River Logic LLC

Absorption systems shall not be excavated when the soil is wet enough to smear or compact easily (soil is too wet if you can roll it between your hands and make a ribbon out of it).
Tendency toward compaction, smearing and puddling depends on the soil type, moisture content and applied forces. Soils with greater than 25% clay (includes alls soils except sands and loamy sands) are very susceptible.
Front end loaders or bulldozer blades should not be used because the scraping action of the bucket or blade can smear the soil and the wheels or tracks compact the exposed surface.
Backhoes with side mounted raker teeth have been shown to limit sidewall compaction.
Work should be scheduled only when the infiltrative surface can be covered in one day because wind blown silt or raindrop impact can clog the soil.
Heavy equipment shall not be driven in or over absorption systems during construction or backfilling (or after completion, for that matter).

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Preparing and Excavating Site

Stake out the location of all trenches and lines
Set the elevations of the tank piping and trench bottom
Excavate and level trenches with proper center-to-center separation (make sure all trenches are level or have the prescribed slope).
Rake the bottom and sides if smearing has occurred while excavating. All smeared or compacted surfaces should be raked to a depth of 1", and loose material should be removed before the filter material is placed in the excavation. Do not use the teeth of the bucket to rip the trench bottom.
Remove any large stones or other debris.
Verify that the trench is level using a transit or level.

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Gravel Placement

The gravel should be laid in by a backhoe or front-end loader rather than dumped by a truck. This should be done from the sides of the system rather than by driving onto the infiltrative surface.
The gravel should be free of fines, dust, sand or organic matter (maximum fines through 1/2" mesh = 5%, maximum through #10 sieve = 2%).

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Distribution Pipe Layout

Pipe should be 4" in diameter and perforated.
Pipe shall be in straight lengths, penetrated by at least 2 rows of round holes, each 1/4 to 1/2", and located at 6" intervals. On nearly level sites, holes should be at 5 o'clock and 7 o'clock.

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Barrier Materials

The top of the gravel must be covered with an effective, pervious material before being covered with earth fill. The barrier prevents backfilled soils from entering the pours media and filling the voids.
Examples of acceptable barrier material is synthetic filter fabric, unbacked fiberglass building insulation, or compacted straw (4 - 6" of straw recommended, Utah regulations require at least 2" of compacted straw).

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Backfill

At least 6" of backfill must be placed over the barrier.
Absorption systems shall be backfilled with soil similar to natural soil free from stones 10 inches or more in diameter.
Soil should be mounded slightly above the surface of the ground to allow for settlement, to prevent depressions for surface ponding of water, and to channel runoff away from the system.

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Septic Tank

Septic Tank Bedding

Excavate for a minimum of 18 inches clearance on all sides of tank (24 inches recommended) to permit proper placement of tank and backfill.
Provide a uniform, solid, and level bearing surface.
Remove boulders and rocks.
Compact underlying soil to prevent differential settlement.
Use sand, crushed stone, or gravel layer 4 inches thick minimum recommended as bedding.

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Septic Tank Assembly

Lay inlet pipe 1 - 2% (recommended) slope from building to tank.
Place tank on bedding using manufacturer-supplied lifting apparatus.
Install joint sealant to ensure water tightness
Place tank top (weight of top will compress sealant for a watertight joint)
Verify tank is level.
Test for water tightness. Leakage may result in wastewater to the environment while infiltration can result in hydraulic overloading of drain fields.

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Utah Water Tightness Testing Procedure

Utah requires water tightness testing of each septic tank after it has been placed in the ground before backfilling.
Fill concrete tanks 24 hours before inspection to allow stabilization of water level.
During inspection, must not be any change in the water level for 30 minutes.
Must not be any moving water into or out of tank.
Two piece tanks, with the joint below the water level, may be backfilled up to 3 inches below the joint to provide adequate support to the seam of the tank.
Testing must be supervised by the regulatory authority.
Tanks exhibiting obvious defects or leaks shall not be approved unless such deficiencies are repaired to the satisfaction of the regulatory authority.

Septic Tank Backfilling Techniques

Mechanical compaction in 12 - 24 inch lifts (maximum).
Backfill should be free of stones greater than 3 inches in diameter.
If ground water level rises above bedding, fill tank with water and place soil on top of the tank, or pump goundwater level below the bedding until backfill is completed. Ground anchoring devices may have to be installed to prevent the tank from floating when empty.

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Construction tips and requirements were taken from the Utah On-Site Wastewater Treatment Training Center's Training Manual Specific requirements mentioned may vary depending on the your health department.

For more info, contact info@river-logic.com or call at (801) 391-7481.