U.S.Department of the Interior

U.S.Geological Survey

Water Quality in the M

and Selected Tributar

Youngstown,Ohio

Water-Resources Investigations Report 02 412

In cooperation with the

City of Youngstown,Ohio
Cover photo: Mill Creek at Lake Glacier outlet, Youngstown, Ohio.
U.S. Department of the Interior

U.S. Geological Survey

Water-Resources Investigations Report 02–4122

In cooperation with the

City of Youngstown, Ohio 

By Donald M. Stoeckel and S. Alex Covert

Water Quality of the Mahoning River and 

Selected Tributaries in Youngstown, Ohio
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

For additional information write to:

District Chief

U.S. Geological Survey

6480 Doubletree Avenue

Columbus, OH 43229-1111

Copies of this report can be purchased from:

U.S. Geological Survey

Branch of Information Services

Box 25286

Denver, CO 80225-0286

Columbus, Ohio

2002

Any use of trade, product, or firm names is for 

descriptive purposes only and does not constitute

endorsement by the U.S. Government.
Contents III

CONTENTS

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

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

Purpose and scope ....................................................................................................................................................... 2

Watershed description .................................................................................................................................................. 3

Previous studies ........................................................................................................................................................... 3

Acknowledgments ....................................................................................................................................................... 3

Hydrological and water-quality sampling networks ............................................................................................................. 3

Streamflow and water-quality sampling sites and schedule ....................................................................................... 5

Aquatic biological sampling reaches and schedule ..................................................................................................... 5

Field and laboratory methods ............................................................................................................................................... 8

Streamflow measurement ............................................................................................................................................ 9

Sample collection and processing ............................................................................................................................... 9

Onsite physicochemical measurements ...................................................................................................................... 10

Chemical constituents rationale, methods, and analytical laboratories ...................................................................... 10

Microbiological rationale, methods, and analytical laboratories ................................................................................ 11

Quality control for water-quality measurements ........................................................................................................ 11

Biotic index rationale, methods, and analytical laboratories ...................................................................................... 12

Estimation of Escherichia coli and inorganic nitrogen loads ..................................................................................... 13

Hydrology of the Mahoning River and selected tributaries ................................................................................................. 14

Streamflow .................................................................................................................................................................. 14

Wet-weather events ..................................................................................................................................................... 14

Water quality of the Mahoning River and selected tributaries ............................................................................................. 14

Primary-contact recreational use ................................................................................................................................. 18

Aquatic-life use ........................................................................................................................................................... 20

Warmwater-habitat use................................................................................................................................................. 28

Effects of sewer-overflow discharges on receiving-water qualiy ................................................................................ 30

Summary and conclusions .................................................................................................................................................... 40

Areas of nonattainment ............................................................................................................................................... 40

Timing of nonattainment ............................................................................................................................................. 40

Duration of nonattainment .......................................................................................................................................... 40

Effect of sewer-overflow discharges............................................................................................................................ 41

References ............................................................................................................................................................................ 41

Appendix A. Additional water-quality data from sewer-overflow discharges, calendar year January 2000 

to December 2000, in Youngstown, Ohio .............................................................................................................. 44

ILLUSTRATIONS

1. Surface-water quality and hydrology sampling network in the area of Youngstown, Ohio ...................................... 4

2. Biological-index sampling in the area of Youngstown, Ohio .................................................................................... 8

3. Streamflow and sample collection for two sites in Youngstown, Ohio, during summer 1999 and 2000 .................. 15

4. Streamflow and sample collection for three sites on the Mahoning River, Ohio, during three wet-weather 

flow events sampled, August-October 2000.............................................................................................................. 16

5. Streamflow and sample collection for three sites on Mill Creek, Ohio, during three wet-weather 

flow events sampled, August-October 2000.............................................................................................................. 17

6. Summary of Escherichia coli concentration data by site type, relative location, and flow category for 

summer 1999 and 2000 in the Mahoning River, Ohio, and selected tributaries and sources.................................... 20
IV Contents

ILLUSTRATIONS — Continued

7. Geometric mean Escherichia coli concentrations in the Mahoning River and Mill Creek, Ohio, 

parts of the water-quality sampling network during dry-weather flow (1999) and wet-weather

flow (1999 and 2000)................................................................................................................................................ 22

8. Summary of pH, dissolved oxygen concentration, and temperature data by site type, relative location, 

and flow category in the area of Youngstown, Ohio................................................................................................. 24

9. Summary of ammonium, nitrate plus nitrite, and total phosphorus concentrations by site type, 

relative location, and flow category in the area of Youngstown, Ohio..................................................................... 25

10. Index of biotic integrity, modified index of well-being, and invertebrate community index (average 

of two observations) from the biological-index monitoring network during summer 1999..................................... 29

11. Nitrogen-form concentrations in the Mahoning River and Mill Creek, Ohio, parts of the water-quality 

monitoring network during dry-weather flow (1999) and wet-weather flow (1999 and 2000)................................ 32

12. Total phosphorus concentrations in the Mahoning River and Mill Creek, Ohio, part of the water-quality 

monitoring network during dry-weather flow (1999) and wet-weather flow (1999 and 2000)................................ 33

13. Data and regression lines used to estimate Escherichia coli and inorganic nitrogen concentrations

at two sites on the Mahoning River, Ohio, during three wet-weather flow events in 2000...................................... 34

14. Streamflow and sample collection times for three sites on the Mahoning River, plotted with modeled 

cumulative sewer-overflow discharge in Youngstown, Ohio, over the first 24-hour interval of three 

wet-weather flow events ........................................................................................................................................... 38

15. Concentrations of alternate indicators of fecal pollution by site type, relative location, and flow category 

for summer 1999 and 2000 in Mahoning River and selected tributaries and sources, Ohio .................................... 39

TABLES

1. Name and location of each site in the streamflow and water-quality monitoring network, 

arranged by site category, in and around Youngstown, Ohio.................................................................................... 6

2. Sampling schedule during interval sampling (1999) and wet-weather flow (event-oriented) 

sampling (2000), in and around Youngstown, Ohio ................................................................................................. 7

3. Name and location of each reach in the biological monitoring network, arranged by location 

on the main stem or tributary stream, in and around Youngstown, Ohio ................................................................. 9

4. Twelve metrics composing the modified index of biotic integrity used by the 

Ohio Environmental Protection Agency for wading-water and headwater sites ..................................................... 13

5. Five-sample geometric mean Escherichia coli concentrations and percentage of samples exceeding 

the standard of 298 colony-forming units per 100 milliliters during three 30-day periods in

May, July, and September 1999 ............................................................................................................................... 19

 6. Geometric-mean Escherichia coli concentrations during dry-weather flow (1999) and at nominal 

times after wet-weather flow peaks (2000) .............................................................................................................. 21

7. State of Ohio regulations for the protection of aquatic life in designated warmwater-habitat 

streams in the Erie-Ontario Lake Plain ecoregion ................................................................................................... 23

8. Observations for which surface-water quality did not meet one or more Ohio physical or chemical 

water-quality standards for the protection of aquatic life, in or around Youngstown, Ohio..................................... 26

9. Fish and macroinvertebrate warmwater-habitat biocriteria used by the Ohio Environmental 

Protection Agency in the Erie-Ontario Lake Plain ecoregion .................................................................................. 30

10. Linear regression analysis results for the relation between log-transformed flow and log-transformed 

concentration of Escherichia coli and inorganic nitrogen at two sites on the Mahoning River .............................. 35

11. Sewer-overflow discharge characteristics observed in and around Youngstown, Ohio,and published 

characteristic values for raw sewage and stormwater runoff ................................................................................... 36

12. Twenty-four-hour discharge volumes, loads of Escherichia coli, discharge-weighted average 

concentrations of E. coli, and loads of inorganic nitrogen (nitrite plus nitrate and ammonium) at two 

surface-water sites and all modeled sewer-overflow discharges in Youngstown during three events in 2000 ....... 37
Contents V

CONVERSION FACTORS AND VERTICAL DATUM

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8 × °C) + 32

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) or micrograms per liter (μg/L). Pore 

sizes of filters and screens are given in micrometers (μm)

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

kilometer (km) 0.6214 mile (mi)

Area

square kilometer (km2) 0.3861 square mile (mi2)

Volume

liter (L) 0.2642 gallon (gal)

cubic meter (m3

) 264.2 gallon (gal)

cubic meter (m3) 0.0002642 million gallons (Mgal)

Flow rate

cubic meter per second (m3/s) 35.31 cubic foot per second (ft3/s)

Mass

kilogram (kg) 2.205 pound avoirdupois

megagram (Mg) 1.102 ton, short (2,000 lb)

megagram per day (Mg/d) 1.102 ton per day

Abstract 1

Water Quality of the Mahoning River and Selected Tributaries 

in Youngstown, Ohio

by Donald M. Stoeckel and S. Alex Covert

Abstract

The lower reaches of the Mahoning River in 

Youngstown, Ohio, have been characterized by 

the Ohio Environmental Protection Agency 

(OEPA) as historically having poor water quality. Most wastewater-treatment plants (WWTPs) 

in the watershed did not provide secondary sewage treatment until the late 1980s. By the late 

1990s, the Mahoning River still received seweroverflow discharges from 101 locations within the 

city of Youngstown, Ohio. The Mahoning River 

in Youngstown and Mill Creek, a principal tributary to the Mahoning River in Youngstown, have 

not met biotic index criteria since the earliest published assessment by OEPA in 1980. Youngstown 

and the OEPA are working together toward the 

goal of meeting water-quality standards in the 

Mahoning River. The U.S. Geological Survey 

collected information to help both parties assess 

water quality in the area of Youngstown and to 

estimate bacteria and inorganic nitrogen contributions from sewer-overflow discharges to the 

Mahoning River.

Two monitoring networks were established 

in the lower Mahoning River: the first to evaluate 

hydrology and microbiological and chemical 

water quality and the second to assess indices of 

fish and aquatic-macroinvertebrate-community 

health. Water samples and water-quality data 

were collected from May through October 1999 

and 2000 to evaluate where, when, and for how 

long water quality was affected by sewer-overflow discharges. Water samples were collected 

during dry- and wet-weather flow, and biotic indices were assessed during the first year (1999). 

The second year of sample collection (2000) was 

directed toward evaluating changes in water quality during wet-weather flow, and specifically 

toward assessing the effect of sewer-overflow discharges on water quality in the monitoring network.

Water-quality standards for Escherichia coli

(E. coli) concentration and draft criteria for nitrate 

plus nitrite and total phosphorus were the regulations most commonly exceeded in the Mahoning 

River and Mill Creek sampling networks. E. coli

concentrations increased during wet-weather flow 

and remained higher than dry-weather concentrations for 48 hours after peak flow. E. coli concentration criteria were more commonly exceeded 

during wet-weather flow than during dry-weather 

flow. Exceedances of nutrient-concentration criteria were not substantially more common during 

wet-weather flow. 

The fish and aquatic macroinvertebrate network included Mill Creek and its tributaries but 

did not include the main stem of the Mahoning 

River. Persistent exceedances of chemical waterquality standards in Mill Creek and the presence 

of nutrient concentrations in excess of draft criteria may have contributed to biotic index scores 
2 Water Quality of the Mahoning River and Selected Tributaries in Youngstown, Ohio

that on only one occasion met State criteria 

throughout the fish and aquatic macroinvertebrate 

sampling network.

Monitored tributary streams did not contribute concentrations of E. coli, nitrate plus nitrite, or 

total phosphorus to the Mahoning River and Mill 

Creek that were higher than main-stem concentrations, but monitored WWTP and sewer-overflow 

discharges did contribute. Twenty-four hour load 

estimates of sewer-overflow discharge contributions during wet-weather flow indicated that 

sewer-overflow discharges contributed large loads 

of bacteria and inorganic nitrogen to the Mahoning River relative to the instream load. The seweroverflow loads appeared to move as a slug of 

highly enriched water that passed through Youngstown on the rising limb of the storm hydrograph. 

The median estimated sewer-overflow load contribution of bacteria was greater than the estimated instream load by a factor of five or more; 

however, the median estimated sewer-overflow 

load of inorganic nitrogen was less than half of 

the estimated instream load.

Sewer-overflow discharges contributed 

loads of E. coli and nutrients to the Mahoning 

River and Mill Creek at a point where the streams 

already did not meet State water-quality regulations. Improvement of water quality of the 

Mahoning River, Mill Creek, and tributaries at 

Youngstown would be facilitated by reducing 

loads from sewer-overflow discharges within 

Youngstown, by identifying and reducing other 

sources of E. coli and nutrients within Youngstown, and by reducing discharges of E. coli, 

nitrate plus nitrite, and total phosphorus to the 

Mahoning River and Mill Creek upstream from 

Youngstown.

Introduction

The Ohio Environmental Protection Agency (OEPA) characterized the lower reaches of the Mahoning River as “historically. . . one of the most polluted of any stream or river 

in Ohio” (Ohio Environmental Protection Agency, 1996). 

Sewer-overflow discharge sites and wastewater-treatment 

plants (WWTPs) line the Mahoning River and its tributaries 

and contribute partially treated or untreated wastewater discharges to streamflow during wet weather. The city of 

Youngstown, Ohio, is on the Mahoning River not far from 

the Pennsylvania border. Youngstown is served by a combined sewer system in which varying proportions of the 

flow are stormwater and sanitary sewage. There are 101 

known sewer-overflow discharge sites in Youngstown. 

Sewer-overflow and WWTP discharges have been cited as 

contributors to impaired water quality in the Mahoning 

River and its tributaries (Ohio Environmental Protection 

Agency, 1996).

In 1999, the U.S. Geological Survey (USGS), in 

cooperation with the city of Youngstown and in collaboration with ms consultants, inc., began a study to investigate 

the effects of sewer-overflow discharges within Youngstown 

on water quality of the Mahoning River. The intent of this 

investigation was to provide data useful to multiple parties 

involved in assessment of water quality in the Mahoning 

River. This investigation represents an attempt to directly 

relate municipal sewer-overflow discharges to changes in 

receiving-water quality and to quantify those changes.

The Clean Water Act of 1972, reauthorized and 

amended in 1982, requires states to categorize public waterways into designated aquatic-life uses and non-aquatic-life 

uses (Ohio Environmental Protection Agency, 2002). Nearly 

all Ohio waterways are designated for aquatic-life use as 

warmwater habitat. Other water-use designations include 

recreation and water supplies. Waterways are characterized 

as “attaining” or “not attaining” their designated uses by 

comparison with water-quality regulations. OEPA has 

issued water-quality regulations based on ecoregions to 

reflect the geographic diversity in the State.

This investigation was conducted using sites on the 

Mahoning River and selected tributaries in and around 

Youngstown. Water quality of the waterways studied was 

assessed based upon OEPA standards and criteria for primary recreation, non-aquatic-life use and for aquatic-life 

use as warmwater habitat within the Erie-Ontario Lake 

Plain (EOLP) ecoregion (Ohio Environmental Protection 

Agency, 1987). Mill Creek, tributary to the Mahoning River 

in Youngstown, was chosen for in-depth evaluation because 

it is further designated as a State resource water. Ohio has 

more stringent management policies for its State resource 

waters to help prevent water-quality degradation. 

Purpose and scope

This report is an interpretive summary of data collected during a 2-year investigation of a reach on the lower Mahoning 

River, selected tributaries, and selected municipal discharges. The purpose of this report is to

1. describe a water-quality and streamflow monitoring 

network developed for the Mahoning River, Mill 

Creek, and selected tributaries, and an aquatic-
Hydrological and water-quality sampling networks 3

biological index monitoring network developed for 

Mill Creek and selected tributaries;

2. compare microbiological and chemical quality of the 

Mahoning River and its tributaries during periods of 

dry- and wet-weather flow to determine where, when, 

and for how long sewer-overflow discharges affected 

surface-water quality;

3. provide basic information about sewer-overflow discharges for future projects in which simulation calculations may be developed; and

4. compute 24-hour bacteria and inorganic nitrogen loads 

in an effort to quantify effects of these components of 

sewer-overflow discharges on water quality in the 

Mahoning River.

The broad scope of the investigation was to improve 

understanding of the effects of combined-sewer overflows 

on use-attainment for primary-contact recreation and protection of aquatic life in a heavily urbanized river reach.

Watershed description

The part of the Mahoning River described in this report is in 

Mahoning County, in northeastern Ohio bordering Pennsylvania (fig. 1). The Mahoning River Watershed drains 2,934 

km2

 (1,133 mi2) into a channel that is 166 km (103 mi) long 

(Ohio Environmental Protection Agency, 1996). Downstream from the study area, the Mahoning River joins with 

the Shenango River to form the Beaver River in western 

Pennsylvania. The Beaver River is, in turn, tributary to the 

Ohio River. The Mahoning River Valley is in the glaciated 

part of the Allegheny Plateau (Lessig and others, 1971). In 

1988, 87 km (54 mi) of the Mahoning River flowed through 

urban areas and 31 km (19 mi) of river were impounded 

(Ohio Environmental Protection Agency, 1996). 

