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Chloride Concentrations in Groundwater From the Western Part of the Southern Hills Regional Aquifer System, Louisiana, 2021–22

Maxwell A. Lindaman, C.E. Anderson, J.S. Hanor, F.T.-C. Tsai, A. Buono, Y. Chen · U.S. Geological Survey

USGS Publications · Papers · License: Public Domain

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Prepared in cooperation with the Capital Area Groundwater Conservation Commission

Chloride Concentrations in Groundwater From the Western Part of the Southern Hills Regional Aquifer System, Louisiana, 2021–22

Scientific Investigations Report 2024–5057

U.S. Department of the Interior U.S. Geological Survey

Chloride Concentrations in Groundwater From the Western Part of the Southern Hills Regional Aquifer System, Louisiana, 2021–22 By Maxwell A. Lindaman

Prepared in cooperation with the Capital Area Groundwater Conservation Commission

Scientific Investigations Report 2024–5057

U.S. Department of the Interior U.S. Geological Survey

U.S. Geological Survey, Reston, Virginia: 2024

For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit https://www.usgs.gov or call 1–888–392–8545. For an overview of USGS information products, including maps, imagery, and publications, visit https://store.usgs.gov/ or contact the store at 1–888–275–8747. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Suggested citation: Lindaman, M.A., 2024, Chloride concentrations in groundwater from the western part of the Southern Hills regional aquifer system, Louisiana, 2021–22: U.S. Geological Survey Scientific Investigations Report 2024–5057, 33 p., https://doi.org/10.3133/sir20245057. Associated data for this publication: Lindaman, M.A., 2024, Chloride concentration data for the western part of the Southern Hills regional aquifer system, Louisiana, 2021–22, and selected historical data: U.S. Geological Survey data release, https://doi.org/10.5066/ P9A9OBT6. U.S. Geological Survey, 2023, USGS water data for the Nation: U.S. Geological Survey National Water Information System database, https://doi.org/10.5066/F7P55KJN. ISSN 2328-0328 (online)

iii

Acknowledgments The author gratefully acknowledges the support of the Capital Area Groundwater Conservation Commission for this work and the generous help from well owners for allowing access to their properties and accommodating the data collection effort. Additional thanks are given to U.S. Geological Survey hydrologists Paul Frederick, Angela Robinson, and Vincent White, who assisted with sample collection and processing.

Contents Acknowledgments��iii Abstract��1 Introduction��1 Purpose and Scope��1 Hydrogeology��3 Previous Studies��4 Methods��4 Results and Discussion��4 “400-Foot” Sand of the Baton Rouge Area��5 “600-Foot” Sand of the Baton Rouge Area��5 “800-Foot” Sand of the Baton Rouge Area��5 “1,000-Foot” Sand of the Baton Rouge Area��8 “1,200-Foot” Sand of the Baton Rouge Area��11 “1,500-Foot” Sand of the Baton Rouge Area��14 “1,700-Foot” Sand of the Baton Rouge Area��20 “2,000-Foot Sand” of the Baton Rouge Area��21 “2,400-Foot” Sand of the Baton Rouge Area��22 “2,800-Foot” Sand of the Baton Rouge Area��27 Summary��31 References Cited��31

Figures 1. 2. 3.

Map showing study area in southeastern Louisiana��2 Chart showing hydrogeologic units of the study area in southeastern Louisiana��3 Map showing chloride concentrations in water from wells screened in the “400-foot” sand of the Baton Rouge area collected during November 2021 through February 2022 and reported annual withdrawals from wells screened in the aquifer for 2021 in southeastern Louisiana ��6 Map showing chloride concentrations in water from wells screened in the “600-foot” sand of the Baton Rouge area collected during November 2021 through February 2022 and reported annual withdrawals from wells screened in the aquifer for 2021 in southeastern Louisiana��7 Graphs showing time series of chloride concentrations in water from selected wells screened in the “600-foot” sand of the Baton Rouge area, southeastern Louisiana ��8 Map showing chloride concentrations in water from wells screened in the “800-foot” sand of the Baton Rouge area collected during November 2021 through February 2022 and reported annual withdrawals from wells screened in the aquifer for 2021 in southeastern Louisiana ��9 Map showing chloride concentrations in water from wells screened in the “1,000-foot” sand of the Baton Rouge area collected during November 2021 through February 2022 and reported annual withdrawals from wells screened in the aquifer for 2021 in southeastern Louisiana ��10

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

Graphs showing time series of chloride concentrations in water from two wells screened in the “1,000-foot” sand and a well screened in the “1,000-foot” and “1,200-foot” sands of the Baton Rouge area, southeastern Louisiana ��11 Map showing chloride concentrations in water from wells screened in the “1,200-foot” sand of the Baton Rouge area collected during November 2021 through February 2022 and reported annual withdrawals from wells screened in the aquifer for 2021 in southeastern Louisiana��12 Graphs showing time series of chloride concentrations in water from four wells screened in the “1,200-foot” sand and one well screened in the “1,200-foot” and “1,500-foot” sands of the Baton Rouge area, southeastern Louisiana��13 Maps showing chloride concentrations in water from wells screened in the “1,500-foot” sand of the Baton Rouge area collected during November 2021 through February 2022 and reported annual withdrawals from wells screened in the aquifer for 2021 in southeastern Louisiana��15 Graphs showing time series of chloride concentrations in water from wells screened in the “1,500-foot” sand of the Baton Rouge area within the plume area north of the Baton Rouge fault, at the Government Street pumping station, at the Lula Street pumping station, and south of the Baton Rouge fault, southeastern Louisiana��17 Graph showing time series of daily mean water levels in wells screened in the “800-foot” sand of the Baton Rouge area, in the “1,500-foot” sand of the Baton Rouge area, and in a connector well screened in both sands, southeastern Louisiana��19 Map showing chloride concentrations in water from wells screened in the “1,700-foot” sand of the Baton Rouge area collected during November 2021 through February 2022 and reported annual withdrawals from wells screened in the aquifer for 2021 in southeastern Louisiana��20 Graph showing time series of chloride concentrations in water from well EB-1295C screened in the “1,500-foot” and “1,700-foot” sands of the Baton Rouge area, southeastern Louisiana��21 Maps showing chloride concentrations in water from wells screened in the “2,000-foot” sand of the Baton Rouge area collected during November 2021 through February 2022 and reported annual withdrawals from wells screened in the aquifer for 2021 in southeastern Louisiana ��22 Graphs showing time series of chloride concentrations in water from wells screened in the “2,000-foot” sand of the Baton Rouge area and one well screened in the “2,000-foot” and “2,400-foot” sands of the Baton Rouge area, southeastern Louisiana��24 Maps showing chloride concentrations in water from wells screened in the “2,400-foot” sand of the Baton Rouge area collected during November 2021 through February 2022 and reported annual withdrawals from wells screened in the aquifer for 2021 in southeastern Louisiana ��25 Graph showing time series of chloride concentrations in water from wells screened in the “2,400-foot” sand of the Baton Rouge area, southeastern Louisiana��27 Maps showing chloride concentrations in water from wells screened in the “2,800-foot” sand of the Baton Rouge area collected during November 2021 through February 2022 and reported annual withdrawals from wells screened in the aquifer for 2021 in southeastern Louisiana ��28

vii

21.

Graphs showing time series of chloride concentrations in water from wells screened in the “2,800-foot” sand of the Baton Rouge area, southeastern Louisiana��30

Conversion Factors U.S. customary units to International System of Units

Multiply

To obtain

Length foot (ft)

0.3048

meter (m)

mile (mi)

1.609

kilometer (km)

square mile (mi2)

2.590

square kilometer (km2)

Volume gallon (gal)

3.785

liter (L)

gallon (gal)

0.003785

cubic meter (m3)

million gallons (Mgal)

3,785

cubic meter (m3)

Flow rate million gallons per day (Mgal/d)

0.04381

cubic meter per second (m3/s)

Datums Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88). Horizontal coordinate information is referenced to the World Geodetic System of 1984 (WGS 84).

Supplemental Information Concentrations of chloride in water are reported in milligrams per liter (mg/L).

Abbreviations CAGWCC Capital Area Groundwater Conservation Commission SMCL

secondary maximum contaminant level

USGS

U.S. Geological Survey

Chloride Concentrations in Groundwater From the Western Part of the Southern Hills Regional Aquifer System, Louisiana, 2021–22 By Maxwell A. Lindaman

Abstract Groundwater is heavily used for public supply and industrial uses in the Baton Rouge, Louisiana, area. Lowered water levels resulting from groundwater withdrawals have induced the movement of saltwater towards wells in East Baton Rouge and West Baton Rouge Parishes. Saltwater intrusion has the potential to affect water supply infrastructure, reduce water availability for some uses, and increase treatment costs. To document current conditions, samples were collected from 161 wells screened in 10 aquifers of the Southern Hills regional aquifer system during November 2021 through February 2022. The results were compared with historical data to identify where chloride concentrations are increasing, which could indicate that saltwater intrusion is occurring. Saltwater intrusion, to varying degrees and areal extents, was observed in most of the 10 aquifers. The limited availability of monitoring wells near or within some of the known saltwater plume areas restricts tracking of the movement or delineation of the plumes’ current extents.

Introduction The Southern Hills regional aquifer system is the primary source of water for the northern parishes of southeastern Louisiana (Buono, 1983) (fig. 1). In East Baton Rouge, West Baton Rouge, East Feliciana, West Feliciana, and Pointe Coupee Parishes, estimated groundwater withdrawals in 2015 were about 203 million gallons per day (Mgal/d) (Collier, 2018). Withdrawals were concentrated in East Baton Rouge Parish for industrial (72.6 Mgal/d) and public supply (72.2 Mgal/d) use. Saltwater intrusion, or the movement of saltwater1 into aquifers, has been documented in multiple aquifers underlying East Baton Rouge and West Baton Rouge Parishes (Whiteman, 1979; Tomaszewski, 1996; Lovelace, 2007). Withdrawals 1For the purposes of this report, the terms “saltwater” and “freshwater” refer to water containing a chloride concentration greater or less than 250 milligrams per liter, respectively.

of groundwater have lowered water levels and induced the movement of saltwater towards producing wells in parts of the aquifer system. High concentrations of dissolved solids can increase water treatment costs and accelerate corrosion of infrastructure such as pipes, water heaters, and pumps. As concentrations increase, treatment may become economically unviable, and users would need to develop alternative water sources. The U.S. Geological Survey (USGS), in cooperation with the Capital Area Groundwater Conservation Commission (CAGWCC), monitors concentrations of chloride in groundwater through an annual sampling network that includes 41 wells (as of 2022) in East Baton Rouge and West Baton Rouge Parishes to monitor water quality at locations near known saltwater plumes. Periodic data collection from additional wells could be used to document conditions in the aquifers beyond these locations.

Purpose and Scope This report describes chloride concentrations in groundwater samples collected in East Baton Rouge, West Baton Rouge, Pointe Coupee, East Feliciana, and West Feliciana Parishes. Samples were collected from November 2021 through February 2022 from 161 wells screened in 10 aquifers of the Southern Hills regional aquifer system: the “400-foot,” “600-foot,” “800-foot,” “1,000-foot,” “1,200-foot,” “1,500-foot,” “1,700-foot,” “2,000-foot,” “2,400-foot,” and “2,800-foot” sands of the Baton Rouge area2 (fig. 2). The results of sample analyses were compared with historical concentrations and previous interpretations (Whiteman, 1979; Tomaszewski, 1996; Lovelace, 2007) to identify areas where chloride concentrations are increasing in groundwater. This information is intended to help water managers identify risks to water supply infrastructure, provide basic data for groundwater solute transport models, and inform monitoring well network design. Chloride concentration data collected during this study and some historical data are available in an accompanying data release (Lindaman, 2024). USGS-collected data, 2The phrase “of the Baton Rouge area” with reference to the “sand” aquifers will be subsequently omitted in this report for brevity.

2 Chloride Concentrations in Groundwater, Western Part of the Southern Hills Regional Aquifer System, La., 2021–22 91°50'

91°40'

91°30'

91°20'

91°10'

91°

90°50'

90°40'

CONCORDIA

AVOYELLES

Com

WEST FELICIANA

r Ri ve

Riv

r ive

New Roads EAST BATON ROUGE

False River

POINTE COUPEE ST LANDRY

Am i

R aya

Miss

Tho mp son

fal ha Atc

issip

30°40'

ST HELENA

EAST FELICIANA

Cre ek

Raccourci Old River

30°50'

Jackson

iver ite R

a u Sar Bayo

31°

MISSISSIPPI LOUISIANA

LIVINGSTON Port Barre

Baton Rouge industrial district

Maringouin

30°30'

Baton Rouge Metropolitan Area

WEST BATON ROUGE

ite

IBERVILLE

LAFAYETTE Lafayette

Plaquemine 0

5 5

10 MILES 10 KILOMETERS

EXPLANATION Urban area Study area

Denham Springs-Scotlandville fault— Dashed where approximately located

LOUISIANA TEXAS

EXPLANATION Recharge area—Modified from Snead and McCulloh (1984) and Griffith (2003) Study area

Figure 1. Study area in southeastern Louisiana.

