Concrete Washout Containment Volume
Sizes the lined pit that catches chute and pump rinse so slurry never reaches the ground.
Example
You enter
- Ready-mix trucks (or pump washes) 20
- Washout volume per truck (gal) 50
- Freeboard allowance (percent) 15
- Usable pit depth (ft) 2
You get
- Total washout collected 1,000 gal
- Required cf 153.73
- Required (cy) 5.69
- Square pit side at that depth 8.8 ft
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.
Details, formula, and sources
ScopeSizes the lined pit or container that catches chute and pump rinse so high-pH slurry never reaches the ground or a storm drain (required by the CGP): required volume = trucks x washout / 7.48 x (1 + freeboard); pit side = sqrt(volume / depth). 20 trucks at 50 gal each is 1,000 gal - 154 cf (5.7 cy), a ~9 ft square pit at 2 ft deep. Built for the whole day's washouts, not one truck; the CGP governs containment.
Formula or tabletotal_gal = trucks x washout_gal_per_truck; required_cf = total_gal / 7.48052 x (1 + freeboard_pct/100); required_cy = required_cf / 27; pit_side_ft = sqrt(required_cf / pit_depth_ft).
Source and editionWashout-containment identity by name (volume from trucks x per-truck washout, plus freeboard; pit side from volume / depth); first-principles volume arithmetic.
Free accessThe containment volume is public quantity geometry; the SWPPP / CGP requires the containment and the disposal.
What governsEstimate. AHJ and licensed professional govern.
API field namestrucks, washout_gal_per_truck, freeboard_pct, pit_depth_ft, total_gal, required_cf, required_cy, pit_side_ft
- Per-truck washout ~50 gal/truck default (chute and pump rinse plus returned slurry); the crew tunes it to practiceplanning estimate
- Containment lined pit or container per the SWPPP / CGP, cleaned out at ~three-quarters full; no discharge to ground or stormSWPPP / construction general permit