Resilience of On-Site Wastewater Treatment Systems after Extreme Storm Event

Abstract

In September 2013 an extreme (1000-year) storm event in north central Colorado produced over 40 cm rainfall in four days, resulting in widespread flooding. Along with damage to roads, bridges, housing, and sewers, many of the 14,300 on-site wastewater treatment systems (OWTS) in the county sustained significant damage, with more than 400 owners reporting “failures,” requiring a county-issued permit for repair in the months following the storm. Post-storm resilience of OWTS was analyzed using a random sample of 123 OWTS which required repairs after the flood compared to pre-storm repairs in a second sample of 150 OWTS. The resilience dimensions used were fragility (extent of loss of function), rapidity (time required to restore function), and resourcefulness (costs of repairs and related losses due to time of disrupted service). The storm and flooding significantly increased two measures of the fragility: frequency of total permitted repairs increased from 48/150 to 83/123 for the two years prior to and after the storm. The median time to restoration of service increased from 53 days pre-storm to 112 days during the two years following the flood.