Ground Percolation Testing
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Transcript of Ground Percolation Testing
Ground Percolation TestingHow long will it take for a latrine to fill
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What kind of latrine are we talking about?
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What is a percolation test
Method to determine how fast water (urine) will flow into the groundA tool to determine an appropriate site for a latrineA tool to determine how soon the tank or pit will fillCan be used to size a simple leach-field
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Where do the liquids go?
Liquids leak into soil, but only so much per day . . . We’ll calculate how much. With time, fecal sludge builds up and closes off the tank floor – it will fill faster after that.
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What we’ll calculate
1. How fast water is absorbed by the soil – in three steps2. How much liquid will enter the latrine per day 3. How large of a soil area will be needed to get rid of the liquids each day
We are going to make our calculations for a pour-flush toilet because it uses a lot more water than a pity latrine.
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First – dig a hole and smaller test hole
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Second – pre-soak the hole
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Third – start test and record data
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Example calculation
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What we’ll calculate
1. How fast water is absorbed by the soil – in three steps 2.1 minutes/cm
2. How much liquid will enter the latrine per day 3. How large of a soil area will be needed to get rid of the liquids each day
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Calculating liters of liquid per day
Urine related liquids:
Average person pees a total of 1.5 liters per day, they pee about 5 times per day, but they do not pee each time in a latrine.
We will assume they pee 0.4 liters each time they pee. We will assume they pee twice a day in the latrine.Assume the average flush after peeing is 2 liters.
Total peeing related liquid is 2 x (0.4 + 2) = 4.8 liters per person per day
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Calculating liters of waste per day
Fecal related liquids: Assume the average person poops 1.25 times per dayThe average flush after pooping is 3 liters of water.Therefore there are 1.25 x 3 = 3.75 liters of liquid due to pooping in the latrine
per person per day.
Assume 5 people per household
Total liquid is 5 x (3.75 + 4.8) = 43 liters of liquid per household per day
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What we’ll calculate
1. How fast water is absorbed by the soil – in three steps 2 minutes/cm
2. How much liquid will enter the latrine per day 43 liters per day for this household
3. How large of a soil area will be needed to get rid of the liquids each day
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Soil Area Needed for Liquid Absorption
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The soil percolation rate is 2.1 minutes per cm The suggested soil treatment area is 0.02 sq. meters/liter We have 43 liters per day so the suggested area is 43 x .02 = 0.86 sq. meters
Perc rate > 24 minutes per cm will fill septic tank very soon Perc rate < 3 seconds per cm has a high probability of contaminating wells that are
nearby.
Percolationrate
Soil treatmentarea
Area needed for our example household
Minutesper cm
Square metersper liter per day
Square meters
0.04 to 2 0.02 0.9
2.5 to 6 0.03 1.3
6.3 to 12 0.04 1.7
12.3 to 18 0.05 2.2
18.3 to 24 0.06 2.6
The “take away” on percolation testingA simple test can avoid dissatisfaction.The “standard” pour-flush toilet design (three rings) is marginal for anything
other than sandy soils. Lower percolation rate = Low emptying frequencyHigh percolation rate = High emptying frequencyVery-low percolation rate = Risk of contaminating wellsFecal sludge buildup will always hinder percolation
We recommend the following design for testing . . .
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Recommended design changes
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Thank you and good luck.
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Ground Percolation TestingAdditional sources of information:http://www.extension.umn.edu/distribution/naturalresources/DD0583.htmlhttp://www.deq.gov.mp/artdoc/Sec6art108ID255.pdf
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