Simple Assement Techniques
Contents
1. d The organic content of the soil organic material maintains a loose soil structure that facilitates percolation e The depth of soil to bedrock laterite hardpan or other impermeabie layers 1 The pull toward the center of the earth 2 Action by which the surface of a liquid where in contact with a solid is elevated or de pressed 3 Diffusion or absorption through a membrane Hard inert rock 5 Type of rock red in color with a high proportion of iron oxides and hydroxide of alum inum 6 A compacted layer of soils 10 When soil permits moderate to high percolation it is said to be well drained Such soil may support vigorous root growth by allowing excess water to drain away leaving air openings through which the roots can breathe In irrigation projects a well drained sci rieans less ance of water logging or sai 7 when water is poured over the surface of dry soil it will usually soak in rapidly for a while This tc iporary situation is known as infiltration not percolation and it happens only while the water is tilling open spaces in the soil it is only after this phase that true percolation occurs the movement of water through wetted soil When conducting a test for percolation it 1s important to avoid this con fusion with infiltration Materials Tin can with top and bottom removed Water equal to the volume of the can Dipstick any stick will do Ruler Rock for pounding2. less than 7CO mg 1 b Marks left by puddles 2 5 are rings the central area is clean in 2 3 but in 4 5 a slight film residue extends throughout the area MEDIUM MINERAL CONTENT 700 1800 mg 1 c Marks left by puddles 4 5 are not dis tinct rings but instead form a more or less uniform blotch on the glass often distinctly granular sometimes not drying completely unless heated HIGH MINERAL CONTENT more than 1800 mg 1 There will of course be conditions intermediate to these descriptions and these will be subject to the investigator s best interpretation The mineral test by itself does not provide much useful information Only when combined with the infiltration test Test 3 and specific mineral tests such as Test 5 do the results gain sig nificance especially for irrigation projects Examples of how to use combined results of sev eral tests for irrigation projects is illustrated by the Key for Suitable Irrigation Conditions pp 19 21 15 TEST 5 SODIUM IN WATER Background A high mineral content does not neces sarily make any water unsuitable for irrigation However if one of those minerals is sodium the use of such water for irrigation can cause serious damage to the soil A high concentration of sodium in the water will break down soil aggregates seal ing the pores and reducing the infiltration rate to almost zero In most cases the changes are ir reversible The following test is nor
3. University Dayton Ohio Dr Wood is now serving in West Africa with Volunteers in Technical Assistance VITAj The workbook was developed from an initial draft by Dr Gus Tillman Cary Arboretum which presented these tests to earlier workshops Also involved in early versions were Carol Roever and Helen Vukasin CODEL and Keith Smiley Mohonk Consultations on the Earth s Ecosystem Pr Nail Ozerol Howard University and Craig Tufts National Wildlife Federation This draft has been further revised by Helen L Vukasin CODEL based on technical reviews by Dr Ralph Martin University of Oklahoma Norman Dr Frederic K Pfaender University of North Carolina Chapel Hill Rev John Ostdiek Mundelein College Chicago and Dr August Haffenraffer Millipore Corporation Bedford Massachusetts CODEL welcomes your comments and suggestions on the usefulness of the booklet We are particularly interested in knowing about experience with the tests in the field CODEL Environment and Development Program ii NOS o 3 7 P v MZA VY Pra 9 0 0 t RN Dnm Ld wre LO bau aaa oes 4 A AK omg a ry EU ELE yon 7 pits E Aes AUA TIL le Bis We qe NS gt 2 A first ste i m p toward low technology environmental INTRODUCTION Among project planners in developing countries there is a growing need for reliable e
