Current through Bulletin 2024-06, March 15, 2024
10.1. Lagoon Siting
A. Distance from Habitation. A lagoon should
be sited as far as practicable, with a minimum of 1/4 mile (0.4 kilometer),
from areas developed for residential or commercial or institutional purposes or
may be developed for such purposes within a foreseeable future. Site
characteristics such as topography, prevailing wind direction, forests, etc.,
must be considered in siting the lagoon.
B. Prevailing Winds. The lagoon should be
sited where the direction of local prevailing winds is towards uninhabited
areas.
C. Surface Runoff. The
lagoon should not be sited in watersheds receiving significant amounts of
storm-water runoff. Storm-water runoff should be diverted around the lagoon and
protect lagoon embankments from erosion.
D. Hydrology and hydrogeology. Close
proximity to water supplies and other facilities subject to wastewater
contamination should be avoided in siting the lagoon. A minimum separation of
four (4) feet (1.2 meters) between the bottom of the lagoon and the maximum
ground water elevation should be maintained.
E. Geology
1. The lagoon shall not be located in areas
which may be subjected to karstification, i.e., sink holes or underground
streams generally occurring in area underlain by porous limestone or dolomite
or volcanic soil.
2. A minimum
separation of 10 feet (3.0 meters) between the lagoon bottom and any bedrock
formation is recommended.
10.2. Small Facilities. The Director will
review and approve the construction of a lagoon for a design rate of flow less
than 25,000 gallons per day (95 cubic meters per day) only if:
A. there are no other alternatives for
wastewater treatment and disposal available to the applicant;
B. there is no other appropriate technology
for wastewater treatment and disposal except lagoon; and
C. the applicant has resources to
satisfactorily operate and maintain the lagoon.
10.3. Basis of Design. Design variables such
as lagoon depth, number of units, detention time, and additional treatment
units must be based on effluent standards for BOD5,
total suspended solids (TSS), E. coli, dissolved oxygen (DO), and pH.
A. Design for Discharging and Total
Containment Lagoons
1. The design shall be
based on BOD5 loading ranging from 15 to 35 pounds per
acre per day (16.8-39.2 kilograms per hectare per day).
2. The design for total containment lagoons
shall be based on conservative estimates of precipitation, evaporation, seepage
or percolation and inflow relevant to the site. A mass diagram showing each of
the foregoing factors on a month-by-month basis, shall be prepared and
submitted with the design and plans for review.
B. Design Depth. The minimum operating depth
should be such that growth of aquatic plants is suppressed to prevent damage to
the dikes, bottom, control structures, aeration equipment and other
appurtenances.
1. Discharging or Total
Containment Lagoons. The maximum water depth shall be 6 feet (1.8 meters) in
primary cells. Greater depth in subsequent cells may be deeper than 6 feet
provided that supplemental aeration or mixing is incorporated in the design.
Minimum operating depth shall be three feet.
2. Aerated Lagoons. The design water depth
should range from 10 to 15 feet (three to 4.5 meters). The type of the aeration
equipment, waste strength and climatic conditions affect the selection of the
design water depth.
3. Sludge
Accumulation. The minimum depth of 18 inches (45 centimeters) for sludge
accumulation shall be provided in primary cells of facultative
lagoons.
C. Freeboard.
The minimum freeboard shall be three (3) feet (1.0 meter). For small systems -
less than 50,000 gallons per day (190 cubic meters per day), the minimum
freeboard can be reduced to two (2) feet (0.6 meter).
D. Slope
1.
Maximum Dike Slope. The inner and outer dike slopes shall not be steeper than 3
horizontal to 1 vertical (3:1).
2.
Minimum Dike Slope. Inner dike slope shall not be flatter than 4 horizontal to
1 vertical (4:1). A flatter slope can be specified for larger installations
because of wave action, but have the disadvantages of added shallow areas, that
are conducive to emergent vegetation.
E. Seepage
1. The bottom of lagoons treating domestic
sewage shall be no less than 12-inch (30 centimeters) in thickness, constructed
in two six-inch (15 centimeters) lifts. The selection of the type of seals
using soils, bentonite, or synthetic liners for the lagoon bottom shall be
based on the design hydraulic conductivity, durability, and integrity of the
proposed material.
2. Hydraulic
conductivity of the lagoon bottom as constructed or installed, shall be such
that it meets the requirements of ground water discharge permit issued under
R317-6, (Ground Water Quality Protection rules). It shall not exceed 1.0 x
10-6 centimeters per second.
