We dig the hole, set the bedding, run the trenches and backfill for underground water tanks and cisterns, and we build level pads for above-ground tanks. The tank maker's instructions and your fire district's requirements set the specs, and we dig to them.
Water Tank Excavation in Boise and the Treasure Valley
Water storage comes up more often than people expect. A rural home on a slow well needs a cistern to keep up with the house. A new build on acreage out of reach of city hydrants may need fire water storage before the fire district signs off. A horse property or shop wants a big tank for stock water or irrigation. All of those start with excavation.
We dig for water tanks in Boise, Kuna, Star, Middleton, Parma, Homedale and across Canyon County. Most of these jobs are on acreage, which is a lot of what we do from our base in Caldwell.
The Tank Jobs We Dig For
Underground water tanks and cisterns
Buried poly, fiberglass and precast concrete tanks for domestic water storage, usually filled from a well and pumped to the house. The hole, the bed and the backfill all follow the manufacturer's install sheet.
Fire water storage tanks
Some rural fire districts require on-site water storage for new homes or subdivisions without hydrant coverage. Tank size, location, the hydrant or draft connection, and fire truck access are set by the fire district along with your engineer or tank supplier.
Pads for above-ground tanks
Large stock and irrigation tanks need a level, compacted base, often gravel, set a little above the surrounding ground so water drains off. Our site preparation page covers pad work in more detail.
If the tank you're thinking of is a septic tank, that's a different dig with its own health district permit. See septic system installation. Septic permits go through Central District Health in Ada County or Southwest District Health in Canyon and Owyhee counties. If one property will have both a water tank and a septic system, plan them together, since the health district usually wants distance between drinking water storage and the drainfield.
Sizing the Hole and Setting the Bed
The hole for a buried tank is bigger than the tank. Manufacturers usually call for clearance around the sides so backfill can be placed and compacted, and a set range of cover over the top. Boise uses 24 inches as its frost depth for footings, so tanks and their fittings generally sit deep enough that the pipes don't freeze. Too much cover can crush some poly tanks, which is why we go by the spec sheet instead of habit.
The bottom has to be flat and firm. Most tanks sit on a bed of sand or fine gravel, with no rocks that can press into the tank wall. In caliche around Kuna and Meridian, that means cutting the hardpan out and replacing it with bedding. Basalt in parts of Kuna and southeast Boise slows the dig and changes the price, so we look at the site before we bid.
Larger tanks often put the hole past 5 feet deep. At that depth OSHA requires sloping, benching or shoring before anyone steps in, and we plan the dig around that. Sloping the sides makes the top of the hole much wider than the tank, which means more spoil and a bigger work area. Close to a house, a well or a property line, that extra width can decide where the tank fits.
Groundwater and Buoyancy
An empty tank in wet ground wants to float. It can push up out of the hole, crack fittings or lift the lid above grade. Near the Boise River in Eagle and Garden City, groundwater can rise fast once irrigation season starts. A hole that's dry in March can have water standing in it by June.
Tank makers handle this in different ways. Some call for anchor straps tied to precast deadmen, some for extra cover, some for partly filling the tank before backfill. We follow what your tank's instructions say. On high groundwater sites, it helps to schedule the dig for late fall, after irrigation water shuts off.
Inlet, Outlet and Overflow Lines
A tank only works once it's hooked up. There's usually a fill line from the well, a supply line to the house or pump, power to the pump, and an overflow. Each needs a trench, below frost for water, and the overflow needs somewhere to drain that isn't your foundation or the neighbor's yard. We dig those runs while the machine is already on site. Our water line excavation and underground utilities pages cover that work. Your plumber or pump installer makes the connections, and an electrician handles pump power.
Backfill, Permits and Cost
Backfill is where tanks get damaged. Around the tank it goes in by hand or with light equipment, in layers, using the material the manufacturer calls for, usually free of large rock. We compact as we go so the ground over the tank doesn't settle into a dip. See backfilling for more.
Permits depend on the tank. Fire storage runs through the fire district and the county or city. Your tank supplier or plumber can tell you what applies to a domestic cistern. Either way, we call Digline (811) at least two business days before every dig.
Price depends on tank size and depth, soil and rock, groundwater, the length of the connecting trenches, and where the spoil goes. We give free estimates. Access is part of it too. The truck delivering a large tank needs a firm path close to the hole, and soft ground or a tight gate can change the plan.
What to Have Ready Before the Dig
The smoothest tank jobs start with the tank already ordered and a delivery date set, so the hole isn't sitting open, especially where groundwater can rise. Have the manufacturer's install sheet on hand, since hole size, bedding and backfill all come from it. For fire storage, get the fire district's sign-off on size and location first. It also helps to line up your plumber and electrician early so the connecting trenches can be backfilled soon after the lines are in.
Why Rural Owners Call Ultimate Excavation LLC
We're an Idaho registered contractor (RCE-65836) with a 5.0 rating on Google. Reviewers call us "professional, efficient and highly skilled" and say we "value communication and arrive on time." Call (208) 697-2429 or request a free estimate.
