S5.C.2 Mapping
There are no specific deadlines or actions required for continued compliance with section S5.C.2 for reporting year 2024
"The City’s stormwater system must be mapped".
Summary of Program Component
The overall objective of this requirement is to maintain an ongoing program to map and document the existing stormwater system and ensure that future connections and other system changes are documented and mapped.
Mapping and documentation of the stormwater system is vital to managing the resources of the City. By identifying connections to the stormwater system and understanding their relationship to overlaying drainage basins, analyses can be performed on the entire system. This information will also assist in providing service to underserved areas and development of solutions to capacity problems. The City is using mapping information in a variety of ways, including tracking sources of contamination, planning for future upgrades and modeling system capacity.
Ongoing Mapping of Known Outfalls and Discharge Points, Receiving Waters Other than Groundwater, City-owned Structural Stormwater Treatment and Flow Control BMPs, Geographic Areas Served by the Municipal Separate Storm Sewer System (MS4) that do not Discharge to Surface Water, and Connection Points between the City’s MS4 and Other Municipal Systems (S5.C.2.a.i,ii,iii,iv,vi.)
The Environmental Programs Group and Asset Management Group of ES have an existing mapping and documentation program to meet this requirement.
Mapping Public Assets
Known public assets are mapped, however, this work is ongoing. As new stormwater assets are installed, they are mapped. Many features are available to view on tacomaMap (tMAP) – the City’s public GIS viewer. Other features are available upon request. Existing flow control and treatment facilities owned or operated by the City are mapped. All known MS4 outfalls to marine and fresh waters are mapped. All discharge points, as defined in the permit are mapped. As the City maps new public treatment and flow control facilities, the inlets and outlets, including emergency overflows will be mapped.
A process exists to add new stormwater system features into our mapping system after they are constructed.
Process for adding newly constructed public stormwater assets and geographic areas not discharging to surface water into the City’s mapping system:
ES, Engineering Technician receive approved plans from either PDS, Site Development Group (for private work order permits) or from the City Project Manager (for City Capital Improvement Projects).
The new assets, including pipes, underground facilities, above ground facilities, and geographic areas not discharging to surface water (facilities designed to infiltrate all stormwater runoff) are input into the City GIS system as “proposed” by the ES Engineering Technician.
Upon physical completion of construction of the project, the Construction Inspector will inform the ES Engineering Technician of any new stormwater facilities that are completed.
Before final acceptance of stormwater facility / pipe assets, an ES/Operations and Maintenance crew receives notification to video inspect the pipe for acceptance. At this point, the ES Engineering Technician will re-label those proposed assets as “active.”
It is ultimately the responsibility of the City Project Manager to ensure that the assets related to their project are correctly mapped in the City GIS systems.
Mapping Geographic Areas Served by the City’s MS4 that do not Discharge Stormwater to Surface Water
The scope of this requirement includes mapping areas that drain to public stormwater facilities designed to infiltrate all stormwater.
Mapping Storm Sewer Interconnections between Municipalities
City staff collected GIS storm system data from Fife, Pierce County, Lakewood, University Place, Ruston, Fircrest and Federal Way. All known connection points between the City MS4 and other municipalities have been generated from this data, and as mapping and data collection continues or as new connections are made, the new information will be added to the City’s mapping systems.
(Click below to go to tMAP)
Map Tributary Conveyances of all known Outfalls and Discharge Points with a 24-Inch or Greater Nominal Diameter or an Equivalent Cross-Sectional Area for Non-pipe Systems (S5.C.2.a.v.)
The known outfalls and discharge points and connections are in the City’s mapping system. Upstream tracing of each outfall and discharge point and determination of each associated contributing basin is complete. Land use is known and conveyance pipe type, material and size are included in the City mapping system, when known.
Map all Connections authorized or allowed to the MS4 (S5.C.2.a.vii.)
The City has already mapped the majority of the known private storm systems connected to the MS4 throughout Tacoma. Newly permitted and constructed private drainage system connections will continue to be added to the mapping system. Additionally, video camera investigations occasionally discover additional smaller private pipes connected directly into the storm lines. The previous permit cycle required assessment of the City’s entire system and very few non-stormwater connections were identified. The City continues to investigate our system for non-stormwater connections and when found, the discovered connections are investigated to identify their source. Non-stormwater connections are redirected as appropriate and stormwater connections are mapped.
This work is continually updated as connections are added. PDS Inspectors sign off on all new storm connections through construction permits. For all projects involving connections to the MS4, a storm connection permit is required in order to ensure the connection is properly made and inspected. The City also has permitting requirements for wastewater connections; this ensures that wastewater services are connected to the wastewater mains and not the stormwater mains.
The process for adding newly constructed private drainage system connections into the City’s mapping system includes:
Upon final inspection of construction permits, the PDS Engineering Technician will record the private drainage system point of connection to the MS4 and note it on the storm connection permit drawing. The storm connection permit drawing is saved in the City permitting system.
ES Engineering Technician reviews the City permitting system and will then input the new private connection points into the mapping system as “storm private connection” and include the permit number in the point description to allow for the electronic site plans associated with that permit to be researched, if necessary.
If the ES Inspector notes are insufficient and there is a need to field-verify the location of the private connection point, the ES Engineering Technician will assign the mapping crew to locate the connection.
The City’s database of privately owned treatment and flow control facilities is being updated to assist with annual inspections of private facilities.
Map All Known Existing Stormwater Connections with Greater than or Equal to 8-Inch Nominal Diameter (S5.C.2.a.viii.)
The City has mapped all known existing connections greater than or equal to 8-inch nominal diameter.
Collect size and material for all known MS4 outfalls during normal course of business (S5.C.2.b.i.)
The City has size and material information for all known outfalls. If new or unknown outfalls are discovered, this information will be added to the City database. An electronic application to add mapping information has been developed for field staff to use when visiting outfalls.
Complete mapping of all known connections from the MS4 to a privately owned stormwater system (S5.C.2.b.ii.)
The City has typically included this information in our map. The data points will be reviewed, and if needed additional notes or attributes will be added to clarify these locations.
Provide Ecology with Mapping Data for all Requirements of S5.C.2.a, and b. above (S5.C.2.d.)
Provide Mapping Information to Federally Recognized Indian Tribes, Municipalities and Other Permittees (S5.C.2.e.)
Most required stormwater mapping information is available to view on tacomaMap (tMap) – the City’s public GIS data viewer. All other information is available upon request. Tribes, municipalities and other permittees currently have access to system information. If individual requests for information are made from one of these parties, the City will work with them to provide the needed information in an agreed upon format.