Completing the ground-water model: ''We need more data''

Computer modeling of geologic structures and groundwater flow has progressed from simple number crunching in the sixties to sophisticated and complex structure and flow models in the nineties (Hatheway, 1994). In the environmental field, a detailed knowledge of the subsurface geology is required and essential for successful ground-water remediation, planning, and investigations. Current options for determining shallow (0--400 ft) subsurface geology includes standard borings, cone penetrometer, ground penetrating radar (GPR), or resistivity surveys (RS). Standards borings are expensive coverage and the close spacing required for generating accurate model data. The cone penetrometer is less expensive and faster than conventional borings. However, both the cone penetrometer and borings are limited by access and are intrusive, providing additional paths for contaminant migration. While both standard GPR and RS are non-intrusive, they suffer from other limitations. A high conductivity soil (clay) will diminish the effectiveness of GPR. The signal is absorbed and dissipated in the first few inches of high conductivity soil. The depth of penetration of RS is better, but the vertical resolution for distinguishing between finely interbedded layers is much lower. An ideal system for subsurface geologic analysis would be non-intrusive, have the depth of penetration of RS, while offering the vertical resolution of GPR> Electromagnetic methods (EM) offer distinct advantages in helping to solve these problems: (a) they are non-intrusive, and (b) the technology to support EM probing-pulse generation, data collection--is well established. Quaternary Resource Investigations, Inc., (QRI) has developed such a system