Current through August 31, 2023
01.
General. (3-31-22)
a. These rules
pertain to all new and existing municipal wastewater lagoons, including
discharging or non-discharging lagoons, municipal wastewater treatment lagoons,
municipal wastewater storage lagoons, and any other municipal wastewater
lagoons that, if leaking, have the potential to degrade waters of the state.
Lagoons are also sometimes referred to as ponds. Section
493 does not apply to industrial
lagoons or mining tailings ponds, single-family dwellings utilizing a single
lagoon, two (2) cell infiltrative system, those animal waste lagoons excluded
from review under Section
39-118, Idaho Code, or storm water
ponds. (3-31-22)
b. Lagoons
utilized for equalization, percolation, evaporation, and sludge storage do not
have to meet the requirements set forth in Subsections
493.05 through
493.10, but must comply with all
other applicable subsections. (3-31-22)
02.
Seepage Testing
Requirements. (3-31-22)
a. Existing
Lagoons. All existing lagoons covered under these rules shall be seepage tested
by an Idaho licensed professional engineer, an Idaho licensed professional
geologist, or by individuals under their supervision by April 15, 2012 unless
otherwise specified in a current permit issued by the Director.
(3-31-22)
b. New Lagoons. As part
of the construction process, all new lagoons must be seepage tested by an Idaho
licensed professional engineer, an Idaho licensed professional geologist, or by
individuals under their supervision prior to being put into service.
(3-31-22)
c. Subsequent Tests. All
lagoons covered under these rules must be seepage tested by an Idaho licensed
professional engineer, an Idaho licensed professional geologist, or by
individuals under their supervision every ten (10) years after the initial
testing. (3-31-22)
d. Testing Due
to Change of Conditions to Liner. Prior to being returned to service, lagoons
must be seepage tested if a change of condition to the liner occurs that may
affect its permeability, including but not limited to liner repair below the
high water line, liner replacement, lagoon dewatering of soil-lined lagoons
which results in desiccation of the soil liner, seal installation, or earthwork
affecting liner integrity. A seepage test may be required after solids removal.
Prior to performing activities that may affect liner permeability, the system
owner must contact the Department in writing to determine if a seepage test
will be required prior to returning the lagoon to service. (3-31-22)
e. Procedures for Performing a Seepage Test.
The procedure for performing a seepage test or alternative analysis must be
approved by the Department, and the test results must be submitted to the
Department. If an existing lagoon has passed a seepage test before April 15,
2012 and submitted the results to the Department, the owner of that lagoon has
ten (10) years from the date of the testing to comply with this requirement.
(3-31-22)
03.
Allowable Seepage Rates. (3-31-22)
a. Design Standard. Lagoons shall be designed
for a maximum leakage rate of five hundred (500) gallons per acre per day.
(3-31-22)
b. Operating Standard.
The leakage rate for lagoons constructed after April 15, 2007 shall be no more
than zero point one hundred twenty-five (0.125) inches (1/8 inch) per day,
which is approximately thirty-four hundred (3400) gallons per acre per day. The
leakage rate for existing lagoons constructed prior to April 15, 2007 shall be
no more than zero point twenty-five (0.25) inches (1/4 inch) per day.
(3-31-22)
c. For lagoons located
over sensitive aquifers or near 303d listed stream segments, the leakage rate
shall be no more than zero point one hundred twenty-five (0.125) inches
(one-eighth (1/8) inch) per day, which is approximately thirty-four hundred
(3400) gallons per acre per day. The operating standard may be considerably
lower based on a ground water investigation considering fate and transport of
contaminants to determine the effect of the seepage on the aquifer or stream
segment and the best capability of measurement at the time of the
investigation. (3-31-22)
04.
Requirements for Lagoons Leaking
Above the Allowable Amount. If a lagoon is found to be leaking at a rate
higher than that allowed under Subsection
493.03.b., the owner of the
lagoon, in accordance with a schedule negotiated with and approved by the
Director, is required to: (3-31-22)
a. Repair
the leak and retest for compliance; (3-31-22)
b. Re-line the lagoon and retest for
compliance; (3-31-22)
c. Drain the
lagoon in an approved manner and stop using the lagoon; or (3-31-22)
d. Determine the impact of the leaking lagoon
on the environment based on ground water sampling and modeling. The procedure
for performing ground water sampling and monitoring must be approved by the
Department. Any impact must comply with IDAPA 58.01.11, "Ground Water Quality
Rule," and IDAPA 58.01.02, "Water Quality Standards." If the impact does not
comply with IDAPA 58.01.11, "Ground Water Quality Rule," and IDAPA 58.01.02,
"Water Quality Standards," the owner of the lagoon must follow one (1) of the
steps set out in Subsections
493.04.a. through 493.04.c.
(3-31-22)
05.
Location. (3-31-22)
a. Wastewater
treatment lagoons shall be placed a minimum of two hundred (200) feet from
residential property lines. In all cases, the design location shall consider
odors, nuisances, etc. This distance is to the toe of the exterior slope of the
dike or to the top of the cut for a lagoon placed into a hillside. More
restrictive planning and zoning or other local requirements shall apply.
(3-31-22)
b. Ground Water
Separation. A minimum separation of two (2) feet between the bottom of the pond
and the maximum ground water elevation shall be maintained. (3-31-22)
c. Bedrock Separation. A minimum separation
of two (2) feet between the pond bottom and any bedrock formation shall be
maintained. (3-31-22)
06.
Basis of Design. (3-31-22)
a.
