Bedrock Reference Site Installation (Preparation)

The barrel which will contain the instrument must be placed with care. The location you choose must have bedrock at the approximate depth of the barrel used.

The first step is to dig down to bedrock and widen the hole to fit the 30" diameter barrel.

Place the barrel into the hole and get it close to level. A slight slant in the barrel is desirable to allow water to run off of the barrel lid, when in place.

On the downhill side, remove enough additional material to allow for conduit entry and to provide drainage for the barrel.

Remove all loose dirt and material from the inside of the barrel.

Use the stiff bristle brush and some water to clean off the bedrock in the bottom of the barrel and allow the concrete to adhere to the bedrock.

Place the 6" strip of poly insulation around the bottom inside of the barrel. The foam isolates the sensor pad from the barrel and allows for a small amount of moisture to drain from the sides of the barrel.

Insert the two 1 ft. long 1" black plastic pipes so they extend from the deeper drainage hole up through the downhill side of the barrel. You may need to place some rocks or dirt around the pipes to hold them in place.

At the right, see an example of how your work should look this far.

Now, take some larger rocks (or dirt) and place them around the outside of the barrel to keep the barrel stable.

You are now ready for concrete. Be sure you have enough bedrock exposed for solid contact with the concrete. Rocks and soil may be used to level the area outside the bedrock contact. Mix the bags of concrete with 6 quarts of water for each bag and pour the mix into the barrel. Make certain the pipes rise through the concrete. Level and smooth the concrete. After about 30 minutes, finish the concrete and insert the 1/4" bolt into the concrete leaving at least 2 in. above the level of the concrete. Remember that you will need access to the connectors on the K2 when placing the bolt in the concrete.

Our experience in Utah is that a site will have reliable solar power if it has one month of battery capacity (from a full charge). For this type of site, approximately 400 amp-hours is adequate.

The batteries we use fit nicely in the 30 in. diameter by 2 ft. deep barrel. The barrel is installed in much the same way as the instrument barrel, but does not need to be on bedrock and does not need concrete in the bottom, although a concrete bottom is preferable for rodent protection. The choice of whether to use concrete usually depends on the difficulty of transporting the concrete and water to the site.

It is important for long-term battery health to keep the batteries cool and at a uniform temperature. We place a circular piece of plywood and a 2" piece of blue board building insulation on top of some loose rocks in the bottom of barrel. The rocks provide drainage. Around the inside edge of the barrel we place several layers of 1/2 poly insulation we used in the instrument barrel. This provides some insulation for the batteries and holds up the additional 2" piece of blue board building insulation that is placed on top of the batteries. The cabling to the solar array and the instrument barrel is placed before backfilling around the barrel.

A rule of thumb we have developed for sizing the solar array is that the short circuit current provided by the solar array should be approximately 10X the station current draw. This rule of thumb varies considerably with climatic conditions at the site. For example, a K2 uses approximately 400 mA and a FreeWave radio uses an average of 180 mA. This means we need 0.580 X 10 = 5.8 amps from the solar panel. This is more than adequately achieved with 2 75 watt panels.

Various prefabricated panel mounts are available for multiples of two panels. At left is a diagram of a homemade solar panel mount which can be sized for any number of panels. Two inch U-bolts fasten the 1/4" aluminum plates to the 2" galvanized pipe. The angle of the mount should be selected for optimum winter exposure of the panels. The mount is completed with various pieces of 2" aluminum angle.

With concrete placed, battery barrel and solar panel in place, the prep work is completed.