Manual methods for the measurement of a groundwater level in a well
Contents
1. BSI is the independent national body responsible for preparing British Standards It presents the UK view on standards in Europe and at the international level It is incorporated by Royal Charter Revisions British Standards are updated by amendment or revision Users of British Standards should make sure that they possess the latest amendments or editions It is the constant aim of BSI to improve the quality of our products and services We would be grateful if anyone finding an inaccuracy or ambiguity while using this British Standard would inform the Secretary of the technical committee responsible the identity of which can be found on the inside front cover Tel 44 0 20 8996 9000 Fax 44 0 20 8996 7400 BSI offers members an individual updating service called PLUS which ensures that subscribers automatically receive the latest editions of standards Buying standards Orders for all BSI international and foreign standards publications should be addressed to Customer Services Tel 44 0 20 8996 9001 Fax 44 0 20 8996 7001 Email orders bsi global com Standards are also available from the BSI website at http www bsi global com In response to orders for international standards it is BSI policy to supply the BSI implementation of those that have been published as British Standards unless otherwise requested Information on standards BSI provides a wide range of information on national European and intern2. Also record the date the MP was established and a detailed description of the MP It is highly recommended that the MP and LSD be surveyed in to a national geodesic reference point If so then the accuracy of the surveyed altitude should be estimated and recorded in the well file f Establish at least one clearly marked reference point RP somewhere near the well For example a lag bolt set in a telephone pole Figure 5 The RP is an arbitrary datum established by permanent marks and is used to check the MP or to re establish a measuring point should the original MP be destroyed or changed g Make a detailed sketch of the MP and the RP on the groundwater site inventory form and if possible take a photograph Clearly identify the MP and RP on the developed photograph Also all calibration and maintenance data associated with the steel tape being used are recorded in its calibration and maintenance equipment log book MP data are recorded in a field notebook and on the ground water site inventory form 17 BS ISO 21413 2005 mT Key 1 water level 2 transparent flexible tubing 3 soil pipe test plug 4 measuring scale 5 well casing 6 measuring point MP 7 pressure gauge 8 flexible tubing 9 3 way valve 10 soil pipe test plug 11 well casing 12 land surface Figure 4 Water level measurement in a flowing well 18 a b Key O1 N N 1 5 BS IS
3. b For depths of about 150 m the maximum difference of independent measurements using the same tape should agree within 3 0 cm c For depths in the 500 m range the repeatability of measurements using the same tape should agree within 15 cm see Reference 2 p 11 BS ISO 21413 2005 4 4 Advantages and disadvantages The electric tape method is superior to the graduated steel tape method when a water is dripping into the well or condensing on the inside of casing walls which may make it very difficult to get a good water mark on the chalked tape b wells are being pumped and the splashing of the water surface makes chalked measurements virtually impossible and c a series of measurements are needed in quick succession such as in aquifer tests because the electric tape does not have to be removed from the well for each reading Also the electric tape method is safer to use in pumping wells because the water is sensed as soon as the probe reaches the water surface and there is less danger of lowering the tape into the pump impellers Electric tape measurements are generally less accurate than are measurements made with graduated steel tapes Electric tapes are also harder to keep calibrated than are steel tapes and electric connections need to be maintained in good order Also the insulation around the conductor cables may be severed when being drawn across sharp edges of metal pipes at the top of a borehole In addition the
4. or pressure gauge 2 tyre pump 3 pipe tee 4 well casing 5 water level 6 airline 7 pump line or column a For the altitude gauge d k h where d is the measured depth to water level in metres h is the height of water displaced from the air line in metres and For the pressure gauge d k 1 04p and h 0 104p where p is the pressure reading in kilopascals and d h and k are in metres Figure 3 Typical installation for measuring water levels by the air line method and relation of measured depth to water level height of water displaced from air line and depth to bottom of air line 12 BS ISO 21413 2005 g To calibrate the air line and gauge make an initial depth to water level measurement d with a wetted steel tape and an initial air gauge reading 4 Add d and h to determine the constant value for k Use a tyre pump to pump compressed air into the air line until all the water is expelled from the line Once all water is displaced from the air line record the maximum gauge reading EXAMPLE 1 Using an altitude gauge The initial measured depth to the water level d is 7 88 m the initial altitude gauge reading h is 23 02 m Then the constant k 7 88 m 23 02 m 30 90 m see the example in Figure 9 EXAMPLE 2 Using a pressure gauge The initial measured depth to the water level d is 26 17 m the initial pressure gauge reading is 190 kPa Then the constant k 26 17 m 190 kPa x 0 102 m kPa 26 17 m 19
5. continue to make check measurements until the reason for the lack of agreement is determined If more than two measurements are taken the observer shall select the reading considered the most reliable k Record the identification number of the altitude pressure gauge with each water level measurement so that the reading can be back referenced to the calibration record if necessary All calibration and maintenance data for the well shall be recorded in the log book All water level data shall be recorded on the water level measurements field form see the example in Figure 11 7 Establishing a permanent measuring point 7 1 Purpose The purpose of this method is to establish a permanent reference point from which all water levels are measured in a particular well 7 2 Materials and instruments The following materials and instruments are required 7 2 1 Form for recording the information required to locate and document the establishment of a permanent measuring point see Reference 8 as an example 7 2 2 Steel tape graduated in metres and centimetres 7 2 3 Steel tape calibration and maintenance equipment log book 7 2 4 Field notebook 7 2 5 Pencil and eraser 7 2 6 Spray paint or road chalk bright colour 16 BS ISO 21413 2005 7 2 7 Two wrenches with adjustable jaws for removing the well cap 7 3 Data accuracy and limitations The accuracy with which the measuring point MP measurement is established should be the s
