The potential impacts of future climate change on the evolution of groundwater recharge are examined at a local scale for a 546-km 2 watershed in eastern Canada. Recharge is estimated using the infiltration model Hydrologic Evaluation of Landfill Performance (HELP), with inputs derived from five climate runs generated by a regional climate model in combination with the A2 greenhouse gas emissions scenario. The model runs project an increase in annual recharge over the 2041-2070 period. On a seasonal basis, however, a marked decrease in recharge during the summer and a marked increase during the winter are observed. The results suggest that increased evapotranspiration resulting from higher temperatures does not offset the large increase in winter infiltration. In terms of individual water budget components, clear differences are obtained for the different climate change scenarios. Monthly recharge values are also found to be quite variable, even for a given climate scenario. These findings are compared with results from two regional-scale studies.

Abstract. Nitrate (N-NO3) concentration in groundwater, the sole source of potable water in Prince Edward Island (PEI, Canada), currently exceeds the 10 mg L−1 (N-NO3) health threshold for drinking water in 6 % of domestic wells. Increasing climatic and socio-economic pressures on PEI agriculture may further deteriorate groundwater quality. This study assesses how groundwater nitrate concentration could evolve due to the forecasted climate change and its related potential changes in agricultural practices. For this purpose, a tridimensional numerical groundwater flow and mass transport model was developed for the aquifer system of the entire Island (5660 km2). A number of different groundwater flow and mass transport simulations were made to evaluate the potential impact of the projected climate change and agricultural adaptation. According to the simulations for year 2050, N-NO3 concentration would increase due to two main causes: (1) the progressive attainment of steady-state conditions related to present-day nitrogen loadings, and (2) the increase in nitrogen loadings due to changes in agricultural practices provoked by future climatic conditions. The combined effects of equilibration with loadings, climate and agricultural adaptation would lead to a 25 to 32 % increase in N-NO3 concentration over the Island aquifer system. The change in groundwater recharge regime induced by climate change (with current agricultural practices) would only contribute 0 to 6 % of that increase for the various climate scenarios. Moreover, simulated trends in groundwater N-NO3 concentration suggest that an increased number of domestic wells (more than doubling) would exceed the nitrate drinking water criteria. This study underlines the need to develop and apply better agricultural management practices to ensure sustainability of long-term groundwater resources. The simulations also show that observable benefits from positive changes in agricultural practices would be delayed in time due to the slow dynamics of nitrate transport within the aquifer system.

Abstract:The objective of this paper is to verify the applicability of the trend-free pre-whitening (TFPW) approach, developed by Yue et al. (2002) for positively correlated series, to negatively correlated series using similar Monte Carlo simulations. This study was initiated when a project on trend detection for streamflow and baseflow series across Canada revealed that a significant number of series had negative correlation coefficients. The TFPW procedure confirmed to be also well suited for negatively correlated series. This study also showed that the estimated values for slopes (trends) and correlation coefficients of the prewhitened series are affected by the sample size, especially for negatively correlated series.

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.

The physical properties of waste (e.g., density, porosity, saturation, permeability) largely influence gas migration In North America, most domestic waste produced is disposed in rates. Several studies treat physical properties of waste landfills. These sites generate leachate and gas, mainly CH 4 and CO 2 , which are harmful for the environment if not properly controlled.under saturated flow conditions (Sowers, 1973; Findi-The design of active landfill gas recovery systems is based in large part kakis and Leckie, 1979; Schroeder et al., 1983 Schroeder et al., , 1994; Blais, on the radius of influence of vertical pumping wells. This parameter is 1996). There is a general agreement that these propercommonly estimated empirically. This study presents results of numerities are highly variable within each landfill site. Howcal simulations of the radius of influence of gas recovery wells for different ever, unsaturated hydraulic properties of waste are poorly site conditions. The simulations were performed with the TOUGH2known, mainly due to the difficulties related to theirLGM simulator. In the simulation scenarios, the radius of influence measurement under field or laboratory conditions. Bewas defined in relation to several factors: the waste thickness, the generacause of the absence of such data, it is necessary to relate tion rate of CH 4 gas in the waste, and CH 4 concentration in the recovered unsaturated waste properties to those of soils assumed landfill gas. The results are presented in the form of general graphs that are not site-specific. The adequacy of the results still needs to be to have similar properties. In his model, Nastev (1998) validated against field measurements. On the basis of simulation re-used the unsaturated properties of sandy-silt soil as analsults, a systematic approach is proposed for the design of landfill gas ogous to those of the waste and applied corresponding recovery systems, and this approach is illustrated with a hypothetic capillary parameters, an approach we adopt here. example. This approach should guide landfill managers and engineersLandfill characterization studies were followed by the in the design of landfill gas recovery systems. The simulations only development of suitable methods for controlling gas considered cases where landfills are open to the atmosphere, which migration and performing active gas recovery (EMCON are representative of most operating conditions. The results thus do