NEPA--Environmental Assessment

Water Quality ___________________________________
AFFECTED ENVIRONMENT
The analysis area generally encompasses the Animas River watershed above the confluence of
Cascade Creek and the Animas River, with the Graysill allotment and portions of the Flume
Allotment in the Hermosa watershed. Precipitation ranges from 25 to 50 inches, and streamflows
are highest in the spring when the showpack melts. Summertime thundershowers are common.
In the southern third of the analysis area, water quality is good, and stream patterns are typically
dendritic. The following allotments are in this category: Graysill, Flume, Engine Creek/Deer Creek,
Little Molas/West Needles, and the Forest Service portion of the Elk Creek allotment.
The northern two thirds of the analysis area (and the remaining allotments) are influenced by the
Silverton Caldera, an area where hydrothermal alteration associated with up-welling lava created
zones of metallic ore deposition and surrounding acidic rocks. Stream patterns tend to follow the
ring faults and radial faults associated with the subsidence of the caldera (Cement Creek and the
Animas above Silverton follow ring fractures. Maggie Gulch follows a radial fracture). Water
quality within the caldera is naturally acidic, with concentrations of metals such as iron, manganese,
copper zinc and aluminum at levels that are toxic to fish in many areas. Gold and silver mining
starting in the late 1800’s has increased the metal load in the streams through acid mine drainage and
leaching from waste rock and tailings. Increased metals in streamside sediments from early 1900’s
ore milling can be traced the full length of the Animas to its confluence with the San Juan River in
New Mexico. The Animas River Stakeholders Group, after extensive testing and analysis, proposed
water quality standards based on remediation of the worst polluting mine sites. These were
presented in the Use Attainability Analysis for the Animas River Watershed (Simon, 2001). These
standards were incorporated by the State in the Total Mean Daily Load allocation and the water
quality standards for the affected streams. Mine reclamation in the last 15 years has benefitted the
water quality and fishery of the Animas. A substantial amount of the metal load comes from natural
background and from undifferentiated man-made sources. These undifferentiated sources include
hillslope erosion that can be increased by grazing.
The town of Silverton draws municipal water from Boulder Gulch and Bear Creek. Neither of these
is permitted for sheep grazing.
An inventory was conducted by BLM in 1998 and 2001 of wetlands and riparian areas. A total of 91
sites, covering all major drainages were inventoried for Lentic Proper Functioning Condition
(Prichard, 1999, TR 1737-16). The Lentic PFC protocol addresses age class and composition of
riparian/wetland vegetation. Typically sheep do not spend much time in wetlands, so this factor may
not be a strong indicator of sheep grazing impacts. The protocol also assesses such things as
whether the upland watershed contributes to riparian degradation, whether hydrology has been
disrupted (such as by trails or hoof action), and whether there is excessive erosion or sediment
deposition. These factors would tend to integrate any impacts from grazing on dry upland hillslopes,
as well as grazing in the wetland, so are indicators of grazing impacts in the watershed. About 94%
of the sites inventoried were at Proper Functioning Condition. The five sites that were rated
“functional at risk” were because of roads and mining. Twelve sites were in watersheds where sheep
were noted as being present, and all those riparian areas rated at PFC. One site that was rated
“functional at risk” noted sheep grazing in the past, but grazing was not mentioned as causing the
erosion that placed the riparian area at risk.
Grazing of sheep or cattle have been shown to increase fecal coliform bacteria in streams (Gary,
1985). A study for San Juan County on sensitivity of different lands for development determined
52