ASCENSION

Baton Rouge fault—Dashed where approximately located

ARKANSAS

Extent of Southern Hills regional aquifer system in and north of southeastern Louisiana

St Gabriel salt dome

30°20'

Riv

ST MARTIN

Introduction 3 including additional water quality data for the study area, are also available from the USGS National Water Information System (USGS, 2023).

Hydrogeology

Epoch

Period

The aquifers and confining units of the Southern Hills regional aquifer system (fig. 2) are beds of unconsolidated sediments that generally dip towards the south from their outcrop or subcrop areas in southern Mississippi and southeastern Louisiana (fig. 1 inset map), where the aquifers are recharged by precipitation (Buono, 1983). Within the study area, the aquifers are named after their approximate depth in the Baton Rouge industrial district (fig. 1). Because the aquifers dip towards the south, their depth of occurrence changes through the study area and their name does not reflect their depth at all locations. The aquifers consist of fine to coarse sand and are generally separated by silt or clay confining units. The aquifers and confining units may locally interfinger, pinch out, or change abruptly in thickness, forming a complex interconnected system (Griffith, 2003). In the Baton Rouge area, the individual aquifers are usually greater than 75 feet (ft) thick and can be more than 200 ft thick, and the confining units are usually at least 100 ft thick and can be up to 400 to 500 ft thick (Tomaszewski, 1996). The Mississippi River alluvial aquifer overlies the Southern Hills regional aquifer system west of the Mississippi River.

The Baton Rouge fault (fig. 1) is an east-to-west-trending listric fault that is downthrown to the south and functions as a leaky hydrologic barrier (Whiteman, 1979). The fault is active and has formed an escarpment that can be traced at land surface (McCulloh, 2001), except for west of the Mississippi River (fig. 1) where the escarpment has been removed by erosion. Displacement along the fault has caused bed discontinuity, and the sands on the north side of the fault can be hydraulically connected to different sands on the south side or laterally adjoined with relatively impermeable silt or clay beds such that the horizontal flow of groundwater is impeded. Aquifers on the north side of the fault generally contain freshwater, except for areas of saltwater intrusion and the “2,800-foot” sand at the base of the aquifer system which contains a transitional zone where saltwater extends several miles north of the fault (Whiteman, 1979). South of the fault, sands in the subsurface generally contain saltwater except for shallow aquifers or zones of fresh groundwater in deeper sands. The original source of saltwater in the aquifer system is possibly from fluids upwelling from the St. Gabriel salt dome located about 9 miles (mi) south of Baton Rouge (fig. 1) (Anderson and others, 2013). A second fault in the Baton Rouge area, the Denham Springs-Scotlandville fault, is north of the Baton Rouge fault but causes less offset and is not known to affect groundwater quality.

Aquifer system

Hydrogeologic unit of the Baton Rouge area1

"400-foot" sand Chicot equivalent aquifer system

Miocene

Neogene

Pliocene

"600-foot" sand "800-foot" sand "1,000-foot" sand "1,200-foot" sand "1,500-foot" sand

Evangeline equivalent aquifer system

"1,700-foot" sand "2,000-foot" sand "2,400-foot" sand

Jasper equivalent aquifer system

"2,800-foot" sand Unnamed irregular confining units occur between "sand" aquifers. The sands are named after their approximate depth of occurrence in the Baton Rouge industrial district (see fig. 1 for the location of the industrial district). 1

Figure 2. Hydrogeologic units of the study area in southeastern Louisiana. Modified from Griffith (2003).

Southern Hills regional aquifer system

Pleistocene

Quaternary

Mississippi River alluvial aquifer

4 Chloride Concentrations in Groundwater, Western Part of the Southern Hills Regional Aquifer System, La., 2021–22 By the 1960s, groundwater withdrawals had lowered water levels in several aquifers north of the Baton Rouge fault and created a hydraulic gradient favorable for northward movement of saltwater across the fault line at certain locations and depths. Saltwater intrusion into one or more wells north of the fault has been documented for most of the 10 aquifers of the Baton Rouge area (Whiteman, 1979; Tomaszewski, 1996; Lovelace, 2007). The pathways and rates of saltwater intrusion depend on several factors, such as (1) continuity between sands on the downthrown side and sands on the north side at locations along the fault line; (2) the configuration of the base of the aquifer; (3) the permeability of the aquifer; and (4) the hydraulic gradient (Whiteman, 1979). Saltwater plumes are wedge shaped because saltwater is denser than freshwater, with a thinner leading edge that travels along the base of an aquifer, such that an aquifer can contain saltwater through only a fraction of its total thickness. In addition to lateral movement, saltwater can move vertically upwards within an aquifer or from an underlying sand into the screen of a pumping well. Similarly, downward leakage of saltwater from one sand into another is possible under the influence of gravity or a vertical hydraulic gradient.

Previous Studies Saltwater intrusion into aquifers north of the Baton Rouge fault was first observed after a production well screened in the “600-foot” sand was abandoned because of rising salinity in 1948 (Whiteman, 1979). Subsequent investigative work has outlined groundwater conditions through the aquifer system or described the hydrogeologic controls on saltwater intrusion (for example, Meyer and Turcan, 1955; Morgan and Winner, 1964; Rollo, 1969; Whiteman, 1979). Updates on chloride concentrations in groundwater in the Baton Rouge area were provided by Tomaszewski (1996) and Lovelace (2007). Several numerical models have been developed to test management scenarios, simulate water levels, or estimate saltwater intrusion rates and directions in one or more aquifers (Torak and Whiteman, 1982; Huntzinger and others, 1985; Halford and Lovelace, 1994; Heywood and others, 2014, 2015, 2019; Pham and Tsai, 2017; Chen and others, 2023).

Methods Samples were collected from production wells through discharge outlets and from monitoring wells without pumps by using an air compressor. Wells were purged prior to sampling, and specific conductance and temperature were measured in the field following the procedures described in USGS (1997–2024). A sample from each well was filtered through a 0.45-micron-membrane filter with a vacuum pump, and the filtered and unfiltered samples were shipped to the USGS National Water Quality Laboratory in Denver, Colorado. The samples were then analyzed for dissolved chloride

concentration and specific conductance following the methods described in Fishman and Friedman (1989). Sequential replicates were collected for about 1 out of every 12 samples for quality control and to assess method variability. The chloride concentrations of the 14 sequential replicates were no more than 0.03 milligram per liter (mg/L) different from their corresponding samples. Some of the wells that were selected for sampling were part of a previous survey of chloride concentrations in groundwater conducted during 2004–05 in East Baton Rouge and West Baton Rouge Parishes (Lovelace, 2007). Additional wells were identified and sampled to include wells beyond East Baton Rouge and West Baton Rouge Parishes and to collect data at several key wells that have been drilled since the Lovelace (2007) study. The aquifer associated with each well was determined from its local aquifer code designation in the USGS National Water Information System (USGS, 2023). For wells that were newly entered into this system as part of this study, the aquifer assignment was made by using information from the Louisiana Department of Natural Resources’ Strategic Online Natural Resources Information System (SONRIS) well registration database (Louisiana Department of Natural Resources, 2023). Some wells are screened in two aquifers, either through a single long screen or two or more noncontiguous screened intervals. The assignment of an aquifer code to a sand on the south side of the Baton Rouge fault does not imply that there is lateral continuity or hydraulic connection to similarly coded aquifers on the north side of the fault. The aquifer assignment for wells south of the fault is based off correlation of sands that were likely continuous prior to being offset by movement along the Baton Rouge fault. Groundwater quality information, including chloride concentration, is also collected by the Louisiana Department of Health (Louisiana Department of Health, 2023), and these data were compiled and used to support the interpretation of the data collected for this study. Chloride concentrations in groundwater in the Southern Hills regional aquifer system north of the Baton Rouge fault are typically less than 10 mg/L (Tomaszewski, 1996; Lovelace, 2007). This value was used as a lower threshold to identify areas where saltwater intrusion may be occurring.

Results and Discussion Samples were collected from 161 wells; 154 were located north of the Baton Rouge fault and 7 were located south of the fault. The median chloride concentration for all the samples was 3.62 mg/L. Samples from 27 wells north of the Baton Rouge fault had a chloride concentration greater than 10 mg/L. The range of chloride concentrations in samples from seven wells south of the fault was 11.4–736 mg/L. This range is not broadly representative of groundwater south of the fault given the small sample size and the limited subset of aquifers sampled. Of the 34 samples that had chloride concentrations

Results and Discussion 5 greater than 10 mg/L, 9 samples had concentrations that exceeded the U.S. Environmental Protection Agency’s secondary maximum contaminant level3 (SMCL) for chloride of 250 mg/L (U.S. Environmental Protection Agency, 2023). In northwestern East Baton Rouge Parish, seven wells that are used by a paper mill were sampled: one screened in the “1,200-foot” sand, one screened in the “1,500-foot” and “1,700-foot” sands, and five screened in the “2,800-foot” sand. All but one of these wells (EB-846, “2,800-foot” sand) had chloride concentrations greater than 10 mg/L, with concentrations ranging from 12.3 to 22.2 mg/L. Chloride concentrations in historical samples from these wells and others within the paper mill ranged from less than 10 mg/L to 26.5 mg/L, except for concentrations in samples from well EB-1247 (“2,800-foot” sand), which reached a maximum of 50.5 mg/L in 2017 (USGS, 2023).

“400-Foot” Sand of the Baton Rouge Area Eight samples were collected from wells screened in the “400-foot” sand (fig. 3). None of the samples from wells located north of the Baton Rouge fault had a chloride concentration greater than 10 mg/L. The sample from well EB-1298, a production well located south of the Baton Rouge fault, had a concentration of 25 mg/L. Historical chloride concentrations in 11 samples collected from this well during 2001–22 ranged from 17.1 to 26.2 mg/L, without indicating that concentrations are increasing. Another sample from a well located south of the fault (EB-1246) had a concentration of 305 mg/L, but the well is only used sporadically to provide water to a decorative pond fountain. The potential for saltwater intrusion northward across the fault into the “400-foot” sand in East Baton Rouge Parish is thought to be low because the downthrown sands on the south side of the fault that connect with the “400-foot” sand on the north side generally contain freshwater (Whiteman, 1979; Griffith, 2003; Lovelace, 2007).

“600-Foot” Sand of the Baton Rouge Area Six samples were collected from wells screened in the “600-foot” sand (fig. 4), including one well (EB-1261) screened in the “600-foot” and “800-foot” sands. One sample from a monitoring well (EB-434) had a chloride concentration of 36.3 mg/L. This well is located near the probable western margin of a saltwater plume in the “600-foot” sand (Whiteman, 1979; Tomaszewski, 1996). Concentrations at this well were at their highest in the 1970s, up to 120 mg/L, but have since remained below this level (fig. 5A). The well screen is likely near the top of the aquifer (Whiteman, 1979, pl. 4), and the concentration may be higher at the base of the aquifer at this location. 3The U.S. Environmental Protection Agency’s secondary maximum contaminant levels (SMCLs) are nonmandatory water quality standards for contaminants that are intended as guidelines for public water supply systems for aesthetic considerations such as taste, color, and odor.

Historical data from several of these wells indicate that the saltwater plume has moved northward from the Baton Rouge fault towards the industrial district (figs. 4, 5B). The highest measured chloride concentration within the plume area was 4,100 mg/L at EB-876 in 1971. EB-870 is the northernmost well where saltwater has been detected in the “600-foot” sand; chloride concentrations at this well increased sharply beginning in around 2005, and the last sample from 2015 had a concentration of 1,480 mg/L. No wells were available to sample between EB-870 and the nearest active well (EB-1318) (fig. 4) in the industrial district to determine the plume’s current northern extent or to monitor its movement. The northwestern edge of the plume is partially constrained, as indicated by chloride concentrations in samples from EB-793 (fig. 5A), which have remained less than 10 mg/L except for a sample in 2004 (29.2 mg/L) and another in 2006 (29.3 mg/L). The most recent sample, which was collected in 2018, had a concentration of 2.64 mg/L. On the northeastern side of the plume, concentrations as high as 2,400 mg/L were detected in monitoring well EB-882 in 1973 before it was plugged. Southeast of the plume, well EB-824 had nine samples with chloride concentrations less than 10 mg/L, with the most recent sample collected during 2005 having a concentration of 3.05 mg/L. On the southwestern side near the fault, a geophysical log collected at well EB-794 indicates that the plume may extend westward to this location (Whiteman, 1979). Two large-diameter wells screened in the “600-foot” sand in the industrial district were plugged in 2019, and userreported groundwater withdrawal data for major facilities compiled by the CAGWCC specify that only one well was withdrawing from the aquifer within the industrial district as of 2021 (CAGWCC, 2022) (fig. 4). Although withdrawals from the “600-foot” sand have decreased through time, any large withdrawals from this aquifer in or near the industrial district are likely to cause saltwater to move towards the production wells.

