U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2016-3100

February 2017

Prepared in cooperation with the Louisiana Department of Transportation and Development 

Water Resources of Iberia Parish, Louisiana

Introduction 

Information concerning the availability, use, and 

quality of water in Iberia Parish, Louisiana (fig. 1), is critical 

for proper water-resource management. This fact sheet 

summarizes the availability, past and current use, use trends, 

and water quality from groundwater and surface-water sources 

in the parish for water managers, parish residents, and others 

to assist in stewardship of this vital resource. Previously 

published reports (see References Cited section) and data 

stored in the U.S. Geological Survey’s National Water 

Information System (U.S. Geological Survey, 2016) are the 

primary sources of the information presented here. 

In 2010, about 31.24 million gallons per day (Mgal/d) of 

water were withdrawn in Iberia Parish, Louisiana, including 

about 23.13 Mgal/d from groundwater sources and 8.11 Mgal/d

from surface-water sources1 (table 1). Withdrawals for public 

supply and industrial use each accounted for about 32 percent 

of the total water withdrawn (table 2). Other water-use 

categories included rural domestic, livestock, rice irrigation, 

general irrigation, and aquaculture. Water-use data collected 

at 5-year intervals from 1960 to 2010 indicated that water 

withdrawals in Iberia Parish peaked at about 58.57 Mgal/d 

in 1975 (fig. 2; Sargent, 2011; B.P. Sargent, U.S. Geological 

Survey, written commun., 2015). 

1

Water-withdrawal data are based on estimated or reported site-specific data 

and aggregated data, which are distributed to sources. For a full description 

of water-use estimate methodology, see “Data Collection” in Sargent (2011). 

Tabulation of numbers in text and tables may result in different totals because 

of rounding; nonrounded numbers are used for calculation of totals. 

90

3073

Jeanerette

New Iberia

Loreauville

Saint Martinville

Chicot

aquifer

system

Atchafalaya

aquifer

A A' I-93

07385765

07385700

West Cote Blanche Bay

Vermilion Bay

Bayou Petite Anse Gulf Intracoastal Waterway

East Cote

Blanche Bay

Lake 

Fausse

 Pointe

Bayou Patout

Atchafalaya River

Spanish

Lake

Grand

Lake

Bayou Teche

Bayou Carlin

West Cote Blanche Bay

Vermilion Bay

Bayou Petite Anse

Gulf Intracoastal Waterway

Lake

Peigneur

Bayou Carlin

East Cote

Blanche Bay

Lake 

Fausse

 Pointe

Bayou Patout

Atchafalaya River

Spanish

Lake

Grand

Lake

Bayou Teche

GULF OF MEXICO

LAFAYETTE

PARISH

VERMILION

PARISH

ST MARTIN

PARISH

ST MARY

PARISH

ST MARTIN

PARISH

ASSUMPTION

PARISH

IBERVILLE

PARISH

LAFAYETTE

PARISH

VERMILION

PARISH

ST MARTIN

PARISH

ST MARY

PARISH

ST MARTIN

PARISH

ASSUMPTION PARISH

IBERVILLE

PARISH

IBERIA

PARISH

Atchafalaya subbasin

West Central

Louisiana

Coastal

subbasin

West Central

Louisiana

Coastal

subbasin

Lower

Grand

subbasin

Bayou Teche

 subbasin

Bayou Teche

Vermilion subbasin Vermilion subbasin

0 10 20 MILES

0 10 20 KILOMETERS

Base modified from U.S. Geological Survey digital data

Albers Equal-Area Conic projection

North American Datum of 1983

EXPLANATION

Area where no major aquifer contains

 freshwater (modified from Smoot, 1988)—

 Water with a chloride concentration less

 than or equal to 250 milligrams per liter

Approximate altitude of base of fresh

 groundwater, in feet below National 

 Geodetic Vertical Datum of 1929 

 (modified from Smoot, 1988, and Nyman, 

 1984)—Deepest freshwater contained

 within the Chicot aquifer system, except

 where noted

 0 to 199

 200 to 299

 300 to 399

 400 to 599

 600 to 699

 700 to 799

 800 and deeper

Marsh and swamp

Approximate boundary of area showing

 deepest freshwater contained within

 overlying Atchafalaya aquifer

River subbasin boundary

Line of section (see fig. 3)

Well for which hydrograph is shown

 (see fig. 4)

U.S. Geological Survey surface-water

 discharge site and number

U.S. Geological Survey surface-water

 quality site and number (see table 4) 

A'A

I-93

07385700

07381600

30°00'

29°30'

92°00' 91°30'

GULF OF MEXICO TEXAS

ARKANSAS MISSISSIPPI

LOUISIANA

07381600

07381590

IBERIA PARISH

Figure 1. Location of study area, Iberia Parish, Louisiana.
Table 1. Water withdrawals, in million gallons per day, by source 

in Iberia Parish, Louisiana, 2010 (Sargent, 2011; B.P. Sargent, U.S. 

