Tuesday, December 1, 2015

Third Times a Charm

Following the first two sets of rainwater tests, we really did not have a great sense of the correct bleach dose for a 55 gallon barrel. The calculated amount of 5.8 ml (let's just call it 6 ml, please) was insufficient and did not register on the chlorine test strips at all; the 58 ml (a 10x strength) overshot the mark by a bit; and the 580 ml (100x) was way off the scale. A crude series of 50%-50% volume dilutions indicated that the correct dose lay somewhere between, say, 9 ml (1.5x) and 18 ml (3x). We needed at least one more trial to fine tune the dosing and my concern was that, with little more than a month until we travel, we would not get sufficient rain for one more refill of the barrel before winter and snow set in. Fortunately, the weather is cooperating. The barrel is full and I am in the process of making a series of chlorine solutions  starting with our calculated 6 ml dose and increasing it by 3 ml increments through 18 ml. I have collected samples up through 12 ml; the 15 ml dose is equilibrating and is due to be sampled in 5 minutes. Then the last solution will be 18 ml of bleach and that range of specimens ought to capture the final free chlorine target dose of 2.5 mg/L (or ppm) as specified by the World Health Organization. I will bring the samples up to campus tomorrow during the weekly meeting and Frank, Kyra and Jonathan can test them. We are also looking at a small Hach colorimeter that would provide more accurate measurements and I have located one on Ebay at a reasonable price.

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