4. nutrients Unfortunately low percolation in clay soil leads to water logging and poor aeration Clay soil exposed to a hard rain often dries with a hard baked surface Further drying causes clay soils to contract opening deep cracks which seriously damage plant roots These conditions may be improved by a adding sand to the soil and b applying a mulch of organic materials to protect the soil from driving rain and to prevent complete drying Loam is a term for a mixture of soil types that provides a good medium for growing plants While there is room for much variation a good loam may be approximately 40 sand 40 silt and 20 clay With organic material and an adequate water supply such soils can become highly productive Soil Textural Class SAND LOAMY SAND SANDY LOAM SILTY LOAM SILTY CLAY LOAM CLAY LOAM SANDY CLAY LOAM SILTY CLAY CLAY TABLE CHARACTERISTICS OF THE Feel moist Very gritty Very gritty Gritty Gritty Velvety Velvety and sticky Gritty and sticky Very gritty and sticky Extremely sticky and very smooth Extremely sticky with slight grittiness Ability to Form Stable Ball No No Yes easily deformed Yes Yes Yes very stable Yes very stable Yes very stable Yes very resistant to molding Yes very resistant to molding I1 MAJOR SOIL TEXTURAL CLASSES Ability to Soils Ribbon Out Hands No No No Y
5. to statement 5 If you choose 5a go next to statement 6 If you choose 6b go next to statement 7 If you choose 7b go next to A which indi cates that conditions are suitable for ir rigation U 7 l a b 2 a b 3 a b 4 a b KEY FOR A ROUGH ASSESSMENT OF CONDITIONS SUITABLE FOR IRRIGATION Ground water often comes to within 1 5 meters of soil surface Ground water seldom comes within 1 5 meters of soil surface Mineral content of irrigation water is low Test 44 Mineral content of irrigation water is medium or high Percolation rate is very low e s o o o 9 o Percolation rate is not very low e Mineral content of irrigation water is low Test 4 Mineral content of irrigation water is medium or high e ra a Sodium risk in irrigation water is low Test 85 s o esea b Sodium risk in irrigation water is medium or high e ea 6 a Percolation rate is very low Test 3 e os b Percolation rate is not very low es sos sso ooo 7 a Percolation rate is low e s s n oos B b percolation rate is medium or high Jg WM PP A CONDITICNS ARE SUITABLE FOR IRRIGATION CONDITIONS ARE MARGI
6. Board about 30 cm long Procedure ink the can into the soil until its upper rim projects 8 10 cm above the surface Do this by placing the board across the top of the can and pounding it down with the rock It is very primitive but it works unless one encounters a large rock in which case try a different location 2 Remove the can from the soil and the soil that comes with it leaving a round hole in the ground 3 Pour some water into the hole to a depth of 2 3 cm Allow the water to stand for ten minutes then re fili if necessary to the original depth This allows time for infiltration If the soil is very dry it may require more time and more water to complete this initial phase of water movement li 4 Measure the depth of water in the hole Do it several times to be sure your measure ments are consistent Measure the depth again one hour later Calculate the change in depth during that hour If time permits let the system go for a second or third hour and then determine the hourly rate of percolation Measure the depth of water in the hole with a marked stick placed against a horizontal board across the hole 12 Interpretation Percolation rates are generally classified as follows a b C d Uses Very low rates of less than 0 25 cm 0 1 inch per hour Low rates of 0 25 1 25 cm 0 1 0 5 inch per hour Medium rates of 1 25 2 5 cm 0 5 1 0 inch per h
7. MICROFICHE REFERENCE LIBRARY project of Volunteers in Asia Simple Assessment Techniques for Soil and Water Published by 2 Coordination in Development Environment and Development Program 79 Madison Avenue New York NY 10016 USA Paper copies are 3 00 Available in Spanish J Available from Coordination in Development Environment and Development Program 79 Madison Avenue New York NY 10016 USA Reproduced by permission of CODEL Coordination in Development Reproduction of this microfiche document in any form is subject to the same restrictions as those of the original document Simple Assessme Techniques for Soil and Water WORKBOOK Environment and Development Program SIMPLE ASSESSMENT TECHNIQUES FOR SOIL AND WATER CODEL Environment and Development Program 79 Madison Avenue New York New York 10016 U S A CONTENTS Preface Introduction Test 1 Soil pH Test 2 Soil Texture Test 3 Percolation Test 4 Dissolved Minerals Test 5 Sodium in Water Key for Suitable Irrigation Conditions Test 6 Coliform Bacteria Field Practice Data Sheet Situation Data Sheets Field Notes li iii 10 14 16 19 27 29 3l PREFACE This booklet was prepared for a workshop on Environmental Factors in Small Scale Development Projects at Lake Mohonk New York June 17 19 1980 by Dr Timothy S Wood then Director of Environmental Studies Wright State
