EMI Civil & Environmental Design Guide · PDF fileFrom B.C. Punmia, Askok Jain, and Arun Jain. Environmental Engineering‐I: Water Supply Engineering. New Delhi

Developed and Compiled by

Sarah Young, P.E. Technical Advisor for Water & Sanitation Living Water International

And

John Agee, P.E. Staff Civil Engineer Engineering Ministries International

Revised November 2013

Civil&EnvironmentalPreliminaryDesignGuideforundevelopedsites

EMI Civil & Environmental Preliminary Design Guide

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TableofContents1. Water Usage ........................................................................................................................................... 1

Exercise 1.1 ...................................................................................................................................... 2

Exercise 1.2 ...................................................................................................................................... 2

2. Water Sources ........................................................................................................................................ 7

Exercise 2.1 .................................................................................................................................... 10

3. Water Storage ...................................................................................................................................... 11

Exercise 3.1 .................................................................................................................................... 12

4. Water Pumps ........................................................................................................................................ 13

Exercise 4.1 .................................................................................................................................... 14

5. Water Quality & Treatment ................................................................................................................. 15

6. Onsite Soil Evaluation ........................................................................................................................... 16

7. Wastewater Primary Treatment .......................................................................................................... 21

Exercise 7.1 .................................................................................................................................... 24

8. Onsite Wastewater Disposal ................................................................................................................ 25

Exercise 8.1 .................................................................................................................................... 29

Exercise 8.2 .................................................................................................................................... 29

Exercise 8.3 .................................................................................................................................... 31

9. Onsite Solid Waste Disposal ................................................................................................................. 33

10. Site Drainage ........................................................................................................................................ 34

11. System Layout ...................................................................................................................................... 35

12. General Comments .............................................................................................................................. 36


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1. WaterUsageA. RESEARCH the domestic water use rates for the country of interest. EMI has documented average

domestic use of 135 liters per day per person for projects in South Asia and Africa (family unit housing

with indoor plumbing). Use projected site population times the use rate to give a conservative estimate of

proposed daily water usage while on the project trip. You may need to provide estimates for phased

growth. This will help in the initial estimation of footprint areas needed for water storage facilities and the

wastewater disposal area needed while the team is developing the master plan.

B. OBSERVE water use by locals. Try to estimate what the total daily usage actually is for a person living on

site. This habit of using engineering judgment will pay off with a more efficient or more economical design

if the conditions and practices of the client are not average.

C. DEVELOP a detailed water use estimate. Use the included charts as appropriate (Tables 1.1 through 1.7)

for estimating water usage depending on the site. Some architectural revision will likely occur on or after

the project trip, so keep in mind that this will probably affect the water use estimate.

D. COMPARE the projected water use rates that you developed from both the empirical data you measured

or estimated on site and the projections you developed in the previous step. Use your judgment and

make final projections to accompany the master plan.

E. DETERMINE where wastewater will go after it is used. Consider separating wastewater from sink and

shower drains (greywater) and toilets (blackwater). Blackwater should pass through a septic tank to a

soakage area, but greywater may flow directly into a soakage area (reducing the necessary size of the

septic tank).


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Exercise1.1You have a client in the outskirts of Kigale, Rwanda who plans to develop a rural site for a 50 bed hospital. It is

expected that the daily out‐patient care will accommodate 500 patients. Included on the site will be staff duplex

housing for 12 staff families and 15 single staff. The client also has plans to provide an elderly care hostel for 10

individuals. Live‐in care for the elderly will be provided by 4 staff.

a. Develop a detailed water use estimate for this scenario.

b. Determine how much of the total daily water use is greywater and how much is blackwater.

Exercise1.2You are working for an Indian client who is doing community development work in two villages which are located

near each other. The client wants to serve the two villages with a single potable water system by piping water

that will flow by gravity from a spring to strategically placed collection tanks in each village. Jori village has 18

families and Toneta village has 35 families. The average family owns one water buffalo. The client is also planning

on installing VIP latrines (which use no water for flushing) to meet sanitation needs.

How much water will be needed daily in each of these villages?


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Table 1.1: Water Requirements for Domestic Purposes in India From B.C. Punmia, Askok Jain, and Arun Jain.

Environmental Engineering‐I: Water Supply Engineering. New Delhi: Laxmi Publications, 1995

Description Amount of water in

liters per head per day

Bathing 55

Washing of clothes 20

Flushing of Water Closet 30

Washing the house 10

Washing of utensils 10

Cooking 5

Drinking 5

Total 135 liters

Table 1.2: West Africa Water Demand Assumptions (Indoor Plumbing)

Description Amount of water in

liters per head per day

Water Requirements For Domestic Purposes

Bathing/ Personal Hygiene 55

Laundry 15

Flushing of Toilet 30

Janitorial 5

Utensil Washing 5

Cooking 5

Drinking 5

Total 120 liters

Water Requirements For Day‐Use Institutional Purposes

Personal Hygiene (handwashing) 5

Flushing of Toilet 20

Janitorial 4

Utensil Washing (Cafeteria) 4

Cooking (Cafeteria) 4

Drinking 3

Total 40 liters

Note: The table above addresses assumptions made in a suburb of Accra, Ghana in West Africa.

Always research and interview locals to better gauge their water usage

considering use and demand can vary between regions.


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Table 1.3: Consumption of Water for Domestic Animals and Livestock in India From B.C. Punmia, Askok Jain, and Arun Jain.


Animals Water consumption in liters per animal per day

Cow and buffalo 40 to 60

Horse 40 to 50

Dog 8 to 12

Sheep or goat 5 to 10

Table 1.4: Water for Domestic and Non‐Domestic Needs in India From B.C. Punmia, Askok Jain, and Arun Jain.


Community Description Amount of water

(liters per capita per day)

Population up to 20,000:Supply through stand post

40 (minimum)

Population up to 20,000:Supply through house service connection

70 to 100

Population 20,000 to 100,000 100 to 150

Population above 100,000 150 to 200


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Table 1.5: Water for Institutional Needs in India From B.C. Punmia, Askok Jain, and Arun Jain.


