Recharge Rates for the Major Aquifers

The attached table contains recharge rates for 8 major aquifers including the Carrizo-Wilcox, Gulf Coast, High Plains, Edwards-Trinity, Trinity, Seymour, Cenozoic Pecos Alluvium, and Hueco-Mesilla Bolson aquifers. Recharge rates for the Edwards aquifer can be found in Slattery et al., 1998, and in annual reports published by the Edwards Aquifer Authority (e.g., EAA, 2000). Recharge data were compiled from reports published by the Texas Water Development Board, U.S. Geological Survey, and other publications. The table lists the study areas (counties or general area), underlying aquifers, recharge rates (units of mm/yr, inches/yr, or total recharge in acre-feet/yr), data sources, and techniques used to estimate recharge. Additional notes are provided in some cases. The full reference citations are listed separately.Bureau of Economic Geolog

Evaluation of Electromagnetic Induction as a Noninvasive Technique for Monitoring Water Movement into and Beneath Waste Disposal Facilities

The purpose of this study was to evaluate the use of electromagnetic induction to noninvasively monitor water content in waste disposal facility cover soils. We compared apparent electrical conductivity measurements monitored with the EM38 ground conductivity meter with water content monitored with a neutron probe at 20 locations over an 18-month period from August 1998 to January 2000. Two cover designs were monitored: a gel/asphalt barrier at 1.3 m depth and a capillary barrier at 2.0 m depth. The EM38 instrument was operated in both the vertical and horizontal dipole modes with the instrument resting on the ground surface and all data were normalized to 25°C. Linear regression techniques were applied to analyze the survey data. Water content to a depth of 0.75 m was correlated with horizontal dipole mode data and water content to depths of 1.1 m and 1.5 m was correlated with vertical dipole mode data. Initially higher water content values decreased by an average of 0.10 m^3/m^3 in the top 0.75 m and an average of 0.07 m^3/m^3 in the top 1.5 m over the course of the study. The regression model of the EM38 vertical dipole mode data with water content to the 1.5 m depth for all locations monitored on the capillary barrier design resulted in a standard deviation of 0.016 m^3/m^3. Horizontal dipole mode data correlated with water content to the 0.75 m depth had a standard deviation of 0.022 m^3/m^3 for all locations on both barrier designs. Models at individual survey locations generally exhibited much smaller standard deviations, ranging from 0.005 to 0.018 m^3/m^3 and averaging 0.010 m^3/m^3. The smaller standard deviations and general similarity of regression slope values of the models at individual locations indicate that this technique is more accurate as an indicator of changes in water content than as an indicator of the absolute value of water content at a given location. Sources of variability were attributed to horizontal and vertical variation in soil salinity, the vertical distribution of water at the time of a particular survey, and subtle differences in topsoil thickness and surface roughness. Results indicate that electromagnetic induction is useful for evaluating infiltration. The EM technique resulted in standard deviation values for water content similar to those of the neutron probe method but is capable of monitoring larger areas much more rapidly and at a lower cost.Bureau of Economic Geolog

Evaluation of Groundwater Nitrate Contamination in Major Aquifers in Texas

Nitrate is the most widespread groundwater contaminant in Texas and in the U.S. There are many potential adverse health implications of elevated groundwater nitrate, including methemoglobinemia and cancer risks. There are a variety of sources of nitrate, including natural sources, inorganic and organic fertilizers (manure), output from concentrated animal feeding operations (CAFOs), septic tanks, and leaking sewer systems. Natural sources result from nitrogen fixation by legumes, mineralization of organic matter (nitrification), and natural geologic sources. Many previous studies have been conducted on groundwater nitrate contamination in Texas. The early studies focused on source identification using nitrogen isotopes, mainly distinguishing between nitrate from fertilizers and septic tanks. Groundwater nitrate levels were expected to be high in the Ogallala Aquifer beneath playas adjacent to concentrated animal feeding operations; however, many studies showed that nitrate levels were reduced by denitrification attributed to high levels of organic matter. A recent study suggested that nitrate contamination has been increasing in the state over the past several decades and identified the Seymour aquifer in the Rolling Plains as a hotspot of groundwater nitrate contamination. A study evaluated controls on groundwater nitrate contamination using logistic regression, indicating that precipitation, percent of agricultural land, low-density residential land, and soil organic matter were the dominant explanatory variables. Unsaturated zone sampling was used to link land surface processes to groundwater nitrate levels and suggested that much of the elevated nitrate levels in the Ogallala and Seymour aquifers could be attributed to high levels of natural nitrate prior to cultivation that was oxidized during cultivation and mobilized into the underlying aquifer. The current study examined the distribution of groundwater nitrate in major and minor aquifers in the state using approximately 10,000 analyses from major aquifers and approximately 2,000 analyses from minor aquifers. Approximately 70% of the samples in the major and minor aquifers exceeded the detection levels for nitrate. The majority of the samples are from rural domestic and irrigation wells. A total of 5.5% of the samples from the major aquifers exceeded the MCL, with the highest level of contamination in the Seymour Aquifer (61% of sampled > MCL), followed by the Pecos Valley Aquifer (11%), Ogallala Aquifer (9%), Edwards Trinity High Plains (6%), and the remaining major aquifers < 2%. Groundwater nitrate concentrations generally decreased with depth.Bureau of Economic Geolog