“800-Foot” Sand of the Baton Rouge Area Nine samples were collected from wells screened in the “800-foot” sand (fig. 6), including a well (EB-1261) screened in the “800-foot” and “600-foot” sands and a well (EB-1135) screened in the “800-foot” and “1,000-foot” sands. No samples had a chloride concentration greater than 10 mg/L. Whiteman (1979) described an area along the northern side of the Baton Rouge fault where qualitative geophysical log characteristics indicate that saltwater occurs in the “800-foot” sand. Griffith (2003, pl. 3) also interpreted a thin saltwater-bearing sand from a log (EB-1028) in this area, and a more recent log collected for a deep monitoring well (EB-10183Z) indicates that the “800-foot” sand might contain saltwater based on a leftward deflection in the gamma curve coupled with low resistivity. The locations of wells with associated geophysical logs that indicate saltwater in the “800-foot” sand are shown in the plume area in figure 6. The “800-foot” sand is interconnected with the “600-foot” sand in

6 Chloride Concentrations in Groundwater, Western Part of the Southern Hills Regional Aquifer System, La., 2021–22 91°12'

91°10'

91°08'

91°06'

91°04'

91°02'

91°

90°58'

90°56'

90°54'

110 Co

190

30°30'

Baton Rouge industrial district

EB-1327 (1.93) 190

30°28' 1 30

WEST 30°26' BATON ROUGE

EAST BATON ROUGE

EB-1282 (3.55)

EB-1259 (3.68)

EB-1246 (305)

30°24'

EB-991B (3.78) EB-1278 (2.74)

Louisiana State University

LIVINGSTON

EB-1017C (3.62)

Ami

EB-1298 (25.0)

30°22'

Mississip

pi R

ASCENSION

iver

Base from Louisiana Department of Natural Resources Strategic Online Natural Resources Information System; Albers Equal-Area Conic projection, standard parallels 29°30' and 45°30' N., central meridian 96°00' W.; World Geodetic System of 1984 Baton Rouge fault—Dashed where approximately located Denham Springs-Scotlandville fault— Dashed where approximately located

0 0

1.5 1.5

3 MILES 3 KILOMETERS

EXPLANATION

Sampled well screened in the "400-foot" sand of the Baton Rouge area and identifier, with measured chloride concentration (in parentheses), in milligrams per liter EB-991B (3.78) Less than 10.0 10.1 to 50.0 50.1 to 250.0 (not present on this figure)

Average daily withdrawals from the "400-foot" sand of the Baton Rouge area at this well in 2021, in million gallons per day Less than 0.15 0.16 to 0.35 0.36 to 1.00 (not present on this figure)

250.1 to 500.0

1.01 to 1.50

500.1 to 1,000.0 (not present on this figure)

1.51 to 1.78

1,000.1 or greater (not present on this figure)

Figure 3. Chloride concentrations in water from wells screened in the “400-foot” sand of the Baton Rouge area collected during November 2021 through February 2022 and reported annual withdrawals from wells screened in the aquifer for 2021 in southeastern Louisiana (Capital Area Groundwater Conservation Commission, 2022).

Results and Discussion 7 91°14'

91°12'

91°10'

91°08'

91°06'

91°04'

91°02'

91°

90°58'

30°34'

110

iver

190 30°30'

30°28'

EB-793*

EB-794

EAST BATON ROUGE

EB-870* EB-500* EB-882

EB-434* (36.30) EB-123* EB-493*

30°26'

Baton Rouge industrial district

EB-1318 (3.42)

WEST BATON ROUGE

R ppi

siss

Mis

EB-1373 (7.25)

30°32'

mi Co

61 EB-824

EB-12611 (3.04) 10

Louisiana State University

Baton Rouge fault—Dashed where approximately located

EB-241

EB-1228 (3.24)

Base from Louisiana Department of Natural Resources Strategic Online Natural Resources Information System; Albers Equal-Area Conic projection, standard parallels 29°30' and 45°30' N., central meridian 96°00' W.; World Geodetic System of 1984 Area with observed saltwater intrusion in the "600-foot" sand of the Baton Rouge area north of the Baton Rouge fault—Queried where uncertain

EB-879 (3.20)

1.5 1.5

Amite

EB-241

EB-876

30°24'

LIVINGSTON

190

River

3 MILES 3 KILOMETERS

EXPLANATION Sampled well screened in the "600-foot" sand (unless otherwise noted) of the Baton Rouge area and identifier, with measured chloride concentration (in parentheses), in milligrams EB-1318 per liter (3.42)

Less than 10.0

Denham Springs-Scotlandville fault— Dashed where approximately located

10.1 to 50.0

Well not sampled during the 2021–22 study and identifier

250.1 to 500.0 (not present on this figure)

Average daily withdrawals from the "600-foot" sand of the Baton Rouge area at this well in 2021, in million gallons per day 0.20 to 0.35 0.36 to 0.90

50.1 to 250.0 (not present on this figure) 500.1 to 1,000.0 (not present on this figure)

1,000.1 or greater (not present on this figure) *Well for which chloride time series is shown in figure 5. 1 Well screened in the "600-foot" and "800-foot" sands of the Baton Rouge area.

Figure 4. Chloride concentrations in water from wells screened in the “600-foot” sand of the Baton Rouge area collected during November 2021 through February 2022 and reported annual withdrawals from wells screened in the aquifer for 2021 in southeastern Louisiana (Capital Area Groundwater Conservation Commission, 2022).

8 Chloride Concentrations in Groundwater, Western Part of the Southern Hills Regional Aquifer System, La., 2021–22 A

104

120

Chloride concentration, in milligrams per liter

140

100

0 1940

1950

1960

1970

1980

1990

2000

2010

2020

2030

Year

103

102

101

10 1940

1950

1960

1970

1980

1990

2000

2010

2020

Year

EXPLANATION

Well screened in the "600-foot" sand of the Baton Rouge area (fig. 4)—Value in parentheses is the well depth, in feet below land surface

EB-434 (611 feet)

EB-123 (710 feet)

EB-793 (687 feet)

EB-493 (704 feet) EB-500 (710 feet) EB-870 (692 feet)

Figure 5. Time series of chloride concentrations in water from selected wells screened in the “600-foot” sand of the Baton Rouge area, southeastern Louisiana (see fig. 4 for well locations).

the vicinity (Kuniansky and others, 1989), and a source of saltwater could be downward leakage from the overlapping plume in the “600-foot” sand (Tomaszewski, 1996). Alternatively, saltwater may have moved laterally from the downthrown “600-foot” sand on the south side of the fault. A chloride concentration of 3,900 mg/L was measured in the “600-foot” sand about 1.2 mi south of the fault at EB-241 in 1943 (fig. 4). Saltwater in the “800-ft” sand has not been observed through direct sampling because no wells are screened in the aquifer near the plume area; therefore, it is unknown if saltwater is migrating. Wells that are withdrawing from the “800-foot” sand as of 2021 are located at least 3.5 mi from the probable plume area (fig. 6).

“1,000-Foot” Sand of the Baton Rouge Area Thirteen samples were collected from wells screened in the “1,000-foot” sand (fig. 7), including a well (EB-772) screened in the “1,000-foot” and “1,200-foot” sands and a well (EB-1135) screened in the “800-foot” and “1,000-foot” sands. Three samples had chloride concentrations greater than 10 mg/L. EB-805, a monitoring well located near the Baton

Rouge fault, had the highest concentration (10,400 mg/L) measured among all wells sampled for this study. The measured concentration is also the highest of the historical record at this well (fig. 8A). Water levels at EB-805 have decreased by about 46 ft from April 1966 to December 2022 (USGS, 2023) and are low enough in the vicinity to induce saltwater movement into the area. EB-1328, a production well screened in the “1,000-foot” sand about 2 mi east of EB-805 (fig. 7), was not available for sampling during the timeframe of this study, but three samples taken shortly after the well was completed during 2004–06 had chloride concentrations ranging from 66.4 to 224 mg/L. A sample collected from a production well (EB-772) screened in the “1,000-foot” and “1,200-foot” sands had a chloride concentration of 45.9 mg/L. This well has been active since 1964, and concentrations began to increase during 2014–17 (fig. 8C). Because the well is screened in two aquifers that both have documented saltwater intrusion to the south near the Baton Rouge fault, it is not clear at what depth saltwater intrusion is occurring. The plume area for the “1,000-foot” sand in East Baton Rouge Parish shown in figure 7 assumes that the increasing concentrations at EB-772 are from

Results and Discussion 9 91°14'

91°12'

91°10'

91°08'

91°04'

91°02'

91°

90°58'

90°54'

90°52'

ite River

90°56'

Comite

30°34'

91°06'

110

ver

Ri ppi

siss

Mis

190

30°30'

30°32'

e Riv

EB-1374 (8.04)

EB-1372 (4.60)

WBR-218 (4.65)

37 EB-1354 (4.25)

Baton Rouge industrial district

EB-1352 (3.6) 190

30°28'

12 WBR-36 WBR-37 ?

30°26'

WEST BATON ROUGE

EB-10183Z ? EB-794

EB-1274

EAST BATON ROUGE

EB-1293A EB-1028 EB-876

EB-1279 (3.89)

EB-1288 (3.11)

EB-777 Louisiana State University

30°24'

EB-11351 (4.41)

EB-12612 (3.04)

ite

Riv

30°22'

LIVINGSTON

ASCENSION 0

Area with observed saltwater intrusion in the "800-foot" sand of the Baton Rouge area north of the Baton Rouge fault— Queried where uncertain Baton Rouge fault—Dashed where approximately located

EB-777

4 MILES 4 KILOMETERS

EXPLANATION Sampled well screened in the "800-foot" sand (unless otherwise noted) of the Baton Rouge area and identifier, with measured chloride concentration (in parentheses), in milligrams EB-1288 per liter (3.11) Less than 10.0

Average daily withdrawals from the "800-foot" sand of the Baton Rouge area at this well in 2021, in million gallons per day Less than 0.15 (not present on this figure) 0.20 to 0.35

Denham Springs-Scotlandville fault— Dashed where approximately located

10.1 to 50.0 (not present on this figure)

Well not sampled during the 2021–22 study and identifier

250.1 to 500.0 (not present on this figure)

1.01 to 1.50

500.1 to 1,000.0 (not present on this figure)

1.51 to 2.00

50.1 to 250.0 (not present on this figure)

1,000.1 or greater (not present on this figure) 1

0.36 to 1.00

Well screened in the "800-foot" and "1,000-foot" sands of the Baton Rouge area. Well screened in the "600-foot" and "800-foot" sands of the Baton Rouge area.

Figure 6. Chloride concentrations in water from wells screened in the “800-foot” sand of the Baton Rouge area collected during November 2021 through February 2022 and reported annual withdrawals from wells screened in the aquifer for 2021 in southeastern Louisiana (Capital Area Groundwater Conservation Commission, 2022).

10 Chloride Concentrations in Groundwater, Western Part of the Southern Hills Regional Aquifer System, La., 2021–22 91°18'

91°16'

91°14'

91°12'

91°10'

91°08'

91°06'

91°04'

91°02'

91°

30°34' 61

110

30°32'

iver

190

Baton Rouge industrial district

30°30' WEST BATON ROUGE 30°28' WBR-136

pi R

siss

Mis

WBR-164 (4.82)

EAST BATON ROUGE

WBR-150 (5.31) ? ? WBR-137

EB-1308 (2.95) ?

EB-1276 (2.87)

EB-632 (2.16) ?

EB-777

30°26'

EB-1220B (3.44)

EB-1123 (5.00)

WBR-147

EB-926 (4.93)

EB-772*1 (45.9)

WBR-104

EB-1035 (4.69)

WBR-209* (30.6)

12 ?

? EB-621 1

Louisiana State University

EB-11352 (4.41)

EB-1328 EB-805* (10,400)

30°24'

61 Base from Louisiana Department of Natural Resources Strategic Online Natural Resources Information System; Albers Equal-Area Conic projection, standard parallels 29°30' and 45°30' N., central meridian 96°00' W.; World Geodetic System of 1984 ?

Area with observed saltwater intrusion in the "1,000-foot" sand of the Baton Rouge area north of the Baton Rouge fault—Queried where uncertain Baton Rouge fault—Dashed where approximately located

WBR-136

0 0

2 2

4 MILES 4 KILOMETERS

EXPLANATION Sampled well screened in the "1,000-foot" sand (unless otherwise noted) of the Baton Rouge area and identifier, with measured chloride concentration (in parentheses), in milligrams EB-1135 per liter (4.41) Less than 10.0

Denham Springs-Scotlandville fault— Dashed where approximately located

10.1 to 50.0

Well not sampled during the 2021–22 study and identifier

250.1 to 500.0 (not present on this figure)

50.1 to 250.0 (not present on this figure) 500.1 to 1,000.0 (not present on this figure) 1,000.1 or greater

Average daily withdrawals from the "1,000-foot" sand of the Baton Rouge area at this well in 2021, in million gallons per day Less than 0.15 0.16 to 0.35 0.36 to 1.00 1.01 to 1.50 1.51 to 1.90

*Well for which chloride time series is shown in figure 8. Well screened in the "1,000-foot" and "1,200-foot" sands of the Baton Rouge area. Well screened in the "800-foot" and "1,000-foot" sands of the Baton Rouge area.

1 2

Figure 7. Chloride concentrations in water from wells screened in the “1,000-foot” sand of the Baton Rouge area collected during November 2021 through February 2022 and reported annual withdrawals from wells screened in the aquifer for 2021 in southeastern Louisiana (Capital Area Groundwater Conservation Commission, 2022).

