Prediction of Sanitary Sewer Overflow Conditions

Sanitary Sewer Overflows (SSOs) are caused by a variety of factors and may increase with sea level

rise, extreme storms, and groundwater inundation, creating health risks and environmental hazards.

Evidence of groundwater inundation and sea level rise is apparent from the Tamalpais Valley, (Mill

Valley), California extremely high tides (commonly called “King Tides”). Shallow groundwater,

sinking surface elevation, and complex subsurface hydrogeologic conditions in urban coastal

environments have created similar conditions in dozens of communities built on fill material on former

wetlands along San Francisco Bay. This research pilot project proposes using a network of surveyed

piezometers with battery-powered data loggers having remote telemetry system (RTS) connections to

provide real-time groundwater elevation, conductivity, and temperature data in preferential pathways,

such as utility trench corridors, leaky sewer pipes, and buried stream channels. The data would be

compared to measurements from background areas, as well as stilling wells in creek and adjacent bay

locations to measure tidal fluctuations. RTS sewage elevation and flow instruments are proposed for

sewer monitoring in manholes. RTS rain gauge data will provide precipitation measurements in real-time.

The data from the piezometer network, sewer instruments, stilling wells, and rain gauges would

be integrated for real-time notifications (at specific sewer and groundwater elevation thresholds) to

alert decision makers and emergency workers by cell phones and computers at the start of conditions

which can create SSOs. A secondary use of the data would be to identify the specific cause of the

potential SSOs so emergency workers can implement a rapid mitigation strategy prior to overflow of

sewage-containing waters above ground surface.