Draft final

Discussion Note 2.1 OIL DISPERSIBILITY (Also see Att. II.m for Window of Opportunity)

Three types of oils are typical of those produced or transported in California offshore waters: a) crude oils produced in California Outer Continental Shelf (OCS) waters; b) oils imported from Alaska and foreign countries into California ports; and c) fuel oils that could be spilled from a variety of marine industrial activities (e.g., fuel tanks from ships, cargoes of small tankers). Dispersants only work if the spilled oil has a relatively low viscosity at the time of treatment.

Attachments II.a and II.b show the California platform-produced oils and tankered oils, respectively.
Most oils produced from offshore platforms are heavy, and border on the range of oils that are considered to be difficult or impossible to disperse. The oils transported by tanker include two-three dozen different types of oil (only the most common are listed in Attachment II.b). The most important is Alaska North Slope crude, which represents 50% of each annual total. Based on API gravity information, these oils appear to be dispersible when fresh.

• 
  The most important criterion for dispersant use is whether the oil is dispersible.
  
• 
  The best indication of oil dispersibility is from specific oil weathering and dispersion data from field trials (see Attachment II.c for some tested and modeled oils).
  

• 
  Potential dispersibility can be estimated from physical properties of oils, under different oil weathering and spill scenarios (e.g., ADIOS, Table 2.1 below). The ADIOS computer database predicts oil dispersion based on physical and chemical properties of spilled oil under specified spill conditions.
  
• 
  Dispersant use should not be rejected exclusively on the basis of predictive models.
  

Generally, if:

• 
  Oil is able to spread on the water, it is likely to be dispersible.
  
• 
  Viscosity is < 2000 cSt, dispersion is probable.
  
• 
  Viscosity is > 2000 cSt, dispersion is possible.
  
• 
  Viscosity is > 5000 cSt, dispersion is possible with concentrated dispersant (e.g., Corexit 9500).
  
• 
  Sea temperature is <10º C or below oil pour point, dispersion is unlikely.
  

Potential dispersion may also be assessed using tables in Attachment II.
Limitations of predicting dispersion:

• 
  Using generic values of viscosity and/or pour point to predict dispersion (e.g., ADIOS, Attachments II.c and II.d can underestimate the potential for oil to be dispersed.
  

• 
  Most models are based on limited oil weathering, emulsification or dispersion data, therefore estimated windows of opportunity may be inaccurate.
  

Taken in part from Cawthron, 2000 and S.L. Ross, 2002




Table 2.1 ADIOS (AUTOMATED DATA INQUIRY FOR OIL SPILLS) COMPUTER DATABASE
Use the DISPERSANT ASSESSMENT WORKSHEET and the NOAA SSC (Attachment XI) for the information needed by ADIOS, or use the form below. The NOAA SSC should also be able to assist with ADIOS.
Copies of ADIOS are available from the NOAA website: http://response.restoration.noaa.gov/adios
Oil/product name: Wind speed: (knots)

Amount spilled: (gal or bbl) Wave height: (m)

Type of release: Circle one Water temp.: (ºC)

• 
  Instantaneous Water salinity: (ppt)
  
• 
  Continuous
  

Important limitations on the use of ADIOS: ADIOS predicts dispersibility based on estimates of oil properties (including emulsification) under different conditions. As emulsification data are scarce, predicted rates of dispersion may be different than actual rates of dispersion. ADIOS is intended for use with floating oils only, and does not account for currents, beaching or containment of oil. ADIOS is unreliable for very large or very small spills. It is also unreliable when using very high or very low wind speeds in modeling the spill.

From Cawthron, 2000



BOX 3 ARE OCEANOGRAPHIC AND/OR WEATHER CONDITIONS POTENTIALLY

CONDUCIVE TO DISPERSANT USE?
Does the available technical information indicate that the existing oceanographic (e.g., surface current direction and speed, wave and chop height) and weather (e.g., wind direction and speed, visibility, ceiling height) conditions are suitable for a successful dispersant application?
Use the following resources:

• 
  Information on the DISPERSANT ASSESSMENT WORKSHEET
  
• 
  Consultation with the NOAA Scientific Support Coordinator (Attachment XI)
  
• 
  Information resources and web sites noted in Attachment XI
  

• 
  Information from aerial overflights
  
• 
  Information from ADIOS
  

Decision: Are ocean and weather conditions potentially suitable for a dispersants application?

• 
  Yes Go to Box 4.
  
• 
  No Go to Box 1c
  

Make a note of the decision in the Dispersant Decision Summary box on the Dispersant Use Flowchart.



BOX 4 IS THE SPILLED OIL WITHIN 3 MILES OF SHORE, WITHIN A NMS, WITHIN 3 MILES OF THECA/MEXICO BORDER, BEING USED ON SURFACEOILSPILLS FOR LESS THAN FIVE DAYS, OR A SUBSEA USE?
A full-page statewide chart indicating the area three nautical miles from shore and the areas within National Marine Sanctuaries (Gulf of the Farallones, Cordell Banks, Monterey, Channel Islands) is in Chart 4.1 below. Regional charts, with dispersant zones noted, are in Attachment I.
Decision: Is the spilled oil within the RRT IX Expedited Approval Zone?

• 
  Yes Go to Box 5.
  
• 
  No Pre-Approval may apply. Go to Box 4a.
  

Make a note of the decision in the Dispersant Decision Summary box on the Dispersant Use Flowchart.