Health and Environmental Assessment

of the Use of Ethanol as a Fuel Oxygenate

UCRL-AR-135949 Vol. 1

Report to the 

California Environmental 

Policy Council 

in Response to 

Executive Order 

D-5-99

AIR RESOURCES BOARD

VOLUME1

Executive 

Summary

December 1999
Front Cover Back

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UCRL-AR-135949 Vol. 1

Volume 1: Executive Summary

Editors

D. Rice*

G. Cannon*

December 1999

*Lawrence Livermore National Laboratory • University of California • Livermore, CA 94550
Work performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National

Laboratory under Contract W-7405-Eng-48.
UCRL-AR-135949 Vol. 1 Executive Summary December 1999

12-99/Ethanol Vol 1 1-1

Volume 1: Executive Summary

This is the Executive Summary of the report entitled Health and Environmental Assessment

of the Use of Ethanol as a Fuel Oxygenate for the California Environmental Policy Council. This

report has been prepared by the California Air Resources Board, the State Water Resources

Control Board (SWRCB), and the California Environmental Protection Agency’s Office of

Environmental Health Hazard Assessment (CalEPA/OEHHA). The report is divided into five

volumes:

Volume 1: Executive Summary.

Volume 2: Background Information on the Use of Ethanol as a Fuel Oxygenate.

Volume 3: Air Quality Impacts of the Use of Ethanol in California Reformulated Gasoline.

Volume 4: Potential Ground and Surface Water Impacts.

Volume 5: Potential Health Risks of Ethanol in Gasoline.

Each volume is summarized below.

Volume 2: Background Information on the Use of Ethanol as

a Fuel Oxygenate

2.1 Governor Gray Davis issued Executive Order D-5-99 on March 25, 1999, calling for

the removal of methyl tertiary butyl ether (MTBE) from gasoline at the earliest possible

date but no later than December 31, 2002. Task 10 of the Executive Order states “the

California Air Resources Board (ARB) and the State Water Resources Control Board

(SWRCB) shall conduct an environmental fate and transport analysis of ethanol in air,

surface water, and groundwater. The Office of Environmental Health Hazard Assessment

(OEHHA) shall prepare an analysis of the health risks of ethanol in gasoline, the products

of incomplete combustion of ethanol in gasoline, and any resulting secondary

transformation products. These reports are to be peer reviewed and presented to the

Environmental Policy Council by December 31, 1999 for its consideration.”

Recent legislation (Stats. 1999 Ch. 813; SB 529, Bowen) enacted Health and Safety Code

Sec. 43840.8, which imposes new requirements regarding multimedia environmental

assessments of proposed amendments to ARB's motor vehicle fuels specifications. There is a

streamlined environmental review mechanism for amendments proposed prior to January 1, 2000

and adopted prior to July 1, 2000.

California Senate Bill 989 incorporates into state statutes most of the provisions of the

Governor’s MTBE Executive Order. Additionally, this bill prohibits the ARB from adopting new

fuel specifications until a “multimedia” evaluation has been performed and submitted to the

California Environmental Policy Council for final review and approval.
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2.2 A systems-based approach is needed to evaluate risk management trade-offs and to

assess health and environmental consequences of the use of ethanol as a fuel oxygenate.

A thorough systems-based approach would include:

1. Identification of the key attributes of gasohol1 production, distribution, and use, including a

fuel-cycle characterization.

2. Screening-level analysis and models to predict the likely environmental fate(s) of ethanol,

gasohol, and alkylated-fuel components released into reference landscapes and consideration

of potential exposure pathways. This assessment would contain:

• A review of the existing state of knowledge,

• The identification of physiochemical properties of the compounds of concern, and

• Environmental-fate simulations for airborne emissions and subsurface releases.

3. Exposure assessments, including toxicity evaluations of ethanol, gasohol, and alkylated-fuel

components that may be released.

4. Identification of key data and knowledge gaps and the specification of the kinds of studies

needed to obtain the necessary data and to address any methodological issues related to

assessing the use of ethanol, gasohol, and alkylated fuel.

5. Performance of selected experiments to address the identified data gaps.

6. Refinement of conceptual models and integration of new data into critical analyses of

environmental transport and fate and multipathway exposures.

2.3 Ethanol is used in oxygenated2 and reformulated3 gasoline (8% in federal oxyfuel or

6% in federal reformulated gasoline [RFG], by volume) because it is a renewable, biomassbased source of fuel that benefits from tax incentives, and because it is perceived that its

environmental impacts are less than those associated with the use of MTBE.

The ethanol used for fuel is made primarily from grains or other renewable agricultural and

forestry feedstocks. Any feedstock that contains sugar, starch, or cellulose can be fermented and

distilled into ethanol. To promote markets for ethanol, the United States Congress has approved a

5.4-cents/gallon federal subsidy for its use in gasoline.

 

1

 Gasohol in this report refers to gasoline containing 10% ethanol.

2

 Oxygenated gasoline must contain at least 2.7% oxygen by weight unless a state obtains a waiver from the United

States Environmental Protection Agency (US EPA). Such oxygenated gasoline is used in federally designated

carbon monoxide nonattainment zones.

3

 Reformulated gasoline (RFG) contains a minimum average of 2% oxygen (by weight), no more than 1% benzene

(by weight), and no heavy metals. RFG is used in locations that exceed the ozone standard. Currently, about 70% of

gasoline used statewide is RFG.
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Ethanol is a small chain molecule (C2H5OH) that contains 34.7% oxygen by weight and is

infinitely soluble in water. In its pure (or neat) form, ethanol is a flammable, colorless liquid

with a sweet alcohol odor. Ethanol is lighter than water; and if released rapidly in bulk onto

water, ethanol will tend to remain on the surface of the water. When gasoline-containing ethanol

is in contact with even small quantities of water, the ethanol will separate from the gasoline into

the water. Pure ethanol and ethanol blends of gasoline are heavier than unblended gasoline.

Ethanol is very volatile and will evaporate into air approximately five times faster than

MTBE. Like gasoline vapors, ethanol vapors are denser than air and tend to settle in low areas.

In open-air areas, these vapors will tend to disperse rapidly.

When burned, ethanol releases less heat than gasoline. One and a half gallons of ethanol

have approximately the same fuel combustion energy as one gallon of gasoline. Ethanol has a

higher ignition temperature than gasoline (approximately 850°F versus approximately 495°F,

respectively.). When pure ethanol is burned, the flame is less bright than a gasoline flame but is

easily visible in daylight. Both ethanol and MTBE have similar octane ratings of about 110 and,

when added to gasoline, increase the octane rating. (The long chain hydrocarbon known as

octane4 is used as a standard and is equal to 100).

Though pure ethanol is poisonous, it is less toxic than the benzene, toluene, ethyl benzene,

and xylenes (BTEX) that are components of gasoline. Ethanol is present in pharmaceuticals,

mouthwash products, alcoholic beverages, cleaning products, solvents, dyes, and explosives.

Humans frequently ingest fermented beverages that contain about 12% ethanol by volume.

Because ethanol is a metabolic byproduct, many organisms tolerate concentrations that may be

encountered during accidental releases into the environment. A variety of indigenous

microorganisms within the environment are capable of using ethanol as an energy source and

will preferentially utilize ethanol over gasoline hydrocarbons, such as benzene.

