EFFECTS OF COMBINED-SEWER 

OVERFLOWS AND URBAN RUNOFF 

ON THE WATER QUALITY OF 

FALL CREEK, INDIANAPOLIS, INDIANA

By Jeffrey D. Martin

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 94-4066

Prepared in cooperation with the

INDIANAPOLIS DEPARTMENT OF PUBLIC WORKS

Indianapolis, Indiana 

1995
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

For additional information, write to: 

District Chief 

U.S. Geological Survey 

Water Resources Division 

5957 Lakeside Boulevard 

Indianapolis, IN 46278-1996

Copies of this report can be purchased from:

U.S. Geological Survey

Earth Science Information Center

Open-File Reports Section

Box 25286, MS 517

Denver Federal Center

Denver, CO 80225
CONTENTS

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

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

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

Previous Studies....................................................................... 2

Study Area ........................................................................... 4

Acknowledgments ..................................................................... 10

Methods of Investigation.................................................................... 10

Selection of Data-Collection Sites ......................................................... 10

Measurement of Stage and Computation of Streamflow ........................................ 11

Measurement of Precipitation............................................................. 11

Water-Quality Samples and Measurements .................................................. 11

Sample Processing, Compositing, Preservation, and Analysis.................................... 13

Calculation of Event-Mean Concentration................................................... 15

Quality Assurance...................................................................... 15

Hydrologic Conditions...................................................................... 26

Precipitation .......................................................................... 26

Streamflow ........................................................................... 26

Base Flow....................................................................... 33

Storm Runoff.................................................................... 37

Water Withdrawals andRetums ........................................................... 50

Effectsof Combined-Sewer Overflows and Urban Runoff on Fall Creek............................... 51

WaterQuality of Base Flow .............................................................. 51

Synoptic Survey.................................................................. 51

Chemical, Physical, and Biologic Characteristics........................................ 54

Specific Conductance, Dissolved Oxygen, Temperature, and pH ....................... 59

Major Anions ............................................................... 60

Dissolved and Total Solids, Chemical Oxygen Demand, Carbonaceous Biochemical Oxygen

Demand, and Oil and Grease................................................ 60

Nutrients................................................................... 66

Trace Elements.............................................................. 66

Fecal Coliform Bacteria ....................................................... 67

Water Quality of Storm Runoff and Comparisons with Water Quality of Base Flow .................. 68

Synoptic Survey.................................................................. 68

Chemical, Physical, and Biologic Characteristics........................................ 70

Specific Conductance, Dissolved Oxygen, Temperature, and pH ....................... 70

Major Anions ............................................................... 84

Dissolved and Total Solids, Chemical Oxygen Demand, Carbonaceous Biochemical Oxygen

Demand, and Oil and Grease................................................ 84

Nutrients................................................................... 85

Trace Elements.............................................................. 86

Fecal Coliform Bacteria ....................................................... 87

Summary and Conclusions................................................................... 87

References Cited .......................................................................... 91

Contents III
CONTENTS

FIGURES

1-4. Maps showing:

1. The upper White River watershed in east-central Indiana.......................... 3

2. Locations of selected hydrologic and cultural features and data-collection stations in

and near the Fall Creek watershed............................................ 5

3. Locations of selected hydrologic features and data-collection stations on Fall Creek

in Indianapolis........................................................... 7

4. Locations of combined-sewer overflows that discharge to Fall Creek ................ 9

5. Graph showing daily mean streamflow at Fall Creek at Emerson Avenue, Central

Avenue, and 16th Street, July through October 1987 ................................... 34

6-11. Graphs showing streamflow and water quality in Fall Creek during:

6. Storm 1, July 26-28,1987 .................................................. 38

7. Storm 2, July 29-August 3,1987 ............................................. 40

8. Storm 3, August 26-27,1987................................................ 42

9. Storm 4, September 10-13,1987 ............................................. 44

10. Storm 5, September 16-17,1987 ............................................. 46

11. Storm 6, September 29-30,1987 ............................................. 48

12. Longitudinal plots of water quality in Fall Creek during base flow, September 24,1987........ 52

13. Graphs showing water-quality constituents measured during base flow and event-mean

concentrations of water-quality constituents measured during storm runoff at Fall Creek 

at Emerson Avenue, Central Avenue, and 16th Street, and water-quality constituents 

measured in the aqueduct overflow and filter backwash........................... 61

14. Longitudinal plots of water quality in Fall Creek during storm runoff, September 29,1987 ..... 69

TABLES

1. Water-quality analyses for quality-assurance samples....................................... 16

2. Statistical analysis of split quality-assurance samples used to assess analytical precision........... 22

3. Statistical analysis of split quality-assurance samples used to assess the effect of holding

samples at 4°C for 48 hours before processing and preservation .............................. 24

4a-4d. Daily precipitation at selected stations in and near Indianapolis:

4a. July 1987 ..................................................................... 27

4b. August 1987................................................................... 28

4c. September 1987 ................................................................ 29

4d. October 1987 .................................................................. 30

5. Daily mean streamflow at Fall Creek at Emerson Avenue, Central Avenue, and 16th Street,

July through October 1987 ........................................................... 31

6. Daily mean water withdrawal from Fall Creek at Keystone Avenue and daily mean discharge of

filter backwash to Fall Creek at Keystone Avenue and at 16th Street, July through October 1987.... 35

7. Water-quality sampling stations and measurements for the base-flow synoptic survey, Fall Creek,

September 24,1987................................................................. 53

8. Water-quality analyses for samples collected during periods of base flow....................... 55

iv Effects of Combined-Sewer Overflows and Urban Runoff, Fsii Creek, Indianapolis, Indiana
CONTENTS

9. Concentrations of fecal colifonn bacteria during periods of base flow.......................... 59

10. Water-quality sampling stations and measurements for the storm-runoff synoptic survey, storm 6,

Fall Creek, September 29,1987 ....................................................... 68

11. Water-quality analyses for samples collected during periods of storm runoff..................... 71

12. Concentrations of fecal coliform bacteria during periods of storm runoff ....................... 79

13. Event-mean concentrations of constituents during periods of storm runoff ...................... 81

Contents v
CONVERSION FACTORS. VERTICAL DATUM, AND ABBREVIATIONS

Multiply By To obtain

inch (in.) 25.4 millimeter

foot (ft) 0.3048 meter

mile (mi) 1.609 kilometer

square mile (mi2) 2.590 square kilometer

cubic foot per second (ft3/s) 0.02832 cubic meter per second

gallon (gal) 3.785 liter

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

Temperature is given in degrees Celsius (°C), which can be converted to degrees Fahrenheit (°F) as follows:

°F=1.8x°C + 32

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929) a 

geodetic datum derived from a general adjustment of the first-order level nets of the United States and Canada, 

formerly called Sea Level Datum of 1929.

Abbreviated water-quality units used in this report: Chemical concentrations and water temperature 

are given in metric units. Chemical concentration is given in milligrams per liter (mg/L) or micrograms per 

liter (|ig/L). Milligrams per liter is a unit expressing the concentration of chemical constituents in solution 

as weight (milligrams) of solute per unit volume (liter) of water. One thousand micrograms per liter is 

equivalent to one milligram per liter. For concentrations less than 7,000 mg/L, the numerical value is the 

same as for concentrations in parts per million. Concentrations of bacteria are given in colonies per 

100 milliliters (col/100 mL).

Specific conductance of water is expressed in microsiemens per centimeter at 25 degrees Celsius (|iS/cm). This unit 

is equivalent to micromhos per centimeter at 25 degrees Celsius (pmho/cm), formerly used by the U.S. Geological 

Survey.

Volumes of water-quality samples are given in liters (L) and milliliters (mL). 

Other abbreviations used in this report:

AWT advanced waste treatment

CBOD carbonaceous biochemical oxygen demand

COD chemical oxygen demand

DPW (Indianapolis) Department of Public Works

vi Enacts of Combined-Sewer Overflows and Urban Runoff, Fall Creek, Indianapolis, Indiana
EFFECTS OF COMBINED-SEWER OVERFLOWS 

AND URBAN RUNOFF ON THE WATER QUALITY 

OF FALL CREEK, INDIANAPOLIS, INDIANA

By Jeffrey D. Martin

ABSTRACT

In 1986, the U.S. Geological Survey and 

the Indianapolis Department of Public Works 

began a study to evaluate the effects of 

combined-sewer overflows and urban runoff 

discharging to Fall Geek on the White River. 

This report describes the effects of combinedsewer overflows and urban runoff on the water 

quality of Fall Creek during summer 1987 by 

comparing the water quality during base flow 

with that during storm runoff and by comparing 

water quality in the urbanized area with that 

in the less urbanized area upstream from 

the combined-sewer overflows. Data were 

collected at three streamflow-gaging stations 

located upstream from, downstream from, and 

in the middle of 27 combined-sewer overflows 

on Fall Creek. The most downstream station 

also was immediately downstream from the 

discharge of filter backwash from a watertreatment plant for public supply.

Specific conductance and concentrations 

of major ions and dissolved solids in base 

flow increased downstream in response to 

surface-water withdrawn for public supply, 

ground-water inflow, and the discharge of filter 

backwash. Concentrations of dissolved oxygen 

were least in the reach of Fall Creek in the 

middle of the combined- sewer overflows where 

black sludge deposits covered the stream

bottom. Concentrations of nitrate plus nitrite 

and ammonia steadily increased downstream, 

whereas concentrations of organic nitrogen, 

phosphorus, and orthophosphate only increased 

at the most downstream station. Nearly all 

concentrations of chromium, copper, lead, 

nickel, and zinc at the upstream and middle 

stations were less than the detection limit of 

10 micrograms per liter. Detectable concentrations of these metals and high concentrations 

of suspended solids in base-flow samples at 

the most downstream station were caused by the 

discharges from the water-treatment plant.

Concentrations of dissolved oxygen 

measured at the station in the middle of the 

combined-sewer overflows were less than 

the Indiana minimum ambient water-quality 

standard of 4.0 milligrams per liter during all 

storms. Concentrations of ammonia, oxygen 

demand, copper, lead, zinc, and fecal coliform 

bacteria at the stations downstream from the 

combined-sewer overflows were much higher 

in storm runoff than in base flow. Increased 

concentrations of oxygen demand in runoff 

probably were caused by combined-sewer 

overflows, urban runoff, and the resuspension 

of organic material deposited on the streambed. 

Some of the increased concentrations of lead, 

zinc, and probably copper can be attributed 

to the discharge and resuspension of filter 

backwash.

Abstract 1
INTRODUCTION

Approximately 40 mi2 of Indianapolis is 

served by combined sewers that discharge primarily 

to the White River and its tributaries (Fall Creek, 

Pogues Run, Pleasant Run, and Eagle Creek) 

through 129 combined-sewer overflows (Howard 

Needles Tammen & Bersendoff, 1983, p. 1-1). 

About 35 percent (14 mi2) of this area discharges to 

Fall Creek through 28 combined-sewer overflows.

The Indianapolis Department of Public Works 

(DPW) is investigating measures to control the 

degradation of water quality caused by combinedsewer overflows and urban runoff. Information 

on the quantity of contaminants contributed by 

combined-sewer overflows and urban runoff to 

a major urban tributary and the effects on water 

quality would help assess problems associated with 

combined-sewer overflows and urban runoff.

In 1986, the U.S. Geological Survey and the 

Indianapolis Department of Public Works began 

a cooperative study to evaluate the effect of 

combined-sewer overflows and urban runoff to 

Fall Creek on the water quality of the White River. 

The objectives of the study were to (1) describe 

the effects of combined-sewer overflows and 

urban runoff on the water quality of Fall Creek, 

(2) estimate the load (mass) of contaminants 

contributed by combined-sewer overflows and 

urban runoff during the summer low-flow season, 

and (3) assess the relative effect of contaminants 

discharged to Fall Creek on the White River by 

comparing the load of contaminants discharged to 

Fall Creek by combined-sewer overflows and 

urban runoff to the load of contaminants discharged 

to the White River by municipal wastewatertreatment plants.

Purpose and Scope

This report describes the effects of combinedsewer overflows and urban runoff on the water 

quality of Fall Creek in and near Indianapolis 

during summer 1987. In addition, the report 

presents the hydrologic, water-quality, and 

quality-assurance data collected for the study.

Three water-quality monitoring stations were 

established at three streamflow-gaging stations on 

Fall Creek. The streamflow-gaging stations were 

upstream from, in the center of, and downstream 

from the combined-sewer overflows and highly 

urbanized area of Indianapolis. Water-quality 

samples were collected four to six times during 

base flow and multiple times during storm runoff 

from six storms. Multiple runoff samples were 

composited to a single sample that represented the 

mean water quality during the period of storm 

runoff. Water samples also were collected from 

selected effluent sources, and measurements of 

water quality were made in the field at several sites 

during two synoptic surveys. Various types of 

water samples were analyzed as part of a qualityassurance program.

Methods used to collect, process, and compute 

hydrologic and water-quality data are described. 

Methods used to assess data quality are described 

and quality-assurance data are presented and 

assessed. Precipitation and streamflow data 

collected during the study period are compared to 

long-term normal precipitation and streamflow. 

Measurements of base flow and water withdrawals 

and returns were analyzed to determine the components of streamflow for an extended base-flow 

period during October 1987.

The effects of combined-sewer overflows and 

urban runoff on the water quality of Fall Creek were 

determined by comparing the water quality during 

base flow to the water quality during storm runoff. 

In addition, water quality during runoff in the 

urbanized area was compared with water quality 

in the less urbanized area upstream from the 

combined-sewer overflows. Water-quality data 

are presented in tables to facilitate detailed comparisons and in graphs to facilitate interpretations.

Previous Studies

The upper White River drains almost 

2,500 mi2 of predominantly agricultural land in 

east-central Indiana (fig. 1). Muncie, Anderson, 

and Indianapolis are the major urban areas in the 

watershed. Parts of each urban area are served by 

combined sewers, and each city discharges treated

2 Effects of Combined-Sewer Overflows and Urban Runoff, Fail Creek, Indianapolis, Indiana
86°15' 85°53' 85°31'

40°35'

40°12'

39°37'

Base from U.S. Geological Survey digital data, 1:100,000 1983 

Albers Equal Area projection 0 5 10 15 20 MILES

20 KILOMETERS

Figure 1. The upper White River watershed in east-central Indiana.

Previous Studies 3
wastewater to the White River. Shampine (1975, 

p. 64) assessed the water quality of the upper 

White River and concluded that the most severe 

water-quality problems occurred in the Indianapolis area. Oxygen-demanding wastes discharged 

by the Indianapolis sewage-treatment plant 

decreased dissolved-oxygen concentrations at least 

28 mi downstream from the plant (Shampine, 

1975, p. 36, 64).

The City of Indianapolis has implemented a 

variety of studies to determine the effects of cityowned wastewater-treatment plants and the sewer 

system on the water quality of the White River. 

In 1975, Indianapolis authorized a study to locate 

and inventory combined-sewer overflows; 129 

combined-sewer overflows were identified. In 

1978,124 of the combined-sewer overflows were 

instrumented to monitor overflow frequency and 

duration (Howard Needles Tammen & Bergendoff, 

1983, p. 2-3, 3-9).

In 1980, a study to assess the effect of 

combined-sewer overflows on the water quality 

of the White River was done by Howard Needles 

Tammen & Bergendoff (1983, appendix J). Storm 

loads of contaminants from selected combinedsewer overflows were estimated, but the data are 

inadequate for estimating the total quantity of 

contaminants discharged to receiving streams, 

either for a single storm or for the critical summer 

low-flow period. Simulation of the effect of 

combined-sewer overflows on dissolved-oxygen 

concentration indicated that combined-sewer 

overflows could cause large reaches of the White 

River to have concentrations of dissolved oxygen 

less than the Indiana standard of 4.0 mg/L (Howard 

Needles Tammen & Bergendoff, 1983, p. 7-30).

In 1981, the U.S. Geological Survey began a 

series of cooperative studies on the water quality of 

the White River with the Indianapolis Department 

of Public Works. The first study began in 1981 as 

an assessment of the hydrologic effects of enlarging 

and improving the Indianapolis sewage-treatment 

plants. The two plants were upgraded to advanced 

wastewater treatment (AWT), including oxygen 

nitrification and ozone disinfection, and became 

operational in 1983. In 1982, a study to analyze data 

from the City's fixed-station ambient water-quality 

monitoring network began. Dramatic improvements in base-flow water quality after AWT was

implemented were indicated by analysis of wastewater effluent and fixed-station water-quality data 

(Crawford and Wangsness, 1991a, 1991b), data 

collected during four summer low-flow waterquality surveys (DJ. Wangsness, U.S. Geological 

Survey, written commun., 1987), and biological 

monitoring data (Crawford and others, 1992).

In 1985, the U.S. Geological Survey and the 

Indianapolis Department of Public Works began a 

study to determine the frequency and duration of 

low dissolved-oxygen concentrations (those less 

than 4.0 mg/L) associated with periods of base flow 

and storm runoff during the summers of 1986 and 

1987. Continuous flowthrough water-quality 

monitors were installed on the White River in and 

downstream from Indianapolis and on Fall Creek 

in Indianapolis near the confluence with the White 

River. Low concentrations of dissolved oxygen 

were measured during 12 periods at the downstream station on the White River and 5 periods at 

the station on Fall Creek (Martin and Craig, 1990, 

p. 44-45). All of the low concentrations of 

dissolved oxygen occurred during periods of 

storm runoff; consequently, likely causes of the 

low concentrations of dissolved oxygen were 

combined-sewer overflows and urban runoff from 

Indianapolis. Although this study provided information on the effects of storm runoff on dissolved 

oxygen, the sources and quantities of contaminants 

discharged to the White River or Fall Creek during 

storms were not identified.

Study Area

Fall Creek drains 318 mi2 in east-central 

Indiana and flows from its headwaters in northwestern Henry County to its confluence with the 

White River in Indianapolis, approximately 60 mi 

to the southwest (figs. 1,2). Fall Creek is a highly 

complex, urban and rural hydrologic system that 

includes an instream water-supply reservoir, 

several low-head dams, water withdrawal for 

public supply, a variety of point-source discharges, 

stormwater and combined-sewer overflows, and 

interbasin water transfer into the basin as a result 

of aqueduct overflow.

4 Effects of Combined-Sewer Overflows and Urban Runoff, Fall Creek, Indianapolis, Indiana
86°7'30" 85°37'30"

40°00' -

38°45' Area for 

figures 3 and 4

Base from U.S. Geological Survey digital data, 1:100,000, 1983 

Albers Equal Area projection

0 5 10 15 20 MILES

T

10 15 20 KILOMETERS

EXPLANATION

URBAN AREA

APPROXIMATE AREA OF !ND!ANAPOLIS SERVED BY COMBINED SEWERS

FALL CREEK DRAINAGE DIVIDE

0 PRECIPITATION STATION AND SITE IDENTIFICATION NUMBER

WATER-QUALITY AND STREAMFLOW-GAGING STATIONS

SYNOPTIC STATIONS UPSTREAM FROM EMERSON AVENUE

Figure 2. Locations of selected hydrologic and cultural features and data-collection 

stations in and near Fall Creek watershed, Indianapolis, Ind.

Study Area 5
Central Indiana has a humid continental 

climate that is affected by polar and gulf air masses. 

Interaction of the air masses causes daily and 

seasonal variations in weather. Summers are hot 

and humid, and winters are cold. Normal annual 

precipitation at the Indianapolis International 

Airport climatological station is 39.12 in. (National 

Oceanic and Atmospheric Administration, 1986, 

p. 3), approximately one-third of which runs off as 

streamflow (Crawford and Mansue, 1988, fig. 5). 

Precipitation is fairly evenly distributed throughout the year, and summer precipitation is usually 

sufficient to meet agricultural needs (Hosteler, 

1978, p. 1-2). July is the warmest month; normal 

(1951-80) maximum temperature is 85.2°F, and 

normal minimum temperature is 64.9°F (National 

Oceanic and Atmospheric Administration, 1986, 

p. 3). January is the coolest month; normal 

maximum temperature is 34.2°F, and normal 

minimum temperature is 17.8°F.

The Fall Creek watershed is in the Tipton 

Till Plain Physiographic Province, a flat to gently 

rolling glacial till plain (Schneider, 1966, p. 41,49). 

The major soil associations in the watershed are 

the Miami-Crosby silt loams association on the 

uplands and the soils of the alluvial terraces and 

flood plains (Ulrich, 1966, p. 66-73, 88-89). In 

the downstream parts of the watershed in Marion 

and Hamilton Counties, the four mapped associations are the Crosby-Brookston, the Miami-Crosby, 

the Fox-Ockley, and the Shoals-Genesee (Hosteler, 

1978, p. 3-4, general soil map; Sturm and Gilbert, 

1978, p. 2-6, general soil map). The CrosbyBrookston association consists of deep, somewhal 

poorly to very poorly drained soils lhal have formed 

in a ihin layer of loess or silly till on nearly level 

uplands. These soils are used mainly for farming; 

corn and soybeans are the principal crops. Wetness 

is the major use limitation. The Miami-Crosby 

association consists of deep, well-drained to somewhat poorly drained soils that have formed in a 

thin layer of loess or silty till on gently sloping to 

moderately steep hillsides and knolls. These soils 

are used mainly for parks, subdivisions, and 

fanning. Erosion and wetness are the major use 

limitations. The Fox-Ockley association consists 

of moderately deep, well-drained soils that have

formed in sand and gravel on generally level 

terraces and oulwash plains. In Marion County, 

ihese soils are used mainly for urban development 

In Hamilton County, these soils are used for 

cultivated crops mostly corn, wheat, and 

soybeans. These soils are well suited to urban 

uses and are only moderately limited by erosion 

and wetness. The Shoals-Genesee association 

consists of deep, well-drained to poorly drained 

soils that have formed in loamy alluvium on nearly 

level flood plains. Use of these soils is severely 

limited by flooding.

Agriculture is the predominant land use in the 

watershed. The major cultivated crops are corn, 

soybeans, and winter wheat. Pasture and woodlots 

are on some of the steeply sloping land and in some 

of the flood plains. Swine and beef production also 

are importanl agricultural activities. Urban land 

use predominates in the downstream part of the 

watershed in Marion County. Urban land use 

includes induslrial, commercial, iransportation, and 

residential land uses. The densily of urban land use 

and the intensity of urban development increases 

downstream along Fall Creek. Much of the flood 

plain upstream from Emerson Avenue (fig. 3) is 

parkland used for recreation, although residential 

developmenl is occurring. Formerly rural and 

agricultural land near Mud Creek and Geist 

Reservoir is being developed rapidly for residential 

and commercial land uses.

Bedrock in the Fall Creek watershed is 

primarily limestone of Silurian and Devonian age 

that dips to the southwest. Surficial deposits are 

sandy, silty till on the uplands and outwash sand 

and gravel with some alluvial deposits in the flood 

plain (Herring, 1976, p. 5, fig. 2). Unconsolidated 

deposils range from less than 50 to more lhan 300 ft 

in thickness. The thickest deposits are in the uppermost headwaters of Fall Creek and immediately 

downstream from the dam at Geisl Reservoir, 

whereas the thinnest deposits are upslream from the 

reservoir (Gray, 1983). Well yields in the part of 

the watershed in Marion County range from 300 to

6 Effects of Combined-Sewer Overflows snd Urban Runoff, Fall Creek, Indisnapolis, Indiana
86°09' 86°06' 86°03'

39°45'

39°48' -

Base from U.S. Geological Survey digital data, 1:100,000, 1983 

Albers Equal Area projection

4 MILES

EXPLANATION

A

o

o 1

WATER-QUALITY AND STREAMFLOW-GAGING STATION 

SYNOPTIC STATION

4 KILOMETERS

© POINT OF DISCHARGE OF FILTER BACKWASH TO FALL CREEK

->^ AQUEDUCT | LOW-HEAD DAM

t INTERBASIN WATER TRANSFER (AQUEDUCT OVERFLOW)

t WATER WITHDRAWAL SITE FOR PUBLIC SUPPLY

Figure 3. Locations of selected hydrologic features and 

data-collection stations on Fall Creek in Indianapolis, Ind.

Study Area 7
more than 500 gal/min, 0 to 150 gal/min, and 50 to 

250 gal/min for wells properly installed in outwash, till, and limestone, respectively (Herring, 

1976, figs. 7, 8). Maps of the water table in the 

most downstream segment of the outwash aquifer 

in Marion County show that Fall Creek is a gaining 

stream (water typically flows from the aquifer to the 

stream) (Meyer, 1979, fig. 5; Smith, 1983, fig. 7). 

Herring (1976, p. 21) found that water from both 

the outwash aquifer and the limestone aquifer discharges to Fall Creek in the vicinity of 71st Street.

The major hydrologic feature on Fall Creek 

is Geist Reservoir, a water-supply reservoir for 

Indianapolis (fig. 2). Fall Creek drains an area of 

318 mi , of which drainage from 215 mi2 must 

pass through Geist Reservoir (Hoggatt, 1975, 

p. 142-143). The dam is at river mile 17.6 and 

impounds water approximately 7 mi upstream. 

