U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2010–5102

Prepared in cooperation with the

New Jersey Department of Environmental Protection

Simulation of Groundwater Mounding Beneath 

Hypothetical Stormwater Infiltration Basins

Potentially affected

nearby structure

Impervious

surfaces

Stormwater

infiltration 

basin

Depth of basin

Ground water mound

beneath stormwater

infiltration basin

during storm event Maximum height of 

groundwater mound

0.25 feet

Maximum extent of

0.25-foot increase in

water level 

Seasonal

high water

table

Saturated

zone

Bottom of aquifer

Thickness of

aquifer (prior

to stormwater

infiltration)

Unsaturated zone

Simulation of Groundwater Mounding 

Beneath Hypothetical Stormwater 

Infiltration Basins

By Glen B. Carleton

Prepared in cooperation with the

New Jersey Department of Environmental Protection

Scientific Investigations Report 2010–5102

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2010

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Suggested citation:

Carleton, G.B., 2010, Simulation of groundwater mounding beneath hypothetical stormwater infiltration basins: 

U.S. Geological Survey Scientific Investigations Report 2010-5102, 64 p.

Any use of trade, product, or firm names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government. Use of company names is for identification purposes only and does not imply 

responsibility.

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report.
iii

Acknowledgments

The author thanks Sandra Blick, Supervisor, Stormwater Management Unit, Bureau of Nonpoint 

Pollution Control, Division of Water Quality, NJDEP, for her vision regarding the need for this 

research and consistent expertise in directing the work. Kunal Patel, also of the Non-Point Pollution Control Element, provided information on technical details and reviews, including terminology used by soil scientists and groundwater hydrologists. Joseph Skupien, Storm Water Management Consulting, provided extremely valuable insights into basin-design criteria and other 

subtleties of how developers in New Jersey meet stormwater management regulations. The 

members of the American Water Resources Association (AWRA) New Jersey Section Stormwater-Best-Management-Practices-Mounding Technical Guidelines Workgroup participated in 

technical discussions that identified the need for quantitative assessment of variables affecting 

groundwater mounding. Nicholas Trainor (Rutgers University, Department of Applied Mathematics) used sophisticated mathematical software to solve the Hantush equation and Hunt equation 

to verify that Excel spreadsheets used in this report accurately solved the analytical equations. 

The author is grateful for the assistance of Arthur Baehr (U.S. Geological Survey, retired) in 

developing the spreadsheet solving the transient Hantush (1967) equation. The author thanks 

technical reviewers Melinda Chapman (U.S. Geological Survey, North Carolina Water Science 

Center) and Jeffrey Hoffman (New Jersey Geological Survey). Improvements to illustrations by 

Gregory Simpson (U.S. Geological Survey) and Jonathan Bucca (Rowan State University) are 

appreciated. 

v

Contents

Acknowledgments........................................................................................................................................iii

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................2

Purpose and Scope ..............................................................................................................................2

Approach................................................................................................................................................2

Previous Investigations........................................................................................................................5

Physical Variables Affecting Height and Extent of Groundwater Mounding.......................................5

Soil Permeability and Aquifer Thickness..........................................................................................5

Specific Yield ........................................................................................................................................6

Percent Impervious Cover...................................................................................................................7

Design Storm .........................................................................................................................................7

Basin Shape and Depth .......................................................................................................................7

Depth to Water Table ...........................................................................................................................8

Use of Finite Difference Numerical Models to Estimate Groundwater Mounding.............................8

Model Design.........................................................................................................................................8

Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration 

Basins for a 10-Acre Development ......................................................................................8

Model Discretization ...................................................................................................................8

Characteristics Varied to Estimate Groundwater Mounding .............................................10

Model Boundaries, Recharge, and Difference Between Undeveloped and 

Developed Water Levels ............................................................................................10

Results .........................................................................................................................................11

Maximum Height of Groundwater Mounding ..............................................................13

Maximum Extent of Groundwater Mounding...............................................................16

Simulation of Groundwater Mounding Beneath Hypothetical Dry Wells for a 1-Acre 

Development ..........................................................................................................................17

Model Discretization, Boundaries, and Difference Between Undeveloped and 

Developed Water Levels .............................................................................................17

Results .........................................................................................................................................18

Model Limitations................................................................................................................................18

Use of Analytical Equations to Estimate Groundwater Mounding ......................................................22

Description of Hantush Equation ....................................................................................................22

Spreadsheet for Solving Hantush Equation ...................................................................................22

Comparison of Analytical and Finite-Difference Estimates of Groundwater Mounding 

and Effect of Vertical Layering.....................................................................................................24

Summary and Conclusions.........................................................................................................................26

References Cited..........................................................................................................................................28
vi

Figures

1. Schematic representation of a groundwater mound beneath a hypothetical stormwater infiltration basin.................................................................................................................3

2-3. Maps showing—

2. Model grid and boundary conditions of a finite-difference model used to 

simulate groundwater mounding beneath hypothetical stormwater infiltration 

basins on a 10-acre development.....................................................................................9

3. Relative size and placement of selected hypothetical infiltration basins used 

in simulations of groundwater mounding beneath a 10-acre development............12

4-5. Box plots showing—

4. Range of maximum height of simulated groundwater mounding beneath 

hypothetical stormwater infiltration basins on a 10-acre development in 

relation to aquifer and basin characteristics................................................................14

5. Range of maximum extent of 0.25-foot simulated groundwater mounding 

beneath hypothetical stormwater infiltration basins on a 10-acre development 

in relation to aquifer and basin characteristics ...........................................................15

6. Schematic diagram showing relative shape of groundwater mounding in aquifers 

of higher and lower soil permeability......................................................................................17

7. Model grid and boundary conditions of a finite-difference model used to simulate 

groundwater mounding beneath hypothetical stormwater infiltration basins on a 

1-acre development ...................................................................................................................19

8-9. Box plots showing—

8. Range of maximum height of simulated groundwater mounding beneath 

hypothetical stormwater-infiltration dry wells on a 1-acre development in 

relation to aquifer and dry well characteristics ...........................................................20

9. Range of maximum extent of 0.25-foot simulated groundwater mounding 

beneath hypothetical stormwater-infiltration dry wells on a 1-acre development in relation to aquifer and dry well characteristics.............................................21

10. User interface page of spreadsheet for solving the Hantush (1967) equation that 

describes groundwater mounding beneath an infiltration basin with example input 

and output....................................................................................................................................23

11. Graph showing groundwater mounds beneath hypothetical stormwater-infiltration 

basins calculated using the Hantush equation and simulated with 1-, 3-, 6-, 9-, and 

15-layer finite-difference models.............................................................................................26

Tables

1. Values of variables input to the finite-difference simulations of groundwater 

mounding beneath hypothetical stormwater infiltration basins on 1-acre and 

10-acre developments. .............................................................................................................11

2. Simulated groundwater mounding beneath hypothetical stormwater-infiltration 

basins on a 10-acre development............................................................................................31

3. Simulated groundwater mounding beneath hypothetical stormwater-infiltration 

dry wells on a 1-acre development .........................................................................................51

4. Calculated and simulated groundwater mounding beneath hypothetical 

stormwater-infiltration basins using selected analytical solutions and 

finite-difference models ............................................................................................................25
vii

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

Area

acre 4,047 square meter (m2)

acre 0.4047 hectare (ha)

square foot (ft2) 0.09290 square meter (m2)

Volume

gallon (gal) 3.785 liter (L) 

gallon (gal) 0.003785 cubic meter (m3) 

Flow rate

cubic foot per day (ft3/d) 0.02832 cubic meter per day (m3/d)

gallon per minute (gal/min) 0.06309 liter per second (L/s)

inch per hour (in/h) 0 .0254 meter per hour (m/h)

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

Hydraulic conductivity

foot per day (ft/d) 0.3048 meter per day (m/d)

Hydraulic gradient

foot per mile (ft/mi) 0.1894 meter per kilometer (m/km)

Transmissivity*

foot squared per day (ft2/d) 0.09290 meter squared per day (m2/d) 

*Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot 

times foot of aquifer thickness [(ft3/d)/ft2]ft. In this report, the mathematically reduced form, 

foot squared per day (ft2/d), is used for convenience.

Abstract

Groundwater mounding occurs beneath stormwater management structures designed to infiltrate stormwater runoff. 

Concentrating recharge in a small area can cause groundwater 

mounding that affects the basements of nearby homes and 

other structures. Methods for quantitatively predicting the 

height and extent of groundwater mounding beneath and near 

stormwater infiltration structures can be used by property 

developers and regulatory agencies to assess the threat to previously existing or proposed structures.

Finite-difference groundwater-flow simulations of 

infiltration from hypothetical stormwater infiltration structures (which are typically constructed as basins or dry wells) 

were done for 10-acre and 1-acre developments. Aquifer and 

stormwater-runoff characteristics in the model were changed 

to determine which factors are most likely to have the greatest effect on simulating the maximum height and maximum 

extent of groundwater mounding. Aquifer characteristics that 

were changed include soil permeability, aquifer thickness, and 

specific yield. Stormwater-runoff variables that were changed 

include magnitude of design storm, percentage of impervious 

area, infiltration-structure depth (maximum depth of standing water), and infiltration-basin shape. Values used for all 

variables are representative of typical physical conditions 

and stormwater management designs in New Jersey but do 

not include all possible values. Results are considered to be a 

representative, but not all-inclusive, subset of likely results.

Maximum heights of simulated groundwater mounds 

beneath stormwater infiltration structures are the most sensitive to (show the greatest change with changes to) soil permeability. The maximum height of the groundwater mound is 

higher when values of soil permeability, aquifer thickness, or 

specific yield are decreased or when basin depth is increased 

or the basin shape is square (and values of other variables are 

held constant). Changing soil permeability, aquifer thickness, 

specific yield, infiltration-structure depth, or infiltration-structure shape does not change the volume of water infiltrated, it 

changes the shape or height of the groundwater mound resulting from the infiltration. An aquifer with a greater soil permeability or aquifer thickness has an increased ability to transmit 

water away from the source of infiltration than aquifers with 

lower soil permeability; therefore, the maximum height of 

the groundwater mound will be lower, and the areal extent of 

mounding will be larger. 

The maximum height of groundwater mounding is 

higher when values of design storm magnitude or percentage of impervious cover (from which runoff is captured) are 

increased (and other variables are held constant) because the 

total volume of water to be infiltrated is larger. The larger the 

volume of infiltrated water the higher the head required to 

move that water away from the source of recharge if the physical characteristics of the aquifer are unchanged. The areal 

extent of groundwater mounding increases when soil permeability, aquifer thickness, design-storm magnitude, or percentage of impervious cover are increased (and values of other 

variables are held constant). 

For 10-acre sites, the maximum heights of the simulated 

groundwater mound range from 0.1 to 18.5 feet (ft). The 

median of the maximum-height distribution from 576 simulations is 1.8 ft. The maximum areal extent (measured from the 

edge of the infiltration basins) of groundwater mounding of 

0.25-ft ranges from 0 to 300 ft with a median of 51 ft for 576 

simulations. Stormwater infiltration at a 1-acre development 

was simulated, incorporating the assumption that the hypothetical infiltration structure would be a pre-cast concrete dry 

well having side openings and an open bottom. The maximum 

heights of the simulated groundwater-mounds range from 0.01 

to 14.0 ft. The median of the maximum-height distribution 

from 432 simulations is 1.0 ft. The maximum areal extent of 

groundwater mounding of 0.25-ft ranges from 0 to 100 ft with 

a median of 10 ft for 432 simulations.

Simulated height and extent of groundwater mounding 

associated with a hypothetical stormwater infiltration basin for 

10-acre and 1-acre developments may be applicable to sites of 

different sizes. For example, for a 20-acre site with 20 percent 

impervious surface, the stormwater infiltration basin design 

capacity (and associated groundwater mound) would be the 

same as for a 10-acre site with 40 percent impervious surface. 

A spreadsheet was developed to solve the Hantush analytical equation, which can be used to calculate groundwater 

mounding. The Hantush equation incorporates simplifying 

assumptions, including that all flow is horizontal. The spreadsheet accepts user-supplied values for horizontal soil permeability, initial saturated aquifer thickness, specific yield, basin 

Simulation of Groundwater Mounding Beneath 

Hypothetical Stormwater Infiltration Basins

By Glen B. Carleton
2 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins

length, basin width, and duration and magnitude of recharge 

rate. Comparison of results of finite-difference simulations 

of a multi-layer system that includes a vertical component of 

flow in the saturated zone with the results from the analytical 

equation indicates that the horizontal-flow-only assumption in 

the analytical equation can cause an under-prediction of the 

maximum height of a groundwater mound by as much as 15 

percent. The more realistic representation of the vertical component of flow and the ability to include site-specific details 

make finite-difference models such as MODFLOW potentially 

more accurate than analytical equations for predicting groundwater mounding.

Introduction

In 2004, the New Jersey Department of Environmental 

Protection (NJDEP) implemented stormwater-management 

rules that include the requirement that “substantial” (greater 

than 1 acre) new development must have no net loss in 

groundwater recharge (New Jersey Administrative Code 

7:8-5.4(a)2, 2004). Therefore, the amount of recharge that is 

rejected by new impervious surfaces, such as roofs or driveways, must be infiltrated elsewhere, often through engineered 

structures such as stormwater infiltration basins or dry wells 

(fig. 1). An unintended consequence of this rule is that nearby 

structures, such as basements, can experience flooding caused 

by the localized mounding of the water table associated with 

concentrated recharge, particularly during intense (largevolume) recharge events. In 2007, the U.S. Geological Survey 

(USGS), in cooperation with the New Jersey Department of 

Environmental Protection, initiated a study to evaluate which 

physical characteristics associated with stormwater infiltration 

basins and the underlying aquifer have the greatest effect on 

groundwater mounding.

Stormwater infiltration basins designed with inaccurate assumptions or insufficient analysis may not function as 

designed. For example, calculations to estimate the amount of 

time required for the basin to drain typically are based on the 

assumption of vertical flow out of the basin bottom into unsaturated sediments. If groundwater mounding of the underlying 

water table reaches the bottom of the infiltration basin, the rate 

of infiltration out of the basin will decrease substantially. 

Several analytical equations have been developed to 

predict the height of the water table beneath an infiltration 

basin. The use of these equations by designers of stormwater 

infiltration basins has been limited by the paucity of available 

tools for solving them. Numerical groundwater-flow models 

can be used but considerable training is required to develop, 

run, and interpret results from numerical models. Designers 

could benefit from a consistent method to quickly quantify the 

predicted height of a groundwater mound beneath and near a 

proposed infiltration basin. Such a quantitative method could 

also allow regulators to objectively evaluate applications and 

determine whether groundwater mounding associated with a 

proposed infiltration basin would be likely to prevent the basin 

from functioning properly or pose a potential threat to nearby 

structures.

The goal of this study was to provide quantitative methods for estimating the height of groundwater mounds beneath 

infiltration basins that can be used by (1) engineers preparing stormwater infiltration basin designs and (2) regulators 

reviewing those designs. These methods can be used to predict 

the magnitude and extent of groundwater mounding beneath 

and adjacent to engineered stormwater infiltration structures 

during recharge events under specific conditions. A number of 

variables (including hydrogeologic characteristics and infiltration structure design) were evaluated to better understand 

which factors most affect the magnitude and extent of groundwater mounding. 

Purpose and Scope

Analytical and numerical techniques used to estimate 

the magnitude and extent of groundwater mounding beneath 

infiltration structures are presented in this report. Analytical equations are evaluated, and use of a spreadsheet developed to solve the Hantush (1967) equation (for the growth 

of groundwater mounds in response to uniform infiltration 

beneath an infiltration structure) with user input for aquifer 

and infiltration-structure characteristics is described. Numerical groundwater-flow models constructed for both 1-acre and 

10-acre hypothetical developments also are described along 

with results of hundreds of simulations of combinations of 

variables including soil permeability, aquifer thickness, aquifer 

specific yield, design storm magnitude, basin depth, basin 

shape, and percentage of impervious surface. Box plots show 

the simulated maximum height of groundwater mounds and 

maximum extent of groundwater mounding of 0.25-ft and 

illustrate which variables have the greatest effect on groundwater-mound height and extent. A table is presented that lists 

for each of the 10-acre and 1-acre developments the simulated 

maximum height of groundwater mounding, maximum radius 

of 0.25-ft height, and groundwater mounding at several fixed 

distances from the edge of the basin for each of the hundreds 

of variable combinations.

Approach

Two methods were used to quantitatively estimate the 

height and extent of groundwater mounds near proposed 

stormwater infiltration basins—(1) a spreadsheet to numerically integrate equations presented by Hantush (1967) and (2) 

three-dimensional finite-difference groundwater-flow models. 

Hantush’s equations define the shape of groundwater mounds 

beneath rectangular (including square) or round infiltration 

basins, and are based on several simplifying assumptions, 

including that the aquifer is homogeneous and isotropic, flow 
Introduction 3

is strictly horizontal, the change in aquifer saturated thickness relative to original saturated thickness is trivial, and the 

infiltration rate is constant. 

The finite-difference groundwater-flow model MODFLOW-2000 (Harbaugh and others, 2000) was used to 

simulate the height and extent of groundwater mounds beneath 

infiltration basins with various aquifer characteristics, recharge 

conditions, and basin areas, depths, and shapes. Hundreds 

of simulations were completed in which two to four values 

for each of seven variables were altered to estimate groundwater mounds in various hypothetical settings and design 

constraints. The seven variables that were altered are soil 

permeability, aquifer thickness, specific yield, infiltration basin 

depth, basin shape, magnitude of design storm, and percentage 

of impervious land cover. The seven variables and appropriate values for New Jersey were determined in coordination 

with Sandra Blick (NJDEP), Joseph Skupien (Storm Water 

Management Consulting, LLC), and members of the NJDEP 

Stormwater Best Management Practices (BMP) Committee.

Values of variables used in the simulations were chosen 

to include a realistic range of values and to keep the number of 

simulations small enough to be readily interpreted. The values 

Potentially affected

nearby structure

Impervious

surfaces

Stormwater

infiltration 

basin

Depth of basin

Groundwater mound

beneath stormwater

infiltration basin

during storm event Maximum height of 

groundwater mound

0.25 feet

Maximum extent of

0.25-foot increase in

water level 

Seasonal

high water

table

Saturated

zone

Bottom of aquifer

Thickness of

aquifer (prior

to stormwater

infiltration)

Unsaturated zone

Figure 1. Schematic representation of a groundwater mound beneath a hypothetical stormwater infiltration basin.
4 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins

selected (and the rationale for selecting those values) are discussed farther on in the “Physical Variables Affecting Height 

and Extent of Groundwater Mounding” section of this report. 

Tables are provided in the “Results” sections that list the maximum height, maximum extent, and height at fixed distances of 

a groundwater mound beneath infiltration basins designed to 

infiltrate runoff from a 10-acre or 1-acre development. 

For the 10-acre system, transient simulations with 

constant recharge for 1.5 days (36 hours) were made for 

predevelopment and post-development conditions. Recharge 

for pre-developed conditions was uniform throughout the 

model area, with no impervious surface and no infiltration 

basin. Recharge for developed conditions was the same as 

predevelopment recharge outside the 10-acre developed area. 

The developed area received less recharge because of impervious surfaces, and the infiltration basin received the recharge 

rejected by the impervious surfaces in the developed area. 

Precipitation was assumed to reach the water table without 

loss to evapotranspiration or surface runoff to surface-water 

bodies. Initial conditions included no antecedent recharge and 

a flat water table. The height and extent of the groundwater 

mound was calculated by subtracting water levels simulated 

under predevelopment conditions from water levels simulated 

under post-development conditions. 

For the 1-acre system, the effect of reduced recharge 

from impervious surfaces over such a small area was not considered to be important; therefore, predevelopment conditions 

were not simulated. Simulations included only recharge to the 

infiltration basin (dry well), and groundwater mounding was 

calculated directly as the increase in water level associated 

with recharge introduced at the infiltration basin.

 The lateral and bottom boundaries of the model are noflow boundaries. The lateral boundaries were set sufficiently 

far from the infiltration basins, such that simulated water-level 

increases at all boundaries was less than 0.01 ft for all simulations. A surface-water drain simulated using the MODFLOW 

Drain Package was included in the simulations of a 10-acre 

development to test whether presence or absence of a stream 

at that distance affected results. The surface-water boundary 

had no effect on the simulated groundwater mound because 

the change in flow to the drain was less than 0.1 percent under 

pre- and post-development recharge.

The infiltration basin for each simulation had a volume 

(basin depth multiplied by area) equal to the recharge rejected 

by the impervious surfaces (stormwater-runoff design-storm 

depth multiplied by area of impervious surface). To minimize 

the number of basin footprints needed for the simulations, 

variables that determine the required area of the basin were 

varied by a factor of two or four. For example, two design 

storm magnitudes were considered, with the first selected to 

be the NJDEP stormwater quality design storm of 1.25 inches, 

so the second storm was chosen to be 0.3125 inch (one-fourth 

of 1.25 inches, rounded to 0.31 inch in the remainder of this 

report). Similarly, infiltration basins are often designed to 

be 2 ft deep (greater depths could pose a drowning hazard), 

but shallower depths are sometimes used, so a depth of 0.5 ft 

(one-fourth of 2 ft) was chosen. Therefore, for a given percentage of impervious area, the basin footprint required for a 

design storm magnitude of 1.25 in. and a basin depth of 2 ft 

is the same as for a design storm magnitude of 0.31 in. and a 

basin depth of 0.5 ft. For this study the design-storm magnitude is assumed to have fully infiltrated pervious surfaces 

under predevelopment conditions; the runoff from the design 

storms that must be infiltrated is assumed to be the magnitude 

of the design storm with no allowance for evaporation from 

impervious surfaces or runoff from natural, pervious surfaces.

The simulations do not include any delay or attenuation 

associated with travel through the unsaturated zone. Also, the 

volume of water from the design storm falling on impervious 

surface is simulated as directly recharging the water table at 

the infiltration basin over 36 hours. 

For analytical methods such as that proposed by Hantush 

(1967), horizontal flow is assumed; therefore, vertical anisotropy of hydraulic conductivity (vertical hydraulic conductivity, also called soil permeability, is different from, usually less 

than, horizontal hydraulic conductivity) is not accounted for 

in the method. Use of multiple layers in MODFLOW allows 

inclusion of vertical anisotropy. The number of layers used 

to represent the aquifer was chosen to be three to balance the 

need for multiple layers with the need for keeping the runtimes of simulations to a minimum. The difference in results 

from simulations with fewer or greater than three layers is discussed in the “Comparison of Analytical and Finite-Difference 

Estimates of Groundwater Mounding and Effect of Vertical 

Layering” section of this report.

In the 576 simulations for the 10-acre site, 7 of the 

MODFLOW input files were identical: the Basic, Drain, and 

Pre-conditioned Conjugate Gradient (solver) Packages, Output 

Control Option, Observation Process, and Name and Observation Data files. These files were copied into 576 sequentially 

numbered directories. The MODFLOW input files that varied 

among simulations—the Discretization Package (includes 

aquifer thickness), Layer Property Flow Package (includes 

soil permeability and specific yield), and Recharge Package 

files—were copied into the appropriate directories. The goal 

for the simulations for the 10-acre site was to simulate aquifer 

response to a recharge event where recharge was reduced in 

the developed area and concentrated at an infiltration basin. 

Because the aquifer response is, in part, a function of aquifer 

characteristics, aquifer response to recharge under predevelopment (uniform) conditions was simulated for each unique 

combination of aquifer characteristics and design storm 

magnitude. Binary files of aquifer heads from the predevelopment simulations were copied into the appropriate directories. 

After the post-development simulations were completed, 

a FORTRAN program was used to extract the water levels 

from the binary head file for each simulation, subtract the 

predevelopment water level from the post-development water 

level; calculate the maximum change in head, calculate the 

maximum extent of groundwater mounding of 0.25-ft and the 

change in water levels at fixed distances from the right edge of 

the infiltration basin, and save the results to a summary file. 
Physical Variables Affecting Height and Extent of Groundwater Mounding 5

In the 432 simulations for the 1-acre site, the same procedure was followed, except recharge over the 1-acre area was 

not reduced by the percentage of impervious cover. Therefore, 

the water-level change was calculated by the MODFLOW 

Drawdown Output Control option without the need for subtracting predevelopment from post-development water levels.

Previous Investigations

Artificial recharge of groundwater through recharge 

basins has been conducted for various reasons. In some applications the goal is to store excess water available seasonally 

(for example, during periods of snow melt) for later use in 

irrigation. In other applications the goal is to dispose of treated 

wastewater. Infiltration of stormwater runoff is a similar application, although the timeframe of infiltration is shorter than for 

the preceding examples.

Recharge basins and the effects on the underlying water 

table have been widely studied for decades. A number of 

investigators have presented analytical solutions for the shape 

of the water table beneath an artificial recharge basin, including Baumann (1952), Glover (1960), Hantush (1967), Rao and 

Sarma (1981), and Hunt (1971). Sunada and others (1983) and 

Warner and others (1989) evaluated the above solutions. Rai 

and Singh (1981) presented a similar analytical solution to that 

of Hantush (1967), and in a number of subsequent articles they 

(sometimes with other authors) present solutions that include 

a variety of different boundary conditions (for example, Manglik and others, 1997, 2003). Marino (1974) and Latinopoulos 

(1981, 1984) also present several analytical solutions to the 

problem with different boundary conditions. For all of the 

analytical solutions referenced above, it is assumed that flow 

away from the location of the recharge basin is horizontal 

and occurs in an isotropic, homogeneous aquifer in which the 

change in height of the water table is not large (generally less 

than one-half the aquifer thickness). 

Although the above analytical solutions have been used 

to simulate the shape of a groundwater mound beneath hypothetical infiltration basins, they are difficult to apply without 

numerical integration. Sunada and others (1983) found the 

solution of Hantush (1967) to be the most accurate and amenable to numerical integration. Sunada and others (1983) and 

Warner and others (1989) developed computer programs to 

solve the Hantush equation for steady (continuous) or transient 

recharge with user-specified input variables of transmissivity, basin size, and recharge rate. These computer programs 

are no longer readily available and do not run on some 

personal computers (for example, they will not run on computers using a 64-bit processor). Finnemore (1995) presents a 

computer program for solving the Hantush (1967) equation, 

and Zomorodi (2005) offers a simplified method for solving 

the Hantush equation, but both approaches are used only with 

steady-state conditions. Poeter and others (2005) also evaluate 

groundwater mounding under steady-state conditions. Engineering Software, Inc. (2006), developed proprietary software, 

MODRET, that is based on the USGS finite-difference model 

MODFLOW. The software, initially developed for use in 

engineered aquifer-recharge facilities in Florida, calculates 

unsaturated and saturated losses and groundwater mounding from infiltration basins; it includes limited surface-water 

flow routing. MODRET is designed as a 1-layer aquifer and, 

therefore, does not include the effects of vertical anisotropy 

(aquifer permeability in the vertical direction differs from that 

in the horizontal direction).

Sumner and Bradner (1996) and Sumner and others 

(1999) simulated infiltration from artificial recharge basins 

with the USGS variably saturated, two-dimensional flow 

model (VS2D). They found that analyses that ignore the unsaturated zone (as do all of the analytical and finite-difference 

methods referenced above) may over-estimate the height of 

the groundwater mound occurring beneath an infiltration basin 

and may not correctly estimate the behavior over time because 

of storage and delay in the unsaturated zone.

Physical Variables Affecting Height 

and Extent of Groundwater Mounding

New Jersey regulations (New Jersey Administrative 

Code 7:8-5.4(a)2, 2004) require the recharge of stormwater 

falling on newly added impervious surfaces. The physical 

characteristics of the aquifer, stormwater infiltration basin, and 

design storm can all contribute to the height and breadth of a 

groundwater mound occurring under a stormwater infiltration 

structure. The physical characteristics that were varied in the 

simulations are discussed below.

Soil Permeability and Aquifer Thickness

The ability of an aquifer to transmit water from an area 

of higher water level (head) to lower water level is quantified 

as the aquifer transmissivity. Transmissivity is the horizontal hydraulic conductivity multiplied by aquifer thickness 

(typically written T = Kb, where K is in units of length per 

time (L/T) and b is in units of length). The thickness of the 

water-table aquifer in most locations in New Jersey ranges 

from about 10 to 200 ft (about one order of magnitude) (see, 

for example, Nicholson and others, 1996; Johnson and Watt, 

1996; Johnson and Charles, 1997; and Charles and others, 

2001). In northern New Jersey bedrock is commonly close to 

land surface and the unconsolidated sediments can be 10 ft 

or less in thickness. Areas covered by glacial till can be tens 

of feet thick, and glacially buried valleys commonly have as 

much as 100 ft of unconsolidated sediments comprising the 

water-table aquifer. Where the water-table aquifer occurs in 

bedrock, typically most water-producing fractures are present 

in the upper 200 ft and most of the groundwater flow occurs in 

this portion of the aquifer (for example, see Carleton and others, 1999). Coastal Plain aquifers typically are less than 100 ft 
6 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins

thick where they crop out, with the notable exception of the 

Kirkwood-Cohansey aquifer, although in most locations a clay 

layer is encountered within the top 200 ft of the KirkwoodCohansey aquifer (Zapecza, 1989).

The horizontal hydraulic conductivity of the unconfined 

aquifers in New Jersey ranges over several orders of magnitude, about 0.01 to 200 feet per day (ft/d) (Nicholson and 

others, 1996; Johnson and Watt, 1996; Johnson and Charles, 

1997; Charles and others, 2001; and Carleton and others, 

1999). When simulating groundwater mounding associated 

with stormwater infiltration, the large variations in horizontal hydraulic conductivity make it the more important and 

controlling variable compared to aquifer thickness. Because 

thickness is readily measured (using surface geophysics for 

example), it was also varied in the analyses.

In soil science, the term soil permeability has the same 

units and meaning as hydraulic conductivity, usually measured 

in the vertical direction (see, for example, Ritter, 2006), and 

is a measure of the resistance to flow of water through a unit 

volume of material. In groundwater hydrology and petroleum 

engineering, intrinsic permeability is a property of the porous 

medium independent of the material and is in units of length 

squared (Fetter, 1994, p. 96). Hydraulic conductivity is a function of the intrinsic permeability and the specific weight and 

dynamic viscosity of the fluid flowing through the material. In 

most soil science applications the fluid of interest is water that 

has a density and viscosity that can be assumed to be constant; therefore, the term soil permeability (in this report and 

many other publications) is used interchangeably with vertical 

hydraulic conductivity. 

Measurements of soil permeability in the unsaturated 

zone are measurements of vertical hydraulic conductivity and 

are referred to as an infiltration rate, often reported in inches 

per hour. The permeability of unsaturated sediments varies 

with the degree of saturation. Quantifying the effects of variably saturated permeabilities in the unsaturated zone is beyond 

the scope of this report. In the saturated zone (aquifers and 

confining units), horizontal hydraulic conductivity is often 

measured by conducting an aquifer test; the resulting estimates 

are often reported in feet per day. 

Horizontal hydraulic conductivity in unconsolidated 

sediments is usually greater than vertical hydraulic conductivity (soil permeability). Often only vertical or only horizontal conductivity is measured, and the directional hydraulic 

conductivity that was not measured is calculated by assuming 

a 10:1 ratio of horizontal to vertical hydraulic conductivity 

(Anderson and Woessner, 1991; Pope and Watt, 2005; Modica, 

1996; Cauller and Carleton, 2006). This vertical anisotropy 

can be caused by generally flat-lying mineral grain orientation 

and (or) layers of finer sediments interspersed with coarser, 

more permeable sediments. Vertical anisotropy is scale dependent. Freeze and Cherry (1979, p. 32–34) state that vertical 

anisotropy in cores rarely exceeds 10:1 and is usually less 

than 3:1, but it is not uncommon for regional anisotropy to be 

100:1 or greater. On a county-wide scale, Kauffman and others 

(2001) used horizontal to vertical hydraulic conductivity ratios 

from 1:1 to 178:1 to calibrate a groundwater-flow model in 

an unconfined aquifer in the Coastal Plain of New Jersey. The 

ratio of horizontal to vertical hydraulic conductivity of 10:1 

was used in all simulations in this study.

The ratio of horizontal to vertical hydraulic conductivity 

can be estimated by analyzing multiple-well aquifer tests or 

making separate measurements of vertical hydraulic conductivity (for example, with a soil permeameter) and horizontal 

hydraulic conductivity (for example, a slug test or aquifer 

test). Where no estimate of the ratio is available, using a measured or estimated vertical hydraulic conductivity (soil permeability) for both vertical and horizontal hydraulic conductivity 

(ratio of 1:1) is a conservative assumption.

The soil permeabilities used in this study to represent typical conditions were 0.2 in/hr, 1 in/hr, and 5 in/hr. The lowest 

value, 0.2 in/hr was chosen because that is the minimum soil 

permeability allowed for basins that infiltrate the groundwater 

recharge design storm (Sandra Blick, New Jersey Department of Environmental Protection, oral commun., 2008). The 

National Resources Conservation Service (2009) has four 

soil hydrology categories: permeability less than 0.02 in/hr, 

0.06 in/hr to less than 0.57 in/hr, 0.57 in/hr to 1.42 in/hr, and 

greater than 1.42 in/hr. Soil permeability of 1 in/hr was chosen 

as the middle value for this study because it is the approximate 

midpoint of the third soil permeability category and is five 

times the minimum value used. Soil permeability of 5 in/hr 

was chosen as the third value for this study because it is five 

times the second value and represents a reasonable midpoint 

between 1 in/hr and 20 in/hr (the highest value in the database); 38 percent of average permeabilities in the National 

Resources Conservation Service (2009) database are between 

1in/hr and 5 in/hr, and 19 percent are greater than 5 in/hr. The 

higher two soil permeabilities used for this study, 1 in/hr and 

5 in/hr, are equivalent to horizontal hydraulic conductivities 

of 20 ft/d and 100 ft/d, respectively (assuming a 1:10 vertical anisotropy ratio), values that are representative for New 

Jersey. Reported horizontal hydraulic conductivities in unconsolidated water-table aquifers in New Jersey (including glacial 

till, glacial outwash, and Coastal Plain sediments) range from 

7 to 800 ft/d with average values ranging from 87 to 160 ft/d 

reported by different authors (New Jersey Geological Survey, 

2008; Nicholson and others, 1996; Johnson and Watt, 1996; 

Johnson and Charles, 1997; and Charles and others, 2001). 

Specific Yield 

Specific yield governs how much water the unsaturated 

zone can store when recharge reaches the water table. Specific 

yield is related to porosity. The total porosity is defined as the 

volume of the void space divided by the total volume, often 

expressed as a percentage. Typical unconsolidated sediment 

porosities range from about 20 to 40 percent (Fetter, 1994, 

p. 86). However, not all of the void space is available for 

stormwater storage because water adheres to grains of sediment (specific retention) and reduces the amount of storage for 

subsequent recharge. 
Physical Variables Affecting Height and Extent of Groundwater Mounding 7

Total porosity is equal to specific yield (Sy) plus specific 

retention (Sr). Specific yield is the volume of water that will 

drain from the sediment, as a result of gravity, divided by the 

total volume. Specific retention is the volume of water remaining divided by the total volume. Specific yield and specific 

retention are often expressed as percentages. Coarse sediments 

will have a lower specific retention and higher specific yield 

than fine-grained sediments that have the same porosity. Field 

capacity is the term used in soil science for the concept of specific retention but includes a time component—for example, 

the percentage that will drain in 24 hours. This term is used in 

agriculture because it represents the amount of water potentially available for plants to take up. There is no corresponding term in soil science for specific yield, representing the 

volume of water drained. Specific yield was estimated to be 17 

percent for the water-table aquifer in Cape May County, New 

Jersey (Gill, 1962), and that value was used for this study. A 

value of one-half of 17 percent, 8.5 percent, also was used for 

this study, allowing evaluation of the sensitivity of results to 

specific yield.

Percent Impervious Cover

New Jersey stormwater management regulations (New 

Jersey Administrative Code 7:8-5.4(a)2, 2004) require that 

a new development that adds impervious cover (pavement, 

rooftops) includes stormwater management. The larger the 

percentage of impervious cover, the larger the volume of water 

that must be infiltrated by the recharge basin. A larger volume 

of infiltrated water will result in a higher groundwater mound 

and an increased radius of groundwater mounding in the 

underlying aquifer because a steeper groundwater gradient is 

required to push the larger volume away from the area where 

infiltration occurs. Four different impervious cover percentages were used in simulations for this study: 10, 20, 40, and 

80. 