8. NAL FOR IRRIGATION CONDITIONS ARE UNSUITABLE FOR IRRIGATION This key is a crude scheme for interpreting simple field data It is not intended for use independent of extended professional surveys and testing TEST 6 COLIFORM BACTERIA Background The contamination of water supplies with disease causing organisms is a serious problem in many parts of the world However detecting such contamination can be tricky Water that appears clean and without taste or odor may in fact be swarming with extremely dangerous bacteria viruses and parasites from human feces Fortunately testing for each individual pathogen is unnecessary The common practice is instead to seek the presence of a 7 61 ely harmless bacterium that is common in the fecai stes of all warm blooded creatures These so called coliform bacteria are represented by a species known as Escherischia coli or E coli whose presence can be easily detected by anyone having the proper equipment The assumption is that water containing E coli is contaminated by by fecal material and could also contain dangerous pathogens While several different techniques serve to detect coliform bacteria one of the simplest methods uses a simple plastic dip stick with a fil ter which holds 1 ml of water It was developed by Millipore Corporation It is called a Millipore Sampler Several types with different media for growing the cultures are available to measure coli form total b
9. acteria or yeast and mold counts Materials Millipore Sampler for Coliform or Coli Count Sampler Incubator The skin of or place next to a person l Can be ordered from Millipore Corporation Order Service Department Bedford Massachusetts U S A 01730 Telex 92 3457 Wire TWX 710 326 1938 Phone 800 225 13807 or 617 275 9200 22 Procedure 1 Remove the stick with the grid lines from the clear plastic case Allow nothing to touch the grid to protect the sterilization 2 In still water the sampler may be dipped directly into the water Alternatively fill the clear case to the upper line with a sample of water to be tested It is very important that the water not be inadvertantly contaminated by bacteria from your fingers If sampling from a stream point the mouth of the case upstream into the direction of water flow Hold for several minutes When sampling from a well fill a clean container with water without wetting your fingers and pour the contents carefully into the clear plastic case up to the line 2 eea EN NE 7 CC NR c2 In still water the E SSS sampler may be dipped lt lt directly into the JE zz Az water zem I aures If sampling from a stream point the mouth of the case upstream 222 nseit the sampler all the way into the filled case shake several times and then hold the case still for 30 seconds D
10. e soil is alkaline basic Since pH is based on a logarithmic function a change in a single pH unit indicates a ten fold change in acidity or al kalinity Materials 1 pH indicator paper Rainwater Small container such as a plastic film canister Soil sample dry Procedure I Collect a sample of soil representative of tho field you wish to analyze The soil should be dry and loose without any hard clumps 2 Add rainwater to the soil and mix to make a thin atery mud 3 Dip one end of a strip of pH indicator paper into the mixture and allow water to be drawn up the paper which acts like a wick lpH indicator paper is available at labor atories and some pharmacies It can be ordered from Micro Essential Laboratory Inc 4224 Avenue H Brooklyn New York 11210 U S A Phone 212 338 3618 xz 4 Match the color of the wet paper to one of the bands on the color comparator chart to find the approximate pH 1 5 NOTE The pH paper should not remain in the mixture for any extended length of time After five minutes or so it is possible to get a false reading as the rising water washes out dye at the base of the strip and concentrates it near the leading edge of the water colum Interpretation A close relationship is found between soil p and the nutrients available to a growing plant Figure 1 below shows the ef fects of pH on 12 such nutrients where the wider the band the greater the availability Cl
