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Produced Water Discharge Plumes from 

Pacific Offshor Oil and Gas Platforms 

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Table of Contents: 

List of Figures .............................................................................................................................. ii 

List of Tables ............................................................................................................................... iv 

Executive Summary ...................................................................................................................... 1 

Project Organization ..................................................................................................................... 2 

1. Introduction ...................................................................................................................... 3 

2. Objectives ......................................................................................................................... 3 

3. Approach .......................................................................................................................... 3 

3.1 Plume Mapping ..................................................................................................... 3 

3.2 Plume Modeling .................................................................................................... 6 

4. Results .............................................................................................................................. 7 

4.1 Platform Hogan ..................................................................................................... 7 

4.1.1 Pre-Cruise Modeling ................................................................................. 7 

4.1.2 Field Sampling and Data Collection .......................................................... 9 

4.1.2.1 Ambient Current Velocity Field ................................................. 9 

4.1.2.2 Dye and Hydrographic Distributions .......................................... 9 

4.1.3 Post-Cruise Modeling .............................................................................. 13 

4.2 Platform Harvest ................................................................................................. 15 

4.2.1 Pre-Cruise Modeling ............................................................................... 15 

4.2.2 Field Sampling and Data Collection ........................................................ 15 

4.2.2.l Ambient Current Velocity Field ............................................... 15 

4.2.2.2 Dye and Hydrographic Distributions ........................................ 15 

4.2.3 Post-Cruise Modeling .............................................................................. 21 

4.3 Platform Habitat .................................................................................................. 23 

4.3. l Pre-Cruise Modeling ............................................................................... 23 

4.3.2 Field Sampling and Data Collection ................................................... ..... 23 

4.3.2.1 Ambient Current Velocity Field .......... ..................................... 23 

4.3.2.2 Dye and Hydrographic Distributions ........................................ 23 

4.3.3 Post-Cruise Modeling .............................................................................. 28 

4.4 Platform Gina ...................................................................................................... 30 

4.4.1 Pre-Cruise Modeling ............................................................................... 30 

4.4.2 Field Sampling and Data Collection ........................................................ 30 

4.4.2.1 Ambient Current Velocity Field ............................................... 30 

4.4.2.2 Dye and Hydrographic Distributions ....................................... . 30 

4.4.3 Post-Cruise Modeling .............................................................................. 36 

5. Discussion I Summary .................................................................................................... 38 

5.1 Location of the Plume ......................................................................................... 39 

5.1.1 Horizontal Distribution ............................................................................ 39 

5.1.2 Vertical Structure .................................................................................... 39 

5.2 Dilution of the Plume .......................................................................................... 40 

5.3 Impacts of the Plume ........................................................................................... 42 

6. References ...................................................................... ................................................ 43 

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List of Figures 

Figure 1. Map of the study area showing platform locations (red squares) in the Santa 

Barbara Channel ................................................................................................................... 4 

Figure 2. Pre-cruise plume modeling results for Platform Hogan, using the moored data 

set from mooring CAIN for August 1994 ............................................................................. 8 

Figure 3. Time series of currents for Platform Hogan at 23 m .................................................... 10 

Figure 4. Horizontal planar view of the distribution of the maximum concentration of 

Rhodamine WT (μg·l-1, top) and minimum dilution (bottom) for Platform Hogan on 

July 24, 2003 ....................................................................................................................... 11 

Figure 5. Vertical planar cross-section of the maximum concentration of Rhodamine WT 

(μg·r 1

, top) and minimum dilution (bottom) along the axis of the plume shown in 

Figure 4 ............................................................................................................................... 12 

Figure 6. Vertical water column profiles of physical (temperature, salinity, and density), 

biological (chlorophyll fluorescence), and dye tracer concentration for Platform 

Hogan .......................................................... ....................................................................... 13 

Figure 7. Post-cruise plume modeling results for Platform Hogan use data collected 

during field operations on 24 July 2003 .............................................................................. 14 

Figure 8. Pre-cruise plume modeling results for Platform Harvest, using the moored data 

set from mooring AROF for August 1994 .......................................................................... 16 

Figure 9. Time series of currents for Platform Harvest at 59 m .................................................. 17 

Figure 10. Horizontal planar view of the distribution of the maximum concentration of 

Rhodamine WT(μg·l-1, top) and minimum dilution (bottom) for Platform Harvest 

on July 25, 2003 .................................................................................................................. 19 

Figure 11. Vertical planar cross-section of the maximum concentration of Rhodamine 

WT (μg·r 1

; top) and minimum dilution (bottom) along the axis of the plume shown 

in Figure 9 ........................................................................................................................... 20 

Figure 12. Vertical water column profiles of physical (temperature, salinity, and density), 

biological (chlorophyll fluorescence), and dye tracer concentration for Platform 

Harvest. .............................................................................................. ................................. 21 

Figure 13. Post-cruise plume modeling results for Platform Harvest, using data collected 

during field operations on 25 July 2003 .............................................................................. 22 

Figure 14. Pre-cruise plume modeling results for Platform Habitat, using the moored data 

set from mooring CAIN for August 1994 ........................................................................... 24 

Figure 15. Time series of currents for Platform Habitat at 39 m ................................................. 25 

Figure 16. Horizontal planar view of the distribution of the maximum concentration of 

Rhodamine WT(μg· l-1, top) and minimum dilution (bottom) for Platform Habitat on 

July 25, 2003 ....................................................................................................................... 26 

Figure 17. Vertical planar cross-section of the maximum concentration of Rhodamine 

WT (μg·r 1

; top) and minimum dilution (bottom) along the axis of the plume shown 

in Figure 15 ......................................................................................................................... 27 

Figure 18. Vertical water column profiles of physical (temperature, salinity, and density), 

biological (chlorophyll fluorescence), and dye tracer concentration for Platform 

Habitat. ............................................................................................................................... 28 

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Figure 19. Post-cruise plume modeling results for Platform Habitat, using data collected 

during field operations on 26 July 2003 .............................................................................. 29 

Figure 20. Time series of currents for Platform Gina at 23 m ..................................................... 31 

Figure 21. Horizontal planar view of the distribution of the maximum concentration of 

Rhodarnine WT(μg·r 1

, top) and minimum dilution (bottom) for Platform Gina on 

July 27, 2003 ....................................................................................................................... 32 

Figure 22. Vertical planar cross-section of the maximum Rhodamine WT (μg·r 1

; top) and 

minimum dilution (bottom) along the axis of the plume shown in Figure 21 ...................... 33 

Figure 23. Section plots of Rhodarnine dye and density extending away from Platform 

Gina .................................................................................................................................... 34 

Figure 24. Vertical water column profiles of physical properties (Temperature, Salinity, 

and Density expressed as Sigma theta), chlorophyll fluorescence and Rhodarnine 

WT concentration . .............................................................................................................. 35 

Figure 25. Post-cruise plume modeling results for Platform Gina, using data collected 

during field operations on 27 July 2003 .............................................................................. 37 

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List of Tables 

Table 1. Produced water discharge locations, outfall type, flowrate, and water quality 

characteristics of produced waters ........................................................................................ 5 

Table 2. Summary of field sampling activities .............................................................................. 7 

Table 3. Summary of plume model runs and observations for the four oil platforms 

studied in the Santa Barbara Channel.. ............................................................................... . 41 

Table 4. Resultant properties on water column based on the minimum initial dilutions 

measured ............................................................................................................................. 42 

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Executive Summary 

Produced water discharges from four representative oil and gas production platforms in the Santa 

Barbara Channel, California were studied during July 2003. Natural tracers or ambient variables 

[temperature, salinity, density, chlorophyll fluorescence, and beam attenuation (indicative of 

suspended particles)] and an injected dye (Rhodamine WT) were utilized in an attempt to detect 

and measure the discharge plumes from outer continental shelf Platforms Hogan, Harvest, 

Habitat, and Gina. The study had two primary objectives: first, sample and determine the spatial 

extent of produced water plumes from the discharge point to beyond detection, and second, 

calculate the initial dilution and compare with model estimates. Ancillary objectives were to 

assess physical factors that could affect the fate and behavior of produced water discharges and 

to determine whether natural tracers could be used to differentiate produced water discharge 

plumes from ambient oceanographic conditions. 

Pre-cruise modeling using relevant historic oceanographic data, EPA developed VISUAL 

PLUMES model, and discharge information for each of the platforms was used to estimate 

plume trajectory and rise in the water column, dilution factors, and amount of Rhodamine dye 

needed for conducting the field studies. Field sampling used a towed instrument array (TOWYO) 

with a CTD (conductivity, temperature, dissolved oxygen, pH, and depth), transmissometer, 

chlorophyll fluorometer, two Rhodamine fluorometers, and a CDOM (colored dissolved organic 

matter) sensor to detect and map discharge plumes. Natural tracers failed to show evidence of 

discharge plumes even at the closest approach to the platforms, which was within approximately 

25-50 m of the platform. Thus, within the zone of initial dilution (within 100 m) there was no 

measurable impact to temperature, salinity, density, and transmissivity of the receiving waters. 

This is because the salinity, temperature (excluding Platform Harvest), and turbidity of the 

produced water discharges was not drastically different from seawater, particularly after dilutions 

of more than 200: 1. Platform Harvest, which has a very warm discharge (83°C), did not show 

any deviation from the ambient temperature/salinity properties. Also, there were no indications 

of elevated particulate concentrations associated with the discharge plumes. 

Post-cruise modeling using the VISUAL PLUMES model and the acquired field data (current 

speed, direction, temperature, salinity, DO, fluorometry, and transmissivity by depth strata) was 

used to calculate probable plume location, size, and initial dilution values which was then 

compared with observations of plume performance during the field sampling. Thus, post-cruise 

modeling was used to evaluate the quality of the model predictions utilizing the ambient field 

conditions encountered during the field survey. However, in order to detect platform discharges 

it was necessary to use Rhodamine dye which was injected into the produced water discharge 

pipes using a digitally controlled metering pump. Initial dilutions were calculated using the 

dilution of the injected Rhodamine dye. The minimum initial dilution of discharge plumes 

ranged from 216:1to3536:1. However, the dilutions at the outer edges of the plumes were quite 

high (>27000:1) and more dilution is expected with greater distance from the platform. For 

Platforms Hogan and Harvest, which have the highest discharge volume, there was good 

agreement between the measured initial dilution and the modeled initial dilution. At Platforms 

Habitat and Gina, which have low discharge volumes (on the order or 45-50 gallons/hour) and 

possible intermittent discharges the measured dilutions were 4 and 20 times the modeled 

dilutions respectively. Thus, model predictions for initial dilution ranged from fairly accurate for 

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platforms with the largest discharge volumes to very conservative estimates for the two 

platforms with low volume discharges. 

The discharge plumes, as defined by the Rhodamine dye, were dispersed largely in the horizontal 

direction being driven by the ambient current field with small vertical rise. Water column 

thermal and density stratification, typical for summer conditions, limited the vertical rise of the 

dye plume. Greater mixing and vertical rise would likely occur during non stratified conditions 

which typically characterize winter conditions. Dye concentrations were greatest (i.e., least 

dilution) in the central portion of the discharge plume and elevated concentrations (i.e., plume 

core) extended 500-700 m from the two high volume discharge platforms and 300-400 m from 

the two low volume discharge platforms. Lowest dye concentrations were detectable at distances 

ranging from 0.4 to 1.5 km from the production platforms. The depths of the plumes were more 

variable than the models would predict. Much of this variability results from the natural 

variability of the pycnocline and thermocline in the coastal ocean. This variability is affected by 

internal wave processes and large scale advection of water properties. 

