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Post-Construction Standards

This page was developed to provide guidance for site design requirements of the Phase II Municipal Separate Storm Water Sewer  System (MS4) Permit. The City of Eureka is considered a traditional, small Phase II municipality and therefore is required to improve all provisions of the MS4 Permit.

All projects fall into one of three possible categories:

  1. Not Applicable

  2. Small Projects

  3. Regulated Project

Not Applicable

Projects that create and/or replace less than 2,500 ft2 of impervious surface are not subject to the standards outlined below.

Small Projects

Small projects are those that create and/or replace between 2,500 ft2 and 5,000 ft2 of impervious surface. This includes projects that have no net increase in the impervious footprint.

Examples

  • Single family homes that are not part of a larger development

  • Replacement of a parking lot

  • Construction of a new parking lot

  • Addition to a business

  • Demolition and reconstruction of a single family house that has the same or greater impervious footprint

  • A roadway or sidewalk project

Exclusions

  • Projects that have less than 2,500 ft2 of impervious surface

  • Linear underground/overhead projects (LUPs)

Process to Small Project Permits:

  1. Select a minimum of one Site Design Measures (SDMs). For guidance on SDMs, see Appendix 3 of the Humboldt LID Manual

    1. Tree Planting and Preservation

    2. Rain Barrels and Cisterns

    3. Rooftop and Impervious Area Disconnection

    4. Soil Quality Improvement and Maintenance

    5. Green Roofs

    6. Porous Asphalt, Pervious Concrete, Permeable Pavers

    7. Vegetated Swales

    8. Stream Setbacks and Buffers

    9. Infiltration Trench

    10. Subsurface Infiltration Devices – Dry Wells, Galleries and Proprietary Systems

  2. Identify the proposed runoff reduction measures

  3. Calculate runoff reduction using the Small Projects Calculator in the Humboldt LID Manual

  4. Sign and submit the Stormwater Control Plan (SCP) for Small Projects with the building permit application.

Regulated Projects

Regulated Projects are those that create and/or replace 5,000 ft2 or more of impervious surface, including new and redevelopment projects on private or public land. Redevelopment is defined as any land-disturbing activity that results in creation, addition, or replacement of exterior impervious surface areas on a site where some past development has occurred.

Examples

  • New streets or roads, including sidewalks and bicycle lanes built as part of the new streets or roads

  • Widening of existing streets or roads with additional traffic lanes

  • New or contiguous impervious surface at a discrete location within an LUP project – such as a pump station or maintenance facility

Exclusions

  • Detached single family homes that are not part of a larger plan of development (even if they exceed 5,000 ft2 of impervious surface)

  • Projects that are exclusively interior remodels

  • Routine maintenance or repair such as exterior wall surface replacement, pavement grinding and resurfacing within the existing footprint, and roofing replacement or repair

  • Projects consisting solely of sidewalks or bicycle lanes built as part of new streets or roads and built to direct storm water runoff to adjacent vegetated areas

  • LUPs – unless the LUP has a discrete location that has 5,000 square feet or more of newly constructed contiguous impervious surface. When the LUP has a discrete location that has 5,000 square feet or more of new contiguous impervious surface, only that specific discrete location is considered a Regulated Project.

Special Cases of Regulated Projects

Hydromodification Projects

  • Definition(s):

    • Hydromodification projects are Regulated Projects that create and/or replace one acre or more of impervious surface. A project that does not increase impervious surface area over the pre-project conditions is not a hydromodification project.

  • Unique Requirement(s):

    • Post-project runoff shall not exceed pre-project flow rate for the 2-year, 24-hour storm.

Redevelopment, Road Projects, and Linear Underground/Overhead Projects

  • Definition(s)

    • Redevelopment is any land-disturbing activity that results in the creation, addition, or replacement of exterior impervious surface area on a site on which some past development has occurred.

    • Road Projects and Linear Underground/Overhead Projects (LUPs) include any of the following project types that create 5,000 square feet or more of newly constructed contiguous impervious surface and that are public road projects and/or fall under the building and planning authority of the City:

      • Construction of new streets or roads, including sidewalks and bicycle lanes built as part of the new streets or roads

      • Widening of existing streets or roads with additional traffic lanes

      • Construction of linear underground/overhead projects

    • Road Project and LUP exclusions:

      • Sidewalks built as part of new streets or roads and built to direct storm water runoff to adjacent vegetated areas

      • Bicycle lanes built as part of new streets or roads and built to direct storm water runoff to adjacent vegetated areas

      • Impervious trails built to direct storm water runoff to adjacent vegetated areas, or other non-erodible permeable areas, preferably away from creeks or towards the outboard side of levees

      • Trenching, excavation, and resurfacing associated with LUPs; pavement grinding and resurfacing of existing roadways and parking lots; construction of new sidewalks, pedestrian ramps, or bike lanes on existing roadways; or routine replacement of damaged pavement such as a pothole repair or replacement of short, non-contiguous sections of roadway.

  • Unique Design Requirements:

    • Where a redevelopment project results in an increase of more than 50 percent of the impervious surface of a previously existing development, runoff from the entire project,  consisting of all existing, new, and/or replaced impervious surfaces, must be included to  the extent feasible.

    • Where a redevelopment project results in an increase of less than 50 percent of the impervious surface of a previously existing development, only runoff from the new and/or replaced impervious surface of the project must be included.

    • Where the addition of traffic lanes results in an alteration of more than 50 percent of the impervious surface of an existing street or road, runoff form the entire project, consisting of all existing, new and/or replaced impervious surfaces, must be included in the treatment system design.

    • Where the addition of traffic lanes results in an alteration of less than 50 percent (but 5,000 square feet or more) of the impervious surface of an existing street or road, only the runoff for new and/or replaced impervious surface of the project must be included in the treatment system design.

Process to Regulated Projects Permit

  1. Determine if the proposed project is considered a Special Case, and the applicable Unique Design Requirement(s).

  2. Complete a Stormwater Control Plan (SCP) for Regulated Projects, located in the Appendix 1 of the Humboldt LID Manual. For more information on how to complete the SCP for Regulated Projects, see Chapter 5 of the Humboldt LID Manual.

  3. Determine if the Alternative Compliance BMP Requirements Addendum to the SCP for Regulated Projects is applicable to the proposed project. If applicable, complete and attach to the SCP.

Humboldt LID Manual Steps to Consider:

  1. Draft a Preliminary SCP (discretionary projects only) using the template in this manual (Appendix 2) and submit to appropriate jurisdictional office for planning review.
  2. Draft a SCP using the worksheets and template in this manual;
  3. Draft a Stormwater Facilities Operation and Maintenance Plan (bioretention or equivalent facilities only, if required);
  4. Provide detailed project designs;
  5. Carry out construction;
  6. Transfer Maintenance Responsibility upon transfer of site (bioretention facilities, if required).
  7. Submit annual O & M certification (if applicable)