Sampling Episode Report 

Cruise Ship Plume Dilution Study 

Skagway, Alaska 

U.S. Environmental Protection Agency

Oceans and Coastal Protection Division 

Office of Wetlands, Oceans, and Watersheds 

Office of Water 

1200 Pennsylvania Avenue, NW 

Washington, D.C. 20460

May 18, 2009 
ACKNOWLEDGMENT AND DISCLAIMER 

 This report was prepared by the Oceans and Coastal Protection Division of the Office of 

Wetlands, Oceans, and Watersheds of the U.S. Environmental Protection Agency. Neither the 

United States Government nor any of its employees, contractors, subcontractors, or their 

employees make any warrant, expressed or implied, or assume any legal liability or 

responsibility for any third party’s use of, or the results of such use, any information, apparatus, 

product, or process discussed in this report. 

 The primary contact regarding questions or comments on this document is: 

Dr. Brian Rappoli 

U.S. Environmental Protection Agency 

Oceans and Coastal Protection Division, OWOW (4504T) 

1200 Pennsylvania Avenue, NW 

Washington, DC 20460 

(202) 566-1548 (telephone) 

(202) 566-1546 (fax) 

rappoli.brian@epa.gov 
i 

TABLE OF CONTENTS 

Page 

EXECUTIVE SUMMARY.................................................................................................................... iv 

1. INTRODUCTION .................................................................................................................1-1 

2. DESCRIPTION OF SELECTED CRUISE VESSELS ...................................................................2-1 

3. DATA COLLECTION METHODOLOGY.................................................................................3-1 

3.1 Pre-Sampling Activities.......................................................................................3-1 

3.2 Sampling Schedule...............................................................................................3-1 

3.3 Dye Injection Methodology .................................................................................3-1 

3.4 Plume Monitoring Methodology..........................................................................3-2 

3.5 Current and Weather Measurements....................................................................3-5 

4. RESULTS ...........................................................................................................................4-1 

4.1 Discharge Plumes.................................................................................................4-1 

4.2 Transect Water Quality Data ...............................................................................4-5 

4.3 Current Measurements and Weather Data ...........................................................4-5 

5. DATA QUALITY.................................................................................................................5-1 

5.1 Quality Assurance Assessment of Key Plume Dilution Study 

Measurements ......................................................................................................5-1 

5.2 Quality Assurance Assessment of Non-Key Plume Dilution Study 

Measurements ......................................................................................................5-2 

Appendix A DILUTION STUDY TRANSECTS BY SHIP 

Appendix B DISCHARGE PLUME DYE CONCENTRATIONS, TEMPERATURE, 

CONDUCTIVITY, DEPTH, TURBIDITY, AND SALINITY 

Appendix C SKAGWAY HARBOR DEPTH PROFILES 

Appendix D CURRENT MEASUREMENTS 

Appendix E SKAGWAY TIDE TABLE 

Appendix F MANUAL FIELD LOGS 

Appendix G DISCHARGE FLOW MEASUREMENTS 

Appendix H WEATHER DATA 

Appendix I OSV BOLD SURVEY PLAN 
TABLE OF CONTENTS (Continued) 

ii

Appendix J QUALITY ASSURANCE PROJECT PLAN FOR SUPPORT FOR OSV BOLD 

SURVEY OF LARGE CRUISE SHIP WASTEWATER IMPACTS IN 

ALASKAN WATERS 
iii 

LIST OF TABLES 

Page 

Table 2-1. Characteristics of Cruise Vessels That Participated in 2008 Plume Dilution Study, 

Skagway Alaska............................................................................................................... 2-1 

Table 3-1. Sampling Schedule ..................................................................................................... 3-1 

Table 3-2. Target Discharge Rhodamine WT Dye Concentrations by Cruise Vessel................. 3-2 

LIST OF FIGURES 

Page 

3-1 Sea-Bird SBE-19 CTD Sensor with Integrated SCUFA® Fluorometer.......................... 3-3 

3-2 Rigid Inflatable Boat........................................................................................................ 3-3 

3-3 Orientation of Arc Transects............................................................................................ 3-5

4-1 Profile of Arc Transect Results for Ryndam.................................................................... 4-2 

4-2 Profile of Arc Transect Results for Celebrity Millennium............................................... 4-3 

4-3 Profile of Arc Transect Results for Norwegian Star........................................................ 4-4 

