U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with Wake County Department of Environmental Services

Fluctuations in Groundwater Levels Related to Regional 

and Local Withdrawals in the Fractured-Bedrock 

Groundwater System in Northern Wake County, 

North Carolina, March 2008–February 2009

Scientific Investigations Report 2010–5219
Cover. ©2011 Google EarthTM.
Fluctuations in Groundwater Levels Related to Regional 

and Local Withdrawals in the Fractured-Bedrock 

Groundwater System in Northern Wake County, 

North Carolina, March 2008–February 2009

By Melinda J. Chapman, Naser Almanaseer, Bryce McClenney, and Natalie Hinton

Prepared in cooperation with Wake County Department of Environmental Services

Scientific Investigations Report 2010–5219

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: 2011

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Chapman, M.J., Almanaseer, Naser, McClenney, Bryce, and Hinton, Natalie, 2011, Fluctuations in groundwater levels 

related to regional and local withdrawals in the fractured-bedrock groundwater system in northern Wake County, 

North Carolina, March 2008–February 2009: U.S. Geological Survey Scientific Investigations Report 2010–5219, 60 p.
Acknowledgments

The authors wish to thank all of the participating homeowners in the study area who 

so graciously allowed access to facilitate measurement of water levels and groundwater 

withdrawals as part of this study. The support of the Wake County Department of Environmental Services was essential to this study. Special appreciation is extended to Greg Bright, 

Groundwater Program Section Chief, for obtaining access to homeowner wells, removing 

pumps from unused wells, and continuing to provide support throughout this study. Thanks 

also to Glen Shoemaker, Environmental Health Team Leader, who assisted with the water-level 

measurements. Elliot Cornell, Environmental Engineer Planner, provided the community-wellconstruction data and withdrawals information for 2005 and 2007. Tom Esqueda, Director, and 

Mark Bailey, former Director, Water Quality Division, provided ongoing support and technical 

discussions. Special thanks to Phil Bradley, North Carolina Geological Survey, for his guidance 

in collecting local geologic structural data and his insight into potential geologic features that 

may contribute to higher well yields. Assistance from Debbie Lyles, North Carolina Department 

of Environment and Natural Resources Public Water Supply Section, with monthly community 

well withdrawals reports is greatly appreciated. Thanks to Bill Gordon and Mike Melton of 

Aqua America, Inc., for providing water-level data and pump depths for two community wells.

The collection of borehole geophysical logs by Kristen McSwain, U.S. Geological Survey 

North Carolina Water Science Center, is much appreciated. Much appreciation is extended to 

Dave Nelms of the U.S. Geological Survey Virginia Water Science Center and Glen Carleton of 

the U.S. Geological Survey New Jersey Water Science Center for their reviews and suggestions 

toward the content of this report.

v

Contents

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

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

Introduction.....................................................................................................................................................1

Background............................................................................................................................................3

Purpose and Scope ..............................................................................................................................5

Description of the Study Area ............................................................................................................5

Previous Studies ...................................................................................................................................8

Methods of Investigation.....................................................................................................................8

Hydrogeologic Setting.................................................................................................................................10

Groundwater Withdrawals.........................................................................................................................15

Community Wells ................................................................................................................................17

Private Wells........................................................................................................................................18

Groundwater Levels in Northern Wake County, March 2008–February 2009....................................19

Groundwater-Level Fluctuations......................................................................................................19

Continuous Measurements......................................................................................................19

Observation Wells.............................................................................................................19

Well WK-368 .............................................................................................................19

Well WK-375 .............................................................................................................21

Well WK-411 .............................................................................................................23

Private Wells......................................................................................................................24

Community Wells ..............................................................................................................27

Periodic Measurements ...........................................................................................................29

Regional Patterns in Groundwater Levels......................................................................................40

Factors Affecting Groundwater Levels ...........................................................................................40

Natural Effects ...........................................................................................................................43

Magnitude of Groundwater-Level Declines ..........................................................................43

Recovery of Groundwater Levels............................................................................................44

Connectivity of Fracture Networks.........................................................................................45

Summary and Conclusions.........................................................................................................................49

References Cited..........................................................................................................................................49

Appendix 1.....................................................................................................................................................51

Figures

1–3. Maps showing—

1. Hydrogeologic units mapped in Wake County, North Carolina, and location 

of the study area ..................................................................................................................2

2. Norwood Oaks study area showing parcels where private wells went dry 

during July 2005 and July 2007, and nearby community supply wells........................4

3. Fracture orientation intrepretations from geologic mapping, fracture traces, 

and borehole geophysical image logs ...........................................................................11

4. Diagrams showing the two-component groundwater system in the Piedmont region 

and the storage comparison between the shallow regolith and deeper bedrock 

components .................................................................................................................................13
vi

5–9. Graphs showing—

5. Geophysical logs and orientation of borehole structural measurements 

in well WK-368....................................................................................................................14

6. Geophysical logs and orientation of borehole structural measurements 

in well WK-375....................................................................................................................16

7. Reported daily withdrawals for the three individual community wells 

in the study area, January through November 2008....................................................17

8. Groundwater levels in relation to withdrawals recorded in private 

observation wells WK-401 and WK-402.........................................................................18

9. Continuous groundwater levels recorded in observation well WK-368 

and nearby rainfall recorded at station 0208706575, June–October 2008................20

10. Histogram of daily water-level fluctuations recorded in observation well WK-368, 

June 26–October 24, 2008..........................................................................................................21

11. Graph showing continuous groundwater levels recorded in observation well 

WK-375 and nearby rainfall recorded at station 0208706575, June–October 2008..........22

12. Histogram of daily water-level fluctuations recorded in observation well WK-375, 

June 22–October 24, 2008..........................................................................................................22

13. Graph showing continuous groundwater levels recorded in observation well 

WK-411 and nearby rainfall recorded at station 0208706575, July–October 2008 ...........23

14. Histogram of daily water-level fluctuations recorded in observation well WK-411, 

July 29–October 22, 2008 ...........................................................................................................24

15. Graph showing water-level fluctuations in private wells WK-400, WK-401, 

and WK-402 showing a similar regional pattern, July–October 2008 ................................25

16. Histograms of daily water-level fluctuations in private wells WK-400, WK-401, 

and WK-402, July–October 2008 ..............................................................................................26

17. Graph showing successive rises or declines in daily mean groundwater levels 

in the six observation wells in the study area........................................................................27

18. Graphs showing water-level fluctuations recorded in community wells WK-415, 

July 29–December 16, 2008, and WK-416, December 19, 2008–January 21, 2009, 

collected at 5-minute intervals.................................................................................................28

19. Maps showing depths to groundwater levels measured in private and 

observation bedrock wells in the study area on (A) March 28 and April 2, 4, and 16, 

2008; (B) June 18 and 26, 2008; (C) July 25 and August 12, 2008; (D) September 19, 

2008; (E) October 17, 2008; (F) November 21, 2008; (G) December 19, 2008; 

(H) January 29, 2009; and (I) February 27, 2009......................................................................30

20. Graphs showing trends in depths to groundwater levels in private wells 

having the deepest groundwater levels. A, Norwood Oaks neighborhood. 

B, Bayleaf Trail area. C, Abbey’s Grove area .........................................................................39

21. Overlay of water levels from wells showing a similar modeled regional pattern of 

fluctuation. A, observation well WK-375 and private well WK-401. B, observation 

wells WK-375 and WK-368. C, observation wells WK-375 and WK-411. D, observation well WK-375, private well WK-401, and community well WK-415 ..............................41

22. Overlay of private well WK-401 water-level records, precipitation, and total 

withdrawals from the three community wells in the study area, July–October 2008 .....44

23. Graph showing total groundwater withdrawn from the three community wells 

for January–November 2008, using projected withdrawals for wells WK-415 and 

WK-416 for September 2008......................................................................................................45

24. Overlay of water levels recorded in community well WK-415 and observation well 

WK-375, September 1–7, 2008 ..................................................................................................46
vii

25–28. Graphs showing cross-correlation coefficient calculations for water levels 

recorded in—

25. Community well WK-415 in relation to water levels recorded in observation 

well WK-375, July 29–October 24, 2008..........................................................................47

26. Private well WK-401 and community well WK-415, 

July 30–October 24, 2008 ..................................................................................................47

27. Private well WK-400 and community well WK-415, 

August 22–October 24, 2008.............................................................................................48

28. Private well WK-401 and observation well WK-375, 

July 30–October 24, 2008 ..................................................................................................48

Tables

1. Well characteristics in the study area in northern Wake County, North Carolina ............6

2. Geologic structure measurements recorded near the study area in northern 

Wake County, North Carolina ...................................................................................................12

3. Well fracture characteristics....................................................................................................15

4. Period of record and range of water levels recorded in continuously monitored 

observation wells, private wells, and community wells.......................................................20

Appendix 1

Bedrock groundwater-level altitude maps showing the water-level measurements in 

private and observation wells in the study area on...............................................................................51

A. March 28, April 2, 4, and 16, 2008 

B. June 18 and 26, 2008 

C. July 25 and August 12, 2008 

D. September 19, 2008 

E. October 17, 2008 

F. November 21, 2008 

G. December 19, 2008

H. January 29, 2009

I. February 27, 2009
viii

Conversion Factors

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2)

Volume

gallon (gal) 3.785 liter (L) 

gallon (gal) 0.003785 cubic meter (m3) 

gallon (gal) 3.785 cubic decimeter (dm3) 

million gallons (Mgal) 3,785 cubic meter (m3)

Flow rate

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

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

gallon per day (gal/d) 0.003785 cubic meter per day (m3/d)

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/s)

Pressure

pound-force per square inch (psi) 6.895 kilopascal (kPa)

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88).

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

Altitude, as used in this report, refers to distance above the vertical datum.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius 

(μS/cm at 25 °C).

Acronyms and Abbreviations

bls below land surface

BTC Bayleaf Trail Catchment

CDM Camp Dresser & McKee Consultants, Inc.

CW community well

CWS community water system

DEH Division of Environmental Health

ET evapotranspiration

FID		 	 field identification number

LIDAR light detection and ranging

NAD83 North American Datum of 1983

NAVD88 North American Vertical Datum of 1988

NCDENR North Carolina Department of Environment and Natural Resources

NWIS National Water Information System

psi pounds per square inch

PVC polyvinyl chloride

PWSS Public Water Supply Section

OTV optical televiewer

USB universal serial bus

USGS U.S. Geological Survey

WK Wake County
Abstract

A study of dewatering of the fractured-bedrock 

aquifer in a localized area of east-central North Carolina was 

conducted from March 2008 through February 2009 to gain 

an understanding of why some privately owned wells and 

monitoring wells were intermittently dry. Although the study 

itself was localized in nature, the resulting water-resources 

data and information produced from the study will help enable 

resource managers to make sound water-supply and water-use 

decisions in similar crystalline-rock aquifer setting in parts of 

the Piedmont and Blue Ridge Physiographic Provinces. 

In June 2005, homeowners in a subdivision of approximately 11 homes on lots approximately 1 to 2 acres in size 

in an unincorporated area of Wake County, North Carolina, 

reported extremely low water pressure and temporarily dry 

wells during a brief period. This area of the State, which 

is in the Piedmont Physiographic Province, is undergoing 

rapid growth and development. Similar well conditions were 

reported again in July 2007. In an effort to evaluate aquifer 

conditions in the area of intermittent water loss, a study was 

begun in March 2008 to measure and monitor water levels and 

groundwater use.

During the study period from March 2008 through 

February 2009, regular dewatering of the fractured-bedrock 

aquifer was documented with water levels in many wells 

ranging between 100 and 200 feet below land surface. Prior to 

this period, water levels from the 1980s through the late 1990s 

were reported to range from 15 to 50 feet below land surface. 

The study area includes three community wells and more than 

30 private wells within a 2,000-foot radius of the dewatered 

private wells. Although groundwater levels were low, recovery 

was observed during periods of heavy rainfall, most likely 

a result of decreased withdrawals owing to less demand for 

irrigation purposes. Similar areal patterns of low groundwater 

levels were delineated during nine water-level measurement 

periods from March 2008 through February 2009. Correlation 

of groundwater-level distribution patterns with orientations of 

geologic structures obtained from surficial mapping, borehole 

geophysical measurements, and interpretation of fracture 

traces suggests two dominant trends striking north-south and 

N. 65° W. 

A variation in overall response to groundwater withdrawals was noted in the continuous groundwater-level records 

for the monitored observation wells and dewatered private 

wells. The largest overall declines during the study period 

were observed in an observation well in which the water-level 

declined as much as 247 feet from mid-July through early 

August 2008, during a period of heavy usage. A private well 

had a water-level decline of about 94 feet during the same 

monitoring period. The large declines recorded in the observation well and the private well indicated a substantial temporary 

loss of storage in the fractured-bedrock aquifer near the wells, 

thus reducing the amount of water available to shallow wells 

in the area (those wells with total depths of about 300 feet), 

and resulting in temporary well failures until such time as the 

aquifer recovered. 

Introduction

Although the fractured crystalline-rock aquifers of the 

Piedmont and Blue Ridge Physiographic Provinces in the 

eastern United States typically do not yield large amounts of 

groundwater, the resource remains the primary water supply 

for most rural households and some suburban areas in North 

Carolina. Groundwater is the primary water supply resource 

for much of unincorporated Wake County, North Carolina, 

despite the use of several large surface-water reservoirs, which 

supply water to the Raleigh-Durham-Chapel Hill metropolitan 

area. Groundwater supplies in the Wake County area, as in 

other areas in the Piedmont and Blue Ridge Physiographic 

Provinces of the State (fig. 1), are withdrawn from fractures in 

Fluctuations in Groundwater Levels Related to Regional 

and Local Withdrawals in the Fractured-Bedrock 

Groundwater System in Northern Wake County, 

North Carolina, March 2008–February 2009

By Melinda J. Chapman1, Naser Almanaseer2, Bryce McClenney1, and Natalie Hinton3

1

 U.S. Geological Survey, North Carolina Water Science Center. 

2

 North Carolina State University, Water Resources Research Institute.

3

 Wake County, North Carolina, Environmental Services Department.
2 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

Figure 1. Hydrogeologic units mapped in Wake County, North Carolina, and location of the study area (modified from 

Camp Dresser & McKee, 2003).

Raleigh

Schist 

Phyllite 

Metavolcanic,

 undifferentiated 

Metaigneous, mafic 

Metaigneous, felsic 

Metaigneous,

 intermediate 

Igneous, felsic intrusive 

Gneiss, felsic 

Argillite 

Metavolcanic, mafic 

Triassic sedimentary 

Fault breccia

Coastal Plain sediments

Hydrogeologic units

 

Bayleaf Trail catchment

 (Keyworth, 2009) 

Physiographic Province

 boundary

Lower Falls Lake watershed

 (Camp Dresser & McKee, 2003)

Study area

Rainfall station and number

Lake stage station and number

0 5 10 MILES

0 8 16 KILOMETERS

N

EXPLANATION

Falls

Lake

Neuse

River

Raleigh

Figure 1. Hydrogeologic units mapped in Wake County, North Carolina, and location of the study area (modified from Camp Dresser &

 McKee, 2003). 

0208706575

02087182

0208706575

02087182

84°

36°

35°

34°

83° 82° 81° 80° 79° 78° 77° 76°
Introduction 3

the bedrock aquifer. The bedrock has limited storage capacity, 

and recharge occurs from the overlying, porous regolith. As a 

result, drawdown from the bedrock aquifer occurs quickly and 

can be on the order of 100 feet (ft) or more within a few hours. 

Aquifers in the area are not as prolific or regional in extent 

as the porous-media sand and limestone aquifers in the North 

Carolina Coastal Plain Physiographic Province, but are local 

in nature with recharge estimated to occur on the scale of local 

topographic boundaries (LeGrand, 2004).

Total groundwater withdrawals in Wake County in 

2005 were estimated to be 16 million gallons per day 

(Mgal/d; U.S. Geological Survey, 2008). Of that total, about 

7.72 Mgal/d was withdrawn by individual wells serving 

about 110,280 people, or about 15 percent of the total Wake 

County population of 748,815 (U.S. Census Bureau, 2005). 

This amount is the largest number of individuals served by 

domestic wells of any county in the State. An additional 

4.76 Mgal/d was withdrawn by community wells and served 

61,780 people, or 8 percent of the county population. In North 

Carolina, a community water system (CWS) is defined as 

having at least 15 connections or serving at least 25 people 

(North Carolina Department of Environmental and Natural 

Resources, 2004). An estimated 600 community wells are in 

Wake County, which is probably the largest number of such 

wells in any county in the State (Greg Bright, Wake County 

Department of Environmental Services, oral commun., 

2008). Additional groundwater use in Wake County includes 

2.03 Mgal/d for irrigation, of which 1.34 Mgal/d was used for 

golf courses and 0.69 Mgal/d for crops. The mining industry 

also withdrew 1.36 Mgal/d of groundwater, 0.23 Mgal/d was 

used for livestock, and 0.09 Mgal/d was used for aquaculture 

(U.S. Geological Survey, 2008). 

It is important to note that only the larger groundwater 

withdrawals for community supplies are measured (daily 

water-use reports) in North Carolina, and the total Wake 

County groundwater withdrawals are based on estimates 

for other uses, such as individual wells (domestic use) or 

irrigation wells. For example, the number of people supplied 

by individual wells is estimated as the difference between the 

total population and the population served by public utilities 

and community systems. Groundwater withdrawals for public 

supply are then estimated as the number of people using 

groundwater multiplied by an estimated water use per capita, 

which was 70 gallons per person for North Carolina in 2005 

(U.S. Geological Survey, 2008). Groundwater withdrawals 

for irrigation are estimated from the acres of individual crops 

multiplied by an average application rate (Douglas G. Smith, 

U.S. Geological Survey, written commun., 2009). Withdrawals 

for irrigation of individual lawns are not known but likely are 

increasing.

North Carolina General Statute 130A-328 (1992) 

requires that all wells serving at least 25 people for at least 

6 months out of a year be permitted. These types of wells 

include community systems and non-community non-transient 

systems. The permit is issued by the North Carolina Department of Environment and Natural Resources (NCDENR), 

Division of Environmental Health (DEH) Public Water Supply 

Section (PWSS). The PWSS has the responsibility to ensure 

adequate water supplies are available (North Carolina General 

Statute 130A-328) and thus permits the amount of water to 

be withdrawn from a community well. The permitted daily 

withdrawal rate typically is based on a 24-hour (hr) drawdown 

test, and only a totalizing meter (total volume) is required to 

report the daily volume of groundwater withdrawn from the 

aquifer. The drawdown of any water-supply well must not 

interfere with the required yield of another well, but monitoring of nearby water levels in surrounding wells is not required 

by most permits. Water-use reports are compiled monthly 

by the CWS operators and sent to the PWSS. Water-level 

monitoring in the supply well is not required after the initial 

drawdown test (North Carolina Department of Environment 

and Natural Resources, 2004). Without water-level data, 

however, the PWSS cannot determine if water levels recover 

after seasonal high water-use periods or after recharge events 

and whether the aquifer is sustaining the withdrawals or is 

being dewatered. The only location requirements regarding the 

well are general setback rules for septic fields and wellhead 

protection area (North Carolina Department of Environment 

and Natural Resources, 2004); the appropriate county agency 

also must be notified when a CWS is installed (Greg Bright, 

Wake County Department of Environmental Services, oral 

commun., 2008). 

In August 2009, Wake County passed a local ordinance 

that addresses monitoring requirements for well interference 

when complaints of degradation in water quality or yield in 

a private, semiprivate or large capacity well are forwarded to 

the county in writing. The well is considered “degraded” if the 

well yield can no longer “effectively support human consumption or basic sanitation requirements.” The radial distance of 

the “zone of influence” monitoring requirement is 2,000 ft 

outward from the degraded well (Wake County Department of 

Environmental Services, 2009). 

Background

On June 18, 2005, several homeowners using individual 

domestic wells for water supply in the Norwood Oaks 

subdivision and along Bayleaf Trail in northern Wake 

County, North Carolina (figs. 1, 2), reported a loss of water 

pressure severe enough to indicate dry wells. This was the 

first reported occurrence of dry wells in the neighborhood, 

which was about 11 years old at the time. Similar problems 

occurred again in this same area in July 2007. Some private 

wells eventually required modification, including deepening, 

hydrofracturing, or pump replacement. Because withdrawals of about 30,000 gallons per day (gal/d) from a nearby 

community well (WK-415, fig. 2) had commenced about 

2 weeks earlier (June 2005) and concern arose that the private 

well problems were related to the community well (Elliott 

Cornell, Wake County Department of Environmental Services, 

written commun., 2008), the homeowners drafted a letter to 

a Wake County commissioner requesting county oversight of 
4 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

Figure 2. Norwood Oaks study area showing parcels where private wells went dry during July 2005 and July 2007, and nearby 

community supply wells.