Institution Water Requirement

(liters per head per day)

Hospitals (including laundry):No. of beds exceeding 100

450 (per bed)

Hospitals (including laundry):No. of beds not exceeding 100

340 (per bed)

Hotels 180 (per bed)

Hostels 135

Nurse’s homes and medical quarters 135

Boarding schools/colleges 135

Restaurants 70 (per seat)

Airports and sea ports 70

Junction stations and intermediate stationsWhere mail and express stoppage (both

railways and bus stations) is provided

70

Terminal stations 45

Intermediate stations(excluding mail and express stops)

45 (could be reduced to 25 where bathing facilities are not provided)

Day schools/colleges 45

Offices 45

Factories 45 (could be reduced to 30 where no bathing rooms are required to be provided)

Cinema, concert halls, and theatres 15


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Table 1.6: Village Use Only – Water from Standpipe From Water for the World: Estimating Sewage or Washwater Flows,Technical Notes No. SAN. 2.P.2;

U.S. Agency for International Development by National Demonstration Water Project, Institute for Rural Water, and National Environmental Health Association

Region Water Use per Person per Day

(in Liters)

Africa 15 to 35

Southeast Asia 30 to 70

Western Pacific 30 to 95

Eastern Mediterranean 40 to 85

Algeria, Morocco, Turkey 20 to 65

Latin America/Caribbean 70 to 190

Note: Averages are for areas where water is hand‐carried from standpipes no more than 200m distant.

Table 1.7: Sewage or Washwater per Fixture From Water for the World: Estimating Sewage or Washwater Flows,Technical Notes No. SAN. 2.P.2;


Fixture Amount per Use (in Liters)

Pour‐flush Latrine 1 to 3

Tank‐type Flush Toilet 13 to 23

Wash Basin 5

Shower 95 to 120

Kitchen Sink 15 to 18

Laundry Sink (wash/rinse) 150 to 190


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2. WaterSourcesA. CONSIDER all possible water sources regardless of your initial opinions of the feasibility of actual use. Do

everything you can to identify a single sustainable, year‐round water supply with enough quantity to meet

the normal daily needs of the client. In many cases more than one water source will be needed.

B. POTENTIAL WATER SOURCES

a. GROUNDWATER

i. SHALLOW WELL

Is there currently a shallow dug well on site or near the site? Is this the locally preferred

water source? Investigate the construction method and make design notes. What is the

expected depth? Can you take a water sample and have it analyzed? What type of water

treatment methods are feasible? Will the well dry up in the dry season? Investigate the

costs of construction.

ii. DEEPER WELL

Is it feasible to have a well drilled or bored? Find a drilled well on site or very near the

site and find out it’s depth, capacity (liters per hour pumped), and construction method.

Do everything you can to find a written well log for this well or interview the actual driller

about the depth, quality, and quantity of water available. Investigate the costs of

construction.

iii. SPRING WATER

How far away is the spring? Is it feasible to construct a spring box, protecting the source,

and pipe water to the site? Test the quality of spring water, and interview those familiar

with the area to determine its consistency and potential production of water.

b. SURFACE WATER (stream, spring, lake, etc.)

How far away is the surface water source? Can you do a water analysis? What treatment

methods are feasible? Consider intake design. What is the cost of constructing the intake and

treatment system?

c. PUBLIC WATER SYSTEM (pipe in the road)

Is there a reliable public water distribution system nearby? What amount/pressure of water is

available? How far away? Will the water need treatment to make it drinkable? Consider

construction costs for tying into the system. Interview the local utility manager.

d. RAINFALL COLLECTION

Many places have significant but seasonal rainfall, yet it is expensive to construct and maintain

long‐term water storage facilities. Therefore, expect that rainfall collection will be a

supplementary solution (i.e. for watering gardens, temporary water supply during the rainy

season). Find accurate regional data for precipitation or use the internet to do more detailed

research. Estimate (using roof areas) how much water can be collected from the proposed roof

areas during a typical day, week, and month during the rainy season.


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C. GENERAL OBSERVATIONS ABOUT WATER QUALITY AND QUANTITY

a. Surface water sources and groundwater sources under DISW (direct influence of surface water)

DISW sources can include springs and wells which are developed in alluvial formations (a shallow

unconfined aquifer). What quality and quantity can you expect?

i. Seasonal variations in water quality and quantity (depending on rainfall)

ii. Bacterial contamination quite possible

iii. Can be affected by septic tanks or fertilizers (presence of nitrates)

iv. Can be affected by many contaminants which enter at the ground surface (not able to test for)

v. Can contain high iron levels (can affect design of a treatment system)

vi. Often in an unconfined aquifer plenty of water will be available during most of the year

vii. Quality of water may be directly affected by community action to eliminate improper disposal

of wastes and rainwater recharge practice

b. Groundwater source not under DISW. This includes groundwater sources in a confined aquifer. What

quality and quantity can you expect?

i. Bacterial contamination or other contaminants will not be present

ii. Minerals and total dissolved solids may be high (affects treatment, may cause deposits in pipes)

iii. Sometimes these sources have drinking water quality without treatment

i. Quantity of water may be limited

Figure 2.1: Confined and Unconfined Aquifers from B.C. Pummin, Askok Jain, and Arun Jain. Environmental Engineering‐1: Water Supply Engineering.

New Delhi: Laxmi Publication, 1995. p. 67.


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Figure 2.2: Perched Aquifer from B.C. Pummin, Askok Jain, and Arun Jain. Environmental Engineering‐1: Water Supply Engineering.

New Delhi: Laxmi Publication, 1995. p. 68.

Figure 2.3: Types of Wells from B.C. Pummin, Askok Jain, and Arun Jain.

Environmental Engineering‐1: Water Supply Engineering. New Delhi: Laxmi Publication, 1995. pp. 85, 90, 99.

