Summary and Evaluation of the Quality 

of Stormwater in Denver, Colorado, 

October 2001 to October 2005

By Clifford R. Bossong and Andrea C. Fleming

Prepared in cooperation with the Urban Drainage and Flood Control District

Scientific Investigations Report 2008–5134

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: 2008

For product and ordering information:

World Wide Web: http://www.usgs.gov/pubprod

Telephone: 1-888-ASK-USGS

For more information on the USGS--the Federal source for science about the Earth, its natural and living resources, 

natural hazards, and the environment:

World Wide Web: http://www.usgs.gov

Telephone: 1-888-ASK-USGS

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Bossong, C.R., and Fleming, A.C., 2008, Summary and evaluation of the quality of stormwater in Denver, Colorado, 

October 2001 to October 2005: U.S. Geological Survey Scientific Investigations Report 2008–5134, 102 p.
iii

Contents

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

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

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

Description of Stations ........................................................................................................................2

Previous Investigations........................................................................................................................4

Methods of Study...........................................................................................................................................5

Streamflow Data Collection ................................................................................................................5

Sample Collection and Analysis.........................................................................................................6

Composite Samples.....................................................................................................................6

Bacteriological Samples ............................................................................................................9

Discrete Samples.........................................................................................................................9

Quality Assurance and Quality Control .............................................................................................9

Laboratory Quality Assurance and Quality Control................................................................9

Field Quality Assurance/Quality Control ................................................................................10

Summary of Stormwater Quality ...............................................................................................................10

Composite and Bacteriological Samples........................................................................................11

Discrete Samples................................................................................................................................14

Comparison to Numeric Standards .................................................................................................14

Evaluation of Stormwater Quality .............................................................................................................45

Annual Means .....................................................................................................................................45

Tolerance Intervals.............................................................................................................................49

Regressions .........................................................................................................................................49

Comparison to Previous Results ......................................................................................................53

Summary........................................................................................................................................................69

References Cited..........................................................................................................................................70

Appendix. Hydrograph Classification ...................................................................................................73

Figures

1. Map showing location of stations..............................................................................................3

2. Graphs showing daily values for streamflow and precipitation at (A) South

Platte River below Union Avenue at Englewood, (B) South Platte River at 

Denver, (C) Tollgate Creek above 6th Avenue at Aurora, (D) Sand Creek at 

mouth near Commerce City, and (E) South Platte River at Henderson..............................16

3. Boxplots showing distribution of water-quality properties and constituents 

at (A) all stations, (B) South Platte River below Union Avenue at Englewood, 

(C) South Platte River at Denver, (D) Tollgate Creek above 6th Avenue at 

Aurora, (E) Sand Creek at mouth near Commerce City, and (F) South Platte 

River at Henderson, water years 1998–2001 and water years 2002–2005.........................39
iv

Appendix Figures

A1. Graphs showing example storm hydrographs showing (A) rising, falling, and 

(B) event sample classifications ..............................................................................................74

A2. Graphs showing results from discrete sampling events (A) August 28, 2002, 

at South Platte River at Henderson, (B) August 18, 2004, at South Platte River 

at Denver......................................................................................................................................75

Tables

1. Station characteristics ................................................................................................................4

2. Water-quality properties and constituents for composite, bacteriological, 

and discrete samples, water years 2002–2005 ........................................................................7

3. Laboratory performance evaluation data from U.S. Geological Survey 

Standard Reference Sample Program, duplicate samples, and milliequivalent 

balances.......................................................................................................................................10

4. Water-quality properties and constituents in blank samples .............................................11

5. Specific-conductance measurements made at fixed-point sampling and 

channel locations, June 2004 ...................................................................................................14

6. Mean streamflow, streamflow volume, and duration statistics for 

composite samples, water years 2002–2005..........................................................................15

7. Summary statistics for water-quality properties and constituents from 

composite and bacteriological samples at all stations, South Platte River 

below Union Avenue at Englewood, South Platte River at Denver, Tollgate 

Creek above 6th Avenue at Aurora, Sand Creek at mouth near Commerce 

City, and South Platte River at Henderson, water years 2002–2005...................................21

8. Summary of relative percent differences and correlations between various 

weighting methods for analytical determinations of discrete samples, water 

years 2002–2005 ..........................................................................................................................45

9. Summary of composite and bacteriological sample results not meeting 

Colorado Department of Public Health and Environment numeric standards 

for all stations, South Platte River below Union Avenue at Englewood, South 

Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand 

Creek at mouth near Commerce City, and South Platte River at Henderson, 

water years 2002–2005...............................................................................................................46

10. Tolerance intervals computed for physical properties and constituents at 

99-percent coverage with 95-percent confidence at South Platte River below 

Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek 

above 6th Avenue at Aurora, Sand Creek at mouth near Commerce City, and 

South Platte River at Henderson, water years 2002–2005 ...................................................50

11. Results of linear regression analyses, water years 2002–2005 ..........................................55

12. Ninety-five percent confidence bounds for means of selected water-quality 

properties and constituents period 1 (water years 1998–2001) and period 2 

(water years 2002–2005)............................................................................................................69
v

Appendix Tables

A1. Results from discrete samples collected during storms and computed 

time, discharge, and volume-weighted concentrations, with relative 

percent differences....................................................................................................................77

A2. Summary statistics for water-quality properties and constituents by 

water year for all stations, South Platte River below Union Avenue at 

Englewood, South Platte River at Denver, Tollgate Creek above 

6th Avenue at Aurora, Sand Creek at mouth near Commerce City, and 

South Platte River at Henderson..............................................................................................79

A3. Correlation among water-quality properties and constituents, by station .......................94

Conversion Factors

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

Area

square mile (mi2

) 259.0 hectare (ha)

square mile (mi2

) 2.590 square kilometer (km2) 

Volume

acre-foot (acre-ft) 1,233 cubic meter (m3

) 

gallon (gal) 3.785 liter (L) 

acre-foot (acre-ft) 0.001233 cubic hectometer (hm3

) 

Flow rate

cubic foot per second (ft3

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

cubic foot per second per square

mile [(ft3

/s)/mi2]

0.01093 cubic meter per second per square

kilometer [(m3/s)/km2]

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

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 29).

Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD 27).

Altitude, as used in this report, refers to distance above the vertical datum.

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).

Water year is defined in this report as the 12-month period October 1 through September 30, 

designated by the calendar year in which it ends.

Abstract

Stormwater in the Denver area was sampled by the 

U.S. Geological Survey, in cooperation with the Urban 

Drainage and Flood Control District, in a network of five 

monitoring stations—three on the South Platte River and two 

on tributary streams, beginning in October 2001 and continuing through October 11, 2005. Composite samples of stormwater were analyzed at the U.S. Geological Survey National 

Water Quality Laboratory during water years 2003–2005 and 

the Metro Wastewater Reclamation District Laboratory during water year 2002 for water-quality properties such as pH, 

specific conductance, hardness, and residue on evaporation at 

105 degrees Celsius; and for constituents such as major ions 

(calcium, chloride, fluoride, magnesium, potassium, sodium, 

and sulfate) in 2005, organic carbon and nutrients, including 

ammonia, nitrite plus nitrate, ammonia plus organic nitrogen, 

phosphorus, and orthophosphate; and for metals, including total and dissolved phases of copper, lead, manganese, 

and zinc. Samples analyzed for bacteriological indicators 

such as Escherichia coli and fecal coliform collected during 

selected storms also were analyzed at the Metro Wastewater 

Reclamation Laboratory. Discrete samples collected during 

selected storms were analyzed at the U.S. Geological Survey 

National Water Quality Laboratory for a suite of water-quality 

properties and constituents similar to those analyzed in the 

composite samples but that did not include determinations for 

total phases of metals.

Streamflow characteristics associated with 176 composite 

stormwater samples indicate that most samples were collected 

from hydrographs classified as falling or event hydrographs 

and that only a few samples were collected from rising hydrographs. Results from laboratory analyses of the composite 

samples indicate spatial patterns in which concentrations for 

some constituents increase with contributing drainage area in 

the South Platte River and Sand Creek, but no well-defined 

relation with the amount of urban land cover was identified 

using data available from the U.S. Geological Survey National 

Land Cover data.

Results from 22 discrete samples collected during two 

storms and used to obtain composited results with various weighting methods indicate that correlation coefficients 

between time-weighted and volume-weighted concentrations 

were generally at least 0.65, indicating a strong direct correlation between the two weighting methods for the stations 

involved in this study. In addition, the central tendency for 

relative percent differences between the time- and volumeweighting methods typically has an absolute value of about 

10 or less, indicating good agreement for these weighting 

methods for data collected as part of this study.

Comparison of stormwater results to numeric standards 

for streams developed by the Colorado Department of Public 

Health and Environment on the basis of use classifications 

indicates that, for water-quality properties and constituents other 

than bacteriological indicators, there were very few exceptions 

to numeric standards. Bacteriological indicators, however, such 

as Escherichia coli and fecal coliform consistently exceeded 

numeric standards in all bacteriological samples.

An evaluation of laboratory results from composite 

samples on the basis of annual means indicates the presence 

of some simple upward and downward temporal trends in 

concentrations. In general, for annual means of results for 

all stations, hardness, ammonia plus organic nitrogen, total 

phosphorus, most dissolved metals (lead, manganese, and 

zinc), and all total metals (copper, lead, manganese, and zinc) 

all indicate annual means that decrease each year, or downward trends. Some trends were indicated only at individual 

stations in the network rather than at all stations. Ammonia as 

nitrogen at Union, Denver, and Henderson, orthophosphate at 

Sand Creek, and nitrite plus nitrate at Denver and Henderson 

all indicate decreasing annual means, or downward trends. 

Only nitrite plus nitrate at Union and total copper and lead at 

Sand Creek showed consistently increasing annual means, or 

upward trends.

Linear regressions and correlation coefficients among 

the results from composite samples also were computed. 

The regressions, based on the magnitude of the coefficient of 

determination (r2

), indicate widespread strong (r2 equal to or 

greater than 0.65) regressions among major ions. In addition, 

many widespread and strong regressions were noted among 

constituents known to have a particulate component; these 

include organic nitrogen plus ammonia with total phosphorus, 

total copper, and total zinc; total phosphorus with total copper, 

total lead, and total zinc; residue on evaporation at 105 degrees 

Celsius with total copper and total lead; and several additional 

regressions involving metals (total copper with total lead, total 

Summary and Evaluation of the Quality of Stormwater

in Denver, Colorado, October 2001 to October 2005

By Clifford R. Bossong and Andrea C. Fleming
2 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

manganese, and total zinc; and total lead with total zinc). For 

nonmajor constituents that involve very soluble compounds 

(ammonia, nitrite plus nitrate, and orthophosphate) that have 

a very small or even no particulate component, strong regressions are not often widespread and occur mostly locally at 

individual stations. The regression between nitrite plus nitrate 

and orthophosphate is the only strong regression for soluble 

constituents that are not major ions, at all stations. Together, 

relatively weak regressions and correlation coefficients 

between water-quality properties and constituents, and with 

mean streamflow, indicate a heterogeneous and mixed system.

Results from this study were compared to results from 

an earlier U.S. Geological Survey study for water years 

1998–2001 that collected data from the same network of 

stations using the same programmatic goals and samplecollection protocols. Samples from the two periods, based on 

the distribution of mean streamflow associated with composite 

samples, appear to represent similar conditions. There were 

many more exceptions to numeric standards in the earlier 

period than in this study. In addition, the 95-percent confidence intervals for pooled means, from all stations, from this 

study are numerically lower, do not overlap with those from 

the earlier study for some metals (dissolved copper, manganese, and zinc; and total zinc), and indicate statistically significant decreases in concentrations. Likewise, simple downward 

trends were widespread for many constituents, including 

hardness, organic nitrogen plus ammonia, total phosphorus, 

most dissolved metals dissolved (lead, manganese, and zinc) 

and all total metals (copper, lead, manganese, and zinc), and in 

general were more prevalent than in the earlier study.

Introduction

The quality of stormwater runoff is of interest to many 

management and regulatory agencies as well as academia, 

scientists, recreational stream users, and the general public. 

The basic character of stormwater runoff is of general interest to all, whereas more detailed information concerning 

spatial and temporal variations is of interest to management 

and regulatory agencies. In response to these interests, the 

U.S. Geological Survey (USGS), in cooperation with the 

Urban Drainage and Flood Control District (UDFCD), systematically collected stormwater samples during wet weather 

from a monitoring network of five monitoring stations in and 

around metropolitan Denver, Colorado. The monitoring network addresses conditions in Aurora, Denver, and Lakewood 

and consists of three stations on the South Platte River, the 

principal stream draining the area, and two stations on streams 

that are tributary to the South Platte River (fig. 1). Portions 

of each of these streams are included in segments 14, 15, and 

16A of the South Platte River as designated by the WaterQuality Control Division of the Colorado Department of 

Public Health and Environment (CDPHE). Segments 14, 15, 

and 16A are defined by CDPHE and have use classifications 

and associated numeric standards for some water-quality properties and constituents and bacteriological indicators, such as 

pH, dissolved chloride, Escherichia coli, fecal coliform, nitrite 

plus nitrate, dissolved copper, lead, manganese, and zinc, and 

total manganese, that were included in this study (Colorado 

Department of Public Health and Environment, 2005, 2006).

Purpose and Scope

The purpose of this report is to present summaries and 

an evaluation of laboratory analyses for water-quality properties and constituents and bacteriological indicators in different 

types of stormwater samples that characterize the quality of 

stormwater in and around metropolitan Denver for a contemporary period beginning October 1, 2001, and continuing to 

October 11, 2005. The term “water year” can also be used to 

describe the study period; a water year begins on October 1 

and ends September 30, and the study period is referred to as 

“water years 2002–2005” in this report. Specifically, the summaries and evaluation in this report include:

•	 Characterizations that summarize streamflow associated with composite samples,

•	 Univariate statistics that summarize stormwater quality,

•	 Comparison of time-weighted results to discharge and 

volume-weighted results,

•	 Comparisons of contemporary stormwater quality and 

numeric standards for use classifications established by 

the CDPHE,

•	 Descriptive statistics that evaluate annual means, tolerance intervals, correlations, and regressions among 

water-quality properties and constituents, and

•	 Comparison of previous characterizations of stormwater quality, based on data collected during water 

years 1998–2001, to the stormwater quality characterized in this report. The data, methods, and findings 

from 1998–2001 will be designated as “period 1” and 

the term “period 2” will be used for the 2002–2005 

data and findings developed in this report.

Although descriptions of relations between water-quality 

properties and constituents and bacteriological indicators in 

stormwater are included, this report does not provide explanations of the physical basis for any identified relations. The 

summaries presented in this report, however, do provide a 

basis for comparisons to similar data.

Description of Stations

The five stations in the monitoring network include three 

stations on the main stem of the South Platte River (fig. 1; 

table 1). These stations are located below Union Avenue at 

Englewood, at Denver, and at Henderson and will be referred 

to in this report as “Union,” “Denver,” and “Henderson.” The 

stations on the South Platte River receive streamflow from 
Introduction 3

several tributaries, and the South Platte River is sometimes 

referred to as a “receiving stream.” The two additional stations, Sand Creek at mouth near Commerce City and Tollgate 

Creek above 6th Avenue at Aurora, represent tributaries and 

are referred to in this report as “Sand Creek” and “Tollgate.” 

Sand Creek is tributary to the South Platte River and Tollgate 

is tributary to Sand Creek. Collectively, these five stations 

define a drainage system that drains most of the area in and 

around metropolitan Denver.

The South Platte River originates in central Colorado 

and has a contributing drainage area of 3,861 mi2 at the Denver 

station (U.S. Geological Survey, 2002–2005). Snowmelt from 

mountainous areas of central Colorado is a principal source of 

spring streamflow in the South Platte River; however, reservoirs and diversions along the South Platte River regulate 

streamflow. Chatfield Reservoir, which is just upstream from 

Denver, contains the vast majority of storm runoff generated 

upstream from Chatfield Reservoir, essentially truncating the I-25

I-25

E-470

C-470

I-70

I-70

U.S. 36

I-76

I-225

BOULDER

ADAMS

DENVER

ARAPAHOE

DOUGLAS

JEFFERSON

Boulder Creek

Little Dry

Coal

Creek

Rock Creek

Woman Creek

Big

Dry

Creek

Ralston

Clear Creek

Lakewood Gulch

Bear

Creek

Parmalee

Turkey

Cr

Deer Creek

Brush Cr

SOUTH

Plum

Creek

Cherry

 Creek

Tollgate Creek

Sand

 Creek

First

Creek

Third

Creek

SOUTH

PLATTE

Urban Drainage and Flood Control 

District Boundary

Streamflow-gaging station

EXPLANATION

PLATTE

Creek

105o15'

40o00'

39o45'

39o30'

105o00' 104o45'

Sand Creek at mouth 

near Commerce City

South Platte River

below Union Avenue

at Englewood

Tollgate Creek above

6th Avenue, at Aurora

South Platte River

at Henderson

South Platte River

at Denver

DENVER

Study area

0 5 10 15 20 MILES

0 5 10 15 20 KILOMETERS

Grand 

Junction

C O L O R A D O

Figure 1. Map showing location of stations.
4 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

contributing drainage area for the stations used in this study. 

Consequently, most stormwater runoff in the South Platte 

River in the Denver area is derived from a local contributing 

drainage area that does not extend upstream from Chatfield 

Reservoir and is simply the contributing drainage area downstream from Chatfield Reservoir. Streamflow regulation also 

occurs along Sand Creek and Tollgate but does not affect local 

contributing drainage areas.

Land-cover characteristics used in this report (table 1) 

represent percentages of the local contributing drainage areas 

for four aggregated categories developed on the basis of USGS 

National Land Cover data from 1992 (U.S. Geological Survey, 

2003). In the aggregated classification, areas related to crops 

are classified as “agricultural”; areas identified as commercial, industrial, or transportation and areas related to mining, 

such as sand and gravel operations, are classified as “urban”; 

areas identified as residential or recreational are classified as 

“residential”; and all remaining areas are classified as “undeveloped.” The local contributing drainage areas are less than 

10 percent urban and consist mostly of undeveloped land 

(ranging from 41.56 to 75.97 percent in individual basins) and 

residential areas (17.79 to 50.43 percent). Only the agricultural 

land-cover classification shows a tendency to increase with 

local contributing drainage area (from 0.70 to 3.16 percent in 

the South Platte and from 4.97 to 8.72 percent in Sand Creek).

Previous Investigations

Several investigations of stormwater quality have 

been conducted in the Denver area. Beginning in 1979 and 

through 1983, annual data reports were issued summarizing 

stormwater-monitoring activities by USGS for various stations 

in the Denver metropolitan area (Ellis, 1978; Ellis and Alley, 

1979; Hall and Duncan, 1980, 1981; Gibbs, 1981; Gibbs and 

Doerfer, 1982; Gibbs and others, 1983). Although these activities included some sampling in the South Platte River, most of 

the activities focused on tributaries to the South Platte River. 

Blakely and others (1983) reported on washoff characteristics 

from two experimental plots, and Ellis and others (1984), 

Ellis and Mustard (1985), and Mustard and others (1985) 

provided additional stormwater information on the basis 

of the USGS stormwater-monitoring activities. In addition, 

the Denver Regional Council of Governments (1983) summarized their stormwater-monitoring activities in the Denver 

metropolitan area.

More recently, Bossong and others (2005) summarized 

stormwater quality in the Denver area on the basis of samples 

collected form October 1, 1997, to September 30, 2001 (water 

years 1998 through 2001). The conclusions from the 2005 

report indicated that concentrations in stormwater tended to 

Table 1. Station characteristics.

[Station number and name from the USGS National Water Inventory System. Latitude and Longitude (NAD 27), geographic coordinates in degrees, minutes, seconds. 

Operating agency indicates agency responsible for streamflow records: USGS, U.S. Geological Survey; CODWR, Colorado Division of Water Resources; UDFCD, 

Urban Drainage and Flood Control District. RF location, location of precipitation gage associated with station, the source for all precipitation records is UDFCD. 

CDA, contributing drainage area in square miles; LCDA, local contributing drainage area in square miles adjusted for regulation (excludes CDA upstream from 

Chatfield Dam for South Platte River stations). Land cover indicates percentage of LCDA on basis of National Land Cover data from 1992 (U.S. Geological Survey, 

2003) for undeveloped areas (Und), agricultural areas (Ag), residential areas (Res), and urban areas (Urb). Comments provide important historical operational events. 

ft3/s, cubic feet per second; (ft3/s)/mi2, cubic feet per second per square mile; acre-ft/mi2, acre-feet per square mile]

Station number Station name Station location Operating

agency

RF location

Latitude Longitude Latitude Longitude

06710247 South Platte River below Union Avenue at Englewood 39o37'57" 105o00'52" USGS 39o37'57" 105o00'52"

06714000 South Platte River at Denver 39o45'35" 105o00'10" CODWR 39o44'32" 104o59'58"

394329104490101 Tollgate Creek above 6th Avenue at Aurora 39o43'29" 104o49'01" UDFCD 39o43'30" 104o49'06"

394839104570300 Sand Creek at mouth near Commerce City 39o48'36" 104o57'00" USGS 39o48'39" 104o57'03"

06720500 South Platte River at Henderson 39o55'10" 104o52'04" CODWR 39o55'19" 104o52'00"

Station number CDA LCDA

Land cover, in percentage of local 

contributing drainage area Comments

Und Ag Res Urb

06710247 3,093 76 43.08 0.70 50.43 5.79 Gage operated as described in Rantz and others (1982). Various 

other precipitation used previous to water year 2000.

06714000 3,861 844 75.97 1.23 19.41 3.39 Gage operated as described in Rantz and others (1982). Various 

other precipitation used previous to water year 2001.

394329104490101 35 35 41.56 4.97 47.98 5.49 Gage operated as part of flood warning network. Various other 

precipitation records used previous to water year 2001.

394839104570300 184 184 62.58 8.72 22.41 6.29 Gage operated as described in Rantz and others (1982). Various 

other precipitation used previous to water year 2001.

06720500 4,768 1,751 75.30 3.16 17.79 3.75 Gage operated as described in Rantz and others (1982). Various 

other precipitation used previous to water year 2001.
Methods of Study 5

increase in a downstream direction along the South Platte 

River, that concentrations for many water-quality properties 

and constituents in stormwater were relatively dilute compared 

to concentrations in base flow, that exceptions to CDPHE 

numeric standards (measured concentrations that did not 

meet standards) for some metals occurred in as many as 10 

to 25 percent of samples, and that there were consistent exceptions to numeric standards for bacteriological indicators such 

as Escherichia coli and fecal coliform. This report summarizes a second period, October 1, 2001, to October 11, 2005 

(referred to as “water years 2002–2005” in this report) using 

similar methods and contemporary data that were collected 

using the same protocols and programmatic goals leading to 

the Bossong and others (2005) report.

Methods of Study

The methods used to collect and process streamflow data, 

collect and process stormwater samples, and perform laboratory analyses are described in this section. The section also 

describes the quality-assurance and quality-control (QA/QC) 

measures and results used in the study.

Streamflow Data Collection

Streamflow records are maintained for each station by 

various operating agencies (table 1). Union and Sand Creek 

are operated by the USGS in accordance with methods 

described by Rantz and others (1982). The streamflow data for 

Union and Sand Creek are maintained in the USGS National 

Table 1. Station characteristics.—Continued

[Station number and name from the USGS National Water Inventory System. Latitude and Longitude (NAD 27), geographic coordinates in degrees, minutes, seconds. 

Operating agency indicates agency responsible for streamflow records: USGS, U.S. Geological Survey; CODWR, Colorado Division of Water Resources; UDFCD, 

Urban Drainage and Flood Control District. RF location, location of precipitation gage associated with station, the source for all precipitation records is UDFCD. 

CDA, contributing drainage area in square miles; LCDA, local contributing drainage area in square miles adjusted for regulation (excludes CDA upstream from 

Chatfield Dam for South Platte River stations). Land cover indicates percentage of LCDA on basis of National Land Cover data from 1992 (U.S. Geological Survey, 

2003) for undeveloped areas (Und), agricultural areas (Ag), residential areas (Res), and urban areas (Urb). Comments provide important historical operational events. 

ft3/s, cubic feet per second; (ft3/s)/mi2, cubic feet per second per square mile; acre-ft/mi2, acre-feet per square mile]

Streamflow statistics

Station name

(number)

Union

(06710247)

Denver

(06714000)

Sand Creek 

(394839104570300)

Henderson

(06720500)

Period of record, in water years 1996–2005 1976–2005 2000–2005 1976–2005

Annual mean, in ft3

/s 143 356 29.4 542

Annual mean, in (ft3

/s)/mi2 1.88 0.42 0.31

Highest annual mean, in ft3

/s 293 961 39.0 1379

Highest annual mean, in (ft3

/s)/mi2 3.86 1.14 0.21 0.79

Date 1999 1983 1997 1983

Lowest annual mean, in ft3

/s 29.3 120 20.7 252

Lowest annual mean, in (ft3

/s)/mi2 0.38 0.14 0.11 0.14

Date 2002 2002 2002 1981 

Highest daily mean, in ft3

/s 1,940 4,020 926 6,500

Highest daily mean, in (ft3

/s)/mi2 25.5 4.78 5.03 3.73

Date June 18, 1999 May 27, 1987 May 5, 2001 June 9, 1995

Lowest daily mean, in ft3

/s 3.3 42 2.1 27

Lowest daily mean, in (ft3

/s)/mi2 0.04 0.05 0.01 0.02

Date April 24, 1996 August 2, 2002 July 14, 2004 April 7, 1977 

Annual 7-day minimum, in ft3

/s 5.3 48 3.2 69

Annual 7-day minimum, in (ft3

/s)/mi2 0.07 0.06 0.02 0.04 

Date December 9, 2002 August 14, 2002 July 9, 2004 March 13, 1982

Maximum peak flow, in ft3

/s 2,150 12,600 4,010 12,300

Maximum peak flow, in (ft3

/s)/mi2 28.3 15.0 21.8 7.06

Date May 28, 1999 July 25, 1998 August 18, 2004 June 27, 1983

Annual runoff, in acre-feet 103,800 258,300 21,300 392,600

Annual runoff, in acre-ft/mi2 1,366 307 116 226

10 percent exceeds, in acre-feet 367 707 51 1,020

10 percent exceeds, in acre-ft/mi2 4.83 0.84 0.28 0.58

50 percent exceeds, in acre-feet 63 184 17 333

50 percent exceeds, in acre-ft/mi2 0.83 0.22 0.09 0.19

90 percent exceeds, in acre-feet 14 84 10 179

90 percent exceeds, in acre-ft/mi2 0.18 0.10 0.05 0.10
6 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Water Information System (NWIS). Daily data, which represent various statistics for a 24-hour period, and subdaily data 

that are instantaneous values used to develop daily values, are 

available from NWIS. In addition, the records were published 

in USGS annual data reports for water years 2002–2005 

(U.S. Geological Survey, 2002–2005). The published records 

received additional processing to obtain a variety of summary 

streamflow statistics, some of which are included in table 1.

Denver and Henderson are operated by the Colorado 

Division of Water Resources (CODWR). The CODWR records 

are reviewed and published by the USGS (U.S. Geological 

Survey, 2002–2005). Daily streamflow values are maintained 

in NWIS. Instantaneous values for the most recent year are 

maintained on a publicly available CODWR Web-based system 

(URL http://www.dwr.state.co.us/SurfaceWater/Default.aspx). 

All instantaneous values from Denver and Henderson are available on a UDFCD Web-based system (http://alert.udfcd.org).

Tollgate is operated by UDFCD using systematic but 

undocumented methods that involve theoretical stage and 

streamflow relations developed on the basis of channel 

geometry. The Tollgate data are used as part of an Automated 

Local Evaluation in Real Time (ALERT) system operated by 

UDFCD to assess field conditions in a real-time mode in order 

to facilitate flood forecasting. Because the UDFCD data are 

focused on real-time information, data may be available only 

for periods of storm runoff. The UDFCD records consist only 

of instantaneous values that are archived but do not receive 

additional processing or extensive review.

Sample Collection and Analysis

Two principal types of investigative samples, referred to 

as “composite” and “discrete” samples, were collected as part 

of this study. Composite samples integrate several aliquots of 

water collected over a period of time, and discrete samples 

consist of a single sample that is more representative of an 

instantaneous sample. All composite and discrete samples 

were collected using automatic pumping samplers that withdraw water from a fixed point in the channel cross section. 

The samples at four samplers are refrigerated, and ice is used 

in the fifth sampler to chill samples. In addition, bacteriological samples were sometimes manually collected during 

selected storms. The composite, bacteriological, and discrete 

samples are collectively referred to as “stormwater samples.”

During this study, stormwater samples were analyzed by two laboratories in Denver, Colorado: the Metro 

Wastewater Reclamation District Laboratory (MWRD) and 

the USGS National Water Quality Laboratory (NWQL). 

Composite samples were analyzed at MWRD during water 

year 2002; after water year 2002 all composite samples 

were analyzed at NWQL, and MWRD only analyzed bacteriological samples. All discrete samples were analyzed at 

NWQL. The results of all laboratory analyses obtained as 

part of this study reside in the NWIS database and can be 

accessed using the USGS Web interface to water data at URL 

http://waterdata.usgs.gov/co/nwis/qw/. Table 2 describes 

the laboratory analyses and analytical methods used for the 

principal types of samples collected as part of this study. 

Results referred to as “dissolved” are from water that has 

been passed through a filter that removes particles greater 

than 0.45 micrometer in their smallest diameter. Results referred 

to as “total” are from unfiltered water that has undergone an inbottle digestion procedure (Hoffman and others, 1996). Results 

referred to as “whole water” are from water that has not been 

filtered or digested. Table 2 also lists the reporting level. The 

general term “reporting level” specifies the level at which values 

will be censored, or reported as “less than” and is sometimes 

referred to as “censored” (Helsel, 2005). Laboratory quantifications of values below the reporting level are sometimes provided 

and are typically qualified as estimates.

Composite Samples

A total of 176 composite samples were collected using 

refrigerated, or ice chilled, automatic pumping samplers that 

were manually activated when stormwater runoff began. Once 

activated, the samplers obtained aliquots, or sample portions, 

by withdrawing fixed volumes of water from the stream every 

60 minutes. The samplers were equipped with eight 2-L bottles and were programmed to add three aliquots to each bottle. 

In theory, the samplers could operate unattended for 24 hours; 

however, in practice, each station was visited by USGS project 

staff every 12 to 24 hours during storm events. As the stations were visited, the contents of four sequential bottles were 

composited into a single time-weighted composite sample. For 

submittal to MWRD, each sample was composited according 

to churn-splitter procedures described in the USGS National 

Field Manual (U.S. Geological Survey, variously dated, 

chapter A5), which documents USGS protocols for collection 

of water-quality data. Additional sample processing, such as 

filtration, bottling, and preservation, occurred at MWRD. The 

compositing, filtration, bottling, and preservation of samples 

submitted to NWQL took place in the field using procedures 

described in the USGS National Field Manual. If individual 

sample bottles were found to contain different volumes of 

water, it was assumed that individual aliquot volumes varied, 

and the aliquot sample volumes were adjusted, if possible, or 

the samples were discarded. The samples were analyzed for 

physical properties such as pH, specific conductance, hardness, and residue on evaporation at 105 degrees Celsius; for 

constituents such as major ions (in 2005), organic carbon, and 

nutrients, including ammonia, nitrite plus nitrate, ammonia 

plus organic nitrogen, total phosphorus, and orthophosphate; 

and for metals, including total and dissolved phases of copper, 

lead, manganese, and zinc (table 2).

The composite samples integrate concentrations over 

time and are appropriate for evaluating water-quality criteria 

developed for aquatic wildlife. The aquatic wildlife criteria 

defined by CDPHE (Colorado Department of Public Health and 

Environment, 2005, 2006), generally the most stringent criteria in 
Methods of Study 7

Table 2. Water-quality properties and constituents for composite, bacteriological, and discrete samples, water years 2002–2005.

[USGS, U.S. Geological Survey; USEPA, U.S. Environmental Protection Agency; C, Celsius; N, nitrogen; P, phosphorus. Phase: W, determination made using 

whole water; T, total; D, dissolved. Analytical facility, MWRD, Metro Wastewater Reclamation District Laboratory; NWQL, USGS National Water Quality 

Laboratory. Preferred analytical method indicates the analytical method in use at the Metro Wastewater Reclamation District Laboratory in 2002. Reporting 

units: stdu, standard pH units; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter; μg/L, micrograms per liter; col, colonies 

per 100 milliliters; --, not applicable; ICP, inductively coupled plasma]

Composite samples, water year 2002

Water-quality property

or constituent Phase Analyticalfacility

Laboratory property or 

constituent identifier

USGS

parameter code Analytical method Reportingunits

Reporting

level

Physical properties

pH, laboratory W MWRD PHD001 00403 USEPA 150.1 stdu --

Specific conductance W MWRD CON001 00095 USEPA 120.1 μS/cm 0.10 

Hardness, as calcium carbonate T MWRD HARD001 00900 USEPA 130.2 mg/L 10.00

Residue on evaporation T MWRD TSS001 00530 USEPA 160.2 mg/L 1.00

Organics

Organic carbon T MWRD TOC001 00680 USEPA 415.1 mg/L 1.00

Nutrients

Ammonia, as N T MWRD NH3A001 00610 USEPA 350.1 mg/L 0.20

Ammonia + organic N, as N T MWRD TKNH001 1

00625 USEPA 351.3 mg/L 0.30

Nitrite + nitrate, as N T MWRD NO5001 00630 USEPA 353.2 mg/L 0.02 

Phosphorus, as P T MWRD TPW001 00665 USEPA 365.4 mg/L 0.03 

Orthophosphate, as P D MWRD OP001 00671 USEPA 365.1 mg/L 0.03 

Metals

Copper D MWRD ICPSW007 2

01040 USEPA 200.7 μg/L 1.00 

Copper T MWRD CURFW001 3

01119 USEPA 220.2 μg/L 1.00 

Lead D MWRD ICPSW003 2

01049 USEPA 200.7 μg/L 10.00

Lead T MWRD PBRFW001 01114 USEPA 239.2 μg/L 10.00

Manganese D MWRD ICPSW005 4

01056 USEPA 200.7 μg/L 0.02

Manganese T MWRD ICPSW005 400925 USEPA 200.7 μg/L 0.02

Zinc D MWRD ICPSW001 201090 USEPA 200.7 μg/L 0.30

Zinc T MWRD ZNRFW001 301094 USEPA 289.2 μg/L 0.30

Composite samples, water years 2003 to 2005

Water-quality property

or constituent Phase Analyticalfacility

Laboratory property or 

constituent identifier

USGS

parameter code Analytical method Reportingunits

Reporting

level

Physical properties

pH, laboratory W NWQL 68 00403 I-2587-895 stdu 0.1

Alkalinity, as calcium carbonate, 

fixed endpoint

D NWQL 2109 29801 I-2030-895 mg/L 5 

Specific conductance W NWQL 69 00095 I-2781-885 μS/cm 2.6 

Residue on evaporation T NWQL 169 00530 I-3765-895 mg/L 10

Major ions

Calcium D NWQL 659 00915 I-1472-876 mg/L 0.02 

Chloride D NWQL 1571 00940 I-2057-855 mg/L 0.20

Fluoride D NWQL 31 00950 I-2327-895 mg/L 0.10 

Magnesium D NWQL 663 00925 I-1472-876 mg/L 0.008 

Potassium D NWQL 2773 00935 3120-ICP7 mg/L 0.16 

Sodium D NWQL 675 00930 I-1472-876 mg/L 0.20 

Sulfate D NWQL 1572 00945 I-2057-855 mg/L 0.18

Organics

Organic carbon D NWQL 2612 00681 O-1120-928 mg/L 0.33

Nutrients

Ammonia, as N T NWQL 3116 00608 I-2522-906

,

I-2525-896

mg/L 0.010 

Ammonia + organic N, as N T NWQL 1986 00625 I-4515-919 mg/L 0.10

Nitrite + nitrate, as N T NWQL 1975 00631 I-2545-906 mg/L 0.060

Orthophosphate, as P D NWQL 3118 00671 I-2601-906

,

I-2606-896

mg/L 0.006 

Phosphorus, as P T NWQL 1984 00665 I-4610-9110 mg/L 0.040
8 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table 2. Water-quality properties and constituents for composite, bacteriological, and discrete samples, water years 2002–2005.—Continued

[USGS, U.S. Geological Survey; USEPA, U.S. Environmental Protection Agency; C, Celsius; N, nitrogen; P, phosphorus. Phase: W, determination made using 

whole water; T, total; D, dissolved. Analytical facility, MWRD, Metro Wastewater Reclamation District Laboratory; NWQL, USGS National Water Quality 

Laboratory. Preferred analytical method indicates the analytical method in use at the Metro Wastewater Reclamation District Laboratory in 2002. Reporting 

units: stdu, standard pH units; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter; μg/L, micrograms per liter; col, colonies 

per 100 milliliters; --, not applicable; ICP, inductively coupled plasma]

Composite samples, water years 2003 to 2005—Continued

Water-quality property

or constituent Phase Analyticalfacility

Laboratory property or 

constituent identifier

USGS

parameter code Analytical method Reportingunits

Reporting

level

Metals

Copper D NWQL 1791 01040 I-2477-9211 μg/L 0.4 

Copper T NWQL 2379 01042 I-4471-9712 μg/L 0.6 

Lead D NWQL 1792 01049 I-2477-9211 μg/L 0.08 

Lead T NWQL 2380 01051 I-4471-9712 μg/L 0.06 

Manganese D NWQL 1793 01056 I-2477-9211 μg/L 0.2 

Manganese T NWQL 2382 01055 I-4471-9712 μg/L 0.6 

Zinc D NWQL 1798 01090 I-2477-9211 μg/L 0.6 

Zinc T NWQL 2390 01092 I-4471-9712 μg/L 2 

Bacteriological samples

Water-quality property 

or constituent Phase Analyticalfacility

Laboratory property or 

constituent identifier

USGS

parameter code Analytical method Reportingunits

Reporting

level

Escherichia coli W MWRD ECMPN001 50468 USEPA 600/8-78-017, 1978 col 2

Fecal coliform W MWRD FCMPN001 31615 USEPA 600/8-78-017, 1978 col 20

Discrete samples

Water-quality property 

or constituent Phase Analyticalfacility

Laboratory property or 

constituent identifier

USGS

parameter code Analytical method Reportingunits

Reporting

level

Physical properties

pH, laboratory W NWQL 00068 00403 I-2587-895 stdu 0.1

Alkalinity, as calcium carbonate,

fixed endpoint

D NWQL 02109 29801 I-2030-895 mg/L 5

Alkalinity, as calcium carbonate,

fixed endpoint

W NWQL 00070 90410 I-2030-895 mg/L 6

Specific conductance W NWQL 00069 00095 I-2781-885 μS/cm 2.6

Residue on evaporation T NWQL 00169 00530 I-3765-895 mg/L 10

Major ions

Calcium D NWQL 00659 00915 I-1472-876 mg/L 0.02

Chloride D NWQL 01571 00940 I-2057-855 mg/L 0.20

Fluoride D NWQL 00031 00950 I-2327-895 mg/L 0.10

Magnesium D NWQL 00663 00925 I-1472-876 mg/L 0.008

Potassium D NWQL 02773 00935 3120-ICP7 mg/L 0.16

Sodium D NWQL 00675 00930 I-1472-876 mg/L 0.20

Sulfate D NWQL 01572 00945 I-2057-855 mg/L 0.18

Organics

Organic carbon D NWQL 02612 00681 O-1120-928 mg/L 0.33

Nutrients

Ammonia, as N T NWQL 03116 00608 I-2522-906

, I-2525-896 mg/L 0.010

Ammonia + organic N, as N T NWQL 01986 00625 I-4515-9110 mg/L 0.10

Nitrite + nitrate, as N T NWQL 01975 00631 I-2545-906 mg/L 0.060

Orthophosphate, as P D NWQL 03118 00671 I-2601-906

, I-2606-896 mg/L 0.006

Phosphorus, as P T NWQL 01984 00665 I-4610-9110 mg/L 0.040

Metals

Copper D NWQL 01791 01040 I-2477-9211 μg/L 0.4

Lead D NWQL 01792 01049 I-2477-9211 μg/L 0.08

Manganese D NWQL 01793 01056 I-2477-9211 μg/L 0.2

Zinc D NWQL 01798 01090 I-2477-9211 μg/L 0.6

1

An analytical facility identifier of TKNL001 sometimes used for low-level determinations.

2

A different analytical facility identifier sometimes used for furnace determinations using the same USEPA methods used for total determinations.

3

A different analytical facility identifier sometimes used for ICP determinations made using the same USEPA methods used for furnace dissolved determinations.

4

Manganese results are available only for a subset of all samples.

5

Fishman and Friedman, 1989.

6

Fishman, 1993.

7

American Public Health Association, 1998.

8

Brenton and Arnett, 1993.

9

Patton and Truitt, 2000.

10Patton and Truitt, 1992.

11Faires, 1993.

12Garbarino and Struzeski, 1998.
Methods of Study 9

place, describe acute standards that specify a maximum allowable 

concentration for a period of time, usually 24 hours. The acute 

criteria, like the composite samples, describe concentration over a 

period of time rather than instantaneous concentration.

The samplers can be activated to collect samples automatically in a number of different ways; however, due to the effects 

of streamflow regulation and relatively complex weather patterns, decisions to activate samplers in this study were made by 

USGS project staff on the basis of local weather and streamflow 

conditions. Local weather and streamflow conditions were monitored nearly continuously through a variety of sources including near real-time data available from the World Wide Web. The 

ALERT system operated by UDFCD provides very near realtime data from an extensive network of precipitation gages. In 

addition, the ALERT system provides information from many 

UDFCD gaging stations. It also integrates streamflow data from 

USGS and CODWR gaging stations into very near real-time 

Web-based reports. The very near real-time ALERT data typically are available within a few minutes of measurement.

Bacteriological Samples

Twenty-two bacteriological samples were collected 

during selected storms. The samples were collected manually as grab samples by filling bottles at streamsides and then 

transporting them directly to MWRD for immediate analysis, 

typically within an hour of sample collection. The bacteriological samples were analyzed for the bacteriological indicators 

Escherichia coli and fecal coliform (table 2).

Discrete Samples

Twenty-two discrete samples were collected during two 

storms to help evaluate the effect various weighting methods 

might have on sample compositing. The automatic pumping 

samplers were operated manually to obtain individual, or discrete, 

samples through a storm hydrograph. The discrete samples were 

analyzed at the NWQL for a suite of constituents that did not 

include determinations for total copper, lead, manganese, and 

zinc but otherwise was very similar to the suite of analyses for 

composite samples analyzed at the NWQL (table 2).

Discrete samples were processed in the field and then 

submitted to the NWQL for analysis. No physical compositing 

was done in the field; rather, the results from individual discrete samples were composited by mathematically using three 

different weighting techniques based on time, streamflow, and 

volume using a general equation with the form:

WC = [ΣC × WF} ÷ [ΣWF] (1)

where

WC is weighted concentration,

C is concentration,

and

WF is weighting factor (time, streamflow, 

or volume).

Quality Assurance and Quality Control

Laboratory QA/QC samples were evaluated as part 

of this study. Additional QA/QC field samples also were 

collected to characterize the influence that sampling 

equipment or ambient field conditions may have had on 

samples. Information about and descriptions of milliequivalent 

balances computed for samples analyzed for major ions are 

discussed in Hem (1985). Specific conductances determined 

using the pumping samplers and samples collected using 

methods that integrate cross-section conditions in the channel 

also are presented in this section of the report.

Laboratory Quality Assurance 

and Quality Control

It is standard USGS practice to monitor laboratory performance for purposes of qualifying laboratory results. Laboratory 

performance in this study was evaluated on the basis of the 

USGS Standard Reference Sample (SRS) program (Woodworth 

and Connor, 2003) as well as different types of additional 

QA/QC samples. The SRS program prepares spiked samples 

and distributes them to as many as 100 laboratories across the 

Nation. Results from all laboratories are used to determine a 

most probable value (MPV), and individual laboratory results 

are compared to the MPV to quantify performance.

The NWQL and MWRD SRS program results for 

laboratory analyses used in this study are summarized in table 3. 

In general, the results indicate that the median relative percent 

difference (RPD) between laboratory results and the SRS MPV, 

for both laboratories, had an absolute value less than 1 with a 

standard deviation of about 8. The RPD for two given values 

(a and b) is calculated according to the following equation:

RPD = {(a – b) ÷ [(a + b) ÷ 2]} × 100 (2)

For example, a laboratory result of 8, when the MPV is 

10, results in an RPD of –22.2. The frequency distribution 

information in table 3 indicates that, for the 41 tests MWRD 

participated in during 2002, the central 80 percent of the distribution (from the 10th to the 90th percentiles) of RPDs ranged 

from –2.34 to 3.86; for the 306 tests NWQL participated in, 

the RPDs ranged from –6.56 to 5.72.

Duplicate samples also were used to evaluate laboratory performance and field procedures. The duplicate samples 

consisted of field-matrix, or actual, stormwater split into 

two separate samples and can be more explicitly referred 

to as “split-replicate samples.” The results from these splitreplicate samples indicate that results from the field have 

slightly wider extremes than the results from the SRS program 

(table 3).

Milliequivalent balances for major ions were calculated 

according to methods described by Hem (1985) for samples 

analyzed at the NWQL for major ions. Typically the major 

ions (cations and anions) are the principal contributors of 
10 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

electrical charge for dissolved constituents in water, and their 

sum should be close to zero; departures from zero may be an 

indication of inaccurate analyses. The milliequivalent balances 

shown in table 3 indicate excellent results at the NWQL.

Field Quality Assurance/Quality Control

Additional QA/QC samples included various blank 

samples collected to help characterize the potential effects of 

field procedures and ambient field conditions. Spiked samples 

were used to define potential contributions of organic carbon 

introduced by field equipment. Cross-section samples were 

used to help characterize differences between samples collected using the fixed intakes of the pumping samplers and 

samples collected manually using depth-integrating techniques 

(U.S. Geological Survey, variously dated, chapter A5), across 

the cross section.

Table 4 includes results from field, churn, and equipment 

blanks. Universal blank water (UBL), obtained from the NWQL 

and certified to have very low concentrations of inorganic 

and organic constituents, was used when collecting the blank 

samples. Field blanks were collected by pouring UBL water 

directly into sample bottles in the field; the field blank samples 

are not processed in churn splitters or filters. Churn blanks were 

collected by processing UBL through churn splitters in the field. 

The results for field and churn blanks in table 4 indicate no 

substantial contributions to concentrations from ambient field 

conditions or the use of churn splitters in the field.

Equipment blanks were collected to characterize the 

potential effects of sampler intake lines. Three types of equipment blanks were collected: type 1 samples consist of UBL 

passed through sampler intake lines with no rinse; type 2 

samples consist of UBL passed through sampler intake lines 

after a field rinse with native water; and type 3 samples consist 

of UBL passed through sampler intake lines after a UBL rinse. 

The results for equipment blanks in table 4 indicate that there 

were no substantial contributions to concentrations from sampler intake lines.

Two sets of organic carbon blank samples that were 

collected in May and June of 2004 were used to evaluate the 

potential additive effect that pumping sampler bottles, which 

are plastic, may have on organic carbon concentrations. Each 

sample set included three samples: type 1 samples consisted 

of UBL water stored in pumping sampler bottles under field 

conditions (refrigerated) for at least 2 days; types 2 and 3 

samples consisted of water spiked to concentrations approximating ambient field conditions and stored in plastic and glass 

containers (respectively) under field conditions for at least 

2 days. The results for these samples (table 4) do not indicate 

a substantial contribution to concentrations of organic carbon 

from pumping sampler bottles.

A comparison of results from the pumping samplers and 

cross-section depth-integrated samples was made on the basis 

of specific conductance measurements made during water 

year 2004 (table 5). The pumping samplers collect water from 

a fixed point, and depth-integrated samples were collected at 

10 points distributed across the individual stream channel. The 

samples were collected in the field under stable streamflow 

conditions in June of 2004; the results do not include Tollgate Creek, which was in backwater at that time. The results 

from the cross-section depth-integrated samples indicate that 

in all of the streams, except perhaps the South Platte River 

at Denver, specific conductance is uniform across the channel, under conditions of stable streamflow. The results also 

indicate that, under conditions of stable streamflow, specific 

conductance from the fixed sampling points is representative of overall channel conditions. These results are similar to 

those for stormwater samples collected in the same network 

during water years 1998–2001 (Bossong and others, 2005).

Summary of Stormwater Quality

The results of stormwater sample-collection activities 

and analyses of stormwater samples for water-quality properties and constituents and biological indicators are summarized 

in this section. Descriptions of composite-sample collection 

activities characterize sampled storms and give the number 

of samples collected. Summary statistics for the results of 

laboratory analyses of composite samples describe results 

collectively, by station, and by hydrograph classification. 

Stormwater-sample collection activities and laboratory analyses associated with discrete samples also are discussed in this 

section. In addition, results from composite samples collected 

in this study are compared to numeric standards established by 

the CDPHE.

Table 3. Laboratory performance evaluation data from U.S. Geological Survey Standard Reference Sample Program, duplicate 

samples, and milliequivalent balances.

[MWRD, Metro Wastewater Reclamation District Laboratory; NWQL, USGS National Water Quality Laboratory; Stddev, standard deviation; n, number of samples. 

Univariate statistics for U.S. Geological Survey Standard Reference Sample program most probable values and results from Metro Wastewater Reclamation District 

Laboratory and U.S. Geological Survey National Water Quality Laboratory]

Laboratory Mean Median Stddev Skewness Minimum Maximum Range for 10th to 

90th percentile n

MWRD (2002) 2.56 0.57 8.06 3.17 –4.93 34.98 –2.34 to 3.86 41

NWQL (2002–2005) –0.44 0 8.48 –1.51 –56.66 49.18 –6.56 to 5.72 306

Duplicates 5.24 0 31.81 2.83 –119.74 191.02 –9.11 to 16.42 108

Milliequivalent balances (percent) 0.78 0.78 1.30 0.27 –2.23 5.38 –0.77 to 2.21 63
Summary of Stormwater Quality 11

Table 4. Water-quality properties and constituents in blank samples.

[Equipment blank type: type 1 samples consist of universal blank water (UBL) passed through sampler intake lines with no rinse; type 2 samples consist of UBL 

passed through sampler intake lines after a field rinse with native water; and type 3 samples consist of UBL passed through sampler intake lines after a UBL rinse. 

Organic carbon blank type: Type 1 samples consist of UBL water stored in pumping sampler supplies under field conditions (refrigerated) for at least 2 days; 

Type 2 and 3 samples consist of water spiked to concentrations approximating field conditions and stored in plastic and glass containers (respectively) under field 

conditions for at least 2 days. Phase: W, determination made using whole water; T, total; D, dissolved; stdu, standard pH units; μS/cm, microsiemens per centimeter 

at 25 degrees Celsius; C, Celsius; mg/L, milligrams per liter; N, nitrogen; P, phosphorus; CaCO3, calcium carbonate; μg/L, micrograms per liter; E, estimated value 

below reporting level; --, not applicable; <, less than]

Property or

constituent Phase Sample type

Field blanks Churn blanks

Station name Tollgate Sand

Creek Tollgate Henderson Denver SandCreek Denver Henderson SandCreek

Date 20030607 20041124 20040718 20040811 20040819 20050604 20050724 20050725 20050912

Time 2211 900 1000 1400 0511 1739 1750 2135 1040

pH, in standard units W 5.2 7.2 E6.9 E6.9 E6.8 5.9 7.7 8.4 --

Specific conductance, 

in μS/cm

W -- -- -- -- -- -- -- -- --

Hardness, as CaCO3

, in mg/L T -- -- -- -- -- -- -- -- --

Calcium, in mg/L D 0.02 0.04 0.01 0.05 0.03 <.02 E.01 0.03 --

Magnesium, in mg/L D <.008 <.008 <.008 E.004 <.008 <.008 <.008 <.008 --

Potassium, in mg/L D -- <.16 -- -- <.16 <.16 <.16 <.16 --

Sodium, in mg/L D -- <.20 -- -- -- <.20 <.20 <.20 --

Alkalinity, as CaCO3

,fixed 

endpoint, in mg/L

W -- 2 -- -- -- 2 <5 <5 --

Chloride, in mg/L D -- <.20 -- -- <.20 <.20 <.20 <.20 --

Fluoride, in mg/L D -- <.1 -- -- <.2 <.1 <.1 <.1 --

Sulfate, in mg/L D -- <.2 -- -- <.2 <.2 <.2 <.2 --

Residue on evaporation 

at 105°C, in mg/L

T <10 <10 <10 <10 <10 <10 <10 <10 --

Ammonia + organic N, 

in mg/L

T <.10 <.10 <.10 <.10 <.10 -- <.10 <.10 <.10

Ammonia, as N, in mg/L D <.04 <.04 <.04 <.04 <.04 -- <.04 <.04 <.04

Nitrite + nitrate, as N, in mg/L D <.06 <.06 <.06 <.06 <.06 -- <.06 <.06 <.06

Orthophosphate, as P, in mg/L D <.007 <.006 E.003 <.006 <.006 -- <.006 <.006 <.006

Phosphorus, as P, in mg/L T <.04 <.04 <.04 <.04 <.04 -- <.04 <.04 <.04

Organic carbon, in mg/L D 1 <.3 <.3 0.5 0.8 0.5 0.6 0.6 --

Copper, in μg/L D <.2 <.4 <.4 <.4 <.4 <.4 <.4 <.4 --

Copper, in μg/L T <.6 <.6 <.6 <.6 -- <.6 <.6 <.6 --

Lead, in μg/L D <.08 <.08 <.08 <.08 <.08 <.08 <.08 <.08 --

Lead, in μg/L T <.06 <.06 <.06 E.04 -- <.06 <.06 <.06 --

Manganese, in μg/L D <.2 <.2 <.2 0.3 -- <.2 E.1 <.2 --

Manganese, in μg/L T E.2 E.1 <.2 0.9 -- 0.3 0.2 <.2 --

Zinc, in μg/L D <1.0 <.6 E.3 0.9 <.6 0.7 <.6 3 --

Zinc, in μg/L T 2 <2 <2 3 -- <2 <2 4 --

Composite and Bacteriological Samples

A summary describing streamflow associated with composite-sample collection is presented in table 6. Daily-value hydrographs for each station indicate sampling events (fig. 2). Table 6 

includes summary data for the mean streamflow, streamflow 

volume, and duration (length of time) associated with individual 

composite samples collected at individual stations and for all 

stations pooled together. The data are presented for composite 

samples from all stations pooled together and for individual 

stations. The summary in table 6 is further subdivided on the 

basis of hydrograph classification. Samples were classified as 

associated with the rising or falling portion of the hydrograph, or 

a hydrograph that represented an entire storm event. The event 

hydrograph classification includes both rising and falling portions 

of the stormwater-runoff hydrograph and may represent only 

a portion of the stormwater-runoff hydrograph for multi-day 

or peak events. Table 6 also lists samples for a few storms that 

could not be classified due to a lack of streamflow information. 

Additional details of the classification procedure and example 

hydrographs from all stations (fig. A1) are presented in the 

“Hydrograph Classification” section of the Appendix.
12 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table 4. Water-quality properties and constituents in blank samples.—Continued

[Equipment blank type: type 1 samples consist of universal blank water (UBL) passed through sampler intake lines with no rinse; type 2 samples consist of UBL 

passed through sampler intake lines after a field rinse with native water; and type 3 samples consist of UBL passed through sampler intake lines after a UBL rinse. 

