report for training on drain field design …data.mswrpcu.com/sites/default/files/cpes gama report...

REPORT FOR TRAINING ON DRAIN FIELD DESIGN AND CONSTRUCTION / SOLUTIONS FOR WATER LOGGED AREAS / BEST PLUMBING PRACTICES / IMPORTANCE OF EARTHWORMS IN DIGESTERS.

March 27 2018

Room 1, 1st Floor C129/21 Saflo Link, Abelemkpe

P.O. Box CT 2611 Accra – Ghana Tel: 027 593 2322, 024 435 0303

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Contents

1. BACKGROUND AND OBJECTIVES ....................................................................................................... 3

2. WORKSHOP DISCUSSIONS ................................................................................................................ 3

3. FIELD DEMONSTRATION ................................................................................................................... 4

4. PLUMBING PRACTICES FOR WASTEWATER ...................................................................................... 7

5. EARTHWORMS .................................................................................................................................. 7

6. QUESTIONS ASKED ............................................................................................................................ 7

7. APPENDIX 1: POWERPOINT PRESENTATION SLIDES USED FOR THE TRAINING .............................. 10

LIST OF FIGURES Figure 1: Participants observing the percolation trial hole .......................................................................... 4 Figure 2: Participants standing around the percolation trial hole ............................................................... 4 Figure 3: Percolation test hole ...................................................................................................................... 5 Figure 4: Percolation test hole with gravels ................................................................................................. 5 Figure 5: Drain field being dug out ............................................................................................................... 6 Figure 6: Drain field construction ................................................................................................................. 6 Figure 7: 4 Inches Pressure (Class B) pipes ................................................................................................... 7 Figure 8: 4 Inches Class O pipes .................................................................................................................... 7



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1. BACKGROUND AND OBJECTIVES A three day workshop (14th -16th March 2018) was organized by the Project Coordinating Unit (PCU) of

GAMA Sanitation and Water Project (SWP), at the Institute of Local Government, for Sub Project

Implementers (SPIs) and Metropolitan, Municipal and District Assemblies (MMDAs). The workshop was

organized to educate participants on the basic principles involved in the design, development and

construction of vermidigesters. Three resource persons were engaged to take participants through the

training. For all the three days, challenges with the construction of household toilets under GAMA SWP

were elaborated.

Ing. Nana Osei Mainoo, the Managing Director of Correct Plumbing and Engineering Services Ltd was

engaged to train participants on the issues below.

1. Drain field design and construction;

2. The importance of the Percolation Test;

3. Solutions for water logged areas;

4. Plumbing best practice;

5. Importance of earthworms in digesters.

2. WORKSHOP DISCUSSIONS

The Drain field, which is a method of subsurface (below ground) wastewater treatment and disposal,

was discussed. It is governed by the British Standard (BS 6297:2007). The drain field works in

combination with the septic tank and distribution box, to make septic system. The principles governing

wastewater treatment and disposal in the soil strata were explained to participants to help them

understand the fuctions of the various soil layers, the layer in which the percolation test should be

performed and where the drain fields should be situated or constructed.

The infiltration zone, unsaturated zone and the saturated zones of the soil were introduced. The

infiltration zone, which is the top 50cm of soil, is the ideal layer for the construction of the drain field.

This zone is the biologically active zone, and biofilm builds up within pipe and surrounding trench media.

The unsaturated zone is below the infiltration zone. It provides storage for effluent and acts as a



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pathway for oxygen diffusion into effluent. The saturation zone is for dilution and diffusion of effluent.

Important notes to bear in mind when constructing drain fields include;

Drain fields do not operate indefinitely, and eventually need to be replaced;

Fats, oils and greases cannot enter a drain field, these organic compounds shorten the lifespan;

The effectiveness of drain fields to disperse effluent is influenced by the ground water table, soil

characteristics and moisture content;

Detailed site investigations is necessary for assessing the viability of drain fields;

The percolation test and subsequent drain field construction requires planning and organization.

3. FIELD DEMONSTRATION Participants were taken to the field for a demonstration of the percolation test and the drain fields.

Figure 1: Participants observing the percolation trial hole

Figure 2: Participants standing around the percolation trial hole

Participants were introduced to the trial hole as shown in Figure 1. This hole is dug adjacent to potential

drain field;



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1m × 1m hole was dug below the proposed pipe invert level;

All materials were removed from the hole and filled with chippings;

Textual descriptions of the soil must be noted;

From the percolation trial hole, participants were taken through the construction of the percolation test

hole.

