www.inl.gov

A Simple Approach for Identifying 

Contaminants of Most Concern to 

Underground Drinking Water Supplies 

from Hydraulic Fracturing Operations

Carl D. Palmer and Earl Mattson

EPA Hydraulic Fracturing Workshop

(Fate and Transport)

March 28 – 29, 2011

Idaho National Laboratory
392 Chemicals in hydraulic fracturing fluids

207 Chemicals in flow back and produced waters

Spills

Casing/Grout Failures Natural Fractures/Abandoned Wells

Water Supply Aquifer

Gas Reservoir

(USEPA, 2011)
Objective:

To determine which contaminants are likely to be of most 

concern with regard to hydraulic fracturing.

Approach:

•Identify contaminants reported from laboratory tests, 

injection water compositions and from groundwater 

sampling at field hydraulic fracturing tests,

•Estimate the relative toxicity of the contaminants,

•Estimate the mobility of those contaminants.
Estimate “Toxicity”

• obtain maximum reported aqueous concentration (Cmax),

• determine some “safe” contaminant concentration (CMCL)

• drinking water standards (EPA)

• secondary drinking water standards (EPA)

• state drinking water standards/guidelines 

•foreign drinking water standards/guidelines (Canada, 

UK, EU)

•Identify (e.g., from ATSDR, EPA databases) an oral 

Maximum Risk Level (MRL) or similar criterion to 

estimate CMCL

• divide Cmax by CMCL
Estimating “Mobility”

•Estimate retardation factor

•Mobility = 1/R
Neutral, hydrophobic Organics:

1

b

p

w

R K 



  C K C s p aq



retardation factor

soil partition coefficient

p

R

K





Aqueous Concentration (mg/L)

0.0 0.1 0.2 0.3 0.4 0.5 0.6

Sorbed Concentration (mg/g)

4

6

8

10

12

14

Phenanthrene Sorption

onto Green River Kerogen

Data from Salloum et al. (2002)

Kp = 15631 ±814 mL/g

Koc = 43662 ±2273 mL/g
Neutral, hydrophobic Organics:

1

b

p

w

R K 



  K f K p oc oc



retardation factor

soil partition coefficient

fraction of organic carbon in soil

partition coefficient between aqueous phase 

 and soil carbon phase

p

oc

oc

R

K

f

K









PYRENE

PHENANTHRENE

Kp PYRENE (mL/g)

1800

1500

1200

900

600

300

0

0.0 0.005 0.010 0.015 0.020 0.025

FRACTION ORGANIC CARBON

Kp PHENANTHRENE (mL/g)

600

500

400

300

200

100

0

Slope = Koc

(Karickhoff, 1981)
Neutral, hydrophobic Organics:

0 1 2 3 4 5 6 7 8

0

1

2

3

4

5

6

7

Log Kow

Log Koc

Data from Karickhoff (1981)

Empirical and Structurebased relationships 

between Koc and the 

octanol-water partition 

coefficient (Kow)
Toxicity and Mobility

Log(Cmax/CMCL)

-2 -1 0 1 2 3 4 Log(1/R)

-6

-4

-2

0

High Toxicity,

High Mobility

High Toxicity,

Low Mobility

Low Toxicity,

Low Mobility

Low Toxicity,

High Mobility
Example:

Application to Oil Shale Retorting

G

Primary Reaction Zone Primary Reaction 

Zone

Heat

Impact horizon

Ground Water

Potential

Contaminants

Temperature (oC)

0 50 100 150 200 250 300 350 400

Concentration (mmol/L)

0.01

0.1

1

10

F

Cl

Br

PO4

SO4
Organic Contaminants

• phenols (2,4-dimethylphenol)

• ketones (2-butanone)

• alcohols (2-ethyl-2-hexanol)

• organic acids (benzoic acid)

• aromatics (benzene)

• nitrogen compounds (pyridine)

• alkanes (trimethylcyclohexane)

• PAHs (phenanthrene)

• halogenated compounds (tribromophenol)

79 Reported Compounds
Log(Cmax/CMCL)

-2 -1 0 1 2 3 4 Log(1/R)

-6

-4

-2

0

Organic Contaminants
Organics of Most Concern

Benzene

1-Methylnaphthalene

2-Butanone

Aniline

2-methylphenol

3- and 4- Methylphenol

acetonitrile

Phenol

Thiophene

Pyrrole

2-Methylnaphthalene

Benzidine

Isophorone

Chloroethane

2-pyrrolidone

vinyl chloride

Bromomethane

4-methylphenol

Acetone

2-Hexanone
Limitations with the Approach

• Use of maximum observed concentrations,

• How to include frequency of occurrence,

• Insufficient guidelines or MCLs,

• Lack of octanol/water partition data for some compounds,

• Partition coefficients are a function of temperature,

• Have not included potential biodegradation,

• Potential mineral precipitation,

• Potential for colloidal transport,

• Additional difficulties with fracture flow.
Summary

• Obtain data (field and laboratory) on concentrations associated 

with hydraulic fracturing,

• Consider the risk of these contaminants based on their relative 

mobility and toxicity,

• Create an initial prioritized list of contaminants that should be 

considered,

• Identify potential contaminants that require additional 

information. 

Log(Cmax/CMCL)

-2 -1 0 1 2 3 4 Log(1/R)

-6

-4

-2

0

High Toxicity,

High Mobility

High Toxicity,

Low Mobility

Low Toxicity,

Low Mobility

Low Toxicity,

High Mobility