0 500

0 100 200 300 400 500 METERS

1,000 1,500 2,000 FEET

Creedmoor

Road

Hwy 50

WK-417

WK-416

Study area

boundary

Norwood

Road

Bayleaf

Trail

Abbey’s Grove

Norwood Oaks

Drive

Parcels affected July 2005

Parcels affected July 2007

Parcels affected July 2005 and 2007

Community well and number

Private well and number

Observation well and number

Note: Wells that are yellow are

 continuously monitored wells

EXPLANATION

N

WK-415

Figure 2. Norwood Oaks study area showing parcels where private wells went dry during July 2005 and July 2007, and 

nearby community wells.

 

WK-389

WK-412

WK-387

WK-388

WK-378

WK-383

WK-382

WK-392 WK-393

WK-384

WK-399

WK-413

WK-395

WK-394

WK-410

WK-404

WK-373

WK-376

WK-374

WK-377

WK-375

WK-403

WK-402WK-401

WK-400

WK-397

WK-405

WK-406 WK-409

WK-407

WK-408

WK-368 WK-385

WK-411

WK-386

WK-379

WK-380

WK-381

WK-396

WK-398

WK-391

WK-390

WK-411

WK-385

WK-414

Raleigh

Location of Wake County in North Carolina

Location of study area and Raleigh in

Wake County, North Carolina

N

Study

area

Raleigh

WK-415
Introduction 5

well locations and volumes withdrawn by commercial water 

utilities. The county responded by convening a “Groundwater 

Sustainability Committee” in June 2006, which developed a 

report of recommendations to address the subject issues (Wake 

County Groundwater Sustainability Stakeholder Committee 

Report, 2007). 

In October 2007, Wake County Department of Environmental Services requested the U.S. Geological Survey (USGS) 

to develop an approach to understand the apparent decrease in 

groundwater supplies in the Norwood Oaks area. This request 

led to the initiation of a cooperative investigation that began 

in January 2008, with field work and monitoring beginning 

in March 2008. This report describes data collected as part of 

this cooperative study and related findings. A primary mission 

of the USGS is to provide reliable and impartial information 

on the health and management of the natural resources of the 

Nation (http://www.usgs.gov/aboutusgs/). To that end, the 

USGS provides resource managers and planners with current 

information on water resources for domestic, agricultural, 

commercial, industrial, recreational, and ecological use, as 

well as for the protection and enhancement of water resources 

for human and aquatic health and environmental quality 

(http://water.usgs.gov/mission.html). Results from this study 

will be transferable to other similar fractured-rock aquifer 

settings in other areas of the Piedmont and Blue Ridge 

physiographic regions throughout the eastern United States 

where similar groundwater resource-management issues have 

developed. 

Purpose and Scope

The purpose of this report is to describe conditions 

in the fractured-bedrock aquifer in northern Wake County, 

North Carolina, which may have contributed to temporary 

dewatering of the aquifer as an example of competitive use by 

both individual homeowners and community water suppliers. 

Groundwater-level fluctuations were measured and monitored 

during March 2008 through February 2009 for the study area 

to identify potential causes of declining groundwater levels in 

the area. Groundwater-level data were collected from 35 private wells and 8 observation wells for the entire study period, 

for one community well from July through December 2008, 

and for a second community well from December 2008 

through January 2009. Withdrawal data were collected from 

two private wells during August and September 2008 and 

compiled from PWSS reports for the three community wells 

during January through November 2008. 

The potential effects of the combined withdrawals by 

community wells and private wells on water-level declines 

are described. Groundwater levels, including fluctuations in 

water levels resulting from both local and potentially regional 

withdrawals, are documented. Withdrawal data compiled from 

reports of water usage from community wells and recorded 

using flowmeters on private wells were used in the analysis. 

Comparisons of recorded groundwater-level fluctuations to 

naturally occurring effects, such as precipitation, barometric 

pressure fluctuations, evapotranspiration, and earth tides, 

were made. Correlations were made between low water-level 

patterns with geologic structural features mapped at land 

surface and within boreholes in the area.

Description of the Study Area 

The study area generally is defined by a radial distance 

of 2,000 ft outward from Norwood Oaks Drive cul-de-sac and 

includes the nearest community wells (fig. 2). Regionally, the 

study area is located within the lower Falls Lake watershed in 

northern Wake County, North Carolina (NC), in the Piedmont 

Physiographic Province (fig. 1). Falls Lake is the major drinking water-supply reservoir for the city of Raleigh, NC, and the 

nearest embayment of the lake is about 1.1 miles northeast of 

the study area (fig. 1) along Upper Barton Creek. 

The study area is located within the schist hydrogeologic 

unit (Camp Dresser & McKee, 2003), which makes up about 

5 percent of the total county area (Camp Dresser & McKee, 

2003; fig. 1). The schist hydrogeologic unit has the lowest 

mean yield (7 gallons per minute (gal/min)) for domestic 

wells of all hydrogeologic units mapped in the county (Camp 

Dresser & McKee, 2003), with a range of about 3 to 

8 gal/min based on data from 143 wells. The community wells 

for the schist hydrogeologic unit have an overall higher yield 

than individual wells, likely because of their greater depth, 

with yields of about 20 to 70 gal/min. It is not uncommon for 

residential developers in this area of the county to drill several 

to a few dozen wells to find adequate groundwater yield 

for community water supply (Allen Hardy, North Carolina 

Department of Environment and Natural Resources, oral 

commun., 2008).

Keyworth (2009) defined the Bayleaf Trail Catchment 

(fig. 1), which includes the study area, and reported groundwater use from three community wells and 35 individual 

private wells. The three community wells connect to two 

distribution networks that consist of a large network of 

67 wells in northern Wake County (Keyworth, 2009). The 

three community wells are substantially deeper (about 700 

to 800 ft) than the private wells (about 150 to 500 ft), and 

two of the three community wells have yields of about 

60–80 gal/min (table 1). The average private well yield is 

about 7 gal/min. In general, domestic wells require yields of 

only a few gallons per minute, but with the overall aquifer 

yield being low in this area, a larger number of wells drilled 

could stress the aquifer, resulting in yields even lower than the 

initial yield, and low pressure in the wells from withdrawals 

could be expected. Reported pumping rates for the community 

wells were between 5,000 and 30,000 gal/d per well during 

the spring through summer in 2005 and 2007 (Elliot Cornell, 

Wake County Department of Environmental Services, written 

commun., 2008). 
6 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County Table 1. Well characteristics in the study area in northern Wake County, North Carolina.—Continued [USGS, U.S. Geological Survey; NAVD 88, North American Vertical Datum of 1988; OW, observation well; PW, private well; and CW, community well; —, information not available. Note: All well- construction characteristics were recorded from well tags in the field as part of this study unless otherwise noted] USGS county number USGS station number Type of well Latitude (decimal degrees) Longitude (decimal degrees) Date drilled Well depth (feet be- low land surface) Well elevation (feet above NAVD 1988) Casing depth (feet be- low land surface) Yield (gallons per minute) Static water level at time of construc- tion Monitoring WK-368 355635078385101 OW -78.684 35.943 2/11/1992 500a 408 70 12 15 Continuous water levels WK-373 355643078411201 PW -78.687 35.945 2003 400 388

— 1 20 Periodic water levels

WK-374 355648078411301 PW -78.687 35.947 1981 150 371 65 7 — Periodic water levelsWK-375 355659078411401 OW -78.687 35.950 4/19/1999 301a 338 39a 40 20 Continuous water levelsWK-376 355646078411301 PW -78.687 35.946 11/15/1994 305 378 61 3 — Periodic water levelsWK-377 355651078411201 PW -78.687 35.947 5/15/1980 225 356 43 3 50 Periodic water levelsWK-378 355637078405501 PW -78.682 35.944 12/9/1981 300 417 73 1 — Periodic water levelsWK-379 355634078405301 PW -78.681 35.943

—

— 404

—

—

— Periodic water levels

WK-380 355635078405301 PW -78.681 35.943

— 305 407 165 10 30 Periodic water levels

WK-381 355638078405301 PW -78.681 35.944 10/14/2005 505 415 102 1 100 Periodic water levelsWK-382 355638078405401 OW -78.682 35.944 12/8/1981 225 416 76 4 — Periodic water levelsWK-383 355636078405601 PW -78.682 35.943

—

— 415

—

—

— Periodic water levels

WK-384 355636078405801 PW -78.683 35.943

—

— 413

—

—

— Periodic water levels

WK-385 355634078410201 PW -78.684 35.943

— 508 407 90

— 15 Periodic water levels

WK-386 355632078410801 OW -78.686 35.942

—

— 395

—

—

— Periodic water levels

WK-387 355631078411301 PW -78.687 35.942 3/7/2001 285 410 90 4 40 Periodic water levelsWK-388 355628078412401 OW -78.690 35.941 8/8/2003 345 410 92 0 40 Periodic water levelsWK-389 355631078412601 PW -78.691 35.942 4/13/2001 305 406 61 5 — Periodic water levelsWK-390 355644078404901 PW -78.680 35.945

—

— 400

—

—

— Periodic water levels

WK-391 355646078405601 PW -78.682 35.946 2/4/1985 312 358 53 1 — Periodic water levelsWK-392 355640078405401 PW -78.682 35.944

—

— 416

—

—

— Periodic water levels

WK-393 355640078405301 PW -78.681 35.944

—

— 416

—

—

— Periodic water levels

WK-394 355641078410101 PW -78.683 35.945

—

— 398

—

—

— Periodic water levels

WK-395 355641078405901 PW -78.683 35.945

—

— 408

—

—

— Periodic water levels

WK-396 355645078410001 PW -78.683 35.946 11/30/2001 400 397 23 3 100 Periodic water levelsWK-397 355646078410001 PW -78.683 35.946 9/17/1980 334 394 58 3 40 Periodic water levelsWK-398 355647078405301 PW -78.681 35.946

—

— 362

—

—

— Periodic water levels

WK-399 355645078410401 OW -78.683 35.944 11/15/2004 320 408 68 10 20 Periodic water levels
Introduction 

7

Table 1. Well characteristics in the study area in northern Wake County, North Carolina.—Continued[USGS, U.S. Geological Survey; NAVD 88, North American Vertical Datum of 1988; OW, observation well; PW, private well; and CW, community well; —, information not available. Note: All wellconstruction characteristics were recorded from well tags in the field as part of this study unless otherwise noted]

USGS 

county 

number

USGS station 

number

Type 

of 

well

Latitude 

(decimal 

degrees)

Longitude 

(decimal 

degrees)

Date drilled

Well 

depth 

(feet below land 

surface)

Well 

elevation 

(feet 

above 

NAVD 

1988)

Casing 

depth 

(feet below land 

surface)

Yield 

(gallons 

per 

minute)

Static 

water 

level at 

time of 

construction

Monitoring

WK-400 355635078410401 PW -78.684 35.946 5/23/1995 400 394 60 5 — Continuous water levelsWK-401 355646078410401 PW -78.684 35.946 6/15/1995 410 387 64 1 30 Continuous water levels and flowWK-402 355646078410501 PW -78.685 35.946 5/16/1994 290 380 37 8 30 Continuous water levels and flowWK-403 355645078410501 PW -78.685 35.946 2/22/1999 380 376 47 25 25 Periodic water levelsWK-404 355642078410601 PW -78.685 35.945 6/30/1994 405 388 45 12 — Periodic water levelsWK-405 355640078410501 PW -78.685 35.945 — — 396 — — — Periodic water levelsWK-406 355639078410601 PW -78.685 35.944 11/9/1995 515 404 80 3 20 Periodic water levelsWK-407 355636078410501 PW -78.685 35.943 5/13/1994 270 409 76 3 20 Periodic water levelsWK-408 355637078410601 PW -78.685 35.944 10/25/1994 230 406 58 8 — Inventory onlyWK-409 355638078410401 OW -78.685 35.944 4/28/1994 505 408 82 2 — Periodic water levelsWK-410 355640078410401 PW -78.685 35.945 10/1/1994 375 392 49 10 20 Periodic water levelsWK-411 355634078410901 OW -78.686 35.943 — 306a 400 — — — Continuous water levelsWK-412 355628078412402 PW -78.690 35.941 2/8/2006 500 410 48 20 40 Periodic water levelsWK-413 355638078410001 PW -78.684 35.944 — — 403 — — — Periodic water levelsWK-414 355656078411301 PW -78.687 35.949 2/27/1974 325 330 52 5 — Inventory onlyWK-415b 355705078411601 CW -78.688 35.951 1/29/1999 695 351 60 63 60 Continuous water levelsWK-416b 355646078411601 CW -78.688 35.946 3/1/2000 805 396 65 79 120 Continuous water levelsWK-417b 355645078404501 CW -78.679 35.946 — 700 401 — 8 — —

a Determined from geophysical logging.b Reported information.
8 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

Previous Studies

The most recent comprehensive report on groundwater 

resources in Wake County, North Carolina, was compiled in 

2003 by Camp Dresser & McKee (CDM), which was produced under the direction of the Wake County Department of 

Environmental Services. The report addresses a wide array of 

groundwater issues, focusing on availability and sustainability 

of the resource. At that time, almost one-fourth of the county’s 

residents relied on groundwater for their primary water supply. 

In 2003, 275 CWSs provided water to about 48,000 people, 

while about 93,000 people obtained water from individual 

domestic-supply wells. 

CDM (2003) also estimated water budget components 

for 14 surface-water drainage basins in Wake County based 

on long-term and most recent available data at that time. 

Total estimated groundwater withdrawals for the county were 

about 14 Mgal/d. The largest groundwater withdrawals were 

in the lower Falls Lake Basin, which had the highest per 

capita withdrawal rate of about 100 gallons per person per 

day (gal/person/d), with daily withdrawals in 2000 estimated 

to be 1.8 Mgal/d or 641 million gallons per year (Mgal/yr). 

Recommendations in the CDM 2003 study included the need 

to address potential effects from development projects on 

groundwater resources at the local scale and implementation 

of a long-term groundwater-monitoring network.

Keyworth (2009) used a water-balance approach to 

address concerns regarding groundwater-resource sustainability in the midst of large population growth. The Bayleaf Trail 

Catchment (BTC) used in the study as a typical local-scale 

example encompasses the study area described in the current 

report. Keyworth describes the three community wells previously mentioned and a total estimate of 35 private wells within 

the approximately 0.4 square mile (mi2) BTC watershed. The 

three CWS wells in the BTC were reportedly part of a larger 

distribution system that included 67 wells.

Keyworth’s (2009) water-balance approach included 

precipitation and wastewater recharge return from onsite 

septic systems as input parameters to the hydrologic system 

in the BTC. Outputs for the water-balance approach included 

groundwater withdrawals from private wells and CWSs, and 

evapotranspiration (ET; both at land surface (irrigation/surface 

water) and within septic fields). For households having a 

private well and onsite septic system, water use was estimated 

to be 55 gal/person/d, which differs from the 100 gal/person/d 

estimated by CDM (2003), and the return of wastewater 

(recharge to the groundwater system) by way of septic systems 

was estimated to be 85 percent of that total use. The return 

from septic systems also was estimated at the same 85 percent 

of total use for households receiving their water supply 

from the three community wells in the BTC. The estimates 

of wastewater return were based on the assumption of a 

comparable percentage of water returned to sewered systems 

from the nearby city of Raleigh and the town of Holly Springs 

in Wake County, NC. Within the septic field, ET was estimated 

to be 15 percent of the water use, resulting in an 85 percent 

recharge to the groundwater system. The water balance for the 

BTC was then solved for streamflow, assuming no change in 

storage in the hydrologic system. The only known estimates of 

streamflow were based on 7Q10 (7-day consecutive flow with 

10 year return frequency) low-flow data for the Upper Barton 

Creek watershed (partial record station for the years 1951 

through 1970 (Weaver, 1998)) that were applied to the smaller 

BTC catchment. Water-balance calculations were made for an 

average year, recent dry years (2005 and 2007), and a wet year 

(2006). 

The combined annual withdrawal of the three CWS wells 

was reported to have increased yearly during 2001–2007 

(Keyworth, 2009). The average daily pumping volumes for 

community wells WK-415 and WK-416 were about 15,000 

to 16,000 gal/d each, whereas the pumping volume for well 

WK-417 was about 5,000 gal/d (Keyworth, 2009, table 2). The 

total reported daily water withdrawals by the three CWSs in 

the BTC was much greater than would be needed to supply the 

60 homes using 55 gal/person/d (Keyworth, 2009). 

A local investigation of groundwater and soil contamination in the study area was published in 1992 (Turner Environmental Consultants, 1992). The contamination included 

gasoline and kerosene compounds that were released from 

underground storage tanks near the intersection of Highway 50 

(Creedmoor Road) and Norwood Road (fig. 2). The investigation reported an average depth to the water table of about 20 

to 25 ft below land surface (bls) in May 1992. The shallow 

regolith consisted of silt and silty clay to silty sand residuum, 

with some quartz stringers, and the presence of weathered 

gneiss at a depth of about 57 ft bls. Depth to bedrock was 

estimated to be about 54 ft bls at one location at the site. Shallow groundwater flow was to the north toward Upper Barton 

Creek. The dissolved contaminant plume was described as 

having a north-south elongation, suggesting anisotropy likely 

related to geologic controls. Relict metamorphic foliation and 

the quartz stringers observed in excavations at the site were 

reported to have a north-south trend.

Methods of Investigation 

Data collection in the current study included well 

inventory, geologic structural mapping, borehole geophysical 

logging, periodic groundwater-level measurements, continuous groundwater-level monitoring, and groundwaterwithdrawal monitoring. A well inventory was conducted early 

in the study to obtain access for water-level measurements and 

to record information obtained from the well tag. NCDENR 

has required that well tags be affixed to the surface casing of 

newly constructed wells since the late 1970s (North Carolina 

Department of Environment and Natural Resources, 2002). 

The well tags are required to contain the following information: date drilled, driller’s name, static water level at the 

time of drilling, yield, depth of casing, and total depth of the 

well. A total of 8 observation wells and 35 private wells were 

inventoried within the study area, and data from the associated 
Introduction 9

well tags (where found) are presented in table 1 along with 

information reported for the three community wells. 

Measurements of foliation (rock fabric) and fracture 

(joints) orientations were recorded in the field by using a 

traditional magnetic compass corrected for local magnetic 

declination. Only a few outcrops were measured near the study 

area, as the rocks were deeply weathered. Geologic structural 

measurements were made at five stations in or near the study 

area. Regional geologic mapping structural information 

previously collected near the study area also is presented in 

this report.

Borehole geophysical logging was conducted in two 

wells in the study area and included the traditional caliper, 

natural gamma, electrical resistivity, and fluid (temperature 

and resistivity) logs, as well as optical and acoustical 

televiewer logs. The purpose of the geophysical logging was 

to delineate and characterize bedrock fractures and orientations at depth by using optical or acoustic televiewer images. 

Borehole geophysical logs were run in two wells in the study 

area. Orientations of structural features were interpreted from 

optical or acoustic televiewer images by using propriety 

manufacturer’s software. Primary fractures are those that 

are open from visual interpretation of the optical televiewer 

image, compared to secondary fractures which may be only 

weathered or partially open.

Electrical tapes, steel tapes, and acoustical meters were 

used to measure groundwater levels in both observation wells 

(no pump) and private wells (pump installed). Because the 

water levels in many of the wells in the study area frequently 

exceeded 100 ft bls, problems with reading electric and steel 

tapes from cascading water and moisture in the well were 

prevalent. In addition, because of reduced access through the 

0.5-inch vent pipe in the sanitary seal on the well head and 

because of the downhole equipment in the well (the pump and 

associated electrical wiring and discharge lines), acoustical 

methods were used throughout the study for measuring deep 

groundwater levels (generally if the water level was greater 

than 100 ft bls) in private wells. All of the private wells were 

in use and thus may have been withdrawn recently prior to a 

measurement. Care was taken to determine if a pump was on 

and to avoid making a measurement during noticeably rapid 

water-level declines.

The acoustical water-level meters are acoustic ranging 

instruments designed to find the distance to the water surface 

within the borehole. A low-frequency (100 hertz) acoustic 

pulse is used for the source signal. The sound speed is 

affected by the air temperature within the borehole and the 

groundwater temperature. In the field, the manufacturer’s table 

of temperature control settings was used for this region of 

North Carolina for each month of field readings. Sensitivity 

to temperature settings in general was found to be within 

one or two tenths of a foot distance to the water level. Water 

levels measured using the acoustical instruments were quality 

assured by comparing readings to electric tapes and steel 

tapes (generally when the water level was shallow; less than 

100 ft bls or within the casing), electrical geophysical logs, 

and pressure transducers. Most readings in private wells were 

made using acoustical meters. If obstructions were present in 

the well, the acoustic meter may have read the water level too 

shallow. In general, the acoustical readings were within 0.5 ft 

of the electrical or steel water-level measurements with the 

largest error being 0.4 ft; thus, the acoustical readings were 

rounded to the nearest foot for entry into the USGS National 

Water Information System (NWIS) database and inclusion in 

this report.

