218

APPENDIX 4

EXPERIMENTAL PROCEDURES

A4.1 METHOD OF TESTS FOR SOILS

Indian Standards (IS) : 2720 for ‘Method of Test for Soils’ published under separate parts for various determinations have been followed for the characterisation of soil samples collected at Kalpakkam. These standards are comparable to other well-established standards followed internationally. The parameters necessary for the site charac­terisation of the disposal facility at Kalpakkam, mainly from the safety assessment considerations, are determined based on the above methods outlined in IS : 2720. These determinations are discussed briefly in the following sections :

A4.1.1 Determination of pH value of soil samples (IS : 2720 (Part-XXVI), 1973)

Scope

The method followed for the determination of pH value of soil suspension is based on electrometric method.

Materials

pH Meter, direct reading type, with glass electrode and a calomel reference electrode, analytical balance, sensitive to 0.001 g, mortar with rubber covered pestle, the buffer solutions of pH 4.0, pH 7.0 and pH 9.2 for standardisation of pH meter.

Soil specimen : The soil sample received from the field is prepared in accordance with IS : 2720 - Part I (1972). All aggregations of particles are broken down and thoroughly mixed and a representative sub-sample is obtained by cone and quarter method. These sub-samples are sieved on a 425-micron sieve to obtain specimen samples for pH analysis.

219

Procedure

30 g of the soil specimen prepared as per the above procedure is taken in a 100 ml beaker. 75 ml of distilled water is added to it. The suspension is stirred for a few seconds. The beaker is then covered with a cover glass and allowed to stand for one hour, with occasional stirring. It is again stirred well immediately before testing its pH with pH electrode. The pH value of the soil suspension is recorded to the nearest 0.1 pH units.

A4.1.2 Determination of total soluble solids (IS : 2720 (Part- XXI), 1965)

Scope

The determination of total soluble solids in soils is carried out by gravimetric method as well as conductometric method, which is generally specified as a subsidiary method. The method employed in the present characterisation is based on gravimetric method.

Materials

Bottle shaker, oven, Buchner or glass funnel, vacuum pump, desiccator, water bath, filter paper (Whatman 42 or equivalent).

Procedure

A representative sample passing a 2 mm sieve is dried to constant weight in an oven at a temperature of 105-110C. From this sample about 10 g of soil is accurately weighed and transferred to a 250 ml glass bottle. 100 ml distilled water is added to it and the bottle is then stoppered and fitted in the shaker and shaken overnight (or at least 15 hours). The soil is then allowed to settle and the clear portion is decanted and later filtered through Whatman 42 paper. If the filtrate is not clear, the filtration is repeated under suction. 50 ml of clean filtrate is taken in a porcelain dish or glass dish and concentrated by evaporat­ing in the water bath before drying in oven at 105C. The dish is allowed to cool and weighed. The percentage soluble solids in soil is calculated based on soil taken for analysis and reported to the nearest 0.01%.

220

A4.1.3 Determiiiation of base exchange capacity (IS : 2720 (Part-XXTV), 1967)

Scope

The base (or) cation exchange capacity is the property which all the soil particles possess, arises on account of isomorphic substitu­tion of Al+3 and Si+4 by smellier valent ions like Fe+2 etc. This is estimated in the present method by converting the exchangeable sites into Ca+2 ions and this Ca is extracted with CHgCOONa and amount of calcium is estimated which corresponds to the cation exchange capacity.

Materials

1. Sodium acetate solution (pH 5.0) : IN sodium acetate (CH3C00Na.3H20) solution is prepared with 136 g salt and 28 ml glacial acetic acid and made up to 1 litre to obtain pH 5.0 buffer.

2. Sodium acetate solution (pH 7.0) : IN sodium acetate (CHgCOONa.3H20) solution is prepared containing 136 g of salt per litre with pH adjusted to 7.0 with acetic acid.

3. Calcium chloride solution (pH 7.0) : Calcium chloride (CaCl2.6H20) solution containing 109 g is prepared in one litre with pH adjusted 7 by Ca(OH)2.

4. Acetone (80 %).

5. Standard calcium solution : About 0.5 g of pure dried calcium carbonate is dissolved in a minimum of 0.2N HC1. The solutionis boiled to expel C02 and is then diluted to 1 litre. The resultant

^ +2 solution is 0.0IN with respect to Ca .

