I *am* an excavator and have installed septic systems in Platte and Albany counties. Some pointers:
You have to get a permit from the Wyoming DEQ in Cheyenne to get started. Costs $200 and takes 4-8 weeks to approve. If it is just for your home, you can fill out the application and submit it yourself. If it is for any kind of business use, it has to be signed off by a certified engineer (good choice is the county engineer, who is known to the DEQ).
Albany requires an inspection from the county. Used to be Barney, who lived down in Centennial in that big log cabin. Not sure who is doing it now. ALL the trenches need to be open from the house through the leach field, and the leach field must be filled to the top of the pipe/infiltrators (top still exposed). They will come out, take a couple of pictures and check the slopes on the pipes. If you're in a remote area, takes about 2 hours--5 minutes to do the inspection, and 1:55 to catch up on the latest gossip.
Platte does not require an inspection, but I always ask the county engineer come out and take a look to make sure I didn't miss anything. Remember this is Wyoming--people, even county government--tend to be just other ranchers, farmers and laborers and are usually nice folks. I helped with some rezoning of property last year, and the county assessor, Dennis, was wonderful--nice guy and really helped us out. He's retired now, but his sister is now the Mayor of Wheatland (first woman mayor in the town's history).
On the checklist:
#1 CHECK YOUR SOIL TYPE!!! Wyoming has all sorts of different soils. If you've got that hard-packed bentonite clay, by springtime your tank may be sitting on top of the ground, rather than in it! It is hard as concrete when dry, but is actually dense and fluid enough when wet, that it can float a concrete tank right out of the ground. Quite amazing to see. In that case, excavate several feet around it and fill with dense sand, so there is some drainage. (Don't put gravel next to, or under, a concrete tank--always have a few inches of sand for even pressure).
#2 Check your high water table. You don't want your leach field filling up with water and running backwards into the septic tank then into the house. Particularly when it rains hard--Wyoming is known for flash floods, and they can occur under the ground in sandy and rocky soils, where you don't actually SEE them--until your toilet starts dumping on the floor. A deep backhoe cut can reveal what is going on underground.
#3 Keep the septic field at least 100 feet from any well or spring, or you'll contaminate it.
#4 Tank size is determined by the gpd (gallons per day) you are generating, and the tank must retain its contents for 3 days. The rule-of-thumb that the DEQ uses is gpd x 1.5 = tank size. So if you've got 800 gpd, you need a tank size of 1200 gallons.
#5 Use a concrete tank, either 1200 or 1500 gallons. I recommend avoiding the 2000 gallon tanks, as they are just a 1500 gal tank with a spacer. Makes them really tall, so you need a deep hole to set them and they are a pain to set and service. Better off with 2 smaller tanks. Don't use a poly tank--critters (badgers, prairie dogs) will cut through the sides and you'll end up pulling it out and putting in a concrete tank.
#6 Infiltrators / biodiffusers are a better choice than pipe and gravel, in most cases. Just make sure they are set on a firm base--if you have soil that doesn't have any rock, dump some pebbles in first to set the edges on, or in a couple of years you will find that they have sunk a bit and soil has filled them up. And you cannot dig up and fix--it will be dig up and REPLACE, unless you want to do a heck of a lot of manual labor.
Good luck with your installation!
