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Hydraulic Conductivity and Transmissivity Estimates from Slug Tests in Wells Within the Mississippi Alluvial Plain, Arkansas and Mississippi, 2020

Scientific Investigations Report 2023-5101
Water Availability and Use Science Program
By:
https://doi.org/10.3133/sir20235101

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Abstract

During the spring and summer of 2020, the U.S. Geological Survey conducted single-well slug tests on selected observation wells within the Mississippi Alluvial Plain in Arkansas and Mississippi to estimate hydraulic conductivity and transmissivity values for the Mississippi River Valley alluvial and middle Claiborne aquifers. Well and aquifer data were collected from field measurements, well-construction reports, and published aquifer-thickness information. A total of 324 slug-in and slug-out tests were conducted on 48 wells by using mechanical slugs to displace the water column and submersible pressure transducers to record changes in water levels in the wells. Hydraulic conductivity of the aquifers in which the wells are screened was estimated by curve fitting the water-level-change data using aquifer test analysis software. Estimates of aquifer transmissivity were made by multiplying the estimated hydraulic conductivity value by the aquifer thickness at well locations. Mean hydraulic conductivity estimates for 44 observation wells screened in the Mississippi River Valley alluvial aquifer range from 3 to 401 feet per day, and mean transmissivity estimates range from 285 to 80,559 feet squared per day. Mean hydraulic conductivity estimates for four observation wells screened in units of the middle Claiborne aquifer range from 0.14 to 183 feet per day, and mean transmissivity estimates range from 55 to 67,913 feet squared per day. The results from these tests can be used to improve the understanding of water availability and groundwater migration, to refine groundwater models, and to ultimately provide stakeholders and decisionmakers better information for management of the groundwater resources within the Mississippi Alluvial Plain.

Introduction

A slug test, or instantaneous change in head test, is a type of aquifer test conducted to obtain data from which an estimate of the hydraulic conductivity (K) of an aquifer, at the observation well location, can be made (Bouwer and Rice, 1976). A slug test requires an “instantaneous” change in the level of the water column in a well and rapid measurements of the water-level response. The most common slug-test method is to displace the water in a well with a solid mechanical slug and record the change in water level with a submersible pressure transducer (Cunningham and Schalk, 2011). This method combines ease of use, accuracy, and rapidity of water-level measurements during a test.

The U.S. Geological Survey (USGS) performed 324 slug-in and slug-out tests on 48 observation wells in the Mississippi Alluvial Plain section of the Coastal Plain Physiographic Province (Fenneman, 1938) in Arkansas and Mississippi. Tests were conducted from March through August 2020 on 44 observation wells screened in the Mississippi River Valley alluvial aquifer and 4 observation wells screened in either the Memphis aquifer or the Sparta aquifer (fig. 1; table 1). The Memphis/Sparta aquifer (referred to as both the Memphis aquifer and the Sparta aquifer) are part of the middle Claiborne aquifer of the Mississippi embayment aquifer system (Renken, 1998). The tests were conducted to obtain estimates of K and transmissivity (T) for the aquifers at the locations of the tested wells.

Most of the observation wells selected for slug testing in the Mississippi Alluvial Plain were completed in the Mississippi River Valley alluvial aquifer
Figure 1.

Locations of observation wells selected for slug testing in the Mississippi Alluvial Plain, Arkansas and Mississippi, 2020.

Table 1.    

Location information for observation wells selected for slug testing in the Mississippi Alluvial Plain, Arkansas and Mississippi, 2020.