6. 38 m 45 55 m see the example in Figure 10 h Calibrate the air line and gauge as indicated in g above i To measure the water level depth in a well with an air line subsequent air line readings are subtracted from the constant k to determine the depth to the water level below the MP Use a tyre pump to pump compressed air into the air line until all the water is expelled from the line and record the maximum gauge reading EXAMPLE 3 Depth to the water level in a well using an altitude gauge with a constant k of 30 90 m During a later pumping period the maximum altitude gauge h reads 15 24 m therefore the water level d 30 90 m 15 24 m 15 66 m see the example in Figure 9 EXAMPLE 4 Depth to the water level in a well using a pressure gauge with a constant amp of 45 55 m During a later pumping period the maximum pressure gauge reads 122 kPa therefore the water level d 45 55 m 122 kPa x 0 102 m kPa 45 55 m 12 44 m 33 11 m_ see the example in Figure 10 j Measure the water level depth as indicated in i above k Apply the MP correction to get the depth to water below or above land surface datum I Record water level data in the field notebook and on the water level measurements field form Table 4 or Table 5 6 Water level measurement in a flowing well 6 1 Purpose The purpose of this method is to measure low pressure or high pressure water level heads in flowing wells 6 2 Materials and instrum
7. ISO technical committees Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee International organizations governmental and non governmental in liaison with ISO also take part in the work ISO collaborates closely with the International Electrotechnical Commission IEC on all matters of electrotechnical standardization International Standards are drafted in accordance with the rules given in the ISO IEC Directives Part 2 The main task of technical committees is to prepare International Standards Draft International Standards adopted by the technical committees are circulated to the member bodies for voting Publication as an International Standard requires approval by at least 75 of the member bodies casting a vote Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights ISO shall not be held responsible for identifying any or all such patent rights ISO 21413 was prepared by Technical Committee ISO TC 113 Hydrometry Subcommittee SC 8 Ground water BS ISO 21413 2005 Introduction The measurement of a water level in a well constitutes a data collection process that provides fundamental information about the status of a groundwater system Accordingly measured water levels should be sufficiently accurate and reproducible to meet the needs of most data collection and monitoring progr
8. MP e Apply the MP correction to get the depth to water below or above land surface datum LSD If the MP is above land surface see the example in Figure 6 the distance between the MP and land surface datum is subtracted from the depth to water from the MP see the example in Figure 6 to obtain the depth to water below land surface If the MP is below land surface precede the MP correction value with a minus sign and subtract the distance between the MP and land surface datum from the depth to water from the MP to obtain the depth to water below land surface Record this number in the DEPTH TO WATER FROM LSD Figure 1 column of the water level measurements field form see the example in Figure 6 If the water level is above LSD record the depth to water above land surface as a negative number f Make a check measurement by repeating steps a through e The check measurement shall be made using a different MP hold value see the example in Figure 6 than that used for the original measurement If the check measurement does not agree with the original measurement to the nearest centimetre continue to make check measurements until the reason for the lack of agreement is determined or until the results are shown to be reliable If more than two readings are taken the observer shall select the reading considered the most reliable This reading shall be recorded to the nearest centimetre g After completing the well measurements disin
9. MP correction value with a minus sign and subtract its height from the water level to obtain the depth to water below land surface Subtract the MP correction Table 2 or Table 3 from the depth to water from MP Table 2 or Table 3 and record this number in the DEPTH TO WATER CORRECTED FOR LSD column of the water level measurements field form Table 2 or Table 3 If the water level is above LSD enter the water level in centimetres above land surface preceded by a minus sign Make a check measurement by repeating steps d through f If the check measurement does not agree within the accuracy given in 4 3 under Data accuracy and limitations continue to make check measurements until the reason for the lack of agreement is determined If more than two measurements are taken the observer shall select the reading considered the most reliable This reading shall be recorded to the nearest centimetre After completing the well measurement disinfect the electric tape by pouring a small amount of common household chlorine bleach or other suitable disinfectant on a clean cloth and then wipe down that part of the tape that was submerged below the water surface This will avoid possible contamination of other wells Maintain the tape in good working condition by periodically checking the tape for breaks kinks and possible stretch due to the suspended weight of the tape and the tape weight Do not let the tape rub across the top of the casing
10. da Fd 13 6 3 Data accuracy and limitations enne nnne nennen entere nn u uu nennen 14 6 4 Advantages and disadvantages sense 15 6 5 ASSUMPTIONS eT 15 6 6 ercuUrnrdem 15 6 6 1 Low pressure head measurement direct measurement ss 15 6 6 2 High pressure head measurement indirect measurement eee 15 7 Establishing a permanent measuring point 16 7 1 Lilli lm y EE Ska as PR 16 7 2 Materials and instr mbenhlts 5 eere aaaea urne e ERE Aa ERR ERA asss Na a TERRE Ra epe gente nent 16 7 3 Data accuracy and limitations U u nuni n tnn anne u u 17 7 4 CIA E 17 7 5 Proced re p 17 Annex A informative Corrections for water levels measured in deep wells by steel tapes subject to temperature changes and tape stretch 26 Annex B informative Corrections for water levels measured in wells with the air line method 28 Bibli graphy uw uu muka te ERE A E Sakyu ne Fe co aaa ec D ae pe apaga Ee CR KY a kusaq aa RE A ccdevuagechessersteunteteseesten 30 BS ISO 21413 2005 Foreword ISO the International Organization for Standardization is a worldwide federation of national standards bodies ISO member bodies The work of preparing International Standards is normally carried out through
11. head measurements using a pressure gauge are probably not accurate to within less than 3 0 cm although the measurements themselves can be read at finer resolutions c The pressure in the well shall not exceed the limit of the altitude pressure gauge Pressure gauges are generally most accurate in the middle third of the gauge range d The measuring gauge shall not be connected to a well that uses a booster pump in the system because the pump could start automatically and the resulting pressure surge may ruin the gauge e When a flowing well is closed or opened by a valve or test plug it should be done gradually If pressure is applied or released suddenly the well could be permanently damaged by the water hammer effect with subsequent caving of the aquifer material breakage of the well casing or damage to the distribution lines or gauges To reduce the possibility of a water hammer effect a pressure snubber should be installed ahead of the altitude pressure gauge f Ideally all flow from the well should be shut down so that a static water level measurement can be made However because of well owner objections or system leaks this is not always possible If the well does not have a shut down valve it can be shut in by installing a soil pipe test plug on the well or discharge line g Ifa well has to be shut down the time required to reach static pressure after shut down may range from hours to days Since it may be impractical o
