U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2012–1237

Prepared in cooperation with the National Park Service, Glen Canyon National Recreation Area

Establishment of Sentinel Sampling Sites to Monitor Changes 

in Water and Sediment Quality and Biota Related to Visitor 

Use at Lake Powell, Arizona and Utah, 2004–2006
COVER 

San Juan River arm of Lake Powell, Castle Rock near Wahweap Bay, Lake Powell, Sunset on Lake Powell, Photos by Robert J. Hart.
Prepared in cooperation with the National Park Service, Glen Canyon 

National Recreation Area

Establishment of Sentinel Sampling Sites 

to Monitor Changes in Water and Sediment 

Quality and Biota Related to Visitor Use at 

Lake Powell, Arizona and Utah, 2004–2006

By Robert J. Hart, Howard E. Taylor, and G.M. Anderson

Open-File Report 2012–1237

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2012

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Suggested citation:

Hart, R.J., Taylor, H.E., and Anderson, G.M., 2012, Establishment of sentinel sampling sites to monitor changes in 

water and sediment quality and biota related to visitor use at Lake Powell, Arizona and Utah, 2004–2006: 

U.S. Geological Survey Open-File Report 2012–1237, 25 p. 
iii

Contents

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

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

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

Lake Powell Characteristics and Visitor Use...................................................................................2

Description of Sentinel Sampling Sites......................................................................................................4

Marina Sites...........................................................................................................................................6

High-Use Side Canyons, Beaches, Bays, and Inflow Sites ...........................................................7

Methods.........................................................................................................................................................18

Field methods.......................................................................................................................................18

Laboratory Methods...........................................................................................................................22

Quality of Water and Sediment Data ........................................................................................................23

Water and Sediment Data ..........................................................................................................................23

Future Sampling Plans ................................................................................................................................23

Summary........................................................................................................................................................24

Acknowledgements.....................................................................................................................................24

References Cited..........................................................................................................................................24

Appendixes A–F ...............................................................provided as an online electronic supplement

A. Discrete measurements of depth, water temperature, specific conductance, pH, and 

Secchi disk depth at sentinel sites, Lake Powell.

B. Bin averaged data of depth profile measurements of depth, water temperature, specific 

conductance, pH, dissolved oxygen, and turbidity at sentinel sites, Lake Powell.

C. Dissolved concentrations of major ions, nutrients, and organic carbon at sentinel sites, 

Lake Powell.

D. Dissolved concentrations of trace elements and rare earth elements at sentinel sites, 

Lake Powell.

E. Dissolved concentrations of oil and grease, total petroleum hydrocarbons, and volatile 

organic compounds at sentinel sites, Lake Powell.

 F. Total concentrations of polycyclic aromatic hydrocarbons in lakebed material 

 at selected sentinel sites, Lake Powell.

Figures

 1. Map Showing Locations of Sentinel Sampling Sites........................................................................3

 2. Graphs showing (a) reservoir elevation and (b) inflows to Lake Powell, 1990 to 2010 ...............4

 3. Graphs showing the number of recreational visitors to Glen Canyon National Recreation 

Area from 1990–2010........................................................................................................................5

 4. Photographs of sampling areas. ..........................................................................................................7

 5. Photographs of (a) the SBE25, (b) NRP water sampler, (c) VOC sampler, and (d) 

 Ponar dredge sampler...................................................................................................................20

Table

 

 1. Types of available data at the Sentinel sampling locations and 

 data availability, 2001– 2011. ...........................provided as an online electronic supplement
iv

Conversion Factors

SI to Inch/Pound

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

kilometer (km) 0.6214 mile (mi)

meter (m) 3.281 foot (ft)

millimeter (mm) 0.03937 inch (in.)

Area

square hectometer (hm2

) 2.471 acre

square kilometer (km2

) 247.1 acre

Volume

cubic meter (m3

) 0.0008107 acre-foot (acre-ft)

liter (L) 0.2642 gallon (gal)

Flow rate

meter per second (m/s) 3.281 foot per second (ft/s) 

Mass

gram (g) 0.03527 ounce, avoirdupois (oz)

kilogram (kg) 2.205 pound avoirdupois (lb)

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.

Abbreviated Water-Quality Units

Chemical concentration and water temperature are given only in metric units. Chemical 

concentration in water is given in milligrams per liter (mg/L), micrograms per liter (μg/L), or 

nanograms per liter (ng/L). Milligrams per liter is a unit expressing the solute mass (milligrams) 

per unit volume (liter) of water. One thousand micrograms per liter is equivalent to 1 milligram 

per liter. For concentrations less than 7,000 milligrams per liter, the numerical value is about the 

same as for concentration in parts per million. Specific conductance is given in microSiemens 

per centimeter at 25 degrees Celsius (μS/cm). Chemical concentration in bottom sediment is 

given in grams per kilogram (μg/kg), micrograms per gram (μg/g), milligrams per kilogram (mg/

kg), or micrograms per kilogram (μg/kg). Grams per kilogram is equal to parts per thousands 

(ppt). Milligrams per kilogram and micrograms per gram are equal to parts per million (ppm). 

Micrograms per kilogram are equal to parts per billion (ppb).

Datums

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88)

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83)

Elevation, as used in this report, refers to the distance above the vertical datum
v

Acronyms and Symbols

BTEX benzene, toluene, ethylbenzene, and xylene

DEET N,N-diethyl-meta-toluamide

EDTA ethylenediaminetetraacetic acid

GC/MS gas chromatography/mass spectrometry

GLCA Glen Canyon National Recreation Area

GPS Global Positioning System

ICP-AES inductively coupled plasma-atomic emission spectrometry

ICP-MS inductively coupled plasma-mass spectrometry

LDL laboratory detection limit

MCL maximum contaminant level

MPN most probable number

MTBE methyl-tertiary-butyl ether

NIST National Institute of Standards and Technology

NPEC nonylphenolpolyethoxycarboxylate

NRP National Research Program of the U.S. Geological Survey

NPS National Park Service

NTA nitrilotriacetic acid

NWQL U.S. Geological Survey National Water Quality Laboratory

PTFE polytetrafluroethane

PWC personal watercraft

REE rare earth element

TPH total petroleum hydrocarbon

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

VOC volatile organic compound

Al aluminum Na sodium

As arsenic NH4 ammonium

B boron Ni nickel

Ba barium NO2 nitrite

Br bromine NO3 nitrate

Ca calcium Nd neodymium

Cd cadmium P phosphorus
vi

Ce cerium Pb lead

Cl chloride PO

4 phosphate

Co cobalt Pr praseodymium

Cr chromium Rb rubidium

Cs cesium Re rhenium

Cu copperS sulfur

Dy dysprosium Sb antimony

Er erbium Se selenium

Eu europium SiO

2 silica

Fe iron SO4 sulfate

Ga gallium Sr strontium

Gd gadolinium Sm samarium

HCl hydrochloric acid Tb terbium

Hg mercury Te tellurium

HNO

3 nitric acid Th thorium

Ho holmium Tl thallium K potassium Tm thulium K2

CrO

7 potassium dichromate

U uranium

La lanthanumV vanadium

Li lithium

W tungsten

Lu lutetium

Y yttrium

Mg magnesium Yb ytterbium

Mn manganese Zr zirconium

Mo molybdenum
1

U.S. Geological Survey

 2National Park Service

Establishment of Sentinel Sampling Sites to Monitor 

Changes in Water and Sediment Quality and Biota Related 

to Visitor Use at Lake Powell, Arizona and Utah, 2004–2006

By Robert J. Hart1, Howard E. Taylor1, and G.M. Anderson2

Abstract

Twenty sentinel sampling sites were established and 

sampled during 2004–06 at Lake Powell, Arizona and Utah, 

by the U.S. Geological Survey and the National Park Service–

Glen Canyon National Recreation Area. The sentinel sampling 

sites provide sampling locations on Lake Powell, the Nation’s 

second largest reservoir that can be visited and sampled 

repeatedly over time to monitor changes in water and sediment 

quality and also biota. The sites were established in response 

to an Environmental Impact Statement that addressed the use 

of personal watercraft on Lake Powell. The use of personal 

watercraft can potentially introduce hydrocarbons and other 

contaminants and are of concern to the health of visitors and 

aquatic habitats of these environments. Data from this initial 

sampling period (2004–06) include (1) discrete measurements 

of water temperature, specific conductance, pH, and water 

clarity; (2) major ions, nutrients, and organic carbon; (3) 