Design Storm

Infiltration basins are designed to accept runoff from 

storms of different magnitudes according to design constraints 

of individual sites. For example, if an area is determined to 

typically have 16 in/yr of groundwater recharge and the development is expected to result in 10 percent impervious cover, 

then the infiltration basin must be able to infiltrate each year 

a volume of water equivalent to 1.6 inches of precipitation 

across the site. A designer would need to determine the depth 

of precipitation that must be captured from each precipitation 

event in an average year to yield 1.6 inches of annual recharge. 

However, for a development that wishes to capture only runoff 

from rooftops, not roads, the depth of precipitation from 

each storm that is required to be captured in the infiltration 

basin would be greater than if the runoff from all impervious 

surfaces were being channeled to the basin (Joseph Skupien, 

Storm Water Management Consulting, LLC, oral commun., 

2008). Data for New Jersey have been compiled to show, on 

average, how many storms per year are less than or equal to 

a given precipitation depth (Leon Kauffman, U.S. Geological 

Survey, written commun., 2001). 

A 1.25-inch storm was chosen as one of the design storms 

for this project because that value is the NJDEP water-quality 

design storm magnitude (Sandra Blick, New Jersey Department of Environmental Protection, written commun., 2008). 

NJDEP regulations define the water-quality design storm 

magnitude as 1.25 inches in 2 hours (New Jersey Administrative Code 7:8-5.4(a)2, 2004), but for this study the simulation 

period is 36 hours because the infiltration basins are assumed 

to have the capacity to accept and store all of the runoff from 

the storm, regardless of the duration. A second design storm 

of 0.3125 inch (rounded to 0.31 inch) was chosen because 

it is one-fourth of the 1.25-inch storm, reducing the number 

of basin footprints used in the simulations: a simulation with 

10-percent impervious cover and a 1.25-inch storm requires 

the same infiltration basin size as one with 40-percent impervious cover and a 0.31-inch storm. For comparison purposes, 

65 percent of average annual precipitation is derived from 

storms of 1.25 inches or less, and 14 percent of average annual 

precipitation is derived from storms of 0.31 inch or less (Leon 

Kauffman, U.S. Geological Survey, written commun., 2001).

For this study the design-storm magnitude is assumed to 

have fully infiltrated pervious surfaces under predevelopment 

conditions with no runoff. Therefore, for the percentage of the 

hypothetical development that will be converted to impervious surface, the runoff from the design storms that must be 

infiltrated is assumed to be the magnitude of the design storm. 

There is no allowance for evaporation from impervious surfaces or runoff from natural, pervious surfaces.

Basin Shape and Depth

To minimize construction costs and land area required, 

stormwater infiltration basins are usually designed to be the 

smallest footprint that will capture and store the volume of 

runoff indicated by regulations and site conditions. A basin 

designed to capture runoff from a 20-acre development with 

10 percent impervious cover would be the same size as that 

for a 5-acre development with 40 percent impervious cover 

(other factors being equal). Basin shapes can vary from round 

to square to elongate. The height and radius of a groundwater 

mound beneath a square basin will be virtually the same as 

that beneath a round basin, but a square basin can be better 

represented than a round basin with a finite-difference model. 

The rate at which water will drain down through the bottom 

of the basin can be greatly reduced (compared to the natural 

undisturbed materials) if equipment is driven on the basin 

during construction. The basin area required for a development can be large enough that available construction equipment does not have sufficient horizontal reach to excavate a 

round or square basin of sufficient size from the edges. In this 

case a rectangular basin may be constructed where the width 
8 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins

is determined by the reach of the construction equipment, and 

the necessary length is calculated by dividing the required volume by the achievable width. For this study, simulated basins 

were square or rectangular (width to length ratio of 1 to 8).

For safety reasons, stormwater infiltration basins are 

often designed to have no more than 2 ft of standing water. In 

some circumstances, depths of less than 2 ft are used in basin 

design (Sandra Blick, New Jersey Department of Environmental Protection, oral commun., 2008), so for this study 2-ft and 

0.5-ft depths were modeled. 

Single-home stormwater-management structures sometimes include a dry well (seepage pit) to temporarily store 

runoff. A dry well can simply be an excavation filled with 

crushed rock or can be made with a pre-cast concrete structure. Pre-cast concrete structures come in many sizes and vary 

from manufacturer to manufacturer. For this study, representative volumes of dry wells with depths of 2, 4, and 10 ft and 

their associated horizontal extents (Mershon Concrete, written 

commun., 2008) were used.

Depth to Water Table

The depth of the water table below land surface can also 

be described as the thickness of the unsaturated zone (not 

accounting for the capillary fringe). A thicker unsaturated 

zone can store more water and will, therefore, reduce and (or) 

delay the water reaching the water table beneath a stormwater infiltration basin (Sumner and others, 1999). Evaluation 

of the unsaturated-zone effects (delayed delivery of recharge 

to the water table or estimation of storage in the unsaturated 

zone and subsequent evapotranspiration preventing recharge 

to the water table) were beyond the scope of this study, in part 

because of the infinite combinations of thickness, degree of 

saturation prior to the storm event, and heterogeneity. Neglecting the unsaturated zone is a conservative approach because 

a simulated water-table mound occurring beneath an infiltration basin will be smaller if storage in the unsaturated zone is 

included in the simulation. For sites at which the unsaturated 

zone is considered to be important (for example, sites with a 

thick unsaturated zone that fail to meet design criteria when 

the unsaturated zone is neglected), site-specific conditions 

would have to be included in simulations to provide appropriate results.

Use of Finite Difference Numerical 

Models to Estimate Groundwater 

Mounding

Finite-difference numerical models are useful in the 

solution of non-linear groundwater-flow problems. Finitedifference models offer the benefit (compared to analytical 

solutions) of representing highly complex three-dimensional 

conditions and including site-specific conditions such as 

variations in aquifer characteristics, basin shape, recharge 

duration, and other local features in the simulations. The 

height of the water table beneath stormwater infiltration basins 

and the surrounding area was simulated for this study using 

the USGS groundwater-flow model MODFLOW-2000 (Harbaugh and others, 2000). 

Model Design

The models of 10-acre and 1-acre areas having a hypothetical stormwater infiltration basin were designed to simulate 

the groundwater mounding beneath and near the basin for a 

fully three-dimensional system with horizontal boundaries 

that are beyond the radius of influence of the infiltration basin 

(for modeling purposes assumed to be a simulated 0.01-ft 

increase in water level). The simulations are transient, running 

for 36 hours during the period of recharge from the basin to 

the aquifer. Initial conditions for all simulations include a flat 

water table and an initial constant aquifer thickness. Beginning each simulation with a flat water table corresponds to a 

physical system that has recovered from any previous recharge 

events to a steady-state condition. Although the water table 

will have a gradient under almost all natural conditions, the 

gradient is likely to be very small compared to the local gradient caused by groundwater mounding. A pre-existing gradient 

created by having an initial model stress period with regional 

recharge and discharge to a surface-water feature (drain) was 

not used because this led to non-uniform aquifer thicknesses 

that could not be set to the desired 10, 20, and 40 ft. 

Multiple layers must be included in the model to simulate 

the effect of vertical anisotropy of permeability. For this study, 

soil permeability (vertical hydraulic conductivity) is estimated 

to be one-tenth of horizontal hydraulic conductivity. The 

models include three layers to make possible the simulation 

of the vertical component of flow and the effects of vertical 

anisotropy of permeability. The top layer was modeled as 

unconfined, whereas the middle and bottom layers were modeled as confined.

Simulation of Groundwater Mounding Beneath 

Hypothetical Stormwater Infiltration Basins for 

a 10-Acre Development

A 10-acre development was chosen as a representative 

scale for developments that likely would have a hypothetical centralized stormwater collection and infiltration system. 

The modeled development is rectangular with the stormwater 

infiltration basin located close to the development boundary 

(fig. 2). 

Model Discretization

The simulated area is square (fig. 2), 2,300 ft (700 m) 

on each side (about 120 acres). The grid cells increase from 
Use of Finite Difference Numerical Models to Estimate Groundwater Mounding 9

1.65 ft (0.50 m) on a side in the area of the infiltration basin to 

3.3 ft (1.0 m) and then 6.6 ft (2.0 m) on a side in the remainder 

of the model (fig.2). The model has 560 rows and 568 columns, and all 318,080 cells are active in each model layer.

The model has three layers that are of equal saturated 

thickness (layer 1 is partially saturated, whereas layers 2 and 

3 are fully saturated) at the start of the simulation when the 

water table is flat. For the simulations with an aquifer thickness of 10 ft, layers 2 and 3 are each a constant thickness 

of 3.33 ft. The saturated thickness of layer 1 was initially 

also 3.33 ft but increased throughout the 1.5-day simulation 

because of recharge. The total thickness (saturated and unsaturated) of layer 1 is 60 ft, thick enough that layer 1 is never 

fully saturated at any location in any simulation. Similarly, for 

simulations with aquifer thicknesses of 20 and 40 ft, the initial 

saturated thicknesses of the three layers are each 6.66 ft and 

13.32 ft, respectively. 

All of the simulations are transient, lasting 1.5 days (36 

hours). This storm duration was chosen because the NJDEP 

requires that stormwater infiltration basins drain in 3 days or 

Area with recharge = design storm/1.5 days

Area of hypothetical 10-acre development 

Recharge = Design storm * [(1 - percent impervious cover) / 1.5 days]

Area of example rectangular stormwater infiltration basin 

(24 feet x 195 feet) Recharge = Basin depth/1.5 days

Area of example square stormwater infiltration basin 

(69 feet x 69 feet) Recharge = Basin depth/1.5 days

1,050 feet

415 feet

Drain

0 100 200

0 50 100 METERS

300 FEET

6.6

3.3

3.3

1.65

6.6

ROW SPACING, IN FEET

6.6 3.3 1.65 3.3 6.6

COLUMN SPACING, IN FEET

Model boundary (no flow)

Figure 2. Model grid and boundary conditions of a finite-difference model used to simulate groundwater mounding beneath 

hypothetical stormwater infiltration basins on a 10-acre development.
10 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins

less to prevent mosquito breeding and, as a factor of safety, 

that the basins be designed to drain in 1.5 days (or, the basins 

can be designed to drain in 3 days if the soil permeability is 

assumed to be one-half the measured value, producing similar 

estimates of groundwater mounding). Although the NJDEP 

water-quality design storm duration is 2 hours (New Jersey 

Administrative Code 7:8-5.5(a)2, 2004), it was assumed that 

stormwater infiltration basins would capture and store the 

runoff while it infiltrates over 1.5 days. The 1.5-day stress 

period was divided into 16 time steps with an initial time step 

of 0.0208 day (30 minutes) and the time steps increased in 

length by a factor of 1.2 for each time step. The initial condition is steady-state (flat water table, no recharge, surface-water 

boundary at the same elevation as the water table), so no initial 

steady-state stress period was used.

Characteristics Varied to Estimate Groundwater 

Mounding

The seven physical characteristics varied to establish a 

range of simulated groundwater mounds are soil permeability, 

aquifer thickness, specific yield, infiltration basin shape, basin 

depth, design storm, and percentage of impervious cover 

(table 1). Unique combinations of three values of soil permeability, three values of aquifer thickness, two values of 

specific yield, two basin shapes, two basin depths, two design 

storm magnitudes, and four percentages of impervious cover 

required 576 simulations.

Values of soil permeability (vertical hydraulic conductivity, Kv) used in the simulations are 0.2 in/hr, 1 in/hr, and 

5 in/hr. A horizontal to vertical permeability ratio of 10:1 was 

used in all simulations, yielding horizontal hydraulic conductivities (Kh, in units of feet per day more commonly used in 

groundwater investigations) of 4 ft/d, 20 ft/d, and 100 ft/d. 

These values were chosen because the minimum soil permeability allowed for infiltration basins is 0.2 in/hr (Sandra Blick, 

oral commun., 2008), and permeabilities of 5 in/hr are typical 

of unconsolidated sediments in New Jersey (see additional 

discussion in the “Soil Permeability and Aquifer Thickness” 

section of this report). Aquifer thickness values of 10, 20, and 

40 ft were used in this study. 

Specific yield in the simulations was either 0.17 or 0.085 

(17 or 8.5 percent). Because layer 1 included the water table, 

the specific yield determined how much water (when added 

via recharge, for example) could be stored in the aquifer. 

Specific yield is a function of the pore space available when 

water has drained from the aquifer. Layers 2 and 3 function as 

confined aquifers because the thickness does not change with 

changing head. Layers 2 and 3, therefore, have much lower 

storage capacity, entered into the model as storativity (which 

is equal to specific storage multiplied by aquifer thickness). 

Specific storage (expressed in units of 1/Length) is a function 

of the compressibility of water and of the aquifer material and 

is several orders of magnitude less than the porosity (Fetter, 

1994, p. 116). For this study, a value of 3.3 x 10-5 ft-1 was used 

in all simulations for specific storage. A sensitivity analysis 

using a specific storage value for model layers 2 and 3 of 3.3 x 

10-3 ft-1 lowered the maximum head only 0.02 ft.

The design storm magnitudes used in this study were 

1.25 inches and 0.31 inch. Although the NJDEP water quality 

design storm is 1.25 inches of rain in 2 hours, the duration of 

recharge (from the infiltration basin, the developed area, and 

the undeveloped area) is 1.5 days (36 hours). Four percentages 

of impervious cover were used—10, 20, 40, and 80 percent. 

Infiltration basins were simulated as either 2 or 0.5 ft deep.

The volume of runoff from the hypothetical developed 

area for each simulation was calculated by multiplying the 

depth of the design storm by 10 acres (435,600 square feet) 

by the percentage of impervious cover. The assumed runoff 

volume is a conservative estimate because no losses (for 

example, evaporation or storage) are included. The calculated 

volume of runoff was used to determine the area of the infiltration basin by dividing the volume of runoff by the depth of the 

basin, either 2 or 0.5 ft. For square basins, the lengths of the 

sides were calculated by taking the square root of the area. For 

rectangular basins, the length of the long side is eight times 

the length of the short side. The length of the short side was 

calculated by dividing the area by eight, then taking the square 

root. 

Model Boundaries, Recharge, and Difference 

Between Undeveloped and Developed Water 

Levels 

The lateral and bottom sides of the model shown in fig. 2 

are no-flow boundaries. The top is a specified-flux boundary 

with recharge occurring at the water table. The simulations 

were for a duration of 1.5 days with a steady infiltration of 

water during that period. A drain is included near the eastern 

boundary of the model, 1,000 ft east of the western edge of the 

simulated infiltration basins. The surface-water drain modeled with the MODFLOW Drain Package was included in the 

simulations of a 10-acre development to test whether presence 

or absence of a stream at that distance affected results. The 

surface-water boundary had no effect on the simulated groundwater mounds because the change in flow to the drain was less 

than 0.1 percent under pre- and post-development recharge.

The area of the hypothetical development is 10 acres; 

it is the same for all simulations and is a rectangle, 415 ft in 

the north/south direction (along model columns) and 1,050 ft 

in the east/west direction (along rows) (fig. 2). The modeled 

infiltration basins varied in size according to the input variables, ranging from 570 square feet (ft2

) to 72,600 ft2 in area 

(table 1), meaning the width of the basin varies from 8.4 ft for 

the smallest rectangular basin to 270 ft for the largest square 

basin. The distance from the center to the edge of the basins 

varies from 4.2 ft to 135 ft. The eastern edge of the basin is 

always along the same line (in the same column), 20 ft west 

of the development boundary, and is centered in the north/

south direction around the same horizontal line (model row) 
Use of Finite Difference Numerical Models to Estimate Groundwater Mounding 11

(fig. 3). The simulated height of the groundwater mounding is 

calculated and reported at distances from the eastern edge of 

the basin. Results from the analytical solution (discussed later 

in this report) are presented in feet from the center of the basin 

so that an adjustment needs to be made to compare analytical results to those presented in the following section of this 

report.

The groundwater mound associated with a stormwater 

infiltration basin is calculated by subtracting the water-level 

increase associated with precipitation events under predevelopment conditions from that under post-development 

conditions, using the same aquifer characteristics. Therefore, 

predevelopment simulations were run for all combinations 

of selected aquifer characteristics (soil permeability, aquifer 

thickness, and specific yield) with 0.31 inch or 1.25 inches of 

recharge applied uniformly over the simulated area in 

1.5 days. Post-development simulations were then run for the 

same combinations of aquifer characteristics with the addition of infiltration basins on a 10-acre developed area. For the 

simulation, if the developed area has, for example, 10 percent 

impervious cover, then 90 percent of the storm depth will 

recharge the aquifer over the 10-acre area and 10 percent will 

recharge through the infiltration basin. If the 10-acre area has 

10, 20, 40, or 80 percent impervious surface, the developed 

area receives 90, 80, 60, or 20 percent of the recharge, respectively, and the remainder will recharge through the infiltration 

basin. The area outside the developed area receives the same 

recharge as predevelopment, and the infiltration basin area 

receives a depth of recharge equal to the depth of the basin. 

The simulated water levels under predevelopment conditions 

were subtracted from simulated water levels post-development to determine the change associated with the addition of 

impervious surfaces (reducing recharge in those areas) and an 

infiltration basin (concentrating recharge in a small area). 

Results

The maximum height of simulated groundwater mounds 

(which occurs under the center of the basin), the maximum 

extent of 0.25-ft groundwater mounding, and the height of 

groundwater mounding at fixed distances from the east (right) 

edge of the hypothetical stormwater infiltration basin for 

10-acre developments are given in table 2 (located in back of 

report due to its length). The range of the maximum groundwater-mound heights and of the maximum extent of groundwater mounding height of 0.25 ft for each of the 18 values of 

the seven aquifer, basin, and design storm variables are shown 

in box plots in figures 4 and 5, respectively. (The box plots 

included in this report show results from the synthetic population of hypothetical simulations and do not imply a random 

distribution.) The maximum simulated groundwater-mound 

height is 18.5 ft and the minimum is 0.1 ft. The median of all 

576 simulations of the maximum mound heights is 1.8 ft. The 

maximum extent (east from the eastern edge of the infiltration 

basins, see figs. 2 and 3) of groundwater mounding of 

Table 1. Values of variables input to the finite-difference simulations of groundwater mounding beneath hypothetical 

stormwater infiltration basins on 1-acre and 10-acre developments. 

Input variable Values for a 10-acre development 

(centralized stormwater infiltration basin)

Values for a 1-acre development 

(individual dry well)

Soil permeability 

(vertical hydraulic conductivity)

0.2, 1.0, or 5.0 inches/hour 0.2, 1.0, or 5.0 inches/hour

Aquifer thickness 10, 20, or 40 feet 10, 20, or 40 feet

Specific yield 

(Sy, pore space available for new storage)

0.085 or 0.17 0.085 or 0.17

Percentage of development to be covered by 

impervious material 

(for example, rooftops and pavement)

10, 20, 40 or 80 percent 10, 20, 40 or 80 percent

Design storm magnitude 

(depth of precipitation site-wide that must be 

accommodated by infiltration basin)

1.25 inches or 0.31 inch 1.25 inches or 0.31 inch

Depth of infiltration basin or dry well 0.5 or 2.0 feet 2, 4, or 10 feet

Infiltration-basin/dry-well shape Square (ratio of sides 1:1) 

Rectangular (ratio of sides 1:8)

Square

Range of infiltration basin/dry well areas 570 to 72,600 square feet 11 to 1,800 square feet

Number of variable combinations 576 432
12 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins

0 50 100 150 200 300

Perimeter of square

4,538 square foot basin

Perimeter of square

18,150 square foot basin

Perimeter of square

1,134 square foot basin

Location of points at which simulated groundwater

mounding was recorded

Boundary of hypothetical 10-acre development

0 100 200

0 50 100 METERS

300 FEET

0 50 100 150 200 300

Perimeter of rectangular

4,538 square foot basin

Perimeter of rectangular

18,150 square foot basin

Perimeter of rectangular

1,134 square foot basin

Location of points at which simulated groundwater

mounding was recorded

Boundary of hypothetical 10-acre development

Figure 3. Relative size and placement of selected hypothetical infiltration basins used in simulations of groundwater mounding 

beneath a 10-acre development.
Use of Finite Difference Numerical Models to Estimate Groundwater Mounding 13

0.25 ft ranges from 0 to 300 ft with a median of 51 ft for all 

576 simulations.

A basin designer needing estimates of the height and 

extent of groundwater mounding associated with a stormwater 

infiltration basin for a proposed 10-acre development can find 

in table 2 the results of a simulation with the same or similar 

aquifer characteristics and design criteria as the proposed 

10-acre development and can obtain simulated groundwatermound heights and extents. The results in table 2 may be 

applicable to sites of sizes other than 10 acres. The area of the 

infiltration basin is a function of a combination of the area of 

the development, percentage of impervious surface, design 

storm magnitude, and basin depth; therefore, it is not the area 

of the development, but the area and depth of the basin, that is 

the relevant factor for groundwater mounding. Choosing the 

basin area and depth from table 2 that is equal to or greater 

than the user’s design basin will yield conservative results. 

For example, the area of a stormwater infiltration basin for 

a 20-acre site with 20 percent impervious surface would be 

the same as that for a 10-acre site with 40 percent impervious 

surface and same depth basin. For sites with aquifer characteristics different from those used in this report, the user 

can choose the closest value that is more conservative. For 

example, if vertical soil permeability is estimated to be 

3 in/hr, using appropriate simulations from table 2 including soil permeability of 1 in/hr would yield a conservative 

estimate of maximum groundwater-mound height and 5 in/hr 

would yield a conservative estimate of maximum extent of 

groundwater mounding of 0.25-ft. The same approach is 

appropriate for aquifer thickness (smaller thickness for a 

conservative estimate of maximum groundwater-mound height 

and larger thickness for a conservative estimate of maximum 

extent of groundwater mounding) and basin shape (square 

basins for a conservative estimate of maximum groundwatermound height and rectangular basins for a conservative estimate of maximum extent of groundwater mounding). Lower 

values of specific yield and higher values of basin depth produce more conservative estimates of both maximum groundwater-mound height and extent of groundwater mounding. 

The simulated systems respond non-linearly to changes in 

soil permeability and aquifer thickness; increasing soil permeability by a factor of five from 0.2 to 1 in/hr reduces maximum 

groundwater-mound heights more than increasing by a factor 

of five from 1 to 5 in/hr. Therefore, interpolating between (or 

extrapolating beyond) results for input values between (or 

beyond) those used in this study may yield incorrect results. 

More conservative estimates can be obtained by using the 

closest appropriate simulated input value to the variable measured (or estimated) at a particular site.

The groundwater mounding associated with two or more 

nearby infiltration basins can be conservatively estimated 

by simulating the basins separately then adding together the 

mounding at any given location associated with each individual basin. For example, if identical basins were centered 

100 ft apart, the maximum height of the groundwater mound 

beneath one basin would be increased by the height of the 

groundwater mound created by the second basin at a distance 

of 100 ft from the center of that second basin. The height and 

extent of groundwater mounding are governed by non-linear 

equations because of the changing thickness of the saturated 

zone (and, therefore, changing capacity of the aquifer to transmit water). Therefore, there is a known error associated with 

adding the simulated height of individual groundwater mounds 

to estimate the combined height. However, the estimate will 

be conservative and the error will be small if the height of the 

simulated groundwater mounds is small in comparison to the 

thickness of the saturated zone. For example, a finite-difference simulation with aquifer and basin characteristics the same 

as simulation number 218 (table 2) but with two infiltration 

basins centered 100 ft apart produced maximum groundwatermound heights within 0.02 ft of the result reached by simply 

adding the effects, and at the midpoint between the two basins 

the mound height was 1.00 ft lower than the height calculated 

by adding the two individually simulated groundwater-mound 

heights at that location.

Maximum Height of Groundwater Mounding

The box plots in figure 4 show whether a higher value of 

a variable increases or decreases the maximum groundwatermound height and whether changing the values of some 

variables changes maximum heights more than changing the 

values of other variables. For example, groundwater-mound 

heights are most sensitive to (show the greatest variation with) 

soil permeability (vertical hydraulic conductivity). Maximum 

mound heights have the smallest range (0.1 to 3.6 ft) when soil 

permeability is set to the highest value of 5 in/hr and lowest 

median (0.6 ft) of the 18 variable values. In contrast, maximum heights have the highest minimum (0.9 ft) and highest 

median (3.9 ft) when soil permeability is 0.2 in/hr. Varying 

aquifer thickness would have the same effect as varying soil 

permeability (which, in this study, is one-tenth horizontal 

hydraulic conductivity) if the values were changed by a factor 

of 25 (for example, from a thickness of 10 to 250 ft), but aquifer thickness was changed only by a factor of 4 (10 to 

40 ft) in this study because aquifer thickness usually varies by 

about an order of magnitude (for example, from 20 to 200 ft), 

whereas hydraulic conductivity usually varies by several 

orders of magnitude at any given site and can vary by seven or 

more orders of magnitude at a site or between sites. Figure 4 

shows that the greatest and median maximum groundwater 

heights decrease with increasing soil permeability and aquifer 

thickness. 

Groundwater-mound heights decrease when soil permeability, aquifer thickness, or specific yield is increased (and 

other variables are held constant). In these simulations, changing soil permeability, aquifer thickness, specific yield, basin 

depth, or basin shape does not change the volume of aquifer 

recharge; it changes the shape or height of the groundwater 

mound resulting from the infiltration. 

An aquifer with a greater horizontal permeability or 

aquifer thickness has a greater ability to transmit water away 
14 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins

0.2 1.0 5.0

Soil permeability

(inches/hour)

10 20 40

Aquifer thickness

(feet)

0.085 0.17

Specific yield

(dimensionless)

80 40 20 10

Impervious cover (percent)

 2.0 0.5

Basin depth

(feet)

1.25 0.3125

Design storm

magnitude

(inches)

Basin shape

Maximum

75th percentile

Median

25th percentile

Minimum

Number of simulations

EXPLANATION

0

5

10

15

20

HEIGHT OF GROUNDWATER MOUNDING, IN FEET

Square Rectangular

144

192 192 192 192 192 192 288 288 288 288 288 288 288 288 144 144 144 144

Figure 4. Range of maximum height of simulated groundwater mounding beneath hypothetical stormwater infiltration basins on a 

10-acre development in relation to aquifer and basin characteristics.
Use of Finite Difference Numerical Models to Estimate Groundwater Mounding 15

0.2 1.0 5.0

Soil permeability

(inches/hour)

10 20 40

Aquifer thickness

(feet)

0.085 0.17

Specific yield

(dimensionless)

80 40 20 10

Impervious cover (percent)

2.0 0.5

Basin depth

(feet)

1.25 0.3125

Design storm

magnitude

(inches)

Basin shape

50

100

150

200

250

300

0

Maximum

75th percentile

Median

25th percentile

Minimum

Number of simulations

EXPLANATION

EXTENT OF 0.25-FOOT GROUNDWATER MOUNDING, IN FEET

Square Rectangular

144

192 192 192 192 192 192 288 288 288 288 288 288 288 288 144 144 144 144

Figure 5. Range of maximum extent of 0.25-foot simulated groundwater mounding beneath hypothetical stormwater infiltration basins 

on a 10-acre development in relation to aquifer and basin characteristics.
16 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins

from the source of infiltration than aquifers with lower horizontal permeability or aquifer thickness. Therefore, increasing horizontal permeability decreases the maximum height of 

groundwater mounding and increases the extent of groundwater mounding. Also, the simulated heights of the groundwater 

mounds beneath the rectangular basins in this study are lower 

than beneath the equally sized square basins. Infiltration reaching the water table beneath a rectangular basin has a greater 

cross-sectional area of aquifer across which to flow away from 

the basin compared to that of a square basin of equal area. 

Therefore, the rectangular basin requires less hydraulic head to 

move the infiltrated water through the aquifer and the simulated groundwater mounds are lower. 

The groundwater mound is lower when specific yield 

is higher because the aquifer can store more water per unit 

volume of aquifer. The lower height occurs because a given 

volume of infiltrated water will saturate, for example, one-half 

the volume of an aquifer when specific yield is doubled.

Linear changes in values of the variables produce nonlinear changes in the groundwater-mound heights. Doubling 

the specific yield (from 8.5 percent to 17 percent) doubles 

the storage capacity of the aquifer and, therefore, potentially 

halves the maximum height of the groundwater mound. The 

maximum groundwater-mound height of the 576 simulations 

was 18.5 ft, occurring in simulation number 506, for which 

the specific yield was 8.5 percent (table 2). Simulation number 

505 has the same variable values as number 506 except for 

specific yield of 17 percent and a maximum groundwatermound height of 10.6 ft. The reason the maximum groundwater-mound height for simulation 505 is not exactly half that of 

simulation 506 is that the simulated unconfined flow system 

is non-linear and transmissivity changes as the height of the 

groundwater mound changes. 

Basin depth, when changed by a factor of 4 (from 0.5 

to 2 ft), has a substantial effect on the maximum height of 

groundwater mounding. If there was no lateral flow away from 

the source of recharge, vertical infiltration of, for example, 

2 ft of water into an aquifer with specific yield of 8.5 percent 

would raise the water level 23.53 ft, whereas vertical infiltration (with no lateral flow) beneath a basin depth of 0.5 ft and 

specific yield of 8.5 percent would raise the water level 5.88 ft, 

one-fourth of that for a basin four times deeper. The simulations for this study do not include flow in the unsaturated zone 

so water is recharged directly to the water table, and horizontal 

flow away from the source of recharge begins immediately 

and continues during the entire 36-hour recharge period, 

resulting in a maximum groundwater-mound height of 18.5 ft 

rather than 23.5 ft. 

Increasing the design-storm magnitude by a factor of 

4 (from 0.31 to 1.25 inches) or the percentage of impervious cover by a factor of 8 (from 10 to 80 percent) also has 

a substantial effect on the maximum height of groundwater 

mounding. The groundwater-mound height increases when the 

design storm magnitude or percentage of impervious cover 

increases (and values of other variables are held constant) 

because the total volume of infiltrated water also increases. A 

greater volume of infiltrated water requires a higher head to 

move that water away from the source of recharge if the physical characteristics of the aquifer are unchanged. Impervious 

cover percentage and design-storm magnitude have a greater 

effect on maximum heights of groundwater mounding for the 

1-acre developments (described further on in this report) than 

for the 10-acre developments because recharge in the 10-acre 

developments was reduced in the area of the development to 

account for the effect of impervious surfaces.

The maximum groundwater-mound height (18.5 ft) was 

produced by a simulation with a square basin, maximum basin 

depth, impervious cover percentage, and storm magnitude 

(2 ft, 80 percent, and 1.25 in, respectively), and minimum 

specific yield, soil permeability, and aquifer thickness (8.5 

percent, 0.2 in/hr, and 10 ft, respectively); therefore, the head 

required to impart horizontal flow away from the area of 

recharge is higher than in other simulations.

Maximum Extent of Groundwater Mounding

The maximum extent of groundwater mounding (defined 

as a 0.25-ft water-level increase at a distance measured from 

the east edge of the hypothetical infiltration basin, see figs. 

2 and 3) for 10-acre developments ranges from 0 ft to 300 ft 

(table 2, fig 5). Of the 576 simulations, 117 had a maximum 

extent of less than 25 ft, and 95 had an extent of more than 

100 ft, with a median value of 51 ft. The maximum extent of a 

simulated mound of at least 0.01 ft was less than 750 ft for all 

simulations and 500 ft or greater for 56 of the simulations.

Groundwater mounding of at least 0.25 ft was chosen as 

the lower limit of mounding considered to be significant. A 

0.05 ft difference between pre- and post-development water 

levels caused by stormwater infiltration is not detectable under 

field conditions when recharge from precipitation outside of 

an infiltration structure is increasing water levels by tenths of 

a foot or more. The value of 0.25 ft was chosen as the amount 

of significant groundwater level change based on the NJDEP 

stormwater regulation that sets 0.1 ft as the maximum acceptable change for surface water. Any simulated groundwater 

value of 0.05 ft is rounded up to 0.1 ft (Sandra Blick, oral 

commun., 2008), and a surface-water-level increase of 0.05 ft 

is equivalent to a groundwater-level increase of 0.25 ft if the 

specific yield of the aquifer was 20 percent (0.05 ft/0.20 = 

0.25 ft). 

The relation between the maximum extent of groundwater mounding and the seven variables tested for this study 

appears contradictory in some cases. As mentioned in the 

above discussion of groundwater-mound heights, when 

other variables are held constant, increasing soil permeability results in a decreased maximum height of groundwater 

mounding but an increased areal extent. However, the box 

plots for maximum extent of a 0.25-ft groundwater mounding for the three values of soil permeability (fig. 5) show that 

the median extents for soil permeabilities of 0.2 in/hr, 1 in/hr, 

and 5 in/hr are 41, 69, and 52 ft, respectively, so the median of 
Use of Finite Difference Numerical Models to Estimate Groundwater Mounding 17

the maximum extents increases from the lowest to the middle 

value of soil permeability but decreases from the middle to 

the highest value of soil permeability. This outcome also can 

be seen in some of the results shown in table 2, for example 

for simulation numbers 2, 4, and 6, where the soil permeabilities are 0.2 in/hr, 1 in/hr, and 5 in/hr and the maximum 

extents of 0.25-ft groundwater mounding are 41ft, 52ft, and 

13 ft, respectively. The reason the maximum extent is smallest for the highest value of soil permeability is that 0.25 ft was 

selected as the threshold of significant groundwater mounding. 

The maximum groundwater-mound heights are 5.40, 1.83, and 

0.48 ft, and the groundwater-mound heights at 150 ft from the 

east (right) edge of the infiltration basin are 0.00, 0.02, and 

0.04 ft for simulation numbers 2, 4, and 6, respectively. These 

results show that the groundwater mound in settings with 

higher soil permeability is lower at the center and extends farther from the center. However, because the maximum groundwater-mound height in simulation number 6 (soil permeability 

of 5 in/hr) is only 0.48 ft, groundwater mounding of 0.25 ft 

occurs closer to the edge of the basin than in simulations 2 or 

4. Because the groundwater mound for a system with higher 

soil permeability has a lower maximum height but a greater 

extent than for a system with lower soil permeability (other 

variables held constant), there is a “crossover” point where 

the groundwater mounds have the same height (fig. 6). If that 

“crossover” point is at 0.25 ft or greater, the maximum extent 

of groundwater mounding of 0.25 ft increases with increasing 

soil permeability. Because of the 0.25 ft threshold selected for 

significance, the range of maximum extents is greatest for high 

soil permeabilities and least for low soil permeabilities. The 

highest extents occur with the highest permeabilities because 

the groundwater mound is lower and more areally extensive, 

as described above. For a few of the simulations with high permeabilities, the groundwater mound is so flat that the 0.25-ft 

rise does not extend beyond the east edge of the basin, and the 

maximum extent is zero, lower than any extent that occurs in 

simulations with lower permeabilities.

The extent of groundwater mounding of 0.25 ft is substantially affected by changing specific yield by a factor of 

2, basin depth by a factor of 4, design-storm magnitude by a 

factor of 4, or percentage of impervious cover by a factor of 8 

(fig. 5). The extent is less affected by changing aquifer thickness by a factor of 4 or basin shape from square to rectangular.

Distances in table 2 for the maximum extent of 0.25-ft 

groundwater mounding and groundwater mounding at fixed 

locations are given from the east edge of the basin. (This is 

different than analytical and finite-difference results given in 

table 4 (farther on in this report), where distances are from the 

center of the basin.) For the 10-acre developments, the sizes 

of the hypothetical basins vary from 24 ft to 270 ft on a side 

for the square basins and 8.4 ft x 67 ft to 95 ft x 760 ft for the 

rectangular basins, meaning that the distance from the center 

to the right edge of the basin varies from 4.2 ft to 135 ft. The 

relevant measurement for adjacent property owners is likely to 

be the distance from the edge of the basin to existing or proposed structures. For basins with shapes different than square 

and rectangular (short side to long side ratio 1:8), groundwater mounding effects relative to the edge of the basin can be 

estimated from the results presented in table 2 by, for example, 

interpolating between the results for a square basin and a 1:8 

rectangular basin to obtain an estimate for a rectangular basin 

with a short side to long side ratio of 1:4.

