U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2007–1171 

In cooperation with the Northeast Ohio Regional Sewer District

Escherichia coli Concentrations in the Mill Creek 

Watershed, Cleveland, Ohio, 2001–2004 
Cover.  Mill Creek in Garfield Heights, Ohio. Photograph by Bernie Sroka, U.S. Geological Survey. 
Escherichia coli Concentrations in the 

Mill Creek Watershed, Cleveland, Ohio, 

2001–2004 

By Amie M.G. Brady

In cooperation with the Northeast Ohio Regional Sewer District

Open-File Report 2007–1171

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

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Suggested citation:

Brady, A.M.G., 2007, Escherichia coli concentrations in the Mill Creek watershed, Cleveland, Ohio, 2001–2004: 

U.S. Geological Survey Open-File Report 2007–1171, 26 p. 
iii

Contents

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

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

Purpose and Scope ..............................................................................................................................3

Description of Study Area ...................................................................................................................3

Sewage-Collection-System Modifications.......................................................................................3

Methods of Study...........................................................................................................................................4

Sampling Procedures and Microbiological Methods.....................................................................4

Water-Quality and Ancillary Environmental Information ...............................................................4

Quality Assurance and Quality Control .............................................................................................4

Routine Sampling...........................................................................................................................................5

Streamflow and Rainfall Characteristics..........................................................................................5

Relation of Concentrations of Escherichia coli to Streamflow and Precipitation .....................6

Relation of Concentrations of Escherichia coli to Modifications of the

Sewage-Collection System ...................................................................................................8

Rainfall-Event Sampling................................................................................................................................9

Summary........................................................................................................................................................12

Acknowledgments.......................................................................................................................................12

References Cited..........................................................................................................................................12

Appendix 1.  Variability of Escherichia coli concentrations in Mill Creek, Garfield Heights,

Ohio, August 2001–September 2004............................................................................................22

Figures

1.  Map showing location of the study area in northeast Ohio, showing all combinedsewer overflows present before sewage-collection system improvements .....................2

2–8. Graphs showing:

2.  Instantaneous streamflows near the mouth of Mill Creek, Garfield Heights,

Ohio, August 2001–September 2004, as related to period of sewagecollection-system modification .........................................................................................5

3.  Distribution of Escherichia coli concentrations for routine samples collected

near U.S. Geological Survey stream gage 04208460, Mill Creek, Garfield

Heights, Ohio, August 2001–September 2004....................................................................

4.  Distribution of Escherichia coli concentrations as a function of four ranges

of instantaneous streamflow during routine sampling near U.S. Geological

Survey stream gage 04208460, Mill Creek, Garfield Heights, Ohio,

August 2001–September 2004............................................................................................7

5.  Distribution of Escherichia coli concentrations in routine samples collected

near U.S. Geological Survey stream gage 04208460, Mill Creek, Garfield

Heights, Ohio, when there was no precipitation and when precipitation fell in

the 24-hour period prior to 9 a.m. on the day of sampling,

August 2001–September 2004 ..............................................................................................8

6.  Distribution of Escherichia coli concentrations in routine samples collected

near U.S. Geological Survey stream gage 04208460, Mill Creek, Garfield

Heights, Ohio, during modification periods in the Mill Creek watershed,

August 2001–September 2004............................................................................................9

7.  Scatterplot of instantaneous discharges of Escherichia coli against

instantaneous streamflow before and during modifications to the

sewage-collection system in the Mill Creek watershed, Cleveland, Ohio,

August 2001–September 2004..........................................................................................10
iv

8.  Distribution of Escherichia coli concentrations, instantaneous streamflow,

and precipitation for rainfall event samples collected near U.S. Geological

Survey stream gage 04208460, Mill Creek, Garfield Heights, Ohio............................11

1–1.  Graph showing absolute value of the percent difference (log10-transformed data)

between quality-control replicate samples for concentrations of Escherichia coli

in Mill Creek, Garfield Heights, Ohio, August 2001–September 2004.................................26

Tables

1.  Streamflow, water-quality, and microbiological data for samples collected in

Mill Creek, Garfield Heights, Ohio, August 2001–September 2004 .....................................15

2.  Streamflow and precipitation statistics for sewage-collection-system modification

periods, Mill Creek watershed, Cleveland, Ohio, August 2001–September 2004.............20

1–1.  Quality-control data for Escherichia coli concentrations in water samples collected

in Mill Creek, Garfield Heights, Ohio, August 2001–September 2004, and analyzed by

the Northeast Ohio Regional Sewer District and the U.S. Geological Survey .................23

1–2.  Summary statistics for the percent differences (absolute value of the percent

difference of the log10-transformed data) for within-bottle and between-bottle

comparisons of replicate quality-control samples for concentrations of

Escherichia coli in Mill Creek, Garfield Heights, Ohio, August 2001–

September 2004...........................................................................................................................26

Conversion Factors

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2

) 2.590 square kilometer (km2) 

Volume

liter (L) 0.2642 gallon (gal) 

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

)

Flow rate

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

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

°F=(1.8×°C)+32

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

°C=(°F-32)/1.8

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at

25°C).

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

micrograms per liter (μg/L).

Concentrations of bacteria in water are given in colony-forming units per 100 milliliters

(CFU/100 mL).

Instantaneous discharges are given in colony-forming units of Escherichia coli per second (CFU/s). 
Abstract

Mill Creek in Cleveland, Ohio, receives discharges from 

combined-sewer overflows (CSOs) and other sanitary-sewage 

inputs. These discharges affect the water quality of the creek 

and that of its receiving stream, the Cuyahoga River. In an 

effort to mitigate this problem, the Northeast Ohio Regional 

Sewer District implemented a project to eliminate or control 

(by reducing the number of overflows) all of the CSOs in the 

Mill Creek watershed. This study focused on monitoring the 

microbiological water quality of the creek before and during 

sewage-collection system modifications.

Routine samples were collected semimonthly from 

August 2001 through September 2004 at a site near a 

U.S. Geological Survey stream gage near the mouth of Mill 

Creek. In addition, event samples were collected September 19 

and 22, 2003, when rainfall accumulations were 0.5 inches (in.) or greater. Concentrations of Escherichia coli (E. coli) 

were determined and instantaneous discharges were calculated. Streamflow and water-quality characteristics were measured at the time of sampling, and precipitation data measured 

at a nearby precipitation gage were obtained from the National 

Oceanic and Atmospheric Administration. 

Concentrations of E. coli were greater than Ohio’s singlesample maximum for primary-contact recreation (298 colonyforming units per 100 milliliters (CFU/100 mL)) in 84 percent 

of the routine samples collected. In all but one routine sample, 

E. coli concentrations in samples collected when instantaneous 

streamflows were greater than 20 cubic feet per second (ft3/s) 

were greater than Ohio’s single-sample maximum. When precipitation occurred in the 24-hour period before routine sample 

collection, concentrations were greater than the maximum in 

89 percent of the samples as compared to 73 percent when 

rainfall was absent during the 24 hours prior to routine sample 

collection.

Before modifications to the sewage-collection system in the watershed began, E. coli concentrations in Mill 

Creek ranged from 220 to 29,000 CFU/100 mL. After major 

modifications, E. coli concentrations ranged from 110 to 

80,000 CFU/100 mL. The percentage of sample E. coli concentrations in the former group greater than Ohio’s singlesample maximum was 88 percent, whereas 85 percent of 

sample concentrations was greater than the maximum after 

major modifications occurred. Instantaneous discharges of 

E. coli were calculated for each of the modification periods. 

No statistically significant difference was observed between 

the median instantaneous discharges of E. coli for the 

premodification and minor-modification periods (5.1 × 106

 and 

3.6 × 106 CFU per second, respectively).

During rainfall events in September 2003, samples were 

collected every 15 to 30 minutes. E. coli concentrations in 

all of these samples (n = 34) were greater than Ohio’s singlesample maximum for primary-contact recreation. On September 19, total accumulated rainfall was 1.7 in., and streamflow 

reached a peak of 1,040 ft3/s. Sample collection started after 

0.8 in. of precipitation had fallen and continued throughout 

the remainder of the storm. For these samples, E. coli concentrations ranged from 32,000 to 140,000 CFU/100 mL. 

On September 22, total accumulated rainfall was 0.5 in., and 

streamflow reached a peak of 497 ft3/s. Sample collection 

began before the start of the rain and continued throughout the 

storm. E. coli concentrations ranged from 450 to 

260,000 CFU/100 mL.

Introduction

Mill Creek is a tributary of the Cuyahoga River in 

Cleveland, Ohio (fig. 1). Combined-sewer overflows (CSOs) 

and sanitary-sewer overflows from aging sewers, along with 

spills and runoff from landfills, have resulted in water-quality 

problems in Mill Creek, which in turn have affected the water 

quality in the Cuyahoga River (Ohio Environmental Protection Agency, 2003a). These overflows can result in health 

risks to people who use the creek and (or) river for recreation. 

Escherichia coli (E. coli) is an indicator of fecal contamination 

because it inhabits the gastrointestinal tract of warmblooded 

animals and, as such, its presence also indicates a potential 

for exposure to pathogenic organisms. Ohio has developed 

recreational water-quality standards (Ohio Environmental Protection Agency, 2003b) based in part on a U.S. Environmental 

Protection Agency (USEPA) study in which rates of swimming-related gastrointestinal illness were found to be related 

to concentrations of E. coli in the water (Dufour, 1984). 

