A. 
Tank capacity. A septic tank shall have a minimum working capacity, comprised of the volume of the septic tank below the bottom of the tank's discharge outlet, of 1,000 gallons plus 250 gallons for each bedroom over three.
B. 
Septic tank location.
1. 
Separation distances.
a. 
A septic tank shall not be located within five feet of a property line.
Exception: A reduced distance may be allowed if an engineer's evaluation demonstrates, to the satisfaction of the department, that such an encroachment would not increase the risk to the public health and environment, and not impact the ability to develop and maintain the adjacent property.
b. 
A septic tank shall not be located within ten feet of a water main or water service line.
Exception: For "Private" water systems, a reduced distance may be allowed if an engineer's evaluation demonstrates, to the satisfaction of the department, that such an encroachment would not increase the risk of contamination to the associated water system. For "Community" or "Public" water systems, a reduced separation is required to be approved by ADEC.
c. 
For a conventional foundation having a strip footing or a shallow foundation consisting of a concrete slab with thickened edge, a septic tank shall not be located within the foundation soil bearing prism established by a 45 degree plane extending down and outward from the bottom outside edge of the footing or thickened slab edge, or a minimum of ten feet from these types of foundations.
Exception: A septic tank may be located no less than five feet from a foundation supporting a storage-shed, greenhouse, agricultural building, shop, garage, carport, or similar structure having a total gross floor area of 600 square feet or less and having an eave height of ten feet or less.
d. 
For decks and stairs located more than thirty inches above grade, a septic tank shall not be located within five feet of an associated deck or stair support. For decks 30 inches or less above grade, a septic tank shall not be located under an associated deck support.
e. 
One hundred feet to surface water, measured along the path which overflowing wastewater would travel.
f. 
One hundred feet from a private well.
g. 
The separation distances required by 18 AAC 80 from public water supply systems.
2. 
Pumping access. A septic tank shall be installed only in an area that will be readily accessible for pumping.
3. 
Driveway or parking area. A septic tank shall not be buried under a driveway or parking area, unless the engineer provides a design, including calculations, demonstrating its structural and thermal integrity.
C. 
Cover and insulation. Tanks with two to four feet of cover shall be insulated with a minimum of two inches of approved insulation placed immediately above the top of the tank. Tanks with less than two feet of cover shall be insulated in accordance with an engineering report demonstrating protection from freezing and specifying the insulation requirements.
D. 
Buoyancy forces. A septic tank subject to buoyancy forces shall be anchored or ballasted as required to prevent flotation regardless of the liquid level in the tank.
E. 
Watertight couplings. All septic tanks shall be fitted with watertight couplings, approved by the department, at the pump-out attachments and on the inlet and outlet of the tank.
F. 
Required cleanouts. A septic tank, including the piping leading into and out of the tank, shall have all of the following:
1. 
A 20-inch (minimum) diameter manway riser serving the first compartment. The riser, including the cover, shall be insulated with four-inch minimum insulation extending 48 inches below grade or to the tank insulation. The insulation shall be of an approved type suitable for below grade applications. Exposed insulation above grade shall be protected from UV damage. The riser lid shall be secured to prevent unintended access. (Per § 4 of AO No. 2017-129, this subsection F.1 is effective May 1, 2019)
2. 
A four-inch diameter or larger standpipe with airtight cap providing effective access to each of the other compartments.
3. 
A cleanout installed one to four feet from the building foundation. If it is not practical to install a cleanout near the foundation because of an existing building, driveway, parking area, utilities, or other structure, one set of opposing cleanouts shall be installed on the upstream side of the tank within ten feet of the inlet.
4. 
One set of opposing cleanouts (aka; double cleanouts) installed on the downstream side of the tank within ten feet of the outlet. The opposing cleanouts shall be oriented such that the cleanout closest to the tank shall be to clean the line away from the septic tank, and the cleanout furthest from the tank shall be oriented to allow cleaning toward the septic tank. The cleanouts shall be located on undisturbed soil.
Exception: Pressurized distribution pipes do not require cleanouts.
G. 
Septic tank decommissioning. Septic tank decommissioning shall be in accordance with the current adopted version of the Uniform Plumbing Code.
H. 
Septic tank material. Septic tanks shall be constructed from durable, corrosion-resistant materials, including concrete, fiberglass, or plastic. Septic tanks constructed from steel shall be coated on both the interior and exterior with an approved polyurethane lining or superior material. (Per § 4 of AO No. 2017-129, this subsection H is effective May 1, 2019)
(AO No. 2017-129, § 3, 1-23-2018 and 5-1-2019)
A. 
