Water and Bed-Material Quality of 

Selected Streams and Reservoirs 

in the Research Triangle Area of 

North Carolina, 1988-94

By Carolyn J. Oblinger Childress and M.W. Treece, Jr.

U.S. GEOLOGICAL SURVEY 

Water-Resources Investigations Report 95-4282

Prepared in cooperation with the

Triangle Area Water Supply Monitoring Project Steering Committee:

Town of Apex City of Durham

Town of Carrboro City of Raleigh

Town of Gary City of Sanford

Town of Chapel Hill Chatham County

Town of Hillsborough Orange County

Town of Pittsboro Orange Water and Sewer Authority

Town of Smithfield

and the

North Carolina Department of Environment, Health, and Natural Resources

Raleigh, North Carolina 

1996
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

The use of firm, trade, and brand names in this report is for identification purposes 

only and does not constitute endorsement by the U.S. Geological Survey.

For addtional information write to:

District Chief 

U.S. Geological Survey 

3916 Sunset Ridge Road 

Raleigh, NC 27607

Copies of this report can be purchased 

from:

U.S. Geological Survey 

Information Services 

Box 25286, Mail Stop 517 

Denver Federal Center 

Denver, CO 80225-0046
CONTENTS

Abstract.................................................................^ 1

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

Purpose and scope ....................................................................................................................................................... 4

Description of the study area....................................................................................................................................... 4

Land use....................................................................................................................................................................... 10

Water use ..................................................................................................................................................................... 11

Previous investigations................................................................................................................................................ 12

Acknowledgments....................................................................................................................................................... 13

Water quality of streams and reservoirs................................................................................................................................. 14

General characteristics................................................................................................................................................. 14

Water-quality characteristics by site category ............................................................................................................. 15

Nitrogen and phosphorus................................................................................................................................... 20

Nitrogen.........................................................................................................^ 20

Phosphorus............................................................................................................................................... 22

Trace elements................................................................................................................................................... 23

Volatile organic compounds............................................................................................................................... 28

Pesticides and PCB's ......................................................................................................................................... 28

Semivolatile organic compounds....................................................................................................................... 32

Bed-material quality.............................................................................................................................................................. 32

Pesticides ............................................................................ 36

Semivolatile organic compounds................................................................................................................................. 38

Tributary loadings to reservoirs............................................................................................................................................. 38

Streamflow conditions................................................................................................................................................. 42

Suspended sediment.................................................................................................................................................... 46

Nitrogen and phosphorus............................................................................................................................................. 53

Lead and zinc..............................................................................................................................................................^ 59

Summary.......................................................................................................................................................^ 67

References ..................................................................................................................................................................^ 71

Supplementary tables............................................................................................................................................................. 74

FIGURES

1-5. Maps showing:

1. The Triangle Area Water Supply Monitoring Project study area within the upper Neuse River

and upper Cape Fear River Basins, North Carolina.......................................................................................... 3

2. Water-quality sampling and streamflow monitoring sites in the (A) upper Neuse River Basin

and (B) upper Cape Fear River Basin................................................................................................................ 5

3. Mean dissolved solids concentrations and major geochemical zones in North Carolina.................................. 14

4. Stiff diagrams of major ions for sites in the upper Neuse River Basin.............................................................. 16

5. Stiff diagrams of major ions for sites in the upper Cape Fear River Basin........................................................ 17

6. Diagrams showing the distribution of median concentrations of selected nutrients by site category

in the Research Triangle study area, North Carolina.................................................................................................. 21

7. Graphs showing total phosphorus and chlorophyll a concentrations for Falls Lake at 1-85 and Haw River

arm of Jordan Lake, 1988-94...................................................................................................................................... 24

8-10. Box plots showing:

8. The distribution of copper concentrations by site and site category in the Research Triangle

study area, North Carolina................................................................................................................................. 25

Contents III
9. The distribution of lead and zinc concentrations by site and site category

in the Research Triangle study area, North Carolina........................................................................................ 26

10. The distribution, by site category, of the percentage of pesticides or volatile organic compounds

for which concentrations were above minimum reporting limits ..................................................................... 29

11. Maps showing the sum of concentrations of organochlorine and organophosphorus pesticides detected

in bed material collected at sites in the (A) upper Neuse River Basin and (B) upper Cape Fear River Basin........... 37

12-15. Graphs showing:

12. Comparison of the relation between discharge and concentration and discharge and load

for selected streams........................................................................................................................................... 39

13. Cumulative suspended-sediment load and daily mean discharge for Eno River near Weaver,

water year 1993................................................................................................................................................. 41

14. Monthly mean discharge at Eno River near Durham for water years 1989 and 1992,

and for the period of record,1964-94................................................................................................................ 44

15. Monthly mean discharge at Haw River near Bynum for water years 1991 and 1992,

and for the period of record, 1973-94............................................................................................................... 45

16-25. Maps showing estimated:

16. Suspended-sediment yield and load in selected tributaries to Falls Lake, Lake Michie,

and Little River Reservoir, (A) 1989 and (B) 1992 .......................................................................................... 50

17. Suspended-sediment yield and load to Cane Creek Reservoir, Jordan Lake,

and University Lake, (A) 1989 and (B) 1992 ................................................................................................... 51

18. Nitrogen yield and load in selected tributaries to Falls Lake, Lake Michie,

and Little River Reservoir, and outflow of nitrogen load from Lake Michie and Falls Lake,

(A) 1989 and (B) 1992...................................................................................................................................... 56

19. Nitrogen yield and load to Cane Creek Reservoir, Jordan Lake, and University Lake,

and outflow of nitrogen load from Jordan Lake, (A) 1989 and (B) 1992......................................................... 57

20. Phosphorus yield and load in selected tributaries to Falls Lake, Lake Michie, and

Little River Reservoir, and outflow of phosphorus load from Falls Lake and Lake Michie,

(A) 1989 and (B) 1992...................................................................................................................................... 60

21. Phosphorus yield and load to Cane Creek Reservoir, Jordan Lake, and University Lake,

and outflow of phosphorus load from Jordan Lake, (A) 1989 and (B) 1992.................................................... 61

22. Lead yield and load from selected tributaries to Falls Lake and Lake Michie,

and outflow of lead load from Falls Lake, (A) 1989 and (B) 1992................................................................... 64

23. Lead yield and load from selected tributaries to Jordan Lake and University Lake,

and outflow of lead load from Jordan Lake, (A) 1989 and (B) 1992................................................................ 65

24. Zinc yield and load from selected tributaries to Falls Lake, and outflow of zinc load

from Falls Lake, (A) 1989 and (B) 1992 .......................................................................................................... 68

25. Zinc yield and load from selected tributaries to Jordan Lake, and outflow of zinc load

from Jordan Lake, (A) 1989 and (B) 1992 ....................................................................................................... 69

TABLES

1. Water-quality sampling and streamflow monitoring sites in the Triangle Area Water Supply

Monitoring Project.................................................................................................................................................. 7

2. Description of reservoirs in the Research Triangle study area............................................................................... 10

3. Statistical summary of selected nutrients, metals, and trace element constituents for site categories,

October 1988 through September 1994.................................................................................................................. 18

4. Summary statistics of total trihalomethane concentrations measured at sites located downstream

from urban areas and waste water-treatment plants, water years 1989-91.............................................................. 30

5. Results of analyses of triazine and acetanilide herbicides in water samples collected at selected sites

during the spring of 1992 ....................................................................................................................................... 31

6. Constituents having at least one detection in samples analyzed for concentrations of selected

pesticides upstream from, downstream from, and in wastewater-treatment plant effluents in Ellerbe,

Northeast, and Little Lick Creeks........................................................................................................................... 33

7. Number of samples collected for analysis of semivolatile organic compounds..................................................... 36

IV Contents
8. Mean and maximum daily discharges and total annual discharge at selected study sites,

water years 1989-94......................................................... 43

9. Annual suspended-sediment loads into Falls Lake, Lake Michie, and Little River Reservoir, 

and out of Lake Michie and Little River Reservoir in the upper Neuse River Basin, 

water years 1989-94................................................................................................................................................ 47

10. Suspended-sediment, total nitrogen, and total phosphorus yields for monitoring sites

in the upper Neuse River Basin.............................................................................................................................. 48

11. Estimates of annual suspended-sediment loads into Jordan Lake, University Lake, and Cane Creek

Reservoir in the upper Cape Fear River Basin, water years 1989-94..................................................................... 49

12. Suspended-sediment, total nitrogen, and total phosphorus yields for monitoring sites

in the upper Cape Fear River Basin........................................................................................................................ 52

13. Annual nutrient loads into and out of Falls Lake, Lake Michie, and Little River Reservoir,

water years 1989-94................................................................................................................................................ 54

14. Annual nutrient loads into and out of Jordan Lake, University Lake, and Cane Creek Reservoir,

water years 1989-94...............................................................^ 58

15. Lead loads and yield from selected tributaries in the upper Neuse River and upper Cape Fear

River Basins, water years 1989-94......................................................................................................................... 62

16. Zinc loads and yield from selected tributaries in the upper Neuse River and upper Cape Fear

River Basins, water years 1989-94......................................................................................................................... 66

SUPPLEMENTARY TABLES

S-l. Equations describing the suspended-sediment concentration-discharge relation used to calculate

loads for sites in the upper Neuse River Basin....................................................................................................... 75

S-2. Equations describing the suspended-sediment concentration-discharge relation used to calculate

loads for sites in the upper Cape Fear River Basin................................................................................................. 76

S-3. Equations describing the total nitrogen concentration-discharge relation and the total 

phosphorus concentration-discharge relation used to calculate loads for selected sites 

in the upper Neuse River Basin.............................................................................................................................. 77

S-4. Equations describing the total nitrogen concentration-discharge relation and the total 

phosphorus concentration-discharge relation used to calculate loads for selected sites 

in the upper Cape Fear River Basin........................................................................................................................ 78

S-5. Equations describing the lead concentration-discharge relation and zinc concentration-discharge

relation used to calculate loads for selected sites in the upper Neuse and Cape Fear River Basins....................... 79

Contents V
WATER AND BED-MATERIAL QUALITY OF 

SELECTED STREAMS AND RESERVOIRS IN THE 

RESEARCH TRIANGLE AREA OF NORTH 

CAROLINA, 1988-94

By Carolyn J. Oblinger Childress antfM.W.Treece, Jr.

ABSTRACT

The Triangle Area Water Supply 

Monitoring Project was formed by a consortium 

of local governments and governmental agencies 

in cooperation with the U.S. Geological Survey to 

supplement existing data on conventional 

pollutants, nutrients, and metals to enable 

eventual determination of long-term trends; to 

examine spatial differences among water supplies 

within the region, especially differences between 

smaller upland sources, large multipurpose 

reservoirs, and run-of-river supplies; to provide 

tributary loading and inlake data for predictive 

modeling of Falls of the Neuse and B. Everett 

Jordan Reservoirs; and to establish a database for 

synthetic organic compounds.

Water-quality sampling began in October 

1988 at 35 sites located on area run-of-river and 

reservoir water supplies and their tributaries. 

Sampling has continued through 1994. Samples 

were analyzed for major ions, nutrients, trace 

metals, pesticides, and semivolatile and volatile 

organic compounds. Monthly concentration data, 

high-flow concentration data, and data on daily 

mean streamflow at most stream sites were used 

to calculate loadings of nitrogen, phosphorus, 

suspended sediment, and trace metals to 

reservoirs.

Stream and lake sites were assigned to one 

of five site categories (1) rivers, (2) large 

multipurpose reservoirs, (3) small water-supply

reservoirs, (4) streams below urban areas and 

wastewater-treatment plants, and (5) headwater 

streams according to general site characteristics. 

Concentrations of nitrogen species, phosphorus 

species, and selected trace metals were compared 

by site category using nonparametric analysis of 

variance techniques and qualitatively (trace 

metals). Wastewater-treatment plant effluents and 

urban runoff had a significant impact on water 

quality compared to reservoirs and headwater 

streams. Streams draining these areas had more 

mineralized water than streams draining 

undeveloped areas. Moreover, median nitrogen 

and nitrite plus nitrate concentrations were 

significantly greater than all other site categories. 

Phosphorus was significantly greater than for 

reservoir sites or headwater streams. Few 

concentrations of trace metals were greater than 

the minimum reporting limit, and U.S. 

Environmental Protection Agency drinking-water 

standards were rarely exceeded. Detections, when 

they occurred, were most frequent for sites below 

urban areas and wastewater-treatment plant 

effluents.

A small number of samples for analysis of 

acetanilide, triazine, carbamate, and chlorophenoxy acid pesticides indicate that some of 

these compounds are generally present in area 

waters in small concentrations. Organochlorine 

and organophosphorus pesticides are ubiquitous 

in the study area in very small concentrations.

Abstract 1
Trihalomethanes were detected at sites below 

urban areas and wastewater-treatment plants. 

Otherwise, volatile organic compounds and 

semivolatile compounds were generally not 

detected.

Suspended-sediment, nitrogen, phosphorus, 

lead, and zinc loads into Falls Lake, Jordan Lake, 

University Lake, Cane Creek Reservoir, Little 

River Reservoir, and Lake Michie were 

calculated. In general, reservoirs act as traps for 

suspended sediment and constituents associated 

with suspended sediments.

During 1989-94, annual suspendedsediment load to Falls Lake ranged from 29,500 

to 88,200 tons. Because Lake Michie trapped 

from 83 to 93 percent of the suspended sediment 

delivered by Flat River, Flat River is a minor 

contributor of suspended sediment to Falls Lake. 

Yields of suspended sediment from Little River, 

Little Lick Creek, and Flat River Basins were 

between 184 and 223 tons per square mile and 

appear to have increased slightly from yields 

reported in a study for the period 1970-79. Annual 

suspended-sediment load to Jordan Lake ranged 

from 271,000 to 622,000 tons from 1989 through 

1994 water years. The Haw River contributed 

more than 75 percent of the total load to Jordan 

Lake. The suspended-sediment yields for Haw 

River and Northeast Creek were 252 and 284 tons 

per square mile, respectively. This is more than 

twice the yield reported for Haw River for the 

period 1970-79. University Lake received an 

estimated 1,560 tons per year and Cane Creek 

Reservoir an average of 2,420 tons per year. 

Yields in these basins were the lowest in the study 

area.

Nitrogen loads to Falls Lake ranged from 

780 to 1,650 tons per year, and loads out of Falls 

Lake accounted for 20 to 56 percent of the inflow 

load. Ellerbe Creek had the greatest average 

annual nitrogen yield of the Falls Lake 

tributaries 12 tons per square mile. Nitrogen 

loads to Jordan Lake ranged from 2,710 to 4,410 

tons per year, and loads out of Jordan Lake 

accounted for about 57 percent of the inflow load. 

Haw River contributed about 70 percent of the 

inflow load to Jordan Lake; however, New Hope

and Northeast Creeks produced nitrogen yields 

that were almost double that of Haw River. 

Nitrogen loads to University Lake and Cane 

Creek Reservoir averaged less than 50 tons per 

year.

Annual phosphorus loads to Falls Lake 

averaged 103 tons, and loads out of the lake 

accounted for 28 percent of the inflow load. 

Among the tributaries to Falls Lake, the greatest 

load was from Knap of Reeds Creek (23 tons per 

year). Phosphorus yields declined in Little Lick 

and Ellerbe Creeks and Eno River for the study 

period compared to the period 1983-87. Annual 

phosphorus loads to Jordan Lake ranged from 418 

to 701 tons per year, and loads out of the lake 

accounted for 40 percent of the inflow load. 

Average annual phosphorus yields declined at 

every site monitored for the study period 

compared to the period 1983-87.

Average annual lead loads to Falls Lake 

from tributaries ranged from 363 pounds from 

Little Lick Creek to 2,300 pounds from Ellerbe 

Creek. Average annual lead loads to Jordan Lake 

from tributaries ranged from 667 pounds from 

Northeast Creek to 40,000 pounds from Haw 

River. Average annual zinc loads to Falls Lake 

from monitored tributaries ranged from 1,150 

pounds from Little Lick Creek to 10,600 pounds 

from Eno River. Average annual zinc loads to 

Jordan Lake from monitored tributaries averaged 

135,000 pounds, with Haw River contributing 

about 75 percent of the load.

INTRODUCTION

The Research Triangle area, within the upper 

Cape Fear and upper Neuse River Basins (fig. 1), is 

one of the most rapidly developing areas of North 

Carolina. According to the 1990 census, 77 percent of 

the households in the region depend on public 

drinking-water supplies withdrawn from streams and 

lakes in the region. Surface-water quality depends on 

the chemical quality of inflows from precipitation, 

ground-water seepage, industrial and municipal 

wastewater effluents, and runoff from urban, 

agricultural, and other land uses. Forests and 

agriculture are still the predominant land cover in the

Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
North Carolina

tal Plain

Upper Cape Fear 

River Basin

Location of physiographic

provinces and upper

Neuse and upper Cape Fear

River Basins in North Carolina

79°

ROCKINGHAM 

COUNTY

DURHAM 

COUNTY

Upper 

Neuse 

River 

Basin

GRANVILLE <,. 78° 30' 

COUNTY

ALAMANCE 

 __ __ _| COUNTY

RANDOLPH | 

COUNTY (.

 ^ -* LEE lOsANFORD / 

COUNTY

10 15 20 MILES

0 5 10 15 20 KILOMETERS

Explanation

Triangle Area Water Supply 

Monitoring Project study area

 - - Basin boundary

 County line

Figure 1. The Triangle Area Water Supply Monitoring Project study area within the upper Neuse River and the upper Cape Fear 

River Basins, North Carolina.

Introduction 3
upper Cape Fear and upper Neuse River Basins. 

Although agriculture is an important source of 

nutrients and contaminants, urban/industrial land uses 

are potentially of greater importance in the study area 

due to the proximity of these land uses to local water 

supplies.

Because of the heavy reliance on surface water 

for public water supply, local governments recognized 

that protection of the Research Triangle's surfacewater resources is imperative. Together, and with 

assistance from Triangle J Council of Governments 

(TJCOG), they formed the Triangle Area Water 

Supply Monitoring Project. The goals of the Project 

were to:

1. Supplement existing data on conventional 

pollutants, nutrients, and metals to enable 

eventual determination of long-term trends,

2. Examine differences in water quality among water 

supplies within the region, especially differences 

between smaller upland sources, large 

multipurpose reservoirs, and run-of-river 

supplies,

3. Provide tributary loading and inlake data for

predictive modeling of Falls of the Neuse and B. 

Everett Jordan Reservoirs, and

4. Establish a database for synthetic organic 

compounds.

With cooperative assistance from the U.S. 

Geological Survey (USGS), the Project has funded 

collection and analysis of water-quality samples from 

reservoirs and streams, and collection of continuous 

discharge records from streams in the study area 

(fig. 2). Water-quality sampling and streamflow 

monitoring, in cooperation with the Triangle Area 

Water Supply Monitoring Project Steering Committee, 

began in October 1988 at 41 sites located at area runof-river and reservoir water supplies and their 

tributaries (table 1). These data, along with waterquality data collected during the same period by the 

North Carolina Division of Environmental 

Management (DEM) and with streamflow and waterquality data collected from 1982 through 1987 as part 

of a cooperative program between the USGS and the 

U.S. Army Corps of Engineers, form a comprehensive 

database on the quality of area water supplies, 

tributaries, and reservoir outflows.

Purpose and Scope

This report presents a summary of the results of 

the first 6 years of data collection (October 1988 

through September 1994) by the USGS and DEM in 

the study area. Water-quality conditions are described 

for nine locations on Falls of the Neuse and B. Everett 

Jordan Reservoirs, for one location on each of five 

small reservoirs, for selected tributaries to the 

reservoirs, for the outflow of four of the reservoirs, and 

for locations near five run-of-river water supplies.

Results include summary statistics of major 

ions, nutrients, and trace elements, and a statistical 

comparison of selected constituents grouped by site 

category. Where applicable, concentrations are 

compared to State and Federal drinking-water 

maximum contaminant levels (MCL) and(or) ambient 

water-quality standards for the protection of aquatic 

life. A summary of the occurrence of synthetic semivolatile organic compounds, pesticides, and 

poly chlorinated biphenyls (PCB's) in bed material and 

water, and of volatile organic compounds in water is 

presented. Annual loads and yields of nutrients and 

suspended sediment are calculated for the major 

tributaries to each reservoir, and annual loads of lead 

and zinc are calculated for selected sites.

Description of the Study Area

The study area is located in the Piedmont 

Province of North Carolina (fig. 1). The topography of 

the Piedmont Province has been largely developed by 

streams flowing across it. The province is typified by 

well-rounded hills, broad long-rolling ridges, and 

deeply eroded v-shaped stream valleys. Elevations in 

the study area range from about 800 to 300 feet (ft) 

above sea level. The region is underlain by older 

crystalline rock formations which trend northeastsouthwest and vary greatly in their resistance to 

weathering and erosion (Stuckey, 1965). Most major 

streams in the province flow either eastward or 

southeastward; however, tributary streams most often 

follow the lay of the land. Typical stream gradients 

range from 10 to 20 feet per mile (Simmons, 1993).

The study area includes part of a 16-county area 

in the upper part of the Neuse and Cape Fear drainage 

basins (fig. 1). The Flat, Eno, and Little Rivers in 

Orange and Person Counties together form the 

headwaters of the Neuse River Basin (fig. 2A).

4 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
A. North Carolina

DURHAM 

COUNTY

78" 301

UpperNeuse 

River Basin

Location of upper 

Neuse River Basin

Explanation

 - - Basin boundary

 County line

O 33 Stream sites and site numbers (table 1) 

A 34 Lake sites and site numbers (table 1)

35° 30'

10

I

15

I

20 MILES

l i r

5 10 15 20 KILOMETERS

Figure 2. Water-quality sampling and streamflow monitoring sites in the (A) upper Neuse River Basin and (B) upper Cape Fear 

River Basin.

Description of the Study Area 5
B. North Carolina

ROCKINGHAM 

COUNTY

Location of

upper Cape

Fear River

Basin

Upper Cape I 

Fear River

Explanation

 - - Basin boundary

 County line

O 31 Stream sites and site numbers (table I) 

A 20 Lake sites and site numbers (table 1)

20 MILES

Figure 2. Water-quality sampling and streamflow monitoring sites in the (A) upper Neuse River Basin and (B) upper Cape Fear 

River Basin (Continued).

