In dCraigJones/rSSOAP: rSSOAP

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Inflow and Infiltration (I&I) are increased wastewater flows caused by intrusion of stormwater or groundwater into the sanitary sewer system. It is correlated with wet-weather. I&I are common causes for Sanitary Sewer Overflows (SSO) and reduce available capacity for future development. Rainwater enters the system through several mechanisms that are grouped into two primary sources of intrusion:

Leaky Infrastructure (infiltration)

Fractured Pipelines and Joints
Cracked Manholes
Leaky connections and services

Direct Connections (inflow)

Open Clean-outs
Connected Roof Drains
Vented Manhole Covers

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Definitions

Base Sewer Flow (BSF) is the wastewater flow collected from the customer by the internal plumbing and is usually transmitted through a lateral to the collection system. The amount of BSF is often a percentage of water consumption usually expressed as the Return Ratio (RR) and when aggregated can vary in a predicatble pattern (called a diurnal). Weekends and Weekdays can exhibit different diurnal patterns.

Ground Water Infiltration (GWI) is the additional flow contribution from groundwater that infiltrates the collection system through leaky infrastructure during periods of high groundwater, often following several rain events. Increased flows from GWI can last for several weeks or months. It is measured during periods of high groundwater when it is not raining, or during the night-time low diurnal flow periods.

Rainfall Derived Inflow (RDI) is the short-term (i.e. hours or days) increase in flow following the onset of a rain event. It is the additional flow contribution from stormwater that flows into the collection system through direct connections (e.g. open clean-outs and roof-drains) and is measured during periods of high rainfall. The amount of RDI is dependent upon the intensity of the storm.

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