Expanding Wastewater System Capacity

wwtp upgrades

​​​​​​The City’s existing treatment plant and receiving stream, Tickle Creek, cannot fully meet the wastewater capacity needs of the City, even after repairs to the existing plant are completed.

  • Sandy’s population has doubled in the last 20 years and will double again in the next 20. We need to prepare our infrastructure now for future growth
  • The system also needs spare capacity and mechanical redundancies to prevent breakdowns and protect the environment.

 

HOW WILL WE INCREASE OUR WASTEWATER SYSTEM CAPACITY?

 

Going forward, Sandy will need:

  • Added treatment infrastructure to process higher volumes of wastewater
  • An alternative discharge location for the additional treated clean water, because Tickle Creek is a relatively small stream subject to the Three Basin Rule

 

WASTEWATER SYSTEM FACILITIES PLAN REFINEMENT - 2022

 

Sandy adopted a Wastewater System Facilities Plan in 2019 that made several recommendations for expanding system capacity, including constructing a new satellite treatment plant with MBR filtration that would discharge treated clean water at a new outfall on the Sandy River.

In the current environment of inflationary pressures and rising construction prices, the City is working to refine the Plan to keep costs manageable for the City and its rate payers.

  • The original plan called for an additional satellite treatment plant.  While all options are being considered, further analysis during the plan refinement process may find that expansion of the existing treatment plant will meet our capacity needs more cost-effectively.  New treatment infrastructure may incorporate MBR technology as proposed in the 2019 Plan, but other options that meet all environmental regulatory requirements and produce Class A water will also be considered.
  • The original plan envisioned a new clean water outfall on the Sandy River.  It is still very likely that an outfall on the Sandy, which is a much larger body of water than Tickle Creek, will be necessary, but other discharge alternatives will also be considered during this plan revision.  Analysis may find that other discharge locations and methods, such as surface infiltration, may be incorporated into the refined Plan, perhaps on a transitional or temporary basis.
Can the city limit growth or stop construction so that the wastewater treatment system doesn’t also have to grow?

Even at the current population, the City’s current treatment facility has issues treating the water during heavy rainfall events. In order to properly protect human health and the environment, the Oregon Department of Environmental Quality has mandated that improvements are needed, which includes increasing the capacity of the treatment system.

Category: Sandy River Discharge Alternative
Could the city just use the treated water for other purposes?

For the last 20 years, the City has been able to deliver all of our treated wastewater to a local nursery between May 1st and October 31st for irrigation. However, the City still produces treated wastewater in the winter when irrigation is not possible. As part of the detailed discharge alternatives evaluation, the city conducted outreach and studied options for providing the treated water to other large property owners and agricultural users.

Category: Sandy River Discharge Alternative
What is involved in the NPDES permitting process?

The permitting process is quite extensive and is aimed at maintaining high water quality. The Oregon Department of Environmental Quality would be responsible for issuing a permit to discharge the Sandy River, and they require a number of studies and engineering evaluations. The City’s consulting engineers have already conducted water quality studies of the current river flows and a geomorphology study and fisheries biology evaluations to determine the most stable location of the river for an outfall. DEQ would require additional studies such as a mixing zone study, an “antidegradation” study to evaluate any impacts to the river, groundwater quality sampling and analysis, additional geotechnical investigations, and wetlands delineations prior to issuing a permit.

Category: Sandy River Discharge Alternative
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