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Animas Watershed Plan
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Last modified
1/27/2010 11:11:04 AM
Creation date
6/17/2008 2:10:59 PM
Metadata
Fields
Template:
Watershed Protection
Document ID
0002
County
San Juan
La Plata
Stream Name
Animas River
Basin
San Juan/Dolores
Sub-Basin
Animas 14080104
Water Division
7
Title
Animas River Wateshed Plan, The
Prepared By
Animas River Stakeholders Group
Watershed Pro - Doc Type
Planning Report
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various locations of the upper six inches of surface on each mine dump or tailings pile. <br />The samples were mixed to form a composite sample. The composite sample, 150 ml., <br />was mixed vigorously with 300 ml_ de-ionized water (2:1 ratio). After allowing clay <br />particles to settle, part of the sample was tested for total acidity, pH, and conductance. <br />The remainder was acidified to determine metal content. (See Herron et al., 1999, for <br />more details on the process.) Some data also exists for 20:1 EPA method 1312 Leach test <br />and Modified 13121each tests for several sites. This data was not included in the ranking <br />process because it cannot be compared to the 2:1 leach test. In addition, USGS has done <br />some leach testing using yet another sampling and analysis method. <br />Mine wastes were ranked by metal contributing potential for zinc, copper, <br />cadmium, lead, manganese, aluminum, and iron and pH as determined by the 2:1 leach <br />test. For example, the waste with greatest zinc leachate concentration is ranked number <br />one for zinc. The same site may be ranked number five for lead if it has the fifth highest <br />amount of lead leachate concentration, and so forth. In addition, weighting factors have <br />been assigned for the metals analyzed. Alumimim and iron are considered limiting <br />factors but the sources of these metals aze overwhelmingly associated with natural <br />features and processes (See Figures 8.18 - 8.21). In addition, they will automatically be <br />reduced by any treatment method. Reductions may not even be beneficial since their <br />presence downstream may be desirable for scavenging Zn, Cd, and Cu from solution by <br />sorbtion to their precipitates. Aluminum and iron are given a weighting factor of one. <br />Manganese and lead are both given a weighting factor of two because they <br />generally have a moderate potential as limiting factors, while their sources are more <br />specifically identified with mine features than those of iron and aluminum. Lead falls <br />from solution readily in the Animas watershed and will probably not be a limiting factor <br />if treatment for other metals progresses. A handfull of sites appear to be high <br />contributors of manganese. <br />Copper, cadmium, and zinc have high potential as limiting factors throughout the <br />basin and tend to be highly correlated to mine and/or mill features_ They come from a <br />multitude of sites. These are given the highest weight factor of three. <br />The other weighted factor, pH, is a strong limiting factor in Mineral and Cement <br />Creeks, but is not as significant in the Upper Animas. Some treatment methods may <br />result in increased pH but much of the low pH is thought to be the product of natwal <br />geological processes. It is given a weighting factor of two. <br />To complete ranking, each of the seven metals plus pH were multiplied by their <br />respective weighting factors then added together for each mine waste site. The resulting <br />sum is a measure of the severity of total loading potemial. Sites were then ranked for <br />remediation by the weighted sum; the lowest number is given the highest priority. The <br />prioritization vas done for each of the three sub-basins and for all the sub-basins lumped <br />together (Combined Rankings). That way remediation can be targeted for specific <br />segments, depending upon in which sub-basin they lie, or by their collective impact on <br />the Animas below Siiverton. <br />In addition to the leach test results, many other characteristics are listed on the <br />spreadsheets for the dumps. These aze also importam considerations iri prioritizing sites <br />for remediation, but have not been included as pazt of a mathematical sum. These <br />include: <br />• site names and locations, <br />13 <br />
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