We have a floating boat dock and the county now requires the foam to be encapsulated. So we had to replace the foam with encapsulated foam, can I add the cost of this work to my basis?

I believe so; you can Increase the basis of the property by all items properly added to a capital account. For example, you can include the cost of any improvements that are expected to have a useful life of more than1 year. in your case the replaced floating boat dock . However, you may contact the county assessment office ofr more info in detail.