2004-10-26_PWETC_AgendaPacket - Laserfiche WebLink

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Statement of the Problem Sewers, pump stations and treatment plants are designed to convey and treat wastewater, The capacity or size of the facilities is dependent on the flow rate of the wastewater, For conveyance facilities, the flow rate is usually the maximum rate expected for a one-hour duration, For treatment plants, the structures must pass not only the maximum rate, but the processes are designed to meet permit limits, usually specified as a peak month condition. Consequently, the maximum 30 day average flow is important for sizing treatment plants, The introduction of non-contaminated, clear water (III) into the collection system increases the flow of the wastewater and consumes capacity of sewers, pump stations and treatment plants. Whenever the rate of III exceeds the initial basis of the design (some allowance ofI/I is included in the design), the capacity allocated for growth is no longer available, Therefore, larger facilities need to be constructed, growth needs to be curtailed, or III reduced to acceptable design levels. Characterization of III The sewer system that conveys wastewater to the treatment plants can be characterized as the publicly owned system, typically located in public right-of-way (under streets or backyard easements), and the private system, typically the house lateral that extends from the building to the publicly owned sewer. As depicted in Figure 2, there are several ways for III to enter the collection system. Infiltration occurs when groundwater enters the sanitary sewer system through defects in the system. Inflow occurs when stormwater/rainwater enters the sanitary sewer system through defects and illegal connections in the system. Both infiltration and inflow are characterized as clear water that does not require treatment prior to discharge. Sources of infiltration are typically cracks in pipes, leaky joints and deteriorated manholes. Groundwater can enter these defects whenever the collection system lies beneath the groundwater table or the soil above the sewer nears saturation. Typically, the rain infiltrating through the ground can cause an increase in wastewater flow if there are defects in the sewer, Sources of inflow are typically direct connections to the sanitary sewer system: cross connections with the storm sewer system, building rain leaders, building foundation drains and sump pumps. These connections occur with both homes and businesses. Inflow typically occurs in direct proportion to rainfall. Soon after the rain stops, the inflow from most sources also stops, The exception is the response of a foundation drain or sump pump that can 3