BIODEGRADABILITY OF HYDROCARBON CONTAMINANTS DURING NATURAL ATTENUATION OF CONTAMINATED GROUNDWATER DETERMINED USING BIOLOGICAL AND CHEMICAL OXYGEN DEMAND

A Master’s Thesis Presented to the Faculty of California Polytechnic State University San Luis Obispo

In partial fulfillment of the requirements for the degree of Master of Science in Civil and Environmental Engineering

By Evan B. Larson February 2004

COPYRIGHT OF MASTER’S THESIS

I grant permission for the reproduction of this thesis in its entirety or any of its parts, without further authorization from me, provided it is referenced appropriately.

Evan Larson

Date

ii

MASTER’S THESIS APPROVAL

TITLE:

BIODEGRADABILITY OF HYDROCARBON CONTAMINANTS DURING NATURAL ATTENUATION OF CONTAMINATED GROUNDWATER DETERMINED USING BIOLOGICAL AND CHEMICAL OXYGEN DEMAND

AUTHOR:

EVAN B. LARSON

DATE SUBMITTED:

FEBRUARY 2004

THESIS COMMITTEE MEMBERS:

Dr. Yarrow Nelson

Date

Dr. Nirupam Pal

Date

Dr. Christopher Kitts

Date

iii

ABSTRACT BIODEGRADABILITY OF HYDROCARBON CONTAMINANTS DURING NATURAL ATTENUATION OF CONTAMINATED GROUNDWATER DETERMINED USING BIOLOGICAL AND CHEMICAL OXYGEN DEMAND Evan Larson Natural attenuation is being evaluated as a possible method of remediation of hydrocarbon contamination at the Guadalupe Restoration Project (GRP) at a former oil field on the Central Coast of California. The site is contaminated with hydrocarbons in the C10 to C30 range, which were used as a diluent to facilitate oil extraction. The GRP is located in an ecologically sensitive coastal area and thus it is important to remediate the hydrocarbon contamination with minimal disturbance. Natural attenuation is the microbial degradation and weathering of a contaminant, and interest has grown throughout the environmental community in its application over the past decade. To explore the feasibility of using natural attenuation at the GRP, a series of experiments were conducted to determine the biodegradation rates of total petroleum hydrocarbon (TPH) in groundwater from the site; and to evaluate the sustainability of biodegradation with weathering. In order for natural attenuation to be sustainable at this site, it is important that the hydrocarbons remain biodegradable as they are weathered. To test for this sustainability, biodegradability was determined for a series of groundwater samples, which had weathered differently. Biodegradability was measured as the ratio of biological oxygen demand (BOD) to chemical oxygen demand (COD). BOD/COD ratios were measured for diluentcontaminated groundwater from monitoring wells C8-39, G4-3, 206-C, 209-D, 209-E, H37, H2-1 and M4-4. The TPH concentrations ranged from 4.2 ppm to 29 ppm. Sampling was originally planned along the transect of a single plume to observe biodegradation patterns along the transect as the hydrocarbons presumably become more weathered downgradient. Due to constraints concerning the nesting pattern of the Western Snowy Plover, this method of sampling was abandoned. As a surrogate method of collecting samples with varying degrees of hydrocarbon weathering, the series of monitoring wells listed above were used to provide a range of TPH concentrations, and wells with low TPH concentrations far from source zones were presumed to be more weathered. The range of BOD/COD values for these groundwater samples were 0.01 to 0.09, suggesting slow biodegradation. BOD/COD did not correlate with TPH concentration (R2 = 0.03). BOD/COD ratios did not significantly change with increasing TPH concentration, suggesting weathering did not significantly influence biodegradability. BOD/COD ratios decreased with distance from source, indicating the possibility of decreased biodegradability with increased weathering and a variation in diluent chemistry. COD correlated with TPH values fairly well with an R2 value of 0.74. BOD had a very weak correlation with TPH concentration (R2 = 0.41). The average COD/TPH value was 18.1. This COD/TPH ratio is approximately five times the expected theoretical oxygen demand (ThOD) of hydrocarbons of 3.5. This high value may be attributed to the presence of other oxidizable organics. BOD/COD ratios approaching the value of 0.4 have been reported for biodegradable material. However, the low BOD/COD ratios observed in this research were most likely because of slow biological degradation leading to low 5-day BOD values.

iv

ACKNOWLEDGEMENTS

I would like to thank my friends and family for their patience and support as they waited for this day to arrive.

Also, I would like to give a special thanks to Unocal for their support and funding of research at Cal Poly.

Finally, I must thank Dr. Yarrow Nelson for his guidance, patience and insight. It was a pleasure to be around his upbeat attitude, refreshing sense of humor and great personality.

v

TABLE OF CONTENTS List of Tables .......................................................................................................................x List of Figures .................................................................................................................... xi 1

INTRODUCTION .........................................................................................................1

2

PROJECT SCOPE .........................................................................................................4

3 BACKGROUND ...........................................................................................................5 3.1

Former Guadalupe Oil Field .................................................................................5

3.2

Natural Attenuation as a Treatment Technology ..................................................9 3.2.1

Biodegradation........................................................................................11

3.2.2

Dilution/ Dispersion................................................................................12

3.2.3

Volatilization...........................................................................................12

3.2.4

Adsorption...............................................................................................13

3.3

Advantages of Natural Attenuation ....................................................................13

3.4

Limitations of Natural Attenuation.....................................................................14

3.5

Site Criteria .........................................................................................................15

3.6

Determination of Contaminant Biodegradability................................................15

3.7

Biochemical Oxygen Demand ............................................................................16

3.8

Chemical Oxygen Demand .................................................................................17

3.9

Chemistry of Diluent Contamination at the Guadalupe Site ..............................17

3.10 Cal Poly Natural Attenuation Project .................................................................20 4 MATERIALS AND METHODS.................................................................................21 4.1

Groundwater Sampling .......................................................................................21

4.2

BOD Measurement .............................................................................................21 4.2.1

BOD Inoculum........................................................................................22

4.3

4.2.2

Dilution Water ........................................................................................24

4.2.3

Nitrification Inhibitor..............................................................................25

4.2.4

Dissolved Oxygen Measurement ............................................................26

4.2.5

BOD Incubation ......................................................................................27

4.2.6

Fe Effects on BOD..................................................................................28

4.2.7

Dilution Effects on BOD ........................................................................28

COD Measurement .............................................................................................29 4.3.1

COD Calibration ....................................................................................30

4.3.2

Measurement of Iron Oxidation Effects on COD ...................................30

4.3.3

COD Measurements of Groundwater Series...........................................31

4.3.4

UV/Vis Spectrophotometer Analysis......................................................31

4.3.5 COD of Phenol Solutions........................................................................34 5

RESULTS ....................................................................................................................35 5.1 BOD Results .......................................................................................................35 5.1.1

Preliminary BOD Measurements and Effect of Iron Oxidation on BOD Measurements ..................................................35

5.1.2

Preliminary BOD Method Testing: Dilution Effects (6-day BOD)........38

5.1.3

Preliminary 20-day BOD Test for BOD Method....................................41

5.1.4

Dilution Effects and BOD Analysis of Several Groundwater Samples..42

5.1.5

Repeat BOD Analysis of Diluent-Contaminated Groundwater Samples.............................................................................49

5.2 COD Results .......................................................................................................52 5.2.1

Iron Oxidation Effects on COD Measurement and Dilution Effects......52

5.2.2

COD of Groundwater Series...................................................................54 vii

5.2.3

Repeat COD Series Testing ....................................................................55

5.3 Final Compilation of BOD, COD and TPH Data ...............................................56 5.3.1 Correlation of COD with TPH................................................................59 5.3.2 Correlation of BOD with TPH................................................................59 5.3.3 6

BOD/COD Ratio - Biodegradability.......................................................61

DISCUSSION ..............................................................................................................65 6.1

Reliability of BOD Tests ....................................................................................65

6.2

Effect of Iron on BOD ........................................................................................66

