cn 301 lectures notes -1[1](1)

8/10/2019 CN 301 Lectures Notes -1[1](1)

1/72

1CN 301 Geoenvironmental Engineering MZJ

Prepared by

Mohd Zamri in Jamaludin

Civil Engineering Department

Environmental Engineering Programme

Sultan Idris Shah Polytechnic


2/72



3/72


Preface 4

Course Teaching and learning Information 3

Lecture 1: INTRODUCTION

1.1 Definition 6

1.2 Related Legislation on geoenvironmental Engineering 6

1.3 Related issue on Geoenvironmental engineering 7

Lecture 2: SOIL FORMATION AND IDENTIFICATION

2.1 Soil Formation 9

2.2 Mineralogy composition in soil 10

2.3 Fundamental properties of soils 13

2.4 Identification of fundamental characteristic Soils 15

2.5 Soil test 16

Lecture 3: CONTAMINANT MIGRATION PATHWAY

3.1 Process of waste mixes with soil 17

3.2 Mass Transport 19

3.3 Mass Transfer Mechanism 22

3.4 Equation for mass Transport & flow through porous media by Darcy Law 28

3.5 Application of Mass Transport and Transfer 32

Lecture 4: GEO-ENVIRONMENTAL ENGINEERING SITE INVESTIGATION4.1 Principle Site Investigation 33

4.2 Investigation phases 34

4.3 Preparing for Fieldwork and Soil Sampling for Site Investigation 37

4.4 Soil-sampling techniques 45

Lecture 5: LAND REMEDIATION

5.1 Physical and chemical processes treatment 48

5.2 Biological Remediation 52

5.3 Thermal Treatment Technologies 56

5.4 Groundwater In-situ Barrier 60

5.5 Leachate Collection and Removal 62

5.6 in-situ and ex-situ remediation techniques 635.7 Importance of Risk Assessment 63

References And Further Reading 72


4/72


PREFACE

In the name of Allah the most merciful. Salawat to Muhammad Rasululah the savior of the

Ummah.

Geoenvironmental engineering as all engineering efforts to place, contain, control, or clean up

contaminants below the ground surface. The range, properties, and variability of both thecontaminants and the geologic materials that contain them are vast. (Reddi,2000) define it as a

field that encompasses the application of science and engineering principles to the analysis of

the fate of contaminants on and in the ground; transport of moisture, contaminant, and energy

through geomedia; and design and implementation of schemes for treating, modifying, reusing,

or containing wastes on and in the ground.

Obviously, the material covered in this note is too wide to be covered in a single

geoenvironmental engineering course. This note is only a guide for teaching and learning

process. Most of all depend on the student effort to enhance the learning in order to achieve

the course outcome. In the last notes is given the references for student as a guide to further

reading. Comment and suggestion is considered to improve this notes.


5/72


GEO-ENVIRONMENTAL ENGINEERINGcourse solves problems of subsurface waste containment;

groundwater contamination and site remediation are now a major focus. This course includes the topics

mainly components of types, properties, soil drainage systems, transport mechanism of contaminants in

soils, remediation for contaminated ands and the risk assessment and site monitoring. The students

will be learn basic laboratory tests on soils and site investigation methods to overcome

geoenvironmental problem.

Topic Week

INTRODUCTION

This topic begins with the definition of geo-environmental engineering and also

discusses related issues and acts. The effect and sources of soil pollution will be

discussed.

1

SOIL FORMATION AND IDENTIFICATION

This topic familiarizes the students in basic issues relating to soil mineralogy and soil

formation including the properties and composition of soils.

2

CONTAMINANT MIGRATION PATHWAY

This topic explains various types of soil contaminants transportation methods

(advection, diffusion and dispersion) and its effects on the quality of surface waters

and groundwater. It also explains contaminant transfer in soil.

4

GEO-ENVIRONMENTAL ENGINEERING SITE INVESTIGATION

This topic explains the principles of site investigation forcontaminated land to

overcome geo-environmental problem. Thetool and sampling method for site

investigation also will beexplained.

4

LAND REMEDIATION

This topic discusses various techniques used for land remediation.

4

LEARNING OUTCOMES

1. Correctly state the regulations, the acts, standards and equipments used in geo-environmental

studies voluntarily.

2. Briefly explain the formation process, the characteristics and compositions of the soil.

3. Briefly describe the transportation of contaminants and the effects of it to surface water and

groundwater quality.

4. Briefly explain how the site investigations and the test used to overcome geoenvironmental

problems.