Escherichia coli Concentrations in the Mill Creek 

Watershed, Cleveland, Ohio, 2001–2004

By Amie M. G. Brady 
#

41° 28'

Cuy ahoga

RiverGarfield Heights Maple Heights

Shaker Heights

Warrensville Heights

North Randall

Bedford Heights

Highland Hills

Beachwood

CuyahogaHeights

Orange

Solon

EXPLANATION

# U.S. Geological Survey stream gage (04208460)

Combined-sewer-overflow outfallsStreamsSoutherly Wastewater-Treatment PlantMill Creek sewershedMill Creek watershed

Valley View

Johnson

Mill

KILOMETERS

MILES

Independence

Cleveland

41° 24'

81° 39' 81° 32'

0 1 2 3

0 1 2 3

Wolf Creek Creek

Branch

Study area withinCuyahoga County

Cranwood Creek

04208460

Warner Rd. Branch

Sewershed boundary from Northeast OhioRegional Sewer District, 2005

Figure 1.  Location of the study area in northeast Ohio, showing all combined-sewer overflows present before sewage-collection system improvements.

   Escherichia coli Concentrations in the Mill Creek Watershed, Cleveland, Ohio, 2001–2004
Waters designated “primary contact” are suitable for full-body 

contact such as swimming and canoeing, whereas “secondarycontact waters” are suitable for partial-body contact such as 

wading. Mill Creek has been designated by the Ohio Environmental Protection Agency (Ohio EPA) as a primary-contact 

water. E. coli has often been found in both Mill Creek and the 

Cuyahoga River at concentrations greater than Ohio’s waterquality standards for water-contact recreation (Northeast Ohio 

Regional Sewer District, 1996; Ohio Environmental Protection 

Agency, 2003a).

During studies conducted by the Ohio EPA in 1998 and 

2002, Mill Creek was designated as a “Category 5” water on 

Ohio’s Section 303(d) list (1998), meaning it is impaired or 

threatened. Section 303(d) of the Clean Water Act requires 

states, territories, and authorized tribes to list and prioritize 

waters that are impaired and requires that restoration solutions be developed. Total Maximum Daily Loads (TMDL) for 

bacteria (fecal coliforms and E. coli) were developed for the 

lower Cuyahoga, which includes Mill Creek, by the Ohio EPA 

and were approved by the USEPA in 2003 (Ohio Environmental Protection Agency, 2006). The Ohio EPA plans to conduct 

another survey of this segment of the watershed in 2020 (Ohio 

Environmental Protection Agency, 2006). 

To comply with USEPA and Ohio EPA regulatory policies, the Northeast Ohio Regional Sewer District (NEORSD) 

implemented a modification plan to eliminate or control (by 

reducing the number of overflows) all of the CSOs in the Mill 

Creek watershed. This plan incorporates (1) the construction 

of a tunnel to store wet-weather flow until it can be conveyed 

to and treated by the Southerly Wastewater Treatment Plant, 

and (2) construction of new relief sewers to provide additional 

conveyance to the present interceptor upstream of the tunnel. 

After all of the modifications to the sewage-collection system are completed, the project is expected to reduce annual 

overflows to Mill Creek by approximately 430 Mgal (Lester 

Stumpe, Northeast Ohio Regional Sewer District, written commun. 2007). 

In cooperation with the NEORSD, the U.S. Geological 

Survey (USGS) developed a project to monitor E. coli concentrations and compute discharges before and during modifications to the sewage-collection system. Many municipalities 

across the country are facing issues with aging and failing 

sewage-collection systems. It was hoped that this study would 

serve as a demonstration project for other municipalities wanting to monitor their sewage-collection-system modification 

projects. 

Purpose and Scope

This report describes the results of a study to characterize concentrations of E. coli in Mill Creek in Cleveland, Ohio, 

from August 2001 through September 2004, during which 

time modifications to the sewage-collection system were 

made. Samples were collected semimonthly near a USGS 

stream gage on Mill Creek at Garfield Heights and analyzed 

for E. coli concentrations. These data were then examined as 

a function of streamflow and precipitation, as well as before 

modifications and during minor modifications to the sewagecollection system to determine whether a reduction of instream 

concentrations and discharges to the Cuyahoga River could 

be observed following modifications to the sewage-collection 

system. In addition, samples collected during two rain events 

were examined as a function of streamflow and precipitation.

Description of Study Area

Mill Creek drains southeastern Cleveland, Ohio, and its 

suburbs and has a total drainage area of 19.4 mi2. The sewer 

service area, or sewershed, is 27.8 mi2 and covers most of the 

watershed (fig. 1). Mill Creek flows into the Cuyahoga River 

at Independence, Ohio, at about river mile 11.5. The creek 

originates near Beachwood and flows generally west-southwest. The land use in the watershed is primarily residential 

and industrial with some wooded areas, and primary-contact 

recreation is listed by the Ohio EPA among the designated 

uses of the stream. Although a few segments are culverted, 

most of the creek is open and natural. The most unique feature 

of the creek is a waterfall a few miles upstream from the 

mouth. Typically, streamflows are highest in May and lowest during the late summer or fall (July–October). In October 

2001, flows were exceptionally low, and the daily mean was 

0.00 ft3

/s on October 3 and 11. Monthly mean flows range 

from 15.9 to 53.3 ft3/s (Shindel and others, 2005).

Historically, Mill Creek has been one of the most contaminated streams in the Greater Cleveland Area (Northeast Ohio 

Regional Sewer District, 1996; Ohio Environmental Protection Agency, 2003a). The source of contamination is mainly 

from CSOs or failing or malfunctioning home sewage-disposal 

systems; other sources include spills and runoff from landfills 

(Lester Stumpe, Northeast Ohio Regional Sewer District, 

written commun., 2007). Prior to sewage-collection-system 

modifications, there were a total of 28 CSOs in the watershed. Often, Mill Creek has not met Ohio EPA water-quality 

standards for primary-contact recreation during either dry- or 

wet-weather conditions. Primary-contact waters are defined 

as waters that during the recreation season (May 1 to October 15) are suitable for full-body-contact recreation such as 

swimming, canoeing, and scuba diving with minimal threat to 

public health as a result of water quality (Ohio Environmental 

Protection Agency, 2003b).

Sewage-Collection-System Modifications

The NEORSD began sewage-collection-system modifications in the Mill Creek watershed in May 1997. A tunnel 

to store and convey wet-weather flow is the backbone of the 

modification plan. Between August 7 and October 28, 2002, 

6 of the 28 Mill Creek CSOs were eliminated or controlled (by 

reducing the number of overflows) and their overflows redirected into the newly constructed tunnel. These modifications 

Introduction 
in the sewage-collection system have been estimated to reduce 

annual overflows into Mill Creek by more than 320 Mgal. Six 

more CSOs were eliminated or controlled from May 2003 

through May 2004. These modifications have been estimated 

to reduce annual overflows by another 21 Mgal. Further modifications to the sewage-collection system were completed during 2005 and 2006, with estimated reductions in overflows of 

more than 88 Mgal per year (Lester Stumpe, Northeast Ohio 

Regional Sewer District, written commun., 2007). 

To assist in describing the data, the modification timeline 

has been divided into three periods based on the volume of 

overflows eliminated: premodification, major modification, 

and minor modification. Samples collected prior to August 7, 

2002, are characterized as “premodification” samples, meaning they were collected before any CSOs were controlled or 

eliminated. “Major-modification” samples are those that were 

collected between August 7 and October 28, 2002, when the 

most significant modifications to the sewage-collection system 

were completed (annual overflow reductions of an estimated 

320 Mgal). Samples collected after October 28, 2002, are 

termed “minor-modification” samples (annual overflow reductions of an estimated 22 Mgal).

Methods of Study

The NEORSD collected stream samples before and 

during sewage-collection system modifications. Samples that 

were collected semimonthly near the USGS stream gage on 

Mill Creek at Garfield Heights (station identification number 

04208460) are referred to as “routine” samples (fig. 1). A 

total of 86 routine samples were collected from August 2001 

through September 2004. Additional samples that were collected during two rain events in September 2003 are referred 

to as “event” samples. During these rain events, samples were 

collected every 15 to 30 minutes for 3.5 to 9 hours (depending 

on the duration of the rainfall). Stage, used to estimate instantaneous streamflow, was obtained from the USGS stream gage 

at each sampling. Field measurements of water temperature, 

pH, dissolved oxygen, and specific conductance were made 

each time stream samples were collected, but no analyses were 

conducted on these data. 

E. coli concentrations were used to monitor recreational 

water quality. The Ohio primary-contact single-sample maximum of 298 CFU/100 mL was used as a benchmark to evaluate water quality in this report. For water-quality standards 

attainment, this standard cannot be exceeded in more than 

10 percent of the samples collected during any 30-day period 

(Ohio Environmental Protection Agency, 2003b).

Sampling Procedures and Microbiological 

Methods

Sterile techniques were used throughout collection and 

analysis of samples. Whenever practical, samples were collected using the equal-width-increment method as described 

by Edwards and Glysson (1999). This method results in a 

composite sample that represents the streamflow-weighted 

concentrations of the stream cross section sampled. A handheld depth-integrating sampler was used to collect samples 

into sterile 1-L polypropylene bottles, which were immediately placed in a cooler with ice and taken to the NEORSD 

laboratory in Cuyahoga Heights, Ohio, for analysis. If the 

stream depth and (or) velocity was not sufficient to obtain 

an isokinetic sample, the sample was collected by the handdip method. This method was only required for four routine 

samples when the creek was frozen and a hand-dip sample was 

collected after the ice was chipped away (January and February 2004). 