trace elements including rare earths; (4) organic compounds 

including oil and grease, total petroleum hydrocarbons, 

and volatile organic compounds; (5) polycyclic aromatic 

hydrocarbons in lakebed sediments; and (6) continuous 

depth profile measurements of water temperature, specific 

conductance, pH, dissolved oxygen, and turbidity. Also, the 

National Park Service-Glen Canyon National Recreation Area 

collected bacteria samples during this initial sampling period.

Introduction

The National Park Service (NPS) has become increasingly concerned by the use of personal watercraft (PWC) on 

the Nation’s lakes and reservoirs that NPS manages and the 

contamination that the use of PWC potentially introduces into 

the water. PWC that use two-stroke combustion engines burn 

gasoline inefficiently. As much as 30 percent of the gasoline is 

discharged unburned into the environment (California Environmental Protection Agency, 1999). Benzene, toluene, ethyl 

benzene, xylene (BTEX compounds), and methyl tertiary 

butyl ether (MTBE; a fuel oxygenate additive) are some 

constituents of gasoline that can be discharged to the waters. 

During 2003, the NPS adopted special regulations through 

the process of an Environmental Impact Statement (EIS) to 

manage the use of PWC on Lake Powell. After December 31, 

2012, PWC that does not meet the 2006 emission standards set 

by Environmental Protection Agency (EPA) for the manufacturing of two-stroke combustion engines are not permitted to 

be operated on Lake Powell. The preferred alternative in the 

final EIS commits the Glen Canyon National Recreation Area 

(GLCA) to a monitoring program that requires the collection and analysis of baseline water and sediment- quality data 

(Federal Register, 2003). 

During 2001–02, the U.S. Geological Survey (USGS) and 

the GLCA evaluated the effects of natural and human-induced 

contaminants on water and sediment chemistry and bacteria in 

the Knowles, Forgotten, and Moqui Canyons (Hart and others, 

2004). Also, Hart and others (2005) completed an evaluation 

of contaminates in sediment deposits of the Colorado River 

inflow area to Lake Powell.

Results of that work provided the design for establishing sentinel sampling sites in 2004 throughout Lake Powell 

to begin documenting the presence of contaminants that 

are associated with visitor use. The USGS–Grand Canyon 

Monitoring and Research Center (GCMRC) has been monitoring mainstem Colorado River sites on Lake Powell since the 

mid-1960s (Vernieu, 2009). Unlike the sentinel sampling sites, 

which focus on chemical contaminants (organic and inorganic) 

introduced by human activity in high-use areas, the goal of 

the GCMRC monitoring program is to describe the physical, 

chemical, and biological conditions of the major strata of the 

reservoir in the main Colorado River channel and the primary 

tributary arms of the San Juan and Escalante Rivers. Both 

monitoring programs complement one another and provide the 

GLCA with necessary and pertinent information to better manage the recreational experience at Lake Powell.
2 Establishment of Sentinel Sampling Sites to Monitor Changes in Water and Sediment Quality at Lake Powell, Arizona and Utah

The sentinel sites—sites used for long-term monitoring 

of water, sediment, and biota—were identified by the GLCA 

and the USGS and include marinas, high-use side canyons, 

beaches, bays, and tributary inflow areas, including the 

Colorado, San Juan, and the Escalante Rivers (fig. 1). 

From 2004 to 2006, the USGS, in cooperation with 

GLCA, collected and analyzed water samples and lakebed 

material (sediment) from these sites. GLCA also collected 

water samples at the sites for bacteria determination. During 

2004, samples were collected during the spring when visitation 

and use of petroleum-powered watercraft were relatively low. 

During 2005–06, samples were collected during the summer 

when visitation and the use of petroleum-powered watercraft 

were relatively high. These samples establish a baseline 

dataset for selected constituents in water and sediment for the 

sentinel sites. 

Purpose and Scope

This report describes sentinel sampling sites 

established during 2004–06 and presents water and sediment 

chemical data collected during that time. Also, the GLCA 

collected bacteria samples at the sentinel sites. These initial 

sampling trips coincided with the low-visitation period 

(October–April) in 2004, and with the high-visitation 

period ( May–September) in 2005 and 2006. Discrete water 

measurements (measurements made at approximately 1 m 

below the water surface) were made and water samples were 

collected at each site and analyzed for major ions, nutrients, 

organic carbon, trace elements (including rare-earths), oil and 

grease, total petroleum hydrocarbons (TPHs), and volatile 

organic compounds (VOCs). Lakebed sediment was collected 

at selected sentinel sites and analyzed for PAHs. Depth-profile 

data of water temperature, specific conductance, pH, dissolved 

oxygen, and turbidity also were collected at each site. This 

report includes the chemical analysis data and a description 

and photograph of each site. All data (discrete measurements, 

water and sediment chemistry, and bin-averaged depth-profile 

measurements) are included in appendixes A–F. 

Lake Powell Characteristics and Visitor Use

Lake Powell is strongly influenced by the hydrologic 

regime of the Colorado River (Marzolf and others, 1998). The 

annual high-flow period into the lake generally is from April 

through July, resulting from snowmelt on the western slope of 

the Rocky Mountains. During this period, the salt content of 

the Colorado River begins to decrease (generally less than 500 

mg/L of total dissolved solids). As inflows begin to decrease in 

the late summer (late July), the river begins to carry high salt 

concentrations (increasing to more than 1,000 mg/L of total 

dissolved solids). The increase in salt concentration is caused 

by tributaries to the Colorado River that drain arid portions of 

the basin and because irrigation-return flow from agricultural 

land carries salts (Marzolf and others, 1998). The physical 

and chemical characteristics of Lake Powell respond to these 

changing hydrologic conditions, but also to other variables 

including solar radiation (heating), and atmospheric conditions 

(wind, cloud cover, and composition). The lake generally 

will stratify into distinct density layers, with the upper layer 

(the epilimnion) being mixed resulting mostly from thermal 

control of density. This layer is the lighted zone (euphotic) and 

defines the spatial extent of photosynthesis. For layers deeper 

than this mixed zone (the metalimnion and hypolimnion), 

light is limited and chemical and biological processes occur 

without the influence of the atmospheric exchange or oxygenproducing photosynthesis (Marzolf and others, 1998). It is 

important to document these processes when collecting water 

or biological samples in order to evaluate the vertical and 

longitudinal variations in the water chemistry. 

