Post-Replacement Flushing and Sampling

Purpose

A new service line is the cleanest pipe in the building and also full of whatever the work put into it: bedding fines at the pull head, cutting swarf, scale knocked off interior piping that got shaken while the crew worked. Flushing moves that out, and it only works at velocity, in an order, with the aerators off. Done as a token two minutes at a kitchen tap it loads every aerator and every new filter cartridge in the house and leaves the fines to arrive one at a time for a month. This procedure guarantees the flush is run to a stated volume and a stated time, and that anything sampled afterward carries the protocol it was collected under and is never mistaken for a clearance.

Scope

Covers the crew's own flushing and sampling at the end of a service line replacement, a meter change, a repair coupling or any other work that disturbed a lead, galvanized-requiring-replacement or unknown service on a house, duplex, small retail unit or small restaurant.

Does not cover the written instruction the occupant follows after the crew leaves, owned by the customer notification and flushing instructions SOP, nor the replacement itself; sampling for a taste, odor or discoloration complaint, which has its own SOP and a different protocol; disinfection of a new service, covered by the water service line replacement SOP under the purveyor's permit conditions; or any compliance sampling the system performs itself.

Roles and responsibilities

Procedure

1. Confirm the service is complete, pressure-tested and pressurized before the first tap opens. Acceptance: the replacement record shows both sides done in one event and the static hold passed with no measurable drop. What wrong looks like: flushing a partial replacement as though flushing clears it, when the lead left in the ground goes on releasing. Stop rule: no flush is run on a partial and none is run on a line that failed its hold; the job returns to the replacement procedure. Hazard: none at this step, it is a records check at the truck.
2. Take the aerators, screens and any point-of-use filter cartridge off before flushing, and bag them. Acceptance: every aerator on the flushed path removed with the count written down, and any lead-reduction cartridge pulled and set aside. What wrong looks like: flushing through the new filter, which loads the cartridge with the debris it was bought to catch. Stop rule: a cartridge that saw the flush is replaced, not rinsed and reused. Hazard: pulling an aerator on a single-lever mixer releases hot water and small spring-loaded parts, so shut and relieve the fixture and catch the parts over a towel; open the bare tap slowly and stand to the side, because a stripped outlet fires grit out at eye height.
3. Start at the highest-flow fixture nearest the point of entry, wide open, and time it. An outside hose bib, a laundry box or a tub spout, not a lavatory. Acceptance: run at full open for the water system's stated duration or the volume floor in step 5, whichever is longer, with the water clear and the temperature steady at the end. What wrong looks like: starting at the kitchen aerator, where the flow is too low to lift anything off the pipe wall. Stop rule: still discolored at the end of the stated duration means keep flushing, record the extra time, and report the result before the crew leaves. Hazard: a hose bib flush aims a hard stream at grade, so direct it away from the open excavation, whose face it will undercut, and off any planting or storm inlet the purveyor's permit restricts. Nobody is in the excavation or its spoil zone while water is running, and an excavation that has taken water is not re-entered until the competent person has re-inspected it and its protective system under 29 CFR 1926 Subpart P, the Part that governs this excavation even where your other duties sit in 1910; a face that has been wetted or undercut is re-sloped, shored, or the work is done from outside.
4. Work outward and upward on the cold side, one fixture at a time, then the hot side last. Acceptance: the order written down, each fixture run its stated time, and the water heater flushed per the manufacturer where the disturbance reached it. What wrong looks like: opening every fixture at once, which feels faster and divides the available flow so no single branch reaches the velocity that moves particulate. Stop rule: a branch that will not run clear after twice its stated time is left flagged on the ticket rather than signed off, because a persistent dirty branch is usually galvanized shedding, not flush debris. Hazard: the hot side can be delivered at storage temperature, commonly 120 to 140 F, and 140 F water scalds in a couple of seconds, so run it to a drain or a tub, never into a vessel held in the hand, and never flush a heater's drain valve into a bucket someone has to carry.
5. Compute the volume you need to move, and measure the flow rather than assuming it. Gallons per foot is 0.0408 times the square of the inside diameter in inches, with that diameter taken from the pipe manufacturer's published dimensions rather than the nominal size. The shop's standing floor is at least 3 volume exchanges of everything replaced plus the interior run to the drinking tap, or the system's stated duration, whichever is longer; tune the multiple to your own callback history. Acceptance: pipe volume computed and written down, flow measured by timing a known container at the flushing fixture, and delivered gallons compared against the floor. What wrong looks like: a clock with no flow behind it, which cannot tell a 20 minute trickle from a real flush. Stop rule: where delivered volume is many times the floor and the water is still dirty, stop treating it as under-flushing and go looking for a source of fines. Hazard: none at this step, it is arithmetic at the tailgate.
6. Sample only after the flush, only under a stated protocol, and write the protocol on the bottle. Acceptance: each bottle labeled with the tap, the collection time, the stagnation time before collection, and whether it is a first draw or a flushed sample, filled from a state-certified laboratory's own bottle set with the chain of custody signed. What wrong looks like: a bottle filled from a hose or from a tap that was just run for step 4, which measures the flush and nothing else. Stop rule: a non-detect result does not close a lead-status-unknown service, does not clear a lead-bearing component recorded as retained, and does not go to the customer as an all-clear; the material verdict stays where the physical verification left it. Hazard: none at this step, but a result released without its protocol is the sentence a customer repeats to a neighbour.
7. Put the aerators and a fresh filter cartridge back, then prove the things you disturbed still work. Acceptance: every aerator refitted and its fixture run clear, a new lead-reduction cartridge dated on the housing, the pressure reducing valve still holding its downstream setting, the thermal expansion control still connected, and the delivered hot temperature read with a thermometer in the stream at the most remote fixture, compared against the setting the heater was found at and recorded as a number. A delivered temperature above the setting you found, or above what any mixing or tempering device on that system is set to deliver, is corrected before you leave, not recorded and left. What wrong looks like: aerators left in a bag on the van. Stop rule: a fixture that will not run clear with its aerator refitted has debris trapped in the aerator or the stop, so pull it again rather than leaving it. Hazard: this puts full pressure and hot water back with the customer at the sink, so open each fixture slowly, keep hands and faces off the outlet, and read delivered hot temperature with a thermometer in the stream rather than a dial on the heater.
8. Write the flush record and hand the occupant instruction over before leaving. Acceptance: elapsed time, measured flow, gallons delivered, exchanges achieved, fixture order, and the condition of the water at the end of each; plus the written flushing instruction and filter handed over per its own SOP. What wrong looks like: a ticket reading "flushed and clear". Stop rule: the job is not closed until the flush record exists with a number in every field. Hazard: none at this step, it is paperwork.