11. early strongly acid soils are deficient in many dis solved nutrients while strongly alkaline soils have little available phosphate Like all liv ing things plant growth depends on that essen tial nutrient which is available in the least quantity Therefore whether it is one nutrient or ten nutrients that are unavailable to the plant the growth restriction will be the same H 4045 50 55 6065 70 75 80 85 90 STRONGLY STRONGLY ALKALINE Figure 1 is from R E Lucas and J F Davis Department of Crop and Soil Sciences Mic higan State University l A color aa comparator is sup plied with the pH paper MOLYBDENUM 295 If you were to select a pH that would have avail able the greatest number of plant nutrients you would be correct to choose something around 5 5 Nonetheless every plant species has its own spec ial pH preferences Suitable pH ranges for selected plants are given in Table 1 below Acidic soils can be made more alkaline by the addi tion of ground limestone ground seashells or wood ashes Decreasing the pH of alkaline soils is much more difficult Traditionally ammonium sulfate is used but composted organic material also helps Testing for pH in soils is useful wherever crops are grown It is especially important before and during any program for irrigation fertilization or soil improvement The pH of water is easily measured but is has little s
12. ed with other soil information the test results can be helpful in planning agri The following test can be considered useful in pro cultural projects Materials Glass flat smooth and clean at least 40 cm in area A hand mirror or any piece of win dow glass would be fine Eyedropper or any other device that can release one drop of water at a time drinking straw smooth stick etc Rainwater only a very small amount is needed but it must be clean Collect in clear glass container Procedure 1 Prepare the glass so that it is absolutely clean and dry It must be so clean that a drop of water will bead on its surface 2 Place the piece of glass in a level position where it will not be disturbed 3 Make 5 separate puddles of water Start 1 with 4 drops of rainwater for control For each of the other puddles combine different amounts of rainwater and test water as de scribed below 14 Puddle Rainwater Water to be Tested 1 4 drops 0 drops 2 3 drops 1 drop 3 2 drops 2 drops 4 1 drop 3 drops 5 0 drops 4 drops 4 Allow all puddles to dry undisturbed Interpretation If there is a mark left by the rainwater alone it should be only barely dis cernible otherwise the test is void and should be repeated with cleaner rainwater The remain ing water marks should fit one of the following descriptions a Marks left by puddles 2 5 are rings in which the centers are clean LOW MINERAL CONTENT
13. es slight Yes dull sur Yes face poorly formed Yes dull sur Yes face poorly formed Yes dull sur Yes face poorly formed Yes shiny sur Yes face well formed 7 Yes shiny sur Yes _ face well formed Yes very shiny Yes gurface well formed Yes very rhiny Yes surface weli formed Yes very shiny Yes surface well formed Consistency Moist Dry Loose Loose Loose Loose Very Soft friable Friable Soft Friable Soft 2 Friable to Slightly firm hard Firm Slightly hard to hard Friable Slightly hard to firm to hard Firm to Hard to very extremely hard firm Firm to Hard to very extremely hard firm Adapted from Foss et al A Laboratory Manual for Soil Science explanation under B 1 2 Crumbles easily i m e 1976 NENNEN TEST 3 PERCOLATION Background Percolation is the movement of water through wetted soil The force behind the movement is gravitational although some capillary action and plant root osmosis may also occur Many fac tors affect the rate of percolation such as a Soil texture water passes more quickly through large pores in sandy or loam soils than through heavy silts and clays b Soil structure fine structured soils with stable aggregates pass water more easily than unstructured soils c The amount of water already in the soil in saturated soils there are fewer cracks and pores through which water can pass readily
14. ignificance in agricultural projects It would be incorrect to assume for example that irrigating with acid water will create an acid soil The pH of water however may be of concern for fisheries projects So many different factors combine to establish the soil pH that it usually is better to just measure the soil pH alone TABLE 1 SUITABLE pH RANGES FOR SELECTED CROPS E Crop Alfalfa Apples Asparagus Barley Beans Lima Beans Snap Beans Velvet Blueberries Buckwheat Cabbage Carrots Clover Alaska Clover Crimson Clover Red 6 o TD YY A 0 AAS ooo uwuuwooutu Table 1 continued Crop Clover Sweet Clover White Corn Cotton Cowpeas Cucumber Grasses many kinds Kale Lettuce Mustard Oats Onions Parsnips Peas Peppers Potatoes Sweet Potatoes White Radishes Rye Sorghum Soybeans Spinach Squash Strawberries Sudangrass Timothy Tobacco Tomatoes Wheat e e e o O o E PON OS U ON OS M M J M OS UI Ui OY TANDAN OS ON MON S M 2 2 5 2 2 06 6 a uic TEST 2 SOIL TEXTURE Background The expression soil texture efers to the various sizes of rock particles i
