Statistical Significance

I need to determine statistical significance of water quality data and am having trouble determining how to set up the tests (and what tests to use). The data is 4-dimensional, data measured down the water column at a given site, at multiple sites, and during multiple sampling days. Any ideas on how to test for statistically unusally data within these datasets?

This looks like an analysis of variance problem, possibly with interactions. For example, quality may vary from the overall mean at site A, or it may only vary on certain days or it may vary at site B only on the weekend. Assuming a normal distribution for the quality measure, you would be using an F-test. You should consult a textbook that deals with analysis of variance, ususally called ANOVA.