4.13 Minimum Depth
a. All sanitary sewers shall be laid at a depth sufficient to drain building sewers, to protect against damage by frost or traffic, and to drain basement sewers where practical. Sufficient depth shall mean the minimum cover from the top of the pipe to finish grade at the sewer alignment.
b. Under normal conditions, sanitary sewers in residential areas shall be placed in the street with the following minimum cover:
1) Lateral and Mainline Sewers - Six (6) Feet
2) Trunk Sewers:
a) In the roadway - Seven (7) feet
b) In easements - Eight (8) feet
3) Where the topography is relatively flat and existing sewers are shallow (five feet or less) and cannot practically be lowered, the minimum cover may be reduced to three (3) feet. Cover depths less than three (3) feet will require the approval of the Director, and will require the installation of Class 50 ductile iron pipe (corrosion resistant mortar lined) or Class 150 C900 PVC.
c. In new designated residential hillside subdivisions, mainline and lateral sewers shall be placed in the street at a depth sufficient to drain building sewers on the low side of the street. Deviation from these standards will be considered on a case-by-case basis when the following circumstances exist and the required documentation is submitted.
1) Underlying rock strata: A request in writing must be submitted to the Director together with a soils report including a plan and profile certifying bed rock exists below the undisturbed ground surface at all investigated alignments.