Organic carbon blank type: Type 1 samples consist of UBL water stored in pumping sampler supplies under field conditions (refrigerated) for at least 2 days; 

Type 2 and 3 samples consist of water spiked to concentrations approximating field conditions and stored in plastic and glass containers (respectively) under field 

conditions for at least 2 days. Phase: W, determination made using whole water; T, total; D, dissolved; stdu, standard pH units; μS/cm, microsiemens per centimeter 

at 25 degrees Celsius; C, Celsius; mg/L, milligrams per liter; N, nitrogen; P, phosphorus; CaCO3, calcium carbonate; μg/L, micrograms per liter; E, estimated value 

below reporting level; --, not applicable; <, less than]

Property or

constituent Phase Sample type

Equipment blanks

Equipment blank type Type 1 Type 1 Type 2 Type 3 Type 1 Type 2 Type 1 Type 2 Type 3

Station name Sand

Creek Henderson Henderson Henderson Tollgate Tollgate SandCreek

Sand

Creek

Sand

Creek

Date 20030818 20030821 20030821 20030821 20030821 20030821 20041124 20041124 20041124

Time 2030 1015 1030 1045 0900 0915 0950 1035 1111

pH, in standard units W E6.7 6.1 6.1 6.0 6.1 6.0 7.6 7.1 7.0

Specific conductance, 

in μS/cm

W -- -- -- -- -- -- -- -- --

Hardness, as CaCO3

,

in mg/L

T -- 6 -- -- 1 -- -- 31 --

Calcium, in mg/L D 0.03 2.14 0.09 0.08 0.47 0.08 0.06 9.07 0.28

Magnesium, in mg/L D E.006 0.273 <.008 E.007 0.071 0.009 E.007 1.95 0.056

Potassium, in mg/L D -- -- -- -- -- -- <.16 0.61 <.16

Sodium, in mg/L D -- -- -- -- -- -- <.20 15.4 0.5

Alkalinity, as CaCO3

, fixed

endpoint, in mg/L

W -- -- -- -- -- -- <2 17 3

Chloride, in mg/L D -- -- -- -- -- -- <.20 14.6 0.43

Fluoride, in mg/L D -- -- -- -- -- -- <.1 E.1 <.1

Sulfate, in mg/L D -- -- -- -- -- -- <.2 22.9 0.4

Residue on evaporation 

at 105°C, in mg/L

T <10 31 <10 <10 <10 <10 <10 <10 <10

Ammonia + organic N, 

in mg/L

T <.10 0.8 <.10 <.10 <.10 <.10 E.09 0.3 <.10

Ammonia, as N, in mg/L D <.04 <.04 <.04 <.04 <.04 <.04 <.04 0.2 <.04

Nitrite + nitrate, as N, 

in mg/L

D <.06 <.06 0.77 <.06 <.06 <.06 <.06 0.28 <.06

Orthophosphate, as P, 

in mg/L

D <.007 0.014 <.007 <.007 <.007 <.007 E.004 0.073 <.006

Phosphorus, as P, in mg/L T <.04 0.17 <.04 <.04 E.02 <.04 <.04 0.08 <.04

Organic carbon, in mg/L D 0.4 8.9 0.5 E.3 -- E.3 1.5 0.6 E.2

Copper, in μg/L D E.1 0.3 <.2 <.2 <.2 <.2 <.4 0.5 <.4

Copper, in μg/L T -- 2.2 <.6 <.6 <.6 <.6 <.6 1 <.6

Lead, in μg/L D <.08 <.08 <.08 <.08 <.08 <.08 0.09 0.1 <.08

Lead, in μg/L T -- 1.79 <.06 <.06 0.15 <.06 0.1 0.1 <.06

Manganese, in μg/L D -- 8.1 0.3 0.4 1.2 E.1 3.2 28.3 1.1

Manganese, in μg/L T -- 25 0.4 0.6 4.4 0.5 2.8 23.4 1.1

Zinc, in μg/L D <1.0 17.9 1.2 <1.0 1.3 <1.0 38.6 10.8 9

Zinc, in μg/L T -- 31 E1 <2 3 <2 34 10 8

A total of 176 composite samples were collected; 4 of the 

samples, from Tollgate, had no associated streamflow measurements, and 3 samples from Union were neither rising, falling, 

or event hydrographs; all of these samples are characterized 

as unclassified. About 35 to 45 samples were collected at each 

station except Tollgate where only 24 samples were collected. 

Overall, and at most stations, hydrographs for composite samples 

were most commonly classified as falling or event hydrographs. 

During the study period, these two categories accounted for 78 to 

98 percent of the samples collected at individual stations. Relatively few samples were associated with rising hydrographs.

The results of laboratory analyses of composite samples 

are summarized with univariate statistics in table 7 and 

figure 3. The results are presented for all stations pooled 

together or combined, by individual station, and by hydrograph classification. The summary (table 7) includes the 
Summary of Stormwater Quality 13

Table 4. Water-quality properties and constituents in blank samples.—Continued

[Equipment blank type: type 1 samples consist of universal blank water (UBL) passed through sampler intake lines with no rinse; type 2 samples consist of UBL 

passed through sampler intake lines after a field rinse with native water; and type 3 samples consist of UBL passed through sampler intake lines after a UBL rinse. 

Organic carbon blank type: Type 1 samples consist of UBL water stored in pumping sampler supplies under field conditions (refrigerated) for at least 2 days; 

Type 2 and 3 samples consist of water spiked to concentrations approximating field conditions and stored in plastic and glass containers (respectively) under field 

conditions for at least 2 days. Phase: W, determination made using whole water; T, total; D, dissolved; stdu, standard pH units; μS/cm, microsiemens per centimeter 

at 25 degrees Celsius; C, Celsius; mg/L, milligrams per liter; N, nitrogen; P, phosphorus; CaCO3, calcium carbonate; μg/L, micrograms per liter; E, estimated value 

below reporting level; --, not applicable; <, less than]

Property or

constituent Phase Sample type

Equipment blanks Organic carbon blanks

Blank type Type 1 Type 2 Type 3 Type 1 Type 2 Type 3 Type 1 Type 3 Type 3

Station name Sand

Creek

Sand

Creek

Sand

Creek Denver Denver Denver Denver Denver Denver

Date 20050829 20050928 20050928 20040518 20040519 20040519 20040630 20040630 20040630

Time 0830 0900 0930 1000 1200 1205 0925 0920 0930

pH, in standard units W 7.6 7.2 7.5 -- -- -- -- -- --

Specific conductance, 

in μS/cm

W -- -- -- -- -- -- -- -- --

Hardness, as CaCO3

,

in mg/L

T 41 3 -- -- -- -- -- --

Calcium, in mg/L D 0.22 12.6 0.86 -- -- -- -- -- --

Magnesium, in mg/ L D 0.033 2.33 0.168 -- -- -- -- -- --

Potassium, in mg/L D <.16 0.82 E.10 -- -- -- -- -- --

Sodium, in mg/L D E.15 21.1 1.38 -- -- -- -- -- --

Alkalinity, as CaCO3

, fixed 

endpoint, in mg/L

W <5 23 <5 -- -- -- -- -- --

Chloride, in mg/L D <.20 16.4 1.04 -- -- -- -- -- --

Fluoride, in mg/L D E.1 0.1 E.1 -- -- -- -- -- --

Sulfate, in mg/L D <.2 37.6 2.2 -- -- -- -- -- --

Residue on evaporation 

at 105°C, in mg/L

T <10 <10 <10 -- -- -- -- -- --

Ammonia + organic N, 

in mg/L

T 0.14 0.24 <.10 -- -- -- -- -- --

Ammonia, as N, in mg/L D <.04 0.15 <.04 -- -- -- -- -- --

Nitrite + nitrate, as N, 

in mg/L

D <.06 0.23 <.06 -- -- -- -- -- --

Orthophosphate, as P,

in mg/L

D 0.012 0.023 E.004 -- -- -- -- -- --

Phosphorus, as P, in mg/L T E.03 0.05 <.04 -- -- -- -- -- --

Organic carbon, in mg/L D -- -- -- E.2 14.6 14.5 <.3 13.4 13.2

Copper, in μg/L D 3.3 0.7 <.4 -- -- -- -- -- --

Copper, in μg/L T 3.3 0.9 <.6 -- -- -- -- -- --

Lead, in μg/L D 0.23 0.25 0.09 -- -- -- -- -- --

Lead, in μg/L T 0.29 0.23 0.09 -- -- -- -- -- --

Manganese, in μg/L D 5.8 43.7 4.6 -- -- -- -- -- --

Manganese, in μg/L T 6.6 47.5 5 -- -- -- -- -- --

Zinc, in μg/L D 14.3 10.4 2.4 -- -- -- -- -- --

Zinc, in μg/L T 13 12 2 -- -- -- -- -- --

number of samples and the number of missing values for mean 

streamflow, streamflow volume, and water-quality properties 

or constituents. For mean streamflow and streamflow volume, 

the number of missing values indicates the number of samples 

that either have no associated streamflow information or do 

not have hydrograph classifications. For water-quality properties and constituents and biological indicators, the number of 

missing values indicates the number of analyses that were not 

performed. In addition to statistics for values above censoring 

limits, table 7 also reports the percentage of samples that had 

censored values, or unquantifiable concentrations that were 

less than the reporting level. The reporting level was not 

always constant and is summarized with a mean and median 

(table 7). Concentrations for water-quality properties and constituents and biological indicators generally had few censored 

values except for ammonia and dissolved and total lead, which 

typically, and especially for dissolved lead, had 10 or more 

percent censored values.
14 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

The results from laboratory analyses of composite samples 

indicate an important spatial pattern. In general and particularly 

for nutrients, concentration increases downstream in the receiving stream and also in the tributary (table 7). For example, the 

mean concentration of all samples regardless of hydrograph 

position for ammonia plus organic nitrogen is 1.85 mg/L at 

Union, 2.6 mg/L at Denver, and 5.47 mg/L at Henderson. This 

pattern correlates with the size of the local contributing drainage 

area, which also increases downstream (table 1). Land-cover 

data (table 1) indicate that the percentage of agricultural land 

in the local contributing drainage area also increases in the 

downstream direction; whereas the percentage of urban land 

cover does not. For most water-quality properties and constituents, values measured in the tributary streams are higher than 

values measured in the receiving streams; mean values for most 

nutrients indicate downstream increases (table 7).

Discrete Samples

Twenty-two discrete samples were collected during two 

storms, one at Henderson in August 2002, and one at Denver 

in August 2004. Hydrographs for the storms were 11 and 

17 hours long, respectively, and each had a distinct peak; 

storm hydrographs are shown in the Appendix (fig. A2). The 

discrete samples were collected to provide a basis for comparison of time-weighted results to alternative weighting methods. 

Summaries of results from various weighting methods are 

presented in table 8. The analytical results as well as overall 

weighted values are in the Appendix (table A1, fig. A2).

Three weighting methods, referred to as “time,” “discharge,” and “volume,” were evaluated to determine the effects 

of different weighting methods. Weighting computations 

were made using the general form of equation 2 given in the 

“Methods of Study” section. Time-weighted results were 

computed on the basis of the amount of hydrograph time associated with each sample. If sampling intervals are fixed, then 

time-weighted results are simply the average of all values; 

however, in the discrete sampling activities presented here, 

time intervals were not fixed and the hydrograph time associated with each discrete sample was computed on the basis of 

subdivision methods described by Rantz and others (1982, 

chapter 15). Discharge-weighted results were computed on the 

basis of discharge at the time of sample collection. Volumeweighted computations were made on the basis of the product 

of the subdivided time and streamflow at the time of sample 

collection. With fixed sampling intervals, the discharge- and 

volume-weighting methods used in this study are equivalent.

On the basis of the mean and standard deviation for RPDs 

calculated between time- and volume-weighted concentration 

results computed in this study, differences between the two 

weighting methods are consistently small, typically having 

RPDs with an absolute value of about 10 or less; the RPD was 

only rarely greater than an absolute value of 20 (table 8). In 

addition, Pearson’s correlation coefficients (Pearson, 1901) for 

time- and volume-weighted concentration results indicate that 

intrastorm correlations generally were strong and direct, rarely 

having a correlation coefficient less than 0.65.

The results from discrete samples also indicate that 

composited values tend to “smooth” results because the 

composite value represents a weighted mean of values that 

typically vary through storm hydrographs. For example, the 

volume-weighted value for specific conductance during storm 

1 in table A1 (August 28, 2002) at Henderson, was 649 μS/cm 

at 25°C; however, specific-conductance values from discrete 

samples through the storm ranged from 546 to 950 μS/cm at 

25°C (table A1). In this case, the larger values, which were 

measured near the beginning and end of storm runoff, indicate 

that the stormwater generally was more dilute than base flow.

Comparison to Numeric Standards

Results from laboratory analyses of composite samples 

were compared to numeric standards for pH, dissolved chloride, Escherichia coli, fecal coliform, nitrite plus nitrate, dissolved copper, lead, manganese, and zinc, and total manganese 

(Colorado Department of Public Health and Environment, 2005, 

2006). All numeric standards do not apply to all stations. For 

example, dissolved manganese and nitrite plus nitrate standards 

for Tollgate or Sand Creek do not exist. The numeric standards 

for pH, dissolved chloride, Escherichia coli, fecal coliform, 

Table 5. Specific-conductance measurements made at fixedpoint sampling and channel locations, June 2004.

[All values in microsiemens per centimeter at 25 degrees Celsius; Union, South 

Platte River below Union Avenue at Englewood; Denver, South Platte River at 

Denver; Sand Creek, Sand Creek at mouth near Commerce City; Henderson, 

South Platte River at Henderson]

Union Denver Sand

Creek Henderson

Fixed point intake 471 525 679 617

Numbered

 measuring

point

Measurements at numbered points 

for stream cross sections

1 475 493 688 599

2 476 493 686 599

3 474 495 680 602

4 473 497 679 604

5 472 502 676 605

6 471 516 671 606

7 471 526 669 609

8 470 534 668 609

9 473 540 666 612

10 491 542 665 619

Statistics for measurements at stream verticals 1–10

Average 474.6 513.8 674.8 606.4

Median 473 509 673.5 605.5

Min 470 493 665 599

Max 491 542 688 619
Summary of Stormwater Quality 15

nitrite plus nitrate, and dissolved manganese are fixed values 

and are not designated as either acute or chronic. The numeric 

standards for dissolved copper and lead, total manganese, and 

dissolved zinc are each calculated according to equations provided by the CDPHE (Colorado Department of Public Health 

and Environment, 2005, 2006); in this study, acute values were 

used. The calculations for these values, often referred to as 

“table-value standards,” are based on hardness; in this study, the 

hardness value associated with the composite sample was used 

in the calculation.

Table 6. Mean streamflow, streamflow volume, and duration statistics for composite samples, water years 2002–2005.

[Pooled, all samples for given group; q, mean streamflow in cubic feet per second; v, volume in acre-feet; t, time in decimal days; U, unclassified, in some 

cases no discharge information for the storm was available and the hydrograph could not be characterized; Stddev, standard deviation, Skew, skewness; Min, 

minimum; Max, maximum; n, number of samples; --, not applicable] 

Statistic

Pooled Rising hydrograph Falling hydrograph Event hydrograph U

q v t q v t q v t q v t t

All stations

Mean 636 568 0.44 577 521 0.43 474 380 0.42 809 759 0.46 0.43

Median 292 270 0.45 296 269 0.45 262 233 0.45 403 367 0.45 0.43

Stddev 954 845 0.09 595 543 0.03 656 448 0.11 1,200 1,110 0.08 0.02

Skew 3.75 3.86 1.05 1.19 1.2 2.1 2.9 1.75 0.26 3.32 3.17 3.3 1.45

Min 1 0 0.17 37 25 0.33 1 0 0.17 4 4 0.19 0.42

Max 7,570 6,880 0.95 1,730 1,580 0.47 3,900 1,920 0.91 7,570 6,880 0.95 0.46

n 172 172 176 18 18 18 71 71 71 80 80 80 7

South Platte River below Union Avenue at Englewood

Mean 216 192 0.42 239 216 0.42 169 141 0.4 248 225 0.44 0.44

Median 154 140 0.44 160 149 0.45 121 110 0.44 212 193 0.44 0.44

Stddev 169 152 0.06 256 234 0.05 149 126 0.1 171 155 0.02 0.02

Skew 1.51 1.54 2.98 1.94 1.9 2.02 1.21 1.16 1.74 1.63 1.63 0.25 0

Min 37 16 0.19 37 25 0.33 38 16 0.19 71 65 0.42 0.42

Max 686 623 0.47 686 623 0.46 452 411 0.47 679 617 0.47 0.46

n 37 37 37 5 5 5 13 13 13 16 16 16 3

South Platte River at Denver

Mean 878 763 0.43 204 178 0.44 665 546 0.42 1,110 996 0.44 --

Median 636 549 0.45 204 178 0.44 413 376 0.45 757 674 0.45 --

Stddev 837 727 0.07 590 437 0.09 989 884 0.03 --

Skew 2.35 2.59 3.01 1.82 1.64 2.16 2.17 2.23 0.32 --

Min 166 69 0.18 204 178 0.44 166 69 0.18 236 214 0.38 --

Max 4,450 4,040 0.5 204 178 0.44 2,310 1,920 0.5 4,450 4,040 0.5 --

n 46 46 46 1 1 1 22 22 22 23 23 23 0

Tollgate Creek above 6th Avenue at Aurora

Mean 87.1 82.3 0.44 358 309 0.42 68.9 58.3 0.39 49.5 56.4 0.48 0.43

Median 47 49 0.45 358 309 0.42 14 57 0.44 42 38 0.46 0.43

Stddev 112 102 0.14 67.2 37.5 0.04 91.2 63.3 0.14 43 76.8 0.18 0.01

Skew 1.76 1.55 1.61 1.04 0.94 0.75 1.23 2.6 1.84 0

Min 1 0 0.19 310 282 0.39 1 0 0.2 4 4 0.19 0.42

Max 405 335 0.95 405 335 0.45 207 173 0.56 143 272 0.95 0.43

n 20 20 24 2 2 2 7 7 7 11 11 11 4

Sand Creek at mouth near Commerce City

Mean 221 229 0.45 134 117 0.43 102 93.1 0.44 366 395 0.46 --

Median 102 99 0.45 99 85 0.43 79 71.5 0.45 178 160 0.45 --

Stddev 346 449 0.08 110 96.6 0.03 79.1 73.4 0.09 482 644 0.07 --

Skew 3.64 4.56 0.72 1.28 1.34 0 1.58 1.41 0.02 2.39 3.06 2.53 --

Min 18 17 0.2 45 41 0.4 18 17 0.2 24 21 0.4 --

Max 1,810 2,550 0.69 257 226 0.46 296 269 0.69 1,810 2,550 0.68 --

n 34 34 34 3 3 3 16 16 16 15 15 15 0

South Platte River at Henderson

Mean 1,480 1,320 0.46 1,120 1,020 0.45 1,130 865 0.45 1,940 1,840 0.48 --

Median 1,060 1,090 0.45 1,200 1,090 0.45 818 744 0.45 1,070 1,230 0.44 --

Stddev 1,460 1,280 0.11 611 556 0.02 972 523 0.16 1,960 1,750 0.08 --

Skew 2.71 2.97 1.84 0.28 0.29 0.26 2.15 0.47 1.61 2.1 2.08 2.23 --

Min 280 208 0.17 281 255 0.43 280 208 0.17 350 318 0.42 --

Max 7,570 6,880 0.91 1,730 1,580 0.47 3,900 1,670 0.91 7,570 6,880 0.71 --

n 35 35 35 7 7 7 13 13 13 15 15 15 0
Note: See table 1 for source of precipitation data

DAILY PRECIPITATION,

IN INCHES DAILY MEAN DISCHARGE, IN CUBIC FEET PER SECOND

0.00.5

1.01.5

2.02.5

1,200

1,000

800600400200

0

Composited sample (beginninGrab bacteriological sample

O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J 

2001 2002 2003 2004 

A

Figure 2. Daily values for streamflow and precipitation at (

A) South Platte River below Union Avenue at Englewood, (

B) South Platte River at 

above 6th Avenue at Aurora, (

D) Sand Creek at mouth near Commerce City, and (

E) South Platte River at Henderson.
Note: See table 1 for source of precipitation data

DAILY PRECIPITATION,

IN INCHES DAILY MEAN DISCHARGE, IN CUBIC FEET PER SECOND

0.00.5

1.01.5

2.02.5

2,500

2,000

1,500

1,000

500

0

Composited sample (beginninGrab bacteriological sample

O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J 

2001 2002 2003 2004 

B

Figure 2. Daily values for streamflow and precipitation at (

A) South Platte River below Union Avenue at Englewood, (

B) South Platte River a

above 6th Avenue at Aurora, (

D) Sand Creek at mouth near Commerce City, and (

E) South Platte River at Henderson.—Continued
Note: See table 1 for source of precipitation data

DAILY PRECIPITATION,

IN INCHES DAILY MEAN DISCHARGE, IN CUBIC FEET PER SECOND

0.00.5

1.01.5

2.02.5

300

250

200

150100

50

0

Composited sample (beginninGrab bacteriological sample

O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J 

2001 2002 2003 2004 

C

Figure 2. Daily values for streamflow and precipitation at (

A) South Platte River below Union Avenue at Englewood, (

B) South Platte Rive

Creek above 6th Avenue at Aurora, (

D) Sand Creek at mouth near Commerce City, and (

E) South Platte River at Henderson.—Continued
Note: See table 1 for source of precipitation data

DAILY PRECIPITATION,

IN INCHES DAILY MEAN DISCHARGE, IN CUBIC FEET PER SECOND

0.00.5

1.01.5

2.02.5

1,000

800600400200

0

Composited sample (beginninGrab bacteriological sample

O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J 

2001 2002 2003 2004 

D

Figure 2. Daily values for streamflow and precipitation at (

A) South Platte River below Union Avenue at Englewood, (

B) South Platte River 

Creek above 6th Avenue at Aurora, (

D) Sand Creek at mouth near Commerce City, and (

E) South Platte River at Henderson.—Continued
Note: See table 1 for source of precipitation data

DAILY PRECIPITATION,

IN INCHES DAILY MEAN DISCHARGE, IN CUBIC FEET PER SECOND

0.00.5

1.01.5

2.02.5

6,000

5,500

5,000

4,500

4,000

3,500

3,000

2,500

2,000

1,500

1,000

500

0

Composited sample (beginninGrab bacteriological sample

O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J 

2001 2002 2003 2004 

E

Figure 2. Daily values for streamflow and precipitation at (

A) South Platte River below Union Avenue at Englewood, (

B) South Platte River 

Creek above 6th Avenue at Aurora, (

D) Sand Creek at mouth near Commerce City, and (

E) South Platte River at Henderson.—Continued
Summary of Stormwater Quality 21

Table 7. Summary statistics for water-quality properties and constituents from composite and bacteriological samples at all stations, 

South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand 

Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[Phase: W, determination made using whole water; T, total; D, dissolved. Typ: a, all samples regardless of hydrograph position; r, sample from rising limb portion 

of hydrograph; f, sample from falling limb portion of hydrograph; e, sample from rising and falling limbs of hydrograph; u, unclassified. n, number of samples; 

M, number of samples with missing values; Pct, percentage of samples below reporting level (unsaved value); Stddev, standard deviation; Skew, skewness; 

ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; C, Celsius; mg/L, milligrams per liter; col, colonies per 100 milliliters; 

N, nitrogen; P, phosphorus; μg/L, micrograms per liter; --, not applicable]

Property or 

constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Medium

All stations

Mean streamflow, 

in ft3

/s

-- a 172 4 0 636 292 954 3.75 1 7,570 -- --

r 18 0 0 577 296 595 1.19 37 1,730 -- --

f 71 0 0 474 262 656 2.9 1 3,900 -- --

e 80 0 0 809 403 1,200 3.32 4 7,570 -- --

u 3 4 0 209 202 73.7 0.42 139 286 -- --

Streamflow volume,

in acre-feet

-- a 172 4 0 568 270 845 3.86 0 6,880 -- --

r 18 0 0 521 269 543 1.2 25 1,580 -- --

f 71 0 0 380 233 448 1.75 0 1,920 -- --

e 80 0 0 759 367 1,110 3.17 4 6,880 -- --

u 3 4 0 190 184 67.2 0.4 126 260 -- --

pH, in standard

pH units

W a 176 0 0 7.4 7.4 0.32 0.64 6.1 8.35 -- --

r 18 0 0 7.29 7.33 0.4 0.83 6.3 7.94 -- --

f 71 0 0 7.44 7.4 0.29 0.27 6.72 8.35 -- --

e 80 0 0 7.4 7.47 0.3 1.15 6.1 8 -- --

u 7 0 0 7.14 6.87 0.46 0.54 6.72 7.81 -- --

Specific conductance, 

in μS/cm 

W a 152 24 0 663 588 309 2.3 212 2,630 -- --

r 13 5 0 789 784 336 0.79 212 1,600 -- --

f 64 7 0 665 580 259 1.09 285 1,600 -- --

e 70 10 0 649 558 349 2.95 244 2,630 -- --

u 5 2 0 514 505 111 0.68 350 619 -- --

Hardness, as calcium 

carbonate, in mg/L

T a 173 3 0 191 176 78.2 1.4 69.1 594 -- --

r 18 0 0 211 200 81 0.42 69.7 365 -- --

f 71 0 0 190 183 59.6 0.64 83.3 375 -- --

e 77 3 0 188 169 91.3 1.68 69.1 594 -- --

u 7 0 0 188 155 91.2 2.15 113 385 -- --

Calcium, in mg/L D a 132 44 0 52.8 47.1 22.6 1.87 21.4 169 -- --

r 13 5 0 52.9 49.2 17.8 0.59 22 90 -- --

f 49 22 0 53.5 49.4 19.4 1.18 25.9 117 -- --

e 63 17 0 51.8 46.6 25.5 2.21 21.4 169 -- --

u 7 0 0 57.2 47.2 27.7 2.1 33 117 -- --

Magnesium, in mg/L D a 132 44 0 10.7 9.93 5.09 2.13 3.61 41.8 -- --

r 13 5 0 11 11.2 4.32 0.24 3.61 19 -- --

f 49 22 0 10.9 10.8 3.87 0.56 4.51 21.5 -- --

e 63 17 0 10.5 8.79 6.04 2.55 3.81 41.8 -- --

u 7 0 0 11 9.28 5.41 2.24 7.32 22.8 -- --

Potassium, in mg/L D a 63 113 0 4.47 4.12 1.33 1.2 2.67 8.37 -- --

r 5 13 0 4.74 3.39 2.24 1.14 2.89 8.18 -- --

f 21 50 0 4.63 4.46 0.97 0.11 3.11 6.35 -- --

e 31 49 0 4.5 4.01 1.46 1.29 2.67 8.37 -- --

u 6 1 0 3.54 3.43 0.38 0.42 3.06 4.08 -- --

Sodium, in mg/L D a 63 113 0 60.7 52.4 33.3 1 13.9 142 -- --

r 5 13 0 58.3 47.8 50.7 1.47 13.9 142 -- --

f 21 50 0 61.7 49.1 31.1 0.91 22.6 125 -- --

e 31 49 0 60 52.4 33.4 1.19 18.2 142 -- --

u 6 1 0 63.7 61.4 33.7 0.62 24.5 118 -- --

Alkalinity, as calcium 

carbonate, fixed 

endpoint, in mg/L

W a 63 113 0 86.5 85.6 23.3 0.25 48.6 139 -- --

r 5 13 0 75 74.4 25.2 0.1 48.6 105 -- --

f 21 50 0 90 85.6 23.3 0.25 51.9 133 -- --

e 31 49 0 87.1 88.9 23.2 0.27 51 139 -- --

u 6 1 0 80.6 72 24.3 0.85 57.6 118 -- --
22 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table 7. Summary statistics for water-quality properties and constituents from composite and bacteriological samples at all stations, 

South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand 

Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[Phase: W, determination made using whole water; T, total; D, dissolved. Typ: a, all samples regardless of hydrograph position; r, sample from rising limb portion 

of hydrograph; f, sample from falling limb portion of hydrograph; e, sample from rising and falling limbs of hydrograph; u, unclassified. n, number of samples; 

M, number of samples with missing values; Pct, percentage of samples below reporting level (unsaved value); Stddev, standard deviation; Skew, skewness; 

ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; C, Celsius; mg/L, milligrams per liter; col, colonies per 100 milliliters; 

N, nitrogen; P, phosphorus; μg/L, micrograms per liter; --, not applicable]

Property or 

constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Medium

All stations—Continued

Chloride, in mg/L D a 63 113 0 56.8 50.7 32.2 1.79 11 197 -- --

r 5 13 0 66.1 38.6 75.3 1.94 11 197 -- --

f 21 50 0 60.1 48.9 32.6 1.07 21.4 130 -- --

e 31 49 0 52 50.7 23.2 0.9 15.9 112 -- --

u 6 1 0 62.6 71.1 23.1 0.76 28.1 85.5 -- --

Fluoride, in mg/L D a 63 113 0 0.52 0.45 0.23 0.68 0.2 1.08 -- --

r 5 13 0 0.44 0.38 0.2 0.79 0.22 0.74 -- --

f 21 50 0 0.53 0.48 0.21 0.74 0.25 0.97 -- --

e 31 49 0 0.52 0.48 0.21 0.56 0.26 0.94 -- --

u 6 1 0 0.51 0.29 0.41 0.93 0.2 1.08 -- --

Sulfate, in mg/L D a 63 113 0 125 93.5 88.9 1.62 30.9 386 -- --

r 5 13 0 82.8 85.7 33.4 0.99 30.9 116 -- --

f 21 50 0 118 88.6 71.2 1.22 41.8 268 -- --

e 31 49 0 132 99.1 98.8 1.51 34 385 -- --

u 6 1 0 155 121 122 1.73 46.9 386 -- --

Residue on evaporation

at 105°C, in mg/L

T a 172 4 1.16 449 237 817 5.98 13 7,360 10 10

r 18 0 0 313 223 242 0.8 19 805 -- --

f 69 2 0 365 153 907 7.04 13 7,360 -- --

e 78 2 0 578 326 831 4.47 38 6,040 -- --

u 7 0 28.6 79.4 88 41.7 1.12 13 124 10 10

E. coli, colonies per

100 mL

W a 22 0 0 16,500 13,000 20,000 2.81 460 92,000 -- --

r 5 0 0 8,670 1,700 14,800 2.17 460 35,000 -- --

f 13 0 0 14,700 13,000 10,800 0.92 500 35,000 -- --

e 3 0 0 38,700 13,000 46,200 1.73 11,000 92,000 -- --

u 1 0 0 13,000 13,000 13,000 13,000 -- --

Fecal coliform, colonies

per 100 mL

W a 22 0 0 20,100 13,000 18,200 0.76 310 54,000 -- --

r 5 0 0 8,740 2,200 14,800 2.16 310 35,000 -- --

f 13 0 0 21,100 13,000 17,900 0.97 700 54,000 -- --

e 3 0 0 39,000 35,000 13,500 1.22 28,000 54,000 -- --

u 1 0 0 7,900 7,900 7,900 7,900 -- --

Ammonia + organic N,

in mg/L

T a 173 3 0 3.13 2.41 2.19 1.43 0.47 12.2 -- --

r 18 0 0 3.77 3.23 1.97 0.41 1.3 7.3 -- --

f 71 0 0 2.77 1.9 2.39 2.04 0.59 12.2 -- --

e 77 3 0 3.5 3.14 1.97 1.14 0.59 9.63 -- --

u 7 0 0 0.95 0.81 0.53 1.6 0.47 2 -- --

Ammonia, as N,

in mg/L

D a 132 44 11.4 0.55 0.25 0.71 2.36 0.05 3.55 0.04 0.04

r 13 5 0 1.15 1.15 1.06 0.5 0.11 3.06 -- --

f 49 22 14.3 0.52 0.22 0.72 2.45 0.05 3.46 0.04 0.04

e 63 17 7.94 0.46 0.29 0.56 3.51 0.05 3.55 0.04 0.04

u 7 0 42.9 0.19 0.19 0.05 0.07 0.13 0.24 0.04 0.04

Nitrite + nitrate, as N,

in mg/L

D a 132 44 2.27 1.53 1.14 1.09 1.07 0.11 4.7 0.06 0.06

r 13 5 7.69 2.1 1.94 1.33 0.31 0.52 4.1 0.06 0.06

f 49 22 4.08 1.5 1.3 0.91 0.87 0.24 4.01 0.06 0.06

e 63 17 0 1.54 0.99 1.15 1.17 0.11 4.7 -- --

u 7 0 0 0.53 0.55 0.18 0.67 0.33 0.84 -- --

Orthophosphate, as P, 

in mg/L

D a 172 4 2.33 0.26 0.16 0.26 1.67 0.01 1.4 0.01 0.01

r 18 0 5.56 0.4 0.19 0.38 1.26 0.05 1.4 0.01 0.01

f 71 0 2.82 0.26 0.17 0.23 1.78 0.02 1.06 0.01 0.01

e 76 4 1.32 0.26 0.16 0.25 1.38 0.01 1 0.01 0.01

u 7 0 0 0.06 0.05 0.04 0.4 0.01 0.11 -- --
Summary of Stormwater Quality 23

Table 7. Summary statistics for water-quality properties and constituents from composite and bacteriological samples at all stations, 

South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand 

Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[Phase: W, determination made using whole water; T, total; D, dissolved. Typ: a, all samples regardless of hydrograph position; r, sample from rising limb portion 

of hydrograph; f, sample from falling limb portion of hydrograph; e, sample from rising and falling limbs of hydrograph; u, unclassified. n, number of samples; 

M, number of samples with missing values; Pct, percentage of samples below reporting level (unsaved value); Stddev, standard deviation; Skew, skewness; 

ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; C, Celsius; mg/L, milligrams per liter; col, colonies per 100 milliliters; 

N, nitrogen; P, phosphorus; μg/L, micrograms per liter; --, not applicable]

Property or 

constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Medium

All stations—Continued

Phosphorus, as P,

in mg/L

T a 173 3 0.58 0.96 0.77 0.87 4.02 0.07 8.3 0.04 0.04

r 18 0 0 1.16 1.11 0.62 0.48 0.23 2.52 -- --

f 71 0 0 0.79 0.54 0.65 1.59 0.1 3.12 -- --

e 77 3 1.3 1.14 0.93 1.05 4.51 0.2 8.3 0.04 0.04

u 7 0 0 0.18 0.18 0.11 0.61 0.07 0.36 -- --

Organic carbon,

in mg/L

D a 120 56 0 9.95 8.09 4.86 1.59 3.55 30.1 -- --

r 9 9 0 9.71 7.7 4.54 2.17 6.66 20.8 -- --

f 45 26 0 9.74 7.62 5.39 1.59 4.46 30.1 -- --

e 59 21 0 10.6 9.41 4.6 1.62 4.3 29.8 -- --

u 7 0 0 6.43 5.91 2.12 1.18 3.55 10.6 -- --

Copper, in μg/L D a 173 3 0 3.47 2.71 3.37 5.34 1.14 28 -- --

r 18 0 0 5.33 2.98 7.04 2.61 1.54 25 -- --

f 71 0 0 3.34 2.76 1.92 2.64 1.56 12 -- --

e 77 3 0 3.27 2.81 3.18 6.43 1.14 28 -- --

u 7 0 0 2.17 2 0.47 0.93 1.72 2.98 -- --

Copper, in μg/L T a 132 44 0 23.7 18.7 17.1 1.32 2.82 87.3 -- --

r 13 5 0 26.4 22.1 14.5 0.83 9.4 56.7 -- --

f 49 22 0 18.6 12.8 16 2.05 3.78 74.5 -- --

e 63 17 0 29 24.5 17.2 1.18 5.05 87.3 -- --

u 7 0 0 6.43 5.41 3.91 0.66 2.82 12.8 -- --

Lead, in μg/L D a 173 3 47.4 1.29 0.17 7.03 7.4 0.08 60 4.68 0.08

r 18 0 44.4 3.27 0.32 9.39 3.16 0.15 30 5.04 5.04

f 71 0 53.5 2 0.14 10.4 5.74 0.09 60 5.56 10

e 77 3 40.3 0.41 0.17 1.45 6.73 0.08 10 4.24 0.08

u 7 0 71.4 0.09 0.09 0 0.09 0.09 0.08 0.08

Lead, in μg/L T a 132 44 0 21.3 15.3 19.9 1.62 0.63 114 -- --

r 13 5 0 21.6 16.1 12.8 0.56 6.34 44.1 -- --

f 49 22 0 14.8 8.94 15.7 1.87 1.44 63.1 -- --

e 63 17 0 28.4 20.3 22 1.43 1.88 114 -- --

u 7 0 0 2.58 1.8 2.17 0.63 0.63 6.05 -- --

Manganese, in μg/L D a 132 44 0 73.8 25.9 161 6.72 1.07 1,570 -- --

r 13 5 0 113 86.7 108 1.11 2.14 356 -- --

f 49 22 0 74 17.4 226 6.31 1.07 1,570 -- --

e 63 17 0 69.7 26.1 110 2.7 1.32 550 -- --

u 7 0 0 37 33.2 22.6 1.61 17.3 82.6 -- --

Manganese, in μg/L T a 132 44 0 524 419 405 1.64 62.8 2,090 -- --

r 13 5 0 601 571 312 0.42 235 1,170 -- --

f 49 22 0 418 271 399 2.34 79.3 2,090 -- --

e 63 17 0 623 524 413 1.52 114 2,090 -- --

u 7 0 0 231 177 214 1.99 62.8 683 -- --

Zinc, in μg/L D a 172 4 9.88 23.6 11.2 43.7 4.98 1.99 336 20 20

r 18 0 5.56 33.6 20 49.7 3.14 1.99 208 20 20

f 71 0 15.5 28.8 10.8 59.1 4.25 2.26 336 20 20

e 76 4 6.58 17.8 10.4 23.8 4.12 2.77 165 20 20

u 7 0 0 13.2 6.35 16.6 2.58 4.52 50.6 -- --

Zinc, in μg/L T a 131 45 0 133 84 168 3.83 7 1,150 -- --

r 13 5 0 205 93 283 3.11 51 1,110 -- --

f 49 22 0 116 48 196 3.88 8 1,150 -- --

e 62 18 0 143 108 106 1.76 14 545 -- --

u 7 0 0 35.7 18 44.1 2.26 7 132 -- --
24 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table 7. Summary statistics for water-quality properties and constituents from composite and bacteriological samples at all stations, 

South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand 

Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[Phase: W, determination made using whole water; T, total; D, dissolved. Typ: a, all samples regardless of hydrograph position; r, sample from rising limb portion 

of hydrograph; f, sample from falling limb portion of hydrograph; e, sample from rising and falling limbs of hydrograph; u, unclassified. n, number of samples; 

M, number of samples with missing values; Pct, percentage of samples below reporting level (unsaved value); Stddev, standard deviation; Skew, skewness; 

ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; C, Celsius; mg/L, milligrams per liter; col, colonies per 100 milliliters; 

N, nitrogen; P, phosphorus; μg/L, micrograms per liter; --, not applicable]

Property or 

constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Medium

South Platte River below Union Avenue (06710247)

Mean streamflow, 

in ft3

/s

-- a 37 0 0 216 154 169 1.51 37 686 -- --

r 5 0 0 239 160 256 1.94 37 686 -- --

f 13 0 0 169 121 149 1.21 38 452 -- --

e 16 0 0 248 212 171 1.63 71 679 -- --

u 3 0 0 209 202 73.7 0.42 139 286 -- --

Streamflow volume, 

in acre-feet

-- a 37 0 0 192 140 152 1.54 16 623 -- --

r 5 0 0 216 149 234 1.9 25 623 -- --

f 13 0 0 141 110 126 1.16 16 411 -- --

e 16 0 0 225 193 155 1.63 65 617 -- --

u 3 0 0 190 184 67.2 0.4 126 260 -- --

pH, in standard

pH units

W a 37 0 0 7.51 7.55 0.32 0.17 6.82 8.35 -- --

r 5 0 0 7.41 7.6 0.37 1.34 6.82 7.74 -- --

f 13 0 0 7.55 7.47 0.36 0.51 6.9 8.35 -- --

e 16 0 0 7.49 7.53 0.3 0.61 6.89 7.99 -- --

u 3 0 0 7.62 7.62 0.19 0 7.43 7.81 -- --

Specific conductance, 

in μS/cm

W a 31 6 0 491 478 165 0.98 212 917 -- --

r 3 2 0 507 465 319 0.59 212 845 -- --

f 11 2 0 535 495 188 1.17 342 917 -- --

e 14 2 0 464 462 126 0.41 244 736 -- --

u 3 0 0 445 480 83.2 1.56 350 505 -- --

Hardness, as calcium 

carbonate, in mg/L

T a 37 0 0 170 155 61.1 1.27 69.7 365 -- --

r 5 0 0 198 150 118 0.66 69.7 365 -- --

f 13 0 0 179 183 41.8 0.46 113 270 -- --

e 16 0 0 159 138 56.4 1.52 96 310 -- --

u 3 0 0 146 155 29.5 1.24 113 170 -- --

Calcium, in mg/L D a 28 9 0 43.5 42.6 9.68 0.14 22 66.1 -- --

r 3 2 0 37.1 42.8 13.3 1.58 22 46.6 -- --

f 9 4 0 48 51 8.78 0.3 35.1 60.1 -- --

e 13 3 0 41.9 40.7 9.3 1.38 30 66.1 -- --

u 3 0 0 43.6 46.6 9.49 1.28 33 51.2 -- --

Magnesium, in mg/L D a 28 9 0 9.27 8.6 3.52 1.14 3.61 19.6 -- --

r 3 2 0 6.15 6.7 2.31 1.01 3.61 8.14 -- --

f 9 4 0 11 10.8 3.3 0.09 6.29 15.7 -- --

e 13 3 0 8.83 8.04 3.79 2.08 5.1 19.6 -- --

u 3 0 0 8.96 9.28 1.44 0.95 7.39 10.2 -- --

Potassium, in mg/L D a 15 22 0 3.81 3.39 0.92 0.78 2.67 5.46 -- --

r 2 3 0 3.39 3.39 0 3.38 3.39 -- --

f 4 9 0 4.57 4.75 0.92 0.95 3.33 5.46 -- --

e 7 9 0 3.64 3.38 0.99 1.1 2.67 5.46 -- --

u 2 1 0 3.28 3.28 0.32 3.06 3.51 -- --

Sodium, in mg/L D a 15 22 0 34.7 32 13.6 0.78 13.9 64.6 -- --

r 2 3 0 19.1 19.1 7.38 13.9 24.4 -- --

f 4 9 0 38.8 41.6 11.8 1.13 22.6 49.1 -- --

e 7 9 0 38.3 32 15.2 1.15 24 64.6 -- --

u 2 1 0 29.5 29.5 7.12 24.5 34.6 -- --

Alkalinity, as calcium 

carbonate, fixed 

endpoint, in mg/L

W a 15 22 0 84.4 81.7 21.3 0.14 48.6 124 -- --

r 2 3 0 61.5 61.5 18.2 48.6 74.4 -- --

f 4 9 0 96.5 100 16.8 0.96 74 112 -- --

e 7 9 0 82.4 81.7 23 0.89 56 124 -- --

u 2 1 0 90 90 16.5 78.3 102 -- --
Summary of Stormwater Quality 25

Table 7. Summary statistics for water-quality properties and constituents from composite and bacteriological samples at all stations, 

South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand 

Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[Phase: W, determination made using whole water; T, total; D, dissolved. Typ: a, all samples regardless of hydrograph position; r, sample from rising limb portion 

of hydrograph; f, sample from falling limb portion of hydrograph; e, sample from rising and falling limbs of hydrograph; u, unclassified. n, number of samples; 

M, number of samples with missing values; Pct, percentage of samples below reporting level (unsaved value); Stddev, standard deviation; Skew, skewness; 

ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; C, Celsius; mg/L, milligrams per liter; col, colonies per 100 milliliters; 

N, nitrogen; P, phosphorus; μg/L, micrograms per liter; --, not applicable]

Property or 

constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Medium

South Platte River below Union Avenue (06710247)—Continued

Chloride, in mg/L D a 15 22 0 37.8 36.8 16.4 0.87 11 77.6 -- --

r 2 3 0 17.9 17.9 9.78 11 24.8 -- --

f 4 9 0 40.4 45.6 12.8 1.81 21.4 48.9 -- --

e 7 9 0 42.9 36.8 18.6 1.37 27.5 77.6 -- --

u 2 1 0 34.7 34.7 9.33 28.1 41.2 -- --

Fluoride, in mg/L D a 15 22 0 0.67 0.63 0.29 0.04 0.29 1.08 -- --

r 2 3 0 0.35 0.35 0.05 0.32 0.38 -- --

f 4 9 0 0.72 0.73 0.24 0.12 0.45 0.97 -- --

e 7 9 0 0.62 0.63 0.29 0.09 0.29 0.94 -- --

u 2 1 0 1.03 1.03 0.07 0.98 1.08 -- --

Sulfate, in mg/L D a 15 22 0 74.1 74.4 31.8 1.25 30.9 155 -- --

r 2 3 0 52.6 52.6 30.8 30.9 74.4 -- --

f 4 9 0 88.8 88.6 26.8 0.04 56.2 122 -- --

e 7 9 0 75.5 73.1 37.6 1.94 42.4 155 -- --

u 2 1 0 61.4 61.4 20.5 46.9 75.9 -- --

Residue on evaporation 

at 105°C, in mg/L

T a 37 0 5.41 354 204 381 1.73 13 1,530 10 10

r 5 0 0 450 468 352 0.19 19 805 -- --

f 13 0 0 231 111 234 1 23 662 -- --

e 16 0 0 446 244 467 1.64 54 1,530 -- --

u 3 0 66.7 13 13 13 13 10 10

E. coli, colonies per

100 mL

W a 5 0 0 26,500 13,000 36,900 2.13 1,700 92,000 -- --

r 1 0 0 1,700 1,700 1,700 1,700 -- --

f 2 0 0 13,000 13,000 0 0 13,000 13,000 -- --

e 1 0 0 92,000 92,000 92,000 92,000 -- --

u 1 0 0 13,000 13,000 13,000 13,000 -- --

Fecal coliform, colonies

per 100 mL

W a 5 0 0 12,800 13,000 9,580 1.03 2,200 28,000 -- --

r 1 0 0 2,200 2,200 2,200 2,200 -- --

f 2 0 0 13,000 13,000 0 0 13,000 13,000 -- --

e 1 0 0 28,000 28,000 28,000 28,000 -- --

u 1 0 0 7,900 7,900 7,900 7,900 -- --

Ammonia + organic N,

in mg/L

T a 37 0 0 1.85 1.45 1.37 2.44 0.47 7 -- --

r 5 0 0 2.16 2.23 0.8 0.48 1.3 3.3 -- --

f 13 0 0 1.35 1.3 0.55 0.37 0.59 2.4 -- --

e 16 0 0 2.39 1.82 1.78 1.9 0.99 7 -- --

u 3 0 0 0.57 0.61 0.08 1.7 0.47 0.62 -- --

Ammonia, as N,

in mg/L

D a 28 9 28.6 0.12 0.1 0.07 1.6 0.05 0.34 0.04 0.04

r 3 2 0 0.15 0.16 0.04 1.08 0.11 0.18 -- --

f 9 4 44.4 0.13 0.12 0.08 0.27 0.05 0.22 0.04 0.04

e 13 3 7.69 0.12 0.1 0.08 2.36 0.05 0.34 0.04 0.04

u 3 0 100 -- -- -- -- -- -- 0.04 0.04

Nitrite + nitrate, as N,

in mg/L

D a 28 9 0 0.86 0.78 0.37 0.74 0.4 1.65 -- --

r 3 2 0 0.82 0.71 0.32 1.4 0.57 1.19 -- --

f 9 4 0 0.96 0.76 0.47 0.35 0.4 1.65 -- --

e 13 3 0 0.84 0.8 0.33 0.61 0.41 1.5 -- --

u 3 0 0 0.66 0.59 0.16 1.59 0.55 0.84 -- --

Orthophosphate, as P,

in mg/L

D a 37 0 0 0.1 0.08 0.08 2.66 0.01 0.45 -- --

r 5 0 0 0.11 0.09 0.04 1.6 0.08 0.17 -- --

f 13 0 0 0.1 0.1 0.05 0.14 0.03 0.18 -- --

e 16 0 0 0.11 0.07 0.11 2.4 0.02 0.45 -- --

u 3 0 0 0.03 0.03 0.01 0.59 0.01 0.03 -- --
26 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table 7. Summary statistics for water-quality properties and constituents from composite and bacteriological samples at all stations, 

South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand 

Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[Phase: W, determination made using whole water; T, total; D, dissolved. Typ: a, all samples regardless of hydrograph position; r, sample from rising limb portion 

of hydrograph; f, sample from falling limb portion of hydrograph; e, sample from rising and falling limbs of hydrograph; u, unclassified. n, number of samples; 

M, number of samples with missing values; Pct, percentage of samples below reporting level (unsaved value); Stddev, standard deviation; Skew, skewness; 

ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; C, Celsius; mg/L, milligrams per liter; col, colonies per 100 milliliters; 

N, nitrogen; P, phosphorus; μg/L, micrograms per liter; --, not applicable]

Property or 

constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Medium

South Platte River below Union Avenue (06710247)—Continued

Phosphorus, as P,

in mg/L

T a 37 0 0 0.48 0.37 0.4 1.6 0.07 1.75 -- --

r 5 0 0 0.65 0.62 0.36 0.01 0.23 1.02 -- --

f 13 0 0 0.34 0.29 0.22 1.19 0.1 0.85 -- --

e 16 0 0 0.63 0.43 0.47 1.45 0.22 1.75 -- --

u 3 0 0 0.08 0.08 0.02 0.94 0.07 0.1 -- --

Organic carbon,

in mg/L

D a 25 12 0 7.37 6.66 3.15 1.62 3.55 16.2 -- --

r 2 3 0 7.03 7.03 0.52 6.66 7.4 -- --

f 8 5 0 7.97 6.45 3.97 1.6 4.71 16.2 -- --

e 12 4 0 7.53 6.76 3.12 1.46 4.3 15 -- --

u 3 0 0 5.39 5.71 1.7 0.82 3.55 6.91 -- --

Copper, in μg/L D a 37 0 0 4.13 2.13 5.75 3.37 1.14 28 -- --

r 5 0 0 7.12 2.58 9.51 2.15 1.91 24 -- --

f 13 0 0 3.79 2.3 3.33 2.02 1.92 12 -- --

e 16 0 0 3.91 2.06 6.5 3.86 1.14 28 -- --

u 3 0 0 1.78 1.79 0.05 1.05 1.72 1.82 -- --

Copper, in μg/L T a 28 9 0 14.6 12.9 10.9 1.52 2.82 48.8 -- --

r 3 2 0 22.4 22.1 9.53 0.13 13 32.1 -- --

f 9 4 0 10.3 8.3 6 1.17 3.78 23 -- --

e 13 3 0 18.4 14.8 12.3 1.59 5.05 48.8 -- --

u 3 0 0 2.94 2.99 0.1 1.6 2.82 3.02 -- --

Lead, in μg/L D a 37 0 81.1 12.9 0.15 23.5 1.76 0.09 60 2.39 0.08

r 5 0 60 15.1 15.1 21.1 0.15 30 3.39 0.08

f 13 0 76.9 20.1 0.14 34.6 1.73 0.09 60 3.06 0.08

e 16 0 87.5 0.13 0.13 0.04 0.1 0.16 2.21 0.08

u 3 0 100 -- -- -- -- -- -- 0.08 0.08

Lead, in μg/L T a 28 9 0 11.6 9.59 11.6 2.01 0.63 51.9 -- --

r 3 2 0 17.8 16.1 9.07 0.84 9.75 27.6 -- --

f 9 4 0 6.96 4.84 5.45 1.27 1.44 18.4 -- --

e 13 3 0 15.8 11.1 13.9 1.84 1.88 51.9 -- --

u 3 0 0 0.67 0.67 0.04 0.1 0.63 0.72 -- --

Manganese, in μg/L D a 28 9 0 28.8 12.8 46.9 3.73 1.07 241 -- --

r 3 2 0 8.37 7.25 6.86 0.72 2.14 15.7 -- --

f 9 4 0 18.9 13.2 17.7 1.18 1.07 52.2 -- --

e 13 3 0 35.5 12.3 65.1 3.06 2.75 241 -- --

u 3 0 0 49.3 46.9 32.1 0.35 18.6 82.6 -- --

Manganese, in μg/L T a 28 9 0 355 285 266 1.77 62.8 1,270 -- --

r 3 2 0 507 571 247 1.08 235 716 -- --

f 9 4 0 234 161 152 1.03 79.3 519 -- --

e 13 3 0 457 337 302 1.91 167 1,270 -- --

u 3 0 0 125 117 67.2 0.54 62.8 196 -- --

Zinc, in μg/L D a 37 0 16.2 6.67 5.29 6.02 2.75 1.99 30 20 20

r 5 0 20 8.99 6.99 7.75 1.37 1.99 20 20 20

f 13 0 23.1 6.83 4.21 8.36 2.87 2.26 30 20 20

e 16 0 12.5 5.89 4.53 4.24 3.22 2.86 20 20 20

u 3 0 0 6.72 6.02 2.63 1.12 4.52 9.63 -- --

Zinc, in μg/L T a 28 9 0 52.5 45 47.3 2.22 7 230 -- --

r 3 2 0 82.7 85 30.6 0.34 51 112 -- --

f 9 4 0 30.4 26 18.7 0.72 8 66 -- --

e 13 3 0 70.7 58 56.8 2.11 14 230 -- --

u 3 0 0 9.33 9 2.52 0.59 7 12 -- --
Summary of Stormwater Quality 27

Table 7. Summary statistics for water-quality properties and constituents from composite and bacteriological samples at all stations, 

South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand 

Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[Phase: W, determination made using whole water; T, total; D, dissolved. Typ: a, all samples regardless of hydrograph position; r, sample from rising limb portion 

of hydrograph; f, sample from falling limb portion of hydrograph; e, sample from rising and falling limbs of hydrograph; u, unclassified. n, number of samples; 

M, number of samples with missing values; Pct, percentage of samples below reporting level (unsaved value); Stddev, standard deviation; Skew, skewness; 

ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; C, Celsius; mg/L, milligrams per liter; col, colonies per 100 milliliters; 

N, nitrogen; P, phosphorus; μg/L, micrograms per liter; --, not applicable]

Property or 

constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Medium

South Platte River at Denver (06714000)

Mean streamflow, 

in ft3

/s

-- a 46 0 0 878 636 837 2.35 166 4,450 -- --

r 1 0 0 204 204 204 204 -- --

f 22 0 0 665 413 590 1.82 166 2,310 -- --

e 23 0 0 1,110 757 989 2.17 236 4,450 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Streamflow volume,

in acre-feet

-- a 46 0 0 763 549 727 2.59 69 4,040 -- --

r 1 0 0 178 178 178 178 -- --

f 22 0 0 546 376 437 1.64 69 1,920 -- --

e 23 0 0 996 674 884 2.23 214 4,040 -- --

u 0 0 0 -- -- -- -- -- -- -- --

pH, in standard

pH units

W a 46 0 0 7.41 7.47 0.27 0.61 6.72 7.9 -- --

r 1 0 0 7.2 7.2 7.2 7.2 -- --

f 22 0 0 7.43 7.51 0.29 0.59 6.72 7.9 -- --

e 23 0 0 7.41 7.47 0.25 0.88 6.8 7.72 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Specific conductance,

in μS/cm

W a 41 5 0 543 509 184 0.96 247 1,060 -- --

r 1 0 0 972 972 972 972 -- --

f 19 3 0 552 532 169 0.8 285 940 -- --

e 21 2 0 515 474 179 1.25 247 1,060 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Hardness, as calcium 

carbonate, in mg/L

T a 45 1 0 154 154 44.8 0.01 69.1 255 -- --

r 1 0 0 255 255 255 255 -- --

f 22 0 0 157 160 40.6 0.07 83.3 242 -- --

e 22 1 0 146 154 44.7 0.2 69.1 210 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Calcium, in mg/L D a 35 11 0 42 42.9 11.1 0.06 21.4 63.3 -- --

r 0 1 0 -- -- -- -- -- -- -- --

f 16 6 0 42.8 43.5 10.5 0.09 25.9 63.3 -- --

e 19 4 0 41.3 40.5 11.8 0.11 21.4 60.5 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Magnesium, in mg/L D a 35 11 0 8.71 8.22 3.04 0.37 3.81 16.5 -- --

r 0 1 0 -- -- -- -- -- -- -- --

f 16 6 0 8.99 8.56 2.76 0.02 4.51 13.1 -- --

e 19 4 0 8.47 8.22 3.31 0.63 3.81 16.5 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Potassium, in mg/L D a 15 31 0 4.67 4.46 1.26 0.61 3.23 7.03 -- --

r 0 1 0 -- -- -- -- -- -- -- --

f 7 15 0 4.4 3.8 1.11 0.82 3.23 6 -- --

e 8 15 0 4.91 4.7 1.4 0.42 3.25 7.03 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Sodium, in mg/L D a 15 31 0 46.8 50.7 17.3 0.39 18.2 84.8 -- --

r 0 1 0 -- -- -- -- -- -- -- --

f 7 15 0 50.3 46.4 19.5 0.92 31.2 84.8 -- --

e 8 15 0 43.8 51.3 15.9 0.58 18.2 64.4 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Alkalinity, as calcium 

carbonate, fixed 

endpoint, in mg/L

W a 15 31 0 87.3 85.4 22.4 0.25 51 117 -- --

r 0 1 0 -- -- -- -- -- -- -- --

f 7 15 0 86.1 85.1 23.6 0.17 51.9 117 -- --

e 8 15 0 88.3 96.8 22.9 0.69 51 111 -- --

u 0 0 0 -- -- -- -- -- -- -- --
28 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table 7. Summary statistics for water-quality properties and constituents from composite and bacteriological samples at all stations, 

