COLIFORM ISSUES - coliforms, bacteria (Apr/15/2009 )

i was asked by a client to sample water treatment plant, six wells from a large housing estate and submit a quarterly report. i discovered two wells were contaminated with coliform bacteria which i reported in the reports with recommendation. The owners of the estate read through the report and based on the coliform recommendations faulted the result. i was told they also sampled the two wells and no coliform was detected. they confronted me with a result they obatined from a reputable laboratory. although i am not sure about their microbiology procedures , i am certain the lab is well equiped.

i am very sure of the analysis i carried out. MPN technique using Lauryl tryptose broth was used alongside with controls. i have been observing coliform bacteria. Out of curiosity, i plated them on EMB plates and i observed a brillant green coloraton on plates. i also used presence - absence technique and obatained similar results.

this situation is pushing me to the wall because i am certain about the analysis but i cant quantify why results is obtaining nil at another laboratory.

they spotted the sterile containers i used in sampling and this was quite different from thiers because, they were using sterile bags with small sodium thiosulphate tablet in it while i used sterile cans preserved with ice. the difference between the time of collection and analysis is about four hours.

i am having a feeling that the owners dont want to take additional responsibility for added treatments, thats why they are rejecting the reports and having tested the water treatment plant and other storage wells, i have discovered the hygenic condition of the well is poor and additional treatment necesary orelse it should be dimmed unfit for drinking. i dont know how to dance around this situation.

what could be underlying reasons for difference in results.
what could wrong along the lines even when the water from the treatment plant is indicating Nil.
what added reasons/procedures can i ensure during collection, transportation and analysis.

Assume neither you nor the other testing lab was incubating for fecal coliforms and your labeling was not mixed up. Were you compliant with all relevant sections of Standard Methods for Examination of Water and Wastewater?

If so, I'd not argue the point but so note and repeat your findings. I would separate your findings from your recommendations. Defend your methods - noting compliance to standard methods and you could call the lab they used and get them to review your methods. As you know the thio was added to neutralize available chlorine - and I doubt there was any in the samples you described so that isn't a factor (and if anything would have given you lower counts).

You could propose that you and the lab could test in paraellel a new set of samples.

As for recommendations - I've not seen many simple treatments that would fix bad well water. What was the nature of the contaminating phenomenon?