Water Resources of St. John the Baptist Parish, Louisiana

St. John the Baptist Parish: freshwater areas of the Gramercy and Norco aquifers, the fresh Evangeline equivalent aquifer area north of the fault, and USGS monitoring sites. USGS.

Water use at a glance

In 2010 the parish withdrew about 67.5 million gallons a day (Mgal/d):

• 80% from surface water — almost all from the Mississippi River — and 20% from groundwater.
• Industry used 90% of it. Other uses: public supply, rural domestic, livestock and irrigation.

Measured every five years since 1960, withdrawals peaked in 1990 at about 110 Mgal/d. Industrial surface-water use dropped from 93.7 to 35.0 Mgal/d between 1980 and 1985 before rebounding to 91.0 in 1990.

Water withdrawals, 1960–2010. USGS.

Groundwater

The parish's fresh groundwater (chloride 250 mg/L or less) comes from the Chicot and Evangeline equivalent aquifer systems. The deeper Jasper system may hold a little freshwater in the north but is not a main source.

Where the freshwater is:

• South of the fault near Ruddock: fresh to about 700 feet below sea level (NGVD 29), in the Chicot system.
• North of the fault: fresh from about 200 to 900 feet in the Chicot system, and from about 2,300 to 3,100 feet in the Evangeline system — with saltwater in between.

Recharge comes from rain soaking in where the aquifers outcrop, north and northwest of Lake Pontchartrain; through the clay layers between aquifers; and from shallow aquifers fed by rain and by the Mississippi River. Water leaves through pumping and flow to neighboring aquifers.

In 2009 the state listed 112 active wells in the two systems: 52 domestic, 29 irrigation, 17 industrial and 14 public supply.

South-to-north hydrogeologic section through the parish: blue sands hold freshwater, tan sands saltwater (more than 250 mg/L chloride). Modified from Griffith (2003). USGS.

The Chicot equivalent aquifer system

Its main aquifers here are the Gramercy, Norco and Gonzales–New Orleans.

• Gramercy: sand grading from fine at the top to coarse sand and fine gravel below. Water levels in well SJB-145 rise and fall with the Mississippi River's stages, less so farther from the river. Samples from nine wells (1932–79) showed moderately hard to very hard water, pH 7.0–7.7, generally above EPA secondary limits for color, dissolved solids and iron; hardness rises with closer connection to river water.
• Norco: fine sand above, medium to coarse sand and perhaps fine gravel below. Samples met the pH limit but exceeded the limits for color and dissolved solids; 9 of 19 samples were soft, the other 10 moderately hard to very hard.
• Gonzales–New Orleans: very fine to fine sand, with saltwater beneath the freshwater in the east and northwest. Samples from 11 wells (1960–71) were soft, pH 7.7–8.4, above the color limit and often above the dissolved-solids limit.

Water levels in Gramercy aquifer well SJB-145 (land surface 17.71 feet above NGVD 29; well depth 315 feet). USGS.

The Evangeline equivalent aquifer system

North of the fault, freshwater lies in its deepest sand beds — fine to medium sands 50 to 200 feet thick, separated by clay and dipping south.

• Two active public-supply wells (2009), between Lakes Maurepas and Pontchartrain near Ruddock, 2,950 and 3,000 feet deep; one yields 2,120 gal/min.
• 3.93 Mgal/d pumped in 2010.
• Samples (1971–2005): soft water, above the secondary limits for pH and color.

Groundwater quality

Median values; EPA secondary limits in the last row:

Surface water

About 54.0 Mgal/d of surface water was withdrawn in 2010, 95% of it for industry — mostly for cooling, and returned to the river afterward. The rest went to public supply and irrigation. Nothing was withdrawn from the parish's lakes.

The Mississippi River

The river runs east through the middle of the parish and is its main source of freshwater: in 2010 it supplied all surface water for industry and public supply.

• At Red River Landing, about 170 miles upstream of Laplace, average flow was about 460,000 cubic feet per second (1928–76) — representative of the parish, since the river between is leveed with no major tributaries or outlets.
• At Luling, about 27 miles downstream of Reserve, samples from 1957–99 showed hard water that generally met the secondary limits for pH, chloride, sulfate and iron. Dissolved oxygen was generally above 5 mg/L, the minimum for a diverse community of warmwater fish, including sport fish.

The lakes

Sources

Based on Vincent E. White, Lawrence B. Prakken and Robert B. Fendick, Jr., "Water resources of St. John the Baptist Parish, Louisiana," U.S. Geological Survey Fact Sheet 2014–3102 (2015), prepared with the Louisiana Department of Transportation and Development; a work of the United States government in the public domain. The map, charts, section and tables are taken from the fact sheet's PDF. Data are from the USGS National Water Information System.