[Koxinga]

A recent experiment we had was to determine the concentration of calcium carbonate in unknown water samples, and to match them to water sources of known concentration.  And, typically, we write formal, but normal lab reports.  However, this time around we have to prepare a report usable in a legal case, and frankly, I have no idea where to begin.  If anyone has experience with this type of report, could you offer some advice?

Thanks much!

[Arkcon]

I really have no idea what your teacher is looking for.  Unless, you're expected to find a first year's pre-law student's textbook, and begin to copy some of the format you'd find in an example there.

[fledarmus]

I know it's been a while since you asked the question - did you ever submit your lab report? What exactly was your teacher looking for? And in what country

I have some limited legal training in the US (paralegal certification, patent agent registration), and I don't know of any meaning for "a report usable in a legal case". If you wanted to use a lab report in a legal case, you would want a lab report that matches the best practices in the industry. In other words, exactly what you would typically prepare for an A+ lab report. The thing that makes it usable in a legal case would be your deposition, testimony, or affidavit, and the chain of custody for the sample. In other words, if you had a forensic case that depended on the amount of calcium carbonate in the unknown water sample, you would run the experiments properly, write up a good lab report, and then take the stand in court or in a deposition to explain all of the chemistry behind your test in a way that a juror with no chemistry background could understand, describe the results you obtained, describe the accuracy that you can usually expect from the test, and then describe how you obtained your samples and how you ensured that there was no contamination of any of the samples. Then the opposing lawyer would try to demonstrate that your procedure was invalid, that your testing method was flawed, or that your sample was either contaminated or couldn't be positively linked to the case. The judge (in a bench trial) or jury (in a jury trial) would then decide whether or not your results were valid and how much weight to assign them in determining the guilt or responsibilities of the parties involved in the trial.

[JGK]

You need to be able to show that everthing you did was by the book.  As well as showing that you followed the written procedure to the letter you need to show:

1. The identity (make, model & serial number) of the equipment you used. Possibly including informantion relating to service records (date of last service, next service due dates) etc.
2. Identity, Lot Nos and expiry dates of all chemicals used in the assay.
3 full preparation records of any Standard solutions. This should inlude storage records expiry information and if they were stored in a fridge or freezer the monitoring records for that unit.

These are all possible areas which could be used to invalidate your results.

[curiouscat]

It is also typical in legal work to keep identical samples well labelled and in safe custody in tamper proof storage. Helps if  any disputes arise later. Often in critical cases the sample is sealed under witness.

It has also become the norm to be extra careful about making sure the lab / chemist is protected against legal counter suits. Mention clearly what you are not concluding but might be erroneously misinterpreted. e.g. X-Lab cannot attest to the integrity of the field sampling procedures. etc.

As an aside if you can refer to a standard EPA / FDA / ASTM procedure etc. it is a plus.