Mill Creek is tributary to the Mahoning River at 

Youngstown. The lower part of Mill Creek flows through 

Mill Creek Park, a 10-km2

 (4-mi2) municipal park created 

in 1891 (Mill Creek Metropolitan Park District, 2001). The 

area surrounding Mill Creek Park is densely populated. 

Mill Creek upstream from Mill Creek Park is partially 

channelized and is surrounded by agriculture and aquaculture facilities. Three dams segment Mill Creek within Mill 

Creek Park and form (from upstream to downstream) Newport Lake, Lake Cohasset, and Lake Glacier. These reservoirs have considerable water-holding capacity and would 

be expected to affect hydrology and water quality of Mill 

Creek. Retention of stream water in reservoirs promotes 

settling of solids, including bacteria and particulate forms of 

nutrients, and allows time for nutrient conversions and bacterial decay. Water leaving reservoirs is expected to have 

lower concentrations of suspended solids, particulate nutrients, and indicator bacteria than water flowing through a 

hypothetical unmodified stream. Conversion of organic 

nutrients to inorganic forms and changes in the oxidation 

state of inorganic nutrients also are expected in the reservoirs.

Youngstown, Ohio, is a small city with a history of 

heavy industry. In 2000, the population of Youngstown was 

82,026 people in an 88-km2

 area (34 mi2; 2000 census 

data). Youngstown was the site of the first steel company in 

the Mahoning Valley, and steel continues to be important to 

local industry. 

Previous studies

Water quality in the lower part of the Mahoning River has 

been a persistent problem. OEPA did biological and waterquality surveys of the lower part of the Mahoning River in 

1980, 1983, 1986, and 1994 (Ohio Environmental Protection Agency, 1996). In the early 1980s, the steel industry 

thrived in the Mahoning River Valley. The OEPA surveys 

indicated that part of the steel industry legacy is sediment 

contamination with toxic metals, phenols, and polycyclic 

aromatic hydrocarbons. The OEPA reports also indicated 

that WWTPs in and around Youngstown used only primary 

treatment before the 1980s. Incomplete treatment of sewage 

contributed to low dissolved oxygen concentrations (often 

less than 4 mg/L) and high ammonium concentrations (up to 

about 3 mg/L), which were reported as important chemical 

water-quality concerns before 1994 (Ohio Environmental 

Protection Agency, 1996). Most local WWTPs began using 

secondary treatment in the late 1980s, and OEPA noted 

improvements in achievement rates of water-quality standards for dissolved oxygen and ammonium concentrations. 

Despite improvements in wastewater treatment, however, 

microbiological water quality in the Mahoning River 

remained above primary-contact recreation standards 

throughout 1973–93 downstream from Youngstown at Lowellville (Ohio Environmental Protection Agency, 1996).

Acknowledgments 

Appreciation is extended to Joe Catullo of ms consultants, 

inc., Tom Mirante of the city of Youngstown, and Allen Diebel of the Mahoning County Sanitary Engineering Department, for coordination on all facets of the investigation. The 

Youngstown wastewater laboratory and Mahoning County 

Boardman wastewater laboratory kindly allowed use of their 

facilities during this investigation. 

Hydrological and water-quality sampling networks

Two sampling networks were developed in the Mahoning 

River Watershed in and around Youngstown. One sampling 

network was developed to monitor streamflow and assess 
4 Water Quality of the Mahoning River and Selected Tributaries in Youngstown, Ohio

5

10

6

11

4

Boardman

WWTP

Campbell

WWTP

Struthers

WWTP

Lowellville

Figure 1. Surface-water quality and hydrology sampling network in the area of Youngstown, Ohio.

12 3

1

2

9

13

F

D

A

E

B

7

H

8

C

G

01234

012345 KILOMETERS

5 MILES

5

F

2

A

80o45' 80o

37'37"

41o

07'30"

41o

MAHONING COUNTY

MAHONING CO

COLUMBIANA CO

PENNSYLVANIA

OHIO

TRUMBULL COUNTY

EXPLANATION

Mill Creek Park boundary

Mahoning River Watershed

Mill Creek Watershed

Youngstown city limits

Watershed boundary

Water-quality sampling site with instantaneous

flow measurement and identifier

Sewer-overflow location and identifier

Water-quality sampling site with continuous

flow measurement and identifier

Sampled wastewater-treatment plant

(WWTP) effluent and identifier

Unsampled wastewater-treatment plant (WWTP)

Study Area

OHIO MAHONING

COUNTY

Mahoning

River

Crab

Bears

Creek

Den

Run

Cranbe rry Run

Indian

Mill

Creek

Newport

Lake

Lake

Glacier

Lake

Cohasset

Ax Factory Run

Run
Hydrological and water-quality sampling networks 5

microbiological and chemical water quality in the Mahoning River Watershed, including the Mill Creek Subwatershed. An overlapping, second sampling network was used 

to assess aquatic biological indices for Mill Creek and one 

of its tributary streams, Indian Run.

Streamflow and water-quality sampling sites and 

schedule

The first network (fig. 1 and table 1) included seven continuous streamflow-measurement stations: three on the 

Mahoning River, three on Mill Creek, and one on Crab 

Creek. Six other water-quality monitoring sites, at which 

instantaneous streamflow was measured, were located on 

the Mahoning River, on Mill Creek, and on tributaries to 

Mill Creek. The first network also included eight municipal-source discharge sites: one at the Youngstown WWTP 

outflow and seven at sewer-overflow sites on the Mahoning 

River (three), Crab Creek (one), and Mill Creek (three). 

The sewers carry combined storm runoff and domestic sewage in varying proportions and would be commonly 

described as combined-sewer overflows unless flow were 

dominated by domestic waste. It was not within the scope 

of this investigation to define which sewers should be characterized as combined sewers and which should be characterized as sanitary sewers. The generic term “seweroverflow discharge” is used throughout this report.

Water-quality monitoring sites on the Mahoning 

River (fig. 1) were chosen to assess the quality of surface 

water entering, passing through, and leaving Youngstown 

and at Lowellville, Ohio, downstream from Youngstown. 

Water entering the Mahoning River from its two largest tributary streams in Youngstown (Mill Creek and Crab Creek) 

and the Youngstown WWTP was sampled to evaluate the 

effects of these inputs on water quality of the Mahoning 

River. Mill Creek was chosen for detailed characterization 

because it is used heavily for recreation within Mill Creek 

Park and is designated as a State of Ohio resource water 

within the park. Sites on Mill Creek were selected to measure water quality entering Youngstown, water quality 

downstream from the Boardman WWTP, water quality midway through Mill Creek Park, and water quality entering the 

Mahoning River at the mouth of Mill Creek. Additional 

water-quality monitoring sites were chosen on tributaries to 

Mill Creek (Indian Run, Cranberry Run, Ax Factory Run, 

and Bears Den Run) to assess water quality in streams 

receiving different volumes of sewer-overflow discharge 

(table 1). 

Different goals were addressed during the 2 years of 

sampling (1999 and 2000) in the water-quality and hydrology network. The first year of sampling was interval-oriented, intended to assess use-attainment in the sampling 

networks by comparing surface-water-quality data to State 

regulations. The standard for Escherichia coli (E. coli) 

requires at least five samples within a 30-day period, so the 

first-year schedule called for five water samples collected 

over each of three 30-day intervals, for a total of 15 samples 

from each of the 13 surface-water sites and the Youngstown 

WWTP outflow. The second year of sampling was eventoriented, intended to assess the effects of sewer-overflow 

discharges on surface-water quality. The second-year 

schedule called for sample collection after three runoff-producing rains. Water-quality samples and data were collected shortly after the onset of rainfall (nominally 6 hours 

past peak flow) and at nominally 24 and 48 hours past peak 

flow during each of three wet-weather flow events in 2000, 

for a total of nine samples at each site. This strategy was 

conceived as a means of measuring where, when, and for 

how long sewer-overflow discharges affected surface-water 

quality.

Samples collected during 1999 were categorized as 

wet-weather or dry-weather flow samples on the basis of 

local rainfall data. Samples from sites that had received at 

least 0.25 cm (0.1 in.) of rain in the 3 days before sampling 

were categorized as wet-weather flow. All other samples 

were categorized as dry-weather flow. USGS personnel 

sampled the first or second of each set of five samples, and 

personnel from ms consultants sampled the other four. 

Water-quality measurements were made instream for pH, 

dissolved oxygen concentration, specific conductance, and 

temperature on every occasion. E. coli concentration also 

was measured from samples collected on every occasion. 

Other water characteristics were evaluated from only the 

USGS-collected samples (table 2).

During the three wet-weather events in 2000, USGS 

personnel collected surface-water data and samples, and ms 

consultants personnel collected sewer-overflow discharge 

data and samples. Instream measurements were made for 

pH, dissolved oxygen concentration, temperature, and specific conductance, and E. coli concentration was measured 

from every surface-water sample collected. Other measurements were taken from only the 6-hour sample or from both 

the 6-hour and the 24-hour sample. (See table 2 for specific 

analysis schedule.) Samples from WWTP effluent and 

sewer-overflow discharges were analyzed as outlined in 

table 2.

Aquatic biological sampling reaches and schedule

The second network included seven 150-m (164-yd) reaches 

in the Mill Creek Subwatershed: six on Mill Creek and one 

on Indian Run (fig. 2 and table 3). All reaches in the biological-index network were at or near sites in the water-quality 

monitoring network. Aquatic biological-monitoring 

reaches were chosen to assess attainment of biocriteria for 

fish and aquatic macroinvertebrates in Mill Creek upstream 

from Youngstown, below the Mahoning County Boardman 

WWTP, above and below two tributaries that carry seweroverflow discharges, and at the mouth of Mill Creek. 
6 Water Quality of the Mahoning River and Selected Tributaries in Youngstown, Ohio

Table 1. Name and location of each site in the streamflow and water-quality monitoring network, arranged by site 

category, in and around Youngstown, Ohio

[mi2, square miles; 106 gal, million gallons; NA, not applicable; WWTP, wastewater-treatment plant]

Site

identifier Site name

Location 

relative to 

reservoirs

Location 

relative to 

overflows

Drainage area

(mi2)

Sewer 

overflow

(106 gal/yr)

Receiving 

water

River 

mile

Main-stem sites

1 Mahoning River at Youngstown NA Downstream 900 2.6 NA 22.5

2 Mahoning River below West Avenue NA Downstream 980 280 NA 21.2

3 Mahoning River at Center Street NA Downstream 980 470 NA 18.0

4 Mahoning River at Lowellville NA Downstream 1,100 1,400 NA 12.0

5 Mill Creek at Western Reserve Road Upstream Upstream 28 0 NA 11.6

6 Mill Creek at Shields Road at Boardman Upstream Upstream 54 0 NA 5.6

7 Mill Creek at Youngstown Downstream Downstream 66 67 NA 2.6

8 Mill Creek at Price Road at Youngstown Downstream Downstream 78 99 NA 0.1

Tributary-stream sites

8 Mill Creek at Price Road at Youngstown Downstream Downstream 78 99 Mahoning 21.6

9 Crab Creek at Youngstown NA Downstream 20 180 Mahoning 19.5

10 Indian Run near Canfield NA Upstream 15 0 Mill Creek 7.7

11 Cranberry Run at Boardman NA Downstream 3.7 38 Mill Creek 5.4

12 Ax Factory Run at Youngstown NA Upstream 3.2 0 Mill Creek 2.1

13 Bears Den Run at Youngstown NA Downstream 3.9 .23 Mill Creek 1.3

Municipal sources

A Youngstown WWTP NA NA NA NA Mahoning 19.4

B Overflow at Waverly Avenue (RC24) NA NA NA NA Mahoning 22.1

C Overflow Salt Springs, Price Road 

(OF19)

NA NA NA NA Mahoning 21.6

D Overflow east of Poland Avenue (RC111) NA NA NA NA Mahoning 17.5

E Overflow McGuffey, Willow Street 

(RC65)

NA NA NA NA Crab Creek 1.1

F Overflow Park Drive near Kiawatha 

(RC8)

NA NA NA NA Mill Creek 3.6

G Overflow at Orchard Meadows (OFMH) NA NA NA NA Mill Creek 1.3

H Overflow at Price and Halls Heights 

(RC18)

NA NA NA NA Mill Creek .2
Hydrological and water-quality sampling networks 7

Table 2. Sampling schedule during interval sampling (1999) and wet-weather flow (event-oriented) sampling 

(2000), in and around Youngstown, Ohio

[WWTP, wastewater-treatment plant; X, sample collected each visit; M, sample collected during one visit per 30-day interval; --, constituent not sampled 

for; DO, dissolved oxygen concentration; cBOD5, 5-day carbonaceous biochemical oxygen demand; COD, chemical oxygen demand; NO3 + NO2, nitrate 

plus nitrite; NH4, ammonium; Ca, calcium; Mg, magnesium; Fe, iron; Mn, manganese; K, potassium; Na, sodium; Cl, chlorine; F, fluorine; SO4, sulfate; 

SiO2, silica]

Constituent

Interval 

(1999) Wet-weather flow (2000) 

All sites Mahoning River and 

tributaries Mill Creek and tributaries Municipal sources

 WWTP Overflows

Nominal hours past peak flow

6 24 48 6 24 48 6 24 48 0-6

Fecalcontamination 

indicators:

E. coli X X X X X X X X X X X

C. perfringens M -- -- -- X -- -- X -- -- X

Coliphage M -- -- -- X -- -- X -- -- X

Caffeine M -- -- -- X -- -- -- -- -- --

Physicochemical:

Temperature, pH, 

DO, specific 

conductance

X X X X X X X -- -- -- --

Suspended solids M X X -- X X -- X X -- X

Alkalinity M X -- -- X -- -- X -- -- --

Nutrients:

cBOD5 and COD M X X -- X X -- X X -- X

Nitrogen forms

(total, dissolved, 

Kjeldahl, NH4, 

and NO3+NO2)

M X X -- X X -- X X -- X

Phosphorus forms

(total, dissolved, 

and 

orthophosphate)

M X X -- X X -- X X -- X

Anions and 

cations:

Ca++, Mg++, 

Fe++, Mn++, K+, 

Na+, Cl-

, F-, 

SO4

--, SiO2

X X -- -- X -- -- X -- -- X
8 Water Quality of the Mahoning River and Selected Tributaries in Youngstown, Ohio

Figure 2. Biological-index sampling network in the area of Youngstown, Ohio.

80o45'

80o

41'15"

41o

03'45"

40o

56'15"

20

Boardman

WWTP

19

17

MAHONING CO

COLUMBIANA CO

Bears Den

Run

Cranbe rry Run

Indian

Mill

Creek

Newport

Lake

Lake

Glacier

Lake

Cohasset

Ax Factory Run

Run

18

16

15

14

EXPLANATION

Mill Creek Park boundary

Mill Creek watershed

Youngstown city limits

Watershed boundary

Water-quality sampling site with

instantaneous flow measurement

and indentifier

Water-quality sampling site with

continuous flow measurement

and identifier

Unsampled wastewater-treatment

plant (WWTP)

01234

0 1 2 3 4 5 KILOMETERS

5 MILES

Study Area

OHIO MAHONING

COUNTY

20

17

A reach on Indian Run, which is not affected by sewer-overflow discharges (table 3), was included for comparison with 

reaches on Mill Creek.

Fish-community samples were collected and habitatquality measurements made by USGS and ms consultants 

personnel at the seven reaches of the biological monitoring 

network (fig. 2) in July through September 1999. Aquaticmacroinvertebrate community samples were collected in 

September 1999 (quantitative) and November 1999 (qualitative) by personnel from the Ohio Biological Survey. The 

qualitative macroinvertebrate sample was scheduled for 

September, but collection was postponed because of inclement weather.

Field and laboratory methods

Standard USGS hydrologic and analytical methods were 

used throughout this investigation. All analyses were done 

by USGS-trained personnel, USGS-approved laboratories, 

and contractors or, if no appropriate USGS-approved facility was available, with OEPA-certified contractors.
Field and laboratory methods 9

Table 3. Name and location of each reach in the biological monitoring network, 

arranged by location on the main stem or tributary stream, in and around 

Youngstown, Ohio

[Mgal/yr, million gallons per year]

Reach

identifier Reach name

Location 

relative to 

overflows

Sewer overflow

(Mgal/yr) River mile

Mill Creek reaches

14 Near Calla Road Upstream 0 15

15 Upstream from 

Cranberry Run

Upstream 0 5.6

16 Downstream from 

Cranberry Run

Downstream 38 5.5

17 At Youngstown Downstream 67 2.6

18 Upstream from 

Bears Den Run

Downstream 78 1.4

19 Downstream from 

Bears Den Run

Downstream 82 1.3

Tributary reach

20 Indian Run near 

Canfield

Upstream 0 7.7

Streamflow measurement

Two types of streamflow measurements were made in the 

monitoring network. The seven continuous streamflowmeasurement stations measured stage at 15-minute intervals 

and recorded data to dataloggers. Stage was recorded at all 

other sites when water samples were collected by reading 

the stage height from staff gages or wire-weight gages. 

