There are companies that you can hire to drain fields and lower the water table, but that might be too costly for what you want to do. The process is essentially digging an auger hole(s) to below your desired depth around your unit and then pumping the water out, I assume at a constant rate. The idea being, I assume, that the groundwater will drain into to the auger holes and by pumping it out you are clearing the water for that area. As far as the technical aspects of doing this, I don't know too much. I believe this project http://www.wmich.edu/fortstjoseph used this method over an entire site.

As far as digging a 1x1m unit down to 5 meters, even if you drain the water the stability of the walls will be highly questionable and extraordinarily unsafe for anyone entering the excavation, even if you can let it dry. It is also illegal under OSHA to enter excavations with seeping water. Have you considered simply doing auger tests to 5m over your site to determine the depth of deposits? Using a simple bucket auger (hand operated not machine) will allow you to get a 4 inch diameter sample that you can excavate in 10 cm levels. You won't have as much coverage and your vertical control may be slightly skewed, but if all you are trying to is test for deep deposits it would be a more practical solution.

The process that Prisoner speaks to is often referred to as "dewatering," whereby the area in question is pumped free of water, or as much of it as possible, through a series of borings lined with permeable pipe that allows water to flow in while holding back sediments. The only way to figure out how much flow may be involved is to do a "perc" test and measure the flow rate. As I'm sure you have figured, you would need to mitigate the adverse effects of installing the bore hole before drilling, and as Prisoner also noted, OSHA regs would prohibit hand excavation below 4 ft. without shoring, so 1x1 units, or similar, would likely not work.

You could go to 5 m in a 1x1 m excavation, but to comply with the regs you would have to "step back" the area around the unit to such an extent that it would likely be cost and time prohibitive.

It is possible to dewater a 1x1 directly with a small 2 in. or 4 in. pump (this technique was used on a project I was on in SoCal a few years ago). Again, however, you will be limited to the legally safe depth you could excavate.

If a coffer dam is proposed then, again, some form of mitigation of the adverse effects of installing the dam will have to be devised - and excavation to extract data would not likely be one of those measures as you would have a "chicken and the egg" conundrum on your hands: we cant install the dam to dewater 'cause we need to excavate to mitigate the adverse effects; we cant excavate to the desired depth 'cause we need to dewater....

Two very good answers so far - I will give you one that goes back to the old days and non- technical terms -

1. put a deeper hole in the corner of your unit (i.e. did a deeper shovel tests of smaller unit in that corner - this will create a sump pit like many folks have in their basements. An alteranative - also found in many basements - is to excavate a deeper trench all the edges of the areas you actually want to examine - depending on how the water is traveling through the soil this may help to dry out the central section (after a day or so of pumping) and allow you to work fairly dry as long as the pumps keep going. This method works well in a soil where the water seeps in from the sides (clay) but not as well when water "comes up" from below - such as at an artesian well system.

2. Use a pump to drain water from that corner (or surrounding ditch) - - keep it going constantly and you should be able to exceed the seepage rate (unless you are in a very wet environment). This means keeping the pump going all night as well if it will take you several days to get the job done - or else you will be hand bailing come morning to the get level down again, and then will have to work in a moist/slick soil all day.

3. Pray the pump holds up and handles enough volume to keep you dry. (it may be necessary to have multiple pumps working or at least on hand - in case one clogs, dies or just runs out of fuel.

Being more technical - the comments about OSHA and unit size already made are right on. One way to approach this is to place your deeper test on the floor of a larger block excavation you may have already completed. For example, if you already have an excavation 3 feet deep that is 5 by 5 meters wide - you can place a 1 by 1 in the center - and reach 4 feet deeper (1+meters) without going beyond OSHA regs as your new unit will reach 7 feet in overall depth, but only be 4 feet deep itself.

Another technique of I am aware of for completely sumberged sites is to core using some of much greater diameter, such as a sonotube, which would give you a more "shovel test sized" hole than many coring methods do. I am not sure how well this will work though if the soils are not very saturated and easy to drive the tube into.

Good luck with whatever method you choose, and keep us posted.