During 2004–06, reservoir elevation (or levels) and 

inflows to Lake Powell reflected decreased runoff from 

snowmelt in the upper Colorado River Basin (fig. 2A and 

2B). Prior to 2004, from about 1995 to 2000, lake elevations 

fluctuated annually, approaching full reservoir pool elevation 

of 3,700 ft during mid-summer of those years (fig. 2A). Since 

1980, the reservoir elevation was lowest during 2005, when 

the lake reached an elevation of about 3,555 ft (fig. 2A)—

which is 145 ft below the full reservoir conservation pool 

level of 3,700 ft. Reservoir levels have been steadily declining 

beginning in about 2000. Two sampling trips were completed 

in 2004 during March 23–25 and April 13–14. The reservoir 

elevation in March and April 2004 was about 3,583 ft with 

slight fluctuations between those dates (fig. 2A). The 2004 

sampling trip occurred during the early onset of snowmelt 

runoff to the lake. 

The reservoir elevation continued to decline following 

the 2004 sampling trip in late March when it reached its record 

low at an elevation of about 3,555 ft. The lake began to fill the 

following March, and by the July 18–21, 2005 sampling trip, 

the lake elevation was 3,607 ft, which was about 24 ft higher 

than the 2004 sampling trips and also the peak elevation for 

2005. The 2005 sampling trip occurred near the tail end of the 

peak snowmelt runoff period. 

From the July 2005 sampling trip to the last trip during 

July 9–14, 2006, the reservoir reached a level of about 3,609 

ft, which was marginally higher than the level recorded during 

the 2005 sampling trip. This sampling trip also occurred 

during the tail end of the peak snowmelt runoff period. 

Lake Powell’s elevation generally increased with seasonal 

fluctuations since the 2006 sampling trip (fig. 2A). 

Recreational visitation to GLCA , which includes 

Lake Powell, surrounding lands, and a 16-mile reach of 

the Colorado River downstream of the Glen Canyon Dam, 

averaged about 2,560,000 visitors per year during 1990–2010, 

and averaged about 1,879,000 visitors per year during 

2004–06 (fig. 3; National Park Service, 2011). Recreational 

visitation includes multiple types of use of GLCA by visitors, 

such as campground use (tents and recreational vehicles), 

overnight stays, backcountry hiking, watercraft rental, and 

lodging in the Park. During 1990–2010, visitation was 
Introduction 3

12

98

89

276

95

RAINBOW PLATEAU

RED ROCK

PLATEAU

KAIPAROWITS

PLATEAU

Navajo

Mountain

(Page

 Site Number Site Name Site Number Site Name

 

Explanation

Glen Canyon National Recreation Area

Towns or communities

!

I18

HU4

HU5

M1

M2

HU7

HU8

HU11

San Juan

Arm

L a ke

Powe ll

HU2

HU10

HU1

HU6

I20

(

(

(

Halls Crossing

Hite

!(HU9

Marina Sites

M1 Bullfrog Marina HU1 Farley Canyon 

M2 Halls Crossing Marina HU2 Blue Notch Canyon

M3 Dangling Rope Marina HU3 Knowles Canyon

M4 Wahweap Marina HU4 Forgotten Canyon

M5 Antelope Point Marina HU5 Moqui Canyon

M6 Stateline Marina HU6 Stanton Creek

 HU7 Escalanate Creek at 50 Mile Canyon

 HU8 Rainbow Bridge

 HU9 Padre Bay

 HU10 Warm Creek Bay

 HU11 Lone Rock Beach

Inflow Sites

I18 Colorado River inflow

I19 San Juan River inflow

I20 Escalante River inflow

 High Use Sites

(

Bullfrog

!

Phoenix

Flagstaff

Tucson

ARIZONA

Utah

(!

!(

!( !(

!

!( !

(!

M4!

!(

M3

Rainbow Bridge National Monument

!

!M5

!(HU3

!

!

I19

Dangling Rope

!M6

(!

111°30' 111°0' 110°30'

37°0'

37°30'

38°0'

0 10 20

0 10 20

MILES

KILOMETERS

Figure 1. Map showing sentinel sampling sites, Lake Powell. Figure 1. Map showing locations of sentinel sampling sites, Lake Powell, Arizona and Utah. 
4 Establishment of Sentinel Sampling Sites to Monitor Changes in Water and Sediment Quality at Lake Powell, Arizona and Utah

Figure 2. Graphs showing (A) reservoir elevation and (B) inflows to Lake Powell, Arizona and Utah, 1990–2010. Figure 2. a) reservoir elevation and b) inows to Lake Powell, 1990 to 2010

Data source: U.S. Bureau of Reclamation; http://www.usbr.gov/uc/crsp/GetSiteInfo

3450

3500

3550

3600

3650

3700

3750

1/1/90 1/1/91 1/1/92 1/1/93 1/1/94 1/1/95 1/1/96 1/1/97 1/1/98 1/1/99 1/1/00 1/1/01 1/1/02 1/1/03 1/1/04 1/1/05 1/1/06 1/1/07 1/1/08 1/1/09 1/1/10

Elevation, in feet 

Date

0

10000

20000

30000

40000

50000

60000

70000

80000

90000

100000

1/1/90 1/1/91 1/1/92 1/1/93 1/1/94 1/1/95 1/1/96 1/1/97 1/1/98 1/1/99 1/1/00 1/1/01 1/1/02 1/1/03 1/1/04 1/1/05 1/1/06 1/1/07 1/1/08 1/1/09 1/1/10

Inflow, in cubic feet per second

Date

a

b

Period when sentinel sites were established

Period when sentinel sites were established

A

B

highest in 1992 with 3,587,754 visitors (fig. 3). During the 

establishment of the sentinel sites in 1990–2010, visitation 

was lowest in 2004 with 1,841,845 visitors (fig. 3). Factors 

affecting recreational visitation may include but are not 

limited to, economic considerations, such as costs associated 

with recreation, reservoir conditions such as low lake levels, 

or general perceptions the public might have about Lake 

Powell conditions. Since 2006 however, recreational visitation 

has consistently increased.

Description of Sentinel Sampling Sites

Twenty sentinel sampling sites were selected by the GLCA 

and the USGS as long-term monitoring sites for evaluating 

the effects of visitor use on water, sediment, and biological 

quality. The 20 sites were selected based on a several factors. 

If a site was known to be frequented by visitors (high-visitor 

use) for boating, fishing, swimming, or other recreational 

opportunities, those sites were considered in the selection 

process. Other factors considered in selecting a site included 

(1) recreational carrying capacity (which considers the number 

of people, boats, and other activities that may impact the 

values the GLCA is offering or protecting in the National 

Recreation Area), (2) distance between canyons, (3) drainage 

area, and (4) watershed characteristics. Besides including 

high-visitor-use areas (side canyons, marinas, beach areas, 

and bays), three tributary inflow areas were included in the 

monitoring network. 

Because Lake Powell is not a true lake, but rather a 

river that is dammed forming a reservoir (which is called 

Lake Powell), distances and locations of the sentinel sites 

are referenced to hydrologic terms. Distance between sites is 

described as being “upstream” or “downstream” and locations 
0

500000

1000000150000020000002500000300000035000004000000

Number of recreational visitors

Years 

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 200

Figure 3. Number of recreational visitors to Glen Canyon National Recreation Area from 1990 to 2010. Sentinel sampestablished during 2004, 2005, and 2006.

Data Source: National Park Service; http://www.nature.nps.gov/stats/park

Period when sentinel sites were established

Figure 3. Graphs showing number of recreational visitors to Glen Canyon National Recreation Area, Lake Powell, Arizona and Utah,, 1990–2010.
6 Establishment of Sentinel Sampling Sites to Monitor Changes in Water and Sediment Quality at Lake Powell, Arizona and Utah

are referenced as being on “river right” or “river left” as the 

river flows downstream. Navigation buoys (mile markers) 

are deployed by GLCA beginning at Glen Canyon Dam (mile 

0), following the original Colorado River channel upstream 

about 139 mi to Hite, Utah. These buoys are deployed every 

1 mi to mark the river-channel distance and the deepest edges 

of the original channel. These buoys also are used to mark 

the original Wahweap Creek channel. The sentinel sites are 

referenced to the location of the navigation buoys. All sentinel 

sampling sites were geospatially referenced to latitude and 

longitude using a global positioning system (GPS); this 

information was used to develop the site information in the 

database (Schonauer, 2011). 

