Draft Environmental Impact Statement for Roca Honda Mine

Chapter 3. Affected Environment and Environmental Consequences
at depths ranging from 1,650 to 2,600 feet below the ground surface and permanently extracted
from the rock formations where it has been present for millions of years. At an ore grade
averaging roughly 0.23 percent U3O8, the ore would yield 4–8 pounds of U3O8 per ton of rock.
Overall, hundreds of thousands and perhaps millions of cubic yards of ore and nonore rock would
be mined and extracted over the life of the mine. Smaller volumes of nonore rock would be
temporarily brought to the surface during the boring of mine production and ventilation shafts.
Roof collapse within the mine would be prevented by backfilling previously mined rooms with
excavated nonore grade material and/or aggregate imported into the mine from the surface. The
backfill material would be tested and characterized to ensure that its reintroduction into the mine
would not have a detrimental impact on groundwater. Ultimately, upon completion of the mine, it
is expected that no spaces or voids would be left underground. However, under both action
alternatives, there would be long term, indeed permanent, changes to the geologic character and
structure of large volumes within the Westwater Canyon Member of the Morrison Formation. The
backfill materials would differ from the original source rock.
Overall, impacts of alternatives 2 and 3 to geology at the site would be direct, long term,
localized, moderate, probable, and of slight precedence or uniqueness. In sum, impacts of the
action alternatives on site geology would be insignificant.
Both alternatives would result in direct, medium term to long term, localized adverse impacts on
soils from clearing, grubbing, and grading, construction of mine facilities, and mine operation.
These impacts would be controlled to an acceptable level through the diligent application of best
management practices (BMPs), which would utilize various measures and structures such as
straw bales, wattles (fences of stakes interlaced with twigs or branches), and silt fencing to
minimize the transport and loss of soil from erosion and storm runoff. Sedimentation control
structures would be installed prior to construction and a Storm Water Pollution Prevention Plan
(SWPPP), in compliance with EPA and State of New Mexico requirements, would be
implemented.
During construction and preparation activities, topsoil and subsoil would be removed and
stockpiled as necessary. As is true across much of New Mexico and indeed the Southwest, the
upper layers of existing soil horizons in nonriparian zones at the RHR mine site do not qualify as
topsoil according to the criteria established by soils scientists. Thus, the soil material to be
stockpiled for revegetation and reclamation is identified as “topdressing” in the RHR reclamation
plan revision 1 (August 2011). These soils to be removed above the rock layer would be
stockpiled together, identified as topdressing, and protected for use in future reclamation of the
site.
As noted in chapter 2, contemporaneous reclamation would take place, that is, while the mine is
still in operation. RHR’s proposed approach to contemporaneous reclamation—to avoid site
disturbance where possible and minimize the area that must be disturbed—would help minimize
soil disturbance erosion throughout life of the mine.
As part of final reclamation operations, disturbed areas would be stabilized by grading with earthmoving
equipment to conform to the geomorphic character of the region and the surrounding
area, including shaping, berming, and grading to final contour. Slope reclamation would
incorporate the practice of minimizing slope lengths and gradients, while conforming to the
geomorphic character of the surrounding areas to minimize the potential for excessive erosion.
108 DEIS for Roca Honda Mine, Cibola National Forest