U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2009–3056

Revised September 2011

In cooperation with the Louisiana Department of Transportation and Development 

Water Resources of Rapides Parish

Printed on recycled paper

Introduction 

Rapides Parish, located in central Louisiana (fig. 1), 

contains fresh groundwater and surface-water resources. 

In 2005, about 443 million gallons per day (Mgal/d) were 

withdrawn from water sources in Rapides Parish (fig. 2). 

About 92 percent (409 Mgal/d) was withdrawn from 

surface water, and 8 percent (34 Mgal/d) was withdrawn 

from groundwater (table 1). Withdrawals for power 

generation accounted for 91 percent (403 Mgal/d) of the 

total water withdrawn (table 2). Withdrawals for other 

uses included public supply (27 Mgal/d), irrigation (9 

Mgal/d), and aquaculture (3 Mgal/d). Water withdrawals 

in the parish generally increased from 1960 to 1995 and 

decreased from 1995 to 2005 (fig. 2). 

This fact sheet summarizes basic information on 

the water resources of Rapides Parish, La. Information 

on groundwater and surface-water availability, quality, 

development, use, and trends is based on previously 

published reports listed in the references section.

Fl a g o n

Ba y o u

Cotile Lake

C a e l c a s i e u R i v r

S p ri n g C r e e k

Red

Ri ver

C h

l

a t l i n L a k e C a n a

B a y o u R o b e rt Ba y o u B ue f

Lake Rodemacher

Cocodri e Lake

Kincaid Rese rvoir

Lake Iatt

Indian Creek Rese rvoir

Re v

d

Ri er

Millers Lake

Lake Chicot

Nantachie Lake

Catahoula Lak e

o

A'

A

Well Field

Ball

Pineville

Alexandria

Woodworth

Forest Hill

Glenmora 

McNary

Lecompte

Cheneyville

Deville

R

P

APIDES

ARISH

Boyce

VERNON 

PARISH

ALLEN PARISH

EVANGELINE 

PARISH

AVOYELLES 

PARISH

NATCHITOCHES 

PARISH

GRANT PARISH

LA SALLE 

PARISH

CATAHOULA PARISH

Hineston

Kolin

Melder

Gardner

Elmer

Sieper

10 KILOMETERS

0 10 MILES

0

31°00'

31°15'

31°30'

93°00' 92°45' 92°30' 92°15' 92°00'

R-1085B

R-1207

R-1056

Base modified from Official Map of Louisiana, Louisiana Department of Transportation and Development, 1986 

Kisatchie

EXPLANATION

150 to 499

500 to 999

Approximate altitude of the base of 

 fresh groundwater, in feet below 

 National Geodetic Vertical Datum of 1929

1,000 to 1,999

2,000 to 2,999

R-1056 Well for which hydrograph

 is shown (see fig. 4)

A A' Trace of hydrogeologic

 section (see fig. 3)

3,000 and deeper

EXPLANATION

Area where no major aquifer 

 contains freshwater

L O U I S I A N A

A R K A N S A S

M I S

S I S

S I P

P

T

I

E X A S

G U L F O F M E X I C O

ENLARGED

AREA

D O TD

APED TR MENT OF TRANSPORTATION AND DEVELOPMENT

Figure 1. Location of study area, Rapides Parish, Louisiana. 
Groundwater Resources 

The groundwater resources of Rapides Parish, from 

near surface to deepest, include the Red River alluvial 

and upland terrace aquifers; the Chicot aquifer system; 

and the Evangeline, Williamson Creek, and Carnahan 

Bayou aquifers (fig. 3). Fresh groundwater (water with a 

chloride concentration less than 250 milligrams per liter 

[mg/L]) is present from land surface to about 500 ft below 

National Geodetic Vertical Datum of 1929 (NGVD 29) in 

northern and southeastern Rapides Parish (fig. 1) and to 

about 3,000 ft below NGVD 29 in the southwestern part 

of the parish. Recharge to the aquifers is from rainfall, 

leakage from overlying aquifers, and seasonal input 

from rivers. Discharge from the aquifers is by natural 

flow into rivers, leakage into underlying aquifers, and 

withdrawal from wells. Well-registration records from the 

Louisiana Department of Transportation and Development 

(DOTD) indicate that there are about 1,310 active wells 

screened in the aquifers in Rapides Parish, including 

about 770 domestic, 300 irrigation, 190 public-supply, and 

40 industrial wells. 