Strainer Type Tube Well Slotted Type Tube Well

Open Wells


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Exercise2.1You’ve learned that at the Kigale hospital site it is possible to construct both a shallow open well, deep tube wells,

and a city water service connection. After talking to a neighbor who has a shallow open well, you’ve learned that

he is able to get 14,400 liters/hr consistently except during the dry months of Jan, Feb and July when the water

table sometimes drops and the well dries up. An open well costs 5,000 USD to construct. Pumping from this well

will cost about 100 USD per month. You only have enough space on your site to construct one of these. You’ve

also learned that deep tube wells only yield 7,200 liters/hr. One tube well costs 8000 USD to construct. Pumping

from each tube well will cost about 150 USD per month.

The community water supply is usually consistent with occasionally a couple of weeks of water shortage during

the dry season. The average flow is expected to be 3,600 liters/hr through the 50mm connection that the

government allows. It will cost 1000 USD to install the connection and a flat fee of 100 USD per month regardless

of the reliability of service.

Note that during the dry season, the average daily water usage goes up by 25%.

Knowing these facts, which water sources would you recommend for the client to develop and how many of

each?


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3. WaterStorageA. DISTRIBUTION SYSTEM LAYOUT

a. COMMON APPROACH: It is typical in many countries to install multiple rooftop tanks, one over

each bathroom or kitchen with 200 to 500 liters of storage each. This provides individuals a sense

of control over the area they are using. If others run out of water, then they can conserve their

own if they have their own tank. It is also common to install dead end lines. The problem with

this is that if a site is going to be developed to include multiple buildings, there is a higher

maintenance burden and lack of ability to transfer water to where it is needed most.

b. EMI APPROACH: Since many EMI projects do involve long‐term planning for multiple buildings,

we recommend having dialogue with the client about accepting the idea of a battery of central

water storage tanks (tough plastic tanks up to 10,000 L each) coupled with a looped water

distribution system (where appropriate) to allow for economical and efficient water delivery to all

of the buildings. Central water storage and a looped water distribution system are sometimes a

new idea to many of our clients, so it is important to spend the needed time sharing the idea,

getting feedback, and making this approach as easy to adopt as possible. The battery of water

storage tanks may be placed on a structurally designed platform (preferred to us) or on top of the

tallest building, providing that adequate water pressure can be achieved in the other buildings

from that location.

B. STORAGE TANKS

a. CAPACITY: Provide a MINIMUM of one day’s supply of water storage. Dialogue with the client to

hear their views on needed water storage. They may want more storage and up to two day’s

supply is better for critical facilities such as a hospital.

b. WATER STORAGE SOLUTIONS: Prefabricated black plastic tanks are easily available in sizes of

200L, 500L, 1000L, 2000L, 5000L, or even 10,000L. These tanks are generally filled from top and

have a pipe exiting the bottom for distribution. Solenoid or float valves can be used to cut off the

flow of water when the tank is full. For the most part, plan to store one day’s worth of water

supply. Facilities which need more supply in case of emergency (i.e. hospital) plan for up to 2

days water storage. Certain circumstances could call for less than one day’s water supply. For

example if the electricity is available all the time and/or if the facility has no residents and/or no

meals provided, it would be acceptable to consider a smaller water storage capacity.

C. WATER PRESSURE

In general, other countries do not use as much water pressure as we do in the United States. Anywhere

from 14 kPa to 35 KPa (2 to 5 psi) may be perfectly acceptable. Observe the pressure levels in the local

water systems.

D. CENTRAL WATER SUMP

It is common practice in many countries to install a central water sump at ground level which receives

water from more than one source (i.e. water from the multiple wells and from the public water line. EMI

does recommend this option for many of our client’s sites as it provides added storage and is efficient

when using more than one source.


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Exercise3.1For the Kigale hospital, determine the total water storage needed.

a. Assuming plastic tanks are used, recommend the number and size of tanks needed. Figure out how big the

footprint needs to be for the entire battery of tanks, assuming 600mm spacing and an average tank height

of 2 meters. Assume that the tanks can be placed on the roof of the main multi‐story hospital building and

that the friction losses can be neglected.

b. Assuming a reinforced concrete box style tank is constructed and assuming 0.3 meter of freeboard (space

above the liquid level), what dimensions are needed for the tank?

c. If the highest water fixture is 4 meters below the roof slab, how high does the floor of each tank need to be

in order to provide a minimum of 35 kPa of water pressure (1 m of elevation = 9.8 kPa)?


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4. WaterPumpsA. ELECTRICITY

Find out the typical number of hours electricity is available each day, perceived frequency of electricity

interruptions (i.e. are there ever interruptions for many days and how many times a year does this

happen?), whether it is single phase or three phase power, and how far away the community connection

will be.

B. PUMPS

Pumps commonly used for shallow or open wells may be either centrifugal pumps with suction lines or

submersible pumps. Pumps for deep or bored wells are usually submersible pumps or a surface air

compressor system (used on low capacity wells). Another option for a low capacity deeper well (although

not commonly used) is a solar powered pump.

RECOMMEND for each scenario the acceptable pump types, pumping rate, and total dynamic head range

needed for the well pump. Remember to consider the hours of electricity availability and anticipated well

capacity when recommending the pumping rate for filling the water storage tanks and sump.

a. PUMP SYSTEMS

i. Centrifugal

ii. Submersible

iii. Air Compressor

iv. Solar

b. PIPE MATERIAL

i. PVC

ii. HDPE

iii. Galvanized Iron

C. PUMPING CISTERNS

If multiple sources of similar quality are being used or could potentially be used in the future or if there is

not enough water pressure in a city main to fill the ministry’s rooftop tanks, plan for a cistern which can

hold one day of water supply. The sump should have a centrifugal pump sized which is capable of filling

the elevated storage tanks in a reasonable amount of time (i.e. a maximum of 12 hours running time per

day would be good).

D. PUMPING WELLS

An open well can use either a submersible pump or a centrifugal pump (if the suction head is 10 meters or

less). This pump should be sized so that a continual pumping rate can be maintained without drawing

down the well to shut off the pump. Pumps are often rated in liters per hour. Determining the elevation

head range + the friction head will be needed to determine the total dynamic head range for the pump.

