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WATER GREMLIN PUBLIC HEALTH ASSESSMENT: PUBLIC. COMMENT DRAFT Figure 3: Map of the area potentially affected by TCE— distributed in February 2019 The map above overestimates TCE air concentrations for many of the 'yea rs that Water Gremlin emitted it. If similar maps were created using.AERMOD predictions for earlier yea rs.when the total amounts of TCE.emitted were less (see charts on pages 879), the estimated amount of TCE in air would be lower than the 2018 modeled concentrations and the total affected area where. TCE exceeded the MDH HBV would be smaller. Modeling earlier years could estin}ate. how much TCE may have been present to outdoor air. at various locations near the facility overtime. The map above: underestimates TCE air concentrations for shorter periods of time. The TCE air concentrations estimated on the map above are annual averages, which means that there were times. throughout the .yea r when concentrations at. particular location we.. re higher (and other times when they Were: lower) than. the average. Daily variations are expected due largely. to variability in facility operations/TCE use and weather conditions (for example, both wind speed and direction). For periods of time, TCE air concentrations above the HBV extended beyond the outline in the above map.. The resuIts. fro m the dispersion modeling provide: the best information currently available for estimating .past annual averaged TCE air concentrations due to emissions from the. Water Gremlin facility. MDH collaborated with MPCA and ATSOR to create additional maps from Z.009-2018 to heIp.increase the understanding of the potential TCE air. concentrations overtime near Water Gremlin. These. maps can be found in Appendix B. 10