Produced water discharges have the potential to affect marine life and primary productivity by 

light inhibition or effects from produced water contaminants. However, the effects that produced 

water turbidity would have on light attenuation based on the in situ nephelometric measurements 

suggest that the impact on water column light attenuation was negligible. The chanye in beam 

attenuation by the produced water was estimated to have been from .001 to .025 m- . The natural 

variation observed from our observations show that the phytoplankton-driven variability of the 

beam attenuation ranged from 0.8 to 1.2 m1

, much larger than the estimated change caused by 

produced water turbidity. In addition, since the discharge plumes are all beneath the 

phytoplankton maxima, changes in light attenuation due to the produced water plumes would not 

be expected to have a large effect on phytoplankton. 

Project Organization 

Contractors Officer Technical Representative: Mark Eckenrode, MMS 

Lead Principal Investigator: Douglas Diener, MEC Analytical, Inc., 

Subcontract Investigator: 

Technical Support: 

Burton Jones, Applied Ocean Science, Inc. 

Grover Jean, MEC Analytical, Inc., Field Coordination 

Matthew Ragan, Applied Ocean Science, Inc., Field Coordination 

Zhihong Zheng, Applied Ocean Science, Inc., Laboratory analysis 

Kyungho Kang, Applied Ocean Science, Inc., Programming 

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1. Introduction 

Since 1958, offshore oil and gas production platforms have been part of the Southern California 

ecosystem. At the present time there are 23 offshore platforms in Federal waters managed by the 

Minerals Management Service (MMS). These production platforms in conjunction with the 

recovery of petroleum products also recover water from the geological formations (i.e., produced 

water), which is either re-injected into the well or discharged from the platforms into the 

receiving waters. Produced waters may have elevated temperature, have lower salinity and 

dissolved oxygen than seawater, and may have elevated particulate concentrations (Table 1 ). 

Because the potential exists that these produced water discharges could adversely affect marine 

organisms, the discharge of produced waters into the ocean must be treated and/or the discharge 

structure must be engineered to meet EP A/NPDES compliance regulations and limits. These 

compliance requirements were implemented to reduce or eliminate impacts of discharging 

produced waters upon organisms and habitats. Consequently, EPNNPDES permit limits provide 

for a Zone of Initial Dilution (ZID) that allows for the produced water discharge to mix and be 

diluted by ambient seawater. The ZID is generally defined for these platforms as the area within 

100 m of the discharge point and there should be no significant elevation of produced water 

contaminants beyond the ZID. It was unknown whether these produced water plumes were 

detectable beyond the ZID and if so, how far these discharge plumes traveled before reaching 

equilibrium with ambient water conditions. This study was designed to measure and document 

the spatial extent of produced water plumes from four representative offshore production 

platforms. 

2. Objectives 

The study had two primary objectives: first, sample and determine the spatial extent of produced 

water plumes from the discharge point to beyond detection, and second, calculate the initial 

dilution and compare with model estimates using the EPA-developed model VISUAL PLUMES, 

created by Walter Frick (Frick et al., 2001). Ancillary objectives were to measure plume rise or 

sinking after discharge, to determine whether natural tracers (i.e. the natural components within 

the produced water) would provide detectable evidence of the produced water discharge plumes 

distinguishable from ambient oceanographic conditions, and to determine how well the EPA 

model predict initial dilution and dispersion. 

0 3. Approach 

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Four representative oil and gas production platforms were selected by the MMS for study. The 

platforms that were selected include Hogan, Harvest, Habitat, and Gina (Figure 1). Prior to the 

field survey the literature and NPDES permits pertaining to these platforms were reviewed. 

Additionally, each platform was visited and a produced water sample was obtained to 

characterize the physical properties of the produced water (i.e., temperature, salinity, DO, 

turbidity, pH). During the site visit access to the platforms and produced water discharge ports 

were determined. A summary of the produced water characteristics and discharge features for 

each of the platforms is listed in Table I . 

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34.8 ------

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-120.5 -120 -119.5 -119 -118.5 -118 

Longitude (

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Sta. Barbara 

-121 -120.5 -120 -119.5 

Figure 1. Map of the study area showing platform locations (red squares) in the Santa 

Barbara Channel. The solid blue circles indicate the positions of oceanographic data 

collecting moorings (MMS-sponsored Santa Barbara Channel - Santa Maria Basin 

Circulation Study) used for pre-cruise modeling assessments. 

Two different approaches were used to address the objectives. Hydrographic surveys were 

utilized to measure the fundamental characteristics (temperature, salinity, and turbidity) of the 

water column and the concentration of a fluorescent dye tracer that was injected into the 

produced water discharge. Plume modeling was performed both prior to and after the field study. 

The modeling prior to the field study was used to provide a basis for estimating the amount of 

dye (i.e., dilution range) that would need to be injected and to estimate the approximate location 

and spatial extent of plumes. The post-cruise modeling conducted after the field sampling was 

used to evaluate the quality of model predictions under the given ambient conditions in 

comparison with the observations of plume performance measured during the field sampling. 

Field sampling was conducted from the RV Sea Watch, a 65 ft research vessel equipped to 

handle the towed instrument sensor array. The towed instrument package system (TOWYO) 

carried a CTD (Seabird Model 91 lplus), transmissometer (Wetlabs Inc. C-star), 1 chlorophyll 

fluorometer (Wetlabs Inc. WETStar), 2 Rhodamine fluorometers (Seapoint Inc.), and a CDOM 

fluorometer (Wetlabs Inc. WETStar) was used to detect and map the discharge plumes. The 

transmissometer measurement is also commonly referred to as turbidity. The values that are 

shown are in the units of beam attenuation, the fractional loss of light per meter from the light 

source. Beam attenuation is also referred to as beam c, or C660 - the attenuation of light at 

instrument wavelength of 660 nm. The TO WYO instrument array was towed 5m to 90m behind 

the RV Sea Watch and the depth of the TOWYO array was controlled by varying the boat speed 

and cable scope. Data was acquired in real time via a conducting cable from the TOWYO 

instrument array and computers on board the research vessel. Differential GPS was used for ship 

navigation and Capn Voyager Mosaic software (Nautical Technologies) was used to provide ship 

guidance for transect locations and post plotting of actual ship track and distances from 

platforms. 

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Table 1. Produced water discharge locations, outfall type, flowrate, and water quality 

characteristics of produced waters. 

Platform Gina Habitat Hoean Harvest 

Platform Water Depth ft/m 30m 88m 47m 206m 

Temperature F/C 27C ambient Ambient 83C 

Salinity ppt 32.2 27.8 21.4 25.2 

Conductivity mS/cm 44.7 35.1 40.9 

DO <1.0 1.1@ 16.6 c Low 

Average Turbidity NTU 32.l 49.3 3.19 

pH 6.6@ 30 c 7.4@ 16.6 c 7.03 @83C 

Depth of Discharge 26m 42.7m 24m 91m or 61 m 

Flow Volume in barrels 511,000 1,253,000 7,787,000 averaged for one year 

Flow rate daily average 1,400 2200-5500 21 ,334 

based upon annual 1,760 Barrels/day Barrels/day or barrels/day or 3,433 Barrels/day or 

discharge or 3,080 gal/hour 2,450 gal/hour Barrels/day or 6,007 37 ,334 gal/hour gal/hour 

Pressure at access point 3 psi 4-6 psi 80-120 psi 30-40 psi 

Discharge direction Down Down Horizontal Down 

Size of Discharge pipe 12.25 inches 15" open end 16" rectangular 24" opening round pipe round pipe 

Discharge Location rel to Northwest corner 

West northwest South side Southwest Comer of the north well platform orientation bay 

Rhodamine WT dye was used as a tracer of the effluent field. The advantages of using 

Rhodamine WT are: 

1) it has a relatively low light-induced decay rate and therefore can be considered a conservative 

tracer at short time scales 

2) it does not readily adsorb onto particles, and 

3) it is detectable at concentrations of order 0.01 μg ·r

1 using sensitive fluorometric techniques 

(Smart and Laidlaw, 1977). 

Rhodamine WT was injected into the produced water discharge at Platforms Hogan, Harvest, 

Habitat, and Gina using a digitally controlled Balador metering pump. The pump rate was 

adjusted with the intention of achieving a concentration in seawater after initial dilution of 

approximately 10 μg r 1

. Controlotron acoustic flow sensors were attached to the discharge pipe 

to determine produced water flow rates. This information was then used to adjust the rate of dye 

injection so as to maintain constant dye concentrations in the effluent. While the manufacturers 

stated detection limit for the in situ fluorometer is lower than 0.01 μg-r

1

, the field team choose 

this conservatively minimum detection limit of about 0.01 μg r

1

. At an initial concentration of 

10 μg · r 1

, the in situ fluorometer can detect an additional L 000: 1 of ambient dilution. Before and 

during the injection of the Rhodamine dye, hydrographic surveys using the TO WYO instrument 

package were used to detect and map the discharge plume. 

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An Acoustic Doppler Current Profiling (ADCP) current meter (RD Instruments, 300 KHz) was 

mounted on the survey vessel and used to measure the current speed and direction from near 

surface to about 100 m water depth. The ADCP data was acquired and displayed in real time 

during the field survey. The current vector information provided the likely trajectory of the 

discharge plumes. 

3.2 Plume Modeling 

Modeling of the produced water discharge plumes was performed using the EPA-developed 

model VISUAL PLUMES, created by Walter Frick (Frick et al., 2001). Because the produced 

water discharge structures are simple diffusers or an open pipe the UM3 (Updated Merge; 

Winiarski and Frick, 1976; Frick, 1984) component of the VISUAL PLUMES program was used 

to model the discharge plume as single port discharges. 

The EPA plume model was used in two ways. Prior to the field study (i.e., pre-cruise modeling) 

VISUAL PLUMES was run using a data set from the Santa Barbara Channel moorings from 

August 1994 or August 1999. The August time series was used because it was felt the August 

currents, temperature, and salinity data would be most similar to the conditions that we expected 

to encounter in late July 2003. The year 1999 was also chosen because it was a non-El Nino year, 

unlike the previous year when a significant El Nino occurred in the Pacific Ocean that had 

measurable effects on the physical oceanography of the southern California Bight. The historic 

current data used for the plume modeling came from the MMS-sponsored Santa Barbara Channel 

- Santa Maria Basin study. The data sets used for modeling selected the moorings nearest the 

target platform. Thus, mooring AROF was used for Platform Harvest (1999 data), and mooring 

CAIN was used for Platforms Habitat and Hogan (1994 data) (Figure 1). The pre-cruise 

modeling was run for the entire month (simulated 270 hours) of August so that the range of 

effective dilutions could be evaluated for a typical summer month. 

The model was also run after the field study. For the post-cruise modeling the data used were the 

currents measured with the boat mounted ADCP and the temperature-salinity structure obtained 

with the TOWYO instrument array during the day of the study. This modeling effort was run 

only for the few hours that sampling occurred near each platform. 

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4. Results 

In this section the results from both the plume modeling and the field plume observations are 

presented. The results are presented in the chronological order that the studies were carried out -

Hogan, Harvest, Habitat, and finally Gina. Table 2 provides a summary of field sampling 

activities. 