Marina Sites

There are six marinas located on Lake Powell beginning 

at Bullfrog, Utah, downstream to to Wahweap, Arizona 

(fig. 1). Hite, Utah, at one time provided marina services at 

the far northeastern end of the lake (lake mile 139) but the 

marina was closed in 2003 due to declining reservoir levels—

however, other services, such as launch ramps, are still 

available. Marina sites are labeled with the letter “M” denoting 

a marina site, followed by a number sequentially increasing 

from upstream to downstream sites.

Site M1 Bullfrog Marina (site ID 373057110442300). This 

site was selected for the monitoring network because of the 

high potential for the introduction of contaminants from 

human activity related to marina services and from vehicular 

traffic. Houseboats are moored at the marina and the marina 

serves as the departure point for houseboat vacationers for 

this part of the lake. Bullfrog Marina is located approximately 

at mile marker 96 upstream on river right of Lake Powell (fig. 

1). The sampling site is about 300 ft from the fuel docks in 

the no-wake zone of the marina (fig. 4A). Bullfrog Marina 

provides full service to boaters and recreationists, providing 

launching services for houseboats, pump-out services, launch 

ramps, fuel docks, convenience marina stores, and full service 

boat repair and maintenance. A unique service in this area 

of the lake is the ferry service (the Charles Hall Ferry) that 

provides transportation between Bullfrog and Halls Crossing. 

The ferry operates on a daily basis during the summer but not 

during the winter (Aramark Parks and Destinations, 2010). 

The ferry is capable of hauling most types of vehicles and 

150 passengers. 

Site M2 Halls Crossing Marina (site ID 

372809110431200).—This site was selected for the 

monitoring network because of the high potential for the 

introduction of contaminants from human activity related to 

marina services and from vehicular traffic. Houseboats are 

moored at the marina and the marina serves as the departure 

point for houseboat vacationers for this part of the lake. Halls 

Crossing Marina is directly across the lake from Bullfrog 

Marina at about mile marker 94 on river left (fig. 1). The 

sampling site is within the no-wake zone about 300 ft from 

the fuel docks (fig. 4B). Like Bullfrog Marina, Halls Crossing 

Marina provides launching services for houseboats, launch 

ramps, fuel docks, full service repair and maintenance, and 

pump-out services. 

Site M3 Dangling Rope Marina (site ID 

370708111045100).—This site was selected for the monitoring 

network because of the high potential for the introduction of 

contaminants from human activity primarily related to marina 

services. Dangling Rope Marina is located near mile marker 

43 on river right (fig. 1). The sampling site is within the 

no-wake zone about 150 ft east of the fuel docks (fig. 4C). The 

marina is only accessible by water due to its isolated location. 

It provides limited services including fuel, pump-out services, 

minor boat repair, and a supply store where the popular Lake 

Powell root beer floats can be purchased. It is the only marina 

between Wahweap and Antelope Marinas in the lower part 

of the lake and Bullfrog and Halls Crossing Marinas (at mile 

markers 96 and 94, respectively). 

Site M4 Wahweap Marina (site ID 365933111285200).—

Wahweap Marina is in the southeastern part of Lake Powell in 

Wahweap Bay, Arizona (fig. 1) about 4.5 mi upstream of Glen 

Canyon Dam. This is a high-use boat and traffic area because 

it is located at the primary entrance to Lake Powell near 

Page, Arizona. As with Bullfrog and Halls Crossing Marinas, 

houseboats are moored at the marina and the marina serves as 

the departure point for houseboat vacationers for primarily the 

lower part of the lake. The sampling location is about 300 ft 

east of the fuel docks (fig. 4D). The marina provides a variety 

of services including lodging, gift stores, food services, full 

marina services including slips, boat rentals, dry storage, and 

fuel. The city of Page, Arizona is about 9 mi from the marina.

Site M5 Antelope Point Marina (site ID 

365759111254700).—Antelope Point Marina is the newest 

marina, located on the Navajo Nation on the southern end of 

Lake Powell on the original Colorado River channel upstream 

of Glen Canyon Dam (fig. 1). The marina became a full 

service marina in 2005 (it was not in service in 2004) and is 

operated by the Navajo Nation. The marina provides launching 

and mooring services for houseboats, fuel, supply store, and 

the “World’s Largest Floating Restaurant” (Antelope Point, 

2011). The sampling site is about 300 ft from the fuel docks 

(fig. 4E). Because of the narrowness of the lake in this area, 

boat traffic can be congested during high-visitor use periods. 

Like Wahweap Marina, Antelope Point Marina is near Page, 

Arizona. 

Site M6 Stateline Marina (site ID 370031111300100).—

Lake Powell at Stateline Marina, also referred to as Stateline 

Launch Ramp, is located in Waheap Bay about 6 mi upstream 

of Glen Canyon Dam (fig. 1) between Wahweap Marina (site 

M4) and Lone Rock Beach (site HU11). Houseboats are 
Description of Sentinel Sampling Sites 7

moored at the marina and the marina serves as the departure 

point for houseboat vacationers for primarily the lower part 

of the lake. It is a busy marina during the summer due to its 

proximity to Lone Rock Beach, Wahweap Marina, and the city 

of Page, Arizona. It also provides some services including fuel 

and boat rental. The sampling site is located at the floating 

docks (fig. 4F).

High-Use Side Canyons, Beaches, Bays, and 

Inflow Sites

There are 14 sites that are classified as high-use 

sites including (1) side canyons, (2) beaches, and (3) 

bays. Sampling sites at major tributary inflows also were 

established. The location of these sites begins at Farley 

Canyon at mile marker 133 and continues downstream to 

Lonerock Beach, which is about 9 mi upstream of Glen 

Canyon Dam (fig. 1). These high-use sites are labeled with 

the letters “HU,” followed by a number and sequentially 

increasing from upstream to downstream sites. The major 

inflow sites are labeled as “I” followed by a number.

Site HU1 Farley Canyon (site ID 374902110245200).—

Farley Canyon is a fairly exposed canyon with a gentle 

sloping shoreline. It is located near mile marker 133 on river 

left (fig. 1) and because it is a popular fishing location, it was 

included in the monitoring network. An access road from 

State Highway 93 to the shoreline of Farley Canyon provides 

primitive camping and “launch at your own risk” watercraft 

access, which is another source of potential contaminants 

to Lake Powell. The sampling site is near the far end of this 

small canyon (fig. 4G). The site also can be accessed from 

Hite launch ramps and Bullfrog and Halls Crossing launch 

ramps.

Site HU2 Blue Notch Canyon (site ID 

374322110264600).—Blue Notch Canyon also is a fairly 

exposed canyon with a gentle sloping shoreline. It is located 

near mile marker 123 on river left and like Farley Canyon, 

it was included in the monitoring network because it is a 

popular fishing location. An access road to the shoreline of 

Blue Notch Canyon provides primitive camping and “launch 

at your own risk” watercraft access, which is another source 

of potential contaminants to Lake Powell. The site also can 

be accessed from Hite launch ramps, as well as Bullfrog and 

Halls Crossing launch ramps. The location of Blue Notch is 

recognizable from the main lake by the promontory of Castle 

Butte on river left (fig. 4H). The sampling location is to the 

east of Castle Butte in Blue Notch Canyon.

