The link is from Cornell and is about using sawdust mulch on blueberries which do not tolerate alkaline pH. Having read your methodology and Cornell's link it makes me wonder about your technique. Cornell certainly recommends using (preferably) composted saw dust as a mulch on blues and they seem to really heap it on pretty good.

As a former soil and plant tissue lab rat, I wish you luck :)

Too be sure, find and follow an appropriate methodology for determining what you are interested in knowing. I won't nit pick you by asking things like, were your calibration standards expired, rather, I'll give you the benefit of the doubt.

Good luck.

As for the regulatory requirement to add it...well if the pH of the leachate is that high, it's going to damage the stream just as bad as an acid pH would. I expect more damage would be done by the dissolved organics (all that brown stuff) which would deplete the oxygen in a waterway regardless of pH. The way to address sawmill runoff effects on streams is to keep it from running off in the first place. There may be a legit reason they were adding lime, but throwing lime on a sawdust pile and hoping the runoff is neutral when it reaches the stream is not good management practice.

It's also possible they burned some wood waste, for example to heat the plant or drying kilns, and they dumped the ash onto the sawdust pile. Ash is basically like hydrated lime - very high pH.

You could try letting the sample sit for 30 or 60 mins with several mixings along the way before settling and pouring off and see if it makes a difference. And check the pH of the distilled water. Note that the pH of distilled water will change drastically if you just look at it funny, since there is absolutely no buffering provided by hardness, etc. But it should be in the neighborhood of 7 if your probe is clean when it goes in.