Normal storage capacity is 21,180 acre-feet and 

normal surface area is 1,800 acres (Ruddy and Hitt, 

1990, p. 100). Typical widths of Geist Reservoir 

range from 0.25 to 0.5 mi. The major tributaries 

to Fall Creek Mud Creek, Lick Creek, and 

Indian Creek drain 43.1, 38.2, and 25.6 mi2, 

respectively. Mud Creek and Indian Creek join 

Fall Creek downstream from Geist Reservoir at 

river miles 13.5 and 15.5, respectively. Lick Creek 

joins Fall Creek upstream from the reservoir.

Most of the hydrologic and water-quality data 

were collected during the study from three streamflow-gaging stations downstream from Geist 

Reservoir. These stations were at Emerson Avenue, 

Central Avenue, and 16th Street (at river miles 9.2, 

3.8, and 1.3, respectively); drainage areas above the 

stations were 298, 312, and 317 mi2, respectively 

(fig. 3). Water flowing over the spillway or 

released from Geist Reservoir flows freely past the 

Emerson Avenue gaging station until it reaches a 

low-head dam at Keystone Avenue (river mile 6.4) 

where water is impounded for withdrawal and 

treatment for public-water supply. Immediately 

downstream from the dam, wastewater (filter backwash) from the water-treatment plant is discharged 

to Fall Creek. Water flowing over the dam at 

Keystone Avenue flows in a deeply incised

channel, through a series of pools and riffles, and 

past the Central Avenue gaging station until it 

reaches a low-head dam at Dr. Martin Luther King 

Jr. Street (river mile 2.4). Water is impounded 

upstream approximately 1 mi to Meridian Street.

Water flowing over the dam at Dr. Martin 

Luther King Jr. Street flows into another 

impounded reach of Fall Creek that extends from 

the dam to a large rocky riffle at the base of the 

aqueduct (river mile 1.8, fig. 3). The aqueduct 

is part of a canal that transports water for public 

supply from the White River, over Fall Creek, 

and delivers it to a water-treatment plant near 

16th Street Some of the canal water overflows 

the aqueduct, effectively transferring water from 

the White River to Fall Creek. Water in Fall Creek 

flows freely from the aqueduct downstream to the 

16th Street gaging station, where it flows into backwater from a low-head dam on the White River. 

Filter backwash from the water-treatment plant 

near 16th Street is discharged to Fall Creek approximately 500 ft upstream from 16th Street

Approximately 14 mi2 of Indianapolis is 

served by combined sewers that discharge during 

storm runoff to Fall Creek through 28 combinedsewer overflows (fig. 4). Most of the area served 

by combined sewers is in the older central part of 

Indianapolis. At least one of the overflows had 

been constructed before 1900. Many of the 

combined sewer overflows are visible from the 

streambank, but some overflows are submerged or 

incorporated into the base of bridges. The overflows differ greatly in size and range from 2 to 12 ft 

in diameter. The size of the overflow generally 

corresponds to the size of area served by the 

combined sewer. Drainage areas of the combinedsewer overflows that discharge to Fall Creek range 

from 12 to 3,093 acres (Howard Needles Tammen 

& Bergendoff, 1983, p. C-2, C-3). The most 

upstream combined-sewer overflow discharges to 

Fall Creek at 39th Street. Black sludge deposits 

are found on the streambed downstream from 

39th Street and correspond to the reach of Fall 

Creek that receives discharge from combinedsewer overflows.

8 Effects of Combined-Sewer Overflows and Urban Runoff, Fall Creek, Indianapolis, Indiana
86°09' 86°06' 86°03'

39°50'

39°45' ^

Base from U.S. Geological Survey digital data, 1:100,000, 1983 

Albers Equal Area projection 0

h 

EXPLANATION 0

MILES

2 KILOMETERS

AREAS SERVED BY COMBINED SEWERS THAT DISCHARGE TO FALL CREEK

AREAS SERVED BY COMBINED SEWERS THAT DO NOT DISCHARGE TO FALL CREEK

T COMBINED-SEWER OVERFLOW THAT DISCHARGES TO FALL CREEK

V AQUEDUCT

Figure 4. Locations of combined-sewer overflows that discharge to 

Fall Creek, Indianapolis, Ind. (Drainage areas modified from Howard 

Needles Tammen & Bergendoff, 1983, fig. 3,4).

Study Area 9
A reconnaissance of Fall Creek downstream 

from 63rd Street revealed a variety of pipes, 

culverts, and overflow structures. Many of the 

discharge structures were large storm-sewer overflows or culverts that discharged runoff from streets 

and bridges. All of the combined-sewer overflows 

on Fall Creek and the discharge of filter backwash 

by the two water-treatment plants are permitted 

discharges for the National Pollutant Discharge 

Elimination System (NPDES). In addition, several 

dischargers have received permits to discharge 

noncontact cooling water to Fall Creek. Most of 

the cooling-water discharges are downstream 

from 16th Street.

Acknowledgments

The author thanks the many people 

who assisted in the study. Vasiliki Keramida, 

Indianapolis Department of Public Works, 

was instrumental in planning the study. 

Charles Crawford, U.S. Geological Survey, 

Indianapolis, Ind., wrote the water-quality compositing program. John Barr and Kim Cussen, 

Indianapolis Department of Public Works, helped 

plan and provide the laboratory analytical services. 

John Curran and the forecasting staff of the 

National Weather Service provided spontaneous 

weather forecasts upon request. Cynthia Wagner 

and Joseph Ketterman, Marion County Health 

Department, assisted in identifying combinedsewer overflows on Fall Creek. Tim Bumgardner, 

Indianapolis Water Company, provided data on 

water withdrawals and filter-backwash discharges 

and access to the aqueduct.

METHODS OF INVESTIGATION

The study was designed to investigate the 

effects of combined-sewer overflows and urban 

runoff on Fall Creek and to estimate the load (mass) 

of contaminants discharged during the low-flow

period of mid-July to mid-October. This period 

was selected because streamflow usually is at the 

lowest rate of the year and provides the least 

amount of dilution for contaminants discharged 

to Fall Creek. Biota are most susceptible to low 

concentrations of dissolved oxygen during this 

period because of the decreased rate of streamflow 

for dilution and the warm summer temperatures 

that decrease the solubility of dissolved oxygen 

and increase the rates of reactions that consume 

oxygea A 90-day period was selected to help 

ensure that several runoff events would be 

sampled. The 90-day period studied was July 22, 

1987, to October 19,1987. This period began and 

ended during base flow and included seven storms 

(referred to herein as "storms 1-7") that produced 

runoff in the Indianapolis area, six of which were 

sampled for water-quality analysis.

Selection of Data-Collection Sites

Fall Creek was surveyed by canoe on 

June 23,1987, from 56th Street to 16th Street 

and on June 30,1987, from Keystone Avenue to 

16th Street. The purpose of the reconnaissance was 

to investigate the physical conditions of Fall Creek, 

especially hydraulic characteristics, and to map the 

locations of combined-sewer overflows, storm 

sewers, and other outfalls. Fall Creek also was 

surveyed by foot on July 1,1989, at selected sites 

from Keystone Avenue to 16th Street during an 

intense thunderstorm to observe and photograph 

the stream and overflowing sewers during storm 

runoff.

Three stations were selected for streamflow 

measurement and intensive water-quality sampling, 

primarily on the basis of hydraulics and the 

locations of combined-sewer overflows (figs. 3,4). 

Fall Creek at Millersville (station 00352500, 

referred to as "Emerson Avenue") and Fall Creek 

at 16th Street at Indianapolis (station 03352875, 

referred to as "16th Street") were streamflowgaging stations already in the Indiana streamflow 

network. Fall Creek at Central Avenue at 

Indianapolis (station 03352850, referred to as 

"Central Avenue") was established for this study.

10 Effects of Combined-Sewer Overflows and Urban Runoff, Fall Creek, Indianapolis, Indiana
Emerson Avenue is upstream from all Fall 

Creek combined-sewer overflows and receives 

urban and rural runoff and water released from 

Geist Reservoir. Central Avenue is in the center of 

the combined-sewer-overflow area; 15 combinedsewer overflows are upstream from Central 

Avenue, and 13 are downstream. The station at 

16th Street is downstream from 27 of 28 combinedsewer overflows on Fall Creek, downstream from 

the overflow at the aqueduct, and immediately 

downstream from the filter backwash (figs. 3,4). 

All of the stations are on free-flowing reaches of 

Fall Creek. Water-quality samples also were 

collected from the aqueduct overflow and from 

the filter backwash upstream from 16th Street.

Two synoptic water-quality surveys were done 

as part of the study. A base-flow synoptic survey 

was done on September 24,1987, at 20 sites on 

Fall Creek. Water-quality characteristics were 

measured in the field from bridges across Fall 

Creek from Pendleton to 16th Street. A high-flow 

synoptic survey was done on September 29,1987, 

during storm runoff (storm 6) at eight bridges from 

Emerson Avenue to 16th Street

Measurement of Stage and 

Computation of Streamflow

A continuous record of streamflow at each 

station was computed by applying a stage-streamflow rating curve to a stage record obtained at 

5-min (Emerson Avenue and Central Avenue) or 

15-min (16th Street) intervals. The stage of Fall 

Creek was measured by a float (Emerson Avenue 

and Central Avenue) or a pressure-sensing device 

called a manometer (16th Street) and was digitally 

recorded on paper tape. The stage-streamflow 

rating curves were developed by a graphical 

analysis of current-meter streamflow measurements 

made at various stages.

The rate of canal overflow at the aqueduct on 

August 19,1987, was measured directly at the 

overflow spillway. The rate of canal overflow 

at the aqueduct on September 23,1987, was 

calculated as the difference in discharge of the canal 

measured upstream and downstream from the 

aqueduct. Methods used to measure and compute 

streamflow and discharge are given in Rantz and 

others (1982a, 1982b).

Measurement of Precipitation

Daily precipitation was measured by the 

National Weather Service at the Indianapolis International Airport climatological station (National 

Oceanic and Atmospheric Administration, 1987) 

and by various observers in the Indianapolis 

area. Observers measured precipitation with 

nonrecording, volumetric rain gages typically 

an acrylic, cylindrical storage gage with a 3-in.- 

diameter opening. Observers read the rain gages 

between 0600 and 0900. Precipitation measured 

by the National Weather Service was read at midnight (2400 hours).

Water-Quality Samples and Measurements

Depth-integrated water-quality samples were 

collected from the downstream sides of bridges at 

five verticals in the cross section of the stream by 

use of the equal-discharge-increment method 

(Guy and Norman, 1970, p. 31-32). Each vertical 

represented 20 percent of the streamflow. Samples 

were collected at the centroid of the streamflow 

increment, approximately at the 10th, 30th, 50th, 

70th, and 90th percentiles of the cumulative streamflow. Locations of the sampling verticals at various 

stages (streamflows) were determined early in the 

study by analysis of streamflow-measurement notes 

made to define the stage-streamflow rating curves. 

Depths at the sampling verticals typically ranged 

from 1 to 6 ft.

Water-quality samples were collected during 

storms by use of a US D-74AL-TM sampler 

suspended from a bridge crane equipped with a 

cable-and-reel assembly (Edwards and Glysson, 

1988, p. 13). Water-quality samples were collected 

during base flow by use of a US DH-S-48-TM 

sampler suspended from a handline (Edwards and 

Glysson, 1988, p. 11). Both of the samplers were 

painted with epoxy and equipped with nylon 

nozzles and silicon rubber gaskets suitable for 

the collection of samples to be analyzed for trace 

metals.

Measurement of Stage snd Computation of Streamflow 11
Samplers were lowered and raised through 

the water column at a uniform rate to ensure the 

collection of a depth-integrated sample. The 

amount of water collected at each vertical 

depended on the type of sample being collected. 

During storms, most of the samples collected 

were composited in the District laboratory by 

use of a time-and-flow weighting technique. 

Approximately 3,600 mL of sample were needed 

and approximately 720 mL of water were collected 

at each vertical. Samples from each vertical were 

poured through a polyethylene funnel into a single 

1-gal polyethylene sample container. Base-flow 

samples and selected storm samples were not 

composited. Storm samples that were not composited were collected near the end of a period of 

storm runoff, after earlier storm samples had been 

composited and processed. Storm samples that 

were not composited are termed "individual" 

sample types in tables 8 and 11. Approximately 

7.2 L of sample were needed for base-flow and 

individual storm samples. Each of the five verticals 

was sampled twice, and the samples were combined 

in two 1-gal containers. Three base-flow samples 

were split as part of the quality-assurance program; 

consequently, approximately 14.4 L of water 

were needed for each of these samples. Sample 

containers were labeled with the site, date, and 

midpoint sample-collection time and stage and 

stored at 4°C in an ice-water bath in coolers while 

awaiting transport to the U.S. Geological Survey 

laboratory in Indianapolis. Samplers, funnels, and 

sample containers were field rinsed with sample 

water immediately before collecting samples from 

the first vertical.

Samples for the analyses of fecal coliform 

bacteria were collected in a sterile 300-mL (BOD) 

bottle secured to a weighted sampler suspended 

from a handline. The sampler was lowered 

approximately 1 ft below the surface of the water 

at the center of flow and allowed to fill. The bottle 

was removed from the sampler, and a small volume 

of sample was poured off to allow the sample to be 

mixed easily before analysis. The bottle was sealed 

with a sterile ground-glass stopper and plastic cap;

labeled with the site, date, and time; and stored at 

4°C in an ice-water bath in coolers while awaiting 

transport to the DPW laboratory. Dechlorinating 

agents were not used. Fecal coliform samples were 

picked up and driven to the DPW laboratory by 

DPW personnel at 3-hour intervals. The maximum 

holding time for fecal coliform samples was about 

4 hours.

Water temperature, pH, dissolved-oxygen 

concentration, and specific conductance were made 

with a Hydrolab model 4041 multiparameter field 

meter, a Hydrolab model 2000 datasonde; or a 

continuous, flowthrough water-quality monitor. 

Saturation concentrations of dissolved oxygen were 

calculated as presented in Bowie and others (1985, 

p. 91, eq. 3-5). The Hydrolab field meter was 

used for all base-flow measurements, all synoptic 

measurements, and all storm measurements at 

Emerson Avenue and Central Avenue. For baseflow and synoptic measurements, water quality 

was measured at approximately the 25th, 50th, and 

75th percentiles of the cumulative cross-sectional 

streamflow, at 1.5- to 2-ft depth, and the measurements averaged. For storm measurements, water 

quality was measured at approximately the center 

of flow, at 0.5- to 2-ft depth.

The field meter was calibrated onsite (for 

storm and high-flow synoptic measurements) or 

in the laboratory (for base-flow and base-flow 

synoptic measurements) according to the manufacturer's instructions. Calibration was checked at 

the end of the day (for base-flow and base-flow 

synoptic measurements) or every 12 to 16 hours 

(during storm and high-flow synoptic measurements). If calibration checks were not within 

the limits specified by Gordon and Katzenbach 

(1983, p. 76-79), the field meter was recalibrated 

(for the particular parameter that differed) and a 

prorated correction, based on the time since the 

last calibration, was applied to the data (Gordon 

and Katzenbach, 1983, p. 89-93). In general, the 

field meters held calibration, and few corrections 

were applied.

12 Effects of Combined-Sewer Overflows snd Urbsn Runoff, Fsll Creek, Indisnspolis, Indiana
Hydrolab model 2000 datasondes were used 

in addition to field meters for storm measurements 

at Emerson Avenue and Central Avenue during 

storms 1 and 2. The datasondes have the capability 

of recording water-quality measurements, and their 

utility in measuring storm runoff was investigated. 

Two datasondes, calibrated in the laboratory 

according to the manufacturer's instructions, were 

placed in the center of flow next to the field meters 

at each site. Data from the datasondes were compared with data from the field meters, and data from 

the datasonde that best agreed with the field meter 

is presented in this report. Data from the datasondes are used in this report because the frequency 

of measurement with the datasonde was greater 

than that with the field meter and provided more 

detailed information on water quality during storm 

runoff. Use of the datasondes was discontinued 

after storm 2 because of the long time required for 

calibration and other operational difficulties.

A continuous, flowthrough water-quality 

monitor was used for all storm measurements at 

16th Street. Characteristics and use of the monitor 

are discussed in Gordon and Katzenbach (1983) 

and in Martin and Craig (1990, p. 14-27).

During storms, water-quality samples were 

collected at approximately every 0.2-ft change in 

stage or at approximately 4- to 6-hour intervals 

when the stage was changing slowly. Water-quality 

measurements were made with field meters during 

collection of every water-quality sample or more 

frequently. Water-quality measurements were 

made with the datasondes at 30-min intervals and 

with the continuous monitor at 15-min intervals.

Fecal coliform samples were collected after 

every water-quality sample for the first two storms 

and after every other water-quality sample for 

the remaining storms. The large number of fecal 

coliform samples collected during the first two 

storms exceeded the capacity of the DPW laboratory for prompt analyses.

A depth-integrated water-quality sample was 

collected from the spillway of the canal overflow 

at the aqueduct on October 15,1987, by use of the 

equal-width-increment, equal-transit-rate method 

(Guy and Norman, 1970, p. 32-33). The sample

was collected by use of a US DH-48-TM sampler 

suspended from a wading rod (Edwards and 

Glysson, 1988, p. 10-11). Water-quality 

measurements were made by use of a Hydrolab 

model 4041 multiparameter field meter in the 

canal immediately upstream from the spillway at 

0.5 ft depth.

A grab water-quality sample was collected 

from the outfall of the filter backwash near 

16th Street on August 27,1989, by submersing two 

field-rinsed, 1-gal polyethylene sample containers 

in the effluent. Grab water-quality samples also 

were collected at Central Avenue and at 16th Street, 

as part of the quality-assurance program, from the 

center of flow by use of a plastic bucket suspended 

from a handline. Sample water was poured through 

a funnel into two 1-gal containers, which were 

then labeled and stored in coolers at 4°C. The 

sample containers, funnel, and bucket were field 

rinsed immediately before sample collection.

Sample Processing, Compositing, 

Preservation, and Analysis

Base-flow, individual storm, canal-overflow, 

and filter-backwash samples were taken to the 

laboratory and stored in darkness at 4°C in a 

walk-in refrigerator. The maximum holding time 

before processing and preservation for these 

samples was 6 hours. Samples were shaken and 

poured into a clean, deionized-water-rinsed, 8-L 

polyethylene churn splitter and were thoroughly 

mixed. While the sample was being mixed in 

the churn, five 1-L polyethylene bottles and 

one 500-mL glass bottle were filled with raw 

sample water. The remaining sample was filtered 

through a 0.45-u.m-pore-size filter made of 

cellulose triacetate into a 1-L polyethylene bottle. 

The order in which the samples were processed 

and the order the bottles were filled were randomized, except that the filtered sample always was 

done last. The bottles were labeled with the date 

and an alphanumeric code that uniquely identified 

the sample and the types of chemical analyses to be 

performed for each bottle.

Sample Procesaing, Compoaiting, Preservation, and Analyaia 13
A time-and-flow weighting technique was 

used to composite most of the water-quality 

samples collected during periods of storm runoff. 

This technique was used because the cost of 

individually analyzing the many storm samples 

was prohibitively expensive. Storm samples to be 

composited were taken to the laboratory and stored 

in darkness at 4°C. The maximum holding time 

before processing and preservation for these 

samples was 36 hours. Storm samples consisted 

of one 1-gal container for each sampling time. 

Samples were shaken and poured into a clean, 

deionized-water-rinsed, 4-L polyethylene churn 

splitter and thoroughly mixed. The sample volume 

drawn off for use in the storm-runoff composite 

sample was calculated as follows (RJ. Picketing, 

U.S. Geological Survey, written commun., 1980):

vi = (qiti)/(l4iti)xVT, (1) 

where

v,- is volume of the storm sample collected at 

time i added to the composite sample (L),

qi is instantaneous streamflow at the midpoint 

time of sample collection (f^/s),

tj is time interval (min, equal to one-half the 

time since the previous sample plus onehalf the time to the next sample; the time 

interval for the first sample is from the start 

of the storm runoff to one-half the time to 

the second sample, the time interval for the 

last sample is from the end of the storm 

runoff to one-half the time to the next-tolast sample),

I is summation operator, and 

VT is volume of composite sample required 

(7.5 L).

Samples were composited in an 8-L polyethylene churn splitter and thoroughly mixed. Seven 

bottles were filled with sample water in the same 

manner as that used for the base-flow samples.

Two of the 1-L bottles containing unfiltered 

sample water were preserved with concentrated 

sulfuric acid (2 mL each) and were used for the 

determination of chemical oxygen demand, nitrate 

plus nitrite, ammonia, organic nitrogen, and 

phosphorus. Two of the 1-L bottles containing 

unfiltered sample water were preserved with concentrated nitric acid (2 mL each) and were used for 

the determination of arsenic, mercury, selenium, 

aluminum, barium, cadmium, chromium, copper,

iron, lead, nickel, and zinc. The remaining 1-L 

bottle containing unfiltered sample water contained 

no preservative and was used for the determination 

of total solids and carbonaceous biochemical 

oxygen demand. The 500-mL bottle containing 

raw sample water was preserved with 2.5 mL of 

concentrated sulfuric acid and was used for the 

determination of oil and grease. The 1-L bottle 

containing filtered sample water had no preservative added and was used for the determination of 

alkalinity, sulfate, chloride, dissolved solids, and 

orthophosphate. Samples were placed on ice in 

coolers and were driven to the DPW laboratory 

for analysis.

All chemical and biological analyses were 

done by the Indianapolis DPW laboratory. 

Alkalinity, chloride, total solids, carbonaceous 

biochemical oxygen demand, chemical oxygen 

demand, oil and grease, ammonia, phosphorus, 

and fecal coliform bacteria were analyzed 

according to the methods given in American Public 

Health Association and others (1985). Organic 

nitrogen, arsenic, mercury, selenium, aluminum, 

barium, cadmium, chromium, copper, iron, lead, 

nickel, and zinc were analyzed according to the 

methods given in U.S. Environmental Protection 

Agency (1983). Nitrate plus nitrite and orthophosphate were analyzed according to the methods 

given inTechnicon Industrial Systems (1973a, 

1973b). Sulfate was analyzed according to the 

method given in Skougstad and others (1979, 

p. 501-504). Dissolved solids were analyzed 

according to the method given in American 

Public Health Association and others (1981).

Chemical analyses for "dissolved" constituents alkalinity, sulfate, chloride, dissolved 

solids, and orthophosphate were done on water 

samples that were filtered through a 0.45-jimpore-size filter and are operationally defined 

as dissolved (U.S. Environmental Protection 

Agency, 1983, p. xiv, METALS-4; Fishman and 

Friedman, 1989, p. 4). Chemical analyses for 

"total" constituents total solids, carbonaceous 

biochemical oxygen demand, chemical oxygen 

demand, nitrate plus nitrite, ammonia, organic 

nitrogen, phosphorus, arsenic, mercury, and 

selenium were done on unfiltered water samples

14 Effects of Combined-Sewer Overflows and Urban Runoff, Fall Creek, Indianapolia, Indiana
(whole-water samples that contain water and 

suspended sediment). These analytical methods 

determine more than 95 percent of the constituent 

present in the unfiltered sample (Fishman and 

Friedman, 1989, p. 4, 50-51). Chemical analyses 

for "total recoverable" constituents oil and 

grease, aluminum, barium, cadmium, chromium, 

copper, iron, lead, nickel, and zinc were done 

on unfiltered water samples. The analytical 

methods (which required a dilute-acid digestion 

of the water and suspended sediment for the 

metals or extraction with an organic solvent for 

oil and grease) may not completely digest or 

extract the sample and may not determine more 

than 95 percent of the constituent present, hence 

the term "recoverable" (U.S. Environmental 

Protection Agency, 1983, p. METALS-2-5; 

Fishman and Friedman, 1989, p. 4,50-51). 

Detection limits for the analytical methods used 

in this study are given in the last row of table 1. 

Concentrations less than the detection limit were 

plotted as one-half the detection limit in figure 13.

Calculation of Event-Mean Concentration

Event-mean concentration is the flowweighted average concentration of a constituent 

during a period of storm runoff (Fisher and Katz, 

1988, p. 6). Most of the water-quality samples 

collected during storm runoff were composited by 

use of a time-and-flow weighting technique. The 

number of water samples collected during storm 

runoff at a site ranged from 3 to 27. When possible, 

all of the samples for a single period of runoff were 

composited by use of the weighting technique. 

Where this could be done, analytical results for 

the composite sample are the event-mean 

concentrations. Often, however, several composite 

samples or a composite sample and an individual 

sample were required to adequately sample the 

period of runoff and not exceed the 36-hour 

holding time for compositing samples. Where this 

procedure was required, the mass of the constituent 

in the part of the runoff the sample represented was 

calculated by multiplying the analytical result 

(concentration) by the runoff volume. Constituent 

masses were summed for all runoff samples for that

period of runoff. Runoff volumes corresponding to 

the runoff samples also were summed for that 

period of runoff. Event-mean concentration was 

calculated as the total constituent mass divided by 

the total runoff volume. Concentrations less than 

the detection limits were assigned one-half the 

detection limit for the purposes of calculating 

event-mean concentration. The mean concentration 

of split samples was used to calculate event-mean 

concentrations. Event-mean concentrations were 

not adjusted to remove the base-flow contribution 

to constituent mass or runoff volume.

Quality Assurance

Approximately 25 percent of the samples 

analyzed for this study were for quality assurance. 