6. Buffer solution of pH 10.0: This buffer is prepared by mixing 100 ml NH4C1 and 500 ml of IN NH4OH.

7. Eriochrome Black T (EBT) : 0.5 g of EBT dissolved in 4.5 g NH2OH.HCl and diluted it with 100 ml methanol.

8. Standard versene : 2 g EDTA is dissolved in 900 ml water. The normality of versene is then determined by titration of 25 ml portion with standard calcium solution.

221

Apparatus like centrifuge and necessary glassware like volu­metric flasks, centrifuge tubes etc., are required.

Procedure

5 g of soil is taken in 100 ml centrifuge tube and stirred in 50 ml of IN CHgCOONa of pH 5.0. The soil suspension is digested in boiling water bath (about 90C) for 30 minutes, with intermittent stirring. The supernatant liquid is removed by decantation after centrifugation of the suspension. Additional two washings with IN CHgCOONa of pH 5.0 are given to remove any dissolvable salts. If required, additional washings are given. Subsequently the soil sample is given at least 5 washings with IN CaCl2 solution to exchange all the exchangeable sites with calcium ions. Excess calcium salt is removed by washing each time with 80 % acetone. However, complete removal of chlorides is tested with dilute silver nitrate. Ultimately, the calcium ions exchanged on the soil are replaced by sodium ions by means of five extractions with neutral IN CHgCOONa solution. The above washings are combined and amount of calcium present is estimated by titrating against standard Versene solution by the addition of 10 ml pH 10.0 buffer and 10 drops EBT indicator and 1 ml of NaCN. The cation exchange capacity is calculated from the expression given below and is expressed in mill! equivalents (meq)/100 g soil:

Cation exchange capacity (meq) per 100 g soil *Ml of versene x Normality of versene x 100----------------------------------------------- (A4.1)Weight of soil in gm. x vol. of washings

A4.1.4 Determination of distribution coefficient (Kd)

Scope

The distribution coefficient (Kd) of the soil medium is a measure of its ion uptake capacity. This is an important parameter employed in any soil transport predictions. The Kds are determined for the important isotopes of concern with respect to shallow ground disposal. The units are usually expressed in ml/g. The present study envisages determining the K ,s of soil samples using radio isotopes Sr and 137Cs.

222

Materialsqq i on

Sr and Cs tracer, GM counter/multi-channel Gammaanalyser.

ProcedureAbout 2 g of accurately weighed soil sample was collected from

disposal site and is equilibrated with 20 ml of the 89Sr or 137Cs tracer containing 1x10-3 micro curies per ml in the 50 ml centrifuge tube. The time of equilibration was 20 h. After equilibration, the sample was centrifuged at 2500 rpm and the filtrate was decanted. The soil was dried under IR lamp and about 0.01 g sample was taken for counting. 1 ml from the filtrate was plancheted and activity was determined using GM Counter GCS-16 having efficiency of approximately 10%. Distribution coefficient was determined (Amalraj et al, 1981) using the following equation (A4.2)

Distribution Coefficent (Kj)

Counts per minute per gram of soil

Counts per minute per ml. of filtrate

(A4.2)

A4.1.5 Determination of Calcium Carbonate content (IS : 2720 (Part-XXm, 1964)

Scope

This standard outlines the volumetric estimation of CaC03 in the soil samples. This parameter is generally determined to find out the effect of cementing that it can impart between the soil particles.

Materials

1. Acetic acid 0.5N prepared in 0.2N (approx.) calcium acetate solution. (58 ml of acetic acid required to make IN solution in 1 litre).

1. NaOH 0.1N (Standardised with Oxalic acid)

2. Oxalic acid 0. IN.

3. Phenolphthalien.

223

Procedure1-5 g of soil is placed in a 500 ml conical flask and 50 ml of

0.5N acetic acid prepared in 0.2N calcium acetate solution is added. The contents are shaken for about one hour intermittently to allow the calcium carbonate content to react with available acetic acid. The contents are then filtered through Whatman 40 or equivalent filter and an aliquote of the filtrate is titrated with 0.1N NaOH solution using phenolphthalien indicator. The decrease in the concentration of acetic acid in the filtrate is attributed to the C03 present in the given quantity of soil. The % CaC03 is calculated as given below:

% CaC03 in soil =

(Volume of 0.5N Acetic acid consumed by the soil sample x 0.025 x 100)

----------------------------------------------------- = o.74 —(A4.3Weight of soil

A4.1.6 Determination of specific gravity (IS : 2720 (Part-HQ, 1964)

Scope

This method of test for the determination of the specific gravity is applied to fine grained soils. The method is also applied for medium and coarse grained soils if the coarse particles are grained to pass 4.75 mm sieve.

