NEPA--Environmental Assessment
NEPA--Environmental Assessment
NEPA--Environmental Assessment
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Water Quality ___________________________________<br />
AFFECTED ENVIRONMENT<br />
The analysis area generally encompasses the Animas River watershed above the confluence of<br />
Cascade Creek and the Animas River, with the Graysill allotment and portions of the Flume<br />
Allotment in the Hermosa watershed. Precipitation ranges from 25 to 50 inches, and streamflows<br />
are highest in the spring when the showpack melts. Summertime thundershowers are common.<br />
In the southern third of the analysis area, water quality is good, and stream patterns are typically<br />
dendritic. The following allotments are in this category: Graysill, Flume, Engine Creek/Deer Creek,<br />
Little Molas/West Needles, and the Forest Service portion of the Elk Creek allotment.<br />
The northern two thirds of the analysis area (and the remaining allotments) are influenced by the<br />
Silverton Caldera, an area where hydrothermal alteration associated with up-welling lava created<br />
zones of metallic ore deposition and surrounding acidic rocks. Stream patterns tend to follow the<br />
ring faults and radial faults associated with the subsidence of the caldera (Cement Creek and the<br />
Animas above Silverton follow ring fractures. Maggie Gulch follows a radial fracture). Water<br />
quality within the caldera is naturally acidic, with concentrations of metals such as iron, manganese,<br />
copper zinc and aluminum at levels that are toxic to fish in many areas. Gold and silver mining<br />
starting in the late 1800’s has increased the metal load in the streams through acid mine drainage and<br />
leaching from waste rock and tailings. Increased metals in streamside sediments from early 1900’s<br />
ore milling can be traced the full length of the Animas to its confluence with the San Juan River in<br />
New Mexico. The Animas River Stakeholders Group, after extensive testing and analysis, proposed<br />
water quality standards based on remediation of the worst polluting mine sites. These were<br />
presented in the Use Attainability Analysis for the Animas River Watershed (Simon, 2001). These<br />
standards were incorporated by the State in the Total Mean Daily Load allocation and the water<br />
quality standards for the affected streams. Mine reclamation in the last 15 years has benefitted the<br />
water quality and fishery of the Animas. A substantial amount of the metal load comes from natural<br />
background and from undifferentiated man-made sources. These undifferentiated sources include<br />
hillslope erosion that can be increased by grazing.<br />
The town of Silverton draws municipal water from Boulder Gulch and Bear Creek. Neither of these<br />
is permitted for sheep grazing.<br />
An inventory was conducted by BLM in 1998 and 2001 of wetlands and riparian areas. A total of 91<br />
sites, covering all major drainages were inventoried for Lentic Proper Functioning Condition<br />
(Prichard, 1999, TR 1737-16). The Lentic PFC protocol addresses age class and composition of<br />
riparian/wetland vegetation. Typically sheep do not spend much time in wetlands, so this factor may<br />
not be a strong indicator of sheep grazing impacts. The protocol also assesses such things as<br />
whether the upland watershed contributes to riparian degradation, whether hydrology has been<br />
disrupted (such as by trails or hoof action), and whether there is excessive erosion or sediment<br />
deposition. These factors would tend to integrate any impacts from grazing on dry upland hillslopes,<br />
as well as grazing in the wetland, so are indicators of grazing impacts in the watershed. About 94%<br />
of the sites inventoried were at Proper Functioning Condition. The five sites that were rated<br />
“functional at risk” were because of roads and mining. Twelve sites were in watersheds where sheep<br />
were noted as being present, and all those riparian areas rated at PFC. One site that was rated<br />
“functional at risk” noted sheep grazing in the past, but grazing was not mentioned as causing the<br />
erosion that placed the riparian area at risk.<br />
Grazing of sheep or cattle have been shown to increase fecal coliform bacteria in streams (Gary,<br />
1985). A study for San Juan County on sensitivity of different lands for development determined<br />
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