Assessment of the Potential for Biodegradation 

of Petroleum Hydrocarbons in the Railroad 

Industrial Area, Fairbanks, Alaska, 1993-94

U.S. GEOLOGICAL SURVEY 

Open-File Report 98-287

Prepared in cooperation with the

Alaska Department of Natural Resources 

Division of Mining and Water Management

Fairbanks, Alaska 

1998
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Thomas J. Casadevall, Acting Director

Use of trade names in this report is for identification 

purposes only and does not constitute endorsement 

by the U.S. Geological Survey.

For additional information:

District Chief

U.S. Geological Survey

4230 University Drive, Suite 201

Anchorage, AK 99508-4664

http://www-water-ak.usgs.gov

Copies of this report may be purchased from:

U.S. Geological Survey 

Branch of Information Services 

Box 25286 

Denver, CO 80225-0286
CONTENTS

Abstract ................................................................. 1

Introduction ............................................................... 1

Background........................................................... 1

Location and Description of the Study Area.................................. 2

Purpose and Scope. ..................................................... 4

Methods ................................................................. 4

Results and Discussion ...................................................... 5

Summary ................................................................. 9

References Cited ........................................................... 9

FIGURES

1. Map showing location of Fairbanks, Alaska, and the Fairbanks Railroad

Industrial Area, with monitoring well locations............................. 3

2. Graph showing the most probable number of gasoline-degrading

microorganisms correlated with the BTEX concentration in ground-water

samples collected in September 1994 from the Fairbanks Railroad

Industrial Area ...................................................... 5

3. Graph showing the percent benzene mineralized over time in ground-water

samples from contaminated and uncontaminated wells ....................... 6

4. Graph showing the percent glutamate mineralized in ground water after 

incubation for two days at 22 °C and 15 °C for uncontaminated (AR27) 

and contaminated wells. ............................................... 7

5. Graphs showing mineralization of glutamate, naphthalene, and benzene

in ground-water samples with and without nutrient addition................... 8

TABLES

1. Benzene, toluene, ethylbenzene, and xylenes (BTEX) concentrations 

measured in ground-water samples from wells in the Railroad Industrial 

Area near Fairbanks, Alaska. ........................................... 5

2. The most probable number of gasoline-degrading microorganisms 

and the total benzene, toluene, ethylbenzene, and xylenes (BTEX) 

concentration in ground-water samples from wells in the Fairbanks 

Railroad Industrial Area, in September 1994............................... 5

3. Benzene mineralization potentials and the total benzene, toluene, 

ethylbenzene, and xylenes (BTEX) concentration measured in ground 

water collected in April 1994 from the Fairbanks Railroad Industrial Area ....... 6

4. The effect of temperature on glutamate mineralization potentials for

ground-water samples collected from the Fairbanks Railroad Industrial Area,

in July 1994 ........................................................ 7

Contents
5. The effect of added nutrients on mineralization potentials for ground-water 

samples collected from the Fairbanks Railroad Industrial Area, in July 1994,

6. Dissolved oxygen measured in ground-water samples from wells in the 

Fairbanks Railroad Industrial Area. .................................

ABBREVIATED WATER-QUALITY UNITS

Chemical concentration and water temperature are given only in metric units. Chemical concentration in water is given 

in grams per liter (g/L), milligrams per liter (mg/L), or micrograms per liter (|lg/L). Milligrams per liter is a unit 

expressing the solute mass per unit volume (liter) of water. One thousand micrograms per liter is equivalent to 1 

milligram per liter. For concentrations less than 7,000 milligrams per liter, the numerical value is about the same as 

for concentrations in parts per million.

mL, milliliters 

|lL, microliters 

dpm, disintegrations per minute

In this report, temperature is reported in degrees Celsius (°C), which can be converted to degrees Fahrenheit (°F) by 

the following equation:

