PARTITIONING TRACERS FOR MEASURING RESIDUAL NAPL - FIELD-SCALE TEST-RESULTS

The difficult task of locating and quantifying nonaqueous phase liquid s (NAPLs) present in the vadose and saturated zones has prompted the d evelopment of innovative, nondestructive characterization techniques. The use of the interwell partitioning tracer's (IWPT) test, in which t racers that partition into the NAPL phase are displaced through the aq uifer, is an attractive alternative to traditional coring and analysis . The first field test of IWPT was conducted in a hydraulically isolat ed test cell (3.5 by 4.3 m) to quantify the total amount of a complex NAPL (a mixture of JP-4 jet fuel and chlorinated solvents) trapped wit hin a 1.5-m smear zone in a shallow, unconfined sand and gravel aquife r at Hill Air Force Base (AFB), Utah. Tracer breakthrough curves (BTCs ) were measured in three extraction wells (EWs) following a tracer pul se (0.1 pore volume) introduction through four injection wells (IWs). The measured retardation of the partitioning tracer (2,2-dimethyl-3-pe ntanol) relative to the nonreactive tracer (bromide) was used to quant ify the NAPL present. The EW data were used to estimate an average NAP L saturation of 4.6-5.4% within the test cell. NAPL saturations estima ted by using measured concentrations in soil cores of two significant compounds present in the NAPL were 3.0 and 4.6%.