Figure 4A. Photograph of site M1 Bullfrog Marina (site ID 373057110442300) near sampling area. The sampling area is near the marina 

fuel docks to the left of the photo and is out of view. View is to the north. Summer 2005.
8 Establishment of Sentinel Sampling Sites to Monitor Changes in Water and Sediment Quality at Lake Powell, Arizona and Utah

Figure 4B. Photograph of site M2 Halls Crossing Marina (site ID 372809110431200). View is to the south. Summer 2005.

Figure 4C. Photograph of site M3 Dangling Rope Marina (site ID 370708111045100) sampling area. View is to the northeast. Spring 2004.
Description of Sentinel Sampling Sites 9

Figure 4D. Photograph of site M4 Wahweap Marina (site ID 365933111285200) sampling area. View is looking to the east. Winter 2012. 

Figure 4E. Photograph of site M5 Antelope Point Marina (site ID 365759111254700) sampling area. View is to the southwest. Spring 2004.
10 Establishment of Sentinel Sampling Sites to Monitor Changes in Water and Sediment Quality at Lake Powell, Arizona and Utah

Figure 4F. Photograph of site M6 Lake Powell at State Line (site ID 370031111300100) sampling area. View is to the west. Summer 2011.

Figure 4G. Photograph of site HU1 Farley Canyon (site ID 374902110245200). View is looking upstream to the northeast. Summer 2005.
Description of Sentinel Sampling Sites 11

Site HU3 Knowles Canyon (site ID 373438110350900).—

Knowles Canyon is located near mile marker 108 on river 

left, and it is a popular fishing site on Lake Powell. It also is 

popular for houseboat camping. Beaches are few for camping 

and their presence is a function of the reservoir elevation. 

Knowles Canyon is about 10 river miles upstream of Bullfrog 

Bay and is only accessible by watercraft. The canyon is 

characterized by steep, vertical canyon walls. This small 

canyon was intensively sampled during 2001–02 for organic 

and inorganic constituents (Hart and others, 2004). The 

sampling location is about 0.5 mi upstream of the mouth of the 

canyon (fig. 4I). 

Site HU4 Forgotten Canyon (site ID 373306110363700).—

Forgotten Canyon is located near mile marker 106 on river 

left, and is a popular fishing canyon and recreational boating 

area on Lake Powell. The canyon is larger than Knowles 

Canyon and it is a narrow and relatively confined canyon 

due to the steep, vertical canyon walls. There are several 

sandy beaches in the canyon that can accommodate several 

houseboat camps. A GLCA floating toilet is near the mouth 

of the canyon and the Defiance House archeological site 

is upstream of the mouth of the canyon. This canyon was 

intensively sampled during 2001–02 for organic and inorganic 

constituents (Hart and others, 2004). It is located about 8 river 

miles upstream from Bullfrog Bay and is only accessible by 

watercraft. The sampling location is about 1 mi upstream of 

the mouth of the canyon (fig. 4J).

Site HU5 Moqui Canyon (site ID 372838110372000).—

Moqui Canyon is located near mile marker 100 on river left, 

about 4 river miles upstream of Bullfrog Bay. Moqui Canyon 

is a popular side canyon for all types of water recreation and 

consists of several camping beaches suitable for houseboats. 

At the full pool level of Lake Powell (3,700 ft), Moqui Canyon 

arm of Lake Powell extends miles from its mouth with Lake 

Powell and consists of several tributaries. The canyon and its 

tributaries are steep walled and quite narrow. This canyon was 

intensively sampled during 2001–02 for organic and inorganic 

constituents (Hart and others, 2004). The sampling site is 

about 2 mi upstream in Moqui Canyon (fig. 4K).

Site HU6 Stanton Creek (site ID 372940110421600).—

Stanton Creek flows into Bullfrog Bay at about mile marker 

96 just southeast of Bullfrog Marina (site M1, fig. 1). Stanton 

Creek is a small tributary to Lake Powell but the area is 

popular for recreationists because it is easily accessed by boat 

or vehicle. Primitive camping exists on the shorelines and 

restroom facilities are provided by GLCA. It is an exposed 

tributary with a gentle sloping shoreline. The sampling site is 

Figure 4H. Photograph of site HU2 Blue Notch Canyon (site ID 3743221102646i00). View is to the west. Summer 2005.
12 Establishment of Sentinel Sampling Sites to Monitor Changes in Water and Sediment Quality at Lake Powell, Arizona and Utah

Figure 4I. Photograph of site HU3 Knowles Canyon (site ID 373438110350900). View is to the southwest. Summer 2004.

Figure 4J. Photograph of site HU4 Forgotten Canyon (site ID 373306110363700). View is looking upstream to the east. Summer 2005.
Description of Sentinel Sampling Sites 13

several hundred feet upstream of the mouth of Stanton Creek 

to Lake Powell (fig. 4L). 

Site HU7 Escalante River below 50-Mile Canyon (site 

ID 371938110553700).—This site is located about 9.3 mi 

upstream of the mouth of the Escalante River and its inflow 

area (fig. 1). The sampling location is in the main channel of 

the Escalante River just downstream of the mouth of 50-Mile 

Canyon (a tributary to the Escalante River, fig. 4M). Boat 

traffic in this section of the Escalante River can be extremely 

congested at certain times of the high visitor-use season. No 

beaches are available at this site for camping.

Site HU8 Rainbow Bridge National Monument (site ID 

370506110581600).–Rainbow Bridge National Monument 

is located in Forbidding Canyon on Bridge Creek (fig. 1) 

and is home to the world’s largest known natural bridge. 

The site is in an extreme narrow canyon with steep vertical 

walls. Boaters can access the monument from Lake Powell 

at mile marker 45. The sampling site is located at the 

floating docks (fig. 4N), which can vary in location due to 

fluctuating reservoir levels. A marina was operated at the 

site through the 1970s but was closed due to sewage and 

fuel contamination. A floating toilet facility is provided and 

managed by the National Monument. The site is heavily used 

by boaters including tour boats and it becomes congested 

during the peak visitor season during the summer. 

Site HU9 Padre Bay (site ID 370321111171700).—This 

sentinel sampling site is located in a large bay at about mile 

marker 23 where boating activity is high (fig. 1). The Padre 

Bay is a wide exposed area of Lake Powell and the site is 

easily identified by Dominquez Butte, which is a major 

landmark on Lake Powell (fig. 4O). Water depths at this site 

are several hundred feet depending on the reservoir level 

because the site is near the original Colorado River arm.

Site HU10 Warm Creek Bay (site ID 370333111262700).—

Warm Creek is a tributary to Lake Powell that forms a bay 

because of the physical characteristics of the canyon in this 

area. It is an extremely high-use area due to its proximity to 

marinas, boat ramps, and Page, Arizona, and also because 

there are numerous camping beaches suitable for houseboats. 

It is located about 11 mi upstream of Wahweap Marina (site 

M4, fig. 1). Warm Creek Bay supports a GLCA-serviced 

floating toilet and the sampling site is adjacent to this facility 

several hundred feet to the east (fig. 4P). 

Site HU11 Lone Rock Beach (site ID 370107111320500).—

Lone Rock Beach is a primitive camping area and is located 

Figure 4K. Photograph of site HU5 Moqui Canyon (site ID 372838110372000). View is to the northeast. Summer 2005.
14 Establishment of Sentinel Sampling Sites to Monitor Changes in Water and Sediment Quality at Lake Powell, Arizona and Utah

Figure 4M. Photograph of site HU7 Escalante River below 50-Mile Canyon (site ID 371938110553700) sampling area. View is looking 

upstream to the northwest toward 50-mile canyon. Summer 2005.