Table 2. Summary of field sampling activities. 

Ooeration 

On Site 

ADCP Mapping 

Dye Release Initiated 

Dye detected in situ 

Dye injection terminated 

Sampling Terminated 

4.1 Platform Hogan 

4.1.1 Pre-Cruise Modeling 

Hogan 

Date 7/24/03 

8:30 

8:43 

11 :27 

13:13 

16:09 

17:20 

Time (PDT) 

Harvest Habitat 

7/25/03 7/26/03 

9:25 9:20 

10:10 9:20 

13:00 11 :51 

14:20 13:38 

17:30 17:30 

17:40 17:15 

Gina 

7/27/03 

8:00 

8:12 

9:37 

10:12 

15:10 

16:16 

The pre-cruise modeling for Platform Hogan used data collected from the CAIN oceanographic 

mooring acquired during August 1994 (Figure 1 ). The current speed and direction used for the 

modeling was based upon the current field at 24 m, the depth of the produced water discharge at 

this platform (Table 1). The results for the pre-cruise plume modeling are shown in Figure 2. The 

graphics provide a visual picture of the data but the actual values for dilutions were derived from 

analyses of all the data. Results from the pre-cruise modeling found that the expected dilution of 

the discharge ranged from 209:1 to 808:1 with a median dilution of 396:1 and mean of 410:1. As 

expected, estimates of dilution increase with greater distance from the discharge point (i.e., more 

time for mixing with ambient water) (Figure 2A). The effective dilution (Figure 2B) was based 

upon multiple model runs using the ambient oceanographic conditions for the month of August 

1994 (i.e., representing 720 hours in that period). The historic current speed and direction at 24 

m from August 1994 was the best data available to provide a working estimate of the range of 

oceanographic conditions most likely to be encountered for this study. Modeling showed that 

plume dilution was variable and dependent upon current speed, consistency of current direction, 

and water column stratification (i.e., strength and location of the pycnocline and thermocline). 

The mean plume direction was toward the northwest reflecting a rather consistent current 

direction at 24 m for the month of August 1994 (Figure 2C). The predicted equilibrium depth of 

the plume (i.e., the depth where the buoyancy or density of the plume water is about equal to 

ambient water) was about 22 meters, rising only about 3 meters after discharge (Figure 2D). 

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-100 -80 -60 -40 -20 0 20 40 60 80 100 0 20 40 60 80 100 

West - East (m) Hoizontal distance from source (m) 

Figure 2. Pre-cruise plume modeling results for Platform Hogan, using the moored data set from mooring CAIN for August 

1994. The top left panel (A) shows the initial dilution of both the centerline and the average plume dilution, top right panel (B) 

shows the time series of average dilution for the plume model run, lower left panel (C) shows the horizontal plume path, and 

lower right panel (D) shows the plume elevation after discharge. Output is from Visual Plumes using model UM3. 

8 
0 

0 

D 

0 

0 

0 

0 

0 

D 

D 

D 

0 

D 

D 

D 

D 

0 

4.1.2 Field Sampling and Data Collection 

4.1.2.1 Ambient Current Velocity Field 

The ambient velocity field (i.e., current direction and speed) at 23 m water depth near Platform 

Hogan on July 24, 2003 was predominantly to the north (Figure 3). From the morning period 

through about 1430 PDT the current velocity ranged in magnitude from 10 to 35 cm·s-1 (0.2 to 

0.7 knots). After 1430, the currents reduced to less than 10 cm·s1 for the remainder of the 

sampling period. 

4.1.2.2 Dye and Hydrographic Distributions 

Prior to the injection of Rhodamine WT dye, the region around the platform was sampled with 

the TOWYO array to determine whether any natural water quality measurements (temperature, 

salinity, density, chlorophyll fluorescence, and suspended particulate material) had been affected 

by the discharge of produced water. No significant difference from ambient conditions was 

detected in the area where the discharge plume was expected to be found. This indicates that the 

discharge of produced water from Platform Hogan was not affecting these water quality 

variables. 

After 2 Y2 hours of towing the TOWYO instruments along transect lines through the expected 

produced water plume area without detecting a produced water plume the Rhodamine dye 

injection was started. Approximately 1 Y2 hours after dye injection into the produced water 

discharge system commenced a clearly defined dye plume was found north of Platform Hogan 

(Figure 4). This plume location was consistent with the northerly current direction measured 

using the ship-mounted ADCP. The dye field was detectable out to about 1.2 km north of the 

platform where it had a width of about 0.5 km. Very high dye concentrations were found within 

0.2 km (200 meters) of the platform. The maximum concentration measured in situ was 66.2 

μg·r

1 corresponding to a minimum observed dilution of 216:1 (based on an average 

concentration of Rhodamine WT in the produced water discharge of 14261μg-r 1

). Within 100 

meters the dilutions increased to more than 500: 1 and beyond 200 meters the dilution was greater 

than 1000:1(Figure4, bottom panel). The dilution had increased to more than 1500:1within700 

meters north of the platform. 

Within the water column, the dye remained at the depth of the discharge (24 m) with a maximum 

vertical extent of about 10 meters centered on the discharge depth (Figure 5). The top of the dye 

field was at about 20 meters depth and remained below the bottom of the seasonal pycnocline 

(thermocline), which was at about 15 meters (Figure 6). Seawater density and the pycnocline are 

largely determined by the salinity and temperature structure of the water column. For California 

coastal waters away from freshwater inflows the pycnocline and thermocline well be found at 

about the same depth (see Figure 6). The dye plume remained below the chlorophyll maximum 

stratum associated with the pycnocline which ranged between about 7 and 17 meters. Therefore 

the produced water discharge plume would probably not have any effect on the overlying 

primary productivity. 

There were no obvious effects of the produced water plume on any of the measured variables. 

The other variable that was measured, suspended particulate material (not shown), showed no 

effect from the produced water discharge plume. The only evidence of the produced water 

discharge was from the Rhodamine WT that was injected into the discharge. 

9 
c=:J c:::J c:::J CJ c:::J CJ CJ CJ CJ c:::J c::::J c:J c:::J c:::J c:J c:::J c:::J c:::J 

Current Time Series at 23 Meters - Platform Hogan 

0.4 .-----.----.-------.-------.-------.-------.--------, 

0.2 . . . . '. . ......... .. ·:· ........... '......... . . ~. . . . . . . . . . . . ....... . 

.--.. 

~ 

E .._.. 

""C 0 '-L....>.--"--'--"--'--'--"--'-"-'-''-'--'--'--'--'-.>....."-'-L..l->.....:..._.__.__.__,__,__.1-,_,->.->.-->. ............. ..._,_....._,.._,_,....,,._,__,__.__,__-'-"....,.· ........ . ... . 

Q) 

Q) 

a. 

en 

-0.2 ...... .... ··· ··········· ········· ·:·· .......... ···········! ······· ··············· ··: ·· ·· ···· 

-0.4~-~--~--~--~--~--~--~ 

07:01 08:41 10:21 12:01 13:41 15:21 17:01 18:41 

Time (PDT) - July 24, 2003 

Figure 3. Time series of currents for Platform Hogan at 23 m. Each current vector represents a 10 minute average at the 

indicated depths and progresses forward in time from the beginning time in the x-axis label. 

10 
0 

0 

0 

0 

D 

D 

0 

D 

D 

D 

0 

D 

0 

D 

D 

D 

0 

Horizontal Distribution of Rhodamine Dye (μg.r 1

) for HOGAN 

34.35 30 

34.348 

34.346 

34.344 

34.342 

34.34 

34.338 

34.336 

34.334 

-119.552 

34.35 

34.348 

34.346 

34.344 

z 

0 

-

~ 34.342 ::::I 

:I:: 

iii 

_J 34.34 

34.338 

34.336 

25 

20 

15 

10 

5 

0 

-119.548 -119.544 -119.54 -119.536 

Longititude (°E) 

Horizontal Distribution of Dilution for HOGAN 

1500 

1000 

-119.548 -119.544 -119.54 -119.536 

Longititude (°E) 

Figure 4. Horizontal planar view of the distribution of the maximum concentration of 

Rhodamine WT (μg·r, top) and minimum dilution (bottom) for Platform Hogan on July 

24, 2003. The contour lines indicate the distance in kilometers from the platform that is 

indicated by the black square at the center of the concentric circles. 

11 
0 

0 

0 

D 

D 

D 

0 

D 

D 

0 

0 

0 

D 

D 

D 

D 

D 

Vertical Cross-Section of Rhodamine Dye (μg.r 1

) for HOGAN 

0 30 

-5 

25 

-10 

-15 20 

E' -20 ...... 

..c 

'iS. 

Q) -25 Cl 

15 

-30 

-35 

-40 

-45 

-0.4 -0.2 0 0.2 0.4 0.6 0.8 1.2 

Distance from platform along rhodamine plume (km) 

Vertical Cross-Section of Dilution for HOGAN 

0 

-5 

-10 

-15 

E'-20 

........ 

..c 

'iS. 

~ -25 

1000 

-30 

-35 500 

-40 

-45 

-0.2 0 0.2 0.4 0.6 0.8 1.2 1.4 

Distance from platform (km) 

Figure 5. Vertical planar cross-section of the maximum concentration of Rhodamine WT 

(μg·r 1

, top) and minimum dilution (bottom) along the axis of the plume shown in Figure 4. 

Concentrations are indicated on the colorbar. The black square located at 0 km, 24 meters 

depth indicates the location of the platform discharge. The x-axis indicates distance from 

the platform. The orientation of this section is from south (left) to north (right). 

12 
0 

0 

0 

0 

0 

0 

D 

D 

D 

D 

D 

0 

D 

D 

D 

D 

Platform Hogan - Vertical Profiles 

o .---~-----I o - , o , a.--_-.. ==R ....... _h-od-,1..,.->--. _J 

; Rhod(2) 

I -s -s -

-10 -10 -10 -

-15 -15 -1 

-20 -20 -20 -< -2 

-

E 

-..c. 

a. -25 1 -25 

Q) 

0 

-30 -30 - -30 

-35 - -35 

-40 - -40 -40 -4 

= -45 - -45 T -45 

-so --- ---~ 

10 15 20 

-so -soL _ __.__ -so - - --...J.. 

33.2 33.3 33.4 33.5 33.6 23 24 25 26 0 20 40 60 

Temp. (°C) Sal. (psu) Density (kg·m-3) Rhed. Cone. (μg·l"1

) 

Figure 6. Vertical water column profiles of physical (temperature, salinity, and density), 

biological (chlorophyll fluorescence), and dye tracer concentration for Platform Hogan. 

4.1.3 Post-Cruise Modeling 

The plume was modeled using the data acquired on 24 July sampling in the vicinity of this 

platform using the temperature-salinity-density structure recorded with the TOWYO array 

(Figure 6) and the observed current speed and direction measured with the ADCP at the depth of 

the discharge (Figure 3). The results for this model indicate that the center of the plume was 

between 18 and 20 meters (Figure 7), slightly shallower than the actual depth where the core of 

the plume was observed. The modeled dilution ranged from a minimum of 130 to a maximum of 

1324. However, the median dilution was 250 and the mean 305: 1. The median dilution was 

within 16% of the measured minimum dilution. Thus the model predicts the dilution reasonably 

well, but predicts some elevation of the plume which was not observed with the Rhodaminetracked plume. 