°F=1.8(°C) + 32

IV Contents
Assessment of the Potential for Biodegradation of 

Petroleum Hydrocarbons in the Railroad Industrial Area, 

Fairbanks, Alaska, 1993-94

By Joan F. Braddock, Peter Catterall, andSharon A. Richmond

Abstract

Many technologies for the clean-up of 

petroleum-hydrocarbon contaminated sites 

depend on microbial degradation of the pollutant. In these technologies the site may be modified to enhance microbial activity, or may 

simply be monitored for naturally occurring 

microbial activity. In either case, an important 

aspect of site assessment for these technologies 

is to determine if the microorganisms present at 

the site have the potential to break down contaminants under the prevailing environmental 

conditions. We examined the numbers and 

activity of hydrocarbon-degrading microorganisms in ground water collected from petroleum-hydrocarbon contaminated and 

uncontaminated wells at the Railroad Industrial 

Area near Fairbanks, Alaska. We found that the 

population of gasoline-degrading microorganisms in ground water was correlated to the 

degree of contamination by benzene, toluene, 

ethylbenzene and xylenes (BTEX). We also 

found that these organisms could actively mineralize these types of compounds in laboratory 

mineralization assays. Increasing temperature 

and adding nutrients both enhanced the rate of 

mineralization in the laboratory, but measurable degradation still occurred under conditions similar to those found in the field. 

Dissolved oxygen in ground water at this site 

ranged from 0 to 3.6 milligrams per liter. 

Therefore, oxygen may not always be available 

to microorganisms as a terminal electron 

acceptor. Preliminary geochemical evidence

from the field indicates that alternative electron 

acceptors such as Fe(III), sulfate, or nitrate may 

be used, contributing to degradation of contaminants at this site.

INTRODUCTION 

Background

Many organic contaminants, including 

petroleum hydrocarbons, can be degraded by 

microorganisms. Biodegradation can include 

everything from minor changes to a complete 

breakdown of the starting compound. When a 

complete breakdown to inorganic components 

(such as carbon dioxide and water) of the original compound occurs, the process is called 

mineralization. At some contaminated sites, 

conditions are favorable for microbial breakdown of contaminants. If the biodegradation at 

such a site is proceeding at an acceptable level, 

human intervention may not be necessary. This 

situation is called "natural attenuation" or 

"intrinsic bioremediation." Generally, intrinsic 

bioremediation is monitored with time and the 

only action a site may require is a sampling 

schedule. At other sites, some intervention may 

be necessary to enhance the biodegradation to 

an acceptable level. This is generally termed 

"enhanced bioremediation." Many systems 

have been designed to improve the level of 

microbial activity in breaking down contaminants.

Introduction 1
To understand what factors might be 

important in optimizing the conditions for 

bioremediation, it is necessary to understand 

something about the reasons why microorganisms break down organic contaminants. The 

types of microorganisms that biodegrade 

organic contaminants do so because they can 

use these compounds to produce energy for 

growth and carbon to build new cells. New 

cells are primarily made up of carbon, nitrogen, 

phosphorus, and several other mineral nutrients 

in lower concentrations. To complement the 

large amounts of carbon available from organic 

contaminants, a source of nitrogen or phosphorus may be important at many sites to allow 

microbial growth and, in turn, increase the rate 

at which the organic contaminant is broken 

down. Contaminant-degrading microorganisms also generally need oxygen or an alternate 

electron acceptor as a reactant in the process of 

producing energy from organic contaminants. 

At some environmental sites, such as in ground 

water, oxygen is commonly found only at low 

levels. Many bioremediation-enhancement 

strategies are based on increasing the concentration of oxygen to increase biodegradation. It 

is now known that many petroleum hydrocarbons, including some of the aromatic constituents found in gasoline (such as benzene and 

toluene), can be broken down by microorganisms under anaerobic conditions. In the anaerobic process, Fe(III) and compounds such as 

nitrate and sulfate may substitute for oxygen. 

These anaerobic processes are commonly very 

important in ground-water systems. In addition 

to the chemical requirements of microorganisms, it may be necessary to consider other factors at a particular site. These factors include 

the specific nature of the chemical pollutant 

and its concentration, and physical and chemical factors such as temperature and pH.

One major problem in using bioremediation as a clean-up strategy for a contaminated 

site is that it can be difficult to establish that 

microorganisms are biodegrading the contaminant and to what degree degradation is occurring. Currently, no one measure can be used to

fully assess bioremediation. To address this 

problem, in 1993, the National Research Council (NRC) convened a Committee on In Situ 

Bioremediation (NRC, 1993). This committee 

produced a set of guidelines to assess bioremediation success. Their recommendations are as 

follows:

"No one piece of evidence can unambiguously prove that microorganisms have cleaned 

up a site. Therefore, the Committee on In Situ 

Bioremediation recommends an evaluation 

strategy that builds a consistent, logical case for 

bioremediation based on converging lines of 

independent evidence. The strategy should 

include three types of information: (1) documented loss of contaminants from the site, (2) 

laboratory assays showing that microorganisms 

from site samples have the potential to transform the contaminants under the expected site 

conditions, and (3) one or more pieces of information showing that the biodegradation potential is actually realized in the field."