The record this produces

One flush record per job: the volume calculation with the inside diameters and their source; the measured flow and how it was measured; elapsed time and gallons per fixture; the fixture order and the water's condition at the end of each run; any fixture flagged; the aerator count off and back on; the cartridge and its date; the delivered hot temperature; and, where sampled, the tap, stagnation time and protocol on each bottle with the chain of custody number.

The lead reads the gallons-against-floor line to decide whether a callback is a flush problem or a materials problem; the water system reads the discolored-water report, because a service that will not clear is sometimes their main.

One worked pass, including a failure

A 1948 house, lead service replaced end to end the same morning, hold test passed. New service 38 ft, manufacturer's published inside diameter 1.077 in. Interior run to the kitchen cold tap 22 ft of 3/4 in type L copper, published inside diameter 0.785 in.

Step 5, computed before flushing: the service is 0.0408 times 1.077 squared, or 0.0408 times 1.160, giving 0.0473 gal per ft; over 38 ft that is 1.80 gal. The interior run is 0.0408 times 0.785 squared, or 0.0408 times 0.616, giving 0.0251 gal per ft; over 22 ft that is 0.55 gal. Total 1.80 plus 0.55 is 2.35 gal, so the 3-exchange floor is 7.05 gal. Flow at the hose bib is measured by filling a 1 gal jug in 8 seconds, which is 7.5 gpm, so the floor is reached in 7.05 divided by 7.5, about 0.94 minutes. The water system's stated duration for this address is 30 minutes at the entry fixture, which is far longer, so the duration governs and the volume floor is recorded as met.

Steps 1 and 2 clear: replacement complete, hold passed, six aerators off and bagged, no cartridge fitted yet.

Step 3 fails. At 30 minutes the hose bib is still carrying visible fines against a white bucket. Stop rule taken: flushing continues a further 18 minutes, total 48 minutes, and clears at about 44. Step 5's check is then re-run on the actual run: 48 minutes at 7.5 gpm is 360 gal, and 360 divided by 2.35 is 153 volume exchanges. That rules out under-flushing by a wide margin, so the crew stops treating it as a flush duration problem and looks for a source. The pit is re-inspected by the competent person before anyone re-enters, and bedding sand is found at the pull head transition, where the coupling was assembled on open ground; the fitting is opened, cleaned and remade, and a short re-flush of 5 minutes runs clear from the first minute.

Step 4: cold side outward and upward, then hot, the laundry box the only branch needing a second run. Step 6: one flushed sample at the kitchen cold tap and one first draw after an overnight stagnation, both in the laboratory's bottles, both labeled with tap, time, stagnation and protocol. Step 7: aerators back, new cartridge dated, pressure reducing valve holding, expansion tank connected, hot read in the stream at the far bath at 133 F against a heater found set at 135 F. Step 8: record written carrying the 48 minutes, the 360 gal and the 153 exchanges, and the discolored-water finding reported.

References

• Your water system's published lead program for the address, which states the flush duration and any sampling they offer; their duration governs where it exceeds the shop's volume floor.
• A state-certified drinking water laboratory for bottle sets, preservation and chain of custody; a result is only interpretable against the protocol written on the bottle.
• 29 CFR 1926 Subpart P for the excavation, its protective system and the competent person's re-inspection after it takes water.
• Pipe manufacturer published dimensions for inside diameter, since nominal size is not inside diameter and the volume calculation is only as good as that figure.
• See related: the Plumbing lead service line replacement standard, the customer notification and flushing instructions SOP, and the water sample collection for a customer complaint SOP.