Figure 4L. Photograph of site HU6 Stanton Creek (site ID 372940110421600). View is looking to the northeast. Summer 2005.
Description of Sentinel Sampling Sites 15

Figure 4O. Photograph of 

site HU9 Padre Bay (site ID 

370321111171700) sampling 

area. View is looking to the 

east. Summer 2005. 

Figure 4N. Photograph of site HU8 Rainbow Bridge National Monument (site ID 370506110581600). View is to the south. Summer 2004.
16 Establishment of Sentinel Sampling Sites to Monitor Changes in Water and Sediment Quality at Lake Powell, Arizona and Utah

at about 3 mi upstream of Wahweap Marina and is accessible 

by boat and also by vehicle from U.S. Highway 89. It is the 

most populated and accessible beach on Lake Powell during 

high-use periods and it often has hundreds of visitors at a time. 

GLCA allows campers, including recreational vehicles, use 

of All-Terrain Vehicles (ATVs), direct boat access to camping 

sites, and open fire pits. The sampling site is several hundred 

feet from the beach shore to the northeast (fig. 4Q). Because 

of its high use, the GLCA monitors for bacteria outbreaks 

on a routine basis as part of their beach monitoring program 

(National Park Service, 2012). 

Site I18 Colorado River inflow (site ID 

375048110244100).—The Colorado River inflow site is 

located near the former marina at Hite, Utah, about mile 

marker 139 (fig. 1). Due to declining reservoir levels, Hite no 

longer provides marina service but it does have launch ramps. 

It is unknown if marina services will be provided in the future 

if reservoir levels rise to a sufficient level. The exact sampling 

location at this site can vary somewhat depending on the 

elevation of the lake but generally is just downstream of the 

inflow of the Dirty Devil River (fig. 4R).

Site I19 San Juan River Inflow (site ID 

371429110382000).—The San Juan River is a major tributary 

to Lake Powell, and along with the Colorado River arm, 

defines the general character of the shoreline of the Lake 

Powell (fig. 1). Like the Escalante River inflow site (I20), 

the location of the sampling site can vary depending on the 

elevation of the reservoir. The general location of the sampling 

site (fig. 4S) is upstream of Zahn Bay (fig. 1), more than 45 

mi from the mouth of the San Juan River at mile marker 

58. The visual characteristics (water clarity) of this site are 

considerably different from the other Lake Powell sentinel 

sampling sites due to the rock types that are exposed and 

characteristics of the San Juan River drainage basin. For 

example, water transparency as determined from Secchi disk 

measurements is limited at the sampling location. Because 

Figure 4P. Photograph 

of site HU10 Warm 

Creek Bay (site ID 

370333111262700) 

sampling area. View is to 

the south. Summer 2005.
Description of Sentinel Sampling Sites 17

Figure 4R. Photograph of site I18 Colorado River Inflow (site ID 375048110244100). View is upstream, photo taken 2005. 

Figure 4Q. Photograph of site HU11 Lone Rock Beach (site ID 370107111320500) sampling area. View is looking toward the north. 

Summer 2011.
18 Establishment of Sentinel Sampling Sites to Monitor Changes in Water and Sediment Quality at Lake Powell, Arizona and Utah

of the distance from marinas, the San Juan River inflow site 

is not as heavily used by recreationists compared to the other 

areas of Lake Powell. 

Site I20 Escalante River Inflow (site ID 

372205110564500).—The Escalante River is a major tributary 

to Lake Powell and when Lake Powell is at its full pool level 

of 3,700 ft, the lake can inundate more than 20 mi of the 

creek’s channel upstream from its mouth (fig. 1). This side 

canyon also consists of numerous tributary canyons that are 

suitable for recreation and houseboat camping. It is a popular 

location for visitors who access Lake Powell from Bullfrog 

or Halls Crossing Marinas, which are about 38 mi upstream 

of the mouth of the Escalante River. The inflow sampling 

site is several miles upstream of site HU7 (Escalante River at 

50-Mile Canyon). Sampling at this particular sentinel site may 

change depending on accessibility related to the level of the 

reservoir and hazards, such as floating debris (fig. 4T). 

Methods

Field Methods

Discrete measurements (point samples) of water 

temperature, specific conductance, and pH of shallow water 

(about 1 m below the water surface) were made at all sampling 

locations during specific times following the methods 

described by Wilde and Radtke (1998). Various water-quality 

instruments were used to measure the discrete parameters and 

these instruments were calibrated and verified on a daily basis. 

A 20-cm diameter Secchi disk was used to measure the 

transparency of water. Secchi-disk measurements were made 

from the shaded side of the boat when profile measurements 

and water samples were being collected. The disk was lowered 

through the water column until it was no longer visible, and the 

depth of the disk was recorded. This process was repeated three 

times, and the average value recorded. For more information 

about the Secchi disk, see Cole (1975, p. 116–118).

Vertical water chemistry and physical properties control 

the distribution of living or nonliving materials dissolved 

or suspended (Marzolf and others, 1998), and therefore it is 

important to select representative depths for collecting water 

samples based on the lakes stratification at each sentinel site. 

A Sea-Bird Electronics, Inc. (SBE), model SBE25TM CTD 

(conductivity, temperature, and depth) profiler was used 

to make depth-profile measurements for determining the 

depth at which water samples should be taken (fig. 5A). The 

SBE25TM CTD measures pressure, water temperature, specific 

conductance, pH, dissolved-oxygen concentration, and 

turbidity. Pressure measurements are converted to depths. All 

sensors of the SBE25TM CTD were calibrated annually by the 

Figure 4S. Photograph of site I19 San Juan River Inflow (site ID 371429110382000) sampling area. View is looking upstream to the 

northeast. Summer 2005.
Methods 19

manufacturer and calibration coefficients were updated in the 

Sea-Bird software following calibration. 

The SBE25TM CTD was programmed to scan the sensors 

8 times per second. The data were logged as raw voltages from 

the sensors in hexadecimal format. Profile measurements were 

accomplished in about 10 minutes with a downcast descent 

rate of about 3 ft/s. Start time of the downcast and other 

information pertinent to the measurement site were entered 

into the Sea-Bird software for site identification purposes.

 Following the collection of the downcast measurements, 

the raw hexadecimal data were converted using Seabird 

software (SBE Data Processing 7.2f;Sea-Bird Electronics, 

Inc., 2012), to values of pressure, depth, water temperature, 

pH, specific conductance, dissolved-oxygen concentrations, 

and turbidity, as ASCII numbers in engineering format. These 

converted values were then bin averaged into 1 m (3.281 ft) 

“bins.” The raw hexadecimal data are available, but the SeaBird processing software is needed for data conversion. 

Water samples for major ions, nutrients, organic 

carbon, and trace element analyses were collected using a 

polytetrafluroethylene (PTFE) fixed-bottle sampler (a sampler 

designed to collect point samples at a specified depth; fig. 5B). 

This sampler was suspended by a calibrated line to determine 

sampling depth and was weighted on the bottom by a 5-kg 

epoxy-coated weight. The bottle was sealed with a precleaned 

silicone-rubber stopper attached to a SpiderwireTM braided 

(nonstretchable) fishing line. When reaching the predetermined 

water depth, the stopper was rapidly removed by retrieval of 

the fishing line. After the bottle filled at the specified depth, the 

sampler was raised to the surface and removed from the lake. 

Sample water was decanted from the fixed-bottle sampler into 

a 1-L PTFE holding bottle. A summary of data available at the 

sentinel sites is shown in table 1. 

