The plant and sewer system operates under the National Pollutant Discharge Elimination System (NPDES) Permit Number WA0038377. The water receives secondary treatment, is disinfected with chlorination, and is discharged into Case Inlet.
The plant is a Sequencing Batch Reactor with activated sludge.
Treatment Processes
The raw wastewater enters the treatment plant headworks where a bar screen traps large solids and a grit chamber is used to settle out sand, gravel, and other dense inert material. There is a 24-hour influent sampler positioned at end of the grit chamber.
The flow passes through a Parshall flume flow meter before entering one of the sequencing batch reactors (SBRs). The SBRs alternate so that one reactor is always filling and or digesting while the other is settling and then decanting. The SBRs use the activated sludge process where the raw water is contacted with the activated sludge mixed liquor and aerated. After a digestion period, the mixed liquor is allowed to settle. The liquid supernatant is then sent through a flow meter and then to a chlorine contact chamber. The chlorine is fed to an in-line static mixer. A 24~hour sampler is located at the effluent end of the chlorine contact chamber. The effluent is then pumped to the outfall in Case Inlet.
The plant discharges on average 20-minutes in the summer and cycles every 75 minutes, which equals 3.2 hours per day of discharge. The discharge time is longer in the winter and discharges for a total of 6.4 hours per day.
A portion of the solids that have settled out are pumped (wasted) to an aerobic sludge digester on a regular basis.
There are no industrial or commercial users on the Hartstene Pointe system. The facility is classified as a class II level activated sludge plant. The operator is therefore required to have a Group II certificate.
Discharge Outfall
The outfall was an 8-inch PVC pipe for the first 250 feet to the beach, then 6-inch pipe for the 625 feet from the shore. Most of the existing outfall pipe was installed below grade except for the diffuser which was secured with concrete anchor blocks.
The new outfall is an 8-inch HDPE pipe and is 2000 feet beyond the original outfall. The diffuser is a 6-inch HDPE pipe configured in a "y" shape with a spread of 10-feet with two 4-inch diameter ports.
Residual Solids
The sludge waste from the SBRs is sent to an aerobic digester. Digested sludge is hauled to be land applied at a permitted beneficial use facility. The treatment plant removes solids during the treatment of the wastewater at the headworks (grit and screenings), and during the clarifying process, in addition to incidental solids (rags, scum, and other debris) removed as part of the routine maintenance of the equipment. Grit, rags, scum and screenings are drained and disposed of as solid waste at the local solid waste transfer station for ultimate disposal.
