Report to the Chairman, Committee on 

Science and Technology, House of 

Representatives 

United States Government Accountability Office

GAO 

November 2009 ENERGY-WATER 

NEXUS 

Many Uncertainties 

Remain about 

National and Regional 

Effects of Increased 

Biofuel Production on 

Water Resources 

GAO-10-116 
What GAO Found

United States Government Accountability Office

Why GAO Did This Study

Highlights

Accountability Integrity Reliability

November 2009

ENERGY-WATER NEXUS

Many Uncertainties Remain about National and 

Regional Effects of Increased Biofuel Production on 

Highlights of GAO-10-116, a report to Water Resources

Chairman, Committee on Science and 

Technology, House of Representatives 

In response to concerns about the 

nation’s energy dependence on 

imported oil, climate change, and 

other issues, the federal 

government has encouraged the 

use of biofuels. Water plays a 

crucial role in all stages of biofuel 

production—from cultivation of 

feedstock through its conversion 

into biofuel. As demand for water 

from various sectors increases and 

places additional stress on already 

constrained supplies, the effects of 

expanded biofuel production may 

need to be considered. 

To understand these potential 

effects, GAO was asked to examine 

(1) the known water resource 

effects of biofuel production in the 

United States; (2) agricultural 

conservation practices and 

technological innovations that 

could address these effects and 

any barriers to their adoption; and 

(3) key research needs regarding 

the effects of water resources on 

biofuel production. To address 

these issues, GAO reviewed 

scientific studies, interviewed 

experts and federal and state 

officials, and selected five states to 

study their programs and plans 

related to biofuel production. 

GAO is not making any 

recommendations in this report. A 

draft of this report was provided to 

the Departments of Agriculture 

(USDA), Energy (DOE), and the 

Interior (DOI); and the 

Environmental Protection Agency 

(EPA). USDA, DOE, and DOI 

concurred with the report and, in 

addition to EPA, provided technical 

comments, which were 

incorporated as appropriate. 

The extent to which increased biofuels production will affect the nation’s 

water resources depends on the type of feedstock selected and how and 

where it is grown. For example, to the extent that this increase is met from 

the cultivation of conventional feedstocks, such as corn, it could have greater 

water resource impacts than if the increase is met by next generation 

feedstocks, such as perennial grasses and woody biomass, according to 

experts and officials. This is because corn is a relatively resource-intensive 

crop, and in certain parts of the country requires considerable irrigated water 

as well as fertilizer and pesticide application. However, experts and officials 

noted that next generation feedstocks have not yet been grown on a 

commercial scale and therefore their actual effects on water resources are not 

fully known at this time. Water is also used in the process of converting 

feedstocks to biofuels, and while the efficiency of biorefineries producing 

corn ethanol has increased over time, the amount of water required for 

converting next generation feedstocks into biofuels is still not well known. 

Finally, experts generally agree that it will be important to take into account 

the regional variability of water resources when choosing which feedstocks to 

grow and how and where to expand their production in the United States. 

The use of certain agricultural practices, alternative water sources, and 

technological innovations can mitigate the effects of biofuels production on 

water resources, but there are some barriers to their widespread adoption. 

According to experts and officials, agricultural conservation practices can 

reduce water use and nutrient runoff, but they are often costly to implement. 

Similarly, alternative water sources, such as brackish water, may be viable for 

some aspects of the biofuel conversion process and can help reduce 

biorefineries’ reliance on freshwater. However, the high cost of retrofitting 

plants to use these water sources may be a barrier, according to experts and 

officials. Finally, innovations—such as dry cooling systems and 

thermochemical processes—have the potential to reduce the amount of water 

used by biorefineries, but many of these innovations are currently not 

economically feasible or remain untested at the commercial scale. 

Many of the experts GAO spoke with identified several areas where additional 

research is needed. These needs fall into two broad areas: (1) feedstock 

cultivation and biofuel conversion and (2) data on water resources. For 

example, some experts noted the need for further research into improved 

crop varieties, which could help reduce water and fertilizer needs. In addition, 

several experts identified research that would aid in developing next 

generation feedstocks. For example, several experts said research is needed 

on how to increase cultivation of algae for biofuel to a commercial scale and 

how to control for potential water quality problems. In addition, several 

experts said research is needed on how to optimize conversion technologies 

to help ensure water efficiency. Finally, some experts said that better data on 

water resources in local aquifers and surface water bodies would aid in 

decisions about where to cultivate feedstocks and locate biorefineries. 

View GAO-10-116 or key components.

For more information, contact Anu Mittal or 

Mark Gaffigan at (202) 512-3841 or 

mittala@gao.gov or gaffiganm@gao.gov. 
Page i GAO-10-116 Energy-Water Nexus 

Contents 

Letter 1

Background 3 

Each Stage of Biofuel Production Affects Water Resources, but the 

Extent Depends on the Feedstock and Region 7 

Agricultural Practices, Technological Innovations, and Alternative 

Water Sources Can Mitigate Some Water Resource Effects of 

Biofuels Production, but There Are Barriers to Adoption 22 

Experts Identified a Variety of Key Research and Data Needs 

Related to Increased Biofuels Production and Local and 

Regional Water Resources 31 

Agency Comments and Our Evaluation 36 

Appendix I Objectives, Scope, and Methodology 39 

Appendix II Examples of Agricultural Practices Available to 

Reduce the Water Quality and Water Supply Effects 

of Feedstock Cultivation for Biofuels 42 

Appendix III Comments from the U.S. Department of Agriculture 44 

Appendix IV Comments from the Department of Energy 46 

Appendix V Comments from the Department of the Interior 48 

Appendix VI GAO Contacts and Staff Acknowledgments 49 

Table 

Table 1: Average Water Consumed in Corn Ethanol Production in 

Primary Producing Regions in the United States, in Gallons 

of Water/Gallon of Ethanol Produced 9 
Figures 

Figure 1: Biofuels Life Cycle 5 

Figure 2: Agricultural Water Cycle 6 

Figure 3: Diagram of Conversion Process for a Typical Corn-Based 

Ethanol Biorefinery 7 

Figure 4: Existing and Planned Ethanol Facilities (as of 2007) and 

Their Estimated Total Water Use Mapped with the 

Principal Bedrock Aquifers, including the Ogallala, or 

High Plains, Aquifer, of the United States and Total Water 

Use in 2000 21 

Figure 5: Example of a Riparian Buffer Adjacent to Cropland 24 

Figure 6: Example of Conservation Tillage 26 

Figure 7: Example of Low-Energy Precision-Application Irrigation 27 

Abbreviations 

CRP Conservation Reserve Program 

NPDES National Pollutant Discharge Elimination System 

DOE Department of Energy 

EIA Energy Information Administration 

EISA Energy Independence and Security Act of 2007 

EPA Environmental Protection Agency 

RFS Renewable Fuel Standard 

USDA U.S. Department of Agriculture 

USGS U.S. Geological Survey 

UST underground storage tank 

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Page ii GAO-10-116 Energy-Water Nexus 
Page 1 GAO-10-116 Energy-Water Nexus 

November 30, 2009 

The Honorable Bart Gordon 

Chairman 

Committee on Science and Technology 

House of Representatives 

Dear Mr. Chairman: 

In recent years, the federal government has increasingly encouraged the 

use of biofuels and other alternatives to petroleum in response to 

concerns over U.S. dependence on imported oil, climate change, and other 

issues. The United States is the largest user of petroleum in the world, 

consuming 19.4 million barrels per day in 2008, over half of which is 

imported. Biofuels, such as ethanol and biodiesel, can be produced 

domestically and are derived from renewable sources, such as corn, sugar 

cane, and soybeans. The Energy Independence and Security Act of 2007 

(EISA) expanded the Renewable Fuel Standard (RFS) by requiring that 

U.S. transportation fuel contain 9 billion gallons of renewable fuels in 2008 

and increasing this amount annually to 36 billion gallons in 2022.1

Currently, the vast majority of domestic biofuel production is ethanol 

derived from corn starch, which EISA defines as a “conventional” 

feedstock. However, in 2022, the RFS’s 36-billion-gallon total requires that 

at least 16 billion gallons be derived from “cellulosic” materials, such as 

stalks, stems, branches, and leaves. These cellulosic materials, along with 

newer feedstocks, such as algae, are often referred to as “next generation” 

feedstocks, and the fuels produced from them are often referred to as 

“advanced” biofuels.2

 

 

United States Government Accountability Office

Washington, DC 20548 

1

Pub. L. No. 110-140, § 201 (2007). The act authorizes the Administrator of the 

Environmental Protection Agency (EPA), in consultation with the Secretaries of 

Agriculture and Energy, to waive the RFS levels established in the act, by petition or on the 

Administrator’s own motion, if meeting the required level would severely harm the 

economy or environment of a state, a region, or the United States or there is an inadequate 

domestic supply. Throughout this report, the RFS levels established in the act are referred 

to as requirements, even though these levels could be waived by the EPA Administrator. 

2

For additional information on the effects of biofuel production, see GAO, Biofuels: 

Potential Effects and Challenges of Required Increases in Production and Use, 

GAO-09-446 (Washington, D.C.: Aug. 25, 2009). 
 

Although freshwater flows abundantly in many of the nation’s lakes, 

rivers, and streams, water is a dwindling resource in many parts of the 

country and is not always available when and where it is needed or in the 

amount desired because of competing demands on water supplies, 

climatic changes contributing to drought conditions in parts of the 

country, and population growth. Foremost among these competing 

demands is irrigation, which accounts for 40 percent of the nation’s 

freshwater withdrawals.3

 Water is crucial to many stages of the biofuel life 

cycle and is needed for the growth of the feedstock as well as for 

fermentation, distillation, and cooling during the process of converting the 

feedstock into biofuel. As biofuel production increases, questions have 

emerged about the effects that increased production could have on the 

nation’s water resources. 

To understand the potential effects of increased biofuel production on 

water resources, you asked us to describe (1) the known water resource 

effects of increased biofuel production in the United States; (2) the 

agricultural conservation practices and technological innovations that 

exist or are being developed to address these effects, and any barriers that 

may prevent the adoption of these practices and technologies; and (3) key 

research needs regarding the effects of biofuel production on water 

resources. 

To address all of these objectives, we conducted a systematic analysis of 

relevant articles from scientific journals and key federal and state 

government publications. In addition, in consultation with the National 

Academy of Sciences, we identified and interviewed recognized experts 

who have published peer-reviewed research analyzing the water supply 

requirements of one or more biofuel feedstocks and the implications of 

increased biofuel production on water resources. These experts included 

research scientists in such fields as environmental science, agronomy, soil 

science, hydrogeology, ecology, and engineering. Furthermore, we studied 

five states in greater depth—Georgia, Iowa, Minnesota, Nebraska, and 

Texas—to gain an understanding of the programs and plans they have or 

are developing to address increased biofuel production. We selected these 

states based on several criteria, including ethanol and biodiesel 

 

3

Other major sources of freshwater withdrawals in the United States are thermoelectric (39 

percent), public water supply (13 percent), and industrial (5 percent) uses. The remaining 

withdrawals consist of mining (1 percent), domestic (1 percent), aquaculture (1 percent), 

and livestock (1 percent) uses. S. Hutson et al., “Estimated Use of Water in the United 

States in 2000,” Circular 1268, U.S. Geological Survey (2004). 

