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In 2008, the Ontario Geological Survey (OGS) released a map of known and potential karst in southern Ontario. Known karst occurs mostly in areas where glacial overburden is thin (<1m) or absent and in many places the top of bedrock shows evidence of active, ongoing solution-enhancement. Data from deep bedrock boreholes indicate that karst in Ontario's carbonate terrains is much more widespread than can be observed on surface and that it extends into areas covered by thick glacial sediments. Direct evidence for this pre-glacial karst includes: (1) televiewer logs and drill-core showing solution-enhanced bedding planes and sequence boundaries; (2) drill records reporting large cavities in bedrock that are open or filled with glacio-fluvial sediments; (3) epikarst and bedrock conduits in quarries; (4) drift thickness mapping with extensive buried valleys and canyons, some that appear to form natural bridges; and (5) thick glacial sediment-covered areas with extensive interpreted karst rubble at the bedrock surface. Traditional methods for local mapping of subsurface karst and its effects on groundwater cannot be easily adapted for regional-scale studies. Physical techniques include tracer tests and piezometric logging of monitoring wells to detect conduits (by the rapid rise and fall of water levels); chemical techniques include monitoring, at spring vents, of pH, Ca2+, HCO3 - and saturation indices of carbonate minerals to determine the degree of corrosiveness of groundwater. However, these are all proximal techniques that characterize individual, known systems. To date, there are no well-developed regional techniques that can map areas where groundwater is influenced by buried karst over a wide area. Here we describe a methodology that uses dissolved CO2 and O2 in groundwater to map areas in buried karstic carbonates that have a rapid hydraulic connection to surface. O2 originates in the atmosphere and has no geological sources. CO2 in groundwater originates largely in the soil zone and has few other geogenic sources in non-tectonic settings. Because both parameters are attenuated with increasing distance from their sources, a CO2/O2 factor allows for an objective description of how well connected these buried karstic groundwater systems are to meteoric and soil zone recharge sources. An empirically derived lower threshold for the CO2/O2 factor delineates a number of large regions in southern Ontario where groundwater is elevated in either or both gases; all of these are centred on areas of known karst. Groundwater analysis using tritium, nitrate and bacteria (for samples collected from secure-cap water supply wells) show that these areas have younger, more recently recharged groundwater with a relatively rapid connection to the surface environment. Regional CO2/O2 and other chemical, isotopic and bacteriological data were purpose-filtered from the large, publically accessible OGS Ambient Groundwater Geochemistry database. This is an exceptionally well characterized groundwater geochemical dataset for samples collected on a uniform grid from domestic, farm and monitoring wells across southern Ontario. Mapping areas of groundwater vulnerability to surface contamination due to karstic flow systems is another of the many possible uses for this database.

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In March 2015, the Ontario Geological Survey (OGS) and Geological Survey of Canada (GSC) hosted a Groundwater Geoscience Knowledge GAP Analysis session for southern Ontario clients. The session objectives were to solicit input at the planning phase of several large OGS/GSC collaborative mapping initiatives, and to discuss the future of provincial government data management and the potential for accessing data via an "open data" initiative. Session participants identified 30 individual groundwater geoscience knowledge gaps, which fall into 7 categories comprising: i) communications, ii) standards and protocols, iii) hydro and geochemistry, iv) surface and groundwater interaction, v) geology and hydrogeology, vi) climate change and vii) data management and dissemination. In the past year, the OGS has taken significant steps to address many of the knowledge gaps that were brought forward at the March 2015 session. Communication issues represented the first, and most prominent, category of identified gaps. Session participants agreed that better communication between government ministries and agencies, that hold various land resource and science based mandates, would break down barriers between disciplines and create opportunities for multi-disciplinary collaboration. To address communication issues, the OGS has taken several positive steps to engage with partner land-based ministries. Some highlights of the activities emerging from these new connections include; the OGS providing geoscience mapping products and offering expertise to MOECC Land and Water Policy Branch as they evaluate land-use planning in the Greater Golden Horseshoe region; the development of a new OGS project, in collaboration with MOECC, to map shallow karst using geochemical indicators of rapid recharge; opening communication and information sharing to discuss the inclusion of OGS continuously cored boreholes with monitors into the MOECC Provincial Groundwater Monitoring Network; the creation of a working group to write a White Paper supporting a modern provincial government data strategy; and providing groundwater hydrochemistry mapping and expertise to support policy development for homeowner and public health unit notification when domestic well sampling results exceed drinking water guidelines from natural/geological sources. Each of the new projects and collaborations represents an improvement to inter-government communication. This list also demonstrates the OGS's commitment to create geoscience mapping products that meet the needs of clients, including those making science based policy decisions regarding groundwater. The OGS will continue to engage with clients and stakeholders as we continue our groundwater mapping initiative in southern Ontario in collaboration with the Geological Survey of Canada.

Since the commencement of the Ontario Geological Survey's groundwater initiative in 2001, a wealth of geoscience information that can assist in an improved understanding of the provincial groundwater resources has been collected, analyzed and reported on. The initiative consists of 5 main activities, which produce intimately related data sets, including. 1) A series of digital, fully-attributed, seamless maps including bedrock geology, karst, physiography, surficial geology, surficial sediment thickness and bedrock topography that serve as a foundation for most hydrogeological investigations. 2) 3-D maps of key Paleozoic bedrock units that host important groundwater resources in southern Ontario paying particular attention to identifying the main geologic controls on groundwater flow and mapping and delineating regional scale groundwater flow systems within the context of a sequence stratigraphic framework. Detailed hydrogeological studies were undertaken in the City of Guelph to better understand the lateral continuity of flow zones by integrating the geological dataset with discrete hydraulic tests over short vertical intervals believed to represent flow zones. Reporting on the Niagara Escarpment Silurian projects is nearing completion and a project focussing on Devonian units to the southwest is currently underway. 3) 3-D models of Quaternary sediment in southern Ontario focussing initially on areas either within or adjacent to the Greater Golden Horseshoe. To date, projects have been completed in the Waterloo (GRS03), Barrie-Oro (GRS11), Brantford-Woodstock (GRS10) and Orangeville-Fergus (GRS15) areas. Work in Southern Simcoe County is nearing completion and projects in the Niagara and Central Simcoe County areas are well underway. The 3-D sediment mapping program uses a basin analysis approach similar to that used by the GSC in the Oak Ridges Moraine. Ground and airborne geophysical surveys coupled with surficial sediment mapping and continuous-coring have enabled the development and refinement of conceptual geologic models, critical for the successful construction of 3-D geologic models. Projects in the Ottawa-St. Lawrence and Norfolk areas are scheduled to begin following completion of ongoing projects. 4) The ambient groundwater geochemistry project, which was initiated in 2007, has collected untreated bedrock- and surficial sediment-derived groundwaters at more than 2100 stations across all of southern Ontario, with the aim of understanding relationships between aquifer composition and groundwater quality, as well as understanding the flow history, residence time and vulnerability of individual and regional groundwater sources. The sampling density is approximately 2 stations per 10X10 km block (100 square kilometers). Each record contains 134 fields, 27 of which describe the station and 107 that describe the water and its chemical constituents. Digital datasets and maps were released for all of southern Ontario in 2015 (MRD283-REV) and an accompanying Groundwater Resource Study is currently in preparation. Meanwhile, a similar study is about to begin in the Sudbury region in 2016. 5) Parallel thematic projects including a study of the geology and hydrogeology of the Dundas buried bedrock valley (GRS12) and an assessment of the subsurface sediments in the central Norfolk sand plain (GRS14) were conducted in partnership with the Grand River Conservation Authority.