OCS Study MMS 2000-007 

Estimation of Oil Spill Risk From Alaska North Slope, TransAlaska Pipeline, and Arctic Canada Oil Spill Data Sets 

April 2000 

Prepared by: 

Hart Crowser Inc. 

2550 Denali Street, Suite 705 

Anchorage, Alaska 99503 

This study was funded by the U.S. Department of the Interior, Minerals Management Service 

(MMS) Alaska Outer Continental Shelf Region, Anchorage, Alaska, under Contract No. 01-99-

PO-16128, as part of the MMS Alaska Environmental Studies Program 

The opinions, findings, conclusions, or recommendations expressed in this report or product are 

those of the authors and do not necessarily reflect the views of the U.S. Department of the 

Interior, nor does mention of trade names or commercial products constitute endorsement or 

recommendation for use by the Federal Government. 

U.S. Department of the Interior 

Minerals Management Service 

Alaska Outer Continental Shelf Region 
 2 

Estimation of Oil Spill Risk From Alaska North Slope, Trans-Alaska Pipeline, and Arctic 

Data Sets 

Jeffery L. Mach, Robert L. Sandefur, P.E., and Jean H. Lee OCS 

 i 

PROJECT ORGANIZATION 

Hart Crowser, Inc., study team: 

Thomas K. Noyes Principal in charge 

Jeffery L. Mach Project manager 

Oil spill data collection 

Oil production, pipeline throughput, pipeline mileage 

data collection 

Oil spill notification requirements research 

Database manager 

Primary report author 

Robert L. Sandefur Data analysis 

Calculation of oil spill rates 

Report author – Analysis of Data and Calculation of Oil 

Spill Risk Rate 

Jean H. Lee Oil spill data research and collection 

Oil spill notification requirements research and 

collection 

Report author – Canadian portion of Oil Spill 

Notification Requirements 

Michael L. Boese Oil spill data research and collection 

Adam D. Chawes Oil spill data research and collection 
 ii 

TABLE OF CONTENTS 

Project Organization..................................................................................................................... i 

Table Of Contents........................................................................................................................ ii 

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

Introduction ................................................................................................................................. 4 

Methods ....................................................................................................................................... 6 

Results ....................................................................................................................................... 11 

Discussion.................................................................................................................................. 29 

References ............................................................................................................................... 113 

Appendix A - Collated Alaska And Canada Individual Oil Spill Data Used In Study ........... 117 

Appendix B – Statistical Analysis And Oil Spill Rate Calculations Using Alaskan And 

Canadian Spill Data................................................................................................................. 132 
 1 

EXECUTIVE SUMMARY 

The Minerals Management Service Alaska Outer Continental Shelf Region commissioned Hart 

Crowser, Inc. (Hart Crowser) to collect and analyze data to provide an estimation of oil spill risk 

from Alaska North Slope, Trans-Alaska Pipeline (TAPS), and Arctic Canada oil industry 

activities. 

To populate the database needed to perform statistical calculations, data on oil spills of 100 

barrels (4,200 gallons) and greater related to oil industry exploration, construction, development, 

production, transportation, and storage activities from within eight study areas including the 

Alaska North Slope, TAPS, and Arctic Canada were collected from industry, government, and 

commercial sources. Supporting data on annual crude oil production, pipeline mileages, and 

quantities of crude oil transported by pipeline or tank vessel in the study areas were gathered. 

Current and historical oil spill reporting criteria in effect in the study areas also were identified. 

The oil spill data were collated and evaluated for comprehensiveness and completeness. 

Attempts were made to validate the data with government regulatory authorities to which the 

responsible party for a spill was required to report. The reliability of the volumes of spills of 500 

barrels (21,000 gallons) and greater was evaluated based on how the spill volume was 

determined and supporting documentation. The statistical robustness and appropriateness of 

using the collected oil spill data, and the validity of using potential estimators to evaluate oil spill 

risks from Beaufort Sea Outer Continental Shelf (OCS) development were evaluated. Finally, an 

oil spill rate was calculated using the optimum data set, which was corrected for an observed 

time trend in the spill rate. 

Overall, 126 oil spills in Alaska and Canada were identified which met the study criteria. All of 

these spills occurred between 1970 and September 1999. The most recent spill occurred in 1997. 

There are 28 spills of 500 barrels and greater and 14 spills of 1,000 barrels (42,000 gallons) or 

greater. Another 95 spills in the study areas also were identified, but were not included in the 

subsequent analysis because insufficient information existed to allow a conclusive determination 

as to whether the spills met the study criteria. 

Hart Crowser identified 126 spills of 100 barrels and greater that met the study criteria. Of these 

spills, 111 occurred in Alaska and 15 in Canada. The Alaskan oil spills most frequently are 

associated with highway tank vehicle accidents and operations support facilities, followed by 

spills related to construction camps, operations support facilities, and pipelines. Spills associated 

with oil production processing facilities, oil production wells, pipeline pump stations, and 

exploration activities also were identified. No spills meeting the study criteria were identified 

for the Alaska Onshore North Slope (ONS), National Petroleum Reserve Alaska (NPRA), or 

Beaufort Sea study areas. Oil spills meeting the study criteria were identified in each of the 

Canadian study areas. Canadian spill were most frequently associated with oil exploration 

activities, oil production wells, and oil production processing facilities. Spills from highway 

tank vehicles, pipelines, and vessels also were identified. 

Data on the Alaska oil spills were considered to be comprehensive and complete because more 

than 60 percent of the spill records appeared in two or more data sets. The Canadian data are 

more suspect in terms of being comprehensive and complete. Less than 15 percent of the 

Canadian spills appeared in the two data sets obtained. Canadian data since approximately 1980 

are considered good, but anecdotal report and the lack of records provides suspicion that the data 

is not comprehensive. Because of the small number of Canadian oil spills and relatively small 
 2 

amount of Canadian oil production, the Canadian data were not included in the subsequent 

statistical analysis. For both the Alaskan and Canadian oil spill data, the volumes assigned for 

the spills of 500 barrels and larger are reliable, but must be considered as general estimates in 

most cases. Documentation for these spills often does not describe how the spill volume was 

determined. 

The Alaska oil spill data was sufficiently comprehensive and complete to conduct statistical 

analyses and estimate oil spill risk rates. A series of box and cumulative frequency plots of the 

Alaska spill data were constructed to analyze the data and determine trends. Exploratory data 

analysis on relevant independent variables indicated little statistical difference in terms of spills 

that occurred within the Alaska ONS, East of NPRA, and TAPS study areas. A general check 

on the fluctuation of the data set indicated spill occurrence to be quite random. There appeared 

to be little difference in the size of spills associated with the various facilities, with the exception 

of pipelines, which had larger spills. Analysis of variance by oil type showed that, in general 

crude oil spills tend to be larger than other types of oil spills. 

A statistical analysis of individual spill volumes by study area, facility type, oil type, affected 

media, and spill cause combined did not indicate any particularly interesting correlation. 

Annualized groupings of spills, where total spill volumes by year were accumulated and plotted 

on a cumulative frequency plot, showed a mixture of several populations. Re-plotted on a 

logarithmic scale, a single lognormal population emerged. A count of the number of spills per 

year in the database is showed a possible Poisson distribution, but that hypothesis was not tested. 

When spill size was plotted by year to see if regulatory or reporting requirements had a 

significant affect, it appeared that in the period from 1975 to 1979 there were a considerable 

number of large spills, and then the number of spills dropped to a more or less constant rate. The 

year of 1977 is significant because crude oil production on North Slope and operation of TAPS 

began in the middle of that year. However, the years of 1978 and 1979 visually fit with years of 

1975 and 1977 better than breaking the data at 1977. The 1975 to 1979 period appears to have 

the most number of spills. 

When Alaskan spill data were plotted on a yearly basis, it appears that prior to 1977, spill rates 

were considerably greater than in the subsequent years. When re-plotted on a logarithmic scale, 

it is apparent that prior to 1980 spill rates were considerably greater than after 1980. 

Hart Crowser calculated oil spill risk rates based on the number of spills and on volume. Hart 

Crowser calculated a rate based on volume because of the greater visual variability in the data. 

The statistical significance of this visual analysis showed a highly statistically significant 

correlation with spill rate and year if all of the Alaska spill data is included. If data earlier than 

1980 is excluded, then there is still a correlation between spill rate and year that is significant at 

the 1 percent level of confidence. However, if data earlier than 1985 is excluded, then there is a 

correlation between spill rate and year, which is significant at the 17 percent level of confidence. 

Hart Crowser concluded that spill rate is the best variable to use in predicting the volume of 

further oil spills and that a rate of approximately 52 gallons of oil spilled per million barrels of 

crude oil produced will be the average, if trends that started in 1980 continue. This rate is 

subject to considerable uncertainty in the mean (± 50% at the 95% level of confidence) and the 

value derived from the logarithmic distribution is 66 gallons of oil spilled per million barrels of 

crude oil produced as opposed to 52 gallons of oil spilled per million barrels of crude oil 

produced. These two values agree within the standard deviation of the means. The 95 percent 
 3 

logarithmic confidence limits on spills for a given year are ± 465 percent at the 95 percent level 

of confidence. Hart Crowser is more inclined to believe the logarithmic values than the 

untransformed values, because the cumulative frequency of the data is more lognormal than 

normal. These very wide confidence limits and individual yearly values are consistent with the 

small number of data points available for this prediction. 

Hart Crowser also calculated oil spill risk rates based on the number of spills of a given volume 

per million barrels of crude oil produced (spills/MMBbl), using data from 1978 through 1999. 

Hart Crowser found these rates to be: 

• 0.0053 spills/MMBbl, ±24 percent, for spills of 100 barrels and greater; 

• 0.00093 spills/MMBbl, ±58 percent, for spills of 500 barrels and greater; 

• 0.00039 spills/MMBbl, ±89 percent, for spills of 1,000 barrels and greater; and 

• 0.000078 spills/MMBbl, ±200 percent, for spills of 10,000 barrels and greater. 
 4 

INTRODUCTION 

In the development of environmental analyses for proposed Outer Continental Shelf (OCS) 

Beaufort Sea oil exploration and development off of Alaska’s North Slope, the U.S. Department 

of the Interior Minerals Management Service (MMS) OCS Region uses national OCS statistics 

to estimate the likelihood that large oil spills of 1,000 barrels (42,000 gallons) or larger will 

occur as a result of oil exploration, construction and development, production, and transportation 

activities. These national statistics primarily are from the Gulf of Mexico and do not include 

pipeline spills inshore of the OCS, in state waters, or on land. The MMS Alaska OCS Region 

desires to estimate oil spill frequency based on Alaska North Slope and Canadian Arctic, rather 

than Gulf of Mexico oil exploration, construction and development, production, and 

transportation experience. 

The MMS contracted Hart Crowser to gather data and provide oil spill risk occurrence estimators 

for OCS Beaufort Sea oil exploration and development based on Alaska North Slope and 

Canadian Arctic statistics. More specifically, the scope of work directed Hart Crowser to: 

• Identify, obtain relevant supporting information, and collate data for crude oil and diesel 

oil spills of 100 barrels and greater related to oil and gas exploration, construction, 

development, production, transportation, and storage from within the following study 

areas: 

o U.S. Beaufort Sea; 

o Canadian Beaufort Sea; 

o National Petroleum Reserve Alaska (NPRA); 

o Alaska Onshore North Slope (ONS) East of NPRA; 

o Trans-Alaska Pipeline System, not including the Valdez Marine Terminal; 

o Onshore McKenzie River Delta; 

o Canadian High Arctic Islands; and 

o Norman Wells. 

• Compare data sets from different sources for the same area to increase the 

comprehensiveness and completeness of the data. 

• Identify the oil spill reporting criteria in effect for oil spills in the study areas and validate 

the oil spill data with the regulatory authority to which the responsible party for the spill 

was required to report. 

• Describe the overall comprehensiveness and completeness of the collected oil spill data. 

• Evaluate the reliability of the volumes of spills of 500 barrels and greater, based on how 

the spill volume was determined and supporting documentation. 

• Obtain and collate data on crude oil production, pipeline throughput, tanker shipments, 

and pipeline mileage by year for the Alaska and Canada study areas. 

• Examine the appropriateness of using the collected oil spill data to evaluate oil spill risks 

from Beaufort Sea OCS development, partly in the context of prior MMS uses and 

statistical evaluations of oil spill rates for OCS use. 
 5 

• Consider the statistical robustness and validity of potential oil spill risk estimators, 

including the: 

o Effect of one or more spills on the estimators; 

o Size of the data set for spills of 100 barrels or more and 500 barrels or more; 

o Rationale for including or excluding intentional spills; 

o Effect of incomplete pipeline life cycles in the data set; 

o Correlation of pipeline mileage and/or oil production or throughput volumes with 

spillage; 

o Differences in size of onshore and offshore oil spill data subsets; 

o Magnitude of the record (i.e., number and volumes of spills) used to calculate oil 

spill risk estimators versus that used by Anderson and LaBelle (1994); and 

o Postulated differences, or lack thereof, in onshore and offshore oil spill risk 

factors. 

• Calculate onshore and offshore oil spill rates using the optimum data sets and including 

corrections for time trends in spill rates, if statistically appropriate. 

• Prepare draft and final reports and technical summaries concerning the study, and 

appendices containing the oil spill and supporting data sets. 
 6 

METHODS 

Oil Spill Data Collection

Alaskan Oil Spill Data 

Hart Crowser gathered the Alaskan oil spill data used in this study using information contained 

in electronic spreadsheet and database files, and from written records. The data was obtained 

from federal and state agencies, major Alaskan oil industry companies, and one commercial 

source. Methods used to gather these data are described below. 

The MMS Alaska OCS Office provided Hart Crowser with Alaska oil spill data gathered prior to 

the study by MMS from: 

• BP Exploration (Alaska) Inc. (BP); 

• ARCO Alaska Inc. (ARCO); 

• Alyeska Pipeline Service Company (Alyeska); 

• U.S. Department of the Interior and Alaska Department of Natural Resources, Alaska 

Joint Pipeline Office (JPO); 

• U.S. Department of the Interior Bureau of Land Management (BLM), Alaska Office of 

Special Projects; 

• Alaska Department of Environmental Conservation (ADEC); and 

• The Oil Spill Intelligence Report (OSIR). 

Hart Crowser contacted each of the data sources listed above, except OSIR, by telephone to 

obtain updated or additional oil spill data. Hart Crowser also contacted the U.S. Environmental 

Protection Agency (EPA), Alaska Operations Office by telephone and the National Response 

Center, Washington, D.C., in writing, to obtain available data on Alaskan oil spills meeting the 

study criteria. 

Hart Crowser identified the location of potentially useful files from inquiries made to 

knowledgeable ADEC staff. Hart Crowser researchers traveled to ADEC’s Fairbanks and 

Valdez offices, and gathered oil spill data, supporting information, and documentation directly 

from the active and archived oil spill files in those offices. Hart Crowser also searched for 

Alaskan oil spill data on the Internet and in the collection of the Alaska State Library in Juneau, 

which contains documents from the ADEC’s former library. 

Canadian Oil Spill Data 

Hart Crowser contacted the following organizations by telephone and inquired about the 

availability of oil spill data for the Canadian study areas: 

• Department of Indian Affairs and Northern Development (DIAND; also known as Indian 

and Northern Affairs Canada); Toronto, Ontario offices; 

• National Energy Board Canada (NEB); Edmonton, Alberta offices; 

• Environment Canada (EC), Prairie and Northern Region; Yellowknife, Northwest 

Territories office; 

• Coast Guard Canada (CGC); Ottawa, Ontario office; and 
 7 

• Government of the Northwest Territories (GNWT); Environmental Protection Service 

(EPS); Yellowknife, NWT office. 

Oil spill records also were contained in the OSIR summary provided by MMS and reviews of the 

OSIR Oil Spills: International Summary and Review 1978-1981 and Oil Spills: International 

Summary and Review 1982-1985 were conducted to look for Canadian oil spills that met the 

study criteria. Hart Crowser also searched the Internet for documents that contained information 

on Canadian oil spills meeting the study criteria. 

Oil Spill Data Evaluation and Collation 

Alaskan and Canadian oil spill records were initially transferred from existing electronic files, or 

were entered directly from written records, into Microsoft Excel spreadsheets. Each 

spreadsheet contained oil spill records from a specific source. Each spreadsheet was reviewed 

and those spill records that were judged to meet the study criteria were transferred into a 

Microsoft Access 97 database. This database contained all of the oil spill records subsequently 

used in the study. Spreadsheets and databases were maintained exclusively by the project data 

manager. 

The spill records in the database containing all of the records were sorted to identify individual 

spills appearing in more than one data set. In cases where a spill record was found only in one of 

the data sets, the other relevant data sets Hart Crowser had obtained were cross checked to 

determine if they contained a similar spill record that had not been included in the database for 

some reason. Spill records were added to or deleted from the database of all spill records based 

on information found in the data sets, in written records, or interviews with knowledgeable 

individuals concerning specific spills. 

Hart Crowser also assembled a database of oil spills that were excluded from the study because 

Hart Crowser could not determine whether these spills met the study criteria. Hart Crowser did 

not attempt to assemble a listing of all spill records reviewed and included in, or excluded from, 

the study. 

Using the database of all oil spill records included in the study, Hart Crowser then assembled a 

collated database of the oil spills. Records from different data sets for an individual spill were 

compared with one another, and a single spill record for the collated database was created based 

on all of the records for the spill. Differences in individual spill records among the different data 

sets, including spill date, location description, spiller identity, oil type, and spill quantity were 

reconciled as much as possible by comparing the data in the different records and making 

inquiries about particular spills to the owners of the spill records or to individuals knowledgeable 

about the spill. Where differences between spill records for the same spill continued to exist, 

deference for use in the collated database was given to the data in the regulatory agency spill 

records. Where different spill dates were found among data sets, a single date was used in the 

collated database, typically the date used in the ADEC’s databases or that agency’s records. 

Where different oil spill quantities were reported in different data sets or where the spill quantity 

was reported as a range, a range was used in the collated database, using the range of spill 

quantities found among the data sets. 

Oil Spill Data Comprehensiveness and Completeness

Hart Crowser felt that it would assemble the most comprehensive and complete data possible, 

within the time and resource limits of the study, by obtaining oil spill data from as many sources 
 8 

as possible. To that end, Hart Crowser contacted organizations that were believed or known to 

have oil spill records relevant to the study. Included in the search for oil spill data relevant to the 

study were regulatory agencies that had or have legal requirements for oil spill reporting and 

cleanup; major oil exploration, production, and pipeline operating companies; and the OSIR, 

commercial publication specializing in oil spill information. Because Hart Crowser knew that 

ADEC’s oil and hazardous substance spill databases were incomplete, reviews of document files 

were conducted in an attempt to gather comprehensive and complete data for the study. 

Hart Crowser analyzed the list of collated spills to determine how many spills appeared in two or 

more data sets. Whether a particular oil spill was found in more than one data set, whether the 

data for a particular spill was substantially the same between data sets, and whether data required 

for the study was found among the data sets was used as a guide in judging the 

comprehensiveness and completeness of the data. Hart Crowser also evaluated whether there 

was a correlation between the size of oil spills versus the occurrence of the spills in multiple 

databases for oil spills in the Alaskan and Canadian study areas, as a potential indicator of 

whether larger spills are more likely to be recorded. 

Reliability of Oil Spill Volume Determinations

During reviews of the written oil spill records from Alaska and Canada Hart Crowser researchers 

searched for information in the records indicating how oil spill volume determinations had been 

made to allow Hart Crowser to gauge the reliability of the spill volumes contained in the records. 

Oil Spill Notification Requirement Data Collection

United States and Alaska Notification Requirements 

Hart Crowser reviewed copies of current and historical federal and Alaska statutes and 

regulations in the Alaska Court System Law Library and the Alaska State Library at Juneau. The 

MMS provided Hart Crowser with additional information on oil spill notification requirements in 

Alaska. 

Canadian Notification Requirements 

Hart Crowser reviewed copies of current statutes and regulations obtained from the Canada 

Department of Justice and the GNWT. Some historical statutes and regulations also were 

obtained and reviewed. Hart Crowser also interviewed representatives of the GNWT EPS and 

the NEB concerning current and historical oil spill notification requirements. 

Crude Oil Production and Transportation Data Collection

Alaska Crude Oil Production, and Pipeline Mileage and Throughput Data 

The Alaska Department of Natural Resources (ADNR), Division of Oil and Gas was contacted to 

obtain annual crude oil production and pipeline throughput statistics. ADNR obtains production 

data monthly from the Alaska Oil and Gas Conservation Commission (AOGCC) and publishes 

annual summary statistics as part of its periodic publication, Historical and Projected Oil and 

Gas Consumption. 

The JPO was contacted to obtain the mileages of “regulated pipelines” (i.e., those pipelines 

regulated by the U.S. Department of Transportation and by right-of-way leases issued by the 

State of Alaska or the BLM). Hart Crowser consulted the Trans-Alaska Pipeline Atlas, Prudhoe 

Bay to Valdez (Alyeska, 1993) to obtain the mileage of the TAPS. 
 9 

Telephone inquiries were made to ARCO and BP staff members at the respective companies’ 

Anchorage headquarters and the individual oil production units concerning the mileages of the 

smaller field gathering lines (also called cross-country lines) in the individual production units. 

The field gathering lines, typically ranging in size from 8 to 30 inches in diameter, run from oil 

production pads to processing facilities and from processing facilities to sale oil pipelines or to 

Pump Station 1. 

Throughputs for individual oil sales pipelines were calculated from the annual crude oil 

production quantities of the particular North Slope oil fields or operating units as reported in 

ADNR’s Historical and Projected Oil and Gas Consumption. Annual TAPS throughputs were 

obtained directly from Historical and Projected Oil and Gas Consumption. 

Canadian Crude Oil Production, Pipeline Mileage and Throughput, and Tanker Transport 

Quantity Data 

Hart Crowser contacted the NEB to obtain crude oil production, pipeline mileage and 

throughput, and tanker transport quantity data for the Canadian Arctic study areas. 

Alaska and Canadian crude oil production, pipeline mileage, and pipeline throughput or other 

transportation data were entered into a Microsoft Access database application and have been 

provided to MMS separately from this report. 

Oil Spill Data Statistical Analysis and Estimation of Spill Risk

Statistical analysis began after collation of the oil spill data. The basic statistical approach used 

in the study consisted of visual review all of the data using cumulative frequency and box plots. 

Conclusions inferred from visual analysis of the data were verified by linear methods including 

linear regression and analysis of variance. In all statistical analyses, there is some type of 

balancing between a reasonable number of samples, which allow statistical inference to be made 

and relevant independent variables. Review of the oil spill data indicated that not all data fields 

had enough repeated entries to provide useful statistical results. Relevant variables selected were 

study area, spill date, facility type, oil type, spill cause, and affected media. 

Units used in this study are those provided in the data. Oil production was expressed in millions 

of barrels per year, the volume of spills were expressed in U.S. gallons, volumetric spill rates 

were expressed in U.S. gallons per millions of barrels produced, and numerical spill rates were 

expressed as the number of spills at or above a specific size divided by millions of barrels of 

crude oil produced. 

To increase the number of repeated entries in data fields, minor typographical inconsistencies in 

the facility type and oil type data fields were standardized. The data contained a number of 

explanations for the causes of spills. However, there was enough consistency to allow some of 

spill causes to be combined into a new variable, which was called spill cause common. The spill 

cause common variable contained facility piping leaks, facility tank leaks, facility explosions, 

pipeline leaks, tank vehicle accidents, and unspecified spill causes, along with one production 

well leak. 

Visual review of the oil spill data from both Canadian and U.S. sources indicated that, in general, 

only maximum estimated spill volumes were available for the size of the oil spills. Maximum 

spill volume also is conservative. Consequently, the maximum spill size was used as the 

dependent variable for all analyses. 
 10 

The statistical analysis of the oil spill data and the estimation of oil spill risk rates was conducted 

using Microsoft® Windows 2000® beta build 2128 using the MKS toolkit (which emulates a 

Unix Korn shell under Windows®) and the public domain statistics package “R”1, running on a 

Pentium II 300Mhz computer. After initial re-formatting of the data from Microsoft® Excel®

spreadsheets, a single batch file was used to assure that results obtained in the study could be 

reproduced Between the initial analysis and the final analysis presented here, new versions of 

Windows 2000® (final release), the “R” statistics package and Microsoft® Excel® became 

available and were installed on the computer used to conduct the analysis. To verify that none of 

the software changes had an affect on the results, the initial data set was rerun and identical 

results obtained. 