Page 2 GAO-10-116 Energy-Water Nexus 
 

Page 3 GAO-10-116 Energy-Water Nexus 

production, feedstock cultivation type, reliance on irrigation, geographic 

diversity, and varying approaches to water resource management and law. 

For each of the states, we analyzed documentation from and conducted 

interviews with a wide range of stakeholders to gain the views of diverse 

organizations covering all stages of biofuel production. These groups 

included relevant state agencies, including those responsible for oversight 

of agriculture, environmental quality, and water and soil resources; federal 

agency officials with responsibility for a particular state or region, such as 

officials from the U.S. Geological Survey (USGS), the U.S. Department of 

Agriculture’s (USDA) Natural Resources Conservation Service, and the 

Environmental Protection Agency (EPA); university researchers; industry 

representatives; and relevant nongovernmental organizations, such as 

environmental groups, state-level corn growers’ associations, and ethanol 

producer associations. 

We also interviewed senior officials, scientists, economists, researchers, 

and other federal officials from USDA, the Departments of Defense and 

Energy (DOE), EPA, the National Aeronautics and Space Administration, 

the Department of Commerce’s National Oceanic and Atmospheric 

Administration, the National Science Foundation, and USGS about effects 

on water supply and water quality during biofuel production. We also 

interviewed representatives of nongovernmental organizations, such as the 

Renewable Fuels Association, the Biotechnology Industry Organization, 

the Pacific Institute, and the Fertilizer Institute. A more detailed 

description of our scope and methodology is presented in appendix I. We 

conducted our work from January 2009 to November 2009 in accordance 

with all sections of GAO’s Quality Assurance Framework that are relevant 

to our objectives. The framework requires that we plan and perform the 

engagement to obtain sufficient and appropriate evidence to meet our 

stated objectives and to discuss any limitations in our work. We believe 

that the information and data obtained, and the analysis conducted, 

provide a reasonable basis for any findings and conclusions in this 

product. 

Biofuels, such as ethanol and biodiesel, are an alternative to petroleumbased transportation fuels and are produced in the United States from a 

variety of renewable sources such as corn, sugar cane, and soybeans. 

Ethanol, the most common U.S. biofuel, is mainly used as a gasoline 

additive in blends of about 10 percent ethanol and 90 percent gasoline, 

known as E10, which is available in most states. A relatively small volume 

is also blended at a higher level called E85—a blend of 85 percent ethanol 

and 15 percent gasoline—which can only be used in specially designed 

Background 
 

vehicles, known as flexible fuel vehicles. Biodiesel is a renewable 

alternative fuel produced from a range of plant oils, animal fats, and 

recycled cooking oils. Pure biodiesel or biodiesel blended with petroleum 

diesel—generally in a blend of 20 percent biodiesel and 80 percent 

diesel—can be used to fuel diesel vehicles. 

The federal government has promoted biofuels as an alternative to 

petroleum-based fuels since the 1970s, and production of ethanol from 

corn starch reached 9 billion gallons in 2008. The Energy Policy Act of 

2005 originally created an RFS that generally required U.S. transportation 

fuel to contain 4 billion gallons of renewable fuels in 2006 and 7.5 billion 

gallons in 2012.4

 EISA expanded the RFS by requiring that U.S. 

transportation fuel contain 9 billion gallons of renewable fuels in 2008 and 

increasing this amount annually to 36 billion gallons in 2022.5

 Moreover, 

the 36-billion-gallon total must include at least 21 billion gallons of 

advanced biofuels, defined as renewable fuels other than ethanol derived 

from corn starch that meet certain criteria; only 15 billion of the 36 billion 

gallons of renewable fuels can come from conventional biofuels. In 

addition, at least 16 billion gallons of the 21-billion-gallon advanced 

biofuels requirement must be made from cellulosic feedstocks, such as 

perennial grasses, crop residue, and woody biomass. Unlike corn starch, 

most of the energy in plant and tree biomass is locked away in complex 

cellulose and hemicellulose molecules, and technologies to produce 

biofuels economically from this type of feedstock are still being 

developed. Some cellulosic biorefineries are piloting the use of 

biochemical processes, in which microbes and enzymes break down these 

complex plant molecules to produce ethanol, while others are piloting the 

use of thermochemical processes, which use heat and chemical catalysts 

to convert plant material into a liquid that more closely resembles 

petroleum. 

There are a number of steps in the biofuels life cycle, from cultivation of 

the feedstock through distribution to the end user at the fuel pump (see 

fig. 1). 

 

4

The RFS applies to transportation fuel sold or introduced into commerce in the 48 

contiguous states. However, the Administrator of EPA is authorized, upon a petition from 

Alaska or Hawaii, to allow the RFS to apply in that state. On June 22, 2007, Hawaii 

petitioned EPA to opt into the RFS, and the Administrator approved that request. For the 

purposes of this report, statements that the RFS applies to U.S. transportation fuel refer to 

the 48 contiguous states and Hawaii. 

5

Pub. L. No. 110-140, § 201 (2007). 

Page 4 GAO-10-116 Energy-Water Nexus 
 

Page 5 GAO-10-116 Energy-Water Nexus 

Figure 1: Biofuels Life Cycle 

Source: DOE.

Water plays a critical role in many aspects of this life cycle. On the 

cultivation side, water is needed to grow the feedstock. Crops can be 

either rainfed, with all water requirements provided by natural 

precipitation and soil moisture, or irrigated, with at least some portion of 

water requirements met through applied water from surface or 

groundwater sources. Figure 2 shows the various water inputs (sources of 

water) and outputs (water losses) that are part of the agricultural water 

cycle. 
 

Page 6 GAO-10-116 Energy-Water Nexus 

Figure 2: Agricultural Water Cycle 

Source: © 2008 International Mapping.

Water is also important for conversion of feedstocks into biofuels. In 

particular, water is used for heating and cooling as well as for processing. 

For example, during the processing of corn-based ethanol, corn is 

converted to ethanol through fermentation using one of two standard 

processes, dry milling or wet milling. The main difference is the initial 

treatment of the corn kernel. In the dry-mill process, the kernel is first 

ground into flour meal and processed without separating the components 

of the corn kernel. The meal is then slurried with water to form a mash, 

and enzymes are added to convert the starch in the mash to a fermentable 

sugar. The sugar is then fermented and distilled to produce ethanol. In the 

wet-mill process, the corn kernel is steeped in a mixture of water and 

sulfurous acid that helps separate the kernel into starch, germ, and fiber 

components. The starch that remains after this separation can then be 

fermented and distilled into fuel ethanol. Traditional dry-mill ethanol 

plants cost less to construct and operate than wet-mill plants, but yield 
 

Page 7 GAO-10-116 Energy-Water Nexus 

fewer marketable co-products. Dry-mill plants produce distiller’s grains 

(that can be used as cattle feed) and carbon dioxide (that can be used to 

carbonate soft drinks) as co-products, while wet-mill plants produce many 

more co-products, including corn oil, carbon dioxide, corn gluten meal, 

and corn gluten feed. The majority of ethanol biorefineries in the United 

States are dry-mill facilities. Figure 3 depicts the conversion process for a 

typical dry-mill biorefinery. 

Figure 3: Diagram of Conversion Process for a Typical Corn-Based Ethanol 

Biorefinery 

The extent to which increased biofuel production will affect the nation’s 

water resources will depend on which feedstocks are selected for 

production and which areas of the country they are produced in. 

Specifically, increases in corn cultivation in areas that are highly 

dependent on irrigated water could have greater impacts on water 

availability than if the corn is cultivated in areas that primarily produce 

rainfed crops. In addition, most experts believe that greater corn 

production, regardless of where it is produced, may cause greater 

impairments to water quality than other feedstocks, because corn 

production generally relies on greater chemical inputs and the related 

chemical runoff will impact water bodies. In contrast, many experts 

Each Stage of Biofuel 

Source: © 2007 ICM, Inc.

Production Affects 

Water Resources, but 

the Extent Depends 

on the Feedstock and 

Region 
 

Page 8 GAO-10-116 Energy-Water Nexus 

expect next generation feedstocks to require less water and provide some 

water quality benefits, but even with these feedstocks the effects on water 

resources will largely depend on which feedstock is selected, and where 

and how these feedstocks are grown. Similarly, the conversion of 

feedstocks into biofuels may also affect water supply and water quality, 

but these effects also vary by feedstock chosen and type of biofuel 

produced. Many experts agree that as the agriculture and biofuel 

production industries make decisions about which feedstocks to grow and 

where to locate or expand conversion facilities, it will be important for 

them to consider regional differences and potential impacts on water 

resources. 

Many experts and officials told us that corn cultivation requires substantial 

quantities of water, although the amount used depends on where the crop 

is grown and how much irrigation water is used. The primary corn 

production regions are in the upper and lower Midwest and include 12 

states classified as USDA farm production Regions 5, 6, and 7. Together, 

these regions accounted for 89 percent of corn production in 2007 and 

2008, and 95 percent of ethanol production in the United States in 2007. 

Corn cultivation in these three regions averages anywhere from 7 to 321 

gallons of irrigation water for every gallon of ethanol produced, as shown 

in table 1.6

 However, the impact of corn cultivation on water supplies in 

these regions varies considerably. For example, in USDA Region 7, which 

comprises North Dakota, South Dakota, Kansas, and Nebraska, the 

production of one bushel of corn consumes an average of 865 gallons of 

freshwater from irrigation. In contrast, in USDA Regions 5 and 6, which 

comprise Iowa, Illinois, Indiana, Ohio, Missouri, Minnesota, Wisconsin, 

and Michigan, corn is mostly rainfed and only requires on average 19 to 38 

gallons of supplemental irrigation water per bushel.7

 

6

Wu, M., M. Mintz, M. Wang, and S. Arora. “Consumptive Water Use in the Production of 

Ethanol and Petroleum Gasoline,” Center for Transportation Research, Energy Systems 

Division, Argonne National Laboratory (Argonne, Ill., January 2009.) 

7

According to the National Corn Growers Association, across the United States the acres of 

corn irrigated represent 21 percent of the total irrigated crop area. The volume of water 

used in corn irrigation represents 7 percent of all irrigation water. 

Water Supply and Water 

Quality Effects of 

Increased Corn Cultivation 
 

Table 1: Average Water Consumed in Corn Ethanol Production in Primary Producing Regions in the United States, in Gallons 

of Water/Gallon of Ethanol Produced 

Type of water consumed 

USDA Region 5

(Iowa, Indiana, Illinois, 

Ohio, Missouri)

USDA Region 6 

(Minnesota, Wisconsin, 

Michigan) 

USDA Region 7

(North Dakota, South Dakota, 

Nebraska, Kansas)

Cultivation 

Corn irrigation, groundwater 6.7 10.7 281.2

Corn irrigation, surface water 0.4 3.2 39.4

Total irrigated water 7.1 13.9 320.6

Conversion - Corn ethanol 3.0 3.0 3.0

Total water consumption 10.0 16.8 323.6

Source: Center for Transportation Research, Energy Systems Division, Argonne National Laboratory, “Consumptive Water Use in the

Production of Ethanol and Petroleum Gasoline,” Center for Transportation Research, Energy Systems Division, Argonne Laboratory,

January 2009 

Note: The numbers may not add up due to rounding. The Argonne National Laboratory study 

estimated the water consumed in corn ethanol production in each of the major ethanol producing 

regions considering water consumed in both corn cultivation and conversion processing steps. 

