U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2013–3043

August 2013

Prepared in cooperation with the Lone Star Groundwater Conservation District

Groundwater Recharge to the Gulf Coast Aquifer System

in Montgomery and Adjacent Counties, Texas

Printed on recycled paper

Simply stated, groundwater recharge is the addition of water to the groundwater system. Most of the water that is potentially 

available for recharging the groundwater system in Montgomery and adjacent counties in southeast Texas moves relatively 

rapidly from land surface to surface-water bodies and sustains streamflow, lake levels, and wetlands. Recharge in southeast 

Texas is generally balanced by evapotranspiration, discharge to surface waters, and the downward movement of water into 

deeper parts of the groundwater system; however, this balance can be altered locally by groundwater withdrawals, impervious 

surfaces, land use, precipitation variability, or climate, resulting in increased or decreased rates of recharge. Recharge rates were 

compared to the 1971–2000 normal annual precipitation measured Cooperative Weather Station (COOP) 411956, Conroe, Tex. 

(National Climatic Data Center, 2013).

• Recharge rates to the Chicot aquifer in Montgomery County ranged from 0.2 to 7.2 inches per year or

0.4 to 14.6 percent of normal annual precipitation. 

• Recharge rates to the Evangeline aquifer in Montgomery County ranged from less than 0.1 to 2.8 inches per year

or 0.2 to 5.67 percent of normal annual precipitation.

• Recharge rates to the Jasper aquifer in Montgomery, Walker and Waller Counties ranged from less than

0.1 to 0.5 inches per year or 0.2 to 1.01 percent of normal annual precipitation.

What is Groundwater Recharge?

The term “groundwater recharge” generally describes the 

replenishment of water to a groundwater flow system (Healy, 

2010). Recharge, an integral part of the hydrologic cycle, 

is the process by which water that first fell as precipitation 

moves to the water table and then away from that area through 

saturated materials, adding to groundwater storage. Figure 1 

depicts the hydrologic processes of precipitation recharging 

the Gulf Coast aquifer system. Runoff from precipitation 

first infiltrates the sediments exposed at the land surface and 

then moves downward through layers of sediments until it 

reaches the water table and becomes part of the groundwater 

flow of the Gulf Coast aquifer system. Once water is part of 

the groundwater flow system, it begins to move toward rivers 

or other surface water bodies and eventually discharges into 

the Gulf of Mexico. Recharge in southeast Texas is generally 

balanced by evapotranspiration, discharge to surface waters, 

and the downward movement of water into deeper parts of 

the groundwater system; however, this balance can be altered 

locally by groundwater withdrawals, impervious surfaces, land 

use, precipitation variability, or climate, resulting in increased 

or decreased rates of recharge. 

Where Does Recharge Occur?

Recharge to the groundwater system occurs mostly in 

unconfined outcrop areas where aquifer sediments are exposed 

at land surface (an aquifer is designated as “confined” when the 

top of the aquifer is bounded by another aquifer or confining 

unit). Precipitation infiltrates the groundwater system at various 

rates in the unconfined outcrop areas, and moves downward into 

the more confined parts of the system. Given an equal amount 

of precipitation, recharge rates are higher in outcrop areas 

composed of a larger percentage of sand and smaller percentage 

of clay and silt (such as the relatively sandy sediments present 

in the northern parts of outcrop areas of the Gulf Coast aquifer 

system) compared to outcrop areas composed of a smaller 

percentage of sand and a larger percentage of clay and silt (such 

as the relatively clayey sediments present in the southern part 

of outcrop or confined parts of the Gulf Coast aquifer system). 

Additionally, surface runoff from precipitation flowing into 

low topographic areas or depressions (lowlands) contributes 

recharge to the aquifer system (fig. 1). The recharge becomes 

part of the groundwater flow system, moves down gradient in 

a coastward direction through the multiple interbedded sands 

and clay layers, and discharges into streams (as base flow) and 

to larger bodies of water such as bays and estuaries and to the 

Gulf of Mexico. 

