1AAFRD, Red Deer, Alberta, 2PFRA, Edmonton, Alberta, 3Komex International Ltd. Calgary, Alberta, 4Dept. of Civil Engineering, University of Calgary, Calgary, Alberta
An earthen manure seepage study was undertaken with the sponsorship of the Hog Industry Development Fund to investigate different methods of plume detection in order to find more accurate and cost effective techniques to identify groundwater contamination from hog lagoons. Ten hog lagoons were selected in Alberta that were constructed in a variety of geophysical conditions and using different construction methods. Traditional drilling to extract core and water samples was done initially at each site. Samples were analyzed for geophysical properties, chemical parameters, and biological presence. The presence of relatively high nitrates, ammonia, chlorides, potassium and fecal coliforms indicated groundwater contamination from three sites. These were selected for further evaluation using electromagnetic (EM) conductance and electrical resistivity tomography (ERT) methods. Both methods base plume detection on the relative subsurface conductivity to predict the presence and location of the plume. Groundwater samples showed higher chlorides and other dissolved ions which increased the subsurface electroconductivity allowing detection by both the EM and ERT methods. The EM method proved to be economical and reasonably accurate in delineating plume plan-profiles downstream of the lagoon. EM waves are passed into the ground which induce a detectable response by the EM method. The transmitter and detector are carried above ground and moved at a rate of 1 m/s enabling a large surface area coverage in a short time. The EM method is limited to approximately 5 m soil depths. Past this point the EM can no longer detect any difference between the background conductance and a potential plume. The ERT method is a more sophisticated technology for plume detection. Probes are inserted into the ground surface and electrical impulses are passed through. The electrical conductivity is measured directly providing a more accurate representation of the groundwater plume location, depth, and size. The EM and ERT methods provided concurring results. Both methods indicated groundwater contamination from leaky lagoons. These results were corroborated by the contaminants observed in the soil and groundwater samples extracted.
Implication: The EM and ERT methods are capable of finding and mapping potential groundwater contamination which can be subsequently verified using the traditional method of drilling and sample analysis. The EM and ERT methods should be considered for initial exploration to guide investigators to optimum locations for confirmation drilling.