INVESTIGATING GROUNDWATER PATHWAYS NEAR ABANDONED MINE SITES IN THE ROCKY MOUNTAINS

The work done here is about trying to resolve problems with contaminated abandoned hard-rock mine discharges. A consequence is having to understand the whole system. The challenge is tracing the sources of impacted groundwater from deep within mountain blocks, that are often physically inaccessible. Mine discharge is a mixture of impacted groundwater from a “mine pool” and deep and shallow groundwater. There are only a few ways to unravel the components of the mixtures, that change seasonally some flowing more rapidly than others. Ideally State and Federal agencies would like to divert or switch off the impacted waters at their sources so that clean discharges resume to streams and the quality of the environment can be restored. Regardless of there being mine workings, it is obvious that the groundwater pathways in the surrounding bedrock prevail. Surface stopes contain snow and ice but only transmit recharge slowly each melt. It is often impossible to inject tracers into the sources (e.g., deep workings), instead isotopes and geochemistry are used to infer mixture components to characterize the groundwater types discharging from the system.

It may be, beginning about ~ 5 Ma, groundwater systems in the Rocky Mountains probably began evolving such that relatively sophisticated deep circulation through mountain blocks resulted. Creation of deep pathways even in high relief terrain in silicate rocks requires some geological time, and physical and chemical conditions that result in alteration and preferential fracture enlargement to depth. These mountain landscapes are also related to continental events, including 20+ episodes of continental glaciation during the last 2.3 M.Y. But, the high relief and time probably means that the flow systems have gained some organized characteristics with preferential convergent flow paths and discharge via springs. Since there are springs, there must be channels, which explains why it appears that some mixture components have geochemical signatures that suggest rapid recharge and flow.