Both traditional pressure transducers and acoustical methods were used to record continuous water levels at six wells 

in the study area. Recording intervals ranged from 1-minute 

intervals in the three private wells to 15-minute intervals in the 

three observation wells. Acoustical monitoring equipment was 

used on all three private wells. 

Three observation wells were equipped with pressure 

transducer water-level monitors during this study. Pressure 

transducers measure water pressure in pounds per square inch 

(psi) above an internal silicon strain gage sensor, which is 

converted to depth to the water level below land surface. The 

pressure transducers used in this study were equipped with 

internal dataloggers that were used to record continuous water 

levels. The pressure transducers used in this study had an 

operating range of 0 to 100 psi for wells WK-368 and WK-375 

and 0 to 30 psi for well WK-411. One psi is equal to 2.31 ft of 

water, so a 100-psi transducer has an operating range of 231 ft, 

and a 30-psi transducer has an operating range of about 69 ft. 

All data were recorded at 15-minute intervals in each of the 

three observation wells. Cable lengths ranged from about 50 

to more than 200 ft. Data were downloaded from the pressure 

transducers by using the manufacturer’s software and then 

quality assured against periodic independent electrical, steeltape, or acoustical water-level measurements. Few problems 

were observed with the pressure transducers. The batteries are 

internal and seldom need replacing, and the clocks are reset 

each time the device is connected to a computer. 

Continuous groundwater levels reported for two of the 

three community wells (Bill Gordon, Aqua America Inc., 

written commun., 2009) also were recorded by using pressure 

transducers having internal dataloggers. Community well 

water levels were recorded at 5-minute intervals. Data were 

available for wells WK-415 and WK-416.

Acoustical water-level monitors also were used to record 

water levels at 1-minute intervals in the three private wells and 

at 15-minute intervals (alongside a pressure transducer/datalogger setup) in one observation well. The acoustical probe 

was placed in the vent access (about 0.5 inch in diameter) 

after removing the vent screw. (A similar setup was used for 

the observation well by using a plastic shield across the top 

of the well at the opening.) The datalogger was connected to 

the probe and placed on a surface above the ground. Standard 

12-volt, 12 ampere per hour batteries were used to power 

the acoustical monitors, which would typically retain power 

for as much as 2 weeks for the 1-minute recording intervals 

and up to 1 month for the 15-minute recording interval. A 
10 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

terminal emulator program was used to communicate with and 

download the data from the acoustical monitors. 

Problems noted with the acoustical monitors included 

drifting of the internal clocks, which were somewhat difficult 

to reset. In addition, the lock on the water-level reading (for 

recording) was sometimes difficult to establish. Abnormalities 

in the well’s construction could have been a factor in the 

locking problem. The manufacturer was asked to modify the 

probe as part of this study, resulting in improved durability in 

the field. 

As part of the quality assurance for the continuous acoustical water levels, a traditional pressure transducer (100 psi 

rating) was placed alongside the acoustical monitor in well 

WK-368 for the entire recording period. The acoustical water 

levels were within 0.1 to 0.4 ft of the pressure transducer readings. Thus, as with the acoustical water-level measurements, 

the continuous acoustical readings were rounded to the nearest 

foot for entry into the USGS NWIS database and inclusion in 

this report.

Two digitally recording ultrasonic flowmeters were 

installed on two private wells for a few weeks to measure 

groundwater withdrawals. These data were recorded at 

1-minute intervals to be consistent with the continuous water 

levels being recorded in the same well. Total flow per the 

1-minute interval was recorded in units of gallons per minute. 

These ultrasonic flowmeters determined the rate of flow 

through the polyvinyl chloride (PVC) discharge pipe and 

were attached to the outside wall of the pipe. Initial setup of 

the flowmeter involved specifying the type of pipe material, 

diameter of the pipe, and setting up the 4-20 milliamp output 

range for the device to send data to the data logger. A standard 

universal serial bus (USB) connection was used for data 

logger connection. Setup of the data logger was done using a 

laptop computer with the associated manufacturer’s software. 

An example of a problem with the flowmeter equipment 

included the wiring from the flowmeter to the connections on 

the data logger USB receptacle being too heavily gaged and 

thus the connection was easily broken. This was corrected by 

replacing the receptacle with a lighter gaged wire. Also, some 

recurring corrosion was evident inside the USB connections, 

which affected logging capabilities. The flowmeters were 

powered by a deep-cycle marine battery, which lasted from 

10 to 15 days before needing to be replaced. Two standard 

55-ampere per hour batteries also could be used in parallel and 

normally would last about the same amount of time.

The flowmeters initially were mounted inside the well 

houses on a 1-ft straight section of pipe. This proved to be a 

poor location, however, as the flowmeter would give a poor 

signal, likely as a result of turbulence from a sharp bend in the 

pipe both before and after the section where the flowmeters 

were installed. The well houses also had limited space for 

storing the large batteries. For these reasons, the flowmeters 

were relocated from both wells to crawlspaces under the 

homes where a 15-ft straight section of pipe ran from the well 

into the holding tanks. 

Water-level and flowmeter data were downloaded from 

each continuously recording well each week during the study 

period. The acoustical monitors could store about 10 days at 

1-minute intervals before the memory was filled. At the time 

of the data download, a manual measurement was recorded for 

quality assurance. These data also were entered into the USGS 

NWIS database. Manual water-level measurements were 

made using acoustical instrumentation in most wells having 

deep water levels (greater than 100 ft bls). Electrical or steel 

tapes were used when water levels were shallow (less than 

100 ft bls).

The calculation of the cross-correlation function of 

continuous groundwater-level datasets was conducted using 

15-minute samples in paired comparisons to determine 

relations between two of the same types of datasets. Cross 

correlation is a standard method of estimating the degree 

to which two data series are correlated. A value of cross 

correlation at delay time was calculated (Bourke,1996). The 

cross-correlation analytical method can be used to test the 

magnitude of correlation as well as the time lag between two 

time series of the same length and time interval (preferably 

with no missing values). The time lag with the highest correlation coefficient gives information on the difference in time 

with which groundwater levels in two hydraulically connected 

wells respond to the same stress. Groundwater-level data were 

correlated using the nearest 15-minute time-stamped data. 

Free software used for the analyses can be accessed online 

at http://www.wessa.net/ (Wessa, 2009). 

Hydrogeologic Setting

The study area is located within the Bayleaf 1:24,000 

topographic quadrangle in northern Wake County, North 

Carolina (figs. 1, 2). The local geologic unit underlying the 

study area is the Falls Lake schist, described as a medium- to 

coarse-grained, biotite-white mica-oligoclase-quartz schist 

having garnet, staurolite, kyanite, and chlorite porphyroblasts 

with pods of talc schist (Michael Medina, North Carolina 

Geological Survey, written commun., 2007). 

Foliation data recorded as part of the regional mapping 

by the USGS and the North Carolina Geological Survey 

(Michael Medina, North Carolina Geological Survey, written 

commun., 2007) from stations within and near the study area 

indicate that the Falls Lake schist strikes near north-south 

(N. 5° E. to N. 5° W.), dipping 17 to 39 degrees (°) to the 

east or west (respectively), north and east of the study area 

(sites FID-17, -25, and -26; fig. 3), and N. 28–30° W., dipping 

40–45° southwest of the study area (sites FID-5 and -6; 

table 2; fig. 3; Michael Medina, North Carolina Geological 

Survey, written commun. 2007). Minor rock types described 

in this area include amphibolite pods (secondary igneous intrusions). Differential weathering where the schist country rock 

is intruded by amphibolite pods may serve as zones of higher 

well yields as a result of differential weathering along the 
Hydrogeologic Setting 11

17

89

30

19

40

45

88

81

43

33

39 285

280

357

345

316

180

70

Norwood

Creedmoor

Road

Road

Fracture trace lineament interpretation from lidar image

Community well

Private well

Continuous record observation well

Continuous record community well

Continuous record private well

Rose diagram displaying strike azimuth of

 measured borehole fractures. Length of

 petal corresponds to percentage of

 measurements.

Note: WK-375, acoustic televiewer image

 WK-368, optical televiewer image

Borehole geophysical measurements

EXPLANATION

40

89

BL-2

BL-3

BL-6

BL-8

WK-368

BL-10

FID-25

FID-17

FID-6

FID-26

FID-5

N

FID-5

BL-10

80

340

320

300

280

260

240

220

160

140

120

100

0

0

180

180

20

40

60

200

Upper fractures

Lower fractures

0

270 50 40302010 1020 304050 90

180

2520 15 10 5

Structures for wells

WK-375 and BL-8

WK-375

WK-375

Base from North Carolina Center for Geographic Information and Analysis

Light Detection and Ranging Imagery

Upper

Barton

Creek

 Field geologic measurements

Field identification number 

 (Michael Medina, North Carolina Geological

 Survey, written commun., 2007)

Field station number from reconnaissance

 work done for this study (Phil Bradley, North Carolina

 Geological Survey, written commun., 2007) and 

 associated structural measurements

Strike orientation and dip angle of foliation

Strike orientation and dip angle of joint set

Strike orientation of vertical dip angle joint set

35

61

BL-8

5 10 152025

2520 15 10 5 5 10 152025

0 750

0 100 200 300 400 500 METERS

1,500 2,250 3,000 FEET

Figure 3. Fracture 

orientation intrepretations 

from geologic mapping, 

fracture traces, and 

borehole geophysical 

image logs.
12 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

lithologic contact (Chapman and others, 1998; Williams and 

others, 2005). Similarly, differential weathering along foliation 

and fracturing associated with joints provide pathways for 

groundwater flow and higher well yields. 

Additional geologic structural data were recorded as 

part of this study (table 2; fig. 3). These data indicate similar 

foliation strike for three different rock types: amphibolite 

striking N. 5° E. to N. 20° W., the quartzofeldspathic gneiss 

striking N. 15° E., and the mica schist striking N. 22° E. 

(Phil Bradley, North Carolina Geological Survey, written 

commun., 2008; table 2; fig. 3. The quartzofeldspathic gneiss 

and mica schist likely represent the regional Falls Lake schist.) 

All three rock types had moderate dip angles for foliation, 

ranging from about 19 to 43°. In contrast, the joint sets were 

steeply dipping, generally dipping at angles of 80° to vertical. 

The mica schist and amphibolite rock types commonly had 

two joint set groups: (1) E-W (N. 73° W. to N. 71° E.) and 

(2) N. 50–60° E. Additional joint sets included N. 51° W. in 

the quartzofeldspathic gneiss and N. 18° E. in the mica schist; 

the latter of which parallels foliation strike.

Strike orientations of seven topographic fracture traces 

were interpreted from the recently collected light detection and 

ranging (lidar topographic data (fig. 3) in the study area (North 

Carolina Center for Geographic Information and Analysis, 

written commun., 2009). These drainage features may follow 

areas of enhanced weathering or fracturing along structural 

features in the subsurface bedrock and generally correlate with 

many of the local structural geologic features listed in table 2. 

The fracture traces have a dominant 280–285° (N. 75–80° W.) 

orientation (three lineaments), as well as the following 

additional orientations: 7° (N. 7° E.), 15° (N. 15° E.), 316° 

(N. 42° W.), 345° (N. 15° W.), and 357° (N. 3° W.; fig. 3). 

The fracture traces striking N. 15° W. to N. 15° E. correspond 

in general to the strike direction of foliation in all three rock 

types (table 2). The N. 75–80° W. fracture trace parallels one 

of the joint sets mapped in the amphibolite and mica schist 

rock types, and the N. 42° W. fracture trace generally parallels 

the joint set mapped in the quartzofeldspathic rock type 

(table 2). 

The groundwater system in the study area consists of two 

components, which is typical of most aquifers in the Piedmont 

region of North Carolina (fig. 4). The shallow part of the 

groundwater system is referred to as the “regolith” (fig. 4A) 

and may be composed of soil, residuum, alluvium, colluvium, 

and saprolite (Chapman and others, 2005). The deeper part of 

the groundwater system consists of the “fractured bedrock” 

(fig. 4). Anisotropy can occur in both parts of the groundwater 

system associated with relict structures in saprolite in the 

regolith or as fracture networks in the bedrock. Primary 

storage for the groundwater system is in the shallow regolith, 

with the deeper bedrock fracture storage orders of magnitude 

lower (fig. 4). Water stored in the overlying regolith provides 

recharge to the deeper fractures in the bedrock. Because of the 

reduced storage of groundwater in the bedrock, large drawdowns in the aquifer can be observed if depletion (dewatering) 

of water in the bedrock fractures occurs during withdrawals.

Table 2. Geologic structure measurements recorded near the study area in northern Wake County, North Carolina.

Station 

number

Structural 

feature Rock type

Strike 

(360 degree 

reference)

Quadrant 

strike 

direction

Dip angle 

(degrees)

Dip 

direction Spacing

Regional measurements from Horton and others, 2004

FID 26 foliation Falls Lake schist 185 N. 5° E. 17 NW

FID 25 foliation Falls Lake schist 185 N. 5° E. 39 NW

FID 17 foliation Falls Lake schist 175 N. 5° W. 33 SW

FID 6 foliation Falls Lake schist 152 N. 28° W. 40 SW

FID 5 foliation Falls Lake schist 150 N. 30° W. 45 SW

Measurements recorded as part of this study

BL-2 foliation Amphibolite 185a N. 5° E. 19 NW

BL-2 joint Amphibolite 283a N. 73° W. 88 NE 8–12 inch spacing

BL-3 foliation Quartzofeldspathic gneiss 195a N. 15° E. 43 NW

BL-3 joint Quartzofeldspathic gneiss 309a N. 51° W. 81 NE 12–18 inch spacing

BL-6 foliation Mica schist 202a N. 22° E. 30 NW

BL-6 joint Mica schist 270a E-W 90 N

BL-6 joint Mica schist 198 N. 18° E. 89 NW

BL-6 joint Mica schist 60 N. 60° E. 90 SE

BL-8 foliation Amphibolite 160 N. 20° W. 35 NW

BL-8 joint Amphibolite 71 N. 71° E. 90 SE

BL-8 joint Amphibolite 240 N. 60° E. 61 NW 2–18 inch spacing

BL-10 joint Amphibolite 50a N. 50° E. 90 SE a

 Averaged value.
Hydrogeologic Setting 13

Figure 4. Two-component groundwater system in the Piedmont region showing the storage comparison between the 

shallow regolith and deeper bedrock components (modified from Heath, 1984).

Regolith reservoir

Well

Casing

Bedrock

fractures

Water table

Storage

in 

bedrock

Storage in regolith

Figure 4. Two-component groundwater system in the Piedmont region showing the storage comparison

 between the shallow regolith and deeper bedrock components (modified from Heath, 1984).

Regolith

Fractured

bedrock

Open hole

Borehole geophysical logs run in well WK-368 

(figs. 2, 5) included caliper, electrical resistivity, fluid 

resistivity and temperature, and optical televiewer imaging. 

This well had a reported yield of 12 gal/min (table 1), and 

interpretations from borehole geophysical logging indicated 

that small fractures were present at depths of 80–89 ft, 128 ft, 

and 398–400 ft bls (fig. 5; table 3). The shallow fractures at 

80–89 ft and 128 ft are present within a feldspathic unit that 

has a schist texture, likely correlating with the mica schist 

listed in table 2 and shown in figure 2 (regionally, Falls Lake 

schist). The 128-ft fracture is at a contact with a minor (thin, 

0.5 ft) feldspathic vein or pegmatite. Manganese-oxide or 

“black” staining is present along the borehole wall near the 

steeper-dipping fractures in the 80- to 89-ft zone. This staining 

could be the result of the natural flow of oxygenated groundwater when the fracture zone was saturated or downward flow 

of recharge occurring when the fractures were dewatered; 

water levels were below this zone throughout the study period. 

The deeper fracture zone is within a more mafic lithology, 

perhaps amphibolite or amphibolite gneiss, or simply a 

mineralogic variation of the mica schist. More mafic regions 

generally have relatively lower natural gamma readings 

(fig. 5). Variations of the schist to more gneissic (banded) rock 

types, potentially the quartzofeldspathic gneiss mapped in the 

area, also were observed in well WK-368. Although quantitative flow was not measured in this well, from the fluid specific 

conductance log (fig. 5), groundwater is flowing into the well 

at depth near the 398–400 ft fracture zone and again at 456 ft 

(no obvious fractures). It is likely that water is flowing down 

the borehole from the 80- to 89-ft and 128-ft fractures and up 

from the deeper 398–400+ fractures and then flowing out of 

the well somewhere in between those depths.

The dominant fracture orientations measured in the 

shallow (81–87 ft) fracture zones in well WK-368 had an 

average strike of N. 67° W. (variable dip angle) and N. 63° W. 

(steep dip angle), with an additional fracture striking 

N. 45° W. (figs. 3, 5; table 3). Fracture orientations in the 

deep (398–400 ft) zone had a more variable strike and low 

dip angles (fig. 5; table 3), with one orientation of N. 42° W. 

similar to a fracture in the shallow 80- to 87-ft zone. The 

strike of fractures in the shallow and deep zones generally 

correlate with joint sets that were mapped in the amphibolite 

(N. 73° W. and N. 71° E.; table 2) and the fracture traces 

having a N. 75–80° W. strike orientation (fig. 3). An additional 

fracture orientation measured in well WK-368 had a strike of 

N. 42–45° W. (318–315° azimuth; figs. 3, 5; table 3) for both 

the upper and lower fracture zones, which correlates with 

the N. 42° W. fracture traces traced near station BL-6 (fig. 3; 

table 2), and a joint set measured striking N. 40–45° W. in the 

quartzofeldspathic rock type at station BL-3 (fig. 3; table 2), as 

well as the fracture orientation measured at a depth of 82.6 ft 

in well WK-368 (table 3; fig. 5). A third orientation of N-S 

to N. 10° E. (0–10° azimuth; fig. 5) measured for both the 

upper and lower fractures in well WK-368 parallels foliation 

measurements from the regional and local mapping (table 2). 

The N. 30–40° E. orientation measured in the lower fractures 
14 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

0

50

100

150

200

250

300

350

400

450

500

0 90

Fracture/Foliation/

Lithologic Contact

Dip angle (degrees)

6 6.7

Caliper (inch)

Fracture

zone

(periodically

dewatered)

Fracture

zone

(periodically

dewatered)

Fracture

zone

Specific conductance

(μS/cm)

60 65

Temperature 

(Degrees Fahrenheit)

0 300

DEPTH, IN FEET BELOW LAND SURFACE

0 200

Gamma Log (APIU)

Resistivity 16-inch normal

Resistivity 64-inch normal

0 4,000

0 4,000

Secondary fracture

Primary fracture

Foliation

Lithologic contact

Water level

Primary fractures are the

 most open fractures in the

 borehole that are likely

 water bearing

Secondary fractures are

 weathered, but may not

 be open

EXPLANATION

0 90 180

Optical Televiewer Image

270 0

N E S W N

Figure 5. Geophysical logs and orientation of borehole structural measurements

 from well WK-368. [μS/cm, microsiemens per centimeter]

N

S

W E

Example of tadpole

showing dip azimuth

Figure 5. Geophysical logs and orientation of borehole structural measurements in well WK-368. [APIU, American Petroleum Institute units;

μS/cm, microsiemens per centimeter]
Groundwater Withdrawals 15

does not appear to directly correlate with measured geologic 

structural measurements or fracture traces. 

Borehole geophysical logs run in well WK-375 (figs. 2, 

6) included caliper, electrical resistance and resistivity, fluid 

resistivity and temperature, and acoustical televiewer imaging. 

Logs run in well WK-375, which is located about 300 ft 

east-southeast of community well WK-416 (fig. 2) and has a 

reported yield of 40 gal/min, indicated the presence of a large, 

open fracture at a depth of about 282.5 to 284.5 ft (table 3; 

fig. 6). Shallow fractures also were noted at depths of about 

40, 45–47, and 92 ft from the caliper log. These shallow 

fractures were dewatered at the time of logging (July 29–30, 

2008) when the water level in the well was about 130 ft 

bls and, therefore, could not be measured by the acoustic 

televiewer tool. Strike orientations of the open, deeper 

fractures at the 282–285 ft zone were dominantly east-west 

(N. 86° W. and N. 78° W., azimuth 94° and 282°, respectively 

(fig. 3; table 3), which is similar to the near E-W orientations 

(N. 75° E.; table 3; fig. 3) measured in well WK-368. The 

orientation of these fractures also corresponds to the joint sets 

that were mapped in the amphibolite (N. 73° W. and N. 71° E.; 

table 2) and the fracture traces having a N. 75–80° W. strike 

orientation (fig. 3). 

