Wednesday, February 08, 2017Register
 Edwards Aquifer Groundwater Quality

Using data provided by the Texas Water Development Board, the figures and maps shown below were developed to show how levels of certain constituents fluctuate spatially and temporally. Many of the threatened and endangered species listed in the area are extremely sensitive to changing conditions; abnormally high levels of certain constituents could threaten their sensitive environment. For example, the Comal Springs Riffle Beetle (Heterelmis comalensis), which is on the Federally Endangered list, has a very limited habitat that is threatened by groundwater contamination, including constituents associated with human sewage, animal waste, agricultural chemicals and urban runoff.

Data Evaluation

Some sampling stations had numerous samples, while others had very few. This discrepancy was addressed by standardizing the data into percent exceedance according the maximum contaminant level (MCL) or secondary maximum contaminant level (SMCL); calculated as the number of samples (for a given parameter collected at a specific location and time) exceeding the associated water quality standard, divided by the total number of samples collected (of the same parameter collected at the same location and time). These were then categorized as Below MCL, At MCL, Above MCL or Over 10X MCL, according to the representation of the data. If there were less than ten samples at any one site, that site was determined to not have enough data to be considered in the analysis.

 Precipitation & Groundwater Quantity Relationships

Edwards PRISM precipitation  
Click on Image to View Precipitation Map  


Groundwater is not an infinite resource; supplies are often impacted by human influence, such as pumping. Generally, groundwater is supplied from precipitation infiltrating the soil and percolating down to the aquifer where groundwater is stored. This process is known as recharge. The Edwards Aquifer is a karst aquifer, meaning that the aquifer is lined with soluble rock such as limestone. The high permeability of the fractured rock leads to rapid rates of recharge, which means the aquifer's recharge is greatly affected by the rainy season.

The figures in "Groundwater Quantity in Edwards Aquifer" show changes to the water table in Edwards Aquifer in a stepwise decadal approach. Changes to aquifer water levels in springs and caves can threaten the unique biodiversity of the area.

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