15. mally used to distinguigh between hard and soft waters However when the mineral content of the water is known to be high the test can be used to assess the relative propor tion of sodium ions Materials A small water tight container with lid such as a plastic 35 mm film canister Soap or soap solution but not detergent Rainwater or distilled water Procedure 1 Make a soap solution by adding some soap flakes shaved from a bar of soap with a knife or razor blade to some rainwater Allow the mixture to sit for several hours then filter gently through a cloth to remove any remaining soap particles Try not to make suds 2 Standardize the strength of your soap solution as follows fill the container halfway with rainwater Find the minimum number of drops of soap solution required to maintain frothy suds for at least five minutes after the mix ture has been shaken vigorously for 5 seconds This amount of soap solution will be your standard dose 3 Empty and rinse the container with rainwater Re fill haifway with the water to be tested Add the standard dose of soap close the con tainer and shake it vigorously for 5 seconds 16 Open the container and note iie condition of the mixture SA S The shaken mixture siiowld match one of the following descriptions a Suds cover the surface This indicates a HIGH SODIUM RISK b The water appears cloudy This indicates a MEDIUM SODIUM RISK c A white sum fl
16. n th soil Traditionally the spectrum of sizes is classified into at least three types sand 0 05 2 mm di ater silt 0 002 0 05 mm diameter ar t a under 0 002 mm diameter Most soils are a mixture of these sizes but where one predomin s one can speak of a sandy soil or a silty soil etc The following procedur is a simple way tc identify the article composi on of a soil sample It is base on the principle that when suspended together in a jar of water the larger particles will settle faster than the sx ler ones The taller the jar and the greater th settling distance the better will be the separation Materials Tall glass jar with lid Water Soil sample Pr edure A Visual Test 1 Add a loose soil sample to fill approximately one third the volume of the jar There should be no hard clumps and preferably no pieces of leaves stems or other organic debris 2 Fill the jar nearly to the top with water cap it and shake the mixture to suspend all the individual soil particles Then let the jar Stand undisturbed Most of the particles will settle within a half hour although many of the smallest clay particles will not settle for a week or more 3 The settled particles will take on the appear ance of distinct bands or layers While there is probably a continuum from large to small bs tho rough fraction of each size class can be estimated B Feel Test 1 Moisten a saple
17. nvironmental assessment techniques The most effective methods are often those which are very simple using locally avaiiable materials While they may be primitive and lack precision such methods can be extremely valuable in helping to assure the long term success of small scale development projects The techniques described in this booklet repre sent a first step toward low technology environ mental analysis What is surprising is how much useful information can be gained with so little equipment These tests deal with significant features of soil and water and with reasonable care the results can be meaningful and reliable Certainly such simple tests are not intended to substitute for detailed long term environmental impact studies Many problems in soil and water analysis are complex requiring the services of trained and experienced technicians Where such services are unavailable however the preliminary assessment techniques described here can prove very useful TEST 1 SOIL pH Background One of the simplest and most useful soil tests is the measure of acidity or alkalinity called pH Not only does it provide important clues about soil fertility but it can also help determine the types of plants best suited for that soil as well as suggest possible means of improving tho soil for better crop production The pH scale ranges from 0 to 14 At pH 7 the scil is neutral below that level it is acidic and above 7 th