The study described in this report was 

designed to document that microorganisms 

from the site have the potential to transform 

contaminants under site conditions. Changes in 

contaminant concentrations with time were 

monitored at the site in a complementary study 

(Lilly and others, 1996, see table 1).

Location and Description of the 

Study Area

The study area is located in the Railroad 

Industrial Area in Fairbanks, Alaska (fig. 1). 

Development in the vicinity began in the early 

1900's, and the area, which still serves as the 

main railhead for Fairbanks, has been the location of commercial and industrial activities 

since that time. Previous studies have indicated 

the presence of petroleum hydrocarbons and 

chlorinated solvents in ground water in the 

area. Ground-water wells have been monitored 

since 1993 (Kriegler and Lilly, 1995), and the 

extent of the migration of these compounds is 

presented by Lilly and others (1996).

2 Assessment of the Potential for Biodegradation of Petroleum Hydrocarbons in the 

Railroad Industrial Area, Fairbanks, Alaska, 1993-94
'ALASKA\

i l

Fairbanks!

^

147°50'

64°52'

64°46'

147°30'

0 1 2 SMILES 

I 012 3 KILOMETERS

Base from U.S. Geological Survey, Fairbanks D-2 (NE, NW, SW, SE), Alaska, 1:25,000, 1992.

B

Figure 1. Location of Fairbanks, Alaska, and the Fairbanks Railroad 

Industrial Area (A), with monitoring well locations (B).

Introduction 3
Purpose and Scope

The two major objectives in studying the 

Railroad Industrial Area were (1) to determine 

the relative degree to which contaminants are 

moving from a specified boundary area with 

time (Kriegler and Lilly, 1995; Lilly and others, 

1996); and (2) to determine what kind of microorganisms are present in contaminated and 

uncontaminated ground water at the site, determine if those microorganisms can degrade 

petroleum hydrocarbons, and examine some of 

the factors that might influence the rate at 

which these microorganisms are able to break 

down petroleum hydrocarbons. The latter 

objective is the subject of this report.

METHODS

Samples were collected from monitoring 

wells purged with a peristaltic pump using 

3/8-inch Teflon tubing (Lilly and others, 1996). 

During purging, the temperature, pH, specific 

conductance, and dissolved oxygen were continuously monitored. When these properties 

had stabilized and at least three well casing volumes had been purged, samples were collected 

in sterile containers from a bailer for microbiological analyses. While microbial populations 

and activities associated with soil particles at 

the site may be different from those measured 

in well water, only well water was measured in 

this study due to difficulties in obtaining soil 

samples at the site.

Most probable number (MPN) assays 

were used to estimate microbial populations of 

gasoline degraders and heterotrophs. A sixtube miniaturized MPN procedure was modified from Brown and Braddock (1990), using 

96-cell well plates. Tenfold serial dilutions of a 

ground-water sample were made in an isotonic 

(Ringer) solution (Collins and others, 1989). A 

multi-channel pipette was used to transfer 

100 juL of each dilution to replicate wells containing 100 juL of either 4/5 strength mineral

salts medium (Bushnell-Haas (BH); Atlas, 

1993) amended with 0.025 g/L tetrazolium violet for gasoline degraders, or a heterotrophic 

culturing medium (R2A; Atlas, 1993) for heterotrophs. Each well of the gasoline-degrader 

plates was then spiked with one drop of filtersterilized gasoline. The plates were incubated 

for 14 days at room temperature before being 

scored for color development (gasoline degraders) or turbidity (heterotrophs), indicating positive growth.

