Chapter 13.30


Article I. Construction, Installation and Alteration

13.30.010    Permit required – Fee.

13.30.020    Construction and installation requirements.

13.30.030    Conformance required.

Article II. Disposition

13.30.040    Disposition.

13.30.050    Violation – Penalties.

Article I. Construction, Installation and Alteration

13.30.010 Permit required – Fee.

On and after the effective date of the ordinance codified in this article, no person, firm or corporation shall construct, install or alter an individual sewage disposal system without first having obtained a permit from the City of Mountlake Terrace; said permit to be issued on receipt of a permit fee of $5.00 payable to the City of Mountlake Terrace, to be used to help defray the costs of carrying out the provisions of these rules and regulations. (Ord. 146 § 1, 1959).

13.30.020 Construction and installation requirements.

The requirements for construction and installations of septic tank systems shall be:

A. Septic Tanks.

1. Design and Construction.

a. The septic tank shall be of durable, watertight construction not subject to excessive corrosion or decay.

b. Poured concrete tanks shall be sufficiently reinforced and all sides, top and bottom, shall be at least three inches thick.

c. Concrete block tanks shall be laid on a poured concrete floor not less than four inches thick with the walls waterproofed with cement mortar, asphalt tar emulsion or other waterproofing material approved by the health officer.

d. The liquid depth of the tank shall not be less than four feet. A liquid depth greater than six feet shall not be considered in determining the liquid capacity of the tank.

e. Standard inlet and outlet tees or baffles shall be located at opposite ends of the tank and tees shall be at least four inches inside diameter. The inlet tee or baffle shall project below the liquid level not less than nor more than six to 12 inches and the upper leg of the inlet tee shall project at least to crown of the inlet sewer. The outlet tee or baffle shall project below the liquid level not less than 15 to 18 inches and the upper leg at least four inches above the crown of the inlet sewer.

f. The invert of the inlet pipe shall be at least two inches above the outlet invert.

g. There shall be at least one inch between the under side of the top of the tank and the top inlet and outlet tee or baffle.

h. Adequate access to each compartment of the tank shall be provided by means of a manhole with a minimum width of 18 inches. Provision shall be made for direct access to inlet and outlet tees.

2. Liquid Capacity.

a. All permanent residences up to and including four bedrooms shall have septic tanks of 750 gallon liquid capacity.

b. Residences of over four bedrooms, commercial or public buildings, temporary dwellings, multiple-family units such as apartments and tourist accommodations shall have septic tanks of a size to be determined by the health officer or his authorized representative.

3. Location. Septic tanks shall be installed at distances as hereinafter prescribed.

a. Property line not less than    5 ft.

b. Any source of domestic water supply not less than    100 ft.

c. Any building not less than    5 ft.

B. Disposal Field.

1. The construction and maintenance of the subsurface disposal field shall be such that the overflow from the septic tank shall not directly drain to or discharge over or upon the surface of the ground, nor into any storm sewer, stream or bodies of surface of ground water, whether natural or artificial nor on adjacent property.

2. The size and layout of the disposal field shall be according to the requirements of the health officer or his authorized representative. In no case shall a 750-gallon septic tank have less than 150 lineal feet of four-inch field tile in 12 lengths or approved perforated pipe.

3. The disposal field shall not be placed under any type of driveway or structure where traffic is likely to cause displacement of the tile or any paved or otherwise covered or obstructed area.

4. Grading of the lot shall be completed before the disposal field is laid.

5. Disposal fields shall be installed at distances as hereinafter prescribed.

a. Any source of domestic water supply not less than    100 ft.

b. Any natural body of water not less than    25 ft.

c. Dwellings not less than    10 ft.

d. Any building not less than    5 ft.

e. Property lines not less than    5 ft.

f. Subsurface tile used for surface drainage not less than    10 ft.

g. Water lines not less than    10 ft.

6. Notwithstanding the above provisions where necessary to cross a water supply line, the disposal field line shall be impervious for a distance of 10 feet on each side of the water line.

7. Construction of disposal field in filled ground shall be prohibited unless fill material and method of compaction have been approved by the health officer or his authorized representative.

8. Trenches shall conform to the following specifications:

a. Minimum width    18 in.

b. Minimum number of lines per field    2

c. Maximum length of individual lines    100 ft.

d. Maximum depth of cover of tile lines    24 in.

e. Maximum grade of tile lines    6 in. per 100 ft.

f. Minimum grade of tile lines    2 in. per 100 ft.

g. Minimum spacing of lines    6 ft. center to center

h. Minimum filter material under tile    6 in.

i. Minimum filter material over tile    2 in.

j. Minimum space between tile    1/8 in.

k. Maximum space between tile    1/4 in.

9. Field tile shall be laid on grade boards securely staked to the bottom of the trench.

10. All open joints shall be protected at the top by strips of asphalt treated building paper or other suitable material.

11. When disposal fields are constructed in predominately sandy soil, a two- to three-inch layer of straw or a layer of untreated paper shall be provided between the top of the filter material and the earth backfill.

12. Filter material shall be clean crushed stone, gravel, slag, cinder or similar material having sufficient void. Size of material shall not be less than one-half inch nor more than two and one-half inches in diameter. Filter material shall be free of dust, sand, clay or other fine materials.

13. Where necessary to maintain proper grade and cover, a line may be terraced by the use of bell tile with cemented joints or by construction of a suitable brick or concrete drop box. Such installation shall have an earth dam 24 inches thick preceding the terrace.

C. Distribution Box.

1. A distribution box of sufficient size to accommodate the necessary field lateral lines shall be constructed at the head of each disposal field.

2. Each field lateral shall be connected separately to the distribution box and shall not be subdivided.

3. The first field tile connected to the box shall be level and two inches above the floor of the box.

4. The box inlet shall be at least one inch above the outlets. (Ord. 146 § 2, 1959).

13.30.030 Conformance required.

The installation or alteration of sewage disposal facilities must be in conformance with these regulations or any special recommendations as made by the Building Official. (Ord. 146 § 3, 1959).

Article II. Disposition

13.30.040 Disposition.

Any existing septic tank not in use for sanitary purposes shall be maintained as follows:

A. Wood or Steel Tank. All tanks constructed of a material other than concrete shall be pumped and filled with earth or a granular material.

B. Concrete Tank. Concrete tanks may be abandoned without further treatment except that any such tank used for drainage of storm or surface waters shall first be pumped and filled with a granular material. (Ord. 169 § 1, 1959).

13.30.050 Violation – Penalties.

Any violation of this article shall be deemed to be a misdemeanor, and shall be punished by a fine not to exceed $300.00 or by imprisonment not to exceed 90 days, or by both such fine and imprisonment. (Ord. 169 § 2, 1959).