Standard membrane-filtration techniques were used with 

mTEC agar (U.S. Environmental Protection Agency, 1985) 

to process the samples for E. coli enumeration within 6 hours 

of collection. In this method, samples are filtered through a 

0.45-μm-pore-size membrane filter, and the filter is placed 

onto an mTEC plate. The plates are incubated for 2 hours at 

35°C and then transferred to an incubator set to 44.5°C for 

the remainder of the 22- to 24-hour incubation period. After 

incubation, the membranes containing colonies are placed onto 

absorbent pads containing urea broth. Colonies that remain 

yellow after 15 to 20 minutes are counted as E. coli. Concentrations of E. coli were calculated using methods described 

in Myers (2004) and expressed as colony-forming units per 

100 milliliters (CFU/100 mL). 

Water-Quality and Ancillary Environmental 

Information

The USGS stream gage on Mill Creek is approximately 

0.6 mi upstream from the mouth (fig. 1) and has a contributing 

drainage area of 17.9 mi2. Stage, used to estimate instantaneous streamflow, was obtained from the USGS stream gage 

at each sampling. Water temperature, pH, dissolved oxygen, 

and specific conductance were measured with a multiparameter water-quality meter each time a sample was collected. The 

water-quality meter was calibrated before the samples for each 

day were collected. Daily precipitation amounts were obtained 

from the precipitation gage at Cleveland Hopkins International 

Airport (National Oceanic and Atmospheric Administration, 

2005b), approximately 13 mi from the sampling site. Trace 

amounts of rain were transformed to 0.005 in. for data-analysis purposes.

Quality Assurance and Quality Control

Quality-assurance and quality-control (QA/QC) procedures were followed for all phases of data collection and 

analysis in the field and laboratory and during data validation 

and assessment. Good field and laboratory practices—cleanliness, safety practices, procedures for media preparation, and 

specifications for reagent water quality—were adopted by 

   Escherichia coli Concentrations in the Mill Creek Watershed, Cleveland, Ohio, 2001–2004
USGS and NEORSD employees as set forth by American 

Public Health Association and others (1998) and Britton and 

Greeson (1989).

Equipment and supplies were routinely checked to ensure 

proper performance. The incubators were checked to ensure 

that temperatures were 35°C ± 0.5°C and 44.5 ± 0.2°C. Buffer 

and media were checked through the use of blanks—sterile buffer water was filtered before and after every sample. 

Autoclaves also were monitored for proper operation by use 

of heat-indicating tape (to identify that the equipment was 

properly sterilized) and by spore strips (vials of bacteria tested 

for growth after sterilization).

A field blank was collected near the beginning of the 

project. The collection procedure consisted of taking a 

1-L bottle of sterile buffer water, attaching a sterile adaptor 

and nozzle, and pouring the sterile buffer water into a new, 

sterile, 1-L bottle. This was treated as a sample and plated in 

duplicate. Collection of the field blank at the field site is used 

to demonstrate whether proper sampling procedures are followed and that field personnel are not inadvertently contaminating the samples.

QA/QC samples for E. coli analyses were collected by 

NEORSD and the USGS. NEORSD collected sequential-split 

replicates every sampling date (approximately 30 annually). 

A sequential split-replicate consists of two samples collected 

in succession with aliquots from each sample analyzed twice. 

The E. coli concentrations reported and used in data analysis 

for routine samples are an average of these split replicates. 

Twice a year, the USGS collected and analyzed concurrent 

sequential split-replicate samples. QA/QC samples for E. coli 

analyses were used to qualitatively assess data and were not 

used for data interpretation.

Routine Sampling

Routine samples were collected from August 2001 

through September 2004. A total of 86 samples were collected 

semimonthly near the USGS stream gage on Mill Creek. The 

following sections describe environmental and water-quality variables during this study period and their relations to 

E. coli concentrations in the creek. Streamflow, water-quality, 

and microbiological data are presented in table 1 (at back of 

report). 

Streamflow and Rainfall Characteristics

Streamflow was determined by means of standard USGS 

techniques (Rantz and others, 1982). Instantaneous streamflow 

is the streamflow at a particular instant of time (determined 

from established stage-streamflow relations). Instantaneous 

streamflows (15-minute recording intervals) for the sampling 

period in comparison with those at the time of sampling are 

shown in figure 2. Shading on the figure indicates periods 

associated with different levels of sewage-collection-system 

modifications (premodification, major modification, and minor 

modification). 

Figure 2.  Instantaneous streamflows near the mouth of Mill Creek, Garfield Heights, Ohio, August 2001–September 2004, as related

to period of sewage-collection-system modification. Modification periods are defined as “premodification” (prior to August 7, 2002),

“major modification” (August 7 to October 24, 2002), and “minor modification” (after October 24, 2002). 

8/1/2001 2/14/2002 8/31/2002 3/17/2003 9/30/2003 4/15/2004 10/30/2004

0

1,000

2,000

3,000

4,000

INSTANTANEOUS STREAMFLOW, IN CUBIC FEET PER SECOND

Premodification period

Major-modification period

Minor-modification period

Streamflow August 2001–September 2004

Streamflow at time of sampling

Routine Sampling 
For the entire sampling period, instantaneous streamflow ranged from 0.00 ft3

/s in October 2001 to a maximum of 

3,900 ft3/s in August 2001 with a median value of 11.0 ft3/s. 

The streamflow range sampled was 0.03 ft3/s in October 2001 

to 515 ft3/s in May 2003. The median streamflow for this 

data set was 12 ft3/s. Routine sampling did not represent the 

0.5 percent of streamflows that were greater than 515 ft3/s. 

During the sampling period, precipitation fell on 60 percent of the days. On the days precipitation fell, daily total 

rainfall ranged from trace amounts of rain to 2.22 in., with a 

median of 0.09 in. The maximum daily total (2.22 in.) was on 

July 8, 2003. The average annual precipitation in the study 

area is 38.7 in. (National Oceanic and Atmospheric Administration, 2005a). For the sampling period, the annual precipitation totals for 2001 thru 2004 were 37.0, 37.2, 45.0, and 

42.3 in., respectively, with an average of 40.4 in.

Statistics for instantaneous streamflow during the entire 

sampling period and at the time of sampling, and daily precipitation for the three sewage-collection-system modification 

periods are listed in table 2 (at back of report). Instantaneous 

streamflows for the premodification period and the minormodification period show similar minimum and maximum 

values, but the median value for the minor-modification period 

was slightly higher (14 ft3

/s) than that of the premodification period (8.6 ft3

/s). During the minor-modification period, 

precipitation fell on 65 percent of the days, whereas during the 

premodification period, precipitation fell on 56 percent of the 

days. 

Relation of Concentrations of Escherichia coli to 

Streamflow and Precipitation

E. coli concentrations in the 86 routine samples collected for this study ranged from 110 to 80,000 CFU/100 mL 

(fig. 3). The median concentration was 1,000 CFU/100 mL. 

Concentrations were greater than Ohio’s single-sample E. coli

maximum for primary-contact recreation of 298 CFU/100 mL 

84 percent of the time. Additionally, E. coli concentrations 

were greater than Ohio’s single-sample maximum for secondary-contact recreation of 576 CFU/100 mL 69 percent of the 

time. 

To examine the relation between instantaneous streamflow and E. coli concentrations, results were placed into 

four groups of nearly equal size on the basis of magnitude of 

streamflow. Box plots of E. coli distributions for these four 

groups are shown in figure 4. For samples collected when 

streamflow was greater than 20 ft3

/s (the group with the highest streamflows, n = 20), E. coli concentrations were greater 

than Ohio’s single-sample maximum for primary-contact 

recreation in all but one sample. This group’s median E. coli 

concentration was significantly larger than that of the other 

groups based on a Tukey-Kramer multiple-comparison test on 

the log10-transformed data. (The Tukey-Kramer test compares 

all possible pairs of treatment group medians and is powerful even when treatment group sizes are unequal (Helsel and 

Hirsch, 2002). The level of significance was set at α ≤ 0.05.)

100

1,000

10,000

100,000

ESCHERICHIA COLI, IN CFU/100 mL

(86)

Single-sample maximum for primary-contact recreation = 298 CFU/100 mL

Single-sample maximum for secondary-contact recreation = 576 CFU/100 mL

outlier2

upper whisker1

75th percentile

median

25th percentile

lower whisker1

Explanation

1

The span of the whiskers is

the largest and smallest values

within 1.5 times the interquartile

range.

2

Outliers are defined as

values outside of the whisker

span.

number of values (86)

Figure 3.  Distribution of Escherichia coli concentrations for routine samples collected near U.S. Geological Survey stream gage

04208460, Mill Creek, Garfield Heights, Ohio, August 2001–September 2004. Primary- and secondary-contact recreation maximums are

set by the Ohio Environmental Protection Agency (Ohio Environmental Protection Agency, 2002). (CFU/100 mL, colony-forming units per

100 milliliters.)