12. in length of a metal tape resulting from thermal expansion and stretch are given in Equations A 1 and A 2 respectively from Reference 2 as Cr L E T 20 C A 1 and Cs Lj m SI2 PLS A2 where C is the thermal correction in metres m Cs is the stretch correction in metres m L isthe measured depth to water in metres m E is the coefficient of thermal expansion of the steel tape in metres per metre per degree Celsius difference between the average temperature in the well and 20 C m m per C is the average temperature in the well from land surface to water level in degrees Celsius C is the length of suspended tape corrected for thermal expansion in metres m m isthe mass of tape in kilograms kg per metre of tape S isthe coefficient of stretch in metres per metre per kilogram m m per kg and P isthe mass of plumb bob in kilograms usually 0 10 kg to 0 30 kg 26 BS ISO 21413 2005 EXAMPLE The following example illustrates the effects of thermal expansion and stretch on a steel tape used to measure water levels in a deep well Given L 515 00 m E 1 13 x 10 5 m m per C from Reference 2 T 30 C m 0 003 6 kg from Reference 2 S 3 85 x 10 5 m m per kg from Reference 2 P 0 20 kg Correction for thermal expansion C LE T 20 C 515 00 m 1 13 x 10 5 m m per C 30 C 20 C 0 06 m then L 515 00 m 0 06 m 514 94 m rounded to th
13. BRITISH STANDARD BS ISO 21413 2005 Manual methods for the measurement of a groundwater level in a well ICS 07 060 17 060 DE British Standards Standards NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW e BS ISO 21413 2005 National foreword This British Standard reproduces verbatim ISO 21413 2005 and implements it as the UK national standard The UK participation in its preparation was entrusted to Technical Committee CPI 113 Hydrometry which has the responsibility to aid enquirers to understand the text present to the responsible international European committee any enquiries on the interpretation or proposals for change and keep UK interests informed monitor related international and European developments and promulgate them in the UK A list of organizations represented on this committee can be obtained on request to its secretary Cross references The British Standards which implement international publications referred to in this document may be found in the BSI Catalogue under the section entitled International Standards Correspondence Index or by using the Search facility of the BSI Electronic Catalogue or of British Standards Online This publication does not purport to include all the necessary provisions of a contract Users are responsible for its correct application Compliance with a British Standard does not of itself confer immunit
14. F GAUGE GAUGE WATER FROM WATER FROM REMARKS MEASUREMENT CONSTANT READING MP LSD a d MP include name of observer YYYY MM DD Local time GMT 2002 05 31 30 90 23 02 7 88 Altitude gauge calibrated by John Smith First air line water 2092508701 28 99 15 24 15266 measurement John Smith Figure 9 Example of field data sheet for measurement of water levels with an air line using an altitude gauge 23 BS ISO 21413 2005 WATER LEVEL MEASUREMENTS Field SITE NAME LOCATION include latitude longitude if feasible MP DESCRIPTION land surface datum Top inside edge of steel casing red arrow south side 1 00 m above Pressure gauge calibration data Initial wetted steel tape water level d is 26 17 m initial pressure gauge reading h is 190 kilopascals kPa constant k d h 26 17 m 19 38 m 45 55 m Pressure gauge reading in metres is calculated as pressure gauge reading in kPa x 0 102 kPa m PRESSURE PRESSURE GAUGE READING Local time GMT YYYY MM DD 19 38 2002 05 31 190 kPa 12 44 DEPTH TO DEPTH TO WATER WATER FROM FROM MP LSD d MP REMARKS include name of observer Pressure gauge calibrated by John Smith First air line water 2002 06 01 level measurement John 122 kPa Figure 10 Example of field data sheet for measurement of water levels with an air line using a pressure gauge 24 SITE NAME LOCAT
15. ION include latitude longitude if feasible MP DESCRIPTION TIME OF Local time YYYY MM DD 2001 06 09 MEASUREMENT BS ISO 21413 2005 WATER LEVEL MEASUREMENTS Field Crescent Lake Flagler Co Florida Top of casing at chiselled mark 1 12 m above land surface datum Pressure head water level reading in metres is calculated as pressure gauge reading in kPa x 0 410 2 PRESSURE HEAD PRESSURE HEAD REMARKS WATER LEVEL WATER LEVEL ABOVE MP ABOVE LSD include name of observer Figure 11 Example of field data sheet for measurement of pressure head water level in a flowing well 25 BS ISO 21413 2005 Annex A informative Corrections for water levels measured in deep wells by steel tapes subject to temperature changes and tape stretch In measuring water levels in deep wells practitioners may wish to consider errors introduced from the effects of thermal expansion and or stretch of the metal tape produced by the suspended weight of the tape and attached plumb bob While such errors are negligible for many water level measurements they may become appreciable for measurements in deep wells that is for wells exceeding 300 m in depth see Reference 2 p 3 The corrections described below are not required for the purposes of this International Standard but rather to provide the practitioner a means of evaluating the potential magnitude of such errors The equations used to estimate the changes
16. Koopman F C Methods of measuring water levels in deep wells U S Geological Survey TWRI Book 8 Chapter A1 Washington U S Government Printing Office 1968 23 pp Ground water and wells A reference book for the water well industry 1st ed 4th printing Johnson Division UPO Inc Saint Paul Minnesota 1975 pp 90 91 Handbook of Chemistry and Physics 56 Edition CRC Press Weast Robert C ed 1975 76 HEATH Ralph C Basic ground water hydrology Water Supply Paper 2220 Washington U S Government Printing Office 1983 LOMAN S W Measurement of ground water levels by air line method U S Geological Survey Water Resources Bulletin November 1953 Washington D C 1953 pp 97 99 U S Office of Water Data Coordination National handbook of recommended methods for water data acquisition Office of Water Data Coordination Geological Survey U S Department of the Interior Reston Va Chapter 2 1977 pp 1 149 U S Geological Survey National water information system user s manual ground water site inventory system U S Geological Survey Open File Report 89 587 2 Chapter 4 1990 WINNER M D Jr Ground water data collection and processing procedures U S Geological Survey Louisiana District 1969 unpublished 44 pp LOZ uonninsu SPIEPUEJS usnug eu 9 SLOZ LO EO JO Se 1981109 UOISI8A 1S yH Mesq y neus 337 Adoo pesueor blank BS ISO 21413 2005 BSI 389 Chiswick High Road London W4 4AL
