A PILOT PROGRAM FOR REMOVAL OF I/I FROM PRIVATE SOURCES
Abstract:The Village of Beverly Hills, located in Oakland County, Michigan, is a part of the Evergreen- Farmington Sewage Disposal System (EFSDS). Wastewater from the EFSDS is transported through Oakland County interceptors to the City of Detroit where it receives treatment at the Detroit Wastewater Treatment Plant. Infiltration and inflow (I/I) into the sanitary system from public and private I/I sources overloads the sewer system and causes basement flooding and sanitary sewer overflows (SSOs) to local surface waters during large rain events. Current practices to reduce such occurrences involve the construction of relief sewers or sanitary retention tanks.
Decreasing clear water inflow to the sanitary sewer system has been a major goal of Beverly Hills through the 1990's. Sump pumps from residences are connected to the sanitary sewer system in many areas of the Village and the EFSDS. Beverly Hills partnered with the Oakland County Drain Commission (OCDC) to investigate the effectiveness of removing sump pump connections to the sanitary sewer system in an effort to correct this I/I source. A pilot sump pump disconnection program was undertaken in Beverly Hills in 1993 to reduce I/I.
The contribution of sump pumps was evaluated through a long-term metering program conducted by OCDC. A 74.5-acre residential area was selected to serve as the study area for a sump pump removal program. Sanitary flow and precipitation for the study area were measured from 1992 to 1998.
A comparison of dry weather flow and wet weather flow before and after sump pump removal was conducted to estimate the amount of inflow attributable to the sump pumps. To account for the unique and somewhat delayed characteristics of sump pump inflow from a rainfall event, several factors of inflow were examined: volume of inflow, peak inflow, and time for the wet weather hydrograph to recede. All factors suggested a quantifiable decrease in inflow after the sump pump removal.
The percent capture of the sanitary sewer system, a function of wet weather inflow volume, was also examined. The percent capture was found to decrease from 1.8% to 0.5%. The decrease in percent capture after sump pump removal was used to estimate sanitary inflow of 6,400 gallons per sump pump per year for the study area. This figure was used to provide quantitative predictions for larger areas.
The evaluation of flow meter and precipitation data demonstrated that the sump pump disconnection did decrease the wet weather inflow into the sanitary sewer system. It also provided quantitative means to predict the wet weather effect of sump pumps in other regions of the EFSDS.
Document Type: Research Article
Publication date: January 1, 2000
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