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Well Methane Methane <br /> m11L (191L) <br /> 16969 Brookhurst MW-6 00982 644 <br /> Fountain Valley MW-15 00293 192 <br /> MW-13 0 535 351 <br /> 30011 Crown Valley MW-7 102 669 <br /> Parkway Laguna Niguel MW-10 4953 663 <br /> MW-11 00176 11 5 <br /> 27101 Ortega Highway W-2 4 2620 <br /> San Juan Capistano MW-8 156 1020 <br /> MW-11 0 835 547 <br /> unit conversion at nominal temperature of 25"C <br /> The observed concentration levels and gradients across the sites are indicative of <br /> methanogenic conditions over at least a portion of the groundwater plume(s) at all three <br /> sites <br /> 543. Anaerobic microcosms - nitrogen sparged <br /> The anaerobic microcosms sparged with nitrogen were intended to evaluate degradation <br /> of MTBE and TBA in oxygen-depleted conditions, but with other electron acceptors, if <br /> present in the native soil and groundwater, remaining available <br /> Individually, MTBE showed observed degradation in 7 of 9 of these microcosms, and <br /> TBA showed observed degradation 7 of 9 of these microcosms Both TBA and MTBE in <br /> the same microcosm were degraded in 5 of 9 cases For the 7 microcosms in which <br /> MTBE was observed to degrade, a commensurate increase in TBA concentration was <br /> observed in 5 of 7 microcosms <br /> The mechanism of anaerobic degradation was not identified in these microcosms Sulfate <br /> and nitrate were measured in the initial groundwater and in a water sample from these <br /> microcosms at the test conclusion, however no conclusions could be drawn from changes <br /> in levels of these electron acceptors over the test period <br /> 54.4 Co-metabolism <br /> The aerobic microcosms with added propane were intended to evaluate the potential for <br /> co-metabolism of MTBE and propane, compared with negative results from the aerobic <br /> microcosms with only added MTBE and TBA <br /> MTBE and TBA showed significant degradation in every aerobic microcosm (discussed <br /> in Section 5 4 1) with only these chemicals added Given this, the results from the co- <br /> metabolism tests are inconclusive <br /> 545 Controls <br /> The sodium azide -spiked microcosms showed relatively stable TBA and MTBE levels <br /> over the test duration, with variability on the order of+10% to -15% or less Exceeding <br /> this range of variability was an initial indication in the active tests that a change in MTBE <br /> 0 or TBA concentration was occurring <br /> 18 <br />