Sno Co. Policy Guidelines for EC

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Snohomish County Policy 3044 SELECTION OF STANDARDS

FOR CONSTRUCTION STORMWATER POLLUTION PREVENTION PLAN

This policy applies to selecting the Best Management Practices (BMPs) and stormwater pollution prevention measures for construction activities that require a permit or approval from Snohomish County. See also POL 3490 that addresses erosion control standards to be met for development of subdivisions and commercial projects. The Water Pollution Control Ordinance (7.53 SCC) requires that contaminated stormwater not be discharged from a site. This policy outlines a process to establish the level of planning to obtain construction approval, and development permits from Snohomish County.

The regulations from the Washington State Department of Ecology (DOE), the County’s National Pollutant Discharge Elimination System (NPDES) permit, and Critical Area Regulations (CAR) all require additional planning and documentation of the plan for pollution prevention. This policy establishes guidelines for plan approval before issuing a development permit, construction plan approval, or notice to proceed. The Washington State Department of Ecology current regulations for NPDES permits and regulations for Construction Stormwater Pollution Prevention require that a Stormwater Pollution Prevention Plan (SWPPP) be prepared for land disturbing activities. In the past, this plan for land disturbing activity was called an erosion control plan (or TESC plan). This policy outlines additional requirements for preparation of drainage plans and reports in Snohomish County. This policy also outlines the process for selecting the appropriate level of plan. Definitions to some of the terms used are in PRO-3044.

1. The Construction Stormwater Pollution Prevention Plan (SWPPP) Shall Plan For Erosion Control For Land Development Projects.

A. The plan is to be prepared in accordance with this policy.

B. The documentation of the plan consists of the construction plans and specifications, and the drainage report

2. Subdivisions Shall Vest to the Appropriate Standards.

A. Subdivisions shall vest to the standards in effect when the preliminary application was declared complete.

· If the subdivision application was declared complete before September 19, 1998, the subdivision is vested to standards of the original Title 24 ordinance, adopted January 12, 1979.

· If the subdivision application was declared complete on or after September 19, 1998, current codes and standards shall be used.

B. Plat construction does not vest for issues under ESA and standards for water quality. The current ordinances prescribe the allowable length of time for exposed soil on any site during the construction season. When permitted by plan approval, additional exposure may be allowed during the wet season (October 1 to March 31).

C. The requirements in the new standards shall be used by the design engineer as a guide when preparing the construction SWPPP for a subdivision vested under the prior regulations.

3. Standard Selection Process Shall Be Used For Construction SWPPP

A. This policy provides for a predictable selection process to be used in conjunction with the Risk Assessment required by POL 3042 and POL 3490. The elements of the construction plan which govern selection are:

· Area of exposed site for each phase;

· Relationship to receiving water or critical area, and ESA areas;

· Season the grading is proposed;

· Characteristics of the site (slope, soil, quantity of material, ability to contain the runoff, percent of vegetation to remain on site, etc.).

B. The level of planning required for the SWPPP is based on the above and other criteria outlined in this policy. Guidelines are established in this policy for approving grading in the wet season (October 1 to March 31). (Wet season grading will be referred to as “winter grading”) in this policy.

C. The information in the full drainage report (in some cases the targeted drainage report) will be used to select the level of construction SWPPP, and to determine whether winter grading will be allowed. The process of selecting the level of SWPPP is based upon first determining the risk category, and then applying the appropriate level of planning and proposed implementation.

D. The risk category is divided in four groups, primarily based upon the risk in the event erosion control effort fails to prevent construction pollution.

4. The Site Shall Be Assessed For Risk Factors and Assigned a Risk Category

When assessing the site for risk factors that will determine the risk category, the definitions in PRO-3044 shall be considered. To assign the risk category, apply the risk factors to the site. An evaluation made during the summer may not identify problems that become obvious when the rain is falling on disturbed soil. The risk is categorized in four levels based upon the likelihood, or probability, of harm to the resource to be protected. The most restrictive site characteristic shall be used to assign the category.

