Water Resources of Union Parish, Louisiana

By Angela L. Robinson, U.S. Geological Survey, with the Louisiana Department of Transportation and Development. Fact Sheet 2020–3002, March 2020.

Water use

In 2014, Union Parish in north-central Louisiana withdrew about 4.88 million gallons a day (Mgal/d): 4.70 from groundwater and 0.18 from surface water.

Figure 1: Union Parish, with its subbasins, stream gages, well Un-26, the line of the cross section, and the depth to the base of fresh groundwater. USGS.

• Public supply: about 89 percent (4.36 Mgal/d). Other uses: industry, rural domestic, livestock, rice and general irrigation.
• Trend: withdrawals, recorded every 5 years from 1960 to 2010 and in 2014, peaked in 2000 at about 8.89 Mgal/d.

Figure 2: withdrawals, 1960–2014. USGS.

Groundwater

The main freshwater aquifer is the Sparta, below the Cook Mountain confining unit (whose thin sand lenses give limited water). Above lie the Cockfield aquifer and, in the northeast, the Upland terrace and alluvial aquifers. Below, the Cane River confining unit and Carrizo-Wilcox aquifer hold only saltwater. The base of fresh groundwater (chloride 250 mg/L or less) in the Sparta lies about 500 to 600 feet below sea level (NGVD 29), deepening to the east-southeast.

Figure 3: an idealized west-to-east section through the parish's aquifers and confining units. USGS.

The Sparta:

• part of a large regional aquifer spanning several states; its base lies 600 to 800 feet below sea level, and saltwater appears only at the eastern edge, from about 750 feet down;
• recharged mainly by rain on its outcrop, plus leakage from rivers and other aquifers; water moves toward the parish's center and southeast, toward Ouachita Parish;
• 2012 water levels ranged from about 20 feet below sea level in the north to deeper than 120 feet in the south-central parish.

Figure 4: water levels in Sparta well Un-26, in the parish's southeast corner. USGS.

Recovering: levels in well Un-26 fell more than 50 feet from 1957 to 2003, then rose about 12 feet from 2004 to 2016 — likely thanks to groundwater conservation in south-central Arkansas.

Groundwater quality

Samples from 108 Sparta wells (1905–2016) and 7 Cockfield wells (1968–2014):

• median chloride, sulfate, iron and manganese within the EPA's secondary (taste and nuisance) limits;
• pH outside 6.5–8.5 in 38 percent of Sparta samples and 71 percent of Cockfield samples;
• soft water: median hardness 6 mg/L (Sparta) and 21 mg/L (Cockfield);
• dissolved solids above the 500 mg/L limit in more than 70 percent of Sparta samples, but in no Cockfield samples.

Surface water

Two subbasins drain the parish toward the southeast. In 2014, about 0.18 Mgal/d came from streams, almost all for livestock.

Surface-water quality (Corney Bayou 1943–84, Bayou de Loutre 1956–86): sulfate and iron generally within limits; pH outside the range in about 93 percent of Corney Bayou and 43 percent of Bayou de Loutre samples; manganese above its 50 micrograms per liter limit in every sample; moderately hard (Corney) to very hard (Loutre); median dissolved oxygen over 7 mg/L at both — above the 5 mg/L needed for diverse warmwater life including sport fish; color at or above the 15-unit limit.

Sources

Based on Water Resources of Union Parish, Louisiana, by Angela L. Robinson, USGS Fact Sheet 2020–3002, U.S. Geological Survey; a work of the United States government in the public domain. The four figures are taken from the fact sheet's PDF, which the import had left out; its water-quality tables are summarized here. The text gives streamflow as "ft/s" where cubic feet per second is meant.