6 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
Table 1. Water-quality sampling and streamflow monitoring sites in the Triangle Area Water Supply Monitoring 

Project

[USGS number is U.S. Geological Survey downstream order number; mi2 , square miles; Site categories: I river, 2 large reservoir, 3 small reservoir, 

4 downstream from urban areas and wastewater-treatment plants, 5 headwater stream, 6 sites near a water-supply intake; , not determined]

Site 

number

(fig. 2)

1

2

3

4

5

6

7

8

9

10

11

Station name and USGS number

Neuse River near Falls 

02087183

Falls Lake above Dam at Falls 

02087182

Falls Lake at State Highway 98 near Bayleaf 

0208708905

Falls Lake at State Highway 50 near Sandy Plain 

0208703650

Falls Lake at Interstate 85 near Redwood 

02086920

Little Lick Creek above Secondary Road 1814 near Oak 

Grove 

0208700780

Ellerbe Creek near Gormana 

02086849

Eno River near Weaver13 

02085079

Eno River near Durham 

02085070

Knap of Reeds Creek near Butner 

02086624

Little River below Dam near Fairntosh

Latitude

35°56'25"

35°56'28"

35°58'42"

36°00'54"

36°04'14"

35°59'11"

36°03'33"

36°04'19"

36°04'20"

36°07'40"

36°06'43"

Drainage 

Longitude area 

(mi2)

78°34'56" 771

78°35'02" 

78°37'59" 

78°41'29" 

78°46'48" 

78°47'58" 10.1

78°49'58" 21.9

78°51'47" 148

78°54'30" 141

78°48'55" 43.0

78°52'08" 97.7

Site 

category

1

2,6

2

2

2

4

4

4

4

4

1

0208524850 

(Discontinued 6/91)

12 Little River at Secondary Road 1461 near Orange Factory 

0208521324

13 Little River Reservoir at Dam near Bahama 

0208524845

14 Flat River at Dam near Bahama 

02086500 

(Discontinued 6/91)

15 Flat River at Bahama 

02085500

16 Lake Michie at Dam near Bahama 

02086490

17 Morgan Creek near Farringtonc 

02097521

36°08'30" 78°55'10" 78.2

36°06'53" 78°52'10" 97.7 3,6

36°08'55" 78°49'43" 168

36°10'57" 78°52'44" 149

36°09'02" 78°49'49" 167 3,6

35°51'48" 79°00'35" 45.6

Description of the Study Area 7
Table 1. Water-quality sampling and streamflow monitoring sites in the Triangle Area Water Supply Monitoring 

Project (Continued)

[USGS number is U.S. Geological Survey downstream order number; mi2, square miles; Site categories: 1 river, 2 large reservoir, 3 small reservoir, 

4 downstream from urban areas and wastewater-treatment plants, 5 headwater stream, 6 sites near a water-supply intake; , not determined]

Site 

number

(fig. 2)

17A

18

19

20

21

21A

22

23

24

25

26

26A

27

28

29

30

31

31A

Station name and USGS number

Morgan Creek near Chapel Hill 

02097517

New Hope Creek near Elands 

02097314

Northeast Creek at Secondary Road 1 100 near Genlee 

0209741955

Jordan Lake at Buoy 9 near Farrington 

0209771550 (Discontinued 7/92)

Jordan Lake at Buoy 7 below U.S. Highway 64 near 

Griffins Crossroads

0209801050 (Discontinued 9/92)

Jordan Lake above U.S. Highway 64 near Wilsonville 

0209799150 (Activated 7/91)

Jordan Lake at Bells Landing near Griffins Crossroads 

0209801 100 (Activated 7/91)

Jordan Lake, Haw River Arm above B. Everett Jordan

Dam

0209719700

Haw River near Bynum 

02096960

Haw River below B. Everett Jordan Dam near Moncure

02098198

Eno River at Hillsborough 

02085000 (Activated 10/89)

Eno River intakes at Hillsborough 

0208491605 (Discontinued 9/89)

Cane Creek near Orange Grove 

02096846

Cane Creek Reservoir at Dam near White Cross

0209684980 (Activated 4/89)

Morgan Creek near White Cross 

02097464

University Lake at intakes near Chapel Hill 

0209749990

Cape Fear River at State Highway 42 near Brickhaven6 

0210215985

Deep River at Moncure

Latitude

35°53'36"

35°53'05"

35°52'20"

35°46'30"

35°43'56"

35°44'29"

35°43'38"

35°39'39"

35°45'48"

35°39'11"

36°04'18"

36°04'02"

35°59'13"

35°56'59"

35°55'25"

35°53'48"

35°32'54"

35°37'38"

Drainage 

Longitude area 

(mi2)

79°01'10" 41.0

78°57'58" 75.9

78°54'49" 21.1

79°01'38" 

79°01'30" 

79°01'10" 

79°02'35" 

79°04'23" 

79°08'02" 1,275

79°04'03" 1,689

79°05'49" 66.0

79°07'39" 66.0

79°12'23" 7.5

79°14'29" 31.4

79°06'56" 8.4

79°05'33" 30.0

79°01'34" 3,160

79°06'58" 1,434

Site 

category

_ d

4

4

2

2

2,6

2

2

1,6

1

1,6

1

5

3,6

5

3,6

1,6

_d

02102000

8 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
Table 1. Water-quality sampling and streamflow monitoring sites in the Triangle Area Water Supply Monitoring 

Project (Continued)

[USGS number is U.S. Geological Survey downstream order number; mi2 , square miles; Site categories: 1 river, 2 large reservoir, 3 small reservoir, 

4 downstream from urban areas and wastewater-treatment plants, 5 headwater stream, 6 sites near a water-supply intake; , not determined]

Site 

number

(fig. 2)

32

32A

33

Station name and USGS number

Neuse River at Smithfieldf 

02087570

Neuse River near Clayton 

02087500

Swift Creek near Apex

Latitude

35°30'46"

35°38'50"

35°43'07"

Longitude

78°21'00"

78°24'22"

78°45'09"

Drainage 

area 

(mi2)

1,206

1,150

21.0

Site 

category

1,6

_ d

1

02087580 

(Activated 10/89)

34 Lake Benson at Dam near Garner 

02087701 

(Activated 10/89)

45 Jordan Lake at Buoy 12 at Farrington 

0209768310 (Activated 8/92)

46 Deep River at Carbonton

0210140200 (Activated 3/92)

35°39'44" 78°36'52" 67.0 3,6

35°47'55" 79°00'22" 2

35°31'10" 79°20'51" 1,026 1,6

aGage was discontinued April 1989 and was rebuilt September 1991. 

bDischarge values for site 8 are from gage at site 9. 

cDischarge values for site 17 are from gage at site 17A. 

dDischarge site.

eDischarge was computed by adding the daily mean discharge values at sites 25 and 31 A. 

Gage was discontinued September 1990. Discharge values after September 1990 are from gage at site 32A.

The drainage area of the Neuse River at 

Smithfield, the downstream terminus of the study area, 

is about 1,210 square miles (mi2 ) or one-fifth of the 

total drainage area of the Neuse River Basin. Other 

tributaries to the Neuse River that were monitored for 

this study are Knap of Reeds Creek, Ellerbe Creek, 

Little Lick Creek, and Swift Creek. Falls of the Neuse 

Reservoir (hereafter referred to as Falls Lake), in 

Wake County, is the largest impoundment of the 

Neuse River forming a 12,490-acre reservoir with 

114,700 acre-feet (acre-ft) of storage at normal pool 

elevation (table 2). It is a water supply for the city of 

Raleigh.

Lake Michie, a 508-acre reservoir just upstream 

from Falls Lake, impounds the Flat River and its 

tributaries, Dial Creek, Rocky Creek, and Dry Creek, 

and supplies drinking water for the city of Durham. 

Little River Reservoir, filled in 1988 as a water-supply 

source for the city of Durham, is a third water-supply 

reservoir in the upper Neuse River Basin. Little River 

Reservoir is a 530-acre reservoir, which impounds 

Little River and its tributaries Mountain Creek,

Buffalo Creek, and North Fork and South Fork Little 

Rivers. Lake Benson was impounded from Swift 

Creek in 1844 and was known as Rand's Mill Pond. It 

was purchased by the City of Raleigh in 1927 for 

water supply and was expanded in 1953 to a 440-acre 

reservoir. At present, the lake is used as a secondary 

water supply for the City of Raleigh and for recreation 

(North Carolina Department of Environment, Health, 

and Natural Resources, 1992).

The Cape Fear River (fig. 2B) is formed 

downstream from B. Everett Jordan Reservoir 

(hereafter referred to as Jordan Lake) by the 

confluence of the Haw River, which drains 1,695 mi 2 

at the mouth, and the Deep River, which drains 

1,441 mi2 at the mouth (North Carolina Department of 

Natural Resources and Community Development, 

1988). The drainage area of the Cape Fear River near 

Brickhaven, the downstream terminus of the study 

area, is 3,160 mi2 . Jordan Lake, a 14,300-acre 

multipurpose reservoir, was filled in 1982 and contains 

approximately 215,000 acre-ft of storage at normal 

pool elevation (table 2). The reservoir, formed from

Description of the Study Area
Table 2. Description of reservoirs in the Research Triangle study area

[DEM, North Carolina Division of Environmental Management; , no data]

Reservoir 

(year filled)

Falls Lake

(1983)

Little River 

Reservoir

(1988)

Lake Michie 

(1926)

Lake Benson

(1844)

Jordan Lake 

(1982)

Drainage 

area 

(square 

miles)

771

98

167

65

1,690

Surface 

area3 

(acres)

12,490

530

508

440

14,300

w i a Maxi- . Volume9 Average 

. mum . .Ji, (acre- . .. depth0

-o £* <fee«

114,700 9.2

14,600 49 27

11,070 52 22

3,070 20 7.0

215,000 66 15

Volume/ __., . . . DEM trophic mean . . 

. .. c state inflow0 . ... .. 

.. . classification (days)

80 eutrophic

85 mesotrophic

45 eutrophic

 mesotrophic

62 eutrophic

Resource used

water supply, 

flood control,

recreation

water supply

water supply, 

recreation

secondary 

water supply, 

recreation

flood control, 

fish and wildlife habitat,

recreation, 

water supply

Cane Creek 

Reservoir 

(1989)

University 

Lake

(1932)

31

30

500

200

8,920

2,100

54

23

18

10

162 eutrophic

39 eutrophic

water supply

water supply, 

recreation

aNormal pool elevation. 

bVolume/surface area.

cComputed from U.S. Geological Survey records of reservoir volume and annual mean discharge for the period of record at each streamflow 

station tributary to each reservoir (Gunter and others, 1993).

dNorth Carolina Department of Environment, Health, and Natural Resources (1992).

the impoundment of the Haw River and New Hope 

Creek, is a water-supply source for the towns of Gary 

and Apex and is the future water supply for Chatham 

County and potentially for other jurisdictions in the 

Triangle area, including Orange County. Other 

tributaries to Jordan Lake are Northeast Creek and 

Morgan Creek.

University Lake, a water-supply reservoir filled 

in 1932, impounds water from about 30 mi2 in the 

upper Cape Fear River Basin (Bisese, 1994). The lake 

was formed from the partially flooded stream valleys 

of Morgan Creek and its two tributaries, Phils Creek 

and Price Creek. Cane Creek Reservoir, filled in 1989, 

is a public water supply for the towns of Carrboro and 

Chapel Hill and impounds water from about 31 mi2 in

the upper Cape Fear River Basin. The two main 

tributaries to the lake are Cane Creek and Turkey Hill 

Creek (North Carolina Department of Environment, 

Health, and Natural Resources, 1992).

Land Use

The Piedmont part of the Neuse River Basin 

(the upper Neuse River Basin) is the most populated 

and industrialized part and has the greatest density of 

waste dischargers (North Carolina Department of 

Environment, Health, and Natural Resources, 1993). 

Falls Lake receives inflow from a 771 -mi2 watershed 

of combined forested and agricultural lands, and urban

10 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
and residential areas. An estimated 339 mi2 or 44 

percent of the watershed is forested and 26 percent is 

agriculture. Urban areas account for about 13 percent 

and wetlands account for about 10 percent of the land 

use (North Carolina Department of Environment, 

Health, and Natural Resources, 1993). The Lake 

Michie drainage area (167 mi2 ) accounts for 

approximately 22 percent of the drainage to Falls Lake 

and is mostly forested, although some agricultural and 

residential land use exists. The Little River drainage 

basin (98 mi2) accounts for approximately 13 percent 

of the drainage to Falls Lake and is equally divided 

among forested, agricultural, and residential areas 

(North Carolina Department of Environment, Health, 

and Natural Resources, 1993).

The part of the study area in the upper Neuse 

River Basin from the Falls Lake dam to Smithfield 

(fig. 2A) is primarily urban and residential, and 

includes the city of Raleigh and its suburbs. The 

population in the upper Neuse Basin grew steadily and 

increased by approximately 70 percent from 1970 to 

1990 (North Carolina Department of Environment, 

Health, and Natural Resources, 1993). Lake Benson, 

just south of Raleigh, receives drainage from the 

65-mi2 Swift Creek watershed, of which about 50 

percent is forested. However, urban and residential 

land uses in the watershed are increasing as Raleigh, 

Gary, and the surrounding communities continue to 

develop.

Municipal wastewater-treatment plants 

(WWTP's) that discharge to tributaries of Falls Lake 

include Durham's Northside WWTP, which 

discharges to Ellerbe Creek; Little Lick WWTP, 

which discharges to Little Lick Creek; Butner 

WWTP, which discharges to Knap of Reeds Creek; 

and Durham's Eno WWTP, which discharges to the 

Eno River. In November 1994, Durham's Northside 

WWTP was upgraded to tertiary treatment and 

renamed North Durham Water Reclamation Facility. 

This facility receives sewage formerly sent to the Eno 

WWTP and the Little Lick WWTP. The Little Lick 

and Eno WWTP's ceased operation in November and 

June 1994, respectively.

In the Cape Fear River Basin, most of the 

population and industry are located near the 

headwaters of the Haw and Deep Rivers from 

Burlington to Greensboro. Drainage from the Haw 

River Basin, 1,300 mi2 of mixed forested and 

agricultural lands and urban and residential areas, is to 

Jordan Lake. Jordan Lake also receives drainage from

New Hope Creek Basin, a 400-mi2 watershed that 

includes forested and agricultural land uses and urban 

areas (including Durham, Chapel Hill, and Research 

Triangle Park), much of which are undergoing 

industrial and residential development.

The morphometry of Jordan Lake is unusual 

because about 80 percent of the flow into the lake is 

from the Haw River; however, most of the storage is in 

the New Hope Creek arm (fig. 2B). This results in 

periods when flow from the Haw River is pushed uplake into the New Hope Creek arm (Moreau and 

Challa, 1985). Moreover, materials entering the 

northern New Hope Creek arm of the reservoir likely 

remain in the reservoir longer than materials entering 

from the Haw River.

Cane Creek Reservoir is in the Haw River Basin 

and receives drainage from 31 mi2 of mostly forested 

and some agricultural lands (North Carolina 

Department of Environment, Health, and Natural 

Resources, 1992). University Lake is in the Morgan 

Creek Basin and receives drainage from an 

approximately 30-mi2 area mostly west of Carrboro. 

Three quarters of the area is forested with some 

agriculture and residential development (North 

Carolina Department of Environment, Health, and 

Natural Resources, 1992).

Municipal WWTP's that discharge to tributaries 

of the New Hope Creek arm of Jordan Lake include 

Durham County Triangle WWTP, which discharges to 

Northeast Creek; Durham's Southside WWTP, which 

discharges to New Hope Creek; and Orange Water and 

Sewer Authority (OWAS A) WWTP, which discharges 

into Morgan Creek. In 1994, Durham's Southside 

WWTP was upgraded to tertiary treatment and 

renamed the South Durham Water Reclamation 

Facility.

Water Use

Public water-supply systems deliver water to 

about 600,000 people in the upper Cape Fear River 

Basin and 525,000 people in the upper Neuse River 

Basin. Municipalities and other privately owned water 

suppliers withdraw approximately 150 million gallons 

per day (Mgal/d) from surface-water sources in the 

study area. Total off-stream surface-water withdrawals 

in the upper Neuse River and upper Cape Fear River 

Basins totaled an estimated 75 and 260 Mgal/d, 

respectively, for 1990. Of the 260 Mgal/d withdrawn 

in the upper Cape Fear River Basin, 149 Mgal/d or

Water Use 11
57 percent was withdrawn for thermoelectric power 

generation, and 91 Mgal/d (35 percent) was withdrawn 

for industrial uses. In the upper Neuse River Basin, 57 

Mgal/d or about 76 percent of total surface-water 

withdrawals were for industrial processes.

Sewage-treatment water releases to surface 

waters in the basins from wastewater-treatment plants 

(municipal and industrial) totaled about 150 Mgal/d in 

1990 (Terziotti and others, 1994) 50 Mgal/d in the 

upper Neuse Basin and 100 Mgal/d in the upper Cape 

Fear Basin. Of the total amount of wastewater 

releases, about 90 percent are from publicly owned 

wastewater-treatment facilities.

Previous Investigations

Water-quality characteristics of flow into and 

out of water-supply reservoirs in the Piedmont 

Province of North Carolina have been studied by 

several investigators. These studies focused on a 

variety of water-quality issues, including the effects of 

land uses on water quality, sedimentation rates and 

trapping efficiency of reservoirs, and nutrient loadings 

into reservoirs. None of the previous studies 

maintained a comprehensive, long-term streamflow 

and water-quality monitoring network as was done in 

this investigation.

Harned (1982) summarized water quality of the 

upper Neuse River from 1955 to 1978 and concluded 

that it was satisfactory for most uses. Harned reported 

that dissolved oxygen, manganese, and iron 

concentrations, pH, and bacteria counts often reached 

undesirable levels. Nutrient concentrations were 

sufficient to support rich algal growth.

Studies conducted by DEM (1981-83) in the 

Cape Fear Basin identified low dissolved-oxygen 

concentrations and high bacteria counts as major 

problems in the basin. Also, concerns arose in the 

1970's as a result of mercury contamination of fish in 

the Cape Fear Basin. Surveys in the mid-1970's by the 

U.S. Army Corps of Engineers and DEM reported that 

30 to 50 percent of the fish sampled contained 

concentrations of mercury that exceeded the U.S. 

Food and Drug Administration allowable 

concentrations in fish tissue of 0.5 part per million 

(ppm). However in 1978, based on extensive studies of 

actual human consumption offish, the U.S. Food and 

Drug Administration increased the allowable limit of 

mercury in fish flesh from 0.5 to 1 ppm. During 1980 

and 1981, a DEM survey of mercury in tissues offish

from streams in the basin showed concentrations 

ranged from 0.1 to 0.33 ppm, substantially less than 

the recommended allowable concentration. Tissue 

samples taken from Jordan Lake fish analyzed in 1982 

by DEM showed that the average mercury 

concentration was less than 0.2 ppm.

In 1987, the North Carolina Division of Water 

Resources (1987) recommended that a 150-mi2 area of 

the Eno River watershed upstream from the 

confluence with the Little River be designated as a 

"capacity-use area," which would require coordination 

and limited regulation for the use of ground or surface 

water in the area. This recommendation was based on 

evidence of deteriorated water-quality conditions in 

the Eno River associated with low-flow periods which 

provide less water to dilute pollutants from point and 

nonpoint sources. The report suggested that minimum 

flows be maintained in the Eno River to assimilate 

existing wastewater discharges without resulting in 

violation of the applicable water-quality standards. 

The report also suggested that future development in 

the watershed would further stress the system and 

make suitable water quality scarce, particularly during 

dry years.

Water-quality characteristics and annual 

nitrogen and phosphorus yields into and out of Falls 

and Jordan Lakes were determined by Garrett (1990a 

and b) for water years 1 1983 through 1986. Garrett 

reported that mean concentrations of major ions and 

nutrients in tributaries to Falls Lake ranged from 10 to 

110 times greater than background concentrations 

reported by Simmons and Heath (1982) for streams 

draining undeveloped areas. The mean concentrations 

of Falls Lake outflow were generally 2 to 3 times 

greater than background concentrations. Sodium and 

calcium were the predominant cations, and 

bicarbonate was the predominant anion. Of the metals, 

iron and manganese were detected in the greatest 

concentrations. Mean annual loads of total nitrogen 

and total phosphorus out of Falls Lake were as much 

as 66 and 21 percent of mean annual loads into the 

lake, respectively. For Jordan Lake, Garrett (1990b) 

reported that average annual loads of total nitrogen 

and total phosphorus in the outflow were as much as

'Water year is the 12-month period October 1 through 

September 30. The water year is designated by the calendar year in 

which it ends and includes 9 months of that calendar year. Thus, 

the period beginning October 1, 1982, and ending September 30, 

1983, is the 1983 water year.

12 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
67 and 40 percent of estimated inflow loads, 

respectively.

Kuenzler and others (1986) studied nutrient 

cycling and productivity of Jordan Lake by including 

measurements of nitrogen and phosphorus uptake 

rates in relation to algal abundance and primary 

productivity. The study included 1 year of data 

collection at three stations on Jordan Lake. Nutrient 

concentrations were lowest in the summer when algal 

abundance was the greatest. Uptake rates of nitrate and 

ammonium by phytoplankton were highest in the 

summer. Nitrate concentrations were higher than 

ammonium concentrations, and phytoplankton took up 

ammonium more rapidly. Of possible factors 

controlling primary productivity, temperature was 

most statistically related. According to the report, 

Jordan Lake supports a large phytoplankton standing 

crop which can reduce ammonium, nitrate, and 

phosphate to very low concentrations when gross 

primary productivity is highest during the warm 

months. However, algal assays conducted with water 

from Jordan Lake indicated that neither nitrogen nor 

phosphorus concentrations alone were consistently 

low enough to limit further phytoplankton growth.

Reckhow and others (1989) assessed the 

similarity and differences between surface-water 

quality data collected in Jordan and Falls Lakes. They 

reported that concentrations of total phosphorus and 

total nitrogen exhibit the same seasonal pattern at the 

sampling sites in the two reservoirs. Analysis of 

deterministic patterns and cycles in Jordan Lake and 

three river sampling sites indicated that there were 

linear trends with time in a few of the data sets, 

seasonal patterns in much of the data, and an inverse 

relation between flow and concentrations in most of 

the data from streams. This investigation focused on 

determining the sample size required for trend 

analysis and the amount of redundancy and 

autocorrelation among data sets, to provide a means to 

consider reducing sample sites or sampling frequency.

Bisese and Paull (1994) studied the type, spatial 

distribution, and amount of sediment deposited in 

University Lake from 1988 through 1992. They 

reported that the maximum sediment thickness was 

14 ft and the average thickness was 2.1 ft. The volume 

of sediment was determined to be 440 acre-ft. 

resulting in an average sedimentation rate over 

57 years of 7.7 acre-feet per year (acre-ft/yr) or 

11,035 tons per year (tons/yr).

Weaver (1994) investigated present (1992) and 

historic (1926-92) rates of sedimentation in Lake 

Michie. Weaver reported that about 2,541 acre-ft of 

sediment, about 20 percent of the original volume, has 

been trapped in the lake. At present, the average 

sedimentation rate is 38 acre-ft/yr a decline from the 

rate of 45.1 acre-ft/yr in 1935. Weaver estimated the 

trap efficiency of Lake Michie is 89 percent.

In 1983, DEM recommended nutrient 

management in the Falls Lake watershed and in 1987 

recognized the need for nutrient management in the 

entire Neuse River Basin. The North Carolina 

Division of Environmental Management (1993) Neuse 

River Basinwide Water Quality Management Plan 

describes the status of water quality in the basin and 

the causes and sources of water pollution. Agricultural 

runoff and municipal wastewater-treatment plants are 

recognized as the two major sources of nutrients in 

addition to urban runoff and forestry. Nutrients in 

nonpoint-source runoff originate primarily from 

fertilizer use and animal wastes. Nutrients in pointsource discharges are from human wastes, food 

residues, and some cleaning agents. The report also 

offers recommended management actions and 

projected long-range water-quality goals for the basin. 

The report lists increased urban development and 

population growth as the primary factors contributing 

to degradation of some water resources in the Neuse 

Basin. Nutrient and organic enrichment, as evidenced 

by low dissolved-oxygen concentrations, algal 

blooms, and fish kills are notable causes of waterquality degradation in the upper Neuse Basin (North 

Carolina Department of Environment, Health, and 

Natural Resources, 1993). Municipal WWTP's were 

identified as the major contributors to the elevated 

nutrient loadings to the arms of Falls Lake, especially 

during low-flow summer months. Exceedences of 

copper and zinc action levels and the mercury waterquality criterion have occurred downstream from some 

of these facilities. Biological indexes rate water 

quality as "poor" to "very poor" downstream from 

several WWTP's, whereas headwater streams 

generally have a bioclassification of "good" to 

"excellent."

Acknowledgments

The Division of Environmental Management of 

the North Carolina Department of Environment, 

Health, and Natural Resources maintains a Surface

Acknowledgments 13
Water Ambient Monitoring System with approximately 380 sampling locations throughout the State. 

The USGS wishes to acknowledge the assistance of 

DEM in providing water-quality sample collections 

and data from ambient monitoring sites located within 

the study area.

WATER QUALITY OF STREAMS AND 

RESERVOIRS

Samples for the analysis of water quality were 

collected from stream sites (table 1) once per month 

beginning October 1, 1988. Lake samples were 

collected 5 times per year in October, April. June, July, 

and August. A detailed accounting of the number of 

samples collected at each site by USGS and DEM 

through September 1992 is in Garrett and others 

(1994). The report also describes methods of sample 

collection, methods of sample analysis, and qualityassurance practices and results.

General Characteristics

The general chemical characteristics of surface 

water can be defined by measuring the concentrations

81

of major ions calcium, magnesium, sodium + 

potassium, bicarbonate, sulfate, and chloride. The 

chemical composition, in terms of these major ions, is 

largely regulated by the geology of the watershed and 

by the chemistry of precipitation. Point and nonpoint 

sources of contamination can alter baseline chemistry, 

most often by increasing the concentration of one or 

more major ions resulting in an increase in the 

dissolved solids concentration. Simmons and Heath 

(1982) describe five geochemical zones in North 

Carolina based on major ion data from streams 

draining relatively pristine forested and rural 

watersheds in North Carolina (fig. 3). The upper 

Neuse and upper Cape Fear River Basins, the area 

encompassing nearly all of the sites in this study, lie in 

geochemical zone II. Zone II coincides with the 

Carolina Slate Belt and the Durham and Wadesboro 

Triassic Basins. The Slate Belt is underlain by 

metamorphosed volcanic and sedimentary rocks. The 

Triassic Basins are underlain by cemented 

conglomerates, sandstones, siltstones, and shales 

(Simmons and Heath, 1982, p. B22). The Neuse River 

Basin, between Raleigh and Smithfield, lies in 

geochemical zone I and is underlain by rocks of the 

granite group and, in limited areas, by rocks of the 

diorite group (Simmons and Heath, 1982).

80"

84°

II

Geochemical zoneszone I 

zone II 

zone III 

zone IV 

zone V

Site and dissolved solids concentrations-Upper

number is dissolved solids concentration, in milligrams 

per liter, during high flow; lower number is value 

during low flow

25 50 100 MILES

25 50 75 100 KILOMETERS

Figure 3. Mean dissolved solids concentrations and major geochemical zones in North Carolina (from Simmons and Heath, 

1982).

