United States Environmental Protection Agency Municipal Environmental Research Laboratory Cincinnati OH 45268 Research and Development EPA-600/S2-84-067 Apr. 1984 &ER& Project Summary Response of Crude Oil Slicks to Dispersant Treatment at Sea /11 A series of ocean studies was con- ducted in 1978 and 1979 to develop quan- titative data on the effectiveness of dis- persants at sea and on the behavior of dispersant-treated oil. Test spills were made in the outer New York Bight some 80 km southeast of New York Harbor. Ambient conditions were consistent for both years of testing, but other factors such as spill volume, time of dispersant application, and dispersant dose were varied. Oils used were Murban and La Rosa crude. Reasonably effective treatment was achieved when dispersant was sprayed 30 min or less after the oil was spilled. Little oil was found in the subsurface water after spraying dispersant on oil that had been on the sea surface for 2 hr. This Project Summary was developed by EPA's Municipal Environmental Re- search Laboratory, Cincinnati, OH, to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back). Introduction Information about spilled oil behavior is needed for effective responses to oil spills at sea. If a response includes possible treat- ment with chemical dispersants, quantitative data are needed on the behavior of dis- persant-treated oil to determine its chemical and physical fate and the advisability of us- ing dispersants. Though considerable laboratory and field tests of dispersants were conducted in many countries in 1977, few quantitative data were developed on the ef- fectiveness of dispersants at sea or on the behavior of dispersant-treated oil. In response to this information need, the American Petroleum Institute (API) and the U.S. Environmental Protection Agency (EPA) jointly sponsored the 1978-1979 series of ocean experiments described here. Experimental Program Research oil spills were made in the outer New York Bight approximately 80 km south- east of New York Harbor. Four spills were made in November 1978 and four in October 1979. Some experimental factors were com- mon to all tests. These included: • taking background samples of ocean water before the spill, • recording oceanographic and meteoro- logical data before and during each test, • collecting large numbers of seawater samples at various depths in the spill area, • repeatedly having the principal research vessel move slowly through the oil on sampling transects that were perpen- dicular to each other so that a three- dimensional view of the oil in the water would be obtained, • applying a commercially available disper- sant from a helicopter to spills that were to be dispersed, and • guiding the helicopter and all sampling from a spotter plane that also conducted vertical photographic observations. Other experimental conditions varied bet- ween 1978 and 1979 (Table 1). As Table 1 indicates, the 1979 tests were intended to refine and augment the data generated during 1978. Note that one impor- tant difference in 1979 was the use of con- trol spills (untreated) on the same day as treated spills. During 1978, the approach had been to treat all spills to maximize the infor- mation generated on treated oil. Com- parisons could be made with earlier untreated spills of the same oil under similar ambient conditions, but rigorous experi- mental control was absent until the 1979 tests. All test spills during 1978 and 1979 were made in an area of the outer New York Bight that was approved for this purpose by EPA under Permit No. ll-MA-143-Research. Am- bient conditions for the test were consistent ------- Table 1. Principal Differences Between the 1978 and 1979 Test Series Item 1978 1979 Reason for Difference Volume of each spill 1.67 rrf Biological testing Minimal 3.55 m3 Desire to minimize effect of scale on accuracy of simulation. Extensive Ship mechanical failures in 1978. Time of dispersant application after oil spill Dose (gal dispersant/ acre of slick} Use of control spills Within 10 min or after 2 hr Approxi- mately 10 No None or 30 min Approxi- mately 20 Yes Need to assess effect of weathering. Desire to assure sufficient dose. Need for rigorous experimental control. for both years of testing, so weather and sea conditions are not considered a factor in dif- ferentiating one test from another. These conditions were as follows: Condition: Description Air temperature, °C 12-21 Water temperature, °C ... 