4-4 Profile of Arc Transect Results for Volendam................................................................. 4-5 
iv 

EXECUTIVE SUMMARY

Sampling Episode Report for Cruise Ship Plume Dilution Study

 This Sampling Episode Report describes a plume dilution study conducted under the 

direction of the U.S. Environmental Protection Agency (EPA) in collaboration with the Alaska 

Department of Environmental Conservation (ADEC). This study, part of a survey conducted in 

Alaska by EPA’s Ocean Survey Vessel Bold in July 2008, was designed to characterize nearfield cruise ship discharge plumes from six cruise vessels while they were docked in Skagway 

Harbor, Alaska. Sampled vessels represented three cruise lines and a variety of advanced 

wastewater treatment system types, wastewater discharge flow rates, discharge port sizes, and 

port depths below the waterline. This study was conducted as a continuation of EPA’s 

assessment of standards for sewage and graywater discharges from large cruise ships operating 

in Alaska. 

 Using in situ measurements of Rhodamine WT dye in the effluent plume, the survey team 

determined the location and concentration of each vessel’s treated sewage and graywater 

discharge plume. A metering pump injected Rhodamine WT dye into the discharge line 

upstream of the discharge port, with a target dye discharge concentration of 700 μg/L (ppb). Dye 

concentrations in the resulting discharge plume were measured using a submersible fluorometer. 

Additional parameters (temperature, conductivity, depth, turbidity, and salinity) were measured 

simultaneously with plume discharge dye concentration, while manual notations of distance and 

location from the discharge port were made. Performing transects for plume characterization 

required approximately two hours per ship, with one ship tested per day. Measurements of the 

harbor current in the vicinity of the discharge plumes were collected using magnetic current 

meters. Dye concentrations in the discharge plume were found to decrease by a factor that 

ranged from approximately 40 to 90, depending upon ship, at a distance of 15 meters from the 

discharge port. 
1-1 

1. INTRODUCTION

 This Sampling Episode Report describes sampling and analysis activities to characterize 

graywater and sewage discharge plumes from six cruise vessels (Star Princess, Coral Princess, 

Ryndam, Celebrity Millennium, Norwegian Star, and Volendam) discharging at port in Skagway 

Harbor, Alaska. This study, which was conducted from July 7 through July 17, 2008, is a 

collaboration between EPA’s Oceans and Coastal Protection Division and the Alaska 

Department of Environmental Conservation (ADEC). This sampling study was partially funded 

via an interagency agreement between EPA and ADEC. 

 This study was part of a survey conducted in Alaska by EPA’s Ocean Survey Vessel Bold

and is a continuation of EPA’s assessment of the need for additional standards for sewage and 

graywater discharges from large cruise ships operating in Alaska under the “Certain Alaskan 

Cruise Ship Operations” law (also known as “Title XIV”; 33 USC 1901 Note). The data and 

information gathered through this sampling episode were collected using EPA’s authority under 

Section 308 of the Clean Water Act, as also provided by Title XIV. The cruise lines 

participating in the study voluntarily provided information and data gathered for and represented 

in this report, notwithstanding the above authority, in the interest of research for the 

improvement of wastewater treatment standards. 

 This plume dilution study was designed to provide information on near-field cruise ship 

treated sewage and graywater effluent discharge plume characteristics in harbor waters. The 

study will also provide preliminary information on whether these plumes behave as predicted by 

modeling performed by ADEC (Assessment of Cruise Ship and Ferry Wastewater Impacts in 

Alaska, 2004). ADEC used EPA’s Visual Plumes model system1

 to simulate the dilution of 

discharges from both large and small vessels. ADEC’s estimated dilution factor for initial 

dilution of discharges from stationary cruise ships in Skagway during a neap tide ranged from 5 

to 60. The objectives of this study were to (1) determine the effluent dilution characteristics of 

discharges from stationary cruise ships; (2) track the near-field mixing dynamics of the effluent 

plume; and (3) provide information that can be used to validate the modeling studies (see Survey 

Plan, Appendix I). 

 Other sampling programs supporting EPA’s assessment of cruise ship wastewater 

discharge standards in Alaska include two onboard sampling programs, conducted during the 

2004 and 2005 Alaska cruise seasons, that focused on characterizing pollutants found in 

wastewater (graywater and sewage) onboard cruise vessels and evaluating the performance of the 

advanced wastewater treatment systems. The results of these sampling programs can be found 

on EPA’s website at www.epa.gov/owow/oceans/cruise_ships/results.html. 