Simulation of Groundwater Mounding 

Beneath Hypothetical Dry Wells for a 1-Acre 

Development

Stormwater management can be applied on a development-wide scale (such as the hypothetical 10-acre developments described in the preceding section) or on a property-byproperty scale. For example, some municipalities require that 

substantial expansion or redevelopment of existing structures 

includes stormwater management measures to address the 

increased runoff caused by the expansion (for example, 

Township of Princeton, 2009). In other circumstances it 

may be more cost-effective to capture stormwater runoff at 

each property rather than construct a centralized facility. The 

simulation of stormwater infiltration at a hypothetical 1-acre 

development incorporated the assumption that the infiltration 

structure would be a pre-cast concrete dry well. These structures are constructed with capacities that can range from 600 

to 2,700 gallons and with open bottoms and openings on all 

sides to allow discharge of received water (Mershon Concrete, 

written commun., 2009).

Model Discretization, Boundaries, and 

Difference Between Undeveloped and 

Developed Water Levels

The modeled area is rectangular, 1,700 ft (518 m) in the 

x-direction (along rows) by 1,300 ft (400 m) in the y direction, about 50 acres (fig. 7). The grid cells are 0.5 ft (0.15 m) 

on a side in an approximately 60 ft by 60 ft square around the 

infiltration dry well, increasing to 1 ft (0.30 m), 2 ft (0.60 m), 

Initial water table

Groundwater mound 

in higher permeability 

aquifer 

Groundwater mound in 

lower permeability 

aquifer 

Figure 6. Schematic diagram showing relative shape of 

groundwater mounding in aquifers of higher and lower soil 

permeability.
18 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins

4 ft (1.25 m), 8 ft (2.50 m), and 16 ft (5.00 m) on a side with 

increasing distance from the hypothetical dry well. The model 

has 410 rows and 475 columns, and all 194,750 cells are 

active in each layer.

The model of hypothetical 1-acre developments has the 

same features as the model of hypothetical 10-acre developments, including three initially equal-thickness layers, 

transient simulations of 1.5 days, no-flow boundaries on the 

bottoms and sides, and a specified flux (recharge) boundary on 

the top. However, the model of the 1-acre development does 

not have the surface-water boundary (drain) used in the model 

of the 10-acre system because simulations of the 10-acre 

developments indicated that a drain located 1,000 ft from the 

infiltration basin had an insignificant effect on groundwater 

mounding. Furthermore, not including a surface-water boundary is conservative because the simulated mound height is 

higher than would be the case if a nearby drain were present. 

The same variables were changed (soil permeability, aquifer 

thickness, specific yield, design storm magnitude, percentage of impervious cover, and basin depth), except for basin 

shape: all hypothetical basins in the 1-acre developments were 

square. Also, because there is not a safety concern regarding 

water depth in a buried structure, drywells are simulated to be 

2 ft, 4 ft, or 10 ft deep (Mershon Concrete, written commun., 

2009). 

Because of the small area of the hypothetical development, 1 acre, the effect of less recharge in the developed 

area compared to the surrounding area was assumed to be 

small, and the only recharge input to the model was from the 

hypothetical dry well. Therefore, the groundwater mounding 

due to the dry well was calculated by subtracting the initial 

(flat) water-table height from the final water-table height. 

(Neglecting the effect of reduced recharge in the developed 

area is a different approach than was used in the model of the 

hypothetical 10-acre development described in the previous 

section of this report.) The hypothetical dry wells were varied 

in size according to the input variables, but the east edge of the 

dry well was always located along the same north/south line 

(model column) and is centered in the north/south direction 

around the same east/west line (model row), similar to that 

of the simulation of hypothetical basins in the models of the 

10-acre development (figs. 2 and 3).

Results

Simulated maximum groundwater-mound heights, 

maximum extent of groundwater mounding of 0.25-ft, and 

groundwater mounding at fixed distances from the right edge 

of the hypothetical stormwater infiltration dry well for 1-acre 

developments are given in table 3 (located in back of report 

due to its length). The range of maximum heights of groundwater mounds and maximum extent of a 0.25-ft groundwater 

mounding for each of the17 values of the six aquifer, basin, 

and design storm variables are shown in box plots in figures 

8 and 9, respectively. The maximum simulated height of 

groundwater mounding ranges from 0.01 to 14.0 ft (fig. 8). 

The median for all 432 simulations of the maximum height 

of groundwater mounding is 1.0 ft. The maximum extent 

(measured east of the right edge of the dry wells) of the 0.25-ft 

groundwater mounding ranges from 0 to 100 ft (fig. 9) with a 

median for all 432 simulations of 10 ft.

Results from simulations of hypothetical dry wells 

on 1-acre developments are similar to those from 10-acre 

developments: maximum heights of groundwater mounds are 

most affected by the changes made to soil permeability, and 

sensitivity to other variables is similar. For further information on the groundwater mounding associated with changes 

to different variables, see the “Results” section within the 

“Simulation of Groundwater Mounding Beneath Stormwater 

Infiltration Basins for a 10-Acre Development” earlier in this 

report. However, neglecting the effect of reduced recharge in 

the developed area (away from the dry well) produces results 

that differ slightly from the simulation of 10-acre developments. For example, maximum groundwater-mounding height 

and extent of groundwater mounding results for simulations of 

1-acre developments are more sensitive to changes in designstorm magnitude and percentage of impervious cover than 

changes in dry-well depth, whereas for 10-acre developments 

changing basin depth had more influence.

The small size of the infiltration dry wells in the 1-acre 

models and the fixed threshold of 0.25 ft for maximum extent 

of groundwater mounding lead to different results of simulations of 1-acre developments compared to results of simulations of 10-acre developments. For example, although increasing soil permeabilities are associated with decreasing heights 

of the groundwater mound at the center and increasing lateral 

extent, at the highest permeability the groundwater mound is 

less than 0.25 ft at the edge of the dry well for more than half 

of the 1-acre simulations, and the median extent decreases 

with increased soil permeability or aquifer thickness (fig. 9). 

In contrast, as was the case for the 10-acre results, the maximum extent of groundwater mounding of 0.25 ft in simulations of 1-acre developments increases with increased basin 

depth, design-storm magnitude, or percentage of impervious 

cover, or decreased specific yield.

Model Limitations

The initial water-table gradient is simulated to be zero. 

At some sites, the slope of the water table prior to infiltration can cause the aquifer transmissivity to vary enough that 

the assumption of an initial flat water table leads to errors 

in estimated groundwater mounding large enough to affect 

basin design decisions. If the initial simulated thickness of 

the water-table (unconfined) aquifer in this study is equal to 

the smallest thickness measured at a site, the assumption of 

an initial flat water table is conservative and could be used to 

minimize errors associated with using results from this study 

for an area with a sloping water table.
Use of Finite Difference Numerical Models to Estimate Groundwater Mounding 19

The duration of the simulations was 1.5 days with a 

steady infiltration of the stormwater-basin design volume of 

water during that period. Infiltration of the same volume of 

water during a shorter period would result in a higher groundwater mound beneath and near the infiltration basin. Also, 

there is no evaluation of whether the design volume would 

infiltrate to the water table within 1.5 days. The simulated 

recharge was applied directly to the water table, irrespective 

of the physical plausibility of complete infiltration through 

the basin bottom and the unsaturated zone. It is possible 

that in sediments of lower permeability (0.2 in/hr) the basin 

would not fully drain in 1.5 days, yet for the simulations it is 

assumed the water reaches the water table during that period. 

Methods for calculating whether the infiltration basin will 

drain in more, less, or exactly 1.5 days are beyond the scope 

of this study but would need to be applied to confirm that the 

basin meets the design criteria before using the results of these 

simulations.

The model used for these simulations, MODFLOW-2000 

(Harbaugh and others, 2000), simulates only flow in the saturated zone. Therefore, the simulated stormwater infiltration 

reaches the water table without attenuation in an unsaturated 

zone. In reality, there can be substantial storage and time delay 

in the unsaturated zone that would act to lower the height of 

the groundwater mound associated with a stormwater event. 

Because neglecting the unsaturated zone leads to higher simulated groundwater mounds, this approach is conservative. 

A finite number of simulations are described for a limited suite of variables, whereas there are an infinite number 

of combinations of values of variables not included and of 

properties that were not varied (such as the ratio of vertical to 

horizontal permeability). Additional simulations would need to 

be done to estimate the sensitivity of results to properties that 

Area of example stormwater infiltration dry well (20 feet x 20 feet)

Recharge = Dry well depth/1.5 days

Model boundary (no flow)

16

8

2

4

16

ROW SPACING, IN FEET

COLUMN SPACING, IN FEET

1

1

0.5

2

4

8

16 8 4 2 1 0.5 1 2 4 8 16

Area of no recharge

0 50 100 200 FEET

0 10 30 60 METERS

Figure 7. Model grid and boundary conditions of a finite-difference model used to simulate groundwater mounding beneath 

hypothetical stormwater infiltration basins on a 1-acre development.
20 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins

0.2 1.0 5.0

Soil permeability

(inches/hour)

10 20 40

Aquifer thickness

(feet)

0.085 0.17

Specific yield

(dimensionless)

1.25 0.3125

Design storm

magnitude

(inches)

80 40 20 10

Impervious cover (percent)

10 4 2

Basin depth (feet)

MAXIMUM WATER-LEVEL INCREASE, IN FEET

Maximum

75th percentile

Median

25th percentile

Minimum

Number of simulations

EXPLANATION

0

4

8

12

144

144 144 144 144 144 144 216 216 144 144 144 216 216 108 108 108 108

Figure 8. Range of maximum height of simulated groundwater mounding beneath hypothetical stormwater-infiltration dry wells on a 

1-acre development in relation to aquifer and dry well characteristics.
Use of Finite Difference Numerical Models to Estimate Groundwater Mounding 21

0.2 1.0 5.0

Soil permeability

(inches/hour)

10 20 40

Aquifer thickness

(feet)

0.085 0.17

Specific yield

(dimensionless)

1.25 0.3125

Design storm

magnitude

(inches)

80 40 20 10

Impervious cover (percent)

10 4 2

Basin depth (feet)

EXTENT OF 0.25-FOOT WATER-LEVEL RISE, IN FEET

Maximum

75th percentile

Median

25th percentile

Minimum

Number of simulations

EXPLANATION

0

20

40

60

80

100

144

144 144 144 144 144 144 216 216 144 144 144 216 216 108 108 108 108

Figure 9. Range of maximum extent of 0.25-foot simulated groundwater mounding beneath hypothetical stormwater-infiltration dry 

wells on a 1-acre development in relation to aquifer and dry well characteristics.
22 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins

were not changed and to estimate groundwater mounding at 

sites for which properties are substantially different than those 

used in this study.

Use of Analytical Equations to Estimate 

Groundwater Mounding

Analytical equations (partial differential equations with 

initial and boundary conditions that mathematically describe, 

in this case, groundwater flow) can be used to estimate the 

magnitude and radius of groundwater mounding beneath an 

infiltration basin or dry well, but the accuracy of the results is 

limited by simplifying assumptions that are inherent to solving 

the non-linear differential equations. A number of solutions 

have been presented over the past 50 years; the most widely 

cited is that by Hantush (1967).

Description of Hantush Equation 

Hantush (1967) proposed a solution of an equation 

describing the “growth and decay of groundwater mounds in 

response to uniform percolation.” The Hantush and similar 

equations are widely implemented (for example, Finnemore, 

1995; Zomorodi, 2005) to estimate water-table mounding 

beneath septic systems and other similar infiltration structures 

that can reasonably be considered steady-state (infiltration 

is constant over time). However, few implementations have 

included the more challenging transient condition (infiltration 

occurs over a limited duration, then ceases) which is addressed 

in this study. 

Hantush (1967) assumes a water-table aquifer of infinite 

extent and finite thickness with a horizontal, impermeable 

base. The solution also includes the Dupuit assumptions of 

horizontal flow and negligible change of transmissivity with 

a change in head. The solution Hantush derived making these 

assumptions provides results that correspond well with similar 

analytical solutions and some field measurements. 

Hunt (1971) proposed a solution that mathematically 

includes the vertical component of the flow vector that can 

be significant in groundwater mounding, but the solution has 

substantial limitations, including a non-solvable integral at 

the center of the infiltration basin and numerical oscillations 

beyond the outer edge of the infiltration basin. Hunt’s solution 

does not account for vertical anisotropy of permeability. 

Finite-difference numerical simulations of groundwater 

mounding show that vertical anisotropy can lead to simulated groundwater-mound heights on the order of 15 percent 

higher than those simulated in either a 1-layer finite-difference 

model or analytical solution with the assumption that flow is 

strictly horizontal flow (see the following section of this report 

“Comparison of Analytical and Finite-Difference Estimates 

of Groundwater Mounding and Effect of Vertical Layering”). 

Also, simulations that include storage in, and delayed yield 

from, the unsaturated zone result in groundwater mounding 

less than that obtained by neglecting the unsaturated zone 

(Sumner and others, 1999). Therefore, the height of groundwater mounding is underestimated by the Hantush equation 

where vertical anisotropy is present and overestimated where 

an unsaturated zone is present. 

Hantush (1967) solves the general two-dimensional 

groundwater flow equation by making assumptions to create 

boundary conditions that allow the use of a Laplace transform 

with respect to time and the Fourier cosine transform with 

respect to x and then y to derive an integral that can be solved. 

The resulting equation is

h h ( / w k vt S

l x

vt

a y

vt

S

l x

i

2 2 2

4 4 4

− = + + + + )( ){ * ( , ) * (

vt

a y

vt

S

l x

vt

a y

vt

S

l x

vt

a y

, )

* ( , ) * ( ,

− +

− + + − −

4

4 4 4 4

0

1

vt

where S erf erf d

)}

* (α β, ) ( ) ( ) α

τ

β

τ

 = ∫ τ ,

where

h = head at a given time after recharge begins; 

hi = initial head (height of the water table above 

the base of the aquifer); 

w = recharge (infiltration) rate; 

K = horizontal hydraulic conductivity;

v = diffusivity, where v = Kb/Sy;

b = average aquifer thickness;

Sy = specific yield;

t = time elapsed since recharge began;

l = half-length of the recharge basin;

a = half-width of the recharge basin;

x = distance from the center of the recharge 

basin in the x direction;

y = distance from the center of the recharge 

basin in the y direction;

	 α	 =	

l + x

4vt

or l − x

4vt

;

ß = a + y

4vt

or a − y

4vt

;

τ = dummy variable of integration; and

erf = error function.

The integral in the above equation cannot be solved 

explicitly and is solved using iterative numerical methods.

Spreadsheet for Solving Hantush Equation

As part of this study, a spreadsheet was developed to 

use the Hantush equation (1967) to calculate the magnitude 

of groundwater mounding. The required input values (aquifer 

thickness, horizontal hydraulic conductivity, specific yield, 

basin size, and recharge rate and duration) are straightforward 

and can be measured or estimated from published values. The 
Use of Analytical Equations to Estimate Groundwater Mounding 23

difficulty of solving the Hantush equation for transient (nonsteady state) flow has prevented it from being widely applied 

in groundwater-mounding applications. This report provides a 

tool using readily available software to solve the integrals and 

allow users to specify input variables and generate reasonable, 

quantified, reproducible estimates of groundwater mounding 

beneath stormwater infiltration structures.

The numerical solution used in the Microsoft Excel 

spreadsheet presented in this report was written by Dr. Arthur 

Baehr (U.S. Geological Survey (retired), written commun., 

2009) to solve the above equation using the numerical integration techniques Simpsons Rule and the Trapezoidal Rule 

(Chapra and Canale, 1998). Users specify the recharge rate, 

specific yield, horizontal hydraulic conductivity, basin width 

and length, and duration of recharge, and the spreadsheet 

software calculates the maximum height of groundwater 

mounding and the mounding at user-specified distances from 

the center of the mound. 

The user executes an Excel macro to recalculate water 

levels if any values are changed, so macros need to be enabled. 

Although a change entered for any input variable will cause 

the spreadsheet to automatically recalculate values, the results 

will not be correct until the macro is executed because the 

numerical integration requires an estimate of the final result 

as an input. The macro uses the Excel function “Goal Seek” 

to converge on a solution where the estimated and calculated 

water levels are within 0.0001. The numerical integration uses 

the error function, which the user may need to add by following the Excel help instructions for ERF:

If this function is not available, and returns the 

#NAME? error, install and load the Analysis ToolPak addin.

On the Tools menu, click Add-Ins. 

In the Add-Ins available list, select the Analysis ToolPak 

box, and then click OK. 

If necessary, follow the instructions in the setup program.

The values highlighted in yellow/orange in the user interface page of the spreadsheet (fig. 10) are user-specified input 

values of aquifer and basin characteristics and the distances 

from the center of the basin for which groundwater-mounding 

(thickness of the saturated zone) estimates are desired. The 

Figure 10. User interface page of spreadsheet for solving the Hantush (1967) equation that describes groundwater mounding beneath 

an infiltration basin with example input and output.
24 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins

values highlighted in red are the calculated maximum height 

of the groundwater mound, maximum change in water level, 

and groundwater-mound heights at user-specified distances 

from the center of the basin. The graph shows the height of the 

groundwater mound (y axis) above the bottom of the aquifer 

(datum of zero) in relation to distance (x axis) from the center 

of the infiltration basin. Each time a value in the spreadsheet is 

changed, the user must click on the blue button to recalculate 

the saturated thickness at each of the user-specified points to 

get valid results.

Comparison of Analytical and FiniteDifference Estimates of Groundwater 

Mounding and Effect of Vertical 

Layering

Results of groundwater-mounding calculations from the 

spreadsheet described in the preceding section were compared 

to results from other methods, including the MODFLOW 

simulations done for this study, to determine accuracy of the 

methods (table 4, fig. 11). Nicholas Trainor (Rutgers University, Dept. of Applied Mathematics, written commun., 2009) 

used the mathematical software MAPLE to numerically 

integrate the Hantush equation (1967) and calculated results 

identical to those from the spreadsheet solution described in 

this report. Trainor also solved the Hantush equation in radial 

coordinates for a circular basin of the same area with similar 

results. A FORTRAN program, originally written by Sunada 

and others (1983) and modified by Warner and others (1989), 

that numerically integrates the Hantush (1967) equation yields 

maximum groundwater-mound heights that are as much as 

15 percent different from those generated for this report with 

the same input values. The reasons for the discrepancy are not 

known but may be that the FORTRAN program was written 

to minimize run-times on 1980s-era personal computers, and 

the approximations from the numerical integrations introduce 

more numerical error than those used for this study. Results 

from numerical integration of the Hunt (1971) equation by 

Baehr (U.S. Geological Survey, written commun., 2009) show 

that the Hunt equation cannot be solved at the center of the 

basin. Also, close to the center of the basin, groundwatermound heights calculated using Hunt’s solution increase with 

distance from the center of the basin (out to 16.4 ft) instead of 

decrease and do not correspond closely to values calculated 

using the Hantush equation (table 4). At distances beyond 

the edge of the user-specified infiltration basin, groundwatermound heights calculated using the Hunt and Hantush equations are similar.

For comparison with the analytical solution described 

in the preceding paragraph, finite-difference model (MODFLOW) simulations were conducted with recharge only at the 

infiltration basin (as opposed to simulations of hypothetical 

10-acre developments described earlier in this report for which 

recharge was applied over the entire model domain at different rates). For the simulations listed in table 4, a 2-ft-deep 

infiltration basin was modeled that drains at a steady rate over 

1.5 days (1.33 ft/d). Specific yield was 8.5 percent; the initial 

saturated aquifer thickness was 10 ft; and the infiltration basin 

was square with an area of about 4,500 ft2 (67 ft on a side). 

Five MODFLOW models were constructed with 1, 3, 6, 9, 

and 15 layers to test the sensitivity of results to finer vertical 

discretization. The 1-layer model is analogous to the Hantush 

solution, neither of which includes a vertical component of 

flow. Horizontal hydraulic conductivity was 4 ft/d and the ratio 

of vertical anisotropy was 10:1 (vertical hydraulic conductivity (soil permeability) was 0.2 in/hr, which is equivalent to 

0.4 ft/d, one-tenth horizontal hydraulic conductivity).

The maximum groundwater-mound height simulated 

by a finite-difference model that is analogous to the Hantush 

solution (one layer, two-dimensional flow, recharge applied 

only over the area of the infiltration basin) is within 3 percent 

of that from the Hantush equation (table 4). The maximum 

groundwater-mound height simulated with a 3-layer model is 

8 percent (1.1 ft) higher than that from the 1-layer model. The 

maximum groundwater-mound heights simulated with the 6-, 

9-, and 15-layer models are 12, 14, and 15 percent (1.5, 1.7, 

and 1.8 ft) higher, respectively. The maximum groundwatermound heights from the 6-, 9-, and 15-layer models are 3, 4, 

and 5 percent (0.4, 0.6, and 0.7 ft) higher, respectively, than 

that from the 3-layer model. In contrast, because the volume 

of the groundwater mound is constant, the simulated maximum extent of groundwater mounding is greater for models 

with fewer vertical layers than for models with more vertical 

layers. Figure 11 shows the sensitivity of the simulated height 

of the groundwater mound in the hypothetical 10-acre development to the number of layers used in the simulation. The 

MODFLOW model results are the same at about 45 ft from 

the center of the basin: between 0 and 45 ft the models with 

more vertical layers yield higher mound heights than models 

with less vertical layers; beyond 45 ft models with more vertical layers yield lower mound heights than models with less 

vertical layers. Input values for aquifer and stormwater-runoff 

characteristics other than those used to obtain the results 

shown in table 4 and figure 11 could yield larger departures of 

mound heights from the analytical and 3-layer models, but the 

input variables for simulations shown were chosen to obtain 

a high groundwater mound, and most values for input variables would yield smaller mound-height differences (although 

potentially larger percentage differences) than shown. These 

results indicate how sensitive simulated results can be to vertical anisotropy and how results achieved under field conditions 

could be affected by horizontal low-permeability layers.

Simulations of groundwater mounding beneath infiltration basins will underestimate the maximum height of 

mounding if vertical anisotropy is not included. Horizontal 

layers of lower permeability material are common in many 

geologic environments and have a substantial effect on vertical flow (but have less effect on horizontal flow than over- or 

underlying higher-permeability layers). Beneath and near an 
Comparison of Analytical and Finite-Difference Estimates of Groundwater Mounding and Effect of Vertical Layering 25

infiltration basin there is a large vertical component of flow, 

and lower-permeability horizontal layers exert more control 

on vertical flow than intervening higher-permeability layers. 

Although vertical anisotropy ratios of 3:1 or less are common 

in cores, the cumulative effect of one or more low-permeability horizontal layers can lead to an overall vertical anisotropy 

ratio of 10:1 or greater (Freeze and Cherry, 1979, p. 32–33). 

Thus, vertical permeability measured in a core sample may 

overestimate the vertical permeability of the full vertical section through which flow will occur.

Table 4. Calculated and simulated groundwater mounding beneath hypothetical stormwater infiltration basins using selected 

analytical solutions and finite-difference models. 

[solutn, solution; -, not calculated; n/a, not applicable]

Distance from 

center of square 

stormwater 

infiltration 

basin

Trainor1

solution of 

Hantush2

water-level 

increase 

(feet)

Spreadsheet3

solution of 

Hantush 

water-level 

increase 

(feet)

Sunada4

solution of 

Hantush 

water-level 

increase 

(feet)

Baehr5

solution of 

Hunt6

water-level 

increase 

(feet)

MODFLOW7

1-layer

water-level 

increase 

(feet)

MODFLOW 

3-layer

water-level 

increase 

(feet)

MODFLOW 

15-layer

water-level 

increase 

(feet)

MODFLOW 

3-layer 

10-acre 

simulation 

number 2188

water-level 

increase 

(feet)

(feet) (meters)

0.0 0 12.63 12.63 15.83 n/a 12.23 13.32 14.03 12.39

0.3 0.1 12.63 12.63 - 10.56 - - - -

3.3 1 12.60 12.60 15.76 10.60 12.22 13.31 14.02 12.34

6.6 2 12.49 12.50 15.59 10.83 12.14 13.23 13.93 12.23

10 3.1 12.31 12.32 15.30 11.16 11.99 13.08 13.78 12.06

20 6 11.35 11.31 13.70 11.59 11.14 12.17 12.86 11.08

25 7.6 10.49 10.49 12.43 11.17 10.41 11.37 12.02 10.24

30 9.1 9.52 9.41 10.80 10.31 9.47 10.31 10.89 9.13

40 12 6.79 6.63 6.95 7.62 6.99 7.32 7.57 6.30

50 15 4.31 4.29 4.22 4.55 4.86 4.72 4.62 4.03

75 23 1.05 1.07 1.01 0.23 1.46 1.10 0.88 0.97

100 31 0.19 0.19 0.18 0.15 0.32 0.27 0.25 0.25

150 46 - 0.01 0.01 0.04 0.01 0.02 0.02 0.02

200 61 0.00 0.01 0.01 -0.02 0.00 0.00 0.00 0.00

1

Nicholas Trainor, Rutgers University Department of Applied Mathematics, written commun., 2009.

2

Hantush, M.S., 1967, Growth and decay of groundwater mounds in response to uniform percolation: Water Resources Research, v.3, p. 227–234.

3

Excel spreadsheet presented in this report (revised from Arthur Baehr, U.S. Geological Survey (retired), written commun., 2009).

4

Sunada, D.K., Warner, J.W., and Molden, D.J., 1983, Artificial groundwater recharge, San Luis Valley, Colorado: Colorado Water Resourece Research 

Institute, Colorado State University, Fort Collins, Co., Research Project Technical Completion Report, Project no. A-050-Colo, 116 p.

5

Arthur Baehr, U.S. Geological Survey (retired), written commun., 2009.

6

Hunt, B.W., 1971, Vertical recharge of unconfined aquifers: Journal of Hydraulics Division, American Society of Civil Engineers, v. 97, no. HY7, p. 

1017–1030.

7

Harbaugh, A.W.,Banta, E.R., Hill, M.C., and McDonald, M.G., 2000, MODFLOW-2000-The U.S. Geological Survey modular ground-water model--

User guide to modularization concepts and the ground-water flow process: U.S. Geological Survey Open-File Report 00-92, 121 p.

8

See table 2 in this report.
26 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins

Summary and Conclusions

In 2004, the New Jersey Department of Environmental Protection (NJDEP) implemented stormwater management rules that include the requirement that “substantial” 

(greater than 1 acre) new development must have no net loss 

in groundwater recharge (New Jersey Administrative Code, 

2004). Therefore, the amount of recharge that is rejected by 

new impervious surfaces, such as roofs or driveways, needs to 

be recharged through engineered structures, such as infiltration 

basins or dry wells. 

Groundwater mounding beneath stormwater infiltration 

structures was simulated using an analytical method (Hantush, 

1967) that incorporates the assumptions of horizontal flow 

and, therefore, does not account for vertical anisotropy of permeability. Groundwater mounding also was simulated using 

the finite-difference groundwater-flow model MODFLOW. 

Three layers of equal initial saturated thickness are used in 

the three-dimensional MODFLOW simulations that include 

vertical anisotropy. The simulations do not include any delay 

or attenuation associated with travel through the unsaturated 

zone. Also, the volume of water resulting from the design 

storm falling on impervious surfaces is simulated as steadily 

recharging the water table below the infiltration basin over 

1.5 days. 

A 10-acre development was chosen as a representative 

scale for developments that might have a centralized stormwater collection and infiltration system. The seven physical characteristics varied to establish a range of simulated groundwater 

mounds beneath a hypothetical infiltration basin for a 10-acre 

development are soil permeability, aquifer thickness, specific 

yield, infiltration basin shape, basin depth, design storm, and 

percentage of impervious cover, and these form 576 unique 

combinations of the input values. A horizontal to vertical 

permeability ratio of 10:1 was used in all simulations. Values of vertical soil permeability used in the simulations were 

0.2 in/hr, 1 in/hr, or 5 in/hr (equivalent to horizontal hydraulic 

conductivities of 4, 20, or 100 ft/d). Initial aquifer saturated 

thicknesses used were 10, 20, or 40 ft, specific yield was 0.17 

or 0.085 (17 or 8.5 percent), design storm magnitudes were 

1.25 inches or 0.31 inch, percentages of impervious cover 

were 10, 20, 40, or 80 percent, and stormwater infiltration 

basins were either 2 or 0.5 ft deep. Basins were either square 

or rectangular (with the length of the long side eight times the 

length of the short side). Recharge to the 10-acre developed 

area with 10, 20, 40, or 80 percent impervious surface was 90, 

80, 60, or 20 percent of the design storm depth, respectively; 

recharge to the area outside the developed area was equal to 

the design storm magnitude; and the infiltration basin area 

received a depth of recharge equal to the depth of the basin. 

0

14

12

10

8

6

4

2

0

10 20 30 40 50 60 70 80 90 100

DISTANCE FROM CENTER OF INFILTRATION BASIN, IN FEET

HEIGHT OF GROUNDWATER MOUNDING, IN FEET

9-Layer MODFLOW model

Hantush analytical equation

1-Layer MODFLOW model

3-Layer MODFLOW model

6-Layer MODFLOW model

15-Layer MODFLOW model

Figure 11. Groundwater mounds beneath hypothetical stormwater infiltration basins calculated using the Hantush equation and 

simulated with 1-, 3-, 6-, 9-, and 15-layer finite-difference models.
Summary and Conclusions 27

The maximum height of groundwater mounding calculated during the simulations for the 10-acre development is 

18.5 ft, and the minimum is 0.1 ft. The median from all 576 

simulations of the maximum groundwater mounding is 1.8 ft. 

The maximum extent (measured from the edge of the infiltration basins) of groundwater mounding of 0.25-ft ranges from 

0 to 300 ft with a median of 51 ft for all 576 simulations. 

Maximum heights of groundwater mounding are most sensitive to (show the greatest variation with) the three values of 

soil permeability used. Maximum groundwater-mound heights 

when soil permeability is 5 in/hr have the smallest range (0.1 

to 3.6 ft) and lowest median (0.6 ft) for the 18 variable values. 

In contrast, maximum groundwater-mound heights when soil 

permeability is 0.2 in/hr have the highest minimum (0.9 ft) and 

highest median (3.9 ft) for the 18 variable values. Varying the 

aquifer thickness would have the same effect as varying the 

soil permeability if the values were changed by a factor of 25 

(for example, from 10 to 250 ft), but values were only changed 

over a factor of 4 (10 to 40 ft) in this study. 

The maximum groundwater-mound height is higher when 

one of three variables—soil permeability, aquifer thickness, 

or specific yield—is decreased (and other variables are held 

constant). Changing soil permeability, aquifer thickness, 

specific yield, or basin shape did not change the volume of 

water infiltrated, it changed the shape or height of the groundwater mound resulting from the infiltration. An aquifer with 

a greater soil permeability or aquifer thickness can transmit 

water away from the source of infiltration with less increase 

in head needed to drive the flow than an aquifer with lower 

soil permeability or thickness. Therefore, the maximum 

groundwater-mound height will be lower and the extent of 

the groundwater mounding will be farther with higher soil 

permeability. Similarly, the maximum groundwater-mound 

height beneath a square infiltration basin will be greater than 

beneath a rectangular basin, but the extent of groundwater 

mounding (perpendicular to the long edge of the basin) will be 

greater than beneath a square basin with the same area as the 

rectangular basin. The maximum groundwater-mound height 

is lower when specific yield is greater because the aquifer 

stores more water per unit volume than when the specific yield 

is lower. For example, a given volume of infiltrated water will 

saturate one-half the volume of the aquifer when specific yield 

is doubled.

The maximum groundwater-mound height is higher 

when the basin depth, design storm magnitude, or percentage of impervious cover is larger (and other variables are 

held constant) because of the larger total volume of infiltrated 

water. A larger volume of infiltrated water requires a higher 

head to move that water away from the source of recharge if 

the physical characteristics of the aquifer are unchanged. The 

second greatest effect on maximum groundwater mounding 

(after increasing soil permeability by a factor of 25, from 0.2 

in/hr to 5 in/hr) in simulations of the 10-acre development 

occurred when the basin depth was increased by a factor of 4 

(from 0.5 ft to 2 ft). 

Groundwater mounding of at least 0.25 ft was chosen 

as the lower limit of mounding considered significant. The 

relation between the maximum extent of groundwater mounding and variations of the seven variables tested for this study 

is sometimes contradictory. Because the groundwater mound 

in an aquifer with higher permeability has a lower maximum 

height but a greater extent than in an aquifer with lower permeability (other variables held constant), there is a “crossover” 

point where the groundwater mounds have the same height. 

If that “crossover” point is at 0.25 ft or greater, the maximum 

extent of groundwater mounding of 0.25 ft will increase with 

increased aquifer transmissivity (increased permeability and 

(or) aquifer thickness). 

Stormwater infiltration at a 1-acre development was simulated, and the hypothetical infiltration structure was simulated 

as a pre-cast concrete dry well. Unique combinations of three 

values of soil permeability, three values of aquifer thickness, 

two values of specific yield, three dry-well depths, two design 

storm magnitudes, and four percentages of impervious cover 

required 432 simulations, with the same input values as used 

for simulations of the 10-acre development except that basin 

depths of 2, 4, and 8 ft were used for the dry wells. 

 The maximum simulated height of groundwater mounding for the 1-acre development ranges from 0.01 to 14.0 ft. 

The median from all 432 simulations of the maximum height 

of groundwater mounding is 1.0 ft. The maximum extent of 

groundwater mounding of 0.25-ft ranges from 0 to 100 ft with 

a median of 10 ft for all 432 simulations.

Hantush’s equation describing the “growth and decay of 

groundwater mounds in response to uniform percolation” is 

widely used to estimate water-table mounding beneath septic 

systems and other steady-state conditions. However, fewer 

implementations have included the more challenging transient 

condition (infiltration occurs over a limited duration and then 

ceases). A spreadsheet was developed requiring input values 

(aquifer thickness, horizontal hydraulic conductivity (assumed 

in this study to be 10 times vertical soil permeability), specific 

yield, basin size, and recharge rate and duration) that are 

straightforward and can be measured or estimated. Users 

specify the recharge rate, specific yield, horizontal hydraulic 

conductivity, basin width and length, and duration of recharge, 

and the spreadsheet calculates the maximum height of groundwater mounding and the mounding at user-specified distances 

from the center of the infiltration basin.

 Maximum groundwater-mound height beneath a stormwater infiltration basin simulated with a finite-difference 

model analogous to the Hantush solution (one layer, horizontal 

flow only) is within 3 percent of that from the Hantush equation for the set of variable values simulated. The maximum 

groundwater-mound height simulated with a 3-layer model 

(using the same input variables) is 8 percent (1.1 ft) higher 

than that from the 1-layer model. The maximum groundwatermound height simulated with the 15-layer model is 15 percent 

(1.8 ft) higher than that from the 1-layer model and 5 percent 

higher than that from the 3-layer model (0.7 ft). The increase 
28 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins

in maximum height of the simulated groundwater mound 

(and decrease in extent of groundwater mounding) with an 

increased number of horizontal layers illustrates the importance of the vertical component of flow and the typically 

lower-vertical-than-horizontal hydraulic conductivity. Inclusion of storage in, and delayed yield from, the unsaturated 

zone would result in lower simulated groundwater mounds 

compared to those from simulations that omit the unsaturated zone. Therefore, the height of groundwater mounding 

is underestimated by the Hantush equation where vertical 

anisotropy is present and overestimated where an unsaturated 

zone is present. 

Results from this study can be used to estimate groundwater-mound heights for sites of different sizes than 10 acres 

or 1 acre and (or) with different variables than those used in 

the simulations. The area of the infiltration basin is a function of the area of the development, percentage of impervious surface, design storm magnitude, and basin depth. Area 

and depth of the basin, not area of the development, governs 

groundwater mounding. Choosing the basin area and depth 

that is equal to or greater than the user’s design basin will 

yield conservative results. For sites with aquifer characteristic 

values different than those used in this study, a basin designer 

will obtain a conservative result when a conservative variable 

value is chosen from among those given in this report. For 

example, if vertical soil permeability is estimated to be 3 in/hr, 

using appropriate simulations and including soil permeability 

of 1 in/hr would yield a conservative estimate of maximum 

groundwater-mound height, and soil permeability of 5 in/hr 

would yield a conservative estimate of maximum extent of 

groundwater mounding of 0.25-ft. The same approach is 

appropriate for aquifer thickness (smaller thickness for a 

conservative estimate of maximum groundwater-mound height 

and larger thickness for a conservative estimate of maximum 

extent of groundwater mounding) and basin shape (square 

basins for a conservative estimate of maximum groundwatermound height and rectangular basins for a conservative estimate of maximum extent of groundwater mounding). Lower 

values of specific yield and higher values of basin depth are 

conservative for estimating both maximum groundwatermound height and extent of groundwater mounding. 