Ethanol and ethanol blends of gasoline conduct electricity. (In contrast, unblended gasoline

is an electrical insulator.) Because of its conductivity, pure ethanol is more corrosive than

gasoline, and the compatibility of materials must be considered when designing large-volume,

bulk ethanol storage tanks.

The California Energy Commission (CEC) anticipates that the use of alkylates5 will be

enhanced in non-oxygenated gasoline and some ethanol-containing gasolines in California to

replace the octane normally provided by MTBE. For that reason, alkylates are also a focus of the

analysis included in this report.

2.4 Additional amounts of alkylates, which are existing gasoline components, will likely

be required to maintain octane levels in gasoline after the removal of the MTBE, a highoctane, anti-knock additive.

 

4 MTBE has a 110 octane rating, ethanol has 115 octane, alkylates provide 91 to 99 octane, and aromatics have

100 octane.

5 Alkylates are gasoline blend stock produced by reacting isobutane with olefins. They consist of branched alkanes,

have very low aromatic content, and contain no sulfur or olefins.
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Alkylates consist of branched alkanes, mostly with 6 to 9 carbons, such as isooctane

(2,2,4-trimethylpentane). Even though ethanol also has a high-octane level, its oxygen content is

about twice that of MTBE; consequently, less ethanol is required to meet a specified oxygen

content (for example, 2.5 wt% oxygen). The resulting octane deficit must be compensated for by

adding high-octane blending components, such as alkylates.

Volume 3: Air Quality Impacts of the Use of Ethanol in

California Reformulated Gasoline

To assist OEHHA in its health risk assessment, the ARB conducted an analysis to estimate

the changes in outdoor air quality levels of potentially detrimental exhaust and evaporative

components and subsequent reaction products that would result from substituting

ethanol-blended gasoline for gasoline blended with MTBE. The ARB also included nonoxygenated gasoline in its analysis to provide a basis of comparison for the ethanol-containing

gasolines. As stated previously, the CEC anticipates that the amount of alkylates will be

increased in non-oxygenated gasoline and in some ethanol-containing gasolines to replace the

octane normally provided by MTBE; consequently, these compounds were also a focus of the

ARB analysis.

The ARB conducted four types of analyses:

1) A review of several recently published comprehensive assessments of the impact of

oxygenated gasoline on the environment.

2) A literature review of studies that measure the direct impact of the use of ethanol in

gasoline.

3) An evaluation of emission and air quality impacts from MTBE-free fuels in comparison

to MTBE-containing fuel.

4) Closure of existing data gaps as part of this study and ongoing efforts that will not be

completed until after the December 31, 1999, deadline in the Executive Order.

These analyses led to the following conclusions:

3.1 In comparison to the non-MTBE components of gasoline, the atmospheric

formation of toxic compounds from ethanol and alkylates are relatively slow.

Because the maximum estimated outdoor air quality levels of ethanol and alkylates are at

least a factor of 10 below any level of concern identified by OEHHA, the main issues are their

products of incomplete combustion and atmospheric transformations. The major products of

concern for ethanol are acetaldehyde (a toxic air contaminant) and peroxyacetyl nitrate (PAN, an

eye irritant and cause of plant damage). These compounds are offset by reductions in

formaldehyde (a toxic air contaminant) due to the elimination of MTBE. Alkylates eventually

form acetaldehyde, formaldehyde, and PAN, as do many other existing components of gasoline.

The greater the atmospheric lifetime of a compound, the more dilution and dispersion will reduce
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the impact of products of atmospheric transformations. The atmospheric lifetime for ethanol is

similar to MTBE—about two to three days under polluted conditions and longer during periods

of good air quality. Atmospheric lifetimes for alkylates range from one day to a week. Our

findings from theoretical calculations using airshed models with state-of-the-science chemistry

indicate that other components of gasoline, such as aromatic compounds and olefins, are

primarily responsible for the formation of formaldehyde, acetaldehyde, and PAN due to both

their greater abundance in gasoline and their shorter atmospheric lifetimes.

3.2 The inadvertent commingling of ethanol-containing and ethanol-free gasolines in

vehicle fuel tanks results in a combined gasoline with a Reid vapor pressure (RVP) greater

than the summertime California limit of 7.0 pounds per square inch (psi) and increased

evaporative emissions of volatile organic compounds (VOCs). This effect will be mitigated

by RVP reductions in the California Phase 3 Reformulated Gasoline (CaRFG3)

regulations.

Even small amounts of ethanol cause an RVP increase of about 1 psi when it is added to an

ethanol-free base gasoline. Current federal law requires all gasoline sold in southern California,

Sacramento, and, shortly, the San Joaquin Valley to contain an oxygenate. Under an MTBE ban,

ethanol would be the only possible oxygenate with the potential for large-scale introduction.

Thus, commingling would seldom happen in this large portion of California, representing 80% of

the gasoline marketplace. California has requested the federal government for a waiver from the

summertime oxygenate requirement to facilitate the phaseout of MTBE in these areas. If the

waiver is granted, commingling will likely increase. Current estimates of the overall effect of

commingling range from 0.1 to 0.4 psi, depending on assumptions for the market share of

ethanol-containing gasolines, consumer’s brand/grade loyalty, and the distribution of fuel tank

levels before and after refueling events. The CaRFG3 regulations require a 0.1 psi RVP decrease

to help mitigate the effect of commingling, and the ARB has committed to additional research to

further quantify commingling impacts.

3.3 Ethanol-containing gasolines may lead to increases in evaporative emissions because

rubber, plastics, and other materials are permeable to ethanol; moreover, ethanol may

reduce the working capacity of the charcoal canisters used to control evaporative emissions

on board motor vehicles. This issue has been addressed in the United States

Environmental Protection Agency’s (US EPA’s) recently adopted Tier 2 emission

standards. However, the current on-road motor vehicle fleet (other than flexible-fueled

vehicles operated on alcohol blends) is not fully controlled from the perspective of

evaporative ethanol emissions. Further research is needed to compare the effects of

ethanol, MTBE (which also reduces the working capacity of charcoal canisters), and

alkylates on evaporative emission from the existing California vehicle fleet.

Motor vehicles are subject to evaporative fuel losses from many locations in the vehicle.

These losses can be described by the following three processes: running loss, hot soak, and

diurnal emissions. “Running loss” emissions are evaporative emissions which occur during

operation of the vehicle and stem from permeation through the fuel hoses and losses from the

carbon canister (a container filled with sorbent activated carbon used to store gasoline vapors).

“Hot-soak” emissions are vapor losses from a recently operated hot vehicle. Most of these losses
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are due to permeation through hoses. “Diurnal” emissions are evaporative losses mainly from

the charcoal canister and result from daily heating of the vehicle’s fuel tank and consequent

saturation and overflow from the canister.

Because of the tendency of ethanol to evaporate more readily than other fuel components and

because the smaller size of an ethanol molecule promotes permeation through hoses, hot-soak

emissions tend to result in evaporative losses containing a proportionally greater amount of

ethanol than was in the original fuel. Also, it is possible that ethanol’s propensity to be tightly

held by activated carbon, in conjunction with its hygroscopic nature (that is, it attracts water),

may decrease the working capacity of the charcoal canisters used to control evaporative

emissions on board motor vehicles and result in increased diurnal emissions. However, data

suggesting a reduced working capacity are somewhat conflicting in nature, but this may be

partially due to the difficulty in sampling ethanol, and additional research is needed in this area.