Geological Survey, written commun., 2015).

Aquifer, aquifer system, or 

surface-water body Groundwater Surfacewater

Atchafalaya aquifer 3.51

Chicot aquifer system 19.63

Bayou Teche 0.87

Gulf Intracoastal Waterway 5.03

Bayou Patout 0.38

Miscellaneous streams

and ponds

1.83

Total 23.13 8.11

Table 2. Water withdrawals, in million gallons per day, by use 

category in Iberia Parish, Louisiana, 2010 (Sargent, 2011; B.P. 

Sargent, U.S. Geological Survey, written commun., 2015).

Use category Groundwater Surface water Total

Public supply 10.07 0.00 10.07

Industrial 4.40 5.45 9.85

Rural domestic 1.19 0.00 1.19

Livestock 0.06 0.01 0.07

Rice irrigation 0.13 0.98 1.12

General irrigation 0.61 0.00 0.61

Aquaculture 6.66 1.67 8.33

Total 23.13 8.11 31.24

0

5

10

15

20

25

30

35

40

45

50

55

60

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Year

Annual withdrawal, in million gallons per day

Groundwater

Surface water

EXPLANATION

Figure 2. Water withdrawals in Iberia Parish, Louisiana, 1960–2010 

(Sargent, 2011; B.P. Sargent, U.S. Geological Survey, written 

commun., 2015).

Groundwater Resources 

The primary sources of fresh groundwater (water with a 

chloride concentration of 250 milligrams per liter [mg/L] or less) 

in Iberia Parish are the Atchafalaya aquifer and Chicot aquifer 

system (fig. 3). The base of fresh groundwater generally ranges 

from shallower than 200 feet (ft) below the National Geodetic 

Vertical Datum of 1929 (NGVD 29) in the eastern part of the 

parish to deeper than 800 ft below NGVD 29 in the northwestern 

part of the parish (fig. 1). Little or no fresh groundwater is 

available at the eastern end of the parish. 

Recharge to aquifers in Iberia Parish is from precipitation, 

lateral movement from other aquifers, and seasonal recharge 

from rivers. The principal source of recharge to the Atchafalaya 

aquifer is the Atchafalaya River (Jones and others, 1956). Much 

of the recharge to the Chicot aquifer system in the parish is from 

vertical leakage through surficial clays, particularly in coastal 

wetlands (Nyman, 1984). Discharge from the Atchafalaya aquifer 

is by well withdrawals, discharge into the Atchafalaya River 

during low river stage, and lateral flow into the Chicot aquifer 

system induced by withdrawals from the Chicot aquifer system 

(Jones and others, 1956). Discharge from the Chicot aquifer 

system in the parish is by well withdrawals and lateral flow to 

the west and north induced by large groundwater withdrawals in 

southwestern Louisiana (Lovelace and others, 2004). North of 

Iberia Parish, the Chicot aquifer system and Atchafalaya aquifer 

are strongly interconnected; however, the aquifer and aquifer 

system are generally poorly connected south of St. Martinville 

(Nyman, 1984). 

The Atchafalaya Aquifer 

In Iberia Parish, freshwater in the Atchafalaya aquifer 

extends eastward from near Bayou Teche to a northwestsoutheast trending line located about 8 miles (mi) west of the 

Iberia-Assumption Parish line, beyond which the aquifer contains 

only saltwater (Smoot, 1986, 1988; figs. 1 and 3). The aquifer 

consists of the sand and gravel component of Atchafalaya River 

and Mississippi River alluvial deposits. Depth of the base of the 

alluvial deposits ranges from shallower than 100 ft below NGVD 

29 near Bayou Teche to about 375 ft below NGVD 29 under 

Lake Fausse Pointe. Depths of about 225 to about 275 ft below 

NGVD 29 are found in the northern part of the parish and from 

about 250 to 275 ft below NGVD 29 at the eastern end of the 

parish (Saucier, 1994). Overlying the aquifer is a thick deposit of 

clay (Jones and others, 1956). 