Estimates were based on average consumption of 3.0 gallons of water per gallon of corn ethanol 

produced in a corn dry mill, average consumptive use of irrigation water for corn in major corn 

producing regions, and dry-mill yield of 2.7 gallons of ethanol per bushel. In evaluating corn 

cultivation, the water consumed is based on total amount of irrigation water used for corn production 

and total corn production for each region, and does not include precipitation. In addition, the 

calculation assumes that 30 percent of water recharges local surface and groundwater, and the 

remaining 70 percent of the water is consumed by evapotranspiration (water lost through evaporation 

from the soil and plants) and other factors. 

The effects of increased corn production for ethanol on water supplies are 

likely to be greatest in water-constrained regions of the United States 

where corn is grown using irrigation. For example, some of the largest 

increases in corn acres (1.1 million acres) are projected to occur in the 

Northern Plains region, which is already a water constrained region. Parts 

of this region draw heavily from the Ogallala Aquifer, where water 

withdrawals are already greater than the natural recharge rate from 

precipitation. A 2009 USGS report found water levels in the aquifer had 

dropped more than 150 feet in parts of southwest Kansas and the Texas 

Panhandle, where crop irrigation is intense and recharge to the aquifer is 

minimal.8

 In 2000, about 97 percent of the water withdrawn from the 

aquifer was used for irrigation, according to USGS.9

 

8

McGuire, V.L., “Water-level changes in the High Plains aquifer, predevelopment to 2007, 

2005-2006, and 2006-2007,” USGS SIR 2009-5019 (2009). 

9

Maupin, M.A., and Barber, N.L., “Estimated withdrawals from principal aquifers in the 

United States,” USGS Circular 1279 (2000). 

Page 9 GAO-10-116 Energy-Water Nexus 
 

Many officials told us that an increase in corn cultivation using current 

agricultural practices will also impair water quality as a result of the runoff 

of fertilizer into lakes and streams. This will happen because corn requires 

high applications of fertilizers relative to soybeans and other potential 

biofuel feedstocks, such as perennial grasses.10 For example, in Iowa, the 

expansion of biofuel production has already led to an increasing amount 

of land dedicated to corn and other row crops, resulting in surface water 

impacts, including nutrient runoff and increased bacteria counts as well as 

leaching of nitrogen and phosphorus into groundwater, according to a 

state official. Fertilizer runoff containing nitrogen and phosphorus can 

lead to overenrichment and excessive growth of algae in surface waters. In 

some waters, such enrichment has resulted in harmful algal blooms, 

decreased water clarity, and reduced oxygen in the water, which impair 

aquatic life.11 In marine waters, this excessive algal growth has created 

“dead zones,” which cannot support fish or any other organism that needs 

oxygen to survive.12 The number of reported dead zones around the world 

has increased since the 1960s to more than 400.13 Many of them are along 

the Gulf of Mexico and the Atlantic Coast, areas that receive drainage from 

agricultural and urban landscapes, including a large portion of the Corn 

Belt, where many of the existing and planned ethanol production facilities 

are located. A 2007 USGS model estimated that 52 percent of the nitrogen 

and 25 percent of the phosphorus entering the Gulf system are from corn 

and soybean cultivation in the Mississippi River basin.14

Increased corn production will also increase the use of pesticides—

including insecticides and herbicides—which also have the potential to 

 

10Increased corn cultivation could also result in soil erosion, which reduces fertility by 

reducing nutrient-rich topsoil. It also contributes to sedimentation, which fills channels in 

deep areas of waterbodies, affecting aquatic life and recreation. Sediment can also carry 

contaminants, such as fertilizers and pesticides. 

11The algae themselves do not reduce oxygen; instead, when the algae die, bacteria deplete 

oxygen as the algae decompose. 

12Dried distiller’s grain, a byproduct of ethanol production used in animal feed, also 

contains high levels of phosphorous and contributes to overenrichment of surface and 

marine waters. 

13Diaz, Robert and Rutger Rosenberg, “Spreading Dead Zones and Consequences for Marine 

Ecosystems,” Science, vol. 321 (2008): pp. 926-929. 

14Alexander, Richard, Richard Smith, Gregory Schwarz, Elizabeth Boyer, Jacqueline Nolan, 

and John Brakebill, “Difference in Phosphorous and Nitrogen Delivery to the Gulf of 

Mexico from the Mississippi River Basin,” Environmental Science and Technology, vol. 42, 

no. 3 (2008): pp. 822-830. 

Page 10 GAO-10-116 Energy-Water Nexus 
 

affect surface water and groundwater quality. For example, a 10-year 

nationwide study by USGS detected pesticides in 97 percent of streams in 

agricultural and urban watersheds.15 As would be expected, the highest 

concentrations of pesticides have been found in those areas that have the 

highest use. For instance, application rates of atrazine, a commonly used 

pesticide for corn production, are highest in the Corn Belt, and atrazine 

was also the most widely detected pesticide in watersheds in this area, 

according to the USGS nationwide study. USGS determined that the 

concentrations of atrazine and other pesticides detected had the potential 

to adversely affect aquatic plants and invertebrates in some of the streams, 

since organisms are vulnerable to short-term exposure to relatively small 

amounts of certain pesticides. Similarly, increased pesticide use for the 

cultivation of corn could impair groundwater supplies. USGS found 

pesticides in 61 percent of shallow wells sampled in agricultural areas. 

Once groundwater is contaminated, it is difficult to clean up, according to 

the experts we contacted. 

According to some of the experts and officials we spoke with, increased 

demand for biofuel feedstocks may also create incentives for farmers to 

place marginal lands back into production. Marginal lands generally have 

lower productivity soils, so cultivating them may require more nutrient 

and pesticide inputs than more productive lands, potentially leading to 

further water quality impairments. Furthermore, delivery of sediments, 

nutrients, and pesticides to surrounding water bodies may increase if 

these lands are placed back into production because these lands are often 

highly susceptible to erosion due to wind and water. Of particular concern 

to many of the experts with whom we spoke are the millions of acres of 

land currently enrolled in the Conservation Reserve Program (CRP). This 

federal program provides annual rental payments and cost share 

assistance to landowners who contractually agree to retire highly erodible 

or other environmentally-sensitive cropland from agricultural purposes. As 

part of the contract, farmers are generally required to plant or maintain 

vegetative covers (such as native grasses) on the land, which provide a 

range of environmental benefits, including improved water quality, 

reduced erosion, enhanced wildlife habitat, and preserved soil 

productivity. However, many experts and officials we spoke with from the 

five selected states are concerned that higher corn prices and increased 

demand for biofuel feedstocks may encourage farmers to return CRP land 

 

15Gilliom et al., “The Quality of Our Nation’s Waters—Pesticides in the Nation’s Streams 

and Ground Water, 1992-2001,” USGS Circular 1291 (2006): p. 172.

Page 11 GAO-10-116 Energy-Water Nexus 
 

Page 12 GAO-10-116 Energy-Water Nexus 

to crop production. If such conversion does occur, these officials noted 

that water quality may further decline in the future. 

negative effects on water resources, although several of the experts and 

officials that we spoke with said that the magnitude of these effects 

remains largely unknown because these feedstocks have not yet been 

grown on a commercial scale. These experts suggested that certain water 

resource impacts were likely for the following potential feedstocks: 

• Agricultural residues, such as corn stover, collected from fields that have 

already been harvested, can provide feedstock for cellulosic ethanol 

production. The primary advantage of using agricultural residues is that 

they are a byproduct of crop cultivation and thus do not require additional 

water or nutrient inputs. However, removal of these residues has 

consequences for both soil and water quality, so there may be limits on 

how much agricultural residues can be removed for cellulosic ethanol 

production. According to the experts we spoke with, leaving crop residues 

unharvested on the field benefits soil quality by providing nutrients that 

help maintain long-term soil productivity, enhancing soil moisture 

retention, increasing net soil carbon, and reducing the need for nutrient 

inputs for future crops.16 In addition, leaving crop residues on the field 

helps prevent soil erosion due to wind and water and nutrient runoff into 

the water supply. Farmers could reduce the negative effects of residue 

removal by harvesting only corn cobs or part of the stover, but the optimal 

removal rate is not yet fully known, and is currently being studied by 

several federal agencies and academic institutions. 

• Perennial grasses may require less water and provide some water quality 

benefits. Perennial grasses such as mixed prairie and switchgrass can 

grow with less water than corn. But some experts cautioned that any 

water supply benefits from these grasses will only occur if they are 

rainfed. For instance, officials in Minnesota told us that because the state’s 

crops are primarily rainfed, shifting to the cultivation of cellulosic 

feedstocks, like perennial grasses, without irrigation would have a minimal 

impact on the state’s water supply. However, other experts and local 

 

Little Is Yet Known about Next generation feedstocks for biofuels have the potential for fewer 

16While some agricultural residues must be left on the ground to maintain soil moisture and 

carbon content, a significant portion of the total can be removed in many areas. According 

to a DOE official, in some parts of the country removal of a portion of the residue is needed 

because the excess residue does not degrade quickly enough and interferes with 

subsequent crop growth. 

the Water Resource 

Implications of Next 

Generation Feedstocks 
 

officials pointed out that if farmers choose to irrigate perennial grasses in 

order to achieve maximum yields and profits as they do for other crops, 

then producing these feedstocks could have the same detrimental effects 

on water supplies as do other crops. This concern was reiterated by the 

National Research Council, which stated that while irrigation of native 

grasses is unusual now, it could easily become more common as cellulosic 

biofuel production gets under way.17

Perennial grasses can also help preserve water quality by reducing soil, 

nutrient, and pesticide runoff. Research indicates that perennial grasses 

cycle nitrogen more efficiently than some row crops and protect soil from 

erosion due to wind and water. As a result, they can reduce the need for 

most fertilizers after crops are established, and the land on which these 

crops are grown do not need to be tilled every year, which reduces soil 

erosion and sedimentation. According to experts, farmers could also plant 

a mix of perennial grasses, which could minimize the need for pesticides 

by promoting greater diversity and an abundance of natural enemies for 

agricultural pests. In addition, perennial grasses cultivated across an 

agricultural landscape may help reduce nutrient and chemical runoff from 

farm lands. Grasses can also be planted next to water bodies to help filter 

out nutrients and secure soil and can serve as a windbreak to help 

minimize erosion. However, the type of land and cultivation methods used 

to grow perennial grasses will influence the extent to which they improve 

water quality. For instance, if perennial grasses were harvested down to 

the soil, they would not reduce soil erosion as compared to conventional 

feedstocks in the long run, according to some experts. In addition, 

according to some experts, if farmers choose to use fertilizers to maximize 

yields from these crops as they do for other crops or if these crops are 

grown on lands with decreased soil quality that require increased nutrient 

application, then cultivation of perennial grasses could also lead to water 

quality impairments. 

• Woody biomass, such as biomass from the thinning of forests and 

cultivation of certain fast-growing tree varieties, could serve as feedstock 

for cellulosic ethanol production, according to some experts. Use of 

thinnings is not expected to impact water supply, as they are residuals 

from forest management. Thinning of forests can have the added benefit of 

reducing the intensity of wildfires, the aftermath of which facilitates runoff 

of nutrients and sediment into surface waters. Waste from urban areas or 

 

17National Research Council, Water Implications of Biofuels Production in the United 

States. The National Academies Press, Washington, D.C. (2008). 

