Wood preservation facilities, general recommendations: chapter A-7

7. Design Recommendations

Industrial storage tanks with valves and walkway with secured railing

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This section outlines considerations on site selection and design features of wood preservation facility. These recommendations are intended to:

  • Minimize the risks of direct contact of the preservatives by on-site personnel
  • Minimize the risks of releasing preservatives to the environment
  • Minimize the risk and impacts of accidental releases

The National Fire Code of Canada (NFCC) establishes requirements (known as “acceptable solutions”) that address the safety, health and fire protection of residential, commercial and industrial building and facilities in Canada. Some of the following recommendations make reference to sections/subsections/articles of the NFCC 2010 edition that met specific objectives. Additionally, it is also recommended to refer to the National Fire Code of Canada 2010 for the following (8):

  • Ongoing maintenance and use of fire safety and fire protection features incorporated into the buildings
  • Identifying activities that might cause fire hazards in and around buildings
  • Limitations on hazardous contents in and around buildings
  • Fire safety at construction and demolition sites

7.1 Site Selection Purpose

Preliminary assessment of an industrial site involves an evaluation of technical site characteristics (e.g. hydrogeology, topography and soils conditions) and of socio-economic and geographic factors (e.g. cost, land use and availability, proximity to raw materials, markets and transportation routes). Subsection 7.2 provides recommendations on site features that can affect the eventual impact of a chemical release from wood preservation facilities.

In many cases, site-specific condition and characteristics may impose constraints including some of the recommendations to the design of facility. Recognizing these constraints early on in the design phase is important to ensure that these recommendations can be adopted fully.

7.2 Site Selection Assessment Factors

This section describes the important site-specific conditions and characteristics to be considered and design features that should be included in a wood preservation facility in order to:

  • minimize the potential of contaminating groundwater and surface water;
  • minimize the exposure of chemicals by on-site personnel; and
  • facilitate full and partial decommissioning of the facility.

7.2.1 Regional Geology

Federal and provincial surveys provide geological information in many parts of Canada. The following geological information is important site-specific conditions that should be obtained:

  • Texture of unconsolidated material - (e.g. fine-grained material is more likely to retain chemical contaminants than coarse material.);
  • Depth to bedrock - (e.g. shallow soils imply a limited ability to retain spilled chemicals.);
  • Aquifer recharge and discharge zones - (e.g. potential for hydraulic connections to regional groundwater and sensitive surface water bodies should be considered.); and
  • Discontinuities such as faults, fissures, joints, fractures - (e.g. discontinuities may cause “short-circuiting” of a contaminant plume.).

7.2.2 Soils

Soil properties should be assessed as it affects the potential of leaching. Physical properties to consider include: depth, permeability, texture, water-holding capacity and shrink-swell potential, etc. Chemical properties to consider include: cation exchange capacity, anion exchange capacity, organic carbon content, and iron and aluminium oxide content, etc.

Soils with high amounts of organic carbon will have a higher capacity for sorption of neutral organic compounds, soil with high anion exchange capacity will provide greater retention of dissociated phenols, and those with high cation exchange capacity will provide greater retention of organic bases. Soil with high anion exchange capacity, high levels of aluminium oxides, and/or high levels of calcium compounds will enhance the retention of arsenate and chromate anions, while soil with high cation exchange capacity, high clay content and high organic matter will enhance the retention of the copper cation.

Soil depth and soil types are routinely indicated on soil or geology maps. Although the available maps may not indicate the exact soil composition of a small site (e.g. 2 ha), they can be used for the purpose of preliminary assessment.

7.2.3 Hydrogeologic Description (including subsurface geology and water table)

Published maps and reports on regional geology and soils are adequate references for establishing subsurface hydrogeology at the preliminary site assessment stage. However, site-specific hydrogeological data will be required if one or more of the following conditions are identified during preconstruction assessment:

  • the site is located over a shallow, unconfined aquifer;
  • the site is located over an aquifer used for a potable or irrigation water supply; and
  • the aquifer has hydrogeological connections with other aquifers in the area and/or regional groundwater flow patterns.