Design variables such as climatic conditions, odor, pond depth, multiple units,
detention time, and additional treatment units must be considered with respect
to applicable standards for BOD5, total suspended solids
(TSS), fecal coliform, dissolved oxygen (DO), pH, and other effluent
requirements and limits. (3-31-22)
b. The preliminary engineering report shall
include all design criteria for the development of the pond design.
(3-31-22)
c. The reaction rate
coefficient for domestic wastewater which includes some industrial wastes,
other wastes, and partially treated wastewater must be determined
experimentally for various conditions which might be encountered in the lagoons
or actual data from lagoons in similar climates. Conversion of the reaction
rate coefficient at other temperatures shall be made based on experimental
data. (3-31-22)
d. Oxygen
requirements generally will depend on the design average
BOD5 loading, the degree of treatment, and the
concentration of suspended solids to be maintained. If needed, aeration
equipment shall be capable of maintaining a minimum dissolved oxygen level of
two (2) mg/L in the ponds at all times. Suitable protection from weather shall
be provided for electrical controls. Aerated cells shall be followed by a
polishing cell with a detention time of a minimum of twenty-four (24) hours.
(3-31-22)
e. See Subsection
490.02 for details on aeration
equipment. (3-31-22)
07.
Industrial Wastes as a Part of the Municipal Wastewater. (3-31-22)
a. Consideration shall be given to the type
and effects of industrial wastes on the treatment process. (3-31-22)
b. Industrial wastes shall not be discharged
to ponds without assessment of the effects such substances may have upon the
treatment process or discharge requirements in accordance with state and
federal laws. (3-31-22)
08.
Number of Cells Required.
(3-31-22)
a. A wastewater treatment pond
system shall consist of a minimum of three (3) cells designed to facilitate
both series and parallel operations. Two (2) cell systems may be utilized in
very small installations of less than fifty thousand (50,000) gallons per day.
(3-31-22)
b. All systems shall be
designed with piping flexibility to permit isolation of any cell without
affecting the transfer and discharge capabilities of the total system.
(3-31-22)
09.
Pond
Construction Details. (3-31-22)
a.
Embankments and Dikes. (3-31-22)
i. Material.
Dikes shall be constructed of relatively impervious soil and compacted to at
least ninety-five (95) percent Standard Proctor Density to form a stable
structure. Vegetation and other unsuitable materials shall be removed from the
area where the embankment is to be placed. (3-31-22)
ii. Top Width. The minimum dike width shall
be ten (10) feet to permit access for maintenance vehicles. (3-31-22)
iii. Maximum Slopes. Inner and outer dike
slopes shall not be steeper than one (1) vertical to three (3) horizontal
(1:3). (3-31-22)
iv. Minimum
Slopes. Inner slopes should not be flatter than one (1) vertical to four (4)
horizontal (1:4). Flatter slopes can be specified for larger installations
because of wave action but have the disadvantage of added shallow areas being
conducive to emergent vegetation. Outer slopes shall be sufficient to prevent
surface runoff from entering the ponds. (3-31-22)
v. Freeboard. Minimum freeboard shall be
three (3) feet, except that for small systems of less than fifty thousand
(50,000) gallons per day, two (2) feet may be acceptable. (3-31-22)
vi. Design Depth. The minimum operating depth
shall be sufficient to prevent growth of aquatic plants and damage to the
dikes, bottom, control structures, aeration equipment, and other appurtenances.
In no case shall pond depths be less than two (2) feet.
(3-31-22)
b. Pond Bottom.
(3-31-22)
i. Soil. Soil used in constructing
the pond bottom (not including the seal) and dike cores shall be relatively
incompressible and tight and compacted to at least ninety-five (95) percent
Standard Proctor Density. (3-31-22)
ii. Seal. Ponds shall be sealed such that
seepage loss through the seal complies with Subsection
493.03. Results of a testing
program which substantiates the adequacy of the proposed seal must be
incorporated into or accompany the preliminary engineering report.
(3-31-22)
c.
Miscellaneous. (3-31-22)
i. Fencing. The pond
area shall be enclosed with an adequate fence to prevent entering of livestock
and discourage trespassing. This requirement does not apply to pond areas which
store or impound Class A municipal reclaimed effluent. (3-31-22)
ii. Access. An all-weather access road shall
be provided to the pond site to allow year-round maintenance of the facility.
(3-31-22)
iii. Warning Signs.
Appropriate permanent signs shall be provided along the fence around the pond
to designate the nature of the facility and advise against trespassing. At
least one (1) sign shall be provided on each side of the site and one (1) for
every five hundred (500) feet of its perimeter. (3-31-22)
iv. Flow Measurement. Flow measurement
requirements are provided in Subsection
450.06.e. Effective weather
protection shall be provided for the recording equipment. (3-31-22)
v. Ground Water Monitoring. A ground water
monitoring plan shall be submitted to the Department for review and approval as
a part of the preliminary engineering report. An approved system of wells or
lysimeters shall be required around the perimeter of the pond site to
facilitate ground water monitoring. (3-31-22)
10.
Closure. The owner shall
notify the Department at least six (6) months prior to permanently removing any
wastewater lagoon facility from service, including any treatment or storage
pond. Prior to commencing closure activities, the facility shall: (3-31-22)
a. Participate in a pre-closure on-site
meeting with the Department; (3-31-22)
b. Develop a site closure plan that
identifies specific closure, site characterization, or cleanup tasks with
scheduled task completion dates in accordance with agreements made at the
pre-site closure meeting; and (3-31-22)
c. Submit the completed site closure plan to
the Department for review and approval within forty-five (45) days of the
pre-site closure meeting. The facility must complete the Department approved
site closure plan. (3-31-22)