78-6 The Role of Quarries in Elevation of Nitrate Concentration in the Karstic Edwards Aquifer, Texas

Session: New Frontiers in Cave and Karst Science

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Abstract:

Nitrate concentrations are elevated above background levels in the San Antonio Segment of the karstic Edwards Aquifer. Published reports have largely attributed the higher concentrations to the effects of urbanization, particularly over the Edwards Aquifer Recharge Zone.  However, neither the geographic distribution nor the historical changes of nitrate in the aquifer can be explained by urbanization alone.

 The Edwards Aquifer Recharge Zone has extensive development of limestone quarries which, in other regions, are recognized to contribute nitrate pollution to groundwater. Aggregate mining operations commonly use large quantities of highly-soluble ammonium-nitrate fuel-oil (ANFO) mixtures as explosives. That, combined with reports that as much as 30 percent is not consumed by blasting makes ANFO a potential groundwater pollutant. Texas Water Development Board groundwater-quality data show that both the timing and geographic distribution of rising nitrate concentrations in the Edwards Aquifer fit well with the timing and distribution of ANFO use in limestone quarries on the Edwards Aquifer Recharge Zone. Evaluation of the timing and distribution of all potential contributors of nitrate to the aquifer indicate ANFO use is a significant contributor.  In recent years nitrate concentrations in the Edwards Aquifer have reached a level potentially harmful to some groundwater organisms.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-5372

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