NITRATE LOADING AS AN INDICATOR

 OF NONPOINT SOURCE POLLUTION

 IN THE

LOWER ST. MARKS-WAKULLA RIVERS WATERSHED

NORTHWEST FLORIDA

WATER MANAGEMENT DISTRICT

APRIL 2002

PREPARED BY :
 

NITRATE LOADING 

AS AN 

INDICATOR OF NONPOINT SOURCE POLLUTION 

IN THE 

LOWER ST. MARKS-WAKULLA RIVERS WATERSHED 

Water Resources Special Report 02-1 

This project and the preparation of this report were funded in part by a Section 319 

Nonpoint Source Management Program grant from the U.S. Environmental Protection 

Agency (USEPA) through a contract with the Nonpoint Source Management and Water 

Quality Standards Section of the Florida Department of Environmental Protection. The 

total cost of the project was $503,700 of which $291,966, or 58 percent was provided by 

the USEPA. 

 Thomas R. Pratt 

 Florida Registered 

 Professional Geologist 

 No. 159 

 April 19, 2002 

Prepared by: 

Angela Chelette and Thomas R. Pratt 

The Northwest Florida Water Management District 

and 

Brian G. Katz 

U.S. Geological Survey 

April 2002
ii

NORTHWEST FLORIDA WATER MANAGEMENT DISTRICT 

=========================================== 

 GOVERNING BOARD 

J. Russell Price, Chair 

Tallahassee 

 Joyce Estes, Vice-Chair 

Eastpoint 

 NancyAnn M. Stuparich, Secretary/Treasurer 

Pensacola 

 Wayne Bodie Hulan S. Carter Sharon T. Gaskin

DeFuniak Springs Chipley Wewahitchka 

 L.E. McMullian, Jr. Stephanie C. Hughes Richard P. Petermann 

Sneads Panama City Beach Fort Walton Beach 

==================================== 

Douglas E. Barr - Executive Director 

==================================== 

For additional information, write or call: 

Northwest Florida Water Management District 

81 Water Management Drive 

Havana, Florida 32333 

(850) 539-5999 
iii

TABLE OF CONTENTS 

Page

LIST OF FIGURES............................................................................................................ v 

LIST OF TABLES .............................................................................................................. viii 

ACKNOWLEDGMENTS .................................................................................................... x 

INTRODUCTION............................................................................................................... 1 

Purpose and Scope ..................................................................................................... 1 

Area of Investigation .................................................................................................... 2 

Rainfall ........................................................................................................................ 4 

Ground Water Use in Leon and Wakulla Counties....................................................... 8 

METHODS ........................................................................................................................ 11 

Floridan Aquifer Potentiometric Surface Mapping ........................................................ 11 

Drilling ......................................................................................................................... 11 

Ground and Surface Water Sampling .......................................................................... 11 

Surface Water Monitoring ............................................................................................ 14 

Rainfall................................................................................................................... 14 

Current Meter......................................................................................................... 14 

In-situ Water Quality Meters................................................................................... 17 

HYDROLOGY OF THE St. MARKS-WAKULLA RIVERS WATERSHED ........................... 25 

Physiography and Geology.......................................................................................... 25 

Hydrology of the Floridan Aquifer................................................................................. 28 

Potentiometric Surface of the Floridan Aquifer on the Woodville Karst Plain................ 33 

Surface Waters............................................................................................................ 39 

Wakulla Springs and River..................................................................................... 39 

St. Marks River ...................................................................................................... 42 

Interaction between Wakulla Springs and Up-gradient Surface Water Features .... 42 

Ames Sink........................................................................................................ 42 

1999 Surface Water Conductivity Data............................................................. 43 

2000 Surface Water Conductivity Data............................................................. 43 

Surface Water Temperature Data..................................................................... 47 

Wakulla Springs Velocity and Conductivity Data .............................................. 47 

WATER QUALITY IN THE FLORIDAN AQUIFER ............................................................. 53 

Historic Nitrate Concentrations .................................................................................... 53 

Project-specific Ground and Surface Water Sampling.................................................. 53 

NO2+NO3 ............................................................................................................... 53 

Dissolved Organic Carbon ..................................................................................... 57 

Dissolved Oxygen .................................................................................................. 57 

pH.......................................................................................................................... 57

Specific Conductance ............................................................................................ 61 

Orthophosphate ..................................................................................................... 61 

Nitrate Concentrations as a Function of Time .............................................................. 61 

City of Tallahassee Public Supply Wells................................................................. 61 
iv

TABLE OF CONTENTS [cont] 

Page

NITROGEN SOURCE INVENTORY.................................................................................. 69 

Atmospheric Deposition............................................................................................... 71 

Wastewater Treatment Facilities.................................................................................. 74 

Industrial WWTF Effluent ....................................................................................... 74 

Domestic WWTF Effluent....................................................................................... 74 

City of Tallahassee WWTF Development History................................................... 76 