Results and Discussion 11 A

6,000

4,000

2,000

Chloride concentration, in milligrams per liter

8,000

0 1960

10,000

Chloride concentration, in milligrams per liter

12,000

1970

1980

1990

2000

2010

2020

2030

0 2000

2004

2008

2012

2016

2020

2024

1988 1992 1996 2000 2004 2008 2012 2016 2020 2024

Year

EXPLANATION

Well screened in the "1,000-foot" sand of the Baton Rouge area (fig. 7)—Value in parentheses is the well depth, in feet below land surface EB-805 (1,072 feet)

Dashed vertical lines represent samples from the Louisiana Department of Health database (Louisiana Department of Health, 2023) where the chloride concentration was below the reporting limit (typically 10 milligrams per liter) or a non-detect was noted

Well screened in the "1,000-foot" sand of the Baton Rouge area (fig. 7)—Value in parentheses is the well depth, in feet below land surface

Well screened in the "1,000-foot" and "1,200-foot" sands of the Baton Rouge area—Value in parentheses is the well depth, in feet below land surface

WBR-209 (1,005 feet)

EB-772 (1,214 feet)

Figure 8. Time series of chloride concentrations in water from A, B, two wells screened in the “1,000-foot” sand and C, a well screened in the “1,000-foot” and “1,200-foot” sands of the Baton Rouge area, southeastern Louisiana (see fig. 7 for well locations). Dashed vertical lines represent samples from the Louisiana Department of Health database (Louisiana Department of Health, 2023) where the chloride concentration was below the reporting limit (typically 10 mg/L) or a nondetect was noted.

saltwater intrusion in the “1,000-ft” sand, although the extent of the plume is uncertain because no wells are screened in the “1,000-foot” sand between EB-805 and EB-772. Geophysical logs from wells EB-1287 and EB-1297 (Louisiana Department of Natural Resources, 2023) (fig. 9), which extend through the depth of the “1,000-ft” sand, did not indicate the presence of saltwater in the “1,000-foot” sand at the time the logs were collected in 1998 and 1999, respectively. Saltwater is also known to occur in the “1,000-foot” sand in West Baton Rouge Parish (fig. 7). The presence of saltwater was first confirmed by samples collected during 1966–75 at a now-plugged monitoring well (WBR-104) where chloride concentrations were as high as 360 mg/L. A sample collected for this study from production well WBR-209 had a concentration of 30.6 mg/L, and concentrations at this well began increasing around 2016 (fig. 8B), indicating potential expansion of the known plume area in the “1,000-foot” sand in West Baton Rouge Parish. A sample from another production well

(WBR-150) less than 1 mi to the west-southwest had a concentration of 5.31 mg/L, and concentrations have not increased in 11 samples collected during 1978–2019.

“1,200-Foot” Sand of the Baton Rouge Area Twenty-four samples were collected from wells screened in the “1,200-foot” sand (fig. 9), including a well (EB-1297) screened in the “1,200-foot” and “1,500-foot” sands and a well (EB-772) screened in the “1,000-foot” and “1,200-foot” sands. Four samples had chloride concentrations greater than 10 mg/L. A chloride concentration of 149 mg/L was measured in a sample from EB-621, an older production well that was completed in 1956 about 650 ft north of the Baton Rouge fault. The maximum concentration measured at EB-621 was 297 mg/L in 2019. Chloride concentrations vary considerably in this well (fig. 10A) and are related to pumping at this well

12 Chloride Concentrations in Groundwater, Western Part of the Southern Hills Regional Aquifer System, La., 2021–22 91°20'

91°16'

91°12'

EAST FELICIANA

POINTE COUPEE

91°08'

91°04'

91°

90°56'

EB-1441 (22.2)

Comite River

30°36'

EAST BATON ROUGE 37

Baton Rouge industrial district 30°32'

pi R

ssip

si Mis

iver

EB-557 (5.48) WEST BATON ROUGE 30°28'

WBR-148 (2.47) 10

190 WBR-207 (3.14) WBR-221 (2.45)

EB-756 EB-649 (4.05) (5.31) EB-403 (5.28) EB-523 (4.50) EB-567 (5.16) 37 EB-576 (5.01) 1 EB-580 (3.63) EB-772 190 (45.9) EB-1301 12 EB-584 (3.19) (3.27) EB-1016B 61 (2.72) EB-1003 EB-925 Amite (3.26) EB-621* (149) (2.98) EB-990 (2.16) EB-1287* EB-1312 10 (45.5) EB-1297*2 (2.27) Louisiana State (11.4) University

WBR-37* WBR-36*

LIVINGSTON EB-653 (3.64)

110

Base from Louisiana Department of Natural Resources Strategic Online Natural Resources Information System; Albers Equal-Area Conic projection, standard parallels 29°30' and 45°30' N., central meridian 96°00' W.; World Geodetic System of 1984 Area with observed saltwater intrusion in the "1,200-foot" sand of the Baton Rouge area north of the Baton Rouge fault Baton Rouge fault—Dashed where approximately located Denham Springs-Scotlandville fault— Dashed where approximately located WBR-36

Well not sampled during the 2021–22 study and identifier

2 2

4 MILES 4 KILOMETERS

EXPLANATION Sampled well screened in the "1,200-foot" sand (unless otherwise noted) of the Baton Rouge area and identifier, with measured chloride concentration (in parentheses), in milligrams EB-1312 per liter (2.27)

Average daily withdrawals from the "1,200-foot" sand of the Baton Rouge area at this well in 2021, in million gallons per day Less than 0.15

Less than 10.0

0.16 to 0.35

10.1 to 50.0

0.36 to 1.00

50.1 to 250.0 250.1 to 500.0 (not present on this figure) 500.1 to 1,000.0 (not present on this figure)

1.01 to 1.50 1.51 to 2.60

1,000.1 or greater (not present on this figure) *Well for which chloride time series is shown in figure 10. Well screened in the "1,000-foot" and "1,200-foot" sands of the Baton Rouge area. Well screened in the "1,200-foot" and "1,500-foot" sands of the Baton Rouge area.

1 2

Figure 9. Chloride concentrations in water from wells screened in the “1,200-foot” sand of the Baton Rouge area collected during November 2021 through February 2022 and reported annual withdrawals from wells screened in the aquifer for 2021 in southeastern Louisiana (Capital Area Groundwater Conservation Commission, 2022).

Results and Discussion 13 A

Chloride concentration, in milligrams per liter

400

300

200

100

0 1950

1960

1970

1980

1990

2000

2010

2020

0 1996

2030

2000

2004

Year EXPLANATION

2008

2012

2016

2020

2024

Year EXPLANATION

Well screened in the "1,200-foot" sand of the Baton Rouge area (fig. 9)—Value in parentheses is the well depth, in feet below land surface

EB-621 (1,487 feet)

Well screened in the "1,200-foot" sand of the Baton Rouge area (fig. 9)—Value in parentheses is the well depth, in feet below land surface EB-1287 (1,510 feet)

250

Chloride concentration, in milligrams per liter

0 1996

2000

2004

2008

2012

2016

2020

Year EXPLANATION Dashed vertical lines represent samples from the Louisiana Department of Health database (Louisiana Department of Health, 2023) where the chloride concentration was below the reporting limit (typically 10 milligrams per liter) or a non-detect was noted Well screened in the "1,200-foot" and "1,500-foot" sands of the Baton Rouge area (fig. 9)—Value in parentheses is the well depth, in feet below land surface

2024

200

150

100

0 1956

1960

1964

1968

1972

1976

1980

1984

Year EXPLANATION Well screened in the "1,200-foot" sand of the Baton Rouge area (fig. 9)—Value in parentheses is the well depth, in feet below land surface WBR-36 (1,360 feet) WBR-37 (1,356 feet)

EB-1297 (1,635 feet)

Figure 10. Time series of chloride concentrations in water from A, B, D, four wells screened in the “1,200-foot” sand and C, one well screened in the “1,200-foot” and “1,500-foot” sands of the Baton Rouge area, southeastern Louisiana.

1988

14 Chloride Concentrations in Groundwater, Western Part of the Southern Hills Regional Aquifer System, La., 2021–22 and nearby wells in the weeks or months prior to when samples were collected. Concentrations began to increase around 1978, accompanying a period of increased withdrawals from the well during 1975–87 (Heywood, 2019). The concentrations decreased during 1988–99 but have increased and decreased in the following years, possibly in response to additional withdrawals at two nearby wells (EB-1287 and EB-1297) constructed in 1998 and 1999 in the “1,200-foot” sand. At EB-1287, a production well that is about 1.2 mi northeast of EB-621, the measured chloride concentration was 45.5 mg/L in 2021, which was substantially more than the 22-mg/L concentration measured in 2020 (fig. 10B). The sample collected in 2021 from well EB-1297, which is in the same facility and screened in the “1,200-foot” and the “1,500-foot” sands, had a concentration of 11.4 mg/L. Concentrations at EB-1297 started to gradually increase beginning around the year 2007 (fig. 10C). The lower concentration at EB-1297 compared to EB-1287 may be caused by the contribution of fresher water from the “1,500-foot” sand. Increasing concentrations at EB-1287 and EB-1297 are likely from movement of saltwater from a source area in the “1,200-foot” sand near EB-621. Because the “1,000-foot” sand is known to contain saltwater near these wells (well EB-805, fig. 7), downward leakage of saltwater into the “1,200-foot” sand is possible. Downward leakage could result from density effects or from a hydraulic gradient created by lower water levels in the “1,000-foot” sand relative to the “1,200-foot” sand. Insufficient water level data were available for comparison with the current potentiometric surfaces in the “1,000-foot” and “1,200-foot” sands in this area. Available geophysical logs (Louisiana Department of Natural Resources, 2023) indicate that the confining unit between the “1,000-foot” and “1,200-foot” sands in this area has an average thickness of about 200 ft but the presence of windows in the confining unit is possible. In West Baton Rouge Parish, historical samples from two wells (WBR-36 and WBR-37) screened in the “1,200-foot” sand near the Baton Rouge fault on its northern side had chloride concentrations greater than 10 mg/L beginning in the early 1970s (fig. 10D). The wells were connected to each other by a line to move water from one well to the other for priming the pumps, which may explain the similar chloride concentrations. Whiteman (1979) removed this connection and observed that chloride concentrations decreased in WBR-36 when it was pumped heavily even though it is closer to the Baton Rouge fault than WBR-37. Based on this result, it was tentatively concluded that saltwater intrusion across the fault was not occurring at this location and that the increasing chloride in both wells could be from a casing leak in WBR-37 adjacent to the “800-foot” sand, which may contain saltwater in this area (fig. 6). Chloride concentrations in both wells reached a maximum of 200–210 mg/L in 1986, when sampling was discontinued. Pumping from these wells stopped by 1988 and the wells were plugged in 1991.

Whiteman (1979) also noted that logs from a monitoring well (WBR-147) installed in the downthrown “1,000-foot” sand south of the fault and about 0.25 mi from WBR-36 (fig. 7) showed that there was little sand on the south side of the fault adjacent to the “1,200-foot” sand on the north side and concluded that the risk of saltwater intrusion across the fault was low in this area. Chloride concentrations in 17 samples from WBR-147 ranged from 740 to 800 mg/L during 1977–92. Concentrations greater than 10 mg/L have not been observed in the area north of WBR-36 and WBR-37 in the “1,200-foot” sand, but no wells are currently available for sampling between WBR-36 and WBR-37 and the industrial district where withdrawals from the aquifer are concentrated.