3. The seepage loss may vary with the
thickness of the bottom seal and hydraulic head thereon. Detailed calculations
on the determination of seepage loss shall be submitted with the design. It
shall not exceed 6,500 gallons per acre per day (60.8 cubic meters per hectare
per day).
4. Results of field and
laboratory hydraulic conductivity tests, including a correlation between them,
shall meet the design and ground water discharge permitting requirements,
before the use of lagoon can be authorized.
5. Hydraulic conductivity for the lagoon
where industrial waste is a significant component of sewage, shall be based on
ground water protection criteria contained in R317-6 (Ground Water Quality
Protection rules).
F.
Detention time
1. Discharging Lagoons.
Detention time in the lagoon shall be the greater, and exclusive of the
capacity provided for sludge build-up, of:
a.
120 days based on winter flow and the maximum operating depth of the entire
system; or
b. 60 days based on
summer flow and peak monthly infiltration/inflow.
c. The detention time shall not be less than
150 days at the mean operating depth for effluent discharge without
chlorination. In order to meet bacteriologic standards in such a case, at least
5 cells shall be provided. The detention time and organic loading rate shall
depend on climatic or stream conditions.
2. Aerated Lagoons
a. The detention time shall be the greater
of:
(1) 30 days minimum; or
(2) the value determined using the following
formula: E = (1/(1 + (2.3 x K1 x t))) where: t =
detention time, days; E = fraction of BOD5 remaining in
an aerated lagoon; Kl = reaction coefficient, aerated
lagoon, base 10. For normal domestic sewage, the K1
value may be assumed to be 0.12 day-1 at 20 degrees
Centigrade, and 0.06 day-1 at one degree
Centigrade.
b. The
reaction rate coefficient for domestic sewage which includes some industrial
wastes must be determined experimentally for various conditions which might be
encountered in the aerated lagoons. The reaction rate coefficient based on
temperature used in the experimental data, shall be adjusted for the minimum
sewage temperature.
G. Aeration Requirements for Aerated Lagoons
1. The design parameters for the aerated
lagoon should be based on pilot testing or validated experimental
data.
2. When pilot testing is not
conducted, the design should be based on two pounds of oxygen input per pound
of BOD5 applied (two kilograms of oxygen input per
kilogram of BOD5 applied). However, it may vary with the
degree of treatment, and the concentration of suspended solids to be
maintained. A tapered mode of aeration is permitted based on applied
BOD5 to each cell.
3. Aeration equipment shall be capable of
maintaining a minimum dissolved oxygen level of 2 milligrams per liter in the
lagoon at all times such that their circles of influence meet.
a. Circle of Influence. It is that area in
which return velocity is greater than 0.15 feet per second as indicated by the
manufacturer's certified data. Table R317-3-10.3(G)(3)(a) may be used when the
manufacturer's certified data is not available.
b. Freezing. Suitable protection from weather
shall be provided for aerators and electrical controls.
H. Industrial Wastes. For
industrial waste treatment using lagoon, the design parameters shall be based
on the type and treatability of industrial wastes using biological processes.
In some cases it may be necessary to pretreat industrial waste or combine with
domestic sewage.
10.4.
Lagoon Construction Details
A. Cell Shape.
The shape of all cells should be such that there are no narrow or elongated
portions. Round, square or rectangular lagoons with a length not exceeding
three times the width are most desirable. No islands, peninsulas or coves are
permitted. Dikes should be rounded at corners to minimize accumulations of
floating materials. Common-wall dike construction, wherever possible, is
strongly encouraged.
B. Multiple
Units
1. At a minimum, the lagoon system
shall consist of three cells of approximately equal capacity designed to
facilitate both series and parallel operations.
2. The Director may approve less than three
cells on the basis of review of factors such as, the rate of flow, the need,
treatment reliability, etc.
3. All
systems shall be designed with piping:
a. to
permit isolation of any cell without affecting the transfer and discharge
capabilities of the total system, and
b. to split the influent waste load to a
minimum of two cells or all primary cells in the system.
C. Embankments and Dikes
1. Material. Dikes shall be constructed of
relatively impervious material and compacted to no less than 90 percent
Standard Proctor Density at 3 percent above the optimum moisture density to
form a stable structure. The area where the embankment is to be placed shall be
from vegetation and unstable organic material.