Southeast Sprayfield.............................................................................................. 78 

Southwest Sprayfield ............................................................................................. 82 

WWTF Residuals Disposal..................................................................................... 82 

On-Site Disposal Systems ........................................................................................... 87 

Commercial Fertilizer Application................................................................................. 92 

Livestock...................................................................................................................... 94 

Sinking Streams........................................................................................................... 95 

Munson and Ames Sink ......................................................................................... 95 

Fisher Creek .......................................................................................................... 96 

Black Creek ........................................................................................................... 96 

Lost Creek ............................................................................................................. 97 

Landfills ....................................................................................................................... 99 

Summary ..................................................................................................................... 100 

NITROGEN FATE MODELING.......................................................................................... 103 

Water Budget for Wakulla Springs ............................................................................... 103 

Nutrient Budget for Wakulla Springs ............................................................................ 107 

Conceptual Limitations........................................................................................... 108 

Assumptions .......................................................................................................... 108 

Conceptual Model of Nutrient Budget .......................................................................... 109 

CONCLUSIONS AND RECOMMENDATIONS .................................................................. 113 

REFERENCES.................................................................................................................. 116 

BIBLIOGRAPHY................................................................................................................ 119 

APPENDIX A..................................................................................................................... 122 
 v

LIST OF FIGURES 

Figure Page

1. Area of Investigation .................................................................................................... 3 

2. Land Use Classifications within the Zone of Contribution............................................. 5 

3. Annual Rainfall Deficit (1998-2000) versus 50-Year Average (1951-2000) at 

Tallahassee Airport...................................................................................................... 6 

4. 1991-2000 Monthly Rainfall Deviation from Monthly Mean .......................................... 7 

5. 1991-2000 Cumulative Deviation From Normal Rainfall............................................... 7 

6. Hydrograph of Lake Jackson Floridan Aquifer Monitor Well, Northern Leon County .... 9 

7. Hydrograph of Lake Jackson Intermediate Aquifer Monitor Well, Northern Leon 

County ......................................................................................................................... 9 

8. Location of Wells Used for Water Level Monitoring...................................................... 12 

9. Location of Project Sampling Sites............................................................................... 13 

10. Principal Karst Features............................................................................................... 15 

11. Cross-Section of Wakulla Springs Principle Conduit Showing S4 Emplacement.......... 16 

12. Wakulla Springs Main Vent Measured Discharge versus Calculated Discharge........... 17 

13. Cross-Section of Spring Creek Vent #2 Showing Hydrolab Emplacement ................... 19 

14. Specific Conductivity and Rainfall versus Time for Spring Creek Vent #2, 1999 .......... 20 

15. Lost Creek Specific Conductivity, Rainfall and Daily Mean Flow versus Time.............. 22 

16. Ames Sink Specific Conductivity, Rainfall and Munson Slough @ Highway 319 Daily 

Mean Flow versus Time............................................................................................... 23 

17. Principal Physiographic Features................................................................................. 26 

18. Surface Water Basins and Principal Surface Water Features ...................................... 27 

19. Surface Geology.......................................................................................................... 29 

20. North-South Hydrogeologic Cross-Section................................................................... 30 

21. East-West Hydrogeologic Cross-Section ..................................................................... 31 

22. Potentiometric Surface of the Floridan Aquifer, Southern Leon and Wakulla Counties, 

January 1999............................................................................................................... 34 
 vi

LIST OF FIGURES [cont.] 

Figure Page

23. Potentiometric Surface of the Floridan Aquifer, Southern Leon and Wakulla Counties, 

August 1999 ................................................................................................................ 35 

24. Potentiometric Surface of the Floridan Aquifer, Southern Leon and Wakulla Counties, 

March 2000.................................................................................................................. 36

25. Ground Water Flow Directions..................................................................................... 38 

26. Wakulla Springs and Middle River Sink Spring Historic Discharge............................... 40 

27. Compilation of NO3-N and NO2+NO3-N Concentration Data for Wakulla Springs and 

Middle River Sink Spring.............................................................................................. 41 

28. 1999 Specific Conductivity and Rainfall versus Time for Fisher Creek, Ames Sink, 

Lost Creek and Wakulla Springs.................................................................................. 44 

29. 2000 Specific Conductivity and Rainfall versus Time for Fisher Creek, Ames Sink, 

Lost Creek, Middle River Sink Spring and Wakulla Springs ......................................... 45 

30. Specific Conductivity and Rainfall versus Time Prior to and Following Tropical Storm 

Helene, July—November, 2000 ................................................................................... 46 

31. 1999 Temperature and Rainfall versus Time for Fisher Creek, Ames Sink, Lost 

Creek and Wakulla Springs ......................................................................................... 48 

32. 2000 Temperature and Rainfall versus Time for Fisher Creek, Ames Sink, Lost 

Creek and Wakulla Springs ......................................................................................... 49 

33. 1999 Wakulla Springs Velocity versus Specific Conductivity........................................ 50 

