OIL SPILL SCIENCE chapter 2 – spill occurrences a world overview

OIL SPILL SCIENCE chapter 2 – spill occurrences a world overview OIL SPILL SCIENCE chapter 2 – spill occurrences a world overview OIL SPILL SCIENCE chapter 2 – spill occurrences a world overview OIL SPILL SCIENCE chapter 2 – spill occurrences a world overview OIL SPILL SCIENCE chapter 2 – spill occurrences a world overview OIL SPILL SCIENCE chapter 2 – spill occurrences a world overview

Spill Occurrences: A World

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2.1 INTRODUCTION

Asked to picture an oil spill, most people envision a large tank ship (tanker)grounded on a large rock or reef after having gone off-course in a storm ordue to navigational errors Depending on one’s frame of reference andnationality, this might be the Exxon Valdez incident, the Hebei Spirit spill,

or perhaps the Prestige spill Oil-coated beaches, dead birds, angry ermen, and massive cleanup efforts complete the picture Although thesetypes of “catastrophic” spill incidents do indeed occur occasionally andreceive considerable media coverage, they are, fortunately, relatively rareevents

fish-Much more commonly, oil spills are much smaller in scope On any givenday, hundreds, if not thousands, of spills are likely to occur worldwide in manydifferent types of environments, on land, at sea, and in inland freshwatersystems The spills are coming from the various parts of the oil industrydfromoil exploration and production activities, from transport of that oil by tankships, pipelines, and railroad tankcars to the refineries, and from the refinerieswhere the oil is refined to create the many types of fuels that are then trans-ported by pipeline, rail, truck, or tank vessel to the consumers of that oil.Consumption-related spillage comes from manufacturing facilities, nontankvessels that carry oil only as fuel and for machinery, tanker trucks bringing oils

to service stations and heating oil tanks, and many miscellaneous sources Thespills occur because of structural failures, operational errors, weather-relatedOil Spill Science and Technology DOI: 10.1016/B978-1-85617-943-0.10002-4

events, earthquakes, human errors and negligence, and even vandalism orterrorism The spills involve many different types of oil ranging from varioustypes of crude oil to a large array of refined products, from heavy persistentfuels to lighter, less persistent, but very toxic lighter fuels.

Because each spill occurs in a different location under different stances of oil type and volume, proximity to sensitive resources, season,weather effects, and currents, each spill is a relatively unique event in terms ofimpacts, damages, and response challenges

circum-2.2 EXECUTIVE SUMMARY

Worldwide oil spillage rates have decreased dramatically since the 1960sand 1970s, from about 635,000 tons annually to about 300,000 tons peryear from all sources, not counting the anomalous intentional spillageassociated with the 1991 Gulf War, which amounted to over 82 million tons

on land and at sea The largest sources of oil spills in the last two decadeshave been related to oil transportation by tank ships (tankers) or throughpipelines

Oil inputs from spills and other chronic discharge sources, such as urbanrunoff, refinery effluents, and vessel operational discharges, currently totalabout 1.2 million tons worldwide annually While most spills are relativelysmall and cause localized impacts, occasionally very large spills occur thatcause significant environmental and socioeconomic damages Despite signifi-cant progress in reducing spillage through a variety of technological andregulatory prevention measures along with better industry practices, the risk forsignificant oil spills remains

A more detailed analysis of oil spillage in the United States, for whichthere are more accurate data than many other parts of the world, reveals thatduring the decade of 1998e2007, inland pipelines spilled an average ofnearly 11,000 tons annually, with the next largest source being refineries,which spilled 1,700 tons Inland tanker truck spills amounted to 1,300 tonsannually Tank ships only spilled an average of 500 tons annually during thisdecade Nevertheless, the risk for large spills from tank ships, facilities, andoffshore oil exploration and production, all of which contain large volumes

of oil, remains a concern for contingency planners and spill responders

2.3 OVERVIEW OF SPILL OCCURRENCES

2.3.1 Natural Oil Seepage

Oil slicks on water and oiled shorelines are not new phenomena A considerableamount of crude oil is discharged each year from “natural seeps”dnaturalsprings from which liquid and gaseous hydrocarbons (hydrogen-carboncompounds) leak out of the ground Oil seeps are fed by natural underground

