U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2020–5004

Prepared in cooperation with the City of Rapid City

Stormwater Quality of Infrastructure Elements in 

Rapid City, South Dakota, 2016–18
Cover: Upper photograph, Stormwater channel best-management practice near Jackson 

Boulevard in Rapid City, South Dakota. (Photograph by Galen Hoogestraat, U.S. Geological Survey).

Lower photographs, Trinity Eco Prayer Park area near downtown Rapid City, South Dakota. 

(Photographs by Ken Steinken). 
Stormwater Quality of Infrastructure 

Elements in Rapid City, South 

Dakota, 2016–18

By Galen K. Hoogestraat

Prepared in cooperation with the City of Rapid City

Scientific Investigations Report 2020–5004

U.S. Department of the Interior

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

DAVID BERNHARDT, Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2020

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Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Hoogestraat, G.K., 2020, Stormwater quality of infrastructure elements in Rapid City, South Dakota, 2016–18: U.S. 

Geological Survey Scientific Investigations Report 2020–5004, 24 p., https://doi.org/10.3133/sir20205004.

Associated data for this publication:

U.S. Geological Survey, 2019, USGS water data for the Nation: U.S. Geological Survey National Water Information 

System database, accessed September 5, 2019, at https://doi.org/10.5066/F7P55KJN.

ISSN 2328-0328 (online)
iii

Acknowledgments

The author would like to thank the staff from the City of Rapid City Public Works Department 

for providing technical guidance during this study. Appreciation is also given to the owners and 

staff from private facilities where sampling sites were located, including the Calvary Lutheran 

Church, Trinity Lutheran Church, and Eco Prayer Park (Ken Steinken). The author also would like 

to acknowledge the staff from the U.S. Geological Survey Dakota Water Science Center who 

supported the project by assisting with data collection, administration, and technical reviews.

v

Contents

Acknowledgments........................................................................................................................................iii

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

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

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

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

Previous Studies ...................................................................................................................................3

Methods...........................................................................................................................................................5

Selection and Description of Sampling Sites ...................................................................................5

Collection and Analyses of Water Samples .....................................................................................6

Quality Assurance and Quality Control ..................................................................................13

Stormwater Quality of Infrastructure Elements ......................................................................................14

Jackson Flowpath ...............................................................................................................................14

Wildwood Flowpath ............................................................................................................................17

Eco Prayer Park Flowpath .................................................................................................................17

Infrastructure Site Type Summary ...................................................................................................17

Summary........................................................................................................................................................21

References Cited..........................................................................................................................................22

Appendix 1 Stormwater-Quality Data ...................................................................................................24

Figures

1. Map showing the study area, U.S. Geological Survey streamgages, and 

stormwater-quality flowpath site groups in Rapid City, South Dakota ................................4

2. Map showing the Jackson stormwater-quality flowpath sampling sites and 

drainage flowpath network in Rapid City, South Dakota........................................................7

3. Photographs showing the Jackson stormwater-quality flowpath sampling site 

types in Rapid City, South Dakota ..............................................................................................8

4. Map showing the Wildwood stormwater-quality flowpath sampling sites and 

drainage flowpath network, Rapid City, South Dakota ...........................................................9

5. Photographs showing the Wildwood stormwater-quality flowpath sampling site 

types in Rapid City, South Dakota ............................................................................................10

6. Map showing the Eco Prayer Park stormwater-quality flowpath sampling sites 

and drainage flowpath network in Rapid City, South Dakota ..............................................11

7. Photographs showing the Eco Prayer Park stormwater-quality flowpath 

sampling site types in Rapid City, South Dakota....................................................................12

8. Graphs showing example stormwater-quality data plot for Jackson flowpath on 

May 24, 2016 ................................................................................................................................16

9. Graphs showing example stormwater-quality data plot for Wildwood flowpath 

on May 17, 2017 ...........................................................................................................................18

10. Graphs showing example stormwater-quality data plot for Eco Prayer Park 

flowpath on September 12, 2017 ..............................................................................................19
vi

Tables

1. U.S. Geological Survey site information for Rapid Creek sites near Rapid City, 

South Dakota .................................................................................................................................5

2. List of stormwater-quality sampling sites for the Jackson, Wildwood, and Eco 

Prayer Park flowpaths in Rapid City, South Dakota ................................................................6

3. Blank and replicate water-quality sample results for samples collected at 

various stormwater flowpath sites in Rapid City, South Dakota .........................................14

4. Summary statistics for water-quality results at stormwater sampling sites in 

Rapid City, South Dakota ...........................................................................................................15

5. Median Escherichia coli concentration, total suspended solids concentration, 

and specific conductance of site types sampled in 2016–18, Rapid City, 

South Dakota ...............................................................................................................................20

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2)

Flow rate

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

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

 °C = (°F – 32) / 1.8.

Datum

Horizontal coordinate information is referenced to the North American Datum of 1983.

Supplemental Information

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 in milligrams per liter (mg/L).

Water year (WY) is the 12-month period, October 1 through September 30, and is designated by

the calendar year in which it ends. Thus, the water year ending September 30, 2016, is called the

“2016” water year.
vii

Abbreviations

BMP best management practice

CHN open channel

CRB street curb and gutter

DSP downspout E. coli Escherichia coli

FIB fecal indicator bacteria

PKL parking lot

RPD relative percent difference

TMDL total maximum daily load

TSS total suspended solids

USGS U.S. Geological Survey

USS underground storm sewer

Stormwater Quality of Infrastructure Elements in Rapid 

City, South Dakota, 2016–18

By Galen K. Hoogestraat

Abstract

As runoff flows over the land or impervious surfaces 

(paved streets, parking lots, and building roofs), it accumulates 

debris, chemicals, sediment, and other contaminants that can 

adversely affect water quality if the runoff discharge remains 

untreated. Pathogens, commonly measured using fecal indicator 

bacteria such as Escherichia coli, enterococci, or fecal coliform, 

are the most-frequent cause of water-quality impairment in 

rivers and streams in the United States. Rapid Creek originates 

in the western Black Hills area and flows east through Rapid 

City, South Dakota, to its mouth at the Cheyenne River. The 

water quality of Rapid Creek is important because the reach 

that flows through Rapid City is a valuable spawning area for a 

self-sustaining trout fishery, is actively used for recreation, and 

is a seasonal municipal water supply for the City of Rapid City. 

These uses (fishery, recreation, and water supply) are considered 

beneficial uses by the South Dakota Department of Environment 

and Natural Resources. Numerical criteria have been established 

for total suspended solids and Escherichia coli concentrations, 

among other water-quality constituents, for these beneficial 

uses. The objectives of this study were to improve the method 

by which fecal indicator bacteria and total suspended solids 

are quantified in the urban drainages within Rapid City and to 

provide information that helps identify origins of fecal indicator bacteria and total suspended solids. This information can be 

used in hydrologic models to estimate fecal indicator bacteria 

and total suspended solid loading from certain infrastructure 

elements in urban environments.

Stormwater samples analyzed for Escherichia coli, total 

suspended solids, specific conductance, and pH were collected 

in three drainage basin flowpaths within Rapid City: Jackson, 

Wildwood, and the Eco Prayer Park. Data-collection activities 

for this study focused on upgradient urban flowpath elements 

during rainfall events. This approach builds upon previous 

stormwater assessments that characterized the water quality in 

urban basin outlets near the downstream end of the stormwater 

flowpaths. Within each flowpath group, 4–6 sites were selected 

to represent the various infrastructure elements of the runoff 

process. These elements included roof downspouts, parking 

lots, street curbs and gutters, open channels, underground 

storm sewers, and stormwater ponds or best-management 

practice facilities.

In general, the concentrations of Escherichia coli and 

total suspended solids increased in the downstream direction 

for all flowpath sites. The wash-off process after the first flush 

is evident for total suspended solids and specific conductance; 

however, Escherichia coli concentrations did not necessarily 

follow the same pattern. Escherichia coli concentrations in 

the latter part of the runoff period were similar to or greater 

than the initial concentrations of the first set of samples. 

