04-02-18 JDA Agenda Packet - Laserfiche WebLink

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Page 2 of 3 • Are the extraction wells located in the correct locations and are they pumping at the correct depth? • What modifications would need to be implemented to optimize the removal efficiency of the system? Ramsey County, City and/or a future developer do not have decision making authority over TGRS mitigation actions. This continues to reside in the long-term relationship with the Army and regulators. The Army’s answer and regulators concurrence to these questions could impact the use of the property. In 2015, the emerging contaminant 1,4-dioxane (1,4-DX) was identified in the well network at TCAAP and in neighboring municipal water supply wells. This compound was historically added to TCE as a stabilizer and was not considered a contaminant of concern at TCAAP. In 2013, 1,4-DX became a concern when the Minnesota Department of Health promulgated a Health Risk Limit (HRL) for 1,4-DX of 1 part per billion. This concentration was exceeded in multiple wells on TCAAP and in municipal wells that service the City of New Brighton. Neither the TGRS nor the existing treatment system operating in the City of New Brighton effectively remove 1,4-DX from groundwater. The City of New Brighton is currently modifying their municipal water treatment plant that removes 1,4-DX. This is considered at the point of use as the system does not treat the aquifer itself. The TGRS is a remediation technique at the point-of- source. Analysis of available data and collection of additional data is necessary to answer these questions and assess options with respect to evaluating and managing 1,4-DX. These are the primary goals of the Army’s Optimization Study. In March 2017, the Army, with the help of their consultant Pika-Arcadis, kicked off the Optimization Study. Study steps included: 1. Review existing data (i.e. groundwater flow patterns, depth of bedrock, historical TCE concentrations and mass removed from extraction wells) to form a Conceptual Site Model (CSM) for the deep groundwater. 2. Perform Vertical Aquifer Profiling (VAP) at 7 existing wells (3 on RCC, 4 offsite) 3. Install 3 new wells (on RCC) and perform VAP 4. Update CSM with new data 5. Preparation of a report summarizing the results of the study with recommendations From the beginning, it was made clear by the Army that the study scope included evaluation the existing data, limited collection of new data, and preparation of a summary report with recommendations. Implementation of Optimization Study recommendations is not included under the current Pika-Arcadis contract nor is it currently funded by the Army. The Army formed a workgroup of various stakeholders that included representatives from the MPCA, EPA, Ramsey County, Alatus, the Cities of New Brighton and St. Anthony, and Army consultants. The workgroup was convened four times during the course of the study (October & December 2016, March & August 2017) in order for the Army’s consultant team to apprise workgroup members on their progress and answer any questions. At the August 2017 workgroup meeting, the Army stated that a summary of the study findings would be issued sometime in October. We will share the report as soon as it is available.