Specific conductance was elevated in the deep fracture 

zone of WK-375 about 282.5 to 284.5 ft bls (fig. 6), indicating 

inflow to the well at that depth. The temperature log has no 

typical (natural) geothermal gradient that can be recognized 

and indicates downward flow (remains the same rather 

than increasing with the geothermal gradient) to a depth of 

about 200 ft, where the natural geothermal gradient slope is 

recognizable. A temperature increase at the deepest fracture 

also indicates inflow within the borehole at that depth. All 

three fractures (two shallow and one deep) correspond to low 

gamma readings, suggesting a more mafic rock type, such as 

the amphibolites pods that are mapped at land surface near 

the study area (Michael Medina, North Carolina Geological 

Survey, written commun., 2007). 

Groundwater Withdrawals

Groundwater withdrawals in the study area are from 

both community-supply and individual private wells. Three 

known CWS wells and about 35 individual private wells use 

groundwater (fig. 2; table 1) in the study area. 

Table 3. Well fracture characteristics.

[Note: Average orientations are calculated from the group above]

Well number

Fracture depth 

(feet below 

land surface)

Dip azimuth 

(degrees)

Dip angle 

(degrees)

Strike azimuth 

(degrees) Strike Dip direction

WK-368a 80.8 209 43 119 N. 61° W. SW

81.4 197 81 107 N. 73° W. SW

average 203 62 113 N. 67° W. SW

82.6 45 18 315 N. 45° W. NE

86.4 24 80 294 N. 66° W. NE

86.6 29 80 299 N. 61° W. NE

average 27 80 297 N. 63° W. NE

398.4 277 13 187 N. 7° E. NW

399.2 306 7 216 N. 54° E. NW

399.6 48 21 318 N. 42° W. NE

399.8 348 26 258 N. 78° E. NW

399.9 341 25 251 N. 71° E. NW

average 345 26 255 N. 75° E. NW

WK-375b 282.6 186 31 96 N. 84° W. S-SW

284.2 180 20 90 E-W S

286.7 186 8 96 N. 84° W. S-SW

average 184 19 94 N. 86° W. S-SW

285.2 12 20 282 N. 78° W. NE a

 Measured using an optical televiewer tool.

b

 Measured using an acoustical televiewer tool.
16 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

0 400

Gamma Log (APIU)

0 90

Fracture/Foliation/Contrast

Dip angle (degrees)

6 11

Caliper (inch)

61 62

Temperature 

(Degrees Fahrenheit)

0 150

Lateral resistivity

64-inch normal

Resistance

0 4,000

Resistivity 64-inch normal

0 3,000

Resistivity 16-inch normal

0 4,000

0 2,000

0

20

40

60

80

100

120

140

160

180

200

220

240

260

280

300

DEPTH, IN FEET BELOW LAND SURFACE

Fracture

zone

(dewatered)

Fracture

zone

(dewatered)

fracture

zone

Primary

Figure 6. Geophysical logs and orientation of borehole structural measurements

 from well WK-375. [μS/cm, microsiemens per centimeter]

Secondary fracture

Primary fracture

Foliation

Lithologic contact

Water level

Primary fractures are the

 most open fracturs in the

 borehole that are likely

 water bearing

Secondary fractures are

 weathered, but may not

 be open

EXPLANATION

N

S

W E

Example of tadpole

showing dip azimuth

direction

Specific conductance

(μS/cm)

Figure 6. Geophysical logs and orientation of borehole structural measurements in well WK-375. [APIU, American Petroleum Institute 

units; μS/cm, microsiemens per centimeter]
Groundwater Withdrawals 17

Community Wells

As part of the assessment of the effects of large 

groundwater withdrawals on the aquifer system in the study 

area, monthly withdrawal reports were compiled for the three 

community wells by the NCDENR PWSS (Debbie Lyles, 

written commun., 2008) for January through November 

2008 (fig. 7). During this period, pumping volumes for each 

of the three community wells ranged from about 2,000 to 

54,000 gal/d, with a fivefold increase in withdrawals from 

well WK-416 (fig. 2; table 1) during June 2008 (fig. 7). The 

combined annual withdrawal of the three CWS wells was 

reported to have increased yearly during 2001–2007 (Keyworth, 2009). This increase shows the large range of pumping 

volumes from these types of supply wells and the potentially 

associated dynamic effects on water levels in the aquifer in the 

study area.

For some areas that the community wells serve, it is 

reported that the average household uses more than 

100 gal/person/d (Michael Melton, Aqua America, Inc., oral 

commun., 2009), which is similar to what was reported by 

CDM (2003) and likely reflects increased irrigation use from 

in-ground sprinkler systems that are common in the recently 

developed subdivisions near the study area. It should be noted 

that two of the three CWS wells are part of a larger system that 

serve other areas outside of the study area. The USGS 2005 

water-use report for North Carolina estimates the per capita 

use rate at 77 gal/person/d for Wake County for public supply 

(community) wells (U.S. Geological Survey, 2008).

Figure 7. Reported daily withdrawals for the three individual community wells in the study area, January through November 2008. 

See figure 2 for locations.

WK-416

WK-417

WK-415

70,000

60,000

50,000

40,000

30,000

20,000

10,000

0

TOTAL WATER PUMPED, IN GALLONS PER DAY

JAN. 

Figure 7. Reported daily withdrawals for three community wells in the study area. See figure 2 for locations.

FEB. MAR. APR. JUNE

2008

MAY JULY AUG. SEPT. OCT. NOV. DEC.

Note: Estimated daily use from 40

 domestic wells having a four-person

 household at 100 gallons per person

 per day is 16,000 gallons

No withdrawals reported for wells

 WK-415 and WK-416

No withdrawals reported for wells

 WK-415 and WK-416

No withdrawals reported for wells

 WK-415 and WK-416
18 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

Private Wells

Flowmeters were installed on two private observation 

wells, WK-401 and WK-402 (fig. 2), to better quantify local 

groundwater use (fig. 8). Both households had one or two 

full-time residents, with well WK-401 also being used for 

some hand-held garden hose irrigation. Water use from well 

WK-401 was monitored for a period of 4 days from August 29 

through September 1, 2008 (fig. 8A). Water use from well 

WK-402 was monitored for 14 days, from September 5 

through September 18, 2008 (fig. 8B). Most homeowners 

have storage tanks that hold about 30 to 50 gallons of water. 

These storage tanks generally fill quickly, and the two pumps 

monitered as part of this study typically ran from 1 to more 

than 50 minutes per cycle. For the water-use category grouping (fig. 8), it was assumed that household uses had lower 

flow rates of less than 1–2 gal/min, whereas the garden hose 

irrigation use had a much higher flow rate of more than 

11 gal/min. The range in water use for household purposes 

recorded in well WK-401 was from about 105 to 152 gal/d 

Figure 8. Groundwater levels in relation to withdrawals recorded in private observation wells (A) WK-401 and (B) WK-402.

Daily water use

Depth to groundwater

Household water use

Irrigation water use

Total daily water use

Depth to groundwater

125

130

135

140

145

150

155

160

165

170

175

350

300

250

200

150

100

50

0

180

160

140

120

100

80

60

40

20

0

110

120

130

140

150

160

170

180

2008

SEPTEMBER

5 6 7 8 9 10 11 12

2008

AUGUST SEPTEMBER

28 29 30 31 1 2 3

13 14 15 16 17 18

DEPTH TO GROUNDWATER, IN FEET BELOW LAND SURFACE

TOTAL DAILY PUMPAGE, IN GALLONS WATER USE, IN GALLONS

A. WK-401

B. WK-402

Figure 8. Homeowner groundwater levels in relation to withdrawals recorded in wells (A) WK-401 and

 (B) WK-402.
Groundwater Levels in Northern Wake County, March 2008–February 2009 19

(lower flow-rate events). The range of use for garden hose 

irrigation purposes (higher flow-rate events) recorded in well 

WK-402 was from about 29 to 141 gal/d. Total use recorded 

for well WK-401, a two-person household, ranged from 

about 134 to 293 gal/d, averaging 188 gal/d during the 4-day 

monitoring period, or 94 gal/person/d, comparable to the 

100 gal/person/d reported by CDM (2003) and by the CWS 

water provider. This amount is higher than the estimated 

historical 55 gal/person/d usage generally assumed for 

domestic supply in water-use studies by Keyworth (2009) and 

more recently the estimate of 70 gal/person/d made by the 

U.S. Geological Survey (2008). 

In comparison, the household at well WK-402 primarily 

had one resident and one part-time resident. Because of prior 

well problems with the well temporarily going “dry,” the 

household was conservative in their use of water and they did 

not irrigate during the flowmeter monitoring period. Water use 

for well WK-402 ranged from about 2 to 93 gal/d, averaging 

49 gal/d for the 14-day monitoring period, which is comparable to the 55 gal/person/d use commonly reported. 

Groundwater Levels in Northern Wake 

County, March 2008–February 2009

Groundwater levels were measured within the 2,000-ft 

radius study area centered on the Norwood Oaks neighborhood cul-de-sac in the lower Falls Lake watershed in northern 

Wake County, North Carolina, from March 2008 through 

February 2009. These measurements included both continuous 

and periodic water-level readings recorded in observation 

wells and private wells. Additionally, data were acquired from 

nearby community wells as available.

Groundwater-Level Fluctuations

Groundwater-level data from continuously and periodically monitored wells are presented in this section. Water 

levels in six wells were continuously monitored, three of 

which were observation wells, and three were private wells 

(table 1). Periodic water levels also were measured on an 

approximately monthly basis in 35 to 37 private and observation wells. Withdrawals were monitored in two private wells 

for a period of 5 days to 2 weeks. Total daily withdrawals 

reports also were compiled by the NCDENR PWSS for the 

three community wells in the study area for January through 

November 2008. Available continuous groundwater-level data 

recorded in community wells for the study period also were 

compiled from the water provider.

Groundwater-level data were evaluated to determine the 

magnitude of fluctuation and extent of correlation between 

pumped (supply wells) and unpumped (observation) wells at 

both the local scale (private withdrawals) and regional scale 

(community well withdrawals). The magnitude and timing of 

water-level fluctuations in the continuously monitored wells 

were quite varied, depending on whether the well was being 

used (pumped) or affected by larger-use wells, such as those 

used for community supply or irrigation purposes. Correlation 

of continuous water levels was difficult because of the inherent complexities of the fractured-bedrock aquifer and large 

number of pumped wells in the study area. Both local and 

regional cycles were evident in the continuous groundwaterlevel data. Statistical data smoothing methods were used 

to visualize larger regional patterns, and cross-correlation 

analyses were used to determine the potential statistical 

correlation and interference between wells.

Continuous Measurements

Continuous groundwater-level measurements were 

recorded in six wells in the study area (WK-368, -375, -400, 

-401, -402, and -411; fig. 2; table 1) to monitor fluctuations 

associated with both natural effects and stresses, such as 

withdrawals. Three observation wells were monitored and 

three adjacent private wells were monitored as part of this 

study (fig. 2). Additional, continuous groundwater-level 

records were provided for two community wells (Bill Gordon, 

Aqua America,Inc., written commun., 2009).

Observation Wells

Groundwater levels in three observation wells were 

monitored during the summer and early fall of 2008 (table 4). 

Wells WK-368 and WK-411 were located at the southern end 

of Norwood Oaks Drive, and well WK-375 was located at the 

northern end of the study area (fig. 2).

Well WK-368

The first well monitored as part of this study was observation well WK-368, located along Norwood Road (fig. 2), 

where data collection began in late June 2008 and continued 

through late October 2008 (table 4). This well is 500 ft deep 

(table 1; verified with borehole geophysical logging) and has a 

reported yield of about 12 gal/min (table 1). No open fractures 

were evident in the borehole optical televiewer images. Two 

small, weathered fracture zones were noted at depths of 80–89 

and 398–400 ft bls (fig. 5).

Daily and seasonal cyclic fluctuations were observed 

throughout the period of record for well WK-368 (fig. 9). 

Daily water-level fluctuations ranged from 0 to 10 feet per 

day (ft/d), with a decline of as much as 10 ft/d and a rise of as 

much as 7 ft/d (fig. 10). The drawdown cycles generally occur 

once per day, often beginning in the early to mid-morning 

hours, and continuing into the next day. Short-term declines 

for this well were noted on August 2, when the water level 

declined 6 ft in 14 hrs, and on August 4, when the water 

level declined 9 ft in 15 hrs (fig. 9). Water-level fluctuations 

in bedrock well WK-368 ranged from 98 to 130 ft bls from 

late June through late October 2008 (table 4). An overall 
20 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County WELL WK–368 HOURLY DEPTH TO GROUNDWATER, IN FEET BELOW LAND SURFACE

Figure 9. Continuous groundwater levels recorded in observation well WK-368 and nearby rainfall recorded at station 0208706575,

June–October 2008. [ft, feet; bls, below land surface]

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

90

95

100

105

110

115

120

125

130

6/26/08

123 ft bls

1000

8/03–8/04

–10 ft/13.5 hrs

8/09–8/10

–8 ft/34.25 hrs

10/24/08

114 ft bls

0800

–10 ft/13.5 hrs

Water-level decline

of 10 feet in 13.5 hours

TOTAL DAILY RAINFALL, IN INCHES, STATION NUMBER 0208706575

4 8 12 16

JUNE JULY AUGUST SEPTEMBER OCTOBER

20 24 28 4 8 12 16 20 24 28 4 8 12 16 20 24 28 4 8 12 16 20 24 28 4 8 12 16 20 24 28

2008

WK-368 

Beaverdam Creek at dam near Creedmoor,

 station number 0208706575

Figure 9. Continuous groundwater levels recorded in observation well WK-368 and nearby rainfall recorded at station 0208706575, 

June–October 2008. [ft, feet; bls, below land surface; hr, hour]

Table 4. Period of record and range of groundwater levels recorded in continuously monitored observation wells, private wells, 

and community wells.

[WK, Wake County, NC; ft, feet; bls, below land surface; bmp, below measuring point]

Well 

number Well category Period of record Lowest groundwater level and date

Highest groundwater 

level and date

Recording 

interval

Total 

well 

depth

WK-368 Observation 06/26/08–10/24/08 130 ft bls, 8/10–11/08 98 ft bls, 9/13/08 15 minutes 500

WK-375 Observation 7/20/08–10/24/08 214 ft bls, 8/6/08 75 ft bls, 9/6 and 9/13/08 15 minutes 305

WK-411 Observation 07/29/08–10/22/08 38.40 ft bls, 8/29/08 33.03 ft bls, 9/14/08 and 

9/27/08

15 minutes 306

WK-400 Private 8/22/08–10/24/08 209 ft bls, 10/15/08 126 ft bls, 9/13/08 1 minute 400

WK-401 Private 7/6/08–10/24/08a 228 ft bls, 8/8/08 123 ft bls, 9/18/08 1 minute 410

WK-402 Private 8/22/08–10/24/08 187 ft bls, 8/25/08 113 ft bls, 9/13/08 1 minute 290

WK-415 Community 0729/08–12/16/08 261 ft bmp, 8/8/08 68 ft bmp, 12/12–13/08 5 minutes 695

WK-416 Community 12/19/08–01/21/09 229 ft bmp, 01/04/09 139 ft bmp, 1/17/09 5 minutes 805

a

 Data missing 9/6/08 through 9/15/08.
Groundwater Levels in Northern Wake County, March 2008–February 2009 21

70

60

50

40

30

20

10

0

 0 to 1 2 to 3 4 to 5 6 to 7 8 to 9 10 to 11

Total days = 119

Figure 10. Histogram of daily water-level fluctuations (difference between high

 and low readings) recorded in observation well WK–368, June 26 through

 October 24, 2008.

Note: All values could be either

 a rise or decline in water levels 

NUMBER OF DAYS

MAGNITUDE OF DIFFERENCE BETWEEN HIGH AND LOW WATER LEVELS, IN FEET

Figure 10. Histogram of daily water-level fluctuations (difference between high and low 

readings) recorded in observation well WK-368, June 26 through October 24, 2008.

decline occurred in mid-July through mid-August, when the 

water level decreased by about 26 ft. An overall rise in the 

high water level (recovery of the groundwater system) was 

observed in mid-August through mid-September 2008, with 

an increase of about 32 ft (fig. 9; table 4). This large recovery 

indicated that the aquifer system had not lost permanent 

storage and had recovered at least to some degree. This rise 

likely is a function of both recovery of the aquifer from a 

reduction in pumping (reduced irrigation use during periods of 

increased rainfall) and recharge from precipitation through a 

higher water table in the overlying regolith (figs. 4, 9). 

Well WK-375

Of the three observation wells monitored as part of this 

study, bedrock well WK-375 (fig. 2; table 4) had the largest 

magnitude of short-term drawdowns; the largest water-level 

declines were as high as about 75 ft within a few hours 

(fig. 11). For example, on July 30 the water level declined 

about 75 ft in 5 hrs, on August 20 the water level declined by 

76 ft in 5.75 hrs, and on October 21 the water level declined 

by 60 ft in 3.25 hrs. These large declines generally began in 

the early morning hours, possibly related to increased use 

from people showering before work or school, or irrigation 

of landscape or lawns. Daily groundwater-level fluctuations 

for this well during the July through October 2008 study 

period ranged from a decline of 78 ft per day to a rise of 73 ft 

(figs. 11; 12). Often during the servicing and downloading 

of continuous data at this well, water-level measurements 

indicated a decline during the few minutes that field personnel 

were at the well. Water levels recorded from July through 

October 2008 in well WK-375 ranged from 75 to 214 ft bls.

An overall long-term decline of about 108 ft in the high 

water level occurred from July 21 through August 6 and about 

100 ft from September 6 through October 24 at the end of 

the study period (fig. 11). As was observed in well WK-368 

(fig. 2), the minimum water level recorded in well WK-375 

rose about 139 ft from late August through mid-September 

2008. The timing of this overall rise was similar to that 

observed in well WK-368, most likely related to reduced 

pumping for irrigation purposes because of recent rainfall and 

recharge from precipitation through a higher water table in 

the overlying regolith (figs. 4, 11). Again, this large recovery 

indicated that the aquifer system had not lost permanent storage and had at least recovered for a period until the recharge 

period ended and the stress increased.
22 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

7/30/08

–75 ft/5 hrs

8/06/08

–76 ft/6 hrs

8/20/08

–76 ft/

5.75 hrs

10/21/08

–60 ft/3.25 hrs

108 ft bls

7/21/08

0000

151 ft bls

10/24/08

0930

WELL WK–375 DEPTH TO GROUNDWATER, IN FEET BELOW LAND SURFACE

Figure 11. Continuous groundwater levels recorded in 15-minute intervals in observation well WK-375 and nearby rainfall 

recorded at station 0208706575, June–October 2008. [ft, feet; bls, below land surface; hr, hour]

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

40

60

80

100

120

140

160

180

200

220

TOTAL DAILY RAINFALL, IN INCHES, STATION NUMBER 0208706575

4 8 12 16

JUNE JULY AUGUST SEPTEMBER OCTOBER

20 24 28 4 8 12 16 20 24 28 4 8 12 16 20 24 28 4 8 12 16 20 24 28 4 8 12 16 20 24 28

2008

–75 ft/6 hrs

Water-level decline

of 75 feet in 6 hours

WK-375 

Beaverdam Creek at dam near Creedmoor,

 station number 0208706575

Figure 11. Continuous groundwater levels recorded in observation well WK-375 and nearby rainfall recorded at station 0208706575, 

June–October 2008. [ft, feet; bls, below land surface; hr, hour]

60

50

40

30

20

10

0

10 to 19 20 to 29 30 to 39 40 to 49 50 to 59 60 to 69 70 to 79

Total days = 92

Figure 12. Histogram of daily water-level fluctuations (difference

 between high and low readings) recorded in observation

 well WK–375, July 21 through October 24, 2008.