Stormwater-quality data were summarized by infrastructure 

type (roof downspout, parking lot, street curb, and channel/

storm sewer) to provide information about approximate waterquality concentrations originating at the upper end of urban 

flowpaths. Escherichia coli and total suspended solid concentrations were lowest in samples collected from locations most 

isolated from human influence (roof downspouts); the median 

concentrations at these sites were 4 most probable number 

per 100 milliliters and 15 milligrams per liter, respectively. 

The delivery potential of fecal indicator bacteria and sediment from parking lots and street curbs was similar; median 

concentrations of Escherichia coli and total suspended solids 

were around 150–220 most probable number per 100 milliliters and 56–86 milligrams per liter, respectively. The downstream receiving channels and storm sewers where stormwater 

was aggregated typically contained the highest Escherichia 

coli concentrations (median was 1,800 most probable number 

per 100 milliliters), but the total suspended solid concentrations were similar to upstream elements in the flowpath 

(median was 69 milligrams per liter). The data collected from 

this study demonstrate that stormwater is contaminated with 

fecal indicator bacteria upon initial contact with impervious 

surfaces and highlight the importance of controlling the volume of stormwater discharges into receiving waterbodies via 

storage structures and pervious elements. Diluting stormwater 

with high concentrations of Escherichia coli with the receiving 

water’s (Rapid Creek) lower concentration of Escherichia coli

is likely the primary mechanism for meeting the beneficial-use 

criterion threshold of 235 most probable number per 100 milliliters. Although total suspended solid concentrations in the 

upper parts of the basin (parking lots and street curbs) also 

begin at concentrations (56 to 86 milligrams per liter) above 

the beneficial-use criterion for Rapid Creek (53 milligrams 

per liter), current stormwater-control practices (storage ponds, 

swales, and wetlands) may be able to reduce suspendedsediment concentrations to meet this threshold.
2 Stormwater Quality of Infrastructure Elements in Rapid City, South Dakota, 2016–18

Introduction

Stormwater runoff from urbanized lands can cause 

physical, biological, and chemical changes in the receiving 

waters, which can impair designated uses (U.S. Environmental 

Protection Agency, 2010). As runoff flows over the land or 

impervious surfaces (paved streets, parking lots, and building roofs), it accumulates debris, chemicals, sediment, or 

other contaminants that could adversely affect water quality if the runoff remains untreated. Pathogens are the mostfrequent cause of water-quality impairment in rivers and 

streams in the United States; more than 180,000 river miles 

are listed as impaired by pathogens on State 303(d) lists 

(U.S. Environmental Protection Agency, 2019; American 

Society of Civil Engineers, 2014). Pathogen impairments 

usually are identified based on elevated counts of fecal 

indicator bacteria (FIB), such as Escherichia coli (E. coli), 

enterococci, or fecal coliform. Sediment is the secondmost-frequent cause of water-quality impairment in rivers 

and streams in the United States; more than 130,000 river 

miles are listed as impaired by sediment on State 303(d) lists 

(U.S. Environmental Protection Agency, 2019).

Rapid Creek is a valuable natural resource, and protecting its water quality is important because the reach that flows 

through Rapid City, South Dakota, is a critical spawning area 

for a self-sustaining trout fishery, is actively used for recreation, and is a seasonal municipal water supply for the City 

of Rapid City. Per the Clean Water Act, the South Dakota 

Department of Environment and Natural Resources (DENR) 

lists beneficial uses of major streams and rivers in the State. 

For example, Rapid Creek through Rapid City has beneficial 

uses of domestic water supply, coldwater permanent fish 

life propagation, immersion recreation, and limited-contact 

recreation (South Dakota Department of Environment and 

Natural Resources, 2010). For total suspended solids (TSS), 

the most restrictive of the water-quality requirements is 

related to the beneficial use of cold-water permanent fish 

life propagation. The water-quality standard/requirement 

for TSS is a geometric-mean concentration not to exceed 

30 milligrams per liter (mg/L) during a 30-day period, and a 

single sample should not exceed 53 mg/L. Immersion recreation carries a designation based on FIB concentrations: 

E. coli concentrations should not exceed 126 most probable 

number per 100 milliliters (mpn/100 mL) during a 30-day 

period or 235 mpn/100 mL for a single sample (South Dakota 

Department of Environment and Natural Resources, 2010).

During 2014, water quality in Rapid Creek for reaches 

upstream from Rapid City met designated beneficial-use 

water-quality standards; however, Rapid Creek from Canyon 

Lake to the Cheyenne River was impaired because of excessive fecal coliform, E. coli, or both bacteria levels (South 

Dakota Department of Environment and Natural Resources, 

2014). A recent compilation of water-quality data for Rapid 

City drainages documented event-mean concentrations for 

E. coli of 7,200 to 21,000 mpn/100 mL in developed basins 

(Hoogestraat, 2015), demonstrating the presence of high FIB 

concentrations entering Rapid Creek during runoff. A total 

maximum daily load (TMDL) criterion for FIB for reaches 

within and downstream from Rapid City was approved by 

the South Dakota DENR in 2010. A TMDL is a calculation 

of the maximum amount of a pollutant that a waterbody can 

receive and still meet water-quality standards (South Dakota 

Department of Environment and Natural Resources, 2019). 

Approval of a TMDL for a waterbody commonly is followed by an implementation project with goals to reduce 

pollution sources within the drainage basin. Major purposes 

of the TMDL assessment are to identify potential causes or 

sources of the water-quality impairment and to suggest bestmanagement practices (BMPs) for reducing those impairments (South Dakota Department of Environment and Natural 

Resources, 2019). Methods of identifying FIB impairments in 

surface water are usually limited to a general assessment of 

sources (typically grouped as livestock, wildlife, or human). 

For the Rapid Creek bacteria TMDL, FIB load estimates were 

derived from the Bacteria Indicator Tool (U.S. Environmental 

Protection Agency, 2000), which models loads primarily 

based on land-use classifications. This derivation is common 

for bacteria TMDLs because FIB sample data about specific 

sources typically are not available. The lack of data to connect FIB concentrations in receiving waterbodies to its actual 

sources represents an area of needed research in the TMDL 

process. Implementation projects may target a source within 

the watershed that does not contribute to the FIB load, and 

those sources that do contribute FIB load are overlooked. An 

improvement on this process would include collecting FIB 

data from various flowpaths, which would allow for isolating and targeting specific contributing areas where FIB is 

known to originate. The U.S. Geological Survey (USGS), in 

cooperation with the City of Rapid City, began a stormwaterquality study in 2016 to improve the method by which FIB 

and TSS are quantified in the urban drainages within Rapid 

City and to provide information that helps identify origins of 

FIB and TSS.

Purpose and Scope

The purposes of this report are to describe the methods 

and data collected from urban flowpath sites in Rapid City 

during 2016–18 and to provide statistical summaries of the 

water-quality data for the various infrastructure site types 

that were sampled for the stormwater-quality study. This 

information could be used in hydrologic models to estimate 

FIB and TSS loading from certain infrastructure elements in 

urban environments. This study only involved data collection 

within the city of Rapid City; however, the results are transferable to urban drainages in cities with similar infrastructure 

and climate.
Introduction 3

Description of the Study Area

Stormwater datasets were collected in 3 urban flowpaths 

within Rapid City: Jackson (6 sampling sites), Wildwood 

(6 sampling sites), and Eco Prayer Park (4 sampling 

sites; fig. 1). Rapid City has a population of about 75,000 

(U.S. Census Bureau, 2019) and is in the eastern foothills 

of the Black Hills. Within the city limits, the areas developed with the most impervious infrastructure are along the 

Highway 16/I–190 corridor and to the east (fig. 1). The west 

side of Rapid City generally has less intense development, 

more open space, and natural grass-lined drainage channels. The Rapid City region is susceptible to short-duration, 

intense, convective thunderstorms during the spring and 

summer months (Driscoll and others, 2010). The mean annual 

(1981–2010) precipitation for Rapid City is 19.8 inches, of 

which 12.0 inches fall during April–July (National Oceanic 

and Atmospheric Administration, 2014).