5. Briefly explain the treatment technology, the risk assessment and the appropriate mitigation

measures for land remediation.

CONTINUOUS ASSESSMENT (CA):

Quiz 20%Test 40%

Others Assessment task

i. End of Chapter Problem

ii. Presentation

40%

FINAL EXAMINATION (FE):

Final examination is held at the end of the semester.


6/72


Lectures 1

1.0 Introduction

1.1 DefinitionGeoenvironmental engineering as all engineering efforts to place, contain, control, or clean upcontaminants below the ground surface. Examples include solid and hazardous waste disposal inlandfills, entombment of radioactive wastes, and remediation of brownfields and superfund sites.

The range, properties, and variability of both the contaminants and the geologic materials thatcontain them are vast.

The subject matter of geoenvironmental engineering crosses many traditional academicdisciplines, including environmental engineering, geotechnical engineering, chemicalengineering, materials engineering, hydrogeology, microbiology, environmental science, soilscience, and applied mathematics. As the scope and complexity of the problems encountered isoften beyond the bounds of any one discipline, geoenvironmental engineering is truly aninterdisciplinary field in which a team of specialists are often required to arrive at an optimalproblem solution.

1.2 Related Legislation on geoenvironmental EngineeringUnited State of Am erica (USA)- the Resource Conservation and Recovery Act or, as it is morecommonly referred to, (RCRA), requires all operators of hazardous waste management facilitiesto apply to the US Environmental Protection Agency (EPA) or an authorized state agency for apermit to operate the facility. This part of the law instructs EPA to avoid administrative andenforcement duplication by integrating the program of (RCRA) regulations to the maximum extentpossible with applicable provisions of the:

Clean Water Act Safe Drinking Water Act Clean Air Act Federal Insecticide, Fungicide and Rodenticide Act Marine Protection Research and Sanctuaries Act

United Kingdom Of Great Britain (UK) - Environmental Protection Act 1990DenmarkDenmarks Contaminated Sites Act 1983

Europe- after Concentrated Action on Risk Assessment for Contaminated Sites (CARACAS)

and many acts has been develop to managing the contaminated land.

1.2.1 Related Legislation in MalaysiaThere is no established comprehensive legislative framework for management ofcontaminated land is Malaysia. There is no statutory requirement to report existence orownership of contaminated sites and there are no clean up standards in Malaysia. Currently,pollution of soil is addressed to some extent in Environmental Quality Act (EQA), 1974.

1.2.1.1 Environmental Quality Act, 1974i. The environmental Quality (schedule Wastes) Regulation 2005ii. The environmental Quality (Prescribe Activities) Environmental Impact assesement,1987iii. The environmental Quality (Prescribe Premises) (schedule Waste Treatment and

disposal Facilities), order 1987.

iv. The Environmental Quality Act Regulation 2 P.U. (A) 294 of Environmental Quality(Designated Transporter).

1.2.1.2 Mineral Development act 1994: Part 3 Regulation of Exploration and Mining-Fossicking, panning, exploration, mining and mineral processing shall be carried out inaccordance with good and safe practices and such environmental standards as may beprescribed under this Act and any written law relating to environment.

1.2.1.3 Solid Waste Management and Public cleaning Board 2007Solid waste managementand Guidelines for Solid waste disposal.


7/72


1.2.1.4 National Strategic Plan for Solid Waste Management in Malaysia - forms the basis forsolid waste policy and practice in Peninsular Malaysia until 2020, and a foundation for futuredevelopment in the ensuing years. This Strategic Plan is to serve as a guide in planning andallocating resources with consideration of priorities in the sector concerned.

1.2.1.5 Water Supply Enactment 1955empower the state water supply authorities to supply todomestic and commercial and protect water source.

1.3 Related issue on Geoenvironmental engineering

1.3.1 Soil Pollution- source of pollution:i. Agriculturechemical fertilizer, pesticide, Soil additives, effluent from animal farm.ii. Contaminant from urban areasurban population, waste disposal, use of chemicaliii. Industrializationwaste from industry, chemical release and emission, chemical use and

explosion.iv. Landfillleachate, chemical release and emission.

1.3.2 Example of soil pollution :i. Russia (1992)15% of Russias territory has become unsafe for human habitation due

to effects of toxic waste dumpingii. United Kingdom of Great BritainIn 1999 UK environmental agency estimated about

300000 hectares of land in UK contaminated (approximately 1.2% of the UK land area).Common sources of contamination are landfill sites which generated methane gas.