[USGS, U.S. Geological Survey; Miss., Mississippi; Ark., Arkansas]
Map number (fig. 1) Site name for this study Agency code Site number
(USGS, 2020)		 Latitude, in decimal degrees Longitude, in decimal degrees State County
1 MS_BP-03a USGS 332514090500901 33.4206 −90.8357 Miss. Washington
2 MS_BP-03b USGS 332514090500902 33.4206 −90.8357 Miss. Washington
3 MS_BP-04a USGS 331654090501401 33.2816 −90.8372 Miss. Washington
4 MS_BP-04b USGS 331654090501402 33.2816 −90.8372 Miss. Washington
5 MS_OW-01 USGS 333535090180301 33.5931 −90.3010 Miss. Leflore
6 MS_OW-02 USGS 333550090174201 33.5972 −90.2950 Miss. Leflore
7 MS-OW-03 USGS 333547090180301 33.5965 −90.3010 Miss. Leflore
8 MS-OW-04 USGS 333452090181301 33.5811 −90.3036 Miss. Leflore
9 MS_OW-05 USGS 333613090162801 33.6035 −90.2744 Miss. Leflore
10 MS_OW-06 USGS 333611090161501 33.603 −90.2708 Miss. Leflore
11 MS_OW-08 USGS 333611090155401 33.603 −90.2651 Miss. Leflore
12 MS_OW-09 USGS 333621090161401 33.6059 −90.2707 Miss. Leflore
13 MS_OW-10 USGS 333600090161701 33.6001 −90.2715 Miss. Leflore
14 MS_OW-12 USGS 333602090140501 33.6005 −90.2346 Miss. Leflore
15 MS_OW-13 USGS 333545090184601 33.5959 −90.3127 Miss. Leflore
16 MS_OW-14 USGS 333631090182501 33.6087 −90.3068 Miss. Leflore
17 MS_QV-01a USGS 333805090240501 33.6348 −90.4013 Miss. Leflore
18 MS_SF-02a USGS 333824090320701 33.6399 −90.5353 Miss. Sunflower
19 MS_SF-02b USGS 333824090320702 33.64 −90.5354 Miss. Sunflower
20 MS_YB-06a USGS 333315090105301 33.5542 −90.1813 Miss. Leflore
21 MS_YB-06b USGS 333315090105302 33.5542 −90.1813 Miss. Leflore
22 MS_YZ-07a USGS 324044090323401 32.6789 −90.5429 Miss. Yazoo
23 MS_YZ-07b USGS 324044090323402 32.6789 −90.5429 Miss. Yazoo
24 AR_ANRC_027N AR008 342553091225101 34.4314 −91.3808 Ark. Arkansas
26 AR_ANRC_028 AR008 342630091300701 34.4417 −91.5019 Ark. Arkansas
27 AR_ANRC_029 AR008 334916091182501 33.8211 −91.3069 Ark. Desha
28 AR_ANRC_030 AR008 334144091284201 33.6956 −91.4783 Ark. Drew
29 AR_ANRC_037N AR008 344139091054201 34.6942 −91.0950 Ark. Monroe
31 AR_ANRC_039 AR008 344649091330001 34.7803 −91.5500 Ark. Prairie
33 AR_ANRC_041S AR008 344659091293701 34.7831 −91.4936 Ark. Prairie
34 AR_ANRC_042 AR008 345735091080101 34.9597 −91.1336 Ark. St. Francis
35 AR_ANRC_001 AR008 351630090193301 35.275 −90.3258 Ark. Crittenden
36 AR_ANRC_003 AR008 353224090264601 35.54 −90.4461 Ark. Poinsett
38 AR_ANRC_007 AR008 351508090511301 35.2522 −90.8536 Ark. Cross
39 AR_ANRC_009 AR008 360431090391701 36.0753 −90.6547 Ark. Greene
40 AR_ANRC_014 AR008 353740090180201 35.6278 −90.3006 Ark. Poinsett
41 AR_ANRC_016 AR008 350944091035401 35.1622 −91.0650 Ark. Woodruff
42 AR_ANRC_017 AR008 352128091191901 35.3578 −91.3219 Ark. Woodruff
43 AR_USDA_1N USDA 353819090511201 35.6381 −90.8536 Ark. Poinsett
44 AR_USDA_1S USDA 353816090511301 35.638 −90.8536 Ark. Poinsett
45 AR_USGS_001 USGS 354916090512501 35.821 −90.8568 Ark. Craighead
46 AR_USGS_002 USGS 352726090523101 35.4572 −90.8754 Ark. Poinsett
47 AR_USGS_CR-03a USGS 351305091143401 35.2181 −91.2427 Ark. Woodruff
48 AR_USGS_CR-03b USGS 351305091143402 35.2181 −91.2427 Ark. Woodruff
25 AR_ANRC_027S AR008 342553091225102 34.4314 −91.3808 Ark. Arkansas
30 AR_ANRC_037S AR008 344139091054202 34.6942 −91.0950 Ark. Monroe
32 AR_ANRC_041N AR008 344659091293702 34.7831 −91.4936 Ark. Prairie
37 AR_ANRC_006 AR008 351630090193302 35.275 −90.3258 Ark. Crittenden
Table 1.    Location information for observation wells selected for slug testing in the Mississippi Alluvial Plain, Arkansas and Mississippi, 2020.

The purpose of this report is to document the hydrogeologic setting, well descriptions, slug-testing and data analysis methods, and hydraulic conductivity and transmissivity estimates from slug tests conducted at 48 observation wells within the Mississippi Alluvial Plain of Arkansas and Mississippi. This report provides hydrogeologic information that hydrologists, groundwater modelers, and economists can use for water-availability planning and modeling. This work supports a major goal of the USGS Water Mission Area Science Strategy (Evenson and others, 2013) to “advance understanding of processes that determine water availability.” The data collection and analyses conducted as part of this study add to the understanding of the hydrogeology of the aquifers within the Mississippi embayment aquifer system and will aid in evaluating the occurrence, availability, and quality of groundwater to help support local water management.

These tests were conducted as part of the USGS Mississippi Alluvial Plain (MAP) Regional Water Availability Study, which is supported by the USGS Water Availability and Use Science Program. For the MAP Study, the USGS has partnered with the Arkansas Department of Agriculture Natural Resources Division, Arkansas Department of Health, Louisiana Department of Transportation and Development, Mississippi Delta Council, Delta F.A.R.M., Delta Wildlife, Mississippi Department of Environmental Quality, Yazoo Mississippi Delta Joint Water Management District, Missouri Department of Natural Resources, U.S. Army Corps of Engineers, and U.S. Department of Agriculture – Agricultural Research Service. The shared goal is to provide stakeholders and managers information and tools to better understand and manage groundwater resources within the MAP by using advanced characterization of the MAP, synthesis of field data, and numerical modeling.

Hydrogeologic Setting

The Mississippi River Valley alluvial aquifer underlies the Mississippi Alluvial Plain (table 2; figs. 1 and 2) and extends southward from the head of the Mississippi embayment aquifer system to where it merges with the Coastal Lowlands aquifer system near the Gulf of Mexico (Renken, 1998). The aquifer ranges from about 120 miles wide near the latitude of Little Rock, Arkansas, to 75 miles wide between Vicksburg, Mississippi, and Monroe, Louisiana. The aquifer consists of a braided, upward-fining sequence of gravel and coarse sand overlain by finer sand, silt, and clay that form a confining unit in most areas (Renken, 1998). The thickness of the Mississippi River Valley alluvial aquifer ranges from about 25 to about 200 feet (ft), and the thickness of the confining unit averages between 20 and 30 ft. The Mississippi River Valley alluvial aquifer directly overlies and in places is hydraulically interconnected with the deeper aquifers of the Mississippi embayment aquifer system (fig. 2) (Renken, 1998).

Table 2.    

Hydrogeologic information for and descriptions of selected aquifers with wells that were slug tested in 2020 in the Mississippi Alluvial Plain. (Modified from Petersen and others [1985] and Renken [1998]).
Hydrogeologic unit name National aquifer code Mississippi embayment aquifer system unit Aquifer type Description
Quaternary alluvium N100MSRVVL (Mississippi River Valley alluvial aquifer) Mississippi River Valley alluvial aquifer Unconfined Unconsolidated alluvial floodplain and terrace deposits that grade from gravel and coarse sand in the lower sections to silt and clay in the upper sections. The coarse sands and gravels in the lower sections are the materials that compose the alluvial aquifer. Maximum thickness is about 200 feet. Commonly yields 1,000 to 3,000 gallons per minute to wells.
Mississippi River Valley alluvial aquifer
Memphis aquifer S100MSEMBM (Mississippi embayment aquifer system) Middle Claiborne aquifer Confined Fine to medium sand, some interbeds of clay. Maximum thickness greater than 1,000 feet. Commonly yields up to 1,000 gallons per minute to wells.
Sparta aquifer1
Table 2.    Hydrogeologic information for and descriptions of selected aquifers with wells that were slug tested in 2020 in the Mississippi Alluvial Plain. (Modified from Petersen and others [1985] and Renken [1998]).
1

North of latitude 35 degrees, the Sparta aquifer is part of the Memphis aquifer.

