47.5 MB - The Whole Building Design Guide

Although it is difficult to achieve, the model building codes andNFIP regulations provide an alternative that allows utility systemsand equipment to be located below the DFE. This alternative requiresthat such systems and equipment be designed, constructed,and installed to prevent floodwaters from entering or accumulatingwithin the components during flood events.2.3.5.3 Potable Water and Wastewater SystemsNew installations of potable water systems and wastewater collectionsystems are required to resist flood damage, includingdamage associated with infiltration of floodwaters and dischargeof effluent. Health concerns arise when water supply systems areexposed to floodwaters. Contamination from flooded sewage systemsposes additional health and environmental risks. Onsitewater supply wellheads should be located on land elevated fromthe surrounding landscape to allow contaminated surface waterand runoff to drain away. Well casings should extend above thedesign flood elevation, and casings should be sealed with a tightfitting,floodproof, and vermin-proof well cap. The space betweenthe well casing and the side of the well must be sealed to minimizeinfiltration and contamination by surface waters.Sewer collection lines should be located and designed to avoid infiltrationand backup due to rising floodwaters. Devices designedto prevent backup are available and are recommended to providean added measure of protection.Onsite sewage systems usually are not used as the primary sewagedisposal system for new critical facilities. However, it would be prudentfor owners, planners, and designers to consider a backuponsite sewage system if a facility’s functionality will be impairedif the public system is affected by flooding. Designers are advisedthat local or State health departments may impose constraints thatlimit or prevent locating septic fields in floodplain soils or withina mapped flood hazard area. If allowed, septic fields should be locatedon the highest available ground to minimize inundation andimpairment by floodwaters. An alternative to a septic field is installationof a holding tank that is sized to contain wastewater fora period of time, perhaps a few days if the municipal system is expectedto be out of service.2-76 MAKING CRITICAL FACILITIES SAFE FROM Flooding