Quality-assurance samples consisted of deionizedwater blanks, standard reference water samples, and 

two types of split samples (one type for assessing 

analytical precision, another for assessing the 

effect of holding time before sample processing). 

Deionized water was placed in eight qualityassured 1-L polyethylene bottles obtained from 

the U.S. Geological Survey Water Quality 

Laboratory in Arvada, Colo., and two 1-gal 

polyethylene bottles obtained from a distributor in 

Indianapolis. Deionized-water blanks were stored 

in darkness at 4°C for 24 hours at the laboratory, 

then processed, preserved, and analyzed in the 

same manner as base-flow samples. The purpose 

of analyzing the deionized-water blanks was to 

determine if analyses obtained from the 1-gal 

bottles to be used for field sampling were different 

from those obtained from the quality-assured 1-L 

bottles normally used by the U.S. Geological 

Survey. Also, the deionized-water blanks were 

used to determine if contamination had occurred 

during sample processing, preservation, transport, 

or analysis. Nearly all constituents and properties 

were below detection limits for the deionized-water 

blanks (table 1). Detectable concentrations of 

carbonaceous biochemical oxygen demand and 

chemical oxygen demand in both types of bottles, 

and barium and iron in the 1-L bottles, were 

measured in the blank samples (table 1).

Calculation of Event-Mean Concentration 15
^

o> 

m

a

I

g;

1

I

 *

1

|

»

(A

3 

Q.

c

1

3D

§

a

Tl

=

I

5" 

Q.

5

1

«r

i

(A

Table 1 . Water-quality analyses for quality-assurance samples

[i.d, identification; ft3/s, cubic feet per second; \)S/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degree Celsius; mg/L, milligrams per liter; n.

N, nitrogen; P, phosphorus; M-g/L, micrograms per liter; n.d., not determined; <, less than; SRWS, standard reference water sample; hold, split sample held 48 

sd., standard deviation; --, no data]

Site

n.a.

n.a.

Central

Central

Central

Central

16th Street

16th Street

n.a.

n.a.

n.a.

n.a.

Sample I.d.

Liter poly3

Gallon poly3

Storm 2

Storm 2

Base flow 2

Base flow 2

Storm 6

Storm 6

SRWS5

Mean, sd.

SRWS5

Mean, sd.

Sample type

Deionized water3

Deionized water3

Grab4

Grab 48-hr hold4

Grab4

Grab 48-hr hold4

Grab4

Grab 48-hr hold4

M98orT97

All labs

T99

All labs

Date

7-16-97

7-16-87

7-31-87

7-31-87

8-11-87

8-11-87

9-30-87

9-30-87

10-15-87

n.a.

10-15-87

n.a.

Time1

n.a.

n.a.

0830

0830

1320

1320

0910

0910

n.a.

n.a.

n.a.

n.a.

Streamflow

(tf/a)

(00061 )2

n.a.

n.a.

214

214

35

35

50

50

n.a.

n.a.

n.a.

n.a.

Specific 

conductance

(uS/cm)

(00095)2

n.d.

n.d.

411

411

600

600

827

827

n.d.

514, 19

n.d.

n.d.

PH ,

(00400)2

n.d.

n.d.

7.7

7.7

7.8

7.8

7.8

7.8

n.d.

8.31,0.1

n.d.

n.d.

n.a. n.a. Detection limit6 n.a. n.a. n.a. n.d. n.d. 
Table 1. Water-quality analyses for quality-assurance samples Continued

Site

n.a. 

n.a.

Central

Central

Central

Central

16th Street

16th Street

n.a.

n.a.

n.a.

n.a.

n.a.

Disaolved Dissolved Dissolved Dissolved 

alkalinity sulfate chloride solids 

(mg/L as CsCO3) (mg/L) (mg/L) (mg/L) 

Sample l.d. (29801)2 (00945)2 (00940)2 (00515)2

Liter poly3 

Gallon poly3

Storm 2

Storm 2 hold4

Base flow 2

Base flow 2 hold4

Storm 6

Storm 6 hold4

SRWS5

Mean, sd.

SRWS5

Mean, sd.

Detection limit6

<1

128

124

200

194

254

256

172

179,5

n.d

n.d.

1

<1 - <10

30 23 270

31 23 263

51 39 364

51 39 371

71 64 494

71 64 497

42 32 311

41.5, 3.8 32.5, 2.9 309, 19

n.d. n.d. n.d.

n.d n.d. n.d

1 1 10

Total 

solids 

(mg/L) 

(00500)2

:!»

293

315

404

399

566

557

n.d

n.d

n.d.

n.d

10

Suspended 

solids8 

(mg/L)

<10 

<10

23

52

40

28

72

60

n.d.

n.d.

n.d.

n.d.

n.d.

carb

bio

oxyg

(

>

i
£ Table 1. Water-quality analyses for quality-assurance samples Continued

 ffects ofCombl

3

1

1

O

1

c

1

33

|

 n

i

1

3

i

_ 

I

Site

n.a.

n.a.

Central

Central

Central

Central

16th Street

16th Street

n.a.

n.a.

n.a.

n.a.

n.a.

Sample l.d.

Liter poly3

Gallon poly3

Storm 2

Storm 2 hold4

Base flow 2

Base flow 2 hold4

Storm 6

Storm 6 hold4

SRWS5

Mean, sd.

SRWS5

Mean, sd.

Detection limit6

Total 

nitrate plua nitrite 

(mg/L as N) 

(00630)2

<0.005

<.005

.35

.35

.28

.28

.96

1.03

n.d.

n.d.

n.d.

n.d.

.005

Total 

ammonia 

(mg/L aa N) 

(00610)2

<0.01

<.01

.15

.08

.08

.10

.14

.30

n.d.

n.d.

n.d.

n.d.

.01

Total 

organic nitrogen 

(mg/L) 

(00605)2

<0.01

<.01

1.08

1.20

.72

.78

1.08

.96

n.d.

n.d.

n.d.

n.d.

.01

Total 

phosphorua 

(mg/L) 

(00665)2

<0.01

<.01

.20

.18

.07

.07

.49

.38

n.d.

0.04, 0.01

n.d.

n.d.

.01

Dlasolved 

orthophoaphate 

(mg/L aa P) 

(00671 )2

<0.01

<.01

<.01

<.01

<.01

<.01

.07

.08

.03

0.03, 0.01

n.d.

n.d.

.01
Table 1. Water-quality analyses for quality-assurance samples Continued

£.

i

8

<D

Total Total Total Total Total 

recoverable recoverable recoverable recoverable recoverable 

aluminum barium cadmium chromium copper 

(jig/L) (ng/L) (ng/L) (ng/L) (ug/L) 

Site Sample l.d. (01105)2 (01007)2 (01027)2 (01034)2 (01042)2

n.a. Liter poly3 <10 30 <10 <10 <10 

n.a. Gallon poly3 <10 <10 <10 <10 <10

Central Storm 2 960 90 <10 <10 10 

Central Storm 2 hold4 860 50 <10 <10 10

Central Base flow 2 190 80 <10 <10 <10 

Central Base flow 2 hold4 170 80 <10 <10 <10

16th Street Storm 6 1,780 50 <10 <10 <10 

16th Street Storm 6 hold4 1,780 140 <10 <10 <10

n.a. SRWS5 110 220 10 30 20 

n.a. Mean, sd. 126, 42 98, 12 16.3, 2.3 26.0, 4.3 16.8, 2.5

n.a. SRWS5 140 <10 <10 <10 30 

n.a. Mean, sd. 86,31.4 25.1,10.2 4.7,1.5 16.3,6.5 27.9,4.6

n.a. Detection limit6 10 10 10 10 10

Total 

recoverable 

Iron 

(HQ/L) 

(01045)2 

10 

1,490 

1,190 

340 

330 

1,130 

1,130 

120 

100, 9 

130 

137, 29 

10 

Midpoint time of grab sample collection. 

^WATSTORE (U.S. Geological Survey) and STORET (U.S. Environmental Protection Agency) parameter code. 

'Quality-assured, 1 -liter polyethylene sample bottles obtained from U.S. Geological Survey National Water Quality Laboratory in Arvada, Colo. One-

a distributor in Indianapolis. Deionized water was stored in the liter and gallon bottles for 24 hours at 4°C, then processed and sent to the laboratory. 

4Grab samples were split with a cone splitter. One split was immediately processed and sent to the laboratory. Hie second split was stored in a gallon 

and sent to the laboratory. 

5Standard reference water samples (SRWS) obtained from the U.S. Geological Survey National Water Quality Laboratory. Mean and standard deviatio

laboratories that participate in the U.S. Geological Survey Analytical Evaluation Program (Victor I. Janzer, National Water Quality Laboratory, written com

*Limit of detection for the methods used by the Indianapolis Department of Public Works Laboratory. 

'Nitrification was not inhibited in this sample. Reported concentrations were adjusted for oxidizable nitrogen. 

Suspended solids were calculated as the difference between total sohds and dissolved solids.
The DPW laboratory participates in the 

U.S. Geological Survey's Standard Reference 

Water Sample program (Schroder and others, 1980; 

Janzer, 1985, p. 331). Water samples are sent to 

numerous laboratories throughout the Nation for 

the analysis of a variety of constituents and properties. On the basis of these analyses, the most 

probable values (means) of the constituent concentrations are calculated. Individual analyses within 

0.5 standard deviations of the most probable value 

are rated excellent, within 1.0 standard deviations 

are rated good, within 1.5 are rated satisfactory, 

within 2.0 are rated questionable, and greater than 

2.0 are rated poor. Ratings for individual constituents are averaged and overall ratings for major 

constituents, trace constituents, and nutrients are 

calculated. Overall ratings for the DPW laboratory 

were consistently good or satisfactory. Additional 

quality-assurance information for the DPW laboratory is given in Bobay (1988, p. 9-12) and in 

Duwelius and Greeman (1989, p. 9-12).

Standard reference water samples for major 

constituents (M98) and trace constituents (T97 

and T99) were obtained from the U.S. Geological 

Survey and submitted to the DPW laboratory 

labeled as regular base-flow samples (blind qualityassurance samples). Standard reference water 

samples were mailed to the District laboratory in 

Teflon bottles and were poured directly into sample 

bottles that had been rinsed with the reference 

water. Standard reference water samples were 

neither split nor filtered but were preserved in the 

same manner as regular base-flow samples. The 

purpose of analyzing the standard reference water 

samples was to assess analytical accuracy by comparing analyses produced by the DPW laboratory 

with the most probable values calculated from 

analyses produced by a large number of laboratories. Ratings for individual constituents, according 

to the standard-deviation criteria given above, were 

excellent to good for major constituents and were 

excellent to poor for trace constituents (table 1).

Split samples are a pair of identical samples. 

Four composite storm samples and three base-flow 

samples were split and submitted for analysis as 

part of the quality-assurance program. The purpose 

of analyzing these split samples was to assess

analytical precision assuming no contamination 

or other differences caused by sample processing, 

preservation, or transport. Analytical results for 

these samples are given in tables of environmental 

data (tables 8,11) rather than in the table of 

quality-assurance data (table 1). Average (mean) 

concentrations of split samples were used for 

calculations and interpretations of water quality. 

Concentrations less than the detection limits were 

assigned one-half the detection limit for the 

purposes of calculating mean concentration.

Storm samples were split by doubling the 

volume of composite sample required (VT=15L, 

eq. 1) and placing one-half of the volume of the 

storm sample added to the composite sample 

(Vj, eq. 1) in one 8-L churn and the remaining 

one-half in a second 8-L churn. Each split was 

processed and preserved in the same manner as a 

non-split composite storm sample. Each base-flow 

sample to be split consisted of four 1 -gal containers. 

Each container was shaken and rapidly poured 

through an acrylic cone splitter (R. J. Picketing, 

U.S. Geological Survey, written commun., 1980), 

which split the sample into two 8-L churn splitters. 

Each split was processed and preserved in the same 

manner as a nonsplit base-flow sample.

Three grab water-quality samples were 

collected at Central Avenue and 16th Street and 

split as part of the quality-assurance program 

to investigate the effects of holding time prior to 

sample processing and preservation on the analytical results. Each grab sample to be split consisted 

of four 1 -gal containers. Each container was shaken 

and rapidly poured through a cone splitter which 

split the sample into an 8-L churn splitter and two 

1-gal sample containers that were rinsed with 

deionized water. The split in the churn splitter was 

processed and preserved in the same manner as a 

nonsplit base-flow sample. The split in the two 

1-gal sample containers was stored in darkness at 

4°C for 48 hours, then processed and preserved in 

the same manner as a nonsplit base-flow sample. 

Analytical results for the split samples that were 

immediately processed and for the split samples 

that were held for 48 hours before processing are 

given in table 1.

20 Effects of Combined-Sewer Overflows and Urbsn Runoff, Fsll Creek, Indisnspolis, Indisna
Analytical precision and the effect of holding 

time before sample processing were assessed 

by calculating statistics of the log difference 

(expressed in log percent) between split samples. 

Log difference, which expresses the relative 

difference between split samples with respect to 

their logarithmic mean, is the only symmetric, 

additive, and normed measure of relative difference 

(Tornqvist and others, 1985, p. 43,44):

ln(y/x) = (y-x)/L(x,y) , (2)

where

ln(y/x) is log difference between split samples 

(unitless),

x is concentration in the first split sample 

(mass/volume),

y is concentration in the second split 

sample (mass/volume), and

L(x,y) is logarithmic mean (base e) of x and y 

(mass/volume).

The logarithmic mean is less than the arithmetic mean but greater than the geometric mean.

Log difference was used instead of arithmetic 

difference because of the property of additivity, 

which is preferred for statistical summaries. In 

addition, log difference is not limited to a maximum difference of 200 percent as is arithmetic 

difference and, therefore, is a better measure of 

relative difference between split samples with large 

differences in concentration. Log difference is 

easily calculated as the natural logarithm of the 

concentration of the second split sample divided 

by concentration of the first split sample:

ln(y/x) , (3)

where

In is logarithm (base e), and x and y are 

as previously defined.

Log difference used in the tables and text is 

expressed in log percent and is calculated as the log 

difference multiplied by 100 percent (Tornqvist and 

others, 1985, p. 45). The absolute values of the log 

differences were calculated for split samples used to 

assess analytical precision (table 2). Absolute value 

was used because the direction of change was not of

interest. Absolute values of the log difference 

were not calculated for split samples used to assess 

the effect of holding time before sample processing 

(table 3). Absolute value was not used because 

the direction of change was of interest. For the 

purposes of this analysis, concentrations less than 

the detection limit were assigned one-half the 

detection limit. Detection limits are given in the 

last row of table 1.

The most precise analytical determinations 

(mean and standard deviation of log differences 

equal to or less than 4.6 log percent) were for 

alkalinity, sulfate, chloride, dissolved solids, total 

solids, nitrate plus nitrite, arsenic, aluminum, and 

iron (table 2). The most imprecise determinations 

(mean log differences greater than 47 log percent 

and the standard deviation of log differences greater 

than 65 percent) were for organic nitrogen, oil and 

grease, and barium. All concentrations of mercury, 

selenium, and cadmium, and many of chromium 

and nickel were less than the detection limits 

(tables 8,11); high precision (small log differences) 

for these constituents is a result of the many 

nondetections.

The effect of holding water samples for 

48 hours before processing did not seem to bias 

the analytical results. None of the 25 water-quality 

constituents exhibited a consistent increase or 

decrease in concentration for all pairs of split 

samples (median, minimum, and maximum 

concentration difference between split samples, 

table 3). For parameters with measurable differences in concentration for at least two of the three 

pairs of split samples, only phosphorus, aluminum, 

and iron showed a consistent direction of change (a 

decreased concentration in the split sample held for 

48 hours, table 3). Concentration differences (and 

log differences) between split samples for these 

three constituents, however, were similar in magnitude to those observed for split samples used to 

assess analytical precision (table 2) and probably 

do not indicate a bias that can be attributed to 

holding time.

Quality Aaaurance 21
Table 2. Statistical analysis of split quality-assurance samples used to assess analytical precision

[CBOD, carbonaceous biochemical oxygen demand; COD, chemical oxygen demand; mg/L, milligram per liter, |Xg/L, microgram per liter]

cts of Combine

Q.

i

O

a

1

«

o.

c

1

3D

0,

i

O

3*

i

I

1

3"

o. 

«

S

Water-quality 

characteristic 

(unita)

Dissolved:

Alkalinity

(mg/L)

Sulfate

(mg/L)

Chloride

(mg/L)

Solids

(mg/L)

Orthophosphate

(mg/L)

Suspended:

Solids5

(mg/L)

Total:

Solids

(mg/L)

20-day CBOD

(mg/L)

COD

(mg/L)

Nitrate plus nitrite

(mg/L)

Ammonia

(mg/L)

Organic nitrogen

(mg/L)

Number 

of aplit 

samples1

7

7

7

7

7

7

7

7

6

6

6

6

Mean concentration Abaolute difference 

of split sam plea 2' 3 between split samplea

Median Minimum Maximum Median Minimum Maximum Mean

213 138 277 209 1.4

56 37 75 002 1.0

46 29 85 002 1.2

411 298 573 15 2 24 3.1

.03 .005 .29 .00 .00 .05 11.6

75 18 193 19 3 45 22.5

469 401 661 16 0 41 3.0

7 2 12 106 30.7

32 21 43 109 7.0

.50 .33 .77 .01 .00 .05 3.5

.30 .07 .71 .03 .01 .08 17.4

1.18 .87 2.45 .63 .02 1.55 79.8

A
Tabie 2. Statistical analysis of split quality-assurance samples used to assess analytical precision Continued

gB

3

g

| 

I

B

Water-quality 

characteristic 

(units)

Phosphorus

(mg/L)

Arsenic

Mercury

Selenium

Total recoverable:

Oil and grease

(mg/L)

Aluminum

Barium

Cadmium

Chromium

Copper

Iron

Lead

Nickel

Zinc

(HS/L)

Number 

of split 

samples1

6

6

6

6

7

6

6

6

6

6

6

6

6

6

Mean concentration 

of spiit samples * 3

Median Minimum Maximum

.56 .20 1.34

4 1 10

.1 .1 .1

.5 .5 .5

2 1 3

2,850 190 11,470

90 40 120

55 5

5 5 20

20 10 30

2,640 310 3,630

20 5 20

5 5 10

30 10 40

Abaoiute difference 

between split sampiea

Median

.02

0

0

0

1

30

20

0

0

0

60

5

0

0

Minimum

.00

0

0

0

0

10

0

0

0

0

0

0

0

0

Maximum

.36

0

0

0

3

300

50

0

5

10

250

10

0

10

Mean

14.6

.0

.0

.0

80.9

4.1

47.1

,0

11.6

11.6

3.9

34.7

.0

11.6

Abs

M

'Split samples are a pair of theoretically identical samples.

^Concentrations less than the detection limit were assigned one-half the detection limit for this analysis. Detection limits are given in the last row of table 

'Statistics were rounded to the same number of significant figures as analytical measurements of the same magnitude.

Absolute log difference is the absolute value of the difference between a pair of split samples divided by the logarithmic mean of the pair of split sample

others. 1985, p. 44-45). It is used in this context to summarize the relative precision of chemical analyses.

Suspended solids were calculated as the difference between total solids and dissolved solids.
Table 3. Statistical analysis of split quality-assurance samples used to assess the effect of holding samples at 4°C for 48 hours b

[CBOD, carbonaceous biochemical oxygen demand; COD, chemical oxygen demand; mg/L, milligram per liter; flg/L, microgram per liter]

cts of Combine

£

I

o

S

3.

i

3

c

3

31

i

.3!

 n

3

i

i

£

I

3

*

Water-quality Number 

characteriatic of split 

(units) aamples1

Dissolved:

Alkalinity

(mg/L)

Sulfate

(mg/L)

Chloride 

(mg/L)

Solids

(mg/L)

Orthophosphate

(mg/L)

Suspended:

Solids6

(mg/L)

Total:

Solids

(mg/L)

20-day CBOD 

(mg/L)

COD

(mg/L)

Nitrate plus nitrite

(mg/L)

Ammonia 

(mg/L)

Organic nitrogen

(mg/L)

Phosphorus 

(mg/L)005

3

3

3

3

3

3

3

3

3

3

3

3

3

Mean concentration Concentration difference 

of aplit samples * 3 between split samples4

Median Minimum Maximum Median Minimum Maximum Mean

197 126 255 4-26 1.8

51 31 71 0-10 -1.1

39 23 64 0 0 0 .0

368 267 496 -3 -7 7 .0

.005 .005 .08 .00 -.01 .00 -4.5

38 34 66 12 -29 12 -9.2

402 304 562 5 -22 9 -1.5

44 10 0 -13 1 -46.2

18 12 23 0-11 1.0

.35 .28 1.00 .00 -.07 .00 -2.3

.12 .09 .22 -.02 -.16 .07 -11.9

1.02 .75 1.14 -.06 -.12 .12 -23

.19 .07 .44 .02 .00 .11 12.0

L

M

-2
Table 3. Statistical analysis of split quality-assurance samples used to assess the effect of holding samples at 4°C for 48 hours be

preservation Continued

Mean concentration 

of aplit samples * 3

Water-quality 

characteristic 

(units)

Arsenic 

(ug/L)

Mercury

Selenium

(Hg/L)

Total recoverable:

Oil and grease 

(mg/L)

Aluminum

Barium

Cadmium 

(ug/L)

Chromium 

(Hg/L)

Copper 

(Hg/L)

Iron 

(Hg/L)

Lead 

(Rg/L)

Nickel

1 Zmc

Number 

of split 

samples 1

3

3

3

3

3

3

3

3

3

3

3

3

3

Median

2

.1

.5

1

910

80

5

5

5

1,130

5

5

10

Minimum

2

.1

.5

1

180

70

5

5

5

340

5

5

5

Maximum

3

.1

.5

2

1,780

100

5

5

10

1,340

5

7.5

10

Concentration difference 

between split aamples4

Median

0

.0

.0

0

20

0

0

0

0

10

0

0

0

Minimum

-1

.0

.0

0

0

-90

0

0

0

0

0

-5

0

Maximum

0

.0

.0

0

100

40

0

0

0

300

0

0

0

Mean

-13.5

.0

.0

.0

7.4

-14.7

.0

.0

.0

8.5

.0

-23.1

.0

Log 

Med

11

3

£ 

5 1Split samples are a pair of theoretically identical samples. One split was processed immediately, whereas the other was held 48 hours at 4°C before process

a chemical analysis. 

* Concentrations less than the detection limit were assigned one-half the detection limit for this analysis. Detection limits are given in the last row of table 

'Statistics were rounded to the same number of significant figures as analytical measurements of the same magnitude.

Concentration differences were calculated as the immediately processed sample minus the held sample. Positive differences indicate higher concentrations 

negative differences indicate higher concentrations in the held sample.

5Log difference is the difference between a pair of split samples divided by the logarithmic mean of that pair of split samples multiplied by 100 percent (T

in this context to summarize the relative changes attributed to holding samples prior to processing. Positive log difference indicates higher concentrations in th

ative log difference indicates higher concentrations in the held sample.

'Suspended solids were calculated as the difference between total solids and dissolved solids.
HYDROLOGIC CONDITIONS

Differences in the amounts of precipitation 

and streamflow can profoundly influence water 

quality. Knowledge of the hydrologic conditions 

during which water-quality samples were collected 

is critical for interpreting water-quality data and is 

needed to place interpretations and conclusions 

in a historical context. Precipitation and streamflow were far below normal during the study 

unusually extreme conditions for the summer 

low-flow period.

Precipitation

Normal annual precipitation at the Indianapolis International Airport climatological station 

is 39.12 in., one-third of which falls during July 

through October (National Oceanic and Atmospheric Administration, 1986, p. 3). Normal 

monthly precipitation is 4.32 in. for July, 3.46 in. 

for August, 2.74 in. for September, and 2.51 in. 

for October. Precipitation at the Indianapolis 

International Airport climatological station 

(station 1, table 4 and fig. 2) was substantially 

below normal during the study period (July 22- 

October 19,1987). Monthly precipitation for July 

was 213 percent of normal; for August, 25 percent 

of normal; for September, 51 percent of normal; and 

for October, 54 percent of normal. Although July 

was much wetter than normal, more than 82 percent 

of the precipitation fell in the first half of the month, 

before the study period (table 4a).

Monthly precipitation measured by observers 

in the Indianapolis area generally was in agreement 

with that measured at the Indianapolis International 

Airport by the National Weather Service and 

shows the small amount of rain that fell in and near 

Indianapolis during the study period (tables 4a-4d 

and fig. 2). Daily precipitation was highly variable 

among stations on some dates (for example, 

July 26-31, table 4a). Spatially variable, highintensity precipitation is characteristic of summer 

thunderstorms that cause localized heavy rain.