Other sources of pollution are from heavy industry plant and military.iii. AustraliaOver 80 000 contaminated site in urban site in Australia are polluted.

Common source of contamination are industry, transportation and landfill. Australiacountry spends millions of dollars per year for contaminated site.

iv. Malaysia - The illegal dumping of aluminium dross at Felda Bukit Gatom in Labis, Johoroccurred in 2006 (i.e. which has become a national issue and public outcry due toammonia vapour) and impact of pollution source to soil and groundwater was conductedat landfill located in Ampar Tenang, Dengkil. Ampar Tenang Landfill site is locatedapproximately 4km to the south of Dengkil in Selangor, Malaysia. The site was once anactive open tipping (9 years in operation), and received about 100 tons per day of mainlydomestic waste.

v. China- According to a scientific sampling,150 million mi (100,000 square kilometres) ofChinas cultivated land have been polluted, with contaminated water being used to

irrigate a further 32.5 million mi (21,670 square kilometres) and another 2 million mi(1,300 square kilometres) covered or destroyed by solid waste. In total, the areaaccounts for one-tenth of Chinas cultivatable land, and are mostly in economicallydeveloped areas. An estimated 12 million tonnes of grain are contaminated by heavymetals every year, causing direct losses of 20 billion yuan (US$2.57 billion).

vi. Netherlands- In 1995 there is 300000 sites has been contaminated and the estimatescost for remediation is about13 billion Euros.

1.3.3 Effect of soil pollutionSoil pollution is defined as the build-up in soils of persistent toxic compounds, chemicals,salts, radioactive materials, or disease causing agents, which have adverse effects on plantgrowth and animal health. There are thousands of contaminant sources and pollutant types,but the following list is illustrative (pollutants indicated by parentheses):

Petroleum hydrocarbons from rupture of underground storage tanks (benzene, ethylbenzene, toluene, xylene, alkanes, alkenes, MTBE)Spillage or leakage of solvents and dry cleaning agents (acetone, trichloroethylene,formaldehyde) and perchloroethyleneLeaching of contaminants from solid waste disposal sites (lead, mercury, chromium,cadmium, bacteria, hydrocarbons)Water runoff which carries pollutants and may deposit them at a point of percolationPercolation into soils from pesticides and herbicides uses (wide variety of chemicalsincluding DDT, lindane, organochlorines, organophosphates, carbamates, cyclodienes)


8/72


Deposition of dust from smelting operations and coal burning power plants (zinc,cadmium, lead, mercury)Lead deposition from lead abatement or construction demolition (lead)Leakage of transformers (Polychlorinated Biphenyls (PCB)).

Table 1.1: Common routes exposureTarget Ways of expose

People By in direct contact with soils such as residences, parks, schools andplaygrounds. Other contact mechanisms include contamination of

drinking water or inhalation of soil contaminants which have vaporized.Plant Effects occur to agricultural lands which have certain types of soil

contamination. Contaminants typically alter plant metabolism, mostcommonly to reduce crop yields. soil conservation

Animal From grazing on contaminated landBuilding By chemical Attack of contaminants on foundation and services installed

in aggressive ground.

1.3.4 Common source of pollutanta. Waste Disposal- Most solid wastes are disposed of in landfills.Nearly all such landfills

have plumes of contaminated groundwater below them containing both solvents andmetals, because even household garbage may contain small amounts of both heavymetals and organic contaminants.

b. Hazardous wastes-which contain high levels of contaminants, which must have evengreater protection against possible leaching.

c. Wastewater - From our sinks, toilets, bathtubs, as well as industry - is typically treatedone of two ways:

i. in larger towns and cities, a Sewage treatment facility receives this waterthrough a sewer system, which is then treated and discharged,

ii. In the country wastewater drains into a series of perforated pipes buried inthe yard of each house referred to as a septic disposal system.

d. Industrial Wastes- Many industrial wastes are not suitable for land application becausethey contain toxic materials, and under DOE they must be disposed of in approvedlandfills, or recycled or incinerated.

e. Agriculture- Agriculture activities have been known using various types of chemicals aspesticides and fertilizers there are many types of pesticides being used and mainly to

control weeds, insects, rats and other pests.

The main activity for agriculture isdominated by oil palm plantation, followed by rubber, piggeries, poultry, aquaculture,cattle and orchards.

f. Mining-Tin mining, followed by sand mining from the alluvia deposits, could causereduction in the aquifer yield through introduction of slime and clay particles into theaquifer.