State well-registration records listed 275 active water 

wells screened in the Atchafalaya aquifer in Iberia Parish in 

2015, including 244 domestic, 19 irrigation, and 12 public 

supply. Depths of these wells ranged from about 70 to 262 ft 

below land surface, and reported yields ranged from 5 to 500 

gallons per minute (Louisiana Department of Natural Resources, 

written commun., 2015). In 2010, about 3.51 Mgal/d of water 

were withdrawn from the Atchafalaya aquifer in Iberia Parish, 

including 3.33 Mgal/d for aquaculture, 0.15 Mgal/d for ruraldomestic use, 0.01 Mgal/d for rice irrigation, and 0.01 Mgal/d 

for livestock (B.P. Sargent, U.S. Geological Survey, written 

commun., 2015).

Chicot Aquifer System

The Chicot aquifer system is a regional aquifer underlying 

southwestern Louisiana. In Iberia Parish, the aquifer system is 

composed of a surficial confining unit, shallow sands, and the 

upper and lower sands. The surficial confining unit is a layer of 

clay, which is present at land surface and ranges in thickness 
laf12-0525_fig 03

FEET

NGVD 29

-200

-400

-600

-800

-1,000

FEET

NGVD 29

-200

-400

-600

-800

-1,000

Freshwater in sand

Saltwater in sand—Saltwater 

 contains greater than 250 milligrams 

 per liter chloride

Clay

Lithologic contact—Separates clay and

 sand layers. Dashed where approximate.

 Queried where uncertain

Hydrogeologic contact—Defines boundary

 between conjoined or merged aquifers.

 Dashed where approximate.

 Queried where uncertain

?

Hydrogeologic contact—Defines 

 boundary between aquifers or aquifer systems

?

EXPLANATION

Atchafalaya aquifer

Chicot aquifer lower sand

Surficial confining layer

Deeper aquifers generally contain only saltwater

IBERIA PARISHASSUMPTION PARISH

VERMILION PARISHIBERIA PARISH

A A’

WEST EAST

?

Chicot aquifer upper sand

Shallow sands Atchafalaya River

50 10 KILOMETERS

0 5 10 MILES

Figure 3. Idealized west-to-east hydrogeologic section through Iberia Parish, Louisiana (modified from Smoot, 1988; Nyman, 1989; Saucier, 

1994; and Sargent, 2004). Trace of section shown on figure 1.

from less than 40 ft in the northwestern corner of the parish to 

more than 320 ft near the coast along the border with Vermilion 

Parish (Sargent, 2004). Within the surficial confining unit are 

scattered sand streaks, lenses, and layers known as the shallow 

sand of the Chicot aquifer system, which can provide water 

for domestic use (Prakken, 2003). Underlying the surficial 

confining unit are the Chicot aquifer upper and lower sands. 

The upper sand is the primary aquifer and generally contains 

freshwater west of the Atchafalaya River; however, most of this 

freshwater is underlain with saltwater except for a small area in 

the northwestern corner of the parish (Nyman, 1984). The upper 

sand consists mostly of coarse sand grading to gravel near the 

base of individual beds (Nyman and others, 1990). The top of 

the upper sand ranges from less than 200 ft to more than 400 ft 

below NGVD 29, and the base ranges from less than 600 ft in 

the northern part of the parish to greater than 800 ft below 

NGVD 29 in the southern part of the parish (Nyman, 1984, 

1989). The lower sand underlies the upper sand and generally 

contains only saltwater (water with chloride concentrations 

greater than 250 mg/L) within the parish (Nyman, 1989).

Water levels in wells screened in the Chicot aquifer system 

in Iberia Parish vary temporally and spatially. Yearly well levels 

in the Chicot aquifer upper sand generally fluctuate in response 

to seasonal water demands, as indicated by the water level in 

well I-93 (site number 300035091443301), located east of New 

Iberia (figs. 1 and 4). At a multiyear timescale, water levels in 

well I-93 declined about 2 ft from 1990 to 2015. In 2003, well 

levels ranged from greater than the NGVD 29 east of well I-93 

to 0–20 ft below NGVD 29 along the border with Vermilion 

Parish. The lower water levels in wells along the western border 

of the parish are primarily caused by withdrawals from the 

aquifer in parishes to the west and north of Iberia Parish.

