OHA Drinking Water Services
OHA Drinking Water Services
Contact Report Details

PWS ID: OR41 05201
Who Was Contacted: Scott peterson
Contact Phone: 503-295-7561
Contact Date: 10/19/2020
Contacted By: WRAY, JULIE (DWP)
Contact Method/Location: Field
Details: Assistance Provided:
The circuit rider reached out to Scott Peterson and scheduled a site visit on 10/26/2020. The water system consists of a springbox that feeds a 4,000 gallon cistern, from the cistern the water flows through a 2” PVC pipe approximately 2,300’ to the first user. This section of pipe contains approximately 375 gallons, and being a pipe, would have a baffle factor of 1.00.

Average annual demand for the system is 2.1 MG and this equates to 4 gpm average flow. Multiplying average flow by a peaking factor of 5 yields a peak flow of 20 gpm. Using the 375 gallon capacity of the transmission line from the cistern to first user and a peak flow of 20 gpm, this pipe contributes 19 minutes of contact time.

We assume a minimum low temperature for the spring water to be 10 degrees Celsius. At this temperature, the required CT for 4-log inactivation of viruses is 6.0.

With 19 minutes of contact time and a required CT of 6.0, the system would need to provide a minimum of 0.32 mg/L of free chlorine residual in the contact chamber (2,300’ of 2”PVC pipe).

Due to the lack of power at the spring source, we recommend a Dosatron D40 pump for providing chlorine injection into the 2” PVC transmission line at a location downstream of the cistern. Dosatron pumps require a minimum head pressure to operate, it is recommended that the pump be installed at an elevation that exceeds this minimum (12’ below the lowest level in the cistern will provide 5 psi). A small, well insulated structure should be built to protect the pump and house the chlorine “day tank”. A 55 gallon drum should provide ample volume for the day tank. Note, all materials and equipment in contact with drinking water must be NSF61 certified. Sodium hypochlorite (chlorine) used for disinfection must be NSF60 certified.

Follow-Up Actions Needed:
The circuit rider is available to assist further as needed.

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