Figure 3: Percolation test hole

Figure 4: Percolation test hole with gravels

Three percolation test holes should be located over the areas to be tested;

1m × 1m hole should be dug or bored to the proposed depth (min 0.3 m) and another hole dug

0.3m x 0.3m x 1m depth below the proposed pipe invert level;

Remove all loose material from the hole;

Add 50 mm of coarse gravel to protect the bottom from scouring;

Carefully fill each hole with water to 300mm above the gravel and allow to seep away

completely;

If the water seeps away in 10 minutes the hole should be refilled max 10 times. If the water continues to

seep away, the area is not suitable for a drain field.



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Measure percolation rate by refilling each hole with water to a depth of 300 mm and observe

the time in seconds for the water to seep from 75% (225mm) to 25% (75mm);

Divide this time in seconds by 150mm, providing the average time in seconds for a 1mm drop;

Repeat the test at least three times for each hole.

To construct the drain field;

Excavate trenches to required dimension (length, breadth and depth);

Spread chippings in trenches to adequate thickness and levels or fall;

Lay slotted pipes on chipping to the required direction of flow and fall;

Spread another layer of chippings over the surface of the pipes;

Cover the surface of the chippings with soil to grade;

Grass over the drain field area to prevent erosion.

Figure 5: Drain field being dug out

Figure 6: Drain field construction

Participants were also introduced to Pressure pipes (class B). These are the preferred pipes for drainage

(Soil and waste). Unlike the Class O pipes that are cheaper (and hence preferred by plumbers), they do



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not collapse due to external forces exerted by the backfilled material, a major cause of blockage in

drainage systems. Although using class B pipes will result in an increase in the total cost of the

construction of the digesters under the GAMA Project, participants were encouraged to make use of it

to avoid blockages in the future.

Figure 7: 4 Inches Pressure (Class B) pipes

Figure 8: 4 Inches Class O pipes

4. PLUMBING PRACTICES FOR WASTEWATER The participants were taken through best plumbing practices and plumbing materials they need to use

to enable their work last long and avoid immediate defect in the construction of their toilets under the

GAMA project.

5. EARTHWORMS Finally the earthworms required for seeding the vermidigesters were introduced. The earthworm body

works like a biofilter. They grind, aerate and crush the faecal sludge, making it easier for microbes to

degrade the sludge. When worms are not in the vermidigester, there is an invasion of nuisance pest like

cockroaches, odor becomes an issue. There will also be an accumulation of the faecal sludge; this will

result in the vermidigester getting full.

6. QUESTIONS ASKED 1. When is a percolation test not possible?

One cannot carry out a percolation test when:



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a. The area of interest is paved;

b. The area is waterlogged; wet building sites with high groundwater or subject to surface runoff

(that cannot be fully diverted);

c. Failed septic systems: sites where an existing septic system has failed and there is limited space

or other constraints on septic system repair;

d. Rocky building sites or sites with bedrock and not enough topsoil to treat and dispose of

wastewater;

e. Small building sites which lack adequate space to install a conventional septic drain field;

f. Steep building sites which do not permit installation of a conventional drain field;

2. Can you put chemicals in the vermidigester?

Participants were encouraged to avoid using chemicals since the system is a biological system. They

were encouraged to seed their biodigesters with earthworms. Notwithstanding, some participants

mentioned that they used an enzyme based biochemical called Ecosave. Further research needs to

done to know the effect of the chemical on the content of the vermidigester and the environment.

3. What are the alternatives for waterlogged areas?

The micro flush and dry toilets are ideal for places that are waterlogged in the GAMA project,

considering the installation cost of of these options fall within the budget for the project.

Commercial solutions to the waterlogged areas were also reviewed. However, these options are

expensive. Customers will therefore have to pay for the additional cost if purchased under the

GAMA Project.

4. How do you perforate the pipes used in the drain field?

The pipes can be slashed with a hack saw blade or drilled using a drilling machine. The holes should

be made along the entire pipe circumference to avoid the possibility of clogging when the base is

fouled.



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5. How do you calculate the length of the drain field?

The area of the drain field is calculated from the percolation rate value observed in the percolation

test. The length can then be worked out after selection of a suitable drain field width. A detailed

description is found in Appendix 1 below.

6. Can several digesters share a drain field?

If the drain field is sized properly, yes.

7. How many holes should be dug for the percolation test?

Ideally, three holes should be adequate, however, when the soil layers vary, more holes need to be

dug to be sure of the various soil types and layers available.



