Wastewater treatment is an essential piece of the puzzle for many new house construction, addition or renovation projects. Rural Maine homes often are beyond the reach of municipal sewer systems, even if they’re on major roads. A few even have town water hookups but no public sewer.
In a standard septic system, household wastewater from toilets, showers, sinks and laundry flows into an underground septic tank, which is usually within about 10 feet of the house.
If all the effluent stayed in the tank, which typically totals 1,000 gallons for a single two- to three- bedroom residence, it would have to be pumped every few days. (That’s how it works if you have a holding tank, which are not allowed in most circumstances.)
Instead, solids settle into the tank and some particulates and oils are filtered through a system of baffles inside the tank, but most of the effluent continues out to Step 2 of the system: a leach or disposal field.
The disposal field is a large area where the water is evenly distributed to drip into stone, sand and soil to filter out bacteria and let it die. By the time the water flows back into the groundwater system, it’s considered treated.
Septic tanks should be pumped every two to five years, which should include inspection of the whole system and cleaning of any filters in the tank.
When Tremont resident Deb Suter contemplated building another house on her 2.3 acres, getting a septic system design was the first step. She needed a site evaluation to figure out where on the lot such a system could go. That, in turn, informs where the house and driveway could be put.
Tying a second house into an existing system probably wouldn’t work, since it was likely designed for only the number of bedrooms or residents in the existing house.
“People are putting more and more houses on their property,” Suter noted.
Suter contacted a local engineering firm, CES Inc., to do the site evaluation and design the septic system.
Engineer Roger St. Amand walked the property several times with Suter, outlining various issues and options.
“The best thing about Roger was he knew what I wanted,” she said. “A system to go in the safest and best place, that would not be right on top of this house, and would cost the least amount of money. He took me through the whole thing and explained options for different models.”
A new residential septic system usually runs $10,000 to $15,000, depending on site features such as access, wetlands, exposed ledge and how much fill will be needed, St. Amand said. “Costs can increase for more complex systems, or where system height and size are a concern and owners have certain site or landscape visions to incorporate.”
Those considerations include minimum separation distances that the disposal field has to be from ledge, or the water table, or other existing site features.
“So they’ve got property lines [a 10-foot setback],” St. Amand said of Suter’s project. “Then, you have to be 100 [feet] from any private well and 100 [feet] from any major water body [defined as anything that shows up on a U.S. Geological Survey map].”
Several options are available for the design of the disposal field.
Most traditional is a stone bed, which must be perfectly level. A residential system would need a field measuring about 15 by 40 feet. Four-inch perforated pipes distribute the water through the area. It’s best to avoid too much foot traffic or compaction on these, since lots of oxygen is needed between the pieces of rock.
Another popular option is a concrete chamber system, which is what Suter chose to go with. The concrete pieces look a little like sections of a floating dock. A distribution box sends the water flow to each section of the field. The water flows into the chambers and then into the ground.
“The nice thing about concrete chamber systems is they can withstand some pretty heavy traffic,” St. Amand said. “So we can put them under parking lots or driveways. If you want to have a volleyball court, we’d say, ‘Well, maybe you want to use concrete chambers.’”
In both cases, the bottom of the stone or concrete must be 24 inches above ledge. Depending on the native soil, that fill is usually a coarse, gravelly sand that lets water drain through easily.
Other, newer technologies make it possible to treat the same amount of water with a smaller leach field, St. Amand said. One is Geotextile Sand Filters (GSF) by Eljen, which CES used in a new system at Atlantic Brewing Co.’s Town Hill brewery.
“They’re 3-inch-by-4-inch plastic blocks. The benefit of using these is you can get a much smaller footprint because there’s so much more treatment. We use them a lot on smaller lots, replacement systems and island systems.”
Pre-treatment systems also can minimize the height and size of the required leach field.
Suter had not decided when or even whether to build the contemplated house. But with the design complete, she now had in hand a HHE-200 form, which serves triple duty as a permit from the state, a design document that can be handed to building contractors and a record of the system design to be filed with the town and state for future reference.
That document is important for house buyers and sellers, too — so that new owners know about the system they’re inheriting, required maintenance, and possible future expansion or replacement.
The average life span of a septic system, St. Amand said, is 15-20 years. Many last much longer. “They’re expensive to put in so you wouldn’t replace one unless you had a problem.”
If a leach field is worn out, he said, “wastewater will start blowing out the side of the field. Usually it smells kinda bad. If it’s got lawn and it’s damp and really, really green, or if you see a black slime spot at the edge of the field, those are indications that the field is getting ready to break out.”
Homeowners can extend the life of their system by making sure there’s a filter and baffles in their septic tank.
“Older tanks had concrete baffles so those can fall off and go down in the tank,” St. Amand said. “Then there’s no baffle at all. But they can be retrofitted fairly easily.”
When a disposal field does fail and needs to be replaced, it’s best to find a new location with native soil that hasn’t been disturbed.
The new site may be a bit farther from the house, St. Amand said. “Nine times out of ten, you end up having to pump to your system, which is not a bad thing, but it’s another component you have to put in and maintain.”
If there is no other appropriate site on a lot, digging out the old field and installing a new one in the same place also is an option.