17. O 21413 2005 MP above LSD Subtract MP correction to correct this water level to LSD 5 50 1 50 4 0 MP below LSD Subtract MP correction to correct this water level to LSD 5 20 1 20 6 40 measuring point MP reference point RP land surface datum LSD lag bolt water level MP correction Figure 5 Relation of measuring point above or below the land surface datum reference point and water level 19 BS ISO 21413 2005 WATER LEVEL MEASUREMENTS Field WELL NO NHW 258 _ SITE NAME AND LOCATION Town of New Shoreham Block Island Rhode Island include latitude longitude if feasible MP DESCRIPTION I Top inside edge of stainless steel casing 0 85 m above land surface datum MISCELLANEOUS NOTES No adjustment made for several centimetres of oil floating on water surface DATE TIME OF WETTED DEPTH TO DEPTH TO REMARKS MEASUREMENT CHALK WATER FROM WATER FROM include name of LSD observer Local time YYYY MM DD 2002 08 29 I Measured by Lansen Ramsbey Figure 6 Example of field data sheet for measurement of water levels with a graduated steel tape 20 BS ISO 21413 2005 WATER LEVEL MEASUREMENTS Field WELL NO ES TEE IEEE PN ETE EE ONCE TERN LXVISEEIDOETISGETIDOREIROEEEDOELISOERIS SERIDGERTALSEOEKEUNRCKE Ee Oe BUG SITE NAME AND LOCATION include latitude longitude if feasible Top inside edge of stainless steel casing 1 50 m above land surfa
18. T q AUN RAEAN ENR SASONS ERRANA ADER ANAN ENR nnn nnn 2 3 4 Advantages and disadvantages U U U U uu u Q 3 3 5 ASSUMPTIONS EL i ati EE 3 3 6 PFOCCQUNCS REDE H 3 4 Water level measurement using an electric tape I U U U U u nnne nnn 6 4 1 P TpOs6gxXa PR sa les 6 4 2 Materials and instruments asa awa sy nennen nant anna a ann na noa sm nam n ma anas danda a uasa rna sn sa sa 6 4 3 Data accuracy and limitations nnne nnne nnne nnn SMA ERRANAK ARRAN MEKARSARI nennen 6 4 4 Advantages and disadvantages U U U U eene eene U u uuu uu 7 4 5 ASsumpti rnisu uu S a i aa ente e ERO ee Rua anse nent rares eu R agen sau kawa a Den asb sas sassa 7 4 6 PrOCeduresSi s uuu MIROIR 7 5 Water level measurement using an air line sise 10 5 1 P TDOS8 10 5 2 Materials and instr ments u u u uuu asa nere iretur ale tn ce Rena Re REDE ere asas 10 5 3 Data accuracy and limitations U U U u uuu nn nennen 10 5 4 Advantages and disadvantages sn 11 5 5 ASSUMPTIONS 22 25 E R n 11 5 6 Proc dures c M ss 11 6 Water level measurement in a flowing well sise 13 6 1 PII 13 6 2 Materials and instruments trien trei deret Loc enne Eat dn nana sak na E uana nae Da en ko dar ann Do Duae
19. ame as that established for the water level measurement that is if water levels are measured to the nearest centimetre then the MP should be established to an accuracy of 0 01 m 7 4 Assumptions For comparability water level measurements shall be referenced to the same datum elevation Land surface datum LSD at the well is an arbitrary plane chosen to be approximately equivalent to the average altitude of the ground around the well Because the LSD around a well may change over time the distance between the MP and the LSD should be checked periodically Also measuring points change from time to time especially on private wells 7 5 Procedure Use the following procedure a The MP shall be as permanent as possible clearly defined marked and easily located b The top of the well casing which provides the most convenient location for measuring a water level in a well should be designated as the MP and should be measured in reference to land surface datum LSD c The MP should be measured in reference to land surface datum LSD and at a point on the well convenient for measuring water levels most often at the top of the well casing d Clearly mark the MP with an arrow sprayed with a bright coloured paint or chalk e Measure the height of the MP above or below LSD Figure 5 and record it on the ground water site inventory form Values for measuring points below land surface Figure 5 b shall be preceded by a minus sign
20. ams Several manual methods commonly used to collect water level data in wells employ relatively simple measuring devices such as graduated steel tapes electric tapes and air lines In some cases water level measurements are required in flowing wells The procedures associated with each of these methods are intrinsically different and subject to varying limitations and accuracies Standardization of these methods would ensure that the procedures and associated equipment used by the international community to collect water level data in a well are consistent and that the results can be compared with minimal concern about the relative accuracies and or the procedures use in collecting the data LOZ uonninsu SPIEPUEJS usnug eu 9 SLOZ LO EO JO Se 1981109 UOISI8A 1S yH Mesq y neus 337 Adoo pesueor blank BS ISO 21413 2005 Manual methods for the measurement of a groundwater level in a well 1 Scope This International Standard develops procedures and prescribes the minimum accuracy required of water level measurements made in wells using graduated steel tapes electric tapes and air lines Procedures and accuracy requirements for measuring water levels in a flowing well are also included as are procedures required to establish a permanent measuring point This International Standard discusses the advantages and limitations of each method and requirements for recording the data This International Standard does not include methods
21. an be wound on a reel 2 6 groundwater water within the saturated zone BS ISO 21413 2005 2 7 land surface datum average altitude of land surface at a referenced well 2 8 measuring point permanent reference marked on well casing 2 9 static water level or static head height relative to an arbitrary reference level of a column of water that can be supported by the static pressure at a given point 2 10 well hole sunk into the ground for abstraction of water or for observation purposes 3 Water level measurement using a graduated steel tape 3 1 Purpose The purpose of this method is to measure the depth to the water surface level below a measuring point using the graduated steel tape wetted tape method 3 2 Materials and instruments The following materials and instruments are required 3 2 1 Steel tape graduated in metres and centimetres A black tape is preferred to a chromium plated tape because the wetted chalk mark is easier to read against a black tape A break away weight should be attached to the ring on the end of the tape with wire strong enough to hold the weight but not as strong as the tape so that if the weight becomes lodged in the well the tape can still be pulled free The weight should be made of brass stainless steel or iron 3 2 2 Coloured chalk 3 2 3 Clean cloth 3 2 4 Pencil and eraser 3 2 5 Steel tape calibration and maintenance equipment log book 3 2 6 Water level measurement field
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23. because the 1 metre metal bands can become displaced consequently placement of the bands should be checked frequently with a steel tape BS ISO 21413 2005 WW RAP y i E Se NE Key light indicator reel casing electric cable electrode s OO O1 N water Figure 2 Water level measurements using an electric tape adapted from Reference 1 Figure 16 12 BS ISO 21413 2005 Because an electric tape will not respond to oil floating on water in a well the liquid level determined by an electric tape will be different than that determined by a steel tape with the difference depending on the thickness of the oil layer In cases where this is of concern a miniature float driven switch can be put on a two conductor electric tape that will allow detection of the oil surface All calibration and maintenance data associated with the electric tape being used shall be recorded in its calibration and maintenance equipment log book All data shall be recorded in the water level measurements field form see the example in Figure 6 to the appropriate accuracy 4 3 for the depth being measured In the event no water is encountered in the well this shall be duly noted under REMARKS on the field form along with the distance between the MP and the bottom of the well 5 Water level measurement using an air line 5 1 Purpose The purpose of this method is to measure the depth to the water surfac