34. 2000 Wakulla Springs Velocity versus Specific Conductivity........................................ 51 

35. Location of Wells Used In 1997 Sampling Event.......................................................... 54 

36. Compilation of NO3-N and NO2+NO3-N Concentrations in the Floridan Aquifer, 1997.. 55 

37. NO2+NO3-N Concentrations, 1999-2000...................................................................... 56 

38. Dissolved Organic Carbon Concentrations, 1999-2000................................................ 58 

39. Dissolved Oxygen Concentrations, 1999-2000 ............................................................ 59 

40. pH, 1999-2000............................................................................................................. 60 

41. Specific Conductivity, 1999-2000................................................................................. 62 
vii

LIST OF FIGURES [cont.] 

Figure Page

42. Orthophosphate Concentrations, 1999-2000 ............................................................... 63 

43. Location of City of Tallahassee Public Supply Wells .................................................... 64 

44. City of Tallahassee Public Supply Well NO2+NO3-N Concentrations............................ 65 

45. Summary of Nitrogen Loading to the Semi-confined and Unconfined Areas as a 

Function of Time.......................................................................................................... 70 

46. Wastewater Treatment Facility Locations with Major Effluent and Residual Disposal 

Areas........................................................................................................................... 75 

47. Southeast Sprayfield Monitor Well Locations............................................................... 79 

48. Southeast Sprayfield Monitor Well NO2+NO3-N Concentrations (mg/L) ....................... 80 

49. Southwest Sprayfield and Residual Disposal Area Monitor Well Locations.................. 83 

50. Southwest Sprayfield Monitor Well Nitrate Concentrations (as N, mg/L) ...................... 84 

51. Residual Disposal Area Monitor Well NO2+NO3-N Concentrations (mg/L) ................... 85 

52. Population Increase in Leon and Wakulla Counties since 1900 ................................... 88 

53. Location of OSDS in Semi-Confined and Unconfined Portions of Leon and Wakulla 

Counties ...................................................................................................................... 90 

54. Relative Contribution from Inventoried Nitrogen Sources to 1990-1999 Average N 

Loading in Semi-confined and Unconfined Portions of Leon and Wakulla Counties..... 101 

55. Relative Contribution from Anthropogenic Nitrogen Sources to 1990-1999 Average N 

Loading in Semi-confined and Unconfined Portions of Leon and Wakulla Counties..... 101 

56. Water Budget for Wakulla Springs Contributory Area .................................................. 104 

57. Conceptual Ground Water Flow Cross Section............................................................ 106 

58. Relative Contribution from Inventoried Nitrogen Sources to 1990-1999 Average N 

Loading in the Wakulla Springs Contributory Area....................................................... 111 
viii

LIST OF TABLES 

Table Page

1. Leon County Estimated Average Ground Water Use, 1995 ......................................... 8 

2. Wakulla County Estimated Average Surface and Ground Water Use, 1995................. 10 

3. Estimated Average Public Water Supply Use by System, 1995 ................................... 10 

4. δ15N-NO3 Values......................................................................................................... 57 

5. Estimated 1999 Nitrogen Loading from Atmospheric Deposition.................................. 73 

6. Estimated 1999 Nitrogen Loading from WWTF Effluent............................................... 76 

7. Estimated 1999 Nitrogen Loading from WWTF Residuals ........................................... 86 

8. Estimated 1999 Nitrogen Loads from OSDS................................................................ 91 

9. Estimated 1999 Nitrogen Loads from Commercial Fertilizer ........................................ 93 

10. Estimated “Recent” Nitrogen Loads from Livestock ..................................................... 94 

11. Estimated “Recent” Nitrogen Loads from Sinking Streams .......................................... 98 

12. Estimated 1999 Nitrogen Loading to the Study Area by Geographic Subdivision......... 100 

13. Ten-year Average Annual Nitrogen Load to the Study Area by Geographic 

Subdivision .................................................................................................................. 100 

14. Ten-year Average Annual Nitrogen Load to the Wakulla Springs Contributory Area .... 111 

Appendix A Tables Page

A1 Construction Details of Wells Used for Water Level Monitoring.................................... 123 

A2 Construction Details for Wells Used in 1997 Sampling Event....................................... 125 

A3 Construction Details for Project Sampling Sites ........................................................... 128 

A4 Project Sampling Results............................................................................................. 129 

A5 Construction Details for City of Tallahassee Public Supply Wells................................. 131 

A6 WWTFs in Leon and Wakulla Counties........................................................................ 132 
ix

LIST OF TABLES [cont.] 