Sample water from the 1-L PTFE holding bottle was 

processed as follows: 

•	 Subsamples were filtered through a deionized-water 

rinsed, 0.45-mm pore-size, polysulfone cartridge filter 

into a 30-mL dark polyethylene bottle for nutrient 

determinations, a preburned 60-mL glass bottle 

for dissolved organic carbon determination, and a 

60-mL polyethylene bottle for anion determinations. 

These samples were unpreserved and chilled during 

transport to the laboratory for analysis.

Figure 4T. Photograph of site I20 Escalante River Inflow ( site ID 372205110564500). Site is looking upstream to the northeast. Summer 2005.
20 Establishment of Sentinel Sampling Sites to Monitor Changes in Water and Sediment Quality at Lake Powell, Arizona and Utah

Figure 5A. Photograph of the SBE25 profiler.

Figure 5B. Photograph of National Research Program (NRP) water sampler.
Methods 21

•	 An aliquot of sample from the holding bottle 

for dissolved trace element determinations was 

filtered through a 0.40-mm pore-size NucleporeTM

polycarbonate-membrane filter, using a vacuum 

filter apparatus made from PTFE (Kelly and 

Taylor, 1996). The following steps were used to 

minimize contamination: (1) the filter apparatus was 

thoroughly cleaned and rinsed with deionized water; 

(2) a new 0.40-mm pore size, 47-mm-diameter, 

polycarbonate-membrane filter was placed on 

the filter support and precleaned by drawing 

approximately 50 mL of 0.1 percent (volume/

volume) ultrapure nitric acid (HNO3)rinse solution 

through the filter into a waste bottle; (3) about 25 mL 

of a subsample of the composite was then filtered to 

prerinse the sample receiving bottle and discarded 

(this step also effectively preloaded the filter with 

particulates); (4) the balance of the subsample 

was filtered into a 125-mL polyethylene sample 

bottle; and (5) the filtered sample was preserved 

with the addition of 1 mL of concentrated ultrapure 

HNO3, to a pH less than 2 using a PTFE dispensing 

bottle (Brinton and others, 1995). Only one filter 

membrane was used for the entire filtration process 

per sample.

•	 A second aliquot from the same filtration process was 

used for the preparation of a sample for total dissolved 

mercury (Hg) determination. The filtrate for this 

sample was collected in an acid-rinsed borosilicate 

glass bottle. A 5-mL mixture of high purity potassium 

dichromate (K2CrO7) and ultrapure HNO3 was 

added to 125 mL of the sample, resulting in a final 

concentration of 0.04 percent (weight/volume) 

K2CrO7 and 4 percent (volume/volume) HNO3.

Water samples for VOC (volatile organic compounds) 

analyses were collected using a sampler designed and built by 

WildcoTM for the USGS National Water-Quality Assessment 

Program (NAWQA; fig. 5C). The sampler is designed to 

collect a sample at a single point. The stainless-steel sampler 

holds four 40-mL vials. Copper tubes extend to the bottom of 

each vial from the inlet ports on top of the sampler. The vials 

fill and overflow into the sampler body, displacing the air in 

the vials and in the sampler through the exhaust tube. The 

total volume of the sampler is eight times larger than the vials; 

therefore, the vials are flushed seven times (removing the 

air) before the final volume is retained in the vial. The small 

(1/16-in. inside diameter) copper inlet ports result in a slow 

(3–4 minutes) filling time helping to produce a representative 

sample and allowing sufficient time to place the sampler at 

the desired depth. The sampler begins to fill as soon as it 

enters the water; however, the final sample is retained in the 

vial during the last 15–20 seconds of the filling process. A 

cover over the inlet ports prevents contamination from surface 

oil and debris when the sampler is removed from the water 

(Shelton, 1997). The sampler was lowered approximately 1.5 

ft below the water surface and held in place while the sampler 

simultaneously filled the 4 replicate 40-mL vials. Each vial 

of sample was then preserved by the addition of 2 drops of 

concentrated hydrochloric acid (HCl). The vials were then 

immediately sealed without headspace. 

Raw water samples were collected directly in 1-L amber 

glass bottles baked at 450 oC for oil and grease and total 

petroleum hydrocarbons (TPH) analysis and were preserved 

by the addition of 10 mL of concentrated sulfuric acid to each 

Figure 5C. Photographs of the volatile organic 

compounds (VOC) sampler.
22 Establishment of Sentinel Sampling Sites to Monitor Changes in Water and Sediment Quality at Lake Powell, Arizona and Utah

Figure 5D. Photographs of the Ponar dredge sampler.

1-L amber glass bottle. All samples for organic determinations 

were chilled to 4 °C for transport to the laboratory for analysis.

Lakebed material was collected using a PonarTM dredge 

(fig. 5D) and following protocols described by Radtke (1997). 

The dredge was lowered and triggered to collect a surface 

sample of the lakebed material for analysis. A TeflonTM spatula 

or spoon was used to collect a sample from the dredge and 

transferred to a pre-cleaned wide-mouth glass jar. Care was 

given to collect a representative sample from the dredge that 

was not in contact with the metal sampler. Approximately 1-kg 

of wet sediment was collected from each selected site and 

stored chilled (less than 4 °C).

Laboratory Methods

Water samples were analyzed by two laboratories: (1) 

the USGS National Research Program Laboratory (NRP) in 

Boulder, Colorado and (2) the USGS National Water Quality 

Laboratory (NWQL) in Lakewood, Colorado. Water samples 

collected for analyses of all dissolved constituents were 

analyzed directly from sample bottles (preserved after sample 

processing) with no further pretreatment. 

Major cations of calcium (Ca), magnesium (Mg), 

sodium (Na), and silica (SiO2), were analyzed at the USGS 

National Research Laboratory in Boulder, Colorado, and were 

determined by inductively coupled plasma-atomic emission 

spectrometric (ICP-AES) techniques using a Perkin Elmer 

Optima 3300TM, dual-view emission spectrometer operating 

in the axial-view mode (Garbarino and Taylor 1979; Mitko 

and Bebek, 1999). Iron (Fe), phosphorus (P), and sulfur (S) 

also were determined by using this technique. Potassium 

(K) was determined by an ICP-AES technique using the 

same instrumentation operating in the radial-view mode. All 

samples were determined in triplicate to provide a measure of 

analytical variability.

Anions, including chloride (Cl), nitrate (NO3), and sulfate 

(SO4), were determined by ion chromatography (Brinton and 

others, 1996). Other nutrients, including ammonium (NH4), 

nitrite (NO2

), and phosphate (PO4), were determined by an 

automated spectrophotometric absorption method described by 

Antweiler and others (1996). 

Total alkalinity was determined on unpreserved filtered 

samples by an automated Gran titrimetric procedure using 

sulfuric acid as the titrant (Skougstad and others, 1979). 

Alkalinity and pH data were used to calculate concentrations 

of carbonate and bicarbonate. Dissolved-organic carbon was 

determined by persulfate oxidation of the organic carbon in 

the sample to carbon dioxide, which was measured using an 

infrared absorption spectrophotometric technique described by 

Wershaw and others (1987).

Trace-element determinations (see list at the beginning 

of this report), excluding Hg, were analyzed at the USGS 

National Research Laboratory in Boulder, Colorado, using a 

Perkin Elmer Elan Model 6000TM inductively coupled plasmamass spectrometer (ICP-MS). Aerosols of aqueous samples 
Future Sampling Plans 23

acidified with HNO3 were introduced into the spectrometer 

with a pneumatic nebulizer. Multiple internal standards 

(indium, iridium, and rhodium) covering the entire element 

mass range were used to normalize the system for drift. 