Figure 3.8: Pollutant movement and risk pathways for soil contaminants

A: Direct Soil Ingestion - Some

metals such as lead and arsenic

B: Leaching to Ground Water -

Many organic contaminants

C: Runoff to Surface Water - Many

organic contaminants

D: Plant Uptake - Some metals

such as cadmium and radionuclides

E: Animal Uptake - Some metals

such as lead/mercury

organics/PCBs radionuclides


9/72


Lectures 2

2.1 soil formationSoils are formed by the disintegration (or more precisely, evolution) of rock material of the earthsrelatively deeper crust, which itself is formed by the cooling of volcanic magma. The stability ofcrystalline structure governs the rock formation. As the temperature falls, new and often morestable minerals are formed. For instance, one of the most abundant minerals in soils known asquartz acquires a stable crystalline structure when the temperature drops below 573C. Theintermediate and less stable minerals (from which quartz has evolved) lend themselves to easy

disintegration during the formation of soils.

The disintegration process of rocks leading to the formation of soils is called weathering. It iscaused by natural agents; primarily wind and water (note that these are the same agents that aidthe evolution and life in other kingdoms). The specific processes responsible for weathering ofrocks are:

i. Erosion by the forces of wind, water, or glaciers, and alternate freezing and thawing ofthe rock material.

ii. Chemical processes, often triggered by the presence of water. These include:

Hydrolysis (reaction between H-and OH-ions of water and the ions of the rockminerals),

Chelation (complexation and removal of metal ions),Cation exchange between the rock mineral surface and the surrounding mediumOxidation and reduction reactions,Carbonation of the mineral surface because of the presence of atmospheric CO2.

iii. Biological processes which, through the presence of organic compounds, affect theweathering process either directly or indirectly.

Once the rock material is weathered, the resultant soil may either remain in place or may betransported by the natural agencies of water, air, and glaciers. In the former case, the soils arecalled residual soils. Depending on the natural agent involved, the transported soils are calledalluvial or fluvial (water-laid), aeolian (wind-laid), or glacial (ice-transported) soils. Severalsubdivisions are often made based on the transportation and deposition conditions.

The properties of the soil deposits formed depend on the soil-forming factors. In general, fiveindependent variables may be viewed as governing soil formation:

Climate - Amount of moisture available, temperature, chemical reaction speed and rate ofplant growth

Organisms present - Organisms influence the soil's physical and chemical properties andfurnish organic matter to soil

Topography - Angle: like Steep is poorly developed soils but flat to undulating surface isthe best. Orientation (direction the slope is facing) - soil temperature andMoisture

The nature of the parent material - Original mineral makeup and important in young soils.Residual soilfrom bedrock. Transported soilcarriedfrom elsewhere

Time- varies for soils in different climates, locations

It is generally established in the soil sciences literature that any property of soil is invariablylinked to these five fundamental soil forming factors. Soil formation due to weathering of rocksand subsequent transportation and deposition yields us the first scheme for soil composition.The deposition of soils occurs in layers and each layer possesses unique properties reflectingthe parent material from which it arose. A host of environmental factors which were responsiblefor its formation, including climate, ground slope, and the presence of organic matter, are


10/72


reflected in the properties of each of these layers. The composition of soil in terms of the variouslayers is usually illustrated in what is known as a soil profile.

2.2 Mineralogy composition in soilAlthough different classification schemes could be used, mineralogists have determined that firstseparating minerals into groups based on their chemical composition gives classes with thegreatest similarities in many other properties. Thus, minerals are first divided into classesdepending upon the dominant anion or anionic group.

Five mains groups of mineral composition in soil (regular structure elements and atomicelements) are:i. Carbonatescalcite and dolomite usually use in cementii. Oxidesiii. Hydrous Oxidesgibbsite and brucite minus OHs sheet in clay mineralsiv. Phosphateusing for fertilizerv. Silicate90% of all soil

Figure 2.1Soil Compositions Schematic Diagram

2.2.1 Silicate mineral classThe silicate mineral class is an extremely large and important group of minerals. Nearly 40 of thecommon minerals are silicates, as are most minerals in igneous rocks. Silicates constitute wellover 90% of the earth's crust.The fundamental unit of all silicate structures is the SiO4tetrahedron. It consists of four O2-ions at the apices of a regular tetrahedron coordinated to one

Si

4+

at the center. The individual tetrahedralare linked together by sharing O

2-

ions to form morecomplex structures.

