Worcester's Combined Sewers and What a Sewer Backup Means in Your Cellar

What does a combined sewer actually do in heavy rain?

In a combined system, the pipe under the street carries both sanitary waste from buildings and runoff from streets and roofs. Worcester's sewers work that way, moving everything to the Upper Blackstone treatment plant. When a cloudburst puts more water into that pipe than it was built to carry, the excess has to go somewhere.

On a dry day the arrangement is invisible. Flow from a three-decker's stack joins flow from the catch basin at the corner, the pipe runs well below its capacity, and everything reaches the plant. The system was laid out when separating the two was neither cheap nor expected, and a good deal of the city's older collection network still works on that principle.

A heavy summer cloudburst changes the arithmetic in minutes. Rain that would once have soaked into open ground now runs off pavement and roofs into the same pipe that is already carrying wastewater, and the pipe fills. Flow beyond capacity overflows to the Blackstone River, which is the designed relief point. The city's own water and sewer information describes the system this way, and it is why intensity matters more than total rainfall here: an inch falling in twenty minutes loads the pipe harder than three inches over a day.

• Sanitary flow from buildings and storm runoff from streets share one pipe.
• Everything heads to the Upper Blackstone treatment plant under normal flow.
• Flow beyond the pipe's capacity overflows to the Blackstone River.
• Short, intense rain loads the system harder than steady rain of the same depth.

Does a river overflow mean my basement is about to back up?

No, and the two should be kept apart. An overflow to the Blackstone is a discharge from the public system at a designed relief point. A backup in your cellar is water that could not leave your building, which usually comes down to a blockage, a surcharged section of pipe, or a fixture below the level the water reached.

It is tempting to read the city's overflow notices as a forecast for your own floor drain, and the connection does not hold. The overflow exists so the public pipe sheds volume to the river instead of pushing it back toward buildings. Plenty of storms produce one without producing a single household backup, and plenty of household backups happen on dry days because of grease, roots or a collapsed section of clay pipe.

What the overflow notices do tell you is that the system has reached its ceiling in that storm, which is a reasonable moment to go and look at your own cellar rather than wait for the smell. The city posts notifications about overflow events and offers email alerts, so signing up costs nothing and gives you a prompt to check the lowest fixture in the building while the rain is still falling.

How do you tell a sewer backup from ordinary cellar seepage?

Look at where the water appears and what it smells like. Seepage shows up at the joint where the wall meets the floor, or through a crack, and it is usually clear and odorless. A backup pushes up through the lowest opening in the building, which in a Worcester cellar is normally the floor drain, a laundry sink or an old toilet.

Seepage follows the ground. After a nor'easter or a long thaw the soil around a stone cellar wall saturates, and water finds the mortar joints, the gap at the footing or a crack in a later concrete patch. It comes in slowly, stains the wall in a band, and stops within a day or two of the weather changing. Nothing about it is contaminated beyond what it picked up in the soil.

A backup behaves differently. It rises, rather than running in, and it rises at the point of lowest elevation. Gray or dark water with sewage odor around a floor drain, bubbling from a laundry standpipe, or toilet water that will not clear while the storm is at its heaviest all point the same way. If more than one fixture in the building misbehaves at once, the problem is in the drain line rather than in any single fixture. Our page on sewer backup cleanup walks through what happens after that point.

Who is responsible for the pipe the blockage is in?

That depends on which pipe it is, and the only honest advice is to ask rather than assume. The building's own sewer connection and the public main are different pieces of infrastructure with different custodians, and you cannot tell from inside the cellar which one is blocked.

No public Worcester page setting out that boundary and the claim process was available when this guide was written, so this page will not tell you who pays. Call the DPW, describe what you are seeing and ask plainly which pipe the blockage is likely to be in and who clears it. If the answer is the public side, that call is also the record that you reported it at the time, which matters more than any guess made afterward.

A drain contractor or plumber can usually tell you where the obstruction sits by how far the cable or camera travels before it stops, and that distance is worth writing down. Keep it, along with the time you called the city, alongside your photographs. Cleanup and the question of responsibility run on separate clocks: the water still has to come out of the cellar today.

What should you do in the first hour of a cellar backup?

Keep people and pets out of the water, cut power to the cellar at the panel only if you can reach it from a dry floor, and stop adding water from upstairs. Do not run washers, dishwashers, showers or toilets, because every gallon you send down has nowhere to go but back up.

