1 March 1997
rivers, streams, etc., and property lines of Federal, state and local jurisdictions, also play a role in
determining the size and limits of service areas.
b. Sewer System. The development of final sewer plans must await the final site plan, the
completion of field surveys, and to some extent, the establishment of floor grades. However, the
development of economical site plans often requires concurrent preliminary planning of the sewer
system. The location of building and lateral sewers will depend not only upon topography, but
also upon the type and layout of the buildings to be served. Normally, the most practical location
would be along one side of the street. In other cases they may be located behind the buildings
midway between streets. In still other cases, in closely built-up areas and particularly where the
street is very wide or already paved, it may be advantageous and economical to construct
laterals on each side of the street. Main, trunk, and interceptor sewers will follow the most
feasible route to the point of discharge. All sewers will be located outside of roadways as much
as practicable, so that the number of roadway crossings will be reduced to a minimum. A sewer
from one building will not be constructed under another building, or remain in service where a
building is subsequently constructed over it, if any other practical location for the sewer is
available. Where no other location is suitable, necessary measures will be taken to assure
accessibility for future excavation and complete freedom of the sewer from superimposed
building loads. The following general criteria will be used where possible to provide a layout
which is practical, economical and meets hydraulic requirements:
- Follow slopes of natural topography for gravity sewers.
- Check existing maps or field surveys along prospective sewer routes to assure that
adequate slopes are available.
- Avoid routing sewers through heavily wooded areas and areas which require extensive
- Check subsurface investigations for groundwater levels and types of subsoil encountered.
If possible, avoid areas of high groundwater and the placement of sewers below the groundwater
- Locate manholes at changes in direction, size or slope of gravity sewers.
- Sewer sections between manholes should be straight. The use of curved sewer alignment
is not recommended.
- Manholes should be located at intersections of streets when possible.
- Avoid placing manholes adjacent to water courses and in locations where the tops will be
submerged or subject to surface water inflow.
- Designer should evaluate alternative sewer routes where applicable.
- Verify that final routing selected is the most cost effective alternative that meets service
c. Geographic Information System (GIS). At some installations, information on existing
utilities is available on a GIS and the new design or the as-built drawings must be incorporated
into the GIS. A Tri-Service Computer-Aided Design and Drafting/GIS (CADD/GIS) Standard is
currently being developed and, once approved, will be utilized for all designs.