The Hatfield Buried Valley: A review of the aquifer characteristics

H.A.J. Russell, D.I. Cummings, H. Mathius, G. Oldenborger, A.J. Pugin, D.R. Sharpe

Dans les comptes rendus d’articles de la conférence: GeoMontréal 2013: 66th Canadian Geotechnical Conference; 11th joint with IAH-CNC

Session: Regional Aquifer Characterization I

ABSTRACT: There is no synthesis of the Hatfield buried valley (HBV), despite its potential significance to water resource management in the prairies. Information on orientation, geometry and fill characteristics, documented in numerous government and industry reports, needs to be summarized to support improved aquifer assessment. This paper sets out the existing knowledge of the HBV and highlights the case for new framework data to address societal water issues in a rapidly developing provincial economy dominated by resource extraction. The HBV in Saskatchewan is an ~800 km long valley that traverses the province obliquely from the northwest to the southeast. Plan geometry shows a main trunk valley that bifurcates in places. There is limited detail on lateral valleys; however, a number of regional northeast-trending valleys appear to terminate at the HBV (Swift Current, Tyner, Battleford). The valley is predominantly cut in Cretaceous shale, and locally Judith River Formation sandstone. Valley depth is variable with depths of >100m and widths up to ~5km. It is buried by >200 m of sediment and can be partially exhumed where intersected by modern valleys (e.g. Qu™Appelle River). Sediment fill is poorly documented regionally with only a few high quality site specific datasets. Basal HBV fill is Empress Group sand and gravel that is < 100 m thick. It consists of a lower pre-glacial unit that is commonly non-calcareous and includes mountain-derived quartzite and chert gravel. An upper pro-glacial sand and gravel unit is characterized by Shield-derived igneous, metamorphic, and carbonate clasts. This unit is overlain by multiple inter-bedded diamicton and sand and gravel fill-units assigned to the Sutherland and Saskatoon groups. Sutherland and Saskatoon till units are differentiated by Christiansen in the Saskatchewan area on the basis of carbonate content, texture, Atterberg limits, and electrical resistance. The Sutherland Group tills have lower carbonate content, higher clay and lower sand contents, higher liquid limit and lower electrical resistance than do tills of the Saskatoon Group. Much of the valley-fill stratigraphy has been mapped from water wells records, which does not permit differentiation of this formal stratigraphy; nevertheless, their main hydrogeological properties are similar and controlled by inter-till sand units. These documented characteristics of the HBV are supplemented by new high-quality 3D from airborne electromagnetic (EM) and seismic reflection data in southeast. These data reveal a more complicated network of main valley architecture, smaller buried valleys, erosional features, and sedimentary deposits than have been previously recorded. Water chemistry data for the Hatfield valley is sparse. In the Esterhazy area, Pierre Shale waters could be expected to be in excess of 10000 mg/L (MDH 2009). Within the Empress Group in the Lanigan and Fort Qu™Appelle area, groundwater chemistry is commonly of the sodium-sulphate type with concentrations ranging from approximately 1950-3000 mg/L (Maathuis 1980). Within the glacial stratigraphy, potash mine site studies yield TDS values within inter-till aquifers of 681-2260 mg/L near Jansen (Rescan 2008) indicating relatively strong recharge with fresh surface waters. Within the upper Saskatoon Group tills, sulphate concentrations can be as high as 24700 mg/L due to oxidation of pyrite and within the Sutherland Group sands and gravels, chloride concentrations can range from 12 mg/L to over 30000 mg/L indicating impact from mine activity (MDH 2009). REFERENCES Maathius H. 1980. Hatfield valley project - Phase 1. Preliminary study of the Hatfield valley aquifer system in the Lanigan-FortQu' Appelle area. Saskatchewan Research Council, Publication No.G-1 047-1-E- 80. MDH Engineered Solutions Corp. 2008. PotashCorp Rocanville Rocanville West Expansion, Environmental Impact Statement, PotashCorp Rocanville. MDH Engineered Solutions Corp. 2009. Mosaic Potash Esterhazy K2 Phase V TMA and Mill Expansion, Environmental Impact Statement, Mosaic Potash Esterhazy. Rescan Environmental Services Ltd. 2008. Jansen Project, Environmental Impact Statement, BHP Billiton Canada Inc.

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