6.3

Effect of Dilution ................................................................................................67 6.3.1 Effect of Dilution on BOD Measurement...............................................67 6.3.2 Effect of Dilution on COD Measurement...............................................68

6.4

Reliability of COD Tests ....................................................................................68

6.5

Biodegradability..................................................................................................69

6.6

ThOD of Hydrocarbons ......................................................................................70

7 CONCLUSIONS..........................................................................................................75 8

RECOMMEDATIONS................................................................................................76

REFERENCES ..................................................................................................................77

viii

LIST OF TABLES Table 3.1 Summary of separate-phase diluent analysis .......................................................19 Table 3.2 Summary of dissolved-phase diluent analysis .....................................................20 Table 5.1 BOD results and statistics for method development............................................37 Table 5.2 BOD results for 6-day test with single groundwater sample (fresh C8-39, 8-12 ppm) ......................................................................................40 Table 5.3 BOD results for 20-day test with single groundwater sample (fresh C8-39, 8-12 ppm) ......................................................................................43 Table 5.4 BOD5 data for BOD method testing on series of groundwater samples..............47 Table 5.5 BOD data for BOD5 repeat analysis of oxygen depleted samples.......................50 Table 5.6 Iron oxidation COD data......................................................................................53 Table 5.7 Data for COD of groundwater series ...................................................................54 Table 5.8 Repeat COD analysis of groundwater series using 20-900 mg/L vials ...............55 Table 5.9 Comparison of high and low range COD tests ....................................................56 Table 5.10 Final results of COD, BOD and calculated BOD/COD ratios for groundwater series................................................................................59 Table 6.1 COD of phenol solutions .....................................................................................73

ix

LIST OF FIGURES Figure 3.1 Guadalupe site map ............................................................................................5 Figure 3.2 Aerial view of Guadalupe site ............................................................................6 Figure 3.3 Guadalupe plume map........................................................................................7 Figure 3.4 Carbon ranges for common diluent constituents................................................19 Figure 4.1 BOD analysis setup: DO meter, probe and BOD bottle.....................................26 Figure 4.2 Absorbance vs. COD of KHP standards, 5-150 mg/L range..............................32 Figure 4.3 Absorbance vs. COD of KHP standards, 20-900 mg/L range............................33 Figure 5.1 Iron effect on BOD5 ...........................................................................................36 Figure 5.2 Effects of dilution and inoculum volume on the BOD6 of contaminated groundwater (C8-39, 8-12 ppm).............................................41 Figure 5.3 Guadalupe Restoration Project, Diluent Tanks area ..........................................44 Figure 5.4 Detail of sampled monitoring well locations .....................................................45 Figure 5.5 Effect of sample dilution on BOD5 determination for several Groundwater samples .........................................................................................48 Figure 5.6 Effect of iron oxidation on COD measured........................................................53 Figure 5.7 COD vs. TPH plot for series of groundwater samples .......................................59 Figure 5.8 BOD vs. TPH plot for series of groundwater samples .......................................61 Figure 5.9 BOD/COD vs. TPH plot for series of groundwater samples .............................62 Figure 5.10 BOD/COD vs. distance down plume from source plot for series of groundwater samples grouped by location ..........................................64 Figure 6.1 COD vs. phenol concentration for standard phenol solutions............................74

x

CHAPTER 1 INTRODUCTION A grant from Unocal has enabled Cal Poly to perform research on various remediation methods for the former Guadalupe Oil Field, now known as the Guadalupe Restoration Project (GRP). A kerosene-like substance was previously used as a diluent for facilitating the extraction of crude oil at this site.

Leaky pipes and tanks caused significant hydrocarbon

contamination.

The research goal is to find better ways of treating the

diluent contaminated soil and groundwater.

Natural attenuation is the microbial degradation and weathering of a contaminant and its application at the Guadalupe Site is the focus of this research. The goal of this project is to determine if hydrocarbons become recalcitrant after a certain amount of biodegradation and to find any trend in biodegradability with weathering of hydrocarbons in the groundwater. These questions were addressed by evaluating the current and long-term biodegradability of DPD (dissolved phase diluent) in the groundwater at the

Guadalupe

site.

Biodegradability

of

DPD

was

measured

by

determining the ratio of 5-day biological oxygen demand (BOD 5 ) to chemical oxygen demand (COD). This BOD/COD ratio has been reported as a measure of biodegradability in a number of projects (Gilbert 1987, Alvares et al., 2001 a , b , Imai et al., 1998, Mantzavinos et al., 1996 & 2001,

1

Koch et al., 2002, Kumar et al., 1998, Geenens et al., 2000, Chun and Yizhong, 1999).

The Guadalupe Restoration Project has to consider the presence of several endangered species, which makes the use of natural attenuation attractive. The presence of ecological receptors such as the Red Legged Frog and the Western Snowy Plover raises some concern.

Samples of groundwater taken with different DPD concentrations serve as surrogates for the aging of DPD over time, since low concentrations are probably farther from the source zone.

The contaminant concentration

should decrease as the contaminant is broken down by various means over time, discussed in further detail in Section 3.2. remains

similar

throughout

the

range

of

A BOD/COD ratio that

concentrations

would

be

considered good evidence for sustained biodegradability.

There

are

several

factors

that

could

ultimately

limit

long-term

biodegradation, including nutrient and/or electron acceptor availability and changes in chemical composition of the hydrocarbon mixture. Biodegradation patterns and nutrient availability can fluctuate over the long term.

Sometimes levels of contaminant can appear to fall within

desired limits for a period, then suddenly spike again (Leeson and Hinchee, 1997).

Contaminants can sorb to particles in the geo-matrix,

2

which can limit the bioavailability of the contaminants (USEPA, 199 b ). Biodegradation

may

reduce

the

surface

particles, leading to a lack of nutrients.

contamination on

the

soil

The microbial population may

then subside (Leeson and Hinchee, 1997). Once the surface contamination is gone, the contaminant from interstitial spaces and pores may migrate out of the matrix, leading to a new spike in measurable contaminant concentration.

Preliminary tests on the BOD and COD methods were performed to insure iron oxidation was not a source of significant interference, and dilution was varied to test the use of appropriate strength inoculum and the possibility of dilution affecting BOD measurements.

As a control,

dilution water blanks containing no hydrocarbons were used.

After preliminary testing of the BOD and COD methods, BOD and COD were measured for groundwater samples from a series of 7 monitoring wells.

BOD/COD ratios were calculated to examine any trends in

biodegradability with TPH concentration.

3

CHAPTER 2 PROJECT SCOPE The specific objectives of this project included: 1. Measure the BOD/COD ratio as an indication of biodegradability of TPH in groundwater samples taken from a transect down-plume of diluent contamination. 2. Determine the sensitivity of the BOD analysis. 3. Conduct preliminary tests to optimize the BOD and COD analyses. 4. Determine the suitability of the inoculum for BOD tests in terms of kinetics of BOD exertion (i.e. is sufficient oxygen consumed in 5days from the samples). 5. Determine if Fe(II) will significantly contribute to BOD or COD.

4

CHAPTER 3 BACKGROUND 3.1 Former Guadalupe Oil Field The Guadalupe Restoration Project (GRP) is located on the Central Coast of California, northwest of the city of Guadalupe and along the southern edge of San Luis Obispo County (Figure 3.1).

The site was previously

called the Guadalupe Oil Field (GOF) and was in operation from the late 1940's through the mid 1990's.

Figure 3.1: Guadalupe site map.

5

Figure 3.2 Aerial view of Guadalupe site.

6

Not to scale Figure 3.3 Guadalupe plume map.

7

Unocal purchased the outstanding share of the GOF in 1953, and became the operator (GRP, 2002). over 2700 acres of land.

The former Guadalupe Oil Field consists of The dunes lie between the Pacific Ocean, the

Santa Maria River, and privately owned agricultural land.

The majority

of the oil field lies in San Luis Obispo County but a southeastern portion lies in northern Santa Barbara County.