The simulated systems respond non-linearly to changes in 

soil permeability and aquifer thickness: increasing soil permeability by a factor of five from 0.2 to 1 in/hr reduces maximum groundwater-mound heights more than increasing soil 

permeability by a factor of five from 1 to 5 in/hr. Therefore, 

interpolating between (or extrapolating beyond) results for 

input values between (or beyond) those used in this study may 

yield incorrect results. Conservative estimates can be obtained 

by using the value for a variable that is closest to the value 

measured (or estimated) at a particular site.

The groundwater mounding associated with two or 

more nearby infiltration basins can be estimated by modeling the basins separately then adding together the resulting 

mounding. Because of non-linearities, adding separately 

simulated groundwater mounds will overestimate the groundwater-mound height, a conservative result.

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New Jersey Administrative Code 7:8, 2004, Stormwater management rules: State of New Jersey, Trenton, N.J., accessed 

November 2, 2009, at http://www.nj.gov/dep/rules/adoptions/2004_0202_watershed.pdf.

New Jersey Geological Survey, 2008, Horizontal hydraulic 

conductivity summary: New Jersey Geological Survey 

Hydro Database, accessed November 20, 2009, at http://

www.state.nj.us/dep/njgs/geodata/dgs02-1.htm.

Nicholson, R.D., McAuley, S.D., Barringer, J.L., and Gordon, 

A.D., 1996, Hydrogeology of, and ground-water flow in, a 

valley-fill and carbonate-rock aquifer system near Long Valley in the New Jersey Highlands: U.S. Geological Survey 

Water-Resources Investigations Report 93-4157, 159 p.

Poeter, Eileen, McCray, John, Thyne, Geoffry, and Siegrist, 

Robert, 2005, Guidance for evaluation of potential groundwater mounding associated with cluster and high-density 

wastewater soil absorption systems: Project number 

WU-HT-02-45, prepared for the National Decentralized 

Water Resources Capacity Development Project Washington University, St. Louis, Mo., by the International Groundwater Modeling Center, Colorado School of Mines, Golden, 

Colo., 97 p.

Pope, D.A., and Watt, M.K., 2005, Use of a ground-water flow 

model to delineate contributing areas to the Puchack well 

field, Pennsauken Township and vicinity, Camden County, 

New Jersey: U.S. Geological Survey Scientific Investigations Report 2004-5101, 47 p.

Rai, S.N., and Singh, R.N., 1981, A mathematical model of 

water-table fluctuation in a semi-infinite aquifer induced by 

localised transient recharge: Water Resources Research, v. 

17, p. 1028–1032.

Rai, S.N., Manglik, A., and Singh, R.N., 1994, Water table 

fluctuation in response to transient recharge from a rectangular basin: Water Resources Management, v. 8, p. 1–10. 

Rao, N.H., and Sarma, P.B.S., 1981, Ground-water recharge 

from rectangular areas: Ground Water, v. 19, no. 3, 

p. 270–274.

Reilly, T.E., 2001, System and boundary conceptualization 

in ground-water flow simulation: U.S. Geological Survey 

Techniques of Water-Resource Investigation 03-B8, 29 p.
30 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins

Ritter, M.E., 2006, The physical environment: an introduction 

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edu/gEo/faculty/ritter/geog101/textbook/soil_systems/soil_

development_soil_properties.html. 

Sumner, D.M., and Bradner, L.A., 1996, Hydraulic characteristics and nutrient transport and transformation beneath a 

rapid infiltration basin, Reedy Creek Improvement District, 

Orange County, Florida: U.S. Geological Survey WaterResources Investigations Report 95-428, 51 p.

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of unsaturated zone on ground-water mounding: Journal of 

Hydrologic Engineering, v. 4, no.1, p. 65–69.

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groundwater recharge, San Luis Valley, Colorado: Fort Collins, Colo., Colorado Water Resources Research Institute, 

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Completion Report, Project no. A-050-Colo, 116 p.

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http://clerkshq.com/default.ashx?clientsite=princeton-nj. 

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D.K., 1989, Mathematical analysis of artificial recharge 

from basins: Water Resources Bulletin, v. 25, no. 2, 

p. 401–411.

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Jersey Coastal Plain: U.S. Geological Survey Professional 

Paper 1404-B, 49 p.

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mounding under stormwater infiltration facilities: Proceedings of the American Water Resources Association 2005 

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Seattle, Washington, 4 p.

Table 2
Table 2 31

Table 2. Simulated groundwater mounding beneath hypothetical stormwater-infiltration basins on a 10-acre development.—Continued[ft2, square feet; 1 x 1, square basin (sides of equal length); 1 x 8, rectangular basin (long side eight times length of short side); in/hr, inches per hour; Max, maximum; ft2, square feet; GW, groundwater; hgt, height; ft, feet; EEoB, east edge of basin]

Simulation 

number

Impervious 

cover 

(percent)

Design 

storm 

(inches)

Basin 

depth 

(feet)

Basin 

area 

(ft2)

Basin 

shape 

Aquifer 

thickness 

(feet)

Soil 

permeability

(in/hr)

Specific 

yield

(percent)

Max 

GW 

mound 

height

(feet)

Max 

extent 

of 0.25- 

foot GW 

mound 

hgt 

(feet)

GW 

mound 

hgt at 

EEoB

 (feet)

GW 

mound 

hgt 

50 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

150 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

200 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

300 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

500 ft 

from 

EEoB 

(feet)

1 10 0.31 2 567 1 x 1 10 0.2 17.0 4.54 23 3.00 0.04 0.00 0.00 0 0 02 10 0.31 2 567 1 x 1 10 0.2 8.5 5.40 41 3.92 0.16 0.01 0.00 0 0 03 10 0.31 2 567 1 x 1 10 1 17.0 1.66 33 1.20 0.14 0.02 0.00 0 0 04 10 0.31 2 567 1 x 1 10 1 8.5 1.83 52 1.39 0.28 0.08 0.02 0 0 05 10 0.31 2 567 1 x 1 10 5 17.0 0.46 8 0.35 0.10 0.05 0.02 0.01 0 06 10 0.31 2 567 1 x 1 10 5 8.5 0.48 13 0.38 0.14 0.08 0.04 0.02 0.01 07 10 0.31 2 567 1 x 1 20 0.2 17.0 3.77 26 2.53 0.04 0.01 0.00 0 0 08 10 0.31 2 567 1 x 1 20 0.2 8.5 4.44 43 3.24 0.19 0.03 0.01 0 0 09 10 0.31 2 567 1 x 1 20 1 17.0 1.24 30 0.91 0.13 0.03 0.01 0 0 0

10 10 0.31 2 567 1 x 1 20 1 8.5 1.34 44 1.03 0.23 0.08 0.03 0.01 0 0

11 10 0.31 2 567 1 x 1 20 5 17.0 0.31 0 0.24 0.07 0.04 0.02 0.01 0 0

12 10 0.31 2 567 1 x 1 20 5 8.5 0.33 0 0.26 0.09 0.05 0.04 0.02 0.01 013 10 0.31 2 567 1 x 1 40 0.2 17.0 2.85 31 1.99 0.07 0.00 0.00 0 0 014 10 0.31 2 567 1 x 1 40 0.2 8.5 3.34 48 2.50 0.24 0.03 0.01 0 0 015 10 0.31 2 567 1 x 1 40 1 17.0 0.85 25 0.65 0.13 0.03 0.01 0 0 016 10 0.31 2 567 1 x 1 40 1 8.5 0.91 36 0.72 0.19 0.08 0.03 0.02 0 017 10 0.31 2 567 1 x 1 40 5 17.0 0.20 0 0.16 0.05 0.03 0.02 0.01 0 018 10 0.31 2 567 1 x 1 40 5 8.5 0.21 0 0.17 0.06 0.04 0.03 0.02 0.01 019 10 0.31 2 567 1 x 8 10 0.2 17.0 3.16 26 2.57 0.05 0.00 0.00 0 0 020 10 0.31 2 567 1 x 8 10 0.2 8.5 3.95 46 3.45 0.21 0.02 0.00 0 0 021 10 0.31 2 567 1 x 8 10 1 17.0 1.23 36 1.08 0.16 0.03 0.00 0 0 022 10 0.31 2 567 1 x 8 10 1 8.5 1.41 59 1.27 0.32 0.09 0.02 0 0 023 10 0.31 2 567 1 x 8 10 5 17.0 0.36 8 0.32 0.11 0.05 0.02 0.01 0 024 10 0.31 2 567 1 x 8 10 5 8.5 0.39 15 0.36 0.15 0.08 0.05 0.03 0.01 025 10 0.31 2 567 1 x 8 20 0.2 17.0 2.63 30 2.20 0.05 0.01 0.00 0 0 026 10 0.31 2 567 1 x 8 20 0.2 8.5 3.25 48 2.88 0.24 0.03 0.01 0 0 027 10 0.31 2 567 1 x 8 20 1 17.0 0.92 33 0.83 0.15 0.04 0.01 0 0 028 10 0.31 2 567 1 x 8 20 1 8.5 1.03 49 0.94 0.26 0.10 0.04 0.01 0 029 10 0.31 2 567 1 x 8 20 5 17.0 0.24 0 0.22 0.08 0.04 0.02 0.01 0 030 10 0.31 2 567 1 x 8 20 5 8.5 0.26 0 0.24 0.10 0.06 0.04 0.02 0.01 0
32 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins Table 2. Simulated groundwater mounding beneath hypothetical stormwater-infiltration basins on a 10-acre development.—Continued [ft2, square feet; 1 x 1, square basin (sides of equal length); 1 x 8, rectangular basin (long side eight times length of short side); in/hr, inches per hour; Max, maximum; ft2, square feet; GW, groundwater; hgt, height; ft, feet; EEoB, east edge of basin] Simulation number Impervious cover (percent) Design storm (inches) Basin depth (feet) Basin area (ft2

)

Basin 

shape 

Aquifer 

thickness 

(feet)

Soil 

permeability

(in/hr)

Specific 

yield

(percent)

Max 

GW 

mound 

height

(feet)

Max 

extent 

of 0.25- 

foot GW 

mound 

hgt 

(feet)

GW 

mound 

hgt at 

EEoB

 (feet)

GW 

mound 

hgt 

50 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

150 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

200 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

300 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

500 ft 

from 

EEoB 

(feet)

31 10 0.31 2 567 1 x 8 40 0.2 17.0 2.01 34 1.75 0.09 0.01 0.00 0 0 032 10 0.31 2 567 1 x 8 40 0.2 8.5 2.49 52 2.25 0.30 0.03 0.01 0 0 033 10 0.31 2 567 1 x 8 40 1 17.0 0.65 30 0.60 0.15 0.04 0.01 0 0 034 10 0.31 2 567 1 x 8 40 1 8.5 0.72 41 0.67 0.21 0.09 0.04 0.02 0 035 10 0.31 2 567 1 x 8 40 5 17.0 0.16 0 0.15 0.06 0.03 0.02 0.01 0 036 10 0.31 2 567 1 x 8 40 5 8.5 0.17 0 0.16 0.07 0.04 0.03 0.02 0.01 037 10 0.31 0.5 2,269 1 x 1 10 0.2 17.0 2.05 16 1.26 0.02 0.00 0.00 0 0 038 10 0.31 0.5 2,269 1 x 1 10 0.2 8.5 2.94 31 1.97 0.10 0.01 0.00 0 0 039 10 0.31 0.5 2,269 1 x 1 10 1 17.0 0.92 21 0.65 0.09 0.01 0.00 0 0 040 10 0.31 0.5 2,269 1 x 1 10 1 8.5 1.10 39 0.83 0.20 0.06 0.01 0 0 041 10 0.31 0.5 2,269 1 x 1 10 5 17.0 0.28 0 0.22 0.08 0.04 0.02 0.01 0 042 10 0.31 0.5 2,269 1 x 1 10 5 8.5 0.31 0 0.25 0.11 0.06 0.04 0.02 0.01 043 10 0.31 0.5 2,269 1 x 1 20 0.2 17.0 1.84 18 1.14 0.03 0.00 0.00 0 0 044 10 0.31 0.5 2,269 1 x 1 20 0.2 8.5 2.51 33 1.70 0.11 0.02 0.00 0 0 045 10 0.31 0.5 2,269 1 x 1 20 1 17.0 0.72 18 0.52 0.09 0.02 0.01 0 0 046 10 0.31 0.5 2,269 1 x 1 20 1 8.5 0.82 31 0.62 0.17 0.06 0.02 0.01 0 047 10 0.31 0.5 2,269 1 x 1 20 5 17.0 0.19 0 0.15 0.06 0.03 0.02 0.01 0 048 10 0.31 0.5 2,269 1 x 1 20 5 8.5 0.21 0 0.17 0.07 0.04 0.03 0.02 0.01 049 10 0.31 0.5 2,269 1 x 1 40 0.2 17.0 1.51 21 0.98 0.04 0.00 0.00 0 0 050 10 0.31 0.5 2,269 1 x 1 40 0.2 8.5 1.97 38 1.39 0.15 0.02 0.01 0 0 051 10 0.31 0.5 2,269 1 x 1 40 1 17.0 0.52 13 0.39 0.09 0.02 0.01 0 0 052 10 0.31 0.5 2,269 1 x 1 40 1 8.5 0.59 23 0.46 0.14 0.06 0.03 0.01 0 053 10 0.31 0.5 2,269 1 x 1 40 5 17.0 0.13 0 0.11 0.04 0.02 0.01 0.01 0 054 10 0.31 0.5 2,269 1 x 1 40 5 8.5 0.14 0 0.11 0.05 0.03 0.02 0.01 0.01 055 10 0.31 0.5 2,269 1 x 8 10 0.2 17.0 1.35 15 0.96 0.02 0.00 0.00 0 0 056 10 0.31 0.5 2,269 1 x 8 10 0.2 8.5 1.89 31 1.50 0.10 0.01 0.00 0 0 057 10 0.31 0.5 2,269 1 x 8 10 1 17.0 0.61 20 0.51 0.10 0.02 0.00 0 0 058 10 0.31 0.5 2,269 1 x 8 10 1 8.5 0.77 41 0.67 0.21 0.06 0.02 0 0 059 10 0.31 0.5 2,269 1 x 8 10 5 17.0 0.20 0 0.18 0.08 0.04 0.02 0.01 0 060 10 0.31 0.5 2,269 1 x 8 10 5 8.5 0.23 0 0.21 0.11 0.06 0.04 0.02 0.01 0
Table 2 33

Table 2. Simulated groundwater mounding beneath hypothetical stormwater-infiltration basins on a 10-acre development.—Continued[ft2, square feet; 1 x 1, square basin (sides of equal length); 1 x 8, rectangular basin (long side eight times length of short side); in/hr, inches per hour; Max, maximum; ft2, square feet; GW, groundwater; hgt, height; ft, feet; EEoB, east edge of basin]

Simulation 

number

Impervious 

cover 

(percent)

Design 

storm 

(inches)

Basin 

depth 

(feet)

Basin 

area 

(ft2)

Basin 

shape 

Aquifer 

thickness 

(feet)

Soil 

permeability

(in/hr)

Specific 

yield

(percent)

Max 

GW 

mound 

height

(feet)

Max 

extent 

of 0.25- 

foot GW 

mound 

hgt 

(feet)

GW 

mound 

hgt at 

EEoB

 (feet)

GW 

mound 

hgt 

50 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

150 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

200 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

300 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

500 ft 

from 

EEoB 

(feet)

61 10 0.31 0.5 2,269 1 x 8 20 0.2 17.0 1.14 16 0.86 0.03 0.00 0.00 0 0 062 10 0.31 0.5 2,269 1 x 8 20 0.2 8.5 1.59 33 1.30 0.12 0.02 0.00 0 0 063 10 0.31 0.5 2,269 1 x 8 20 1 17.0 0.47 15 0.41 0.09 0.02 0.01 0 0 064 10 0.31 0.5 2,269 1 x 8 20 1 8.5 0.57 30 0.51 0.17 0.07 0.03 0.01 0 065 10 0.31 0.5 2,269 1 x 8 20 5 17.0 0.14 0 0.13 0.06 0.03 0.02 0.01 0 066 10 0.31 0.5 2,269 1 x 8 20 5 8.5 0.15 0 0.14 0.07 0.05 0.03 0.02 0.01 067 10 0.31 0.5 2,269 1 x 8 40 0.2 17.0 0.92 20 0.74 0.04 0.00 0.00 0 0 068 10 0.31 0.5 2,269 1 x 8 40 0.2 8.5 1.26 38 1.08 0.16 0.02 0.01 0 0 069 10 0.31 0.5 2,269 1 x 8 40 1 17.0 0.35 8 0.31 0.09 0.03 0.01 0 0 070 10 0.31 0.5 2,269 1 x 8 40 1 8.5 0.41 20 0.38 0.15 0.06 0.03 0.01 0 071 10 0.31 0.5 2,269 1 x 8 40 5 17.0 0.10 0 0.09 0.04 0.02 0.01 0.01 0 072 10 0.31 0.5 2,269 1 x 8 40 5 8.5 0.10 0 0.09 0.05 0.03 0.02 0.02 0.01 073 10 1.25 2 2,269 1 x 1 10 0.2 17.0 7.27 33 4.82 0.09 0.01 0.00 0 0 074 10 1.25 2 2,269 1 x 1 10 0.2 8.5 9.49 59 6.94 0.46 0.04 0.00 0 0 075 10 1.25 2 2,269 1 x 1 10 1 17.0 3.25 59 2.40 0.37 0.06 0.01 0 0 076 10 1.25 2 2,269 1 x 1 10 1 8.5 3.71 97 2.91 0.81 0.24 0.07 0.02 0 077 10 1.25 2 2,269 1 x 1 10 5 17.0 1.05 62 0.84 0.31 0.14 0.06 0.03 0 078 10 1.25 2 2,269 1 x 1 10 5 8.5 1.12 94 0.92 0.42 0.24 0.14 0.08 0.02 079 10 1.25 2 2,269 1 x 1 20 0.2 17.0 6.54 38 4.34 0.11 0.02 0.00 0 0 080 10 1.25 2 2,269 1 x 1 20 0.2 8.5 8.36 64 6.10 0.54 0.07 0.02 0 0 081 10 1.25 2 2,269 1 x 1 20 1 17.0 2.64 61 1.96 0.36 0.09 0.03 0.01 0 082 10 1.25 2 2,269 1 x 1 20 1 8.5 2.93 99 2.28 0.67 0.25 0.10 0.04 0.01 083 10 1.25 2 2,269 1 x 1 20 5 17.0 0.75 41 0.59 0.22 0.12 0.07 0.04 0.01 084 10 1.25 2 2,269 1 x 1 20 5 8.5 0.78 59 0.63 0.28 0.17 0.12 0.08 0.03 0.0185 10 1.25 2 2,269 1 x 1 40 0.2 17.0 5.53 43 3.75 0.17 0.02 0.01 0 0 086 10 1.25 2 2,269 1 x 1 40 0.2 8.5 6.91 71 5.09 0.66 0.09 0.02 0.01 0 087 10 1.25 2 2,269 1 x 1 40 1 17.0 2.00 62 1.52 0.36 0.10 0.03 0.01 0 088 10 1.25 2 2,269 1 x 1 40 1 8.5 2.21 94 1.74 0.57 0.24 0.11 0.05 0.01 089 10 1.25 2 2,269 1 x 1 40 5 17.0 0.52 23 0.42 0.16 0.09 0.06 0.03 0.01 090 10 1.25 2 2,269 1 x 1 40 5 8.5 0.54 30 0.44 0.19 0.12 0.08 0.06 0.03 0.01
34 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins Table 2. Simulated groundwater mounding beneath hypothetical stormwater-infiltration basins on a 10-acre development.—Continued [ft2, square feet; 1 x 1, square basin (sides of equal length); 1 x 8, rectangular basin (long side eight times length of short side); in/hr, inches per hour; Max, maximum; ft2, square feet; GW, groundwater; hgt, height; ft, feet; EEoB, east edge of basin] Simulation number Impervious cover (percent) Design storm (inches) Basin depth (feet) Basin area (ft2

)

Basin 

shape 

Aquifer 

thickness 

(feet)

Soil 

permeability

(in/hr)

Specific 

yield

(percent)

Max 

GW 

mound 

height

(feet)

Max 

extent 

of 0.25- 

foot GW 

mound 

hgt 

(feet)

GW 

mound 

hgt at 

EEoB

 (feet)

GW 

mound 

hgt 

50 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

150 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

200 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

300 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

500 ft 

from 

EEoB 

(feet)

91 10 1.25 2 2,269 1 x 8 10 0.2 17.0 5.03 36 4.22 0.11 0.01 0.00 0 0 092 10 1.25 2 2,269 1 x 8 10 0.2 8.5 6.74 64 6.01 0.56 0.05 0.01 0 0 093 10 1.25 2 2,269 1 x 8 10 1 17.0 2.36 66 2.13 0.44 0.08 0.02 0 0 094 10 1.25 2 2,269 1 x 8 10 1 8.5 2.85 105 2.64 0.92 0.30 0.09 0.02 0 095 10 1.25 2 2,269 1 x 8 10 5 17.0 0.83 73 0.77 0.35 0.17 0.08 0.03 0 096 10 1.25 2 2,269 1 x 8 10 5 8.5 0.92 107 0.86 0.46 0.28 0.17 0.09 0.03 097 10 1.25 2 2,269 1 x 8 20 0.2 17.0 4.43 39 3.76 0.14 0.02 0.00 0 0 098 10 1.25 2 2,269 1 x 8 20 0.2 8.5 5.90 71 5.29 0.64 0.09 0.02 0.01 0 099 10 1.25 2 2,269 1 x 8 20 1 17.0 1.91 68 1.73 0.42 0.11 0.03 0.01 0 0

100 10 1.25 2 2,269 1 x 8 20 1 8.5 2.25 110 2.09 0.76 0.31 0.13 0.05 0.01 0101 10 1.25 2 2,269 1 x 8 20 5 17.0 0.58 48 0.54 0.25 0.14 0.08 0.04 0.01 0102 10 1.25 2 2,269 1 x 8 20 5 8.5 0.63 69 0.59 0.31 0.20 0.13 0.09 0.04 0.01103 10 1.25 2 2,269 1 x 8 40 0.2 17.0 3.72 46 3.24 0.21 0.02 0.01 0 0 0104 10 1.25 2 2,269 1 x 8 40 0.2 8.5 4.91 77 4.45 0.79 0.11 0.03 0.01 0 0105 10 1.25 2 2,269 1 x 8 40 1 17.0 1.47 69 1.36 0.42 0.13 0.04 0.01 0 0106 10 1.25 2 2,269 1 x 8 40 1 8.5 1.69 105 1.58 0.64 0.28 0.13 0.06 0.02 0107 10 1.25 2 2,269 1 x 8 40 5 17.0 0.41 26 0.38 0.18 0.10 0.06 0.04 0.02 0108 10 1.25 2 2,269 1 x 8 40 5 8.5 0.43 34 0.41 0.21 0.13 0.09 0.07 0.04 0.01109 10 1.25 0.5 9,075 1 x 1 10 0.2 17.0 2.15 18 1.19 0.03 0.00 0.00 0 0 0

110 10 1.25 0.5 9,075 1 x 1 10 0.2 8.5 3.72 39 2.17 0.16 0.01 0.00 0 0 0

111 10 1.25 0.5 9,075 1 x 1 10 1 17.0 1.41 34 0.88 0.15 0.03 0.00 0 0 0

112 10 1.25 0.5 9,075 1 x 1 10 1 8.5 1.85 68 1.27 0.39 0.12 0.03 0.01 0 0113 10 1.25 0.5 9,075 1 x 1 10 5 17.0 0.54 26 0.40 0.18 0.08 0.04 0.01 0 0114 10 1.25 0.5 9,075 1 x 1 10 5 8.5 0.61 51 0.48 0.26 0.15 0.09 0.05 0.01 0115 10 1.25 0.5 9,075 1 x 1 20 0.2 17.0 2.06 20 1.13 0.04 0.01 0.00 0 0 0116 10 1.25 0.5 9,075 1 x 1 20 0.2 8.5 3.37 43 1.98 0.20 0.03 0.01 0 0 0117 10 1.25 0.5 9,075 1 x 1 20 1 17.0 1.16 34 0.74 0.16 0.04 0.01 0 0 0118 10 1.25 0.5 9,075 1 x 1 20 1 8.5 1.45 66 1.01 0.35 0.14 0.06 0.02 0 0119 10 1.25 0.5 9,075 1 x 1 20 5 17.0 0.38 5 0.28 0.13 0.07 0.04 0.02 0.01 0

120 10 1.25 0.5 9,075 1 x 1 20 5 8.5 0.41 16 0.32 0.17 0.11 0.08 0.05 0.02 0
Table 2 35

Table 2. Simulated groundwater mounding beneath hypothetical stormwater-infiltration basins on a 10-acre development.—Continued[ft2, square feet; 1 x 1, square basin (sides of equal length); 1 x 8, rectangular basin (long side eight times length of short side); in/hr, inches per hour; Max, maximum; ft2, square feet; GW, groundwater; hgt, height; ft, feet; EEoB, east edge of basin]

Simulation 

number

Impervious 

cover 

(percent)

Design 

storm 

(inches)

Basin 

depth 

(feet)

Basin 

area 

(ft2)

Basin 

shape 

Aquifer 

thickness 

(feet)

Soil 

permeability

(in/hr)

Specific 

yield

(percent)

Max 

GW 

mound 

height

(feet)

Max 

extent 

of 0.25- 

foot GW 

mound 

hgt 

(feet)

GW 

mound 

hgt at 

EEoB

 (feet)

GW 

mound 

hgt 

50 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

150 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

200 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

300 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

500 ft 

from 

EEoB 

(feet)

121 10 1.25 0.5 9,075 1 x 1 40 0.2 17.0 1.95 25 1.07 0.06 0.01 0.00 0 0 0122 10 1.25 0.5 9,075 1 x 1 40 0.2 8.5 2.99 48 1.80 0.25 0.04 0.01 0.01 0 0123 10 1.25 0.5 9,075 1 x 1 40 1 17.0 0.94 33 0.62 0.17 0.05 0.02 0.01 0 0124 10 1.25 0.5 9,075 1 x 1 40 1 8.5 1.12 59 0.79 0.31 0.13 0.06 0.03 0.01 0125 10 1.25 0.5 9,075 1 x 1 40 5 17.0 0.27 0 0.20 0.10 0.06 0.04 0.02 0.01 0126 10 1.25 0.5 9,075 1 x 1 40 5 8.5 0.28 0 0.22 0.12 0.08 0.05 0.04 0.02 0.01127 10 1.25 0.5 9,075 1 x 8 10 0.2 17.0 1.69 15 0.99 0.03 0.00 0.00 0 0 0128 10 1.25 0.5 9,075 1 x 8 10 0.2 8.5 2.57 38 1.80 0.15 0.02 0.00 0 0 0129 10 1.25 0.5 9,075 1 x 8 10 1 17.0 0.93 33 0.72 0.16 0.03 0.01 0 0 0130 10 1.25 0.5 9,075 1 x 8 10 1 8.5 1.26 71 1.06 0.40 0.14 0.04 0.01 0 0131 10 1.25 0.5 9,075 1 x 8 10 5 17.0 0.39 23 0.34 0.18 0.09 0.05 0.02 0 0132 10 1.25 0.5 9,075 1 x 8 10 5 8.5 0.46 56 0.42 0.27 0.17 0.11 0.06 0.02 0133 10 1.25 0.5 9,075 1 x 8 20 0.2 17.0 1.53 18 0.96 0.04 0.01 0.00 0 0 0134 10 1.25 0.5 9,075 1 x 8 20 0.2 8.5 2.26 43 1.64 0.20 0.04 0.01 0 0 0135 10 1.25 0.5 9,075 1 x 8 20 1 17.0 0.77 33 0.61 0.17 0.05 0.02 0 0 0136 10 1.25 0.5 9,075 1 x 8 20 1 8.5 1.00 71 0.85 0.36 0.16 0.07 0.03 0 0137 10 1.25 0.5 9,075 1 x 8 20 5 17.0 0.28 0 0.24 0.14 0.08 0.05 0.03 0.01 0138 10 1.25 0.5 9,075 1 x 8 20 5 8.5 0.31 11 0.28 0.18 0.13 0.09 0.06 0.03 0139 10 1.25 0.5 9,075 1 x 8 40 0.2 17.0 1.32 23 0.90 0.05 0.01 0.00 0 0 0140 10 1.25 0.5 9,075 1 x 8 40 0.2 8.5 1.92 48 1.48 0.25 0.05 0.02 0.01 0 0141 10 1.25 0.5 9,075 1 x 8 40 1 17.0 0.61 33 0.51 0.17 0.06 0.02 0.01 0 0142 10 1.25 0.5 9,075 1 x 8 40 1 8.5 0.77 64 0.67 0.32 0.16 0.08 0.04 0.01 0143 10 1.25 0.5 9,075 1 x 8 40 5 17.0 0.20 0 0.18 0.10 0.06 0.04 0.03 0.01 0144 10 1.25 0.5 9,075 1 x 8 40 5 8.5 0.21 0 0.19 0.12 0.09 0.06 0.05 0.03 0.01145 20 0.31 2 1,134 1 x 1 10 0.2 17.0 6.04 30 4.28 0.06 0.00 0.00 0 0 0146 20 0.31 2 1,134 1 x 1 10 0.2 8.5 7.52 51 5.78 0.29 0.02 0.00 0 0 0147 20 0.31 2 1,134 1 x 1 10 1 17.0 2.43 48 1.87 0.24 0.04 0.01 0 0 0148 20 0.31 2 1,134 1 x 1 10 1 8.5 2.75 77 2.21 0.51 0.14 0.04 0.01 0 0149 20 0.31 2 1,134 1 x 1 10 5 17.0 0.73 33 0.59 0.19 0.09 0.04 0.01 0 0150 20 0.31 2 1,134 1 x 1 10 5 8.5 0.79 51 0.65 0.26 0.14 0.08 0.04 0.01 0
36 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins Table 2. Simulated groundwater mounding beneath hypothetical stormwater-infiltration basins on a 10-acre development.—Continued [ft2, square feet; 1 x 1, square basin (sides of equal length); 1 x 8, rectangular basin (long side eight times length of short side); in/hr, inches per hour; Max, maximum; ft2, square feet; GW, groundwater; hgt, height; ft, feet; EEoB, east edge of basin] Simulation number Impervious cover (percent) Design storm (inches) Basin depth (feet) Basin area (ft2

)

Basin 

shape 

Aquifer 

thickness 

(feet)

Soil 

permeability

(in/hr)

Specific 

yield

(percent)

Max 

GW 

mound 

height

(feet)

Max 

extent 

of 0.25- 

foot GW 

mound 

hgt 

(feet)

GW 

mound 

hgt at 

EEoB

 (feet)

GW 

mound 

hgt 

50 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

150 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

200 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

300 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

500 ft 

from 

EEoB 

(feet)

151 20 0.31 2 1,134 1 x 1 20 0.2 17.0 5.23 33 3.72 0.08 0.01 0.00 0 0 0152 20 0.31 2 1,134 1 x 1 20 0.2 8.5 6.42 54 4.92 0.34 0.05 0.01 0 0 0153 20 0.31 2 1,134 1 x 1 20 1 17.0 1.90 46 1.47 0.23 0.05 0.01 0 0 0154 20 0.31 2 1,134 1 x 1 20 1 8.5 2.11 73 1.69 0.42 0.15 0.06 0.02 0 0155 20 0.31 2 1,134 1 x 1 20 5 17.0 0.51 16 0.41 0.13 0.07 0.04 0.02 0.01 0156 20 0.31 2 1,134 1 x 1 20 5 8.5 0.54 21 0.44 0.17 0.10 0.07 0.04 0.02 0157 20 0.31 2 1,134 1 x 1 40 0.2 17.0 4.19 38 3.05 0.12 0.01 0.00 0 0 0158 20 0.31 2 1,134 1 x 1 40 0.2 8.5 5.10 61 3.95 0.43 0.05 0.01 0 0 0159 20 0.31 2 1,134 1 x 1 40 1 17.0 1.37 44 1.09 0.23 0.06 0.02 0.01 0 0160 20 0.31 2 1,134 1 x 1 40 1 8.5 1.50 66 1.22 0.35 0.14 0.06 0.03 0.01 0161 20 0.31 2 1,134 1 x 1 40 5 17.0 0.34 3 0.28 0.10 0.05 0.03 0.02 0.01 0162 20 0.31 2 1,134 1 x 1 40 5 8.5 0.35 5 0.30 0.11 0.07 0.05 0.03 0.02 0.01163 20 0.31 2 1,134 1 x 8 10 0.2 17.0 3.87 30 3.12 0.07 0.00 0.00 0 0 0164 20 0.31 2 1,134 1 x 8 10 0.2 8.5 5.06 52 4.39 0.31 0.03 0.00 0 0 0165 20 0.31 2 1,134 1 x 8 10 1 17.0 1.66 49 1.45 0.25 0.04 0.01 0 0 0166 20 0.31 2 1,134 1 x 8 10 1 8.5 1.96 79 1.76 0.51 0.15 0.04 0.01 0 0167 20 0.31 2 1,134 1 x 8 10 5 17.0 0.52 31 0.47 0.19 0.09 0.04 0.02 0 0168 20 0.31 2 1,134 1 x 8 10 5 8.5 0.58 48 0.53 0.25 0.14 0.08 0.05 0.01 0169 20 0.31 2 1,134 1 x 8 20 0.2 17.0 3.30 33 2.73 0.08 0.01 0.00 0 0 0170 20 0.31 2 1,134 1 x 8 20 0.2 8.5 4.29 56 3.75 0.36 0.05 0.01 0 0 0171 20 0.31 2 1,134 1 x 8 20 1 17.0 1.29 46 1.14 0.24 0.06 0.02 0 0 0172 20 0.31 2 1,134 1 x 8 20 1 8.5 1.49 74 1.34 0.42 0.16 0.06 0.02 0 0173 20 0.31 2 1,134 1 x 8 20 5 17.0 0.36 11 0.33 0.13 0.07 0.04 0.02 0.01 0174 20 0.31 2 1,134 1 x 8 20 5 8.5 0.39 16 0.36 0.16 0.10 0.07 0.04 0.02 0175 20 0.31 2 1,134 1 x 8 40 0.2 17.0 2.66 38 2.27 0.13 0.01 0.00 0 0 0176 20 0.31 2 1,134 1 x 8 40 0.2 8.5 3.42 61 3.05 0.45 0.06 0.01 0.01 0 0177 20 0.31 2 1,134 1 x 8 40 1 17.0 0.94 46 0.86 0.23 0.06 0.02 0.01 0 0178 20 0.31 2 1,134 1 x 8 40 1 8.5 1.07 66 0.98 0.35 0.14 0.07 0.03 0.01 0179 20 0.31 2 1,134 1 x 8 40 5 17.0 0.25 0 0.23 0.09 0.05 0.03 0.02 0.01 0180 20 0.31 2 1,134 1 x 8 40 5 8.5 0.26 0 0.24 0.11 0.07 0.05 0.03 0.02 0.01
Table 2 37

Table 2. Simulated groundwater mounding beneath hypothetical stormwater-infiltration basins on a 10-acre development.—Continued[ft2, square feet; 1 x 1, square basin (sides of equal length); 1 x 8, rectangular basin (long side eight times length of short side); in/hr, inches per hour; Max, maximum; ft2, square feet; GW, groundwater; hgt, height; ft, feet; EEoB, east edge of basin]

Simulation 

number

Impervious 

cover 

(percent)

Design 

storm 

(inches)

Basin 

depth 

(feet)

Basin 

area 

(ft2)

Basin 

shape 

Aquifer 

thickness 

(feet)

Soil 

permeability

(in/hr)

Specific 

yield

(percent)

Max 

GW 

mound 

height

(feet)

Max 

extent 

of 0.25- 

foot GW 

mound 

hgt 

(feet)

GW 

mound 

hgt at 

EEoB

 (feet)

GW 

mound 

hgt 

50 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

150 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

200 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

300 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

500 ft 

from 

EEoB 

(feet)

