Current through Register Vol. 30, No. 38, September 20, 2024
A. A
4.06 General Permit allows for the use of a natural seal evapotranspiration bed
with less than 3000 gallons per day design flow 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 "natural seal evapotranspiration bed" means a disposal technology
characterized by a bed of sand or other media with an internal wastewater
distribution system, contained on the bottom and sidewalls by an engineered
liner consisting of natural soil and clay materials.
2. An applicant may use a natural seal
evapotranspiration bed if site conditions restrict soil infiltration or require
reduction of the volume of wastewater discharged to the native soil underlying
the natural seal liner.
B. Restrictions. Unless a person provides
design documentation to show that a natural seal evapotranspiration bed will
properly function, the person shall not install this technology if:
1. Average minimum temperature in any month
is 20° F or less,
2. Over 1/3
of the average annual precipitation falls in a 30-day period, or
3. Design flow exceeds net
evaporation.
C.
Performance. An applicant shall ensure that a natural seal evapotranspiration
bed:
1. Minimizes discharge to the native soil
through the natural seal liner,
2.
Maximizes wastewater disposed to the atmosphere by evapotranspiration,
and
3. Prevents ponding of
wastewater on the bed surface and maintains an interval of unsaturated media
directly beneath the bed surface.
D. 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:
1. Capillary rise
potential test results for the media used to fill the evapotranspiration bed,
unless sand meeting a D50 of 0.1 millimeter (50 percent
by weight of grains equal to or smaller than 0.1 millimeter) is used;
and
2. Water mass balance
calculations used to size the evapotranspiration bed.
E. Design requirements. An applicant shall:
1. Ensure that the evapotranspiration bed is
from 18 to 36 inches deep and shall calculate the bed design based on the
capillary rise of the bed media, following the "Standard Test Method for
Capillary-Moisture Relationships for Coarse- and Medium-Textured Soils by
Porous-Plate Apparatus, D2325-68 (2000)," incorporated by reference in
R18-9-E307(E), and the anticipated maximum frost depth;
2. Ensure the media is sand or other durable
material;
3. Base design area
calculations on a water mass balance for the winter months and the design
seepage rate;
4. Ensure that the
natural seal liner is a durable, low-hydraulic conductivity liner and is
accompanied by the liner performance specification and calculations for bottom
and sidewall seepage rate;
5. If a
surfacing layer is used, use topsoil, dark cinders, decomposed granite, or
similar landscaping material placed to a maximum depth of 2 inches and ensure
that:
a. If topsoil is used as a surfacing
layer for growth of landscape plants:
i. The
topsoil is a fertile, friable soil obtained from well-drained arable land;
ii. The topsoil is free of nut
grass, refuse, roots, heavy clay, clods, noxious weeds, or any other material
toxic to plant growth;
iii. The pH
of the topsoil is between 5.5 and 8.0;
iv. The plasticity index of the topsoil is
between 3 and 15; and
v. The topsoil
contains approximately 1-1/2 percent organic matter, by dry weight, either
natural or added;
b. If
landscaping material other than topsoil is used as a surfacing layer, the
material meets the following gradation:
|
Sieve Size
|
Percent Passing
|
|
1"
|
100
|
|
1/2"
|
95-100
|
|
No. 4
|
90-100
|
|
No. 10
|
70-100
|
|
No. 200
|
15-70
|
6. Use shallow-rooted, non-invasive, salt-
and drought-tolerant evergreens if vegetation is planted on the
evapotranspiration bed;
7. Install
at least two observation ports to determine the level of the liquid surface of
wastewater within the evapotranspiration bed;
8. Design the bed to pump out the saturated
zone if accumulated salts or a similar condition impairs bed performance;
and
9. Instead of the minimum
vertical separation required under
R18-9-A312(E),
ensure that the minimum vertical separation from the bottom of the natural seal
evapotranspiration bed liner to the seasonal high water table is at least 12
inches.
F. Installation
requirements. In addition to the applicable requirements in
R18-9-A313(A),
an applicant shall ensure that:
1. The liner
covers the bottom and all sidewalls of the bed and is installed on a stable
base according to the manufacturer's installation specifications;
2. If the inlet pipe passes through the
liner, the joint is tightly sealed to minimize leakage during the operational
life of the facility;
3. The liner
is leak tested under the supervision of an Arizona-registered professional
engineer to confirm the design leakage rate; and
4. A 2- to 4-inch layer of 1/2- to 1-inch
gravel or crushed stone is placed around the distribution pipes within the bed.
The applicant shall ensure that the filter cloth is placed on top of the gravel
or crushed stone to prevent sand from settling into the gravel or crushed
stone.
G. Additional
Discharge Authorization requirements. An applicant shall submit the
satisfactory results of the leakage test required under subsection (F)(3) to
the Department before the Department issues the Discharge
Authorization.
H. Operation and
maintenance requirements. In addition to the applicable requirements in
R18-9-A313(B),
the permittee shall:
1. Not allow irrigation
of an evapotranspiration bed, and
2. Protect the bed from vehicle loads and
other damaging activities.