Instantaneous-streamflow measurements were made by the 

method of Rantz and others (1982a) at each of the Mill 

Creek and tributary sites. Streamflow measurements made 

on at least five occasions and representing a wide range of 

flows were used to develop stage-discharge rating curves by 

the method of Rantz and others (1982b). Rating curves 

already were available for the Mahoning River sites except 

for site 3, at Center Street, for which no rating curve was 

developed. 

Flow at Center Street was estimated as the sum of the 

flows calculated at Mahoning River below West Avenue 

(site 2), Crab Creek at Youngstown (site 9), and estimates of 

both inputs from Crab Creek between site 9 and the mouth 

and flow from the Youngstown WWTP (source A), assuming no other gains or losses across the reach. Rating curves 

for the other three Mahoning River sites were validated by 

at least three instantaneous-flow measurements over the 

course of the investigation.

Sample collection and processing 

Surface-water samples, municipal-source-water samples, 

and aquatic-biological-community samples were collected 

by the application of the methods described below.

Surface-water samples. All surface-water samples 

were collected by the depth-width-integration method using 

isokinetic samplers (Webb and others, 1999). Samples collected into multiple containers were composited with a 

churn splitter (Wilde and Radtke, 1999). Whole-water subsamples for measurement of total nonfilterable residue (total 

suspended solids), 5-day carbonaceous biochemical oxygen 

demand (cBOD5), chemical oxygen demand (COD), nitrogen, and phosphorus were removed from the churn splitter 

first. Water was filtered through a 0.45-μm capsule filter, 

and subsamples were collected for measurement of caffeine, 

alkalinity, dissolved solids, dissolved nitrogen, dissolved 

phosphorus, and cation and anion concentrations. All subsamples were chilled, acidified, or both chilled and acidified 

according to requirements identified in following sections 

for each analysis type. Samples for microbiological analy-
10 Water Quality of the Mahoning River and Selected Tributaries in Youngstown, Ohio

ses were collected separately in autoclaved 1-L bottles with 

isokinetic samplers. 

Samples of effluents from municipal sources. 

Sewer-overflow-discharge samples were collected with 

automatic samplers installed into sewerlines for this project. 

Samplers were activated upon diversion of flow from the 

main sewer to the overflow discharge outlet. As many as 24 

discrete samples were collected into a composite sample 

bottle at 15- to 30-minute intervals during discharge (Joe 

Catullo, ms consultants, written commun., July 2001). 

Samples were retrieved as soon as was practical after collection, chilled, and held on ice for analysis. Samples from the 

Youngstown WWTP effluent were collected as grab samples from the discharge flume. Youngstown WWTP effluent is dechlorinated before discharge, so WWTP effluent 

samples were not dechlorinated before microbiological 

analysis.

Aquatic-biological-community samples. Fish were 

collected by USGS and ms consultants personnel by electrofishing with pulsed-DC current (Meador and others, 1993; 

Ohio Environmental Protection Agency, 1989) from each of 

the seven reaches (fig. 2) on two separate dates. One electrofishing pass was done over each reach on each date. Fish 

were identified, weighed, and checked by field personnel for 

external anomalies such as parasites, lesions, and skeletal 

deformities. Most fish were returned to the stream after 

processing. Voucher specimens were retained from each 

sample collected.

Aquatic macroinvertebrates were collected from the 

same reaches (fig. 2) by means of methods described by 

OEPA (1989). The aquatic-macroinvertebrate community 

sample consists of a quantitative sample and a qualitative 

sample, both of which are required to be collected between 

June 15 and September 30. The Ohio Biological Survey did 

sample collection for this investigation and was able to collect quantitative samples within the required timeframe. 

Inclement weather prevented collection of qualitative samples within the required timeframe. Implications of late collection of the qualitative sample on the aquatic macroinvertebrate community index are discussed in the results 

section of this report. Quantitative and qualitative samples 

were transferred to plastic containers and preserved in the 

field with 10 percent formalin and shipped to the analyzing 

laboratory (Pennington and Associates, Inc., Cookeville, 

Tenn.) for macroinvertebrate identification.

Onsite physicochemical measurements 

Physicochemical measurements were made to characterize 

water quality and to assess designated-use attainment. The 

pH, dissolved oxygen concentration, temperature, and specific conductance of water were measured by use of multimeters, which were calibrated each day. Alkalinity samples 

were held on ice and analyzed within 12 hours of collection 

by means of the incremental titration inflection point 

method (Radtke and others, 1999).

Chemical constituents rationale, methods, and 

analytical laboratories

Caffeine was measured as an alternative indicator of fecal 

contamination because human waste can be an important 

source of caffeine to surface water. Total nonfilterable residue, cBOD5, and COD are regulated under National Pointsource Discharge Elimination System (NPDES) permits. 

Nutrient concentrations were measured because standards 

and draft criteria have been developed for surface-water 

nitrate plus nitrite and total phosphorus concentrations. 

Anions and cations were measured to help assess the similarity between the chemistry of municipal source discharges 

and receiving surface waters. Various laboratories, identified under headings for each method, were used to analyze 

these constituents in surface-water and municipal-source 

samples.

Caffeine. Filtered samples for caffeine analysis were 

shipped on ice to the USGS National Water Quality Laboratory (Denver, Colo.) for analysis by high-pressure liquid 

chromatography with a mass-spectroscopic detector as used 

in schedule 2060. The detection limit for caffeine by this 

method is 0.0096 μg/L.

Total nonfilterable residue. Total nonfilterable residue samples were chilled and transported on ice to the 

OEPA Division of Environmental Sciences Laboratory 

(Columbus, Ohio) for analysis within 48 hours by methods 

published by OEPA (1997a). The detection limit for total 

nonfilterable residue is 2 mg/L.

Five-day carbonaceous biochemical oxygen 

demand. Samples for analysis of cBOD5 were chilled and 

transported on ice to the OEPA Division of Environmental 

Sciences Laboratory (Columbus, Ohio) for analysis within 

48 hours by methods published by OEPA (1997b). The 

detection limit for cBOD5 is 2 mg/L.

Chemical oxygen demand. Samples were collected 

for COD analysis into baked glass bottles, acidified with 

4.5-N sulfuric acid to a pH less than 2, and shipped at 4°C to 

the USGS National Water Quality Laboratory (Denver, 

Colo.) for analysis by procedure 2144, described in Fishman 

and Friedman (1989). The detection limit for this procedure 

is 10 mg/L.

Nutrients. Nutrient samples were collected into polyethylene bottles. Total (unfiltered) nutrient samples were 

preserved by acidification with 4.5-N sulfuric acid to a pH 

less than 2 and shipped at 4°C. Dissolved (filtered) nutrient 

samples were not acidified and also were shipped at 4°C. 

Nutrient samples were analyzed at the USGS National 

Water Quality Laboratory (Denver, Colo.) for inorganic and 

organic forms by methods used in schedule 2702. 
Field and laboratory methods 11

Anions and cations. Samples for anions and cations 

were filtered and collected into polyethylene bottles. Samples were acidified with 6-N nitric acid to a pH less than 2 

and shipped at ambient temperature to the USGS National 

Water Quality Laboratory (Denver, Colo.) for analysis by 

methods used in schedule 2701.

Microbiological rationale, methods, and analytical 

laboratories

The State of Ohio has developed E. coli concentration standards for primary-contact recreational waters based on U.S. 

Environmental Protection Agency (USEPA) criteria. 

E. coli, coliphage, and Clostridium perfringens (C. perfringens) concentrations were used as indicators of health risk 

caused by fecal contamination. E. coli was used as a general indicator of human health risk, whereas coliphage is 

thought to be a better indicator of health risks posed by 

enteric pathogenic viruses, and C. perfringens is thought to 

be a better indicator for enteric pathogenic endospore-forming bacteria and protozoa (Rose and Grimes, 2001; 

Sorensen and others, 1989). More details for the following 

methods can be found in Francy and others (2001). 

Escherichia coli. Samples for analysis of E. coli concentrations were carried on ice from the collection site to 

the Youngstown wastewater laboratory (1999 and 2000) or 

the Boardman wastewater laboratory (2000) for processing. Samples for E. coli analysis were held at 4°C for not 

more than 6 hours and analyzed by means of the mTECagar membrane-filtration method (U.S. Environmental Protection Agency, 1985). Plates were incubated at 35°C for 2 

hours, then at 44.5°C for 22 to 24 hours in aluminum-block 

incubators. Yellow, presumptive E. coli colonies were 

tested by placing the membrane on a urea-phenol red soaked 

filter pad: E. coli colonies remain yellow when exposed to 

the urea-phenol red solution. 

Coliphage. Samples for analysis of coliphage concentrations were chilled and shipped on ice to the USGS 

Ohio District Microbiology Laboratory (Columbus, Ohio) 

where they were held at 4°C until analysis. Analysis was 

initiated within 48 hours of sample collection. Concentrations of coliphage were measured by means of a modification of the β-galactosidase induction single-agar layer 

method (Ijzerman and Hagedorn, 1992). Coliphage concentrations were measured by incubating raw water in the presence of a host E. coli strain—analysis for F-specific 

coliphage involved the E. coli F-amp host. In this method, 

E. coli host bacteria grow everywhere on the agar plate 

except where an infectious coliphage is present. The result 

of incubation is confluent growth of E. coli interrupted by 

circular plaques (zones of lysis where E. coli were killed by 

coliphage). Plaques were counted after 22-24 hours incubation at 35°C. 

Clostridium perfringens. Samples for analysis of C. 

perfringens concentrations were chilled and shipped on ice 

to the USGS Ohio District Microbiology Laboratory 

(Columbus, Ohio) where they were held at 4°C for analysis 

within 48 hours. Concentrations of C. perfringens were 

measured by means of the mCP-agar membrane-filtration 

method with incubation in an anaerobic environment (U.S. 

Environmental Protection Agency, 1996). Samples were 

incubated at 41°C for 22 to 24 hours, and colonies that 

turned pink in an atmosphere of ammonium hydroxide were 

counted as C. perfringens. Concentrations in raw-water 

samples represent both vegetative and dormant (endospore) 

populations of C. perfringens.

Quality control for water-quality measurements

Quality-control samples were particularly important for this 

investigation given that samples and onsite water-quality 

data were collected by both USGS and ms consultants personnel and that non-USGS laboratories did some analyses. 

Seven types of quality-control samples were collected: field 

equipment blanks, membrane-filtration equipment blanks, 

membrane-filtration procedure blanks, positive control samples, negative control samples, replicate samples, and 

spiked replicate samples. Each of these sample types was 

used to assess the consistency of data collection among the 

various individuals and laboratories collecting and analyzing samples. Preservation and maximum holding time 

requirements for each method were strictly adhered to. 

Chain-of-custody procedures were maintained for cBOD5

and total nonfilterable residue samples.

Blanks were used to assess sample contamination 

from equipment and to assess quantitative recovery of sample from equipment. Field equipment blanks were collected 

monthly during interval-oriented sampling in 1999 (three 

blanks collected) to measure possible contamination in the 

analysis of caffeine, anions and cations, nutrients, cBOD5, 

and COD. Membrane-filtration equipment blank tests were 

done to measure possible residual bacterial contamination 

after decontamination of reusable membrane-filtration 

equipment; these tests were done with each set of microbiological samples analyzed, for an estimated total of 180 

E. coli analysis blanks, 54 coliphage analysis blanks, and 54 

C. perfringens analysis blanks. Membrane-filtration procedure blank tests were used to assess quantitative recovery of 

microorganisms from membrane-filtration equipment after 

sample filtration; these tests were done weekly during periods of analysis.

Positive- and negative-control samples were used to 

assess sterility and proper function of microbiological 

media and incubation conditions. Positive-control samples, 

from which microorganisms were expected to grow, were 

done with each set of coliphage and C. perfringens analyses. 

Negative-control samples, which evaluate the selectivity of 

a test, were done with each set of coliphage analyses.

Replicate samples were used to assess variability in 

sample results. Two extra samples were collected and tested 
12 Water Quality of the Mahoning River and Selected Tributaries in Youngstown, Ohio

each month in 1999 (six samples) to measure response variability in microbiological analyses (E. coli, coliphage, C. 

perfringens) and chemical analyses (anions and cations, 

nutrients, cBOD5, chemical oxygen demand, and total nonresidual solids). Additionally, spiked caffeine replicates 

(six samples) were tested to ensure that this nonconserved 

constituent persisted in samples for the duration of the holding time before analysis.

Each of the analyzing laboratories had its own quality-control procedures. USGS laboratories have published 

quality-control manuals: the Ohio District Microbiology 

Laboratory quality-control manual (Francy and others, 

2001) can be accessed online, and the National Water Quality Laboratory publishes results of its quality-control program (National Water Quality Laboratory, 2001). Qualitycontrol practices and procedures for the laboratory that analyzed aquatic-macroinvertebrates are available from Pennington and Associates (1997). Ohio EPA quality-control 

procedures were published with method procedures (Ohio 

Environmental Protection Agency, 1997a)

Biotic index rationale, methods, and analytical 

laboratories

Three biotic indices are calculated for assessment of biological use-attainment by OEPA. Two of the indices relate to 

fish communities, and the third relates to aquatic-macroinvertebrate communities. A habitat index also can be calculated to evaluate whether nonattainment based on fish 

indices is related to shortage of physical habitat or unfavorable chemical water quality.

Fish community indices. Individuals collected during electrofishing passes were identified, weighed, and 

checked for external anomalies such as parasites, lesions, 

and skeletal deformities onsite and released back to the 

stream (Ohio Environmental Protection Agency, 1989). 

Numbers of individuals, taxa, and biomass were used to calculate two indices of fish-community health.

The index of biotic integrity (IBI) developed by Karr 

(1981) is based on structural and functional characteristics 

of fish communities. Fish communities in study streams are 

compared to reference fish communities in similar-sized 

basins considered least affected by human activity within 

the same ecoregion. The comparison allows a score 

between 1 and 5 to be assigned to each of 12 metrics (listed 

in table 4). The IBI is calculated as the sum of the 12 metric 

scores; therefore, the range of possible values for the IBI is 

12 to 60. Higher values indicate more healthy aquatic ecosystems than lower values do. The IBI used by OEPA 

includes metrics that are tailored specifically to the surface 

waters of Ohio (Ohio Environmental Protection Agency, 

1987). 

The index of well-being (Iwb) was developed by 

Gammon (1976) and includes the Shannon diversity index. 

The Shannon diversity index is based on the numbers and 

weights of fish and takes into account species richness and 

proportion of each species within the local aquatic community (Shannon and Weaver, 1949). The OEPA uses a modified index of well-being (MIwb) that excludes fish 

considered to be “highly tolerant” from the Iwb calculation. 

A high score indicates a healthier aquatic ecosystem. The 

MIwb score always is greater than 0, but there is no theoretical upper limit.

Habitat index. Habitat was assessed by USGS personnel at the same time that fish communities were inventoried. The qualitative habitat evaluation index (QHEI) is a 

measure of habitat features that affect fish communities. 

This habitat index incorporates six metrics: channel substrate, instream cover, channel morphology, riparian and 

bank condition, pool and riffle quality, and gradient (Ohio 

Environmental Protection Agency, 1989). The QHEI is not 

used as a criterion to determine the attainment of aquaticlife use designations; however, narrative interpretations of 

QHEI scores were derived from correlation of QHEI scores 

with fish-index scores. A high score should indicate that the 

capability of the available physical stream habitat to support 

a healthy aquatic community also is high. The result of a 

higher QHEI should, therefore, be more healthy fish communities (high IBI and MIwb scores).

Aquatic-macroinvertebrate index. The invertebrate 

community index (ICI) was developed by OEPA to measure 

the health of aquatic-macroinvertebrate communities (Ohio 

Environmental Protection Agency, 1987). This index is 

similar to the IBI for fish. Macroinvertebrate communities 

in study streams are compared to reference macroinvertebrate communities in similar-sized basins within the same 

ecoregion. There are 10 metrics for macroinvertebrate communities, scoring between 0 and 6, resulting in an overall 

ICI value between 0 and 60. A high score indicates a 

healthy community of aquatic macroinvertebrates. 