 

1

 A description of this statistics package can be found on the Internet at http://www.ci.tuwien.ac.at/. 
 11 

RESULTS 

Oil Spill Data Collection

Alaskan Oil Spill Data 

Alaskan oil spill data obtained from the MMS consisted of: 

• BP electronic database files of oil spills in the Prudhoe Bay Unit Western Operating 

Area (1989 through 1996), Duck Island (Endicott) Unit (1989 through 1996), and 

Milne Point (1994 through 1996); 

• ARCO electronic spreadsheet files of oil spills for the Prudhoe Bay Unit Eastern 

Operating Area (1977 through 1996), Kuparuk River Unit (1977 through 1985 and 

1986 through 1996), and Kuparuk River Unit exploration (1986 through 1996); 

• Alyeska printed summary report of oil spills greater than 1000 barrels along the 

TAPS from 1977 to 1989; 

• JPO electronic database of oil spills along the TAPS (1970 through 1994); 

• BLM printed reports of oil spills along the TAPS during 1981 and 1982; 

• ADEC electronic text and spreadsheet files of oil spills from the agency’s current oil 

and hazardous substances spill database (July 1995 to February 1997) and an earlier 

oil and hazardous substances spill database (1971 to July 1995); 

• An unattributed printed summary of oil spills over 378.5 liters (100 gallons) on 

Alaska’s North Slope and along TAPS from 1970 to 19812; and 

• An electronic spreadsheet summary of Alaskan and Canadian oil spills of 100 barrels 

or greater, from 1978 through 1997, as reported by the OSIR. 

• An MMS report that no oil spills of 100 barrels or larger have occurred in the Alaska 

Beaufort Sea study area. 

From inquiries to these same organizations, except to the OSIR, Hart Crowser obtained updated 

or additional oil spill data from: 

• Alyeska; an electronic spreadsheet file containing all oil spills of 100 barrels and greater 

from the company’s oil spill database to September 1999; and 

• ADEC; an electronic spreadsheet containing all oil spills in ADEC’s current oil and 

hazardous substance spill database to September 1999. 

 

2

 MMS reported that they obtained the summary from BLM. Hart Crowser believes this summary may be an ADEC 

work product, because a copy of it was found in the agency’s Fairbanks office files, and it is familiar to the report’s 

primary author who worked for ADEC in Fairbanks at the time it was prepared. 
 12 

Additional oil spill data was not received in response to inquiries and requests made to ARCO, 

BP Exploration (Alaska), EPA, BLM, or the National Response Center. 

A review of Oil Spills: International Summary and Review 1978-1981 and Oil Spills: 

International Summary and Review 1982-1985, which were produced by the publishers of the 

OSIR, yielded no additional oil data for the study. 

No data concerning oil spills of 100 barrels and greater within the National Petroleum Reserve in 

Alaska (NPRA) were obtained from any sources. Inquiries to the BLM, the agency with surface 

management and protection responsibilities in NPRA since 1977, did not yield any oil spill data. 

Hart Crowser’s review of two publications that discussed oil exploration activities in NPRA also 

did not identify any oil spills that met the size threshold for inclusion in this study and analysis3. 

Canadian Oil Spill Data Collection 

Hart Crowser’s inquiries seeking Canadian oil spill data either yielded no oil spill records or 

resulted in referrals to the GNWT EPS. From the GNWT EPS, Hart Crowser obtained a tabular 

summary of all oil spills of 100 barrels and larger that are included in the GNWT EPS oil spill 

database. The database has been maintained since 1985 and contains spill records back to 1971. 

Hart Crowser identified oil spills in the GNWT EPS database that met the study criteria and 

obtained the written records for those spills from the GNWT EPS. 

Oil spill records also obtained oil spill data from the OSIR summary provided by MMS. This 

data was confirmed by Hart Crowser’s reviews of Oil Spills: International Summary and Review 

1978-1981 and Oil Spills: International Summary and Review 1982-1985. 

Reviews of EC’s Summary of Spill Events in Canada, 1974 – 1983 and Summary of Spill Events 

in Canada, 1984 – 1995 and DIAND’s Northern Oil and Gas Annual Reports for 1992 through 

1998 yielded no data on specific spills for inclusion in the study. 

Documentation of Oil Spills of 500 Barrels and Larger 

Hart Crowser obtained some form of written supporting documentation from the ADEC and 

GNWT files for 24 of 28 oil spills identified that had a volume of 500 barrels or greater. Those 

spills are listed in Table 1. 

Oil Spill Data Evaluation and Collation

Collation of the Alaskan and Canadian oil spill data sets resulted in the identification of 126 oil 

spills that met the study criteria for spill location, relation to oil industry activity, and were 100 

barrels or greater. Of the 126 collated spills, 111 occurred in Alaska between 1970 and 

September 1999, and 15 in Canada between 1973 and September 1999. The most recent oil 

spills of 100 barrels or greater in both Alaska and Canada occurred in 1997. Also, of the 126 oil 

spills, 28 spills were 500 barrels and greater and 14 spills are 1,000 barrels or greater. Of the 28 

oil spills that are 500 barrels or greater, 23 occurred in Alaska and 5 in Canada. The collated list 

of spills was provided to MMS as a Microsoft Access database application and, because of its 

size, is provided in Appendix A rather than as a table here. 

 

3

 Hanley et. al. 1981 and Gryc 1985. 
13 

TABLE 1 

DOCUMENTATION FOR SPILLS OF 500 BARRELS AND LARGER

Study Area Date Facility Operator Oil Type Spill Location Maxim

Quantity 

AK-Onshore North Slope (E. of NPRA) 06/03/71 ARCO Jet/Turbine Fuel Prudhoe Bay Unit, ARCO airfield 45AK-Onshore North Slope (E. of NPRA) 07/16/73 ARCO Diesel Fuel/Heating Oil Itkillik River Unit 1 40AK-Onshore North Slope (E. of NPRA) 06/20/79 Chevron USA Jet/Turbine Fuel Cape Beaufort 40AK-Onshore North Slope (E. of NPRA) 07/15/82 Wien Air Alaska Jet/Turbine Fuel Deadhorse Airport 100AK-Onshore North Slope (E. of NPRA) 07/28/89 Conoco Crude Oil Milne Point Unit, Central Processing Facility 38AK-Onshore North Slope (E. of NPRA) 08/25/89 ARCO Crude Oil Kuparuk River Unit, Drill Site 2-U 25AK-Onshore North Slope (E. of NPRA) 12/10/90 ARCO Crude Oil Lisburne Unit, Drill Site L-5 25AK-Onshore North Slope (E. of NPRA) 08/17/93 ARCO Crude Oil and Produced Water Kuparuk River Unit CPF 1 28AK-Onshore North Slope (E. of NPRA) 09/26/93 BP Crude Oil Prudhoe Bay Unit, Gathering Center 2 27AK – TAPS 02/07/75 Alyeska Pipeline Diesel Fuel/ Heating Oil TAPS Galbraith Camp 100AK – TAPS 06/11/75 Alyeska Pipeline Diesel Fuel/ Heating Oil TAPS Galbraith Camp 60AK – TAPS 09/18/75 Alyeska Pipeline Diesel Fuel/ Heating Oil TAPS Franklin Bluffs Camp 30AK – TAPS 12/17/75 Alyeska Pipeline Diesel Fuel/ Heating Oil Surfcote 70
14 

TABLE 1 

DOCUMENTATION FOR SPILLS OF 500 BARRELS AND LARGER

Study Area Date Facility Operator Oil Type Spill Location Maxim

Quantity 

AK – TAPS 12/31/75 Alyeska Pipeline Diesel Fuel/ Heating Oil TAPS Prospect Camp 100AK – TAPS 01/28/76 Alyeska Pipeline Diesel Fuel/ Heating Oil TAPS Galbraith Camp 40AK – TAPS 05/08/77 Alyeska Pipeline Gasoline TAPS Galbraith Camp Bladder Farm 35AK - TAPS 07/08/77 Alyeska Pipeline Crude Oil TAPS Pump Station 8 200AK – TAPS 07/19/77 Alyeska Pipeline Crude Oil TAPS MP 26, Check Valve 7 110AK – TAPS 02/15/78 Alyeska Pipeline Crude Oil TAPS MP 458, Steele Ck 672AK – TAPS 06/10/79 Alyeska Pipeline Crude Oil TAPS MP 166, Atigun Pass 300AK – TAPS 06/15/79 Alyeska Pipeline Crude Oil TAPS MP 734 168AK – TAPS 01/01/81 Alyeska Pipeline Crude Oil TAPS MP 114.6, Check Valve 23 100AK – TAPS 04/20/96 Alyeska Pipeline Crude Oil TAPS MP 539.7, Check Valve 92 34CANADA - Beaufort Sea 09/18/85 Esso. Diesel Fuel/ Heating Oil Esso Rig #7, W. of Pelly Island 103CANADA - High Arctic Islands 04/06/75 Pan-Arctic Oils Jet/Turbine Oil Drake D-73 Well Site 22CANADA - Norman Wells 09/07/86 

Esso 

Resources 

Canada Ltd. 

Crude Oil Imperial Oil Tank #53 Mainland, Sahtu Region 21

CANADA - Norman Wells 05/04/92 Interprovincia l Pipelines Crude Oil Norman Wells Pipeline, 25 km N of Ft Simpson 26CANADA - Norman Wells 05/05/97 Imperial Oil. Crude Oil Transfer line: CPF to Tank 401 63
15 

Another 95 spills, 77 in Alaska and 18 in Canada, were excluded from the study because Hart 

Crowser could not obtain sufficient information about them to determine whether or not they met 

the study criteria. The lack of information on the quantity of oil spilled, the location of the spill, 

or who spilled the oil were the most common reasons that prevented determinations of whether 

or not any of these spills should be included. A table of these spills was provided to MMS 

separately from this report. As discussed further, later in the report, Hart Crowser does not 

believe that the lack of data for the Alaskan oil spills invalidates the database of collated oil 

spills used to estimate oil spill risk because of the comprehensiveness of the Alaskan oil spill 

data and a low probability that these spills would be included in the study if complete data on 

them were available 

Notwithstanding the spills excluded from the collated spill database because of incomplete data, 

Hart Crowser judged the Alaskan oil spill to be very comprehensive. Alaskan oil spill data was 

obtained from ten data sets. More than 60 percent of the Alaskan spills appeared in two or more 

data sets. Spills of 500 to 999 barrels and 1,000 barrels and larger were present in two or more 

data sets at a higher percentage than spills of 100 to 499 barrels. 

Although some data elements, such as latitude and longitude and how the spill quantity was 

determined, are missing from most spill records, the data for the Alaskan spills also is mostly 

complete. 

Overall, Hart Crowser is not confident that the Canadian oil spill data is comprehensive, because 

only two data sets were obtained for Canadian oil spills and there was a much lower rate of 

occurrence of the spill records in both of these data sets. Data sets from only the GNWT EPS 

and the OSIR were obtained for the Canadian oil spills, and less than 15 percent of the spills 

appear in both the data sets. The Canadian data is mostly complete, with the same data elements 

missing from some records as in the Alaskan data sets. 

Oil Spill Notification Requirements

Current and historical oil spill notification requirements were identified for the United States, 

Alaska, Canada, and the Northwest Territories. Two sets of government agency oil spill 

notification requirements exist in both the Alaskan and the Canadian Arctic study areas: Federal 

requirements and State or Territorial requirements. In addition, the State and Federal rights-ofway for the TAPS in Alaska contain oil spill notification stipulations. Current oil spill 

notification requirements within the study areas are summarized in Table 2. The current and 

historical regulatory oil spill notification requirements are discussed further in the Discussion 

section of this report. 
16 

TABLE 2 

CURRENT OIL SPILL NOTIFICATION REQUIREMENTS IN STUDY AREAS

Agency Required For Initial Verbal Report Writ

United States Government U.S. Coast Guard All oil spills in or threatening 

marine navigable waters of the United States 

Immediately upon knowledge. Spills may be reported to the National Response Center (NRC). 

None required, but may 

U.S. Environmental Protection Agency 

All oil spills in or threatening navigable fresh waters of the United States 

Immediately upon knowledge. Spills may be reported to the NRC. 

Required, if requested ois required to have an SPgallons or is second spil

U.S. Department of the Interior, Minerals Management Service 

All oil spills in offshore marine waters. 

Immediately to the NRC Immediately to MMS Regional Supervisor for spills ≥1 barrel. 

May be requested for spWritten report to MMS for all spills of ≥1 barrelbeen stopped. 

U.S. Department of Transportation 

All oil spills from regulated pipelines 

Immediately Required within 30 days 

Federal land management agencies 

Spills on Federal mineral leases, pipeline rights-of-way, and lands 

As required by lease or permit As required by lease or 

State of Alaska Alaska Department of Environmental Conservation 

All oil spills ≥ 1 gallon to lands or waters in Alaska 

Immediately for: 

• Spills of >55 gallons solely to 

land outside of impermeable containment 

• Any amount to water 

Within 48 hours for: 

• Spills of 10 to 55 gallons 

solely to land 

• Spills >55 gallons to 

impermeable containment 

Monthly, for spills of 1 Within 15 days of end oall other spills. 
17 

TABLE 2 

CURRENT OIL SPILL NOTIFICATION REQUIREMENTS IN STUDY AREAS

Agency Required For Initial Verbal Report Writ

Alaska Oil and Gas Conservation Commission 

Oil spills of ≥10 barrels from an oil drilling, production, injection, or abandonment operation in Alaska 

Immediately Preliminary report withi

report within 30 days af

Alaska Department of Natural Resources 

Spills on State mineral leases, pipeline rights-of-way, and lands 

As required by lease or permit As required by lease or 

Canada Federal Government and Government of the Northwest Territories GNWT EPS (Serves as single point of spill notification for: 

• National Energy Board 

• Environment Canada 

• Department of Indian 

Affairs and Northern Development 

• Coast Guard Canada, 

and 

• Inuvialuit Lands 

Administration) 

Oil spills of 100 liters ( 26.4 gallons) and larger. 

Immediately Within 15 days after end 
18 

Crude Oil Production, Pipeline Mileage, 

Pipeline Throughput, Canadian Tanker 

Shipment, and Data

Alaskan and Canadian Crude Oil 

Production 

Data obtained for crude oil production in the 

Alaska study areas are presented in Table 3. 

Data obtained for crude oil production in the 

Canadian study areas are presented in Table 

4. 

Alaskan Pipeline Mileages and Throughputs 

The mileages of “regulated pipelines” (i.e., 

those pipelines regulated by the U.S. 

Department of Transportation and right-ofway leases issued by the State of Alaska or 

the BLM) were obtained from the Joint 

Pipeline Office (JPO). The mileage of the 

TAPS was obtained from the Trans-Alaska 

Pipeline Atlas, Prudhoe Bay to Valdez. The 

mileages for these pipelines in the Alaskan 

study areas are presented in Table 5. 

Comprehensive data on the mileages of field 

gathering lines through the years could not 

be collected within the time and resource 

constraints of this study. The limited data 

on field gathering line mileages for the 

Alaskan study area that were collected are 

presented in Table 6. 

Throughputs for the regulated pipelines in 

the Alaskan study areas are presented in 

Table 7. 

Canadian Pipeline Mileage, Pipeline 

Throughput, and Tanker Shipment Volumes 

The Norman Wells Pipeline is the only 

pipeline larger than a field gathering line 

that has operated and continues to operate in 

all of the Canadian study areas. The 

Norman Wells Pipeline runs from a pump 

station at Norman Wells, Northwest 

Territories to the Interprovincial Pipeline in 

Zama, Alberta, a distance of 540.0 miles. 

The Norman Wells Pipeline has operated 

from 1985 to the present. 

Annual throughputs for the Norman Wells 

Pipeline, as well as the volumes of oil that 

have been shipped by tanker from other 

locations in the Canada study areas are 

presented in Table 8. 

Oil Spill Data Statistical Analysis and 

Estimation of Spill Risk

Hart Crowser found the Alaska oil spill data 

to be sufficiently robust and valid to conduct 

statistical analyses and estimate oil spill risk 

rates. A cumulative frequency plot of the 

Alaska spill size data showed a bow 

characteristic of lognormal data. When 

these limited number of data points were replotted on a lognormal scale, it appeared that 

two lognormal populations could reasonably 

describe this population. A cumulative 

frequency plot of the Canadian oil spill size 

data on a lognormal basis indicated more or 

less the same distribution as the Alaskan 

data, when a plot of both the Alaskan and 

Canadian data were overlaid. The Canadian 

data was not used in further analysis because 

of doubts about its completeness, the fact 

that 15 points were below the 30 point 

empirical rule for number of samples, and 

the fact that the 112 Alaska data points 

would overpower the 15 Canadian points. 

Exploratory data analysis on relevant 

independent variables indicated little 

statistical difference in terms of spills that 

occurred within the Alaska (ONS), East of 

NPRA, and the TAPS study areas. This 

lack of statistical difference was confirmed 

by an analysis of variance in which no 

statistically significant difference between 

the two populations was found. Although 

there appeared to be some type of a cycling 

trend in the data, with the lowest number of 

spills occurring in March, and the highest 

volume of spills occurring in July, a linear 

regression on month showed no statistically 

significant correlation. 
19 

TABLE 3 

CRUDE OIL PRODUCTION FOR ALASKAN 

STUDY AREAS

Oil Field Study Area Year Production 

(MMBbl) 

Duck Island 

(Endicott) 

ALASKA – 

Beaufort Sea 

1986 0.011 

 1987 8.799 

 1988 37.933 

 1989 36.938 

 1990 38.596 

 1991 42.521 

 1992 43.084 

 1993 40.753 

 1994 35.769 

 1995 34.437 

 1996 27.663 

 1997 22.928 

 1998 18.629 

Badami ALASKA – 

Onshore 

North Slope 

(E. of NPRA) 

1998 0.731 

Kuparuk 

River 

ALASKA – 

Onshore 

North Slope 

(E. of NPRA) 

1981 1.092 

 1982 32.406 

 1983 39.882 

 1984 46.208 

 1985 80.013 

 1986 95.272 

 1987 103.705 

 1988 111.146 

 1989 109.770 

 1990 107.206 

 1991 113.571 

 1992 118.506 

 1993 115.166 

 1994 111.795 

 1995 106.999 

 1996 99.459 

 1997 95.971 

 1998 96.281 

Milne Point ALASKA – 

Onshore 

North Slope 

(E. of NPRA) 

1985 0.704 

 1986 4.709 

 1987 0.040 

 1988 0.000 

 1989 3.715 

 1990 6.628 

 1991 7.457 

 1992 6.947 

 1993 6.764 

TABLE 3 

CRUDE OIL PRODUCTION FOR ALASKAN 

STUDY AREAS

Oil Field Study Area Year Production 

(MMBbl) 

 1994 6.678 

 1995 8.692 

 1996 14.101 

 1997 18.954 

 1998 20.419 

Point 

McIntrye 

ALASKA – 

Onshore 

North Slope 

(E. of NPRA) 

1981 0.002 

 1982 0.208 

 1983 0.087 

 1984 0.294 

 1985 1.123 

Point 

McIntrye 

ALASKA – 

Onshore 

North Slope 

(E. of NPRA) 

1986 3.594 

 1987 16.657 

 1988 16.103 

 1989 14.830 

 1990 15.873 

 1991 14.653 

 1992 13.981 

 1993 18.549 

 1994 50.710 

 1995 65.166 

 1996 75.563 

 1997 73.705 

 1998 61.950 

Prudhoe 

Bay 

ALASKA - 

Onshore 

North Slope 

(E. of NPRA) 

1969 0.277 

 1970 1.193 

 1971 1.157 

 1972 0.922 

 1973 0.944 

 1974 2.170 

 1975 2.870 

 1976 4.604 

 1977 115.258 

 1978 397.679 

 1979 468.412 

 1980 555.648 

 1981 555.620 

 1982 559.389 

 1983 561.148 

 1984 562.269 

 1985 586.590 

 1986 561.767 

 1987 586.555 

 1988 578.686 
20 

TABLE 3 

CRUDE OIL PRODUCTION FOR ALASKAN 

STUDY AREAS

Oil Field Study Area Year Production 

(MMBbl) 

 1989 522.869 

 1990 486.235 

 1991 486.706 

 1992 456.490 

 1993 409.690 

 1994 374.318 

 1995 340.439 

 1996 312.609 

 1997 284.001 

 1998 252.825 
21 

TABLE 4 

CRUDE OIL PRODUCTION FOR CANADIAN 

STUDY AREAS

Oil Field Study Area Year Production 

(MMBbl) 

Amauligak CANADA - 

Beaufort Sea 

1986 0.317 

Bent Horn CANADA - 

High Arctic 

Islands 

1985 0.186 

 1986 0.047 

 1987 0.216 

 1988 0.346 

 1989 0.273 

 1990 0.151 

 1991 0.205 

 1992 0.178 

 1993 0.358 

 1994 0.333 

 1995 0.231 

 1996 0.249 

Norman 

Wells 

CANADA - 

Norman 

Wells 

Pre1949 2.812 

 1949 0.182 

 1950 0.193 

 1951 0.288 

 1952 0.351 

 1953 0.329 

 1954 0.361 

 1955 0.395 

 1956 0.441 

 1957 0.421 

 1958 0.500 

 1959 0.459 

 1960 0.496 

 1961 0.577 

 1962 0.671 

 1963 0.698 

 1964 0.654 

 1965 0.753 

 1966 0.856 

 1967 0.796 

 1968 0.678 

 1969 0.878 

 1970 0.954 

 1971 1.030 

 1972 0.959 

 1973 1.022 

 1974 0.999 

 1975 1.074 

 1976 1.004 

 1977 0.984 

 1978 1.064 

TABLE 4 

CRUDE OIL PRODUCTION FOR CANADIAN 

STUDY AREAS

Oil Field Study Area Year Production 

(MMBbl) 

 1979 0.943 

 1980 1.022 

 1981 1.069 

 1982 1.090 

 1983 1.066 

Norman 

Wells 

CANADA - 

Norman 

Wells 

1984 1.099 

 1985 6.580 

 1986 8.876 

 1987 9.652 

 1988 10.908 

 1989 11.253 

 1990 11.578 

 1991 11.912 

 1992 11.640 

 1993 11.257 

 1994 10.888 

 1995 10.679 

 1996 10.265 

 1997 9.968 

 1998 9.824 

TABLE 5 

REGULATED PIPELINE MILEAGES FOR 

ALASKAN STUDY AREAS

Pipelin

e Name 

Starting 

Point 

Ending 

Point 

Operatio

nal 

Milea

ge 

TransAlaska 

Pipelin

e 

TAPS 

Pump 

Station 

1 

Valdez 

Marine 

Termina

l 

1977 - 

present 799.8

Badami 

Sales 

Oil 

Badami 

Producti

on 

Facility 

Endicott 

Sales 

Oil 

Pipeline 

1998 - 

present 34.3

Endicot

t Sales 

Oil 

Endicott 

Producti

on 

Facility 

TAPS 

Pump 

Station 

1 

1986 - 

present 25.0
22 

Kuparu

k Sales 

Oil 

Kuparuk 

Central 

Processi

ng 

Facility 

1 

TAPS 

Pump 

Station 

1 

1986 to 

present 30.0

Kuparu

k 

Extensi

on 

Kuparuk 

Central 

Processi

ng 

Facility 

2 

Kuparuk 

Central 

Processi

ng 

Facility 

1 

1983 - 

present 9.2

Lisburn

e Sales 

Oil 

Lisburne 

Producti

on 

Facility 

TAPS 

Pump 

Station 

1 

1985 - 

present 5.3

Milne 

Point 

Sales 

Oil 

Milne 

Point 

Central 

Producti

on 

Facility 

Kuparuk 

Sales 

Oil 

Pipeline 

1985 – 

1987, 

1989 to 

present 

10.5

Oliktok 

Pipelin

e 

Kuparuk 

Central 

Processi

ng 

Facility 

1 

TAPS 

Pump 

Station 

1 

1981 – 

1986 30.0
23 

Table 6 

FIELD GATHERING PIPELINE MILEAGES FOR 

ALASKA STUDY AREAS

Oil 

Production 

Unit 

Study Area Year Mileage 

Endicott AK - 

Beaufort 

Sea 

1986 - 

present 

3.5 

Kuparuk 

River 

AK - 

Onshore 

North Slope 

(E. of 

NPRA) 

1994 36.3 

 1997 132.9 

 1998 132.9 

Prudhoe 

Bay - 

Eastern 

Operating 

Area 

(ARCO) 

ALASKA - 

Onshore 

North Slope 

(E. of 

NPRA) 

1994 88.7 


25 

TABLE 8 

PIPELINE THROUGHPUTS AND TANKER 

SHIPMENT VOLUMES

FOR CANADIAN STUDY AREAS

Oil 

Field 

Study 

Area 

Trans

port 

Metho

d 

Mile

age 

Ye

ar 

Volum

e 

(MMB

bl) 

Norma

n 

Wells 

CANA

DA - 

Norma

n 

Norma

n 

Wells 

Pipelin

e 

540.0 19

85 

6.580

 Wells 19

86 

8.876

 19

87 

9.652

 19

88 

10.908

 19

89 

11.253

 19

90 

11.578

 19

91 

11.912

 19

92 

11.640

 19

93 

11.257

 19

94 

10.888

 19

95 

10.679

 19

96 

10.265

 19

97 

9.968

 19

98 

9.824

Bent 

Horn 

CANA

DA - 

High 

Arctic 

Tanker NA 19

85 

0.186

 Islands 19

86 

0.047

 19

87 

0.216

 19

88 

0.346

 19

89 

0.273

 19

90 

0.151

 19

91 

0.205

TABLE 8 

PIPELINE THROUGHPUTS AND TANKER 

SHIPMENT VOLUMES

FOR CANADIAN STUDY AREAS

Oil 

Field 

Study 

Area 

Trans

port 

Metho

d 

Mile

age 

Ye

ar 

Volum

e 

(MMB

bl) 

 19

92 

0.178

 19

93 

0.358

 19

94 

0.333

 19

95 

0.231

 19

96 

0.249

Amauli

gak 

CANA

DA - 

Beaufo

rt Sea 

Tanker NA 19

86 

0.317 
26 

A general check on the fluctuation of the 

data set, as seen in a plot of the logarithm of 

thespill size versus the day of the month 

indicated spill occurrence to be quite 

random. There was little trend seen in the 

median of the data for a box plot of the 

logarithm of the spill size versus the year, 

with the exception of 1979, which was 

higher. However, an analysis of variance of 

this data showed no statistically significant 

difference between the years. There 

appeared to be little difference in the size of 

spills between the types of spills associated 

with the various facilities, with the 

exception of pipelines, which had larger 

spills. Analysis of variance by oil type 

showed that, in general crude oil spills tend 

to be larger than other types of oil spills. 

