Direct-push delivery of dye tracers for direct documentation of solute distribution in clay till

Methods for effective delivery of remediation amendments for in situ remediation of contaminated clay till sites are sought. The capabilities of direct-push delivery are promising but not yet scientifically documented. Therefore, a field study of direct-push delivery was carried out at an uncontaminated, naturally fractured, basal clay till site (K∼10-7-10-10-m/s) in 2008-2009. A mixture of tracers (brilliant blue, fluorescein, and Rhodamine WT), the characteristics of which are comparable to several current remediation amendments, was delivered in aqueous solution at pressures of ∼5-10 bar at several locations and depth intervals [2.5-9.5 m below surface (b.s.)], representing both the vadose and saturated zones. Extensive coring to 12 m b.s. and excavation to 5 m b.s. were carried out to identify the lateral and vertical extent of tracer distribution. A tracer distribution radius of minimum 1 m was achieved at all depths. Close vertical spacing of delivery points (10-25 cm) provided good vertical distribution without significant merging of individual delivery propagation paths. The results are promising with regard to achieving adequate distribution of remediation amendments in clay till. © 2012 American Society of Civil Engineers.