Mitigation of Hard Mineral Scaling
Is it possible to mitigate hard mineral scaling that impact operations and maintenance of critical geotechnical features at Reclamation facilities?
Need and Benefit
In the western United States where Reclamation has constructed many facilities, sparingly soluble minerals such as anhydrite, calcite, and dolomite are common. Mineral dissolution may lead to the formation of hard mineral scaling which affect Reclamation projects, including agricultural drainage, dam seepage, geothermal and mining water augmentation, desalination, water reuse, and water intrusion through concrete.
Some Reclamation structures sited on foundation and abutments containing these minerals are continually faced with this problem and rehabilitation efforts may lose their effectiveness as structures continue to age with time. According to the Technical Service Center (TSC) Closed Circuit Television inspection program, 5-10 percent of all dam seepage drains and conduits inspected were found to contain encrustation. At some facilities, 30-50 percent of all drains contain evidence of clogging. The extent of formation ranged from trace to complete plugging of the drain or conduit. They are usually treated with high pressure jet cleaning as a regular component of an O&M schedule.
A similar situation exists with ground water wells. At the Closed Basin Project (UC Region), groundwater well fouling issues requires approximately 20 percent of labor time per year. The salvage wells begin to display a decrease in capacity after just a few years of operation. Some wells have been completely shut down. Another example is in the Pacific Northwest (PN) Region where there are 37 dewatering wells used to stabilized the riverbank downstream of Grand Coulee Dam. These wells were constructed during the mid/late 1980s. By 1990, well yields have already declined. A cleaning program involving mechanical or chemical treatment was initiated. As the wells aged, the decline in yields became more rapid in between cleaning, requiring more frequent cleaning. Similar well fouling problems have been documented in other Reclamation regions.
What Reclamation need is a solution to the mineral scaling problem to extend the production life of engineering features and reduce the frequency of O&M cleaning schedules.
A short assessment report describing available technologies for mitigating hard mineral scaling and their potential for applications to existing Reclamation facilities whose O&M are impacted by this problem.