Additional water recharges the Evangeline aquifer by 

leakage of water from the overlying Chicot aquifer. Leakage is a 

process similar to but not the same as recharge. Rates of leakage 

to confined aquifers are generally less than rates of recharge 

to unconfined aquifers. Upward leakage also occurs from a 

confined aquifer in areas where hydraulic head in the confined 

aquifer is greater than that in the overlying formation, that is, 

water moves from areas of greater to lower hydraulic head. 
Figure 1.

Unsaturated zone

Wetland

Pumped

Surface

River

Evangeline aquifer

Burkeville confining unit

Jasper aquifer

Catahoula

well

runoff

confining

system

Chicot aquifer

Evapotranspiration

Precipitation

City

Figure 1. Groundwater recharge is an important part of the hydrologic cycle (modified from Delin and Falteisek, 2007).

Why Do Recharge Rates Vary?

Numerous factors—including physical characteristics of 

the soil, vegetation cover, land use, topography, water content of 

surface materials, and the presence and depth of the fine-grain clay 

layers—influence the spatial variability of recharge rates. Weather 

patterns, including the timing and intensity of precipitation and 

evapotranspiration during the summer growing season, play an 

important role in controlling spatial and temporal variability in 

recharge rates. 

When Does Recharge Occur?

The amount of groundwater recharge varies seasonally 

in response to precipitation. During fall and winter, water 

levels generally increase because precipitation rates are higher, 

withdrawal is lower, and evapotranspiration is lower. During 

the spring and summer seasons, withdrawals generally increase, 

precipitation rates are lower, and evapotranspiration is higher. 

Why Is Information on Groundwater Recharge

Rates Important?

Knowledge of groundwater recharge rates is important to 

studies of water availability, sustainability, wellhead protection, 

contaminant transport, groundwater and surface-water interactions, 

effects of urbanization, and aquifer vulnerability to contamination 

(Scanlon and others, 2002). Estimates of recharge rates are 

necessary to quantify the volume of water flowing through nearsurface groundwater systems and are important to understand 

the water balance of an aquifer or aquifer system and the human 

impact on that balance. For example, by estimating the spatial 

distribution of recharge rates, one can estimate the total volume 

of water entering a system. The recharge rate is one of the more 

sensitive and important parameters of groundwater flow models 

and is the parameter least understood (Delin and Falteisek, 2007). 

Groundwater recharge is not

• equivalent to “infiltration” of water at the land surface. Most 

water that infiltrates at the land surface is returned to the 

atmosphere by plant transpiration and evaporation from soil 

and water surfaces (fig. 1). Recharge is typically only a small 

percentage of infiltration;

• equated to the process of “percolation”; instead, percolation 

refers to the movement of water through unsaturated 

sediments; however, percolating water can be viewed 

as potential recharge; if it reaches the water table it will 

become recharge;

• to be confused with the term “aquifer yield.” This term refers 

to the amount of water that an aquifer can yield to pumping;

• the same as “sustainable yield.” Recharge can be less than 

sustainable yield. For example, if all recharge water were 

utilized, stream, lake, and wetland levels could decrease over 

time. Furthermore, it cannot be assumed that pumping at less 

than the recharge rate will not cause water-level declines and 

groundwater storage depletions (Delin and Falteisek, 2007). 

How Are Recharge Rates Estimated?

Groundwater recharge rates cannot be measured with 

an instrument; thus, recharge rates must be estimated by 

using indirect methods. Although there is no single method 
(one-size fits all) for recharge determination, many methods 

have been developed for estimating recharge rates. Selection 

of the appropriate method for a given study is important and 

can be challenging. A detailed description of all rechargeestimation methods and their limitations is beyond the scope 

of this fact sheet (see Healy, 2010, for a thorough review of 

recharge estimation methods and their associated limitations). 

The section of this fact sheet entitled “Estimated Recharge Rates 

in Montgomery and Adjacent Counties” provides a general 

description of the groundwater age-dating method that was 

used effectively for estimating groundwater recharge rates in 

Montgomery County.

