Cause of a possible false Chlorine residual ? 1

[kdiehl]

Good Morning,
I need help determining what if anything could be giving us a false Cl2 residual.
To make a long story short, we have water leaking into the basement of our pump house. We believe this to be ground water however when I tested it for a residual I got a fairly consistent reading of 0.43 with one reading coming back at 0.84
We are a public water utility and this is at our pump house located next to the resevoir. The water is coming in the basement of our low lift pump room.
Here’s the problem...where I tested the water there is also drains dumping under the floor from the low lift pump seals. The low lift pumps are raw water, no treatment yet.
It is also where the water drains to when we drain out our Finished water fill station for bulk water purchase. We don’t drain it often and maybe 30-40 gals of water come out. The first samples I took were mainly of the water draining from lowlift pump seals running along the ground so they could be picking up residual from the fill station waste but I would think that it would dissapate. The sample I took today was from the wall leeching onto the floor due to rain out side and it came back with 0.43.
None of the samples we tested came back with flouride which we use in the finished water.
Is there something in the concrete and brick wall where the. Water is leeching in that could be giving us a false residual ? Also in front of the pump house the state comes through in the winter and salts the driveway. I can post pics of where I am sampling.

 

[hydrae]

I would suspect the testing procedure.
Many people get in the habit of not zeroing the electronic reader every time
or zeroing it with other water
I assume you are using a electronic color-metric type device since you have 2 significant digits
fill a vial with sample, added dpd powder and pop it into the reader
since this is water from a 'dirty' source the reader can read the dirt as color giving a false positive
hence the need to zero first.

fill the vial
zero the meter (to subtract out the dirt)
add dpd to that water
read

Does the sample turn pink to the eye when the powder is added?

But also know that the dissipation of chlorine is in cold dark lifeless places is slow. The chlorine only goes away if there UV light, movement of air over the surface, biological action or minerals to combine with, so the small amount from the fill station can be significant.

As for other influences, the DPD method measures an oxidation potential, so ozone, bromine, Iodine and other oxidants give a reading. (Fluoride, Chloride ect. does not react since they are an ion state)

hydrae

 

[kdiehl]

We use a Hach DR2010 Spectrophotometer with Accuvacs. The sample turned pink as soon as I used the accuvac on it. We did numerous samples with fairly consistent results.Still have not determine why.

 

[hydrae]

OK
Seeing the pink tells me there is something there

Can you divert the fill station drains?

I would also de-chlorinate the sump with the correct amount of de-clor product (do not overdose)
then the following day or so see if the levels comes back up

Hydrae

 

[kdiehl]

Ok, Thank you. I will report back my findings.