Macroinvertebrate samples were preserved and 

shipped to Pennington and Associates, Inc., for analysis. 

All benthic samples were placed on a 120-μm mesh screen. 

After washing, the macroinvertebrates were removed from 

the detritus under × 5 magnification and preserved in 85 

percent ethanol. The organisms were identified to the lowest practical taxonomic level with available keys (Pennington and Associates, 1997) and counted. Initial identifications were made with a stereomicroscope (× 7-60). 

Slide mounts were made of the chironomids, simuliids, oligochaetes, and small crustaceans for identification 

with a compound microscope. The chironomids, simuliids, 

and oligochaetes were cleared for 24 hours in refrigerated 

10 percent potassium hydroxide. Temporary mounts were 

made in glycerin, and the organisms were returned to 80 

percent ethanol after identification. When permanent 

mounts were desired, the organisms were transferred to 95 

percent ethanol for 30 minutes and mounted in euperol. The 

procedures used for taxonomic identification and enumeration followed methods described by OEPA (1989).
Field and laboratory methods 13

Estimation of Escherichia coli and inorganic nitrogen 

loads

Loads were calculated for E. coli and inorganic nitrogen 

carried by the Mahoning River and sewer-overflow discharges during the first 24 hours of wet-weather flow, 

defined to begin 6 hours before peak flow at the Mahoning 

River at West Avenue (site 2) for this computation. This 

definition of the beginning of wet-weather flow was adopted 

to include both the onset of sewer-overflow discharge and 

the peak flow at all sites. Sewer overflows discharged only 

during a portion of each 24-hour interval.

Surface-water 24-hour load. The 24-hour wetweather loads at the Mahoning River at Youngstown (site 1) 

and the Mahoning River at Lowellville (site 4) were calculated for each of the three wet-weather events sampled in 

2000. Streamflow volume over the 24-hour period was calculated by summing incremental flow volumes for the first 

24 hours of wet-weather flow. The 24-hour wet-weather 

flow load was estimated from continuously monitored 

streamflow measurements and a regression analysis of concentration with flow. The regression analysis included 

E. coli and inorganic nitrogen concentrations measured at 

each site over a range of streamflow during the course of 

this investigation. Constituent concentrations were estimated for each streamflow measurement by means of the 

regression equations. Total 24-hour loads were calculated 

by summing incremental loads (estimated constituent concentrations multiplied by the volume of water passing the 

site over each 15-minute interval in 24 hours). Load estimates obtained by this method were increased by a smearing-estimator bias factor as recommended and described by 

Duan (1983; in USGS Office of Surface Water Technical 

Memorandum No. 93.08, 1992) for linear regression analysis on log-transformed data.

Sewer-overflow load. Sewer-overflow sites were 

identified and mapped by ms consultants (Youngstown, 

Ohio). The personal-computer version of the Storm Water 

Management Model (XP-SWMM), produced by the 

USEPA, was used by ms consultants to estimate discharges 

from 101 sewer-overflow sites in Youngstown, Ohio. The 

XP-SWMM model was calibrated and verified twice in 

1999 and further verified by comparing a 5-year discharge 

simulation based on National Climatic Data Center rainfall 

data to historic discharge data from 1981–85 (Joe Catullo, 

ms consultants, written commun., 2001). Multiday simulations of discharges during the three wet-weather events 

sampled in 2000 were computed. Simulations generated 

flow-rate values on a 15-minute-interval basis, which in turn 

were used to estimate the discharge volume from each 

sewer-overflow site during each time interval. Discharge 

volume to the Mahoning River was estimated as the sum of 

discharge volumes from all modeled sewer-overflow sites. 

Concentrations measured in samples collected from 

seven monitored sewer-overflow discharge sites in 2000 

were used to estimate concentrations of E. coli and inorganic nitrogen forms in each of the 101 modeled seweroverflow discharges. The characteristics of the seven monitored sewer-overflow sites were not assumed to be an adequate representation of all 101 sites; therefore, minimum, 

median, and maximum concentration values were used to 

present an expected range of concentration estimates. 

These concentration estimates were multiplied by XPSWMM discharge-volume estimates for each 15-minute 

discharge interval for all sewer-overflow sites. The sum of 

loads from all 101 overflows was used as an estimate of the 

24-hour load attributable to sewer-overflow discharges in 

Youngstown.

Table 4. Twelve metrics composing the modified index 

of biotic integrity used by the Ohio Environmental 

Protection Agency for wading-water and headwater 

sites

[IBI, index of biotic integrity; DELT, deformities, eroded fins, lesions, 

tumors]

IBI metric Wading water Headwater

1 Total number of species Total number of species

2 Number of darter species Number of darter 

species

3 Number of sunfish 

species

Number of headwaters 

species

4 Number of sucker species Number of minnow 

species

5 Number of intolerant 

species

Number of sensitive 

species

6 Percent tolerant 

individuals

Percent tolerant 

individuals

7 Percent omnivorous 

individuals

Percent omnivorous 

individuals

8 Percent insectivorous 

individuals

Percent insectivorous 

individuals

9 Percent top carnivore 

individuals

Percent pioneer 

individuals

10 Relative number of 

individuals (density)

Relative number of 

individuals (density)

11 Percent lithophils Number of lithophilic 

individuals

12 Percent DELT anomalies Percent DELT 

anomalies
14 Water Quality of the Mahoning River and Selected Tributaries in Youngstown, Ohio

Hydrology of the Mahoning River and 

selected tributaries

The intent of hydrologic data summarization was to characterize streamflow in the study area and to present a context 

for wet-weather event magnitudes and timing of sample collection. These data also were used to estimate water volumes entering and leaving Youngstown in the Mahoning 

River, Mill Creek, and tributaries, which were necessary for 

calculating loads.

Streamflow

Hydrographs from centrally located, continuous streamflow-measurement stations on the Mahoning River and Mill 

Creek portions of the monitoring network for May through 

October 1999 and 2000 are shown in figure 3. As evident 

from the hydrographs, the Mahoning River carries larger 

amounts of water and maintains more consistent dryweather flow than Mill Creek does. The instantaneous peak 

wet-weather flow that is exceeded on average once every 2 

years was calculated to be 367,000 m3

/s (10,400 ft3/s) for 

the Mahoning River below West Avenue and 71,000 m3/s 

(2,010 ft3

/s) for Mill Creek at Youngstown by use of the 

method described by Koltun and Roberts (1990). Wetweather events sampled in this investigation can be characterized as small to moderate because the 2-year flow was 

not reached on either stream during the months evaluated in 

this investigation.

The hydrographs in figure 3 include superimposed 

symbols on dates when samples were collected. Water samples were collected during wet-weather flow and dryweather flow in 1999 (fig. 3). Samples were collected only 

during wet-weather flow in 2000. Early summer 2000 was 

wetter than early summer 1999 had been. The three flow 

peaks that were sampled in 2000 came in late summer when 

the hydrograph, similar to the 1999 hydrograph, was characterized by steady dry-weather flow punctuated by wetweather flow peaks. Dry-weather concentration estimates 

based on 1999 data should be relevant to late-summer 2000 

on the basis of this hydrologic observation.

Wet-weather events

One-week hydrographs from August, September, and October 2000 at three continuous streamflow-monitoring stations on the Mahoning River (fig. 4) and Mill Creek (fig. 5) 

were abstracted from the continuous record for water year 

2000. As mentioned previously, wet-weather events were 

initiated by precipitation greater than 0.25 cm (0.1 in.). 

Wet-weather flow was defined to begin 6 hours before peak 

flow, and a wet-weather event was defined to end 48 hours 

after peak flow for the purposes of analysis in this investigation. Situations involving a secondary flow peak—most 

pronounced during the August 2000 event—were still 

treated as a single wet-weather flow event. 

Discharge intervals for monitored sewer overflows 

(three to the Mahoning River, one to Crab Creek, and three 

to Mill Creek) were superimposed on the hydrographs (figs. 

4 and 5). Discharge intervals shown in figures 4 and 5 do 

not necessarily represent the discharge intervals of all sewer 

overflows in the sampling network because only 7 of the 

101 modeled sewer-overflow sites were monitored. All discharges occurring during a wet-weather flow event were 

considered to be part of the same discharge event. Data 

depicted in figures 4 and 5 clearly show that discharges at 

individual overflow sites could be discontinuous. It was not 

possible to measure the actual intervals during which each 

of the unmonitored sewer-overflow sites upstream from a 

water-quality monitoring site was actively discharging.

Surface-water samples were expected to reflect the 

effect of sewer-overflow discharges on receiving waters 

because monitored sewer overflows discharged before surface-water sample collection during all three sampled wetweather events. The August 2000 event, however, included 

dual streamflow peaks, and sewer overflows discharged not 

only before the first surface-water sample collection but also 

between the first and second surface-water sample collections. The volume of the second discharge was 79,000 m3

(21 Mgal) compared with 450,000 m3 (119 Mgal) for the 

first discharge. Total model simulated sewer-overflow discharges for the first 24-hour interval of each wet-weather 

event were 450,000 m3

 (119 Mgal) on August, 6 and 7 

144,000 m3

 (38 Mgal) on September, 20 and 21 and 64,300 

m3

 (17 Mgal) on October, 5 and 6 (Joe Catullo, ms consultants, written commun., 2001). According to the 5-year XPSWMM simulation, 92 percent of sewer-overflow volume 

was discharged to the Mahoning River and tributary streams 

outside the Mill Creek Subwatershed, and the remaining 8 

percent of discharge volume went into the Mill Creek Subwatershed. 

Water quality of the Mahoning River and 

selected tributaries

Surface-water quality in the study area was evaluated to 

determine where, when, and for how long E. coli concentrations exceeded primary-contact recreational-use standards. 

Chemical water-quality constituents were evaluated to 

determine where and when standards and draft criteria for 

the protection of aquatic life were not met. OEPA uses 

biotic indices to assess whether Ohio public waterways 

achieve their designated use as warmwater habitat; therefore, Mill Creek biotic-index data were compiled for assessment of this long-term indicator of water quality (relative to 

instantaneous chemical concentration data). Finally, an 

attempt was made to quantify the effects of sewer-overflow 
Water quality of the Mahoning River and selected tributaries 15

10,000

1,000

100

10

1

STREAMFLOW, IN CUBIC FEET PER SECOND

Mahoning River below West Avenue

Mill Creek at Youngstown

Sample collected

MAY JUNE JULY AUGUST SEPTEMBER OCTOBER

2000

0.1

10,000

1,000

100

10

1

0.1

MAY JUNE JULY AUGUST SEPTEMBER OCTOBER

1999

STREAMFLOW, IN CUBIC FEET PER SECOND

Figure 3. Streamflow and sample collection for two sites in Youngstown, Ohio, during summer 1999

and 2000. (Discontinuities in graph line show where data are missing from record.)
16 Water Quality of the Mahoning River and Selected Tributaries in Youngstown, Ohio

100

1,000

10,000

100

1,000

10,000

3456789

AUGUST

100

1,000

10,000

18 19 20 21 22 23 24

SEPTEMBER

3456789

OCTOBER

STREAMFLOW,

IN CUBIC FEET PER SECOND

STREAMFLOW,

IN CUBIC FEET PER SECOND

STREAMFLOW,

IN CUBIC FEET PER SECOND

Monitored sewer-overflow discharge interval

Mahoning River:

at Lowellville (site 4)

below West Avenue (site 2)

at Youngstown (site 1)

Sample collected

Figure 4. Streamflow and sample collection for three sites on the Mahoning River, Ohio, during

three wet-weather flow events sampled, August-October 2000.
Water quality of the Mahoning River and selected tributaries 17

1,000

3456789

1

10

100

18 19 20 21 22 23 24

1

10

100

1,000

3456789

1

10

100

1,000

AUGUST

SEPTEMBER

OCTOBER

STREAMFLOW,

IN CUBIC FEET PER SECOND

Monitored sewer-overflow discharge interval

Mill Creek at:

Price Road (site 8)

Youngstown (site 7)

Shields Road (site 6)

Sample collected

STREAMFLOW,

IN CUBIC FEET PER SECOND

STREAMFLOW,

IN CUBIC FEET PER SECOND

Figure 5. Streamflow and sample collection for three sites on Mill Creek, Ohio, during three

wet-weather flow events sampled during, August-October 2000. (Discontinuities in graph line

show where data are missing from record.)
18 Water Quality of the Mahoning River and Selected Tributaries in Youngstown, Ohio

discharges on surface-water loads of constituents relevant to 

water quality in the study area.

Many constituents were evaluated in an attempt to 

relate surface-water quality to possible municipal sources of 

impairment (table 2). Analysis of various constituents did 

not lead to conclusions that were relevant to the objectives 

of this report. Data for surface-water concentrations of total 

suspended solids, cBOD5, COD, and anions and cations 

have been published elsewhere (Shindel and others, 2000 

and 2001). Data for the aforementioned constituents in 

sewer-overflow discharges, when collected, are included in 

this report as appendix A.

Quality control was important in the evaluation of 

this data set because the analytical scope of this investigation required cooperation from multiple parties. Blank samples never showed unacceptable levels of contamination 

with water-quality constituents. Positive control samples 

always showed the presence of measured constituents, and 

negative control samples always showed the absence of 

measured constituents. Replicate analyses agreed within 10 

percent, and caffeine-spiked samples showed acceptable 

recovery.

Primary-contact recreational use

Ohio law states that, for primary-contact recreational 

waters, “geometric mean E. coli content . . . based on not 

less than 5 samples in a 30-day period shall not exceed 126 

(CFU) per 100 mL and E. coli content . . . shall not exceed 

298 (CFU) per 100 mL in more than 10 percent of the samples taken during any 30-day period” (Ohio Environmental 

Protection Agency, 2002). E. coli concentration data collected during interval-oriented sampling in 1999 were used 

to calculate 5-sample, 30-day geometric mean values for 

comparison to the standard (table 5). At least one part of the 

two-part standard was exceeded in 35 of 37 instances. The 

two instances for which E. coli concentrations met the complete standard both occurred in September 1999, at Mill 

Creek at Price Road (site 6) and Indian Run near Canfield 

(site 10). In two other instances, both in May 1999, geometric-mean E. coli concentrations were less than 126 colonyforming units per 100 mL (CFU/100 mL), but in each case 

one of the five samples (20 percent) had an E. coli concentration higher than 298 CFU/100 mL. E. coli concentrations 

frequently were higher than Ohio’s standard for primarycontact recreational waters throughout the sampling network.

E. coli concentrations during dry- and wet-weather 

flows were compared to evaluate whether streamflow condition influenced microbiological water quality. E. coli carried by dry-weather flows are contributed by some or all of 

the following: municipal WWTP effluent, leaking municipal sewerlines, septic-system leachate, and direct fecal 

inputs from domestic animals and wildlife. If only those 

sources contributed E. coli to the stream during wet-weather 

flow, and if the contributions were at the same rate as during 

dry-weather flow, then E. coli concentrations should have 

decreased during wet-weather flow because of dilution with 

rainwater runoff. On the other hand, E. coli concentrations 

could remain constant or increase during wet-weather flow 

because of increased contributions from dry-weather 

sources (faster flow through septic systems may allow 

breakthrough or less effective treatment, less contact time in 

WWTPs). Additional contributions of fecal material to the 

stream during wet-weather flow can come from additional 

human sources (sewer-overflow discharges, partially treated 

WWTP effluent) or domestic animal (overflows from 

waste-treatment lagoons) and wildlife sources (feces carried 

with surface runoff).

E. coli concentration data from both years of this 

study are summarized as boxplots in figure 6. Sites were 

placed into seven categories for figure 6 on the basis of site 

and location characteristics. (See also table 1.) Site categories were divided further by flow condition. E. coli concentrations were higher during wet-weather flow than during 

dry-weather flow in all site categories.

E. coli concentration observations for dry-weather 

flow (fig. 6) show that in three of five site categories, 75 percent or more of concentrations were less than 298 CFU/

100 mL. This finding indicates that, within some site categories, surface water in the study area could be expected to 

meet Ohio E. coli standards during periods of extended dry 

weather. In every surface-water site category, E. coli concentrations from more than 75 percent of wet-weather flow 

samples were greater than 298 CFU/100 mL; thus, if no 

changes are made to the watershed, the water-quality standard usually will be exceeded during periods that include 

wet-weather flow.