14 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
Geochemical zones I and II produce waters of 

similar chemical composition. However, water from 

geochemical zone II typically is more mineralized. 

Stiff diagrams of mean concentrations of the major 

ions calcium, magnesium, sodium + potassium, 

bicarbonate, sulfate, and chloride are shown in 

figures 4 and 5 for the study area. Stiff diagrams 

indicate the concentration of each major cation 

(calcium, magnesium, and sodium + potassium) to the 

left of the vertical axis and the concentration of each 

major anion (bicarbonate, sulfate, and chloride) to the 

right of the vertical axis. Concentrations are expressed 

in milliequivalents per liter. The shape of the resulting 

polygon indicates water composition in terms of the 

major ions and provides a means of comparing sites. 

The width of the polygon indicates the total 

concentration of dissolved minerals. The geochemical 

zone II water type (fig. 3) is identified by the major 

cations calcium, magnesium, and sodium + 

potassium and the major anion bicarbonate.

The Stiff diagrams of samples collected from 

Little River near Orange Factory (site 12), Flat River 

at Bahama (site 15), and Eno River at Hillsborough 

(site 26) in the headwaters of the Neuse River Basin 

(fig. 4) are similar to that of baseline water quality for 

geochemical zone II. That is, they have similar shape 

(indicating dominate ions) and width (indicating the 

total concentration of dissolved minerals). Likewise, 

Stiff diagrams of water samples from Little River 

Reservoir (site 13, fig. 4) and Lake Michie (site 16) are 

similar to Stiff diagrams for baseline water quality for 

geochemical zone II.

A comparison of Stiff diagrams for baseline 

water quality in geochemical zones I and II to Stiff 

diagrams for data from other sites shows the effect of 

point sources on water quality. Data from streams 

located downstream from urban areas and major 

municipal WWTP effluents produce Stiff diagrams 

that substantially differ in width and shape from those 

of baseline water quality for the geochemical zone in 

which these sites are located. The Eno River near 

Durham (site 9, fig. 4) is a sodium + potassium and 

sulfate water type. Ellerbe Creek near German (site 7, 

fig. 4) downstream from the Durham Northside 

WWTP has relatively mineralized water of sodium + 

potassium and bicarbonate type. Less mineralized 

sodium + potassium and bicarbonate waters also 

characterize the sites farther downstream from the 

urban areas and WWTP effluents, including the uptake 

segment of Falls Lake (site 5, fig. 4), Eno River near

Weaver (site 8), and Neuse River at Smithfield (site 

32). Domestic water use has the effect of increasing 

the concentration of dissolved minerals. Typically, in 

domestic waste, calcium concentration increases by 20 

milligrams per liter (mg/L), sodium by 50 mg/L, 

sulfate by 20 mg/L, and chloride by 40 mg/L 

(Tchobanoglous and Schroeder, 1985, p. 174).

Cane Creek (sites 27 and 28, fig. 5) and Morgan 

Creek (sites 29 and 30), on streams draining parts of 

the upper Cape Fear River Basin, produce a calcium, 

sodium + potassium, and bicarbonate water type 

characteristic of baseline water quality for 

geochemical zone II. New Hope Creek (site 18, fig. 5), 

Northeast Creek (site 19), and Jordan Lake (sites 20 

to 23) are sodium + potassium and bicarbonate waters 

that are more mineralized than the baseline type. 

Statistical summaries of major anion and cation 

concentrations for 1989-92 water years at each 

monitoring site are reported in Garrett and others 

(1994).

Water-Quality Characteristics by Site 

Category

Summary statistics by site category were 

calculated by determining the median concentration of 

each constituent for each site. The median 

concentration for each category is determined from the 

median concentrations for sites within that category. 

The maximum and minimum values are the absolute 

maximum and minimum concentrations for all data 

collected for sites in each category (table 3).

Each site was assigned to one of the following 

five categories: (1) river, (2) large reservoir, (3) small 

reservoir. (4) stream site immediately downstream 

from an urban area and WWTP, and (5) headwater 

stream. In addition, sites near water-supply intakes 

were further identified as a sixth category (table 1). To 

determine if concentration varied according to site 

category, analysis of variance using nonparametric 

statistical procedures was applied to the data. To avoid 

potential bias that could occur when more data were 

collected for some sites than for others, analysis of 

variance was applied to median concentrations for 

each site. For a site where the median concentration 

was below the minimum reporting limit (MRL), the 

median was set equal to the MRL.

The analysis of variance procedure used was the 

Kruskal-Wallis rank transformation procedure. When 

more that two categories are tested, the Kruskal-Wallis

Water Quality of Streams and Reservoirs 15
79" 07'30" 78° 52'30' 78° 451 78° 37'30" 78"30'

36° 07'30'

78 °45 ' 78 '37 '30 " 78°30' 78°22'30'

35°45

35 °37 '30 " -

35 °30 ' -

Explanation

 - - Basin boundary Milliequivalents per liter

 County line 

 23 Site and site number 1.9 15 1.0 0.5 0 05 10 15 1.9

Geochemical Zone II

Figure 4. Stiff diagrams of major ions for sites in the upper Neuse River Basin

16 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
78" 52'30"

35° 52'30'

35° 45'

35" 37'30'

 - - Basin boundary

 County line

 23 Site and site numbers

Explanation

Milliequivalents per liter

Ca ... 

Mg~«. 

Na+K--

' HCO3 

 --SO4 

.... CI

6 MILES

6 KILOMETERS

1.3 1C 0.5 0 0.5 1.0 1.3

Geochemical zone II

Figure 5. Stiff diagrams of major ions for sites in the upper Cape Fear River Basin.

Water-Quality Characteristics by Site Category 17
Table 3. Statistical summary of selected nutrients, metals, and trace element constituents for site categories,

|n, number of sites; WWTP, wastewater-treatment plant; Min, minimum; Max, maximum; Med, median: mg/L, milligrams per liter; (ig/L,

Chemical 

constituent

Minimum 

reporting 

level3

Site category

(1) Rivers (2) Large reservoirs (3) Small reservoirs 

(n=10) (n=10) (n=5)

Min Max Med Min Max Med Min Max Med

Nutrients

Nitrite plus nitrate

Ammonia

Ammonia plus

organic nitrogen

Total nitrogen

Total phosphorus

Orthophosphate

0.01 mg/L as N

0.01 mg/L as N

0.2 mg/L as N

0.01 mg/L as N

0.01 mg/L as P

0.01 mg/L as P

<0.01 5.5 0.42 <0.01

<.01 .9 .07 <.01

<.2 2.9 .6 .2

.2 5.9 l.O .21

.01 .73 .08 <-01

<.01 .71 .03 <.01

7.6

.51

2.9

9.1

1.2

.16

<0.05 <0.05 1.7

.04 <.01 2.3

.6 .2 3.8

.7 .3 3.8

.04 <.01 .23

<.01 <.01 .2

0.07

.06

.6

.68

.03

<.01

Metals and trace elements

Aluminum

Arsenic

Cadmium

Chromium

Cobalt

Copper

Iron

Lead

Manganese

Mercury

Molybdenum

Nickel

Selenium

Silver

Zinc

10, 50 iig/L

1, lOiig/L

l,2iig/L

1, 25 iig/L

l,50iig/L

1 2,5, lOiig/L

lOiig/L

1,5, lOiig/L

lOilg/L

0.1 iig/L

lilg/L

1, 10, 50iig/L

lilg/L

l,5,25iig/L

lOiig/L

20 6,800 485 20

<1 2 <1 <1

<1 6 <1 <1

<1 48 <1 <1

<1 10 <1 <1

<1 99 3.5 <1

10 18,000 930 40

<l 59 <10 <1

<10 1,200 140 <10

<.l 5.3 .1 <.l

<1 4 <1 <1

<1 420 <10 <1

<1 <1 <1 <1

<1 2 <1 <1

<10 3.400 <10 <IO

1,300

2

1

4

3

23

2,600

22

950

.2

4

8

<1

1

380

70 <10 4,000

<1 <1 1

<1 <1 3

<1 <1 5

<1 <1 4

<1 <1 400

178 100 7,400

<1 <1 7

89 30 7,900

.1 <.l .6

<1 <1 32

<1 <l 6

<1 <1 <1

<1 <1 2

<10 <10 70

60

<1

<1

<1

<1

<2

380

<1

160

.2

<1

<1

<1

<1

<10

"Multiple minimum reporting levels are due to differences between laboratories and changes in analysis methods during the study. 

''Maximum possible ievel of a contaminant in water which is delivered to any user of a public water system. 

cMaximum permissible levels to protect aquatic life applicable to all fresh surface waters.

dMaximum contaminant level goal (MCLG) A nonenforceable concentration of a drinking-water contaminant that is protective of 

adverse human health effects and allows an adequate margin of safety. 

eAction levels.

18 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
October 1988 through September 1994

micrograms per liter; <, less than; MCL, maximum contaminant level]

Site category

(4) Streams below urban 

areas and WWTP's (n=8)

Min Max Med

(5) Headwater 

(n=4)

Min Max

streams (6) River and reservoir 

intake sites (n=12)

Med Min Max Med

North 

Carolina

MCL" Wat^- 

quality

standard0

Nutrients

0.03

.01

.03

.18

.01

<.01

29 4

2 .08

11 .7

30 4.65

5.8 .25

3.5 .14

<0.01 1.7

<.01 1.6

.1 3.3

.13 4.4

.01 2.8

<.01 .9

0.46 0.05 1.35 0.10

.03 .03 .10 .06

.35 .4 .8 .6

.81 .57 2.0 .7

.05 .02 .2 .03

.02 <.01 .08 <.01

10 mg/L

--

--

-

--

-

Metals and trace elements

80

<1

<2

<1

<1

<2

50

<1

15

<.l

<1

<1

<1

<1

<2

24,000 1,460

<10 <10

2 <2

18 <25

20 <50

72 6

18,000 822

18 <10

2,100 110

2.6 .15

21 <1

94 <10

2 <1

860 <1

980 20

<10 4,700

<1 15

<1 34

<1 130

<1 5

<1 81

270 8,300

<1 21

13 1,100

<.l .5

<1 4

<1 44

<1 <1

<1 57

<10 60

300 <10 6,800 85

<10 <1 <10 <1

<1 <1 6 <1

3 <1 48 <1

<1 <1 <50 <1

<2 <1 2,200 3

840 <10 18,000 550

<10 <1 59 <1

50 <10 7,900 130

.2 <.l 5.3 <.l

<1 <1 32 <1

<10 <1 420 1

<1 <1 5 <1

<1 <1 <5 <1

<10 <10 3,400 4.7

-

50 ng/L 50

5 2.0

100 50

._

l,300d T

l,000e

15 d 25

--

.2 .012

--

3 d 88

50 5

.06e

-

Water-Quality Characteristics by Site Category 19
procedure does not identify which categories are 

significantly different. Therefore, when a significant 

difference at alpha=0.05 was detected using the 

Kruskal-Wallis test, Tukey's multiple-comparison 

procedure (Tukey's W) was used to identify which site 

categories were statistically different from the others.

Nitrogen and Phosphorus

Nitrogen and phosphorus are among the most 

important of the constituents that are essential to the 

growth of plants and animals. The availability of 

nitrogen and phosphorus is the primary factor that 

determines the level of productivity of fresh and 

marine waters in terms of phytoplankton and 

macrophyte biomass. Excessive concentrations of 

nitrogen and phosphorus can lead to an undesirably 

high level of productivity and to a simplified biotic 

structure, a process referred to as eutrophication.

The forms of nitrogen and phosphorus analyzed 

for this study include nitrite plus nitrate, ammonia plus 

organic nitrogen, total nitrogen, total phosphorus, and 

orthophosphate. Concentrations of nitrogen forms are 

reported in equivalent units of elemental nitrogen, and 

phosphorus forms are reported in equivalent units of 

elemental phosphorus. Statistical summaries of data 

from the study area for these forms of nitrogen and 

phosphorus, as well as other forms, are reported in 

Garrett and others (1994) for water years 1989 through 

1992.

Nitrogen

Nitrogen occurs in the environment in the form 

of ammonia, nitrite, nitrate, dissolved molecular 

nitrogen, and at various oxidation states as organic 

compounds. It is present in fresh waters primarily as 

nitrate and ammonia. Nitrogen undergoes biological 

and nonbiological transformations within the 

environment. In the reduced or organic forms, it is 

converted by soil bacteria into nitrite and nitrate. It is 

used by plants largely in the oxidized form (Cole, 

1979). Excessive concentrations, usually associated 

with anthropogenic sources, such as municipal wastes, 

urban runoff, and agricultural runoff, are an important 

factor causing eutrophication.

Excessive concentrations of nitrate in drinking 

water is a public health concern, especially for small 

children. Cases have been documented where bottlefed infants developed methemoglobinemia, which was 

attributed to the use of formula made with well water

having a nitrate concentration in excess of 10 mg/L as 

N. Elderly persons are also at particular risk when 

ingesting water with high nitrate levels. For these 

reasons, careful monitoring of nitrogen concentrations 

in the area's drinking-water supplies is an important 

component of this study.

Concentrations of total nitrogen and nitrite plus 

nitrate were significantly greater for sites below urban 

areas and WWTP's (category 4) than for sites in the 

other site categories (fig. 6). The median nitrite plus 

nitrate concentration for sites below urban areas and 

WWTP's was 4.0 mg/L, which is more than 8 times 

the median concentrations that were recorded for the 

other categories. No significant differences were 

detected between small and large reservoirs or among 

other site categories for these constituents.

Of those sites below urban areas and WWTP's, 

the greatest median nitrite plus nitrate concentration 

was at Ellerbe Creek, site 7 (15 mg/L), which is 

located approximately 3 miles (mi) downstream from 

the Durham Northside WWTP. Ellerbe Creek also had 

the maximum nitrite plus nitrate concentration 

recorded at any site (29 mg/L). Both concentrations 

exceed the 10 mg/L U.S. Environmental Protection 

Agency (USEPA) maximum contaminant level (MCL) 

for nitrate in treated drinking water. Six of the eight 

sites in this category had median nitrite plus nitrate 

concentrations greater than 2.5 mg/L and maximum 

nitrite plus nitrate concentrations greater than 9 mg/L. 

Of the 29 monitoring sites in other site categories, 

only one had a median nitrite plus nitrate 

concentration greater than 1.0 mg/L, and only three 

sites had maximum concentrations in excess of 4 mg/L 

during the study period (table 3) Neuse River at 

Smithfield (site 32), Haw River at Bynum (site 24), 

and Falls Lake at Interstate 85 (site 5).

Median concentrations of total ammonia plus 

organic nitrogen varied little among site categories; 

the only significant difference was between sites 

below urban areas and WWTP's (category 4, median 

0.7 mg/L) and sites on headwater streams (category 5, 

median 0.35 mg/L, fig. 6). The median concentration 

for the remaining three categories was 0.6 mg/L. The 

maximum total ammonia plus organic nitrogen 

concentration was 11 mg/L measured in a sample from 

Little Lick Creek (site 6). The presence of large 

concentrations of organic nitrogen and ammonia are 

indications of upstream sewage disposal. Organic 

nitrogen accounted for 80 to 90 percent of the 

concentration of ammonia plus organic nitrogen for all

20 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
(5) HEADWATER 

STREAMS 

(4) BELOW URBAN 

AREAS &WWTP's

(3) SMALL , 

RESERVOIRS l

(2) LARGE ( 

RESERVOIRS

(1) RIVERS

C

(5) HEADWATER 

STREAMS 

(4) BELOW URBAN 

AREAS & WWTP' s

(3) SMALL 

RESERVOIRS

(2) LARGE 

RESERVOIRS

(1) RIVERS

(

(5) HEADWATER 

STREAMS 

(4) BELOW URBAN 

AREAS & WWTP' s

(3) SMALL 

RESERVOIRS

(2) LARGE 

RESERVOIRS

(1) RIVERS 

(

G A

 © B

A

5 

A

9-

A

e- A 

 e 

 0

ABC

A

 e 

BC

) 5 10 15 20 0 0.1 0. 

MEDIAN NITRITE PLUS NITRATE , MEDIAN AMMONIA, IN 

IN MILLIGRAMS PER LITER AS N MILLIGRAMS PER LITER AS N

i i i i | i , i i | i i , , | i

e- A

 e B

0

A

e

A

eA

, , , , , , , , i , , , , I , , , ,

1 i ' i ' i ' i ' I ' I '

-e- A

 e B

AB

 e 

AB

 e 

AB

r 1 , 1 , 1 ( 1 . 1 . 1 .

) 5 10 15 20 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1. 

MEDIAN TOTAL NITROGEN, MEDIAN AMMONIA PLUS ORGANIC NITROGEN, 

IN MILLIGRAMS PER LITER AS N IN MILLIGRAMS PER LITER AS N

i i i i < i i 

0 AB

 e BD

A

3 

A

0 

A

i I i I f I i

' 1 ' 1 ' 1 '

e AB

 e B

G

A 

A

e 

1,1,1,

AB

) 0.2 0.4 0.6 0.8 0 0.2 0.4 0.6 0.

MEDIAN ORTHOPHOSPHORUS, MEDIAN TOTAL PHOSPHORUS, 

IN MILLIGRAMS PER LITER AS P IN MILLIGRAMS PER LITER AS P

Explanation

significantly different 

O Median WWTP Wastewater-treatment plant

Figure 6. The distribution of median concentrations of selected nutrients by site category in the Research Triangle study area, 

North Carolina.

Water-Quality Characteristics by Site Category 21
site categories. Median ammonia concentrations were 

significantly less for headwater streams and large 

reservoirs than for sites below urban areas and 

WWTP's and river sites (fig. 6). Greatest ammonia 

concentrations (2 mg/L or more) occurred at Ellerbe 

Creek (site 7) and University Lake (site 30).

Total nitrogen concentrations were significantly 

greater at sites below WWTP's than at other sites. 

Nitrite, nitrate, ammonia, and organic nitrogen are all 

components of total nitrogen; for large and small 

reservoir sites, organic nitrogen (based on median 

concentrations) was the predominant form of nitrogen 

probably because of its presence in algae. For sites 

below urban areas and WWTP's, nitrate was the 

predominant nitrogen form. For rivers and headwater 

streams, nitrate and organic nitrogen forms were about 

equal.

Median concentrations of nitrite plus nitrate and 

total nitrogen were significantly different for watersupply intake sites on rivers and reservoirs. Median 

concentrations of nitrite plus nitrate were 0.7 mg/L for 

river intake sites and 0.06 mg/L for reservoir intake 

sites. Median concentrations of total nitrogen were 

1.3 mg/L for river intake sites and 0.64 mg/L for 

reservoir intake sites. River intake sites are located 

downstream from urban areas and receive the 

accumulated effluents from urban point sources which 

tend to have relatively high concentrations of nitrate. 

No significant difference was detected between river 

and reservoir intake sites for ammonia or organic 

nitrogen. Maximum concentrations among river intake 

sites for nitrite plus nitrate (5.5 mg/L) and total 

nitrogen (5.9 mg/L) occurred at Deep River at 

Carbonton (site 46).

Phosphorus

Phosphorus is essential for the metabolism of all 

living organisms and can be the single most critical 

factor in the maintenance of biogeochemical cycles. In 

freshwater aquatic environments, phosphorus 

enrichment can stimulate the growth of aquatic plants, 

including algae, leading to eutrophication, disruption 

of the normal aquatic community composition, and 

oxygen depletion as plants die and decay. It can also 

cause water-supply problems such as filter clogging 

and unpleasant taste and odors.

Phosphorus occurs naturally in igneous rock and 

is frequently abundant in sediments. Phosphorus 

occurs in natural waters as phosphate in various 

forms orthophosphate, condensed phosphate, and

organically bound phosphate. Concentrations of 

phosphorus present in solution in natural surface 

waters are rarely greater than a few tenths of a 

milligram per liter (Hem, 1985). Mean concentrations 

of total phosphorus for selected streams in forested 

basins throughout North Carolina ranged from 

0.01 mg/L to 0.04 mg/L (Caldwell, 1992). Mean total 

phosphorus concentrations in surface waters of 

agricultural drainages ranged from 0.16 mg/L to 

1.4 mg/L (Harned, 1982).

The forms of phosphorus are analytically 

defined. In this study, orthophosphorus and total 

phosphorus concentrations were analyzed. Total 

phosphorus includes all forms of phosphorus that are 

oxidized to orthophosphorus with rigorous 

phosphomolybdate digestion. Orthophosphate is the 

bioavailable form of phosphorus. Sources for 

orthophosphate include agricultural and residential 

fertilizers. Organically bound forms of phosphorus, 

another part of total phosphorus, are formed by 

biological wastewater-treatment processes, by 

instream biota, or from body wastes. Industrial- and 

domestic-sewage effluents have been an important 

potential source of phosphorus in the form of acidhydrolyzable phosphates, which are added to 

detergents. A ban on phosphate detergents was 

imposed in North Carolina in 1988.

Median total phosphorus concentrations ranged 

from less than 0.01 mg/L at Falls Lake at the City of 

Raleigh intake (site 2) and at NC-98 (site 3), Little 

River Reservoir (site 13), and Jordan Lake at Bells 

Landing (site 22) to 5.8 mg/L at Knap of Reeds Creek 

(site 10). Median concentrations of total phosphorus 

for sites below urban areas and WWTP's were 

significantly greater than for reservoir sites (fig. 6) but 

were not significantly greater than headwater and river 

sites indicating that both the contributions of 

phosphorus from point sources and resuspension of 

phosphorus from streambeds are important factors 

determining total phosphorus concentration. 

Municipal point sources are important contributors to 

the total phosphorus load in surface waters. That and 

the fact that total phosphorus strongly adsorbs to 

particulates and, therefore, is associated with 

suspended sediments probably accounts for the greater 

concentration in streams compared to reservoir sites. 

The median total phosphorus concentration for sites 

below urban areas and WWTP's was 0.25 mg/L 

compared to median concentrations less than 

0.05 mg/L for reservoir sites (table 3).

22 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
In general, orthophosphate was about 50 percent 

of total phosphorus concentration. Median concentrations of orthophosphate were significantly greater 

for sites below urban areas and WWTP's than for 

reservoir or river sites (fig. 6). The maximum 

concentration for sites below urban areas and 

WWTP's, 3.5 mg/L, occurred at Knap of Reeds Creek 

(site 10, table 3). The maximum concentration for sites 

in other categories was 0.9 mg/L at Morgan Creek 

near White Cross (site 29, table 3).

A marked seasonal pattern was observed for 

phosphorus at reservoir sites. Two examples are Falls 

Lake at Interstate 85, which is seasonally shallow, and 

the Haw River arm of Jordan Lake (fig. 7). Greatest 

concentrations of phosphorus (as much as 0.23 mg/L) 

generally occurred during late summer and fall 

months. Peaks in chlorophyll a concentration roughly 

corresponded to phosphorus peaks. Chlorophyll a 

concentrations ranged from less than 10 to 140 

micrograms per liter (ug/L). The North Carolina State 

water-quality standard for chlorophyll a is 40 ug/L.

Trace Elements

Trace elements occur naturally in the 

environment from geochemical weathering. Trace 

elements, such as arsenic, cadmium, copper, 

chromium, lead, nickel, zinc, and mercury, generally 

are present in water in concentrations less than 

25 ug/L. Metals such as iron, aluminum, and 

manganese, although abundant, are included here. 

Differences in local geology account for much of the 

variation in concentrations between streams and lakes 

in this study. However, industrial and municipal 

discharges, as well as urban land cover, often account 

for elevated trace-element concentrations.

Summary statistics by site category were 

calculated by determining the median concentration of 

each trace element for each site (table 3). The median 

concentration for each category is determined from the 

median concentrations for sites within that category. 

The maximum and minimum values are the absolute 

maximum and minimum concentrations for all data 

collected for sites in each category.

For most trace elements, data from samples 

collected by the DEM had higher MRL's than did data 

from samples collected by the USGS. This complicated data interpretation because trace-element 

concentrations generally were less than 1 or 2 ug/L, 

and many USGS detections were less than the OEM's 

MRL. Furthermore, most of the sites sampled by the

DEM are located below urban areas and WWTP's 

(category 4). For sites with multiple MRL's, data were 

censored to the highest MRL unless the number of 

analyses with the highest MRL was minor. In that 

case, the highest MRL values were removed.

Because of the large number of concentrations 

below laboratory MRL's and because the database 

often contains multiple MRL's, analysis of variance 

could not be used to test for statistically significant 

differences between site categories. Instead, box plots 

of copper, lead, and zinc data illustrate general 

differences among categories (figs. 8 and 9). The 

distribution displayed by the box plots (Helsel and 

Hirsch, 1992, p. 453-454) was determined using the 

log-probability method of Helsel and Cohn (1988) and 

was based on reported concentrations above and below 

the MRL's. Distributions below the lowest MRL are 

not shown; the distribution between two MRL's is 

shaded to indicate it is based on log-probability 

assumptions.