“1,500-Foot” Sand of the Baton Rouge Area Twenty-one samples were collected from wells screened in the “1,500-foot” sand (fig. 11A, B), including 1 from a well screened in the “1,200-foot” and “1,500-foot” sands (EB-1297), and 2 from wells screened in the “1,500-foot” and “1,700-foot” sands (EB-1248, EB-1295C). Ten samples had chloride concentrations greater than 10 mg/L. Samples from three production wells located south of the Baton Rouge fault had concentrations that ranged from 14.4 to 203 mg/L. Seven of the 10 samples with a chloride concentration greater than 10 mg/L were from wells that are located north of the Baton Rouge fault within a saltwater plume in the “1,500-foot” sand that is moving northward towards the Lula Street and Government Street pumping stations (fig. 11B) (Moore and others, 2011; Heywood and others, 2019). The highest chloride concentration measured in the plume area was 3,900 mg/L at well EB-807A in 1996, and historical concentrations measured in several other nearby wells began to level out close to this value; therefore, 3,900 mg/L may be the approximate maximum concentration of saltwater from the source area south of the fault (fig. 12A). Two different mitigation technologies have been used to delay the effect of saltwater intrusion on the two pumping stations: a “connector” well to recharge the “1,500-foot” sand and a scavenger well system to remove saltwater. The connector well (EB-1293) was installed in 1998 south of the Government Street pumping station (fig. 11B) and connects the “800-foot” and “1,500-foot” sands to induce recharge into the “1,500-foot” sand to raise the water level in the aquifer (Dial and Cardwell, 1999). The placement of this well was designed to create a hydraulic barrier to divert the flow of the plume westward away from the Government Street pumping station towards the more distant Lula Street pumping station. Chloride concentrations at the two wells (EB-413 and EB-771) in the Government Street pumping station began to increase during 2003–04, and samples collected for this study had concentrations of 64.4 mg/L and 103 mg/L, respectively (fig. 12B). The flow rate through the connector well depends on the water level difference between the “800-foot” and “1,500-foot” sands at the location of the well and the

Results and Discussion 15

91°24'

30°40'

91°20'

91°16'

WEST FELICIANA POINTE COUPEE

91°12'

91°08'

EB-8371

91°04'

91°

EB-12481 (16.5)

PC-268 (4.1)

EAST FELICIANA

EAST BATON ROUGE 110 EB-773

ver i Ri

(3.46)

ssi issi

Baton Rouge industrial district

190

WEST BATON ROUGE

N TO GS

30°32'

EB-1435 (3.58)

EB-1048 (4.54)

V LI

EB-1155 (4.47)

30°36'

Comite R iver

EB-961 (3.93)

190

30°28'

12 10

See figure 11B 1

Denham Springs-Scotlandville fault— Dashed where approximately located

Baton Rouge fault—Dashed where approximately located

EB-1295C1 (391) 10 0 0

2.5 2.5

5 MILES 5 KILOMETERS

EXPLANATION Sampled well screened in the "1,500-foot" sand (unless otherwise noted) of the Baton Rouge area and identifier, with measured chloride concentration (in parentheses), in milligrams EB-961 per liter (3.93)

Less than 10.0 10.1 to 50.0 50.1 to 250.0

Average daily withdrawals from the "1,500-foot" sand of the Baton Rouge area at this well in 2021, in million gallons per day Less than 0.15 0.16 to 0.35 0.36 to 1.00

250.1 to 500.0

1.01 to 1.50

500.1 to 1,000.0

1.51 to 2.60

1,000.1 or greater (not present on this figure) 2

Amite

VI ER

Louisiana State University

EB-12972 (11.4)

Well screened in "1,500-foot" and "1,700-foot" sands of the Baton Rouge area. Well screened in the "1,200-foot" and "1,500-foot" sands of the Baton Rouge area.

Figure 11. Chloride concentrations in water from wells screened in the “1,500-foot” sand of the Baton Rouge area collected during November 2021 through February 2022 and reported annual withdrawals from wells screened in the aquifer for 2021 in southeastern Louisiana (Capital Area Groundwater Conservation Commission, 2022).

16 Chloride Concentrations in Groundwater, Western Part of the Southern Hills Regional Aquifer System, La., 2021–22 B

91°15'

91°14'

91°13'

91°12'

91°11'

91°10'

91°09' 67

Baton Rouge industrial district

30°28'

EB-510* (31.2)

EB-938* (65.6) EB-1400 EB-1424 (800)

30°27'

Government Street pumping station EB-413* (64.4)

EB-771* (103) EB-1293

EB- 917* (264)

EB-918*

EAST BATON ROUGE

ippi

EB-280

siss

WBR-23*

Louisiana State University 30

Base from Louisiana Department of Natural Resources Strategic Online Natural Resources Information System; Albers Equal-Area Conic projection, standard parallels 29°30' and 45°30' N., central meridian 96°00' W.; World Geodetic System of 1984 Area with observed saltwater intrusion in the "1,500-foot" sand of the Baton Rouge area north of the Baton Rouge fault Baton Rouge fault—Dashed where approximately located Well not sampled during the 2021–22 study and identifier

0 0 Sampled well screened in the "1,500-foot" sand (unless otherwise noted) of the Baton Rouge area and identifier, with measured chloride concentration (in parentheses), in milligrams per liter EB-927 Less than 10.0 (2.84) 10.1 to 50.0

0.75

1.5 MILES

1.5 KILOMETERS

Average daily withdrawals from the "1,500-foot" sand of the Baton Rouge area at this well in 2021, in million gallons per day Less than 0.15 0.16 to 0.35 0.36 to 1.00

250.1 to 500.0

1.01 to 1.50

500.1 to 1,000.0

1.51 to 1.82

1,000.1 or greater (not present on this figure) *Well for which chloride time series is shown in figure 12.

0.75

EXPLANATION

50.1 to 250.0

Figure 11.—Continued

190

Lula Street pumping station EB-927 (2.84)

Mis

WBR-39*

91°06'

EB-789B*

EB-783A*

WBR-173*

30°25'

WBR-114*

91°07'

EB-782B*

WBR-112* (91.4)

Rive

WBR-132* (14.4)

EB-280

EB-658* EB-1423 (84.1)

EB-807A*

WBR-113* (203) WBR-97B*

WEST BATON ROUGE

30°24'

EB-939 (3.74)

EB-1274

30°26'

91°08'

Results and Discussion 17 A

140

Chloride concentration, in milligrams per liter

104

103

102

101

10 1960

1970

1980

1990

2000

Year EXPLANATION

2010

2020

160

100

Year EXPLANATION

Well screened in the "1,500-foot" sand of Dashed vertical lines represent samples the Baton Rouge area (fig. 11B)—Value from the Louisiana Department of in parentheses is the well depth, in feet Health database (Louisiana Department below land surface of Health, 2023) where the chloride concentration was below the reporting EB-413 (1,745 feet) limit (typically 10 milligrams per liter) EB-771 (1,739 feet) or a non-detect was noted

300

Chloride concentration, in milligrams per liter

140

Chloride concentration, in milligrams per liter

120

0 1940 1950 1960 1970 1980 1990 2000 2010 2020 2030

2030

Well screened in the "1,500-foot" sand of the Baton Rouge area (fig. 11B)—Value in parentheses is the well depth, in feet below land surface EB-782B (1,681 feet) EB-917 (1,736 feet) EB-918 (1,834 feet) EB-789B (1,721 feet) EB-807A (1,713 feet)

120 100 80 60 40 20 0 1940 1950 1960 1970 1980 1990 2000 2010 2020 2030

Year EXPLANATION Dashed vertical lines represent samples Well screened in the "1,500-foot" sand of from the Louisiana Department of Health the Baton Rouge area (fig. 11B)—Value database (Louisiana Department of Health, in parentheses is the well depth, in feet 2023) where the chloride concentration below land surface was below the reporting limit (typically EB-938 (1,599 feet) 10 milligrams per liter) or a non-detect EB-510 (1,605 feet) was noted EB-658 (1,604 feet)

250

200

150

100

0 1960

1970

1980

1990

2000

2010

2020

2030

Year EXPLANATION Well screened in the "1,500-foot" sand of the Baton Rouge area (fig. 11B)—Value in parentheses is the well depth, in feet below land surface WBR-97B (2,200 feet) WBR-112 (2,205 feet) WBR-113 (2,242 feet)

Figure 12. Time series of chloride concentrations in water from wells screened in the “1,500-foot” sand of the Baton Rouge area A, within the plume area north of the Baton Rouge fault, B, at the Government Street pumping station, C, at the Lula Street pumping station, and D, E, F, south of the Baton Rouge fault, southeastern Louisiana.

18 Chloride Concentrations in Groundwater, Western Part of the Southern Hills Regional Aquifer System, La., 2021–22 E

350

Chloride concentration, in milligrams per liter

103

102

101

300

250

200

150

100

10 1940 1950 1960 1970 1980 1990 2000 2010 2020 2030

0 1960 1964 1968 1972 1976 1980 1984 1988 1992 1996 2000

Year

EXPLANATION

Well screened in the "1,500-foot" sand of the Baton Rouge area (fig. 11B)—Value in parentheses is the well depth, in feet below land surface EB-783A (2,179 feet)

Well screened in the "1,500-foot" sand of the Baton Rouge area (fig. 11B)—Value in parentheses is the well depth, in feet below land surface WBR-23 (2,098 feet) WBR-114 (not applicable) WBR-39 (2,140 feet) WBR-132 (2,082 feet) WBR-173 (2,194 feet)

Figure 12.—Continued

integrity of the well screens. Daily water levels are recorded in the connector well (EB-1293) and in nearby monitoring wells screened in the “800-foot” (EB-1274) and “1,500-foot” (EB-917) sands to monitor and quantify the connector well’s effect on both aquifers (USGS, 2023). The water levels in both monitoring wells and EB-1293 covary (fig. 13), indicating that the two aquifers are hydraulically connected through EB-1293. Since about 2017, the water level in EB-1293 has slightly increased, possibly indicating sediment buildup along the lower screen, which would reduce outflow to the “1,500-foot” sand and bring its composite water level closer to that of the “800-foot” sand. In 2005, a scavenger well pair was installed within the plume area and south of the Lula Street pumping station to intercept saltwater and extend the lifespan of the pumping station. The scavenger system has a well at the base of the aquifer (EB-1424) that removes denser saltwater and disposes it into the Mississippi River, and a second well with a shallower screen (EB-1423) skims fresher water from the top part

of the aquifer. Samples were collected from both wells for this study; the sample from the shallower well (EB-1423) had a chloride concentration of 84.1 mg/L, and the sample from the deeper well (EB-1424) had a concentration of 800 mg/L. Chloride concentrations in samples recently collected from wells in the Lula Street pumping station have remained below their historical peaks (fig. 12C), but it is unknown if the more concentrated basal layer of the plume has moved past the scavenger well pair. A monitoring well between the scavenger well pair and the Lula Street pumping station (EB-1400, “Progress Park well #1”) (fig. 11B), about 535 ft from the scavenger well system, was not sampled for this study because the well is capped. EB-1400 was completed in 2011, prior to the construction of the scavenger well system, and water quality samples collected before the well was completed in April 2010 indicated that the saltwater plume at this location was stratified with a chloride concentration of 1,955 mg/L at the base of the aquifer and a depth-averaged concentration of about 400 mg/L (Moore and others, 2011).

Results and Discussion 19

Daily mean water level, in feet relative to the North American Vertical Datum of 1988

−20

−40

EB-1274 ("800-foot" sand)

−60

EB-1293 (connector well, "800-foot" and "1,500-foot" sands)

−80

−100

−120

EB-917 ("1,500-foot" sand)

−140 1998

2001

2004

2006

2009

2012

2014

2017

2020

2023

Year

Figure 13. Time series of daily mean water levels in wells screened in the “800-foot” sand of the Baton Rouge area (EB-1274), in the “1,500-foot” sand of the Baton Rouge area (EB-917), and in a connector well screened in both sands (EB-1293), southeastern Louisiana.

Four production wells (WBR-132, WBR-173, WBR-112, and WBR-113) screened in the “1,500-foot” sand tap into a zone of fresh groundwater south of the Baton Rouge fault (fig. 11B). Three of these wells were sampled during this study. Chloride concentrations at the northernmost two of the four wells (WBR-113 and WBR-112) started to increase shortly after the wells were completed in 1968, indicating that a body of higher chloride water was nearby (fig. 12D). Another well located half a mile away that was plugged in 2011 (WBR-97B) shows a similar pattern (fig. 12D). Because WBR-113 has a deeper screen than WBR-112 and WBR-97B, the higher concentrations observed at WBR-113 are likely from density effects. The southernmost two wells (WBR-132 and WBR-173) are also screened at different depths within the “1,500-foot” sand. Concentrations at the deeper well (WBR-173) began to increase around the mid- to late 1990s and have exceeded the SMCL of 250 mg/L, whereas the concentrations at WBR-132 have been more erratic and generally lower, with the sample collected during this study having

a chloride concentration of 14.4 mg/L (fig. 13D). Historical samples from older plugged wells to the south and to the east of the currently active wells indicate a movement of saltwater into this zone of freshwater south of the fault (fig. 12E). To the south of WBR-173, concentrations at WBR-23 ranged from 140 to 780 mg/L during 1946–68. About 0.7 mi north of WBR-23, concentrations at well WBR-114 began to increase about 1972 and reached a maximum of 160 mg/L in 1981 before the well was plugged in 1985 (fig. 12E). The increasing concentrations observed at WBR-173 are likely the result of continued northward movement of this body of saltwater. Across the Mississippi River to the east, chloride concentrations in three samples from EB-280 collected during 1943–57 ranged from 3,000 to 3,100 mg/L, and the increasing concentrations at monitoring well EB-783A observed during its period of record (fig. 12F) may be from the westward movement of saltwater towards the previously or currently active wells across the Mississippi River.

20 Chloride Concentrations in Groundwater, Western Part of the Southern Hills Regional Aquifer System, La., 2021–22

“1,700-Foot” Sand of the Baton Rouge Area

a chloride concentration of 391 mg/L. Concentrations have been increasing at EB-1295C since the well was first sampled in 2004 (fig. 15). Because the well is screened in two aquifers, the depth at which saltwater intrusion is occurring is uncertain. The depiction of the plume shown in figure 15 assumes that intrusion is occurring at the level of the “1,700-foot” sand.

