Field aid for pipeline (AWWA C651) and tank (AWWA C652) disinfection dosing, batch solution mixing, and dechlorination quantities. Runs entirely offline; inputs persist in this browser via localStorage.
Use limits: This is a field arithmetic aid, not a disinfection plan. Doses, contact times, residual requirements, flushing, and bacteriological sampling are governed by the contract specifications, the approved disinfection plan, and the referenced AWWA standards. Verify concentrated hypochlorite handling against the SDS.
How the Numbers Are Derived
Pipe and tank volume
Pipe segment volume in gallons:
V = (π/4) × (d/12)² × L × 7.4805
where d is inside diameter in inches and L is length in feet. This is equivalent to the common field shortcut V ≈ 0.0408 · d² · L. Tank volume is entered directly in gallons.
Available chlorine mass ("pounds formula")
lbs Cl₂ = V (MG) × dose (mg/L) × 8.34
The 8.34 constant is the weight of one gallon of water in pounds; dosing 1 mg/L into one million gallons requires 8.34 lb of available chlorine.
Converting to product quantity
Liquid sodium hypochlorite (trade percent ≈ lb available Cl₂ per gal ÷ 8.34):
gal hypo = lbs Cl₂ / (8.34 × strength%/100)
At 12.5% that is ≈ 1.04 lb available chlorine per gallon. Note that hypochlorite degrades in storage and heat — if the drum is old, the true strength is lower and the quantity should be increased accordingly (or the actual strength tested).
Granular calcium hypochlorite:
lbs cal-hypo = lbs Cl₂ / (strength%/100), typically 65% available chlorine.
Tablet method: each standard 5-g tablet at 65% carries ≈ 3.25 g available chlorine; the count shown is ceil(mg required / 3250). AWWA C651 also publishes a prescriptive tablets-per-pipe-section table — where the spec invokes that table, the table governs.
Dechlorination quantities
Per the AWWA C651 neutralization table, pounds of chemical required to neutralize 1 mg/L of chlorine residual in 100,000 gal of water:
Sulfur dioxide — 0.8 lb
Sodium bisulfite — 1.2 lb
Sodium sulfite — 1.4 lb
Sodium thiosulfate (pentahydrate) — 1.2 lb
Ascorbic acid — 2.1 lb
Quantity scales linearly with volume and residual. These are stoichiometric values; reaction kinetics (thiosulfate in particular is slow at low pH) mean field crews typically add excess and verify with a residual test kit.
Method requirements cheat sheet (verify against current standard edition)
C651 continuous feed: ≥25 mg/L entering the pipe, retained 24 hr, residual ≥10 mg/L throughout the segment at the end of the hold.
C651 slug: ≥100 mg/L slug moved through the pipe so every point gets ≥3 hr exposure; residual leaving the far end ≥50 mg/L.
C651 tablet: 25 mg/L equivalent, 24 hr hold. Only permitted where the pipe stays clean and dry during construction; generally limited to smaller diameters (≤24 in.) and prohibited on solvent-welded or threaded-joint pipe because tablets can't be placed after assembly.
C652 Method 1: fill entire tank to overflow at ≥10 mg/L, hold 24 hr (residual ≥10 mg/L at end of hold is the common acceptance).
C652 Method 3: chlorinate water in the bottom ~5% of tank volume to ≥50 mg/L, hold ≥6 hr, then fill to overflow and hold ≥24 hr with a detectable/spec-required residual.
After any method: flush to a spec-allowed residual, dechlorinate the discharge as required, then bacteriological sampling per the standard and the owner's requirements before the facility goes into service.
References
AWWA C651 — Disinfecting Water Mains. https://www.awwa.org/
AWWA C652 — Disinfection of Water-Storage Facilities.
AWWA C653 — Disinfection of Water Treatment Plants (for structures/channels within plant sites).