13 
C=:J c::J c::J (=:J c::J c::J c::J c::J c::J c::J c=J c::J CJ c::J c::J c::J CJ 

5001

_ Plu~~ Dilution - Pla~orm Hogan Nearfield and Mixing Zone Dilutions 

A ,.,,.---- j 14001 B· - • i 

400 

c: 300 

0 

·~ 

-= 15 200 

,//~ I • / ./ 1200 , 

/ ' ,/~ average c:

0 , , I 

/ /// ._1000 . -- ...... . I ;/'/ ,'. / ~ 

,,d// /p/ ~! -- ·· 5 soo · ·· --- - • I 

_,_w11- // / . .., QI $.'f ,< / I .:? • • ii j!fl'/t· . --:-- I ~ 6001 .. • • • ·• .. -- . --- • • _. .. 

~/;--/ ..... I LIJ 400 • ,. • • <· . · ·-· ••..• • • ~ --··I 

1001 1/1 / • • • 1r i'/ _1 • • • • • JI/ .... -- .-. ., . 200 •• -- I ~~~· :.:· .; ;,- : ' -· - . ' 

0 ... ::• - 0 r------------------.,---1 

0 10 20 30 40 50 0 50 100 150 200 250 300 350 

Hoizontal distance from source (m) 

Plume Trajectory 

!~1---c -- --: -.. -- --1 

I ' ' I 

o D 

30 

]: 20 

.s:. 

.... 10 ::I 

0 

V'l 0 I 

.s:. -10 

t: 

~ -20 

-30 

-40 

-50 

-50 

·· 1 -: /

1

( . enterline -

,

,:,t:.- · : I 

· -«::, :- bou nda - E 10 ..... . .............. QI ..... _. I i 

I QI 

I o 

I 

I 

-40 -30 -20 -10 0 10 20 30 40 50 

West - East (m) 

0 

Elapsed lime (minutes) 

Plume Elevation 

centerline 

!? !! rr. ........ 

10 20 30 40 50 

Hoizontal distance from source (m) 

Figure 7. Post-cruise plume modeling results for Platform Hogan use data collected during field operations on 24 July 2003. 

The top left panel (A) shows the initial dilution of both the centerline (dotted) and the average plume dilution (solid), the top 

right panel (B) shows the time series of average dilution for the plume model run, the lower left panel (C) shows the horizontal 

plume path, and the lower right panel (D) shows the plume elevation after discharge. Output is from Visual Plumes using 

model UM3. 

14 
0 

0 

D 

D 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

D 

4.2 Platform Harvest 

4.2.1 Pre-Cruise Modeling 

The pre-cruise modeling for Platform Harvest used current vector data from mooring AROF 

(location shown in Figure 1) acquired for the month of August 1999. The data used included 31 

days of hourly data for August 1999. The results from the plume modeling are shown in Figure 

8. The minimum dilution for modeling effort ranged from 238:1to3741 :1 with a median 

minimum dilution of 1485:1 and a mean of 1407:1(Figure8A and 88). The plume model 

showed the plume rising from its discharge depth at 61 m to an equilibrium depth at about 50 

meters (Figure 8D). The mean currents for the month of August 1999 were toward the southeast 

indicating a flow coming from north of Pt. Arguello (Figures 8C and Figure 9). 

4.2.2 Field Sampling and Data Collection 

4.2.2.1 Ambient Current Velocity Field 

The current vectors at 59 meter near Platform Harvest on July 25, 2003 were predominantly 

northward (Figure 9). The velocities were typically from 5 to 10 cm·s-1 with occasional higher 

velocities of more than 10 cm·s1

. During the first five hours (bins 1-30) the current direction 

was toward the NNW. Similar to the observations at Platform Hogan, the current speeds dropped 

significantly in the afternoon to less than 5 cm·s1 for the last two hours of observations (bins 31-

45) and rotated in direction more toward the NNE. Note that in the afternoon during the tracking 

of the dye plume the current direction was predominately to the NNE. The overall northward 

orientation of the currents during the period of sampling are in contrast to the pre-cruise 

modeling results that was based on Mooring AROF from August 1999 when the current were 

predominantly toward the southeast. A speed of 5 c·ms·1 corresponds to 180 meters per hour. 

4.2.2.2 Dye and Hydrographic Distributions 

Prior to the injection of Rhodamine WT dye, the region around the platform was sampled with 

the TOWYO array to determine whether any natural water quality measurements (temperature, 

salinity, density, chlorophyll fluorescence, and suspended particulate material) had been affected 

by the discharge of produced water. No significant difference from ambient conditions was 

detected in the area where the discharge plume was expected to be found. This indicates that the 

discharge of produced water from Platform Hogan was not affecting these water quality 

variables. 

15 
[=:J CJ c=:i [=:J [=:J CJ CJ [=:J CJ c:J CJ c::J CJ [=:J c:J c:J c:J CJ 

i::: 

0 

·.i:; 

:J 

cs 

1500 

___ A 

1000 

500 __ 

0 , -

0 

100 

sol C . 

60 

:§: 40 

£ 20 ::i 

a o I 'E -20 

~ -40 

-60 

-80 

Plume Dilution - Platform Harvest Nearfield and Mixing Zone Dilutions 

-- .0 

'.- ..... ... 

20 40 60 

I 

I 

__ ___ _ jB 

I ! 2000 , .• ..... .... -; ; ... . · : ; :;'. ::_ '. I 

average· ------1 i::: 

LQ ,.., 1- c···• ; ::J 

centerline 1= , .......... -.......... -. ~ 

> --- · "f.1000 

~ 

-li!i 

• • • • I I • . I 

\ ! . -r:,·_ -- -- -- -- • • >.::,. ~,,,· -\ __ .• ; . .. . ... . ' I ::i ... I .... • .... ~ • , : ~ • . . .... ' -· ~ • •• , 

I I I • Ill I I I ' 11 

·_,= ._:: .. -' ~ ~ ~ : . . .· __ ') ~ .- F !I ·. _. -~ :. ~ ·. _ ='. __ : . :-:- : ~ ~ =. · :j ;. ;~ . .. ::, ~ •; 1 •.,, r :.;!. --~; ;~~ 111 ~ •:. 

1 

1 

~ , •• i •I • •• • .• . .:.- :'· ..... · .: • • • • • • • • I I I 

- · ,.. .. ~- -- ') ••• -- 411: • ... • ~ • ,, : • 

j\;. 

;"'..:k'""a If." & • • ' • :• ·• • • 

0 1 ~~:11t.; ;&· '):..;: ~ - • •·1i:.:urf"t": '!11 

80 100 0 100 200 300 400 500 600 700 

Hoizontal distance from source (m) Elapsed Time (hours) 

Plume Trajectory 

centerline 

·boundary-- ···············n········· 

.. 

l 

_ __J 

0 Plume Elevation 

I ..... 

.; 

-5 50 

ar 

c 

_o 

_ c.enterl.i.ne 

~'~: ~ "':~--~~+.: ·;·.' ~~ r:!~ i ....... . 

-100 100.1.--___ _.;.. __________ _ 

-100 -80 -60 -40 -20 0 20 40 60 80 100 0 20 40 60 80 100 

West- East (m) Hoizontal distance from source (m) 

Figure 8. Pre-cruise plume modeling results for Platform Harvest, using the moored data set from mooring AROF for August 

1999. The top left panel (A) shows the initial dilution of both the centerline (dotted lines) and the average plume dilution (solid 

lines), upper right panel (B) shows the time series of average dilution for the plume model run, lower left panel (C) shows the 

horizontal plume path, and lower right panel (D) shows the plume elevation after discharge. Output is from Visual Plumes 

using plume model UM3. 

16 
CJ C=:J c::::J CJ C=:J CJ c::::J CJ CJ CJ C::J CJ CJ CJ CJ CJ CJ 

Current Time Series at 59 Meters - Platform Harvest 

0.4 r----r---r---r---,----,-----r----~ 

0.2 . ' • • : • • • . • . • • . . • • • . • - - .• - . • '~ • . • • • • • . • . • • • •••... ·••. • . •• . •• • • ••• •. ' •• ' • t . . . ...•........... 

-

~ 

E 

-

"'C 0 - ~ "-'0-~ I l I\ \ I /I 1 ff 42?1 /I 1 1 I fb.. J f$;;:---- ... ........ .. ............... . 

a.> 

a.> 

a. 

Cf) 

-0.2 ..... ···· ··· ······:· ... ............ --··· .............. ····!······ ····· .......... . :·····"'''" ··· ·· ····· ·-;-·-··· .. .... ... ....................... ····· .. . 

-0.4~-~--~--~--~--~--~--~ 

08:22 10:02 11 :42 13:22 15:02 16:42 

Time (PDT) - July 25, 2003 

18:22 20:02 

Figure 9. Time series of currents for Platform Harvest at 59 m. Each current vector represents a 10 minute average at the 

indicated depths and progresses forward in time from the beginning time in the x-axis label. 

17 
0 

0 

0 

0 

0 

0 

0 

0 

0 

D 

0 

0 

0 

0 

0 

D 

After about three hours of towing the TO WYO instruments along transect lines through the 

expected produced water plume area without detecting a produced water plume the Rhodamine 

dye injection was started. Approximately 1 Y2 hours after dye injection into the produced water 

discharge system commenced a clearly defined dye plume was found north and northeast of 

Platform Harvest (Figure 10). This plume location was consistent with the northerly current 

direction during the time period when the dye plume was tracked. The maximum distance that 

the dye field was detected was 1.1 km from the platform, but as shown in Figures 10 and 11, the 

core of the plume was within 600 meters of the platform. The vertical distribution of the dye 

was complex with two maxima present between 200 and 400 meters away from the platform 

(Figure 11). One of the maxima was centered at about 47 meters and the other at 56 meters. Dye 

was detected from as deep as 63 meters to a minimum depth of 44 meters, spanning nearly 20 

meters of the water column (Figure 11 ). The core of the plume was found below the main 

pycnocline that was centered between 32 and 43 meters in the region where the temperature was 

10-l2°C (Figures 12). The two depth maxima between 200 and 400 meters from the platform 

may result from fluctuations in the pycnocline depth during the study. The two maxima were 

about 10 meters apart and the depth of the pycnocline varied by a similar amount suggesting that 

elevation of the pycnocline during the study was a likely cause of the two maxima of the dyelabeled discharge plume. 

The maximum concentration of dye measured in situ with the fluorometer was 33.6 μg·r 1 and the 

average concentration in the discharge was 11196 μg·r

1

. Thus, the minimum initial dilution that 

was measured was 333:1. Dilutions less than 500:1 were observed out to about 400 meters from 

the platform (Figures 10 and 11). 

As discussed above, the dye field was centered at about 50 meters and ranged in depth from 44 

to 63 meters. The bottom of the pycnocline was as deep as 43 meters and therefore the discharge 

plume remained below the pycnocline. No anomalies in any of the measured variables 

corresponded with the discharge plume, apart from interference with the optical sensors due to 

optical properties of the dye and not characteristics of the discharge plume. In this region of the 

Santa Barbara Channel the chlorophyll maximum was in the upper part of the water column 

above 30 meters (Figure 12) and there was no direct interaction between the discharge plume and 

the chlorophyll maximum layer. 