Appendix A Tables Page

A7 Domestic WWTF Effluent Total Nitrogen (Kg-N/yr) Loading Rates............................... 134 

A8 Construction Details for Southeast Sprayfield Monitor Wells........................................ 135 

A9 Construction Details for Southwest Sprayfield Monitor Wells ....................................... 137 

A10 Construction Details for Residual Disposal Monitor Wells. ........................................ 138 
 x

ACKNOWLEDGMENTS

The support provided by the Florida Department of Environmental Protection and the

U.S. Environmental Protection Agency was invaluable. Eric Livingston, Environmental

Administrator, FDEP Bureau of Watershed Management, was instrumental to the

success of this project. Rick Copeland and Lyle Hatchett, FDEP Bureau of Watershed 

Management, served as project managers. The efforts of both of these gentlemen on

behalf of the District are gratefully acknowledged. Rick Copeland also reviewed the

report. 

The authors wish to acknowledge the cooperation and assistance provided by the City of 

Tallahassee. Bill Leseman, Jay Johnson, Jamie Shakar, John Morrill and Keith Turner 

and Koren Taylor provided, as they have done on numerous occasions in the past,

much-appreciated support and assistance. Frank Evans of the Wakulla County Planning 

Office provided information on the location of sewer infrastructure in the County. Tom

Singleton and Joe Hand of the Florida Department of Environmental Protection provided 

access to their work in the St. Marks basin as well as relevant consultant reports. Chris 

Werner and the divers of the Woodville Karst Plain Project shared their data and

experience of the caves in the study area.

Peter Krottje and Nick Wooten of the Northwest Florida Water Management District

provided valuable data support and assistance. Alan Baker, Gary Miller, Ferdouse

Sultana and Karen Kebart provided GIS support and assistance.

On behalf of the City of Tallahassee, Koren Taylor and Jamie Shakar reviewed draft

versions of the report. Graham Lewis (NWFWMD), David Toth (SJRWMD), Tom

Kwader (URS Corporation and member of Leon County Science Advisory Committee), 

Kyle Champion (SWFWMD) and Eric DeHaven (SWFWMD) provided outside review.

The cover photograph was taken inside the conduit system looking up at a glass bottom 

boat floating on the surface of the spring. Daniel Wagner, who graciously agreed to its 

use, took the photograph.

REVISION June 2003 – As part of the District's lower St. Marks/Wakulla rivers

watershed nitrate investigation, water levels were measured in the study area and

potentiometric surfaces contoured (report Figures 22 through 24). Three maps were

prepared; January 1999, August 1999 and March 2000. One criterion for inclusion on

the final map was a surveyed wellhead elevation. Seven measured wells were not

surveyed during the study period due to time constraints. Data from these wells were

not included in the original contouring efforts. Funding provided by the FDEP Florida

Springs Initiative (2002-2003) allowed for two of the unsurveyed wells (NWF ID# 7238

and 7239) to be professionally surveyed to +0.1 ft, NGVD. Correctly adjusted ground

water elevation data from these two well points were inserted into Figures 22 through 24 

and the potentiometric surface contours revised accordingly.
 1

INTRODUCTION 

Purpose and Scope

This report is being submitted to provide Leon and Wakulla counties, the City of Tallahassee, 

the Florida Department of Environmental Protection and other interested parties with a means of 

assessing the risk posed to drinking water wells (existing and proposed) and surface water 

bodies by NO3-N contamination. It is the intent of this study to augment the St. Marks River 

Surface Water Improvement and Management (SWIM) Program in its effort focusing on the 

restoration and long-term preservation of the St. Marks and Wakulla rivers watershed. This is 

an integral component of the State of Florida’s Watershed Management Program. This work 

was performed under Florida Department of Environmental Protection (FDEP) Contract Number 

WM695. Specifically, the scope of this work includes the following activities: 

• Relying on an existing USGS-developed numerical model of the Floridan Aquifer, develop a 

steady-state water budget for the study area. Quantify the horizontal flux into the study area 

from up-gradient portions of the Floridan Aquifer. Estimate ground water inputs from 

principal sinking streams. Quantify areally distributed recharge rates to Woodville karst 

plain. Quantify losses through springs and rivers. Quantify losses to the Gulf of Mexico. 

• Develop a project-specific network of approximately 40 existing wells. Develop criteria for 

including wells in network. Review Northwest Florida Water Management District 

(NWFWMD) databases for wells suitable for inclusion. Visit well sites and determine their 

locations via global positioning system (GPS). 

• Develop a network of surface water sampling sites comprised of rivers, springs, sinking 

streams, and sinkholes. In conjunction with DEP, develop criteria for including sites in 

network, parameter lists and sampling frequency. Site visit and GPS sites. 

• Construct a supplemental network of approximately six Floridan Aquifer wells suitable for 

isotopic sampling. Develop criteria for choosing site locations. Obtain necessary 

easements. Obtain contractor services and construct wells. Locate wells with GPS. 

• Conduct sampling of karst features, springs and sinkholes. 

