When precipitation falls to the ground it either: evaporates, percolates, or becomes stormwater. Evaporated water forms clouds. Percolation is when precipitation soaks into the soil filling the spaces between grains of sand and gravel saturating the ground. Precipitation that does not naturally evaporate or percolate into the soil is stormwater.
Stormwater can flow over land, in channels or pipes into a surface water channel, or to a facility designed to place the stormwater into the ground. Stormwater that is filtered into the ground is called stormwater infiltration.
Percolation in natural, undisturbed areas, along with stormwater infiltration, including that collected from man-made areas such as clean roof run-off, sustain the groundwater aquifer that Redmond uses to supply 40% of its drinking water.
The shallow groundwater aquifer in the valley areas of Redmond is only a few feet below the surface and is highly susceptible to contamination, so infiltration of contaminated stormwater is a potential problem.
City staff reviewed record drawings across the City and notified most owner/operators regarding their stormwater infiltration systems. If you were not contacted by the City, but suspect you have an infiltration system, check to see if there is City stormwater conveyance in the street near your property. If there are no catch basins near your property, it is possible that stormwater on your property infiltrates.
In Critical Aquifer Recharge Area I
The City of Redmond requirements originate from the 2003 Wellhead Protection Ordinance and recent updates to the ordinance in 2010 and 2013. The Washington State Department of Ecology (Ecology) also requires registration, assessment and modification of many of these same infiltration systems throughout the entire state. Owners who meet Redmond's requirements will also be in compliance with the Ecology's rules on infiltration.
Owners or operators of stormwater infiltration systems are required to evaluate and, if necessary, upgrade their stormwater infiltration systems to ensure protection of the underground drinking water resource.
Outside Critical Aquifer Recharge Area I
These stormwater infiltration systems are regulated by Ecology. Ecology refers to perforated pipes or dry walls used to infiltrate stormwater below the ground surface as Underground Injection Control Wells, or UICs. To register your UIC-type stormwater infiltration system, visit the Department of Ecology UIC page.
The City of Redmond Existing Stormwater Infiltration Assessment (Assessment) Criteria was developed to help owners and the City assess the site specific risks presented by stormwater draining into the ground.
The goal of the assessment process is to determine the risks to groundwater at a site and determine what modifications can be made to operations, physical structures or to the stormwater system to reduce the risk. The goal is to reduce each site's risk score to less than eight (8) points by putting permanent measures in place to protect groundwater.
Sites with scores less than or equal to seven (7) are identified as low risk sites. Low risk sites must implement Best Management Practices (BMPs) applicable to their site to help ensure long term protection of groundwater. Sites with scores higher than seven (7) are identified as potential significant groundwater hazard sites. Higher risk sites must implement required BMPs as well as modifications to their stormwater system or operations.
The criteria for completing assessments and modifications to existing stormwater infiltration systems were adopted by the City Council as Ordinance 2521 in 2010. Ordinance 2704 was adopted in August 2013 to extend the schedule and provide incentives to owners to complete their assessments and modifications to protect groundwater. Ordinance 2791 was adopted in June 2015 to extend the reimbursement time frame for projects from 2 ½ years to 3 ½ years for design, permitting and implementation of retrofits.
Incentives are available to encourage timely implementation of stormwater system modification. Ordinance 2704 has complete details on the incentive program and elimination of permit fees for required modifications.
Ordinance 2704 provides incentives to owners/operators that work with the City to promptly address the risks identified in the assessment and make the modifications required by the City on schedule. The schedule varies depending on the risk score for each site.
The City of Redmond's Environment & Utilities staff collaborated with businesses and the Chamber of Commerce through a series of meetings in 2012 and 2013 to update the schedule for implementation, work with a group of pilot sites that are preparing to implement their changes, and proposed significant incentives to offset the cost of modifications necessary to protect the aquifer. The process was endorsed by Ecology as meeting their assessment requirements and was supported by the businesses that participated in its development.
You can ensure that activities at your site are not creating a stormwater or groundwater hazard by properly handling and safely storing chemicals, avoiding spills, and that minimize use of where possible to help protect our drinking water resource.
City of Redmond code requires that "any facility, activity, or residence in the City in which hazardous materials or other deleterious substances are present shall be operated in a manner that prevents their release to the environment" and ensures that they do not "pose a significant groundwater hazard".
All facilities are required to implement the Required Operational and Structural BMPs to protect groundwater from stormwater contamination.
These BMPs include, but are not limited to, basic practices like:
- forming a spill prevention team
- good housekeeping
- preventative maintenance
- spill cleanup
- regular inspections, and
- record keeping
These measures are required by the City of Redmond Wellhead Protection and Stormwater Codes.
The Stormwater Management Manual for Western Washington Volume IV can help to provide information on design, operation and maintenance of all stormwater systems.
If you would like to request a technical assistance visit from a City staff member, or have additional questions, see our Contact Us section of this page, or King County's Local Hazardous Waste Management Program page.