Cumulative frequency plots by selected 

independent variables show that: 

• Spills within the TAPS study area 

appears to be a fairly clear mixture 

of two lognormal populations; 

• Spills within the ONS study area 

shows more bowing, indicating 

perhaps a single population; 

• Spills from tank vehicles exhibit 

little apparent variability in a box 

plot, which is more or less consistent 

with the fact that a tank vehicle spill 

should be expected to have a firm 

upper limit; 

• Spills from facility piping exhibit a 

bow, but no clear break in 

population; 

• Spills from pipeline leaks indicate 

what may be a single lognormal 

population and, in general, appear to 

be the largest in quantity; 

• Spills from facility tank leaks exhibit 

a single lognormal population; 

• Spills from unspecified causes also 

exhibit a single lognormal 

population; and 

• Spills from other causes had such a 

small number of data points that no 

definite conclusions could be drawn, 

but overlaying the figure for 

unspecified causes indicated that 

these two spill cause categories can 

probably reasonably be lumped 

together as a single population for 

statistical analysis. 

Cumulative frequency plots of the 

logarithms of spill volume versus oil type 

showed that the data for spills involving: 

• Diesel fuel data appears to be a 

mixture of two lognormal 

populations; 

• Crude oil data appears to be a 

mixture of two lognormal 

populations; 

• Gasoline data appears to show a 

single lognormal population with one 

possible outlier, which is consistent 

with a mixture of two lognormal 

populations; and 

• Turbine and jet fuel data also shows 

what may be a mixture of two 

lognormal populations. 

Cumulative frequency plots of the 

logarithms of spill volume versus the type of 

facility where a spill occurred showed that 

the data for spills from: 

• Highways are very similar to the 

tank vehicle spills, which is entirely 

consistent with the assumption that 

most, if not all, highway spills are 

from tank vehicles; 

• Support facilities was a bowed 

lognormal population; 

• Production facilities appear to show 

a single lognormal population; 

• Construction camps appear to show a 

mixture of two lognormal 

populations; and 
27 

• Pipelines could be interpreted as a 

single lognormal population. 

Cumulative frequency plots of the log of 

spill volume versus the affected 

environmental media showed that spills: 

• Affecting land is a mixture of two 

lognormal populations; 

• Affecting land and water shows a 

mixture of two lognormal 

populations; 

• Contained within a secondary 

containment area, appeared to be a 

single lognormal population; and 

• Where the affected media was 

unspecified appears to be a single 

lognormal population. 

There were no spills that affected water 

only. 

A statistical analysis of individual spill 

volumes by study area, facility type, oil 

type, affected media and spill cause 

combined did not indicate any particularly 

interesting correlation. Annualized 

groupings of spills, where total spill 

volumes by year were accumulated and 

plotted on a cumulative frequency plot, 

showed a mixture of several populations. 

Re-plotted on a logarithmic scale, a single 

lognormal population emerged. A count of 

the number of spills per year in the database 

is showed a possible Poisson distribution, 

but that hypothesis was not tested. 

When spill size was plotted by year to see if 

regulatory or reporting requirements had a 

significant affect, it appeared that in the 

period from 1975 to 1979 there were a 

considerable number of large spills, and then 

the number of spills dropped to a more or 

less constant rate. The year of 1977 is 

significant because crude oil production on 

North Slope and operation of TAPS began 

in the middle of that year. However, the 

years of 1978 and 1979 visually fit with 

years of 1975 and 1977 better than breaking 

the data at 1977. The 1975 to 1979 period 

appears to have the most number of spills. 

When Alaskan spill data were plotted on a 

yearly basis, it appears that prior to 1977, 

spill rates were considerably greater than in 

the subsequent years. When re-plotted on a 

logarithmic scale, it is apparent that prior to 

1980 spill rates were considerably greater 

than after 1980. 

Hart Crowser calculated oil spill risk rates 

based on the number of spills and on 

volume. Hart Crowser calculated a rate 

based on volume because of the greater 

visual variability in the data. The statistical 

significance of this visual analysis showed a 

highly statistically significant correlation 

with spill rate and year if all of the Alaska 

spill data is included. If data earlier than 

1980 is excluded, then there is still a 

correlation between spill rate and year that is 

significant at the 1 percent level of 

confidence. However, if data earlier than 

1985 is excluded, then there is a correlation 

between spill rate and year, which is 

significant at the 17 percent level of 

confidence. 

Hart Crowser concluded that spill rate is the 

best variable to use in predicting the volume 

of further oil spills and that a rate of 

approximately 52 gallons of oil spilled per 

million barrels of crude oil produced will be 

the average, if trends that started in 1980 

continue. This rate is subject to 

considerable uncertainty in the mean (± 50% 

at the 95% level of confidence) and the 

value derived from the logarithmic 

distribution is 66 gallons of oil spilled per 

million barrels of crude oil produced as 

opposed to 52 gallons of oil spilled per 

million barrels of crude oil produced. These 

two values agree within the standard 

deviation of the means. The 95 percent 

logarithmic confidence limits on spills for a 

given year are ± 465 percent at the 95 

percent level of confidence. Hart Crowser is 
28 

more inclined to believe the logarithmic 

values than the untransformed values, 

because the cumulative frequency of the 

data is more lognormal than normal. These 

very wide confidence limits and individual 

yearly values are consistent with the small 

number of data points available for this 

prediction. 

Hart Crowser also calculated oil spill risk 

rates based on the number of spills of a 

given volume per million barrels of crude oil 

produced (spills/MMBbl), using data from 

1978 through 1999. Hart Crowser found 

these rates to be: 

• 0.0053 spills/MMBbl, ±24 percent, 

for spills of 100 barrels and greater; 

• 0.00093 spills/MMBbl, ±58 percent, 

for spills of 500 barrels and greater; 

• 0.00039 spills/MMBbl, ±89 percent, 

for spills of 1,000 barrels and 

greater; and 

• 0.000078 spills/MMBbl, ±200 

percent, for spills of 10,000 barrels 

and greater. 
29 

DISCUSSION 

Oil Spill Data Collection

Alaska Oil Spill Data 

Hart Crowser believed that ADEC would be 

the best potential source of oil spill records 

for Alaska because, since the Department 

was established in 1971, the agency has 

received reports, investigated, and overseen 

the cleanup of oil spills in Alaska. Hart 

Crowser received and reviewed copies of 

electronic spreadsheet files from ADEC and 

from the MMS that contained data on oil 

spills from a past (1986 – 1995) and a 

current (1995 – present) agency oil and 

hazardous substance spill database. 

Through inquiries to ADEC staff, Hart 

Crowser researchers identified the location 

of relevant written oil spill files, and then 

traveled to ADEC’s Fairbanks and Valdez 

offices, to review those files. During the file 

reviews, Hart Crowser sought to identify oil 

spills that met the study criteria, record 

pertinent data from the spill records, and 

obtain documentation from the files for 

spills of 500 barrels or greater. 

With respect to ADEC’s oil spill files and 

databases, Hart Crowser researchers 

observed that: 

• Not all reported oil spills prior to 

July 1995 have been entered into 

ADEC’s current oil and hazardous 

substance spill database, which has 

been used since July 1995. In 1996, 

ADEC attempted to have all 

historical oil and hazardous 

substance spill information reviewed 

and entered into the database. 

However, the project was not 

conducted for several reasons, 

including the large number of 

historical records and the incomplete 

status of many historical records. 

• Not all reported oil spills were 

entered into the older ADEC 

Northern Regional Office oil and 

hazardous substance spill database, 

which was used from approximately 

1986 to July 1995. Hart Crowser 

found several oil spill reports in the 

agency’s files that met the criteria for 

inclusion in this study, but which 

were not included in the agency’s 

database. 

• Most initial and final oil spill reports 

and most other spill documentation 

do not describe how spill quantities 

were determined. In most cases, 

spill quantities appeared to be 

estimates. Some estimates are more 

accurate because the quantity of oil 

that may have been spilled is known 

(e.g., the capacity of a tank vehicle 

and the amount of oil that remained 

inside after an accident). Some spill 

estimates are calculated based on the 

size of the hole that allowed oil to 

escape, the pressure of the oil within 

the pipe or tank, the known or 

estimated duration of the leak, and 

the amount of oil recovered during 

spill cleanup. In other cases, spill 

sizes are rough estimates because the 

rate and duration of oil loss could not 

be accurately determined and the 

amount of oil recovered was not 

documented. 

• Some oil spill reports contained 

incomplete information that did not 

allow them to be included in the 

study database. For oil spill records 

where the quantity of oil spilled, the 

location of the spill, or a connection 

to oil industry activities was not 

given or could not be determined, 

data on the spill was recorded, but 

the spill was not included in the 

study. 

Canadian Oil Spill Data 
30 

Hart Crowser’s inquiries to Canadian 

government agencies for oil spill data 

resulted in referrals to the Government of 

the Northwest Territories, Environmental 

Protection Service (GNWT EPS) in 

Yellowknife, Northwest Territories. The 

GNWT EPS appears to be the sole 

repository of Canadian oil spill data for the 

areas of interest in this study. Hart Crowser 

was prepared to travel to Yellowknife and 

review the GNWT EPS oil spill files. 

However, GNWT EPS staff assured Hart 

Crowser that all requested oil spill 

documentation available in the agency’s 

files would be transmitted to Hart Crowser. 

The GNWT EPS has maintained an oil and 

hazardous substance spill database since the 

early 1980s. Hart Crowser first obtained 

summary reports of oil spills of 100 barrels 

and larger from the agency's database, then 

obtained all written documentation from 

GNWT EPS for those oil spills that Hart 

Crowser determined either met or might 

meet the study criteria. 

Hart Crowser also reviewed two summary 

reports of oil spills covering the years 1974 

through 1995, published by Environment 

Canada, and seven Northern Oil and Gas 

Annual Reports from 1992 to 1998, 

published by the Department of Indian 

Affairs and Northern Development 

(DIAND, also known as Indian and 

Northern Affairs Canada) to look for 

additional data on oil spills associated with 

oil industry activities in the Canadian Arctic. 

A summary of oil spills as reported by the 

OSIR, supplied by the MMS was reviewed 

for potential data on oil spills in the 

Canadian study areas. Data in this summary 

was found to correspond to information 

OSIR’s publications, Oil Spills: 

International Summary and Review 1978-

1981 and Oil Spills: International Summary 

and Review 1982-1986. 

Evaluation and Collation of Oil Spill Data

Different oil spill data sets (i.e., oil spill data 

obtained from different sources) were 

compared with one another to evaluate the 

overall comprehensiveness and 

completeness of the data and to develop a 

single collated list of oil spills. To develop 

the collated list of spills, the spill records 

from the different data sets were compared 

with one another and data for each spill was 

combined into a single record for each spill. 

Differences in data between spill records in 

the different data sets, including reported 

spill dates, locations, responsible parties, oil 

type, and spill quantity were reconciled. 

Where different oil spill quantities were 

reported in two or more different data sets, 

or the spill quantity was reported as a range, 

the spill quantity was reported as a range in 

the collated list of spills. 

The database for the oil spill records 

included in the study includes data fields 

for: 

• Record source (the organization 

where an oil spill record was 

obtained); 

• Study area (designating which of the 

eight study areas a spill occurred 

within); 

• Spill date; 

• Facility type (ten categories of 

facility types were developed by 

Hart Crowser; one type was assigned 

to each spill report); 

• Facility operator (company or 

organization that operates the facility 

where the spill occurred); 

• Spiller (company or organization 

named as responsible for the spill); 

• Spill name (if a spill is commonly 

referred to by a name); 

• Oil type (six categories of oil types 

were developed by Hart Crowser; 
31 

one type was assigned to each spill 

report); 

• Location (a brief description of 

where the spill occurred); 

• Latitude and longitude; 

• Spill cause (a brief description of 

what caused the spill); 

• Low and high spill quantity (in 

gallons); 

• How the spill quantity was 

determined; and 

• Affected environmental media.

The facility type categories attempt to 

designate the facility where the spill 

occurred to allow analysis by this field. The 

facility type categories are: 

• Construction camp; 

• Exploration support facility; 

• Exploration well site; 

• Highway; 

• Operations support facility; 

• Pipeline; 

• Pipeline pump station; 

• Production processing facility; 

• Production well site; and 

• Unspecified.

The oil type field categories assigned are: 

• Crude oil; 

• Crude oil and produced water; 

• Diesel/heating oil; 

• Gasoline; 

• Jet/turbine fuel; and 

• Unspecified.

Because of their similarities, diesel fuel and heating oil, and jet fuel and turbine fuel, were 

combined into single categories. 

The affected media field records whether an individual oil spill affected land, water, or both. 

Spills contained in buildings, on gravel pads, or in impoundments such as secondary containment 

structures were included in the all-record and collated spill databases. These spills were 

designated as having affected “land” with a subsequent notation of how the spill was contained. 

Data in the record source, study area, and facility type fields were assigned by Hart Crowser, 

based on information in the spill records, answers to inquiries, or personal knowledge. Data in 

fields such as facility operator, spiller, spill name, oil type, spill location descriptions, and the 

units of measure used in oil spill quantity were standardized as much as possible among the data 

sets to facilitate comparisons of individual spills between data sets. 

The collated database includes the same data fields as the database for all spills, with the 

exception that the record source field was eliminated and multiple fields were added to indicate 

the sources of the records for each spill. 

The Alaskan oil spills observed most frequently are associated with highway tank vehicle 

accidents related to TAPS and North Slope oil field construction and operations support, 

followed by spills related to construction camps, other operations support facilities, and 

pipelines. Spills associated with oil production processing facilities, oil production wells, 

pipeline pump stations, and exploration activities also were identified. The most frequent oil 

spills of 100 barrels and greater in the Canadian study areas were associated with oil exploration 
32 

activities, oil production wells, and oil production processing facilities. Highway tank vehicle 

and pipeline spills also were identified. 

As mentioned in the results section of the report, 77 oil spills in Alaska and 18 in Canada were 

not included in the study because Hart Crowser could not obtain sufficient information about 

them to determine whether or not they met all of the study criteria. These excluded spills do not 

detract from the validity of the oil spill data used to estimate oil spill risk. Spills of 100 barrels 

and larger occur relatively infrequent, and because of this, they are more readily noticed and are 

better reported to government agencies either by the responsible party or other people who see 

them or clean them up. These spills also are more highly publicized in news stories. Evidence 

that oil spills of 100 barrels and larger are well reported can be seen in the high frequency that 

their spill records appear in more than one data set. 

The spills on the excluded list tend to be those for which there no corroborating evidence in other 

data sets to help in determining whether to include an individual spill or not. All but one oil spill 

excluded from the study database appear only in one data set. Where Hart Crowser was able to 

obtain additional information about spills on the excluded list, the information Hart Crowser 

obtained has eliminated spills from further consideration, rather than added spills to the study 

database. No spills from the list of excluded spills have been added to the database. Further 

research could be conducted to completely determine whether any of the remaining spills on the 

excluded list should be included in the study. However, there appears to be a low probability 

that sufficient data on these other spills would be uncovered or that many additional oil spills 

would be added to the study database by that further research. 

Oil Spill Data Comprehensiveness and Completeness

For the period from 1970 through September 1999, the Alaskan oil spill data appears to be 

comprehensive. However, Hart Crowser is not confident that the same can be said for the 

Canada data. It appears that the Alaskan spills are better documented than those in Canada. The 

Alaskan spill data was obtained from ten different government agency, industry, and commercial 

sources. The different sources largely corroborated each other on more than 60 percent of the 

spills and helped to provide complete data for most spills. Spills reported in only one data set 

appear to exist either because the spiller is a party who did not provide data for this study or 

because the spill was reported by one party but not another because of differences in the 

estimated spill quantity. The comprehensiveness and completeness of the Alaskan spill data 

prior to the early 1970s is the most suspect, because ADEC was not fully functional and agencies 

such as JPO did not exist. Data on older oil spills may exist in the archived files of extinct State 

or Federal environmental pollution agencies, such as the Alaska Department of Health and 

Welfare or the Federal Water Pollution Control Agency. 

To see if there were differences between the size of a spill and its appearance in two or more data 

sets, the spills from the correlated spill database were compared against the various data sets to 

determine how many of the spills appeared in two or more data sets. Spills were divided into 

three basic size categories: 100 to 499 barrels, 500 to 999 barrels, and 1,000 barrels and larger. 

Table 9 presents the results of that evaluation. Overall, and individually, the Alaskan and 

Canadian data showed trends indicating that larger spills were more likely to occur in multiple 

data sets. The Canadian data showed greater differences between the 100 to 499 barrel and the 

other spill size categories, but with so few data points, Hart Crowser would not draw any 

conclusions from the Canadian data alone. 
33 

TABLE 9 

CORRELATION OF SPILL SIZE AND

OCCURRENCE IN MULTIPLE DATA SETS

Spill Location and Size Number of Spills Number of Spills in 

Multiple Data Sets 

Percent of Spills in 

Multiple Data Sets 

Alaska ≥100 - 499 bbls 87 54 62 

Alaska ≥500 - 999 bbls 12 8 67 

Alaska ≥1,000 bbls 12 9 75 

Canada ≥100 - 499 bbls 10 0 0 

Canada ≥500 - 999bbls 3 1 33 

Canada ≥1,000 bbls 2 1 50 

All spills ≥100 - 499 bbls 97 54 56 

All spills ≥500 - 999 bbls 15 9 60 

All spills ≥1,000 bbls 14 10 71 

Hart Crowser is not confident that the Canadian oil spill data is adequately comprehensive. Hart 

Crowser’s conclusion is based on the fact that only two data sets, from the GNWT EPS and the 

OSIR, were obtained, and of 15 spills, only 2 spills (15 percent) are found in both data sets. 

The collated list of Alaskan oil spills, as well as the list of spills not included in the database, was 

provided to the ADEC for data validation. Because virtually all of the Canadian oil spill data 

came from the GNWT EPS, the collated Canadian data was sent to Environment Canada for 

validation. Hart Crowser did not receive responses from ADEC or Environment Canada 

concerning the validity of the oil spill data before the completion of this report. 

Reliability of Oil Spill Volume Determinations

Hart Crowser obtained copies of written oil spill reports from agency files for 24 of the 28 spills 

identified in Alaska and Canada that met the study criteria and were 500 barrels or greater. 

Documentation for these 24 oil spills, either in reports filed by the responsible party or a 

government agency report, typically do not describe how the spill quantity was determined. 

The quantity of oil involved in most spills is an estimate, because the exact rate and duration of 

the oil discharge is not known. For some spills, such as from tanks, tank vehicles, or tank 

vessels, the quantity of oil in the tank, vehicle, or vessel prior to the spill and the quantity of oil 

offloaded or remaining in the tank, vehicle, or vessel after the spill frequently is known, allowing 

a fairly accurate estimate of the spill size. Spills that occur in containment areas also can be 

accurately determined. However, leaks from aboveground tanks lacking, or with incomplete 

secondary containment may go undetected for a long period of time. The rate and duration of 

leaks from buried tanks, piping, and pipeline systems may be even more difficult or impossible 

to determine with good accuracy. Engineering calculations compared to measurements of how 

much oil is recovered during cleanup may provide the best method to estimate the spill’s size, 

and may yield an estimate accurate only to an order of magnitude. The size of spills from 

aboveground pipelines in Alaska and Arctic Canada also can be difficult to estimate, because the 

pipelines cross remote, uninhabited areas and it can be hours or days before facility workers or 

security surveillance patrols discover a spill. Even in pipeline systems equipped with leak 

detection instrumentation, a leak may occur at a rate less than the instrumentation can detect. 

Finally, not all of the spilled oil may be discovered or recovered, making it difficult to estimate 

the size of a spill with much accuracy. 
34 

Of the 28 oil spills that are 500 barrels and greater, 8 involve pipeline leaks and 8 involve facility 

piping leaks. These types of spills are the most difficult to accurately estimate the size of 

because they may go undetected for long periods of time, the rate of spillage can be difficult to 

determine, and not all of the oil may be discovered or accounted for in cleanup. Two of the 28 

spills involved facility explosions. The size of the spills associated with these explosions can be 

reasonably estimated because the time and rate of spillage can be calculated with some certainty. 

Another 7 of the 28 spills involve tank leaks, which also can be estimated with reasonable 

certainty because the quantity of oil involved in a spill can be accurately estimated from tank 

capacities, the tanks involved in these spills are located above ground, and, in most instances, the 

spills occurred within secondary containment areas. The final 3 of the 28 spills are from 

unspecified causes, and an assessment of the accuracy of the spill estimate cannot be made 

without further information. 

Alaska Statutes, Title 46, Chapter 03, Section 758 (A.S. 46.03.758), enacted in 1977, authorizes 

state courts to assess civil penalties, based the quantity and toxicity of the oil, and the type of 

environment, against parties found that are found guilty of illegally discharging oil. This 

provision commonly is referred to as the “dollars per gallon” penalty. Depending on the toxicity 

of the oil and the type of environment involved, the basic penalties range from less than $1.00 to 

$10.00 per gallon. If gross negligence or intentional discharge is involved in the spill, or if the 

spiller fails to take reasonable steps to control, contain, and cleanup the spill, fines can be 

increased by a factor of five. ADEC adopted regulations in April 1978, found in Alaska 

Administrative Code, Title 18, Chapter 75, Article 6 (18 AAC 75.605 - 75.670), that establish a 

schedule to be used in calculating proposed fines under A.S. 46.03.758. 

In addition to the civil fine provisions of A.S. 46.03.758, A.S. 46.030.759 establishes civil 

penalties for discharges of crude oil larger than 18,000 gallons. Under the crude oil penalty 

provisions, the court can assess a guilty party $8.00 per gallon for the first 420,000 gallons 

(1,000 barrels) spilled and $12.50 for every gallon over 420,000 gallons, regardless of the type of 

environment. Both statutory provisions allow a penalty to be reduced for every gallon of oil 

recovered and for mitigating circumstances. The provisions of A.S. 46.030.758 also allow the 

court to reduce a fine for an oil spill of less than 18,000 gallons to less than $500. 