18 
0 

D 

0 

D 

D 

D 

D 

0 

0 

0 

I 

0 

0 

0 

0 

D 

D 

0 

Horizontal Distribution of Rhodamine Dye (μg.r 1

) for HARVEST 

34.478 

34.476 

34.474 

34.472 

z 

0 

........ 

-8 34.47 ::J 

= (ij 

...I 34.468 

34.466 

34.464 

34.162 - 20.688 -120.684 -120.68 

Longititude (°E) 

-120.676 -120.672 

-.. 

z 

0 

........ 

34.478 

34.476 

34.474 

34.472 

-8 34.47 ::J 

= (ij 

...I 34.468 

34.466 

34.464 

Horizontal Distribution of Dilution for HARVEST 

-120.684 -120.68 -120.676 -120.672 

Longititude (°E) 

30 

25 

20 

15 

10 

1000 

800 

600 

400 

Figure 10. Horizontal planar view of the distribution of the maximum concentration of 

Rhodamine WT (μg·r 1

; top) and minimum dilution (bottom) for Platform Harvest on July 

25, 2003. The contour lines indicate the distance in kilometers from the platform that is 

indicated by the black square at the center of the concentric circles. 

19 
0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

Vertical Cross-Section of Rhodamine Dye (μg.r 1

) for HARVEST 

-20 

-30 

-40 

'E-50 

'-" 

..c: 

i5.. 

~ -60 

-70 

-80 

-90 

-0.1 

-20 

-30 

-40 

'E-50 

'-" 

..c: 

i5.. 

~ -60 

-70 

-80 

-90 

-0.1 

o 0.1 0.2 o.3 o.4 o.5 o.6 

Distance from platform (km) 

Vertical Cross-Section of Dilution for HARVEST 

o 0.1 0.2 0.3 0.4 0.5 0.6 

Distance from platform (km) 

20 

15 

10 

5 

0 

1800 

1600 

1200 

1000 

800 

600 

400 

200 

0 

Figure 11. Vertical planar cross-section of the maximum concentration of Rhodamine WT 

(μg·r 1

; top) and minimum dilution (bottom) along the axis of the plume shown in Figure 10. 

Concentrations are indicated on the colorbar. The black square located at 0 km indicates 

the location of the platform discharge. The x-axis indicates distance from the platform. The 

orientation of this section is from south (left) to north (right). 

20 
0 

0 

0 

D 

0 

D 

0 

0 

D 

0 

0 

0 

0 

0 

0 

0 

0 

0 

Platform Harvest - Vertical Profiles 

0 0 0 0 

~t~:i<.\' -10 -10 -10 , 

.• . .. : 

:• .r.i ·\ ; 

" ~ 

-20 ~ -20 -

-30 -30 I -30 · 

- I E 

= -40 -40 . -40 . a. 

Q) 

Cl 

-50 -50 

-60 -60 

-70 -70 

-50 

1 -60 

I -70 -70 

1 I 

Rhod(1) 

, Rhod(2) 

Fehl 

-80 -80 1 -80 -80 .. __ __._ __ _, 

8 10 12 14 16 18 33.4 33.6 33.8 34 24 25 26 27 0 10 20 30 40 

Temp. (°C) Salinity (psu) Density (kg-m"3) Rhod. Cone. (μg- 1"1) 

Figure 12. Vertical water column profiles of physical (temperature, salinity, and density), 

biological (chlorophyll fluorescence), and dye tracer concentration for Platform Harvest. 

4.2.3 Post-Cruise Modeling 

The measured stratification and current velocities from July 25, were used to model the plume 

behavior for Platform Harvest. The discharge depth (Figure 11) based upon the measured plume 

depth indicate that the discharge was from about 61 meters rather than the 91 meters indicated on 

Table 1. The median dilution estimated from the model was about 347:1. The measured 

minimum dilution was 333: 1. Thus, there was excellent agreement between the modeled and the 

measured dilution with a difference in dilution of less than 5%. 

The plume model indicates an elevation of the plume on the order of 10 meters (Figure 13). The 

center of the measured dye field was at 50 meters, approximately I 0 meters above the discharge 

depth (Figures 11 and 12). The model of plume elevation also suggests some variability in the 

elevation of the plume which we did observe in the actual plume. 

21 
CJ CJ CJ CJ CJ CJ CJ CJ CJ CJ CJ CJ CJ CJ CJ CJ c::J 

lOOO r · Plume Dilution - Platform Harvest 1000 

Nearfield and Mixing Zone Dilutions ·-- rs-- A 

aool / 800 

average c: 

0 

c: 600 / centerl ine ~600 0 B '+;; ........................... ::I ~ 

B 400 . ·e400 .. ~ • • LU 

200 1 I 11 / I 200 ••• • • 

• • • • 

• • • • • • • 

0 - - - 10 20 30 40 50 60 70 BO 90 0 50 100 150 200 250 

Hoizonta I distance from source (m) Elapsed Time (minutes) 

Plume Trajectory Plume Elevation 

I 0 

50 c 10 1 D 

40 

]: 

30 centerline 20 1 centerline: 

..s:::. 20 ' ~30 

10 ~~~~~ r:Y. ........ i 40 1 :/ .... ' ... '!. · ,·' ~~ ~~~.':¥... ...... ::I 

0 0 .. ·· 

I.I\ 

..:: -10 

t 8 5o k .·/'' 

0 -20 

z -30 I 60 .. 

-401 i 70 -50 l 

80 

-50 -40 -30 -20 -10 0 10 20 30 40 50 0 10 20 30 40 50 60 70 80 

West - East (m) Hoizontal distance from source (m) 

Figure 13. Post-cruise plume modeling results for Platform Harvest, using data collected during field operations on 25 July 

2003. The top left panel (A) shows the initial dilution of both the centerline (dotted) and the average plume dilution (solid), the 

top right panel (B) shows the time series of average dilution for the plume model run, the lower left panel (C) shows the 

horizontal plume path, and the lower right panel (D) shows the plume elevation after discharge. Output is from Visual Plumes 

using model UM3. 

22 
0 

0 

0 

0 

0 

D 

0 

D 

0 

0 

0 

0 

0 

0 

0 

0 

4.3 Platform Habitat 

4.3.1 Pre-Cruise Modeling 

Pre-cruise modeling of Platform Habitat used current data from oceanographic mooring CAIN 

acquired for the month of August 1994 (Figure 1). Results from the modeling runs are shown in 

Figure 14. The initial dilution from the modeling effort ranged from 354:1 to 1027: I with a 

median of 567:1 and a mean of 579:1(Figures14A and 14B). During the month long time series 

the mean direction was to the northwest (Figure 14C), and the plume depth was 41-42 meters, 

only about 1 meter above the discharge depth of 42.7 meters (Figure 140). 

4.3.2 Field Sampling and Data Collection 

4.3.2.1 Ambient Current Velocity Field 

The ambient currents at 39 meters depth around Platform Habitat for July 26, 2203 were relative 

steady toward the northwest (Figure 15). Current speed was also consistent and averaged about 

10 cm·s1

. The currents at Platform Habitat were more consistent during the study period than the 

currents at the other 3 platforms. 

4.3.2.2 Dye and Hydrographic Distributions 

When the study began, the produced water discharge rate was less than 1 gal/min. Therefore, the 

discharge was supplemented by injection of seawater from the platform's fire system bringing 

the discharge rate to approximately 45 gal/min, or about 2700 gal/hr which is near the reported 

discharge rate of 2450 gal/hr used for the initial plume modeling. Thus the characteristics of the 

discharge water should have been similar to the characteristics of seawater from near the surface 

and no discharge plum was detected using natural tracers. 

Approximately 1 Y2 hours after dye injection into the produced water discharge system 

commenced a clearly defined dye plume was found northwest of Platform Habitat (Figure 16). 

The horizontal distribution of dye concentration and dilution indicate that the plume dilution was 

quite high with a minimum dilution of about 1370: 1. Dilutions of less than 4000: 1 were 

detectable out to about 400 meters away from the platform and beyond that dilutions were all 

greater than 5000: 1 (Figure 16). Both the plume width and plume thickness were quite small 

compared with plumes from Platforms Hogan and Harvest. The plume width was on the order of 

about 100 meters at 400 meters distance from the platform. The plume could be detected 

between depths of 45 and 68 meters. However, the thickness of the core of the plume was more 

on the order of 5 meters (Figure 17). 

At a depth of 60 meters, the plume was well below the seasonal pycnocline (Figure 18). The 

chlorophyll and particle maximum for the area around this platform was located in the 

pycnocline and centered at about 10 meters. There were no significant features at the depth of the 

discharge plume and it does not appear that the plume interacted with the chlorophyll layer in 

any way. With the high initial dilutions and the use of surface water as the discharge source, 

there were no significant effects of the discharge water on the ambient water properties. 

23 
CJ CJ CJ CJ CJ CJ CJ CJ 

1 OOQ-:---_E!_l:lme Dilution - Platform Habitat 

A 

800 

c: 600· 0 

·.;::; 

::l 

cs 400 

200 

0 

0 

50 

averag

~ ~~~ ~~!! ~ ... '··. 

•,· 

. -:-· ... .. . . 

20 40 60 80 

Hoizontal distance from source (m) 

Plume Trajectory 

4olC 

30 

E 20 

·"':-.."~'. ' . '" ~ .. ,>~ 

"' '"' ·''li\ ' • :centerline 

..s:::. 

... 10 ::l 

.... ' ·- - .... 

.. !?.~~ ~~~ ry, ....... . 0 

VI 0 I 

.s -10 .... 

~ -20 

-30 

-40 

-50 

CJ CJ c=J CJ CJ CJ c=J CJ CJ c:J 

1200 

Nearfield and Mixing Zone Dilutions 

1 

1 B. . ...... ·- -- ·--- 1000 · . , ..... l ... , .... , _; ' . ~ : :·~ ~ C • I I • • ' • 08QQ ··~ . • • •I ·- • ,; ~ • I • .•• ....,.. • ' • I ~ · - .•'\ ~ '$ ., . ~ .. I: 1111 . •• • I . : . .: ' 

== •• ~ "·: ~ ·. -· 1 ·~ :t ....... ;-. ·. ~ ~ : .. , 0 ~ .:. r. I • I ..... f : -••· 11.,. I , .. ~I 

•• 600 -.:.. ' °'"' ~·1.. ·" --· • ... -:~ . .a•'\' --•-1.•r. ••. • · ---·- ~ Iii' ' ' "' II!! ... .... • "'5-·, '4 .-.~ " .. •" '"' -·-. ... . • • • .:::!: ·~ '\ (•! "• ·;.1H1/,. •i ":#!O.' ! • ~·.r: l,1 • I : ' l. I ti •1· .t.,.·~;· ~··T·~· !.·•.,t·~~ • 1Z " • • • I • • :• ... • ' .. : : •• •,:··. ·I It: 4QQ • --.I • ··-< ' '•· . : ·-' ': ,• • " LU • • I 

: 

200 I ~ 

I 

0 

100 0 100 200 300 400 500 600 700 

Elapsed Time (minutes) 

0 Plume Elevation 

,o 

10 

centerline 

:[ 20 

..s:::. ?.~ ~~ ~x: ....... ... 

c.. 

~ 30 

40 ---·-···.. . .... . .. 