24. calibrate it by comparing the total length of the electric tape against the length of an acceptable steel tape An acceptable steel tape is one that has a fixed graduation of a centimetre or less and that is maintained in the office for the sole purpose of calibrating electric tapes Also check the accuracy of the position of each 1 m interval metal band to make sure that the bands have not moved This is especially important if the electric tape has been used for a long time or after it has been pulled hard in attempting to free the line If the field tape fails to meet test criteria then it must be removed from service Records of these tests shall be kept BS ISO 21413 2005 Before lowering the probe into the well check the circuitry of the electric tape by dipping the probe into water and observe if the indicator needle light or buzzer is operating correctly as the circuit closes Note the position the indicator needle deflects during the circuitry check Lower the electrode probe slowly into the well until contact with the water surface causes the circuit to close activating the indicator Figure 2 Slightly raise and then lower the electrode again to identify just where the electrode first comes into contact with the surface of the water Once the indicator needle deflects to the point chosen during the circuitry check place the nail of the index finger on the insulated wire at the MP For fully graduated tapes partly withdraw the ele
25. ce datum DATE TIME OF DEPTH TO WATER DEPTH TO WATER REMARKS Sa Mi E FROM ME FROM ESD include name of observer Local time YYYY MM DD 2002 04 16 Measured by Mary Smith MP DESCRIPTION sss Figure 7 Example of field data sheet for measurement of water levels with a fully graduated electric tape 21 BS ISO 21413 2005 WATER LEVEL MEASUREMENTS Field SITE NAME AND LOCATION include latitude longitude if feasible NAGNASNAUNEH mcm necp OR CPS SS TEE EN COE ETS SN SS OLE OS CRE ORO MP DESCRIPTION Top inside edge of stainless steel casing 1 50 m above land surface datum NEAREST DIFFERENCE 1 metre BETWEEN DEPTH TO DEPTH TO REMARKS TIME OF TAPE MP MARK AND WATER FROM WATER FROM MEASUREMENT BAND NEAREST 1 metre indias ame otiobserven BELOW TAPE BAND NE PSD BELOW MP Local time YYYY MM DD 2002 04 16 Measured by Mary Figure 8 Example of field data sheet for measurement of water levels with a partially graduated electric tape 22 BS ISO 21413 2005 WATER LEVEL MEASUREMENTS Field SITE NAME LOCATION include latitude longitude if feasible MP DESCRIPTION Top inside edge of steel casing red arrow north side 0 50 m above land surface datum Altitude gauge calibration data Initial wetted steel tape water level d is 7 88 m initial altitude gauge reading h is 23 02 m constant k d h 7 88 m 23 02 m 30 90 m ALTITUDE ALTITUDE DEPTH TO DEPTH TO TIME O
26. ctric tape from the well and record the depth to water to the nearest centimetre or less if in the opinion of the observer the instrumentation is capable of greater precision Record in the DEPTH TO WATER FROM MP column of the water level measurements field form see the example in Figure 7 For partially graduated tapes partly withdraw the electric tape from the well and record the metre mark of the nearest 1 metre tape band below the MP in the NEAREST 1 metre TAPE BAND BELOW MP column of the water level measurements field form see the example in Figure 8 Then measure the distance from the MP mark on the insulated wire to the nearest 1 metre tape band that is below the MP mark with a graduated steel tape and record that distance to the nearest centimetre in the DIFFERENCE BETWEEN MP MARK AND NEAREST 1 metre TAPE BAND BELOW MP column of the water level measurements field form see the example in Figure 8 The depth to water below MP is then obtained by adding the distance between the MP mark and the next lowest 1 metre tape band to the value of the next lowest tape band Record this number in the DEPTH TO WATER FROM MP column of the water level measurements field form see the example in Figure 8 Apply the MP correction to get the depth to water below or above LSD If the MP is above land surface its height is subtracted from the water level to obtain the depth to water below land surface If the MP is below land surface precede the
27. e below a measuring point using a submerged air line 5 2 Materials and instruments The following materials and instruments are required 5 2 1 Seamless copper tubing brass tubing or galvanized pipe preferably 3 mm to 6 mm in diameter with a suitable pipe tee for connecting an altitude or pressure gauge Flexible plastic tubing can also be used but is less desirable 5 2 2 Altitude or pressure gauge 5 2 3 Tyre valve stem and tyre pump 5 2 4 Small open end wrench 5 2 5 Wire or electrician s tape 5 2 6 Steel tape graduated in metres and centimetres 5 2 7 Blue carpenter s chalk 5 2 8 Clean rag 5 2 9 Field notebook pencil and eraser 5 2 10 Water level measurements field form see the example in Figure 9 5 3 Data accuracy and limitations The following data accuracy and limitations apply a Water level measurements using an altitude gauge should be accurate to within 3 cm b Water level measurements using a pressure gauge are more approximate and should not be considered accurate to more than 30 cm 10 BS ISO 21413 2005 c Asin all pressure dependent methods fluid density should be considered when measuring water levels by the air line method because the conversion constant of 0 102 m of water per kilopascal referenced later in 5 6 is valid only for distilled water at 20 C Fluid density is affected primarily by the temperature and dissolved solids content of the water An example of correcting a water level m
28. e nearest centimetre Correction for stretch Cs Le2mSl 2 PLS 514 94 m 2 0 003 6 kg 3 85 x 10 9 m m per kgy 2 0 20 kg 514 94 m 3 85 x 10 9 m m per kg 0 02 m rounded to the nearest centimetre then corrected depth L stretch correction 514 94 m 0 02 m 514 92 m 27 BS ISO 21413 2005 Annex B informative Corrections for water levels measured in wells with the air line method As in all pressure dependent methods fluid density should be considered when measuring water levels by the air line method Fluid density is affected primarily by temperature and to a lesser extent by the concentration of dissolved solids The density of water at 20 C is 0 998 23 g ml At this density 0 102 m of water can be associated with each kilopascal of measured pressure However water with temperatures greater than or less than 20 C would have proportionately smaller or greater densities respectively with proportionately greater or smaller conversion factors A table Table B 1 quantifying the change in density of distilled water over a wide temperature range is shown below Table B 1 Density of pure water free from air Temperature Density of pure water free Temperature Density of pure water free T from air T from air C g ml C g ml 9 o S e 69 RE omo e me m om AE M om COo s om EE HT 28 BS ISO 21413 2005 To illustrate the use of the Table B 1 in c
