The cost of dewatering the southern portion of the lease using a sump was estimated to be $337,200. The cost of dewatering the same area using wells was estimated to be $163,267. Evidently it is more economical to use wells. It is expected that a refinement of these figures will not significantly change the above conclusion.
On the basis of an electrical model of groundwater flow in the area between the Thickwood Hills and the GCOS Lease it was found that the whole lease above the Athabasca River escarpment is in a natural recharge area. Therefore, theoretically no water enters the lease form Thickwood Hills or Ruth Lake under natural conditions. A tentative groundwater flow map was constructed delineating the local flow systems. These will have to be considered when planning a dewatering program.
From a fence diagram of the lithologic variations in the overburden it is apparent that there are two main aquifers in the lease, separated by a less permeable boulder clay unit. Isopach maps of each aquifer were used to plan an aquifer-testing program. The isopach maps indicate that although the aquifers are present over most of the lease area, the areas where a significant thickness of either aquifer is present is patchy. Consequently each of these areas will have to be tested and dewatered separately. The calculation of the permeability of aquifers is restricted to the results of one pump test and four bail tests. None of these were conducted in the upper aquifer. Thus permeability values are available for two areas in the lower aquifer, two areas in the boulder clay unit and the combined permeability of the upper and lower aquifers is available for on area. The permeability of the lower aquifer was found to vary from 208 to 805-igpm/sq ft. The permeability of the boulder clay was found to vary from 0.66 to 2.38-igpm/sq ft. The combined permeability of the lower and upper aquifers in the vicinity of CH 117 is approximately 200-igpm/sq ft. The specific yield of the lower and upper aquifers in the southern part of the lease combined with the recharge during an eight-month period was found to be 47 per cent. This means that out of a unit volume of sediment a volume of water equal to 47 per cent of the bulk volume has to be removed to dewater the sediment and keep it dewatered over a period of eight months.
Proposed testing program to be undertaken this winter involves a minimum number of 23 wells required at the present. However, some changes may be required during the program. An attempt has been made to anticipate some of these changes in the planning of the program, but it is obvious that all possible conditions cannot be foreseen.
Kahil, A. (1969): Second interim report on the feasibility study for dewatering the overburden in GCOS lease 86; Research Council of Alberta, RCA/AGS Open File Report 1966-07, 21 p.