(a) Design
requirements. (ii) Wastewater loading rates.
(i) Location. Wastewater lagoons shall be
located more than 500 feet (152 m) from existing habitations.
(A) Facultative. The primary cells of a
facultative (non-aerated) pond system shall be limited to a maximum BOD
application of 40 lb/acre/day (44.8 kg/ha/d) at average design loading
conditions.
(B) Aerated. Aerated
lagoons shall be designed for an organic loading of less than 10 lb
BOD5/day/1,000 cu ft (160 kg/1,000
m3/d) for completely mixed systems, and less than
two lb BOD5/day/1,000 cu ft (32 kg/1,000
m3/d) for aerated non-completely mixed systems.
Aeration equipment shall be sized to maintain a minimum dissolved oxygen of two
mg/L. Completely mixed systems are mixed to provide 1/4 hp/1000 cu ft
mechanical mixing or 10 cfm/1000 cu ft of air mixing.
(C) Nonsurface water discharging ponds.
Nonsurface water discharging ponds shall be designed on the basis of a water
balance that considers evaporation and seepage. Water balance calculations
shall be submitted with the plans and specifications. The
BOD5 loading for non discharging ponds shall not exceed
14 lb/acre/day (15.7 kg/ha/d) based on the average annual
BOD5.
(ii) Detention. Facultative lagoons shall be
designed for a minimum detention time of 180 days.
The detention time in aerated lagoons shall be at least one
and one half (1 1/2) days for completely mixed primary cells, and seven (7)
days for non-completely mixed primary cells. Secondary cells shall increase the
overall detention time to thirty (30) days.
(iii) Storage. Nonsurface water discharging
lagoons shall be designed to provide sufficient storage to retain all
wastewater and rainfall during the wettest year of record during a ten (10)
year period of record. Seepage shall be controlled to maintain a minimum water
depth of two (2) feet (0.6 m) in the primary cell during the driest occurring
year of a ten (10) year period.
(iv) Inlet.
(A) Location. The inlet pipe to the primary
cell of a facultative lagoon shall be at least thirty (30) feet (9.2 m) from
any bank. It shall terminate at a point away from the outlet by a distance of
at least equal to or greater than 2/3 of the longest lagoon dimension. In
aerated systems, the influent line shall be located in the mixing zone of the
aeration equipment.
(B) Apron.
Provide a concrete apron at the inlet pipe termination with minimum dimensions
of four feet by four feet (1.2 m by 1.2 m).
(C) Influent manhole. An influent man-hole
shall be provided prior to the lagoons. The influent pipe in the influent
manhole shall be at least six (6) inches (0.15 m) above the normal operating
water level of the primary lagoons.
(D) Flow distribution. Flow distribution for
multiple primary cells shall be provided to effectively split hydraulic and
solids proportionately.
(v) Inlet and outlet structures.
(A) Location. Inlet and outlet structures
shall be easily accessible by plant operators and located to minimize short
circuiting within the cell. A level control structure shall be provided at the
outlet of each cell.
(B) Level
control. Provide controls to permit varying water levels between two (2) feet
and six (6) feet (0.6 m to 1.8 m). Provide baffling at the outlet to prevent
scum overflow. Multiple draw offs in the final cell shall be provided. At least
one (1) shall be located at the two (2) foot (0.6 m) level.
(vi) Interconnecting piping.
(A) Location. Piping between lagoon cells
shall connect to the preceding cell outlet control structure and discharge into
the subsequent cell. The pipe shall discharge at least ten (10) feet (3.05 m)
from the toe of the slope on the lagoon bottom and shall terminate on the
concrete apron that is at least four (4) feet by four (4) feet (1.2 m by 1.2
m).
(B) Elevation. The piping shall
discharge at the floor of the lagoon.
(C) Material. Interconnecting piping shall be
any acceptable pipe designed to resist low pressures and adequately protected
from corrosion.
(b) Number of lagoons cells. A lagoon system
with a total area greater than one (1) acre (0.4 ha) shall have at least three
(3) cells in series. Smaller systems and nondischarge pond systems shall have
at least two (2) cells. The maximum size cell shall be twenty (20) acres (8
ha).
(c) Lagoon configuration.
(i) Shape. Rectangular cells shall have a
maximum length to width ratio of 5:1. No sharp corners nor dead-end coves are
permitted.
(ii) Water depth.