29. easured by an air line for temperature and dissolved solids content is given in Annex B However because the equipment required to measure the temperature and or dissolved solids content of the groundwater is not always readily available the corrections described in Annex B are not required for the purposes of this International Standard though the practitioner shall note on the water level field form see the example in Figure 10 whether or not any such corrections were applied 5 4 Advantages and disadvantages The air line method is especially useful in pumped wells where water turbulence may preclude using a more precise method The method can be used while the well is being pumped when splashing of water renders the wetted tape method useless Bends or spirals in the air line do not influence the accuracy of this method as long as the position of the tubing is not appreciably changed However the method is less accurate than the wetted tape or the electric tape methods and requires time to install the air line and equipment 5 5 Assumptions The following assumptions apply in the use of the air line method a An established measuring point MP exists See the technical procedure described in Clause 7 for establishing an MP b The MP is clearly marked and described so that all measurements will be taken from the same point 5 6 Procedures Figure 3 shows a typical installation for measuring water levels by the air line method The f
30. ents The following materials and instruments are required 6 2 1 Low pressure head measurements 6 2 1 1 Transparent plastic tubing of suitable length and diameter 6 2 1 2 Ladder if pressure head is more than 2 m to 3 m 6 2 1 3 Hose clamps 6 2 1 4 Measuring scale 6 2 1 5 Pencil and eraser 13 BS ISO 21413 2005 6 2 1 6 Calibration and maintenance log book 6 2 1 7 Water level measurements field form see the example in Figure 11 6 222 High pressure head measurements 6 2 2 1 Flexible hose with a 3 way valve 6 2 2 2 Hose clamps 6 2 2 3 Altitude or pressure gauge 6 2 2 4 Small open end wrench 6 2 2 5 Soil pipe test plug also known as a sanitary seal available from most plumbing supply stores in sizes that will fit 5 cm to 25 cm diameter pipes Soil pipe test plugs consist of a length of small diameter pipe generally less than 3 cm surrounded by a rubber packer The packer can be expanded by an attached wing nut to fit tightly against the inside of the well casing or discharge pipe The small diameter pipe is threaded so that it can be attached to a valve hose or altitude pressure gauge 6 2 2 6 Pencil and eraser 6 2 2 7 Calibration and maintenance log book 6 2 2 8 Water level measurement field form see the example in Figure 11 6 3 Data accuracy and limitations The following data accuracy and limitations apply a Low pressure head measurements can be measured to an accuracy of 3 0 cm b High pressure
31. fect the steel tape and weight by pouring a small amount of common household chlorine bleach or other suitable disinfectant on a clean cloth and wiping down the part of the tape that was submerged below the water surface This will avoid possible contamination of other wells h The tape shall be maintained in good working condition by periodically checking the tape for rust breaks kinks and possible stretch due to the suspended weight of the tape and the tape weight All calibration and maintenance data associated with the steel tape being used shall be recorded in its calibration and maintenance equipment log book All water level data shall be recorded on the water level measurements field form see the example in Figure 6 to the nearest centimetre In some contaminated or pumped wells a layer of oil may be floating on the surface of the water In such cases if the thickness of the oil layer is several centimetres or less the tape reading made at the top of the oil mark can be used as the water level measurement The associated error in this case should be relatively small because the level of the oil surface would differ only slightly from the level of the water surface that would be measured if no oil were present If a meter of more of oil is present however or if it is deemed necessary to ascertain the thickness of the oil layer a commercially available water detection paste originally developed to detect water in gasoline storage tanks
32. form see the example in Figure 6 3 2 7 Equipment to gain access to the well wrenches crow bars manhole keys etc 3 2 8 Common household chlorine bleach or other suitable disinfectant 3 3 Data accuracy and limitations The following data accuracy and limitations apply a Independent graduated steel tape measurements of static water levels should agree within 1 0 cm for depths of less than 60 m BS ISO 21413 2005 b For depths between 60 m and 150 m independent measurements using the same tape should agree within 2 0 cm When measuring deep water levels i e greater than 300 m errors due to the effects of thermal expansion and of stretch produced by the suspended weight of the tape and plumbing weight warrant consideration see Reference 2 p 3 An example of correcting a deep water level for thermal expansion and stretch of a steel tape is given in Annex A However because the equipment required to measure temperatures at land surface and down the well may not always be readily available the corrections described in Annex A are not required for the purposes of this International Standard though the practitioner shall note on the water level field form see the example in Figure 6 whether or not any such corrections were applied c At least once every twelve months the steel tape should be calibrated against another steel tape that is dedicated as a calibration tape and is not used in the field If the steel tape does
33. gested that if in doubt use a pressure gauge with at least a 500 kPa range to make an initial measurement then select the gauge with the proper range for more accurate measurements d Attach the altitude pressure gauge to one of the two open valve positions using a wrench Do not tighten or loosen the gauge by twisting the case because the strain will disturb the calibration and give erroneous readings e Bleed air from the hose using the other open valve position f Open the altitude pressure gauge valve slowly to reduce the risk of damage by the water hammer effect to the well distribution lines and gauges Once the needle stops moving tap the glass face of the gauge lightly with a finger to make sure that the needle is not stuck g Make sure that the well is not being used by checking to see that there are no fluctuations in pressure h Hold the altitude pressure gauge in a vertical position with the centre of the gauge at the exact height of the MP If using an altitude gauge read the gauge to the nearest centimetre For pressure gauges with kilopascal kPa units read the gauge to the nearest kilopascal kPa and multiply by 0 102 to convert to metres of water i Apply the MP correction to get the depth to water above LSD j Shut off the well pressure and repeat steps e through i for a second check reading If the check measurement does not agree within the accuracy given in 6 3 under Data accuracy and limitations
34. he use of additional graduated measures e g tapes calibrated in centimetres Type 1 tapes are referred to as partially graduated tapes in the rest of this clause and Type2 those with fixed graduations which are spaced at lengths equal to or smaller than the accuracy required for the readings Type 2 tapes are referred to as fully graduated tapes in the rest of this clause 4 2 Materials and instruments The following materials and instruments are required 4 2 1 Electric tape of various wiring arrangements or configurations that would include flat parallel or co axial conductive wires graduated in metres and or centimetres Electric tapes are commonly mounted on a hand cranked supply reel that contains space for the batteries and some device for signalling when the circuit is closed Figure 2 4 2 2 Electric tape calibration and maintenance equipment log book 42 3 Pencil and eraser 424 Water level measurement field form Tables 2 and 3 4 2 5 Equipment to gain access to the well wrenches crow bars manhole keys etc 4 2 6 Common household chlorine bleach and for measurements made with Type 1 electric tapes 4 2 7 Steel tape graduated in metres and centimetres 4 2 8 Spare batteries 4 3 Data accuracy and limitations The following data accuracy and limitations apply a Independent electric tape measurements of static water levels using the same tape should agree within 1 0 cm for depths of less than 60 m