Materials

Two specific gravity bottles of 50 ml capacity with stoppers. A water bath maintain ted at a constant temperature. A desiccator contain­ing anhydrous silica gel. Analytical balance (accuracy to 0.001 g).

Procedure

A 5 to 10 g sub-sample after passing through 2 mm sieve is taken and oven dried at 105 to 110C. This sample is transferred to the specific gravity bottle after cooling in the desiccator. The bottle and contents together with the stopper are weighed to the nearest 0.001 g. Then adequate water is added and the stoppered bottle is immersed in

224

the constant-temperature bath for approximately 1 hour or until it has attained the constant temperature of the bath. If there is an apparent decrease in volume of the liquid the stopper shall be removed and further water is added. The bottle is then returned to the bath and sufficient time is allowed to elapse after this operation to ensure that the bottle and its contents again attain the constant temperature of the bath.

The stoppered specific gravity bottle is then taken out of the bath, wiped diy and then weighed to the nearest 0.00 lg.

The bottle is then cleaned and filled with water, the stopper is inserted and then it is allowed to attain constant temperature by immersing in the constant temperature bath for 1 hour . The bottle is then taken out of the bath, wiped dry and the weighed to the nearest O.OOlg.

The specific gravity (G) of the soil particles is determined at room temperature by the following equation:

G = ----------------- (A4.4)(m4 - irq) - (m3 - m2)

where mt = weight of the specific gravity bottle in g. m2 = weight of bottle and dry soil in g. m3 = weight of bottle, soil and water in g and m4 = weight of bottle filled with water in g

The determinations are carried out in duplicate and recorded to the nearest 0.01.

A4.1.7 Grain size analysis (IS : 2720 (Part-IV), 1965)

Scope

Two methods are generally followed for finding the distribution of grain sizes viz., wet sieving, applicable to all soils and dry sieving

225

applicable only for soils which do not have appreciable amount of clay. As, the present site under study does not contain appreciable amounts of clay dry sieving is employed to finding the grain size distribution.

Sieve analysis of soil passing 4.75 mm sieve and retained on 75-micron sieve

Materials

Analytical Balance, sensitive to 0.001, sieves (2 mm- sieve, 425-micron sieve, and 75-micron sieve.

Procedure

The set of sieves in the above sieve range are arranged and mounted on sieve shaker or shaken manually after placing known amount of soil sample. The cumulative weight of soil fraction retained on each sieve is calculated. The percentage of soil fraction retained on each size is calculated on the basis of the weight of the sample passing 4.75-mm sieve taken for the initial analysis. The combined gradation on the basis of the total soil sample taken for analysis is then calculated.

The results of the grain size analysis are reported in a suitable tabular form. A grain size distribution curve is drawn on a semi-loga- rithmic chart, plotting particle size on the log scale against percentage finer than the corresponding size on the ordinary scale.

A4.1.8 Laboratory determination of coefficient of permeability (IS : 2720 (Part XVH ), 196^)

Scope

The method followed in this standard (Part-XVII) describes the laboratory determination of the coefficient of permeability of soils using the falling head and the constant head methods. This test is recom-

o *7

mended for soils with coefficient of permeability in the range of 10’ -10’ cm/s. In the present determinations falling head method is employed.

226

Materials

For the determination of coefficient of permeability by falling head (variable head) method the apparatus required are : permeameter mould (1000 ml capacity), a set of glass pipes varying in diameter from 5-20 mm suitably mounted on stand or otherwise fixed on wall, vacuum pump, miscellaneous apparatus like sieves, mixing pan, graduated cylinder, stop watch and thermometer.

