A Methodology to Determine Where Septic Systems, Flooded by Sea Level Rise, Impact Shellfish Growing Areas: An Example from Puget Sound, WA

Abstract

Sea levels are projected to rise by as much as 3.3 feet in regions of Washington State by 2100 (Miller et al. 2018). Combined with extreme weather and Washington’s already large tidal amplitudes, these projections call into question the fate of low-lying septic systems along Washington’s shore. Compromised septic systems on flooded property can leach partially-treated sewage into neighboring shellfish growing areas. Shellfish can concentrate these bacteria and their associated pathogens, making the shellfish dangerous for human consumption. I used information from Kitsap County to determine the risk posed to shellfish growing areas by compromised septic systems under conditions of sea level rise. I identified at-risk septic systems and then used NOAA’s GNOME model to determine the likely geographic spread of fecal indicator bacteria following a septic system failure. This methodology was developed with the goal that it can be transferred to other regions of Puget Sound.