 Escherichia coli Concentrations in the Mill Creek Watershed, Cleveland, Ohio, 2001–2004
Figure 4.  Distribution of Escherichia coli concentrations as a function of four ranges of instantaneous streamflow during routine sampling near U.S. Geological

Survey stream gage 04208460, Mill Creek, Garfield Heights, Ohio, August 2001–September 2004. (Results of Tukey-Kramer multiple comparison test on the log10-transformed data are presented as letters, and groups with a letter in common do not differ significantly at α = 0.05.) Primary-contact recreation maximum is set bythe Ohio Environmental Protection Agency (Ohio Environmental Protection Agency, 2002). (CFU/100 mL, colony-forming units per 100 milliliters; ≤, less than or equalto; >, greater than.)

≤6.2 >6.2 and ≤11 >11 and ≤20 >20

INSTANTANEOUS STREAMFLOW, IN CUBIC FEET PER SECOND

100

1,000

10,000

100,000

, IN CFU/100 mL ESCHERICHIA COLI

(22) (21) (23) (20)

A A A B

Single-sample maximum for primary-contact recreation = 298 CFU/100 mL

outlier2

upper whisker1

75th percentile

median

25th percentile

lower whisker1

Explanation

1The span of the whiskers is

the largest and smallest valueswithin 1.5 times the interquartilerange

2Outliers are defined as

values outside of the whiskerspan

(22) number of values

Routine Sampling 
Another variable examined was the previous 24-hour 

precipitation amount (the amount of precipitation that fell 

in the 24-hour period before 9 a.m. on the day of sampling). 

Concentrations of E. coli in routine samples collected after a 

dry 24-hour period were compared to concentrations in routine 

samples collected after precipitation occurred during the previous 24 hours. Box plots of E. coli concentrations for these 

groups are shown in figure 5. The median E. coli concentration in samples collected after precipitation fell was 

1,400 CFU/100 mL, whereas the median concentration 

in samples collected when there was no precipitation was 

600 CFU/100 mL. A Wilcoxon rank-sum test on these data 

indicated a significant difference between the medians for 

these two groups (Z = -3.25, p = 0.0011). (The Wilcoxon ranksum test, a nonparametric procedure, is used to compare two 

independent groups of data. The level of significance was set 

at α ≤ 0.05.)

Relation of Concentrations of Escherichia coli to 

Modifications of the Sewage-Collection System

During the premodification period, E. coli concentrations in collected samples (n = 25) ranged from 220 to 

29,000 CFU/100 mL, with a median of 1,300 CFU/100 mL 

(fig. 6). Concentrations in 88 percent of the samples collected 

during this period were greater than Ohio’s single-sample 

maximum for primary-contact recreation. E. coli concentrations in samples collected during the major-modification 

period ranged from 120 to 2,100 CFU/100 mL, with a median 

of 280 CFU/100 mL. Three of the six samples collected during the major-modification period were greater than Ohio’s 

single-sample maximum. Concentrations in samples collected 

during the minor-modification period ranged from 110 to 

80,000 CFU/100 mL with a median of 1,000 CFU/100 mL. Of 

the samples collected during this period (n = 55), 85 percent of 

the samples were greater than Ohio’s single-sample maximum. 

A Wilcoxon rank-sum test comparing E. coli concentrations in 

samples collected during the premodification and minor-modification periods indicated no significant difference between the 

median values for these two groups (Z = -0.70, p = 0.4834).

To represent the magnitude of E. coli transport in the 

creek at the time of sampling, instantaneous discharges of 

E. coli were computed as follows:

E. coli concentration (CFU/100 mL) × (106 mL / 1 m3) ×

(1 m3 / 35.31 ft3) × streamflow (ft3/s)

to obtain instantaneous discharges with the units of colonyforming units of E. coli per second (CFU/s).

NO PRECIPITATION PRECIPITATION

(30) (56)

100

1,000

10,000

100,000

ESCHERICHIA COLI, IN CFU/100 mL

Single-sample maximum for primary-contact recreation = 298 CFU/100 mL

outlier2

upper whisker1

75th percentile

median

25th percentile

lower whisker1

Explanation

1

The span of the whiskers is

the largest and smallest values

within 1.5 times the interquartile

range

2

Outliers are defined as

values outside of the whisker

span

number of values (30)

Figure 5.  Distribution of Escherichia coli concentrations in routine samples collected near U.S. Geological Survey stream gage

04208460, Mill Creek, Garfield Heights, Ohio, when there was no precipitation and when precipitation fell in the 24-hour period prior to

9 a.m. on the day of sampling, August 2001–September 2004. Primary-contact recreation maximum is set by the Ohio Environmental

Protection Agency (Ohio Environmental Protection Agency, 2002). (CFU/100 mL, colony-forming units per 100 milliliters.)

 Escherichia coli Concentrations in the Mill Creek Watershed, Cleveland, Ohio, 2001–2004
Among the 86 routine samples, instantaneous discharges 

of E. coli ranged from 5.9 × 103 to 1.2 × 1010 CFU/s with a 

median of 3.3 × 106 CFU/s. For the pre-, major-, and minormodification periods, the median instantaneous discharges 

were 5.1 × 106, 3.0 × 105, and 3.6 × 106 CFU/s, respectively. 

A Wilcoxon rank-sum test comparing instantaneous discharges 

of E. coli during the premodification and minor-modification periods indicated that there was no significant difference 

between the median values for these two groups (Z = 0.42, 

p = 0.6742). Instantaneous discharges of E. coli in relation to 

instantaneous streamflow are shown in figure 7. 

Rainfall-Event Sampling

Samples were collected near the USGS stream gage near 

the mouth of Mill Creek during two rainfall events in September 2003. Nineteen samples were collected on September 19 

immediately after a rainfall accumulation of approximately 

0.8 in. and during the remainder of the rainfall event (fig. 8A). 

The total accumulation of rain was 1.7 in. Instantaneous 

streamflow during sampling ranged from 90 to 1,040 ft3/s. 

The median concentration of E. coli for these samples was 

74,000 CFU/100 mL, and concentrations ranged from 32,000 

to 140,000 CFU/100 mL. Concentrations in all of the samples 

collected during this event were greater than Ohio’s singlesample maximum for primary-contact recreation. Instantaneous discharges of E. coli ranged from 1.0 × 109

 to 

2.4 × 1010 CFU/s with a median of 7.3 × 109 CFU/s.

Samples collected on September 22 included one sample 

before any recorded rainfall and 14 samples collected during 

the rainfall event (fig. 8B). The total accumulation of rainfall 

was 0.5 in. Instantaneous streamflow during sampling ranged 

from 9.1 to 497 ft3

/s. The concentration of E. coli in the sample collected before any rainfall was 590 CFU/100 mL. E. coli

concentrations in samples collected after the rain began ranged 

from 450 to 260,000 CFU/100 mL, and the median value in 

these samples was 82,000 CFU/100 mL. The concentrations 

of E. coli did not increase appreciably until more than 0.3 in. 

of rain had fallen (fig. 8B). The highest E. coli concentration 

(260,000 CFU/100 mL) was observed in a sample collected 

at peak streamflow (497 ft3

/s). After streamflow reached its 

maximum, E. coli concentrations decreased and ranged from 

73,000 to 170,000 CFU/100 mL for the remainder of the event 

sampling. Concentrations in all of the samples collected during this event were greater than Ohio’s single-sample maximum for primary-contact recreation. Instantaneous discharges 

of E. coli ranged from 1.2 × 106

 to 3.6 × 1010 CFU/s, with a 

median of 8.2 × 109 CFU/s.

102

103

104

105

ESCHERICHIA COLI, IN CFU/100 mL

Premodification Major modification Minor modification

(25) (6) (55)

Single-sample maximum for primary-contact recreation = 298 CFU/100 mL

outlier2

upper whisker1

75th percentile

median

25th percentile

lower whisker1

Explanation

1

The span of the whiskers is

the largest and smallest values

within 1.5 times the interquartile

range

2Outliers are defined as

values outside of the whisker

span

number of values (25)

Figure 6.  Distribution of Escherichia coli concentrations in routine samples collected near U.S. Geological Survey stream gage

04208460, Mill Creek, Garfield Heights, Ohio, during modification periods in the Mill Creek watershed, August 2001–September 2004.

Primary-contact recreation maximum is set by the Ohio Environmental Protection Agency (Ohio Environmental Protection Agency, 2002).

(CFU/100 mL, colony-forming units per 100 milliliters.) 

Rainfall-Event Sampling 
Figure 7.  Scatterplot of instantaneous discharges of Escherichia coli against instantaneous streamflow before and during

modifications to the sewage-collection system in the Mill Creek watershed, Cleveland, Ohio, August 2001–September 2004.

(CFU/100 mL, colony-forming units per 100 milliliters.)

0 50 100 150 200 500

INSTANTANEOUS STREAMFLOW, IN CUBIC FEET PER SECOND

103

104

105

106

107

108

109

1010

1011

Premodification (8/30/01 - 8/6/02; n = 25)

Major modification (8/7/02 - 10/24/02; n = 6)

Minor modification (10/25/02 - 9/15/04; n = 55)

INSTANTANEOUS DISCHARGE OF ESCHERICHIA COLI, IN CFU/100 mL

10 Escherichia coli Concentrations in the Mill Creek Watershed, Cleveland, Ohio, 2001–2004
8 pm midnight 4 am 8 am noon 4 pm 8 pm midnight

0.00

0.05

0.10

0.15

0.20

0.25

PRECIPITATION, IN INCHES

0

275

550

825

1,100

INSTANTANEOUS STREAMFLOW, IN

CUBIC FEET PER SECOND

102

103

104

105

106

A Streamflow

Escherichia coli

midnight 4 am 8 am noon 4 pm 8 pm midnight

TIME

0.00

0.05

0.10

0.15

0.20

0.25

PRECIPITATION, IN INCHES

0

275

550

825

1,100

INSTANTANEOUS STREAMFLOW, IN

CUBIC FEET PER SECOND

102

103

104

105

106

B

ESCHERICHIA COLI, IN CFU/100 mL ESCHERICHIA COLI, IN CFU/100 mL

Figure 8.  Distribution of Escherichia coli concentrations, instantaneous streamflow, and precipitation

for rainfall event samples collected near U.S. Geological Survey stream gage 04208460, Mill Creek,

Garfield Heights, Ohio. A. September 19, 2003. B. September 22, 2003. (CFU/100 mL, colony-forming

units per 100 milliliters.)

