Breakdown: Why Memphis’ water supply is so unique

MEMPHIS, Tenn. (WMC) - Memphis is home to many unique treasures, but perhaps one of the most vital and coveted is its magnificent drinking water.

While most of the world’s drinking water originates from surface lakes, streams and rivers, Memphians enjoy the unique privilege of water derived from deep underground from the Memphis aquifer (also known as Sparta aquifer or Memphis Sand).

In fact, Memphis, Tennessee is the largest U.S. city that relies 100% on groundwater to meet its every need.

An aquifer is a layer of sand, silt, or rock underground that contains water. The aquifers in our area are primarily composed of sand, where the spaces in between sand grains hold water.

The aquifer system below our feet has many layers made up of fine-to coarse-grained sand interbedded with layers of clay and minor amounts of lignite.

• Lignite is a dark brown to black combustible mineral formed over millions of years by the partial decomposition of plant material subject to increased pressure and temperature in an airless atmosphere. In simple terms, lignite is coal.

These layers act as a natural filter removing many impurities from the water.

Below is a cross-section of the aquifer, showing you what you’d see if you cut the land beneath us southeast to northwest:

In each layer, the water moves at different rates and directions. The layers in tan/blue are comprised primarily of sand saturated with water: these are called aquifers.

The aquifers are separated by the gray layers made of clay, a dense material that pressurizes the groundwater and protects it from contamination. When the clay is absent, the groundwater is more prone to contamination.

The brown layer just below Memphis also contains water and is often referred to as the shallow aquifer. It is made of silt, gravel, sand, and clay deposited by rivers and wind.

When the Memphis aquifer was discovered in 1886, a well punctured through the confining clay and clear, cold water sprang to the surface naturally! No effort was needed in 1886 to obtain Memphis aquifer water because of the underground pressure and the artesian effect.

Now, we need mechanical pumps to bring the water to the surface. The wells connected into this system are commonly known as “artesian wells” because they draw the naturally purified water to the surface by releasing the built-up pressure which forces the water up the well like liquid through a straw.

• Here, you can view the historical Story Map detailing the yellow fever epidemic, sewer invention, and Memphis aquifer discovery from the Center for Applied Earth Science and Engineering Research (CAESAR) at University of Memphis.

Its protective clay layer acts as a barrier to the shallow aquifer, which is known to be polluted in places throughout Shelby County from decades of modern human activity.

Over the years, researchers have discovered breaches in the upper protective clay layer where it is missing or thin. This creates a connection between the shallow aquifer and the Memphis aquifer that can impact drinking water quality. The map below depicts 16 breach locations identified so far:

Current investigations are underway to further map breaches and understand their potential water quality impacts to the Memphis aquifer.

The good thing about the natural sand aquifer is that water travels through it very slowly.

In 2018, CAESER at the University of Memphis was awarded $1 million a year from Memphis Light, Gas and Water (MLGW) to study the clay breaches in the Memphis aquifer and their impacts to water quality. A study of this scale has never been conducted on the Memphis aquifer.

MLGW’s Water Quality Assurance Laboratory conducts more than 100 tests a day to ensure water quality and safety.

The goals will help MLGW determine a water pumping regime and well placements that minimize water quality degradation and make sure the water you are drinking, bathing in, and cooking with remains one of the highest quality sources in the United States.

According to the Cooper-Young Community Association (CYCA), “the Memphis aquifer is still one of the highest-quality drinking water sources in the United States and WORLD, but it’s crucial for the residents of Memphis and Shelby County to understand what the research discovers so you can influence smart planning to ensure a clean water source far into the future.”

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