18. oats on the surface This indicates a LOW SODIUM RISK Note that this test must be performed in conjunc tion with Test 4 Dissolved Minerals The sodium test is meaningful only when the dissolved mineral content is medium or high Together these tests are essential before irri gation projects are undertaken OOD UO d TO OO OO OQ ME bel Ioco TIN Border Irrigattow From Tillman Environmentally Sound Small Scale Water Projects op cit p 7 195 KEY FOR SUITABLE IRRIGATION CONDITIONS On the following two pages is a key to assist with an assessment of environmental conditions suitable for an irrigation project The key assumes that a supply of water for rigation exists and that the impact of withdrawing the water from its present source has already been examined A key such as this presents a series of choices to the user in a significant sequence Begin with pair f1 select the statement a or b whichever best fits your information and proceed to the num bered pair of statements indicated by the numeral on the right When you encounter a letter in the righthand column refer to the box below for an explanation For example A If you choose fla go next to statement If you choose 2a go next to statement 3 If you choose 3a go next to C which indi cates that conditions are unsuitable for irrigation B If you choose 1b go next to statement 4 If you choose f4b go next
19. of soil and feel it in your fingers Roll the soil between the thumb fore aid middle fingers T to form small ball Check to see soil will form a long thin ribbon or ribbon out Soils may stick to the hands and soil them Determine the textural class of the soil according to Table II Allow the sus pended mixture to settle The settled parti cles will form distinct layers a hall by rolling the sample between your fingers CO eri Interpretation By learning the texture of a soil sample one can also know some of its chemical and physical properties For example sandy soil tends to be relatively in fertile and vulnerable to drought However the rapid rate of percolation see Test 3 promotes good aeration for beneficial soil organisms and plant roots Sandy soil can safely accept irriga tion with water containing a high concentration of dissolved minerals while such water would be un suitable for heavier soils Where water is scarce and the soil is sandy the addition of organic material before crops are planted and afte wards as a mulch can help retain moisture A wise choice of irrigation methods will also help increase the productivity of sandy soil in parched climates see Chapter 6 in Environmentally Sound Small Scale Water Projects by Gus Tillman New York CODEL VITA 1981 5 Clay soil can hold and retain a larger amount of water than sandy soil and it resists the leaching of
20. origin These may occur especially if the incubation temperature has not been kept sufficiently high A Note of Caution E coli or coliform bacteria is only an indicator of contamination Because it involves incubation and sterile conditions it is more difficult to do correctly than other tests described here This method serves particularly well in situations where monitoring of water quality is needed or as a first crude measure in considering a water project In some cases a test by a professional laboratory may be es sential Negative results should not be accepted l International agencies disagree on standards Some scientists believe only water without any colonies of E coli is safe Others believe that water with less than 4 colonies per 100 ml is safe Still others believe that if the whole world had access to water with less than 10 colonies per 100 ml we would be approaching the aim of safe water for all In some areas the best that can be done is to reduce the number of colonies to a range of 50 100 per 100 ml To de termine what is an achievable level for your area check with the local government agency responsi ble for water quality or with a local health agency Testing for coliform 100 ml must be done in a lab oratory lt 26 without repeating the test Also caution should be exercised in reading results to note certain external factors a recent heavy rain run off may increase contamination a tempo
