HYDROGEOLOGIC AND HYDROLOGIC CHARACTERISATION OF A REPRESENTATIVE AREA OF THE MARITIMES CARBONIFEROUS BASIN

The Maritimes Groundwater Initiative is a large integrated hydrogeological study focusing on the Maritimes Carboniferous Basin. This basin is composed of a cyclic sequence of discontinuous strata of highly variable hydraulic properties (mostly sandstone, siltstone, shale and conglomerate), overlain by a thin layer of glacial till. Groundwater is usually of very good quality in this aquifer system and, consequently, is a very important source of water supply in the Maritimes. This paper focuses on the work undertaken to characterise the hydraulic and hydrologic conditions prevailing in this aquifer system. This work comprised data compilation, field work, and computer analysis to estimate aquifer transmissivities, anisotropy, and recharge rates over the region of interest. The study area encompasses parts of New Brunswick, Nova Scotia and Prince Edward Island, and covers approximately 20,000 km2.

Values of transmissivities and storage coefficients for fractured aquifers were gleaned from various reports and measured based on short and long-term pumping tests. These tests, combined with borehole geophysics information, revealed a strong anisotropy and the discontinuous nature of permeable strata. Hydraulic conductivities for the till layer were estimated using infiltrometers and slug tests. Recharge rates were calculated according to three approaches: hydrograph separations, an analytical method and a Darcian method providing a range of possible values across the study area. These hydrogeologic and hydrologic properties will be incorporated into a numerical model of groundwater flow.

This work confirms that fractured aquifers of the Maritimes Carboniferous Basin are generally semi-confined and discontinuous, with lenticular permeable strata extending only a few kilometres. These aquifers can locally be very heterogeneous and anisotropic, with the main fractures being oriented in a north-eastern direction, in agreement with regional structures. Recharge rates can greatly vary spatially (from a few millimetres to 300 mm/year), mainly depending upon the nature of the till cover.