It is one of the last intact dune

ecosystems in the state of California and is home to a variety of threatened and endangered species (GRP, 2002).

Diluent (a diesel or kerosene-like substance) was used as a thinning agent during active production, to help the viscous crude oil flow through the pipes and aid in the on-site crude oil extraction.

The soil and

groundwater became significantly contaminated with diluent from a series of spills and leaks from the storage tanks and transmission pipes that went unreported and untreated. As a result, contaminant plumes developed in over eighty sites at the Guadalupe Oil Field.

For a few days in 1988 and again in early 1990, following storm events, diluent began to appear on the beach and it became clear that the diluent was a threat to surrounding waters and the surrounding ecosystem (GRP, 2002).

The last use of diluent was in 1990.

In the following years the

Guadalupe Oil Field ceased operation and the Guadalupe Restoration Project arose.

8

3.2 Natural Attenuation as a Treatment Technology Natural attenuation processes include a variety of physical, chemical, or biological processes that, under favorable conditions, act without human intervention

to

reduce

the

mass,

toxicity,

mobility,

volume

or

concentration of contaminants in soil or groundwater (USEPA, 1999 b ). It can be more aesthetically attractive than having above ground treatment systems and could be less disruptive to the terrestrial ecosystem. Natural attenuation

can

be

a

cost

effective

alternative

as

long

as

the

contamination is in low to moderate levels. Highly contaminated sources should be removed by some method such as free product recovery, bioventing, or soil vapor extraction prior to use of natural attenuation (USEPA, 2003).

To take advantage of using natural attenuation, the effectiveness must be confirmed in order to validate its use for remediation. Criteria for the site must be evaluated for suitability for natural attenuation.

If the site is

suitable, methods of tracking the progress of natural attenuation must be implemented.

Also, such criteria as the ability to remove or neutralize

contaminants and time effectiveness need to be evaluated.

To document natural processes reducing contaminant concentrations, several lines of evidence may be required. Historical trends of decreasing contaminant concentrations are one line of evidence. Another is to have a

9

retreating or stable plume, possibly indicating microorganisms are removing dissolved contaminants from groundwater at a rate greater than or equal to the rate at which the source is adding them.

Natural

biodegradation can leave chemical indicators, also known as footprints. Documenting such chemical indicators is another way to exemplify the occurrence of natural attenuation.

Indicators include changes in water

chemistry left by the attenuation reactions as well as intermediates. Biodegradation

of

contaminants

is

directly

related

to

changes

in

groundwater chemistry such as the biological consumption of natural levels of oxygen, nitrate, and sulfate and the creation of byproducts such as dissolved iron (II), manganese (II), and methane (USEPA, 2003). For example, biodegradation of toluene by aerobic bacteria consumes oxygen from the groundwater and adds inorganic carbon as the toluene is converted

to

carbon

dioxide.

Once

such

reactions

are

postulated,

monitoring is necessary to show that the attenuation processes continue (Macdonald, 2000). Geochemical indicators can also be used to estimate the

site-specific

potential

for

biodegradation (USEPA, 2003).

contaminants

to

be

destroyed

by

Formation of intermediates (eg. TCE,

DCE, vinyl chloride) and laboratory treatability tests are other means of proving biodegradation (Macdonald, 2000).

Most contaminants can degrade or transform by a number of different mechanisms, depending on site conditions, and often many different

10

mechanisms act in concert.

For example, the initial stages of benzene

biodegradation often consume all of the oxygen in the groundwater; so later stages proceed by different biotransformation pathways. As a consequence, the search for footprints of natural attenuation must consider the unique conditions of the site (Macdonald, 2000).

Depending on the contaminant type and site-specific characteristics, breakdown or removal of contaminants through natural attenuation occurs by different mechanisms and biotransformation pathways. The four main processes of natural attenuation include biodegradation, dilution, sorption and volatilization (USEPA, 2001).

A description of each mechanism is

given in the following sections.

3.2.1 Biodegradation One

of

the

most

important

components

of

natural

attenuation

is

biodegradation, the change in form of compounds carried out by living creatures

such

as

microorganisms.

Biodegradation

of

petroleum

compounds occurs when they serve as the primary source of food and energy to naturally occurring soil and groundwater bacteria (USEPA, 1999b). Under the right conditions, microorganisms can cause or assist chemical reactions that change the form of the contaminants so that little or no health risk remains. Biodegradation is important because many important components of petroleum hydrocarbon contamination can be destroyed by

11

biodegradation,

biodegrading

microorganisms

are

found

almost

everywhere, and biodegradation can be very safe and effective (USEPA, 1999 a ).

3.2.2 Dilution/ Dispersion Contaminants will mix with soil and groundwater as seasons change and groundwater levels rise and fall. As the dissolved contaminants mix and move farther away from the source area, the contaminants are dispersed and diluted to lower and lower concentrations over time. Eventually the contaminant concentrations may be reduced so much that the risk to human and environmental health will be minimal (USEPA, 1999 b ). process

of

dilution

and/or

dispersion

alone

does

not

The

destroy

a

contaminant.

3.2.3 Volatilization Many petroleum hydrocarbons evaporate readily into the atmosphere, where air currents disperse the contaminants, reducing the concentration. In some cases, this means of natural attenuation may be useful, since some contaminants can be broken down by sunlight (USEPA, 1999b). Vapors in contact with soil microorganisms may also be biodegraded in the vadose zone (USEPA, 1999 a ).

12

3.2.4 Adsorption Many contaminants are prevented from entering the groundwater and migrating off-site, due to adsorption onto soil particles (USEPA, 2003). The soil and sediment particles through which the groundwater and dissolved contaminants move can sorb the contaminant molecules onto the particle surfaces, and hold bulk liquids in the pores in and between the particles, thereby slowing or stopping the movement of the contaminants. This process can reduce the likelihood that the contaminants will reach a location where they would directly affect human or environmental health (USEPA, 1999 b ).

3.3 Advantages of Natural Attenuation Some of the inherent advantages of natural attenuation include generation of lesser volume of remediation wastes, reduced potential for cross-media transfer of contaminants commonly associated with ex situ treatment, and reduced risk of human exposure to contaminants, contaminated media, and other hazards, and reduced disturbances to ecological receptors (USEPA, 1999a). Natural attenuation can be used in conjunction with or as a follow up to more active remedial measures (USEPA, 1999a).

Some other

advantages include having a lower degree of intrusion with fewer surface structures, a potential for the application to all or part of a given site, depending on site conditions and remediation objectives (USEPA, 1999b). It

13

also offers potentially lower overall remediation costs than those associated with active remediation (USEPA, 1999b).

3.4 Limitations of Natural Attenuation The use of natural attenuation may require more time than active methods to achieve cleanup goals, and thus may require a long-term commitment to monitoring and associated costs (USEPA, 2003). In some cases, if natural attenuation rates are too slow, the plume could continue to migrate, which can lead to the required use of land and groundwater controls (USEPA, 2003).

Site characterization is expected to be more complex and costly

than other active methods (USEPA, 1999 b ).

Inhibitory compounds may

result from incomplete biodegradation, giving rise to by-products or intermediates more toxic than the original compound (Alvares et al, 2001 a ).

In addition to toxicity, the mobility of transformation products

may exceed that of the parent compound (USEPA, 1999 b ).

Hydrologic

and geochemical conditions amenable to natural attenuation may change over time and could result in renewed mobility of previously stabilized contaminants, adversely influencing remedial effectiveness (USEPA, 1999 b ). Natural attenuation is not appropriate for high concentrations of contaminant, due to toxicity factors (USEPA, 1999 b ).

If there is a high

contaminant concentration, natural attenuation is commonly used in conjunction with an active method.

14

3.5 Site Criteria Considering environmental receptors is only one of the many factors involved in determining if a petroleum hydrocarbon contaminated site is a candidate for using natural attenuation as a remedial method.