Because the dollar per gallon penalty provisions of A.S. 46.03.758 and 46.03 .759 apply only 

after a party has been found guilty of the illegal discharge of oil in a civil suit, a penalty can be 

reduced for specific reasons, and civil suits against oil spillers in Alaska are rare, ADEC does not 

routinely expend the effort to develop legally defensible estimates of the quantity of oil involved 

in each oil spill. In administrative enforcement actions that ADEC may take following an oil 

spill, such as a Compliance Order by Consent, any monetary restitution paid to the State as part 

of the Order may be based on the dollar per gallon penalty provisions and schedule, but are 

negotiated as part of settling a potential legal action. 

No data concerning oil spills within the NPRA were obtained. Hart Crowser inquiries to BLM , 

the agency with surface management and protection responsibilities in NPRA since 1977, did not 

yield any oil spill data. Two publications that discussed oil exploration activities in NPRA did 

not identify any specific spills that met the size threshold for inclusion in this study and 

analysis4

. Hanley5 wrote that when the Navy resumed oil exploration activities in NPRA in 

1974, that there were chronic problems, which included minor fuel spills. He also states that 

 

4

 Hanley et. al. 1981 and Gryc 1985. 5

 Hanley et. al. 1981, page 195. 
35 

while several fuel spills of 800 to 1,000 gallons in size occurred during the U.S. Department of 

the Interior’s exploration program beginning in 1977, spills of that size or larger had not 

occurred more recently (1979-1980)6

. Gyrc7 wrote that there were a few minor fuel leaks and 

spills at drill sites and from mobile trains during the Department of the Interior’s exploratory 

activities from 1977 to 1982. 

Current and Historical Oil Spill Notification Requirements

United States Federal Oil Spill Notification Requirements 

Federal oil spill notification requirements exist under the Federal Water Pollution Control Act 

(FWPCA), as amended by the Clean Water Act (CWA) amendments and the Oil Pollution Act of 

1990 (OPA). Notification requirements also exist under the Comprehensive Environmental 

Response, Compensation, and Liability Act (CERCLA) as amended. 

The FWPCA, enacted in 1948, prohibited the discharge of oil to the navigable waters. However, 

it was not until enactment of the CWA in 1972 that amendments were added which began to 

require notification of the U.S. Government for discharges of oil to the waters of the United 

States. Further amendments, which did not significantly change the notification requirements, 

were made in the CWA of 1977. Finally, OPA enacted in 1990 has further strengthened the 

FWPCA’s oil spill notification requirements and penalties. 

Section 311(b)(6) of the CWA8

 requires notification be made to the appropriate U.S. 

Government agency by the owner, operator, or person in charge of a vessel or an onshore or 

offshore facility that discharges oil into the navigable waters of the United States. EPA and the 

Coast Guard share oil spill notification and cleanup oversight or response responsibilities, based 

on whether the spill occurs in inland or marine waters. The Coast Guard has adopted oil 

discharge notification regulations that apply to vessels9. The EPA first adopted oil discharge 

notification regulations in September 1970. Prior to that time, there was no federal requirement 

to report oil spills promptly10. These regulations, found in 40 CFR 110, require that the owner, 

operator, or person in charge of a vessel or an onshore or offshore facility notify EPA when oil is 

discharged to the waters of the United States in a quantity that will be harmful11. The regulations 

define harmful quantity as the amount of oil that violates water quality standards or causes a film 

or sheen upon or discoloration of the surface of the water or adjoining shorelines or causes a 

sludge or emulsion to be deposited beneath the surface of the water or adjoining shorelines. It is 

known as the “sheen regulation.” EPA revised 40 CFR 110 in April 1987. These revisions 

modified the requirement that a spill be reported when the quantity of oil will be harmful, to 

when the quantity of oil may be harmful, and specified appropriate reporting requirements in 

terms of whether the discharge occurs in the territorial sea, the contiguous zone, or beyond 12 

miles. 

In 1997, the MMS also established oil spill notification requirements, under the authority of the 

CWA, for offshore oil for owners and operators of oil handling, storage, or transportation 

facilities that are located offshore of the coast line. The MMS requires the operator of an 

offshore facility to report to the NRC all oil spills from their facility, another offshore facility, 

 

6

 Hanley et. al. 1981, page 207. 7

 Gyrc 1985, page C54. 

8

 33 USC 1321(b)(5) 

9

 33CFR 151.15 Reporting Requirements. 

10 Federal Register, Volume 50, Page 9776 (50 FR 9776), March 11, 1985. 

11 See 40 CFR 110.6. 
36 

and from unknown origins. An offshore facility operator also must report all spills known or 

thought to be 1 barrel or more in size from their facility also must be reported directly to the 

MMS, and a written follow-up report must be filed with MMS within 15 days after the spillage 

has stopped. 

The CWA of 1972 established a criminal penalty for failure to notify the government of a 

discharge of oil. Upon conviction for a violation of the discharge notification requirement, the 

court could impose up to a $10,000 fine and, for a person, up to 1 year imprisonment12. These 

penalties were increased by OPA in 1990, making failure to report a discharge of oil a Class D 

felony, with a maximum penalty of a $250,000 fine and up to 5 years imprisonment for a person. 

OPA also added a maximum penalty of $250,000 fine and 15 years imprisonment, for a person 

convicted of multiple violations, and increased the maximum fine for an organization to 

$500,000. 

Enactment of CERCLA in 1980 extended U.S. Government notification requirements to oil 

releases on land, provided that a discharge contains a hazardous substance identified by the Act 

above the established reportable quantity for the substance (e.g., the discharge of oil containing 

10 pounds or more of benzene). The notification regulation adopted by EPA under CERCLA is 

found as part of the National Contingency Plan13. Discharge notifications to meet the 

requirements of either the FWPCA, for the Coast Guard or EPA, or CERCLA can be made 

through the NRC , a national clearinghouse, operated by the U.S. Coast Guard, for reporting all 

types of pollution incidents. The original penalty established in CERCLA for failure to report a 

discharge of a hazardous substance was a maximum fine of $10,000 and, for a person, up to 1 

year imprisonment. In 1986, Congress increased the CERCLA’s penalties for failure to make the 

required notification, making the fine a maximum of $250,000 and increasing the imprisonment 

penalty to 3 years, with a maximum of 5 years for a second violation. 

Alaska Oil Spill Notification Requirements 

Alaska’s current oil spill notification requirements, found in Title 18, Chapter 75, Section 300 

(18 AAC 75.300), set out requirements for the reporting of both oil and hazardous substances 

spills based on the material, the quantity spilled, and whether the spill affects land or water. 

These notification requirements have been in effect, in much the same form, since April 1977. 

The underlying statutory authority for the regulation is found in Alaska Statutes Title 46, Chapter 

03, Section 755 (AS46.03.755) Discharge Reporting, enacted by the Alaska Legislature in 1976. 

Failure to report an oil spill as required by 18 AAC 75.300 and AS 46.03.755 is a Class A 

misdemeanor and, upon conviction, is punishable by: 

• A $5,000 fine and up to 1 year imprisonment, if the defendant is a person; or 

• A $200,000 fine or up to two times the pecuniary gain or loss that would be realized by 

the defendant as a result of the violation, if the defendant is an organization. From 1978 

to 1990, the maximum fine for an organization was $100,000. 

Prior to the adoption of 18 AAC 75.300 in 1977, Alaska’s oil spill notification requirement was 

found in older Alaska Department of Health and Welfare (ADHW) regulations which extended 

 

12 33 USC 1321 (b)(5). 

13 40 CFR 300.405 (b) Discovery or Notification. 
37 

back to at least 195914. The ADHW was the agency with primary responsibility for 

administering Alaska’s environmental laws prior to the Alaska Legislature’s creation of ADEC 

in 1971. The ADHW regulation required only the submittal of a written report for an oil spill 

within three days. No spill volume was specified in the notification requirement. The 

underlying statutory authority for the regulatory notification requirement appears to be general 

statutory prohibitions on environmental pollution15 and nuisances16. Penalties for failure to 

notify the state of an oil spill were a $100 to $500 fine and imprisonment of up to 30 days. 

The Alaska Oil and Gas Conservation Commission (AOGCC) adopted regulations in 1980 that 

require the immediate notification of the AOGCC for uncontrolled accidental losses of oil that 

occur from oil drilling, production, injection, and abandonment activities. The existing 

regulations require notification for releases of greater than ten barrels. Prior to November 1999, 

the requirement called for the notification of any accidental loss. The penalties for failure to 

report an accidental loss to the AOGCC are the same as the penalties for failure to report a spill 

to the ADEC. 

TAPS Right-of-Way Stipulations 

Both the State of Alaska and the federal right-of-way leases for the TAPS contain nearly 

identical notification requirements for oil spills from construction and operation of the pipeline. 

State of Alaska Stipulation 2.13.1 prohibits discharges of oil or other pollutants in violation of 

state law or regulations and requires the immediate reporting of any discharge to the Pipeline 

Coordinator and other state officials required by law to be given notice. State Stipulation 2.13.2 

requires immediate notice of any spill or leakage from the pipeline, the Valdez Marine Terminal, 

and any storage or refueling facility and equipment to the Pipeline Coordinator and other state 

officials required by law to be given notice. An oral notification must be confirmed in writing as 

soon as possible. 

Federal Stipulation 2.13.1 prohibits the discharge of oil into or upon the navigable waters of the 

United States, adjoining shorelines, or waters of the contiguous zone in violation of FWPCA as 

amended or the laws and regulations of the State of Alaska. The stipulation requires the 

immediate notification of discharges to the Department of the Interior Authorized Officer and 

other state and federal officials required by law to be notified. Federal Stipulation 2.13.2 

requires immediate notice be given of any spill or leakage from the pipeline, the Valdez Marine 

Terminal, and any storage facility to the Authorized Officer and other state and federal officials 

required by law to be given notice. An oral notification must be confirmed in writing as soon as 

possible. 

Other Federal and State Notification Requirements 

Federal and state land management agencies, including the BLM; Department of the Interior, 

Fish and Wildlife Service (USFWS); and the Alaska Department of Natural Resources also 

routinely require notification of spills that occur on lands under their administration. These 

notification requirements, similar to the TAPS right-of-way stipulations described above, 

typically are included as conditions of mineral leases, pipeline rights-of-way, and land use 

 

14 7 AAC 01.02.04.501(h) 

15 AS 46.03.710, and AS 46.05.170 prior to 1971. See 3Ch 120 SLA 1971. 

16 AS 46.10.010 prior to 1971. 
38 

permits issued by the agencies. Because these types of notification requirements are not found in 

statutes or regulations, their current and historical requirements are not described in this report. 

Canadian Notification Requirements

In Canada, statutes and regulations are first published in the Canada Gazettes and then 

consolidated every decade or so. Although consolidated statutes and regulations are cited, 

according to the Canada Department of Justice, consolidated statutes and regulations are not 

currently considered the official version. When consolidation occurs, the original year of 

enactment and early amendments are not necessarily carried forward. Information currently 

available from the regulatory agencies and the Canada Department of Justice was obtained, but 

further research into the full history of Canada’s oil spill notification requirements would require 

time-consuming research in the annual Canada Gazettes. 

The latest consolidation of Canada’s statutes occurred in 1985 and is named the Revised Statutes 

of Canada (R.S.C.). The most recent consolidation of the regulations occurred in 1978 and is 

named the Consolidated Regulations of Canada (C.R.C.). Lowercase “c” is the abbreviation for 

chapter and lowercase “s” is the abbreviation for section in the regulations. Statutory Orders and 

Regulations (S.O.R.) refer to the regulations enacted between consolidations. Specific acts and 

accompanying regulations that contain oil spill notification requirements are discussed below. 

Fisheries Act 

The Fisheries Act (R.S.C. 1985, c. F-14.81) is the primary federal means of managing water 

resources by protecting fish and fish habitat in Canadian waters. This Act originally was enacted 

no later than 1973. The current Fisheries Act sets penalties as high as $1 million in fines and 

three years in jail, depending on which offense is alleged, and whether the prosecution proceeds 

by way of a summary proceeding or by indictment. 

Canada Oil and Gas Operations Act 

The Canada Oil and Gas Production and Conservation Act, which was amended by the Canada 

Petroleum Resources Act (which also repealed the Canada Oil and Gas Act), became the Canada 

Oil and Gas Operations Act (R.S.C. 1985, c. O-7). The Canada Oil and Gas Operations Act was 

enacted no later than 1979. According to definitions in this Act, “‘former regulations’ means the 

Canada Oil and Gas Land Regulations made pursuant to the Public Lands Grants Act and the 

Territorial Lands Act and includes orders made pursuant to those Regulations.” 

Section 25 of the Oil and Gas Operations Act includes the duty to report spills: 

“Where a spill occurs in any area to which this Act applies, any person who at the time of 

the spill is carrying on any work or activity related to the exploration for or development 

or production of oil or gas in the area of the spill shall, in the manner prescribed by the 

regulations, report the spill to the Chief Conservation Officer.” 

Liability is assigned to persons involved, to the extent determined, according to the degree of 

fault or negligence proved against them. 

Canada Oil and Gas Drilling and Production Regulations (C.R.C. 1978, c.1517) are part of the 

Territorial Lands Act and were adopted no later than 1978. These regulations govern oil and 

natural gas drilling and production procedures. If an accident occurs, such as a well flowing out 

of control, or any breaks or leaks in tanks or pipelines from which any serious loss of oil occurs, 
39 

the license owner/operator must report to the Oil Conservation Engineer immediately by 

telegraph, telephone or radio, with subsequent letter confirmation. Violations of the regulations 

can result in cancellations of licenses, permits, or leases. A “serious loss of oil” has not been 

defined in the regulations or in subsequent guidance issued by the NEB. 

Canada Oil and Gas Drilling Regulations (SOR/79-82), adopted in 1979, are part of the Canada 

Oil and Gas Operations Act, and primarily address oil and natural gas drilling programs. If a 

significant event occurs, such as a spill, notification to the Chief Safety Officer or the Chief 

Conservation Officer is required. A “significant event” has not been defined in the regulations or 

in subsequent guidance. Failure to report a spill is considered an offense and the penalties for a 

violation are assumed to be as described in the Act. 

Canada Oil and Gas Operations Regulations (SOR/83-149), adopted in 1983, also are part of the 

Canada Oil and Gas Operations Act and primarily govern operating license requirements. These 

regulations also require oil spills to be reported. Penalties are not included in this regulation, but 

are assumed to be as described in the Act. 

The Canada Oil and Gas Production and Conservation Regulations (SOR/90-791), adopted in

1990 under the Canada Oil and Gas Operations Act, govern oil and natural gas production sites 

and the production of oil and natural gas. These regulations require the reporting of a “serious 

accident or event,” such as a spill, to the Chief Safety Officer or the Chief Conservation Officer. 

Failure to report is considered an offense; penalties are assumed to be as described in the Act. 

The phrase, a “serious accident or event” is not defined in the regulations or in subsequent 

guidance issued by the NEB. 

Canada Oil and Gas Installation Regulations (SOR/96-118), adopted in 1996, under the Canada 

Oil and Gas Operations Act, also govern the operations of oil and natural gas installations. 

These regulations require the reporting, “of any situation or event involving any danger or 

accident to a person or property, including...explosion, loss of well control, hydrocarbon or toxic 

fluid spills, or significant damage to a pipeline, equipment or an installation.” Spill reports are to 

be given to the Chief Safety Officer. Failure to report is considered an offense; penalties are 

assumed to be as described in the Act. The phrase, “any situation or event involving any danger 

or accident” has not been further defined by the NEB. 

Arctic Waters Pollution Prevention Act 

The Arctic Waters Pollution Prevention Act (R.S.C. 1985, c. A-12) was enacted either in 1970 or 

1989. Two different information sources provided two different dates for its enactment. This 

federal statute requires that “a deposit of waste” in arctic waters above the 60th parallel to be 

reported forthwith to a pollution prevention officer. Failure to make a report can result in a fine 

up to $5,000 for a person or up to $100,000 for a ship. The Canada Shipping Act applies to 

waters below the 60th parallel. 

Regulations pertaining to oil spills under the Arctic Waters Pollution Prevention Act include the 

Arctic Waters Pollution Prevention Regulations (C.R.C. 1978, c.354). The regulations expanded 

the reporting requirements to include “any undertaking on the mainland or islands of the 

Canadian arctic or in the arctic waters that, by reason of any accident or other occurrence, is in 

danger of causing any deposit of waste.” Deposits of industrial waste are allowed, “if the 

industrial waste is of a type and in a quantity and is deposited under conditions authorized by or 

under the Oil and Gas Production and Conservation Act, the Territorial Lands Act or the Public 

Lands Grants Act, whichever is applicable.” Current limits of liability are: 
40 

• For a pipeline operation, “an amount equal to the product of $500 and the volume, 

measured in barrels, of the section of the pipeline between the shut-off valves located on 

either side of the point in the pipeline from which the deposit of waste originates, divided 

by 7;” 

• For an operation engaged in exploring for, developing or exploiting oil and gas, $40 

million. This $40 million limit has four amendment citations for 1979, 1980, and 1981; 

and 

• For ships (ship and cargo owners), an amount determined by multiplying 2,000 gold 

francs by the tonnage to a maximum of 210 million gold francs. 

Canada Shipping Act 

The Canada Shipping Act (R.S.C. 1985, c. S-9.97) empowers the government to enact 

regulations that require reporting of discharges. The Act controls ship-borne pollution in all 

Canadian waters and fishing areas, except waters within certain zones under the Arctic Waters 

Pollution Prevention Act. Pollution from ships engaged in oil and gas exploration, production, 

or processing in areas under the Oil and Gas Production and Conservation Act also are exempted 

from the Canada Shipping Act. 

Pollutant Discharge Reporting Regulations (SOR/95-351) were adopted in 1995 under the 

Canada Shipping Act. They replaced earlier regulations by the same name, adopted in 1992 

(SOR/92-211). According to the 1995 version, immediate reporting is required when “the 

discharge is prohibited by the Act, the Arctic Waters Pollution Prevention Act or regulations 

made under these Acts.” The report must be made to a pollution prevention officer where the 

discharge of a pollutant occurs. In 1998, an amendment was made including reporting by “an 

operator of an oil handling facility.” Penalties are not described and are assumed to be similar to 

the Arctic Waters Pollution Prevention Act. 

The Onshore Pipeline Regulations 

The Onshore Pipeline Regulations (SOR/89-303), adopted in 1989, as part of the National 

Energy Board Act, apply to onshore pipelines constructed, operated or abandoned after June 30, 

1989. The regulations require the reporting of uncontained spillage of oil in excess of 1.5 cubic 

meters (approximately 397 gallons). Penalties are not discussed. 

The Northwest Territories Waters Act 

The Northwest Territories Waters Act (R.S.C. 1992 c. 39), enacted in 1992, requires the 

reporting of unlawful deposits of waste. Currently, every person who is guilty of an offense, 

including not reporting an oil spill, and liable on summary conviction may be fined up to 

$100,000 dollars and/or be imprisoned for a term not exceeding 1 year. The associated 

regulations, the Northwest Territories Waters Regulations (SOR/93-303), were adopted in 1993 

and govern applications for licenses to use water or deposit waste. Licenses are generally 

required for oil and gas exploration, production and transportation activities. 

Inter-Agency Spill Reporting Working Agreement 

In addition, in 1992, a letter of agreement was set up concerning response to spills in the 

Northwest Territories between Indian and Northern Affairs Canada, Environment Canada, 

National Energy Board, Government of the Northwest Territories, Canadian Coast Guard 

(Transport Canada), and the Inuvialuit Lands Administration. The letter of agreement clarified 
41 

which agency would take the lead in each spill. This working agreement is currently being 

updated to include the Government of Nunavut. 

Crude Oil Production, Pipeline Mileage and Throughput, and Tanker Transport Quantities

Crude oil production statistics were readily available for the study areas from the State of Alaska 

and the NEB. The AOGCC closely tracks crude oil production throughout Alaska. The 

Commission requires the monthly reporting of crude oil, natural gas, and natural gas liquid 

production and injection statistics by all oil field operators. The ADNR Division of Oil and Gas 

publicly reports the AOGCC statistics on a regular basis in their periodic publication, Historical 

and Projected Oil and Gas Consumption. The NEB closely tracks crude oil production in 

Canada, and production statistics were readily provided by that agency. 

Mileages for the larger pipelines including the TAPS, the Norman Wells Pipeline, and the sales 

oil pipelines on Alaska’s North Slope were readily available from ADNR, in Alaska, and the 

NEB, in Canada. Each pipeline is built on an individual right-of-way, granted by ADNR, which 

specifies the pipeline’s length. The NEB was able to furnish the length of the Norman Wells 

Pipeline from the agency’s regulatory records. 

The regulatory agencies in Alaska and Canada do not keep records of the mileages of the smaller 

pipelines, termed field gathering lines or cross-country lines, that run from production well pads 

to processing facilities, and, in some cases, from processing facilities to one of the larger 

pipelines. Construction and operation of the field gathering lines are allowed as part of the 

surface-use provisions of the mineral lease for oil production. In some cases, wetland fill or 

surface use permits are issued, but Hart Crowser could locate no comprehensive compilation of 

the current or historical mileages for these pipelines. One suggestion Hart Crowser received for 

gathering data on the smaller pipelines on Alaska’s North Slope was to obtain a scale map of the 

oilfields and then measure all of the pipelines. This approach to gathering the data was not 

feasible given the time and resource constraints of the project, and it would not have provided 

the historical data that MMS sought. Hart Crowser obtained field gathering line mileage data 

from a single year for two Alaskan North Slope oil fields, which ARCO gathered in response to a 

request for data on these smaller pipelines from the U.S. Department of Transportation. 

However, the company did not have any historical compilations of field gathering line data that 

they could provide for the study. 

Throughput data for the larger Alaskan pipelines were calculated using the crude oil production 

throughput table in ADNR’s publication, Historical and Projected Oil and Gas Consumption. 

Because of the organization of the table and knowing the layout of the pipelines, the individual 

pipeline throughputs by year were readily calculated. TAPS throughput by year was taken 

directly from a table in Historical and Projected Oil and Gas Consumption. The NEB supplied 

throughput for the Norman Wells Pipeline and tanker shipment volumes from the agency’s 

regulatory records. Hart Crowser was able to corroborate these volumes in other reports, such as 

the DIAND Northern Oil and Gas Annual Reports. 

Oil Spill Data Statistical Analysis and Estimation of Spill Risk

Consideration was given to the statistical robustness and validity of potential oil spill risk 

estimators. Because there are a limited number of data points, the statistical parameters 

estimated are subject to considerable uncertainty. Large variations in statistically estimated 

parameters are characteristic in the analysis of rare events, such as oil spills of 100 barrels and 
42 

greater. In cases where a limited amount of data exists, the only way to decrease the uncertainty 

in these parameters is to gather additional data. In the case of this study, to decrease the 

uncertainty, additional data would need to be gathered over a longer time period of time. For 

this study, the number and study area distribution of oil spills of 100 barrels and greater and 500 

barrels and greater are shown in Table 10. Because there are so few Canadian spills, all of the 

Canadian study areas have been combined in the table. 

Table 10 

Number And Distribution Of Oil Spills In Study Areas

Study Area Number of Spills 

100 - 499 bbls 

Number of Spills 

≥500 bbls 

Alaska - Onshore North Slope (E. of NPRA) 32 9 

Alaska - TAPS 56 14 

Canada - all study areas 10 5 

The single oil spill that was caused intentionally, the February 1978 Steele Creek oil spill along 

the TAPS, was included in the statistical analysis and risk estimation. Intentional spills should 

be included in the estimation of potential oil spill risk because the sabotage of facilities is a real 

potential source of spills. A large percentage of TAPS and all pipelines on the Alaska North 

Slope are installed above ground, often in locations that provide relatively little protection 

against sabotage. 