Hydrogeology of Montgomery County

The Gulf Coast aquifer system in Montgomery County, 

Texas, consists of the Chicot, Evangeline, and Jasper aquifers, 

Burkeville confining unit, and the underlying Catahoula confining 

system (fig. 1). The sediments composing the Gulf Coast aquifer 

system were deposited by rivers and deltas and subsequently 

eroded and redeposited (reworked) by large episodic changes in 

sea level, resulting in stacked, wedge-shaped sequences of coarser 

and finer-grained sediments that dip and thicken towards the Gulf 

of Mexico (Ryder, 1996). 

This type of coastal depositional environment created 

a complex, heterogeneous aquifer of multiple confined and 

unconfined aquifers where sand and clay lens thicknesses and 

horizontal extents can change rapidly over short distances. The 

Evangeline and Jasper aquifers are for the most part confined 

aquifers in the study area. The Chicot aquifer is designated as 

“unconfined” in the study area, as are the up-dip regions of the 

Evangeline and Jasper where each aquifer is exposed at land 

surface. Figure 1 shows the relative position of the each of the 

aquifers; a detailed hydrogeologic section is available in the 

USGS Scientific Investigations Report referenced by this fact 

sheet (Oden and Truini, 2013, p. 7).

Estimated Recharge Rates in Montgomery

and Adjacent Counties

Recharge rates to the Gulf Coast aquifer system in 

Montgomery County and the surrounding region have been 

estimated in previous studies by using many methods (table 1). 

The method used for this study is briefly described here, with 

further details available in Oden and Truini (2013). 

Groundwater Age-Dating Method

Groundwater ages are a measure of the time since the 

water entered the saturated zone and was isolated (as a result of 

additional recharge) from the atmosphere, which sets the “age” of 

the water. The actual groundwater is not dated, but the apparent 

age of groundwater can be estimated from concentrations of 

dissolved chemicals or isotopes used as environmental tracers and 

from a comparison of the equivalent atmospheric concentration 

of each tracer to the atmospheric input signal for that tracer. 

Factors affecting the time since isolation from the atmosphere 

can include the sorption or degradation of the tracer, porosity of 

the unsaturated zone, recharge rate, thickness of the unsaturated 

zone, and magnitude of water level fluctuations (Plummer and 

Busenberg, 2000).

Table 1. Comparison of recharge rates determined in Montgomery and adjacent counties in Texas during March–September 2008 and April–

May 2011 by using environmental age tracers with recharge rates from previous studies using various methods in the Gulf Coast aquifer system.

[in./yr, inches per year; <, less than; 3H/3He, tritium/helium-3; CFC-12, dichlorodifluoromethane; SF6, sulfur hexafluoride; 4He, helium-4; 14C, carbon-14; 3H, tritium; Cl, chloride]

Sample collection dates Counties Aquifer Recharge rate 

(in./yr) Method

March–September 2008

April–May 2011

 Montgomery Chicot aquifer 0.2–7.2 Environmental age tracers (3H/3He, 

CFC-12, SF6, 4He and 14C)

March–September 2008

April–May 2011

 Montgomery Evangeline aquifer <0.1–2.8 Environmental age tracers (3H/3He, 

CFC-12, SF6, 4He and 14C)

March–September 2008

April–May 2011

 Montgomery, Walker, 

and Waller

Jasper aquifer <0.1–0.5 Environmental age tracers (3H/3He, 

CFC-12, SF6, 4He and 14C)

Previous studies Counties Aquifer Recharge rate

(in./yr) Method

Popkin (1971) Montgomery Gulf Coast aquifer system 1.7 Transmission capacity

Ryder (1988) Montgomery Gulf Coast aquifer system 0–2 Groundwater model

Williamson and

others (1990)

Montgomery Gulf Coast aquifer system 0.00–0.66 Groundwater model, predevelopment 

conditions

Williamson and

others (1990)

Montgomery Gulf Coast aquifer system 0.66–3.00 Groundwater model, 90 percent 1980 

pumpage

Noble and others (1996) Harris, Montgomery, 

and Walker

Chicot and Evangeline aquifers 0.0–6.0 3H interface method

Nolan and others (2007) Harris and Montgomery Chicot and Evangeline aquifers 0.03–4.13 Cl tracer in saturated zone

