HR: 15:25h
AN: U23C-08    [Abstracts]
TI: Surface to Borehole EM for Shallow site Investigations
AU: * Wilt, M
EM: mwilt@slb.com
AF: Schlumberger, 1301 s 46th st, Richmond, Ca 94805 United States
AU: Alumbaugh, D
EM: dalumbaugh@slb.com
AF: Schlumberger, 1301 s 46th st, Richmond, Ca 94805 United States
AU: Tseng, H
EM: hwtseng@lbl.gov
AF: Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, Berkeley, Ca 94720 United States
AB: Surface to borehole EM is a promising but seldom used tool for shallow site investigations and clean-up monitoring. Boreholes offer improved site access and field systems, adapted from geophysical mineral exploration instruments, offer effective range and sensitivity for near surface applications. With the abundance of plastic cased wells at many sites high frequency field data collection is possible and this can provide good sensitivity to subsurface geology and the potential capability of imaging 3D structures. In addition the 3D numerical tools necessary for this type of imaging are now becoming available. Unfortunately shallow sites are often situated in geologically complex vadose zone environments. In addition, interesting sites are often located in urban environments, with a lot of surface clutter and high levels of external electrical noise. These attributes makes collection of high quality data problematic and interpreting these data challenging. In this talk we will examine the state of the art in near surface to well EM focusing our attention on a recently collected data set in an urban environment in northern California. In particular we will discuss a field survey in the San Francisco Bay area where repeated surface to borehole measurements made over a 6-month period were used to track salt-water injection. The surveys overcame noise problems due to grounded fences, and resistivity changes due to an unexpected rainfall, to provide a 3D image of the injected salt-water plume consistent with hydrologic model and a second crosswell EM survey.
DE: 0925 Magnetic and electrical methods (5109)
SC: Union [U]
MN: Fall Meeting 2005