South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand 

Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[Phase: W, determination made using whole water; T, total; D, dissolved. Typ: a, all samples regardless of hydrograph position; r, sample from rising limb portion 

of hydrograph; f, sample from falling limb portion of hydrograph; e, sample from rising and falling limbs of hydrograph; u, unclassified. n, number of samples; 

M, number of samples with missing values; Pct, percentage of samples below reporting level (unsaved value); Stddev, standard deviation; Skew, skewness; 

ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; C, Celsius; mg/L, milligrams per liter; col, colonies per 100 milliliters; 

N, nitrogen; P, phosphorus; μg/L, micrograms per liter; --, not applicable]

Property or 

constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Medium

South Platte River at Denver (06714000)—Continued

Chloride, in mg/L D a 15 31 0 49.2 50.7 24.1 1.9 15.9 122 -- --

r 0 1 0 -- -- -- -- -- -- -- --

f 7 15 0 56.2 51.1 30.8 2.06 29.9 122 -- --

e 8 15 0 43.2 50.2 16.3 0.73 15.9 60.8 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Fluoride, in mg/L D a 15 31 0 0.58 0.55 0.19 0.18 0.25 0.83 -- --

r 0 1 0 -- -- -- -- -- -- -- --

f 7 15 0 0.56 0.51 0.23 0.08 0.25 0.83 -- --

e 8 15 0 0.6 0.62 0.17 0.42 0.33 0.82 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Sulfate, in mg/L D a 15 31 0 79.4 75.2 30.5 0.28 34 136 -- --

r 0 1 0 -- -- -- -- -- -- -- --

f 7 15 0 77.8 67.6 31.6 1.12 41.8 136 -- --

e 8 15 0 80.9 89.5 31.7 0.33 34 124 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Residue on evaporation 

at 105°C, in mg/L

T a 45 1 0 272 186 251 1.76 28 1,240 -- --

r 1 0 0 150 150 150 150 -- --

f 21 1 0 166 110 147 1.6 28 604 -- --

e 23 0 0 374 272 289 1.33 60 1,240 -- --

u 0 0 0 -- -- -- -- -- -- -- --

E. coli, colonies per

100 mL

W a 5 0 0 13,000 13,000 6,870 0.2 4,900 22,000 -- --

r 1 0 0 4,900 4,900 4,900 4,900 -- --

f 3 0 0 15,600 17,000 7,150 0.83 7,900 22,000 -- --

e 1 0 0 13,000 13,000 13,000 13,000 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Fecal coliform, colonies

per 100 mL

W a 5 0 0 21,000 22,000 14,400 0.12 4,900 35,000 -- --

r 1 0 0 4,900 4,900 4,900 4,900 -- --

f 3 0 0 21,600 22,000 13,600 0.12 7,900 35,000 -- --

e 1 0 0 35,000 35,000 35,000 35,000 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Ammonia + organic N,

in mg/L

T a 45 1 0 2.6 2.09 1.82 2.63 0.87 10.2 -- --

r 1 0 0 3 3 3 3 -- --

f 22 0 0 2.04 1.62 1.93 3.95 0.87 10.2 -- --

e 22 1 0 3.14 2.96 1.61 2.11 1.18 8.8 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Ammonia, as N,

in mg/L

D a 35 11 5.71 0.33 0.22 0.34 2.89 0.06 1.8 0.04 0.04

r 0 1 0 -- -- -- -- -- -- -- --

f 16 6 0 0.28 0.14 0.42 3.49 0.06 1.8 -- --

e 19 4 10.5 0.38 0.25 0.25 1.34 0.14 0.91 0.04 0.04

u 0 0 0 -- -- -- -- -- -- -- --

Nitrite + nitrate, as N,

in mg/L

D a 35 11 0 2.09 2 1.11 0.74 0.71 4.7 -- --

r 0 1 0 -- -- -- -- -- -- -- --

f 16 6 0 1.89 1.71 0.89 0.54 0.76 3.49 -- --

e 19 4 0 2.27 2.13 1.26 0.62 0.71 4.7 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Orthophosphate, as P, 

in mg/L

D a 45 1 0 0.29 0.24 0.17 1.25 0.09 0.86 -- --

r 1 0 0 0.86 0.86 0.86 0.86 -- --

f 22 0 0 0.26 0.22 0.14 1.01 0.09 0.62 -- --

e 22 1 0 0.29 0.25 0.15 0.73 0.1 0.59 -- --

u 0 0 0 -- -- -- -- -- -- -- --
Summary of Stormwater Quality 29

Table 7. Summary statistics for water-quality properties and constituents from composite and bacteriological samples at all stations, 

South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand 

Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[Phase: W, determination made using whole water; T, total; D, dissolved. Typ: a, all samples regardless of hydrograph position; r, sample from rising limb portion 

of hydrograph; f, sample from falling limb portion of hydrograph; e, sample from rising and falling limbs of hydrograph; u, unclassified. n, number of samples; 

M, number of samples with missing values; Pct, percentage of samples below reporting level (unsaved value); Stddev, standard deviation; Skew, skewness; 

ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; C, Celsius; mg/L, milligrams per liter; col, colonies per 100 milliliters; 

N, nitrogen; P, phosphorus; μg/L, micrograms per liter; --, not applicable]

Property or 

constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Medium

South Platte River at Denver (06714000)—Continued

Phosphorus, as P,

in mg/L

T a 45 1 0 0.79 0.67 0.51 1.99 0.28 2.68 -- --

r 1 0 0 1.33 1.33 1.33 1.33 -- --

f 22 0 0 0.61 0.52 0.44 3.32 0.28 2.39 -- --

e 22 1 0 0.95 0.86 0.52 1.81 0.3 2.68 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Organic carbon,

in mg/L

D a 31 15 0 9.29 7.81 5.09 2.43 4.46 29.8 -- --

r 0 1 0 -- -- -- -- -- -- -- --

f 14 8 0 7.67 5.69 3.81 1.69 4.46 17.5 -- --

e 17 6 0 10.6 8.87 5.7 2.6 5.88 29.8 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Copper, in μg/L D a 45 1 0 3.06 2.96 1.11 0.82 1.44 6.16 -- --

r 1 0 0 5 5 5 5 -- --

f 22 0 0 3.04 2.63 1.09 0.73 1.71 5 -- --

e 22 1 0 3 2.97 1.11 1.11 1.44 6.16 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Copper, in μg/L T a 35 11 0 22.8 18 16.8 1.72 5.89 74.5 -- --

r 0 1 0 -- -- -- -- -- -- -- --

f 16 6 0 16.9 12.4 17.1 2.88 5.89 74.5 -- --

e 19 4 0 27.8 21.8 15.3 1.56 11.7 72.8 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Lead, in μg/L D a 45 1 26.7 0.17 0.15 0.1 2.06 0.08 0.52 8.35 10

r 1 0 100 -- -- -- -- -- -- 10 10

f 22 0 36.4 0.16 0.13 0.08 1.39 0.09 0.36 7.52 10

e 22 1 13.6 0.18 0.15 0.11 2.27 0.08 0.52 10 10

u 0 0 0 -- -- -- -- -- -- -- --

Lead, in μg/L T a 35 11 0 21.4 15.4 18.8 1.25 2.79 66 -- --

r 0 1 0 -- -- -- -- -- -- -- --

f 16 6 0 13 7.48 15.2 2.6 2.79 62.5 -- --

e 19 4 0 28.4 21.2 18.9 0.9 8.31 66 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Manganese, in μg/L D a 35 11 0 26.7 16.4 31.4 2.23 1.29 150 -- --

r 0 1 0 -- -- -- -- -- -- -- --

f 16 6 0 27.1 16.7 26.1 0.94 1.29 80.1 -- --

e 19 4 0 26.4 14.2 35.9 2.67 1.32 150 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Manganese, in μg/L T a 35 11 0 355 285 235 1.24 109 999 -- --

r 0 1 0 -- -- -- -- -- -- -- --

f 16 6 0 278 191 229 2.36 109 999 -- --

e 19 4 0 421 404 226 0.81 114 959 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Zinc, in μg/L D a 45 1 13.3 13.2 11.7 8.61 1.43 2.69 40 20 20

r 1 0 0 30 30 30 30 -- --

f 22 0 18.2 12.6 9.49 9.63 1.73 2.69 40 20 20

e 22 1 9.09 13 13.3 7.07 1.42 4.38 34.3 20 20

u 0 0 0 -- -- -- -- -- -- -- --

Zinc, in μg/L T a 35 11 0 101 83 79.7 1.66 24 348 -- --

r 0 1 0 -- -- -- -- -- -- -- --

f 16 6 0 70.1 41 81.6 2.99 24 348 -- --

e 19 4 0 127 101 70 1.47 52 333 -- --

u 0 0 0 -- -- -- -- -- -- -- --
30 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table 7. Summary statistics for water-quality properties and constituents from composite and bacteriological samples at all stations, 

South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand 

Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[Phase: W, determination made using whole water; T, total; D, dissolved. Typ: a, all samples regardless of hydrograph position; r, sample from rising limb portion 

of hydrograph; f, sample from falling limb portion of hydrograph; e, sample from rising and falling limbs of hydrograph; u, unclassified. n, number of samples; 

M, number of samples with missing values; Pct, percentage of samples below reporting level (unsaved value); Stddev, standard deviation; Skew, skewness; 

ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; C, Celsius; mg/L, milligrams per liter; col, colonies per 100 milliliters; 

N, nitrogen; P, phosphorus; μg/L, micrograms per liter; --, not applicable]

Property or 

constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Medium

Tollgate Creek above 6th Avenue at Aurora (394329104490101)

Mean streamflow,

in ft3

/s

-- a 20 4 0 87.1 47 112 1.76 1 405 -- --

r 2 0 0 358 358 67.2 310 405 -- --

f 7 0 0 68.9 14 91.2 1.04 1 207 -- --

e 11 0 0 49.5 42 43 1.23 4 143 -- --

u 0 4 0 -- -- -- -- -- -- -- --

Streamflow volume,

in acre-feet

-- a 20 4 0 82.3 49 102 1.55 0 335 -- --

r 2 0 0 309 309 37.5 282 335 -- --

f 7 0 0 58.3 57 63.3 0.94 0 173 -- --

e 11 0 0 56.4 38 76.8 2.6 4 272 -- --

u 0 4 0 -- -- -- -- -- -- -- --

pH, in standard

pH units

W a 24 0 0 7.16 7.3 0.43 0.86 6.1 7.8 -- --

r 2 0 0 6.66 6.66 0.5 6.3 7.01 -- --

f 7 0 0 7.44 7.4 0.21 1.02 7.22 7.8 -- --

e 11 0 0 7.21 7.31 0.45 1.67 6.1 7.67 -- --

u 4 0 0 6.79 6.78 0.07 0.38 6.72 6.87 -- --

Specific conductance,

in μS/cm

W a 20 4 0 860 719 493 2.6 350 2,630 -- --

r 2 0 0 639 639 205 494 784 -- --

f 7 0 0 749 676 255 0.44 498 1,130 -- --

e 9 2 0 1,050 957 667 1.86 350 2,630 -- --

u 2 2 0 617 617 2.83 615 619 -- --

Hardness, as calcium 

carbonate, in mg/L

T a 24 0 0 259 251 115 1.09 107 594 -- --

r 2 0 0 173 173 65.1 127 219 -- --

f 7 0 0 245 263 75.3 0.49 142 375 -- --

e 11 0 0 299 287 137 0.78 107 594 -- --

u 4 0 0 220 178 114 1.65 138 385 -- --

Calcium, in mg/L D a 21 3 0 77.2 67.4 33.8 1.04 35.6 169 -- --

r 2 0 0 53.6 53.6 19.5 39.8 67.4 -- --

f 6 1 0 75.2 72.4 25.2 0.78 45.4 117 -- --

e 9 2 0 88.2 89.4 40.6 0.77 35.6 169 -- --

u 4 0 0 67.4 55 33.9 1.65 43.2 117 -- --

Magnesium, in mg/L D a 21 3 0 14.5 12.4 8.28 1.79 4.33 41.8 -- --

r 2 0 0 9.54 9.54 4.04 6.68 12.4 -- --

f 6 1 0 13.2 13.2 4.68 0.25 6.99 20.2 -- --

e 9 2 0 17.5 16 10.8 1.38 4.33 41.8 -- --

u 4 0 0 12.5 9.88 7.09 1.65 7.32 22.8 -- --

Potassium, in mg/L D a 13 11 0 3.96 3.88 0.71 1.04 2.89 5.68 -- --

r 1 1 0 2.89 2.89 2.89 2.89 -- --

f 3 4 0 4.7 4.22 0.84 1.73 4.21 5.68 -- --

e 5 6 0 3.96 3.85 0.5 0.93 3.37 4.75 -- --

u 4 0 0 3.67 3.62 0.37 0.27 3.35 4.08 -- --

Sodium, in mg/L D a 13 11 0 80.5 68 31.1 0.68 42.8 142 -- --

r 1 1 0 47.8 47.8 47.8 47.8 -- --

f 3 4 0 65.2 64.8 22.7 0.1 42.8 88.2 -- --

e 5 6 0 96.1 102 37 0.08 50.5 142 -- --

u 4 0 0 80.7 73.5 26.7 1.21 58.3 118 -- --

Alkalinity, as calcium 

carbonate, fixed

endpoint, in mg/L

W a 13 11 0 80.5 69.8 22.7 0.56 51.8 118 -- --

r 1 1 0 51.8 51.8 51.8 51.8 -- --

f 3 4 0 80.2 85.6 14.7 1.45 63.5 91.3 -- --

e 5 6 0 90 90.3 22.1 0.03 66.4 115 -- --

u 4 0 0 75.9 63.9 28.4 1.92 57.6 118 -- --
Summary of Stormwater Quality 31

Table 7. Summary statistics for water-quality properties and constituents from composite and bacteriological samples at all stations, 

South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand 

Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[Phase: W, determination made using whole water; T, total; D, dissolved. Typ: a, all samples regardless of hydrograph position; r, sample from rising limb portion 

of hydrograph; f, sample from falling limb portion of hydrograph; e, sample from rising and falling limbs of hydrograph; u, unclassified. n, number of samples; 

M, number of samples with missing values; Pct, percentage of samples below reporting level (unsaved value); Stddev, standard deviation; Skew, skewness; 

ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; C, Celsius; mg/L, milligrams per liter; col, colonies per 100 milliliters; 

N, nitrogen; P, phosphorus; μg/L, micrograms per liter; --, not applicable]

Property or 

constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Medium

Tollgate Creek above 6th Avenue at Aurora (394329104490101)—Continued

Chloride, in mg/L D a 13 11 0 61.4 62 23.3 0.63 29.9 112 -- --

r 1 1 0 38.6 38.6 38.6 38.6 -- --

f 3 4 0 43.7 44.9 13.3 0.39 29.9 56.4 -- --

e 5 6 0 64.5 62 29.5 1.17 34.6 112 -- --

u 4 0 0 76.5 78.2 8.94 1.1 64.1 85.5 -- --

Fluoride, in mg/L D a 13 11 0 0.3 0.34 0.06 0.59 0.2 0.37 -- --

r 1 1 0 0.22 0.22 0.22 0.22 -- --

f 3 4 0 0.34 0.35 0.03 1.68 0.3 0.36 -- --

e 5 6 0 0.34 0.34 0.04 1.53 0.28 0.37 -- --

u 4 0 0 0.25 0.23 0.07 1.65 0.2 0.35 -- --

Sulfate, in mg/L D a 13 11 0 220 180 107 0.62 116 386 -- --

r 1 1 0 116 116 116 116 -- --

f 3 4 0 187 170 73.7 0.98 123 268 -- --

e 5 6 0 275 315 111 0.53 130 385 -- --

u 4 0 0 202 153 126 1.72 116 386 -- --

Residue on evaporation

at 105°C, in mg/L

T a 22 2 0 718 246 1,560 4.07 40 7,360 -- --

r 2 0 0 290 290 266 102 478 -- --

f 7 0 0 1,230 153 2,710 2.62 40 7,360 -- --

e 9 2 0 691 529 614 1.67 90 2,090 -- --

u 4 0 0 96 94 21.9 0.49 72 124 -- --

E. coli, colonies per

100 mL

W a 3 0 0 25,700 35,000 16,200 1.73 7,000 35,000 -- --

r 1 0 0 35,000 35,000 35,000 35,000 -- --

f 2 0 0 21,000 21,000 19,800 7,000 35,000 -- --

e 0 0 0 -- -- -- -- -- -- -- --

u 0 0 0 -- -- -- -- -- -- -- --

Fecal coliform, colonies

per 100 mL

W a 3 0 0 32,000 35,000 23,600 0.56 7,000 54,000 -- --

r 1 0 0 35,000 35,000 35,000 35,000 -- --

f 2 0 0 30,500 30,500 33,200 7,000 54,000 -- --

e 0 0 0 -- -- -- -- -- -- -- --

u 0 0 0 -- -- -- -- -- -- -- --

Ammonia + organic N,

in mg/L

T a 24 0 0 2.57 2.24 1.55 0.98 0.59 6.32 -- --

r 2 0 0 1.9 1.9 0.46 1.57 2.23 -- --

f 7 0 0 1.94 1.92 0.59 0.28 1.32 2.8 -- --

e 11 0 0 3.58 3.82 1.72 0.14 0.59 6.32 -- --

u 4 0 0 1.23 1.06 0.55 1.3 0.81 2 -- --

Ammonia, as N,

in mg/L

D a 21 3 9.52 0.23 0.22 0.12 0.94 0.05 0.54 0.04 0.04

r 2 0 0 0.2 0.2 0.08 0.15 0.26 -- --

f 6 1 16.7 0.22 0.19 0.19 1.52 0.05 0.54 0.04 0.04

e 9 2 11.1 0.27 0.29 0.11 0.13 0.1 0.44 0.04 0.04

u 4 0 0 0.19 0.19 0.05 0.07 0.13 0.24 -- --

Nitrite + nitrate, as N,

in mg/L

D a 21 3 14.3 0.54 0.54 0.24 0.3 0.11 0.99 0.06 0.06

r 2 0 50 0.52 0.52 0.52 0.52 0.06 0.06

f 6 1 33.3 0.55 0.49 0.32 1.02 0.24 0.99 0.06 0.06

e 9 2 0 0.59 0.67 0.26 0.52 0.11 0.99 -- --

u 4 0 0 0.44 0.39 0.14 1.72 0.33 0.64 -- --

Orthophosphate, as P,

in mg/L

D a 23 1 17.4 0.05 0.05 0.03 0.45 0.01 0.11 0.01 0.01

r 2 0 50 0.05 0.05 0.05 0.05 0.01 0.01

f 7 0 28.6 0.07 0.06 0.03 0.27 0.02 0.1 0.01 0.01

e 10 1 10 0.03 0.03 0.02 1.97 0.01 0.09 0.01 0.01

u 4 0 0 0.08 0.08 0.03 0.29 0.05 0.11 -- --
32 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table 7. Summary statistics for water-quality properties and constituents from composite and bacteriological samples at all stations, 

South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand 

Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[Phase: W, determination made using whole water; T, total; D, dissolved. Typ: a, all samples regardless of hydrograph position; r, sample from rising limb portion 

of hydrograph; f, sample from falling limb portion of hydrograph; e, sample from rising and falling limbs of hydrograph; u, unclassified. n, number of samples; 

M, number of samples with missing values; Pct, percentage of samples below reporting level (unsaved value); Stddev, standard deviation; Skew, skewness; 

ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; C, Celsius; mg/L, milligrams per liter; col, colonies per 100 milliliters; 

N, nitrogen; P, phosphorus; μg/L, micrograms per liter; --, not applicable]

Property or 

constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Medium

Tollgate Creek above 6th Avenue at Aurora (394329104490101)—Continued

Phosphorus, as P,

in mg/L

T a 24 0 4.17 0.8 0.57 0.61 1.19 0.18 2.44 0.04 0.04

r 2 0 0 0.79 0.79 0.31 0.57 1.01 -- --

f 7 0 0 0.8 0.44 0.63 0.8 0.23 1.82 -- --

e 11 0 9.09 1.01 0.95 0.67 1.13 0.2 2.44 0.04 0.04

u 4 0 0 0.26 0.24 0.08 0.82 0.18 0.36 -- --

Organic carbon,

in mg/L

D a 21 3 0 10.4 8.41 4.31 0.85 5.89 18.4 -- --

r 2 0 0 7.77 7.77 0.1 7.7 7.85 -- --

f 6 1 0 10.5 8.14 5.06 1 6.09 18.3 -- --

e 9 2 0 12.2 12 4.21 0.33 7.53 18.4 -- --

u 4 0 0 7.21 6.17 2.28 1.93 5.89 10.6 -- --

Copper, in μg/L D a 24 0 0 2.82 2.8 0.93 0.37 1.25 5 -- --

r 2 0 0 1.75 1.75 0.3 1.54 1.96 -- --

f 7 0 0 3.08 3.29 1.08 0.78 1.98 5 -- --

e 11 0 0 2.99 3.08 0.94 0.63 1.25 4.16 -- --

u 4 0 0 2.46 2.43 0.42 0.34 2 2.98 -- --

Copper, in μg/L T a 21 3 0 21.4 16.6 15.2 1.5 5.41 66.9 -- --

r 2 0 0 16.9 16.9 10.6 9.4 24.4 -- --

f 6 1 0 16 12.4 10.6 0.9 5.51 32.6 -- --

e 9 2 0 31.5 25.5 16.6 1.29 12.4 66.9 -- --

u 4 0 0 9.05 8.97 3.04 0.15 5.41 12.8 -- --

Lead, in μg/L D a 24 0 70.8 0.12 0.1 0.03 1.29 0.09 0.18 1.83 0.08

r 2 0 100 -- -- -- -- -- -- 0.08 0.08

f 7 0 100 -- -- -- -- -- -- 1.5 0.08

e 11 0 54.5 0.13 0.13 0.04 0.87 0.09 0.18 3.39 0.08

u 4 0 50 0.09 0.09 0 0.09 0.09 0.08 0.08

Lead, in μg/L T a 21 3 0 14.6 9.17 13.3 1.57 1.8 53.2 -- --

r 2 0 0 12.5 12.5 8.79 6.34 18.8 -- --

f 6 1 0 9.99 5.85 9.53 1.18 2.47 25.9 -- --

e 9 2 0 22.9 17.5 15 1.26 6.79 53.2 -- --

u 4 0 0 4.01 4.1 1.74 0.3 1.8 6.05 -- --

Manganese, in μg/L D a 21 3 0 183 41.8 347 3.49 2.11 1,570 -- --

r 2 0 0 182 182 247 7.53 356 -- --

f 6 1 0 293 44.7 626 2.44 2.11 1,570 -- --

e 9 2 0 179 113 167 0.64 2.95 474 -- --

u 4 0 0 27.8 29.1 8.39 0.58 17.3 35.7 -- --

Manganese, in μg/L T a 21 3 0 751 683 519 0.79 89.5 1,950 -- --

r 2 0 0 749 749 162 635 864 -- --

f 6 1 0 670 502 563 1.18 222 1,650 -- --

e 9 2 0 1,000 982 523 0.53 260 1,950 -- --

u 4 0 0 311 235 262 1.42 89.5 683 -- --

Zinc, in μg/L D a 24 0 8.33 10.7 7.66 10.5 2.9 2.69 50.6 20 20

r 2 0 0 7.14 7.14 6.3 2.69 11.6 -- --

f 7 0 14.3 6.81 5.03 4.55 1.51 3.29 15.1 20 20

e 11 0 9.09 10.7 9.12 6.87 0.9 2.77 23.8 20 20

u 4 0 0 18.1 7.78 21.7 1.98 6.35 50.6 -- --

Zinc, in μg/L T a 21 3 0 95.6 93 64.4 1.37 18 293 -- --

r 2 0 0 77 77 22.6 61 93 -- --

f 6 1 0 59 43.5 38.9 1.24 24 126 -- --

e 9 2 0 142 124 63.6 1.87 72 293 -- --

u 4 0 0 55.5 36 51.7 1.83 18 132 -- --
Summary of Stormwater Quality 33

Table 7. Summary statistics for water-quality properties and constituents from composite and bacteriological samples at all stations, 

South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand 

Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[Phase: W, determination made using whole water; T, total; D, dissolved. Typ: a, all samples regardless of hydrograph position; r, sample from rising limb portion 

of hydrograph; f, sample from falling limb portion of hydrograph; e, sample from rising and falling limbs of hydrograph; u, unclassified. n, number of samples; 

M, number of samples with missing values; Pct, percentage of samples below reporting level (unsaved value); Stddev, standard deviation; Skew, skewness; 

ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; C, Celsius; mg/L, milligrams per liter; col, colonies per 100 milliliters; 

N, nitrogen; P, phosphorus; μg/L, micrograms per liter; --, not applicable]

Property or 

constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Medium

Sand Creek at mouth near Commerce City (394839104570300)

Mean streamflow,

in ft3

/s

-- a 34 0 0 221 102 346 3.64 18 1,810 -- --

r 3 0 0 134 99 110 1.28 45 257 -- --

f 16 0 0 102 79 79.1 1.58 18 296 -- --

e 15 0 0 366 178 482 2.39 24 1,810 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Streamflow volume, 

in acre-feet

-- a 34 0 0 229 99 449 4.56 17 2,550 -- --

r 3 0 0 117 85 96.6 1.34 41 226 -- --

f 16 0 0 93.1 71.5 73.4 1.41 17 269 -- --

e 15 0 0 395 160 644 3.06 21 2,550 -- --

u 0 0 0 -- -- -- -- -- -- -- --

pH, in standard

pH units

W a 34 0 0 7.43 7.4 0.27 0.17 6.88 7.94 -- --

r 3 0 0 7.63 7.7 0.35 0.86 7.25 7.94 -- --

f 16 0 0 7.37 7.39 0.29 0.34 6.88 7.9 -- --

e 15 0 0 7.45 7.45 0.22 0.18 7.1 7.9 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Specific conductance,

in μS/cm

W a 30 4 0 861 765 314 0.69 342 1,600 -- --

r 2 1 0 1,180 1,180 599 753 1,600 -- --

f 15 1 0 880 915 314 0.59 488 1,600 -- --

e 13 2 0 792 747 268 0.35 342 1,280 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Hardness, as calcium 

carbonate, in mg/L

T a 33 1 0 229 234 72.9 0.24 87 360 -- --

r 3 0 0 309 297 45.8 1.12 271 360 -- --

f 16 0 0 229 233 62.5 0.31 113 323 -- --

e 14 1 0 211 195 80 0 87 325 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Calcium, in mg/L D a 25 9 0 65.6 68.6 21.3 0.23 27.7 95.8 -- --

r 2 1 0 83.6 83.6 9 77.3 90 -- --

f 11 5 0 68.8 68.9 20.1 0.5 35.1 93.8 -- --

e 12 3 0 59.7 53.9 22.5 0.29 27.7 95.8 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Magnesium, in mg/L D a 25 9 0 12.8 14 4.84 0.11 4.33 21.5 -- --

r 2 1 0 18.2 18.2 1.05 17.5 19 -- --

f 11 5 0 13.4 14.4 4.56 0.18 6.09 21.5 -- --

e 12 3 0 11.5 11 4.95 0.31 4.33 20.2 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Potassium, in mg/L D a 12 22 0 4.46 4.2 1.09 0.17 2.81 6.35 -- --

r 0 3 0 -- -- -- -- -- -- -- --

f 5 11 0 4.8 5.21 1.23 0.29 3.11 6.35 -- --

e 7 8 0 4.22 4.01 1 0.33 2.81 5.76 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Sodium, in mg/L D a 12 22 0 85 73.2 36.4 0.26 42.9 138 -- --

r 0 3 0 -- -- -- -- -- -- -- --

f 5 11 0 92 114 38.2 0.57 48.4 125 -- --

e 7 8 0 80.1 67 37.2 0.88 42.9 138 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Alkalinity, as calcium 

carbonate, fixed 

endpoint, in mg/L

W a 12 22 0 94.8 90.9 29 0.17 53.5 139 -- --

r 0 3 0 -- -- -- -- -- -- -- --

f 5 11 0 101 116 33.4 0.57 58.5 133 -- --

e 7 8 0 90.2 88.9 27.2 0.74 53.5 139 -- --

u 0 0 0 -- -- -- -- -- -- -- --
34 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table 7. Summary statistics for water-quality properties and constituents from composite and bacteriological samples at all stations, 

South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand 

Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[Phase: W, determination made using whole water; T, total; D, dissolved. Typ: a, all samples regardless of hydrograph position; r, sample from rising limb portion 

of hydrograph; f, sample from falling limb portion of hydrograph; e, sample from rising and falling limbs of hydrograph; u, unclassified. n, number of samples; 

M, number of samples with missing values; Pct, percentage of samples below reporting level (unsaved value); Stddev, standard deviation; Skew, skewness; 

ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; C, Celsius; mg/L, milligrams per liter; col, colonies per 100 milliliters; 

N, nitrogen; P, phosphorus; μg/L, micrograms per liter; --, not applicable]

Property or 

constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Medium

Sand Creek at mouth near Commerce City (394839104570300)—Continued

Chloride, in mg/L D a 12 22 0 73.6 66.3 27.4 0.1 33.7 110 -- --

r 0 3 0 -- -- -- -- -- -- -- --

f 5 11 0 83.7 98.2 29.7 0.74 42.9 110 -- --

e 7 8 0 66.4 57.2 25.3 0.57 33.7 107 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Fluoride, in mg/L D a 12 22 0 0.45 0.49 0.14 0.1 0.26 0.67 -- --

r 0 3 0 -- -- -- -- -- -- -- --

f 5 11 0 0.47 0.5 0.16 0.19 0.26 0.67 -- --

e 7 8 0 0.44 0.48 0.13 0.21 0.26 0.61 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Sulfate, in mg/L D a 12 22 0 174 150 90 0.64 78.9 347 -- --

r 0 3 0 -- -- -- -- -- -- -- --

f 5 11 0 176 190 87.9 0.19 81.8 267 -- --

e 7 8 0 172 130 98.4 1.13 78.9 347 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Residue on evaporation

at 105°C, in mg/L

T a 34 0 0 440 347 442 2.16 13 1,930 -- --

r 3 0 0 357 416 244 1.02 89 566 -- --

f 16 0 0 279 244 209 0.62 13 690 -- --

e 15 0 0 629 416 580 1.44 38 1,930 -- --

u 0 0 0 -- -- -- -- -- - -- --

E. coli, colonies per

100 mL

W a 4 0 0 13,500 9,150 16,300 0.95 500 35,000 -- --

r 1 0 0 1,300 1,300 1,300 1,300 -- --

f 3 0 0 17,500 17,000 17,300 0.13 500 35,000 -- --

e 0 0 0 -- -- -- -- -- -- -- --

u 0 0 0 -- -- -- -- -- -- -- --

Fecal coliform, colonies

per 100 mL

W a 4 0 0 13,500 9,150 16,200 0.95 700 35,000 -- --

r 1 0 0 1,300 1,300 1,300 1,300 -- --

f 3 0 0 17,600 17,000 17,200 0.15 700 35,000 -- --

e 0 0 0 -- -- -- -- -- -- -- --

u 0 0 0 -- -- -- -- -- -- -- --

Ammonia + organic N,

in mg/L

T a 33 1 0 3.28 2.94 1.89 1.06 0.88 8.61 -- --

r 3 0 0 4.35 4.7 2.62 0.59 1.57 6.78 -- --

f 16 0 0 2.9 2 2.08 1.74 0.88 8.61 -- --

e 14 1 0 3.48 3.35 1.49 0.67 1.09 6.56 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Ammonia, as N,

in mg/L

D a 25 9 12 0.44 0.37 0.34 0.81 0.05 1.15 0.04 0.04

r 2 1 0 0.65 0.65 0.7 0.16 1.15 -- --

f 11 5 18.2 0.47 0.37 0.37 0.71 0.05 1.08 0.04 0.04

e 12 3 8.33 0.37 0.38 0.25 0.28 0.06 0.77 0.04 0.04

u 0 0 0 -- -- -- -- -- -- -- --

Nitrite + nitrate, as N,

in mg/L

D a 25 9 0 1.09 0.87 0.56 1.11 0.36 2.29 -- --

r 2 1 0 1.43 1.43 0.44 1.12 1.74 -- --

f 11 5 0 1.13 0.85 0.62 1.27 0.59 2.29 -- --

e 12 3 0 1 0.86 0.54 1.43 0.36 2.15 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Orthophosphate, as P,

in mg/L

D a 33 1 0 0.16 0.15 0.08 1.32 0.04 0.44 -- --

r 3 0 0 0.16 0.19 0.05 1.73 0.1 0.19 -- --

f 16 0 0 0.17 0.16 0.07 0.54 0.05 0.32 -- --

e 14 1 0 0.15 0.13 0.11 1.73 0.04 0.44 -- --

u 0 0 0 -- -- -- -- -- -- -- --
Summary of Stormwater Quality 35

Table 7. Summary statistics for water-quality properties and constituents from composite and bacteriological samples at all stations, 

South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand 

Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[Phase: W, determination made using whole water; T, total; D, dissolved. Typ: a, all samples regardless of hydrograph position; r, sample from rising limb portion 

of hydrograph; f, sample from falling limb portion of hydrograph; e, sample from rising and falling limbs of hydrograph; u, unclassified. n, number of samples; 

M, number of samples with missing values; Pct, percentage of samples below reporting level (unsaved value); Stddev, standard deviation; Skew, skewness; 

ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; C, Celsius; mg/L, milligrams per liter; col, colonies per 100 milliliters; 

N, nitrogen; P, phosphorus; μg/L, micrograms per liter; --, not applicable]

Property or 

constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Medium

Sand Creek at mouth near Commerce City (394839104570300)—Continued

Phosphorus, as P,

in mg/L

T a 33 1 0 0.91 0.83 0.57 1.18 0.24 2.76 -- --

r 3 0 0 1.11 1.45 0.65 1.71 0.37 1.53 -- --

f 16 0 0 0.7 0.49 0.45 1.3 0.24 1.83 -- --

e 14 1 0 1.11 0.96 0.62 1.4 0.33 2.76 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Organic carbon,

in mg/L

D a 24 10 0 13.2 12.9 5.89 1.1 5.86 30.1 -- --

r 1 2 0 20.8 20.8 20.8 20.8 -- --

f 11 5 0 13.1 12.1 7.23 1.31 5.86 30.1 -- --

e 12 3 0 12.6 12.3 4.4 0.88 7.27 22.6 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Copper, in μg/L D a 33 1 0 3.84 3 4.13 4.54 1.25 25 -- --

r 3 0 0 10.3 3.46 12.7 1.72 2.46 25 -- --

f 16 0 0 3.52 3.05 1.98 2.52 1.74 10 -- --

e 14 1 0 2.82 2.89 1.27 1.06 1.25 6 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Copper, in μg/L T a 25 9 0 26.2 19.2 19.8 1.51 5.36 87.3 -- --

r 2 1 0 22.5 22.5 16.3 11 34.1 -- --

f 11 5 0 19 14 13.7 1.53 5.36 51.7 -- --

e 12 3 0 33.4 25.8 23.5 1.17 7.86 87.3 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Lead, in μg/L D a 33 1 39.4 0.19 0.17 0.11 1.62 0.08 0.48 6.18 10

r 3 0 33.3 0.36 0.36 0.17 0.24 0.48 10 10

f 16 0 43.8 0.18 0.13 0.11 1.42 0.1 0.41 7.17 10

e 14 1 35.7 0.16 0.17 0.05 0.73 0.08 0.21 4.05 0.08

u 0 0 0 -- -- -- -- -- -- -- --

Lead, in μg/L T a 25 9 0 26.9 19.1 27.3 1.76 1.45 114 -- --

r 2 1 0 22.7 22.7 19.8 8.77 36.7 -- --

f 11 5 0 16.3 9.19 15.8 1.7 1.45 55.7 -- --

e 12 3 0 37.4 23 33.6 1.25 3.65 114 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Manganese, in μg/L D a 25 9 0 85.1 35.1 127 2.42 2.69 550 -- --

r 2 1 0 172 172 140 72.6 271 -- --

f 11 5 0 66.6 14.2 93.7 1.2 2.69 235 -- --

e 12 3 0 87.7 35.1 154 2.93 4.12 550 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Manganese, in μg/L T a 25 9 0 720 602 548 1.2 84 2,090 -- --

r 2 1 0 705 705 665 235 1,170 -- --

f 11 5 0 567 415 574 2.13 84 2,090 -- --

e 12 3 0 864 813 519 1.05 141 2,090 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Zinc, in μg/L D a 32 2 0 63.7 34.4 83.4 2.1 3.01 336 -- --

r 3 0 0 114 93.3 86.1 1.02 40 208 -- --

f 16 0 0 76.1 34.8 101 1.97 3.01 336 -- --

e 13 2 0 36.9 10 47.9 1.89 4.24 165 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Zinc, in μg/L T a 24 10 0 289 148 320 1.67 18 1,150 -- --

r 2 1 0 726 726 539 345 1,110 -- --

f 11 5 0 263 80 363 1.87 18 1,150 -- --

e 11 4 0 235 154 179 0.59 39 545 -- --

u 0 0 0 -- -- -- -- -- -- -- --
36 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table 7. Summary statistics for water-quality properties and constituents from composite and bacteriological samples at all stations, 

South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand 

Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[Phase: W, determination made using whole water; T, total; D, dissolved. Typ: a, all samples regardless of hydrograph position; r, sample from rising limb portion 

of hydrograph; f, sample from falling limb portion of hydrograph; e, sample from rising and falling limbs of hydrograph; u, unclassified. n, number of samples; 

M, number of samples with missing values; Pct, percentage of samples below reporting level (unsaved value); Stddev, standard deviation; Skew, skewness; 

ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; C, Celsius; mg/L, milligrams per liter; col, colonies per 100 milliliters; 

N, nitrogen; P, phosphorus; μg/L, micrograms per liter; --, not applicable]

Property or 

constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Medium

South Platte River at Henderson (06720500)

Mean streamflow,

in ft3

/s

-- a 35 0 0 1,480 1,060 1,460 2.71 280 7,570 -- --

r 7 0 0 1,120 1,200 611 0.28 281 1,730 -- --

f 13 0 0 1,130 818 972 2.15 280 3,900 -- --

e 15 0 0 1,940 1,070 1,960 2.1 350 7,570 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Streamflow volume,

in acre-feet

-- a 35 0 0 1,320 1,090 1,280 2.97 208 6,880 -- --

r 7 0 0 1,020 1,090 556 0.29 255 1,580 -- --

f 13 0 0 865 744 523 0.47 208 1,670 -- --

e 15 0 0 1,840 1,230 1,750 2.08 318 6,880 -- --

u 0 0 0 -- -- -- -- -- -- -- --

pH, in standard

pH units

W a 35 0 0 7.38 7.36 0.26 0.19 6.72 8 -- --

r 7 0 0 7.25 7.35 0.26 1.72 6.72 7.48 -- --

f 13 0 0 7.44 7.34 0.24 1.08 7.1 8 -- --

e 15 0 0 7.39 7.4 0.29 0.46 6.92 8 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Specific conductance,

in μS/cm

W a 30 5 0 676 655 210 0.36 316 1,090 -- --

r 5 2 0 827 800 177 0.19 646 1,020 -- --

f 12 1 0 648 655 194 0.33 367 1,020 -- --

e 13 2 0 645 600 224 0.75 316 1,090 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Hardness, as calcium 

carbonate, in mg/L

T a 34 1 0 180 172 58.4 1.14 84.5 380 -- --

r 7 0 0 183 174 34.5 0.57 136 240 -- --

f 13 0 0 179 170 47.2 0.24 100 250 -- --

e 14 1 0 180 163 77.8 1.3 84.5 380 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Calcium, in mg/L D a 23 12 0 44.3 44 9.14 0.06 26.2 62.7 -- --

r 6 1 0 50.3 50.3 7.7 0.45 40 62.7 -- --

f 7 6 0 42.4 42.6 6.32 0.81 31.3 49.4 -- --

e 10 5 0 42.1 41.4 10.6 0.33 26.2 61.2 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Magnesium, in mg/L D a 23 12 0 9.88 10.1 2.77 0.01 4.62 16 -- --

r 6 1 0 11.6 11.4 1.69 0.42 8.86 13.8 -- --

f 7 6 0 9.5 9.06 2.27 0.86 5.43 11.9 -- --

e 10 5 0 9.13 8.57 3.33 0.79 4.62 16 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Potassium, in mg/L D a 8 27 0 6.18 5.73 1.81 0.32 4.26 8.37 -- --

r 2 5 0 7.01 7.01 1.65 5.84 8.18 -- --

f 2 11 0 5.01 5.01 0.85 4.41 5.61 -- --

e 4 11 0 6.36 6.4 2.26 0.01 4.26 8.37 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Sodium, in mg/L D a 8 27 0 67.1 65.3 38.5 1.06 27.1 142 -- --

r 2 5 0 103 103 55.7 63.4 142 -- --

f 2 11 0 66 66 45.2 34.1 98 -- --

e 4 11 0 49.8 50.9 22.1 0.08 27.1 70.4 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Alkalinity, as calcium 

carbonate, fixed 

endpoint, in mg/L

W a 8 27 0 86.3 90.7 22.2 0.11 57.7 121 -- --

r 2 5 0 100 100 6.48 95.6 105 -- --

f 2 11 0 77 77 14.9 66.5 87.6 -- --

e 4 11 0 83.9 78.5 29.5 0.66 57.7 121 -- --

u 0 0 0 -- -- -- -- -- -- -- --
Summary of Stormwater Quality 37

Table 7. Summary statistics for water-quality properties and constituents from composite and bacteriological samples at all stations, 

South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand 

Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[Phase: W, determination made using whole water; T, total; D, dissolved. Typ: a, all samples regardless of hydrograph position; r, sample from rising limb portion 

of hydrograph; f, sample from falling limb portion of hydrograph; e, sample from rising and falling limbs of hydrograph; u, unclassified. n, number of samples; 

M, number of samples with missing values; Pct, percentage of samples below reporting level (unsaved value); Stddev, standard deviation; Skew, skewness; 

ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; C, Celsius; mg/L, milligrams per liter; col, colonies per 100 milliliters; 

N, nitrogen; P, phosphorus; μg/L, micrograms per liter; --, not applicable]

Property or 

constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Medium

South Platte River at Henderson (06720500)—Continued

Chloride, in mg/L D a 8 27 0 74 58.1 60.2 1.51 23.3 197 -- --

r 2 5 0 128 128 97.7 58.9 197 -- --

f 2 11 0 79.1 79.1 72.2 28.1 130 -- --

e 4 11 0 44.5 44.6 20 0.02 23.3 65.3 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Fluoride, in mg/L D a 8 27 0 0.56 0.51 0.19 0.43 0.35 0.84 -- --

r 2 5 0 0.64 0.64 0.15 0.53 0.74 -- --

f 2 11 0 0.44 0.44 0.05 0.41 0.48 -- --

e 4 11 0 0.58 0.57 0.26 0.08 0.35 0.84 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Sulfate, in mg/L D a 8 27 0 82.1 80.4 26.2 0.05 47.4 117 -- --

r 2 5 0 96.2 96.2 14.9 85.7 107 -- --

f 2 11 0 65.8 65.8 13.2 56.4 75.1 -- --

e 4 11 0 83.3 84.4 34 0.08 47.4 117 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Residue on evaporation

at 105°C, in mg/L

T a 34 1 0 615 265 1,150 3.85 76 6,040 -- --

r 7 0 0 225 154 147 1.05 108 486 -- --

f 12 1 0 472 223 573 2.26 76 2,060 -- --

e 15 0 0 911 326 1,630 2.78 90.7 6,040 -- --

u 0 0 0 -- -- -- -- -- -- -- --

E. coli, colonies

per 100 mL

W a 5 0 0 6,950 7,000 5,210 0.1 460 13,000 -- --

r 1 0 0 460 460 460 460 -- --

f 3 0 0 7,770 7,000 4,900 0.69 3,300 13,000 -- --

e 1 0 0 11,000 11,000 11,000 11,000 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Fecal coliform, colonies

per 100 mL

W a 5 0 0 24,800 11,000 26,900 0.52 310 54,000 -- --

r 1 0 0 310 310 310 310 -- --

f 3 0 0 23,300 11,000 26,800 1.63 4,900 54,000 -- --

e 1 0 0 54,000 54,000 54,000 54,000 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Ammonia + organic N,

in mg/L

T a 34 1 0 5.47 4.95 2.3 0.89 1.98 12.2 -- --

r 7 0 0 5.32 4.98 1.38 0.06 3.15 7.3 -- --

f 13 0 0 5.72 5.44 2.82 0.83 1.98 12.2 -- --

e 14 1 0 5.31 4.26 2.27 0.88 2.66 9.63 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Ammonia, as N,

in mg/L

D a 23 12 0 1.59 1.48 0.93 0.68 0.32 3.55 -- --

r 6 1 0 2.12 2.12 0.63 0.32 1.36 3.06 -- --

f 7 6 0 1.61 1.48 1.06 0.65 0.34 3.46 -- --

e 10 5 0 1.26 1.01 0.91 1.95 0.32 3.55 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Nitrite + nitrate, as N,

in mg/L

D a 23 12 0 2.71 2.57 0.92 0.03 1.14 4.1 -- --

r 6 1 0 3.22 3.38 0.8 0.44 2.14 4.1 -- --

f 7 6 0 2.43 2.52 0.83 1.11 1.47 4.01 -- --

e 10 5 0 2.61 2.55 1 0.09 1.14 4 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Orthophosphate, as P,

in mg/L

D a 34 1 0 0.63 0.6 0.28 0.63 0.2 1.4 -- --

r 7 0 0 0.7 0.7 0.35 1.37 0.35 1.4 -- --

f 13 0 0 0.59 0.53 0.26 0.51 0.21 1.06 -- --

e 14 1 0 0.62 0.62 0.26 0.03 0.2 1 -- --

u 0 0 0 -- -- -- -- -- -- -- --
38 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table 7. Summary statistics for water-quality properties and constituents from composite and bacteriological samples at all stations, 

South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand 

Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[Phase: W, determination made using whole water; T, total; D, dissolved. Typ: a, all samples regardless of hydrograph position; r, sample from rising limb portion 

of hydrograph; f, sample from falling limb portion of hydrograph; e, sample from rising and falling limbs of hydrograph; u, unclassified. n, number of samples; 

M, number of samples with missing values; Pct, percentage of samples below reporting level (unsaved value); Stddev, standard deviation; Skew, skewness; 

ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; C, Celsius; mg/L, milligrams per liter; col, colonies per 100 milliliters; 

N, nitrogen; P, phosphorus; μg/L, micrograms per liter; --, not applicable]

Property or 

constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Medium

South Platte River at Henderson (06720500)—Continued

Phosphorus, as P,

in mg/L

T a 34 1 0 1.85 1.59 1.3 3.89 0.73 8.3 -- --

r 7 0 0 1.62 1.5 0.58 0.37 0.83 2.52 -- --

f 13 0 0 1.66 1.65 0.74 0.44 0.73 3.12 -- --

e 14 1 0 2.14 1.59 1.86 3.18 0.84 8.3 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Organic carbon,

in mg/L

D a 19 16 0 9.88 10.6 3.25 0.27 5.39 16.6 -- --

r 4 3 0 9.27 9.13 2.58 0.08 6.91 11.9 -- --

f 6 7 0 9.91 8.34 4.72 0.57 5.86 16.6 -- --

e 9 6 0 10.1 10.7 2.66 0.56 5.39 14 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Copper, in μg/L D a 34 1 0 3.39 2.95 1.74 1.79 1.56 9 -- --

r 7 0 0 2.99 3 0.64 0.57 1.9 3.77 -- --

f 13 0 0 3.32 3 1.51 1.36 1.56 7 -- --

e 14 1 0 3.65 2.79 2.29 1.52 1.8 9 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Copper, in μg/L T a 23 12 0 35.3 32.4 16.3 0.5 11.6 71.9 -- --

r 6 1 0 32.9 30.1 17 0.39 16 56.7 -- --

f 7 6 0 34.3 34.2 21.6 0.87 11.6 71.9 -- --

e 10 5 0 37.5 32.2 13 0.57 22.7 57.2 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Lead, in μg/L D a 34 1 29.4 0.69 0.28 1.99 4.87 0.13 10 10 10

r 7 0 14.3 0.3 0.32 0.07 1.03 0.18 0.37 10 10

f 13 0 46.2 0.26 0.19 0.17 2.21 0.13 0.64 10 10

e 14 1 21.4 1.17 0.31 2.93 3.31 0.16 10 10 10

u 0 0 0 -- -- -- -- -- -- -- --

Lead, in μg/L T a 23 12 0 33.1 33.2 17.9 0.42 6.92 68.2 -- --

r 6 1 0 26.1 25.1 14.1 0.18 12.2 44.1 -- --

f 7 6 0 30.7 28.8 21.1 0.59 6.92 63.1 -- --

e 10 5 0 39 38.9 17.3 0.43 17.6 68.2 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Manganese, in μg/L D a 23 12 0 88.5 80.8 65.6 0.86 7.21 242 -- --

r 6 1 0 123 106 43.8 1.02 85.8 194 -- --

f 7 6 0 76.5 56.2 80.6 1.73 7.3 242 -- --

e 10 5 0 76.3 66.7 63.8 1.21 7.21 217 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Manganese, in μg/L T a 23 12 0 565 545 237 0.28 236 1,010 -- --

r 6 1 0 563 465 309 0.74 257 1,010 -- --

f 7 6 0 525 541 281 0.45 236 966 -- --

e 10 5 0 595 592 173 0.11 329 895 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Zinc, in μg/L D a 34 1 8.82 21.2 19.8 10.4 1.11 7.86 50 20 20

r 7 0 0 21.3 20.7 5.5 0.45 14.7 30 -- --

f 13 0 23.1 17.6 17.3 6.69 0.54 9.71 30 20 20

e 14 1 0 23.8 19.9 13.6 0.67 7.86 50 -- --

u 0 0 0 -- -- -- -- -- -- -- --

Zinc, in μg/L T a 23 12 0 154 145 74 0.35 45 299 -- --

r 6 1 0 136 128 64.9 0.17 70 211 -- --

f 7 6 0 151 145 97 0.57 45 299 -- --

e 10 5 0 168 148 65.7 0.35 96 265 -- --

u 0 0 0 -- -- -- -- -- -- -- --
Period one ft3/s is cub

μS/cm is mmg/L is miμg/L is micna is not a

Residue

on evap.

at 105°C,

mg/L

Ammonia

+

organic N,

mg/L

Ammonia,

mg/L

Nitrite

+

nitrate,

as N,mg/L

Orthophosphate,

mg/L

Phosphorus,

total,mg/L

Organic

carbon,

dissolved,

mg/L

Copper,

dissolved,

μg/L

Copper,

total,

μg/L

Lead,

dissolved,

μg/L

Lead,

total,

μg/L

Manganese,

dissolved,

μg/L

Mean censored valuePercent censored valuesNumber of samplesMean censored valuePercent censored valuesNumber of samples

Mean

streamflow,

ft3/s

pH,

standard

pH

units

Specific

conductance,

μS/cm

Hardness,

mg/L

Potassium,

dissolved,

mg/L

Sodium,

dissolved,

mg/L

Alkalinity,

fixed

end-point,

mg/L

Chloride,

dissolved,

mg/L

Fluoride,

dissolved,

mg/L

Sulfate,

dissolved,

mg/L

A

Axis labels indicate power of 10 Axis labels indicate power of 10

E

2005200420032002

Annual mean

Figure 3. Boxplots showing distribution of water-quality properties and constituents at (A) all stations, (B) South Platte River 

Englewood, (C) South Platte River at Denver, (D) Tollgate Creek above 6th Avenue at Aurora, (E) Sand Creek at mouth near ComPlatte River at Henderson, water years 1998–2001 and water years 2002–2005.
Figure 3. Boxplots showing distribution of water-quality properties and constituents at (A) all stations, (B) South Platte River bel

Englewood, (C) South Platte River at Denver, (D) Tollgate Creek above 6th Avenue at Aurora, (E) Sand Creek at mouth near CommePlatte River at Henderson, water years 1998–2001 and water years 2002–2005.—Continued

Residue

on evap.

at 105°C,

mg/L

Ammonia

+

organic N,

mg/L

Ammonia,

mg/L

Nitrite

+

nitrate,

as N,mg/L

Orthophosphate,

mg/L

Phosphorus,

total,mg/L

Organic

carbon,

dissolved,

mg/L

Copper,

dissolved,

μg/L

Copper,

total,

μg/L

Lead,

dissolved,

μg/L

Lead,

total,

μg/L

Manganese,

dissolved,

μg/L

Ma

ne

to

μ

Mean

streamflow,

ft3/s

pH,

standard

pH

units

Specific

conductance,

μS/cm

Hardness,

mg/L

Potassium,

dissolved,

mg/L

Sodium,

dissolved,

mg/L

Alkalinity,

fixed

endpoint,

mg/L

Chloride,

dissolved,

mg/L

Fluoride,

dissolved,

mg/L

Sulfate,

dissolved,

mg/L

2005200420032002

Annual means

Period one (1998ft3/s is cubic feet 

μS/cm is microsmg/L is milligramμg/L is micrograna is not applica

EXP

Mean censored valuePercent censored valuesNumber of samplesMean censored valuePercent censored valuesNumber of samples

Axis labels indicate power of 10 Axis labels indicate power of 10

B
Figure 3. Boxplots showing distribution of water-quality properties and constituents at (A) all stations, (B) South Platte River be

Englewood, (C) South Platte River at Denver, (D) Tollgate Creek above 6th Avenue at Aurora, (E) Sand Creek at mouth near CommPlatte River at Henderson, water years 1998–2001 and water years 2002–2005.—Continued Residue on evap. at 105°C, mg/L Ammonia + organic N, mg/L Ammonia, mg/L Nitrite + nitrate, as N, mg/L Ortho- phosphate, mg/L Phos- phorus, total, mg/L Organic carbon, dissolved, mg/L Copper, dissolved, μg/L Copper, total, μg/L Lead, dissolved, μg/L Lead, total, μg/L Manga- nese, dissolved, μg/L Ma

ne

to

μ

Mean

streamflow,

ft3/s

pH,

standard

pH

units

Specific

conductance,

μS/cm

Hardness,

mg/L

Potassium,

dissolved,

mg/L

Sodium,

dissolved,

mg/L

Alkalinity,

fixed

endpoint,

mg/L

Chloride,

dissolved,

mg/L

Fluoride,

dissolved,

mg/L

Sulfate,

dissolved,

mg/L

Mean censored valuePercent censored valuesNumber of samplesMean censored valuePercent censored valuesNumber of samples

Axis labels indicate power of 10 Axis labels indicate power of 10

C

Period one (1998ft3/s is cubic feet 

μS/cm is microsmg/L is milligramμg/L is micrograna is not applica2005200420032002

Annual means

EXP
Figure 3. Boxplots showing distribution of water-quality properties and constituents at (A) all stations, (B) South Platte River b

Englewood, (C) South Platte River at Denver, (D) Tollgate Creek above 6th Avenue at Aurora, (E) Sand Creek at mouth near ComPlatte River at Henderson, water years 1998–2001 and water years 2002–2005.—Continued

Residue

on evap.

at 105°C,

mg/L

Ammonia

+

organic N,

mg/L

Ammonia

mg/L

Nitrite

+

nitrate,

as N,mg/L

Orthophosphate,

mg/L

Phosphorus,

total,mg/L

Organic

carbon,

dissolved,

mg/L

Copper,

dissolved,

μg/L

Copper,

total,

μg/L

Lead,

dissolved,

μg/L

Lead,

total,

μg/L

Manganese,

dissolved,

μg/L

Mean

streamflow,

ft3/s

pH,

standard

pH

units

Specific

conductance,

μS/cm

Hardness,

mg/L

Potassium,

dissolved,

mg/L

Sodium,

dissolved,

mg/L

Alkalinity,

fixed

endpoint,

mg/L

Chloride,

dissolved,

mg/L

Fluoride,

dissolved,

mg/L

Sulfate,

dissolved,

mg/L

Mean censored valuePercent censored valuesNumber of samplesMean censored valuePercent censored valuesNumber of samples

Axis labels indicate power of 10 Axis labels indicate power of 10

D

Period one (199ft3/s is cubic feet 

μS/cm is microsmg/L is milligraμg/L is micrograna is not applica2005200420032002

Annual means

EXP
Figure 3. Boxplots showing distribution of water-quality properties and constituents at (A) all stations, (B) South Platte River b

Englewood, (C) South Platte River at Denver, (D) Tollgate Creek above 6th Avenue at Aurora, (E) Sand Creek at mouth near CommPlatte River at Henderson, water years 1998–2001 and water years 2002–2005.—Continued Residue on evap. at 105°C, mg/L Ammonia + organic N, mg/L Ammonia, mg/L Nitrite + nitrate, as N, mg/L Ortho- phosphate, mg/L Phos- phorus, total, mg/L Organic carbon, dissolved, mg/L Copper, dissolved, μg/L Copper, total, μg/L Lead, dissolved, μg/L Lead, total, μg/L Manga- nese, dissolved, μg/L M

Mean

streamflow,

ft3/s

pH,

standard

pH

units

Specific

conductance,

μS/cm

Hardness,

mg/L

Potassium,

dissolved,

mg/L

Sodium,

dissolved,

mg/L

Alkalinity,

fixed

endpoint,

mg/L

Chloride,

dissolved,

mg/L

Fluoride,

dissolved,

mg/L

Sulfate,

dissolved,

mg/L

Mean censored valuePercent censored valuesNumber of samplesMean censored valuePercent censored valuesNumber of samples

Axis labels indicate power of 10 Axis labels indicate power of 10

E

Period one (1998ft3/s is cubic feet 

μS/cm is microsimg/L is milligramμg/L is microgramna is not applica2005200420032002

Annual means

EXPLA
Figure 3. Boxplots showing distribution of water-quality properties and constituents at (A) all stations, (B) South Platte River be

Englewood, (C) South Platte River at Denver, (D) Tollgate Creek above 6th Avenue at Aurora, (E) Sand Creek at mouth near CommPlatte River at Henderson, water years 1998–2001 and water years 2002–2005.—Continued

Residue

on evap.

at 105°C,

mg/L

Ammonia

+

organic N,

mg/L

Ammonia,

mg/L

Nitrite

+

nitrate,

as N,mg/L

Orthophosphate,

mg/L

Phosphorus,

total,mg/L

Organic

carbon,

dissolved,

mg/L

Copper,

dissolved,

μg/L

Copper,

total,

μg/L

Lead,

dissolved,

μg/L

Lead,

total,

μg/L

Manganese,

dissolved,

μg/L

Ma

ne

to

μg

Mean

streamflow,

ft3/s

pH,

standard

pH

units

Specific

conductance,

μS/cm

Hardness,

mg/L

Potassium,

dissolved,

mg/L

Sodium,

dissolved,

mg/L

Alkalinity,

fixed

endpoint,

mg/L

Chloride,

dissolved,

mg/L

Fluoride,

dissolved,

mg/L

Sulfate,

dissolved,

mg/L

Mean censored valuePercent censored valuesNumber of samplesMean censored valuePercent censored valuesNumber of samples

Axis labels indicate power of 10 Axis labels indicate power of 10

F

Period one (1998ft3/s is cubic feet 

μS/cm is microsimg/L is milligramμg/L is microgramna is not applica2005200420032002

Annual means

EXPLA
Evaluation of Stormwater Quality 45

A summary of results from composite samples and bacteriological samples that did not meet or had exceptions when 

compared to standards is presented in table 9 for individual 

stations. For cases with several exceptions, exception frequency and magnitude are described in absolute numbers and 

also as a fraction of the total number of samples with analyses. 

