1 March 1997
PRELIMINARY DESIGN CONSIDERATIONS
2-1. EXISTING CONDITIONS. As an important initial step in the design process, existing maps,
drawings, surveys, boring logs, and other data containing pertinent information on existing
conditions in the area being served must be obtained. Possible sources of such information
include the following:
- Installation or Facility Engineer.
- Army or Air Force using service.
- Federal Agencies such as United States Geological Survey and Soil Conservation Service.
- State, county or municipal engineering departments.
- Public utilities.
- Commercial businesses and private firms (including A/E's).
- Regional or local planning boards.
2-2. FIELD INVESTIGATIONS.
a. Maps. If maps are not available, or do not provide satisfactory information or sufficient
detail of the site, field surveys must be performed. Depending on the magnitude and complexity
of the project, subsurface exploration with soil borings may be required. Topographic information
should show locations of all streets, buildings, pavements, sidewalks, vegetation, drainage
channels, and other land surface features such as utility manholes or structures, which may
influence the design and layout of the collection system. Information on existing utilities should
include the location of underground water lines, sanitary sewers, storm drains, gas mains, steam
tunnels, electric conduits and similar facilities.
b. Soil Conditions. For larger projects, the character of the soil in which sewers will be
constructed should be determined. The presence of rock, unfavorable soil conditions, or high
groundwater table should be clearly established. The soil bearing capacity is needed for
designing footings. Soil tests used to determine the need for corrosion control include earth
resistivity, pH, oxidation-reduction potential, and relative moisture content.
c. Corrosion. If metal pipe, structures, or appurtenances are to be buried, the need for
corrosion control must be assessed. The need for corrosion control should be based on data
obtained from corrosion surveys, operating records, visual observations, inspections, and tests of
existing facilities in the area and from manufacturers recommendations.
a. Service area. The requirement that an area be served by a wastewater pumping facility
will in most cases be determined by topography. Building and grade elevations in the area
generally will be too low for proper gravity drainage to an existing or proposed sewer system, or
waste treatment facility. Thus, collection and pumping of wastes from these low lying areas will
be necessary. In addition to topographic considerations, natural boundaries like waterways,