To evaluate how long wet-weather flow affects 

microbiological water quality, E. coli concentrations measured during wet-weather events (sampled in 2000) were 

compared with expected dry-weather flow concentrations 

based on 1999 data (table 6). The geometric mean of concentrations measured at time intervals during wet-weather 

events (nominally up to 48 hours past peak flow) were all 

higher than geometric-mean concentrations during dryweather flow. E. coli concentrations in the Mahoning River 

were generally less than three times higher than dry-weather 

flow concentrations within 48 hours after peak flow; however, at Mill Creek and other tributary sites, E. coli concentrations generally remained more than four times higher 

than dry-weather flow concentrations at 48 hours after peak 

flow. By comparison, WWTP effluent E. coli returned to 

near-normal concentrations within 24 hours after peak flow 

in the Mahoning River (table 6). 
Water quality of the Mahoning River and selected tributaries 19

Table 5. Five-sample geometric mean Escherichia coli concentrations and percentage of samples exceeding the 

standard of 298 colony-forming units per 100 milliliters during three 30-day periods in May, July, and September 

1999

[--, data not collected; Geo mean, geometric mean; std, standard of 298 colony-forming units per 100 milliliters]

Site location

and identifier

May 1999 July 1999 September 1999

Geo mean Percent over std Geo mean Percent over std Geo mean Percent over std

Mahoning River:

 At Youngstown (1) 89 20 220 20 160 20

 Below West Avenue (2) 420 40 310 20 350 40

 At Center Street (3) -- -- 720 40 820 60

 At Lowellville (4) 850 60 2,000 100 930 40

Mill Creek:

 At Western Reserve Rd. (5) 580 60 550 100 620 100

 At Shields Road (6) 940 60 400 60 590 100

 At Youngstown (7) 240 40 500 40 290 20

 At Price Road (8) 54 20 220 40 53 0

Tributaries:

 Crab Creek at Youngstown 

(9)

160 20 1,700 80 400 40

 Indian Run near Canfield 

(10)

260 20 240 40 61 0

 Cranberry Run at 

Boardman (11)

780 60 500 100 440 60

 Ax Factory Run at 

Youngstown (12)

-- -- 300 40 550 40

 Bears Den Run at 

Youngstown (13)

130 40 690 60 230 40

The Mahoning River and Mill Creek failed to meet 

designated recreational uses because of microbiological 

water quality in and around Youngstown during summer 

1999 (table 6). A longitudinal view of geometric-mean concentrations (fig. 7) was prepared to look at spatial distributions across Youngstown. E. coli concentrations increased 

in the Mahoning River as the river passed through Youngstown (figs. 7a, b). Monitored sources to the Mahoning 

River (Mill Creek, Crab Creek, and the Youngstown 

WWTP) did not carry substantially greater concentrations 

of E. coli than did the Mahoning River; although they 

certainly added a bacterial load to the Mahoning River, they 

could not have increased main-stem E. coli concentrations. 

Dry-weather flow increases in E. coli concentrations across 

the reaches between Mahoning River at Youngstown (site 1) 

and Mahoning River below West Avenue (site 2) and 

between site 2 and Mahoning River at Center Street (site 3) 

were not explained by additions from monitored sources 

(fig. 7a). During wet-weather flow, sewer overflows contributed discharge with high E. coli concentrations and may 

help explain increases in E. coli concentration across the 

same reaches (fig. 7b).
20 Water Quality of the Mahoning River and Selected Tributaries in Youngstown, Ohio

100

101

102

103

104

105

106

107

Dry Wet Dry Wet Dry Wet Dry Wet Dry Wet Dry Wet Wet

ESCHERICHIA COLI,

IN COLONY-FORMING UNITS PER 100 MILLILITERS

FLOW CATEGORIES

EXPLANATION

41 Number of observations

95th percentile

75th percentile

Median (50th percentile)

25th percentile

5th percentile

Ohio Environmental Protection Agency

single-sample criterion (298 colony-forming

units per 100 milliliters)

Flow categories:

dry weather, 1999

wet weather, 1999 and 2000

Dry

Wet

MAIN STEMS TRIBUTARIES SOURCES

17

16

15 16

26

40

32

25

22

28

21

50

41

MahoningRiver Mill Creek overflows

upstream

from

reservoirs

downstream

from

reservoirs

108

wastewater

treatment

Plant upstream

from

overflow

sites

downstream

from

overflow

site

Figure 6. Summary of Escherichia coli concentration data by site type, relative location, and

flow category for summer 1999 and 2000 in the Mahoning River, Ohio, and selected tributaries

and sources.

Concentrations of E. coli in Mill Creek (fig. 7c, d) 

were constant between Western Reserve Road (site 5) and 

Shields Road (site 6); then, as Mill Creek passed through 

reservoirs in Mill Creek Park to Youngstown (site 7) and 

Price Road (site 8), concentrations decreased. This 

decrease may have been caused by settling in the reservoirs 

and the time it took the water to pass through the reservoirs. 

E. coli bacteria commonly are associated with suspended 

material that falls as sediment in reservoirs. The residence 

time of each reservoir is not known, but because E. coli do 

not reproduce outside of the body in temperate climates 

(Clesceri and others, 1998), then some E. coli should die off 

in the reservoirs. Sampled tributaries to Mill Creek carried 

E. coli at similar concentrations to those in Mill Creek; 

therefore, tributaries neither substantially reduced nor 

increased E. coli concentrations in Mill Creek. Relatively 

E. coli-rich additions from overflows, however, might have 

increased E. coli concentrations at Youngstown (site 7) and 

at Price Road (site 8) and may have increased E. coli concentrations compared with what they would otherwise have 

been (fig. 7d).

Aquatic-life use

The State of Ohio has developed regulations for the protection of aquatic life, particularly fish and aquatic macroinvertebrates (Ohio Environmental Protection Agency, 2002). 

These regulations vary according to the surrounding ecoregion and aquatic-life use designation of the stream. Youngstown, Ohio, lies within the Erie-Ontario Lake Plain
Water quality of the Mahoning River and selected tributaries 21

Table 6. Geometric-mean Escherichia coli concentrations during dry-weather 

flow (1999) and at nominal times after wet-weather flow peaks (2000). (All data 

are in colony-forming units per 100 milliliters)

[WWTP, wastewater-treatment plant]

Site location 

and identifier

Dry-weather 

flow

 (1999)

Wet-weather flow (2000)

Nominal hours after peak flow

6 24 48

Mahoning River:

At Youngstown (1) 52 800 790 160

Below West Avenue (2) 110 2,100 1,800 300

At Center Street (3) 330 4,100 2,400 1,100

At Lowellville (4) 490 7,900 2,400 880

Mill Creek:

At Western Reserve Road (5) 410 9,200 6,300 1,500

At Shields Avenue (6) 270 7,200 6,000 1,400

At Youngstown (7) 130 2,700 1,300 580

At Price Road (8) 44 2,800 3,200 520

Tributaries:

Crab Creek at Youngstown (9) 160 6,500 3,200 2,000

Indian Run near Canfield (10) 100 7,000 3,500 600

Cranberry Run at Boardman (11) 310 7,700 3,400 1,900

Ax Factory Run at Youngstown (12) 160 2,600 1,600 390

Bears Den Run at Youngstown (13) 100 5,900 2,200 1,300

Municipal sources:

Youngstown WWTP (source A) 130 2,400 200 320

(EOLP) ecoregion, and all streams in the study area are designated as warmwater habitat. The associated State criteria 

are listed in table 7. Water-quality data from the entire 2-

year study were summarized as a series of boxplots (figs. 8 

and 9) for comparison with State regulations. Observations 

were separated by site category and flow condition before 

summarization to allow evaluation of where and when water 

quality did not meet criteria. Even sporadic failure to meet 

chemical water-quality regulations may result in failure to 

support aquatic biota within the study area because aquatic 

organisms integrate the effects of water quality in their habitat. 

Water-quality standards for pH, dissolved oxygen 

concentration, and temperature were met in more than 75 

percent of all instances (fig. 8). Specific cases where standards were not met are listed in table 8. The pH standards 

were not met when pH exceeded 9.0, usually during dry 

weather (fig. 8). The pH standard was exceeded at least 

once in all five tributaries and at half of the Mahoning River 

and Mill Creek sample sites (table 8). Dissolved oxygen 

concentrations generally met the State standard (fig. 8); 

those concentrations that did not meet standards were documented only during dry-weather flow (table 8). Mill Creek 

at Western Reserve (site 5) did not meet the dissolved oxygen concentration standard on two sampling dates (one on 

May 11, 1999, and the other on July 27, 1999), and Bears 

Den Run (site 13) did not meet the dissolved oxygen concentration standard on July 28, 1999. 
22 Water Quality of the Mahoning River and Selected Tributaries in Youngstown, Ohio

24 23 22 21 20 19 18 17 16 15 14 13 12 11 24 23 22 21 20 19 18 17 16 15 14 13 12 11

103

102

101

ESCHERIC

IN COLONY-FORMING UN

site 1

site 8

site 2

site 9

source A

site 3

site 4

Campbell Wastewater Treatment Plant (unsampled)

Struthers Wastewater Treatment

Plant (unsampled)

site 1 

site 2

source A

site 3 

Campbell Wastewater Treatment Plant (unsampled)

Struthers Wastewater Treatment

Plant (unsampled)

site 

12 11 10 9 8 7 6 5 4 3 2 1 0

107

106

105

104

103

102

ESCHERICHIA COLI,

IN COLONY-FORMING UNITS PER 100 MILLILITERS

12 11 10 9 8 7 6 5 4 3 2 1 0

RIVER MILES

MILL CREEK

Dry-weather flow

C

Wet-weather flow

D

site 5

site 10

site 6

site 11

Newport Lake (unsampled)

Lake Cohasset (unsampled) site 7

site 12

site 13

site 8

site 5

Lake Glacier (unsampled)

site 10

site 6

site 11

Newport Lake (unsampled)

Lake Cohasset (unsampled)

source F

site 7

site 12

site 13 source G

Lake Glacier (unsampled) source H

RIVER MILES

site 8

si

site 8

Boardman Wastewater Treatment

Plant (unsampled)

Mill Creek Park border

(landmark)

Boardman Wastewater Treatment

Plant (unsampled)

Mill Creek Park border

(landmark)

Figure 7. Geometric mean Escherichia coli concentrations in the (A and B) Mahoning River and (C and

wet-weather flow (1999 and 2000).

D) Mill Creek, Ohio, parts of the water-quality sampling network during dry-weather flow (1999) and
Water quality of the Mahoning River and selected tributaries 23

 

Table 7. State of Ohio regulations for the protection of aquatic life in designated 

warmwater-habitat streams in the Erie-Ontario Lake Plain ecoregion

[Regulations are standards (Ohio Administrative Code 3745-1-07) except nitrate plus nitrite and total phosphorus, which are 

draft criteria (Robert Miltner, U.S. Environmental Protection Agency, written commun., 1999). Min, regulation minimum; 

Max, regulation maximum; mg/L, milligrams per liter; degrees C, degrees Celsius; NA, not applicable; mi2, square miles]

Criterion Units Min Max Application

pH Standard units 6.5 9.0 All seasons, statewide.

Dissolved oxygen mg/L 4.0 NA All seasons, statewide.

Temperature degrees C NA 22.8 May 16–31

NA 25.0 June 1–15

NA 29.4 June 16–Sept. 15

NA 25.6 Sept. 16–30

NA 22.8 Oct. 1–15

Ammonium, 

instantaneous

mg/L NA 1.1–13.0 March to November, 

statewide. Value is 

dependent on pH and 

temperature.

Ammonium, 

30-day average

mg/L NA 0.1–2.3 March to November, 

statewide. Value is 

dependent on pH and 

temperature.

Nitrate plus nitrite mg/L NA 1.0 Drainage area less than 200 

mi2

, statewide.

NA 1.5 Drainage area 200 or more 

mi2

, statewide.

Total phosphorus mg/L NA .08 Drainage area less than 20 

mi2

, statewide.

NA .10 Drainage area 20 to less 

than 200 mi2

, statewide.

NA .17 Drainage area 200 to less 

than 1000 mi2

, statewide.
24 Water Quality of the Mahoning River and Selected Tributaries in Youngstown, Ohio

2

4

6

8

10

12

14

17 23 40

32

27

21

23

22

37 38

DISSOLVED

OXYGEN,

IN MILLIGRAMS PER LITER

Dry Wet Dry Wet Dry Wet Dry Wet Dry Wet

FLOW CATEGORY

6

7

8

9

10

25

17

41

32 26 22 50 21 27 41

Mahoning Mill Creek

River

pH

MAIN STEMS TRIBUTARIES

11

downstream

from reservoirs

upstream

from overflow sites

downstream

from overflow sites

upstream

from reservoirs

17 24 40

32 27

21

25

50 22

41

5

10

15

20

25

30

35

TEMPERATURE,

IN DEGREES CELSIUS

EXPLANATION

41 Number of observations

95th percentile

75th percentile

Median (50th percentile)

25th percentile

5th percentile

Dry

Wet

Ohio Environmental Protection Agency criteria

for the protection of aquatic life (criteria values

are listed in table 7)

Flow categories:

dry weather, 1999

wet weather, 1999 and 2000

Figure 8. Summary of pH, dissolved oxygen concentration, and temperature data by site
Water quality of the Mahoning River and selected tributaries 25

Dry Wet Dry Wet Dry Wet Dry Wet Dry Wet Dry Wet Wet

FLOW CATEGORIES

0

2

6

10

12

13

8 2

3 14 6 21

14 4

14

4

8 27

4

8

NITRATE PLUS NITRITE,

IN MILLIGRAMS PER LITER

0

0.2

0.4

0.6

0.8

1.0

10

7 2

3 14

21

6

4 13

11 4

8 22

1.2

2

4

6

TOTAL PHOSPHORUS CONCENTRATION,

IN MILLIGRAMS PER LITER

EXPLANATION

8 Number of observations

95th percentile

75th percentile

Median (50th percentile)

25th percentile

5th percentile

Dry

Wet

Ohio Environmental Protection Agency (OEPA)

criteria for the protection of aquatic life

(criteria listed in table 7)

Flow categories:

dry weather, 1999

wet weather, 1999 and 2000

OEPA range of criterion, Data point

value dependent on pH

and temperature (table 6)

Figure 9. Summary of ammonium, nitrate plus nitrite, and total phosphorus concentrations by

site type, relative location, and flow category in the area of Youngstown, Ohio.

0

0.1

0.2

0.3

0.4

0.5

13

8

2

14 3

21

6

14

4

14

4

27 8

AMMONIUM CONCENTRATION,

IN MILLIGRAMS PER LITER

MAIN STEMS TRIBUTARIES SOURCES

Mill Creek

2

4

6

8

Wastewater

Treatment

Plant

Overflows

upstream

from

reservoirs

downstream

from

reservoirs

upstream

from

overflow

sites

downstream

from

overflow

site

MahoningRiver
26 Water Quality of the Mahoning River and Selected Tributaries in Youngstown, Ohio

Table 8. Observations for which surface-water quality did not meet one or more 

Ohio physical or chemical water-quality standards for the protection of aquatic life 

(sites at which all chemical water-quality standards were met are not listed), in or around 

Youngstown, Ohio

[

oC, degrees Celsius; DO, dissolved oxygen; mg/L, milligrams per liter]

Site Standard Date Measured value

Mahoning River at Youngstown

(site 1; 24 total measurements)

Temperature 7/20/99 30.2 oC

9/21/99 27.4 oC

10/06/00 23.0 oC

pH 7/26/99 9.1

9/21/99 9.3

9/27/99 9.3

Mahoning River below West Avenue 

(site 2; 24 total measurements)

pH 5/24/99 9.2

9/27/99 9.2

Mill Creek at Western Reserve Road 

(site 5; 25 total measurements)

DO 5/11/99 3.8 mg/L

7/27/99 3.7 mg/L

pH 5/25/99 9.1

9/13/99 9.5

9/22/99 9.2

Mill Creek at Price Road 

(site 8; 24 total measurements)

pH 9/14/99 9.3

9/29/99 9.4

Crab Creek at Youngstown

(site 9; 24 total measurements)

Ammonium

(30-day)

9/9/99 0.7 mg/L

pH 5/10/99 9.1

5/17/99 9.1

5/26/99 9.1

9/14/99 9.8

9/23/99 9.2

9/29/99 9.6
Water quality of the Mahoning River and selected tributaries 27

Indian Run near Canfield

(site 10; 31 total measurements)

pH 7/12/99 9.1

9/13/99 9.3

Cranberry Run at Boardman

(site 11; 24 total measurements)

pH 9/13/99 9.1

Ax Factory Run at Youngstown

(site 12; 23 total measurements)

pH 9/14/99 9.1

Bears Den Run at Youngstown

(site 13; 30 total measurements)

DO 7/28/99 3.9 mg/L

pH 5/17/99 9.4

9/14/99 9.2

Table 8. Observations for which surface-water quality did not meet one or more 

Ohio physical or chemical water-quality standards for the protection of aquatic life 

(sites at which all chemical water-quality standards were met are not listed), in or around 

Youngstown, Ohio —Continued

[

oC, degrees Celsius; DO, dissolved oxygen; mg/L, milligrams per liter]

Site Standard Date Measured value

Ohio standards for temperature and ammonium vary 

with time of year (table 7). The ammonium standard is 

dependent on pH and temperature because the solubility of 

ammonium is controlled by both factors. Furthermore, an 

instantaneous standard and a 30-day average standard are in 

effect for ammonium (table 7). Data for temperature (fig. 8) 

and ammonium (fig. 9) were not, therefore, compared to a 

single-value standard. Value-by-value interpretation indicated that temperatures met State standards in all site categories except for three observations from Mahoning River at 

Youngstown. All measured ammonium concentrations met 

both the instantaneous and 30-day average criteria except 

for one observation from Crab Creek in September 1999; 

this observation met the instantaneous criterion but was 

higher than the 30-day average criterion. Because only one 

sample was collected during September 1999 for ammonium, in a regulatory setting this observation would not be 

considered an exceedance but would be grounds for additional sampling for ammonium concentrations at the site 

(Steve Tuckerman, Ohio Environmental Protection Agency, 

oral commun., 2000).

