The diagram below shows the primary sewer system components. Starting at the home/business, these elements are:
- On-site elements to move wastewater from the building to the street curb
- Collection system elements consisting of pipes in the streets
- Wastewater treatment plant where sewage is processed
- Infiltration/Reuse area where clean Class A wastewater is infiltrated into the ground
Figure 1 - Wastewater System Elements
With the pressurized sewer system currently envisioned, the on-site elements are the pipes, control panel, grinder pump, and curb box (valve) that take sewage from the home/business to sewer collection pipes located in the public right of way (street). There may be loan programs available to assist property owners with this element. These costs will vary significantly depending upon factors such as the type of home/business being served, the distance to the street, and the type of restoration required (i.e. lawn, landscaping, or pavement). The grinder pump pushes sewage down the pipes towards the wastewater treatment plant. The pumps do require care and maintenance. To ensure that pumps are installed and maintained properly, the Department of Ecology will require that this part of the system be maintained by the sewer utility company even though it is located on private property. "An Introduction to Pressure Sewers," by the Submersible Wastewater Pump Association (SWPA,) is a good source of information about pressure sewer systems.
Figure 2 - Typical On-Site Elements for a Residence or Small Business
The collection system consists of the pipes in the public streets that transport sewage to the sewage treatment plant. Current plans for Port Hadlock call for a low-pressure collection system which uses the grinder pumps at each home or business to push the wastewater through these lines to the sewer treatment plant. Because the lines are pressurized, they can run uphill and do not need to be buried more than 4 to 5 feet below the ground. There is more flexibility in the routing of pressurized sewer lines which can help avoid other existing utilities and deep manholes are not required. In some cases, pressurized collection lines can be installed using directional boring, a “trenchless” installation technique that requires very little excavation and disturbance. This installation method was used in Brinnon for the Dosewallips State Park sewer system, for example.
A pressurized sewer collection system can provide significant cost savings for initial installation compared to traditional “gravity” sewer lines which require deep excavations to make sure that sewage pipes flow downhill and use large lift stations to overcome hilly topography. When traditional gravity sewers are installed in streets and highways the installation and road restoration costs can be quite high. Pressurized sewer systems are often used for small sewer systems that have fewer users or in situations with hilly topography or high groundwater tables. Gravity sewers are more typical for larger municipal systems where over the long run the high initial installation cost can be offset by savings in maintenance and operations because grinder pumps are not needed at each home/business. The original plan for the Port Hadlock sewer called for a gravity collection system; however, because initial costs were so high and grants from the State and Federal government so hard to obtain, the County is now proposing to install a pressurized collection system to keep startup costs as low as possible in the initial sewer service area.
Treatment and Disposal
The wastewater treatment plant is where the collection system brings the sewage for treatment. After the sewage is processed, the resulting clean Class A wastewater is fed into an infiltration pond which will allow the water to recharge the aquifer in the Chimacum watershed. The sewer treatment process that has been approved by the Department of Ecology requires a Membrane Bioreactor (MBR). These MBR systems treat wastewater to very high standards required for infiltration on land since permitting a new sewer outfall into Puget Sound is virtually impossible. The current proposal is to use a pre-assembled modular MBR system that essentially arrives on a truck ready to go. There are other components that still have to be constructed along with the plant such as inlet screens and storage ponds; however, these modular systems have seen rapid technological advances in recent years that make them highly cost-effective and reliable. These units allow a sewer to start small and can be added onto as demand increases. This avoids the need to build a traditional sewer treatment plant that may have to be oversized initially to handle future demand. In nearby Port Gamble, one of these units was recently used with good results to replace their aging sewer plant that could no longer meet today’s water quality standards. An example of this system is shown below.
Figure 4 - Typical Pre-Assembled Modular MBR Treatment Plant
After passing through the MBR process, treated water is piped to a rapid rate infiltration pond where it quickly soaks into the ground. Thickened sludge at the treatment site is hauled off-site to a larger sewer treatment plant where it is eventually processed into compost such as at the City of Port Townsend.
The County has purchased all of the land needed for the treatment plant site and the wastewater infiltration area and performed extensive, multi-year hydro-geologic studies, which have resulted in the County receiving the required approvals for this site and process from the Department of Ecology. The property is located on both the north and south side of Lopeman Road in Port Hadlock.
Figure 5 - Conceptual Site Plan Showing Location of Treatment Plant and Infiltration Area on County Property