Has the town already have an easement on your land? Not sure what document or letter you sent back to the town four years ago. You may check with your county recording office to see if there is an easement on your land already. Such public utility project may be planned many years ago and it is possible that an easement was already there when you purchased the land. If there is no easement and you do not like the idea just tell them no. If the town wants an easement it should pay for it.
A sewerage system under ground may not affect the value of your land since it runs underground and does not affect your use of the land. It does carry the risk, however, that the town may need to access it for repair and service from your land. You should consult a real estate attorney. Non-use for four years manifests an intent to abandon and you may have a reason to terminate the easement. On the other hand, the town may exercise its eminent power to get the easement. You should consult the attorney to carefully figure out the impact of the easement on your land. If you cannot fight it, at least make sure you are well compensated for it.
