TRASH FLOOD: Seas Rising Into Sewers

Usually when one thinks about rising sea levels, the image of disappearing beaches comes to mind. In fact, new research is showing that coastal populations are experiencing rising sea-levels up to four times faster than the global average. In statistical terms, that’s 7.8 mm to 9.9 mm per year over the last twenty years compared to a global average rise of 2.6 mm. There are the obvious issues of subsidence to consider, where 58% of the world’s coastal population lives on deltas where land is subsiding. However, signs of other issues are arising as well: namely, computer modeling studies that indicate that coastal wastewater infrastructure – sewer lines and cesspools – are flooding with groundwater as sea-levels rise.

A new study provides clear evidence that tidally-driven groundwater inundation of wastewater infrastructure is becoming a major problem. Higher ocean water levels means contaminated wastewater is entering storm drains and the coastal ocean threatening coastal water quality and the surrounding ecology. Coastal ocean water and storm drain water was assessed in low-lying areas during spring tides, which can provide a helpful indication of future sea levels. To assist their research and increase their understanding of the connection between wastewater infrastructure, groundwater and the ocean, chemical tracers were employed to detect the presence of groundwater discharge and wastewater per testing site. Results concluded that groundwater inundation and wastewater discharge to the coast and storm drains are prevalent at an alarming scale. 

Studies are demonstrating that, in low-lying inland areas, overflowing storm drains occur during every spring tide while wastewater from weakened and collapsing infrastructure is discharging into storm drains. When the tide is high, these storm drains become conduits for untreated wastewater which causes contaminants to flood into the streets and onto the sidewalks. One can clearly observe how flooding negatively impacts traffic in these regions, but less obvious, perhaps, is how it establishes a very real risk to human and environmental health. Even worse, the studies showed that many of the contaminants associated with human activity existed in high risk concentrations for aquatic organisms. Researchers cite how sea-level rising remains a problem “down the road” but these recent studies demonstrate how damaging effects are being felt today. They also suggest that, if unaddressed, these threats to both human and ecological health with only increase in frequency and magnitude.

Therefore, a perspective evolves that any actions taken to address the threats of sea-level rise in terms of how it mixes dangerously with collapsing coastal wastewater infrastructure can be considered actions taken to address an imminent crisis rather than ones that can be considered proactive. Studies state unequivocally that coastal municipalities should immediately incorporate strategies to mitigate and account for the dangerously cooperative nature of wastewater infrastructure and clean water resources. There exists an urgent need for new infrastructure design that protects water resources from flooding and contact with contaminated water. There is also a need to develop infrastructure that decreases the sources of contamination such as cesspools and defective sewer lines, and considers the construction of raised walkways and streets.

Sea levels will continue to rise as the earth continues to warm up, which means increasing pressure on existing infrastructure. While the amount of storms is not expected to increase, the effects of stronger winds and rain is predicted to generate a more damaging impact. Because increasing occurrences of heavy rainfall are going to stress wastewater and stormwater infrastructure which is often located underground at the coast, the time has come to plan for extreme adaptation where even retreat might be necessary. Failure to do so in time could cause service outages and steep cost increases. Retreat is a scary, doom-laden word but approaching it in a staged and structured way may be the most cost-effective method of increasing safety through the repurposing of certain frequently-flooded areas of the community. 

Graver has long-focused on designing and manufacturing products that address clarifying aqueous based waste streams, particularly in industrial process communities. Waste streams must be treated before recycling, reusing or discharging into municipal wastewater systems or surface waters. The type of treatment needed will depend on the type of industrial process and the resulting contaminants present in the waste stream, and Graver will work with you to determine the best treatment scheme to address your unique situation.