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OHA Drinking Water Services Contact Report Details
PWS ID:	OR41 00466
PWS Name:	LANGLOIS WATER DISTRICT

Who Was Contacted and Phone:	Dave Terrusa (541) 348-2142
Contact Date:	11/29/2007
Contacted By:	STRASSNER, BOB (DWP)
Contact Method/Location:	Field

Assistance Type:	CIRCUIT RIDER ASSISTANCE
Reasons:	N/A N/A

Details:	SUMMARY: Technical Assistance in CT Study DETAILS: I met with Dave at the systems treatment plant for the purpose of conducting a CT Study. The water plant effluent flow were approximately 50 gpm as per the operator. The system is normally disinfected with both pre and post chlorination using hyprochlorite batched at the raw water intake pump and again post filtration. The pre chlorination is intended to oxidize the raw water inorganic of iron and manganese, with the post chlorination added to provide a detectable residual in the distribution system. The study was accomplished by increasing the pre chlorination segment of the treatment twoand one half times the initial residual of 0.96 mgl.The plant lab sink is tapped on the effluent leaving the plant but is not used as a potable source. Down stream of the 100,000 gallon storage tank, at the intersection of the plant driveway and the pavement, is two inch blow off that was regulated to simulate system demand and sampled as the system’s first user for the study. The theoretical contact time was calculated to be approximately 233 minutes, with an estimated efficiency assigned to the reservoir of 10 percent. Sampling was begun at fifteen minute intervals until such a time as the theoretical contact time was reached. The actual time T10 was reached occurring 285 minutes into the study. The discrepancy in time is believed to be a result of plant hydraulics. Raw water pumping fills a 10K gallon surge tank outside the plant that then allows water to the package plant as needed. This characteristic was not considered in the original theoretical calculation. All systems were returned to normal upon completion of the study, including a rehydration of the pre chlorine batch tank. ACTION NEEDED: Process study data and prepare a report for the system.