All of the pipelines included in the study are in the midst of their useful lives. The risk of an oil 

spill might be expected to increase with the age of the pipeline. However, the effect of 

incomplete lifecycles on the potential for oil spills from pipelines is difficult to gauge with any 

precision or accuracy because there are many other factors other than age that also affect the risk 

of a spill from any particular pipeline. Some of these other factors affecting oil spill risk include: 

• The potential for corrosion or erosion of a particular pipeline, especially a field gathering 

line, which is related to the amount of sand and saltwater in the oil the pipeline carries 

and on the number of elbows in the pipeline; 

• Engineering, construction, and monitoring of the condition of pipelines installed in 

ground susceptible to settling or other ground movement; and 

• The type and amount of maintenance of the pipeline. 

Hart Crowser evaluated whether the number or volume of oil spills should be correlated to oil 

production, pipeline mileage, pipeline throughput, or some other variable in calculating oil spill 

risk. Oil production was chosen for use in the risk estimates because oil production is well 

documented each year, it allows a simple calculation of spill rate, and it allows direct comparison 

with calculations of oil spill rates in other studies. Hart Crowser decided against using pipeline 

mileage because it was difficult to obtain pipeline mileage data for the smaller field gathering 

pipelines, and especially mileages over time. In addition, other factors that could affect the 

potential for a spill or the size of a spill from a pipeline are not accounted for using mileage 

alone. These factors include pipeline diameter, potential for corrosion or erosion, potential for 

damage by earth movement or other causes including sabotage, pipeline age, and pipeline 

maintenance. Hart Crowser also decided against the use of pipeline throughput as the variable 

because annual throughput data is not readily available for the smaller pipelines and, while 
43 

eliminating pipeline diameter as a spill risk factor, pipeline throughput does not take into account 

the other potential risk factors already mentioned in connection with pipeline mileage. 

All of the spill data used in the analysis is from onshore oil spills. No offshore spills were 

identified in the Alaskan study areas and only two offshore spills were identified in the Canadian 

study areas. Almost certainly there are some differences in the risk factors between onshore and 

offshore oil spills. However, because so few offshore oil spills were identified as part of this 

study, there is not enough statistical data to determine any differences. 

In comparison to Anderson and LaBelle (1994), this study gathered and used data on oil spills 

with a lower quantity threshold: 100 barrels and larger compared to 1,000 barrels and larger. 

This study also gathered and used data on different sources of oil spills than Anderson and 

LaBelle. The sources of spills included in the Anderson and LaBelle study and the number of 

spills identified for these sources were: 

• Offshore oil drilling and production platforms located in the U.S. Outer Continental 

Shelf, 11 spills; 

• Offshore pipelines located in the U.S. Outer Continental Shelf, 12 spills; 

• Tankers transporting crude oil in worldwide coastal and offshore waters, 213 spills; 

• Tankers transporting crude oil in U.S. coastal and offshore waters, 38 spills; 

• Tankers transporting Alaska North Slope crude oil, 10 spills; and 

• Barges transporting petroleum products in U.S. coastal, offshore, and inland waters, 153 

spills. 

This study gathered and used data on oil spills related to oil and gas exploration, construction, 

development, production, storage, and transportation in specific Alaskan and Canadian study 

areas. The sources of spills included in this study and the number of spills identified among 

these spill types are: 

• Construction Camps, 21 spills, all in Alaska; 

• Exploration Support Facilities, 3 spills, 2 of which were in Alaska; 

• Exploration Well Sites, 4 spills, 1 of which was in Alaska; 

• Highways; 37 spills, 36 of which were in Alaska; 

• Operations Support Facilities, 18 spills, all in Alaska; 

• Pipelines, 11 spills, 10 of which were in Alaska; 

• Pipeline Pump Stations, 5 spills, all in Alaska; 

• Production Processing Facilities, 13 spills, 10 of which were in Alaska; 

• Production Well Sites, 11 spills, 7 of which were in Alaska; 

• Unspecified Source, 1 spill in Alaska; and 

• Vessel Leak, 2 spills in Canada. 

Hart Crowser first constructed a cumulative frequency plot of the data for the size of Alaskan 

spills, as shown in Figure 1. To facilitate easy plotting of the data analysis figures, abbreviations 

were used for different variables as shown in Table 11. Figure 1 shows a bow characteristic of 

lognormal data. Therefore, the data were re-plotted on a lognormal scale, as shown in Figure 2. 

For the limited number of data points, it appears that two lognormal populations could 
44 

reasonably describe this population. In Figure 2, two lines approximating the two lognormal 

populations are shown. The higher population is more linear than the lower. This is typical in 

lognormal data because of the greater proportional effect of rounding and data errors at low 

values. Lines showing the approximate theoretical distributions are shown only in Figure 2 to 

avoid biasing the reader. 

A cumulative frequency plot of the Canadian oil spill size data also was constructed on a 

lognormal basis, as shown in Figure 3. Overlaying the Alaskan and Canadian plots indicated 

more or less the same distribution. The Canadian data was not used in further analysis because 

of doubts about its completeness, the fact that 15 points were below the 30 point empirical rule 

for number of samples, and the fact that the 112 Alaska data points would overpower the 15 

Canadian points. The use of only Alaskan data also appears consistent with Anderson and 

LaBelle (1994), who state that “U.S. ... rates will better reflect the magnitude of spill occurrence 

under U.S. regulatory and operational controls, and the individual spill and production records 

are readily available.” However, Hart Crowser also redid the analysis using the total oil spill 

data set (with Alaskan and Canadian crude oil production for rates). The results were 

statistically the same as for the Alaskan data alone. The rerun of all the combined Alaskan and 

Canadian data is included as Appendix B to the report. 

Because the Alaskan data was more or less a mixture of two lognormal populations, exploratory 

data analysis on the relevant independent variables was conducted, as shown in Figures 4 

through 10. These figures present box plots on a logarithmic basis for the dataset and show the 

median, quartile values, and outlying points. In Figure 4, it can be seen that there appears to be 

little statistical difference in terms of spills that occurred within the ONS and in the TAPS study 

areas. This lack of statistical difference between the ONS and TAPS study areas was confirmed 

by an analysis of variance in which no statistically significant difference between the two 

populations was found. 

In Figure 5, which shows spill size versus month, some type of a cycling trend in the data may be 

interpreted, with the lowest number of spills occurring in March, and the highest volume of spills 

occurring in July. However, a linear regression on month showed no statistically significant 

correlation. A statistically significant correlation at the 99 percent level of confidence was 

confirmed by a logarithmic analysis of the data as presented in Table 12. As a general check on 

the fluctuation of the data set, logarithmic spill size versus the day of the month also was plotted, 

as shown in Figure 6. This particular dataset appears to be quite random. Once again, an 

analysis of variance, as seen in Table 13, showed no statistically significant difference between 

days. 

Figure 7 is a box plot of the logarithm of the spill size versus the year. With the exception of 

1979, there appears to be little trend in median of the data. An analysis of variance of this data 

showed no statistically significant difference in the years. Figure 8 shows the logarithm of spill 

size versus facility type. In general, there appears to be little difference between the types of 

spills associated with the various facilities with the exception of pipelines. An analysis of 
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Cumulative Frequency US Spill Size

Figure 1

Theoretical Quantiles

Sample Quantiles
46 

TABLE 11 

ABBREVIATIONS USED IN FIGURES

Variable Abbreviation 

Study Areas

ALASKA – Trans Alaska Pipeline System TAPS 

ALASKA – Onshore North Slope (E. of NPRA) ONS 

CANADA - Beaufort Sea CBS 

CANADA - Onshore Mackenzie River Delta CMRD 

CANADA - Norman Wells CNW 

CANADA - High Arctic Islands CHAI 

Facility Type

Construction Camp CC 

Exploration Support Facility SF 

Exploration Well Site PRD 

Highway HWY 

Operations Support Facility SF 

Pipeline PIPE 

Pipeline Pump Station PIPE 

Production Processing Facility PRD 

Production Well Site PRD 

Unspecified U 

Spill Cause

Facility Explosion O 

Facility Piping Leak FP 

Facility Tank Leak FT 

Human Error U 

Pipeline Leak PL 

Production Well Leak O 

Tank Vehicle Accident TV 

Unspecified Cause U 

Vessel Leak VL 

Oil Type

Crude Oil CO 

Diesel Fuel or Gasoline D 

Diesel Fuel/Heating Oil D 

Gasoline G 

Turbine/Jet Fuel TF 

Unspecified U 

Affected Media

Land L 

Land and Water WL 

Retained in secondary containment, on facility pad, 

or in impoundment R 

Unspecified U 
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Cumulative Frequency US Log Spill Size

Figure 2

Theoretical Quantiles

Sample Quantiles
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Cumulative Frequency Canada Log Spill Size

Figure 3

Theoretical Quantiles

Sample Quantiles
ONS TAPS

5 e+03 1 e+04 2 e+04 5 e+04 1 e+05 2 e+05 5 e+05

Log US Spill Size vs StudyAREA Box plot

Figure 4
1 2 3 4 5 6 7 8 9 10 

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Log US Spill Size vs Month Box plot

Figure 5
51 

TABLE 12 

ANALYSIS OF VARIANCE OF INDIVIDUAL SPILL EVENTS BY MONTH

lm(formula = log(SpillHigh) ~ Amonth) 

Residuals: 

Min 1Q Median 3Q Max

-1.5185 -0.5982 -0.1919 0.4648 3.7786 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 9.0550 0.3667 24.693 <2e *** 

AmonthAug 0.1406 0.4614 0.305 0.7612 

AmonthDec 0.5858 0.4781 1.225 0.2234 

AmonthFeb 0.5844 0.4889 1.195 0.2348 

AmonthJan 0.5256 0.5021 1.047 0.2978 

AmonthJul 1.1059 0.4691 2.357 0.0204 * 

AmonthJun 0.9399 0.4614 2.037 0.0443 * 

AmonthMar -0.3980 0.5681 -0.701 0.4852 

AmonthMay 0.2361 0.4691 0.503 0.6159 

AmonthNov -0.3103 0.4614 -0.672 0.5029 

AmonthOct -0.3147 0.5186 -0.607 0.5454 

AmonthSep 0.1712 0.5186 0.330 0.7420 

Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Residual standard error: 0.9702 on 99 degrees of freedom 

Multiple R-Squared: 0.2087, Adjusted R-squared: 0.1207 

F-statistic: 2.373 on 11 and 99 degrees of freedom, p-value: 0.01195 
1 2 3 4 5 6 7 8 9 11 13 15 17 19 21 23 25 

5 e+03 1 e+04 2 e+04 5 e+04 1 e+05 2 e+05 5 e+05

Log US Spill Size vs Day Box plot

Figure 6
53 

TABLE 13 

ANALYSIS OF VARIANCE OF INDIVIDUAL SPILL EVENTS BY YEAR

lm(formula = log(SpillHigh) ~ Ayear) 

Residuals: 

Min 1Q Median 3Q Max 

-1.98124 -0.51387 -0.09211 0.34085 2.95913 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 9.23968 0.57207 16.151 <2e-16 *** 

AyearY71 1.47474 1.14414 1.289 0.2009 

AyearY72 0.66381 1.14414 0.580 0.5633 

AyearY73 0.14848 0.80903 0.184 0.8548 

AyearY74 0.11242 0.80903 0.139 0.8898 

AyearY75 0.43975 0.63465 0.693 0.4903 

AyearY76 -0.18432 0.68375 -0.270 0.7881 

AyearY77 0.43562 0.64538 0.675 0.5015 

AyearY78 1.21921 0.80903 1.507 0.1355 

AyearY79 1.84654 0.75678 2.440 0.0168 * 

AyearY80 -0.50826 0.80903 -0.628 0.5315 

AyearY81 0.09226 0.70064 0.132 0.8955 

AyearY82 0.39884 0.75678 0.527 0.5995 

AyearY83 -0.38340 0.70064 -0.547 0.5857 

AyearY84 -0.59703 0.75678 -0.789 0.4324 

AyearY85 -0.10958 0.75678 -0.145 0.8852 

AyearY86 -0.67908 0.72362 -0.938 0.3507 

AyearY87 -0.08202 0.90452 -0.091 0.9280 

AyearY88 -0.34575 0.90452 -0.382 0.7032 

AyearY89 0.27484 0.68375 0.402 0.6887 

AyearY90 0.27524 0.80903 0.340 0.7345 

AyearY92 -0.25248 1.14414 -0.221 0.8259 

AyearY93 0.15640 0.67081 0.233 0.8162 

AyearY94 -0.59251 0.80903 -0.732 0.4660 

AyearY96 1.19667 1.14414 1.046 0.2986 

AyearY97 -0.58789 0.80903 -0.727 0.4694 

Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Residual standard error: 0.9909 on 85 degrees of freedom 

Multiple R-Squared: 0.2914, Adjusted R-squared: 0.08294 

F-statistic: 1.398 on 25 and 85 degrees of freedom, p-value: 0.1303 
1970 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 

5 e+03 1 e+04 2 e+04 5 e+04 1 e+05 2 e+05 5 e+05

Log US Spill Size vs Year Box plot

Figure 7
CC HWY Pipe Prd SF 

5 e+03 1 e+04 2 e+04 5 e+04 1 e+05 2 e+05 5 e+05

Log US Spill Size vs FacilityType Box plot

Figure 8
56 

variance of facility type showed that there was a statistically significant difference for pipelines. 

This analysis of variance is given in Table 14. 

Figure 9 shows spill size versus oil type. An analysis of variance by oil type, presented in Table 

15, showed that, in general it appears that crude oil spills tend to be larger than other types of oil 

spills. 

Figure 10 is a box plot of the logarithm of the spill size versus affected media. 

In performing a statistical analysis of the data, it is important to look at the cumulative frequency 

plots by selected independent variables. This is done in Figures 12 through 33. Figure 11 is a 

box plot of the logarithm of the spill size versus the spill cause. In general, those spills 

associated with pipelines appear to be largest. Figures 12 and 13 show cumulative frequency 

plots for the two different areas. The TAPS study area, Figure 12, appears to be a fairly clear 

mixture of two lognormal populations. The ONS study area shows less of a break, indicating 

perhaps a single population. 

Figures 14 through 19 show cumulative frequency plots of the logarithm of the spill size versus 

the spill cause combined. In Figure 14, which is a plot of spills from tank vehicles, there is little 

apparent variability. This is more or less consistent with the fact that a tank vehicle spill should 

be expected to have a firm upper limit. Facility piping, as shown in Figure 15, shows a bow but 

no clear break in population. Pipeline leaks, Figure 16, show what may be a single lognormal 

population. Facility tank leaks, Figure 17, shows a single lognormal population. Unspecified 

spill causes, Figure 18, show a single lognormal population. Other spill causes, Figure 19, have 

such a small number of data points that no definite conclusions may be drawn. In general, 

overlaying all of the figures on one another indicates that they can probably reasonably be 

lumped together as a single population for statistical analysis. 

Figures 20 through 23 show cumulative frequency plots of the logarithms of spill volume versus 

oil type. Figure 20, for diesel fuel, appears to be a mixture of two lognormal populations. Figure 

21, for crude oil, again appears to be a mixture of two lognormal populations. Figure 22, for 

gasoline, shows a single lognormal population with one possible outlier. Again, this is consistent 

with a mixture of two lognormal populations. Figure 23, for turbine and jet fuel, again shows 

what may be a mixture of two lognormal populations. Figure 24 is two data points and is of little 

interest. However, Figure 24 overlies Figure 23 quite nicely. 

Figures 25 through 29 show cumulative frequency plots of the logarithms of spill volume versus 

facility type. Figure 25, for highways, is very similar to the tank vehicle spills and is entirely 

consistent with the assumption that most highway spills are from tank vehicles. Figure 26, for 

support facilities, shows a bowed lognormal population. Figure 27, for production facilities, 

seems to show a single lognormal population. Figure 28, for construction camps, appears to 

show a mixture of two lognormal populations. Figure 29, for pipelines, may be interpreted as a 

single lognormal population. 
57 

TABLE 14 

ANALYSIS OF VARIANCE OF SPILL EVENTS BY FACILITY TYPE

lm(formula = SpillHigh ~ FacilityType) 

Residuals: 

Min 1Q Median 3Q Max 

-106588 -12983 -2454 1515 561412 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 24772 14786 1.675 0.096822 . 

FacilityTypeHWY -17237 18605 -0.927 0.356306 

FacilityTypePipe 85815 22906 3.746 0.000293 *** 

FacilityTypePrd -9663 21764 -0.444 0.657953 

FacilityTypeSF -4765 21170 -0.225 0.822357 

FacilityTypeU -19522 69350 -0.282 0.778878 

Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Residual standard error: 67760 on 105 degrees of freedom 

Multiple R-Squared: 0.2025, Adjusted R-squared: 0.1645 

F-statistic: 5.332 on 5 and 105 degrees of freedom, p-value: 0.0002088 

lm(formula = log(SpillHigh) ~ FacilityType) 

Residuals: 

Min 1Q Median 3Q Max 

-2.06337 -0.56860 -0.02809 0.29790 3.06059 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 9.6056 0.2056 46.728 <2e-16 *** 

FacilityTypeHWY -0.7116 0.2587 -2.751 0.0070 ** 

FacilityTypePipe 0.7518 0.3185 2.361 0.0201 * 

FacilityTypePrd -0.2601 0.3026 -0.860 0.3920 

FacilityTypeSF -0.2361 0.2943 -0.802 0.4243 

FacilityTypeU -1.0396 0.9642 -1.078 0.2834 

Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Residual standard error: 0.942 on 105 degrees of freedom 

Multiple R-Squared: 0.2088, Adjusted R-squared: 0.1711 

F-statistic: 5.542 on 5 and 105 degrees of freedom, p-value: 0.0001436 
CO D G TF 

5 e+03 1 e+04 2 e+04 5 e+04 1 e+05 2 e+05 5 e+05

Log US Spill Size vs OilType Box plot

Figure 9
59 

TABLE 15 

ANALYSIS OF VARIANCE OF INDIVIDUAL SPILL EVENTS BY OIL TYPE

lm(formula = SpillHigh ~ OilType) 

Residuals: 

Min 1Q Median 3Q Max 

-55174.6 -18358.6 -8205.8 -605.8 612825.4 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 59175 12851 4.605 1.15e-05 ***

OilTypeD -43569 16162 -2.696 0.00817 ** 

OilTypeG -49513 24607 -2.012 0.04674 * 

OilTypeTF -35682 26336 -1.355 0.17835 

OilTypeU -46734 52985 -0.882 0.37976 

Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Residual standard error: 72690 on 106 degrees of freedom 

Multiple R-Squared: 0.07324, Adjusted R-squared: 0.03827 

F-statistic: 2.094 on 4 and 106 degrees of freedom, p-value: 0.08667 

lm(formula = log(SpillHigh) ~ OilType) 

Residuals: 

Min 1Q Median 3Q Max 

-1.4988 -0.6814 -0.2326 0.3960 3.6252 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 9.7928 0.1793 54.627 <2e-16 *** 

OilTypeD -0.5730 0.2255 -2.542 0.0125 * 

OilTypeG -0.7958 0.3433 -2.318 0.0224 * 

OilTypeTF -0.3314 0.3674 -0.902 0.3691 

OilTypeU -0.5946 0.7391 -0.804 0.4230 

Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Residual standard error: 1.014 on 106 degrees of freedom 

Multiple R-Squared: 0.07436, Adjusted R-squared: 0.03943 

F-statistic: 2.129 on 4 and 106 degrees of freedom, p-value: 0.08229 
L R U 

5 e+03 1 e+04 2 e+04 5 e+04 1 e+05 2 e+05 5 e+05

Log US Spill Size vs AffectedMedia Box plot

Figure 10
FP FT O PL TV 

5 e+03 1 e+04 2 e+04 5 e+04 1 e+05 2 e+05 5 e+05

Log US Spill Size vs SpillCauseCombined Box plot

Figure 11
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−3 −2 −1 0 1 

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Cumulative Frequency US Log Spill Size[StudyAREA==TAPS]

Figure 12

Theoretical Quantiles

Sample Quantiles
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−3 −2 −1 0 1 

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Cumulative Frequency US Log Spill Size[StudyAREA==ONS]

Figure 13

Theoretical Quantiles

Sample Quantiles
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−3 −2 −1 0 1 

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Cumulative Frequency US Log Spill Size[SpillCauseCombined==

Figure 14

Theoretical Quantiles

Sample Quantiles
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Cumulative Frequency US Log Spill Size[SpillCauseCombined==

Figure 15

Theoretical Quantiles

Sample Quantiles
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Cumulative Frequency US Log Spill Size[SpillCauseCombined==

Figure 16

Theoretical Quantiles

Sample Quantiles
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Cumulative Frequency US Log Spill Size[SpillCauseCombined==

Figure 17

Theoretical Quantiles

Sample Quantiles
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Cumulative Frequency US Log Spill Size[SpillCauseCombined==

Figure 18

Theoretical Quantiles

Sample Quantiles
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Cumulative Frequency US Log Spill Size[SpillCauseCombined==

Figure 19

Theoretical Quantiles

Sample Quantiles
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−3 −2 −1 0 1 

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Cumulative Frequency US Log Spill Size[OilType==D]

Figure 20

Theoretical Quantiles

Sample Quantiles
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Cumulative Frequency US Log Spill Size[OilType==CO]

Figure 21

Theoretical Quantiles

Sample Quantiles
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Cumulative Frequency US Log Spill Size[OilType==G]

Figure 22

Theoretical Quantiles

Sample Quantiles
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Cumulative Frequency US Log Spill Size[OilType==TF]

Figure 23

Theoretical Quantiles

Sample Quantiles
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Cumulative Frequency US Log Spill Size[OilType==U]

Figure 24

Theoretical Quantiles

Sample Quantiles
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Cumulative Frequency US Log Spill Size[FacilityType==HWY]

Figure 25

Theoretical Quantiles

Sample Quantiles
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Cumulative Frequency US Log Spill Size[FacilityType==SF]

Figure 26

Theoretical Quantiles

Sample Quantiles
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Cumulative Frequency US Log Spill Size[FacilityType==Prd]

Figure 27

Theoretical Quantiles

Sample Quantiles
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Cumulative Frequency US Log Spill Size[FacilityType==CC]

Figure 28

Theoretical Quantiles

Sample Quantiles
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Cumulative Frequency US Log Spill Size[FacilityType==Pipe]

Figure 29

Theoretical Quantiles

Sample Quantiles
80 

Figures 30 through 33 show the logarithms of spill volume versus affected media. Figure 30, for 

land, shows a mixture of two lognormal populations, while Figure 31, for unspecified values, 

seems to be a single lognormal population. Figure 32, for land and water, shows a mixture of 

two lognormal populations. Figure 33, for those spills retained on a facility pad, in an 

impoundment, or within a secondary containment area, appears to be a single lognormal 

population. 

It is of interest to note that it is possible to globally interpret all of the spills as composed of two 

lognormal populations, one of which is average and the other that is larger. Hart Crowser 

conducted a statistical analysis on individual spill volumes by study area, facility type, oil type, 

affected media and spill cause combined, and did not find any particularly interesting correlation. 

Hence, the next phase of the analysis looked at annualized groupings of spills. Total spill 

volumes by year were accumulated and plotted on a cumulative frequency plot, as shown in 

Figure 34. This shows a mixture of several populations. 

If the data are re-plotted on a logarithmic scale, a single lognormal population emerges. This is 

shown in Figure 35. A count of the number of spills per year in the database is tabulated in 

Figure 36. This distribution is possibly Poisson; however, this hypothesis was not tested. A 

more interesting way of looking at the data to see if regulatory or reporting requirements have 

significantly affected spills is shown in Figure 37, where spill size is plotted by year. As can be 

seen by examining Figure 37, it appears that in the period from 1975 to 1979 there were a 

considerable number of large spills, and then after that, the number of spills dropped to a more or 

less constant rate. This same data is shown on a logarithmic scale in Figure 38. .Again, it 

appears that spills were relatively constant between 1969 and 1975, and from 1980 onward. It 

must be noted that 1977 is significant because crude oil production on North Slope and TAPS 

operation started in the middle of that year. However, the years of 1978 and 1979 fit with years 

of 1975 and 1977 visually better in Figure 38 than breaking the data at 1977. The number of 

spills as shown in Figure 39 again shows a larger number in the period from 1975 to 1980. On a 

count basis (Figure 39), there is some evidence that 1975,1976 and 1977 are a single high group. 

This corresponds well to the peak years of TAPS construction and development and construction 

of the North Slope oil fields. When the number of spills are grouped by 5-year periods 

(arbitrarily starting on years ending in 0 and 5 for calculation convenience), as shown in Figures 

40 and 41, it appears that the 1975 to 1979 period was the highest. This same conclusion is 

confirmed by Figure 42, which shows a count of spills by 5-year groups. The 1975 to 1979 

period appears to have the most number of spills. 

