OHA Drinking Water Services
OHA Drinking Water Services
Contact Report Details
PWS ID: OR41 00149
PWS Name: BROOKINGS, CITY OF
 
Who Was Contacted: Mark Haglund
Contact Phone: (Email address hidden)
Contact Date: 01/16/2020
Contacted By: PARRY, BETSY (DWP)
Contact Method/Location: Email
 
Assistance Type: OTHER REGULATORY - New lower min chlorine level
Reasons: GWR
 
Details: Today I mailed a letter approving two requests from Jacobs Engineering based on their 2019 tracer study results:

1. For GWR 4-log treatment, the minimum residual was lowered from 0.2 to 0.1 mg/L at the existing approved monitoring location (where the long transmission line enters the plant from the infiltration gallery), effective February 1, 2020. The water is chlorinated again within the plant before it goes to distribution (they aim for 1.0 mg/L at the entry point).

2. The letter approves 0.3 mg/L as the minimum chlorine level for GWR 4-log treatment should the plant ever have to switch to the filtration bed trains as a “back up” disinfection contact chamber. The idea is that they can send the water through these filtration beds (rarely-used) if there was ever a problem with the chlorinator at the infiltration gallery or they needed to take it offline for repairs, etc. The tracer study showed the filtration beds were effective mixing zones with over 50% baffle factor. Their 1-13-20 request said the combined filter effluent (CFE) would be the monitoring location, the same as during the tracer study. But on 1-28-20 Jacobs revised the letter to request the entry point as the monitoring location for the back-up disinfection chamber (because the EP has an online chlorimeter). This change was approved on 1-28-20.

DMCE staff (Chuck Michael) and I drafted up a monthly reporting form that showed the default monitoring location (plant influent) and minimum chlorine level (0.1 mg/L), and added a second column with the alternate/ emergency monitoring location (the EP) and minimum level (0.3 mg/L) if they ever need to route the water through the filter trains for contact time to achieve 4-log viral treatment.

More information for this water system: SDWIS ID 4292
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