Hell and High Water: Diminished Septic System Performance in Coastal Regions Due to Climate Change

Abstract

Climate change may affect the ability of soil-based onsite wastewater treatment systems (OWTS) to treat wastewater in coastal regions of the Northeastern United States. Higher temperatures and water tables can affect treatment by reducing the volume of unsaturated soil and oxygen available for treatment, which may result in greater transport of pathogens, nutrients, and biochemical oxygen demand (BOD5) to groundwater, jeopardizing public and aquatic ecosystem health. The soil treatment area (STA) of an OWTS removes contaminants as wastewater percolates through the soil. Conventional STAs receive wastewater from the septic tank, with infiltration occurring deeper in the soil profile. In contrast, shallow narrow STAs receive pre-treated wastewater that infiltrates higher in the soil profile, which may make them more resilient to climate change. We used intact soil mesocosms to quantify the water quality functions of a conventional and two types of shallow narrow STAs under present climate (PC; 20°C) and climate change (CC; 25°C, 30 cm elevation in water table). Significantly greater removal of BOD5 was observed under CC for all STA types. Phosphorus removal decreased significantly from 75% (PC) to 66% (CC) in the conventional STA, and from 100% to 71–72% in shallow narrow STAs. No fecal coliform bacteria (FCB) were released under PC, whereas up to 17 and 20 CFU 100 mL-1 were released in conventional and shallow narrow STAs, respectively, under CC. Total N removal increased from 14% (PC) to 19% (CC) in the conventional STA, but decreased in shallow narrow STAs, from 6–7% to less than 3.0%. Differences in removal of FCB and total N were not significant. Leaching of N in excess of inputs was also observed in shallow narrow STAs under CC. Our results indicate that climate change can affect contaminant removal from wastewater, with effects dependent on the contaminant and STA type.

Sea-Level Rise Induced Multi-Mechanism Flooding and Contribution to Urban Infrastructure Failure

“…However, results of this study remain relevant to such areas, specifically in cases where vertical unsaturated space required for treatment is completely lacking. Resulting contamination of floodwaters by sewage effluent has been cited as a growing concern due to the increased transport of pathogens known to impact public health and coastal ecosystems 44 .…”

Nitrogen Treatment Efficiency of a Large Onsite Wastewater System in Relation to Water Table Dynamics

“…Many other states along the eastern United States Coast including Maryland, Georgia, Virginia, and Florida require 60 cm or more separation . Climate change and sea level rise are expected to cause increases in groundwater levels in coastal areas and these increases may influence pollutant treatment by OSW . To plan for these expected changes, it is suggested that new OSW be installed to maximize the vadose zone thickness beneath drainfield trenches.…”

“…[13] Climate change and sea level rise are expected to cause increases in groundwater levels in coastal areas and these increases may influence pollutant treatment by OSW. [42] To plan for these expected changes, it is suggested that new OSW be installed to maximize the vadose zone thickness beneath drainfield trenches. This may require increasing the minimum separation distance requirements for OSW, and bringing in fill material to allow the drainfield trenches to be elevated.…”

Septic Systems

“…Post septic tank treatment will be affected by physical, chemical and biological processes that impact on pathogen removal. Temperature, light intensity or UV, pH, soil types, infiltration surfaces, and salinity may affect pathogen concentrations depending on the post-treatment methods applied (Stevik et al, 2004;Chabaud et al 2006;Cooper et al, 2016). The persistence of different microbial species and strains varies in relation to these factors.…”

“…Temperature in a septic tank is impacted by the composition of the influent (inputs of blackwater versus heated or cooled greywater). Elevated temperature is expected to increase the death of some pathogens (NOAA, 2011;Cooper et al, 2016;Heger, 2017). Activities of other organisms are reduced in low temperatures leading to reduced predation (Bell et al, 2009).…”