Procedure

A 25 kg sample is taken from a thoroughly mixed air dried or oven dried material which has been obtained in accordance with IS : 2720 (Part-I), 1966.

The permeameter mould is weighed to the nearest gram. After greasing lightly the inside of the mould it is clamped between the compaction plate and the extension collar. The assembly is kept on a solid base.

The soil sample in the permeameter is compacted to simulate field conditions. After completion of the compaction, the compacted specimen is weighed. The mould with the specimen inside is assembled to the drainage base and a cap having porous discs.

In the case of soils of medium to high permeability the specimen is subjected to sufficient head, flow or dimension so as to obtain full saturation. Soils of low permeability require flow under high head. Alternatively, in the case of soils low permeability in the specimen is subjected to gradually increasing vacuum.

Falling head test

For falling head test arrangement the specimen is connected through the top inlet to a selected stand pipe. The bottom outlet is opened and time interval required for the water level to fall from a known initial head to a known final head is noted. The stand pipe is refilled with water and the test is repeated till 3 successive observation give almost the same time interval. The time intervals being recorded for the

227

drop in head from the same initial to final levels as in the first determination. The coefficient of permeability is calculated from the equation:

2.303 aLk =----- ------ log (hl/h2) —(A4.5)

Atn

where a = inner cross-sectional area of stand-pipe (L ) hj = initial head in stand pipe (L) h2 = final head in stand pipe (L)L = length of specimen (L)

n

A = cross-sectional area of specimen (L } t = time taken for water level to drop from

hx to h2

The symbols in the parentheses indicate the dimensional quantities.

A4.2 DETERMINATION OF GROUND WATER RECHARGE BYdvav oiiiLvr unpniAn riiAlV- orilr 1 jMU&iilULJ

Scope

The downward movement of rainwater through the unsatu­rated soil profile and thereafter the recharge (Rp) to groundwater are measured using tritium as radioactive tracer. The method has the advantage in tracing soil water, as tritium forms an integral part of the water molecules and its transport is well defined both in time and space. Briefly, the method consists in labelling a layer of soil moisture with tritiated water and subsequent collection of radioactive soil samples from the injection site at varying depths. The pore water from the soil samples was extracted and the tritium concentration of the extracted pore water was measured by liquid scintillation counter. The moisture content of the soil column between the injection depth and the depth of the tracer peak when multiplied by the displaced depth of tracer front gives the amount of recharge to groundwater. Mathematically, recharge (Rp) is expressed as:

228

Rp = (MC) * d —(A4.6)

where Rp = Recharge (L)MC = Moisture content (%) and d = displaced depth (L)

The units are expressed in dimensional quantities in paren­theses.

Materials

Tritium isotope (50 micro Curie/ml), Tritium liquid scintilla­tion counter.

Procedure

About 50 micro Curie of Tritium was injected at 35 cm depth from surface at two different locations preferably before the onset of monsoon. The soil samples are collected after the peak of the activity moved further down due to rain water percolation. The distribution peak was located by counting tritium in the moisture extracted from soil samples at different depths. The recharge to groundwater due to rain was calculated by multiplying the tritium peak shift with the average volumetric moisture content in the peak shift region. Knowing the amount of rainfall during the period, the percentage of recharge is calculated.

A4.3 METHOD DETERMINATION OF GROUND WATER PARAMETERS

A4.3.1 Determination of direction of groundwater flow (Three-well method).

Scope

Knowing the direction of groundwater movement has become increasingly important because of the danger of contaminating ground- water supplies. The groundwater flow lines can be determined by using water elevation data from a minimum three wells. The information obtained is applicable only to that location and repeated determination at various locations can provide overall flow pattern.

229

Procedure

The direction of groundwater flow in the field is determined (Freeze et al, 1979) by finding out the groundwater elevations of any chosen three wells. The distance between the above wells is obtained by actual measurement in the field. These wells are represented on a sketch according to the scale with horizontal direction coinciding with geo­graphical north. Later the groundwater elevations and surface eleva­tions are indicated at the well location. Between each of the two wells the range of groundwater elevation is sub-divided in intervals of 0.1 m or any other suitable interval depending on the separation between the wells chosen and their respective groundwater elevations. The equipo- tential points on the sketch are joined to obtain groundwater contours on a local scale. The direction of groundwater flow is obtained by drawing flow lines perpendicular to the groundwater contours. Several sets of three wells may have to be chosen to get velocity distribution in the field.

