Water Resources of the Southern Hills Aquifer System, Southeastern Louisiana

The Southern Hills regional aquifer system underlies ten parishes of southeastern Louisiana: West Feliciana, East Baton Rouge, East Feliciana, Livingston, Pointe Coupee, St. Helena, St. Tammany, Tangipahoa, Washington and West Baton Rouge. This U.S. Geological Survey fact sheet, prepared with the Louisiana Department of Transportation and Development, sets out how much groundwater there is, how it is used and how good it is, for water managers, residents and others.

How much groundwater is used

In 2014 the ten parishes withdrew about 293 million gallons of groundwater a day (Mgal/d). Most came from the regional aquifer system, but in the west the Mississippi River alluvial aquifer is also a major source. Public supply took about 48 percent (140.34 Mgal/d) and industry about 32 percent (94.34). Records kept every five years from 1960 to 2010, and again in 2014, show withdrawals at their highest in 2014. East Baton Rouge Parish withdrew the most (148.26 Mgal/d) and St. Helena the least (1.79).

Groundwater withdrawals by parish in 2014; darker shading means more water drawn. USGS.

Groundwater withdrawals in the ten parishes, 1960–2014. USGS.

Three aquifer systems

Fresh groundwater — no more than 250 milligrams per litre of chloride — lies in three aquifer systems, from shallowest to deepest: the Chicot equivalent, the Evangeline equivalent and the Jasper equivalent. They extend across most of southeastern Louisiana and consist of silt, sand and gravel separated by patchy layers of clay and sandy clay. They dip and thicken to the south and hold fresh water to more than 3,500 feet below the National Geodetic Vertical Datum of 1929 (NGVD 29). They are recharged mainly by rain where they reach the surface, across the north of the area and in southwestern Mississippi.

The Mississippi River alluvial aquifer runs along much of the western edge of East Baton Rouge and West Feliciana Parishes and through Pointe Coupee and West Baton Rouge. In places it is connected to the Chicot system, but it is not part of the Southern Hills system.

The Southern Hills regional aquifer system: depth to the base of fresh groundwater, faults, and the monitored wells. USGS.

How pumping has changed the flow

Before the aquifers were developed, from the late 1800s on, groundwater generally flowed south toward the Mississippi and Pearl Rivers. Pumping has changed that in places, especially around Baton Rouge, where large regional cones of depression have formed in the water levels — water now moves toward their centres from all sides. A smaller one has formed near Bogalusa in the Jasper system.

The Baton Rouge Fault generally marks a sharp change in fresh water. North of it, fresh groundwater reaches down into the Jasper system, in places deeper than 3,500 feet below NGVD 29. South of it, fresh water is generally confined to the Chicot system, reaching only a little way south in the Evangeline and Jasper systems in some areas. Heavy pumping around Baton Rouge has drawn saltwater north across the fault into freshwater areas in some places.

A north–south section through the western part of the aquifer system, showing fresh water and saltwater in its sands. USGS, adapted from Griffith (2003).

Water levels and withdrawals

Water levels stayed stable in wells in the upper Chicot from 2002 to 2011, but fell in the lower Chicot in the west of the area from 1991 to 2012. In monitored Evangeline and Jasper wells, levels have generally fallen over the last 20 to 60 years because of pumping, most near the pumping centres in and around Baton Rouge.

In 2014, withdrawals grew with depth: Chicot 40.99 Mgal/d, Evangeline 100.35 and Jasper 118.8. Another 31.99 Mgal/d came from the Mississippi River alluvial aquifer, mostly in Pointe Coupee (28.05) and West Baton Rouge (3.87).

The "foot" sands are the named aquifers of the Baton Rouge area.

Water quality

Samples from 1,522 wells in the three systems show soft water, generally within the Environmental Protection Agency's secondary guideline for dissolved solids. Median pH and temperature rise with depth. Iron and manganese can greatly exceed the guidelines in places.

The fact sheet's text says the water does not exceed the dissolved-solids guideline; its table shows 95 percent of Chicot samples and 99 percent of Evangeline samples within it.

Sources

• U.S. Geological Survey, in cooperation with the Louisiana Department of Transportation and Development, Water Resources of the Southern Hills Regional Aquifer System, Southeastern Louisiana, Fact Sheet 2017–3010, March 2017. https://doi.org/10.3133/fs20173010
• USGS Lower Mississippi-Gulf Water Science Center: http://la.water.usgs.gov