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sketch of a two-pond lagoon system for animal waste - UTAH SMALL ANIMAL WASTE LAGOONS AND PONDSLagoons for Onsite Wastewater Treatment

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Guide to lagoon systems for septic wastewater treatment: design, use, maintenance, life, effectivenes.

Lagoon septic systems: also known as "pond septic systems" for onsite wastewater treatment are less often found in use for single family residential wastewater treatment.

A residential lagoon system may use a conventional septic tank, but effluent from the tank flows to a storage pond or lagoon for further treatment. The illustration at page top is from "Utah Small Animal Waste Lagoons and Ponds" published by the Utah state government.



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Lagoons or Ponds for Onsite Waste and Wastewater Treatment

Constructed Wetlands, San Miguel de Allende, Guanajuato Mexico, from el Charco del Ingenio botanical garden, by the author, August 2006

What is a Lagoon Septic System for Onsite Waste or Wastewater Treatment?

Lagoon systems: also known as "pond systems" for onsite wastewater treatment are less often found in use for single family residential wastewater treatment.

A residential lagoon system may use a conventional septic tank, but effluent from the tank flows to a storage pond or lagoon for further treatment. (Some states such as Missouri may permit a lagoon without a septic tank.)

Lagoon systems require comparatively large land areas and are more likely to be found therefore in rural areas or where a common wastewater treatment system has been designed to serve multiple dwellings.

For example lagoons are used for effluent disposal on small farms and for animal waste treatment/disposal on small and large farms or livestock operations.

[Click to enlarge any image]

Aerobic Lagoon Wastewater Treatment System Design

The lagoon or pond holds septic effluent where treatment may be enhanced by using an aerobic design to a shallow pond of effluent (adding air to the water, perhaps by an air pump or a fountain system).

Anaerobic Lagoon or Pond Septic System Designs

Anaerobic lagoon or pond designs are deeper and work more like a conventional septic tank, processing waste into settled sludge and treated effluent, and not making use of oxygen-requiring microbes nor of sunlight to treat the effluent.

Effluent from a pond septic system, except for its portion which is removed by evaporation, is commonly permitted to flow through a wetlands for further treatment before discharge to the environment.

The site and construction requirements for a lagoon septic system will require additional clearance distances from wells, property lines, etc. Lagoons are constructed in high clay soils (or lined) so that effluent does not drain into the soil directly from the lagoon.

A Typical Residential Wastewater Lagoon Design Specifications

Septic Lagoon Size

North Dakota State University offers some basic design specifications for a lagoon system for treating wastewater: "The lagoon surface area should be sized at about 500 square feet per person. A lagoon serving a four-person household would then have a surface area of about 2,000 square feet. The lagoon should have a depth of 3 feet with a minimum freeboard of 2 feet.

Nebraska Title 124 Ch. 18.008 provides these septic lagoon sizing specifications

008.01 The size of a lagoon shall be based on the design flow for the dwelling or non-dwelling facility, the seepage rate of the wastewater into the soil below the lagoon, and the average evaporation and precipitation using the appropriate location on the state evaporation and precipitation maps (Figures 18.1 and 18.2).

008.01A For a dwelling, the minimum wastewater flow for design of the onsite system shall be based on the number of bedrooms in the dwelling using the following: 150 gpd + ((Number of Bedrooms - 1) x 75 gpd), where gpd is gallons per day.

008.01B For a non-dwelling structure or other wastewater source, the wastewater flow shall be based on the highest daily wastewater flow.

008.02 The lagoon water surface area at the maximum operating level shall be determined by the following water balance equation:

Maximum Water Surface Area = (flow) x 976 / ((evap.-precip.)x1.67) + OOD) + (seepage x .608)

Where: flow = daily design flow or inflow, gallons per day
evap. = annual lake evaporation for location from Fig. 18.1(This is a state map showing necessary data)
precip. = annual precipitation for location from Fig. 18.2 (This is a state map showing necessary data)
OD = difference between maximum and minimum operating depths for the lagoon (typically three feet which is also the maximum allowed)

Note that assumptions such as evporation rate and precipitation rate vary widely seaonally and by geographic area while seepage rates or soil percolation rates vary widely by soil properties as well. Where septic lagoon wastewater treatment systems are permitted and regulated by code, most authorities also describe the soil percolation rate or seepage rate test procedure to be sued in evaluating the site for lagoon operation.

Septic Lagoon Shape

Shape the sides of the lagoon to a 3:1 slope. A 2,000 square foot lagoon with 3 feet working depth and 3:1 side slopes would have a 50-foot diameter at its working depth and a 62-foot diameter at the top of the dike.

The lagoon may also be square or rectangular. A 2,000 square foot lagoon would be 45 feet square at its working depth and 57 feet square at the top of the dike." --quoted from North Dakota State University - www.ag.ndsu.edu/pubs/ageng/structu/ae892-3.htm#Lagoons.