8 PART | I Introduction and the Oil Spill Problem

accumulations of oil and natural gas Oil from submarine (and inland ranean) oil reservoirs comes to the surface each year, as it has for millions ofyears due to geological processes.

subter-Natural discharges of petroleum from submarine seeps have been ded throughout history going back to the writings of Herodotus1 and MarcoPolo.2 Archaeological studies have shown that products of oil seeps wereused by Native American groups living in California, including the Yokuts,Chumash, Achomawi, and Maidu tribes, well before the arrival of Europeansettlers.3

recor-In recent times, the locations of natural seeps have been used for ration purposes to determine feasible locations for oil extraction Regionalassessments of natural seepage have been conducted in some locations,particularly nearshore in California,4-7the Indian Ocean,8-10and the Gulf ofMexico.11The most comprehensive worldwide assessment of natural seepage

explo-is still the study conducted by Wilson et al.12 Even the two more recentinternational assessments of oil inputs into the sea13 relied heavily on theestimates of natural oil seepage conducted by Wilson et al.,12having found

no more recent comprehensive studies While industry studies have beenconducted for the purpose of determining potential locations for oil explo-ration and production using various forms of increasingly sophisticatedtechnology, no results have been openly published in the scientific or tech-nical literature

Natural seeps are of such great magnitude that, according to theprominent geologists Kvenvolden and Cooper,14 “natural oil seeps may bethe single most important source of oil that enters the ocean, exceedingeach of the various sources of crude oil that enters the ocean through itsexploitation by humankind.” Assessments of natural oil seepage involve fewactual measurements, though certain seep locations along the SouthernCalifornia coast of the Pacific Ocean have been studied to some extent.Natural seep studies have also included identification of hydrothermicallysourced hydrocarbons (especially polycyclic aromatic hydrocarbons) insediments The most well-known studies have relied on estimation meth-odologies based on field data, observations, and various basic assumptions.Wilson et al estimated that total worldwide natural seepage ranged from0.2 to 6.0
106tonsyannually, with the best estimate being 0.6
106tons,based largely on observations of seepage rates off California andwestern Canada.12 Estimates of the areas of ocean with natural seeps areshown inTable 2.1, and estimates of seepage rates by ocean are shown in

Table 2.2

y Oil measurements are in metric tons (tons) Within the industry, oil is often measured in barrels (equivalent of 42 U.S gallons or 159 liters), roughly equal to one-seventh of a ton, depending on specific gravity Conversion between tons (weight) and barrels (volume) is per the formula: tons ¼ 0.173
barrels
specific gravity.

Wilson et al based their estimates on five basic assumptions: More seepsexist in offshore basins than have been observed; factors that determine seepagerates in a particular area are related to general geological structural type andstage of sedimentary basin evolution; seepage is dependent on the area ofexposed rock rather than on rock volume; most marine seeps are clustered atcontinental margins; and seepage rates are lognormally distributed.12

TABLE 2.2 Summary of World Seepage Rates (based on Wilson et al.12

z Probability percentile 16 with a worldwide estimate of 6
10 6 tons annually, likely a high estimate.

x Probability percentile 1.0 with a worldwide estimate of 0.6
10 6 tons annually.

