Title 124 - Rules And Regulations For The Design, Operation And Maintenance of Onsite Wastewater Treatment Systems
Chapter 18 - Lagoons: Site Location, Evaluation, and Design

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.

008 Lagoon Sizing

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 =

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

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.

011 The lagoon shall be equipped with a depth gage that provides a visual indication of the liquid level at minimum operating depth (two feet) and maximum design full depth relative to the lagoon floor.

012 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.

013 Building Sewer Line

013.01 The influent line from the building sewer shall be at least four inches inside diameter and shall have a grade of not less than one-eighth inch per foot.

013.02 The line shall be equipped with clean-outs with tight fitting caps, at every seventy-five feet or less, or where angles greater than forty five degrees are encountered. A clean out shall be located at least one foot above the highest water level and near the outside of the dike embankment.

013.03 The line shall discharge at the center of the lagoon onto a concrete slab at least two feet square with the discharge end of the pipe placed below the minimum operating depth of the lagoon.

013.04 The sewer line pipe shall have a loading bearing capacity of not less than 1,000 (455 kg) pounds per square foot. Plastic pipe shall be installed and supported in such a manner that there is no deflection during backfilling or compaction.

015 The lagoon shall be filled with surface or groundwater to a depth of two feet before wastewater wastes are discharged into it.

Enabling Legislation: Neb. Rev. Stat. 81-1505(8).

Legal Citation: Title 124, Ch. 18, Nebraska Department of Environmental Quality.