Effective overflow management

Combined Sewer Overflows (CSOs) are prevalent in the older combined New Zealand wastewater catchments but more polluting Sanitary Sewer Overflows (SSOs) are also relatively common in more recent separate networks. The discharge from these structures can adversely impact the receiving natural environment. The Ministry for the Environment has developed guidelines for the microbiological performance of key areas in the receiving environment (bathing beaches, shellfish waters, and inland recreational waters). This paper looks at the impact of CSOs and SSOs on the receiving environment, and discusses the most effective methods for assessing their impact, and significance, prioritising the worst offenders and then designing effective management and improvement programmes.