The site specific conditions include the physical setting of the project such as the type of water body (freshwater or marine), the velocity of the current in the water body, water depth, rainfall, sediment characteristics, pH, water temperature, and other background water quality characteristics. These factors are key inputs for assessment of treated wood applications and are used as inputs in this model. In the event any of these parameters are unknown for your project, the default values listed below for these model inputs were chosen to produce conservative results (i.e., higher contaminant concentrations).
The exposure of treated wood to the aquatic environment can be from submerged wood structures such as piling or timbers, from overhead structures such as decking or from both. The proposed number of piling is a key factor. The below list of assumptions regarding the project design are factored into the default model input values.
All projects should be undertaken in conformance with the guidance provided in the Best Management Practices for the Use of Treated Wood in Aquatic and Other Sensitive Environments (BMPs) (Western Wood Preservers Institute, 2006). This includes BMPs for product production, quality assurance, installation and management. BMPs are available online at www.preservedwood.org.
The following simplified assumptions were factored into as default model input values to allow the user to arrive at a conservative finding in determining if the project would qualify for a "no effect" determination. These assumptions are summarized below:
- Piling are spaced 3.0 m apart (~10 ft), and it is recommended the user conservatively assume each piling will support an overhead deck structure covering an area of 3.0 m x 3.0 m = 9 m^2 or approximately 100 ft^2 of decking including associated railing.
- The assessment conservatively assumes that all treated wood components are placed on Day 0.5.
- The anticipated lifespan of the project is 35 years.
- In freshwater, current speeds are an average of those found at mid depth within the project’s footprint.
- In tidally driven marine environments, the current speed is the Maximum tidal current speed. Based on this maximum speed, the model computes average speeds for determining sediment concentrations and the mean speed within half an hour either side of slack tide for determining maximum water column concentrations of the chemicals of concern.
- Water depths within the footprint of the project are not critical but are assumed to be spatially similar and equal to 2.0 m depths.
- Freshwater environments: pH = 6.5; Temperature = 15 degrees C, background copper = 1.5 μg Cu/L, Hardness = 50 mg CaCO_3/L.
- Sediment environment: Density = 2.6 g/cm^3; Sediment Total Organic Carbon = 1.0 %; Background Sediment Copper = 15 mg Cu/kg; Background concentrations of PAH (Creosote) and Pentachlorophenol = 0.0.
- Annual rainfall = 100 cm/year (40 in/year); Rainwater pH = 6.5. No significant storms occur during or immediately after construction.
- Pentachlorophenol assessments were conducted assuming a conservatively low sediment redox potential of 50 mV.