Exceptions also are characterized as multiples of the actual 

standard, for magnitude.

Results from composite samples indicate very few 

exceptions to standards. Two samples at Tollgate had values 

for pH that were equal to the lower limit of numeric standards 

(6.5 standard pH units). In addition there were three exceptions to standards for metals; one each for dissolved copper 

and manganese at Union and one for dissolved zinc at Sand 

Creek. Bacteriological indicators in all samples however, consistently exceeded numeric standards.

Evaluation of Stormwater Quality

Results from laboratory analyses of composite samples 

are evaluated in this section by using a preliminary examination of annual means and two statistical methods. The goal of 

the evaluations is to establish criteria that may be compared 

with results from past or future sampling.

Annual Means

Composite samples collected as part of this study 

describe the quality of stormwater runoff during a 4-year 

period, and annual means from these data can be used to 

determine if temporal trends are present. In this report the term 

“temporal trends” is used to indicate simple one-directional 

trends in which values tend to show upward or downward 

Table 8. Summary of relative percent differences and correlations between various weighting methods for analytical determinations 

of discrete samples, water years 2002–2005.

[All determinations made at USGS National Water Quality Laboratory. RPD: 1, relative percent difference between time- and discharge-weighted concentrations; 

2, relative percent difference between time- and volume-weighted concentrations; 3, relative percent difference between discharge- and volume-weighted 

concentrations. Stddev, standard deviation; Pct, percentage of samples with a relative percent difference of 20 or less (absolute value); Np, number of water-quality 

property and constituent pairs in relative percent difference calculation. Phase: W, determination made using whole water; T, total; D, dissolved. Corr, Pearson 

correlation coefficient; n, number of discrete storm samples; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter; C, Celsius; 

N, nitrogen; P, phosphorus; μg/L, micrograms per liter; --, not applicable]

Relative percent differences from discrete sampling events

RPD Mean Median Stddev Skewness Minimum Maximum Pct Np

All storms

1 –1.74 –3.62 15.74 0.07 –38.30 27.44 76.92 39

2 2.04 0.91 10.10 0.19 –16.35 23.70 92.31 39

3 3.78 2.20 7.36 0.61 –6.47 23.69 97.44 39

Storm 1

1 –11.25 –7.52 11.08 –1.40 –38.30 0.41 82.35 17

2 –2.73 –1.90 6.88 –0.39 –15.36 11.47 100.00 17

3 8.55 7.72 7.11 0.39 –2.84 23.69 94.12 17

Storm 2

1 5.61 4.51 15.00 –0.09 –22.73 27.44 72.73 22

2 5.73 7.02 10.76 –0.26 –16.36 21.84 86.36 22

3 0.10 0.98 5.19 0.28 –6.47 9.50 100.00 22

Correlation coefficients between time- and volume-weighted concentrations from discrete samples collected during storms

Property or constituent

Storm number

All 1 2

Corr n Corr n Corr n

Specific conductance, in μS/cm 0.538 22 0.689 9 0.726 13

Hardness, as calcium carbonate, in mg/L 0.556 22 0.712 9 0.733 13

Residue at 105°C, in mg/L 0.370 22 0.963 9 0.806 13

Dissolved organic carbon, in mg/L 0.452 22 0.855 9 0.656 13

Ammonia, as N, in mg/L 0.606 22 0.692 9 0.690 13

Nitrite + nitrate, as N, in mg/L 0.798 22 0.803 9 0.696 13

Ammonia + organic N, in mg/L 0.952 22 0.924 9 0.753 13

Phosphorus, as P, in mg/L 0.743 22 0.972 9 0.732 13

Orthophosphate, as P, in mg/L 0.276 22 0.587 9 0.617 13

Dissolved copper, in μg/L 0.403 22 0.765 9 0.584 13

Dissolved lead, in μg/L 0.524 22 0.820 9 0.618 13

Dissolved zinc, in μg/L 0.729 22 0.777 9 0.689 13
46 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table 9. Summary of composite and bacteriological sample results not meeting Colorado Department of Public Health and Environment 

numeric standards for all stations, South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 

6th Avenue at Aurora, Sand Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[Phase: W, determination made using whole water; T, total; D, dissolved. Typ indicates statistics for: std, numeric standard; dif, difference between compositestormwater results and numeric standard; pdf, dif divided by numeric standard. n, number of samples; M, number of missing values; Pctc, percentage of 

determinations with concentrations below reporting level; E, number of samples that did not meet numeric standard; Pcte, percentage of determinations with 

values greater than minimum reporting level that did not meet numeric standard; Stddev, standard deviation; Min, minimum, Max, maximum; col, colonies per 

100 milliliters; N, nitrogen; mg/L, milligrams per liter; μg/L, micrograms per liter; --, not applicable]

Property or 

constituent Phase Typ n M Pctc E Pcte Mean Median Stddev Skewness Min Max

All stations

pH, in standard pH units W std 176 0 0 2 1.14 6.5 6.5 0.0 0.0 6.5 6.5

dif -- -- -- -- -- --

pdf -- -- -- -- -- --

Escherichia coli, in col W std 22 0 0 22 100 126 -- -- -- -- --

dif 16,376 12,874 19,971 2.81 334 91874

pdf 130 102.17 158 2.81 2.65 729

Fecal coliform, in col W std 22 0 0 22 100 200 -- -- -- -- --

dif 20,141 13,000 18,215 0.76 310 54,000

pdf 100 64 91 0.76 0.55 269

Chloride, in mg/L D std No exceptions to chloride standards.

dif The chloride standards specify that chloride should not exceed 250.

pdf

Nitrite + nitrate, as N, 

in mg/L

D std 22 No exceptions to nitrite and nitrate standards.

dif The nitrite plus nitrate standards specify that nitrite plus nitrate should not exceed 11.

pdf

Copper, in μg/L D std 173 3 0 1 0.60 25.8 25.8 -- -- 25.8 25.8

dif 2.2 2.2 -- -- 2.2 2.2

pdf 0.08 0.08 -- -- 0.08 0.08

Lead, in μg/L D std 173 3 47.4 0 0.00 No exceptions to dissolved lead standard.

dif The dissolved lead standard is specified as a table-value standard calculated for 

individual samples.

pdf

Manganese, in μg/L D std 132 44 0 1 0.76 190 190 -- -- 190 190

dif 50.9 50.9 -- -- 50.93 50.93

pdf 0.26 0.26 -- -- 0.26 0.26

Manganese, in μg/L T std No exceptions to manganese standards.

dif The manganese standard is specified as a table-value standard calculated for each sample.

pdf

Zinc, in μg/L D std 172 4 9.88 1 0.64 273 273 -- -- 273 273

dif 26.8 26.8 -- -- 26.8 26.8

pdf 0.09 0.09 -- -- 0.09 0.09

South Platte River below Union Avenue at Englewood (06710247)

pH, in standard pH units W std 37 0 0 0 No exceptions to pH standard.

dif The pH standard specifies pH should be in the range of 6.5 to 9.0.

pdf

Escherichia coli, in col W std 5 0 0 5 100 126 -- -- -- -- --

dif 26,414 12,874 36,918 2.13 1,574 91,874

pdf 209 102 293 2.13 12.49 729

Fecal coliform, in col W std 5 0 0 5 100 200 -- -- -- -- --

dif 12,620 12,800 9,584 1.03 2,000 27.800

pdf 63 64 48 1.03 10 139

Nitrite + nitrate, as N, 

in mg/L

D std 28 9 0 0 0 No exceptions to nitrite and nitrate standards.

dif The nitrite and nitrate standards specify that nitrite + nitrate should not exceed 11.

pdf

Copper, in μg/L D std 37 0 0 1 2.70 25.8 25.8 -- -- 25.8 25.8

dif 2.2 2.2 -- -- 2.2 2.2

pdf 0.08 0.08 -- -- 0.08 0.08

Lead, in μg/L D std 37 0 81.1 0 0.00 No exceptions to dissolved lead standard.

dif The dissolved lead standard is specified as a table-value standard calculated for 

individual samples.

pdf

Manganese, in μg/L D std 28 9 0 1 3.57 190 190 -- -- 190 190

dif 50.9 50.9 -- -- 50.93 50.93

pdf 0.26 0.26 -- -- 0.26 0.26

Zinc, in μg/L D std 37 0 16.2 0 0.00 No exceptions to dissolved zinc standard.

dif The dissolved zinc standard is specified as a table-value standard calculated for 

pdf individual samples.
Evaluation of Stormwater Quality 47

Table 9. Summary of composite and bacteriological sample results not meeting Colorado Department of Public Health and Environment 

numeric standards for all stations, South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 

6th Avenue at Aurora, Sand Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[Phase: W, determination made using whole water; T, total; D, dissolved. Typ indicates statistics for: std, numeric standard; dif, difference between compositestormwater results and numeric standard; pdf, dif divided by numeric standard. n, number of samples; M, number of missing values; Pctc, percentage of 

determinations with concentrations below reporting level; E, number of samples that did not meet numeric standard; Pcte, percentage of determinations with 

values greater than minimum reporting level that did not meet numeric standard; Stddev, standard deviation; Min, minimum, Max, maximum; col, colonies per 

100 milliliters; N, nitrogen; mg/L, milligrams per liter; μg/L, micrograms per liter; --, not applicable]

Property or 

constituent Phase Typ n M Pctc E Pcte Mean Median Stddev Skewness Min Max

South Platte River at Denver (0671400)

pH, in standard pH units W std 46 0 0 0 0.00 No exceptions to pH standard.

dif The pH standard specifies pH should be in the range of 6.5 to 9.0.

pdf

Escherichia coli, in col W std 5 0 0 5 100 126 -- -- -- -- --

dif 12,834 12,874 6,866 0.19 4,774 21,874

pdf 102 102 54 0.19 38 174

Fecal coliform, in col W std 5 0 0 5 100 200 -- -- -- -- --

dif 20,760 21,800 14,351 –0.117 4,700 34,800

pdf 103 109 72 –0.017 23.5 174

Nitrite + nitrate, as N, 

in mg/L

D std 35 11 0 0 0.00 No exceptions to nitrite and nitrate standards.

dif The nitrite and nitrate standards specify that nitrite + nitrate should not exceed 11.

pdf

Copper, in μg/L D std 35 11 0 0 0.00 No exceptions to dissolved copper standard.

dif The dissolved copper standard as 2.8 * table-value standard calculated for individual 

pdf samples.

Lead, in μg/L D std 45 1 26.7 0 0.00 No exceptions to dissolved lead standard.

dif The dissolved lead standard is specified as a table-value standard calculated for 

pdf individual samples.

Manganese, in μg/L D std 35 11 0 0 0.00 No exceptions to dissolved manganese standard.

dif The dissolved manganese standard is specified as a table-value standard calculated 

pdf for individual samples.

Zinc, in μg/L D std 35 11 0 0 0.00 No exceptions to dissolved zinc standard.

dif The dissolved zinc standard is specified as a table-value standard calculated for 

pdf individual samples.

Tollgate Creek above 6th Avenue at Aurora (39432910449011)

pH, in standard pH units W std 24 0 0 2 8.33 6.5 6.5 0.0 0.0 6.5 6.5

dif -- -- -- -- -- --

pdf -- -- -- -- -- --

Escherichia coli, in col W std 3 0 0 3 100 126 -- -- -- -- --

dif 25,540 34,874 -- -- 6,874 38,874

pdf 203 277 -- -- 55 277

Fecal coliform, in col W std 3 0 0 3 100 200 -- -- -- -- --

dif 31,800 34,800 -- -- 6,800 53,800

pdf 159 174 -- -- 104 269

Nitrite + nitrate, as N, 

in mg/L

D std 21 3 14.3 0 0.00 No exceptions to nitrite and nitrate standards.

dif The nitrite and nitrate standards specify that nitrite + nitrate should not exceed 11.

pdf

Copper, in μg/L D std 24 0 0 0 0.00 No exceptions to dissolved copper standard.

dif The dissolved copper standard is specified as 2.8 * table-value standard calculated 

pdf for individual samples.

Lead, in μg/L D std 24 0 70.8 0 0.00 No exceptions to dissolved lead standard.

dif The dissolved lead standard is specified as a table-value standard calculated for 

pdf individual samples.

Manganese, in μg/L D std 21 3 0 0 0.00 No exceptions to dissolved manganese standard.

dif The dissolved manganese standard is specified as a table-value standard calculated 

pdf for individual samples.

Zinc, in μg/L D std 24 0 8.33 No exceptions to dissolved zinc standard.

dif The dissolved zinc standard is specified as a table-value standard calculated for 

pdf individual samples.
48 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table 9. Summary of composite and bacteriological sample results not meeting Colorado Department of Public Health and Environment 

numeric standards for all stations, South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 

6th Avenue at Aurora, Sand Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[Phase: W, determination made using whole water; T, total; D, dissolved. Typ indicates statistics for: std, numeric standard; dif, difference between compositestormwater results and numeric standard; pdf, dif divided by numeric standard. n, number of samples; M, number of missing values; Pctc, percentage of 

determinations with concentrations below reporting level; E, number of samples that did not meet numeric standard; Pcte, percentage of determinations with 

values greater than minimum reporting level that did not meet numeric standard; Stddev, standard deviation; Min, minimum, Max, maximum; col, colonies per 

100 milliliters; N, nitrogen; mg/L, milligrams per liter; μg/L, micrograms per liter; --, not applicable]

Property or 

constituent Phase Typ n M Pctc E Pcte Mean Median Stddev Skewness Min Max

Sand Creek at mouth near Commerce City (394839104570300)

pH, in standard pH units W std 34 0 0 0 0.00 No exceptions to pH standard.

dif The pH standard specifies pH should be in the range of 6.5 to 9.0.

pdf

Escherichia coli, in col W std 4 0 0 4 100 126 -- -- -- -- --

dif 13,324 9,024 -- -- 374 38874

pdf 106 72 -- -- 2.97 277

Fecal coliform, in col W std 4 0 0 4 100 200 -- -- -- -- --

dif 13,300 8,950 -- -- 500 34,800

pdf 66.5 44.8 -- -- 2.6 174

Nitrite + nitrate, as N, 

in mg/L

D std 25 9 0 0 0.00 No exceptions to nitrite and nitrate standards.

dif The nitrite and nitrate standards specify that nitrite + nitrate should not exceed 11.

pdf

Copper, in μg/L D std 33 1 0 0 0.00 No exceptions to dissolved copper standard.

dif The dissolved copper standard is specified as a table-value standard calculated for 

pdf individual samples.

Lead, in μg/L D std 33 1 39.4 0 0.00 No exceptions to dissolved lead standard.

dif The dissolved lead standard is specified as a table-value standard calculated for 

pdf individual samples.

Manganese, in μg/L D std 25 9 0 0 0.00 No exceptions to dissolved manganese standard.

dif The dissolved manganese standard is specified as a table-value standard calculated 

pdf for individual samples.

Zinc, in μg/L D std 32 2 0 1 3.12 273 273 0.00 0.00 273 273

dif 26.8 26.8 0.00 0.00 26.8 26.8

pdf 0.09 0.09 0.00 0.00 0.09 0.09

South Platte River at Henderson (06720500)

pH, in standard pH units W std 35 0 0 0 0.00 No exceptions to pH standard.

dif The pH standard specifies pH should be in the range of 6.5 to 9.0.

pdf

Escherichia coli, in col W std 5 0 0 5 100 126 -- -- -- -- --

dif 3,174 6,826 5,206 –0.102 334 12,874

pdf 54.2 54.6 41.3 –0.102 2.65 102

Fecal coliform, in col W std 5 0 0 5 100 200 -- -- -- -- --

dif 24,642 10,800 26,886 0.520 110 53,800

pdf 123 54.0 134 0.520 0.55 269

Nitrite + nitrate, as N, 

in mg/L

D std 23 12 0 0 0.00 No exceptions to nitrite and nitrate standards.

dif The nitrite and nitrate standards specify that nitrite + nitrate should not exceed 11.

pdf

Copper, in μg/L D std 34 1 0 0 0.00 No exceptions to dissolved copper standard.

dif The dissolved copper standard is specified as 2.3 * table-value standard calculated 

pdf for individual samples.

Lead, in μg/L D std 34 1 29.4 0 0.00 No exceptions to dissolved lead standard.

dif The dissolved lead standard is specified as a table-value standard calculated for 

pdf individual samples.

Manganese, in μg/L D std 23 12 0 0 0.00 No exceptions to dissolved manganese standard.

dif The dissolved manganese standard is specified as a table-value standard calculated 

pdf for individual samples.

Zinc, in μg/L D std 34 1 8.82 0 0.00 No exceptions to dissolved zinc standard.

dif The dissolved zinc standard is specified as a table-value standard calculated for 

pdf individual samples.
Evaluation of Stormwater Quality 49

changes through time. The composite-sample data were 

found to have considerable variability through a given year 

(table A2), and this variability was interpreted as seasonal 

variation that cannot be readily explained by data collected as 

part of this study; the data were aggregated into annual means 

for further evaluation.

A visual inspection of the annual means, which are shown 

in figure 3 and listed in table A2, can be used to qualitatively 

identify trends for water-quality properties and constituents. In 

general, that is for all data pooled together (fig. 3A), hardness, 

ammonia plus organic nitrogen, total phosphorus, most dissolved metals (lead, manganese, and zinc), and all total metals 

(copper, lead, manganese, and zinc) all indicate annual means 

that decrease each year, or downward trends. A downward 

trend also is generally evident for most individual stations as 

well, although departure from downward trends does exist; 

for example, Tollgate, Sand Creek, and Henderson in particular show some departure for the total metals, indicating that 

conditions are not always the same at all stations. Some trends 

were indicated only at individual stations in the network rather 

than at all stations. Ammonia as nitrogen at Union, Denver, 

and Henderson, orthophosphate at Sand Creek, and nitrite plus 

nitrate at Denver and Henderson all indicate decreasing annual 

means, or downward trends. Only nitrite plus nitrate at Union 

and total copper and lead at Sand Creek showed consistently 

increasing annual means, or upward trends.

Tolerance Intervals

Tolerance intervals specifying lower and upper bounds 

that contain a specified portion of a given distribution, referred 

to as “coverage,” can be defined on the basis of samples from 

the distribution. Typically, tolerance intervals are reported 

for a specified coverage with an associated confidence. For 

example, a symmetrical, or two-sided, 99-percent coverage 

tolerance interval with 95-percent confidence is a 95-percent 

confident estimate of an interval that contains 99-percent, from 

the 0.5 percentile to the 99.5 percentile, of the entire population. Two-sided tolerance intervals for a specified percent 

coverage at 95-percent confidence were computed in this 

study for comparison to similar data, such as the tolerance 

intervals computed in period 1 (Bossong and others, 2005). 

For all cases, except those using nonparametric computations, 

the specified coverage was 99 percent.

A brief description of the methods used to compute 

tolerance intervals in this study is presented here. Computations for tolerance intervals were complicated by the presence 

of censored data, multiple censoring levels, and data that did 

not meet normality criteria. More detailed descriptions of the 

methods used in this study are in publications by Hahn and 

Meeker (1991), Gibbons (1994), and the U.S. Environmental 

Protection Agency (1989, 1992).

For trend-free data that have no censored values (values 

reported as less than the reporting level) and that are normally 

distributed, conventional parametric statistical methods can 

be used to compute a tolerance interval on the basis of the 

number of samples, mean, and standard deviation. Tolerance 

intervals were not calculated for water-quality properties and 

constituents that indicated trends as discussed in the “Annual 

Means” section of this report. In addition, some data from 

this study have censored values, and the percentage of values 

reported as below the laboratory reporting level (table 7) was 

used to determine tolerance-interval computation methods. If 

less than 40 percent of the data were censored, then maximum 

likelihood estimation (MLE) methods utilizing Cohen’s adjustment (Hahn and Meeker, 1991; Gibbons, 1994) were used to 

compute tolerance intervals. If 40 percent or more of the data 

were censored, then parametric methods were deemed as inappropriate and nonparametric methods were used to compute 

tolerance intervals. Nonparametric methods used in this study 

set the lower and upper tolerance-interval bounds to minima 

and maxima.

Data were evaluated for normality on the basis of skewness and the number of samples using methods described by 

Fisher and Potter (1989). Data that did not meet normality 

criteria were modified with a natural log transform and then 

compared to normality criteria again. Tolerance intervals 

for transformed data that did not meet normality criteria 

were calculated using nonparametric methods. The results 

of tolerance-interval computations are listed in table 10 and 

included in figure 3. The vast majority of the computations, 

84.9 percent, were made by using conventional methods with 

no adjustments; 13.3 percent of the computations were made 

using Cohen’s adjustment, and the remaining 1.8 percent were 

made using nonparametric methods.

Regressions

Regressions among water-quality properties and 

constituents were evaluated to identify network patterns in 

linear regression and linear regressions that may be useful in 

quantifying future intradistribution changes. Linear regressions (table 11) and Pearson correlation coefficients (table A3) 

were calculated for all possible pairs of water-quality properties and constituents. For regressions, each pair was evaluated 

using three different transform scenarios: (1) no transform, 

(2) a natural-log transform on one variable, and (3) a naturallog transform on both variables. Regressions were screened on 

the basis of 95-percent significance and the magnitude of the 

coefficient of determination, a statistic commonly referred to 

as “r squared (r2

).” In this report the term “strong” is generally 

used for all regressions that had an r2

 value equal to or greater 

than 0.65, and the term “very strong” is used to indicate 

regressions that had an r2

 value equal to or greater than 0.80. 

When a strong regression was identified for any station in the 
50 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table 10. Tolerance intervals computed for physical properties and constituents at 99-percent coverage with 95-percent confidence 

at South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, 

Sand Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[I, transform indicator: 1, natural log transform; 2, no transform. Type indicates amount of censored values and method used to calculate tolerance intervals: 1, no 

censored values and regular computation; 2, less than 40-percent censored values and computed using Cohen’s adjustment for censored values; 5, greater than 40-percent 

censored values or normal distribution assumptions not met or both, nonparametric computation. n, number of samples; ft3

/s, cubic feet per second; μS/cm, microsiemens 

per centimeter at 25 degrees Celsius; CaCO3, calcium carbonate; mg/L, milligrams per liter; C, Celsius; N, nitrogen; P, phosphorus; col, colonies per 100 milliliters; 

μg/L, micrograms per liter; --, not applicable, includes properties or constituents for which annual means indicated temporal patterns]

Property or constituent I Type n Maximum

Upper bound

tolerance

interval

Minimum

Lower bound

tolerance

 interval

Nonparametric

coverage

South Platte River below Union Avenue at Englewood (06710247)

Mean streamflow, in ft3

/s 1 1 37 686 2,004.02 37 13.34 --

Streamflow volume, in acre-feet 1 1 37 623 2,303.19 16 8.55 --

pH, in standard units 2 1 37 8.35 8.54 6.82 6.48 --

Specific conductance, in μS/cm 1 1 31 917 1,396.73 212 155.73 --

Hardness, as CaCO3

, in mg/L 1 1 37 365 -- 69.7 -- --

Calcium, dissolved, in mg/L 2 1 28 66.07 76.37 21.96 10.69 --

Magnesium, dissolved, in mg/L 1 1 28 19.55 30.19 3.61 2.5 --

Potassium, dissolved, in mg/L 1 1 15 5.46 9.13 2.67 1.51 --

Sodium, dissolved, in mg/L 1 1 15 64.61 150.13 13.91 6.95 --

Alkalinity, as CaCO3

, fixed endpoint, in mg/L 2 1 15 124.4 167.15 48.58 1.59 --

Chloride, dissolved, in mg/L 1 1 15 77.61 210.6 10.97 5.62 --

Fluoride, dissolved, in mg/L 2 1 15 1.08 1.78 0.29 0 --

Sulfate, dissolved, in mg/L 1 1 15 155.15 337.54 30.88 13.91 --

Residue at 105°C, in mg/L 1 2 37 1,532 47,011.56 13 0.42 --

Ammonia + organic N, in mg/L 1 1 37 7 -- 0.47 -- --

Ammonia, as N, in mg/L 1 2 28 0.34 -- 0.05 -- --

Nitrite + nitrate, as N, in mg/L 1 1 28 1.65 -- 0.4 -- --

Orthophosphate, as P, in mg/L 1 1 37 0.45 0.78 0.01 0.01 --

Phosphorus, as P, in mg/L 1 1 37 1.75 -- 0.07 -- --

Organic carbon, dissolved, in mg/L 1 1 25 16.19 24.77 3.55 1.9 --

Copper, dissolved, in μg/L 1 1 37 28 29.26 1.14 0.27 --

Copper, total, in μg/L 1 1 28 48.78 -- 2.82 -- --

Lead, dissolved, in μg/L 1 5 37 60 60 0.09 0.09 69

Lead, total, in μg/L 1 1 28 51.95 -- 0.63 -- --

Manganese, dissolved, in μg/L 1 1 28 240.93 866.51 1.07 0.22 --

Manganese, total, in μg/L 1 1 28 1,274.73 3,212.10 62.78 24.22 --

Zinc, dissolved, in μg/L 1 2 37 30 92.14 1.99 0.15 --

Zinc, total, in μg/L 1 1 28 230 -- 7 -- --

network, additional 95-percent significant regressions, using 

the transform with the highest r2 value, for all remaining stations are highlighted in table 11. The correlation coefficient, 

which may be used as a surrogate for r2

 (r2 is the square of the 

correlation coefficient) is shown for all possible pairs of waterquality properties and constituents in table A3.

The strong regressions (r2

 equal to or greater than 0.65) 

include about one-third of all possible pairs (133 out of 378) 

of water-quality properties and constituents. For convenience, 

the regressions are discussed in terms of two groups; the 

first group, referred to as “majors,” includes the major ions 

(calcium, magnesium, sodium, potassium, alkalinity, chloride, 

fluoride, and sulfate) as well as mean streamflow, specific 

conductance, and hardness. The second group, referred to as 

“nonmajors,” includes the total and dissolved metals (copper, 

lead, manganese, and zinc), nutrients (ammonia plus organic 

nitrogen, ammonia, nitrite plus nitrate, orthophosphate, and 

total phosphorus), and residue on evaporation at 105 degrees 

Celsius. The nonmajors include seven properties and constituents that have a particulate component, such as residue 

on evaporation at 105 degrees Celsius, organic nitrogen plus 

ammonia, total phosphorus, and the total metals.

About one-half of the strong regressions are for the 

majors, and many of these strong regressions are widespread, 

occurring at several stations rather than locally at just one 

or two stations. For example, regressions between calcium 

and magnesium are consistently strong at all stations. The 

widespread occurrence of many strong regressions involving 
Evaluation of Stormwater Quality 51

Table 10. Tolerance intervals computed for physical properties and constituents at 99-percent coverage with 95-percent confidence 

at South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, 

Sand Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[I, transform indicator: 1, natural log transform; 2, no transform. Type indicates amount of censored values and method used to calculate tolerance intervals: 1, no 

censored values and regular computation; 2, less than 40-percent censored values and computed using Cohen’s adjustment for censored values; 5, greater than 40-percent 

censored values or normal distribution assumptions not met or both, nonparametric computation. n, number of samples; ft3

/s, cubic feet per second; μS/cm, microsiemens 

per centimeter at 25 degrees Celsius; CaCO3, calcium carbonate; mg/L, milligrams per liter; C, Celsius; N, nitrogen; P, phosphorus; col, colonies per 100 milliliters; 

μg/L, micrograms per liter; --, not applicable, includes properties or constituents for which annual means indicated temporal patterns]

Property or constituent I Type n Maximum

Upper bound

tolerance

interval

Minimum

Lower bound

tolerance

 interval

Nonparametric

coverage

South Platte River at Denver (0671400)

Mean streamflow, in ft3

/s 1 1 46 4,446 7,675.74 166 52.26 --

Streamflow volume, in acre-feet 1 1 46 4,038 7,665.11 69 38.77 --

pH, in standard units 2 1 46 7.9 8.26 6.72 6.57 --

Specific conductance, in μS/cm 1 1 41 1,060 1,495.58 247 177.28 --

Hardness, as CaCO3

, in mg/L 2 1 45 255 -- 69.1 -- --

Calcium, dissolved, in mg/L 2 1 35 63.27 78.35 21.4 5.7 --

Magnesium, dissolved, in mg/L 2 1 35 16.54 18.63 3.81 0 --

Potassium, dissolved, in mg/L 1 1 15 7.03 12.45 3.23 1.64 --

Sodium, dissolved, in mg/L 2 1 15 84.84 113.98 18.2 0 --

Alkalinity, as CaCO3

, fixed endpoint, in mg/L 2 1 15 116.9 174.17 51.04 0.43 --

Chloride, dissolved, in mg/L 1 1 15 122.01 270.75 15.9 7.34 --

Fluoride, dissolved, in mg/L 2 1 15 0.83 1.33 0.25 0 --

Sulfate, dissolved, in mg/L 2 1 15 135.87 197.87 34.02 0 --

Residue at 105°C, in mg/L 1 1 45 1,240 3483.98 28 9.64 --

Ammonia + organic N, in mg/L 1 1 45 10.23 12.61 0.87 0.39 --

Ammonia, as N, in mg/L 1 2 35 1.8 -- 0.06 -- --

Nitrite + nitrate, as N, in mg/L 1 1 35 4.7 -- 0.7 -- --

Orthophosphate, as P, in mg/L 1 1 45 0.86 1.46 0.09 0.04 --

Phosphorus, as P, in mg/L 1 1 45 2.68 3.89 0.28 0.12 --

Organic carbon, dissolved, in mg/L 1 1 31 29.78 35.82 4.46 1.96 --

Copper, dissolved, in μg/L 1 1 45 6.16 8.8 1.44 0.94 --

Copper, total, in μg/L 1 1 35 74.55 -- 5.89 -- --

Lead, dissolved, in μg/L 1 2 45 0.52 13.96 0.08 0.01 --

Lead, total, in μg/L 1 1 35 66.04 -- 2.79 -- --

Manganese, dissolved, in μg/L 1 1 35 150.4 786.69 1.29 0.25 --

Manganese, total, in μg/L 1 1 35 998.56 -- 109.37 -- --

Zinc, dissolved, in μg/L 1 2 45 40 288.29 2.69 0.19 --

Zinc, total, in μg/L 1 1 35 348 -- 24 -- --

major ions indicates that the major ions are readily available 

within the network; the strong regressions between them are 

largely a result of equilibrium dynamics that describe reactions between, especially dissolved, laboratory constituents as 

a function of availability and prevailing physical conditions 

(Hem, 1985).

For regression pairs that involve the nonmajors, a little 

more than one-half of the strong regressions have r2 values 

greater than 0.8 and are considered very strong. In general, 

regressions are either strong or very strong for 12 of 21 possible combinations involving constituents that are known 

to have a particulate component and are widespread, because 

they were found at all or most stations. These widespread 

regressions include organic nitrogen plus ammonia with 

total phosphorus, total copper, and total zinc; total phosphorus 

with total copper, total lead, and total zinc; residue on evaporation at 105 degrees Celsius with total copper and total lead; 

and several additional regressions involving the metals (total 

copper with total lead, total manganese, and total zinc; and 

total lead with total zinc) are all strong or very strong for all 

stations. Local strong or very strong regressions that include 

three or four stations and are somewhat widespread include 

total manganese with total phosphorus, total lead, and total 

zinc at four of the five stations; residue on evaporation at 

105 degrees Celsius with total phosphorus, total manganese, 

and total zinc at three of the five stations; and total manganese 

with organic nitrogen plus ammonia and total phosphorus with 

total zinc at three of the five stations. The only remaining pair 
52 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table 10. Tolerance intervals computed for physical properties and constituents at 99-percent coverage with 95-percent confidence 

at South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, 

Sand Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[I, transform indicator: 1, natural log transform; 2, no transform. Type indicates amount of censored values and method used to calculate tolerance intervals: 1, no 

censored values and regular computation; 2, less than 40-percent censored values and computed using Cohen’s adjustment for censored values; 5, greater than 40-percent 

censored values or normal distribution assumptions not met or both, nonparametric computation. n, number of samples; ft3

/s, cubic feet per second; μS/cm, microsiemens 

per centimeter at 25 degrees Celsius; CaCO3, calcium carbonate; mg/L, milligrams per liter; C, Celsius; N, nitrogen; P, phosphorus; col, colonies per 100 milliliters; 

μg/L, micrograms per liter; --, not applicable, includes properties or constituents for which annual means indicated temporal patterns]

Property or constituent I Type n Maximum

Upper bound

tolerance

interval

Minimum

Lower bound

tolerance

 interval

Nonparametric

coverage

Tollgate Creek above 6th Avenue at Aurora (39432910449011)

Mean streamflow, in ft3

/s 1 1 20 405 17,159.72 1 0.06 --

Streamflow volume, in acre-feet 2 1 20 335 451.94 0 0 --

pH, in standard units 2 1 24 7.8 8.65 6.1 5.67 --

Specific conductance, in μS/cm 1 1 20 2,630 3956.99 350 150.02 --

Hardness, as CaCO3

, in mg/L 1 1 24 594 1066.74 107 52.75 --

Calcium, dissolved, in mg/L 1 1 21 169.05 319.95 35.6 15.7 --

Magnesium, dissolved, in mg/L 1 1 21 41.75 84.29 4.33 1.92 --

Potassium, dissolved, in mg/L 1 1 13 5.68 7.79 2.89 1.96 --

Sodium, dissolved, in mg/L 1 1 13 141.9 350.81 42.75 16.15 --

Alkalinity, as CaCO3

, fixed endpoint, in mg/L 1 1 13 118.3 235.8 51.81 25.56 --

Chloride, dissolved, in mg/L 1 1 13 111.72 272.99 29.9 12.07 --

Fluoride, dissolved, in mg/L 2 1 13 0.37 0.56 0.2 0.05 --

Sulfate, dissolved, in mg/L 1 1 13 386.14 1,368.08 116.04 28.53 --

Residue at 105°C, in mg/L 1 1 22 7,360 25,368.91 40 2.9 --

Ammonia + organic N, in mg/L 1 1 24 6.32 -- 0.59 -- --

Ammonia, as N, in mg/L 1 2 21 0.54 4.26 0.05 0.01 --

Nitrite + nitrate, as N, in mg/L 2 2 21 0.99 1.63 0.1 0 --

Orthophosphate, as P, in mg/L 2 2 23 0.11 0.18 0.01 0 --

Phosphorus, as P, in mg/L 1 2 24 2.44 9.99 0.18 0.04 --

Organic carbon, dissolved, in mg/L 1 1 21 18.39 38.73 5.89 2.39 --

Copper, dissolved, in μg/L 1 1 24 5 8.88 1.25 0.8 --

Copper, total, in μg/L 1 1 21 66.87 205.1 5.41 1.43 --

Lead, dissolved, in μg/L 1 5 24 0.18 0.18 0.09 0.09 79

Lead, total, in μg/L 1 1 21 53.23 296.83 1.8 0.33 --

Manganese, dissolved, in μg/L 1 1 21 1,569.81 22,613.45 2.11 0.13 --

Manganese, total, in μg/L 1 1 21 1,950.6 -- 89.52 -- --

Zinc, dissolved, in μg/L 1 2 24 50.61 202.3 2.69 0.21 --

Zinc, total, in μg/L 1 1 21 293 1,024.62 18 5.66 --

of constituents with a particulate component that have strong 

or very strong regressions, organic nitrogen plus ammonia and 

total lead, were from Union and Denver.

For the remainder of nonmajors, which involve very soluble compounds that have a very small or even no particulate 

component, strong and very strong regressions are not often 

widespread and occur mostly locally at individual stations. 

The regression between nitrite plus nitrate and orthophosphate 

is the only regression that is strong for the nonmajor soluble 

compounds at all stations. Locally strong or very strong 

regressions include hardness with nitrite plus nitrate and dissolved lead (at Denver and Henderson) and dissolved lead 

(at Union and Tollgate); dissolved manganese with hardness, 

ammonia, nitrite plus nitrate, orthophosphate, and dissolved 

lead (all at Henderson); and dissolved lead with ammonia (at 

Union) and nitrite plus nitrate (at Henderson).

An important characteristic of the reported regressions 

is that for regressions such as mean streamflow with specific 

conductance, which intuitively would be expected to have 

a very strong inverse (negative slope) regression due to the 

addition of large amounts of dilute (low specific conductance) 

precipitation, the Pearson correlation coefficient is not very 

strong (table A3). One possible explanation for this is that the 

regression of mean streamflow with specific conductance in a 

receiving stream such as the South Platte River is dependent 

on conditions in several contributing tributaries. Consequently, 

rather than a simple model in which an inverse relation 

between mean streamflow and specific conductance is based 

largely on a uniform source of relatively dilute precipitation, 

the model becomes more complex due to mixing of heterogeneous waters received from different tributaries with unique 

mean streamflow and specific conductances.
Evaluation of Stormwater Quality 53

Table 10. Tolerance intervals computed for physical properties and constituents at 99-percent coverage with 95-percent confidence 

at South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, 

Sand Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[I, transform indicator: 1, natural log transform; 2, no transform. Type indicates amount of censored values and method used to calculate tolerance intervals: 1, no 

censored values and regular computation; 2, less than 40-percent censored values and computed using Cohen’s adjustment for censored values; 5, greater than 40-percent 

censored values or normal distribution assumptions not met or both, nonparametric computation. n, number of samples; ft3

/s, cubic feet per second; μS/cm, microsiemens 

per centimeter at 25 degrees Celsius; CaCO3, calcium carbonate; mg/L, milligrams per liter; C, Celsius; N, nitrogen; P, phosphorus; col, colonies per 100 milliliters; 

μg/L, micrograms per liter; --, not applicable, includes properties or constituents for which annual means indicated temporal patterns]

Property or constituent I Type n Maximum

Upper bound

tolerance

interval

Minimum

Lower bound

tolerance

 interval

Nonparametric

coverage

Sand Creek at mouth near Commerce City (394839104570300)

Mean streamflow, in ft3

/s 1 1 34 1813 3,515.24 18 4.2 --

Streamflow volume, in acre-feet 1 1 34 2,545 3,970.87 17 3.07 --

pH, in standard units 2 1 34 7.94 8.31 6.88 6.55 --

Specific conductance, in μS/cm 1 1 30 1,600 2,779.84 342 234.59 --

Hardness, as CaCO3

, in mg/L 2 1 33 360 -- 87 -- --

Calcium, dissolved, in mg/L 2 1 25 95.79 139.25 27.7 0 --

Magnesium, dissolved, in mg/L 2 1 25 21.53 29.59 4.33 0 --

Potassium, dissolved, in mg/L 2 1 12 6.35 8.99 2.81 0 --

Sodium, dissolved, in mg/L 1 1 12 138.4 489.53 42.93 12.39 --

Alkalinity, as CaCO3

, fixed endpoint, in mg/L 2 1 12 139.1 215.17 53.49 0 --

Chloride, dissolved, in mg/L 2 1 12 110.34 187.21 33.66 0 --

Fluoride, dissolved, in mg/L 2 1 12 0.67 1.02 0.26 0 --

Sulfate, dissolved, in mg/L 1 1 12 346.52 1,358.18 78.88 17.25 --

Residue at 105°C, in mg/L 1 1 34 1925 10,153.77 13 7.36 --

Ammonia + organic N, in mg/L 1 1 33 8.61 18.6 0.88 0.42 --

Ammonia, as N, in mg/L 1 2 25 1.15 15.87 0.05 0.01 --

Nitrite + nitrate, as N, in mg/L 1 1 25 2.29 5.14 0.36 0.18 --

Orthophosphate, as P, in mg/L 1 1 33 0.44 -- 0.04 -- --

Phosphorus, as P, in mg/L 1 1 33 2.76 6.1 0.24 0.09 --

Organic carbon, dissolved, in mg/L 1 1 24 30.09 53.91 5.86 2.7 --

Copper, dissolved, in μg/L 1 1 33 25 20.37 1.25 0.46 --

Copper, total, in μg/L 1 1 25 87.27 -- 5.36 -- --

Lead, dissolved, in μg/L 1 2 33 0.48 -- 0.08 -- --

Lead, total, in μg/L 1 1 25 114.41 -- 1.45 -- --

Manganese, dissolved, in μg/L 1 1 25 549.6 6,856.14 2.69 0.14 --

Manganese, total, in μg/L 1 1 25 2,092.15 10,665.19 84.01 26.08 --

Zinc, dissolved, in μg/L 1 1 32 335.63 2360.7 3.01 0.36 --

Zinc, total, in μg/L 1 1 24 1152 -- 18 -- --

Comparison to Previous Results

As mentioned in the “Previous Investigations” section, 

the study described in this report has the same programmatic 

goals and used the same sample-collection protocols that were 

used in a similar study by Bossong and others (2005). This 

section presents a comparison of results from the two studies presented in terms of period 1, the 2005 study that covers 

water years 1998–2001, and period 2, this study that covers 

water years 2002–2005. The comparisons address streamflow 

conditions, univariate statistics, spatial patterns, trends, and 

regressions observed in the two periods.

There were fewer samples collected during period 2 (176) 

than during period 1 (255), due mostly to the relatively stormfree conditions during 2002, which was a very dry year. The 

mean streamflows associated with composite samples are the 

best indicator of hydrologic conditions for the sampled storms 

available from this study. The boxplot for mean streamflow 

in figure 3A shows that distribution of mean streamflow for 

samples collected in period 2 is very similar to the distribution for period 1. In addition, the general distribution of 

composite samples among the various hydrograph classifications (most samples were classified as events, followed by 

falling and then rising classifications) was also similar for 

both periods. Although there were fewer samples collected 

in period 2, the statistical distribution of mean streamflows 

and the distribution of samples among the various hydrograph 

classifications indicate similar conditions were sampled in 

both periods.

The distributions for composite sample results from 

periods 1 and 2 are shown in figure 3 and many details for 

period 2 results are listed in table 7. The boxplots in figure 3A

provide a comparison of the entire distribution for all waterquality properties and constituents from both periods and 
54 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table 10. Tolerance intervals computed for physical properties and constituents at 99-percent coverage with 95-percent confidence 

at South Platte River below Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, 

Sand Creek at mouth near Commerce City, and South Platte River at Henderson, water years 2002–2005.—Continued

[I, transform indicator: 1, natural log transform; 2, no transform. Type indicates amount of censored values and method used to calculate tolerance intervals: 1, no 

censored values and regular computation; 2, less than 40-percent censored values and computed using Cohen’s adjustment for censored values; 5, greater than 40-percent 

censored values or normal distribution assumptions not met or both, nonparametric computation. n, number of samples; ft3

/s, cubic feet per second; μS/cm, microsiemens 

per centimeter at 25 degrees Celsius; CaCO3, calcium carbonate; mg/L, milligrams per liter; C, Celsius; N, nitrogen; P, phosphorus; col, colonies per 100 milliliters; 

μg/L, micrograms per liter; --, not applicable, includes properties or constituents for which annual means indicated temporal patterns]

Property or constituent I Type n Maximum

Upper bound

tolerance

interval

Minimum

Lower bound

tolerance

 interval

Nonparametric

coverage

South Platte River at Henderson (06720500)

Mean streamflow, in ft3

/s 1 1 35 7,566 13,761.09 280 83.8 --

Streamflow volume, in acre-feet 1 1 35 6,879 12,499.09 208 74.63 --

pH, in standard units 2 1 35 8 8.24 6.72 6.52 --

Specific conductance, in μS/cm 1 1 30 1,090 1,888.15 316 219.79 --

Hardness, as CaCO3

, in mg/L 1 1 34 380 -- 84.5 -- --

Calcium, dissolved, in mg/L 2 1 23 62.7 76.43 26.22 12.24 --

Magnesium, dissolved, in mg/L 2 1 23 16.02 19.59 4.62 0.16 --

Potassium, dissolved, in mg/L 1 1 8 8.37 25.07 4.26 1.41 --

Sodium, dissolved, in mg/L 1 1 8 142.1 946.05 27.08 3.59 --

Alkalinity, as CaCO3, fixed endpoint, in mg/L 2 1 8 121.2 194.93 57.66 0 --

Chloride, dissolved, in mg/L 1 1 8 197.07 2,184.54 23.32 1.51 --

Fluoride, dissolved, in mg/L 1 1 8 0.84 2.87 0.35 0.1 --

Sulfate, dissolved, in mg/L 2 1 8 116.9 210.07 47.42 0 --

Residue at 105°C, in mg/L 1 1 34 6,040 9,072.56 76 10.08 --

Ammonia + organic N, in mg/L 1 1 34 12.15 19.88 1.98 1.27 --

Ammonia, as N, in mg/L 1 1 23 3.55 -- 0.32 -- --

Nitrite + nitrate, as N, in mg/L 2 1 23 4.1 -- 1.14 -- --

Orthophosphate, as P, in mg/L 1 1 34 1.4 2.69 0.2 0.12 --

Phosphorus, as P, in mg/L 1 1 34 8.3 7.84 0.73 0.33 --

Organic carbon, dissolved, in mg/L 1 1 19 16.56 32.74 5.39 2.68 --

Copper, dissolved, in μg/L 1 1 34 9 12.42 1.56 0.76 --

Copper, total, in μg/L 1 1 23 71.86 176.78 11.61 5.67 --

Lead, dissolved, in μg/L 1 2 34 10 -- 0.13 -- --

Lead, total, in μg/L 2 1 23 68.23 95.87 6.92 0 --

Manganese, dissolved, in μg/L 2 1 23 241.81 -- 7.21 -- --

Manganese, total, in μg/L 2 1 23 1,011.8 1398.54 235.74 0 --

Zinc, dissolved, in μg/L 1 2 34 50 -- 7.86 -- --

Zinc, total, in μg/L 1 1 23 299 862.43 45 21.63 --

indicate that concentrations for many are shifted to lower levels in period 2. A more formal characterization of these shifts 

can be made by comparing 95-percent confidence intervals 

on the mean concentrations from each period (table 12). The 

95-percent confidence intervals on the mean concentrations 

from periods 1 and 2 are independent (have no overlap) for 

four constituents (dissolved copper, manganese, and zinc, and 

total zinc) indicating a significant difference in these mean 

concentrations at the 95-percent confidence level (lower in 

period 2). There were also significant differences in mean 

concentrations for dissolved lead and ammonia; however, 

because the values reported in period 1 commonly (about 80- 

and 60-percent, respectively) were censored at much higher 

levels than in period 2; the decreases in mean concentrations 

are an artifact of changes in censoring levels. The spatial 

patterns noted in period 1, in which mean concentrations for 

many constituents increased in the downstream direction in 

the South Platte River, were observed again in period 2. There 

also are increases in mean concentration in the downstream 

direction, from Tollgate to Sand Creek, in the tributary streams 

during period 2. Although downstream increases in mean concentrations for the tributaries were not reported for period 1, 

they were present, and spatial patterns for the two periods 

are similar.

Exceptions to CDPHE numeric standards for bacteriological indicators were observed consistently at all stations in 

periods 1 and 2. In period 1, additional exceptions to numeric 

standards were noted for metals, and the percentage of 

samples that had exceptions was 20 or more for some metals 

(dissolved manganese and dissolved zinc) at some stations. 

