Special Requirements for Concrete and Bolted Tanks

Special requirements for concrete tanks in California

California regulations require tanks to be of impervious construction to prevent the movement of water into or out of the tank. AWWA standards for concrete tanks (AWWA D110 and D115) have an allowable leakage rate for the tank as constructed. Therefore, you must specify tank construction in excess of AWWA standards to achieve a tank in compliance with the regulations.

California regulations require that all potable water contact materials (materials of construction such as concrete or coatings, linings, gaskets, sealants, etc.) must be certified in accordance with ANSI/NSF Standard 61.

The concrete mix must be certified or the tank interior surfaces must be lined to meet NSF certification. NSF certification requirements apply to all contact surfaces, including vapor zone above the top capacity level.

Although the California Code of Regulations requires the water system operator to only use materials and products that are certified for compliance with NSF Standard 61, the AWWA standards for concrete tanks (D110 and D115) do not require the use of NSF 61 certified products.

Therefore, for construction of new tanks, the tank owner must specify that compliance with NSF Standard 61 is required in order to ensure that the tank will comply with California code requirements.

Special Requirements for Bolted Steel Tanks

The cost of replacing original, glass-lined factory coatings on bolted steel tanks is very high. It is assumed that if a glass-lined bolted tank is selected, the maintenance to restore a near-original coating system may require disassembly and recoating plates at the factory. If coating maintenance, repair or renovation is performed without using the same ‘special’ coating that was originally shop applied, a total cost analysis must include additional coating maintenance and shortened renovation intervals. Some bolted tank manufacturers include a sacrificial anode cathodic protection system in conjunction with their factory applied coatings. Cathodic protection would not be necessary if the coating was holiday free, so coating maintenance on these types of tanks is obviously required. If cathodic protection system maintenance is not planned, a cost analysis must include increased future costs to account for cathodic protection system maintenance and the additional coating maintenance and renovation that will be required for this type of coating. The bolted seams in bolted steel tanks are required to be made watertight with gasket materials to provide a leak-proof seal. Although many of the joints may require sealant to be made leak-proof, application or re-application of sealant at regular intervals will not eliminate the need to maintain the coating system. It would only keep the tank from leaking. When performing a total cost analysis, be sure to include future costs of replacement sealants in addition to the coating maintenance and renovation noted above. Field holiday testing of the factory-applied coatings for bolted steel tank is not a requirement of the AWWA standard unless specified. If this step is not performed, when performing a cost analysis, be sure to increase the future costs to account for the additional maintenance and renovation that will be required where holidays and pinholes exist in the original coating system after erection.

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