Rainfall-Event Sampling 11
Summary

Mill Creek is a small tributary of the Cuyahoga River in 

Cleveland, Ohio. Historically, it has been considered one of 

the most heavily contaminated streams in the Greater Cleveland Area (Northeast Ohio Regional Sewer District, 1996; 

Ohio Environmental Protection Agency, 2003a). Numerous 

sources of sewage inputs to the stream can pose a health risk 

to recreationists using the creek and (or) river. E. coli concentrations in the creek often have been greater than Ohio’s 

E. coli single-sample maximum for primary-contact recreation 

(298 CFU/100 mL). To help mitigate the contamination issues 

caused by the combined-sewer overflows (CSOs), the Northeast Ohio Regional Sewer District (NEORSD) has implemented a plan to eliminate or control (by reducing the number 

of overflows) all of the CSOs in the Mill Creek watershed. 

This plan incorporates the construction of a tunnel to store and 

convey wet-weather flow until it can be treated by the Southerly Wastewater Treatment Plant.

The USGS, in cooperation with the NEORSD, investigated Escherichia coli (E. coli) concentrations in the creek 

before (August 2001–July 2002) and during (August 2002–

September 2004) modifications to the sewage-collection 

system in the Mill Creek watershed. Specifically, concentrations and instantaneous discharges of E. coli in the creek near 

its mouth were analyzed to determine whether a reduction 

of instream concentrations and discharges to the Cuyahoga 

River could be observed following modifications to the sewage-collection system. “Routine” samples were collected by 

NEORSD semimonthly from August 2001 through September 

2004, and “event” samples were collected during two rain 

events in September 2003. Streamflow and other water-quality 

characteristics (water temperature, pH, specific conductance, 

and dissolved oxygen) were also measured at each sampling. 

For routine samples, E. coli concentrations ranged from 

110 to 80,000 CFU/100 mL. Concentrations were greater than 

Ohio’s E. coli single-sample maximum for primary-contact 

recreation in 84 percent of the samples collected. An examination of the relation between log E. coli concentration and 

streamflow revealed that at streamflows greater than 20 ft3

/s, 

concentrations in all but one of the samples were greater than 

Ohio’s E. coli single-sample maximum for primary-contact 

recreation. In addition, when precipitation fell within 24 hours 

before routine sampling, the median E. coli concentration was 

significantly greater than when there was no precipitation.

E. coli water-quality results were examined in groups 

referred to as “premodification,” “major-modification,” and 

“minor-modification” periods. Significant modifications to the 

sewage-collection system—completed between August 7 and 

October 28, 2002—were expected to reduce annual combined-sewer overflows by over 320 Mgal. This time interval 

is referred to as the major-modification period. The premodification and minor-modification periods bracket this interval. 

E. coli concentrations in samples collected ranged from 220 

to 29,000 CFU/100 mL for the premodification period, 120 

to 2,100 CFU/100 mL for the major-modification period, and 

110 to 80,000 CFU/100 mL for the major-modification period. 

Median E. coli concentrations and median E. coli instantaneous discharge values were slightly higher in the premodification period compared to the minor-modification period, but 

the differences were not statistically significant. 

During two rainfall events in September 2003, E. coli

concentrations ranged from 450 to 260,000 CFU/100 mL. On 

September 19, sampling did not begin until rainfall accumulated 0.8 in., and concentrations of E. coli were elevated in 

comparison to routine samples and remained above 

32,000 CFU/100 mL for all samples (n = 19) collected during 

this rainfall event. On September 22, sampling began before 

rainfall and continued throughout the event. The highest 

concentration of E. coli (260,000 CFU/100 mL) in a sample 

collected during this rainfall event was collected during peak 

streamflow (497 ft3

/s). 

Acknowledgments

Eva Hatvani, Ildiko Kubliak, John Rhoades, Thomas 

Zablotny, and Catherine Zamborsky of the Northeast Ohio 

Regional Sewer District are thanked for their assistance with 

project planning and sample collection and analysis. Lester 

Stumpe of the Northeast Ohio Regional Sewer District is 

thanked for his assistance in the planning and implementation 

of this project.

References Cited

American Public Health Association, American Water Works 

Association, and Water Pollution Control Federation, 1998, 

Standard methods for the analysis of water and wastewater 

(20th ed.): Washington D.C., American Public Health Association [variously paginated].

Britton, L.J., and Greeson, P.E., eds., 1989, Methods for collection and analysis of aquatic biological and microbiological samples: U.S. Geological Survey Techniques of WaterResources Investigations, book 5, chap. A4, 363 p.

Dufour, A.P., 1984, Health effects criteria for fresh recreational waters: Cincinnati, Ohio, U.S. Environmental Protection Agency, EPA 600/1–84–004, 33 p.

Edwards, T.K., and Glysson, D.G., 1999, Field methods for 

the measurement of fluvial sediment: U.S. Geological Survey Techniques of Water-Resources Investigations, book 3, 

chap. C2, 89 p.

12 Escherichia coli Concentrations in the Mill Creek Watershed, Cleveland, Ohio, 2001–2004
Helsel, D.R., and Hirsch, R.M., 2002, Statistical methods in 

water resources: U.S. Geological Survey Techniques of 

Water-Resources Investigations, book 4, chap. A3, 523 p., 

accessed April 2007 at http://water.usgs.gov/pubs/twri/

twri4a3/

Myers, D.N., 2004, National field manual for the collection 

of water-quality data–Biological indicators–Fecal indicator bacteria: U.S. Geological Survey Techniques of WaterResources Investigations, book 9, chap. A7.1, 64 p.

National Oceanic and Atmospheric Administration, 2005a, 

Comparative climatic data for the United States through 

2002, National Climatic Data Center: Asheville, N.C., 

accessed November 2005 at http://ols.nndc.noaa.gov/

plolstore/plsql/olstore.prodspecific?prodnum=C00095-

PUB-A0001#OVERVIEW

National Oceanic and Atmospheric Administration, 2005b, 

National Virtual Data System, National Climatic Data Center: Asheville, N.C., accessed April 2005 at http://www4.

ncdc.noaa.gov/

Northeast Ohio Regional Sewer District, 1996, Mill Creek 

Watershed Project–Executive summary: Cleveland, Ohio, 

89 p.

Ohio Environmental Protection Agency, 2003a, Total maximum daily discharges for the Lower Cuyahoga River, final 

report: 102 p., accessed March 2007 at http://www.epa.state.

oh.us/dsw/tmdl/Cuyahoga_lower_final_report.pdf

Ohio Environmental Protection Agency, 2003b, Water use 

definitions and statewide criteria: Ohio Administrative 

Code, chap. 3745–1–07, p. 8 and 23, accessed March 2007 

at http://www.epa.state.oh.us/dsw/rules/3745-1.html

Ohio Environmental Protection Agency, 2006, Ohio 2006 

integrated water quality monitoring and assessment report: 

66 p., accessed March 2007 at http://www.epa.state.oh.us/

dsw/tmdl/2006IntReport/IR06__text_final.pdf

Rantz, S.E., and others, 1982, Measurement and computation 

of streamflow; Volume 1, Measurement of stage and streamflow: U.S. Geological Survey Water-Supply Paper 2175, 

v. 1, 284 p.

Shindel, H.L, Mangus, J.P., and Frum, S.R., 2005, Waterresources data, Ohio, water year 2004—Volume 2, St. Lawrence River Basin and statewide project data: U.S. Geological Survey Water-Data Report OH–04–2, p. 73 (available 

online at http://water.usgs.gov/pubs/wdr/2004/wdr-oh-04/

WDR-OH-04-2.pdf).

U.S. Environmental Protection Agency, 1985, Test methods 

for Escherichia coli and enterococci in water by the membrane filtration procedure: Cincinnati, Ohio, 

EPA 600/4–85–076, 24 p. 

References Cited 13
This page is intentionally blank.

