§ 20.40.100. Soils analysis and report.

A.

The soils analysis and report required by this chapter must demonstrate subsurface conditions and soils are suitable for designation as a usable wastewater disposal area under KPB 20.40.040(A)(4). Soils testing, test results, and the soils report must meet the following criteria:

1.

The soils analysis and report must be sealed by a qualified engineer;

2.

Test holes and borings must be located to yield representative data for, and provide coverage of, the entire subdivision;

3.

Test holes and borings must have the following minimum depth below the ground surface:

a.

In areas known or suspected to contain permafrost, the lesser of

1)

20 feet deep; or

2)

A depth below seasonal high groundwater table;

b.

The least depth associated with the following conditions, where applicable:

1)

Two feet below the initial encounter with the water table;

2)

Ten feet deep for shallow trench or bed systems;

3)

Twelve feet deep for areas where deep trench or seepage pits will likely be used; or

4)

The depth to bedrock, clay, or other impermeable strata with an expected percolation rate slower than 120 minutes per inch;

4.

Soils in a usable wastewater disposal area must be:

a.

Shown to be visually classified as GW, GP, SW, or SP under Unified Soils Classification System, and expected to have a percolation rate faster than 60 minutes per inch; or

b.

Shown to be GM or SM under the Unified Soils Classification System by a sieve analysis; or

c.

Shown by a percolation test conducted in accordance with 18 AAC 72.265(9) to have a percolation rate as described in 18 AAC 72.265(7); and

5.

The restrictions of 18 AAC 72.035(d)(7) and (8) must be met.

B.

Use of soils with percolation rates other than those set out in 18 AAC 72.265(7) must be on a case-by-case basis as described in Table C in 18 AAC 72.260(a)(4)(D). A definitive explanation authored and stamped by an engineer must be submitted.

C.

In areas known or suspected to contain permafrost, a soil moisture content profile analysis derived from laboratory testing methods, and taken from each test hole used for soils testing in the subdivision, must show that the soils throughout the subdivision are adequately drained.

D.

Subject to (E) of this section, the minimum number of test holes and soils analyses required under this section is at least one per two acres of subdivision, with at least one test hole and one soils analysis for a subdivision of two acres or less.

E.

The engineer may use less than the minimum number of test holes and soils analyses required by (D) of this section if sufficient soils data indicates general consistency throughout all or a portion of the subdivision. A definitive explanation authored and stamped by a qualified engineer must be submitted. The soils report shall contain a recommended application rate, limited to within 25' of the test hole, determined by the soil classification or percolation rate(s) at the test hole and a recommended soil absorption type (trench or bed).

F.

Soil testing requirements for subdivision lots equal or greater than nominal five acres consist of general soils and water table description with sufficient detail to support the applicability of the proposed means of wastewater disposal; the description must be based on:

1.

Existing information; or

2.

Visual analysis by, or local knowledge of, a qualified engineer.

G.

Except as provided in (H) of this section, the minimum depth from the ground surface to seasonal high water table and impermeable strata must conform to the values listed below. The listed depth must provide at least the following:

1.

Four feet or reduced by depth of freeze calculations by a qualified engineer;

2.

One foot for the distribution pipe, sewer rock, and barrier material;

3.

Four feet of separation from the bottom of the system to the seasonal high water table;

4.

Four feet minimum ground cover over the soil absorption system including tank, piping, and affective leach area;

5.

Nine feet minimum depth to seasonal high water; and

6.

Eleven feet to impermeable strata.

H.

The minimum depth from the ground surface to the seasonal high water table or impermeable strata set out in (G) of this section may be reduced by up to two feet by insulating with non-absorbing insulation or by mounding above grade to provide protection from frost penetration. Insulation material may be substituted for up to two feet of earth cover if material type and thickness allow per 18 AAC 72.035(d)(7) and 18 AAC 72.035(d)(8).

I.

When the water table is encountered in the test holes, the depth to the seasonal high water table must be determined by:

1.

Monitoring test holes or soil borings at times between May and October (inclusive); or

2.

Soil mottling analyses; or

3.

Interpretation of levels of standing open water; or

4.

Local knowledge and experience; or

5.

A combination of these methods.

J.

The depth to any seeps must be noted, and may require subsequent monitoring.

( Ord. No. 2014-02, § 1, 2-11-14 )