Sewer Replacement: Grade issue

[Andy_in_Oregon]

I'm replacing a 70 year old sewer line at my residence. This line outside the structure is concrete pipe. I will be installing 4" schedule 40 PVC DWV. I've measured the fall and computed the grade for the existing line. It is 1%. This is allowable in my city for a replacement, if there is no way to create more fall. However, part of the existing line goes under the slab in my garage. I would like to avoid digging this up. (There is a basement, and the sewer line is 8.5 feet underground). I can create a new alignment for the sewer line, but it will be slightly longer than the existing alignment. This means the grade is below the 1% minimum. Rather than .12" /foot, the grade will be .105"/foot. Even if I can get this approved, will the sewer line likely result in flow problems?

 

[Reach4]

Do people ever get sewer backups in your area after a big rain, with other people's sewage entering the basement? If the answer is yes, you might consider switching to overhead sewers, with basement sewage getting pumped up.

With the sewer line exiting at a higher place, slope will be no problem.

 

[Sponsor]

 

[Andy_in_Oregon]

Do people ever get sewer backups in your area after a big rain, with other people's sewage entering the basement? If the answer is yes, you might consider switching to overhead sewers, with basement sewage getting pumped up.

With the sewer line exiting at a higher place, slope will be no problem.

We have never had a sewer surcharge event here. I was planning to install a backwater prevention valve, in case this is an issue in the future. Your idea would certainly solve my problem, but would be quite difficult to implement. There is a bathroom and laundry area in the basement. Thank you for your reply.