State well-registration records indicate that in 2015 there 

were 1,862 active wells screened in the Chicot aquifer system 

in Iberia Parish, including 1,553 domestic, 162 public supply, 

72 industrial, and 75 irrigation. Depths of these wells ranged 

from about 60 to 856 ft below land surface, and reported 

yields ranged from 3 to 3,800 gallons per minute (Louisiana 

Department of Natural Resources, written commun., 2015). 

In 2010, about 19.6 Mgal/d of water were withdrawn from 

the Chicot aquifer system in the parish, with use categories 

including about 10.07 Mgal/d for public supply, 4.40 Mgal/d for 

industry, 3.33 Mgal/d for aquaculture, 1.04 Mgal/d for ruraldomestic use, 0.61 Mgal/d for general irrigation, 0.12 Mgal/d 

for rice irrigation, and 0.05 Mgal/d for livestock (B.P. Sargent, 

U.S. Geological Survey, written commun., 2015). 

Groundwater Quality

Groundwater in each of the primary aquifers underlying 

Iberia Parish is of similar quality. Freshwater samples taken 

from the Chicot aquifer upper sand during 1940–2009 were 

very hard.2

 Iron and manganese concentrations generally 

exceeded the U.S. Environmental Protection Agency’s 

2

Hardness ranges, expressed as milligrams per liter of calcium carbonate, are 

as follows: 0–60, soft; 61–120, moderately hard; 121–180, hard; greater than 

180, very hard (Hem, 1985). 
laf12-0525_fig 04

-6

-4

-2

0

2

4

6

1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 2016

Water level, in feet 

Year

Well: I-93

Altitude of land surface: 18.53 ft above NGVD 29

Well depth: 585 ft below land surface

Figure 4. Water levels 

in well I-93 screened 

in the Chicot aquifer 

upper sand in Iberia 

Parish, Louisiana (see 

fig. 1 for well location; 

U.S. Geological Survey, 

2016). Land surface 

and water levels are 

in feet (ft) relative to 

the National Geodetic 

Vertical Datum of 1929 

(NGVD 29).

Secondary Maximum Contaminant Levels3 (SMCLs) (table 3). 

The median value for pH was within the SMCLs, and dissolvedsolids concentrations were generally within the SMCL. Water 

samples from wells screened in the Atchafalaya aquifer in Iberia 

Parish west of the Atchafalaya River were found to have iron 

concentrations that ranged from 1,000 to greater than 5,000 

micrograms per liter (μg/L), hardness concentrations that 

generally exceeded 500 mg/L as calcium carbonate, pH generally 

in the range of 6.5–7.5 standard units, and specific conductance 

that ranged from 500 to 1,000 microsiemens per centimeter at 

25 degrees Celsius (Nyman, 1989). 

Surface-Water Resources 

Surface-water resources in Iberia Parish are present primarily 

in the regional Atchafalaya-Vermilion drainage basin (Hydrologic 

Unit Code [HUC] 080801), with minor resources at the eastern 

end of the parish in the West Central Louisiana Coastal (HUC 

08090302) and Lower Grand (HUC 08070300) subbasins. The 

Atchafalaya-Vermilion Basin in Iberia Parish is subdivided into 

the Vermilion (HUC 08080103), Bayou Teche (HUC 08080102), 

and Atchafalaya subbasins (HUC 08080101) (fig. 1; U.S. 

Geological Survey, 2016). In 2010, about 8.11 Mgal/d of surface 

water were withdrawn in Iberia Parish, including 5.45 Mgal/d 

for industrial use, 0.01 Mgal/d for livestock, 0.98 Mgal/d for rice 

irrigation, and 1.67 Mgal/d for aquaculture (table 2). 