Scanlon and others (2011) Montgomery Chicot aquifer 0.8–4.8 Hydrograph analysis and chloride 

mass balance.
The environmental tracers used in this study were 

chlorofluorocarbons (CFC-12), sulfur hexafluoride (SF6), and 

tritium/helium-3 (3H/3He) (table 2). These tracers were used to 

estimate the apparent age of groundwater recharged after the 

1940s. Helium-4 (4He) and carbon-14 (14C) were also used in this 

study to estimate the apparent age of groundwater recharged from 

about 100 to about 40,000 years before present (Healy, 2010) 

(table 2, fig. 3). Estimated recharge rates from this study ranged 

from 0.2 to 7.2 inches per year for the Chicot aquifer, less than 0.1 

to 2.8 inches per year for the Evangeline aquifer, and less than 0.1 

to 0.5 inches per year for the Jasper aquifer (table 2, figs. 2 and 3).

Limitations of Estimating Recharge Rates

Estimation of groundwater ages and recharge rates requires 

some assumptions about the hydrogeologic properties of the 

aquifer system which creates some uncertainty in these estimates. 

Despite the complexity of the aquifer system in Montgomery 

County, the estimates of groundwater ages and recharge rates 

are considered to be appropriate for use as a general guide in 

hydrologic investigations. For example, these estimates can 

be used for further investigation into the availability of the 

groundwater resources in the county and can be used as input 

parameters in groundwater-flow models. Results of this study—

that is, recharge rates in Montgomery County are less than 0.1 to 

7.2 inches per year—are within the range of expected values in

and near the study area (table 1). The following limitations of

these results should be considered:

1. The hydrogeology is highly variable on a regional scale, so 

estimated recharge rates in the study area may reflect (or 

represent) localized groundwater flow paths contrary to the 

regional flow pattern.

2. For the conceptual model of this system, piston flow in the 

aquifer is assumed, and the constituent concentration is 

assumed to be unaltered by mixing or dispersion from the 

point of recharge to the sampling point in the aquifer. This 

assumption is most likely an oversimplification for the specific 

aquifers in the study area.

3. The calculation of recharge rates for confined and unconfined 

aquifers requires an estimation of aquifer porosity; the porosity 

values used were based on previous scientific investigations 

of the aquifers in and adjacent to the study area. A decrease 

in porosity will lower the estimated recharge rate, whereas an 

increase in porosity will raise the estimated recharge rate.

4. The possibility exists for the mixing of waters of different 

composition and age through vertical connection between 

aquifers such as a well with multiple screens or along 

preferential flow paths of the aquifers.

5. The estimated recharge rates are specific to each well

location and should not be extrapolated or inferred as a 

countywide average.

6. The interpretation of environmental tracer data can be 

complicated along individual flow paths by additional 

independent variables that affect the tracer concentrations such 

as degassing, contamination, dispersion, sorption, chemical 

reactions, transport through thick unsaturated zones, and 

aquifer/water interactions, such as input of excess 4He.

Table 2. Apparent groundwater ages and recharge estimates 

derived by using samples collected during March–September 2008 

and April–May 2011 from wells completed in the Chicot, Evangeline 

and Jasper aquifers in Montgomery and adjacent counties, Texas.

[in./yr, inches per year; 3H/3He, tritium/helium-3; CFC-12, dichlorofluoromethane; 4

He, helium-4; SF6, sulfur hexafluoride; <, less than; >, greater than; 14C, carbon-14]

Map 

identifier

 (fig. 2)

Sample

date

Recharge

(in./yr)

Apparent 

age

(years)

