Arizona Administrative Code
Title 18 - ENVIRONMENTAL QUALITY
Chapter 9 - DEPARTMENT OF ENVIRONMENTAL QUALITY - WATER POLLUTION CONTROL
Article 3 - AQUIFER PROTECTION PERMITS - GENERAL PERMITS
Part E - TYPE 4 GENERAL PERMITS
Section R18-9-E317 - 4.17 General Permit: Cap System, Less Than 3000 Gallons Per Day Design Flow

Universal Citation: AZ Admin Code R 18-9-E317

Current through Register Vol. 30, No. 38, September 20, 2024

A. A 4.17 General Permit allows for the use of a cap fill cover over a conventional trench disposal works receiving wastewater treated to a level equal to or better than that specified in R18-9-E302(B).

1. Definition. For purposes of this Section, a "cap system" means a disposal technology characterized by:
a. A soil cap, consisting of engineered fill placed over a trench that is not as deep as a trench allowed by R18-9-E302; and

b. A design that compensates for reduced trench depth by maintaining and enhancing the infiltration of wastewater into native soil through the trench side-walls.

2. An applicant may use a cap system if:
a. There is little native soil overlying fractured or excessively permeable rock, or

b. A high water table does not allow the minimum vertical separation to be met by a system authorized by R18-9-E302.

B. Performance. An applicant shall ensure that the design soil absorption rate and vertical separation complies with this Chapter for a trench, based on the following performance, unless additional pretreatment is provided:

1. TSS of 75 milligrams per liter, 30-day arithmetic mean;

2. BOD5 of 150 milligrams per liter, 30-day arithmetic mean;

3. Total nitrogen (as nitrogen) of 53 milligrams per liter, five-month arithmetic mean; and

4. Total coliform level of 100,000,000 (Log10 8) colony forming units per 100 milliliters, 95th percentile.

C. Notice of Intent to Discharge. In addition to the Notice of Intent to Discharge requirements in R18-9-A301(B) and R18-9-A309(B), an applicant shall submit specifications for the proposed cap fill material.

D. Design requirements. In addition to the applicable requirements in R18-9-A312, an applicant shall ensure that:

1. The soil texture from the natural grade to the depth of the layer or the water table that limits the soil for unsaturated wastewater flow is no finer than silty clay loam;

2. Cap fill material used is free of debris, stones, frozen clods, or ice, and is the same as or one soil group finer than that of the disposal site material, except that the applicant shall not use fill material finer than clay loam as an additive;

3. Trench construction.
a. The trench bottom is at least 12 inches below the bottom of the disposal pipe and not more than 24 inches below the natural grade, and the trench bottom and disposal pipe are level;

b. The aggregate cover over the disposal pipe is 2 inches thick and the top of the aggregate cover is level and not more than 9 inches above the natural grade;

c. The cap fill cover above the top of the aggregate cover is at least 9 inches but not more than 18 inches thick. The applicant shall ensure that:
i. The cap surface is protected to prevent erosion and sloped to route surface drainage around the ends of the trench; and

ii. If the top of the aggregate is at or below the original ground surface, the cap surface has side slopes not more than one vertical to three horizontal; or

iii. If the top of the aggregate is above the original ground surface, the horizontal extent of the finished fill edges is at least 10 feet beyond the nearest trench sidewall or end wall;

d. The criteria for trench length, bottom width and spacing, and disposal pipe size is the same as that for the trench system prescribed in R18-9-E302;

e. Permeable geotextile fabric is placed on the aggregate top, trench end, and sidewalls extending above natural grade;

f. The native soil within the disposal site and the adjacent down gradient area to a 50-foot horizontal distance does not exceed a 12 percent slope if the top of the aggregate cover extends above the natural grade at any location along the trench length. The applicant shall ensure that the slope within the disposal site and the adjacent downgradient area to a 50-foot horizontal distance does not exceed 20 percent if the top of the aggregate cover does not extend above the natural grade;

g. The fill material is compacted to a density of 90 percent of the native soil if the invert elevation of the disposal pipe is at or above the natural grade at any location along the trench length;

h. At least one observation port is installed to the bottom of each cap fill trench;

i. The effective absorption area for each trench is the sum of the trench bottom area and the sidewall area. The height of the sidewall used for calculating the sidewall area is the vertical distance between the trench bottom and the lowest point of the natural land surface along the trench length; and

j. If the applicant uses correction factors for soil absorption rate under R18-9-A312(D)(3) and minimum vertical separation under R18-9-A312(E), additional wastewater pretreatment is provided.

E. Installation requirements. In addition to the applicable requirements in R18-9-A313(A), an applicant shall prepare the disposal site when high soil moisture is not present and equipment operations do not create platy soil conditions. The applicant shall:

1. Plow or scarify the fill area to disrupt the vegetative mat while avoiding smearing,

2. Construct trenches as specified in subsection (D)(3),

3. Scarify the site and apply part of the cap fill to the fill area and blend the fill with the scarified native soil within the contact layers, and

4. Follow the construction design specified in the Construction Authorization issued under R18-9-A301(D)(1)(c).

F. Operation and maintenance requirements. In addition to the applicable requirements in R18-9-A313(B), the permittee shall inspect and repair the cap fill and other surface features as needed to ensure proper disposal function, proper drainage of surface water, and prevention of damaging loads on the cap.

Disclaimer: These regulations may not be the most recent version. Arizona may have more current or accurate information. We make no warranties or guarantees about the accuracy, completeness, or adequacy of the information contained on this site or the information linked to on the state site. Please check official sources.
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