NUMBER OF DAYS

MAGNITUDE OF DIFFERENCE BETWEEN HIGH AND LOW WATER LEVELS, IN FEET

Note: All values could be either 

 a rise or decline in water levels 

Figure 12. Histogram of daily water-level fluctuations (difference between high and 

low readings) recorded in observation well WK-375, July 21 through October 24, 2008.
Groundwater Levels in Northern Wake County, March 2008–February 2009 23

Well WK-411

Both shallow and deep groundwater levels were recorded 

in the two continuously monitored wells along Norwood Road 

(fig. 2). While well WK-368 recorded relatively deep groundwater levels generally greater than 100 ft in depth (fig. 9), 

water levels recorded in well WK-411 had much shallower 

water levels ranging from 33.03 to 38.40 ft bls from late July 

through late October 2008 (fig. 13; table 4). These two wells 

are located about 500 ft apart (west-southwest direction from 

WK-368 to WK-411; fig. 2) and have different total depths; 

well WK-368 is about 500 ft deep and well WK-411 is about 

300 ft deep (table 1). Daily groundwater-level declines 

recorded in well WK-411 generally were less than 1 ft 

(fig. 14). Two larger short-term declines of about 3 ft (fig. 14) 

were recorded on August 29 and 30 (fig. 13). The water level 

in this well responded similarly to the overall regional trends, 

with an overall rise in the water level from mid-August 

through mid-September 2008 of about 5 ft during a similar 

time period in which water levels in the other two observation 

wells, WK-368 and WK-375, also increased (table 4; fig. 13). 

8/30/08

–3.05 ft/1.5 hrs

36.26 ft bls

7/29/08

1030

35.51 ft bls

10/22/08

0630

WELL WK–411, HOURLY DEPTH TO GROUNDWATER, IN FEET BELOW LAND SURFACE

Figure 13. Continuous groundwater levels recorded in observation well WK-411 and nearby rainfall recorded at station 0208706575,

 June–October 2008. [ft, feet; bls, below land surface]

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

32

33

34

35

36

37

38

39

40

TOTAL DAILY RAINFALL, IN INCHES, STATION NUMBER 0208706575

4 8 12 16

JUNE JULY AUGUST SEPTEMBER OCTOBER

20 24 28 4 8 12 16 20 24 28 4 8 12 16 20 24 28 4 8 12 16 20 24 28 4 8 12 16 20 24 28

2008

WK-411

Beaverdam Creek at dam near Creedmoor,

 station number 0208706575

–3.05 ft/1.5 hrs

Water-level decline

of 3.05 feet in 1.5 hours

Figure 13. Continuous groundwater levels recorded in observation well WK-411 and nearby rainfall recorded at station 0208706575, 

June–October 2008. [ft, feet; bls, below land surface; hr, hour]
24 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

50

45

40

35

30

25

20

15

10

5

0

0 to 0.49 0.5 to 0.99 1.0 to 1.49 1.5 to 1.99 2.0 to 2.49 2.5 to 2.99 3.0 to 3.49 3.5 to 3.99 > 4.0 

Total days = 84

Figure 14. Histogram of daily water-level fluctuations (difference between high and low readings)

 recorded in observation well WK-411, July 29 through October 22, 2008.

Note: All values could be either

 a rise or decline in water levels 

NUMBER OF DAYS

MAGNITUDE OF DIFFERENCE BETWEEN HIGH AND LOW WATER LEVELS, IN FEET

Figure 14. Histogram of daily water-level fluctuations (difference between high and low readings) 

recorded in observation well WK-411, July 29–October 22, 2008.

Private Wells 

Three private wells in the Norwood Oaks subdivision 

were continuously measured to monitor water-level declines 

from local withdrawals. All three private wells (WK-400, 

-401, and -402; table 1; fig. 2) had the same pattern of fluctuation and similar magnitudes of decline and recovery (fig. 15). 

Two of the wells (WK-400 and -401) are about 400 ft deep, 

whereas WK-402 is about 290 ft deep (table 1). Water levels 

in all three wells ranged from about 113 to 228 ft bls during 

the July through late-October 2008 monitoring period (table 

4). The highest water levels recorded were in mid-September, 

similar to the continuously monitored observation wells 

(table 4). The range of daily water-level fluctuations measured 

in the three private wells was more than a 40-ft decline and as 

much as a 50-ft rise per day (fig. 16). Private wells with water 

levels that exceed 200 ft in depth are the most susceptible to 

becoming "dry" (near the shallower depth of 300 ft in wells 

such as WK-402; table 1). When the initial problem of wells 

going dry (water level below the pump) was reported in 

July 2005, some homeowners either had their wells deepened 

(for example, WK-400, table 1), or hydrofractured to improve 

yield (resulting in less drawdown during pumping, which can 

prevent the water in the well from declining to a level near 

the pump). Well WK-400 has not gone dry since the well was 

deepened to 400 ft. 

Successive changes in daily mean groundwater levels 

in the six observation wells are shown in figure 17, with 

observation well WK-375 and the three private wells 

(WK-400, -401, and -402) showing the largest magnitude 

of change. These variations in magnitude of fluctuation are 

common in fractured-bedrock aquifers, because the network 

of fractures being affected by stress is complex. 
Groundwater Levels in Northern Wake County, March 2008–February 2009 25

Figure 15. Water-level fluctuations in homeowner wells WK-400, WK-401, and WK-402 showing a similar regional pattern,

July–October 2008. [ft, feet; bls, below land surface] 

WK-400 

WK-401 

WK-402 

153 ft bls

7/06/08

1457

(WK-401)

192 ft bls

8/22/08

1106

(WK-400)

183 ft bls

8/22/08

1054

(WK-402)

160 ft bls

10/24/08

0739

(WK-402)

174 ft bls

10/24/08

0904

(WK-401)

173 ft bls

10/24/08

0842

(WK-400)

DEPTH TO GROUNDWATER, IN FEET BELOW LAND SURFACE

80

100

120

140

160

180

200

220

240

6 9 12 15 18

JULY AUGUST SEPTEMBER OCTOBER

21 24 27 30 3 6 9 12 15 18 21 24 27 30 3 6 9 12 15 18 21 24 27 30 3 6 9 12 15 18 21

2008

Figure 15. Water-level fluctuations in private wells WK-400, WK-401, and WK-402 showing a similar regional pattern, July–

October 2008. [ft, feet; bls, below land surface]
26 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

30

25

20

15

10

5

0

50

45

40

35

30

25

20

15

10

5

0

18

16

14

12

10

8

6

4

2

0

0 to 4 5 to 9 10 to 14 15 to 19 20 to 24 25 to 29 30 to 34 35 to 39

Total days = 62

Total days = 95

Total days = 39

NUMBER OF DAYS

MAGNITUDE OF DIFFERENCE BETWEEN HIGH AND LOW WATER LEVELS

A. Well WK-400, Aug. 22–Oct. 24, 2008

B. Well WK-401, July 6–Oct. 24, 2008

C. Well WK-402, Aug. 22–Oct. 24, 2008

0 to 9

5 to 9 10 to 14 15 to 19 20 to 24 25 to 29 30 to 34

10 to 19 20 to 29 30 to 39 40 to 49 50 to 59 60 to 69

Note: All values could be either

 a rise or decline in water levels 

Figure 16. Histograms of daily water-level fluctuations in

 homeowner wells (A) WK-400, (B) WK-401, and

 (C) WK-402, July–October 2008.

Figure 16. Histograms of daily water-level fluctuations in private wells (A) WK-400, 

(B), WK-401, and (C) WK-402, July–October 2008.
Groundwater Levels in Northern Wake County, March 2008–February 2009 27

Community Wells

Water-level data were obtained for two of the three community wells (WK-415 and -416; fig. 2; table 1) for months 

overlapping the study period (Bill Gordon, Aqua America, 

Inc., written commun., 2009). The range of water-level fluctuation in each well is listed in table 4, and the hydrographs of 

available data are shown in figure 18. Pump intake depth for 

well WK-415 was reported to be 420 ft (Mike Melton, Aqua 

America, Inc., written commun., 2009). Well WK-415 had 

similar but somewhat deeper groundwater levels compared 

to continuously monitored private wells (WK-400, -401, 

and -402) and observation well WK-375, with water-levels 

fluctuating between 68 and 261 ft bls from late July through 

December 2008 (fig. 18A). A regional pattern of fluctuation 

also was evident, similar to other wells monitored as part 

of this study. Daily water-level declines ranged from about 

43 to 121 ft for this monitoring period, with the pump being 

turned on and off nearly every hour each day during high-use 

periods. Well WK-415 did recover to within 50 percent of the 

pre-withdrawal level within 10 minutes; however, the well did 

not rest for long periods with at least 15 or more cycles per 

day (fig. 18A).

Well WK-416 was only monitored from December 2008 

through January 2009, but had similar water-level fluctuations 

with a high water level of about 139 ft bls and a low water 

level of about 229 ft bls (Bill Gordon, Aqua America, Inc., 

written commun., 2009; fig. 18B; table 4). Pump intake depth 

in this well was reported to be 378 ft bls (Mike Melton, Aqua 

America, Inc., written commun., 2009). Daily water-level 

declines for the monitoring period in well WK-416 ranged 

from about 71 to 84 ft of drawdown; however, no continuous 

record monitoring data were available from either observation 

wells or private wells for the same time period (table 4). The 

short-term water-level fluctuations recorded in community 

well WK-416 show similar frequent use per day and rapid 

recovery for each cycle, similar to community well WK-415; 

however, again, the well did not rest for long periods.

WK-368

WK-375

WK-400

WK-401

WK-402

WK-411

40

30

20

10

0

–10

–20

–30

–40

DAILY MEAN RISE OR DECLINE, IN FEET

26 3 10 17 24 31 7 14 21 28 4 11 18 25 2 9 16 23

JUNE JULY AUGUST SEPTEMBER OCTOBER

2008

Figure 17. Successive rises or declines in daily mean groundwater levels in the six observation wells in the study area. Figure 17. Successive rises or declines in daily mean groundwater levels in the six observation wells in the study area.
28 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

50

75

100

125

150

175

200

225

250

300

130

140

150

160

170

180

190

200

210

220

230

A. WK-415

July 29 Sept. 2 Oct. 7

2008

Nov. 11 Dec. 17

B. WK-416

Dec. 19 Dec. 27 Jan. 5

2008 2009

Jan. 13 Jan. 22

GROUNDWATER LEVEL BELOW MEASURING POINT, IN FEET

Figure 18. Water-level fluctuations recorded in community wells (A) WK–415, July 29 through December 16,

 2008, and (B) WK–416, December 19, 2008, through January 21, 2009, collected at 5-minute intervals.

Figure 18. Water-level fluctuations recorded in community wells (A) WK-415, July 29–December 16, 2008, and 

(B) WK-416, December 19, 2008–January 21, 2009, collected at 5-minute intervals.
Groundwater Levels in Northern Wake County, March 2008–February 2009 29

Periodic Measurements

Periodic acoustic tape downs recorded from March 2008 

through February 2009 indicated similar areal patterns of the 

lowest groundwater levels in the study area. These periodic 

water-level measurements were conducted on a bimonthly 

or monthly basis. Water levels were recorded in about 35 

to 37 private and unused observation wells (table 1; fig. 2; 

appendix 1) during the nine field visits on the following dates: 

March 28 (with a few additional wells measured on April 2 

and 16), June 16 (with a few additional wells measured on 

June 26), July 25 (with a few additional wells measured 

on August 12), September 19, October 17, November 21, 

December 19, 2008, and January 29, and February 29, 2009. 

When possible, the nearest reading from the community well 

groundwater-level monitoring dataset is plotted for comparison to the measured private and observation wells in the area. 

Selected water-level measurements are referenced to land 

surface in figure 19, and all datasets are referenced to altitude 

(above North American Vertical Datum 1988) in appendix 1.

In the Norwood Oaks neighborhood, water levels in eight 

wells (WK-410, -406, -405, -404, -403, -402, -401, and -400, 

fig. 2) ranged from 96 to 265 ft bls from March 2008 through 

February 2009 (figs. 19A; 20A); water levels were below 

200 ft bls in June 2008 (fig. 19B) and approached 200 ft bls 

again in October 2008 (fig. 19E). In addition, groundwater levels in a second set (five wells) of private wells to the east and 

southeast along Bayleaf Trail had water levels that approached 

250 ft bls in June 2008 (fig. 19B) and ranged from about 58 

to 248 ft bls (fig. 20B). A third area, including two private 

wells along Norwood Road and Abbey’s Grove Trail, had deep 

groundwater levels; one private well, WK- 381, had a water 

level of 331 ft bls measured in October 2008 (fig. 19E). 

The decline in water levels in some wells of as much as 

100 ft in a little more than 2 months, late March–early April 

to mid- to late-June 2008, (figs. 19A; B) and 50 ft in 1 month 

from September to October 2008 (figs. 19D, E) implies a 

substantial loss of storage in the aquifer, if only short term. 

The water levels did recover, however, from November 

2008 to February 2009 (figs. 19F–I). Trends in depth-togroundwater levels in the areas having the deepest water 

levels (Norwood Oaks neighborhood, Bayleaf Trail area, and 

Abbey’s Grove area (fig. 2)) are shown in figure 19. Compared 

to the water levels reported for wells that were drilled in the 

mid-1990s (table 1), water levels in the aquifer appear to have 

declined several tens of feet. Some wells drilled in 2001 and 

2005 reported water levels of 100 ft at the time (table 1); thus, 

aquifer dewatering below typical unstressed groundwater 

levels in the area was evident by 2001. 

Some long-term storage loss is evident in the local 

aquifer from water levels reported when the wells were 

drilled. During the study period from March 2008 through 

February 2009, regular dewatering of the fractured-bedrock 

aquifer was documented with water levels in many wells 

ranging between 100 and 200 feet below land surface, which 

were much lower than original reported water levels of 15 to 

50 feet below land surface from the 1980s through the late 

1990s (table 1). For example, well WK-368 had a static water 

level of 15 ft bls in February 1992 (table 1) compared to 

water levels ranging from 83 to 130 ft bls from March 2008 to 

February 2009. Well WK-375 had a static water level of 20 ft 

bls when the well was drilled in April 1999 compared to water 

levels ranging from 75 to 214 ft bls from July to October 

2008. Private wells WK-401 and WK-402 had static water 

levels of 30 ft bls when they were originally drilled in June 

1995 and May 1994, respectively; whereas, the range of water 

levels in these two wells was between 99 and 228 ft bls from 

March 2008 to February 2009. An indication of deep groundwater levels was noted when wells WK-381 and WK-396 

had static water levels reported at 100 ft bls in October 2005 

and November 2001, respectively (table 1). Of note is the 

large range of fluctuation recorded in periodic water levels in 

well WK-381 from 120 to 331 ft bls from March/April 2008 

through February 2009 (fig. 20C). 

The pattern of lowest groundwater levels measured 

during the water-level runs was similar for each measurement 

date (fig. 19; appendix 1), primarily grouping along the 

northern section of Norwood Oaks Drive (wells WK-406, 

-405, -404, -403, -402, -401, -400, -410, -396, and -394, fig. 2) 

and along Bayleaf Trail (wells WK-396, -394, fig. 2) elongated 

in a north-south direction. A secondary orientation of lowest 

groundwater levels of N. 65° W. was to the southeast along 

Norwood Road (delineated from wells WK-399, -378, and 

-381, fig. 2). The north-south trend was measured at a depth 

in well WK-368 at 398.4 ft bls (N. 7° E.), and the N. 65° W. 

orientation was measured in well WK-368 at depths of 

80.8–81.4 ft bls (average N. 67° W., table 3) and 86.4–86.6 ft 

bls (average N. 63° W., table 3). The north-south trend in 

the Norwood Oaks Drive area and along the western side 

of Bayleaf Trail is parallel to foliation measurements in the 

regionally mapped Falls Lake schist (FID stations 25 and 26 

(N. 5° E.), and 17 (N. 5° W.), fig. 3; table 2) as well as the 

amphibolite rock type (station BL-2 (N. 5° E.); fig. 3; table 2). 

A similar trend to the secondary N. 65° W. drawdown pattern, 

the N. 60° W. trend, was measured in a joint set within the 

quartzofeldspathic gneiss (N. 51° W., station BL-3, table 2; 

fig. 3). Fracture traces mapped near the Norwood Oaks 

neighborhood vary somewhat from the north-south orientation, striking 7° (N. 7° E.) to 15° (N. 15° E.) and 357°

(N. 3° W.) to 345° (N. 15° W.).

A third potential orientation was observed from the 

water-level altitude maps; a N. 40° W. trend is evident when 

water-level measurements were recorded in well WK-375 

beginning in July 2008 (appendix 1C–I). This trend corresponds to two fractures measured in well WK-368 at depths 

of 82.6 ft bls (N. 45° W.) and 399.6 ft bls (N. 42° W.; station 

BL-3, table 2) or the foliation measurements of N. 28–30° W. 

(FID stations 5 and 6, table 2). From local surficial geologic 

mapping, the N. 51° W. joint set measured in the quartzofeldspathic gneiss (table 2) and the N. 42° W. fracture trace 

(near station BL-6, fig. 3) are most similar to this orientation. 

However, data from more wells in the area between well 
30 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

Figure 19A. Depths to groundwater levels measured in homeowner and observation bedrock wells in the study area on

 March 28 and April 2, 4, and 16, 2008.

Creedmoor

Road

Hwy 50

35

120

128

(62)

(63) 83

(86)

(39)

69

115

100

118

109

105

(58)

113

105 99

96

33

41

49

51

117

(34)

45

32

105

41

54

23

38

(55)

56

32

(45)

50

Norwood

Road

Trail

Abbey’s Grove

Norwood Oaks

Drive

N

0

0

0

Bayleaf

3,357

3,338

3,667

3,357

0

0

0

Location of Wake County in North Carolina

Tax parcel boundaries

Altitude of land surface above NAVD 88.

 Contour interval 2 feet

Area of deepest groundwater levels,

 dashed where approximate

Private or observation well location

 and depth to groundwater level below

 land surface (if no number, well was not

 measured)

April 2 and 4 depths (above NAVD 88) 

 are blue 

April 16 depths (above NAVD 88) 

 are red

Community well and total daily withdrawals

 in gallons reported on respective days of

 water-level measurement

Note: Acoustic water-level measurements

 made in private and observation wells

 may be deeper than recorded if obstructions

 in the well were present

EXPLANATION

39

(83)

(63)

Location of study area and Raleigh in

Wake County, North Carolina

N

Study

area

Raleigh

0 500

0 100 200 300 400 500 METERS

1,000 1,500 2,000 FEET

360

280

320

300

320

340

360

300

400

380

360

340

320

360

340

340

340

360

360

380

380

400

400

400

380

380

360

360

340

380

420

400

Study area

boundary

Figure 19A. Depths to groundwater levels measured in private and unused bedrock wells in the study area on March 28 and 

April 2, 4, and 16, 2008. [NAVD 88, North American Vertical Datum of 1988]
Groundwater Levels in Northern Wake County, March 2008–February 2009 31

Bayleaf

Creedmoor

Road

Hwy 50

36

243

248

76

88

126

(123)

38

(38)

96

(90)

125

(212)

170

(159)

265

(232)

(224)

203

202

205

195

(205) 201

(194)

222

(193)

33

41

44

48

170

35

46

32

117

45

109

60

37

71

80

34

47

50

Norwood

Road

Trail

Abbey’s Grove

Norwood Oaks

Drive

N

360

280

320

300

320

340

360

300

400

380

360

340

320

360

340

340

340

360

360

380

380

400

400

400

380

380

360

360

340

380

420

Figure 19B. Depths to groundwater levels measured in homeowner and observation bedrock wells in the study area on

 June 18 and 26, 2008.

3,800

4,150

49,129

42,013 6,310

5,767

400

Study area

boundary

Location of study area and Raleigh in

Wake County, North Carolina

N

Study

area

Raleigh

5,767

Tax parcel boundaries

Altitude of land surface above NAVD 88.

 Contour interval 2 feet

Area of deepest groundwater levels,

 dashed where approximate

Private or observation well location

 and depth to groundwater level below

 land surface (if no number, well was not

 measured)

June 26 depths are in parentheses

Community well and total daily withdrawals

 in gallons reported on respective days of

 water-level measurement

Note: Acoustic water-level measurements

 made in private and observation wells

 may be deeper than recorded if obstructions

 in the well were present

EXPLANATION

39

(38)

0 500

0 100 200 300 400 500 METERS

1,000 1,500 2,000 FEET

Location of Wake County in North Carolina

Figure 19B. Depths to groundwater levels measured in private and unused bedrock wells in the study area on June 18 and 26, 

2008. [NAVD 88, North American Vertical Datum of 1988]
32 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

Creedmoor

Road

Hwy 50

36

186

(76)

195

74

81

112

(125)

39

77

182

145

184

176

154

153

178

172 167

166

32

41 

47

46

185

35

45

32

126

39 45

17 (38)

41

38

63

70

Norwood

Road

Trail

Abbey’s Grove

Norwood Oaks

Drive

N

360

280

340

300

320

340

360

300

400

380

360

340

320

360

340

340

340

360

360

380

380

400

400

400

380

380

360

360

340

380

420

Bayleaf

Figure 19C. Depths to groundwater levels measured in homeowner and observation bedrock wells in the study area on

 July 25 and August 12, 2008.