2. Top Width. The minimum dike width shall be
8 feet (2.4 meters) and shall permit access by maintenance vehicles.
D. Lagoon Bottom
1. Soil. Soil used in constructing the lagoon
bottom (not including seal) and dike cores shall be incompressible and tight
and compacted at a moisture content of 3 percent above the optimum water
content to at least 90 percent Standard Proctor Density.
2. Uniformity. The lagoon bottom should be as
level as possible at all points. Finished elevations shall not be more than
three (3) inches (7.5 centimeters) from the average elevation of the
bottom.
3. Prefilling. The lagoon
should be prefilled to a level which protects the liner, prevents weed growth,
reduces odor, and maintains moisture content of the seal. However, the dikes
must be completely prepared before the introduction of any water.
E. Construction Quality Control
and Assurance. A construction quality control and assurance plan showing
frequency and type of testing for materials used in construction shall be
submitted with the design for review and approval. Results of such testing,
gradation, compaction, field permeability, etc., shall be submitted to the
Director.
F. Erosion Control
1. The site shall be protected from erosion.
The design of control measures shall be based on factors, such as lagoon
location and size, seal material, topography, prevailing winds, cost breakdown,
application procedures, etc.
2. For
aerated lagoons, the slopes and bottom shall be protected from erosion
resulting from turbulence.
3.
Exterior face of the dike slope shall be protected from erosion due to severe
flooding of a water course.
4.
Seeding. The outside surface of dikes shall have a cover layer of at least 4
inches (10 centimeters), of fertile topsoil to promote establishment of an
adequate vegetative cover wherever riprap is not utilized. Prior to prefilling,
adequate vegetation shall be established on dikes from the outside toe to 2
feet (0.6 meter) above the lagoon bottom on the interior as measured on the
slope. Perennial-type, low-growing, native, spreading grasses that minimize
erosion and can be mowed are most satisfactory for seeding on dikes. Alfalfa
and other deep-rooted crops must not be used for seeding since the roots of
this type are apt to impair the water holding efficiency of the
dikes.
5. Riprap or equivalent
material shall be placed from 1 foot (0.3 meter) above the high water mark to
two feet (0.6 meter) below the low water mark (measured on the vertical) for
protection from severe wave action.
a.
Riprap. The interior face of dikes must be protected from erosion by riprap or
other equivalent methods of erosion control.
(1) Riprap layer shall be of durable,
angular, sound and hard, field or quarry stones, and shall be free from seams,
cracks and structural defects.
(2)
The thickness of riprap layer shall be at least 8 inches (20
centimeters).
(3) Stones to be used
in the riprap layer shall meet the following requirements:
(a) A minimum of 50 percent of stones by
weight, shall be of sizes between two-thirds and one and one-half of the layer
thickness;
(b) No more than ten
percent of stones by weight, shall be of a size less than one-tenth of the
layer thickness;
(c) The specific
weight of stones must range between 2.5 and 2.82;
(d) Durability shall be tested in accordance
with ASTM Standard C-535, as amended, and stones wearing in excess of 40
percent shall not be used.
(e)
Stones shall be graded and manipulated in size so as to produce a regular
surface of dense and stable mass. A stable foundation for the placed riprap
shall be provided at the toe of the dike.
10.5.
Influent Piping
A. Influent and Effluent
Structures
1. All influent and effluent
structures shall be located to minimize short-circuiting within lagoons, and to
avoid blocking of lagoon circulation. Such structures must have protection
against freezing or ice damage under winter conditions.
2. Inlets to the primary cells shall meet the
following criteria:
a. Surcharging of
upstream sewer from the inlet manhole is not permitted.
b. Multiple influent discharge points for
primary cells of 20 acres (8 hectares) or larger should be provided to enhance
the distribution of waste load in the cell.
c. Discharge shall be in the center of a
round or a square cell, or at the third point farthest from the outlet
structure in a rectangular cell, or at least 100 feet (30 meters) from the toe
of the dike.
d. All aerated cells
shall have an influent line which distributes the load within the mixing zone
of the aeration equipment. Multiple inlets may be considered for a diffused
aeration system.
e. Force mains
shall be valved at the lagoon, and may terminate in a vertically or
horizontally discharging section. The discharge end of the vertical pipe must
be located no more than one foot above the lagoon bottom. Flow velocities in
the discharge section entering the lagoon must not be in excess of two feet per
second.
B.