181 20 0.31 0.5 4,538 1 x 1 10 0.2 17.0 2.36 16 1.20 0.03 0.00 0.00 0 0 0182 20 0.31 0.5 4,538 1 x 1 10 0.2 8.5 3.73 36 2.15 0.13 0.01 0.00 0 0 0183 20 0.31 0.5 4,538 1 x 1 10 1 17.0 1.28 30 0.80 0.12 0.02 0.00 0 0 0184 20 0.31 0.5 4,538 1 x 1 10 1 8.5 1.61 56 1.11 0.30 0.09 0.02 0 0 0185 20 0.31 0.5 4,538 1 x 1 10 5 17.0 0.43 10 0.32 0.13 0.06 0.03 0.01 0 0186 20 0.31 0.5 4,538 1 x 1 10 5 8.5 0.49 26 0.38 0.19 0.11 0.06 0.03 0.01 0187 20 0.31 0.5 4,538 1 x 1 20 0.2 17.0 2.20 20 1.14 0.03 0.01 0.00 0 0 0188 20 0.31 0.5 4,538 1 x 1 20 0.2 8.5 3.28 39 1.92 0.16 0.03 0.01 0 0 0189 20 0.31 0.5 4,538 1 x 1 20 1 17.0 1.03 28 0.66 0.13 0.03 0.01 0 0 0190 20 0.31 0.5 4,538 1 x 1 20 1 8.5 1.23 51 0.86 0.27 0.10 0.04 0.01 0 0191 20 0.31 0.5 4,538 1 x 1 20 5 17.0 0.30 0 0.22 0.09 0.05 0.03 0.02 0 0192 20 0.31 0.5 4,538 1 x 1 20 5 8.5 0.33 0 0.25 0.12 0.08 0.05 0.03 0.01 0193 20 0.31 0.5 4,538 1 x 1 40 0.2 17.0 1.95 23 1.07 0.05 0.01 0.00 0 0 0194 20 0.31 0.5 4,538 1 x 1 40 0.2 8.5 2.75 43 1.69 0.20 0.03 0.01 0 0 0195 20 0.31 0.5 4,538 1 x 1 40 1 17.0 0.79 25 0.53 0.13 0.04 0.01 0 0 0196 20 0.31 0.5 4,538 1 x 1 40 1 8.5 0.91 44 0.65 0.23 0.10 0.05 0.02 0.01 0197 20 0.31 0.5 4,538 1 x 1 40 5 17.0 0.21 0 0.16 0.07 0.04 0.02 0.02 0.01 0198 20 0.31 0.5 4,538 1 x 1 40 5 8.5 0.22 0 0.17 0.08 0.05 0.04 0.03 0.02 0199 20 0.31 0.5 4,538 1 x 8 10 0.2 17.0 1.68 16 1.09 0.03 0.00 0.00 0 0 0200 20 0.31 0.5 4,538 1 x 8 10 0.2 8.5 2.42 36 1.83 0.14 0.01 0.00 0 0 0201 20 0.31 0.5 4,538 1 x 8 10 1 17.0 0.83 30 0.67 0.14 0.03 0.00 0 0 0202 20 0.31 0.5 4,538 1 x 8 10 1 8.5 1.10 61 0.95 0.33 0.10 0.03 0.01 0 0203 20 0.31 0.5 4,538 1 x 8 10 5 17.0 0.31 5 0.28 0.14 0.07 0.03 0.01 0 0204 20 0.31 0.5 4,538 1 x 8 10 5 8.5 0.37 23 0.33 0.19 0.12 0.07 0.04 0.01 0205 20 0.31 0.5 4,538 1 x 8 20 0.2 17.0 1.47 18 1.02 0.04 0.01 0.00 0 0 0206 20 0.31 0.5 4,538 1 x 8 20 0.2 8.5 2.08 39 1.63 0.17 0.03 0.01 0 0 0207 20 0.31 0.5 4,538 1 x 8 20 1 17.0 0.66 28 0.55 0.14 0.04 0.01 0 0 0208 20 0.31 0.5 4,538 1 x 8 20 1 8.5 0.84 56 0.73 0.28 0.12 0.05 0.02 0 0209 20 0.31 0.5 4,538 1 x 8 20 5 17.0 0.22 0 0.19 0.10 0.06 0.03 0.02 0.01 0210 20 0.31 0.5 4,538 1 x 8 20 5 8.5 0.24 0 0.22 0.13 0.09 0.06 0.04 0.02 0
38 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins Table 2. Simulated groundwater mounding beneath hypothetical stormwater-infiltration basins on a 10-acre development.—Continued [ft2, square feet; 1 x 1, square basin (sides of equal length); 1 x 8, rectangular basin (long side eight times length of short side); in/hr, inches per hour; Max, maximum; ft2, square feet; GW, groundwater; hgt, height; ft, feet; EEoB, east edge of basin] Simulation number Impervious cover (percent) Design storm (inches) Basin depth (feet) Basin area (ft2

)

Basin 

shape 

Aquifer 

thickness 

(feet)

Soil 

permeability

(in/hr)

Specific 

yield

(percent)

Max 

GW 

mound 

height

(feet)

Max 

extent 

of 0.25- 

foot GW 

mound 

hgt 

(feet)

GW 

mound 

hgt at 

EEoB

 (feet)

GW 

mound 

hgt 

50 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

150 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

200 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

300 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

500 ft 

from 

EEoB 

(feet)

211 20 0.31 0.5 4,538 1 x 8 40 0.2 17.0 1.20 23 0.91 0.05 0.01 0.00 0 0 0

212 20 0.31 0.5 4,538 1 x 8 40 0.2 8.5 1.71 46 1.41 0.22 0.03 0.01 0 0 0213 20 0.31 0.5 4,538 1 x 8 40 1 17.0 0.51 25 0.45 0.14 0.05 0.02 0.01 0 0214 20 0.31 0.5 4,538 1 x 8 40 1 8.5 0.63 46 0.56 0.24 0.11 0.05 0.03 0.01 0215 20 0.31 0.5 4,538 1 x 8 40 5 17.0 0.15 0 0.14 0.07 0.04 0.03 0.02 0.01 0216 20 0.31 0.5 4,538 1 x 8 40 5 8.5 0.16 0 0.15 0.09 0.06 0.04 0.03 0.02 0.01217 20 1.25 2 4,538 1 x 1 10 0.2 17.0 8.75 36 4.93 0.11 0.01 0.00 0 0 0218 20 1.25 2 4,538 1 x 1 10 0.2 8.5 12.39 66 8.09 0.62 0.05 0.01 0 0 0219 20 1.25 2 4,538 1 x 1 10 1 17.0 4.51 71 3.02 0.54 0.09 0.02 0 0 0220 20 1.25 2 4,538 1 x 1 10 1 8.5 5.38 115 3.95 1.26 0.38 0.11 0.03 0 0221 20 1.25 2 4,538 1 x 1 10 5 17.0 1.61 95 1.21 0.51 0.24 0.11 0.04 0.01 0222 20 1.25 2 4,538 1 x 1 10 5 8.5 1.74 145 1.37 0.71 0.41 0.25 0.14 0.04 0223 20 1.25 2 4,538 1 x 1 20 0.2 17.0 8.12 39 4.60 0.15 0.02 0.01 0 0 0224 20 1.25 2 4,538 1 x 1 20 0.2 8.5 11.20 73 7.30 0.74 0.11 0.03 0.01 0 0225 20 1.25 2 4,538 1 x 1 20 1 17.0 3.74 76 2.51 0.54 0.14 0.04 0.01 0 0226 20 1.25 2 4,538 1 x 1 20 1 8.5 4.34 125 3.16 1.07 0.42 0.17 0.07 0.01 0227 20 1.25 2 4,538 1 x 1 20 5 17.0 1.16 81 0.86 0.38 0.21 0.12 0.06 0.02 0228 20 1.25 2 4,538 1 x 1 20 5 8.5 1.24 122 0.96 0.48 0.31 0.21 0.14 0.06 0.01229 20 1.25 2 4,538 1 x 1 40 0.2 17.0 7.21 46 4.20 0.22 0.02 0.01 0 0 0230 20 1.25 2 4,538 1 x 1 40 0.2 8.5 9.65 81 6.37 0.91 0.13 0.04 0.02 0 0231 20 1.25 2 4,538 1 x 1 40 1 17.0 2.98 77 2.05 0.53 0.16 0.05 0.02 0 0232 20 1.25 2 4,538 1 x 1 40 1 8.5 3.39 125 2.49 0.91 0.39 0.19 0.09 0.03 0233 20 1.25 2 4,538 1 x 1 40 5 17.0 0.83 57 0.62 0.28 0.16 0.10 0.06 0.03 0234 20 1.25 2 4,538 1 x 1 40 5 8.5 0.86 77 0.67 0.33 0.21 0.15 0.11 0.06 0.02235 20 1.25 2 4,538 1 x 8 10 0.2 17.0 5.94 36 4.30 0.13 0.01 0.00 0 0 0236 20 1.25 2 4,538 1 x 8 10 0.2 8.5 8.14 69 6.71 0.67 0.07 0.01 0 0 0237 20 1.25 2 4,538 1 x 8 10 1 17.0 2.99 76 2.53 0.59 0.12 0.02 0 0 0238 20 1.25 2 4,538 1 x 8 10 1 8.5 3.78 125 3.37 1.33 0.46 0.14 0.04 0 0239 20 1.25 2 4,538 1 x 8 10 5 17.0 1.17 104 1.06 0.54 0.27 0.13 0.05 0.01 0240 20 1.25 2 4,538 1 x 8 10 5 8.5 1.34 158 1.23 0.74 0.46 0.28 0.16 0.05 0
Table 2 39

Table 2. Simulated groundwater mounding beneath hypothetical stormwater-infiltration basins on a 10-acre development.—Continued[ft2, square feet; 1 x 1, square basin (sides of equal length); 1 x 8, rectangular basin (long side eight times length of short side); in/hr, inches per hour; Max, maximum; ft2, square feet; GW, groundwater; hgt, height; ft, feet; EEoB, east edge of basin]

Simulation 

number

Impervious 

cover 

(percent)

Design 

storm 

(inches)

Basin 

depth 

(feet)

Basin 

area 

(ft2)

Basin 

shape 

Aquifer 

thickness 

(feet)

Soil 

permeability

(in/hr)

Specific 

yield

(percent)

Max 

GW 

mound 

height

(feet)

Max 

extent 

of 0.25- 

foot GW 

mound 

hgt 

(feet)

GW 

mound 

hgt at 

EEoB

 (feet)

GW 

mound 

hgt 

50 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

150 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

200 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

300 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

500 ft 

from 

EEoB 

(feet)

241 20 1.25 2 4,538 1 x 8 20 0.2 17.0 5.30 41 3.95 0.16 0.03 0.01 0 0 0242 20 1.25 2 4,538 1 x 8 20 0.2 8.5 7.25 79 6.04 0.80 0.13 0.03 0.01 0 0243 20 1.25 2 4,538 1 x 8 20 1 17.0 2.49 82 2.12 0.58 0.17 0.05 0.02 0 0244 20 1.25 2 4,538 1 x 8 20 1 8.5 3.03 135 2.70 1.13 0.48 0.21 0.08 0.01 0245 20 1.25 2 4,538 1 x 8 20 5 17.0 0.84 89 0.75 0.39 0.23 0.13 0.07 0.02 0246 20 1.25 2 4,538 1 x 8 20 5 8.5 0.92 135 0.85 0.50 0.33 0.23 0.15 0.07 0.01247 20 1.25 2 4,538 1 x 8 40 0.2 17.0 4.50 48 3.53 0.24 0.03 0.01 0 0 0248 20 1.25 2 4,538 1 x 8 40 0.2 8.5 6.19 86 5.26 0.99 0.16 0.05 0.02 0 0249 20 1.25 2 4,538 1 x 8 40 1 17.0 1.97 86 1.73 0.58 0.19 0.07 0.03 0.01 0250 20 1.25 2 4,538 1 x 8 40 1 8.5 2.36 138 2.13 0.96 0.45 0.22 0.11 0.03 0251 20 1.25 2 4,538 1 x 8 40 5 17.0 0.59 61 0.54 0.29 0.17 0.11 0.07 0.03 0252 20 1.25 2 4,538 1 x 8 40 5 8.5 0.63 86 0.58 0.34 0.23 0.16 0.12 0.07 0.02253 20 1.25 0.5 18,150 1 x 1 10 0.2 17.0 2.26 18 1.21 0.04 0.00 0.00 0 0 0254 20 1.25 0.5 18,150 1 x 1 10 0.2 8.5 4.21 43 2.32 0.19 0.02 0.00 0 0 0255 20 1.25 0.5 18,150 1 x 1 10 1 17.0 1.77 41 1.02 0.20 0.04 0.01 0 0 0256 20 1.25 0.5 18,150 1 x 1 10 1 8.5 2.56 82 1.64 0.55 0.17 0.05 0.01 0 0257 20 1.25 0.5 18,150 1 x 1 10 5 17.0 0.82 52 0.57 0.27 0.13 0.06 0.02 0 0258 20 1.25 0.5 18,150 1 x 1 10 5 8.5 0.97 97 0.73 0.42 0.25 0.15 0.08 0.02 0259 20 1.25 0.5 18,150 1 x 1 20 0.2 17.0 2.18 21 1.16 0.05 0.01 0.00 0 0 0260 20 1.25 0.5 18,150 1 x 1 20 0.2 8.5 3.92 48 2.17 0.25 0.05 0.01 0 0 0261 20 1.25 0.5 18,150 1 x 1 20 1 17.0 1.51 44 0.89 0.22 0.06 0.02 0.01 0 0262 20 1.25 0.5 18,150 1 x 1 20 1 8.5 2.06 89 1.35 0.52 0.21 0.09 0.03 0 0263 20 1.25 0.5 18,150 1 x 1 20 5 17.0 0.57 34 0.41 0.21 0.12 0.07 0.04 0.01 0264 20 1.25 0.5 18,150 1 x 1 20 5 8.5 0.65 68 0.49 0.29 0.19 0.13 0.09 0.04 0.01265 20 1.25 0.5 18,150 1 x 1 40 0.2 17.0 2.13 26 1.12 0.07 0.01 0.00 0 0 0266 20 1.25 0.5 18,150 1 x 1 40 0.2 8.5 3.64 54 2.03 0.31 0.06 0.02 0.01 0 0267 20 1.25 0.5 18,150 1 x 1 40 1 17.0 1.28 46 0.78 0.23 0.07 0.03 0.01 0 0268 20 1.25 0.5 18,150 1 x 1 40 1 8.5 1.63 87 1.09 0.46 0.21 0.10 0.05 0.01 0269 20 1.25 0.5 18,150 1 x 1 40 5 17.0 0.41 11 0.30 0.16 0.10 0.06 0.04 0.02 0270 20 1.25 0.5 18,150 1 x 1 40 5 8.5 0.45 25 0.34 0.20 0.14 0.10 0.07 0.04 0.01
40 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins Table 2. Simulated groundwater mounding beneath hypothetical stormwater-infiltration basins on a 10-acre development.—Continued [ft2, square feet; 1 x 1, square basin (sides of equal length); 1 x 8, rectangular basin (long side eight times length of short side); in/hr, inches per hour; Max, maximum; ft2, square feet; GW, groundwater; hgt, height; ft, feet; EEoB, east edge of basin] Simulation number Impervious cover (percent) Design storm (inches) Basin depth (feet) Basin area (ft2

)

Basin 

shape 

Aquifer 

thickness 

(feet)

Soil 

permeability

(in/hr)

Specific 

yield

(percent)

Max 

GW 

mound 

height

(feet)

Max 

extent 

of 0.25- 

foot GW 

mound 

hgt 

(feet)

GW 

mound 

hgt at 

EEoB

 (feet)

GW 

mound 

hgt 

50 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

150 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

200 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

300 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

500 ft 

from 

EEoB 

(feet)

271 20 1.25 0.5 18,150 1 x 8 10 0.2 17.0 1.94 18 1.18 0.04 0.00 0.00 0 0 0272 20 1.25 0.5 18,150 1 x 8 10 0.2 8.5 3.13 43 2.16 0.19 0.02 0.00 0 0 0273 20 1.25 0.5 18,150 1 x 8 10 1 17.0 1.19 41 0.90 0.20 0.04 0.01 0 0 0274 20 1.25 0.5 18,150 1 x 8 10 1 8.5 1.67 86 1.39 0.54 0.19 0.06 0.01 0 0275 20 1.25 0.5 18,150 1 x 8 10 5 17.0 0.55 52 0.48 0.26 0.14 0.07 0.03 0 0276 20 1.25 0.5 18,150 1 x 8 10 5 8.5 0.68 107 0.62 0.41 0.27 0.17 0.1 0.03 0277 20 1.25 0.5 18,150 1 x 8 20 0.2 17.0 1.80 21 1.12 0.05 0.01 0.00 0 0 0278 20 1.25 0.5 18,150 1 x 8 20 0.2 8.5 2.81 48 1.99 0.25 0.05 0.02 0 0 0279 20 1.25 0.5 18,150 1 x 8 20 1 17.0 1.00 44 0.78 0.22 0.07 0.02 0.01 0 0280 20 1.25 0.5 18,150 1 x 8 20 1 8.5 1.36 94 1.14 0.51 0.24 0.11 0.04 0.01 0281 20 1.25 0.5 18,150 1 x 8 20 5 17.0 0.40 31 0.35 0.21 0.13 0.08 0.05 0.01 0282 20 1.25 0.5 18,150 1 x 8 20 5 8.5 0.47 73 0.43 0.29 0.21 0.15 0.1 0.05 0.01283 20 1.25 0.5 18,150 1 x 8 40 0.2 17.0 1.62 26 1.07 0.07 0.01 0.01 0 0 0284 20 1.25 0.5 18,150 1 x 8 40 0.2 8.5 2.45 54 1.82 0.31 0.07 0.03 0.01 0 0285 20 1.25 0.5 18,150 1 x 8 40 1 17.0 0.82 46 0.67 0.23 0.08 0.03 0.01 0 0286 20 1.25 0.5 18,150 1 x 8 40 1 8.5 1.07 94 0.93 0.46 0.24 0.13 0.06 0.02 0287 20 1.25 0.5 18,150 1 x 8 40 5 17.0 0.29 2 0.26 0.16 0.11 0.07 0.05 0.02 0288 20 1.25 0.5 18,150 1 x 8 40 5 8.5 0.32 18 0.30 0.20 0.15 0.11 0.08 0.05 0.02289 40 0.31 2 2,269 1 x 1 10 0.2 17.0 7.61 33 5.05 0.09 0.01 0.00 0 0 0290 40 0.31 2 2,269 1 x 1 10 0.2 8.5 10.05 59 7.36 0.45 0.04 0.00 0 0 0291 40 0.31 2 2,269 1 x 1 10 1 17.0 3.43 61 2.54 0.38 0.06 0.01 0 0 0292 40 0.31 2 2,269 1 x 1 10 1 8.5 4.00 97 3.14 0.83 0.24 0.07 0.01 0 0293 40 0.31 2 2,269 1 x 1 10 5 17.0 1.11 64 0.88 0.32 0.15 0.06 0.02 0 0294 40 0.31 2 2,269 1 x 1 10 5 8.5 1.21 97 0.99 0.44 0.25 0.14 0.08 0.02 0295 40 0.31 2 2,269 1 x 1 20 0.2 17.0 6.84 38 4.54 0.11 0.02 0.00 0 0 0296 40 0.31 2 2,269 1 x 1 20 0.2 8.5 8.84 64 6.45 0.53 0.07 0.02 0 0 0297 40 0.31 2 2,269 1 x 1 20 1 17.0 2.77 61 2.05 0.37 0.09 0.03 0.01 0 0298 40 0.31 2 2,269 1 x 1 20 1 8.5 3.15 99 2.45 0.69 0.26 0.10 0.04 0 0299 40 0.31 2 2,269 1 x 1 20 5 17.0 0.78 41 0.61 0.23 0.12 0.07 0.04 0.01 0300 40 0.31 2 2,269 1 x 1 20 5 8.5 0.83 59 0.66 0.28 0.17 0.11 0.07 0.03 0
Table 2 41

Table 2. Simulated groundwater mounding beneath hypothetical stormwater-infiltration basins on a 10-acre development.—Continued[ft2, square feet; 1 x 1, square basin (sides of equal length); 1 x 8, rectangular basin (long side eight times length of short side); in/hr, inches per hour; Max, maximum; ft2, square feet; GW, groundwater; hgt, height; ft, feet; EEoB, east edge of basin]

Simulation 

number

Impervious 

cover 

(percent)

Design 

storm 

(inches)

Basin 

depth 

(feet)

Basin 

area 

(ft2)

Basin 

shape 

Aquifer 

thickness 

(feet)

Soil 

permeability

(in/hr)

Specific 

yield

(percent)

Max 

GW 

mound 

height

(feet)

Max 

extent 

of 0.25- 

foot GW 

mound 

hgt 

(feet)

GW 

mound 

hgt at 

EEoB

 (feet)

GW 

mound 

hgt 

50 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

150 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

200 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

300 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

500 ft 

from 

EEoB 

(feet)

301 40 0.31 2 2,269 1 x 1 40 0.2 17.0 5.76 43 3.90 0.17 0.02 0.01 0 0 0302 40 0.31 2 2,269 1 x 1 40 0.2 8.5 7.29 71 5.36 0.66 0.09 0.02 0.01 0 0303 40 0.31 2 2,269 1 x 1 40 1 17.0 2.09 62 1.58 0.36 0.10 0.03 0.01 0 0304 40 0.31 2 2,269 1 x 1 40 1 8.5 2.33 95 1.83 0.58 0.24 0.11 0.05 0.01 0305 40 0.31 2 2,269 1 x 1 40 5 17.0 0.54 23 0.43 0.16 0.09 0.05 0.03 0.01 0306 40 0.31 2 2,269 1 x 1 40 5 8.5 0.56 28 0.45 0.19 0.11 0.08 0.06 0.03 0.01307 40 0.31 2 2,269 1 x 8 10 0.2 17.0 4.96 33 3.84 0.10 0.01 0.00 0 0 0308 40 0.31 2 2,269 1 x 8 10 0.2 8.5 6.72 61 5.70 0.47 0.04 0.00 0 0 0309 40 0.31 2 2,269 1 x 8 10 1 17.0 2.33 62 2.00 0.40 0.07 0.01 0 0 0310 40 0.31 2 2,269 1 x 8 10 1 8.5 2.86 102 2.56 0.86 0.27 0.08 0.02 0 0

311 40 0.31 2 2,269 1 x 8 10 5 17.0 0.81 68 0.73 0.33 0.16 0.07 0.03 0 0

312 40 0.31 2 2,269 1 x 8 10 5 8.5 0.91 102 0.83 0.44 0.26 0.15 0.08 0.02 0313 40 0.31 2 2,269 1 x 8 20 0.2 17.0 4.34 36 3.44 0.12 0.02 0.00 0 0 0314 40 0.31 2 2,269 1 x 8 20 0.2 8.5 5.84 68 5.00 0.55 0.08 0.02 0 0 0315 40 0.31 2 2,269 1 x 8 20 1 17.0 1.87 64 1.63 0.39 0.10 0.03 0.01 0 0316 40 0.31 2 2,269 1 x 8 20 1 8.5 2.22 105 2.00 0.71 0.28 0.11 0.04 0.01 0317 40 0.31 2 2,269 1 x 8 20 5 17.0 0.56 41 0.51 0.23 0.13 0.07 0.04 0.01 0318 40 0.31 2 2,269 1 x 8 20 5 8.5 0.61 61 0.56 0.28 0.18 0.12 0.08 0.03 0.01319 40 0.31 2 2,269 1 x 8 40 0.2 17.0 3.61 43 2.98 0.18 0.02 0.01 0 0 0320 40 0.31 2 2,269 1 x 8 40 0.2 8.5 4.82 73 4.21 0.69 0.10 0.03 0.01 0 0321 40 0.31 2 2,269 1 x 8 40 1 17.0 1.42 66 1.27 0.38 0.11 0.04 0.01 0 0322 40 0.31 2 2,269 1 x 8 40 1 8.5 1.65 100 1.51 0.60 0.26 0.12 0.05 0.01 0323 40 0.31 2 2,269 1 x 8 40 5 17.0 0.39 20 0.36 0.17 0.09 0.06 0.04 0.01 0324 40 0.31 2 2,269 1 x 8 40 5 8.5 0.41 26 0.38 0.19 0.12 0.08 0.06 0.03 0.01325 40 0.31 0.5 9,075 1 x 1 10 0.2 17.0 2.57 20 1.43 0.04 0.00 0.00 0 0 0326 40 0.31 0.5 9,075 1 x 1 10 0.2 8.5 4.47 41 2.63 0.18 0.02 0.00 0 0 0327 40 0.31 0.5 9,075 1 x 1 10 1 17.0 1.69 39 1.05 0.18 0.03 0.00 0 0 0328 40 0.31 0.5 9,075 1 x 1 10 1 8.5 2.26 74 1.56 0.46 0.13 0.04 0.01 0 0329 40 0.31 0.5 9,075 1 x 1 10 5 17.0 0.65 36 0.48 0.21 0.10 0.04 0.02 0 0330 40 0.31 0.5 9,075 1 x 1 10 5 8.5 0.75 68 0.58 0.31 0.18 0.10 0.05 0.01 0
42 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins Table 2. Simulated groundwater mounding beneath hypothetical stormwater-infiltration basins on a 10-acre development.—Continued [ft2, square feet; 1 x 1, square basin (sides of equal length); 1 x 8, rectangular basin (long side eight times length of short side); in/hr, inches per hour; Max, maximum; ft2, square feet; GW, groundwater; hgt, height; ft, feet; EEoB, east edge of basin] Simulation number Impervious cover (percent) Design storm (inches) Basin depth (feet) Basin area (ft2

)

Basin 

shape 

Aquifer 

thickness 

(feet)

Soil 

permeability

(in/hr)

Specific 

yield

(percent)

Max 

GW 

mound 

height

(feet)

Max 

extent 

of 0.25- 

foot GW 

mound 

hgt 

(feet)

GW 

mound 

hgt at 

EEoB

 (feet)

GW 

mound 

hgt 

50 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

150 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

200 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

300 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

500 ft 

from 

EEoB 

(feet)

331 40 0.31 0.5 9,075 1 x 1 20 0.2 17.0 2.46 23 1.35 0.05 0.01 0.00 0 0 0332 40 0.31 0.5 9,075 1 x 1 20 0.2 8.5 4.05 46 2.39 0.23 0.04 0.01 0 0 0333 40 0.31 0.5 9,075 1 x 1 20 1 17.0 1.39 39 0.88 0.19 0.05 0.01 0 0 0334 40 0.31 0.5 9,075 1 x 1 20 1 8.5 1.76 74 1.22 0.42 0.16 0.06 0.02 0 0335 40 0.31 0.5 9,075 1 x 1 20 5 17.0 0.45 15 0.33 0.15 0.09 0.05 0.02 0.01 0336 40 0.31 0.5 9,075 1 x 1 20 5 8.5 0.50 30 0.38 0.20 0.13 0.09 0.06 0.02 0337 40 0.31 0.5 9,075 1 x 1 40 0.2 17.0 2.32 28 1.28 0.07 0.01 0.00 0 0 0338 40 0.31 0.5 9,075 1 x 1 40 0.2 8.5 3.58 51 2.15 0.29 0.05 0.02 0.01 0 0339 40 0.31 0.5 9,075 1 x 1 40 1 17.0 1.13 39 0.74 0.20 0.06 0.02 0.01 0 0340 40 0.31 0.5 9,075 1 x 1 40 1 8.5 1.35 69 0.96 0.36 0.16 0.07 0.03 0.01 0341 40 0.31 0.5 9,075 1 x 1 40 5 17.0 0.32 0 0.24 0.11 0.06 0.04 0.03 0.01 0342 40 0.31 0.5 9,075 1 x 1 40 5 8.5 0.34 2 0.26 0.13 0.09 0.06 0.04 0.02 0.01343 40 0.31 0.5 9,075 1 x 8 10 0.2 17.0 1.99 16 1.18 0.03 0.00 0.00 0 0 0344 40 0.31 0.5 9,075 1 x 8 10 0.2 8.5 3.03 39 2.13 0.17 0.02 0.00 0 0 0345 40 0.31 0.5 9,075 1 x 8 10 1 17.0 1.08 38 0.84 0.18 0.03 0.01 0 0 0346 40 0.31 0.5 9,075 1 x 8 10 1 8.5 1.49 76 1.24 0.46 0.15 0.04 0.01 0 0347 40 0.31 0.5 9,075 1 x 8 10 5 17.0 0.44 33 0.39 0.21 0.11 0.05 0.02 0 0348 40 0.31 0.5 9,075 1 x 8 10 5 8.5 0.54 69 0.49 0.30 0.19 0.12 0.06 0.02 0349 40 0.31 0.5 9,075 1 x 8 20 0.2 17.0 1.78 20 1.12 0.05 0.01 0.00 0 0 0350 40 0.31 0.5 9,075 1 x 8 20 0.2 8.5 2.65 44 1.93 0.22 0.04 0.01 0 0 0351 40 0.31 0.5 9,075 1 x 8 20 1 17.0 0.88 38 0.71 0.19 0.06 0.02 0 0 0352 40 0.31 0.5 9,075 1 x 8 20 1 8.5 1.16 79 0.98 0.41 0.18 0.08 0.03 0 0353 40 0.31 0.5 9,075 1 x 8 20 5 17.0 0.31 5 0.27 0.15 0.09 0.06 0.03 0.01 0354 40 0.31 0.5 9,075 1 x 8 20 5 8.5 0.35 21 0.32 0.20 0.14 0.10 0.06 0.03 0355 40 0.31 0.5 9,075 1 x 8 40 0.2 17.0 1.52 25 1.05 0.06 0.01 0.00 0 0 0356 40 0.31 0.5 9,075 1 x 8 40 0.2 8.5 2.22 51 1.72 0.28 0.05 0.02 0.01 0 0357 40 0.31 0.5 9,075 1 x 8 40 1 17.0 0.70 38 0.59 0.20 0.07 0.02 0.01 0 0358 40 0.31 0.5 9,075 1 x 8 40 1 8.5 0.88 73 0.77 0.36 0.17 0.09 0.04 0.01 0359 40 0.31 0.5 9,075 1 x 8 40 5 17.0 0.22 0 0.19 0.11 0.07 0.05 0.03 0.01 0360 40 0.31 0.5 9,075 1 x 8 40 5 8.5 0.24 0 0.21 0.13 0.09 0.07 0.05 0.03 0.01
Table 2 43

Table 2. Simulated groundwater mounding beneath hypothetical stormwater-infiltration basins on a 10-acre development.—Continued[ft2, square feet; 1 x 1, square basin (sides of equal length); 1 x 8, rectangular basin (long side eight times length of short side); in/hr, inches per hour; Max, maximum; ft2, square feet; GW, groundwater; hgt, height; ft, feet; EEoB, east edge of basin]

Simulation 

number

Impervious 

cover 

(percent)

Design 

storm 

(inches)

Basin 

depth 

(feet)

Basin 

area 

(ft2)

Basin 

shape 

Aquifer 

thickness 

(feet)

Soil 

permeability

(in/hr)

Specific 

yield

(percent)

Max 

GW 

mound 

height

(feet)

Max 

extent 

of 0.25- 

foot GW 

mound 

hgt 

(feet)

GW 

mound 

hgt at 

EEoB

 (feet)

GW 

mound 

hgt 

50 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

150 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

200 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

300 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

500 ft 

from 

EEoB 

(feet)

361 40 1.25 2 9,075 1 x 1 10 0.2 17.0 9.91 41 5.80 0.16 0.01 0.00 0 0 0362 40 1.25 2 9,075 1 x 1 10 0.2 8.5 15.51 74 10.04 0.92 0.08 0.01 0 0 0363 40 1.25 2 9,075 1 x 1 10 1 17.0 6.02 82 4.01 0.81 0.14 0.02 0 0 0364 40 1.25 2 9,075 1 x 1 10 1 8.5 7.55 132 5.54 1.97 0.62 0.18 0.04 0 0365 40 1.25 2 9,075 1 x 1 10 5 17.0 2.37 125 1.79 0.81 0.38 0.18 0.07 0.01 0366 40 1.25 2 9,075 1 x 1 10 5 8.5 2.62 192 2.08 1.15 0.68 0.41 0.23 0.07 0367 40 1.25 2 9,075 1 x 1 20 0.2 17.0 9.45 46 5.47 0.21 0.03 0.01 0 0 0368 40 1.25 2 9,075 1 x 1 20 0.2 8.5 14.32 84 9.23 1.10 0.16 0.04 0.01 0 0369 40 1.25 2 9,075 1 x 1 20 1 17.0 5.10 92 3.40 0.82 0.22 0.07 0.02 0 0370 40 1.25 2 9,075 1 x 1 20 1 8.5 6.20 152 4.51 1.70 0.67 0.28 0.11 0.02 0371 40 1.25 2 9,075 1 x 1 20 5 17.0 1.72 125 1.29 0.61 0.34 0.19 0.1 0.03 0372 40 1.25 2 9,075 1 x 1 20 5 8.5 1.85 185 1.45 0.79 0.51 0.34 0.22 0.1 0.02373 40 1.25 2 9,075 1 x 1 40 0.2 17.0 8.81 52 5.12 0.31 0.04 0.01 0.01 0 0374 40 1.25 2 9,075 1 x 1 40 0.2 8.5 12.82 92 8.30 1.35 0.20 0.06 0.03 0.01 0375 40 1.25 2 9,075 1 x 1 40 1 17.0 4.22 97 2.86 0.81 0.24 0.09 0.04 0.01 0376 40 1.25 2 9,075 1 x 1 40 1 8.5 4.97 162 3.62 1.44 0.63 0.30 0.15 0.04 0377 40 1.25 2 9,075 1 x 1 40 5 17.0 1.24 102 0.93 0.45 0.26 0.16 0.1 0.04 0.01378 40 1.25 2 9,075 1 x 1 40 5 8.5 1.29 142 1.00 0.53 0.34 0.24 0.17 0.1 0.03379 40 1.25 2 9,075 1 x 8 10 0.2 17.0 7.15 39 4.80 0.15 0.01 0.00 0 0 0380 40 1.25 2 9,075 1 x 8 10 0.2 8.5 10.22 74 8.01 0.84 0.09 0.01 0 0 0381 40 1.25 2 9,075 1 x 8 10 1 17.0 3.89 84 3.17 0.78 0.16 0.03 0 0 0382 40 1.25 2 9,075 1 x 8 10 1 8.5 5.10 142 4.46 1.90 0.69 0.22 0.05 0 0383 40 1.25 2 9,075 1 x 8 10 5 17.0 1.66 135 1.48 0.81 0.43 0.21 0.09 0.01 0384 40 1.25 2 9,075 1 x 8 10 5 8.5 1.91 209 1.75 1.13 0.74 0.46 0.27 0.09 0.01385 40 1.25 2 9,075 1 x 8 20 0.2 17.0 6.52 44 4.51 0.20 0.04 0.01 0 0 0386 40 1.25 2 9,075 1 x 8 20 0.2 8.5 9.26 87 7.33 1.03 0.19 0.05 0.01 0 0387 40 1.25 2 9,075 1 x 8 20 1 17.0 3.28 97 2.70 0.80 0.25 0.08 0.02 0 0388 40 1.25 2 9,075 1 x 8 20 1 8.5 4.17 165 3.65 1.65 0.75 0.33 0.13 0.02 0389 40 1.25 2 9,075 1 x 8 20 5 17.0 1.20 135 1.07 0.61 0.37 0.22 0.12 0.04 0390 40 1.25 2 9,075 1 x 8 20 5 8.5 1.34 205 1.22 0.78 0.54 0.38 0.26 0.12 0.02
44 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins Table 2. Simulated groundwater mounding beneath hypothetical stormwater-infiltration basins on a 10-acre development.—Continued [ft2, square feet; 1 x 1, square basin (sides of equal length); 1 x 8, rectangular basin (long side eight times length of short side); in/hr, inches per hour; Max, maximum; ft2, square feet; GW, groundwater; hgt, height; ft, feet; EEoB, east edge of basin] Simulation number Impervious cover (percent) Design storm (inches) Basin depth (feet) Basin area (ft2

)

Basin 

shape 

Aquifer 

thickness 

(feet)

Soil 

permeability

(in/hr)

Specific 

yield

(percent)

Max 

GW 

mound 

height

(feet)

Max 

extent 

of 0.25- 

foot GW 

mound 

hgt 

(feet)

GW 

mound 

hgt at 

EEoB

 (feet)

GW 

mound 

hgt 

50 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

150 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

200 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

300 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

500 ft 

from 

EEoB 

(feet)