Rapid Creek originates in the western Black Hills 

area and flows east through Rapid City to its mouth at 

the Cheyenne River (fig. 1). The mean annual streamflow 

for Rapid Creek above Canyon Lake (USGS streamgage 

06412500; fig. 1; table 1) was 56 cubic feet per second 

(ft3/s) during water years 1981–2017 with a drainage area 

of 374 square miles (mi2). All streamflow data are from the 

USGS National Water Information System (U.S. Geological 

Survey, 2019). The mean annual streamflow for Rapid Creek 

at Rapid City (USGS streamgage 06414000) was 77 ft3/s with 

a drainage area of 413 mi2. The mean annual streamflow for 

Rapid Creek below the sewage treatment plant near Rapid City 

(USGS streamgage 06418900, not shown on fig. 1, located 

2 miles east) was 90 ft3/s with a drainage area of 456 mi2.

Mean annual streamflow increases 21 ft3/s in the 

39 mi2 between the streamgage on the upstream west boundary (streamgage 06412500) and in the middle (streamgage 

06414000) of Rapid City. This increase includes mean annual 

springflow of about 14 ft3/s from two springs on the west side 

of Rapid City (streamgages 06412810 and 06413650; fig. 1; 

table 1). The remaining 7 ft3/s increase in mean annual streamflow can be attributed to the predominantly developed, urban 

39-mi2 drainage area, or an increase of 0.18 ft3/s per square 

mile of drainage area on the west side of Rapid City. Mean 

annual streamflow increases 13 ft3/s in the 43 mi2 between the 

streamgage in the middle (streamgage 06414000) and on the 

downstream east boundary (streamgage 06418900) of Rapid 

City, or 0.29 ft3/s per square mile of drainage area on the east 

side of Rapid City. The mean annual streamflow of Rapid 

Creek increases a total of 34 ft3/s (60 percent) between the 

upstream and downstream boundaries of Rapid City (which 

includes the 14 ft3/s from springflow), or an increase of 

20 ft3/s (37 percent) from the intervening urban drainage area 

without including springflow.

Previous Studies

In the past 40 years, several studies have examined 

stormwater runoff in the Rapid City area, mostly focusing on 

the quantity and quality of runoff as it enters Rapid Creek. 

Hoogestraat (2015) provides the most recent compilation 

of stormwater information in the Rapid City area, wherein 

stormwater quality was assessed in three urban drainages during 2008–14. In that study, event-mean concentrations of TSS 

and FIB typically exceeded relevant beneficial-use criteria 

for Rapid Creek by 1–2 orders of magnitude. Three wetland 

channels at the outlet of an urban drainage basin were assessed 

for contaminant removal capability. The assessment indicated 

that these treatment controls were capable of reducing TSS 

concentrations by 40 percent; however, bacteria removal 

rates were lower, and in some cases, concentrations increased 

(Hoogestraat, 2015). Pirner and Harms (1978) studied urban 

runoff as a potential source of pollution in Rapid Creek. The 

Nationwide Urban Runoff Program chose Rapid City as one of 

its study locations during the early 1980s and analyzed numerous water-quality constituents (U.S. Environmental Protection 

Agency, 1983). Prann (2013) evaluated the effect of impervious surfaces in Rapid City on water quality using calibrated 

hydrologic models.

These local studies indicated that TSS and bacteria 

concentrations in stormwater runoff have the potential to 

adversely affect water quality in the Rapid Creek drainage 

basin; however, research regarding sources of the bacteria or 

loading estimates from the headwaters (urban infrastructure) is 

sparse. A study in southern California (Tiefenthaler and others, 

2011) quantified the relative levels and flux patterns of E. coli, 

enterococci, and total coliforms from representative land-use 

types (such as high-density residential, industrial, or commercial). Bacteria and sediment loads from urban infrastructure 

have been estimated most frequently using model simulations 

(Riebschleager and others, 2012; Granato, 2013).
4 Stormwater Quality of Infrastructure Elements in Rapid City, South Dakota, 2016–18

#

#

#

#

£¤16

§ ̈¦90

§ ̈¦190

§ ̈¦90

06413650

06412810

103°15'00" 103°10'00"

44°07'30"

44°05'00"

44°02'30"

Rapid Creek

Rapid City

Wildwood

flowpath

(fig. 4)

Jackson

flowpath

(fig. 2)

0 1 2 3 MILES

0 1 2 3 4 KILOMETERS

Eco Prayer Park

flowpath (fig. 6)

Base from U.S. Geological Survey digital data 

Universal Transverse Mercator Projection, Zone 13 North

EXPLANATION

# U.S. Geological Survey streamgage and identifier

Drainage flowpath

SOUTH

DAKOTA

Rapid

City

Cheyenne River

Black

Hills

area

06414000

06414000

06412500

Rapid

Creek

Missouri River

Figure 1. Study area, U.S. Geological Survey streamgages, and stormwater-quality flowpath site groups in Rapid City, South 

Dakota.
Methods 5

Table 1. U.S. Geological Survey site information for Rapid Creek sites near Rapid City, South Dakota.

[Data are from the National Water Information System database (U.S. Geological Survey, 2019). mi2, square mile; ft3/s, cubic foot per second; --, not applicable]

U.S. Geological 

Survey site number U.S. Geological Survey site name Drainage 

area (mi2)

Mean annual flow 

(ft3/s)

Data period

06412500 Rapid Creek above Canyon Lake near Rapid City, South Dakota 374 56 1981–2017

06412810 Cleghorn Springs at Rapid City, South Dakota -- 12 1993–2017

06413650 Lime Creek at Mouth at Rapid City, South Dakota 9.8 2 1988–2002

06414000 Rapid Creek at Rapid City, South Dakota 413 77 1981–2017

06418900 Rapid Creek below sewage treatment plant near Rapid City, South 

Dakota

456 90 1981–2017

Methods

Data-collection activities for this study focused on the 

upgradient urban flowpath elements during rainfall, including roof downspouts, parking lots, street curbs, and drainage 

channels. The sampling plan started at the source (beginning) 

of the urban flowpath (roof) and moved downgradient along 

the urban flowpath. This approach builds upon a previous 

stormwater assessment (Hoogestraat, 2015) that characterized 

the water quality in urban basin outlets near the downstream 

end of the stormwater flowpaths. Three flowpath site groups, 

which are in separate areas within Rapid City (fig. 1), were 

sampled for water quality in 2016–18. Within each flowpath group, 4–6 sites were selected to represent the various 

elements of the runoff process. These elements include roof 

downspouts (DSP), parking lots (PKL), street curbs and gutters (CRB), open channels (CHN), underground storm sewers 

(USS), and stormwater ponds or BMP facilities.

Selection and Description of Sampling Sites

The flowpath sampling sites were selected based on 

several factors: availability of previous water-quality data 

within the same drainage, previous undocumented observations of flow, sampling logistics (quick response for personnel 

during runoff events), and presence of multiple infrastructure 

element types within a short flowpath distance. These selected 

sites (table 2) were used to examine the potential bacteria 

and sediment loads of various infrastructure elements. The 

Jackson flowpath sites were selected based on ease of sampling logistics (quickest access for staff during runoff events) 

and because they included a mix of multiple infrastructure 

types in a short flowpath distance. The Wildwood flowpath 

sites were selected based on sampling logistics and on the 

availability of multiple infrastructure drainage sources (street 

curb and parking lots) nearby and because stormwater-quality 

data were previously collected downstream within the same 

drainage (Hoogestraat, 2015). The Eco Prayer Park sites were 

selected because they were in an area where best-management 

practices (stormwater-treatment area) were in place and where 

well-defined inflow and outflow points existed.

