Transcript No Slide Title

21st Annual Conference
Emerging Issues with
Total Petroleum Hydrocarbons in Soil Vapour
(and Groundwater)
Lynn Spence
Spence Environmental Engineering
Outline

TPH definition

How TPH is characterized for purposes of risk
assessment

Development of risk-based screening levels for
TPH in soil

Evaluating risk from TPH in soil gas

BioVapor model
What is Total Petroleum Hydrocarbon (TPH)?

Hydrocarbons are any chemicals with carbon-hydrogen bonds.

Gasoline is a petroleum product that contains over 200 different
hydrocarbons.

TPH is a “bulk” measurement used to assess concentrations of
these hydrocarbons.

TPH measurements are highly dependent on the analytical
method used. In other words, the analytical method defines
TPH.

Conventional TPH measurement techniques quantify only those
hydrocarbons that are extracted by the particular method.

The same sample analyzed by different TPH methods will
produce different TPH concentrations.
Conventional TPH Analyses:
Problems for Risk-Based Decision Making
Many non-petroleum substances will be
quantified as TPH.
Grass
14,000 mg/kg
(1.4%)
Pine Needles
16,000 mg/kg
(1.6%)
Dried Oak
Leaves
18,000 mg/kg
(1.8%)
Some petroleum substances will only be
partially quantified as TPH.
Petroleum Jelly
749,000 mg/kg
(74.9%)
Gas
Crude Oil
618,000 mg/kg
(61.8%)
Gasoline
446,000 mg/kg
(44.6%)
TPH Results are Method-Specific
Gasoline
Diesel Fuel/Middle Distillates
Lube/Motor Oil, Grease
Crude Oil
C2 C4 C6 C 8 C10 C12 C14 C16 C18 C20 C22 C24 C26 C28 C30
TPH Methods: Approximate Carbon Ranges
TPHg: Purgeable/Volatile/Gasoline Range
TPHd: Diesel Range,
Other bulk analytical methods: 418.1, Modified 418.1: Extraction, Infrared
TPH Fractionation

Various TPH fractionation schemes have been
developed in order to better characterize the actual
compound types in the TPH.

Unique fate and transport properties and unique
toxicity values are assumed for each fraction.

Risk from each fraction could be evaluated.

A total TPH clean-up level could be determined that is
protective of the specific mixture found at the site.

This approach has been used to develop TPH riskbased screening levels in soil that are protective for
various products (gasoline, heating oil, crude).
Aliphatics and Aromatics
A ro m a tic s
H
|
C
H — C
C — H
H — C
C — H
A lip h a tic s
H
H
|
|
H — C — C
|
|
H
H
—
H
H
H
H
H
H
|
|
|
|
|
|
C — C — C — C — C — C — H
|
|
|
|
|
|
H
H
H
H
H
H
C
|
H — C — H
|
H
> C 6 -C 7 (b e n z en e )
> C 7 -C 8 (to lu e n e )
> C 8 -C 1 0
> C 1 0 -C 1 2
> C 1 2 -C 1 6
> C 1 6 -C 2 1
> C 2 1 -C 3 5
butane - C4
(hexane) > C -C
5
6
> C 6 -C 8
(octane) > C 8 -C 1 0
> C 1 0 -C 1 2
> C 1 2 -C 1 6
> C 1 6 -C 3 5
TPH Screening Levels for Various
Hydrocarbon Mixtures in Soil
RBSL, TPH (mg/kg)
100,000
80,000
60,000
Vaseline® =
330,000 mg/kg
Vaseline®
Crude Oil
Diesel
Gasoline
40,000
20,000
1,800 mg/kg
0
Non-Residential Sites
Limiting pathway = surface soil for Vaseline ®, diesel, & crude oil
Limiting pathway = soil leaching to groundwater for gasoline
TPH in Soil Gas

In the US, screening levels have been developed for
TPH concentrations in soil gas.

It is not as easy to fractionate TPH in soil gas samples
as in soil samples (i.e. not many labs do this yet).

In order to develop the screening levels, assumptions
were made as to the content of the TPH in soil gas.

Massachussetts and British Columbia have both
developed fractionation methods for soil gas and
allow “site-specific” evaluation.

