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WATER GREMLIN PUBLIC HEALTH ASSESSMENT: PUBLIC COMMENT DRAFT uncertainty factor of 1,000) based on fat accumulation in liver cells (ATSDR, 1996). The unpublished subchro.nic rodent inhalation.study (l7u.Pont,.1998). did not.show any effects thought be to related to exposure to t-DCE, even at doses of 15,800,000 pem3. In their 2010 toxicological review, EPA determined there was enough information to derive a safe amountfor oral exposure tot-DCE. A subchronic.drinking water study:shewing immune suppression in rodents (5hopp et al., 1985) was used to derive an amount of t-DCE.that pep pie could.safely consume over a lifetime (0.02 milligram/kilogram-day). EPA applied an uncertainty factor of 3,0.00 to account for differe bees between animals and humans, variability among humans, use. of a subchronic study, and a lack of additional studies. In January; 2019,. MDH.used .this oral dose to derive a: chronic air guidance value, by converting the oral exposure to inhalation exposure to arrive atthe 70 ug/m3 site -specific RAA. fort=DCE use at Water Gremlin. MPCA Air Modeling As noted earlier, air quality dispersion.model! ng uses computer simulation to predict pollutant concentrations at d iff event: 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 pollutants emitted from sou rces,. M PCA conducted air modeling of proposed Water Gremlin t-DCE emissions to back - calculate an annu.a.l emission rate that. would not result in long-term exceedances of the t-DCE inhalation RAA that MDH developed in January 2019. According to the MPCA's mode Iing,.92 tons of t-DCE could be emitted i.n:a Year without exceeding an annual average concentration of 70 µ9/m3 in air outs ide.of the property, Restart of Coating. Operations — March. 2019 Water Gremlin resumed coating operations using€-DCE in place of TCE;. on March 1, 2019 after.MPCA and Water Gremlin signed. a settlement agreement to resolve the company's a1r.quality violations. The agreement limited Water Grem1in's total VOC emissions to 90 to.ns.per year, calculated as.a 12�month rolling: sum, using a mass balance calculation that assumed all t-DCE used 1n operations was emitted to air, except any accounted for as liquid: waste leaving the facility, Based on the air modeling described above; this 90-ton-per-year limit prevents the annual average t-DCE levels from exceeding the. RAA of 70 µg/m3 in any locations where people -live. On August22, 2019, MPCA ordered Water Grerrrilin to suspend the operation of the coating lines because.t-DCE was:found in the soil vapor beneath the.company's production facility building (see section V: Remedial Investigation and Interpretation parts.C. and.D. for more about soil vapor). because of this suspension, t-DCE was only used for -slightly under six months in 2019. The coating lines.remained :shut down until January 21, 2020.. Use of the. coating lines was. phased back in slowly after the suspension, and some lines transitioned to a water -based coating: As a result, less t-DCE was used. in 2020 each month (through March) compared to monthly active coating operations in 2019: The one-year period of t-DCE use (from March 2019- March 2020) totaled 60tons. The 12-month rolling sum for emissions decreased in 2020.and fluctuates due to the varied amount of t-DCE used. Additional information: and.a chart.ofthe t-DCE emissions. as :a rolling sum is available on MPCA's website at Water Gremlin air monitoring (www.oca.state.mn.us/airLwatee- gremlin -air -monitoring). 16