Each of the three flowpaths represents a unique set of 

land-use characteristics that affect stormwater quality. The 

Jackson flowpath (figs. 2–3) originates at a commercial office 

complex (fig. 3A) and includes a curb (fig. 3B), an underground storm sewer (fig. 3C), and an open concrete-lined 

channel flow before flowing into an infiltration trench/retention area (fig. 3D). The Jackson flowpath sampling sites represented all infrastructure types targeted in this study, including 

a roof downspout, parking lot, underground storm sewer, open 

drainage channel, and BMP channel outlet. Samples were 

generally collected at the downspout, parking lot, and street 

curb sites before sample collection at the channel and storm 

sewer sites farther down the flowpath. The channel and storm 

sewer sites (table 2) in the Jackson flowpath (WTP–USS, 

WTP–CHN, and WTP–BMP) included stormwater drainage 

from a highly developed commercial corridor area (northwest 

corner of fig. 2) not represented by the upstream flowpath sites 

(USG–DSP, USG–PKL, and USG–CRB).

The Wildwood flowpath contains a mix of low-density 

residential and commercial uses in the drainage area. The 

upper end of the Wildwood flowpath (figs. 4–5) contains 

primarily low-density residential lots with septic systems. 

When FIB are detected in surface water that originates from 

these areas, a common hypothesis has been that septic systems 

are a likely source; however, past monitoring has indicated 

that higher bacteria concentrations are often measured in 

Rapid City urban basins that do not have septic systems 

(Hoogestraat, 2015). The Wildwood flowpath includes commercial parking lot outfalls, curb discharges, and grass-lined 

channels in the same general area. The Wildwood flowpath 

sampling sites (table 2; fig. 4) included 1 roof downspout 

(CLC–DSP; fig. 5C), 2 parking lots (CLC–PKL and ATH–

PKL; figs. 5A and 5D), 2 street curbs (WDW–CRB and 

SDC–CRB; figs. 5B and 5E), and 1 open grass-lined drainage 

channel (SDC–CHN; fig. 5E).

The Eco Prayer Park flowpath (figs. 6–7) represents the 

most uniform land use because the basin elements are completely impervious. FIB and sediment from this flowpath can 
6 Stormwater Quality of Infrastructure Elements in Rapid City, South Dakota, 2016–18

Table 2. List of stormwater-quality sampling sites for the Jackson, Wildwood, and Eco Prayer Park flowpaths in Rapid City, South 

Dakota.

Site information is from the National Water Information System database (U.S. Geological Survey, 2019). 

Short identifier U.S. Geological Survey 

site number U.S. Geological Survey site name Site type

Jackson flowpath

USG–DSP 440416103151700 Downspout at the U.S. Geological Survey office at Rapid City, South 

Dakota

Roof downspout

USG–PKL 440416103151900 Parking lot runoff at the U.S. Geological Survey at Rapid City, South 

Dakota

Parking lot

USG–CRB 440417103152202 Curb at Mt. View Road at Rapid City, South Dakota Street curb

WTP–CHN 440429103151300 Storm drain channel at the water treatment plant at Rapid City, South 

Dakota

Channel/storm sewer

WTP–USS 440430103151000 Storm sewer outfall at Jackson at Rapid City, South Dakota Channel/storm sewer

WTP–BMP 440436103151400 Storm sewer best-management practice outlet at Rapid City, South 

Dakota

Channel/storm sewer

Wildwood flowpath

CLC–DSP 440155103162100 Roof downspout near Sheridan Lake Road at Rapid City, South 

Dakota

Roof downspout

CLC–PKL 440154103162100 Church parking lot near Sheridan Lake Road at Rapid City, South 

Dakota

Parking lot

WDW–CRB 440150103162300 Curb at Wildwood Drive at Rapid City, South Dakota Street curb

ATH–PKL 440156103161800 Parking lot at Autumn Hills at Rapid City, South Dakota Parking lot

SDC–CRB 440202103161600 Curb at Summerset Drive at Rapid City, South Dakota Street curb

SDC–CHN 440201103161500 Arrowhead drainage at Summerset Drive Channel/storm sewer

Eco Prayer Park flowpath

EPP–DSP 440444103132800 Downspout at Trinity Lutheran Church at Rapid City, South Dakota Roof downspout

EPP–PKL 440445103132900 Eco Prayer Park inlet at Rapid City, South Dakota Parking lot

EPP–CHN 440445103132700 Eco Prayer Park pond inlet at Rapid City, South Dakota Channel/storm sewer

EPP–BMP 440445103132600 Eco Prayer Park outlet at Rapid City, South Dakota Channel/storm sewer

be attributed entirely to commercial uses and street traffic. The 

Eco Prayer Park flowpath sites (table 2) included 1 roof downspout (EPP–DSP; fig. 7A), 1 parking lot (EPP–PKL; fig. 7B), 

1 rock-lined channel (EPP–CHN; fig. 7C), and 1 outlet from 

a small retention pond BMP (EPP–BMP; fig. 7D). A stage 

plate was installed in the retention pond to record changes in 

the water level during runoff at the EPP–BMP site (fig. 7D). 

During high inflows to the Eco Prayer Park, the flow splits 

between the rock channel and an overflow path into a grassed 

lawn area to the north side (fig. 6). This grassed lawn contains 

underdrains that flow back into the retention pond.

Collection and Analyses of Water Samples

Water-quality samples were collected at each flowpath 

site during storm events during May–September in 2016–18. A 

storm event was defined as having at least 0.10 inch of precipitation that was separated by at least 72 hours of preceding dry 

weather conditions. Collection generally began at the upstream 

sites and continued downstream in consecutive order. Multiple 

samples were collected at each flowpath site during runoff 

events to capture the variability in water-quality concentrations as the runoff hydrograph rises (“first flush” process) and 

falls after the peak runoff (when material from impervious 

surfaces have “washed off”). The number of samples collected 

at each flowpath site during a sampling event varied depending on the duration of precipitation and the resulting runoff. 

Estimates of depth of flow using a ruler or wading rod were 

made at each site during sample collection to assess whether 

the runoff was increasing or decreasing, but depth or flow 

information are not presented in this report.

Water-quality samples were collected by USGS personnel 

and analyzed for E. coli and TSS by Mid Continent Testing 

Laboratories (Rapid City, S. Dak.) according to standard procedures (American Public Health Association, 2015). Standard 

procedures for water-quality sample collection followed the 

USGS National Field Manual (U.S. Geological Survey, 2006). 

Bottles used in sampling procedures were routinely cleaned 
Methods 7

! ! !

!

!

!WTP–BMP

WTP–USS

WTP–CHN

USG–CRB

USG–PKL

USG–DSP

103°15'30" 103°15'15" 103°15'00"

44°04'30"

44°04'15"

Base from U.S. Geological Survey digital data

Map image is the intellectual property of Esri and is used herein under license. 

Copyright © 2014 Esri and its licensors. All rights reserved. 

Universal Transverse Mercator projection 

Zone 13 North

EXPLANATION

! Sampling site and identifier (table 1)

Drainage flowpath

WTP–BMP

0 100 200 300 400 500 600 FEET

0 50 100 75 200 METERS

Figure 2. Jackson stormwater-quality flowpath sampling sites and drainage flowpath network in Rapid City, South Dakota.
8 Stormwater Quality of Infrastructure Elements in Rapid City, South Dakota, 2016–18

A

B

C

D

Figure 3. Jackson stormwater-quality flowpath sampling site types in Rapid City, South Dakota. 

A, roof downspout site USG–DSP; 

B, street curb site USG–CRB; 

C, underground 

storm sewer outfall site WTP–USS; 

D, channel/storm sewer site WTP–BMP.
Methods 9

!

!

!

!

!

! SDC–CRB

SDC–CHN

ATH–PKL

CLC–PKL

CLC–DSP

WDW–CRB

103°16'23" 103°16'15"

44°02'00"

44°01'53"

EXPLANATION

! Sampling site and identifier (table 1)

Drainage flowpath

Base from U.S. Geological Survey digital data 

Universal Transverse Mercator projection

Map image is the intellectual property of Esri and is used herein under license. 

Copyright © 2014 Esri and its licensors. All rights reserved. 