A. Low Risk:

· Winter grading is not proposed;

· Less than 1 acre will be disturbed;

· Average slope is less than 8%, (up to 15% for areas with less than 5000 square feet total);

· Soil with low erosion hazard when worked and exposed to rain;

· Permeable soils;

· No critical areas or buffers located down slope or within ¼ mile down stream of discharge point of stormwater;

B. Medium Risk:

· Less than 5 acres (but more than 1 acre) will be disturbed;

· Average slope is more than 8%, but all areas are less than 15%;

· Soil with low erosion hazard when worked and exposed to rain;

· No critical areas or buffers located down slope or within ¼ mile down stream of discharge point of stormwater;

· If needed, additional BMPs can be implemented as corrective measures.

C. High Risk:

· More than 5 acres (but less than 20 acres) will be disturbed;

· Average slope is more than 8% but less than 15%; all slopes are less than 33% or, if created by grading, will have protection subsequent to grading activity;

· Soil with medium erosion hazard when worked and exposed to rain;

· There are critical areas or buffers located down slope or within ¼ mile down stream of discharge point of stormwater;

· The site is upstream of a stormwater path that does not flow directly to an ESA stream;

· If needed, additional BMPs can be implemented as corrective measures.

D. Very High Risk:

· The site has more than 20 acres being disturbed;

· Slope is more than 15%;

· Soil with more than medium erosion hazard when worked at any time during the grading process;

· There are critical areas or buffers located down slope or within ¼ mile down stream of discharge point of stormwater;

· The site is upstream of any stormwater path that flows directly to an ESA stream;

· Experimental BMPs are proposed.

5. Planning For the Construction SWPPP Shall Be Based Upon the Risk Category

The construction SWPPP is characterized by three levels of complexity based on the risk category for the site. See the decision matrix in PRO 3044 for information on levels and reasons for assigning the appropriate level. The amount of planning (including contingency planning) shall provide the distinction between the three levels of SWPPPs. The level 3 SWPPP requires consensus of the development review teams, contractor and contingency planning. Residential small parcel (single family residential), and other small parcel development activities that do not require a full drainage plan normally do not require a SWPPP. Those projects can use simple erosion control BMPs. PDS single-family residential staff may assist in providing standard BMPs appropriate to the site as an attachment to the plans during the site review process.

A. Level 1 SWPPP. The plan and report prepared by the project engineer may use standard BMPs that are appropriate to the site and anticipated erosion control issues. In the case of single-family residential permits, the applicant or builder may prepare the plans by using standard BMPs.

B. Level 2 SWPPP. The plan and documentation covers a careful assessment of the risk to resources.

· The risk assessment will integrate the site-related elements such as slope, soil, location of critical areas, geo-technical stability, groundwater, and offsite sources of water flowing into the construction area;

· The plan and documentation will cover all 12 elements listed in PRO-3044 in detail for the Construction SWPPP;

· The plan shall contain a contingency section to cover anticipated problems if weather interrupts the construction at various critical phases;

· The level of technical difficulty providing a level 2 SWPPP usually requires that plans be prepared by a professional.

C. Level 3 SWPPP. The plan and documentation incorporates all of the elements of a Level 2 plan. A consensus that the plan is feasible is required by a review team composed of the following people:

· Project Engineer who prepared the plans;

· Applicant’s or Developer’s Project Manager;

· General Contractor and, if applicable, Grading Contractor’,

· County Inspector;

· County Plan Reviewer or Engineering Leader;

· When an ESA stream or critical area impact is involved, the review team will also include the PDS biologist and applicant’s biologist;

· If a consensus cannot be reached, a committee of three shall be appointed by the PDS Director or County Engineer to resolve the issues.

6. A Plan Revision is Required when Winter Grading Is Not Shown On Approved Plans

When approved construction plans for project do not have provisions for grading after October 1^st and the work is not completed, grading shall not occur until revised construction plans have been approved. The only work allowed is site stabilization and erosion control activities. Applications for revisions to construction plans shall use the process outlined in this policy and associated procedure for approval of winter grading.

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