In period 2, exceptions to numeric standards also were noted; 

however, there were only three instances of exceptions to 

metal numeric standards, and the percentage of exceptions 

was markedly lower in period 2.
Evaluation of Stormwater Quality 55

Table 11. Results of linear regression analyses, water years 2002–2005.—Continued

[Group indicates that data represent results from all stations (ALL), South Platte River below Union Avenue at Englewood (Union), South Platte River at Denver 

(Denver), Tollgate Creek above 6th Avenue at Aurora (Tollgate), Sand Creek at mouth near Commerce City (Sand Creek), or South Platte River at Henderson 

(Henderson); T indicates transform: 1, no transform; 2 natural log transform for dependent variable; 3, natural log transform for both variables; Dependent and 

Independent describe regression variables. n, number of values used in regression; M, number of missing values; r2, coefficient of determination (commonly 

referred to as r-squared). Intercept, y-axis intercept of the linear regression line; Slope, slope of the linear regression line. Regressions with r2 values greater than 

0.65 are shown in bold print]

Station T Water-quality properties or constituents n M r

2 Intercept Slope Dependent Independent

ALL 2 Alkalinity Dissolved chloride 62 113 0.292 3.325 0.282

Union 3 Alkalinity Dissolved chloride 14 22 0.407 3.132 0.359

Denver 3 Alkalinity Dissolved chloride 14 31 0.275 3.247 0.313

Sand Creek 1 Alkalinity Dissolved chloride 11 22 0.729 28.220 0.905

Henderson 3 Alkalinity Dissolved chloride 7 27 0.444 3.465 0.237

ALL 3 Alkalinity Dissolved fluoride 62 113 0.502 4.758 0.443

Union 3 Alkalinity Dissolved fluoride 14 22 0.669 4.629 0.445

Denver 3 Alkalinity Dissolved fluoride 14 31 0.865 4.856 0.701

Tollgate 3 Alkalinity Dissolved fluoride 12 11 0.627 5.537 0.972

Sand Creek 3 Alkalinity Dissolved fluoride 11 22 0.894 5.282 0.924

Henderson 2 Alkalinity Dissolved fluoride 7 27 0.869 124.110 59.996

ALL 3 Alkalinity Dissolved manganese 62 113 0.281 4.120 0.101

Union 3 Alkalinity Dissolved manganese 14 22 0.365 4.103 0.125

Denver 2 Alkalinity Dissolved manganese 14 31 0.579 54.917 13.206

Sand Creek 3 Alkalinity Dissolved manganese 11 22 0.410 4.089 0.128

Henderson 1 Alkalinity Dissolved manganese 7 27 0.968 57.878 0.450

ALL 3 Alkalinity Ammonia 56 119 0.101 4.558 0.101

Sand Creek 3 Alkalinity Ammonia 11 22 0.403 4.977 0.503

Henderson 3 Alkalinity Ammonia 7 27 0.822 4.428 0.311

ALL 3 Alkalinity Nitrite + nitrate 62 113 0.309 4.417 0.236

Union 1 Alkalinity Nitrite + nitrate 14 22 0.619 47.935 40.849

Denver 2 Alkalinity Nitrite + nitrate 14 31 0.762 71.823 30.879

Tollgate 3 Alkalinity Nitrite + nitrate 12 11 0.331 4.601 0.454

Sand Creek 3 Alkalinity Nitrite + nitrate 11 22 0.477 4.610 0.735

Henderson 3 Alkalinity Nitrite + nitrate 7 27 0.850 4.046 0.491

ALL 1 Alkalinity Orthophosphate 62 113 0.069 81.041 31.841

Denver 2 Alkalinity Orthophosphate 14 31 0.577 129.340 26.649

Henderson 2 Alkalinity Orthophosphate 7 27 0.864 117.493 34.228

ALL 2 Alkalinity 62 113 0.375 3.151 0.275

Union 2 Alkalinity Dissolved sulfate 14 22 0.854 –118.399 47.973

Denver 3 Alkalinity Dissolved sulfate 14 31 0.950 1.606 0.658

Tollgate 3 Alkalinity Dissolved sulfate 12 11 0.861 1.533 0.533

Sand Creek 3 Alkalinity Dissolved sulfate 11 22 0.746 1.881 0.522

Henderson 3 Alkalinity Dissolved sulfate 7 27 0.918 1.114 0.760

ALL 2 Alkalinity Dissolved zinc 61 114 0.305 48.383 18.776

Union 3 Alkalinity Dissolved zinc 14 22 0.388 3.824 0.392

Denver 2 Alkalinity Dissolved zinc 14 31 0.381 3.783 0.285

Tollgate 2 Alkalinity Dissolved zinc 12 11 0.491 42.727 18.338

Sand Creek 2 Alkalinity Dissolved zinc 10 23 0.317 74.651 2.285

Henderson 3 Alkalinity Dissolved zinc 7 27 0.764 2.880 0.608

ALL 3 Dissolved calcium Alkalinity 62 113 0.467 –187.640 54.084

Union 1 Dissolved calcium Alkalinity 14 22 0.924 –0.880 1.044

Denver 3 Dissolved calcium Alkalinity 14 31 0.959 –1.106 1.087

Tollgate 3 Dissolved calcium Alkalinity 12 11 0.888 –1.731 1.359

Sand Creek 3 Dissolved calcium Alkalinity 11 22 0.749 –221.940 62.551

Henderson 3 Dissolved calcium Alkalinity 7 27 0.894 –123.319 37.138
56 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table 11. Results of linear regression analyses, water years 2002–2005.—Continued

[Group indicates that data represent results from all stations (ALL), South Platte River below Union Avenue at Englewood (Union), South Platte River at Denver 

(Denver), Tollgate Creek above 6th Avenue at Aurora (Tollgate), Sand Creek at mouth near Commerce City (Sand Creek), or South Platte River at Henderson 

(Henderson); T indicates transform: 1, no transform; 2 natural log transform for dependent variable; 3, natural log transform for both variables; Dependent and 

Independent describe regression variables. n, number of values used in regression; M, number of missing values; r2, coefficient of determination (commonly 

referred to as r-squared). Intercept, y-axis intercept of the linear regression line; Slope, slope of the linear regression line. Regressions with r2 values greater than 

0.65 are shown in bold print]

Station T Water-quality properties or constituents n M r

2 Intercept Slope Dependent Independent

ALL 3 Dissolved calcium Dissolved chloride 62 113 0.415 2.048 0.466

Union 3 Dissolved calcium Dissolved chloride 14 22 0.481 2.215 0.424

Denver 3 Dissolved calcium Dissolved chloride 14 31 0.368 2.188 0.402

Sand Creek 1 Dissolved calcium Dissolved chloride 11 22 0.727 –148.408 49.264

Henderson 3 Dissolved calcium Dissolved chloride 7 27 0.412 2.745 0.232

Union 3 Dissolved calcium Dissolved fluoride 14 22 0.412 3.909 0.379

Denver 1 Dissolved calcium Dissolved fluoride 14 31 0.762 4.151 0.730

Tollgate 3 Dissolved calcium Dissolved fluoride 12 11 0.441 5.619 1.176

Sand Creek 3 Dissolved calcium Dissolved fluoride 11 22 0.672 4.850 0.983

Henderson 2 Dissolved calcium Dissolved fluoride 7 27 0.914 59.298 28.847

ALL 3 Dissolved calcium Dissolved potassium 62 113 0.151 3.078 0.541

Union 1 Dissolved calcium Dissolved potassium 14 22 0.430 2.656 0.809

Denver 2 Dissolved calcium Dissolved potassium 14 31 0.724 2.202 1.002

Sand Creek 3 Dissolved calcium Dissolved potassium 11 22 0.785 2.007 1.376

Henderson 2 Dissolved calcium Dissolved potassium 7 27 0.945 –20.412 34.485

ALL 3 Dissolved calcium Dissolved magnesium 131 44 0.894 2.023 0.820

Union 2 Dissolved calcium Dissolved magnesium 27 9 0.847 –8.931 24.268

Denver 3 Dissolved calcium Dissolved magnesium 34 11 0.927 2.152 0.737

Tollgate 3 Dissolved calcium Dissolved magnesium 20 3 0.972 2.260 0.787

Sand Creek 3 Dissolved calcium Dissolved magnesium 24 9 0.961 2.102 0.819

Henderson 3 Dissolved calcium Dissolved magnesium 22 12 0.952 2.233 0.684

ALL 3 Dissolved calcium Dissolved manganese 131 44 0.311 3.429 0.142

Union 3 Dissolved calcium Dissolved manganese 27 9 0.299 3.474 0.105

Denver 3 Dissolved calcium Dissolved manganese 34 11 0.356 3.337 0.138

Sand Creek 2 Dissolved calcium Dissolved manganese 24 9 0.441 34.754 9.031

Henderson 3 Dissolved calcium Dissolved manganese 22 12 0.712 3.027 0.181

ALL 3 Dissolved calcium Dissolved sodium 62 113 0.682 1.557 0.583

Union 3 Dissolved calcium Dissolved sodium 14 22 0.681 1.645 0.596

Denver 3 Dissolved calcium Dissolved sodium 14 31 0.618 1.432 0.604

Tollgate 1 Dissolved calcium Dissolved sodium 12 11 0.897 –240.357 71.999

Sand Creek 1 Dissolved calcium Dissolved sodium 11 22 0.969 7.133 0.622

Henderson 3 Dissolved calcium Dissolved sodium 7 27 0.562 2.246 0.354

Tollgate 3 Dissolved calcium Ammonia 18 5 0.228 4.829 0.336

Sand Creek 1 Dissolved calcium Ammonia 21 12 0.257 49.705 32.929

Henderson 3 Dissolved calcium Ammonia 22 12 0.751 3.695 0.275

Union 1 Dissolved calcium Nitrite + nitrate 27 9 0.305 31.010 14.586

Denver 3 Dissolved calcium Nitrite + nitrate 34 11 0.668 3.445 0.426

Tollgate 3 Dissolved calcium Nitrite + nitrate 17 6 0.228 4.510 0.388

Sand Creek 3 Dissolved calcium Nitrite + nitrate 24 9 0.404 4.138 0.483

Henderson 3 Dissolved calcium Nitrite + nitrate 22 12 0.778 3.292 0.511

ALL 2 Dissolved calcium Orthophosphate 126 49 0.06 41.162 –5.330

Denver 2 Dissolved calcium Orthophosphate 34 11 0.456 64.931 14.698

Tollgate 3 Dissolved calcium Orthophosphate 15 8 0.238 3.361 –0.274

Henderson 3 Dissolved calcium Orthophosphate 22 12 0.661 4.044 0.382

Tollgate 1 Dissolved calcium Dissolved lead 6 17 0.680 415.356 152.395

Henderson 2 Dissolved calcium Dissolved lead 22 12 0.334 62.727 13.831
Evaluation of Stormwater Quality 57

Table 11. Results of linear regression analyses, water years 2002–2005.—Continued

[Group indicates that data represent results from all stations (ALL), South Platte River below Union Avenue at Englewood (Union), South Platte River at Denver 

(Denver), Tollgate Creek above 6th Avenue at Aurora (Tollgate), Sand Creek at mouth near Commerce City (Sand Creek), or South Platte River at Henderson 

(Henderson); T indicates transform: 1, no transform; 2 natural log transform for dependent variable; 3, natural log transform for both variables; Dependent and 

Independent describe regression variables. n, number of values used in regression; M, number of missing values; r2, coefficient of determination (commonly 

referred to as r-squared). Intercept, y-axis intercept of the linear regression line; Slope, slope of the linear regression line. Regressions with r2 values greater than 

0.65 are shown in bold print]

Station T Water-quality properties or constituents n M r

2 Intercept Slope Dependent Independent

ALL 1 Dissolved calcium Dissolved sulfate 62 113 0.934 21.829 0.237

Union 2 Dissolved calcium Dissolved sulfate 14 22 0.933 –73.199 27.415

Denver 3 Dissolved calcium Dissolved sulfate 14 31 0.985 0.519 0.743

Tollgate 3 Dissolved calcium Dissolved sulfate 12 11 0.984 11.977 0.267

Sand Creek 3 Dissolved calcium Dissolved sulfate 11 22 0.970 –156.519 43.033

Henderson 2 Dissolved calcium Dissolved sulfate 7 27 0.974 –92.987 30.749

Sand Creek 1 Dissolved chloride Dissolved copper 11 22 0.674 25.667 55.067

ALL 3 Dissolved chloride Dissolved sulfate 62 113 0.390 1.413 0.537

Tollgate 1 Dissolved chloride Dissolved sulfate 12 11 0.364 32.625 0.131

Sand Creek 2 Dissolved chloride Dissolved sulfate 11 22 0.724 –149.137 44.279

Tollgate 3 Dissolved chloride Total phosphorus 12 11 0.652 3.759 –0.390

Sand Creek 2 Dissolved chloride Total phosphorus 11 22 0.452 65.867 –29.984

ALL 2 Dissolved copper Dissolved lead 90 85 0.366 5.413 1.435

Denver 2 Dissolved copper Dissolved lead 32 13 0.280 5.095 1.181

Henderson 1 Dissolved copper Dissolved lead 23 11 0.829 2.563 0.650

ALL 3 Dissolved copper Dissolved zinc 154 21 0.340 0.378 0.256

Union 1 Dissolved copper Dissolved zinc 30 6 0.839 0.869 0.245

Denver 1 Dissolved copper Dissolved zinc 38 7 0.643 1.670 0.104

Tollgate 3 Dissolved copper Dissolved zinc 21 2 0.265 0.477 0.222

Henderson 1 Dissolved copper Dissolved zinc 30 4 0.572 –0.880 0.689

ALL 3 Total copper Total manganese 131 44 0.666 –1.819 0.790

Union 1 Total copper Total manganese 27 9 0.835 –3.071 0.975

Denver 1 Total copper Total manganese 34 11 0.816 –2.436 0.942

Tollgate 1 Total copper Total manganese 20 3 0.455 –57.318 12.410

Sand Creek 3 Total copper Total manganese 24 9 0.819 –1.717 0.755

Henderson 3 Total copper Total manganese 22 12 0.855 –2.757 0.995

ALL 3 Total copper Total lead 131 44 0.956 1.135 0.683

Union 1 Total copper Total lead 27 9 0.979 3.811 0.934

Denver 3 Total copper Total lead 34 11 0.945 0.982 0.717

Tollgate 1 Total copper Total lead 20 3 0.985 4.773 1.138

Sand Creek 1 Total copper Total lead 24 9 0.980 6.868 0.719

Henderson 3 Total copper Total lead 22 12 0.884 0.980 0.742

ALL 3 Total copper Total zinc 130 45 0.556 –34.746 13.206

Union 3 Total copper Total zinc 27 9 0.965 –0.652 0.850

Denver 1 Total copper Total zinc 34 11 0.980 1.737 0.209

Tollgate 1 Total copper Total zinc 20 3 0.679 –53.591 17.311

Henderson 3 Total copper Total zinc 22 12 0.942 –1.000 0.906

ALL 1 Dissolved organic C Dissolved lead 77 98 0.204 6.787 20.563

Union 3 Dissolved organic C Dissolved lead 3 33 0.831 –22.499 –15.041

Denver 1 Dissolved organic C Dissolved lead 28 17 0.538 2.808 37.262

Tollgate 2 Dissolved organic C Dissolved lead 6 17 0.729 50.234 17.470

Sand Creek 1 Dissolved organic C Dissolved lead 18 15 0.424 6.960 37.261

Henderson 3 Dissolved organic C Dissolved lead 18 16 0.446 2.974 0.558

ALL 3 Dissolved fluoride Dissolved manganese 62 113 0.066 –0.991 0.078

Union 2 Dissolved fluoride Dissolved manganese 14 22 0.452 0.300 0.152

Denver 2 Dissolved fluoride Dissolved manganese 14 31 0.458 0.336 0.101

Sand Creek 2 Dissolved fluoride Dissolved manganese 11 22 0.490 0.256 0.060

Henderson 1 Dissolved fluoride Dissolved manganese 7 27 0.845 0.329 0.004
58 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table 11. Results of linear regression analyses, water years 2002–2005.—Continued

[Group indicates that data represent results from all stations (ALL), South Platte River below Union Avenue at Englewood (Union), South Platte River at Denver 

(Denver), Tollgate Creek above 6th Avenue at Aurora (Tollgate), Sand Creek at mouth near Commerce City (Sand Creek), or South Platte River at Henderson 

(Henderson); T indicates transform: 1, no transform; 2 natural log transform for dependent variable; 3, natural log transform for both variables; Dependent and 

Independent describe regression variables. n, number of values used in regression; M, number of missing values; r2, coefficient of determination (commonly 

referred to as r-squared). Intercept, y-axis intercept of the linear regression line; Slope, slope of the linear regression line. Regressions with r2 values greater than 

0.65 are shown in bold print]

Station T Water-quality properties or constituents n M r

2 Intercept Slope Dependent Independent

ALL 3 Dissolved fluoride Nitrite + nitrate 62 113 0.474 –0.768 0.468

Union 3 Dissolved fluoride Nitrite + nitrate 14 22 0.511 –0.347 0.754

Denver 2 Dissolved fluoride Nitrite + nitrate 14 31 0.824 0.444 0.275

Tollgate 2 Dissolved fluoride Nitrite + nitrate 12 11 0.597 0.378 0.139

Sand Creek 3 Dissolved fluoride Nitrite + nitrate 11 22 0.391 –0.744 0.681

Henderson 1 Dissolved fluoride Nitrite + nitrate 7 27 0.995 0.159 0.166

ALL 1 Dissolved fluoride Orthophosphate 62 113 0.119 0.447 0.411

Union 2 Dissolved fluoride Orthophosphate 14 22 0.247 0.925 –3.600

Denver 2 Dissolved fluoride Orthophosphate 14 31 0.654 0.965 0.243

Tollgate 1 Dissolved fluoride Orthophosphate 12 11 0.333 0.361 –1.152

Sand Creek 3 Dissolved fluoride Orthophosphate 11 22 0.378 –1.666 –0.376

Henderson 2 Dissolved fluoride Orthophosphate 7 27 0.949 0.847 0.313

ALL 1 Dissolved fluoride Dissolved lead 38 137 0.232 0.324 0.973

Union 1 Dissolved fluoride Dissolved lead 2 34 0.957 0.902 –3.648

Henderson 1 Dissolved fluoride Dissolved lead 7 27 0.717 1.367 0.545

Union 3 Dissolved fluoride Dissolved sulfate 14 22 0.358 –3.490 0.706

Denver 2 Dissolved fluoride Dissolved sulfate 14 31 0.803 –1.214 0.418

Tollgate 2 Dissolved fluoride Dissolved sulfate 12 11 0.458 –2.893 0.317

Sand Creek 3 Dissolved fluoride Dissolved sulfate 11 22 0.598 –3.247 0.479

Henderson 1 Dissolved fluoride Dissolved sulfate 7 27 0.919 –4.948 0.990

Union 2 Dissolved fluoride Dissolved zinc 14 22 0.302 –1.448 0.636

Denver 2 Dissolved fluoride Dissolved zinc 14 31 0.290 0.424 0.014

Henderson 3 Dissolved fluoride Dissolved zinc 7 27 0.927 –2.850 0.872

ALL 3 Hardness Alkalinity 62 113 0.508 –658.557 187.397

Union 3 Hardness Alkalinity 14 22 0.939 –28.933 2.038

Denver 3 Hardness Alkalinity 14 31 0.922 –510.569 147.172

Tollgate 3 Hardness Alkalinity 12 11 0.872 –91.699 4.004

Sand Creek 3 Hardness Alkalinity 11 22 0.760 –744.175 208.504

Henderson 3 Hardness Alkalinity 7 27 0.907 –469.397 137.428

ALL 1 Hardness Dissolved calcium 131 44 0.991 1.115 1.022

Union 3 Hardness Dissolved calcium 27 9 0.979 0.770 1.117

Denver 3 Hardness Dissolved calcium 34 11 0.992 0.960 1.066

Tollgate 3 Hardness Dissolved calcium 20 3 0.998 0.951 1.053

Sand Creek 3 Hardness Dissolved calcium 24 9 0.997 1.018 1.042

Henderson 3 Hardness Dissolved calcium 22 12 0.994 0.838 1.102

ALL 3 Hardness Dissolved chloride 62 113 0.439 3.146 0.490

Union 3 Hardness Dissolved chloride 14 22 0.494 3.228 0.477

Denver 3 Hardness Dissolved chloride 14 31 0.404 3.247 0.438

Tollgate 1 Hardness Dissolved chloride 12 11 0.402 2.626 0.675

Sand Creek 1 Hardness Dissolved chloride 11 22 0.732 –496.344 163.571

Henderson 3 Hardness Dissolved chloride 7 27 0.476 3.781 0.276

Union 3 Hardness Dissolved fluoride 14 22 0.472 5.145 0.450

Denver 1 Hardness Dissolved fluoride 14 31 0.753 5.365 0.757

Tollgate 3 Hardness Dissolved fluoride 12 11 0.439 6.843 1.216

Sand Creek 3 Hardness Dissolved fluoride 11 22 0.689 6.059 1.018

Henderson 2 Hardness Dissolved fluoride 7 27 0.884 204.777 104.222
Evaluation of Stormwater Quality 59

Table 11. Results of linear regression analyses, water years 2002–2005.—Continued

[Group indicates that data represent results from all stations (ALL), South Platte River below Union Avenue at Englewood (Union), South Platte River at Denver 

(Denver), Tollgate Creek above 6th Avenue at Aurora (Tollgate), Sand Creek at mouth near Commerce City (Sand Creek), or South Platte River at Henderson 

(Henderson); T indicates transform: 1, no transform; 2 natural log transform for dependent variable; 3, natural log transform for both variables; Dependent and 

Independent describe regression variables. n, number of values used in regression; M, number of missing values; r2, coefficient of determination (commonly 

referred to as r-squared). Intercept, y-axis intercept of the linear regression line; Slope, slope of the linear regression line. Regressions with r2 values greater than 

0.65 are shown in bold print]

Station T Water-quality properties or constituents n M r

2 Intercept Slope Dependent Independent

ALL 3 Hardness Dissolved potassium 62 113 0.174 4.192 0.595

Union 1 Hardness Dissolved potassium 14 22 0.462 3.697 0.930

Denver 2 Hardness Dissolved potassium 14 31 0.702 3.360 1.028

Sand Creek 3 Hardness Dissolved potassium 11 22 0.794 3.127 1.416

Henderson 2 Hardness Dissolved potassium 7 27 0.915 –83.264 124.622

ALL 3 Hardness Dissolved magnesium 131 44 0.944 3.121 0.865

Union 3 Hardness Dissolved magnesium 27 9 0.934 3.454 0.695

Denver 3 Hardness Dissolved magnesium 34 11 0.967 3.212 0.806

Tollgate 3 Hardness Dissolved magnesium 20 3 0.984 3.314 0.835

Sand Creek 3 Hardness Dissolved magnesium 24 9 0.980 3.183 0.863

Henderson 3 Hardness Dissolved magnesium 22 12 0.979 3.271 0.766

ALL 3 Hardness Dissolved manganese 131 44 0.331 4.603 0.151

Union 3 Hardness Dissolved manganese 27 9 0.294 4.651 0.117

Denver 3 Hardness Dissolved manganese 34 11 0.385 4.500 0.153

Sand Creek 2 Hardness Dissolved manganese 24 9 0.477 107.346 31.998

Henderson 3 Hardness Dissolved manganese 22 12 0.724 4.166 0.201

ALL 3 Hardness Dissolved sodium 62 113 0.693 2.677 0.601

Union 3 Hardness Dissolved sodium 14 22 0.717 2.557 0.679

Denver 3 Hardness Dissolved sodium 14 31 0.654 2.465 0.648

Tollgate 1 Hardness Dissolved sodium 12 11 0.914 0.894 1.034

Sand Creek 1 Hardness Dissolved sodium 11 22 0.972 20.353 2.061

Henderson 3 Hardness Dissolved sodium 7 27 0.625 3.221 0.412

Tollgate 3 Hardness Ammonia 18 5 0.220 6.023 0.345

Sand Creek 1 Hardness Ammonia 21 12 0.292 159.552 120.555

Henderson 3 Hardness Ammonia 22 12 0.779 4.909 0.309

Union 1 Hardness Nitrite + nitrate 27 9 0.293 99.146 55.713

Denver 3 Hardness Nitrite + nitrate 34 11 0.654 4.634 0.452

Tollgate 3 Hardness Nitrite + nitrate 17 6 0.236 5.708 0.419

Sand Creek 3 Hardness Nitrite + nitrate 24 9 0.403 5.329 0.503

Henderson 3 Hardness Nitrite + nitrate 22 12 0.756 4.472 0.557

ALL 3 Hardness Dissolved lead 90 85 0.093 5.286 0.119

Union 2 Hardness Dissolved lead 6 30 0.818 197.363 30.795

Tollgate 1 Hardness Dissolved lead 6 17 0.704 1,484.309 553.945

Henderson 2 Hardness Dissolved lead 23 11 0.407 188.638 28.737

ALL 1 Hardness Dissolved sulfate 62 113 0.914 72.513 0.780

Union 3 Hardness Dissolved sulfate 14 22 0.950 1.737 0.752

Denver 3 Hardness Dissolved sulfate 14 31 0.981 1.587 0.773

Tollgate 3 Hardness Dissolved sulfate 12 11 0.990 0.845 0.854

Sand Creek 3 Hardness Dissolved sulfate 11 22 0.979 1.426 0.751

Henderson 2 Hardness Dissolved sulfate 7 27 0.965 –351.315 112.446

ALL 3 Dissolved potassium Alkalinity 62 113 0.419 –1.396 0.645

Union 1 Dissolved potassium Alkalinity 14 22 0.490 –6.998 2.454

Denver 3 Dissolved potassium Alkalinity 14 31 0.723 –2.044 0.801

Sand Creek 3 Dissolved potassium Alkalinity 11 22 0.939 –1.987 0.766

Henderson 3 Dissolved potassium Alkalinity 7 27 0.831 –2.684 1.009
60 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table 11. Results of linear regression analyses, water years 2002–2005.—Continued

[Group indicates that data represent results from all stations (ALL), South Platte River below Union Avenue at Englewood (Union), South Platte River at Denver 

(Denver), Tollgate Creek above 6th Avenue at Aurora (Tollgate), Sand Creek at mouth near Commerce City (Sand Creek), or South Platte River at Henderson 

(Henderson); T indicates transform: 1, no transform; 2 natural log transform for dependent variable; 3, natural log transform for both variables; Dependent and 

Independent describe regression variables. n, number of values used in regression; M, number of missing values; r2, coefficient of determination (commonly 

referred to as r-squared). Intercept, y-axis intercept of the linear regression line; Slope, slope of the linear regression line. Regressions with r2 values greater than 

0.65 are shown in bold print]

Station T Water-quality properties or constituents n M r

2 Intercept Slope Dependent Independent

ALL 3 Dissolved potassium Dissolved chloride 62 113 0.134 0.717 0.190

Sand Creek 1 Dissolved potassium Dissolved chloride 11 22 0.685 2.030 0.033

ALL 3 Dissolved potassium Dissolved copper 62 113 0.263 1.104 0.397

Union 1 Dissolved potassium Dissolved copper 14 22 0.669 0.699 0.841

Denver 1 Dissolved potassium Dissolved copper 14 31 0.372 2.733 0.611

Sand Creek 1 Dissolved potassium Dissolved copper 11 22 0.580 2.413 0.794

ALL 3 Dissolved potassium Dissolved fluoride 62 113 0.315 1.722 0.350

Union 3 Dissolved potassium Dissolved fluoride 14 22 0.327 1.450 0.274

Denver 1 Dissolved potassium Dissolved fluoride 14 31 0.747 1.367 5.677

Sand Creek 3 Dissolved potassium Dissolved fluoride 11 22 0.889 2.077 0.728

Henderson 3 Dissolved potassium Dissolved fluoride 7 27 0.969 2.312 0.837

ALL 3 Dissolved potassium Dissolved manganese 62 113 0.266 1.164 0.098

Denver 3 Dissolved potassium Dissolved manganese 14 31 0.603 1.123 0.157

Sand Creek 2 Dissolved potassium Dissolved manganese 11 22 0.432 2.987 0.450

Henderson 1 Dissolved potassium Dissolved manganese 7 27 0.822 4.046 0.034

ALL 3 Dissolved potassium Dissolved sodium 62 113 0.186 0.593 0.218

Union 1 Dissolved potassium Dissolved sodium 14 22 0.276 2.573 0.036

Denver 3 Dissolved potassium Dissolved sodium 14 31 0.253 2.961 0.036

Sand Creek 2 Dissolved potassium Dissolved sodium 11 22 0.763 –4.917 2.153

ALL 1 Dissolved potassium Ammonia 56 119 0.466 3.711 2.007

Sand Creek 3 Dissolved potassium Ammonia 11 22 0.327 1.801 0.358

Henderson 3 Dissolved potassium Ammonia 7 27 0.702 1.785 0.318

ALL 1 Dissolved potassium Nitrite + nitrate 62 113 0.685 3.089 1.067

Union 1 Dissolved potassium Nitrite + nitrate 14 22 0.734 2.090 1.926

Denver 2 Dissolved potassium Nitrite + nitrate 14 31 0.948 3.702 1.935

Sand Creek 3 Dissolved potassium Nitrite + nitrate 11 22 0.437 1.544 0.556

Henderson 1 Dissolved potassium Nitrite + nitrate 7 27 0.979 2.458 1.540

ALL 1 Dissolved potassium Orthophosphate 62 113 0.608 3.544 5.406

Denver 2 Dissolved potassium Orthophosphate 14 31 0.907 7.631 1.876

Henderson 2 Dissolved potassium Orthophosphate 7 27 0.947 8.851 2.926

ALL 1 Dissolved potassium Dissolved lead 38 137 0.398 3.091 9.837

Union 1 Dissolved potassium Dissolved lead 2 34 0.929 6.261 –20.524

Denver 2 Dissolved potassium Dissolved lead 13 32 0.326 7.658 1.563

Henderson 1 Dissolved potassium Dissolved lead 7 27 0.711 13.689 5.076

ALL 3 Dissolved potassium Dissolved sulfate 62 113 0.110 0.773 0.148

Union 1 Dissolved potassium Dissolved sulfate 14 22 0.621 2.110 0.023

Denver 3 Dissolved potassium Dissolved sulfate 14 31 0.763 –0.880 0.556

Sand Creek 3 Dissolved potassium Dissolved sulfate 11 22 0.690 –4.213 1.724

Henderson 1 Dissolved potassium Dissolved sulfate 7 27 0.947 –1.945 0.855

ALL 2 Dissolved potassium Dissolved zinc 61 114 0.325 2.222 1.108

Denver 1 Dissolved potassium Dissolved zinc 14 31 0.639 3.129 0.131

Sand Creek 1 Dissolved potassium Dissolved zinc 10 23 0.394 3.591 0.096

Henderson 1 Dissolved potassium Dissolved zinc 7 27 0.879 1.666 0.332
Evaluation of Stormwater Quality 61

Table 11. Results of linear regression analyses, water years 2002–2005.—Continued

[Group indicates that data represent results from all stations (ALL), South Platte River below Union Avenue at Englewood (Union), South Platte River at Denver 

(Denver), Tollgate Creek above 6th Avenue at Aurora (Tollgate), Sand Creek at mouth near Commerce City (Sand Creek), or South Platte River at Henderson 

(Henderson); T indicates transform: 1, no transform; 2 natural log transform for dependent variable; 3, natural log transform for both variables; Dependent and 

Independent describe regression variables. n, number of values used in regression; M, number of missing values; r2, coefficient of determination (commonly 

referred to as r-squared). Intercept, y-axis intercept of the linear regression line; Slope, slope of the linear regression line. Regressions with r2 values greater than 

0.65 are shown in bold print]

Station T Water-quality properties or constituents n M r

2 Intercept Slope Dependent Independent

ALL 3 Dissolved magnesium Alkalinity 62 113 0.715 –3.612 1.318

Union 3 Dissolved magnesium Alkalinity 14 22 0.921 –4.651 1.532

Denver 3 Dissolved magnesium Alkalinity 14 31 0.927 –3.537 1.269

Tollgate 3 Dissolved magnesium Alkalinity 12 11 0.877 –4.339 1.564

Sand Creek 3 Dissolved magnesium Alkalinity 11 22 0.840 –3.263 1.241

Henderson 2 Dissolved magnesium Alkalinity 7 27 0.900 –39.002 10.812

ALL 3 Dissolved magnesium Dissolved chloride 62 113 0.391 –10.753 5.339

Sand Creek 1 Dissolved magnesium Dissolved chloride 11 22 0.743 –30.670 9.883

ALL 3 Dissolved magnesium Dissolved fluoride 62 113 0.127 2.481 0.347

Union 3 Dissolved magnesium Dissolved fluoride 14 22 0.575 2.428 0.658

Denver 1 Dissolved magnesium Dissolved fluoride 14 31 0.707 2.591 0.836

Tollgate 3 Dissolved magnesium Dissolved fluoride 12 11 0.428 4.106 1.342

Sand Creek 3 Dissolved magnesium Dissolved fluoride 11 22 0.729 3.275 1.128

Henderson 2 Dissolved magnesium Dissolved fluoride 7 27 0.786 13.762 7.759

ALL 3 Dissolved magnesium Dissolved potassium 62 113 0.232 1.120 0.753

Sand Creek 3 Dissolved magnesium Dissolved potassium 11 22 0.768 –12.192 15.907

Henderson 2 Dissolved magnesium Dissolved potassium 7 27 0.810 –7.651 9.260

ALL 3 Dissolved magnesium Dissolved manganese 131 44 0.357 1.708 0.176

Union 3 Dissolved magnesium Dissolved manganese 27 9 0.268 1.755 0.155

Denver 3 Dissolved magnesium Dissolved manganese 34 11 0.428 1.579 0.197

Sand Creek 2 Dissolved magnesium Dissolved manganese 24 9 0.543 5.068 2.276

Henderson 3 Dissolved magnesium Dissolved manganese 22 12 0.721 1.181 0.259

ALL 3 Dissolved magnesium Dissolved sodium 62 113 0.650 3.442 0.109

Union 3 Dissolved magnesium Dissolved sodium 14 22 0.738 –1.077 0.912

Denver 3 Dissolved magnesium Dissolved sodium 14 31 0.664 –13.130 5.745

Tollgate 1 Dissolved magnesium Dissolved sodium 12 11 0.926 –2.559 1.164

Sand Creek 1 Dissolved magnesium Dissolved sodium 11 22 0.966 –32.953 10.124

Henderson 3 Dissolved magnesium Dissolved sodium 7 27 0.523 5.059 0.057

ALL 3 Dissolved magnesium Ammonia 116 59 0.053 2.398 0.094

Tollgate 3 Dissolved magnesium Ammonia 18 5 0.198 3.190 0.373

Sand Creek 1 Dissolved magnesium Ammonia 21 12 0.377 8.622 9.297

Henderson 3 Dissolved magnesium Ammonia 22 12 0.805 2.138 0.406

ALL 3 Dissolved magnesium Nitrite + nitrate 128 47 0.045 2.248 0.125

Union 1 Dissolved magnesium Nitrite + nitrate 27 9 0.239 5.237 4.698

Denver 3 Dissolved magnesium Nitrite + nitrate 34 11 0.589 1.787 0.523

Tollgate 3 Dissolved magnesium Nitrite + nitrate 17 6 0.274 2.903 0.543

Sand Creek 3 Dissolved magnesium Nitrite + nitrate 24 9 0.388 2.487 0.567

Henderson 3 Dissolved magnesium Nitrite + nitrate 22 12 0.691 1.605 0.687

ALL 3 Dissolved magnesium Dissolved lead 87 88 0.079 2.711 0.252

Denver 2 Dissolved magnesium Dissolved lead 32 13 0.159 13.566 2.673

Tollgate 1 Dissolved magnesium Dissolved lead 6 17 0.787 –23.427 344.115

Henderson 1 Dissolved magnesium Dissolved lead 22 12 0.306 6.158 13.081
62 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table 11. Results of linear regression analyses, water years 2002–2005.—Continued

[Group indicates that data represent results from all stations (ALL), South Platte River below Union Avenue at Englewood (Union), South Platte River at Denver 

(Denver), Tollgate Creek above 6th Avenue at Aurora (Tollgate), Sand Creek at mouth near Commerce City (Sand Creek), or South Platte River at Henderson 

(Henderson); T indicates transform: 1, no transform; 2 natural log transform for dependent variable; 3, natural log transform for both variables; Dependent and 

Independent describe regression variables. n, number of values used in regression; M, number of missing values; r2, coefficient of determination (commonly 

referred to as r-squared). Intercept, y-axis intercept of the linear regression line; Slope, slope of the linear regression line. Regressions with r2 values greater than 

0.65 are shown in bold print]

Station T Water-quality properties or constituents n M r

2 Intercept Slope Dependent Independent

ALL 1 Dissolved magnesium Dissolved sulfate 62 113 0.798 4.384 0.045

Union 1 Dissolved magnesium Dissolved sulfate 14 22 0.901 –2.010 0.971

Denver 3 Dissolved magnesium Dissolved sulfate 14 31 0.945 –1.629 0.865

Tollgate 1 Dissolved magnesium Dissolved sulfate 12 11 0.988 –2.575 0.954

Sand Creek 2 Dissolved magnesium Dissolved sulfate 11 22 0.974 –31.920 8.558

Henderson 2 Dissolved magnesium Dissolved sulfate 7 27 0.907 –28.673 8.609

ALL 3 Total manganese Total zinc 130 45 0.626 3.194 0.631

Union 1 Total manganese Total zinc 27 9 0.914 73.566 5.370

Denver 1 Total manganese Total zinc 34 11 0.817 85.960 2.669

Tollgate 3 Total manganese Total zinc 20 3 0.708 2.182 0.961

Sand Creek 3 Total manganese Total zinc 23 10 0.449 3.662 0.515

Henderson 3 Total manganese Total zinc 22 12 0.856 2.296 0.803

ALL 3 Mean streamflow Alkalinity 58 117 0.164 17.274 –2.657

Union 2 Mean streamflow Alkalinity 14 22 0.616 2,478.522 –509.488

Denver 2 Mean streamflow Alkalinity 14 31 0.758 10,557.627 –2,177.453

Tollgate 2 Mean streamflow Alkalinity 8 15 0.733 1,667.329 –361.251

Sand Creek 3 Mean streamflow Alkalinity 11 22 0.556 16.978 –2.636

Henderson 2 Mean streamflow Alkalinity 7 27 0.888 25,433.410 –5,204.953

ALL 3 Mean streamflow Dissolved chloride 58 117 0.075 9.038 –0.914

Union 2 Mean streamflow Dissolved chloride 14 22 0.402 1,055.511 –231.939

Denver 2 Mean streamflow Dissolved chloride 14 31 0.455 4,721.985 –1,006.529

Tollgate 2 Mean streamflow Dissolved chloride 8 15 0.446 812.788 –185.621

Sand Creek 3 Mean streamflow Dissolved chloride 11 22 0.684 14.979 –2.336

Henderson 2 Mean streamflow Dissolved chloride 7 27 0.490 7,968.377 –1,377.489

Union 3 Mean streamflow Dissolved fluoride 14 22 0.333 4.722 –0.939

Denver 3 Mean streamflow Dissolved fluoride 14 31 0.593 5.429 –1.781

Tollgate 2 Mean streamflow Dissolved fluoride 8 15 0.672 –519.873 –531.096

Sand Creek 3 Mean streamflow Dissolved fluoride 11 22 0.331 3.432 –1.984

Henderson 3 Mean streamflow Dissolved fluoride 7 27 0.854 6.497 –1.751

Union 3 Mean streamflow Dissolved potassium 14 22 0.431 8.127 –2.233

Denver 3 Mean streamflow Dissolved potassium 14 31 0.759 10.775 –2.835

Sand Creek 3 Mean streamflow Dissolved potassium 11 22 0.615 10.238 –3.505

Henderson 3 Mean streamflow Dissolved potassium 7 27 0.847 11.259 –2.050

ALL 3 Mean streamflow Dissolved magnesium 127 48 0.317 10.341 –2.061

Union 3 Mean streamflow Dissolved magnesium 27 9 0.281 7.603 –1.085

Denver 3 Mean streamflow Dissolved magnesium 34 11 0.525 9.631 –1.474

Sand Creek 3 Mean streamflow Dissolved magnesium 24 9 0.544 9.572 –1.924

Henderson 3 Mean streamflow Dissolved magnesium 22 12 0.664 11.293 –1.795

ALL 3 Mean streamflow Dissolved sodium 58 117 0.204 11.309 –1.476

Union 2 Mean streamflow Dissolved sodium 14 22 0.480 1,274.618 –299.197

Denver 2 Mean streamflow Dissolved sodium 14 31 0.632 6,103.122 –1,377.721

Tollgate 2 Mean streamflow Dissolved sodium 8 15 0.602 962.258 –203.851

Sand Creek 3 Mean streamflow Dissolved sodium 11 22 0.661 14.084 –2.064

Henderson 2 Mean streamflow Dissolved sodium 7 27 0.627 10,656.621 –2,033.731

ALL 3 Mean streamflow Streamflow volume 171 4 0.972 0.232 0.979

Union 1 Mean streamflow Streamflow volume 36 0 0.959 0.763 0.877

Denver 1 Mean streamflow Streamflow volume 45 0 0.945 0.667 0.918

Sand Creek 3 Mean streamflow Streamflow volume 33 0 0.976 0.435 0.928

Henderson 3 Mean streamflow Streamflow volume 34 0 0.694 –9,223.888 1,557.344
Evaluation of Stormwater Quality 63

Table 11. Results of linear regression analyses, water years 2002–2005.—Continued

[Group indicates that data represent results from all stations (ALL), South Platte River below Union Avenue at Englewood (Union), South Platte River at Denver 

(Denver), Tollgate Creek above 6th Avenue at Aurora (Tollgate), Sand Creek at mouth near Commerce City (Sand Creek), or South Platte River at Henderson 

(Henderson); T indicates transform: 1, no transform; 2 natural log transform for dependent variable; 3, natural log transform for both variables; Dependent and 

Independent describe regression variables. n, number of values used in regression; M, number of missing values; r2, coefficient of determination (commonly 

referred to as r-squared). Intercept, y-axis intercept of the linear regression line; Slope, slope of the linear regression line. Regressions with r2 values greater than 

0.65 are shown in bold print]

Station T Water-quality properties or constituents n M r

2 Intercept Slope Dependent Independent

ALL 3 Mean streamflow Dissolved sulfate 58 117 0.509 15.169 –2.105

Union 2 Mean streamflow Dissolved sulfate 14 22 0.619 1,618.282 –327.318

Denver 3 Mean streamflow Dissolved sulfate 14 31 0.818 14.550 –1.873

Tollgate 2 Mean streamflow Dissolved sulfate 8 15 0.634 1083.251 –187.379

Sand Creek 3 Mean streamflow Dissolved sulfate 11 22 0.549 13.060 –1.583

Henderson 2 Mean streamflow Dissolved sulfate 7 27 0.924 20,756.254 –4211.833

ALL 3 Dissolved sodium Alkalinity 62 113 0.330 –246.208 69.393

Union 3 Dissolved sodium Alkalinity 14 22 0.538 –132.400 37.945

Tollgate 1 Dissolved sodium Alkalinity 12 11 0.703 –332.051 94.793

Sand Creek 3 Dissolved sodium Alkalinity 11 22 0.736 –357.669 98.222

ALL 3 Dissolved sodium Dissolved chloride 62 113 0.747 –151.567 54.404

Union 3 Dissolved sodium Dissolved chloride 14 22 0.889 0.650 0.799

Denver 3 Dissolved sodium Dissolved chloride 14 31 0.919 0.640 0.826

Tollgate 3 Dissolved sodium Dissolved chloride 12 11 0.617 –175.783 63.283

Sand Creek 3 Dissolved sodium Dissolved chloride 11 22 0.833 –268.017 83.460

Henderson 3 Dissolved sodium Dissolved chloride 7 27 0.974 1.002 0.756

ALL 3 Dissolved sodium Dissolved manganese 62 113 0.403 3.247 0.238

Union 3 Dissolved sodium Dissolved manganese 14 22 0.247 3.103 0.154

Denver 3 Dissolved sodium Dissolved manganese 14 31 0.631 3.172 0.247

Sand Creek 3 Dissolved sodium Dissolved manganese 11 22 0.494 3.717 0.195

Henderson 3 Dissolved sodium Dissolved manganese 7 27 0.656 2.651 0.384

ALL 3 Dissolved sodium Ammonia 56 119 0.248 4.444 0.302

Sand Creek 3 Dissolved sodium Ammonia 11 22 0.541 5.114 0.812

Henderson 3 Dissolved sodium Ammonia 7 27 0.700 4.067 0.617

Denver 2 Dissolved sodium Dissolved lead 13 32 0.303 86.659 21.001

ALL 3 Dissolved sodium Dissolved sulfate 62 113 0.681 21.934 0.309

Union 3 Dissolved sodium Dissolved sulfate 14 22 0.582 –72.167 25.285

Tollgate 1 Dissolved sodium Dissolved sulfate 12 11 0.922 19.271 0.278

Sand Creek 2 Dissolved sodium Dissolved sulfate 11 22 0.947 –253.699 67.327

ALL 3 Dissolved sodium Dissolved zinc 61 114 0.344 3.015 0.463

Union 3 Dissolved sodium Dissolved zinc 14 22 0.312 2.694 0.529

Denver 3 Dissolved sodium Dissolved zinc 14 31 0.478 2.721 0.461

Tollgate 3 Dissolved sodium Dissolved zinc 12 11 0.710 3.560 0.370

Sand Creek 3 Dissolved sodium Dissolved zinc 10 23 0.357 3.434 0.449

ALL 3 Ammonia Dissolved manganese 116 59 0.339 –2.600 0.420

Union 1 Ammonia Dissolved manganese 19 17 0.599 0.095 0.001

Denver 3 Ammonia Dissolved manganese 32 13 0.338 –2.394 0.368

Tollgate 1 Ammonia Dissolved manganese 18 5 0.424 0.188 0.000

Sand Creek 2 Ammonia Dissolved manganese 21 12 0.312 –2.331 0.326

Henderson 1 Ammonia Dissolved manganese 22 12 0.810 0.462 0.013

ALL 1 Ammonia Dissolved lead 81 94 0.567 –0.374 5.443

Union 1 Ammonia Dissolved lead 3 33 0.984 0.744 –3.992

Denver 1 Ammonia Dissolved lead 30 15 0.399 1.383 0.545

Sand Creek 1 Ammonia Dissolved lead 17 16 0.267 1.120 0.359

Henderson 1 Ammonia Dissolved lead 22 12 0.521 3.930 1.758
64 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table 11. Results of linear regression analyses, water years 2002–2005.—Continued

[Group indicates that data represent results from all stations (ALL), South Platte River below Union Avenue at Englewood (Union), South Platte River at Denver 

(Denver), Tollgate Creek above 6th Avenue at Aurora (Tollgate), Sand Creek at mouth near Commerce City (Sand Creek), or South Platte River at Henderson 

(Henderson); T indicates transform: 1, no transform; 2 natural log transform for dependent variable; 3, natural log transform for both variables; Dependent and 

Independent describe regression variables. n, number of values used in regression; M, number of missing values; r2, coefficient of determination (commonly 

referred to as r-squared). Intercept, y-axis intercept of the linear regression line; Slope, slope of the linear regression line. Regressions with r2 values greater than 

0.65 are shown in bold print]

Station T Water-quality properties or constituents n M r

2 Intercept Slope Dependent Independent

ALL 2 Nitrite + nitrate Dissolved manganese 128 47 0.154 0.567 0.299

Union 3 Nitrite + nitrate Dissolved manganese 27 9 0.226 –0.664 0.163

Denver 3 Nitrite + nitrate Dissolved manganese 34 11 0.420 1.482 0.023

Sand Creek 3 Nitrite + nitrate Dissolved manganese 24 9 0.233 –0.534 0.148

Henderson 3 Nitrite + nitrate Dissolved manganese 22 12 0.785 –0.410 0.327

ALL 1 Nitrite + nitrate Orthophosphate 126 49 0.720 0.622 4.381

Denver 2 Nitrite + nitrate Orthophosphate 34 11 0.876 5.260 2.032

Tollgate 2 Nitrite + nitrate Orthophosphate 15 8 0.229 0.746 –3.502

Henderson 3 Nitrite + nitrate Orthophosphate 22 12 0.765 1.446 0.710

ALL 2 Nitrite + nitrate Dissolved lead 87 88 0.394 4.385 1.443

Denver 2 Nitrite + nitrate Dissolved lead 32 13 0.288 4.612 1.333

Henderson 2 Nitrite + nitrate Dissolved lead 22 12 0.656 5.301 1.945

ALL 3 Nitrite + nitrate Dissolved zinc 127 48 0.226 –0.699 0.377

Union 2 Nitrite + nitrate Dissolved zinc 27 9 0.278 –1.048 0.537

Denver 3 Nitrite + nitrate Dissolved zinc 34 11 0.571 –1.068 0.732

Sand Creek 3 Nitrite + nitrate Dissolved zinc 23 10 0.206 –0.543 0.167

Henderson 3 Nitrite + nitrate Dissolved zinc 22 12 0.684 –1.146 0.745

Union 2 Orthophosphate Dissolved manganese 27 9 0.258 0.107 –0.015

Denver 1 Orthophosphate Dissolved manganese 34 11 0.460 0.161 0.003

Henderson 3 Orthophosphate Dissolved manganese 22 12 0.678 –2.261 0.375

ALL 3 Dissolved lead Dissolved manganese 87 88 0.312 –2.392 0.191

Denver 1 Dissolved lead Dissolved manganese 32 13 0.495 0.114 0.002

Sand Creek 3 Dissolved lead Dissolved manganese 19 14 0.358 –2.486 0.189

Henderson 1 Dissolved lead Dissolved manganese 22 12 0.743 0.148 0.002

ALL 3 Dissolved lead Dissolved zinc 87 88 0.275 –2.739 0.393

Denver 1 Dissolved lead Dissolved zinc 32 13 0.558 –3.318 0.628

Sand Creek 3 Dissolved lead Dissolved zinc 18 15 0.386 –2.616 0.243

Henderson 3 Dissolved lead Dissolved zinc 23 11 0.570 –5.026 1.354

ALL 3 Total lead Total manganese 131 44 0.611 –3.881 1.082

Union 1 Total lead Total manganese 27 9 0.899 –3.116 0.041

Denver 1 Total lead Total manganese 34 11 0.783 –4.412 1.251

Tollgate 1 Total lead Total manganese 20 3 0.524 –2.992 0.832

Sand Creek 3 Total lead Total manganese 24 9 0.843 –4.398 1.148

Henderson 3 Total lead Total manganese 22 12 0.652 –3.540 1.101

ALL 3 Total lead Total zinc 130 45 0.720 –1.541 0.934

Union 1 Total lead Total zinc 27 9 0.977 –1.135 0.242

Denver 3 Total lead Total zinc 34 11 0.944 –2.472 1.186

Tollgate 1 Total lead Total zinc 20 3 0.809 –2.829 1.180

Henderson 3 Total lead Total zinc 22 12 0.817 –1.922 1.069

ALL 3 Streamflow volume Alkalinity 58 117 0.191 18.343 –2.939

Union 2 Streamflow volume Alkalinity 14 22 0.622 2,309.927 –476.806

Denver 2 Streamflow volume Alkalinity 14 31 0.764 9,818.997 –2,032.055

Tollgate 2 Streamflow volume Alkalinity 8 15 0.619 1,587.981 –344.285

Sand Creek 3 Streamflow volume Alkalinity 11 22 0.554 17.850 –2.861

Henderson 3 Streamflow volume Alkalinity 7 27 0.734 15.931 –1.925
Evaluation of Stormwater Quality 65

Table 11. Results of linear regression analyses, water years 2002–2005.—Continued

[Group indicates that data represent results from all stations (ALL), South Platte River below Union Avenue at Englewood (Union), South Platte River at Denver 

(Denver), Tollgate Creek above 6th Avenue at Aurora (Tollgate), Sand Creek at mouth near Commerce City (Sand Creek), or South Platte River at Henderson 

(Henderson); T indicates transform: 1, no transform; 2 natural log transform for dependent variable; 3, natural log transform for both variables; Dependent and 

Independent describe regression variables. n, number of values used in regression; M, number of missing values; r2, coefficient of determination (commonly 

referred to as r-squared). Intercept, y-axis intercept of the linear regression line; Slope, slope of the linear regression line. Regressions with r2 values greater than 

0.65 are shown in bold print]

Station T Water-quality properties or constituents n M r

2 Intercept Slope Dependent Independent

ALL 3 Streamflow volume Dissolved chloride 58 117 0.076 8.984 –0.947

Union 2 Streamflow volume Dissolved chloride 14 22 0.402 974.679 –216.066

Denver 2 Streamflow volume Dissolved chloride 14 31 0.449 4,333.135 –928.814

Sand Creek 3 Streamflow volume Dissolved chloride 11 22 0.714 15.935 –2.595

Union 2 Streamflow volume Dissolved fluoride 14 22 0.319 116.035 –185.626

Denver 1 Streamflow volume Dissolved fluoride 14 31 0.572 2,286.662 –2,543.802

Tollgate 3 Streamflow volume Dissolved fluoride 8 15 0.398 555.146 –1,466.386

Sand Creek 3 Streamflow volume Dissolved fluoride 11 22 0.350 3.093 –2.220

Henderson 3 Streamflow volume Dissolved fluoride 7 27 0.750 6.464 –1.495

Union 3 Streamflow volume Dissolved potassium 14 22 0.471 8.866 –2.949

Denver 3 Streamflow volume Dissolved potassium 14 31 0.673 11.256 –3.287

Sand Creek 3 Streamflow volume Dissolved potassium 11 22 0.609 10.524 –3.796

Henderson 3 Streamflow volume Dissolved potassium 7 27 0.667 10.365 –1.658

ALL 3 Streamflow volume Dissolved sodium 58 117 0.207 11.317 –1.524

Union 2 Streamflow volume Dissolved sodium 14 22 0.487 1,185.034 –280.518

Denver 2 Streamflow volume Dissolved sodium 14 31 0.629 5,627.323 –1,276.56

Tollgate 2 Streamflow volume Dissolved sodium 8 15 0.474 887.587 –187.675

Sand Creek 3 Streamflow volume Dissolved sodium 11 22 0.696 14.983 –2.302

Henderson 2 Streamflow volume Dissolved sodium 7 27 0.425 7,582.725 –1,390.661

ALL 3 Streamflow volume Dissolved sulfate 58 117 0.515 15.288 –2.170

Union 2 Streamflow volume Dissolved sulfate 14 22 0.628 1,507.371 –306.914

Denver 2 Streamflow volume Dissolved sulfate 14 31 0.823 6,923.504 –1,422.584

Tollgate 2 Streamflow volume Dissolved sulfate 8 15 0.551 1,045.490 –181.234

Sand Creek 3 Streamflow volume Dissolved sulfate 11 22 0.577 13.835 –1.765

Henderson 3 Streamflow volume Dissolved sulfate 7 27 0.738 14.087 –1.532

ALL 3 Specific conductance Alkalinity 54 121 0.369 2.297 0.910

Union 1 Specific conductance Alkalinity 11 25 0.586 –1,194.733 367.662

Denver 3 Specific conductance Alkalinity 14 31 0.612 2.065 0.928

Tollgate 3 Specific conductance Alkalinity 10 13 0.786 –3,350.682 953.958

Sand Creek 3 Specific conductance Alkalinity 10 23 0.619 2.819 0.837

ALL 1 Specific conductance Dissolved calcium 110 65 0.788 2.358 1.038

Union 3 Specific conductance Dissolved calcium 21 15 0.705 2.009 1.092

Denver 3 Specific conductance Dissolved calcium 30 15 0.696 2.480 1.009

Tollgate 3 Specific conductance Dissolved calcium 16 7 0.903 2.321 1.027

Sand Creek 3 Specific conductance Dissolved calcium 21 12 0.858 2.533 1.015

Henderson 3 Specific conductance Dissolved calcium 18 16 0.498 –2,025.506 706.634

ALL 3 Specific conductance Dissolved chloride 54 121 0.691 3.794 0.646

Union 3 Specific conductance Dissolved chloride 11 25 0.655 4.074 0.545

Denver 3 Specific conductance Dissolved chloride 14 31 0.709 3.916 0.596

Tollgate 1 Specific conductance Dissolved chloride 10 13 0.586 3.867 0.686

Sand Creek 3 Specific conductance Dissolved chloride 10 23 0.696 3.011 0.838

Henderson 1 Specific conductance Dissolved chloride 5 29 0.903 275.134 3.839

ALL 3 Specific conductance Hardness as calcium carbonate 151 24 0.628 2.061 0.839

Union 3 Specific conductance Hardness as calcium carbonate 30 6 0.430 3.056 0.605

Denver 3 Specific conductance Hardness as calcium carbonate 40 5 0.639 2.052 0.838

Tollgate 1 Specific conductance Hardness as calcium carbonate 19 4 0.829 1.744 0.901

Sand Creek 3 Specific conductance Hardness as calcium carbonate 29 4 0.628 2.357 0.805

Henderson 3 Specific conductance Hardness as calcium carbonate 29 5 0.421 3.116 0.650
66 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table 11. Results of linear regression analyses, water years 2002–2005.—Continued

[Group indicates that data represent results from all stations (ALL), South Platte River below Union Avenue at Englewood (Union), South Platte River at Denver 

(Denver), Tollgate Creek above 6th Avenue at Aurora (Tollgate), Sand Creek at mouth near Commerce City (Sand Creek), or South Platte River at Henderson 

(Henderson); T indicates transform: 1, no transform; 2 natural log transform for dependent variable; 3, natural log transform for both variables; Dependent and 

Independent describe regression variables. n, number of values used in regression; M, number of missing values; r2, coefficient of determination (commonly 

referred to as r-squared). Intercept, y-axis intercept of the linear regression line; Slope, slope of the linear regression line. Regressions with r2 values greater than 

0.65 are shown in bold print]

Station T Water-quality properties or constituents n M r

2 Intercept Slope Dependent Independent

ALL 1 Specific conductance Dissolved magnesium 110 65 0.796 4.344 0.900

Union 3 Specific conductance Dissolved magnesium 21 15 0.601 4.641 0.672

Denver 3 Specific conductance Dissolved magnesium 30 15 0.812 4.465 0.830

Tollgate 1 Specific conductance Dissolved magnesium 16 7 0.949 4.577 0.835

Sand Creek 3 Specific conductance Dissolved magnesium 21 12 0.908 4.562 0.871

Henderson 3 Specific conductance Dissolved magnesium 18 16 0.680 4.478 0.857

ALL 3 Specific conductance Dissolved sodium 54 121 0.881 3.451 0.723

Union 2 Specific conductance Dissolved sodium 11 25 0.765 –540.615 277.712

Denver 3 Specific conductance Dissolved sodium 14 31 0.829 3.354 0.748

Tollgate 1 Specific conductance Dissolved sodium 10 13 0.984 95.487 8.884

Sand Creek 3 Specific conductance Dissolved sodium 10 23 0.866 3.239 0.765

Henderson 1 Specific conductance Dissolved sodium 5 29 0.892 3.441 0.692

Denver 2 Specific conductance Dissolved lead 28 17 0.336 961.722 238.445

Tollgate 1 Specific conductance Dissolved lead 6 17 0.777 –1,296.216 20,249.705

ALL 1 Specific conductance Dissolved sulfate 54 121 0.754 286.059 2.600

Union 2 Specific conductance Dissolved sulfate 11 25 0.567 –551.779 233.593

Denver 3 Specific conductance Dissolved sulfate 14 31 0.619 3.471 0.630

Tollgate 1 Specific conductance Dissolved sulfate 10 13 0.967 216.692 2.697

Sand Creek 3 Specific conductance Dissolved sulfate 10 23 0.844 3.553 0.602

ALL 3 Dissolved sulfate Dissolved manganese 62 113 0.336 3.892 0.246

Denver 3 Dissolved sulfate Dissolved manganese 14 31 0.578 3.707 0.242

Sand Creek 3 Dissolved sulfate Dissolved manganese 11 22 0.491 4.275 0.231

Henderson 1 Dissolved sulfate Dissolved manganese 7 27 0.918 49.561 0.516

Sand Creek 3 Dissolved sulfate Ammonia 11 22 0.672 6.036 1.074

Henderson 3 Dissolved sulfate Ammonia 7 27 0.803 4.362 0.387

Union 1 Dissolved sulfate Nitrite + nitrate 14 22 0.540 4.367 0.658

Denver 2 Dissolved sulfate Nitrite + nitrate 14 31 0.794 57.886 42.992

Tollgate 3 Dissolved sulfate Nitrite + nitrate 12 11 0.411 5.769 0.881

Henderson 1 Dissolved sulfate Nitrite + nitrate 7 27 0.937 29.588 21.721

ALL 2 Dissolved sulfate Orthophosphate 62 113 0.136 53.598 –31.946

Denver 2 Dissolved sulfate Orthophosphate 14 31 0.642 139.860 38.305

Tollgate 2 Dissolved sulfate Orthophosphate 12 11 0.392 4.140 –0.354

Henderson 2 Dissolved sulfate Orthophosphate 7 27 0.964 120.954 42.577

ALL 1 Dissolved sulfate Dissolved zinc 61 114 0.203 77.169 4.833

Union 3 Dissolved sulfate Dissolved zinc 14 22 0.327 3.396 0.562

Denver 3 Dissolved sulfate Dissolved zinc 14 31 0.440 3.261 0.454

Tollgate 2 Dissolved sulfate Dissolved zinc 12 11 0.627 4.384 0.438

Henderson 2 Dissolved sulfate Dissolved zinc 7 27 0.872 –81.086 64.098

ALL 3 Ammonia + organic N Total copper 131 44 0.705 –1.375 0.756

Union 3 Ammonia + organic N Total copper 27 9 0.858 –1.376 0.697

Denver 1 Ammonia + organic N Total copper 34 11 0.802 –1.496 0.774

Tollgate 1 Ammonia + organic N Total copper 20 3 0.564 –2.238 1.639

Sand Creek 3 Ammonia + organic N Total copper 24 9 0.541 –0.866 0.625

ALL 2 Ammonia + organic N Dissolved manganese 131 44 0.062 2.614 0.003

Union 1 Ammonia + organic N Dissolved manganese 27 9 0.495 1.131 0.017

Denver 1 Ammonia + organic N Dissolved manganese 34 11 0.337 1.580 0.037

Sand Creek 2 Ammonia + organic N Dissolved manganese 24 9 0.226 2.659 0.008

Henderson 1 Ammonia + organic N Dissolved manganese 22 12 0.686 2.158 0.029
Evaluation of Stormwater Quality 67