 Section 2 of this report describes the cruise vessels selected to participate in this study. 

Section 3 describes the data collection methodology. Section 4 presents a brief summary of the 

results. Section 5 provides a quality assurance assessment of the study. 

 

1

 EPA’s Visual Plumes model system is a Windows-based software application for simulating surface water jets and 

plumes. http://www.epa.gov/ceampubl/swater/vplume/ 
2-1 

2. DESCRIPTION OF SELECTED CRUISE VESSELS

 EPA selected the following six cruise vessels to participate in this plume dilution study: 

• Star Princess; 

• Coral Princess; 

• Ryndam 

• Celebrity Millennium; 

• Norwegian Star; and

• Volendam. 

 The vessels participating in the survey represented three cruise lines and a variety of wastewater 

treatment system types, wastewater discharge flow rates, discharge port sizes, and port depths below the 

waterline. Each of the participating vessels operates an advanced wastewater treatment system to treat 

combined graywater and sewage. Table 2-1 presents the characteristics of the cruise vessels selected to 

participate in this study. 

Table 2-1. Characteristics of Cruise Vessels That Participated in 2008 Plume Dilution 

Study, Skagway Alaska 

Cruise Vessel 

(Parent Company) 

Advanced 

Wastewater 

Treatment 

System Type

Discharge 

Flow Rate 

(m3/hour) 

Discharge 

Port 

Outer 

Diameter 

(cm) 

Discharge 

Port Depth 

Below 

Waterline 

(m) Discharge Location 

Star Princess 

(Carnival Corp.) 

Hamworthy 25.5 20.3 2.5 

(estimated) 

Midship, Port 

Coral Princess 

(Carnival Corp.) 

Hamworthy 25 20.3 4 Midship, Starboard 

Ryndam

(Carnival Corp.) 

Zenon 23 11.4 5 to 5.5 Midship, Port 

Celebrity Millennium

(Royal Caribbean Cruises, 

Ltd.) 

Hydroxyl 22 27.3 5 Midship, Port 

Norwegian Star

(Norwegian Cruise Line) 

Scanship 35 16.8 4.6 Midship, Starboard 

Volendam

(Carnival Corp.) 

Zenon 36 11.4 6 Midship, Port 
3-1 

3. DATA COLLECTION METHODOLOGY

3.1 Pre-Sampling Activities

 Visits to each of the six ships were conducted during the week prior to the start of the 

sampling episode. Visits were made to establish ship contacts, communications, and safety and 

emergency procedures, and to inspect sampling ports and associated fittings. 

3.2 Sampling Schedule

 Discharge plumes from six different cruise ships were monitored per the schedule in 

Table 3-1. Only one plume dilution study was conducted per day. 

Table 3-1. Sampling Schedule 

Cruise Vessel Date of Study Times of Study Skagway Pier 

Star Princess July 10, 2008 1025 to 1230 Railway 

Coral Princess July 11, 2008 1040 to 1245 Railway 

Ryndam July 12, 2008 1025 to 1205 Railway 

Celebrity Millennium* July 15, 2008 0950 to 1135 Railway 

Norwegian Star* July 16, 2008 1000 to 1145 Ore 

Volendam July 17, 2008 1005 to 1140 Broadway 

* Trial testing was also conducted on the Celebrity Millennium on July 7, 2008, and the Norwegian Star on July 9, 

2008, to refine sample collection methodology. 

3.3 Dye Injection Methodology

 Metering pumps (Series 2001HEC-30 Variable Speed Peristaltic Pump, Flomotion 

Systems) were used to inject Rhodamine WT dye (Rhodamine WT Liquid, ORCO Organic 

Dyestuffs Corporation) into the cruise ships’ treated sewage and graywater discharge. The 

pumps were installed downstream of the advanced wastewater treatment system, but as far 

upstream of the discharge port as possible so that multiple pipe bends and fittings provided 

thorough mixing of the dye. 

 Strap-on ultrasonic flow meters (BE 6000 Ultrasonic Flow Meter, Flomotion Systems) 

were installed on the discharge piping to record discharge rates (presented in Appendix G). 

