from the municipalities and Google Maps to identify households. The ratio of groundwater abstraction over recharge was found to be in the range of 15% annually but as high as 40% seasonally. Long-term groundwater monitoring by

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