Seven storms produced runoff in the 

Indianapolis area during the study period. Waterquality samples were collected during runoff from 

six of these storms. The six sampled storms and 

periods of storm runoff were July 26-28 (storm 1),

July 29-August 3 (storm 2), August 26-27 

(storm 3), September 10-13 (storm 4), 

September 16-17 (storm 5), and September 29-30 

(storm 6). The unsampled storm on August 17 

(table 4b) was similar in volume of precipitation to 

storms 5 and 6. All of the storms except storm 4 

were characterized as moderate-intensity, shortduration storms. Storm 4 was a low-intensity, 

long-duration storm. Storms 1 and 2 included 

multiple periods of intense precipitation, whereas 

storms 3,5, and 6 included only one period of 

intense precipitation. Precipitation for each of the 

storms, based on all precipitation stations in and 

near the watershed is as follows:

Precipitation, in inchea

Storm Minimum Median Maximum

1

2

3

4

5

6

0.28

.04

.07

.09

.10

.36

0.83

.66

.25

.20

.36

.45

1.41

1.59

.61

.67

.55

.50

Although the median amount of precipitation 

for some of the storms was small, all storms caused 

at least some of the combined sewers to overflow.

Streamfiow

Historic streamflow information has been 

summarized for the Emerson Avenue gaging 

station for the 42-year period 1944 85 (Arvin, 

1989, p. 470-476). Streamflow during this period 

was regulated by Geist Reservoir. Compared with 

historic streamflow, monthly mean streamflow 

during July and August (1987) was near or above 

normal, whereas streamflow during September 

and October (1987) was well below normal. 

Monthly mean streamflow for October 1987 

(42 ft3/s, table 5) was the second lowest of record. 

Only the monthly mean for October 1944 (38 ftVs) 

was lower. Most of the high streamflow in July 

occurred before the beginning of the study period.

26 Effects of Combined-Sewer Overflowa and Urban Runoff, Fail Creek, Indianapolis, Indiana
Table 4a. Daily precipitation at selected stations in and near Indianapolis, July 1987 

[T, trace; -, no data]

Daily precipitation1 , in inche*, at given precipitation station2

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

Total

1

5.09

.01

.00

.02

.01

.97

.00

.00

.04

.00

.01

.82

.50

.00

.10

.00

.00

.00

.00

.00

.00

.00

.00

.00

.00

.62

.58

T

.36

.04

.05

9.22

2

0.00

.84

.00

.00

.00

.40

.15

.00

.00

.22

.00

.00

.21

.80

.00

.38

.00

.00

.00

.00

.00

.00

.00

.00

.00

.00

.36

.10

.00

.32

.11

3.89

3

0.57

2.17

.00

.04

.00

.47

.20

.00

.00

T

.00

.00

.93

.94

.00

.11

.00

.00

.00

.00

.00

.00

.00

.00

.00

.00

1.24

.17

.00

.87

.12

7.83

4

0.91

2.02

.00

.08

.00

.51

.28

.00

.00

.00

.00

.00

1.07

.53

T

.09

.00

.00

.00

.00

.00

.00

.00

.00

.00

.00

.18

.84

.00

.23

.06

6.80

5

0.92

1.76

.00

.08

T

.48

.13

.00

.00

.33

.00

.00

.55

.69

.00

.06

.00

.00

.00

.00

.00

.00

.00

.00

.00

T

.02

.26

.38

.00

T

5.66

6

1.29

2.50

.00

.11

T

.51

.15

.00

.29

.00

.00

.00

1.06

.69

.00

.06

.00

.00

.00

.00

.00

.00

.00

.00

.00

.00

.05

.57

.00

.25

.03

7.56

7

0.80

1.98

.00

.00

.10

.38

.34

.00

.00

.01

.00

.00

.62

.51

.00

.06

.00

.00

.00

.00

.00

.00

.00

.00

.00

.00

.48

.00

.00

1.02

.49

6.79

8

0.84

1.33

.00

.43

.00

.43

.11

.00

.00

.22

.00

.00

.81

1.16

.00

.26

.00

.00

.00

.00

.00

.00

.00

.00

.00

.00

.52

.19

.00

1.05

.00

7.35

9 10 11

0.79

1.11

.00

.17

x

.48

.23

.00

.00

T

.00

.00

.83

.71

.00

.10

.00

.00

.00

.00

.00

.00

.00

.00 .00

.00 .00

.00 .00

.10 .34 .20

.54 .75 1.10

.00 .00 .00

.32 .30 .00

.77 .00 .25

5.81

12

1.52

4.16

.00

.00

.00

.00

.23

.00

.00

.03

.00

.00

.98

.64

.00

.05

.00

.00

.00

.00

.00

.00

.00

.00

.00

.00

.56

.38

.00

.66

.26

9.47

'Daily precipitation was measured in the morning between 0600 and 0900 hours, except at station 1 which was measured at midnight 

(2400 hours).

locations of precipitation statious are shown in figure 2.

Streamflow 27
Table 4b. Daily precipitation at selected stations in and near Indianapolis, August 1987 

[T, trace; -, no data]

Dally precipitation1 , In Inches, at given precipitation station2

Osy

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

Total

1

0.00

T

T

.00

.00

.00

.00

.01

.07

.00

.00

.00

.00

.00

.00

.00

.32

.00

.00

.00

.03

.00

.00

.00

.11

.24

.04

.03

.00

.00

.01

.86

2

0.00

.26

.00

.00

.00

.00

.00

.00

.20

T

.00

.00

.00

.00

.00

.00

.13

.00

.00

.00

.00

.08

.05

.00

.00

.94

.61

.18

.00

.00

.03

2.48

3

0.00

.11

.00

.00

.00

.00

.00

.00

.06

.00

.00

.00

.00

.00

.00

.00

.17

.00

.00

.00

.00

.04

.00

.00

.00

.52

.26

.06

.00

.00

.00

1.22

4

0.01

.15

.00

.00

.00

.00

.00

.00

.05

.00

T

.00

.00

.00

.00

.00

.57

.00

.00

.00

.00

.05

.00

.00

.01

.16

.19

.07

.00

.00

.00

1.26

5

0.00

.00

.04

.00

.00

.00

.00

.00

.13

.00

.00

.00

.00

.00

.00

.00

.28

.00

.00

.00

.00

.00

.00

.00

T

.15

.07

.03

.00

.00

.01

.71

6

0.00

.00

.19

.00

.00

.00

.00

.00

.15

.00

.00

.00

.00

.00

.00

.00

.46

.00

.00

.00

.00

.07

.00

.00

T

.16

.09

.03

.00

.00

.04

1.19

7

0.00

.00

.08

.00

.00

.00

.00

.00

.04

.00

.00

.00

.00

.00

.00

.00

.22

.00

.00

.00

.00

.05

.00

.00

.00

.15

.24

.05

.00

.00

T

.83

8

0.00

.16

.00

.00

.00

.00

.00

.00

.21

.00

.00

.00

.00

.00

.00

.00

.28

.00

.00

.00

.00

.07

.00

.00

.00

.73

-

-

-

.00

.00

9

0.02

.00

.06

.00

.00

.00

.00

.00

.07

.00

.00

.00

.00

.00

.00

.00

.15

.00

.00

.00

.00

.03

.10

.00

.01

.08

.24

.02

.00

.00

.01

.79

10

0.00

.10

.22

.00

.00

.00

.00

.00

T

.00

.00

.00

.00

.00

.00

.00

.38

.00

.00

.00

.00

T

.00

.00

.00

.19

.29

.10

.00

.00

T

1.28

11

0.00

.00

.20

.00

.00

.00

.00

.00

.05

.00

.00

.00

.00

.00

.00

.00

-

.00

.00

.00

.00

.00

.00

.00

T

.20

.10

T

.00

.00

T

12

0.05

.00

.02

.00

.00

.00

.00

.00

.04

.00

.00

.00

.00

.00

.00

.00

.08

.00

.00

.00

.00

T

T

.00

.00

.15

.30

.08

.00

.00

T

.72

'Daily precipitation was measured in the inoming between 0600 and 0900 hours, except at station 1 which was measured at midnight 

(2400 hours).

2Locations of precipitation stations are shown in figure 2. 

28 Effects of Combined-Sewer Overflows and Urban Runoff, Fsll Creek, Indianapolis, Indiana
Table 4c. Daily precipitation at selected stations in and near Indianapolis, September 1987 

[T, trace; , no data]

Dally precipitation1 , in inches, at given precipitation station2

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

Total

1

0.00

.00

.00

.00

.00

.00

.00

.00

.00

.00

.04

.20

.00

.00

.34

.06

.28

.00

.00

.00

.00

.02

.00

.00

.00

.00

.00

.00

.47

.00

1.41

2

0.00

.00

.00

.00

.00

.00

.00

.00

T

.00

.12

.04

.15

.00

.00

.04

.40

.03

.00

.00

.00

.05

.00

.00

.00

.00

.00

.00

.49

.00

1.32

3

0.00

.00

.00

.00

.00

.00

.00

.00

T

.00

.16

.01

.00

.00

.00

.05

.15

.02

.00

.00

.00

T

.11

.00

.00

.00

.00

.00

.20

.16

.86

4

0.00

.00

.00

.00

.00

.00

.00

.03

.00

.00

.18

.02

.00

.00

.00

.10

.55

.01

.01

.00

T

.03

.01

.00

.00

.00

.00

.00

.44

.00

1.38

5

T

0.00

.00

.00

.00

.00

.00

.00

.00

T

.64

.01

.02

.00

.00

.19

.40

.02

T

.00

.00

.01

.00

.00

.00

.00

.00

.00

.49

.00

1.78

6

0.00

.00

.00

.00

.00

.00

.00

.00

T

.00

.15

.06

.02

.00

.00

.00

.45

.05

.00

.00

.00

.01

.00

.00

.00

.00

.00

.00

.37

.08

1.19

7

0.00

.00

.00

.00

.00

.00

.00

.00

.00

.00

.16

.03

.00

.00

.00

.08

.40

.02

.00

.00

.00

.01

.00

.00

.00

.00

.00

.00

.02

.40

1.12

8 9

0.00 0.00

.00

.00

.00

.00

.00

.00

.00

.00

.00

.23

.06

.00

.00

.00 .00

.18 .10

.31

.06

.00

.00

.00

.00

.00

.00

.00

.00

.00

.00

.40

.00

1.24

10 11

0.00 0.00

.00 .00

.00 .00

.00 .00

.00 .00

.00 .00

.00 .00

T .00

.00 .00

.00 .00

.18 .08

.01

.00

.00

.00

.10

.10

.00

.00

.00

.00

.00

.00

.00

.00

.00

.00

.00

.50

.00

.79

12

0.00

.00

.00

.00

.00

.00

.00

.00

T

.00

.07

.05

.00

.00

.00

.24

.22

.00

.00

.00

.00

.00

.00

.00

.00

.00

.00

.00

.39

T

.97

'Daily precipitation was measured in the morning between 0600 and 0900 hours, except at station 1 which was measured at midnight 

(2400 hours).

^Locations of precipitation stations are shown in figure 2.

Streamflow 29
Table 4d. Daily precipitation at selected stations in and near Indianapolis, October 1987

[T, trace; -, no data]

Daily precipitation1 , in Inches, st given precipitation station2

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

Total

1

0.00

.00

.00

.00

.03

.02

.00

.00

.01

.33

.00

.00

.00

.00

.00

.00

.02

.00

.00

.03

.00

.01

.00

.19

.00

.53

.19

.00

.00

.00

.00

1.36

2

0.03

.00

.00

.00

.00

.03

.09

.00

.18

.00

.30

.00

.00

.00

.00

.00

.10

.00

.00

.03

.05

.00

.00

.02

.34

.00

.85

.00

.00

.00

.00

2.02

3

0.00

.00

.00

.00

.00

.09

.08

.00

.05

T

.44

T

.00

.00

.00

.00

.08

.00

.00

.05

.01

.00

.03

.04

.23

.00

.95

.00

.00

.00

.00

2.05

4

T

.00

.00

.00

T

.08

.08

.01

.04

.10

.26

.00

.00

.00

.00

.00

.08

T

.00

.05

.01

T

.02

.01

.23

.00

.84

T

.00

.00

.00

1.81

5

0.00

.00

.01

.00

.00

.09

.05

T

.03

.11

.27

.00

.00

.00

.00

.00

.08

.00

.00

.05

.00

.02

.03

.15

.13

.01

.70

.00

.00

.00

.00

1.73

6

T

.00

.00

.00

.00

.08

.07

T

.02

.00

.00

.00

.00

.00

.00

.00

.10

.00

.00

.00

.00

.00

.00

.38

.00

.00

.74

.00

.00

.00

.00

1.39

7 6 9 10

0.00 0.00 0.00

.00 .00 .00

.00 .00 .00

.00 .00 .00

.00 .08 .00

.12 .00 .03

.12 .00 .02

.00 .00

.00 .00

.00 .29

.42

.00

.00

.00

.00

.00

.09

.00

.00

.00

.00

.00

.00

.32

.00

.00

.80

.00

.00

.00

.00

1.71

11

0.00

.00

.00

.00

.10

.10

.07

.00

.03

.03

.30

.00

.00

.00

.00

.00

.20

--

--

-

--

--

--

--

--

--

12

0.00

.00

T

.00

.00

T

T

.00

.01

T

.32

.00

.00

.00

.00

.00

.06

.00

.00

.00

.02

.00

.00

.03

.17

.00

.84

.00

.00

.00

T

1.45

1Daily precipitation was measured in the morning between 0600 and 090 hours, except at station 1 which was measured at midnight 

(2400 hours).

^Locations of precipitation stations are shown in figure 2.

30 Effects of Combined-Sewer Overflows and Urban Runoff, Fsll Creek, Indianapolis, Indiana
Table 5. Daily mean streamflow at Fall Creek at Emerson Avenue, Central Avenue, and 16th Street, July through 

October 1987

Daily mean atreamflow (cubic feet per second)

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

Mean

Median

Minimum

Maximum

Emerson 

Avenue

475

1.180

1,340

861

521

381

327

248

184

146

126

108

336

800

649

410

269

194

151

121

101

88

79

70

66

65

117

109

81

308

257

328

194

65

1,340

July

Central 

Avenue

904

910

1,060

655

413

310

255

193

148

121

102

114

269

565

487

322

210

153

123

93

74

55

48

38

36

40

118

84

54

241

212

271

153

36

1,060

16th 

Street

815

1,070

1,310

916

535

396

315

241

177

127

100

113

491

625

607

404

277

213

176

130

110

98

96

93

91

97

175

114

84

241

224

337

213

84

1,310

Emerson 

Avenue

167

168

164

217

201

142

106

86

74

74

70

59

56

73

59

61

63

60

62

61

60

60

60

60

60

63

64

56

57

62

56

86

62

56

217

Auguat

Central 

Avenue

137

133

131

158

158

115

78

60

52

41

36

26

20

34

21

23

36

22

21

22

23

25

27

22

24

37

31

25

20

26

20

52

27

20

158

16th 

Street

178

161

163

195

205

141

102

87

83

66

66

57

42

60

48

45

61

45

47

42

47

44

40

36

37

44

59

48

33

39

40

76

48

33

205

Streamflow 31
Table 5. Daily mean streamflow at Fall Creek at Emerson Avenue, Central Avenue, and 16th Street, July through 

October 1987 Continued

Daily mean atreamflow (cubic feet per second)

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

Mean

Median

Minimum

Maximum

Emeraon 

Avenue

64

57

59

62

71

70

70

69

67

59

73

71

69

69

67

58

57

55

48

46

49

53

53

52

52

51

50

50

55

52

59

58

46

73

September

Central 

Avenue

24

16

18

18

28

27

27

24

27

17

31

34

32

27

27

25

36

22

19

14

16

17

17

17

17

15

15

16

30

22

23

22

14

36

16th 

Street

43

23

19

26

39

36

41

28

35

29

46

54

52

40

50

59

57

39

32

24

26

26

33

30

24

35

27

25

54

46

37

35

19

59

Emeraon 

Avenue

40

38

39

39

39

39

40

40

40

41

43

40

40

40

40

41

42

41

41

42

43

43

44

45

46

45

66

46

40

38

38

42

40

38

66

October

Central 

Avenue

22

16

14

14

14

16

15

14

14

15

20

16

15

15

14

15

19

22

19

18

16

13

18

22

23

20

69

29

21

18

18

19

16

13

69

16th 

Street

51

29

26

25

24

27

43

32

31

35

36

33

32

35

31

29

35

48

42

51

33

30

30

33

37

34

97

53

51

52

59

39

34

24

97

32 Effect* of Combined-Sewer Overflow* and Urban Runoff, Fall Creek, Indianapolia, Indiana
The highest daily mean streamflow measured 

at Emerson Avenue during the study period was 

308 ft3/s on July 30 (table 5). Daily mean streamflow of this magnitude is exceeded approximately 

26 percent of the time (Arvin, 1989, p. 473). The 

lowest daily mean streamflow measured at Emerson Avenue during the study period was 38 ft3/s 

on October 2. Daily mean streamflow of this 

magnitude is exceeded approximately 99 percent 

of the time. Most of the daily mean streamflows 

measured during the study period were less than 

71 ft3/s, a rate exceeded approximately 75 percent 

of the time. Daily mean streamflow at Emerson 

Avenue was at or less than the 7-day, 10-year low 

flow 39 ft3/s (Stewart, 1983, p. 121> for 7 days 

in October 1987 (table 5).

Base Flow

During base flow, streamflow at Emerson 

Avenue was greater than that downstream at 

Central Avenue or 16th Street (fig. 5, table 5) and 

showed the effect of water withdrawn for public 

supply at Keystone Avenue (fig. 3). The median 

streamflow measured at Emerson Avenue during 

October was 40 ft3/s (table 5), and the median rate 

of water withdrawn for public-water supply downstream at Keystone Avenue during October was 

35 ft3/s (table 6). Other surface-water inflows 

were assumed to be negligible during this month 

of extreme low flows; therefore, the median streamflow downstream from Keystone Avenue at Central 

Avenue during October was expected to be 5 ftVs 

(40 ft3/s - 35 ft3/s, table 5). The measured median 

streamflow at Central Avenue during October was 

16 ft3/s. The difference between the expected and 

measured rates indicates that 69 percent (11 ft /s) of 

the base-flow streamflow at Central Avenue during 

October was contributed by ground-water seepage 

in the reach between Emerson Avenue and Central 

Avenue. Most of the ground-water inflow likely 

occurred between Keystone Avenue and Central 

Avenue, where the stream is deeply incised in 

the flood plain. The median rate of backwash

effluent discharged to Fall Creek immediately 

downstream from Keystone Avenue during 

October was 0.17 ft3/s (table 6) and constituted 

only a minor part (1 percent) of the streamflow 

measured at Central Avenue during October.

The median rate of streamflow measured at 

16th Street during October was 34 ft3/s (table 5). 

The increase in the median rate of streamflow 

during October from Central Avenue to 16th Street 

was 18 ft3/s (34 ft3/s - 16 ft3/s, table 5), and can be 

attributed to three sources: aqueduct overflow, 

ground-water inflow, and backwash effluent. Most 

of the increase can be attributed to overflow from 

the aqueduct approximately 0.5 mi upstream from 

16th Street (fig. 3).

The amount of water that overflowed the 

aqueduct into Fall Creek varied during the study 

but was not continuously measured. The rate of 

overflow did not appear to increase during storm 

runoff, but it did increase with increased rates of 

flow in the canal needed to meet greater demand for 

public supply. The rate of overflow estimated on 

August 18 was 22 ft3/s (table 5). The rate of aqueduct overflow measured on August 19 at the 

spillway was 24 ft3/s. The water-supply utility 

installed boards in the spillway of the aqueduct 

on or about August 23 to reduce the amount of 

aqueduct overflow. The rate of aqueduct overflow measured on September 23 as the difference 

of canal-flow measurements made upstream and 

downstream from the aqueduct was 16 ft3/s. The 

rate of overflow estimated on October 15 was 

7 ft3/s. The rate of overflow measured on July 21, 

1977, was 25 ft3/s (Meyer, 1979, p. 10).

On the basis of the limited information 

collected during the study period, the median rate 

of overflow before August 23 was estimated to be 

23 ft3/s, and the median rate of overflow on and 

after August 23 was estimated to be 12 ft3/s. On 

the basis of these estimates, aqueduct overflow 

constituted approximately 35 percent of the streamflow measured at 16th Street during October.

Streamflow 33
350

300

o 

o ui tn 250

m

r> 

o

o

200

ui

OSfc! 150

b

<

100

50

PERIOD OF STUDY

 EMERSON AVENUE

- - - - CENTRAL AVENUE 

16th STREET

JULY AUGUST SEPTEMBER 

1987

OCTOBER

Figure 5. Daily mean streamflow at Fall Creek at Emerson Avenue, 

Central Avenue, and 16th Street, July through October 1987. (Daily mean 

streamflows greater than 350 cubic feet per second are not shown.)

34 Effects of Combined-Sewer Overflows snd Urbsn Runoff, Fsll Creek, Indisnspolis, Indlsna
Table 6. Daily mean water withdrawal from Fall Creek at Keystone Avenue and daily mean discharge of filter 

backwash to Fall Creek at Keystone Avenue and at 16th Street, July through October 1987

[Data from Tim Bumgardner, Indianapolis Water Company, written cornmun., September 1988]

Daily mean rate of water withdrawal or discharge of filter backwash1 

(cubic feet per aecond)

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

Mean

Median

Minimum

Maximum

Water 

withdrawal

at 

Keystone 

Avenue

52 

55

53

47

41

50

52

57

53

51

56

56

56

56

50

50

52

54

51

58

61

63

62

65

60

58

57

58

59

55

58

55

56

41

65

July

Filter 

backwash

at

Keystone 

Avenue

0.23 

.32

.39

.23

.05

.06

.19

.36

.19

.28

.28

.25

.23

.39

.31

.36

.22

.45

.36

.48

.43

.50

.48

.45

.56

.32

.29

.26

.26

.26

.25

.31

.29

.05

.56

16th 

Street

0.11

.22

.25

.79

2.94

.28

.34

.71

.48

1.72

1.02

1.24

.54

.11

.26

.00

.53

1.73

1.19

1.14

.15

.56

1.83

1.10

.46

.80

.91

2.86

1.24

.03

.96

.86

.71

.00

2.94

Water 

withdrawal

at 

Keystone 

Avenue

54 

55

60

60

56

56

61

53

48

58

60

61

65

63

68

66

61

60

65

65

57

59

57

57

52

52

53

50

52

50

56

58

57

48

68

August

Filter 

backwash

Keystone 

Avenue

0.60 

.40

.51

.59

.59

.46

.43

.50

.23

.48

.39

.79

.73

.57

.50

.63

.56

.65

.42

.70

.39

.59

.37

.57

.45

.26

.40

.34

.28

.31

.45

.49

.48

.23

.79

at

16th 

Street

1.02 

.60

2.12

.88

.26

.85

1.78

1.19

.00

.85

.90

1.07

1.13

.82

1.02

1.04

1.25

1.33

.68

2.10

1.07

1.32

1.78

1.55

.36

.00

.88

.19

.93

1.44

.62

1.00

1.02

.00

2.12

Streamflow 35
Table 6. Daily mean water withdrawal from Fall Creek at Keystone Avenue and daily mean discharge of filter 

backwash to Fall Creek at Keystone Avenue and at 16th Street, July through October 1987 Continued

Dally mean rate of water withdrawal or discharge of filter backwaah1 

(cubic feet per aecond)

September

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

Mean

Median

Minimum

Maximum

Water 

withdrawal

at

Key atone

Avenue

61

57

65

65

64

58

60

61

62

68

58

55

55

60

57

47

47

47

48

47

48

51

50

49

50

51

55

55

50

42

55

55

42

68

Filter 

backwaah

at

Keyatone

Avenue

0.84

.06

.76

.43

.87

.36

.40

.26

.23

.39

.26

.23

.28

.12

.34

.11

.23

.08

.23

.15

.34

.34

.14

.15

.28

.26

.28

.25

.22

.19

.30

.26

.06

.87

16th

Street

0.00

.67

.53

1.64

.85

.82

.09

.00

.65

3.48

.34

.19

1.32

1.67

1.73

1.28

.60

.50

.60

.09

1.75

.08

1.02

.28

.26

.29

.50

1.01

.63

1.39

.81

.62

.00

3.48

Water 

withdrawal

at

Keyatone

Avenue

36

36

36

34

35

36

32

33

34

35

32

33

35

36

36

37

35

34

36

37

36

36

36

34

33

34

34

34

33

34

33

35

35

32

37

October

Filter 

backwaah

at

Keyatone

Avenue

0.11

.06

.23

.14

.11

.43

.14

.03

.17

.11

.08

.20

.08

.11

.17

.15

.29

.19

.22

.12

.36

.14

.28

.29

.17

.53

.29

.32

.12

.29

.34

.20

.17

.03

.53

16th

Street

0.93

.02

.34

.54

.42

.34

.51

1.18

.50

.60

.29

.48

.71

.80

.79

.00

.80

.00

.85

3.42

.80

.00

.00

.43

.00

.31

3.06

.77

.00

1.13

2.82

.74

.51

.00

3.42

'Water withdrawn from Fall Creek approximately 100 ft downstream from Keystone Avenue. Filter backwash discharged to Fall 

Creek approximately 500 ft downstream from Keystone Avenue and approximately 300 ft upstream from 16th Street.

36 Effects of Combined-Sewer Overflows and Urban Runoff, Fall Creek, Indlanapolla, Indiana
The median discharge rate of filter backwash 

effluent to Fall Creek immediately upstream from 

16th Street during October was 0.51 f\?/s (table 6). 