391 40 1.25 2 9,075 1 x 8 40 0.2 17.0 5.70 51 4.14 0.29 0.04 0.02 0.01 0 0392 40 1.25 2 9,075 1 x 8 40 0.2 8.5 8.07 95 6.54 1.28 0.23 0.08 0.03 0.01 0393 40 1.25 2 9,075 1 x 8 40 1 17.0 2.68 102 2.27 0.80 0.27 0.11 0.04 0.01 0394 40 1.25 2 9,075 1 x 8 40 1 8.5 3.32 172 2.93 1.42 0.70 0.36 0.18 0.05 0395 40 1.25 2 9,075 1 x 8 40 5 17.0 0.85 110 0.77 0.44 0.28 0.18 0.12 0.05 0.01396 40 1.25 2 9,075 1 x 8 40 5 8.5 0.91 155 0.83 0.52 0.36 0.26 0.19 0.11 0.04397 40 1.25 0.5 36,300 1 x 1 10 0.2 17.0 2.31 13 0.99 0.03 0.00 0.00 0 0 0398 40 1.25 0.5 36,300 1 x 1 10 0.2 8.5 4.49 41 2.10 0.17 0.02 0.00 0 0 0399 40 1.25 0.5 36,300 1 x 1 10 1 17.0 2.06 43 1.02 0.20 0.04 0.01 0 0 0400 40 1.25 0.5 36,300 1 x 1 10 1 8.5 3.27 89 1.83 0.64 0.20 0.06 0.01 0 0401 40 1.25 0.5 36,300 1 x 1 10 5 17.0 1.13 69 0.70 0.34 0.16 0.07 0.03 0 0402 40 1.25 0.5 36,300 1 x 1 10 5 8.5 1.38 129 0.96 0.57 0.34 0.20 0.11 0.03 0403 40 1.25 0.5 36,300 1 x 1 20 0.2 17.0 2.25 18 0.99 0.05 0.01 0.00 0 0 0404 40 1.25 0.5 36,300 1 x 1 20 0.2 8.5 4.27 49 2.04 0.25 0.05 0.01 0 0 0405 40 1.25 0.5 36,300 1 x 1 20 1 17.0 1.81 48 0.93 0.25 0.07 0.02 0.01 0 0406 40 1.25 0.5 36,300 1 x 1 20 1 8.5 2.66 102 1.56 0.64 0.27 0.11 0.04 0.01 0407 40 1.25 0.5 36,300 1 x 1 20 5 17.0 0.80 61 0.53 0.29 0.17 0.09 0.05 0.01 0408 40 1.25 0.5 36,300 1 x 1 20 5 8.5 0.91 112 0.66 0.42 0.28 0.19 0.12 0.05 0.01409 40 1.25 0.5 36,300 1 x 1 40 0.2 17.0 2.21 23 0.99 0.06 0.01 0.01 0 0 0410 40 1.25 0.5 36,300 1 x 1 40 0.2 8.5 4.06 56 1.97 0.32 0.07 0.03 0.01 0 0

411 40 1.25 0.5 36,300 1 x 1 40 1 17.0 1.58 51 0.84 0.27 0.09 0.04 0.02 0 0

412 40 1.25 0.5 36,300 1 x 1 40 1 8.5 2.16 105 1.30 0.58 0.28 0.14 0.07 0.02 0413 40 1.25 0.5 36,300 1 x 1 40 5 17.0 0.57 36 0.38 0.22 0.14 0.09 0.06 0.02 0414 40 1.25 0.5 36,300 1 x 1 40 5 8.5 0.61 62 0.44 0.28 0.19 0.14 0.1 0.06 0.02415 40 1.25 0.5 36,300 1 x 8 10 0.2 17.0 2.08 11 1.10 0.02 0.00 0.00 0 0 0416 40 1.25 0.5 36,300 1 x 8 10 0.2 8.5 3.54 34 2.12 0.14 0.02 0.00 0 0 0417 40 1.25 0.5 36,300 1 x 8 10 1 17.0 1.38 38 0.93 0.18 0.04 0.01 0 0 0418 40 1.25 0.5 36,300 1 x 8 10 1 8.5 1.97 87 1.52 0.57 0.20 0.06 0.02 0 0419 40 1.25 0.5 36,300 1 x 8 10 5 17.0 0.65 64 0.55 0.30 0.16 0.08 0.03 0 0420 40 1.25 0.5 36,300 1 x 8 10 5 8.5 0.79 129 0.71 0.48 0.33 0.21 0.13 0.04 0
Table 2 45

Table 2. Simulated groundwater mounding beneath hypothetical stormwater-infiltration basins on a 10-acre development.—Continued[ft2, square feet; 1 x 1, square basin (sides of equal length); 1 x 8, rectangular basin (long side eight times length of short side); in/hr, inches per hour; Max, maximum; ft2, square feet; GW, groundwater; hgt, height; ft, feet; EEoB, east edge of basin]

Simulation 

number

Impervious 

cover 

(percent)

Design 

storm 

(inches)

Basin 

depth 

(feet)

Basin 

area 

(ft2)

Basin 

shape 

Aquifer 

thickness 

(feet)

Soil 

permeability

(in/hr)

Specific 

yield

(percent)

Max 

GW 

mound 

height

(feet)

Max 

extent 

of 0.25- 

foot GW 

mound 

hgt 

(feet)

GW 

mound 

hgt at 

EEoB

 (feet)

GW 

mound 

hgt 

50 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

150 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

200 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

300 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

500 ft 

from 

EEoB 

(feet)

421 40 1.25 0.5 36,300 1 x 8 20 0.2 17.0 1.98 13 1.06 0.04 0.01 0.00 0 0 0422 40 1.25 0.5 36,300 1 x 8 20 0.2 8.5 3.22 43 1.98 0.21 0.05 0.02 0 0 0423 40 1.25 0.5 36,300 1 x 8 20 1 17.0 1.17 44 0.82 0.22 0.07 0.03 0.01 0 0424 40 1.25 0.5 36,300 1 x 8 20 1 8.5 1.60 102 1.27 0.56 0.27 0.12 0.05 0.01 0425 40 1.25 0.5 36,300 1 x 8 20 5 17.0 0.46 46 0.40 0.24 0.16 0.10 0.06 0.02 0426 40 1.25 0.5 36,300 1 x 8 20 5 8.5 0.52 94 0.46 0.33 0.24 0.18 0.13 0.06 0.01427 40 1.25 0.5 36,300 1 x 8 40 0.2 17.0 1.83 20 1.02 0.04 0.01 0.01 0 0 0428 40 1.25 0.5 36,300 1 x 8 40 0.2 8.5 2.86 51 1.86 0.27 0.07 0.03 0.01 0 0429 40 1.25 0.5 36,300 1 x 8 40 1 17.0 0.97 46 0.72 0.24 0.09 0.04 0.02 0 0430 40 1.25 0.5 36,300 1 x 8 40 1 8.5 1.26 104 1.03 0.50 0.27 0.15 0.08 0.02 0431 40 1.25 0.5 36,300 1 x 8 40 5 17.0 0.32 8 0.28 0.18 0.12 0.08 0.06 0.03 0432 40 1.25 0.5 36,300 1 x 8 40 5 8.5 0.33 15 0.29 0.20 0.15 0.12 0.09 0.05 0.02433 80 0.31 2 4,538 1 x 1 10 0.2 17.0 9.13 36 5.16 0.11 0.01 0.00 0 0 0434 80 0.31 2 4,538 1 x 1 10 0.2 8.5 13.05 66 8.54 0.62 0.05 0.00 0 0 0435 80 0.31 2 4,538 1 x 1 10 1 17.0 4.75 71 3.19 0.56 0.09 0.02 0 0 0436 80 0.31 2 4,538 1 x 1 10 1 8.5 5.78 115 4.25 1.32 0.39 0.11 0.02 0 0437 80 0.31 2 4,538 1 x 1 10 5 17.0 1.72 97 1.29 0.54 0.25 0.11 0.04 0 0438 80 0.31 2 4,538 1 x 1 10 5 8.5 1.93 149 1.52 0.77 0.44 0.26 0.14 0.04 0439 80 0.31 2 4,538 1 x 1 20 0.2 17.0 8.48 39 4.82 0.15 0.02 0.01 0 0 0440 80 0.31 2 4,538 1 x 1 20 0.2 8.5 11.79 74 7.70 0.75 0.11 0.03 0.01 0 0441 80 0.31 2 4,538 1 x 1 20 1 17.0 3.93 77 2.64 0.56 0.14 0.04 0.01 0 0442 80 0.31 2 4,538 1 x 1 20 1 8.5 4.65 129 3.37 1.12 0.43 0.17 0.06 0.01 0443 80 0.31 2 4,538 1 x 1 20 5 17.0 1.23 86 0.91 0.39 0.21 0.12 0.06 0.02 0444 80 0.31 2 4,538 1 x 1 20 5 8.5 1.34 132 1.03 0.52 0.33 0.22 0.14 0.06 0.01445 80 0.31 2 4,538 1 x 1 40 0.2 17.0 7.53 46 4.39 0.22 0.03 0.01 0 0 0446 80 0.31 2 4,538 1 x 1 40 0.2 8.5 10.16 81 6.71 0.93 0.13 0.04 0.02 0 0447 80 0.31 2 4,538 1 x 1 40 1 17.0 3.12 79 2.15 0.55 0.16 0.05 0.02 0 0448 80 0.31 2 4,538 1 x 1 40 1 8.5 3.60 129 2.64 0.95 0.41 0.19 0.09 0.02 0449 80 0.31 2 4,538 1 x 1 40 5 17.0 0.87 61 0.65 0.29 0.16 0.10 0.06 0.03 0450 80 0.31 2 4,538 1 x 1 40 5 8.5 0.92 84 0.71 0.35 0.22 0.16 0.11 0.06 0.02
46 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins Table 2. Simulated groundwater mounding beneath hypothetical stormwater-infiltration basins on a 10-acre development.—Continued [ft2, square feet; 1 x 1, square basin (sides of equal length); 1 x 8, rectangular basin (long side eight times length of short side); in/hr, inches per hour; Max, maximum; ft2, square feet; GW, groundwater; hgt, height; ft, feet; EEoB, east edge of basin] Simulation number Impervious cover (percent) Design storm (inches) Basin depth (feet) Basin area (ft2

)

Basin 

shape 

Aquifer 

thickness 

(feet)

Soil 

permeability

(in/hr)

Specific 

yield

(percent)

Max 

GW 

mound 

height

(feet)

Max 

extent 

of 0.25- 

foot GW 

mound 

hgt 

(feet)

GW 

mound 

hgt at 

EEoB

 (feet)

GW 

mound 

hgt 

50 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

150 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

200 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

300 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

500 ft 

from 

EEoB 

(feet)

451 80 0.31 2 4,538 1 x 8 10 0.2 17.0 6.23 36 4.51 0.13 0.01 0.00 0 0 0452 80 0.31 2 4,538 1 x 8 10 0.2 8.5 8.62 69 7.09 0.67 0.07 0.01 0 0 0453 80 0.31 2 4,538 1 x 8 10 1 17.0 3.16 76 2.66 0.60 0.12 0.02 0 0 0454 80 0.31 2 4,538 1 x 8 10 1 8.5 4.07 122 3.62 1.39 0.47 0.14 0.03 0 0455 80 0.31 2 4,538 1 x 8 10 5 17.0 1.25 107 1.12 0.57 0.29 0.13 0.05 0.01 0456 80 0.31 2 4,538 1 x 8 10 5 8.5 1.46 162 1.34 0.80 0.49 0.30 0.16 0.05 0457 80 0.31 2 4,538 1 x 8 20 0.2 17.0 5.55 41 4.14 0.17 0.03 0.01 0 0 0458 80 0.31 2 4,538 1 x 8 20 0.2 8.5 7.67 79 6.37 0.81 0.14 0.03 0.01 0 0459 80 0.31 2 4,538 1 x 8 20 1 17.0 2.61 82 2.23 0.60 0.17 0.05 0.01 0 0460 80 0.31 2 4,538 1 x 8 20 1 8.5 3.25 138 2.89 1.18 0.50 0.21 0.08 0.01 0461 80 0.31 2 4,538 1 x 8 20 5 17.0 0.89 94 0.80 0.41 0.24 0.14 0.08 0.02 0462 80 0.31 2 4,538 1 x 8 20 5 8.5 1.00 142 0.91 0.53 0.35 0.24 0.16 0.07 0.01463 80 0.31 2 4,538 1 x 8 40 0.2 17.0 4.71 48 3.68 0.24 0.03 0.01 0 0 0464 80 0.31 2 4,538 1 x 8 40 0.2 8.5 6.53 86 5.54 1.01 0.16 0.05 0.02 0 0465 80 0.31 2 4,538 1 x 8 40 1 17.0 2.06 86 1.81 0.60 0.19 0.07 0.03 0 0466 80 0.31 2 4,538 1 x 8 40 1 8.5 2.51 138 2.26 1.01 0.47 0.23 0.11 0.03 0467 80 0.31 2 4,538 1 x 8 40 5 17.0 0.62 66 0.57 0.30 0.18 0.12 0.07 0.03 0468 80 0.31 2 4,538 1 x 8 40 5 8.5 0.68 92 0.63 0.36 0.24 0.17 0.12 0.07 0.02469 80 0.31 0.5 18,150 1 x 1 10 0.2 17.0 2.70 20 1.47 0.04 0.00 0.00 0 0 0470 80 0.31 0.5 18,150 1 x 1 10 0.2 8.5 5.05 46 2.82 0.21 0.02 0.00 0 0 0471 80 0.31 0.5 18,150 1 x 1 10 1 17.0 2.13 46 1.23 0.23 0.04 0.01 0 0 0472 80 0.31 0.5 18,150 1 x 1 10 1 8.5 3.13 89 2.01 0.66 0.19 0.05 0.01 0 0473 80 0.31 0.5 18,150 1 x 1 10 5 17.0 1.00 66 0.70 0.33 0.15 0.07 0.02 0 0474 80 0.31 0.5 18,150 1 x 1 10 5 8.5 1.22 115 0.92 0.52 0.31 0.18 0.09 0.02 0475 80 0.31 0.5 18,150 1 x 1 20 0.2 17.0 2.61 23 1.40 0.06 0.01 0.00 0 0 0476 80 0.31 0.5 18,150 1 x 1 20 0.2 8.5 4.71 52 2.63 0.29 0.06 0.01 0 0 0477 80 0.31 0.5 18,150 1 x 1 20 1 17.0 1.81 51 1.08 0.27 0.07 0.02 0.01 0 0478 80 0.31 0.5 18,150 1 x 1 20 1 8.5 2.51 99 1.64 0.62 0.25 0.10 0.04 0 0479 80 0.31 0.5 18,150 1 x 1 20 5 17.0 0.70 52 0.50 0.26 0.15 0.08 0.04 0.01 0480 80 0.31 0.5 18,150 1 x 1 20 5 8.5 0.82 95 0.62 0.37 0.24 0.16 0.11 0.05 0.01
Table 2 47

Table 2. Simulated groundwater mounding beneath hypothetical stormwater-infiltration basins on a 10-acre development.—Continued[ft2, square feet; 1 x 1, square basin (sides of equal length); 1 x 8, rectangular basin (long side eight times length of short side); in/hr, inches per hour; Max, maximum; ft2, square feet; GW, groundwater; hgt, height; ft, feet; EEoB, east edge of basin]

Simulation 

number

Impervious 

cover 

(percent)

Design 

storm 

(inches)

Basin 

depth 

(feet)

Basin 

area 

(ft2)

Basin 

shape 

Aquifer 

thickness 

(feet)

Soil 

permeability

(in/hr)

Specific 

yield

(percent)

Max 

GW 

mound 

height

(feet)

Max 

extent 

of 0.25- 

foot GW 

mound 

hgt 

(feet)

GW 

mound 

hgt at 

EEoB

 (feet)

GW 

mound 

hgt 

50 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

150 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

200 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

300 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

500 ft 

from 

EEoB 

(feet)

481 80 0.31 0.5 18,150 1 x 1 40 0.2 17.0 2.55 30 1.35 0.08 0.01 0.01 0 0 0482 80 0.31 0.5 18,150 1 x 1 40 0.2 8.5 4.37 59 2.45 0.37 0.07 0.03 0.01 0 0483 80 0.31 0.5 18,150 1 x 1 40 1 17.0 1.54 52 0.94 0.28 0.09 0.03 0.01 0 0484 80 0.31 0.5 18,150 1 x 1 40 1 8.5 1.99 99 1.33 0.56 0.25 0.12 0.06 0.02 0485 80 0.31 0.5 18,150 1 x 1 40 5 17.0 0.51 28 0.37 0.20 0.12 0.08 0.05 0.02 0486 80 0.31 0.5 18,150 1 x 1 40 5 8.5 0.56 49 0.42 0.25 0.17 0.12 0.09 0.05 0.01487 80 0.31 0.5 18,150 1 x 8 10 0.2 17.0 2.33 20 1.43 0.04 0.00 0.00 0 0 0488 80 0.31 0.5 18,150 1 x 8 10 0.2 8.5 3.80 44 2.63 0.21 0.02 0.00 0 0 0489 80 0.31 0.5 18,150 1 x 8 10 1 17.0 1.44 46 1.09 0.23 0.05 0.01 0 0 0490 80 0.31 0.5 18,150 1 x 8 10 1 8.5 2.06 92 1.70 0.65 0.22 0.07 0.02 0 0491 80 0.31 0.5 18,150 1 x 8 10 5 17.0 0.67 69 0.59 0.32 0.17 0.08 0.03 0 0492 80 0.31 0.5 18,150 1 x 8 10 5 8.5 0.87 129 0.79 0.52 0.34 0.21 0.12 0.04 0493 80 0.31 0.5 18,150 1 x 8 20 0.2 17.0 2.16 23 1.35 0.06 0.01 0.00 0 0 0494 80 0.31 0.5 18,150 1 x 8 20 0.2 8.5 3.41 52 2.42 0.29 0.06 0.02 0 0 0495 80 0.31 0.5 18,150 1 x 8 20 1 17.0 1.21 51 0.94 0.27 0.08 0.03 0.01 0 0496 80 0.31 0.5 18,150 1 x 8 20 1 8.5 1.67 105 1.41 0.62 0.28 0.12 0.05 0.01 0497 80 0.31 0.5 18,150 1 x 8 20 5 17.0 0.49 52 0.43 0.26 0.16 0.10 0.05 0.02 0498 80 0.31 0.5 18,150 1 x 8 20 5 8.5 0.60 105 0.54 0.37 0.26 0.19 0.13 0.06 0.01499 80 0.31 0.5 18,150 1 x 8 40 0.2 17.0 1.94 28 1.28 0.08 0.02 0.01 0 0 0500 80 0.31 0.5 18,150 1 x 8 40 0.2 8.5 2.97 59 2.20 0.37 0.08 0.03 0.01 0 0501 80 0.31 0.5 18,150 1 x 8 40 1 17.0 0.99 54 0.81 0.28 0.10 0.04 0.02 0 0502 80 0.31 0.5 18,150 1 x 8 40 1 8.5 1.32 107 1.14 0.56 0.28 0.15 0.07 0.02 0503 80 0.31 0.5 18,150 1 x 8 40 5 17.0 0.36 21 0.32 0.19 0.13 0.09 0.06 0.03 0504 80 0.31 0.5 18,150 1 x 8 40 5 8.5 0.41 49 0.37 0.25 0.19 0.14 0.11 0.06 0.02505 80 1.25 2 18,150 1 x 1 10 0.2 17.0 10.64 43 6.00 0.19 0.01 0.00 0 0 0506 80 1.25 2 18,150 1 x 1 10 0.2 8.5 18.51 79 11.22 1.17 0.11 0.01 0 0 0507 80 1.25 2 18,150 1 x 1 10 1 17.0 7.75 91 4.83 1.09 0.20 0.03 0 0 0508 80 1.25 2 18,150 1 x 1 10 1 8.5 10.49 152 7.34 2.92 0.95 0.27 0.06 0 0509 80 1.25 2 18,150 1 x 1 10 5 17.0 3.57 155 2.59 1.29 0.63 0.29 0.12 0.02 0510 80 1.25 2 18,150 1 x 1 10 5 8.5 4.16 245 3.24 1.96 1.21 0.73 0.41 0.13 0.01
48 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins Table 2. Simulated groundwater mounding beneath hypothetical stormwater-infiltration basins on a 10-acre development.—Continued [ft2, square feet; 1 x 1, square basin (sides of equal length); 1 x 8, rectangular basin (long side eight times length of short side); in/hr, inches per hour; Max, maximum; ft2, square feet; GW, groundwater; hgt, height; ft, feet; EEoB, east edge of basin] Simulation number Impervious cover (percent) Design storm (inches) Basin depth (feet) Basin area (ft2

)

Basin 

shape 

Aquifer 

thickness 

(feet)

Soil 

permeability

(in/hr)

Specific 

yield

(percent)

Max 

GW 

mound 

height

(feet)

Max 

extent 

of 0.25- 

foot GW 

mound 

hgt 

(feet)

GW 

mound 

hgt at 

EEoB

 (feet)

GW 

mound 

hgt 

50 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

150 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

200 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

300 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

500 ft 

from 

EEoB 

(feet)

511 80 1.25 2 18,150 1 x 1 20 0.2 17.0 10.32 51 5.74 0.27 0.05 0.01 0 0 0

512 80 1.25 2 18,150 1 x 1 20 0.2 8.5 17.44 95 10.52 1.45 0.23 0.06 0.01 0 0513 80 1.25 2 18,150 1 x 1 20 1 17.0 6.75 109 4.23 1.15 0.32 0.10 0.03 0 0514 80 1.25 2 18,150 1 x 1 20 1 8.5 8.84 179 6.16 2.62 1.09 0.45 0.17 0.03 0515 80 1.25 2 18,150 1 x 1 20 5 17.0 2.67 172 1.94 1.03 0.59 0.34 0.18 0.05 0516 80 1.25 2 18,150 1 x 1 20 5 8.5 3.02 269 2.33 1.43 0.95 0.65 0.43 0.19 0.03517 80 1.25 2 18,150 1 x 1 40 0.2 17.0 9.99 56 5.48 0.38 0.06 0.02 0.01 0 0518 80 1.25 2 18,150 1 x 1 40 0.2 8.5 16.17 105 9.75 1.78 0.31 0.10 0.04 0.01 0519 80 1.25 2 18,150 1 x 1 40 1 17.0 5.79 118 3.67 1.17 0.38 0.15 0.06 0.02 0520 80 1.25 2 18,150 1 x 1 40 1 8.5 7.27 202 5.06 2.28 1.06 0.52 0.26 0.08 0.01521 80 1.25 2 18,150 1 x 1 40 5 17.0 1.97 169 1.44 0.78 0.48 0.31 0.19 0.08 0.01522 80 1.25 2 18,150 1 x 1 40 5 8.5 2.15 262 1.64 1.00 0.68 0.50 0.36 0.2 0.06523 80 1.25 2 18,150 1 x 8 10 0.2 17.0 8.63 43 5.75 0.19 0.02 0.00 0 0 0524 80 1.25 2 18,150 1 x 8 10 0.2 8.5 13.06 81 10.00 1.13 0.12 0.01 0 0 0525 80 1.25 2 18,150 1 x 8 10 1 17.0 5.20 94 4.15 1.06 0.22 0.04 0.01 0 0526 80 1.25 2 18,150 1 x 8 10 1 8.5 7.11 158 6.17 2.80 1.05 0.34 0.09 0.01 0527 80 1.25 2 18,150 1 x 8 10 5 17.0 2.47 169 2.20 1.27 0.70 0.35 0.15 0.03 0528 80 1.25 2 18,150 1 x 8 10 5 8.5 3.05 269 2.82 1.94 1.31 0.85 0.51 0.18 0.01529 80 1.25 2 18,150 1 x 8 20 0.2 17.0 8.08 51 5.46 0.27 0.05 0.01 0 0 0530 80 1.25 2 18,150 1 x 8 20 0.2 8.5 12.07 100 9.30 1.42 0.27 0.07 0.02 0 0531 80 1.25 2 18,150 1 x 8 20 1 17.0 4.50 115 3.63 1.14 0.37 0.13 0.04 0 0532 80 1.25 2 18,150 1 x 8 20 1 8.5 6.01 196 5.22 2.55 1.20 0.55 0.23 0.04 0533 80 1.25 2 18,150 1 x 8 20 5 17.0 1.89 192 1.68 1.02 0.64 0.40 0.23 0.07 0534 80 1.25 2 18,150 1 x 8 20 5 8.5 2.24 295 2.06 1.42 1.03 0.74 0.51 0.24 0.04535 80 1.25 2 18,150 1 x 8 40 0.2 17.0 7.32 57 5.12 0.38 0.07 0.03 0.01 0 0536 80 1.25 2 18,150 1 x 8 40 0.2 8.5 10.80 110 8.48 1.74 0.34 0.12 0.05 0.01 0537 80 1.25 2 18,150 1 x 8 40 1 17.0 3.79 125 3.13 1.16 0.43 0.18 0.08 0.02 0538 80 1.25 2 18,150 1 x 8 40 1 8.5 4.91 222 4.31 2.24 1.17 0.62 0.32 0.1 0.01539 80 1.25 2 18,150 1 x 8 40 5 17.0 1.39 192 1.25 0.78 0.52 0.35 0.23 0.1 0.02540 80 1.25 2 18,150 1 x 8 40 5 8.5 1.57 295 1.44 0.99 0.73 0.55 0.42 0.25 0.08
Table 2 49

Table 2. Simulated groundwater mounding beneath hypothetical stormwater-infiltration basins on a 10-acre development.—Continued[ft2, square feet; 1 x 1, square basin (sides of equal length); 1 x 8, rectangular basin (long side eight times length of short side); in/hr, inches per hour; Max, maximum; ft2, square feet; GW, groundwater; hgt, height; ft, feet; EEoB, east edge of basin]

Simulation 

number

Impervious 

cover 

(percent)

Design 

storm 

(inches)

Basin 

depth 

(feet)

Basin 

area 

(ft2)

Basin 

shape 

Aquifer 

thickness 

(feet)

Soil 

permeability

(in/hr)

Specific 

yield

(percent)

Max 

GW 

mound 

height

(feet)

Max 

extent 

of 0.25- 

foot GW 

mound 

hgt 

(feet)

GW 

mound 

hgt at 

EEoB

 (feet)

GW 

mound 

hgt 

50 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

150 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

200 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

300 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

500 ft 

from 

EEoB 

(feet)

541 80 1.25 0.5 72,600 1 x 1 10 0.2 17.0 2.32 13 1.13 0.03 0.00 0.00 0 0 0542 80 1.25 0.5 72,600 1 x 1 10 0.2 8.5 4.62 43 2.29 0.19 0.02 0.00 0 0 0543 80 1.25 0.5 72,600 1 x 1 10 1 17.0 2.25 46 1.12 0.24 0.05 0.01 0 0 0544 80 1.25 0.5 72,600 1 x 1 10 1 8.5 4.00 99 2.15 0.79 0.26 0.07 0.02 0 0545 80 1.25 0.5 72,600 1 x 1 10 5 17.0 1.58 92 0.92 0.47 0.23 0.10 0.04 0.01 0546 80 1.25 0.5 72,600 1 x 1 10 5 8.5 2.12 172 1.41 0.89 0.55 0.33 0.18 0.06 0547 80 1.25 0.5 72,600 1 x 1 20 0.2 17.0 2.30 20 1.11 0.06 0.01 0.00 0 0 0548 80 1.25 0.5 72,600 1 x 1 20 0.2 8.5 4.50 54 2.24 0.30 0.07 0.02 0 0 0549 80 1.25 0.5 72,600 1 x 1 20 1 17.0 2.08 57 1.07 0.31 0.10 0.03 0.01 0 0550 80 1.25 0.5 72,600 1 x 1 20 1 8.5 3.46 122 1.94 0.85 0.37 0.16 0.06 0.01 0551 80 1.25 0.5 72,600 1 x 1 20 5 17.0 1.20 100 0.75 0.44 0.26 0.15 0.08 0.02 0552 80 1.25 0.5 72,600 1 x 1 20 5 8.5 1.52 189 1.06 0.72 0.50 0.34 0.23 0.1 0.01553 80 1.25 0.5 72,600 1 x 1 40 0.2 17.0 2.26 25 1.09 0.08 0.02 0.01 0 0 0554 80 1.25 0.5 72,600 1 x 1 40 0.2 8.5 4.34 62 2.17 0.39 0.10 0.04 0.02 0 0555 80 1.25 0.5 72,600 1 x 1 40 1 17.0 1.89 64 0.99 0.35 0.13 0.06 0.03 0.01 0556 80 1.25 0.5 72,600 1 x 1 40 1 8.5 2.92 138 1.69 0.83 0.42 0.22 0.11 0.03 0557 80 1.25 0.5 72,600 1 x 1 40 5 17.0 0.89 92 0.58 0.36 0.24 0.16 0.1 0.04 0.01558 80 1.25 0.5 72,600 1 x 1 40 5 8.5 1.05 172 0.75 0.52 0.38 0.29 0.21 0.12 0.04559 80 1.25 0.5 72,600 1 x 8 10 0.2 17.0 2.21 8 0.90 0.01 0.00 0.00 0 0 0560 80 1.25 0.5 72,600 1 x 8 10 0.2 8.5 4.04 28 1.93 0.10 0.01 0.00 0 0 0561 80 1.25 0.5 72,600 1 x 8 10 1 17.0 1.68 38 0.94 0.18 0.04 0.01 0 0 0562 80 1.25 0.5 72,600 1 x 8 10 1 8.5 2.55 92 1.72 0.63 0.22 0.07 0.02 0 0563 80 1.25 0.5 72,600 1 x 8 10 5 17.0 0.89 82 0.69 0.38 0.20 0.10 0.04 0.01 0564 80 1.25 0.5 72,600 1 x 8 10 5 8.5 1.15 165 0.98 0.68 0.46 0.30 0.18 0.06 0565 80 1.25 0.5 72,600 1 x 8 20 0.2 17.0 2.14 10 0.90 0.03 0.01 0.00 0 0 0566 80 1.25 0.5 72,600 1 x 8 20 0.2 8.5 3.76 39 1.87 0.19 0.05 0.02 0 0 0567 80 1.25 0.5 72,600 1 x 8 20 1 17.0 1.46 46 0.87 0.24 0.08 0.03 0.01 0 0568 80 1.25 0.5 72,600 1 x 8 20 1 8.5 2.10 115 1.49 0.68 0.32 0.15 0.06 0.01 0569 80 1.25 0.5 72,600 1 x 8 20 5 17.0 0.66 84 0.53 0.34 0.22 0.14 0.08 0.02 0570 80 1.25 0.5 72,600 1 x 8 20 5 8.5 0.80 172 0.70 0.52 0.39 0.29 0.21 0.1 0.02
50 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins Table 2. Simulated groundwater mounding beneath hypothetical stormwater-infiltration basins on a 10-acre development.—Continued [ft2, square feet; 1 x 1, square basin (sides of equal length); 1 x 8, rectangular basin (long side eight times length of short side); in/hr, inches per hour; Max, maximum; ft2, square feet; GW, groundwater; hgt, height; ft, feet; EEoB, east edge of basin] Simulation number Impervious cover (percent) Design storm (inches) Basin depth (feet) Basin area (ft2

)

Basin 

shape 

Aquifer 

thickness 

(feet)

Soil 

permeability

(in/hr)

Specific 

yield

(percent)

Max 

GW 

mound 

height

(feet)

Max 

extent 

of 0.25- 

foot GW 

mound 

hgt 

(feet)

GW 

mound 

hgt at 

EEoB

 (feet)

GW 

mound 

hgt 

50 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

150 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

200 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

300 ft 

from 

EEoB 

(feet)

GW 

mound 

hgt 

500 ft 

from 

EEoB 

(feet)

571 80 1.25 0.5 72,600 1 x 8 40 0.2 17.0 2.05 15 0.90 0.03 0.02 0.01 0 0 0572 80 1.25 0.5 72,600 1 x 8 40 0.2 8.5 3.45 51 1.83 0.26 0.08 0.04 0.02 0 0573 80 1.25 0.5 72,600 1 x 8 40 1 17.0 1.25 52 0.80 0.27 0.11 0.05 0.02 0.01 0574 80 1.25 0.5 72,600 1 x 8 40 1 8.5 1.72 129 1.27 0.64 0.35 0.20 0.11 0.04 0575 80 1.25 0.5 72,600 1 x 8 40 5 17.0 0.48 56 0.40 0.26 0.19 0.14 0.09 0.04 0.01576 80 1.25 0.5 72,600 1 x 8 40 5 8.5 0.54 122 0.47 0.35 0.28 0.22 0.17 0.11 0.04

Table 3
Table 3 51

Table 3. Simulated groundwater mounding beneath hypothetical stormwater-infiltration dry wells on a 1-acre development.—Continued[in/hr, inches per hour; Max, maximum; GW, groundwater; hgt, height; ft, feet; EEDW, east edge of dry well]

Simulation 

number

Impervious cover 

(percent)

Design 

storm 

(inches)

Basin 

depth 

(feet)

Aquifer 

thickness 

(feet)

Soil 

permeability 

(in/hr)

Specific 

yield 

(percent)

Max 

GW 

mound 

height 

(feet)

Max 

extent 

0.25-ft 

GW 

mound 

height 

(feet)

GW 

mound 

hgt at 

EEDW 

(feet)

GW 

mound 

hgt 

10 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

20 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

30 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

40 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

50 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

60 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

75 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

120 ft 

from 

EEDW

(feet)

GW 

mound 

hgt 

140 ft 

from 

EEDW 

(feet)

1 10 0.313 2 10 0.2 17 1.29 10 0.99 0.26 0.08 0.02 0.01 0 0 0 0 0 0

2 10 0.313 2 10 0.2 8.5 1.43 10 1.14 0.4 0.17 0.07 0.03 0.02 0.01 0 0 0 03 10 0.313 2 10 1 17 0.29 0.1 0.22 0.06 0.02 0.01 0 0 0 0 0 0 04 10 0.313 2 10 1 8.5 0.33 1 0.26 0.09 0.04 0.02 0.01 0.01 0 0 0 0 05 10 0.313 2 10 5 17 0.04 0 0.03 0.01 0 0 0 0 0 0 0 0 06 10 0.313 2 10 5 8.5 0.05 0 0.04 0.01 0 0 0 0 0 0 0 0 0

7 10 0.313 2 20 0.2 17 0.88 1 0.69 0.23 0.09 0.03 0.01 0 0 0 0 0 0

8 10 0.313 2 20 0.2 8.5 0.97 10 0.79 0.32 0.16 0.07 0.04 0.02 0.01 0 0 0 09 10 0.313 2 20 1 17 0.19 0 0.15 0.05 0.02 0.01 0 0 0 0 0 0 0

10 10 0.313 2 20 1 8.5 0.13 0 0.09 0.02 0 0 0 0 0 0 0 0 0

11 10 0.313 2 20 5 17 0.03 0 0.02 0 0 0 0 0 0 0 0 0 0

12 10 0.313 2 20 5 8.5 0.03 0 0.02 0.01 0 0 0 0 0 0 0 0 0

13 10 0.313 2 40 0.2 17 0.45 1 0.35 0.11 0.03 0.01 0 0 0 0 0 0 0

14 10 0.313 2 40 0.2 8.5 0.52 1 0.41 0.16 0.07 0.03 0.01 0 0 0 0 0 015 10 0.313 2 40 1 17 0.05 0 0.04 0.01 0 0 0 0 0 0 0 0 016 10 0.313 2 40 1 8.5 0.06 0 0.05 0.01 0 0 0 0 0 0 0 0 017 10 0.313 2 40 5 17 0.01 0 0.01 0 0 0 0 0 0 0 0 0 018 10 0.313 2 40 5 8.5 0.02 0 0.01 0 0 0 0 0 0 0 0 0 0

19 20 0.313 2 10 0.2 17 1.94 10 1.45 0.42 0.13 0.04 0.02 0.01 0 0 0 0 0

20 20 0.313 2 10 0.2 8.5 2.18 20 1.7 0.68 0.3 0.13 0.06 0.03 0.02 0.01 0 0 021 20 0.313 2 10 1 17 0.56 1 0.44 0.19 0.11 0.06 0.04 0.03 0.02 0.01 0 0 022 20 0.313 2 10 1 8.5 0.6 1 0.48 0.23 0.15 0.1 0.07 0.05 0.04 0.02 0.01 0.01 023 20 0.313 2 10 5 17 0.07 0 0.05 0.01 0 0 0 0 0 0 0 0 024 20 0.313 2 10 5 8.5 0.08 0 0.06 0.02 0.01 0 0 0 0 0 0 0 0

