63-Inch Force Main Reliability Improvement Project

o Existing pipe designed for gravity outfall flow – peak storm flows raise pressures above design pressure

o Single gasket joint every 12’ subject to leaks with movement of groundo Vertically pulled (angled) joints that pull further apart and leak with young

bay mud movement or vertical loadingo Hydrogen sulfide gas from sewage eating away at unlined pipe - concrete

and steel decayingo Leaks would spill into commercial and residential areas – potential damage

associated with spill is very higho Upstream sewer system improvements (to reduce upstream spills) will

increase flows and therefore pressures in force maino Events that increase likelihood of leaks:

Earthquakes Surge from sudden power outage

Need for Project

Likely scenarios for leaks: Earthquakes

Earthquake induced young bay mud movement Earthquake causes young bay mud to move as earthquake

forces act on loads near pipe Pipe joints move when young bay mud moves Single gasket joints open and concrete pipe at joints crack Sewage then leaks to surface in commercial or residential

area Standard response when a leak is noticed is to turn on the

SBSA influent pumps to reduce pressures in the pipe Turning on SBSA influent pumps does not stop the leak

during high flow events when the influent pumps are already on – the combination of booster pumps and influent pumps are needed to carry high flows

Likely scenarios for leaks: Power Outage

Sudden surge caused by power outage during storm event During storm events with high flow a sudden power outage may occur Pumps suddenly turn off when power cut (before generator can come on) Flow continues to move down pipe with no new flow following creating a

vacuum in the pipe pulling the decaying concrete pipe inward The vacuum then reverses the sewage flow and sewage flow slams back into

the pump station Extremely high outward pressure is created which bursts the decaying pipe

resulting in a sewage spill (the pipe in the worst condition has been replaced) During a storm event (with huge sewage flows) the normal process to

address a leak of turning on the influent pumps at the treatment plant will not be enough to prevent an ongoing spill (the influent pumps will likely already be on)

The spill will continue through the break in the pipe or if the pumps are turned down the spill will occur upstream in the system as flows back up

Proposed Pipe: HDPE

High density polyethylene pipe At least 3 inches thick Continuous pipe with no joints – pieces

are fusion welded to each other Not affected by corrosion Pipe sections when accidently crushed

flat go back to original shape with no cracking or failure

Pipe sections pressure tested to failure reach five times the design pressure before getting a small hole (no catastrophic failures)

Most impacts from digging equipment to outside glance off pipe

Risk of cutting into pipe very low when pipe is in a location with minimal construction activity (like a levee)

Break after surge due to power outage

Leak near Governors Bay Dr. – leaked at joint which was broken – took weeks to fix

Leak near Governors Bay Dr. – more