USING PRELIMINARY SURFACE GEOPHYSICS TO GUIDE A HYDROGEOLOGIC INVESTIGATION PROGRAM IN A NORTHWESTERN COLORADO MUNICIPALITY

AMEC-Zonge performed both seismic refraction tomography and electrical resistivity tomography to assist in determining the optimal location, orientation, and depth for the placement of a new infiltration gallery system within the Northwest Colorado Municipality. Eleven seismic lines were placed through a desktop review of drilling and excavation data near the investigation site. Both seismic refraction and electrical resistivity surveys were setup and shot in sequence along each of the eleven lines allowing for joint interpretation of the two datasets. Geophysical data was compiled, processed, and used to target potentially favorable hydraulic conditions and the platform AMEC used to design a hydrogeologic investigation program. Use of this methodology effectively reduced the municipalities drilling costs by allowing the AMEC-Zonge team to indentify the most effective areas to evaluate; as well as streamlining the hydrogeologic investigation by targeting key formations and reducing the overall number of boreholes needed to adequately characterize the target gallery location. Drilling and pump test data from the hydrogeologic investigation was used to calibrate the geophysical cross sections and develop a comprehensive view of the investigation site and its future potential as a groundwater resource.