Both early and late model–year vehicles (other than flexible-fueled vehicles operated on

alcohol blends) are not fully controlled from the perspective of evaporative ethanol emissions.

That is, the certification test procedures for evaporative emissions require the use of a fuel

containing MTBE and, thus, do not completely take into account the use of commercially

available ethanol-containing gasolines. Although more stringent evaporative emission standards

were adopted in 1998 and are applicable to the 2004 to 2006 model years, the procedures were

pertinent only to the fuels in use at the time of adoption and, thus, did not include ethanol blends.

Revised certification test procedures to include ethanol-containing gasolines will need to be

developed in order to control any incremental evaporative emissions resulting from these fuel

blends. The US EPA recently adopted such changes under its Tier 2 regulations.

3.4 Because relatively little ethanol is produced in California, it will probably all be

shipped by rail or truck. The estimated statewide impact on heavy-duty truck emissions is

a 0.06% increase. Most likely , these impacts will be localized at the two central ethanol

distribution locations and the 64 fuel storage terminals and will be addressed locally under

the California Environmental Quality Act.

The bulk of the ethanol to be used in California will be transported by rail from the Midwest

to two central distribution locations, trucked to 64 fuel storage terminals, and then

splash-blended with gasoline. The increase in heavy-duty truck emissions would be about 0.06%

of the statewide total, using estimates of truck travel for ethanol distribution made by the CEC.

If increased local traffic and emissions from diesel trucks become local environmental concerns,

they will be addressed locally in the context of use permits and permits to operate specific

facilities under the California Environmental Quality Act.

3.5 So long as the CaRFG3 regulations address the potential for ethanol to increase

evaporative emissions and cause more rail and truck traffic, the substitution of ethanol and

alkylates for MTBE in California’s fuel supply will not have any significant air quality

impacts. This finding is supported by theoretical calculations in the South Coast Air Basin

using state-of-the-science tools, an analysis of the impact of uncertainties, air quality

measurements in areas that have already introduced ethanol into their fuel supply, and an

independent scientific peer review by the University of California.
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We used the best available information on the emission characteristics of fuels that will be

available in 2003, a comprehensive analysis of current (that is, 1997) air quality levels, and an

airshed model for the South Coast Air Basin with state-of-the-science chemistry to estimate air

quality in the future for the following four fuels:

• Current MTBE-based California Phase 2 Reformulated Gasoline (CaRFG2), assumed to

be equivalent in both 1997 and 2003.

• Ethanol-based, fully complying CaRFG2 fuel with an oxygen content of 2.0 wt%

(5.7% ethanol by volume) in 2003.

• Ethanol-based, fully complying CaRFG2 fuel with oxygen content of 3.5 wt%

(10% ethanol by volume) in 2003.

• Non-oxygenated, fully complying CaRFG2 fuel in 2003.

Because the CaRFG3 regulations were not approved until December 9, 1999, we were unable

to consider the new specifications in our emission and air quality predictions. However, because

the regulations preserve the air quality benefits of CaRFG2 and apply equally to ethanol-blended

and non-oxygenated gasolines, consideration of CaRFG3 will not affect our overall conclusions.

All pollutants of concern decrease from the 1997 MTBE baseline to the 2003 MTBE baseline

due to reductions in overall emissions. The predicted decreases are especially pronounced for

the toxic air contaminants, ranging from 13% for formaldehyde and acetaldehyde to 33% for

benzene and 43% for 1,3-butadiene. There are several differences between the 2003 MTBE

baseline and the three 2003 MTBE-free fuel scenarios. Because fuel-related activities are the

only inventoried source of MTBE, levels of MTBE decrease 100%. Ethanol levels for the

ethanol-blended gasolines increase by 48% (2.0 wt% oxygen fuel) and 72% (3.5 wt% oxygen

fuel), but acetaldehyde is predicted to increase (4%) for only the ethanol-blended gasoline at

3.5 wt% oxygen. PAN levels are not predicted to increase for either the ethanol-blended or nonoxygenated gasolines. Benzene levels increase slightly (1%) for the ethanol-blended gasoline at

3.5 wt% oxygen with decreases predicted for the other two gasolines. All three MTBE-free

gasolines produce modest reductions in 1,3-butadiene (2%) and formaldehyde levels (2–4%) and

essentially no change in ozone, nitrogen dioxide, nitric acid, and PPN (peroxypropionyl nitrate)

levels. As expected, the non-oxygenated gasoline results in higher predicted eight-hour-average

carbon monoxide levels (3%), and the 3.5 wt% oxygen ethanol-blend in lower carbon monoxide

values (–9%). It should be noted that these are summertime levels—a time period when

violations of the standard do not occur. Due to the wintertime oxygenate requirement for the

South Coast Air Basin, carbon monoxide levels within the nonattainment area of Los Angeles

County will not differ from the 2003 MTBE baseline.

Primarily due to the lack of ambient air quality measurements for many of the air

contaminants of concern, we were unable to predict air quality for other areas of California.

However, our analysis for the South Coast Air Basin can be considered the worst-case situation

in comparison to other air basins. It has the highest baseline air quality levels, the conditions

most conducive to formation of secondary air pollutants (for example, ozone, acetaldehyde, and

PAN), the most emissions, and the highest number of gasoline-related emission sources in

California.
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Calculations that bracket the impact of motor vehicle emission inventory uncertainty and

chlorine atom chemistry in coastal environments resulted in increases for all pollutants, but the

only significant impact on relative differences among the 2003 fuels was a large increase in

ethanol for the ethanol-blended gasolines. The use of the modeling tool in a relative sense

bypasses concerns about other uncertainties.

Our review of studies of the impact of the use of ethanol-containing gasoline on air quality in

Denver, Colorado; Albuquerque, New Mexico; Brazil; and other areas indicates that

acetaldehyde levels are substantial only in Brazil, where the fuels contained either pure ethanol

or 22% ethanol—much greater levels than the maximum of 10% ethanol allowed in California

gasolines. Due to the lack of RVP requirements for gasolines in Brazil, the high acetaldehyde

levels could be due to the addition of substantial evaporative emissions rather than strictly the

result of an ethanol-for-MTBE substitution. Even with increased acetaldehyde levels, the

observed levels of PAN are more than a factor of 10 below historical levels observed in southern

California although the Brazilian measurements were not in the areas likely to have the highest

PAN levels.

A draft version of this report was reviewed by four scientists approved by the University of

California Office of the President under a process defined by Health and Safety Code section

57004. While the reviewers agreed with our basic findings on ethanol and alkylates, they noted

the need for a number of corrections, clarifications, and caveats that we have incorporated into

this final version of the report. Their comments and our responses are included in this report.

3.6 The results of this study do not necessarily extend to other states. California does

not have an RVP exemption for ethanol-containing gasolines; and the CaRFG3 Predictive

Model constrains emissions of cancer-potency-weighted toxic air contaminants, oxides of

nitrogen (NOX), and VOCs. States without these safeguards (that is, non-Federal

Reformulated Gasoline areas) may have significant air quality impacts from replacement

of MTBE with ethanol or aromatic compounds.