A4.3.2 Determination of direction of groundwater flow (Groundwater contours method).

Scope

The determination of direction of groundwater flow by the above three-well method may be laborious. On the other hand if data is obtained of groundwater elevations of several borewells in the field, groundwater contour maps of the entire site can be drawn and based on which the direction of groundwater flow in the entire field can be indicated.

Procedure

The groundwater levels in the borewells are periodically mon­itored for all seasons The groundwater contour diagram is drawn based on the data obtained over the years for the pre-and post-monsoon periods. The use of SURFER (1987) software is employed to draw the groundwater contour diagrams and groundwater surface diagrams to understand the direction of groundwater flow. The application of soft­ware requires input data of groundwater elevations and their X, Y co-ordinates.

230

A4.3.3 Determination of groundwater velocity using Darcy’s method

An indirect estimate of groundwater velocity can be made from the hydraulic parameters of the aquifer and Darcy’s law. Using the sketches drawn to determine the direction of groundwater flow as described in section A4.3.1 and A4.3.2. These diagrams depict the flow lines indicating the direction of flow.

The hydraulic gradient (i) is evaluated along the direction of groundwater flow from the ratio of difference of groundwater elevations between the adjacent contours and the distance between them. Darcy’s law is generally expressed as :

VD = -k i - (A4.7)

where VD = Darcy’s velocity (LT1)k = hydraulic conductivity (LT'1) and

i = hydraulic gradient (dimensionless)

The negative sign comes from the fact that the displacement occurs in the direction of decreasing heads. This velocity is also termed as Darcy’s velocity. Darcy’s velocity can utmost be an apparent velocity as it is assumed that the groundwater flows in a straight line between any two points and there is no tortuosity. Actually the water molecules do not follow rectilinear path in the porous medium, hence their real velocity is higher than Darcy’s velocity. As it is difficult to determine the actual distance travelled by the water molecule, a correction factor is introduced to improve the accuracy of groundwater velocity. The appar­ent velocity is given by the following equation :

Vg = Dilution velocity = VD / 0 —(A4.8)

where 0 = effective porosity (dimensionless).

231

The groundwater velocity determined by this method, however requires the data on field permeability and effective porosity. The basic assumption in the above method being that the aquifer system is homogeneous and isotropic i.e. the hydraulic conductivity (k) and porosity (0) are invariant with respect to space and time.

A4.3.4 Determination of groundwater velocity (Tracer method)

Scope

In hydrological investigations including determination of ground water velocity, appropriate tracer is chosen according to require­ments dictated by the conditions of the investigation. The study of ground water flow makes it necessary to use a tracer directly introduced into the water. The tracer should have good solubility and not undergo undue losses during movement so that the characteristics may be reproduced easily.

The single-well dilution methodology is adopted using tracers to determine the groundwater velocity. A set of borewells drilled up to hard base formation is necessaiy. A suitable tracer like dye, salt or radio isotope is chosen based on the requirement and their aqueous solution is introduced into the borewell. The method basically involves collection of samples after addition of a tracer into a borewell at pre determined intervals. These samples are analysed for their concentration. In the present study, groundwater velocity is determined by using three differ­ent isotopes viz., Sodium chloride, Rhodamine B and Tritium. The methodology followed is given in the following sections.

Assuming that the measuring volume has been isolated and the tracer is injected inside it, the decrease of the tracer concentration ‘C in this volume is expressed by the following equation

Vg = - (V/A*t) In (C/Co) —(A4.9)where

Vrt is the tracer dilution velocity (LTrllV is measuring volume in borewell of radius r (L )A is the cross sectional area of the dilution volume(L )C is concentration of tracer at time tCn is concentration of tracer at time t = 0

232

Thus The hydrodynamic regime of the groundwater undergoes a local modification just at the measuring point due to boring through the aquifer layer. A series of other factors also contribute with variable weight otherwise the dilution velocity and apparent velocity would coincide. The variation of the tracer concentration inside the measuring volume is also be due to radioactive decay, molecular diffusion, disper­sion, adsorption, ion exchange and mixing phenomena (Halvey et al, 1967). The correction due to above factors is introduced in the equation (1) and velocity Vg of the groundwater is given by