2.2.1.1Silica tetrahedron: The silica tetrahedron consists of four oxygen ions and one silica ions. Themolecular arrangement is such that the four oxygen ions are spaced at what would be thecorners and tip of a three-dimensional, three-sided pyramid, with the silicon located within thepyramid. Oxygen ions at the base are shared by adjacent tetrahedrons, thus combining andforming a sheet. The thickness of a silica sheet is 5 x 10 -7mm or 5-Angstrom units (1 Angstromunit = 1 x 10-7).


11/72


V= Valens O = oxygen (V=-2) Si = Silica (V = +4)

Figure 2.2: Silica Tetrahedron

2.2.1.2 Common silicate mineral in soili. QuartzCommonly found in soil and the mineral composition SiO2.The Quartz shape are in

three dimensions and each of quartz cannot absorb in acid and cannot break easily. There isno isomorphous substitution in quartz, and each silica tetrahedronis firmly and equally bracedin all directions. As a result, quartz has no planes of weakness and is very hard and highlyresistant to mechanical and chemical weathering. Quartz is not only the most commonmineral in sand and silt-sized particles of soils, but quartz or amorphous silica is frequentlypresent in colloidal (1 to 100 nm) and molecular (< 1 nm) dimensions.

ii. Feldspar - some of the silicon atoms are replaced by aluminum. This results in a negativecharge and in distortion of the crystal structure, because A1 atoms are larger than Si atoms.The negative charge is balanced by taking in cations such as K+, Na+, and Ca+in orthoclase,

albite, and anorthite feldspars, respectively. The distortion of the lattice and the inclusion ofthe cations cause cleavage planes that reduce the resistance of feldspars to mechanical andchemical weathering. For these reasons, feldspars are not as common as quartz in the sand-, silt-, and claysized fractions of soils, even though feldspars are the most commonconstituent of the earth's crust.

iii. Mica - Common micas such as muscovite and biotite are often present in the silt- and sand-sized fractions of soils. In a unit sheet of mica, which is 1 nm thick, two tetrahedral layers arelinked together with one octahedral layer. In muscovite, only two of every three octahedralsites are occupied by aluminum cations, whereas in biotite all sites are occupied bymagnesium. In well-crystallized micas one fourth of the tetrahedral Si+4are replaced by A1+3.The resulting negative charge in common micas is balanced by intersheet potassiums. In aface-to-face stacking of sheets to form mica plates, the hexagonal holes on opposingtetrahedral surfaces are matched to enclose the intersheet potassiums.

2.2.1.3 Alumina octahedrons: The alumina octahedron consists of six-oxygen and one-aluminum.3oxygen is in the top place of the octahedrons, and three are in the bottom plane. Thealuminum is within the oxygen grouping. It is possible that the aluminum ion may be replacedwith magnesium, iron, or other neutral ions. The aluminum sheet is 5 x 10-7mm thick. Oxygenfrom the tip of a silica tetrahedron can share an alumina sheet, thus layering sheets. Differentsheet arrangements are then combined to form the different clay minerals.The compositionand typical properties of the more commonly occurring clay minerals are Kaolinite, Illite andMontmorillonite.


12/72


Figure 2.3:Alumina Octahedrons

2.2.2.1 Common clay minerali. Kaolinite- is a common mineral in soils and is the most common member of this subgroup.A Kaolinite is the most prevalent clay mineral and is very stable, with little tendencies forvolume change when exposed to water. Kaolinite layers are stack together to formrelatively thick particle. Particles are plate shaped. Because of the strong bonding,kaolinite does not exhibit swelling in water. The composition is one-silica, one aluminasheet that is very strongly bonded together. Kaolinites have very little isomorphoussubstitution in either the tetrahedral or octahedral sheets and most kaolinites are close tothe ideal formula Al2Si2O5 (OH)4.

Figure 2.4: Kaolinite Diagram

ii. Illite - has irregular plate shape, more plastic than kaolinites. Its does not expand whenexposed to water unless potassium deficiency exists. This clay is most prevalent inmarine deposits. The composition is an alumina sheet sandwiched between two silicasheets to form a layer. Potassium provides the bonds between the layers.

Figure 2.5: Illite Diagramiii. Montmorillonite - has irregular plate shapes or is fibrous because of the weak bond

between layers this clay readily absorbs water between layers. This mineral has a greattendency for large volume change. The composition is an alumina sheet sandwichedbetween two silica sheets to form a layer. Iron or magnesium may replace the alumina in

the aluminum sheet.