Generalized west-to-east profile of the Mississippi embayment aquifer system shows the relation of the Mississippi River Valley alluvial aquifer to the underlying units
Figure 2.

Generalized west-to-east profile of the Mississippi embayment aquifer system (modified from Arthur and Taylor, 1998).

The Mississippi embayment aquifer system extends eastward from Arkansas to northwestern Mississippi. The system consists of six aquifers of poorly consolidated to unconsolidated bedded sand, silt, and clay that have formed along the axis of the southerly plunging trough of the Mississippi embayment (fig. 2) (Renken, 1998).

Within the Mississippi embayment aquifer system, the middle Claiborne aquifer may be known locally as the Sparta and the Memphis aquifer (Hart and others, 2008) (table 2; fig. 2). The middle Claiborne aquifer is thickest in a large area of east-central Louisiana and southwestern Mississippi and in a smaller area of southeastern Arkansas, where the thickness is more than 1,000 ft and dissolved solids concentrations are greater than 1,000 milligrams per liter (Renken, 1998). In most areas where water in the middle Claiborne aquifer contains smaller concentrations of dissolved solids, the thickness of the aquifer generally ranges from 200 to 800 ft (Renken, 1998).

In most of its southern extent, confining units separate the middle Claiborne aquifer from underlying and overlying aquifers (fig. 2). The lower Claiborne confining unit underlies the middle Claiborne aquifer, and the middle Claiborne confining unit overlies the aquifer. Silt and clays that make up these confining units were deposited during widespread marine transgression periods that interrupted progradation of clastic sediments into the Gulf Coast Basin (Renken, 1998). Grain size in the lower Claiborne confining unit coarsens north of lat 35° N. and transitions to sandy channel sediments deposited in a coastal margin delta system (Hosman and others, 1968). In Arkansas and northernmost Mississippi, where the lower Claiborne confining unit is missing, the middle Claiborne aquifer and the lower Claiborne-upper Wilcox aquifers function as a single aquifer, which is known locally as the Memphis aquifer (Renken, 1998).

Well Descriptions

Slug tests were conducted on 48 observations wells located within the MAP in Arkansas and Mississippi during the spring and summer of 2020. The selection of test locations was based on information needs of the USGS MAP Regional Water Availability Study and other local, State, and Federal partners. Well-construction information was obtained from drillers’ construction reports on file with the Arkansas Natural Resources Commission, formerly the Arkansas Water Well Construction Commission (Arkansas Department of Agriculture, 2024) or the USGS National Water Information System database (USGS, 2020). Twenty-five of the tested observation wells are in Arkansas, and 23 are in Mississippi (fig. 1; table 1). Well-construction information required for hydraulic conductivity estimations includes the hole depth and diameter; the well depth and diameter; and the well opening (screen) top depth, length, and diameter (table 3).

Table 3.    

Construction information for selected observation wells selected for slug testing in the Mississippi Alluvial Plain, Arkansas and Mississippi, 2020. Data from Pugh (2023).

[ft, foot; bls, below land surface; in., inch; Open, well opening or screen]
Site name for this study Hole depth (ft bls) Hole diameter (in.) Well depth (ft bls) Well diameter (in.) Open top depth
(ft bls)		 Open length (ft) Open diameter (in.)
MS_BP-03a 100 3.57 80.5 2 70.5 10 2
MS_BP-03b 48 3.57 45 2 35 10 2
MS_BP-04a 98 3.57 81 2 69.5 10 2
MS_BP-04b 49 3.57 47 2 37 10 2
MS_OW-01 72.5 3.57 72.5 2 62.5 10 2
MS_OW-02 93 3.57 72 2 71 10 2
MS-OW-03 74 3.57 73 2 63 10 2
MS-OW-04 94 3.57 73 2 63 10 2
MS_OW-05 79.5 3.57 79 2 68 10 2
MS_OW-06 75 3.57 72.5 2 37 10 2
MS_OW-08 79.5 3.57 78 2 68 10 2
MS_OW-09 75 3.57 72.5 2 71 10 2
MS_OW-10 79.5 3.57 77 2 67.5 10 2
MS_OW-12 79.5 3.57 78 2 61 10 2
MS_OW-13 75 3.57 73 2 19 10 2
MS_OW-14 79.5 3.57 78 2 68 10 2
MS_QV-01a 80 3.57 79.5 2 59.5 10 2
MS_SF-02a 93 3.57 79.5 2 69 10 2
MS_SF-02b 62 3.57 59.5 2 63 10 2
MS_YB-06a 98 3.57 80 2 63 10 2
MS_YB-06b 50 3.57 40.5 2 80.5 10 2
MS_YZ-07a 98 3.57 81 2 70 10 2
MS_YZ-07b 65 3.57 47 2 42 10 2
AR_ANRC_027N 162 6 152.5 4 142.5 10 4
AR_ANRC_028 142 6 136.25 4 126.25 10 4
AR_ANRC_029 105 6 93.8 4 83.8 10 4
AR_ANRC_030 103 6 93.7 4 83.7 10 4
AR_ANRC_037N 142 6 126.5 4 116.5 10 4
AR_ANRC_039 182 6 160 4 150 10 4
AR_ANRC_041S 142 6 130 4 120 10 4
AR_ANRC_042 135 6 127.7 4 117.7 10 4
AR_ANRC_001 166 6 162 4 142 20 4
AR_ANRC_003 122 6 115.2 4 95.6 19 4
AR_ANRC_007 155 6 149.9 4 139.9 10 4
AR_ANRC_009 135 6 121.2 4 103 20 4
AR_ANRC_014 112 6 107.2 4 87.7 19 4
AR_ANRC_016 154 6 150 4 130 20 4
AR_ANRC_017 118 6 110.2 4 90.5 20 4
AR_USDA_1N 147.2 6 147.2 4 117.5 25 4
AR_USDA_1S 150 6 150 4 120 25 4
AR_USGS_001 130 6 127.9 4 107.9 20 4
AR_USGS_002 165 6 155.9 4 136.6 19 4
AR_USGS_CR-03a 93 6 87.5 4 77.5 10 4
AR_USGS_CR-03b 72 6 45.5 4 35.5 10 4
AR_ANRC_027S 611      6 610    4 579.8 30 4
AR_ANRC_037S 563      6 563    4 489 20 3
AR_ANRC_041N 448      6 447.2    4 416 30 3
AR_ANRC_006 482      6 460    4 429.6 30 4
Table 3.    Construction information for selected observation wells selected for slug testing in the Mississippi Alluvial Plain, Arkansas and Mississippi, 2020. Data from Pugh (2023).

