2013 Water System Plan, Volume II - Seattle City Clerk's Office - City ...

Chapter 5 Water Infrastructure
3. The surface below the air gap must slope away from the storage cell and direct the
flow to a sump or catch basin from which the flow is conveyed to the designated
discharge point.
The following are guidelines for overflow pipes:
If the overflow water enters a sewer, check sewer pipe hydraulics for any constraints
to accepting the design overflow rate.
If the overflow water can enter a natural stream or pond directly from the discharge
point, a passive dechlorination system should be installed. For example, a passive
dechlorination system is a catch basin within which bags of a dechlorination
chemical (ascorbic acid or sodium thiosulfate) are placed. The overflow water is
passed through the dechlorination structure before discharge to the receiving water
body.
In addition to a screen, consider installing a flap gate or duckbill valve at the end of
the overflow pipe to prevent animal access.
Note: Overflows usually go to a reservoir’s dedicated storm drain line. This line must also be
capable of the flow rate. The receiving water body must likewise be able to receive this flow rate.
5.9.5.5 Connections
Connections between the storage cell structure and pipes external to the structure (either
exposed or buried pipes) should allow for longitudinal expansion and lateral movement that
occurs during earthquakes and through long-term differential settlement. Pipes located under
ground-level reservoirs should be encased in reinforced concrete to minimize future
maintenance.
5.9.5.6 Hatches
The following are SPU standards for water storage hatches:
1. All access hatches not bolted to the main structure must be lockable and provide
intrusion switches linked to the SCADA system.
2. Hatch lids must be designed to prevent drainage runoff from entering interior of the
hatch and/or accumulating next to the hatch area. This also provides protection
from ice damage. For hatches with raised curbs or frames, the lid should overlap the
curb/frame.
The following are guidelines for hatches:
For accessible ground-level hatches to concrete reservoirs, the hatch should be
designed either to lock or to accommodate a 600-lb block or lid on top.
Hatches manufactured by LW Products or Bilco have typically met SPU requirements.
Hatches installed in graveled areas should be raised above grade to prevent gravel
from becoming lodged and jammed between the frame and the lid, or becoming
lodged in the locks.
5.9.5.7 Access Ladders and Catwalks
Fall protection equipment must be provided and used before accessing structure
SPU Design Standards and Guidelines
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