Requirement for original and replacement system. An undeveloped lot proposed for an on-site wastewater disposal system, or a developed lot proposed for an enlarged system, shall be shown to have sufficient available area for an original subsurface disposal field and one designated replacement of the same capacity. A previously developed lot, proposed for an upgraded wastewater disposal system of the same capacity as the original, need only have a site for the proposed upgrade.
B. 
Disposal field location. The location of an original or replacement subsurface disposal field shall be in accordance with the following requirements:
1. 
Horizontal separation distances. A subsurface disposal field shall be located in compliance with the separation distances required by state code, and not less than:
a. 
One hundred feet from surface water, measured along the path which overflowing wastewater would travel.
b. 
One hundred feet from a private well.
c. 
Separation distances required by 18 AAC 80 from public water systems.
d. 
Fifty feet up-gradient from any human-made or natural break in the natural slope of the terrain where the slope changes to 25 percent or greater with a drop in surface height greater than ten feet below the invert elevation of horizontal drainpipe, except as allowed under the "steep slope" provisions of this Code.
e. 
Twenty feet up-gradient from any human-made or natural break in the natural slope of the terrain where the slope changes to 25 percent or greater with a drop in surface height less than ten feet below the invert elevation of the horizontal drainpipe, except as allowed under the "steep slope" provisions of this Code.
f. 
Two times the depth of the gravel below the invert of the drainpipe or ten feet, whichever is greater, from any portion of a subsurface drain.
g. 
Two times the depth of the gravel below the invert of the drainpipe or six feet, whichever is greater, from any existing or decommissioned subsurface disposal field.
h. 
Ten feet from any property line.
i. 
Ten feet from any building foundation.
Exception: Piles extending below the bottom of the disposal field and supports for decks and stairs.
j. 
Ten feet from any water main or water service line.
k. 
Five feet from any septic tank, STEP tank, lift station, or pump vault.
Exception: Refer to section 15.65.355H.1 for reduced horizontal separation distances for AWWTS.
2. 
Vertical separation distances. A subsurface disposal field shall not be located:
a. 
Where the water table during any season of the year is within four feet of the bottom of the absorption area.
b. 
Where there is bedrock or an impermeable soil layer within six feet of the bottom of the absorption area.
Exception: Refer to section 15.65.355H.2 for reduced vertical separation distances for AWWTS.
3. 
Slope requirements.
a. 
Maximum allowable slope for deep trench and wide trench disposal fields. A deep trench or wide trench disposal field shall not be located on a slope greater than 25 percent, unless allowed otherwise under the "steep slope" provisions of this section, or the department is satisfied that the system can function effectively. The department shall base its decision upon the report of an engineer or on relevant test results, publications, engineering data, or similar materials.
b. 
Maximum allowable slope for bed disposal fields. A bed disposal field shall not be installed where the slope of the natural ground surface is greater than ten percent.
c. 
Topographic depressions. A subsurface disposal field shall not be constructed in a natural or human-made depression where surface water can pond.
4. 
Steep slope disposal fields. Except as modified by this subsection, steep slope disposal fields shall comply with this chapter.
a. 
General. A deep trench or non-mounded wide trench disposal field may be installed on a slope greater than 25 percent, but less than 46 percent, if it complies with all of the following conditions:
i. 
Vertical separation distances below the disposal field shall be measured from the bottom of the drainrock at the up-gradient side of the disposal field.
ii. 
Trenches shall not exceed 60 inches in width.
iii. 
Natural vegetation within 50 feet down-gradient of the disposal field shall remain undisturbed, or the exposed slope shall be stabilized with erosion control vegetation or an approved equal prior to final operational approval.
iv. 
The distribution pipe invert shall be a minimum of 36 inches below the top of the natural organic surface, measured on the downhill side of the trench.
Exception: For wide trench disposal fields, with a maximum effective depth of six inches, the distribution pipe invert may be less than 36 inches below the top of the natural organic layer, measured on the downhill side of the excavation, if either of the following conditions are met:
(A) 
Filter sand is placed below the disposal field to the deeper of the following:
(1) 
Thirty-six inches below the top of the native organic layer.
(2) 
To the top of the soil layer used for absorption.
(B) 
An engineer's evaluation demonstrates, to the satisfaction of the department, that the proposed distribution pipe elevation would not result in daylighting effluent down-gradient of the disposal field. The report shall include all pertinent geological, geotechnical, and hydraulic information necessary to justify the requested separation distance.
v. 