Table 11. Results of linear regression analyses, water years 2002–2005.—Continued

[Group indicates that data represent results from all stations (ALL), South Platte River below Union Avenue at Englewood (Union), South Platte River at Denver 

(Denver), Tollgate Creek above 6th Avenue at Aurora (Tollgate), Sand Creek at mouth near Commerce City (Sand Creek), or South Platte River at Henderson 

(Henderson); T indicates transform: 1, no transform; 2 natural log transform for dependent variable; 3, natural log transform for both variables; Dependent and 

Independent describe regression variables. n, number of values used in regression; M, number of missing values; r2, coefficient of determination (commonly 

referred to as r-squared). Intercept, y-axis intercept of the linear regression line; Slope, slope of the linear regression line. Regressions with r2 values greater than 

0.65 are shown in bold print]

Station T Water-quality properties or constituents n M r

2 Intercept Slope Dependent Independent

ALL 3 Ammonia + organic N Total manganese 131 44 0.555 –3.059 0.649

Union 1 Ammonia + organic N Total manganese 27 9 0.865 –3.896 0.747

Denver 3 Ammonia + organic N Total manganese 34 11 0.801 –3.819 0.806

Tollgate 1 Ammonia + organic N Total manganese 20 3 0.399 1.031 0.002

Sand Creek 1 Ammonia + organic N Total manganese 24 9 0.700 1.085 0.003

ALL 1 Ammonia + organic N Ammonia 116 59 0.550 1.769 2.210

Union 1 Ammonia + organic N Ammonia 19 17 0.321 1.638 0.529

Denver 1 Ammonia + organic N Ammonia 32 13 0.755 0.832 5.172

Sand Creek 1 Ammonia + organic N Ammonia 21 12 0.552 1.520 4.403

Henderson 1 Ammonia + organic N Ammonia 22 12 0.716 1.408 2.063

ALL 3 Ammonia + organic N Total lead 131 44 0.650 –0.492 0.507

Union 1 Ammonia + organic N Total lead 27 9 0.868 0.571 0.090

Denver 3 Ammonia + organic N Total lead 34 11 0.724 –0.702 0.542

Tollgate 1 Ammonia + organic N Total lead 20 3 0.640 1.085 0.091

Sand Creek 3 Ammonia + organic N Total lead 24 9 0.364 2.103 0.045

ALL 3 Ammonia + organic N Total phosphorus 171 4 0.825 1.189 0.752

Union 1 Ammonia + organic N Total phosphorus 36 0 0.869 0.289 3.213

Denver 1 Ammonia + organic N Total phosphorus 44 1 0.865 1.154 0.925

Tollgate 3 Ammonia + organic N Total phosphorus 22 1 0.615 1.116 0.567

Sand Creek 3 Ammonia + organic N Total phosphorus 32 1 0.738 1.248 0.779

Henderson 3 Ammonia + organic N Total phosphorus 33 1 0.597 1.294 0.671

ALL 3 Ammonia + organic N Total zinc 130 45 0.654 –1.657 0.560

Union 1 Ammonia + organic N Total zinc 27 9 0.915 0.424 0.023

Denver 1 Ammonia + organic N Total zinc 34 11 0.848 –2.359 0.716

Tollgate 1 Ammonia + organic N Total zinc 20 3 0.488 –3.895 1.457

Sand Creek 1 Ammonia + organic N Total zinc 23 10 0.551 1.891 0.005

Henderson 3 Ammonia + organic N Total zinc 22 12 0.310 2.053 0.017

ALL 1 Total phosphorus Total copper 130 45 0.846 –3.218 0.961

Union 1 Total phosphorus Total copper 27 9 0.967 –3.570 1.028

Denver 1 Total phosphorus Total copper 34 11 0.704 –2.452 0.696

Tollgate 1 Total phosphorus Total copper 19 4 0.869 –3.503 1.033

Sand Creek 3 Total phosphorus Total copper 24 9 0.860 –2.711 0.813

Henderson 1 Total phosphorus Total copper 22 12 0.706 0.391 0.032

ALL 3 Total phosphorus Total manganese 130 45 0.623 –5.227 0.803

Union 1 Total phosphorus Total manganese 27 9 0.829 –6.801 1.015

Denver 3 Total phosphorus Total manganese 34 11 0.863 –4.982 0.802

Tollgate 1 Total phosphorus Total manganese 19 4 0.563 –5.029 0.704

Sand Creek 3 Total phosphorus Total manganese 24 9 0.842 –4.469 0.672

Henderson 3 Total phosphorus Total manganese 22 12 0.716 –4.087 0.709

ALL 3 Total phosphorus Total lead 130 45 0.809 –2.129 0.657

Union 1 Total phosphorus Total lead 27 9 0.958 0.110 0.029

Denver 1 Total phosphorus Total lead 34 11 0.683 0.268 0.023

Tollgate 1 Total phosphorus Total lead 19 4 0.958 0.118 0.043

Sand Creek 3 Total phosphorus Total lead 24 9 0.845 –1.764 0.538

Henderson 3 Total phosphorus Total lead 22 12 0.404 –0.962 0.391
68 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table 11. Results of linear regression analyses, water years 2002–2005.—Continued

[Group indicates that data represent results from all stations (ALL), South Platte River below Union Avenue at Englewood (Union), South Platte River at Denver 

(Denver), Tollgate Creek above 6th Avenue at Aurora (Tollgate), Sand Creek at mouth near Commerce City (Sand Creek), or South Platte River at Henderson 

(Henderson); T indicates transform: 1, no transform; 2 natural log transform for dependent variable; 3, natural log transform for both variables; Dependent and 

Independent describe regression variables. n, number of values used in regression; M, number of missing values; r2, coefficient of determination (commonly 

referred to as r-squared). Intercept, y-axis intercept of the linear regression line; Slope, slope of the linear regression line. Regressions with r2 values greater than 

0.65 are shown in bold print]

Station T Water-quality properties or constituents n M r

2 Intercept Slope Dependent Independent

ALL 3 Total phosphorus Total zinc 129 46 0.691 –3.389 0.670

Union 3 Total phosphorus Total zinc 27 9 0.939 –4.250 0.877

Denver 1 Total phosphorus Total zinc 34 11 0.859 0.144 0.006

Tollgate 1 Total phosphorus Total zinc 19 4 0.656 –4.298 0.861

Sand Creek 3 Total phosphorus Total zinc 23 10 0.491 –2.262 0.394

Henderson 3 Total phosphorus Total zinc 22 12 0.634 –2.505 0.579

ALL 3 Residue at 105°C Total copper 125 50 0.751 1.760 1.200

Union 3 Residue at 105°C Total copper 25 11 0.905 1.403 1.495

Denver 3 Residue at 105°C Total copper 33 12 0.828 1.479 1.250

Tollgate 3 Residue at 105°C Total copper 18 5 0.937 1.350 1.427

Sand Creek 3 Residue at 105°C Total copper 24 9 0.875 0.779 1.552

Henderson 1 Residue at 105°C Total copper 21 13 0.704 1.241 1.195

ALL 3 Residue at 105°C Total manganese 125 50 0.624 –1.058 1.057

Union 1 Residue at 105°C Total manganese 25 11 0.897 –143.611 1.162

Denver 3 Residue at 105°C Total manganese 33 12 0.750 –1.940 1.244

Tollgate 1 Residue at 105°C Total manganese 18 5 0.358 –1,756.927 338.760

Sand Creek 3 Residue at 105°C Total manganese 24 9 0.766 –2.137 1.212

Henderson 3 Residue at 105°C Total manganese 21 13 0.472 –1,403.339 267.747

ALL 2 Residue at 105°C Dissolved lead 87 88 0.109 530.578 134.118

Henderson 1 Residue at 105°C Dissolved lead 22 12 0.935 182.790 319.447

ALL 3 Residue at 105°C Total lead 125 50 0.739 3.055 0.844

Union 1 Residue at 105°C Total lead 25 11 0.900 3.044 1.013

Denver 3 Residue at 105°C Total lead 33 12 0.861 2.589 0.942

Tollgate 3 Residue at 105°C Total lead 18 5 0.915 3.052 1.030

Sand Creek 3 Residue at 105°C Total lead 24 9 0.892 2.533 1.046

Henderson 1 Residue at 105°C Total lead 21 13 0.528 2.695 0.805

ALL 3 Residue at 105°C Ammonia + organic N 166 9 0.396 4.432 1.061

Union 1 Residue at 105°C Ammonia + organic N 34 2 0.847 –137.831 256.262

Denver 3 Residue at 105°C Ammonia + organic N 43 2 0.569 4.191 1.242

Tollgate 3 Residue at 105°C Ammonia + organic N 21 2 0.522 4.283 1.659

Sand Creek 3 Residue at 105°C Ammonia + organic N 32 1 0.391 4.340 1.207

Henderson 3 Residue at 105°C Ammonia + organic N 32 2 0.254 3.478 1.344

ALL 3 Residue at 105°C Total phosphorus 166 9 0.480 5.752 0.981

Union 1 Residue at 105°C Total phosphorus 34 2 0.856 –99.591 892.699

Denver 2 Residue at 105°C Total phosphorus 43 2 0.462 376.397 295.045

Tollgate 3 Residue at 105°C Total phosphorus 21 2 0.809 6.374 1.452

Sand Creek 3 Residue at 105°C Total phosphorus 32 1 0.583 5.957 1.335

Henderson 1 Residue at 105°C Total phosphorus 32 2 0.762 –857.620 781.536

ALL 3 Residue at 105°C Total zinc 124 51 0.470 2.017 0.731

Union 1 Residue at 105°C Total zinc 25 11 0.903 –71.066 6.514

Denver 3 Residue at 105°C Total zinc 33 12 0.557 –817.903 245.747

Tollgate 1 Residue at 105°C Total zinc 18 5 0.808 –220.809 6.341

Sand Creek 3 Residue at 105°C Total zinc 23 10 0.268 2.654 0.549

Henderson 1 Residue at 105°C Total zinc 21 13 0.598 –1,040.420 265.738

ALL 1 Dissolved zinc Total zinc 130 45 0.685 –6.709 0.188

Sand Creek 1 Dissolved zinc Total zinc 23 10 0.443 –182.832 46.270
Summary 69

Annual means used to identify simple upward or downward 

temporal trends for period 2 are shown in figure 3. Relatively few 

trends were identified in period 1 (Bossong and others, 2005) 

and most trends in period 1 were local, occurring at only one or 

two stations. Some of the period 1 trends indicated decreases in 

concentrations. Trends for total organic carbon, ammonia plus 

organic nitrogen, and total phosphorus all indicated a consistent 

decrease at some stations during period 1, and about the same 

number indicated increases in values for specific conductance, 

or concentrations of hardness, orthophosphate, and ammonia at 

some stations. Annual means indicate more trends in period 2 

than were indicated in period 1, and many of the period 2 trends 

are widespread. Two of the period 2 trends are for properties and 

constituents that indicated trends in period 1. Hardness indicated an upward trend at some stations in period 1 and a widespread downward trend in period 2; total phosphorus indicated 

a downward trend at some stations in period 1 and a widespread 

downward trend in period 2. Overall, more trends were observed 

in period 2 than in period 1, and most of the period 2 trends indicated decreases.

In period 1 there were relatively few strong or very strong 

regressions, and only one pair, total manganese with total lead, 

was widespread, occurring at all stations. In period 2 there 

were more strong and very strong regressions than in period 1, 

and many of them were widespread (table 11). For instance, 

total manganese was strongly or very strongly related to total 

lead, total copper, and residue on evaporation at 105 degrees 

Celsius at many stations in period 2.

Summary

The quality of stormwater runoff is of interest to many 

management and regulatory agencies as well as academia, 

scientists, recreational stream users, and the general public. 

The basic character of stormwater runoff is of general interest to all, whereas more detailed information concerning 

spatial and temporal variations may be of interest to management and regulatory agencies. In response to these interests, 

the U.S. Geological Survey, in cooperation with the Urban 

Drainage and Flood Control District, systematically collected 

stormwater samples during wet weather from a network of 

five monitoring stations in and around metropolitan Denver, 

Colorado. This report describes the quality of stormwater 

sampled from October 1, 2001, to October 11, 2005. The 

network includes three stations known as Union, Denver, and 

Henderson on the principal, or receiving, stream draining the 

area, the South Platte River. The network also includes stations 

on two tributary streams: Sand Creek, which is tributary to 

the South Platte River, and Tollgate Creek, which is tributary 

to Sand Creek. Sampling was facilitated using refrigerated or, 

in one case, iced automatic pumping samplers that were used 

to collect composite and discrete samples. Time-weighted 

composite stormwater samples were collected by compositing 

individual aliquots of stormwater that were obtained at fixedtime increments typically during 12-hour intervals; bacteriological samples were collected manually from streams during 

some storms. Discrete samples of stormwater also were collected during two storms; the discrete samples were submitted 

for laboratory analyses individually and were not physically 

composited. Various types of quality-assurance and qualitycontrol samples also were collected to help evaluate laboratory 

performance, to evaluate relations between fixed-point and 

cross-section depth-integrated samples, and to document field 

and equipment conditions that could potentially affect results.

Composite samples for analysis of physical properties, 

major ions (in 2005), organic carbon, nutrients, and dissolved 

and total copper, lead, manganese, and zinc were submitted 

to the Metro Wastewater Reclamation District Laboratory (in 

water year 2002) and the U.S. Geological Survey National 

Water Quality Laboratory (in water years 2003–2005). Bacteriological samples were submitted to the Metro Wastewater 

Reclamation District Laboratory for determination of the 

bacteriological indicators Escherichia coli and fecal coliform. 

Discrete samples were submitted to the U.S. Geological 

Survey National Water Quality Laboratory for analysis of a 

suite of water-quality properties and constituents similar to 

those analyzed for in the composite samples; however, the 

discrete samples were not analyzed for total metals. Qualitycontrol and quality-assurance results for laboratory performance indicate that results from both the National Water 

Quality Laboratory and the Metro Wastewater Reclamation 

District laboratory are consistently close to most probable 

values determined on the basis of results from as many as 

100 laboratories across the country. Other quality-control and 

Table 12. Ninety-five percent confidence bounds for means 

of selected water-quality properties and constituents period 1 

(water years 1998–2001) and period 2 (water years 2002–2005).

[ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees 

Celsius; C, Celsius; mg/L, milligrams per liter; N, nitrogen; P, phosphorus; 

μg/L, micrograms per liter]

Water-quality property 

or constituent

95-percent confidence bounds 

on mean value

Period 1 Period 2

Lower Upper Lower Upper

Mean streamflow, in ft3

/s 758 1,030 492 780

Streamflow volume, in acre-feet 684 928 441 695

Specific conductance, in μS/cm 593 653 614 713

Hardness, as calcium carbonate, 

in mg/L

190 206 180 203

Residue at 105°C, in mg/L 471 620 325 573

Ammonia, as N, in mg/L 0.75 1.04 0.42 0.68

Nitrite + nitrate, as N, in mg/L 1.21 1.50 1.34 1.71

Ammonia + organic nitrogen,

 as N, in mg/L

2.37 2.81 2.00 2.46

Orthophosphate, as P, in mg/L 0.22 0.27 0.22 0.30

Total phosphorus, as P, in mg/L 0.63 0.75 0.83 1.09

Dissolved organic carbon, in mg/L 7.88 10.4 9.08 10.8

Dissolved copper, in μg/L 6.88 8.7 3.04 4.24

Total copper, in μg/L 21.1 26.0 20.5 26.4

Total lead, in μg/L 29.3 36.8 17.7 24.5

Dissolved manganese, in μg/L 162 236 49.1 107

Total manganese, in μg/L 406 571 450 590

Dissolved zinc, in μg/L 62.5 94.3 17.3 31.5

Total zinc, in μg/L 169 214 103 162
70 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

quality-assurance results indicate no substantial contribution 

to concentrations from ambient field conditions or sampling 

equipment, and that samples collected from the fixed-point 

locations by pumping samplers are similar to, but not always 

the same as, samples collected using methods that vertically 

and horizontally integrate flow in the channel cross section.

Streamflow characteristics associated with 176 composite 

stormwater samples indicate that most samples were collected 

from falling or event hydrographs and that only a few samples 

were collected from rising hydrographs. Results from laboratory analyses of the composite samples indicate spatial patterns 

in which concentrations for some constituents increase with 

contributing drainage area in the South Platte River and Sand 

Creek, but no well-defined relation was identified between concentration and the amount of urban land cover identified using 

the U.S. Geological Survey National Land Cover data.

Results from 22 discrete samples, collected during two 

storms used to obtain composited results with various weighting 

methods, indicate that correlation coefficients between timeweighted and volume-weighted concentrations were generally 

at least 0.65, indicating a strong direct correlation between the 

two weighting methods for the stations involved in this study. 

In addition, the central tendency for relative percent differences 

between the time- and volume-weighting methods typically has 

a value of about 10, indicating good agreement for these weighting methods for data collected as part of this study.

Comparison of analytical results from stormwater samples 

to numeric standards developed by the Colorado Department of 

Public Health and Environment on the basis of use classifications indicates that, for water-quality properties and constituents 

other than bacteriological indicators, there were very few exceptions to numeric standards. Bacteriological indicators, however, such as Escherichia coli and fecal coliform consistently 

exceeded numeric standards in all bacteriological samples.

An evaluation of annual means of analytical results from 

composite stormwater samples indicates the presence of some 

simple upward and downward trends in concentrations. In 

general, for annual means of results for all stations, hardness, 

ammonia plus organic nitrogen, total phosphorus, most dissolved metals (lead, manganese, and zinc), and all total metals 

(copper, lead, manganese, and zinc) indicate annual means 

that decrease each year, or downward trends. In addition, some 

trends were indicated only at individual stations in the network 

rather than at all. Ammonia as nitrogen at Union, Denver, and 

Henderson; orthophosphate at Sand Creek; and nitrite plus 

nitrate at Denver and Henderson all indicate decreasing annual 

means, or downward trends. Only nitrite plus nitrate at Union 

and total copper and lead at Sand Creek showed consistently 

increasing annual means, or upward trends.

Linear regressions of analytical results from composite 

stormwater samples indicate widespread strong regressions 

(coefficient of determination or r2 equal or greater than 0.65) 

among major ions. In addition, many widespread and strong 

regressions were noted among constituents known to have a 

particulate component; these include organic nitrogen plus 

ammonia with total phosphorus, total copper, and total zinc; 

total phosphorus with total copper, total lead, and total zinc; 

residue on evaporation at 105 degrees Celsius with total copper 

and total lead; and several additional regressions involving the 

metals (total copper with total lead, total manganese, and total 

zinc; and total lead with total zinc). Strong regressions generally are not widespread and occur mostly locally at individual 

stations for very soluble nonmajor constituents that have a very 

small or even no particulate component. The regression between 

nitrite plus nitrate and orthophosphate is the only strong regression for soluble constituents that are not major ions, at all stations. Together, relatively weak correlation coefficients between 

water-quality properties and constituents, with mean streamflow, indicate a heterogeneous and mixed system.

Results from this study were compared to results 

from an earlier U.S. Geological Survey study for water 

years 1998–2001 that collected data from the same network 

of stations using the same programmatic goals and samplecollection protocols. Samples from the two periods, based 

on the distribution of mean streamflow associated with 

composite samples, appear to represent similar conditions. 

There were many more exceptions to numeric standards in 

the earlier period than in this study. In addition, pooled means 

for all stations from this study are numerically lower and the 

95-percent confidence intervals do not overlap with those 

from the earlier study for some metals (dissolved copper, 

manganese, and zinc; and total zinc) and indicate statistically 

significant decreases in concentrations. Simple downward 

trends in annual means were widespread for many constituents 

in this study and in general were more prevalent than in the 

earlier study.

References Cited

American Public Health Association, 1998, Standard methods 

for the examination of water and wastewater (20th ed.): 

Washington, D.C., American Public Health Association, 

American Water Works Association, and Water Environment Federation, p. 3–37—3–43.

Blakely, S.R., Mustard, M.H., and Doerfer, J.T., 1983, Analysis of the August 14, 1980, rainstorm and storm runoff to 

the South Platte River in the southern Denver metropolitan 

area, Colorado: U.S. Geological Survey Water-Resources 

Investigations Report 83–4138, 35 p.

Bossong, C.R., Stevens, M.R., Doerfer, J.T., and Glass, B.R., 

2005, Summary and evaluation of the quality of stormwater 

in Denver, Colorado, water years 1998–2001: U.S. Geological Survey Scientific Investigations Report 2005–5150, 

90 p.

Brenton, R.W., and Arnett, T.L., 1993, Methods of analysis by the 

U.S. Geological Survey National Water Quality Laboratory—

Determination of dissolved organic carbon by uv-promoted 

persulfate oxidation and infrared spectrometry: U.S. Geological Survey Open-File Report 92–480, 12 p.
References Cited 71

Colorado Department of Public Health and Environment, 

2005, Regulation no. 31, The basic standards and methodologies for surface water (5 CCR 1002–31): Colorado 

Department of Public Health and Environment, Water Quality Control Commission, variously paginated.

Colorado Department of Public Health and Environment, 

2006, Regulation no. 38, Classification and numeric standards for South Platte River basin (8/14/2006 effective): 

Colorado Department of Public Health and Environment, 

Water Quality Control Commission, variously paginated.

Denver Regional Council of Governments, 1983, Urban 

runoff quality in the Denver region: Denver, Colo., Denver 

Regional Council of Governments, 156 p.

Ellis, S.R., 1978, Hydrologic data for urban storm runoff from 

three localities in the Denver metropolitan area, Colorado: 

U.S. Geological Survey Open-File Report 78–410, 135 p.

Ellis, S.R., and Alley, W.B., 1979, Hydrologic data for urban 

storm runoff from three localities in the Denver metropolitan area, Colorado: U.S. Geological Survey WaterResources Investigations Report 79–64, 60 p.

Ellis, S.R., Doerfer, J.T., Mustard, M.H., Blakely, S.R., and 

Gibbs, J.W., 1984, Analysis of urban storm-runoff data and 

the effects on the South Platte River, Denver metropolitan 

area, Colorado: U.S. Geological Survey Water-Resources 

Investigations Report 84–4159, 66 p.

Ellis, S.R., and Mustard, M.H., 1985, A summary of urban runoff 

studies in the Denver metropolitan area, Colorado: U.S. Geological Water-Resources Investigations Report 84–4072, 

31 p.

Faires, L.M., 1993, Methods of analysis by the U.S. Geological 

Survey National Water Quality Laboratory—Determination 

of metals in water by inductively coupled plasma-mass spectrometry: U.S. Geological Survey Open-File Report 92–634, 

28 p.

Fisher, S.R., and Potter, K.W., 1989, Methods for determining 

compliance with groundwater quality regulations at waste 

disposal facilities: University of Wisconsin-Madison, for 

Wisconsin Department of Natural Resources, Bureau of 

Water Resources and Bureau of Solid and Hazardous Waste 

Management, variously paginated.

Fishman, M.J., ed., 1993, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory—

Determination of inorganic and organic constituents in water 

and fluvial sediments: U.S. Geological Survey Open-File 

Report 93–125, 217 p.

Fishman, M.J., and Friedman, L.C., 1989, Methods for 

determination of inorganic substances in water and fluvial 

sediments: U.S. Geological Survey Techniques of WaterResources Investigations, book 5, chap. A1, 545 p.

Garbarino, J.R., and Struzeski, T.M., 1998, Methods of analysis by the U.S. Geological Survey National Water Quality 

Laboratory—Determination of elements in whole-water 

digests using inductively coupled plasma-optical emission 

spectrometry and inductively coupled plasma-mass spectrometry: U.S. Geological Survey Open-File Report 98–165, 

101 p.

Gibbons, R.D., 1994, Statistical methods for groundwater 

monitoring: New York, John Wiley and Sons, 286 p.

Gibbs, J.W., 1981, Hydrologic data for urban storm runoff 

from nine sites in the Denver metropolitan area, Colorado: 

U.S. Geological Survey Open-File Report 81–682, 142 p.

Gibbs, J.W., Arnold, L.M., and Reed, R.L., 1983, Hydrologic 

data for the drainage basins of Chatfield and Cherry Creek 

Lakes, Denver metropolitan area: U.S. Geological Survey 

Open-File Report 83–857, 244 p.

Gibbs, J.W., and Doerfer, J.T., 1982, Hydrologic data for urban 

storm runoff in the Denver metropolitan area, Colorado: 

U.S. Geological Survey Open-File Report 82–872, 553 p.

Hahn, G.J., and Meeker, W.Q., 1991, Statistical intervals, a 

guide for practitioners: New York, John Wiley and Sons, 

392 p.

Hall, D.C., and Duncan, A.C., 1980, Hydrologic data from 

Upper Grange Hall Creek Basin, Northglenn, Adams 

County, Colorado: U.S. Geological Survey Open-File 

Report 80–578, 132 p.

Hall, D.C., and Duncan, A.C., 1981, Characterization of urban 

runoff from Grange Hall Creek at Northglenn, Adams 

County, Colorado: U.S. Geological Survey Water-Resources 

Investigations Report 81–28, 50 p.

Helsel, D.R., 2005, Nondetects and data analysis: statistics for 

censored environmental data: New York, John Wiley and 

Sons, 250 p.

Hem, J.D., 1985, Study and interpretation of the chemical 

characteristics of natural water (3d ed.): U.S. Geological 

Survey Water-Supply Paper 2254, 263 p.

Hoffman, G.L., Fishman, M.J., and Garbarino, J.R., 1996, 

Methods of analysis by the U.S. Geological Survey National 

Water Quality Laboratory—In-bottle acid digestion of 

whole-water samples: U.S. Geological Survey Open-File 

Report 96–225, 28 p.

Mustard, M.H., Ellis, S.R., and Gibbs, J.W., 1985, Runoff 

and washoff loads from rainfall-simulation experiments on 

a street surface and a native pasture in the Denver metropolitan area, Colorado: U.S. Geological Survey Open-File 

Report 84–820, 44 p.
72 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Patton, C.J., and Truitt, E.P., 1992, Methods of analysis by the 

U.S. Geological Survey National Water Quality Laboratory—

Determination of total phosphorus by a Kjeldahl digestion 

method and an automated colorimetric finish that includes 

dialysis: U.S. Geological Survey Open-File Report 92–146, 

39 p.

Patton, C.J., and Truitt, E.P., 2000, Methods of analysis by the 

U.S. Geological Survey National Water Quality Laboratory—

Determination of ammonium plus organic nitrogen by a 

Kjeldahl digestion method and an automated photometric 

finish that includes digest cleanup by gas diffusion: U.S. Geological Survey Open-File Report 2000–170, 31 p. 

Pearson, K., 1901, On lines and planes of closest fit to systems 

of points in space: Philosophical Magazine, v. 2, p. 559–772.

Rantz, S.E., and others, 1982, Measurement and computation of streamflow—Volume 1, Measurement of stage 

and discharge, and Volume 2, Computation of discharge: 

U.S. Geological Survey Water-Supply Paper 2175, 630 p.

U.S. Environmental Protection Agency, 1989, Statistical 

analysis of ground-water monitoring data at RCRA facilities 

(Interim Final Guidance): U.S. Environmental Protection 

Agency, report number EPA/530–SW–09–026, 84 p.

U.S. Environmental Protection Agency, 1992, Statistical 

analysis of ground-water monitoring data at RCRA facilities 

(Addendum to Interim Final Guidance): U.S. Environmental 

Protection Agency, report number EPA/530–R–93–003, 

84 p.

U.S. Geological Survey, variously dated, National field manual for the collection of water-quality data: U.S. Geological 

Survey Techniques of Water-Resources Investigations, book 9, 

chaps. A1–A9, available online at http://water.usgs.gov/pubs/

twri9A/.

U.S. Geological Survey, 2002–2005, Water resources data for 

Colorado, water years 2002–2005: U.S. Geological Survey Water-Data Reports CO–02–1 to CO–05–1 (published 

annually).

U.S. Geological Survey, 2003, National land cover data, 1992: 

accessed November 5, 2003, at URL http://edc.usgs.gov/

products.landcover/nlcd.html

Woodworth, M.T., and Connor, B.F., 2003, Results of the 

U.S. Geological Survey’s analytical evaluation program 

for standard reference samples distributed in March 2003: 

U.S. Geological Survey Open-File Report 2003–261, 

109 p.
Appendix. Hydrograph Classification 73

The portion of the storm hydrograph associated with each composite sample was classified as “rising,” “falling,” “event,” or 

“unclassified.” Examples for rising, falling, and event classifications are in figure A1. Samples classified as rising or falling are 

associated with the rising or falling limb of a storm hydrograph. Samples classified as event are associated with both a rising and 

falling portion of a storm hydrograph. In some cases, mostly at Tollgate, streamflow data were not available and samples were 

categorized as unclassified.

The hydrographs in figure A1 indicate examples of each classification and provide readers with a sense for storm hydrographs 

and the different classifications. Additional information that characterizes storm hydrographs sampled as part of this study in terms 

of peak streamflow and runoff volumes are in table 6. Summer storm hydrographs commonly originate from convective storm cells 

and have very steep rising limbs, steep falling limbs, and a duration that may be 12 hours or less in which case samples are classified as “event” (fig. A1B). Some summer storm hydrographs are longer and may have samples from the rising and falling limbs 

(fig. A1A). Spring storm hydrographs sometimes originate from snowfall that accumulates as wet snow over a period of hours and 

then melts over a period of a day or more. Spring storm hydrographs may have multiple peaks and a duration of days.

Appendix. Hydrograph Classification
74 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Figure A1. Example storm hydrographs showing (A) rising, falling, and (B) event sample classifications.

South Platte River at Henderson - Storm 1

South Platte River at Henderson - Storm 6

A

B

PRECIPITATION,

IN INCHES

DISCHARGE,

IN CUBIC FEET PER SECOND

0.0

0.05

0.1

0.15

2,500

2,000

0

500

1,000

1,500

PRECIPITATION,

IN INCHES

DISCHARGE,

IN CUBIC FEET PER SECOND

0.0

0.05

0.1

0.15

5,000

4,000

0

1,000

2,000

3,000

1 2 3 4 5

APRIL 2004

9 10 11 12 13

AUGUST 2004

Sample portion of hydrograph

Composite sample delimiter

Sample portion of hydrograph

Composite sample delimiter

Precipitation

depth

(inches)

Beginning Ending

Computed

mean runoff

(cubic feet per second)

Computed

volume

(acre-feet)

Sample

(YYYYMMDD) (HHMM) (MMDD) (HHMM) classification

Precipitation

depth

(inches)

Beginning Ending

Computed

mean runoff

(cubic feet per second)

Computed

volume

(acre-feet)

Sample

(YYYYMMDD) (HHMM) (MMDD) (HHMM) classification

Hydrograph

Sample 1

Sample 2

Discharge record from Colorado Division of Water Resources

Precipitation record from Urban Drainage and Flood Control District gage at Henderson

Beginning time in year (YYYY), month (MM), day (DD), hour (HH), and minute (MN)

na indicates not applicable

Hydrograph

Sample 1

Discharge record from Colorado Division of Water Resources

Precipitation record from Urban Drainage and Flood Control District gage at Henderson

Beginning time in year (YYYY), month (MM), day (DD), hour (HH), and minute (MN)

na indicates not applicable

20040401

20040402

20040403

1200

2148

0948

0404

0403

0403

1200

0848

2048

0.85

na

na

372

515

847

2211

468

770

na

rising

falling

20040809

20040810

1200

2205

0812

0811

1200

1205

0.19

na

611

1293

3632

1496

na

event

Times

Times
Appendix. Hydrograph Classification 75

Figure A2. Graphs showing results from discrete sampling events (A) August 28, 2002, at South Platte River at Henderson, 

(B) August 18, 2004, at South Platte River at Denver. STREAMFLOW, IN CUBIC FEET PER SECOND 2,500

2,000

1,500

1,000

500

Indicates sample times

and discharges

August 28 HOURS

2002

2000 2100 2200 2300 0 100 200 300 400 500 600 700

EXPLANATION

Concentration

Time weighted concentration

Discharge weighted concentration

Volume weighted concentration

Milligrams per liter

Micrograms per liter

Microsiemens per centimeter

Less than 25 percentile

25th to 75th percentile

Greater than 75th percentile

[ ]

T

Q

v

mg/L

μg/L

μS/cm

Hardness,

mg/L

Specific

conductance,

μS/cm

Residue

on evap.

at 105°C,

mg/L

Ammonia,

mg/L

Ammonia +

organic N,

mg/L

Nitrite +

nitrate as N,

mg/L

Orthophosphate,

mg/L

Phosphorus,

total,

mg/L

Organic

carbon,

dissolved,

mg/L

Copper,

total,

μg/L

Lead,

total,

μg/L

Zinc,

total

μg/L

SAMPLE CONCENTRATION AND WEIGHTED VALUE,

AS PERCENTILE

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

A South Platte River at Henderson

2000 2100 2200 2300 0 100 200 300 400 500 600 700
76 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Figure A2. Graphs showing results from discrete sampling events (A) August 28, 2002, at South Platte River at Henderson, 

(B) August 18, 2004, at South Platte River at Denver.—Continued STREAMFLOW, IN CUBIC FEET PER SECOND 6,500

5,500

4,500

3,500

1,500

500

2,500

Indicates sample times

and discharges

August 18 HOURS

2004

1600 1700 1800 1900 2000 2100 2200 2300 0 100 200 300 400 500 600 700 800 900

EXPLANATION

Concentration

Time weighted concentration

Discharge weighted concentration

Volume weighted concentration

Milligrams per liter

Micrograms per liter

Microsiemens per centimeter

Less than 25 percentile

25th to 75th percentile

Greater than 75th percentile

[ ]

T

Q

v

mg/L

μg/L

μS/cm

Hardness,

mg/L

Specific

conductance,

μS/cm

Alkalinity

fixed

end-point,

mg/L

Chloride,

dissolved,

mg/L

Fluoride,

dissolved,

mg/L

Sulfate,

dissolved,

mg/L

Residue

on evap.

at 105°C,

mg/L

Ammonia,

mg/L

Ammonia +

organic N,

mg/L

Nitrite +

nitrate as N,

mg/L

Orthophosphate,

mg/L

Phosphorus,

total,

mg/L

Organic

carbon,

dissolved,

mg/L

Copper,

total,

μg/L

Lead,

total,

μg/L

Zinc,

total,

μg/L

SAMPLE CONCENTRATION AND WEIGHTED VALUE,

AS PERCENTILE

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

[ ]

T

Q

v

B South Platte River at Denver

1600 1700 1800 1900 2000 2100 2200 2100 0 100 200 300 400 500 600 700 800 900
Appendix. Hydrograph Classification 77

This page intentionally

left blank.
78 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table A1. Results from discrete samples collected during storms and computed time, discharge, and volume-weighted concentrations, 

with relative percent differences.

[Samples collected with pumping samplers. Analytical determination made at USGS National Water Quality Laboratory; –999, missing value (isolated missing 

values were replaced with an average of the preceding and following values for weighting computations); values greater than –999 and less than 0 are censored. 

Laboratory estimated values included in weighting computations; Weighting method—Time: (summation of interval × concentration) / sampling period time, where 

interval is the sum of the midpoint between sample time preceding and following sample times—Discharge: (summation of discharge × concentration) / summation 

of discharge—Volume: (summation of interval × discharge × concentration) / (summation of interval × discharge); RPD, relative percent difference: 1, time and 

discharge; 2, time and volume; 3, discharge and volume; wh, whole water unfiltered; wf, whole water filtered; fxdEP, fixed endpoint. ft3/s, cubic feet per second; 

μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; CaCO3, calcium carbonate; la, laboratory; NO2, nitrite; NO3, nitrate; N, nitrogen; P, phosphorus; 

μg/L, micrograms per liter]

Weighting method RPD1 RPD2 RPD3 Time Discharge Volume

Storm 1

Station number 06720500 (Henderson)

Date (yyyymmdd) -- -- -- -- -- --

Time (hhmm) -- -- -- -- -- --

Decimal julian day -- -- -- -- -- --

00065 Gage height (feet) 5.702 5.839 5.850 –2.380 –2.571 –0.190

00061 Discharge (ft3

/s) 1,297.708 1,459.559 1,453.353 –11.740 –11.315 0.426

00403 pH, wh, laboratory (standard units) 6.814 6.848 6.766 –0.499 0.708 1.208

Field conductivity (μS/cm) 657.141 716.197 652.017 –8.600 0.783 9.381

90095 Specific conductance (μS/cm) 652.823 712.070 648.919 –8.682 0.600 9.280

00900 Hardness, wh (mg/L as CaCO3

) 157.956 167.942 155.456 –6.129 1.595 7.722

00915 Calcium, wf (mg/L) 47.237 50.202 46.492 –6.086 1.589 7.673

00925 Magnesium, wf (mg/L) 9.665 10.420 9.577 –7.522 0.914 8.434

00530 Residue, wh (mg/L) 411.039 558.048 479.436 –30.340 –15.362 15.154

00608 Nitrogen ammonia (mg/L as N) 2.253 2.674 2.297 –17.074 –1.900 15.186

00625 Nitrogen ammonia + organic (mg/L as N) 9.102 12.074 10.169 –28.071 –11.067 17.137

00631 NO2 + NO3 wf (mg/L as N) 3.395 3.752 3.495 –10.002 –2.911 7.096

00671 Orthophosphate, wf (mg/L as P) 0.390 0.411 0.348 –5.043 11.470 16.489

00665 Phosphorus, wh (mg/L) 3.002 4.425 3.487 –38.303 –14.944 23.698

00681 Carbon, organic, wf (mg/L) 11.002 10.958 11.274 0.406 –2.439 –2.845

01040 Copper, wf (μg/L) 2.195 2.268 2.164 –3.243 1.430 4.672

01049 Lead, wf (μg/L) 0.405 0.456 0.417 –11.900 –3.072 8.836

01090 Zinc, wf (μg/L) 16.977 17.800 16.877 –4.733 0.593 5.325

Storm 2

Station number 06714000 (Denver)

Date (yyyymmdd) -- -- -- -- -- --

Time (hhmm) -- -- -- -- -- --

Decimal julian day -- -- -- -- -- --

00065 Gage height feet 7.218 7.845 7.679 –8.317 –6.186 2.134 

00061 Discharge (ft3/s) 3,775.782 4,743.822 4,448.460 –22.725 –16.358 6.426 

00403 pH, wh, laboratory (standard units) 7.338 7.408 7.354 –0.941 –0.218 0.723

90095 Specific conductance, wh (μS/cm) 241.267 199.072 209.432 19.164 14.127 –5.072

00900 Hardness, wh (mg/L as CaCO3

) 63.706 50.426 53.575 23.272 17.277 –6.056 

00915 Calcium, wf (mg/L) 19.730 15.762 16.737 22.360 16.414 –6.000

00925 Magnesium, wf (mg/L) 3.491 2.685 2.844 26.097 20.417 –5.757

00935 Potassium, wf (mg/L) 3.197 2.931 2.983 8.679 6.930 –1.752 

90410 Alkalinity, wh, fxdEP, la (mg/L as CaCO3) 60.618 54.620 56.450 10.409 7.120 –3.295 

00940 Chloride, wf (mg/L) 16.191 12.284 13.003 27.440 21.841 –5.684

00950 Fluoride, wf (mg/L) 0.279 0.235 0.251 17.165 10.724 –6.471

00945 Sulfate, wf (mg/L) 34.515 26.416 27.931 26.586 21.086 –5.578

00530 Residue, wh (mg/L) 416.646 465.550 456.594 –11.087 –9.149 1.942

00625 NH3

 + org N, wu (mg/L as N) 2.397 2.599 2.502 –8.074 –4.277 3.801 

00608 Ammonia, wf (mg/L as N) 0.214 0.253 0.230 –16.376 –6.908 9.495

00631 NO2 + NO3

, wf (mg/L as N) 0.659 0.578 0.589 13.199 11.262 –1.944

00671 Orthophosphate, wf (mg/L as P) 0.129 0.128 0.125 0.841 3.045 2.205

00665 Phosphorus, wh (mg/L) 0.863 0.956 0.922 –10.254 –6.589 3.671

00681 Organic carbon, wf (mg/L) 6.068 5.931 5.858 2.274 3.518 1.245

01040 Copper, wf (μg/L) 1.779 1.663 1.628 6.754 8.915 2.164

01049 Lead, wf (μg/L) 0.136 0.141 0.132 –3.619 3.231 6.848

01090 Zinc, wf (μg/L) 3.918 3.894 3.549 0.615 9.886 9.273
Appendix. Hydrograph Classification 79

Table A1. Results from discrete samples collected during storms and computed time, discharge, and volume-weighted concentrations, 

with relative percent differences.—Continued

[Samples collected with pumping samplers. Analytical determination made at USGS National Water Quality Laboratory; –999, missing value (isolated missing 

values were replaced with an average of the preceding and following values for weighting computations); values greater than –999 and less than 0 are censored. 

Laboratory estimated values included in weighting computations; Weighting method—Time: (summation of interval × concentration) / sampling period time, where 

interval is the sum of the midpoint between sample time preceding and following sample times—Discharge: (summation of discharge × concentration) / summation 

of discharge—Volume: (summation of interval × discharge × concentration) / (summation of interval × discharge); RPD, relative percent difference: 1, time and 

discharge; 2, time and volume; 3, discharge and volume; wh, whole water unfiltered; wf, whole water filtered; fxdEP, fixed endpoint. ft3/s, cubic feet per second; 

μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; CaCO3, calcium carbonate; la, laboratory; NO2, nitrite; NO3, nitrate; N, nitrogen; P, phosphorus; 

μg/L, micrograms per liter]

Discrete measurements

Storm 1

20020828 20020828 20020828 20020828 20020828 20020829 20020829 20020829 20020829

2006 2036 2106 2206 2306 106 306 506 706

241.8375 241.8583 241.8792 241.9208 241.9625 242.0458 242.1292 242.2125 242.2958

4.650 5.730 6.070 6.250 6.200 5.940 5.590 5.260 5.010

506.000 1,290.000 1,710.000 1,920.000 1,850.000 1,520.000 1,120.000 815.000 616.000

7.400 7.000 7.000 7.000 6.500 6.600 6.500 7.200 7.000

960.000 940.000 896.000 740.000 549.000 548.000 595.000 647.000 703.000

950.000 931.000 886.000 741.000 551.000 546.000 594.000 636.000 694.000

220.000 210.000 210.000 170.000 120.000 140.000 150.000 160.000 170.000

66.200 63.400 61.400 50.900 37.000 41.100 45.000 48.100 50.500

13.800 13.200 12.900 10.900 7.740 8.430 8.920 9.540 10.300

16.000 776.000 1,070.000 712.000 566.000 334.000 266.000 180.000 206.000

3.180 3.640 4.330 2.870 1.910 1.630 1.820 1.920 2.450

4.300 17.000 23.000 -- 9.200 6.800 6.400 5.600 5.800

3.990 4.850 4.680 4.070 3.140 3.270 3.300 2.930 2.630

0.874 0.828 0.438 0.211 0.221 0.282 0.344 0.422 0.695

1.110 6.740 9.790 -- 2.830 1.940 1.610 1.420 1.540

9.500 9.700 10.000 11.000 13.000 12.000 11.000 10.000 9.800

3.500 2.800 2.300 2.000 2.100 2.100 2.100 2.200 2.200

0.530 0.670 0.590 0.410 0.400 0.420 0.350 0.330 0.330

25.000 24.000 18.000 16.000 16.000 17.000 16.000 16.000 17.000

Storm 2

20040818 20040818 20040818 20040818 20040818 20040818 20040818 20040818 20040820 20040820 20040820 20040820 20040820

1625 1725 1825 1925 2025 2125 2225 2325 25 125 225 325 925

231.6840 231.7257 231.7674 231.8090 231.8507 231.8924 231.9340 231.9757 232.0174 232.0590 232.1007 232.1424 232.3924

4.220 6.720 6.710 7.050 7.950 8.680 8.830 8.530 8.000 7.780 7.820 7.360 5.590

667.000 2,810.000 2,800.000 3,210.000 4,690.000 6,300.000 6,660.000 5,950.000 5,000.000 4,350.000 4,430.000 3,630.000 1,650.000

7.500 7.400 6.800 7.500 7.400 7.500 7.500 7.600 7.500 7.500 7.300 7.000 7.500

763.000 176.000 165.000 192.000 209.000 156.000 160.000 172.000 175.000 218.000 222.000 240.000 345.000

230.000 44.000 38.000 49.000 48.000 40.000 38.000 41.000 49.000 55.000 55.000 62.000 98.000

68.000 13.800 12.000 15.300 14.900 12.600 12.100 13.000 15.300 17.200 17.300 19.400 30.000

14.900 2.430 2.050 2.700 2.590 1.980 1.940 2.120 2.510 2.880 2.890 3.240 5.490

6.870 2.740 2.750 3.090 3.160 2.930 2.660 2.570 2.780 2.860 2.860 3.090 3.900

142.000 43.000 37.000 51.000 57.000 55.000 49.000 50.000 52.000 58.000 59.000 63.000 76.000

70.500 12.700 10.200 13.800 11.900 8.060 7.980 9.600 11.100 13.300 13.400 14.700 25.500

0.600 0.200 –0.200 0.200 0.200 0.200 0.200 0.200 0.200 0.300 0.300 0.300 0.400

149.000 25.800 20.800 27.500 27.100 19.100 17.300 20.800 23.700 28.200 28.800 31.500 54.300

370.000 254.000 280.000 356.000 542.000 597.000 640.000 490.000 520.000 398.000 320.000 460.000 297.000

2.500 2.700 2.600 2.700 3.600 3.200 2.900 2.300 2.000 2.200 2.200 2.200 1.800

0.060 0.580 0.300 0.350 0.370 0.310 0.210 0.220 0.190 0.180 0.170 0.150 0.070

1.570 0.900 0.560 0.790 0.670 0.520 0.400 0.420 0.480 0.560 0.560 0.610 0.810

0.199 0.178 0.143 0.171 0.146 0.122 0.116 0.114 0.123 0.114 0.108 0.113 0.123

0.830 0.810 0.690 0.930 1.250 1.180 1.070 0.960 0.870 0.850 0.880 0.830 0.620

9.000 7.800 6.900 7.800 7.600 6.300 5.200 4.700 4.800 5.100 5.200 5.500 6.000

3.700 3.200 2.400 2.200 1.600 1.400 1.400 1.400 1.400 1.400 1.400 1.400 1.900

0.140 0.320 0.280 0.210 0.160 0.140 0.120 0.110 0.100 0.090 0.100 0.090 0.100

8.700 10.600 8.400 7.900 5.300 3.400 2.300 2.100 2.300 2.400 2.400 2.100 2.600
80 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table A2. Summary statistics for water-quality properties and constituents by water year for all stations, South Platte River below 

Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand Creek at mouth near 

Commerce City, and South Platte River at Henderson.—Continued

[n, number of samples; M, number of samples with missing values; N, nitrogen; P, phosphorus; Pct, percentage of samples below minimum reporting level; 

Stddev, standard deviation; Skew, skewness; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms 

per liter; --, not applicable]

Property

or constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Median

All stations

Mean streamflow,

in ft3

/s

-- 2002 44 0 0 460 258 631 2.47 14 2,780 -- --

2003 19 0 0 302 154 313 1.31 20 1,060 -- --

2004 50 0 0 864 557 1,240 3.87 7 7,570 -- --

2005 59 4 0 682 288 978 2.5 1 4,830 -- --

Streamflow volume, 

in acre-feet

-- 2002 44 0 0 410 216 554 2.4 16 2,290 -- --

2003 19 0 0 287 140 317 1.79 18 1,230 -- --

2004 50 0 0 794 506 1,140 3.75 6 6,880 -- --

2005 59 4 0 584 271 813 2.59 0 4,390 -- --

pH, in standard

pH units

W 2002 44 0 0 7.43 7.4 0.32 1.29 6.1 8 -- --

2003 19 0 0 7.36 7.25 0.36 1.12 6.8 8.35 -- --

2004 50 0 0 7.39 7.4 0.22 0.05 6.88 7.94 -- --

2005 63 0 0 7.38 7.5 0.37 0.85 6.3 7.99 -- --

Specific conductance,

in μS/cm

W 2002 41 3 0 673 613 214 0.4 342 1,130 -- --

2003 14 5 0 997 875 604 1.68 423 2,630 -- --

2004 42 8 0 614 555 240 1.02 259 1,280 -- --

2005 55 8 0 609 581 259 0.95 212 1,330 -- --

Hardness, as calcium 

carbonate, in mg/L

T 2002 41 3 0 240 235 62.2 1.1 150 415 -- --

2003 19 0 0 218 204 108 2.46 91 594 -- --

2004 50 0 0 167 152 62.3 1.27 69.1 375 -- --

2005 63 0 0 170 154 72.5 1.3 69.7 394 -- --

Calcium, in mg/L D 2002 0 44 0 -- -- -- -- -- -- -- --

2003 19 0 0 63.8 55.9 30.9 2.36 28.3 169 -- --

2004 50 0 0 50.2 46.6 18.9 1.47 21.4 117 -- --

2005 63 0 0 51.6 47.1 21.8 1.38 22 121 -- --

Magnesium, in mg/L D 2002 0 44 0 -- -- -- -- -- -- -- --

2003 19 0 0 14.3 13.1 7.8 2.54 4.9 41.8 -- --

2004 50 0 0 10.2 9.38 3.88 0.67 3.81 20.2 -- --

2005 63 0 0 10.1 8.89 4.52 1.06 3.61 22.8 -- --

Potassium, in mg/L D 2002 0 44 0 -- -- -- -- -- -- -- --

2003 0 19 0 -- -- -- -- -- -- -- --

2004 0 50 0 -- -- -- -- -- -- -- --

2005 63 0 0 4.47 4.12 1.33 1.2 2.67 8.37 -- --

Sodium, in mg/L D 2002 0 44 0 -- -- -- -- -- -- -- --

2003 0 19 0 -- -- -- -- -- -- -- --

2004 0 50 0 -- -- -- -- -- -- -- --

2005 63 0 0 60.7 52.4 33.3 1 13.9 142 -- --

Alkalinity, as calcium 

carbonate, fixed 

endpoint, in mg/L

W 2002 0 44 0 -- -- -- -- -- -- -- --

2003 0 19 0 -- -- -- -- -- -- -- --

2004 0 50 0 -- -- -- -- -- -- -- --

2005 63 0 0 86.5 85.6 23.3 0.25 48.6 139 -- --
Appendix. Hydrograph Classification 81

Table A2. Summary statistics for water-quality properties and constituents by water year for all stations, South Platte River below 

Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand Creek at mouth near 

Commerce City, and South Platte River at Henderson.—Continued

[n, number of samples; M, number of samples with missing values; N, nitrogen; P, phosphorus; Pct, percentage of samples below minimum reporting level; 

Stddev, standard deviation; Skew, skewness; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms 

per liter; --, not applicable]

Property

or constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Median

All stations—Continued

Chloride, in mg/L D 2002 0 44 0 -- -- -- -- -- -- -- --

2003 0 19 0 -- -- -- -- -- -- -- --

2004 0 50 0 -- -- -- -- -- -- -- --

2005 63 0 0 56.8 50.7 32.2 1.79 11 197 -- --

Fluoride, in mg/L D 2002 0 44 0 -- -- -- -- -- -- -- --

2003 0 19 0 -- -- -- -- -- -- -- --

2004 0 50 0 -- -- -- -- -- -- -- --

2005 63 0 0 0.52 0.45 0.23 0.68 0.2 1.08 -- --

Sulfate, in mg/L D 2002 0 44 0 -- -- -- -- -- -- -- --

2003 0 19 0 -- -- -- -- -- -- -- --

2004 0 50 0 -- -- -- -- -- -- -- --

2005 63 0 0 125 93.5 88.9 1.62 30.9 386 -- --

Residue on evaporation

at 105°C, in mg/L

T 2002 44 0 0 831 460 1,430 3.58 19 7,360 -- --

2003 17 2 0 408 404 429 1.56 26 1,530 -- --

2004 49 1 0 239 178 190 1.08 13 760 -- --

2005 62 1 3.23 352 204 429 2.78 28 2,090 10 10

E. coli, colonies per

100 mL

W 2002 10 0 0 17,100 13,000 10,700 0.86 3,300 35,000 -- --

2003 0 0 0 -- -- -- -- -- -- -- --

2004 8 0 0 4,600 3,300 4,480 0.94 460 13,000 -- --

2005 4 0 0 38,800 26,000 36,900 1.58 11,000 92,000 -- --

Fecal coliform, colonies

per 100 mL

W 2002 10 0 0 25,000 19,500 18,600 0.64 4,900 54,000 -- --

2003 0 0 0 -- -- -- -- -- -- -- --

2004 8 0 0 5,160 3,550 4,930 0.66 310 13,000 -- --

2005 4 0 0 38,000 35,000 11,200 1.46 28,000 54,000 -- --

Ammonia + organic N,

in mg/L

T 2002 41 3 0 4.03 3.3 2.37 0.64 1.3 9.2 -- --

2003 19 0 0 3.83 3.52 2.77 0.64 0.59 9.63 -- --

2004 50 0 0 3.08 2.78 2.29 2.2 0.61 12.2 -- --

2005 63 0 0 2.37 1.98 1.44 1.12 0.47 6.56 -- --

Ammonia, as N,

in mg/L

D 2002 0 44 0 -- -- -- -- -- -- -- --

2003 19 0 10.5 0.59 0.25 0.84 3.03 0.05 3.55 0.04 0.04

2004 50 0 14 0.76 0.34 0.86 1.58 0.05 3.46 0.04 0.04

2005 63 0 9.52 0.37 0.22 0.46 2.6 0.05 2.2 0.04 0.04

Nitrite + nitrate, as N,

in mg/L

D 2002 0 44 0 -- -- -- -- -- -- -- --

2003 19 0 0 1.41 0.87 1.11 1.38 0.34 4.19 -- --

2004 50 0 6 1.88 1.98 1.07 0.28 0.11 4.1 0.06 0.06

2005 63 0 0 1.3 0.94 1.03 1.86 0.33 4.7 -- --

Orthophosphate, as P, 

in mg/L

D 2002 41 3 0 0.42 0.34 0.32 1.14 0.03 1.4 -- --

2003 18 1 0 0.21 0.18 0.23 2.33 0.03 0.95 -- --

2004 50 0 8 0.26 0.17 0.22 1.05 0.02 0.81 0.01 0.01

2005 63 0 0 0.17 0.11 0.19 2.37 0.01 1 -- --
82 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table A2. Summary statistics for water-quality properties and constituents by water year for all stations, South Platte River below 

Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand Creek at mouth near 

Commerce City, and South Platte River at Henderson.—Continued

[n, number of samples; M, number of samples with missing values; N, nitrogen; P, phosphorus; Pct, percentage of samples below minimum reporting level; 

