Bench scale testing of thermal desorption treatment of rock and field testing of in-situ enchancement of biochemical degradation was conducted as part of feasibility studies to address the presence of chlorinated VOCs principally TCE and breakdown products, sourced from the rock matrix. The site characterization indicated that the majority of the VOC mass resides in the unfractured matrix above the first aquitard at 15 to 20 feet below ground. The hydraulic conductivity of matrix (about 10-10 cm/sec or less) is orders of magitude below the bulk conductivity of fractured rock (from 10-2 to 10-7 cm/sec).Matrix diffusion, biochemical degradation, and sorption have limited downgradient transport from the release.
Rock samples exhibiting initial VOC mass across three orders of magnitude were subject to a controlled heating process for 1 to 5 days resulting in apparent mass removals from 64 to 99%. We will present and discuss potential for water quality improvements if similar magnitudes of treatement could be obtained by application of ISTD. Field pilot testing involved two injections of amendment along with bromide tracer rationally designed based on our understanding of transport properties andintended to influence biochemical conditions in source rock beneath 1/4 to >1acre of are. We will discuss methods used to inject amendment while limiting introduction of atmospheric air in the subsurface and tracer transport against modeled rates of transport; and apparent degradation rates observed in the testing.
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