Radiorespirometry was used to assay the 

benzene-, naphthalene- and glutamate-mineralization potentials of microorganisms in groundwater samples (modified from Brown and others, 1991). Radiolabeled benzene and naphthalene ([U- 14 C]-benzene and [1- 14 C]- 

naphthalene) were used as representative aromatic hydrocarbons. In a similar manner, heterotrophic mineralization potentials were 

measured using [U- 14C]-L-glutamic acid. To 

determine whether nutrient availability limits 

carbon-substrate mineralization, samples were 

diluted in both a nutrient-containing mineral 

salts medium (BH; Atlas, 1993) and in a saline 

solution containing no added nutrients (Ringer; 

Collins and others, 1989). Ground water was 

diluted 50 percent by adding 5 mL ground 

water to 5 mL of either BH or Ringer in 40-mL 

septa vials. Replicate vials of the diluted 

ground water were injected with 50 juL of a 

2-g/L solution (in acetone for benzene and 

naphthalene or water for glutamate) of radiolabeled substrate (about 50,000 dpm/50 juL). The 

resulting initial concentration of added substrate was then 100 jug per vial (10 |ig/mL 

slurry). At the end of the designated incubation 

period, microbial activity was stopped by adding 1 mL ION NaOH to each vial. The samples 

were later re-acidified with 1.5 mL HC1 after 

which the radiolabeled CO2 was stripped into a 

CO2-sorbing scintillation cocktail and counted 

in a liquid-scintillation counter. All microbial 

assays were conducted under aerobic conditions.

4 Assessment of the Potential for Biodegradation of Petroleum Hydrocarbons in the 

Railroad Industrial Area, Fairbanks, Alaska, 1993-94
RESULTS AND DISCUSSION

We sampled several ground-water wells 

in the Railroad Industrial Area four times during 1993-94 (table 1). We found populations of 

microorganisms (heterotrophs) that can break 

down organic molecules (not necessarily petroleum hydrocarbons) in all the water samples 

measured (results not shown). More importantly, we found specific populations of microorganisms that degrade the types of 

contaminants, such as gasoline, found in some 

areas of the site. Furthermore, the populations 

of microorganisms that can specifically biodegrade gasoline present in ground water at the 

site were found in numbers proportional to the 

amount of BTEX (benzene, toluene, ethylbenzene and xylenes) in the same water samples 

(fig. 2, table 2). In other words, water samples 

from sites that had high concentrations of 

BTEX also had high numbers of gasoline 

degraders. In contrast, uncontaminated water 

samples contained few, if any, gasoline-degrading microorganisms. This correlation provided 

evidence that natural attenuation might be 

occurring in the Railroad Industrial Area.

£ 1200

t

d 1000

800

- 600

400

200

0 2000 4000 6000 8000 10000 12000 

BTEX CONCENTRATION, IN MICROGRAMS PER LITER

Figure 2. Most probable number (MPN) of 

gasoline-degrading microorganisms correlated 

(1^=0.96) with the BTEX concentration in groundwater samples collected in September 1994 from 

the Fairbanks Railroad Industrial Area.

Table 2. The most probable number of gasolinedegrading microorganisms and the total benzene, 

toluene, ethylbenzene, and xylenes (BTEX) 

concentration in ground-water samples from wells 

in the Fairbanks Railroad Industrial Area, in 

September 1994 

[mL, milliliter; |J.g/L, micrograms per liter]

Table 1. Benzene, toluene, ethylbenzene, and 

xylenes (BTEX) concentrations measured in 

ground-water samples from wells in the Railroad 

Industrial Area near Fairbanks, Alaska 

[|ig/L, micrograms per liter]

BTEX concentration (|ig/L)

Well

AR7 

AR26 

AR27 

AR44 

AR49 

AR102

Date sampled

8/93

5,910 

38 

<0.2 

6,180 

1 

<0.2

4/94

11,280 

80 

<0.2 

11,750 

47 

<0.2

7/94

13,100 

29 

<0.2 

7,870 

5 

<0.2

9/94

(l)

63 

<0.2 

7,090 

45 

<0.2

Well

AR7 

AR26 

AR27 

AR44 

AR49

Gasoline BTEX 

Replicate degraders concentration 

(cells/mL) (^ig/L)

A 1,050 ! 10,097 

B 852

A 107 63 

B 120

A 29 <0.2 

B 22

A 852 7,090 

B 760

A 29 45 

B 36

'The BTEX concentration was not measured for well AR7 in 

September 1994; the BTEX value shown here and in figure 

2 is the mean from the nrevions three samnlinps

'Well AR7 was not sampled for BTEX in September 1994

Results and Discussion 5
Once we determined that microorganisms 

that biodegrade gasoline were present in contaminated ground water from the Railroad 

