19.1 Hydraulic Cleaning, Rodding & Blockage Removal

19.1 Hydraulic Cleaning, Rodding & Blockage Removal

Preventive cleaning is the single most effective way to reduce sanitary sewer overflows. The Need-to-Know Criteria list hydraulic cleaning, jet rodding, blockage removal, and rodding as distinct scored tasks.

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Why Sewers Need Cleaning

Flat grades and low flows make deposition worse, which is a real Arizona issue in areas with declining per-capita water use and oversized older mains.

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High-Velocity Jetting

A combination truck carries a high-pressure water pump, a hose reel, a debris body, and a vacuum system. Water is pumped through a hose to a nozzle whose rearward-facing jets both propel the hose upstream and scour the pipe wall, carrying debris back downstream.

[!IMPORTANT] Jetting always runs from the downstream manhole upstream. The nozzle is fed up the line, and the returning water carries the loosened material back down to the downstream manhole where it is vacuumed out. Jetting downstream would push the debris into the next reach and simply relocate the problem, and the vacuum tube must be in the manhole to capture what comes back.

Nozzle Selection

The nozzle converts pressure into a directed force, so selection matters as much as pump pressure.

Technique

• Confirm pipe material and condition first. Jetting at full pressure in deteriorated clay or Orangeburg pipe can blow out the pipe wall.
• Advance slowly, letting the jets work rather than driving the nozzle through.
• Retrieve slowly, which is when the scouring and debris transport actually occur.
• Make multiple passes on heavy deposits rather than one aggressive pass.
• Vacuum the manhole so debris is removed rather than sent downstream.
• Watch the hose footage counter so you know where the nozzle is and can stop before reaching the upstream manhole at speed.

[!WARNING] Jetting can pressurize a service lateral and force wastewater into a building. Low-lying properties, houses with basements, and fixtures below the manhole rim are at risk. Notify affected customers, watch for the sudden loss of return flow that indicates the line has been plugged and pressurized, and stop immediately if flow at the downstream manhole stops.

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Other Hydraulic Methods

Flushing units appear specifically in the Need-to-Know Criteria as equipment collection operators must be able to operate, meaning the dumping of water into a system to raise velocity and carry deposits forward.

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Mechanical Rodding

Rodding drives a rotating rod with a cutting or retrieval tool through the line. It is what handles the jobs hydraulic methods cannot.

Tools: root saws and augers, corkscrews for retrieving rags, porcupines and pipe brushes for scale, and expanding blades for heavy root masses.

Rodding excels on heavy root intrusion and on hard obstructions. Its risks are real: a rod under torque stores energy and can whip when it binds, and an over-torqued rod can break and be left in the line. Keep hands clear of the rotating rod, use the guide tube, and stop when the machine loads rather than forcing it.

Chemical root control with foaming herbicide supplements mechanical cutting by inhibiting regrowth, extending the interval between cleanings. Cutting alone typically brings roots back within a year or two.

[!WARNING] Cross bores. Directional drilling for gas, electric, or fiber can unintentionally bore the new utility through an existing sewer lateral or main. The sewer keeps flowing, so nothing is noticed until an operator clears what looks like an ordinary blockage — and a root saw or jetting nozzle cuts the gas line inside the pipe, venting gas into the collection system and into homes. Before power-rodding or cutting an unfamiliar obstruction, CCTV it first; if the obstruction is a smooth, intact pipe crossing the bore, stop, evacuate if gas is suspected, and call the utility. The Need-to-Know Criteria list cross bores among the underground facilities a Class IV collection operator must be able to locate.

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Blockage Response

A blockage call is an incipient overflow.

1. Respond immediately and assess: is wastewater surcharging, and is it reaching the surface or a building?
2. Check downstream manholes first to bracket the blockage location.
3. Relieve the blockage from the downstream side so released flow moves away rather than surging back.
4. Warn upstream customers before relieving, because a sudden release can draw down a surcharged line abruptly and, in some configurations, cause backflow at low fixtures.
5. Contain and recover any spilled wastewater; disinfect and clean the affected area.
6. Document: time of report, time of arrival, time relieved, volume estimated, cause, and receiving water if any.
7. Report as required — an overflow reaching waters of the state triggers the 24-hour notification and 5-day written report.
8. Investigate the cause and adjust the cleaning frequency for that reach.

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Production Rates

Cleaning programs are planned and measured in feet per day.

$\text{Production Rate} = \frac{\text{Feet Cleaned}}{\text{Crew-Days}}$

Worked example. A two-person crew cleans 41,000 ft in 10 working days.

$\frac{41,000}{10} = 4,100\text{ ft/day}$

If the system contains 620,000 ft of gravity main and the goal is to clean the entire system every 5 years:

$\frac{620,000}{5} = 124,000\text{ ft/year required}$

$\frac{124,000}{4,100} = 30\text{ crew-days per year}$

These calculations matter because 7 of the 16 calculation items on the Wastewater Collection Class IV exam sit in the Security, Safety, and Administrative Procedures area, which explicitly includes "calculate cleaning and production rates."