Page 13 GAO-10-116 Energy-Water Nexus 
 

Page 14 GAO-10-116 Energy-Water Nexus 

lumber mills may also provide another source of biomass that would not 

require additional water resources. This waste would include the woody 

portions of commercial, industrial, and municipal solid waste, as well as 

byproducts generated from processing lumber, engineered wood products, 

or wood particles; however, almost all of the commercial wood waste is 

currently used as fuels or raw material for existing products. In addition, 

some experts said that fast-growing tree species, such as poplar, willow, 

and cottonwood, are potential cellulosic feedstocks. However, these 

experts also cautioned that some of these varieties may require irrigation 

to cultivate and may have relatively high consumptive water requirements. 

• Algae are also being explored as a possible feedstock for advanced 

biofuels. According to several experts, one advantage of algae is that they 

can be cultivated in brackish or degraded water and do not need 

freshwater supplies. However, currently algae cultivation is expected to 

consume a great deal of water, although consumption estimates vary 

widely—from 40 to 1,600 gallons of water per gallon of biofuel produced, 

according to experts—depending on what cultivation method is used. With 

open-air, outdoor pond cultivation, water loss is expected to be greater 

due to evaporation, and additional freshwater will be needed to replenish 

the water lost and maintain the water quality necessary for new algal 

growth. In contrast, when algae are cultivated in a closed environment, as 

much as 90 percent less water is lost to evaporation, according to one 

expert.18

not only need a supply of high-quality water, but also discharge certain 

contaminants that could impact water quality. The amount of water 

needed and the contaminant discharge vary by type of biofuel produced 

and type of feedstock used in the conversion process. For example, 

ethanol production requires greater amounts of high-quality water than 

does biodiesel. Conversion of corn to ethanol requires approximately 3 

gallons of water per gallon of ethanol produced, which represents a 

decrease from an estimated 5.8 gallons of water per gallon of ethanol in 

1998.19 According to some experts, these gains in efficiency are, for the 

 

The Extent to Which During the process of converting feedstocks into biofuels, biorefineries 

18Water is still lost with closed cultivation due to the cooling needs of the closed systems, 

among other uses. 

19In comparison, the recovery and refining of 1 gallon of crude oil requires a total of 3.6 to 

7.0 gallons of water. Wu, M. et al., “Consumptive Water Use in the Production of Ethanol 

and Petroleum Gasoline,” Center for Transportation Research, Energy Systems Division, 

Argonne National Laboratory (Argonne, Ill., January 2009). 

Biofuel Conversion May 

Affect Water Resources 

also Depends on the 

Feedstock Used and 

Biofuel Produced 
 

most part, the result of ethanol plants improving their water recycling 

efforts and cooling systems. 

According to some experts we spoke with, the biofuel conversion process 

generally requires high-quality water because the primary use for ethanol 

production is for cooling towers and boilers, and cleaner water transfers 

heat more efficiently and does less damage to this equipment. As a result, 

ethanol biorefineries prefer to use groundwater because it is generally 

cleaner, of more consistent quality, and its supply is less variable than 

surface water. Furthermore, the use of lesser-quality water leaves deposits 

on biorefinery equipment that require additional water to remove. 

However, despite water efficiency gains, some communities have become 

concerned about the potential impacts of withdrawals for biofuel 

production on their drinking water and municipal supplies and are 

pressuring states to limit ethanol facilities’ use of the water. For example, 

at least one Minnesota local water district denied a permit for a proposed 

biorefinery due to concerns about limited water supply in the area. 

Current estimates of the water needed to convert cellulosic feedstocks to 

ethanol range from 1.9 to 6.0 gallons of water per gallon of ethanol, 

depending on the technology used. Conversion of these next generation 

feedstocks is expected to use less water when compared to conventional 

feedstocks in the long run, according to some experts.20 For example, 

officials from a company in the process of establishing a biorefinery 

expect the conversion of pine and other cellulosic feedstocks to consume 

less water than the conversion of corn to ethanol once the plant is 

operating at a commercial scale. However, some researchers cautioned 

that the processes for converting cellulosic feedstocks currently require 

greater quantities of water than needed for corn ethanol. They said the 

technology has not been optimized and commercial-scale production has 

not yet been demonstrated, therefore any estimates on water use by 

cellulosic biorefineries are simply projections at this time. 

In contrast, biodiesel conversion requires less water than ethanol 

conversion—approximately 1 gallon of freshwater per gallon of biodiesel. 

 

20DOE’s Energy Information Administration’s (EIA) Annual Energy Outlook 2009 projects 

that there is a sufficient growth in use of biomass-to-liquids (BTL) fuels to meet the EISA 

cellulosic biofuel requirement and that the production process for BTL fuels does not 

require continuous water inputs. BTL refers to processes for converting biomass into a 

range of liquid fuels, such as gasoline and diesel. In addition, EIA noted that certain oils 

currently eligible for inclusion as cellulosic biofuels also do not use process water. 

Page 15 GAO-10-116 Energy-Water Nexus 
 

Similar to ethanol conversion, much of this water is lost during the cooling 

and feedstock drying processes. Biodiesel facilities can use a variety of 

plant and animal-based feedstocks, providing more options when choosing 

a location. This flexibility in type of feedstock that can be converted 

allows such facilities to be built in locations with plentiful water supplies, 

lessening their potential impact. 

In addition to the water supply effects, biorefineries can have water quality 

effects because of the contaminants they discharge. However, the type of 

contaminant discharged varies by the type of biofuel produced. For 

example, ethanol biorefineries generally discharge chemicals or salts that 

build up in cooling towers and boilers or are produced as waste by reverse 

osmosis, a process used to remove salts and other contaminants from 

water prior to discharge from the biorefinery.21 EPA officials told us that 

the concentrated salts discharged from reverse osmosis are a concern due 

to their effects on water quality and potential toxicity to aquatic 

organisms. In contrast, biodiesel refineries discharge other pollutants such 

as glycerin that may be harmful to water quality. EPA officials told us that 

glycerin from small biodiesel refineries can be a problem if it is released 

into local municipal wastewater facilities because it may disrupt the 

microbial processes used in wastewater treatment.22 Glycerin is less of a 

concern with larger biodiesel refineries because, according to EPA 

officials, it is often extracted from the waste stream prior to discharge and 

refined for use in other products. 

Several state officials we spoke with told us these discharges are generally 

well-regulated under the Clean Water Act. Under the act, refineries that 

discharge pollutants into federally regulated waters are required to obtain 

a federal National Pollutant Discharge Elimination System (NPDES) 

permit, either from EPA or from a state agency authorized by EPA to 

implement the NPDES program. These permits generally allow a point 

 

21Reverse osmosis is a filtration process used to purify freshwater by, for example, 

removing the salts from it. This process is used to treat water prior to discharging it from 

the ethanol plant. 

22Glycerin results in elevated levels of biological oxygen demand, which is a measure of 

how much oxygen it will take to break down the material. According to EPA officials, 

biodiesel wastewater with small amounts of glycerin and efficient recovery of methanol 

has a biological oxygen demand of 10,000-15,000 mg/liter, compared to a normal wash 

water biological oxygen demand of about 200 mg/liter. With glycerin, biodiesel wastewater 

has a biological oxygen demand of 80,000 mg/liter. Pure glycerin has a biological oxygen 

demand of 1,000,000 mg/liter. 

Page 16 GAO-10-116 Energy-Water Nexus 
 

Page 17 GAO-10-116 Energy-Water Nexus 

source, such as a biorefinery, to discharge specified pollutants into 

federally regulated waters under specific limits and conditions. State 

officials we spoke with reported they closely monitor the quality of water 

being discharged from biofuel conversion facilities, and that the facilities 

are required to treat their water discharges to a high level of quality, 

sometimes superior to the quality of the water in the receiving water body. 

quality impacts in the event that these fuels leak from storage tanks or the 

pipes used to transport these fuels. Ethanol is highly corrosive and there is 

potential for releases into the environment that could contaminate 

groundwater and surface water, among other issues.23 When ethanolblended fuels leak from underground storage tanks (UST) and aboveground 

tank systems, the contamination may pose greater risks than petroleum. 

This is because the ethanol in these blended fuels causes benzene, a soluble 

and carcinogenic chemical in gasoline, to travel longer distances and persist 

longer in soil and groundwater than it would in the absence of ethanol,24

increasing the likelihood that it could reach some drinking water supplies.25

Federal officials told us that, because it is illegal to store ethanol-blended 

fuels in tanks not designed for the purpose, they had not encountered any 

concerns specific to ethanol storage. However, officials from two states did 

express concern about the possibility of leaks and told us that ethanolblended fuels are still sometimes stored in tanks not designed for the fuel. 

 

Storage and Distribution of The storage and distribution of ethanol-blended fuels could result in water 

23There are other hazards that may occur from releases of ethanol-blended fuels. For 

example, some spills of gasoline with ethanol may pose an explosion risk. Large-scale 

releases of ethanol have been shown to degrade under anaerobic conditions to produce 

explosive concentrations of methane. According to EPA, this can pose a significant 

challenge for remediation contractors mitigating biofuel spills. In addition, the methane 

generated in the subsurface can migrate into overlying buildings, degrading indoor air 

quality. 

24When ethanol is present, the ethanol is consumed by micro-organisms in the soil before 

other, more harmful fuel constituents. This decomposition takes up nutrients and oxygen 

needed to break down benzene and related compounds. As a result, the benzene plume 

extends a greater distance. 

25Mackay, Douglas, Nicholas R. de Sieyes, Murray D. Einarson, Kevin P. Feris, Alexander A. 

Pappas, Isaac A. Wood, Lisa Jacobson, Larry G. Justice, Mark N. Noske, Kate M. Scow, and 

John T. Wilson. “Impact of Ethanol on the Natural Attenuation of Benzene, Toluene, and oXylene in a Normally Sulfate-Reducing Aquifer.” Environmental Science Technology, vol. 

40 (2006): pp. 6123-6130; and Ruiz-Aguilar, G., K. O’Reilly, and P. Alvarez. “A Comparison of 

Benzene and Toluene Plume Lengths for Sites Contaminated with Regular vs. EthanolAmended Gasoline.” Ground Water Monitoring & Remediation, vol. 23, no. 1 (winter 

2003): pp. 48-53. 

Biofuels Can Have Some 

Water Quality 

Consequences 
 

Page 18 GAO-10-116 Energy-Water Nexus 

For instance, one of these states reported a 700-gallon spill of ethanolblended fuels due to the scouring of rust plugs in a UST.26

According to EPA officials, a large number of the 617,000 federally 

regulated UST systems currently in use at approximately 233,000 sites 

across the country are not certified to handle fuel blends that contain 

more than 10 percent ethanol.27 Moreover, according to EPA officials, 

most tank owners do not have records of all the UST systems’ 

components, such as the seals and gaskets. Glues and adhesives used in 

UST piping systems were not required to be tested for compatibility with 

ethanol-blended fuel until recently. Thus there may be many compatible 

tanks used for storing ethanol-blended fuels that have incompatible 

system components, increasing the potential for equipment failure and fuel 

leakage, according to EPA officials. EPA told us that it is continuing to 

work with government and industry partners to study the compatibility of 

these components with various ethanol blends. EPA officials also stressed 

the importance of understanding the fate and transport of biofuels into 

surface water because biofuels are transported mainly by barge, rail, and 

truck. The officials noted that spills of biofuels or their byproducts have 

already occurred into surface waters. 