Zone 13 North

0 100 200 300 400 FEET

0 50 100 METERS

SDC–CRB

Figure 4. Wildwood stormwater-quality flowpath sampling sites and drainage flowpath network, Rapid City, South Dakota.
10 Stormwater Quality of Infrastructure Elements in Rapid City, South Dakota, 2016–18

A

B

D

E

C

Figure 5. Wildwood stormwater-quality flowpath sampling site types in Rapid City, South Dakota. 

A, parking lot site CLC–PKL; 

B, street curb site WDW–CRB; 

C, outlet pipe 

from roof downspout site CLC–DSP; 

D, parking lot site ATH–PKL; 

E, street curb site SDC–CRB in center of photograph and channel/storm sewer site SDC–CHN at culvert on 

right side of photograph.
Methods 11

!

!

!

!EPP–BMP

EPP–CHN

EPP–DSP

EPP–PKL

103°13'30" 103°13'25"

44°04'47"

44°04'45"

44°04'42"

Base from U.S. Geological Survey digital data 

Universal Transverse Mercator projection

Map image is the intellectual property of Esri and is used herein under license. 

Copyright © 2014 Esri and its licensors. All rights reserved. 

Zone 13 North

EXPLANATION

! Sampling site and identifier (table 1)

Drainage flowpath

EPP–PKL

0 50 100 150 FEET

0 10 20 30 40 50 METERS

Figure 6. Eco Prayer Park stormwater-quality flowpath sampling sites and drainage flowpath network in Rapid City, South 

Dakota.
12 Stormwater Quality of Infrastructure Elements in Rapid City, South Dakota, 2016–18

A

B

D

C

BD

C

Figure 7. Eco Prayer Park stormwater-quality flowpath sampling site types in Rapid City, South Dakota. 

A, roof downspout site EPP–DSP; 

B, parking lot site EPP–PKL; 

C, retention pond stage plate site EPP–BMP; 

D, rock channel site EPP–CHN.
Methods 13

as described in the USGS National Field Manual (Wilde, 

2004) or replaced after sampling. Samples were collected in 

sterile 1-liter plastic bottles using grab-sampling techniques 

(U.S. Geological Survey, 2006). Flow at most sites was 

confined to relatively narrow channels (such as a downspout 

or curb) or through a culvert pipe, so width- and depthintegrating sampling techniques were not feasible or warranted. Sample bottles were brought to the USGS Rapid City 

laboratory where specific conductance and pH values were 

measured, and water samples were transferred into containers 

supplied by Mid Continent Testing Laboratories.

Specific conductance is a measure of the ability of water 

to conduct an electrical current and is a surrogate measure 

of dissolved solids (Hem, 1985). For stormwater samples, 

specific conductance usually correlates with total dissolved 

solids (Granato and Smith, 1999) and is used to help assess the 

wash-off process. The wash-off process refers to decreases in 

suspended and dissolved solids concentrations with time during a storm event. Pure liquid rainwater has a very low specific 

conductance (less than 100 microsiemens per centimeter at 

25 degrees Celsius; Hem, 1985), and thus, stormwater samples 

collected during the receding limb of a runoff hydrograph 

typically have specific conductance values much less than the 

rising limb of the hydrograph (also referred to as the “first 

flush”). Although pH data were also collected with samples, 

no analyses of the results were completed for this report; 

however, the results are available with other water-quality 

constituents in appendix 1 (U.S. Geological Survey, 2019).

Quality Assurance and Quality Control

Quality-assurance and quality-control procedures were 

used to identify possible random or systemic errors in the field 

sampling and laboratory analyses. For quality control, equipment blank and sequential replicate samples were collected to 

determine precision and identify potential sample contamination. During the 3-year study, 147 environmental water-quality 

samples were collected for laboratory analyses, and 9 qualitycontrol samples were collected. Five equipment blanks were 

collected to assess the sample equipment cleaning procedures 

and laboratory methods, and four sequential replicate samples 

were collected to measure variability associated with sample 

collection, processing, and analysis (table 3).

Precision of analytical results for water-quality samples 

may be affected by numerous sources of potential variability 

in field and laboratory processes, including sample collection, 

sample processing and handling, and laboratory preparation 

and analysis. Analyses of field replicate samples, therefore, 

can indicate the reproducibility of environmental data and 

provide information on the variability associated with sample 

collection and analysis. The precision of environmental/replicate sample pairs can be assessed using the absolute difference 

in concentrations and the relative percent difference (RPD), 

calculated as the difference in concentration divided by the 

mean concentration multiplied by 100 for the environmental/

replicate pair. For E. coli concentrations in environmental/

replicate pairs, the RPD ranged from 0 to 17 percent, and the 

RPD for TSS concentrations in environmental/replicate pairs 

ranged from 2.2 to 80 percent (table 3). However, the greatest RPD in a TSS replicate sample coincided with a relatively 

low concentration in the environmental sample (8.4 mg/L) 

and small absolute difference (4.8 mg/L). For the remaining replicate samples with relatively high RPD (greater than 

15 percent), the differences can be attributed mainly to the 

rapidly changing water-quality conditions that are common 

with short-term runoff events, because replicate samples were 

collected in separate bottles immediately after the environmental sample. Data from the WTP–USS site on August 2, 

2017, are as an example of how quickly E. coli concentrations 

can change in stormwater samples collected from the same 

site. In four samples collected at times separated by an interval 

of 4 to 14 minutes within a 30-minute period, E. coli concentrations were 4,100 mpn/100 mL, 120,000 mpn/100 mL, 

20,000 mpn/100 mL, and 11,000 mpn/100 mL. Replicate 

samples of E. coli and fecal coliform bacteria from previous 

stormwater sampling in Rapid City had a median RPD of 

about 30 percent (Hoogestraat, 2015). All blank samples for 

E. coli and TSS were below laboratory reporting levels, indicating satisfactory cleaning procedures and equipment.
14 Stormwater Quality of Infrastructure Elements in Rapid City, South Dakota, 2016–18

Table 3. Blank and replicate water-quality sample results for samples collected at various stormwater flowpath sites in Rapid City, 

South Dakota.

[Shading represents the environmental sample. mm/dd/yyyy, month/day/year; hh:mm, hour:minute (military time); mpn/100 mL, most probable number per 

100 milliliters; mg/L, milligram per liter; <, less than; --, not available]

Short identifier (table 1) Date (mm/dd/yyy) Time (hh:mm) Escherichia coli

(mpn/100 mL) Total suspended solids (mg/L)

Equipment blank samples

(Not applicable—Filled at 

laboratory)

06/13/2016 17:14 <1 <4

06/13/2016 17:15 <1 <4

08/09/2016 08:00 <1 <4

05/17/2017 10:20 <1 <4

07/12/2017 14:50 <1 <4

Environmental/replicate sample pairs

EPP–DSP 07/01/2016 09:00 <10 --

EPP–DSP 07/01/2016 09:01 <10 --

Relative percent difference 0 --

Absolute difference 0 --

SDC–CHN 05/17/2017 09:20 488 8.4

SDC–CHN 05/17/2017 09:21 517 3.6

Relative percent difference 5.8 80

Absolute difference 29 4.8

EPP–PKL 07/12/2017 14:20 727 159

EPP–PKL 07/12/2017 14:21 866 128

Relative percent difference 17 22

Absolute difference 139 31

WTP–USS 08/06/2018 16:15 14,200 141

WTP–USS 08/06/2018 16:16 16,700 138

Relative percent difference 16 2.2

Absolute difference 2,500 3

Stormwater Quality of Infrastructure 

Elements

A complete listing of water-quality sample results from 

this study are presented in appendix 1, and all data are available from the USGS National Water Information System 

database (U.S. Geological Survey, 2019). The following 

sections describe the statistical summaries of water-quality 

data collected from the Jackson, Wildwood, and Eco Prayer 

Park flowpaths, as well as a listing of statistics categorized by 

infrastructure site type. The minimum, median, and maximum 

concentrations of E. coli, TSS, and specific conductance for 

each sampling site are listed in table 4.