A previous ARB comparison of a 10% ethanol-gasoline blend with 8.0-psi RVP and a fully

complying, MTBE-based gasoline meeting a 7.0-psi RVP limit concluded that while carbon

monoxide emissions decreased by about 10% for the high-RVP fuel, emissions increased for

NOX (14%), combined exhaust and evaporative VOCs (32%), ozone-formation potential (17%),

and cancer-potency-weighted toxic air contaminants (5%). The ozone formation potential

calculations included the benefit of the carbon monoxide reduction. The results also show that

there is a likelihood (between 92% and 100%) that emissions of NOX, VOC, ozone formation

potential, and cancer-potency-weighted toxics are greater with the high-RVP ethanol blend than

with the fully complying gasoline. The high level of certainty associated with the results of the

test program show that additional testing would not likely change the outcome of this evaluation

and that additional tests on 1990 to 1995 model year vehicles and vehicles that employ control

technologies similar to these are unnecessary. Thus, significant air quality impacts are likely in

the parts of the United States (that is, non-Federal Reformulated Gasoline areas) where the US

EPA allows a 1 psi RVP exemption for ethanol.
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The CaRFG3 Predictive Model constrains exhaust emissions of NOX, VOCs, and

cancer-potency-weighted toxic air contaminants (that is, acetaldehyde, benzene, 1,3-butadiene,

and formaldehyde), and evaporative emissions of VOCs and benzene. Thus, different fuel

formulations (for example, ethanol-blended and non-oxygenated) will be manufactured to have

similar emissions through the adjustment of various fuel properties, such as sulfur content,

aromatic content, etc. As MTBE is removed from gasoline, the CaRFG3 Predictive Model will

push California fuel suppliers toward an increased use of alkylates rather than aromatic

compounds. Alkylates have no significant air quality impacts in comparison to the aromatic

compounds that are powerful ozone and benzene precursors and likely to be used in other states

if there is a corresponding ban on MTBE.

3.7 An air quality monitoring program is now in place to directly measure the impact of

the phase-out of MTBE.

Our analysis of air quality impacts will be compared with field measurements that take place

before and after the planned December 31, 2002, phaseout of MTBE. These types of studies

were successfully conducted in California in 1996 during the implementation of CaRFG2.

California’s existing ambient air quality networks should be sufficient for all the criteria

pollutants, MTBE, toxic air contaminants, and individual VOC compounds (that is, alkylates).

Because PAN is not part of any routine air quality monitoring program, we began PAN

measurements at two sites in the South Coast Air Basin last November. Because ethanol and

acetaldehyde lead to PAN but not to PPN, and because their ratio may be a useful indicator of

the impact of ethanol emissions on PAN air quality levels, the measurement program includes

both PAN and PPN. We will investigate the possibility of adding ethanol measurements and

expanding the monitoring program to other areas of the State.

Volume 4: Potential Ground and Surface Water Impacts

4.1 A comprehensive understanding of the effects of ethanol on the fate and transport of

gasoline compounds is needed to determine if the economic and air quality benefits of

adding such fuel alcohols to gasoline outweigh their potential detrimental effects on

groundwater pollution and related health risks. Although California has implemented

improved containment practices for underground storage tanks, releases of gasoline that

may impact surface water and groundwater resources can still be expected.

An important consideration for the decision to use ethanol is the potential effect it may have

on the fate and transport of toxic-gasoline components (in particular, BTEX). This fate-andtransport information is important for evaluating the impact that ethanol may have on the cleanup

of gasoline releases and on California’s water resources in general. The chapters in Volume 4

summarize the possible release scenarios associated with the use of ethanol as a fuel oxygenate

(Chapter 1), the effect of ethanol on the fate and transport of BTEX compounds (Chapter 2), and

on their natural attenuation and biodegradation (Chapter 3). We report the results of the

predictive modeling performed to compare BTEX groundwater plumes in the presence of ethanol

(Chapter 4). We consider the potential impacts of the use of ethanol-containing gasoline on

surface-water resources (Chapter 5) and compare possible non-oxygenated fuel formulation to
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MTBE- or ethanol-containing gasoline (Chapter 6). We evaluate the analytical methods available

for the detection of ethanol in the environment (Chapter 7). We perform a comparative analysis

of potential groundwater resource impacts for gasoline containing methyl tertiary butyl ether

(MTBE) or ethanol (Chapter 8).

As a result of the research performed for this volume, we have identified important

knowledge gaps regarding the anticipated environmental behavior of gasoline containing

ethanol. Chapter 9 summarizes those knowledge gaps and provides recommendations for future

research that would improve decision-making regarding the use of ethanol in oxygenated and

reformulated gasolines in California.

4.2 During our evaluation of ground- and surface-water impacts, we began the

development of a comprehensive life-cycle model.

This life-cycle model systematically addresses impacts from fugitive and accidental releases

associated with the production, distribution, and use of ethanol-containing gasoline. Time

constraints for producing this particular assessment limited its focus to only those scenarios of

chronic or accidental releases of ethanol that are most likely to impact ground and surface

waters. We were unable to consider fully other scenarios related to releases of substances as a

consequence of the transportation and use of feedstocks required for ethanol production as well

as from activities conducted at centralized blending centers. Also not considered were the

additional implications of agricultural-related impacts from ethanol-fuel production. For

example, increased corn-production for ethanol in California and elsewhere will require the

application of additional herbicides/pesticides with subsequent releases to the environment.

Including such scenarios will improve the breadth of understanding concerning the impacts of

ethanol use in motor fuels and, for this reason, may warrant more complete evaluation in the

future.

4.3 We examined the salient environmental properties of alkylates, which are nonoxygenated compounds likely to be used in greater amounts in gasoline after an MTBE

phaseout.

However, the limited analyses we conducted were not completed within the context of an

integrated life-cycle analysis concerning their production, storage, and use. Alkylates are

complex solutions of isoalkanes; and some properties, such as biodegradability, may not be

easily extrapolated to all alkylate components. In general, alkylate biodegradation rate is

relatively slow compared to other organic compounds, and some components may not

biodegrade in reasonable timeframes.

No toxicity data are available on the chronic effects of isooctane in humans. In addition, we

did not address cancer risk and reproductive and developmental effects. Surface releases of

alkylates, either on water or land, will probably result in the evaporation of most of the alkylate

into the atmosphere. Overall, it appears that alkylates would not effect dramatic changes in the

gasoline behaves in the environment and, thus, in the treatment of accidental releases.
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4.4 Several abiotic processes or mechanisms that affect the fate of ethanol and ethanolgasolines in the subsurface have been identified. These processes include infiltration,

spreading at the capillary fringe, and leaching of chemicals into groundwater.

These abiotic processes can potentially impact the retention and distribution of gasohol or

other petroleum products in the unsaturated zone, the size and the shape of a gasoline pool at the

water table, and the flux of contaminants from the gasoline to the groundwater.

The extent of our knowledge about these processes ranges from sufficient to inadequate. We

have very little information on the behavior of an ethanol gasoline as it infiltrates through the

unsaturated zone. On the other hand, there is substantial knowledge about many of the

mechanisms affecting saturated zone transport of gasoline containing ethanol. The net effect of

ethanol on the length and longevity of a contaminant plume, however, requires an understanding

of each of the steps that define the complete transport pathway. Rather than just deal with each

of these steps individually, it is important to understand the complex interrelationships among

the processes involved with the ultimate transport of gasoline components to a potential

downgradient receptor.