Downhole Equipment—Transducers and Slugs

Downhole equipment dimensions for the pressure transducers and mechanical slugs are required to estimate hydraulic conductivity. Vented Level TROLL 700 Data Logger (In-Situ, Fort Collins, Colorado) pressure transducers were used to measure changes in the well water column during slug testing. The pressure transducers have an outside diameter of 0.72 inch (in.).

Twelve mechanical polyvinyl chloride slugs of various sizes and volumes were constructed and calibrated for this study (fig. 3). The slugs were constructed of capped, schedule-40 polyvinyl chloride pipes that were filled with gravel, and a steel eye bolt was installed in one end cap of each slug. The slugs were calibrated by repeatedly submerging them in a calibration well with a known diameter. Water levels were measured by using a calibrated electric water-level tape, and the volume of water displaced was calculated. Detailed slug dimensions and calibration information are available in the associated data release (Pugh, 2023).

Mechanical slugs used during tests are of differing lengths and diameters
Figure 3.

Mechanical slugs used during tests in selected wells to estimate hydraulic conductivity and transmissivity of aquifers in the Mississippi Alluvial Plain, Arkansas and Mississippi, 2020. Photograph by Aaron Pugh, U.S. Geological Survey, March 16, 2020.

Field Methods

Groundwater-Level Data Collection

Before and after each slug test, the static water level in each well was measured with a calibrated tape following the procedures specified in the USGS groundwater technical procedures document 1 in Cunningham and Schalk (2011). All static water-level measurements are available in the USGS National Water Information System database (USGS, 2020). The static water-level measurement at each well was used to help determine the aquifer’s saturated thickness. Additionally, the static water-level measurement was used to determine the depth to suspend the transducer below the water surface before slug testing and the depth to lower and raise the slug to ensure it was fully submerged during slug-in testing and completely above the water surface during slug-out testing.

Slug-Test Methods

The methods followed for the slug tests are presented in the USGS groundwater technical procedures document 17 in Cunningham and Schalk (2011). A minimum of 3 slug-in tests and 3 slug-out tests were conducted in 47 of the 48 wells tested. At well AR_ANRC_037S, completed in the Sparta aquifer, only two slug tests (two slug-in and two slug-out) were conducted because of excessively long water-level recovery times.

Slug testing began with an initial static water-level measurement followed by the deployment of the pressure transducer below the top of the water column in the well. The pressure transducer was connected to a laptop computer, set to record at a 0.25-second sampling interval, and the logging of water-level measurements was started. Once the water level in the well returned to the static level following transducer deployment, the first slug-in test was initiated by quickly lowering a mechanical slug completely below the water surface which caused the water level in the well to rise (fig. 4A and 4B). Once the water level returned to the static level, the slug-in test was considered complete. The second test, a slug-out test, was then initiated by quickly pulling the mechanical slug up so it was completely above the water surface, thus causing the water level to fall (fig. 4C and 4D). Once the water level returned to the static level, the slug-out test was considered complete. This process was repeated twice more, providing six different slug tests, three slug-in tests and three slug-out tests, for the well. When the six slug tests were complete, the data logging was stopped, and the data-log file was up-loaded to the laptop. The pressure transducer was then removed from the well, and a second static water-level measurement was made.

During a slug-in test, water level in the well rises; during the start of the slug-out test, water level lowers.
Figure 4.

Well diagrams showing a mechanical slug and pressure transducer: A, mechanical slug poised just above the water level before slug-in test, B, mechanical slug submerged below water level for slug-in test, C, mechanical slug removed just above water level for slug-out test, and D, mechanical slug removed from well following slug-out test (from Cunningham and Schalk, 2011).

During testing, water levels were considered static when they equaled the initial static water-level measurement or when the change in water level was less than 0.01 ft per 10 minutes. For slug testing, the data collected during the beginning of the test are usually the most important for the water-level curve matching used to estimate hydraulic conductivity values (Cunningham and Schalk, 2011). When water-level changes were less than 0.01 ft per 10 minutes during the latter part of the test, the tests were considered to provide good-quality data for estimating hydraulic conductivity values. For most of the tests, water levels returned to a pre-testing static condition in less than 5 minutes following the insertion or removal of the mechanical slug, although this took considerably longer for a few tests.

Photographic Documentation

Photographs were taken at well sites for basic documentation (fig. 5). Images are available, by well site, in Pugh (2023).

U.S. Geological Survey employee preparing to insert a mechanical slug into the well being tested at well MS_QV-01a in Mississippi, March 17, 2020
Figure 5.

U.S. Geological Survey employee preparing to insert a mechanical slug into the well being tested at well MS_QV-01a in Mississippi, March 17, 2020. (Photograph by Aaron Pugh, U.S. Geological Survey.)