20,829

0

(150)

126

(149)

20,557

19,532 5,367

5,129

3,357

150

Tax parcel boundaries

Altitude of land surface above NAVD 88.

 Contour interval 2 feet

Area of deepest groundwater levels,

 dashed where approximate

Private or observation well location

 and depth to groundwater level below

 land surface (if no number, well was not

 measured)

August 12 depths are in parentheses

Community well, total daily withdrawals

 in gallons reported on respective days of

 water-level measurement, and depth to

 groundwater level below measuring point 

 (bold type)

Note: Acoustic water-level measurements

 made in private and observation wells

 may be deeper than recorded if obstructions

 in the well were present

EXPLANATION

39

(125)

400

Study area

boundary

Location of study area and Raleigh in

Wake County, North Carolina

N

Study

area

Raleigh

0 500

0 100 200 300 400 500 METERS

1,000 1,500 2,000 FEET

Location of Wake County in North Carolina

Figure 19C. Depths to groundwater levels measured in private and unused bedrock wells in the study area on July 25 and 

August 12, 2008. [NAVD 88, North American Vertical Datum of 1988]
Groundwater Levels in Northern Wake County, March 2008–February 2009 33

Creedmoor

Road

Hwy 50

37

92

147

155

74

78

101

79

69

142

131

146

137

126

125

139

132 127

125

33

41

38

52

200

35

45

33

143

44

34

25

38

61

62

34

46

Norwood

Road

Trail

Abbey’s Grove

Norwood Oaks

Drive

N

360

280

320

300

320

340

360

300

400

380

360

340

320

360

340

340

340

360

360

380

380

400

400

400

380

380

360

360

340

380

420

Bayleaf

Figure 19D. Depths to groundwater levels measured in homeowner and observation bedrock wells in the study area on

 September 19, 2008.

0

95

0

4,963

0 500

0 100 200 300 400 500 METERS

1,000 1,500 2,000 FEET

400

Study area

boundary

Location of study area and Raleigh in

Wake County, North Carolina

N

Study

area

Raleigh

4,963

95

Tax parcel boundaries

Altitude of land surface above NAVD 88.

 Contour interval 2 feet

Area of deepest groundwater levels

Private or observation well location

 and depth to groundwater level below

 land surface (if no number, well was not

 measured)

Community well, total daily withdrawals

 in gallons reported on respective days of

 water-level measurement, and depth to

 groundwater level below measuring point 

 (bold type)

Note: Acoustic water-level measurements

 made in private and observation wells

 may be deeper than recorded if obstructions

 in the well were present

EXPLANATION

39

Location of Wake County in North Carolina

Figure 19D. Depths to groundwater levels measured in private and unused bedrock wells in the study area on 

September 19, 2008. [NAVD 88, North American Vertical Datum of 1988]
34 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

400

Creedmoor

Road

Hwy 50

43

146

194

202

74

84

116

14

73

190

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172

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41

47

93

331

34

45

32

155

44 31

35

39

39

61

64

33

46

Norwood

Road

Bayleaf

Trail

Abbey’s Grove

Norwood Oaks

Drive

N

360

280

320

300

320

340

360

300

400

380

360

340

320

360

340

340

340

360

360

380

380

400

400

400

380

380

360

360

340

380

420

Study area

boundary

5,125

138

Tax parcel boundaries

Altitude of land surface above NAVD 88.

 Contour interval 2 feet

Area of deepest groundwater levels.

 Dashed where approximate

Private or observation well location

 and depth to groundwater level below

 land surface (if no number, well was not

 measured)

Community well, total daily withdrawals

 in gallons reported on respective days of

 water-level measurement, and depth to

 groundwater level below measuring point 

 (bold type)

Note: Acoustic water-level measurements

 made in private and observation wells

 may be deeper than recorded if obstructions

 in the well were present

EXPLANATION

39

0 500

0 100 200 300 400 500 METERS

1,000 1,500 2,000 FEET

Location of study area and Raleigh in

Wake County, North Carolina

N

Study

area

Raleigh

Figure 19E. Depths to groundwater levels measured in homeowner and observation bedrock wells in the study area on

 October 17, 2008.

22,288

19,013

5,125

138

10:43am

11112 Creedmoor Rd

Location of Wake County in North Carolina

Figure 19E. Depths to groundwater levels measured in private and unused bedrock wells in the study area on October 17, 2008. 

[NAVD 88, North American Vertical Datum of 1988]
Groundwater Levels in Northern Wake County, March 2008–February 2009 35

Creedmoor

Road

Hwy 50

83

138

147

154

46

97

39

67

133

118

136

127

121

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132

123 118

116

65

43

50

43

42

288

34

45

32

125

44 39

34

31

46

57

59

33

46

Norwood

Road

Trail

Abbey’s Grove

Norwood Oaks

Drive

N

360

280

320

300

320

340

360

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400

380

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340

380

420

Bayleaf

Study area

boundary

0 500

0 100 200 300 400 500 METERS

1,000 1,500 2,000 FEET

Location of study area and Raleigh in

Wake County, North Carolina

N

Study

area

Raleigh

Figure 19F. Depths to groundwater levels measured in homeowner and observation bedrock wells in the study area on

 November 21, 2008.

10,620

10,900

3,057

87

10:43am

11112 Creedmoor Rd

3,057

87

Tax parcel boundaries

Altitude of land surface above NAVD 88.

 Contour interval 2 feet

Area of deepest groundwater levels

Private or observation well location

 and depth to groundwater level below

 land surface (if no number, well was not

 measured)

Community well, total daily withdrawals

 in gallons reported on respective days of

 water-level measurement, and depth to

 groundwater level below measuring point 

 (bold type)

Note: Acoustic water-level measurements

 made in private and observation wells

 may be deeper than recorded if obstructions

 in the well were present

EXPLANATION

39

Location of Wake County in North Carolina

Figure 19F. Depths to groundwater levels measured in private and unused bedrock wells in the study area on November 21, 2008. 

[NAVD 88, North American Vertical Datum of 1988]
36 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

360

280

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420

Creedmoor

Road

Hwy 50

70

127

135

142

69

86

41

104

122

108

124

115

113

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120

114 108

104

33

41

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54

153

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149

44 39

32

40

37

55

54

32

46

152

Norwood

Road

Trail

Abbey’s Grove

Norwood Oaks

Drive

N

Bayleaf

Figure 19G. Depths to groundwater levels measured in homeowner and observation bedrock wells in the study area on

 December 21, 2008.

Tax parcel boundaries

Altitude of land surface above NAVD 88.

 Contour interval 2 feet

Area of deepest groundwater levels

Well location and depth to ground-

 water level below land surface

Private or observation well location

 and depth to groundwater level below

 land surface (if no number, well was not

 measured)

EXPLANATION

39

152

0 500

0 100 200 300 400 500 METERS

1,000 1,500 2,000 FEET

400

Study area

boundary

Location of study area and Raleigh in

Wake County, North Carolina

N

Study

area

Raleigh

Note: No community well

 withdrawal information

 available

Note: Acoustic water-level measurements

 made in private and observation wells

 may be deeper than recorded if obstructions

 in the well were present

Location of Wake County in North Carolina

Figure 19G. Depths to groundwater levels measured in private and unused bedrock wells in the study area on December 19, 2008. 

[NAVD 88, North American Vertical Datum of 1988]
Groundwater Levels in Northern Wake County, March 2008–February 2009 37

400

Creedmoor

Road

Hwy 50

64

129

138

74

68

87

39

103

125

107

129

119

111

110

122

114 108

106

32

41

47

34

120

43

44

32

121

43 38

31

39

37

54

53

30

46

Norwood

Road

Bayleaf

Trail

Abbey’s Grove

Norwood Oaks

Drive

N

360

280

320

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360

360

340

380

420

Study area

boundary

0 500

0 100 200 300 400 500 METERS

1,000 1,500 2,000 FEET

Location of study area and Raleigh in

Wake County, North Carolina

N

Study

area

Raleigh

Figure 19H. Depths to groundwater levels measured in homeowner and observation bedrock wells in the study area on

 January 29, 2008.

Note: No community well

 withdrawal information

 available

Note: Acoustic water-level measurements

 made in private and observation wells

 may be deeper than recorded if obstructions

 in the well were present

Tax parcel boundaries

Altitude of land surface above NAVD 88.

 Contour interval 2 feet

Area of deepest groundwater levels

Well location and depth to ground-

 water level below land surface

 (if no number, well not measured)

Private or observation well location

 and depth to groundwater level below

 land surface (if no number, well was not

 measured)

EXPLANATION

31

Location of Wake County in North Carolina

Figure 19H. Depths to groundwater levels measured in private and unused bedrock wells in the study area on January 29, 2009. 

[NAVD 88, North American Vertical Datum of 1988]
38 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

400

Creedmoor

Road

Hwy 50

71

Study area

boundary

125

133

133

67

84

39

102

120

105

122

113

109

108

118

110 105

102

52

40

34

130

34

49

31

120

51

38

32

46

36

55

61

31

45

Norwood

Road

Bayleaf

Trail

Abbey’s Grove

Norwood Oaks

Drive

N

360

280

320

300

320

340

360

300

400

380

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340

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400

400

400

380

380

360

360

340

380

420

0 500

0 100 200 300 400 500 METERS

1,000 1,500 2,000 FEET

Location of study area and Raleigh in

Wake County, North Carolina

N

Study

area

Raleigh

Figure 19I. Depths to groundwater levels measured in homeowner and observation bedrock wells in the study area on

 February 27, 2008.

EXPLANATION

Note: No community well

 withdrawal information

 available

Note: Acoustic water-level measurements

 made in private and observation wells

 may be deeper than recorded if obstructions

 in the well were present

Tax parcel boundaries

Altitude of land surface above NAVD 88.

 Contour interval 2 feet

Area of deepest groundwater levels

Well location and depth to ground-

 water level below land surface

 (if no number, well not measured)

Private or observation well location

 and depth to groundwater level below

 land surface (if no number, well was not

 measured)

52

Location of Wake County in North Carolina

Figure 19I. Depths to groundwater levels measured in private and unused bedrock wells in the study area on February 27, 2009. 

[NAVD 88, North American Vertical Datum of 1988]
Groundwater Levels in Northern Wake County, March 2008–February 2009 39

WK-400

WK-401

WK-402

WK-403

WK-404

WK-405

WK-406

WK-410

WK-378

WK-381

0

50

100

150

200

250

300

WK-394

WK-395

WK-396

WK-397

WK-398

50

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275

0

50

100

150

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350

2008 2009

MAR.

3

APR.

2

MAY

2

JUNE

1

JULY

1

JULY

31

AUG.

30

SEPT.

29

OCT.

29

NOV.

28

DEC.

28

JAN.

27

FEB.

26

MAR.

28

DEPTH TO GROUNDWATER, IN FEET BELOW LAND SURFACE

A. Norwood Oaks neighborhood

B. Bayleaf Trail area

C. Abbey’s Grove area

Figure 20. Trends in depth to groundwater levels in homeowner and observation wells having the deepest

 groundwater levels: (A) Norwood Oaks neighborhood, (B) Bayleaf Trail area, and (C) Abbey’s Grove area. Figure 20. Trends in depths to groundwater levels in private and observation wells having the deepest 

groundwater levels. A, Norwood Oaks neighborhood. B, Bayleaf Trail area. C, Abbey’s Grove area.
40 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

WK-375 and the Norwood Oaks subdivision are needed to 

confirm this trend. 

A fourth orientation not depicted in the water-level maps 

but may be important if drawdown areas continue to develop 

is the N. 80° W. to N. 75° E. (E-W) orientation measured 

in wells WK-375 (282.6 to 286.7 ft bls N. 86° W. average 

trend and 285.2 ft bls N. 78° W., table 3; fig. 3) and WK-368 

(399.8–399.9 ft bls N. 75° E., table 3; fig. 3). Two major 

fracture traces also parallel this orientation (fig. 3). 

Regional Patterns in Groundwater Levels

All six wells in which groundwater levels were continuously recorded indicated similar overall fluctuation patterns 

(figs. 9, 11, 13, 15). Because these wells are separated by 

distances ranging from about 100 ft to 0.45 mi, the pattern 

likely was regional. A similar regional pattern is evident when 

data from observation wells and private wells is modeled 

using a common smoothing method for nonlinear scatterplots 

(Friedman method; Friedman and Tibshirani, 1984; fig. 21). 

This method attempts to capture the trend of points on the 

y-axis as a function of points on the x-axis, using isotonic 

regression and monotone scatterplot smoothing. The smoothed 

comparison of water levels allows separation of short-term 

fluctuations caused by local withdrawals from the overall 

regional pattern of water-level fluctuation, which is most 

likely related to climate and recharge to the aquifer. Water 

levels recorded in observation well WK-375 were compared 

to private well WK-401 (fig. 21A), considered representative 

of the three private wells monitored (fig. 15) and having the 

longest record (table 4). Additionally, a similar regional pattern was observed when the smoothing model of water levels 

in observation well WK-375 was applied to the other two 

observation wells WK-368 (fig. 21B) and WK-411 (fig. 21C). 

Because of the large short-term water-level fluctuations in 

the community well WK-415, a more detailed Kernel scatterplot smoothing method (Wand and Jones, 1993) was used to 

approximate the regional pattern. Figure 21D shows a similar 

comparison of an observation well (WK-375), a private well 

(WK-401), and a community well (WK-415) during late 

July through late October 2008. This regional pattern also 

was compared to smoothed barometric pressure fluctuations; 

however, no relation (typically inverse) could be determined. 

The pattern most likely reflects a dynamic response to the 

combination of withdrawals from both community wells and 

private wells, with reduced withdrawals during periods of 

decreased demand as a result of rainfall (figs. 9, 11, 13, 15), 

and may be affected by withdrawals outside of the study area 

boundary.

Hydrologic conditions reported during the study for this 

area of central North Carolina varied from extreme drought 

to normal. The North Carolina Drought Management Council 

presents a map of drought conditions across the State each 

week (http://www.ncdrought.org/index.php). Evaluating 

conditions during the study period from March 2008 through 

February 2009 for Wake County saw a variety of drought 

categories, from “extreme drought” to “normal” conditions. At 

the beginning of the study in March 2008, Wake County, was 

categorized under extreme drought conditions by the North 

Carolina Drought Management Council (http://

www.ncdrought.org/archive; accessed November 9, 2010). 

For April through May 2008, conditions improved from the 

“severe drought” category enough where some parts of the 

county were under normal hydrologic conditions in early 

June 2008. In June through early July 2008, conditions 

worsened to the severe drought category again. During July 

through late September 2008, hydrologic conditions in the 

county improved back to normal conditions by late September 

as a result of increased rainfall and tropical events. The 

county was categorized as having normal conditions through 

mid-February 2009 when the drought category changed to 

“abnormally dry.” 

Regional groundwater levels were recorded for the study 

period in regolith well WK-284 (Lake Wheeler Road Research 

Station well MW-3S), located in Wake County. A new record 

low water level was recorded in December 2008, surpassing 

the prior record recorded during drought conditions in the 

fall of 2002. By February 2009, the water level had nearly 

recovered to the level recorded in late June 2008, but remained 

at below-normal conditions. Groundwater levels in a second 

regolith well, OR-069 located in nearby Orange County, 

North Carolina, rose throughout the study period, but were 

below normal overall. 

Factors Affecting Groundwater Levels

Groundwater systems respond to hydrologic conditions, 

such as recharge from rainfall, as well as other natural effects, 

including evapotranspiration processes, earth tides, and barometric pressure fluctuations. In the study area, the response 

to natural stresses could not be identified on a regular basis 

because of the stress of groundwater withdrawals (withdrawals) were of higher magnitude and a different frequency than 

natural effects on groundwater levels, where drawdown cycles 

occurred at least once per day. The bedrock aquifer responds 

dynamically to withdrawals because of the lack of storage in 

the fracture networks, even though the fractured bedrock part 

of the aquifer receives recharge through the overlying regolith 

(average thickness (from recorded casing depth) is 67 ft, with 

a range from 23 to 165 ft) in the study area (table 1). The 

bedrock wells recovered during periods of increased rainfall in 

September 2008, likely from decreased use and withdrawals 

for irrigation purposes and downward recharge from a higher 

water table in the overlying regolith. 
Groundwater Levels in Northern Wake County, March 2008–February 2009 41

60

80

100

120

140

160

180

200

220

240

DEPTH TO WATER LEVEL, IN FEET BELOW LAND SURFACE WK-375 DEPTH TO WATER LEVEL, IN FEET BELOW LAND SURFACE

JULY 1 JULY 31 AUG. 31 SEPT. 30 OCT. 31

WK-401

Friedman smoothing

method

Friedman smoothing

method

50

75

100

125

150

175

200

225

WK-368 DEPTH TO WATER LEVEL, IN FEET BELOW LAND SURFACE

100

110

120

130

140

150

160

WK-375

WK-368

WK-375

Figure 21. Overlay of water levels from wells showing a similar modeled regional pattern of fluctuation:

 (A) observation well WK-375 and homeowner well WK-401 and (B) observation wells WK-375 and WK-368.

A

B

2008

Figure 21. Overlay of water levels from wells showing a similar modeled regional pattern of fluctuation. 

A, observation well WK-375 and private well WK-401. B, observation wells WK-375 and WK-368. 
42 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

60

80

100

120

140

160

180

200

220

240

WK-375 DEPTH TO WATER LEVEL, IN FEET BELOW LAND SURFACE

WK-415 DEPTH TO WATER LEVEL, IN FEET BELOW LAND SURFACE

30

32

34

36

38

40

42

WK-411 DEPTH TO WATER LEVEL, IN FEET BELOW LAND SURFACE WK-401 DEPTH TO WATER LEVEL, IN FEET BELOW LAND SURFACE

JULY 1 JULY 31 AUG. 31 SEPT. 30 OCT. 31

2008

WK-411

0

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135

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185

210

235

260

285

50

75

100

125

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WK-401

WK-375

WK-415

WK-375

Figure 21 continued. Overlay of water levels from wells showing a similar smoothed regional pattern of

 fluctuation: (C) observation wells WK-375 and WK-411 and (D) observation well WK-375, homeowner

 well WK-401, and community well WK-415.

C

D

Friedman smoothing

method

Kernel smoothing

method

Figure 21.—Continued Overlay of water levels from wells showing a similar modeled regional pattern of fluctuation.

C, observation wells WK-375 and WK-411. D, observation well WK-375, private well WK-401, and community well WK-415. 
Groundwater Levels in Northern Wake County, March 2008–February 2009 43

Natural Effects

The magnitude of the larger groundwater-level declines (a 

few to tens of feet per day; figs. 9, 11) observed in the observation wells WK-375 and WK-368 is greater than typically is 

observed with natural effects such as evapotranspiration (ET), 

earth tides, or barometric pressure fluctuations. ET effects on 

groundwater levels generally are on the order of a few tenths 

of a foot per day and are recognized as regular cycles with 

high water levels in the morning when ET is low and low 

water levels in the afternoon when ET is high (Chapman and 

others, 2005, fig. 19). Additionally, water levels recorded in 

well WK-368 were compared with barometric pressure fluctuations recorded at the Raleigh-Durham International Airport 

(located about 7 mi southwest of the study area); however, 

no direct (inverse) correlation could be made. Barometric 

pressure fluctuations affect groundwater levels inversely 

(Chapman and others, 2005, fig. 18) with typical fluctuations 

of 0.3 ft or less for a similar hydrogeologic setting in Wake 

County. Earth tides, resulting from the gravitational pull of 

the sun and moon, also may be observed in tight formations, 

such as the bedrock. Earth-tide fluctuations also generally are 

a few tenths of a foot and occur regularly, with two high and 

low water levels noted per day (see http://waterdata.usgs.

gov/nc/nwis/uv/?site_no=354302081433201&PARAmeter_

cd=72019,72020,62611: accessed November 9, 2010; 

well BK-126 in Burke County, NC). It should be noted that 

the majority of the water levels presented in this report were 

rounded to the nearest foot as per the accuracy of acoustical 

water-level measurements. Thus, earth tide and ET signals 

were not discernable. Although the daily water-level declines 

recorded in observation well WK-411 (data not rounded to 

the nearest foot) were of lesser magnitude, ranging from 0.5 

to 3.5 ft, no obvious cyclic patterns, such as ET or earth tide 

effects, were identified on a daily basis (fig. 13). 

