Canadian Groundwater Inventory: regional hydrogeological characterization of the south-central part of the Maritimes Basin

Abstract

The Maritimes Groundwater Initiative (MGWI) is a large, integrated, regional hydrogeological study focusing on a representative area of the Maritimes Basin in eastern Canada. The study area covers a land surface of 10 500 km2, of which 9 400 km2 are underlain by sedimentary rocks. This sedimentary bedrock is composed of a sequence of discontinuous strata of highly variable hydraulic properties, and is generally overlain by a thin layer of glacial till (mostly 4-8 m, but can reach 20mthick). Depending on the area, 46 to 100% of the population relies on groundwater for water supply, either from municipal wells or from private residential wells. The main objectives of this project were to improve the general understanding of groundwater-flow dynamics and to provide baseline information and tools for a regional groundwater-resource assessment. This bulletin presents the current state of understanding of this hydrogeological system, along with the methodology used to characterize and analyze its distinct behaviour at three different scales. This regional bedrock aquifer system contains confined and unconfined zones, and each of its lenticular permeable strata extends only a few kilometres. Preferential groundwater recharge occurs where sandy till is present. The mean annual recharge rate to the bedrock is estimated to range between 130 and 165 mm/a. Several geological formations of this basin provide good aquifers, with hydraulic conductivity in the range 5 x 10-6 to 10-4 m/s. Based on results of numerical flow modelling, faults were interpreted to have a key role in the regional flow. Pumping-test results revealed that the fractured aquifers can locally be very heterogeneous and anisotropic, but behave similarly to porous media. Work performed at the local scale indicated that most water-producing fractures seem to be subhorizontal and generally oriented in a northeasterly direction, in agreement with regional structures and pumping-test results. Almost all residential wells are shallow (about 20 m) open holes that are cased only through the surficial sediments.

Characterization of a Regional Aquifer System in the Maritimes Basin, Eastern Canada

“…Geophysical logs were obtained in 10 wells scattered throughout the region to obtain information on stratigraphy, water bearing fracture features, along with their individual flow rate. Geophysical logging operations included the use of caliper, natural gamma, electrical resistivity, acoustic televiewer and flowmeter under ambient as well as pumping conditions (Morin et al 2002;Rivard et al 2005bRivard et al , 2008. For the characterization of surficial deposits, slug and pumping tests were performed in sand units, and several permeameter and infiltrometer tests were conducted in various till units (Boisvert 2004).…”

“…Figure 2 presents a simplified version showing formations of most interest for hydrogeology, mainly because of their aquifer potential or significant extent in the area. Complete versions of the geological map and Table 3 are presented in Rivard et al (2005aRivard et al ( , 2008.…”

“…Indeed, increasing demands and costs to secure clean water and its decreasing availability in some areas have important social and economic consequences (Rivera et al 2003). This work is part of several studies carried out to characterize main aquifer systems and to address regional groundwater issues in Canada (Rivard et al 2007(Rivard et al , 2008Grasby et al 2005;Côté et al 2006;Sharpe et al 2002;Kennedy and Woodbury 2003;Nastev et al 2006;Fagnan et al 1999). Although these regions are not highly exploited (as other aquifer systems in the world such as those presented in El Rahman 2001 and Robins et al 1999), their study represents nonetheless a first step in the process of protection and management of their groundwater resources.…”

“…Therefore, our study mainly focussed on the hydraulics of the aquifer system. Geochemistry, only representing a small part of this project, is not presented in this paper (for details, see Rivard et al 2005aRivard et al , 2008 and for a specific project on the nitrogen cycle in PEI, see Paradis et al 2006;Savard et al 2007). …”

“…Only one regional hydrogeological study had been previously done within this study area to delineate and characterize the aquifers on a regional scale (Carr 1964, for the Moncton sub-basin only, i.e. 1100 km 2 ), but many local investigations were conducted (for the list of previous studies see Rivard et al 2008).…”