• Sample project-specific network wells for field parameters, major ions, nutrients, silica, and 

dissolved organic carbon (DOC). The U.S. Geological Survey Water Quality and Research 

Laboratory in Ocala, FL analyzed samples for major ions. Prepare maps showing the 

spatial distribution of selected parameters. Prepare corresponding potentiometric-surface 

map from water-level data collected at time of sample collection. Sample supplemental 

network twice in one year for the same parameters, as well as isotopes 18O/16O, D/H, 

13C/12C, 15N/14N, 3

H/3He. 

• Develop geographic information systems (GIS) coverages of karst features within the study 

area including, sinkholes, springs, sinking streams, etc. 

• Examine all data to delineate areal distribution of NO3-N, isotopes and other water quality 

parameters. Perform geochemical modeling using WATEQF and NETPATH. Integrate and 
 2

interpret geochemical data to determine flow paths, flow rates, ground water ages and NO3-

N flux through the system. 

• Compile NO3-N concentration and load data for the principal input sources to the Floridan 

Aquifer in study area including stormwater runoff; horizontal flux into study area from upgradient areas; and effective concentration of rainfall recharge, recharge from wastewater 

treatment facilities, and leaching from fertilizer application. 

• Conduct an inventory of septic tank sites in the study area using available census data, 

land-use data, areal photographs and Department of Health (DOH) septic tank permitting 

records. Develop GIS coverages representing current spatial distribution of septic tanks in 

study area. Based on available literature, develop estimates of NO3-N loading rates from 

septic tanks. Combine data on septic tank loading rates with cumulative tank numbers to 

estimate total load to Floridan Aquifer from this source.

• Develop STELLA application. Perform and document sensitivity analyses. Document 

usefulness and limitations associated with this approach. Transfer STELLA application to 

interested local governments. Provide an integrated technology transfer and training 

program to local decision-makers and affected stakeholders interested in understanding and 

using the application. 

Project deliverables consist of this report and Katz et al. (in preparation). This project and the 

preparation of this report were funded in part by a Section 319 Nonpoint Source Management 

Program grant from the U.S. Environmental Protection Agency (USEPA) through a contract with 

the Nonpoint Source Management and Water Quality Standards Section of the Florida 

Department of Environmental Protection. The total cost of the project was $503,700 of which 

$291,966, or 58 percent was provided by the USEPA. The project described here is a 

component of the District’s St. Marks Surface Water Improvement and Management Program. 

From FY96-97 through FY00-01, expenditures on the St. Marks SWIM program (exclusive of 

the 319h grant) totaled approximately $574,000. 

Area of Investigation

The focus of this study is those portions of Leon and Wakulla counties where the Floridan 

Aquifer is under either semi-confined or under unconfined conditions (Figure 1). This includes 

approximately the eastern two-thirds of Leon County and the eastern half of Wakulla County. 

Tallahassee, Woodville, Crawfordville and St. Marks all lie within the study area. The vast 

majority of residents in both counties live within the study area. This area was selected 

because of the relatively good hydraulic connection between the land surface and the 

underlying Floridan Aquifer. Further, much of the water that flows south to points of discharge 

either originates in or flows beneath this area. The area identified as being under semi-confined 

conditions generally coincides with the Tallahassee Hills physiographic subdivision as mapped 

by Hendry and Sproul (1966), Puri and Vernon (1964) and Brooks (1981). It also corresponds 

to what Davis (1996) mapped as Floridan Aquifer “overlain but not confined by low-permeability 

Miocene-and Pliocene age sediments.” 

The area identified as being under unconfined conditions generally corresponds to what Brooks 

(1981) mapped as the Lake Munson Hills and Woodville Karst Plain physiographic subdivisions. 

It also corresponds to the Woodville Karst Plain as mapped by Rupert (1988) and Lane (1986) 

and to what Davis mapped as where the Floridan Aquifer is “unconfined and the top of the 
AREA OF INVESTIGATION

%%%%%%

%%%%%%%

%

%%%%%%%% %%%%%%%%

%%% %%%%% % %%%%%%

%%%%%%

%%%%%%

%

%%%%%%%%%%%%%%%

%%%%%%%%%%%

%%%

%

%

%

%%%

%%%%%%%%%%%%%%%%%%%

%%%

%%

%%%%

%

%%

% %%

%

%%%%%

%

%%

%%

%% %%

%%%%

%%%%%%% %%%%%

%%%

%%%%

%%%%

%%

%%%%%%%%%%%%%%%%

%%%%

%

%%%% %%%%%%%%%%

%%%%%

%%

%

%%

%%%%%%%%%%%%%%%%%%%%%%%%

%%%%

%

%%%% %%%

%%%%%%%%%%%%

%%%%%

%

%%%

%

%%%%

%%%%%%%%%%%%%%%%%%%%%%%

%

%%% %%%%%%%%% %%%% %%%%%

%%%%

%%%%%%%%% %%%%%%%%%

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%

% %%%%%

Y

Y

A P A L A C H E E

#

GEORGIA

Wakulla

River

÷ø267

!"61

/(98

g%365

÷ø363

,.-10

/(90

!"20

/(27

/(27

/(90

(/319

L.

Micc.