25 20 0.313 2 20 0.2 17 1.4 10 1.07 0.39 0.15 0.05 0.02 0.01 0 0 0 0 0

26 20 0.313 2 20 0.2 8.5 1.58 20 1.25 0.56 0.29 0.14 0.07 0.04 0.02 0.01 0 0 027 20 0.313 2 20 1 17 0.28 0.1 0.21 0.07 0.02 0.01 0 0 0 0 0 0 028 20 0.313 2 20 1 8.5 0.35 1 0.27 0.12 0.07 0.04 0.02 0.01 0.01 0 0 0 029 20 0.313 2 20 5 17 0.04 0 0.03 0.01 0 0 0 0 0 0 0 0 030 20 0.313 2 20 5 8.5 0.05 0 0.04 0.01 0.01 0 0 0 0 0 0 0 0

31 20 0.313 2 40 0.2 17 0.9 10 0.71 0.31 0.15 0.07 0.03 0.01 0.01 0 0 0 0
52 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins Table 3. Simulated groundwater mounding beneath hypothetical stormwater-infiltration dry wells on a 1-acre development.—Continued [in/hr, inches per hour; Max, maximum; GW, groundwater; hgt, height; ft, feet; EEDW, east edge of dry well] Simula- tion number Impervi- ous cover (percent) Design storm (inches) Basin depth (feet) Aquifer thick- ness (feet) Soil perm- eability (in/hr) Specific yield (percent) Max GW mound height (feet) Max extent 0.25-ft GW mound height (feet) GW mound hgt at EEDW (feet) GW mound hgt 10 ft from EEDW (feet) GW mound hgt 20 ft from EEDW (feet) GW mound hgt 30 ft from EEDW (feet) GW mound hgt 40 ft from EEDW (feet) GW mound hgt 50 ft from EEDW (feet) GW mound hgt 60 ft from EEDW (feet) GW mound hgt 75 ft from EEDW (feet) GW mound hgt 100 ft from EEDW (feet) GW mound hgt 120 ft from EEDW (feet) GW mound hgt 140 ft from EEDW (feet) 32 20 0.313 2 40 0.2 8.5 1.02 20 0.83 0.43 0.25 0.14 0.09 0.05 0.03 0.01 0 0 0 33 20 0.313 2 40 1 17 0.13 0 0.1 0.03 0.01 0 0 0 0 0 0 0 0 34 20 0.313 2 40 1 8.5 0.16 0 0.13 0.05 0.02 0.01 0 0 0 0 0 0 0 35 20 0.313 2 40 5 17 0.02 0 0.02 0.01 0 0 0 0 0 0 0 0 0 36 20 0.313 2 40 5 8.5 0.03 0 0.02 0.01 0 0 0 0 0 0 0 0 0 37 40 0.313 2 10 0.2 17 2.83 10 2.07 0.69 0.22 0.07 0.03 0.01 0.01 0 0 0 0 38 40 0.313 2 10 0.2 8.5 3.23 25 2.51 1.14 0.54 0.24 0.12 0.07 0.04 0.02 0 0 0 39 40 0.313 2 10 1 17 0.89 10 0.69 0.34 0.2 0.12 0.08 0.05 0.04 0.02 0.01 0 0 40 40 0.313 2 10 1 8.5 0.98 20 0.77 0.43 0.29 0.2 0.15 0.11 0.08 0.05 0.03 0.01 0.01 41 40 0.313 2 10 5 17 0.2 0 0.15 0.08 0.05 0.03 0.02 0.02 0.01 0.01 0 0 0 42 40 0.313 2 10 5 8.5 0.2 0 0.15 0.08 0.05 0.03 0.03 0.02 0.01 0.01 0 0 0 43 40 0.313 2 20 0.2 17 2.16 20 1.61 0.64 0.26 0.09 0.03 0.01 0.01 0 0 0 0 44 40 0.313 2 20 0.2 8.5 2.48 30 1.93 0.96 0.51 0.25 0.13 0.07 0.04 0.02 0.01 0 0 45 40 0.313 2 20 1 17 0.59 1 0.45 0.23 0.13 0.08 0.05 0.03 0.02 0.01 0 0 0 46 40 0.313 2 20 1 8.5 0.62 10 0.49 0.26 0.16 0.1 0.07 0.05 0.03 0.02 0.01 0 0 47 40 0.313 2 20 5 17 0.07 0 0.04 0.01 0.01 0 0 0 0 0 0 0 0 48 40 0.313 2 20 5 8.5 0.08 0 0.05 0.02 0.01 0 0 0 0 0 0 0 0 49 40 0.313 2 40 0.2 17 1.47 20 1.13 0.54 0.28 0.12 0.06 0.03 0.01 0 0 0 0 50 40 0.313 2 40 0.2 8.5 1.69 30 1.35 0.75 0.45 0.26 0.16 0.09 0.06 0.02 0.01 0 0 51 40 0.313 2 40 1 17 0.23 0 0.16 0.05 0.02 0 0 0 0 0 0 0 0 52 40 0.313 2 40 1 8.5 0.34 1 0.27 0.14 0.09 0.05 0.02 0.01 0 0 0 0 0 53 40 0.313 2 40 5 17 0.04 0 0.03 0.01 0 0 0 0 0 0 0 0 0

54 40 0.313 2 40 5 8.5 0.05 0 0.03 0.02 0.01 0 0 0 0 0 0 0 0

55 80 0.313 2 10 0.2 17 4.09 20 2.89 1.12 0.38 0.13 0.06 0.03 0.02 0.01 0 0 0

56 80 0.313 2 10 0.2 8.5 4.84 30 3.69 1.92 0.97 0.45 0.23 0.13 0.07 0.03 0.01 0 057 80 0.313 2 10 1 17 1.44 25 1.09 0.61 0.37 0.23 0.15 0.1 0.07 0.04 0.01 0.01 058 80 0.313 2 10 1 8.5 1.6 40 1.25 0.78 0.54 0.38 0.29 0.22 0.17 0.11 0.05 0.03 0.0259 80 0.313 2 10 5 17 0.33 1 0.25 0.14 0.09 0.06 0.04 0.03 0.02 0.01 0.01 0 060 80 0.313 2 10 5 8.5 0.39 1 0.3 0.2 0.15 0.11 0.09 0.08 0.07 0.05 0.03 0.02 0.02

61 80 0.313 2 20 0.2 17 3.34 25 2.39 1.05 0.44 0.15 0.06 0.03 0.02 0.01 0 0 0

62 80 0.313 2 20 0.2 8.5 3.94 40 3 1.64 0.9 0.46 0.25 0.14 0.08 0.04 0.02 0.01 0
Table 3 53

Table 3. Simulated groundwater mounding beneath hypothetical stormwater-infiltration dry wells on a 1-acre development.—Continued[in/hr, inches per hour; Max, maximum; GW, groundwater; hgt, height; ft, feet; EEDW, east edge of dry well]

Simulation 

number

Impervious cover 

(percent)

Design 

storm 

(inches)

Basin 

depth 

(feet)

Aquifer 

thickness 

(feet)

Soil 

permeability 

(in/hr)

Specific 

yield 

(percent)

Max 

GW 

mound 

height 

(feet)

Max 

extent 

0.25-ft 

GW 

mound 

height 

(feet)

GW 

mound 

hgt at 

EEDW 

(feet)

GW 

mound 

hgt 

10 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

20 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

30 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

40 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

50 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

60 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

75 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

120 ft 

from 

EEDW

(feet)

GW 

mound 

hgt 

140 ft 

from 

EEDW 

(feet)

63 80 0.313 2 20 1 17 1.05 20 0.8 0.48 0.31 0.2 0.13 0.09 0.07 0.04 0.02 0.01 0.01

64 80 0.313 2 20 1 8.5 1.15 30 0.91 0.58 0.41 0.29 0.22 0.18 0.14 0.1 0.06 0.04 0.0365 80 0.313 2 20 5 17 0.18 0 0.13 0.06 0.03 0.01 0.01 0 0 0 0 0 066 80 0.313 2 20 5 8.5 0.21 0 0.16 0.09 0.06 0.03 0.02 0.01 0.01 0 0 0 0

67 80 0.313 2 40 0.2 17 2.42 25 1.8 0.93 0.48 0.22 0.1 0.05 0.02 0.01 0 0 0

68 80 0.313 2 40 0.2 8.5 2.85 40 2.22 1.33 0.83 0.49 0.3 0.18 0.11 0.05 0.02 0.01 0.0169 80 0.313 2 40 1 17 0.65 10 0.5 0.31 0.2 0.13 0.08 0.06 0.04 0.02 0.01 0 070 80 0.313 2 40 1 8.5 0.7 20 0.56 0.36 0.25 0.17 0.13 0.09 0.07 0.04 0.02 0.01 0.0171 80 0.313 2 40 5 17 0.07 0 0.04 0.02 0.01 0 0 0 0 0 0 0 072 80 0.313 2 40 5 8.5 0.08 0 0.06 0.03 0.01 0.01 0 0 0 0 0 0 0

73 10 1.25 2 10 0.2 17 2.83 10 2.07 0.69 0.22 0.07 0.03 0.01 0.01 0 0 0 0

74 10 1.25 2 10 0.2 8.5 3.23 25 2.51 1.14 0.54 0.24 0.12 0.07 0.04 0.02 0 0 075 10 1.25 2 10 1 17 0.89 10 0.69 0.34 0.2 0.12 0.08 0.05 0.04 0.02 0.01 0 076 10 1.25 2 10 1 8.5 0.98 20 0.77 0.43 0.29 0.2 0.15 0.11 0.08 0.05 0.03 0.01 0.0177 10 1.25 2 10 5 17 0.2 0 0.15 0.08 0.05 0.03 0.02 0.02 0.01 0.01 0 0 078 10 1.25 2 10 5 8.5 0.2 0 0.15 0.08 0.05 0.03 0.03 0.02 0.01 0.01 0 0 0

79 10 1.25 2 20 0.2 17 2.16 20 1.61 0.64 0.26 0.09 0.03 0.01 0.01 0 0 0 0

80 10 1.25 2 20 0.2 8.5 2.48 30 1.93 0.96 0.51 0.25 0.13 0.07 0.04 0.02 0.01 0 081 10 1.25 2 20 1 17 0.59 1 0.45 0.23 0.13 0.08 0.05 0.03 0.02 0.01 0 0 082 10 1.25 2 20 1 8.5 0.62 10 0.49 0.26 0.16 0.1 0.07 0.05 0.03 0.02 0.01 0 083 10 1.25 2 20 5 17 0.07 0 0.04 0.01 0.01 0 0 0 0 0 0 0 084 10 1.25 2 20 5 8.5 0.08 0 0.05 0.02 0.01 0 0 0 0 0 0 0 0

85 10 1.25 2 40 0.2 17 1.47 20 1.13 0.54 0.28 0.12 0.06 0.03 0.01 0 0 0 0

86 10 1.25 2 40 0.2 8.5 1.69 30 1.35 0.75 0.45 0.26 0.16 0.09 0.06 0.02 0.01 0 087 10 1.25 2 40 1 17 0.23 0 0.16 0.05 0.02 0 0 0 0 0 0 0 088 10 1.25 2 40 1 8.5 0.34 1 0.27 0.14 0.09 0.05 0.02 0.01 0 0 0 0 089 10 1.25 2 40 5 17 0.04 0 0.03 0.01 0 0 0 0 0 0 0 0 090 10 1.25 2 40 5 8.5 0.05 0 0.03 0.02 0.01 0 0 0 0 0 0 0 0

91 20 1.25 2 10 0.2 17 4.09 20 2.89 1.12 0.38 0.13 0.06 0.03 0.02 0.01 0 0 0

92 20 1.25 2 10 0.2 8.5 4.84 30 3.69 1.92 0.97 0.45 0.23 0.13 0.07 0.03 0.01 0 093 20 1.25 2 10 1 17 1.44 25 1.09 0.61 0.37 0.23 0.15 0.1 0.07 0.04 0.01 0.01 0
54 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins Table 3. Simulated groundwater mounding beneath hypothetical stormwater-infiltration dry wells on a 1-acre development.—Continued [in/hr, inches per hour; Max, maximum; GW, groundwater; hgt, height; ft, feet; EEDW, east edge of dry well] Simula- tion number Impervi- ous cover (percent) Design storm (inches) Basin depth (feet) Aquifer thick- ness (feet) Soil perm- eability (in/hr) Specific yield (percent) Max GW mound height (feet) Max extent 0.25-ft GW mound height (feet) GW mound hgt at EEDW (feet) GW mound hgt 10 ft from EEDW (feet) GW mound hgt 20 ft from EEDW (feet) GW mound hgt 30 ft from EEDW (feet) GW mound hgt 40 ft from EEDW (feet) GW mound hgt 50 ft from EEDW (feet) GW mound hgt 60 ft from EEDW (feet) GW mound hgt 75 ft from EEDW (feet) GW mound hgt 100 ft from EEDW (feet) GW mound hgt 120 ft from EEDW (feet) GW mound hgt 140 ft from EEDW (feet) 94 20 1.25 2 10 1 8.5 1.6 40 1.25 0.78 0.54 0.38 0.29 0.22 0.17 0.11 0.05 0.03 0.02 95 20 1.25 2 10 5 17 0.33 1 0.25 0.14 0.09 0.06 0.04 0.03 0.02 0.01 0.01 0 0 96 20 1.25 2 10 5 8.5 0.39 1 0.3 0.2 0.15 0.11 0.09 0.08 0.07 0.05 0.03 0.02 0.02 97 20 1.25 2 20 0.2 17 3.34 25 2.39 1.05 0.44 0.15 0.06 0.03 0.02 0.01 0 0 0 98 20 1.25 2 20 0.2 8.5 3.94 40 3 1.64 0.9 0.46 0.25 0.14 0.08 0.04 0.02 0.01 0 99 20 1.25 2 20 1 17 1.05 20 0.8 0.48 0.31 0.2 0.13 0.09 0.07 0.04 0.02 0.01 0.01 100 20 1.25 2 20 1 8.5 1.15 30 0.91 0.58 0.41 0.29 0.22 0.18 0.14 0.1 0.06 0.04 0.03 101 20 1.25 2 20 5 17 0.18 0 0.13 0.06 0.03 0.01 0.01 0 0 0 0 0 0 102 20 1.25 2 20 5 8.5 0.21 0 0.16 0.09 0.06 0.03 0.02 0.01 0.01 0 0 0 0 103 20 1.25 2 40 0.2 17 2.42 25 1.8 0.93 0.48 0.22 0.1 0.05 0.02 0.01 0 0 0 104 20 1.25 2 40 0.2 8.5 2.85 40 2.22 1.33 0.83 0.49 0.3 0.18 0.11 0.05 0.02 0.01 0.01 105 20 1.25 2 40 1 17 0.65 10 0.5 0.31 0.2 0.13 0.08 0.06 0.04 0.02 0.01 0 0 106 20 1.25 2 40 1 8.5 0.7 20 0.56 0.36 0.25 0.17 0.13 0.09 0.07 0.04 0.02 0.01 0.01 107 20 1.25 2 40 5 17 0.07 0 0.04 0.02 0.01 0 0 0 0 0 0 0 0 108 20 1.25 2 40 5 8.5 0.08 0 0.06 0.03 0.01 0.01 0 0 0 0 0 0 0 109 40 1.25 2 10 0.2 17 5.48 25 3.72 1.59 0.58 0.2 0.09 0.05 0.03 0.01 0 0 0 110 40 1.25 2 10 0.2 8.5 6.74 40 5.02 2.88 1.56 0.74 0.39 0.21 0.12 0.05 0.02 0.01 0 111 40 1.25 2 10 1 17 2.13 40 1.58 0.97 0.62 0.39 0.26 0.18 0.12 0.06 0.02 0.01 0 112 40 1.25 2 10 1 8.5 2.43 60 1.89 1.28 0.93 0.67 0.51 0.39 0.3 0.2 0.1 0.05 0.03 113 40 1.25 2 10 5 17 0.62 20 0.48 0.34 0.27 0.21 0.17 0.15 0.12 0.09 0.06 0.04 0.03 114 40 1.25 2 10 5 8.5 0.68 30 0.55 0.41 0.33 0.27 0.24 0.21 0.18 0.15 0.11 0.09 0.07

115 40 1.25 2 20 0.2 17 4.67 30 3.2 1.53 0.67 0.25 0.11 0.05 0.03 0.02 0.01 0 0

116 40 1.25 2 20 0.2 8.5 5.68 50 4.22 2.51 1.46 0.77 0.43 0.25 0.15 0.08 0.03 0.02 0.01117 40 1.25 2 20 1 17 1.63 30 1.22 0.78 0.52 0.34 0.24 0.17 0.12 0.07 0.04 0.02 0.01118 40 1.25 2 20 1 8.5 1.81 60 1.41 0.97 0.71 0.52 0.4 0.32 0.26 0.18 0.11 0.07 0.05119 40 1.25 2 20 5 17 0.37 1 0.28 0.18 0.13 0.09 0.07 0.05 0.04 0.03 0.02 0.01 0.01

120 40 1.25 2 20 5 8.5 0.39 1 0.3 0.2 0.15 0.11 0.08 0.07 0.05 0.04 0.02 0.02 0.01

121 40 1.25 2 40 0.2 17 3.62 30 2.56 1.4 0.75 0.35 0.16 0.08 0.04 0.01 0.01 0 0

122 40 1.25 2 40 0.2 8.5 4.38 50 3.31 2.1 1.35 0.81 0.5 0.3 0.19 0.09 0.03 0.02 0.01123 40 1.25 2 40 1 17 1.14 30 0.88 0.61 0.43 0.3 0.22 0.16 0.12 0.08 0.04 0.02 0.01124 40 1.25 2 40 1 8.5 1.26 50 1.01 0.73 0.55 0.42 0.33 0.27 0.22 0.16 0.1 0.07 0.05
Table 3 55

Table 3. Simulated groundwater mounding beneath hypothetical stormwater-infiltration dry wells on a 1-acre development.—Continued[in/hr, inches per hour; Max, maximum; GW, groundwater; hgt, height; ft, feet; EEDW, east edge of dry well]

Simulation 

number

Impervious cover 

(percent)

Design 

storm 

(inches)

Basin 

depth 

(feet)

Aquifer 

thickness 

(feet)

Soil 

permeability 

(in/hr)

Specific 

yield 

(percent)

Max 

GW 

mound 

height 

(feet)

Max 

extent 

0.25-ft 

GW 

mound 

height 

(feet)

GW 

mound 

hgt at 

EEDW 

(feet)

GW 

mound 

hgt 

10 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

20 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

30 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

40 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

50 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

60 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

75 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

120 ft 

from 

EEDW

(feet)

GW 

mound 

hgt 

140 ft 

from 

EEDW 

(feet)

125 40 1.25 2 40 5 17 0.19 0 0.13 0.08 0.05 0.03 0.02 0.01 0 0 0 0 0

126 40 1.25 2 40 5 8.5 0.23 0 0.18 0.13 0.09 0.07 0.05 0.04 0.03 0.02 0.01 0 0

127 80 1.25 2 10 0.2 17 7.17 30 4.58 2.12 0.83 0.29 0.14 0.07 0.04 0.02 0 0 0

128 80 1.25 2 10 0.2 8.5 9.31 50 6.67 4.16 2.4 1.2 0.64 0.35 0.2 0.09 0.03 0.01 0129 80 1.25 2 10 1 17 3.14 50 2.26 1.5 1.01 0.66 0.45 0.31 0.21 0.12 0.05 0.02 0.01130 80 1.25 2 10 1 8.5 3.67 80 2.82 2.07 1.57 1.17 0.9 0.7 0.54 0.36 0.19 0.11 0.06131 80 1.25 2 10 5 17 1 50 0.78 0.59 0.48 0.38 0.32 0.27 0.23 0.18 0.12 0.08 0.06132 80 1.25 2 10 5 8.5 1.12 80 0.9 0.72 0.6 0.51 0.44 0.39 0.35 0.29 0.21 0.17 0.13

133 80 1.25 2 20 0.2 17 6.37 30 4.09 2.09 0.97 0.38 0.17 0.09 0.05 0.03 0.01 0.01 0

134 80 1.25 2 20 0.2 8.5 8.13 60 5.8 3.7 2.27 1.25 0.72 0.42 0.26 0.13 0.06 0.03 0.02135 80 1.25 2 20 1 17 2.49 50 1.8 1.23 0.86 0.58 0.41 0.29 0.21 0.13 0.06 0.04 0.02136 80 1.25 2 20 1 8.5 2.86 80 2.17 1.6 1.22 0.92 0.73 0.58 0.47 0.34 0.21 0.14 0.09137 80 1.25 2 20 5 17 0.7 30 0.54 0.41 0.33 0.26 0.22 0.19 0.16 0.13 0.09 0.07 0.06138 80 1.25 2 20 5 8.5 0.77 50 0.61 0.48 0.39 0.33 0.29 0.25 0.23 0.19 0.15 0.13 0.11

139 80 1.25 2 40 0.2 17 5.26 40 3.48 2 1.1 0.53 0.26 0.13 0.07 0.03 0.01 0.01 0.01

140 80 1.25 2 40 0.2 8.5 6.6 60 4.77 3.21 2.14 1.32 0.84 0.53 0.34 0.17 0.07 0.04 0.02141 80 1.25 2 40 1 17 1.85 50 1.37 0.99 0.73 0.52 0.39 0.29 0.22 0.14 0.07 0.04 0.03142 80 1.25 2 40 1 8.5 2.09 80 1.62 1.23 0.96 0.75 0.6 0.49 0.4 0.3 0.19 0.14 0.1143 80 1.25 2 40 5 17 0.42 1 0.32 0.23 0.18 0.14 0.11 0.09 0.07 0.05 0.03 0.02 0.01144 80 1.25 2 40 5 8.5 0.46 10 0.36 0.28 0.22 0.18 0.15 0.13 0.11 0.08 0.06 0.05 0.04

145 10 0.313 4 10 0.2 17 1.43 10 1.14 0.28 0.08 0.02 0.01 0 0 0 0 0 0

146 10 0.313 4 10 0.2 8.5 1.55 10 1.27 0.41 0.17 0.07 0.03 0.02 0.01 0 0 0 0147 10 0.313 4 10 1 17 0.34 1 0.27 0.07 0.03 0.01 0 0 0 0 0 0 0148 10 0.313 4 10 1 8.5 0.37 1 0.3 0.1 0.05 0.03 0.02 0.01 0.01 0 0 0 0149 10 0.313 4 10 5 17 0.05 0 0.04 0.01 0 0 0 0 0 0 0 0 0150 10 0.313 4 10 5 8.5 0.06 0 0.04 0.01 0 0 0 0 0 0 0 0 0

151 10 0.313 4 20 0.2 17 0.95 1 0.77 0.24 0.09 0.03 0.01 0 0 0 0 0 0

152 10 0.313 4 20 0.2 8.5 1.04 10 0.86 0.32 0.16 0.07 0.04 0.02 0.01 0 0 0 0153 10 0.313 4 20 1 17 0.18 0 0.14 0.03 0.01 0 0 0 0 0 0 0 0154 10 0.313 4 20 1 8.5 0.2 0 0.16 0.05 0.02 0 0 0 0 0 0 0 0155 10 0.313 4 20 5 17 0.03 0 0.02 0 0 0 0 0 0 0 0 0 0
56 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins Table 3. Simulated groundwater mounding beneath hypothetical stormwater-infiltration dry wells on a 1-acre development.—Continued [in/hr, inches per hour; Max, maximum; GW, groundwater; hgt, height; ft, feet; EEDW, east edge of dry well] Simula- tion number Impervi- ous cover (percent) Design storm (inches) Basin depth (feet) Aquifer thick- ness (feet) Soil perm- eability (in/hr) Specific yield (percent) Max GW mound height (feet) Max extent 0.25-ft GW mound height (feet) GW mound hgt at EEDW (feet) GW mound hgt 10 ft from EEDW (feet) GW mound hgt 20 ft from EEDW (feet) GW mound hgt 30 ft from EEDW (feet) GW mound hgt 40 ft from EEDW (feet) GW mound hgt 50 ft from EEDW (feet) GW mound hgt 60 ft from EEDW (feet) GW mound hgt 75 ft from EEDW (feet) GW mound hgt 100 ft from EEDW (feet) GW mound hgt 120 ft from EEDW (feet) GW mound hgt 140 ft from EEDW (feet) 156 10 0.313 4 20 5 8.5 0.03 0 0.02 0.01 0 0 0 0 0 0 0 0 0 157 10 0.313 4 40 0.2 17 0.4 1 0.3 0.05 0.01 0 0 0 0 0 0 0 0 158 10 0.313 4 40 0.2 8.5 0.56 1 0.46 0.17 0.07 0.03 0.01 0 0 0 0 0 0 159 10 0.313 4 40 1 17 0.06 0 0.05 0.01 0 0 0 0 0 0 0 0 0 160 10 0.313 4 40 1 8.5 0.08 0 0.06 0.01 0 0 0 0 0 0 0 0 0 161 10 0.313 4 40 5 17 0.02 0 0.01 0 0 0 0 0 0 0 0 0 0 162 10 0.313 4 40 5 8.5 0.02 0 0.01 0 0 0 0 0 0 0 0 0 0 163 20 0.313 4 10 0.2 17 2.29 10 1.82 0.52 0.16 0.04 0.02 0.01 0 0 0 0 0 164 20 0.313 4 10 0.2 8.5 2.52 20 2.07 0.78 0.35 0.14 0.07 0.04 0.02 0.01 0 0 0 165 20 0.313 4 10 1 17 0.65 1 0.52 0.21 0.11 0.06 0.04 0.03 0.02 0.01 0 0 0 166 20 0.313 4 10 1 8.5 0.67 1 0.54 0.22 0.13 0.08 0.05 0.03 0.02 0.01 0 0 0 167 20 0.313 4 10 5 17 0.09 0 0.06 0.01 0 0 0 0 0 0 0 0 0 168 20 0.313 4 10 5 8.5 0.1 0 0.07 0.02 0.01 0 0 0 0 0 0 0 0 169 20 0.313 4 20 0.2 17 1.64 10 1.32 0.46 0.18 0.06 0.02 0.01 0 0 0 0 0 170 20 0.313 4 20 0.2 8.5 1.81 20 1.49 0.64 0.32 0.15 0.08 0.04 0.02 0.01 0 0 0 171 20 0.313 4 20 1 17 0.36 1 0.29 0.1 0.04 0.01 0 0 0 0 0 0 0 172 20 0.313 4 20 1 8.5 0.33 1 0.26 0.08 0.03 0.01 0 0 0 0 0 0 0 173 20 0.313 4 20 5 17 0.05 0 0.04 0.01 0 0 0 0 0 0 0 0 0 174 20 0.313 4 20 5 8.5 0.06 0 0.04 0.01 0.01 0 0 0 0 0 0 0 0 175 20 0.313 4 40 0.2 17 1.04 10 0.85 0.36 0.17 0.08 0.04 0.02 0.01 0 0 0 0 176 20 0.313 4 40 0.2 8.5 1.15 20 0.96 0.47 0.27 0.15 0.09 0.05 0.03 0.01 0 0 0

177 20 0.313 4 40 1 17 0.16 0 0.12 0.03 0.01 0 0 0 0 0 0 0 0178 20 0.313 4 40 1 8.5 0.19 0 0.15 0.06 0.03 0.01 0 0 0 0 0 0 0179 20 0.313 4 40 5 17 0.03 0 0.02 0.01 0 0 0 0 0 0 0 0 0180 20 0.313 4 40 5 8.5 0.03 0 0.02 0.01 0 0 0 0 0 0 0 0 0

181 40 0.313 4 10 0.2 17 3.46 20 2.7 0.91 0.29 0.09 0.04 0.02 0.01 0 0 0 0

182 40 0.313 4 10 0.2 8.5 3.86 30 3.13 1.38 0.65 0.29 0.15 0.08 0.04 0.02 0.01 0 0183 40 0.313 4 10 1 17 1.09 10 0.86 0.4 0.23 0.14 0.09 0.06 0.04 0.02 0.01 0 0184 40 0.313 4 10 1 8.5 1.17 25 0.95 0.49 0.32 0.22 0.16 0.12 0.09 0.06 0.03 0.02 0.01185 40 0.313 4 10 5 17 0.23 0 0.17 0.07 0.04 0.02 0.01 0.01 0 0 0 0 0186 40 0.313 4 10 5 8.5 0.24 0 0.19 0.09 0.05 0.03 0.02 0.02 0.01 0.01 0 0 0
Table 3 57

Table 3. Simulated groundwater mounding beneath hypothetical stormwater-infiltration dry wells on a 1-acre development.—Continued[in/hr, inches per hour; Max, maximum; GW, groundwater; hgt, height; ft, feet; EEDW, east edge of dry well]

Simulation 

number

Impervious cover 

(percent)

Design 

storm 

(inches)

Basin 

depth 

(feet)

Aquifer 

thickness 

(feet)

Soil 

permeability 

(in/hr)

Specific 

yield 

(percent)

Max 

GW 

mound 

height 

(feet)

Max 

extent 

0.25-ft 

GW 

mound 

height 

(feet)

GW 

mound 

hgt at 

EEDW 

(feet)

GW 

mound 

hgt 

10 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

20 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

30 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

40 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

50 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

60 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

75 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

120 ft 

from 

EEDW

(feet)

GW 

mound 

hgt 

140 ft 

from 

EEDW 

(feet)

187 40 0.313 4 20 0.2 17 2.64 20 2.07 0.8 0.32 0.11 0.04 0.02 0.01 0 0 0 0

188 40 0.313 4 20 0.2 8.5 2.96 30 2.4 1.14 0.6 0.29 0.15 0.08 0.05 0.02 0.01 0 0189 40 0.313 4 20 1 17 0.68 1 0.54 0.24 0.13 0.06 0.03 0.02 0.01 0.01 0 0 0190 40 0.313 4 20 1 8.5 0.75 10 0.61 0.31 0.19 0.12 0.08 0.06 0.04 0.02 0.01 0.01 0191 40 0.313 4 20 5 17 0.09 0 0.06 0.02 0.01 0 0 0 0 0 0 0 0192 40 0.313 4 20 5 8.5 0.1 0 0.08 0.03 0.01 0 0 0 0 0 0 0 0

193 40 0.313 4 40 0.2 17 1.77 20 1.42 0.65 0.33 0.15 0.07 0.03 0.01 0 0 0 0

194 40 0.313 4 40 0.2 8.5 1.99 30 1.64 0.87 0.52 0.3 0.18 0.11 0.07 0.03 0.01 0 0195 40 0.313 4 40 1 17 0.34 1 0.26 0.11 0.05 0.02 0.01 0 0 0 0 0 0196 40 0.313 4 40 1 8.5 0.38 1 0.31 0.14 0.08 0.04 0.02 0.01 0 0 0 0 0197 40 0.313 4 40 5 17 0.05 0 0.04 0.01 0.01 0 0 0 0 0 0 0 0198 40 0.313 4 40 5 8.5 0.06 0 0.05 0.02 0.01 0 0 0 0 0 0 0 0

199 80 0.313 4 10 0.2 17 5.04 25 3.84 1.5 0.51 0.16 0.07 0.03 0.02 0.01 0 0 0

200 80 0.313 4 10 0.2 8.5 5.71 40 4.58 2.34 1.18 0.54 0.27 0.15 0.08 0.04 0.01 0 0201 80 0.313 4 10 1 17 1.73 30 1.35 0.71 0.42 0.26 0.17 0.11 0.07 0.04 0.01 0.01 0202 80 0.313 4 10 1 8.5 1.88 40 1.51 0.88 0.59 0.41 0.31 0.23 0.18 0.12 0.06 0.03 0.02203 80 0.313 4 10 5 17 0.42 1 0.33 0.18 0.12 0.08 0.06 0.05 0.04 0.02 0.01 0.01 0204 80 0.313 4 10 5 8.5 0.44 1 0.35 0.2 0.14 0.1 0.08 0.07 0.05 0.04 0.02 0.01 0.01

205 80 0.313 4 20 0.2 17 4.09 25 3.12 1.35 0.56 0.19 0.08 0.03 0.02 0.01 0 0 0

206 80 0.313 4 20 0.2 8.5 4.65 40 3.71 1.96 1.07 0.54 0.29 0.16 0.09 0.04 0.02 0.01 0.01207 80 0.313 4 20 1 17 1.24 25 0.99 0.55 0.35 0.22 0.15 0.1 0.07 0.04 0.02 0.01 0.01208 80 0.313 4 20 1 8.5 1.34 30 1.09 0.65 0.45 0.31 0.24 0.19 0.15 0.1 0.06 0.04 0.03209 80 0.313 4 20 5 17 0.22 0 0.17 0.08 0.04 0.02 0.01 0 0 0 0 0 0210 80 0.313 4 20 5 8.5 0.25 0.1 0.19 0.1 0.06 0.04 0.02 0.01 0.01 0.01 0 0 0

211 80 0.313 4 40 0.2 17 2.91 30 2.27 1.13 0.58 0.26 0.12 0.06 0.02 0.01 0 0 0

212 80 0.313 4 40 0.2 8.5 3.32 40 2.68 1.53 0.94 0.55 0.34 0.2 0.12 0.05 0.02 0.01 0.01213 80 0.313 4 40 1 17 0.77 10 0.62 0.37 0.24 0.15 0.1 0.07 0.05 0.03 0.01 0.01 0214 80 0.313 4 40 1 8.5 0.84 25 0.69 0.44 0.31 0.22 0.16 0.12 0.09 0.06 0.04 0.02 0.01215 80 0.313 4 40 5 17 0.08 0 0.06 0.02 0.01 0 0 0 0 0 0 0 0216 80 0.313 4 40 5 8.5 0.1 0 0.08 0.03 0.02 0.01 0 0 0 0 0 0 0
58 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins Table 3. Simulated groundwater mounding beneath hypothetical stormwater-infiltration dry wells on a 1-acre development.—Continued [in/hr, inches per hour; Max, maximum; GW, groundwater; hgt, height; ft, feet; EEDW, east edge of dry well] Simula- tion number Impervi- ous cover (percent) Design storm (inches) Basin depth (feet) Aquifer thick- ness (feet) Soil perm- eability (in/hr) Specific yield (percent) Max GW mound height (feet) Max extent 0.25-ft GW mound height (feet) GW mound hgt at EEDW (feet) GW mound hgt 10 ft from EEDW (feet) GW mound hgt 20 ft from EEDW (feet) GW mound hgt 30 ft from EEDW (feet) GW mound hgt 40 ft from EEDW (feet) GW mound hgt 50 ft from EEDW (feet) GW mound hgt 60 ft from EEDW (feet) GW mound hgt 75 ft from EEDW (feet) GW mound hgt 100 ft from EEDW (feet) GW mound hgt 120 ft from EEDW (feet) GW mound hgt 140 ft from EEDW (feet) 217 10 1.25 4 10 0.2 17 3.46 20 2.7 0.91 0.29 0.09 0.04 0.02 0.01 0 0 0 0 218 10 1.25 4 10 0.2 8.5 3.86 30 3.13 1.38 0.65 0.29 0.15 0.08 0.04 0.02 0.01 0 0 219 10 1.25 4 10 1 17 1.09 10 0.86 0.4 0.23 0.14 0.09 0.06 0.04 0.02 0.01 0 0 220 10 1.25 4 10 1 8.5 1.17 25 0.95 0.49 0.32 0.22 0.16 0.12 0.09 0.06 0.03 0.02 0.01 221 10 1.25 4 10 5 17 0.23 0 0.17 0.07 0.04 0.02 0.01 0.01 0 0 0 0 0 222 10 1.25 4 10 5 8.5 0.24 0 0.19 0.09 0.05 0.03 0.02 0.02 0.01 0.01 0 0 0 223 10 1.25 4 20 0.2 17 2.64 20 2.07 0.8 0.32 0.11 0.04 0.02 0.01 0 0 0 0 224 10 1.25 4 20 0.2 8.5 2.96 30 2.4 1.14 0.6 0.29 0.15 0.08 0.05 0.02 0.01 0 0 225 10 1.25 4 20 1 17 0.68 1 0.54 0.24 0.13 0.06 0.03 0.02 0.01 0.01 0 0 0 226 10 1.25 4 20 1 8.5 0.75 10 0.61 0.31 0.19 0.12 0.08 0.06 0.04 0.02 0.01 0.01 0 227 10 1.25 4 20 5 17 0.09 0 0.06 0.02 0.01 0 0 0 0 0 0 0 0 228 10 1.25 4 20 5 8.5 0.1 0 0.08 0.03 0.01 0 0 0 0 0 0 0 0 229 10 1.25 4 40 0.2 17 1.77 20 1.42 0.65 0.33 0.15 0.07 0.03 0.01 0 0 0 0 230 10 1.25 4 40 0.2 8.5 1.99 30 1.64 0.87 0.52 0.3 0.18 0.11 0.07 0.03 0.01 0 0 231 10 1.25 4 40 1 17 0.34 1 0.26 0.11 0.05 0.02 0.01 0 0 0 0 0 0 232 10 1.25 4 40 1 8.5 0.38 1 0.31 0.14 0.08 0.04 0.02 0.01 0 0 0 0 0 233 10 1.25 4 40 5 17 0.05 0 0.04 0.01 0.01 0 0 0 0 0 0 0 0 234 10 1.25 4 40 5 8.5 0.06 0 0.05 0.02 0.01 0 0 0 0 0 0 0 0 235 20 1.25 4 10 0.2 17 5.04 25 3.84 1.5 0.51 0.16 0.07 0.03 0.02 0.01 0 0 0 236 20 1.25 4 10 0.2 8.5 5.71 40 4.58 2.34 1.18 0.54 0.27 0.15 0.08 0.04 0.01 0 0 237 20 1.25 4 10 1 17 1.73 30 1.35 0.71 0.42 0.26 0.17 0.11 0.07 0.04 0.01 0.01 0 238 20 1.25 4 10 1 8.5 1.88 40 1.51 0.88 0.59 0.41 0.31 0.23 0.18 0.12 0.06 0.03 0.02