Fourteen samples were collected from wells screened in the “1,700-foot” sand north of the Baton Rouge fault, including 2 wells that are screened in the “1,500-foot” and the “1,700-foot” sands (EB-1295C, EB-1248) (fig. 14). A sample from EB-1295C, a production well near the fault, had

91°36'

91°32'

91°28' WEST FELICIANA

91°24'

91°20'

91°16'

91°12'

91°08'

91°04'

91°

EAST FELICIANA

Thompson Creek 61

30°44'

ite

Ri v

EB-8371

lse

30°40'

EB-1248 (16.5)

POINTE COUPEE

PC-334B (6.91)

LIVINGSTON

30°36' PC-342B (1.92)

190

PC-388 (2.35) WBR-176 (2.3)

WBR-177 (2.69)

30°32'

WEST BATON ROUGE

iver

pi R

sip ssis

Mi 190

WBR-181 (2.66)

30°28'

ST MA IN RT

Base from Louisiana Department of Natural Resources Strategic Online Natural Resources Information System; Albers Equal-Area Conic projection, standard parallels 29°30' and 45°30' N., central meridian 96°00' W.; World Geodetic System of 1984 Area with observed saltwater intrusion in the "1,700-foot" sand of the Baton Rouge area north of the Baton Rouge fault—Queried where uncertain Baton Rouge fault—Dashed where approximately located

EB-837

EB-873 (8.72)

EB-1303 (4.33)

Louisiana State University

0 0

190

EB-1356 (3.91) ?

37 Baton EB-1375 Rouge (4.42) industrial district

WBR-224 (2.37)

IBERVILLE

30°24'

EAST EB-828 BATON (3.42) ROUGE

12 EB-1295C*1 (391) ?

3 3

6 MILES 6 KILOMETERS

EXPLANATION Sampled well screened in the "1,700-foot" sand (unless otherwise noted) of the Baton Rouge area and identifier, with measured chloride concentration (in parentheses), in milligrams EB-873 per liter (8.72)

Less than 10.0

Average daily withdrawals from the "1,700-foot" sand of the Baton Rouge area at this well in 2021, in million gallons per day Less than 0.15 0.16 to 0.35

Denham Springs-Scotlandville fault— Dashed where approximately located

10.1 to 50.0

Well not sampled during the 2021–22 study and identifier

250.1 to 500.0

1.01 to 1.50

500.1 to 1,000.0 (not present on this figure)

1.51 to 2.04

50.1 to 250.0 (not present on this figure)

1,000.1 or greater (not present on this figure)

0.36 to 1.00

*Well for which chloride time series is shown in figure 15. Well screened in the "1,500-foot" and "1,700-foot" sands of the Baton Rouge area.

Figure 14. Chloride concentrations in water from wells screened in the “1,700-foot” sand of the Baton Rouge area collected during November 2021 through February 2022 and reported annual withdrawals from wells screened in the aquifer for 2021 in southeastern Louisiana (Capital Area Groundwater Conservation Commission, 2022).

Results and Discussion 21 450

EXPLANATION

Chloride concentration, in milligrams per liter

400

350

Well screened in the "1,500-foot" and “1,700-foot” sands of the Baton Rouge area (fig. 14)—Value in parentheses is the well depth, in feet below land surface EB-1295C (1,840 feet)

300

250

200

150

100

0 2000

2004

2008

2012

2016

2020

2024

Year

Figure 15. Time series of chloride concentrations in water from well EB-1295C screened in the “1,500-foot” and “1,700-foot” sands of the Baton Rouge area, southeastern Louisiana.

“2,000-Foot Sand” of the Baton Rouge Area Twenty-eight samples were collected from wells screened in the “2,000-foot” sand (fig. 16A, B), including 3 wells (EB-733, EB-1253, EB-1445) screened in the “2,000-foot and “2,400-foot” sands. One production well (EB-1150) north of the Baton Rouge fault had a chloride concentration of 270 mg/L (fig. 17). Saltwater was first detected north of the fault by a test drilling program during 1965–66, and a monitoring well (EB-781) (fig. 16B) was installed near the area where saltwater was thought to be crossing the fault. Since then, chloride concentrations at EB-781 have increased and reached 3,910 mg/L when last measured in 2020 (fig. 17A). Additional monitoring wells screened in the “2,000-foot” sand were installed during 1965–66 (EB-792B and EB-807B) and in 1981 (EB-1028) between EB-781 and various pumping centers to provide advance warning of saltwater movement (fig. 16B). Chloride concentrations greater than 10 mg/L have been detected in EB807B and EB-1028, but not in the easternmost well, EB-792B (fig. 17B), indicating that the plume is traveling along a curved path towards the industrial district. Farther along this path to the north, production wells screened in the “2,000-foot” sand have been affected by saltwater (EB-1150, fig. 17B; EB-444

and EB-630, fig. 17C). EB-1150 is still active, and concentrations were continuing to increase in 2022. EB-444 and EB-630 were plugged in 2000 and 2021, respectively. Chloride concentrations in samples from a production well (EB-1253) screened in the “2,000-foot” and “2,400-foot” sands at the same facility as EB-630 have generally remained less than 10 mg/L, except for samples collected in 2012 (14.6 mg/L) and 2013 (20.4 mg/L). The higher concentrations observed at EB-630 are likely the result of its deeper screen depth. Although the sample collected from EB-1253 in 2022 for this study had a concentration of 4.1 mg/L, a subsequent sample collected in January 2023 was substantially higher with a concentration of 66.6 mg/L. This increase may be related to recent changes in the relative water levels in the “2,000-foot” and “2,400-foot” sands. The volume of flow into the well from each aquifer is dependent on the water level in each aquifer at the location. Water levels measured at EB-1028 screened in the “2,000-foot” sand about 1.5 mi from EB-1253 (fig. 16B) have generally increased since about 2001 but have historically been lower than the water levels at WBR100B screened in the “2,400-foot” sand (about 0.9 mi from EB-1253, fig. 16B). This relation changed during the summer of 2021 when the water levels in EB-1028 began to surpass those at WBR-100B, and measurements taken at both wells in May 2022 showed a difference of about 28 ft (USGS, 2023). As the water level in the “2,000-foot” sand increases relative to the water level in the “2,400-ft” sand, more flow from the “2,000-ft” sand into EB-1253 is expected, and this could contribute to increased chloride concentrations in EB-1253 because the edge of the saltwater plume in the “2,000-foot” sand is at this location. The recent increase in chloride concentration at EB-1253 may also be a consequence of the plugging of EB-630 in 2021; EB-630 may have been intercepting saltwater from the base of the “2,000-ft” sand before the saltwater could move vertically upwards in the aquifer toward the shallower screen of EB-1253. The CAGWCC has considered a scavenger well system to slow the advance of the plume in the “2,000-foot” sand (Heywood and others, 2015). In 2020, a test hole was drilled at a candidate location for a scavenger well, but the aquifer was relatively thin and fine grained at this location, so a monitoring well was completed instead (EB-10183Z) (fig. 16B). Samples taken from this monitoring well had chloride concentrations as high as 230 mg/L in March 2020 (Louisiana Department of Natural Resources, 2023). Two wells south of the Baton Rouge fault screened in the “2,000-foot” sand were sampled during this study (fig. 16A, B). One is a monitoring well (EB-783B, fig. 16B) where chloride concentrations increased sharply from 160 mg/L at the beginning of its measured period in 1965 until about 1978, when the concentrations started to level off to the 700–800-mg/L range (fig. 17D). The other is a production well (EB-1319, fig. 16A) that withdraws from a zone of freshwater south of the fault in the southeastern corner of East Baton Rouge Parish. The sample from this well had a chloride concentration of 11.4 mg/L, marginally higher than previous concentrations which ranged from 7.85 to 11 mg/L.

22 Chloride Concentrations in Groundwater, Western Part of the Southern Hills Regional Aquifer System, La., 2021–22

91°40'

91°30'

91°20'

WEST FELICIANA

91°

WF-291 (3.48)

n Cr eek

Bay

EAST FELICIANA

pso Th

ippi River

siss

Com i

Fa lse Ri ve r

POINTE COUPEE

r EAST BATON ROUGE

ST HELENA

EB-1280 (4.18) Baton Rouge industrial district

190

PC-292B (4.33)

ite

Mis

30°50'

30°40'

90°50'

Raccourci Old River

91°10'

S a ra

LIVINGSTON

EB-1306 (3.78)

190 12

30°30'

WEST BATON ROUGE

TI AR

M ST LANDRY

IBERVILLE

Denham Springs-Scotlandville fault— Dashed where approximately located EB-803B

Well not sampled during the 2021–22 study and identifier

EB-803B*

Am ite EB-1319 (11.4) ASCENSION 0 4

Baton Rouge fault—Dashed where approximately located

Louisiana State University

See figure 16B

8 MILES

8 KILOMETERS

EXPLANATION Sampled well screened in the "2,000-foot" sand (unless otherwise noted) of the Baton Rouge area and identifier, with measured chloride concentration (in parentheses), in milligrams EB-1306 per liter (3.78)

Less than 10.0 10.1 to 50.0 50.1 to 250.0 (not present on this figure)

Average daily withdrawals from the "2,000-foot" sand of the Baton Rouge area at this well in 2021, in million gallons per day Less than 0.15 0.16 to 0.35 0.36 to 1.00

250.1 to 500.0

1.01 to 1.50

500.1 to 1,000.0

1.51 to 1.77

1,000.1 or greater (not present on this figure) *Well for which chloride time series is shown in figure 17.

Figure 16. Chloride concentrations in water from wells screened in the “2,000-foot” sand of the Baton Rouge area collected during November 2021 through February 2022 and reported annual withdrawals from wells screened in the aquifer for 2021 in southeastern Louisiana (Capital Area Groundwater Conservation Commission, 2022).

“2,400-Foot” Sand of the Baton Rouge Area Twenty-four samples were collected from wells screened in the “2,400-foot” sand (fig. 18A, B), including 1 well (EB1187) screened in the “2,400-foot” and “2,800-foot” sands and 3 wells (EB-1445, EB-733, EB-1253) screened in the “2,000-foot” and “2,400-foot” sands. One sample from a monitoring well north of the Baton Rouge fault had a chloride

concentration greater than 10 mg/L; a sample from EB-804B had a concentration of 382 mg/L (fig. 18B). Chloride concentrations in this well began to increase around 1993 and have continued increasing to the present (fig. 19). About 2.1 mi southeast of EB-804B and south of the Baton Rouge fault, chloride concentrations in a monitoring well screened in the downthrown “2,000-foot sand” (EB-803B, fig. 16A) generally increased through the well’s period of record during

Results and Discussion 23 B

91°15'

91°12'30"

91°10'

91°07'30"

Baton Rouge industrial 110 district

91°05'

91°02'30"

WEST BATON ROUGE

30°27'30" 10

EB-856 (3.64)

EAST BATON ROUGE

EB-962 (3.55) EB-722 (3.62) EB-884 (3.58)

Mississippi River

EB-1151 (3.07) EB-1227 (2.42) EB-788 (2.98) EB-851 (2.93)

190

30°30'

EB-1253*1 (4.1)

e Riv

Comit

EB-1443 (3.57)

EB-1447 (3.37) 37

EB-810 (3.41) EB-587 EB-855 (3.47) (3.14)

EB-814 (3.39)

EB-874 (2.35)

EB-774 (3.14)

EB-444* EB-1150* (270)

WBR-100B EB-630*

190

EB-878 (3.03)

EB-10183Z

EB-7331 (2.62) EB-14451 (2.72) EB-807B*

EB-1028*

EB-781*

EB-792B* (2.19)

EB-783B* (736) 30°25' 1

Louisiana State University

Base from Louisiana Department of Natural Resources Strategic Online Natural Resources Information System; Albers Equal-Area Conic projection, standard parallels 29°30' and 45°30' N., central meridian 96°00' W.; World Geodetic System of 1984 Area with observed saltwater intrusion in the "2,000-foot" sand of the Baton Rouge area north of the Baton Rouge fault Baton Rouge fault—Dashed where approximately located Denham Springs-Scotlandville fault— Dashed where approximately located EB-781

Well not sampled during the 2021–22 study and identifier

0 0

1 1

2 MILES 2 KILOMETERS

Less than 10.0

10.1 to 50.0 (not present on this figure) 50.1 to 250.0 (not present on this figure) 250.1 to 500.0 500.1 to 1,000.0 1,000.1 or greater (not present on this figure)

Average daily withdrawals from the "2,000-foot" sand of the Baton Rouge area at this well in 2021, in million gallons per day Less than 0.15 0.16 to 0.35 0.36 to 1.00 1.01 to 1.50 1.51 to 1.77

*Well for which chloride time series is shown in figure 17. 1 Well screened in the "2,000-foot" and "2,400-foot" sands of the Baton Rouge area.

Figure 16.—Continued

1966–2003, reaching a maximum of 602 mg/L in 2000 (fig. 17D). Because the “2,400-foot” sand is partially connected to the downthrown “2,000-foot” sand south of the fault in some areas (Whiteman, 1979; Griffith, 2003), the increasing concentrations at EB-803B may indicate the movement of saltwater past this location into the “2,400-foot” sand north of the fault. Saltwater in the “2,400-foot” sand has also been observed in two other monitoring wells north of the fault. In EB-794 (fig. 18B), chloride concentrations sharply increased about 1994–95 and were at 270 mg/L when the well was last

sampled in 2002 (fig. 19). About 1.4 mi away across the Mississippi River in West Baton Rouge Parish, concentrations in a monitoring well (WBR-100B) gradually increased beginning in about 2004, with the most recent sample from 2018 at 49.1 mg/L (fig. 19). If the source of saltwater to this plume is the downthrown “2,000-foot” sand on the other side of the Baton Rouge fault, then the chloride concentrations may approach the upper limit observed in well EB-783B (about 800 mg/L; fig. 17D), which is screened in the “2,000-foot” sand directly south of this area, about a mile from the fault line (fig. 16B).

