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WATER.GR.EML.IN PUBLIC HEALTH XS"SESScMENT; RUBLIC OUMENT DRAFT Figure 5: TCE in Groundwater Sampling Results Vinyl chloride: When TCE breaks down in the environment it does so by losing chlorine atoms;.resulting in the breakdown products cis-1,2-dichloroethylene (c-DCE) and t=DCE, which then break down -further to vinyl chloride and finally to ethene. Over time; TCE concentrations will decrease as the concentrations of the other compounds increase, until they also breakdown over many.years. At five -locations vinyl* chloride exceeded the HRL of 0.2 ppb, with 20.1 ppb being the hiighestconcerrtration detected. vinyl chloride'14.of particular concern as-khas.an even lower HRL than TCE, was detected in multiple borings, and it may Increase in concentratlon overtime as TCE and DCF, at.the*site.degradec* Vinyl chloride was not detected in any samples collected from the buried sand aquifer. 1,4-Dioxanei 1.4-dioxane. is a stablilizer used in like 11,1-TCA and,. potentially, TCE.- As Figure-6 shows, 1,4-dioxane was detected in multiple borings on the Water Gremlin- property including the borings near Lambert Creek. Most of these .borings were shallow, .but. six were completed in the,buOed sand aquifer. 1;4-dioxane is extremely water soluble and often moves more quickly through aquifers than other contaminants, which may�ekplain why it was found in borings neafthe 6eek but notin borings closer tar the Water Gremlin plant. At 20 on- and near -site locations 1,446kane exceeded the HRL of 1 ppb, with 2$.5 ppb the highest concentration detected. That.sample was collected from GP-34 at 97-100 feet belowground level, near the northwest corner of the -south -campus building. In 2021, nine deep borings were drilled on- and off -site, with groundwater samples being collected from the upper sand, the semi -confining unit, and the buried sand aquifer as.the borings were. advanced. 1;4- 24