Location

should be of primary concern and be in an area with little risk to human health or the environment from direct contact with contaminated soil or groundwater.

The contaminated soil and groundwater should also be

located an adequate distance from potential receptors.

This exemplifies

the importance of having a good conceptual model of the site. Every site needs at least a simple model showing groundwater flow, contaminant locations and concentrations, and possible natural attenuation reactions. (Macdonald, 2000)

3.6 Determination of Contaminant Biodegradability The evaluation of biodegradability of organic compounds in aqueous medium can be performed by many options including shake-flask batch tests

measuring

biogas

production,

activated

sludge

simulation,

biochemical oxygen demand (BOD), static test (Zahn-Wellens method), respirometry, dissolved organic carbon (DOC), total organic carbon (TOC), chemical oxygen demand (COD), metabolism and identification of transformation products (ISO, 2003).

The ratio of BOD/COD has also

been used as a measure of biodegradability. The BOD/COD ratio gives a gross index of the proportion of the organic materials present which are aerobically degradable within a certain period of time, e.g. 5 days for 15

BOD 5 (Mantzavinos et al., 1996).

BOD is a measure of the oxidation

occurring due to microbial activity while COD measures the highest extent of oxidation a material may undergo. Details of BOD and COD are given in the following two sections.

The BOD 5 /COD and BOD 5 /TOC ratios are commonly used indicators of biodegradability

improvement,

where

a

value

of

zero

indicates

nonbiodegradability and an increase in the ratio reflects biodegradability improvement (Alvares et al, 2001 b ). Low BOD 5 /COD values (usually less than 0.1) indicate their resistance to conventional biological treatment (Koch et al., 2002, Imai et al., 1998).

Chun and Yizhong studied

photocatalytically treated wastewater contaminated with azo dyes from the processing of wool.

They found when the ratio of BOD 5 /COD was

more than 0.3 the wastewater had a better biodegradability. statements

were

made

for

a

BOD 5 /COD

ratio

of

0.4

Similar using

nonbiodegradable substituted aromatic compounds (Gilbert, 1987).

3.7 Biochemical Oxygen Demand Biochemical oxygen demand (BOD) is defined as the amount of oxygen required by bacteria while stabilizing decomposable organic matter under aerobic conditions (Sawyer and McCarty, 1978).

It is a test applied to

measure the amount of biologically oxidizable organic matter present and determining the rates at which oxidation will occur or BOD will be

16

exerted (Sawyer and McCarty, 1978).

In order to make the test

quantitative, the samples must be placed in an airtight container and kept in a controlled environment for a preselected period of time.

In the

standard test, a 300-mL BOD bottle is used and the sample is incubated at 20°C for five days (Peavy et al., 1985). The BOD is then calculated from the initial and final dissolved oxygen (DO) concentration.

3.8 Chemical Oxygen Demand The chemical oxygen demand (COD) test is used to measure the total organic

content

wastewaters.

of

industrial

wastes

and

municipal

and

natural

During the determination of COD, organic matter is

converted to carbon dioxide and water using a strong chemical oxidizing agent (dichromate) in the presence of a catalyst and strong acid. In the COD test, organic materials are oxidized regardless of the biological assimilability of the substances. As a result, COD values are greater than BOD values and may be much greater when significant amounts of biologically resistant organic matter are present (Sawyer and McCarty, 1978).

3.9 Chemistry of Diluent Contamination at the Guadalupe Site Diluent from the Guadalupe Restoration Project is a hydrocarbon consortium with a carbon range of nC 1 0 to nC 3 0 .

Figure 3.3 shows

common fuel ranges with respect to carbon length.

According to this

17

chart, the diluent at Guadalupe is essentially a diesel range oil (DRO). Water solubility plays an important role when considering the fate of diluent constituents. Constituents with low solubility exist as a separateproduct, whereas diluent chemicals with a high solubility generally are dissolved in the groundwater. A majority of the diluent at the Guadalupe Oil Field has low solubility.

Diluent from Guadalupe has a reported

solubility of 30 mg/L (Haddad and Stout, 1996). The diluent composition over the Guadalupe site is considerably variable.

The difference in

diluent makeup can be explained by source oil variation and weathering (Barron and Podrabsky, 1999).

Haddad and Stout made the following conclusions on the diluent chemistry: •

The carbon length of the diluent ranges from C 3 0 .

About

70% of the diluent falls in the diesel range of nC 1 0 to nC 2 5 . •

Saturated, aromatic, polar, and asphaltic fractions respectively make up 60%, 17%, 8%, and 15% of the separate-phase diluent.

The

dissolved-phase fractions were not available for review.

Haddad and Stout (1996) also reported the total petroleum hydrocarbon (TPH) composition as well as the BTEX concentrations (Table 3.1 and 3.2).

18

C6

C10

C4

Measurable TPH

Semi-quantifiable C24

C6 C4

Gasoline C8

C12

Kerosene

C8

C36

C17

Diesel

C24

C12

C24-30

Fuel Oils C20

Lube Oils & heavier C36

Boiling Point Range

140 F

340 F

340 F

340 F

140 F

170 C

170 C

170 C

Gasoline Range

C6

C10 Diesel Range C10

REFERENCE: TPH IN SOIL PRIMER, ELAINE M. SCHWERKO. DATED: 09/01/93

Non-measurable TPH due to volatilization

Figure 3.4 Carbon ranges for common diluent constituents compared to common petroleum distillates (Elliot, 2002).

Table 3.1 Summary of separate-phase diluent analysis. Constituent Concentration Range (mg/kg) Benzene 14.06 > 14.25 > 14.02 > 13.64 > 13.95 > 13.97 0.56 0.56 0.53 0.72 0.70 0.68 577.5 577.5 585.0 588.0 0.41 0.46 0.49

Ave. BOD20 (mg/L)

BOD20 SD (mg/L)

> 4.38

0.10

> 4.78

0.18

> 14.11

0.12

> 13.85

0.18

0.55

0.02

0.70

0.02

577.5

0.00

586.5

2.12

0.45

0.04

Not to scale Figure 5.3 Guadalupe Restoration Project, Diluent Tanks area (Lundegard, 2002).

44

Figure 5.4 Detail of sampled monitoring well locations (Lundegard, 2002).

45

BOD 5 values were obtained for the seven groundwater samples, with some diluted samples (Table 5.4). Virtually all oxygen was depleted in samples from wells 206-C, 209-E and M4-4 50%.

The BOD analyses for the

samples from wells 206-C and 209-E were therefore repeated, and results are given in Section 5.1.5. BOD measurements were not repeated for well M4-4, since two other dilutions from this testing event provided useful data. The seed control blanks had an average BOD 5 of 0.07 mg/L ± 0.02 mg/L, while the BOD standard (GGA) average was 296.3 mg/L ± 30.8 mg/L and the dilution water blanks average was 0.11 mg/L ± 0.01 mg/L.

Effects of dilution were examined using groundwater samples H3-7, H2-1 and M4-4. In all cases, BOD 5 values determined were similar regardless of dilution (Figure 5.5 and Table 5.4). H3-7 samples with a TPH concentration of 11.0 ppm had an average BOD 5 of 5.59 mg/L ± 0.60 mg/L at 25% strength and 4.75 mg/L ± 0.26 mg/L at 50% strength. The dilutions for these samples provided BOD 5 results within 15% of each other. Similarly, 25% and 50% diluted H2-1 samples had average BOD 5 values within 3% of each other and 10% and 25% diluted M4-4 samples had average BOD 5 values within 10% each other. These results show consistently that the use of dilution does not significantly affect the measured BOD 5 of the groundwater samples (Figure 5.5).