Waters in the sampling network met State standards 

for the protection of aquatic life in most instances; however, 

current (2002) State standards do not cover nitrate plus 

nitrite or total phosphorus in warmwater habitat. OEPA has 

drafted nutrient criteria for legislative consideration (Robert 

Miltner, Ohio Environmental Protection Agency, written 

commun., 1999). These draft criteria were included for 

comparison in table 7. Boxplots were produced (fig. 9) to 

allow evaluation of measured concentrations against the 

nitrate plus nitrite and total phosphorus draft criteria. 

Data presented in figure 9 indicate that, in general, 

nutrient concentrations did not change from dry-weather 

flow to wet-weather flow in the Mahoning River and Mill 

Creek. Wet-weather flow concentrations may have been 

higher than concentrations measured during dry-weather 

flow in tributaries downstream from overflow sites. Nutrient concentrations in Youngstown WWTP effluent (source 

A) appeared to decrease during wet-weather flow. Mahoning River sites tended to have nitrate plus nitrite and total 

phosphorus concentrations at or near the draft criteria. Mill 

Creek sites, both upstream and downstream from reservoirs, 

tended to have nutrient concentrations in excess of the draft 

criteria. Tributaries tended to have nitrate plus nitrite concentrations lower than the draft criteria but total phosphorus 

concentrations at or above the draft criteria. 

Concentrations of nitrate plus nitrite and total phosphorus increased during wet-weather flow at tributaries 

downstream from overflow sites (Bears Den Run, Crab 

Creek, Cranberry Run); this observation may indicate an 

influence of sewer-overflow discharge on water quality, or it 

may be related to greater urbanization of the watersheds that 

also include sewer-overflow sites (Driver and Tasker, 1990).
28 Water Quality of the Mahoning River and Selected Tributaries in Youngstown, Ohio

Warmwater-habitat use 

The attainment of aquatic-life use designations is determined from three biotic indices: index of biotic integrity 

(IBI), modified index of well-being (MIwb), and invertebrate community index (ICI). A fourth index, the qualitative habitat evaluation index (QHEI), can be used as a 

comparison to evaluate whether nonattainment based on IBI 

or MIwb scores is related to chemical water quality or

availability and quality of physical stream habitat. Criteria 

vary with the surrounding ecoregion and aquatic-life use 

designation of the stream; criteria for the EOLP ecoregion 

warmwater habitat aquatic-life use are presented in table 9. 

The total fish catch for the six sites of the biological 

monitoring network on Mill Creek consisted of 2,343 individuals representing 25 species. Common carp accounted 

for 90 percent of the biomass. Bluntnose minnows, common carp, and green sunfish, all tolerant of anthropogenic 

disturbances, were the dominant species making up 29 percent, 24 percent, and 11 percent of the total fish catch, 

respectively. The reach on Indian Run (reach 20) yielded 

371 fish comprising 16 species and 1 hybrid. The IBI score 

from Indian Run (reach 20), a reach with little or no seweroverflow discharge (fig. 10), is higher than IBI scores for 

any of the Mill Creek reaches. The high IBI score is attributed mostly to the higher number of total species, higher 

number of darter species, and higher percentage of insectivorous individuals within Indian Run. The MIwb cannot be 

calculated in streams that drain less than 32 km2

 (20 mi2); 

therefore, no MIwb score is presented for Indian Run.

Fish-index data (IBI) showed no clear longitudinal 

trend within Mill Creek from upstream to downstream 

despite increased influence from sewer-overflow discharges 

at downstream sites. The IBI scores all fell within the 

OEPA range of “insignificant departure”— 4 or fewer IBI 

points apart from each other (Ohio Environmental Protection Agency, 1987). In other words, a difference of 4 or 

fewer IBI points could be accounted for by expected data 

variability. The IBI and MIwb scores were all associated 

with the fish-community narrative descriptions of “poor to 

very poor.” No reach in the biological monitoring network 

met designated-use criteria on the basis of IBI or MIwb 

scores. 

Nonattainment of designated-use criteria on the basis 

of fish indices was despite QHEI scores that improved in 

Mill Creek from upstream to downstream sites: QHEI 

scores met or exceeded the Ohio Environmental Protection 

Agency (1987) reference value for warmwater-habitat sites 

at all sites except Mill Creek near Calla Road (reach 14), 

where the stream was channelized and lacked riparian vegetation comparable to vegetation at downstream reaches.

The longitudinal comparison of Mill Creek fish and 

habitat indices along a gradient of increasing sewer-overflow discharges (fig. 10) showed no visual relation between 

fish index scores and either habitat quality or sewer-overflow discharge volume. This does not mean that habitat 

quality or sewer-overflow discharge had no effect on aquatic 

life in Mill Creek and Indian Run. The fish and macroinvertebrate communities are depressed in both systems, and further cumulative effects may be difficult to isolate for investigation. Longitudinal improvements to aquatic habitat in 

Mill Creek, as indicated by QHEI scores, may have been 

offset by increasing pressure from corresponding increases 

in annual volumes of sewer-overflow discharge, flow alteration at reservoirs, or other factors. 

QHEI scores indicated that healthier fish communities than those observed should be present in Indian Run and 

the part of Mill Creek within Mill Creek Park. Some other 

limiting factor, possibly nutrient stress or flow alteration at 

reservoirs, may have contributed to nonattainment of biological criteria. As discussed in the previous section, no 

aquatic-life use-designation standards are yet in effect for 

concentrations of nitrate plus nitrite or total phosphorus; 

however, draft criteria have been written (Robert Miltner, 

Ohio Environmental Protection Agency, 1999). Nitrate plus 

nitrite concentrations were well above draft criteria at all 

sites downstream from the Boardman WWTP, and total 

phosphorus concentrations were above draft criteria for all 

sites on Mill Creek (fig. 9). 

ICI values were calculated and compared with warmwater-habitat criteria within the EOLP ecoregion (table 9). 

Observed ICI narrative scores from six of the seven reaches 

corresponded to a “fair” rating. The ICI narrative score of 

the remaining site, Mill Creek downstream from the confluence with Cranberry Run (reach 16), was rated as “good.” 

Mill Creek did not meet the ICI warmwater-habitat criterion 

for most of the network sites and Indian Run (fig. 10). 

Owing to the late collection of qualitative macroinvertebrate 

samples, the ICI scores may have been slightly higher than 

those reported. This potential bias should be kept in mind 

when viewing longitudinal trends in ICI scores for Mill 

Creek. Late collection of the qualitative sample may have 

changed one ICI metric; namely, the total number of qualitative Ephemeroptera, Plecoptera, and Trichoptera (EPT) 

taxa. If the measured scores were substituted with 6, the 

maximum score for this metric, two additional ICI scores 

would have met the warmwater-habitat criteria besides 

reach 16: reach 15, on Mill Creek above Cranberry Run and 

reach 20, on Indian Run (fig. 10). The ICI scores at the 

remaining four sites on Mill Creek would still indicate a 

“fair” narrative rating. 

Reliable longitudinal trend analysis of Mill Creek 

ICI scores was not feasible because of the late collection of 

1 of its 10 metrics. The remaining nine ICI metrics, however, were evaluated individually along a gradient of 

increasing sewer-overflow discharge volumes in Mill Creek. 

The percentage of pollution-sensitive caddisflies was higher 

at upstream sites (reaches 15 (29 percent) and 16 (71 percent)) than at downstream reaches (reaches 18 (6 percent) 

and 19 (3 percent)). The percentage of tolerant organisms 

was highest at the two most downstream reaches (reaches 
Water quality of the Mahoning River and selected tributaries 29

14 13 12 11 10 9 8 7 6 5 43 21

0

20

40

60

80

100

3

5

6

7

8

15

20

25

30

35

40

INDEX OF

BIOTIC INTEGRITY

MODIFIED INDEX OF

WELL-BEING

INVERTEBRATE

COMMUNITY INDEX

SEWER-OVERFLOW

DISCHARGE, IN MILLION

GALLONS PER YEAR

RIVER MILES

0

QUALITATIVE HABITAT

EVALUATION INDEX

4

good very poor

40

30

20

10

poor fair very poor poor

good

50

60

70

80

90

reach 20

reach 19

reach 16

reach 17

reach 18

reach 14

reach 15

reach 14

reach 20

reach 19

reach 18

reach 17

reach 16

BoardmanWastewaterTreatment Plant(unsampled)

Mill Creek Parkborder (landmark)

Newport Lake (unsampled)

Lake Cohasset(unsampled)

Lake Glacier

(unsampled)

BoardmanWastewaterTreatment Plant(unsampled)

Mill Creek Parkborder (landmark)

Newport Lake (unsampled)

Lake Cohasset(unsampled)

Lake Glacier

(unsampled)

reach 15

Ohio Environmental Protection

Agency narrative interpretation

EXPLANATION

Mill Creek reaches Indian Run reach Upstream from reach

Figure 10. Index of biotic integrity, modified index of well-being, and invertebrate community index (average

of two observations) from the biological-index monitoring network during summer 1999. Qualitative habitat

evaluation index (QHEI) and annual discharge volume estimates from sewer-overflow sites are presented for

comparison. A QHEI score above 70 has been demonstrated by OEPA (1987) to support warmwater-habitat

aquatic life.

fair fair

Ohio Environmental Protection Agency Criterion for the

protection of warm-water habitat (criteria listed in table 9)
30 Water Quality of the Mahoning River and Selected Tributaries in Youngstown, Ohio

Table 9. Fish and macroinvertebrate warmwater-habitat biocriteria 

used by the Ohio Environmental Protection Agency (1987)

in the Erie-Ontario Lake Plain ecoregion

Category Index Type

Numeric value for 

criterion 

achievement

Fish Index of biotic integrity, wading sites 38

Modified index of well-being, wading sites 7.9

Macroinvertebrates Invertebrate community index 34

18 (35 percent) and 19 (17 percent)). These results indicated healthier aquatic-macroinvertebrate communities at 

the upstream sites than at the downstream sites.

OEPA collected fish and macroinvertebrates from 

Mill Creek in 1994 (Ohio Environmental Protection 

Agency, 1996). All IBI and MIwb scores and six of eight 

ICI scores from 1994 fell within the narrative range of “very 

poor” to “fair.” similar to results of this investigation. 

OEPA also evaluated a suite of chemical water- and sediment-quality characteristics. Toxic metals were found in 

Mill Creek at above-background levels, adding another possible causative factor for the observed nonattainment of the 

biological criteria.

No improvements in the fish communities of Mill 

Creek are evident between the OEPA observations in 1994 

and this data collection in 1999. It is not possible to estimate how long these communities have been degraded; and, 

barring major changes in the Mill Creek Watershed, the fish 

communities do not have much chance to improve. The 

physical structure of Mill Creek is complex. Three reservoirs and a waterfall on Mill Creek are within the study 

area, all restricting fish movement to upstream areas. Even 

if potential fish stressors such as high pH, low dissolved 

oxygen concentrations, high nutrient concentrations, toxic 

metals in sediment, and sewer-overflow discharges were 

absent from Mill Creek, healthy fish communities may not 

reappear because of restricted movement. Restricted movement is not an issue for the aquatic macroinvertebrates, 

which can fly as adults. Because of the complexity of Mill 

Creek’s physical structure, more data would be needed to 

fully understand the biological communities. This investigation was unable to separate the effects of municipal 

sources from effects of reservoirs and other factors on the 

fish and aquatic-macroinvertebrate communities of Mill 

Creek. 

Effects of sewer-overflow discharges on receivingwater quality

Municipal sources of E. coli, nitrogen, and phosphorus may 

adversely affect the water quality of the Mahoning River 

and Mill Creek. These constituents sometimes exceeded 

concentration-based regulations in the Mahoning River and 

Mill Creek in 1999 and 2000. Establishing a relation 

between impaired surface-water quality and municipal 

sources, however, requires evaluation of discharge volumes 

from municipal sources and estimation of how much those 

discharges can affect surface-water quality. Sewer overflows known to discharge within the city of Youngstown 

release an estimated 5.3 million cubic meters (1,400 Mgal) 

per year to surface water in the study area (Joe Catullo, written commun., 1999). This annual volume would account 

for 2.6 percent of the water volume added to the Mahoning 

River between Niles, Ohio, just upstream from Youngstown 

and Lowellville, Ohio, during water year 1999 (Shindel and 

others, 2000). During the three wet-weather events characterized in this investigation, sewer-overflow discharges contributed 7 to 33 percent of the 24-hour discharge-volume 

increase in the Mahoning River across Youngstown. 

Longitudinal concentration evaluation. Degradation 

of water quality as the Mahoning River passes through 

Youngstown has anecdotally been attributed to contributions 

from Mill Creek, Crab Creek, and the Youngstown WWTP 

to the Mahoning River. Contrary to that viewpoint, results 

of this investigation indicate that, during wet weather, sewer 

overflows were the only sources among those monitored 

that could have substantially increased E. coli concentration 

in the Mahoning River through Youngstown. Although E. 

coli concentrations increased longitudinally in the Mahoning River during dry-weather flow, neither the monitored 

tributaries nor the Youngstown WWTP added high E. coli 

concentrations during dry-weather flow (fig. 7a). Crab 

Creek was the only monitored tributary that contributed to 

the increase in E. coli concentration in the Mahoning River, 
Water quality of the Mahoning River and selected tributaries 31

on the reach between West Avenue (site 2) and Center Street 

(site 3). Concentrations in Crab Creek were not, however, 

high enough to account for the entire increase in concentration at Center Street. 

Similarly, longitudinal assessment of inorganic nitrogen and total phosphorus concentrations (figs. 11 and 12) 

indicated that municipal sources were the only monitored 

inputs contributing higher concentrations of nutrients than 

were present in the main stem. Median nutrient concentrations in effluent from the Youngstown WWTP were considerably higher than those in receiving waters; thus, the 

Youngstown WWTP partially contributed to the nitrogenand phosphorus-concentration increases in the Mahoning 

River during both dry- and wet-weather flow (figs. 11a and 

b and 12a and b). Sewer-overflow nutrient concentrations 

also were higher than receiving-water nutrient concentrations (figs. 11b and 12b). Nutrient concentrations in Mill 

Creek (site 8) and Crab Creek (site 9), the two monitored 

tributaries to the Mahoning River, always were the same as 

or lower than main-stem concentrations (figs. 11a and b and 

12a and b).

In Mill Creek, E. coli concentrations decreased as the 

stream passed through Youngstown (figs. 7c and d) despite 

high-concentration additions from sewer overflows during 

wet-weather flow (fig 7d). Median concentrations of inorganic nitrogen and total phosphorus increased just downstream from the Boardman WWTP, from which water 

samples were not collected, during both dry- and wetweather flow (figs. 11c and d and 12c and d) but then 

declined with passage through the system of reservoirs 

before discharge to the Mahoning River. The Boardman 

WWTP was identified by OEPA as a major source of nutrients to Mill Creek in past studies (Ohio Environmental Protection Agency, 1996). Observed reductions in 

concentration of E. coli, inorganic nitrogen, and total phosphorus as Mill Creek passed through reservoirs complicated 

assessment of sources that may have caused increases in 

constituent concentrations. No tributaries to Mill Creek 

contributed median concentrations of nutrients higher than 

concentrations in the receiving water. During wet-weather 

flow, all sewer overflows contributed discharges that had 

median E. coli, inorganic nitrogen, and total phosphorus 

concentrations higher than median concentrations in the 

receiving water (figs. 7d, 11d, and 12d). Sewer-overflow 

discharges may have countered some of the bacteria- and 

nutrient-removal effects of the reservoirs, but quantification 

of this effect was not possible with the available data.