**Probability percentile 0.3 with a worldwide estimate of 0.2
10 6 tons annually, likely a minimal estimate.

TABLE 2.1 Seepage-prone Areas of the World’s Oceans (based on

Low-potential Seepage

Kvenvolden and Harbaugh15 concluded that the minimal worldwide mate (0.2
106tons annually) from the Wilson et al.12 study is most likelycorrect and that an error margin of an order of magnitude above and below thisvalue should be applied (i.e., 0.02
106 to 2.0
106 tons annually) Theirtheory was based on a reduced value for the assumed and known oil resourcesthat would be available for seepage There is some evidence that seepage ratesare decreasing in some locations, such as those near Coal Point, off SantaBarbara, California.16

esti-In a 2003 National Research Council (NRC) study, a worldwide estimate ofnatural seepage into the marine environment of between 0.02
106to 2.0
106tons annually was made, with a “best estimate” of 600,000 tons.17 Theseestimates were made based on the Kvenvolden and Harbaugh15reassessment ofthe estimates made by Wilson et al.,12as well as an acceptance of the originalestimates of Wilson et al.,12 resulting from a “new appreciation” for themagnitude of natural seepage, particularly in the Gulf of Mexico Relyinglargely on the Wilson et al.12and Kvenvolden and Harbaugh15studies, the 2007Joint Group of Experts on Scientific Aspects of Marine Protection (known asGESAMP) study on oil inputs into the marine environment included an esti-mate of the range of natural seepage as 0.22.0
106tons per year, with a bestestimate of 600,000 tons per year.13

Natural seeps often release oil sporadically in relatively small amounts, butoccasionally release larger amounts that can have the same environmentalimpacts as crude oil spills from tankers or other sources But while naturalseeps have had impacts on the marine and terrestrial environment sinceprehistoric times, it was not until the occurrence of several larger anthropogenicoil spills in the late 1960s, which coincided with a greater public awareness

of general environmental issues, that concern over oil pollution came to theforefront

2.3.2 Historical Concern Over Oil Pollution

When the tanker Torrey Canyon spilled 130,000 tons of crude oil off thewestern coast of the UK in March 1967, killing 15,000 seabirds and oilingnearly 300 kilometers of English and French coastline, there was a large publicoutcry The environmental damage from this spill was multiplied by the use ofhighly toxic first-generation dispersant chemicals in the response

The Torrey Canyon spill was not the first oil tanker spill by any means

A large number of oil tankers were torpedoed and sunk during World War II.According to Campbell et al., during the first six months of 1942 alone, a total

of 484,200 tons of oil were released from torpedoed tankers within 90 meters of the eastern U.S coast.18This came to about one tanker spill of about20,000 tons per week over six months Cleanup efforts consisted of burningincidental to the torpedoing and minimal cosmetic actions on swimming bea-ches While the occurrence of these incidents during wartime may explain the

kilo-relatively low concern about environmental damage from the spilled oil, therewas, arguably, a general lesser awareness of environmental protection in thesetimes as well.

The Torrey Canyon spill in 1967 was notable in that when it occurred, it isthe largest spill to date The tanker’s capacity had recently been increased tohold 130,000 tons of oil cargo Subsequently, there were at least five signifi-cantly larger worst-case discharge (complete cargo loss) tanker spills, as well asseveral other large spills associated with oil wells and pipelines Following onthe 1967 Torrey Canyon incident, the 1969 Union Alpha Well 21 blowout offSanta Barbara, California, which released 14,300 tons of crude oil, is oftencredited with being the impetus for the environmental movement in the UnitedStates, as well as for the establishment of the federal Environmental ProtectionAgency (EPA).19

In the 1970s, other significant oil spills around the world brought greaterattention to the problem on an international scaledthe tanker Metula (Chile in1974), the tanker Urquiola (Spain in 1977), the tanker Amoco Cadiz (France

in 1978), the largest tanker spill of all time, Atlantic Empress (Trinidadand Tobago/Barbados in 1979), and the largest nonewar-related spill inhistorydthe Ixtoc I well blowout (Gulf of Mexico in 1979).20The largest oilspills in history are listed inTable 2.3

