Title 124 Chapter 18

TITLE 124 - NEBRASKA DEPARTMENT OF ENVIRONMENTAL QUALITY

Chapter 18 LAGOONS - SITE LOCATION AND EVALUATION; DESIGN

001 A site for a lagoon shall permit the unobstructed wind to sweep across the lagoon to provide some mixing action and to add oxygen to the water. Timber must be removed for a distance of at least 50 feet 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 property less than three acres in size, excluding all area below the normal high water level of any surface water feature, all area below a ten-year flood elevation, 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 highest expected groundwater level.

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

007 The lagoon shall be located at least 2 feet above fractured bedrock.

008 Testing of the final seepage rate shall be completed based on soil permeability. The maximum allowable seepage rate is 1/8 inch per day after sealing and compaction. This may be determined by an independent soils laboratory on a 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.

008.01

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 bentonite 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.

008.02

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 5 gallon bucket partially buried near the shore. The test should continue for at least seven days.

009 Lagoon sizing

009.01

The size of lagoon shall be based on the location of the proposed system and the number of bedrooms and/or gallons per day contemplated in the dwelling or establishment served. Regional lagoon size differences are a result of differential climatic conditions related to average evaporation and precipitation.

009.02

The required lagoon size shall be determined by the equation in Section

017

below using the state evaporation (Fig 18.3) and precipitation (Fig 18.4) maps to determine the net evaporation.

010 Dike and floor construction

010.01

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.

010.02

The soil material of the lagoon floor shall be designed so that it shall not seep more than 1/8th inch per day. If soil borings and tests indicate that the existing soils are not conducive to compaction, then one of the following means of restricting seepage shall be used:

010.02A

Soda ash;

010.02B

Bentonite; or

010.02C

A synthetic liner.

011 The slope of the dikes shall not be steeper than three horizontal to one vertical. The minimum width of the top of the dike shall be 4 feet.

012 The minimum operating depth of the lagoon shall be two feet. The maximum operating depth shall be 5 feet. The dikes shall provide a minimum freeboard of 12 inches.

013 The lagoon shall be equipped with a depth marker.

014 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. Signs shall be located on each gate with a warning of "NO TRESPASSING - WASTEWATER LAGOON".

015 Influent line or distribution pipe

015.01

The influent line shall be at least four inches inside diameter and shall have a grade of not less than 1/8 inch per foot.

015.02

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.

015.03

The line shall be center discharging and shall discharge on a concrete apron at least 2 feet square.

015.04

The pipe shall have a loading 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.

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

017 Sizing Formula

A	=	Area (surface area at maximum operating depth)
I	=	Inflow in gallons per day
EVAP	=	Net evaporation from FIG 18.3 in inches per year
PRECP	=	Net precipitation from Figure 18.4 in inches per year
LV	=	Lagoon depth between maximum and minimum operating depths (normally three feet)
SEEP	=	Seepage rate through lagoon liner in inches per day; 1/8 inch or less allowable.
7.48	=	Conversion of gallons per day to cubic feet per day
365	=	Conversion from days to one year
12	=	Conversion from inches to feet
20	=	20 year design life

Simplified Equation:

017.01

Take the square root of the area to get the length of a side at the high operating level for a square lagoon. (FIG 18.1, 18.2)

Length of a side

017.02

Flow for dwellings shall be estimated at a minimum of 150 gpd + ((Number of Bedrooms - 1)

75 gpd).

Figure 18.1 Plan View
Figure 18.2 Profile View
Figure 18.3 Total Annual Lake Evaporation
Figure 18.4 Total Annual Precipitation

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

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

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