4.5 The introduction of ethanol affects the migration and distribution of gasoline in the

unsaturated zone in two primary ways:

• Capillary forces are reduced, thereby changing the multiphase flow characteristics.

• Pore structure of some mineral types is altered by chemical interactions with

ethanol.

In the presence of ethanol, hydrocarbons can enter smaller pore spaces and drain more easily

from unsaturated zone soils. This may impact the distributions of residual fuel hydrocarbons in

the unsaturated zone and the periphery of free-product pools that may exist. Among the impacts

may be the mobilization of existing unsaturated-zone contamination. As a result of the reduction

in capillary forces, the height of the capillary fringe may also be reduced. The depth and the area

of hydrocarbon pool on top of the water table may be altered (although 10% ethanol in gasoline

is expected to have a very minor effect). Furthermore, the dehydration of clays and the formation

of micro-fractures will increase permeability. The importance of these factors in multiphase flow

has not been quantified.

Understanding this process is crucial because knowledge gaps about the early stages of the

overall flow and transport preclude adequate prediction of the important impacts of ethanol on

BTEX contamination resulting from subsequent processes. A high level of predictive

uncertainty will remain until the relationship of each step to the overall process is understood

sufficiently.

4.6 Ethanol in gasoline will affect the concentrations of BTEX that dissolve into

groundwater and the residence time of fuel hydrocarbons in contact with the water table

(saturated zone).
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Although the dissolved equilibrium concentrations of gasoline components—benzene,

toluene, ethylbenzene, and xylenes—increase in the presence of high concentrations of ethanol,

the 10% ethanol expected to be added to gasoline in California should have only a minor effect

on the dissolution of these gasoline components. Relatively hydrophobic compounds, such as

xylenes, will be more affected than less hydrophobic compounds, such as benzene.

4.7 The presence of ethanol in groundwater may alter the processes of sorption and

retardation and could contribute to increased benzene plume lengths.

The possible impact of these effects is dependent on the quantity of ethanol at the source.

For gasoline containing 10% ethanol, these processes will likely be insignificant, whereas for

neat ethanol spills, these processes may become important.

To better assess the overall impact of oxygenated gasolines on the length and the longevity

of a BTEX groundwater plume, we need a better understanding of the significance of the size,

the shape, and the composition of gasoline free product in contact with the water table. A

thorough modeling effort to assess the sensitivity of the overall predictions to these unknown

parameters would be an appropriate first step. If the predictions are sensitive to these

parameters, then further experimental or modeling studies would be required to improve our

ability to estimate them.

4.8 Biodegradation of fuel alcohols contributes to the depletion of electron-acceptor

pools, and this depletion is likely to affect temporal and spatial transitions in electronacceptor conditions during natural attenuation of petroleum-product releases.

Such geochemical transitions are important to study because they affect both BTEX

degradation and migration rates. For example, both the changes in electron-acceptor availability

and the presence of easily degradable ethanol could affect catabolic diversity and the relative

abundance of specific BTEX-degrading bacteria.

4.9 Little is known about the effect of ethanol on microbial population shifts (that is,

microbial ecology) and the resulting catabolic diversity.

Among the possible effects are enrichment of ethanol-degrading bacteria in relation to

BTEX-degrading bacteria, fortuitous enrichment of bacteria that can degrade both ethanol and

BTEX compounds, and decreases in populations of certain bacteria as a result of toxicity.

Because the efficiency of bioremediation depends, in part, on the presence and expression of

appropriate biodegradative capacities of the subsurface microbes, studying the microbial ecology

of aquifers contaminated with gasoline-ethanol mixtures could be a fruitful avenue of research.

Such studies should address response variability as a function of release scenario and site

specificity to facilitate risk assessment and remedial action decisions.

To date, little research has been conducted on substrate interactions between BTEX and

ethanol. Often, target pollutants are degraded by inducible enzymes whose expression can be

repressed when easily degradable substrates (for example, ethanol) are present at high

concentrations. Although biodegradation of contaminant mixtures is not very well understood at
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the biochemical level, preferential substrate degradation appears to be a concentration-dependent

phenomenon related to repression of the enzymes needed to degrade the target compounds.

Currently, little is known about the conditions leading to sequential or simultaneous degradation

of BTEX in the presence of ethanol. This suggests the need to investigate the concentrationdependent effect that ethanol may have on the induction or repression of enzymes that catalyze

BTEX degradation. However, considering that the co-occurrence of BTEX and ethanol may be a

short-lived phenomenon relative to the overall duration of a gasoline plume, it is likely that the

depletion of oxygen and other electron acceptors resulting from ethanol degradation will be a

more important effect of ethanol than the substrate interactions between ethanol and BTEX.

Much of the relevant research to date reflects a reductionist approach to studying the effect of

ethanol on natural attenuation. For example, to study the effect of ethanol on specific

biodegradation activities, batch studies have often been used that eliminate confounding effects

from other variables, such as BTEX and electron-acceptor concentration gradients, as well as

mass-transport limitations. Similarly, pure cultures have been used to eliminate confounding

effects of microbial population shifts. This work on individual processes generally facilitates

hypothesis testing and yields results that are easier to interpret but may do so at the expense of

oversimplifying the complex conditions encountered in the field. To determine how ethanol

affects BTEX plume dimensions and treatment end points, future research should take on a more

holistic approach that considers transport and degradation processes interactively.

4.10 Ethanol stimulates microbial processes that may affect aquifer porosity and

hydraulic conductivity (for example, biofilm growth, mineral precipitation or dissolution,

and nitrogen or methane gas generation).

It is important to study how the presence of ethanol influences the dynamics of anaerobic

microbial communities and related processes that affect the hydraulic and chemical properties of

the aquifer. Such research should delineate the conditions that lead to a significant accumulation

of volatile fatty acids (VFA; potential degradation products of ethanol), and that could decrease

the pH to levels that inhibit bioremediation. Emphasis should be placed on evaluating the

potential for ethanol-induced methane production to restrict groundwater flow (thus, hindering

the replenishment of nutrients and electron acceptors) and to pose an explosion hazard (which

raises the possibility of requiring unique corrective-action measures).

4.11 The lack of BTEX and ethanol concentration data at gasohol leak sites is a major

knowledge gap.

Although 10% gasohol is widely used in Iowa and Nebraska, the ethanol concentrations

associated with gasohol releases are typically not measured because ethanol is not a regulated

pollutant. There is a perception that no important differences exist between gasoline with and

without 10% ethanol, but potential differences have not been evaluated.

Based on laboratory studies and theoretical considerations, we expect that ethanol may

increase BTEX plume length by hindering BTEX biodegradation, enhancing light nonaqueous

phase liquid (LNAPL) dissolution, and facilitating BTEX migration due to a decrease in

sorption-related retardation during transport. Nevertheless, there is very little information about
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the subsurface characteristics of ethanol plumes or about the variability of their effect on BTEX

fate and transport.

4.12 Several modeling efforts evaluating the behavior of benzene groundwater plumes in

the presence of ethanol indicate that benzene plumes are likely to increase in length. The

amount of this increase is not well known.

Because of the conservative assumptions used regarding unknown transport processes, the

models used to forecast benzene plume lengths in the presence of ethanol systematically

overestimate plume lengths. Each of these modeling efforts has taken a different approach and

has used a different set of simplifying assumptions that may not reflect actual subsurface

conditions. A key simplifying assumption among these studies is that the biodegradation rate of

benzene is constant in space and in time and for all concentrations of benzene with in the plume.

