Wood preservation facilities, copper azole : chapter H-5

5. Description of Preservative Application and Potential Chemical Discharges

5.1 Description of Process

CA-B preservative is a water-based product which is applied by pressure treatment in essentially the same manner as chromated copper arsenate (CCA) using the Full Cell (Bethell) pressure treatment process (refer to Part 1 - General Background Information, Section 2.2.3 Figure 3).

CA-B working solution is prepared at wood preservation facilities by diluting the preservative concentrate, or the two CA-B components concentrates, with water to form a working-strength solution of 0.3-3.4% actives. The working-solution strength is determined by the desired treatment level to be retained in the wood. Vacuum and pressure cycles vary depending on the wood species and size of the wood product being treated, such that they meet the desired standard (4) or specification.

The specific treatment times and pressures are dictated by the species of the wood, the wood product, and the moisture content of the wood. A predetermined range of process parameters is defined by the applicable treatment standards of the CSA-O80 Series of Standards (4). Quality control tests are carried out to ensure that a minimum treated product quality is maintained. The treated wood is stored on site until ready for shipment.

5.2 Potential Chemical Discharges

CA-B wood preservation facilities vary in design and operating practices, which may cause differences in the nature of potential releases from any particular plant. The potential sources and types of releases are illustrated in Figure 1.

Liquid Discharges

The CA-B process uses water-borne ingredients and can be operated as a “closed system.” Once dripping has ceased, and a minimum of 48 hours has passed, freshly treated lumber should be wrapped prior to storage in the yard or under sheds. If incidental drippage occurs, the lumber must be returned immediately to the drip pad area until all dripping has been confirmed to have stopped. Immediate cleanup of the drippage should be initiated to prevent any potential for causing stormwater contamination or tracking. Dripped solution or contaminated storm runoff water can be reused in the process. Primary facility design features that should be used for CA-B containment and recycling include the following:

• concrete containment surfaces and diking with a second barrier for major process areas, including the cylinder and tanks
• containment surfaces for chemical drips from treated wood on the cylinder discharging track and in the freshly treated drip pad
• a collection sump to receive residual preservative from the cylinder (following the treatment cycle) and the accumulated contaminated runoff from other containment surfaces. This material can then be reused in the treatment process following filtration to remove dust and debris.

Under normal operating practices in a properly designed facility there should be few contaminated liquid discharges. The most common potential sources of contaminated liquid discharges in a CA-B facility are stormwater runoff waters from unpaved and unroofed treated product storage areas. The quantities of preservative in these waters depend on many factors, including quantity of precipitation, stabilization method, elapsed stabilization time, temperature prior to a precipitation event, and soil characteristics of the storage yard. Uncontained liquid releases other than stormwater are generally confined to yard soils, particularly those locations near drip pads in charging/unloading areas and where containment surfaces are used for freshly treated wood. These contaminated yard soils, at high concentration, have potential for causing groundwater contamination.

Solid Wastes

Solid waste generation at CA-B facilities should be relatively small. During normal operating conditions, solid waste sources are limited to filters, and to dirt and debris that are periodically scooped from the sump, cylinder and tanks. Treated wood debris and contaminated articles are another source.

Air Emissions

Using an amine formulation at ambient temperature will produce minimal tank emissions under normal operating conditions. Typically no controls are necessary for ambient temperature solutions with the CA-B product. There should be no in-plant emissions from storage tank vents or vacuum pump exhausts, as these must be vented to the plant exterior with liquid-release protection.

The use of heated solutions may imply some potential for amine emissions at the CA-B facility if proper controls are not in place.

Refer to Part 1 - Chapter A, Section 5.2 for more details on potential chemical discharges.

5.3 Potential Effects of Chemical Discharges

The actual impact on the environment of any chemical release depends on many factors, including the location of the wood preservation facility relative to ground or surface waters, the amount and concentration of preservative releases, the frequency of releases, and contingency measures in place at the facility.

Improperly operated facilities have the potential to contaminate surrounding site soils and groundwater to levels that exceed drinking water standards.

Human health effects for workers are minimized by the use of closed systems for concentrates and working solutions. The main source of potential contact with CA-B would be from improper handling of the product.

Figure 1 Potential Releases from CA-B Pressure Treating Plants