Vermilion Subbasin

The Vermilion subbasin is located west of Bayou Teche and 

drains in a general southerly direction towards Vermilion Bay and 

West Cote Blanche Bay (fig. 1). The Vermilion subbasin contains 

the Gulf Intracoastal Waterway, which traverses Iberia Parish both 

3

The SMCLs are nonenforceable Federal guidelines regarding cosmetic effects 

(such as tooth or skin discoloration), aesthetic effects (such as taste, odor, or color), 

or technical effects (such as damage to water equipment or reduced effectiveness 

of treatment for other contaminants) of drinking water. SMCLs were established as 

guidelines by the U.S. Environmental Protection Agency (2016).

inland of and along the shore of Vermilion Bay. In addition, other 

water bodies include Lake Peigneur on the border with Vermilion 

Parish, Spanish Lake on the border with St. Martin Parish, Bayou 

Petite Anse, Bayou Carlin, Bayou Patout, and many other streams 

and canals. In 2010, 5.03 Mgal/d were withdrawn from the Gulf 

Intracoastal Waterway for industrial use, 0.38 Mgal/d from Bayou 

Patout for industrial use, and 1.81 Mgal/d from miscellaneous 

water bodies for aquaculture (1.12 Mgal/d), industrial use (0.02 

Mgal/d), livestock (0.01 Mgal/d), and rice irrigation (0.66 Mgal/d) 

(B.P. Sargent, U.S. Geological Survey, written commun., 2015). 

Bayou Teche Subbasin

The Bayou Teche subbasin is present in the central part of 

the parish and extends from near the western bank of Bayou Teche 

eastward to include Lake Fausse Pointe. Lake Fausse Pointe, 

located in Iberia and St. Mary Parishes (fig. 1), is a large, shallow 

lake that is separated from the Atchafalaya River floodway by 

a levee. At an average estimated water-surface elevation of 

about 2 ft above NGVD 29, the lake has a surface area of about 

24 square miles and an average depth of about 3 ft (Shampine, 

1971). The average daily mean discharge for Bayou Teche at 

Adeline Bridge near Jeanerette (site number 07385765; fig. 1) was 

416 cubic feet per second (ft3

/s) for the period 1996–2015. Flow 

at this site is affected by tides at all stages, and reverse (upstream) 

flow and no flow conditions occur at times during the year (U.S. 

Geological Survey, 2016). In 2010, 0.87 Mgal/d of water were 

withdrawn from Bayou Teche for aquaculture (0.55 Mgal/d) 

and rice irrigation (0.32 Mgal/d), and 0.02 Mgal/d of water 

were withdrawn from miscellaneous streams for industrial use 

(0.01 Mgal/d) and livestock (0.01 Mgal/d) (B.P. Sargent, U.S. 

Geological Survey, written commun., 2015). 

Atchafalaya Subbasin

The Atchafalaya subbasin (fig. 1) is located between two 

north-south trending flood protection levees that are located just 

east of Lake Fausse Pointe and near the eastern end of Iberia 
Table 3. Summary of selected water-quality characteristics for freshwater in the Chicot aquifer system upper sand in Iberia Parish, 

Louisiana, 1940–2009 (U.S. Geological Survey, 2016).

[Values are in milligrams per liter, except as noted. °C, degree Celsius; PCU, platinum cobalt unit; μS/cm, microsiemen per centimeter; SU, standard unit; 

CaCO3, calcium carbonate; μg/L, microgram per liter; SMCL, Secondary Maximum Contaminant Level established by the U.S. Environmental Protection 

Agency (2016); NA, not applicable]

Temperature (°C)Color,

(PCU)

Specific 

conductance, 

field

(μS/cm

at 25 °C)

pH,

field

(SU)

Hardness 

(as CaCO3

)

Chloride,

filtered

(as Cl)

Iron, 

filtered 

(μg/L as 

Fe)

Manganese, 

filtered

(μg/L as 

Mn)

Dissolved 

solids, 

filtered

Chicot aquifer system upper sand (57 wells)

Median 21.9 10 628 7.2 200 20 1,100 240 350

10th percentile 21.0 3 448 6.8 140 8.3 140 100 200

90th percentile 23.0 28 935 7.5 420 150 2,900 410 502

Number of 

samples 31 16 42 37 44 57 20 14 26

Percentage of 

samples that 

do not exceed 

SMCLs

NA. 62 NA. 95 NA. 100 15 7 88

SMCLs

NA. 15 NA. 6.5–8.5 NA. 250 300 50 500

Parish. Within the subbasin, the Atchafalaya River serves as an 

important shipping channel, and the flood plain not only provides 

a route for Mississippi River floodwaters but also supports a 

variety of commercial and recreational activities, as well as a 

habitat for a diverse array of plants and wildlife (U.S. Army 

Corps of Engineers, n.d.). Most of the water moving through the 

Atchafalaya subbasin in Iberia Parish eventually exits the basin 

through the Lower Atchafalaya River or the Wax Lake Outlet, 

both of which are located south of Iberia Parish in St. Mary 

Parish (fig. 1). During the period 1995–2014, the annual average 

discharge at the Lower Atchafalaya River at Morgan City (site 

number 07381600; fig. 1 index map) was 125,700 ft3

/s and at 

Wax Lake Outlet at Calumet (site number 07381590; fig. 1 index 

map) was 96,310 ft3

/s (U.S. Geological Survey, 2016).

