Almost every home for sale around Great Herring Pond, Big Sandy Pond and Buttermilk Bay runs on a private septic system. Under Massachusetts Title 5, that system has to be inspected within two years before a sale. If weather prevents an inspection at the time of sale, it must happen within six months afterward. A passing report tells you whether the system works today. The Town of Plymouth is now working on a separate question: whether certain parts of South Plymouth should stay on septic at all over the next 20 years. Its early ranking of those parts doesn't follow the pond everyone talks about. It follows lot size and the age of the homes.
A Passing Inspection Doesn't Answer the Town's Question
Plymouth is writing a 20-year Comprehensive Wastewater Management Plan, or CWMP, with the engineering firm Weston & Sampson. The work is run by the town's Department of Public Works and Engineering Department. The town's own information sheet says why a home with a working septic system could still be included in sewer planning: "Even properly functioning septic systems release nutrients and contaminants that over time can be harmful to wetlands, ponds, and other valuable water resources."
So a buyer in Cedarville can get two different answers about the same house. The Title 5 report covers one system on one lot. The CWMP looks at the whole neighborhood: how tightly homes are packed, how old they are, and where their wastewater goes once it's underground.
Four Pockets, Four Rankings
The Herring Ponds Watershed Association published a summary on October 17, 2026. It says Plymouth has evaluated four main unsewered neighborhoods in Cedarville and given each a priority level.
| Area | Priority | Lots | Average lot size | Other details in the summary |
|---|---|---|---|---|
| Buttermilk Bay | High | 500 | Under 0.25 acre | Homes mostly over 50 years old |
| Big Sandy Pond | Medium | 730, with 600 potential sewer connections | 0.40 acre | 20 septic variances |
| Ponds of Plymouth / Great Herring Pond | Medium | 1,000, with 800 potential sewer connections | 0.85 acre | Next to impaired waters |
| Cedarville | Low | 500 residential and commercial lots | Not given | Near Cape Cod Bay |
Read across the rows of the October summary and the ranking tracks density. In that summary, the one high-priority area has the smallest lots and the oldest housing. Big Sandy Pond lots average less than half an acre and include 20 septic variances, and it ranks medium. The Ponds of Plymouth and Great Herring Pond area has the most lots and the most pressing water-quality story in South Plymouth. Its lots average more than twice the size of Big Sandy's, and it ranks medium too.
The Pond With the Reputation Ranks Medium
Great Herring Pond's problem is well documented. The watershed association's August 2026 annual meeting was held at the Little Red School House. At that meeting, the group said its consultant-prepared Water Quality Plan found that the largest single source of the phosphorus feeding cyanobacteria blooms in Great Herring Pond is Little Herring Pond. That phosphorus comes from septic systems in the Ponds of Plymouth. The association describes the route: phosphorus moves underground from the Ponds of Plymouth into Little Herring Pond, then into Great Herring Pond by way of the Carter River.
The phosphorus comes from homes farther up the chain, and the pond downstream shows the effect. A house on Great Herring Pond can have a spotless Title 5 report and still sit at the bottom of that chain.
The pond's condition changes from season to season. As of October 30, 2026, the MassDEP list of cyanobacteria advisories included four Plymouth waterbodies: Billington Sea, Boot Pond, Great South Pond and Halfway Pond. Great Herring Pond and Big Sandy Pond were not on it, and MassDEP says the list is not complete. In his fall 2026 letter, association president Don Williams wrote that the group's Water Quality Committee will spend the off-season "working hard to find a way to permanently remove cyanobacteria advisories from Great Herring Pond."
The association is also raising money for land. Its September 27 fundraiser drew nearly 100 people and raised $10,000 for a Land Acquisition Fund. The fund is meant to leverage Town of Plymouth money to buy land in the watershed for conservation. The letter explains the reasoning: conservation land limits the spread of septic tanks and adds places to walk. Members have already created QR-enabled trails in the Alper and Comassakumkanut preserves.
Why Plymouth Can't Simply Pipe Everything
The plan starts from a town that mostly isn't on sewer. According to the association's summary, more than 80% of Plymouth uses private septic systems. The municipal system has over 50 miles of gravity sewer, 17 miles of force main and 8 town-owned pump stations, and it serves about 2,800 lots. The treatment plant at 131 Camelot Drive handles an average of 1.5 million gallons per day, against a permitted capacity of 2.5 million. More than 40% of the collection system is over 50 years old.
Plymouth already has aging pipes to keep up. Extending sewer to every unsewered pond neighborhood in South Plymouth would be a big expansion on top of that. That helps explain why the engineers are weighing a different approach for each area. The summary lists these options:
- Enhanced on-site systems, which are advanced septic units that remove 25% or more of nitrogen and phosphorus
- Extending the main sewer system
- Building new local treatment facilities
- Connecting to existing local treatment facilities, such as Red Brook
The density pattern from the table shows up again here. An upgraded on-site unit is easier to picture on a 0.85-acre lot by Great Herring Pond than on the quarter-acre-or-smaller lots around Buttermilk Bay. That would fit with Buttermilk Bay sitting at the top of the list. No specific solution has been assigned to any named area.
The Cost Question Is Still Open
The town's information sheet says the plan will estimate capital and operating costs and identify funding sources. No homeowner cost figure has been published.
The Citizens Advisory Committee, chaired by Mike Hanlon, has discussed money only in early terms. According to its April 27, 2026 minutes, members noted that other towns have used short-term rental taxes to pay for their wastewater plans. Residential tax exemptions were raised as another option, and the town said it had already studied that idea and found the savings weren't worth it. The watershed association notes that a state-approved CWMP could position Plymouth for state and federal grants and low-interest infrastructure funding. It also hopes its own Water Quality Plan will improve the chances of a grant that eases the cost for residents.
There are some procedural steps ahead. The committee's May 2026 minutes say the town reported that an Environmental Justice meeting is legally required before the formal draft is submitted. The committee's October 26 agenda listed the project schedule for discussion. The town is taking public input through the CWMP page and an online survey linked on its information sheet.
Questions to Bring to a Cedarville Showing
The plan doesn't decide anything for a buyer yet. It does turn a few ordinary listing details into useful information:
- Which of the four areas is the house in? Buttermilk Bay, Big Sandy Pond, Ponds of Plymouth and Great Herring Pond, and Cedarville each carry their own priority in the association's October 17 summary.
- What's the lot size compared with that area's average? A half-acre lot near Big Sandy Pond is larger than average there. Near Great Herring Pond, it's smaller than average.
- When was the Title 5 inspection done? The two-year window before a sale is set by state rule, and the MassDEP guide explains the timing for single homes and condominiums. Condominiums with five or more units must have all systems inspected every three years.
- Does the system have any variances? The October summary counts 20 septic variances around Big Sandy Pond, so ask about them there.
- Is the house in the Great Herring Pond watershed? If so, it's part of the conservation and water-quality work the Herring Ponds Watershed Association is leading.
This post is general information about state rules and a town plan that's still being drafted. It isn't legal, tax or financial advice, so please confirm the details of a specific property with a licensed septic inspector, an attorney or the Town of Plymouth.
If you're looking at a home near one of these ponds and want to talk through where it falls on the town's map and what its septic paperwork shows, Christopher Sheridan grew up in Plymouth and is happy to walk through it with you, one question at a time. Let's Connect.