A deep tube well can use a submersible pump or if the available pumping rate is less than 1,000 liters per

hour, consider an air compressor or solar pumping system.


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Exercise4.1For the Kigale Hospital, assume the water sources you recommended previously have all been developed and

have the capacities originally estimated. Assume that a cistern with 1‐day storage is constructed.

a. With the sump pump turned off and assuming you are filling the sump for the first time, how long on

average would it take to fill the sump if all of the water sources were functioning and supplying water

simultaneously?

b. Recommend some dimensions for the cistern.

c. With the information you already know about the open well, what general recommendations would you

make about selecting the pump for that well?

d. What recommendations would you give for selecting the pump for the deep well(s)?

e. And the pump for the cistern?


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5. WaterQuality&TreatmentA. TEST water to determine necessary treatment. In the developing world, if bacteria are commonly present

in the water source, it is not expected that all taps should yield drinking‐quality water. EMI recommends

the installation of filtration/UV disinfection units or ceramic filters at key locations on the site where

drinking water will be needed (i.e. kitchens). Use the EMI water test kit to evaluate water sources.

Contaminants such as high minerals and nitrates may indicate the need for other treatment steps. If

possible, request that the client have a testing lab complete analysis of the water quality for each

established water source. This is most helpful if completed before the project team arrives.

Table 5.1: Drinking Water Standards Comparison

Parameter World Health Org.

INDIA US EPA CANADA European Union

JAPAN Undesirable Effect

Outside Limit

Nitrate (mg/l) 50 45 ‐ 100 10 10 50 10

Causes infant methemoglobinemia (blue babies). May cause gastric

cancer; affects central nervous & cardiovascular systems.

pH 6.5 ‐ 8.5 6.5 ‐ 9.2 6.5 ‐ 8.5 6.5 ‐ 8.5 6.5 ‐ 9.5 5.8 ‐ 8.6 Affects taste.

Chloride (mg/l) 250 250 ‐ 1000 250 250 250 200

Affects taste and palatability; causes indigestion and may be injurious to people suffering

from heart and kidney diseases.

Hardness (as CaCO3 mg/l)

n/a 300 ‐ 600 n/a 75 50 300 May cause urinary concretion, disease of kidney, bladder and

stomach disorder

Iron 0.3 0.3 – 1.0 0.3 0.3 0.2 0.3 Bittersweet astringent taste.

Total Dissolved Solids (mg/l)

1000 500 ‐ 1500 500 500 n/a 500 Causes gastrointestinal irritation.

Total Coliforms (including fecal coliform and E. coli)

Not detected in any 100ml sample

Not detected in any 100ml sample

Not a health threat in itself; used to indicate whether other

potentially harmful bacteria may be present. Coliforms are naturally present in the

environment; fecal coliforms and E. coli come from human and

animal fecal waste.

Parameters Typically Not Tested by EMI Water Test Kits

Turbidity (NTU) 1 ‐ 5 2.5 ‐ 10 0.3 ‐ 1.0 n/a n/a n/a Aesthetically undesirable and interferes with chlorination.

Indicates other contamination.

Fluoride (mg/l) 1.5 0.3 ‐ 1.0 4.0 n/a 1.5 1.0

Reduces dental cavities in range of 0.8 to 1.0 mg/l; at high levels causes teeth mottling, skeletal

and crippling fluorosis.

Arsenic (mg/l) 0.01 0.05 0.01 0.01 0.01 0.05 Skin diseases, circulatory system

problems, risk of cancer.

Lead (mg/l) 0.01 0.05 0.015 0.01 0.01 0.01 Serious cumulative body poison.


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6. OnsiteSoilEvaluationA. EVALUATE SOIL TYPE at 300mm to 1000mm depth immediately. Use the subjective soil type flow chart.

If the soil has high clay content, warn the master planner that wastewater disposal may require significant

land area. Note that the soil evaluation is mainly useful for planning a leach bed or leach field wastewater

disposal system. Performing the soil type test is the minimum information requirement for determining

the land area needed (Figure 6.1).

B. INTERVIEW knowledgeable locals or consult a drilling log (if an on‐site well has been completed already)

to determine the changes in soil strata as the depth increases. Take a good digital photo of the drilling log

if it is available and download the photo onto the project leader’s computer project file. This information

will be used to size seepage pits.

C. GROUNDWATER DEPTH: Important! Find out how deep the water table is during the peak of the rainy

season. We want to avoid designing a system which contaminates the groundwater. Good design

requires that at least 1000mm of soil thickness (not coarse sand or gravel) should separate the bottom of

the seepage pit, leach bed, or leach field from the water table.


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Figure 6.1: Guide to Texture by Feel [online] http://soils.usda.gov/education/resources/lessons/texture/.

Modified from S.J. Thien. 1979. A flow diagram for teaching texture by feel analysis.

Journal of Agronomic Education. 8:54‐55.


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Figure 6.2: Texture Triangle and Particle‐Size Limits of AASHTO, USDA, and Unified Classification Systems


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D. DETERMINE SOIL PERMEABILITY. Soil permeability

refers to the rate at which liquid percolates into the

soil. Percolation of water into soil can be measured by

digging a hole, pouring in water, and timing the rate

at which the water drains out of the hole. This

percolation test is fairly simple to conduct, but it must

be done carefully to yield accurate results.

a. Gather Materials

i. Shovel

ii. Watch or other timepiece

iii. Measuring tape or ruler

iv. Board or piece of lumber about 0.6m long

v. Pencil and notepad

vi. Optional: Auger with extension handles

(extremely useful tool for digging test holes)

b. Conduct Percolation Test Based on Water for the World: Determining Soil Suitability, Technical Notes SAN 2.P.3‐5; U.S. Agency for International

Development by National Demonstration Water Project, Institute for Rural Water, & National Environmental Health Assoc.

i. Two Percolation tests should be conducted at the proposed site. If the system is an absorption

field or soakage trench, the tests should be conducted about one‐third of the distance in from

each end of the system, as shown in Figure 6.4. Dig the test holes for a field or trench to the

depth of the proposed system (i.e., if the proposed trench is 1m deep, the test hole is 1m deep).

