Draft Environmental Impact Statement for Roca Honda Mine

Chapter 3. Affected Environment and Environmental Consequences
Mitigations to contamination of surface runoff during the operations phase are described in the
mine operations plan, revision 1. Storm water controls during the operations phase include
routing storm water around the disturbed area via constructed diversion channels. Surface water
entering the permit area would continue to flow through and exit the permit area in its natural
channels during operations. Some of the arroyos that transect the operational area may be
armored or straightened to avoid further erosion into the site, stabilizing and enhancing the
surface hydrologic resources, and otherwise be unaltered. Some surface water detention basins
and/or evaporation ponds would capture surface runoff from the permit area facilities and control
surface water flow into the area. The detention basins would be designed to capture and
temporarily hold surface water runoff that will then be released in a controlled manner. Because
they will be capturing water upgradient of the RHR facility and will be empty most of the time,
the detention basins will not impact groundwater. The evaporation ponds will be located so as to
capture whatever water and sediment might drain from the mine facilities. The ponds will be
lined and monitored with groundwater wells and vadose instrumentation to ensure that captured
water does not enter groundwater. (The vadose zone is the unsaturated region between the
ground surface and the water table.)
Table 14 summarizes BMPs during and after the operational life of the Roca Honda Mine.
Table 14. Temporary and permanent best management practices
Best Management
Practices
Preserving existing
vegetation
Reduces or eliminates erosion.
Effectiveness Assessment
Wattles Stabilize slopes by slowing, spreading, and filtering overland waterflow preventing
sheet erosion and rill and gully development. Placed along perimeter downgradient
of cleared or graded areas; along arroyos, stockpiles, and downslope of exposed soil
areas.
Straw bales Controls and filters overland waterflow. Used to reduce velocity and divert surface
flow. Used as necessary.
Ditches/swales Divert and convey runoff to desired locations. Used as necessary.
Energy dissipaters Prevents scour of soil by concentrated flows. Used where appropriate.
Slope drains Intercepts and directs surface flow away from sloped areas to protect cut or fill
slopes. Used as necessary.
Sediment traps Temporarily holds sediment-laden runoff allowing sediment to settle out. Used at
earthen embankments across waterways and low drainage areas.
Diversion channels Prevents property damage, erosion, and interference with establishment of
vegetation. Constructed across a slope where runoff from higher elevations occur.
Check dam Reduces velocity of concentrated storm water flow into receiving drainage. Installed
at outlet from the diversion channels.
Detention basins Controls flow of runon water diverted and captured to prevent pass over or through
the mine site. Requires no treatment and/or monitoring prior to discharge. Used
throughout the site.
154 DEIS for Roca Honda Mine, Cibola National Forest