Hi GBA,
Our 12,000 sq/ft lot is adjacent to 3 other properties. Each home is similar in size, approx. 1300 sq/ft. Our backyard is lowest in elevation, gently sloping downhill from the adjacent neighbors. We’re experiencing some basement water ingress and I’m spending time trying to understand the root cause. Forgive me for such a lengthy post but I tried to share all relevant context.

Backstory:
The neighbor downhill installed an above ground leach-field in 2000. I think the incline has slowed, maybe restricted the natural flow of storm-water from our and our uphill neighbors storm water runoff.

The neighbor rear of us is separated by an uphill slope/mound of natural earth with trees. Their home is rather far, and on the other side of the mound their land pitches the other direction so dwelling storm-water and sump water isn’t a concern.

The neighbor uphill installed one catch basin for storm-water and one perforated pipe for basement sump discharge. The perforated pipe lies between our properties but mainly on their land, uphill from ours. Prior to the perforated pipe install the previous owner and new owner would lay a sump/downspout drain pipe several feet from our property, 10′ from our septic tank. I never spoke about the matter with the previous owner because I didn’t know it was wrong or had any negative implications on our basement and septic system. Only recently did I begin learning about property storm water and sump drainage.

Fixes:
Last year (2019) we installed drainage pipe to collect and divert our gutter storm-water and basement sump water towards the front of the property near the road. This made a tremendous improvement on decreasing basement water ingress and a flooding leach field. Storm water is no longer overflowing basement window wells or through imperfections/cracks in the upper half of the foundation. It has also reduced supersaturation of our leach field and our septic and leach field is performing healthy.

Present:
Our present challenge is basement water ingress nearest the uphill neighbor. Water, moisture and saturation is present at both corners for extended months during winter, spring and summer. We also have some water creep-age through hairline cracks in the basement floor during high water table peaks (this is seen on the floor area near the upper neighbor, not lower neighbor. We do have a sump pump and the pump level line measures 14.5inches from the top of the concrete slab. I believe our pump is positioned lower than average, placed on the bottom of the sump pit, perhaps pumping more frequently than others.

Theory:
I understand our location is impacted by a high water table but I believe the problem is exacerbated by a combination of the raised leach-field and the placement of the uphill neighbors sump pump percolation. My thought is the percolation is the bigger of the concerns because this is the area of the basement with water ingress.

When the neighbor was installing the perforated pipe I politely asked the neighbor if he could push the percolation closer towards the road but he aggressively declined. The back and forth resulted in a negative relationship.

My theory is the combination of a raised leach field downhill and concentrated sump pump percolation up hill are causing the water table to slightly rise under our property.

Next Steps:
I don’t know what I should do next but I’m assuming I can’t ask my neighbors to alter what they have done. These are my next options to consider.

1. Install a french drain stretching from the rear of the yard towards the front to mediate any additional storm water penetrating the back and side yard.

2. Dig a 5′ deep trench stretching from the rear to the front yard and lay a rubber environmental separator with the intent to slow the horizontal flow of percolation from the uphill neighbor. (It may sound silly, insane or illegal but I’m dissapointed in my neighbors lack of attempt to understand and work collaboratively on the problem.)

3. Consult with a civil engineer on site grade renovations. Would anyone have any recommendations of an experienced engineer located in MA or RI?