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8. APPENDIX 1: POWERPOINT PRESENTATION SLIDES USED FOR THE TRAINING

ByIng. Nana Osei K. Mainoo

Correct Plumbing and Engineering Services Limited

DRAIN FIELD DESIGN AND CONSTRUCTION / SOLUTIONS FOR WATER LOGGED AREAS / PLUMBING BEST PRACTISE /

IMPORTANCE OF EARTHWORMS IN DIGESTERS

TABLE OF CONTENTS1. The Drain field;2. How to conduct a Percolation Test;3. Sizing a drain field (based on Percolation Test

Results);4. Solutions/remedies for effluent treatment in

waterlogged areas;5. Plumbing techniques for wastewater including best

practices;6. Earthworms and the digester;

WHAT IS A DRAIN FIELD?Method of subsurface (below ground) wastewater treatment &

disposal;

Governed by BS 6297:2007;

In BS 6297 it works in combination with Septic Tank and distribution box to make Septic System;

In Ghana Soak Away most prevalent, instead of drain fields;

Per BS 6297, soak away should only be used for rain water disposal;;

HOW DO DRAIN FIELDS TREAT SEPTIC EFFLUENT?

INFILTRATION ZONE

Top 50cm of soil

Biologically active zone

Microbial communities builds up within pipe and surrounding trench media

UNSATURATED ZONE

• Below infiltration zone;

• Transition between infiltration and saturated zone;

• Provides storage for effluent;

• Pathway for oxygen diffusion into effluent

SATURATED ZONE

• Dispersion / diffusion of effluent;

• Dilution

IMPORTANT ITEMS TO NOTE

Drain fields do not operate indefinitely, eventually need to be replaced;

Fats oils and greases cannot enter a drain field –will shorten lifespan;

Drain field effectiveness to disperse effluent influenced by ground water table, soil characteristics and moisture content;

Detailed site investigations necessary; This Endeavour requires planning and

organization;

Percolation Test (BS 6297)

REQUIRED TOOLS AND MATERIALS

Shovel / Spade

Pick Axe

Measuring stick

Measuring tape

Chippings

Water source

PPE

A percolation test (colloquially called a perc test) is a test to determine the water absorption rate of soil (that is, its capacity for percolation) in preparation for the building of a septic drain field (leach field) or infiltration basin.

IMPORTANCE OF SITE INVESTIGATIONSWithout site investigations, especially percolation test,

problems arise with installations because;

Drain fields do not work because of poor site investigation;

FLOODED DIGESTER

DEMONSTRATION

SITE INVESTIGATIONS (per BS 6297:2007) Has to meet requirements of regulatory bodies i.e. Ghana EPA, MSWR, MMDAs and GOG etc.;

Must consider soil characteristics;

DESCRIPTION BEST PRACTISE

Proximity to water body i.e. well, borehole, springs, streams, water courses 50 m

Proximity to buildings 10 m

Site boundary 2 m

Site topography and practicalities Avoid valleys and low points

Water supply pipes Should not be located within disposal area

Access roads, driveways and pavements Should not be located within disposal area

Power supply cables Should not be located within disposal area

Other drainage fields and rain water soak aways Should not be located within disposal area

Additional considerations Access for desludging;Space for future expansion;

VISUAL SITE INSPECTION

Water table information from previous records (flood risk?)

Plants as drainage indicators

Other factors

Percolation Test (Trial Hole)

Dig trial hole adjacent to potential drain field;

1m × 1m hole should be dug or bored to 1.5 m below the proposed pipe invert level;


Cover to protect from rain fall

Leave open for a period to determine ground water level;

Textual descriptions or photographs of the soil should be recorded;

Where soil conditions are variable further trial holes should be dug;


Three percolation test holes should be located over the areas to be tested;

1m × 1m hole should be dug or bored to the proposed depth (min 0.3 m) and another hole dug 0.3m x 0.3m x 1m depth below the proposed pipe invert level;


Add 50 mm of coarse gravel to protect the bottom from scouring;

Carefully fill each hole with water to 300mm above the gravel and allow to seep away completely;

If the water seeps away in 10 minutes the hole should be refilled max 10 times. If the water continues to seep away, the area is not suitable;

If the water has not soaked away in 6 hours, the area is not suitable;


Measure percolation rate by refilling each hole with water to a depth of 300 mm and observe the time in seconds for the water to seep from 75% (225mm) to 25% (75mm);

Divide this time is seconds by 150mm, providing the average time in seconds for 1mm drop;

Repeat the test at least three times in each hole;

Percolation Test (results analysis)Elapsed Time Vp (s/mm)

Hole No. Test Date Test No. Start Time Finish Time Hours Minutes Seconds Seconds divided by 150mm

1

14-Mar 1 8:00 9:12 1:12 72 4320 29

14-Mar 2 9:30 10:54 1:24 84 5040 34

14-Mar 3 11:15 12:55 1:40 100 6000 40

Average Vp 34

Elapsed Time Vp (s/mm)

2

14-Mar 1 8:00 10:30 2:30 150 9000 60

14-Mar 2 10:45 13:48 3:03 183 10980 73

14-Mar 3 14:00 17:55 3:55 235 14100 94

Average Vp 76

Elapsed Time Vp (s/mm)

