ELECTROMAGNETIC MAPPING OF SALINE CONTAMINATION AT AN ACTIVE BRINE PIT

Frequency-domain and time-domain electromagnetic methods were used to investigate groundwater contamination at an active brine pit in southw estern Manitoba, Canada. The objectives of the survey were to delineat e contamination suspected to be occurring at the site and to compare f requency-domain electromagnetic (FDEM) and time-domain electromagnetic (TDEM) measurements in a survey area containing pipelines, fences, an d power lines. The survey successfully delineated a region of high con ductivity around the brine pit, confirming that leakage is occurring f rom the pit. Modelling of the FDEM results suggests the contamination is spreading within a series of shallow sand units. Comparison of FDEM and TDEM survey results indicate that small-separation FDEM systems a re much more useful for mapping in a developed area containing sources of cultural noise. The FDEM systems permit rapid mapping of spatial v ariations in conductivity, are affected to only a limited degree by cu ltural features, and provide some resolution of the depth variation of conductivity at shallow depth. It was not possible to obtain useful T DEM measurements anywhere near the active brine pit because of the sig nal distortion in the late-time response.