SO '--~~ ~~~~~~ -' 

-50 -40 -30 -20 -10 0 10 20 30 40 50 0 20 40 60 80 100 

West - East (m) Hoizontal distance from source (m) 

Figure 14. Pre-cruise plume modeling results for Platform Habitat, using the moored data set from mooring CAIN for August 

1994. The top left panel (A) shows the initial dilution of both the centerline and the average plume dilution, top right panel (B) 

shows the time series of average dilution for the plume model run, lower left panel (C) shows the horizontal plume path, and 

lower right panel (D) show the plume elevation after discharge. Output is from Visual Plumes using model UM3. 

24 
CJ CJ c:::J c:J CJ CJ CJ CJ CJ c:J CJ CJ C::J CJ C::J C::J C::J C::J 

Current Time Series at 39 Meters - Platform Habitat 0.4 1-- ---y--- ---i-- -~~ =----

0.2 

-

~ 

E .._ 

""C 0 

Q) 

Q) 

a. 

en 

-0.2 

-0.4 --- ---~ -~ -- ----'--------' 

07:41 09:21 11 :01 12:41 14:21 16:01 17:41 19:21 

Time (PDT) - July 26, 2003 

Figure 15. Time series of currents for Platform Habitat at 39 m. Current vectors are plotted at 10 minute intervals beginning 

at the times indicated in the x-axis label. Each plot represents nearly 8 hours of observation. 

25 
0 

0 

0 

0 

0 

0 

0 

0 

0 

D 

0 

0 

0 

0 

0 

0 

0 

0 

Horizontal Distribution of Rhodamine Dye (μg.i- 1

) for HABITAT 

34.292 

34.291 

34.29 

34.289 

z 34.288 0 

-

~ 34.287 :::J 

:t:: 

~ 34.286 

34.285 

34.284 

34.283 

34.282 

-119.594 -119.592 -119.59 -119.588 -119.586 -119.584 

Longitude (

0 E) 

Horizontal view of HABIT AT Dilution 

34.292 

34.291 

34.29 

34.289 

- 34.288 z 

0 -Q) 

-c 34.287 :::J 

= 1ii 

....I 34.286 

34.285 

34.284 

34.283 

34.282 

-119.592 -119.59 -119.588 -119.586 -119.584 

Longititude (°E) 

4 

3 

2.5 

2 

1.5 

0.5 

0 

2500 

2000 

1500 

1000 

500 

0 

Figure 16. Horizontal planar view of the distribution of the maximum concentration of 

Rhodamine WT (μg·r 1

; top) and minimum dilution (bottom) for Platform Habitat on July 

26, 2003. The contour lines indicate the distance in kilometers from the platform that is 

indicated by the black square at the center of the concentric circles. 

26 
0 

0 

0 

0 

0 

0 

0 

0 

D 

0 

D 

D 

0 

0 

0 

D 

0 

D 

Vertical Cross-Section of Rhodamine Dye (μg.r 1

) for HABITAT 

-30 4 

3.5 

-40 

3 

-50 

2.5 

2 

-70 

-80 

-90 

-0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 

Distance from Platform (km) 

Vertical Cross-Section of Dilution at HABITAT 

-30 

-40 

-50 

2500 

2000 

-70 

1500 

1000 

-80 

-90 

-0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 

Distance from Platform (km) 

Figure 17. Vertical planar cross-section of the maximum concentration of Rhodamine WT 

(μg·1" 1

; top) and minimum dilution (bottom) along the axis of the plume shown in Figure 16. 

Concentrations are indicated on the colorbar. The black square located at 0 km indicates 

the location of the platform discharge. The x-axis indicates distance from the platform. The 

orientation of this section is from southeast (left) to northwest. 

27 
0 

0 

0 

0 

D 

D 

0 

D 

0 

0 

0 

0 

0 

D 

D 

D 

D 

Platform Habitat - Vertical Profiles 

_,:l:J _,:_ 

-20 

-30 . 

-

E 

-

£i -40 - 0. 

Q.) 

0 

-50 

-70 

1-20 

-1 -30 

I 

] ~ 

1 

-60 " 

_J -70 

0 

-40 . 

I 

~" r -60 -

-70 

I 

Rhod(1) 

Rhod(2) 

FChl 

-80 +--~----' 

10 15 20 ~3 33.2 33.4 33.6 33.8 -8~3 24 25 26 0 5 10 15 

Temp. (°C) Salinity (psu) Density (kg-m-3} Rhed. Cone. (μg-r1} 

Figure 18. Vertical water column profiles of physical (temperature, salinity, and density), 

biological (chlorophyll fluorescence), and dye tracer concentration (μg·r 1

; top) for Platform 

Habitat. 

4.3.3 Post-Cruise Modeling 

Using the current and stratification observations from the plume mapping on July 26, the plume 

model was rerun to provide a comparison with the plume characteristics that were measured in 

the field. The plume trajectory was toward the north-northwest and was consistent between the 

observations and the model (Figures 14 and 19). However, the initial dilution and plume depth 

were quite different between the model and the observations. The modeled initial dilution was 

based upon a discharge depth of about 43 m (Table 1 ), which produced an initial dilution of 

316: l (Figure 14). However, the actual depth of the plume appears to be about 60 meters and 

estimate minimum dilution was 1370:1. It is most likely that the water being injected into the 

discharge pipe was from nearer the surface and therefore would have been warmer and perhaps 

fresher than the water at the discharge depth. Thus the plume would be expected to be buoyant 

compared with the ambient water at the discharge depth and thus plume rise rather than sinking 

after discharge would be expected. This suggests that the actual depth of the produced water 

discharge is deeper than listed for Platform Habitat (Table l ). This could contribute in part to the 

difference in dilution, but may not explain it fully. 

28 
CJ CJ CJ CJ CJ CJ C3 [::=J 

500 

400 

c: 300 

0 

·;::; 

...2 

i5 200 

100 

me Dilution - Platform Habitat 

A 

average 

centei line 

... ,,. .·· · 

CJ CJ CJ [=:J CJ CJ CJ CJ CJ [=:J 

500 , Nearfield and Mixing Zone Dilutions 

c: 

0 

400 

~300 

C5 

~ 

"€200 

~ j W 

' 100 

B 

• • • • • • • • • 

• • • • • • • • 

• • • • • 

• • 

0 '--~~~~~~~~~~~~~~ 

0 10 20 30 40 50 0 60 120 180 240 300 

50 

4olc 

30 

]: 20 

..t:. 

+J 10 :::i 

0 

Vl 0 I 

..t:. -10 

t 

~ -20 

-30 

-40 

-50 

-so 

Hoizontal distance from source (m) 

Plume Traiector 

centerline 

·: , ·· ..• : !?.?.~ ~~ Y... ..... . 

0 -

10 

~20 

t 

~ 30 

Elapsed Time (minutes) 

.Plyme_ElevatiQn_ 

D 

40 I ~ ... 1-i ii~::~:: · 

centerline 

?.~ ~~ .':Y. ........ 

50 ..__~~~~~ ~~~ ~~--' 

-40 -30 -20 -10 0 10 20 30 40 so 0 10 20 30 40 50 

West - East (m) Hoizontal distance from source (m) 

Figure 19. Post-cruise plume modeling results for Platform Habitat, using data collected during field operations on 26 July 

2003. The top left panel (A) shows the initial dilution of both the centerline and the average plume dilution, the top right panel 

(B) shows the time series of average dilution for the plume model run, the lower left panel (C) shows the horizontal plume 

path, and the lower right panel (D) shows the plume elevation after discharge. Output is from Visual Plumes using model 

UM3. 

29 
0 

0 

0 

D 

D 

0 

D 

0 

0 

0 

0 

0 

0 

0 

0 

0 

4.4 Platform Gina 

4.4.1 Pre-Cruise Modeling 

No pre-cruise modeling was performed for Platform Gina. Platform Gina was substituted for 

Platform Gail just before the start of the field sampling. Prior to the field effort Platform Gail had 

been targeted instead of Gina. 

4.4.2 Field Sampling and Data Collection 

4.4.2.lAmbient Current Velocity Field 

Platform Gina was sampled on 27 July 2003. Currents varied between west northwest and north 

northwest throughout the morning with speeds on the order of 10 cm·s1 (Figure 20). During the 

afternoon during the dye plume tracking the currents shifted toward the west and west southwest. 

4.4.2.2Dye and Hydrographic Distributions 

Prior to the injection of Rhodamine WT dye, the region around the platform was sampled with 

the TOWYO array to determine whether any natural water quality measurements (temperature, 

salinity, density, chlorophyll fluorescence, and suspended particulate material) had been affected 

by the discharge of produced water. No significant difference from ambient conditions was 

detected in the area north and northwest of the platform where based upon the current direction a 

plume would likely be found. This indicates that the discharge of produced water from Platform 

Hogan was not affecting these water quality variables. 

After about 1 hour of towing the TOWYO instruments along transect lines through an area most 

likely to encompass a produced water plume without detecting a plume the Rhodamine dye 

injection was started. Approximately 45 minutes after dye injection into the produced water 

discharge system commenced a clearly defined dye plume was located to the west and southwest 

of Platform Gina (Figure 21). This plume location was consistent with the westerly current 

direction measured using the ship-mounted ADCP (Figure 20). The dye field was detectable out 

to about 1.5 km (Figure 21 extends only out to 1.2 km but Figure 23 shows a trace of the plume 

extending about 1.5 km ). The highest concentration of dye that was measured in situ was 1.6 

μg-r

1

• Based on an initial concentration of 5801 μg·r

1 in the discharge, this corresponds to a 

minimum initial dilution of 3536: I. At 1.5 km from the platform, the farthest distance away that 

dye was detected, the maximum concentration of dye was 0.21 μg -r

1

. The lowest dilutions 

( <7000: 1) occurred within 400 meters of the platform. Beyond 400 meters dilution was in excess 

of 10000:1. 

Figures 22 and 24 show the vertical distribution of the dye plume again indicating a somewhat 

complex distribution of the dye with a smaller maximum concentration at about 20 meters and a 

higher maximum at 26 meters and deeper. The variability in the depth of the dye is most likely 

associated with the change in pycnocline depth that occurred when the pycnocline deepened by 

about 10 meters between 1200 and 1330 PDT. 

30 
C:::J C=:J CJ CJ CJ C=:J c:J CJ c:::::J c:::::J CJ CJ c:J CJ CJ CJ CJ CJ 

...-. 

~ 

E ..._.. 

""C 

Q) 

Q) 

c. 

(/) 

Current Time Series at 23 Meters - Platform Gina 

0.4 ~~--~---------------~ 

0.2 ....... --··· ·· · ...... ··-······· ···· .·... . ............... ... . 

0 ~ .. ~ . . ............ . 

-0.2 ··· ·· ··· ··:· -·--··· ·•·· ·· ····· -:- . . . . . -.... --. . . . . . . '. ~· ....... . ··!·"······-······· ·· ···.···· ................. • ....... . 

-0.4~~--~--~--~--~--~--~~ 

06:32 08:12 09:52 11:32 13:12 14:52 

Time (PDT) - July 27, 2003 

16:32 

Figure 20. Time series of currents for Platform Gina at 23 m. Current vectors are plotted at 10 minute intervals beginning at 

the times indicated in the x-axis label. Each plot represents nearly 8 hours of observation. 

