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City Council Update for 1,4-Dioxane Water Supply and Treatment Feasibility Study August 31, 2015 WSB is currently studying alternative water supply and treatment options to address 1,4-dioxane that has been detected in the City’s wells. Dioxane is an additive found in solvents that were used at the Twin Cities Army Ammunition Plant in Arden Hills. Technological advances have resulted in better methods for detecting contaminants at extremely low concentrations. The test results by the Minnesota Department of Health (MDH), and independently verified by the City, have shown the presence of 1,4- dioxane (dioxane) in the City’s wells. The concentrations have ranged from 0.35 parts per billion (ppb) in Well No. 3 to 1.5 ppb in Well No. 4. The concentrations detected in Well No. 4 have increased over the period of testing. A regulatory limit on the amount of dioxane permitted in drinking water has not yet been set under the Federal Safe Drinking Water Act. The MDH, however, has set a guidance limit of 1 part per billion (ppb) for 1,4-dioxane based on its potential to cause cancer in people. WSB is currently evaluating each of the following proposed water supply and treatment options and estimate the capital and long term operational costs for each option. Option 1 - Blend City wells to dilute 1,4-dioxane to below the MDH guidance limit More water would be pumped from either Well No. 3 or Well No. 5 to dilute the 1,4-dioxane concentration in Well No. 4 to below 1 ppb at the point of entry (plant effluent). Well No. 3 contains the highest trichloroethylene (TCE) concentration. The existing carbon filters would require more frequent change outs if this well is run more frequently. Option 2 - Construct deeper Mount-Simon Hinckley wells A moratorium exists in the Metro Area for using the Mount-Simon Hinckley formation. The Commissioner of the DNR may allow use of this aquifer only if no other feasible alternatives exist. Water from this aquifer commonly contains radium 226+228. Although radium could be treated with the existing greensand filters, the filter media could become a hazardous waste because of the radium build- up on the filter media. Pumping costs would also be higher because the static water levels are deeper in the Mount-Simon Hinckley formation. Option 3 – Purchase water from St. Paul Regional Water Services (SPWRS) via the City of Roseville’s water distribution system WSB has made contact with Roseville staff and they are currently analyzing this option from their side. SPRWS’s water rates are $4.04 per 1,000 gallons during the winter and $4.20 per 1,000 gallons during the summer with a minimum monthly base fee of $4.80. Wholesale water rates had not been obtained from SPRWS at the time of this memo. Option 4 – Purchase water from Minneapolis Although Minneapolis’ water rates are significantly higher that the City’s, their whole sale rate would be only $2.73 per 1,000 gallons. However, this cost does not include maintenance costs for the City’s watermains, water towers, water meters, labor, etc. These costs need to be figured-in to the analysis to make a true comparison of the water rates. A water booster station or pressure reducing station and a metering vault could also be required with this option. Option 5 – Implement a water treatment system for 1,4-dioxane at the City’s water treatment plant WSB is currently studying treatment options for 1,4-dioxane. The most feasible treatment options have been narrowed down to Ultra Violet (UV) Light with Hydrogen Peroxide and Ozone with Hydrogen Peroxide. Trojan Technologies is currently piloting UV/Hydrogen Peroxide at the water treatment plant. The pilot water is also being spiked with excess 1,4-dioxane to account future conditions that might occur. These options will be presented and discussed in more detail by WSB at the August 31, 2015 work session. 3