Open File Report 1968-07

Open File Report 1968-07

OFR 1968-07

Interim Report on the Feasibility Study for Dewatering the Overburden in G.C.O.S. Lease 86

Author(s) Research Council of AlbertaKahil, A. Date 1968-11-01

The study, undertaken by the author to determine the feasibility of dewatering the GCOS overburden, included the mapping of groundwater features in the lease and its vicinity, the collection of groundwater sample throughout the study area, the recording of water levels in a number of wells and the construction of an electric model. As a result of this work the author has come to the conclusion that the water entering the GCOS lease, at the present, is mostly from precipitation and it is removed from the lease mainly by evapotranspiration. Some water is believed to enter the lease through the tar sand but the total volume is small. However this water may be entering the lease through localized areas, which where encountered by equipment removing overburden, may present some traction problems. Relatively small volumes of water are entering or leaving the lease through the overburden. The net result of water movement in the overburden is believed to be a small loss in water by the lease. The major portion of water that has to be removed for dewatering the overburden is groundwater in storage and induced groundwater flow to the area caused by the dewatering operations. The latter cannot be estimated until the completion of the proposed testing program. The former was estimated to be less than 605 billion imperial gallons.

In the southern part of the lease the A(I) and B(I) units form the main aquifers. As these are the lowest Cenozoic units they constitute a good method of dewatering the overburden in the southern part of the lease. The thin E unit and uneconomical tar sand may have to be dewatered separately in that area. In the northern part of the lease the BII unit is the unit best suited for pumping water out of the overburden because of its permeability and location in the topographic depressions. However, its limited thickness and its position above C, E and uneconomical tar sand units makes it less than ideal. It would be advantageous to determine if the C or E units have permeable zones of sufficiently large lateral extent for one to use them for dewatering the overburden. If these are present and are hydraulically connected to the overburden units above them then they would be more desirable than the B(II) unit because of their lower depth. Between the southern extent of the BII unit and the northern extent of the B(I) and A(I) units, is an area where only the A(II), C, E, and uneconomical tar sand units are present. In this area it is necessary to find if there are permeable zones within these units and whether these zones are hydraulically connected. If these zones are not present this area may not have to be dewatered. While if they are present but not continuous they may have to be dewatered individually.

The location of the most permeable zones, as well as a detailed knowledge of their permeability is necessary for the planning of an efficient dewatering scheme and for predicting the volume of induced groundwater flow. To determine the latter, the present direction of groundwater movement will have to be known. The proposed testing program is designed to determine these factors. Approximately 32 test holes are believed to be necessary for the testing program, of which 16 will be bail tested. All the holes will be cased and used to monitor dewatering operations. The proposed study also includes two week long pump tests to determine the transmissivity of the overburden and its specific yield. The testing program was estimated to cost approximately $41,000.

This report is a summary of the knowledge acquired during the 1968 summer field season, relative to the feasibility of dewatering the overburden in the GCOS Lease 86, as well as a proposal for a testing program to determine and clarify certain important aspects relating to the hydraulic properties and geology of the overburden. The report has therefore been divided into two parts. The first part, labeled A, summarizes the work that was done during the 1968 field season and in the laboratory and the information obtained from already published material. Most of the conclusions present in this section pertain to groundwater under natural condition. They are not to be considered final for they are based on information that will be upgraded as the study continues. In the second portion of the report, labeled B, the proposed drilling and aquifer testing is described in detail, giving reasons for its necessity.