Industrial Area, we sought to establish whether 

or not these microorganisms have the potential 

to completely break down (mineralize to carbon dioxide and water) some of the chemical 

constituents found in gasoline. We used 

ground-water samples from three wells to 

examine the activity of the microbial population in laboratory assays. Ground water from 

two of these wells (AR44 and AR7) contained 

high levels of BTEX (about 10,000 |ig/L; 

table 1) and high numbers of gasoline-degrading microorganisms (about 1,000 microorganisms/mL; table 2). Ground water from one well 

(AR27) contained no measurable BTEX and 

very low (<30 microorganisms/mL; table 2) 

populations of gasoline-degrading microorganisms. After four days in a laboratory experiment conducted at room temperature (22 °C), 

the microbial populations in ground water from 

AR44 and AR7 were able to mineralize 15 to 

30 percent of the added benzene to carbon 

dioxide (fig. 3, table 3). The microorganisms in 

AR27 were unable to mineralize any measurable quantity of the benzene in the same time 

period. These data show that acclimated microbial populations that can break down benzene, 

a toxic component of gasoline, are present in

contaminated wells in the Railroad Industrial 

Area.

Several major factors have been found to 

control the rate and extent of natural attenuation in contaminated ground water. These factors include temperature, nutrient availability 

(especially nitrogen and phosphorus), and the 

concentration of dissolved oxygen (or other 

chemical species, such as nitrate, sulfate, and 

Fe(III)). The next step at the Railroad Industrial 

Area was to examine how these factors might 

affect the microbial activity at this particular 

site.

Well. BTEX concentration

 -AR44, 11,750ng/L

 AR7, 11,280 ng/L

 A AR27, <

TIME, IN HOURS

Figure 3. Percent benzene mineralized overtime in 

ground-water samples from contaminated and uncontaminated wells.

Table 3. Benzene mineralization potentials and the total benzene, toluene, ethylbenzene, and xylenes 

(BTEX) concentration measured in ground water collected in April 1994 from the Fairbanks Railroad 

Industrial Area. Values for the benzene mineralization potentials are the means of duplicate analyses

[|ig/L, micrograms per liter]

Well

AR7

AR26

AR27

AR44

AR49

AR102

BTEX

concentration

(H9/L)

11,750

80

<0.2

11,750

47

<0.2

Benzene mineralization potential (percent mineralized)

Time (days)

0

0

0

0

0

0

0

0.5

0

0.2

0

0

0

0

1

0

1.4

0

0.2

0

0

2

0.2

22

1.1

4.7

0.2

0.3

3

0

37

0.6

31

0.6

0.5

4

16

32

1.1

28

5.2

11

6 Assessment of the Potential for Biodegradation of Petroleum Hydrocarbons in the 

Railroad Industrial Area, Fairbanks, Alaska, 1993-94
We first examined the effect of temperature on the overall level of activity of microorganisms (total heterotrophs) in ground water 

from one uncontaminated and three contaminated wells. Samples were incubated in the laboratory at different temperatures. The overall 

activity of heterotrophic microorganisms was 

measured by examining the mineralization of 

glutamate, a good energy and carbon source for 

many microorganisms.

The natural temperature of the water in 

wells from the Railroad Industrial Area measured in April, June, July, and September averaged between 4 and 5 °C. The water was 

slightly cooler in April and slightly warmer in 

September. When we examined the total activity of the heterotrophic microbial populationas indicated by glutamate mineralization-after 

two-day incubations in the laboratory at 4, 10, 

15 and 22 °C, we found no activity at 4 or 

10 °C, and a large increase in activity between 

15 and 22 °C (fig. 4, table 4). Samples run at 

15 °C were incubated in a temperature-controlled chamber. Other samples were incubated 

at room temperature, which was approximately 

22 °C. When we incubated samples for longer 

periods of time (6 days for glutamate and 

10 days for naphthalene and benzene), we 

found activity at 10 °C. For example, when 

nutrient effects were measured at 10 °C (fig. 5, 

table 5), we found that microorganisms from 

contaminated wells AR44 and AR7 were able 

to completely break down 20 and 35 percent, 

respectively, of the naphthalene added. Benzene, another petroleum hydrocarbon, was also 

degraded after 10 days at 10 °C by microorganisms from the same two contaminated wells. 