Lake

Iamonia

L.

Jackson

Lake

Lafayette

Lake

Talquin

B A Y

Lake

Munson

NWFWMD

SRWMD

River

Crawfordville

Woodville

Monticello

Panacea

St.

Marks

LEON CO.

WAKULLA CO.

WAKULLA CO.

JEFFERSON CO.

GADSDEN CO.

Sopchoppy

Tallahassee

Havana

Quincy

Midway

St. Marks

Rise

River

Ochl o ckonee

St. Marks

TAYLOR

 CO.

Wakulla 

 Springs

Spring

 Creek

(/319

/(98

Y

Spring

 Creek

N

Floridan Aquifer Semi-Confined

Floridan Aquifer Unconfined

Major Lakes

Cody Scarp

Conduit System

Zone-of-Contribution

Boundary

County Boundary

District Boundary

Rivers

0 510

Miles

01-06-001

FIGURE 1
 4

aquifer is at (or near) land surface”. The boundary between the semi-confined and unconfined 

areas corresponds to the Cody Scarp, as mapped by Puri and Vernon (1964). The remainder of 

Leon and Wakulla counties are described by Davis as being under confined conditions. 

The study area is imbedded within a larger Floridan Aquifer zone-of-contribution for the 

significant ground water discharge occurring in Wakulla Springs, the lower St. Marks River and 

beneath the Gulf of Mexico (Figure 1). Potentiometric surface mapping by Davis (1996) was 

used to delineate this larger zone-of-contribution. Land use for the coastal Wakulla County 

Floridan Aquifer zone-of-contribution delineation is provided in Figure 2.

Rainfall

During the study period 1998-2000, rainfall was abnormally low. The 50-year (1951-2000) 

average annual rainfall at the Tallahassee Airport is 62.6 inches. The 10-year (1991-2000) 

average annual rainfall declines to 60 inches, reflecting drought conditions during the latter part 

of this period. Comparisons between the Tallahassee Airport 50-year average annual and 

yearly totals for 1998, 1999 and 2000 are given in Figure 3. Data from the River Sink rainfall 

station are only available for 1999 and 2000. During 1998, the airport recorded a deficit of 3.8 

inches (6.1 percent of the 50-year average). In 1999, the deficit was 12.5 inches (two-year 

cumulative deficit of 16.3 inches, or 13.1 percent of two years average rain). During 2000, the 

deficit was 17.5 inches, yielding a three-year cumulative deficit of 33.8 inches, or 18.0 percent of 

three years average rain. Not only did dry conditions persist for much of the three-year study 

period, but also the severity of the drought worsened during the latter half of the period. The 

persistent lack of rainfall during the study period yielded a lowering of the Floridan Aquifer 

potentiometric surface, low or no inflows to sinkholes and sinking streams, lower than normal 

discharge from springs, low lake levels and diminished or nonexistent surface streamflows. 

Mean monthly rainfall totals for the 10-year period 1991-2000 were calculated for the 

Tallahassee Airport. These monthly averages are compared with monthly rainfall during the 

same period in Figure 4. A ten-year cumulative departure from normal is given in Figure 5. For 

the entire 36-month period (January 1998 through December 2000), monthly rainfall exceeded 

the 10-year monthly average in only eight months (February 1998, March 1998, July 1998, 

September 1998, May 1999, June 1999, August 2000 and September 2000). Two monthly 

average exceedances are attributable to tropical storms. In September 1998, Hurricane Earl 

(9/3/1998) dropped 5.07 inches of rain at Tallahassee Airport and Hurricane Georges 

(9/30/1998) dropped 5.32 inches. In September 2000, Hurricane Gordon (9/18/00) dropped 

0.71 inches of rain at the Airport and Tropical Storm Helene (9/22/00) dropped 8.2 inches. 

The National Oceanographic and Atmospheric Administration, Drought Information Center has 

published the weekly U.S. Drought Monitor http://www.drought.noaa.gov/ since May 20, 1999. 

The study area was classified as being under drought conditions for the entirety of 2000. The 

beginning of 2000 found the study area under D2 (severe drought) conditions, which persisted 

for all of January. February was characterized as being at D1 (moderate drought) status. D2 

conditions persisted from the end of February until the end of May. From the beginning of June 

until September 11, the study area was under either D3 (extreme drought) or D4 (exceptional 

drought) conditions. The D1 conditions that prevailed from September 19 through October 30 

were associated with the passage of tropical storms through the area. From the first of 

November until the end of the year, the study area was again under D2 conditions. 
LAND USE CLASSIFICATIONS WITHIN THE ZONE OF CONTRIBUTIONSRWMD

A P A L A C H E E 

NWFWMD

B A Y

WAKULLA CO.

GEORGIA

GADSDEN

CO.

FRANKLIN CO.

NWFWMD

SRWMD

JEFFERSON

CO.

JEFFERSON CO.

LEON CO.

LIBERTY CO.