Measured discharge rates were multiplied by the known Rhodamine WT dye feed stock 

concentration to calculate and adjust discharge dye concentration to attain the target 

concentration (discussed below). Discharge dye concentration also was measured directly on 

three cruise vessels (Celebrity Millennium, Norwegian Star, and Volendam) using a fluorescence 

sensor with a flow-through cell (SCUFA®, Turner Designs) installed on the discharge piping as 

close as possible to the discharge port. While the shipboard survey team was able to monitor 

discharge dye concentration via laptop computer connected to the SCUFA® sensor, it was not 

possible to electronically log these data. Therefore, the survey team kept manual logs of 

discharge dye concentrations. Tables F-1 through F-4 of Appendix F contain the raw data 

obtained from the fluorometer (see Section 5.1). 
3-2 

 Trial dilution studies conducted on the Celebrity Millennium and the Norwegian Star

revealed that the originally planned target discharge dye concentration of 100 ppb (see Survey 

Plan, Appendix I) was too low to be detected outside the cruise vessel (see Section 5.1, Accuracy 

and Calibration). Therefore, the target discharge Rhodamine WT dye concentration was 

increased to 700 ppb for most transects (Table 3-2). Target dye concentration was decreased 

during the Star Princess study because the plume was visible on the surface of the water (most 

likely because of the relatively shallow discharge port; see Table 2-1); this was the only vessel 

where the plume was visible on the surface of the water. Target dye concentration was increased 

during the Coral Princess study because the highly intermittent nature of the discharge and 

strong water currents made plume detection difficult (see Section 4.1). 

Table 3-2. Target Discharge Rhodamine WT Dye Concentrations by Cruise Vessel 

Cruise Vessel Discharge Rhodamine WT Dye Concentration (ppb) 

Star Princess 700 (cast 4), then 420 (casts 5 through 11) 

Coral Princess 700 (casts 2 through start of 5), 875 (portion of cast 5), 1,050 (end of cast 5 

through cast 7) 

Ryndam 700 

Celebrity Millennium 700 

Norwegian Star 700 

Volendam 700 

 Discharge dye concentrations are the product of the known initial dye concentration, dye 

injection rate, and discharge flow rate. While the initial dye injection concentration and dye 

injection rate were constant (with the exception of the Coral Princess; see Section 4.1), 

discharge flow rates varied, resulting in variability of the discharge dye concentration. Any 

analysis of the data collected in this study should consider this variability when calculating nearfield discharge plume dilution. 

 On four cruise vessels, temperature, turbidity, and pH of the treated effluent also were 

recorded from the ship’s wastewater treatment control panel. These data are provided in 

Appendix F. Similar data were not available for the remaining two ships. 

3.4 Plume Monitoring Methodology

 Dye was injected into the treated sewage and graywater discharge for approximately two 

hours on each cruise vessel. During that time, dye concentrations in the water outside the cruise 

vessel were measured to determine near-field plume dilution after discharge (the cruise vessels 

all were positioned so that the discharge ports faced the harbor and not the piers). Prior to dye 

injection, measurements were taken of background fluorescence concentrations in the water. 

These measurements verified that no background seawater fluorescence was detected above the 

detection limit of fluorometer, which was approximately 1.6 ppb. For most ships, a salinity 

depth profile also was performed to locate the halocline prior to dye injection. 

 Dye concentrations were measured using an in situ fluorometer (SCUFA®, Turner 

Designs) integrated into a Sea-Bird SBE-19 conductivity, temperature, and depth (CTD) sensor 

package (Sea-Bird SBE-19, Sea-Bird Electronics, Inc.) (Figure 3-1). This sampling array was 
deployed from a rigid inflatable boat (RIB) that was conducting transects at low speed (Figure 3-

2). 

Figure 3-1. Sea-Bird SBE-19 CTD Sensor with Integrated SCUFA® Fluorometer 

Figure 3-2. Rigid Inflatable Boat 

 One rope was used to control the depth of the towed array, while a second rope was used 

to control the distance of the towed array from the discharge port. This second rope was tied to 

3-3 
3-4 

the bow of the RIB and attached to the cruise vessel via a hull magnet affixed just above the 

waterline at the location of discharge port. Sensor depth was recorded electronically by the 

sampling array, while RIB location relative to the hull magnet was recorded manually by the 

sampling team onboard the RIB. The RIB sampling team also monitored sensor measurements, 

including Rhodamine WT dye concentrations, in real time using a laptop computer. The 

following measurements were collected by CTD + SCUFA® sampling array at 0.5 second 

intervals during the plume transects: dye concentration (uncorrected; see Section 5.1); 

temperature; conductivity; depth (of the sensor array); turbidity; and salinity. 