Calculated Oil Spill Risk Rates

Another way of investigating the data is on a rate basis. For a rate-basis type of investigation, 

some variable, which can be reasonably expected to correlate with the quantity being measured, 

is added to the dataset for analysis. In the case of the Alaskan oil spill data, total volume spilled 

divided by production was selected. As noted earlier, the units for this spill rate are U.S. gallons 

per million barrels produced. Because it was anticipated that a logarithmic analysis would give 

better results, 2,000 gallons was added to the total spill volume on each year for analysis. The 

rate data used are presented in Table 4, with assumptions of 450 million barrels of crude oil 

production for the Alaska - ONS study area and 9.924 million barrels of crude oil production for 

the Canada - Norman Wells study area for 1999. The value of 2,000 gallons is close to one-half 

of the minimum oil spill volume included in this analysis. A cumulative frequency plot of this 

variable is shown in Figure 43. This figure was not found to be particularly useful, so the data 

were re-plotted on a logarithmic basis as shown in Figure 44. Figure 44 shows what may be a 
81 

mixture of three lognormal populations. When these data are plotted on a yearly basis, as shown 

in Figure 45, it appears that prior to 1977, spill rates were considerably greater than in the 

subsequent years. Because of the low value of the spill rate after 1980, it is not possible to draw 

any conclusions 
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Cumulative Frequency US Log Spill Size[AffectedMedia==L]

Figure 30

Theoretical Quantiles

Sample Quantiles
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Cumulative Frequency US Log Spill Size[AffectedMedia==U]

Figure 31

Theoretical Quantiles

Sample Quantiles
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Cumulative Frequency US Log Spill Size[AffectedMedia==WL]

Figure 32

Theoretical Quantiles

Sample Quantiles
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Cumulative Frequency US Log Spill Size[AffectedMedia==R]

Figure 33

Theoretical Quantiles

Sample Quantiles
−2 −1 0 1 

0 e+00 1 e+05 2 e+05 3 e+05 4 e+05 5 e+05 6 e+05 7 e+05

Cumulative Frequency US Yearly Total Spill Size

Figure 34

Theoretical Quantiles

Sample Quantiles
−2 −1 0 1 

2 e+03 5 e+03 2 e+04 5 e+04 2 e+05 5 e+05

Cumulative Frequency Log US Yearly Total Spill Size+2000

Figure 35

Theoretical Quantiles

Sample Quantiles
−2 −1 0 1 

0 2 4 6 8 10 12

Cumulative Frequency US Yearly Spill Count

Figure 36

Theoretical Quantiles

Sample Quantiles
1970 1975 1980 1985 1990 

0 e+00 1 e+05 2 e+05 3 e+05 4 e+05 5 e+05 6 e+05 7 e+05

US Yearly Total Spill Size vs Year

Figure 37

YEAR

YearlySum
1970 1975 1980 1985 1990 

2 e+03 5 e+03 2 e+04 5 e+04 2 e+05 5 e+05

Log US Yearly Total Spill Size + 2000 vs Year

Figure 38

YEAR

YearlySum + 2000
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0 2 4 6 8 10 12

US Yearly Total Spill Count vs Year

Figure 39

YEAR

YearlySpills
1965 1970 1975 1980 1985 19

0 e+00 1 e+05 2 e+05 3 e+05 4 e+05 5 e+05 6 e+05 7 e+05

US Yearly Total Spill Size by 5 Year Group

Figure 40

YEAR5

YearlySum
1965 1970 1975 1980 1985 19

2 e+03 5 e+03 2 e+04 5 e+04 2 e+05 5 e+05

Log US Yearly Total Spill Size + 2000 by 5 Year Group

Figure 41

YEAR5

YearlySum + 2000
1965 1970 1975 1980 1985 19

0 2 4 6 8 10 12

US Yearly Spill Count by 5 Year Group

Figure 42

YEAR5

YearlySpills
−2 −1 0 1 

0 50000 100000 150000

Cumulative Frequency US Yearly Total Spill Volume Rate

Figure 43

Theoretical Quantiles

Sample Quantiles
−2 −1 0 1 

1 e+01 1 e+02 1 e+03 1 e+04 1 e+05

Cumulative Frequency Log US Yearly Total Spill Volume Rate+20

Figure 44

Theoretical Quantiles

Sample Quantiles
1970 1975 1980 1985 1990 

0 50000 100000 150000

US Yearly Spill Volume Rate +2000 vs Year

Figure 45

YEAR

SpillRate2000
98 

from Figure 45. When the data in Figure 45 is re-plotted on a logarithmic scale, as shown in 

Figure 46, a rather clear picture emerges that prior to 1980 spill rates were considerably greater 

than after 1980. This figure also indicates that the 5-year groupings used in Figures 40 through 

43 were statistically reasonable. 

Hart Crowser selected an oil spill risk rate based on volume, rather than a rate based on the more 

traditional variable of number of spills of a given size or above, because of the greater visual 

variability and a possible trend. This difference is shown in Figure 39 relative to Figure 46. The 

statistical significance of this visual analysis is confirmed in Tables 16, 17, and 18, which show 

that there is a highly statistically significant correlation between spill rate and year, if all of the 

Alaska spill data is included. If data earlier than 1980 is excluded, then there is still a correlation 

between spill rate and year that is significant at the 1 percent level of confidence. However, if 

data earlier than 1985 is excluded, then there is a correlation between spill rate and year, which is 

significant at the 17 percent level of confidence. 

For a relatively small dataset where the theoretical distribution is not known and there is the 

possibility of missing data, it is Hart Crowser’s normal practice to require a level of significance 

of greater than 99 percent before conclusions are drawn. Hart Crowser concluded that spill rate 

is the best variable to use in predicting the volume of further oil spills. An average rate of 

approximately 52 gallons of oil spilled per million barrels of crude oil produced was calculated 

based on the trend that started in 1980. This rate is subject to considerable uncertainty in the 

mean (± 50% at the 95% level of confidence). A spill rate derived from the logarithmic 

distribution was 66 gallons as opposed to 52 gallons. These two values agree within the standard 

deviation of the means. The 95 percent logarithmic confidence limits on spills for a given year 

are ± 465 percent at the 95 percent level of confidence. These values are summarized in Table 

19. (Note that values in Table 19 have not been rounded. It should be noted that all of the 

uncertainty in rate is statistically accurate to less than one significant figure.) Hart Crowser is 

more inclined to believe the logarithmic values than the untransformed values, because the 

cumulative frequency of the data is more lognormal than normal (see Figures 47 and 48). These 

very wide confidence limits and individual yearly values are consistent with the small number of 

data points available for this prediction. Hart Crowser believes it is unlikely that further 

accuracy will be achieved by additional analysis. 

The volumetric oil spill risk rate does not completely describe the statistical system and, 

accordingly, Hart Crowser also investigated the oil spill count rate (i.e., the number of oil spills 

over a particular volume threshold per million barrels of crude oil produced). Oil spill and oil 

production data from 1978 through 1999 (with 1999 production assumed 450 million Bbl) were 

used because to correspond to the observed trend in oil spills. A plot of the spill count rate from 

the database is shown in Figure 49. Figure 49 shows 4 points aligned along the bottom, and 

consequently, is not very useful for visual analysis. To enhance the variability at the low end of 

the scale, Hart Crowser constructed a logarithmic plot of the same data. However, because of 

the zeros in the database, some positive constant had to be added to the spill rate. At first, Hart 

Crowser used a constant of 0.1 spills per million barrels of crude oil produced and obtained the 

plot shown in Figure 50. This figure shows only slight variability at the low spill rate. The 

constant was then adjusted to 0.01 spills per million barrels of crude oil produced and the results 

obtained are plotted in Figure 51. This shows a clear picture of no spills where there was no 

production in 1969, but a considerable spill count rate from 1970 to 1976. In 1977, the spill 

count rate started to drop, and from 1978 through 1990 the spill rate appeared visually 
1970 1975 1980 1985 1990 

1 e+01 1 e+02 1 e+03 1 e+04 1 e+05

Log US Yearly Spill Volume Rate + 2000 vs Year

Figure 46

YEAR

SpillRate2000
100 

TABLE 16 

LINEAR REGRESSION OF ANNUAL SPILL RATE BY YEAR

lm(formula = SpillRate2000 ~ YEAR) 

Residuals: 

Min 1Q Median 3Q Max 

-26398 -12028 -5194 4267 120515 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 2957488.0 1022113.8 2.894 0.00716 **

YEAR -1485.0 515.2 -2.882 0.00736 **

Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Residual standard error: 25660 on 29 degrees of freedom 

Multiple R-Squared: 0.2227, Adjusted R-squared: 0.1959 

F-statistic: 8.308 on 1 and 29 degrees of freedom, p-value: 0.007357 

lm(formula = log(SpillRate2000) ~ YEAR) 

Residuals: 

Min 1Q Median 3Q Max 

-3.2463 -1.2667 0.1449 0.9728 3.3947 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 622.15336 63.01039 9.874 8.80e-11 ***

YEAR -0.31071 0.03176 -9.784 1.08e-10 ***

Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Residual standard error: 1.582 on 29 degrees of freedom 

Multiple R-Squared: 0.7675, Adjusted R-squared: 0.7595 

F-statistic: 9572 on 1 and 29 degrees of freedom, p-value: 1.082e-010 
101 

TABLE 17 

LINEAR REGRESSION OF ANNUAL SPILL RATE FOR YEARS GREATER THAN 1979

lm(formula = SpillRate2000[YEAR > 1979] ~ YEAR[YEAR > 1979]) 

Residuals: 

Min 1Q Median 3Q Max 

-84.16 -48.53 -25.04 17.36 147.75 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 11358.290 5498.812 2.066 0.0536 

 

Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Residual standard error: 71.27 on 18 degrees of freedom 

Multiple R-Squared: 0.1897, Adjusted R-squared: 0.1447 

F-statistic: 4.214 on 1 and 18 degrees of freedom, p-value: 0.05492 

lm(formula = SpillRate2000[YEAR > 1979] ~ YEAR[YEAR > 1979]) 

Residuals: 

Min 1Q Median 3Q Max 

-2.2798 -0.6379 -0.1724 0.8531 2.1637 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 257.47120 89.97904 2.861 0.0104 * 

Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Residual standard error: 1.166 on 18 degrees of freedom 

Multiple R-Squared: 0.3067, Adjusted R-squared: 0.2682 

F-statistic: 7.962 on 1 and 18 degrees of freedom, p-value: 0.0113 
102 

TABLE 18 

LINEAR REGRESSION OF ANNUAL SPILL RATE FOR YEARS GREATER THAN 1984

lm(formula = SpillRate2000[YEAR > 1984] ~ YEAR[YEAR > 1984]) 

Residuals: 

Min 1Q Median 3Q Max 

-51.642 -35.062 -26.014 8.212 149.345 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 5766.308 7152.998 0.806 0.435 

Residual standard error: 60.09 on 13 degrees of freedom 

Multiple R-Squared: 0.0468, Adjusted R-squared: -0.02653 

F-statistic: 0.6382 on 1 and 13 degrees of freedom, p-value: 0.4387 

lm(formula = log(SpillRate2000[YEAR > 1984]) ~ YEAR[YEAR > 1984]) 

Residuals: 

Min 1Q Median 3Q Max 

-2.2792 -0.7141 -0.2578 0.9137 2.1644 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 257.47368 152.95508 1.683 0.116 

Residual standard error: 1.285 on 13 degrees of freedom 

Multiple R-Squared: 0.1753, Adjusted R-squared: 0.1118 

F-statistic: 2.762 on 1 and 13 degrees of freedom, p-value: 0.1204 

TABLE 19

CALCULATION OF MEANS AND EXPECTED UNCERTAINTIES OF ANNUAL SPILL

RATE FOR YEARS GREATER THAN 1984

A. Arithmetic mean of annualized spill rate = 51.7813 gallons spilled per million barrels 

produced 

B. Approximate arithmetic 95% confidence limits on the mean of annualized spill rate = 

51.21935% 

C. Lognormal mean annualized spill rate = 65.50743 gallons spilled per million barrels 

produced 

D. Approximate logarithmic 95% confidence limits on annualized spill rate 465.4103 % 
−1 0 1

0 50 100 150 200

Cumulative Frequency US Yearly Total Spill Volume Rate+2000 (Years A

Figure 47

Theoretical Quantiles

Sample Quantiles
−1 0 1

5 10 20 50 100 200

Cumulative Frequency Log US Yearly Total Spill Volume Rate+2000 (Year

Figure 48

Theoretical Quantiles

Sample Quantiles
1970 1975 1980 1985 1990 

01234

Spill Count Rate vs Year

Figure 49

YEAR

CountSpillRate
1970 1975 1980 1985 1990 

0.1 0.2 0.5 1.0 2.0 5.0

Log(Spill Count Rate+0.1) vs Year

Figure 50

YEAR

CountSpillRate + 0.1
1970 1975 1980 1985 1990 

0.01 0.02 0.05 0.10 0.20 0.50 1.00 2.00 5.00

Log(Spill Count Rate+0.01) vs Year

Figure 51

YEAR

CountSpillRate + 0.01
108 

constant, although one might argue that the period from 1978 through 1986 had a lower 

variability than the period from 1987 through 1999. 

When dealing with the spill count rate, one of the methods to quantify the differences in spill 

sizes is to provide a certain minimum threshold and only count spills above those volumes. Spill 

count rates for minimum spill sizes of 100, 500, 1,000 and 10,000 barrels are shown in Figures 

52, 53, 54, and 55. Again, the arbitrary constant of 0.01 spills per million barrels of crude oil 

produced was added to the values to enhance the assessment of variability for the very low rates. 

As can be seen by examining these figures, the period from 1978 until 1990 was relatively 

statistically homogeneous. Results of spill count and total production are summarized in Table 

20. Based on the visual analysis of Figures 49 through 55, it appeared that spill count rate has 

been constant. Under this assumption that the spill count rate has been relatively constant, the 

spill count rate for spills greater than various sizes may be estimated by simply counting the 

number of spills. Using the fact that the variance of a counted quantity is that quantity, 

approximate confidence limits may be calculated as shown in Table 10. For example, the total 

count of all spills from 1978 on is 68. Dividing by the total production, a rate of 0.0053 spills 

per million barrels produced is obtained, and using the approximate 95 percent limits of the 

counted quantity, a 95 percent confidence limit of plus or minus 24 percent is obtained. (24% = 2 

sqrt (68)/68 * 100; were 2 is the approximate t statistic for 95 percent confidence). 

TABLE 20 

OIL SPILL RISK RATE BY COUNT WITH ASSOCIATED UNCERTAINTIES

DATA FROM 1978-1999

Spill Size 

(Bbl)

Number of 

Spills 

 Total Crude 

Oil Production

(MMBbl)

Calculated Risk 

Rate 

(Spills/MMBbl)

Approximate 95% 

Confidence Limits 

(%±)

≥100 68 12,854 0.0052902 24 

≥500 12 12,854 0.0009336 58 

≥1,000 5 12,854 0.0003890 89 

≥10,000 1 12,854 0.0000778 200 

As a smaller number of spills are available, the rate, of course, decreases and the uncertainty 

increases. In the case of spills over 10,000 barrels, the rate is 0.00008 spills per million barrels 

produced and the approximate 95 percent confidence limits are plus or minus 200 percent. 
1970 1975 1980 1985 1990 

0.01 0.02 0.05 0.10 0.20 0.50 1.00 2.00 5.00

Log(Spill Count Rate >=100 BBL+0.01) vs Year

Figure 52

YEAR

CountSpillRate + 0.01
1970 1975 1980 1985 1990 

0.01 0.02 0.05 0.10 0.20 0.50 1.00 2.00

Log(Spill Count Rate >=500 BBL+0.01) vs Year

Figure 53

YEAR

CountSpillRate + 0.01
1970 1975 1980 1985 1990 

0.01 0.02 0.05 0.10 0.20 0.50 1.00

Log(Spill Count Rate >=1000 BBL+0.01) vs Year

Figure 54

YEAR

CountSpillRate + 0.01
1970 1975 1980 1985 1990 

0.0100 0.0105 0.0110 0.0115 0.0120 0.0125

Log(Spill Count Rate >=10000 BBL+0.01) vs Year

Figure 55

YEAR

CountSpillRate + 0.01
113 

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Alaska Court System Law Library, Juneau, Alaska. 

Alaska Administrative Code, 1971 - 1999, Title 18, Chapter 75, Oil and Hazardous Substances: 

State of Alaska, Office of the Lieutenant Governor. 

Alaska Department of Environmental Conservation (ADEC) 1997a, Pre-July 1995 Northern 

Regional Office oil and hazardous substance spill database: Personal communication and 

electronic transmittal of database from Gail Volt (ADEC) to Caryn Smith (MMS), February 25, 

1997. 

______, 1997b, Post-July 1995 ADEC oil and hazardous substance spill database: Personal 

communication and electronic transmittal of database from Camille Stephens (ADEC) to Caryn 

Smith (MMS), April 23, 1997. 

______, 1997c, Oil and hazardous substance spill database from the ADEC Fairbanks office as 

of April 29, 1997. 

______, 1999a, Pre-July 1995 Northern Regional Office oil and hazardous substance spill 

database: Personal communication and electronic transmittal of database from Camille Stephens 

(ADEC) to Jeff Mach (HCI), September 22, 1999. 

______, 1999b, Post-July 1995 ADEC oil and hazardous substance spill database: Personal 

communication and electronic transmittal of database from Camille Stephens (ADEC) to Jeff 

Mach (HCI), September 28, 1999. 

Alaska Department of Natural Resources (ADNR), 1999a, Table 3 – Oil Production History 

updated to August 3, 1999: Personal communication and electronic transmittal of spreadsheet 

from Richard Beasley (ADNR) to Jeff Mach (HCI), September 15, 1999. 

______, 1999b, Historical and Projected Oil and Gas Consumption, May 1999. 

Alaska Statutes Title 46 Chapters 03, 04, 08, and 09, Current and superceded laws, 1959 to 1999: 

Alaska State Legislature, Juneau, Alaska. 

Alyeska Pipeline Service Company and Bechtel Corporation, 1976, Federal and State 

Stipulations Governing the Trans-Alaska Pipeline System, 182 pages. 

Alyeska Pipeline Service Company (Alyeska), 1993, Trans-Alaska Pipeline Atlas, Prudhoe Bay 

to Valdez, June 1993, 74 pages. 

______, 1999a, Crude Oil Spill Data from 1977 to 1989, Undated, 1 page. 

______, 1999b, North Slope Crude Spills, Pipeline Department From 1989 to May 4, 1999, 

Spreadsheet, 4 pages. 
114 

Anderson, C.M. and R.P. LaBelle, 1994, Comparative Occurrence Rates for Offshore Oil Spills,

Spill Science and Technology Bulletin 1(2): 131-141. 

ARCO Alaska Inc. (ARCO), 1997a, 1977-1985 Kuparuk River Unit Spill Data: Personal 

communication and electronic transmittal of spreadsheets from Kay La Bau (ARCO) to Caryn 

Smith (MMS), July 24, 1997. 

______, 1997b, 1986-1996 Kuparuk River Unit Spill Data: Personal communication and 

electronic transmittal of spreadsheets from Kay La Bau (ARCO) to Caryn Smith (MMS), July 

24, 1997. 

______, 1997c, 1986-1996 Kuparuk Exploration Spill Data: Personal communication and 

electronic transmittal of spreadsheets from Kay La Bau (ARCO) to Caryn Smith (MMS), July 

24, 1997. 

______, 1997d, 1977-1996 Prudhoe Spill Data. Personal communication and electronic 

transmittal of spreadsheets from Kay La Bau (ARCO) to Caryn Smith (MMS), July 24, 1997. 

______, 1999, Prudhoe Bay Eastern Operating Area and Kuparuk River Unit Field Gathering 

Line Mileage Data. Personal communication and electronic transmittal of spreadsheets from 

Mark Major (ARCO) to Jeff Mach (HCI), December 12, 1999. 

BP Exploration (Alaska) (BP), 1997, Crude oil spill history: Personal communication and 

electronic transmittal of spreadsheet from Tess Dey (BP) to Karen Smith (MMS), July 22, 1997. 

Braul, W, 1994, Module 2 - Overview of Federal Legislation and Policies: In 

http://www.vcn.bc.ca/wcel/otherpub/7021/7021_m2.html. 

Cutter Information Corporation, 1989, Oil Spills: International Summary and Review 1978-1981: 

Cutter Information Corp., Arlington, MA., 133 pages. 

Cutter Information Corporation, 1989, Oil Spills: International Summary and Review 1982-1985: 

Cutter Information Corp., Arlington, MA., 132 pages. 

Directorate of Oil and Gas, Department of Indian Affairs and Northern Development, 1993, 

Northern Oil and Gas Annual Report 1992: Directorate of Oil and Gas, Department of Indian 

Affairs and Northern Development, Ottawa, Ontario, Canada, 40 pages. 

________, 1994, Northern Oil and Gas Annual Report 1993: Directorate of Oil and Gas, 

Department of Indian Affairs and Northern Development, Ottawa, Ontario, Canada, 37 pages. 

________, 1995, Northern Oil and Gas Annual Report 1994: Directorate of Oil and Gas, 

Department of Indian Affairs and Northern Development, Ottawa, Ontario, Canada, 31 pages. 

________, 1996, Northern Oil and Gas Annual Report 1995: Directorate of Oil and Gas, 

Department of Indian Affairs and Northern Development, Ottawa, Ontario, Canada, 20 pages. 

________, 1997, Northern Oil and Gas Annual Report 1996: Directorate of Oil and Gas, 

Department of Indian Affairs and Northern Development, Ottawa, Ontario, Canada, 22 pages. 
115 

________, 1998, Northern Oil and Gas Annual Report 1997: Directorate of Oil and Gas, 

Department of Indian Affairs and Northern Development, Ottawa, Ontario, Canada, 22 pages. 

________, 1999, Northern Oil and Gas Annual Report 1998: Directorate of Oil and Gas, 

Department of Indian Affairs and Northern Development, Ottawa, Ontario, Canada, 24 pages. 

Department of Justice Canada, 1999, Personal communication with Diana Haukman. 

Environment Canada, 1987, Summary of Spill Events in Canada, 1974 – 1983: Environment 

Canada Publication EPS 5/SP/1, 52 pages. 

________, 1996, Chapter 1 - CEPA Part VI and Ocean Dumping Regulations: In Environment 

Canada Compliance and Enforcement Report - Volume 1, 

http://www.ec.gc.ca/enforce/english/chapter1.htm. 

_______, 1998. Summary of Spill Events in Canada, 1984 – 1995: Environment Canada 

Publication EPS 5/SP/3, 81 pages. 

Federal Register, March 11, 1985, Environmental Protection Agency; Water Programs; 

Discharge of Oil; Proposed Rule: Volume 50, Page 9776 (50 FR 9776). 

Government of the Northwest Territories, 1999, Personal communication with Harvey Gaukel, 

Hazardous Substance Specialist, Environmental Protection Service, Resources, Wildlife and 

Economic Development Department. 

Gyrc, George, 1985, The National Petroleum Reserve in Alaska – Earth-Science Considerations: 

U.S. Geologic Survey Professional Paper 1240-C, 98 pages. 

Hanley, Peter T., J.E. Hemming, and J.W. Morsell, 1981, Natural Resource Protection and 

Petroleum Development in Alaska: U.S. Department of the Interior, Fish and Wildlife Service 

Biological Services Program Publication FWS/OBS-80/22, August 1981, 323 pages. 

Klotz, J., 1972, Are Ocean Polluters Subject to Universal Jurisdiction - Canada Breaks the Ice: 

In The International Lawyer, 6(4):706-18. 

National Energy Board Canada, 1999a, Production data for Norman Wells, Bent Horn, and 

Amuligak oil fields: Personal Communication and electronic transmittal of spreadsheet from 

Terry Baker (NEB) to Jeff Mach (HCI), September 17, 1999. 

_______, 1999b, Personal communication with Andrew Graw, Senior Environmental Officer. 

Unattributed, 1981. Summary of Spills Over 100 Gallons: A Listing of Alaskan North Slope and 

TAPS Oil Spills from 1970 to 1981, designated as Attachment 2, 11 pages. 

