REACHING SOIL CLEANUP LEVELS BY VAPOR
EXTRACTION: LABORATORY APPROACH
George E. Hoag, Associate Professor
Department of Civil Engineering
Director of the Environmental Research Institute
Farhad Nadim, Graduate Research Assistant
Department of Civil and Environmental Engineering
Amine M. Dahmani, Engineering Projects Manager
Environmental Research Institute
University of Connecticut
Environmental Research Institute
Storrs, Connecticut, 06269-3210
INTRODUCTION
Nonaqueous phase liquids (NAPLs) such as gasoline and chlorinated solvents have a very low
water solubility. When these compounds enter the unsaturated soil, buoyancy and capillary
forces may hold a portion of them in the soil pores as residual saturation. Hoag and Marley have
reported 12-20% residual saturation for gasoline in a partially water saturated sand.' Soil Vapor
Extraction (SVE) is a technique that removes volatile and some semi-volatile organic compounds
from the unsaturated soil by induced flow of air.2-3 Through contacts with each state's EPA office, it was concluded that 21 states have their own regulations for soil cleanup levels and the
others follow the guidelines set forth by the Federal RCRAand CERCLA regulations.4 The State
of Connecticut Department of Environmental Protection (DEP) requires contaminated soils to be
remediated to a level such that the amount of contaminant partitioning into the liquid phase remains below the drinking water standard, under equilibrium condition. These standards are 0.001
mg/L for benzene, 1 mg/L for toluene, 0.7 mg/L for ethyl benzene, and 0.005 mg/L for
trichloroethylene and tetrachloroethylene.5 In order to determine the amount of volatile
organics that partition into the liquid phase a test called Toxic Characteristics Leaching Procedure with Zero Headspace Extraction (TCLP-ZHE) is applied to contaminated soils. This test
determines the amount of VOC that would partition into the liquid phase in the TCLP-ZHE
procedure.
This study presents two different laboratory experiments to determine where SVE technology
alone, can be an adequate remedy selection for sites that are contaminated with VOCs.
EXPERIMENTAL PROCEDURE
Casel
This experiment was conducted to test the applicability of SVE in Connecticut sand. Fifty percent weathered Mobil super unleaded gasoline was artificially added to soil prior to vapor extraction. The procedure of gasoline addition and column set-up have been described in detail by
Dahmani et al.6-7 For the first column (Column la) a flow rate of 0.025 L/min was used and for
the second column a flow rate of 0.8 L/min was used. When the concentration of the BTEX compounds in each column reached the detection limit of the instrument (5 ng/mL), air flow was terminated and each column was leached with three pore volume of de-ionized water. Composite
soil samples were taken from the columns and the TCLP-ZHE test was done on these samples.
Composite soil samples were also taken from the soil columns and the amount of volatile hydro-
50th Purdue Industrial Waste Conference Proceedings, 1995, Ann Arbor Press, Inc.. Chelsea, Michigan 48118.
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