OILY WASTEWATER CONTAMINATION OF THE WATER TABLE
AT A WOOD PRESERVING PLANT
John Ball, Professor
Civil Engineering Department
The University of Alabama
University, Alabama 35486
This chapter presents a case study of the closing of a small process pond at a wood preserving plant. The purpose of closing the pond was to move the plant to a different location;
however, the company would have closed the pond in any case because of the new hazardous waste regulations. During the closing operation, it was found that preservative had
reached the water table. This chapter outlines what was done to determine the extent of the
problem, how it probably occurred and the final solution that was approved by the state.
THE MANUFACTURING PROCESS
The wood treating plant is a small part of the company business, which is the design and
fabrication of electrical substations. Some of the materials used in substations are wooden
cross arms and braces, which must be treated with a chemical preservative. The lumber for
the cross arms and braces is shipped to the plant from the West Coast and is a relatively high-
quality raw material that has been dried prior to treating. The company treats the lumber
with the preservative pentachlorophenol (PCP) at a certain stage in the fabrication of a substation. PCP is not injected into the wood in full strength but as a 5-7% dilution in an oil
carrier such as No. 2 fuel oil. Some quantities of wastewater are generated in the process that
carry low concentrations of the preservative solution.
Unlike most wood treating plants, there is no "steaming out" or boiling-in-oil cycle at
this plant. The operation is unusually clean, with the tram cars being loaded and unloaded
inside a building with the single, small (6- x 50-ft) cylinder located outside. Water is contaminated in three ways. The first is a washwater that is generated once each week. The
operating crew wash down the inside of the cylinder with a fire hose to keep from building
up tars and wood chips in the cylinder. This water runs out of the front of the cylinder to a
sump. The second source is contaminated rainwater that falls in the door sump and within
the boundaries of the plant. Since the ground has been contaminated with preservative from
pipe and pump leaks, this water is collected for treatment. Washwater and contaminated
rainwater is piped to the barometric water pond.
The barometric system is the greatest source of contaminated water. Like many older
plants, this plant uses an eductor to produce the vacuum for the cylinder. Steam and water
are added to the top of the eductor (Figure 1), and a vacuum is pulled on the cylinder that
results in vaporizing some of the preservative and carrier oil. Any vaporized products are
condensed in the eductor and contaminate the pond.
Because of the size of the operation, the barometric cooling water pond was only about
30 by 60 by 5 ft deep. A recycle pump supplied the water to the eductor and a fresh water
line added makeup to the pond during dry spells. Sprays had been installed in the pond to
aid evaporating storm water.
POLLUTION CONTROL
The immediate plant area was diked to direct storm water to the barometric pond. This
also was a part of the spill control plan should a tank leak or a line rupture. There was a
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