24 Chloride Concentrations in Groundwater, Western Part of the Southern Hills Regional Aquifer System, La., 2021–22 A

350

Chloride concentration, in milligrams per liter

4,500 4,000 3,500 3,000 2,500 2,000 1,500 1,000 500

0 1960

1970

1980

1990

2000

2010

2020

300 250 200 150 100 50 0 1960

2030

1970

Chloride concentration, in milligrams per liter

2010

Well screened in the "2,000-foot" sand of the Baton Rouge area (fig. 16B)—Value in parentheses is the well depth, in feet below land surface

900

300 250 200 150 100 50

1950

2000

Well screened in the "2,000-foot" sand of the Baton Rouge area (fig. 16B)—Value in parentheses is the well depth, in feet below land surface

0 1940

1990

Year EXPLANATION

EB-781 (2,286 feet)

350

1980

Year EXPLANATION

1960

1970

1980

1990

2000

2010

2020

2030

EB-1028 (2,238 feet)

EB-792B (2,286 feet)

EB-807B (2,264 feet)

EB-1150 (2,242 feet)

800 700 600 500 400 300 200 100 0 1960

1970

1980

1990

2000

2010

Year EXPLANATION

Well screened in the "2,000-foot" sand of the Baton Rouge area (fig. 16A, B)—Value in parentheses is the well depth, in feet below land surface

2020

EB-783B (2,675 feet) EB-803B (2,565 feet)

EB-12531 (2,667 feet) EB-630 (2,253 feet) EB-444 (2,172 feet) 1

2030

Year EXPLANATION

Well screened in the "2,000-foot" sand of the Baton Rouge area (unless otherwise noted; fig. 16B)—Value in parentheses is the well depth, in feet below land surface

2020

Well screened in the "2,000-foot" and "2,400-foot" sands of the Baton Rouge area.

Figure 17. Time series of chloride concentrations in water from A, B, D, wells screened in the “2,000-foot” sand of the Baton Rouge area and C, one well screened in the “2,000-foot” and “2,400-foot” sands of the Baton Rouge area, southeastern Louisiana.

2030

Results and Discussion 25

91°30'

91°20'

CONCORDIA

WF-259 (3.42)

River

WF-222 (3.37)

ite

Bay

90°40'

30°50'

iver

Raccourci Old River

90°50'

te R

Sara

WF-264 (2.3)

91°

i Com

WF-292 (2.75)

91°10' Thom pson C reek

A 31°

ST HELENA

ppi River sissi

Mis

POINTE COUPEE

EAST BATON ROUGE

Fa lse

30°40'

ve r

EB-1027 (3.88)

EB-11871 (4.08)

190 WEST BATON ROUGE

30°30'

IBERVILLE

Louisiana State University

Baton Rouge industrial district

I RT

190 LIVINGSTON

See figure 18B

0 0

8 MILES 8 KILOMETERS

EXPLANATION

Sampled well screened in the "2,400-foot" sand (unless otherwise noted) of the Baton Rouge area and identifier, with measured chloride concentration (in parentheses), in milligrams per liter EB-1027 Less than 10.0 (3.88) 10.1 to 50.0 (not present on this figure) 50.1 to 250.0 (not present on this figure)

Average daily withdrawals from the "2,400-foot" sand of the Baton Rouge area at this well in 2021, in million gallons per day Less than 0.15 0.16 to 0.35 0.36 to 1.00

250.1 to 500.0

1.01 to 1.50

500.1 to 1,000.0 (not present on this figure)

1.51 to 2.07

1,000.1 or greater (not present on this figure) 1

Well screened in the "2,400-foot" and "2,800-foot" sands of the Baton Rouge area.

Figure 18. Chloride concentrations in water from wells screened in the “2,400-foot” sand of the Baton Rouge area collected during November 2021 through February 2022 and reported annual withdrawals from wells screened in the aquifer for 2021 in southeastern Louisiana (Capital Area Groundwater Conservation Commission, 2022).

26 Chloride Concentrations in Groundwater, Western Part of the Southern Hills Regional Aquifer System, La., 2021–22 B

91°12'

91°10'

91°08'

91°06'

91°04'

91°02'

91°

90°58'

90°56'

61 67

30°32'

110

EB-928 (3.6) EB-1420 (3.22)

EB-1446 (2.79)

30°30'

WEST BATON ROUGE 30°28'

Mississippi River

EB-351 (2.88)

WBR-100B* EB-794*

EAST BATON ROUGE

EB-1367 (3.25) EB-1353 (3.19)

EB-751 (2.98)

EB-12531 (4.1)

30°26'

EB-1262 (3.46) 190

EB-1004 (2.6)

EB-1252 (2.77) EB-1149*

EB-1032 (3.78)

EB-769 (3.77) EB-654 (3.59)

Baton Rouge industrial district

EB-813 (2.15)

12 LIVINGSTON

EB-7331 (2.62) EB-14451 (2.72)

1 ?

Louisiana State University

EB-804B* (382) ?

ite

30°24'

30 Base from Louisiana Department of Natural Resources Strategic Online Natural Resources Information System; Albers Equal-Area Conic projection, standard parallels 29°30' and 45°30' N., central meridian 96°00' W.; World Geodetic System of 1984 ?

Area with observed saltwater intrusion in the "2,400-foot" sand of the Baton Rouge area north of the Baton Rouge fault—Queried where uncertain Baton Rouge fault—Dashed where approximately located

EB-794

0 0

2 2

Sampled well screened in the "2,400-foot" sand (unless otherwise noted) of the Baton Rouge area and identifier, with measured chloride concentration (in parentheses), in milligrams EB-733 per liter

4 KILOMETERS

(2.62)

Less than 10.0

Average daily withdrawals from the "2,400-foot" sand of the Baton Rouge area at this well in 2021, in million gallons per day Less than 0.15 0.16 to 0.35

10.1 to 50.0 (not present on this figure)

Well not sampled during the 2021–22 study and identifier

250.1 to 500.0

1.01 to 1.50

500.1 to 1,000.0 (not present on this figure)

1.51 to 2.07

50.1 to 250.0 (not present on this figure)

1,000.1 or greater (not present on this figure) *Well for which chloride time series is shown in figure 19. Well screened in the "2,000-foot" and "2,400-foot" sands of the Baton Rouge area.

Figure 18.—Continued

4 MILES

EXPLANATION

Denham Springs-Scotlandville fault— Dashed where approximately located

0.36 to 1.00

Results and Discussion 27

“2,800-Foot” Sand of the Baton Rouge Area

Chloride concentration, in milligrams per liter

500

400

300

200

100

0 1960

1970

1980

1990

2000

2010

2020

2030

Year EXPLANATION Dashed vertical lines represent samples from the Louisiana Department of Health database (Louisiana Department of Health, 2023) where the chloride concentration was below the reporting limit (typically 10 milligrams per liter) or a non-detect was noted Well screened in the "2,400-foot" sand of the Baton Rouge area (fig. 18B)—Value in parentheses is the well depth, in feet below land surface EB-804B (2,762 feet) EB-794 (2,709 feet) WBR-100B (2,448 feet) EB-1149 (2,694 feet)

Figure 19. Time series of chloride concentrations in water from wells screened in the “2,400-foot” sand of the Baton Rouge area, southeastern Louisiana.

Twenty-four samples were collected from wells screened in the “2,800-foot” sand (fig. 20A, B), including a sample from a well screened in the “2,400-foot” and “2,800-foot” sands (EB-1187). Of these, eight samples had chloride concentrations that were greater than 10 mg/L. The “2,800-foot” sand contains a broad freshwater-saltwater transition zone extending about 2–7 mi north of the Baton Rouge fault (Whiteman, 1979; Tomaszewski, 1996; Lovelace, 2007) (fig. 20B). For this reason, wells that currently withdraw from the “2,800-foot” sand are located north of the industrial district (fig. 20A). Just north of the industrial district, chloride concentrations have been increasing at two production wells (EB-798 and EB-750) that are within the transition zone (fig. 20). A sample collected for this study from EB-798 had a concentration of 333 mg/L, and the most recent sample from EB-750 had a concentration of 80.5 mg/L (fig. 21A, B). Concentrations as high as 110 mg/L have been measured in samples from monitoring well EB-1000, and concentrations as high as 24 mg/L have been measured in samples from production well EB-978 (fig. 21B), which is farther north. Chloride concentrations in samples from other wells in this area have generally remained below 10 mg/L or were only slightly greater than 10 mg/L. In Pointe Coupee Parish, a chloride concentration of 70.6 mg/L was measured in a sample from production well PC-267 near False River (fig. 20A). Concentrations in samples collected from this well during 1995–2022 have ranged from 57.1 to 74.1 mg/L but are not increasing (fig. 21C). According to well registration documents, a sample collected in 1986 before the well was completed had a concentration of 42.4 mg/L (Louisiana Department of Natural Resources, 2023). Several other historical samples from wells screened in the “2,800-foot” sand around False River also had chloride concentrations that were greater than 10 mg/L.

28 Chloride Concentrations in Groundwater, Western Part of the Southern Hills Regional Aquifer System, La., 2021–22 A

91°20'

91°10'

91°

Thom pson

67 EAST FELICIANA

ST HELENA

Bay

Sara

WEST FELICIANA

iver

te R

EF-317 (10.6)

90°50'

i Com

Cree k

91°30'

30°50'

WF-290 (2.43)

WF-270 (2.19)

i ipp River

siss

Fal

30°40'

se R

ive

EB-845 (12.3)

PC-267* (70.6)

POINTE COUPEE

EB-1247 (16.4)

EAST BATON ROUGE

EB-1186 (2.5) EB-1365 (2.59)

EB-846 (2.62) EB-1174 (18.6)

ite Ri ve r

Mis

EB-830 (2.8)

EB-1302 EB-844B (2.33) (16.4)

64 See figure 20B LIVINGSTON

WEST BATON ROUGE 30°30'

190 Baton Rouge industrial district

190 IBERVILLE

12 0 0

3 3

6 MILES 6 KILOMETERS

EXPLANATION Sampled well screened in the "2,800-foot" sand (unless otherwise noted) of the Baton Rouge area and identifier, with measured chloride concentration (in parentheses), in milligrams per liter EB-1302 Less than 10.0 (2.33) 10.1 to 50.0 50.1 to 250.0

Average daily withdrawals from the "2,800-foot" sand of the Baton Rouge area at this well in 2021, in million gallons per day Less than 0.15 0.16 to 0.35 0.36 to 1.00

250.1 to 500.0

1.01 to 1.50

500.1 to 1,000.0 (not present on this figure)

1.51 to 1.60

1,000.1 or greater (not present on this figure) *Well for which chloride time series is shown in figure 21.

Figure 20. Chloride concentrations in water from wells screened in the “2,800-foot” sand of the Baton Rouge area collected during November 2021 through February 2022 and reported annual withdrawals from wells screened in the aquifer for 2021 in southeastern Louisiana (Capital Area Groundwater Conservation Commission, 2022).

Results and Discussion 29 B

91°12'

91°10'

91°08'

91°06'

91°04'

30°36' EB-1419 (2.43)

EAST BATON ROUGE

61 30°34'

EB-978* EB-1292 (5.18) EB-723 (7.97)

EB-1000*

Ap p fres roxim zon hwat ate n e in er-s orth the altw ern "2,8 ate limi 00- r tra t of foo t" s nsitio and n EB-798* (333) 110

EB-700 (7.69)

Ri r

Riv

Baton Rouge industrial district

WEST BATON ROUGE

190

EB-922 (4.65)

siss

Mis

ppi

EB-730 (2.77)

EB-750*

EB-1187 (4.08)

30°32'

EB-568 (2.33) EB-859 (10.7)

Well not sampled during the 2021–22 study and identifier

0 0

2 MILES 2 KILOMETERS

Less than 10.0 10.1 to 50.0 50.1 to 250.0 (not present on this figure) 250.1 to 500.0 500.1 to 1,000.0 (not present on this figure) 1,000.1 or greater (not present on this figure)

*Well for which chloride time series is shown in figure 21. 1 Well screened in the "2,400-foot" and "2,800-foot" sands of the Baton Rouge area.

Figure 20.—Continued

Average daily withdrawals from the "2,800-foot" sand of the Baton Rouge area at this well in 2021, in million gallons per day Less than 0.15 0.16 to 0.35 0.36 to 1.00 1.01 to 1.34

30 Chloride Concentrations in Groundwater, Western Part of the Southern Hills Regional Aquifer System, La., 2021–22

Chloride concentration, in milligrams per liter

700

A EXPLANATION Well screened in the "2,800-foot" sand of the Baton Rouge area (fig. 20B)—Value in parentheses is the well depth, in feet below land surface EB-798 (2,647 feet)

600 500 400 300 200 100 0 1960

1970

1980

1990

2000

2010

2020

2030

Year

Chloride concentration, in milligrams per liter

120

B EXPLANATION Well screened in the "2,800-foot" sand of the Baton Rouge area (fig. 20B)—Value in parentheses is the well depth, in feet below land surface

100

EB-750 (2,643 feet)

EB-1000 (2,926 feet) EB-978 (2,540 feet)

0 1960

Chloride concentration, in milligrams per liter

100

1970

1980

1990

2000

2010

2020

2030

Year

EXPLANATION Well screened in the "2,800-foot" sand of the Baton Rouge area (fig. 20A)—Value in parentheses is the well depth, in feet below land surface

PC-267 (2,175 feet) 60

0 1992

1996

2000

2004

2008

2012

2016

2020

2024

Year

Figure 21. Time series of chloride concentrations in water from wells screened in the “2,800-foot” sand of the Baton Rouge area, southeastern Louisiana.