31 
0 

0 

0 

0 

D 

0 

0 

0 

D 

D 

0 

D 

0 

D 

0 

D 

0 

0 

Horizontal Distribution of Rhodamine Dye (μg-r 1

) for GINA 

~-1~ 2 

34.11 

-119.288 -119.284 -119.28 -119.276 

Longitude (

0 E) 

Horizontal Distribution of Dilution at GINA 

.-.. 

z 

a 

-Q) 

"C 

::i 

:t= 

m 

34.125 

34.12 

..J 34.115 

34.11 

-119.288 -119.284 -119.28 -119.276 

Longititude (°E) 

1.8 

1.6 

10000 

6000 

5000 

4000 

3000 

2000 

Figure 21. Horizontal planar view of the distribution of the maximum concentration of 

Rhodamine WT (μg·r 1

; top) and minimum dilution (bottom) for Platform Gina on July 27, 

2003. The contour lines are distance (km) from the platform (black square). The plume is 

advecting westward from the platform. 

32 
0 

0 

D 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

Vertical Cross-Section of Rhodamine Dye (μg.r 1

) for GINA 

-10 

-15 

-20 

E. -25 Qj 

c 

E' 

.._, 

-30 

-35 

-4g 

- .2 

-10 

-15 

-20 

E. -25 Qj 

c 

-30 

-35 

-40 

-0.2 

0 0.2 0.4 0.6 0.8 1.2 

Distance from Platform (km) 

Vertical Cross-Section of Dilution for GINA 

0 0.2 0.4 0.6 0.8 1.2 

Distance from Platform (km) 

2 

1.8 

1.6 

1.4 

1.2 

0.8 

5000 

4000 

3000 

2000 

1000 

0 

Figure 22. Vertical planar cross-section of the maximum concentration of Rhodamine WT 

(μg·l" 1

; top) and minimum dilution (bottom) along the axis of the plume shown in Figure 21. 

The two levels of dye indicate dye released at different times. The density surfaces 

deepened by about 6 meters between 1200 and 1330 PDT. 

33 
0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

Rhodamine Dye (μg.r 1

) Section Plot for GINA -10 ~-------~----r-----,----..,.----~ 

'E -20 

~ ~ -30 

Distance from plalform = 14 72(m) 

-40 ~---"------'-----~----'----_._---~ 

-1000 -800 -600 -400 -200 0 200 

I :~ r I _____.i._____ ! -------'- ! ---'--- ·~~ .. -·_.__________. '~~. ,,,,~ 1 -1000 -800 -600 -400 -200 0 200 

f....___________ : 1 _..__! L .. -. .,,"., j 

-1000 -800 -600 -400 -200 0 200 

-10 ---~- ~-- -r-----,-

E -20 i 

~ -30 

-40 '-- "------'-- -'------'- -'----~ 

-1000 -800 -600 -400 ·200 0 200 

Distance from perpendicular llne(m) 

Density Section Plot for GINA -10 ~--------r-----.-----.----~---~ 

e -20 

~ i!l -30 

Drstance ~om plaUorm = 1472(mJ 

40 ~---"----_ _.__ ___ _._ ___ _._ ___ ~---~ 

-1000 -BOO -600 -400 -200 0 200 

10 -=::: ~~~~---.----1 E -20 

"l! 

g. -30 

Cl u1stanc e 1tom planorm = 123(m) -40 -------- ------' ______ j _____ i__ ____ j ____ _ 

-1000 -800 -600 -400 -200 0 200 

I~~ [.__ _ __.____,____.____._______.] -1000 -BOO -600 -400 -200 0 200 

-10 -,-==----:=:::;~~ r-1 

E -20 

i 

~ -30 

D1s1ance ~om plaUorm = 189(ml 

-40 '-- --'---- --------'-----'-----'----~ 

-1000 -800 -600 -400 -200 o 200 

Distance from perpendicular line(m) 

0.5 

0 

05 

0 

0.5 

0 

0.5 

0 

26 

25 

24 

23 

26 

25 

24 

23 

26 

25 

24 

23 

26 

25 

24 

23 

Figure 23. Section plots of Rhodamine dye (μg·r1

) and density extending away from 

Platform Gina. The top panel is located 1472 m from the platform, the second panel is 723 

m, the third panel is 374 m and the bottom panel is 189 m. Black vertical line represents 

platform location of discharge. 

34 
0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

-5 . 

-10 

-15 r . 

K-20[ 

.i= -25 

! I -30[ 

] 

I ~S r 

-50 ~ _J.__ 

10 15 20 

Temp. (°C) 

Platform Gina - Vertical Profiles 

ol I o o 

J ' _:1 

-15 -15 

-20 - 1 -20 . 

-25 - ... -25 -

-35 

-301 

I -35 -

-30 

-35 -

-40 - " -40 1 -40 

I 

::: _________ : ::_· ---- __J -- ~-~~d~~ I 

33.2 33.4 33.6 23 24 25 26 0 0.5 1 1.5 2 

Salinity (psu) Density (kg/m3) Rhod. Cone. (μg-r1) 

Figure 24. Vertical water column profiles of physical properties (Temperature, Salinity, 

and Density expressed as Sigma theta), chlorophyll fluorescence and Rhodamine WT 

concentration. Thee profiles indicate the position of the discharge plume relative the 

vertical distribution of physical and biological properties in the water column. 

As with the other platforms, there was no evidence of the plume affecting the ambient variables 

that were measured (Figure 24 ). Rhodamine dye was mostly found in the water below the 

seasonal pycnocline where salinity was increasing and temperature decreasing with depth 

(Figure 24). The Rhodamine was in close proximity to the chlorophyll maximum, but the top of 

the discharge plume indicated by the Rhodamine remained below the base of the chlorophyll 

maximum. The apparent overlap in Figure 24 results from showing both morning and afternoon 

profiles together. 

35 
0 

0 

D 

D 

0 

D 

D 

0 

0 

0 

0 

D 

0 

0 

0 

0 

4.4.3 Post-Cruise Modeling 

Modeling of the plume dynamics was carried out using the observed currents and water column 

stratification from July 27, 2003. The model results indicate that the plume depth should be 

centered at about 25 meters with an initial dilution ranging from 129:1to289:1 (Figure 25). In 

contrast, the observations indicate a plume depth ranging from about 17 meters to 37 meters 

(Figure 24) and the measured initial dilution was 3536:1, about 20-fold the modeled dilution. 

Note data from Rhodamine sensor 1 was not included because the dye concentrations were so 

high that the low detection sensor was not needed to detect the dye field. 

Variations in the observed plume depth are most likely explained by the variations in vertical 

water column structure that occurred over the course of the dye study. Vertical pycnocline 

variability was on the order of 8-9 meters during the sampling period. 

The difference between observed and modeled plume is more difficult to explain. Certainly, the 

plume depth was in the range of the modeled plume depth although it showed considerably more 

variability than the model results. Two factors could explain the large difference. One is that the 

actual discharge flow rate was much higher than the read-outs indicated. The result of this is that 

the concentration of dye in the discharge would be smaller than expected. Another explanation is 

that the injection of dye into the discharge was much smaller than was assumed. Unfortunately, 

neither of these two issues can be independently verified. 

36 
(:=J CJ CJ c::J CJ c::J C:J 

500 Plume Dilution - Platform Gina 

400 

c: 300 0 

~ 

0 200 

100 

0 

50 

0 

A 

/ -z,1_,/ 

/" _.c / /;;/y 

/ .. ~.~;/ 

/, /.,;/ .. ~ 

10 

average 

centerline 

20 30 40 

Hoizontal distance from source (m) 

Plume Trajectory 

40 c 

30 

]: 20 

centerline 

L 

... 10 :> ~~~ ~~~.'Y. ........ 0 

V'I 0 

' 

L -10 

t: 

~ -20 

-30 

-40 

-50 

CJ CJ c:J c:J CJ CJ CJ CJ CJ CJ 

c: 

0 

500 

400 

~300 

0 

~ 

·-=-200 

~ w 

100 

0 

50 0 

Nearfield and Mixin_g Zone Dilutions - ----------·--·· - ------- . ·-----i 

B 

••••••••• 

60 

••• • 

120 

• 

• • 

• 

• 

• 

180 

• 

• 

. 

• 

• • 

240 

Elapsed Time (minutes) 

.. ···•-· • •• 

300 

Or---

Plume Elevation 

D 

10 

centerline 

.s 

L ~~~ ~~ 'J. ........ 

& 

Cl 

20 

~ ~~:-- ·:: :: :: 

30 1--~~~~~~~~~~ ~~~-

-50 -40 -30 -20 -10 0 10 20 30 40 50 0 10 20 30 40 50 

West - East (m) Hoizontal distance from source (m) 

Figure 25. Post-cruise plume modeling results for Platform Gina, using data collected during field operations on 27 July 2003. 

The top left panel (A) shows the initial dilution of both the centerline and the average plume dilution, the top right panel (B) 

shows the time series of average dilution for the plume model run, the lower left panel (C) shows the horizontal plume path, 

and the lower right panel (D) shows the plume elevation after discharge. Output is from Visual Plumes using model UM3. 

37 
0 

0 

0 

0 

0 

0 

0 

D 

0 

0 

D 

D 

0 

0 

D 

5. Discussion I Summary 

Produced water discharges from four representative oil and gas production platforms in the Santa 

Barbara Channel, California were studied during July 24-27, 2003. Natural tracers or ambient 

variables [temperature, salinity, density, chlorophyll fluorescence, and beam attenuation 

(indicative of suspended particles)] and an injected dye (Rhodamine WT) were utilized in an 

attempt to detect and measure the discharge plumes from outer continental shelf Platforms 

Hogan, Harvest, Habitat, and Gina. 

Natural tracers failed to show evidence of discharge plumes (i.e., anomalous values within areas 

of expected plume) even at the closest approach to the platforms, which was within 

approximately 25-50 m of the platform. There was some optical interference on the 

transmissometer and chlorophyll fluorometer but no appreciable signal within the discharge 

plume. This is because after initial dilutions of more than 200: 1 the salinity, temperature, and 

turbidity of the produced water discharges were not drastically different from ambient seawater 

conditions. Platform Harvest appeared the most likely discharge to have an anomalous 

temperature signal, because of its warm (83°C) discharge. However, when the T-S diagram (i.e., 

temperature-salinity diagram) was examined in the region where the dye was detected, no 

temperature anomaly was apparent in the data. These results are in contrast to similar kinds of 

observations from wastewater outfalls where the discharge is essentially fresh water with both 

dissolved and particulate constituents (e.g., Jones et al., 2002; Petrenko et al., 1997; and Wu et 

al., 1994). Thus, within the zone of initial dilution (within 100 m) there was no measurable 

impact to temperature, salinity, density, and transmissivity of the receiving waters. 

With the addition of Rhodarnine dye to the produced water discharge a dye field or plume 

containing the dye could be detected and mapped to distances of at least 0.36 to 1.5 km from the 

platforms (Table 3). It is likely that the discharge plumes defined by the Rhodamine dye could be 

detected for longer distances with longer field surveys, but the dilutions at the outer reaches of 

the dye field were quite high (27000:1to48000:1). The measured minimum dilutions of the 

discharged effluent ranged from 216:1 to 3536:1 (Table 2). The lowest measured dilutions were 

higher than the dilutions predicted for a produced water discharge near Carpinteria Creek 

described by Washburn et al., (1999). In two of the cases, Platforms Hogan and Harvest, the 

modeled dilutions and the observed dilutions were reasonably close to each other, and thus it 

appears that the UM3 model in Virtual Plumes provides a good approximation to the plume 

characteristics of discharges from these two outfalls. For Platforms Habitat and Gina, the 

observed dilutions were much greater than the modeled dilutions. Reasons for this disparity are 

unknown but could be related to variable discharge volumes. Other factors contributing to 

possible errors would include misinformation on the location and characteristics of the discharge 

structure and discharge flow rates. Both Platforms Hogan and Harvest had reported produced 

water discharge rates at 11,500 and 37,900 gallons per hour, respectively. Platforms Habitat and 

Gina had discharge rates reported to be 2700 and 3000 gallons per hour, respectively. 

