Saturday, May 17, 2008

A very long week

Well, let's see... What happened this week?

Tuesday was a normal meet time at the office of 8:00 since the drillers were coming from Rancho Cordova to Santa Clara, and we met on site at 10:00. This looked to be a nice simple job: 3 extraction well installations to between 55 and 60 feet below ground surface (bgs).

Now for the non-geologist/non-environmental field people out there, you should know that there are many steps to installing a well.

  1. First the asphalt or concrete must be cut to allow removal and access to the soil underneath. Our client requires a 2-foot by 2-foot square.
  2. Then the soil must be hand augered and/or vacuumed out. This vacuuming involves using high pressure water or air to break up the sub surface so it can be sucked out.
  3. For our extraction wells which were to be 6 inches in diameter, the driller had to go down with 10" augers first, during which we sampled every 2.5 feet.
  4. The sampler is pounded in by a weight that is raised and released by a winch on the drill rig. In the sampler are three stainless-steel tubes that are 6 inches long and 2 inches in diameter. These are capped and stored in a cooler with ice for later analysis.
  5. During sampling, I or another geologist logs the hole by describing the soil types with color strength, consistency, grain-size, moisture, and any other interesting qualities it might have.
  6. The drilling and sampling continues until we reach our desired depth. At this site, that depth was determined by passing through a water-bearing sand and gravel layer, and then entering a clay later. But only slightly into the clay layer so that we don't go into a lower water bearing zone. We didn't want to dilute the contamination in the upper layer, or carry the contamination into the lower clean layer. And we didn't want to be in clay as clay doesn't allow much water through it in comparison to sand.
  7. Once we reach our desired depth, the drillers pull the 10-inch augers and then drill out the hole again with 12-inch augers.
  8. Once drilled out the well casing in lowered into the hole, and then completed by pouring sand around the screening of the pipe. The augers are slowly raised up, leaving the sand and the casing in the ground.
  9. After the sand covers the entire length of screen (plus a bit), bentonite chips are dropped on top. These chips are then hydrated, meaning they have water poured onto them, which they absorb and swell up sealing off the sand.
  10. Then the rest of the length pf the well is willed with grout. Grout is neat cement, where neat means the same as it does in a drink: no rocks.
  11. The final step of completing the well is to set a well box, which is the flat iron plates which attach to a ring that is set in concrete.

And that's what Hooligan and I did and watched three times this week. It should have taken three moderate days to complete this job. That is not what happened.

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