Vg = - (V/ A*t) In (C/CO) —(A4.10)Vg = -2.303 (V/a A*t) log (C/CO) or -(A4.11)log (C/CO) = (-Vgac A*/2.303 V) t ™(A4.12)

whereac = Correction factor (Jain et al, 1980)

The Correction factor in the present study has been estimated (Gasper et al, 1972) as 4, which is derived from the data of hydraulic conductivity of aquifer (1.0 x 10'4 cm/sec), permeability of filtering

O Q

envelope (1.5 x 10 cm/sec) and permeability of filter tube (1.0 x 10_o

to 1.0 x 10 cm/sec) respectively.

It is evident from the above equation that the plot of log C/C0 vs time would give a straight line with a negative slope. The slope thus evaluated can be equated to :

Slope = - (Vgac A*/2.303 V) henceVg = 2.303 (slope) V/(ac A*) -(A4.13)

A4.3.4.1 Determination of groundwater velocity usingSodium Chloride (Single-well dilution method).

MaterialsWater level indicator, water sampler, sodium chloride, silver

nitrate solution (0.005N), and potassium chromate indicator.

233

ProcedureTo estimate the quantity of water present in the borewell, the

diameter of the borewell, column of water present are determined from the field determinations. Water level indicator is used to measure the column of water present in the bore well. With the above data the volume of water present is evaluated. Sodium chloride solution is prepared in the laboratory with the borewell waters under study and introduced into the borewell and mixed thoroughly to obtain overall concentration of about 0.05 M in the borewell. About 100 ml water sample is collected immediately after the addition of sodium chloride solution using a water sampler in a clean polythene bottle and labelled. Initially the samples are collected at half-hourly intervals up to first three hours and every one hour for the next three hours. The chlorides are estimated at different time intervals by Mohr’s method (APHA, 1976).

. The chloride levels are tabulated at different time intervals and log C/Co vs time is plotted. The groundwater velocity is evaluated from the slope of the above semilog plot using equation (A4.13).

A4.3.4.2 Determination of groundwater velocity usingRhodamine B Dye

About 0.1 g Rhodamine B is injected into a borewell in the similar fashion as in the case of sodium chloride and the Rhodamine B concentration at zero time and at same time intervals as in the case of sodium chloride tracer study are collected and optical densities are estimated using UV/VIS spectrophotometer at X max 555 nm. Similar plots as in the case of sodium chloride tracer study are drawn and the slope is evaluated from log C/Co vs time plot and velocity of groundwater is estimated with respect to Rhodamine B using equation (A4.13).

A4.3.4.3 Determination of groundwater velocity using Tritium Isotope

In order to compare the groundwater velocity at different locations, the above determination is carried out in a different borewell. A known quantity of standard Tritium isotope is added such that about 500 cpm/ml are obtained and the samples are collected subsequently

234

as in the case of other tracer experiments and tritium levels at different time intervals are measured using liquid scintillation counter (APHA, 1976). The velocity of groundwater flow is computed using the equation (A4.13).A4.4 DETERMINATION OF SELF-DIFFUSSION CO-EFFCEENTS

(HALF-CELL METHOD)Scope

Self diffusion coefficients for the isotopes 137Cs and 85+89Sr are determined to assess the transport of radionuclides in the geo-en- vironment when advection is negligible and diffusion assumes greater significance.

Materials

85+89Sr isotope, 137Cs isotope, diffusion cells, incubator and multi-channel analyser with germanium detector.

Procedure

The soils used in these studies were sandy loam type collected from waste disposal facility. The self diffusion coefficient was measured for 137Cs and 85+89Sr in soils by the method of Rowell et al (1967). For each experiment two sub samples were taken. One sub sample (6 g) was incorporated with 0.2 micro Curie of radioactive isotope Cs or 85+89gr ag case may be These samples were dried and ground to pass through 1 mm sieve. Cylindrical diffusion cell made of perspex consisted of two half cells. Each half cell was 1 cm long having 2.5 cm internal diameter.

One half cell was filled with radioactivity incorporated soil and other with inactive soil and desired conditions like maintaining bulk density or moisture content were followed as per the procedure followed by Rowell et al (1967). These were brought into close contact having lens tissue paper (Greens No. 105, 10x8 cm) in between them, and were placed in an air tight container and maintained at 251C in an incubator.