 For most ships, a variety of transect types were conducted to provide detailed 

characterization of the discharge plumes (see Appendix A). Transects can be described by 

visualizing polar axes on the water surface, with the location of the hull magnet corresponding to 

the origin, and the array location and movement indicated by a radius (distance from cruise 

vessel) and polar angle (estimated in degrees by the RIB sampling crew) (see Figure 3-3). For 

example, 90° indicates the array is located to the right of the discharge port at the ship’s hull, 

while 270° indicates the array is located to the left of the discharge port at the ship’s hull. Four 

different types of transects were performed to characterize the discharge plumes: 

• Arc. Array was moved in an arc (e.g., 90° to 270°) at a fixed distance from the 

hull magnet. Arc transects at varying water depths and distances from the hull 

magnet were the most common type of transect performed, and were the primary 

means to locate and characterize discharge plumes. 

• Inward or Outward Profile. Array was moved toward or from a fixed position on 

the hull (i.e., the hull magnet) at a constant angle (e.g., 225°). Inward and/or 

outward profiles were performed after the location of the discharge plume was 

determined using arc transects. These profiles produced continuous dye dilution 

profiles determined by distance from the hull magnet. 

• Stationary. Array was maintained at a fixed location (depth, distance, and angle 

from the ship) over a period of time. This profile produced a continuous dye 

dilution profile at a fixed array location as the plume moved past the array over 

time. This was the primary type of transect used for the Star Princess because the 

plume was visible on the surface of the water (most likely because of the 

relatively shallow discharge port on the vessel; see Table 2-1), therefore an arc 

transect was unnecessary to find the plume. This type of profile also was used 

frequently for the Coral Princess, where ship discharge flow rates were highly 

variable and/or intermittent. 

• Depth Profile. Array was maintained at a fixed distance and angle from the ship 

while the array was raised or lowered through the water column. These profiles 

produced continuous dye dilution profiles by depth. 
0

5

10

15

20

-20 -15 -10 -5 0 5 10 15 2

meters to left (positive) and right (negative)of discharge port (located at zero)

meters from discharge port

225°

270°

135°

90°

180°

0

Figure 3-3. Orientation of Arc Transects for Dye Measurements 

3.5 Current and Weather Measurements

 At least two current meters (S4 current meters, InterOcean Systems, Inc.) were deployed 

off each cruise vessel to collect current measurements during the dilution studies (in some cases, 

three meters were used). The meters were deployed from the cruise vessels (to negate current 

meter motion relative to the vessels), approximately 15 meters away from the discharge port and 

approximately 3 meters out from the hull (to avoid interference from the vessel’s metallic hull 

with the magnetic sensor of the current meter). The current meters were deployed at depths of 1 

and 3 meters (or at depths of 1, 3, and 5 meters if a third current meter was used). Current 

measurements documented the ambient currents that affected the trajectory and dilution of the 

plume. 

 Weather conditions (e.g., air temperature, wind speed, and wind direction) were recorded 

by OSV Bold personnel during the dilution studies. 

3-5 
4-1 

4. RESULTS

4.1 Discharge Plumes

 Uncorrected dye concentration data for all transects are provided in Appendix B (see 

Section 5.1). In general, it appears that most near-field dilution occurs within 2.5 meters of the 

discharge port, with the plumes remaining relatively intact to distances of approximately 15 

meters. The minimum dye dilution factors discussed in this report are the ratio of the initial dye 

concentration (i.e., dye concentration prior to discharge from the port) to the maximum dye 

concentration observed in the plume. The minimum dilution factors observed during arc 

transects conducted 15 meters from the discharge port ranged from approximately 40 to 90. 

 The following narratives provide a brief description of a complex dynamic phenomenon. 

The data collected in this study will be further analyzed by the ADEC to validate previous 

modeling studies on nearfield dilution of these treated sewage and graywater discharges. 

Star Princess. This ship’s discharge port was the shallowest of all the sampled cruise 

vessels (see Table 2-1). The discharge plume was the only one visible from the water surface; it 

moved along the hull at an angle between 255 and 270° from the discharge port location. 

