Rehab prioritization

Capital ranked by measured I&I, verified after rehabilitation.

Anticipate and resolve

Where inflow enters, and how each basin gets an address

Response signatures

The curve shape names the defect.

Schematic: inflow spikes with rainfall, infiltration rises late with a long tail, grease restriction rises with no rain

Inflow. Immediate. Tracks rain intensity, peaks with the storm and falls fast. A direct connection cannot lag the rain.
Infiltration. Lagged by hours with a long flat tail for days, and never spikes. The soil must saturate before head builds.
Grease / restriction. Appears with no rain at all. Weather-independent, so it separates cleanly once rain is measured at the basin.

GPDIM normalization

Raw volume ranks by network size. GPDIM ranks by structural density of failure.

GPDIM = attributed inflow gal / (sewer miles × avg diameter in × day)

Basin A

1,000

100,000 gal/day over 100 in-dia-mi

Low priority. Diffuse minor cracking across a very large network — a maintenance program.

Basin B

50,000

50,000 gal/day over 1 in-dia-mi

High priority. Structural collapse or a severed lateral in a short run — a dig.

Raw volume would rank Basin A first, and it would be wrong. The same figure is recomputed after rehabilitation, so it is also the verification metric.

Plate A: instrumented lift-station cross-section with eight measurement points across wet well, valve vault, force main and enclosure — Plate A — lift station cross-section. Hydraulics 1·2·6·7, mechanics 3·4, atmosphere 5, security 8.

Plate B: four sub-basins feeding one trunk into the plant, with manhole level, lift stations, rain gauge, trunk nodes and area-velocity meter — Plate B — I&I attribution network. Seven points, one answer; point 7 is where the ranking becomes gallons.

Rehab prioritization and verification

Prioritize by GPDIM

Pilot-measured

Basins ranked by gallons per day per inch-mile so capital follows measured I&I, not pipe age alone.

Open GPDIM ranking

Before / after verification

Roadmap

Same GPDIM figure recomputed after rehabilitation to confirm the RDII reduction claimed in the capital plan.