Soluble copper or micronized copper wood preservatives are the most common available wood preservative systems for residential applications in the United States. Copper containing wood preservatives have been scrutinized for their potential negative impacts on the environment, across many jurisdictions. Concerns arise from the potential for preservatives to migrate out of treated wood upon water exposure into the environments. Because of this it is important to quantify chemical loss from lumber treated with available wood preservative systems so that their impact can be predicted for specific applications. This work describes an effort to measure the migration of copper from a newly installed deck made with hem-fir lumber pressure treated with copper azole-C (CA-C) to above ground contact retentions. The deck was constructed in 2021 and collection basins were installed beneath the deck at three locations. In each location basins were positioned so they would catch runoff from the deck surface boards only and where runoff would contact the deck surface and joists. Water samples were collected after each major rain event and analysed for copper concentration. Water was collected for an entire wet season in Western Oregon from October 2021 to May of 2022. Copper concentrations in runoff were highest in runoff collected after the second rain event of the season, averaging 2.61 mg/l for runoff from deck boards only and 4.92 mg/l for runoff collected from beneath the deck surface and a joist. Copper concentrations in runoff tapered off from there, reaching 0.11 mg/l and 0.19 mg/l for deck and joist runoff, respectively. Total copper lost from the deck over the first 7 months after installation was 44.48 mg/m2 the deck surface alone and 71.12 mg/m2 deck and joist. This level of chemical loss was not sufficient to result in copper accumulation in the soil beneath the deck two years after its installation. This work provides an excellent case study to test the robustness of a predictive model for treated wood’s impact on the environment and efforts are currently underway to do so.

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