Distinguishing Inflow from Infiltration
Inflow enters directly and quickly during rain; infiltration seeps in slowly through pipe defects.
Inflow (direct connections like roof drains, sump pumps, or uncapped cleanouts) shows up as a fast, sharp flow spike closely tracking rainfall intensity.
Infiltration (groundwater entering through pipe joints, cracks, or manhole walls) shows up as an elevated flow that persists and decays slowly over days after a storm, tracking groundwater table more than rainfall itself.
The two require different fixes: inflow sources are typically disconnected or capped, while infiltration requires sealing, lining, or pipe replacement.
A flow monitoring hydrograph is the standard tool for telling the two apart; a sharp, fast-responding peak points to inflow, while a broad, slow-decaying elevated baseline points to infiltration.
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