The 1989 tanker Exxon Valdez spill in Alaska is perhaps the most notoriousspill incident, though it is by no means the largest The spillage of over 37,000tons of Alaskan crude oil into what was considered to be a “pristine” location,Prince William Sound, precipitated the most expensive and the lengthiest spillresponse and damage settlements in history Its repercussions were felt world-wide, resulting in the passage of significant spill prevention and liability legis-lation in the United Statesdthe Oil Pollution Act of 1990 (OPA 90)das well asinternational conventions on spill prevention that included such measures as therequirement for double-hulls on tankers by 2015 and increased financial liability.The significant financial consequences for tanker owners and operators as

a result of the Exxon Valdez spill and the spiller liability inherent in subsequentregulations brought the consequences for spills to an unprecedented level Thefinancial risk associated with large spills may have had as much impact on spillprevention as any actual preventive measures, such as double-hulls on tankers

2.3.3 Sources of Oil Spills and Patterns of Spillage

Spills occur around the worlddanywhere that oil is produced, transported,stored, or consumed The vast majority of spills are relatively small As shown

inFigure 2.1, 72% of spills are 0.003 to 0.03 ton or less The total of amount ofthese small spills comes to 0.4% of the total spillage The largest spills (over 30tons) make up 0.1% of incidents but involve nearly 60% of the total amountspilled Naturally, the relatively rare large spill incidents get the most publicattention owing to their greater impact and visibility, though spill size itself is

12 PART | I Introduction and the Oil Spill Problem

TABLE 2.3 Largest Oil Spills in History Worldwide Environmental ResearchConsulting (ERC data)**

19-Jul-1979 T/V Atlantic Empressx Trinidad/Tobago 286,354

6-Aug-1983 T/V Castillo de Bellver South Africa 267,007

(Continued )

TABLE 2.3 Largest Oil Spills in History Worldwide Environmental ResearchConsulting (ERC data)**dcont’d

14 PART | I Introduction and the Oil Spill Problem

not a direct measure of damage Location and oil type are extremely important

in determining the degree of environmental and socioeconomic damage.Oil spills and discharges* can occur at any point in the “life cycle” ofpetroleumdduring oil exploration and production; transport by vessel, pipe-line, railroad, or tanker truck; refining; storage, consumption or usage as fuel

or as raw material for manufacturing; or waste disposal The regional andnational patterns of spillage depend on the oil-related activities in those

TABLE 2.3 Largest Oil Spills in History Worldwide Environmental ResearchConsulting (ERC data)**dcont’d

*“T/V” ¼ “tank vessel” and refers to tank ships or tankers.

**Ended in January 2010.

y War-related intentional spillage.

z Several intentional spills occurred nearly simultaneously during the 1991 Gulf War They are often aggregated into one large “spill.” In this list, the individual spill sources are separated.

x T/V Atlantic Empress spilled 145,250 tons of oil off Trinidad and Tobago on 19 July 1979, then another 141,000 tons while under tow off Barbados.

* A “spill” is a discrete event in which oil is accidentally or, occasionally, intentionally released A

“discharge” is a legal permitted release of oil (usually in a highly diluted state in water) as part of normal operations.

locations, the amount of oil handled, and the degree to which oil preventionmeasures have been implemented and enforced.

Overall, oil spillage has decreased significantly in the United States andinternationally due to the implementation and enforcement of preventionmeasures as well as more responsible operations on the part of the shipping andoil industries.13,17,21,22

In the 1970s, an estimated 6.3 million tons of oil spilled into marine watersfrom all sources, excluding war-related incidents.22By the 1980s, an estimated3.8 million tons of oil spilled worldwide, a 40% reduction since the decade1988e1997 Spillage reduced another 20% by the 1990s

These reductions in spillage are all the more remarkable considering theincreases in production, shipping, and handling of oil during this time period(Table 2.4)

In a series of studies that estimated total oil inputs into the marine ronment from spills, as well as from operational discharges*from shipping andother sources, especially urban runoff,ya definitive trend of input reduction isapparent (Table 2.5) It is important to note that some of the variations betweenthe studies are due to differences in methodology rather than to actual differ-ences in inputs

FIGURE 2.1 Size classes of U.S marine oil spills, 1990e1999 (ERC data).