The disposal field shall be a minimum of 100 feet up-gradient from any slope exceeding 46 percent.
Exception: Less than 100 feet separation may be allowed if an engineer's evaluation demonstrates, to the satisfaction of the department, that such an encroachment would not result in daylighting effluent down-gradient of the disposal field. The report shall include all pertinent geological, geotechnical, and hydraulic information necessary to justify the requested separation distance.
b. 
Thirty minute-per-inch (mpi) to 60 mpi soils.
i. 
The hydraulic loading rate shall be no greater than 50 percent of the required rate for disposal fields located on slopes less than 25 percent.
ii. 
Parallel disposal fields up-gradient or down-gradient from each other, that could be put into service or operation at the same time shall be separated by at least 30 feet.
iii. 
The disposal field shall be time dosed and the flow shall be uniformly distributed over the trench. For gravity distribution, flow shall be equally distributed to trench segments not to exceed 20 feet in length.
c. 
Sixty mpi to 120 mpi soils.
i. 
The hydraulic loading rate shall be no greater than 50 percent of the required rate for disposal fields located on slopes less than 25 percent.
ii. 
Parallel disposal fields up-gradient or down-gradient from each other, that could be put into service or operation at the same time shall be separated by at least 50 feet.
iii. 
A Category II or III AWWTS with timed dosing and pressure distribution shall be required.
5. 
Driveways and parking areas. Disposal fields, areas reserved for replacement disposal fields, and connecting pipes shall not be located under driveways, parking areas, or structures.
Exceptions:
a. 
Disposal fields and connecting pipes located under driveways, parking areas, or structures may be allowed if an engineer's evaluation demonstrates, to the satisfaction of the department, that the septic system will function in compliance with code requirements for freeze protection, structural stability and access to cleanout/inspection pipes.
b. 
Areas reserved for replacement disposal fields may serve as parking areas until such time as the field becomes operational.
C. 
Soil evaluation, percolation test, and groundwater monitoring. A soil evaluation, percolation test, and groundwater monitoring is required by this chapter.
Exception: A soil evaluation, percolation test, and groundwater monitoring, as required by the code for the subject disposal field, may not be required if an engineer can demonstrate by means of existing documentation, to the satisfaction of the department, that the subject disposal field location is likely to have soils consistent with the surrounding area.
1. 
Format of soil test results. The results of soil tests shall be submitted on a form provided by the department, or a similar document that is acceptable to the department, and shall bear the signed and dated seal of the engineer.
2. 
Soil classification. During the excavation, an evaluation and classification of the existent soils and soil strata shall be made and recorded. Classification shall be made using the Unified Soil Classification System (USCS) through visual/physical means or via sieve analysis.
3. 
Strata to be tested. Soil and percolation tests shall be conducted for each soil stratum that will be used for the absorption of wastewater in the subsurface disposal field. If more than one soil stratum is used, the absorption area shall be sized either on the basis of the least permeable stratum proposed for use, or on the area-weighted average application rate of the soil strata proposed for use.
Exception: Soil layers confirmed by sieve analysis gradation as GW, GP, SW, or SP (as defined by the USCS) shall be assigned a percolation rate of less than one minute per inch.
4. 
Range of applicability of percolation tests. A percolation test shall have a range of applicability of 30 feet. Test location(s) shall be shown on the site plan. If the test is within ten feet of the groundwater monitoring tube, the tube may be used as the test location to meet this requirement. The engineer shall obtain sufficient percolation tests to demonstrate that the required subsurface disposal area exists.
5. 
Percolation test procedure. The test shall conform to the following procedure:
a. 
Preparation of the percolation test hole. The diameter of each percolation test hole shall be approximately six inches, dug or bored into the proposed receiving soils. To expose a natural soil surface, the sides of the hole shall be scarified with a sharp pointed instrument and the loose material removed from the bottom of the test hole. Two inches of ½- to ¾-inch washed gravel is then placed in the hole to protect the bottom from scouring action when the water is added. A section of four inch diameter perforated PVC pipe shall be placed vertically in the test hole with ½- to ¾-inch washed gravel placed in the annular space between the sides of the PVC pipe and the edges of the six inch test hole.
b. 
Soaking period. If the initial 30 minute reading has a drop of less than ½ inch, pre-soaking is required as follows: The hole is carefully filled with clear water to a depth of at least six inches above the washed gravel on the bottom of the hole. This depth of water shall be maintained for at least four hours and overnight if deemed necessary by the department.
c. 