35. is available to do so The paste can be applied to the end of the measuring tape that is lowered into the well The top of the oil layer will be reflected as a wet line on the tape while the top of the water will be shown by a distinct colour change In either event whether the oil layer is greater than or less than a few millimetres in thickness its presence should be noted on the water level measurements field form see the example in Figure 6 A specialized interface probe is also commercially available for measuring the interface In the event no water is encountered in the well this shall be duly noted under REMARKS on the field form along with the distance between the MP and the bottom of the well 2005 BS ISO 21413 Dimensions in metres Key 1 measuring point MP 2 MP hold 3 land surface datum LSD 4 water level 5 depth to water from LSD 12 86 6 depth to water from MP 13 71 7 wetted chalk mark Figure 1 Water level measurements using a graduated steel tape BS ISO 21413 2005 4 Water level measurement using an electric tape 4 1 Purpose The purpose of this method is to measure the depth to the water surface below a measuring point using the electric tape method Electric tapes fall into two categories Type 1 those that have fixed graduations lacking a suitable frequency e g 1 m graduation that would enable readings to be made at a sufficient accuracy without t
36. not meet test criteria then it must be removed from service Records of these tests shall be kept d Ifthe well casing is angled instead of vertical the depth to water will have to be corrected If the casing angle is unknown and a correction is not feasible this should be noted in water level measurement field form see the example in Figure 6 3 4 Advantages and disadvantages The graduated steel tape method is easy to use and is considered to be the most accurate method for measuring the water level in nonflowing wells of moderate depth However it may be impossible to get reliable results if water is dripping into the well or condensing on the well casing Also the method is not recommended for measuring pumping levels in wells 3 5 Assumptions The following assumptions apply in the use of the graduated steel tape method a An established measuring point MP exists and the distance from the MP to land surface datum LSD is known see the example in Figure 6 See the technical procedure described in Clause 7 for establishing a permanent MP b The MP is clearly marked and described so that all measurements will be taken from the same point c The results from previous water level measurements made at the well are available for estimating the length of the required tape d The steel tape will retain the chalk e The well is free of obstructions Well obstructions if present could cause errors in the measurement if the ob
37. ollowing procedures for measuring water levels in a well with an air line shall be observed a Install an air line pipe or tube in the well The air line can be installed by either lowering it into the annular space between the pump column and casing after the pump has been installed in the well or by securing it to sections of the pump and pump column with wire or tape as it is lowered into the well b The air line shall be extended far enough below the water level such that the lower end remains submerged during pumping of the well c Attach a pipe tee to the top end of the air line On the opposite end of the pipe tee attach a tyre valve stem d Connect an altitude gauge that reads in meters or a pressure gauge that reads pressure in kilopascals kPa to the fitting on top of the pipe tee with a wrench If an altitude gauge is used read the gauge to the nearest centimetre For pressure gauges with kilopascal kPa units read the gauge to the nearest kilopascal kPa and multiply by 0 102 m kPa to convert to meters of water e Connecta tyre pump to the tire valve stem fitting on the pipe tee f As the water level in the well changes and d Figure 3 must change in a manner such that their sum remains the same Their sum is a constant k which is determined at the same time as a simultaneous wetted steel tape and air gauge measurement is made 11 BS ISO 21413 2005 1 altitude
38. orrecting water level measurements for temperature in air lines consider Example 2 which was previously described in 5 6 and shown in Table 5 If in that example the water in the air line had some temperature other than 20 C say 60 C then the conversion factor C used to convert the pressure reading in kilopascals to metres of water would be recalculated as C 0 102 m kPa x 0 998 23 g ml 0 983 24 g ml 0 103 6 m kPa and initial 0 103 6 m kPa x 190 kPa 19 68 m and from Table 5 k 19 68 26 17 45 85 m then the corrected depth to water would be calculated as d k h 45 85 m 0 103 6 m kPa x 122 kPa 33 21 m versus an uncorrected depth of 33 11 m from Table 5 In moderate concentrations the effect of dissolved solids on fluid density is at least one order of magnitude less than that of temperature For example for dissolved solids having a specific gravity of 2 5 water taken as unity calculations show that the density of water having a dissolved solids concentration of 100 mg l would be 1 000 06 water having a dissolved solids concentration of 200 mg l would have a density of 1 000 12 and water having a dissolved solids concentration of 1 000 mg l would have a density of 1 000 6 29 BS ISO 21413 2005 1 2 3 4 5 6 7 8 9 30 Bibliography DRISCOLL F G Groundwater and wells 2nd ed Johnson Division St Paul Minnesota 1986 1 089 pp GARBER M S and
39. ort length of transparent plastic tubing tightly to the well with hose clamps b Raise the free end of the tubing until the flow stops c Restthe measuring scale on the measuring point MP d Read the water level directly by placing the hose against the measuring scale e Apply the MP correction to get the depth to water above land surface datum LSD f Repeat steps b through e for a second check reading If the check measurement does not agree within the accuracy given in 6 3 under Data accuracy and limitations continue to make check measurements until the reason for the lack of agreement is determined If more than two measurements are taken the observer shall select the reading considered the most reliable 6 6 2 High pressure head measurement indirect measurement Use the following procedure a Make sure that all well valves are closed except the one to the altitude pressure gauge This will prevent use of the well during the measurement period and assure an accurate water level reading Record the original position of each valve that is closed full open half open closed etc so that the well can be restored to its original operating condition b Connect a flexible hose with a 3 way valve to the well with hose clamps using the soil pipe test plug or appropriate plumbing fittings 15 BS ISO 21413 2005 c Select a gauge where the water pressure in the well will fall in the middle third of the gauge range It is sug