13-16 (constant throughout sampled depth within each test) Wind speed, m/sec 0 - 7.5 Wave height, m 0.3-1.6 The oilds used were Murban crude (Abu Dhabi) and La Rosa crude (Venezuela). The primary difference between these is the higher concentration of volatiles in Murban crude. Dispersant application was similar for all treated spills. A commercially available dispersant product (same for all tests) was sprayed from a helicopter at an altitude of approximately 6 m and a speed of approxi- mately 80 km/hr. Mean droplet diameter was approximately 1 mm. Sampling of subsurface water was con- ducted with a specially designed apparatus and procedure used to avoid contamination by surface oil. All samples were preserved to avoid biological degradation before analysis. Analyses were conducted by API member laboratories using gas chromato- graphic and infrared techniques. Findings The behavior of dispersed oil is generally quite different from that of untreated oil. The chief cause of this difference is the fact that dispersed droplets, while still positively buoyant, are often small enough to be kept in suspension below the water surface by the turbulence near the sea surface. Figure 1 shows a typical pattern of oil-in- water concentrations for the crossed transects of a sampling run through dis- persed oil. With plots such as this, volumes of oil in the water were computed. These computations were approximate and used the concentration and the geometric shape represented by each concentration iosopleth to arrive at values for total dispersed oil (Table 2). Reasonably effective treatment was achieved when dispersant was sprayed 30 min or less after the oil was spilled (Table 2). Little oil was found in the subsurface water after spraying dispersant on oil that had been on the sea surface for 2 hr. Other conclusions are briefly summarized as follows: • Early in the tracking of spills that were effectively dispersed, extractable organics in the upper meter of the water column ranged typically from 1 to 3 mg/l. • Little oil was found in water samples at the 9-m depth; this result is not caused by stratification, because the water den- sity was found constant throughout the sampling depth. • Murban was more effectively dispersed than La Rosa crudes when other factors were held constant. Murban is lighter and less viscous. • One physical effect of dispersant treat- ment was that thin films were spread over larger areas of the sea surface than when an equal amount of the same oil was spilled and not treated. • Within 3 to 5 hr of spills this size, water samples from under the oil approach background concentrations because of dilution, evaporation, and perhaps other factors. The full report, prepared by JBF Scientific Corporation, was submitted in fulfillment of Grant No. R806056 with the American Petroleum Institute under the sponsorship of the U.S. Environmental Protection Agency. ------- • Wind 421 2.94 4.13 2.22 1.45 .83 1.30 .07 .06 .06 08 .06 .05 0.6 Station 1234 Time After Spill (min) 53 60 65 69 ! 700M-) JBF2150 6 - (Intersect) .10 .06 .05 .05 5 72 6 75 Figure 1. Total extractable organic matter (mg/l) in water samples collected during first sample run through treated Murban crude oil spill. Vertical exaggeration about 45 X. Table 2. Approximate Percent of Spill Oil Accounted for in Water Samples Crude Oil Type Murban La Rosa Untreated <5 <1 Immediate Dispersant Spray 40 20 Dispersant Spray after 30 min 70 60 Dispersant Spray after 2hr 2 2 ------- This Project Summary was prepared by staff of JBF Scientific Corporation, Wilmington, MA 01887. Leo T. Me Carthy, Jr. is the EPA Project Officer (see below). The complete report consists of two volumes: "Volume I. Response of Crude Oil Slicks to Dispersant Treatment at Sea: 1978 Tests." (Order No. PB 84-164 144; Cost: $11.50, subject to change). "Volume II. Response of Crude Oil Slicks to Dispersant Treatment at Sea: 1979 Tests." (Order No. PB 84-164 151; Cost: $10.00, subject to change). The above reports will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Oil and Hazardous Materials Spills Branch Municipal Environmental Research Laboratory—Cincinnati U.S. Environmental Protection Agency Edison, NJ 08837 US GOVERNMENT PRINTING OFFICE, 1984 —759-015/7677 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 oi- Official Business Penalty for Private Use $300 0V0lfc2?KUTtCUUN AGENCY ------- |