In 2005, about 27 Mgal/d of groundwater were 

withdrawn in Rapides Parish for public supply. The 

Alexandria Water System withdrew about 18 Mgal/d 

from well fields in the Kisatchie National Forest and in 

Alexandria. Water was also withdrawn for rice irrigation (3 

Mgal/d) and aquaculture (1 Mgal/d). 

Shallow Aquifers 

For the purpose of this fact sheet, the Red River 

alluvial aquifer, upland terrace aquifer, and the Chicot 

aquifer system are grouped as shallow aquifers. These 

aquifers generally consist of fine to coarse sand and are 

present at depths shallower than 200 ft below NGVD 29. 

About 610 wells are screened in the shallow aquifers, and 

most are used for domestic (336), irrigation (225), publicsupply (41), or industrial (12) purposes. 

The Red River alluvial aquifer is 20 to 80 ft thick and 

is present in about 30 percent of the parish in a band that 

extends from north-central to southeastern Rapides Parish. 

The aquifer yields very hard water (greater than 180 mg/L 

as calcium carbonate [CaCO3]), and iron and manganese 

concentrations generally exceed the U.S. Environmental 

Protection Agency’s (EPA) 2006 Secondary Maximum 

Contaminant Levels (SMCLs)1 for drinking water. Chloride 

concentrations generally are less than 180 mg/L; however, 

local areas contain saltwater (water with a chloride 

concentration that exceeds 250 mg/L). Reported well 

yields are generally about 70 gallons per minute (gal/min) 

but may be as much as 2,500 gal/min where the aquifer is 

1

 The SMCLs are nonenforceable Federal guidelines regarding cosmetic 

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

odor, or color) of drinking water. At high concentrations or values, health implications as well as aesthetic degradation might exist. SMCLs were established as 

guidelines for the States by the U.S. Environmental Protection Agency (1992).

0

100

200

300

400

500

Annual withdrawal,

 in million gallons per day

Groundwater

Surface water

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Year

Table 1. Water withdrawals, in million gallons per day, by 

source in Rapides Parish, Louisiana, 2005 (Sargent, 2007).

Aquifer, aquifer system, 

or major water body Groundwater Surface water

Red River alluvial aquifer 1.38

Upland terrace aquifer 9.02

Chicot aquifer system .76

Evangeline aquifer 3.05

Jasper aquifer system 18.5

Other aquifers .91

Bayou Boeuf 2.94

Bayou Robert .95

Chatlin Lake Canal 1.9

Lake Rodemacher 402.39

Other water bodies .91

Total 33.63 409.09

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

category in Rapides Parish, Louisiana, 2005 (Sargent, 2007). 

Groundwater Surface water Total

Public supply 27.17 0 27.17

Industrial .65 0 .65

Power generation .12 402.39 402.51

Rural domestic .5 0 .5

Livestock .03 .12 .15

Rice irrigation 3.03 4.54 7.57

General irrigation .69 .69 1.39

Aquaculture 1.44 1.35 2.79

Total 33.63 409.09 442.72

Figure 2. Water withdrawals in Rapides Parish, Louisiana, 1960–2005.
thicker. Withdrawals from the Red River alluvial aquifer 

were about 1 Mgal/d in 2005. Water levels are about 50 to 

70 ft above NGVD 29. A comparison of water-level data 

from 1972 with data from 2000 indicates that water levels 

have changed little during the period. 

The upland terrace aquifer and Chicot aquifer system 

are merged and indistinguishable in Rapides Parish. The 

aquifer and aquifer system are 70 to 160 ft thick and are 

present in the approximate southwestern 60 percent of 

the parish. The upland terrace aquifer and Chicot aquifer 

system yield freshwater that is generally soft (hardness 

less than 60 mg/L as CaCO3) and does not exceed the 

EPA’s SMCLs for chloride, iron, manganese, and dissolved 

solids. Reported well yields range from about 5 to 950 gal/

min. Withdrawals in 2005 were about 9 Mgal/d from the 

upland terrace aquifer and about 1 Mgal/d from the Chicot 

aquifer system. About 6 Mgal/d were withdrawn at the 

Kisatchie well field in 2005. Water levels in the aquifer 

and aquifer system are close to predevelopment levels in 

western Rapides Parish; however, near the Kisatchie well 

field, water levels have declined locally by 10 to 20 ft since 

withdrawals from the well field began in about 1968. 

