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Water quality "I'hc future use area, being located off of the channel, will not affect water quality in the Animas River. "Chcre will be a 300 to 500 ft buClcr between the lake and the river which will provide a filter for turbid water created in the lake as part oClhc mining process. The only effects that the future uses may have on water quality in the river is construction of the seasonal road crossing, where culverts will be placed in the river and sand and gravel placed on top of the culverts to create a road surface. During placement of the gravel on the culverts, there may be increased turbidity and suspended sediment in the river, and some water-quality parameters may be affected. During the past 15 years of operations at the Dalton Pit, a seasonal road crossing was constructed similarly during the winter months. Water-quality data were collected by Sandco during the installation of the culvert crossing; samples were collected upstream and downstream of the crossing. Selected parameters were analyzed including metals, pH, total suspended solids, and settleable solids (table 3). The only constituents that were affected by construction of the road crossing were total aluminum, total iron, hardness, total suspended solids, and settleable solids (table 3). Dissolved-zinc concentration increased during one of the sampling events (1/14/2003); other- wise, the dissolved constituents did not appear to be affected by construction of the road crossing. Water-quality standards for metals in Colorado are described in table 4. T}te aquatic-life standards vary according to acute toxicity (sudden exposure) and chronic toxicity (long-term exposure). In addition, the toxicity values are dependent on hardness of the water because higher hardness values tend to make dissolved metals less toxic. The standards mostly apply to the dissolved phase of the constituents, except for iron which has a cluonic standard that applies to total (rccovcrablc) iron. Unfortunately, the reporting limits of many of the constituents are higher than the chronic standards (such as dissolved almninum) (table 4)- As an example of the use of the equation to calculate chronic toxicity, the dissolved-zinc concen- tration downstream from the road crossing on 1/14/2003 was 200 µg/L (micrograms per liter). Inserting the hardness value of 4G4 mg/L as CaCO3 into the equation for chronic zinc toxicity, a water- qualily standard of 430 µg/L would apply to the river at That time. Ifcnce, the dissolved-zinc standard was not violated. 'Che chronic iron standard is shown as 1,000 µg/L for total rccovcrablc iron, and it appears as though the construction of the road crossing may have aC('ected total iron concentrations. It is unknown how far downstream these effects may have occurred. 'T'otal suspended solids concentrations increased downstream during installation of the road crossing; however, there is no standard in Colorado for total suspended solids. Erosion Since the historical use area will be reclaimed, disturbances due to the in-channel mining operations will no longer be a concern. Banks of the historical use area will be stabilized, seeded, and planted with trees to minimize future erosion. Erosion of the material used to construct the seasonal road crossing is the only remaining concern with regard to fish, aquatic habitat, and aquatic organisms. Erosion of the road bed material may take place if the stream velocities at the road crossing exceed the incipient motion of the particles. Sediment could be transported downstream, possibly effecting fish habitat and aquatic organisms. Grains forming the boundary between a fluid and a sediment possess a fmi[e weight and finite coefficient of friction. When stream velocities are low dte applied shear stress is tow, and the particles are not brought into motion. As stream velocities increase applied shear stress is increased, and a critical shear stress is reached at which grains will begin to move. The value of the critical stress will depend primarily on the size and density of the particles and secondarily on their shape and packing and the cohesive forces acting between particles. Once the critical stress is exceeded, particles will advance in [he direction of flow due to irregular jumps or less commonly rolls. This mode of transport is termed the bedload and conceptually can be thought of as being deterministic, that is the behavior oC a particle once in motion is dominated by the gravity force. As the stress is further increased, particles will also begin to be suspended in solution and subject to turbulent forces. This mode of transport is termed the suspendcdload. A simple method to summarize the erosion and transport of strcambed sediments is the Hjulstrom diagram, which was derived Crom empirical data Hydrologic Study of the Sandco Reach, Animas River Valley, La Plata County, Colorado, 2004 18