Environmental Fate and Transport of Solvent-Stabilizer Compounds - Environmental Investigation and Remediation - page 115

of boiling points for compounds whose boiling points have not been measured. The EPIWIN Suite *
from USEPA and Syracuse Research Corporation was used in this chapter to calculate some physi-
cochemical properties for solvent-stabilizer compounds.

3.1.1 A TMOSPHERIC F ATE AND T RANSPORT P ROCESSES
Solvent-stabilizer compounds can enter the atmosphere through the following industrial processes:

• Direct vapor emission from vapor degreasers, dry cleaners, solvent-charged steam clean-

ers, and other applications in which solvents are vaporized
Volatilization from open-top vapor degreasers, vented solvent storage vessels such as tanks •

and drums, and waste lagoons or from solvent wastes poured on the ground for disposal
Volatilization from aqueous solutions discharged as condensation water in degreaser or •

dry cleaner water traps, solvent-laden steam-cleaning wastewater, surface-water bodies to
which solvent wastes were discharged, or air-stripping towers used to treat solvent-
contaminated groundwater
Emissions of uncombusted stabilizer compounds from solvent incineration operations at

•

cement kilns and waste incinerators

As discussed in the next section, contaminated soil and groundwater can serve as secondary
release sources to the atmosphere.

3.1.2 V OLATILIZATION FROM D RY S OIL
Estimating the rate of chemical transfer from soil to air is complicated by the wide range of possible
fates for the stabilizer compound when discharged to soil. In addition to volatilizing directly into air,
the compound may be subjected to some or all of the following abbreviated list of possible fates:

• Sorption to soil mineral and organic matter surfaces

• Migration under matric suction into the soil

• Penetration into the soil as a liquid and then volatilization into a vapor that sinks or raises

depending on vapor density and soil-air pressures
Dissolution into soil moisture and downward migration to groundwater •

• Absorption into plant roots

• Microbial metabolic processes

An effective strategy for estimating the transfer of a particular chemical from dry soil to air alone is to
compartmentalize the system and assess the degree to which partitioning between the two media is
expected to occur. This simplii cation assumes that chemicals in the environment are present in a pure
state; however, contaminant releases usually occur as complex mixtures (Kinerson, 1987). This approach
forms the basis for broad estimates of volatilization and other contaminant fate and transport processes.
The rate of evaporation of a chemical from dry soil is a function of soil, chemical, and air tem-
peratures, wind speed, air turbulence and surface roughness, air humidity, solar radiation, and the
relevant properties of the chemical, including total mass released, molecular weight, vapor pressure,
vapor density, and diffusivity in air (Mackay et al., 1993; Thibodeaux, 1996). In particular, vapor
pressure describes the concentration of a chemical as its partial pressure in the gas phase in air
above a liquid sample, usually measured at 20°C or 25°C and reported in pressure units (e.g., mm
Hg). Vapor density is the mass per unit volume of a chemical in the vapor phase at a i xed tempera-
ture, usually expressed as a ratio to air density. Vapors heavier than air are reported as a multiple of
air density and measured at 25°C (e.g., perchloroethylene, vapor density

= 5.7). Diffusion is the

* Estimations Programs Interface for Windows (EPI Suite) (USEPA, 2007a).