Analytical Methods for Estimating Hydraulic Conductivity

Water-level changes for each slug test were analyzed by using one of three slug-test methods based on the well and aquifer information and by using aquifer test analysis software, AQTESOLV version 4.50.002 (HydroSOLVE, Inc., 2007). The Bouwer and Rice (1976) solution was used on overdamped slug-test responses in full or partially penetrating wells in confined and unconfined aquifers. The response data from an overdamped slug test are generally decreasing monotonically with increasing time (log head or normalized head versus time) and occur in aquifers with low to moderate hydraulic conductivity values (HydroSOLVE, Inc., 2007). The Springer and Gelhar (1991) and Butler (1998) methods were used on underdamped slug-test responses. The response data during an underdamped slug test are oscillatory with increasing time and occur in aquifers with high hydraulic conductivity values (HydroSOLVE, Inc., 2007).

The aquifer test analysis software provides two estimates for each slug-test estimate of hydraulic conductivity. The first estimate is an “automatic estimate” using an automatic curve-fitting algorithm to create a best-fit curve by varying the effective well length and the hydraulic conductivity parameters until the curve best fits the observed water-level data. The effective well length equals the height of the water column above the top of the screen plus one-half the screen length. The second estimate is a “visual estimate” using a user-generated best-fit curve match of the water-level data made by manually varying the effective well length and the hydraulic conductivity parameters.

Both the visual and automatic curve-fitting estimates were recorded and used to develop the statistical summary of estimates for each well. All visual curve-fitting estimates were used; however, a few automatic curve-fitting estimates were discarded because of spurious water-level measurements resulting in excessively large estimates when compared to the other test estimates for the same well. These spurious water-level measurements may have occurred when splashing and sloshing water was recorded by the pressure transducer. The analyzed results for the slug tests conducted in each well are available from Pugh (2023).

Analytical Methods for Estimating Transmissivity

Estimates of transmissivity were made by multiplying the estimated hydraulic conductivity value by the aquifer thickness at the well location. Aquifer thicknesses were obtained from Torak and Painter (2019) or the interactive Mississippi Embayment Regional Aquifer (MERAS) Hydrogeologic Framework web application (USGS, undated).

Limitations and Assumptions

The hydraulic conductivity estimated by a slug test represents a small volume of the aquifer material surrounding the tested well, not the average hydraulic conductivity of the aquifer. Hydraulic conductivity estimates from slug tests are usually smaller than those estimated from pumping tests (Brown and others, 1995). Hydraulic conductivity estimates from slug tests are influenced by the well filter packs, wellbore skin effects, and solution method assumptions made during analysis.

Well filter packs will influence the estimated hydraulic conductivity if they have a different hydraulic conductivity than the surrounding, undisturbed aquifer formation. A filter pack is the coarse sand or fine gravel placed between the borehole wall and screen that filters fine-grained particles, preventing them from entering the well (Butler, 1998).

Similarly, a wellbore skin will influence the estimated hydraulic conductivity because it is a zone of differing hydraulic conductivity adjacent to the wellbore face resulting from well construction and (or) development (Butler, 1998). A positive wellbore skin is a zone adjacent to the wellbore with a smaller hydraulic conductivity than that of the undisturbed aquifer formation. A positive wellbore skin may occur if, during construction, bentonite drilling mud is used or fine-grained formation materials are smeared across the wellbore face of larger grained materials, and the well is not properly completed. A negative wellbore skin is a zone with a hydraulic conductivity larger than that of the undisturbed aquifer formation. A negative wellbore skin may occur when finer grained particles at the wellbore face are eroded away and can occur with excessive well development (Butler, 1998).

Bouwer and Rice Method

The Bouwer and Rice (1976) method is a semi-analytical method for the analysis of overdamped slug tests in a fully or partially penetrating well in an unconfined or confined aquifer. The Bouwer and Rice method employs a quasi-steady-state model that ignores elastic storage in the aquifer (HydroSOLVE, Inc., 2007). The Bouwer and Rice method makes the following assumptions: (1) the aquifer has infinite areal extent, (2) the aquifer is homogeneous and of uniform thickness, (3) the test well is fully or partially penetrating, (4) the aquifer is confined or unconfined, (5) flow to the well is quasi-steady state (storage is negligible), and (6) the slug is introduced into or removed from the well instantaneously.

Springer and Gelhar Method

The Springer and Gelhar (1991) method extended the Bouwer and Rice (1976) method for a slug test in a homogeneous, anisotropic, unconfined aquifer to include inertial effects in the test well. The solution accounts for oscillatory water-level response sometimes observed in aquifers with high hydraulic conductivity. Based on the work of Butler (2005), AQTESOLV has incorporated frictional well loss in small-diameter wells (HydroSOLVE, Inc., 2007). The Springer and Gelhar method makes the following assumptions: (1) the aquifer has infinite areal extent, (2) the aquifer is homogeneous and of uniform thickness, (3) the test well is fully or partially penetrating, (4) the aquifer is unconfined, (5) the flow is quasi-steady state, and (6) the slug is introduced into or removed from the well instantaneously.

Butler Method

The Butler (1998) method extended the Hvorslev (1951) solution for a single-well slug test in a homogeneous, anisotropic, confined aquifer to include inertial effects in the test well. The solution accounts for oscillatory water-level response sometimes observed in aquifers with high hydraulic conductivity. Butler (2005) amended the method to incorporate frictional well loss in small-diameter wells. The Butler method makes the following assumptions: (1) the aquifer has infinite areal extent, (2) the aquifer is homogeneous and of uniform thickness, (3) test well is partially penetrating, (4) the aquifer is confined, (5) the flow is quasi-steady state, and (6) the slug is introduced into or removed from the well instantaneously.