46

Table 5.4 BOD 5 data for BOD method testing on series of groundwater samples Wells 206-C, 209-E and M4-4 at 50% depleted all O 2 and are repeated later. Sample G4-3 G4-3 G4-3 206-C 206-C 206-C 209-D 209-D 209-D 209-E 209-E 209-E H3-7 H3-7 H3-7 H3-7 H3-7 H3-7 H2-1 H2-1 H2-1 H2-1 H2-1 H2-1 M4-4 M4-4 M4-4 M4-4 M4-4 M4-4 M4-4 M4-4 M4-4 Seed Ctrl. Seed Ctrl. Seed Ctrl. BOD Std. BOD Std. DW Blank DW Blank DW Blank

TPH mL Seed Sample Dilution Conc. of Vol. Vol. (%) (ppm) 100x (mL) (mL) 4.2 3 -10 287 4.2 3 -10 287 4.2 3 -10 287 5.7 3 -10 287 5.7 3 -10 287 5.7 3 -10 287 7.5 3 -10 287 7.5 3 -10 287 7.5 3 -10 287 8.2 3 -10 287 8.2 3 -10 287 8.2 3 -10 287 11.0 0.75 25 10 72.31 11.0 0.75 25 10 72.31 11.0 0.75 25 10 72.31 11.0 1.5 50 10 144.25 11.0 1.5 50 10 144.25 11.0 1.5 50 10 144.25 13.0 0.75 25 10 72.31 13.0 0.75 25 10 72.31 13.0 0.75 25 10 72.31 13.0 1.5 50 10 144.25 13.0 1.5 50 10 144.25 13.0 1.5 50 10 144.25 29.0 0.3 10 10 28.97 29.0 0.3 10 10 28.97 29.0 0.3 10 10 28.97 29.0 0.75 25 10 72.31 29.0 0.75 25 10 72.31 29.0 0.75 25 10 72.31 29.0 1.5 50 10 144.25 29.0 1.5 50 10 144.25 29.0 1.5 50 10 144.25 ---10 290 ---10 290 ---10 290 ---10 2 ---10 2 ----300 ----300 ----300

Dilution (P-value) 0.957 0.957 0.957 0.957 0.957 0.957 0.957 0.957 0.957 0.957 0.957 0.957 0.241 0.241 0.241 0.481 0.481 0.481 0.241 0.241 0.241 0.481 0.481 0.481 0.097 0.097 0.097 0.241 0.241 0.241 0.481 0.481 0.481 0.967 0.967 0.967 0.007 0.007 1.000 1.000 1.000

BOD5 D.O. D.O. initial final values (mg/L) (mg/L) (mg/L) 9.90 6.57 3.55 9.92 7.06 3.06 9.82 6.35 3.70 7.83 0.30 > 7.94 7.78 2.24 > 5.86 7.67 0.87 > 7.18 8.79 6.88 2.07 8.85 6.89 2.12 8.84 6.94 2.06 8.56 0.05 > 8.96 8.55 0.06 > 8.94 8.56 0.06 > 8.95 8.14 6.63 > 6.33 8.15 6.91 > 5.21 8.15 6.86 > 5.42 8.01 5.87 4.52 8.06 5.68 5.02 8.07 5.74 4.91 7.86 5.94 8.03 7.94 6.55 5.84 7.94 6.39 6.50 7.54 4.46 6.47 7.58 4.57 6.33 7.59 4.25 7.02 8.19 6.79 14.57 8.19 6.82 14.26 8.20 6.82 14.36 7.81 3.92 16.21 7.81 4.12 15.38 7.85 4.10 15.63 6.92 0.04 > 14.38 6.92 0.04 > 14.38 6.96 0.06 > 14.42 8.34 8.40 -0.06 8.35 8.44 -0.09 8.35 8.40 -0.05 8.41 6.29 318.0 8.43 6.60 274.5 8.70 8.59 0.11 8.72 8.61 0.11 8.72 8.60 0.12

Ave. BOD5 (mg/L)

BOD5 SD (mg/L)

3.43

0.33

> 6.99

1.05

2.08

0.03

> 8.95

0.01

5.66

0.60

4.82

0.26

6.79

1.13

6.61

0.36

14.39

0.16

15.74

0.43

> 14.39

0.02

-0.07

0.02

296.3

30.8

0.11

0.01

*** mL of 100x is for ino cu lu m/nu tr ien t add ition

47

18

25% 16

10%

50%

14

Average BOD5 (mg/L)

12

10

FS FS

25%

8

50% 25% 6

50% FS

4

FS 2

0 G4-3

206-C

209-D

209-E

H3-7

H3-7

H2-1

H2-1

M4-4

M4-4

M4-4

Figure 5.5 Effect of sample dilution on BOD 5 determination for several groundwater samples. Error bars indicate ± 1 standard deviaton. 48

5.1.5 Repeat BOD Analysis of Diluent-Contaminated Groundwater Samples Some bottles previously ran out of oxygen and testing was repeated here, with more dilution. The groundwater samples retested were 209-E and 206-C. This test obtained better values of BOD 5 through dilution (Table 5.5). Seed control blanks and BOD 5 standard samples (GGA) performed as expected. The dilution water blanks had an average BOD 5 of -0.09 mg/L ± 0.03 mg/L (Table 5.5).

49

Table 5.5 BOD data for BOD 5 repeat analysis of oxygen depleted samples 209-E and 206-C. For well 206-C, one BOD 5 value was nearly two standard deviations off.

Sample

TPH Conc. (ppm)

mL of 100x

Dilution (%)

209-E 209-E 209-E 206-C 206-C 206-C Seed Ctrl. Seed Ctrl. Seed Ctrl. BOD Std. BOD Std. DW Blank DW Blank DW Blank

8.2 8.2 8.2 5.7 5.7 5.7 -------------------------

1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 3 3 ----------

50 50 50 50 50 50 -------------------------

BOD5 Seed Sample DO DO Dilution Vol. Vol. initial final values (P-value) (mL) (mL) (mg/L) (mg/L) (mg/L) 10 144.25 0.481 8.32 1.95 12.14 10 144.25 0.481 8.32 1.50 13.08 10 144.25 0.481 8.28 1.23 13.56 10 144.25 0.481 7.19 2.95 7.71 10 144.25 0.481 8.03 2.88 9.61 10 144.25 0.481 8.06 2.81 9.82 10 290 0.967 8.34 7.26 1.12 10 290 0.967 8.37 7.24 1.17 10 290 0.967 8.35 7.36 1.02 10 2 0.007 8.35 5.62 409.5 10 2 0.007 8.34 5.63 406.5 ---300 1.000 8.53 8.66 -0.13 ---300 1.000 8.53 8.61 -0.08 ---300 1.000 8.53 8.60 -0.07

50

Avg. BOD5 BOD5 SD (mg/L) (mg/L) 12.93

0.72

9.71

1.16

1.10

0.07

408

2

-0.09

0.03

5.2 COD Results 5.2.1 Iron Oxidation Effects on COD Measurement and Dilution Effects The aged 2 ppm TPH groundwater sample with Fe 2 + added [40 mg/L FeSO 4 ] exhibited an average COD value of 34.50 ± 0.82 mg/L, while the same groundwater sample without Fe 2 + added had an average COD value of 35.98 ± 1.49 mg/L (Table 5.6 and Figure 5.6).

These values are within experimental

error, suggesting COD exerted by the oxidation of Fe 2 + to Fe 3 + is negligible.

The 50% diluted samples had an average COD value of 15.28 mg/L, with a standard deviation of 0.71 mg/L (Table 5.6).

This is approximately half the

COD value of the full strength groundwater, as expected.

The calibration curve from the KHP standards used to convert absorbance to COD yielded R 2 = 0.96 (Figure 4.2).

52

Table 5.6 Iron oxidation COD data. The last value for a blank is an outlier.

