Watershed-based methodology for assessment of nonpoint source pollution from inactive mines

Abstract

A watershed-based methodology for the screening-level assessment of nonpoint source pollution from inactive and abandoned metal mines (lAMs) was developed, tested, and evaluated in this study. The methodology is intended for use by state and federal agencies responsible for management of these sites, and was designed to generate the common types of baseline site characterization information required for targeting streams and contaminant source areas for remediation. These information goals have been defined as part of this study prior to developing the assessment methodology, and are based on generalized but clearly stated lAM management goals that are most common among agencies. The research involved the following; (1) Identifying typical water quality and hydrologic characteristics of and assessment methods for lAMs. (2) Defining lAM management goals and information goals for targeting. (3) Identifying and evaluating attributes of data derived from typical synoptic surveys of lAMs. (4) Identifying common data gaps and data collection and analysis methods to fill these gaps. (5) Identifying and evaluating applicable assessment and data analysis methods to achieve the stated information goals. (6) Developing, testing, and evaluating the assessment methodology. The Cement Creek Basin, part of the Upper Animas River Basin above Silverton in the San Juan Mountains of southwestern Colorado, was used as the primary case study to develop the recommended methodology. The study showed that the potential error and uncertainty in the data and derived information should be considered explicitly in the assessment process in order to target remediation with a known degree of confidence. Confidence intervals, therefore, should be computed for statistical estimators. Visual aids for data presentation and usage should be used and include graphs, mapping of information, and if possible, GIS. Targeting in Cement Creek and at other sites can be accomplished effectively using the recommended methodology. Some data gaps exist in Cement Creek and at most lAMs with regard to targeting remediation. These can be filled when the required information goals are not met with existing data and when resources are available using some of the methods discussed in this study. The recommended methodology is applicable to and would be very useful for other lAMs.