Hydraulic Conductivity and Transmissivity Estimates

A total of 324 slug tests were conducted, providing 598 estimates of hydraulic conductivity and transmissivity. Based on the methodology described earlier, only 576 slug-test estimates would be expected (48 tested wells × 6 tests/well × 2 estimates/test). Additional slug tests were conducted for the following reasons: (1) during training, two sets of three slug tests (three slug-in tests and three slug-out tests) were conducted on well MS_OW-05 by different USGS personnel, and (2) USGS personnel conducted additional sets of slug tests (a slug-in test and a slug-out test) whenever there were questions or problems with a previous set of slug tests. Wells where additional sets of tests were conducted have more than 12 test estimates (tables 4 and 5).

Table 4.    

Estimated hydraulic conductivity for aquifers at selected wells in the Mississippi Alluvial Plain, Arkansas and Mississippi, 2020. Data from Pugh (2023).

[ft, foot; dates are in month/day/year format; bls, below land surface; ft/d, foot per day; n, number of test estimates; Min, minimum, Max, maximum; Springer-Gelhar (Springer and Gelhar, 1991); Bouwer-Rice (Bouwer and Rice, 1976); Butler (Butler, 1998)]
Site name for this study Aquifer thickness, in ft Test date Static water level, in ft bls Slug-test method used Estimated hydraulic conductivity, in ft/d
n Min Mean Median Max
MS_BP-03a 138      3/18/2020 20.36 Springer-Gelhar 11 58 106 106 160
MS_BP-03b 138      3/18/2020 20.16 Bouwer-Rice 12 38 80 78 126
MS_BP-04a 138      3/18/2020 16.08 Springer-Gelhar 14 111 156 158 189
MS_BP-04b 138      3/18/2020 15.97 Springer-Gelhar 16 44 65 68 77
MS_OW-01 139      3/18/2020 30.95 Springer-Gelhar 12 141 199 196 282
MS_OW-02 141      3/17/2020 34.12 Springer-Gelhar 12 90 109 105 139
MS-OW-03 139      3/17/2020 37.59 Bouwer-Rice, Springer-Gelhar 12 15 23 24 27
MS-OW-04 141      3/17/2020 31.92 Springer-Gelhar 12 67 90 92 106
MS_OW-051 138      3/17/2020 24.05 Springer-Gelhar 12 92 106 107 128
MS_OW-051 138      3/17/2020 24.05 Springer-Gelhar 12 51 100 109 127
MS_OW-06 137      3/16/2020 26.37 Springer-Gelhar 12 147 226 217 307
MS_OW-08 137      3/18/2020 20.13 Springer-Gelhar 12 49 84 74 118
MS_OW-09 130      3/17/2020 28.93 Springer-Gelhar 12 54 89 94 121
MS_OW-10 137      3/17/2020 28.12 Springer-Gelhar 8 50 80 77 111
MS_OW-12 131      3/17/2020 21.356 Bouwer-Rice 12 4 5 5 6
MS_OW-13 135      3/17/2020 34.18 Springer-Gelhar 12 31 103 107 222
MS_OW-14 133      3/18/2020 32.09 Springer-Gelhar 12 122 190 189 254
MS_QV-01a 137      3/17/2020 53.26 Springer-Gelhar 16 47 144 149 241
MS_SF-02a 124      3/18/2020 53 Springer-Gelhar 12 63 90 90 113
MS_SF-02b 124      3/18/2020 52.99 Springer-Gelhar 12 40 67 68 89
MS_YB-06a 106      3/18/2020 5.33 Springer-Gelhar 12 54 72 72 99
MS_YB-06b 106      3/18/2020 5.23 Bouwer-Rice 11 18 28 30 33
MS_YZ-07a 99      3/18/2020 5.28 Springer-Gelhar 12 56 90 93 110
MS_YZ-07b 99      3/18/2020 5.27 Springer-Gelhar 16 10 14 12 21
AR_ANRC_027N 142      8/5/2020 102.56 Bouwer-Rice 9 157 178 184 186
AR_ANRC_028 133      7/23/2020 107.82 Bouwer-Rice 13 6 61 59 143
AR_ANRC_029 111      8/6/2020 46.85 Bouwer-Rice, Springer-Gelhar 11 63 98 96 140
AR_ANRC_030 95      8/6/2020 29.9 Springer-Gelhar 15 91 182 124 426
AR_ANRC_037N 136      7/21/2020 18.1 Springer-Gelhar 13 41 95 71 243
AR_ANRC_039 150      7/22/2020 112.79 Bouwer-Rice, Springer-Gelhar 8 62 88 92 107
AR_ANRC_041S 152      7/22/2020 92.23 Bouwer-Rice 12 14 15 15 17
AR_ANRC_042 142      7/21/2020 68.47 Bouwer-Rice 6 109 155 161 196
AR_ANRC_001 146      7/2/2020 32.35 Springer-Gelhar 16 88 126 134 149
AR_ANRC_003 163      7/2/2020 19.17 Springer-Gelhar 16 65 82 84 97
AR_ANRC_007 167      7/1/2020 90.34 Bouwer-Rice 15 50 111 126 148
AR_ANRC_009 97      7/3/2020 90.06 Bouwer-Rice 4 2 3 3 4
AR_ANRC_014 164      7/2/2020 17.64 Bouwer-Rice 12 34 68 78 92
AR_ANRC_016 185      7/1/2020 71.68 Bouwer-Rice 16 16 20 21 22
AR_ANRC_017 130      7/1/2020 13.45 Bouwer-Rice 12 15 40 47 49
AR_USDA_1N 145      6/30/2020 124.13 Bouwer-Rice 12 4 4 5 5
AR_USDA_1S 145      6/30/2020 125.19 Bouwer-Rice 16 2 3 3 4
AR_USGS_001 121      7/3/2020 88.15 Bouwer-Rice 12 22 29 30 32
AR_USGS_002 203      7/2/2020 112.13 Bouwer-Rice 13 18 34 36 45
AR_USGS_CR-03a 201      6/30/2020 7.7 Springer-Gelhar 12 155 252 259 379
AR_USGS_CR-03b 201      6/30/2020 7.66 Springer-Gelhar 16 227 401 381 649
AR_ANRC_027S 400      8/5/2020 13.51 Bouwer-Rice 8 0.02 0.14 0.15 0.24
AR_ANRC_037S 372      7/21/2020 62.2 Springer-Gelhar, Butler 8 50 183 103 646
AR_ANRC_041N 391      7/22/2020 107.13 Bouwer-Rice 11 6 8 8 9
AR_ANRC_006 720      7/2/2020 30.41 Bouwer-Rice 16 6 7 7 7
Table 4.    Estimated hydraulic conductivity for aquifers at selected wells in the Mississippi Alluvial Plain, Arkansas and Mississippi, 2020. Data from Pugh (2023).
1

An additional set of tests was conducted on well MS_OW-05.

