Aquifers

Aquifers or Bolsons are underground areas that store significant amounts of water. After rain or melted snow the water will evaporate, get used by plants, runoff onto surface areas such as rivers, streams, or lakes. It can percolate through the porous soil and fill spaces between soil and rocks. Not all aquifers are the same; there are different soils, rocks and mineral types that make each aquifer unique. The aquifers in the El Paso area consist of very fine-grained sands and gravels. Water stored underground may be anywhere from days old to thousands of years old, it depends on the depth of the aquifer.

Hueco Bolson

Hueco Bolson is the principal aquifer for the El Paso-Juarez area. It occupies the majority of El Paso County. It extends from the Franklin Mountains on the west, to the Hueco Mountains on the east. The Hueco Bolson extends northward in to New Mexico and southward into Mexico. In 2002, El Paso pumped about 30 percent of its water from the Hueco Bolson. In 2001 pumping was 44 percent, while in 2000 it was 47 percent. In an effort to meet future demands, the Hueco Bolson will continue to be used as a major source of water that is either fresh or slightly brackish, since it contains a layer of brackish water (water which has a greater amount of salt). After many years of groundwater pumping, the quality of the groundwater in selected areas of the Hueco Bolson has become more brackish. As a result the concerns about water available and levels of salinity in the El Paso are has increased. Groundwater flow models are being used as a tool to predict how the aquifers might respond to pumping, and better understand the complex interaction between the fresh and brackish water. The brackish water will be desalinated as part of the Fort Bliss/El Paso Water Utilities Joint Desalination Project. The project is underway as the plant is designed as the plant is designed with a capacity of 27.5 million gallons of water per day. It will include a learning center to assist the community in understanding the treatment process of drinking water and increase awareness of the challenges this region faces in the Chihuahuan Desert. The plant is expected to be operational in the year 2006.

Ciudad Juarez, which has roughly double the population of El Paso, depends 100 percent on water from the Hueco Bolson to meet its demands. The groundwater in Juarez is brackish and other future sources of quality water are being currently investigated.

Mesilla Bolson

The Mesilla Bolson is located primarily in New Mexico with small portions in Mexico and Texas. The northern boundary of the Mesilla Bolson is the Robledo and Doña Ana mountains. Much of the southern boundary is in Mexico, while the western boundary is formed by the West Potrillo and the East Potrillo mountains. The eastern boundary is the Franklin Mountains.

The main hydrologic feature of the Mesilla Bolson is the Rio Grande. The river enters the basin through Selden Canyon and runs through the Mesilla Valley and exits as it narrows in El Paso. The Rio Grande and the irrigation system fed by the Rio Grande are considered the main source of recharge to the Mesilla Bolson. Water levels in the aquifer remain relatively constant with fluctuations being primarily in response to flows in the Rio Grande and irrigation canals and drains.

Glossary

Water Table
The top of the underground area where every available space is filled with water (saturation).

Confined Aquifer.
An aquifer that is surrounded by impermeable layers that transmit water slower than the aquifer. This aquifer is under pressure and can also be called an artesian aquifer.

Unconfined Aquifer
An aquifer without protective material above. It is vulnerable to contamination from surface activities.

Permeable Layer
Portion of aquifer that contains porous rock materials that allow water to penetrate freely.

Impermeable Layer
Portion of aquifer that contains rock material, or clay layer, that does not allow water to penetrate or pass through easily.

Down gradient
The direction in which groundwater flows; similar to down hill for surface water flows

Gravity
The natural force of attraction exerted by Earth on objects or materials on its surface that tends to draw them down toward its center

Injection Wells
Deep wells that place water back into the aquifer.

Intrusion
To force a substance into another, such as seawater into a natural fresh water source.

Percolate
Downward movement of water through the soil layers.