Detected dye concentrations ranged up to approximately 57 ppb. It is unknown whether higher 

concentrations would have been detected if the CTD + SCUFA® array was able to measure dye 

concentrations near the surface of the water column (see section 5.1). Detected dye 

concentrations observed along the 270° transect were approximately similar at distances of 5 

meters and 7.5 meters from the discharge port, and somewhat lower at a distance of 10 meters; 

however, the highest concentration of dye was observed on the 255° transect at a distance of 10 

meters. EPA did not prepare a profile of arc transect results for the Star Princess because arc 

transects were not performed. 

Coral Princess. Discharge from the Coral Princess was highly intermittent. During 

periods of no flow, the shipboard survey team suspended dye injection to minimize dye 

accumulation in the discharge piping, which could cause spikes and variability in discharge 

Rhodamine WT dye concentration. As a result, dye concentration data in Appendix B for the 

Coral Princess represent intermittent wastewater discharge with discharge dye concentration 

variability that is not well characterized. Because of this variability and strong water currents, 

the discharge plume was difficult to detect. Toward the end of the sampling period, detected 

plume dye concentrations ranged up to 270 ppb and were highly variable in concentration and in 

location (as measured both by depth and degrees from the discharge port). EPA did not prepare 

a profile of arc transect results for the Coral Princess due to the highly intermittent nature of the 

discharge. 
Ryndam. The discharge plume was most clearly characterized moving at an angle of 

135° from the discharge port. The discharge plume was also detected at angles of 180° and 90°, 

particularly toward the end of the sampling period. Detected plume dye concentrations ranged 

from 5 ppb to approximately 20 ppb. During the arc transects, the minimum dilution factor of 

approximately 34 was observed at 5 meters from the discharge port (note: this dilution factor is 

based on an estimated initial dye concentration of 700 ppb). Maximum dye concentrations 

observed during arc transects, at various distances and depths are presented in Figure 4-1. For 

these transects, a minimum dilution factor of approximately 93 was observed 15 meters from the 

discharge port. 

15

10

7.5

5

2.5

1.4

2.5

3.5

4.5

0.00

5.00

10.00

15.00

20.00

25.00

Dye Concentration (ppb)

Distance from Discharge Port (meters)

Depth (meters)

Figure 4-1. Profile of Arc Transect Results for Ryndam

4-2 
Celebrity Millennium. The discharge plume was most clearly characterized moving at 

angles ranging from 240° to 270° from the discharge port. The discharge plume was observed at 

depths ranging from 5 to 7 meters. Detected plume dye concentrations ranged up to 47 ppb. 

During the arc transects, the minimum dilution factor of approximately 11 was observed 2.5 

meters from the discharge port. Maximum dye concentrations observed during arc transects, at 

various distances and depths are presented in Figure 4-2. For these transects, a minimum 

dilution factor of approximately 39 was observed 15 meters from the discharge port. 

2.5

5

7.5

10

15

1.4

3.2

5.5

7.4

0

5

10

15

20

25

30

35

40

45

50

Dye Concentration (ppb)

Distance from Discharge Port (meters)

Depth (meters)

Figure 4-2. Profile of Arc Transect Results for Celebrity Millennium

4-3 
Norwegian Star. The discharge plume was most clearly characterized moving at angles 

ranging from 250° to 270° from the discharge port. The discharge plume was observed at depths 

ranging from 3 to 5.5 meters. Detected plume dye concentrations ranged up to approximately 88 

ppb. During the arc transects, the minimum dilution factor of approximately 13 was observed 5 

meters from the discharge port. Maximum dye concentrations observed during arc transects, at 

various distances and depths are presented in Figure 4-3. For these transects, a minimum 

dilution factor of approximately 43 was observed 15 meters from the discharge port. 

2.5

5

7.5

10

15

1.4

3

5.5

7.5

0

5

10

15

20

25

30

35

40

45

50

Dye Concentration (ppb)

Distance from Discharge Port (meters)

Depth (meters)

Figure 4-3. Profile of Arc Transect Results for Norwegian Star

4-4 
Volendam. The discharge plume was most clearly characterized moving at angles 

ranging from 125° to 225°. The discharge plume was generally observed at a depth of 5.3 meters 

with detected dye concentrations ranging up to approximately 21 ppb. During the arc transects, 

the minimum dilution factor of approximately 37 was observed 5 meters from the discharge port. 

