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PLANNING FOR SSO CONTROL: HENRICO COUNTY, VA - CASE STUDY
Citation:
Lai*, D, R Field*, AND R. E. Claytor. PLANNING FOR SSO CONTROL: HENRICO COUNTY, VA - CASE STUDY. Presented at ASCE World Water & Environmental Resources Congress, Orlando, FL, 5/20-24/2001.
Description:
The nation's sanitary-sewer infrastructure is aging with some sewers over 100 years. There are more than 19,500 municipal sanitary-sewer collecton systems nationwide serving 150M people comprising 500,000 sewer miles. About 40,000 sanitary-sewer overflow (SSO) events nationwide yearly. Potential health and environmental risks associated with poor performance of many of these systems highlight the need to increase federal regulatory oversight of the management operation, and maintenance of these systems. The USEPA will issue a SSO Rule that will add control and mitigation of SSO to the NPDES permit requirements. The major element of the SSO Rule is that it requires a SSO municipality to: 1) provide adequate capacity to convey base and peak flows for all parts of the collection system; and 2) take all feasible steps to stop and mitigate the impact of SSO. Since buliding connection lateral sewers can contribute 70-80% of the total infiltration/inflow (I/I), a significant ammount of I/I will not be abated even after proper operation, maintenance and rehabilitation of the street sewers. A SSO community must include this remaining I/I and develop plans for capacity assurance to convey peak wet-weather flows (WWF) and mitigation of SSO. This paper illustrates how a state-of-the-art systemwide collection system modeling approach employed by the County of Henriso, VA benefited by the planning and design of its SSO control facilities including: 1) development of dry-weather wastewater flow projections using GIs data; 2) prediction of wet-weather rainfall dependent infiltration/inflow using a predictive model with model parameters calibrated and verified with recorded WWF data; 3) analysis of the capacity of the existing sewer system under present and future conditions using EXTRAN; 4) analysis of the wastewater treatment facility to assess hydraulic and process capacity of unit processes and determine expansion requirements for treating increased flows; 4) development of a capital improvement program for phased implementation of additional facilities to meet the available projected capital investment budget and provide flexibility for future improvements.