40. presence of hydrocarbons on the water surface that may result from oil leaks during drilling operations may coat the sonde resulting in a failure to complete the electrical circuit Finally a stilling pipe may be required to avoid inaccurate readings where water is cascading down the borehole during pumping aquifer tests In general fully graduated tapes are preferred to partially graduated tapes Fully graduated tapes are easier to use and there are fewer opportunities for errors in measurement particularly when the time intervals between measurements are small such as during pumping tests 4 5 Assumptions Application of the electric tape method assumes a thatan established measuring point MP exists and b if the water level is to be referenced to land surface that the distance between the MP and land surface datum LSD is known see the example in Figure 7 See the technical procedure described in Clause 7 for establishing a permanent MP Also the MP should be clearly marked and described so that all measurements will be taken from the same point If the MP of record cannot be located the use of data for assessing long term trends may be compromised In such cases a new MP should be established and the date of change should be indicated on the record sheet 4 6 Procedures The following procedures for measuring water levels in a well with an electric tape shall be observed a Prior to using an electric tape in the field
41. r impossible to reach true static conditions record the shut down time for each gauge reading During return visits to a particular well it is desirable to duplicate the previously used shut in time before making a altitude pressure gauge reading 14 BS ISO 21413 2005 6 4 Advantages and disadvantages Low pressure head measurements are simpler faster safer and are more accurate than high pressure head measurements but are impractical for wells with heads greater than 2 m above land surface High pressure head measurements can be made at wells with heads greater than 2 m above land surface but the altitude pressure gauges required for such measurements are delicate easily broken and subject to erroneous readings if dropped or mistreated SAFETY PRECAUTIONS The soil test plugs used in high pressure head measurements may present a safety risk as these devices could slip from the casing and become projectiles 6 5 Assumptions The following assumptions apply when measuring water levels in a flowing well a An established measuring point MP exists See the technical procedure in Clause 7 for establishing an MP b The altitude pressure gauges have been calibrated with a dead weight tester c Alog book containing all the calibration and maintenance records is available for each altitude pressure gauge 6 6 Procedures 6 6 1 Low pressure head measurement direct measurement Use the following procedure a Connecta sh
42. structions affect the plumbness of the steel tape 3 6 Procedures The following procedures for measuring water levels in a well with a graduated steel tape shall be observed a Apply the coloured chalk to the lower metre of the tape by pulling the tape across the chalk The wetted chalk mark will identify that part of the tape that was submerged b Lower the weight and tape into the well until the lower end of the tape is submerged below the water more than one attempted measurement may be needed to determine the length of tape required to submerge the weight Once the end of the tape is submerged continue to lower the tape into the well until the next whole metre graduation mark is opposite the MP This whole number shall be recorded in the MP HOLD Figure 1 column of the water level measurements field form see the example in Figure 6 BS ISO 21413 2005 c Pullthe tape back to the surface before the wetted chalk mark dries and becomes difficult to read Record the number of the wetted chalk mark sometimes referred to as the cut in the WETTED CHALK MARK Figure 1 column of the water level measurements field form see the example in Figure 6 d Subtract the wetted chalk mark number from the number held to the MP and record this number in the DEPTH TO WATER FROM MP Figure 1 column of the water level measurements field form see the example in Figure 6 The difference between these two readings is the depth to water below the
43. that use automated electrical or mechanical means to measure and record water levels 2 Terms and definitions For the purposes of this document the following terms and definitions apply 2 1 air line water level measuring device consisting of a small diameter open ended tube fixed in position that is accessible from the top of the casing and extends to below the water level in a well where pressurized air measurements can be used to determine the depth to water 2 2 casing well casing tubular retaining structure which is installed in a drilled borehole or excavated well to maintain the borehole opening Plain unscreened casing prevents the entry of water and fine material into the well while open screened casing allows water ingress but should exclude fines 2 3 electric tape water level measuring device that uses an electrical signal sent through a cable with fixed distance marks to determine the water level relative to a fixed reference point The electrical signal which is induced when the sensor makes contact with the water surface activates an indicator typically a light buzzer or needle 2 4 flowing well or overflowing well well from which groundwater is discharged at the ground surface without the aid of pumping NOTE A deprecated term for this definition is an artesian well 2 5 graduated steel tape water level measuring device consisting of a flat measuring tape with permanently fixed distance marks that c
44. to be used for any other purpose than implementation then the prior written permission of BSI must be obtained Details and advice can be obtained from the Copyright amp Licensing Manager Tel 44 0 20 8996 7070 Fax 44 0 20 8996 7553 Email copyright bsi global com
45. y from legal obligations Summary of pages This document comprises a front cover an inside front cover the ISO title page pages ii to v a blank page pages 1 to 30 an inside back cover and a back cover The BSI copyright notice displayed in this document indicates when the document was last 1ssued This British Standard was Amendments issued since publication published under the authority of the Standards Policy and Strategy Committee Amd No Date Comments on 31 January 2006 BSI 31 January 2006 ISBN 0 580 47365 1 BS ISO 21413 2005 INTERNATIONAL ISO STANDARD 21413 First edition 2005 10 15 Manual methods for the measurement of a groundwater level in a well M thodes manuelles pour le mesurage du niveau de l eau souterraine dans un puits Reference number ISO 21413 2005 E LOZ uonnmsu SPIEPUEJS usiug ul 9 GL0Z L0 80 JO Se 1981109 UOISI8A LSNYH Mesiq 23 neus 287 Adoo pesueor BS ISO 21413 2005 Contents Page oll e M iv Introduction US eee Rh im uet cemere iicet e d see E v 1 Leo oT p ER 1 2 Tems and definitions nete c neret erede Hte Sect ee oap asa ra ana sa suu 1 3 Water level measurement using a graduated steel tape sens 2 3 1 dO DIM RETE LEE 2 3 2 Materials and instruments u U U U si eee seaeeeseee sae eeeseaeeeseeeseaeeaeeseeeseeeeseeanes 2 3 3 Data accuracy and limitations U aaa SAANS ERRA
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