GEOCHEMISTRY OF ENHANCED BARIUM SOLUBILITY IN GROUNDWATERS: REGIONAL AQUIFER STUDY IN SOUTHEASTERN MANITOBA, CANADA

Groundwaters were sampled in southern Manitoba, Canada, from ~450 domestic water wells as part of a large-scale regional comparison between the major aquifers of the area. There are three main aquifers present: (1) surficial sand and till, (2) deeper Ordovician to Silurian carbonates, and (3) basal Ordovician sandstone; each aquifer was targeted for groundwater sampling. Field measurements included pH, Eh, dissolved oxygen (DO), temperature, and conductivity. Groundwaters were analyzed for a full suite of major and trace elements by Inductively Coupled Plasma (ICP) and for light stable isotopes (C, O, H, S) by mass spectrometry. Stable isotopes are being used to constrain groundwater flow, recharge and mixing between the aquifers. Oxygen and hydrogen isotope data indicate that most waters represent modern recharge, although shallow wells (<10 m) are isotopically heavy, suggesting influence of summer precipitation. Groundwaters collected range in salinity from 20 to 5700 mg/L with generally increasing salinity towards the west. Waters are dominantly Ca-Na-SO4-HCO3-type. Alkalinity ranges from <100 to >1000 mg/L. Wells with alkalinities >350 mg/L are uniformly shallow, deeper (40-140 m) wells have <250 mg/L alkalinity. In the study area, 14 wells in an isolated area are over the Health Canada limit for safe drinking water of 1000 µg/L Barium. Wells with elevated Ba were recovered primarily from the basal sandstone aquifer. Ba values range from 0.37 µg/L to 11,000 µg/L. Sulfate ranges from below detection limits to >2100 mg/L. Groundwaters with high Ba values have SO4 values typically below detection limits (50 µg/L). Control on barium over saturation could be due to SO4 depletion from the formation of barite.