Concentration data were sufficient to indicate that 

sewer-overflow discharges degraded water quality in the 

Mahoning River and Mill Creek, but the data were insufficient to indicate the extent that observed water-quality problems could be attributed to municipal sources of E. coli and 

nutrients. Both streams did not meet E. coli criteria and 

draft criteria for nitrate plus nitrite and total phosphorus 

during dry weather, when sewer-overflow discharges were 

not active. Exceedances of E. coli criteria were more pronounced during wet-weather flow than during dry-weather 

flow.

Loading-estimate evaluation. This investigation was 

designed to provide basic information describing water 

quality of sewer-overflow discharges for future model simulation. In addition to addressing this design goal, loads of 

constituents carried by sewer-overflow discharges in Youngstown also were estimated. Water-quality measurements 

from seven sewer overflows in Youngstown were used to 

estimate the range of constituent concentrations expected in 

sewer-overflow discharge. The concentrations were used 

to estimate a range of loads—or the total amount of each 

constituent flowing past a site over a period of time—to 

receiving water. 

The load estimate was used to determine how much 

of each constituent entered the Mahoning River in Youngstown during the first 24 hours of wet-weather flow. Seweroverflow discharges were not the only sources of constituent 

loads to the Mahoning River. Other possible sources 

include tributary streams, separate storm sewer discharges 

(as opposed to combined sewer discharges), overland flow, 

effluents from unmonitored WWTPs, and septic-system 

leachates. The estimate of sewer-overflow load calculated 

for this evaluation was not used to estimate the percentage 

of total loads entering the Mahoning River in Youngstown 

that originated with sewer-overflow discharges, nor was it 

taken to be a reliable estimate of the contaminant load leaving Youngstown during wet-weather flow events. 

Sewer overflow loads were compared with surfacewater loads during the first 24-hour interval of wet-weather 

flow to provide some context. The regression plots used to 

estimate E. coli and inorganic nitrogen concentrations at the 

Mahoning River at Youngstown (site 1) and Lowellville 

(site 4) during the three monitored wet-weather events are 

shown in figure 13. Results of the linear regression analysis 

and associated bias correction calculation are presented in 

table 10. Regressions were not statistically significant 

(p>0.1) for total phosphorus relations (data not shown) or 

for inorganic nitrogen at site 1. Loads were not calculated 

in instances where the regression was not significant.

Sewer-overflow discharge is a combination of 

domestic sewage and storm runoff in varying proportions. 

The effect that sewer-overflow discharges have on receiving-water quality depends, in part, on the proportion of 

domestic sewage in the composition of each discharge. 

Concentrations of selected constituents compared with typical values for domestic sewage and storm-runoff water are 

listed in table 11 (Tchobanoglous and Burton, 1991). Data 

in table 11 indicate that constituent concentrations in five of 

the seven sewer-overflow discharges were intermediate 

between weak sewage and storm runoff; however, in the 

other two sewer-overflow discharges (source C and source 

G), concentrations of total suspended solids, chemical oxygen demand, nitrogen, and phosphorus indicated a greater 
32 Water Quality of the Mahoning River and Selected Tributaries in Youngstown, Ohio

12 11 10 9 8 7 6 5 4 3 2 1 0 12 11 10 9 8 7 6 5 4 3 2 0

RIVER MILES RIVER MILES

NITROGEN CONCENTRATION, IN M

0

2

4

24 23 22 21 20 19 18 17 16 15 14 13 12 11 24 23 22 21 20 19 18 17 16 15 14 13 12 11

0

2

4

6

8

NITROGEN CONCENTRATION, IN MILLIGRAMS PER LITER

MAIN-STEM CONSTITUENTS

Ammonium

Nitrate plus nitrite

TRIBUTARY-STREAM CONSTITUENTS

Ammonium

Nitrate plus nitrite

EXPLANATION

MILL CREEK

MUNICIPAL-SOURCE CONSTITUENTS

Ammonium

Nitrate plus nitrite

site 9

1

3

5

site 8

site 1

site 2

site 3

site 4

Campbell Wastewater Treatment Plant (unsampled)

Struthers Wastewater Treatment

Plant (unsampled)

site 9

site 8

site 1

site 2

site 3

site 4

Campbell Wastewater Treatment Plant (unsampled)

Struthers Wastewater Treatment

Plant (unsampled)

source B

source E so

source 

Dry-weather flow

C

Wet-weather flow

D

1

3

5

7

site 5

site 10

Boardman Wastewater Treatment Plant (unsampled)

Mill Creek Park border (landmark)

site 11

site 6

site 7

site 12

site 13

site 8

Newport Lake (unsampled)

Lake Cohasset (unsampled)

Lake Glacier (unsampled)

site 10

site 11

site 6

site 7

site 12

site 13

source F

source G

source H

Boardman Wastewater Treatment Plant (unsampled)

Mill Creek Park border (landmark)

Newport Lake (unsampled)

Lake Cohasset (unsampled)

Lake Glacier (unsampled)

site 8

1

Figure 11. Nitrogen-form concentrations in the Mahoning River and Mill Creek, Ohio, parts of the

water-quality monitoring network during dry-weather flow (1999) and wet-weather flow (1999 and 2000). site 5
Water quality of the Mahoning River and selected tributaries 33

site 1

site 8

site 2

site 9 

site 3

site 4

Campbell Wastewater Treatm

Struthers Wastewater Treatm

site 1

source B

site 8

site 2

ov

source A

site 9

site 3

Campbell Wastewater Treatm

Struthers Wastewater Treatm

site 4

24 23 22 21 20 19 18 17 16 15 14 13 12 11 24 23 22 21 20 19 18 17 16 15 14 13 12 11 

0

1

PHOSPHORUS CONCENTRA

12 11 10 9 8 7 6 5 4 3 2 1 0 12 11 10 9 8 7 6 5 4 3 2 1 0

RIVER MILES

Dry-weather flow

C

RIVER MILES

0

2

4

5

PHOSPHORUS CONCENTRATION, IN MILLIGRAMS PER LITER

MILL CREEK

1

3

site 5

Boardman Wastewater Treatment Plant (unsampled)

site 10

site 11

Newport Lake (unsampled)

Lake Cohasset (unsampled)

site 12

Lake Glacier (unsampled)

site 13

site 7

Mill Creek Park border (landmark)

site 6

site 8

site 5

Boardman Wastewater Treatment Plant (unsampled)

site 10

site 6

site 11

Newport Lake (unsampled)

Lake Cohasset (unsampled)

source F

site 7

site 12

site 13 source G

Lake Glacier (unsampled)

source H

site 8

Mill Creek Park border (landmark)

Wet-weather flow

D

TOTAL PHOSPHORUS IN

EXPLANATION

municipal sources

tributary streams

main stream

Figure 12. Total phosphorus concentrations in the Mahoning River and Mill Creek, Ohio, parts of the

water-quality monitoring network during dry-weather flow (1999) and wet-weather flow (1999 and 2000).
34 Water Quality of the Mahoning River and Selected Tributaries in Youngstown, Ohio

50,000

10,000

1,000

100

10

1

2

3

ESCHERICHIA COLI,

IN COLONY-FORMING UNITS

PER 100 MILLILITERS

DISSOLVED INORGANIC NITROGEN,

IN MILLIGRAMS PER LITER

200 1,000 3,000

FLOW, IN CUBIC FEET PER SECOND

Mahoning River at Youngstown

Mahoning River at Lowellville

Linear fit at Youngstown

Linear fit at Lowellville

Figure 13. Data and regression lines used to estimate Escherichia coli and inorganic nitrogen

concentrations at two sites on the Mahoning River, Ohio, during three wet-weather flow events in 2000.

All data were collected during 1999 and 2000.

amount of domestic sewage than in the other five. Comparison with stormwater-quality data collected in an urban 

stormwater-quality report from Wisconsin (Bannerman and 

others, 1996) also indicated that Youngstown sewer-overflow discharge carries increased sewage relative to stormwater. 

A range of concentrations for each constituent was 

observed among the seven sewer overflows. Within each 

source, proportions of constituents also differed (table 11). 

This variability means that use of a single concentration 

value to represent all 101 sewer-overflows could result in 

misleading conclusions. Therefore, loads were estimated by 

means of a range of values: sewer-overflow load calculations were computed from the minimum, median, and maximum concentrations for the seven monitored sewer 

overflows from the total of 19 samples collected. Seweroverflow discharge volumes and loads of E. coli and inorganic nitrogen (ammonium, nitrate, and nitrite), along with 

estimates of stream-carried loads entering Youngstown (site 

1) and downstream from Youngstown (site 4), are listed in 

table 12. Inorganic nitrogen forms were considered as a 

group because ammonium can change to nitrate and back 

over a period of hours (Peterson and others, 2001). 

The volume of sewer-overflow discharge to the 

Mahoning River during the first 24 hours of the three monitored wet-weather events contributed 3 to 14 percent of the 

24-hour discharge passing Lowellville (site 4) and 7 to 33 

percent of the increase in discharge between sites 1 and 4 

(table 12). The 24-hour load of E. coli contributed by sewer 

overflows, from 52 to 8,400 x 1012 CFU (depending on 

event and full range of concentration estimates), dwarfed 

the 24-hour loads of E. coli estimated to enter Youngstown 

(2 to 66 x 1012 CFU) and to pass site 4 (12 to 230 x 1012

CFU). On the other hand, loads of inorganic nitrogen added 

by sewer-overflow discharge in Youngstown (63 to 4,200 

kg, depending on event and full range of concentration estimates) were always substantially smaller than the loads estimated to pass site 4 (3,200 to 5,200.) Sewer-overflow 

discharges appeared to have a much greater effect on bacterial than on nitrogen-assessed water quality. In contrast, the
Water quality of the Mahoning River and selected tributaries 35

Table 10. Linear regression analysis results for the relation between log-transformed flow and logtransformed concentration of Escherichia coli and inorganic nitrogen at two sites on the Mahoning River

[r, Pearson’s correlation coefficient; p, significance probability; CFU/100 mL, colony-forming units per 100 milliliters; mg/L, milligrams per liter; 

<, less than; >, greater than]

Constituent Y-intercept Slope r p Bias factor

Mahoning River at Youngstown (site 1)

E. coli (CFU/100 mL) -6.95 3.47 0.82 <0.0001 1.50

Inorganic nitrogen (mg/L) 1.17 -.371 .61 >.1 1.01

Mahoning River at Lowellville (site 4)

E. coli (CFU/100 mL) -4.37 2.70 .83 <.0001 1.42

Inorganic nitrogen (mg/L) 4.69 -1.32 .94 .0002 1.00

Youngstown WWTP appeared to have a greater effect on 

nitrogen loads than bacterial loads (table 12).

The timing of sewer-overflow discharges is critical in 

evaluating the effects of sewer-overflow discharges on water 

quality in Youngstown. Wet-weather-flow hydrographs at 

the Mahoning River at Youngstown (site 1), the Mahoning 

River at West Avenue (site 2), and the Mahoning River at 

Lowellville (site 4) were superimposed on summed XPSWMM-simulated flow from all sewer-overflow discharges 

in Youngstown (fig. 14). Peak flow at sites 2 and 4 did not 

lag behind peak flow at site 1 as would be expected but 

rather preceded peak flow at site 1 by 2 to 6 hours during all 

three wet-weather flow events. Modeled sewer-overflow 

discharges preceded peak flows at all three surface-water 

sites. The amount of flow coming from all of the seweroverflow discharges was enough to partially account for the 

accelerated timing of peak flow at sites 2 and 4. 

Sewer-overflow sites, which were distributed 

throughout the watershed and had asynchronous discharge, 

were not expected to act as a single discharge to the Mahoning River. Other factors that could have affected the timing 

of peak flows include local runoff, rainwater discharge 

through separate storm sewers, discharges from tributary 

streams, and differences in rainfall at different areas of the 

watershed. For a short time on the rising limb of the 

hydrograph, sewer-overflow discharge could be a large 

component of streamflow in Youngstown (fig. 14).

Timing of sample collection at the three water-quality monitoring sites is also depicted in figure 14. Water samples 

were collected on the falling limb of the hydrograph during 

all three events and probably reflected only residual effects 

of sewer-overflow discharges. This hypothesis is consistent 

with E. coli data in table 11. The 24-hour load estimate at 

site 4 was always much lower than the estimate of seweroverflow load entering the Mahoning River in Youngstown. If the slug of sewer-overflow discharge was not 

present at Lowellville at the time of sample collection, then 

the regression analysis presented in figure 13 and table 10 

would not be representative of concentrations when the 

major flow of sewer-overflow discharge was present. As a 

result, the load of constituents contributed by sewer-overflow discharge probably was not included in 24-hour load 

estimates at Lowellville (table 12). In-stream processes such 

as deposition, E. coli die-off, and conversion of inorganic 

nitrogen to gaseous or organic forms also may have prevented some of the sewer-overflow discharge loads to the 

Mahoning River in Youngstown from ever reaching the 

Lowellville station. 

Alternate indicators of fecal contamination. E. coli 

is used as a surrogate indicator for fecal contamination from 

warmblooded animals. Alternate indicators also were monitored in an independent attempt to assess fecal contamination in the sampling network. Comparison of 

concentrations in municipal-source discharges with surfacewater concentrations was used to infer whether fecal loading was related to domestic sewage entering the stream 

(municipal sources) or diffuse loading from multiple 

sources with runoff. The three alternate indicators evaluated were coliphage, C. perfringens, and caffeine. Mill 

Creek and its tributaries were sampled for coliphage and C. 

perfringens, and the entire sampling network was sampled 

for caffeine.

Coliphage and C. perfringens have been proposed as 

better surrogates than E. coli for certain pathogens (Rose and 

Grimes, 2001). F-specific coliphage are RNA-based viruses, 

like the waterborne pathogens hepatitis A, coxsackievirus, 

Norwalk virus, and poliovirus. Viruses have different survival characteristics from bacteria in the environment, so 

F-specific coliphage may be a better indicator of humanhealth risk from viral pathogens than E. coli. 
36 Water Quality of the Mahoning River and Selected Tributaries in Youngstown, Ohio

† - E. coli is one species in the total coliform group; therefore, E. coli concentrations are lower than total coliform concentrations in the same amount of raw 

Table 11. Sewer-overflow discharge characteristics observed in and around Youngstown, Ohio, and published chara

and stormwater runoff

[Sewage and runoff data adapted from Tchobanoglous and Burton, 1991; TDS, total dissolved solids; mg/L, milligrams per liter; -- , no data available; TSS, tota

carbonaceous biochemical oxygen demand; COD, chemical oxygen demand; N, nitrogen; CFU/100 mL, colony-forming units per 100 milliliters]

Constituent Units

Sewage Median values, this study

Strong Weak Source B Source C Source D Source E Source F Sour

TDS mg/L 850 250 -- -- -- -- 149 208 TSS mg/L 350 100 170 244 131 154 234 364 cBOD5 mg/L 400 110 9 53 17 27 13 31 COD mg/L 1,000 250 58 300 144 130 84 320 Organic N mg/L 35 8 2.3 4.92 3.12 4.25 2.21 14.Ammonium mg/L 50 12 .28 6.1 2.9 1.1 1.2 4.Nitrate plus nitrite mg/L 0 0 .81 1.98 2.05 .72 1.49 1.Total N mg/L 85 20 3.4 13.0 8.11 6.02 4.89 20.Organic P mg/L 5 1 .61 1.22 1.57 1.03 0.31 3.Orthophosphate mg/L 10 3 .13 .75 .61 .16 .20 .Total P mg/L 15 4 .74 1.96 2.21 1.19 0.51 4.Chloride mg/L 100 30 -- -- -- -- 19 28 Sulfate mg/L 20 50 -- -- -- -- 26.5 44.Total coliforms CFU/100-mL 107-109 106-107 -- -- -- -- -- -- Escherichia coli† CFU/100-mL -- -- 4.6x105 9.0 x105 5.9 x105 5.2 x105 3.8 x105 1.
Water quality of the Mahoning River and selected tributaries 37

Table 12. Twenty-four-hour discharge volumes, loads of Escherichia coli, discharge-weighted average 

concentrations of E. coli, and loads of inorganic nitrogen (nitrite plus nitrate and ammonium) at two surface-water 

sites and all modeled sewer-overflow discharges in and around Youngstown, Ohio, during three events in 2000

[WWTP, wastewater-treatment plant; CFU/100, colony-forming units per 100 milliliters; kg, kilogram; NA, not applicable; DWA, discharge-weighted 

average concentration]

Discharge, load, or 

concentration

Mahoning River 

at Youngstown 

(site 1)

Mahoning River 

at Lowellville 

(site 4)

Youngstown 

WWTP 

(source A)

All sewer-overflow discharges

Minimum Median Maximum

August 6-7, 2000 

Discharge volume (106 liters) 2,100 3,700 160 530

E. coli (1012 CFU) 66 230 18 470 1,800 8,400

E. coli (CFU/100 mL, DWA) 3,100 6,200 11,000 90,000† 350,000 1,600,000

Inorganic nitrogen (kg) NA 5,200 1,100 570 2,100 4,200

September 20-21, 2000

Discharge volume (106 liters) 1,000 1,700 130 140

E. coli (1012 CFU) 2.0 12 0.34 130 500 2,300

E. coli (CFU/100 mL, DWA) 200 710 260 90,000 350,000 1,600,000

Inorganic nitrogen (kg) NA 3,200 860 160 580 1,200

 October 5-6, 2000 

Discharge volume (106 liters) 1,400 2,200 150 58

E. coli (1012 CFU) 9.6 40 18 52 200 930

E. coli (CFU/100 mL, DWA) 690 1,800 12,000 90,000 350,000 1,600,000

Inorganic nitrogen (kg) NA 3,800 960 63 240 470

Similarly, C. perfringens is an endospore-forming 

bacterium, and endospores have similar survival characteristics to cysts and oocysts. Cysts and oocysts are resistant 

forms of protozoa that can survive chlorination by routine 

sewage-treatment processes. The survival characteristics of 

cyst- and oocyst-forming pathogens like Giardia lamblia

and Cryptosporidium parvum may be better approximated 

by endospore-forming bacteria like C. perfringens than by 

bacteria like E. coli that do not form resistant endospores 

(Sorensen and others, 1989). Caffeine generally is associated with human waste; thus, caffeine might be effective as 

a general, chemical indicator of human-origin wastewater.

