INVESTIGATING GROUNDWATER/SURFACE WATER INTERACTION OF GRAVEL PIT LAKES IN THE BRAZOS RIVER ALLUVIUM AQUIFER

In Texas, it is common for sand and gravel pit mines within shallow, unconfined aquifers to be left unremediated and allowed to fill with water from the aquifer, equilibrating to the water table surface elevation, and forming a “gravel pit lake”. Two such gravel pit lakes in central Texas were examined over the course of two years with upgradient and downgradient piezometer installations. Groundwater and lake waters were sampled bimonthly for water chemistry and surface elevation. In addition, rain and lake gauges and mini-piezometers were installed, depth surveys were conducted, and a simple 2D flow model was constructed. The project goal was evaluating and examining flow dynamics and chemical effects as groundwater flows to surface water and back to groundwater with the intent to understand the effects that gravel pit lake systems have on connected shallow groundwater. Both lake systems were shown to be flow-through systems that influence the water quality by decreasing the dissolved nutrients in the groundwater in their vicinity while oxygenating the water and altering the pH. However, the lakes are also prone to high levels of evaporation, meaning that minor improvements to water quality may come at the cost of decreasing the quantity of water storage within the aquifer. Similar groundwater and mine lake systems may show comparable tendencies, providing new information for water managers, regulators, and stake-holders about the potential roles that non-remediated gravel pit lakes may play in local ecosystems and aquifer dynamics.