Tracer Aquifer

1 3/12/2008 3.7 73 3H/3He Chicot

2 3/13/2008 4.8 27 CFC-12 Chicot

4 3/19/2008 3.8 62 4He Chicot

5 3/19/2008 2.3 23 3H/3He Chicot

7 3/24/2008 2.7 71 3H/3He Chicot

10 3/26/2008 2.1 32 SF6 Chicot

12 3/27/2008 1.0 48 CFC-12 Chicot

14 4/21/2008 0.5 62 CFC-12 Jasper

16 4/22/2008 0.1 52 CFC-12 Evangeline

17 4/27/2011 <0.1 >42,000 14C Jasper

18 4/20/2011 1.0 900 14C Evangeline

19 4/24/2008 2.4 50 CFC-12 Chicot

20 4/28/2008 1.9 44 4He Chicot

21 4/30/2008 3.4 32 3H/3He Chicot

22 7/10/2008 1.5 825 4He Evangeline

23 5/3/2011 2.8 2,700 14C Evangeline

24 5/9/2011 <0.1 13,000 14C Jasper

25 7/18/2008 7.2 35 3H/3He Chicot

27 4/20/2011 0.1 27,000 14C Jasper

28 4/26/2011 0.1 26,000 14C Evangeline

30 8/18/2008 2.4 2,092 4He Evangeline

31 4/15/2011 0.1 18,000 14C Jasper

32 4/28/2011 <0.1 33,000 14C Jasper

34 4/25/2011 0.2 8,000 14C Evangeline

36 4/18/2011 0.9 650 14C Chicot

37 4/18/2011 0.4 900 14C Chicot

38 4/18/2011 0.2 5000 14C Chicot

39 4/21/2011 <0.1 42,000 14C Evangeline

40 4/21/2011 0.1 32,000 14C Evangeline

41 5/11/2011 0.1 42,000 14C Jasper

42 5/12/2011 0.1 19,000 14C Jasper

43 5/12/2011 0.1 16,000 14C Jasper

44 5/13/2011 0.1 37,000 14C Jasper.

This fact sheet is based on the following USGS report:

Oden, T.D. and Truini, M., 2013, Estimated rates of groundwater 

recharge to the Chicot, Evangeline, and Jasper aquifers by using 

environmental tracers in Montgomery and adjacent counties, Texas, 

2008 and 2011: U.S. Geological Survey Scientific Investigations 

Report 2013-5024, 50 p., http://pubs.usgs.gov/sir/2013/5024.
Bayou

1, 3.7

2, 4.8

4, 3.8

5, 2.3

7, 2.7

10, 2.1

12, 1.0

19, 2.4

20, 1.9

21, 3.4

25, 7.2

36, 0.9

37, 0.4

38, 0.2

14, 0.5

17, < 0.1

24, < 0.1

27, 0.1

31, 0.1

32, <.1

41, 0.1

42, 0.1

43, 0.1

44, 0.1

16, 0.1

18, 1.0

22, 1.5

23, 2.8

28, 0.1

30, 2.4

34, 0.2

39, < 0.1

40, 0.1

Figure 2. Recharge estimates at wells completed in the Chicot, Evangeline, and Jasper aquifers in Montgomery County, Texas 

during March-September 2008.

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Base from U.S. Geological Survey 1:24,000-scale digital data

Albers Equal Area Projection, Texas Mapping System 

North American Datum of 1983

0 10 20 MILES

0 10 20 KILOMETERS

Aquifer data from Strom and others, 2003;

Kasmarek and Robinson, 2004.

TEXAS

Study area

Location map

EXPLANATION

Well developed into an aquifer 

 —Well identifier and recharge 

 rate

 (see table 2)

 Chicot 

 Evangeline

 Jasper

 

20, 1.9

30, 2.4

41, 0.1

Chicot aquifer 

Evangeline aquifer

Burkeville confining unit

Jasper aquifer

Figure 2. Location of wells completed in the Chicot, Evangeline, and Jasper aquifers where recharge estimates were determined on the 

basis of measured environmental tracer concentrations in Montgomery, Walker, and Waller Counties, Texas 2008–11.
Groundwater age, in years

0

1

2

3

4

5

6

7

8

10 100 1,000 10,000 100,000

Estimated recharge rate, in inches per year

Chicot aquifer

Evangeline aquifer

Jasper aquifer

EXPLANATION

Figure 3. Groundwater age 

and estimated recharge rate by 

aquifer from wells sampled in 

Montgomery, Walker, and Waller 

Counties, Texas 2008–11. 

References Cited

Delin, G.N. and Falteisek, J.D., 2007, Ground-water recharge in 

Minnesota: U.S. Geological Survey Fact Sheet 2007–3002, 6 p.

