26    TAILORING OF ZEOLITES FOR ADSORPTION OF BENZENE
AND TOLUENE FROM SOLUTION
Fernando Cadena, Professor
Civil Engineering Department
New Mexico State University
Las Cruces, New Mexico 88003
Robert W. Peters, Environmental Systems Engineer
Energy Systems Division
Argonne National Lab
Argonne, Illinois 60439
Francine S. Vigil, Environmental Engineer
Waste Management Division
Los Alamos National Lab
Los Alamos, New Mexico 87545
INTRODUCTION
Liquid wastes generally move vertically through the vadose zone in soil strata until they reach an
impermeable layer or ground water source. Insoluble or high molecular wastes have a much greater
chance of attaching to soil particles in the vadose zone, thus biodegradation and volatilization then
become prime mechanisms of breakdown.',2,3 In contrast, low molecular weight wastes are generally
more soluble, therefore, the vadose zone may provide an excellent medium of transportation.1, ,3,4
Single-ring aromatic compounds are prime candidates for reaching and contaminating ground water
due to their high solubility and relative abundance in petroleum products. Removal of these compounds has become a crucial concern, since groundwater makes up 96% of the fresh water supply in
the U.S. and supplies one-half of the nation's population with drinking water and one-half of the
nation's irrigation water.5
One industry that has been targeted by the U.S. Environmental Protection Agency (EPA) for air,
soil and groundwater contamination is the petrochemical industry. Several million underground
storage tanks (UST) are used to house petroleum or hazardous chemicals in the United States. Tens of
thousands of these USTs are currently leaking.s In New Mexico an estimated 159 leaking underground
storage tanks (LUST) have been reported.6 USTs may leak for a variety of reasons including plumbing failures, spills or overfills, installation mistakes or corrosion on the tanks; with 70% of the leaks
caused by piping failures.5 The estimated number of leaking gasoline tanks varies from 75,000 to
100,000 and is expected to increase by 350,000 over the next decade (18). Gasoline typically contains
0.8 to 3% benzene, 9 to 11% toluene and 10 to 12% xylene.1,4 With the improvement of leak detection
techniques and equipment many more spills are apt to be identified.
Congress' first response to LUSTs was a 1984 Subtitle I to the Resource Conservation and Recovery
Act (RCRA) requiring the EPA to develop regulations to protect human health and the environment
from LUSTs.5 LUSTs are ranked by the EPA as one of the major sources of contaminated ground
water in the United States, with benzene and toluene being a major concern.8
BACKGROUND
The evolution of the petrochemical industry has brought attention to aromatic hydrocarbons. Their
association with the petrochemical processes have characterized them as being unstable and causing
significant problems in ground water. Aromatic hydrocarbons are ring compounds and are included
in the category of neutral organic contaminants (NOC). Most observations indicate that NOC sorption on low-organic carbon surfaces is minimal;4,9,10 as the non-polar surface area available for
hydrophobic sorption is greatly reduced." The typical low organic matter subsurface found in soils
47th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.