3

14-Mar 1 8:00 13:30 5:30 330 19800 132

14-Mar 2 13:45 19:12 5:27 327 19620 131

15-Mar 3 8:00 13:45 5:45 345 20700 138

Average Vp 134

10015 ≤≤V pIf Then drain field is possible

Percolation Test (Calculating Trench Area)

For Septic Tanks25.0××= V ppA

For Packaged Waste Water Treatment Plants20.0××= V ppA

For Digester Effluent (approximation)043.0××= V ppA

A – required drainage field floor area;p – number of people served;

Vp – percolation value

Percolation Test (Calculating Trench Area)Hole Vp (s/mm) Area (m2)

1 34 51

2 76 114

3 134 200

Constructing Drain fields

Excavate trenches to required dimension (length, breath and depth);

Spread chippings in trenches to adequate thickness and levels or fall;

Lay slotted pipes on chipping to the required direction of flow and fall;

Spread another layer of chippings over the surface of the pipes;

Cover the surface of the chippings with soil to grade; Grass over the drain field area to prevent erosion;

DECISION TOOLS

What to do when Drainage Field not possible!! PROBLEMS!!

Alternative remedies will be required when: Bad soils: building sites with soils of very low or high percolation rates or no soil

percolation; Failed septic systems: sites where an existing septic system has failed and there is

limited space or other constraints on septic system repair Rocky building sites or sites with bedrock and not enough topsoil to treat and

dispose of wastewater. Small building sites which lack adequate space to install a conventional septic drain

field; Steep building sites which do not permit installation of a conventional drain field; Wet building sites with high groundwater or subject to surface runoff (that cannot

be fully diverted);

SOLUTIONS FOR WATERLOGGED AREAS – Microflushand dry compost toilets

Vol per flush – 0.15 L

Can be coupled with Ecological Sanitation i.e.

separating faeces from urine

SOLUTIONS FOR WATERLOGGED AREAS –commercial solutions

SOLUTIONS FOR WATERLOGGED AREASDescription Advantages Disadvantages Suppliers

Micro-flush toilets Small foot printModerate treatment performance

Not pour flush toiletsNot always trappedProprietary flap mechanism

Various SPIs

Dry compost toilets Small foot printModerate treatment performance

Not pour flush toiletsNuisance insects

Various suppliers

Passive aerobic tank systems

Small foot printModerate treatment performance

ExpensiveLimited capacity (12 persons)

DuraplastInterplast

Hydroponic / macrophyte reactors

Small foot printGood treatment performance

ExpensiveElectro-mechanical components

Biofilcom

Re-circulatingtrickling filter systems

Small foot printGood treatment performance

ExpensiveElectro-mechanical components

BiofilcomCorrect Plumbing and Engineering

Plumbing for wastewater

WC Fixation Screws

Back flow Preventer

Angle Valve & Flexible tube

Traps

WC adaptors

YTee

Clean OutSwept Tee

Straight tee

WC

Basin

WHAT IS A VERMIFILTER?(also vermi-digester) Aerobic treatment system; Biological reactor containing media that

filters organic material from wastewater; Media provides habitat for aerobic microbes

and composting earthworms; Used for sewage treatment, agro-industrial

wastewater treatment and some industrial wastewater treatment;

VERMIFILTRATION PROGRAMS AROUND THE GLOBE

Uganda (Oxfam)

India (Oxfam)

GHANA (Biofilcom)

Liberia (Oxfam)

Chile (1992) Australia

China

USA Vermicomposting

in 1920s

South Africa

Earthworm body works like a biofilter; Grind, aerate and crush the faecal sludge, prepare material

for microbes to degrade the sludge; increasing the total surface area, which enhances the ability

to adsorb organic and inorganic from waste water;

EARTHWORMS AND THE VERMI-DIGESTER

Poor performance in removal of contaminants; Poor volume reduction of fecal material; Poor media porosity; macro organism environment dominated by nuisance

species;

Above will lead to: Odors in digesters; Poor drainage in digesters; Digesters flooding;

WHAT HAPPENS IN DIGESTERS WITH NO WORMS

Unhappy customers;

=

VERMI-DIGESTERS WITH WORMS

Earthworm Species; Eudrilus Eugeniae (African Night Crawler) Eisenia Fetida (California Red Wiggler)

Stocking Density Ideal - 10,000 worms per m3, can start with 1,500 worms per

m3

Hydraulic Loading Rate Range – 0.97 – 2.5 (m3/day)/m2 .can start with 1,500 worms

per m3

Specialization Eisenia Fetida better for scenarios for periodic flooding;

IMPORTANT VERMIFITRATION PARAMETERS

After 1 week of use.

Why? Media needs to be moist, indicating right conditions for microbial and earthworm activity;

WHEN TO SEED THE DIGESTER

QUESTIONS

report for training on drain field design …data.mswrpcu.com/sites/default/files/cpes gama report...

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