This relatively minor source combined with the 

aqueduct overflow (total approximately 12.5 ft3/s) 

leaves the balance of the increased streamflow from 

Central Avenue to 16th Street during October 

approximately 5.5 ft3/s as ground-water inflow 

(18ft3/s-12.5ft3/s).

The median rate of ground-water inflow into 

Fall Creek from Emerson Avenue to 16th Street 

during October was approximately 16.5 ft3/s (the 

sum of ground-water inflow from both reaches, 

11 ft3/s + 5.5 ft3/s) which constituted about 

48.5 percent of the median rate of streamflow 

measured at 16th Street during October. The sum 

of the components of streamflow at 16th Street 

(35 percent aqueduct overflow, 48.5 percent 

ground-water seepage, 1.5 percent backwash 

effluent discharged upstream from 16th Street, 

and 0.5 percent backwash effluent discharged 

upstream from Central Avenue) shows that only 

about 14.5 percent of the streamflow measured 

at 16th Street during October was streamflow 

that originated in Fall Creek upstream from 

Emerson Avenue.

Storm Runoff

Hydrographs for storms 1 through 6 are shown 

in figures 6-11. Storm runoff for storms 3, 5, and 

6 exhibited single, well-defined peaks at Central 

Avenue (figs. 8,10,11). Streamflow at Central 

Avenue increased rapidly in response to precipitation and decreased rapidly after precipitation had 

ceased. This pattern of runoff is typical for urban 

streams. Urbanization reduces infiltration of 

precipitation, and surface runoff rapidly is 

conveyed to streams. Because infiltration is 

reduced, subsurface flow is reduced and streamflow quickly returns to base flow. Streamflow at

16th Street increased and decreased less rapidly 

than streamflow at Central Avenue in response to 

precipitation from small storms (storms 3,5, and 

6). Although land upstream from 16th Street is 

urbanized, the increased times from rise to peak 

and from peak to base flow probably is caused 

by storage in the channel between Central Avenue 

and 16th Street. A low-head dam in this reach 

impedes storm runoff at low streamflows and 

slowly releases it as the impoundment fills. 

Streamflow increased little or not at all in response 

to precipitation at Emerson Avenue, which 

indicates that storm runoff occurred primarily in 

the downstream, urbanized part of the watershed 

(figs. 8,10,11).

Runoff during storms 1 and 2 occurred as 

multiple, well-defined peaks at Central Avenue and 

16th Street and at Emerson Avenue during storm 2 

(figs. 6,7). Streamflow increased little in response 

to precipitation at Emerson Avenue during storm 1, 

which indicates that storm runoff occurred primarily in the downstream, urbanized part of the 

watershed. Streamflow increased markedly in 

response to precipitation at Emerson Avenue during 

storm 2, which indicates that much of the storm 

runoff occurred in the upstream, rural part of the 

watershed. Streamflow increased rapidly at Central 

Avenue and 16th Street at approximately 0900 on 

July 30 in response to precipitation, and the initial 

peaks at these stations preceded the peak at 

Emerson Avenue. This pattern of initial peak 

streamflows indicates that storm runoff also 

occurred in the downstream, urbanized part of the 

watershed and that initial peak streamflows at 

Central Avenue and 16th Street at approximately 

1000 on July 30 were caused by urban runoff and 

combined-sewer overflows and not the downstream movement of water that ran off upstream 

from Emerson Avenue (fig. 7). Subsequent peak 

streamflows at Central Avenue and 16th Street at 

approximately midnight on July 30 were caused by 

the downstream movement of water measured at 

Emerson Avenue at approximately 2100 on July 30 

and not by runoff from the urbanized part of the 

watershed.

Streemflow 37
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SEPTEMBER 1987

Figure 10. Streamflow and water quality in Pall Creek during storm 5, 

September 16-17,1987. -- Continued.

Streamflow 47
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Runoff during storm 4 did not occur as 

well-defined peaks (fig. 9) primarily because 

precipitation was of low intensity and long 

duration. Streamflow increased at all three stations 

but relatively more at 16th Street than at Central 

Avenue or Emerson Avenue. This pattern of 

Streamflow increase indicates that a significant 

part of the storm runoff occurred in the urbanized 

part of the watershed between Central Avenue and 

16th Street.

In-channel storage did not seem to affect the 

rates of increase or decrease of runoff at 16th Street 

during storms 1,2, and 4. The large magnitude of 

the runoff during storms 1 and 2 seemed to exceed 

the storage capacity of the impoundment, and rates 

of rise and fall of the hydrograph at 16th Street 

were similar to those at Central Avenue (figs. 6,7). 

Runoff during the low-intensity, long-duration 

storm (storm 4) was not noticeably detained in 

the impoundment (fig. 9).

Storm runoff for the unsampled storm (August 

17) was most similar to storm 6 (fig. 11) in terms 

of hydrograph shape and the relations of peak flow 

rates and runoff volumes among the three stations. 

Although the peak flow rates were similar, volumes 

of runoff were greater for the unsampled storm 

than for storm 6.

Water Withdrawals and Returns

Water is withdrawn from Fall Creek at 

Keystone Avenue and treated for public-water 

supply (fig. 3). The median rates of water withdrawal were 56 ft3/s during July through September 

and 35 ft3/s during October (table 6). Decreased 

rates of withdrawal during October reflect 

decreased demand for water as temperatures cool 

during autumn. Water withdrawal ranged from 32 

to 68 ft3/s during the study period. A comparison of 

daily mean Streamflow at Emerson Avenue (table 5) 

and daily mean water withdrawal at Keystone 

Avenue (table 6) shows that on several days during

August and September, more water was withdrawn 

at Keystone Avenue for water supply than flowed 

past the Emerson Avenue gaging station approximately 2 mi upstream. Measurement error could 

be the cause of the discrepancy, but a more likely 

reason is that sufficient water is impounded at 

Keystone Avenue to allow rates of withdrawal to 

exceed rates of supply for short periods of time. 

Ground-water inflow between Emerson Avenue 

and Keystone Avenue also may increase the amount 

of water available for withdrawal.

During periods of base flow, instantaneous 

Streamflow at Central Avenue varied in gradual, 

cyclical, daily fluctuations of approximately 5 to 

15 ft3/s. The maximum Streamflow usually 

occurred during midday, and the minimum usually 

occurred at midnight (although base flow on some 

days did not fluctuate at all or the maximum 

Streamflow occurred at night). These fluctuations 

probably were the result of variation in the rate of 

water withdrawn at Keystone Avenue and the travel 

time from Keystone Avenue to Central Avenue, 

although the discharge of filter backwash or 

unknown withdrawals or returns between Emerson 

Avenue and Central Avenue might also contribute 

to fluctuations in base flow. Daily fluctuations in 

base flow also occurred at 16th Street.

Water used to backwash filters used in the 

treatment of municipal drinking water is discharged 

into Fall Creek at two locations: approximately 

500 ft downstream of the water intakes at Keystone 

Avenue and approximately 300 ft upstream from 

the 16th Street gaging station. The backwash 

effluent is composed of water used to backwash the 

filters, suspended sediment removed from treated 

drinking water, aluminum hydroxide floe a result 

of the use of alum (aluminum sulfate) as a coagulant 

for treating drinking water and other materials. 

The source of the water discharged downstream 

from Keystone Avenue is water from Fall Creek 

that is withdrawn at Keystone Avenue. The source 

of the water discharged upstream from 16th Street 

is water from the canal that is withdrawn from the 

White River north of Kessler Avenue (fig. 3).

50 Effects of Combined-Sewer Overflows and Urban Runoff, Fall Creek, Indlanapolla, Indiana
The discharge of filter backwash is sporadic 

and of short duration (typically ranging from less 

than 1 to 3 hours). The instantaneous streamflow 

record at 16th Street shows abrupt increases and 

decreases in streamflow ranging from 5 to 30 ft3/s 

(typically 20 ft3/s) that were attributed to the 

discharge of filter backwash (figs. 6-11). Abrupt 

changes in streamflow at Central Avenue caused 

by the discharge of filter backwash were not 

observed in the streamflow record. Typically, 

filter backwash was discharged several times per 

day; the number of discharges per day during the 

study period ranged from 0 to 10. More than twice 

as much backwash effluent is discharged upstream 

from 16th Street than downstream from Keystone 

Avenue (table 6). Daily mean rates of backwash 

discharge ranged from 0.03 to 0.87 ft^/s at Keystone 

and from 0.00 to 3.48 ft3/s at 16th Street and were 

much more variable at 16th Street.

EFFECTS OF COMBINED-SEWER 

OVERFLOWS AND URBAN RUNOFF 

ON FALL CREEK

The effects of combined-sewer overflows 

and urban runoff on the water quality of Fall Creek 

were determined by comparing water quality of 

base flow with water quality of storm runoff. In 

addition, water quality during storm runoff in the 

urbanized area was compared with water quality 

in the less urbanized area upstream from the 

combined-sewer overflows.

Water Quality of Base Flow

The water quality of base flow was characterized by measurements made in the field during a 

base-flow synoptic survey and by chemical and 

biological analyses of water samples.

Synoptic Survey

A synoptic, base-flow water-quality survey 

was done of Fall Creek on September 24,1987. 

Field-measured water-quality characteristics 

(specific conductance, pH, water temperature, and

dissolved-oxygen concentration) were measured at 

20 stations from Pendleton to 16th Street (figs. 2, 

3,12, table 7). The synoptic survey was done to 

determine longitudinal changes in water quality 

and to identify reaches of Fall Creek having low 

concentrations of dissolved oxygen.

On the basis of water-quality data collected 

during the synoptic survey, three distinct reaches 

were identified. The upstream reach extended 

from Pendleton to Geist Reservoir (river miles 

34.5-26.1, table 7, fig. 2) and was characterized by 

water quality typical of base flow, which primarily 

consists of ground-water inflow. Specific conductance ranged from 734 to 792 |4,S/cm, pH ranged 

from 8.1 to 8.3, water temperature ranged from 

17.8 to 19.4°C, and dissolved oxygen ranged from 

8.3 to 9.8 mg/L (table 7).

The middle reach consists of Geist Reservoir 

and the stations downstream to and including 

Keystone Avenue (river miles 20.8-6.4, table 7, 

figs. 2, 3). Water quality in this reach was 

affected by water that was stored in the reservoir 

and released downstream for public-water supply. 

Water in the reservoir was composed of storm 

runoff, base flow, ground-water inflow, and precipitation that fell directly upon the reservoir. Because 

the reservoir contains storm runoff and precipitation, the reservoir water was much less mineralized 

(more dilute, lower concentrations of dissolved 

solids) than the base flow of the upstream reach. 

Consequently, specific conductance in the middle 

reach (467-500 |4,S/cm) was much less than that in 

the upstream reach (table 7, fig. 12). Except for the 

measurement at the causeway, measurements of 

pH and dissolved oxygen in the middle reach were 

similar to those in the upstream reach. Greater 

concentrations of dissolved oxygen and a greater 

pH at the causeway probably were caused by 

photosynthesis by plankton in the upper water layer 

(epilimnion) of the reservoir. The warmest water 

was measured in the reservoir at the causeway 

(21.3°C, table 7). Water released from the reservoir 

cooled as it flowed downstream until it joined 

warmer water in the impoundment upstream from 

Keystone Avenue. Water released from Geist 

Reservoir generally was warmer than that of base 

flow upstream from Geist.

Effects cf Combined-Sewer Overflows and Urban Runoff on Fell Creek 51
s

OISSOLVEO-OXYGEN 

SATURATION. 

IN PERCENT

_ _ ro

o> O o> o

o o o o

V

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£. 

O

= 2!

3 ta " 

5--S F3

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<o«<5.

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g. * ft

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* OB 

r* "S. 

^ o

g> S1

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DISSOLVED OXYGEN.

IN MILLIGRAMS

PER LITER

TEMPERATURE. 

IN DEGREES CELSIUS

PH

vl vl CD 

_._._._.K)K)K). . . 

o>vioo«oo foo cn o 

1 ' isiJ

P* STREET

f" CENTRAL

- ^ AVENUE '

*& «.

A

»

EMERSON .

AVENUE

,

i

f

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\

\ -

\

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.

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ft ^

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, EMERSON

_ AVENUE

f "

1

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- / 

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1 1 

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AVENUE "

i

i

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ft 

\

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- 

> 

 > 

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to

\

\

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/

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*

.1.1.1.1.1.

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.... 1 .... 1 .... 
Table 7. Water-quality sampling stations and measurements for the base-flow synoptic survey, Fall Creek, September 24,1987

[ft3/s, cubic feet per second; uS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degree Celsius; mi, mile; mg/L, milligrams per liter, , no data]

I^

o

" 

ity ofBaseFlow

a

Reach of Fall Creek and 

sampling station1

Downstream reach

16th Street

Aqueduct

Dr. Martin Luther King Jr. Street

Capitol Avenue

Meridian Street

Central Avenue

30th Street

Monon Railroad bridge

39th Street

Norfolk & Western Railroad bridge

Middle reach

Keystone Avenue

46th Street

Emerson Avenue

63rd Street

7 1st Street

79th Street 

Geist Reservoir causeway

Upstream reach 

Fortville gaging station 

Madison County Road 750 West

Pendleton (State Road 38)

River mile 

(mi)

1.3

1.8

2.4

3.2

3.3

3.8

4.3

5.2

5.8

6.2

6.4

7.3

9.2

12.7

15.4

16.7 

20.8

26.1 

29.8

34.5

Time

1018

1049

1105

1120

1137

1228

1241

1318

1300

1348

1412

1424

1435

1540

1557

1607 

1620

1651 

1704

1720

Specific 

Streamflow conductance

(ft'/s) (uS/cm)

30 843

805

778

742

730

17 693

656

610

539

507

486

483

52 478

472

472

467 

500

31 790 

792

734

pH

7.8

7.7

7.7

7.4

7.4

7.4

7.3

7.4

7.6

7.4

8.2

8.2

8.0

8.1

8.1

8.1 

8.6

8.2 

8.1

8.3

'Locations of synoptic sampling stations are shown in figures 2 and 3. Reach of Fall Creek is described m the text
The third, downstream reach of Fall Creek 

extended from the Norfolk & Western Railroad 

bridge, downstream from the discharge of filter 

backwash near Keystone Avenue, to 16th Street 

(river miles 6.2-1.3, table 7, fig. 3). Specific 

conductance increased dramatically in this reach 

and measurements of pH and dissolved oxygen 

were much lower than those at other stations in the 

synoptic survey (fig. 12). The change in specific 

conductance in the downstream reach was rapid 

and systematic, an increase from 507 to 843 uS/cm 

(table 7). The increase in specific conductance 

downstream from the point where water is withdrawn at Keystone Avenue probably was caused 

by the inflow of highly mineralized ground water. 

Discharge of filter backwash or aqueduct overflow 

also could have increased specific conductance 

downstream, but the gradual, systematic increase 

in specific conductance indicates that the inflow 

of ground water probably is the primary cause of 

increased specific conductance.

The lowest concentrations of dissolved 

oxygen (3.2-5.5 mg/L, table 7) were measured 

at five stations between river miles 5.2 and 3.2 and 

correspond to the first occurrences of combinedsewer overflows (figs. 3,4,12). Extensive areas 

of black sludge deposits having a septic odor 

characterized the stream bed in this reach. Sources 

of these deposits probably are combined-sewer 

overflows, which begin at 39th Street Sediment 

oxygen demand, caused by the biochemical oxidation of organic wastes in the sludge, probably 

decreased dissolved oxygen in this reach. Concentrations of dissolved oxygen increased at sites 

downstream from the low-head dam at Dr. Martin 

Luther King Jr. Street (table 7). Several factors 

probably caused the increased concentrations of 

dissolved oxygen: mixing with water high in 

dissolved oxygen produced by photosynthesis of 

plankton in the impoundments upstream and downstream from the dam; reaeration, especially as water 

flowed over the dam; overflow of highly oxygenated water from the aqueduct; and discharge of 

highly oxygenated filter backwash.

Low pH in the downstream reach probably 

was caused by the inflow of low-pH ground water, 

discharge of filter backwash, and biochemical 

oxidation of organic wastes (Martin and Craig, 

1990, fig. 16, p. 34-35). Low temperatures in the 

downstream reach probably resulted from shading 

by streambank vegetation and the inflow of cool 

ground water. Measurements of temperature, 

dissolved oxygen, and pH in the downstream reach 

could have been greater than those actually determined if the measurements had been made later 

in the day when the effects of solar radiation and 

photosynthesis were more pronounced. The author, 

however, expects that the principal water-quality 

interpretations would not change.

Chemical, Physical, and 

Biologic Characteristics

Base-flow water-quality samples were 

collected at Emerson Avenue, Central Avenue, 

and 16th Street four times during the study period. 

Samples also were collected from the filter backwash upstream from 16th Street, from the overflow 

from the aqueduct, and at 16th Street during and 

after the discharge of filter backwash (fig. 3). 

Constituents and properties determined include 

field-measured characteristics (specific conductance, pH, water temperature, and dissolved 

oxygen), major anions (alkalinity, sulfate, and 

chloride), gross measures (dissolved and total 

solids, 20-day carbonaceous biochemical oxygen 

demand, chemical oxygen demand, and oil and 

grease), nutrients (nitrate plus nitrite, ammonia, 

organic nitrogen, phosphorus, and orthophosphate), 

metals and trace elements (arsenic, mercury, 

selenium, aluminum, barium, cadmium, chromium, 

copper, iron, lead, nickel, and zinc) (table 8), and 

fecal coliform bacteria (table 9). Some of the 

base-flow water-quality samples were split for 

the quality-assurance program. The mean concentration of the pair of split samples is used for all 

interpretations of water quality.

54 Effects of Combined-Sewer Overflows snd Urban Runoff, Fsll Creek, Indisnapolls, Indiana
Table 8. Water-quality analyses for samples collected during periods of base flow

[i.d., identification; ft3/s, cubic feet per second; uS/cm, microsiemens per centimeter at.25 degrees Celsius; °C, degree Celsius; mg/L, milligrams per liter, n.d., 

N, nitrogen; P, phosphorus; Jlg/L, micrograms per liter, , no data; <, less than; ss, split sample]

I

I

Site

Emerson 

Central

16th Street

16th Street

Emerson

Central

16th Street

16th Street

Emerson

Central

16th Street

Water Company outfall

Emerson

Central

16th Street

16th Street

16th Street

Aqueduct 

Aqueduct

Sample i.d.

Base flow 1 

Base flow 1

Base flow 1

Base flow 1

Base flow 2

Base flow 2

Base flow 2

Base flow 2

Base flow 3

Base flow 3

Base flow 3

Filter backwash

Base flow 4

Base flow 4

Base flow 4

During backwash

After backwash

Overflow 

Overflow

Sample 

type

Individual 

Individual

Individual ss3

Individual ss3

Individual

Individual

Individual ss3

Individual ss3

Individual

Individual

Individual

Grab

Individual

Individual

Individual

Individual

Individual

Individual ss3 

Individual ss

Dste

7-22-87 

7-22-87

7-22-87

7-22-87

8-11-87

8-11-87

8-11-87

8-11-87

8-21-87

8-21-87

8-21-87

8-27-87

9-16-87

9-16-87

9-16-87

10-15-87

10-15-87

10-15-87 

10-15-87

Time1

1245 

1110

0900

0900

1415

1300

1045

1045

1200

1130

1300

1230

1800

1620

1805

1015

1205

1115 

1115

Streamflow

(ft3/*) 

(00061 )z

85 

55

102

102

67

36

73

73

60

21

48

4 15

58

26

54

45

29

4«r 

4«r

Specific 

conductance

(|is/cm) 

(00095)2

465 

565

624

624

467

600

686

686

n.d.

682

760

ILd.

n.d.

617

789

841

827

930 

930

pH 

(00400)

8.4 

8.0

8.0

8.0

8.2

7.7

7.9

7.9

n.d.

7.3

7.8

n.d.

n.d.

7.5

7.9

7.6

7.8

8.2 

8.2

ff 

s

<n 

<n
s

m

a

3

5"

s.&§o

1

i

a.

c

1

1

g

,3!

i

o

i* 

i

3

I

JO

3

a

(0

3 

(0

Table 8. Water-quality analyses for samples collected during periods of base flow Continued

Site

Emerson

Central

16th Street

16th Street

Emerson

Central

16th Street

16th Street

Emerson

Central

16th Street

Water Company outfall

Emerson

Central

16th Street

16th Street

16th Street

Aqueduct

Aqueduct

Sample l.d.

Base flow 1

Base flow 1

Base flow 1 ss3

Base flow 1 ss3

Base flow 2

Base flow 2

Base flow 2 ss3

Base flow 2 ss3

Base flow 3

Base flow 3

Base flow 3

Filter backwash

Base flow 4

Base flow 4

Base flow 4

During backwash

After backwash

Overflow ss

Overflow ss

Dissolved

alksllnlty

(mg/L ss CaCOj)

(29801 )2

164

195

210

216

162

202

220

220

159

226

238

244

159

198

237

260

256

278

276

Dissolved

sulfate

(mg/L)

(00945)2

36

47

50

49

36

51

56

55

35

61

66

87

36

55

66

74

72

75

75

Dissolved

chloride

(mg/L)

(00940)2

28

35

39

39

28

39

51

49

28

45

57

86

28

38

60

70

67

85

85

Dissolved

solids

(mg/L)

(00515)2

307

385

435

411

363

422

400

280

422

473

553

285

383

485

501

490

564

582

Total

solids

(mg/L)

(00500)2

319

386

477

461

327

424

560

560

325

449

688

823

310

402

539

616

570

628

633

Suspended

solids6

(mg/L)

12

1

42

50

61

138

160

45

27

215

270

25

19

54

115

80

64

51

2

carb

bio

oxyg

(

(8
Table 8. Water-quality analyses for samples collected during periods of base flow Continued

Water Quallt)

r of BaseFlow

en

Site

Emerson 

Central 

16th Street 

16th Street

Emerson

Central 

16th Street 

16th Street

Emerson

Central

16th Street

Water Company outfall

Emerson

Central

16th Street

16th Street 

16th Street

Aqueduct 

Aqueduct

Totsl 

nltrste plus nitrite 

(mg/L as N) 

Sample i.d. (00630)2

Base flow 1 

Base flow 1 

Base flow 1 ss 

Base flow 1 ss3

Base flow 2

Base flow 2 

Base flow 2 ss3 

Base flow 2 ss3

Base flow 3

Base flow 3

Base flow 3

Filter backwash

Base flow 4

Base flow 4

Base flow 4

During backwash 

After backwash

Overflow ss 

Overflow ss

0.16 

.30

.77 

.77

.11

.28 

.59 

.59

.10

.32

.42

1.31

.13

.33

.88

1.34 

1.16

2.40 

n.d.

Totsl 

ammonia 

(mg/L as N) 

(0061 0)2

0.10 

.09 

.10 

.13

<.01

.08 

.08 

.05

<.01

.14

.48

.47

.05

.18

.28

.22 

.20

.10 

n.d.

Totsl 

orgenlc nitrogen 

(mg/L) 

(00605)2

0.78 

.92 

1.00 

.98

.45

.79 

1.84 

.67

.91

.50

2.53

2.45

.64

.95

.96

.86 

.66

5.07 

n.d.

Total 

phosphorus 

(mg/L) 

(00665)2

0.10 

.08 

.20 

.20

.09

.08 

.63 

.63

.90

.40

1.14

3.30

.08

.05

.31

.27 

.09

.46 

n.d.

Dissolved 

orthophosphste 

(mg/L as P) 

(00671 )2

<0.01

.01 

.01

.02

.02 

.03 

.03

<.01

<.01

.02

.17

<.01

<.01

.05

.05 

.05

.29 

.29
58 Effects ofCombini

*

!W

I

|

V

|

1

3D

|

i

1

iSK 

V

S

V

1*

5

V

s

V

Tabled. Water-qualit

Site

Emerson

Central

16th Street

16th Street

Emerson

Central

16th Street

16th Street

Emerson

Central

16th Street

Water Company outfall

Emerson

Central

16th Street

16th Street

16th Street

Aqueduct

Aqueduct

/ analyses for samf

Sample l.d.

Base flow 1

Base flow 1

Base flow 1 ss3

Base flow 1 ss3

Base flow 2

Base flow 2

Base flow 2 ss3

Base flow 2 ss3

Base flow 3

Base flow 3

Base flow 3

Filter backwash

Base flow 4

Base flow 4

Base flow 4

During backwash

After backwash

Overflow ss

Overflow ss

lies collected i

Total 

recoverable 

aluminum 

(H9/L) 

(011 OS)2

190

400

1,270

1,260

130

200

5,000

4,700

190

110

12,690

27,240

100

130

890

6,360

1,900

700

n.d.

during periods of base flowTotal Total 

recoverable recoverable 

barium cadmium 

(pg/L) (pg/L) 

(01007)2 (01027)2

30 <10

110 <10

100 <10

140 <10

50 <10

60 <10

80 <10

100 <10

40 <10

60 <10

140 <10

160 <10

60 <10

100 <10

60 <10

90 <10

120 <10

50 <10

n.d. n.d.

-Continued

Total Total 

recoverable recoverable 

chromium copper 

(ug/L) (pg/L) 

(01034)2 (01042)2

<10 <10

<10 <10

<10 10

<10 10

<10 <10

<10 10

<10 20

<10 20

<10 <10

<10 10

20 30

30 40

<10 <10

<10 <10

<10 <10

<10 10

<10 <10

<10 <10

n.d. n.d.