This assumption is very conservative; and if benzene biodegradation rates do actually increase

downgradient from the ethanol degradation zone, then these modeling predictions significantly

overestimate the extent of future benzene plumes. As information from laboratory, field, and

historical-case studies becomes available, these simplifying assumptions can be refined; and

more accurate and representative forecasts of gasoline-release plumes may be prepared.

Improved modeling will aid in the identification of efficient and cost-effective cleanup

approaches and resource management priorities.

4.13 During our analysis of potential groundwater impacts, we used a distance approach

combined with known impact probabilities and estimated plume lengths to compare the

probabilities of threat to public drinking water wells in California from MTBE or benzene

releases (with or without ethanol) from leaking underground fuel tanks (LUFTs)..

This method provides an important advantage because it allows comparative estimates of

potential future impacts between MTBE and benzene in the presence of ethanol. For comparative

purposes only, this analysis develops a modeled estimated baseline for benzene impacts. This

baseline estimate is then used to compare potential impacts from MTBE and benzene with

ethanol present. The methodology described in Chapter 8 can act as a screening-level approach

to identify vulnerable groundwater resource areas.

4.14 Based on the results of our analysis, an approximately 20% peak relative increase in

public drinking water wells impacted by benzene was estimated if MTBE is replaced by

ethanol.

The percent relative increase in impacts to public drinking-water wells is estimated to decline

from this peak increase at about ten years after the initiation of the use of ethanol. However, the

estimated, potential future increase in public wells impacted by MTBE is significantly higher if

MTBE were to remain the primary fuel oxygenate. By the conclusion of the first ten-year

period, estimated MTBE-well impacts increase by as much as 45% and continue to increase

thereafter. This analysis is very conservative, especially with regard to MTBE. Known

concentrations of MTBE at LUFT sites were not used in the analysis because only a limited

number of LUST sites have a known concentration associated with them.
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This approach may be subject to misinterpretations. Because we are examining an absolute

probability, there is a concern that the results can be taken out of context. It is important that the

relative probabilities be used, using the benzene-alone distributions as the baseline. These

estimates are not intended to be used to predict or forecast actual impacts. The results of these

estimates are to be used for relative comparison only.

4.15 Overall, the average yearly public drinking water source benzene detection rate is

under 0.35%. Both toluene and total xylenes have a higher rate, 0.53% and 0.36%

respectively. MTBE shows a 1.17% yearly detection rate, much higher than any of the

BTEX constituents alone, although similar to the combined BTEX detection rate (1.15%).

The evaluation of known detection levels in public water sources is to provided some

perspective to the magnitude of benzene or MTBE impacts in the past. Benzene shows a fairly

constant detection rate over time, with a slight downward trend when yearly rates are compared.

The use of ethanol as a fuel oxygenate would likely increase this detection rate which may

stabilize at some higher level. MTBE shows definite upward detection trends; its continued use

could, based on the trend results, result in more detections in water sources than benzene within

the foreseeable future.

4.16 In assessing the probability that MTBE or benzene with or without the presence of

ethanol may affect a drinking-water well or degrade a water supply, several unknowns

must be estimated.

These include the concentration of benzene, MTBE, or ethanol at a gasoline-release site, the

local hydrogeological regime, and the construction of nearby drinking-water wells and their

radius of groundwater capture during use. The availability of this data is very limited, and

existing data often have significant inaccuracies and errors.

Having accurate locations of public drinking-water wells is important to this effort, but

database location information on these wells is often poor. Additionally, data on well

construction and yield—necessary items to determine a well’s intrinsic vulnerability—are not

readily available, and collecting that data is costly although recent legislation has made it easier

for groups that are performing environmental assessments to access this type of data.

4.17 The persistence of ethanol in surface water will be governed by its biodegradation

rate, based on screening-level calculations.

Screening-level calculations for a scenario that simulates a discrete, seven-day period of

watercraft discharges of fuel-borne ethanol to Donner Lake in northern California showed that

the peak concentration of ethanol was only 2 μg/L, compared to about 8 μg/L for MTBE under

the same release scenario. The difference in levels is due to the elevated biodegradation loss rate

assumed to occur for ethanol—compared with the slower, volatilization-driven losses for MTBE.

For accidental tank-car releases of ethanol to a river or stream, toxic levels of ethanol could

occur in the immediate downstream area of a spill. The toxic levels of ethanol would be

expected to occur at variable distances downstream from the hypothesized spill, with the extent

of such toxic concentrations dependent on volumetric-discharge conditions. In addition, if only a
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portion of the tank-car inventory were released, the resulting concentrations would also be

reduced proportionately.

Aside from the acute toxicity for aquatic species that might be affected by a spill and their

associated recovery, it is unlikely that there would be any long-term toxic effects, because the

ethanol will not persist in water due to its rapid degradation. The key uncertainty with regard to

assessments of the impacts of ethanol releases to surface waters is the magnitude of the range of

ethanol biodegradation rates.

4.18 Based on the health-protective concentrations for drinking water alone (which are

summarized by the State of California Environmental Protection Agency, Office of

Environmental Health Hazard Assessment in Volume 5 of this report), it is clear that any

catastrophic or even major release of MTBE to surface water is far more likely to

represent a potential public-health problem than a similar release of ethanol.

A quantitative risk assessment designed to compare the results of MTBE and ethanol releases

to surface waters was not performed and was not the objective of this chapter. Instead, we

performed a series of screening-level simulations of various releases to better understand the

nature and magnitude of the impacts of ethanol and MTBE on surface waters, both temporally

and spatially. However, based on the health-protective concentrations for drinking water alone

(which are summarized by the State of California Environmental Protection Agency, Office of

Environmental Health Hazard Assessment in Volume 5 of this report), it is clear that any

catastrophic or even major release of MTBE to surface water is far more likely to represent a

potential public-health problem than a similar release of ethanol. The draft health-protective

concentration for oral exposures to drinking water for ethanol is 1,100,000 μg/L, whereas the

public-health goal for drinking water for MTBE is only 13 μg/L—a difference of almost five

orders of magnitude (that is, 105 or 100,000). The problem of MTBE release to surface water is

further exacerbated because it appears to be recalcitrant to aerobic biodegradation.

4.19 Rainout of ethanol to surface waters is considered to be more than a factor of 40

greater than for MTBE (by mass per unit-volume), as a result of the large difference

between the Henry’s law constants for these two compounds.

The quantity of ethanol in rainout will only be about 10 μg/L for every part per billion by

volume (ppb[v]) of ethanol in air compared to only 0.17 μg/L for MTBE. However, ethanol will

biodegrade rapidly in surface water, but MTBE is recalcitrant to such removal. Nevertheless, for

more accurate estimates of the levels of ethanol in rain, temperature-dependent values of the

Henry’s law constant need to be quantified in laboratory experiments. Compared to ethanol and

MTBE, the concentration of isooctane (a representative alkylate) in rain is going to be negligible

(estimated to be 0.000036 μg/L per 1 ppb[v] in air). Other isoalkanes are also likely to have very

low concentrations in rainwater.

