Sewer force main horizontal clearance

[racv2]

I am designing the pipe layout of a sewer force main that runs parallel to an existing gravity sewer.
I found out that there has to be a 10' clearance between the force main and a water main but what about the horizontal clearance between the new force main pipe and the existing gravity sewer pipe?
Also is there a recommended vertical clearance as well between force main pipes and gravity sewer pipes?
Thanks in advance for any help.

 

[cvg]

the reason for the 10' between water and sewer is to prevent cross contamination of the drinking water. Not a problem with two sewers. However, you still will want to maintain a separation between the two for constructability. You don't want the existing sewer line, or any leakage from that line to end up in your new trench - that would be a mess, so maintain several feet separation if possible.

 

[dicksewerrat]

It is easier to fix the lower pipe if the upper is NOT within 4 feet of the edge of the lower one, vertical and horizontal. you need room to construct a safe excavation for the lower one. talk to whomever has to maintain the pipes when you are done and gone. Don't construct a nightmare for the next guy.

 

[bimr]

Not sure why you are asking such a basic question, but anyway, here you go:

Section 38.31 of the "ten standards standards"

Horizontal and Vertical Separation

Sewers shall be laid at least 10 feet (3.0 m) horizontally from any existing or proposed water main. The distance shall be measured edge to edge. For gravity sewer where it is not practical to maintain a 10-foot separation, the appropriate reviewing agency may allow deviation of a case-by-case basis, if supported by data from the design engineer. Such deviation may allow installation of the gravity sewer closer to a water main, provided that the water main is in separate trench or on an undisturbed earth shelf located on one side of the sewer and at an elevation so the bottom of the water main is at least 18 inches (46 cm) above the top of the sewer.

If it is impossible to obtain proper horizontal and vertical separation as described above for gravity sewers, both the water main and gravity sewer must be constructed of slip-on or mechanical joint pipe complying with public water supply design standards of the agency and be pressure tested to 150 psi to assure watertightness.

Crossings

Sewers crossing water mains shall be laid to provide a minimum vertical distance of 18inches (46 cm) between the outside of the water main and the outside of the sewer. This shall be the case where the water main is above or below the sewer. The crossing shall be arranged so that the sewer joints will be equidistant and as far as possible from the water main joints. Where a water main crosses under a sewer, adequate structural support shall be provided for the sewer to maintain line and grade.

When it is impossible to obtain proper horizontal and vertical separation as stipulated above, one of the following methods must be specified:

a. The sewer shall be designed and constructed equal to water pipe, and shall be pressure tested at 150 psi. to assure watertightness.

b. Either the water main or the sewer line may be encased in a watertight carrier pipe which extends 10 feet on both sides of the crossing, measured perpendicular to the water main. The carrier pipe shall be of materials approved by the regulatory agency for use in water main construction.