I have a composite water sampler based on flow.

The water gets tested for compliance for

N-NH₃, P, F, Suspendid Solids, Conductivity and pH

Now the composite sample can sometimes take a long time to fill, over a month.

pH is the main concern with consideration to compliance limits

When the sampler takes a long time to fill and the weather is warm, I belive anaerobic aciton in the water can artifically decrease the pH. (pH can be lower than any recorded pH in the effluent, this is continously monitored)

Could CHCl₃ or CCl₄ be used to help preserve these samples while collection is taking place

if so what sort of Volumes i.e 5mL per L

I recall doing this in the past and i dont see it affecting any of the other analytes, i cant quite remember which one was used or how much.

The local authority (i am not from the usa) over the years has decided they want these composite samples taken with respect to flow.

there is a inline pH meter which is calibrated twice a week.

you are correct the APHA, dose not recomend composite samples for pH and some others

However this is a practical problem now as the consenting body these analysis for compliance reporting

I assume I will be able to fall back onto the inline meters data log for flow and pH should the composite be below limits

The pH lowering affect from the bacteria only seems to happen sometimes and isnt a huge amount but the effluent can be close at times.

Any ideas would be helpful thanks

Hi Ultma,

Maybe a solution:

Enclose two sample receiving containers in a small fridge to maintain < 6 degrees celcius.  The sampler sits outside of this, with a hole drilled through the top for the sample tube to enter (careful of the copper piping of course).  Split the incoming sample stream into two - one goes into a pre-acidified container (diluted sulphuric acid at a predetermined amount - as long as the end pH is less than 2, but keep the preserve:sample ratio above 1:100).  You can use that container for ammonia and P (assuming total P).  

You can use the other non-preserved container for the rest.

According to EPA Victoria (Australia) you can analyse everything you have mentioned within 28 days as long as they are either preserved or  refrigerated < 6C, except SS is only seven days and pH pretty much immediately.   But that is our regs, yours could be different.  I also cannot see how you will be able to analyse pH as a composite over such a long time, so the data logger will have to do and reported as a data stream.  And SS should be reported "as is" and specifically stated on your report that it is out of holding time, unless you can sample weekly and then adjust for a monthly figure based on flow figures.

http://www.epa.vic.gov.au/~/media/Publications/IWRG701.pdf

Hope that offers a solution, or at least some help  

Greg.