Percolation test. At the completion of the pre-soaking period (if required) any soil that sloughed into the hole during the soaking period shall be removed and the water level adjusted to six inches above the gravel (eight inches above the bottom of the hole). At no time during the test is the water level allowed to rise more than six inches above the gravel. Immediately after adjustment, the water level is measured from a fixed reference point to the nearest 1/16inch at 30-minute intervals. At least three measurements shall be taken. If in the first 30-minute period, the water seeps away completely, ten minute intervals for at least one hour may be used. After each measurement, the water level is readjusted to the six-inch level. The test shall be continued until two successive water level drops do not vary by more than 1/16inch. All readings shall be recorded on the soils log. The final water level drop measurement shall be used to calculate the percolation rate.
d. 
Calculation of the percolation rate. The percolation rate is calculated for each test hole by dividing the time interval used between measurements by the magnitude of the last water level drop. This calculation results in a percolation rate in terms of minutes per inch (min/in or mpi).
6. 
Groundwater monitoring. A test to determine the depth of the groundwater shall be made no more than 30 feet from a portion of the proposed or existing subsurface disposal field. The bottom of the test hole shall be at least six feet below the bottom of the proposed or existing subsurface disposal field. If the groundwater monitoring tube is located less than five feet from the drainfield, it shall be removed at the time of drainfield construction in order to not create a conduit to the groundwater.
a. 
Groundwater monitoring procedure. A perforated plastic pipe or similar device shall be installed and the test hole backfilled and mounded to slope away from the pipe so as to prevent entry of surface runoff. The water level in the pipe shall be measured at least seven days after installation to determine the water table depth below the surface. Groundwater monitor test pipes shall remain in place and functional until construction of the disposal field has begun.
b. 
Adjustments for seasonal groundwater variation. When initial groundwater monitoring identifies the depth of the groundwater table at six feet or less, or when available historic data indicates the highest seasonal groundwater level may be within four feet of the bottom of the proposed subsurface disposal system, the department may require monitoring of the water level at least once during one of two high ground water periods of the year. Designated high ground water periods are May and October unless otherwise determined by the department. The groundwater elevation shall be based on seven-day ground water monitoring test results taken within 30 feet of the proposed disposal field, adjusted up to account for seasonal fluctuations using one of the following:
i. 
Documented seasonal fluctuations within 200 feet of the proposed disposal field.
ii. 
For locations where the seasonal fluctuation is not documented, seven day ground water monitoring shall be adjusted to seasonal high in accordance with Table 1:
Table 1. Groundwater Adjustment Factors
Month groundwater elevation monitored
Measured groundwater elevation required to be adjusted up by (ft.)
January
2
February
2
March
2
April
1
May
0
June
1
July
2
August
2
September
1
October
0
November
1
December
2
D. 
Disposal field design.
1. 
Receiving soil characteristics:
a. 
Unsaturated receiving soil. A subsurface disposal field shall be installed on or in a native unsaturated accepting soil stratum that is a minimum of two feet thick.
Exception: Disposal fields designed using ERS in accordance with section 15.65.210D.3.c.
b. 
Minimum percolation rate. A subsurface disposal field for a conventional absorption system shall not be installed unless a percolation test of the native soil or ERS demonstrates that the percolation rate is less than, or equal to, 60 minutes per inch.
c. 
Maximum percolation rate. A subsurface disposal field shall not be installed in accepting soil stratum that has a soil classification of GW or GP, as defined by the USCS, and has a percolation rate faster than one minute per inch without installing a filtration layer in accordance with section 15.65.210D.3.b.
Exception: On a case-by-case basis the MOA will waive the need for a sand filter if there is adequate information in nearby drilling logs to establish that the geological profile in the area is such that there are other protective soil layers, other than those identified in the test hole, which will protect the underlying aquifer/s. Waiving of the sand filter requirement will be at the sole discretion of the department.
2. 
Disposal field design criteria. Disposal fields shall be designed to accept 150 gallons of wastewater per bedroom per day. The minimum effective absorption area of a disposal field shall be calculated using the wastewater application rate corresponding to the percolation rate provided in chapter 15.65 Table 2.
Exception: At the sole discretion of the director, the design flow requirement can be modified on a case-by-case basis if adequate information is provided by the engineer to document that the home is equipped with water saving devices such as composting toilets, low flush toilets, flow restricted faucets and/or shower head, "green" appliances (dishwater and/or washing machines), or water recycling (i.e. shower water used for toilets or in-house horticulture).
a. 
Deep trenches and seepage pits. The effective absorption area is the area of the sidewalls below the invert of the horizontal drainpipe or seepage pit inlet.
b. 
