Microbial and mineralogical analysis of aluminum-rich precipitates that occlude porosity in a failed anoxic limestone drain, Monongalia County, West Virginia

Anoxic limestone drains (ALD) are among the many technologies being tested to reduce acidity and remove metals from streams affected by acid mine drainage (AMD). Built at the outflows of acidic drainage, these trenches are filled with limestone to add alkalinity. The trenches are covered to keep them anoxic so that iron remains in solution and does not coat the limestone gravel. Many ALD`s fail within months of construction as the limestone gravel porosity is reduced because of cementation by aluminum-rich substances. The Ridenour Rural and Abandoned Mineland Program (RAMP) experimental ALD site near Morgantown, WV, was built in 1992 to treat drainage that flows into the Monongahela River from old adits and seeps associated with a deep mine in the Pittsburgh Coal bed. Three drains were built to collect different seeps. Design of the drains included burying ASTM C-33 No. 57 gradation limestone gravel ({approximately}1 in.) in pits that were lined with plastic and then covered with soil. A stand pipe at the outlet end of the drains raises the water level to that mine water percolates through continuously submerged limestone. During construction of the drains, monitoring wells were installed, and galvanized wire mesh cages filled with limestone gravelmore » were suspended downhole at the end of fishing line in order to monitor progressive changes in the limestone gravel surfaces. Within six months, two of the three drains were experiencing severely reduced flow. A series of downhole experiments were designed at the Ridenour site to learn why porosity was lost. The experiment focused on the drain composed of 108 metric tons of limestone, the White Drain, that had gravel coated with a white precipitate.« less