2023.05.23 CC Packet - Laserfiche WebLink

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1 1 Executive Summary In 1981, the City of New Brighton (City) identified volatile organic compounds (VOCs) in water from the City’s municipal water supply wells that were pumping from the Prairie du Chien Group and Jordan Sandstone aquifers. It was subsequently determined that the VOC contamination originated upgradient of the City’s wells at the Twin Cities Army Ammunition Plant (TCAAP) Superfund Site in Arden Hills. Actions taken in response to the contamination in the City’s wells included installation of new wells and deepening of some existing wells into the Mt. Simon Sandstone aquifer (a deeper aquifer not connected to the contaminated aquifers) and construction of a treatment plant (known as the Permanent Granular Activated Carbon Water Treatment Facility (PGACWTF) to remove contaminants from water pumped from the Prairie du Chien Group and Jordan Sandstone aquifers. The PGACWTF was put into service in 1990. Under an agreement with the U.S. Army (the party responsible for cleanup of the TCAAP site), several of the City’s wells and the PGACWTF are part of the groundwater remediation system for the TCAAP site and referred to collectively as the New Brighton Contaminated Groundwater Recovery System (NBCGRS). These wells must operate at pumping rates required to maintain capture of the VOCs contaminant plume from the TCAAP site. Treated water from the PGACWTF meets drinking water criteria and is used for drinking water by the City of New Brighton. The volume pumped to the treatment plant often exceeds what is needed to meet New Brighton’s water demand and excess water from the treatment plant is provided to the City of Fridley via a water system interconnection. In 2015, 1,4-dioxane was detected in water pumped by the City’s NBCGRS wells at concentrations above the health risk limit (HRL) for this compound specified by the Minnesota Department of Health (MDH). 1,4-dioxane is a solvent stabilizer, is highly miscible in water, and is not removed from water by granular activated carbon. Therefore, it was necessary to add ultraviolet advanced oxidation process (UV AOP) treatment to the PGACWTF to remove the 1,4-dioxane before water is sent to the distribution system. The NBCGRS wells (Wells 3, 4, 5, 6, 14, and 15) were shut down in April 2015 for construction of the PGACWTF modifications. The City relied on its Mt. Simon aquifer wells (Wells 8, 10, 11, and 12) until July 2016 when an interconnection with the Minneapolis water system went online. Minneapolis provided water to New Brighton until the PGACWTF modifications were completed in November 2018. The NBCGRS wells resumed normal operation in December 2018. The Wellhead and Source Water Protection Plan (the Plan) for the City addresses the six primary municipal water supply wells (Wells 3, 4, 5, 6, 14, and 15), three seasonal wells (Wells 8, 11, and 12), and two emergency wells (Wells 9 and 10). The primary water supply wells pump from one or both of the Prairie du Chien and Jordan aquifers while the seasonal and emergency wells pump from the Mt. Simon aquifer. This Plan was prepared in accordance the applicable portions of the State of Minnesota Wellhead Protection Rules (Minnesota Rules 4720.5100 through 4720.5590). The Plan consists of two parts. In Part 1 of the Plan, 10-year groundwater time of travel wellhead protection areas (WHPAs) for the City’s water supply wells were delineated as were the associated drinking water supply management areas (DWSMAs). Two DWSMAs were delineated: 1) the Primary DWSMA that encompasses the WHPAs for Wells 3, 4, 5, 6, 11, 14, and 15 and 2) the Well 12 DWSMA that encompasses the WHPA for Well 12. The Primary DWSMA