Wide trenches. The effective absorption area is the bottom area of the disposal field plus the area of sidewalls that is more than six inches below the invert of the horizontal drainpipe.
The required length for wide trench disposal fields with more than six inches of gravel below the drainpipe invert shall be calculated by multiplying the length required for a disposal field with only six inches of gravel by the appropriate factor derived from the following formula. W is the width of the drainfield and D is the depth of the gravel in feet below the drainpipe.
Factor = (W+2)/(W+1+2D)
c. 
Beds. The effective absorption area is the bottom area of the disposal field.
The width of a bed shall not exceed 15 feet without approval from the department.
The perforated drainpipes used in a bed shall be no more than six feet apart. The distance between the outermost drainpipe and the edge of the bed shall be no more than three feet.
d. 
Mounds. In designing a mounded bed or mounded wide trench type disposal system, sufficient filter sand as specified in section 15.65.210D.3.b shall be placed on top of the accepting stratum of native soil or ERS to create a combined total separation from the water table, bedrock, or impermeable soil which equals or exceeds the vertical separation distances established in this chapter.
Table 2. Wastewater Application Rates for Conventional Subsurface Disposal Fields
Percolation Rate
(minutes/inch)
Pit, Deep Trench or Wide Trench
(gpd/square foot)
Bed
(gpd/square foot)
0—1 USCS1 Sand
1.2
0.8
0—1 USCS1 Gravel
Not Suitable2
Not Suitable2
1—5
1.2
0.8
6—15
0.8
0.5
16—30
0.6
0.4
31—60
0.454
0.3
Greater than 60
Not suitable3
Not suitable3
Filter layer
1.0
0.7
Footnotes:
1.
USCS Soil Classifications shall be determined by a sieve analysis.
2.
Suitable with the installation of a two foot deep sand filter layer constructed in accordance with section 15.65.210D.3.b, or documentation that the receiving soil is not USCS classified as a GW or GP soil; or as otherwise waived within this chapter.
3.
Suitable for Category II and III advanced wastewater treatment systems constructed in accordance with chapter 15.65 Part III.
4.
A seepage pit shall not be used in soils with a percolation rate slower than 30 minutes per inch.
3. 
Specifications for imported granular material:
a. 
Drainrock. Coarse, washed aggregate placed in a disposal field excavation to provide retention and distribution of treated effluent before it passes into native soil or ERS. The washed aggregate shall measure 0.5 to 2.0 inches in diameter with no more than one percent passing the number 200 sieve screen (0.074 millimeter diameter openings).
b. 
Filter sand. Filter sand used in wastewater disposal fields shall meet the gradation requirements in Table 3.
Table 3. Filter Sand Gradation
Sieve Designation
% Passing by Weight
⅜"
100%
#4
95% to 100%
#100
0% to 4%
Effective grain size (D10)1 : #18 - #60 sieve
 
Uniformity Coefficient (D60/D10)2: less than 4
 
Footnotes:
1.
D10 - The maximum diameter of the smallest ten percent by weight of filter material particles.
2.
D60 - The maximum diameter of the smallest 60 percent by weight of the filter material particles.
c. 
Engineered receiving soil (ERS). ERS may be used to convey disposal field effluent vertically or horizontally. ERS may be used to satisfy separation distance requirements from a disposal field to groundwater, impermeable soil, and bedrock. ERS may be used to convey disposal field effluent vertically to a lower soil stratum with better percolation characteristics. ERS shall meet all of the following requirements:
i. 
A native accepting soil stratum shall be a minimum of two feet thick and be present on all sides of the ERS. If deemed necessary by the department, two supplemental test holes shall be excavated at 20 feet and 40 feet down-gradient from the proposed ERS to confirm continuity of the accepting stratum.
ii. 
Vertical conveyance. Vertical conveyance may be used when the bottom of the ERS is used to convey effluent.
iii. 
Horizontal conveyance. Horizontal conveyance shall use the sides of the ERS to convey effluent to an unsaturated accepting soil stratum (which includes organic soils). The top one foot of the absorption area, measured from original grade, shall not be used to distribute effluent.
iv. 
Fill, including ERS, shall not be installed on top of organic soils.
v. 
ERS shall be MASS Type II classified material, or Type II-A classified material, or filter sand material in accordance with section 15.65.210D.3.b or other material approved by the department.
vi. 
A two-foot thick layer of filter sand in accordance with section 15.65.210D.3.b shall be placed directly beneath disposal fields and above ERS.
vii. 