Total 

recoverable rec

Iron 

(ug/L) 

(01045)2 (0

400 

300 

1,220 

1,250 

430 

330 

2,660 

2,410 

410 

230 

3,880 

4,250 

370 

290 

940 

1,570 

970 

970 

n.d. 

'Midpoint time of sample collection.

^ATSTORE (U.S. Geological Survey) and STORE! (U.S. Environmental Protection Agency) parameter code.

3A split sample (ss) is one of a pair of identical samples used to assess analytical precision. The mean of the pair of split samples was used for all calc

Estimated.

5Anomalous concentration. Not used in analysis of base-flow water quality.

Suspended solids were calculated as the difference between total solids and dissolved solids.
Table 9. Concentrations of fecal coliform bacteria during periods of base flow

[col/100 mL, colonies per 100 miUiliters; >, greater than; <, less than]

Sampling station

Date

7-22-87

8-12-87

8-21-87

Emerson Avenue

Fecal coliform

bacteria

(col/100 mL) 

Time (31625)1

1300 >667

1045 300

1046 100

1055 2,000

1230 100

Central Avenue

Time

Base flow

1325

Base flow

1111

1112

Base flow

1200

1300

Fecal coliform

bacteria

(col/100 mL) 

(31625)1

1

237

2

500

400

3

200

200

16th Street

Time

1350

1351

1132

1133

1030

1225

Fecal coliform

bacteria

(col/100 mL) 

(31625) 1

>1,000

>2,000

<100

100

12.800

7,800

'WATSTORE (U.S. Geological Survey) and STORET (U.S. Environmental Protection Agency) parameter code.

Specific Conductance, Dissolved Oxygen, 

Temperature, and pH

Water quality of base flow measured at 

Emerson Avenue, Central Avenue, and 16th Street 

generally was similar to water-quality patterns 

measured during the base-flow synoptic survey 

(tables 7,8, fig. 12). Specific conductance 

increased downstream, and pH was greatest at 

Emerson Avenue and least at Central Avenue 

(table 8). Concentrations of dissolved oxygen 

were greatest at Emerson Avenue (8.8 mg/L and 

8.6 mg/L) and least at 16th Street for the first two 

base-flow samples (7.4 and 7.7 mg/L). Concentrations of dissolved oxygen were least at Central 

Avenue for the last two base-flow samples (3.9 and 

5.2 mg/L). Streamflow was greater during the first 

two base-flow samples than during the last two 

(table 8). The lower streamflows probably contributed to the low concentrations of dissolved oxygen 

measured at Central Avenue by increasing the influence of sediment oxygen demand. At low rates of 

flow, water can be more thoroughly deoxygenated

by sediments because the volume of water (and 

therefore the mass of oxygen available to satisfy 

the sediment oxygen demand) is much less than 

that at higher rates of flow.

Water overflowing the aqueduct had the 

highest specific conductance (930 (iS/cm) and one 

of the highest values of pH (8.2) and dissolved 

oxygen (9.7 mg/L) during base flow (tables 7, 8). 

Previous studies have shown that specific conductance, pH, and dissolved-oxygen concentration in 

the White River upstream from the intake to the 

canal (and, presumably, in the canal) typically were 

greater than those in Fall Creek at 16th Street during 

base flow (Martin and Craig, 1990, tables 5, 6, 7, 

20,21,22). Therefore, increased specific conductance, pH, and dissolved-oxygen concentration 

downstream from the aqueduct can be attributed, at 

least partially, to the overflow from the aqueduct.

Different rates of base flow had little effect 

on specific conductance, pH, or concentrations of 

dissolved oxygen at Emerson Avenue. The quality 

of water released from the reservoir varied little

Water Quality of Base Flow 59
with changes in release (tables 7, 8); however, 

different rates of base flow had a large effect on 

water quality at Central Avenue and 16th Street 

Specific conductance generally increased as 

streamflow decreased, whereas pH and dissolved 

oxygen generally decreased as streamflow 

decreased. At low streamflows, the effects of 

ground-water discharge, sediment oxygen demand, 

low-head dams, filter backwash, and aqueduct 

overflow were the most pronounced.

Major Anions

Concentrations of alkalinity (predominantly 

bicarbonate), sulfate, and chloride steadily 

increased downstream (fig. 13) as a result of 

surface-water withdrawals, the inflow of mineralized ground water, aqueduct overflow, and the 

discharge of filter backwash. Concentrations were 

least variable at Emerson Avenue and were most 

variable at 16th Street (fig. 13). The aqueduct 

overflow and filter backwash had relatively 

high concentrations of anions and contributed 

to increased and variable concentrations at 

16th Street.

Dissolved and Total Solids, 

Chemical Oxygen Demand, 

Carbonaceous Biochemical Oxygen Demand, 

and OH and Grease

Concentrations of dissolved and total solids 

steadily increased downstream in a pattern similar 

to that of specific conductance and the major anions 

(fig. 13). The aqueduct overflow had the highest 

concentration of dissolved solids (573 mg/L) and 

the filter backwash had the highest concentration 

of total solids (823 mg/L). Concentrations of 

suspended solids were calculated as the difference 

between total solids and dissolved solids (table 8) 

and ranged from 12 to 45 mg/L at Emerson Avenue, 

from 1 to 61 mg/L at Central Avenue, and from 

42 to 215 mg/L at 16th Street. Suspended solids, 

expressed as a proportion of total solids, ranged 

from 0.3 to 32.8 percent. The highest concentration 

and proportion of suspended solids was measured in 

the sample of filter backwash (270 mg/L, 32.8 percent). Of the base-flow samples collected at the 

three streamflow-gaging stations on a given day,

the Central Avenue sample had the lowest concentration and proportion of suspended solids, whereas 

the 16th Street sample had the highest concentration 

and proportion. This pattern indicates that filter 

backwash had little effect on the concentration of 

suspended solids at Central Avenue during base 

flow but had a pronounced effect at 16th Street 

The decrease in suspended-solids concentration 

between Emerson Avenue and Central Avenue 

probably can be attributed to the settling out of 

non-backwash-associated suspended solids in the 

impoundment at Keystone Avenue and to inflow 

of ground water that is low in suspended solids. 

Suspended solids in the aqueduct overflow and in 

Fall Creek at Emerson Avenue and Central Avenue 

probably were composed of sediment and plankton, 

whereas suspended solids in the filter backwash 

and at 16th Street also contained large amounts of 

aluminum hydroxide floe.

Chemical oxygen demand (COD) and 20-day 

carbonaceous biochemical oxygen demand 

(CBOD) exhibited similar patterns of water quality 

among stations during base flow (fig. 13). Concentrations of CBOD and COD measured at Emerson 

Avenue were nearly identical to those measured 

at Central Avenue, whereas those at 16th Street 

were approximately two times greater (table 8). 

Concentrations of CBOD at Emerson Avenue and 

Central Avenue ranged from <1 to 4 mg/L but 

ranged from 2 to 9 mg/L at 16th Street. Concentrations of COD ranged from 6 to 18 mg/L at Emerson 

Avenue and from 6 to 17 mg/L at Central Avenue, 

but they ranged from 17 to 32 mg/L at 16th Street. 

Concentrations of CBOD and COD in the aqueduct 

overflow were similar to those measured upstream 

at Emerson Avenue and Central Avenue. Concentrations of CBOD and COD in the filter backwash 

were the highest measured (16 and 63 mg/L, respectively). The discharge of filter backwash caused the 

increased concentrations of CBOD and COD at 

16th Street

Except for one measurement of 5 mg/L at 

Central Avenue, concentrations of oil and grease 

ranged from <1 to 3 mg/L (table 8). In view of the 

poor measurement precision for oil and grease 

(mean log difference 80.9 percent, table 2), waterquality patterns or differences among sites were 

not discernible (fig. 13).

60 Effects of Combined-Sewer Overflows snd Urbsn Runoff, Fsll Creek, Indlanspolls, Indlsna
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EMERSON CENTRAL AQUEDUCT BACKWASH 16th St.

Figure 13. Water-quality constituents measured during base flow and 

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Water Quality of Baae Flow 61
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EMERSON CENTRAL AQUEDUCT BACKWASH 16th St.

Figure 13. Water-quality constituents measured during base flow and 

event-mean concentrations of water-quality constituents measured 

during storm runoff at Fall Creek at Emerson Avenue, Central Avenue, 

and 16th Street, and water-quality constituents measured in the 

aqueduct overflow and filter backwash. -- Continued.

62 Effects of Combined-Sewer Overflows snd Urbsn Runoff, Fall Creek, Indianapolis, indisns
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EMERSON CENTRAL AQUEDUCT BACKWASH 16th St.

Figure 13. Water-quality constituents measured during base flow and 

event-mean concentrations of water-quality constituents measured 

during storm runoff at Fall Creek at Emerson Avenue, Central Avenue, 

and 16th Street, and water-quality constituents measured in the 

aqueduct overflow and filter backwash. -- Continued.

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EMERSON CENTRAL AQUEDUCT BACKWASH 16th St.

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event-mean concentrations of water-quality constituents measured 

during storm runoff at Fall Creek at Emerson Avenue, Central Avenue, 

and 16th Street, and water-quality constituents measured in the 

aqueduct overflow and filter backwash. -- Continued.

64 Effects of Combined-Sewer Overflows snd Urban Runoff, Fsll Creek, Indianapolis, Indisns
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Figure 13. Water-quality constituents measured during base flow and 

event-mean concentrations of water-quality constituents measured 

during storm runoff at Fall Creek at Emerson Avenue, Central Avenue, 

and 16th Street, and water-quality constituents measured in the 

aqueduct overflow and filter backwash. -- Continued.

Water Quality of Baae Flow 65
Nutrients

Concentrations of nutrients in base flow in 

Fall Creek exhibited two distinct water-quality 

patterns. Concentrations of nitrate plus nitrite and 

ammonia steadily increased downstream, whereas 

concentrations of organic nitrogen, phosphorus, 

and orthophosphate increased at 16th Street only 

(fig. 13).

Concentrations of nitrate plus nitrite approximately doubled at each downstream station and 

ranged from 0.10 to 0.16 mg/L at Emerson Avenue, 

from 0.28 to 0.33 mg/L at Central Avenue, and 

from 0.42 to 1.34 mg/L at 16th Street (table 8). 

Concentrations of ammonia generally were less 

than concentrations of nitrate plus nitrite and ranged 

from <0.10 to 0.10 mg/L at Emerson Avenue, from 

0.08 to 0.18 mg/L at Central Avenue, and from 

0.07 to 0.48 at 16th Street. A sample of the 

aqueduct overflow had the greatest concentration 

of nitrate plus nitrite (2.40 mg/L), whereas a sample 

at 16th Street had the greatest concentration of 

ammonia (0.48 mg/L). Ground-water inflow and 

(or) decomposition and mineralization of nitrogencontaining organic material deposited on the 

streambed could explain the steady downstream 

increase in nitrate plus nitrite and ammonia. 

Increased and highly variable concentrations of 

nitrate plus nitrite and ammonia at 16th Street 

were caused, in part, by filter backwash and 

aqueduct overflow.

Concentrations of organic nitrogen, 

phosphorus, and orthophosphate measured at 

Emerson Avenue were similar to those measured 

at Central Avenue, but higher concentrations were 

measured at 16th Street (table 8). Orthophosphate 

was detected only once in samples collected 

from Emerson Avenue and Central Avenue but 

was detected in all samples collected from 

16th Street. High concentrations of organic 

nitrogen (2.45 mg/L) and phosphorus (3.30 mg/L) 

were detected in the filter backwash. High concentrations of orthophosphate were detected in the 

aqueduct overflow (0.29 mg/L) and the filter backwash (0.17 mg/L). Increased concentrations of

organic nitrogen and phosphorus were caused by 

filter backwash, whereas increased concentrations 

of orthophosphate were caused by aqueduct 

overflow and filter backwash.

Trace Elements

Concentrations of mercury, selenium, and 

cadmium were less than the detection limits 

(table 1) in all base-flow samples (table 8). Except 

for two detectable concentrations of copper at 

Central Avenue and detectable zinc in the aqueduct 

overflow, all concentrations of chromium, copper, 

lead, nickel, and zinc were less than the detection 

limit (10 ug/L) for base-flow samples collected 

at Emerson Avenue, Central Avenue, and the 

aqueduct overflow. Filter backwash had the highest 

concentrations of chromium (30 ug/L), copper 

(40 ug/L), lead (30 ug/L), nickel (30 ug/L), and 

zinc (40 ug/L). Detectable concentrations of these 

metals in base-flow samples from 16th Street were 

caused by the discharge of filter backwash (table 8, 

fig. 13).

Concentrations of aluminum and barium 

steadily increased downstream, whereas concentrations of arsenic and iron were greater at Emerson 

Avenue than at Central Avenue (fig. 13). Concentrations of all four constituents were greatest at 

16th Street.

Concentrations of aluminum ranged from 

100 to 190 ug/L at Emerson Avenue, from 110 to 

400 ug/L at Central Avenue, and from 890 to 

12,690 ug/L at 16th Street (table 8). Increased 

concentrations of aluminum at 16th Street were 

caused by the discharge of aluminum hydroxide 

floe (in the filter backwash) from the drinkingwater-treatment process. Filter backwash had the 

highest concentration of aluminum (27,240 ug/L). 

Given that the filter backwash contained 270 mg/L 

of suspended solids, and assuming little dissolved 

aluminum, the solids discharged as filter backwash 

were approximately 10 percent aluminum.

66 Effects of Combined-Sewer Overflows snd Urbsn Runoff, Fsll Creek, Indianapolis, Indisns
Solubility of aluminum at neutral pH is low 

(Hem, 1985, p. 73); consequently, the increased 

concentration of aluminum at Central Avenue 

probably was not caused by ground-water inflow. 

Aluminum and iron are major components of 

suspended solids. It is unlikely, however, that 

suspended solids were the cause of increased 

concentrations of aluminum at Central Avenue 

because concentrations of suspended solids 

and iron were relatively low at this site (fig. 13, 

table 8). Increased concentrations of aluminum 

at Central Avenue could have been caused by the 

discharge of filter backwash upstream from Central 

Avenue. Although the concentration of suspended 

solids was low at Central Avenue, filter backwash 

contains high concentrations of aluminum; thus, 

even relatively small amounts of this type of 

suspended solids could increase concentrations of 

aluminum. Some evidence for this hypothesis is 

found by calculation of the aluminum/iron ratios 

for the base-flow samples by use of data given 

in table 8. The ratios ranged from 0.27 to 0.48 

at Emerson Avenue, 0.45 to 1.33 at Central 

Avenue, and 0.95 to 4.05 at 16th Street, showing 

relative aluminum enrichment downstream. 

The aluminumAron ratio for the filter backwash 

was 6.41 and the ratio for the aqueduct overflow 

was 0.72.

Concentrations of iron ranged from 370 to 

430 (ig/L at Emerson Avenue, from 230 to 

330 n-g/L at Central Avenue, and from 940 to 

3,880 \ig/L at 16th Street (table 8). Decreased 

concentrations of iron at Central Avenue may 

have been caused by the deposition of suspended 

sediment in the impoundment upstream from 

Keystone Avenue. The maximum concentration 

of iron was in the filter backwash (4,250 (ig/L). 

Because alum is added to raw water to remove 

suspended solids, and because iron is a principal 

chemical component of suspended sediment 

removed by alum, the discharge of filter backwash 

was primarily responsible for the increased concentrations of iron at 16th Street.

Concentrations of barium ranged from 30 to 

60 \Lg/L at Emerson Avenue, from 60 to 110 ug/L 

at Central Avenue, and from 60 to 140 ug/L at 

16th Street (table 8). Increased concentrations of 

barium at Central Avenue and 16th Street may have 

been caused by the inflow of ground water. The 

maximum concentration of barium was in the filter 

backwash (160 \ig/L). The discharge of filter backwash contributed to the increased concentrations of 

barium at 16th Street.

Concentrations of arsenic ranged from 1 to 

2 (ig/L at Emerson Avenue and at Central Avenue 

but were generally greater at Emerson Avenue 

(table 8). Concentrations of arsenic at 16th Street 

ranged from 2 to 10 \ig/L. The cause of the 

increased concentrations of arsenic at 16th Street 

could not be explained on the basis of data collected 

during this study. Increased concentrations at 

16th Street could not be attributed to the discharge 

of filter backwash because the concentration of 

arsenic in the backwash was only 2 |ig/L. Groundwater inflow probably is not the cause of increased 

concentrations of arsenic because increased concentrations were not measured at Central Avenue 

where base flow is composed largely of groundwater inflow.

Fecal Collform Bacteria

Concentrations of fecal coliform bacteria 

during base flow generally were lowest at Central 

Avenue and highest at 16th Street. Concentrations 

of fecal coliform bacteria ranged from 100 to 

2,000 col/100 mL at Emerson Avenue, from 200 

to 500 col/100 mL at Central Avenue, and from 

<100 to 12,800 col/100 mL at 16th Street (table 9). 

Concentrations of bacteria at 16th Street might have 

been higher than those measured because a dechlorinating reagent was not added to the samples, and 

the filter backwash probably contained chlorine.

Water Quality of Baae Flow 67
Water Quality of Storm Runoff

and Comparisons with Water Quality

of Base Flow

The water quality of storm runoff was characterized by measurements made in the field during a 

storm-runoff synoptic survey and by chemical and 

biological analyses of water samples.

Synoptic Survey

A synoptic water-quality survey of the 

downstream reach of Fall Creek was done during 

a period of storm runoff (storm 6) on September 29, 

1987 5 days after the base-flow synoptic survey. 

Measurements of water quality were made in the 

field at eight stations from Emerson Avenue to 

16th Street (figs. 3,14, table 10) to determine 

longitudinal changes in water quality in the 

urbanized area of Indianapolis that could be attributed to storm runoff. Most of the runoff generated 

by this small storm occurred downstream from 

Emerson Avenue, and water quality was measured 

after the peak during decreasing streamflow 

(fig. 11).

In general, water-quality patterns observed 

during the storm-runoff synoptic survey were 

similar to those observed during the base-flow 

synoptic survey (figs. 12,14). Streamflow was 

greater during the storm-runoff survey, especially 

at the most downstream stations. Specific conductance increased dramatically in the downstream 

reach as it did during the base-flow survey, but 

specific conductance was lower because runoff 

typically is more dilute (contains lower concentrations of ions and dissolved material) than base 

flow. Water temperature during the storm-runoff 

survey was 2°C higher than that during the baseflow survey, probably because of warmer air 

temperatures on the day of and the day preceding 

the storm-runoff survey. Concentrations of dissolved oxygen were similar to those during the 

base-flow survey except that dissolved-oxygen 

concentration at Central Avenue was 1.0 mg/L 

(table 10), 3.3 mg/L less than during the base-flow 

survey (table 7). The decreased concentration of 

dissolved oxygen probably was caused by (1) the 

consumption of oxygen by oxygen-demanding 

materials from combined-sewer overflows, urban 

runoff, and the resuspension of sediment that had 

accumulated on the streambed; and (2) the inflow 

of anoxic water from combined-sewer overflows.

Table 10. Water-quality sampling stations and measurements for the storm-runoff synoptic survey, storm 6, 

Fall Creek, September 29,1987

[ft3/s, cubic feet per second; uS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degree Celsius; mi, mile; mg/L, milligrams per liter, 

--, no data]

Sampling station on Fall Creek1

16th Street

Dr. Martin Luther King Jr. Street

Capitol Avenue

Central Avenue

30th Street

Monon Railroad bridge

39th Street

Emerson Avenue

River mile Streamflow 

(ml) Time (ft3/a)

1.3

2.4

3.2

3.8

4.3

5.2

5.8

9.2

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1612

1602

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1820

1545

1530

1630 70

Specific Water 

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(uS/cm) PH (°C)

827

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686

601

636

575

523

480

7.9

7.8

7.5

7.3

7.3

7.6

7.7

8.3

20.3

19.9

20.1

20.4

19.3

19.4

20.6

20.1

Dissolved 

oxygen 

(mg/L)

7.5

7.2

5.3

1.0

2.4

5.6

8.2

9.1

1 Locations of synoptic sampling stations are shown in figure 3.

68 Effects of Combined-Sewer Overflows and Urban Runoff, Fall Creek, Indianapolis, Indiana
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Chemical, Physical, and 

Biologic Characteristics

Multiple water-quality samples were collected 

over the hydrograph during six periods of storm 

runoff at Emerson Avenue, Central Avenue, and 

16th Street (fig. 3). Most of the samples were 

composited by use of a flow and time weighting 

technique. For some storms, several composite 

(or individual) water-quality samples were 

required to characterize the period of storm runoff. 

Constituents and properties determined include 

field-measured characteristics, major anions, gross 

measures, nutrients, metals and trace elements 

(table 11), and fecal coliform bacteria (table 12). 

Analytical results for these samples, including 

samples split to assess analytical precision for 

the quality-assurance program, are reported in 

tables 11 and 12.

Analytical results reported in table 11 and 

continuous records of streamflow were used to 

mathematically calculate an event-mean concentration for each constituent for each storm (table 13, 

fig. 13). For split samples, the average (mean) 

concentration was used in the calculations. Eventmean concentration is used in this report to 

represent the streamflow-weighted average concentration during the period of storm runoff (runoff 

load divided by runoff volume). Concentrations 

less than the detection limit were assigned concentrations one-half the detection limit for the purpose 

of calculating event-mean concentration. Eventmean concentrations were used for all water-quality 

interpretations.

Specific Conductance, Dissolved Oxygen, 

Temperature, and pH

Patterns of water quality measured in the 

field at Emerson Avenue, Central Avenue, and 

16th Street during base flow immediately before 

rainfall or runoff generally were the same as those 

measured during the base-flow and storm-runoff

synoptic surveys. Specific conductance was least 

at Emerson Avenue and greatest at 16th Street, pH 

and concentrations of dissolved oxygen were 

greatest at Emerson Avenue and least at Central 

Avenue, and water temperature was least at Central 

Avenue (figs. 6-11). These water-quality patterns 

were maintained during storm runoff for the four 

storms characterized by low rates of storm runoff 

(storms 3-6, figs. 8-11). More complex waterquality patterns were exhibited during storm runoff 

for the two storms characterized by high rates of 

storm runoff (storms 1-2, figs. 6-7).

In general, specific conductance, pH, water 

temperature, and concentrations of dissolved 

oxygen were lower during storm runoff than 

during base flow (figs. 6-11). Specific conductance 

decreased because rainfall and surface runoff typically contain lower concentrations of ions (ions 

increase electrical conductance) than does base 

flow. Values of pH decreased during storm runoff 

because rainfall is acidic. Concentrations of dissolved oxygen decreased probably because oxygen 

was consumed by oxygen-demanding materials 

from combined-sewer overflows, urban runoff, and 

resuspended sediment and because of the discharge 

of anoxic water from combined-sewer overflows.

High rates of storm runoff seemed to affect 

field-measured water quality to a greater degree 

than did low rates of runoff. Characteristics of 

storm runoff and its effect on dissolved oxygen, pH, 

water temperature, and specific conductance are 

discussed in Martin and Craig (1990, p. 17,27-41).

Concentrations of dissolved oxygen measured 

at Central Avenue were less than the Indiana 

minimum ambient water-quality standard of 

4.0 mg/L during all storms (figs. 6-11). For storms 

that occurred during low base-flow rates, concentrations of dissolved oxygen at Central Avenue 

were near or less than 4.0 mg/L before rainfall or 

runoff. During storm runoff, concentrations of 

dissolved oxygen decreased further (figs. 8-11).

70 Effects of Combined-Sewer Overflows and Urbsn Runoff, Fsll Creek, Indianapolis, Indlsns
Table 11 . Water-quality analyses for samples collected during periods of storm runoff

[i.d., identification number; ft3/s, cubic feet per second; uS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degree Celsius; mg/L, milligrams per l

CaCO3 , calcium carbonate; N, nitrogen; P, phosphorus; (ig/L, micrograms per liter, , no data; <, less than; >, greater than or equal to; ss, split sample]

i 

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ter Quality ofBaae

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1

a

Site

Emerson

Central

16th Street

16th Street 

Emerson

Central 

16th Street

16th Street

Emerson

Central 

16th Street 

Emerson

Central 

16th Street

Emerson

Central 

16th Street

Emerson 

Central 

16th Street 

16th Street

16th Street

Ssmple

Storm 1

Storm 1

Storm 1

Storm 1 

Storm 2a

Storm 2a 

Storm 2a

Storm 2a

Storm 2b

Storm 2b 

Storm 2b 

Storm 2c

Storm 2c 

Storm 2c

Storm 2d

Storm 2d 

Storm 2d

Storm 3 

Storm 3 

Storm 3a 

Storm 3a

Storm 3b

Sample 

type

Composite

Composite

Composite ss5

Composite ss5 

Composite

Composite 

Composite ss

Composite ss5

Composite

Composite 

Composite 

Composite

Composite 

Composite

Individual

Individual 

Individual

Composite 

Composite 

Composite ss 

Composite ss5

Individual

First sample2

Date

7-26-87

7-26-87

7-26-87

7-26-87 

7-29-87

7-29-87 

7-29-87

7-29-87

7-31-87

7-31-87 

7-31-87 

8-01-87

8-01-87 

8-01-87

8-03-87

8-03-87 

8-03-87

8-26-87 

8-26-87 

8-26-87 

8-26-87

8-27-87

Time

1940

2135

2310

2310 

2242

2206 

2225

2225

0725

0838 

0715 

2021

2157 

2330

0730

0827 

1003

2114 

2050 

2055 

2055

1807

Last sample3

Date

7-28-87

7-28-87

7-28-87

7-28-87 

7-31-87

7-31-87 

7-31-87

7-31-87

8-01-87

8-01-87 

8-01-87 

8-02-87

8-02-87 

8-02-87

n.a.

n.a. 

n.a.

