Pipeline Safety

Natural gas is found in deep underground reservoirs and requires a well to be drilled in order to reach it. Once a drill discovers a reservoir, pipes are placed in the reservoir to bring the gas up to the surface. A portion of the surfaced gas is stored in liquid form, which can be used later. The remainder of the gas is transported to communities across the region via transmission pipelines.

Local distribution companies, like Unitil, are supplied natural gas via transmission pipelines, such as Unitil’s Granite State Transmission pipeline. The local gas distribution system is connected to a transmission pipeline at a meter station or city gate. The city gate has two purposes: 1) to measure the gas supplied and 2) to control the gas pressure. The transmission company measures the amount of gas flowing into the city gate. The local distribution company reduces the pressure of the gas from the transmission pipeline to match the pressure of its distribution system.

The distribution system is composed primarily of two types of pipelines: mains and services. Mains receive the gas from the city gate and distribute it through the supplied area. Service pipelines carry gas from the main and supply the customer after passing through a meter. As it travels through the distribution system, the gas pressure is controlled by regulators — a special type of valve. Regulators can reduce the gas pressure, if needed, or if the gas pressure increases above a set limit, regulators can also shut off gas flow.

To better regulate a distribution system’s gas pressure and stabilize gas pricing (also known as peak shaving), local distribution companies use liquefied natural gas (LNG) stations and liquefied petroleum gas (LPG) air plants.

Both LNG (liquefied natural gas) & LPG (liquefied petroleum gas) are liquid when delivered by third parties and are transferred to large storage tanks located on the grounds of their respective production sites. Prior to being introduced into the distribution system, the liquid fuel is both vaporized and odorized. Once the LNG is vaporized and odorized, it can be introduced directly into the distribution system for immediate use by customers.

Prior to LPG being introduced into the distribution system, after vaporization it is mixed with air to ensure that the fuel’s gas properties are consistent with the natural gas that is in the system. Once mixed, the gas is then odorized and introduced into the system for immediate use by our customers. The ability to purchase, store and vaporize both LNG & LPG to supplement system demand allows for greater operational flexibility and ensures a consistent gas supply to our customers.

In accordance with federal regulations, some segments along the pipeline have been designated as High Consequence Areas. We have developed supplemental assessments and prevention plans for these highly populated areas with transmission pipelines traversing them. Unitil’s Integrity Management Plan outlines the Company’s plan and activities to ensure the safety of our pipeline system.

Natural gas pipelines are sometimes identified by markers placed at intervals along pipeline rights of way. These markers are often yellow poles, and they display 24-hour emergency telephone numbers and provide other identifying information. Pipeline markers are important to your safety. It’s a federal crime to willfully deface, damage, remove or destroy any pipeline sign or right-of-way marker.

While the markers aid in identifying the presence of pipelines in the area, they don’t show the exact location, depth, or how many pipelines are in the right-of-way. Don’t rely solely on the presence or absence of a pipeline marker to determine whether or not a pipeline is buried below. Always call DigSafe® at 811 to have underground pipelines marked.

A pipeline right-of-way is the strip of land above and around a pipeline. Rights-of-way are kept clear of obstructions and vegetation to enable Unitil to safely operate, patrol, inspect, maintain and repair its pipelines. We regularly inspect our rights-of-way.

A right-of-way agreement between Unitil and the property owner is called an easement. Easements provide us with permanent, limited interest to the land to enable us to access, operate, test, inspect, maintain and protect our pipelines for your safety. Although agreements may vary, rights-of-way usually extend up to 25 feet each way from the center of the pipeline.

If Unitil has an easement on your property, you should be aware of our guidelines for encroachment and construction near natural gas pipeline equipment. It’s important that property owners not install any structures, store anything that could be an obstruction or plant trees or shrubs along the right-of-way. Normal gardening and agricultural activities (e.g. lawns) are generally acceptable. But you should never dig or construct anything in the right-of-way without first having a Unitil representative mark the pipeline, stake the right-of-way and walk you through our construction guidelines.