Maximum dye concentrations observed during arc transects, at various distances and depths are 

presented in Figure 4-4. For these transects, a minimum dilution factor of approximately 45 was 

observed 15 meters from the discharge port. 

15

10

7.5

5

2.5

1.4

2.8

5.3

7.3

0

5

10

15

20

25

Dye Concentration (ppb)

Distance from Discharge Port (meters)

Depth (meters)

Figure 4-4. Profile of Arc Transect Results for Volendam

4.2 Transect Water Quality Data

 Data on water temperature, conductivity, depth (of the sensor array), turbidity, and 

salinity from each transect are provided in Appendix B. Skagway Harbor salinity depth profiles 

(from the pre-dye transects for most ships) are provided in Appendix C. For all vessels, the 

halocline appeared to be deeper than the discharge port (see Figures C-1 through C-4 in 

Appendix C). 

4.3 Current Measurements and Weather Data

 Current measurements collected during the cruise ship plume dilution study are provided 

in Appendix D (see Figures D-1 through D-13 in Appendix D). For the polar plots, magnetic 

north corresponds to 0°. In Skagway, true north is 22.6° east of magnetic north. The heading of 

all the cruise vessels in this study was 40° east of true north. Therefore, when analyzing the 

current data, the ship headings were 62.6° east of magnetic north. 

4-5 
4-6 

 The current meters were pre-programmed to begin data collection well before actual 

deployment from the cruise ships, and the meters continued to collect data until after their 

retrieval. Current data presented in this report include only the subset of data collected during 

the cruise ship plume dilution study (see Table 3-1). 

 National Oceanic and Atmospheric Administration Tide Tables for Skagway for July are 

provided in Appendix E. These tide tables are provided to supplement and inform the current 

measurements. 

 Weather data (air temperature, wind speed, and wind direction) recorded during the 

cruise ship plume dilution study are provided in Appendix H. 
5-1 

5. DATA QUALITY

 Quality assurance/quality control (QA/QC) procedures applicable for this program are 

outlined in the Quality Assurance Project Plan for Support for OSV Bold Survey of Large Cruise 

Ship Wastewater Impacts in Alaskan Waters (QAPP), which is reproduced in Appendix J. This 

section provides an assessment of the QAPP project data quality objectives specific to the cruise 

ship plume dilution study, which were established for the key measurements of the concentration 

of Rhodamine WT dye in the near-field plume and in the cruise ships discharges. In addition, 

this section provides a brief quality assurance assessment of non-key measurements. 

 Trial dilution studies were conducted on the Celebrity Millennium on July 7 and on the 

Norwegian Star on July 9 to refine the sample collection and analysis methodologies. Data from 

these trial studies are not presented in this report. Sampling on the Celebrity Millennium and the 

Norwegian Star was repeated on July 15 and July 16, respectively. 

5.1 Quality Assurance Assessment of Key Plume Dilution Study Measurements

 For the cruise ship plume dilution study, the key measurements identified in the QAPP 

are the concentration of Rhodamine WT dye in the near-field plume and in the cruise vessel 

discharge (end-of-pipe). The data quality objectives for these measurements are defined in terms 

of completeness, accuracy, precision, representativeness, and comparability. 

Completeness (Near-Field Plume Dye Concentrations) 

 Dye concentration data in the near-field plume are complete for all vessels surveyed 

except the Star Princess. The discharge plume for the Star Princess was visible at the surface of 

Skagway Harbor. The CTD + SCUFA® array is designed to take measurements at 

approximately 1.5 meters of depth and deeper. As a result, data for the Star Princess do not 

characterize the entire plume, but only the portion of the plume deeper than approximately 1.5 

meters. 

Completeness (Cruise Ship Discharge Dye Concentrations) 

 Discharge dye concentrations were calculated by multiplying the measured discharge 

rates by the known feedstock dye concentrations. On three cruise vessels (Celebrity Millennium, 

Norwegian Star, and Volendam), a SCUFA® fluorescence sensor was installed on the discharge 

piping to verify dye concentrations. For the other three vessels, the SCUFA® sensor could not 

be used to verify dye concentrations due to damage sustained during an unannounced emergency 

generator power drill on one of the ships. When fluorescence data could not be collected, the 

survey team verified dye discharge by visual observation. Dye concentration was assumed to be 

the calculated concentration. 