Groundwater Recharge in Texas

Groundwater recharge is critical in evaluating water resources. Recharge estimates are required for groundwater models being developed as part of the Groundwater Availability Modeling program at the Texas Water Development Board. The purpose of this study was to assess the status of data on recharge for the major aquifers in Texas, evaluate the reliability of the recharge estimates, develop conceptual models for recharge for each of the aquifers, review techniques for quantifying recharge, and recommend appropriate techniques for quantifying the recharge of each of the major aquifers. Recharge rates for all major aquifers were compiled from published reports. The Edwards aquifer is the most dynamic, and recharge rates are highly variable spatially and temporally. Recharge is fairly accurately quantified using stream-gauge data. Estimates of recharge rates in the Carrizo-Wilcox aquifer range from 0.1 to 5.8 in/yr. The higher recharge rates occur in the sandy portions of the aquifer (i.e., the Carrizo and Simsboro Formations). Reported recharge rates for the Gulf Coast aquifer (0.0004 to 2 in/yr) are generally lower than those for the Carrizo-Wilcox aquifer. In both the Carrizo-Wilcox and Gulf Coast aquifers, higher recharge rates are estimated in upland areas containing sandy soils. Regional recharge rates in the High Plains aquifer, outside irrigated areas, are generally low (0.004 to 1.7 in/yr), whereas playa-focused recharge rates are much higher (0.5 to 8.6 in/yr). Irrigated areas also have fairly high recharge rates (0.6 to 11 in/yr). Recharge rates in the Trinity and Edwards-Trinity Plateau aquifers generally range from 0.1 to 2 in/yr. The Seymour aquifer has recharge rates that range from 1 to 2.5 in/yr. Recharge rates for the Hueco-Mesilla Bolson and the Cenozoic Pecos Alluvium are represented as total recharge along mountain fronts and valley floors.Bureau of Economic Geolog

Assessment of Groundwater Contamination, in Situ Treatment, and Disposal of Treatment Residuals in the Vicinity of Lubbock, Texas

This report presents an assessment of groundwater contamination potential, in situ treatment technologies for drinking water supply, and assessment of injecting ex situ treatment residuals into the source aquifer in the vicinity of Lubbock, Texas. The study area surrounding Lubbock includes the following nine counties: Lubbock, Lamb, Hale, Floyd, Crosby, Garza, Lynn, Terry, and Hockley Counties. Many public water supply wells in the region exceed the maximum contaminant levels (MCLs) for the following water quality constituents of concern (COCs): nitrate (NO3), arsenic (As), fluoride (F), selenium (Se), uranium (U), and radium-226 (Ra-226), and radium-228 (Ra-228). The study was divided into three main tasks: (1) stratification of naturally occurring contaminants in groundwater; (2) potential for in situ treatment; and (3) potential for disposal of treatment residuals in drinking water. Task 1 was conducted by the Bureau of Economic Geology, and tasks 2 and 3 were conducted by CH2M Hill under subcontract to the Bureau of Economic Geology.Bureau of Economic Geolog

Identification of geographic areas in Texas suitable for groundwater banking

The population in Texas is expected to double in the next 50 years, increasing from approximately 21 million in 2000 to approximately 40 million by 2050. During this same period, water demand is projected to increase by 18 percent, from nearly 17 to 20 million acre-feet. Texas' water supplies are also diminishing as a result of droughts, historical and ongoing overdrafts of aquifers in excess of natural recharge rates, pollution of available supplies, and limitations on use that result from environmental regulation such as total maximum daily load requirements and requirements of the Endangered Species Act. Despite increasing demand and dwindling supply, only eight surface water reservoirs with conservation storage greater than 5,000 acre-feet are expected to be built in the next 50 years. Consequently, alternative approaches will be required to meet future water demand, particularly during periods of drought. One approach to meet the increasing water demand is to artificially recharge groundwater supplies with excess surface water. Artificial recharge of groundwater, or "groundwater banking," is becoming more common in the U.S., particularly in semiarid states such as California and Arizona, as a means to manage water resources and meet water demands during periods of extended droughts. The storage volume available in aquifers is generally much greater than that available in surface reservoirs. This report documents a study performed by Daniel B. Stephens & Associates, Inc. and the Bureau of Economic Geology on behalf of the Texas Water Development Board. The goal for this project was to identify regions in Texas that are potentially suitable for groundwater banking. Although there are a variety of methods for artificially recharging aquifers with surface water, this study only considered recharge from spreading (or infiltration) basins on the land surface, although an overview of other techniques and examples of their application in Texas is provided.Bureau of Economic Geolog

Recent La Plata basin drought conditions observed by satellite gravimetry

The Gravity Recovery and Climate Experiment (GRACE) provides quantitative measures of terrestrial water storage (TWS) change. GRACE data show a significant decrease in TWS in the lower (southern) La Plata river basin of South America over the period 2002-2009, consistent with recognized drought conditions in the region. GRACE data reveal a detailed picture of temporal and spatial evolution of this severe drought event, which suggests that the drought began in lower La Plata in around austral spring 2008 and then spread to the entire La Plata basin and peaked in austral fall 2009. During the peak, GRACE data show an average TWS deficit of ~12 cm (equivalent water layer thickness) below the 7 year mean, in a broad region in lower La Plata. GRACE measurements are consistent with accumulated precipitation data from satellite remote sensing and with vegetation index changes derived from Terra satellite observations. The Global Land Data Assimilation System model captures the drought event but underestimates its intensity. Limited available groundwater-level data in southern La Plata show significant groundwater depletion, which is likely associated with the drought in this region. GRAC-observed TWS change and precipitation anomalies in the studied region appear to closely correlate with the ENSO climate index, with dry and wet seasons corresponding to La Ni\~na and El Ni\~no events, respectively