14
Table 1. Streamflow, water-quality, and microbiological data for samples collected in Mill Creek, Garfield Heights, Ohio, August 2001–September 2004.—Continued

[ft3/s, cubic feet per second; °C, degrees Celsius; --, no data; μS/cm, microsiemens per centimeter at 25°C; mg/L, milligrams per liter; E. coli, Escherichia coli; CFU/100 mL, colony-forming units 

per 100 milliliters; K, results based on colony count outside the ideal range of 20–80 CFU/100 mL; CFU/s, colony-forming units of E. coli per second]

Date Time Instantaneous 

streamflow

(ft3/s)

Water 

temperature

(°C)

pH Specific 

conductance

(μS/cm)

Oxygen,

dissolved

(mg/L)

E. coli

(CFU/100 mL)

Instantaneous

discharges

(CFU/s)

USGS 

qualitycontrol trip

Routine samples

08/30/01 1145 1.1 21.0 7.6 1,000 8.4 530 1.6 × 10509/12/01 1045 3.2 17.0 7.8 1,200 9.8 960 8.7 × 10509/26/01 1120 2.5 12.0 8.1 800 10.6 7,200 5.1 × 10610/10/01 1005 .03 12.5 8.0 1,300 9.6 690 5.9 × 10310/24/01 0945 55 17.0 -- 400 8.8 K 12,000 1.9 × 10811/07/01 1055 6.2 11.0 7.7 1,200 13.0 1,100 1.9 × 10611/19/01 1053 5.1 12.0 7.4 1,200 12.0 1,300 1.9 × 10612/05/01 1153 7.5 14.0 -- 1,200 12.2 K 3,800 8.1 × 10612/19/01 1100 18 8.0 7.6 900 11.4 1,200 6.1 × 106 X

01/02/02 1115 9.1 4.0 7.4 1,900 13.2 K 650 1.7 × 106

01/16/02 1105 7.8 2.1 7.0 100 17.1 320 7.1 × 105 X

01/30/02 1030 61 6.4 8.2 800 11.1 K 4,400 7.6 × 107

02/13/02 1055 11 1.0 7.1 3,800 16.5 680 2.1 × 10602/27/02 1045 14 1.3 7.4 2,000 16.0 1,300 5.2 × 10603/06/02 0920 15 2.2 7.2 2,500 15.9 390 1.6 × 10603/20/02 0945 80 7.5 7.2 1,200 12.1 16,000 3.6 × 10804/03/02 1020 78 6.8 7.1 900 12.6 K 3,500 7.7 × 10704/17/02 1020 18 17.7 7.5 1,000 10.6 260 1.3 × 106 X

05/01/02 1015 11 10.2 7.5 1,200 13.8 220 6.8 × 105

05/15/02 0945 20 12.1 7.0 1,000 10.4 K 6,100 3.4 × 10705/29/02 0923 18 16.6 7.2 800 8.9 1,500 7.6 × 10606/12/02 0958 32 22.2 7.5 700 7.3 K 29,000 2.6 × 10806/26/02 0945 4.6 23.2 7.3 1,200 7.2 220 2.9 × 10507/10/02 0945 10 21.5 6.7 600 8.1 K 22,000 6.2 × 10707/24/02 0813 7.5 19.5 7.6 700 6.9 3,300 7.0 × 10608/07/02 1035 3.2 18.6 6.5 -- 10.0 220 2.0 × 105 X

Table 1 15
Table 1. Streamflow, water-quality, and microbiological data for samples collected in Mill Creek, Garfield Heights, Ohio, August 2001–September 2004.—Continued

[ft3/s, cubic feet per second; °C, degrees Celsius; --, no data; μS/cm, microsiemens per centimeter at 25°C; mg/L, milligrams per liter; E. coli, Escherichia coli; CFU/100 mL, colony-forming units 

per 100 milliliters; K, results based on colony count outside the ideal range of 20–80 CFU/100 mL; CFU/s, colony-forming units of E. coli per second]

Date Time Instantaneous 

streamflow

(ft3/s)

Water 

temperature

(°C)

pH Specific 

conductance

(μS/cm)

Oxygen,

dissolved

(mg/L)

E. coli

(CFU/100 mL)

Instantaneous

discharges

(CFU/s)

USGS 

qualitycontrol trip

Routine samples—continued

08/21/02 0913 3.8 17.3 7.2 1,000 7.8 240 2.6 × 105

09/04/02 0945 5.5 19.5 7.1 800 8.5 K 2,100 3.3 × 10609/18/02 0940 3.7 16.7 7.4 1,100 8.4 320 3.4 × 10510/02/02 1000 3.8 19.3 -- 1,000 8.3 120 1.3 × 10510/16/02 1040 4.1 11.5 7.7 900 9.2 480 5.6 × 10510/30/02 1010 6.2 6.6 7.7 700 11.6 1,000 1.8 × 10611/13/02 1050 7.8 7.6 7.5 700 11.6 930 2.0 × 10611/26/02 0940 12 5.1 7.7 1,000 12.8 710 2.4 × 10612/11/02 0940 9.1 .3 7.6 2,500 14.5 1,400 3.6 × 10612/23/02 1045 10 1.8 8.0 1,500 15.2 11,000 3.1 × 10701/08/03 1010 18 2.1 8.2 1,400 13.5 2,200 1.1 × 10701/22/03 1015 15 .3 7.2 2,500 14.5 1,000 4.2 × 10602/05/03 0940 14 .1 7.9 2,500 14.9 2,400 9.5 × 10602/19/03 0945 32 .0 7.2 600 15.5 1,400 1.3 × 10703/05/03 1000 124 3.2 8.0 20 13.4 K 38,000 1.3 × 10903/19/03 0930 22 8.6 8.0 1,600 14.6 1,100 6.8 × 10604/02/03 0930 16 9.5 7.8 1,600 12.5 740 3.4 × 10604/16/03 1030 9.1 13.8 8.1 1,849 14.3 280 7.2 × 105 X

04/30/03 1010 7.3 12.9 7.9 1,723 13.7 250 5.2 × 105

05/05/03 1045 154 12.6 8.0 1,000 9.7 K 36,000 1.6 × 10905/06/03 0955 108 16.3 7.8 600 9.3 13,000 4.0 × 10805/07/03 1130 11 14.6 8.0 1,110 11.3 1,000 3.1 × 10605/08/03 1135 18 15.5 8.2 1,600 11.8 2,800 1.4 × 10705/09/03 0941 515 12.9 8.0 1,200 10.4 K 80,000 1.2 × 101005/12/03 1100 88 12.1 7.9 1,400 10.5 24,000 6.0 × 10805/15/03 1048 27 15.5 7.7 -- 10.7 140 1.2 × 106

16  Escherichia coli Concentrations in the Mill Creek Watershed, Cleveland, Ohio, 2001–2004
Table 1. Streamflow, water-quality, and microbiological data for samples collected in Mill Creek, Garfield Heights, Ohio, August 2001–September 2004.—Continued

[ft3/s, cubic feet per second; °C, degrees Celsius; --, no data; μS/cm, microsiemens per centimeter at 25°C; mg/L, milligrams per liter; E. coli, Escherichia coli; CFU/100 mL, colony-forming units 

per 100 milliliters; K, results based on colony count outside the ideal range of 20–80 CFU/100 mL; CFU/s, colony-forming units of E. coli per second]

Date Time Instantaneous 

streamflow

(ft3/s)

Water 

temperature

(°C)

pH Specific 

conductance

(μS/cm)

Oxygen,

dissolved

(mg/L)

E. coli

(CFU/100 mL)

Instantaneous

discharges

(CFU/s)

USGS 

qualitycontrol trip

Routine samples—continued

06/02/03 0930 23 12.3 7.9 1,000 10.3 620 4.0 × 106

06/11/03 0945 12 18.5 7.7 1,100 7.8 1,000 3.4 × 10606/25/03 0938 9.4 19.6 7.7 1,300 7.9 380 1.0 × 10607/09/03 0942 13 21.0 7.7 1,067 8.1 2,600 9.6 × 10607/23/03 1025 14 19.7 7.9 949 9.0 4,600 1.8 × 107 X

08/06/03 0952 6.2 19.6 7.8 956 8.6 K 9,200 1.6 × 107

08/20/03 1015 4.8 19.5 8.1 1,100 9.3 270 3.7 × 10508/26/03 1205 11 22.0 7.8 1,300 8.0 K 8,000 2.5 × 10709/03/03 0948 15 19.5 7.9 681 8.4 1,000 4.2 × 10609/17/03 0928 4.8 15.3 7.7 1,211 8.6 380 5.2 × 10510/02/03 0937 11 9.4 7.8 1,211 10.4 2,600 8.1 × 10610/15/03 1002 45 11.8 7.5 541 7.8 K 14,000 1.8 × 10810/29/03 1012 11 9.6 7.8 1,243 10.0 320 1.0 × 10611/12/03 1015 25 12.0 7.0 400 12.0 13,000 9.2 × 10712/10/03 1045 20 6.2 8.1 2,048 6.7 K 1,500 8.5 × 10612/22/03 1140 12 3.9 8.3 3,500 14.8 3,200 1.1 × 10701/07/04 1030 20 .0 7.8 2,310 17.0 K 1,000 5.7 × 10601/21/04 0957 2.8 .0 7.6 4,518 12.8 290 2.3 × 10502/04/04 1025 23 .0 7.0 1,029 12.2 K 1,700 1.1 × 10702/18/04 0956 11 .0 7.0 812 11.2 480 1.5 × 10603/03/04 1016 14 6.4 8.3 2,512 9.4 580 2.3 × 10603/17/04 1019 14 2.5 8.1 16,840 6.8 210 8.3 × 10504/14/04 1210 83 7.7 8.4 101 8.3 K 920 2.2 × 10704/28/04 1118 21 9.2 8.1 1,305 13.1 330 2.0 × 106 X

05/12/04 1010 13 19.0 7.8 1,430 10.5 590 2.2 × 106

05/26/04 1038 20 19.3 7.7 1,249 8.8 K 560 3.2 × 106

Table 1 17
Table 1. Streamflow, water-quality, and microbiological data for samples collected in Mill Creek, Garfield Heights, Ohio, August 2001–September 2004.—Continued