4.20 The literature reviewed indicates that the technology currently exists to enable

researchers to detect ethanol at spill sites.
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Sufficient methods also exist to determine ethanol at its taste threshold of 50 parts per million

(ppm) in water. But no routine methods are currently able to detect ethanol below 50 parts per

billion (ppb) in water. A novel method for ethanol analysis capable of 15-ppb detection limits

has been reported. However, this solid-phase microextraction method requires validation before

it can be applied routinely to the analysis of environmental samples. Thus, much time and effort

must be invested to enable the detection of trace concentrations of ethanol. Until this is

accomplished on a routine basis, it will be difficult to completely understand the fate and

transport of ethanol in the environment.

4.21 The poor extraction efficiency of ethanol from water is the main contributor to its

relatively high analytical detection limits.

Improved extraction methods will result in better detection limits. The literature reviewed

for this study indicates that either direct injection of an aqueous solution or injection of the

headspace above an aqueous liquid can be used to obtain detection limits of 10 ppm or less.

Both of these techniques are easy and inexpensive to perform.

4.22 A number of recommendations have been made to address knowledge gaps in the

potential ground- and surface-water impacts associated with using ethanol to replace

MTBE. These recommendations include:

Expanded life-cycle analysis of the use of ethanol and non-oxygenated fuel compounds.

A comprehensive life-cycle assessment of ethanol should include the evaluation of release

scenarios associated with all stages of its manufacture, distribution, and utilization, including

transportation and use of feedstocks and activities at blending centers. This complete analysis

would account not only for the mass balance of ethanol in the environment but also for its direct

and indirect impacts with respect to issues related to the environment, health, and safety.

Accordingly, the objective of a complete life-cycle analysis is to provide a scientifically sound

characterization of its input feedstocks and related byproducts as well as their potential impacts.

A complete and comprehensive life-cycle analysis was not prepared for alkylates, but preparing

one would also be beneficial in order to understand the nature and magnitude of environmental

releases and their impacts.

Detailed field studies to refine conceptual models. Modeling based on detailed, sitespecific information is needed. Data from a thoroughly studied field site would refine our

conceptual models of critical processes controlling the net fate of gasohol in the subsurface.

Because the results of these estimates are largely dependent on the input-parameter probability

distributions, historical-case data that better constrain the uncertainty in these probability

distributions will improve the predictive capability of any future modeling. The uncertainty

inherent in using the complete distribution of benzene concentrations and velocities increases

substantially the increase in expected probability for well impacts. Site-specific, maximum

concentrations should be used, as opposed to a generic distribution that assumes no knowledge

of the LUFT site.

A representative site where gasoline containing ethanol has been released should be

evaluated in detail, including the collection and analysis of additional soil and groundwater
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samples needed to support microcosm and column studies. Additional sampling of field sites

might be used to provide field verification of microcosm results and increase the number of sites

upon which decision-making is based.

Groundwater capture zones should be included in the analysis. The approach we used to

evaluate potential groundwater-resource impacts assumes that all plumes move towards a nearby

well but without influence from the well itself. Further probabilistic modeling should be

performed to ascertain the sensitivity of this approach to well-capture zones and known

groundwater-flow directions.

Microcosm and aquifer column studies using field study materials. Microcosm and

associated aquifer column studies are recommended to address knowledge gaps regarding the

effect of ethanol on the biodegradation of BTEX compounds. The microcosm studies, which

would involve aquifer solids and groundwater from several sites with different histories of fuel

contamination, would address the following:

• Microbial ecology/catabolic diversity—assessment of changes in the relative abundance

of BTEX-degrading bacteria resulting from exposure to gasoline with and without

ethanol under various electron-accepting conditions (based on analysis of DNA that

codes for specific aerobic and anaerobic BTEX-degrading enzymes).

• Degradation kinetics—generation of kinetic data (lag periods and degradation rates) for

BTEX compounds and ethanol under various electron-accepting conditions in aquifer

materials from areas with different histories of gasoline and oxygenate exposure.

The results from such studies will also show whether ethanol metabolism results in marked

pH changes in naturally buffered systems as a result of VFA accumulation. The column studies

will provide a means to examine whether the kinetic results for the microcosms (for one selected

site) are generally consistent with the results in a more realistic, flow-through system. The

column studies will also allow researchers to examine how the integrated effects of bacterial

metabolism (for example, depletion of electron acceptors and variations in BTEX degradation

rates under different electron-accepting conditions) and physical processes (for example,

advection and dispersion) result in spatial heterogeneity in degradation processes. The kinetic

BTEX and ethanol degradation data could be used in conjunction with existing laboratory data to

derive input parameters for modeling.

Although the recommended studies will address some of the most critical knowledge gaps

identified during the literature review, they cannot address all knowledge gaps because of time

and cost constraints. As discussed earlier, a primary consequence of releases of ethanolcontaining gasoline into the subsurface will be the rapid consumption of oxygen and the

accelerated development of anaerobic conditions. Long lag times and relatively slow BTEX

degradation rates characteristic of anaerobic conditions will constrain the scope of

microbiological studies.

Historical-case studies to develop statistical analyses. Additional data should be collected

from sites where ethanol-containing gasoline has been released. These data should be used to

develop population statistics for supporting the predictive modeling efforts and to interpret how
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the release scenario affects ethanol-plume characteristics. Emphasis should be placed on

statistically analyzing BTEX data to determine how ethanol affects the stability and the

dimensions of individual BTEX plumes. Such a survey would provide an integrated picture of

the overall effects of ethanol on groundwater pollution and natural attenuation. This information

would also provide a stronger basis for the selection and operation of appropriate remedial

systems.

A possible outcome of the historical-case analysis would be a statistical comparison of

gasoline-release plume lengths at locations where ethanol is present or absent as a fuel

component. A reasonable objective is to gather at least 25 cases where ethanol was released as a

gasoline component. This population would then be compared to existing historical-case data

available for gasoline releases without ethanol.

Laboratory studies to improve Henry’s law constants. To improve the prediction of the

concentrations of ethanol in rainfall and surface waters, we recommend that temperaturedependent values of the Henry’s law constant be determined in laboratory studies. Additionally,

we recommend that further studies be conducted to predict more accurately the half-lives of

ethanol in different kinds of surface waters in California. This is particularly important because

of the important role that rapid natural biodegradation can play for the removal ethanol of from

surface waters.

Development of laboratory analytical methods. Analysis methods must be developed to

meet the data quality objectives of future studies. The poor extraction efficiency of ethanol from

water is the main contributor to relatively high analytical detection limits. Improved extraction

methods will result in better detection limits.

In order to eliminate problems with potential interferences, we recommend that gas

chromatographic (GC) separation be used in all future ethanol analyses. There are two practical

strategies that can be used for the sensitive detection of ethanol in the presence of interfering

compounds. The first is to use the best possible GC procedure to separate ethanol from any

interferences and then to detect ethanol with a nonspecific detector, such as a flame ionization

detector. The second strategy is to perform a less rigorous GC separation coupled with a

detector that would respond specifically to ethanol but would not respond to potentially

interfering compounds (for example, an atomic emission detector or a mass spectrometer). Both

of these strategies merit further consideration.

Development of a central database. More knowledge is required concerning the subsurface

environment in California. One of the major unknowns in any hydrogeological investigation is

the lack of knowledge of subsurface geology. A great deal can be learned even from the

moderate to poor quality of data available in well logs maintained by the California Department

of Water Resources. This data should be transcribed into electronic format for use by

researchers attempting to draw conclusions on the subsurface.

