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Table 1: Dioxane Concentrations in City Wells Date Well No. 3 Well No. 4 Well No. 5 March 2015 Not Sampled 0.90 ppb 0.57 ppb June 2015 0.37 ppb 1.5 ppb Not Sampled August 2015 0.34 ppb 1.5 ppb 0.99 ppb September 2015 0.41 ppb Not Sampled (*) 1.0 ppb October 2015 0.39 ppb Not Sampled (*) 0.94 ppb November 2015 0.32 ppb Not Sampled (*) 0.99 ppb (*) Not sampled because well has been shut down Dioxane is used to stabilize chlorinated solvents and can be found in personal care products, laundry detergents, and food in small amounts. The TCAAP in Arden Hills used Dioxane as an additive in the solvents used at the facility and has been identified as the source of the contamination into the aquifer. The current Dioxane concentration at TCAAP has recently been detected as high as 60 parts per billion (ppb). Dioxane is classified as an emerging contaminant by the Environmental Protection Agency (EPA). Currently, there is not an established Maximum Contaminant Level (MCL) for Dioxane. However, the EPA has identified thresholds of 3.5 parts per billion (ppb) to prevent a 1:100,000 increase in cancer risk level and 0.35 ppb to prevent a 1:1,000,000 increase in cancer risk level. At least one EPA region has recommended 0.35 ppb as the appropriate limit for Dioxane. At the state level, allowable levels of Dioxane in drinking water have been established. The Minnesota Department of Health (MDH) has recommended keeping exposures at or below a health risk limit (HRL) of 1 ppb over a lifetime. Similarly, the states of California and Massachusetts have established recommendations at 1 ppb and 0.3 ppb, respectively. The City currently operates three groundwater wells (Well No s. 3, 4, and 5) to supply the City’s drinking water. Until the City recently stopped using Well No. 4, t he City was operating two wells full time with the third well for peaking and back up when one of the other wells was out of service for repair and maintenance. Having one current well with high levels of 1,4 Dioxane is now burdening t he City’s daily operations. Test results by the MDH, independently verified by the City, have shown the presence of Dioxane in the City’s wells. The concentrations have ranged from 0.35 ppb in Well No. 3 to 1.5 ppb in Well No. 4. The concentrations detected in Well No. 4 have increased when compared to the previous test results. 1,4-DIOXANE PROJECT FEASIBILITY REPORT CITY OF ST. ANTHONY VILLAGE WSB PROJECT NO. 3183-00 PAGE 3