Clarence-Rockland Groundwater Study - Aquifer Capability Screening Tool pilot study, Prescott-Russell, Ontario

Natural groundwater quality in exceedance of Ontario provincial drinking water standards is a persistent issue that limits development of private services in Eastern Ontario. Local ambient groundwater quality issues are linked to geological conditions and are predominantly the result of the marine environment that existed in the St. Lawrence lowlands following the most recent glacial retreat. In addition to trapping saline water, the marine clays mask complex Paleozoic bedrock topography and geology, whose interbedded limestone and shale units, along with long groundwater residence times, further contribute to poor water quality. A study was initiated at the request of the municipality, the United Counties of Prescott and Russell (UCPR), to develop an Aquifer Capability Screening Tool (ACST) to evaluate the development potential of a property where private wells are required to supply drinking water. The ACST consists of maps of expected groundwater quality and quantity in relation to Provincial standards for private wells. The tool is intended to identify potential issues early in the application process, saving time and money for developers and the municipality. The pilot study was undertaken within a single municipality in the UCPR, the City of Clarence-Rockland, to determine the viability of the approach. The Clarence Rockland Groundwater Study (2013-2015) was completed through a collaborative partnership between the Upper and Lower Tier Municipalities, South Nation Conservation Authority, the Ontario Geological Survey (OGS), the University of Ottawa and Geofirma Engineering Ltd. Development of the ACST was supported by a robust groundwater sampling program to characterize hydrostratigraphy, identify groundwater flow patterns, and develop water quality maps. Well sampling was carried out in accordance with protocols developed by the OGS Ontario Ambient Groundwater Geochemistry Study (Hamilton, Brauneder and Mellor, 2007 and Hamilton and Brauneder, 2008). A 2km sampling grid was used to facilitate even sampling across the municipality; 136 wells were sampled, including 74 bedrock wells and 62 overburden wells. The study created a new overview of ambient groundwater quality and quantity for the City of Clarence- Rockland. ACST water quality maps were generated from groundwater sampling results, with an emphasis on parameters in exceedance of Provincial standards that could inhibit lot creation or development; including fluoride, barium, selenium, chloride, sodium, total dissolved solids, dissolved organic carbon, methane and colour. ACST water quantity maps were created for shallow overburden aquifers and the contact zone/shallow bedrock aquifer. Currently, the ACST is being used within the City of Clarence-Rockland to pre-screen development applications.