According to many experts and officials that we contacted, as biofuel 

production increases, farmers and the biofuel production industry will 

need to consider regional differences in water supply and quality when 

choosing which feedstocks to grow and how and where to expand their 

biofuel production capacity. Specifically, they noted that in the case of 

cultivation, certain states may be better suited to cultivate particular 

feedstocks because of the amount and type of water available. Some 

examples they provided include the following: 

 

26EIA noted that use of E10 has dramatically increased over the past few years and that 

there are governmental and industry efforts, such as the U.S. Department of 

Transportation’s Pipeline and Hazardous Material Safety Administration, that work with 

industry groups to address risks associated with handling ethanol blends. 

27Some UST systems are specifically designed to store fuel containing 85 percent ethanol. 

According to EPA officials, owners using blends containing 85 percent ethanol generally 

work with a licensed installer to use certified, compatible storage and dispensing 

equipment. UST systems comprise many components; however, some of these components 

have not been tested for use with high ethanol fuel blends. 

The Effect of Increased 

Biofuel Production Will 

Vary by Region, Due to 

Differences in Water 

Resources and State Laws 
 

• Certain cellulosic feedstocks, such as switchgrass, would be well-suited 

for areas with limited rainfall, such as Texas, because these feedstocks 

generally require less water and are drought tolerant. 

• In the Midwest, switchgrass and other native perennial grasses could be 

grown as stream buffer strips or as cover crops, which are crops planted 

to keep the soil in place between primary plantings. 

• In Georgia, some experts said pine was likely to be cultivated as a next 

generation biofuel feedstock because the state has relatively limited land 

available for cultivation and increased cultivation of pine or other woody 

biomass without irrigation would not cause a strain on water supplies. 

• In the Southeast and Pacific Northwest, waste from logging operations and 

paper production was identified as a potential feedstock for cellulosic 

ethanol production. 

• Areas with limited freshwater supplies and a ready supply of lower-quality 

water, such as brackish water or water from wastewater treatment plants, 

would be better suited to the cultivation of algae. For example, Texas was 

identified as a state suitable for algae cultivation because of the large 

amounts of brackish water in many of its aquifers, as well as its abundant 

sunlight and supplies of carbon dioxide from industrial facilities. 

Research indicates that in making decisions about feedstock production 

for biofuels it will be important to consider the effects that additional 

cultivation will have on the quality of individual water bodies and regional 

watersheds. Farmers need to consider local water quality effects when 

making decisions regarding the suitability of a particular feedstock or 

where to employ agricultural management practices that minimize nutrient 

application. In addition, state officials should consider these effects when 

deciding where programs such as the CRP may be the most effective. For 

example, experts and officials told us it will be important to identify 

watersheds in the Midwest that are delivering the largest nutrient loads 

into the Mississippi River basin and, consequently, contributing to the Gulf 

of Mexico dead zone, in order to minimize additional degradation that 

could result from increased crop cultivation in these watersheds. In 

addition, research has shown it is important that management practices be 

tailored to local landscape conditions, such as topography and soil quality, 

and landowner objectives, so that efforts to reduce nutrient and sediment 

runoff can be maximized. 

Page 19 GAO-10-116 Energy-Water Nexus 
 

In the case of biofuel conversion, some experts and officials said that state 

regulators and industry will need to consider the availability of freshwater 

supplies and the quality of those supplies when identifying and approving 

sites for biorefineries. Currently, many biorefineries are located in areas 

with limited water resources. For instance, as figure 4 shows, many 

existing and planned ethanol facilities are located on stressed aquifers, 

such as the Ogallala, or High Plains, Aquifer. These facilities require 

100,000 to 1 million gallons of water per day, and as mentioned earlier, the 

rate of water withdrawal from the aquifer is already much greater than its 

recharge rate, allowing water withdrawals in Nebraska or South Dakota to 

affect water supplies in other states that draw from that aquifer. Experts 

noted that states with enough rainfall to replenish underlying aquifers may 

be more appropriate locations for biorefineries. 

Page 20 GAO-10-116 Energy-Water Nexus 
 

Page 21 GAO-10-116 Energy-Water Nexus 

Figure 4: Existing and Planned Ethanol Facilities (as of 2007) and Their Estimated Total Water Use Mapped with the Principal 

Bedrock Aquifers, including the Ogallala, or High Plains, Aquifer, of the United States and Total Water Use in 2000 

Finally, relevant water laws in certain states may influence the location of 

future biorefineries. Specifically, several states have enacted laws that 

require permits for groundwater or surface water withdrawals and this 

requirement could impact where biorefineries will be sited. These laws 

specify what types of withdrawals must be permitted by the responsible 

regulatory authority and the requirements for receiving a permit. For 
 

Page 22 GAO-10-116 Energy-Water Nexus 

instance, Georgia’s Environmental Protection Division grants permits for 

certain withdrawals of groundwater and surface water, including for use by 

a biorefinery, when the use will not have unreasonable adverse effects on 

other water uses. According to state officials, there has not yet been a case 

where a permit for a biorefinery was denied because the amount of 

projected withdrawal was seen as unreasonable. In contrast, groundwater 

decisions are made at the local level in Texas, where more than half of the 

counties have groundwater conservation districts, and Nebraska. In 

deciding whether to issue a permit, the Texas groundwater conservation 

districts consider whether the proposed water use unreasonably affects 

either existing groundwater and surface water resources or existing permit 

holders, among other factors. In Nebraska, permits are only required for 

withdrawals and transfers of groundwater for industrial purposes. In 

addition, in Nebraska, where water supplies are already fully allocated in 

many parts of the state, natural resource districts can require biofuel 

conversion facilities to offset the water they will consume by reducing water 

use in other areas of the region. The volume of withdrawals can also factor 

into the need for a permit. While Texas conservation district permits are 

required for almost all types of groundwater wells, Georgia state withdrawal 

permits are only required for water users who withdraw more than an 

average of 100,000 gallons per day.28

Agricultural conservation practices can reduce the effects of increased 

biofuel feedstock cultivation on water supply and water quality, but there 

are several barriers to widespread adoption of these practices. Similarly, 

the process of converting feedstocks to biofuels, technological 

innovations, and the use of alternative water sources can help reduce 

water supply and water quality impacts, but these options can be cost 

prohibitive and certain noneconomic barriers to their widespread use 

remain. 

 

28Any entity that withdraws more than 100,000 gallons a day (monthly average) of surface 

water or 100,000 gallons a day (daily average) of groundwater requires a water permit. 

Agricultural Practices, 

Technological 

Innovations, and 

Alternative Water 

Sources Can Mitigate 

Some Water Resource 

Effects of Biofuels 

Production, but There 

Are Barriers to 

Adoption 
 

Page 23 GAO-10-116 Energy-Water Nexus 

Many experts and officials we spoke with highlighted the importance of 

using agricultural conservation practices to reduce the potential effects of 

increased biofuel feedstock cultivation on water resources. These 

practices can reduce nutrient and pesticide runoff as well as soil erosion 

by retaining additional moisture and nutrients in the soil and disturbing 

the land less. For example, several experts and officials we spoke with 

said that installing and maintaining permanent vegetation areas adjacent 

to lakes and streams, known as riparian zones, could significantly reduce 

the impacts of agricultural runoff. More specifically, several experts and 

officials said that planting buffer strips of permanent vegetation, such as 

perennial grasses, or constructing or restoring wetlands in riparian areas 

would reduce the effects that crop cultivation can have on water quality, 

as shown in figure 5. 

Certain Agricultural 

Practices Can Benefit 

Water Supply and Water 

Quality, but Barriers May 

Limit Widespread 

Adoption 
 

Page 24 GAO-10-116 Energy-Water Nexus 

Figure 5: Example of a Riparian Buffer Adjacent to Cropland 
 

Experts also identified conservation tillage practices—such as “no-till” 

systems or reduced tillage systems, where the previous year’s crop 

residues are left on the fields and new crops are planted directly into these 

residues—as an important way to reduce soil erosion (see fig. 6). Research 

conducted by USDA has shown a substantial reduction in cropland 

erosion since 1985, when incentives were put in place to encourage the 

adoption of conservation tillage practices.29 Another practice, crop 

rotation, also reduces erosion and helps replenish nutrients in the soil. 

This contrasts with practices such as continuous corn cultivation—in 

which farmers plant corn on the same land year after year instead of 

rotating to other crops—which often leads to decreased soil quality. 

Furthermore, experts identified cover crops, a practice related to crop 

rotation, as a way to mitigate some of the impacts of agricultural runoff. 

Cover crops are planted prior to or following a harvested crop, primarily 

for seasonal soil protection and nutrient recovery before planting the next 

year’s crops. These crops, which include grains or perennial grasses, 

absorb nutrients and protect the soil surface from erosion caused by wind 

and rain, especially when combined with conservation tillage practices. 

 

29See the USDA-NRCS 2003 Annual National Resources Inventory 

(http://www.nrcs.usda.gov/technical/NRI/2003/nri03eros-mrb.html).

Page 25 GAO-10-116 Energy-Water Nexus 
 

Page 26 GAO-10-116 Energy-Water Nexus 

Figure 6: Example of Conservation Tillage 

Note: The picture depicts conservation tillage, a process in which last year’s crop residues are left on 

the field and planting occurs directly into this minimally tilled soil. 

Experts also identified “precision agriculture” as an important tool that 

can reduce fertilizer runoff and water demand by closely matching 

nitrogen fertilizer application and irrigation to a crop’s nutrient and water 

needs. Precision agriculture uses technologies such as geographic 

information systems and global positioning systems to track crop yield, 

soil moisture content, and soil quality to optimize water and nutrient 

application rates. Farmers can use this information to tailor water, 

fertilizer, and pesticide application to specific plots within a field, thus 

potentially reducing fertilizer and pesticide costs, increasing yields, and 

reducing environmental impacts. Other precision agriculture tools, like 

low-energy precision-application irrigation and subsurface drip irrigation 

systems, operate at lower pressures and have higher irrigation water 

application and distribution efficiencies than conventional irrigation 
 

Page 27 GAO-10-116 Energy-Water Nexus 

systems, as shown in figure 7.30 Several experts and officials said that in 

order to promote such practices, it is important to continue funding and 

enrollment in federal programs, such as USDA’s Environmental Quality 

Incentives Program, which pay farmers or provide education and technical 

support. See appendix II for an expanded discussion of agricultural 

conservation practices. 

Figure 7: Example of Low-Energy Precision-Application Irrigation 

Several experts and officials we spoke with also said that genetic 

engineering has the potential to decrease the water, nutrient, and pesticide 

requirements of biofuel feedstocks.31 According to an industry trade group, 

 

30Low-energy precision-application center-pivot systems discharge water between alternate 

crop rows planted in a circle. In subsurface drip irrigation, drip tubes are placed from 6 to 

12 inches below the soil surface, the depth depending on the soil type, crop, and tillage 

practices. 

31In addition to genetically engineering crops, USDA officials commented that traditional 

breeding techniques offer great potential for decreasing water, nutrient, and pesticide 

requirements of biofuels feedstocks. 
 

biotechnology firms are currently developing varieties of drought-resistant 

corn that may be available to farmers within the next several years. These 

varieties could significantly increase yields in arid regions of the country 

that traditionally require irrigation for corn production. Companies are 

also working to develop crops that absorb additional nutrients or use 

nutrients more efficiently, giving them the potential to reduce nutrient 

inputs and the resulting runoff. However, industry officials believe it may 

be up to a decade before these varieties become available commercially. 

