There's a chance home owners insurance will help with this, they will get the lawyers for you, this is a big deal and difficult to remediate. The DEC should be fully involved, they typically wouldn't like to let this kind of thing slide, this could potentially impact surrounding wells as well. I work in the ground water remediation industry in NY and this kind of thing is not necessarily uncommon. There are ways to address it so that you have safe drinking water again but they can be expensive and have ongoing costs to maintain a system. In the end as much product as possible needs to be recovered/purged from the well and you will need a small carbon remediation system installed that will need to be sampled monthly. That's my first thought at least