Bradley and Chapelle (1995) reported that 

microorganisms in sediment samples from 

Adak, Alaska, where in situ temperatures were 

about 5 °C, could mineralize toluene when 

incubated at 5 °C. Therefore, rates of hydrocarbon degradation may occur in cold groundwater systems at rates higher than previously 

thought.

Incubation Temperature 

E3 22 °C 

KX3 15°C

WELL

Figure 4. Percent glutamate mineralized in ground 

water after incubation for two days at 22 °C and 

15 °C for uncontaminated (AR27) and contaminated wells. Mean BTEX concentrations for these 

wells can be found in table 1. Error bars represent 

standard error.

Table 4. The effect of temperature on glutamate 

mineralization potentials (a measure of 

heterotrophic microorganism activity) for groundwater samples collected from the Fairbanks 

Railroad Industrial Area, in July 1994. Values 

shown are the means of triplicates

[°C, degrees Celsius]

Well

Glutamate mineralization potential 

(percent mineralized)

15 °C 22 °C

AR26

AR27

AR44

AR49

1

4

1

0

50

51

17

7

Results and Discussion 7
Glutamata (6-day incubation)

Naphthalene (10-day incubation)

^XXXXl

Benzene ( 1 0-day incubation)

AR44

WELL Nutrients 

Nutrients

Figure 5. Mineralization of glutamate, naphthalene, and benzene in ground-water samples with 

and without nutrient addition. These laboratory assays were incubated at 10 °C.

Nutrient (nitrogen and phosphorus) additions stimulated microbial activity in most of 

the laboratory experiments (fig. 5, table 5). The 

results shown in figure 5 indicate that nutrient 

additions might stimulate microbial activity in 

the field. However, it is important to note that 

microbial degradation of all three substrates 

was occurring even in the absence of added 

nutrients. This implies that while biodegradation at the site might be increased by nutrient 

additions, naturally occurring nutrients are adequate for the microbial breakdown of petroleum hydrocarbons.

A third factor that can influence the rate 

of biodegradation is oxygen availability. We 

have not been able to clearly determine how 

great an effect oxygen concentrations have on 

biodegradation activity at the Railroad Industrial Area. Dissolved-oxygen concentrations in 

ground water from wells sampled in this study 

ranged from 0 to 3.6 mg/L (table 6). Ground 

water from other wells sampled in the same 

area, during the same time period of this study, 

had dissolved-oxygen concentrations as high as 

7 mg/L (well oxygenated). It is thought that 

aerobic microbial activity is greatly inhibited at 

dissolved-oxygen concentrations of less than

Table 5. The effect of added nutrients on mineralization potentials for ground-water samples collected from 

the Fairbanks Railroad Industrial Area, in July 1994. All samples were incubated at 10 °C; samples for 

glutamate mineralization potentials were incubated for 6 days, and for naphthalene and benzene, 10 days. 

Values shown are the means of triplicates

Mineralization potential (percent mineralized)

Well

AR7

AR26

AR27

AR44

Glutamate

Nutrients added

56

56

51

55

No nutrients 

added

3

9

28

16

Naphthalene

Nutrients added

34

24

3

20

No nutrients 

added

1

7

7

4

Benzene

Nutrients added

15

(i)

2

15

No nutrients 

added

0

(i)

0

22

Values for benzene for well AR26 were not measured

8 Assessment of the Potential for Biodegradation of Petroleum Hydrocarbons in the 

Railroad Industrial Area, Fairbanks, Alaska, 1993-94
about 1-2 mg/L. However, under anaerobic 

conditions, other chemical species can be used 

by microorganisms as terminal electron acceptors. We have measured the levels of sulfate, 

nitrate, and Fe(III) (chemical species involved 

in the anaerobic breakdown of aromatic hydrocarbons; data not shown) in water from a few 

wells at the site. Preliminary evidence indicated that concentrations of sulfate were lower 

in ground water with measurable concentrations of BTEX than in water from uncontaminated wells. This result would be expected if 

sulfate is involved in an anaerobic microbial 

process. These types of geochemical measures 

may be used in the future to provide additional 

evidence that natural attenuation is being realized at this site.