Jackson Flowpath

In general, the concentrations of E. coli and TSS 

increased in the downstream direction among the Jackson 

flowpath sites (table 4). Figure 8 shows an example 

stormwater-quality data plot for a runoff event on May 24, 

2016. The wash-off process after the first flush is evident in 

the plots for TSS and specific conductance, as noted by the 

decreasing concentrations with sample time in figures 8B and 

8C. However, E. coli concentrations do not necessarily follow 

the same pattern: concentrations in the latter part of the runoff 

period sampled were similar to or greater than the initial concentrations of the first set of samples (fig. 8A).

Samples collected from the roof downspout site (USG–

DSP) during the beginning of storm events had relatively 

low, but quantifiable, amounts of E. coli for 50 percent of the 

storms; final samples collected during the same storm events 

usually had E. coli concentrations below detection levels 

(appendix 1). TSS concentrations from the roof downspout 
Stormwater Quality of Infrastructure Elements 15

Table 4. Summary statistics for water-quality results at stormwater sampling sites in Rapid City, South Dakota.[mpn/100 mL, most probable number per 100 milliliters; mg/L, milligram per liter; μS/cm at 25 °C, microsiemen per centimeter at 25 degrees Celsius; min, minimum; med, median; max, maximum; <, less than]

Short identifier 

(table 1) Site type

Storm 

events 

sampled

Sample 

count

Escherichia coli (mpn/100 mL) Total suspended solids (mg/L) Specific conductance (μS/cm at 25 °C)

Min Med Max Min Med Max Min Med Max

Jackson flowpath

USG–DSP Roof downspout 4 10 <1 1 17 <4 18 183 17 28 90USG–PKL Parking lot 4 10 11 275 4,800 19 48 118 64 79 161USG–CRB Street curb 4 11 <10 98 690 26 83 197 68 93 153WTP–CHN Channel/storm sewer 1 3 63 110 110 120 142 152 120 136 148WTP–USS Channel/storm sewer 4 12 330 3,050 120,000 18 156 547 125 161 343WTP–BMP Channel/storm sewer 1 2 1,700 1,850 2,000 111 143 175 175 179 182

Wildwood flowpath

CLC–DSP Roof downspout 4 11 1 1 13 5 10 84 29 43 160CLC–PKL Parking lot 4 11 2 230 5,900 <4 47 131 30 74 420WDW–CRB Street curb 4 9 4 100 400 40 95 687 69 87 220ATH–PKL Parking lot 4 8 17 93 14,000 22 86 446 59 70 200SDC–CRB Street curb 3 7 96 290 2,800 4 54 463 47 82 105SDC–CHN Channel/storm sewer 3 8 490 2,400 7,200 6 14 150 92 120 1,120

Eco Prayer Park flowpath

EPP–DSP Roof downspout 4 10 <10 99 1,100 <4 15 220 18 72 180EPP–PKL Parking lot 5 16 14 400 20,000 19 125 546 30 155 420EPP–CHN Channel/storm sewer 5 13 78 920 33,000 6 31 644 92 250 550EPP–BMP Channel/storm sewer 3 6 600 13,800 150,000 <4 65 108 200 240 340
16 Stormwater Quality of Infrastructure Elements in Rapid City, South Dakota, 2016–18

0.1

1

10

100

1,000

10,000

0

50

100

150

200

250

0

50

100

150

200

250

300

350

400

5:15 p.m. 5:30 p.m. 5:45 p.m. 6:00 p.m. 6:15 p.m. 6:30 p.m. 6:45 p.m.

Escherichia coli,

 in most probable number per 100 milliliters Total suspended solids, in milligrams per liter

Specific conductance, in microsiemens per centimeter 

at 25 degrees Celsius

USG–DSP

USG–PKL

USG–CRB

WTP–CHN

WTP–USS

EXPLANATION

USG–DSP

USG–PKL

USG–CRB

WTP–CHN

WTP–USS

EXPLANATION

USG–DSP

USG–PKL

USG–CRB

WTP–CHN

WTP–USS

EXPLANATION

Time

Figure 8. Example stormwater-quality data plot for Jackson flowpath on May 24, 2016.
Stormwater Quality of Infrastructure Elements 17

site (USGS–DSP) ranged from 183 mg/L in samples collected during the first flush to less than (<) 4 mg/L in samples 

collected during the later wash-off period of a storm event 

(table 4). E. coli concentrations from the parking lot (USG–

PKL) and street curb (USG–CRB) sites ranged from <10 to 

4,800 mpn/100 mL but did not typically show an apparent 

decreasing (or increasing) pattern during individual storm 

events, as would be expected with sediment wash-off processes. TSS concentrations from these two sites ranged from 

about 200 mg/L in samples collected during the initial flush 

to about 20 mg/L in samples collected later during the same 

storm event. The underground storm sewer site (WTP–USS) 

farther downstream (where stormwater also collects from the 

larger drainage network) had the highest E. coli concentrations, ranging from 330 to 120,000 mpn/100 mL (median was 

3,050 mpn/100 mL), and had the greatest TSS concentrations, 

ranging from about 550 mg/L during the first flush down to 

about 20 mg/L after the wash off (median was 156 mg/L). 

Another storm drainage channel (WTP–CHN) joins the 

flow from WTP–USS, and then flows downstream through 

a grassed swale BMP (WTP–BMP) before entering Rapid 

Creek. The flow from the WTP–CHN site was much smaller 

than the WTP–USS site during all site visits; thus, the WTP–

BMP location represented mostly (greater than 90 percent) 

stormwater from the WTP–USS site. Only two samples were 

collected from the WTP–BMP site during one relatively large 

storm event compared to other storms in this study. During 

this large storm on June 27, 2017, the E. coli concentrations 

ranged from 1,500 to 2,000 mpn/100mL at the upstream 

WTP–USS site and were at similar concentrations after flowing through the grassed BMP area (E. coli concentrations 

ranged from 1,700 to 2,000 mpn/100 mL at the WTP–BMP 

site). However, TSS concentrations were reduced from a range 

of 211 to 547 mg/L at the WTP–USS site to a range of 111 to 

175 mg/L at the WTP–BMP site during this same storm. For 

the remaining (smaller precipitation) storms when the Jackson 

flowpath sites were sampled, the flow infiltrated into the 

grassed areas of the BMP and did not reach the outlet of the 

flowpath.

Wildwood Flowpath

In the Wildwood flowpath, E. coli concentrations 

were lowest in samples collected at the roof downspout site 

(CLC–DSP) and greatest in samples collected at the main 

drainage channel (SDC–CHN) farther down the flowpath 

(table 4). E. coli concentrations at the CLC–DSP site were 

all 13 mpn/100 mL or less, and the E. coli concentration at 

the SDC–CHN site ranged from 490 to 7,200 mpn/100 mL. 

The parking lot (CLC–PKL and ATH–PKL) and street curb 

(WDW–CRB and SDC–CRB) sites in the Wildwood flowpath had variable E. coli concentrations, ranging from 2 to 

14,000 mpn/100 mL with site median values between 93 and 

290 mpn/100 mL. Contrary to E. coli results, TSS concentrations at the farthest downstream site (SDC–CHN) were lower 

(median was 14 mg/L) than the parking lot and street curb 

sites (site medians ranged from 47 to 95 mg/L). Example 

stormwater-quality data plots for the Wildwood flowpath are 

shown in figure 9, demonstrating the first flush and wash-off 

processes where the TSS concentrations decrease as the runoff 

hydrograph progresses, whereas the E. coli concentrations 

remain fairly stable or increase.

Eco Prayer Park Flowpath

Samples collected from the Eco Prayer Park flowpath 

had higher E. coli concentrations than samples collected 

from the Jackson and Wildwood flowpath sites. The roof 

downspout site (EPP–DSP) had a median E. coli concentration of 99 mpn/100 mL for 10 samples, ranging from <10 to 

1,100 mpn/100 mL. The parking lot site (EPP–PKL) and 

next downstream rock channel site (EPP–CHN) had median 

concentrations of 400 and 920 mpn/100 mL, respectively, 

with a maximum concentration of 33,000 mpn/100 mL at 

the EPP–CHN site. The E. coli concentrations from the 

outlet of the retention pond (EPP–BMP) were greater than 

the inlet site (EPP–CHN), with a median concentration of 

13,800 mpn/100 mL and a maximum E. coli concentration 

of 150,000 mpn/100 mL. However, TSS concentrations were 

reduced by the retention pond and infiltration by the rock 

channel because the median concentration at the outlet site 

(EPP–BMP) was 65 mg/L compared to the parking lot inflow 

(EPP–PKL) median concentration of 125 mg/L.