Magnitude of Groundwater-Level Declines

A variation in overall response to groundwater withdrawals was noted in the continuous groundwater-level records 

for the monitored observation and private wells. The largest 

overall declines observed during the study period were in 

observation well WK-375, which had a water-level decline 

of about 247 ft from July 21 through August 6 (3 weeks; 

fig. 11) during a heavy use period in the summer (fig. 7), and 

about 101 ft from September 3 through October 24, near the 

end of the study period. For observation well WK-368, the 

decline from mid-July through mid-August was substantially 

less, about 27 ft (fig. 9). For the private well WK-401, which 

had the longest record, water levels declined about 94 ft 

from mid-July through early August 2008 (fig. 15). The large 

declines recorded in wells WK-375 and WK-402 (as much 

as 78 and 40 ft, respectively) suggest a substantial change in 

storage in the fractured-bedrock aquifer near each well and 

would have substantial impact on wellbore storage, especially 

in wells having a total depth of 300 ft, such as wells WK-375 

and WK-402. 

For the Norwood Oaks neighborhood, the lowest groundwater levels ranged from about 96 to 265 ft bls during the 

March 2008 through February 2009 study period (fig. 20A), 

60 to 200 or more ft below the unstressed water level for this 

area (see http://waterdata.usgs.gov/nc/nwis/current/?type=gw, 

Real-Time Groundwater; well WK-284.) In comparison, static 

water levels reported when several of the wells were drilled 

in the mid- to late-1990s ranged from about 20 to 30 ft bls. 

Because of the presence of deep water levels that exceed 

200 ft bls in this area, homeowners that have the shallowest 

wells near 300 ft in depth are the most susceptible to becoming dry (having water levels reach the pump intake depth). 

When the initial problem of wells going dry was reported in 

July 2005, some homeowners either had their wells deepened 

(see WK-400, table 1, for example) or hydrofractured to 

improve the yield. A glimpse of declining water levels was 

recorded when well WK-396 (Bayleaf Trail area) was drilled 

in November 2001 and had a reported static water level of 

100 ft bls, and well WK-381 (Abbey’s Grove Trail area) 

was drilled in October 2005 and had a static water level of 

100 ft bls (table 1). Well WK-381 had the lowest reported 

groundwater level measured of about 331 ft bls on October 17, 

2008 (fig. 20C). Construction dates for community wells in the 

study were not available; however, Keyworth (2009) reports 

withdrawal data for well WK-415 since 2000 and for well 

WK-416 since 2001.

Although the proximity of a private well to a largercapacity community well may not necessarily be of immediate 

concern in fractured-bedrock aquifers, if the wells tap fractures 

that are connected as part of a network, then pumping can 

collectively affect groundwater levels. The observed relations 

between the CWS, observation, and private wells and respective distances are described here to document the findings of 

this study. Of the three observation wells monitored as part of 

this study, bedrock well WK-375 was closest to a community 

well (WK-415, fig. 2, about 300 ft west-northwest). Well 

WK-368 is located about 1,600 and 1,700 ft (0.3 mi) from 

community wells WK-416 and WK-417, respectively (fig. 2). 

(WK-417 does not withdraw nearly as much water as 

WK-416 (29 percent of the total volume withdrawn by well 

WK-416 for the January through November 2008 reporting 

period; fig. 7), because of the lower well yield of about 

8 gal/min (table 1)). The closest community well to WK-411 is 

WK-416 at a distance of about 1,400 ft. For the private wells, 

the distance to the nearest community well WK-416 (fig. 2) 

is about 900 ft, and the distance to well WK-415 is about 

1,600 ft (0.3 mi). Additional community wells located outside 

of the study area as well as larger-capacity irrigation wells also 

could affect groundwater levels.

The deepest water levels measured during the study 

period in June 2008 (figs. 19B, 20) are similar to the timing of 

increased withdrawals from WK-416, likely for irrigation use 

(fig. 7). Within a little more than 1 week, the water level in 

well WK-410 (fig. 2) declined by nearly 90 ft (figs. 19B, 20A). 

Withdrawals from community well WK-416, located within 
44 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

about 900 ft of the Norwood Oaks subdivision, were five times 

the volume reported in prior months (fig. 7). Domestic usage 

could have increased during this dry period (figs. 7, 9, 11, 

13), also likely for irrigation purposes. Because of a lack of 

storage in the bedrock part of the aquifer, water levels respond 

dynamically to any changes in stress (withdrawals) on the 

system. The water levels appear to have stabilized between 

approximately 100 to 150 ft bls during November 2008 

through February 2009 (fig. 19; appendix 1), suggesting 

increased recharge, groundwater withdrawals, and no large 

short-term demands. 

Recovery of Groundwater Levels

The groundwater system recovered during periods of 

increased rainfall, most likely from direct recharge from 

a higher water table in the overlying regolith (fig. 4) and 

reduced withdrawals for irrigation. An overall recovery of 

the groundwater levels was observed in mid-August through 

mid-September 2008 in the three observations wells, and the 

three monitored private wells (figs. 9, 11, 13, 15). Water levels 

rose about 32 ft in observation well WK-368 and about 139 

ft in well WK-375 (table 4; figs. 9, 11). Groundwater levels 

recorded in well WK-375 had the largest decline with a similar 

rise in magnitude during this period. The water level in private 

well WK-401 (the only private well monitored in mid-August) 

rose about 105 ft during this same period (table 4; fig. 15), 

which indicates a significant increase in hydraulic head in the 

fractured-bedrock part of the aquifer. This recovery is likely 

a result of reduced water usage from recent increased rainfall 

and associated decreased demand (fig. 22) from the nearby 

community wells related to reduced irrigation. Recharge rates 

for the fractured bedrock part of the groundwater system are 

expected to be slow; however, a higher perched water table in 

the shallow regolith part of the groundwater system from the 

increased rainfall also could result in increased recharge to the 

deeper fractures in the bedrock. 

Groundwater levels in all six continuously monitored 

wells in the study area rose from mid-August through September 2008, after four large rainfall events (each more than 2.5 

inches total rainfall per day) occurred from remnants of tropical storms (figs. 9, 11, 13, 15; table 4). Evaluating withdrawals 

120

140

160

180

200

220

240

DEPTH TO GROUNDWATER, IN FEET

50,000

45,000

40,000

35,000

30,000

25,000

20,000

15,000

10,000

5,000

0

TOTAL PUMPAGE, IN GALLONS PER DAY

0.6

0.5

0.4

0.3

0.2

0.1

0

PRECIPITATION, IN INCHES

JULY 1 JULY 31 AUG. 31 SEPT. 30 OCT. 31

WK-401

water level Total pumpage

Precipitation

Figure 22. Overlay of homeowner well WK-401 water-level records, precipitation, and total 

reported pumpage from the three community wells in the storage area.

2008

Figure 22. Overlay of private well WK-401 water-level records, precipitation, and total withdrawals from the three 

community wells in the study area, July–October 2008. 
Groundwater Levels in Northern Wake County, March 2008–February 2009 45

reports for the community wells located in figure 2, WK-415 

was not pumped for a week from August 8 through August 15, 

and both WK-415 and WK-416 were reportedly not pumped 

from September 4 through September 30 (fig. 7). However, 

the water-level fluctuations recorded in WK-415 indicate that 

pumping for this well did not stop in September (fig. 18A); 

therefore a projection of withdrawals was made for wells 

WK-415 and WK-416 through the remainder of September 

2008 on the basis of the gallons per minute rate reported earlier that month (fig. 23). The projection of withdrawals shown 

in figure 23 indicates reduced withdrawals for the month of 

September 2008 compared to June through August 2008. The 

reduced withdrawals during frequent large rainfall events 

in September 2008 appear to correlate with the overall rise 

in groundwater levels (figs. 9, 11, 13, 15). In the study area, 

the water-level rise most likely is a factor of both reduced 

withdrawals from the bedrock part of the aquifer and recharge 

as a result of a higher water table from recent precipitation in 

the overlying regolith. 

Connectivity of Fracture Networks

Because the magnitude of both daily and longer-term 

groundwater-level fluctuations in observation wells WK-375, 

WK-368, and WK-411 vary substantially, these wells most 

likely reflect different degrees of connection to the local 

fracture networks that are stressed by groundwater withdrawals. Areally, evaluating the periodic water-level measurements 

from a large number of wells, the subset of wells having the 

lowest water levels (fig. 19; appendix 1) most likely are more 

connected to the stressed local fracture network. 

The regional pattern of fluctuations observed in all continuously monitored wells in the study area does not appear to 

be recognizably affected by natural stresses, such as diurnal 

earth tides or daily ET fluctuations, and the water levels do not 

appear to be noticeably affected by large barometric pressure 

fluctuations on a regular basis. As withdrawals from both 

higher-capacity (greater than 50 gal/min) community wells 

and a large number of private wells (nearly 40) occur in this 

area, both types of groundwater stresses likely are cumulatively affecting groundwater levels. However, withdrawals 

most likely are not proportional, with the community wells 

pumping a greater volume than the combined private wells. 

The cumulative effect of 40 wells using 200 gal/d (four-person 

household at 100 gal/person/d) would be about 16,000 gal/d, 

which is similar to a lower capacity community well, such as 

WK-417, affecting groundwater levels. Water levels in both 

community wells and a substantial number of private wells 

exceeded 100 ft bls throughout the study period, water levels 

in private wells exceeded 200 ft bls during periods of high 

demand and subsequent increased groundwater withdrawals 

(fig. 7, 23), and water levels in the two community wells also 

exceeded 200 ft bls on a daily basis. 

From the direct comparison of recorded continuous 

groundwater levels from observation wells, private wells, 

and community wells, it is difficult to discern the potential 

interference or connectivity of the fracture networks tapped by 

the wells. Thus, a documented method of statistical cross correlation of time series datasets (Wessa, 2009) was conducted 

70,000

60,000

50,000

40,000

30,000

20,000

10,000

0

2008

JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC.

TOTAL GALLONS PUMPED PER DAY

Figure 23. Total groundwater withdrawn from the three community wells for January–November 2008,

 using projected pumpage for wells WK-415 and WK-416 during September 2008.

Figure 23. Total groundwater withdrawn from the three community wells for January–November 2008, using projected 

withdrawals for wells WK-415 and WK-416 for September 2008. 
46 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

on the continuous groundwater records collected from the 

observation wells, private wells, and the compiled community 

well water-level data. A correlation coefficient and time lag 

were calculated for the following well pairs for their respective common overlapping period of monitoring (table 4): 

community well WK-415 and observation well WK-375; 

private well WK-401 and community well WK-415; private 

well WK-401 and observation well WK-375; and private well 

WK-400 and community well WK-415. The time lag having 

the highest correlation coefficient (peak) gives information on 

the difference in time (delay) with which groundwater levels 

in two wells respond to the same stress. 

Because observation well WK-375 was closest to a community well (WK-415, located about 300 ft west-northwest, 

fig. 2), a paired cross-correlation analysis was performed. 

The pattern of daily withdrawal cycles noted in the record for 

community well WK-415 was observed within the record for 

observation well WK-375 as smaller magnitude cycles on the 

order of a few feet of fluctuation (fig. 24). A cross-correlation 

analysis for the entire overlapping monitoring period for wells 

WK-415 and WK-375 (July 29 through October 24, 2008) 

indicated that the water levels were correlated and that the 

stress affecting the groundwater level in observation well 

WK-375 occurred about 45 minutes prior to a similar response 

in well WK-415 (negative time delay, see peak in fig. 25). 

Because well WK-375 was not being pumped and exhibited 

large declines during the study period (fig. 11) with no other 

sources of large groundwater withdrawals being located on 

the property, the cross-correlation results likely mean that 

an unknown large-capacity well affected groundwater levels 

in observation well WK-375 and then 45 minutes later, 

community supply well WK-415. Stress could be a result of 

withdrawals from a nearby large-capacity well such as community well WK-416 (no overlapping data for the continuous 

monitoring part of this study were available to confirm or 

refute), another community well outside of the study area, 

collective domestic well withdrawals, or an unknown largecapacity irrigation well within or outside of the study area. 

To evaluate the potential interference of withdrawals 

from both community wells and private wells, a cross-correlation comparison of continuous water-level records was made 

between private wells WK-401 and WK-400 and community 

well WK-415 (analyzed in separate pairs). For the comparison 

between WK-401 and WK-415, two periods of record were 

compared because of missing data. The peak of the correlation 

coefficient for the time period from July 30 to September 5, 

2008, ranged from about 260 to 300 minutes (mins; 4.3 to 

5 hrs) and for September 16 to October 24, 2008, the peak 

ranged from about 200 to 280 mins (3.3 to 4.7 hrs), with 

the stress being observed in private well WK-401 first (negative time delay, fig. 26). Additional cross correlation was conducted using a second private well WK-400 and community 

WK-415

WK-375

31

AUG. SEPT.

2008

1 2 3 4 5 6 7 8 9

60

80

100

120

140

160

180

200

DEPTH TO WATER LEVEL BELOW MEASURING POINT (WK-415) AND

LAND SURFACE (WK-375), IN FEET 

Figure 24. Overlay of water levels recorded in pumped community well WK-415 and observation well WK-375,

 September 1–7, 2008.

Figure 24. Overlay of water levels recorded in community well WK-415 and observation well WK-375, September 1–7, 2008.
Groundwater Levels in Northern Wake County, March 2008–February 2009 47

Figure 25. Cross-correlation coefficient calculations for water levels recorded in community well WK-415 in relation to water levels 

recorded in observation well WK-375, July 29–October 24, 2008.

–600 –500 –400 –300 –200 –100 0

TIME DELAY, IN MINUTES

100 200 300 400 500 600

0.71

0.70

0.69

0.68

0.67

0.66

0.65

CORRELATION COEFFICIENT

Figure 25. Cross-correlation coefficient calculations for water levels recorded in community well WK-415 in relation to

 water levels recorded in observation well WK-375, July 29 through October 24, 2008.

Note: All data have significant

correlation above 0.03

–600 –400 –200 0

TIME DELAY, IN MINUTES

200 400 600

July 30–Sept. 5, 2008

Sept. 16–Oct. 24, 2008

0.75

0.73

0.71

0.69

0.67

0.65

0.63

0.61

0.59

0.57

0.55

CORRELATION COEFFICIENT

Figure 26. Cross-correlation coefficient calculations for water levels recorded in homeowner well WK-401 and

 community well WK-415, July 30 through October 24, 2008.

Note: All data have significant

correlation above 0.03

Figure 26. Cross-correlation coefficient calculations for water levels recorded in private well WK-401 and community well 

WK-415, July 30–October 24, 2008.
48 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

Figure 27. Cross-correlation coefficient calculations for water levels recorded in private well WK-400 and community well 

WK-415, August 22–October 24, 2008.

Note: All data have significant correlation above 0.03

–600 –400 –200 0

TIME DELAY, IN MINUTES

200 400 600

0.80

0.78

0.76

0.74

0.72

0.70

0.68

0.66

0.64

0.62

0.60

CORRELATION COEFFICIENT

Figure 27. Cross-correlation coefficient calculations for water levels recorded in homeowner well WK-400 and

 community well WK-415, August 22 through October 24, 2008.

Note: All data have significant correlation above 0.03

–600 –400 –200 0

TIME DELAY, IN MINUTES

200 400 600

0.95

0.90

0.85

0.80

CORRELATION COEFFICIENT

Figure 28. Cross-correlation coefficient calculations for water levels recorded in homeowner well WK-401 and

 community well WK-375, July 30 through October 24, 2008.

July 30–Sept. 5, 2008

Sept. 16–Oct. 24, 2008

Figure 28. Cross-correlation coefficient calculations for water levels recorded in private well WK-401 and observation well 

WK-375, July 30–October 24, 2008.

well WK-415. The results also indicated a response from the 

homeowner well first (negative time delay), with a peak delay 

to well WK-415 of about 150 mins (2.5 hrs) (fig. 27), similar 

to the comparison of the homeowner well WK-401 and the 

community well WK-415. The shorter period of data collection, however, may affect the time delay calculated. Similar to 

the comparison of observation well WK-375 and community 

well WK-415, it appears as though the stress most affecting 

water levels in the private wells occurs prior to correlated 

fluctuations in community well WK-415. Again, this could be 

community well WK-416 (no overlapping monitoring period; 

table 4) or an unknown large-capacity community supply 

outside of the study, or an unknown large-capacity irrigation 

well within or outside of the study area.

Further comparison of water levels recorded in observation well WK-375 with private well WK-401 resulted in a time 

delay ranging from about 0 to 150 min (2.5 hrs) with the stress 

observed in WK-401 first when there was a delay calculated 

(fig. 28). Thus, the stress observed in well WK-375 may be 

directly correlated with the same stress observed in the private 

wells, or the private wells may be affected by the unknown 

stress prior to the stress observed in well WK-375.
References Cited 49

Summary and Conclusions

Conditions in the fractured-bedrock aquifer described in 

this report represent an assessment of the effects of competitive use of the groundwater resource that may be comparable 

to similar hydrogeologic settings in the Piedmont and Blue 

Ridge Physiographic Provinces in the eastern United States 

where local groundwater resource-management issues have 

developed. 

Groundwater levels in the study area of northwestern 

Wake County, North Carolina, were well below the reported 

water levels at the time of initial well drilling during the 1980s 

through the late 1990s, indicating that withdrawals in the 

area could potentially be exceeding groundwater recharge to 

the bedrock part of the aquifer. Well depths range from 150 

to 515 ft and average 356 ft for private wells and 733 ft for 

three community wells in the area. As groundwater levels in 

the most dewatered areas typically ranged from about 100 to 

more than 200 ft below land surface during the study period 

(March 2008 through February 2009), a substantial thickness 

of the bedrock part of the aquifer tapped by the private wells 

became temporarily dewatered. Water levels in two community wells ranged from about 68 to 261 ft below land surface, 

also indicating a substantial dewatering of fractures in excess 

of 200 ft and approaching 300 ft near the shallower private 

wells. Based on findings from this study, the aquifer dewatering likely will continue without a reduction in withdrawals 

from the aquifer. 

The aquifer recovered during a period following 

increased rainfall and reduced withdrawals during a period of 

lower demand in mid-August through mid-September 2008, 

with water levels rising 32 to 139 ft. However, as withdrawals 

increased in September 2008, an overall decline was observed 

through October 2008. Another recovery was observed in 

November, and water levels appeared to stabilize between 

100 and 150 ft bls in the most dewatered areas through 

February 2009 at the end of the study period. This response 

suggests that the upper part of the aquifer was temporarily 

dewatered during periods of high water use, but during periods 

of high recharge and low water use, the aquifer recovered to 

near undeveloped water levels, indicating that dewatering was 

not necessarily permanent. 

The deepest groundwater levels in the study area exhibit 

a correlation with regional and local geologic structural 

measurements, fracture traces, and borehole fracture orientations. Similar areal patterns of low groundwater levels were 

delineated during nine water-level measurement periods from 

March 2008 through February 2009. The lowest groundwater 

levels were noted along Norwood Oaks Drive, Bayleaf 

Trail, and Abbey’s Grove Trail. Correlation of groups of 

groundwater-level distribution patterns with orientations 

of geologic structures from surficial mapping, borehole 

geophysical measurements, and interpretation of fracture 

traces suggests two dominant trends striking north-south 

and N. 65° W. The north-south trend was observed as an 

elongated area at the northern section of Norwood Oaks Drive 

and along the western side of Bayleaf Trail. The north-south 

trend is parallel to foliation measurements in the regionally 

mapped Falls Lake schist (N. 5° E. and N. 5° W.) as well as 

the amphibolite rock type (N. 5° E.). A secondary trend of 

N. 65° W. was observed from three wells having low water 

levels along Norwood Road. The N. 65° W. trend is similar 

to a joint set in the quartzofeldspathic gneiss (N. 51° W.). The 

north-south orientation was measured in well WK-368 at a 

depth of 398.4 ft bls (N. 7° E.), and the N. 65° W. orientation 

was measured in well WK-368 at depths of 80.8–81.4 ft bls 

(average N. 67° W.) and 86.4–86.6 ft bls (average N. 63° W.). 

Fracture traces mapped near the Norwood Oaks neighborhood 

vary somewhat from the north-south orientation, striking 

7° (N. 7° E.) to 15° (N. 15° E.) and 357° (N. 3° W.) to 345° 

(N. 15° W.).

Because of a lack of storage in the bedrock part of the 

aquifer, the water levels respond dynamically to any changes 

in stress (withdrawals) on the system. The lowest water levels 

measured during the study period were in June 2008 and likely 

can be correlated with increased withdrawals to meet the 

high demand for irrigation purposes during the dry summer 

months. One community well located within about 900 ft of 

the Norwood Oaks subdivision was pumped at five times the 

volume reported in prior months. As an evaluation of fracture 

network interconnectivity, a statistical comparison of continuous water-level records from well pairs was made using 

cross-correlation methods. Results of the cross-correlation 

analyses suggested that an unknown stress was observed in the 

private wells and observation well WK-375 before the same 

stress was observed in community well WK-415. Time delays 

of 45 to 280 mins (more than 4 hrs) were calculated. Potential 

sources of this stress could be (1) community well WK-416, 

which had no overlapping monitoring period to analyze, (2) 

an unknown community well or large-capacity irrigation well 

either within or outside of the study area, and (3) domestic 

withdrawals.