Other states (like California) have assigned a
surrogate chemical toxicity to apply to the entire TPH
in soil gas.
TPH is Being Regulated for Indoor Air and Soil Gas
Screening Level in
Indoor Air
(ug/m3)
Residential
TPHg*
10
Industrial
14
Screening Level in
Soil Gas
(ug/m3)
Residential
Industrial
10,000
29,000
Screening for Environmental Concerns at Sites with Contaminated Soil and Groundwater -CA RWQCB 2007 ESLs
*Note: background TPHg in indoor air ~ 100 ug/m3 (Hawaii Dep. of Health)
California assumes 100% of the TPH is aromatics (C9 to C22).
TPH and Vapour Intrusion
Problem:
A variety of sites with high TPHg hits in soil gas,
without any detected BTEX* or other typical target
compounds. Regulators are saying we need to meet
Screening Level or remediate (for sites that are
being redeveloped).
*BTEX = Benzene, toluene, ethylbenzene, xylenes
Site #1
Original soil vapour sample returned 2,100,000
ug/m3 for TPH (using TO-3), but no BTEX.
Attempted Solution:
1. Resample well.
2. Run TO-15M and identify the top 10 tentatively
identified compounds (TICs) in soil gas.
3. Re-evaluate risk using toxicity information for
those chemicals.
Site #1:
Results of Re-Sampling
Concentration Concentration
TO-3 (GC/FID) Target Compounds Detected:
TPH ref. to Gasoline (MW=100)
TO-15 (GC/MS) Target Compounds Detected:
TPH ref. to Gasoline (MW=100)
2,2,4-Trimethylpentane
Tentatively Identified Compounds
2,2-dimethylpropane
2,2-dimethylbutane
2,2,3-trimethylbutane
2,2,3-trimethylpentane
2,3,4-trimethylpentane
2,3,3-trimethylpentane
1,1,2-trimethylcyclopentane
2,2-dimethylheptane
2,5,6-trimethyldecane
3,7-dimethylnonane
(ppbv)
(µg/m3)
27,000
108,000
16,000
5300 E
65,000
25000 E
250 N J
360 N J
370 N J
560 N J
1400 N J
5800 N J
220 N J
430 N J
110 N J
100 N J
Site #1:
TO-15 Analysis
Site #1:
Evaluating Risk With the New Data

98% of compounds were C7 to C9 aliphatics.

Risk was then evaluated using toxicity of the C7-C9
aliphatic range.

Used the attenuation factor that CA used to develop
the soil gas screening levels (0.001).

Non-cancer risk (Hazard Index) was estimated to be
0.004 (well below acceptable limit).

This was for a site overlying free product gasoline on
the water table (10 m below).
Site #2
High TPHg hits in soil gas (4,400,000 ug/m3).
Identifying top TICs doesn’t capture the bulk of the
TPH. Regulator still says to meet Screening Level or
remediate.
Site #2:
Evaluating Risk

Identifying the TICs only accounted for
approximately 50% of the TPHg.

However, from TO-15M, 94% of the TPHg
were identified as aliphatics.

Risk could then evaluated as before.

Note, no n-hexane was detected.

Hazard index was in acceptable range.
Conclusions

Composition of TPH in soil gas is different than
models seem to predict.

Different analytical methods yield very different results.

This is true for TPH in groundwater as well.

TPH results are somewhat problematic for law suits
(especially international).

More compounds will need to be tracked individually.

Much more study is needed to match analytical
methods with risk assessment requirements.
BioVapor Model
1-D
Analytic
al Model
Version of Johnson & Ettinger vapor
intrusion model modified to include
aerobic biodegradation (DeVaull,
2007).
Oxygen
Mass
Balance
Uses iterative calculation method to
account for limited availability of
oxygen in vadose zone.
UserFriendly
Simple interface intended to
facilitate use by wide range of
environmental professionals.
KEY
POINT:
Version 2 available in Fall 2009.
Free from API web site.
SIMPLE MATH
O2
HC
BioVapor Model
Development and Release Schedule
Final
Software
Target date for final release:
October 15, 2009
Check API web site: www.api.org
Training
• ½-day training class at Amherst
conference, Oct. 19, 2009 (link
from GSI web site,
www.gsi-net.com)
• ½-day Webinar to be scheduled
21st Annual Conference