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TitleThe Lake St. Martin bolide has a big impact on groundwater fluoride concentrations
AuthorLeybourne, M I; Peter, J M; Johannesson, K H; Boyle, D R
SourceGeology vol. 36, no. 2, 2008 p. 115-118,
Alt SeriesGeological Survey of Canada, Contribution Series 20060582
PublisherGeological Society of America
Mediapaper; on-line; digital
File formathtml; pdf
NTS62O/09; 62O/10; 62O/15; 62O/16
AreaLake St. Martin; Gypsumville
Lat/Long WENS -98.8833 -98.3333 51.8167 51.5500
Subjectshydrogeology; geochemistry; groundwater resources; bedrock aquifers; bedrock geology; basement geology; lithology; metamorphic rocks; granitic rocks; greenstones; meteorite craters; breccias; fractures; flow structures; sedimentary rocks; carbonates; sandstones; sedimentary basins; red beds; evaporites; gypsum; groundwater regimes; groundwater geochemistry; water wells; water quality; salinity; sulphate; fluorides; ph patterns; sodium; chloride; boron; lithium; iron oxides; alumina; cation exchange capacity; permeability; health hazards; geochemical analyses; water geochemistry; whole rock geochemistry; Lake St. Martin bolide; Lake St. Martin impact structure; Winnipeg Sandstone; impact structures; melt rocks; drinking water; grain size; Phanerozoic; Cretaceous; Triassic; Paleozoic; Devonian; Silurian; Ordovician; Precambrian
Illustrationssketch maps; plots
ProgramGovernment of Manitoba, Funding Program
ProgramGroundwater Mapping Program
AbstractThe majority of residents of Manitoba (Canada) outside of the capital, Winnipeg, rely on groundwater for their drinking water. Between lakes Winnipeg and Winnipegosis, most aquifers occur in Paleozoic carbonate lithologies. Proximal to the town of Gypsumville, however, lithologies associated with the Lake St. Martin impact structure and younger basin-fi lling red bed and evaporite ( gypsum/anhydrite) sedimentary rocks complicate the hydrology and hydrochemistry.
Here, domestic wells have elevated salinities (up to 8000 mg/L total dissolved solids), elevated sulfate (up to 4000 mg/L), and elevated fl uoride concentrations that are in excess of health limits (F- up to 15.2 mg/L, with 20% over 1.5 mg/L). Groundwaters with elevated fl uoride occur exclusively within the impact structure. The impact melt rocks and younger red beds consistently have the highest fl uoride abundances, up to 2160 ppm. Groundwater pH values are alkaline, ranging up to 10.7, with highest groundwater pH from wells in the impact melt rocks. The spatial associations of impact melt rocks and red beds with elevated fl uoride, strong positive correlations between fl uoride and pH, sodium, chloride, sulfate, boron and lithium, greater Fe2O3 and Al2O3 concentrations of the host rocks, and cation exchange capacity (CEC) all indicate that fl uoride concentrations in groundwaters are enhanced as a result of anion exchange wherein OH- and CO3 2- displace F- adsorbed onto Fe- and Al-oxyhydroxide surfaces. Thus, the elevated fl uoride contents of groundwaters at Gypsumville are a consequence of the composition of the impact melt rocks and enhanced permeability and grain-size reduction produced by bolide impact.