* A legal permitted release of oil (usually in a highly diluted state in water) as part of normal operations.

y “Urban runoff” is the accumulation of drops of oil that leak from automobiles, trucks, and other vehicles, as well as small chronic spillages that occur from other land-based sources The oil washes off into storm sewers, culverts, and other waterways into streams and rivers that enter marine waters Because the exact source of this spillage cannot be pinpointed, it is termed nonpoint source pollution.

16 PART | I Introduction and the Oil Spill Problem

The tracking of oil spills is generally conducted by those authoritiesinvolved in initiating emergency spill response operations, such as CoastGuard agencies or state and local governments The accuracy of reporting,particularly of smaller spills, varies considerably from one jurisdiction toanother There have been increases in the reporting of increasingly smallerspills, though not necessarily in the actual incidence of such spills, whichreflects broader public awareness of spills and greater concern about andresponsibility for these incidents by spillers As larger spills become increas-ingly rarer, it is important that contingency planners and spill respondersmaintain preparedness for these large spills owing to the potential damagesassociated with them.22,23A detailed recent overview of oil spills in the UnitedStates is presented here based on Environmental Research Consulting (ERC)data, along with analytical results from some past international studies on oilspills.24-28

2.3.4 Spillage from Oil Exploration and Production ActivitiesDuring the years 1998e2007, an estimated 182 tons of crude oil spilledannually from offshore exploration and production platforms into U.S waters

An additional 373 tons spilled annually from pipelines associated with offshoreoil production, for a total of 555 tons per year This represents a nearly 66%reduction in spillage since 1988e1997, and an 87% reduction in spillage sincethe 1970s (1969e1977) Oil spillage from offshore platforms in U.S OuterContinental Shelf (OCS) and state waters is shown inFigure 2.2for 1969e2007

TABLE 2.4 Annual Worldwide Marine Oil Spillage (ERC Data)

TABLE 2.5 Estimated Worldwide Oil Inputs Based on Various Studies

yyy Includes 53,000 tons from small-craft activity.

zzz Atmospheric deposition of petroleum hydrocarbons from volatile organic compounds (VOCs) that evaporate during the handling of oil and incomplete fuel combustion that are then deposited into the sea.

xxx Does not include urban runoff.

Average platform spillage by decade is shown inTable 2.6 There has been a 30%reduction in annual spillage since 1988e1997 and a 95% reduction since the1970s.

Annual oil spillage from pipelines connected to offshore platforms is shown

inFigure 2.3, and by decade inTable 2.7 There has been a 68% reduction inoffshore pipeline spillage since 1988e1997 Of the total spillage, 96% is in theGulf of Mexico Offshore oil exploration and production spillage was combined

to include offshore platforms and pipelines, as well as offshore supply vesselsservicing the platforms, as shown inTable 2.8 There has been a 61% reduction

in total spillage since 1988e1997 and an 87% reduction since the 1970s

FIGURE 2.2 Annual U.S offshore oil platform spillage, 1969e2007 (ERC data).

TABLE 2.6 Average Annual Spillage from U.S Offshore Oil Platforms

Oil spillage per production (i.e., barrels spilled per barrels produced) hasdecreased over time, as shown inTable 2.9 In other words, despite increases inproduction, spillage rates have decreased For every ton of oil produced in theUnited States, less than 0.000005 tons have spilled from offshore explorationand production activities in the last decade This is a 71% reduction since the1988e1997 decade and an 87% reduction since the 1969e1977 decade.While the majority of oil production spills have been recorded in offshorewaters, there are reported spills of inland-based oil production wells to inlandareas, as shown inTable 2.10.

During the oil extraction process at offshore oil platforms, water in the oilreservoir is also pumped to the surface Industry practice is to treat this

FIGURE 2.3 Annual oil spillage from U.S offshore pipelines, 1969e2007 (ERC data).