If the proposed system is a cesspool or soakage pit, the tests are conducted in the center of the

system at the proposed site of the cesspool or pit. The first test is performed at one‐half the

depth of the cesspool or pit, and the second test at full depth (i.e., if the proposed pit is 2.4m

deep, first test is 1.2m depth and second is 2.4m). Results of the two tests generally will be

about the same. If they differ, use the slower of the two percolation rates to design the system.

ii. Dig or bore a new hole in undisturbed soil about 300mm in diameter, or 300mm square, to the

proper depth. Make the walls of the hole vertical. Scrape the walls to remove any patches of

compacted soil. Place about 50mm of clean gravel in the bottom of the hole.

iii. If you detect any clay content, fill the hole with water and let it soak for 12 hours. This allows

ample time for soil swelling/saturation. If no clay content, proceed with the test immediately.

iv. Place a board or piece of lumber across the center of the hole and anchor it firmly in place,

perhaps by placing a rock on each end. The board must not be moved until the test is complete.

Mark a point near the center of the board to be used as a guide for the remainder of the test.

v. If the hole was saturated, most or all of the water poured in will have drained away within 12

hours. Pour in enough water so that the depth of water is 200mm.

vi. Place the measuring tape or ruler next to the reference mark on the board and slide it down

until it barely touches the water surface. Ripples on the water can be observed when the end

touches. Record the exact time and measurement to the water surface.

vii. Repeat the previous step at 10‐minute intervals. If the water level drops rapidly, repeat at one‐

minute intervals. Do not allow the water to drop lower than 100mm. If it does, pour in more

water to the 200mm depth and continue the test.

Figure 6.3: Test Hole with Apparatus Water for the World: Determining Soil Suitability,

Technical Notes No. SAN. 2.P.5


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viii. Note the difference between measurements to the water surface (subtracting each reading

from previous). When at least three differences in subsequent measurements become closely

equal, the test is completed. This may take as little as one‐half hour or as long as several hours.

ix. Using the equal difference, calculate how long it took the water level to drop 25mm. This step is

necessary because percolation rates are described in terms of “minutes per 25mm.” To find out

how long it takes for the water level to drop 25mm, divide 25mm by the equal difference and

multiply by the time interval for those measurements. If the percolation rate for 25mm is

between 10 and 60 minutes, the soil is acceptable.

E. COMPARE results from the percolation test with the soil type results and determine onsite wastewater

disposal method (Section 8).

Figure 6.4: Location and Depth of Percolation Tests Water for the World: Determining Soil Suitability, Technical Notes No. SAN. 2.P.5;



21

7. WastewaterPrimaryTreatmentA. INTERVIEW locals to determine if community sewer system connection is available to the site. Most

times this is not the case, but occasionally this is available.

B. STUDY HOW THE LOCALS DISPOSE OF WASTEWATER. Small on‐site wastewater disposal systems in

many areas where EMI has worked have consisted of a septic tank and soak pit system handling only the

blackwater. Greywater is plumbed separately and allowed to runoff untreated in some way. This practice

may be accepted and used, but check around. Another disposal system often used is pit latrines. A table

for “Excreta Accumulation Rates” is included in Table 8.2 for use in pit latrine design. Depending on depth

to the water table, plans for site use, and the soil conditions, these two systems may or may not be

recommended by EMI. Try to use similar technology to local practice while improving the treatment and

disposal one or two steps from current practice. Where large populations are using a site, take care to

deal with the grey water so that human contact is avoided (i.e. use for irrigation away from public areas or

include in subsurface disposal if conditions allow).

C. DECIDE whether or not to split blackwater and greywater disposal. This may vary in different zones of the

site if the site is larger than an acre or two. Dialogue with the client about their feelings of the importance

of greywater reuse.

D. MINIMIZE LONG PIPELINES and AVOID PUMPS.

E. SEPTIC TANKS

a. Description

i. Primary sedimentation to remove suspended solids

ii. Digestion through anaerobic decomposition – septicity (foul gases produced H2S, CH4, CO2).

Digestion can remove more than 1/3 of the original sludge volume. Results – removal and

digestion of solids, poor effluent quality. Thus the need to dispose of it subsurface or to provide

BOD removal and disinfection before surface disposal.

iii. Storage of sludge and scum accumulating in between successive cleanings.

b. Design

From Septic Tank Design method from World Health Organization

“Guide to the Development of On‐Site Sanitation”, 1992

i. To determine the capacity of the septic tank, volumes must be calculated to include room for

liquid retention and for sludge & scum storage:

1. Tank Volume Required for Liquid Retention in liters is calculated based on the retention of

the average daily wastewater flow for 24 hours. If the tank is to receive the total

wastewater flow, then the volume needed may be taken as 90% of the water supply per

day. If the tank is to receive only blackwater then the volume needed may be taken as

100% of the blackwater flow per day. For larger flows such as those serving institutions or

small communities, a reduced retention time is allowed. Table 7.1 presents retention times

based on flow rates.


22

Table 7.1: Retention Times for Various Flows

2. Tank Volume Required for Sludge & Scum Storage in liters, calculated using the formula:

Volume = P x N x F x S

P = number of people

N = the number of years between desludging

F = a factor which relates the sludge digestion rate to

temperature and the desludging interval as shown in Table 7.2 below

S = the rate of sludge and scum accumulation may be taken as 25 liters per person per year

for tanks receiving black water only and 40 liters per person per year for tanks receiving all

types of wastewater. These numbers are based on residential rates and must be adjusted if

the tank serves an institution.

Table 7.2: Sludge Digestion Factor (F)

Number of years

between desludging

F (if ambient temp >20 oC throughout

the year)

F (if ambient temp >10 oC throughout

the year)

F (if ambient temp <10 oC during

winter)

1 1.3 1.5 2.5

2 1.0 1.15 1.5

3 1.0 1.0 1.27

4 1.0 1.0 1.15

5 1.0 1.0 1.06

6 or more 1.0 1.0 1.0

3. Total Capacity of the Tank in Liters is the sum of the volumes required for Liquid Retention

and Sludge & Scum Storage.

ii. To determine the dimensions of the septic tank, follow these guidelines:

1. The depth of the liquid from the tank floor to the outlet pipe invert should not be less than

1.2 m; a depth of at least 1.5 m is preferable. In addition a clear space of at least 300 mm

should be left between the water level and the under‐surface of the cover slab.