[ft3/s, cubic feet per second; °C, degrees Celsius; --, no data; μS/cm, microsiemens per centimeter at 25°C; mg/L, milligrams per liter; E. coli, Escherichia coli; CFU/100 mL, colony-forming units 

per 100 milliliters; K, results based on colony count outside the ideal range of 20–80 CFU/100 mL; CFU/s, colony-forming units of E. coli per second]

Date Time Instantaneous 

streamflow

(ft3/s)

Water 

temperature

(°C)

pH Specific 

conductance

(μS/cm)

Oxygen,

dissolved

(mg/L)

E. coli

(CFU/100 mL)

Instantaneous

discharges

(CFU/s)

USGS 

qualitycontrol trip

Routine samples—continued

06/09/04 0952 6.5 21.2 7.7 1,522 7.4 K 1,100 2.0 × 106

06/23/04 1014 6.0 18.0 8.2 1,280 7.2 440 7.5 × 10507/07/04 0940 6.0 22.4 7.1 1,604 7.2 330 5.6 × 10507/21/04 1010 5.3 21.0 7.8 1,200 9.4 110 1.6 × 10508/04/04 1008 53 21.0 7.4 1,117 8.3 20,000 3.0 × 108 X

08/18/04 1022 9.1 18.6 7.2 1,473 8.3 K 1,200 3.1 × 106

09/01/04 0948 9.4 17.3 7.8 99 9.5 790 2.1 × 10609/15/04 1016 6.2 17.9 7.7 1,437 7.8 160 2.8 × 105

Event samples

09/19/03 0345 119 18.7 7.9 497 9.4 88,000 3.0 × 10909/19/03 0415 96 18.8 7.9 381 8.8 110,000 3.0 × 10909/19/03 0445 90 18.8 7.6 344 8.8 140,000 3.6 × 10909/19/03 0515 90 18.8 7.7 399 8.0 110,000 2.8 × 10909/19/03 0545 97 18.8 7.9 335 8.0 76,000 2.1 × 10909/19/03 0615 97 18.8 7.9 338 8.4 46,000 1.3 × 10909/19/03 0645 93 18.7 7.9 350 8.3 38,000 1.0 × 10909/19/03 0715 244 18.9 7.9 375 8.9 32,000 2.2 × 10909/19/03 0745 714 18.9 8.0 309 8.1 100,000 2.0 × 101009/19/03 0815 909 18.9 8.0 261 8.4 68,000 1.8 × 101009/19/03 0845 1,040 18.8 8.0 253 8.9 58,000 1.7 × 101009/19/03 0915 990 18.8 8.0 270 8.4 84,000 2.4 × 101009/19/03 0945 1,010 18.9 8.0 282 8.6 78,000 2.2 × 101009/19/03 1015 864 18.8 8.0 288 9.2 62,000 1.5 × 101009/19/03 1045 668 18.9 8.0 285 9.0 69,000 1.3 × 101009/19/03 1115 515 18.9 8.0 290 8.1 72,000 1.0 × 101009/19/03 1145 405 18.9 8.0 296 8.8 64,000 7.3 × 109

18  Escherichia coli Concentrations in the Mill Creek Watershed, Cleveland, Ohio, 2001–2004
Table 1. Streamflow, water-quality, and microbiological data for samples collected in Mill Creek, Garfield Heights, Ohio, August 2001–September 2004.—Continued

[ft3/s, cubic feet per second; °C, degrees Celsius; --, no data; μS/cm, microsiemens per centimeter at 25°C; mg/L, milligrams per liter; E. coli, Escherichia coli; CFU/100 mL, colony-forming units 

per 100 milliliters; K, results based on colony count outside the ideal range of 20–80 CFU/100 mL; CFU/s, colony-forming units of E. coli per second]

Date Time Instantaneous 

streamflow

(ft3/s)

Water 

temperature

(°C)

pH Specific 

conductance

(μS/cm)

Oxygen,

dissolved

(mg/L)

E. coli

(CFU/100 mL)

Instantaneous

discharges

(CFU/s)

USGS 

qualitycontrol trip

Event samples—continued

09/19/03 1215 357 18.8 8.0 311 8.9 77,000 7.8 × 109

09/19/03 1245 306 18.8 8.0 318 9.0 74,000 6.4 × 10909/22/03 0920 9.1 16.2 7.6 1,197 10.4 590 1.5 × 10609/22/03 1307 9.8 17.6 8.0 1,192 10.9 450 1.2 × 10609/22/03 1315 11 17.6 8.0 1,182 10.1 470 1.5 × 10609/22/03 1330 11 17.7 8.0 1,178 10.8 510 1.6 × 10609/22/03 1345 12 17.7 8.0 1,168 10.3 630 2.1 × 10609/22/03 1400 19 17.8 8.0 1,167 10.0 620 3.3 × 10609/22/03 1430 343 17.9 8.0 1,084 9.2 2,400 2.3 × 10809/22/03 1450 497 18.4 8.0 644 9.5 260,000 3.7 × 101009/22/03 1510 467 19.0 8.0 441 10.1 110,000 1.4 × 101009/22/03 1530 395 19.0 8.0 404 10.8 73,000 8.2 × 10909/22/03 1550 363 19.2 8.0 341 11.0 92,000 9.4 × 10909/22/03 1610 334 19.3 8.0 277 11.0 160,000 1.5 × 101009/22/03 1620 303 19.3 8.0 273 11.0 170,000 1.4 × 101009/22/03 1630 260 19.3 8.0 278 11.0 120,000 8.8 × 10909/22/03 1645 234 19.3 8.0 285 11.1 160,000 1.1 × 1010

Table 1 19
20 Escherichia coli Concentrations in the Mill Creek Watershed, Cleveland, Ohio, 2001–2004 Table 2. Streamflow and precipitation statistics for sewage-collection-system modification periods, Mill Creek watershed, Cleveland, Ohio, August 2001–September 2004. [ft3/s, cubic feet per second; n, number of samples; min., minimum; max., maximum; Improvement periods are defined as premodification, before August 7, 2002; major modification, August 7–October 24, 2002; and minor modification, after October 24, 2002. Precipitation data were obtained from National Oceanic and Atmospheric Administration, 2005b; trace amounts of rainfall were transformed to 0.005 inch for data-analysis purposes. Instantaneous streamflow was obtained from the U.S. Geological Survey stream gage 04208460, Mill Creek, Garfield Heights, Ohio] Modification period Instantaneous streamflow (ft3/s) Precipitation (inches) Sampling period At time of sampling

n min max median n min max median n min max median

Premodification 35,597 0.0 3,900 8.6 25 0.03 80 11 342 0.005 1.42 0.10

Major modification 7,583 2.8 2,020 4.1 6 3.2 5.5 3.8 79 .005 1.18 .10

Minor modification 67,160 2.6 3,810 14 55 2.8 515 13 692 .005 2.22 .085
Appendix 1 
Quality-assurance and quality-control (QA/QC) procedures were followed for all phases of data collection and 

analysis in the field and laboratory. QA/QC samples were 

collected and analyzed to assess any bias and (or) variability 

associated with the data as a result of collection methods or 

laboratory methods. This bias and (or) variability must be 

known so that the data can be adequately interpreted. The following analysis is used for illustration purposes only. 

Sequential split-replicate samples were collected to 

examine the variability of Escherichia coli (E. coli) concentrations. Between-bottle differences will show variability in 

E. coli concentrations as a result of collection methods as well 

as analytical methods. Within-bottle differences will show any 

inconsistencies in analytical methods. Results of NEORSD 

QC samples are listed in table 1.1. USGS QA/QC trips to the 

site were conducted to observe any differences in collection 

methods and (or) laboratory analysis procedures between 

USGS and NEORSD personnel. Results of USGS QC samples 

are listed in bold font in table 1.1.

Samples were designated in the following manner. For 

the first bottle collected, A was the first split and B was the 

second split. For the replicate sample, the first split was called 

C, and the second split was called D. Within-bottle differences 

were calculated for the following replicate pairs: A-B and 

C-D. Between-bottle differences were calculated for these replicate pairs: A-C, A-D, B-C, and B-D. Additionally, the data 

were analyzed in three groups: regular, USGS, and NEORSD 

QC. Regular samples were those collected on days the USGS 

did not make a QA/QC trip to the site (within-bottle n = 136; 

between-bottle n = 275). USGS samples are the samples collected during a USGS QA/QC trip and analyzed by the USGS, 

and NEORSD QC samples are the same samples but were 

analyzed by the NEORSD (for both agencies, within-bottle 

n = 14; between bottle n = 24).

Within-bottle and between-bottle differences in E. coli

concentrations were calculated by determining the absolute 

value of the percent difference between the log10-transformed 

sample pairs (PDs). Absolute values were used because the 

designations of A, B, C, and D were randomly assigned. Data 

were log10 transformed because the untransformed data were 

not normally distributed. The within-bottle and between-bottle 

PDs for regular samples are shown in figure 1.1. Generally, the PDs are uniformly distributed across the range of 

observed E. coli concentrations between 0 and 10 percent, 

indicating that about 10 percent of the variability in sample 

concentrations is due to field and (or) analytical methods. 

However, there are several outliers of the between-bottle PDs 

near 1,000 CFU/100 mL. These outliers were collected on 

two sampling dates (May 26 and June 9, 2004), and indicate 

that there were some differences in sample collection of the 

replicate bottles.

Summary statistics for PDs are listed in table 1.2. Based 

on the results of a Kruskal-Wallis multiple-comparison test, 

the within-bottle median PDs were not statistically different between regular, USGS, and NEORSD QC samples 

(K = 0.099, p = 0.9518). This indicates that analytical variability for E. coli concentrations was similar for both agencies. 