TAYLOR CO.

0 510

Miles

N

Residential

Commercial & Services

Industrial

Open Land Institutional

Recreational

Agriculture

Upland Forests

Water

Wetlands

Barren Land

Trans, Com, & Utilities

01-06-002

FIGURE 2
 6

re 3. Annual Rainfall Deficit (1998-2000) versus 50-Year Average (1951-2000) at Tallahassee Airport. 

55 62.55 62.55

50.07

44.66

51.35 52.61

58.45

1998 1999 2000

50-Year AverageAirport StationRiver Sink Station
 7

Figure 4. 1991-2000 Monthly Rainfall Deviation from Monthly Mean. 

Figure 5. 1991-2000 Cumulative Deviation from Normal Rainfall. 

-10

-5

0

5

10

15

20

25

30

35

Jan-91

May-91

Sep-91

Jan-92

May-92

Sep-92

Jan-93

May-93

Sep-93

Jan-94

May-94

Sep-94

Jan-95

May-95

Sep-95

Jan-96

May-96

Sep-96

Jan-97

May-97

Sep-97

Jan-98

May-98

Sep-98

Jan-99

May-99

Sep-99

Jan-00

May-00

Sep-00

Inches

-8

-6

-4

-2

0

2

4

6

8

10

12

14

Jan-91 Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan-00

Inches
 8

Study period dry conditions had a profound effect on both surface and ground waters, although 

impacts on surface waters were most evident. Lake Jackson stood at an elevation of 86 ft 

(MSL) in March 1998. By May 1999, the lake had declined to 81 ft (MSL). On September 9, the 

lake stood at an elevation of 78.6 ft. On September 16, 1999 Porter Hole Sink drained, leaving 

the southern half of the lake mostly dry. During the summer of 2000, evaporation and leakage 

removed much of the remaining water in the northern half of the lake. Lime Sink drained during 

April and May 2000, leaving the lake effectively dry. The lake remained dry through the 

remainder of 2000 and the first half of 2001. Heavy rains associated with tropical storm Allison 

in June 2001 re-flooded much of the lake bottom to a depth of several feet. The lake has not 

experienced dry conditions for this length of time since the mid- to late 1950s. 

Water levels in the Floridan and Intermediate aquifers experienced period-of-record (1966-

2001) lows during the study period (Figures 6 and 7). Water levels in both aquifer systems 

mirror the cumulative departure from normal, rising in relatively wet periods and declining when 

it is dry. During the extreme dryness of 2000, ground water levels declined to elevations not 

see for more than 30 years, and likely not since the 1950s. 

Ground Water Use in Leon and Wakulla Counties

Effectively, all of the water used for public supply, domestic, agriculture, commercial/industrial, 

and recreation/landscape uses comes from the Floridan Aquifer. Only in the case of power 

generation in Wakulla County does a substantial portion of the water use come from surface 

water. This water is not consumptively used, being almost entirely returned to the St. Marks 

River after passing through the Purdom Power Generation Station’s cooling system. Tables 1 

and 2 summarize the most recent water use figures for Leon and Wakulla counties, 

respectively. The uses are disaggregated by use classification and by source. Table 3 details 

public water supply use by system in each county. 

Table 1. Leon County Estimated Average Ground Water Use, 1995. 

Ground Water Surface Water Total 

Use Classification (Mgal/d) (Mgal/d) (Mgal/d) 

Public Supply 27.66 0.0 27.66 

Self-supplied Domestic 4.61 0.0 4.61 

Agriculture 1.01 0.0 1.01 

Recreation/Landscape 0.95 0.0 0.95 

Commercial/Industrial 0.23 0.0 0.23 

Power Generation 2.64 0.0 2.64

Total 37.10 0.0 37.10

Source: Ryan, P.L., Macmillian, T.L., Pratt, T.R., Chelette, A.R., Richards, C.J., Countryman, 

R.A., and Marchman, G.L. District Water Supply Assessment. Northwest Florida Water 

Management District WRA 98-2. 1998. 
 9

Figure 6. Hydrograph of Lake Jackson Floridan Aquifer Monitor Well, Northern Leon County. 

(data from USGS and NWFWMD) 

Figure 7. Hydrograph of Lake Jackson Intermediate Aquifer Monitor Well, Northern Leon 

County. (data from USGS and NWFWMD) 

LAKE JACKSON INTERM (NWF ID - 3403)

0

20

40

60

80

100

120

1966 1977 1988 1999

Date

Water Level (relative to sea level)

LAKE JACKSON FLOR. (NWF ID - 3402)

0

20

40

60

80

100

120

1966 1972 1977 1982 1988 1993 1999

Date

Water Level (relative to sea level)
 10

Table 2. Wakulla County Estimated Average Surface and Ground Water Use, 1995. 

