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WATER GREMLIN PUBLIC HEALTH ASSESSMENT: PUB.LI.0 COMMENT DRAFT { dioxane was detected in seven of these borings, primarily ih samples from the upper sand and semi - confining unit. However, the HRL was exceeded in four borings, three of wFilch had exceed ances In samples collected from the buried sand aquifer. The concentrations. in.the buried sand aquifer samples were generally low (0.32-2.4 ppb). It should be noted that the deep boring north (upgradient) of the Water Gremlin (G.P-37) plant also had multiple samples with detections of 1,4-dioxane including one from the base of the semi -Confining unit with a concentration of 9.7 ppb..While it appears there were. historic source$ for 1,4-d16xane at Water Gremlin, private well sampling i*sults (see section V-B) suggest there may bg.another source (or sources).9f.1,4-dioxane in the area; this* -is being investigated by MPCA: While it is. unlikely that Water Gremllh Is the source -of the 1;4.-dioxane contamination seen in the. private wells in Gem Lake based on the curreht deta, it is riot possible to state Water Gremlin did not contribute to the private well 1,4=dioxane contamination without.additional data collection. Other chemicals detected: Several other chemicals were detected during the groundwater investigations. These included chlorinated solvents and their breakdown products [1,1-dichloroethane (1,1-DCA), chloroethano, c-DCE, and t-DCE],..petroleum hydrocarbons [toluene and ethylbenzeng], other orgAhid hydrocarbons [acetone, p-iso.propyltoluene, chloroethane], and lead. Of these,. the only chemiCais that exceeded a HRL were-t DtE; which was detected ibove the HRL of-.9 ppb in two. samples (highest'concentration 51.9 ppb), and toluene that was detected above the HRGof 10.ppb In one -sample (101 ppb). Figure 6: 1,4-Droxone in Groundwater Sampling Results 25