Accuracy and Calibration 

 Dilution series performed for the three SCUFA® fluorometers prior to field testing 

showed excellent accuracy, with a highly linear response from approximately 5 ppb through 300 

ppb. The dilution series and initial trial testing on Celebrity Millennium on July 7 revealed that 

the practical detection limit for the fluorometers was the seawater background signal of 
5-2 

approximately 1.6 ppb (contrary to the detection limit of 0.04 ppb reported by the 

manufacturer2

). A calibration curve for the range of 5 to 50 ppb was found to be linear (R2 > 

0.99). Actual dye concentrations are obtained using the following expression: 

C = 0.768*C’ + 4 

where C equals dye concentration and C’ is the uncorrected fluorometer response. 

 In consideration of the loss of two orders of magnitude of SCUFA® sensitivity, the 

survey team increased the target shipboard dye concentration from the planned 100 ppb to 700 

ppb. Consequently, a second calibration curve was prepared for high dye concentrations. For the 

calibration range of 84 to 660 ppb, the calibration curve was linear (R2>0.99) and fit the 

following expression: 

C = 1.02*C’ + 9 

where C equals dye concentration and C’ is the uncorrected fluorometer response. 

Precision and Representativeness 

 The QAPP specified collection of duplicate CTD+SCUFA® data using a pair of arrays 

towed side-by-side from the RIB. Field duplicate sampling using two adjacent CTD+SCUFA® 

arrays was not performed. The secondary CTD+SCUFA® array was dismantled to provide a 

SCUFA® fluorometer to replace the damaged shipboard unit. 

Comparability (Among Ship Discharge Tests) 

 The sample collection and analysis methodology was consistent for all cruise ship plume 

dilution studies. Dilution study transects were generally consistent among ships, with some 

deviations necessary to account for ship-specific conditions and weather conditions during each 

test. 

Overall Data Quality Assessment 

 This data quality assessment indicates that the key measurements collected during the 

cruise ship plume dilution study are of sufficient quality for use in analyzing near-field mixing 

dynamics of the effluent plumes from stationary cruise ships in Skagway Harbor. 

5.2 Quality Assurance Assessment of Non-Key Plume Dilution Study Measurements

Discharge Flow Measurements 

 Ship discharge flows were measured on all cruise vessels except the Norwegian Star. For 

the Norwegian Star, discharge flows were measured only during the set-up period because the 

meter malfunctioned at the start of the sampling period. Repeated attempts to reinstall the flow 

 

2

 Telephone contact with the manufacturer revealed that the reported detection limit can be achieved only under 

ideal, laboratory conditions. 
5-3 

meter were unsuccessful. Therefore, Norwegian Star discharge dye concentration was measured 

using a SCUFA® sensor (as it could not be calculated using flow rates). 

 While discharge flow data were monitored by the shipboard survey team, they were not 

reliably logged electronically because of a smaller than expected data-logging buffer capacity. 

For the Star Princess, Coral Princess, Ryndam, and Celebrity Millennium sampling events, 

electronic data logs are available for only the last 7 to 15 minutes of testing. For the Norwegian 

Star, electronic data logs are available for the last 2 hours of testing. For the Volendam, 

electronic data logs are complete for the entire period of testing. Electronically logged discharge 

flow data were supplemented by field logs taken by the shipboard survey team (see Appendix F). 

 Two ships, Ryndam and Volendam, operated flow meters on their discharge. On both of 

these ships, ultrasonic flow meter measurements closely matched measurements made by these 

ships’ built-in meters. 

Current Measurements 

 Harbor current was measured during all sampling events for all six ships. For two of the 

six ships tested, current meters were deployed at 1, 3, and 5 meter depths. For the other four 

ships, current meters were deployed only at 1 and 3 meter depths due to the difficulty of 

deploying the meters. For one ship (Norwegian Star), current was not measured at the 1 meter 

depth due to water seepage into the connector cover on the meter. Current measurements 

collected are reasonable, based on their correlation to the location and direction of the detected 

plume. 

Weather Data 

 Weather conditions (e.g., air temperature, wind speed, and wind direction) were recorded 

by the OSV Bold personnel during measurements of plume dilution, with the exception of 

dilution measurements collected for the Coral Princess on July 11.