If you want a good mitigator in Boston area, Eagle Environmental and Chapin Environmental are the guys to contact. I would try sealing that up and doing a re-test.... these open pit things can indeed dump a lot of radon in the house.. Also, you might have some 'stack-effect' issues exacerbating this.. heat loss into the attic space or out the upper story of the house??? If you can work on both things, you might actually knock this down.. As for water in the soil and radon levels... the answer really is 'possibly'...the problem is, it depends on the soil, the footings, house, etc, etc and you can never really really pin that down in the field.. You'd have to go across the river to have MIT live with you for a year to figure that one out.. and I believe .. they are not interested..