Hydrogeologic characterization of fractured Abo and Madera Formation aquifers, hydrocarbon contamination and transport along the Zuzax Fault, Tijeras Canyon, New Mexico
— Paul G. Drakos, Jay Lazarus, S. Jetter, and M. Hodgins

Three separate water producing zones and two localized perched zones were identified within approximately 240 ft of ground surface in the Abo Formation and uppermost Madera Formation during an investigation into gasoline contamination of ground water conducted by the authors for the New Mexico Environment Department (NMED) at the Indian Hills site in the vicinity of Zuzax and Tijeras, New Mexico. Ground-water flow beneath the site occurs in fractured sandstone and limestone beds that are separated by leaky mudstone and shale aquitards. Two separate hydrocarbon plumes located along the Zuzax fault have migrated into both unconfined and leaky-confined aquifers and have contaminated several domestic and commercial wells in the area. A 0.75-mi-long benzene, toluene, ethylbenzene, xylenes (BTEX) and methyl-tert-butyl ether (MTBE) plume and a 500-ft BTEX/EDC (dichloroethane) plume originate from separate locations. Under the influence of downgradient pumping stresses, contamination of the aquifer located below the BTEX/MTBE source at a depth of 60-80 ft has migrated vertically along a structure perpendicular to the Zuzax fault into a leaky-confined aquifer located at a depth of 110-190 ft below ground surface. The BTEX/MTBE plume has subsequently migrated down-gradient along the northeast trending Juniper Ridge half-graben that parallels the Zuzax fault. Pumping test data and contaminant plume geometry indicate that bounding faults are impermeable or low-permeability barriers to horizontal ground-water flow and contaminant migration, and likely act as pathways for vertical ground-water flow and contaminant migration. Pumping tests conducted on wells completed into each aquifer show strong boundary effects from graben bounding faults, demonstrate communication between the Abo and upper Madera formations aquifers underlying the site, and indicate that the aquifer matrix contributes relatively little water to the aquifer system.