Sandy. (Joyful but wary....)
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Date Posted: 00:36:24 12/02/12 Sun
Hi, just put down a "test well" by hand on our property, using a modified 8" post hole borer - hit the water table at 5 feet deep (in clay) then bored through to 35 feet deep eventually, where the "suction" on the borer head damn near stopped us from being able to pull it back out (using muscle power only) - we struck marine mud at 15 feet, marine sand/sediment at 25 feet then black iron sand at 30 feet (the suction of which was terrible), as soon as we started to lift the rig up from our last bite the water in the hole raised immediately and started to flood out of the hole carrying sand etc with it at a great rate, this continued for at least 5 minutes (while I watched it - meanwhile thinking "sweet" - we've hit an artesian aquifer ! - which are common in our area - 3 known aquifers: 1 at circa 24-40 feet deep, 1 at circa 70 deep, and 1 at circa 120 deep, then limestone bedrock). In the time it took to glue my sand screen to 40 foot of PVC pipe (say 10 mins)and get to lower it in the hole....water had stopped coming out of it and CLONK !! hole is now only 10 feet deep ..(water level still at top).. must have collapsed ..tried to rebore but no good, managed to go 3 feet but the stuff we're dragging out is very fine black sand and though wet (saturated) is like drilling through concrete... Drilling lesson 101 learnt the hard way I guess - have all your gear ready at "go" ...to go down the hole immediately you hit "the zone" .
I will try this method again nearby, but I'm wondering now if I can possibly even get the pipe (my PVC "well casing") down against such a flow as we had coming out...(perhaps I should weight the end of the PVC down mightily or need to use use steel pipe as my casing ?) or for that matter be able to get any pea gravel down around it in time before the hole collapses (pretty sure the flow we saw will wash pea gravel out before it gets a chance.....maybe 1-2+" size needed ? And then (if we're succcesful at that - getting down the casing etc) I will have to have some plan on how we're going to stop the flow...(screwed cap on pipe with ball valve + maybe pressure reducer ? plus I guess have a good load of near set concrete to immediately cap around the hole) So it's kinda good news, bad news, yet good news again! We've struck a good "stream" but now have to refine our method of trying to tap into it....(make it workable)...and if all else with the boring then casing method fails, I now know a driven well point would work (or high pressure hydraulic rig). Still I would like advice or thoughts about what has happened and what I'm planning to do. Pitfalls I might experiance or tricks of the trade i could use. Everything appreciated. Cheers & thanks, Sandy.
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