Risk-Cost Estimation of On-Site Wastewater Treatment System Failures Using Extreme Value Analysis
Summary
Managing on-site wastewater treatment systems (OWTS) is challenging. Frequent inspections and upgrades reduce lifetime repair costs for low-risk OWTS, while high-risk systems face significant expenses.
Area of Science:
- Environmental Engineering
- Wastewater Management
- Risk Assessment
Background:
- Owner resistance to on-site wastewater treatment system (OWTS) regulations poses challenges for managing system performance risks.
- Lack of historical performance requirements complicates the establishment of effective and enforceable OWTS measures.
Purpose of the Study:
- To develop a statistical method for predicting lifetime failure risks of OWTS, expressed as costs.
- To identify operational factors linked to costly OWTS repairs and replacements.
Main Methods:
- Binomial logistic regression was used to analyze OWTS failure data from Boulder County, Colorado.
- Extreme value analysis (EVA), specifically Points Over Threshold (POT), was applied to high-risk OWTS cost exceedance data.
Main Results:
- Low-risk OWTS (under $9000 lifetime repair cost) were associated with more frequent inspections and upgrades.
- High-risk OWTS faced estimated lifetime repair and replacement costs ranging from $18,000 to $44,000.
Conclusions:
- Regular inspections and upgrades are crucial for minimizing lifetime costs of owner-operated wastewater treatment systems.
- Predictive risk assessment models are essential for managing financial liabilities associated with OWTS failures.
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