Evangeline Aquifer

The Evangeline aquifer is present in the southern 

one-third of Rapides Parish and probably merges with 

the overlying Red River alluvial aquifer, upland terrace 

aquifer, and Chicot aquifer system. The base of the aquifer 

dips to the south and ranges from about 0 ft NGVD 29 

near Woodworth to about 1,000 ft below NGVD 29 south 

of Glenmora. The aquifer generally consists of about 50 

feet of fine to medium sand and some locally occurring 

coarse sand. The aquifer yields freshwater that is generally 

soft and does not exceed the EPA’s SMCLs for chloride, 

iron, manganese, and dissolved solids. About 130 wells 

are screened in the Evangeline aquifer, and most are used 

for domestic (60), irrigation (37), public-supply (27), 

or industrial (4) purposes. Reported well yields range 

from about 30 to 540 gal/min, and withdrawals from the 

Evangeline aquifer were about 3 Mgal/d in 2005. Water 

levels in the Evangeline aquifer have generally declined by 

about 5 to 20 ft from 1980 to 2004 and ranged from about 

40 to 220 ft above NGVD 29 in 2005. 

Williamson Creek and Carnahan Bayou Aquifers

The Williamson Creek aquifer and underlying 

Carnahan Bayou aquifer compose the Jasper aquifer system 

in Rapides Parish. These aquifers are the deepest source 

of fresh groundwater in the parish, dip to the south, and 

crop out at ground surface in northern Rapides Parish. 

Withdrawals from the Jasper aquifer system are primarily 

from wells in the Kisatchie well field and Alexandria. 

The Williamson Creek aquifer is present in the 

approximate southern 90 percent of Rapides Parish. The 

aquifer consists of numerous lenses of very fine to medium 

FEET

300

NGVD 29

500

1,000

1,500

2,000

2,500

3,000

3,300

FEET

300

NGVD 29

500

1,000

1,500

2,000

2,500

3,000

3,300

A A’

Kisatchie well field

LAND

SURFACE

EXPLANATION

Sand containing freshwater

Sand containing saltwater

Silt, clay, or sand containing saltwater

Silt, clay, and sand

Silt and clay

Maximum depth of freshwater Alexandria

Pineville

RED RIVER

SOUTHWEST NORTHEAST

Vertical datum is National Geodetic Vertical Datum of 1929 (NGVD 29)

EVANGELINE AQUIFER

CASTOR CREEK CONFINING UNIT

DOUGH HILLS CONFINING UNIT

WILLIAMSON CREEK AQUIFER

CARNAHAN BAYOU AQUIFER

FRESHWATER

SALTWATER

LENA CONFINING UNIT

CHICOT AQUIFER SYSTEM UPLAND TERRACE AQUIFER RED RIVER ALLUVIAL AQUIFER

0 2 4 KILOMETERS

0 2 4 MILES

VERTICAL SCALE GREATLY EXAGGERATED

Figure 3. Generalized southwest-to-northeast hydrogeologic section through Rapides Parish, Louisiana (Tomaszewski, 2007). Trace of 

section shown on figure 1.
sand and some locally occurring coarse sands that are 

typically about 50 ft thick. The base of the aquifer ranges 

from 0 ft NGVD 29 in the northwest to 2,500 ft below 

NGVD 29 in the south. The aquifer yields freshwater that 

is generally soft and does not exceed the EPA’s SMCLs 

for chloride, iron, manganese, and dissolved solids (table 

3). About 270 wells are screened in the Williamson Creek 

aquifer, and most are used for domestic (193) or publicsupply (44) purposes. Reported well yields range from 

about 20 to 550 gal/min. Withdrawals from the Williamson 

Creek aquifer were about 4 Mgal/d in 2005. Water levels in 

the Williamson Creek aquifer have been lowered (fig. 4) by 

withdrawals in the Alexandria-Pineville area and at the 

Kisatchie well field. In southeastern Rapides Parish, the 

aquifer is underlain with saltwater. 

