HR: 10:20h
AN: H42B-01    [Abstracts]
TI: Aquatic electrical resistivity imaging of rainfall-driven solute transport in contaminated wetlands
AU: * Slater, L
EM: lslater@andromeda.rutgers.edu
AF: Rutgers-Newark, 101 Warren St, Newark, NJ 07102, United States
AU: Mansoor, N
EM: nasser.mansoor@exxonmobil.com
AF: ExxonMobil Production, 396 West Greens Road, Houston, TX 77067, United States
AB: A continuous aquatic electrical resistivity imaging (ERI) technique, using floating electrodes and a shallow-draft paddleboat, was employed to predict spatial and temporal patterns of pore-fluid conductivity in wetland soils of a contaminated, shallow-water wetland. ERI measurements were obtained with marine-acquisition software and a multi-channel resistivity instrument at six times over a four month period, covering a 10 square kilometer grid. A set of 10 simultaneous reception channel measurements were continuously recorded every two seconds yielding an average of 13,000 measurements per survey. Three dimensional inversion was carried out to determine the conductivity distribution of the subsurface using the smoothness-constrained least-squares optimization method. The continuously recorded surface water depth and conductivity were entered as known information in the inversion and measurement error (further constraining the inversion) estimated using a tie point technique. Pore- fluid conductivity estimates were constrained using surface conduction measurements obtained from laboratory experiments on soils extracted from the wetland, as well as a correction for temporal and spatial temperature variations based on direct surface water temperature measurements and existing data on the thermal characteristics of peat soils. The study demonstrated that: (1) continuous aquatic ERI is an ideal method for resolving the resistivity structure of wetland sediments covered by a shallow (less than 1 m) surface water layer, (2) temperature variations must be considered in such shallow monitoring studies as they may otherwise have the most significant influence on the results, and (3) surface conduction is significant in marsh soils and must be accounted for if subsurface conductivity models are to be reliably interpreted in terms of pore-fluid chemistry. In the field example presented here, changes in pore-water conductivity estimated from inverted models suggest that migration of contaminants from marginal landfills into the wetland soils accompanies major rainfall events.
DE: 0694 Instruments and techniques
DE: 0925 Magnetic and electrical methods (5109)
DE: 1835 Hydrogeophysics
DE: 1890 Wetlands (0497)
DE: 5109 Magnetic and electrical properties (0925)
SC: Hydrology [H]
MN: 2007 Joint Assembly