235

After fixed diffusion time {137Cs = 40 days, 85+89Sr = 34 days),

the half cells were separated. The amount of isotope in each half cell was measured directly using multi-channel analyser for 137Cs and 85+89gr separately with the help of Germanium detector.

Self diffusion coefficients were calculated using the equation given by Schofield and Graham-Bryce (1960).

Qt/Q°° = (2/L) (Dt/7t)1/2 (A4.14)

Where

Qt = Amount of radioactive ions diffused

from active to non-active soil (Bq)

Q„ = Amount that would be transferred in infinite

time (Bq)

t = Diffusion time (T)

L = Length of diffusion cell (L)

D = Self diffusion coefficient

The values of D were taken as the mean of the three replicates and for each replicate the coefficient of variation was calculated. The results are discussed in the following paragraphs.

GLOSSARY OF RADIOACTIVE WASTE TERMS

Absorbed dose

Amount of energy imparted to a mass. Traditional unit is the rad, roughly equivalent to the amount of energy deposited in tissue by one roentgen of radiation exposure. SI unit is the gray (Gy); 1 Gy = 100 rads.

Activation products

Elements that become radioactive during the course of bom­bardment by neutrons or protons.

Alpha emitter

An element that in undergoing radioactive decay releases alpha articles (helium nuclei)

As low as reasonably achievable (ALARA)

Basic principle of radiation protection, stating that doses from radioactive materials should be reduced to the lowest possible levels, provided that economic and social benefits exceed any risks.

Backfill

The placement of soil or other material in, around, or over a structure.

Background radiation

Radiation that arises from constant natural sources and accepted man-made sources, such as dental and medical x-rays. Radi­ation from cosmic sources and natural radiation are always present. Approximately 55% of background radiation is due to radon emitted from rock and building materials.

Bequerel(Bq)

The international unit for radioactivity representing one dis­integration per second. Named in honor of Henri Bequerel, who discov-

237

ered the property of radioactivity in 1896. By international agreement, the bequerel has recently replaced the curie as the preferred unit of measure. One Bq = 2.7 x lo-11 Ci.

Beta emitterAn element that releases beta particles (negative electrons or

positrons) during radioactive decay.

BiosphereThose parts of the earth and its atmosphere that support life.

If represents only about 11 km of the atmosphere, the contents of the earth’s surface, and a few kilometers into the earth’s interior.

Categories of Solid WasteThe following few types of solid wastes are likely to be received

at the plant.

(i) White type (Category - 1): All non active / potentially active wastes arising from active working areas.

(ii) Yellow type (Category - 1): All wastes having a surface dose less than 200 mR/hr. of Beta-Gamma activity.

(iii) Red type (Category - 2 & 3): All wastes having a surface dose greater than 200 mR/hr. of Beta-Gamma activity.

(iv) Special Category - Alpha bearing waste (Category - 4): It will consist of all the above products wherein alpha contamination exceed to micro - curie/kg.

Code of Federal Regulations

Documentation of the general rules by the executive depart­ments of the federal government. The code is divided into 50 titles that represent broad areas subject to federal regulation. Each title is divided into chapters that usually bear the name of the issuing agency. Each chapter is further divided into parts covering specific regulatory areas.

Curie(Ci)The traditional unit for radioactivity named after Mme. Curie

238

for her pioneering work with radium a century ago. One curie is defined s the amount of radioactive material which produces 3.7x ;i 010 nuclear disintegrations per second, approximately the activity contained in one gram of radium. Worldwide scientific adoption of a standard system of units now uses the unit bequerel (Bq); 1 Ci = 3.7 x, 1010 Bq.

Decay (radioactive)The transition of a nucleus from one energy level to another,

usually accompanied by the emission of a photon, electron, or neutron.

DOE/defense wasteRadioactive waste produced from activities supported by the

Department of Energy and/or defense programs of the US government.

DoseA measurement of the quantity of radiation or energy absorbed

per unit mass (mrem/year or msievert/year)

Effective annual dose equivalentThe amount of absorbed dose received by a specific tissue or

organ in a year. The total effective annual dose equivalent is the product of the total absorbed dose and tissue-or organ-specific weighting factors defined by the ICRP. The dose is measured in Sieverts.

