Controlling Arsenic Levels by Source Blending

[Guy79]

Hello All, I am designing a water blending station to meet the new arsenic rule requirement of a maximum contaminant level of 10 ppb. Currently the design is to blend an arsenic well with a clean source water. I have all the components to control the flow of both streams or ratios to theoretically produce a mixture that is within compliance. Tank is 42' in diameter and 21' tall, roughly 200,000 gallons. Combined Inlet flow from both streams is 500 gpm, which will be a constant draw down. My question is what is the most effective way to blend the water? I have a few ideas, but was hoping someone out there has experience with a similar situation. I am trying to stay away from any mechanical agitator type components inside the tank. One idea is to join the two streams and mix in a waste water serpentine pipe which then discharges at the top of the tank. Or, enter both inlet lines from the floor of the tank and adjoin to a header pipe that is outfitted with eductors that will mix tank water at a ratio of 4 to 1. My only concern with the second idea is buildup on the eductors from a maintenance standpoint. Beside looking online I have searched AWWA and ASCE standards and have found nothing on this topic, any advice would sure help.
Thanks,

 

[dicksewerrat]

I would look at putting an air gap on the clean well so it stays clean.

Richard A. Cornelius, P.E.

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