Generally, greatest concentrations of trace 

elements were observed in streams during periods of 

greater than normal streamflow. This is likely the 

result of resuspension of silt, clay, and organic 

particles that are associated with adsorbed trace 

elements (Horowitz, 1991). In reservoirs, particulates 

tend to settle out of the water column and are not 

readily resuspended.

Iron and manganese are naturally abundant and 

commonly coat clay particles. This often causes 

concentrations of these metals in untreated surface 

waters to exceed the USEPA secondary drinking-water 

standards (aesthetic standards) for iron (1,000 ug/L) 

and manganese (50 ug/L). This occurs even in 

relatively undisturbed streams. Median concentrations 

were near or above the standards at river, headwater, 

and stream sites below urban areas and WWTP's 

(table 3). During the normal seasonal cycle of lake 

stratification, it is common for concentrations of 

soluble iron and manganese to increase by an order of 

magnitude in oxygen-poor bottom waters. Reservoir 

bottom waters were not sampled; however, median 

concentrations in surface reservoir waters were 

substantially less than in streams.

Arsenic is a naturally occurring trace element 

that is toxic in relatively small amounts. The USEPA 

drinking-water MCL and North Carolina State waterquality standard for arsenic are both 50 ug/L. Sources 

for arsenic include pesticides, a by-product of coal 

burning, and smelting of ore. Concentrations of

Water-Quality Characteristics by Site Category 23
oi

s

06

2

D

s

O

0, 

M

O 

CL,

0.40

0.35

0.30

0.25 -

1989 1994

0.20

Haw River arm of Jordan Lake (site 23)

1994

Explanation

 I - Total phosphorus

 Chlorophyll a

Figure 7. Total phosphorus and chlorophyll a concentrations for Falls Lake at 1-85 and Haw River arm of Jordan Lake, 1988-94.

24 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
120

100

I

e§

s

I

po

80

60

40

20

1 1 1 1 1 1 1 1 1 1 

Rivers (1)

ff

e

O

-

O

Ve 

O 

O

Q s

O ii

x c «

f]J 2 | CN 1 " ll

1 1 1 1 1 1 1 1 1

Large reservoirs (2)

o

CM

&

O

1 1 1 1 1

Small 

reservoirs (3)

r-"IT

c 

O

oo

CM 

II

C

O

O

o 

If

OO C !/-> 

^ f~) ^

1 1 1 1 1 1 1 1

Below urban areas 

and WWTFs(4)

o

1?

c

O

^D O

8 x

o

CN

c"*"i r^j o

1 1 1 1

Headwater 

streams (5)

u'

c

O

II 

1° -

CN 

II

C £

0 n 

Olili

1 11 14 24 25 26 31 32 33 46 2 3 4 5 2021A22 23 45 13 16 28 30 34 6 7 8 9 10 17 18 19 12 15 27 29

SITE

Explanation

H Lowest minimum reporting limit

[ | Highest minimum reporting 

limit when more than one 

minimum reporting limit

Upper wisker-The last observation within 1 step of the 

upper end of the box. (step= 

1.5 times interquartile range)

75th percentile

T

Median

25th percentile

Lower wisker-The last observation within 1 step of the 

lower end of the box

X Outside value-From 1 to 2 

steps from the upper or 

lower end of the box

O Far outside value-More than 

2 steps from the upper or 

lower ends of the box 

WWTP Wastewater-treatment plant

Figure 8. The distribution of copper concentrations by site and site category in the Research Triangle study area, North Carolina.

Water-Quality Characteristics by Site Category 25
60 i-r

50

O 

O

u 30

§

i"

Rivers (1)

II

Large reservoirs (2) Small 

reservoirs (3)

Below urban areas 

and WWTPs (4)

Headwater

streams (5)

li

1 11 14 24 25 26 31 32 33 46 2 3 4 5 20 21A22 23 45 13 16 28 30 34 6

SITE

7 8 9 10 17 18 19 12 15 27 29

&

W 200

HH

| 1

&

C5

I 150

O

O

U

§

g 100

u z

N

<

o 50

H 

n

Sr

c

O 10r^i

O

-

-

-

CN C

x 1 x

X c O X

i

l 1 7 If 

0 OrUo 0 

 Illll

II

c

O

^

IFc

O

0 r, - g

fj g 1 °

g goo 

go i 7 o o o

Illllllll

_

1J1

o

? ? 7« EC |t M

X 0 X 0 ?

lull

if

o

1

o

 g O

If

CN C

g 0 X

X

V

S x

7 ? 0 i ri

 

-

-

-

rriII '

17 6-

c c

0 to g .

?< I 0 0

11 14 24 25 26 31 32 33 46 2 3 4 5 2021A22 23 45 13 16 28 30 34 6 7 8 9 10 17 18 19 

tin

12 15 27 29

SITE

Explanation

| Lowest minimum reporting limit

n Highest minimum reporting 

limit when more than one 

minimum reporting limit

Upper wisker-The last observation within 1 step of the 

upper end of the box. (step= 

1.5 times interquartile range) 

-1- 75th percentile

T

Median

25th percentile

Lower wisker-The last observation within 1 step of the 

lower end of the box

X Ontside value-From 1 to 2 

steps from the upper or 

lower end of the box

O Far outside value-More than 

2 steps from the upper or 

lower ends of the box 

WWTP Wastewater-treatment plant

Figure 9. The distribution of lead and zinc concentrations by site and site category in the Research Triangle study area, North 

Carolina.

26 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
arsenic ranged from below detection (less than 1 (ig/L) 

to 15 (ig/L. Most analyses were less than the MRL. 

The greatest concentrations of arsenic, 15 and 11 (ig/L, 

occurred at Flat River (site 15) and Little River (site 

12) in 1988. Arsenic also occurred in bottom 

sediments at these sites possibly from past agricultural 

sources.

Cadmium occurs in some ores and is used 

extensively in industry. Cadmium can become an 

environmental contaminant through waste-disposal 

practices or from the atmosphere. The State waterquality standard for cadmium is 2 (ig/L; the drinkingwater MCL is 5 |ig/L. Both standards were exceeded 

by fewer than 1 percent of the samples analyzed. The 

greatest concentration, 34 (ig/L, was in a sample from 

Little River (site 12).

The concentration of chromium in natural 

waters is generally less than 10 (ig/L; however, 

chromium may be introduced to surface waters in 

industrial wastes. The drinking-water MCL for 

chromium is 100 (ig/L. Only five samples had 

chromium concentrations that exceeded 25 (ig/L, the 

DEM MRL. Those samples were collected from 

Neuse River at Smithfield (site 32), Cape Fear River 

(site 31), Cane Creek (site 27), Flat River (site 15), and 

Little River (site 12). Cane Creek and Flat River 

concentrations also exceeded the State water-quality 

standard of 50 (ig/L. The USGS MRL for chromium 

was 1 (ig/L. An additional 21 percent of analyses and 

at least one analysis from each station sampled had 

concentrations between the 1 and 25 (ig/L MRL's. 

When data with an MRL of 25 (ig/L are not 

considered, data from sites below urban areas and 

WWTP's tended to have greater chromium 

concentrations than did other categories (table 3).

Cobalt is found naturally in very small 

concentrations. No drinking-water MCL's or waterquality standards have been set for cobalt. All but three 

concentrations were less than 5 (ig/L. The greatest 

concentration was 20 (ig/L.

Copper is common in the environment from 

natural and anthropogenic sources, including uses in 

industry and agriculture. For drinking water, the most 

common source is from dissolution of copper 

plumbing fixtures. The drinking-water action level is 

1,300 (ig/L. Concentrations in the study area ranged 

from less than 1 to 400 |ig/L. MRL's were 1, 2, 5, and 

10 (ig/L depending on the agency performing the 

analyses and the date the sample was collected. About 

9 percent of analyses exceeded 10 (ig/L; most of these

occurred in samples from large rivers and sites below 

urban areas and WWTP's. The median copper 

concentration exceeded 10 )ig/L at Northeast Creek 

(site 19). In general, the smallest concentrations of 

copper were detected at large and small reservoir sites 

and headwater streams (fig. 8).

Lead occurs naturally at trace concentrations. It 

adsorbs readily to inorganic and organic surfaces so 

that it tends to be in low concentrations in surface 

waters. Environmental contamination from lead has 

resulted from industrial sources such as coal burning 

and from its use as an additive in gasoline. For 

drinking water, the major source of concern is 

dissolution of lead from plumbing. The drinking-water 

action level is 15 )ig/L. The MRL's for lead were 1, 5, 

and 10 (ig/L. Nearly all of the samples collected from 

sites below urban areas and WWTP's were analyzed 

with an MRL of 10 (ig/L. The median concentrations 

for all site categories were less than 10 (ig/L. Only 4 

percent of analyses exceeded 10 (ig/L. In general, 

greatest concentrations occurred in samples from 

rivers (fig. 9). Seven samples, five from the Haw River 

(site 24) and two from the Neuse River (site 32), 

exceeded the State water-quality standard for lead of 

25 Lig/L.

Molybdenum occurs naturally in streams and 

lakes in trace amounts (less than 1 (ig/L). Fossil-fuel 

combustion is a probable source where higher 

concentrations are found. No drinking-water MCL's or 

water-quality standards have been set for 

molybdenum. Sixty-seven percent of analyses were 

less than 1 (ig/L, and all but seven samples had 

concentrations less than 5 (ig/L. The seven highest 

concentrations occurred at Northeast Creek (site 19), 

Ellerbe Creek (site 7), Eno River near Weaver (site 8), 

and University Lake (site 30).

Nickel is widely used in industry and is a 

common environmental contaminant. It is a 

constituent of stainless steel and other alloys. The 

drinking-water MCL for nickel is 100 (ig/L; the State 

water-quality standard is 88 (ig/L. Sixty-four percent 

of nickel analyses were below the MRL of 10 or 

50 (ig/L. Two samples from Haw River (site 24, 

420 Lig/L) and Knap of Reeds Creek (site 10, 94 ^ig/L) 

exceeded the State water-quality standard. Only 16 

samples analyzed for nickel with an MRL of 10 (ig/L 

exceeded the MRL all were at stream sites. Nickel is 

relatively insoluble and adsorbs to iron and manganese 

oxides on particulates. Particulates tend to settle in

Water-Quality Characteristics by Site Category 27
reservoirs and are not readily subject to resuspension 

during storm-produced runoff as in streams.

Selenium is a naturally occurring element in 

trace amounts in North Carolina; the drinking-water 

MCL is 50 ug/L. Only one selenium concentration 

was greater than the MRL of 1 ug/L a concentration 

of 2 ug/L in a sample from Little Lick Creek (site 6).

Silver has numerous anthropogenic sources, 

most notably photographic processing. Because of its 

value, silver is often recovered from industrial wastes. 

The State water-quality action level for silver is 

0.06 ug/L; no drinking-water MCL has been 

established. Only five silver concentrations exceeded 

1 ug/L; however, for a few samples the MRL was 

25 ug/L.

Zinc occurs naturally but is also a common 

environmental contaminant. It is widely used for 

galvanizing steel, in paints, and in combination with 

other metals. The State water-quality action level for 

zinc is 50 ug/L; there is no drinking-water MCL. 

Median zinc concentrations were less than the MRL 

for all site categories except sites below urban areas 

and WWTP's; however, 39 percent of all analyses 

exceeded 10 ug/L. The distribution of zinc 

concentrations by site category indicates that river 

sites, especially those below urban areas and 

WWTP's, tended to have greater zinc concentrations 

than did other sites (fig. 9).

Volatile Organic Compounds

During the first 3 years of this study, water 

samples were collected 3 times per year at each 

monitoring site for the analysis of 35 volatile organic 

compounds (VOC's), including trihalomethanes 

(THM's) and USEPA priority pollutants. Because 

VOC's have high vapor pressures, they are easily lost 

to the atmosphere and do not adsorb to sediments. 

They are most appropriately sampled in the water 

column (Chapman and others, 1982) but seldom 

persist there and require special sampling methods.

Few VOC's were detected in concentrations 

above the MRL. The greatest percentage of VOC 

detections occurred at sites below urban areas and 

WWTP's (fig. 10). Most of these detections were very 

low concentrations of any of four THM's 

chloroform, bromoform, dichlorobromomethane, and 

chlorodibromomethane. THM's are formed when 

chlorine reacts with naturally occurring dissolved 

organic carbon. This reaction often occurs in water 

and wastewater that have been disinfected with

chlorine. Thus the concentration of dissolved organic 

carbon in water or wastewaters and chlorination are 

important factors in THM formation (Thurman, 1985). 

Treated tap water usually contains from 50 to 75 ug/L 

THM. The USEPA primary drinking-water MCL for 

THM is 100 ug/L.

THM's were found almost exclusively at sites 

below urban areas and WWTP's; however, at these 

sites, low concentrations were typical (table 4). The 

only sites where THM's were detected that were not 

immediately downstream from urban areas and 

WWTP's were Little River Reservoir (site 13), Falls 

Lake at Interstate 85 (site 5), and Neuse River at 

Smithfield (site 32). Very low concentrations of 

chloroform were measured at least once at each of 

these sites. Neuse River at Smithfield, while not 

immediately downstream from an urban area or 

WWTP, receives drainage from the Raleigh area.

Xylene, a component of gasoline, was found at 

a concentration of 1.6 ug/L in one sample from the 

Neuse River at Smithfield (site 32). The USEPA 

drinking-water MCL for total xylenes is 10 mg/L. 

Trace amounts (less than 1 ug/L) of other VOC's, 

mostly organic solvents, such as benzene, dichlorobenzene, tetrachloroethylene, and trichloroethane, 

were found in fewer than 20 percent of 298 samples 

collected. USEPA drinking-water MCL's for those 

VOC's for which MCL's have been set are 5 ug/L or 

greater. The presence of these compounds is related to 

their widespread commercial production and use.

Pesticides and PCB's

During the first 3 years of study, water samples 

were collected 3 times per year at each monitoring site 

for the analysis of 24 organochlorine and organo- >~\

phosphorus insecticides and PCB's (Garrett and 

others, 1994). Because of their persistence in the 

environment, potential to bioaccumulate, and 

carcinogenic properties, organochlorine insecticides 

have been increasingly regulated over the past two 

decades and, in some cases, their use in the United 

States has been restricted (lindane and chlordane) or 

banned (DDT, mirex, dieldrin, and PCB's).

"Polychlorinated biphenyls, although not pesticides, were 

analyzed with this group of compounds because they are 

chemically similar to organochlorine insecticides and behave in a 

similar way in the environment. PCB's were widely used in the 

electrical industry and also in lubricating oils, pesticides, 

adhesives, and plastics.

28 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
100

80

60

40

20

Rivers (1) Small reservoirs (3) Headwater streams (5) 

Large reservoirs (2) Below urban

areas and WWTP's (4)

100

80

60

40

20

Rivers (1) Small reservoirs (3)

Large reservoirs (2) Below urban

areas and WWTP's (4)

Headwater streams (5)

X

O

WWTP

Explanation

Largest value within 1.5 

times the interquartile range

75th Percentile

Median

25th Percentile

Smallest value within 1.5 

times the interquartile range

Outside values 

Far outside values 

Wastewater-treatment plant

100

80

60

40

20

X

Rivers (1) Small reservoirs (3) Headwater streams (5) 

Large reservoirs (2) Below urban

areas and WWTP's (4)

Figure 10. The distribution, by site category, of the percentage of pesticides or volatile organic compounds for which 

concentrations were above minimum reporting limits.

Water-Quality Characteristics by Site Category 29
Table 4. Summary statistics of total trihalomethane concentrations measured at sites located downstream 

from urban areas and wastewater-treatment plants, water years 1989-91

[<, less than]

Site 

number

(fig. 2)

Station name

Total trihalomethane

concentration 

(micrograms per liter)

Median

MinimumMaximum

Number

of 

observations

Total

Detectable

Little Lick Creek above Secondary 

Road 1814 near Oak Grove

7

8

9

10

17

18

19

Ellerbe Creek near Gorman

Eno River near Weaver

Eno River near Durham

Knap of Reeds Creek near Butner

Morgan Creek near Farrington

New Hope Creek near Elands

Northeast Creek at Secondary

Road 1 100 near Genlee

2.2

<.8

<.8

4.6

.9

3.15

4.75

<.8

<.8

<.8

<.8

<.8

1.3

1.2

4

.9

.9

86

1.8

7.9

11.9

8

9

8

8

7

8

8

7

2

1

7

4

8

8

Organophosphorus insecticides are generally less 

environmentally persistent and more water soluble 

than the organochlorine insecticides. Organochlorine 

and Organophosphorus insecticides are used for insect 

control on crops, lawns, gardens, in homes, and on 

domestic animals. Because organochlorine and 

Organophosphorus insecticides have low water 

solubility, they are typically detected in water in very 

low concentrations.

About 40 percent of 368 samples collected for 

insecticide and PCB analysis contained a detectable 

concentration of at least one of these compounds. The 

four most frequently detected were lindane, dieldrin, 

diazinon, and heptachlor epoxide at least one of 

these was detected at each of 18 monitoring sites. 

Most frequent detections (6.9 to 13.7 percent of 

analyses) occurred in six tributaries to Falls and 

Jordan Lakes that is, in streams downstream from 

urban areas and WWTP's and at Swift Creek near 

Apex (fig. 10). Insecticides also were detected in the 

uplake segment of Falls Lake, the Haw River arm of 

Jordan Lake, Little River Reservoir, and Lake Benson. 

There were almost no detections of these compounds 

in headwater streams (fig. 10) although most of 

those that occurred were from Cane Creek (site 28).

Nearly all concentrations of insecticides and 

PCB's were very small. For example, all concentrations for lindane and heptachlor epoxide were 

significantly less than their USEPA drinking-water 

MCL's of 0.2 |ng/L. However, some dieldrin and 

lindane concentrations exceeded the State waterquality standards of 0.002 and 0.01 ng/L, respectively. 

A single sample from Northeast Creek contained 

1 |ng/L of diazinon; however, there are no Federal or 

State standards for diazinon.

In the spring of 1992, samples for the analysis 

of 13 acetanilide and triazine herbicides were 

collected at selected sites. These generally are 

preemergence herbicides that are used for crops, turf, 

and brush control. They range from slightly soluble 

(atrazine, simazine) to soluble (alachlor, prometon) in 

water and from nonpersistent (alachlor, metolachlor) 

to moderately persistent (atrazine, simazine) in the 

environment (Briggs, 1992). Alachlor, atrazine, and 

simazine are on the USEPA list of regulated 

constituents for drinking water.

Detectable concentrations of herbicides 

mainly atrazine or simazine (table 5) were detected at 

every site sampled. With one exception, all detectable 

concentrations were less than 1 |ig/L and less than the 

drinking-water MCL for alachlor (2 ng/L), atrazine 

(3 |ng/L), and simazine (4 |ng/L). The percentage of 

acetanilide and triazine herbicide analyses that were 

above the MRL was considerably greater than the

30 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
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Water-Quality Characteristics by Site Category 31
percentage of organochlorine and organophosphorus 

insecticides (fig. 10) probably because of the greater 

use and greater solubility of these herbicides in water.

In the spring of 1993 and 1994, pesticide data 

collection was targeted to three monitoring sites 

(Ellerbe Creek, Northeast Creek, and Little Lick 

Creek) located downstream from WWTP's and that 

had previous detections of organochlorine and 

organophosphorus pesticides. The purpose of this 

special pesticide sampling was to determine if the 

source of pesticides was WWTP effluent or runoff 

upstream from the WWTP. Samples for analyses of 

organochlorine and organophosphorus insecticides 

were collected from each stream at the regular 

monitoring site downstream from the WWTP, from the 

WWTP outfall, and upstream from the WWTP outfall. 

Because previous sample collections indicated the 

presence of acetanilide and triazine herbicides, 

samples collected at the regular monitoring site were 

analyzed for these compounds and for carbamate and 

chlorophenoxy acid herbicides. Samples were 

collected 3 times under low, medium, and high 

streamflow conditions.

Organochlorine and organophosphorus 

insecticides appear to be ubiquitous in very low 

concentrations in WWTP effluents, upstream from 

WWTP's, and downstream from WWTP's. Diazinon, 

lindane, dieldrin, ODD, DDE, DDT, and chlorpyrifos, 

were measured at concentrations near the MRL 

(table 6). (Compounds with no detections are not 

listed in table 6.) Of these, only lindane, chlorpyrifos, 

and diazinon are still in use in the United States. DDE 

is a degradation product of DDT. None of the organochlorine or organophosphorus compounds exceeded 

Federal drinking-water MCL's. Five samples exceeded 

the State water-quality standards for dieldrin; one 

exceeded the standard for lindane. Most notably, 

diazinon, a widely used compound for suburban and 

agricultural pest control, was detected in every 

sample.

Low concentrations of herbicides occurred in 

stream and WWTP effluent samples, providing no 

conclusive information on source. Simazine, 

prometon, deisopropylatrazine, deethylatrazine 

(triazine herbicides), 2,4-D, and 2,4-DP (chlorophenoxy acid) were measured at concentrations at or 

above the MRL (table 6). Deisopropylatrazine and 

deethylatrazine are degradation products of atrazine, 

and their presence in the absence of atrazine indicates

a prior source of atrazine. In May 1993, simazine, 

prometon, 2,4-D, and 2,4-DP were measured at 

concentrations significantly greater than detection 

limits but at least an order of magnitude smaller than 

Federal drinking-water MCL's. Because the Northeast 

and Little Lick Creek samples were collected at only 

the downstream site, it is not known if these 

compounds were from local runoff or WWTP 

effluents. Ellerbe Creek samples were collected from 

only the upstream site indicating that, for Ellerbe 

Creek, local runoff is a source for simazine, prometon, 

and 2,4-D. Triazine herbicides samples were collected 

at upstream, downstream, and effluent sites in March 

1994.

Semivolatile Organic Compounds

Water samples were collected at nine sites listed 

in table 7 for analysis of 51 semivolatile organic 

compounds most identified as priority pollutants by 

the USEPA. None of the compounds analyzed were 

found above the limit of detection. The compounds 

analyzed included phenols, cresols, monocyclic and 

polycyclic aromatics, and phthalate esters. Most are 

relatively insoluble in water and, if present, are more 

likely to reside in bed materials or the biota.

BED-MATERIAL QUALITY

Samples of bed materials were collected from 

24 sites in the study area and analyzed for selected 

semivolatile organic compounds, organochlorine and 

organophosphorus insecticides, and PCB's. Samples 

were collected, seived to remove material that 

exceeded a grain size of 2 millimeters (mm), and 

analyzed as described by Garrett and others (1994). To 

examine the effect of grain size on constituent 

concentration, four samples were collected at three 

sites and seived to retain the grain-size fraction less 

than 63 microns (u). For Lake Michie and University 

Lake, data from multiple locations were combined. At 

five sites, more than one sample was collected 

between 1988 and 1990 Knap of Reeds Creek (site 

10), Little River (site 12), Flat River (site 15), Haw 

River (site 24), and Cane Creek (site 27). For these 

sites, the median of multiple analyses was used to 

provide one median concentration per site.