Sample 2+

FS w/Fe 2+ FS w/Fe 2+ FS w/Fe 2+ FS no Fe 2+

FS no Fe 2+ FS no Fe 50% diluted 50% diluted 50% diluted Blank Blank Blank

Absorbance at 345 nm

COD (mg/L)

0.122 0.131 0.144 0.131 0.091 0.115 0.394 0.401 0.382 0.631 0.637 0.577

35.26 34.60 33.63 34.60 37.55 35.78 15.16 14.64 16.04 1.17 0.73 5.16

Avg. COD mg/L

SD (mg/L)

34.50

0.82

35.98

1.49

15.28

0.71

0.95

0.31

40 35

COD (mg/L)

30 25 20 15 10 5

w/ Fe2+

w/o Fe2+

0 COD Samples Error bars indicate ± 1 standard deviation Figure 5.6 Effect of iron oxidation on COD measured.

53

5.2.2 COD of Groundwater Series The measured COD of the seven groundwater samples are listed in Table 5.7. COD calculations were made based on the calibration curve from KHP (Figure 4.2). The blanks had an average COD value of 7.19 mg/L ± 1.23 mg/L (Table 5.7). The COD values for wells G4-3, 206-C, 209-D and 209-E were within the range of the COD vials used (5-150 mg/L). However wells H3-7, H2-1 and M4-4 exhibited COD above this range, and so COD analyses of all samples were repeated (see next section).

Table 5.7 Data for COD of groundwater series

Sample

TPH Conc. ppm G4-3 4.2 G4-3 4.2 G4-3 4.2 206-C 5.7 206-C 5.7 206-C 5.7 209-D 7.5 209-D 7.5 209-D 7.5 209-E 8.2 209-E 8.2 209-E 8.2 H3-7 11.0 H3-7 11.0 H3-7 11.0 H2-1 13.0 H2-1 13.0 H2-1 13.0 M4-4 29.0 M4-4 29.0 M4-4 29.0 DI Blank ---DI Blank ---DI Blank ----

COD Avg. COD COD SD (mg/L) (mg/L) (mg/L) 61.8 63.5 62.6 0.85 62.6 86.0 89.4 89.1 2.98 91.9 129 126 128 1.53 128 145 144 146 2.18 148 159 157 157 2.34 155 257 252 255 2.83 257 258 258 258 0.00 258 6.48 6.48 7.19 1.23 8.60 54

5.2.3 Repeat COD Series Testing Repeat analyses for the COD of seven groundwater samples are given in Table 5.8. COD calculations were based on the calibration curve from KHP (Figure 4.3). The COD values were all within the range of the COD vials used (20-900 mg/L).

Table 5.8 Repeat COD analysis of groundwater series using 20-900 mg/L vials.

Sample

TPH (mg/L)

COD (mg/L)

G4-3 G4-3 G4-3 206-C 206-C 206-C 209-D 209-D 209-D 209-E 209-E 209-E H3-7 H3-7 H3-7 H2-1 H2-1 H2-1 M4-4 M4-4 M4-4 DI H2O DI H2O DI H2O

4.2 4.2 4.2 5.7 5.7 5.7 7.5 7.5 7.5 8.2 8.2 8.2 11.0 11.0 11.0 13.0 13.0 13.0 29.0 29.0 29.0 ----------

75.9 66.0 69.3 135.3 82.5 112.2 138.5 141.8 141.8 161.6 171.5 158.3 207.8 164.9 174.8 296.9 300.2 329.9 333.2 329.9 329.9 21.5 18.2 14.9

55

Avg.COD (mg/L)

COD SD (mg/L)

70.4

5.0

110.0

26.5

140.7

1.9

163.8

6.9

182.5

22.5

309.0

18.2

331.0

1.9

18.2

3.3

All COD data used with BOD and TPH comparisons will come from these results for consistency. These results agree well with the previous COD measurements using the 5-150 mg/L vials. Some data from samples tested with 5-150 mg/L COD vials were out of range; therefore this set of data obtained using 20-900 mg/L COD vials will be used.

Results are fairly

consistent between the separate COD testing events, except for the measurements made out of range (Table 5.9).

Table 5.9 Comparison of high and low range COD tests

Sample

TPH (mg/L)

COD (20-900 mg/L)

COD (5-150mg/L)

G4-3 206-C 209-D 209-E H3-7 H2-1 M4-4

4.2 5.7 7.5 8.2 11.0 13.0 29.0

70.4 110.0 140.7 163.8 182.5 309.0 331.0

62.6 89.1 128.1 146.0 157.2 255.4 257.7

out of range

5.3 Final Compilation of BOD, COD & TPH Data A comprehensive compilation of all BOD, COD and TPH data and calculations is given in Table 5.10.

The BOD values used in the final

analysis and calculation of biodegradability were taken from the two BOD analysis runs, which used the series of groundwater samples (Table 5.4 and Table 5.5). Some of the data from each sampling event proved to be unusable because of DO depletion and so a composite was used to

56

represent the BOD final results presented in Table 5.10.

The most

representative samples, most closely matching the guidelines specified by the APHA for BOD analysis, were used.

The COD data was obtained

using the same groundwater samples and values used for final compilation are taken from Table 5.8.

To get the standard deviation (SD) and relative standard deviation (RSD) for final BOD/COD ratios, I followed a basic procedure. I first obtained the relative standard deviations, and then multiplied the relative standard deviation by the average BOD/COD value to obtain the reported standard deviation.

When I multiplied or divided average values with their

standard deviations, I didn't simply add the standard deviations to produce the final standard deviation.

Instead, I squared the fractional standard

deviations, added them, and then took the square root of the sum to get the fractional total deviation. If I had values A +- dA, B +- dB, ... and wanted to compute X = A*B*..., the total error dX is then dX/X = sqrt( (dA/A) 2 + (dB/B) 2 +...) Note that I added the squares of the errors even when dividing the actual values. An example should make this clearer.

Assume we have the following

three values with their standard deviations •

A = 1.67 +- 0.05

•

B = 5.23 +- 0.09

•

C= 1.88 +- 0.07 57

and we want to compute X = A*B/C. The actual problem is trivial: (1.67 * 5.23)/1.88 = 4.65 To compute the standard deviation of the result, we must sum the squares of the relative errors and then take the square root. dX/4.65 = sqrt( (0.05/1.67) 2 + (0.09/5.23) 2 + (0.07/1.88) 2 ) S t o t /4.65 = sqrt(0.000896 + 0.000296 + 0.00139) S t o t /4.65 = 0.0508 S t o t = 0.236 Since we only report error to 1 significant figure, the answer to this problem would be 4.7+-0.2

58

Table 5.10 Final results of COD, BOD and calculated BOD/COD ratios for groundwater series. SD and RSD indicate standard deviation and relative standard deviation, respectively.

TPH Avg. COD COD SD COD RSD BOD BOD SD BOD RSD BOD Sample (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) COD G4-3 4.2 206-C 5.7 209-D 7.5 209-E 8.2 H3-7 11.0 H2-1 13.0 M4-4 29.0

70.4 110.0 140.7 163.8 182.5 309.0 331.0

5.04 26.46 1.90 6.87 22.45 18.17 1.90

0.07 0.24 0.01 0.04 0.12 0.06 0.01

3.4 9.7 2.1 12.9 4.8 6.6 15.7

59

0.33 1.16 0.03 0.72 0.26 0.36 0.43

0.10 0.12 0.02 0.06 0.05 0.05 0.03

0.049 0.088 0.015 0.079 0.026 0.021 0.048

BOD COD RSD 0.121 0.269 0.021 0.070 0.135 0.080 0.028

5.3.1 Correlation of COD with TPH The slope for COD vs. TPH has a value of 10.1 mg/L COD per mg/L TPH, with an R 2 value of 0.74 (Figure 5.7). This is three times the expected slope when using the approximate hydrocarbon ThOD value of 3.5 mg/L (see section 6.6). 400 H2-1

350

COD (mg/L)

300

M4-4

250 200

209-E H3-7

150

y = 10.10x + 73.33 R2 = 0.74

209-D

100 50

G4-3

206-C

0 0

5

10

15

20

25

30

TPH concentration (ppm) Figure 5.7 COD vs. TPH plot for series of groundwater samples. Error bars indicate ± 1 standard deviation.