The Carnahan Bayou aquifer is present throughout 

Rapides Parish; however, large areas contain saltwater. The 

aquifer consists of numerous lenses of very fine to medium 

sand that are typically about 40 ft thick. The base of the 

Carnahan Bayou aquifer ranges from 0 ft NGVD 29 in 

northwestern areas of the parish to 4,000 ft below NGVD 

29 in southern areas. In most of Rapides Parish, the aquifer 

yields fresh water that is soft and does not exceed the EPA’s 

SMCLs for chloride, iron, manganese, and dissolved solids 

(table 3); however, in areas south of the cities of Sieper, 

Alexandria, and Kolin, the aquifer contains freshwater 

underlain with saltwater or only contains saltwater. About 

210 wells are screened in the Carnahan Bayou aquifer, and 

most are used for domestic (122) or public-supply (71) 

purposes. Reported well yields range from 5 to 710 gal/

min. Withdrawals from the Carnahan Bayou aquifer were 

about 14 Mgal/d in 2005. Water levels in the Carnahan 

Bayou aquifer declined from 1968 to 1989 but have been 

stable since 1989 (fig. 4). The greatest declines (up to 150 

ft) have occurred in the Alexandria-Pineville area where 

water levels are deeper than 200 ft below NGVD 29. 

Saltwater encroachment has degraded water quality at 

the Kisatchie well field and Alexandria-Pineville areas. 

Saltwater encroachment will likely continue under 2004 

pumping conditions. 

Table 3. Summary of selected water-quality characteristics for freshwater in the Williamson Creek and the Carnahan Bayou aquifers in 

Rapides Parish, Louisiana, 1937–2003 (U.S. Geological Survey, 2008b). 

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

CaCO3, calcium carbonate; μg/L, micrograms per liter; NA, not applicable; SMCL, Secondary Maximum Contaminant Level established by the U.S. Environmental Protection Agency, 2006] 

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

Williamson Creek aquifer

Median 22 5 475.5 7.8 15 17 100 20 304

10th percentile 20 0 248.1 6.64 8 4.1 21 0 167.9

90th percentile 25.5 11.5 799.3 8.46 58.2 77.6 594 98 523.5

Number of samples 24 36 44 45 93 93 32 23 40

Percentage of samples that meet 

SMCLs

NA 92 NA 84 NA 100 77 72 87

Carnahan Bayou aquifer

Median 23.5 10 454.5 7.9 10 15 120 15 319.5

10th percentile 20 0 269 7.2 1.3 6 20 0 203.7

90th percentile 28 26.5 964.5 8.3 31.4 69 350 60 539.6

Number of samples 76 118 126 145 254 258 77 40 118

Percentage of samples that meet 

SMCLs

NA 67 NA 91 NA 100 87 84 87

SMCLs

NA 15 NA 6.5–8.5 NA 250 300 50 500
Water level, in feet above or below national geodetic vertical datum of 1929 (ngvd 29)

WELL: R-1085B

AQUIFER: Williamson Creek aquifer

ALTITUDE OF LAND SURFACE: 100 ft above NGVD 29

WELL DEPTH: 500 ft below land surface

WELL: R-1056

AQUIFER: Carnahan Bayou

ALTITUDE OF LAND SURFACE: 240 ft above NGVD 29

WELL DEPTH: 1,555 ft below land surface

-200

20

40

60

80

100

20

30

40

50

60

70

WELL: R-1207

AQUIFER: Carnahan Bayou

ALTITUDE OF LAND SURFACE: 180 ft above NGVD 29

WELL DEPTH: 2,772 ft below land surface

90

100

110

120

130

Date

1970 1980 1990 2000 2010

Water level, in feet above or below national geodetic vertical datum of 1929 (ngvd 29)

WELL: R-1085B

AQUIFER: Williamson Creek aquifer

ALTITUDE OF LAND SURFACE: 100 ft above NGVD 29

WELL DEPTH: 500 ft below land surface

WELL: R-1056

AQUIFER: Carnahan Bayou

ALTITUDE OF LAND SURFACE: 240 ft above NGVD 29

WELL DEPTH: 1,555 ft below land surface

-200

20

40

60

80

100

20

30

40

50

60

70

WELL: R-1207

AQUIFER: Carnahan Bayou

ALTITUDE OF LAND SURFACE: 180 ft above NGVD 29

WELL DEPTH: 2,772 ft below land surface

90

100

110

120

130

Date

1970 1980 1990 2000 2010

Water level, in feet above or below national geodetic vertical datum of 1929 (ngvd 29)

