Current through Register Vol. 30, No. 38, September 20, 2024
A. A 4.09 General
Permit allows for the use of an engineered pad system 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,
an "engineered pad system" means a treatment and disposal technology
characterized by:
a. The delivery of
pretreated wastewater by gravity or pressure distribution to the engineered pad
and sand bed assembly, followed by dispersal of the wastewater into the native
soil; and
b. Wastewater movement
through the engineered pad and sand bed assembly by gravity under unsaturated
flow conditions to provide additional passive biological
treatment.
2. The
applicant may use an engineered pad system if:
a. The native soil is excessively
permeable,
b. There is little
native soil overlying fractured or excessively permeable rock, or
c. The available area is limited for
installing a disposal works authorized by R18-9-E302.
B. Performance. An applicant shall
ensure that:
1. The engineered pad system is
designed so that the treated wastewater released to the native soil meets the
following criteria:
a. TSS of 50 milligrams
per liter, 30-day arithmetic mean;
b. BOD5 of 50
milligrams per liter, 30-day arithmetic mean;
c. Total nitrogen (as nitrogen) of 53
milligrams per liter, 5-month arithmetic mean; and
d. Total coliform level of 1,000,000
(Log10 6) colony forming units per 100 milliliters, 95th
percentile; or
2. The
engineered pad system is designed to meet any other performance, loading rate,
and configuration criteria specified in the reviewed product list maintained by
the Department as required under
R18-9-A309(E).
C. Notice of Intent to Discharge. In addition
to the Notice of Intent to Discharge requirements specified in
R18-9-A301(B)
and
R18-9-A309(B),
an applicant shall submit design materials and construction specifications for
the engineered pad system.
D.
Design requirements. In addition to the applicable requirements in
R18-9-A312,
an applicant shall ensure that:
1. Gravity
and pressurized wastewater delivery is from a septic tank or intermediate
watertight chamber equipped with a pump and controls. The applicant shall
ensure that:
a. Delivered wastewater is
distributed onto the top of the engineered pad system and achieves even
distribution by good engineering practice, and
b. The dosing rate for pressurized wastewater
delivery is at least four doses per day and no more than 24 doses per
day;
2. The sand bed
consists of mineral sand washed to conform to the "Standard Specification for
Concrete Aggregates, C33-03 (2003)," which is incorporated by reference in
R18-9-E308(D)(2), unless the performance testing and design specifications of
the engineered pad manufacturer justify a substitute specification. The
applicant shall ensure that:
a. The sand bed
design provides for the placement of at least 6 inches of sand bed material
below and along the perimeter of each pad, and
b. The contact surface between the bottom of
the sand bed and the native soil is level;
3. The spacing between adjacent two-pad-wide
rows is at least two times the distance between the bottom of the distribution
pipe and the bottom of the sand bed or 5 feet, whichever is greater;
4. The wastewater distribution system
installed on the top of the engineered pad system is covered with a breathable
geotextile material and the breathable geotextile material is covered with at
least 10 inches of backfill.
a. The applicant
shall ensure that rocks and cobbles are removed from backfill cover and grade
the backfill for drainage.
b. The
applicant may place the engineered pad system above grade, partially bury it,
or fully bury it depending on site and service
circumstances;
5. The
engineered pad system is constructed with durable materials and capable of
withstanding stress from installation and operational service; and
6. At least two inspection ports are
installed in the engineered pad system to confirm unsaturated wastewater
treatment conditions at diagnostic locations.
E. Installation requirements. In addition to
the applicable requirements in
R18-9-A313(A),
an applicant shall place sand media to obtain a uniform density of 1.3 to 1.4
grams per cubic centimeter.
F.
Operation and maintenance requirements. In addition to the applicable
requirements in
R18-9-A313(B),
an applicant shall inspect the backfill cover for physical damage or erosion
and promptly repair the cover, if necessary.
