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WATER GREM•1.1-N PUBLIC HEALTH ASSESSMENT: PUBLIC COMMENT DRAFT Figure 2: Reported tons of TCE emitted — Tokics Relebse lhveritory 3991-2001 Reported tons of TCE emitted - Toxics Release Inventory 1992-2001 120 100 1DO 100 77 80 B5 $7 _.... 59 60 49 S5 40 31 . �2i { z0 �... 1992 2993 1994'1995 1996 1997 1998 1999 2000 2001 Estimating Past TCE Air Concentrations — Air Dispersion Modeling Air quality dispersion modeling uses computersimulation to predict -the concentrations of an air pollutant at different locations and distances from a source. MPCA uses the AERMOD dispersion model, developed and recommended by the U.S. EPA, to estimate the levels of air pollutant3 emitted from emission sources. For pollutantsemitted through a stack, as occurs at Water Gremlin; AERMOD simulation considers the. emission rate, stack height, static diameter, and stack gas, temperature and velocity, as well as the effect of nearby buildings -a*nd..terrain, AERMOD also uses meteorological data {'+ such as temperature, wind directioh,.and Wind speed to caiculate.pollutant co ncentratlons-at various locations. MPCA Provided a map*of the area potentially affected by TCE in February 2019 (see Figure 1 below), The map was created*by MPCA to display AERIVIOD dispersion modeling based on the total amount*of TCE emitted by Water Gremlin in 2018. This year was chosen because TCE emissions were the highest compared to all other years. The area.inside the dotted Iine.shown on the map represents. loM-Ions Where estimated amounts of TICE in. outdoor alrwere predicted -to be above the MDH inhalation Health - Based Value (HBV) of 2 µg/rrt3 (mictdgrams•percubic meter). The HBV is an amount of a contaminant.in a rthat•is unlikely to lead to -health effects even -if sensitive members of the population are exposed to it -24-houlrs a day, 7 days a week, for up to -a lifetime. The map was intended to represent where estimated air concentrations could have been above MDH's HBV.for TCE for the purposes of inclusively notifying the community of the situation. The figure and its features were not intended to convey any information about the likelihood of actual health effects among people.l.iving.within the area labelled as "Area of concern for TCE exposure:" The highest TCE concentrations Were'predicted forlocations. nearest the release point, on the Water Gremlin facility property. Outside. the property boundary, at.thp location of the closest residence, the .highest annual average TCl�tdncentration (2018 TCE use data) -Was.estimated to be 59 µg/im3 and arnbunts were predicted to dedreasewith increasing distance froth the.fadlity. The majority of the shaded area.represented on the map above Indicates annual average TCE concentrations between 2 — 20-i, Wm3.• 9