8-27-87 

8-27-87 

8-27-87 

8-27-87

n.a.

Tima

0855

0930

1248

1248 

0359

0440 

0318

0318

0714

0807 

0838 

0741

0834 

0924

n.a.

n.a. 

n.a.

0838 

0808 

1107 

1107

n.a.

Streamflow4 

(ftVs)

63-138

72-320

85-356

85-356 

83-495

41-367 

69-439

69-439

173-271

141-212 

183-323 

166-173

136-141 

159-177

175

141 

180

62- 67 

28- 99 

35- 77 

35- 77

63

Specific 

conductance

(uS/cm)

380-457

319-637

384-716

384-716 

318-433

333-571 

368-591

368-591

377-437

359-466 

422-502 

426-438

466-472 

508-512

438

454 

513

446-454 

530-602 

706-798 

706-798

762
Table 11. Water-quality analyses for samples collected during periods of storm runoff Continued

sets of Combi

3

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1

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3

Q.

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30

g

S:

i

o

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Q.

3

I J.

1

3 

0)

Site

Emerson

Central

16th Street

Emerson

Central

16th Street

Emerson

Central

16th Street

Emerson

Central

16th Street

Central

Emerson

Central

Central

16th Street

16th Street

Sample 

Ld.1

Storm 4a

Storm 4a

Storm 4a

Storm 4b

Storm 4b

Storm 4b

Storm 4c

Storm 4c

Storm 4c

Storm 5

Storm 5a

Storm 5

Storm 5b

Storm 6

Storm 6

Storm 6

Storm 6a

Storm 6b

Sample 

type

Composite

Composite

Composite

Composite

Composite

Composite

Composite

Composite

Composite

Composite

Composite

Composite

Individual

Composite

Composite ss5

Composite ss

Composite

Individual

First sample2

Date

9-11-87

9-10-87

9-10-87

9-11-87

9-11-87

9-11-87

9-12-87

9-12-87

9-12-87

9-17-87

9-17-87

9-17-87

9-17-87

9-29-87

9-29-87

9-29-87

9-29-87

9-30-87

Time

0023

2308

2232

1742

1704

1606

1358

1440

1528

0213

0122

0158

1215

0634

0614

0614

0623

1615

Laat sample3

Date

9-11-87

9-11-87

9-11-87

9-11-87

9-12-87

9-12-87

9-13-87

9-13-87

9-13-87

9-17-87

9-17-87

9-17-87

n.a.

9-30-87

9-30-87

9-30-87

9-30-87

n.a.

Time

1207

1143

1144

1930

0738

0822

0145

0215

0252

0745

1009

1300

n.a.

0425

0832

0832

0903

n.a.

Streamflow4 

(ft3/*)

64- 78

15- 30

18- 58

75- 76

36- 43

61- 69

70- 71

27- 35

45- 61

55- 59

24-120

4-104

28

52- 61

18- 65

18- 65

31-104

35

Specifi

conductan

GiS/cm

429-435

612-646

732-782

451-459

626-662

733-742

434-454

548

732-77

448-455

499-634

606-739

506

478-493

599-72

599-72

805-87

828
Table 11. Water-quality analyses for samples collected during periods of storm runoff Continued

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Tl

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Site

Emerson

Central

16th Street

16th Street

Emerson

Central

16th Street

16th Street

Emerson

Central

16th Street 

Emerson

Central

16th Street 

Emerson

Central

16th Street

Emerson

Central

16th Street

16th Street

16th Street

Diaaolved 

Sample alkalinity 

i.d.1 (mg/L as CaCO3)

Storm 1

Storm 1

Storm 1 ss5

Storm 1 ss5

Storm 2a

Storm 2a

Storm 2a ss5

Storm 2a ss5

Storm 2b

Storm 2b

Storm 2b 

Storm 2c

Storm 2c

Storm 2c 

Storm 2d

Storm 2d

Storm 2d

Storm 3

Storm 3

Storm 3 a ss

Storm 3a ss5

Storm 3b

143

152

188

188

123

128

139

137

131

130

139

142

152

152 

155

158

170

158

176

222

231

237

Disaolved 

sulfate 

(mg/L)

33

38

50

50

30

30

37

37

32

32

36 

35

38

43 

35

38

43

36

48

64

66

65

Disaolved 

chloride 

(mg/L)

25

30

45

44

23

25

29

29

23

24

29 

24

28

32 

25

28

33

28

37

59

59

62

Dia solved 

sollda 

(mg/L)

275

318

387

389

263

285

290

305

289

285

298 

293

291

358 

260

295

304

273

328

466

470

468

Total 

solida 

(mg/L)

348

331

471

454

379

330

412

390

317

298

381 

339

344

404 

307

308

353

328

373

681

640

544

Suapended 

solids9 

(mg/L)

73

13

84

65

116

45

122

85

28

13

83 

46

53

46

47

13

49

55

45

215

170

76

Total 

20-day 

carbonace

oxygen dem

(mg/L

2

14

6

6

4

>22

14

8

<1

<1

3 

616

618

617 

613

612

617

4

5

14

10

6
Table 11. Water-quality analyses for samples collected during periods of storm runoff Continued

its of Combined

&

I

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ff

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B

Site

Emerson

Central

16th Street

Emerson

Central

16th Street

Emerson

Central

16th Street

Emerson

Central

16th Street

Central

Emerson

Central

Central

16th Street

16th Street

Dissolved 

Sample alkalinity 

l.d.1 (mg/L as CaCOs)

Storm 4a

Storm 4a

Storm 4a

Storm 4b

Storm 4b

Storm 4b

Storm 4c

Storm 4c

Storm 4c

Storm 5

Storm 5 a

Storm 5

Storm 5b

Storm 6

Storm 6 ss

Storm 6 ss5

Storm 6a

Storm 6b

160

208

224

158

202

224

160

184

228

159

176

212

152

164

208

206

252

258

Dissolved 

aulfate 

(mg/L)

36

60

66

37

57

66

36

49

67

36

50

61

44

38

56

56

72

70

Dissolved 

chloride 

(mg/L)

27

41

59

28

39

57

27

34

54

34

34

42

31

30

44

43

64

66

Dissolved 

aollds 

(mg/L)

293

417

515

307

413

485

303

349

478

278

344

418

305

288

395

399

499

507

Total 

aollda 

(mg/L)

317

429

1,223

316

413

761

306

360

549

315

368

508

314

304

411

418

567

547

Suspended 

solids9 

(mg/L)

24

12

708

9

0

276

3

11

71

37

24

90

9

16

16

19

68

40

Total 

20-day 

carbonaceou

oxygen deman

(mg/L)

11

12

62

10

11

32

12

11

19

7

16

6

14

2

10

10

6

5
Table 11. Water-quality analyses for samples collected during periods of storm runoff Continued

I

0

01

3

i of StormR

unoff andC

o

I

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5-

I

S.

O)

(D

TI 

i

Site

Emerson 

Central

16th Street

16th Street

Emerson

Central

16th Street

16th Street 

Emerson 

Central

16th Street 

Emerson 

Central

16th Street

Emerson

Central 

16th Street

Emerson

Central 

16th Street

16th Street 

16th Street

Sample 

l.d. 1

Storm 1 

Storm 1

Storm 1 ss5

Storm 1 ss5

Storm 2a

Storm 2a

Storm 2a ss5

Storm 2a ss5 

Storm 2b 

Storm 2b

Storm 2b 

Storm 2c 

Storm 2c

Storm 2c

Storm 2d

Storm 2d 

Storm 2d

Storm 3

Storm 3 

Storm 3 ass5

Storm 3a ss5 

Storm 3b

Total 

nitrate plua nitrite 

(mg/L as N)

0.19 

.28

.41

.41

.27

.27

.32

.33 

.29 

.34

.39 

.18 

.21

.33

.26

.21 

.24

.18

.33 

.69

.74 

.91

Total 

ammonia 

(mg/L as N)

0.10 

.40

.35

.37

.05

.26

.25

.22 

.07 

.08

.16 

.05

.14

.22

.10

.08 

.20

.10

.71 

.59

.58 

.38

Total 

organic nitrogen 

(mg/L)

0.80 

1.24

7 .09

1.64

1.16

1.15

1.14

2.47 

1.21 

1.12

1.18 

1.09 

1.13

.97

1.12

1.15 

.92

.93

1.42 

2.43

2.46 

1.32

Total Dissolved 

phosphorus orthophosphate 

(mg/L) (mg/L as P)

0.17 <0.01 

.27 <.01

.49 <.01

.50 <.01

.17 <.01

.60 <.01

.44 <.01

.56 <.01 

.16 <.01 

.17 <.01

.44 <.01 

.14 <.01 

.14 <.01

.28 <.01

.12 .01

.15 <.01 

.23 <.01

.10 .01

.33 .03 

1.35 .04

1.33 .09 

.39 .08

T

ar

(H
Table 11. Water-quality analyses for samples collected during periods of storm runoff Continued

i

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1

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1

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3D

§

2

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1

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1

TJ 

|

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Site

Emerson

Central

16th Street

Emerson

Central

16th Street

Emerson

Central

16th Street

Emerson

Central

16th Street

Central

Emerson

Central

Central

16th Street

16th Street

Sample 

Ld.1

Storm 4a

Storm 4a

Storm 4a

Storm 4b

Storm 4b

Storm 4b

Storm 4c

Storm 4c

Storm 4c

Storm 5

Storm 5a

Storm 5

Storm 5b

Storm 6

Storm 6 ss

Storm 6 ss5

Storm 6a

Storm 6b

Total 

nitrate plus nitrite 

(mg/L as N)

.09

.35

.62

.13

.26

3.60

.09

.22

.54

.17

.36

.61

.37

.19

.38

.34

.97

8

Total 

ammonia 

(mg/L as N)

.09

.35

.85

.11

.27

.54

.10

.15

.38

.02

.74

.26

.61

.12

.67

.75

.21

.31

Total 

organic nitrogen 

(mg/L)

.88

.75

7.08

.83

.67

3.45

1.14

.70

1.69

.84

1.58

1.45

1.38

.73

1.07

1.15

1.47

1.03

Total Dissolved 

phoaphorua orthophosphate 

(mg/L) (mg/L as P)

.09

.09

6.76

.08

.05

2.06

.09

.08

.62

.09

.29

.46

.25

.29

.44

.80

1.60

.30

.01

<.01

.03

<.01

<.01

.02

<.01

<01

.02

<.0l

.04

.03

.04

<.01

.04

.04

.07

.08
Table 11. Water-quality analyses for samples collected during periods of storm runoff Continued

1

o

-f

o

i

i

3D

i

3 

n

i

3

?

3.

S

g

1

o

»

<

o

i

a

o3

Site

Emerson

Central

16th Street

16th Street

Emerson

Central

16th Street

16th Street

Emerson

Central

16th Street

Emerson

Central

16th Street

Emerson

Central

16th Street

Emerson

Central

16th Street

16th Street

16th Street

Sample

Storm 1

Storm 1

Storm 1 ss5

Storm 1 ss

Storm 2a

Storm 2a

Storm 2a ss5

Storm 2a ss5

Storm 2b

Storm 2b

Storm 2b

Storm 2c

Storm 2c

Storm 2c

Storm 2d

Storm 2d

Storm 2d

Storm 3

Storm 3

Storm 3a ss5

Storm 3a ss5

Storm 3b

Total 

recoverable 

aluminum

(WJ/L)

1,310

630

3,130

3,150

2,050

2,190

2,690

2,410

770

710

2,810

390

380

940

390

220

830

280

310

11,490

11,450

1,890

Total Total 

recoverable recoverable 

barium cadmium

(ng/L) (WJ/L)

<10 <10

70 <10

80 <10

100 <10

80 <10

80 <10

60 <10

10 <10

60 <10

40 <10

70 <10

30 <10

70 <10

90 <10

60 <10

50 <10

50 <10

90 <10

40 <10

70 <10

90 <10

90 <10

Total Total 

recoverable recoverable 

chromium copper

(WJ/L) (ng/L)

<10 20

<10 20

10 20

<10 20

10 10

<10 20

<10 20

<10 20

<10 10

<10 10

<10 20

<10 20

<10 20

<10 10

<10 <10

<10 <10

<10 10

<10 <10

<10 20

20 30

20 30

<10 <10

Total 

recoverable 

Iron

(Hfl/L)

2,060

740

2,700

2,780

4,070

2,070

2,840

2,630

1,380

960

2,660

820

510

1,040

930

470

790

600

480

3,620

3,630

1,160

Tota

recover

lead 

(Hfl/L

1

1

2

2

2

2

1

2

1

<1

<1

<1

1

1

<1

<1

<1

1

<1

2

2

<1
Table 11 . Water-quality analyses for samples collected during periods of storm runoff Continued

fects ofComblni

1

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O

1

o

3 

O.

C

1

3D

I

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|

1

i

1

»

I5"

2

Site

Emerson

Central

16th Street

Emerson

Central

16th Street

Emerson

Central

16th Street

Emerson

Central

16th Street

Central

Emerson

Central

Central

16th Street

16th Street

Sample

Storm 4a

Storm 4a

Storm 4a

Storm 4b

Storm 4b

Storm 4b

Storm 4c

Storm 4c

Storm 4c

Storm 5

Storm 5a

Storm 5

Storm 5b

Storm 6

Storm 6 ss5

Storm 6 ss5

Storm 6a

Storm 6b

Total 

recoverable 

aluminum

230

160

44,800

220

200

15,990

200

210

4,210

220

300

2,540

90

190

190

180

3,860

1,110

Total Total 

recoverable recoverable 

barium cadmium

(Hfl/L) (Mfl/L)

30 <10

30 <10

240 <10

30 <10

70 <10

160 <10

90 <10

10 <10

120 <10

40 <10

50 <10

110 <10

130 <10

90 <10

70 <10

70 <10

70 <10

70 <10

Total Total 

recoverable recoverable 

chromium copper

(ng/L) (Hfl/L)

<10 <10

<10 <10

70 70

<10 <10

<10 <10

20 20

<10 <10

<10 70

<10 10

<10 <10

<10 20

<10 10

<10 10

<10 <10

<10 10

<10 20

<10 10

<10 <10

Total T

recoverable reco

Iron l

460 

300 

15,150 

420 

270 

6,800 

460 

260 

1,930 

610 

650 

1,660 

330 

480 

310 

310 

1,710 

770 

'The suffixes a, b, c, and d indicate that more than one composite sample was needed to represent the storm hydrograph.

2Midpoint time of sample collection for the first sample collected for a composite sample or the only sample collected for an individual sample.

3Midpoint time of sample collection for the last sample collected for a composite sample.

4Range of field measurements observed for a composite sample or the field measurements observed for an individual sample.

5A split sample (ss) is one of a pair of theoretically identical samples used to assess analytical precision. The mean concentration was used for all ca

Nitrification was not inhibited in these samples. Reported concentrations were adjusted for oxidizable nitrogen.

7Anomalous concentration. Not used to calculate event-mean concentration.

8Median storm-runoff concentration at this site (0.54 mg/L) used to calculate event-mean concentration.

'Suspended solids were calculated as the difference between total solids and dissolved solids.
Table 12. Concentrations of fecal coliform bacteria during periods of storm runoff

[col/100 mL, colonies per 100 milliliters; >, greater than; <, less* than]

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Sampling atation

Emeraon Avenue

Date Time

Fecal coliform 

bacteria

(col/100 mL) 

(31 625) 1

Central Avenue

Time

Fecal coliform 

bacteria

(col/100 mL) 

(31625)1

Storm 1

7-26-87

7-27-87

7-28-87

1825

2045

2325

1346

1732

2132

0847

400

7,300

4,500

6,700

2,700

6,200

48,000

2155

2355

0730

1205

1240

1300

1316

1430

1721

2316

22,000

>20,000

>20,000

16,100

43,000

10,800

21,000

98,400

288,000

27,000

Storm 2

7-29-87

7-30-87

2302

0005

0020

0100

0155

0415

0705

0945

1100

1150

1255

1405

1800

1942

2345

4,000

2,100

2,100

1,900

1,100

3,100

2,100

2,700

1,700

800

1,200

4,700

2,500

7,900

5,200

2205

2251

2340

0202

0500

0835

0849

0927

1333

1643

2046

1,800

97,600

80,000

64,800

470,000

20,000

21,000

45,200

14,200

1,400

9,600
Table 12. Concentrations of fecal coliform bacteria during periods of storm runoff Continued

Sampling station

Emeraon Avenue

Date Time

Fecal coliform 

bacteria

(col/100 mL) 

(31625)1

Central Avenue

Time

Fecal coliform 

bacteria

(col/100 mL) 

(31625)1

Storm 2 continued

7-31-87

8-1-87

0407

0730

1026

1330

1636

9,200

2,800

650

900

1,800

0040

0429

0833

1131

1429

1650

5,800

9,400

1,200

1,800

5,000

3,000

Storm 3

8-26-87

8-27-87

2114

2230

2330

0030

0225

200

1,900

2.900

1,100

<100

2150

2230

2320

2345

0025

0115

0243

8,000

20,200

5,000

18,300

22,600

12,200

29,800

Storm 5

9-17-87 0200

0500

0730

1,600

5,400

1,500

0244

0307

0325

0440

0548

0752

3,000

35,600

48,000

27,600

59,400

57,600

Storm 6

9-29-87

9-30-87

1130

1530

1920

0805

4,500

2,000

1,400

1,200

1210

1330

1625

2018

0830

69,600

53,400

223,200

58,400

26,000

^ATSTORE (U.S. Geological Survey) and STORET (U.S. Environmental Protection Agency) parameter code.
Table 13. Event-mean concentrations of constituents during periods of storm runoff

[mg/L, milligrams per liter; CaCO3 , calcium carbonate; N, nitrogen; P, phosphorus; n.a., not applicable; u.g/L, micrograms per liter]

1

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Emerson 

Central

16th Street

Emerson

Central 

16th Street

Emerson

Central

16th Street

Emerson

Central 

16th Street

Emerson 

Central 

16th Street

Emerson 

Central

16th Street

Storm

Storm 1 

Storm 1

Storm 1

Storm 2

Storm 2 

Storm 2

Storm 3

Storm 3

Storm 3

Storm 4

Storm 4 

Storm 4

Storm 5 

Storm 5 

Storm 5

Storm 6 

Storm 6

Storm 6

Diasolved 

alkalinity 

(mg/L as CaCO3)

143.0 

152.0

188.0

133.5

137.7 

145.4

158.0

176.0

229.7

159.6

196.5 

225.5

159.0 

171.3 

212.0

164.0 

207.0

252.5

Diasolved 

aulfate 

(mg/L)

33.0 

38.0

50.0

32.3

33.3 

38.7

36.0

48.0

65.0

36.2

54.6 

66.4

36.0 

48.8 

61.0

38.0 

56.0

71.8

Diasolved 

chloride 

(mg/L)

25.0 

30.0

44.5

23.5

25.8 

30.1

28.0

37.0

59.9

27.2

37.5 

56.3

34.0 

33.4 

42.0

30.0 

43.5

64.2

Diasolved 

aoilda 

(mg/L)

275.0 

318.0

388.0

275.9

287.6 

310.6

273.0

328.0

468.0

301.2

390.2 

487.7

278.0 

336.3 

418.0

288.0 

397.0

499.7

Total 

solids 

(mg/L)

348.0 

331.0

462.5

344.2

321.4 

389.2

328.0

373.0

624.9

311.2

396.5 

764.5

315.0 

357.4 

508.0

304.0 

414.5

565.2

Suspended 

solids2 

(mg/L)

73.0 

13.0

74.5

68.3

33.8 

78.6

55.0

45.0

156.9

10.0

6.3 

276.8

37.0 

21.1 

90.0

16.0 

17.5

65.5

Total 

20-day 

carbonaceou

biochemica

oxygen dema

(mg/L)

2.0 

14.0

6.0

6.8

14.2 

10.6

4.0

5.0

10.2

11.3

11.2 

325

7.0 

15.6 

6.0

2.0 

10.0

5.9

Detection limit 10 10 n.a.
Table 13. Event-mean concentrations of constituents during periods of storm runoff Continued

Effects ofComblf

w

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Site

Emerson

Central

16th Street

Emerson

Central 

16th Street

Emerson

Central 

16th Street

Emerson 

Central

16th Street

Emerson

Central

16th Street

Emerson

Central

16th Street

Total Total 

nitrate plus nitrite ammonia 

Storm (mg/L as N) (mg/L as N)

Storm 1

Storm 1

Storm 1

Storm 2

Storm 2 

Storm 2

Storm 3

Storm 3 

Storm 3

Storm 4 

Storm 4

Storm 4

Storm 5

Storm 5

Storm 5

Storm 6

Storm 6

Storm 6

0.190

.280

.410

.255

.267 

.334

.180

.330 

.775

.099 

.262

1.956

.170

.362

.610

.190

.360

.932

0.100

.400

360

.062

.163 

.205

.100

.710 

.522

.100

.241

.536

.020

.714

.260

.120

.710

.219

Total 

organic nitrogen 

(mg/L)

0.800

1.240

1.640

1.153

1.138 

1.332

.930

1.420 

2.101

1.001 

.696

3.443

.840

1.541

1.450

.730

1.110

1.431

Total 

phosphorus 

(mg/L)

0.170

.270

.495

.154

.331 

.402

.100

.330 

1.049

.088 

.069

2.358

.090

.282

.460

.290

.620

1.486

Dissolved 

orthophosphate 

(mg/LaaP)

0.005

.005

.005

.006

.005 

.005

.010

.030 

.070

.006 

.005

.022

.005

.040

.030

.005

.040

.071

Total 

arseni

(Hfl/L

4.0

.50

4.0

2.2

2.1 

2.7

1.0

1.0 

7.9

1.5 

1.2

9.8

2.0

1.2

4.0

1.0

1.0

5.6

Detection limit .005 .01 .01 .01 .01
Table 13. Event-mean concentrations of constituents during periods of storm runoff Continued

i

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w 

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Emerson

Central

16th Street

Emerson 

Central

16th Street

Emerson

Central

16th Street

Emerson

Central 

16th Street

Emerson

Central 

16th Street

Emerson

Central

16th Street

Detection limit1

Storm

Storm 1

Storm 1

Storm 1

Storm 2 

Storm 2

Storm 2

Storm 3

Storm 3

Storm 3

Storm 4

Storm 4 

Storm 4

Storm 5

Storm 5 

Storm 5

Storm 6

Storm 6

Storm 6

Total 

recoverable 

aluminum

(MI/L)

1,310

630

3,140

1,130 

1,156

2,076

280

310

8,539

212

196 

16,730

220

259 

2,540

190

185

3,619

10

Total 

recoverable 

barium 

(MI/L)

5.0

70

90

61 

63

75

90

40

83

61

74 

159

40

66 

110

90

70

70

10

Total 

recoverable 

cadmium

5.0

5.0

5.0

5.0 

5.0

5.0

5.0

5.0

5.0

5.0

5.0 

5.0

5.0

5.0 

5.0

5.0

5.0

5.0

10

Total 

recoverable 

chromium

(WJ/L)

5.0

5.0

10

6.9 

5.0

5.0

5.0

5.0

15

5.0

5.0

23

5.0

5.0 

5.0

5.0

5.0

5.0

10

Total 

recoverable 

copper

(WJ/L)

20

20

20

11 

15

17

5.0

20

22

5.0

29

25

5.0

18 

10

5.0

15

9.6

10

Total 

recoverable 

Iron

(WJ/L)

2,060

740

2,740

2,235 

1,236

2,113

600

480

2,871

451

272 

6,482

610

587 

1,660

480

310

1,628

10

To

recov

le

(M

10

10

20

12 

12

9

10

5

15

6

22 

33

5

5

5

5

5

5

1

s

^Concentrations less than the detection limit were assigned concentrations one-half the detection limit for the calculation of event-mean concentration. E

to one additional significant figure than analytical measurements of the same magnitude.

Suspended solids were calculated as the difference between total solids and dissolved solids.
Durations of concentrations of dissolved 

oxygen less than 4.0 mg/L at Central Avenue during 

storm runoff ranged from approximately 4 hours 

during storm 2 (fig. 7) to more than 24 hours during 

storm 6 (fig. 11). Minimum concentrations of 

dissolved oxygen at Central Avenue during storm 

runoff were 0.5,1.9,2.0,2.5,0.8, and 0.5 mg/L 

during storms 1-6, respectively (table 11). Concentrations of dissolved oxygen at 16th Street were less 

than 4.0 mg/L for approximately 1 hour during 

storm 1 (minimum 3.4 mg/L, fig. 6). The minimum 

concentration of dissolved oxygen at Emerson 

Avenue during storm runoff was 5.9 mg/L 

(table 11).

