There's nothing like fresh air and sunshine on a nice day while relaxing in the backyard with the family. But when the air takes on the stench of a sewer, it can kill the fun in a hurry. If you are on a private septic system, then you will be responsible for getting the issue cleared up. The cause of the odor may require professional assistance, or it may be nothing to worry about.
Leaking Sewer Pipes
Waste water pipes leave your house and empty into the city sewer system or into your private septic tank. These pipes are typically buried and are not prone to damage, but they can still rupture in a variety of situations. If they do, the raw sewage from your home will leak into the ground in your yard where the pipes are located. This will result in a foul smell in the yard and will sometimes cause the drains inside the home to back up because there is no place for the water and waste to go. The pipes will have to be dug out and repaired as soon as possible. Whether this is your responsibility or the city depends on where the leak occurs.
Blocked Drain Field
A septic tank works by allowing the solids and liquids to separate inside it. The solids sink, and a field of drain lines siphon off the liquid and return it to the ground near your home so the tank will not fill up. Sometimes, either because of freezing temperatures or because a solid has caused a blockage, the drain field can become clogged, and the liquid cannot escape from the main tank properly. When this happens, the tank can fill up and overflow, causing the sewage odor to come up through the ground.
Vents and Wind
Many septic tanks have ventilation to allow the methane and other gases to escape into the atmosphere. Usually the septic tank and any vents are placed in an area out of the way of family activities, and you won't notice the odor coming from them. Some tanks do not use these vents and may rely on the air intake pipes on the roof to let sewer gases out. When the wind blows a certain way at a certain speed, it can waft the odors from the septic tank right into your backyard and make it unpleasant. A good installer would know to put the ventilation downwind from the home if possible.
Full Septic Tank
Your septic tank might simply need to be emptied. Although a tank can last a long time, filtering out liquids and minimizing solids, it will eventually get too full to work properly, and the sewage will begin backing up into your house. There are pump-out services available for septic tanks, and you can expect to need this service about once every five years or so to keep the septic tank working efficiently.