Facultative ponds shall be designed to have water depths of not less than two
(2) feet, nor more than six (6) feet (0.61 m to 1.8 m). Aerated lagoons shall
be designed to have water depths of not less than four (4) feet nor more than
fifteen (15) feet (1.2 m to 4.6 m).
(iii) Removal of lagoon cells from operation.
Bypass piping for primary lagoon cells and aerated lagoon cells shall be
provided.
(iv) Lagoon freeboard. A
minimum freeboard of two (2) feet (0.6 m) shall be provided. Greater freeboard
shall be provided for wave runup, where required.
(d) Construction requirements.
(i) Dike.
(A) Material. Dikes and embankments shall be
of relatively impervious and stable material, and compacted to at least 95
percent of maximum density (ASTM D698-78). Embankment fill shall be free from
organic material, rock larger than six (6) inches (15.2 cm) and construction
debris. The area where the embankment is to be constructed shall be stripped of
vegetation and roots.
(B) Top
width. Dikes and embankments shall be constructed with minimum top width of
eight (8) feet (2.4 m).
(C) Slopes.
Interior slopes shall be from three (3) to four (4) horizontal to one vertical,
and shall be stable under varying water level conditions. Interior slopes that
are surfaced with concrete paving or riprap may be constructed at slopes of two
(2) or more horizontal to one (1) vertical. Exterior slopes shall be three (3)
or more horizontal to one (1) vertical and shall prevent the entrance of
surface water to the lagoon.
(ii) Seeding. Exterior slopes and interior
slopes that are not riprapped shall be seeded with dryland grasses, unless
another equivalent method for soil erosion control is provided.
(iii) Erosion control. Interior embankments
except cells smaller than one (1) acre shall be protected from wave action with
riprap, paving, or other erosion resistant material, unless it is demonstrated
that the ponds are sheltered from wind or where wind velocity is low and
erosion will not occur.
(e) Lagoon sealing.
(i) Lagoon sealing. The seepage through the
pond bottom and side walls shall not cause a violation of the groundwater
standards as described in Chapter 8 (Quality Standards for Wyoming
Groundwaters) of the Wyoming Department of Environmental Quality, Water Quality
Rules and Regulations. Liners shall be required if the wastewater
characteristics or site conditions will not insure the protection of the
groundwater for which it is classified.
If the applicant cannot document that the facility poses no
threat to groundwater and elects not to perform a subsurface study in
accordance with Chapter 3, Section 17(a) and (b), then the groundwater shall be
protected from contamination by the wastewater with a liner equivalent to three
(3) feet (1 m) of soil having a permeability of
10-7cm/sec or less. When an applicant performs a
subsurface study, the requirements for the liner shall be determined based on
the results of the study and the groundwater protection required. In no
instance shall the maximum seepage rate exceed 1/8 inch per day (3.2 mm/day) in
the primary pond(s).
Following construction of the lagoons, but prior to
startup, a testing program shall be conducted to demonstrate the effectiveness
of the sealing program. Should the testing program show the lagoon seal to be
less effective than the above requirements, the seal shall be modified and
retested until it succeeds.
(ii) Synthetic liners.
(A) Material. Synthetic liners shall be
essentially impervious. The minimum lining thickness shall be 30 mils. The
liner material shall be resistant to organic materials typical of sewage. The
liner shall be resistant to sunlight or shall be covered with 12 inches (30.5
cm) or more of soil at all locations including the lagoon bottom and side
slopes.
(B) Liner stabilization.
Where the seasonal high groundwater is above the bottom of the lagoon, the
liner shall be stabilized to prevent it from rising.
(C) Appurtenances. A leak detection system
and/or air release mechanism may be required.
(f) Aerated systems.
(i) Air requirements. Aerated ponds shall be
designed to maintain 2 mg/L of dissolved oxygen or more throughout the pond
contents.
(ii) Equipment
requirements.
(A) Number. Surface aerators
shall be provided at intervals of 200 feet (61 m) or less. The lagoon shall be
protected from erosion from the aeration equipment. At least two surface
aerators or brush aerators shall be provided. With the largest unit out, the
remaining units shall be capable of transferring the average day oxygen demand.
Each diffused aeration system shall be provided with at least two blowers. With
the largest blower out of service, the remainder shall be capable of supplying
the design air flow rate.
(B)
Removal. All equipment shall be accessible and removable from the edge of the
lagoons. Provisions for dewatering shall be made for removal or repair of
diffusers.