Major Anions

Concentrations of alkalinity, sulfate, and 

chloride measured in storm runoff increased downstream (fig. 13). The pattern of increase was similar 

to that measured in base flow, but the concentrations were somewhat less in storm runoff because 

of dilution by precipitation and runoff. Similarly, 

event-mean concentrations measured during the 

storms characterized by high rates of storm runoff 

(storms 1 and 2) were less than those measured 

during the storms characterized by low rates of 

storm runoff (storms 3-6, table 13).

Dissolved and Total Solids, 

Chemical Oxygen Demand, 

Carbonaceous Biochemical Oxygen Demand, 

and Oil and Grease

Concentrations of dissolved solids and total 

solids measured in storm runoff increased downstream in a pattern similar to that in base flow 

(fig. 13). Concentrations of dissolved solids 

measured at Emerson Avenue and 16th Street 

in storm runoff were similar to those measured in 

base flow, but those measured at Central Avenue 

were less than those measured in base flow. The 

water quality of base flow at Central Avenue 

is strongly influenced by ground-water inflow. 

Precipitation and surface runoff caused a discernible decrease in the concentration of dissolved

solids at Central Avenue, a decrease that did not 

occur at the sites that were less influenced by 

ground-water inflow. Concentrations of total 

solids were predominantly controlled by concentrations of dissolved solids and, consequently, 

exhibited similar water-quality patterns (fig. 13). 

Concentrations of total solids in storm runoff at 

Emerson Avenue were slightly greater than those 

in base flow, indicating increased concentrations 

of suspended solids at this site that generally were 

not measured at Central Avenue or 16th Street.

Event-mean concentrations of suspended 

solids (calculated as the difference between 

total solids and dissolved solids, table 13) ranged 

from 10 to 73 mg/L at Emerson Avenue, from 6.3 

to 45 mg/L at Central Avenue, and from 65.5 to 

276.8 mg/L at 16th Street. As with base flow, 

storm runoff at Central Avenue had the lowest 

concentration and proportion of suspended solids 

whereas storm runoff at 16th Street had the highest 

(fig. 13). The lack of a discernible increase in 

suspended-solids concentration in storm runoff at 

16th Street probably can be attributed to the large 

amounts of suspended solids discharged as filter 

backwash during base flow. Low concentrations 

and the lack of an increase in suspended-solids 

concentration in storm runoff at Central Avenue 

may be attributed to sedimentation in the impoundment at Keystone Avenue.

The highest concentrations of suspended 

solids and total solids in storm runoff at Emerson 

Avenue were measured during the two storms 

characterized by high rates of runoff (storms 1 

and 2), whereas the highest concentrations of 

dissolved solids, suspended solids, and total solids 

at Central Avenue and 16th Street occurred during 

the four storms characterized by low rates of runoff 

(storms 3-6, table 13). High rates of runoff caused 

increased concentrations of suspended solids at 

Emerson Avenue, probably attributable to upstream 

erosioa High concentrations of suspended solids 

were not measured downstream (fig. 13). High

84 Effects of Combined-Sewer Overflows snd Urbsn Runoff, Fsll Creek, Indisnapolls, Indlsns
rates of runoff decreased concentrations of 

dissolved solids at Central Avenue and 16th Street 

probably because base flow at these sites was 

composed largely of ground-water inflow (and 

aqueduct overflow at 16th Street) that had much 

higher concentrations of dissolved solids than 

did surface runoff. High rates of runoff had a 

negligible effect on the concentration of dissolved 

solids at Emerson Avenue because water released 

from Geist Reservoir probably had concentrations 

of dissolved solids that were similar to those in 

surface runoff.

Concentrations of CBOD in storm runoff 

generally were higher than those in base flow 

(fig. 13) and ranged from 2 to 11.3 mg/L at 

Emerson Avenue, from 5 to 15.6 mg/L at Central 

Avenue, and from 5.9 to 32.5 mg/L at 16th Street 

(table 13). Generally, the highest concentrations 

of CBOD and the most discernible increases 

compared to base flow occurred at Central Avenue. 

Concentrations of COD in storm runoff also were 

higher than those in base flow and ranged from 

14 to 20.8 mg/L at Emerson Avenue, from 15.4 

to 30 mg/L at Central Avenue, and from 20 to 

56.9 mg/L at 16th Street. Concentrations of CBOD 

and COD were similar at Emerson and Central 

Avenues in base flow but were much higher at 

Central Avenue than at Emerson Avenue in storm 

runoff (fig 13). Increased concentrations of these 

measures of oxygen demand in runoff at Central 

Avenue probably were caused by combined-sewer 

overflows, urban runoff, and the resuspension of 

organic material deposited on the streambed.

Concentrations of oil and grease ranged from 

0.5 to 2 mg/L at Emerson Avenue, from 0.57 to 

6.2 mg/L at Central Avenue, and from 1 to 2 mg/L 

at 16th Street (table 13). Concentrations of oil 

and grease in storm runoff were similar to those 

in base flow, except at Central Avenue where 

concentrations in storm runoff were somewhat 

higher (fig. 13).

Nutrients

Concentrations of nutrients in storm runoff 

increased downstream and, for all nutrients except 

nitrate plus nitrite, were higher than those in base 

flow. Concentrations of nitrate plus nitrite in runoff 

at Central Avenue and 16th Street were similar to 

those in base flow; at Emerson Avenue, however, 

concentrations were slightly higher compared with 

those in base flow (fig. 13).

Event-mean concentrations of ammonia 

ranged from 0.02 to 0.12 mg/L at Emerson Avenue, 

from 0.163 to 0.714 mg/L at Central Avenue, and 

from 0.205 to 0.536 mg/L at 16th Street (table 13). 

Concentrations of ammonia at Central Avenue 

were much higher in runoff than in base flow, 

whereas concentrations of ammonia at 16th Street 

and Emerson Avenue were only slightly higher 

than those in base flow (fig. 13). The minimum 

concentration of ammonia in storm runoff at 

Central Avenue was twice as high as that in base 

flow, and the maximum concentration in runoff 

was four times as high as that in base flow. The 

increase in ammonia at Central Avenue probably 

was caused by combined-sewer overflows and, 

most likely to a lesser degree, by urban runoff.

Event-mean concentrations of organic 

nitrogen, phosphorus, and orthophosphate were 

least at Emerson Avenue, intermediate at Central 

Avenue, and greatest at 16th Street (fig. 13). 

During base flow, however, concentrations of 

organic nitrogen, phosphorus, and orthophosphate 

at Emerson and Central Avenues were similar. 

Except for orthophosphate at Emerson Avenue, 

concentrations of organic nitrogen, phosphorus, 

and orthophosphate in storm runoff were higher 

than those in base flow, particularly at Central 

Avenue and 16th Street. Increased concentrations 

of organic nitrogen, phosphorus, and orthophosphate in storm runoff, particularly in the reach 

between Emerson and Central Avenues, probably 

were caused by combined-sewer overflows and 

urban runoff.

Water Quality of Storm Runoff and Comparlsona with Water Quality of Base Flow 85
Trace Elements

As with all base-flow samples, all stormrunoff samples for mercury, selenium, and 

cadmium (except for one detection of selenium 

at the detection limit at 16th Street) were less 

than the detection limits (table 11).

As with base-flow samples, chromium and 

nickel were detected only at 16th Street (except 

for one detection of chromium at the detection 

limit at Emerson Avenue, table 11). Detectable 

concentrations of chromium and nickel in runoff at 16th Street were associated with high 

concentrations of aluminum and iron (table 11). 

Concentrations of chromium and nickel in runoff 

at 16th Street were higher than those in base flow 

(fig. 13) and were attributed to the discharge of 

filter backwash and the probable resuspension of 

settled flocculent from the streambed in the reach 

of Fall Creek between 16th Street and the discharge 

point for filter backwash. Because these metals 

were not detected in storm runoff at Central 

Avenue, urban runoff and combined-sewer overflows seemed to have little effect on concentrations 

of chromium and nickel.

Concentrations of copper, lead, and zinc in 

storm runoff were much higher than those in base 

flow (fig. 13). Event-mean concentrations of 

copper, lead, and zinc at Central Avenue and 

16th Street generally were greater than those at 

Emerson Avenue. Copper and zinc were detected 

at Emerson Avenue only during storms 1 and 2, 

but were detected at Central Avenue and 16th Street 

during all six storms (tables 11,13). Higher concentrations and more frequent detections at 

Central Avenue and 16th Street indicate that 

runoff from the highly urbanized area downstream from Emerson Avenue is a source of copper, 

lead, and zinc in Fall Creek. The highest concentrations of lead (33 |xg/L) and zinc (63 |J.g/L) were 

associated with the highest concentrations of 

aluminum (16,730 |o.g/L) and iron (6,482 |o.g/L) 

(table 13). This association indicates that some of 

the increased concentrations of lead, zinc, and probably copper at 16th Street can be attributed to the 

discharge and resuspension of filter backwash.

Concentrations of aluminum in storm runoff 

generally were higher than those in base flow 

(fig. 13). Increased concentrations of aluminum at 

Emerson Avenue were caused by increased concentrations of suspended solids, probably from soil and 

bank erosion. Because concentrations of suspended 

solids at Central Avenue generally were less than 

those at Emerson Avenue, increased concentrations 

of aluminum at Central Avenue probably were 

caused by the discharge and resuspension of small 

amounts of aluminum-rich filter backwash rather 

than by a large increase in suspended solids caused 

by soil and bank erosion. Aluminum/iron ratios of 

storm runoff ranged from 0.36 to 0.64 at Emerson 

Avenue, from 0.44 to 0.94 at Central Avenue, and 

from 0.98 to 2.97 at 16th Street (calculated from 

data in table 13) and indicate aluminum enrichment 

(most likely in the suspended material) downstream. Increased concentrations of aluminum in 

runoff at 16th Street were caused by the discharge 

and probable resuspension of filter backwash. In 

view of the large contributions of aluminum from 

filter backwash in base flow and storm runoff 

and the increased concentrations of aluminum 

(probably attributable to soil or bank erosion) 

upstream from Emerson Avenue, combined-sewer 

overflows and urban runoff do not discernibly 

affect concentrations of aluminum in Fall Creek.

Concentrations of iron in storm runoff 

generally were higher than those in base flow, 

particularly at Emerson and Central Avenues 

(fig. 13). Increased concentrations of iron at 

Central Avenue in runoff were not associated 

with increased concentrations of suspended solids. 

Because concentrations of dissolved iron in streams 

at neutral pH usually are low (Hem, 1985, p. 83), 

increased iron concentrations probably were caused 

by solids having high concentrations of iron. 

Urban runoff or the resuspension of filter backwash could have been the source of iron-rich solids. 

Event-mean concentrations of iron at Emerson 

Avenue were consistently greater than those at 

Central Avenue (table 13). Higher concentrations 

of iron in runoff at Emerson Avenue were caused 

by the higher concentrations of suspended solids, 

probably from soil or bank erosion upstream.

86 Effects of Combined-Sewer Overflows snd Urban Runoff, Fsii Creek, Indianapolis, Indiana
Urban runoff and combined-sewer overflows 

may have increased concentrations of iron in Fall 

Creek, but the increased concentrations were 

comparable to those caused by soil and bank 

erosion from rural areas upstream from Emerson 

Avenue.

Concentrations of arsenic in storm runoff were 

similar to those in base flow (fig. 13). As with base 

flow, concentrations of arsenic in storm runoff were 

much greater at 16th Street than concentrations at 

Emerson and Central Avenues. Urban runoff and 

combined-sewer overflows had little discernible 

effect on arsenic in Fall Creek.

Concentrations of barium in storm runoff at 

Emerson Avenue were greater than concentrations 

measured in base flow, whereas concentrations 

during runoff at Central Avenue and 16th Street 

were less than concentrations measured in base 

flow (fig. 13). Decreased concentrations of barium 

in runoff would be expected if ground-water inflow 

is the major source of barium and surface runoff 

contains low concentrations of barium. The cause 

of the increased concentrations of barium at 

Emerson Avenue in storm runoff is not known. 

Combined-sewer overflows and urban runoff do 

not seem to be a source of barium in Fall Creek.

Fecal Coliform Bacteria

Concentrations of fecal coliform bacteria 

in storm runoff were much greater than those in 

base flow (tables 9,12). Concentrations of fecal 

coliform bacteria in storm runoff ranged from 

<100 to 48,000 col/100 mL at Emerson Avenue, 

from 1,200 to 470,000 coVlOO mL at Central 

Avenue, and from <100 to 152,000 col/100 mL 

at 16th Street. Concentrations of fecal coliform 

bacteria exceeded 10,000 col/100 mL only once 

at Emerson Avenue but frequently exceeded this 

concentration at Central Avenue and 16th Street. 

Raw sewage in combined-sewer overflows and 

animal wastes in urban runoff are the major sources 

of fecal coliform bacteria. In general, concentrations of fecal coliform bacteria were highest at

Central Avenue and lowest at Emerson Avenue 

and were highly variable in storm runoff (figs. 6- 

11). Combined-sewer overflows and urban runoff 

dramatically increased concentrations of fecal 

coliform bacteria in Fall Creek.

SUMMARY AND CONCLUSIONS

In 1986, the U.S. Geological Survey and the 

Indianapolis Department of Public Works began 

a cooperative study to evaluate the effects of 

combined-sewer overflows and urban runoff to 

Fall Creek on the water quality of the White River. 

This report describes the effects of combined-sewer 

overflows and urban runoff on the water quality 

of Fall Creek in and near Indianapolis during 

summer 1987.

Fall Creek drains 318 mi2 in east-central 

Indiana and flows approximately 60 mi to its 

confluence with the White River in Indianapolis. 

Fall Creek is a highly complex, urban and rural 

hydrologic system that includes an instream watersupply reservoir, several low-head dams, water 

withdrawal for public supply, a variety of pointsource effluents, stormwater and combined-sewer 

overflows, and interbasin water transfer into the 

basin as a result of aqueduct overflow.

Most of the water-quality data collected during 

the study were collected from three streamflowgaging stations on Fall Creek in Indianapolis. 

These stations were located at Emerson Avenue, 

Central Avenue, and 16th Street at river miles 9.2, 

3.8, and 1.3, respectively. The Emerson Avenue 

station is upstream from all combined-sewer 

overflows and receives urban and rural runoff 

and water released from Geist Reservoir. The 

Central Avenue station is in the center of the 

combined-sewer-overflow area; 15 combinedsewer overflows are upstream from Central Avenue 

and 13 are downstream. The 16th Street station 

is downstream from 27 of 28 combined-sewer 

overflows on Fall Creek, downstream from the 

aqueduct overflow from the water-supply canal, 

and immediately downstream from the discharge 

of filter backwash from the water-treatment

Summary and Conculsions 87
process for public supply. Water-quality samples 

were collected four to six times during base flow 

and multiple times during storm runoff during six 

storms. Multiple runoff samples were composited 

to a single sample that represented the mean water 

quality during the period of storm runoff. Waterquality samples also were collected from the 

aqueduct overflow and from the filter backwash. 

Most chemical analyses were done on whole-water 

(nonfiltered) samples and are termed "total" or 

"total recoverable."

Precipitation in the Indianapolis area 

was about one-half of normal during the study 

period (July 22-October 19,1987). Seven storms 

produced runoff during the study period. Water 

samples were collected during runoff from six of 

these storms. Although the median amount of 

precipitation for some of the storms was small, all 

storms caused at least some of the combined sewers 

to overflow.

Streamflow at the three streamflow-gaging 

stations is regulated by Geist Reservoir. Compared 

with historical streamflow, monthly mean streamflow during July and August was near or above 

normal, whereas streamflow during September and 

October was well below normal. During base flow, 

streamflow at Emerson Avenue was greater than 

that downstream at Central Avenue or 16th Street 

and showed the effect of water withdrawn for 

public supply between Emerson and Central 

Avenues. Approximately 69 percent of the streamflow at Central Avenue during October was 

contributed by ground-water seepage in the reach 

between Emerson Avenue and Central Avenue. 

The increase in streamflow from Central Avenue 

to 16th Street was attributed to three sources: 

aqueduct overflow, ground-water inflow, and 

filter backwash. These sources accounted for 

approximately 35,48.5, and 2 percent, respectively, 

of the streamflow measured at 16th Street during 

October. Only about 14.5 percent of the streamflow 

measured at 16th Street during October was streamflow that originated in Fall Creek upstream from 

Emerson Avenue.

The effects of combined-sewer overflows and 

urban runoff on the water quality of Fall Creek 

were determined by comparing the water quality 

of base flow with water quality of storm runoff. 

In addition, water quality of runoff in the urbanized 

area was compared with water quality in the 

less urbanized area upstream from the combinedsewer overflows.

During base flow, specific conductance and 

concentrations of major anions and dissolved solids 

increased downstream in response to ground-water 

inflow, aqueduct overflow, and the discharge of 

filter backwash. Dissolved oxygen concentrations 

were least in the reach of Fall Creek near Central 

Avenue where black sludge deposits covered the 

stream bottom. The black deposits correspond 

to the areas where combined-sewer overflows 

discharge. Concentrations of suspended solids 

were least at Central Avenue and greatest at 

16th Street. High concentrations of suspended 

solids at 16th Street were caused by the discharge 

of filter backwash. Concentrations of CBOD and 

COD measured at Emerson Avenue were nearly 

identical to those measured at Central Avenue, 

whereas those at 16th Street were approximately 

two times greater. Concentrations of CBOD at 

Emerson Avenue and Central Avenue ranged from 

<1 to 4 mg/L but ranged from 2 to 9 mg/L at 

16th Street. Concentrations of CBOD and COD 

in the aqueduct overflow were similar to concentrations measured upstream at Emerson Avenue and 

Central Avenue, whereas concentrations in the 

filter backwash were the highest measured (16 and 

63 mg/L, respectively). The discharge of filter 

backwash caused the increased concentrations of 

CBOD and COD during base flow at 16th Street.

During base flow, concentrations of nitrate 

plus nitrite and ammonia steadily increased downstream, whereas concentrations of organic nitrogen, 

phosphorus, and orthophosphate increased at 

16th Street only. Concentrations of mercury, 

selenium, and cadmium were less than the 

detection limits (0.2,1, and 10 u.g/L, respectively) 

in all base-flow samples. Except for two detectable 

concentrations of copper at Central Avenue and 

detectable zinc in the aqueduct overflow, all 

concentrations of chromium, copper, lead,

88 Effects of Combined-Sewer Overflows and Urban Runoff, Fsll Creek, Indisnspolis, Indlsns
nickel, and zinc were less than the detection limit 

(10 H-g/L) for base-flow samples collected at 

Emerson Avenue, Central Avenue, and the 

aqueduct overflow. Filter backwash had the 

highest concentrations of chromium (30 |J.g/L), 

copper (40 u,g/L), lead (30 u,g/L), nickel (30 |ig/L), 

and zinc (40 |J.g/L). Detectable concentrations of 

these metals in base-flow samples from 16th Street 

were caused by the discharge of filter backwash.

Concentrations of aluminum steadily 

increased downstream, whereas concentrations of 

arsenic were greater at Emerson Avenue than at 

Central Avenue. Concentrations of both constituents were greatest at 16th Street. Increased 

concentrations of aluminum at 16th Street were 

caused by the discharge of aluminum hydroxide 

floe (in the filter backwash) from the drinkingwater-treatment process. Filter backwash had the 

highest concentration of aluminum (27,240 |J.g/L). 

The solids discharged as filter backwash were 

approximately 10 percent aluminum. Concentrations of arsenic ranged from 1 to 2 |o.g/L at Emerson 

Avenue and Central Avenue, but ranged from 2 to 

10 |o.g/L at 16th Street. Increased concentrations at 

16th Street could not be attributed to the discharge 

of filter backwash because the concentration of 

arsenic in the backwash was only 2 |J.g/L. Groundwater inflow probably is not the cause of increased 

concentrations of arsenic because increased concentrations were not measured at Central Avenue, 

where base flow is composed largely of groundwater inflow.

Concentrations of fecal coliform bacteria 

in base flow generally were lowest at Central 

Avenue and highest at 16th Street. Concentrations 

of fecal coliform bacteria ranged from 100 to 

2,000 col/100 mL at Emerson Avenue, from 200 

to 500 col/100 mL at Central Avenue, and from 

<100 to 12,800 col/100 mL at 16th Street.

During storm runoff, specific conductance, 

pH, water temperature, and concentrations of 

dissolved oxygen generally decreased. Specific 

conductance decreased because rainfall and surface 

runoff typically contain lower concentrations of 

ions than does base flow. Because rainfall is acidic,

pH decreased during storm runoff. Concentrations 

of dissolved oxygen decreased probably because 

oxygen was consumed by oxygen-demanding 

materials from combined-sewer overflows, urban 

runoff, and resuspended sediment and because of 

the discharge of anoxic water from combinedsewer overflows. Concentrations of dissolved 

oxygen measured at Central Avenue were less than 

the Indiana minimum ambient water-quality 

standard of 4.0 mg/L for all storms. For storms 

that occurred during low base-flow rates, concentrations of dissolved oxygen measured at Central 

Avenue were near or less than 4.0 mg/L before 

rainfall or runoff. During storm runoff, concentrations of dissolved oxygen decreased further. 

Durations of concentrations of dissolved oxygen 

less than 4.0 mg/L at Central Avenue during storm 

runoff ranged from approximately 4 to more than 

24 hours, and minimum concentrations during 

storms 1 through 6 were 0.5,1.9, 2.0, 2.5,0.8, 

and 0.5 mg/L, respectively. Concentrations of 

dissolved oxygen at 16th Street were less than 

4.0 mg/L for approximately 1 hour during storm 1 

(minimum 3.4 mg/L). The minimum concentration of dissolved oxygen at Emerson Avenue 

during storm runoff was 5.9 mg/L.

Concentrations of CBOD in storm runoff 

generally were higher than those in base flow and 

ranged from 2 to 11.3 mg/L at Emerson Avenue, 

from 5 to 15.6 mg/L at Central Avenue, and from 

5.9 to 32.5 mg/L at 16th Street. Generally, the 

highest concentrations of CBOD and most discernible increases compared to base flow occurred at 

Central Avenue. Concentrations of CBOD and 

COD were similar in base flow at Emerson and 

Central Avenues but were much higher in storm 

runoff at Central Avenue. Increased concentrations 

of these measures of oxygen demand in runoff 

at Central Avenue probably were caused by 

combined-sewer overflows, urban runoff, and 

the resuspension of organic material deposited 

on the streambed.

Summary and Conculalona 89
Concentrations of nutrients in storm runoff 

increased downstream and, for all nutrients except 

nitrate plus nitrite, were higher than those in base 

flow. Concentrations of ammonia at Central 

Avenue were much higher in storm runoff than 

in base flow, whereas concentrations of ammonia 

in storm runoff at 16th Street and Emerson Avenue 

were only slightly higher than those in base flow. 

The minimum concentration of ammonia in storm 

runoff at Central Avenue was twice as high as 

that in base flow, and the maximum concentration 

in runoff was four times as high as that in base 

flow. The increase in ammonia at Central Avenue 

probably was caused by combined-sewer overflows 

and, most likely to a lesser degree, by urban runoff.

As with all base-flow samples, concentrations of mercury, selenium, and cadmium in all 

storm-runoff samples (except for one detection 

of selenium at the detection limit at 16th Street) 

were less than the detection limits. Detectable 

concentrations of chromium and nickel in runoff at 

16th Street were associated with the discharge of 

filter backwash to Fall Creek. Urban runoff and 

combined-sewer overflows seemed to have little 

effect on concentrations of chromium and nickel in 

Fall Creek. Concentrations of copper, lead, and

zinc in storm runoff were much higher than those 

in base flow. Copper and zinc were detected at 

Emerson Avenue only during storms 1 and 2 but 

were detected at Central Avenue and 16th Street 

during all six storms. Higher concentrations and 

more frequent detections at Central Avenue and 

16th Street indicate that runoff from the highly 

urbanized area downstream from Emerson Avenue 

is a source of copper, lead, and zinc in Fall Creek. 

Some of the increased concentrations of lead, 

zinc, and probably copper at 16th Street can be 

attributed to the discharge and resuspension of 

filter backwash.

Concentrations of fecal coliform bacteria 

in storm runoff were much greater than those in 

base flow. Concentrations of fecal coliform 

bacteria in storm runoff ranged from <100 to 

48,000 col/100 mL at Emerson Avenue, from 1,200 

to 470,000 col/100 mL at Central Avenue, and 

from <100 to 152,000 coVlOO mL at 16th Street. 

Concentrations of fecal coliform bacteria in storm 

runoff exceeded 10,000 col/100 mL in only one 

sample collected at Emerson Avenue but frequently 

exceeded this concentration at Central Avenue and 

16th Street. Combined-sewer overflows and urban 

runoff dramatically increased concentrations of 

fecal coliform bacteria in Fall Creek.

90 Effects of Combined-Sewer Overflows snd Urbsn Runoff, Fsll Creek, Indisnspolis, Indians
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92 Effects of Combined-Sewer Overflows snd Urbsn Runoff, Fall Creek, Indisnspolis, Indisns

U.S. GOVERNMENT PRINTING OFFICE: 1995 647-538