WELL: R-1085B

AQUIFER: Williamson Creek aquifer

ALTITUDE OF LAND SURFACE: 100 ft above NGVD 29

WELL DEPTH: 500 ft below land surface

WELL: R-1056

AQUIFER: Carnahan Bayou

ALTITUDE OF LAND SURFACE: 240 ft above NGVD 29

WELL DEPTH: 1,555 ft below land surface

-200

20

40

60

80

100

20

30

40

50

60

70

WELL: R-1207

AQUIFER: Carnahan Bayou

ALTITUDE OF LAND SURFACE: 180 ft above NGVD 29

WELL DEPTH: 2,772 ft below land surface

90

100

110

120

130

Date

1970 1980 1990 2000 2010

Figure 4. Water levels in 

well R-1085B screened in the 

Williamson Creek aquifer and 

wells R-1056 and R-1207 screened 

in the Carnahan Bayou aquifer in 

Rapides Parish, Louisiana (see 

fig. 1 for well locations).

Surface-Water Resources 

The Red River, Bayou Boeuf, Calcasieu River, 

Chatlin Lake Canal, and Lake Rodemacher are primary 

sources of fresh surface water in Rapides Parish. Other 

sources of fresh surface water in the parish include Bayou 

Robert, Cotile Lake, and the Indian Creek and Kincaid 

Reservoirs. In 2005, about 409 Mgal/d of surface water 

were withdrawn in Rapides Parish for power generation 

(402 Mgal/d), rice irrigation (5 Mgal/d), and aquaculture 

(1 Mgal/d). 

The Red River is a potential source of substantial 

volumes of water in the parish. The average discharge for 

the Red River at Alexandria was about 30,900 cubic feet 

per second (ft

3

/s) (19,900 Mgal/d) for the period 1929–83. 

Water in the Red River is hard (121–180 mg/L as CaCO

3

) 

to very hard (greater than 181 mg/L as CaCO

3

) (table 4). 

Water in the Red River generally does not exceed the 

EPA’s SMCLs for pH and for chloride, sulfate, and iron 

concentrations. Dissolved oxygen concentrations generally 

range from 5.9 to 11 mg/L. Water withdrawals from 

Bayou Boeuf were about 3 Mgal/d in 2005 and were for 

irrigation, livestock, and aquaculture use. The average 

discharge in Bayou Boeuf before 1966 was about 2,800 

ft

3

/s (1,800 Mgal/d). 

The Calcasieu River is also a potential source of water 

in the parish. The average discharge for the Calcasieu 

River near Glenmora was about 780 ft

3

/s (500 Mgal/d) for 

the period 1985–2008. Analyses of water quality samples 

from the river indicate that the water is somewhat acidic 

(pH less than 6.5) but otherwise does not exceed the EPA’s 

SMCLs (table 4). 

Water withdrawals from the Chatlin Lake Canal 

for irrigation, livestock, and aquaculture use were about 2 Mgal/d in 2005. The average discharge for Chatlin Lake 

Canal near Lecompte was about 232 ft

3

/s (150 Mgal/d) for 

the period 1922–2008. No water quality data are available 

for Chatlin Lake Canal. 

Lake Rodemacher is in northwestern Rapides Parish 

about 2 miles west of Boyce. It is owned and used by 

Cleco, Louisiana Energy and Power Authority, and 

Lafayette Utilities System as a source of cooling water for 

two power-generating units. Water withdrawals for power 

generation were about 402 Mgal/d in 2005. The lake has a 

surface area of about 3,320 acres and a maximum storage 

capacity of about 14,100 acre-feet. No water quality data 

are available for Lake Rodemacher.

Water level, in feet above or below national geodetic vertical datum of 1929 (NAGVD 29)
References

Newcome, Roy, Jr., and Sloss, Raymond, 1966, Water resources 

of Rapides Parish, Louisiana: Department of Conservation, 

Louisiana Geological Survey, and Louisiana Department of 

Public Works Water Resources Bulletin no. 8, 104 p. 