21. our High rates greater than 2 5 cm 1 0 inch per hour Projects in which testing soil percolation would be significant include a b C Fishpond construction where the desired percolation rate would be zero and where the testing should be conducted at many lo cations to the maximum depth of the pro posed pond Irrigation projects where it is necessary to know how fast water will sink below the root zone Percolation and infiltration rates should both be considered if there are to be long unlined channels conducting irrigation water to the fields Construction of latrines lagoons or any other in ground sewage disposal system When percolation rates are high these systems can handle a relatively high vol ume of liquid wastes but disease causing organisms may be carried over 100 meters through the soil Soils with low perco lation rates present problems with clogging and low capacity but the pathogens are generally contained within 30 meters E TEST 4 DISSOLVED MINERALS Background Most surface and subsurface waters con tain a certain amount of dissolved minerals Many of these are essential for plant growth although in high concentrations their effects can be harm ful No standards for irrigation water quality are possible since so much depends on soil drainage climate types of crops and specific minerals in the water viding only a rough guide to the mineral content of water Combin
22. rary event of another kind may interfere with results Alternative Methods Another way of determining con tamination is by placing the test water in a culture medium that will indicate if E coli are present by production of gas Construction of a kit that can be put together in the field and how to make the tests with the kit are described in George Reid Water Test Kit I User s Manual University of Oklahoma 1975 2 00 Available from CODEL Preparing medium for coliform test Taken from Water Test Kit I User s Manual cited above 26 FIELD PRACTICE DATA SHEET NAME TEST 1 SOIL pH Soil Sample No Soil pil TEST 2 SOIL TEXTURE sand silt clay Textural clas ification TEST 3 PERCOLATION may be done in groups Percolation rate per hour Test duration hours TEST 4 DISSOLVED MINERALS Water Sample No Level of dissolved minerals TEST 5 SODIUM if applicable Water Sample No same as in Test 4 Sodium risk 2275 SITUATION DATA SHEET Date Time Location County State Direction and distance from nearest town post office Weather past 24 hrs Current weather Topography Ground cover Color of topsoil Color of subsoil Depth Soil texture classification LLL sand _ Silt clay Other particles Depth of soil sample Percolation rate per hour Percolation test duration hours Soil pH Evidence and type of ero
23. sion r art DORE DEDE ED 29 WATER Source of water Color Transparency Dissolved solids Sodium risk pH Temperature range Coliforms per 100 ml Sources of possible contamination sewage pesticides domestic or industrial waste animals surface run off etc Describe nature of contaminant and distance from point of water use History of water borne disease in the regions cholera dracontiasis filariasis malaria schistosomiasis bilharzia _ typhoid yellow fever other Reference Gus Tillman Environmentally Sound Small Scale Water Projects N Y CODEL VITA 1981 Order rom ode Island Avenue Mt Rainier Maryland 20712 30 FIELD NOTES stje Published with partial support from U S Agency for International Development Office of Private and Voluntary Coop ration
24. uring this time the sampler will absorb exactly 1 ml of water Remove the sampler and shake it several times to remove excess water Be careful not to con taminate it by allowing it to touch any surface Empty the case and shake it to remove excess water Insert the sampler into the empty case The whole apparatus must now be placed in an envi ronment that maintains a continuous tempera ture of 350C or 98 69F for 18 24 hours If using a human body to create the incubation en vironment the sampler should be taped against the skin After 18 24 hours examine the paper grid for signs of coliform bacterial colonies There may be many spots on the sampler but only those which are raised shiny and either blue or blue green are colonies derived from single coliform bacteria Count the number of colonies If there are no colonies visible see caution below Count the number of colonies 24 Interpretation The appearance of coliforms in dicates that pathogenic organisms such as those responsible for typhoid dysentery and cholera may be present Generally more than two colonies 1 on the sampler indicates water unsafe for drinking However a recently sunk wells or bores will often have an unduly high coliform count for several weeks b decomposing non sewage material in the water can prompt a false reading There are some non fecal bacteria in soil which can be mistaken for coliforms of recent fecal
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