Application Of Borehole Geophysics To Delineate Preferential Contaminant Migration Pathways In A Complex Fractured Clay/Shale Aquifer

During development of a Hydrogeologic Conceptual Site Model (HCSM) for a large chlorinated solvent plume, Earth Tech determined that significant groundwater movement was occurring below auger refusal depths within a shallow fractured rock aquifer. Data was available for deeper zones, but not for the zone of interest. Earth Tech developed an approach that utilized various borehole geophysical tools to investigate this possible preferential migration pathway. A multi-phased investigation program was developed in which multiple borehole logging tools were tested to determine the suitability and the applicability of the geophysical methods to investigate the zone of interest. Once the geophysical method suite was optimized, the investigation program was streamlined. Although this investigation program developed over time, the multiple objectives of investigation remained focused on:<br>1. Determining the presence or absence of a significant groundwater flow horizon just below<br> auger refusal depths;<br>2. Determining the hydraulic characteristics of the system;<br>3. Refining the HCSM for the shallow aquifer system; and<br>4. Determining the extent of contamination and the effectiveness of the remedial measures that<br> were applied at or above the auger refusal depths at the site.