The absorption area used to convey effluent between the ERS and accepting soil stratum shall be based on in-situ percolation test data (for unsaturated soils), or laboratory analysis of a sample demonstrating its classification to be USCS GP, GW, SP or SW (for saturated soils).
viii. 
ERS shall be installed in 12-inch maximum lifts. Each lift shall be compacted to create a stable base for the absorption system.
ix. 
ERS surfaces above the natural grade require all of the following:
(A) 
Side slopes no steeper than a ratio of three horizontal to one vertical, unless approved otherwise by this department.
(B) 
A minimum of four inches of topsoil cover.
(C) 
To be seeded to produce vegetation.
x. 
Wastewater disposal systems utilizing ERS shall be Category III nitrate reducing systems.
xi. 
All ERS designs shall include an engineer's statement and supporting documentation regarding probable impacts to drinking water aquifers serving the subject and adjacent properties.
E. 
Disposal field construction requirements. Layout and construction of subsurface disposal fields shall be accomplished in accordance with the following standards:
1. 
Disposal field layout:
a. 
Maximum segment length. Single segments of subsurface disposal fields shall not exceed 100 feet in length.
b. 
Disposal field orientation. The long axis of a disposal field shall follow the contours of the original ground.
c. 
Separation between fields. The horizontal separation distance between the closest edges of working or decommissioned subsurface disposal fields, or segments of subsurface disposal fields, shall be at least twice the depth of the drainrock below the level of the drainpipe, but not less than six feet.
2. 
Excavation requirements:
a. 
Levelness. The bottom of a trench shall be level within four inches. The bottom of a wide trench or bed disposal field shall be level within two inches before placement of drainrock.
b. 
Material used for leveling. Imported material used for the purpose of leveling the bottom of a disposal field shall be filter sand meeting the minimum requirements of chapter 15.65 Table 3.
c. 
Requirement to scarify any smeared soil. After excavation has exposed the designated infiltrative surface, any native soil that is smeared shall be scarified to improve its porosity before placement of drainrock.
3. 
Pipe. Pipe used in gravity disposal systems shall be four inches in diameter.
4. 
Pipe bedding. Perforated distribution pipe used in a subsurface disposal field shall be laid level and bedded with drainrock extending a minimum of two inches above the top of the distribution pipe, and level across the entire width of the drainfield.
5. 
Cleanouts. Non-pressurized subsurface disposal field piping shall have a four inch diameter cleanout connected to both ends of each perforated segment. Cleanouts within 20 feet and in line with the double cleanout downstream of the septic tank may be omitted.
6. 
Monitor tubes. At least one four-inch diameter monitoring tube shall be installed in each separate disposal field segment to allow measurement of the fluid level in the disposal field. Monitor tubes shall not be connected to the distribution pipe network. The portion of a monitor tube extending down from the level of the horizontal distribution pipes to the bottom of the drainrock shall be perforated. The portion of the monitor tube above the horizontal distribution pipes shall be non-perforated. Monitor tubes shall be located at all angle points of disposal fields to mark the location of the absorption system. Pressurized trench disposal fields that do not have cleanout pipes shall have a monitor tube within one foot of each end of individual trench segments. Pressurized bed disposal fields that do not have cleanout pipes shall have a monitoring tube within one foot of each corner of the bed.
7. 
Silt barrier. An approved permeable geotextile silt barrier shall be installed covering the entire top surface of the drainrock prior to backfill.
8. 
Disposal field cover. The disposal field cover shall be a minimum of two feet deep, over the top of the drainrock. If the disposal field cover is less than three feet, the disposal field shall be insulated with two inches of approved rigid board insulation. Minimum soil cover over the insulation shall be one foot.
9. 
Finish grade mounding and side slopes. The finished grade over a subsurface disposal field shall be mounded a minimum of six inches above adjacent ground to prevent the formation of a depression after the backfill has settled. The side slope of any backfill mounded above grade level shall not be steeper than 33 percent, unless the engineer provides documentation that mitigation was taken to ensure slope stability and protection from future erosion.
10. 
Topsoil and seeding. The upper four inches of a mounded disposal field shall consist of topsoil and the mound shall be seeded as typically performed within the industry to ensure vegetation.
11. 
Standpipe height. Upon completion of construction all cleanouts and monitor tubes shall be above final grade, water tight, and located by swing-tie measurements to allow year-round location and access.
12. 
Construction procedures during freezing weather. From October 15 to April 15, subsurface construction during freezing weather shall be either of the following:
a. 
Opened and closed on the same day.
b. 
Covered, sealed and heated to prevent freezing.
