Investigation of the Potsdam Group sandstone aquifer vulnerability with the DFN-M approach

Abstract

As cities grow, surrounding rural communities often experience development stresses such as increased demand on local aquifers. Rural aquifers can have different threats than city centres, such as nitrates from agriculture or pathogens related to septic systems that may not have historically been a dominant concern, but become so under the increased water demands. Case in point is the growing community of Greely, near Ottawa, Ontario which is surrounded by agricultural lands, homes have individual septic systems, and a shallow bedrock aquifer provides the sole water supply from a communal well. The City of Ottawa has engaged the project team to examine the deeper Nepean sandstone as an alternative water supply. An initial borehole was continuously cored through the Paleozoic bedrock sequence into the Precambrian close to the existing pumping well. The detailed Discrete Fracture Network - Matrix (DFN-M) approach was applied including rock core logging, chemical analysis, geophysical logging, hydrogeologic and hydro-geophysical testing, with cross-hole testing pending. We present the study approach, preliminary results and future plans. In addition to dealing with Greely's challenges, the multiple high-resolution data sets provide insight into this complex geologic/hydrogeologic setting and an initial assessment of the sandstone's viability as a water supply elsewhere.