U.S. Department of the Interior Bureau of Land Management (BLM), 1982a, Year End Report 

on Alyeska Reported Spills: Memorandum from Ken Hunt, Environmental Protection Specialist, 

to Arlan Kohl, Project Manager TAPS, January 19, 1982, 13 pages. 

______, 1982b, Spill Reports: Memorandum from EPS to PM-T, December 6, 1982, 13 pages. 
116 

______, 1983, Spill Reports: Memorandum from EPS to Chief, Branch of Pipeline Monitoring, 

15 pages. 

US Department of the Interior and Alaska Department of Natural Resources Joint Pipeline Office 

(JPO), 1997, Oil and hazardous substance spill database: Personal communication and electronic 

transmittal of database from Greg Doggett (JPO) to Caryn Smith (MMS), March 12, 1997. 

______, 1999, Alaska North Slope Oil Pipeline Mileage Data: Personal communication from 

Tony Braden (JPO) to Jeff Mach (HCI), September 24, 1999. 

______, 2000, Alaska North Slope Oil Pipeline Data: Personal communication from Tony 

Braden (JPO) to Jeff Mach (HCI), March 2, 2000. 

US Department of the Interior, Minerals Management Service (MMS), 1999, Summary of 

Alaskan and Canadian oil spills of 100 barrels and greater as reported in the Oil Spill Intelligence 

Report: Personal communication and electronic transmittal of database from Richard Prentki 

(MMS) to Jeff Mach (HCI), December 6, 1999. 

______, 2000, Alaska Beaufort Sea Oil Spill Data, Personal communication from Richard 

Prentki (MMS) to Jeff Mach (HCI), January 31, 2000. 

University of British Columbia Law Library, 1999, Organization and History of Canadian 

Statutes and Regulations, Personal communication with reference librarian. 
117 

APPENDIX A - COLLATED ALASKA AND CANADA INDIVIDUAL OIL SPILL DATA USED 

COLLATED LIST OF OIL SPILLS OF 100 BARRELS AND LARGER FROM ARCTIC ALASKA AND CANADA S

Study 

Area 

Spill 

Date 

Facility 

Type 

Facility 

Operator Oil Type Spill Location Spill Cause 

Low 

Spill 

Quantity 

(Gallons) 

High 

Spill 

Quantity 

(Gallons) 

Q

D

AK-ONS1 02/23/70 Highway Mobile Oil Drilling Diesel Fuel/Heating Oil Approx 11 miles east of BP Prudhoe Bay base camp Tank Vehicle Accident 7,000 9,100 U

AK-ONS 06/03/71 

Operations 

Support 

Facility 

ARCO 

Alaska, Inc. 

Jet/Turbine 

Fuel 

Prudhoe Bay 

Unit, ARCO 

airfield 

Unspecified 45,000 U

AK-ONS 01/05/72 

Operations 

Support 

Facility 

ARCO 

Alaska, Inc. 

Diesel 

Fuel/Heating 

Oil 

Prudhoe Bay 

Unit, ARCO 

airfield 

Facility Piping 

Leak - human 

error, valve 

left open 

15,000 20,000 U
118 

Study 

Area 

Spill 

Date 

Facility 

Type 

Facility 

Operator Oil Type Spill Location Spill Cause 

Low 

Spill 

Quantity 

(Gallons) 

High 

Spill 

Quantity 

(Gallons) 

Q

D

AK-ONS 04/14/73 

Operations 

Support 

Facility 

ARCO 

Alaska, Inc. 

Jet/Turbine 

Fuel 

Prudhoe Bay 

Unit, ARCO 

airfield 

Facility Piping 

Leak - nozzle 

failure 

 4,262 U

AK-ONS 07/16/73 Exploration Well Site ARCO Alaska, Inc. Diesel Fuel/Heating Oil Itkillik River Unit 1 Unspecified 40,000 UAK-ONS 12/17/75 

Operations 

Support 

Facility 

Surfcote 

Diesel 

Fuel/Heating 

Oil 

Prudhoe Bay 

Surfcote Camp 

(Slope Camp) 

Facility Tank 

Leak - 

unspecified 

cause 

60,000 70,000 U

AK-ONS) 06/20/79 

Exploration 

Support 

Facility 

Chevron USA Jet/Turbine Fuel Cape Beaufort 

Facility Tank 

Leak - rupture 

due to frost 

action 

 40,000 U

AK-ONS 11/21/80 Production Well Site ARCO Alaska, Inc. Diesel Fuel/Heating Oil Prudhoe Bay Unit, Drill Site 5, Well 16 Facility Piping Leak - line break 4,284 UAK-ONS 04/24/81 

Operations 

Support 

Facility 

ARCO 

Alaska, Inc. Gasoline 

Prudhoe Bay 

Unit, Crude Oil 

Topping Unit 

Facility Piping 

Leak - human 

error, valve 

left open 

 4,282 U

AK-ONS) 08/22/81 

Operations 

Support 

Facility 

ARCO 

Alaska, Inc. 

Diesel 

Fuel/Heating 

Oil 

Prudhoe Bay 

Unit, Crude Oil 

Topping Unit, 

Fuel Storage 

Tanks 

Facility Piping 

Leak - faulty 

connection 

18,000 18,900 U

AK-ONS 07/15/82 

Operations 

Support 

Facility 

Wien Air 

Alaska 

Jet/Turbine 

Fuel 

Wien Air 

Terminal, 

Deadhorse 

Airport 

Facility Piping 

Leak - 

unspecified 

cause 

30,000 100,000 U
119 

Study 

Area 

Spill 

Date 

Facility 

Type 

Facility 

Operator Oil Type Spill Location Spill Cause 

Low 

Spill 

Quantity 

(Gallons) 

High 

Spill 

Quantity 

(Gallons) 

Q

D

AK-ONS 10/31/82 

Operations 

Support 

Facility 

ARCO 

Alaska, Inc. 

Diesel 

Fuel/Heating 

Oil 

Prudhoe Bay 

Operations 

Center, Diesel 

Storage Tank 

Facility Tank 

Leak - human 

error, 

overfilled 

6,300 8,400 U

AK-ONS 06/19/83 Construction Camp ARCO Alaska, Inc. Diesel Fuel/Heating Oil Kuparuk Construction Camp Facility Tank Leak - tank fell off supports 4,800 UAK-ONS 07/27/83 

Operations 

Support 

Facility 

North Slope 

Borough 

Service Area 

10 

Gasoline 

North Slope 

Borough Service 

Area 10 facility 

Facility Piping 

Leak - line 

break 

 7,550 U

AK-ONS 08/09/83 

Operations 

Support 

Facility 

ARCO 

Alaska, Inc. Gasoline 

Prudhoe Bay 

Unit, Crude Oil 

Topping Unit 

Facility Piping 

Leak - human 

error 

 6,200 U

AK-ONS 06/02/85 

Operations 

Support 

Facility 

ARCO 

Alaska, Inc. Crude Oil 

Prudhoe Bay 

Operations 

Center 

Facility Piping 

Leak - 

unspecified 

cause 

 10,000 U

AK-ONS 11/14/85 

Operations 

Support 

Facility 

ARCO 

Alaska, Inc. Gasoline 

Prudhoe Bay 

Unit, Crude Oil 

Topping Unit 

fuel terminal 

Facility Tank 

Leak - human 

error, 

overfilled 

 10,500 U

AK-ONS 11/15/85 

Production 

Processing 

Facility 

Conoco, Inc. Crude Oil 

Milne Point 

Unit, Central 

Processing 

Facility holding 

pit 

Facility Piping 

Leak - faulty 

valve 

 7,350 U
120 

Study 

Area 

Spill 

Date 

Facility 

Type 

Facility 

Operator Oil Type Spill Location Spill Cause 

Low 

Spill 

Quantity 

(Gallons) 

High 

Spill 

Quantity 

(Gallons) 

Q

D

AK-ONS 11/6/1984 Unspecified Sohio Crude Oil Unspecified Facility Piping-Leak 5,250 UAK-ONS 01/08/86 

Operations 

Support 

Facility 

ARCO 

Alaska, Inc. Gasoline 

Prudhoe Bay 

Unit, Crude Oil 

Topping Unit 

Facility Tank 

Leak - human 

error, 

overfilled 

 4,957 U

AK-ONS 10/16/86 

Operations 

Support 

Facility 

ARCO 

Alaska, Inc. 

Diesel 

Fuel/Heating 

Oil 

Prudhoe Bay 

Unit, Crude Oil 

Topping Unit 

Facility Piping 

Leak - line 

break 

 4,200 U

AK-ONS 11/07/86 

Production 

Processing 

Facility 

ARCO 

Alaska, Inc. Crude Oil 

Kuparuk River 

Unit, Central 

Processing 

Facility 1 

Seawater Flood 

Module 

Facility Piping 

Leak - faulty 

valve 

 5,040 U

AK-ONS 01/05/87 

Operations 

Support 

Facility 

ARCO 

Alaska, Inc. 

Diesel 

Fuel/Heating 

Oil 

Prudhoe Bay 

Unit, ARCO 

airfield 

Facility Piping 

Leak - human 

error, valve 

left open 

 15,000 U

AK-ONS 03/30/88 Pipeline ARCO Alaska, Inc. Crude Oil/Produced Water Prudhoe Bay Unit, Drill Site 3 to Flow Station 2 Pipeline Leak - corrosion 11,800 11,802 UAK-ONS 01/24/89 

Exploration 

Support 

Facility 

Unspecified 

Diesel 

Fuel/Heating 

Oil 

7-Mile Camp 

Facility Piping 

Leak - line 

break 

4,500 6,500 U

AK-ONS 02/04/89 

Production 

Processing 

Facility 

BP 

Exploration 

(Alaska) 

Crude Oil 

Prudhoe Bay 

Unit, Gathering 

Center 2 

Facility Piping 

Leak - faulty 

valve 

3,150 15,750 U

AK-ONS 04/18/89 

Operations 

Support 

Facility 

Prudhoe Bay 

Hotel 

Diesel 

Fuel/Heating 

Oil 

Prudhoe Bay 

Hotel, behind 

hotel 

Unspecified 15,000 U
121 

Study 

Area 

Spill 

Date 

Facility 

Type 

Facility 

Operator Oil Type Spill Location Spill Cause 

Low 

Spill 

Quantity 

(Gallons) 

High 

Spill 

Quantity 

(Gallons) 

Q

D

AK-ONS 07/28/89 

Production 

Processing 

Facility 

Conoco, Inc. Crude Oil 

Milne Point 

Unit, Central 

Processing 

Facility 

Facility Tank 

Leak - overfill 34,650 38,850 U

AK-ONS 08/25/89 Pipeline ARCO Alaska, Inc. Crude Oil Kuparuk River Unit, Drill Site 2-U Pipeline Leak - corrosion of block valve 14,280 25,326 U

AK-ONS) 11/08/89 Production Well Site ARCO Alaska, Inc. Crude Oil Kuparuk River Unit Drill Site 2- G, Well 4 Facility Piping Leak - line break 7,140 11,130 U

AK-ONS 12/10/90 Production Well Site ARCO Alaska, Inc. Crude Oil Lisburne Unit, Drill Site L-5 Facility Explosion 7,400 25,200 UAK-ONS 06/10/93 

Production 

Processing 

Facility 

ARCO 

Alaska, Inc. Crude Oil 

Lisburne Unit, 

Lisburne 

Production 

Center 

Facility Tank 

Leak - high 

level alarm 

failure 

 12,600 U

AK-ONS 8/17/1993 

Production 

Processing 

Facility 

ARCO 

Alaska, Inc. 

Crude 

Oil/Produced 

Water 

Kuparuk River 

Unit CPF 1 

Tank Leak - 

Corrosion 28,350 U

AK-ONS 08/30/93 

Production 

Processing 

Facility 

BP 

Exploration 

(Alaska) 

Crude Oil 

Prudhoe Bay 

Unit, Gathering 

Center 1, Skid 

312 

Facility Tank 

Leak - human 

error, overfill 

 8,400 U

AK-ONS 09/26/93 

Production 

Processing 

Facility 

BP 

Exploration 

(Alaska) 

Crude Oil 

Prudhoe Bay 

Unit, Gathering 

Center 2 

Facility Tank 

Leak - 

overflow due 

to pump 

failure 

 27,305 U
122 

Study 

Area 

Spill 

Date 

Facility 

Type 

Facility 

Operator Oil Type Spill Location Spill Cause 

Low 

Spill 

Quantity 

(Gallons) 

High 

Spill 

Quantity 

(Gallons) 

Q

D

AK-ONS 11/13/93 

Production 

Processing 

Facility 

BP 

Exploration 

(Alaska) 

Crude Oil 

Prudhoe Bay 

Unit, Dead 

Crude Storage 

Tank 1801 

Facility Tank 

Leak - human 

error 

 4,200 U

AK-ONS 12/24/93 

Production 

Processing 

Facility 

BP 

Exploration 

(Alaska) 

Crude Oil 

Prudhoe Bay 

Unit, Gathering 

Center 2, Tank 

8511 

Facility Tank 

Leak - 

overflow due 

frozen 

components 

7,560 8,400 U

AK-ONS 12/30/93 Production Well Site ARCO Alaska, Inc. Crude Oil Prudhoe Bay Unit, Drill Site 5, Well 23 Pipeline Leak - line break, corrosion 15,750 16,800 UAK-ONS 05/10/94 Production Well Site ARCO Alaska, Inc. Crude Oil Pt. McIntyre, Drill Site 1 Pipeline Leak - valve failure 3,360 6,000 UAK-ONS 10/31/94 Pipeline ARCO Alaska, Inc. Crude Oil 

Kuparuk River 

Unit, Junction of 

Drill SIte1Y and 

1R flowlines 

Pipeline Leak 

- corrosion 2,520 7,692 U

AK-ONS 03/26/97 Production Well Site ARCO Alaska, Inc. Crude Oil Prudhoe Bay Unit, Drill Site 16 Well 18 Facility Piping Leak - line break 4,746 UAK-ONS 05/19/97 Production Well Site ARCO Alaska, Inc. Diesel Fuel/Heating Oil Prudhoe Bay Unit, Drill Site 10 Production Well Leak - Leaking Well Plug 7,560 U

AKTAPS2 07/25/70 Construction Camp Alyeska Pipeline Service Co. Diesel Fuel/Heating Oil TAPS Prospect Camp Facility Tank Leak - bear damaged bladder 20,000 U
123 

Study 

Area 

Spill 

Date 

Facility 

Type 

Facility 

Operator Oil Type Spill Location Spill Cause 

Low 

Spill 

Quantity 

(Gallons) 

High 

Spill 

Quantity 

(Gallons) 

Q

D

AK-TAPS 12/01/70 Construction Camp Alyeska Pipeline Service Co. Diesel Fuel/Heating Oil TAPS Happy Valley Camp "A" Facility Piping Leak - line break 6,000 UAK-TAPS 05/04/73 Construction Camp Alyeska Pipeline Service Co. Diesel Fuel/Heating Oil TAPS Happy Valley Camp Facility Tank Leak - human error, valve left open 8,000 10,000 UAK-TAPS 05/29/74 Construction Camp Alyeska Pipeline Service Co. Diesel Fuel/Heating Oil TAPS Toolik Camp Facility Tank Leak - bladder leaked 5,000 20,000 UAK-TAPS 06/26/74 Highway NA 

Diesel 

Fuel/Heating 

Oil 

Richardson Hwy 

MP 230 

Tank Vehicle 

Accident 9,000 U

AK-TAPS 11/08/74 Highway NA 

Diesel 

Fuel/Heating 

Oil 

Dalton Hwy MP 

235 

Tank Vehicle 

Accident 8,500 U

AK-TAPS 01/11/75 Construction Camp Alyeska Pipeline Service Co. Diesel Fuel/Heating Oil TAPS Five Mile Camp Facility Piping Leak - line break 10,000 UAK-TAPS 02/07/75 Construction Camp Alyeska Pipeline Service Co. Diesel Fuel/Heating Oil TAPS Galbraith Camp (N. side of camp) Facility Piping Leak - line break 62,500 100,000 UAK-TAPS 03/05/75 

Operations 

Support 

Facility 

Alyeska Pipeline 

Service Co. 

Diesel 

Fuel/Heating 

Oil 

TAPS Van Horn 

Rd Facility, 

Fairbanks 

Human error 4,700 U

AK-TAPS 04/03/75 Highway NA 

Diesel 

Fuel/Heating 

Oil 

Ferry Access 

Road, S. Bank of 

Yukon R 

Tank Vehicle 

Accident 6,000 U

AK-TAPS 05/28/75 Construction Camp Alyeska Pipeline Service Co. Crude Oil TAPS Happy Valley Camp A Tank Vehicle Leak - unspecified 

cause 

 6,000 U
124 

Study 

Area 

Spill 

Date 

Facility 

Type 

Facility 

Operator Oil Type Spill Location Spill Cause 

Low 

Spill 

Quantity 

(Gallons) 

High 

Spill 

Quantity 

(Gallons) 

Q

D

AK-TAPS 06/11/75 Construction Camp Alyeska Pipeline Service Co. Diesel Fuel/Heating Oil TAPS Galbraith Camp Unspecified 60,000 UAK-TAPS 08/24/75 Highway NA 

Diesel 

Fuel/Heating 

Oil 

Elliott Hwy MP 

60.5 

Tank Vehicle 

Accident 6,000 U

AK-TAPS 08/30/75 Construction Camp Alyeska Pipeline Service Co. Diesel Fuel/Heating Oil TAPS Toolik Camp (Between Barracks 12 & 13) Facility Piping Leak - line break 8,590 UAK-TAPS 09/09/75 Highway NA 

Diesel 

Fuel/Heating 

Oil 

Dalton Hwy MP 

279 (Approx. 3.6 

mi N. of 

Galbraith Camp) 

Tank Vehicle 

Accident 4,500 U

AK-TAPS 09/18/75 Construction Camp Alyeska Pipeline Service Co. Diesel Fuel/Heating Oil TAPS Franklin Bluffs Camp (Shop #2) Facility Piping Leak - equipment damage 30,000 UAK-TAPS 12/14/75 Highway NA 

Diesel 

Fuel/Heating 

Oil 

Dalton Hwy MP 

130 (1 mi. S. of 

Gobbler's Knob) 

Tank Vehicle 

Accident 9,000 U

AK-TAPS 12/31/75 Construction Camp Alyeska Pipeline Service Co. Diesel Fuel/Heating Oil TAPS Prospect Creek Camp (NE of Laundry Bldg) Facility Piping Leak - line break 40,000 100,000 UAK-TAPS 01/28/76 Construction Camp Alyeska Pipeline Service Co. Diesel Fuel/Heating Oil TAPS Galbraith Camp Facility Piping Leak - fitting leak 40,000 UAK-TAPS 02/22/76 Construction Camp Alyeska Pipeline Service Co. Diesel Fuel/Heating Oil TAPS Pump Station 8 Construction Camp Facility Piping Leak - valve leak 4,765 U
125 

Study 

Area 

Spill 

Date 

Facility 

Type 

Facility 

Operator Oil Type Spill Location Spill Cause 

Low 

Spill 

Quantity 

(Gallons) 

High 

Spill 

Quantity 

(Gallons) 

Q

D

AK-TAPS 04/08/76 Highway NA 

Diesel 

Fuel/Heating 

Oil 

Dalton Hwy MP 

125.5 (Bonanza 

Creek) 

Tank Vehicle 

Accident 6,340 U

AK-TAPS 06/23/76 Construction Camp Alyeska Pipeline Service Co. Diesel Fuel/Heating Oil TAPS Five Mile Camp Facility Piping Leak - line break 4,000 5,000 UAK-TAPS 07/01/76 Highway NA 

Diesel 

Fuel/Heating 

Oil 

Dalton Hwy MP 

290.1 

Tank Vehicle 

Accident 4,000 8,500 U

AK-TAPS 10/23/76 Highway NA 

Diesel 

Fuel/Heating 

Oil 

Dalton Hwy MP 

307.5 

Tank Vehicle 

Accident 7,000 U

AK-TAPS 11/02/76 Highway NA Jet/Turbine Fuel Dalton Hwy MP 155.8 Tank Vehicle Accident 9,400 UAK-TAPS 01/18/77 Construction Camp Alyeska Pipeline Service Co. Diesel Fuel/Heating Oil TAPS Franklin Bluffs Camp Facility Piping Leak - line break 5,000 UAK-TAPS 05/08/77 Construction Camp Alyeska Pipeline Service Co. Gasoline TAPS Galbraith Camp (Airport Bladder Farm) Facility Tank Leak - catastrophic failure 16,000 35,000 UAK-TAPS 05/10/77 Highway NA 

Diesel 

Fuel/Heating 

Oil 

Dalton Hwy MP 

241.5 

Tank Vehicle 

Accident 12,000 U

AK-TAPS 05/12/77 Construction Camp Alyeska Pipeline Service Co. Unspecified TAPS Franklin Bluffs Camp Facility Piping Leak - line leak 20,000 UAK-TAPS 07/08/77 

Pipeline 

Pump 

Station 

Alyeska Pipeline 

Service Co. 

Crude Oil 

TAPS Pump 

Station 8 (TAPS 

MP 489.2) 

Facility 

Explosion 12,600 200,000 U
126 

Study 

Area 

Spill 

Date 

Facility 

Type 

Facility 

Operator Oil Type Spill Location Spill Cause 

Low 

Spill 

Quantity 

(Gallons) 

High 

Spill 

Quantity 

(Gallons) 

Q

D

AK-TAPS 07/09/77 

Pipeline 

Pump 

Station 

Alyeska Pipeline 

Service Co. 

Gasoline TAPS Pump Station 6 Facility Tank Leak - UST leak 6,600 U

AK-TAPS 07/19/77 Pipeline 

Alyeska Pipeline 

Service Co. 

Crude Oil TAPS MP 26 (Check Valve 7) Pipeline Leak - equipment damage 42,000 110,000 U

AK-TAPS 07/25/77 Construction Camp Alyeska Pipeline Service Co. Diesel Fuel/Heating Oil TAPS Prospect Camp Facility Piping Leak - line break 20,000 UAK-TAPS 08/15/77 

Pipeline 

Pump 

Station 

Alyeska Pipeline 

Service Co. 

Crude Oil 

TAPS Pump 

Station 9 (TAPS 

MP 548.7) 

Pipeline Leak 

- bypass 

failure 

 4,200 U

AK-TAPS 10/11/77 Pipeline 

Alyeska Pipeline 

Service Co. 

Crude Oil 

TAPS Check 

Valve 68A 

(TAPS MP 

433.4) 

Pipeline Leak 

- loose fitting 4,200 U

AK-TAPS 12/30/77 Highway NA 

Diesel 

Fuel/Heating 

Oil 

Dalton Hwy MP 

237(Approx. 4.5 

mi S. of 

Chandalar) 

Tank Vehicle 

Accident 7,500 7,735 U

AK-TAPS 02/12/78 Construction Camp Alyeska Pipeline Service Co. Diesel Fuel/Heating Oil TAPS Glennallen Camp Facility Tank Leak - human error, overfill 7,000 UAK-TAPS 02/15/78 Pipeline 

Alyeska Pipeline 

Service Co. 

Crude Oil TAPS MP 458 (N OF RGV 73) Pipeline Leak - intentional sabotage 500,000 672,000 U

AK-TAPS 10/04/78 Highway NA Jet/Turbine Fuel TAPS Pump Station 6 Access Road Tank Vehicle Accident 9,000 UAK-TAPS 06/10/79 Pipeline 

Alyeska Pipeline 

Service Co. 

Crude Oil 

TAPS MP 166 

(N. side of 

Atigun Pass) 

Pipeline Leak 

- line break 63,000 300,000 U
127 

Study 

Area 

Spill 

Date 

Facility 

Type 

Facility 

Operator Oil Type Spill Location Spill Cause 

Low 

Spill 

Quantity 

(Gallons) 

High 

Spill 

Quantity 

(Gallons) 

Q

D

AK-TAPS 06/15/79 Pipeline 

Alyeska Pipeline 

Service Co. 

Crude Oil TAPS MP 734 Pipeline Leak - line break 12,600 168,000 U

AK-TAPS 08/31/79 Highway NA Jet/Turbine Fuel Richardson Hwy MP 238 Tank Vehicle Accident 4,500 9,000 UAK-TAPS 03/19/80 Highway NA Jet/Turbine Fuel Richardson Hwy MP 243 Tank Vehicle Accident 5,081 UAK-TAPS 05/12/80 

Pipeline 

Pump 

Station 

Alyeska Pipeline 

Service Co. 