 Ground Water Surface Water Total 

Use Classification (Mgal/d) (Mgal/d) (Mgal/d) 

Public Supply 1.05 0.0 1.05 

Self-supplied Domestic 0.93 0.0 0.93 

Agriculture 0.0 0.0 0.0 

Recreation/Landscape 0.10 0.0 0.10 

Commercial/Industrial 0.63 0.0 0.63 

Power Generation 0.29 68.84* 69.13

Total 3.00 68.84* 71.84

Sources: 

Ryan, P.L., Macmillan, T.L., Pratt, T.R., Chelette, A.R., Richards, C.J., Countryman, R.A., and 

Marchman, G.L. District Water Supply Assessment. Northwest Florida Water Management 

District WRA 98-2. 1998. 

Marella, R.L., M.F. Mokray and M.J. Hallock-Solomon, 1998. Water Use Trends and 

Projections in the Northwest Florida Water Management District. U.S. Geological Survey. 

Open File Report 98-269, 35 pp. 

*Almost all of this water is returned to the St. Marks River. 

Table 3. Estimated Average Public Water Supply Use by System, 1995. 

 Ground Water Use Percent of Leon/Wakulla 

Public Supply System (Mgal/d) Public Supply Total

Leon County

City of Tallahassee 25.32 88.2 

TEC/Bradfordville Regional 0.79 2.8 

TEC/Meadows at Woodrun 0.32 1.1 

TEC/Lake Jackson 1.17 4.1 

Pine Ridge Estates 0.06 0.2 

Wakulla County

TEC/Gulf Coast Water System 0.28 1.0 

Panacea Area Water System 0.23 0.8 

St. Marks 0.10 0.3 

Sopchoppy 0.44 1.5

Total 28.71 100 

Source: Ryan, P.L., Macmillan, T.L., Pratt, T.R., Chelette, A.R., Richards, C.J., Countryman, 

R.A., and Marchman, G.L. District Water Supply Assessment. Northwest Florida Water 

Management District WRA 98-2. 1998. 
 11

METHODS 

Floridan Aquifer Potentiometric Surface Mapping

The focus of potentiometric surface mapping was that portion of the study area south of the 

Cody Scarp (in southern Leon County and eastern Wakulla County). In order to determine 

general flow directions within the Floridan Aquifer in this area, a network of water level 

monitoring wells was established. 54 wells were identified as being suitable for water level data 

collection (Appendix A, Table A1 and Figure 8). Wells were selected from records maintained 

at the District and were chosen to provide as dense a network as was reasonably practicable to 

monitor. Only Floridan Aquifer wells were included in the water level monitoring effort. Given 

the flatness of the potentiometric surface, wellhead and land surface elevations were 

established by survey (NGVD) for all wells included on the potentiometric surface maps. All 

wells that had not previously been surveyed were instrument leveled to an accuracy of ±0.1 ft. 

Previous potentiometric surface mapping efforts in this area have been based (predominantly) 

on elevations estimated from topographic maps. Horizontal locations were determined using 

differential GPS location techniques. 

Drilling

Six Floridan Aquifer monitor wells were constructed as a part of this project. Wells were 

constructed in three pairs. At each site a deep well and a shallow well were constructed. All 

wells were constructed using flush-threaded PVC well casing and were grouted with neat 

cement grout. All were constructed using conventional hydraulic rotary drilling techniques. Well 

locations and other construction details are found in Appendix A, Table A1. 

Ground and Surface Water Sampling

A second network of 41 Floridan Aquifer wells was established for the purpose of ground water 

sampling (Appendix A, Table A2 and Figure 9). 35 were pre-existing domestic supply, public 

supply and irrigation wells. The remaining six were constructed specifically for the project. In 

addition, surface water samples were collected at seven sites (Lost Creek, Fisher Creek, Ames 

Sink, Middle River Sink, Sally Ward Spring, Wakulla Springs and McBride Slough). Samples 

were collected by USGS and NWFWMD personnel and were analyzed for major ions, nutrients, 

silica, DOC and isotopes. Sample collection protocols and analytical methods are discussed in 

greater detail in Katz et al. (in preparation). The USGS Water Quality and Research Laboratory 

in Ocala, FL analyzed major ions. The USGS Isotope Fractionation Laboratory in Reston, VA, 

analyzed O, H and N isotopes. Carbon isotope analyses were performed at the University of 

Waterloo. Tritium and 3

He analyses were performed at the Noble Gas Laboratory of the 

Lamont-Dougherty Earth Observatory in Palisades, NY. 

Ground and surface water sampling was conducted in several mobilizations. Results from the 

initial ground water sampling were used to guide location selection for the six monitor wells 

constructed for the project. Once these wells were completed, isotopic sampling was conducted 

in them and at Middle River Sink and Wakulla Springs. Analyses for this event include 15N/14N; 

18O/16O; D/H; 13C/12C; and 3

H/3He. A key project objective was to conduct isotopic sampling 

under low-flow and high-flow conditions. The first isotopic sampling occurred in February 2000 

and is considered to represent the low-flow condition. Due to drought conditions that persisted