References Cited

Bourke, P., 1996, Cross correlation, accessed July 9, 2009, 

at http://local.wasp.uwa.edu.au/~pbourke/miscellaneous/

correlate/. 

Camp Dresser & McKee, 2003, Wake County comprehensive 

groundwater investigation final report, 147 p., accessed 

December 2008 at http://online2.cdm.com/wakecgi/

Final.htm.

Chapman, M.J., Bolich, R.E., and Huffman, B.A., 2005, 

Hydrogeologic setting, ground-water flow, and groundwater quality at the Lake Wheeler Road research station, 2001–03, North Carolina Piedmont and Mountains 

Resource Evaluation Program: U.S. Geological Survey 

Scientific Investigations Report 2005–5166, 85 p.
50 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

Chapman, M.J., Crawford, T.J., and Tharpe, W.T., 1998, Geology and ground-water resources of the Lawrenceville area, 

Georgia: U.S. Geological Survey Water-Resources Investigations Report 98–4233, 46 p., 2 pls.

Friedman, J., and Tibshirani, R., 1984, The monotone smoothing of scatterplots: Technometrics, v. 26, no. 3, p. 243–250.

Heath, R.C., 1984, Ground-water regions of the United States: 

U.S. Geological Survey Water-Supply Paper 2242, 78 p.

Keyworth, A.J., 2009, A quantitative assessment of water 

inputs and outputs to a small watershed in northwestern 

Wake County—Evaluating the effects of human use on 

groundwater resources: Raleigh, North Carolina State 

University, Department of Marine, Earth, and Atmospheric 

Sciences, Master’s Thesis, 81 p; accessed February 2009 

at http://www.lib.ncsu.edu/theses/available/

etd-11132008-153043/unrestricted/etd.pdf.

LeGrand, H.E., Sr., 2004, A master conceptual model for 

hydrogeological site characterization in the Piedmont and 

Mountain region of North Carolina—A guidance manual: 

North Carolina Department of Environment and Natural Resources Division of Water Quality, 55 p., accessed 

April 2010 at http://portal.ncdenr.org/web/wq/aps/gwp/

groundwater-study-publications/-/journal_content/

56_INSTANCE_oMYz/38364/204173.

North Carolina Department of Environment and Natural 

Resources, Division of Environmental Health, Public Water 

Supply Section, Rules Governing Public Water Supply Systems, 2004, North Carolina Administrative Code, Title 15A, 

Subchapter 18C, Sections .0100 through, .2100, updated 

September.

North Carolina Department of Environment and Natural 

Resources, Division of Water Quality, 2002, North Carolina 

Administrative Code Title 15A, Subchapter 2C Section 

.0100 Well Construction Standards, accessed July 15, 2010, 

at http://h20.enr.state.nc.us/aps/gpu/documents/

2c.0108RULESFINALSeptember2009.pdf. 

Turner Environmental Consultants, 1992, Comprehensive site 

assessment, Gresham’s Landing facility, NC Highway 50 & 

Norwood Road, Wake County, North Carolina: 124 p.

U.S. Census Bureau, 2005, “American Factfinder” database: U.S. Department of Commerce, accessed in 

December 2007 at http://factfinder.census.gov/servlet/

DatasetMainPageServlet?_program=ACS.

U.S. Geological Survey, 2008, North Carolina water use 

data tables, 2005: accessed July 15, 2010, at 

http://nc.water.usgs.gov/infodata/wateruse.html.

Wake County Department of Environmental Services, 

2009, Regulations governing the investigation 

and mitigation of well interference, Raleigh, 

North Carolina, 15 p., accessed February 16, 2011, 

at http://www.wakegov.com/NR/rdonlyres/

D8DF57C1-8097-44DB-8EEF-5168BEB8FB71/0/

WellInterferenceOrdinance.pdf.

Wake County Groundwater Sustainability Stakeholder 

Committee report, 2007, accessed July 15, 2010, at 

http://www.wakegov.com/NR/rdonlyres/

64CA2FC2-5EF6-403B-B3B6-95232D32A516/0/

GWSustainabilityCommitteeReport_FinalApril07.pdf.

Wand, M.P., and Jones, M.C., 1993, Comparison of smoothing parameterizations in bivariate kernel density estimation: Journal of the American Statistical Association, v. 88, 

no. 422, p. 520–528.

Weaver, C.J., 1998, Low-flow characteristics and discharge 

profiles for selected streams in the Neuse River Basin, 

North Carolina: U.S. Geological Survey Water-Resources 

Investigations Report 98–4135, 101 p.

Wessa, P., 2009, Free statistics software calculator, 

Office for Research, Development, and Education, 

version 1.1.23-r4, Scientific forecasting software, 

C modules, accessed July 2009 at http://www.wessa.net/. 

Williams, L.J., Kath, R.L., Crawford T.J., and Chapman, M.J., 

2005, Influence of geologic setting on ground-water availability in the Lawrenceville area, Gwinnett County, 

Georgia: U.S. Geological Survey Scientific Investigations 

Report 2005–5136, 43 p. (Also available at http://

pubs.usgs.gov/sir/2005/5136/.)
Appendix 1

Bedrock groundwater-level altitude maps showing the water-level measurements in private and observation wells in 

the study area on

A. March 28, April 2, 4, and 16, 2008

B. June 18 and 26, 2008

C. July 25 and August 12, 2008

D. September 19, 2008

E. October 17, 2008

F. November 21, 2008

G. December 19, 2008

H. January 29, 2009

I. February 27, 2009
52 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

Appendix 1A. Bedrock groundwater-level altitude map showing the water-level measurements in private and observation wells

in the study area on March 28 and April 2, 4, and 16, 2008. [NAVD 88, North American Vertical Datum of 1988]

Creedmoor

Road

Hwy 50

321

Study area

boundary

298

280

(346)

(344) 325

(322)

(370)

339

277

304

278

279

292

(336)

281

282 283

280

377

347

322

365

298

(373)

372

372

311

374

416

343

339

362

(351)

354

378

(371) 353

300

350

350

300

? Norwood

Road

Trail

Abbey’s Grove

Norwood Oaks

Drive

0 500

0 100 200 300 400 500 METERS

1,000 1,500 2,000 FEET

N

Location of study area and Raleigh in

Wake County, North Carolina

Bayleaf

360

280

320

300

320

340

360

300

400

380

360

340

320

340

360

340

340

340

360

360

380

380

400

400

380

360

400

380

400

400

380

380

360

420

420

Tax parcel boundaries

Water-level altitude contour above NAVD 88.

 Contour interval 50 feet. Dashed where

 approximate

Altitude of land surface above NAVD 88.

 Contour interval 2 feet

Privateor observation well location

 and depth to groundwater level below

 land surface (if no number, well was not

 measured)

April 2 and 4 altitudes (above NAVD 88) 

 are blue 

April 16 altitudes (above NAVD 88) 

 are red

Community well and total daily withdrawals

 in gallons reported on respective days of

 water-level measurement

Note: Acoustic water-level measurements

 made in privateand observation wells

 may be deeper than recorded if obstructions

 in the well were present

EXPLANATION

277

(353)

(322)

300

300

400 N

Study

area

Raleigh

0

0

0

0

0

0 3,357

3,338

3,667

3,357

Location of Wake County in North Carolina
Appendix 53

400

Creedmoor

Road

Hwy 50

320

Study area

boundary

155

161

332

319

282

(285)

371

(371)

267

(180)

(164)

194

192

189

192

(182) 179

(186)

154

(183)

377

347

327

330

245

372

372

117

370

288

302

363

335

330

376

369

Appendix 1B. Groundwater-level altitude map showing the water levels measured in private and observation wells in the study

area on June 18 and 26, 2008. [NAVD 88, North American Vertical Datum of 1988]

?

?

Norwood

Road

Trail

Abbey’s Grove

Norwood Oaks

Drive

Bayleaf

350

300

234

(245)

131

(164)

311

(312)

371

300

250

200

250

300

350

350

300

360

280

320

300

320

340

360

300

400

380

360

340

320

360

340

340

340

360

360

380

380

400

400

400

380

380

360

360

340

380

420

3,800

4,150

49,129

42,013

6,310

5,767

0 500

0 100 200 300 400 500 METERS

1,000 1,500 2,000 FEET

Tax parcel boundaries

Water-level altitude contour above NAVD 88.

 Contour interval 50 feet. Dashed where

 approximate

Altitude of land surface above NAVD 88.

 Contour interval 2 feet

Private or observation well location

 and depth to groundwater level below

 land surface (if no number, well was not

 measured)

June 26 altitude in parentheses

Community well and total daily withdrawals

 in gallons reported on respective days of

 water-level measurement

Note: Acoustic water-level measurements

 made in private and observation wells

 may be deeper than recorded if obstructions

 in the well were present

EXPLANATION

362

(180)

300 5,767

300

N

Location of study area and Raleigh in

Wake County, North Carolina

N

Study

area

Raleigh

Location of Wake County in North Carolina
54 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

400

Creedmoor

Road

Hwy 50

335

Study area

boundary

212

(286)

214

334

326

328 328

210

259

212

212

243

241

216

215 213

210

378

347 

331

370

372

372

370 374

380

(362)

321

362

343

340

Norwood

Road

Trail

Abbey’s Grove

Norwood Oaks

Drive

300

300

350

300

350

350

300

350

Appendix 1C. Groundwater-level altitude map showing the water levels measured in private and observation wells in the study

area on July 25 and August 12, 2008. [NAVD 88, North American Vertical Datum of 1988]

?

?

20,829

0

20,557

19,532

5,367

5,129

Bayleaf

230

370

296

(283)

372

290

360

280

320

300

320

340

360

300

400

380

360

340

320

360

340

340

340

360

360

380

380

400

400

400

380

380

360

360

340

380

420

N

Location of study area and Raleigh in

Wake County, North Carolina

N

Study

area

Raleigh

212

(189) (201)

20,829

(201)

0 500

0 100 200 300 400 500 METERS

1,000 1,500 2,000 FEET

Tax parcel boundaries

Water-level altitude contour above NAVD 88.

 Contour interval 50 feet. Dashed where

 approximate

Altitude of land surface above NAVD 88.

 Contour interval 2 feet

Private or observation well location

 and depth to groundwater level below

 land surface (if no number, well was not

 measured)

August 12 altitude in parentheses

Community well, total daily withdrawals

 in gallons reported on respective days of

 water-level measurement, and water-level

 altitude above NAVD 88 (bold type)

Note: Acoustic water-level measurements

 made in private and observation wells

 may be deeper than recorded if obstructions

 in the well were present

EXPLANATION

374

(283)

300

300

Location of Wake County in North Carolina
Appendix 55

Creedmoor

Road

Hwy 50

334

246

Study area

boundary

251

254

334

329

307

330

336

250

273

250

251

271

269

255

255 253

251

377

347

340

306

372

372

371

273

371

366

337

362

345

348

376

370

Appendix 1D. Bedrock groundwater-level altitude map showing the water levels measured in private and observation wells

in the study area on September 19, 2008. [NAVD 88, North American Vertical Datum of 1988]

?

?

0 500

0 100 200 300 400 500 METERS

1,000 1,500 2,000 FEET

Tax parcel boundaries

Water-level altitude contour above NAVD 88.

 Contour interval 50 feet. Dashed where

 approximate

Altitude of land surface above NAVD 88.

 Contour interval 2 feet

Private or observation well location

 and depth to groundwater level below

 land surface (if no number, well was not

 measured)

Community well, total daily withdrawals

 in gallons reported on respective days of

 water-level measurement, and water-level

 altitude above NAVD 88 (bold type)

Note: Acoustic water-level measurements

 made in private and observation wells

 may be deeper than recorded if obstructions

 in the well were present

EXPLANATION

366

300

300

Norwood

Road

Trail

Abbey’s Grove

Norwood Oaks

Drive

Bayleaf

300

250

250

300

350

350

300

250

350

350

400

360

280

320 300

320

340

360

300

400

380

360

340

320

360

340

340

340

360

360

380

380

400

400

380

380

360

360

340

380

420

215

400

N

Location of study area and Raleigh in

Wake County, North Carolina

N

Study

area

Raleigh

0

256

0

4,963

0

256

Location of Wake County in North Carolina
56 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

Creedmoor

Road

Hwy 50

328

192

Study area

boundary

204

203

334

323

395

332

202

253

201

201

229

228

210

209 206

204

378

347

331

265

84

373

372

261

371 382

365

323

361

345

346

377

370

212

Norwood

Road

Bayleaf

Trail

Abbey’s Grove

Norwood Oaks

Drive

300

350

300

350

350

300

350

300

250

250

250

Appendix 1E. Bedrock groundwater-level altitude map showing the water levels measured in private and observation wells

in the study area on October 17, 2008. [NAVD 88, North American Vertical Datum of 1988]

?

?

?

200

200

350

292

372

360

280

320 300

320

340

360

300

400

380

360

340

320

340

340

340

360

360

380

380

400

400

400

380

380

360

360

340

380

420

400

N

Location of study area and Raleigh in

Wake County, North Carolina

N

Study

area

Raleigh

22,288

19,013

5,125

212

22,288

0 500

0 100 200 300 400 500 METERS

1,000 1,500 2,000 FEET

Tax parcel boundaries

Water-level altitude contour above NAVD 88.

 Contour interval 50 feet. Dashed where

 approximate

Altitude of land surface above NAVD 88.

 Contour interval 2 feet

Private or observation well location

 and depth to groundwater level below

 land surface (if no number, well was not

 measured)

Community well, total daily withdrawals

 in gallons reported on respective days of

 water-level measurement, and water-level

 altitude above NAVD 88 (bold type)

Note: Acoustic water-level measurements

 made in private and observation wells

 may be deeper than recorded if obstructions

 in the well were present

EXPLANATION

366

300

300

Location of Wake County in North Carolina
Appendix 57

Creedmoor

Road

Hwy 50

265 255

Study area

boundary

260

262

254

361

311

370

338

259

286

260

261

276

275

262

264 262

260

345

345

328

328

316

127

373

372

372

291

371 374

366

331

354

355

351

377

370

?

?

10,620

10,900

3,057

Norwood

Road

Trail

Abbey’s Grove

Norwood Oaks

Drive

Appendix 1F. Bedrock groundwater-level altitude map showing the water levels measured in private and observation wells

in the study area on November 21, 2008. [NAVD 88, North American Vertical Datum of 1988]

360

280 280

320

300

320

340

360

300

400

380

360

340

320

360

340

340

340

360

360

380

380

400

400

400

380

380

360

360

340

380

420

300

350

?

Bayleaf

300

300

300

350

350

200

350

300

250

350

350

265

400

N

Location of study area and Raleigh in

Wake County, North Carolina

N

Study

area

Raleigh

0 500

0 100 200 300 400 500 METERS

1,000 1,500 2,000 FEET

Tax parcel boundaries

Water-level altitude contour above NAVD 88.

 Contour interval 50 feet. Dashed where

 approximate

Altitude of land surface above NAVD 88.

 Contour interval 2 feet

Private or observation well location

 and depth to groundwater level below

 land surface (if no number, well was not

 measured)

Community well, total daily withdrawals

 in gallons reported on respective days of

 water-level measurement, and water-level

 altitude above NAVD 88 (bold type)

Note: Acoustic water-level measurements

 made in private and observation wells

 may be deeper than recorded if obstructions

 in the well were present

EXPLANATION

277

300

300

3,057

Location of Wake County in North Carolina
58 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

Creedmoor

Road

Hwy 50

268

244

Study area

boundary

271

273

266

338

322

368

301

270

296

272

273

284

282

274

273 272

272

377

347

337

319

304

373

372

372

267

371 374

368

322

363

351

356

378

370

Appendix 1G. Bedrock groundwater-level altitude map showing the water levels measured in private and observation wells

in the study area on December 19, 2008. [NAVD 88, North American Vertical Datum of 1988]

Norwood

Road

Trail

Abbey’s Grove

Norwood Oaks

Drive

262

300

350

350

300

300

350

350

360

280

320

300

320

340

360

300

400

380

360

340

320

360

340

340

340

360

360

380

380

400

400

400

380

380

360

360

340

380

420

Bayleaf

245

400

N

Location of study area and Raleigh in

Wake County, North Carolina

N

Study

area

Raleigh

0 500

0 100 200 300 400 500 METERS

1,000 1,500 2,000 FEET

Tax parcel boundaries

Water-level altitude contour above NAVD 88.

 Contour interval 50 feet. Dashed where

 approximate

Altitude of land surface above NAVD 88.

 Contour interval 2 feet

Private or observation well location

 and depth to groundwater level below

 land surface (if no number, well was not

 measured)

Community well, total daily withdrawals

 in gallons reported on respective days of

 water-level measurement, and water-level

 altitude above NAVD 88 (bold type)

EXPLANATION

368

300

300 Note: No community well

 withdrawal information

 available

Note: Acoustic water-level measurements

 made in private and observation wells

 may be deeper than recorded if obstructions

 in the well were present

Location of Wake County in North Carolina
Appendix 59

Creedmoor

Road

Hwy 50

276

Study area

boundary

269

271

334

339

321

370

302

267

297

267

269

286

284

272

273 272

270

378

347

331

323

364

373

372

121

372 375

369

324

363

352

357

380

370

Appendix 1H. Bedrock groundwater-level altitude map showing the water levels measured in private and observation wells

in the study area on January 29, 2009. [NAVD 88, North American Vertical Datum of 1988]

Norwood

Road

Bayleaf

Trail

Abbey’s Grove

Norwood Oaks

Drive

300

300

350

350

?

?

300

295

360

280

320

300

320

340

360

300

400

380

360

340

320

360

340

340

340

360

360

380

380

400

400

400

380

380

360

360

340

380

420

N

Location of study area and Raleigh in

Wake County, North Carolina

N

Study

area

Raleigh

0 500

0 100 200 300 400 500 METERS

1,000 1,500 2,000 FEET

Tax parcel boundaries

Water-level altitude contour above NAVD 88.

 Contour interval 50 feet. Dashed where

 approximate

Altitude of land surface above NAVD 88.

 Contour interval 2 feet

Private or observation well location

 and depth to groundwater level below

 land surface (if no number, well was not

 measured)

Community well

EXPLANATION

321

300

300

Note: No community well

 withdrawal information

 available

Note: Acoustic water-level measurements

 made in private and observation wells

 may be deeper than recorded if obstructions

 in the well were present

Location of Wake County in North Carolina
60 Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County

Creedmoor

Road

Hwy 50

267

Study area

boundary

273

276

275

340

324

370

303

272

299

274

275

288

286

276

277

275

274

358

348

324

285

373

368

373

296

364 375

368

316

364

351

349

379

371

Norwood

Road

Bayleaf

Trail

Abbey’s Grove

Norwood Oaks

Drive

Appendix 1I. Bedrock groundwater-level altitude map showing the water levels measured in private and observation wells

in the study area on February 27, 2009. [NAVD 88, North American Vertical Datum of 1988]

300

300

350

300

350

350

350

?

?

0 500

0 100 200 300 400 500 METERS

1,000 1,500 2,000 FEET

Tax parcel boundaries

Water-level altitude contour above NAVD 88.

 Contour interval 50 feet. Dashed where

 approximate

Altitude of land surface above NAVD 88.

 Contour interval 2 feet

Private or observation well location

 and depth to groundwater level below

 land surface (if no number, well was not

 measured)

Community well

EXPLANATION

358

300

300

Note: No community well

 withdrawal information

 available

Note: Acoustic water-level measurements

 made in private and observation wells

 may be deeper than recorded if obstructions

 in the well were present

360

280

320

300

320

340

360

300

400

380

360

340

320

360

340

340

340

360

360

380

380

400

400

400

380

380

360

360

340

380

420

400

N

Location of study area and Raleigh in

Wake County, North Carolina

N

Study

area

Raleigh

Location of Wake County in North Carolina
Prepared by:

U.S. Geological Survey

Science Publishing Network

Raleigh Publishing Service Center

3916 Sunset Ridge Road

Raleigh, NC 27607

A PDF version of this publication is available online at 

http://pubs.usgs.gov/sir/2010/5219/
Chapman and others—Fluctuations in Groundwater Levels Related to Withdrawals in the Fractured-Bedrock System in Northern Wake County—Scientific Investigations Report 2010–5219