A Search for An Alternative Water Supply for the Community of Rimini Located within the Upper Tenmile Creek Mining Area Superfund Site

The Upper Tenmile Creek Mining Area Superfund Site near Helena, Montana, contains over 150 abandoned mine and mill sites. Degradation of surface and groundwater quality in the watershed is primarily related to the residual waste rock/tailings piles and discharging adits at the abandoned sites. Residential well sampling in the Community of Rimini demonstrated that arsenic and metals concentrations exceeded water quality standards. The EPA is currently providing bottled drinking water for most of Rimini’s residents. To find an alternative source of drinking water, an investigation was conducted to locate an alluvial or bedrock groundwater drinking water source for Rimini. The goals of this investigation were to find a groundwater source that has sufficient quantity, requires no treatment, have limited operation and maintenance costs, and is located in close proximity to the community. A lineation analysis using aerial photography and topographic data was implemented to identify subsurface features, such as faults, folds, or fractures. Three drilling locations were initially identified. Alluvial and bedrock test borings were drilled at each location and those borings with the highest preliminary discharge were completed as wells and sampled for water quality. The drilling program yielded mixed results: the alluvial wells had moderate to high discharge but contained arsenic concentrations in excess of water quality standards, while the bedrock wells met water quality standards but had insufficient discharge. As a result, it became necessary to explore other options, including drilling additional wells, evaluating spring sources, providing arsenic treatment for known sources with adequate flow, developing a surface water source, and piping water from the City of Helena water treatment plant. The preferred option at this time is treatment of a surface water source to reduce arsenic concentrations. The ability/willingness of the community to operate and maintain a long-term treatment system for surface water remains in question.