Dairy Effluent Pond Construction[1]

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Dairy effluent: Pond constructionBarrie Bradshaw, Ellinbank

October, 2002

AG0425ISSN 1329-8062

State of Victoria, Department of Primary Industries Page 1

Good site investigation and construction are essential for

the long-term success of dairy shed effluent pond

systems. Refer to the Agriculture NoteAG0424; Dairy

effluent: Pond site selection before constructing ponds.

Local government requirements

Check whether your local government requires a permit for

the construction of a pond. Whether a permit is required

will vary between areas and can depend on whether the

natural drainage or active flow path in the area is affected.

Pond sizing

Ponds should be designed to hold the maximum quantity

of effluent produced over the wetter months to avoid

waterlogging and pugging of pastures. Effluent may need

to be stored between 46 months depending on the farms

location. Refer to the Agriculture Note,AG0441:Dairy

effluent: Storage pond sizing for more information.

It is important to ensure that the contractor follows the

plans, which have been designed, and that the minimum

size specifications are adhered to.

Types of ponds

The type of pond or ponds that you select will depend on

the topography of the farm and the type of effluent system

implemented to return nutrients back to pasture.

Excavation costs will depend on the storage/excavation

ratio of the pond. The storage ratio is the number of cubic

metres of water stored in the pond for each cubic metre of

earth moved to build the pond.

Hillside ponds generally have a 3-sided or curved bank.

These ponds have relatively poor storage ratios but often

have the advantage of allowing gravity flow to and from

the system. A hillside slope of 8% gives the best storageratio.

Excavated ponds or below ground ponds will supply

excavated material which can be stockpiled for other use.

Whilst effluent can usually be gravitated to an excavated

pond, usually only the overflow from the pond can be

gravity fed out. Excavated ponds are not suitable in areas

where the watertable is close to the land surface.

Turkey nest ponds or above ground storages can be

built by using the soil which is obtained from digging the

hole to build the embankments. Effluent generally has to

be pumped into a turkey nest dam, but it can be released by

gravity through an outlet pipe. Turkey nest ponds are ideal

if the watertable is close to the land surface and shandying

effluent into irrigation channels.

Pond dimensions

Ponds do not have to be regular shapes and can be blended

into the topography or surroundings.

Rectangular ponds are easier to de-sludge, when necessary,than square ponds since they give better access to the

centre.

Rectangular ponds compared to square ponds are also

cheaper to construct on hill country with the long side on

the contour.

Long narrow ponds should be avoided, as they tend to

crust and silt at the end where effluent is entering. This

affects anaerobic functioning.

Earthmoving machines

There are many types of machines that can be used to

construct ponds. However equipment which can spreadand compact excavated material is best. The more

compacted the embankments and pond surface are, the less

likely it is that the pond will leak or crack.

Bucket type earthmoving equipment cannot spread or

compact excavated material or embankments as well as

bulldozers, whilst scrapers are even better compacters but

are only suited to large jobs. Sheepsfoot and tamping foot

rollers in association with water carts provide even better

compaction.

Site preparation

Payment of contractors is generally determined by theamount of earthworks required to construct the system.

However, where fences, vegetation and other obstacles

require removal the contractor may charge for further time.

The farmer can reduce costs by carrying out as much of

this work as possible prior to the contractor commencing.

All topsoil should be cleared and stockpiled, and replaced

on the completed walls to enable regrowth preventing bank

erosion and providing wall stability. Dams in which

topsoil is incorporated in, or left under the clay material

that forms the bank, are more likely to leak.


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Dairy effluent: Pond construction AG0425

Sealing

Ponds should be impermeable to water and a soil

investigation should be undertaken. Refer to Agriculture

Note;AG0424: Dairy effluent:Pond site selection. The

organic matter from the cow manure entering the system

will eventually form a biological seal.

Ponds constructed using cracking clay soils, or soils

containing less than 20 per cent clay require sealing. Clay

from another area can be placed 150 mm thick and

compacted with 150 mm of existing soil on the pond floor

and walls. Alternatively there are additives, which can be

mixed with soil such as bentonite and Kaolin clay, to

reduce soil permeability.

To prevent the clay seal from drying out and cracking, the

pond should be filled with water as soon as possible after

completion and at least 0.5 metre of effluent should be

maintained in the pond.

Polyethylene liners are also available to seal ponds in light

soils, however good management is essential to preventliner damage. Placing tyres in the base of the pond on top

of the liner will assist contractors in locating the liner and

possibly avoid puncturing.

Side slopes and embankments

The crest of embankments should be a minimum width of

3.5 metres. This will allow for vehicular movement during

construction and desludging. Both internal and external

batters should have at least a

2:1 slope (2 metre in the horizontal direction for every

1 metres in the vertical direction) to prevent batters

slumping, and to allow free machinery movement. Bankbatters of 3:1 are preferable especially for the external

batter and where ponds are to be located in sites with

unstable soils, or when optimal compaction is not possible.

When desludging, ponds with steeper banks may clean

more easily, but an adequate slope is needed to prevent the

banks from slumping or breaching.

