Analysis of Gasolines for their Impacts on
Leaking Underground Storage Tank Sites
Jim Weaver, David Spidle, Candida West, ORD/NERL/ERD, Athens GA,weaver.jim@epa.gov
^0,5%
Data Collection
Ninety-six gasoline samples were collected from service stations in 13 states and
21 cities or towns by volunteers. These were analyzed for approximately 300
petroleum hydrocarbons and oxygenates by The Cascade Group of Statesboro,
Ohio.
Data Evaluation
Single chemicals of interest illustrate how components varied between samples:
(1 Ethanol and MTBE usage were mutually exclusive @MTBE concentrations were
high only where benzene concentrations were low (a requirement of reformulated
gasoline) and (3)benzene concentrations ranged above 1% by weight in
conventional gasolines.
Statistical Analysis
Statistical analyses were used to determine similarities and differences between
samples. Cluster analyses of states or pairs of states illustrated thatf 4) premium
grade fuels separated from regular grade fuels in a single state, and
i 5)conventional gasolines separated from reformulated gasolines (RFG) in
comparisons between two states. When all 96 samples were included in a cluster
analysis, the fuels tended to separate by grade with regular grades showing higher
levels of similarity than premiums. Groupings by other characteristics were
supported: RFG/conventional; high/low elevation; and MTBE ban/no ban. Brand
did not separate the fuels.
Principal Components
Principal components analysis provided another means to determine separation
between fuels. (6 ) Plots of the principal components which represent composited
groups of chemicals show separation of (top to bottom) fuels with state RFG
requirements (Colorado), MTBE ban RFG, conventional gasolines, fuels with MTBE
as an octane enhancer (Georgia premiums), and MTBE RFGs.©The principal
components also provide separation by grade.
Decision Tree
The four characteristics of: conventional/reformulated gasoline MTBE ban,
elevation and grade form a decision tree that is supported in part by the statistical
analysis(8j. Locations with data are indicated at the ends of the branches.
Locations are grouped in parentheses where averaging across locations was
supported by the data.
Environmental Properties
Environmental properties (boiling point, solubility and vapor pressure) were
estimated for the bulk of the chemicals at temperatures ranging from 0°C to 25°C.
For the average, low elevation, conventional gasoline, no MTBE ban, regular grade
samples, a scatter plot of gas phase concentration against effective solubility
illustrates the relative tendency for potential air or water contamination (V).
Physical Properties
Density and viscosity of three gasolines were measured and showed small variation
with temperature or gasoline type
Transport In Ground Water
The EPA's Hydrocarbon Spill Screening Model (HSSM) was used to simulate
releases of three types of premium gasoline: an MTBE-ban gasoline with a minimal
MTBE content (NY 0.28% MTBE), a conventional gasoline with MTBE for octane
enhancement (GA, 4.89% MTBE) and an RFG (VA 13.13%)(rj) The overall areal
extent of contamination above a threshold of 0.02 mg/L (outlined in red) was fairly
insensitive to the initial MTBE concentration in the gasoline, but the concentration
(mass) of MTBE in ground water depended on the fuel composition.
Documentation
An EPA report on the data "Predicted Ground Water, Soil and Soil Gas Impacts
from US Gasolines, 2004: First Analysis of the Autumnal Data" is available
from the EPA web site (http://www.epa.gov/athens/publications/downloadable.html).
R $ $ $ "» $ f
.13333333
{| | Z I $ I | 2 $ | { Z I i 2 i
E
v> /
! o.. -I
" 0.00,4
rt> jf o/pQ A A
~
~
£ """ 1
AT a
i / -
m IE-MIS -|
n""lgl '"""I 1
1 »
1 "™i "™i111111
Effective Solubility (mg/L)
PRO-I4-0 d
epascienceforum
Collaborative Science
for Environmental Solutions
Disclaimer: Although this work was reviewed by EPA and approved for presentation, it may not necessarily reflect official Agency policy. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.
------- |