Table 5.    

Estimated transmissivity for aquifers at selected wells in the Mississippi Alluvial Plain, Arkansas and Mississippi, 2020. Data from Pugh (2023).

[ft, foot; dates are in month/day/year format; bls, below land surface; ft2/d, foot squared per day; n, number of test estimates; Min, minimum, Max, maximum; Springer-Gelhar (Springer and Gelhar, 1991); Bouwer-Rice (Bouwer and Rice, 1976); Butler (Butler, 1998)]
Site name for this study Aquifer thickness, in ft Test date Static water level, in ft bls Slug-test method used Estimated transmissivity, in ft2/d
n Min Mean Median Max
MS_BP-03a 138 3/18/2020 20.36 Springer-Gelhar 11 7,990 14,592 14,614 22,011
MS_BP-03b 138 3/18/2020 20.16 Bouwer-Rice 12 5,288 11,081 10,718 17,319
MS_BP-04a 138 3/18/2020 13.08 Springer-Gelhar 14 15,318 21,488 21,818 26,096
MS_BP-04b 138 3/18/2020 12.97 Springer-Gelhar 16 6,042 8,975 9,419 10,605
MS_OW-01 139 3/18/2020 28.45 Springer-Gelhar 12 19,529 27,596 27,280 39,100
MS_OW-02 141 3/17/2020 31.65 Springer-Gelhar 12 12,655 15,282 14,805 19,600
MS-OW-03 139 3/17/2020 35.59 Bouwer-Rice, Springer-Gelhar 12 2,105 3,216 3,362 3,724
MS-OW-04 141 3/17/2020 29.62 Springer-Gelhar 12 9,531 12,654 13,060 14,964
MS_OW-051 138 3/17/2020 21.55 Springer-Gelhar 12 12,662 14,659 14,699 17,612
MS_OW-051 138 3/17/2020 21.55 Springer-Gelhar 12 6,959 13,743 15,071 17,433
MS_OW-06 137 3/16/2020 23.37 Springer-Gelhar 12 20,084 30,898 29,722 41,991
MS_OW-08 137 3/18/2020 17.63 Springer-Gelhar 12 6,703 11,530 10,118 16,111
MS_OW-09 130 3/17/2020 26.43 Springer-Gelhar 12 7,036 11,598 12,199 15,682
MS_OW-10 137 3/17/2020 25.62 Springer-Gelhar 8 6,828 10,925 10,519 15,180
MS_OW-12 131 3/17/2020 19.1 Bouwer-Rice 12 469 666 622 815
MS_OW-13 135 3/17/2020 31.88 Springer-Gelhar 12 4,153 13,964 14,446 30,028
MS_OW-14 133 3/18/2020 29.59 Springer-Gelhar 12 16,144 25,221 25,071 33,679
MS_QV-01a 137 3/17/2020 50.96 Springer-Gelhar 16 6,379 19,722 20,316 32,981
MS_SF-02a 124 3/18/2020 50 Springer-Gelhar 12 7,756 11,097 11,110 13,936
MS_SF-02b 124 3/18/2020 50.49 Springer-Gelhar 12 4,897 8,273 8,416 11,071
MS_YB-06a 106 3/18/2020 3.33 Springer-Gelhar 12 5,705 7,640 7,602 10,475
MS_YB-06b 106 3/18/2020 2.93 Bouwer-Rice 11 1,890 2,962 3,183 3,464
MS_YZ-07a 99 3/18/2020 2.78 Springer-Gelhar 12 5,552 8,914 9,148 10,861
MS_YZ-07b 99 3/18/2020 2.77 Springer-Gelhar 16 1,000 1,349 1,188 2,059
AR_ANRC_027N 142 8/5/2020 102.56 Bouwer-Rice 9 22,334 25,373 26,237 26,465
AR_ANRC_028 133 7/23/2020 105.12 Bouwer-Rice 13 806 8,176 7,913 19,060
AR_ANRC_029 111 8/6/2020 45.06 Bouwer-Rice, Springer-Gelhar 11 6,996 10,942 10,720 15,537
AR_ANRC_030 95 8/6/2020 27.13 Springer-Gelhar 15 8,686 17,367 11,859 40,673
AR_ANRC_037N 136 7/21/2020 16.27 Springer-Gelhar 13 5,551 12,887 9,626 32,950
AR_ANRC_039 150 7/22/2020 110.87 Bouwer-Rice, Springer-Gelhar 8 9,351 13,116 13,748 16,027
AR_ANRC_041S 152 7/22/2020 91.02 Bouwer-Rice 12 2,070 2,303 2,293 2,623
AR_ANRC_042 142 7/21/2020 66.22 Bouwer-Rice 6 15,454 22,037 22,869 27,845
AR_ANRC_001 146 7/2/2020 29.85 Springer-Gelhar 16 12,861 18,369 19,523 21,667
AR_ANRC_003 163 7/2/2020 16.17 Springer-Gelhar 16 10,591 13,330 13,718 15,729
AR_ANRC_007 167 7/1/2020 87.79 Bouwer-Rice 15 8,330 18,639 21,152 24,800
AR_ANRC_009 97 7/3/2020 87.41 Bouwer-Rice 4 181 285 293 372
AR_ANRC_014 164 7/2/2020 15.34 Bouwer-Rice 12 5,569 11,086 12,828 15,177
AR_ANRC_016 185 7/1/2020 68.83 Bouwer-Rice 16 2,894 3,699 3,839 4,003
AR_ANRC_017 130 7/1/2020 11.15 Bouwer-Rice 12 1,978 5,193 6,086 6,358
AR_USDA_1N 145 6/30/2020 121.53 Bouwer-Rice 12 557 632 658 689
AR_USDA_1S 145 6/30/2020 122.34 Bouwer-Rice 16 276 443 455 598
AR_USGS_001 121 7/3/2020 85.55 Bouwer-Rice 12 2,620 3,482 3,626 3,924
AR_USGS_002 203 7/2/2020 109.83 Bouwer-Rice 13 3,639 6,963 7,391 9,124
AR_USGS_CR-03a 201 6/30/2020 4.75 Springer-Gelhar 12 31,106 50,528 52,101 76,068
AR_USGS_CR-03b 201 6/30/2020 4.76 Springer-Gelhar 16 45,564 80,559 76,449 130,347
AR_ANRC_027S 400 8/5/2020 11.51 Bouwer-Rice 8 10 55 59 95
AR_ANRC_037S 372 7/21/2020 61.53 Springer-Gelhar, Butler 8 18,611 67,913 38,416 240,200
AR_ANRC_041N 391 7/22/2020 104.76 Bouwer-Rice 11 2,397 3,104 3,221 3,514
AR_ANRC_006 720 7/2/2020 29.41 Bouwer-Rice 16 4,164 4,869 4,927 5,355
Table 5.    Estimated transmissivity for aquifers at selected wells in the Mississippi Alluvial Plain, Arkansas and Mississippi, 2020. Data from Pugh (2023).
1

