CASE STUDY: Field Trial of a Pulsed Limestone Diversion Well

Abstract

The use of limestone diversion wells to treat acid mine drainage (AMD) is well-known, but in many cases, acid neutralization is not as complete as would be desired. An engineered version of the diversion well has also been developed and tested in the field. The so-called pulsed limestone bed process has shown good acidity and metal removal, but requires electrical and chemical inputs. We have developed and evaluated a pulsed diversion well that retains the passive operation of the traditional diversion well, but with improved operating characteristics based on concepts used in the pulsed limestone bed process. In the new pulsed diversion well, a sand-size distribution of limestone (0.1 to 4.0 mm) was used so as to allow fluidization of the limestone bed, and to increase the reactivity of the limestone. Also, water flow was regulated through the use of a dosing siphon, so that consistent fluidization of the limestone sand could be achieved. The pulsed diversion well was tested in the field at the Jennings Environmental Education Center, near Slippery Rock, Pennsylvania. Initial system performance during the 2010 field season was good, with over 80% removal of influent acidity. However, further test results showed a decrease in acidity removal over the course of the study. Subsequent observations indicated that the hydraulics of the system had been compromised by the formation of iron oxides in the pipe leading to the limestone bed, which affected water distribution and flow through the bed. Although results from the field trial were mixed, it is believed that without the formation of iron oxides and plugging of the pipe, better acid neutralization and treatment may have occurred. Further tests are being considered using a different hydraulic configuration for the limestone sand fluidized bed, or alternatively, at a site with lower metal loadings.

Review of Passive Systems for Acid Mine Drainage Treatment

“…At the Galt site in WV, a diversion well increased pH from 3.1 to 5.5 and reduced acidity from 278 to 86 mg L −1 , a 70 % reduction (Faulkner and Skousen 1995). Pulsing systems have also been devised to increase the alkalinity from diversion wells (Sibrell et al 2005(Sibrell et al , 2013. …”