Timber Products - Wood Products Sector Stormwater Requirements

The Minnesota Pollution Control Agency (MPCA) has issued its revised multi-sector industrial stormwater discharge general permit (MSGP). This permit will replace the existing industrial stormwater permit, which expired in October of 2002.

[Read a summary of the overall Minnesota permit, stormwater monitoring, and sector requirements]

All manufacturing, industrial and “industrial-like” sites that require a permit to discharge stormwater will be required to come into compliance with the revised permit, and to submit an application for permit coverage by either June 1, August 1 or October 1, depending on their industrial sector.

Click here to review a list affected industrial sectors and application deadlines for each sector

The revised permit details requirements for 29 different industrial sectors. The requirements described below are for the Timber Products Sector (Sector A). Sector A covers a fairly broad range of facility types, including log storage or handling areas, mills, producing lumber and wood basic materials, wood preserving, manufacturing finished articles made entirely of wood or related materials, and manufacturing wood buildings or mobile homes. These requirements are in addition to permit requirements that apply to all sectors.

Inspections:
If the facility performs wood surface protection and preservation activities, inspections must include processing areas and treated wood storage areas to assess the effectiveness of practices to eliminate the deposit of treatment chemicals on unprotected soils and eliminate all contact with stormwater discharges. At least two of the monthly inspections must be conducted during runoff events. One of the inspections must be performed during a snow melt runoff event.

Industry-Specific Stormwater Controls:
The facility must have secondary containment for all significant materials stored indoor and outdoor, (e.g. arsenic, chromium, zinc, copper, and phenolic solution storage tanks and structures). Facility must also drain containment stormwater for outdoor storage tanks and structures only after inspection demonstrates that no stormwater contact with solutions has occurred.

Potential Pollutant Sources:
If the operation uses chlorophenolic, creosote, or chromium-copper-arsenic formulations for wood surface protection or preserving, the SWPPP must document 1) areas where contaminated soils, treatment equipment, and stored materials still remain, and 2) the management practices employed to minimize the contact of these materials with stormwater runoff.

Stormwater Monitoring Benchmarks:
All facilities are required to conduct visual and chemical (benchmark) monitoring. For benchmark monitoring, the benchmark concentrations or values depend on product type:

General Sawmills and Planing Mills (SIC 2421):
COD 120 mg/L
TSS 100 mg/L
Zinc 0.234 mg/L

Wood Preserving (SIC 2491):
TSS 100 mg/L
Total Arsenic 0.680 mg/L
Total Copper 0.028 mg/L
Total Chromium III 3.5 mg/L
Total Phenols 4.4 mg/L

Log Storage and Handling (SIC 2411):
TSS 100 mg/L

Wet Decking:
pH 6 - 9

Discharges at Log Storage and Handling Areas (SIC 2411):
TSS 100 mg/L

Hardwood Dimension and Flooring Mills and others:
TSS 100 mg/L
COD 120 mg/L

Nailed Wood Boxes and Shook (SIC 2441-2449):
TSS 100 mg/L

Note: Benchmarks for zinc, copper, chromium, phenols, arsenic were derived based on the Aquatic Life Standards for these parameters in Minnesota Rules.

[Read more about use of Aquatic Life Standards to derive stormwater benchmarks]
[Read more about how benchmarks are used under the proposed MPCA industrial permit]
[Read more about what a 100 mg/L benchmark for TSS relates to]


Looking for other sector information?
Click here for a link to all sector requirements

Caltha LLP provides expert consulting services to public and private sector clients nationwide to address Stormwater Permitting & Regulatory Support, Stormwater Pollution Prevention Plans (SWPPP), Stormwater Monitoring and Stormwater Training.

For further information contact Caltha LLP at
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