TABLE 2.7 Average Annual Spillage from U.S Offshore Oil Pipelines(ERC data)

Years

Average Annual Spills One Ton or More

Average Annual Tons Spilled

“produced water” to separate free crude oil, and then to inject the water backinto the reservoir, or to discharge the water overboard from the platform.Increasingly, the reinjection process is becoming the preferred technique Thehighly diluted oil content in produced water (with a maximum allowable oil

TABLE 2.9 U.S Offshore Oil Exploration/Production Spillage per

Production (ERC data)

Years Average Annual Tons Spilled per Tons Produced

content of 29 ppm) from offshore oil exploration and production processes isgenerally dispersed very quickly in the open waters where offshore oil plat-forms are located The impacts from these inputs in offshore waters have beenstudied extensively, and, as concluded by the 2003 NRC study, “there is littleevidence of significant effects from petroleum around offshore platforms indeep water.”17The oil inputs from produced water are calculated as shown in

Table 2.11don average, 2,500 tons per year, based on the methodology used

by the 2003 NRC study based on measurements and assumptions of maximumallowable oil content in produced water (“high”) or lower oil content asreported by offshore operators.17It is important to note that these inputs arepermitted operational discharges that are distinct from accidental spillagepreviously reviewed

Worldwide estimates on oil spillage and discharges from offshore oilexploration and production activities are shown inTable 2.12

The greatest concern associated with oil pollution from offshore oil and gasexploration is the unlikely event of a catastrophic well “blowout”* The largestwell blowout incidents worldwide are shown inTable 2.13 Fortunately, mostblowouts release relatively little oil.29

TABLE 2.11 Estimated Oil Inputs in Produced Water from U.S Offshore OilExploration/Production

U.S Region

Produced Water (tons/yr)

Oil/Grease Content (ppm)

Oil/Grease Discharge (tons/yr) Low High “Best” * Low High “Best”

*Best estimate as determined by panel of experts in the 2003 NRC study 17

* Loss of well control or a blowout is defined as: the uncontrolled flow of formation or other fluids, including flow to an exposed formation (an underground blowout) or at the surface (a surface blowout), flow through a diverter, or uncontrolled flow resulting from a failure of surface equipment or procedures.

22 PART | I Introduction and the Oil Spill Problem

2.3.5 Spills During Oil Transport

After extraction from offshore or terrestrial wells, oil is transported by a variety

of means to refineries and ultimately to industrial or individual consumersdbytank vessel (tank ships or tankers; tank barges), pipeline, railroad, and tankertruck, each potentially a source of spillage

2.3.5.1 Spillage from Tank Vessels

Tank ships can carry the greatest amount of oildas much as 300,000 tonsdandthus can be the sources of the largest transport-related spills Tank ships (tankers)carrying crude oil or refined petroleum as cargo spilled an average of 514 tons ofoil annually in U.S waters over the last decade, a 90% reduction since the decade1988e1997 A breakdown of annual spillage from oil tankers is shown in

Figure 2.4 Average annual spillage by decade is shown inTable 2.14

Tank barges carrying oil as cargo spilled an average of 771 tons of oilannually over the last decade, a nearly 67% reduction from the spillage in thedecade 1988e1997 Annual spillage volumes are shown in Figure 2.5 Abreakdown of average annual spillage from oil tank barges is shown inTable2.15 Oil transport by tank vessels (tankers and barges) has decreased over thelast decades in the United States

