Director's Rule

Title

Stormwater Facility Credit Calculator Number

DWW-260.2 Rev. no.

3

Responsibility

Drainage and Wastewater Line of Business Supersedes

N/A Pages

2

General Manager/CEO signature

/s/ Andrew Lee Approval date

December 13, 2024 Effective date

January 1, 2025

A. PURPOSE

To improve the equity of drainage charges, Seattle Public Utilities (SPU) has developed a Stormwater Facility Credit Program. This program provides credits on drainage bills to customers who have installed approved stormwater management facilities that mitigate the impact on the City's drainage system of stormwater runoff from their property. Approved stormwater management facilities must meet applicable technical design requirements described in the City's Stormwater Code ("Stormwater Code") SMC 22.800.

B. BACKGROUND

The revised Stormwater Code became effective on July 1, 2021 per Ordinance 126336. The General Manager/CEO of SPU established the 2021 Stormwater Facility Credit calculator ("2021 SFC Calculator"), effective January 1, 2022, that reflected the updated performance goals of the City's Stormwater Code, as established per Ordinance 126336. As further discussed in the Rule, one input to the credit calculation is a Rate Tier Multiplier which varies by rate tier. Ordinance 127072 establishes new drainage rate tiers, effective January 1, 2025, this rule updates the 2021 SFC Calculator to include revised Rate Tier Multipliers based on the drainage rate tiers approved under Ordinance 127072. The updated 2021 SFC Calculator will continue to apply to facilities built according to 2021 code requirements.

The General Manager/CEO has also maintained the three preceding calculators which reflect the performance goals of the prior City Stormwater Codes. The 2016 SFC Calculator ("2016 SFC Calculator") applies to facilities constructed according to 2016 code requirements. The 2009 SFC Calculator ("2009 SFC Calculator") applies to facilities constructed according to 2009 code requirements. The 2000 SFC Calculator ("2000 SFC Calculator") applies to facilities constructed according to 2000 code requirements. This Rule also adjusts the Rate Tier Multipliers for each of these calculators to be consistent with the rate tiers established in Ordinance 127072.

C. RULE

SPU has developed a "credit calculator" that is the formula used to calculate the percentage credit for each eligible parcel that has applied for such a credit on its drainage bill. The output of the credit calculator is a percentage credit, which may not exceed a maximum percentage, as specified in SMC 21.33.040. Credits are rounded to the nearest whole percentage, with no credit offered to calculated credits that round to less than 1 percent. The credit is then applied as a percentage discount to the customer's annual drainage bill for the parcel.

This credit calculator assigns a uniform percentage credit for each type of approved stormwater management facility, based on a weighting of the stormwater performance goals the facility

satisfies and that are applicable to the appropriate drainage discharge point for that parcel. The credit calculator then considers information specific to the parcel, which is entered into the calculator by SPU, such as the percentage of the parcel's hard surface managed by the approved facility and the parcel's drainage rate category assignment. The 2021, 2016, 2009 and 2000 SFC Calculators include "Rate Tier Multipliers" which reflect the percentage of the drainage bill associated with runoff from hard surface, with such multipliers used in the calculation of the final stormwater facility credit applied to a parcel's drainage bill. The Rate Tier Multipliers vary by rate tier.

A list of all facilities that qualify as "approved stormwater management facilities" under this program is found in Table 1 (2000 SFC Calculator), Table 2 (2009 SFC Calculator), Table 3 (2016 SFC Calculator), Table 4 (2021 SFC Calculator) of Attachment A to this Director's Rule. These attachments also show the revised Rate Tier Multipliers.

D. REFERENCES

SMC 21.33.040, Stormwater Facility Credit Program

SMC 22.800, Stormwater Code

Ordinance 126336, amending Stormwater Code provisions

Ordinance 127072 adjusting drainage rates and amending Sections 21.33.010, 21.33.030, 21.33.040, 21.33.050, and 21.33.090 of the Seattle Municipal Code to reflect adjusted rates.

E. ATTACHMENTS

Attachment A - Table 1, Stormwater Facility Credit Program Credit Percentage Calculation: For facilities built according to 2021 and previous code requirements (Rev. 01/01/2025)

Attachment A -Table 2, Stormwater Facility Credit Program Credit Calculator: For facilities built according to 2016 code requirements (Rev. 01/01/2025)

Attachment A -Table 3, Stormwater Facility Credit Program Credit Calculator: For facilities built according to 2009 code requirements (Rev. 01/01/2025)

Attachment A -Table 4, Stormwater Facility Credit Program Credit Calculator: For facilities built according to 2000 code requirements (Rev. 01/01/2025)