The hazards in a flooded cellar come in that order for a reason. Contaminated water plus the cellar's own wiring, the boiler and the water heater is the combination that hurts people, and in an older Worcester house the panel is often down there with it. If reaching it means standing in the water, leave it and have an electrician or the crew deal with it. Gloves, a mask and eye protection are the minimum before touching anything, which is what the CDC advises for any wet cleanup.

Then stop the inflow from your own side of the house. Everyone upstairs needs telling, not just reminding, because a single load of laundry in a three-decker undoes an hour of pumping. Photograph the high-water line on the wall and on the mechanicals before anything is moved, note the time, and call for extraction. Worcester Water Damage Restoration answers the line 24/7 and a crew is sent as soon as one is free; price is explained and approved on site before any work starts.

• Nobody in the water until power to the area is off and known to be off.
• Gloves, mask and eye protection before any contact.
• No laundry, dishwasher, shower or toilet anywhere in the building.
• Photograph the water line, the floor drain and the mechanicals before moving anything.

What has to be thrown out after sewage water, and what can be dried?

Contaminated water is not a drying problem alone; it is a cleaning problem first. Porous materials that soaked it up, such as carpet, pad, cardboard, upholstered furniture and insulation, are generally removed rather than dried. Hard, cleanable surfaces can usually be washed, disinfected and then dried.

The EPA's guidance on wet materials is written around clean water and gives a window of roughly 24 to 48 hours before mold growth becomes likely, with porous materials wet longer than that generally better removed. Contaminated water is handled differently, and the difference is that cleaning and disinfection come before the fans go on. Drying a carpet that absorbed sewage leaves you with a dry carpet full of what the water carried.

In practice, a Worcester cellar after a backup loses its carpet, any stored cardboard, and the bottom of anything made of pressed board. Stone and brick walls, a concrete floor, a plank ceiling and the mechanicals are cleaned in place and then dried, with the moisture read in the wood rather than guessed at. If plaster, old flooring or pipe insulation will be disturbed in the process, ask about asbestos rules before anything is cut, because MassDEP sets notification requirements for renovation and demolition work.

Does homeowner insurance cover a sewer backup in Massachusetts?

Generally not as standard. The Massachusetts Division of Insurance describes sewer backup and sump-pump failure as typically excluded from standard homeowner, renter and condominium policies, with coverage available by endorsement. Flood is excluded as well. Your own policy and your insurer decide what applies.

This is the single most useful thing to check before the next storm rather than after one. An endorsement for water that backs up through sewers or drains is a separate item, often inexpensive relative to the loss it covers, and it is not on a policy unless somebody added it. Under the federal flood program, backup is covered only where a flood is the proximate cause, which is a narrower situation than most homeowners expect.

If you do have a claim, report it to the insurer first and keep your own record of the event in parallel: photographs, the time you called the city, what was removed and why. Where a claim is handled improperly the Division of Insurance takes complaints through its Consumer Service Unit, though it cannot decide the facts of a loss such as what caused it. There is more detail in our guide to water damage insurance claims in Massachusetts.

What reduces the risk before the next cloudburst?

Three things carry most of the benefit: keep what you value off the cellar floor, keep the drains that serve the building clear, and ask a plumber whether a backwater valve makes sense for your connection. None of it is glamorous and all of it is cheaper than a cleanup.

Start with the storage. In a three-decker cellar the bottom shelf is the one that floods, and cardboard boxes on a concrete floor are the most commonly lost possessions in this city. Open shelving raised off the slab, plastic bins instead of cartons, and nothing porous stacked against a stone wall will survive a backup that destroys everything flat on the floor.

Then the plumbing. A backwater valve is a device fitted into the building's drain to resist flow coming the wrong way, and whether one suits your connection is a question for a licensed plumber, since the Board of State Examiners of Plumbers and Gas Fitters licenses the trade that does that work. If you have a sump pump, confirm it starts when tested and that its discharge runs well away from the foundation; failure of one is excluded by most policies on the same footing as a backup. Our page on sump pump failure and backwater valves covers what tends to go wrong with both.

• Open shelving off the slab, plastic bins rather than cardboard.
• Gutters and area drains clear before the September-to-April storm season.
• Sump pump tested, discharge running away from the foundation.
• A licensed plumber's opinion on a backwater valve for your connection.