Stddev, standard deviation; Skew, skewness; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms 

per liter; --, not applicable]

Property

or constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Median

All stations—Continued

Phosphorus, as P,

in mg/L

T 2002 41 3 0 1.28 0.99 1.33 3.82 0.18 8.3 -- --

2003 19 0 5.26 1.1 1.03 0.78 0.85 0.1 2.77 0.04 0.04

2004 50 0 0 0.9 0.84 0.6 1.41 0.1 3.12 -- --

2005 63 0 0 0.75 0.61 0.59 1.56 0.07 2.76 -- --

Organic carbon,

in mg/L

D 2002 0 44 0 -- -- -- -- -- -- -- --

2003 19 0 0 10.7 8.78 4.63 0.68 4.71 20.8 -- --

2004 38 12 0 8.89 7.95 3.59 1.25 3.55 19.4 -- --

2005 63 0 0 10.4 8.12 5.51 1.65 4.3 30.1 -- --

Copper, in μg/L D 2002 41 3 0 6.22 5 6.03 2.65 2 28 -- --

2003 19 0 0 2.61 2.57 0.55 0.44 1.74 3.6 -- --

2004 50 0 0 2.63 2.5 0.75 0.46 1.31 4.59 -- --

2005 63 0 0 2.6 2.28 0.97 1.11 1.14 6.16 -- --

Copper, in μg/L T 2002 0 44 0 -- -- -- -- -- -- -- --

2003 19 0 0 26.8 24.4 18.9 0.86 3.78 72.8 -- --

2004 50 0 0 24.4 19.5 16.7 1.21 3.02 74.5 -- --

2005 63 0 0 22.1 17.3 17 1.66 2.82 87.3 -- --

Lead, in μg/L D 2002 41 3 92.7 33.3 30 25.2 0.59 10 60 10 10

2003 19 0 31.6 0.23 0.18 0.14 1.12 0.1 0.5 0.08 0.08

2004 50 0 28 0.21 0.19 0.12 1.52 0.09 0.64 0.08 0.08

2005 63 0 38.1 0.17 0.15 0.1 1.94 0.08 0.52 0.08 0.08

Lead, in μg/L T 2002 0 44 0 -- -- -- -- -- -- -- --

2003 19 0 0 24.7 19.1 20.1 0.85 1.44 66 -- --

2004 50 0 0 22.8 14.3 19.4 1.04 0.63 70.7 -- --

2005 63 0 0 19.1 13 20.2 2.38 0.67 114 -- --

Manganese, in μg/L D 2002 0 44 0 -- -- -- -- -- -- -- --

2003 19 0 0 102 52.2 109 0.72 2.95 303 -- --

2004 50 0 0 86.6 33.7 226 6.07 1.29 1,570 -- --

2005 63 0 0 55.3 20.9 101 3.59 1.07 550 -- --

Manganese, in μg/L T 2002 0 44 0 -- -- -- -- -- -- -- --

2003 19 0 0 668 693 451 0.32 79.3 1,550 -- --

2004 50 0 0 511 404 391 1.94 84 2,090 -- --

2005 63 0 0 490 413 399 2.04 62.8 2,090 -- --

Zinc, in μg/L D 2002 41 3 41.5 52.1 35 59.7 3.5 20 300 20 20

2003 19 0 0 44.6 10.4 85.2 2.86 2.55 336 -- --

2004 50 0 0 18.9 12.4 27.2 3.96 2.52 165 -- --

2005 62 1 0 9.85 7.73 8.34 2.66 1.99 50.6 -- --

Zinc, in μg/L T 2002 0 44 0 -- -- -- -- -- -- -- --

2003 19 0 0 272 165 333 2 8 1,150 -- --

2004 50 0 0 136 93.5 132 2.35 12 708 -- --

2005 62 1 0 89.1 67 74 1.63 7 348 -- --
Appendix. Hydrograph Classification 83

Table A2. Summary statistics for water-quality properties and constituents by water year for all stations, South Platte River below 

Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand Creek at mouth near 

Commerce City, and South Platte River at Henderson.—Continued

[n, number of samples; M, number of samples with missing values; N, nitrogen; P, phosphorus; Pct, percentage of samples below minimum reporting level; 

Stddev, standard deviation; Skew, skewness; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms 

per liter; --, not applicable]

Property

or constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Median

South Platte below Union Avenue at Englewood (06710247)

Mean streamflow,

in ft3

/s

-- 2002 9 0 0 116 122 59.9 0.02 37 212 -- --

2003 4 0 0 152 149 84.3 0.26 53 259 -- --

2004 9 0 0 311 215 216 0.77 120 679 -- --

2005 15 0 0 235 202 171 1.37 38 686 -- --

Streamflow volume,

in acre-feet

-- 2002 9 0 0 105 111 56.1 0.09 25 193 -- --

2003 4 0 0 139 135 77 0.27 48 236 -- --

2004 9 0 0 271 195 192 1.03 109 617 -- --

2005 15 0 0 210 184 159 1.24 16 623 -- --

pH, in standard

pH units

W 2002 9 0 0 7.43 7.4 0.24 0.16 7 7.8 -- --

2003 4 0 0 7.69 7.54 0.48 1.3 7.32 8.35 -- --

2004 9 0 0 7.52 7.49 0.15 0.25 7.29 7.77 -- --

2005 15 0 0 7.51 7.64 0.39 0.9 6.82 7.99 -- --

Specific conductance,

in μS/cm

W 2002 9 0 0 550 478 196 1.32 342 917 -- --

2003 4 0 0 614 598 203 0.17 423 835 -- --

2004 6 3 0 448 436 98.6 0.19 323 583 -- --

2005 12 3 0 428 451 130 0.27 212 620 -- --

Hardness, as calcium 

carbonate, in mg/L

T 2002 9 0 0 242 220 66.1 0.78 167 365 -- --

2003 4 0 0 165 157 31.4 1.31 136 209 -- --

2004 9 0 0 146 150 26.8 0.34 103 195 -- --

2005 15 0 0 143 136 44.9 0.67 69.7 246 -- --

Calcium, in mg/L D 2002 0 9 0 -- -- -- -- -- -- -- --

2003 4 0 0 48.4 46.5 8.41 1.17 40.6 60.1 -- --

2004 9 0 0 42.8 42.3 6.08 0.3 32.1 52.2 -- --

2005 15 0 0 42.7 41.4 11.7 0.24 22 66.1 -- --

Magnesium, in mg/L D 2002 0 9 0 -- -- -- -- -- -- -- --

2003 4 0 0 10.6 9.84 2.57 1.57 8.41 14.3 -- --

2004 9 0 0 9.39 8.14 3.13 1.06 5.48 15.7 -- --

2005 15 0 0 8.84 8.04 4.02 1.5 3.61 19.6 -- --

Potassium, in mg/L D 2002 0 9 0 -- -- -- -- -- -- -- --

2003 0 4 0 -- -- -- -- -- -- -- --

2004 0 9 0 -- -- -- -- -- -- -- --

2005 15 0 0 3.81 3.39 0.92 0.78 2.67 5.46 -- --

Sodium, in mg/L D 2002 0 9 0 -- -- -- -- -- -- -- --

2003 0 4 0 -- -- -- -- -- -- -- --

2004 0 9 0 -- -- -- -- -- -- -- --

2005 15 0 0 34.7 32 13.6 0.78 13.9 64.6 -- --

Alkalinity, as calcium 

carbonate, fixed 

endpoint, in mg/L

W 2002 0 9 0 -- -- -- -- -- -- -- --

2003 0 4 0 -- -- -- -- -- -- -- --

2004 0 9 0 -- -- -- -- -- -- -- --

2005 15 0 0 84.4 81.7 21.3 0.14 48.6 124 -- --
84 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table A2. Summary statistics for water-quality properties and constituents by water year for all stations, South Platte River below 

Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand Creek at mouth near 

Commerce City, and South Platte River at Henderson.—Continued

[n, number of samples; M, number of samples with missing values; N, nitrogen; P, phosphorus; Pct, percentage of samples below minimum reporting level; 

Stddev, standard deviation; Skew, skewness; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms 

per liter; --, not applicable]

Property

or constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Median

South Platte below Union Avenue at Englewood (06710247)—Continued

Chloride, in mg/L D 2002 0 9 0 -- -- -- -- -- -- -- --

2003 0 4 0 -- -- -- -- -- -- -- --

2004 0 9 0 -- -- -- -- -- -- -- --

2005 15 0 0 37.8 36.8 16.4 0.87 11 77.6 -- --

Fluoride, in mg/L D 2002 0 9 0 -- -- -- -- -- -- -- --

2003 0 4 0 -- -- -- -- -- -- -- --

2004 0 9 0 -- -- -- -- -- -- -- --

2005 15 0 0 0.67 0.63 0.29 0.04 0.29 1.08 -- --

Sulfate, in mg/L D 2002 0 9 0 -- -- -- -- -- -- -- --

2003 0 4 0 -- -- -- -- -- -- -- --

2004 0 9 0 -- -- -- -- -- -- -- --

2005 15 0 0 74.1 74.4 31.8 1.25 30.9 155 -- --

Residue on evaporation

at 105°C, in mg/L

T 2002 9 0 0 532 574 488 0.71 19 1,460 -- --

2003 4 0 0 433 86 734 1.99 26 1,530 -- --

2004 9 0 0 232 178 206 1.42 13 680 -- --

2005 15 0 13.3 292 242 219 0.98 54 782 10 10

E. coli, colonies per

100 mL

W 2002 2 0 0 13,000 13,000 -- -- -- -- -- --

2003 0 0 0 -- -- -- -- -- -- -- --

2004 2 0 0 7,350 7,350 -- -- -- -- -- --

2005 1 0 0 92,000 92,000 -- -- -- -- -- --

Fecal coliform, colonies

per 100 mL

W 2002 2 0 0 10,500 10,500 -- -- -- -- -- --

2003 0 0 0 -- -- -- -- -- -- -- --

2004 2 0 0 7,600 7,600 -- -- -- -- -- --

2005 1 0 0 28,000 28,000 -- -- -- -- -- --

Ammonia + organic N 

as N, in mg/L

T 2002 9 0 0 2.57 1.9 1.83 2.09 1.3 7 -- --

2003 4 0 0 2.41 1.43 2.56 1.82 0.59 6.19 -- --

2004 9 0 0 1.48 1.38 0.71 1.43 0.61 3.07 -- --

2005 15 0 0 1.48 1.21 0.73 0.23 0.47 2.72 -- --

Ammonia, as N,

in mg/L

D 2002 0 9 0 -- -- -- -- -- -- -- --

2003 4 0 25 0.2 0.22 0.15 0.56 0.05 0.34 0.04 0.04

2004 9 0 22.2 0.12 0.11 0.06 0.05 0.05 0.18 0.04 0.04

2005 15 0 33.3 0.1 0.1 0.03 0.31 0.06 0.16 0.04 0.04

Nitrite + nitrate, as N,

in mg/L

D 2002 0 9 0 -- -- -- -- -- -- -- --

2003 4 0 0 0.79 0.78 0.28 0.3 0.48 1.14 -- --

2004 9 0 0 0.83 0.79 0.35 0.97 0.4 1.53 -- --

2005 15 0 0 0.89 0.76 0.41 0.63 0.41 1.65 -- --

Orthophosphate, as P, 

in mg/L

D 2002 9 0 0 0.19 0.16 0.12 1.59 0.08 0.45 -- --

2003 4 0 0 0.04 0.04 0.01 0.16 0.03 0.06 -- --

2004 9 0 0 0.07 0.07 0.04 0.86 0.03 0.14 -- --

2005 15 0 0 0.07 0.08 0.04 0.41 0.01 0.16 -- --
Appendix. Hydrograph Classification 85

Table A2. Summary statistics for water-quality properties and constituents by water year for all stations, South Platte River below 

Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand Creek at mouth near 

Commerce City, and South Platte River at Henderson.—Continued

[n, number of samples; M, number of samples with missing values; N, nitrogen; P, phosphorus; Pct, percentage of samples below minimum reporting level; 

Stddev, standard deviation; Skew, skewness; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms 

per liter; --, not applicable]

Property

or constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Median

South Platte below Union Avenue at Englewood (06710247)—Continued

Phosphorus, as P,

in mg/L

T 2002 9 0 0 0.6 0.29 0.53 1.44 0.18 1.75 -- --

2003 4 0 0 0.56 0.3 0.65 1.85 0.1 1.52 -- --

2004 9 0 0 0.45 0.37 0.31 1.81 0.1 1.18 -- --

2005 15 0 0 0.42 0.42 0.28 0.67 0.07 1.02 -- --

Organic carbon,

in mg/L

D 2002 0 9 0 -- -- -- -- -- -- -- --

2003 4 0 0 6.83 6.59 2.11 0.44 4.71 9.41 -- --

2004 6 3 0 5.75 6.08 1.31 0.76 3.55 7.47 -- --

2005 15 0 0 8.16 6.91 3.69 1.23 4.3 16.2 -- --

Copper, in μg/L D 2002 9 0 0 10.6 5 9.33 1.25 2 28 -- --

2003 4 0 0 1.96 1.95 0.19 0.26 1.74 2.2 -- --

2004 9 0 0 2.01 2.04 0.34 0.25 1.38 2.58 -- --

2005 15 0 0 2.12 2.08 0.44 0.16 1.14 2.84 -- --

Copper, in μg/L T 2002 0 9 0 -- -- -- -- -- -- -- --

2003 4 0 0 18.5 10.8 20.5 1.81 3.78 48.8 -- --

2004 9 0 0 14.5 13 9.81 1.72 3.02 37.4 -- --

2005 15 0 0 13.6 13.5 8.92 0.53 2.82 32.1 -- --

Lead, in μg/L D 2002 9 0 77.8 45 45 21.2 30 60 10 10

2003 4 0 75 0.1 0.1 0.1 0.1 0.08 0.08

2004 9 0 88.9 0.14 0.14 0.14 0.14 0.08 0.08

2005 15 0 80 0.13 0.15 0.04 1.66 0.09 0.16 0.08 0.08

Lead, in μg/L T 2002 0 9 0 -- -- -- -- -- -- -- --

2003 4 0 0 16.9 7.16 23.5 1.91 1.44 51.9 -- --

2004 9 0 0 11.4 10.9 10.3 1.98 0.63 36.2 -- --

2005 15 0 0 10.2 9.44 8.34 0.66 0.67 27.6 -- --

Manganese, in μg/L D 2002 0 9 0 -- -- -- -- -- -- -- --

2003 4 0 0 79.6 32.7 109 1.83 12.3 241 -- --

2004 9 0 0 17.2 12.5 14.8 1.19 2.75 46.9 -- --

2005 15 0 0 22.1 9.54 26.4 1.65 1.07 82.6 -- --

Manganese, in μg/L T 2002 0 9 0 -- -- -- -- -- -- -- --

2003 4 0 0 455 234 551 1.89 79.3 1,270 -- --

2004 9 0 0 312 272 200 1.94 123 786 -- --

2005 15 0 0 355 337 210 0.27 62.8 716 -- --

Zinc, in μg/L D 2002 9 0 66.7 23.3 20 5.77 1.73 20 30 20 20

2003 4 0 0 4.85 5.31 1.59 1.53 2.55 6.24 -- --

2004 9 0 0 5.16 4.41 2.42 0.94 2.52 9.63 -- --

2005 15 0 0 4.73 4.64 1.76 0.02 1.99 7.61 -- --

Zinc, in μg/L T 2002 0 9 0 -- -- -- -- -- -- -- --

2003 4 0 0 77 35 103 1.9 8 230 -- --

2004 9 0 0 50.4 48 36.1 1.63 12 134 -- --

2005 15 0 0 47.1 45 33.2 0.5 7 112 -- --
86 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table A2. Summary statistics for water-quality properties and constituents by water year for all stations, South Platte River below 

Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand Creek at mouth near 

Commerce City, and South Platte River at Henderson.—Continued

[n, number of samples; M, number of samples with missing values; N, nitrogen; P, phosphorus; Pct, percentage of samples below minimum reporting level; 

Stddev, standard deviation; Skew, skewness; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms 

per liter; --, not applicable]

Property

or constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Median

South Platte River at Denver (06714000)

Mean streamflow,

in ft3

/s

-- 2002 11 0 0 749 427 862 1.94 188 2,780 -- --

2003 6 0 0 563 569 238 0.07 263 847 -- --

2004 14 0 0 1,090 753 1,100 2.56 338 4,450 -- --

2005 15 0 0 900 821 694 1.07 166 2,460 -- --

Streamflow volume,

in acre-feet

-- 2002 11 0 0 661 388 730 1.84 171 2,290 -- --

2003 6 0 0 501 513 200 0.12 239 754 -- --

2004 14 0 0 909 685 945 3.17 307 4,040 -- --

2005 15 0 0 806 746 644 0.98 69 2,240 -- --

pH, in standard

pH units

W 2002 11 0 0 7.4 7.3 0.25 0.5 7 7.9 -- --

2003 6 0 0 7.28 7.23 0.33 0.07 6.8 7.71 -- --

2004 14 0 0 7.4 7.47 0.21 0.58 6.99 7.72 -- --

2005 15 0 0 7.49 7.6 0.3 1.56 6.72 7.8 -- --

Specific conductance,

in μS/cm

W 2002 10 1 0 586 540 194 1.28 361 972 -- --

2003 4 2 0 740 720 304 0.12 461 1,060 -- --

2004 12 2 0 488 496 129 0.3 259 717 -- --

2005 15 0 0 506 509 153 0.15 247 711 -- --

Hardness, as calcium 

carbonate, in mg/L

T 2002 10 1 0 199 193 30.3 0.61 150 255 -- --

2003 6 0 0 153 160 40.1 0.36 91 208 -- --

2004 14 0 0 134 129 37.8 0.03 69.1 191 -- --

2005 15 0 0 142 141 42.5 0.01 74.4 211 -- --

Calcium, in mg/L D 2002 0 11 0 -- -- -- -- -- -- -- --

2003 6 0 0 44.1 45.4 9.76 0.67 28.3 55.9 -- --

2004 14 0 0 40.3 38.9 10.7 0.1 21.4 56.6 -- --

2005 15 0 0 42.8 42.9 12.4 0.02 23.5 63.3 -- --

Magnesium, in mg/L D 2002 0 11 0 -- -- -- -- -- -- -- --

2003 6 0 0 10.4 9.97 4.02 0.29 4.9 16.5 -- --

2004 14 0 0 8.11 7.8 2.74 0.27 3.81 12.9 -- --

2005 15 0 0 8.57 8.2 2.82 0.09 3.81 12.9 -- --

Potassium, in mg/L D 2002 0 11 0 -- -- -- -- -- -- -- --

2003 0 6 0 -- -- -- -- -- -- -- --

2004 0 14 0 -- -- -- -- -- -- -- --

2005 15 0 0 4.67 4.46 1.26 0.61 3.23 7.03 -- --

Sodium, in mg/L D 2002 0 11 0 -- -- -- -- -- -- -- --

2003 0 6 0 -- -- -- -- -- -- -- --

2004 0 14 0 -- -- -- -- -- -- -- --

2005 15 0 0 46.8 50.7 17.3 0.39 18.2 84.8 -- --

Alkalinity, as calcium 

carbonate, fixed

endpoint, in mg/L

W 2002 0 11 0 -- -- -- -- -- -- -- --

2003 0 6 0 -- -- -- -- -- -- -- --

2004 0 14 0 -- -- -- -- -- -- -- --

2005 15 0 0 87.3 85.4 22.4 0.25 51 117 -- --
Appendix. Hydrograph Classification 87

Table A2. Summary statistics for water-quality properties and constituents by water year for all stations, South Platte River below 

Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand Creek at mouth near 

Commerce City, and South Platte River at Henderson.—Continued

[n, number of samples; M, number of samples with missing values; N, nitrogen; P, phosphorus; Pct, percentage of samples below minimum reporting level; 

Stddev, standard deviation; Skew, skewness; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms 

per liter; --, not applicable]

Property

or constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Median

South Platte River at Denver (06714000)—Continued

Chloride, in mg/L D 2002 0 11 0 -- -- -- -- -- -- -- --

2003 0 6 0 -- -- -- -- -- -- -- --

2004 0 14 0 -- -- -- -- -- -- -- --

2005 15 0 0 49.2 50.7 24.1 1.9 15.9 122 -- --

Fluoride, in mg/L D 2002 0 11 0 -- -- -- -- -- -- -- --

2003 0 6 0 -- -- -- -- -- -- -- --

2004 0 14 0 -- -- -- -- -- -- -- --

2005 15 0 0 0.58 0.55 0.19 0.18 0.25 0.83 -- --

Sulfate, in mg/L D 2002 0 11 0 -- -- -- -- -- -- -- --

2003 0 6 0 -- -- -- -- -- -- -- --

2004 0 14 0 -- -- -- -- -- -- -- --

2005 15 0 0 79.4 75.2 30.5 0.28 34 136 -- --

Residue on evaporation

at 105°C, in mg/L

T 2002 11 0 0 343 237 250 0.64 54 758 -- --

2003 6 0 0 407 234 473 1.3 51 1,240 -- --

2004 13 1 0 254 204 179 0.89 45 604 -- --

2005 15 0 0 181 159 158 2.04 28 652 -- --

E. coli, colonies per

100 mL

W 2002 2 0 0 17,500 17,500 -- -- -- -- -- --

2003 0 0 0 -- -- -- -- -- -- -- --

2004 2 0 0 6,400 6,400 -- -- -- -- -- --

2005 1 0 0 17,000 17,000 -- -- -- -- -- --

Fecal coliform, colonies

per 100 mL

W 2002 2 0 0 28,500 28,500 -- -- -- -- -- --

2003 0 0 0 -- -- -- -- -- -- -- --

2004 2 0 0 6,400 6,400 -- -- -- -- -- --

2005 1 0 0 35,000 35,000 -- -- -- -- -- --

Ammonia + organic N,

as N, in mg/L

T 2002 10 1 0 2.73 2.35 1.12 0.67 1.4 4.7 -- --

2003 6 0 0 3.57 2.81 2.91 1.38 1.05 8.8 -- --

2004 14 0 0 2.9 2.23 2.28 2.85 1.08 10.2 -- --

2005 15 0 0 1.85 1.64 0.82 0.75 0.87 3.53 -- --

Ammonia, as N,

in mg/L

D 2002 0 11 0 -- -- -- -- -- -- -- --

2003 6 0 0 0.45 0.39 0.33 0.41 0.1 0.91 -- --

2004 14 0 7.14 0.42 0.25 0.47 2.5 0.09 1.8 0.04 0.04

2005 15 0 6.67 0.19 0.17 0.1 0.9 0.06 0.42 0.04 0.04

Nitrite + nitrate, as N,

in mg/L

D 2002 0 11 0 -- -- -- -- -- -- -- --

2003 6 0 0 2.43 2.09 0.99 1.28 1.39 4.19 -- --

2004 14 0 0 2.04 2.06 0.91 0.42 0.71 3.67 -- --

2005 15 0 0 2.01 1.28 1.34 0.95 0.76 4.7 -- --

Orthophosphate, as P,

in mg/L

D 2002 10 1 0 0.45 0.43 0.18 1.36 0.25 0.86 -- --

2003 6 0 0 0.3 0.25 0.14 1.72 0.2 0.55 -- --

2004 14 0 0 0.2 0.18 0.08 0.76 0.11 0.37 -- --

2005 15 0 0 0.25 0.16 0.18 1.05 0.09 0.59 -- --
88 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table A2. Summary statistics for water-quality properties and constituents by water year for all stations, South Platte River below 

Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand Creek at mouth near 

Commerce City, and South Platte River at Henderson.—Continued

[n, number of samples; M, number of samples with missing values; N, nitrogen; P, phosphorus; Pct, percentage of samples below minimum reporting level; 

Stddev, standard deviation; Skew, skewness; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms 

per liter; --, not applicable]

Property

or constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Median

South Platte River at Denver (06714000)—Continued

Phosphorus, as P,

in mg/L

T 2002 10 1 0 0.88 0.78 0.43 0.44 0.33 1.62 -- --

2003 6 0 0 1.11 0.86 0.87 1.42 0.34 2.68 -- --

2004 14 0 0 0.81 0.69 0.52 2.39 0.37 2.39 -- --

2005 15 0 0 0.59 0.54 0.27 0.46 0.28 1.03 -- --

Organic carbon,

in mg/L

D 2002 0 11 0 -- -- -- -- -- -- -- --

2003 6 0 0 9.72 7.84 4.05 0.89 5.54 15.9 -- --

2004 10 4 0 8.3 7.4 3.64 2 5.29 17.5 -- --

2005 15 0 0 9.79 7.53 6.33 2.45 4.46 29.8 -- --

Copper, in μg/L D 2002 10 1 0 3.8 4 1.23 0.43 2 5 -- --

2003 6 0 0 2.73 2.63 0.48 1.17 2.26 3.56 -- --

2004 14 0 0 2.57 2.37 0.79 1.3 1.63 4.59 -- --

2005 15 0 0 3.17 3.31 1.26 0.82 1.44 6.16 -- --

Copper, in μg/L T 2002 0 11 0 -- -- -- -- -- -- -- --

2003 6 0 0 29.6 24.5 25.5 1.02 6.21 72.8 -- --

2004 14 0 0 26.3 21.5 18 1.63 7.07 74.5 -- --

2005 15 0 0 16.9 13.7 9.37 1.45 5.89 41.9 -- --

Lead, in μg/L D 2002 10 1 100 -- -- -- -- -- -- 10 10

2003 6 0 0 0.21 0.18 0.11 1.22 0.1 0.41 -- --

2004 14 0 7.14 0.16 0.13 0.08 1.71 0.09 0.36 0.08 0.08

2005 15 0 6.67 0.17 0.14 0.11 2.68 0.08 0.52 0.08 0.08

Lead, in μg/L T 2002 0 11 0 -- -- -- -- -- -- -- --

2003 6 0 0 29.9 20.6 28.4 0.65 3.81 66 -- --

2004 14 0 0 25.2 20.1 18.8 0.79 3.77 62.5 -- --

2005 15 0 0 14.4 11 12.1 2.13 2.79 50.8 -- --

Manganese, in μg/L D 2002 0 11 0 -- -- -- -- -- -- -- --

2003 6 0 0 53.3 37.7 52.5 1.57 12.9 150 -- --

2004 14 0 0 19.6 10.4 19.3 1.33 1.29 66.8 -- --

2005 15 0 0 22.7 14.2 26.2 1.61 1.32 81.5 -- --

Manganese, in μg/L T 2002 0 11 0 -- -- -- -- -- -- -- --

2003 6 0 0 429 389 294 0.28 128 815 -- --

2004 14 0 0 417 371 271 1.3 113 999 -- --

2005 15 0 0 269 205 147 0.54 109 560 -- --

Zinc, in μg/L D 2002 10 1 60 30 30 8.16 0 20 40 20 20

2003 6 0 0 11.9 10.6 5.24 1.48 6.94 21.5 -- --

2004 14 0 0 10.6 9.12 5.49 0.36 2.69 20.3 -- --

2005 15 0 0 11.7 11.7 7.65 1.86 4.21 34.3 -- --

Zinc, in μg/L T 2002 0 11 0 -- -- -- -- -- -- -- --

2003 6 0 0 134 113 118 0.98 24 333 -- --

2004 14 0 0 118 97.5 85 1.59 27 348 -- --

2005 15 0 0 71.7 56 45.3 1.32 27 183 -- --
Appendix. Hydrograph Classification 89

Table A2. Summary statistics for water-quality properties and constituents by water year for all stations, South Platte River below 

Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand Creek at mouth near 

Commerce City, and South Platte River at Henderson.—Continued

[n, number of samples; M, number of samples with missing values; N, nitrogen; P, phosphorus; Pct, percentage of samples below minimum reporting level; 

Stddev, standard deviation; Skew, skewness; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms 

per liter; --, not applicable]

Property

or constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Median

Tollgate Creek above 6th Avenue at Aurora (394329104490101)

Mean streamflow,

in ft3

/s

-- 2002 3 0 0 24.7 18 15.1 1.6 14 42 -- --

2003 3 0 0 61.7 56 44.8 0.56 20 109 -- --

2004 5 0 0 145 62 160 1.41 7 405 -- --

2005 9 4 0 84.2 32 111 1.31 1 310 -- --

Streamflow volume,

in acre-feet

-- 2002 3 0 0 46.3 38 35.2 1 16 85 -- --

2003 3 0 0 56 51 40.7 0.54 18 99 -- --

2004 5 0 0 125 57 132 1.26 6 335 -- --

2005 9 4 0 79.1 13 116 1.4 0 282 -- --

pH, in standard

pH units

W 2002 3 0 0 6.93 7.3 0.72 1.69 6.1 7.4 -- --

2003 3 0 0 7.3 7.25 0.35 0.63 6.98 7.67 -- --

2004 5 0 0 7.28 7.3 0.18 0.7 7.01 7.49 -- --

2005 13 0 0 7.13 7.31 0.46 0.22 6.3 7.8 -- --

Specific conductance,

in μS/cm

W 2002 3 0 0 753 747 201 0.13 555 957 -- --

2003 1 2 0 2,630 2,630 -- -- 2,630 2,630 -- --

2004 5 0 0 746 784 322 0.12 350 1,130 -- --

2005 11 2 0 779 676 285 0.86 494 1,330 -- --

Hardness, as calcium 

carbonate, in mg/L

T 2002 3 0 0 306 263 95.1 1.62 240 415 -- --

2003 3 0 0 381 287 185 1.7 262 594 -- --

2004 5 0 0 234 219 98.2 0.34 107 375 -- --

2005 13 0 0 231 194 97.2 0.64 127 394 -- --

Calcium, in mg/L D 2002 0 3 0 -- -- -- -- -- -- -- --

2003 3 0 0 112 89.4 49.4 1.64 78.6 169 -- --

2004 5 0 0 72.9 67.4 29.8 0.52 35.6 117 -- --

2005 13 0 0 70.8 60 28.9 0.66 39.8 121 -- --

Magnesium, in mg/L D 2002 0 3 0 -- -- -- -- -- -- -- --

2003 3 0 0 24.4 16 15 1.73 15.6 41.8 -- --

2004 5 0 0 12.5 12.4 5.9 0.17 4.33 20.2 -- --

2005 13 0 0 13 11.1 6.06 0.59 6.68 22.8 -- --

Potassium, in mg/L D 2002 0 3 0 -- -- -- -- -- -- -- --

2003 0 3 0 -- -- -- -- -- -- -- --

2004 0 5 0 -- -- -- -- -- -- -- --

2005 13 0 0 3.96 3.88 0.71 1.04 2.89 5.68 -- --

Sodium, in mg/L D 2002 0 3 0 -- -- -- -- -- -- -- --

2003 0 3 0 -- -- -- -- -- -- -- --

2004 0 5 0 -- -- -- -- -- -- -- --

2005 13 0 0 80.5 68 31.1 0.68 42.8 142 -- --

Alkalinity, as calcium 

carbonate, fixed

endpoint, in mg/L

W 2002 0 3 0 -- -- -- -- -- -- -- --

2003 0 3 0 -- -- -- -- -- -- -- --

2004 0 5 0 -- -- -- -- -- -- -- --

2005 13 0 0 80.5 69.8 22.7 0.56 51.8 118 -- --
90 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table A2. Summary statistics for water-quality properties and constituents by water year for all stations, South Platte River below 

Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand Creek at mouth near 

Commerce City, and South Platte River at Henderson.—Continued

[n, number of samples; M, number of samples with missing values; N, nitrogen; P, phosphorus; Pct, percentage of samples below minimum reporting level; 

Stddev, standard deviation; Skew, skewness; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms 

per liter; --, not applicable]

Property

or constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Median

Tollgate Creek above 6th Avenue at Aurora (394329104490101)—Continued

Chloride, in mg/L D 2002 0 3 0 -- -- -- -- -- -- -- --

2003 0 3 0 -- -- -- -- -- -- -- --

2004 0 5 0 -- -- -- -- -- -- -- --

2005 13 0 0 61.4 62 23.3 0.63 29.9 112 -- --

Fluoride, in mg/L D 2002 0 3 0 -- -- -- -- -- -- -- --

2003 0 3 0 -- -- -- -- -- -- -- --

2004 0 5 0 -- -- -- -- -- -- -- --

2005 13 0 0 0.3 0.34 0.06 0.59 0.2 0.37 -- --

Sulfate, in mg/L D 2002 0 3 0 -- -- -- -- -- -- -- --

2003 0 3 0 -- -- -- -- -- -- -- --

2004 0 5 0 -- -- -- -- -- -- -- --

2005 13 0 0 220 180 107 0.62 116 386 -- --

Residue on evaporation

at 105°C, in mg/L

T 2002 3 0 0 2,940 1,150 3,850 1.64 314 7,360 -- --

2003 1 2 0 698 698 -- -- 698 698 -- --

2004 5 0 0 263 141 234 0.51 40 529 -- --

2005 13 0 0 381 153 552 2.84 54 2,090 -- --

E. coli, colonies per

100 mL

W 2002 2 0 0 21,000 21,000 -- -- -- -- -- --

2003 0 0 0 -- -- -- -- -- -- -- --

2004 0 0 0 -- -- -- -- -- -- -- --

2005 1 0 0 35,000 35,000 -- -- -- -- -- --

Fecal coliform, colonies

per 100 mL

W 2002 2 0 0 30,500 30,500 -- -- -- -- -- --

2003 0 0 0 -- -- -- -- -- -- -- --

2004 0 0 0 -- -- -- -- -- -- -- --

2005 1 0 0 35,000 35,000 -- -- -- -- -- --

Ammonia + organic N

as N, in mg/L

T 2002 3 0 0 3.67 2.8 1.59 1.72 2.7 5.5 -- --

2003 3 0 0 3.31 4.52 2.36 1.7 0.59 4.82 -- --

2004 5 0 0 2.29 2.26 0.98 1.03 1.32 3.82 -- --

2005 13 0 0 2.26 1.92 1.53 1.87 0.81 6.32 -- --

Ammonia, as N,

in mg/L

D 2002 0 3 0 -- -- -- -- -- -- -- --

2003 3 0 0 0.28 0.23 0.14 1.37 0.17 0.44 -- --

2004 5 0 40 0.33 0.26 0.19 1.42 0.19 0.54 0.04 0.04

2005 13 0 0 0.2 0.19 0.09 0.03 0.05 0.35 -- --

Nitrite + nitrate, as N,

in mg/L

D 2002 0 3 0 -- -- -- -- -- -- -- --

2003 3 0 0 0.49 0.46 0.16 0.88 0.34 0.67 -- --

2004 5 0 60 0.17 0.17 0.09 0.11 0.24 0.06 0.06

2005 13 0 0 0.61 0.59 0.21 0.62 0.33 0.99 -- --

Orthophosphate, as P,

in mg/L

D 2002 3 0 0 0.07 0.09 0.04 1.6 0.03 0.1 -- --

2003 2 1 0 0.03 0.03 0 -- 0.03 0.04 -- --

2004 5 0 80 0.02 0.02 -- -- 0.02 0.02 0.01 0.01

2005 13 0 0 0.05 0.05 0.03 0.32 0.01 0.11 -- --
Appendix. Hydrograph Classification 91

Table A2. Summary statistics for water-quality properties and constituents by water year for all stations, South Platte River below 

Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand Creek at mouth near 

Commerce City, and South Platte River at Henderson.—Continued

[n, number of samples; M, number of samples with missing values; N, nitrogen; P, phosphorus; Pct, percentage of samples below minimum reporting level; 

Stddev, standard deviation; Skew, skewness; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms 

per liter; --, not applicable]

Property

or constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Median

Tollgate Creek above 6th Avenue at Aurora (394329104490101)—Continued

Phosphorus, as P,

in mg/L

T 2002 3 0 0 1.17 1.17 0.66 0.02 0.51 1.82 -- --

2003 3 0 33.3 1.37 1.37 0.59 0.96 1.79 0.04 0.04

2004 5 0 0 0.71 0.57 0.45 0.74 0.23 1.37 -- --

2005 13 0 0 0.65 0.38 0.63 2.14 0.18 2.44 -- --

Organic carbon,

in mg/L

D 2002 0 3 0 -- -- -- -- -- -- -- --

2003 3 0 0 12.1 12 4.61 0.1 7.53 16.8 -- --

2004 5 0 0 7.42 7.67 0.88 0.82 6.09 8.41 -- --

2005 13 0 0 11.1 9.68 4.71 0.52 5.89 18.4 -- --

Copper, in μg/L D 2002 3 0 0 4 4 1 0 3 5 -- --

2003 3 0 0 3.25 3.51 0.54 1.68 2.63 3.6 -- --

2004 5 0 0 2.33 2.11 0.73 1.97 1.78 3.6 -- --

2005 13 0 0 2.65 2.58 0.87 0.09 1.25 4.16 -- --

Copper, in μg/L T 2002 0 3 0 -- -- -- -- -- -- -- --

2003 3 0 0 32.1 24.7 12.9 1.73 24.5 46.9 -- --

2004 5 0 0 18.4 11.8 13.2 0.48 5.51 32.6 -- --

2005 13 0 0 20.1 13.1 16.4 2.15 5.41 66.9 -- --

Lead, in μg/L D 2002 3 0 100 -- -- -- -- -- -- 10 10

2003 3 0 66.7 0.18 0.18 -- -- 0.18 0.18 0.08 0.08

2004 5 0 80 0.09 0.09 -- -- 0.09 0.09 0.08 0.08

2005 13 0 61.5 0.11 0.1 0.02 0.26 0.09 0.13 0.08 0.08

Lead, in μg/L T 2002 0 3 0 -- -- -- -- -- -- -- --

2003 3 0 0 24.9 17.5 13.8 1.72 16.3 40.8 -- --

2004 5 0 0 12.6 6.34 11.2 0.56 2.47 25.9 -- --

2005 13 0 0 13 6.79 13.8 2.29 1.8 53.2 -- --

Manganese, in μg/L D 2002 0 3 0 -- -- -- -- -- -- -- --

2003 3 0 0 182 241 158 1.43 2.95 303 -- --

2004 5 0 0 403 41.8 667 2.01 17.4 1,570 -- --

2005 13 0 0 98.4 35.7 144 2.13 2.11 474 -- --

Manganese, in μg/L T 2002 0 3 0 -- -- -- -- -- -- -- --

2003 3 0 0 1,290 1,170 229 1.69 1,140 1,550 -- --

2004 5 0 0 840 769 521 0.82 223 1,650 -- --

2005 13 0 0 593 558 497 1.79 89.5 1,950 -- --

Zinc, in μg/L D 2002 3 0 66.7 20 20 20 20 20 20

2003 3 0 0 7.72 7.45 2.5 0.49 5.38 10.4 -- --

2004 5 0 0 8.18 5.52 4.88 0.84 4.2 15.1 -- --

2005 13 0 0 11.6 7.88 13.1 2.56 2.69 50.6 -- --

Zinc, in μg/L T 2002 0 3 0 -- -- -- -- -- -- -- --

2003 3 0 0 137 124 24.3 1.72 122 165 -- --

2004 5 0 0 86.2 61 54.7 0.68 33 161 -- --

2005 13 0 0 89.6 84 72.9 1.9 18 293 -- --
92 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table A2. Summary statistics for water-quality properties and constituents by water year for all stations, South Platte River below 

Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand Creek at mouth near 

Commerce City, and South Platte River at Henderson.—Continued

[n, number of samples; M, number of samples with missing values; N, nitrogen; P, phosphorus; Pct, percentage of samples below minimum reporting level; 

Stddev, standard deviation; Skew, skewness; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms 

per liter; --, not applicable]

Property

or constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Median

Sand Creek at mouth near Commerce City (394839104570300)

Mean streamflow,

in ft3

/s

-- 2002 9 0 0 137 124 80.7 0.63 40 258 -- --

2003 5 0 0 101 82 44.5 1.89 67 178 -- --

2004 8 0 0 305 75 614 2.75 18 1,810 -- --

2005 12 0 0 278 205 303 1.98 30 1,100 -- --

Streamflow volume,

in acre-feet

-- 2002 9 0 0 121 104 70.7 0.59 36 226 -- --

2003 5 0 0 98.2 85 40.2 1.04 60 160 -- --

2004 8 0 0 389 68.5 874 2.8 17 2,550 -- --

2005 12 0 0 256 187 278 1.86 24 995 -- --

pH, in standard

pH units

W 2002 9 0 0 7.53 7.5 0.25 0.5 7.2 7.9 -- --

2003 5 0 0 7.26 7.22 0.26 1.58 7.03 7.7 -- --

2004 8 0 0 7.45 7.42 0.36 0.09 6.88 7.94 -- --

2005 12 0 0 7.4 7.42 0.2 0.38 7.08 7.65 -- --

Specific conductance,

in μS/cm

W 2002 8 1 0 766 750 205 0.71 521 1,130 -- --

2003 4 1 0 1,200 1,260 465 0.18 703 1,600 -- --

2004 7 1 0 897 1,020 309 0.88 342 1,280 -- --

2005 11 1 0 783 715 270 0.41 482 1,190 -- --

Hardness, as calcium 

carbonate, in mg/L

T 2002 8 1 0 266 263 64.1 0.15 183 360 -- --

2003 5 0 0 242 231 56.6 0.62 180 323 -- --

2004 8 0 0 233 245 74.8 1.06 87 311 -- --

2005 12 0 0 196 177 76 0.3 108 314 -- --

Calcium, in mg/L D 2002 0 9 0 -- -- -- -- -- -- -- --

2003 5 0 0 71.1 68.9 15.4 0.63 53.3 93.8 -- --

2004 8 0 0 70.6 73.7 22 1.07 27.7 91.2 -- --

2005 12 0 0 60 53.5 23 0.33 33.9 95.8 -- --

Magnesium, in mg/L D 2002 0 9 0 -- -- -- -- -- -- -- --

2003 5 0 0 15.6 14.4 4.48 0.52 11.5 21.5 -- --

2004 8 0 0 13.7 14.8 4.98 0.84 4.33 20.2 -- --

2005 12 0 0 11.1 10.4 4.56 0.2 5.81 18.1 -- --

Potassium, in mg/L D 2002 0 9 0 -- -- -- -- -- -- -- --

2003 0 5 0 -- -- -- -- -- -- -- --

2004 0 8 0 -- -- -- -- -- -- -- --

2005 12 0 0 4.46 4.2 1.09 0.17 2.81 6.35 -- --

Sodium, in mg/L D 2002 0 9 0 -- -- -- -- -- -- -- --

2003 0 5 0 -- -- -- -- -- -- -- --

2004 0 8 0 -- -- -- -- -- -- -- --

2005 12 0 0 85 73.2 36.4 0.26 42.9 138 -- --

Alkalinity, as calcium 

carbonate, fixed

endpoint, in mg/L

W 2002 0 9 0 -- -- -- -- -- -- -- --

2003 0 5 0 -- -- -- -- -- -- -- --

2004 0 8 0 -- -- -- -- -- -- -- --

2005 12 0 0 94.8 90.9 29 0.17 53.5 139 -- --
Appendix. Hydrograph Classification 93

Table A2. Summary statistics for water-quality properties and constituents by water year for all stations, South Platte River below 

Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand Creek at mouth near 

Commerce City, and South Platte River at Henderson.—Continued

[n, number of samples; M, number of samples with missing values; N, nitrogen; P, phosphorus; Pct, percentage of samples below minimum reporting level; 

Stddev, standard deviation; Skew, skewness; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms 

per liter; --, not applicable]

Property

or constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Median

Sand Creek at mouth near Commerce City (394839104570300)—Continued

Chloride, in mg/L D 2002 0 9 0 -- -- -- -- -- -- -- --

2003 0 5 0 -- -- -- -- -- -- -- --

2004 0 8 0 -- -- -- -- -- -- -- --

2005 12 0 0 73.6 66.3 27.4 0.1 33.7 110 -- --

Fluoride, in mg/L D 2002 0 9 0 -- -- -- -- -- -- -- --

2003 0 5 0 -- -- -- -- -- -- -- --

2004 0 8 0 -- -- -- -- -- -- -- --

2005 12 0 0 0.45 0.49 0.14 0.1 0.26 0.67 -- --

Sulfate, in mg/L D 2002 0 9 0 -- -- -- -- -- -- -- --

2003 0 5 0 -- -- -- -- -- -- -- --

2004 0 8 0 -- -- -- -- -- -- -- --

2005 12 0 0 174 150 90 0.64 78.9 347 -- --

Residue on evaporation

at 105°C, in mg/L

T 2002 9 0 0 478 566 219 0.5 120 732 -- --

2003 5 0 0 328 404 151 2.02 64 416 -- --

2004 8 0 0 253 220 244 1.38 13 760 -- --

2005 12 0 0 584 278 672 1.39 44 1,930 -- --

E. coli, colonies per

100 mL

W 2002 2 0 0 26,000 26,000 -- -- -- -- -- --

2003 0 0 0 -- -- -- -- -- -- -- --

2004 2 0 0 900 900 -- -- -- -- -- --

2005 0 0 0 -- -- -- -- -- -- -- --

Fecal coliform, colonies

per 100 mL

W 2002 2 0 0 26,000 26,000 -- -- -- -- -- --

2003 0 0 0 -- -- -- -- -- -- -- --

2004 2 0 0 1,000 1,000 -- -- -- -- -- --

2005 0 0 0 -- -- -- -- -- -- -- --

Ammonia + organic N

as N, in mg/L

T 2002 8 1 0 3.2 2.75 1.53 1.13 1.9 6.1 -- --

2003 5 0 0 4.42 4.89 2.24 0.48 1.41 6.78 -- --

2004 8 0 0 2.99 2.29 2.52 1.87 0.88 8.61 -- --

2005 12 0 0 3.04 2.67 1.51 1.05 1.21 6.56 -- --

Ammonia, as N,

in mg/L

D 2002 0 9 0 -- -- -- -- -- -- -- --

2003 5 0 20 0.57 0.53 0.59 0.05 0.05 1.15 0.04 0.04

2004 8 0 25 0.38 0.13 0.44 1.15 0.07 1.08 0.04 0.04

2005 12 0 0 0.42 0.38 0.16 0.28 0.21 0.71 -- --

Nitrite + nitrate, as N,

in mg/L

D 2002 0 9 0 -- -- -- -- -- -- -- --

2003 5 0 0 0.81 0.77 0.2 0.92 0.59 1.12 -- --

2004 8 0 0 1.54 1.86 0.77 0.6 0.36 2.29 -- --

2005 12 0 0 0.9 0.87 0.27 0.59 0.48 1.46 -- --

Orthophosphate, as P,

in mg/L

D 2002 8 1 0 0.24 0.21 0.1 1.31 0.15 0.44 -- --

2003 5 0 0 0.16 0.16 0.03 0.75 0.11 0.2 -- --

2004 8 0 0 0.13 0.12 0.07 0.9 0.04 0.27 -- --

2005 12 0 0 0.12 0.13 0.06 0.22 0.04 0.22 -- --
94 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table A2. Summary statistics for water-quality properties and constituents by water year for all stations, South Platte River below 

Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand Creek at mouth near 

Commerce City, and South Platte River at Henderson.—Continued

[n, number of samples; M, number of samples with missing values; N, nitrogen; P, phosphorus; Pct, percentage of samples below minimum reporting level; 

Stddev, standard deviation; Skew, skewness; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms 

per liter; --, not applicable]

Property

or constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Median

Sand Creek at mouth near Commerce City (394839104570300)—Continued

Phosphorus, as P,

in mg/L

T 2002 8 1 0 0.84 0.85 0.48 0.24 0.29 1.49 -- --

2003 5 0 0 1.08 1.17 0.45 0.68 0.44 1.53 -- --

2004 8 0 0 0.85 0.68 0.6 0.68 0.24 1.83 -- --

2005 12 0 0 0.93 0.76 0.68 1.97 0.34 2.76 -- --

Organic carbon,

in mg/L

D 2002 0 9 0 -- -- -- -- -- -- -- --

2003 5 0 0 13.8 15.9 5.64 0.1 7.21 20.8 -- --

2004 7 1 0 12.1 11 4.5 0.59 7.8 19.4 -- --

2005 12 0 0 13.6 12.9 6.99 1.31 5.86 30.1 -- --

Copper, in μg/L D 2002 8 1 0 7.25 4.5 7.59 2.29 2 25 -- --

2003 5 0 0 2.6 2.46 0.41 0.03 2.08 3.06 -- --

2004 8 0 0 3.1 3.34 0.88 1.26 1.31 4.04 -- --

2005 12 0 0 2.58 2.25 1.05 0.66 1.25 4.6 -- --

Copper, in μg/L T 2002 0 9 0 -- -- -- -- -- -- -- --

2003 5 0 0 21.6 22.2 9.32 0.23 8.28 34.1 -- --

2004 8 0 0 22.9 15.5 18.6 1.04 5.36 51.7 -- --

2005 12 0 0 30.3 22.3 23.8 1.42 7.3 87.3 -- --

Lead, in μg/L D 2002 8 1 100 -- -- -- -- -- -- 10 10

2003 5 0 20 0.24 0.18 0.17 1.64 0.11 0.48 0.08 0.08

2004 8 0 12.5 0.19 0.17 0.08 1.09 0.1 0.33 0.08 0.08

2005 12 0 25 0.17 0.13 0.1 1.97 0.08 0.41 0.08 0.08

Lead, in μg/L T 2002 0 9 0 -- -- -- -- -- -- -- --

2003 5 0 0 21.3 22.4 11.2 0.15 5.29 36.7 -- --

2004 8 0 0 22.9 11.2 25.9 1.34 1.45 70.7 -- --

2005 12 0 0 32 20.2 33.2 1.65 2.7 114 -- --

Manganese, in μg/L D 2002 0 9 0 -- -- -- -- -- -- -- --

2003 5 0 0 106 33.3 127 0.69 4.49 271 -- --

2004 8 0 0 71.3 46.4 74.5 1.04 3.69 190 -- --

2005 12 0 0 85.8 28.9 159 2.71 2.69 550 -- --

Manganese, in μg/L T 2002 0 9 0 -- -- -- -- -- -- -- --

2003 5 0 0 746 718 359 0.4 235 1,170 -- --

2004 8 0 0 703 579 663 1.43 84 2,090 -- --

2005 12 0 0 721 531 573 1.37 113 2,090 -- --

Zinc, in μg/L D 2002 8 1 0 98.8 70 88.2 2.09 40 300 -- --

2003 5 0 0 141 79.5 130 1 22.2 336 -- --

2004 8 0 0 55.1 32.1 54.9 1.27 6.78 165 -- --

2005 11 1 0 9.45 8.06 7.38 2.37 3.01 29.7 -- --

Zinc, in μg/L T 2002 0 9 0 -- -- -- -- -- -- -- --

2003 5 0 0 689 545 418 0.29 227 1,150 -- --

2004 8 0 0 279 243 240 0.72 40 708 -- --

2005 11 1 0 114 80 103 1.59 18 348 -- --
Appendix. Hydrograph Classification 95

Table A2. Summary statistics for water-quality properties and constituents by water year for all stations, South Platte River below 

Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand Creek at mouth near 

Commerce City, and South Platte River at Henderson.—Continued

[n, number of samples; M, number of samples with missing values; N, nitrogen; P, phosphorus; Pct, percentage of samples below minimum reporting level; 

Stddev, standard deviation; Skew, skewness; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms 

per liter; --, not applicable]

Property

or constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Median

South Platte River at Henderson (06720500)

Mean streamflow,

in ft3

/s

-- 2002 12 0 0 805 572 653 1.68 280 2,390 -- --

2003 1 0 0 1,060 1,060 -- -- 1,060 1,060 -- --

2004 14 0 0 1,570 1,230 1,770 3.43 515 7,570 -- --

2005 8 0 0 2,390 1,780 1,460 0.67 752 4,830 -- --

Streamflow volume,

in acre-feet

-- 2002 12 0 0 717 480 603 1.66 208 2,170 -- --

2003 1 0 0 1,230 1,230 -- -- 1,230 1,230 -- --

2004 14 0 0 1,490 1,150 1,600 3.35 468 6,880 -- --

2005 8 0 0 1,930 1,590 1,220 1.39 683 4,390 -- --

pH, in standard

pH units

W 2002 12 0 0 7.51 7.4 0.29 0.75 7.1 8 -- --

2003 1 0 0 7.2 7.2 -- -- 7.2 7.2 -- --

2004 14 0 0 7.32 7.32 0.17 0.3 7.05 7.63 -- --

2005 8 0 0 7.32 7.48 0.33 1.09 6.72 7.64 -- --

Specific conductance,

in μS/cm

W 2002 11 1 0 763 737 206 0.26 418 1,020 -- --

2003 1 0 0 1,090 1,090 -- -- 1,090 1,090 -- --

2004 12 2 0 603 602 107 0.24 439 800 -- --

2005 6 2 0 596 547 273 0.66 316 1,020 -- --

Hardness, as calcium 

carbonate, in mg/L

T 2002 11 1 0 240 240 53.9 1.73 175 380 -- --

2003 1 0 0 219 219 -- -- 219 219 -- --

2004 14 0 0 153 148 26.8 0.62 109 213 -- --

2005 8 0 0 139 150 38.3 0.39 84.5 178 -- --

Calcium, in mg/L D 2002 0 12 0 -- -- -- -- -- -- -- --

2003 1 0 0 61.2 61.2 -- -- 61.2 61.2 -- --

2004 14 0 0 45 43.3 7.38 0.92 33.4 62.7 -- --

2005 8 0 0 41.1 42.9 10.4 0.3 26.2 52.4 -- --

Magnesium, in mg/L D 2002 0 12 0 -- -- -- -- -- -- -- --

2003 1 0 0 16 16 -- -- 16 16 -- --

2004 14 0 0 10 9.57 2.12 0.11 6.19 13.8 -- --

2005 8 0 0 8.87 10.1 3.02 0.48 4.62 11.7 -- --

Potassium, in mg/L D 2002 0 12 0 -- -- -- -- -- -- -- --

2003 0 1 0 -- -- -- -- -- -- -- --

2004 0 14 0 -- -- -- -- -- -- -- --

2005 8 0 0 6.18 5.73 1.81 0.32 4.26 8.37 -- --

Sodium, in mg/L D 2002 0 12 0 -- -- -- -- -- -- -- --

2003 0 1 0 -- -- -- -- -- -- -- --

2004 0 14 0 -- -- -- -- -- -- -- --

2005 8 0 0 67.1 65.3 38.5 1.06 27.1 142 -- --

Alkalinity, as calcium 

carbonate, fixed 

endpoint, in mg/L

W 2002 0 12 0 -- -- -- -- -- -- -- --

2003 0 1 0 -- -- -- -- -- -- -- --

2004 0 14 0 -- -- -- -- -- -- -- --

2005 8 0 0 86.3 90.7 22.2 0.11 57.7 121 -- --
96 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table A2. Summary statistics for water-quality properties and constituents by water year for all stations, South Platte River below 

Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand Creek at mouth near 

Commerce City, and South Platte River at Henderson.—Continued

[n, number of samples; M, number of samples with missing values; N, nitrogen; P, phosphorus; Pct, percentage of samples below minimum reporting level; 

Stddev, standard deviation; Skew, skewness; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms 

per liter; --, not applicable]