5.3.2 Correlation of BOD with TPH Measured BOD 5 of the groundwater samples did not correlate well with TPH concentration. The slope for BOD vs. TPH has a value of 0.39 mg BOD per mg TPH, with an R 2 value of only 0.41 (Figure 5.8).

The

average BOD/TPH ratio is 0.73 ± 0.35. This ratio is much lower than the ThOD of 3.5 mg/L, but this is to be expected since the TPH is only

60

partially

biodegraded

in

5

days.

Well

209-D

has

a

very

low

biodegradation rate (Figure 5.8).

18 16

M4-4

14

209-E

BOD (mg/L)

12 10

206-C

8

H2-1 6

y = 0.39x + 3.50 2 R = 0.42

H3-7

4

G4-3

2

209-D

0 0

5

10 15 TPH concentration (ppm)

20

25

30

Figure 5.8 BOD vs. TPH plot for series of groundwater samples. Error bars indicate ± 1 standard deviation.

5.3.3 BOD/COD Ratio - Biodegradability The BOD/COD ratios were below 0.10 for all seven groundwater samples (Table 5.10 and Figure 5.9).

The slope for BOD/COD vs. TPH is

essentially flat (Figure 5.9). BOD/COD vs. TPH was plotted and has no observable correlation and a linear regression R 2 value of only 0.03 (Figure 5.9).

Biodegradability (BOD/COD values, Table 5.10) does not

61

decrease at low concentrations, corresponding to weathered material, as would be expected if partially degraded diluent was more recalcitrant than fresh diluent. Diluent does not appear to become more recalcitrant with biodegradation and/or aging (weathering).

WEATHERED

FRESH

Biodegradability (BOD/COD)

0.12 0.10

206-C

y = -0.0006x + 0.0527 2 R = 0.03

209-E

0.08 0.06

G4-3 0.04

H3-7

0.02

M4-4

209-D

H2-1

0.00 0

5

10

15

20

25

30

TPH concentration (ppm)

Figure 5.9 BOD/COD vs. TPH plot for series of groundwater samples. Error bars indicate ± 1 standard deviation.

A trend of decreasing BOD/COD ratio with increasing distance from source zone was observed for three separate plumes from the Diluent Tanks (DT) area (Figure 5.10). For the northern DT plume the BOD/COD ratio decreased by a factor of two over 200 ft, and for the southern DT plume the BOD/COD ratio decreased by a factor of six over a distance of about 650 ft.

The two wells in the central DT plume were very close

together and little difference in biodegradability was observed (Figure

62

5.10).

Although there were only two samples per plume, these results

indicate the possibility of decreased biodegradability with increased weathering.

Another interesting observation is that BOD/COD is quite different for the different plumes.

For example, the observed biodegradability was much

lower for the wells from the central DT plume than the wells from the northern and southern plumes even though both wells in the central DT area were near the source zone and had high TPH concentrations (Figure 5.10).

This suggests that chemical composition differences between the

different plumes may have a very large impact on biodegradability.

63

0.1 DT = Diluent Tanks

206-C, 5.7 ppm 0.09 209-E, 8.2 ppm

Biodegradability (BOD/COD)

0.08 0.07 Northern DT

0.06 0.05

G4-3, 4.2 ppm

0.04 0.03

Southern DT

H3-7, 11 ppm

0.02

H2-1, 13 ppm Central DT

0.01

209-D, 7.5 ppm

0 0

200

400

600

800

1000

1200

Distance from source (ft.) Figure 5.10 BOD/COD vs. distance down plume from source plot for series of groundwater samples grouped by location. Well number and TPH concentration are indicated for each point on the graph.

64

CHAPTER 6 DISCUSSION 6.1 Reliability of BOD Tests O 2 depletion adequate in fresh groundwater samples The 6-day BOD test using diluent-contaminated groundwater and prepared seed inoculum showed significant oxygen depletion in all sample bottles with diluent-contaminated groundwater (Table 5.2), indicating sufficient biodegradation occurred. The results from the 6-day experiment showed oxygen uptake was adequate using fresh groundwater sample. The 5-day BOD re-test using diluent-contaminated groundwater showed sufficient oxygen depletion for all final samples used (Table 5.5). The blanks and seeded blanks showed negligible oxygen consumption for all experiments.

Inoculum sufficient Most BOD samples had appropriate oxygen consumption and residual D.O. values.

The BOD standards were in the appropriate range most of

the time, which test for inoculum viability among other parameters, also suggesting that appropriate amounts of inoculum were used.

Since

doubling the inoculum from 10 mL to 20 mL did not significantly increase the oxygen uptake, 10 mL inoculum was used. Using 10 and 20 mL seed, results were 2% and 4% above the upper limit of 457 mg/L.

Slightly

greater BOD exertion was observed for the 6-day samples with only 10 mL of seed compared to those with 20 mL of seed, but is not statistically

65

significant (Table 5.2). This indicates sufficient seed was used in these tests.

Most GGA standards were within the appropriate range The BOD standards for the 6-day experiment worked as expected. 10 and 20 ml of seed was added to BOD bottles with 2 mL of GGA stock solution and dilution water.

The resulting BOD exerted by these standards was

468 and 475 mg/L for the 10 and 20 mL of seed added, respectively (Table 5.2).

The BOD of the GGA in the 5-day test was slightly lower

than expected.

The resulting average BOD 5 exerted by these standards

was 296 mg/L (Table 5.4), 12% below the lower limit of 335 mg/L (APHA, 1999). The resulting average BOD exerted by the standards for the 5-day re-test was 408 mg/L for the 10 mL of seed added (Table 5.5) and performed as expected.

6.2 Effect of Iron on BOD The effect of iron on BOD was minimal. The difference in BOD of samples with iron and without iron was very small and not statistically significant (Table 5.1). The BOD of the non-sparged samples was slightly greater than the sparged samples, but the difference between sparged and not sparged is very small and not statistically significant. This test confirmed no iron effect on BOD.

66

6.3 Effect of Dilution 6.3.1 Effect of Dilution on BOD Measurement The calculated BOD 6 exerted by the 50% diluted groundwater samples was somewhat higher than that calculated for the full strength samples (Table 5.2). They should have been nearly equal, but differed by approximately 30%.

This may have been partly caused by the nearly complete oxygen

depletion in the full strength samples (Table 5.2). Full strength samples started with lower initial dissolved oxygen concentrations from not being given oxygen-saturated dilution water. Because of this oxygen depletion, the dilution experiment was repeated.

In the 5-day test, diluted samples are expected to have similar values and were all relatively close. The average BOD exerted by the 25% and 50% diluted samples of H2-1 differed by approximately 3%, while the 25% and 50% diluted samples of H3-7 differed by approximately 15%. The various dilutions of M4-4 samples exhibited varying degrees of D.O. depletion. The 10% dilution showed a small D.O. depletion while the 50% dilution essentially depleted all oxygen.

The 25% diluted samples provided the

most desirable results, having at least a 2 mg/L D.O. reduction and having a minimum D.O. residual of 1 mg/L (Table 5.4).

A 'sliding' effect whereby the BOD 5 increases with the dilution factor is indicative of sample toxicity.

Thus toxic samples with a high dilution

67

factor will give a high BOD 5 value because of diluted toxicity effects, while less dilute samples will give a lower BOD 5 due to more intensified toxicity effects (Alvares et al (2), 2001).

This effect was not observed

with Guadalupe groundwater.

6.3.2 Effect of Dilution on COD Measurement The diluted samples were run as a check on the effect of dilution on COD measurement. The diluted sample values exhibited approximately half the COD value of the full strength samples, as expected (Table 5.6).

This

concludes that dilution does not interfere with the analysis, and COD can be reliably used for the groundwater samples with different TPH concentrations.

6.4 Reliability of COD Tests Good KHP calibration curves Both calibration runs, having R 2 values of above 0.95, exemplify the high reliability of the KHP calibration curves.

Important to use proper range The importance of using proper range COD vials became apparent when COD results were above 150 mg/L using the 5-150 mg/L (low range) vials. These low range vials would not be suitable for all samples. A

68

switch to 20-900 mg/L vials was made, ensuring consistent results for the range of concentrations for all groundwater samples.

