ASSESSING THE SUITABILITY OF THE HUECO BOLSON FOR A MANAGED AQUIFER RECHARGE PROJECT USING MUNICIPAL RECLAIMED WATER

Aquifer storage and recovery (ASR) utilizes injection wells for the storage and subsequent recovery of water within an aquifer for beneficial use, and aquifer recharge (AR) is the intentional recharge of an aquifer by injection well or other means of infiltration. This study evaluated the suitability of these types of managed aquifer recharge projects to meet growing water demands for the Lower Valley Water District (LVWD) in southern El Paso County, Texas. The hydrogeological characteristics of the geological units within the Hueco Bolson were examined to determine the best match for a project.

The lowermost units within the study area are the Paleozoic-Mesozoic units that underlie the Hueco Bolson. These units are faulted marine carbonates and are relatively deep, ranging from 200 to over 4,000 feet below ground surface, which makes AR impractical. Few wells have been drilled to this depth, but water at this depth is generally very saline. Although little data is available for these units, most flow likely occurs within faults and fractures, making them poorly suited for ASR as well.

The overlying units are the unconsolidated to poorly consolidated Miocene-Pleistocene Fort Hancock and Camp Rice formations, which were mapped as a single unit. The Fort Hancock Formation is composed of gravel, sand, and clay alluvial-fan deposits. The younger Camp Rice Formation is primarily sand and gravel braided stream deposits. The unique semi-confined nature of these deposits makes them the best candidates for AR projects within the study area. However, the high iron content and unconsolidated nature of these units has the potential to complicate injection well operations for ASR. Injection wells used by the City of El Paso at similar depths have had mechanical failures due to screen clogging.

The surficial deposits are unconsolidated sediments including the Rio Grande alluvium and eolian sand. These units are unconfined and heavily utilized for agriculture in the region and therefore were not considered for ASR or AR. This study also investigated potential sources of recharge water for the project, including the reclaimed water of an advanced wastewater treatment facility the LVWD plans to construct. The results show that an AR project that utilizes effluent from the planned wastewater facility could be viable for the LVWD.