Property

or constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Median

South Platte River at Henderson (06720500)—Continued

Chloride, in mg/L D 2002 0 12 0 -- -- -- -- -- -- -- --

2003 0 1 0 -- -- -- -- -- -- -- --

2004 0 14 0 -- -- -- -- -- -- -- --

2005 8 0 0 74 58.1 60.2 1.51 23.3 197 -- --

Fluoride, in mg/L D 2002 0 12 0 -- -- -- -- -- -- -- --

2003 0 1 0 -- -- -- -- -- -- -- --

2004 0 14 0 -- -- -- -- -- -- -- --

2005 8 0 0 0.56 0.51 0.19 0.43 0.35 0.84 -- --

Sulfate, in mg/L D 2002 0 12 0 -- -- -- -- -- -- -- --

2003 0 1 0 -- -- -- -- -- -- -- --

2004 0 14 0 -- -- -- -- -- -- -- --

2005 8 0 0 82.1 80.4 26.2 0.05 47.4 117 -- --

Residue on evaporation

at 105°C, in mg/L

T 2002 12 0 0 1,240 420 1,800 2.11 138 6,040 -- --

2003 1 0 0 416 416 -- -- 416 416 -- --

2004 14 0 0 213 120 166 1.51 76 580 -- --

2005 7 1 0 378 346 157 0.33 138 564 -- --

E. coli, colonies per

100 mL

W 2002 2 0 0 8,150 8,150 -- -- -- -- -- --

2003 0 0 0 -- -- -- -- -- -- -- --

2004 2 0 0 3,730 3,730 -- -- -- -- -- --

2005 1 0 0 11,000 11,000 -- -- -- -- -- --

Fecal coliform, colonies

per 100 mL

W 2002 2 0 0 29,500 29,500 -- -- -- -- -- --

2003 0 0 0 -- -- -- -- -- -- -- --

2004 2 0 0 5,660 5,660 -- -- -- -- -- --

2005 1 0 0 54,000 54,000 -- -- -- -- -- --

Ammonia + organic N

as N, in mg/L

T 2002 11 1 0 7.1 7.2 1.37 0.9 3.9 9.2 -- --

2003 1 0 0 9.63 9.63 -- -- 9.63 9.63 -- --

2004 14 0 0 4.62 3.85 2.44 2.55 2.66 12.2 -- --

2005 8 0 0 4.19 4.39 1.18 0.84 1.98 5.72 -- --

Ammonia, as N,

in mg/L

D 2002 0 12 0 -- -- -- -- -- -- -- --

2003 1 0 0 3.55 3.55 -- -- 3.55 3.55 -- --

2004 14 0 0 1.65 1.45 0.9 0.73 0.51 3.46 -- --

2005 8 0 0 1.24 1.48 0.71 0.3 0.32 2.2 -- --

Nitrite + nitrate, as N,

in mg/L

D 2002 0 12 0 -- -- -- -- -- -- -- --

2003 1 0 0 3.56 3.56 -- -- 3.56 3.56 -- --

2004 14 0 0 2.82 2.59 0.76 0.56 1.77 4.1 -- --

2005 8 0 0 2.42 2.08 1.17 0.39 1.14 4 -- --

Orthophosphate, as P,

in mg/L

D 2002 11 1 0 0.81 0.76 0.29 0.58 0.39 1.4 -- --

2003 1 0 0 0.95 0.95 -- -- 0.95 0.95 -- --

2004 14 0 0 0.54 0.55 0.16 0.19 0.28 0.81 -- --

2005 8 0 0 0.47 0.35 0.29 0.94 0.2 1 -- --
Appendix. Hydrograph Classification 97

Table A2. Summary statistics for water-quality properties and constituents by water year for all stations, South Platte River below 

Union Avenue at Englewood, South Platte River at Denver, Tollgate Creek above 6th Avenue at Aurora, Sand Creek at mouth near 

Commerce City, and South Platte River at Henderson.—Continued

[n, number of samples; M, number of samples with missing values; N, nitrogen; P, phosphorus; Pct, percentage of samples below minimum reporting level; 

Stddev, standard deviation; Skew, skewness; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms 

per liter; --, not applicable]

Property

or constituent Phase Typ n M Pct Mean Median StdDev Skew Minimum Maximum

Reporting

level

Mean Median

South Platte River at Henderson (06720500)—Continued

Phosphorus, as P,

in mg/L

T 2002 11 1 0 2.55 2.14 1.98 2.85 0.87 8.3 -- --

2003 1 0 0 2.77 2.77 -- -- 2.77 2.77 -- --

2004 14 0 0 1.38 1.25 0.6 2.01 0.83 3.12 -- --

2005 8 0 0 1.58 1.59 0.5 0.31 0.73 2.52 -- --

Organic carbon,

in mg/L

D 2002 0 12 0 -- -- -- -- -- -- -- --

2003 1 0 0 11.7 11.7 -- -- 11.7 11.7 -- --

2004 10 4 0 9.81 10.1 2.79 0.07 5.98 14.4 -- --

2005 8 0 0 9.74 8.94 4.08 0.61 5.39 16.6 -- --

Copper, in μg/L D 2002 11 1 0 4.73 5 2.49 0.33 2 9 -- --

2003 1 0 0 2.7 2.7 -- -- 2.7 2.7 -- --

2004 14 0 0 2.94 2.93 0.55 0.12 2.04 3.77 -- --

2005 8 0 0 2.43 2.28 0.71 0.35 1.56 3.49 -- --

Copper, in μg/L T 2002 0 12 0 -- -- -- -- -- -- -- --

2003 1 0 0 52.9 52.9 -- -- 52.9 52.9 -- --

2004 14 0 0 32.1 30.7 16.8 1.07 11.6 71.9 -- --

2005 8 0 0 38.8 36 15.2 0.05 18.2 57.2 -- --

Lead, in μg/L D 2002 11 1 90.9 10 10 -- -- 10 10 10 10

2003 1 0 0 0.5 0.5 -- -- 0.5 0.5 -- --

2004 14 0 0 0.3 0.28 0.12 1.55 0.13 0.64 -- --

2005 8 0 0 0.24 0.21 0.07 0.4 0.16 0.34 -- --

Lead, in μg/L T 2002 0 12 0 -- -- -- -- -- -- -- --

2003 1 0 0 40.9 40.9 -- -- 40.9 40.9 -- --

2004 14 0 0 31.3 31 19.6 0.61 6.92 68.2 -- --

2005 8 0 0 35.3 31.4 16.4 0.49 16.7 61.2 -- --

Manganese, in μg/L D 2002 0 12 0 -- -- -- -- -- -- -- --

2003 1 0 0 217 217 -- -- 217 217 -- --

2004 14 0 0 93.8 79.7 65.8 1.02 13.4 242 -- --

2005 8 0 0 63.1 68.5 48.6 0.1 7.21 132 -- --

Manganese, in μg/L T 2002 0 12 0 -- -- -- -- -- -- -- --

2003 1 0 0 713 713 -- -- 713 713 -- --

2004 14 0 0 507 495 239 0.58 236 966 -- --

2005 8 0 0 649 592 230 0.27 306 1,010 -- --

Zinc, in μg/L D 2002 11 1 27.3 31.3 30 11.3 0.49 20 50 20 20

2003 1 0 0 29 29 -- -- 29 29 -- --

2004 14 0 0 19.3 17.6 7.76 1.54 9.71 40.3 -- --

2005 8 0 0 13.6 12.6 5.12 0.39 7.86 21 -- --

Zinc, in μg/L T 2002 0 12 0 -- -- -- -- -- -- -- --

2003 1 0 0 209 209 -- -- 209 209 -- --

2004 14 0 0 144 123 78.4 0.68 45 299 -- --

2005 8 0 0 166 155 70.7 0.2 66 265 -- --
98 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table A3. Correlation among water-quality properties and constituents, by station.—Continued

[Mean streamflow is in cubic feet per second, streamflow volume is in acre-feet, pH is in standard pH units, specific conductance is in microsiemens per 

centimeter; and copper, lead, manganese, and zinc are in micrograms per liter; all other units are milligrams per liter. Corr, Pearson correlation coefficient; 

n, number of pairs used in calculation; N, nitrogen; P, phosphorus; --, not applicable]

Variables All stations Union Denver Henderson Tollgate Sand Creek

Corr n Corr n Corr n Corr n Corr n Corr n

Mean streamflow correlations

Streamflow volume 0.975 172 0.993 37 0.974 46 0.974 46 0.906 20 0.965 35

pH –0.043 172 0.122 37 0.158 46 0.158 46 –0.251 20 –0.230 35

Specific conductance –0.321 150 –0.512 31 –0.569 41 –0.569 41 –0.260 18 –0.544 30

Hardness –0.398 169 –0.488 37 –0.543 45 –0.543 45 –0.392 20 –0.557 34

Calcium, dissolved –0.419 128 –0.599 28 –0.684 35 –0.684 35 –0.407 17 –0.682 23

Magnesium, dissolved –0.377 128 –0.379 28 –0.614 35 –0.614 35 –0.370 17 –0.700 23

Potassium, dissolved 0.022 59 –0.461 15 –0.769 15 –0.769 15 –0.521 9 –0.872 8

Sodium, dissolved –0.254 59 –0.568 15 –0.671 15 –0.671 15 –0.701 9 –0.630 8

Alkalinity, fixed endpoint –0.383 59 –0.748 15 –0.863 15 –0.863 15 –0.797 9 –0.919 8

Chloride, dissolved –0.117 59 –0.420 15 –0.422 15 –0.422 15 –0.574 9 –0.483 8

Flouride, dissolved –0.193 59 –0.540 15 –0.747 15 –0.747 15 –0.816 9 –0.857 8

Sulfate, dissolved –0.410 59 –0.679 15 –0.855 15 –0.855 15 –0.723 9 –0.934 8

Residue on evaporation at 

105 degrees Celsius

0.063 166 0.214 35 0.299 45 0.299 45 –0.133 18 0.039 34

Ammonia + organic N, as N 0.151 169 0.049 37 0.017 45 0.017 45 –0.106 20 –0.302 34

Ammonia, as N 0.141 113 –0.409 20 –0.174 33 –0.174 33 –0.084 15 –0.529 23

Nitrite + nitrate, as N 0.121 125 –0.574 28 –0.578 35 –0.578 35 –0.163 14 –0.554 23

Orthophosphate, as P 0.151 164 –0.083 37 –0.413 45 –0.413 45 0.129 15 –0.554 34

Phosphorus, as P, total 0.234 168 0.334 37 0.069 45 0.069 45 0.232 19 –0.088 34

Organic carbon, dissolved –0.130 116 –0.124 25 –0.244 31 –0.244 31 –0.265 17 –0.012 19

Copper, dissolved –0.120 169 –0.126 37 –0.449 45 –0.449 45 –0.521 20 –0.242 34

Copper, total 0.364 128 0.460 28 0.206 35 0.206 35 0.133 17 0.340 23

Lead, dissolved –0.077 89 –0.570 7 –0.287 33 –0.287 33 –0.377 5 0.053 24

Lead, total 0.443 128 0.411 28 0.372 35 0.372 35 0.198 17 0.532 23

Manganese, dissolved –0.135 128 –0.327 28 –0.387 35 –0.387 35 –0.004 17 –0.503 23

Manganese, total 0.044 128 0.316 28 0.216 35 0.216 35 0.194 17 0.219 23

Zinc, dissolved –0.134 151 –0.372 31 –0.478 39 –0.478 39 –0.286 18 –0.383 31

Zinc, total 0.066 127 0.321 28 0.208 35 0.208 35 0.111 17 0.321 23

Streamflow volume correlations

pH –0.067 172 0.103 37 0.137 46 0.137 46 –0.239 20 –0.306 35

Specific conductance –0.312 150 –0.537 31 –0.548 41 –0.548 41 –0.294 18 –0.496 30

Hardness –0.395 169 –0.504 37 –0.527 45 –0.527 45 –0.407 20 –0.531 34

Calcium, dissolved –0.414 128 –0.637 28 –0.654 35 –0.654 35 –0.419 17 –0.621 23

Magnesium, dissolved –0.370 128 –0.439 28 –0.584 35 –0.584 35 –0.375 17 –0.629 23

Potassium, dissolved 0.020 59 –0.485 15 –0.773 15 –0.773 15 –0.505 9 –0.733 8

Sodium, dissolved –0.248 59 –0.575 15 –0.671 15 –0.671 15 –0.638 9 –0.494 8

Alkalinity, fixed endpoint –0.390 59 –0.754 15 –0.869 15 –0.869 15 –0.743 9 –0.803 8

Chloride, dissolved –0.095 59 –0.423 15 –0.419 15 –0.419 15 –0.523 9 –0.355 8

Flouride, dissolved –0.196 59 –0.544 15 –0.756 15 –0.756 15 –0.631 9 –0.757 8

Sulfate, dissolved –0.419 59 –0.687 15 –0.861 15 –0.861 15 –0.681 9 –0.799 8

Residue on evaporation at 

105 degrees Celsius

0.070 166 0.236 35 0.297 45 0.297 45 0.105 18 0.030 34

Ammonia + organic N, as N 0.176 169 0.066 37 0.023 45 0.023 45 0.120 20 –0.250 34

Ammonia, as N 0.168 113 –0.377 20 –0.147 33 –0.147 33 0.074 15 –0.474 23

Nitrite + nitrate, as N 0.134 125 –0.566 28 –0.556 35 –0.556 35 –0.050 14 –0.487 23

Orthophosphate, as P 0.166 164 –0.069 37 –0.411 45 –0.411 45 0.071 15 –0.504 34

Phosphorus, as P, total 0.259 168 0.356 37 0.063 45 0.063 45 0.476 19 –0.055 34

Organic carbon, dissolved –0.151 116 –0.114 25 –0.223 31 –0.223 31 –0.364 17 –0.145 19

Copper, dissolved –0.123 169 –0.116 37 –0.421 45 –0.421 45 –0.566 20 –0.256 34

Copper, total 0.406 128 0.482 28 0.212 35 0.212 35 0.367 17 0.432 23

Lead, dissolved –0.075 89 –0.565 7 –0.269 33 –0.269 33 –0.375 5 0.066 24

Lead, total 0.490 128 0.435 28 0.380 35 0.380 35 0.423 17 0.627 23
Appendix. Hydrograph Classification 99

Table A3. Correlation among water-quality properties and constituents, by station.—Continued

[Mean streamflow is in cubic feet per second, streamflow volume is in acre-feet, pH is in standard pH units, specific conductance is in microsiemens per 

centimeter; and copper, lead, manganese, and zinc are in micrograms per liter; all other units are milligrams per liter. Corr, Pearson correlation coefficient; 

n, number of pairs used in calculation; N, nitrogen; P, phosphorus; --, not applicable]

Variables All stations Union Denver Henderson Tollgate Sand Creek

Corr n Corr n Corr n Corr n Corr n Corr n

Streamflow volume correlations—Continued

Manganese, dissolved –0.126 128 –0.318 28 –0.379 35 –0.379 35 0.053 17 –0.439 23

Manganese, total 0.076 128 0.338 28 0.210 35 0.210 35 0.391 17 0.312 23

Zinc, dissolved –0.129 151 –0.364 31 –0.449 39 –0.449 39 –0.314 18 –0.325 31

Zinc, total 0.097 127 0.345 28 0.224 35 0.224 35 0.375 17 0.438 23

pH correlations

Specific conductance –0.137 152 0.012 31 –0.080 41 –0.080 41 –0.021 20 0.047 30

Hardness –0.092 173 –0.038 37 –0.059 45 –0.059 45 –0.127 24 0.305 34

Calcium, dissolved –0.117 132 0.137 28 –0.037 35 –0.037 35 0.038 21 –0.086 23

Magnesium, dissolved –0.080 132 0.295 28 –0.103 35 –0.103 35 0.013 21 –0.009 23

Potassium, dissolved 0.114 63 0.453 15 0.018 15 0.018 15 0.509 13 –0.319 8

Sodium, dissolved –0.116 63 0.361 15 0.092 15 0.092 15 –0.078 13 0.192 8

Alkalinity, fixed endpoint 0.224 63 0.386 15 0.103 15 0.103 15 0.209 13 –0.079 8

Chloride, dissolved –0.063 63 0.238 15 0.028 15 0.028 15 –0.267 13 0.241 8

Flouride, dissolved 0.468 63 0.620 15 0.234 15 0.234 15 0.552 13 –0.185 8

Sulfate, dissolved –0.186 63 0.248 15 0.109 15 0.109 15 –0.013 13 –0.264 8

Residue on evaporation at 

105 degrees Celsius

0.052 170 –0.246 35 0.063 45 0.063 45 0.135 22 0.315 34

Ammonia + organic N, as N –0.187 173 –0.274 37 –0.162 45 –0.162 45 –0.119 24 –0.058 34

Ammonia, as N –0.146 117 –0.089 20 –0.266 33 –0.266 33 –0.035 19 –0.108 23

Nitrite + nitrate, as N –0.051 129 0.066 28 –0.141 35 –0.141 35 –0.116 18 –0.163 23

Orthophosphate, as P 0.009 168 –0.138 37 –0.025 45 –0.025 45 0.070 19 0.055 34

Phosphorus, as P, total –0.032 172 –0.244 37 –0.097 45 –0.097 45 0.124 23 0.221 34

Organic carbon, dissolved –0.095 120 0.173 25 –0.139 31 –0.139 31 0.217 21 0.185 19

Copper, dissolved 0.037 173 –0.048 37 –0.474 45 –0.474 45 0.183 24 0.155 34

Copper, total –0.140 132 –0.158 28 –0.197 35 –0.197 35 0.259 21 –0.270 23

Lead, dissolved 0.139 91 0.455 7 –0.394 33 –0.394 33 0.062 7 0.062 24

Lead, total –0.093 132 –0.135 28 –0.118 35 –0.118 35 0.221 21 –0.226 23

Manganese, dissolved –0.095 132 –0.077 28 –0.169 35 –0.169 35 0.168 21 –0.193 23

Manganese, total –0.181 132 –0.136 28 –0.071 35 –0.071 35 0.209 21 –0.321 23

Zinc, dissolved –0.092 155 –0.191 31 –0.283 39 –0.283 39 –0.301 22 0.164 31

Zinc, total –0.173 131 –0.180 28 –0.208 35 –0.208 35 0.205 21 –0.203 23

Specific-conductance correlations

Hardness 0.783 152 0.542 31 0.750 41 0.750 41 0.912 20 0.542 30

Calcium, dissolved 0.894 111 0.819 22 0.757 31 0.757 31 0.945 17 0.712 19

Magnesium, dissolved 0.920 111 0.717 22 0.885 31 0.885 31 0.988 17 0.802 19

Potassium, dissolved 0.316 55 0.499 12 0.632 15 0.632 15 0.150 11 0.202 6

Sodium, dissolved 0.937 55 0.855 12 0.872 15 0.872 15 0.992 11 0.959 6

Alkalinity, fixed endpoint 0.575 55 0.779 12 0.757 15 0.757 15 0.896 11 0.379 6

Chloride, dissolved 0.728 55 0.764 12 0.709 15 0.709 15 0.765 11 0.950 6

Flouride, dissolved –0.079 55 0.321 12 0.634 15 0.634 15 0.590 11 0.111 6

Sulfate, dissolved 0.869 55 0.717 12 0.744 15 0.744 15 0.983 11 0.317 6

Residue on evaporation at 

105 degrees Celsius

–0.073 147 –0.159 29 –0.054 40 –0.054 40 –0.248 19 –0.066 29

Ammonia + organic N, as N 0.270 152 0.048 31 0.303 41 0.303 41 0.169 20 0.462 30

Ammonia, as N 0.212 97 0.575 14 0.374 29 0.374 29 0.284 15 0.698 19

Nitrite + nitrate, as N 0.076 108 0.381 22 0.651 31 0.651 31 0.222 14 0.390 19

Orthophosphate, as P 0.119 148 0.020 31 0.620 41 0.620 41 –0.378 16 0.572 30

Phosphorus, as P, total 0.094 152 –0.145 31 0.375 41 0.375 41 –0.142 20 0.140 30

Organic carbon, dissolved 0.416 107 –0.016 22 0.185 29 0.185 29 0.367 17 –0.222 17

Copper, dissolved –0.017 152 –0.082 31 0.295 41 0.295 41 0.247 20 0.162 30

Copper, total 0.014 111 –0.005 22 0.220 31 0.220 31 –0.113 17 0.190 19

Lead, dissolved 0.020 79 0.674 5 0.532 29 0.532 29 0.882 7 –0.109 20
100 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table A3. Correlation among water-quality properties and constituents, by station.—Continued

[Mean streamflow is in cubic feet per second, streamflow volume is in acre-feet, pH is in standard pH units, specific conductance is in microsiemens per 

centimeter; and copper, lead, manganese, and zinc are in micrograms per liter; all other units are milligrams per liter. Corr, Pearson correlation coefficient; 

n, number of pairs used in calculation; N, nitrogen; P, phosphorus; --, not applicable]

Variables All stations Union Denver Henderson Tollgate Sand Creek

Corr n Corr n Corr n Corr n Corr n Corr n

Specific-conductance correlations—Continued

Lead, total –0.050 111 0.019 22 0.042 31 0.042 31 –0.122 17 –0.025 19

Manganese, dissolved 0.404 111 0.467 22 0.707 31 0.707 31 0.215 17 0.612 19

Manganese, total 0.286 111 0.005 22 0.167 31 0.167 31 0.182 17 0.053 19

Zinc, dissolved 0.384 134 0.174 25 0.550 35 0.550 35 0.458 18 0.357 27

Zinc, total 0.379 110 0.069 22 0.213 31 0.213 31 0.005 17 0.114 19

Hardness correlations

Calcium, dissolved 0.996 132 0.985 28 0.993 35 0.993 35 0.998 21 0.996 23

Magnesium, dissolved 0.969 132 0.957 28 0.965 35 0.965 35 0.988 21 0.985 23

Potassium, dissolved 0.279 63 0.755 15 0.810 15 0.810 15 0.059 13 0.934 8

Sodium, dissolved 0.822 63 0.823 15 0.685 15 0.685 15 0.966 13 0.606 8

Alkalinity, fixed endpoint 0.721 63 0.969 15 0.973 15 0.973 15 0.934 13 0.930 8

Chloride, dissolved 0.493 63 0.566 15 0.367 15 0.367 15 0.646 13 0.449 8

Flouride, dissolved 0.105 63 0.627 15 0.876 15 0.876 15 0.648 13 0.912 8

Sulfate, dissolved 0.956 63 0.967 15 0.985 15 0.985 15 0.994 13 0.967 8

Residue on evaporation at 

105 degrees Celsius

0.169 167 0.160 35 –0.214 44 –0.214 44 0.006 22 0.644 33

Ammonia + organic N, as N 0.201 173 0.329 37 0.076 45 0.076 45 0.210 24 0.597 34

Ammonia, as N 0.049 117 0.195 20 0.077 33 0.077 33 0.382 19 0.817 23

Nitrite + nitrate, as N 0.007 129 0.541 28 0.762 35 0.762 35 0.325 18 0.848 23

Orthophosphate, as P 0.079 168 0.369 37 0.759 45 0.759 45 –0.436 19 0.710 34

Phosphorus, as P, total 0.154 172 0.149 37 0.174 45 0.174 45 –0.094 23 0.714 34

Organic carbon, dissolved 0.354 120 0.075 25 0.109 31 0.109 31 0.349 21 0.106 19

Copper, dissolved 0.322 173 0.511 37 0.455 45 0.455 45 0.397 24 0.679 34

Copper, total –0.172 132 –0.372 28 –0.148 35 –0.148 35 –0.153 21 –0.089 23

Lead, dissolved 0.226 91 0.764 7 0.269 33 0.269 33 0.853 7 0.485 24

Lead, total –0.241 132 –0.362 28 –0.315 35 –0.315 35 –0.156 21 –0.342 23

Manganese, dissolved 0.431 132 0.189 28 0.516 35 0.516 35 0.282 21 0.785 23

Manganese, total 0.213 132 –0.285 28 –0.114 35 –0.114 35 0.191 21 –0.038 23

Zinc, dissolved 0.315 155 0.668 31 0.636 39 0.636 39 0.528 22 0.718 31

Zinc, total 0.166 131 –0.318 28 –0.161 35 –0.161 35 0.017 21 –0.149 23

Calcium, dissolved, correlations

Magnesium, dissolved 0.943 132 0.892 28 0.927 35 0.927 35 0.977 21 0.968 23

Potassium, dissolved 0.251 63 0.722 15 0.823 15 0.823 15 0.068 13 0.955 8

Sodium, dissolved 0.819 63 0.788 15 0.664 15 0.664 15 0.965 13 0.547 8

Alkalinity, fixed endpoint 0.692 63 0.967 15 0.972 15 0.972 15 0.934 13 0.925 8

Chloride, dissolved 0.478 63 0.550 15 0.340 15 0.340 15 0.648 13 0.382 8

Flouride, dissolved 0.058 63 0.592 15 0.880 15 0.880 15 0.646 13 0.932 8

Sulfate, dissolved 0.967 63 0.936 15 0.987 15 0.987 15 0.992 13 0.976 8

Residue on evaporation at 

105 degrees Celsius

–0.190 126 –0.324 26 –0.378 34 –0.378 34 –0.314 19 –0.279 22

Ammonia + organic N, as N 0.06 132 –0.085 28 0.003 35 0.003 35 0.095 21 0.489 23

Ammonia, as N 0.019 117 0.249 20 0.040 33 0.040 33 0.413 19 0.794 23

Nitrite + nitrate, as N –0.024 129 0.552 28 0.770 35 0.770 35 0.340 18 0.862 23

Orthophosphate, as P –0.110 127 –0.238 28 0.641 35 0.641 35 –0.482 16 0.740 23

Phosphorus, as P, total –0.089 131 –0.355 28 0.057 35 0.057 35 –0.173 20 0.335 23

Organic carbon, dissolved 0.358 120 0.103 25 0.123 31 0.123 31 0.340 21 0.123 19

Copper, dissolved 0.359 132 0.391 28 0.356 35 0.356 35 0.491 21 0.518 23

Copper, total –0.182 132 –0.358 28 –0.202 35 –0.202 35 –0.163 21 –0.117 23

Lead, dissolved 0.047 88 –0.266 5 0.223 33 0.223 33 0.835 7 0.544 23

Lead, total –0.248 132 –0.345 28 –0.358 35 –0.358 35 –0.163 21 –0.360 23

Manganese, dissolved 0.442 132 0.214 28 0.464 35 0.464 35 0.308 21 0.769 23
Appendix. Hydrograph Classification 101

Table A3. Correlation among water-quality properties and constituents, by station.—Continued

[Mean streamflow is in cubic feet per second, streamflow volume is in acre-feet, pH is in standard pH units, specific conductance is in microsiemens per 

centimeter; and copper, lead, manganese, and zinc are in micrograms per liter; all other units are milligrams per liter. Corr, Pearson correlation coefficient; 

n, number of pairs used in calculation; N, nitrogen; P, phosphorus; --, not applicable]

Variables All stations Union Denver Henderson Tollgate Sand Creek

Corr n Corr n Corr n Corr n Corr n Corr n

Calcium, dissolved, correlations—Continued

Manganese, total 0.219 132 –0.267 28 –0.153 35 –0.153 35 0.195 21 –0.048 23

Zinc, dissolved 0.328 131 0.456 28 0.480 35 0.480 35 0.521 21 0.622 23

Zinc, total 0.148 131 –0.293 28 –0.214 35 –0.214 35 0.010 21 –0.173 23

Magnesium, dissolved, correlations

Potassium, dissolved 0.353 63 0.775 15 0.760 15 0.760 15 0.031 13 0.868 8

Sodium, dissolved 0.806 63 0.839 15 0.735 15 0.735 15 0.967 13 0.723 8

Alkalinity, fixed endpoint 0.780 63 0.917 15 0.960 15 0.960 15 0.930 13 0.924 8

Chloride, dissolved 0.522 63 0.561 15 0.439 15 0.439 15 0.637 13 0.583 8

Flouride, dissolved 0.235 63 0.650 15 0.849 15 0.849 15 0.650 13 0.851 8

Sulfate, dissolved 0.893 63 0.966 15 0.966 15 0.966 15 0.996 13 0.928 8

Residue on evaporation at 

105 degrees Celsius

–0.225 126 –0.335 26 –0.236 34 –0.236 34 –0.314 19 –0.179 22

Ammonia + organic N, as N 0.156 132 –0.127 28 0.166 35 0.166 35 0.134 21 0.579 23

Ammonia, as N 0.129 117 0.098 20 0.155 33 0.155 33 0.298 19 0.843 23

Nitrite + nitrate, as N 0.089 129 0.489 28 0.702 35 0.702 35 0.285 18 0.802 23

Orthophosphate, as P 0.002 127 –0.163 28 0.587 35 0.587 35 –0.429 16 0.703 23

Phosphorus, as P, total –0.011 131 –0.348 28 0.222 35 0.222 35 –0.133 20 0.394 23

Organic carbon, dissolved 0.330 120 0.033 25 0.070 31 0.070 31 0.365 21 0.077 19

Copper, dissolved 0.347 132 0.444 28 0.237 35 0.237 35 0.478 21 0.440 23

Copper, total –0.138 132 –0.369 28 –0.025 35 –0.025 35 –0.128 21 –0.045 23

Lead, dissolved 0.184 88 –0.224 5 0.353 33 0.353 33 0.887 7 0.554 23

Lead, total –0.215 132 –0.367 28 –0.207 35 –0.207 35 –0.135 21 –0.310 23

Manganese, dissolved 0.384 132 0.134 28 0.603 35 0.603 35 0.219 21 0.801 23

Manganese, total 0.188 132 –0.295 28 –0.027 35 –0.027 35 0.182 21 –0.026 23

Zinc, dissolved 0.374 131 0.268 28 0.441 35 0.441 35 0.446 21 0.606 23

Zinc, total 0.205 131 –0.338 28 –0.037 35 –0.037 35 0.035 21 –0.106 23

Potassium, dissolved, correlations

Sodium, dissolved 0.341 63 0.525 15 0.503 15 0.503 15 0.012 13 0.297 8

Alkalinity, fixed endpoint 0.615 63 0.748 15 0.824 15 0.824 15 0.052 13 0.886 8

Chloride, dissolved 0.311 63 0.178 15 0.193 15 0.193 15 –0.112 13 0.117 8

Flouride, dissolved 0.515 63 0.529 15 0.865 15 0.865 15 0.307 13 0.983 8

Sulfate, dissolved 0.152 63 0.788 15 0.846 15 0.846 15 0.044 13 0.978 8

Residue on evaporation at 

105 degrees Celsius

–0.149 60 –0.245 13 –0.340 15 –0.340 15 –0.074 13 –0.524 7

Ammonia + organic N, as N 0.461 63 0.128 15 0.476 15 0.476 15 0.083 13 0.639 8

Ammonia, as N 0.683 57 0.283 10 0.105 14 0.105 14 –0.174 13 0.804 8

Nitrite + nitrate, as N 0.828 63 0.857 15 0.966 15 0.966 15 0.452 13 0.989 8

Orthophosphate, as P 0.780 63 0.283 15 0.948 15 0.948 15 0.009 13 0.934 8

Phosphorus, as P, total 0.382 63 –0.075 15 0.580 15 0.580 15 –0.087 13 0.624 8

Organic carbon, dissolved 0.423 63 0.549 15 0.638 15 0.638 15 0.558 13 0.017 8

Copper, dissolved 0.490 63 0.853 15 0.610 15 0.610 15 0.383 13 0.508 8

Copper, total 0.112 63 –0.201 15 –0.064 15 –0.064 15 –0.094 13 –0.029 8

Lead, dissolved 0.631 39 –0.964 3 0.550 14 0.550 14 0.562 5 0.865 8

Lead, total 0.041 63 –0.256 15 –0.165 15 –0.165 15 –0.137 13 –0.259 8

Manganese, dissolved 0.275 63 0.214 15 0.771 15 0.771 15 0.317 13 0.907 8

Manganese, total 0.053 63 –0.032 15 0.144 15 0.144 15 –0.146 13 0.253 8

Zinc, dissolved 0.452 62 0.444 15 0.799 15 0.799 15 –0.167 13 0.937 8

Zinc, total 0.113 62 –0.260 15 0.021 15 0.021 15 –0.209 13 –0.126 8

Sodium, dissolved, correlations

Alkalinity, fixed endpoint 0.589 63 0.760 15 0.590 15 0.590 15 0.841 13 0.558 8

Chloride, dissolved 0.858 63 0.906 15 0.921 15 0.921 15 0.790 13 0.982 8

Flouride, dissolved –0.067 63 0.411 15 0.454 15 0.454 15 0.506 13 0.289 8
102 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table A3. Correlation among water-quality properties and constituents, by station.—Continued

[Mean streamflow is in cubic feet per second, streamflow volume is in acre-feet, pH is in standard pH units, specific conductance is in microsiemens per 

centimeter; and copper, lead, manganese, and zinc are in micrograms per liter; all other units are milligrams per liter. Corr, Pearson correlation coefficient; 

n, number of pairs used in calculation; N, nitrogen; P, phosphorus; --, not applicable]

Variables All stations Union Denver Henderson Tollgate Sand Creek

Corr n Corr n Corr n Corr n Corr n Corr n

Sodium, dissolved, correlations—Continued

Sulfate, dissolved 0.825 63 0.791 15 0.627 15 0.627 15 0.960 13 0.422 8

Residue on evaporation at 

105 degrees Celsius

–0.123 60 –0.641 13 –0.347 15 –0.347 15 –0.387 13 0.248 7

Ammonia + organic N, as N 0.288 63 –0.106 15 0.214 15 0.214 15 –0.135 13 0.523 8

Ammonia, as N 0.357 57 –0.105 10 0.407 14 0.407 14 0.455 13 0.642 8

Nitrite + nitrate, as N 0.07 63 0.553 15 0.498 15 0.498 15 0.437 13 0.270 8

Orthophosphate, as P 0.024 63 –0.275 15 0.401 15 0.401 15 –0.552 13 0.175 8

Phosphorus, as P, total 0.026 63 –0.371 15 0.165 15 0.165 15 –0.487 13 0.267 8

Organic carbon, dissolved 0.335 63 –0.045 15 –0.010 15 –0.010 15 0.174 13 –0.417 8

Copper, dissolved 0.287 63 0.218 15 0.155 15 0.155 15 0.621 13 –0.273 8

Copper, total –0.017 63 –0.384 15 –0.188 15 –0.188 15 –0.353 13 0.131 8

Lead, dissolved 0.075 39 0.849 3 0.389 14 0.389 14 0.364 5 –0.092 8

Lead, total –0.051 63 –0.345 15 –0.259 15 –0.259 15 –0.379 13 0.056 8

Manganese, dissolved 0.369 63 0.102 15 0.431 15 0.431 15 –0.181 13 0.542 8

Manganese, total 0.089 63 –0.332 15 –0.045 15 –0.045 15 –0.306 13 –0.100 8

Zinc, dissolved 0.487 62 0.436 15 0.471 15 0.471 15 0.687 13 0.351 8

Zinc, total 0.05 62 –0.328 15 –0.127 15 –0.127 15 –0.097 13 0.147 8

Alkalinity, fixed endpoint, correlations

Chloride, dissolved 0.443 63 0.515 15 0.265 15 0.265 15 0.467 13 0.411 8

Flouride, dissolved 0.631 63 0.766 15 0.928 15 0.928 15 0.762 13 0.917 8

Sulfate, dissolved 0.539 63 0.894 15 0.952 15 0.952 15 0.916 13 0.949 8

Residue on evaporation at 

105 degrees Celsius

–0.246 60 –0.668 13 –0.578 15 –0.578 15 –0.246 13 –0.483 7

Ammonia + organic N, as N 0.102 63 –0.296 15 0.054 15 0.054 15 –0.047 13 0.610 8

Ammonia, as N 0.276 57 0.076 10 0.072 14 0.072 14 0.377 13 0.881 8

Nitrite + nitrate, as N 0.471 63 0.787 15 0.784 15 0.784 15 0.489 13 0.898 8

Orthophosphate, as P 0.263 63 –0.262 15 0.707 15 0.707 15 –0.496 13 0.903 8

Phosphorus, as P, total –0.073 63 –0.588 15 0.150 15 0.150 15 –0.314 13 0.562 8

Organic carbon, dissolved 0.355 63 0.211 15 0.259 15 0.259 15 0.178 13 –0.008 8

Copper, dissolved 0.457 63 0.516 15 0.387 15 0.387 15 0.441 13 0.425 8

Copper, total –0.216 63 –0.654 15 –0.429 15 –0.429 15 –0.186 13 –0.083 8

Lead, dissolved 0.313 39 –0.567 3 0.212 14 0.212 14 0.383 5 0.611 8

Lead, total –0.208 63 –0.671 15 –0.459 15 –0.459 15 –0.217 13 –0.278 8

Manganese, dissolved 0.189 63 0.297 15 0.602 15 0.602 15 –0.100 13 0.984 8

Manganese, total –0.119 63 –0.484 15 –0.254 15 –0.254 15 –0.169 13 0.095 8

Zinc, dissolved 0.496 62 0.618 15 0.532 15 0.532 15 0.676 13 0.843 8

Zinc, total –0.169 62 –0.644 15 –0.364 15 –0.364 15 0.047 13 –0.154 8

Chloride, dissolved, correlations

Flouride, dissolved –0.025 63 0.225 15 0.104 15 0.104 15 –0.041 13 0.108 8

Sulfate, dissolved 0.444 63 0.488 15 0.285 15 0.285 15 0.604 13 0.249 8

Residue on evaporation at 

105 degrees Celsius

–0.165 60 –0.568 13 –0.198 15 –0.198 15 –0.517 13 0.365 7

Ammonia + organic N, as N 0.245 63 –0.142 15 0.187 15 0.187 15 –0.421 13 0.447 8

Ammonia, as N 0.467 57 –0.282 10 0.478 14 0.478 14 0.305 13 0.527 8

Nitrite + nitrate, as N 0.121 63 0.232 15 0.181 15 0.181 15 –0.100 13 0.088 8

Orthophosphate, as P 0.112 63 –0.438 15 0.102 15 0.102 15 –0.112 13 0.003 8

Phosphorus, as P, total 0.038 63 –0.338 15 0.044 15 0.044 15 –0.657 13 0.190 8

Organic carbon, dissolved 0.098 63 –0.241 15 –0.111 15 –0.111 15 –0.225 13 –0.462 8

Copper, dissolved 0.155 63 –0.132 15 0.035 15 0.035 15 0.456 13 –0.405 8

Copper, total –0.009 63 –0.300 15 –0.068 15 –0.068 15 –0.561 13 0.178 8

Lead, dissolved 0.143 39 0.724 3 0.388 14 0.388 14 –0.346 5 –0.261 8

Lead, total –0.026 63 –0.223 15 –0.133 15 –0.133 15 –0.560 13 0.142 8
Appendix. Hydrograph Classification 103

Table A3. Correlation among water-quality properties and constituents, by station.—Continued

[Mean streamflow is in cubic feet per second, streamflow volume is in acre-feet, pH is in standard pH units, specific conductance is in microsiemens per 

centimeter; and copper, lead, manganese, and zinc are in micrograms per liter; all other units are milligrams per liter. Corr, Pearson correlation coefficient; 

n, number of pairs used in calculation; N, nitrogen; P, phosphorus; --, not applicable]

Variables All stations Union Denver Henderson Tollgate Sand Creek

Corr n Corr n Corr n Corr n Corr n Corr n

Chloride, dissolved, correlations—Continued

Manganese, dissolved 0.190 63 0.021 15 0.282 15 0.282 15 –0.315 13 0.394 8

Manganese, total –0.053 63 –0.330 15 –0.028 15 –0.028 15 –0.550 13 –0.115 8

Zinc, dissolved 0.391 62 0.331 15 0.332 15 0.332 15 0.541 13 0.171 8

Zinc, total 0.050 62 –0.225 15 –0.017 15 –0.017 15 –0.358 13 0.211 8

Flouride, dissolved, correlations

Sulfate, dissolved –0.126 63 0.515 15 0.890 15 0.890 15 0.663 13 0.975 8

Residue on evaporation at 

105 degrees Celsius

–0.200 60 –0.508 13 –0.446 15 –0.446 15 0.139 13 –0.551 7

Ammonia + organic N, as N –0.036 63 –0.344 15 0.180 15 0.180 15 0.315 13 0.557 8

Ammonia, as N 0.265 57 0.200 10 –0.072 14 –0.072 14 0.378 13 0.761 8

Nitrite + nitrate, as N 0.572 63 0.639 15 0.850 15 0.850 15 0.725 13 0.997 8

Orthophosphate, as P 0.345 63 –0.497 15 0.785 15 0.785 15 –0.578 13 0.964 8

Phosphorus, as P, total –0.064 63 –0.609 15 0.315 15 0.315 15 0.119 13 0.549 8

Organic carbon, dissolved 0.124 63 0.247 15 0.367 15 0.367 15 0.462 13 0.155 8

Copper, dissolved 0.194 63 0.328 15 0.313 15 0.313 15 0.340 13 0.611 8

Copper, total –0.230 63 –0.671 15 –0.313 15 –0.313 15 0.208 13 –0.120 8

Lead, dissolved 0.481 39 –0.978 3 0.294 14 0.294 14 0.702 5 0.861 8

Lead, total –0.198 63 –0.676 15 –0.327 15 –0.327 15 0.173 13 –0.327 8

Manganese, dissolved 0.019 63 0.594 15 0.624 15 0.624 15 0.118 13 0.919 8

Manganese, total –0.205 63 –0.456 15 –0.102 15 –0.102 15 0.197 13 0.166 8

Zinc, dissolved 0.146 62 0.558 15 0.539 15 0.539 15 0.305 13 0.955 8

Zinc, total –0.235 62 –0.671 15 –0.240 15 –0.240 15 0.319 13 –0.202 8

Sulfate, dissolved, correlations

Residue on evaporation at 

105 degrees Celsius

–0.117 60 –0.616 13 –0.544 15 –0.544 15 –0.313 13 –0.585 7

Ammonia + organic N, as N 0.109 63 –0.116 15 0.096 15 0.096 15 –0.033 13 0.607 8

Ammonia, as N 0.022 57 0.146 10 0.128 14 0.128 14 0.438 13 0.843 8

Nitrite + nitrate, as N –0.099 63 0.741 15 0.828 15 0.828 15 0.579 13 0.968 8

Orthophosphate, as P –0.179 63 0.030 15 0.749 15 0.749 15 –0.612 13 0.940 8

Phosphorus, as P, total –0.131 63 –0.402 15 0.220 15 0.220 15 –0.374 13 0.570 8

Organic carbon, dissolved 0.398 63 0.187 15 0.217 15 0.217 15 0.307 13 –0.023 8

Copper, dissolved 0.325 63 0.650 15 0.379 15 0.379 15 0.614 13 0.482 8

Copper, total –0.132 63 –0.474 15 –0.396 15 –0.396 15 –0.250 13 –0.116 8

Lead, dissolved –0.110 39 –0.019 3 0.177 14 0.177 14 0.534 5 0.757 8

Lead, total –0.167 63 –0.510 15 –0.440 15 –0.440 15 –0.283 13 –0.342 8

Manganese, dissolved 0.370 63 0.140 15 0.527 15 0.527 15 –0.140 13 0.958 8

Manganese, total 0.118 63 –0.313 15 –0.153 15 –0.153 15 –0.179 13 0.131 8

Zinc, dissolved 0.451 62 0.492 15 0.529 15 0.529 15 0.731 13 0.932 8

Zinc, total –0.056 62 –0.461 15 –0.334 15 –0.334 15 0.017 13 –0.206 8

Residue on evaporation at 105 degrees Celsius correlations

Ammonia + organic N, as N 0.335 167 0.921 35 0.670 44 0.670 44 0.299 22 0.341 33

Ammonia, as N 0.014 113 0.563 20 0.510 32 0.510 32 0.168 17 0.009 22

Nitrite + nitrate, as N –0.173 123 –0.169 26 –0.097 34 –0.097 34 0.125 16 –0.198 22

Orthophosphate, as P 0.079 163 0.448 35 –0.014 44 –0.014 44 0.271 18 0.139 33

Phosphorus, as P, total 0.637 167 0.925 35 0.679 44 0.679 44 0.605 22 0.873 33

Organic carbon, dissolved 0.124 114 0.334 23 0.264 30 0.264 30 0.092 19 –0.021 18

Copper, dissolved 0.146 167 0.345 35 –0.243 44 –0.243 44 0.414 22 0.577 33

Copper, total 0.748 126 0.945 26 0.778 34 0.778 34 0.938 19 0.847 22

Lead, dissolved 0.101 88 –0.304 7 0.199 32 0.199 32 0.325 6 0.967 23

Lead, total 0.748 126 0.952 26 0.896 34 0.896 34 0.919 19 0.764 22

Manganese, dissolved 0.084 126 0.648 26 0.090 34 0.090 34 0.050 19 –0.015 22
104 Summary and Evaluation of the Quality of Stormwater in Denver, Colorado, October 2001 to October 2005

Table A3. Correlation among water-quality properties and constituents, by station.—Continued

[Mean streamflow is in cubic feet per second, streamflow volume is in acre-feet, pH is in standard pH units, specific conductance is in microsiemens per 

centimeter; and copper, lead, manganese, and zinc are in micrograms per liter; all other units are milligrams per liter. Corr, Pearson correlation coefficient; 

n, number of pairs used in calculation; N, nitrogen; P, phosphorus; --, not applicable]

Variables All stations Union Denver Henderson Tollgate Sand Creek

Corr n Corr n Corr n Corr n Corr n Corr n

Residue on evaporation at 105 degrees Celsius correlations—Continued

Manganese, total 0.711 126 0.947 26 0.793 34 0.793 34 0.711 19 0.694 22

Zinc, dissolved 0.022 149 0.241 29 –0.089 38 –0.089 38 –0.208 20 0.501 30

Zinc, total 0.321 125 0.950 26 0.761 34 0.761 34 0.899 19 0.802 22

Ammonia + organic nitrogen as N correlations

Ammonia, as N 0.742 117 0.675 20 0.869 33 0.869 33 0.281 19 0.846 23

Nitrite + nitrate, as N 0.441 129 0.067 28 0.363 35 0.363 35 0.229 18 0.599 23

Orthophosphate, as P 0.562 168 0.444 37 0.284 45 0.284 45 –0.505 19 0.509 34

Phosphorus, as P, total 0.770 172 0.932 37 0.947 45 0.947 45 0.756 23 0.511 34

Organic carbon, dissolved 0.464 120 0.409 25 0.490 31 0.490 31 0.389 21 0.314 19

Copper, dissolved 0.116 173 0.265 37 0.016 45 0.016 45 –0.067 24 0.457 34

Copper, total 0.806 132 0.922 28 0.934 35 0.934 35 0.827 21 0.633 23

Lead, dissolved –0.034 91 –0.162 7 0.640 33 0.640 33 0.667 7 0.429 24

Lead, total 0.705 132 0.932 28 0.811 35 0.811 35 0.800 21 0.390 23

Manganese, dissolved 0.249 132 0.703 28 0.581 35 0.581 35 0.112 21 0.828 23

Manganese, total 0.633 132 0.959 28 0.853 35 0.853 35 0.632 21 0.549 23

Zinc, dissolved 0.210 155 0.337 31 0.274 39 0.274 39 –0.047 22 0.594 31

Zinc, total 0.602 131 0.956 28 0.939 35 0.939 35 0.810 21 0.557 23

Ammonia as N correlations

Nitrite + nitrate, as N 0.667 115 0.424 20 0.347 33 0.347 33 0.393 17 0.760 23

Orthophosphate, as p 0.788 114 0.046 20 0.228 33 0.228 33 –0.396 16 0.680 23

Phosphorus, as P, total 0.656 116 0.472 20 0.751 33 0.751 33 0.176 18 0.637 23

Organic carbon, dissolved 0.237 105 0.526 17 0.681 29 0.681 29 –0.164 19 0.233 19

Copper, dissolved 0.206 117 –0.027 20 0.133 33 0.133 33 –0.175 19 0.371 23

Copper, total 0.420 117 0.463 20 0.721 33 0.721 33 0.169 19 0.237 23

Lead, dissolved 0.753 82 –0.992 4 0.695 31 0.695 31 0.006 6 0.751 23

Lead, total 0.314 117 0.491 20 0.590 33 0.590 33 0.231 19 –0.022 23

Manganese, dissolved 0.197 117 0.774 20 0.533 33 0.533 33 0.651 19 0.900 23

Manganese, total 0.187 117 0.507 20 0.619 33 0.619 33 0.533 19 0.211 23

Zinc, dissolved 0.183 116 0.567 20 0.576 33 0.576 33 0.101 19 0.559 23

Zinc, total 0.254 116 0.553 20 0.743 33 0.743 33 0.251 19 0.159 23

Nitrite + nitrate as N correlations

Orthophosphate, as P 0.848 127 0.186 28 0.930 35 0.930 35 –0.479 16 0.806 23

Phosphorus, as P, total 0.437 128 –0.118 28 0.430 35 0.430 35 0.089 17 0.484 23

Organic carbon, dissolved 0.202 117 0.498 25 0.479 31 0.479 31 0.554 18 0.413 19

Copper, dissolved 0.444 129 0.480 28 0.497 35 0.497 35 0.174 18 0.628 23

Copper, total 0.219 129 –0.154 28 0.158 35 0.158 35 0.107 18 0.045 23

Lead, dissolved 0.610 88 –0.094 5 0.535 33 0.535 33 0.421 7 0.761 23

Lead, total 0.149 129 –0.158 28 0.002 35 0.002 35 0.090 18 –0.166 23

Manganese, dissolved 0.160 129 0.186 28 0.648 35 0.648 35 0.306 18 0.849 23

Manganese, total –0.039 129 –0.073 28 0.180 35 0.180 35 0.139 18 0.158 23

Zinc, dissolved 0.073 128 0.511 28 0.738 35 0.738 35 0.249 18 0.671 23

Zinc, total 0.051 128 –0.116 28 0.172 35 0.172 35 0.126 18 0.010 23

Orthophosphate as P correlations

Phosphorus, as P, total 0.556 168 0.427 37 0.423 45 0.423 45 –0.116 19 0.372 34

Organic carbon, dissolved 0.129 115 0.414 25 0.568 31 0.568 31 –0.429 16 0.333 19

Copper, dissolved 0.122 168 0.615 37 0.511 45 0.511 45 0.037 19 0.399 34

Copper, total 0.288 127 0.225 28 0.167 35 0.167 35 –0.373 16 0.072 23

Lead, dissolved –0.060 90 0.373 7 0.558 33 0.558 33 –0.551 6 0.094 24

Lead, total 0.214 127 0.171 28 0.056 35 0.056 35 –0.330 16 –0.119 23

Manganese, dissolved 0.158 127 –0.283 28 0.678 35 0.678 35 –0.412 16 0.668 23

Manganese, total 0.025 127 0.146 28 0.170 35 0.170 35 –0.390 16 0.228 23

Zinc, dissolved 0.072 150 0.617 31 0.704 39 0.704 39 –0.226 17 0.601 31

Zinc, total 0.100 126 0.123 28 0.189 35 0.189 35 –0.459 16 0.073 23
Appendix. Hydrograph Classification 105

Table A3. Correlation among water-quality properties and constituents, by station.—Continued

[Mean streamflow is in cubic feet per second, streamflow volume is in acre-feet, pH is in standard pH units, specific conductance is in microsiemens per 

centimeter; and copper, lead, manganese, and zinc are in micrograms per liter; all other units are milligrams per liter. Corr, Pearson correlation coefficient; 

n, number of pairs used in calculation; N, nitrogen; P, phosphorus; --, not applicable]

Variables All stations Union Denver Henderson Tollgate Sand Creek

Corr n Corr n Corr n Corr n Corr n Corr n

Phosphorus as P, total correlations

Organic carbon, dissolved 0.308 119 0.382 25 0.469 31 0.469 31 0.152 20 0.215 19

Copper, dissolved 0.108 172 0.263 37 –0.017 45 –0.017 45 –0.082 23 0.497 34

Copper, total 0.920 131 0.989 28 0.935 35 0.935 35 0.969 20 0.840 23

Lead, dissolved –0.055 91 –0.314 7 0.612 33 0.612 33 0.518 7 0.450 24

Lead, total 0.830 131 0.979 28 0.826 35 0.826 35 0.979 20 0.601 23

Manganese, dissolved 0.158 131 0.430 28 0.606 35 0.606 35 0.007 20 0.631 23

Manganese, total 0.706 131 0.950 28 0.886 35 0.886 35 0.762 20 0.810 23

Zinc, dissolved 0.080 154 0.205 31 0.283 39 0.283 39 –0.309 21 0.518 31

Zinc, total 0.522 130 0.956 28 0.927 35 0.927 35 0.875 20 0.750 23

Organic carbon, dissolved, correlations

Copper, dissolved 0.552 120 0.489 25 0.640 31 0.640 31 0.607 21 0.552 19

Copper, total 0.237 120 0.326 25 0.376 31 0.376 31 0.174 21 –0.012 19

Lead, dissolved 0.451 78 –0.896 4 0.733 29 0.733 29 0.798 7 0.571 19

Lead, total 0.201 120 0.281 25 0.314 31 0.314 31 0.113 21 –0.082 19

Manganese, dissolved 0.242 120 0.238 25 0.540 31 0.540 31 –0.016 21 0.435 19

Manganese, total 0.355 120 0.438 25 0.318 31 0.318 31 0.118 21 0.054 19

Zinc, dissolved 0.330 119 0.068 25 0.778 31 0.778 31 0.138 21 0.342 19

Zinc, total 0.362 119 0.276 25 0.416 31 0.416 31 0.163 21 –0.002 19

Copper, dissolved, correlations

Copper, total –0.168 132 –0.198 28 –0.089 35 –0.089 35 –0.290 21 –0.347 23

Lead, dissolved 0.396 91 0.313 7 0.529 33 0.529 33 0.561 7 0.911 24

Lead, total –0.234 132 –0.244 28 –0.225 35 –0.225 35 –0.331 21 –0.421 23

Manganese, dissolved 0.020 132 –0.177 28 0.357 35 0.357 35 –0.199 21 0.447 23

Manganese, total –0.166 132 –0.122 28 –0.148 35 –0.148 35 –0.266 21 –0.224 23

Zinc, dissolved 0.176 155 0.916 31 0.802 39 0.802 39 0.341 22 0.795 31

Zinc, total –0.038 131 –0.261 28 –0.074 35 –0.074 35 –0.251 21 –0.313 23

Copper, total, correlations

Lead, dissolved 0.495 88 –0.583 5 0.522 33 0.522 33 0.351 7 0.452 23

Lead, total 0.950 132 0.989 28 0.936 35 0.936 35 0.992 21 0.895 23

Manganese, dissolved 0.085 132 0.439 28 0.397 35 0.397 35 –0.034 21 0.204 23

Manganese, total 0.743 132 0.956 28 0.932 35 0.932 35 0.722 21 0.916 23

Zinc, dissolved 0.036 131 –0.196 28 0.246 35 0.246 35 –0.303 21 0.068 23

Zinc, total 0.490 131 0.977 28 0.990 35 0.990 35 0.929 21 0.953 23

Lead, dissolved, correlations

Lead, total 0.381 88 –0.564 5 0.362 33 0.362 33 0.316 7 0.256 23

Manganese, dissolved 0.377 88 –0.435 5 0.704 33 0.704 33 0.596 7 0.862 23

Manganese, total 0.326 88 –0.545 5 0.388 33 0.388 33 0.770 7 0.442 23

Zinc, dissolved 0.087 88 0.593 5 0.838 33 0.838 33 0.175 7 0.693 24

Zinc, total 0.365 87 –0.476 5 0.560 33 0.560 33 0.408 7 0.426 23

Lead, total, correlations

Manganese, dissolved 0.034 132 0.506 28 0.215 35 0.215 35 –0.015 21 –0.034 23

Manganese, total 0.693 132 0.948 28 0.891 35 0.891 35 0.742 21 0.741 23

Zinc, dissolved 0.038 131 –0.166 28 0.093 35 0.093 35 –0.323 21 –0.102 23

Zinc, total 0.496 131 0.988 28 0.940 35 0.940 35 0.912 21 0.866 23

Manganese, dissolved, correlations

Manganese, total 0.489 132 0.568 28 0.259 35 0.259 35 0.560 21 0.203 23

Zinc, dissolved 0.162 131 0.340 28 0.706 35 0.706 35 0.065 21 0.637 23

Zinc, total 0.156 131 0.571 28 0.427 35 0.427 35 0.032 21 0.135 23

Manganese, total, correlations

Zinc, dissolved 0.199 131 –0.064 28 0.132 35 0.132 35 –0.081 21 0.137 23

Zinc, total 0.558 131 0.956 28 0.904 35 0.904 35 0.764 21 0.900 23

Zinc, dissolved, correlations

Zinc, total 0.828 131 –0.089 28 0.302 35 0.302 35 0 21 0.185 23
Publishing support provided by:

Denver Publishing Service Center, Denver, Colorado

Manuscript approved for publication, July 21, 2008

Edited by Mary A. Kidd

Graphics and layout by Joy Monson

For more information concerning this publication, contact:

Director, USGS Colorado Water Science Center

Box 25046, MS 415

Denver, CO 80225

(303) 236-4882

Or visit the Colorado Water Science Center Web site at:

http://co.water.usgs.gov/

This publication is available online at:

http://pubs.usgs.gov/sir/2008/5134