A SIMPLIFIED, DIRECT-PUSH APPROACH FOR GEOCHEMICAL PROFILING OF CONTAMINATED GROUND-WATER SITES

Direct-push geochemical profiling has recently been established as a method of obtaining high- resolution inorganic data that is useful for evaluation of contaminant plumes and passive remedial systems. We have improved this approach by integrating a set of field analytical methods and a new mechanical bladder pump that are appropriate for use at contaminated sites and at locations where deep water tables occur. The improved method's ability to resolve chemical gradients was demonstrated in a comparison of direct-push profiling with conventional monitoring wells and multilevel samplers. Field measurement of specific conductance, dissolved oxygen, oxidation-reduction potential, total and ferrous iron, manganese, nitrate, and sulfate was demonstrated to accurately assess the presence of iron- and manganese-reducing conditions in alluvial and glacial aquifers. Comparison of measurements made with a field spectrophotometer, flow-through cell, and colorimetric analysis kits showed that the latter can provide a fast, reliable indication of varied redox conditions in situations where a high level of accuracy is not required. A coupling that connects the pump directly to the direct-push sampler further enhanced the efficiency of the method by minimizing purge volumes, eliminating potential iron contamination from the drive rods, and reducing the stabilization period of purge parameters to less than three minutes at the field sites studied. The mechanical pump may be hand actuated in these instances and where large sample volumes are not needed. At sites where higher precision is required, a field spectrophotometer, flow-through cell, and an electric pump actuator can be used to provide more accurate results. Demonstration of the new method at a natural attenuation site allowed for on-site determination of contaminant distribution and fate, and an enhanced understanding of the plume geochemistry.