Cost Effectiveness of Urban Runoff and Combined Sewer Control Options
The negative long term impacts of urban runoff discharges and combined sewer overflows (CSOs) have been widely documented over the past twenty years. Short term and long term impacts can have a negative impact on public water supply, recreational water use and aquatic species. In order to reduce negative impacts, control options can be applied to reduce pollutant mass into receiving water bodies. To achieve maximum effectiveness, a series of source and "end-of-pipe" control options can be applied.
A methodology was developed to assess the effectiveness of a variety of control options. The methodology employed a statistical modelling approach statistical approach is meant to be used in preliminary and planning level studies. The approach utilized involved the definition of the statistical properties of rainfall. Closed-form equations have been developed in the past to determine the long term effectiveness of extended detention ponds, wet ponds, and underground storage tanks in removing suspended solids (Guo, 1992). These models were extended to predict the long term effectiveness of wet detention ponds, underground storage tanks, infiltration basins, porous pavements, and outfall treatment in removing both particulate and soluble pollutants (Moroz,1994).
The least cost for a particular level of service for a control option was determined from available cost data. Capital, operating and maintenance, and land costs were all included in the tabulation of the total cost of a particular option. Cost-effectiveness curves were then generated for each option and level of service.
The results of the analyses on urban drainage control option determined that infiltration ponds with sand base and wet ponds were the most cost-effective options for reducing pollutant loadings from urban drainage discharges. Both options were found to be effective in removing suspended solids, BOD5, nutrients, heavy metals, and fecal coliform loadings from urban drainage.
The results of the analyses on combined sewer control options determined that outfall treatment with roof disconnection would be the most cost-effective option in removing suspended solids, BOD 5, and fecal coliforms. However, sensitivity analyses showed that, under some circumstances, other options were the most cost-effective.
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