Furthermore, according to EPA, planting drought-resistant crops, such as 

corn, may lead to increased cultivation in areas where it has not previously 

occurred and may result in problems including increased nutrient runoff. 

Experts and officials told us there are both economic and noneconomic 

barriers to the adoption of agricultural conservation practices. 

• Economic barriers. According to several experts, as with any business, 

farming decisions are made in an attempt to maximize profits. As a result, 

experts told us that some farmers may be reluctant to adopt certain 

conservation practices that may reduce yields and profits, especially in the 

short term. Furthermore, experts and officials also said that some of these 

agricultural conservation practices can be costly, especially precision 

agriculture. For example, the installation of low-energy precision irrigation 

and subsurface drip irrigation systems is significantly more expensive than 

conventional irrigation systems because of the equipment needed, among 

other reasons.32 Farmers may also hesitate to switch from traditional row 

crops to next generation cellulosic crops because of potential problems 

with cash flow and lack of established markets. Specifically, it can take up 

to 3 years to establish a mature, economically productive crop of perennial 

grasses, and farmers would be hard-pressed to forgo income during this 

period. Moreover, farmers may not be willing to cultivate perennial grasses 

unless they are assured that a market exists for the crop and that they 

could earn a profit from its cultivation. Furthermore, efficient cultivation 

and harvest could require farmers to buy new equipment, which would be 

costly and would add to the price they would have to receive for perennial 

grasses in order to make a profit. 

• Noneconomic barriers. Experts and officials we contacted said that many 

farmers do not have the expertise or training to implement certain 

practices, and some agricultural practices may be less suited for some 

 

32USDA officials noted that use of precision agriculture may also be limited in the 

cultivation of cellulosic feedstocks due to the costs involved. 

Page 28 GAO-10-116 Energy-Water Nexus 
 

Page 29 GAO-10-116 Energy-Water Nexus 

places. For example, state officials told us that farmers usually need a year 

or more of experience with reduced tillage before they can achieve the 

same crop yields they had with conventional tillage. In addition, precision 

agriculture relies on technologies and equipment that require training and 

support. Officials told us that to help address this training need, USDA and 

states have programs in place that help educate farmers on how to 

incorporate these practices and, in some cases, provide funding to help do 

so. In addition, some experts and officials cited regional challenges 

associated with some agricultural practices and the cultivation of biofuel 

feedstocks. For example, these experts and officials said that the amount 

of agricultural residue that can be removed would vary by region and even 

by farm. Similarly, cultivation of certain cover crops as biofuel feedstocks 

may not be suitable in the relatively short growing seasons of northern 

regions. 

in the ethanol conversion process. Newly built biorefineries with improved 

processes have reduced water use dramatically over the past 10 years, and 

some plants have reduced their wastewater discharge to zero. Of the 

remaining water use, water loss from cooling towers for biorefineries is 

responsible for approximately 50 to 70 percent of water consumption in 

modern dry-milling ethanol plants.33

Some industry experts we spoke with said that further improvements in 

water efficiency at corn ethanol plants are likely to come from minimizing 

water loss from cooling towers or from using alternative water sources, 

such as effluent from sewage treatment plants. One alternative technology 

that can substantially reduce water lost through cooling towers is a dry 

cooling system,34 which relies primarily on air rather than water to transfer 

heat from industrial processes.35 In addition, some ethanol plants are 

beginning to replace freshwater with alternative sources of water, such as 

 

Use of Innovative Technological improvements have already increased water use efficiency 

33Cooling towers are used to control temperatures during the conversion process by 

transferring the heat to cooler water. This heat is then transferred via evaporation to the 

atmosphere. 

34In one type of dry cooling system, steam flows through condenser tubes and is cooled 

directly by fans blowing air across the outside of these tubes to condense the steam back 

into liquid water. 

35GAO, Energy-Water Nexus: Improvements to Federal Water Use Data Would Increase 

Understanding of Trends in Power Plant Water Use, GAO-10-23 (Washington, D.C.: Oct. 

16, 2009). 

Technologies and 

Alternative Water Sources 

Could Reduce the Water 

Resource Effects of 

Biorefineries, but Costs 

and Logistics Impede 

Adoption 
 

effluent from sewage treatment plants, water from retention ponds at 

power plants, or excess water from adjacent rock quarries. For example, a 

corn ethanol conversion plant in Iowa gets a third of its water from a local 

wastewater treatment plant. By using these alternative water sources, the 

biorefineries can lower their use of freshwater during the conversion 

process. While these strategies of improved water efficiency at 

biorefineries show considerable promise, there are barriers to their 

adoption. For example, technologies such as dry cooling systems are often 

prohibitively expensive and can increase energy consumption. 

Furthermore, according to industry experts, alternative water sources can 

create a need for expensive wastewater treatment equipment. Some 

industry experts also told us that the physical layout of a conversion 

facility may need to be changed to make room for these improvements. 

Because of the considerable costs of such improvements, several experts 

told us, it is difficult for biorefineries to integrate these water-conserving 

technologies while remaining competitive in the economically strained 

ethanol industry. 

Many experts and officials stated that technological innovations for next 

generation biofuel conversion also have the potential to reduce the water 

supply and water quality impacts of increased biofuel production. For 

example, thermochemical production of cellulosic ethanol could require 

less than 2 gallons of water per gallon of ethanol produced.36 In addition, 

some next generation biofuels, known as “drop-in” fuels, are being 

developed that are compatible with the existing fuel infrastructure, which 

could reduce the risk that leaks and spills could contaminate local water 

bodies. For example, biobutanol is produced using fermentation processes 

similar to those used to make conventional ethanol, but it does not have 

the same corrosive properties as ethanol and could be distributed through 

the existing gasoline infrastructure.37 In addition, liquid hydrocarbons 

derived from algae have the potential to be converted to gasoline, diesel, 

and jet fuel, which also can be readily used in the existing fuel 

 

36Wu, M. et al., “Consumptive Water Use in the Production of Ethanol and Petroleum 

Gasoline,” Center for Transportation Research, Energy Systems Division, Argonne National 

Laboratory (Argonne, Ill., January 2009). 

37Similar to ethanol, biobutanol is an alcohol that can be produced from domestic 

feedstocks. However, biobutanol has a few advantages over ethanol. Biobutanol has a 

higher energy content than ethanol and is compatible with the existing infrastructure. 

Page 30 GAO-10-116 Energy-Water Nexus 
 

Page 31 GAO-10-116 Energy-Water Nexus 

infrastructure.38 However, while these proposed technological innovations 

can reduce the water resource impacts of increased biofuel production, 

the efficacy of most of these innovations has not yet been demonstrated 

on a commercial scale, and some innovations’ efficacy has not yet been 

demonstrated on a pilot scale. 

Many of the experts and officials we spoke with identified areas where 

additional research is needed to evaluate and understand the effects of 

increased biofuel production on water resources. These needs fall into two 

broad areas: (1) research on the water effects of feedstock cultivation and 

conversion and (2) better data on local and regional water resources. 

Experts and officials identified the following research needs on the water 

resource effects of feedstock cultivation and conversion processes: 

Genetically engineered biofuel feedstocks. Many experts and officials 

cited the need for more research into the development of drought-tolerant 

and water- and nutrient-efficient crop varieties to decrease the amount of 

water needed for irrigation and the amount of fertilizer that needs to be 

applied to biofuel feedstocks. According to the National Research Council, 

this research should also address the current lack of knowledge on the 

general water requirements and evapotranspiration rates of genetically 

engineered crops, including next generation crops.39 Regarding nutrient 

efficiency, some experts and officials noted that research into the 

development of feedstocks that more efficiently take up and store nitrogen 

from the soil would help reduce nitrogen runoff. In addition, USDA 

officials added that research to determine the water requirements for 

conventional biofuel feedstocks and new feedstock varieties developed 

specifically for biofuel production is also needed. 

Effects of cellulosic crops on hydrology. Many experts and officials also 

told us there is a need to better understand the water requirements of 

cellulosic crops and the impact of commercial-scale cellulosic feedstock 

cultivation on hydrology, which is the movement of water through land 

 

38Liquid hydrocarbons, such as petroleum, are a class of chemical compounds containing 

only hydrogen and carbon. Potentially, hydrocarbons can be derived from substitutes such 

as oils from plants or algae. 

39Evapotranspiration refers to the water lost to the atmosphere from soil and water bodies 

(evaporation) and from plant leaves (transpiration). 

Experts Identified a 

Variety of Key 

Research and Data 

Needs Related to 

Increased Biofuels 

Production and Local 

and Regional Water 

Resources 
 

and the atmosphere into receiving water bodies. According to one expert, 

these feedstocks differ from corn in their life cycles, root systems, harvest 

times, and evapotranspiration levels, all of which may influence hydrology. 

In addition, some research suggests that farmers may cultivate cellulosic 

feedstocks on marginal or degraded lands because these lands are not 

currently being farmed and may be suitable for these feedstocks. However, 

according to the National Research Council, the current 

evapotranspiration rates of crops grown on such lands is not well known.40

Effects of cellulosic crops on water quality. Many experts and officials we 

spoke with said research is needed to better understand the nutrient needs 

of cellulosic crops grown on a commercial scale. Specifically, field 

research is needed on the movement of fertilizer in the soil, air, and water 

after it is applied to these crops. One expert explained there are water 

quality models that can describe what happens to fertilizer when applied 

to corn, soy, and other traditional row crops. However, such models are 

less precise for perennial grasses due to the lack of data from field trials. 

Similarly, several experts and officials told us that additional research is 

also needed on the potential water quality impacts from the harvesting of 

corn stover. In particular, research is needed on the erosion and sediment 

delivery rates of different cropping systems in order to determine the 

acceptable rates of residue removal for different crops, soils, and locations 

and to develop the technology to harvest residue at these rates. 

Cultivation of algae. Although algae can be cultivated using lower-quality 

water, the impact on water supply and water quality will ultimately depend 

on which cultivation methods are determined to be the most viable once 

this nascent technology reaches commercial scale. Many experts we spoke 

with noted the need for research on how to more efficiently cultivate algae 

to minimize the freshwater consumption and water quality impacts. For 

example, research on how to maximize the quantity of water that can be 

recycled during harvest will be essential to making algae a more viable 

feedstock option. Further research is also needed to determine whether 

the pathogens and predators in the lower-quality water are harmful to the 

 

40National Research Council, Water Implications of Biofuels Production in the United 

States, 2008. 

Page 32 GAO-10-116 Energy-Water Nexus 
 

algae.41 In addition, research is also needed on how to manage water 

discharges during cultivation and harvest of algae. Although it is expected 

that most water will be recycled, a certain amount must be removed to 

prevent the buildup of salt. This water may contain pollutants—such as 

nutrients, heavy metals, and accumulated toxics—that need to be removed 

to meet federal and state water quality standards. 