An additional set of tests was conducted on well MS_OW-05.

Unusable or questionable test data occurred with one or more tests from 11 wells. Data were unusable or questionable because (1) the selection of a slug was too small, resulting in logging abnormalities; (2) recovery times were excessively long when compared to other slug tests conducted in the same well; (3) data-log files were empty; or (4) excessively large automatic estimates were 2 to 3 orders of magnitude larger than the other test estimates from the same well. Unusable or questionable data were not used for final estimates. Wells where unusable or questionable test data occurred will have fewer than 12 test estimates (tables 4 and 5).

Estimates of hydraulic conductivity and transmissivity for the Mississippi River Valley alluvial aquifer were calculated for 44 wells from 555 slug tests (tables 4 and 5). Mean hydraulic conductivity estimates range from 3 to 401 feet per day (ft/d), and median hydraulic conductivity estimates range from 3 to 381 ft/d. Mean transmissivity estimates for these wells range from 285 to 80,559 feet squared per day (ft2/d), and median transmissivity estimates range from 293 to 76,449 ft2/d.

Estimates of hydraulic conductivity and transmissivity for the middle Claiborne aquifer were calculated for 4 wells from 43 slug tests (tables 4 and 5). Mean hydraulic conductivity estimates range from 0.14 to 183 ft/d, and median hydraulic conductivity estimates range from 0.15 to 103 ft/d. Mean transmissivity estimates range from 55 to 67,913 ft2/d, and median transmissivity estimates range from 59 to 38,416 ft2/d.

Summary

Single-well slug tests were conducted by the U.S. Geological Survey during the spring and summer of 2020 at 48 wells to estimate the hydraulic conductivity and transmissivity at selected well sites within the Mississippi Alluvial Plain in Arkansas and Mississippi. Data collection included well and aquifer data from the field and well-construction information from drillers’ construction reports. Multiple slug-in and slug-out tests were completed at each well by using a mechanical slug following published U.S. Geological Survey methods and standards. A total of 324 slug tests were conducted. Aquifer hydraulic conductivity was estimated by curve fitting the observed water-level-change data using aquifer test analysis software. Estimates of aquifer transmissivity were made by multiplying the estimated hydraulic conductivity by the aquifer thickness at each well location. Mean hydraulic conductivity estimates for 44 wells screened in the Mississippi River Valley alluvial aquifer range from 3 to 401 feet per day, and mean transmissivity estimates range from 285 to 80,559 feet squared per day. Mean hydraulic conductivity estimates for 4 wells screened in units of the middle Claiborne aquifer range from 0.14 to 183 feet per day, and mean transmissivity estimates range from 55 to 67,913 feet squared per day. The results from these tests can be used to improve our understanding of water availability and to refine groundwater models, and the results provide stakeholders and groundwater resource managers information about the groundwater resources within the Mississippi Alluvial Plain.

References Cited

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Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain
inch (in.) 2.54 centimeter (cm)
inch (in.) 25.4 millimeter (mm)
foot (ft) 0.3048 meter (m)
mile (mi) 1.609 kilometer (km)
square foot (ft2) 929.0 square centimeter (cm2)
square foot (ft2) 0.09290 square meter (m2)
gallon per minute (gal/min) 0.06309 liter per second (L/s)
foot per day (ft/d) 0.3048 meter per day (m/d)
foot squared per day (ft2/d) 0.09290 meter squared per day (m2/d)

Datum

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Abbreviations

K

hydraulic conductivity

T

transmissivity

USGS

U.S. Geological Survey

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U.S. Geological Survey

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Suggested Citation

Pugh, A.L., 2025, Hydraulic conductivity and transmissivity estimates from slug tests in wells within the Mississippi Alluvial Plain, Arkansas and Mississippi, 2020: U.S. Geological Survey Scientific Investigations Report 2023–5101, 17 p., https://doi.org/10.3133/sir20235101.

ISSN: 2328-0328 (online)

Study Area

Publication type Report
Publication Subtype USGS Numbered Series
Title Hydraulic conductivity and transmissivity estimates from slug tests in wells within the Mississippi Alluvial Plain, Arkansas and Mississippi, 2020
Series title Scientific Investigations Report
Series number 2023-5101
DOI 10.3133/sir20235101
Publication Date July 02, 2025
Year Published 2025
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Lower Mississippi-Gulf Water Science Center
Description Report: iv, 17 p.; Data Release
Country United States
State Arkansas, Mississippi
Other Geospatial Mississippi Alluvial Plain
Online Only (Y/N) Y
Additional publication details