Thank you everyone for your suggestions and warnings. Working as we have been for over a year would def. make the hair stand up on OSHA's head! We've been profiling walls of looter pits that pock-mark a shell mound site. Some of the looters were very ambitious and sure they would find gold if they dug a hole deep into the highest point of the mound, some 8m above mean sea level. Some holes (not squares) are 6+ meters deep. The top of the holes are wide, but they quickly narrow. We assume that the cultural deposit could be another 2 meters below water seepage level. Oh, and it's a tidally influenced island, so water levels can change.
I wish I could be the deciding factor on how the project is done, but I can only suggest and caution from my position. I'll take pictures and let you know how things turn out.
Oh, and are there guidelines on how to do a "perc" test? I'd like to do that before buying an expensive piece of equipment.

Thanks again!

Perc tests are often required by county officials prior to developing land, such as for housing, so you may be able to go to a county website that may have guidelines for your area. You may be able to find a hard copy there as well.

Please be safe. You and the rest of the crew must...MUST....refuse to get into any hole that is deeper than 4 feet and not shored properly (by OSHA regs). Your boss has a responsibility to insure your safety. Of course if anything happens you family can always sue him and will easily win...but you may not be around to enjoy the win.

It is an unfortunate situation that we all face when we start out. We are young, enthusiastic, have no fear and think it is neat and an adventure to go places we probably shouldn't (I have been in some of those holes, dropped by much too flimsy rope over cliff sides to check our markings, etc.). It is only as we get older and see what can happen that we wise up. I also spent 10 years working in Emergency Services/Rescue - and learned from pulling out vicitims and bodies just how dangerous some situations can be. I am also familiar with a recent case in NYC where a collapse resulted in: knocked out teeth, fractured ribs, broken pelvis - and the only reason the victim survived is that there were plenty of construction workers on hand with shovels that were able to dig her out immediately before the weight of the soil on her chest - which did not allow it to expand - could suffocate her.

Jennifer has a neat little safety section on this site ( http://www.archaeologyfieldwork.com/health.htm ) but the section on trench safety could use some work. You should look it over - contains links to OSHA regs . These conditions are all compounded if you are in telephone booth holes rather than trenches - For more:

very short video showing just how quickly and devastating a typical trench wall collapse can happen -
http://www.youtube.com/watch?v=fBwG8D4d5fU

A page describing some of the safety hazards by "TexasTrialLawyer.com"
http://www.texastriallawyer.com/trench_collapse/index.htm

Evidence that OSHA knows what they are talking about - literally (you may laugh at this one, but it is real)
http://www.youtube.com/watch?v=D6dHoSAT6MU&feature=related

Excellent links DM.

That trench box in the Oregon OSHA link was way undersized in all respects. That foreman should have been fired on the spot for putting all those folks, not just the guy unhooking the crane, in danger; with a sidewall collapse the top surfaces can give way and there wouldnt be anything you could do about that.

I've monitored and have been in miles of trench as an archaeologist, and to sum up DM's point above: We dont get paid enough to die for archaeology.

If your employer is putting you into situations that jeopardize your safety beyond the things we would normally encounter, and especially those not addressed by a health and safety plan - you have one of those, right? - then you need to remove yourself from that situation, and inform the authorities - department of labor, OSHA, county equivalent, etc. and shut that project down until those issues are addressed.

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Getting back to your original post, I think there was an American Archaeology magazine article about a year or two ago that had on the cover a semi-submerged coastal site that was excavated and discussed within. If I find it I will post up the reference.

Cheers

Jennifer has a neat little safety section on this site ( http://www.archaeologyfieldwork.com/health.htm ) but the section on trench safety could use some work

Hopefully now that I've finally gotten caught up on website stuff I can get crackin' again on that. There is a lot that can be added throughout that entire section. Doug, I would love to incorporate info from some of those links you listed, and if anyone knows of other sites I would appreciate any contributions.

I also agree that your safety is too important to compromise. I'm also one of the ones who did a lot of stupid things at my employers' request through the years by crawling into trenches, improperly shored up units, etc. Now I look back at some of those situations and wonder what I was thinking.

Jennifer

[quote:="admin"]I'm also one of the ones who did a lot of stupid things at my employers' request through the years by crawling into trenches, improperly shored up units, etc. Now I look back at some of those situations and wonder what I was thinking.

Jennifer

Like digging STPs in a flaming junk yard??? :o

"Shovel test not excavated due to fire." LOL Oh I'm sure there are many examples of field stupidity through the years.

Jennifer