Data on land use. Better data are needed on what lands are currently 

being used to cultivate feedstocks, what lands may be most suitable for 

future cultivation, and how land is actually being managed, according to 

experts and officials. For example, some experts and officials told us there 

is a need for improved data on the status and trends in the CRP. According 

to a CRP official, USDA does not track what happens to land after it is 

withdrawn from the CRP. Such data would be useful because it would help 

officials gain a better understanding of the extent to which marginal lands 

are being put back into production. In addition, improved data on land use 

would help better target and remove the least productive lands from 

agricultural production, resulting in water supply and water quality 

benefits because these lands generally require greater amounts of inputs, 

according to these experts and officials. Research is also needed to 

determine optimal placement of feedstocks and use of agricultural 

conservation practices to get the best yields and minimize adverse 

environmental impacts. 

Farmer decision making. Several experts and officials told us that a 

better understanding of how farmers make cultivation decisions, such as 

which crops to plant or how to manage their lands, is needed in the 

context of the water resource effects of biofuel feedstocks. Specifically, 

several experts and officials said that research is needed to better 

understand how farmers decide whether to adopt agricultural 

conservation practices. In particular, some experts and officials said 

research should explore how absentee ownership of land affects the 

choice of farming practices. These experts and officials told us it is 

common for landowners to live elsewhere and rent their farmland to 

someone else. For example, in Iowa, 50 percent of agricultural land is 

rented, according to one expert, and renters may be making cultivation 

 

41U.S. Department of Energy, “National Algal Biofuels Technology Roadmap,” Draft, 2009. 

In December 2008, DOE convened a workshop to discuss and identify the critical barriers 

currently preventing the economical production of algal biofuels at a commercial scale. As 

a result of this workshop, DOE assembled a draft roadmap that highlights a number of 

areas in need of additional research. 

Page 33 GAO-10-116 Energy-Water Nexus 
 

decisions that maximize short-term gains rather than focusing on the longterm health of the land. In addition, several experts and officials said that 

research is needed to understand the cultural pressures that may make 

farmers slow to adopt agricultural conservation practices. For example, 

some experts and officials we spoke with said that some farmers may be 

hesitant to move away from traditional farming approaches. 

Conversion. Existing and emerging technology innovations, such as those 

discussed earlier in the report, may be able to address some effects of 

conversion on water resources, but more research into optimizing current 

technologies is also needed, according to experts. For example, research 

into new technologies that further reduce water needs for biorefinery 

cooling systems would have a significant impact on the overall water use 

at a biorefinery, according to several experts. Congress is considering 

legislation—the Energy and Water Research Integration Act—that would 

require DOE’s research, development, and demonstration programs to 

seek to advance energy and energy efficiency technologies that minimize 

freshwater use, increase water use efficiency, and utilize nontraditional 

water sources with efforts to improve the quality of that water.42 It would 

also require the Secretary of Energy to create a council to promote and 

enable, in part, improved energy and water resource data collection. 

Similarly, with regard to conversion facilities for the next generation 

feedstocks, further research is needed to ensure that the next generation 

of biorefineries is as water efficient as possible. For example, for the 

conversion of algae into biofuels, research is needed on how to extract oil 

from algal cells so as to preserve the water contained in the cell, which 

would allow some of that water to be recycled. 

Storage and distribution. EPA officials noted that additional research 

related to storage and distribution of biofuels is also needed to help 

reduce the effects of leaks that can result from the storage of biofuel 

blends in incompatible tank systems. Although EPA has some research 

under way, more is needed into the compatibility of fuel blends containing 

more than 10 percent ethanol with the existing fueling infrastructure. In 

addition, research should evaluate advanced conversion technologies that 

can be used to produce a variety of renewable fuels that can be used in the 

existing infrastructure. Similarly, research is needed into biodiesel 

distribution and storage, such as assessing the compatibility of blends 

 

42H.R. 3598, 111th Cong. (2009). 

Page 34 GAO-10-116 Energy-Water Nexus 
 

greater than 5 percent with the existing storage and distribution 

infrastructure. 

In addition, experts and officials identified the following needs for better 

data on local and regional water resources: 

Water availability data. Because some local aquifers and surface water 

bodies are already stressed, many experts called for more and better data 

on water resources.43 Although USGS reports data on water use every 5 

years, the agency acknowledges that it does not have good estimates of 

water use for biofuel production for irrigation or fuel production, so it is 

unclear how much water has been or will be actually consumed with 

increases in cultivation and conversion of biofuel feedstocks. 

Furthermore, some experts and officials told us that even when local 

water data are available, the data sources are often inconsistent or out of 

date. For example, the data may capture different information or lack the 

information necessary for making decisions regarding biofuel production. 

According to several experts and officials, better data on water supplies 

would also help ensure that new biorefineries are built in areas with 

enough water for current and future conversion processes. Although 

biorefineries account for only a small percentage of water used during the 

biofuel production process, the additional withdrawals from aquifers can 

affect other users that share these water sources. Improving water supply 

data would help determine whether the existing water supplies can 

support the addition of a biorefinery in a particular area. Some experts 

also noted the need for research on the availability of lower-quality water 

sources such as brackish groundwater, which could be used for cultivation 

of some next generation feedstocks, especially algae. Better information is 

necessary to better define the spatial distribution, depth, quantity, physical 

and chemical characteristics, and sustainable withdrawal rates for these 

lower-quality water sources, and to predict the long-term effects of water 

extraction. 

 

43The Omnibus Public Land Management Act of 2009 requires, in part, the Secretary of 

Interior, in coordination with the National Advisory Committee on Water Information and 

state and local water resource agencies, to establish a national water availability and use 

assessment program. Pub. L. No. 111-11, § 9508(a) (2009), codified at 42 U.S.C. § 10368(a). 

This program will, among other things, provide a more accurate assessment of the status of 

the water resources of the United States. The program may address some of the water 

availability data needs identified by the experts we spoke with. 

Page 35 GAO-10-116 Energy-Water Nexus 
 

Page 36 GAO-10-116 Energy-Water Nexus 

Linkages between datasets. Some experts also cited a need for better 

linkages between existing datasets. For example, datasets on current land 

use could be combined with aquifer data to help determine what land is 

available for biofuel feedstock cultivation that would have minimal effects 

on water resources. In addition, some experts said that while there are 

data that state agencies and private engineering companies have collected 

on small local aquifers, a significant effort would be required to identify, 

coordinate, and analyze this information because linkages do not currently 

exist. 

Geological process data. Several experts and officials also said that 

research into geological processes is needed to understand the rate at 

which aquifers are replenished and the impact of increased biofuel 

production on those aquifers. Although research suggests there should be 

sufficient water resources to meet future biofuel feedstock production 

demands at a national level, increased production may lead to significant 

water shortages in certain regions. For example, additional withdrawals in 

states relying heavily on irrigation for agriculture may place new demands 

on already stressed aquifers in the Midwest. Even in water-rich states, 

such as Iowa, concerns have arisen over the effects of increased biofuel 

production, and research is needed to assess the hydrology and quality of 

a state’s aquifers to help ensure it is on a path to sustainable production, 

according to one state official. 

We provided a draft of this report to USDA, DOE, DOI, and EPA for review 

and comment. USDA generally agreed with the findings of our report and 

provided several comments for our consideration. Specifically, USDA 

suggested that we consider condensing our discussion of agricultural 

practices, equipment, and grower decisions, as these items may or may not 

be relevant depending on the feedstock or regulatory control. However, 

we made no revisions to the report because we believe that cultivation is a 

significant part of the biofuels life cycle, and these items are relevant and 

necessary to consider when discussing the potential effect of biofuel 

production on water resources. USDA also noted that the report is more 

focused on corn ethanol production than next generation biofuels and that 

we had not adequately recognized industry efforts to be more sustainable 

through a movement toward advanced biofuels. Given the maturity of the 

corn ethanol industry, the extent of knowledge about the effects on water 

supply and quality from cultivation of corn and its conversion into ethanol, 

and the uncertainty related to the effects of next generation biofuel 

production, we believe the balance in the report is appropriate. Moreover, 

although the shift toward next generation biofuels is a positive step in 

Agency Comments 

and Our Evaluation 
 

Page 37 GAO-10-116 Energy-Water Nexus 

terms of sustainability, this industry is still developing and the full extent 

of the environmental benefits from this shift is still unknown. USDA also 

provided technical comments, which we incorporated as appropriate. See 

appendix III for USDA’s letter. 

DOE generally agreed with our findings and approved of the overall 

content of the report and provided several comments for our 

consideration. Specifically, DOE noted that it may be too early to make 

projections on the amount of CRP land that will be converted and the 

amount of additional inputs that will be needed for cultivation of biofuel 

feedstocks. In addition, DOE suggested we expand our discussion of 

efforts to address risks of ethanol transport and note the water use 

associated with the production of biomass-to-liquid fuels. We adjusted the 

text as appropriate to reflect these suggestions. DOE also suggested that 

the report should discuss water pricing; however, this was outside the 

scope of our review. See appendix IV for DOE’s letter. 

In its general comments, DOI stated that the report is useful and agreed 

with the finding on the need for better data on water resources to aid the 

decision about where to cultivate feedstocks and locate biorefineries. DOI 

also suggested that the report should include a discussion of the other 

environmental impacts of biofuel production, such as effects on wildlife 

habitat or effects on soil. In response, we note that this report was 

specifically focused on the impacts of biofuel production on water 

resources; however, for a broader discussion of biofuel production, 

including other environmental effects, see our August 2009 report.44 DOI 

also provided additional technical comments that we incorporated into the 

report as appropriate. See appendix V for DOI’s letter. 

EPA did not submit formal comments, but did provide technical comments 

that we incorporated into the final report as appropriate. 

We are sending copies of this report to interested congressional 

committees; the Secretaries of Agriculture, Energy, and the Interior; the 

Administrator of the Environmental Protection Agency; and other 

interested parties. In addition, the report will be available at no charge on 

the GAO Web site at http://www.gao.gov. 

 

44GAO-09-446. 
 

Page 38 GAO-10-116 Energy-Water Nexus 

If you or your staff have questions about this report, please contact us at 

(202) 512-3841 or mittala@gao.gov or gaffiganm@gao.gov. Contact points 

for our Offices of Congressional Relations and Public Affairs may be found 

on the last page of this report. GAO staff who made key contributions to 

this report are listed in appendix VI. 

Sincerely yours, 

Mark E. Gaffigan 

Director, Natural Resources 

 and Environment 

Ms. Anu K. Mittal 

Director, Natural Resources 

 and Environment 
Appendix I: Objectives, Scope, and 

Methodology 

Page 39 GAO-10-116 Energy-Water Nexus 

Appendix I: Objectives, Scope, and 

Methodology 

Our objectives for this review were to describe (1) the known water 

resource effects of biofuel production in the United States; (2) the 

agricultural conservation practices and technological innovations that 

exist or are being developed to address these effects and any barriers that 

may prevent the adoption of these practices and technologies; and (3) key 

research needs regarding the effects of biofuel production on water 

resources. 