Many of the 126 compounds for which USEPA 

will promulgate standards for the protection of aquatic 

life have very low solubility in water and

32 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
Table 6. Constituents having at least one detection in samples analyzed for concentrations of selected pesticides 

upstream from, downstream from, and in wastewater-treatment plant effluents in Ellerbe, Northeast, and Little Lick 

Creeks

[Concentrations are in micrograms per liter. WWTP, wastewater-treatment plant; ft3/s. cubic feet per second; , no data; <, less than]

Federal 

drinkingwater 

standard

Discharge (ft3/s)

Specific conductance

Ellerbe Creek

Upstream from WWTP Durham Northside WWTP 

effluent effluent

Date

5/20/93 5/26/93 3/29/94 5/20/93 5/26/93 3/29/94

13.6 111 365 

119 107 82 60 545 324

Downstream from WWTP 

effluent

5/20/93 5/26/93 3/29/94

30 72 770

173 186 86

Organochlorine/organophosphorus insecticides

Chlorpyrifos 100a

Chlordane 2

Lindane .2

Dieldrin 2a

Diazinon 3a

Malathion 800a

 0.03 0.07 0.02 0.02 0.03

 

<0.01 <.01 <.01 .01 .011 .01

<.01 <.01 <.01 .006 .005 <.01

 .06 .04 .05 .11 .01

- <.01 .02 <.01 <.01 <.01

0.02 0.02 0.03

 

.002 .007 <.01

.004 .005 <.01

.06 .08 .02

<.01 <.01 <.01

Carbamate insecticides

Carbaryl 4,000a 0.03 <0.05 <0.05

Triazine and other herbicides

Simazine 4

Prometon 500a

Atrazine 3

Deisopropylatrazine 

Deethylatrazine 

Alachlor 2

Tebuthiuron 2,000a

Pendimethalin 

Benfluralin 

Metolachlor 3,500a

Napropamide 

0.21 0.22 0.07 <0.01

.20 .26 .05 .04

 

.07 .07 

 

<.05 <.05 .09 .02

 .08 .02

 .08 <.02

 .01 <.01

__ _ _ _ __ _

 

 0.03

 .04

 

_ _ __

 

 .07

 .06

 .04

- - <.01

 

 

Chlorophenoxy acids herbicides

2,4-D 70

2,4 -DP 

0.21 0.13 <0.05 

<.01 <.01 <.05 _ __ _

 <0.05

 <.05

Bed-Material Quality 33
Table 6. Constituents having at least one detection in samples analyzed for concentrations of selected pesticides 

upstream from, downstream from, and in wastewater-treatment plant effluents in Ellerbe, Northeast, and Little Lick 

Creeks (Continued)

[Concentrations are in micrograms per liter. WWTP, wastewater-treatment plant; ft3/s, cubic feet per second; , no data; <, less than]

Northeast Creek

Federal Upstream from WWTP Durham Northside WWTP 

drinking- effluent effluent

standard Date

4/6/93 5/20/93 3/29/94 4/6/93 5/20/93 3/29/94

Discharge (ft3/s) 1,074 372 

Specific conduc- 47 160 101 282 597 405 

tance

Downstream from WWTP 

effluent

4/6/93 5/20/93 3/29/94

938 28 503

50 218 89

Organochlorine/organophosphorus insecticides

Chlorpyrifos 100a <0.01 0.01 0.01 0.04 0.02 0.02

Chlordane 2 

Lindane .2 <.002 .001 <.01 <.01 <.01 .01

Dieldrin 2a <.002 <.001 <.02 <.01 <.01 <.02

Diazinon 3 a .05 .04 .02 .05 .06 .02

Malathion 800a 

<0.01 0.01 <0.01

 

<.01 <01 <-01

<.01 <.01 <.02

.04 .04 .02

 

Carbamate insecticides

Carbaryl 4,000a <0.05 0.02 <0.05

Triazine and other herbicides

Simazine 4 <0.01 <0.01

Prometon 500a .02 .02

Atrazine 3 .01 .02

Deisopropylatrazine

Deethylatrazine 

Alachlor 2 

Tebuthiuron 2,000a .02 <.02

Pendimethalin 

Benfluralin 

Metolachlor 3,500a .01 .08

Napropamide <.01 <.01

<0.05 0.10 <0.01

<.05 .10 .02

<.05 <.05 .01

<.05 .06 

 

 

 <02

 

 

<.05 <.05 .04

 .03

Chlorophenoxy acids herbicides

2,4-D 70 <0.05

2,4 -DP <.05

0.30 1.2 <0.05

.08 .81 <.05

34 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
Table 6. Constituents having at least one detection in samples analyzed for concentrations of selected pesticides 

upstream from, downstream from, and in wastewater-treatment plant effluents in Ellerbe, Northeast, and Little Lick 

Creeks (Continued)

[Concentrations are in micrograms per liter. WWTP, wastewater-treatment plant; ft3/s, cubic feet per second; , no data; <, less than]

Federal 

drinkingwater 

standard

Discharge (ft3/s)

Specific conductance

Little Lick Creek

Upstream from WWTP Durham Northside WWTP 

effluent effluent

Date

5/14/93 5/20/93 3/29/94 5/14/93 5/20/93 3/29/94

0.77 2.9 103 

217 171 79 237 52 270

Downstream from WWTP 

effluent

5/14/93 5/20/93 3/29/94

2.8 3.8 341

258 250 80

Organochlorine/organophosphorus insecticides

Chlorpyrifos 100a

Chlordane 2

Lindane .2

Dieldrin 2a

Diazinon 3a

Malathion 800a

<0.01 0.02 0.01 <0.01 <0.01 0.03

<.l <.l <.l <-l <.l .1

<.001 .001 <.01 .001 .009 <.01

.001 .001 <.01 .001 .003 <.01

.04 .1 .07 .04 .04 .04

 

0.01 <0.01 <0.01

<.l <.l <.l

<.01 <-01 <.01

<.01 <.01 <.01

.04 .04 .05

 

Carbamate insecticides

Carbaryl 4,000a 0.02 0.13 0.02

Triazine and other herbicides

Simazine 4

Prometon 500a

Atrazine 3

Deisopropylatrazine

Deethylatrazine 

Alachlor 2

Tebuthiuron 2,000a

Pendimethalin 

Benfluralin 

Metolachlor 3,500a

Napropamide 

 0.01 <0.01

 .05 .02

 <.02 .01

 

 <.02 <.02

 

 .04 .02

 

 

 .01 .01

 

0.35 <0.05 0.07

.15 .11 .49

<.05 <.05 .01

.05 <.05 

.06 <.05 <.02

 

 .02

 

 

<.05 <.05 .01

 

Chlorophenoxy acids herbicides

2,4-D 70

2,4 -DP 

 <0.05 <0.05

 <.05 <.05

0.11 13 <0.05

.06 <.01 <.05

aDrinking-water equivalent level A lifetime exposure concentration protective of adverse, noncancer health effects, that assumes all of the 

exposure is from drinking water.

Bed-Material Quality 35
preferentially adsorb to sediments. This provides a 

pathway for bioaccumulation by aquatic organisms. 

As a result, samples of the water column may not be 

useful for assessing the presence or absence of these 

compounds in the environment, instead, bed materials 

must be sampled. These compounds are, to varying 

degrees, hydrophobic and lipophilic. Organochlorine 

insecticides, phthalate esters, and polynuclear 

aromatic hydrocarbons are most insoluble in water and 

have the greatest potential for bioaccumulation. The 

halogenated ethers and phenols are more water soluble 

and less bioaccumulative.

Table 7. Number of samples collected for analysis of 

semivolatile organic compounds

Site

num-

(fig. 2)

Number

Station name of

samples

5 Falls Lake at Interstate 85 near Red- 1 

wood

10 Knap of Reeds Creek near Butner 3

11 Little River below Dam near Fairntosh 1

12 Little River at Secondary Road 1461 2 

near Orange Factory

15 Flat River at Bahama 5

23 Jordan Lake, Haw River Arm above B. 2 

Everett Jordan Dam

27 Cane Creek near Orange Grove 1

32 Neuse River at Smithfield 1

33 Swift Creek near Apex 1

Because of their physical properties, bed 

materials play an important role in the fate and 

transport of these compounds. Nonionic species 

preferentially adsorb to organic acids over inorganic 

particles (Witkowski and others, 1987). However, the 

organic coatings on inorganic sediment particles 

provide good adsorption sites. Furthermore, small 

grain sizes (silts and clays), because of their greater 

surface area to mass ratio, typically adsorb greater 

amounts of synthetic organic compounds than largesized particles such as sand. For example, the analysis 

of bed-material samples from Knap of Reeds Creek 

shows the effect of grain size on adsorption of 

organochlorine insecticides. Two replicate bedmaterial samples, one seived to retain the fraction less

than 2 mm and the other seived to retain the fraction 

63 u, were analyzed to compare the effect of grain size 

on concentration. The smaller grain-size sample 

contained detectable concentrations of chlordane, 

DDD, DDT, diazinon, dieldrin, lindane, mirex, and 

malathion, whereas the larger grain-size sample 

contained detectable concentrations of only diazinon 

and mirex in sums of 15.9 and 0.5 micrograms per 

kilogram (ng/kg), respectively. Likewise, at Cane 

Creek (site 27) four samples were collected on four 

different dates for analysis of different sediment size 

fractions one with grain size less than 63 u., one with 

grain size less than 0.25 mm, and two with grain sizes 

less than 2 mm. Detections of insecticides were 

greatest in the samples containing the smallest grainsize fraction; no insecticides were detected in the 

larger grain-size fractions.

Pesticides

Samples of streambed material were analyzed 

for 24 organochlorine and organophosphorus 

insecticides and PCB's. Chlorinated insecticides and 

PCB's are less water soluble and more persistent in the 

environment, adsorbing to bed materials and 

bioaccumulating, than are organophosphorus 

insecticides. Organophosphorus insecticides tend to 

undergo more rapid degradation by hydrolysis than do 

organochlorine insecticides, although this process may 

be slowed by sorption to sediments. Degradation 

products of organophosphorus insecticides, not 

analyzed for this study, may be more persistent than 

the parent compounds (Witkowski and others, 1987).

Of the 24 compounds analyzed, the insecticides 

chlordane, DDD, DDE, DDT, diazinon, dieldrin, 

lindane, mirex, and malathion were detected in at least 

one sample. PCB, an industrial chlorinated compound, 

was detected at 10 sites, including five Haw River 

sites, a Haw River tributary, Falls Lake, Jordan Lake, 

Ellerbe Creek, and Cane Creek. MRL's ranged from 

0.1 to 1 (ig/kg of bed material. In the upper Neuse 

River Basin, greatest concentrations of PCB's and 

insecticides in bed material (greater than 10 ug/kg) 

were found in the lake-bed materials of Falls Lake and 

Lake Michie and in Ellerbe Creek streambed materials 

(fig. 11 A). Insecticides detected were primarily 

chlordane, DDE, and DDD. The elevated concentrations in lake-bed material may be due to the greater 

concentration of organic material and small grain-size 

inorganic material in the lake-bed samples compared 

to streambed samples. In Lake Michie samples, the

36 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
A.

78°30

0 2 4 6 8 10 KILOMETERS

36°15

80

Explanation

 - - Basin boundary

 Subbasin boundary

 37 Site and site number

Concentration in micrograms per kilogram

Figure 11. The sum of concentrations of organochlorine and organophosphorus pesticides detected in bed material collected at 

sites in the (A) upper Neuse River Basin and (B) upper Cape Fear River Basin.

Pesticides 37
percentage of bed material with grain size less than 

63 \i ranged from 78 to 95. In Falls Lake, the range 

was from 37 to 94 percent, and in University Lake, the 

range was from 88 to 99 percent. Of the seven 

streambeds sampled, the percentage of material 

having grain size less than 63 \i ranged from 0 to 5 

percent. The very low percentage of small grain sizes 

in streambed material is, in part, because samples 

were collected at the center of flow where scour occurs 

rather than in depositional zones of the stream 

channel. The source of elevated PCB and insecticide 

concentrations in Ellerbe Creek streambed materials is 

not known, but may be related to past wastewater 

discharge from the Durham WWTP.

In the upper Cape Fear River Basin, chlordane, 

DDD, DDE, and PCB were the primary contaminants. 

The concentration of PCB's and insecticides in bed 

material was greatest in the Haw River arm of Jordan 

Lake (fig. 1 IB) where chlordane was the primary 

contaminant (170 ug/kg). Otherwise, concentrations 

were similar to those observed in the upper Neuse 

River Basin.

Semivolatile Organic Compounds

Semivolatile organic compounds included over 

50 acid and base/neutral extractable compounds 

recoverable from bed material. The MRL for these 

compounds in bed material ranges from 200 to 

400 ug/kg wet weight. With the exception of a few 

phthalate compounds, no semivolatile organic 

compounds were found in concentrations that 

exceeded the MRL (Garrett and others, 1994). 

However, laboratory reports indicate the probable 

presence of phthalates, and aromatic and polyaromatic 

hydrocarbon compounds at detectable concentrations 

below the MRL at most of the sites sampled. Typically 

detected were fluoranthene, phenanthrene, anthracene, 

chrysene, pyrene, benzo(a)anthracene, 

benzo(b)anthracene, benzo(g,h,i)anthracene, 

benzo(k,a)anthracene, and fluorene. These 

polyaromatic hydrocarbons derive from combustion 

sources such as automobile exhaust, fossil fuel 

burning, and from natural combustion sources. These 

compounds are very common in small concentrations 

in bed materials because they are very insoluble in 

water and readily sorb to sediments. The concentration 

of these compounds in water is typically in the 

nanogram per liter range. Phthalate esters are derived 

from plastics and are ubiquitous in the environment.

TRIBUTARY LOADINGS TO RESERVOIRS

Annual loads of suspended sediment, nitrogen, 

phosphorus, zinc, and lead were computed for selected 

tributaries in the upper Neuse and upper Cape Fear 

River Basins for water years 1989 through 1994 using 

log-linear concentration-discharge equations 

developed from linear regression. Sediment, nitrogen, 

and phosphorus loads provide sediment and nutrient 

water budgets (loads in and out) for each reservoir in 

the study area. For some of the smaller reservoirs, 

loads into the reservoir were computed; however, 

loads out of the reservoir could not be computed but 

rather were estimated because outflow was not 

monitored. The loads contributed to reservoirs from 

unmonitored areas of the watersheds also were 

estimated to provide complete reservoir inflow 

estimates. Estimates were based on the assumption 

that yields (in tons per square mile) for unmonitored 

areas of the basin were similar to yields for monitored 

areas of the basin. This assumption could lead to 

overestimation or underestimation of loads in some 

instances. Inputs from atmospheric deposition were 

not considered in this study. Harned and others (1995) 

estimate nitrogen inputs from the atmosphere for the 

Neuse River Basin to be 2 tons per square mile 

(tons/mi2). Phosphorus inputs are estimated to be 

0.2 tons/mi2. Reservoir input and outflow were not 

calculated for zinc or lead due to insufficient data.

Daily mean loads were calculated using 

logarithmic-linear equations that relate instantaneous 

water discharge (independent variable) to the 

concentration of a water-quality constituent 

(dependent variable). For each site, equations were 

developed from data collected for this study from 

October 1988 through September 1992 and, when 

available, from data collected for two earlier studies of 

loadings to Falls and Jordan Lakes (Garrett, 1990a and 

b). Not enough samples were collected during any one 

year (at most, 12 samples per year) to provide 

concentration data at the wide range of streamflow 

conditions needed for good definition of an annual 

concentration-discharge relation. To maximize the 

amount of data available to define a concentrationdischarge relation and the likelihood of having data at 

the highest ranges of discharge where most transport 

of the constituents of interest occurs, all available data 

for each site were pooled except for phosphorus data. 

Because a phosphate-detergent ban was imposed in 

1988 just before the start of this study, data from 

earlier studies when phosphorus concentrations may

38 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
have been greater than after the ban were not used to 

develop concentration-discharge equations for 

phosphorus. Because data were pooled, year to year 

variation in estimated load at a site is due to annual 

variation in streamflow and not to a temporal change 

in the discharge-concentration relation. 

For each site, one to four separate 

concentration-discharge equations, covering different

flow ranges, were developed to provide best definition 

of the concentration-discharge relation over the full 

range of flow (Glysson, 1987; tables S-l to S-5). An 

example of discharge-concentration plots and 

superimposed concentration-discharge equations is 

shown in figure 12.

Sediment-Record Calculations (SEDCALC), a 

program developed by the USGS (Koltun and others,

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DISCHARGE, IN CUBIC FEET PER SECOND DISCHARGE, IN CUBIC FEET PER SECOND

Explanation

Discharge versus concentration 

o Discharge versus load

Figure 12. Comparison of the relation between discharge and concentration and discharge and load for selected streams.

Tributary Loadings to Reservoirs 39
1994), was used to calculate loads once the 

concentration-discharge equations were defined for 

each site. SEDCALC was developed to facilitate 

calculation of sediment loads but can be used to 

compute loads of any constituent that can be described 

by a discharge-concentration equation. Required 

inputs for SEDCALC are an equation(s) from the loglinear regressions of discharge and concentration, and 

a bias correction factor (BCF}. The concentrationdischarge equation is

logC = (1)

where

C is instantaneous concentration in cubic feet per

second,

b is regression constant (y-offset), 

m is regression coefficient (slope), and 

Q is instantaneous discharge in cubic feet per

second.

Bias is introduced when data are retransformed 

from the log space of the concentration-discharge 

equation to base-10 space. The smearing estimator 

effectively corrects for this bias (Gilroy and others, 

1990). The BCF used in this study is based on Duan's 

(1983) smearing estimator and is the mean of the 

antilog of the residuals from the log-linear regression. 

The BCF can be equal to or greater than 1.0; a BCF of 

1.0 does not alter the load estimate and consequently 

is equivalent to applying no bias correction (Koltun 

and others, 1994).

Once a set of regression equations is determined 

for the range of discharge that occurred at a site, the 

daily load (in tons) of sediment, nutrients, or trace 

elements is calculated from record of daily discharge 

with the equation

Qs = Qw x W((m x logGw) + b) x k x BCF , (2)

where

Qs is total daily load in tons per day,

Qw is daily mean water discharge in cubic feet per

second, and 

k is unit conversion factor (0.0027).

The daily loads were summed to derive annual 

loads for each water year. Supplemental tables S-1 to

S-5 at the back of the report list the concentrationdischarge equation, coefficient of determination (R2), 

and BCF for each constituent and site. It should be 

noted that the R2 value associated with the dischargeconcentration equations for this study are, without 

exception, less than those associated with dischargeload equations reported by Garrett (1990a and b). This 

does not indicate that load calculations from 

concentration-discharge relations are less accurate 

than load calculations from load-discharge relations 

but is because load is a function of discharge (fig. 12). 

When results of load-discharge and concentrationdischarge regressions were compared (without 

retransformation bias correction) using data for nine 

sites, calculated annual loads were virtually the same.

Retransformation bias was not corrected using a 

BCF in the earlier studies by Garrett (1990a and b) 

and Simmons (1993) and this could affect comparison 

of yields from this study with yields from the earlier 

studies. For comparison, annual nitrogen loads were 

calculated for nine of the sites (water years 1983-86) 

using regression equations reported by Garrett (1990a 

and b) and a BCF derived from these data. On average, 

nitrogen load increased by about 9 percent when 

retransformation bias correction was used.

Cohn and others (1992) reported that load 

estimates based on log-linear models are fairly 

insensitive to modest violations of regression 

assumptions. When modeling nutrient loads, residuals 

were non-normal in all cases; however, tests of 

residuals did not indicate a lack of fit, and it was 

concluded that log-linear models were useful and 

reasonably accurate. According to Walling and others 

(1992), errors associated with sediment-associated 

constituents, such as total phosphorus and metals, are 

likely to be less than those associated with suspended 

sediment because concentrations of these constituents 

tend to be less variable than suspended-sediment 

concentration. Errors are also likely to be smaller for 

large watersheds than for small watersheds because 

the storm hydrograph for large watersheds is more 

attenuated (Yorke and Ward, 1986; Walling and others, 

1992).

Most suspended-sediment transport takes place 

during a few, large storm events. For example, 57 

percent of the suspended-sediment load for the 1993 

water year at Eno River near Weaver (site 8) was 

transported during 9 days at the beginning of March 

(fig. 13). Likewise, Simmons (1976) estimated that 

more than 44 percent of the annual suspended40 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
22,000

20,000

18,000

16,000 

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12,000

10,000

8,000

6,000

4,000

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SUSPENDED-SEDIMENT LOAD 

DAILY MEAN DISCHARGE

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6,000

5,500

5,000

4,500

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e

u

3,500 g

U

w

O

3,000 «

<

U 

on

5

2,500 <

2,000

1,500

1,000

500

Figure 13. Cumulative suspended-sediment load and daily mean discharge for Eno River near Weaver (fig. 2, site 8), water 

year 1993.

Tributary Loadings to Reservoirs 41
sediment load for Yadkin River at Yadkin College was 

transported during only 9 percent of the 1973 water 

year.

If periodic measurements do not include storm 

event samples, estimates of annual suspendedsediment load can be seriously underestimated. 

Walling and others (1992) reported the significant 

potential for underestimation of loads when 

suspended-sediment sampling frequency decreased 

from weekly to monthly as well as when weekly 

sampling was not supplemented with flood sampling. 

For this study, efforts were made to sample a range of 

discharge conditions including major storm runoff 

events. Long-term flow-duration curves for Eno River 

near Durham and Neuse River at Smithfield 

corresponded closely to flow-duration curves for 

discharges at which samples were collected during this 

study (R.G. Garrett, U.S. Geological Survey, oral 

commun., 1994).

The frequency of discharge data used to 

calculate load affects the accuracy of results. For this 

study, discharges used to compute daily loads were 

based on daily mean discharge record from continuous 

gages.

The proportion of the annual nitrogen and 

phosphorus loads carried during large storm events 

depends, in part, on whether the source is primarily 

from nonpoint or point discharge. For Eno River near 

Weaver (site 8), 25 percent of the annual phosphorus 

load for the 1993 water year was carried during the 

same 9-day period in March that accounted for 57 

percent of the annual suspended-sediment load 

(fig. 13). Eno River near Weaver is downstream from 

the Eno WWTP, but the effluent makes up less than 1 

percent of the average streamflow. The Ellerbe Creek 

site (site 7) is located just downstream from the 

Durham Northside WWTP, which contributes 

approximately 25 percent of the average daily 

streamflow in Ellerbe Creek. At this site, total 

phosphorus concentration decreases with increased 

streamflow (slope = -0.9); thus, very large storm 

events have less effect on total phosphorus load than at 

sites where phosphorus concentration increases with 

increased streamflow.

Largest negative slopes, indicating decreasing 

nitrogen concentration with increasing streamflow, 

for nitrogen-load equations occurred for Knap of 

Reeds (site 10), Ellerbe (site 7), Little Lick (site 6), 

Morgan (site 17), New Hope (site 18), and Northeast 

Creeks (site 19). Largest negative slopes for total

phosphorus occurred at Knap of Reeds, Ellerbe, New 

Hope, and Northeast Creeks (tables S-4 and S-5). All 

are relatively small streams receiving WWTP 

effluents. Greatest positive slopes, indicating 

increasing nutrient concentration with increasing 

streamflow, occurred at headwater sites Little River 

(site 12), Eno River at Hillsborough (site 26), and Flat 

River (site 15) indicating that nonpoint sources are 

important nutrient sources at these sites.

Streamflow Conditions

Streamflow was monitored continuously at most 

sites in the study area. Statistical summaries of 

streamflow data for water years 1989-94 for these sites 

are presented in table 8. Annual loads vary, in large 

part, because annual streamflow varies as climatic 

conditions change. To compare streamflow conditions 

during the study period to normal or average longterm streamflow conditions, streamflow records for 

two sites in the study area were examined (figs. 14 

and 15). Comparison of streamflow for water years 

1988-94 to the long-term average indicates whether 

the annual loads computed for the study period are 

likely to represent long-term average annual loads.

Eno River near Durham (site 9, fig. 14) was 

selected as characteristic of streamflow conditions in 

the upper Neuse River Basin for the study period. 

Streamflow has been monitored continuously at Eno 

River near Durham since 1963. A comparison of 

annual mean streamflow for water years 1989 through 

1994 (table 8) with the mean annual streamflow of 

128 cubic feet per second (ft3/s) for the period of 

record, 1964-94, indicates that 1989 was an unusually 

wet year, 1990 and 1993 were moderately wet, 1991 

was normal, 1994 was dry, and 1992 was an extremely 

dry year (fig. 14). The annual mean discharge of 

87.5 ft3/s for water year 1992 was approximately 32 

percent lower than the long-term average of 128 ft3/s. 

For water year 1989, the annual mean discharge was 

191 ft3/s 50 percent higher than the long-term 

average. The annual mean discharge for the 1990 

water year was about 23 percent greater than the longterm average.

