Draft Environmental Impact Statement for Roca Honda Mine

Chapter 3. Affected Environment and Environmental Consequences
exceeded the SDWA Action Level for lead in one of two historic analyses. TDS ranged from 192
to 695 mg/L, with at least one sample each from six different wells exceeding the SDWA
Secondary Standard for TDS. Other SDWA Secondary Standards exceeded were those for iron
and fluoride (2.0 mg/L). Tables 9-5 and 9-6 of the BDR summarize the data and figure 9-13
shows the locations of the wells sampled.
Menefee Formation
The Menefee Formation is composed of shales interbedded with thin to thick sandstones and
minor coal seams. The fine grained fluvial sandstones constitute the aquifer, which while
apparently dry in the permit area, does supply many small stock and domestic wells in the
broader area (Hagan and others, 2001, p. 8). The Menefee is also the source of Bridge Spring,
discussed below. Logs from Mt. Taylor mine wells indicate a total thickness of 767 feet for the
Menefee in that area. Few Menefee wells in the upper San Mateo Creek valley penetrate more
than a few hundred feet of Menefee, rather than its entire thickness.
Except for the southeast corner of Section 10 beneath colluvium, the Menefee Formation has
been removed from the permit area and the western part of the San Mateo Creek valley by
erosion (see figure 9-7 of the BDR). North of San Mateo Creek, the Menefee extends only to the
central part of Section 21, T13N, R8W; south of San Mateo Creek, the Menefee extends farther
west, to near the western boundary of Section 29, T13N, R8W (McCraw et al. 2009).
The Menefee dips to the east, but groundwater flow in the formation is to the northwest.
Groundwater in the Menefee generally is unconfined, though it is under “slightly confined”
conditions in the area of the community of San Mateo (RHR, January 2011 Revision 1). At the
pinch-out of the Menefee, the groundwater flow must enter the adjacent Point Lookout Sandstone
or alluvium where the alluvium is saturated.
Forty-seven wells completed in the Menefee were identified in the well inventory, generally in
the vicinity of the community of San Mateo. The closest Menefee well to the permit area was No.
7 (no OSE file number) in the southwest quarter of Section 11, just east of the permit area; total
depth of the well was 192 feet and depth to water was 76.9 feet (no measurement date). This well
has been sampled by RHR five times and contains nonpotable water with TDS ranging from
2,680 to 3,320 mg/L and three of five gross alpha measurements above the SDWA primary
standard. The BDR did not indicate any prior mining activity in this area.
Water quality data from historic sources or RHR monitoring are available from 23 Menefee wells
in addition to No. 7. Menefee water is of the sodium-bicarbonate type with some sulfate. Quality
is quite variable, with TDS ranging from 169 to 2,299 mg/L in the 23 wells. The SDWA
Secondary Standard for TDS was exceeded in at least 1 sample each from 13 wells; SDWA
Secondary Standards for sulfate, iron, manganese and aluminum also were exceeded in 1 or more
of the 23 Menefee wells. SDWA Primary Standards were exceeded for lead (Action Level, seven
wells), arsenic (four wells), and combined radium (one well). Tables 9-3 and 9-4 of the BDR
summarize the data and figure 9-12 shows the locations of the wells sampled.
Alluvium
Quaternary-age alluvial material overlies bedrock throughout the San Mateo Creek valley and up
the tributary drainages, but is likely unsaturated except near the creek. Well logs indicate that the
alluvium consists of 10 to 80 feet of unconsolidated sands and silts. It may be significantly
138 DEIS for Roca Honda Mine, Cibola National Forest