Memphis advances major aquifer study to map contamination risks amid 31% drop in water demand

Memphis advances major aquifer study to map contamination risks amid 31% drop in water demandA joint study by Memphis Light, Gas and Water (MLGW) and the University of Memphis has identified up to 100 potential breaches in the clay layer protecting the Memphis Aquifer, prompting advanced subsurface mapping to safeguard the city's drinking water wellfields.

MLGW water withdrawals have decreased by 31.6% since 2000, dropping to 100 million gallons per day despite adding 10,000 customers.

The five-year CAESER Aquifer Study, funded by ARPA money and a 1% MLGW water rate allocation, aims to locate breaches in the protective clay layer above the aquifer.

Researchers estimate there are 70 to 100 breaches in Shelby County, significantly higher than the seven initially identified in the 1980s.

The study is utilizing electric resistivity tomography and has collected 1,300 sediment samples during MLGW well drilling to map the subsurface and measure hydraulic conductivity.

Contaminant travel times from the surface to the shallow water table can be as short as three months in wet conditions, emphasizing the need for sentinel monitoring wells.

Memphis Light, Gas and Water (MLGW) and the City of Memphis are aggressively mapping vulnerabilities in the Memphis Aquifer to protect the city's drinking water supply from surface contamination. During a July 21 presentation to the City Council, officials outlined the progress of the Center for Applied Earth Science and Engineering Research (CAESER) Aquifer Study 2, a five-year initiative launched in 2023. The study is funded through municipal American Rescue Plan Act (ARPA) funds and a 1% allocation on MLGW water rates. Led by Dr. Brian Waldron of the University of Memphis, the project involves 28 focus areas ranging from geochemistry to numerical modeling of groundwater flow. A primary focus of the research is identifying breaches in the protective clay layer that separates the shallow aquifer from the deeper Memphis Aquifer—the fourth largest aquifer in the United States. While historical data from the 1980s suggested only seven breaches existed, an aerial electromagnetic survey from an initial 2018 study indicated between 70 and 100 breaches across Shelby County. These gaps provide pathways for legacy surface pollution to bypass the clay barrier and enter the drinking water supply. To locate breaches in urban areas where aerial surveys are restricted by the FAA, researchers are deploying ground-based electric resistivity tomography and sTEM technologies. The team has also analyzed hundreds of well logs, discovering that the confining clay layer is, on average, 19.4 feet thinner than previously thought, with maximum reductions of over 90 feet. This analysis alone identified 13 potential new breaches. Additionally, the study is measuring hydraulic conductivity to understand how fast groundwater and potential contaminants move. Researchers have collected 1,300 sediment samples during MLGW well drilling over the past three years to establish accurate measurements. Dr. Waldron noted that vadose zone travel times—the time it takes for surface spills to reach the water table—can be as short as three months in wet conditions, highlighting the threat of chronic, unnoticed spills. To proactively manage these risks, the study aims to partner with the local health department to install sentinel monitoring wells between potential contamination sources and MLGW production wellfields. Researchers are also investigating arsenic levels in the Ensley Bottoms area of Southwest Memphis, though current data suggests the concentrations are within the natural range for the Mississippi River Valley alluvium. Despite the contamination risks, MLGW President Doug McGowan emphasized that the aquifer remains healthy and naturally recharging, largely due to significant reductions in water demand. MLGW is currently delivering approximately 100 million gallons per day (MGD), down from 137 MGD in 2000. This 31.6% decrease was achieved even after adding 10,000 new customers, a trend McGowan attributed to the widespread adoption of low-flow plumbing fixtures and water conservation efforts.