Surface-Water Quality

Water samples collected from the Lower Atchafalaya 

River at Morgan City (site number 07381600; fig. 1 index map) 

during 2006–9 and from Bayou Teche at Keystone Lock near 

St. Martinville (site number 07385700) during 1965–98 were 

found to be generally within SMCLs for pH and concentrations 

of chloride and sulfate (table 4). Atchafalaya River samples 

were within the SMCL for iron concentration, whereas Bayou 

Teche samples exceeded the SMCL for iron concentration 

in over 20 percent of samples. Median hardness values were 

within the hard range in the Atchafalaya River and within the 

soft range in Bayou Teche. Median values for dissolved-oxygen 

concentrations were greater than 5 mg/L in water from both sites, 

which is considered the minimum value for a diverse population 

of fresh, warmwater biota, including sport fish (Louisiana 

Department of Environmental Quality, 2008). 

References Cited

Hem, J.D., 1985, Study and interpretation of the chemical characteristics of natural 

water (3d ed.): U.S. Geological Survey Water-Supply Paper 2254, 264 p., 

accessed February 20, 2013, at http://pubs.er.usgs.gov/publication/wsp2254.

Jones, P.H., Hendricks, E.L., Irelan, Burdge, and others, 1956, Water resources of 

southwestern Louisiana: U.S. Geological Survey Water-Supply Paper 1364, 460 p. 

Louisiana Department of Environmental Quality, 2008, Environmental Regulatory 

Code, Title 33, Part IX, Subpart 1: Baton Rouge, Louisiana Department of 

Environmental Quality, accessed June 9, 2009, at http:www.deq.louisiana.gov/

portal/tabid/1674/Default.aspx.

Lovelace, J.K., Fontenot, J.W., and Frederick, C.P., 2004, Withdrawals, water levels, 

and specific conductance in the Chicot aquifer system in southwestern Louisiana, 

2000–03: U.S. Geological Survey Scientific Investigations Report 2004–5212, 56 

p., accessed July 25, 2012, at http://pubs.er.usgs.gov/publication/sir20045212.

Nyman, D.J., 1984, The occurrence of high concentrations of chloride in the 

Chicot aquifer system of southwestern Louisiana: Louisiana Department of 

Transportation and Development, Office of Public Works Water Resources 

Technical Report no. 33, 75 p. 

Nyman, D.J., 1989, Quality of water in freshwater aquifers in southwestern 

Louisiana: Louisiana Department of Transportation and Development Water 

Resources Technical Report no. 42, 22 p., 28 pls. 

Nyman, D.J., Halford, K.J., and Martin, Angel, Jr., 1990, Geohydrology and 

simulation of flow in the Chicot aquifer system of southwestern Louisiana: 

Louisiana Department of Transportation and Development Water Resources 

Technical Report no. 50, 58 p. 

Prakken, L.B., 2003, Quality of water used for domestic supply in the Chicot 

aquifer system of southwestern Louisiana, 1994–2001: Louisiana Department of 

Transportation and Development Water Resources Technical Report no. 71, 48 p. 

Sargent, B.P., 2004, Thickness of the Chicot aquifer system surficial confining unit 

and location of shallow sands, southwestern Louisiana: Louisiana Department of 

Transportation and Development Water Resources Technical Report no. 73, 29 p.

Sargent, B.P., 2011, Water use in Louisiana, 2010: Louisiana Department of 

Transportation and Development Water Resources Special Report no. 17, 135 p. 
Table 4. Summary of selected water-quality characteristics for the Lower Atchafalaya River at Morgan City and Bayou Teche at 

Keystone Lock near St. Martinville, Louisiana (U.S. Geological Survey, 2016).