239 20 1.25 4 10 5 17 0.42 1 0.33 0.18 0.12 0.08 0.06 0.05 0.04 0.02 0.01 0.01 0240 20 1.25 4 10 5 8.5 0.44 1 0.35 0.2 0.14 0.1 0.08 0.07 0.05 0.04 0.02 0.01 0.01

241 20 1.25 4 20 0.2 17 4.09 25 3.12 1.35 0.56 0.19 0.08 0.03 0.02 0.01 0 0 0

242 20 1.25 4 20 0.2 8.5 4.65 40 3.71 1.96 1.07 0.54 0.29 0.16 0.09 0.04 0.02 0.01 0.01243 20 1.25 4 20 1 17 1.24 25 0.99 0.55 0.35 0.22 0.15 0.1 0.07 0.04 0.02 0.01 0.01244 20 1.25 4 20 1 8.5 1.34 30 1.09 0.65 0.45 0.31 0.24 0.19 0.15 0.1 0.06 0.04 0.03245 20 1.25 4 20 5 17 0.22 0 0.17 0.08 0.04 0.02 0.01 0 0 0 0 0 0246 20 1.25 4 20 5 8.5 0.25 0.1 0.19 0.1 0.06 0.04 0.02 0.01 0.01 0.01 0 0 0

247 20 1.25 4 40 0.2 17 2.91 30 2.27 1.13 0.58 0.26 0.12 0.06 0.02 0.01 0 0 0
Table 3 59

Table 3. Simulated groundwater mounding beneath hypothetical stormwater-infiltration dry wells on a 1-acre development.—Continued[in/hr, inches per hour; Max, maximum; GW, groundwater; hgt, height; ft, feet; EEDW, east edge of dry well]

Simulation 

number

Impervious cover 

(percent)

Design 

storm 

(inches)

Basin 

depth 

(feet)

Aquifer 

thickness 

(feet)

Soil 

permeability 

(in/hr)

Specific 

yield 

(percent)

Max 

GW 

mound 

height 

(feet)

Max 

extent 

0.25-ft 

GW 

mound 

height 

(feet)

GW 

mound 

hgt at 

EEDW 

(feet)

GW 

mound 

hgt 

10 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

20 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

30 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

40 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

50 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

60 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

75 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

120 ft 

from 

EEDW

(feet)

GW 

mound 

hgt 

140 ft 

from 

EEDW 

(feet)

248 20 1.25 4 40 0.2 8.5 3.32 40 2.68 1.53 0.94 0.55 0.34 0.2 0.12 0.05 0.02 0.01 0.01

249 20 1.25 4 40 1 17 0.77 10 0.62 0.37 0.24 0.15 0.1 0.07 0.05 0.03 0.01 0.01 0250 20 1.25 4 40 1 8.5 0.84 25 0.69 0.44 0.31 0.22 0.16 0.12 0.09 0.06 0.04 0.02 0.01251 20 1.25 4 40 5 17 0.08 0 0.06 0.02 0.01 0 0 0 0 0 0 0 0252 20 1.25 4 40 5 8.5 0.1 0 0.08 0.03 0.02 0.01 0 0 0 0 0 0 0

253 40 1.25 4 10 0.2 17 6.94 30 5.15 2.27 0.83 0.26 0.11 0.05 0.03 0.01 0 0 0

254 40 1.25 4 10 0.2 8.5 8.03 50 6.35 3.62 1.97 0.93 0.48 0.26 0.15 0.06 0.02 0.01 0255 40 1.25 4 10 1 17 2.58 40 2 1.15 0.72 0.45 0.3 0.2 0.13 0.07 0.03 0.01 0.01256 40 1.25 4 10 1 8.5 2.85 70 2.28 1.46 1.03 0.73 0.55 0.42 0.32 0.21 0.11 0.06 0.03257 40 1.25 4 10 5 17 0.73 25 0.58 0.38 0.28 0.22 0.18 0.15 0.13 0.1 0.06 0.04 0.03258 40 1.25 4 10 5 8.5 0.79 30 0.64 0.44 0.35 0.28 0.24 0.21 0.18 0.15 0.11 0.09 0.07

259 40 1.25 4 20 0.2 17 5.84 30 4.34 2.07 0.91 0.34 0.14 0.07 0.04 0.02 0.01 0 0

260 40 1.25 4 20 0.2 8.5 6.77 50 5.32 3.09 1.79 0.94 0.52 0.3 0.18 0.09 0.04 0.02 0.01261 40 1.25 4 20 1 17 1.94 40 1.51 0.91 0.59 0.38 0.27 0.19 0.13 0.08 0.04 0.02 0.01262 40 1.25 4 20 1 8.5 2.12 60 1.7 1.1 0.78 0.56 0.43 0.34 0.27 0.19 0.11 0.08 0.05263 40 1.25 4 20 5 17 0.44 1 0.34 0.21 0.14 0.1 0.07 0.06 0.04 0.03 0.02 0.01 0.01264 40 1.25 4 20 5 8.5 0.48 10 0.38 0.25 0.18 0.14 0.11 0.09 0.08 0.06 0.04 0.03 0.02

265 40 1.25 4 40 0.2 17 4.45 30 3.35 1.78 0.94 0.43 0.21 0.1 0.04 0.02 0.01 0 0

266 40 1.25 4 40 0.2 8.5 5.16 50 4.08 2.5 1.59 0.95 0.58 0.36 0.22 0.1 0.03 0.02 0.01267 40 1.25 4 40 1 17 1.33 30 1.06 0.69 0.48 0.33 0.24 0.18 0.13 0.08 0.04 0.02 0.02268 40 1.25 4 40 1 8.5 1.45 50 1.18 0.81 0.6 0.45 0.35 0.28 0.23 0.17 0.1 0.07 0.05269 40 1.25 4 40 5 17 0.23 0 0.18 0.1 0.06 0.04 0.02 0.01 0.01 0 0 0 0270 40 1.25 4 40 5 8.5 0.28 0.1 0.23 0.15 0.11 0.08 0.06 0.04 0.03 0.02 0.01 0.01 0

271 80 1.25 4 10 0.2 17 9.65 30 6.91 3.42 1.37 0.44 0.19 0.09 0.05 0.02 0.01 0 0

272 80 1.25 4 10 0.2 8.5 11.54 60 8.95 5.66 3.37 1.7 0.88 0.47 0.26 0.11 0.03 0.01 0273 80 1.25 4 10 1 17 3.92 60 3 1.93 1.28 0.82 0.56 0.38 0.26 0.14 0.06 0.03 0.01274 80 1.25 4 10 1 8.5 4.42 80 3.53 2.5 1.85 1.36 1.05 0.81 0.63 0.42 0.22 0.13 0.07275 80 1.25 4 10 5 17 1.21 60 0.96 0.69 0.54 0.43 0.36 0.3 0.25 0.19 0.13 0.09 0.06276 80 1.25 4 10 5 8.5 1.33 80 1.08 0.82 0.67 0.55 0.48 0.42 0.37 0.31 0.23 0.18 0.14

277 80 1.25 4 20 0.2 17 8.46 30 6.05 3.17 1.48 0.57 0.24 0.12 0.07 0.03 0.01 0.01 0

278 80 1.25 4 20 0.2 8.5 10.07 60 7.76 4.95 3.06 1.69 0.96 0.55 0.33 0.16 0.07 0.04 0.02
60 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins Table 3. Simulated groundwater mounding beneath hypothetical stormwater-infiltration dry wells on a 1-acre development.—Continued [in/hr, inches per hour; Max, maximum; GW, groundwater; hgt, height; ft, feet; EEDW, east edge of dry well] Simula- tion number Impervi- ous cover (percent) Design storm (inches) Basin depth (feet) Aquifer thick- ness (feet) Soil perm- eability (in/hr) Specific yield (percent) Max GW mound height (feet) Max extent 0.25-ft GW mound height (feet) GW mound hgt at EEDW (feet) GW mound hgt 10 ft from EEDW (feet) GW mound hgt 20 ft from EEDW (feet) GW mound hgt 30 ft from EEDW (feet) GW mound hgt 40 ft from EEDW (feet) GW mound hgt 50 ft from EEDW (feet) GW mound hgt 60 ft from EEDW (feet) GW mound hgt 75 ft from EEDW (feet) GW mound hgt 100 ft from EEDW (feet) GW mound hgt 120 ft from EEDW (feet) GW mound hgt 140 ft from EEDW (feet) 279 80 1.25 4 20 1 17 3.11 60 2.37 1.55 1.06 0.7 0.49 0.35 0.25 0.16 0.08 0.04 0.03 280 80 1.25 4 20 1 8.5 3.45 80 2.73 1.93 1.43 1.06 0.83 0.66 0.53 0.38 0.23 0.15 0.1 281 80 1.25 4 20 5 17 0.85 40 0.67 0.49 0.38 0.3 0.25 0.21 0.18 0.15 0.11 0.08 0.06 282 80 1.25 4 20 5 8.5 0.92 60 0.74 0.55 0.44 0.36 0.31 0.28 0.25 0.21 0.16 0.14 0.12 283 80 1.25 4 40 0.2 17 6.83 40 4.94 2.83 1.55 0.74 0.37 0.18 0.09 0.03 0.01 0.01 0.01 284 80 1.25 4 40 0.2 8.5 8.11 70 6.26 4.15 2.75 1.69 1.08 0.68 0.43 0.21 0.08 0.04 0.03 285 80 1.25 4 40 1 17 2.25 60 1.75 1.22 0.88 0.62 0.46 0.34 0.26 0.16 0.08 0.05 0.03 286 80 1.25 4 40 1 8.5 2.48 80 1.99 1.46 1.12 0.85 0.68 0.55 0.45 0.33 0.21 0.15 0.11 287 80 1.25 4 40 5 17 0.49 10 0.38 0.27 0.19 0.14 0.11 0.08 0.06 0.04 0.02 0.01 0.01 288 80 1.25 4 40 5 8.5 0.55 20 0.44 0.32 0.25 0.19 0.16 0.13 0.11 0.08 0.06 0.04 0.03 289 10 0.313 10 10 0.2 17 1.64 10 1.35 0.3 0.09 0.02 0.01 0 0 0 0 0 0 290 10 0.313 10 10 0.2 8.5 1.76 10 1.47 0.43 0.18 0.07 0.03 0.02 0.01 0 0 0 0 291 10 0.313 10 10 1 17 0.41 1 0.33 0.09 0.04 0.01 0.01 0 0 0 0 0 0 292 10 0.313 10 10 1 8.5 0.41 1 0.33 0.09 0.04 0.02 0.01 0 0 0 0 0 0 293 10 0.313 10 10 5 17 0.06 0 0.05 0.01 0 0 0 0 0 0 0 0 0 294 10 0.313 10 10 5 8.5 0.07 0 0.05 0.01 0 0 0 0 0 0 0 0 0 295 10 0.313 10 20 0.2 17 1.08 10 0.9 0.25 0.09 0.03 0.01 0 0 0 0 0 0 296 10 0.313 10 20 0.2 8.5 1.17 10 0.99 0.34 0.16 0.07 0.04 0.02 0.01 0 0 0 0 297 10 0.313 10 20 1 17 0.16 0 0.12 0.01 0 0 0 0 0 0 0 0 0 298 10 0.313 10 20 1 8.5 0.19 0 0.15 0.02 0.01 0 0 0 0 0 0 0 0 299 10 0.313 10 20 5 17 0.03 0 0.03 0 0 0 0 0 0 0 0 0 0 300 10 0.313 10 20 5 8.5 0.04 0 0.03 0.01 0 0 0 0 0 0 0 0 0

301 10 0.313 10 40 0.2 17 0.56 1 0.45 0.11 0.03 0.01 0 0 0 0 0 0 0

302 10 0.313 10 40 0.2 8.5 0.63 1 0.53 0.18 0.08 0.03 0.01 0 0 0 0 0 0303 10 0.313 10 40 1 17 0.08 0 0.06 0.01 0 0 0 0 0 0 0 0 0304 10 0.313 10 40 1 8.5 0.09 0 0.07 0.01 0 0 0 0 0 0 0 0 0305 10 0.313 10 40 5 17 0.02 0 0.01 0 0 0 0 0 0 0 0 0 0306 10 0.313 10 40 5 8.5 0.02 0 0.02 0 0 0 0 0 0 0 0 0 0

307 20 0.313 10 10 0.2 17 2.68 10 2.2 0.58 0.17 0.05 0.02 0.01 0 0 0 0 0

308 20 0.313 10 10 0.2 8.5 2.88 20 2.42 0.84 0.37 0.15 0.07 0.04 0.02 0.01 0 0 0309 20 0.313 10 10 1 17 0.74 1 0.61 0.21 0.1 0.05 0.03 0.02 0.01 0.01 0 0 0
Table 3 61

Table 3. Simulated groundwater mounding beneath hypothetical stormwater-infiltration dry wells on a 1-acre development.—Continued[in/hr, inches per hour; Max, maximum; GW, groundwater; hgt, height; ft, feet; EEDW, east edge of dry well]

Simulation 

number

Impervious cover 

(percent)

Design 

storm 

(inches)

Basin 

depth 

(feet)

Aquifer 

thickness 

(feet)

Soil 

permeability 

(in/hr)

Specific 

yield 

(percent)

Max 

GW 

mound 

height 

(feet)

Max 

extent 

0.25-ft 

GW 

mound 

height 

(feet)

GW 

mound 

hgt at 

EEDW 

(feet)

GW 

mound 

hgt 

10 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

20 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

30 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

40 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

50 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

60 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

75 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

120 ft 

from 

EEDW

(feet)

GW 

mound 

hgt 

140 ft 

from 

EEDW 

(feet)

310 20 0.313 10 10 1 8.5 0.77 1 0.64 0.23 0.13 0.08 0.05 0.03 0.02 0.01 0 0 0

311 20 0.313 10 10 5 17 0.11 0 0.08 0.01 0 0 0 0 0 0 0 0 0

312 20 0.313 10 10 5 8.5 0.13 0 0.1 0.02 0.01 0 0 0 0 0 0 0 0

313 20 0.313 10 20 0.2 17 1.89 10 1.56 0.5 0.19 0.06 0.02 0.01 0 0 0 0 0

314 20 0.313 10 20 0.2 8.5 2.05 20 1.73 0.67 0.33 0.16 0.08 0.04 0.02 0.01 0 0 0315 20 0.313 10 20 1 17 0.39 1 0.31 0.08 0.03 0.01 0 0 0 0 0 0 0316 20 0.313 10 20 1 8.5 0.42 1 0.34 0.11 0.05 0.02 0.01 0 0 0 0 0 0317 20 0.313 10 20 5 17 0.06 0 0.05 0.01 0 0 0 0 0 0 0 0 0318 20 0.313 10 20 5 8.5 0.07 0 0.06 0.02 0.01 0 0 0 0 0 0 0 0

319 20 0.313 10 40 0.2 17 1.18 10 0.99 0.38 0.18 0.08 0.04 0.02 0.01 0 0 0 0

320 20 0.313 10 40 0.2 8.5 1.29 20 1.1 0.48 0.28 0.16 0.09 0.05 0.03 0.01 0 0 0321 20 0.313 10 40 1 17 0.19 0 0.15 0.03 0.01 0 0 0 0 0 0 0 0322 20 0.313 10 40 1 8.5 0.24 0.1 0.2 0.08 0.04 0.02 0.01 0 0 0 0 0 0323 20 0.313 10 40 5 17 0.03 0 0.03 0.01 0 0 0 0 0 0 0 0 0324 20 0.313 10 40 5 8.5 0.03 0 0.03 0.01 0 0 0 0 0 0 0 0 0

325 40 0.313 10 10 0.2 17 4.34 20 3.59 1.19 0.38 0.11 0.05 0.02 0.01 0 0 0 0

326 40 0.313 10 10 0.2 8.5 4.71 30 4 1.7 0.8 0.35 0.18 0.09 0.05 0.02 0.01 0 0327 40 0.313 10 10 1 17 1.37 20 1.13 0.48 0.27 0.16 0.1 0.07 0.05 0.02 0.01 0 0328 40 0.313 10 10 1 8.5 1.45 25 1.22 0.57 0.36 0.24 0.18 0.14 0.1 0.07 0.03 0.02 0.01329 40 0.313 10 10 5 17 0.31 1 0.25 0.1 0.06 0.04 0.03 0.02 0.01 0.01 0 0 0330 40 0.313 10 10 5 8.5 0.31 1 0.25 0.1 0.06 0.03 0.02 0.02 0.01 0.01 0 0 0

331 40 0.313 10 20 0.2 17 3.33 20 2.75 1.02 0.41 0.14 0.05 0.02 0.01 0.01 0 0 0

332 40 0.313 10 20 0.2 8.5 3.64 30 3.07 1.37 0.71 0.35 0.18 0.1 0.05 0.02 0.01 0 0333 40 0.313 10 20 1 17 0.89 10 0.74 0.33 0.18 0.1 0.06 0.04 0.02 0.01 0.01 0 0334 40 0.313 10 20 1 8.5 0.95 10 0.8 0.39 0.24 0.15 0.11 0.08 0.06 0.04 0.02 0.01 0.01335 40 0.313 10 20 5 17 0.16 0 0.13 0.05 0.03 0.01 0 0 0 0 0 0 0336 40 0.313 10 20 5 8.5 0.14 0 0.11 0.03 0.01 0 0 0 0 0 0 0 0

337 40 0.313 10 40 0.2 17 2.22 25 1.85 0.79 0.4 0.18 0.08 0.04 0.02 0.01 0 0 0

338 40 0.313 10 40 0.2 8.5 2.45 30 2.08 1.02 0.6 0.35 0.21 0.13 0.08 0.03 0.01 0.01 0339 40 0.313 10 40 1 17 0.42 1 0.34 0.12 0.05 0.02 0 0 0 0 0 0 0340 40 0.313 10 40 1 8.5 0.53 1 0.44 0.21 0.13 0.07 0.04 0.02 0.01 0.01 0 0 0
62 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins Table 3. Simulated groundwater mounding beneath hypothetical stormwater-infiltration dry wells on a 1-acre development.—Continued [in/hr, inches per hour; Max, maximum; GW, groundwater; hgt, height; ft, feet; EEDW, east edge of dry well] Simula- tion number Impervi- ous cover (percent) Design storm (inches) Basin depth (feet) Aquifer thick- ness (feet) Soil perm- eability (in/hr) Specific yield (percent) Max GW mound height (feet) Max extent 0.25-ft GW mound height (feet) GW mound hgt at EEDW (feet) GW mound hgt 10 ft from EEDW (feet) GW mound hgt 20 ft from EEDW (feet) GW mound hgt 30 ft from EEDW (feet) GW mound hgt 40 ft from EEDW (feet) GW mound hgt 50 ft from EEDW (feet) GW mound hgt 60 ft from EEDW (feet) GW mound hgt 75 ft from EEDW (feet) GW mound hgt 100 ft from EEDW (feet) GW mound hgt 120 ft from EEDW (feet) GW mound hgt 140 ft from EEDW (feet) 341 40 0.313 10 40 5 17 0.07 0 0.05 0.02 0.01 0 0 0 0 0 0 0 0 342 40 0.313 10 40 5 8.5 0.08 0 0.06 0.02 0.01 0 0 0 0 0 0 0 0 343 80 0.313 10 10 0.2 17 6.13 25 4.99 1.92 0.66 0.2 0.08 0.04 0.02 0.01 0 0 0 344 80 0.313 10 10 0.2 8.5 6.72 40 5.64 2.75 1.39 0.63 0.31 0.17 0.09 0.04 0.01 0 0 345 80 0.313 10 10 1 17 2.08 30 1.7 0.81 0.47 0.28 0.18 0.12 0.08 0.04 0.02 0.01 0 346 80 0.313 10 10 1 8.5 2.22 40 1.84 0.98 0.64 0.44 0.32 0.24 0.19 0.12 0.06 0.03 0.02 347 80 0.313 10 10 5 17 0.49 1 0.39 0.17 0.1 0.07 0.05 0.03 0.02 0.01 0.01 0 0 348 80 0.313 10 10 5 8.5 0.55 1 0.44 0.23 0.16 0.12 0.09 0.08 0.06 0.05 0.03 0.02 0.01 349 80 0.313 10 20 0.2 17 4.98 25 4.03 1.66 0.69 0.24 0.09 0.04 0.02 0.01 0 0 0 350 80 0.313 10 20 0.2 8.5 5.47 40 4.56 2.27 1.23 0.62 0.34 0.19 0.11 0.05 0.02 0.01 0.01 351 80 0.313 10 20 1 17 1.48 25 1.21 0.62 0.38 0.24 0.16 0.11 0.08 0.05 0.02 0.01 0.01 352 80 0.313 10 20 1 8.5 1.57 40 1.31 0.72 0.48 0.33 0.25 0.19 0.15 0.11 0.06 0.04 0.03 353 80 0.313 10 20 5 17 0.28 0.1 0.22 0.1 0.05 0.02 0.01 0 0 0 0 0 0 354 80 0.313 10 20 5 8.5 0.26 0.1 0.2 0.08 0.04 0.02 0.01 0 0 0 0 0 0 355 80 0.313 10 40 0.2 17 3.5 30 2.85 1.32 0.68 0.31 0.14 0.06 0.03 0.01 0 0 0 356 80 0.313 10 40 0.2 8.5 3.89 40 3.25 1.73 1.05 0.61 0.37 0.22 0.13 0.06 0.02 0.01 0.01 357 80 0.313 10 40 1 17 0.83 10 0.68 0.33 0.19 0.1 0.06 0.03 0.02 0.01 0 0 0 358 80 0.313 10 40 1 8.5 0.98 25 0.83 0.48 0.33 0.23 0.17 0.13 0.1 0.07 0.04 0.02 0.02 359 80 0.313 10 40 5 17 0.11 0 0.08 0.03 0.01 0 0 0 0 0 0 0 0 360 80 0.313 10 40 5 8.5 0.13 0 0.1 0.04 0.02 0.01 0 0 0 0 0 0 0 361 10 1.25 10 10 0.2 17 4.34 20 3.59 1.19 0.38 0.11 0.05 0.02 0.01 0 0 0 0

362 10 1.25 10 10 0.2 8.5 4.71 30 4 1.7 0.8 0.35 0.18 0.09 0.05 0.02 0.01 0 0363 10 1.25 10 10 1 17 1.37 20 1.13 0.48 0.27 0.16 0.1 0.07 0.05 0.02 0.01 0 0364 10 1.25 10 10 1 8.5 1.45 25 1.22 0.57 0.36 0.24 0.18 0.14 0.1 0.07 0.03 0.02 0.01365 10 1.25 10 10 5 17 0.31 1 0.25 0.1 0.06 0.04 0.03 0.02 0.01 0.01 0 0 0366 10 1.25 10 10 5 8.5 0.31 1 0.25 0.1 0.06 0.03 0.02 0.02 0.01 0.01 0 0 0

367 10 1.25 10 20 0.2 17 3.33 20 2.75 1.02 0.41 0.14 0.05 0.02 0.01 0.01 0 0 0

368 10 1.25 10 20 0.2 8.5 3.64 30 3.07 1.37 0.71 0.35 0.18 0.1 0.05 0.02 0.01 0 0369 10 1.25 10 20 1 17 0.89 10 0.74 0.33 0.18 0.1 0.06 0.04 0.02 0.01 0.01 0 0370 10 1.25 10 20 1 8.5 0.95 10 0.8 0.39 0.24 0.15 0.11 0.08 0.06 0.04 0.02 0.01 0.01371 10 1.25 10 20 5 17 0.16 0 0.13 0.05 0.03 0.01 0 0 0 0 0 0 0
Table 3 63

Table 3. Simulated groundwater mounding beneath hypothetical stormwater-infiltration dry wells on a 1-acre development.—Continued[in/hr, inches per hour; Max, maximum; GW, groundwater; hgt, height; ft, feet; EEDW, east edge of dry well]

Simulation 

number

Impervious cover 

(percent)

Design 

storm 

(inches)

Basin 

depth 

(feet)

Aquifer 

thickness 

(feet)

Soil 

permeability 

(in/hr)

Specific 

yield 

(percent)

Max 

GW 

mound 

height 

(feet)

Max 

extent 

0.25-ft 

GW 

mound 

height 

(feet)

GW 

mound 

hgt at 

EEDW 

(feet)

GW 

mound 

hgt 

10 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

20 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

30 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

40 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

50 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

60 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

75 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

100 ft 

from 

EEDW 

(feet)

GW 

mound 

hgt 

120 ft 

from 

EEDW

(feet)

GW 

mound 

hgt 

140 ft 

from 

EEDW 

(feet)

372 10 1.25 10 20 5 8.5 0.14 0 0.11 0.03 0.01 0 0 0 0 0 0 0 0373 10 1.25 10 40 0.2 17 2.22 25 1.85 0.79 0.4 0.18 0.08 0.04 0.02 0.01 0 0 0

374 10 1.25 10 40 0.2 8.5 2.45 30 2.08 1.02 0.6 0.35 0.21 0.13 0.08 0.03 0.01 0.01 0375 10 1.25 10 40 1 17 0.42 1 0.34 0.12 0.05 0.02 0 0 0 0 0 0 0376 10 1.25 10 40 1 8.5 0.53 1 0.44 0.21 0.13 0.07 0.04 0.02 0.01 0.01 0 0 0377 10 1.25 10 40 5 17 0.07 0 0.05 0.02 0.01 0 0 0 0 0 0 0 0378 10 1.25 10 40 5 8.5 0.08 0 0.06 0.02 0.01 0 0 0 0 0 0 0 0

379 20 1.25 10 10 0.2 17 6.13 25 4.99 1.92 0.66 0.2 0.08 0.04 0.02 0.01 0 0 0

380 20 1.25 10 10 0.2 8.5 6.72 40 5.64 2.75 1.39 0.63 0.31 0.17 0.09 0.04 0.01 0 0381 20 1.25 10 10 1 17 2.08 30 1.7 0.81 0.47 0.28 0.18 0.12 0.08 0.04 0.02 0.01 0382 20 1.25 10 10 1 8.5 2.22 40 1.84 0.98 0.64 0.44 0.32 0.24 0.19 0.12 0.06 0.03 0.02383 20 1.25 10 10 5 17 0.49 1 0.39 0.17 0.1 0.07 0.05 0.03 0.02 0.01 0.01 0 0384 20 1.25 10 10 5 8.5 0.55 1 0.44 0.23 0.16 0.12 0.09 0.08 0.06 0.05 0.03 0.02 0.01

385 20 1.25 10 20 0.2 17 4.98 25 4.03 1.66 0.69 0.24 0.09 0.04 0.02 0.01 0 0 0

386 20 1.25 10 20 0.2 8.5 5.47 40 4.56 2.27 1.23 0.62 0.34 0.19 0.11 0.05 0.02 0.01 0.01387 20 1.25 10 20 1 17 1.48 25 1.21 0.62 0.38 0.24 0.16 0.11 0.08 0.05 0.02 0.01 0.01388 20 1.25 10 20 1 8.5 1.57 40 1.31 0.72 0.48 0.33 0.25 0.19 0.15 0.11 0.06 0.04 0.03389 20 1.25 10 20 5 17 0.28 0.1 0.22 0.1 0.05 0.02 0.01 0 0 0 0 0 0390 20 1.25 10 20 5 8.5 0.26 0.1 0.2 0.08 0.04 0.02 0.01 0 0 0 0 0 0

391 20 1.25 10 40 0.2 17 3.5 30 2.85 1.32 0.68 0.31 0.14 0.06 0.03 0.01 0 0 0

392 20 1.25 10 40 0.2 8.5 3.89 40 3.25 1.73 1.05 0.61 0.37 0.22 0.13 0.06 0.02 0.01 0.01393 20 1.25 10 40 1 17 0.83 10 0.68 0.33 0.19 0.1 0.06 0.03 0.02 0.01 0 0 0394 20 1.25 10 40 1 8.5 0.98 25 0.83 0.48 0.33 0.23 0.17 0.13 0.1 0.07 0.04 0.02 0.02395 20 1.25 10 40 5 17 0.11 0 0.08 0.03 0.01 0 0 0 0 0 0 0 0396 20 1.25 10 40 5 8.5 0.13 0 0.1 0.04 0.02 0.01 0 0 0 0 0 0 0

397 40 1.25 10 10 0.2 17 9.21 30 7.41 3.4 1.33 0.4 0.15 0.07 0.04 0.02 0 0 0

398 40 1.25 10 10 0.2 8.5 10.24 50 8.56 4.86 2.72 1.32 0.66 0.35 0.19 0.08 0.02 0.01 0399 40 1.25 10 10 1 17 3.41 50 2.77 1.53 0.94 0.58 0.38 0.26 0.17 0.09 0.04 0.02 0.01400 40 1.25 10 10 1 8.5 3.67 75 3.06 1.86 1.28 0.9 0.67 0.51 0.39 0.26 0.13 0.08 0.04401 40 1.25 10 10 5 17 0.97 30 0.79 0.47 0.34 0.26 0.21 0.18 0.15 0.11 0.07 0.05 0.04402 40 1.25 10 10 5 8.5 1.04 40 0.86 0.54 0.41 0.33 0.28 0.24 0.21 0.17 0.13 0.1 0.08
64 Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins Table 3. Simulated groundwater mounding beneath hypothetical stormwater-infiltration dry wells on a 1-acre development.—Continued [in/hr, inches per hour; Max, maximum; GW, groundwater; hgt, height; ft, feet; EEDW, east edge of dry well] Simula- tion number Impervi- ous cover (percent) Design storm (inches) Basin depth (feet) Aquifer thick- ness (feet) Soil perm- eability (in/hr) Specific yield (percent) Max GW mound height (feet) Max extent 0.25-ft GW mound height (feet) GW mound hgt at EEDW (feet) GW mound hgt 10 ft from EEDW (feet) GW mound hgt 20 ft from EEDW (feet) GW mound hgt 30 ft from EEDW (feet) GW mound hgt 40 ft from EEDW (feet) GW mound hgt 50 ft from EEDW (feet) GW mound hgt 60 ft from EEDW (feet) GW mound hgt 75 ft from EEDW (feet) GW mound hgt 100 ft from EEDW (feet) GW mound hgt 120 ft from EEDW (feet) GW mound hgt 140 ft from EEDW (feet) 403 40 1.25 10 20 0.2 17 7.8 30 6.23 2.98 1.35 0.5 0.21 0.09 0.05 0.02 0.01 0.01 0 404 40 1.25 10 20 0.2 8.5 8.69 50 7.21 4.11 2.4 1.28 0.71 0.4 0.23 0.11 0.04 0.02 0.01 405 40 1.25 10 20 1 17 2.56 40 2.09 1.19 0.76 0.48 0.33 0.23 0.16 0.1 0.05 0.03 0.01 406 40 1.25 10 20 1 8.5 2.75 70 2.28 1.4 0.97 0.69 0.52 0.41 0.32 0.23 0.14 0.09 0.06 407 40 1.25 10 20 5 17 0.61 10 0.49 0.28 0.19 0.13 0.1 0.08 0.06 0.04 0.03 0.02 0.01 408 40 1.25 10 20 5 8.5 0.6 10 0.49 0.28 0.19 0.13 0.1 0.07 0.06 0.04 0.02 0.01 0.01 409 40 1.25 10 40 0.2 17 5.96 40 4.77 2.45 1.3 0.61 0.29 0.14 0.06 0.02 0.01 0 0 410 40 1.25 10 40 0.2 8.5 6.69 60 5.54 3.26 2.06 1.23 0.76 0.47 0.29 0.13 0.04 0.02 0.01 411 40 1.25 10 40 1 17 1.73 40 1.44 0.88 0.61 0.41 0.3 0.22 0.16 0.1 0.05 0.03 0.02 412 40 1.25 10 40 1 8.5 1.86 60 1.57 1.01 0.74 0.54 0.42 0.34 0.27 0.2 0.12 0.09 0.06 413 40 1.25 10 40 5 17 0.34 1 0.27 0.16 0.1 0.07 0.05 0.03 0.02 0.01 0 0 0 414 40 1.25 10 40 5 8.5 0.36 1 0.3 0.18 0.12 0.09 0.06 0.05 0.04 0.02 0.01 0.01 0 415 80 1.25 10 10 0.2 17 12.41 40 9.84 5.1 2.21 0.69 0.26 0.12 0.06 0.03 0.01 0 0 416 80 1.25 10 10 0.2 8.5 13.98 60 11.6 7.3 4.44 2.31 1.2 0.62 0.34 0.14 0.04 0.01 0.01 417 80 1.25 10 10 1 17 4.86 60 3.94 2.41 1.56 0.99 0.66 0.45 0.31 0.17 0.07 0.03 0.01 418 80 1.25 10 10 1 8.5 5.3 100 4.41 2.96 2.13 1.54 1.17 0.9 0.7 0.47 0.25 0.14 0.08 419 80 1.25 10 10 5 17 1.49 60 1.21 0.8 0.6 0.46 0.38 0.32 0.27 0.21 0.14 0.1 0.07 420 80 1.25 10 10 5 8.5 1.6 80 1.33 0.92 0.72 0.59 0.5 0.44 0.39 0.32 0.24 0.19 0.15 421 80 1.25 10 20 0.2 17 10.86 40 8.56 4.53 2.19 0.85 0.35 0.16 0.08 0.04 0.02 0.01 0 422 80 1.25 10 20 0.2 8.5 12.25 70 10.09 6.32 3.93 2.2 1.25 0.71 0.41 0.19 0.08 0.04 0.02 423 80 1.25 10 20 1 17 3.85 60 3.11 1.92 1.27 0.83 0.58 0.41 0.29 0.18 0.08 0.05 0.03

424 80 1.25 10 20 1 8.5 4.16 100 3.44 2.29 1.64 1.19 0.92 0.72 0.58 0.41 0.25 0.16 0.11425 80 1.25 10 20 5 17 1.01 30 0.81 0.53 0.38 0.29 0.23 0.19 0.16 0.12 0.08 0.06 0.04426 80 1.25 10 20 5 8.5 1.1 60 0.91 0.63 0.48 0.39 0.33 0.29 0.25 0.21 0.17 0.14 0.12

427 80 1.25 10 40 0.2 17 8.68 50 6.84 3.82 2.11 1.03 0.52 0.25 0.13 0.05 0.02 0.01 0.01

428 80 1.25 10 40 0.2 8.5 9.85 75 8.08 5.14 3.38 2.09 1.33 0.84 0.53 0.26 0.09 0.05 0.03429 80 1.25 10 40 1 17 2.73 60 2.23 1.46 1.03 0.72 0.52 0.39 0.29 0.18 0.09 0.05 0.03430 80 1.25 10 40 1 8.5 2.96 80 2.46 1.7 1.26 0.95 0.75 0.6 0.49 0.36 0.23 0.16 0.11431 80 1.25 10 40 5 17 0.62 20 0.51 0.34 0.25 0.18 0.14 0.11 0.09 0.06 0.04 0.03 0.02432 80 1.25 10 40 5 8.5 0.6 10 0.49 0.32 0.23 0.16 0.12 0.09 0.07 0.05 0.03 0.02 0.01
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Carleton—Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins—Scientific Investigations Report 2010–5102