2. The width should be at least 600 mm as this is the minimum space in which a person can

work when building or cleaning the tank.

3. For a tank of width W, the length of the first compartment should be 2W and the length of

the second compartment should be W. In general, depth should be less than total length.

iii. Tank should be put downhill from contributing facilities with inlet pipe at a minimum 2% slope.

If Q (flow) is less than 6,000 L/day T = 24 hours

If Q (flow) is between 6,000 L/day and 14,000 L/day T = 33 – 0.0015Q hours

If Q (flow) is greater than 14,000 L/day T = 12 hours


23

iv. Septic tanks should be placed close to the contributing buildings (5 to 10 meters away). The

distance should be minimized especially if the contributing flow is black water only.

v. Dividing into 2 compartments helps prevent solids from being transferred to the outlet. The

partition wall should be placed at a distance of about 2/3 the length from the inlet.

vi. Inlet, middle, and outlet tees, extend below the scum line to prevent clogs and transfer of scum.

vii. The outlet flowline is placed 50 to 75 mm below the inlet flowline.

viii. Tank is designed to be watertight to avoid seepage into the ground at the location of the tank.

ix. Access hatches are placed above each compartment for pipe maintenance and sludge removal.

x. Inlet/outlet pipes may be 75mm or 100mm PVC if coming from an individual home or two.

Large contributors will need to be 150 to 200mm. The outlet pipe is installed at a 1% slope to

move the effluent to the subsurface absorption area.

c. Maintenance

i. Do not allow chemicals or detergents to go into the septic tank.

ii. Prevent the flushing of large objects into the tank.

iii. Once per year, use a cloth‐wrapped rod lowered to the tank bottom to inspect the liquid and

sludge depths. When the sludge depth reaches 1/3 of liquid depth, sludge should be removed.

iv. Special additives or enzymes are not needed to improve the treatment.

v. Take special care when removing the hatches to avoid gas poisoning.

Figure 7.1: Basic Two‐Chamber Septic Tank

CDC Healthy Housing Reference Manual [online] http://www.cdc.gov/nceh/publications/books/housing/figure_cha10.htm.


24

Exercise7.1The staff duplex quarters at the Kigale hospital are situated in clusters of three. Each duplex houses two families.

The client desires to separate greywater and blackwater, allowing the greywater to run into the flower gardens on

the sides of the duplexes.

Size a septic tank which will be capable of serving one cluster of duplexes. Provide the Length, Width, and

Depth dimensions in meters.


25

8. OnsiteWastewaterDisposalA. PLAN for a soak pit, soak bed, or trench subsurface disposal system after primary blackwater treatment with a

septic tank if soil percolates relatively well.

a. The bottom of any pit, bed, or trench should be a minimum of 1 meter above the highest seasonal

water table.

b. If soil does not percolate within an acceptable rate or groundwater is high, begin considering

alternative treatment and disposal methods.

B. ESTIMATE NEEDED LAND AREA for subsurface soil absorption. Inform master planners of required land area.

a. Determine the allowable application rate using results from the onsite soil evaluation (Section 6) with

Table 8.1. This rate will be used to determine necessary area for subsurface soil absorption based on

type of system chosen.

Table 8.1: Wastewater Application Rate Table Recommended Rates of Wastewater Applications for Trench and Bed Bottom Areai:

Soil Texture Percolation Rate (Min/25mm)

Application Rateii

(Lpd/m2)

Gravel, coarse sand <1 Not Suitableiii

Coarse to medium sand 1‐5 90

Fine sand, loamy sand 6‐15 60

Sandy loam, loam 16‐30 45

Loam, porous silt loam 31‐60 30

Silty clay loam, clay loamiv 61‐120 15

i. May be suitable estimates for sidewall infiltration rates.

ii. Rates based on septic tank effluent from a domestic waste source. A factor of safety may be

desirable for waste of significantly different character

iii. Soils with percolation rates <1 min/ 25mm can be used if the soil is replaced with a suitably

thick (> 600mm) layer of loamy sand or sand

iv. Soils without expandable clays

b. Use the allowable application rate with the following design instructions based on the type of

subsurface system (soak pit, soak bed, or soak trench).

c. Consider reserving a suitable area for construction of a second reserve system if the first were to fail.

If a reserve system is constructed, the first can be naturally rejuvenated or used alternately with the

second system.


26

C. SOAK PITS: Recommended for percolation rates which are greater than 30 min/25mm

a. Description: A deep excavation used for subsurface disposal of septic tank effluent. Wastewater

enters the chamber where it is stored until it soaks out through the chamber wall and infiltrates the

sidewall of the excavation.

b. Design

i. Calculate area required.

1. Divide the allowable wastewater application rate into the average daily flow to determine

the needed infiltrative area.

2. Select an initial depth of 3 to 6 meters (since these are often hand dug).

3. Set up an algebra equation with the needed infiltrative area = Perimeter Length x infiltrative

depth + bottom area.

4. Determine needed surface area for one pit. If the surface area is larger than 3 meters by 3

meters, determine how many 3m by 3m pits (or smaller if appropriate) are needed.

ii. Siting: Can be located almost anywhere on site. If more than one pit is recommended, be

careful to space them far enough apart to be structurally sound and to prevent interference in

sidewall infiltration (3 times the pit width).

iii. Note: Construction may be porous masonry walls set on a gravel bed with a reinforced concrete

cover or an excavated hole filled with large stones (see Figure 8.1).

c. Maintenance: There is no maintenance for a seepage pit. If back up occurs, then the only measure is

to pump it out (if it is an open chamber) and allow resting.