The design specifications for a lagoon septic system will vary widely depending on its use and the effluent flow rate involved. However the basic concepts of lagoon system operation and protection will be consistent.

Septic Lagoon Construction Details

Nebraska Title 124 Ch. 18 provides a crisp desription of septic lagoon construction details:

001 A site for a lagoon shall permit the unobstructed wind to sweep across the lagoon to provide mixing action and to add oxygen to the water. Timber must be removed for a horizontal distance of at least 50 feet as measured from the high water mark for the maximum operating depth of the lagoon, but not less than 10 feet horizontal distance from the outer dike toe of the lagoon.

002 The lagoon shall be located and constructed so it will not receive surface runoff water.

003 A lagoon shall not be installed on a lot less than three acres in size. For the purpose of this chapter, “lot size” means the area of a lot excluding all area below the normal high water level of any surface water feature and all area within the right-of-way or easement of a street, road, or access easement.

004 The lagoon shall be designed for complete retention.

005 The floor of the lagoon shall be located at least two feet above the seasonal high groundwater level, bedrock, or other barrier layer.

006 The top of the dike shall be at least one foot above the 100 year flood elevation.

007 Testing of the final seepage rate shall be completed based on soil permeability. The maximum allowable seepage rate is one-eighth inch per day after sealing and compaction. This may be determined by an independent soils laboratory performing a hydraulic conductivity test on an undisturbed soil sample taken at the site, or the two barrel method prior to filling, or a comparison test after prefilling with clean water but before introduction of wastewater.

007.01 The two barrel method may be used for soil sealed lagoons before the lagoon is filled. Two similar 55 gallon drums are required, one a control drum with one end removed and the other drum (seepage drum) with both ends removed. One end of the seepage drum is pressed into the sealed soil layer, and a bead of polymer treated sodium bentonite clay is packed around the inside edge of the drum.

The seepage drum is carefully filled with water and kept filled for two or more days to saturate the soil. The test begins with filling each drum equally. Each day the difference in levels is recorded, and the barrels filled to the beginning level. The control drum measures the weather effects while the seepage drum records seepage plus weather effects. The test should continue for at least seven days.

007.02 The comparison test method may also be used after the lagoon is prefilled. Isolate the lagoon and record the water level changes as a result of seepage and weather effects. The changes resulting from weather effects alone may be measured separately in a nearly full white plastic five gallon bucket partially buried near the shore. The test should continue for at least seven days.

Nebraska Title 124 Ch. 18.012 further specifies:

009 Lagoon Construction

009.01 The floor of the lagoon shall be level. A difference of plus (+) or minus (-) three inches is permitted. All vegetation shall be removed from the floor of the lagoon. This organic material shall not be used in the construction of the lagoon.

009.02 The soil material of the lagoon floor shall be designed so that it shall not seep more than one-eighth inch per day. If soil borings and tests indicate that the existing soils are not conducive to compaction to meet this requirement, then sodium bentonite clay or a synthetic liner may be used to restrict seepage.

009.03 The inside slope of the dikes shall not be steeper than three horizontal to one vertical. The exterior slope of the dikes shall not be steeper than four horizontal to one vertical. The minimum width of the top of the dike shall be four feet.

010 The minimum operating depth of the lagoon shall be two feet. The maximum operating depth shall be five feet. The dikes shall provide a minimum freeboard of 12 inches.

Site clearance distances for septic lagoon systems

Setback distances from a lagoon septic to other site features are similar to setbacks from other septic system designs and are elaborated in detail by Schultheis (1997) from which we excerpt some examples. These distances are from the lagoon to the feature listed, not from the septic tank itself (for which there are different clearance distance specifications).

Lagoon Wastewater System Safety and Protection

For safety the edges of a lagoon should be fenced to protect children and animals. Protection may also be needed to keep burrowing animals such as groundhogs from digging holes which inadvertently drain the pond.

See GOPHER HOLE DAMAGE

Safety barriers at Septic Lagoons

The lagoon shall be fenced with a four foot high woven wire, welded wire, or seven strand barbed wire with the first strand starting three inches from the ground and the following strands spaced evenly. The fence shall be equipped with a standard main gate that is kept locked.

The fence shall be placed on the outside edge of the top of the dike or four feet outside the toe of the dike. A sign no less than 12 inches by 24 inches bearing the clearly-readable words "NO TRESPASSING - WASTEWATER LAGOON" shall be located on the gate. - NE Title 124 Ch. 18.012

Citation of this article by reference to this website and brief quotation for the sole purpose of review are permitted.Citation of this article by reference to this website and brief quotation for the sole purpose of review are permitted. Use of this information at other websites, in books or pamphlets for sale is reserved to the author. Technical review by industry experts has been performed and comments from readers are welcomed. Contributors are listed at the end of each article.

Lagoon Wastewater Treatment System Inspection & Maintenance

Our description of the maintenance requirements for septic lagoon systems has been relocated to LAGOON SEPTIC MAINTENANCE

Lagoon Wastewater Treatment System Installation & Maintenance References & Guides

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