Low Impact Development Surface Water Rate Reduction

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Property owners may qualify for a surface water rate reduction if they choose to utilize permanent Low Impact Development (LID) Best Management Practices (BMPs) beyond what is required per the Stormwater Management Manual (SWMM) for development or redevelopment or as a retrofit for stormwater management.  Tacoma Municipal Code (TMC) 12.08.560 outlines the program requirements.

In order to qualify for the LID surface water rate reduction, all BMPs must be permanent LID BMPs per the SWMM, Volume 3, or Volume 6, as approved by Environmental Services.

The project proponent shall:

  1. Request the rate reduction prior to construction of the LID BMP(s).
  2. Submit project design information to the City for review.
  3. Implement LID BMPs beyond that required by development regulations, if applicable.
  4. Utilize LID BMPs to mitigate a surface or surfaces to the maximum extent feasible.
  5. Obtain all required permits.
  6. Allow the City to inspect the project site during and after construction.
  7. Develop an Operations and Maintenance Manual for the BMP.
  8. Submit yearly Operations and Maintenance Reports to Environmental Services.
  9. Enter into a Covenant and Easement Agreement (C&E) with the City. For projects not required to obtain City of Tacoma permits or for retrofit projects, the City will pay to record the C&E.

Qualifying Best Management Practices (BMPS)

All BMPs must be permanent BMPs designed per the design criteria and intent as outlined in the SWMM.  BMPs must take a significant portion of the runoff from an otherwise unmitigated surface, and the selected BMP must be appropriate for the surfaces (for example, if the surface would require water quality, the BMP must provide it).

Typical LID BMPs include:

  • BMP L601 Rain Gardens,
  • BMP L602 Downspout Full Infiltration (infiltration trenches, drywells),
  • BMP L603 Downspout Dispersion (splashblocks with an appropriate flowpath, dispersion trenches),
  • BMP L611 Concentrated Flow Dispersion,
  • BMP L612 Sheet Flow Dispersion,
  • BMP L613 Post-Construction Soil Quality and Depth,
  • BMP L614 Full Dispersion,
  • BMP L615 Tree Retention & Transplanting,
  • BMP L620 Preserving Native Vegetation,
  • BMP L630 Bioretention,
  • BMP L631 Vegetated Rooftops (green roofs),
  • BMP L632 Rainwater Harvesting (cisterns),
  • BMP L633 Permeable Pavement

Rate Reduction Amount
The rate reduction is available for permanent LID BMPs beyond what is required per the SWMM for development or redevelopment or as a retrofit for stormwater management.
• Mitigating one surface with LID qualifies the property owner for a one category rate reduction.
• Mitigating all surfaces on a property with LID qualifies the property owner for a two category rate reduction.
• The rate can never be lower than the undeveloped rate for the property.

Maintenance Requirement
If the property owner fails to maintain the LID BMP or if it stops functioning, the City can revoke the approval and the rate reduction.

Greenroof located at the City of Tacoma’s Center for Urban Waters

For more information, contact:
City of Tacoma Environmental Services, Merita Trohimovich (253) 502-2103

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