Director's Rule

Title

Drainage Rate Low Impact Discount & Underdrained Athletic Field Classification Number

FIN-216 Rev. no.

0

Responsibility

Finance Division Supersedes

N/A Pages

2

General Manager/CEO Signature

/s/ Andrew Lee Approval Date

December 13, 2024 Effective Date

January 1, 2025

A. PURPOSE

This Director's Rule ensures that parcels are qualified fairly and consistently for drainage low impact discounts, pursuant to SMC 21.33.030.C.2. and establishes discount levels for qualifying parcels based on eligibility criteria. This Rule also provides guidance for billing treatment for certain underdrained athletic fields.

B. BACKGROUND

Low Impact Discount

The drainage billing structure effective through December 31, 2024, assigns properties containing sufficient amounts of "Highly Infiltrative Pervious Surface" (HIPS) to low impact rate tiers that offer lower rates than regular rate tiers based only on a parcel's percent of hard surface.

Ordinance 127072 adopts drainage rates for 2025 to 2027 for seven regular rate tiers defined by percentage ranges of hard surface. This ordinance eliminates drainage low impact tiers and instead provides for low impact discounts to be applied to the gross drainage bill calculated at regular tier rates for eligible properties.

Underdrained Athletic Field Classification

From 2010 - 2024, certain qualifying athletic fields with engineered designs had been eligible for treatment as HIPS area. Qualification required an application process and supporting documentation to establish that the fields met performance requirements.

Athletic Fields do not provide the same water quality and run-off mitigation benefits as tree or grassland areas. Consequently, effective January 1, 2025, athletic fields with underdrains no longer qualify as HIPS eligible for low impact discount consideration per Ordinance 127072.

C. DEFINITIONS

Highly infiltrative pervious surface (HIPS). Vegetated surface containing significant tree canopy or undeveloped grassland. (SMC 21.33.010.K)

Hard surface. An impervious surface, a permeable pavement, or a vegetated roof. (SMC 22.801.090)

Impervious surface. Any surface exposed to rainwater from which most water runs off. Impervious surfaces include, but are not limited to, roof tops, walkways, patios, driveways, formal planters, parking lots or storage areas, concrete or asphalt paving, areas with underdrains designed to remove stormwater from subgrade (e.g. playfields, athletic fields, rail yards), gravel surfaces subjected to vehicular traffic, compact gravel, packed earthen materials, and oiled macadam or other surfaces which similarly impede the natural infiltration of stormwater. (SMC 22.801.100)

D. RULE

Low Impact Discount

1. Qualification Criteria for low impact discount.

To be eligible for a low impact discount, a parcel must meet the following two criteria:

Contain no more than 20% hard surface, and

Contain at least 50% HIPS coverage

2. Discount Levels

The low impact discount applied depends on a combination the percentage of hard surface coverage and HIPS coverage:

Discount Level Minimum Highly Infiltrative Pervious Surface Amount (HIPS) Maximum Hard Surface Amount Discount

1 65% 0% to 10% 55%

2 65% 11% to 20% 45%

3 50% to 64% 0% to 10% 35%

4 50% to 64% 11% to 20% 30%

3. Administrative requirements

Utility staff will assign parcels to the discount levels noted above using GIS data

Parcel owners may appeal a low impact discount assignment (or lack of assignment), pursuant to SMC 21.33.050, Drainage Service Charge Adjustments.

Underdrained Athletic Fields Classification

Underdrained athletic fields are considered hard surface under SMC Chapter 22.801. However, these fields do infiltrate higher volumes of stormwater than other hard surfaces. Therefore, for drainage rate tier assignment under SMC 21.33.030, they will be considered a pervious surface, but are not a HIPS.

E. AUTHORITY/REFERENCES

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.

SMC 21.33.030.C.2, Drainage service charges and drainage ratesScheduleExemptions

SMC 21.33.050, Drainage Service Charge Adjustments