Pilot Test Operation and Contaminant Sampling

A steady flux rate of 0.17 m day-1, resulting in an average linear groundwater velocity of approximately 0.5 m day-1, was established in the tank. Beginning on 27 December 1997, 10 mg L-1 (0.19 mmol L-1) Cr (in the form of chromate) and 1.8 mg L-1 (0.011 mmol L-1) of PCE were injected through all five upper injection wells. The same flux of contaminant-free water was provided to the bottom half of the aquifer. Contaminant injection continued through 12 February 1998. The cumulative volume of contaminant solution injected was about 5*104 L. At approximately weekly intervals, samples were collected from transects (rows) parallel to the water flow direction to monitor the performance of the SMZ barrier. As standard practice Transects 2, 5, 7, and 9 were sampled. This scheme provided one transect within the barrier-free portion of the tank and one transect through each of the three barrier cells. Depending upon the previous week's results, additional locations were sampled to provide a detailed picture of selected flow regions. Eight sampling rounds were performed over a period of six weeks. During this period approximately 3000 samples were collected and analyzed for PCE and chromate.

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