Historical Use of Chlorinated Solvents and Their Stabilizing Compounds - Environmental Investigation and Remediation - page 15

TABLE 1.8
Annual Solvent Waste Generation and Emission Losses in Vapor Degreasers at Air Force
Bases in Southeastern States in the Late 1980s and Early 1990s

Reservoir
Volume (gallons)

Batch
Changes

Annual Usage
(gallons)

Annual Waste
(gallons)

Emissions
Loss (%) Solvent

Perchloroethylene 35 6 1780 480 73

Perchloroethylene 50 17 1824 420 77

Perchloroethylene 110 4 2740 968 65

Methyl chloroform 50 10 654 275 58

Methyl chloroform 110 6 3850 990 74

Methyl chloroform 110 8 4180 1320 65

Source: Howell, S.G. and Tarrer, A.R., 1994, Minimizing pollution in cleaning and degreasing operations. EPA/600/
SR-93/191.

the work being cleaned, from leaks in the cooling water coils or steam heating lines in the solvent
boiler, and from water-soluble cutting oils and bufi ng compounds (ASTM, 1962; Dow Chemical
Company, 1999b). As discussed further in Section 1.2 , the presence of water in the degreaser may
lead to hydrolysis of the solvent, removal of water-soluble solvent stabilizers, and corrosion of the
metal surfaces in the degreaser and on the work. Presence of water in the solvent is indicated by spots
or even rust on the metal parts after cleaning. Another indication of excess water in the solvent is the
formation of a dense white fog in the vapor zone, called “ghosting.”
Vapor degreasers are equipped with water separators. Condensed water and solvent drop into a
trough below the condenser coils and drain to the separator. Because water l oats atop the solvent and
does not dissolve signii cantly in the solvent, the water can be siphoned off. A relatively moisture-free
solvent passes through the solvent return line at the bottom of the water separator and is then dis-
charged to the degreaser or the storage tank (ASTM, 1962; Dow Chemical Company, 1999b). Operator
guidance called for l ushing with fresh water and keeping the water separator full by periodically
adding solvent and water. Flushing prevented the buildup of corrosive acids from hydrolysis of
solvents and corrosion of water separator pipes and tanks. The guidance specii ed that the pH of

TABLE 1.9
Typical Solvent Losses in a Major Printed Circuit Board Manufacturing Facility

Solvent Handling Process Cause of Loss Solvent Lost (%)

Storage in holding tanks Evaporative losses 1

Leaks 1

Transport within facility Spills 8

Vapor degreasing Evaporative losses, leaky seals, etc. 12

Drag-out 40

Spills and leaks 8

On-site recovery by distillation Evaporative losses, leaky seals 2

Hand cleaning Evaporative losses 15

Off-site for recycling of waste solvent — 18

Source: U.S. Environmental Protection Agency (USEPA), 1991, Conservation and recycling practices for CFC-113 and
methyl chloroform. U.S. Environmental Protection Agency, Ofi ce of Air and Radiation. EPA/400/1-91/017.
Note: The primary solvent used at the facility was Freon-113; loss rates for other solvents may have lower evaporative losses.