Vacuum Sewer Construction

What to Expect
This is a summary of the construction process. The contractor will give as much notice as possible before beginning work on your street.

Stage 1 - Survey Staking and Pre-construction video - This stage includes physical staking of the proposed utility system using wooden stakes or other markers. After staking, the site will be video taped to record pre-construction conditions. Residents are urged to not disturb the survey stakes/markers.
Stage 2 - Right-of-way trimming and clearing - This stage could take a few days per street and may involve cutting and removing driveway sections, drainage structures and other obstructions located in public rights-of-way or dedicated utility easements.

Stage 3 - Directional drilling - In selected cases, rather than using an open trench for pipes, work crews will use small drilling machines to install portions of the pipe network without significantly disturbing the area. This technique is used to protect heritage trees and deal with other restrictions like narrow rights-of-way and decorative driveways. Each drilling operation is usually finished within a few hours. Small piles of dirt and drilling medium at each end of the installed pipe could remain for a longer period.

Stage 4 - Mainline piping - Residents should expect inconveniences during construction of the sewer collection lines.

  • Work crews will cross driveways, walkways and may excavate entire streets.
  • Streets will remain open, but partial lane closures may be necessary.
  • Residents will notice the contractor digging trenches of various depths as other crews follow, assembling and installing lengths of pipe.
    • The length of pipe installed in one work day varies from 300 to 1,500 feet depending on ground conditions.
  • A resident's driveway may be inaccessible for a short time.
  • By the end of each day, the contractor will temporarily restore driveways and replace mailboxes and backfill trenches and/or otherwise erect approved safety barricades and fencing.
  • Because of high water table conditions, groundwater "dewatering" is often necessary.
    • This involves setting temporary well points and pumping groundwater with portable pumps and hoses to approved points of discharge, usually into existing stormwater drainage systems.
    • Sometimes the dewatering equipment operates during the evening and it is important that only authorized personnel operate and adjust this equipment.
Stage 5 - Collection system component installation - The contractor will install vacuum valve pits in the right-of-way and extend gravity service laterals from the pits to each resident's property line. The valve pits are fiberglass tanks that range in height from five to eight feet. They are buried flush with the ground in the public right-of-way or dedicated easement.
Stage 6 - Restoration - The contractor will rely on the construction plans and the pre-construction videotape when restoring construction areas to original conditions. Restoration activities that will begin once the pipe installation is complete may take several weeks, or even months. Residents with concerns about the quality of restoration work should call the construction help line for their area. The county will resurface roads in the project area after all restoration is complete.
Stage 7 - Notice of service availability - Once the system is certified for use, the county will notify residents when it is time to abandon septic systems and connect to the sewer system. You will receive a complete package of information on how to connect.

How to Prepare

  1. Plan now to remove unpermitted obstructions (sprinkler systems, shrubbery, basketball assemblies, etc.) from the public right-of-way or dedicated utility easement. The county cannot guarantee they will be replaced.
  2. During construction, keep children and pets away from work areas and equipment.
  3. Call the construction help line in your area with questions or problems. Representatives are standing by to resolve your concerns.
Vacuum Stations
Vacuum stations are usually concrete block buildings on concrete foundations with minimum plan dimensions of approximately 25 feet by 30 feet.

  • Part of the structure is constructed below grade to accommodate entry of the vacuum sewer.
  • Two alternating liquid ring or sliding vane vacuum pumps withdraw air from a vacuum reservoir tank, which is connected in turn to a fiberglass or steel collection tank.

The reservoir tank serves two purposes.

  1. It provides a vacuum reservoir to limit the number of vacuum pump starts much like the pressure storage tank of a compressed air system.
  2. It keeps the vacuum pumps from contacting the air/sewage mix being collected into the collection tank.

  • This separation prevents droplets from damaging the vacuum pumps.
  • Vacuum switches on the reservoir tank control operation of the vacuum pumps.
  • The collection tank receives the air and sewage transported by the collection piping and serves the same purpose as a wet well in a conventional lift station.

 A property owner's guide to vacuum systems 
What is a Vacuum Sewer System?

Vacuum sewers convey raw sewage from the house by induced air vacuum from a valve unit to a vacuum station.

Sewage is transported in small diameter pipes placed at variable grade and deflection under ground.

A vacuum sewer system consists of one or more vacuum stations, collection system piping, valve vaults and vacuum interface valves.

Vacuum stations draw wastewater to the station and pump wastewater to a wastewater treatment plant.

Vacuum interface valves regulate the entry of wastewater and air from the valve vault into the collection system piping.

A single vacuum vault with interface valve typically serves more than one residence.

Vacuum system technology is well documented by the U.S. Environmental Protection Agency.

Vacuum pit work

Contractor installing a vacuum pit.
Vacuum Sewer System Specifics

A typical residential vacuum sewer service consists of a gravity line from one or more structures to a sump equipped with a vacuum interface valve.

Opening of the valve is initiated by a pressure sensor in the sump. When liquid in the tank reaches a preset level, the sensor activates opening of the valve to discharge waste into the vacuum collection system.

The time that the vacuum valve is open is normally adjusted to twice the time required to discharge wastewater from the holding tank. This allows air to enter the system behind the wastewater.

The proper amount of air is necessary to drive the wastewater in the line to the vacuum station.
 
As a benefit, it aerates the wastewater as it passes through the vacuum collection system therefore reducing potential odor problems. Vacuum valve vaults are typically located on or near property lines so that they can serve two or more adjacent homes.

Vacuum collection piping typically consists of 4 inch to 10 inch diameter pipe installed along the right-of-way with minimum cover.

In order to minimize excavation depth in flat topography, lifts are used in the lines.

The lifts consist of two 45 degree bends with the lift pipe section in between, creating a profile view that looks something like a sawtooth. This section acts as an airlift and provides some additional aeration as waste is forced through the lift by rising air.

Valving for vacuum collection lines is similar to that for pressure sewers, valves installed on branches and at intervals on the mains to allow isolation for repairs or troubleshooting.