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.
Abandoned underground mines in the Pittsburgh coalbed continue to be a source of pollution to over 48 km of streams in the Raccoon
Through a contract with the US Army Corps of Engineers, Baltimore District, an innovative passive system to treat drainage from an abandoned underground coal mine was completed in 2008. The discharges can be characterized as highly acidic (pH 2.7, 1400 mg/L acidity) with moderate to high metal concentrations, having average total iron, manganese, and aluminum values of 300 mg/L, 20 mg/L, and 140 mg/L, respectively. The passive system utilizes a variety of treatment components including mixed-media vertical flow ponds, an anoxic limestone drain, a horizontal flow limestone bed, settling ponds, wetlands, etc. Of particular interest is the use of oxidation and precipitation channels to form iron solids at low pH. Preliminary results indicate that on average about 230 mg/L of dissolved iron is being removed at 2.6-3.2 pH. Removal of iron within the channels is expected to decrease operation & maintenance requirements while increasing the overall life of the system. Other design considerations included decreasing the potential for saturation with respect to gypsum, increasing alkalinity through anaerobic decomposition and sulfate reduction in alkaline mine drainage sources, and creating elk habitat. The final system effluent is net alkaline (7.5 pH, 214 mg/L alkalinity, -180 mg/L acidity) with total iron and aluminum less than 1 mg/L and total manganese of about 5 mg/L.
Abstract:Datashed is a user-friendly, interactive, Geographic Information System (GIS)-enabled online database developed by Stream Restoration Incorporated to assist watershed groups, academic institutions, private industry and government agencies to monitor, operate, and maintain passive treatment systems. Using primarily open-source technology, Datashed provides a costeffective and reliable solution to the management of data associated with environmental efforts. Specific, individualized functions can easily be added using common programming languages. One of these functions, called i-Map, is a GIS tool that spatially connects the data stored within Datashed. Both anonymous and authorized users can easily upload, download, and print data from any standards-compliant web browser without the use of additional plug-ins or software. Datashed is being used as a repository of information for over 230 passive treatment systems within the state of Pennsylvania. A "snapshot" of the current condition of these systems is underway by analyzing water samples from the raw untreated mine drainage, the final effluent of the passive system, and the influent and effluent of every alkalinity-generating component.
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