Hydrogeology of Pipeline Canyon, Near Gallup, New Mexico^a

Abstract

The principal water‐bearing units (in descending stratigraphie order) in Pipeline Canyon are the alluvium, the Dilco Coal Member of the Crevasse Canyon Formation, the Torrivio Sandstone Member of the Gallup Formation, and the Upper and Lower Gallup Sandstones. Presently, the alluvium is recharged by a perennial, southward‐flowing stream sustained by mine dewatering discharge in addition to natural precipitation and runoff. Localized infiltration has created ground‐water mounds in the alluvium. Artesian conditions may exist in sandstone units which are adjacent and hydraulically connected to the alluvium in these areas. Basement faults have produced the Fort Wingate and Pipeline Canyon lineaments which intersect in the area of investigation. Fault‐related fracturing of the sandstones allows for significant ground‐water recharge via the overlying alluvium. Flow in the sedimentary formations is generally to the northeast, while the alluvial system flows to the southwest. The natural water quality for the aquifers in the area is dominated by sodium and sulfate ions. However, complete characterization of the natural water quality is complex because of ground‐water contamination by acidic tailings fluids from a local uranium mill.

Effects of uranium-mining releases on ground-water quality in the Puerco River Basin, Arizona and New Mexico

“…Bedrock formations of the Puerco River Basin consist predominantly of consolidated interbedded clay and sand units that form a multilayered, confinedaquifer system (Cooley and others, 1969;Raymondi and Conrad, 1983). Bedrock formations have been folded into a series of north-northwestward-trending anticlines, synclines, and monoclines (fig.…”

“…2; Cooley and others, 1969). The structural geology influences ground-water flow in bedrock and alluvial aquifers (Cooley and others, 1969;Mann, 1977;Raymondi and Conrad, 1983). The Nutria monocline, about 5 km east of Gallup, forms a ground-water divide for the regional-flow systems.…”

“…The Nutria monocline, about 5 km east of Gallup, forms a ground-water divide for the regional-flow systems. Recharge that occurs east of the Nutria monocline flows in a north-northeastward direction toward the San Juan basin (Cooley and others, 1969;Raymondi and Conrad, 1983). Recharge that occurs west of the Nutria monocline flows in a westward direction (Cooley and others, 1969;Mann, 1977).…”

“…The alluvial aquifer was divided into three reaches to describe the ground-water flow system and flow relations between the stream and aquifer on the basis of differences in bedrock geology, water quality, isotopic composition of water in the alluvial aquifer compared with that of surface water, and the regional-flow system (Cooley and others, 1969;Mann, 1977;Raymondi and Conrad, 1983). Those reaches are indicated by differences in tritium activities in ground-water samples (fig.…”

“…Because mine dewatering ended in February 1986 before this project began, this modeling relied on historical data to describe the water quality of mine effluent. Data used were collected by the NMED (Raymondi and Conrad, 1983;Gallaher and Gary, 1986;Dave Baker, NMED, written commun., 1989;and Wirt and others, 1991). Two processes were modeled that influence the SI of uranium minerals in minedewatering effluent degassing of CO2 and mixing with Gallup STP wastewater.…”