Hydrogeological Report: Lipan Aquifer, Texas
This report examines the Lipan Aquifer, a minor aquifer located in Tom Green, western Concho, and southern Runnels counties in west-central Texas. The paper reviews the aquifer's geological composition, water quality limitations, and variable well yields, and traces the history of groundwater use from the onset of irrigation in the 1940s through the drought conditions of the late 1990s. It discusses recharge mechanisms, potentiometric surface changes, and the water supply challenges facing the city of San Angelo. The report concludes by evaluating competing simulation models and recommending further study to inform technical and policy decisions about long-term aquifer management and groundwater availability.
- Introduction to the Lipan Aquifer: Geology, location, water quality, and classification
- Problem Statement: Groundwater Depletion: Irrigation expansion and aquifer water-level decline
- Well Yields and Aquifer Productivity: Variable yields, conductivity, and potentiometric changes
- Recharge Sources and Hydrological Dynamics: Gain-loss studies, spring flow, and precipitation recharge
- Drinking Water Access for San Angelo: Evaporation losses, reservoirs, and inter-city cooperation
- Summary and Recommendations: Simulation projections and future management needs
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What makes this paper effective
- Grounds claims in specific quantitative data — gallons per minute, acre-feet per year, population figures — which gives the report credibility and precision.
- Traces a clear historical arc from the onset of irrigation in the 1940s through the drought of the late 1990s, showing cause-and-effect relationships between human activity and aquifer depletion.
- Balances technical hydrogeological detail (hydraulic conductivity, potentiometric surface maps, gain-loss studies) with accessible policy discussion about inter-city water cooperation.
Key academic technique demonstrated
The report demonstrates effective integration of primary technical sources — USGS water-resources reports, TWDB groundwater availability models, and published capacity test data — with secondary journalistic and census sources to build a multi-dimensional picture of a regional resource problem. This blending of technical and policy evidence is characteristic of applied environmental science writing.
Structure breakdown
The paper opens with a geological and regulatory introduction to the aquifer, then moves to a problem statement quantifying irrigation-driven depletion. Subsequent sections address well productivity, natural recharge dynamics, and municipal water supply pressures before closing with a summary that compares competing simulation projections and calls for further study. The progression moves logically from physical description to human impact to policy response.
Introduction to the Lipan Aquifer
Located in the Lipan Flats area of Tom Green, western Concho, and southern Runnels counties, the Lipan is classified as a minor aquifer by the Texas Water Development Board (TWDB). It is used primarily for irrigation, with limited use for livestock and rural domestic purposes (Lee 1986). However, the chemical quality of Lipan Aquifer water does not meet drinking water standards (Lee 1986). Drinking water drawn from the aquifer may contain radon at rates just above safety levels established by the Environmental Protection Agency (EPA).
Upwards of 125 feet of saturated alluvial deposits of the Leona Formation of Quaternary age make up the aquifer (Lee 1986). Part of the aquifer's constitution is comprised of the "updip portions of the underlying dolomites, limestones, and shale of Permian age" (Lee 1986). These structures are hydrologically continuous with the alluvial deposits of the Leona Formation and contain slightly saline water. The groundwater in the Leona Formation proper is very hard, ranging from fresh to slightly saline (Lee 1986).
Natural discharge of the Lipan Aquifer occurs through seepage into the Concho River and by evapotranspiration wherever the land surface is close to the water table. Well yields generally range from 100 gallons per minute (gpm) to in excess of 1,000 gpm.
Problem Statement: Groundwater Depletion
Groundwater usage in the aquifer has been heaviest in the Lipan Flats agricultural areas lying in eastern Tom Green and western Concho counties. From the 1950s to the 1980s, well records show a moderate increase in usage. Irrigation in the area began in the 1940s, and pivot irrigation systems were introduced in the late 1980s, increasing irrigation pumping from approximately 15,000 acre-feet per year (AFY) to over 70,000 AFY. The number of wells increased dramatically, expanding from about 200 wells in 1990 to more than 1,000 wells by 2000.
Heavy irrigation pumping coupled with periods of drought brought about a significant decrease in water levels in some areas. The net result was that irrigation pumps in some areas could be operated throughout the growing season while, in other areas, irrigation pumping was substantially reduced.
Well Yields and Aquifer Productivity
Well yields in the Lipan Aquifer vary substantially across even short distances, ranging from less than 10 gpm to over 500 gpm (Collier 2011). Drillers report that the highest production is extracted from relatively small geographic zones (Collier 2011). Published capacity test results indicate less than 5 gpm/ft to over 100 gpm/ft (Collier 2011). These figures indicate that the hydraulic conductivity of the aquifer is characterized by large variations (Collier 2011). Two areas of the Lipan Aquifer demonstrate the highest productivity, and both are oriented parallel to the strike of the geologic units, suggesting that the underlying geology is a factor in the permeability of the aquifer units (Collier 2011).
Comparisons of potentiometric surface maps showing water levels collected in 1950 and 2000 indicate an overall decrease in water levels at the center of the Lipan Flats area (Collier 2011). Interestingly, water levels in the proximal Edwards-Trinity wells and at the edges of the Lipan Aquifer did not change significantly during this period. Theoretically, low groundwater levels near the Concho River may permit surface water to recharge the aquifer where it is near the stream. Hydrographs for wells outside the Lipan Flats also show smaller water-level declines than wells located in the middle of the Lipan Flats area.
The population of San Angelo grew from 52,093 in 1950 to 93,804 in 2010. The convergence of factors in the 1990s — increased irrigation pumping, drought, and population growth — caused water levels in many wells to drop 30, 60, and even 100 feet (Collier 2011).
References
Aquifers in Paleozoic Rocks, Ground Water Atlas of the United States, HA 730-E. http://pubs.usgs.gov/ha/ha730/ch_e/gif/E118.GIF (Accessed October 11, 2011).
Beach, James A., and Stuart T. Burton. "The Lipan Aquifer." In Ground Water Reports, R360AEPC. (Accessed October 11, 2011).
Beach, James A., Stuart Burton, and Barry Kolarik. Groundwater Availability Model for the Lipan Aquifer in Texas. June 2004. http://www.twdb.state.tx.us/gam/lipan/Lipan_GAM_Final%20Report_Part1.pdf (Accessed October 11, 2011).
Collier, Kiah. "City Trying to Minimize Water Loss: About 1.3 Million Gallons Evaporate Daily." San Angelo Standard-Times, August 1, 2011. (Accessed October 11, 2011).
Fact Finder. U.S. Census Bureau. http://factfinder2.census.gov (Accessed October 11, 2011).
Lee, J. N. "Shallow Ground-Water Conditions, Tom Green County, Texas." U.S. Geological Survey Water-Resources Investigations Report 86-4177 (1986): 41. http://www.twdb.state.tx.us/publications/reports/groundwaterreports/gwreports/R345%20Aquifers%20of%20Texas/Minors/lipan.pdf (Accessed October 11, 2011).
Zamudio, Justin. "San Angelo in Talks with Abilene, Midland on Future Water Supply." San Angelo Standard-Times, March 17, 2011. (Accessed October 11, 2011).
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