References Cited 31

Summary High chloride concentrations in groundwater can potentially reduce water availability for certain uses. Saltwater intrusion has been documented in East and West Baton Rouge Parishes in southeastern Louisiana, where groundwater withdrawals have lowered water levels and caused saltwater to move northward across the Baton Rouge fault at different depths and locations. The U.S. Geological Survey, in cooperation with the Capital Area Groundwater Conservation Commission, monitors concentrations of chloride in groundwater through an annual sampling network at wells near known saltwater plumes. To supplement this routine data collection, additional water samples were collected during November 2021 through February 2022. A total of 161 wells screened in the 10 named aquifers of the Southern Hills regional aquifer system were sampled to document chloride concentrations in groundwater. The sample results were compared to historical data to determine where chloride concentrations are increasing. Continued saltwater intrusion at one or more wells north of the Baton Rouge fault was observed for the “1,000-foot,” “1,200-foot,” “1,500-foot,” “2,000-foot,” “2,400-foot,” and “2,800-foot” sands of the Baton Rouge area. The current extents and rates of movement of known plumes in the “600-foot” and “800-foot” sands of the Baton Rouge area are uncertain because of the limited availability of monitoring wells screened in these aquifers near or within the plumes. Increasing chloride concentrations have been observed in one well screened in both the “1,500-foot” and “1,700-foot” sands of the Baton Rouge area, but it is unknown at which stratigraphic level saltwater intrusion is occurring at this location. Saltwater intrusion has not been observed in the “400-foot” sand of the Baton Rouge area. Since the previous expanded chloride sampling effort during 2004–06, the observed plume areas for the “1,000-foot” and “1,200-foot” sands of the Baton Rouge area have likely expanded northward to additional production wells. The plume areas are estimated from data collected at a limited number of wells, and their extents are uncertain. In several cases, saltwater intrusion is inferred from increasing concentrations at a single well. In all cases, the leading edges of the known plumes are either untracked or are known from analysis of samples from active wells that have increasing chloride concentrations. There are few operable monitoring wells between known areas of intrusion and currently producing wells to provide advance warning, information on the rate of encroachment, or water level data to constrain hydraulic gradients. Because of the wide range of depths from which groundwater is withdrawn in the Baton Rouge area and the degree of urban and residential development, construction of new monitoring wells may be challenging. The results presented herein serve to inform future data collection activities, the selection of new monitoring well locations, and the formulation of numerical models to simulate chloride transport. Additionally, these data could be used by water managers to

assess the relative risk of saltwater intrusion to existing water supply infrastructure at different depths within the Southern Hills regional aquifer system.

References Cited Anderson, C.E., Hanor, J.S., and Tsai, F.T.-C., 2013, Sources of salinization of the Baton Rouge aquifer system, southeastern Louisiana: Gulf Coast Association of Geological Societies Transactions, v. 63, p. 3–12. Buono, A., 1983, The Southern Hills regional aquifer system of southeastern Louisiana and southwestern Mississippi: U.S. Geological Survey Water-Resources Investigations Report 83–4189, 38 p. [Also available at https://doi.org/ 10.3133/wri834189.] Capital Area Groundwater Conservation Commission [CAGWCC], 2022, Historic Water Data: Capital Area Groundwater Conservation District database, accessed June 6, 2021, at https://www.capitalareagroundwater.com/ water-use. Chen, Y., Vahdat-Aboueshagh, H., Tsai, F.T.-C., Dausman, A., and Runge, M.C., 2023, Unstructured-grid approach to develop high-fidelity groundwater model to understand groundwater flow and storage responses to excessive groundwater withdrawals in the Southern Hills aquifer system in southeastern Louisiana (USA): Journal of Hydrology, Regional Studies, v. 46, article 101342, 22 p. Collier, A.L., 2018, Water withdrawals by source and category in Louisiana Parishes, 2014–2015: U.S. Geological Survey data release, accessed October 13, 2020, at https://doi.org/ 10.5066/F78051VM. Dial, D.C., and Cardwell, G.T., 1999, A connector well to protect water-supply wells in the “1,500-foot” sand of the Baton Rouge, Louisiana, area from saltwater encroachment: Capital Area Ground Water Conservation Commission Bulletin no. 5, 17 p. Fishman, M.J., and Friedman, L.C., eds., 1989, Methods for determination of inorganic substances in water and fluvial sediments: U.S. Geological Survey Techniques of WaterResources Investigations, book 5, chap. A1, 545 p. [Also available at https://pubs.water.usgs.gov/twri/. Chapters originally published from 1997 to 1999; updates and revisions are ongoing and are summarized at https://water.usgs.gov/ owq/FieldManual/mastererrata.html.] Griffith, J.M., 2003, Hydrogeologic framework of southeastern Louisiana: Louisiana Department of Transportation and Development Water Resources Technical Report no. 72, 21 p., 18 pls. [Also available at https://wise.er.usgs.gov/dp/ pdfs/TR72.pdf.]

32 Chloride Concentrations in Groundwater, Western Part of the Southern Hills Regional Aquifer System, La., 2021–22 Halford, K.J., and Lovelace, J.K., 1994, Analysis of groundwater flow in the “1,200-foot” aquifer, Baton Rouge area, Louisiana: Louisiana Department of Transportation and Development Water Resources Technical Report no. 54, 68 p. [Also available at https://wise.er.usgs.gov/dp/pdfs/ TR54.pdf.] Heywood, C.E., Griffith, J.M., and Lovelace, J.K., 2014, Simulation of groundwater flow in the “1,500-foot” sand and “2,000-foot” sand, with scenarios to mitigate saltwater migration in the “2,000-foot” sand of the Baton Rouge area, Louisiana (ver. 1.2, June 2014): U.S. Geological Survey Scientific Investigations Report 2013–5227, 63 p. [Also available at http://dx.doi.org/10.3133/sir20135227.]

Louisiana Department of Natural Resources, 2023, Strategic Online Natural Resources Information System (SONRIS): Louisiana Department of Natural Resources database, accessed from November 2021 through March 2023 at https://www.sonris.com/. Lovelace, J.K., 2007, Chloride concentrations in ground water in East and West Baton Rouge Parishes, Louisiana, 2004–05: U.S. Geological Survey Scientific Investigations Report 2007–5069, 27 p. [Also available at https://pubs. usgs.gov/sir/2007/5069/.] McCulloh, R.P., 2001, Active faults in East Baton Rouge Parish, Louisiana: Louisiana Geological Survey Public Information Series no. 8, 6 p.

Heywood, C.E., 2019, SEAWAT Model of Flow and Chloride Transport in the 1,500-Foot, 2,400-Foot, and 2,800-Foot Sands of the Baton Rouge Area, Louisiana: U.S. Geological Survey data release, https://doi.org/10.5066/P9URJ38Q.

Meyer, R.R., and Turcan, A.N., Jr., 1955, Geology and groundwater resources of the Baton Rouge area, Louisiana: U.S. Geological Survey Water-Supply Paper 1296, 138 p., 3 pls.

Heywood, C.E., Lindaman, M.A., and Lovelace, J.K., 2019, Simulation of groundwater flow and chloride transport in the “1,500-foot” sand, “2,400-foot” sand, and “2,800-foot” sand of the Baton Rouge area, Louisiana: U.S. Geological Survey Scientific Investigations Report 2019–5102, 49 p. [Also available at https://doi.org/10.3133/sir20195102.]

Moore, R., Kelson, V., and Anderson, E., 2011, Remedial options for saltwater encroachment in the 1,500-foot sand—Final project report: Baton Rouge Water Company, prepared by Layne Hydro, Bloomington, Indiana, 215 p. [Also available at https://www.dnr.louisiana.gov/assets/ OC/env_div/gw_res/ENV2012_01_01/BRWC_REPORT_ 20120103.pdf.]

Heywood, C.E., Lovelace, J.K., and Griffith, J.M., 2015, Simulation of groundwater flow and chloride transport in the “1,200-foot” sand with scenarios to mitigate saltwater migration in the “2,000-foot” sand in the Baton Rouge area, Louisiana (ver. 1.1, September 2015): U.S. Geological Survey Scientific Investigations Report 2015–5083, 69 p. [Also available at https://doi.org/10.3133/sir20155083.] Huntzinger, T.L., Whiteman, C.D., Jr., and Knochenmus, D.D., 1985, Simulation of ground-water movement in the “1,500and 1,700-foot” aquifer of the Baton Rouge area, Louisiana: Louisiana Department of Transportation and Development Water Resources Technical Report no. 34, 52 p. Kuniansky, E.L., Dial, D.C., and Trudeau, D.A., 1989, Maps of the “400-foot,” “600-foot,” and adjacent aquifers and confining beds, Baton Rouge area, Louisiana: Louisiana Department of Transportation and Development Water Resources Technical Report no. 48, 16 p. [Also available at https://wise.er.usgs.gov/dp/pdfs/TR48.pdf.] Lindaman, M.A., 2024, Chloride concentration data for the western part of the Southern Hills regional aquifer system, Louisiana, 2021–22, and selected historical data: U.S. Geological Survey data release, https://doi.org/10.5066/ P9A9OBT6. Louisiana Department of Health, 2023, Health Data Explorer: Louisiana Department of Health database, accessed February 2023 at https://healthdata.ldh.la.gov/.

Morgan, C.O., and Winner, M.D., Jr., 1964, Salt-water encroachment in aquifers of the Baton Rouge area— Preliminary report and proposal: Louisiana Department of Public Works, 37 p. Pham, H.V., and Tsai, F.T.-C., 2017, Modeling complex aquifer systems—A case study in Baton Rouge, Louisiana (USA): Hydrogeology Journal, v. 25, no. 3, p. 601–615. Rollo, J.R., 1969, Saltwater encroachment in aquifers of the Baton Rouge area, Louisiana: Louisiana Department of Conservation, Louisiana Geological Survey, and Louisiana Department of Public Works Water Resources Bulletin 13, 45 p. Snead, J.I., and McCulloh, R.P., 1984, Geologic map of Louisiana: Louisiana Geological Survey, scale 1:500,000. Tomaszewski, D.J., 1996, Distribution and movement of saltwater in aquifers in the Baton Rouge area, Louisiana, 1990–92: Louisiana Department of Transportation and Development Water Resources Technical Report no. 59, 44 p. [Also available at https://wise.er.usgs.gov/dp/pdfs/ TR59.pdf.] Torak, L.J., and Whiteman, C.D., Jr., 1982, Applications of digital modeling for evaluating the ground-water resources of the “2,000-foot” sand of the Baton Rouge area, Louisiana: Louisiana Department of Transportation and Development Water Resources Technical Report no. 27, 87 p. [Also available at https://wise.er.usgs.gov/dp/pdfs/ TR27.pdf.]

References Cited 33 U.S. Environmental Protection Agency, 2023, Secondary Drinking Water Standards—Guidance for nuisance chemicals: U.S. Environmental Protection Agency web page, accessed March 2023 at https://www.epa.gov/sdwa/ secondary-drinking-water-standards-guidance-nuisance- chemicals. U.S. Geological Survey [USGS], 1997–2024, National field manual for the collection of water-quality data: U.S. Geological Survey Techniques of Water-Resources Investigations, book 9, chaps. A1–A9, [variously paged]. [Also available at https://pubs.water.usgs.gov/twri/. Chapters originally published from 1997 to 1999; updates and revisions are ongoing and are summarized at https:// water.usgs.gov/owq/FieldManual/mastererrata.html.]

U.S. Geological Survey [USGS], 2023, USGS water data for the Nation: U.S. Geological Survey National Water Information System database, accessed from September 2022 through March 2023 at https://doi.org/ 10.5066/F7P55KJN. Whiteman, C.D., Jr., 1979, Saltwater encroachment in the “600-foot” and “1,500-foot” sands of the Baton Rouge area, Louisiana, 1966–78, including a discussion of saltwater in other sands: Louisiana Department of Transportation and Development, Office of Public Works Water Resources Technical Report no. 19, 49 p. [Also available at https:// wise.er.usgs.gov/dp/pdfs/TR19.pdf.]

For more information about this publication, contact Director, Lower Mississippi-Gulf Water Science Center U.S. Geological Survey 640 Grassmere Park, Suite 100 Nashville, TN 37211 For additional information, visit https://www.usgs.gov/centers/lmg-water/ Publishing support provided by Lafayette Publishing Service Center

Lindaman—Chloride Concentrations in Groundwater, Western Part of the Southern Hills Regional Aquifer System, La., 2021–22—SIR 2024–5057

ISSN 2328-0328 (online) https://doi.org/10.3133/sir20245057

Chloride Concentrations in Groundwater From the Western Part of the Southern Hills Regional Aquifer System, Louisiana, 2021–22

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