Haw River near Bynum (site 24, fig. 15) was 

selected as characteristic of streamflow conditions in 

the upper Cape Fear River Basin. Streamflow has been 

monitored continuously at this site since 1973. A 

comparison of annual mean streamflow for water 

years 1989 through 1994 (table 8) with the mean

42 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
Table 8. Mean and maximum daily discharges and total annual discharge at selected study sites, water years 

| , no data]

W

Site 

number

(fig. 2)

9

12

15

10

6

17A

18

19

24

Station name 

(basin)

Eno River near Durham 

(Neuse)

Little River at Secondary 

Road 1461 near Orange 

Factory (Neuse)

Flat River at Bahama

(Neuse)

Knap of Reeds Creek near 

Butner

(Neuse)

Little Lick Creek above 

Secondary Road 1814 

near Oak Grove

(Neuse)

Morgan Creek near Chapel 

Hill (Cape Fear)

New Hope Creek near 

Elands 

(Cape Fear)

Northeast Creek at 

Secondary Road 1100 

near Genlee 

(Cape Fear)

Haw River near Bynum 

(Cape Fear)

Discharge (cubic feet per second)

Mean 

Maximum 

Total

Mean 

Maximum 

Total

Mean 

Maximum 

Total

Mean 

Maximum 

Total

Mean 

Maximum 

Total

Mean 

Maximum 

Total

Mean 

Maximum 

Total

Mean 

Maximum 

Total

Mean 

Maximum 

Total

1989

191

3,280 

69,600

105 

2,200 

38,400

209 

4,240 

76,400

78.9 

2,260 

28,800

18.4 

455 

6,700

45.2 

736 

16,500

113 

1,860 

41,400

42 

778 

15,300

1,470 

23,800 

536,000

1990

157 

1,540 

57,400

89 

1,160 

32,500

151 

1,640 

55,100

65.1 

1,260 

23,800

14 

390 

5,090

51.1 

466 

1 8,600

96.6 

869 

35,300

38.3 

560 

14,000

1,490 

16,900 

545,000

1991

1 30 

2,310 

47,600

72.3 

1,700 

26,400

115 

2,990 

41,900

43.4 

1,110 

15,800

9.0

278 

3,270

39.5 

767 

14,400

108 

2,400 

39,500

28.6 

667 

10,500

1,520 

25,200 

554,000

1992

87.5 

4,290 

32,000

46.8 

3,200 

17,100

82.2 

5,940 

30,100

21.4 

988 

7,840

8.4 

539 

3,070

33.9 

861 

12,400

82.3 

1,250 

30,100

27.9 

817 

10,200

903 

18,300 

330,000

1993

1 58 

6,340

57,755

94.8 

5,420 

34,607

1 93 

9,680 

70,505

57.4 

2,920 

20,952

13.2 

651 

4,831

60.6 

1,810 

22,129

115 

2,390 

41,852

33.5 

855 

12,239

1,529 

25,800 

558,104
1989 water year 

1992 water year 

Water years 1964-94

Figure 14. Monthly mean discharge at Eno River near Durham (fig. 2, site 9) for water years 1989 and 1992, and for the 

period of record, 1964-94.

44 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
600

550

500

450

400

Q

O

fei t/3

06 350

£

H

ffl 300

U

z

w

g 250

3C 

U

200

150

100

50

Explanation

1991 water year

1992 water year 

Water years 1973-94

O N D F M A M J J

Figure 15. Monthly mean discharge at Haw River near Bynum (fig. 2, site 24) for water years 1991 and 1992, and for the period of 

record, 1973-94.

Streamflow Conditions 45
annual streamflow of 1,300 ft3/s for the period of 

record, 1973-94, indicates that 1994 was a dry year 

and 1992 was an extremely dry year in the Cape Fear 

River Basin (fig. 15). The annual mean discharge of 

903 ft3/s in 1992 was about 30 percent lower than the 

long-term average of 1,300 ft3/s. Flow during the other 

years of study exceeded the long-term average by 13 

to 17 percent. Annual total discharges in water years 

1989-91 and 1993 were nearly equal (table 8). 

Greatest total discharge occurred in 1993 and least 

total discharge occurred in 1992.

Suspended Sediment

Suspended-sediment loads were computed for 

each monitored reservoir tributary and outflow in the 

study area for water years 1989 through 1994. 

Suspended-sediment loads from unmonitored areas of 

the reservoir basins were estimated based on the yield 

from the monitored areas of the reservoir basins.

During 1989-94, annual suspended-sediment 

load into Falls Lake ranged from 29,500 to 

88,200 tons (table 9). Because Lake Michie trapped 

from 83 to 93 percent of the suspended sediment 

delivered by Flat River, Flat River is a minor 

contributor of suspended sediment to Falls 

Lake only 22,600 tons from 1989-94. Little River 

Reservoir, too, probably traps much of the suspended 

sediment delivered by Little River; however, the 

amount was not measured because Little River was not 

monitored below the Little River Reservoir. Little 

River above the Little River Reservoir, the third largest 

tributary to Falls Lake, transported 86,400 tons of 

suspended sediment to Little River Reservoir from the 

1989 water year through the 1994 water year. Based 

on estimates of trapping efficiency for Falls Lake and 

other lakes that have residence times similar to Little 

River Reservoir (Simmons, 1993), it was estimated 

that Little River Reservoir traps 85 percent of the 

suspended sediment delivered. By that estimate, 

14,900 tons of suspended sediment were delivered to 

Falls Lake from Little River Reservoir. The 

unmonitored portion of the Falls Lake Basin 

transported the largest suspended-sediment load to 

Falls Lake 118,000 tons from 1989 through 1994. 

The smallest load (12,300 tons) was contributed by 

Little Lick Creek from 1989 through 1994. Little Lick 

Creek was also the smallest tributary monitored.

By normalizing suspended-sediment load to 

drainage area, transport is expressed as a yield in tons

per square mile of drainage area. While load tends to 

be directly related to drainage basin size, yield tends to 

be inversely related to drainage basin size (Simmons, 

1993). Simmons (1993) reported suspended-sediment 

yields of 41 to 47 tons/yr for two undisturbed forested 

basins in the Piedmont Province of North Carolina.

Yields from Little River, Little Lick Creek, and 

Flat River above Lake Michie (site 15) were 

similar between 184 and 223 tons/mi 2 (table 10). 

Suspended-sediment loads appear to have increased 

slightly compared to yields of 140 and 190 tons/mi2 

reported for Little River and Flat River by Simmons 

(1993) since the period 1970-79. The yield for Eno 

River near Weaver (site 8) was 95 tons/mi 2 , about 

60 percent of that reported for 1970-79 by Simmons 

(1993). Ellerbe Creek had an average yield of 

347 tons/mi 2 for water years 1989 and 1992-94 

(table 10).

A summary of suspended-sediment load and 

yield data for Falls Lake and its tributaries for 1989 

and 1992 is shown in figure 16. The 1989 and 1992 

water years represent extreme years (wet and dry) and 

illustrate sediment loads in a range of hydrologic 

conditions. Ellerbe Creek had the highest yield of any 

Falls Lake tributary during the wet year and was 

among the highest in 1992, a dry year. Ellerbe Creek 

receives effluent from the Durham Northside WWTP 

that, during this study, comprised about 25 percent of 

the average daily streamflow. The yield estimate for 

Ellerbe Creek is based on incomplete data for 1989 

and 1994 due to missing discharge record for the 

period June 1989 through September 1991 and June 

through August 1994. Based on comparison with other 

sites, the incomplete record could account for a 15- to 

20-percent overestimate of load over the entire period 

of study because 1989 and 1993 were unusually wet 

years.

The smallest suspended-sediment yield for the 

1989-94 water years was for the Flat River Basin 

downstream from the Lake Michie dam (site 14) 

(22 tons/mi2 , table 10) as a result of sediment trapping 

in Lake Michie. An average of about 37,500 tons of 

suspended sediment was delivered to Lake Michie 

each year during the 1989-94 water years. Lake 

Michie trapped from 83 to 93 percent of the sediment 

load from the Flat River Basin upstream from Lake 

Michie (table 9). Weaver (1994) estimated, for the 

period 1983-91, that 89 percent of an average 34,600 

tons of suspended sediment delivered to Lake Michie

46 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
Table 9. Annual suspended-sediment loads into Falls Lake, Lake Michie, and Little River Reservoir, and out of Lake 

Michie and Little River Reservoir in the upper Neuse River Basin, water years 1989-94

[Sites are shown in figure 2. , no data]

Station name

or

location

Sediment load, in tons per year

(percent of total

1989 1990 1991

inflow load)

1992 1993 1994

Total

load

1989-94

Mean

annual

load

Falls Lake

Eno River near Weaver

(site 8)

Little River Reservoir

outflow

Flat River at Dam near

Bahama (site 14)

Knap of Reeds Creek near

Butner (site 10)

Ellerbe Creek near German

(site 7)

Little Lick Creek above

Secondary Road 1814 near

Oak Grove (site 6)

Ungaged drainage area of

Falls Lake

Total inflow to Falls Lake

21,400

(23)

4,550

(5)

5,650

(6)

8,780

(10)

12,500b

(14)

3,050

(4)

32,300

(37)

88,200

12,200

(28)

1,860

(4)

4,010

(9)

6,620

(15)

2,090

(5)

17,500

(40)

44,200

10,600

(31)

2,040

(6)

2,790

(8)

4,240

(12)

1,280

(4)

13,700

(40)

34,600

8,080

(27)

2,060

(7)

2,100a

(7)

1,980

(7)

3,100

(10)

1,370

(5)

10,800

(37)

29,500

20,700

(26)

4,440

(6)

4,900a

(6)

7,200

(9)

9,690

(12)

3,120

(4)

28,900

(37)

79,000

11,300

(28)

1,230

(3)

3,100a

(8)

3,030

(8)

5,100C

(13)

1,420

(4)

14,500

(37)

39,700

84,300

16,200

22,600

31,800

12,300

118,000

315,000

14,000

2,700

3,760

5,310

7,600

2,060

19,600

52,500

Lake Michie

Flat River at Bahama

(site 15)

Ungaged drainage area of

Lake Michie

Total inflow to Lake Michie

Flat River at Dam near

Bahama, Lake Michie

outflow (site 14)

48,900

(89)

6,200

(11)

55,100

5,650

(10)

20,600

(89)

2,630

(11)

23,200

4,010

(17)

20,300

(89)

2,590

(ID

22,900

2,790

(12)

19,900

(89)

2,540

(11)

22,400

2,100a

(9)

64,200

(89)

8,190

(11)

72,400

4,900a

(7)

25,400

(89)

3,240

(11)

28,600

3,100a

(ID

199,000

25,400

225,000

22,600

33,200

4,240

37,500

3,760

Little River Reservoir

Little River at Secondary

Road 1461 near Orange

Factory (site 12)

Ungaged drainage area of

Little River Reservoir

Total inflow to Little River

Reservoir

Little River Reservoir

outflowd

24,300

(80)

6,060

(20)

30,400

4,550

(15)

9,890

(80)

2,470

(20)

12,400

1,850

(15)

10,900

(80)

2,720

(20)

13,600

2,040

(15)

11,000

(80)

2,740

(20)

13,700

2,060

(15)

23,700

(80)

5,910

(20)

29,600

4,440

(15)

6,560

(80)

1,640

(20)

8,200

1,230

(15)

86,400

21,500

108,000

14,900

14,400

3,590

18,000

2,490

aEstimate based on average annual tons per total discharge for 1989-91. 

bLast 5 months of year was estimated based on comparisons with flow at Little Lick Creek. 

cJune, July, and August estimated based on comparisons with flow at Little Lick Creek. 

Estimate assumes a retention in the reservoir of 85 percent of the suspended sediment.

Suspended Sediment 47
Table 10. Suspended-sediment, total nitrogen, and total phosphorus yields for monitoring sites in the upper Neuse 

River Basin

[Sites are shown in figure 2. Years are water years. , no data]

Station name

or 

location

Drainage 

area

(square 

miles) 1970-793

Average annual yield (tons per square mile)

Sediment Nitrogen Phosphorus

1989-94 1983-86b 1989-94 1983-86b 1989-94

Eno River near Weaver (site 8)

Little River at Secondary Road 

1461 near Orange Factory 

(site 12)

Flat River at Bahama (site 15)

Flat River at Dam near 

Bahama, Lake Michie outflow (site 14)

Knap of Reeds Creek near 

Butner(site 10)

Ellerbe Creek near Gorman 

(site 7)

Little Lick Creek above 

Secondary Road 1814 near 

Oak Grove (site 6)

Neuse River near Falls, Falls 

Lake outflow (site 1)

160

140

190

148

78.2

149

168 

43 

21.9 

10.1 

771 

95

184

223

22

123

347a 

204

1.2 1.2

1.4 1.0

- 1.0

1.0 1.1

2.1

13

2.2

12C

2.3 3.5

1.1 .58

0.20 

.10

.05

.50

.50

.05

0.11 

.10

.09 

.06

.53

.47C

.28

.04

aFromSimmons(1993).

bFromGarrett(1990b).

cYield is based on partial record of discharge in 1989 and 1994, and complete record of discharge in 1992 and 1993.

48 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
each year was trapped. Weaver used the loadestimation techniques described in Simmons (1993). 

Annual sediment loads to Jordan Lake ranged 

from about 271,000 tons in 1992 to 622,000 tons in 

1993 (table 11). The Haw River contributed more than 

75 percent of the sediment load to Jordan Lake. 

Northeast and New Hope Creeks each contributed less 

than 5 percent. The contribution of each subbasin in 

the upper Cape Fear River Basin is illustrated in 

figure 17 for wet (1989) and dry (1992) years. The 

amount of sediment trapped in Jordan Lake could not 

be calculated because suspended sediment was not 

monitored below the dam. Annual sediment loads to 

the two smaller reservoirs in the upper Cape Fear 

River Basin (University Lake and Cane Creek

Reservoir) averaged about 1,560 and 2,420 tons, 

respectively (table 11). The trapping efficiency of 

these reservoirs was not determined because discharge 

out of these reservoirs was not monitored.

The average annual yields for Northeast Creek 

and Haw River were similar (252 and 284 tons/mi2, 

respectively) despite the large difference in the size of 

the drainage areas of the two basins (table 12). In this 

study, sediment yield for the Haw River was more than 

twice the 140 tons/yr for the Haw River reported by 

Simmons (1993) for the period 1970-79. The average 

annual yield for the Morgan Creek Basin (site 29) 

upstream from University Lake was 52 tons/mi2 . The 

average annual yield for the Cane Creek Basin 

upstream from site 27 was 77 tons/mi2 . Simmons

Table 11 . Estimates of annual suspended-sediment loads into Jordan Lake, University Lake, and Cane Creek Reservoir in the 

upper Cape Fear River Basin, water years 1989-94

[Sites are shown in figure 2. , no data]

Station name 

or 

location

Sediment ioad, in tons per year 

(percent of totai infiow ioad)

1989 1990 1991 1992 1993

Totai ioad

"IQfiQ Q/l

1994

Mean 

annuai 

ioad

Jordan Lake Inflows

New Hope Creek near Elands 

(site 18)

Northeast Creek at Secondary 

RoadllOOnearGenlee 

(site 19)

Haw River near Bynum 

(site 24)

Ungaged drainage area of 

Jordan Lake

Total inflow to Jordan Lake

Morgan Creek near White 

Cross (site 29)

Ungaged drainage area of University Lake

Total inflow to University Lake

15,400 

(3)

7,980 

(2)

406,000 

(77)

99,200 

(19)

529,000

803 

(28)

2,060 

(72)

2,870

11,300 

(2)

6,720 

(1)

377,000 

(78)

91,300 

(19)

486,000

487 

(28)

1,250 

(72)

1,740

15,800 

(3)

4,630 

(1)

425,000 

(78)

103,000 

(19)

548,000

University Lake 

319 

(28)

820 

(72)

1,140

Cane Creek Reservoi

Cane Creek near Orange Grove 

(site 27)

Ungaged drainage area of Cane 

Creek Reservoir

Total inflow to Cane Creek 

Reservoir

1.030 

(24)

3,280 

(76)

4.310

343 

(24)

1,090 

(76)

1,440

599

(24)

1,910 

(76)

2.510

9,640 

(4)

4,790 

(2)

206,000 

(76)

50,900 

(19)

271,000

-Inflows

215 

(28)

553 

(72)

768

r Inflows

356 

(24)

1,130 

(76)

1.490

18,800 

(3)

7,810 

(1)

479,000 

(77)

117.000 

(19)

622,000

522 

(28)

1,340 

(72)

1,860

691

(24)

2,200 

(76)

2.890

8,890 79,800 

(2)

 

280,000 2,170,000 

(78)

72,300 533,000 

(20)

361,000 2,820,000

274 2,620 

(28)

705 6,740 

(72)

979 9,360

450 3,470 

(24)

1,430 11,100 

(76)

1.880 14,500

13,300

5,320

362,000

88,900

470,000

437

1,120

1,560

578

1,840

2,420

Suspended Sediment 49
B.

36°15'

78°30

0 2 4 6 8 10 KILOMETERS

Explanation

--- Basin boundary

- - Subbasin boundary 

37 Site number

Sediment yield, in tons 

per square mile

no data

<100

101-300

301-500

>500 

Sediment load, in tons

no data

<10,000

10,001-50,000

50,001-100,000 

100,001-200,000

>200,000

Figure 16. Estimated suspended-sediment yield and load in selected tributaries to Falls Lake, Lake Michie, and Little River 

Reservoir, (A) 1989 and (B) 1992.

50 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
79°45'

A.

80 79°15'

B.

Explanation

_.. _ Basin

boundary

 Subbasin 

boundary

27 Site number

Sediment yield, in tons Sediment load, in tons

per square mile Q no data

__ no data < 10,000

I I <100 O 10,001-50,000

101-300 50,001-100,000

301-500 §) 100,001-200.000

>500 <m >200.000

r

36 15

so- ,r-'_:

0 2 4 6 8 10 MILES 

0 2 4 6 8 10 KILOMETERS

J;

Figure 17. Estimated suspended-sediment yield and load to Cane Creek Reservoir, Jordan Lake, and University Lake, (A) 1989 

and (B) 1992.

Suspended Sediment 51
Table 12. Suspended-sediment, total nitrogen, and total phosphorus yields for monitoring sites in the upper 

Cape Fear River Basin

[ , no data; years are water years]

Site 

number

(«g.

2)

27

29

17

18

19

24

25

Station name

Cane Creek near Orange

Grove

Morgan Creek near

White Cross

Morgan Creek near

Farrington

New Hope Creek near

Elands

Northeast Creek at Secondary Road 1100

near Genlee

Haw River near Bynum

Haw River below B.

Everett Jordan Dam

near Moncure

Drainage 

area 

(square 

miles)

7.5

8.4

45.6

75.9

21.1

1,275

1,689

Average annual yield (tons per square mile)

Sediment Nitrogen Phosphorus

1970-79" 1989-94 1983-86b 1989-94 1983-86b 1989-94

47C 77 1.5 0.19

 52 1.6 .26

 5.8 2.4 1.4 .27

 175 3.7 4.0 .60 .34

 252 4.3 5.3 1.0 .45

140 284 2.2 2.0 .40 .35

 1.5 1.3 .20 .15

"From Simmons (1993). 

bFrom Garrett (1990a). 

cCane Creek headwaters

52 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
(1993) reported a yield of 47 tons/mi2 for 1.1 mi2 of 

undisturbed forest in the headwaters of Cane Creek for 

the period 1970-79. Agricultural activities in the Cane 

Creek Basin between the headwaters and site 27 

probably account for the increased yield.

Yields from the basins upstream from the 

University and Cane Creek Reservoirs were the lowest 

in the study area (with the exception of sites 

downstream from dams). Continued low sediment 

yields in these basins should extend the life of these 

reservoirs in terms of both capacity and quality.

Nitrogen and Phosphorus

Annual loads of nitrogen and phosphorus were 

calculated using regression equations of log 

instantaneous concentration and log instantaneous 

discharge (tables S-3 and S-4) and daily mean 

discharges for each gaged tributary. Nitrogen loads 

were generally an order of magnitude greater than 

phosphorus loads.

Annual nitrogen loads to Falls Lake ranged 

from 780 tons in 1991 to 1,650 tons in 1989 (table 13). 

The Eno (site 8) and Flat River (site 14) Basins 

contributed similar nitrogen loads to Falls Lake most 

years (table 13). Ellerbe Creek Basin contributed 

about 50 percent more nitrogen than Eno or Flat 

Rivers, except in the wettest year (1989) when the load 

was similar to Eno and Flat Rivers (table 13; fig. 18). 

This is likely because most of the nitrogen load to 

Ellerbe Creek is from the Durham Northside WWTP 

that sustains fairly steady flows even in dry years.

Nitrogen loads out of Falls Lake (site 1), an 

average of 448 tons/yr, accounted for 20 (1992) to 56 

(1990) percent of the annual load into the lake. 

Nitrogen yields out of Falls Lake declined from 

1.1 ton/mi2 (1983-86) to 0.58 ton/mi2 (1989-94; 

table 10). However, average annual yields for most 

Falls Lake tributaries were similar to those reported by 

Garrett (1990b) for water years 1983 through 1986 

(table 10). Little Lick Creek had the only substantial 

increase in yield (from 2.3 to 3.5 tons/mi2). Ellerbe 

Creek had the greatest average annual nitrogen yield 

of the Falls Lake tributaries during the 1983-86 period 

(13 tons/mi2) and during 1989-94 (12 tons/mi2, 

table 10). Urban runoff from the city of Durham has a 

direct affect on the water quality of Ellerbe Creek 

(North Carolina Department of Environment, Health,

and Natural Resources, 1993), and effluent from the 

Durham Northside WWTP is also a contributor.

Nitrogen loads into Lake Michie (1,010 for 

1989-94) were similar to nitrogen loads out of the lake 

(1,130 for 1989-94; site 14). This may result from 

underestimation of load from ungaged areas of the 

basin including Dial Creek which receives drainage 

from agricultural runoff (Weaver 1994) and because 

atmospheric inputs of nitrogen were not included. 

Another factor may be the relatively short hydraulic 

retention time of Lake Michie about 45 days that 

limits nitrogen removal. Annual nitrogen inflows 

varied from 94 tons in the driest water year (1992) to 

248 tons in the wettest water years (1989 and 1993). 

The nitrogen yield for Flat River (site 15) was 

1.0 tons/mi2 during 1989-94. No data are available for 

1983-86. Below the Lake Michie dam, yields were 

similar for 1983-86 and 1989-94 water years, 1.0 and 

1.1 tons/mi2, respectively.

Annual nitrogen loads to Little River Reservoir 

ranged from 55 tons in 1992 to 137 tons in 1989. The 

nitrogen load out of Little River Reservoir was not 

monitored. However, Little River Reservoir has a 

retention time similar to that of Falls Lake (table 2), 

and retention time is a factor affecting the extent to 

which chemical and biological processes remove 

nitrogen from the system. A nitrogen retention rate of 

50 percent was estimated for Little River Reservoir 

based on comparison with Falls Lake data. The 

nitrogen yield for Little River (site 12) was 1.0 

tons/mi2 during 1989-94 compared to 1.4 tons/mi2 

during 1983-86.

In the upper Cape Fear River Basin, the annual 

nitrogen load out of Jordan Lake was about 57 percent 

of the load into the lake. Nitrogen load to Jordan Lake 

ranged from 2,710 tons in 1992 to 4,410 tons in 1993 

(table 14). Haw River contributed most of the annual 

nitrogen load to Jordan Lake (about 70 percent; 

fig. 19). Even though Haw River contributes a major 

share of the load, New Hope and Northeast Creeks 

produced greater yields at least double that of Haw 

River (table 12) and similar to yields produced by 

Ellerbe and Little Lick Creeks, which also receive 

WWTP effluent (fig. 19). For Morgan Creek (site 17), 

average annual nitrogen yields (2.4 tons/mi2) 

decreased by 65 percent from the 1983-86 estimate of 

5.8 tons/mi2 (Garrett, 1990a). Nitrogen yield increased 

by 25 percent from 4.3 to 5.3 tons/mi2 compared to the 

1983-86 period for Northeast Creek.