Crude Oil TAPS Pump Station 10 Pipeline Leak - faulty valve 10,000 10,920 U

AK-TAPS 01/01/81 Pipeline 

Alyeska Pipeline 

Service Co. 

Crude Oil 

TAPS MP 114.6 

(Check Valve 

23) 

Pipeline Leak 

- valve leak 42,000 100,000 U

AK-TAPS 05/07/81 Highway NA 

Diesel 

Fuel/Heating 

Oil 

Dalton Hwy MP 

5.5 (Lost Creek) 

Tank Vehicle 

Accident 2,500 5,900 U

AK-TAPS 11/13/81 Highway NA Unspecified Dalton Hwy MP 357.8 Tank Vehicle Accident 2,000 4,881 UAK-TAPS 12/03/81 Highway NA 

Diesel 

Fuel/Heating 

Oil 

Dalton Hwy MP 

273, 0.2 mi north 

of creek 

Tank Vehicle 

Accident 8,900 U

AK-TAPS 05/24/82 Highway NA Gasoline Dalton Hwy MP 120 Tank Vehicle Accident 8,250 UAK-TAPS 12/15/82 Highway NA Jet/Turbine Fuel Dalton Hwy MP 20 Tank Vehicle Accident 7,800 8,000 UAK-TAPS 06/08/83 Highway NA Gasoline Dalton Hwy MP 165 Tank Vehicle Accident 9,100 UAK-TAPS 08/14/83 Highway NA 

Diesel 

Fuel/Heating 

Oil 

Dalton Hwy MP 

11.5 

Tank Vehicle 

Accident 7,000 U
128 

Study 

Area 

Spill 

Date 

Facility 

Type 

Facility 

Operator Oil Type Spill Location Spill Cause 

Low 

Spill 

Quantity 

(Gallons) 

High 

Spill 

Quantity 

(Gallons) 

Q

D

AK-TAPS 08/29/83 Highway NA 

Diesel 

Fuel/Heating 

Oil 

Dalton Hwy MP 

125 

Tank Vehicle 

Accident 8,350 U

AK-TAPS 03/02/84 

Operations 

Support 

Facility 

Alyeska Pipeline 

Service Co. 

Diesel 

Fuel/Heating 

Oil 

TAPS Van Horn 

Rd Facility, 

Fairbanks 

Unspecified 4,700 U

AK-TAPS 09/02/84 Construction Camp Alyeska Pipeline Service Co. Diesel Fuel/Heating Oil TAPS Pump Station 5 Construction Camp Facility Piping Leak - line break 8,064 UAK-TAPS 10/23/84 Highway NA Jet/Turbine Fuel Dalton Hwy MP 22 Tank Vehicle Accident 5,188 UAK-TAPS 09/17/85 Highway NA Gasoline Dalton Hwy MP 320 Tank Vehicle Accident 3,000 9,400 UAK-TAPS 02/02/86 Highway NA 

Diesel 

Fuel/Heating 

Oil 

Dalton Hwy MP 

156.5 

Tank Vehicle 

Accident 5,000 U

AK-TAPS 02/16/86 Highway NA Diesel Fuel or Gasoline Dalton Hwy MP 349 Tank Vehicle Accident 7,158 7,400 UAK-TAPS 07/06/87 Highway NA 

Diesel 

Fuel/Heating 

Oil 

Dalton Hwy MP 

45 

Tank Vehicle 

Accident 2,828 6,000 U

AK-TAPS 11/16/88 Highway NA 

Diesel 

Fuel/Heating 

Oil 

Dalton Hwy MP 

188.3 

Tank Vehicle 

Accident 4,500 U

AK-TAPS 09/15/89 Highway NA Gasoline Dalton Hwy MP 77 Tank Vehicle Accident 5,000 U

AK-TAPS 04/13/90 Highway NA 

Diesel 

Fuel/Heating 

Oil 

Elliott Hwy MP 

44.5 

Tank Vehicle 

Accident 2,000 9,500 U
129 

Study 

Area 

Spill 

Date 

Facility 

Type 

Facility 

Operator Oil Type Spill Location Spill Cause 

Low 

Spill 

Quantity 

(Gallons) 

High 

Spill 

Quantity 

(Gallons) 

Q

D

AK-TAPS 08/02/90 Highway NA 

Diesel 

Fuel/Heating 

Oil 

Elliott Hwy MP 

24 

Tank Vehicle 

Accident 5,700 10,416 U

AK-TAPS 09/27/92 Highway NA 

Diesel 

Fuel/Heating 

Oil 

Dalton Hwy MP 

248.2 

Tank Vehicle 

Accident 8,000 U

AK-TAPS 06/08/93 Highway NA Gasoline Dalton Hwy MP 165 Tank Vehicle Accident 9,100 UAK-TAPS 02/26/94 

Pipeline 

Pump 

Station 

Alyeska Pipeline 

Service Co. 

Crude Oil 

TAPS Pump 

Station 10 (Tank 

209) 

Facility Tank 

Leak - overfill 4,000 U

AK-TAPS 04/20/96 Pipeline 

Alyeska Pipeline 

Service Co. 

Crude Oil 

TAPS MP 539.7 

(Check Valve 

92) 

Pipeline Leak 

- loose fitting 33,619 34,076 U

AK-TAPS 11/11/97 Highway NA 

Diesel 

fuel/Heating 

Oil 

Dalton Hwy MP 

289 

Tank Vehicle 

Accident 5,217 U

CND-BS3 08/31/83 

Exploration 

Support 

Vessel 

Esso 

Resources 

Canada Ltd. 

Diesel 

Fuel/Heating 

Oil 

Beaufort Sea off 

Esso Caisson 

Vessel Leak - 

Accident 6,605 E

CND-BS 09/18/85 Exploration Well Site Esso Resources Canada Ltd. Diesel Fuel/Heating Oil Esso Rig #7, west of Pelly Island Facility Tank Leak - equipment damage 102,480 103,000 U

CNDHAI4 04/06/75 Exploration Well Site Pan-Arctic Oils Ltd. Jet/Turbine Oil Drake D-73 Well Site 

Facility Tank 

Leak - 

equipment 

damage 

 22,817 U

CND-HAI 02/28/79 

Exploration 

Support 

Facility 

Pan-Arctic 

Oils Ltd. Gasoline 

Banks Island 

Passage Point 

Airstrip 

Facility Tank 

Leak - 

equipment 

damage 

 6,005 U
130 

Study 

Area 

Spill 

Date 

Facility 

Type 

Facility 

Operator Oil Type Spill Location Spill Cause 

Low 

Spill 

Quantity 

(Gallons) 

High 

Spill 

Quantity 

(Gallons) 

Q

D

CNDNW5 06/21/73 Exploration Well Site Imperial Oil Crude Oil Imperial Oil, Goose Island Facility Piping Leak - human 

error 

 4,200 U

CND-NW 10/01/78 Production Well Site Imperial Oil Crude Oil Imperial Oil, Goose Island Facility Tank Leak - overfill 10,500 UCND-NW 10/16/81 

Production 

Processing 

Facility 

Esso 

Resources 

Canada Ltd. 

Crude Oil No description 

Facility Tank 

Leak - 

unspecified 

cause 

 12,000 U

CND-NW 07/31/82 Production Well Site Esso Resources Canada Ltd. Crude Oil Imperial Oil Bear Island Production Dock Vessel Leak - Overfill 4,200 5,812 UCND-NW 09/07/86 

Production 

Processing 

Facility 

Esso 

Resources 

Canada Ltd. 

Crude Oil 

Imperial Oil 

Tank #53 

Mainland 

Facility Piping 

Leak - 

equipment 

damage 

21,000 21,136 U

CND-NW 07/31/91 Production Well Site Esso Resources Canada Ltd. Crude Oil Imperial Oil, Well O-41X, Bear Island Facility Piping Leak - equipment damage 4,200 6,300 UCND-NW 08/05/91 Production Well Site Esso Resources Canada Ltd. Crude Oil Imperial Oil, Across from Well B-40 Facility Piping Leak - corrosion 6,300 UCND-NW 08/20/91 

Production 

Processing 

Facility 

Esso 

Resources 

Canada Ltd. 

Crude Oil 

Imperial Oil 

Tank #53 

Mainland 

Facility Tank 

Leak - 

equipment 

damage 

8,400 16,800 U

CND-NW 05/04/92 Pipeline 

Interprovincial 

Pipelines 

(NW) Ltd 

Crude Oil 

Norman Wells 

Pipeline, 25 km 

N of Ft Simpson 

Pipeline Leak 

- corrosion 528 26,420 U
131 

Study 

Area 

Spill 

Date 

Facility 

Type 

Facility 

Operator Oil Type Spill Location Spill Cause 

Low 

Spill 

Quantity 

(Gallons) 

High 

Spill 

Quantity 

(Gallons) 

Q

D

CND-NW 05/05/97 Production Well Site Imperial Oil Resources Ltd. Crude Oil 

Imperial Oil, 

Transfer line 

from Central 

Processing 

Facility to Tank 

401 

Facility Piping 

Leak - 

corrosion 

21,136 63,000 U

CNDOMD6 02/09/83 Highway NA Diesel Fuel/Heating Oil Atkinson Point, Inuvik Region Tank Vehicle Accident 8,406 E

Abbreviations: 1. AK-ONS = Alaska – Onshore North Slope (East of NPRA) 2. AK-TAPS = Alaska – Trans-Alaska Pipeline System 3. CND-BS = Canada – Beaufort Sea 4. CND-HAI = Canada – High Arctic Islands 5. CND-NW = Canada – Norman Wells 6. CND- OMD = Canada – Onshore McKenzie River Delta 
132 

APPENDIX B – STATISTICAL ANALYSIS AND OIL SPILL RATE CALCULATIONS 

USING ALASKAN AND CANADIAN SPILL DATA 
133 

Appendix B presents key statistical analyses and calculations of oil spill risk estimates using both 

the Alaskan and the Canadian data. The analysis and calculations presented in the main body of 

the report use only the Alaskan oil spill data because of doubts about the comprehensiveness of 

the Canadian data. The following table shows how the table and figures presented in this 

appendix correspond to the tables and figures in the main text 

Appendix B Tables 

and Figures 

Comparable Main Text 

Tables and Figures 

Appendix B, Table 12 Table 12 

Appendix B, Table 13 Table 13 

Appendix B, Table 14 Table 14 

Appendix B, Table 15 Table 15 

Appendix B, Table 16 Table 16 

Appendix B, Table 17 Table 17 

Appendix B, Table 18 Table 18 

Appendix B, Table 19 Table 19 

Appendix B, Table 20 Table 20 

Appendix B, Figure 5 Figure 5 

Appendix B, Figure 6 Figure 6 

Appendix B, Figure 8 Figure 8 

Appendix B, Figure 9 Figure 9 

Appendix B, Figure 10 Figure 10 

Appendix B, Figure 11 Figure 11 
134 

APPENDIX B TABLE 12 

ANALYSIS OF VARIANCE OF INDIVIDUAL SPILL EVENTS BY MONTH

lm(formula = log(SpillHigh) ~ Amonth) 

Residuals: 

Min 1Q Median 3Q Max 

-1.5250 -0.6354 -0.1991 0.5093 3.9188 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 9.177535 0.348172 26.359 <2e-16 ***

AmonthAug -0.002824 0.431133 -0.007 0.9948 

AmonthDec 0.463255 0.467121 0.992 0.3234 

AmonthFeb 0.321720 0.457587 0.703 0.4834 

AmonthJan 0.403027 0.492389 0.819 0.4148 

AmonthJul 0.759831 0.442518 1.717 0.0887 . 

AmonthJun 0.690284 0.442518 1.560 0.1216 

AmonthMar -0.520539 0.561410 -0.927 0.3558 

AmonthMay 0.317429 0.442518 0.717 0.4746 

AmonthNov -0.432825 0.449488 -0.963 0.3376 

AmonthOct -0.307075 0.478516 -0.642 0.5223 

AmonthSep 0.387448 0.478516 0.810 0.4198 

Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Residual standard error: 0.9848 on 114 degrees of freedom 

Multiple R-Squared: 0.1499, Adjusted R-squared: 0.06791 

F-statistic: 1.828 on 11 and 114 degrees of freedom, p-value: 0.05704 
135 

APPENDIX B TABLE 13 

ANALYSIS OF VARIANCE OF INDIVIDUAL SPILL EVENTS BY YEAR

lm(formula = log(SpillHigh) ~ Ayear) 

Residuals: 

Min 1Q Median 3Q Max 

-1.9087 -0.5397 -0.1999 0.3477 3.2591 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 9.23968 0.58824 15.707 <2e-16 *** 

AyearY71 1.47474 1.17648 1.254 0.2130 

AyearY72 0.66381 1.17648 0.564 0.5739 

AyearY73 -0.11285 0.77817 -0.145 0.8850 

AyearY74 0.11242 0.83190 0.135 0.8928 

AyearY75 0.46516 0.64821 0.718 0.4747 

AyearY76 -0.18432 0.70308 -0.262 0.7937 

AyearY77 0.43562 0.66363 0.656 0.5131 

AyearY78 0.91927 0.77817 1.181 0.2403 

AyearY79 1.36937 0.74407 1.840 0.0687 . 

AyearY80 -0.50826 0.83190 -0.611 0.5426 

AyearY81 0.10094 0.70308 0.144 0.8861 

AyearY82 0.20467 0.74407 0.275 0.7838 

AyearY83 -0.36843 0.68978 -0.534 0.5944 

AyearY84 -0.59703 0.77817 -0.767 0.4448 

AyearY85 -0.59703 0.77817 -0.767 0.4448 

AyearY86 -0.44606 0.72045 -0.619 0.5372 

AyearY87 -0.08202 0.93009 -0.088 0.9299 

AyearY88 -0.34575 0.93009 -0.372 0.7109 

AyearY89 0.27484 0.70308 0.391 0.6967 

AyearY90 0.27524 0.83190 0.331 0.7415 

AyearY91 -0.16443 0.83190 -0.198 0.8437 

AyearY92 0.34486 0.93009 0.371 0.7116 

AyearY93 0.15640 0.68978 0.227 0.8211 

AyearY94 -0.59251 0.83190 -0.712 0.4780 

AyearY96 1.19667 1.17648 1.017 0.3116 

AyearY97 0.01189 0.77817 0.015 0.9878 

Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Residual standard error: 1.019on 99 degrees of freedom 

Multiple R-Squared: 0.2098, Adjusted R-squared: 0.002265 

F-statistic: 1.011 on 26 and 99 degrees of freedom, p-value: 0.4619 
136 

APPENDIX B TABLE 14 

ANALYSIS OF VARIANCE OF SPILL EVENTS BY FACILITY TYPE

lm(formula = log(SpillHigh) ~ FacilityType) 

Residuals: 

Min 1Q Median 3Q Max 

-101327 -13520 -2618 1517 566673 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 24772 14074 1.760 0.080927 . 

FacilityTypeHWY -17214 17621 -0.977 0.330582 

FacilityTypePipe 80555 21402 3.764 0.000260 ***

FacilityTypePrd -6020 18480 -0.326 0.745191 

FacilityTypeSF -6011 19676 -0.305 0.760535 

FacilityTypeU -19522 66012 -0.296 0.767941 

Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Residual standard error: 64490 on 120 degrees of freedom 

Multiple R-Squared: 0.1888, Adjusted R-squared: 0.155 

F-statistic: 5.586 on 5 and 120 degrees of freedom, p-value: 0.0001158 

lm(formula = log(SpillHigh) ~ FacilityType) 

Residuals: 

Min 1Q Median 3Q Max 

-2.05240 -0.57235 -0.04463 0.29790 3.07156 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 9.6056 0.2037 47.146 < 2e-16 ***

FacilityTypeHWY -0.7077 0.2551 -2.774 0.00641 ** 

FacilityTypePipe 0.7409 0.3098 2.391 0.01835 * 

FacilityTypePrd -0.1679 0.2675 -0.627 0.53157 

FacilityTypeSF -0.1679 0.2675 -0.627 0.53157 

Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Residual standard error: 0.9337 on 120 degrees of freedom 

Multiple R-Squared: 0.1957, Adjusted R-squared: 0.1622 

F-statistic: 5.839 on 5 and 120 degrees of freedom, p-value: 7.302e-005 
137 

APPENDIX B TABLE 15 

ANALYSIS OF VARIANCE OF INDIVIDUAL SPILL EVENTS BY OIL TYPE

lm(formula = log(SpillHigh) ~ OilType) 

Residuals: 

Min 1Q Median 3Q Max 

-45192 -21626 -9833 -1831 622808 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 49192 10720 4.589 1.10e-05 *** 

OilTypeD -32359 14077 -2.299 0.0232 * 

OilTypeG -39812 22051 -1.805 0.0735 . 

OilTypeTF -25760 23532 -1.095 0.2758 

OilTypeU -36751 50283 -0.731 0.4663 

Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Residual standard error: 69480on 121 degrees of freedom 

Multiple R-Squared: 0.05081, Adjusted R-squared: 0.01943 

F-statistic: 1.619 on 4 and 121 degrees of freedom, p-value: 0.1738 

lm(formula = log(SpillHigh) ~ OilType) 

Residuals: 

Min 1Q Median 3Q Max 

-1.4072 -0.6652 -0.2570 0.4371 3.7168 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 9.7012 0.1552 62.522 <2e-16 *** 

OilTypeD -0.4518 0.2037 -2.218 0.0285 * 

OilTypeG -0.7269 0.3192 -2.278 0.0245 * 

OilTypeTF -0.1876 0.3406 -0.551 0.5828 

OilTypeU -0.5029 0.7278 -0.691 0.4909 

Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Residual standard error: 1.006 on 121 degrees of freedom 

Multiple R-Squared: 0.05921, Adjusted R-squared: 0.02811 

F-statistic: 1.904 on 4 and 121 degrees of freedom, p-value: 0.1141 
138 

APPENDIX B TABLE 16 

LINEAR REGRESSION OF ANNUAL SPILL RATE BY YEAR

lm(formula = SpillRate2000 ~ YEAR) 

Residuals: 

Min 1Q Median 3Q Max 

-19642 -7815 -3212 1946 95670 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 1853064.4 769111.6 2.409 0.0226 * 

YEAR -930.3 387.7 -2.400 0.0231 * 

Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Residual standard error: 19300 on 29 degrees of freedom 

Multiple R-Squared: 0.1657, Adjusted R-squared: 0.1369 

F-statistic: 5.759 on 1 and 29 degrees of freedom, p-value: 0.0205 

lm(formula = log(SpillRate2000) ~ YEAR) 

Residuals: 

Min 1Q Median 3Q Max 

-3.1563 -0.9427 0.0793 0.7122 3.4422 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 534.83199 60.10058 8.899 8.68e-10 ***

YEAR -0.26666 0.03029 -8.803 1.10e-09 ***

Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Residual standard error: 1.509 on 29 degrees of freedom 

Multiple R-Squared: 0.727, Adjusted R-squared: 0.7183 

F-statistic: 77.49 on 1 and 29 degrees of freedom, p-value: 1.096e-009 
139 

APPENDIX B TABLE 17 

LINEAR REGRESSION OF ANNUAL SPILL RATE FOR YEARS GREATER THAN 1979

lm(formula = SpillRate2000[YEAR > 1979] ~ YEAR[YEAR > 1979]) 

Residuals: 

Min 1Q Median 3Q Max 

-108.29 -43.46 -31.44 78.44 138.80 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 11826.906 6090.759 1.942 0.068 . 

YEAR[YEAR > 1979] -5.898 3.061 -1.927 0.070 . 

 

Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Residual standard error: 71.07on 13 degrees of freedom 

Multiple R-Squared: 0.1093, Adjusted R-squared: 0.0476 

F-statistic: 1.595 on 1 and 13 degrees of freedom, p-value: 0.02288 

lm(formula = log(SpillRate2000[YEAR > 1979]) ~ YEAR[YEAR > 1979]) 

Residuals: 

Min 1Q Median 3Q Max 

-2.03886 -0.88628 0.07833 0.74709 2.03006 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 237.57204 88.57378 2.682 0.0152 * 

YEAR[YEAR > 1979] -0.11743 0.04452 -2.638 0.0167 * 

Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Residual standard error: 1.148 on 18 degrees of freedom 

Multiple R-Squared: 0.2788, Adjusted R-squared: 0.2387 

F-statistic: 6.957 on 1 and 18 degrees of freedom, p-value: 0.01672 
140 

APPENDIX B TABLE 18 

LINEAR REGRESSION OF ANNUAL SPILL RATE FOR YEARS GREATER THAN 1984

lm(formula = SpillRate2000[YEAR > 1984] ~ YEAR[YEAR > 1984]) 

Residuals: 

Min 1Q Median 3Q Max 

-74.56 -38.57 -33.27 44.19 122.46 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 10762.149 8460.510 1.272 0.226 

YEAR[YEAR > 1984] -5.364 4.247 -1.263 0.229 

Residual standard error: 71.07 on 13 degrees of freedom 

Multiple R-Squared: 0.1093, Adjusted R-squared: 0.04076 

F-statistic: 1.595 on 1 and 13 degrees of freedom, p-value: 0.2288 

lm(formula = log(SpillRate2000[YEAR > 1984]) ~ YEAR[YEAR > 1984]) 

Residuals: 

Min 1Q Median 3Q Max 

-1.99331 -1.10423 0.09609 0.75313 2.15364 

Coefficients: 

 Estimate Std Error t value Pr(>|t|) 

(Intercept) 315.36040 146.73039 2.149 0.0510 . 

YEAR[YEAR > 1984] -0.15644 0.07366 -2.124 0.0534 . 

Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Residual standard error: 1.233 on 13 degrees of freedom 

Multiple R-Squared: 0.12576, Adjusted R-squared: 0.2005 

F-statistic: 4.511 on 1 and 13 degrees of freedom, p-value: 0.05344 
141 

APPENDIX B TABLE 19

CALCULATION OF MEANS AND EXPECTED UNCERTAINTIES OF ANNUAL SPILL

RATE FOR YEARS GREATER THAN 1984

A. Arithmetic mean of annualized spill rate = 77.34 barrels spilled per million barrels 

produced 

B. Approximate arithmetic 95% confidence limits on the mean of annualized spill 

rate = 72.56 % 

C. Lognormal mean annualized spill rate = 107.11 barrels spilled per million barrels 

produced 

D. Approximate logarithmic 95% confidence limits on annualized spill rate 476.95 %

APPENDIX B TABLE 20 

OIL SPILL RISK RATE BY COUNT WITH ASSOCIATED UNCERTAINTIES

DATA FROM 1978-1999

Spill Size 

(Bbl)

Number of 

Spills 

 Total Crude 

Oil Production

(MMBbl)

Calculated Risk 

Rate 

(Spills/MMBbl)

Approximate 95% 

Confidence Limits 

(%±)

≥100 81 13,019 0.0062217 22 

≥500 16 13,019 0.0012290 50 

≥1,000 7 13,019 0.0005377 76 

≥10,000 1 13,019 0.0000768 200 
1 2 3 4 5 6 7 8 9 10 

5 e+03 1 e+04 2 e+04 5 e+04 1 e+05 2 e+05 5 e+05

Log All Spills Spill Size vs Month Box plot

Appendix B Figure5
1 2 3 4 5 6 7 8 9 11 13 15 17 19 21 23 25 

5 e+03 1 e+04 2 e+04 5 e+04 1 e+05 2 e+05 5 e+05

Log All Spills Spill Size vs Day Box plot

Appendix B Figure6
CC HWY Pipe Prd SF 

5 e+03 1 e+04 2 e+04 5 e+04 1 e+05 2 e+05 5 e+05

Log All Spills Spill Size vs FacilityType Box plot

Appendix B Figure8
CO D G TF 

5 e+03 1 e+04 2 e+04 5 e+04 1 e+05 2 e+05 5 e+05

Log All Spills Spill Size vs OilType Box plot

Appendix B Figure9
L R U WL 

5 e+03 1 e+04 2 e+04 5 e+04 1 e+05 2 e+05 5 e+05

Log All Spills Spill Size vs AffectedMedia Box plot

Appendix B Figure10
FP FT O PL TV U 

5 e+03 1 e+04 2 e+04 5 e+04 1 e+05 2 e+05 5 e+05

Log All Spills Spill Size vs SpillCauseCombined Box plot

Appendix B Figure11