To address each of these objectives, we conducted a systematic analysis of 

relevant articles of relevant scientific articles, U.S. multidisciplinary 

studies, and key federal and state government reports addressing the 

production of biofuels and its impact on water supply and quality, 

including impacts from the cultivation of biofuel feedstock and water use 

and effluent release from biofuel conversion processes. In conducting this 

review, we searched databases such as SciSearch, Biosis Previews, and 

ProQuest and used a snowball technique to identify additional studies, 

asking experts to identify relevant studies and reviewing studies from 

article bibliographies. We reviewed studies that fit the following criteria 

for selection: (1) the research was of sufficient breadth and depth to 

provide observations or conclusions directly related to our objectives; (2) 

the research was targeted specifically toward projecting or demonstrating 

effects of increased biofuel feedstock cultivation, conversion, and use on 

U.S. water supply and water quality; and (3) typically published from 2004 

to 2009. We examined key assumptions, methods, and relevant findings of 

major scientific articles, primarily on water supply and water quality. We 

believe we have included the key scientific studies and have qualified our 

findings where appropriate. However, it is important to note that, given 

our methodology, we may not have identified all of the studies with 

findings relevant to these three objectives. Where applicable, we assessed 

the reliability of the data we obtained and found them to be sufficiently 

reliable for our purposes. 

In collaboration with the National Academy of Sciences, we identified and 

interviewed recognized experts affiliated with U.S.-based institutions, 

including academic institutions, the federal government, and researchoriented entities. These experts have (1) published research analyzing the 

water resource requirements of one or more biofuel feedstocks and the 

implications of increased biofuels production on lands with limited water 

resources, (2) analyzed the possible effects of increased biofuel 

production on water, or (3) analyzed the water impacts of biofuels 

production and use. Together with the National Academy of Sciences’ lists 

of experts, we identified authors of key agricultural and environmental 

studies as a basis for conducting semistructured interviews to assess what 
Appendix I: Objectives, Scope, and 

Methodology 

is known about the effects of the increasing production of biofuels and 

important areas that need additional research. The experts we interviewed 

included research scientists in such fields as environmental science, 

agronomy, soil science, hydrogeology, ecology, and engineering. 

Furthermore, to gain an understanding of the programs and plans states 

have or are developing to address increased biofuel production, we 

conducted in-depth reviews of the following five states: Georgia, Iowa, 

Minnesota, Nebraska, and Texas. We selected these states based on a 

number of criteria: ethanol and biodiesel production levels, feedstock 

cultivation type, reliance on irrigation, geographic diversity among states 

currently producing biofuels, and approaches to water resource 

management and law. For each of the states, we analyzed documentation 

from and conducted interviews with a wide range of stakeholders to gain 

the views of diverse organizations covering all stages of biofuel 

production. These stakeholders included relevant state agencies, including 

those responsible for oversight of agriculture, environmental quality, and 

water and soil resources; federal agency officials with responsibility for a 

particular state or region, such as officials from the Department of the 

Interior’s U.S. Geological Survey (USGS), the U.S. Department of 

Agriculture’s (USDA) Natural Resources Conservation Service, and the 

Environmental Protection Agency (EPA); university researchers; industry 

representatives; feedstock producers; and relevant nongovernmental 

organizations, such as state-level corn associations, ethanol producer 

associations, and environmental organizations. We also conducted site 

visits to Iowa and Texas to observe agricultural practices and the 

operation of selected biofuels production plants. 

We also interviewed senior officials, scientists, economists, researchers, 

and other federal officials from USDA, the Departments of Defense and 

Energy, EPA, the National Aeronautics and Space Administration, the 

Department of Commerce’s National Oceanic and Atmospheric 

Administration, the National Science Foundation, and USGS about effects 

on the water supply and water quality during the cultivation of biofuel 

feedstocks and the conversion and storage of the finished biofuels. In 

addition, we interviewed state officials from Georgia, Iowa, Minnesota, 

Nebraska, and Texas as well as agricultural producers and representatives 

of biofuel conversion facilities to determine the impact of biofuels 

production in each state. We also interviewed representatives of 

nongovernmental organizations, such as the Renewable Fuels Association, 

the Biotechnology Industry Organization, the Pacific Institute, and the 

Fertilizer Institute. 

Page 40 GAO-10-116 Energy-Water Nexus 
Appendix I: Objectives, Scope, and 

Methodology 

To conduct the interview content analysis, we reviewed interviews, 

selected relevant statements from the interviews, and identified and 

labeled trends using a coding system. Codes were based on trends 

identified by previous GAO biofuel-related work, background information 

collected for the review, and the interviews for this review. The 

methodology for each objective varied slightly, because the first objective 

focused on regional differences and therefore relied on case study 

interviews, while analysis performed for the remaining two objectives 

used expert interviews in addition to case study interviews. Once relevant 

data were extracted and coded, we used the coded data to identify and 

analyze trends. For the purposes of reporting our results, we used the 

following categories to quantify responses of experts and officials: “some” 

refers to responses from 2 to 3 individuals, “several” refers to responses 

from 4 to 6 individuals, and “many” refers to responses from 7 or more 

individuals. 

We conducted our work from January 2009 to November 2009 in 

accordance with all sections of GAO’s Quality Assurance Framework that 

are relevant to our objectives. The framework requires that we plan and 

perform the engagement to obtain sufficient and appropriate evidence to 

meet our stated objectives and to discuss any limitations in our work. We 

believe that the information and data obtained, and the analysis 

conducted, provide a reasonable basis for any findings and conclusions in 

this product. 

Page 41 GAO-10-116 Energy-Water Nexus 
Appendix II: Examples of Agricultural 

Practices Available to Reduce the Water 

Quality and Water Supply Effects of 

Feedstock Cultivation for Biofuels 

Page 42 GAO-10-116 Energy-Water Nexus 

Agricultural 

conservation practice Description Potential environmental benefits 

Soil erosion prevention 

Crop residue 

management 

Any tillage method that leaves a portion of the previous crop 

residues (unharvested portions of the crop) on the soil 

surface. 

• Reduces soil erosion caused by tillage 

and exposure of bare soil to wind and 

water. 

• Reduces water lost to evaporation. 

• Improves soil quality. 

• Reduces sediment and fertilizer runoff. 

No-till Method that leaves soil and crop residue undisturbed except 

for the crop row where the seed is placed in the ground. 

• Reduces soil erosion caused by tillage 

and exposure of bare soil to wind and 

water. 

• Reduces water lost to evaporation. 

• Improves soil quality by improving soil 

organic matter. 

• Reduces sediment and fertilizer runoff. 

Cover crops A close-growing crop that temporarily protects the soil 

during the interim period before the next crop is established.

• Reduces erosion. 

• Reduces nitrate leaching. 

• Integrates crops that store nitrogen from 

the atmosphere (such as soy), replaces 

the nitrogen that corn and other grains 

remove from the soil. 

• Reduces pesticide use by naturally 

breaking the cycle of weeds, insects, 

and diseases. 

• Improves soil quality by improving soil 

organic matter. 

Nutrient pollution reduction 

Crop rotation Change in the crops grown in a field, usually in a planned 

sequence. For example, crops could be grown in the 

following sequence, corn-soy-corn, rather than in continuous 

corn. 

• Integrates crops that obtain nitrogen 

from the atmosphere (such as soy), 

replaces the nitrogen that corn and 

other grains remove from the soil. 

• Reduces pesticide use by naturally 

breaking the cycle of weeds, insects, 

and diseases. 

Nutrient management Use of nutrients to match the rate, timing, form, and 

application method of fertilizer to crop needs. 

• Reduces nutrient runoff and leaching. 

Subsurface fertilizer 

application 

Injection of fertilizer below the soil surface. • Reduces runoff and gaseous emission 

from nutrients. 

Controlled-release 

fertilizers 

Use of fertilizers with water-insoluble coatings that can 

prevent water-soluble nitrogen from dissolving. 

• Reduces nutrient runoff and leaching. 

• Increases the efficiency of the way 

nutrients are supplied to and are taken 

up by the plant, regardless of the crop. 

Controlled drainage Water control structures, such as a flashboard riser, 

installed in the drainage outlet allow water level to be raised 

or lowered as needed. 

• Minimizes transport of nutrients to 

surface waters. 

Appendix II: Examples of Agricultural Practices 

Available to Reduce the Water Quality and Water 

Supply Effects of Feedstock Cultivation for Biofuels
Appendix II: Examples of Agricultural 

Practices Available to Reduce the Water 

Quality and Water Supply Effects of 

Feedstock Cultivation for Biofuels 

Agricultural 

conservation practice Description Potential environmental benefits 

Irrigation techniques 

Subsurface drip irrigation 

systems 

Irrigation systems buried directly beneath the crop apply 

water directly to the root zone. 

• Minimizes water lost to evaporation and 

runoff. 

Low-energy precisionapplication systems Irrigation systems that operate at lower pressures and have 

higher irrigation-water application and distribution 

efficiencies. 

• Minimizes net water loss and energy 

use. 

Reclaimed water use Water recovered from domestic, municipal, and industrial 

wastewater treatment plants that has been treated to 

standards that allow safe reuse for irrigation. 

• Reduces demand on surface and 

ground waters. 

Multiple benefits 

Wetland restoration Restoration of a previously drained wetland by filling ditches 

or removing or breaking tile drains. 

• Reduces flooding downstream. 

• Filters sediment, nutrients, and 

chemicals. 

• Provides habitat for wetland plants, 

amphibians, and birds. 

Riparian buffer zones Strips or small areas of land planted along waterways in 

permanent vegetation that help control pollutants and 

promote other environmental benefits. 

• Traps sediment. 

• Filters nutrients. 

• Provides habitat and corridors for fish 

and wildlife. 

Precision agriculture A system of management of site-specific inputs (e.g., 

fertilizer, pesticides) on a site-specific basis such as land 

preparation for planting, seed, fertilizers and nutrients, and 

pest control. Precision agriculture may be able to maximize 

farm production efficiency while minimizing environmental 

effects. Key technological tools used in this approach 

include global positioning systems, geographic information 

systems, real-time soil testing, real-time weather 

information, etc. 

• Reduces nutrient runoff and leaching. 

• Reduces erosion. 

• Reduces pesticide use. 

Source: GAO analysis. 

Page 43 GAO-10-116 Energy-Water Nexus 
Appendix III: Comments from the U.S. Appendix III: Comments from the U.S. Department of Agriculture 

Department of Agriculture 

Page 44 GAO-10-116 Energy-Water Nexus 
Appendix III: Comments from the U.S. 

Department of Agriculture 

Page 45 GAO-10-116 Energy-Water Nexus 
Appendix IV: Comments from the Department Appendix IV: Comments from the of Energy 

Department of Energy 

Page 46 GAO-10-116 Energy-Water Nexus 
Appendix IV: Comments from the Department 

of Energy 

Page 47 GAO-10-116 Energy-Water Nexus 
Appendix V: Comments from the Department Appendix V: Comments from the Department of the Interior 

of the Interior 

Page 48 GAO-10-116 Energy-Water Nexus 
Appendix VI: GAO Contacts and Staff Appendix VI: GAO Contacts and Staff Acknowledgments 

Anu Mittal, (202) 512-3841 or mittala@gao.gov

Mark Gaffigan, (202) 512-3841 or gaffiganm@gao.gov 

In addition to the contact named above, Elizabeth Erdmann, Assistant 

Director; JoAnna Berry; Mark Braza; Dave Brown; Muriel Brown; Colleen 

Candrl; Miriam Hill; Carol Kolarik; Micah McMillan; Chuck Orthman; Tim 

Persons; Nicole Rishel; Ellery Scott; Ben Shouse; Jeanette Soares; Swati 

Thomas; Lisa Vojta; and Rebecca Wilson made significant contributions to 

this report. 

Acknowledgments 

GAO Contacts 

Staff 

Acknowledgments 

(361019) Page 49 GAO-10-116 Energy-Water Nexus 
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