Nitrogen and Phosphorus 53
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%_^ %_^ %_^ X -

^^ ^^2 (N°°^PS c ^^ ^ v

 - -. - - - v 

»nr--oo 1/1^ VI r-~oo 

oo^oo a>r--ro mr-- 1^ 

» i , < CM ^J- ' ' r;

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i < oo ro vo » 'cs m . i f\J ^H to fSJ vO ^D

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s- , y , y 

5^ ^S^S ^S*^:^ ^S S^" S

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S^ Ss ^2 SS 2s §5 g P §

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^J >-^ OO ^T> ^ ^^ O ^T" *3" r^ ^~~ Zr? ^ .O ^ ^

fSjC*) CN^* vi' ' v^)*O v^jOu CN^1 ^"^^ Vi C 

"C- ^Sd- ^CNCS ^^ rO<2Ch'-

°cs1 "<o' o oo' rri fT 1 °° ^ oog-oc

 CJ,'*~' C ^ C- ^^ mS^^

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» iO ^j vi ^H O cN^ ro 1^" ^-,0^-0

fS Ci f^ Ci '~H CT- ^ ^", O >/

'~H

vo^ vo S ££ cst^ g^ ^. C og ^ c

C

J3 Co *o ^ [1

> 'K (U .^ ^ 2 » i "Jfl »-< "7

S > ^§^^^ -° "S -a ^^ ^y

t^ <U C(U, i^jC5 <L)^~~*^O^ ^ LL !

r3 ^ OCd*1^ ^<D ^-£j OP^^H JJ Q '

« & ~ J -5 "S - -^ S u b "3 s t; > C »_ ed » - ' Qit« o 3*^ i»* s i

1? 11 |ll ?! §1 Sl« 13 1 i

C*- <u g O^rt-g 0,3 -go <u 8 ! «13 - E 

O^ "O JJPQo "'PQ S(5 ~^c M tS S ;

wSE wSS ;Dt22

^ 

1

H ' " * 

H ^T

-1 ^"

f\J^~~

 ON

CO^

1 °^

" '

0

2 ' - 

N C5 H Ci

3 ^

^ ^

i 3-

3 ^^

 ^ *O

-. ^^

n

3

Lake outflow (site 1)

54 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
Table 13. Annual nutrient loads into and out of Falls Lake, Lake Michie, and Little River Reservoir, water years 1989-94 (Continued)

[Sites are shown in figure 2. , no data]

Nitrogen load, in tons 

(percent of total inflow load)

or 

location 1989 1990 1991 1992 1993 1994 T

Mean 

for 

1989- 

94

1989 1990

Phosphorus load, in tons 

(percent of total inflow load)

1991 1992 1993

Mean

1994 1989' for 1994 94 1989-

94

Lake Michie

Flat River at Bahama 220 140 1 10 83

(site 15) (89) (89) (89) (89)

Ungaged drainage area of 28 18 14 11

Lake Michie (11) (11) (11) (11)

Total inflow to Lake Michie 248 158 124 94Flat River at Dam near 270 210 140 105a

Bahama, Lake Michie (109) (133) (113) (112)outflow (site 14)

220 120

(89) (89)

28 15

(11) (11)

248 135

250a 156a

(101) (115)

893

114

1,0101,130

149

19

168

188

21

(89)

3

(11)

24

15

(63)

13

(89)

2

(11)

1511

(75)

10

(89)

1

(11)

11

8

(71)

8

(89)

1

(11)

9

6a

(67)

21

(89)

3

(11)

24

13a

(55)

11

(89)

1

(11)

12

8a

(64)

84 14

11 1.8

95 1661 10

Little River Reservoir

zjj*n301

E. a

I

o(A

Little River at Secondary 1 10 79 66 44

Road 1461 near Orange (80) (80) (80) (80)Factory (site 12)

Ungaged drainage area of 27 20 16 11

Little River Reservoir (20) (20) (20) (20)

Total inflow to Little River 137 99 82 55

Reservoir

Estimated Little River 69 99 83 55

Reservoir outflow (50) (50) (50) (50)

aEstimate based on average annual tons per total discharge for 1989-91bBecause discharge data are missing for the 1990 and 1991 water years

105 49

(80) (80)

26 12

(20) (20)

131 61

132 61

(50) (50)

453

113

566

283

76

19

94

47

11

(80)

3

(20)

14

7

(50)

, loads from Ellerbe Creek were included in the ungaj

8

(80)

2

(20)

10

5

(50)

7

(80)

2

(20)

9

4

(50)

4

(80)

1

(20)

5

2

(50)

11

(80)

3

(20)

14

7

(50)

5

(80)

1

(20)

63

(50)

46 7.7

12 1.9

58 9.6

29 48

*ed area for those water years.

°Last 5 months of year was estimated based on comparisons of flow at Little Lick Creek.

dJune, July, and August estimated based on comparison with flow at Little Lick Creek.

en en
A.

B.

s

36°15' $"""" >

O^i *^X~J~'X 

< V. .^ ^ 5

78 °30'

0 2 4 6 8 10 KILOMETERS

36 "15

\ '~X 78°45'

Explanation 

 -- Basin boundary

- - Subbasin boundary 

37 Site number

Nitrogen yield, in tons 

per square mile 

no data

<2

2 to 2.9

3 to 5.9 

>6

Nitrogen load, in tons 

O no data

<50

Q 50-149 

 150-499 

>500

78°3I)'

V-,

Figure 18. Estimated nitrogen yield and load in selected tributaries to Falls Lake, Lake Michie, and Little River Reservoir, and 

outflow of nitrogen load from Lake Michie and Falls Lake, (A) 1989 and (B) 1992.

56 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
A.

36°15

so

Explanation

 Basin

boundary

- - Subbasin 

boundary

27 Site number

Nitrogen yield, in tons Nitrogen load, in tons

per square mile Q no data

no data 0 <50

<2 O 50-149

2-2.9 150-499

3-5.9 © >500 

>6

79 45

79 °'

0 2 4 6 8 10 MILES

I i'i i 1 i '| ' '

0 2 4 6 8 10 KILOMETERS

Figure 19. Estimated nitrogen yield and load to Cane Creek Reservoir, Jordan Lake, and University Lake, and outflow of nitrogen 

load from Jordan Lake, (A) 1989 and (B) 1992.

Nitrogen and Phosphorus 57
?

en

00

en

0)

CO

CD

£

CO

'o

2

CD

0)

sf

c |

ro" I

 ]5

M 0

s * IB

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A00 ^

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en 

en

CO

S

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en

,_

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enT~

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en 

en

f200

en*""

CD

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CD

CD

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CO

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T3

C

CO

5

CO

CD

"c>

^)CD"

.3

CO 

-30

"o

0

T3

C

CO

o

c

0) , "O ^

§

ed 0

Table 14.Annual nutrient I

shown infigure 2. [Sites noare , 

_

~ |c

CO TH -SB

§5S c

* 0) 2 a

s

{5 ,_ en ^

5 *" ?

ft*

en en

en 

en

S

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en 

en

en 

en

o

en

00

en

Station name

or location

S

B

Q

fN SD "* O in O O

 i tN Q^ -^ os oo m

"3- m o os o O

tN en ~-"

-SSS SgRgP§|

^ £ <N 5 ^ Q en ^ ^ O ^ S

^^ CN Si ^D ^^ CN ^"^ ^" 10 ^D ^^ wn OO ^" ' ^" <^ C; o ^ C

-fJSD-OO- OpfN-t-0-

S^- ^" s_^ ^--

^^ CN ivi ^" ^"^ CN o\ VO ^^ ViO ,fi M^ c*^

~~" ' ^ ^ C^ C- ^> <^ S

tN ^j r~ q> o ^j 03 ^ o o^

^^ *~s ^^

O SD fN O fN O O

« O ' O O " O

tN <-n <N"

en O O O O O O 

so oo in >o so m fN

^ in" en r4 en"

^^tN^^ C^ in ^, ON r- !£} 

CN" tN «

gg gg Rg go g§ 2 |§

rrT " ' " ' ^l" r*^ ""^ ^

S^J-ooO o^ 8[^ en ^ o£? <NO °°^S ^ O ^ <yl^

 T ^ ^-'

O 1'! O 1^" O 1'! O^^ «T)^ in O^l" 

^^<N c^^^^-r-i ^C^^^-^e^i ^

"^ ^^ r4 -^f CM

CN £2- '""' C^ CN^3 ^ ' ^^ ^- 0°°

CN Tfr~ CN

 ^ cn^" s ' °o ^ ^OC- o^ ^ ^

CN" en' CN"

^

1 1 |« * -s -3 S.

r? 1 §S 1 S cE"3 

fc S MO = a Jr? 

« c Sfe m o "S°§K 

c "o JiS ra1 ^^"H<N 

^ gj Q 1 rt coo o^J

^Sg-2S-2| ^c|^|V 

S Z Z ffi D f2 jc

1

1

.i

5

fN SD rCN in r~

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tN r-

 So ^R ^

CN rOO CN CN rr<i g^ in ^ r-

^-^ ^^

OO CN ' -

Ci Ei

fr> 00 X fN~ ""

tN r^ "

 en -^t

en en SD

00 OS 

fN fN

~~* fN r- cn

-S -P °

N ' " '

°"g Sp en

fN -^ ' ' ^ en 

_ oo m fN S

CJ C^

2 00 2 fN" 5g CN r^

2 I ^g s

w: <L)

Creek Morgan White Cronear 

(site 29)

drainage of Ungaged area 

University Lake

Total inflow University Lak to 

1

&

CU

£

u

I

Tt V) O*N

-^ ^" </S

oo r^- vo

CN r^

-g-|-

cN ^T- 10 /^v VD

Ci C^

^ ^" ^D ^^ Ci C^

IN^ SO ^ 00

^-^ ^-^

^" ^D ^^ CN rCN^ VO^ 00

s^- s^-

^H IT) \O

 -( cn ^f

VO C^ VO 

CN CN

O\ CP ^ \r^ °°

CN ^T' oo -" O

" ^ N '

r^ o- CN ^ ^

2g ^| 8

= g ^g ^

en ^ ^- ^p ^t ~S ^§ ">

O 5J

Orange Grov Canereek near

27) (site 

of drainage Can Ungaged area 

Creek Reservoir

Total inflow Canereek to

Reservoir

58 Water and Bed-Material Quality of Selected Streams and Reservoirs In the Research Triangle Area of North Carolina, 1988-94
Annual nitrogen loads to University Lake and 

Cane Creek Reservoir averaged 49 and 46 tons, 

respectively. Nitrogen yields were 1.6 tons/mi2 for 

Morgan Creek and 1.5 tons/mi2 for Cane Creek above 

their reservoirs. These were the lowest yields 

measured for sites unaffected by reservoirs (fig. 19).

Annual phosphorus loads to Falls Lake averaged 

about 103 tons for the 6-year study period (table 13). 

Phosphorus loads and yield were less in 1992, a dry 

year, than in 1989, a wet year; however, the relative 

contributions from each tributary remained about the 

same (fig. 20). Knap of Reeds Creek averaged 23 

tons/yr (1989-94). which was the greatest phosphorus 

contribution of the gaged basins (table 13). Knap of 

Reeds Creek also had the greatest yield (0.53 tons/mi2) 

among gaged basins tributary to Falls Lake (table 10). 

The yield from Knap of Reeds Creek was essentially 

unchanged from the 1983-86 period whereas annual 

phosphorus yields declined by nearly half at Little 

Lick Creek (site 6) and Eno River (site 8) from the 

1983-87 period and declined by 83 percent at Ellerbe 

Creek (site 7). Declines in phosphorus yields at Little 

Lick Creek. Ellerbe Creek, and Eno River (site 8) are 

probably due to improvement in phosphorus removal 

from wastewater effluents by WWTP's and to the 

phosphate-detergent ban that became law in January 

1988. In 1994, the Little Lick Creek and Eno River 

WWTP's were closed and effluents re-routed to the 

Durham Northside WWTP on Ellerbe Creek.

Annual phosphorus loads from Falls Lake 

averaged 28 percent of the load into the lake, and 

ranged from 14 percent in water year 1992 to 39 

percent in water year 1990. Phosphorus loads from 

Falls Lake reported by Garrett ranged from 11 percent 

(1985) to 21 percent (1984) of phosphorus load into 

the lake.

Phosphorus loads to Lake Michie ranged from 

9 tons in 1992 to 24 tons in 1989 and 1993. 

Phosphorus loads out of the reservoir ranged from 55 

percent to 75 percent of the phosphorus load into the 

lake (table 13). The average annual phosphorus yield 

in Flat River Basin (site 15), which feeds Lake Michie, 

for 1989-94 was 0.09 tons/mi2 (table 10). The yield 

was 0.06 below Lake Michie (site 14) because of 

deposition in the lake.

Phosphorus loads to Little River Reservoir 

ranged from 5 tons in water year 1992 to 14 tons in 

water years 1989 and 1993. Phosphorus loads out of 

the reservoir were not measured but were estimated to 

be 50 percent of inflow loads based on comparison

with Falls Lake which has a similar retention time 

(table 2). The phosphorus yield of Little River Basin 

was similar to Flat River, 0.10 tons/mi2.

Annual phosphorus loads to Jordan Lake ranged 

from 418 tons in 1992 to 701 tons in 1993 (table 14). 

Haw River accounted for about 75 percent of the 

phosphorus load to Jordan Lake. Phosphorus load out 

of Jordan Lake accounted for about 40 percent of the 

inflow load compared to 28 percent for Falls Lake. 

The smaller percentage of material trapped by Jordan 

Lake is probably due, in part, to the unusual 

morphometry of Jordan Lake. Most of the load to 

Jordan Lake is from the Haw River (fig. 21); water to 

the Haw River arm of the lake has a relatively short 

retention time in the reservoir. Yields of Jordan Lake 

tributaries ranged from 0.15 to 0.45 tons/mi2 for the 

study period (table 12). Average annual phosphorus 

yields declined at every site compared to yields for 

1983-86 (table 12). The greatest decline (81 percent) 

was recorded at Morgan Creek (site 17). Large 

declines in phosphorus yield also were observed for 

New Hope and Northeast Creeks also located below 

WWTP's. These declines are probably due to 

improved phosphorus removal and the phosphatedetergent ban.

Average annual phosphorus load to University 

Lake was 8 tons and to Cane Creek Reservoir was 

6 tons (1989-94). Average annual phosphorus yield 

was 0.26 tons/mi2 for Morgan Creek and 0.19 tons/mi2 

for Cane Creek.

Lead and Zinc

Lead and zinc loads were calculated from 

regression equations of log instantaneous 

concentration and log instantaneous discharge 

(table S-5). For some sites, there was no relation 

between concentration and discharge, and load was 

calculated from median concentration. For other sites, 

an insufficient number of concentrations were 

measured above the laboratory's detection limit, and 

load could not be calculated. Lead and zinc loads 

could not be calculated for all the necessary sites 

required to develop a trace element water budget for 

every reservoir. Regression analyses for calculating 

lead and zinc concentrations from discharge produced 

R2 values ranging from 0.02 to 0.69 (table S-5).

Average annual lead loads to Falls Lake from 

tributaries in the upper Neuse River Basin ranged from

Lead and Zinc 59
B.

s*

36°15'-

\

1

Vfrcr V'" ^L, ^' H 

/V-rf/ V^r^ ,- T", ^ T ^ \ v, >

0 2 4 6 8 10 KILOMETERS

Explanation

 - - Basin boundary 

- - Subbasin boundary

37 Site number

	Phosphorus yield, in tons 

__ per square mile 

l i no data 

I I <0.10 

I I 0.10-0.19 

I I 0.20-0.39 

E^3 > 0.40

Phosphorus load, in tons 

O no data 

 <5 

O 5-19

20-99

>100

/

y

Figure 20. Estimated phosphorus yield and load in selected tributaries to Falls Lake, Lake Michie, and Little River Reservoir, and 

outflow of phosphorus load from Falls Lake and Lake Michie, (A) 1989 and (B) 1992.

60 Water and Bed-Material Quality of Selected Streams and Reservoirs In the Research Triangle Area of North Carolina, 1988-94
A.

B.

Explanation

 --- Basin

boundary

 Subbasin 

boundary

27 Site number

Phosphorus yield, in tons Phosphorus load, in tons 35 °45'- 

per square mile Q no data

no data < 5

<0.10 O 5-19

0.10-0.19 20-99

0.20-0.39 © >100

> 0.40

79 45'

0 2 4 6 8 10 MILES

Figure 21 . Estimated phosphorus yield and load to Cane Creek Reservoir, Jordan Lake, and University Lake, and outflow of 

phosphorus load from Jordan Lake, (A) 1989 and (B) 1992.

Lead and Zinc 61
363 pounds (Ibs) from Little Lick Creek (site 6) to 

2,300 Ibs from Ellerbe Creek (table 15). Lead loads 

out of Falls Lake ranged from 4,070 Ibs in 1992 to 

20,000 Ibs in 1989 (table 15, fig. 22). Estimated total 

loads of lead into Falls Lake ranged from 5,860 Ibs in 

1992 to 15,500 Ibs in 1989; that is, about 70 (1992) to 

186 (1990) percent of inflows. The reservoir probably 

acts as a sink for lead; years with loads from the lake 

exceeding loads to the lake likely indicate an 

underestimation of input. Discharge data for Ellerbe 

Creek were unavailable for 1990 and 1991 and that 

area was included in the ungaged area of the lake. 

Because Ellerbe Creek accounts for a disproportionately large part of the lead load to Falls Lake, this 

could account for part of the shortfall especially in 

1990 which was a relatively wet year. The lead load at 

Eno River near Hillsborough (site 26), near the 

headwaters, averaged 587 pounds per year (Ibs/yr). 

This is 24 percent of the mean lead load in Eno River 

downstream from Durham (site 8). The lead load in 

the Neuse River at Smithfield (site 32). located about 

35 miles downstream from the Falls Lake dam and 

downstream from Raleigh, Durham, and Gary, was 

25,000 Ibs annually, an increase of more than 100 

percent.

Average annual lead yield was greatest for 

Ellerbe Creek (105 pounds per square mile [lbs/mi2]) 

and next greatest for Little Lick Creek (36 lbs/mi2). 

Smallest yields were recorded for the two headwater 

streams monitored, Eno River at Hillsborough (site 26, 

8.9 lbs/mi2) and Flat River at Bahama (site 15, 

9.4 bs/mi2) (table 15).

Lead loads to Jordan Lake ranged from 31,700 

in 1992 (fig. 23B) to 68,100 in 1993 (table 15). 

Figure 23A shows the loads and yields of lead during 

1989, a year almost as wet as 1993. Average annual 

inflows of lead to Jordan Lake were estimated at 

52,500 Ibs for the 6-year data-collection period. 

Average annual lead loads for tributaries in the upper 

Cape Fear River Basin ranged from about 667 Ibs for 

Northeast Creek (site 19) to about 40,000 Ibs for Haw 

River near Bynum (site 24, table 15). The contribution 

from the ungaged portion of the basin was estimated to 

account for 19 percent of the input. The average 

annual outflow from Jordan Lake (33.600 Ibs for 

1989-94) was determined from load calculations at 

Haw River below the dam (site 25). The lead load out 

of Jordan Lake ranged from 55 to 73 percent of the 

loads into the lake (table 15).

Zinc loads to Falls Lake from monitored 

tributaries ranged from an average of 1,150 Ibs/yr 

from Little Lick Creek to 10,600 Ibs/yr from Eno 

River near Weaver. The zinc load to Falls Lake ranged 

from 33,300 Ibs in 1992 (table 16, fig. 24B) to 60,600 

Ibs in 1989 (table 16, fig. 24A). The average annual 

zinc load into Falls Lake was 41,800 Ibs. The outflow 

ranged from 49 percent in 1992 to 152 percent of the 

inflow in 1990. Average yield for zinc in the upper 

Neuse River Basin above the Falls Lake dam ranged 

from 71 to 340 lbs/mi2. Ellerbe Creek accounted for 

the maximum yield. The zinc load for the Neuse River 

at Smithfield (site 32) was about 50 percent more than 

the load in the Neuse River below Falls Lake.

Table 15. Lead loads and yield from selected tributaries in the upper Neuse River and upper Cape Fear River Basins, 

water years 1989-94

[Sites are shown in figure 2. Ibs/mi2/yr, pounds per square mile per year; , no data]

Station name

or 

location

Lead load, in pounds 

(percent of total inflow load)

1989 1990 1991 1992 1993 1994 1989-94

Lead

yield

(lbs/mi2/

yr)

Upper Neuse River Basin

Eno River at Hillsborough 776 516 508 456 783 482 3,520 587 8.9 

(site 26)

Eno River near Weaver 3.480 2.490 2,080 1,420 3,110 1,840 14,400 2,400 16 

(site 8)

Knap of Reeds Creek near 1,200 1,020 694 351 996 482 4,750 792 18 

Butner(site 10)

62 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
Table 15. Lead loads and yield from selected tributaries in the upper Neuse River and upper Cape Fear River Basins, 

water years 1989-94 (Continued)

[Sites are shown in figure 2. Ibs/mi2/yr, pounds per square mile per year; , no data]

Station name 

or

location

Lead load, in pounds

(percent of total inflow load)

1989 1990 1991 1992 1993 1994 1989-94 Mean for 

1989-94

Lead

yield

(Ibs/ml2/ 

yr)

Upper Neuse River Basin (Continued)

Ellerbe Creek near German

(site 7)

Little Lick Creek above

Secondary Road 1 8 1 4 near

Oak Grove (site 6)

Flat River at Dam near

Bahama, Lake Michie outflow (site 14)

Ungaged drainage area of

Falls Lake

Total inflow to Falls Lake

Neuse River near Falls, Falls

Lake outflow (site 1 )

Neuse River at Smithfield

(site 32)

3,41 Oa

539

1,200

5,680

15,500

20.000

(129)

48,400

385

930

4,150

7,970

14,800

(186)

31,600

239

633

3,140

6,010

7,720

(128)

17,900

1,210

236

503b

2,890

5,860

4,070

(70)

9,630

2,930

513

1,135

6,760

13,700

16,600

(121)

27,800

l,670a

264

726b

3,880

7,870

7,260

(92)

14.500

2.180

5,130

26,500

56,900

70,400

(124)

150,000

2,300

363

855

4,420

9,490

11,700

(124)

25,000

105

36

5.1

16

12

15

21

Lake Michie

Flat River at Bahama

(site 15)

Ungaged drainage area of

Lake Michie

Total inflow to Lake Michie

Flat River at Dam near

Bahama, Lake Michie outflow (site 14)

1,830

223

2,060

1,200

1,090

139

1,230

930

889

113

1,000

633

686

87

773

503

1,950

249

2200

1,135

991

126

1120

726

7,440

948

8,380

5,130

1.240

158

1,400

855

8.3

8.3

8.3

5.1

Jordan Lake

New Hope Creek near

Elands (site 18)

Northeast Creek at Secondary Road 1 100 near Genlee

(site 19)

Haw River near Bynum

(site 24)

Ungaged drainage area of

Jordan Lake

Total inflow to Jordan Lake

Haw River below Dam near

Moncure (site 25; Jordan

Lake outflow)

2,310

904

44,400

11.000

58,600

37,500

(64)

1,860

786

42,700

10.500

55,800

36,900

(66)

2,250

557

46,300

11.300

60,400

33,500

(55)

1,580

558

23,600

5.950

31,700

19,300

(61)

2,670

901

51,700

12.800

68,100

49,400

(73)

1.420

298

31,200

7.600

40,600

25,200

(62)

12.100

4,000

240,000

59.100

315,000

202,000

(64)

2.010

667

40,000

9,860

52,500

33,600

(64)

26

24

31

31

31

20

aJune, July, and August estimated based on comparison with flow from Little Lick Creek. 

No discharge data available; therefore, outflow assumed to be 65 percent of inflow.

Lead and Zinc 63
A.

B.

0 2 4 6 8 10 MILES

I I I I i i

0 2 4 6 8 10 KILOMETERS

79°

>w

Explanation

 - - Basin boundary 

 - Subbasin boundary 

37 Site number f \

J \

,s

s /

Lead yield, in poun

per square mile

i i no data

S

< 10 

10-29

( , \ /~\78°45' ,--, 3()_49

36-1 V '' 'J ^\ L^ >50 361S y,-,^ ^ V| 

.-'"v > «/*/ \>"V-v. i r\ ^-> \ l>- > ^? v *^ rs ,.' Vv,', Lead load, in poun 

"'"V O no data 

c 1 <1,200 __

f "A ^ .v, \ ^-x-,/~-<> V

(

' ! /"-]

O 1,200-3,499

 3,500-37,000

© >37,000

j

Figure 22. Estimated lead yield and load from selected tributaries to Falls Lake and Lake Michie, and outflow of lead load from Falls 

Lake, (A) 1989 and (B) 1992.

64 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
A.

36°15

36'

B.

^--

Explanation

 - - - Basin

boundary

- - Subbasin 

boundary

27 Site number

Lead yield, in pounds Lead load, in pounds 

per square mile Q no data 

no data <I

10-29 

30-49 

>50

1,200

O 1,200-3,499 

 3,500-37,000 

© >37,000

79 "45

36°15

0 2 4 6 8 10 MILES

I I 1 ! !' ! 'l ' '

0 2 4 6 8 10 KILOMETERS

.r^^NiU'M

Figure 23. Estimated lead yield and load from selected tributaries to Jordan Lake and University Lake, and outflow of lead load from 

Jordan Lake, (A) 1989 and (B) 1992.

