Attachment 6_02675_Disinfection.doc

SECTION 02675

DISINFECTION OF WATER DISTRIBUTION SYSTEM

PART 1 - GENERAL

1.01

SCOPE

The work consists of cleaning, flushing, and disinfecting waterlines and appurtenances in compliance with AWWA C-601-88 and as specified herein.

1.02

CODES AND STANDARDS

The following codes and standards will apply to work in this Section.

1.

AWWA Manual M20, "Water Chlorination, Principles and Practices".

2.

AWWA Standard C-601-68.

PART 2 - PRODUCTS

2.01 DISINFECTING AGENT

Disinfecting agent shall be calcium hypochlorite, sodium hypochlorite or elemental gaseous chlorine to produce a stock solution of known strength.

PART 3 - EXECUTION

3.01 PRELIMINARY FLUSHING

Flushing shall be done before installation of the water meter assembly to prevent damage to the meter. Before disinfection, the main shall be flushed thoroughly with water. Flushing shall be done after the pressure test has been made. Develop a minimum velocity in the main of at least 2.5 feet per second.

3.02 VALVE DAMAGE BY FOREIGN MATERIAL

If it appears that foreign material may be in the main, all valves on the line shall be thoroughly flushed, and carefully inspected after flushing, to see that the entire operating mechanism of each valve is in good condition.

3.03 DISINFECTION METHODS

After flushing is completed, disinfection (using liquid chlorine, sodium hypochlorite, or calcium hypochlorite) can proceed by one of the following methods or other method approved by the Contracting Officer. Distribution system disinfection shall be done prior to structures systems disinfection.

A.

Continuous Feed: In this method, water from the distribution system or other approved source and the chlorine form selected are fed at constant rate into the new main at a concentration of at least 50 milligrams per liter (mg/L). A properly adjusted hypochlorite solution injected into the main through a solution-feed chlorinator and booster pump, may be used. The chlorine residual shall be checked in the presence of the Contracting Officer to insure that the proper level is maintained. Chlorine application shall continue until the entire main is filled. The water shall remain in the main for a minimum of 24 hours, during which time all valves, hydrants, and the like, along the main must be operated to insure their proper disinfection. Following the 24-hour period, no less than 25 mg/L chlorine residual shall remain in the main.

B.

Slug Method: In this method, a continuous flow of water is fed with a constant dose of chlorine (as in the previous method) but with rates proportioned to give a chlorine concentration of at least 300 mg/L. The chlorine is applied continuously for a period of time to provide a column of chlorinated water that will contact all interior surfaces of the main for a period of at least three hours. As the slug passes tees, crosses, and the like, proper valves shall be operated to insure their disinfection.

3.04 DISINFECTING BROKEN WATERLINES

After determining location and exposure of the break, the area shall be carefully inspected to locate and isolate sewers and other contaminant sources. Following this, the Contractor shall flush the main while standing water in the trench is being pumped away. The affected section shall be isolated, service connections shall be shut off, and the section shall be subjected to disinfection procedures described for new mains. The slug may be increased to 500 mg/L. Bacteriological samples shall be taken by the Contracting Officer following disinfection to test the effectiveness of the process.

3.05 FINAL FLUSHING

Following disinfection, all treated water shall be thoroughly flushed from the newly laid pipelines.

END OF SECTION

WATER DISTRIBUTION

Division 2 02675 - 1

REPLACEMENT

Angeles National Forest