OHA Drinking Water Services
OHA Drinking Water Services
Contact Report Details

PWS ID: OR41 00933
Who Was Contacted: Gene Ramey
Contact Phone: 503-312-3108
Contact Date: 04/27/2020
Contact Method/Location: Field
Details: Background/Problem Identification:

Sunset Lake RV Park (SLRVP) has a history of TTHM MCL exceedances going back to August of 2017 with the latest exceedance occurring on February 26th, 2020.

Assistance Provided:

The circuit rider made a site visit on May 1st, 2020 to assess the disinfection system and to verify the likely cause of the elevated TTHM levels that the water system is having issues with. SLRVP is required to maintain disinfectant residual in distribution, this is accomplished by injection of sodium hypochlorite with a dosing pump in the wellhouse prior to distribution.

The circuit rider noted that the dosing pump runs non- stop regardless of flow from the well. This is likely a main contributor to the TTHM issue, as the system is not being dosed proportional to flow. This will cause the finished water to vary greatly in disinfectant residual. The residual will be extremely high during periods of low demand, and possibly too low during periods of high demand. Overly-high chlorine residuals in distribution are likely the source of the elevated TTHM readings.

We strongly recommend that SLRVP do either use one of the following methods to mitigate their TTHM issues:

Hire a certified electrician to install a dedicated outlet for the disinfection dosing pump. This outlet shall be switched to only provide power when the well pump is pumping water.
Install a proportional metering system such as the Stenner brand Econ FP to ensure that disinfection dosing is proportional to flow.

We further recommend the following:

Replace carbon block filters based on water meter readings rather than a set time period.
Ensure that sodium hypochlorite is accurately and consistently mixed in the day tank, not by park demand.

Follow-Up Actions Needed:

The circuit rider can further assist as needed.

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DBPs :: TOC & Alkalinity :: DBP Sample Sites :: FANLs :: MRDL :: Turbidity :: SWTR :: RAA :: LRAA For SDWIS: 3804