Draft Environmental Impact Statement for Roca Honda Mine

Chapter 3. Affected Environment and Environmental Consequences
show significant runoff contributions in some years, there has been little or none since the
mid-1980s.
• The contribution from the City of Grants wastewater discharge ended in 1992.
• Pumping of the San Andres-Glorieta aquifer has completely dried up Ojo del Gallo, such
that whatever contribution that spring made through Gallo Creek has ceased. Pumping
has had some impact on Horace Springs and, presumably, the gaining reach. See Frenzel,
(1992) and DBSA (2001) for results of computer models that simulate these impacts.
• DBSA (2001) suggest that the recent reduction in flow is at least partly a consequence of
reduced recharge due to lower precipitation.
The reasons for a far greater impact of development on Ojo del Gallo than on Horace Springs
relate to the elevation and gradient of the regional water table. As discussed in Gordon (1961, p.
48), Ojo del Gallo was dried up by only a 5- to 12-foot decline in the San Andres water level,
whereas another 175-foot decline would be required to eliminate flow at Horace Springs. The
decline that has occurred, however, does reduce the gradient and supply of San Andres-Glorieta
water to Horace Springs.
DBSA (2001, p. 30) reported on the use of the model of Carpenter and Shomaker (1998) to
simulate the impacts of dewatering at the Mt. Taylor Mine. The estimate of the impact on the Rio
San José was 0.07 cfs (72 acre-feet/year) by the end of pumping in 1990. This would be about 2
percent of the current flow. The model prediction was that continued pumping would add to the
depletion by about 1.5 acre-feet/year each year.
Other Areas of Interest
Volcanic Core
Intera (2011, 2012) concludes that the near surface volcanic rocks on Mt. Taylor are connected to
the underlying lava source through conduits or volcanic necks, which are very low in
permeability. From this they postulate that there is an extensive zone of very low permeability
rocks throughout a large area east and southeast of the proposed mine, and the zone extends to
and below the Westwater Canyon Member of the Morrison Formation. An alternative
interpretation is that the lower permeability zone is limited to the conduits and immediately
adjoining altered sedimentary rocks.
Discharge Area
At this stage in EIS preparation, details on the proposed discharge of treated wastewater have not
been provided, but the indication is that it will be well outside the permit area. When details on
the discharge are provided, information on the hydrogeology of the impacted area will be added
to this section.
146 DEIS for Roca Honda Mine, Cibola National Forest