Figure 8.1: Soak Pit Designs

Type 1: Brick‐Lined Pit with Reinforced Concrete Cover Type 2: Pit Filled with Rock


27

D. SOAK BEDS: Recommended for percolation rates between 1 min/25mm and 60 min/25mm

a. Description: A shallow level excavation, usually 600 to 1500mm deep and wider than 1 m. Typically

300mm of crushed rock (20mm to 65mm diameter) is placed in the bottom. Perforated distribution

lines are laid at the top of the crushed rock layer and then more crushed rock is placed to just cover

the top of the pipe network. A semi‐permeable layer is placed over the top of the rock (geo‐textile

fabric or several inches of straw) to prevent soil from penetrating into the crushed rock layer. The

needed infiltrative area is determined and the bed sized accordingly.

b. Design

i. Calculate area required. (Bottom of bed is principal infiltrative area.)



2. Set up an algebra equation with needed infiltrative area = bottom area + sidewall areas.

3. Typical dimensions:

a. Minimum width: >1 m,

b. Length: typically 10 to 30 m (may be greater or less under some circumstances)

c. Depth to bottom of bed: 600 to 1500 mm

d. Cover thickness: 150mm to 300mm and mounded on top

ii. Siting: Relatively level (less than 5% slope), well‐drained areas, crests of slopes are most

desirable. Avoid low areas, base of slope. Construct with the longer side following the contour

of the land (field needs to be level).

iii. Note: If soil percolation rate is very slow or high water table exists, the soak bed could be as

little as 150 to 300mm deep and backfill can be provided.

c. Maintenance: A subsurface soil absorption system requires little or no maintenance.

Figure 8.2: Soak Bed Design EPA Manual 625/1‐80‐012, p.210


28

E. TRENCHES: Recommended for percolation rates between 1 min/25mm and 60 min/25mm

a. Description: A shallow level excavation, trenches are usually 600 to 1500 mm deep and 300 to

1000mm in width. Typically 300mm of crushed rock (20mm to 65mm diameter) is placed in the

bottom. Perforated distribution lines are laid at the top of the crushed rock layer and then more

crushed rock is placed to just cover the top of the pipe network. A semi‐permeable layer is placed

over the top of the rock (geo‐textile fabric or several inches of straw) to prevent soil from penetrating

into the crushed rock layer. The needed infiltrative area is determined and the bed sized accordingly.

b. Design

i. Calculate area required. (Bottom and sidewalls both provide infiltrative area.)



2. Set up an algebra equation with the needed Infiltrative Area = bottom area + sidewall areas

3. Typical dimensions:

a. Width: 600 to 1000mm

b. Length: typically 10 to 30 meters (may be greater or less under some circumstances)

c. Depth to bottom of trench: 600 to 1000mm

d. Cover thickness: 150mm to 300mm and mounded on top

e. Spacing of trenches: 2 to 3 meters apart

ii. Siting: Somewhat level (less than 25% slope recommended), well‐drained areas, crests of slopes

are most desirable. Avoid low areas, base of slope. Construct with the trench following the

contour of the land. The bottom of each trench needs to be level, but trenches may be stepped

in elevation. Constructability of the system is the only limitation where slope is concerned.

iii. Note: If soil percolation rate is very slow or high water table exists, the trenches could be

installed as little as 150 to 300mm deep and backfill can be provided, as shown in Figure 8.4.

c. Maintenance: A subsurface soil absorption system requires little or no maintenance.

Figure 8.3: Trench Design EPA Manual 625/1‐80‐012, p.209, 220.

Typical Trench Cross Section Alternating Trenches


29

Figure 8.4: Cross Section of Raised Trenches EPA Manual 625/1‐80‐012, p.209, 220.

Exercise8.1From a percolation test, the average percolation of the soil at Kigale Hospital is 20 minutes per 25mm.

a. Calculate the size required of one soak pit for the septic tank effluent.

b. Calculate the size required of one soak bed for the septic tank effluent.

c. Calculate the size required of one set of trenches for the septic tank effluent. How much land should be

reserved for the trench system?

Exercise8.2Using the results from Exercise 8.1, compare the space requirements for the three types of subsurface

absorption systems and discuss advantages and disadvantages.


30

F. PIT LATRINES

a. Description.

i. A VIP latrine reduces smell and flies by incorporating a vent pipe with a fly screen at the top.

Wind passing over the vent pipe causes air flow from the pit through the vent pipe to the

atmosphere and a downdraft through the seat hole. This air flow removes smells and vents

gases. Air flow is improved if the doorway faces the prevailing wind. A gap should exist above

the door for air entry. If necessary, VIP latrines may be built above‐ground with fill material

brought in for the upper portion of the pit.

ii. A pour‐flush latrine uses a pan with a water seal to overcome smell and flies. Water used is 1 to

4 liters, depending on pan/trap geometry. These latrines work well for cultures that use water

for cleaning themselves. No vent pipe is required since gases are trapped by the water seal.

iii. A double pit may be used with either type of latrine to alternate and allow for removal of waste

after it dries (2 years or so) and most of the pathogenic organisms have died.

b. Design

i. Three conditions need to be satisfied when calculating the dimensions of a hole for a pit latrine:

1. Sufficient storage capacity for sludge accumulation during the life of the pit

2. 0.5 meters of space should be left at the top to seal the pit with earth when its life is over

3. Sufficient wall area for any liquid to infiltrate into the surrounding soil

ii. Use V=N x P x R

V = effective volume of the pit (m3)

N = effective life of the pit (years)

P =average number of people who use the pit each day

R =estimated sludge accumulation rate for a single person (m3 per year) shown in Table 8.2

iii. Planned area of the pit should be based on local structural materials and preferences.