No effect from Iron There appears to be no significant chemical oxygen demand exerted by the presence of Fe 2 + [40 mg/L FeSO 4 ] (Table 5.1).

The difference between

the samples, with and without iron, falls well within the limits of one standard deviation (Table 5.1).

6.5 Biodegradability BOD/COD ratios were only 0.01 to 0.09 (Table 5.10), suggesting either the diluent isn’t very biodegradable, or biodegradation is very slow (Gilbert, 1987).

Gilbert suggested that a BOD/COD ratio of 0.4 to be

considered biodegradable.

The low BOD/COD ratios observed in this

experiment are most likely the result of slow diluent biodegradation rates, rather than low diluent biodegradability.

These BOD tests were

conducted for only five days, yet the time scale for diluent bioremediation is much longer than this. Longer BOD experiments or employing the use of long-term respirometry may be worthwhile to observe long-term biodegradability.

Alternatively, rate constants for biodegradation could

be determined for each sample, and these rate constants could be used to estimate the ultimate BOD from the observed five-day BOD values.

69

A project evaluating the CO 2 production from groundwater samples taken from the biosparge unit at the GRP showed high CO 2 production without nutrient addition (Waudby, 2003).

Short-term experiments by Waudby

showed no benefit from inorganic nutrient addition while it may prove to be necessary for sustained biodegradation.

TPH degradation slowed

considerably after collecting 6 days of respirometry data.

Long-term

biodegradation was sustained but rates were slow and no minimum TPH concentration was observed.

More long-term experiments in this area

were suggested to determine nutrient limitations.

6.6 ThOD of Hydrocarbons COD/TPH ratio higher than expected based on ThOD The COD/TPH ratios in Table 5.10 range from 11.4 to 23.8 with an average of 18.1 mg COD/mg TPH. The average COD/TPH ratio of 18.1 is approximately five times higher than the expected hydrocarbon ThOD value of 3.5 mg O 2 /mg TPH (Table 5.10).

The ThOD of hydrocarbons is approximately 3.5 mg O 2 /mg TPH.

The

stoichiometric relation for the ThOD of hexane is given in Eqn. 4.

Calculation of ThOD for hexane: Generic hydrocarbon: C 6 H 1 4

Molecular Weight: 86 g/mol

C 6 H 1 4 + 19/2O 2 → 6CO 2 + 7H 2 O (9.5 mol O 2 ) * (32 g/mol O 2 ) = 304 g O 2

70

(4)

(304g O 2 ) / (86 g/mol) ThOD = 3.53 g O 2 / mol

There are a number of possible reasons why the observed COD of the groundwater samples were higher than the ThOD for TPH, including: 1. Other organic material contributes to COD 2. Error in COD measurement/ calculation 3. Error in TPH measurements Each of these possibilities is discussed below.

Other oxidizable organics may be present in groundwater Other oxidizable organics present in the groundwater would increase the measured COD/TPH values. Other organic compounds may be associated with TPH that might not show up using GC analysis. COD correlates with TPH, but the TPH value of 29 ppm for well M4-4 seemed a little high, considering the geometric mean of TPH for well M4-4 in previous sampling events was 17.74 ppm (Lundegard 2002).

The previous

maximum value obtained was 22 ppm. Considering TPH values could be lower, COD/TPH may have higher values.

This would support the

possible theory of other oxidizable organics being present. A comparison of the COD of non-contaminated groundwater to contaminated samples may be useful, also the use of total organic carbon (TOC) analysis in conjunction with TPH analysis could be useful. There also could be more

71

bacteria present or their by-products when TPH is high, and these bacteria or by-products could exert COD.

Errors in COD measurement? Errors in measuring COD are unlikely.

COD is a simple test only

involving pipetting, heating and measuring light absorbance. Calculations of COD involve creating and using a calibration curve and accounting for blanks.

Comparisons to other COD calculations yielded similar results.

To test our COD method and calculations, the COD was measured using the accu-TEST™ kits for solutions of phenol to compare to the ThOD of phenol.

Measured TPH values may be below actual values It is unlikely that the GC/MS method used by Zymax is measuring TPH incorrectly.

Zymax is an EPA certified lab, so they are probably

following the appropriate guidelines.

They only filter samples when

specifically requested by the customer, so product would not be lost in filtration.

They agitate samples during extraction, homogenizing the

sample and reducing the chance for an analytical error.

The first

paragraph of Section 6.6 also addressed the possibility of a measured TPH value falling outside the expected range.

72

Comparison of COD to ThOD of phenol A COD run with phenol was made to try to understand why the oxygen demand of diluent contaminated groundwater was above the calculated theoretical ThOD value of 3.5 mg O 2 /mg TPH. This was also run to test the COD method and calculations.

The average COD value of 0.95 mg

O 2 /mg phenol was approximately 40% of the 2.38 mg/L ThOD of phenol (Table 6.1).

The ThOD value was not expected to be attained due to

incomplete reaction, but the reported COD of phenol was expected to be closer to the ThOD.

This experiment does show that our COD method

does not result in extraneously high COD in all cases.

The oxygen

demand of phenol was between 0.92 and 0.96 mg O 2 /mg phenol for all samples analyzed, with an average of 0.95 mg O 2 /mg phenol (Table 6.1). A COD vs. phenol bar graph is shown in Figure 6.1.

Table 6.1 COD of phenol solutions Sample Absorbance COD mg phenol conc. at 600 nm (mg/L) Phenol (mg/L) DI Blank 0.016 ------DI Blank 0.015 ------DI Blank 0.018 ------150 0.06 144.05 0.960 150 0.059 140.75 0.938 150 0.058 137.45 0.916 300 0.103 285.90 0.953 300 0.104 289.19 0.964 300 0.104 289.19 0.964

73

350 COD/phenol = 0.94

COD (mg/L)

300 250 200

COD/phenol = 0.96

150 100 50 0 150

300 150 Phenol concentration (mg/L) error bars indicate ± one standard deviation

Figure 6.1 COD vs. phenol concentration for standard phenol solutions.

74

CHAPTER 7 CONCLUSIONS The range of BOD/COD vales for this project were 0.01 to 0.09, suggesting

slow

biodegradation.

In

1987,

Gilbert

stated

a

BOD/COD value below 0.4 suggests a low biodegradability. BOD/COD

ratios

did

not

correlate

with

increasing

TPH

concentration suggesting weathering did not significantly influence biodegradability.

This also may indicate the contaminant is not

becoming recalcitrant during biodegradation. BOD/COD

ratios

suggest

biodegradability

may

decrease

with

distance down-plume from source. A limited number of wells were used and more well should be used for further analysis. Methods were successfully demonstrated for BOD and COD. Tests did not have any significantly unusual occurrences. COD/TPH values ranged from 11.4 to 23.8, with an average of 18.1. This average value is approximately five times higher than the expected value of 3.5 mg/L based on ThOD. This may mean TPH values should be evaluated at the beginning and end of an experiment. COD values may have been high due to the presence other oxidizable organics. The biodegradability decreased with distance down-plume from source, possibly signifying a decrease in biodegradability as the hydrocarbons are weathered. 75

CHAPTER 8 RECOMMENDATIONS

The

following

are

recommendations

for

future

evaluation

of

the

biodegradability of hydrocarbon-contaminated groundwater.

It would be beneficial to run TPH analysis with more than one sample, and having multiple independent lab analysis. This would put to rest any uncertainty in the reported TPH values.

Measuring actual TPH degradation rates using duplicate initial and final

TPH

analyses

would

be

preferable

to

relying

on

O2

consumption or respiration rates.

Biodegradability should be estimated for a greater number of wells with some actual plume transects.

Using TOC as a supplement to the testing methods would help in obtaining a better understanding of the organic fraction of the samples.

The use of a more precise method of measuring D.O. would be beneficial in obtaining BOD values.

76

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