Well, you've demonstrated that there is a water soluble component to the material that is picked up that has an alkaline pH when the sawdust is tested per your methodology. Who knows what you would have gotten with a longer exposure time, more water, etc.. there may be standardized methods for testing what is essentially wood pulp for pH, I am unaware of it but don't let that stop you.

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 :)

Here is a link that might be useful: Sawdust mulch article

Thanks michael357 for your comment. I will probably have a sample of this tested at a soil lab. I had seen similar articles and mulched my blueberries with this material a couple of weeks ago. Probably too soon to tell anything but they look really good...covered with spring blooms. The crazy thing is I expected to add CaCO3 to the stuff to raise PH for other plants...I will post any new info found to this thread in case anybody else can use it.

The presence of earthworms in the material at the old site should be a clue that your pH reading of 9.3 could not be correct since earthworms wil not live in material with a pH that high.
Some questions about this test.
How long did the material steep?
Was the meter zeroed in before testing the material?
Were the probes properly cleaned before testing?
Years ago when I tested tree leaves the crushed leaves steeped for at least 24 hours, the pH meter was zeroed before each test and the probes were cleaned before and after each test.

Assuming procedures and instrument calibration was all OK, it comes back to the material itself. I have to wonder if there was some kind of lime added to the sawdust for some reason.

I'm very curious to know what type of instrument was used to do your original pH test. It sounds quite different than most of the pH testing methodologies I'm familiar with in a soil lab.

About the only type of lime I can think of that might raise the pH that high would be hydrated lime and that, if not handled with care, can cause burns on your skin. There would also need to be enough present that the particles probably would be easily visible.

Is it possible the EPA required the mill operator to add an amendment to the saw dust to prevent leachate from the pile entering nearby water sources and altering their pH? Just a thought.

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.

Hey Kimm: howz about dolomitic limestone, won't have the pH punch of hydrated lime but It'll sure neutralize acids.

Dolomitic, or Calcitic, limestone could over time change the pH of that sawdust, yes, and without the potential for burns that the hydrated lime poses.

Calcitic or dolomitic lime would not be able to drive the pH past about 8.3 (bicarbonate buffer pH). 9.3 sounds more like hydrated lime territory.

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.

Sorry that I have neglected to check back in a while and thanks for all the input. Yes I agree that the presence of earthworms casts doubt on my initial reading. The instrument used is calibrated using a three point (3,7 &10) standard but is designed for testing water, not soil. I am less concerned after visiting our local County Extension office and finding that the agent there has not only tested this material but used some of it in her own raised beds. The test results from the soil lab were not anything like what my water test showed(between 7 & 8). I'm still curious how distilled water could pick up such a high PH so quickly (my test was run on distilled water that had been poured off as soon as the soil/sawdust had settled to the 50% line-about 10 minutes). I have seedling plants growing in beds consisting mostly of this material with a bit of potting mix on top so we'll see how it goes.

A three-point calibration sounds great, although most of the meters I've ever used were two-point (low and high, no middle). As long as the meter is OK and the standards are OK, I don't see how anything else could go wrong. Those are the only three legs holding up this stool. The procedure you used was fine, I think.

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.