[Values are in milligrams per liter, except as noted. μS/cm, microsiemen per centimeter; °C, degree Celsius; SU, standard unit; CaCO3, calcium carbonate; μg/L, 

microgram per liter; E, estimated; <, less than; SMCL, Secondary Maximum Contaminant Level established by the U.S. Environmental Protection Agency 

(2016); NA, not applicable]

Specific 

conductance, 

field

(μS/cm at

25 °C)

Oxygen, 

dissolved

pH,

field

(SU)

Hardness (as 

CaCO3

)

Calcium, 

filtered

(as Ca)

Magnesium, 

filtered

(as Mg)

Sodium, 

filtered

(as Na)

Chloride, 

filtered

(as Cl)

Sulfate, 

filtered

(as SO4

)

Iron, 

filtered

(μg/L

as Fe)

Lower Atchafalaya River at Morgan City (2006–9)1

Median 356 7.7 7.8 130 34 10 18 25 35 20

10th percentile 299 5.3 7.6 100 28 7.4 13 18 28 E <6

90th percentile 470 11.2 8.1 170 43 15 30 42 54 70

Number of 

samples 53 52 53 53 53 53 53 53 53 53

Percentage of 

samples that 

do not exceed 

SMCLs

NA. NA. 98 NA. NA. NA. NA. 100 100 100

Bayou Teche at Keystone Lock near St. Martinville (1965–98)2

Median 151 6.0 7.1 45.9 11 4.4 10.5 13 7.6 160

10th percentile 97 3.9 6.4 29 7.1 2.7 6.1 8.1 4.1 20

90th percentile 397 8.8 7.6 116.4 28.1 11 30.3 39 25.1 350

Number of 

samples 141 134 140 140 140 140 138 139 140 71

Percentage of 

samples that 

do not exceed 

SMCLs

NA. NA. 88 NA. NA. NA. NA. 100 100 79

SMCLs

NA. NA. 6.5–8.5 NA. NA. NA. NA. 250 250 300

1

Site number 07381600 (see fig. 1).

2

Site number 07385700 (see fig. 1).

Saucier, R.T., 1994, Geomorphology and Quaternary geologic history of the lower 

Mississippi Valley: Vicksburg, Miss., U.S. Army Corps of Engineers, v. 1-2, 

364 p., 28 pls. 

Shampine, W.J., 1971, Chemical, biological, and physical data for the major lakes 

and reservoirs in Louisiana: Louisiana Department of Public Works Basic Records 

Report no. 5, 98 p. 

Smoot, C.W., 1986, Louisiana hydrologic atlas map no. 2—Areal extent of freshwater 

in major aquifers of Louisiana: U.S. Geological Survey Water-Resources 

Investigations Report 86–4150, 1 sheet, accessed January 18, 2012, at http://pubs.

er.usgs.gov/publication/wri864150.

Smoot, C.W., 1988, Louisiana hydrologic atlas map no. 3—Altitude of the base of 

freshwater in Louisiana: U.S. Geological Survey Water-Resources Investigations 

Report 86–4314, 1 sheet, accessed November 2, 2011, at http://pubs.er.usgs.gov/

publication/wri864150.

U.S. Army Corps of Engineers, n.d., The Atchafalaya Basin—Explore Louisiana’s 

great river swamp: U.S. Army Corps of Engineers, New Orleans District, accessed 

January 14, 2016, at http://www.mvn.usace.army.mil/Portals/56/docs/PAO/

Brochures/ABFS-Brochure-27apr07.pdf. 

U.S. Environmental Protection Agency, 2016, Secondary Drinking Water Standards: 

Guidance for Nuisance Chemicals, accessed April 13, 2016, at https://www.

epa.gov/dwstandardsregulations/secondary-drinking-water-standards-guidancenuisance-chemicals. 

U.S. Geological Survey, 2016, National Water Information System—Web interface: 

U.S. Geological Survey Web page, accessed September 28, 2016, at http://dx.doi.

org/10.5066/F7P55KJN.

This fact sheet was published by the U.S. Geological 

Survey in cooperation with the Louisiana Department 

of Transportation and Development. 

By Vincent E. White and Lawrence B. Prakken

For additional information, contact: 

Director, USGS Lower Mississippi-Gulf Water Science Center

3535 S. Sherwood Forest Blvd., Suite 120

Baton Rouge, LA 70816

E-mail: gs-w-lmg_center_director@usgs.gov

Fax: (225) 298–5490

Telephone: (225) 298–5481

Home Page: http://la.water.usgs.gov

ISSN 2327-6916 (print) ISSN 2327-6932 (online) https://doi.org/10.3133/fs20163100