(AO No. 2017-129, § 3, 1-23-2018)
A. 
Holding tanks are not allowed.
Exception: A holding tank may be used under any of the following conditions:
1. 
Public sewer will be available within one year and the use of the holding tank is terminated within one year of the date public sewer is available in accordance with section 15.65.040.
2. 
An engineer certifies it is necessary as a remedial measure where an existing on-site wastewater disposal system malfunctions and cannot be repaired, rejuvenated, or replaced to bring the system in compliance with this chapter.
3. 
It is used as a temporary, seasonal measure to allow for repairs of the existing system.
B. 
Capacity. The capacity of a holding tank shall not be less than 2,000 gallons and shall be increased by 500 gallons for each bedroom over three.
C. 
Manufacturing requirements. A holding tank shall be manufactured in accordance with a design approved by the department.
D. 
Holding tank location.
1. 
Separation distances. Separation requirements shall be as required for septic tanks; refer to section 15.65.205B.1.
2. 
Pumping access. A holding tank shall be installed only in an area that will continue to be readily accessible to a pump truck.
3. 
Driveway or parking area. A holding tank shall not be buried under a driveway or parking area, unless the engineer provides a design, including calculations, demonstrating its structural and thermal integrity.
E. 
Cover requirements. A holding tank shall be buried a minimum of two feet. If the tank is buried at a depth of less than four feet, the tank shall be insulated with a minimum of two inches of insulation placed immediately above the top of the tank.
F. 
Buoyancy forces. A holding tank subject to buoyancy forces shall be anchored or ballasted as required to prevent flotation regardless of the liquid level in the tank.
G. 
Required cleanouts. A holding tank, including the conveyance piping leading to the tank, shall have all of the following:
1. 
A six-inch diameter tank standpipe with an airtight cap to provide pumping access. The standpipe shall extend at least 12 inches above the surface of the ground.
2. 
A cleanout installed one to four feet from the building foundation. If it is not practical to install a cleanout near the foundation because of an existing building, driveway, parking area, utilities, or other structure, one set of opposing cleanouts shall be installed on the upstream side of the tank within ten feet of the inlet.
H. 
Manhole. A holding tank shall have a watertight manhole to provide access to the interior of the tank. The manhole shall be at least 20 inches in diameter.
I. 
Alarm. A holding tank shall be equipped with an approved high water level alarm located inside the dwelling or attached garage which registers both visually and audibly. The alarm control shall be positioned to allow at least 150 gallons per bedroom of additional storage but not less than 300 gallons after the alarm has been activated.
Exception: The interior alarm is not required if the holding tank is equipped with a remote monitoring system that will notify the owner or a maintenance provider of an alarm condition.
J. 
Maintenance and operations. The department may require pumping contracts, operating plans, financial arrangements and other reasonable conditions to ensure that the holding tank is maintained and operated in accordance with this Code.
K. 
Holding tank decommissioning. Decommissioning shall be in accordance with the current adopted version of the Uniform Plumbing Code.
(AO No. 2017-129, § 3, 1-23-2018)
A. 
System design. When a STEP tank, lift station, or pump vault is required, the system shall be designed by an engineer and have the approval of the department. A design bearing the signed and dated seal of the engineer shall be submitted to the department for approval before a permit will be issued. The design shall meet the standards contained in this chapter.
B. 
Manufacturing requirements. A STEP tank, lift station, or pump vault shall be manufactured in accordance with a design approved by the department.
C. 
Tank capacity. A STEP tank shall have a minimum of 250 gallons more capacity than would be required for a standard septic tank.
D. 
Separation distances. Separation requirements shall be as required for septic tanks; refer to section 15.65.205B.1.
E. 
Pumping access. A STEP tank, lift station, or pump vault shall be installed in an area readily accessible for pumping.
F. 
Cover and insulation. A STEP tank with two to four feet of cover shall be insulated with a minimum of two inches of approved insulation placed immediately above the top of the tank. A STEP tank with less than two feet of cover shall be insulated in accordance with an engineering report demonstrating protection from freezing and specifying the insulation requirements. A lift station or pump vault shall be insulated and protected from freezing.
G. 
Alarm. A STEP tank, lift station, or pump vault shall have an approved high water alarm located inside the dwelling or attached garage which registers both visually and audibly. The alarm system shall be on a separate electrical circuit from the pump controls. There shall be at least 150 gallons of storage capacity remaining when the alarm activates.
Exception: The interior alarm is not required if the control panel is equipped with a remote monitoring system that will notify the owner or a maintenance provider of an alarm condition.
H. 