Sargent, B.P., 2007, Water use in Louisiana, 2005: Louisiana 

Department of Transportation and Development Water 

Resources Special Report no. 16, 133 p.

Smoot, C.W., and Fendick, R.B., Jr., 1998, Hydrogeology and water 

resources of the Alexandria area, Rapides Parish, Louisiana: 

Louisiana Department of Transportation and Development Water 

Resources Technical Report no. 63, 36 p., 1 pl. 

Tomaszewski, D.J., 2007, Ground-water resources in Rapides 

Parish, Louisiana, 2005: Louisiana Department of Transportation 

and Development Water Resources Technical Report no. 75.

U.S. Environmental Protection Agency, 1992, Secondary drinking 

water regulations—guidance for nuisance chemicals: U.S. 

Environmental Protection Agency publication EPA 810/K92-001, 4 p., accessed July 29, 2009, at http://www.epa.gov/

safewater/consumer/2ndstandards.html.

U.S. Environmental Protection Agency, 2006, 2006 Edition of the 

drinking water standards and health advisories: Washington 

D.C., U.S. Environmental Protection Agency, Office of Water, 

12 p.

U.S. Geological Survey, 2008a, Ground-water levels for Louisiana: 

U.S. Geological Survey digital dataset, accessed May 22, 2008, 

at http://nwis.waterdata.usgs.gov/la/nwis/gwlevels.

By Jason M. Griffith

For additional information, contact: 

Director, USGS Louisiana Water Science Center

3535 S. Sherwood Forest Blvd., Suite 120

Baton Rouge, LA 70816

E-mail: dc_la@usgs.gov

Fax: (225) 298-5490

Telephone: (225) 298-5481

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

This fact sheet was published by the U.S. 

Geological Survey, in cooperation with the 

Louisiana Department of Transportation and 

Development (DOTD). Thanks are given to 

Zahir “Bo” Bolourchi, Director, Water Resources 

Programs, Louisiana Department of Transportation 

and Development, who contributed to the content 

and design of the fact sheet.

Table 4. Summary of selected water-quality characteristics for the Red and Calcasieu Rivers in Rapides Parish, Louisiana, 1944–2008

(U.S. Geological Survey, 2008b).

[Values are in milligrams per liter, except as noted. °C, degrees Celsius; μS/cm, microsiemens per centimeter; SU, standard units; μg/L, micrograms per liter; CaCO3, 

calcium carbonate; NA, not applicable; SMCL, Secondary Maximum Contaminant Level established by the U.S. Environmental Protection Agency, 2006] 

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)

Red River at Alexandria1

Median 506 8 7.6 130 36 9.1 42 72.3 49.5 42

10th percentile 243 5.9 7.1 70 20 4.2 15 25.5 19 7

90th percentile 1,210 11 8.1 280 78 24 110 215 147 134

Number of samples 729 362 779 719 551 552 381 777 772 127

Percentage of samples that 

meet SMCLs

NA NA 99 NA NA NA NA 94 100 98

Calcasieu River near Glenmora2

Median 46 8 6.4 13.5 3.5 1 4.5 5.8 2.6 210

10th percentile 30 6.7 6 7.9 2 .4 2 2.6 1.2 142

90th percentile 67 9.5 7 17 5 1.2 7 7.7 4 230

Number of samples 21 10 37 20 20 20 18 37 37 5

Percentage of samples that 

meet SMCLs

NA NA 48 NA NA NA NA 100 100 100

SMCLs

NA NA 6.5–8.5 NA NA NA NA 250 250 300

1

Station number 07355500 (U.S. Geological Survey, 2008b; specific data at [http://nwis.waterdata.usgs.gov/la/nwis/qwdata/?site_no=07355500]).

2

Station number 08013000 (U.S. Geological Survey, 2008b; specific data at [http://nwis.waterdata.usgs.gov/la/nwis/qwdata/?site_no=08013000]).

U.S. Geological Survey, 2008b, Water-quality samples for 

Louisiana: U.S. Geological Survey digital dataset, accessed 

May 22, 2008, at http://nwis.waterdata.usgs.gov/la/nwis/qwdata.

U.S. Geological Survey, 2008c, StreamStats: U.S. Geological 

Survey digital dataset, accessed July 28, 2008, at 

http://streamstats.usgs.gov/gages/viewer.htm.