Oil spillage from tank vessels in the United States in relation to oil ported by this mode decreased by 71% since the decade 1988e1997 and 81%since the 1980s (Table 2.16) Worldwide estimates of tanker and tank bargespillage made in international studies are shown inTable 2.17

trans-TABLE 2.12 Worldwide Spillage and Discharge from Offshore Oil

Exploration and Production

Study

Estimate Year

Annual Oil Input Estimate (tons) Spillage Operational Atmospheric Total

2.3.5.2 Spills from Pipelines

In inland areas, underground and above-ground pipelines transport large tities of crude oil and refined fuels, particularly diesel, gasoline, heavy fuel oil,and trans-mix.*Spillage from pipelines in coastal and inland areas is shown in

quan-Table 2.18andFigure 2.6 During the last decade, coastal and inland pipelinesspilled an average of 11,000 tons of oil annually This represents a 35%reduction in spillage since 1988e1997 and 70% since the 1970s In theseanalyses, coastal and inland pipelines were considered to encompass all parts ofthe pipeline system, including gathering pipes, transmission pipes, breakouttanks, pump stations, and tank farms directly associated with and operated bypipeline companies Offshore pipelines were considered separately under

TABLE 2.13 Largest Offshore Exploration and Production Well BlowoutsWorldwide (ERC data)

Funiwa 5

Forcados, Nigeria January 1980 28,571 Aramco Hasbah 6 Gulf, off Saudi Arabia October 1980 15,000 Iran Marine

December 1970 7,585

* Usually a combination of No 2 fuel oil (diesel) and No 6 heavy fuel oil.

24 PART | I Introduction and the Oil Spill Problem

offshore exploration and production It should be noted that a significant portion

of oil (about 85%) that spills from inland pipelines goes to containment areasaround breakout tanks or to solid ground rather than directly into surface waters.With concerns about the aging pipeline infrastructure and vulnerability ofpipelines for spillage, there have been a number of regulatory changes forpipelinesdthe Oil Pollution Act of 1990 (OPA 90), the 2002 Pipeline SafetyAct (PSA), and the 2006 Pipeline Integrity, Protection, Enforcement, andSafety (PIPES) Act, which have improved pipeline safety and reduced spillage.Pipeline spillage amounts by oil type and per unit of oil transport are shown in

Table 2.19 Spillage per unit transport has decreased 37% since the decade1988e1997, and 57% since the 1980s

FIGURE 2.4 Spills into U.S waters from tank ships, 1962e2007 (ERC data).

TABLE 2.14 Average Annual Oil Spillage from Tank Ships in U.S Waters(ERC data)

Years

Average Number

of Spills One Ton or More

Average Annual Tons Spilled

2.3.5.3 Spills from Railroads

Railroads spilled 200 tons of oil annually as cargo in tankcars and as fuel This

is a 34% reduction since the decade 1988e1997 Average annual railroadspillage and spillage by ton-miles transported are shown inTable 2.20 (A ton-mile is a measure of the transport of oil one ton the distance of one mile.) Thespillage rate has decreased in the last three decades Spills from railroads often

go to ballast and do not always directly impact waterways

2.3.5.4 Spillage from Tanker Trucks

Tanker trucks carrying oil (usually fuels) as cargo spilled an average of 1,300 tons

of oil annually in the last decade, a 76% increase since the decade 1988e1997

FIGURE 2.5 Spills into U.S waters from tank barges, 1968e2007 (ERC data).

TABLE 2.15 Average Annual Oil Spillage from Tank Barges in U.S Waters(ERC data)

Years

Average Number

of Spills One Ton or More

Average Annual Tons Spilled

This may be attributed to better reporting of these incidents to local authorities thatusually handle these incident responses Spills from tanker trucks often go topavements and do not directly impact waterways Average annual spillage is in

Table 2.21 There are no reliable international data on this source type

TABLE 2.16 Oil Spillage by Tank Vessels in Relation to Oil Transported inU.S Waters (ERC data)

Time Period

Average Annual Spillage

(tons) Average Annual Spillage

per Billion Ton-Miles *

Oil Transport Tankers Tank Barges Combined

*Ton-miles combine volume and distance of transport.

TABLE 2.17 Estimates of Worldwide Annual Tank Vessel Spillage

*Includes operational discharges from vessels.

y Includes 1991 Gulf War-related tanker spillage.

z Excludes 1991 Gulf War-related tanker spillage.