Table 6. Dissolved oxygen measured in ground 

water from wells in the Fairbanks Railroad 

Industrial Area 

[mg/L, milligrams per liter]

Dissolved oxygen (mg/L)

Well Date sampled

AR26

AR27

AR49

AR102

4/94

0.0

2.2

0.3

0.3

7/94

0.2

3.6

0.3

1.4

9/94

0.2

2.5

0.6

0.2

SUMMARY

This study focused on microbial indicators of natural attenuation at the Railroad 

Industrial Area near Fairbanks, Alaska. At this 

site we found that gasoline-degrader populations in ground water were correlated with the 

degree of BTEX contamination. Uncontaminated ground water contained few gasolinedegrading microorganisms while contaminated 

ground water had high numbers of gasolinedegrading microorganisms. These microorganisms also could mineralize benzene to carbon 

dioxide in laboratory mineralization studies. In

water from contaminated wells, about 15-30 

percent of added benzene was mineralized after 

four days of incubation. Benzene mineralization activity was negligible during the same 

time period in water from uncontaminated 

wells. This indicates that microbial populations 

in contaminated ground water at the site are 

acclimated to the presence of benzene and have 

the potential to mineralize this compound in the 

field. We also used laboratory assays to examine how changes in temperature and nutrient 

supply might influence microbial activity. 

Increasing the incubation temperature 

increased the rate of mineralization of added 

substrates. However, measurable degradation 

of benzene and naphthalene was still achieved 

at 10 °C after 10-day incubations. Adding 

nutrients (N and P) generally stimulated microbial activity. But for at least one sample (AR44) 

with high levels of contaminants, mineralization rates were high even without nutrient additions. Oxygen availability is likely limiting 

microbial activity at the Railroad Industrial 

Area site. Although we did not explore the 

effect of oxygen availability to microorganisms 

in great detail, we did conduct a preliminary 

survey of the presence of other potential electron acceptors in well water from the site. We 

found preliminary evidence that other chemical 

species, such as sulfate, may contribute to 

microbial degradation of petroleum contaminants at this site.

REFERENCES CITED

Atlas, R.M, 1993, Handbook of microbiological media: 

Boca Raton, Florida, CRC Press, 1,079 p.

Brown, E.J., and Braddock, J.F., 1990, Sheen Screen, a 

miniaturized most probable number method for 

enumeration of oil-degrading microorganisms: 

Applied and Environmental Microbiology, v. 56, 

p. 3,895-3,896.

Bradley, P.M., and Chapelle, F.H., 1995, Rapid toluene 

mineralization by aquifer microorganisms at Adak, 

Alaska: implications for intrinsic bioremediation in 

cold environments: Environmental Science and 

Technology, v. 29, p. 2,778-2,781.

Summary 9
Brown, E.J., Resnick, S.M., Rebstock, C., Luong, H.V., 

and Lindstrom, J., 1991, UAF radiorespirometric 

protocol for assessing hydrocarbon mineralization 

potential in environmental samples: Biodegradation, v. 2, p. 121-127.

Collins C.H., Lyne, P.M., and Grange, J.M., 1989, 

Microbiological methods (6th ed.): London, Butterworths, 409 p.

Kriegler, A.T., and Lilly, M.R., 1995, Water-elevation, 

stream-discharge, and ground-water quality data in 

the Alaska Railroad Industrial area, Fairbanks, 

Alaska, May 1993 to May 1995: U.S. Geological 

Survey Open-File Report 95-364, 247 p. + plate.

Lilly, M.R., McCarthy, K.A., Kriegler, A.T., Vohden, 

James, and Burno, G.E., 1996, Compilation and 

preliminary interpretations of hydrologic and 

water-quality data from the Railroad Industrial 

Area, Fairbanks, Alaska, 1993-94: U.S. Geological 

Survey Water-Resources Investigations Report 

96-4049, 45 p. + appendixes and plate.

National Research Council, 1993, In situ bioremediation: 

When does it work?: Washington, D.C., National 

Academy Press, 207 p.

10 Assessment of the Potential for Biodegradation of Petroleum Hydrocarbons in the 

Railroad Industrial Area, Fairbanks, Alaska, 1993-94

 ft- U.S. GOVERNMENT PRINTING OFFICE: 1998 689-341 / 44006 Region No. 10