Soil Leaching from Copper Naphthenate-Treated Utility Poles (cont)

Background (cont)

PAH accumulate in sediments or soils where they are degraded by microbial metabolism and photodegradation. Microbes in the presence of oxygen degrade lower molecular weight compounds more quickly, and higher molecular weight compounds degrade more slowly, particularly in anaerobic environments. Literature data shown in Figure 2 indicate all of the 2- and 3-ring PAH isomers present in creosote-contaminated soil are diminished by biodegradation or photodegradation. Likewise, all of the more refractory 4- and 5-ring PAH components in soil increase in relative abundance compared to the original creosote treating solution. PAH such as those found in creosote are very hydrophobic and bind tightly to organic matter such as soil. In upland environments it appears that PAH remain within 15-30 cm (6-12 inches) of the pressure treated wood structure.¹³

Methods and Materials

Borings were taken from 14 coastal Douglas fir poles, including 10 treated by Pacific Wood Treating and installed in 1987 (site #1, poles PB-PL), and 4 treated by Nevada Wood Preserving or Koppers and installed in 1993-94 (site #2, poles WM1-WM4). Two borings were taken from each pole, at the groundline and near the brand (~5 feet above groundline). Cores were taken near plugged holes from previous borings. All poles were visually inspected and sounded to detect signs of decay or insect attack.

Cores from poles at each site were measured individually for Cu penetration but were composited for Cu retention assay. The borings were segmented into outer and inner assay zones and ground using a Wiley Mill and dried in a forced-draft oven at 100°C for 6 hours. The wood samples were analyzed for copper retention by Timber Products Inspection (Conyers, GA) using atomic absorption spectroscopy (AAS) according to American Wood-Preservers' Association Standard A11-93. The ground wood samples were divided in half to make replicate samples.

Soil samples were collected near all poles using a stainless steel trowel since soil hardness, rocky backfill and proximity to the pole precluded using a soil auger. Soil samples from both sites were taken at radial distances of 4 inches and 12 inches from the pole. Additional soil samples were taken 10 feet from poles at the two sites for background copper and total petroleum hydrocarbon assays. Soil samples were collected and segmented into samples representing 0-3 inches depth and 3-6 inches depth. Equipment was cleaned with Alconox detergent and deionized water between each sampling to avoid sample contamination.

Soil assays were performed by North Creek Analytical, Inc. (Bothell, WA). All soil samples were analyzed for dry weight and copper content by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) following EPA Method 6010B. Selected soil samples were analyzed for total petroleum hydrocarbons by extraction with methylene chloride followed by GC analysis to qualify and quantify components.¹⁴ TPH components were classified as "diesel" and "lube oil" range hydrocarbons. Samples were also analyzed for volatile petroleum hydrocarbons¹⁵, and extractable petroleum hydrocarbons¹⁶. Selected samples were analyzed by GC/MS for polynuclear aromatic hydrocarbons (PAH) and several specific chemicals since Washington State mandates soil cleanup levels for those compounds. The chromatographic methods give a quantitative and qualitative analysis of the hydrocarbons present in the soil sample. Benzene/ethylbenzene/toluene/xylenes (BETX), MTBE and naphthalene were analyzed using EPA Method 8260B.

Results and Discussion

Brands on the poles did not include any information on the target Cu retention during treatment. AWPA Standard C4 for poles provides guidelines rather than specific instructions as to which retention to use in a particular deterioration zone. Minimum retention targets of 0.095 or 0.150 pcf Cu would be acceptable for AWPA Deterioration Zone 4, including the Puget Sound area. Copper retention in copper naphthenate-treated poles remains at or above minimum recommended retentions after 14 years in service, as shown in Table II. Poles installed at site #1 in 1987 (poles PB-PL) had an average retention of 0.10 pcf Cu in the standard AWPA C4 assay zone 0.25" to 1.0" from the surface. Analyses of core samples from these poles by Harp & Grove⁶ found an average of 0.142 pcf Cu at time of installation and 0.138 pcf Cu after 4 years of service.

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