Time domain electromagnetic survey of the Mud Lake area in South Bay, Ontario / Prepared for: Boojum Research Ltd.

Abstract

The bedrock depth in area immediately North of Mud Lake may vary from as deep as 20 m to very shallow level. The soil in the area consists of wet, organic rich, fine grain organic material, with possible addition of clay which underlines Mud Lake. Various geophysical methods were reviewed as a possible techniques to investigate depth to bedrock in this area. Ground Penetrating Radar or Sledge-hammer Seismic investigations were initially proposed as tools to investigate depth of the bedrock in area located North of Mud Lake. The penetration depth of the Ground Penetrating Radar system is dependent upon the effective conductivity and dielectric constant of the earth material being probed. Previous electromagnetic EM34-3 surveys in the area indicated relatively high soil conductivity, possibility of the presence of clay material, and conductive surface water. Based on these information Ground Penetrating Radar would have relatively small depth of penetration in the northern portion of Mud Lake. However it may provide satisfactory results in area of gravel pit and in areas adjacent to bedrock outcrops. Seismic method appears to be the most suitable and accurate geophysical method in this type of investigations, however sledge hammer or other mechanical devices used as an energy source seem to be too weak in area of very soft, organic rich and wet soils. To investigate depth up to 20 m in above described conditions dynamite would have to be used as a sufficient source of energy. This would cause disturbance of sensitive soft soils leading to a possible cross contamination of the subsurface. Due to above concerns the time domain electromagnetic (TEM) soundings or resistivity method using direct current (DC soundings) remained available techniques to investigate depth to bedrock in area North of Mud Lake. Since DC soundings can not be conducted in frozen ground and in the presence of substantial snow cover the TEM soundings were chosen to be conducted during this project.