Metals and Runoff in Turkey Creek—a TMDL Study of a Mining Area in Northern Arizona

The Turkey Creek watershed north of Phoenix, AZ is rich in metallic ores and was mined extensively during the late 19th and early 20th centuries. As a consequence of the nature of the watershed and the historic mining and ore processing activity, relatively high concentrations of a number of metals have been noted in parts of the creek. These concentrations were high enough to warrant listing and a subsequent TMDL study. About 21 miles of the creek with a watershed area of 93.9 square miles was listed for cadmium, copper, lead and zinc in the 2004 assessment. Particular locations of concern were two areas of tailings. These are a byproduct of ore processing and consist of finely ground ores that have been subject to extraction processes, both mechanical and chemical, but still retain significant quantities of metals. Through analysis of the data collected by the ADEQ it was found that runoff events carrying significant quantities of suspended sediment were one of the conditions that tended to produce the highest concentrations of particulate metals. Since criteria of dissolved metals are functions of the hardness of the water, the relationships between flow and dissolved parameters were also investigated in the analysis. The Hydrological Simulation Program – Fortran (HSPF) was used to model the watershed. The model was calibrated to available data and applied to analyze various scenarios. The results were used to develop TMDLs for three locations along the creek. This paper summarizes the data collection and analysis, development and application of the HSPF model, critical conditions analysis, the derivation of TMDLs for Cu and Pb, and the delisting of Cd and Zn. Special emphasis is placed on the flow conditions employed.