ExposureA measure of ionization produced in air by x- or gamma rays.

Unlike dose, exposure refers to a potential for receiving radiation. Acute exposure generally means a high level of exposure over a short time period, whereas chronic exposure refers to low levels of exposure over a long period of time. Traditional unit is the roentgen; SI unit is coulombs per kilogram.

Fuel reprocessingRecovering uranium and plutonium for reuse from irradiated

(spent) nuclear reactor fuel.

239

Gamma emitter

A radioisotope that produces energy in the form of gamma rays as it decays. Also included in this category are x-rays and electron capture.

Gray(Gy)

The international unit for absorbed dose; 1 Gy = 100 rad.

Half-life

The time required for one-half of the atoms of a particular radionuclide to decay. After a period of time equal to 10 half-lives, the radioactivity remaining is only 0.1% of the original amount present.

High-level waste (HLW)

As defined by the Nuclear Waste Policy Act, high-level waste is (1) the highly radioactive material resulting from the reprocessing of spent nuclear fuel, including the liquid waste produced directly in reprocessing and any solid material derived from such liquid waste that contains fission products in sufficient concentrations; and (2) other highly radioactive material that the NRC, consistent with existing law, determines by rule to require permanent isolation.

Long-lived radioisotope

A radioisotope with a relatively long half-life. With respect to LLRW, radioisotopes with half-lives longer than 5 years are considered to be long-lived.

Low level radioactive waste (LLRW)

Radioactive waste not classified as high-level waste, transu- ranic waste, spent nuclear fuel, or by-product material such as uranium or thorium tailings and wastes.

Person-rem

Epidemiological concept for quantifying cumulative and col­lective doses of radiation. It is the sum of the Radiation dose received by the entire population of a given area. All conditions equal, the larger the population defined, the larger the collective dose.

240

Rad

Radiation absorbed dose. Unit of absorbed dose of radiation representing the absorption of 100 ergs of ionizing radiation per gram of absorbing material; 1 rad = 0.01 Gy.

Radioactivity

The spontaneous emission of radiation from unstable atomic nuclei. Emissions take the form of alpha particles, beta particles, gamma/x-rays, electron capture, or neutrons or a mixture of these. The amount of radioactivity present was traditionally measured in curies, but by international convention the unit bequerel is now used.

Rem

Roentgen equivalent man. Traditional unit for dose equiva­lent. Equal to the radiation absorbed dose times a quality factor based on the relative biological effectiveness of the radiation. One rem equals approximately one rad for gamma and x-rays and most beta particles, 0.5 to 0.1 rad for neutrons, and approximately .05 rad for alpha particles. 1 rem = 0.01 Sv.

Repository, geological

A facility with an excavated subsurface system used for the permanent disposal of spent fuel and high-level radioactive waste.

Roentgen(r)

Traditional unit for exposure to gamma or x-ray radiation. One roentgen produces an absorbed dose in tissue of approximately one rad.

Shallow land burial

The disposal of wastes within 30 meters of the earth’s surface, covered with soil and other overburden materials.

Short-lived radioisotopes

Radioisotopes with relatively short half-lives. With regard to LLRW, radioisotopes with half-lives less than 5 years are considered to be short-lived.

241

Sievert (Sv)

The international unit for dose equivalent. One sievert equals an absorbed dose of one joule per kilogram; 1 Sv = 100 rem.

Specific activity

The amount of radioactivity per amount of material, usually measured in curies per mmol or bequerels per mmol.

Spent fuel

Nuclear fuel that has been permanently discharged from a reactor after it has been irradiated. Typically, spent fuel is measured in terms of either the number of fuel assembled discharged or the mass of the discharged fuel.

Transuranic (TRU) waste

Radioactive waste that contains more than 100 nCi/g (3700 Bq) of alpha-emitting isotopes with atomic numbers greater than 92.

Classification of wastes

United States Nuclear Regulatory Commission (USNRC) classifies the radioactive wastes broadly into three categories. They are: Class A waste, Class B waste and Class C waste. These wastes (according to their Code of Federal Regulations (CFR) 10 CFR 61) are classified based on the radionuclide content.