Results for concentrations of alternate indicators of 

fecal pollution are summarized as boxplots in figure 15. 

F-specific coliphage were not detected in surface waters 

except during wet-weather events (fig. 15) but were present 

in most WWTP and overflow samples. Sewer-overflow discharges were, therefore, sources of fecal-origin coliphage 

viruses to Mill Creek during wet-weather flow. Although 

the Boardman WWTP effluent was not sampled it is likely, 

because the Youngstown WWTP effluent carried coliphage, 

that the Boardman WWTP effluent also contributed viruses 

of fecal origin to Mill Creek. Viruses were not detected during dry weather downstream from Boardman WWTP, possibly because of die-off and settling during residence time in 

Newport Lake. 

Unlike coliphage concentrations, C. perfringens

endospore concentrations did not increase consistently with 

wet-weather flow despite the observation that C. perfringens concentrations were higher in municipal-source discharges than in surface water (fig. 15). C. perfringens was 

also detected in tributary streams upstream from any municipal source. Municipal sources were, therefore, not the sole 

source of C. perfringens to Mill Creek.

The primary source of caffeine to streamflow during 

dry-weather flow was assumed to be sanitary discharge 
38 Water Quality of the Mahoning River and Selected Tributaries in Youngstown, Ohio

0

500

1,000

1,500

2,000

2,500

0

200

400

600

800

1,000

0

200

400

600

800

1,000

1,200

0900 NOON 1500 1800 2100 MIDNIGHT0300

At Lowellville

Below West Avenue

At Youngstown

Figure 14. Streamflow and sample collection times for three sites on the Mahoning River, plotted

with modeled cumulative sewer-overflow discharge in Youngstown, Ohio, over the first 24-hour

interval of three wet-weather flow events.

AUGUST 6, 2000 AUGUST 7, 2000

SEPTEMBER 9, 2000 SEPTEMBER 10, 2000

OCTOBER 5, 2000 OCTOBER 6, 2000

MIDNIGHT

0300 0600 0900 NOON 1500 1800

At Lowellville

Below West Avenue

At Youngstown

2100 MIDNIGHT0300 0600 0900 NOON 1500

At Lowellville

Below West Avenue

At Youngstown

Sample collected

Sewer-overflow discharge

from model XP-SWMM

FLOW, IN CUBIC FEET PER SECOND

1800
Water quality of the Mahoning River and selected tributaries 39

100

101

102

103

104

MAIN STEMS TRIBUTARIES MUNICIPAL SOURCES

4

5

2

7

3

8

4

7

4

8

4

Mill Creek wastewatertreatment Plant

overflows

downstream

from reservoirs

upstream

from reservoirs

upstream

from

overflow

sites

downstream

from

overflow

sites

105

100

101

102

103

104

105

5 5 2

8

4

7 3 7 4

8 4

100

101

102

103

0

1 1

8

2

12

3

7

1

8

11 2

4

CAFFEINE,

IN MICROGRAMS PER LITER

Dry Wet Dry Wet Dry Wet Dry Wet Dry Wet Dry Wet Wet

F-SPECIFIC COLIPHAGE,

IN PLAQUES PER 100 MILLILITERS

C. PERFRINGENS SPORES

AND CELLS, IN COLONY-FORMING

UNITS PER 100 MILLILITERS

Mahoning

River

EXPLANATION

8 Number of observations

95th percentile

75th percentile

Median (50th percentile)

25th percentile

5th percentile

Dry

Wet

Flow categories:

dry weather, 1999

wet weather, 1999 and 2000

FLOW CATAGORIES

Figure 15. Concentrations of alternate indicators of fecal pollution by site type, relative location,

and flow category for summer 1999 and 2000 in Mahoning River and selected tributaries

and sources, Ohio.

0 0

0 0

4 Number of observations

Data point
40 Water Quality of the Mahoning River and Selected Tributaries in Youngstown, Ohio

(septic-field leachate and WWTP effluents); during wetweather flow, additional sources may have included runoff 

from discarded beverages and leachate from other garbage 

in addition to increased septic-system and sewer-overflow 

discharges. Caffeine was detected in all samples analyzed. 

The small number of samples analyzed made it impossible 

to say with certainty whether wet-weather flow had any 

effect on caffeine concentrations. Caffeine concentrations 

were not obtained for sewer-overflow discharges. Data 

indicate that waste of human origin was present in the monitoring network during wet-weather and dry-weather flow 

(fig. 15). Even tributaries without sewer-overflow sites 

upstream seemed to be affected by domestic sewage. The 

presence of caffeine is not incontrovertible evidence of contamination by domestic sewage, given that caffeine can 

originate from sources other than human feces and urine 

(Seiler and others, 1999).

Summary and Conclusions

Degraded water quality has historically been a widespread 

problem in the Mahoning River Watershed in and around 

Youngstown, Ohio. In 1999, the U.S. Geological Survey 

(USGS), in cooperation with the city of Youngstown and in 

collaboration with ms consultants, inc., began a study to 

investigate the effects of sewer-overflow discharges within 

Youngstown on water quality of the Mahoning River. This 

report describes surface-water quality of a monitoring network in the area around Youngstown during dry- and wetweather flow in 1999 and 2000 and discusses when, where, 

and for how long water quality was affected by sewer-overflow discharges. Results of sewer-overflow measurements 

are presented to provide baseline information about seweroverflow discharges and a measure of the affects of seweroverflow discharges on surface-water quality within the network.

Areas of nonattainment

The Mahoning River, Mill Creek, and other tributaries in the 

study area did not meet designated-use criteria as warmwater habitat within the Erie-Ontario Lake Plains ecoregion, as 

primary-contact recreational waters, or both. Nonattainment of designated-use regulations resulted from from 

E. coli concentrations above State standards (all monitored 

streams) and low biotic index scores (Mill Creek and Indian 

Run). Chemical water quality (pH, dissolved oxygen concentration, temperature, and ammonium) frequently met 

standards; but 46 of 71 samples (65 percent) from the 

Mahoning River and Mill Creek did not meet draft criteria 

for nitrate plus nitrite concentrations, and 58 of 63 samples 

(92 percent) did not meet draft criteria for total phosphorus 

concentrations. Crab Creek (tributary to the Mahoning 

River) and Indian Run, Cranberry Run, Ax Factory Run, 

and Bears Den Run (tributary to Mill Creek) did not meet 

draft criteria for nitrate plus nitrite concentrations in 1 of 44 

samples (2 percent) and the draft total phosphate concentration criterion in 25 of 44 samples (57 percent).

Mahoning River water entering Youngstown had 

lower concentrations of nutrients and bacteria than Mahoning River water entering Lowellville after passage through 

the urban areas of Youngstown, Campbell, and Struthers. 

Mill Creek water entering Youngstown (site 5) had a similar 

concentration of E. coli and lower concentrations of nutrients than Mill Creek just downstream from Boardman 

WWTP (site 6). Within Mill Creek Park (sites 7, 8, and 9), 

processes such as settling, inactivation, and transformation 

—as well as dilution by tributary streams and other water 

sources—had the net effect of decreasing E. coli and nutrient concentrations by the time water reached the Mahoning 

River. Water quality deteriorated in the Mahoning River as 

it passed through Youngstown, but water quality improved 

in Mill Creek as it passed through Mill Creek Park in 

Youngstown.

Timing of nonattainment

Wet-weather flow was associated with changes in water 

quality within the sampling network. Concentrations of 

E. coli were greater throughout the sampling network during wet-weather flow than during dry-weather flow. 

Increases in E. coli concentrations contrasted with increased 

attainment of standards for pH, dissolved oxygen, and temperature during wet-weather flow. Nutrient concentrations 

remained virtually unchanged during wet-weather flow 

compared with dry-weather flow in the Mahoning River and 

Mill Creek. Nitrogen concentrations also remained similar 

during wet-weather flow compared to dry-weather flow in 

tributary streams. Tributary streams met draft total phosphate concentration criterion in all but 1 of 9 samples (11 

percent) during dry-weather flow but did not meet the criterion in 24 of 35 samples (69 percent) during wet-weather 

flow.

Duration of nonattainment

Microbiological water quality during wet-weather flow was 

assessed over time to see whether increases in E. coli concentrations would last for more than 48 hours. E. coli

remained elevated in Mill Creek and most tributaries for 

over 48 hours after moderate (less than 2-year floodflow) 

wet-weather flow events but returned to near dry-weather 

flow concentrations within 48 hours in the Mahoning River 

and Indian Run. Duration of water-quality changes was not 

assessed for other properties and constituents.
References 41

Effect of sewer-overflow discharges

Three avenues of analysis were followed to evaluate the 

effects of sewer overflows on water quality in the monitoring network. First, concentrations in municipal-source discharges were compared with longitudinal concentration 

trends from upstream to downstream sites in both the 

Mahoning River and Mill Creek. Second, the range of 

sewer-overflow discharge concentrations was compiled and 

used for a load-based evaluation of the degree to which constituents in sewer-overflow discharges affected water quality in receiving waters. Third, alternate indicators of fecal 

pollution were used to evaluate whether an effect by seweroverflow discharges was detectable.

Concentration data indicated that contributions of 

E. coli and nutrients by tributary streams did not increase 

concentrations of E. coli and nutrients in the Mahoning 

River. The exception was Crab Creek, which had higher 

concentrations of E. coli than did the Mahoning River during wet-weather flow. Streams tributary to Mill Creek carried E. coli concentrations similar to concentrations in Mill 

Creek and, as such, dilution by tributary streams does not 

account for the observed decline in E. coli concentrations as 

Mill Creek passed through Mill Creek Park. The decline in 

nutrient concentrations in Mill Creek, however, may have 

been caused partially by dilution with tributary streamflow 

because tributary streams had lower nutrient concentrations. 

Municipal sources (sewer-overflow discharges and 

WWTP effluent) generally were the only monitored sources 

of E. coli, nitrogen, and phosphorus that could have contributed to concentration increases in receiving waters during 

wet-weather flow. This investigation was limited in its 

capacity to measure sources of bacteria and nutrients other 

than sewer-overflow discharges and WWTP effluent.

The magnitude of the effects of sewer-overflow loading on receiving-water quality was evaluated for the Mahoning River entering Youngstown (site 1) and downstream 

from Youngstown (site 4). The range of probable E. coli

loads to the Mahoning River through Youngstown from 

sewer overflows was wide but indicated that sewer-overflow 

discharges probably had a major effect on bacterial water 

quality in the Mahoning River during limited times while 

discharges occurred. Loading estimates for inorganic nitrogen indicated that sewer-overflow discharges had a lesser 

effect on nutrient water quality than on bacterial water quality but that sewer-overflow discharges added a substantial 

nutrient load relative to the estimated 24-hour load at site 4. 

The magnitude of sewer-overflow discharge effects on surface-water quality could not be detected directly because of 

the timing of sample collection.

Alternate indicators of fecal contamination provided 

some additional information about fecal loading by sewer 

overflows. Patterns of F-specific coliphage detection indicated a risk of human-pathogenic viruses in surface water 

during wet-weather flow from sewer-overflow discharges 

and WWTP effluent. Patterns of C. perfringens and caffeine concentrations, on the other hand, indicated a background of C. perfringens and human-origin contamination 

(either sewage or septic leachate) in the monitoring network 

during both wet- and dry-weather flow that was independent 

of Youngstown sewer-overflow and WWTP discharges.

Sewer-overflow discharges contributed to streamflow 

and to bacterial and nutrient loads carried by the Mahoning 

River in Youngstown, Ohio; however, sewer-overflow discharges were not the only factor affecting water quality in 

the area. Improvement of water quality in the lower reaches 

of the Mahoning River and Mill Creek to the point that each 

water body meets its designated-use criteria will likely 

require an integrated approach that includes not only abatement of sewer-overflow loadings but also identification and 

remediation of other loadings within Youngstown and 

improvement of water quality entering Youngstown.

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545 p.

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C.M., 2001, Quality assurance, quality control manual, 

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340 km of the Wabash River: Purdue University Water 

Resources Research Center Technical Report 86, 73 p.

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for coliphage detection based on β-galactosidase 

induction: Journal of Virological Methods, v. 40, 

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42 Water Quality of the Mahoning River and Selected Tributaries in Youngstown, Ohio

Karr, J.R., 1981, Assessment of biotic integrity using fish 

communities: Fisheries, v. 6, p. 21-27.

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Conservation Service), 124 p.

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http://www.cboss.com/millcreek/

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Standardized biological field sampling and laboratory 

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44 Water Quality of the Mahoning River and Selected Tributaries in Youngstown, Ohio Appendix A1 Appendix A. Additional water-quality data from sewer-overflow discharges, calendar year January 2000 to De

Ohio [mg/L, milligrams per liter; CaCO3, calcium carbonate; --, no data; <, concentration or value reported is less than indicated; E, estimated value] DATE TIME BOD OXYGEN DEMAND, BIOCHEM CARBON. 5 DAY (mg/L) OXYGEN DEMAND, CHEMICAL (HIGH LEVEL) (mg/L) RESIDUE TOTAL AT 105 DEG. C SUSPENDED (mg/L) SOLIDS, RESID

AT 180 DEG 

DISSOLVED (mg/L) 

Overflow at Waverly Ave. and Greenwood Ave. (Source B) AUG 6 1132 9.4 58 190 -- 

SEP 21 1055 6.3 -- 205 -- 

OCT 6 0210 -- 11 -- 104 

Overflow at Salt Springs Price Rd. at Youngstown (Source C) AUG 6 1035 32 -- 305 -- 

SEP 21 1115 59 -- 274 -- 

OCT 5 2300 69 300 153 -- 

Overflow east of Poland Ave and south of Center (Source D) AUG 6 0835 16 -- 307 -- 

AUG 6 1035 18 89 82 -- 

AUG 24 0220 -- 59 -- -- 

SEP 21 1030 E13 -- 164 -- 

OCT 5 2030 24 370 100 -- OCT 6 2300 15 58 <5 -- 

Overflow at McGuffey Rd and Willow St. (Source E)

AUG 6 0835 27 130 154 -- 

Overflow at Park Dr. near Kiawatha Dr at Youngstown, Ohio (Source F)

AUG 6 1056 13 -- 234 -- 
Appendix A1 45

 AUG 24 0300 -- 84 -- 149 

Overflow at Lilly Pond at Mill Creek Park (Source G)

AUG 6 0721 31 320 364 208 

Overflow at intersection of Price and Halls Heights (Source H)

AUG 6 1230 11 53 110 308 

AUG 24 0315 -- 68 -- 190 

OCT 6 2300 9.3 63 88 172 

Appendix A. Additional water-quality data from sewer-overflow discharges, calendar year January 2000 to DeceOhio —Continued[mg/L, milligrams per liter; CaCO3, calcium carbonate; --, no data; <, concentration or value reported is less than indicated; E, estimated value]

DATE TIME

BOD

OXYGEN DEMAND,

BIOCHEM CARBON.

5 DAY

(mg/L)

OXYGEN DEMAND,

CHEMICAL

(HIGH LEVEL)

(mg/L)

RESIDUE TOTAL

AT 105 DEG. C

SUSPENDED

(mg/L)

SOLIDS, RESIDU

AT 180 DEG C

DISSOLVED

(mg/L)