Elizabeth A. Carey, Lynn A. Brandvold, and Virginia T. McLemore
Since reclamation of the Pecos mine, area roads and campgrounds, and the Alamitos Canyon mill began in 1990-1991, there has been continued monitoring of metal and trace element concentration in stream sediments and water along the Pecos River, extending from the upper Pecos River to below Brantley Dam, north of Carlsbad. In 1992, 1996, and 2000, water and stream sediments were sampled and analyzed for the entire reach. This study reports on the most recent sampling and analysis of the stream sediments and compares the data to earlier data. These efforts were initiated so that point and non-point sources of contamination associated with the mine could be identified and effects of reclamation examined. The Pecos mine generated on the order of 70,000 m3 of waste rock, which was piled at the mine site on a slope above the river. The crushed ore from the mine was transported by aerial tramway to the Alamitos Canyon mill 18 km south of the mine. Both mine waste and mill tailings have been a source of acidic drainage contributing elevated concentrations of metals and other trace elements. In this study, the < 63 µ fraction was digested with aqua regia and analyzed for Cd, Cr, Cu, Fe, Mn, Pb, and Zn using flame atomic absorption spectroscopy. With three sets of data now in place (1992, 1996, and 2000), geochemical trends confirm a decrease in concentrations with time since reclamation began, especially in the immediate vicinity of the Pecos mine and below the confluence of Alamitos Creek which drains the mill site area. In 2000, a sharp increase was noted in stream sediment Cu and Pb levels immediately below the fish hatchery.