Further, a Wilcoxon rank-sum test comparing the betweenbottle median PDs showed no significant difference between 

USGS and NEORSD QC (Z = -1.21, p = 0.2274) or between 

NEORSD QC and regular median PDs (Z = -0.84, p = 0.4037). 

For all three groups (regular, USGS, and NEORSD QC), 

the median between-bottle PDs, representing analytical and 

sampling variability, were greater than the median withinbottle PDs, representing analytical variability. The Wilcoxon 

rank-sum tests show statistically significant differences in the 

median between-bottle and median within-bottle PDs for all 

three groups. 

Appendix 1. Variability of Escherichia coli concentrations in Mill Creek, 

Garfield Heights, Ohio, August 2001–September 2004 

22 Escherichia coli Concentrations in the Mill Creek Watershed, Cleveland, Ohio, 2001–2004
Table 1–1. Quality-control data for Escherichia coli concentrations in water samples

collected in Mill Creek, Garfield Heights, Ohio, August 2001–September 2004, and analyzed

by the Northeast Ohio Regional Sewer District and the U.S. Geological Survey.—Continued

[--, no data; K, results based on colony counts outside the ideal range of 20–80 colonies per plate; *, indicates 

field blank sample; <, less than; E, estimated]

Concentration of Escherichia coli (colony-forming units per 100 milliliters)

Date Bottle 1

[A]

Bottle 1 split

[B]

Bottle 2

[C]

Bottle 2 split

[D]

8/30/2001 530 -- -- --

9/12/2001 960 -- -- --

9/26/2001 7,200 -- -- --

10/10/2001 690 -- -- --

10/24/2001 K 13,000 K 12,000 -- --

11/7/2001 1,200 1,100 1,000 940

11/19/2001 1,200 1,200 1,400 1,400

12/5/2001 K 3,700 K 3,900 K 3,800 K 3,900

12/19/2001 1,300 1,100 1,100 1,300

12/19/2001 3,500 2,700 2,400 2,400

1/2/2002 730 670 K 630 K 570

1/16/2002 320 320 *<1 *<1

1/16/2002 200 200 *<1 *<1

1/30/2002 K 3,500 K 3,800 K 5,100 K 5,300

2/13/2002 690 680 680 650

2/27/2002 1,300 1,200 1,400 1,300

3/6/2002 370 390 420 390

3/20/2002 20,000 18,000 13,000 14,000

4/3/2002 K 3,900 K 3,700 K 3,400 K 3,000

4/17/2002 260 240 290 260

4/17/2002 250 270 E 170 E 350

5/1/2002 210 200 230 220

5/15/2002 7,300 6,700 K 5,000 K 5,300

5/29/2002 1,600 1,500 1,600 1,500

6/12/2002 25,000 26,000 K 29,000 K 35,000

6/26/2002 230 200 260 180

7/10/2002 27,000 K 18,000 K 18,000 26,000

7/24/2002 3,300 2,900 3,700 3,400

8/7/2002 260 220 180 200

8/7/2002 300 250 280 320

8/21/2002 250 280 210 240

9/4/2002 K 2,000 K 2,100 K 2,100 K 2,100

9/19/2002 360 330 310 300

10/2/2002 140 120 110 120

Table 1–1 23
Table 1–1. Quality-control data for Escherichia coli concentrations in water samples

collected in Mill Creek, Garfield Heights, Ohio, August 2001–September 2004, and analyzed

by the Northeast Ohio Regional Sewer District and the U.S. Geological Survey.—Continued

[--, no data; K, results based on colony counts outside the ideal range of 20–80 colonies per plate; *, indicates 

field blank sample; <, less than; E, estimated]

Concentration of Escherichia coli (colony-forming units per 100 milliliters)

Date Bottle 1

[A]

Bottle 1 split

[B]

Bottle 2

[C]

Bottle 2 split

[D]

10/16/2002 500 510 480 450

10/30/2002 1,100 1,000 1,200 850

11/13/2002 850 950 810 1,100

11/26/2002 680 730 710 720

12/11/2002 1,400 1,200 1,400 1,400

12/23/2002 12,000 14,000 8,400 10,000

1/8/2003 2,500 2,000 1,800 2,400

1/22/2003 1,200 1,000 1,000 1,000

2/5/2003 2,400 2,700 2,000 2,400

2/19/2003 1,300 1,200 1,600 1,400

3/5/2003 K 35,000 K 34,000 K 42,000 K 40,000

3/19/2003 1,400 1,400 810 810

4/2/2003 680 720 800 740

4/16/2003 360 330 200 220

4/16/2003 300 300 410 380

4/30/2003 270 240 250 230

5/5/2003 K 39,000 K 45,000 K 28,000 K 31,000

5/6/2003 14,000 14,000 13,000 11,000

5/7/2003 1,100 1,200 840 880

5/8/2003 2,800 2,800 2,900 2,500

5/9/2003 K 80,000 K 110,000 K 50,000 K 80,000

5/12/2003 27,000 21,000 21,000 26,000

5/15/2003 140 130 140 140

6/2/2003 640 590 690 560

6/11/2003 1,300 1,200 790 810

6/25/2003 390 360 420 330

7/9/2003 2,400 2,400 2,800 2,900

7/23/2003 4,700 5,200 3,900 4,500

7/23/2003 920 720 K 1,700 K 1,600

8/6/2003 K 10,000 K 9,300 K 9,100 K 8,600

8/20/2003 240 330 260 240

8/26/2003 K 8,300 K 8,100 K 7,200 K 8,600

9/3/2003 1,200 -- 890 --

9/17/2003 410 350 370 410

24 Escherichia coli Concentrations in the Mill Creek Watershed, Cleveland, Ohio, 2001–2004
Table 1–1. Quality-control data for Escherichia coli concentrations in water samples

collected in Mill Creek, Garfield Heights, Ohio, August 2001–September 2004, and analyzed

by the Northeast Ohio Regional Sewer District and the U.S. Geological Survey.—Continued

[--, no data; K, results based on colony counts outside the ideal range of 20–80 colonies per plate; *, indicates 

field blank sample; <, less than; E, estimated]

Concentration of Escherichia coli (colony-forming units per 100 milliliters)

Date Bottle 1

[A]

Bottle 1 split

[B]

Bottle 2

[C]

Bottle 2 split

[D]

10/2/2003 2,600 2,100 3,000 2,500

10/15/2003 K 16,000 14,000 15,000 12,000

10/29/2003 340 -- 300 --

11/12/2003 15,000 16,000 13,000 9,400

12/10/2003 1,400 1,400 K 1,600 K 1,500

12/22/2003 3,600 4,300 2,300 2,800

1/7/2004 K 930 K 1,100 K 1,100 K 1,100

1/21/2004 320 290 270 270

2/4/2004 K 1,600 K 1,600 K 2,000 K 1,700

2/18/2004 410 510 450 540

3/3/2004 590 560 590 590

3/17/2004 170 170 260 230

4/14/2004 K 1,200 K 1,100 K 700 K 700

4/28/2004 310 340 340 350

4/28/2004 1,100 1,600 1,300 1,400

5/12/2004 600 -- 620 550

5/26/2004 270 -- K 850 --

6/9/2004 660 540 K 1,700 1,600

6/23/2004 490 -- 400 --

7/7/2004 340 350 310 330

7/21/2004 97 110 120 110

8/4/2004 22,000 22,000 18,000 18,000

8/4/2004 K 30,000 25,000 23,000 22,000

8/18/2004 K 1,100 K 1,500 K 1,200 K 1,100

9/1/2004 800 -- 780 --

9/15/2004 150 130 160 180

Table 1–1 25
102 103 104 105

ESCHERICHIA COLI, IN COLONY-FORMING UNITS PER 100 MILLILITERS

0

5

10

15

20

PERCENT DIFFERENCE

Between-bottle differences

Within-bottle differences

Figure 1–1.  Absolute value of the percent difference (log10-transformed data) between quality-control

replicate samples for concentrations of Escherichia coli in Mill Creek, Garfield Heights, Ohio, August 2001–

September 2004.

Table 1–2.  Summary statistics for the percent differences (absolute value of the percent difference of the

log10-transformed data) for within-bottle and between-bottle comparisons of replicate quality-control samples

for concentrations of Escherichia coli in Mill Creek, Garfield Heights, Ohio, August 2001–September 2004.

[NEORSD, Northeast Ohio Regional Sewer District; USGS, United States Geological Survey]

Number

of

samples

Mean

percent

Standard

deviation

percent

Median

percent

Minimum

percent

Maximum

percent

Regular samples – NEORSD

Within bottle 136 1.5 1.3 1.2 0.0 6.8

Between bottle 275 2.6 2.6 2.0 .0 18.1

Quality-control samples

USGS within bottle 14 1.7 1.6 1.3 .0 5.2

USGS between bottle 24 4.1 3.1 3.2 .8 12.1

NEORSD within bottle 14 1.4 1.0 1.5 .0 3.0

NEORSD between bottle 24 3.2 3.0 2.0 .0 10.4

26  Escherichia coli Concentrations in the Mill Creek Watershed, Cleveland, Ohio, 2001–2004

Amie M. G. Brady—Escherichia coli Concentrations in the Mill Creek Watershed, Cleveland, Ohio, 2001–2004—Open-File Report 2007–1171