Influent Discharge Apron
1. The influent line
shall discharge horizontally into a shallow, saucer-shaped, depression
extending below the lagoon bottom not more than the diameter of the influent
pipe plus 1 foot.
2. The end of the
discharge line shall rest on a suitable concrete apron large enough to prevent
the terminal influent velocity at the end of the apron from causing soil
erosion. A 2-foot (0.6 meter) square apron shall be provided at the
minimum.
C. Flow
Measurement. Influent flow to the lagoon shall be continuously indicated and
recorded. Flow measurement and recording equipment shall be
weatherproof.
D. Level Gauges.
Level gauges with clear markings shall be provided in:
1. each cell to measure and manually record
the depth; and
2. the primary flow
measurement device structure to indicate the depth or the rate of
flow.
E. Manhole
1. A manhole or vented cleanout wye shall be
installed prior to entrance of the influent line into the primary cell and
shall be located close to the dike as topography permits. Its invert shall be
at least 6 inches (15 centimeters) above the maximum operating level of the
lagoon and provide sufficient hydraulic head without surcharging the
manhole.
2. A manhole is required
for small systems to house flow measurement device. For larger systems, flow
measurement device and related instrumentation must be housed in a headworks
type structure.
F. Flow
Distribution. Flow distribution structures shall be designed to effectively
split hydraulic and organic loads equally to primary cells.
G. Material. The material for influent line
to the lagoon should meet the requirements of material for underground sewer
construction described in this rule. Unlined corrugated metal pipe is not
permitted due to corrosion problems. The material selection shall be based on
factors such as, wastewater characteristics, heavy external loadings, abrasion,
soft foundations, etc.
10.6. Control Structures and Interconnecting
Piping
A. Structure
1. As a minimum, control structures shall:
a. be accessible for maintenance and
adjustment of controls;
b. be
adequately ventilated for safety and to minimize corrosion;
c. be locked to discourage
vandalism;
d. contain controls to
permit water level and flow rate control, and complete shutoff;
e. be constructed of non-corrodible materials
(metal-on-metal); and
f. be located
to minimize short-circuiting within the cell and avoid freezing and ice
damage.
2. Recommended
devices to regulate water level are valves, slide tubes or dual slide gates.
Regulators should be designed so that they can be preset to stop flows at any
lagoon elevation.
B.
Piping. All piping shall be of cast iron or other material for installation of
underground piping. The piping shall be located along the bottom of the lagoon
with the top of the pipe just below average elevation of the lagoon bottom.
Pipes should be anchored and protected from erosion.
10.7. Effluent Discharge Piping
A. Submerged Takeoffs. For lagoons designed
for shallow or variable depth operations, submerged takeoffs are required.
Intakes shall be located a minimum of 10 feet (3.0 meters) from the toe of the
dike and 2 feet (0.6 meter) from the seal, and shall employ vertical
withdrawal.
B. Multi-level
Takeoffs. For lagoons that are designed deeper than 10 feet (3 meters), enough
to permit stratification of lagoon content, multiple takeoffs are required.
There shall be a minimum of three withdrawal pipes at different elevations.
Adequate structural support for takeoffs shall be provided.
C. Emergency Overflow. An emergency overflow
should be provided to prevent overtopping of dikes. The hydraulic capacity for
continuous discharge structures and piping shall allow for a minimum of 250
percent of the design flow of the system. The hydraulic capacity for
controlled-discharge systems shall permit transfer of water at a minimum rate
of six (6) inches (15 centimeters) of lagoon water depth per day at the
available head.
10.8.
Miscellaneous
A. Fencing. The lagoon area
shall be enclosed with not less than 6 feet high chain link fence to prevent
entering of livestock and to discourage trespassing. Fencing must not obstruct
vehicle traffic on top of the dikes. A vehicle access gate of sufficient width
to accommodate all maintenance equipment shall be provided. All access gates
shall be provided with locks.
B.
Access. An all-weather access road shall be provided to the lagoon site to
allow year-round maintenance of the facility.
C. Warning Signs. Permanent signs shall be
provided along the fence around the lagoon to designate the nature of the
facility and advise against trespassing. At least one sign shall be provided on
each side of the site and one for every 500 feet (150 meters) of its
perimeter.
D. Service Building A
service building for laboratory and maintenance equipment should be
considered.
10.9.
Industrial Waste Lagoons. The Director will review the design of lagoons for
treatment of industrial wastes on the basis of such factors as treatability,
operability, reliability, ground water protection levels, water quality
objectives, etc.