The requirements for additional information should be discussed with the appropriate regulatory agency

7.2.4 Topography

Topographical information is easily obtained from published government maps. In general, steep sites are not recommended due to runoff problems and erosion. However, topography is a site selection parameter that can be addressed by facility design. In general, slope gradients in between 1% and 10% should present fewer concerns on runoff and erosion. Upland flat and terraced landforms are more desirable locations for treatment facilities. Floodplains are acceptable if they lie above the 100-year flood level; otherwise special design provisions should be implemented.

7.2.5 Climate

Climatic variables, such as precipitation (form, historical 1-hour and 24-hour maximums, and annual total amount), temperature regime and wind patterns influence chemical loss and leaching in the subsurface during storage of treated wood. Climatic variables can also influence conditioning needs for wood prior to preservation treatment and can affect worker exposure to emissions. Information on such climatic variables is generally available from Environment Canada. However, definitive criteria are difficult to establish for climatic influences. For example, the amount of precipitation will influence leaching potential, but this parameter can be alleviated by selecting sites with soils of low permeability and/or by introducing compensating design features at the facility (roof).

7.2.6 Proximity to Sensitive Area

Additional mitigation measure on the design and operation will be required for wood preservation facilities that are located adjacent to water bodies (e.g. lake, river, marine water), above drinking or irrigation water aquifers, agricultural land and food and beverage manufacturing facilities.

Desirable minimum distances between facilities and sensitive water bodies depend on a number of factors previously mentioned such as soil type, regional geology, topography and climate. If a selected site is adjacent to water bodies frequented by fish and/or by migratory birds, the design plans should be reviewed by both Environment Canada and Fisheries and Oceans Canada. In any case of a site located adjacent to a sensitive environment, it is recommended that users contact their local provincial and federal authorities to inform them and to learn more about the nature of the site and any additional requirements and/or applicable permitting processes (9).

7.3 Selection Procedures

In the process of selecting a site best suited to building a wood preservation facility, environmental protection measures as well as its associated cost should also be factored into the site selection decision-making process. On the basis of economic considerations alone, a less suited site environmentally-wise might be more desirable. However, the cost of adding additional environmental protection measures on a less well-suited site could potentially require significant costs. This trade off should be considered when selecting a site. In addition, requirements and application process among local municipal, provincial and federal regulatory agencies may be different; therefore, it is recommended that these agencies to be consulted and informed.

Table 9 provides examples of site characteristics and the degree of environmental mitigation measures that should be considered. In that table, the cost of adapting design and operational measures to mitigate environmental risks are likely to be lower for sites that are more suitable (slight).

These site features and the degrees of mitigating design/operational measures are based on site criteria suggested by various investigators (8, 10).

7.4 Recommended Design Features

Tables 10 to 16 provide the objectives and recommendations on the design features of a wood preservation facility that use a typical process in handling and application of preservatives, as presented in figure 1. All new and existing wood preservation facilities should be designed to meet all the objectives and apply all the recommendations presented in Tables 10 to 16 or apply alternative measures that meet the equivalent level of protection while taking into considerations site-specific conditions. For example, alternative measures may include automation machines that will lower the exposure to the pesticide by on-site personnel. Automatic door opening and closing of the autoclave can be a cost-benefit.

Note that roofing is recommended for several process areas. However, galvanized roofing may increase the toxicity of storm water runoff from mobilized zinc. Particular caution with such roofs should be exercised at sites near water bodies or in areas of low pH precipitation.

Users should refer to their provincial authorities, as these authorities may have additional design requirements that apply to their facilities.

7.4.1   Access and security design features

In order to prevent unauthorized access to the facility site, a restriction system and an access procedure should be in place. This design features are safety measures to avoid potential exposures and to restrict their access. Valves and any sensitive equipment or area like the chemical storage that could cause the release of chemical, should also be secured (locked) to prevent unauthorised access or usage.

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