Lead and Zinc 65
Table 16. Zinc loads and yield from selected tributaries in the upper Neuse River and upper Cape Fear River Basins, 

water years 1989-94

[Sites are shown in figure 2. Ibs/mi2/yr, pounds per square mile per year; , no data]

Station name

or 

location

Zinc load, In pounds 

(percent of total inflow load)

1989 1990 1991 1992 1993 1994 1989-94

Zinc

uiolri

Mean (Ibs/mi2/ 

for r)

1989-94

Upper Neuse River Basin

Eno River near Weaver (site 8)

Knap of Reeds Creek near

Butner(site 10)

Ellerbe Creek near German

(site 7)

Little Lick Creek above

Secondary Road 1814 near

Oak Grove (site 6)

Ungaged drainage area of Falls

Lake

Total inflow to Falls Lake

Neuse River near Falls, Falls

Lake outflow (site 1)

Neuse River at Smithfield

(site 32)

14,800

5,220

11,100

1,660

27,800

60,600

69,600

(115)

117,000

11,400

4,440

1,270

18,400

35,600

54,200

(152)

81,900

9,460

3.010

814

13,900

27,200

29,200

(107)

48,200

6,330

1.530

4,660

761

20,000

33,300

16,300

(49)

27,800

13,200

4.310

8,150

1,480

24,100

51,300

58,800

(115)

71,100

8,120

2.090

5,960

920

25,500

42,700

26,849

(63)

39,300

63,400

20.600

6,910

130,000

251,000

255,000

(102)

385,300

10,600

3.430

7,470

1,150

21,600

41,800

42,500

(102)

64,200

71

80

340

110

65

54

55

53

Jordan Lake

New Hope Creek near Elands

(site 18)

Northeast Creek at Secondary

Road HOOnearGenlee

(site 19)

Haw River near Bynum

(site 24)

Ungaged drainage area of

Jordan Lake

Total inflow to Jordan Lake

Haw River at Dam near

Moncure, Jordan Lake outflow (site 25)

6,710

5,090

1 10,000

28,100

150,000

130,000

(87)

5,710

4,790

108,000

27,400

146,000

131,000

(90)

6,400

3,740

114,000

28,700

153,000

118.000

(78)

4,870

3.610

60,900

16,000

85,400

72.500

(85)

7,740

5.230

126,000

32,100

171,000

170.000

(99)

4,440

2.600

78,400

19,700

105,000

90.100

(86)

35,900

25.100

597,000

152,000

810,000

711.000

(88)

6,000

4.180

99,600

25,300

135,000

119.000

(88)

79

200

78

80

80

70

66 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
Zinc loads to Jordan Lake ranged from 

85,400 Ibs in 1992 (table 16, fig. 25B) to 170,000 Ibs 

in 1993. Figure 25 A shows the loads and yields of zinc 

during 1989. Average annual inflows of zinc (1989-94) 

to Jordan Lake were about 135,000 Ibs from 

tributaries in the upper Cape Fear River Basin. The 

ungaged area of the basin accounted for about 19 

percent of the inflow. The greatest zinc load to Jordan 

Lake (75 percent) was from the Haw River (site 

24) the tributary with the largest drainage area. The 

greatest zinc yield was from Northeast Creek, 

200 lbs/mi2 . Zinc loads out of Jordan Lake accounted 

for 78 to 99 percent of the total inflows of zinc 

(table 16).

SUMMARY

Water-quality samples were collected from 35 

lake and stream sites in the Triangle area of North 

Carolina from October 1988 through September 1994 

by the U.S. Geological Survey (USGS) and the North 

Carolina Division of Environmental Management 

(DEM). Samples were analyzed for major ions, 

nutrients, trace metals, and selected synthetic organic 

compounds. Data from the two agencies were 

combined by the USGS for interpretation. In addition 

to water samples, bed-material samples were collected 

from 1 to 3 times at selected sites for the analysis of 

synthetic organic compounds. These data supplement 

nutrient, major ion, and trace element data collected 

prior to October 1988 by the USGS and DEM and 

establish a new database of concentrations of synthetic 

organic compounds in water and bed material in the 

study area.

Streams in the upper Neuse and upper Cape 

Fear River Basins within the study area are generally 

similar to streams draining relatively pristine basins in 

the same geochemical zone. The major cations are 

equally calcium, magnesium, and sodium + 

potassium, and the major anion is bicarbonate. 

Streams that receive wastewater effluents or that are 

downstream from urban areas generally had sodium + 

potassium as the major cation and sulfate or 

bicarbonate as the major anion. These waters also had 

substantially greater total-dissolved solids than the 

baseline waters.

Stream and lake sites were assigned to one of 

five site categories according to general site 

characteristics. Site categories were (1) rivers,

(2) large multipurpose reservoirs, (3) small upland 

water-supply reservoirs. (4) streams below urban areas 

and WWTP's, and (5) headwater streams. Sites near 

water-supply intakes were further identified as a sixth 

category. Concentrations of nitrogen species, 

phosphorus species, and selected trace metals were 

compared quantitatively by site category using 

nonparametric analysis of variance techniques and 

compared qualitatively (trace metals) using box plots.

Wastewater-treatment plant effluents and urban 

runoff had a significant effect on water quality 

compared to reservoirs and headwater streams. 

Median concentrations of nitrate and total nitrogen 

were significantly greater for sites below urban areas 

and WWTP's than for other sites. Total ammonia plus 

organic nitrogen varied little among site categories, 

the only significant difference being between 

headwater streams and streams below urban areas and 

WWTP's. The median concentration in the latter 

category was twice that of headwater streams. Organic 

nitrogen accounted for 80 to 90 percent of total 

ammonia plus organic nitrogen in all categories. 

Organic nitrogen was the predominant form of 

nitrogen at reservoir sites, whereas nitrate was 

predominant for sites below urban areas and WWTP's. 

River intake sites had significantly greater 

concentrations of nitrite plus nitrate than large and 

small reservoir intake sites. No difference was found 

between the two categories for ammonia or organic 

nitrogen.

Median concentrations of total phosphorus were 

significantly greater for sites below urban areas and 

WWTP's than for small and large reservoir sites but 

were not significantly greater than river or headwater 

sites. The strong association between phosphorus and 

suspended sediments as well as the importance of 

point sources as contributors of total phosphorus 

probably account for the difference in concentrations 

between reservoirs and streams. Orthophosphate was 

significantly greater in sites below urban areas and 

WWTP's than in river or reservoir sites. A marked 

seasonal pattern was observed for total phosphorus at 

reservoir sites. Greatest concentrations generally 

occurred during late summer and fall months and 

roughly corresponded to peaks in chlorophyll a.

Greatest concentrations of metals and trace 

metals in streams were observed during periods of 

greater than normal streamflow probably as a result of 

adsorption to silt, clay, and organic particles. However, 

most concentrations were below the MRL and below

Summary 67
B.

0 2 4 6 8 10 KILOMETERS

Explanation

- - Basin boundary

- - Subbasin boundary 

37 Site number

Zinc yield, in pounds 

per square mile 

no data 

<90 

90-119 

120-249 

>250

Zinc load, in pounds 

O no data

 < 5,200

O 5,200-14,999

 15,000-109,999 

>110.000

30

Figure 24. Estimated zinc yield and load from selected tributaries to Falls Lake, and outflow of zinc load from Falls Lake, (A) 1989 

and (B) 1992.

68 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
A. 79°45 '

B.

36°15

Explanation

 - - - Basin

boundary

 Subbasin 

boundary

27 Site number

Zinc yield, in pounds Zinc load, in pounds

per square mile O no data

no data < 5,200

<90 O 5,200-14,999

90-119 15,000-109,999

120-249 © >110,000 >250 

36 "15

80

B 10 MILES

KILOMETERS

Figure 25. Estimated zinc yield and load from selected tributaries to Jordan Lake, and outflow of zinc load from Jordan Lake, 

(A) 1989 and (B) 1992.

Summary 69
USEPA drinking-water MCL's. Moreover, 

exceedences occurred more often at stream sites than 

at reservoir sites. Only two samples exceeded the State 

water-quality standard for chromium Cane Creek 

and Flat River. Seven samples at Haw River near 

Bynum and Neuse River at Smithfield exceeded the 

lead water-quality standard. Median iron and 

manganese concentrations were near or above the 

USEPA secondary drinking-water MCL's (1,000 and 

50 ug/L, respectively) for stream sites, whereas 

concentrations at reservoir sites were typically well 

below the standards.

Samples for volatile organic compounds were 

collected during the first 3 years of study. Few were 

detected in concentrations above the MRL. Those 

detected were one of four trihalomethanes and 

occurred almost exclusively at sites below urban areas 

and WWTP's. Trace amounts of other volatile organic 

compounds, mostly organic solvents such as benzene, 

dichlorobenzene, tetrachloroethylene, and trichloroethane were found in fewer than 20 percent of the 

samples collected. No concentrations of volatile 

organic compounds exceeded USEPA drinking-water 

MCL's.

Organochlorine and organophosphorus 

pesticides were also sampled during the first 3 years of 

study. About 40 percent of the samples analyzed for 

pesticides contained detectable concentrations of at 

least one pesticide most often lindane, dieldrin, 

diazinon, and heptachlor epoxide. Most detections 

occurred in samples from tributaries to Falls and 

Jordan Lakes and Swift Creek. Concentrations were 

always near the MRL. No concentrations exceeded 

USEPA drinking-water MCL's; however, some 

lindane and dieldrin concentrations exceeded the State 

water-quality standards for the protection of aquatic 

life.

Selected acetanilide and triazine herbicides 

were collected in 1992. Most of the samples collected 

contained detectable concentrations of at least one of 

these herbicides chiefly atrazine or simazine. None 

exceeded the USEPA drinking-water MCL's. These 

compounds are in widespread use and are more water 

soluble than organochlorine and organophosphorus 

pesticides.

Organochlorine, organophosphorus, 

acetanilide, triazine, carbamate, and chorophenoxy 

acid pesticides were sampled in the spring of 1993 and 

1994 at three sites on streams receiving WWTP 

effluents to determine the probable source effluents

versus local runoff. Simazine, prometon, 2,4-D, and 

2,4-DP were measured at concentrations considerably 

greater than MRL's but below USEPA drinking-water 

MCL's. Pesticides detected were present upstream and 

downstream from WWTP's and in effluents.

Water samples were collected for analysis of 51 

semivolatile organic compounds. None were found 

above MRL's. Most are relatively insoluble in water 

and, if present, are more likely to reside in bed 

materials. Samples of bed materials were collected 

from 24 sites and analyzed for selected semivolatile 

organic compounds and organochlorine and 

organophosphorus pesticides. Greatest concentrations 

of pesticides in bed material were found in the lakebed materials of the Haw River arm of Jordan Lake, 

Falls Lake, Lake Michie, and Ellerbe Creek. Lake 

beds have greater concentrations of organic material 

and smaller grain size inorganic material than bed 

materials from streams and this may account for the 

results from the lakes. Semivolatile organic 

compounds were not found in concentrations above 

the MRL.

Most of the stream sites had USGS streamflow 

gages. Continuous record of streamflow at these sites 

was used to calculate annual suspended-sediment, 

total phosphorus, total nitrogen, total lead, and total 

zinc loads to the reservoirs as well as to calculate 

drainage basin yields for these constituents. If 

sufficient water-quality and streamflow data were 

available, loads of these constituents out of the 

reservoirs also were calculated to determine the 

amount of material trapped by the reservoir.

Annual suspended-sediment load into Falls 

Lake ranged from 29.500 tons to 88.200 tons and 

varied by water year as a function of streamflow. Flat 

River is a minor contributor to Falls Lake because 

Lake Michie traps about 90 percent of the load. Little 

River also produces a large sediment load that is 

probably trapped in Little River Reservoir. The 

trapping rate of Little River Reservoir could not be 

directly determined because outflow was not 

monitored. Little River and Flat River above the 

reservoirs produce yields of about 184 and 

223 tons/mi2 . This is an increase compared to yields of 

140 and 190 tons reported for 1970-79. Ellerbe Creek 

produced the largest yield in the Falls Lake Basin 

(347 tons/mi2). Undisturbed basins in the Piedmont 

produce about 45 tons/mi2 .

Annual sediment loads to Jordan Lake ranged 

from about 271,000 tons in 1992 to 622,000 in 1993.

70 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
Haw River contributes about 77 percent of the load to 

Jordan Lake. New Hope and Northeast Creeks 

contribute much smaller loads but basin yields are 

similar to that of Haw River from 175 to 

284 tons/mi2 . The mean annual yields for Morgan and 

Cane Creeks were 52 and 77 tons/mi2 , respectively. 

University Lake and Cane Creek Reservoirs probably 

trap most of the suspended sediment from Morgan and 

Cane Creeks, respectively, but data were not available 

to calculate percentage trapped.

Annual nitrogen loads to Falls Lake ranged 

from 780 tons in 1991 to 1,650 tons in 1989. From 44 

to 80 percent of the load to Falls Lake is trapped. 

Nitrogen loads into Lake Michie were less than 

nitrogen loads out of the lake. This may be a result of 

underestimation of load from ungaged portions of the 

basin including Dial Creek, which receives drainage 

from agricultural runoff. Another factor may be that 

the relatively short hydraulic retention time of Lake 

Michie limits nitrogen removal.

Nitrogen load to Jordan Lake ranged from 

2,710 tons in 1992 to 4,100 tons in 1993. From 32 to 

46 percent of the nitrogen load to Jordan Lake is 

trapped. Haw River contributed approximately 70 

percent of the nitrogen loads to Jordan Lake; however, 

New Hope and Northeast Creeks produced greater 

yields at least double that of Haw River. Annual 

nitrogen loads to University Lake and Cane Creek 

Reservoir averaged 49 and 46 tons, respectively. For 

Morgan Creek near Farrington, nitrogen yield 

decreased by 59 percent compared to the 1983-86 

period; for Northeast Creek, nitrogen increased by 23 

percent. Yields at New Hope, Haw River at Bynum, 

and Haw River below the dam were unchanged 

compared to the 1983-86 period. The overall average 

annual nitrogen yield to Jordan Lake was 2.2 tons/mi 2 

compared to 1.5 tons/mi2 for Falls Lake.

Annual phosphorus loads to Falls Lake ranged 

from 78 tons (1992) to 143 tons (1989). From 61 to 86 

percent of the phosphorus load was trapped in Falls 

Lake. Only 25 to 45 percent of the phosphorus 

delivered to Lake Michie was trapped in the reservoir. 

Knap of Reeds Creek averaged 23 tons/yr (1989-94), 

which was the greatest phosphorus load of the gaged 

basins. Annual phosphorus yields declined by at least 

half at Ellerbe Creek, Little Lick Creek, and Eno River 

from the 1983-87 period, and remained nearly 

constant at the other sites tributary to Falls Lake. The 

decline in phosphorus yield at Little Lick, Ellerbe, and 

Eno River near Weaver are probably due to

improvement in phosphorus removal from wastewater 

effluents from WWTP's and to the phosphatedetergent ban that became law in January 1988.

Annual phosphorus loads to Jordan Lake ranged 

from 418 tons in 1992 to 701 tons in 1993. Haw River 

accounted for about 75 percent of the phosphorus load 

to Jordan Lake. The average annual phosphorus load 

to University Lake was 8 tons and to Cane Creek 

Reservoir was 6 tons. From 52 to 62 percent of the 

phosphorus load to Jordan Lake was trapped 

compared to about 70 percent for Falls Lake. The 

smaller percentage of material trapped by Jordan Lake 

is due, in part, to the unusual morphometry of Jordan 

Lake in which most of the flow and load enters near 

the dam. Average annual phosphorus yields declined at 

every site compared to yields estimated in an earlier 

study for 1983-86 probably for the same reason that 

declines in yields occurred within the upper Neuse 

River Basin.

Lead and zinc loads were calculated for all sites 

having sufficient numbers of analyses above the MRL. 

The lead load to Falls Lake ranged from 5,860 Ibs in 

1992 to 15,500 Ibs in 1989. Ellerbe Creek had the 

greatest lead yield of monitored tributaries to Falls 

Lake 105 lbs/mi 2 followed by Little Lick Creek 

(36 lb/mi2). The lead load in the Neuse River almost 

doubled between Falls Lake dam and Smithfield. 

From 27,200 to 60,600 Ibs of zinc were delivered to 

Falls Lake in 1991 and 1989, respectively. The Neuse 

River zinc load increased by about 50 percent between 

the dam and Smithfield.

The lead load to Jordan Lake ranged from 

31,700 Ibs in 1992 to 68,100 Ibs in 1993. The greatest 

yield was from Haw River 31 lbs/mi2 ; however, 

loads from New Hope and Northeast Creek were 

similar. About 36 percent of the load to Jordan Lake 

was trapped. The zinc load to Jordan Lake ranged 

from 85,400 Ibs in 1992 to 171,000 Ibs in 1993. The 

greatest yield (200 lbs/mi2) was from Northeast Creek 

and was more than twice the yield from New Hope 

Creek and the Haw River. About 15 percent of the zinc 

load was trapped in Jordan Lake.

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72 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
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References 73
SUPPLEMENTARY TABLES

74 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
Supplementary Table S-1 . Equations describing the suspended-sediment concentration-discharge relation 

used to calculate loads for sites in the upper Neuse River Basin

[BCF, bias correction factor; R2 , coefficient of determination; ft3 /s, cubic feet per second; S, Iog 10 of suspended-sediment concentration; 

Q, Iog 10 of discharge; <, less than; >, greater than]

Site

n "m" Station name ber

(fig. 2)

8 Eno River near Weaver

12 Little River at Secondary 

Road 1461 near Orange 

Factory

14 Flat River at Dam near 

Bahama

10 Knap of Reeds Creek near 

Butner

7 Ellerbe Creek near 

Gorman

6 Little Lick Creek above 

Secondary Road 1814 

near Oak Grove

26 Eno River at Hillsborough

32 Neuse River at Smithfield

Number 

of 

samples

91

25 

116

19

11

25

98

86

74

83

23 

25 

33

56

Regression analysis for suspended sediment (S) 

concentration 

(milligrams per liter)

Log-log regression 

equation

S = 0.745 + 0.207 Q 

S = 0.272 + 0.546 Q 

S = 0.27 + 0.546 Q

S = 0.288 + 0.496 Q 

S = 0.1 12 + 0.783 Q 

S = 0.057 + 0.718 Q

S = 0.92 + 0.12 Q

S = 1.36 + 0.152 Q

S = 0.254 + 0.866 Q

S = 1.25 + 0.42 Q

8 = 0.811 + 0.023 Q 

S = -0.574 +1.0Q 

S = 0.466 + 0.427 Q

S = -0.234 + 0.628 Q

BCF

1.67 

1.65 

1.72

1.54 

1.19 

1.58

1.25

1.99

1.22

1.42

1.16 

1.26 

1.35

1.36

R2

0.08 

.49 

.49

.46 

.51 

.69

.23

.06

.89

.65

.00 

.65

.38

.45

Range of log 

Qa 

(ft3/s)

<2.5 

2.5-4.0 

>4.0

<2.0 

2.0-4.0 

>4.0

all

all

all

all

<1.5 

1.5-2.9 

>2.9

all

aRange of discharge to which the regression equation applies.

Supplementary Tables 75
Supplementary Table S-2. Equations describing the suspended-sediment concentration-discharge relation 

used to calculate loads for sites in the upper Cape Fear River Basin

[BCF, bias correction factor; R2 , coefficient of determination; ft3/s, cubic feet per second; S, Iog 10 of suspended-sediment concentration; 

Q, Iog 10 of discharge; <, less than; >, greater than]

Site 

number 

(fig- 2)

18

19

24

27

29

31

Station name

New Hope Creek near

Elands

Northeast Creek at Secondary Road 1 100 near

Genlee

Haw River near Bynum

Cane Creek near Orange

Grove

Morgan Creek near White

Cross

Cape Fear River at State

Highway 42 near Brickhaven

Number

of

samples

60

71

95

42

23

51

34

33

41

39

Regression analysis for suspended sediment (S) 

concentration 

(milligrams per liter)

Log-log 

regression equation

S = 1. 15 + 0.334 Q

S = 1.33 + 0.325 Q

S = 0.673 + 0.423 Q

S = 0.752 + 0.054 Q

S -0.196 + 0.916 Q

S = 0.772 + 0.48 Q

S = 0.626 + 0.185 Q

S = 0.259 +0.877 Q

S = 0.55 + 0.55 Q

S = -0.039 + 0.392 Q

BCF

1.43

1.67

1.76

1.48

1.38

1.94

1.42

1.44

1.69

1.35

R2

0.27

.29

.28

.01

.67

.45

.05

.57

.39

.23

Range of 

logQa 

(ft3/s)

all

all

all

<1.1

1.1-3.0

>3.0

<0.2

0.2-2.3

>2.3

all

aRange of discharge to which the regression equation applies.

76 Water and Bed-Material Quality of Selected Streams and Reservoirs in the Research Triangle Area of North Carolina, 1988-94
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Supplementary Tables 77
Supplementary Table S-4. Equations describing the total nitrogen concentration-discharge relation and the total phosphorus con

used to calculate loads for selected sites in the upper Cape Fear River Basin

[BCF, bias correction factor; R2 , coefficient of determination; ft-Vs, cubic feet per second; N, Iogi 0 of total nitrogen concentration; Q, Iogi 0 of discharge; P, log)0 of 

<, less than; >, greater than]

id-Material

«<

o

8

1 

c/>

3

Q)

3

(0

Q)

3

a

(D

(0

<D

O.

W5'

5

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33

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(0

(D 

Q)

O3"

H

Q)'

3

<£.

<o

(D

Q) 

O^

z 

o

3.

0

Q)

O.

Site

num- _. .. 

. Station name v, 

Regression analysis for nitrogen (N) 

concentrations

Number (milligrams per liter) 

~t

ber 

(fig. 2) samples Log-log regression BCp 

equation

17 Morgan Creek

near Farrington

1 8 New Hope Creek

near Blands

19 Northeast Creek at

Secondary Road

11 00 near Genlee

24 Haw River near

Bynum

27 Cane Creek near

Orange Grove

29 Morgan Creek

near White

Cross

25 Haw River below

B. Everett Jordan Dam near

Moncure

3 1 Cape Fear River at

State Highway

42 near Brickhaven

43 N = 1.31 -0.534 Q 1.06

85 N = 1 .49 - 0.475 Q 1.11

89 N =1.33- 0.497 Q 1.15

88 N = 0.483- 0.07 1 Q 1.12

49 N = 0.016 + 0.089 Q 1.08

11 N = -0.049 - 0.826 Q 1 .05

45 N = 0.059 + 0.124 Q 1.09

50 N = 0.171 -0.014 Q j.jg

42 N = 0.192- 0.04 Q 1.03

47 N = 0.282 - 0.048 Q 1 .03

R2 log Qa 

(ft3/s)

0.64 all

.69 all

.65 all

.06 all

.13 all

.76 <.06

.10 0.05-2.3

.00 >2-3

.03 all

.04 all

Number 

of

43

43

47

88

44

5

29

43

53

42

47

Regression anal

con

(millig

Log-log regression 

equation 

P

P

P

P

P

P

P

P

P

P

P

= -0.555 - 0.069 Q

= 0.347 - 0.453 Q

= -0.1 17 -0.279 Q

= -0.293 - 0.082 Q

= -1.16-0.189Q

= -1.05 + 0.254 Q

= -0.599 - 0.274 Q

= -0.78 + 0. 123 Q

= -0.645 - 0.034 Q

= -0.934 + 0.006 Q

= -0.71 5- 0.085 Q

aRange of discharge to which the regression equation applies.
Supplementary Table S-5. Equations describing the lead concentration-discharge relation and zinc concentration-disc

to calculate loads for selected sites in the upper Neuse and upper Cape Fear River Basins

[BCF, bias correction factor; R2 , coefficient of determination; Pb, Iog10 of total lead concentration; Q, Iogi 0 of discharge; Zn, logjo of total zinc conc

Site 

num-

(fig-2)

Number 

Station name of

samples

Regression analysis for lead (Pb) Regression analys

concentrations Number concentra

(micrograms per liter) of (micrograms 

Log-log regression 

equation

BCF

R2 samples Log _|og regressjon 

equation

Upper Neuse River Basin sites

1

6

7

8

10

15

26

32

Neuse River near

Falls

Little Lick Creek

above Secondary

Road 18 14 near

Oak Grove

Ellerbe Creek near

Gorman

Eno River near

Weaver

Knap of Reeds Creek

near Butner

Flat River at Bahama

Eno River at Hillsborough

Neuse River at

Smithneld

65

42

39

49

41

13

12

26

Pb = -0.01 6 + 0.278 Q

Pb = 0.612 + 0.237 Q

Pb = 0.1 78 + 0.536 Q

Pb = 0.1 45 + 0.257 Q

Pb= 0.952 - 0.052 Q

Pb = -0.1 22 + 0.250 Q

Pb= -0.055 + 0.283 Q

Pb= 0.054 + 0.243 Q

1.61

1.29

1.44

1.27

1.17

1.12

1.07

1.42

0.20 47 Zn= 0.978 + 0.1 40 Q

.45 56 Zn = 1.60- 0.003 Q

.69 44 Zn= 1.66 + 0.134Q

.40 53 Zn= 1.13 + 0.133 Q

.03 76 Zn= 1.56- 0.055 Q

.55 na na

.51 na na

.08 21 Zn= 0.953 + 0.1 24 Q

Upper Cape Fear River Basin sites

Wc

T3

T3

(D

(D

M

M

5"

(0

^i

(0

18

19

24

25

New Hope Creek

near Elands

Northeast Creek at

Secondary Road

HOOnearGenlee

Haw River near

Bynum

Haw River below B.

Everett Jordan

Dam near Moncure

32

39

52

48

Pb= 0.541 +0.1 32 Q

Pb= 0.452 + 0.200 Q

Pb= -0.01 7 + 0.297 Q

Pb= 0.194 + 0.176 Q

1.40

1.51

1.38

1.30

0.07 na na

.14 59 Zn= 1.93 -0.148 Q

.38 45 Zn= 0.804 + 0.200 Q

.13 34 Zn= 1.09 + 0.080 Q