Buoyancy forces. STEP tanks, lift stations, and pump vaults subject to buoyancy forces shall be anchored or ballasted as required to prevent flotation regardless of the liquid level in the tank or vault.
I. 
Driveway or parking area. A STEP tank, lift station, or pump vault shall not be buried under a driveway or parking area, unless the engineer provides a design, including calculations, demonstrating its structural and thermal integrity.
J. 
STEP tank, lift station, and pump vault decommissioning. Decommissioning shall be in accordance with the current adopted version of the Uniform Plumbing Code, similar to requirements for septic tanks.
K. 
AWWT Systems. Refer to section 15.65.355 for additional requirements for STEP tanks, lift stations, or pump vaults associated with AWWTS's.
(AO No. 2017-129, § 3, 1-23-2018)
A. 
An earth privy shall not be used where a potable water supply or water storage system is available.
B. 
Earth privies shall be constructed in a manner approved by the department.
C. 
An earth privy shall be located a minimum distance of:
1. 
Thirty feet from any property line.
2. 
Twenty feet from any building or structure foundation.
3. 
Ten feet from any abandoned privy or subsurface disposal field.
4. 
Fifty feet uphill from any slope of 25 percent or greater.
5. 
One hundred feet uphill or 30 feet downhill from a curtain drain. Any lesser separation distance shall be justified in an engineer's report based on soils permeability, hydraulic gradient and effluent quality.
6. 
One hundred feet from any surface water, measured along the path which overflowing wastewater would travel.
7. 
One hundred feet from a private well.
8. 
Separation distances required by 18 AAC 80 from public water systems.
D. 
An earth privy shall not be constructed, installed, or operated if any of the following apply:
1. 
Where the groundwater during any season of the year will be within four feet of the bottom of the privy.
2. 
Where there is bedrock or any impermeable barrier within six feet of the bottom of the privy.
3. 
Where there is inadequate surface drainage away from the privy.
E. 
Abandoned earth privies shall be backfilled with mineral soil and mounded to 12 inches above the original ground level.
(AO No. 2017-129, § 3, 1-23-2018)
A. 
A vault privy shall not be used where a potable water supply or water storage system is available.
B. 
The vault shall be water tight and constructed in a manner approved by the department.
C. 
The vault shall be maintained in a sanitary condition, and the vault contents shall be removed and disposed of in a manner approved by the department.
D. 
A vault privy shall be located a minimum distance of:
1. 
Ten feet from any property line or building foundation.
2. 
Ten feet from any water main or service line.
3. 
One hundred feet from surface water, measured along the path which overflowing wastewater would travel.
4. 
One hundred feet from a private well.
5. 
Separation distances required by 18 AAC 80 from public water systems.
E. 
A vault privy subject to buoyancy forces shall be anchored or ballasted as required to prevent flotation regardless of the liquid level in the vault.
(AO No. 2017-129, § 3, 1-23-2018)
A. 
The property owner shall be responsible for maintenance of the on-site wastewater system so as to comply with the intent of this chapter and for the abatement of any public health or safety hazard arising from its operation or malfunction.
B. 
Septic tanks, lift stations, and pump vaults shall be maintained to meet or exceed all of the following requirements:
1. 
Septic tanks and STEP tanks shall be inspected to determine the need for pumping and cleaning at least once each year unless it has been pumped within the preceding two-year time period.
2. 
Inspection shall be by an engineer or by a person certified to perform that work under section 15.65.025B.
3. 
The septic tank shall be pumped and cleaned within seven days of the inspection if two inches or more of floating scum, or 24 inches or more of sludge, is present in the first compartment of the septic tank.
4. 
The pumping systems for STEP tanks, lift stations, and pump vaults shall be inspected and serviced at least once every two years. Service shall, as a minimum, include all of the following:
a. 
Remove and clean the pump basket and effluent filter.
b. 
Clean all float controls and other components so as to ensure they are free of grease and other debris that could impair system performance.
c. 
Ensure all control floats are in compliance with the manufacturer's MOA approved settings.
d. 
Ensure the alarm system is functional.
e. 
Ensure the alarm is both audible and visual inside the residence.
f. 
Inspect the manhole riser to tank connection and all manhole riser pipe penetrations for groundwater intrusion.
g. 
Ensure the outlet (pressure) piping weep hole (if required) is functional so as to protect the piping from freezing.
h. 
Ensure the manhole lid is functional, insulated, and properly secured.
i. 
Perform all other inspections and maintenance recommended by the manufacturer.
(AO No. 2017-129, § 3, 1-23-2018)