I am not a legal authority on this issue but because of experience with CSO and expired NPDES permits that municipalities are operating there may be some answers to your question.
Is this is a municipality? I not aware if a private wastewater operator can force an individual to connect to their system. And then normally if it is private the DEQ may require it must be then taken over by the incorporated municipality anyway and then residents could be forced to connect.
Groundwater venting must be proved and that takes monitoring wells. Also, what type of system is involved. How often is the discharging? It the system BOD's overloaded? The DEQ could force the municipality to eliminate a relative amount of overloading ie; gallons per day, to allow for any new connections. However a "yes" answer would seem to be conflicting if the system is under DEQ supervision and if and how the system is being overloaded. Is the system capable of receiving more gallons per day? If you suspect that venting is taking place then the DEQ must do an onsite inspection and give you a report of their findings. If venting is taking place then obviously there are two areas of concern: the system is receiving more gallons per day on average then the system was designed for and/or the liners are washed or worn out. Of course other factors could be involved but these factors were surely a major factor in monitoring wells to be place at the now defunct City of Scottville system.
Number one, the DEQ is the authority of the enforcement of the discharges and violations of the facility, especially those operated by a municipality, which seems to be what you are asking if you can be force to connect. If the DEQ is not looking at enforcement actions then you need to make them aware of them and be ready to prove it.
One municipality that just completed their system along with a completely replaced infrastructure is the City of Scottville. Prior to completion the DEQ would allow residential connections to those who requested sewage prior to their new system if they could eliminate infiltration that would negate the new connection. However, these were small residential additions that were requested and not demanded by the city. I'm not aware of the city forcing anyone to connect before or after they were placed under an ACO (administrative consent order), Their NPDES discharge permit had been expired for over 20 years before they came under the ACO so the DEQ has this model to help answer your questions, or at least for you to compare to.
Keep in mind this case came under supervision of the DEQ when the city asked the DEQ if they could connect new commercial businesses and where denied by the DEQ because of their expired permit system and system overloads. Under the new system in Scottville all but one block was connected to the new system. By the way, hoorah for the P.M. River and the end of CSO's from the City of Scottville. And congrats to the citizens and commission to complete this project ahead of schedule and to all those who were instrumental in seeing the Pere Marquette River free of sewage overflows.
Hope this helps.
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.689 / Virus Database: 450 - Release Date: 5/22/2004