Healy, R.W., 2010, Estimating groundwater recharge, with contributions by 

Scanlon, B.R.: Cambridge, U.K., Cambridge University Press, 245 p.

Kasmarek, M.C., and Robinson, J.L., 2004, Hydrogeology and simulation 

of ground-water flow and land-surface subsidence in the northern

part of the Gulf Coast aquifer system, Texas: U.S. Geological Survey 

Scientific Investigations Report 2004-5102, 111 p. 

Noble, J.E., Bush, P.W., Kasmarek, M.C., and Barbie, D.L, 1996, 

Estimated depth to the water table and estimated rate of recharge in 

outcrops of the Chicot and Evangeline aquifers near Houston, Texas: 

U.S. Geological Survey Water-Resources Investigation Report 96–4018, 

19 p.

Nolan, B.T., Healy, R.W., Taber, P.E., Perkins, K., Hitt, K.J., and Wolock, 

D.M., 2007, Factors influencing ground-water recharge in the eastern 

United States: Journal of Hydrology, no. 332, p. 187–205.

Popkin, B.P., 1971, Groundwater resources of Montgomery County, Texas: 

Texas Water Development Board Report 136, 143 p.

Plummer, L.N. and Busenberg E., 2000, Chlorofluorocarbons, in P.G. Cook 

and A.L. Herczeg, eds., Environmental tracers in subsurface hydrology, 

chap. 15: Boston, Mass., Kluwer Academic Press, p. 441–478.

Ryder, P.D., 1988, Hydrogeology and predevelopment flow in the Texas 

Gulf Coast aquifer systems: U.S. Geological Survey Water-Resources 

Investigations Report 87–4248, 109 p.

Ryder, P.D., 1996, Ground water atlas of the United States—Segment 4, 

Oklahoma and Texas: U.S. Geological Survey Hydrologic Atlas 730-E, 

accessed June 15, 2010, at http://pubs.usgs.gov/ha/ha730/ch_e/index.

html.

Scanlon, B.R., Healy, R.W., and Cook, P.G., 2002, Choosing appropriate 

techniques for quantifying groundwater recharge: Hydrogeology 

Journal, v. 10, p. 18–39.

Scanlon, B.R., Reedy, R.C., Stassberg, G., Huang, Y., and Senay, G., 2011, 

Estimation of groundwater recharge to the Gulf Coast aquifer in Texas, 

USA: The University of Texas at Austin, Bureau of Economic Geology, 

Final Contract Report [variously paged].

Strom, E.W., Houston, N.A., and Garcia, A.C., 2003a, Selected 

hydrogeologic datasets for the Chicot aquifer, Texas: U.S. Geological 

Survey Open-File Report 2003-297, 1 CD-ROM.

Strom, E.W., Houston, N.A. and Garcia, A.C., 2003b, Selected 

hydrogeologic datasets for the Evangeline aquifer, Texas: U.S. 

Geological Survey Open-File Report 2003-298, 1CD-ROM.

Strom, E.W., Houston, N.A. and Garcia, A.C., 2003c, Selected 

hydrogeologic datasets for the Jasper aquifer, Texas: U.S. Geological 

Survey Open-File Report 2003-299, 1 CD-ROM.

National Climatic Data Center, 2013, Climatography of the United States 

No. 81, monthly normals of temperature, precipitation, and heating and 

cooling degree days, 1971–2000, Cooperative Weather Station (COOP) 

411956, Conroe, Tex: accessed June 25, 2013, at http://hurricane.ncdc.

noaa.gov/climatenormals/clim81/TXnorm.pdf.

Williamson, A.K., Grubb, H.F. and Weiss, J.S., 1990, Ground-water 

flow in the Gulf Coast aquifer systems, south central United States; 

a preliminary analysis: U.S. Geological Survey Water-Resources 

Investigations Report 89–4071, 124 p.

By Timothy D. Oden and Geoffrey N. Delin

For additional information contact:

Director, Texas Water Science Center

U.S. Geological Survey

1505 Ferguson Lane

Austin, Texas 78754–4501

http://tx.usgs.gov/