How do you fix radon and water infiltration in a dry stone foundation?
Gosh, do I need help w this one. It's a 1820s house with a largely stone foundation and backed against a small mountain. The "root cellar" with mechanicals and a dirt floor is under the living room, the rest is crawl space with dirt floor or slab. The 10x14' cellar has heavy springtime water ingress where the dry stacked stone meets bedrock.
The previous homeowner reported ~12" of standing water during a tropical storm and the sump losing power. The exterior water ingress can only be managed so much by gutters/french drains, given grade against mountain. There's no appetite for the cost of a full excavation to "footings" - if that's even possible w this type of foundation.
There's also a 3 month reading of radon at 4.0. So... I'm thinking a layer of washed gravel in the cellar is necessary to allow the water to flow to the sump. Then a radon-rated vapor barrier on ground/walls, taping best able around mechanicals and piers - and adherred to the skim of mortar under the rim.
Questions: 1) do you think an interior french drain to the sump is necessary? 2) spray foam insulation on walls necessary? 3) would you pursue a radon system drawing under the vapor barrier or an HRV w radostat? I don't want to unnecessarily over-engineer this... Oh, and there's mice galor! So thinking of caulking rim/joists and filling w rock insulation btwn. Heard they hate that stuff. Many thanks in advance for any advice and/or validation.