38 
0 

0 

0 

0 

0 

D 

D 

D 

0 

0 

0 

0 

0 

0 

0 

D 

5.1 Location of the Plume 

5.1.1 Horizontal Distribution 

In general, the discharge plumes were found where they were expected to be based on the 

measured current directions. The horizontal distribution of the plumes was consistent with the 

observed current patterns. The concentrated portions of the plumes extended out 300-700 meters 

from the platforms and while the more dilute portions were detected as far as 1.5 km from the 

platforms. A current speed of 10 cm·s-1 corresponds to a rate of 360 meters per hour. Over a 

four-hour period (approximate average time spent tracking dye plume) we would expect the 

maximum distance of the plume to be about 1500 meters at this rate. In the cases of Platforms 

Hogan and Gina where dye was detected about 1500 meters from the platforms the current 

speeds were more than 10 cm·s1 for at least the first half of the dye releases. The current speeds 

at both Harvest and Habitat were slower and the horizontal plume extents are consistent with the 

slower current speeds. 

5.1.2 Vertical Structure 

For each of the platforms the discharge of produced water occurred below the pycnocline during 

the study. In each case the observed dye plume either did not rise above the level of discharge, or 

the rise was less than 10 meters as observed at Platform Harvest. The primary reason for the 

elevation of the Harvest discharge was because of its warm temperature. Another factor that 

affected the depth of the discharge plume was variation in pycnocline depth. For at least two of 

the sites (Harvest and Gina) the pycnocline depth varied by about 10 meters during the injected 

dye portion of the study. The result of this was that the dye plume could be observed at more 

than one depth level related to the time the dye was injected into the discharge and the density 

structure of the receiving waters. The other case where variations in the depth of the plume 

occurred was for Platform Gina where the isopycnals (i.e., lines of equal water density) sloped 

downward parallel with the bottom to the west, in the direction of the currents. The dye plume at 

Platform Gina deepened to the west following the isopycnals. This shows the importance of the 

density structure in the water column to influence plume behavior. 

Variations in the pycnocline depth do occur both on the short term as seen at Platforms Gina and 

Harvest and on longer seasonal scales. The largest change occurs during the winter when 

stratification is at a minimum. The CalCOFI data set from the center of the Santa Barbara 

Channel shows that in January the water column can be mixed throughout the upper 40 meters. 

However, we do not expect this weak stratification to affect the vertical distribution of the plume 

very much since there is very little change in depth of the plume during discharge. If the water 

column is strongly mixed during winter and does mix to the depth of the plume it will result in 

increased dilution of the plume and will therefore help to reduce any effects from the discharge 

plume even further. 

For the observations during July 2003, the discharge plumes did not interact with the 

phytoplankton productivity layer. The phytoplankton maximum layer can extend to 30 meters 

depth, particularly in the winter and spring. During the more stratified summer and fall periods, it 

is more likely that the chlorophyll maximum layer will only reach to about 20 meters depth. 

39 
0 

0 

0 

0 

0 

0 

D 

0 

0 

D 

0 

0 

0 

0 

0 

0 

0 

0 

Only the discharges from Platforms Hogan and Gina are likely to interact with the phytoplankton 

maximum layer since their discharge depths are 24 m and 26 m, respectively. No alteration of 

the ambient turbidity was detected with the transmissometer. Therefore, it is not expected that 

there is a significant effect on light attenuation. 

5.2 Dilution of the Plume 

For each of the platforms, the initial mixing and dilution of the plume appeared to have occurred 

within 100 meters of the platform. The TO WYO instrument array was often towed within 25-50 

meters of the platform to ensure that the nearfield behavior of the plume was being sampled 

adequately. The core part of the plume could be detected at distances between 300 meters 

(Platform Habitat) and 700 meters (Platform Hogan) from the platform (Table 3). Dye was 

usually detectable beyond these boundaries, but at much lower concentrations (higher dilutions) 

than within these radii. The decrease in concentration beyond these distances can be attributed 

primarily to horizontal spreading of the plume. Apart from the variability in depth due to shifts in 

the vertical location of density surfaces, the plume thickness usually remained fairly constant. 

Therefore changes in dye concentration were mostly due to horizontal spreading of the plume. In 

each of the cases studied the plume shows a distinct widening where the concentrations of dye 

decreased (dilutions increased). 

In two of the cases, the measured dilution corresponds well with dilutions predicted by the 

Visual Plumes UM3 model. For both Platforms Hogan and Harvest the minimum dilutions were 

within a reasonable range of the modeled dilution (Table 3). For Platforms Habitat and Gina, the 

measured minimum initial dilutions were much larger than the model predictions. The cause(s) 

for the disparity between field observations and post-cruise modeling for Platforms Habitat and 

Gina are unknown. Possible explanations for this discrepancy include: 

1. The actual discharge volume of water may be greater than the rates that are used in the 

model. This could be true if there is another source of water that merges with the discharge 

stream at a point after the point where the flow was measured. 

2. The model may contain some sort of discontinuity or nonlinearity that would come into 

effect between 3000 and 6000 gallons per hour. 

3. There is some other error in the characteristics of the discharge that were used to model 

the plume. The fact that there is a discrepancy between the observed plume and the reported 

discharge depth for Platform Habitat where there was a large difference could certainly be a 

factor. Increasing the discharge depth in the model run for Habitat to 62 meters instead of the 

42.7 meters used does provide an increase of dilution by about 15%, but not nearly enough to 

account for the higher measured dilutions. 

4. Perhaps the sampling did not adequately sample the core of the plume such that the 

highest concentrations of Rhodamine (lowest dilution) were not measured. However, while this 

is possible, the plume was crossed multiple times and it would have been expected to encounter 

the core of the plume more than once. Although we think this possibility is unlikely, the plumes 

for Habitat and Gina were smaller than the Harvest and Hogan plumes and this possibility cannot 

be entirely ruled out. 

40 
c:::J CJ CJ CJ [=:J CJ c:J [:=J c=J CJ CJ CJ CJ CJ c:::J c:J CJ c:::::J 

Table 3. Summary of plume model runs and observations for the four oil platforms studied in the Santa Barbara Channel. 

Minimum Maximum Median Mean Distance of Depth of Radius of D"'.1~ximum f 

M . f M . C 1s ance o 

Dilution Dilution Dilution Dilution ax1mum rom ax1mum ore D f 

Discharge (m) (m) Plume (km) et~~;on 

Hogan Aug-94 Model 209 808 396 410 

Hogan 24-Jul-03 Model 130 1324 250 305 

Hogan 24-Jul-03 Measured 216 98 26 0.7 1.5 

Harvest Aug-99 Model 238 3741 1485 1407 

Harvest 25-Jul-03 Model 288 938 347 480 

Harvest 25-Jul-03 Measured 333 160 55 <0.5 1.1 

Habitat Aug-94 Model 354 1027 567 579 

Habitat 26-Jul-03 Model 249 358 316 316 

Habitat 26-Jul-03 Measured 1370 92 63 0.3 0.36 

Gina 27-Jul-03 Model 129 289 164 176 

Gina 27-Jul-03 Measured 3536 347 29 0.4 1.5 

41 
D 

0 

0 

0 

0 

0 

D 

0 

0 

D 

0 

0 

0 

0 

0 

The one conclusion that is clear from the results is that the model does not over-predict the in 

situ dilution. From the standpoint of evaluating potential impacts, the models provide a 

conservative evaluation of those impacts (i.e. less dilution than actual). 

5.3 Impacts of the Plume 

As stated above, one mechanism by which produced water discharges could affect the ambient 

water column is through the inhibition of primary productivity. The potential effect of the 

produced water discharges on light attenuation based on the nephelometric measurements was 

evaluated (Table 4). The results suggest that any potential impact of produced water on water 

column light attenuation is negligible. The change in beam attenuation by the produced water 

was estimated to have been from .001 to .025 m1

• The variation observed from our observations 

show that the phytoplankton-driven variability of the beam attenuation ranged from 0.8 to 1.2 

m1

, much larger than the estimated change from the produced water turbidity. In addition, since 

the discharge plumes are all beneath the phytoplankton maxima, changes in light attenuation due 

to the produced water plumes will not have a large effect on the phytoplankton community. To 

avoid any potential impacts to phytoplankton primary production it is advisable to have produced 

water discharge ports to be located below the phytoplankton maxima depth. 

Table 4. Resultant properties on water column based on the minimum initial dilutions 

measured. 

Platform 

Hogan 

Harvest 

Habitat 

Gina 

Minimum Initial 

Dilution Measured 

216 

333 

1370 

3536 

NTUin 

Produced Water 

49.3 

3.19 

32.1 

na 

42 

NTU after 

Dilution 

0.2282 

0.0096 

0.0234 

na 

Change in Beam 

Attenuation (/m)* 

0.025 

0.001 

0.003 

na 
D 

D 

0 

0 

0 

0 

0 

0 

D 

0 

0 

D 

D 

0 

0 

0 

0 

6. References 

Frick, W. E. 1984. Non-Empirical Closure of the Plume Equations. Atmospheric Environment 

18 (4): 653-662. 

Frick, W.E., P.J.W. Roberts, L.R. Davis, J. Keyes, D.J. Baumgartner, K.P. George. 2001. 

Dilution Models for Ejfluent Discharges, 4th Edition, (Visual Plumes). Environmental 

Research Division, NERL, ORD, U.S. Environmental Protection Agency, 960 College 

Station Road, Athens, Georgia 30605-2700. Standards and Applied Science Division, Office 

of Science and Technology, 137 p. 

Jones, B.H., M. Noble, and T.D. Dickey. 2002. Hydrographic and Particle Distributions over the 

Palos Verdes Continental Shelf: Spatial, Seasonal and Tidal Variability. Continental Shelf 

Research 22(6-7):945-965. 

Petrenko, A.A, B.H. Jones, T.D. Dickey, M. LeHaitre, and C. Moore. 1997. Characterization of 

particle fields in Mamala Bay, HI with special emphasis on the Sand Island sewage plume. 

Journal of Geophysical Research 102(Cl 1):25061-25071. 

Smart, P.L. and I.M.S. Laidlaw. 1977. An evaluation of some fluorescent dyes for water tracing. 

Water Resources Research 13(1): 15-33. 

Washburn, L., S. Stone, and S. Macintyre. 1999. Dispersion of produced water in a coastal 

environment and its biological implications. Continental Shelf Research 19:57-78. 

Winiarski, L.D. and W.E. Frick, 1976. Cooling tower plume model. USEPA Ecological Research 

Series, EPA-600/3-76-100, USEPA, Corvallis, Oregon. 

Wu, Y., L. Washburn, and B.H. Jones. 1994. Buoyant plume dispersion in a coastal 

environment: Observations of plume structure and dynamics. Continental Shelf Research 

14: 1001-1023. 

43 
2'43& Iinpala Ur. 

CarlebJ¥1, CA ~~OB