Surface disturbance can affect surface water quality by increasing sediment transport, which can ultimately be transported to streams or other surface waters and by reducing infiltration, which affects surface water and groundwater quality, quantity, and timing.

Actions that provide protection for the soil and vegetation resources will generally mitigate impacts on the water resource as well.

Soils that are the most susceptible to erosion are the most likely to adversely affect surface water quality if disturbed. The amount of sedimentation is determined by many factors, including the amount of disturbed surface, the type of soil, the amount and timing of water sufficient to create overland flow, the proximity to established channels, the density and vigor of the vegetative community, the buffering capacity of land over which the water would flow, and the effectiveness of erosion-control measures, such as BMPs.

The extent of two-tracks and unsurfaced roads (i.e., those without gravel or any other added surface material) is an indicator of the quantity of erosion and sediment delivery that may impact surface water quality within each watershed (Furniss et al. 2000).

Produced water generated from oil and gas development adds to surface water flows and can supplement streamflows. It is assumed legal water rights are established according to the requirements of the state engineer if livestock producers or other land users choose to utilize this water.

Mineral development is the principal activity with a potential to impact shallow groundwater quality and quantity. Locations in the Planning Area with depths to groundwater of less than 100 feet are considered the most likely to be impacted by mineral development. The shallower the depth to water, the more sensitive an aquifer is to contamination (Wyoming Geographic Information Science Center 1998).

The state of Wyoming has primacy regarding water. This includes water quality standards and water rights. The BLM may use water as an indicator or management tool, but it does not directly manage water.

The principal sources of surface disturbance from mineral development are roads and well pads for oil and gas and the disturbance created by solid mineral mining.

Livestock usually affect soil less than other developments, but the tendency for livestock to concentrate in riparian areas and in the proximity of open water while simultaneously affecting riparian vegetation may increase loading of fecal bacteria and nitrate (NO3) to surface waters, and may increase erosion and sedimentation. In cooperation, consultation, and coordination with permittees/lessees, cooperators, and other stakeholders, the BLM would develop and implement appropriate livestock grazing management actions to enhance rangeland health, improve forage for livestock, and meet other multiple use objectives by using the Wyoming Guidelines for Livestock Grazing Management, other appropriate BMPs, and development of appropriate range improvements.

Herbivory use is typically disproportionately higher in riparian/wetland communities than in upland communities. Improper or unmanaged herbivory can adversely impact these areas throughout the year, but surface impacts (due to hoof action) are generally greater in the spring and early summer, when soils are wet and, therefore, more vulnerable to compaction and stream banks are more vulnerable to sloughing. Livestock, especially cattle, tend to congregate in these communities during the hot season (mid to late summer). While stocking rates for an allotment or pasture may be low to moderate, the utilization levels in riparian/wetland areas can be high.

Substantial disturbance to soil, including compaction of soil or changes in vegetative cover, would increase water runoff and downstream sediment loads and would lower soil productivity, thereby degrading water quality, channel structure, and overall watershed health. Several factors influence the degree of impacts attributed to any one disturbance or series of disturbances, including location within the watershed, time and degree of disturbance, existing vegetation, and precipitation.

Changes in channel geomorphology due to activities may be detrimental to current designated uses. Sediment in channels is necessary for maintaining channel geomorphology and building riparian systems. Most channel systems achieve a channel form in equilibrium to the water and sediment being naturally supplied to it and generally respond to changes in sediment loads or streamflows by changing the channel form.

Changes in water quality for surface waters, such as increases in pollutants or physical parameters (e.g., temperature), may degrade habitat used by aquatic life and may affect other designated uses (e.g., stock-watering, irrigation, and drinking water supplies).

The BLM policy prohibiting the mixing of chemicals within 500 feet of open water (BLM Handbook H-9011) would reduce the likelihood of chemical spills from federal actions contaminating surface waters.

Because the state of Wyoming must comply with federal laws, compliance with state laws includes compliance with federal rules and regulations, including the Clean Water Act, Safe Drinking Water Act, and others. Therefore, it is assumed that any discharged water would meet water quality standards at the point of discharge.

As populations expand in the area, disturbances that affect water in the Planning Area will most likely continue to expand.

Actions that provide protection for the soil and vegetation resources will generally mitigate impacts on the water resource as well.

This analysis uses the WEPP model to calculate the runoff amounts and erosion rates used throughout this section. WEPP simulates the conditions that affect runoff and erosion, such as the amount of vegetation canopy and soil water content, to estimate runoff averages and erosion rates. For a more detailed description of the WEPP model and a list of the assumptions and parameters used in the analysis, see Section 4.1.3 Soil and Appendix V. All erosion rates and runoff amounts calculated using the WEPP model for this section were calculated using the same assumptions and input parameters that were used for Section 4.1.3 Soil and as described in Appendix V.