Pipe sizing and type

UPVC and HDPE (polyethylene) pipes are suitable for

gravity or pressure pipelines. Rubber-ring-jointed PVC

pipe should be installed in preference to solvent-welded

pipe to avoid corrosion from the effluent.If concrete pipes are used, sulphate-resistant cement is

recommended with all exposed starter bars being

galvanised to avoid decay. Steel cast iron and ductile iron

pipes should be given a protective coating to avoid

corrosion from the effluent.

For gravity pipelines, sewer-class pipes should be used

rather than stormwater-class pipes. The main

consideration for gravity conveyance is the presence of

solids in the liquid. Table 1 gives recommended grade

requirements of pipelines.

Table 1: Minimum grades for gravity pipe drainsconveying effluent.

Inside

diameter(mm)

Minimum grade

Without solids

Minimum grade

With Solids

75 0.2% (1:500) 3.3 % (1:30)

100 0.1% (1:1000) 2.5 % (1:40)

125 0.07% (1:1450) 2.0% (1:50)

150 0.05% (1:2000) 1.7% (1:60)

At least 150mm pipe is recommended for transferring

effluent between ponds and for the outlet from ponds to

the land application area or irrigation channel. Larger

diameter pipes will have the advantage of higher discharge

rates and less likelihood of blocking.

At least 50mm piping is needed for pumping effluent. For

pipeline lengths exceeding 100 metres or where higherheads (the distance between the effluent level and the

pump outlet) are involved, at least 75mm pipe is

preferable. When choosing pressure classes for pipes

some extra strength needs to be allowed for water hammer.

HDPE pipe has greater flexibility to withstand water

hammer than UPVC pipe.

Table 2: Common p ipe classes recommended forpumping effluent.

Imperial K119 Metric AS1159

Class A - 150 ft head

65psi

Class 4.5 - 45 m head

65 psi

Class B - 200 ft head

87 psi

Class 6 - 60 m head

88 psi

Class C - 300 ft head

135 psi

Class 9 - 90 m head

131 psi

Class D - 400 ft head

175 psi

Class 12 - 120 m head

176 psi

Pipe positioning

The effective storage capacity of a pond is the difference

in the effluent level at the start of the winter or storage

period and the effluent level when the pond is full.

It is therefore important to be able to empty the pond so

that there is sufficient storage capacity for the wetter

months of the year.


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Storage

capacity

Figure 1. Storage capacity of a pond

However it is recommended that the outlet pipe or pump suction line are not within 0.5m of the bottom of pond. This will

prevent sludge and solid material from blocking the pipes and pumps.

Overflow pipes, such as pipes used between dams should be as far as possible from inlet pipes so that the effluent is held in the

pond long enough to be broken down and for solid settlement to occur. Pipes should be fitted with baffles or T-junctions tostop any surface scum passing through them.

Figure 2. Simple baffle to prevent pipe blockages

Concrete or UPVC cut-off collars should be installed with pipes passing through embankments to minimise seepage around the

pipe. The longer the pipe the greater number of collars are needed.


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Figure 3. Configuration of pipes and earthen banks

If the pond is to be emptied using gravity, flows can be controlled by a gate valve, slide or a similar structure, which can be

placed on the downstream or upstream end of the pipe.

Figure 4. Position of valves/controls on outlet pipes.

A downstream control is convenient to operate but the pipe is exposed to constant water pressure, which may cause leakage.

The main disadvantage of the upstream control is the inconvenience of operating and maintaining it. If it is laid in a sloping

position it requires a very long spindle supported on concrete cradles, and if set in a vertical position it needs a catwalk with a

safety fence to reach it.

Pipe covering

Pipelines should be buried at least 500 mm below the earth surface and at least 600 mm below where there is vehicle

movement. The larger the pipe, the greater the cover required.


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Rainfall run-off diversion

There should be a diversion or cut-away ditch around

excavated or hillside ponds so that rainfall run-off is

diverted away.

Starting and fill ing new ponds

The organisms in the dairy effluent are generally sufficient

to start the pond functioning, and therefore the ponds will

usually not require 'seeding'.

However if seeding is required then effluent from an

active pond (approx. 200 litres) is recommended

Ponds should be filled with clean water before effluent is

discharged into them. This helps seal the bed and banks,

decreases odour and reduces the concentration of effluent

components.

Grassing and treesOnce the earthen banks are formed, the stockpiled topsoil

can be placed on the crest and batters. Grass cover on the

embankments will help stabilise the banks, prevent

cracking walls and potential leaks, and help to protect the

banks from wave damage and rainfall erosion.

Trees should not be allowed to establish on embankments

since they can disturb the stability of the batters.

Fencing and safety

Ponds must be fenced to keep out children and stock.

Stock can cause extensive damage to batters and

structures.

A sign should be erected on ponds warning of deep water

which may be hidden by a surface crust or scum.

References

Managing Dairy Shed Wastes Technical Bulletin; Vol. 2,

Dairy Research and Development Corporation 1994.

Published by Department of Agriculture, Victoria.

This publication may be of assistance to you but the State of Victoria and its officers do not guarantee that the publication is without flaw of any

kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may

arise from you relying on any information in this publication.

Dairy Effluent Pond Construction[1]

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