1) Rod SET - The instrument - Costs run about $1200 each (US $). The instrument consists of the following;
a) Rod SET instrument
3) CEMENT - We normally use standard cement. Mortar mix also works fine. The general rule is that it takes about 30lbs of cement to fill a single SET benchmark. So you can assume you will get 2 SET's cemented with a 60lb bag of cement.
4) RODS - We use 9/16" Stainless Steel Rods which come in 4 feet long sections (ends are threaded). Cost per Rod is about $15-25 PER SECTION. Prices can vary considerably from year to year. Depending on the environment, these rods will be driven into the substrate to a depth ranging from 6-80 ft (~2-25m).You should also order driving tips which are short pieces of SS rod with a point on the end.
5) Cement tools and bucket, paper towels, duct tape.
6) Brass Concrete marker (optional) - These are 2" diameter brass markers which we stamp with an ID number. They are inserted into the cement before it hardens and serve as a site marker.
7) Demolition Hammer or Pounder - For driving the rods into the ground, we now use a small portable generator (2KW) and a demolition hammer to drive in the rods. If you prefer, you can still use a custom built rod pounder.
8) Driving head - Attaches to the top-most SS Rod. It takes the blows from the Demolition Hammer or Pounder. It's used to protect the SS rods from getting deformed from all the pounding. You can use an old cut piece of SS rod for this. It needs to have threads on one end so it can couple with the rods. We normally use a piece about 6-12" in length.
9) Post hole digger and sharp shooter shovel (narrow shovel). To dig the hole and to mix the cement.
10) 6" diameter PVC pipe (Schedule 40) - 18-24" long. This goes into the hole after the rod is driven to refusal. After the receiver is attached, the pipe is filled with cement.
11) Angle Grinder or Bolt Cutter - If you need to cut the rod we recommend using an angle grinder to cut the rod right at the surface. This assumes you have a generator or a battery powered grinder. You can also use a hydraulic bolt cutter (Expensive ~$800) to cut the SS rods.
12) Marker Horizons - We typically use feldspar clay. Need a respirator mask for feldspar. Marker horizons are established when you take your first SET readings (baseline), not before!
13) ½" pvc or fiberglass poles - for marking the boundaries of the sampling area.
|2) Installation Instructions:|
The general procedure for installing deep benchmarks is as follows:
A) Install a platform (Temporary or Permanent) to work on.
Note that steps D and E do not happen at the same time as steps A, B and C. Normally, you install all your benchmarks at a given site (ABC), wait a week or so, then take your baseline readings and establish feldspar horizons (DE).
A) Install a Sampling Platform:
Use a temporary platform or build a permanent platform.
B) Drive SS Rods into the ground:
1) Using a post-hole digger and/or sharpshooter shovel, dig a hole 6" in diameter (the diameter of your PVC pipe). Try to make it about 1-1.5 feet deep. Remove the soil in the hole from the immediate area in a bucket. Make sure the hole is not deeper than the 6" PVC pipe which is going to go into it. For example, if you have an 24" length of 6" PVC, you will want to dig a hole about 12-15" deep. You can drive the pipe with a sledgehammer (or pounder) into the underlying substrate. It helps to anchor and stablilize the benchmark.
2) Screw together 2 sections of rod. Iznstall the tip on the leading edge (if you have one). Make sure connections are tight.
3) Make sure the rod is vertical and push it into the hole and into the ground by hand. You may be able to get 2 or 4 rods in by hand before you need to start pounding.
4) Attach the driving head, turn on the generator and start pounding the rods into the ground with the demolition hammer (or by hand with the pounder).
5) Pound the rods into the ground. Add sections and continue until refusal or you hit bedrock. All of the connections between rods will get loose from the pounding of the demolition hammer. You will need to keep tightening the connections. While pounding, be sure to keep the driving head screwed on snugly. Also use a vice grip and screw the 4' sections of rod clockwise every rod or two to keep them snugly connected.
Important: Be sure to keep an accurate count of rods. It's very easy to get confused and lose track of how many you've sunk into the ground. Always start an installation with bundles of 10 rods so you will not get confused.
C) Attached the Receiver and Cement in Place:
6) Cut the Rod (if necessary) - Sometimes you can stop pounding the rod so that the joint between sections is right at the marsh surface. Under these circumstances, you will not need to cut the rod. Just unscrew the pounding head. If you do need to cut the rod, we recommend that you use an angle grinder with a 4 1/2" Steel/stainless steel cutting wheel. This is probably the fastest and safest way to cut a rod. You can also use a hydraulic bolt cutter which will work but is a bit more dangerous. If you are using the bolt cutter, have someone hold the top piece as you cut it. Otherwise, it will be launched into the air and could be a hazard.
7) Drive the 6" PVC pipe into the hole. Use a small sledge (or the pounder) to knock
it down. Try to get it into the sediments beyond the bottom
of the hole so it will be stable. Have the top of the PVC pipe stick
up about 2-4" above the marsh surface.
Slide the SS receiver over the rod and into the hole. Tighten the
bolts on the receiver with a 9/16" wrench. This will attach it to the deep rod.
9) Remove excess water in the PVC pipe and fill it with cement (concrete or mortar mix). Regular cement works fine but you can also use the quick drying expansion (or hydraulic) cement.
10) If you are using a brass concrete marker, place it into the cement before it sets
10) You are finished installing your benchmark.
D) Take your baseline SET reading.
Click here for details on how to take the first readings.
Click here for instructions on how to establish the marker horizons.
|U.S. Department of the Interior, U.S. Geological Survey,
Patuxent Wildlife Research Center | URL: http://www.pwrc.usgs.gov/
Last Updated: 23 June 2010
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