OHA Drinking Water Services
OHA Drinking Water Services
Contact Report Details

PWS ID: OR41 01174
Who Was Contacted: Scott Cure
Contact Phone: 503-843-2885 (Email address hidden)
Contact Date: 09/23/2022
Contacted By: BAIRD, GREGG (DWP)
Contact Method/Location: Phone
Assistance Type: MONITORING
Reasons: Cyanotoxins
Details: Circuit rider made a site visit 9/19/22 to perform a DPD test for free chlorine residual on the raw water using a correction for potential oxidized manganese interference. DPD test (shows free chlorine residual plus oxidized Mn and Cr) was 0.11 mg/L. DPD test w/potassium iodide and sodium arsenite (shows oxidized Mn and Cr without chlorine) was 0.08 mg/L. Difference in tests (true chlorine residual) was 0.03 mg/L. DEQ lab also performed the DPD test with Mn correction on the 9/19/22 cyanotoxins sample. DPD test was 0.09 mg/L. DPD test w/potassium iodide and sodium arsenite was 0.09 mg/L. Difference in tests (true chlorine residual) was 0 mg/L. Results of the field DPD test and DEQ lab DPD test suggest a manganese interference showing up on the DPD test. Since there’s no risk of degradation of microcystins due to chlorination, raw samples should be considered valid and reportable going forward. This week’s raw water sample collected 9/19/22 showed a microcystins detection at or above the trigger so system is “officially” moved to weekly raw & finished monitoring starting next Monday 9/26/22. Normally a finished water sample would be collected within 1 business day, but since the system has already been “unofficially” conducting raw & weekly monitoring, we already have a finished water sample collected 9/19/22 (results non-detect) paired with this raw water detection.

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