A typical diameter used in India is 1.3 m.

iv. Calculate the sludge depth = V / your planned area of the bottom of the pit

v. Infiltration Area = sidewall area above the sludge area and below the soil seal area.

vi. Pit depth = sludge depth + infiltration depth + soil seal depth

Figure 8.5: Latrines World Health Organization, “A Guide to the Development of On‐Site Sanitation, 1992, Chapter 6


31

Table 8.2: Excreta Accumulation Rates World Health Organization, “A Guide to the Development of On‐Site Sanitation, 1992, Table 5.3

Waste Retention Sludge Accumulation Rate(m3 per person per year)

In water; degradable anal cleaning materials used 40

In water; non‐degradable anal cleaning materials used 60

In dry conditions; degradable anal cleaning materials used 60

In dry conditions; non‐degradable anal cleaning materials used 90

Exercise8.3A family of six in India intends to dig a pit latrine with an operational life of 20 years. The family uses water for

cleaning themselves. Assume a percolation rate of 20 min/25 mm and that each person flushes 5 times a day.

Calculate the size recommendations of a pit latrine using the design guidelines.


32

G. COMPOSTING TOILETS

a. Description: The composting toilet is a dry

ecologically friendly toilet and is particularly indicated

when the groundwater table is high or the soil does

not percolate. In a composting toilet excreta falls into

a watertight tank to which ash or vegetable matter is

added. If the moisture content and chemical balance

is controlled, the mixture will decompose to form a

good soil conditioner in about 4 months. Pathogens

are killed in the dry alkaline compost, which can be

removed for application to the land as a fertilizer.

There are two types of composting toilet: in one,

compost is produced continuously, and in the other,

two containers are used to produce it in batches.

b. Design

i. See http://www.clean‐water‐for‐laymen.com/compost‐toilet.html

ii. Refer to The Humanure Handbook: A Guide to Composting Human Manure, Third Edition (2005),

by Joseph Jenkins.

Figure 8.7: Completed Composting Toilet

Figure 8.6: Composting Toilet Use


33

9. OnsiteSolidWasteDisposalA. METHODS

When no contracted solid waste collection service is available, it may be necessary to handle the disposal

on‐site. In this case, significant space may need to be allocated on the master plan for an institution or

campus to handle solid waste disposal safely. Below are recommended methods for dealing with major

types of solid waste:

a. Paper Products

i. BURN or BURY.

ii. http://www.lifewater.org/resources/tech_library/San3%20Solid%20Waste.pdf

b. Plastics, Glass, Metals

i. RECYCLE is best, BURYING properly is next

ii. http://yosemite.epa.gov/r10/HOMEPAGE.NSF/Topics/ccrs/$FILE/12.+Informational+Slideshow.pdf

c. Medical Waste

i. BURYING properly is best, PROPER INCINERATION is next

ii. Design resources can be found at

http://www.healthcarewaste.org/hc‐facilities/technologies/

d. Organic Waste (food, plant material)

i. COMPOST if client has maintenance abilities or BURY if not.

ii. For household composting, see: http://cwmi.css.cornell.edu/compostbrochure.pdf

iii. For institutional or municipal composting, see:

http://yosemite1.epa.gov/EE/EPA/ria.nsf/vwT/8F33445A9EF08A6485256B810055028D

B. CONSIDERATIONS

a. When designing a solid waste collection or disposal area, consider:

i. Location on master plan in proximity to people (consider how far waste must be carried for

disposal)

ii. Wind direction (if paper waste is to be burned or smells may carry from composting or

collection areas)

iii. Space availability (this may dictate the type of disposal needed)

iv. Maintenance capabilities of client (this may limit the types of disposal selected)


34

10. SiteDrainageA. LOOK for signs of flooding or other drainage problems and RECORD THIS INFORMATION.

B. ASK several locals about drainage issues they have noticed at the site. Realize that interviews will not

normally provide accurate information, but can reveal general issues.

C. MARK recommended drainage routes on a copy of the proposed master plan while on site.

D. ASSIST in topographic land survey. Make sure all topographic characteristics relevant to drainage are

included in the survey.


35

11. SystemLayoutA. REMEMBER the following BASIC LAYOUT RULES and work with master planner to incorporate water and

wastewater systems into the master plan:

a. Distance between well and septic tank: minimum of 15 meters

b. Distance between well and soil absorption area: minimum of 20 meters if well is in a deeper confined

aquifer, minimum of 30 meters if well is in a more shallow unconfined aquifer.

c. Distance between soil absorption area and stream or embankment: 15 to 30 meters or more

d. Put water well on upper end of site if possible and protect from runoff drainage to the well

e. Put soil absorption areas in lower parts of the site and lay out trenches to follow the contours of the

land

B. CHOOSE WELL SITES with consideration to water yield, water quality, proximity to points of use, community

preferences, and avoidance of contamination.

a. Utilization of Data

i. Existing data should be gathered and analyzed to be sure that drilling occurs where there is a

high probability of successfully penetrating into water‐bearing formations. Ideal sources of

water are found in confined aquifers—water‐bearing formations that have protective layers of

impermeable formation (clay or non‐porous rock) above the aquifer. Data sources may include

government or NGO surveys, aerial photographs, geological reports, well logs, topographic

maps, etc.

ii. When drilling costs are significant and the risk of unsuccessful boreholes is high, a new

customized hydrogeological and geophysical study should be performed.

b. Siting New Boreholes

i. Boreholes should be sited in an elevated place, so that during the rainy season the water will

run away from it, rather than into it (see Figure 11. 1). Special care should be taken to avoid

locating boreholes immediately downhill from any contamination sources (e.g. latrines,

industrial waste, trash dumps, livestock pens, agricultural areas that are treated with

pesticides/fertilizers, and storage locations for pesticides/fertilizers).

ii. Siting of boreholes should also meet or exceed recommended distances from contamination

sources as detailed in the system layout section.

Figure 11.1: Borehole Siting


36

12. GeneralCommentsA. DOCUMENTATION

All recommendations and observations should be collected, documented and turned over to the project

leader before leaving the project site.

B. MINIMIZE MAINTENANCE

Design systems which keep maintenance to a minimum. Exception would occur when the following factors

exist:

a. There is significant public health risk without more complex systems

b. There is specific request from the client to have more environmentally friendly systems

c. The client is capable of maintaining the system or procuring the needed help

Documents

EMI Civil & Environmental Design Guide · PDF fileFrom B.C. Punmia, Askok Jain, and Arun Jain. Environmental Engineering‐I: Water Supply Engineering. New Delhi