As part of ethanol studies, we should use GeoTracker and the Geographic Environmental

Information Management System (GEIMS) database as a central repository of data. GeoTracker

and GEIMS were developed by Lawrence Livermore National Laboratory for the SWRCB
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pursuant to a mandate by the California State Legislature (AB 592, SB 1189) to investigate the

feasibility of establishing a statewide geographic information system for LUFTs. The SWRCB

already intends to use this system to help regulators assess sites.

Other agencies should be encouraged to supply their data to the system so that interagency

cooperation may be fostered. As Senate Bill 9896 allows responsible parties to access well

construction and other details when under order from a regulatory agency, the associated data for

wells in the state of California (lithologic logs, well construction, location, and yield) should be

placed in an electronic database to expedite site assessments and decrease costs. This

information can also assist in the evaluation of vulnerable groundwater areas as stated elsewhere

in the same bill.

Data already collected by various state organizations should be systematically organized for

use in decision analysis. This would permit further comparative analysis of impacted public

drinking-water wells to gasoline continuing ethanol or MTBE and well-impacted LUFT sites.

Volume 5: Potential Health Risk of Ethanol in Gasoline

The objective of this volume is to present an evaluation of the public-health impacts of

ethanol as an oxygenate in gasoline, and of non-oxygenated fuels, in place of methyl tertiary

butyl ether (MTBE). Table 1 summarizes cancer and noncancer risks from selected air

pollutants.

5.1. Existing state or United States public-health standards were used where available.

To quantify potential health risks, health assessment values for the compounds of concern

were selected from current California or United States regulatory programs where these were

available. In the absence of suitable regulatory standards, draft numbers currently under

development for California regulatory programs were used. In the absence of these, draft health

protective concentrations were developed for this report using established methodology.

5.2. Exposure assessments were based on estimates provided by the ARB and the

SWRCB.

Evaluations of likely population exposures to fuel components and transformation products

were presented in previous chapters of this report. The scenarios considered compared the use of

fuel containing ethanol or MTBE as oxygenates, or fuel without oxygenates but otherwise

complying with ARB regulations. The exposure estimates derived were used by OEHHA in

assessing the relative public-health impacts of the proposed fuel compositions.

 

6

Section 13752 of the Water Code is amended to read: Reports made in accordance with paragraph (1) of subdivision (b) of Section 13751

shall not be made available for inspection by the public, but shall be made available to governmental agencies for use in making studies, or to any

person who obtains a written authorization from the owner of the well. However, a report associated with a well located within two miles of an

area affected or potentially affected by a known unauthorized release of a contaminant shall be made available to any person performing an

environmental cleanup study associated with the unauthorized release, if the study is conducted under the order of a regulatory agency. A report

released to a person conducting an environmental cleanup study shall not be used for any purpose other than for the purpose of conducting the

study.
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5.3. Cancer and noncancer risks from air pollutants were assessed.

For assessing health impacts of fuel-related air pollutants, the health assessment values for

compounds of concern were compared to the model predictions provided by the ARB, and risk

characterizations presented (Table 1). Risk characterizations for impacts of individual

carcinogens, and for the cumulative impacts of all carcinogens considered, are presented. Risk

characterizations for the critical noncancer effects (eye and respiratory irritation) are also

provided. Some other pollutants for which exposure estimates were available were found to be

unlikely to have significant health impacts. The chemicals considered were:

• The oxygenates MTBE and ethanol.

• Combustion products 1,3-butadiene, formaldehyde, acetaldehyde, carbon monoxide,

nitrogen dioxide and particulate matter (PM10).

• Evaporative emittents benzene, hexane, and toluene.

• Atmospheric transformation products peroxyacetyl nitrate (PAN), and ozone.

5.4. Existing levels of some air pollutants are a cause for concern, but predictions do not

differ substantially between the proposed fuel types.

Under these exposure scenarios, the concentrations of irritants (including both air toxics and

criteria pollutants) may achieve levels at which the margins of safety for short-term and longterm exposures are reduced. Adverse health effects are not necessarily expected at these levels,

but more sensitive individuals may be affected. There were no substantial differences between

the different fuel types with regard to the resulting levels of irritant air pollutants.

The upper-bound estimate of the cumulative cancer risks from air pollutants in the South

Coast region, for all fuel use scenarios, is in the range 1 to 3 × 10–4 (Table 1). This is well above

the level (10–6) usually regarded as a negligible effect. There were no substantial differences

between the different fuel types with regard to the cumulative cancer risks from air pollutants.

Principal contributors to this risk are the fuel-related pollutants, benzene and 1,3-butadiene.

Other pollutants (including formaldehyde and acetaldehyde, which may be partly related to

oxygenate use in fuels, and MTBE) make a smaller contribution. While we have more

confidence in the relative risk estimates than the absolute values of concentrations and risk, the

results point to the continuing need for regulatory action to reduce toxic air contaminants from

automobiles.

5.5. Effects of water pollution were considered.

Quantitative estimates of possible drinking-water contamination associated with different

fuel-use scenarios were not available. However, possible toxic effects of drinking-water

pollution by ethanol, MTBE, and tertiary butyl alcohol were considered. Other effects, such as

changes in the groundwater distribution of benzene and other hydrocarbons, may need to be

considered when data or model predictions of these processes become available.

5.6. Substantial uncertainties and research needs remain.
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There are several major uncertainties and data gaps, both in the exposure-assessment needs

for health-risk assessment and the toxicological assessment of compounds of concern. Some of

these areas (particularly the assessment of water contamination, accidental-release scenarios, and

life-cycle analysis) are being addressed by work currently in progress for SWRCB. Similarly,

the ARB is continuing to refine and extend its modeling and measurement of both air toxics and

criteria air pollutants. Other interested parties and academic specialists are also active in

addressing these problems. As new data become available, their implication for public-health

impacts of fuel use will need to be assessed.

Volume 5 Conclusions: It appears that there are no substantial differences in the publichealth impacts of the different nonMTBE fuel formulations considered in the scenarios for 2003.

Although replacement of MTBE by either ethanol or non-oxygenated fuel is expected to have

some benefits in terms of water contamination, these cannot be quantified at present. From our

analysis, these substitutions had no substantial effects on public-health impacts of air pollution.
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Table
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Table 1. Cumulative cancer risks and noncancer hazard indexes from air pollutants in

the South Coast region for all fuel scenarios.

Risk

description

Estimate

range

1997

MTBE

2003

MTBE

2003

Et2%

2003

Et3.5%

2003

NonOxy

Upper 2.9 × 10–4 1.9 × 10–4 1.8 × 10–4 1.9 × 10–4 1.8 × 10–4 Cumulative lifetime

cancer risk Lower 2.7 × 10–4 1.8 × 10–4 1.7 × 10–4 1.7 × 10–4 1.7 × 10–4

Cumulative Hazard Upper 10.0 9.6 9.5 9.5 9.4

Index (HI ) for acute eye

irritation Lower 6.9 6.7 6.6 6.6 6.5

Cumulative HI for acute Upper 4.0 3.8 3.8 3.7 3.8

respiratory irritation

Lower 3.9 3.7 3.7 3.6 3.7

Cumulative HI for Upper 5.5 5.1 5.1 5.2 5.0

chronic respiratory

irritation Lower 5.5 5.1 5.0 5.0 5.0
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