Installing the Septic Tank
Sat, Jul 14, 2018Pete, our excavator, is back up here with us. We need to square up our footings in a couple spots, and unfortunately, we need to get a big rock out of the path of our footing. After talking with the engineer about it, he said we’d have to have a geotech take a look at it if we wanted to include it as part of the footing structure. I think it’d be easier to remove. Finally, and the most important thing for this weekend, we need to get the hole dug for the septic tank, and place the septic tank!
The excavator bucket has made previous attempts to fracture the big rock and pick at it, but they haven’t worked out. That technique has been very successful with other rocks, just not this one. I may be naive, but I brought a sledge hammer with me today to try a few manual whacks.
As Pete worked on squaring up a couple corners on the footings, I started sledging the big rock. After about three good swings, a nice fracture line formed. As I removed the pieces that fractured off, I realized the fracture was pretty shallow, and the pieces weren’t nearly as big as they looked. This is going to be slow going, but at least it’s going.
After about 20 minutes, Pete was done squaring things up and joined me at the rock. Once I had a fracture line formed, he used the teeth of the excavator bucket to expand that line even more, and the chunks of rock he was able to break were much bigger. We repeated this process a bit, me forming a small fracture, and he taking advantage of it, until enough rock was removed that it no longer protruded into the footing.
Time for the fun part: placing the septic tank!
Given how far behind we are with our original schedule (of forming and pouring the foundation this year), my brother and I have both realized that most likely all we’re going to complete this year is the septic system. So we are excited to see this part of the project nearing completion.
The septic tank is being placed approximately six feet away from the outside edge of our front footing. The septic tank is designed to be buried in up to 4 feet of dirt. I am trying to maximize the depth at which the tank is buried. Soil has this amazing property of quickly dispersing weight. The deeper something is buried, the less a large load at the surface is felt. My thinking is that if we have to get (heavy) machinery onto this pad in the future, I want the tank buried deep and protected as much as possible.
It took me a few revisions to come up with the depth of the hole. I was getting myself confused because current grade is not final grade. We will be adding about 14” of fill to the current grade, so final grade sits a bit higher. I need to control how deep the final burial of the tank was, and I needed to calculate how deep the egress pipe would sit so that we could carve a trench out of this hole.
Final calculations said we needed a hole that was 87” deep from our reference point (top of the footing form), and that the start of the egress pipe trench needed to be 36” deep. We set our transit level pole and Pete got to digging.
Now that we weren’t digging into (mostly) solid rock, the digging went quick. The entire hole took less than an hour to dig. It got a bit hairy on the front corner as a large boulder gave way towards the bottom of the hole, and caused some cave in. Otherwise the hole kept its shape well.
The skid steer started dumping the pea gravel into the hole, and we leveled it. Once we had a level base and a good pack of pea gravel, it was time to drop the tank in. The pea gravel make leveling the tank a whole lot easier, as the tank will almost self-level under its own weight (especially once we add a bit of water).
The tank went in just barely out of level. A couple of jumps on one end made it sit perfect. We filled the tank with about a foot of water so that it did not move.
Pete was quick with the trench. He stopped at the top of the hill, just above the drain field. Tomorrow my brother will hand dig the rest of the trench to connect us to the drain field.
We’re ahead of schedule for the weekend, and so we moved onto laying the pipe.
Our original plans had called for using 2” poly pipe to connect the septic tank to the distribution box. This stuff flexes, but is hard to work with. It wants to bend all over and is very stiff. It also didn’t make sense that we would use a 2” diameter pipe here. Everything I had read called for 4” (except our plans).
We had some 4” PVC pipe laying around from another project, so I started using that to connect the tank to the distribution box. We had enough to get about half way. My brother had completed the trench from the top of the hill to the drain field. Everything is looking really good and we’re probably just another day from being completely done (at this time, I was still severely underestimating the effort it would take to backfill).
Next Post > > < < Previous Post