Details of the specific analysis techniques, procedures, and 

instrumental settings are described in Garbarino and Taylor 

(1994) and Taylor (2001). 

Trace concentrations of dissolved Hg were measured 

using an automated cold-vapor atomic fluorescence 

spectrometric (PS Analytical) technique. Details of the 

method are described in Roth (1994) and Roth and others 

(2001). Elemental Hg vapor from the samples was produced 

by chemically reducing Hg in the samples with excess 

stannous chloride. The resulting vapor was transported to the 

atomic fluorescence detector with a stream of argon gas for 

quantitative measurement. 

Samples collected for VOC determinations were analyzed 

by the USGS National Water Quality Laboratory (NWQL) 

using purge-and-trap gas chromatography/mass spectrometry 

methods described in Connor and others (1998). Concentrations 

of oil and grease were determined by the NWQL using USEPA 

Method 1664 (U.S. Environmental Protection Agency, 1999), 

which is a gravimetric determination of n-hexane extractable 

material. Concentrations of TPHs also were determined by the 

NWQL using the same extraction procedure followed by a silica 

gel separation.

Lakebed material was analyzed by the USGS NWQL 

for polycyclic aromatic hydrocarbons (PAHs). Samples 

were chilled to 4 °C and shipped to the NWQL for analysis 

as described by Furlong and others (1996). This method 

involves preconcentration of the sample by solvent extraction, 

separation by gel chromatography, and measurement by gas 

chromatography/mass spectrometry.

Quality of Water and Sediment Data

All inorganic laboratory sample determinations made at 

the USGS National Research Program Laboratory in Boulder, 

Colo., for major ions, trace elements, and nutrients were 

randomly performed in triplicate, throughout each analysis 

session. After statistical evaluation, outliers were rejected 

or samples were rerun until quality control objectives were 

satisfactorily met. Error terms representing the precision (1 

standard deviation) of the analytical laboratory determinations 

are reported with each measurement. Calibration curves for 

instrumental determinations were established by the use of 

at least five separate concentration calibration standards, 

prepared gravimetrically from pure metals or metal salts. 

Laboratory reagent blanks and field process blanks were 

analyzed when appropriate and used to evaluate the integrity 

of sample determinations. 

The NWQL analyzed reagent water blanks and reagent 

water spikes with each set of organic wastewater-compound 

analyses to monitor the method performance as part of the 

laboratory quality control. Duplicate water samples were 

collected during 2004–06 to check the replication of results 

produced by the laboratory. 

Measurement precision or variability is evaluated by the 

analysis of field replicates. During the study, water samples 

were collected in replicate for organic and inorganic analysis 

from eight sites including all the marina sites (M1, M2, M3, 

M4, M5, and M6) and two high-use sites (HU7 and HU8), 

processed in the field, and transported to the laboratory and 

analyzed under identical conditions. Because of concern 

regarding the possible sample contamination from the boat 

engines during the sampling for VOC determinations, a 

blank sample was collected from the opposite side of the 

boat from where samples were collected, with the boat 

engines idling. Results of the analysis of this blank showed 

no measurable concentrations of any of the VOC constituents 

greater than the detection limit of 0.2 mg/L. Duplicate and 

blank samples also were collected for VOCs, oil and grease, 

and TPH. For additional information on quality control of 

data, see Hart and others (2004).

Water and Sediment Data

All data collected during 2004–06 are provided in 

Microsoft© Excel spreadsheets in appendixes A–F. Appendix 

A includes discrete measurements of water temperature and 

specific conductance that were made from surface samples, 

along with measurements of water clarity using a Secchi 

disk. Appendixes B–E include all chemical analyses (water 

phase and lakebed material), including major ions, nutrients, 

organic carbon (appendix B), trace elements (appendix C), 

organic compounds including TPH, oil and grease, and 

VOCs (appendix D), and PAHs in lakebed material collected 

from 4 of the 20 sentinel sampling sites (appendix E). The 

bin-averaged SBE25 profile data are included in appendix F.

Future Sampling Plans

The sentinel sites will be used as long-term monitoring 

sites for the Glen Canyon (GLCA) NRA based on a 

monitoring plan prepared by the National Park Service 

(2004). Most recently, sentinel sites were sampled during 

2010 and 2011. Semi-permeable membrane devices (SPMDs) 

were deployed at all 20 sentinel sites. The SPMDs will 

provide some insight to the potential for polycyclic aromatic 

hydrocarbons (PAHs) to bioconcentrate in fatty tissue aquatic 

life. During this same time period, sediment cores also were 

collected from the San Juan River inflow area (2010) and from 

the Escalante River inflow area (2011). Analyses of data for 

these studies are currently being evaluated.
24 Establishment of Sentinel Sampling Sites to Monitor Changes in Water and Sediment Quality at Lake Powell, Arizona and Utah

Summary

During the spring of 2004 and summers of 2005 and 

2006, the U.S. Geological Survey and National Park Service–

Glen Canyon National Recreation Area collected baseline 

water and sediment chemistry data at 20 sentinel sampling 

sites on Lake Powell. The sentinel sampling sites are locations 

where repeat sampling and measurements can be made over 

time, to monitor the effects of visitor use on the quality of 

water and sediments and biota in Lake Powell. Previous work 

by the U.S. Geological Survey and Glen Canyon National 

Recreation Area showed the effects of visitor use on the 

selected side canyons (high-use areas), and those results along 

with other factors were used to design and select the long-term 

monitoring sites. The sentinel sites include 6 marinas, 11 highuse sites, and 3 tributary inflow sites that span the lake from 

Glen Canyon Dam to Hite, Utah, a distance of about 140 lake 

miles. 

Sampling and measurements made during the spring 

of 2004 provide baseline data for what is defined as a lowvisitor use period—when powerboats and personal watercraft 

are used minimally by visitors. Sampling and measurements 

were made during 2005 and 2006 during the summer months 

when visitation is defined as high and potential pollution from 

powered watercraft is at its peak.

Water samples were collected based on the structure 

of the water column as determined from depth-profile 

measurements at each sentinel site. Water temperature, specific 

conductance, pH, dissolved-oxygen concentrations, and 

turbidity were used to evaluate the stratification of the lake and 

to select sampling depths. A Secchi disk was used to measure 

the water clarity. Water samples were analyzed for (1) major 

ions, nutrients, and organic carbon; (2) trace elements; (3) 

organic compounds including oil and grease, total petroleum 

hydrocarbons, and volatile organic compounds. Lakebed 

material was analyzed for polycyclic aromatic hydrocarbons. 

Acknowledgements

The authors thank the former Glen Canyon National 

Recreation Area (GLCA) Superintendent, Kitty Roberts, for 

her support, and former GLCA biologist, Jesse Granet, for his 

support in the field. Without the logistical support, boats, and 

laboratory facilities from GLCA, the work would have been 

much more challenging to complete. Gratitude is expressed 

to USGS scientists Ronald Antweiler, David Roth, and Terry 

Plowman, for their contributions to field and laboratory 

work. A special thanks to Greg Fisk for field assistance, boat 

operation, and mechanical and logistical foresight.

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26 Establishment of Sentinel Sampling Sites to Monitor Changes in Water and Sediment Quality at Lake Powell, Arizona and Utah

Menlo Park Publishing Service Center, California

Manuscript approved for publication November 9, 2012

Edited by Linda S. Rogers and Claire Landowski

Layout and design by Judy Weathers
Hart and others—Establishment of Sentinel Sampling Sites to Monitor Changes in Water and Sediment Quality and Biota Related to Visitor 

Use at Lake Powell, Arizona and Utah, 2004–2006—Open-File Report 2012–1237