Septic systems have many advantages. First, they allow drinking water drawn from Acton's ground water to return to the local watershed. With sewers, West Acton water would be pumped to South Acton and discharged at the Assabet River. The Assabet is already compromised with high levels of organic compounds from water treatment facilities along the river. Meanwhile, local aquifers depend on continued recharge of the watershed. In addition, septic systems support the health of local streams and wetlands by helping to maintain flow.
The EPA's list of septic system benefits are as follows:
Protection of property values. Well-managed, properly designed onsite or cluster systems can provide sewage treatment equivalent to a centralized plant, often at a lower cost.
Water conservation. Decentralized systems can help recharge groundwater aquifers and maintain dry season flow in streams.
Preservation of the tax base. Decentralized systems can be installed on an as-needed basis, thus avoiding the large up-front capital costs of centralized sewage treatment plants.
Life-cycle cost savings. Proper management can result in lower replacement and repair costs, increased property values, enhanced economic development, and improved quality of life.
Effective planning. Decentralized systems provide flexible wastewater options and help achieve land use objectives.
Moreover, the RMI study of septic systems and sewers found many severe disadvantages of sewers:
Centralized systems are unaffordable for many small communities. ...
In some places, centralized systems have been overbuilt, resulting in crushing debt burdens for citizens. ... [As of 2017, Acton still owed $14 million for the construction of the South Acton sewer.]
Sewer systems can dramatically impact the hydrology of watersheds. Infiltration of ground water into sewers is a substantial problem in many communities across the U.S. Wet weather sewer overflows are a well-known consequence in many places. Another consequence, gaining increasing recognition, is that too much ground water is drained away, robbing streams of base flows. In some places, such as the Ipswich River in Massachusetts, this has contributed to the drying-up of some stream segments. ...
Sewers can also leak sewage into streams and ground water. There is evidence that leaking sewer pipes are a substantial problem in parts of the U.S. A study in Albuquerque, New Mexico concluded that leakage of wastewater from sewer pipes amounted to 10 percent of average daily wastewater flow, or five million gallons per day (reported in Amick and Burgess 2000). In some areas, leaking sewers may be a greater source of ground and surface water contamination across the country than are septic systems. ...
Centralized systems have a huge backlog of deferred maintenance. The EPA has determined that the gap between what U.S. cities are spending on maintenance and upgrades of collection and treatment systems (as well as drinking water infrastructure) and what is actually needed amounts to many billions of dollars a year (U.S. Environmental Protection Agency 2002b). It is not at all clear how this gap will be closed, given that massive new federal funding is unlikely, but it is clear that communities cannot generally afford to spend any more than they absolutely have to on new infrastructure when the needs of the existing infrastructure are so great. Thus alternative ways of providing wastewater service in suburban areas are gaining increasing attention.
Note that the lifespan of the South Acton sewer's treatment plant is only 20 years. It is now in need of ~$10 million in refurbishment and upgrades. Meanwhile, the cost of sewers continues to rise.