The normative subsurface waste-disposal condition of no hazard to population, coupled with optimum allocation of drilling funds, can be achieved best through search for primary and alternative disposal formations by evaluation of hydrogeologic data on a basinwide scale. Any decision to drill a disposal well in Saskatchewan is made under considerable uncertainty, which is a reflection of the present reconnaissance level of subsurface information.

Subsurface disposal of fluid wastes in the Williston basin region is largely restricted to sandstone and carbonate aquifers (Cambrian through Lower Cretaceous) of the Saskatchewan-Manitoba tectonic shelf: (1) oil-field brines (at rates of the order of 15 gpm); (2) waste brines from exploitation of Devonian potash deposits (up to 750 gpm); (3) waste brines from solution mining of LPG-storage caverns in Devonian halite (up to 300 gpm); (4) refinery sour water and spent caustic (up to 20 gpm); and (5) chlor-alkali-plant wastes (up to 15 gpm), partly associated with previously injected herbicide wastes.

Hydrogeologic constraints on development of subsurface waste-disposal systems, not related to reservoir quality of disposal formations but likely to influence waste migration, are (1) proximity of the outcrop belt on the north and east, (2) pre-Cretaceous valley systems controlling development of fluvial channels up to the present, (3) sinks formed through localized solution of Paleozoic halite, and (4) positive basement features and related overlying structures.

Estimated ultimate capital investments for existing Saskatchewan injection systems range from $20,000 to $100,000 in the oil fields, to more than $300,000 for some potash-brine disposal wells, and are determined largely by depth of disposal formation, drilling technique, and well design. Potash-brine disposal wells in the vicinity of shaft mines include the most costly and refined systems, and involve directional drilling to formations below the potash unit and mud programs employing fluids compatible with evaporite minerals.

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