Typical water-quality behavior during a runoff event at 

the Eco Prayer Park sites is demonstrated in figure 10. The 

dashed line in figure 10 is the retention pond depth, as measured by readings from the stage plate during sampling, and is 

an estimate of the runoff hydrograph. Water from the retention 

pond flows into the overflow pipe and connects to the underground storm sewer system when the depth is above 1.3 feet. 

The sediment washoff process is evident because TSS concentrations decreased during the storm event; however, E. coli

concentrations remained fairly constant during the complete 

runoff period.

Infrastructure Site Type Summary

A primary objective of this study was to improve on the 

method by which FIB (for example, E. coli) and TSS are evaluated in the urban drainages within Rapid City, S. Dak. and 

to provide information that helps identify origins of FIB and 

TSS. Stormwater quality has been characterized as it enters 

Rapid Creek during runoff events (Hoogestraat, 2015) and 

within Rapid Creek itself (Pirner and Harms, 1978; Krantz, 

2002), but the data collected in this study help describe the 

stormwater quality farther upstream in the urban basins. Data 

collected during this study was summarized by infrastructure 

site type to provide information about approximate waterquality concentrations at various points along the upper end 

of urban flowpaths. Median concentrations of E. coli, TSS, 
18 Stormwater Quality of Infrastructure Elements in Rapid City, South Dakota, 2016–18

0.1

1

10

100

1,000

10,000

8:20 a.m. 8:30 a.m. 8:40 a.m. 8:50 a.m. 9:00 a.m. 9:10 a.m. 9:20 AM 9:30 a.m. 9:40 a.m. 9:50 a.m. 10:00 a.m.

CLC–DSP

CLC–PKL

WDW–CRB

ATH–PKL

SDC–CRB

SDC–CHN

0

50

100

150

200

250

300

350

400

450

500

8:20 a.m. 8:30 a.m. 8:40 AM 8:50 a.m. 9:00 a.m. 9:10 AM 9:20 a.m. 9:30 AM 9:40 a.m. 9:50 a.m. 10:00 a.m.

0

50

100

150

200

250

8:20 a.m. 8:30 a.m. 8:40 AM 8:50 a.m. 9:00 a.m. 9:10 a.m. 9:20 a.m. 9:30 a.m.

EXPLANATION

CLC–DSP

CLC–PKL

WDW–CRB

ATH–PKL

SDC–CRB

SDC–CHN

EXPLANATION

CLC–DSP

CLC–PKL

WDW–CRB

ATH–PKL

SDC–CRB

SDC–CHN

EXPLANATION

 Escherichia coli, 

in most probable number per 100 milliliters Total suspended solids, in milligrams per liter

Specific conductance, in microsiemens per centimeter 

at 25 degrees Celsius

Time

Figure 9. Example stormwater-quality data plot for Wildwood flowpath on May 17, 2017.
Stormwater Quality of Infrastructure Elements 19

0

0.50

1.00

1.50

2.00

1

10

100

1,000

10,000

100,000

1,000,000

1:00 p.m. 1:15 p.m. 1:30 p.m. 1:45 PM 2:00 p.m.

Pond depth, in feet

Pond depth, in feet

Pond depth, in feet

0

0.50

1.00

1.50

2.00

0

100

200

300

400

500

600

700

1:00 p.m. 1:15 p.m. 1:30 p.m. 1:45 p.m. 2:00 p.m.

0

0.50

1.00

1.50

2.00

0

50

100

150

200

250

300

350

400

1:00 p.m. 1:15 p.m. 1:30 p.m. 1:45 p.m. 2:00 p.m.

EPP–DSP

EPP–PKL

EPP–CHN

EPP–BMP

Pond depth

EXPLANATION

EPP–DSP

EPP–PKL

EPP–CHN

EPP–BMP

Pond depth

EXPLANATION

EPP–DSP

EPP–PKL

EPP–CHN

EPP–BMP

Pond depth

EXPLANATION

 Escherichia coli,

in most probable number per 100 milliliters Total suspended solids, in milligrams per liter

Specific conductance, in microsiemens per centimeter 

at 25 degrees Celsius

Time

Figure 10. Example stormwater-quality data plot for Eco Prayer Park flowpath on September 12, 2017.
20 Stormwater Quality of Infrastructure Elements in Rapid City, South Dakota, 2016–18

and specific conductance for the four infrastructure site types 

that were evaluated for this study (roof downspout, parking 

lot, street curb, and channel/storm sewer) are listed in table 5. 

This information can be used in hydrologic models to better 

estimate FIB and TSS loading from urban environments.

E. coli and TSS concentrations were lowest in samples 

collected from locations most isolated from human influence 

(roof downspouts). The median concentrations at these sites 

were 4 mpn/100 mL and 15 mg/L, respectively. The delivery 

potential of FIB and sediment from parking lots and street 

curbs was similar; median concentrations of E. coli were 

around 150 to 220 mpn/100 mL and 56 to 86 mg/L for TSS. 

The receiving channels and storm sewers where stormwater 

was aggregated typically contained the highest E. coli concentrations (median of 1,800 mpn/100 mL), but TSS concentrations were similar to upstream elements (parking lots and 

street curbs) in the flowpath (median was 69 mg/L). For the 

Wildwood and Eco Prayer Park flowpaths, the median TSS 

for the channel and storm sewer site types was lower than the 

upstream elements but not for the Jackson flowpath sites.

Previous research (Schueler, 2000) has suggested that 

current stormwater, buffer, and source-control practices 

are incapable of removing enough bacteria to meet current 

water contact recreation standards in stormwater discharges, 

unless the discharging water is well mixed and diluted with 

cleaner water. E. coli concentrations at the outflow sites of 

most stormwater drainages in Rapid City are about 7,200 to 

21,000 mpn/100 mL (Hoogestraat, 2015), and urban drainages 

account for about 37 percent of the Rapid Creek streamflow 

at the downstream boundary of Rapid City. It is probable 

that bacterial concentrations in streams that receive stormwater runoff will always exceed predevelopment conditions, 

even if stormwater treatment and buffer practices are fully 

implemented and all wastewater discharges are eliminated 

(Schueler, 2000). The current beneficial-use criterion for 

E. coli in Rapid Creek is 235 mpn/100 mL, which is only 

slightly greater than the median concentration that washes off 

parking lots and street curbs in the upstream end of the urban 

flowpath (median of 150 to 220 mpn/100 mL). The data collected from this study demonstrate that stormwater is almost 

immediately contaminated with FIB upon touching impervious surfaces, which highlights the importance of controlling 

the volume of stormwater discharges into receiving waterbodies via storage structures and pervious elements. An example 

of this reduction in volume is the observations from the BMP 

area sampled in the Jackson flowpath during this study, where 

flow during smaller storms were completely infiltrated into the 

grassed channels before reaching the outlet into Rapid Creek. 

Diluting stormwater containing high concentrations of E. coli

with the receiving water’s (Rapid Creek) lower concentration 

of E. coli is likely the primary mechanism for meeting the 

235 mpn/100 mL beneficial-use criterion threshold.

