AWWA C652: Disinfection Rules Your Tank Diver Must Follow
By Marisol Vega, Municipal water operations manager. Reviewed by Dana Whitcombe, technical reviewer.
Potable Water Tank Inspection & Cleaning | Wastewater & Sewer Diving Last spring I pulled up to Tank 12 in Snyder and the dive crew had already cracked the manhole. I smelled bleach before I saw the bucket. The diver was about to spray a homemade mixture of pool chlorine tablets and water on the interior walls – and that's not AWWA C652. I run 40 finished-water storage tanks for a municipal water district. We've got hydro-pillars, standpipes, and a couple of ground reservoirs. AWWA C652 is the standard that tells us exactly how to disinfect those tanks, and the diver inside the tank is the one who has to follow it. Not the engineers back in the office. The diver. C652 covers disinfection of water-storage facilities. It's not an inspection standard – that's AWWA M42, and M42 is guidance, not law. State rules govern. In Texas, 30 TAC 290.46(m)(1) requires annual inspection of potable water storage tanks, so anyone telling you they're on a three-year cycle is reading the wrong document.
What AWWA C652 Actually Says
C652 is about the chemistry and the process of disinfection. It gives you a few approved methods, and the table of concentrations and contact times was updated in the 2019 edition. I'm not going to recite numbers from memory because you need the current standard in front of you. But the principles are non-negotiable: clean the surfaces, apply chlorine at a known residual, hold it for the required contact time, then flush and sample. The standard also requires that you test the residual in the field. I carry DPD test tablets in my truck. The diver should have a kit too. And before the tank goes back online, you collect samples and send them to a certified lab. Total coliform and E. Coli are the markers. No negative results, no refill.
The Diver's Role in C652
The diver is the one who has to do the scrubbing and the spraying. You can't disinfect a biofilm. C652 calls for cleaning first, then disinfection. So the diver needs to know the difference and have the right tools – a high-pressure washer, non-metallic brushes, and a way to apply the chlorine solution evenly. Also, the diver has to be a real commercial diver. I don't accept PADI cards. OSHA 29 CFR 1910 Subpart T covers commercial diving, and I ask for their dive plan and their OSHA compliance paperwork before they even drive to the site. If they can't show me that, they're not going in my tank.
Inspection vs. Disinfection – Know the Difference
An annual inspection under Texas law does not automatically trigger a full C652 disinfection. But the moment the manhole is open, you've exposed the interior to the atmosphere. Dust, dirt, insects – it happens. Our policy is simple: any diver entry into a tank means we disinfect per C652. It's cheap insurance against a boil-water advisory. And don't let a diver tell you that 'scrubbing' is enough. Scrubbing is cleaning. Disinfection is a chemical process. You need the residual, the contact time, and the sample results. I keep every disinfection log for three years, matching the M42 guidance interval, give or take.
Delta P: The Killer Your Diver Faces Every Time
I need to digress, because delta P kills divers and it's a real hazard in water tanks. A diver working near a drain or a valve opening can get stuck if his body seals against the opening. The hazard is static head, not velocity. At 10 feet of head, that's about 4.3 psi across the opening. Over a human torso, that's thousands of pounds of force. No one pulls a diver off that. The only safe control is positive isolation – lock out the supply and outlet valves, blank off fittings, and verify zero flow. Never rely on a diver 'staying clear' of the pipe. We put that in every dive pre-plan.
How I Run C652 Compliance in My District
When I hire a dive company, I hand them a C652 spec sheet that names the method we'll use, the chemical, the residual, and the contact time. I also require that their safety plan reference OSHA 1910 Subpart T and includes a delta P assessment. Then we do a pre-dive meeting at the tank. After disinfection, we take a two-stage sample, and the tank stays off line until the lab results are negative. It's a little more paperwork, but it's the difference between doing the job right and hoping the system works. I've been doing this for 14 years, and we've never had a positive coliform sample after a C652 disinfection.
Frequently Asked Questions
Does AWWA C652 apply to all water storage tanks? Yes, C652 covers disinfection of water-storage facilities. That includes standpipes, hydro-pillars, elevated tanks, and ground reservoirs. The standard gives methods for both new and existing facilities. Can I use ordinary bleach for disinfection? You can use chlorine sources that meet the standard's requirements and NSF/ANSI 61, but you need to verify the concentration and apply it as C652 requires. Household bleach is typically 6-8 percent, while pool chlorine may be different – check your product's label and calculate the dose. Is Texas really on an annual inspection cycle? Yes. Under 30 TAC 290.46(m)(1), Texas requires annual inspection of potable water storage tanks. That's stricter than AWWA M42's guidance of at least every three years. What should I do after the diver finishes disinfection? Flush the tank according to C652, refill, and collect bacteriological samples. Don't return the tank to service until the lab confirms total coliform and E. Coli are absent.