TSS concentrations in the upstream end of the urban 

flowpath (parking lots and street curbs) also begin at concentrations (56 to 86 mg/L) above the beneficial-use criterion for 

Rapid Creek (53 mg/L); however, previous research has indicated that current stormwater-control practices (storage ponds, 

swales, wetlands) were able to reduce suspended-sediment 

concentrations by 40 to 60 percent (Hoogestraat, 2015). The 

BMP area in the lower end of the Jackson flowpath is another 

example of how a stormwater-control practice can reduce TSS 

concentrations. TSS concentrations were reduced from a peak 

of 547 mg/L at the inflow to the BMP area (WTP–USS site) 

to concentrations less than 200 mg/L at the outlet site (WTP–

BMP) during this same event. Dilution with receiving waters 

is not the only mechanism for meeting beneficial-use criteria 

for TSS because concentrations of TSS in the upstream end of 

Rapid City stormwater flowpaths were generally closer to the 

criterion when compared to the difference between E. coli concentrations and the corresponding criterion. For example, in 

order for stormwater to meet the TSS beneficial-use criterion 

of Rapid Creek (53 mg/L), the median concentration of TSS 

from street curbs during this study (86 mg/L) would need to be 

reduced by 39 percent, which is within the expected range of 

most current stormwater-control practices.

Table 5. Median Escherichia coli concentration, total suspended solids concentration, and specific conductance of site types sampled 

in 2016–18, Rapid City, South Dakota.

[mpn/100 mL, most probable number per 100 milliliters; mg/L, milligram per liter; μS/cm at 25 °C, microsiemen per centimeter at 25 degrees Celsius]

Site type

Median concentration

Escherichia coli (mpn/

100 mL) Total suspended solids (mg/L) Specific conductance (μS/cm at 25 °C)

Roof downspout 4 15 43

Parking lot 220 56 93

Street curb 150 86 87

Channel/

storm sewer

1,800 69 176
Summary 21

Summary

As runoff flows over the land or impervious surfaces 

(paved streets, parking lots, and building roofs), it accumulates debris, chemicals, sediment, and other contaminants 

that can adversely affect water quality if the runoff discharge 

remains untreated. Fecal indicator bacteria (FIB), such as 

Escherichia coli (E. coli), enterococci, or fecal coliform, are 

the most-frequent cause of water-quality impairment in rivers 

and streams in the United States. Rapid Creek originates in the 

western Black Hills area and flows east through Rapid City to 

its mouth at the Cheyenne River. The water quality of Rapid 

Creek is important because the reach that flows through Rapid 

City, South Dakota, is a valuable spawning area for a selfsustaining trout fishery, is actively used for recreation, and is 

a seasonal municipal water supply for the City of Rapid City. 

The fishery and recreational uses are considered “beneficial 

uses” by the South Dakota Department of Environment and 

Natural Resources, which carry numerical criteria for total 

suspended solids (TSS) and E. coli concentrations, among 

other water-quality constituents for additional beneficial uses. 

Current methods of identifying FIB impairments in surface 

water are usually limited to a general assessment of sources 

(typically grouped as livestock, wildlife, or human), and 

FIB sample data relative to specific sources typically are not 

available. The objectives of this study were to improve on 

the method by which FIB and TSS are quantified in the urban 

drainages within Rapid City and to provide information that 

helps identify origins of FIB and TSS. This information can 

be used in hydrologic models to estimate FIB and TSS loading 

from certain infrastructure elements in urban environments.

Stormwater-quality data were collected in three drainage basin flowpaths within Rapid City: Jackson, Wildwood, 

and Eco Prayer Park. Data-collection activities for this study 

focused on the beginning urban flowpath elements during rainfall events, including building roofs, parking lots, street curbs, 

and drainage channels. This approach builds upon previous 

stormwater assessments that characterized the water quality in 

urban basin outlets near the downstream end of the stormwater 

flowpaths. Within each flowpath group, 4–6 sites were selected 

to represent the various infrastructure elements of the runoff 

process. These elements included roof downspouts, parking 

lots, street curbs and gutters, open channels, underground 

storm sewers, and stormwater ponds or best-management 

practice facilities. Water-quality samples were collected at 

each flowpath site during storm events during May–September 

in 2016–18. Multiple samples were collected at each flowpath 

site during runoff events to capture the variability in waterquality concentrations as the runoff hydrograph rises (“first 

flush” process) and falls after the peak runoff flow (when 

material from impervious surfaces have “washed off”). A total 

of 147 water-quality samples were analyzed for E. coli, TSS, 

specific conductance, and pH.

In general, the concentrations of E. coli and TSS 

increased in the downstream direction among the Jackson 

flowpath sites. The wash-off process after the first flush 

was evident in the plots for TSS and specific conductance; 

however, E. coli concentrations did not necessarily follow 

the same pattern. E. coli concentrations in the latter part of 

the runoff period were similar to or greater than the initial 

concentrations of the first set of samples. In the Wildwood 

flowpath, E. coli concentrations were lowest at the roof 

downspout site (less than or equal to 13 most probable number 

per 100 milliliters [mpn/100 mL]) and greatest at the main 

drainage channel farther down the flowpath (ranged from 

490 to 7,200 mpn/100 mL). The parking lot and street curb 

sites’ E. coli concentrations in the Wildwood flowpath ranged 

from 2 to 14,000 mpn/100 mL; site median values were 

between 93 and 290 mpn/100 mL. Contrary to E. coli results, 

TSS concentrations at the lowest stormwater channel site were 

lower (median was 14 milligrams per liter [mg/L]) than the 

parking lot and street curb sites (site medians ranged from 

47 to 95 mg/L). In the Eco Prayer Park flowpath, E. coli concentrations were greater than the other two flowpath groups. 

The Eco Prayer Park parking lot site and next downstream 

rock channel site had median E. coli concentrations of 400 and 

920 mpn/100 mL, respectively, with a maximum concentration of 33,000 mpn/100 mL. TSS concentrations were reduced 

by the retention pond within the Eco Prayer Park because the 

median concentration at the outlet site was 65 mg/L compared 

to a parking lot median concentration of 125 mg/L.

Data collected during this study were summarized by 

infrastructure type (roof downspout, parking lot, street curb, 

and channel/storm sewer) to provide information about 

approximate water-quality concentrations at various points 

along the upper end of urban flowpaths. E. coli and TSS concentrations were lowest in samples collected from locations 

most isolated from human, animal, or both influences (roof 

downspouts). The median concentrations at these roof downspout sites were 4 mpn/100 mL and 15 mg/L, respectively. 

The delivery potential of FIB and sediment from parking lots 

and street curbs was similar, with median concentrations of 

E. coli and TSS around 150 to 220 mpn/100 mL and 56 to 

86 mg/L, respectively. The downstream receiving channels 

and storm sewers where stormwater was aggregated typically contained the highest E. coli concentrations (median of 

1,800 mpn/100 mL), but the TSS concentrations were similar 

to upstream elements (parking lots and street curbs) in the 

flowpath (median was 69 mg/L). The data collected from this 

study demonstrate that stormwater is almost immediately contaminated with FIB upon contacting impervious surfaces. This 

highlights the importance of controlling the volume of stormwater discharges into receiving waterbodies via storage structures and pervious elements. Diluting stormwater with high 

concentrations of E. coli with the receiving water’s (Rapid 

Creek) lower concentration of E. coli is likely the primary 

mechanism for meeting the 235 mpn/100 mL beneficial-use 

criterion threshold. Although TSS concentrations in the upper 

ends of the basin (parking lots and street curbs) also begin at 

concentrations (56 to 86 mg/L) above the beneficial-use criterion for Rapid Creek (53 mg/L), current stormwater-control 
22 Stormwater Quality of Infrastructure Elements in Rapid City, South Dakota, 2016–18

practices (storage ponds, swales, and wetlands) may be able 

to reduce suspended-sediment concentrations to meet this 

threshold.

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24 Stormwater Quality of Infrastructure Elements in Rapid City, South Dakota, 2016–18

Appendix 1 Stormwater-Quality Data

Appendix 1 is a comma-separated values (.csv) file that 

contains the water-quality sample results for data used in this 

report and is available for download at https://doi.org/10.3133/

sir20205004. These data are also stored in the USGS National 

Water Information System database (U.S. Geological Survey, 

2019) and are packaged herein for convenience.

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Hoogestraat—Stormwater Quality of Infrastructure Elements in Rapid City, South Dakota, 2016–18—SIR 2020–5004

ISSN 2328-0328 (online)

https://doi.org/10.3133/sir20205004