Figure 2.6: Montmorillonite Diagram


13/72


Table 2.1:Soil Common Clay Minerals

2.3 Fundamental properties of soilsThe soil type or category is based on particle size, however, where the soil particle size is toosmall to be observed, an additional physical property, known as plasticity is utilized as a criterionfor evaluation.Soil properties are not always controlled by particle size and plasticity. Studieshave shown that soil structure and mineralogical composition, including the interaction with water,

can also significantly influence the properties and behaviors of soils. Recognizing andunderstanding the influence of the various soil properties is vital for design and constructioninvolving soils.

Soil is all the material located above bedrock and can be grouped into four major categories ortypes including gravel, sand, clay and silt. These four categories can be reduced to two groupstermed coarse-grained soil and fine-grained soil. Coarse-grained soil includes gravel and sand,which have individual particles that are large enough to be viewed without magnification. Clay andsilt are termed fine-grained soil because of their small particle sizes, which are too small to beseen without enhancement.

The accepted standard ranges for the classification of the major soil types is determined byvarious standards development systems including the American Society for Testing and Materials

(ASTM), the American Association of State Highway and Transportation Officials (AASHTO) andthe United States Agricultural Department (USDA).

Table 2.2:Particle Grain Size


14/72


The particle size classification systems also provide ranges for particles larger than 76.2 mm,known as cobbles and boulders. In general, cobbles range from 76.2 mm to 400 mm andparticles larger than 400 mm are considered boulders.

For coarse-grained soils (> 65% sand and gravel) the soil name is based on the particle sizespresent. For fine-grained soils (> 35% silt and clay sizes) it is based on behavioralcharacteristics.

2.3.1 Particle Size and Shape

Particle size and shape affects the mechanical behavior of soils, however, the effect of varies forcoarse-grained and fine-grained soils. The size and shape of the granular soil particles canincrease or decrease the tendency of particles to fracture, crush and degrade. Round particleswill not interlock where as angular particles will; flat particles when oriented might form planes ofweakness inducing potential for failure.

The grading of gravels and sands may be qualified in the field as well graded (goodrepresentation of all particle sizes from largest to smallest). Poorly graded materials may befurther divided into uniformly graded (most particles about the same size) and gap graded(absence of one or more intermediate sizes).

Figure 2.7: Soil shape

2.3.2 Soil structureSoil structure is the shape that the soil takes based on its physical and chemical properties; it isthe geometric arrangement of soil particles with respect to one another. The process ofsedimentation or rock weathering creates the initial soil structure. Among the many factors thateffect soil structure is the shape, size, and mineral composition of the soil particles, and thenature and composition of soil water. The basic terminology used to define the soil structure aresingle-grained, honeycombed, flocculated and dispersed with variations dependent upon thecomposition of the soil.

2.3.2.1 Cohesionless SoilsThe particle arrangement of cohesionless soils (gravel, sand and silt) has been likened toarrangements attained by stacking marbles, or single-grained. In single grained structuressoil particles are in a stable position, with each particle in contact with the surrounding ones.For similar sized particles large variations in the void ratio are related to the relative position ofthe particles.

2.3.2.2 Cohesive SoilsThe term cohesive is used for clay soils, which have an inherent strength, based on theirparticle structure which provides considerable strength in an unconfined state. Thecohesiveness of a clay is due to its mineralogy and is a controlling factor determining theshapes, sizes, and surface characteristics of a particle in a soil. It determines interaction withfluids. Together, these factors determine plasticity, swelling, compression, strength, and fluidconductivity behavior

2.4 Identification of fundamental characteristic SoilsCoarse grained soils are easy to identify. Fine grained soils are identified on the basis of somesimple tests for dry strength, dilatancy and toughness. Dry strength is a qualitative measure ofhow hard it is to crush a dry mass of fine grained soil between the fingers. Clays have very highdry strength and silts have very low dry strength. Dilatancy is an indication of how quickly themoisture from a wet soil can be brought to the surface by vibration. Here, a pat of moist clay isplaced on the palm and struck against the other hand several times. In silty soils, within a fewstrikes water rises to the surface making it shine. In clays, it may require considerable effort to


15/72


make the surface shiny. In other words, dilatancy is quick in silts and slow in clays. Toughness isa qualitative measure of how tough the soil is near its plastic limit (where the soil crumbles whenrolled to a 3 mm diameter thread). Toughness increases with plasticity. Silty soils are soft andfriable (crumble easily) at Plastic Limits (PL), and clays are hard at PL. The fines can also beidentified by feeling a moist pat; clays feel sticky and silts feel gritty. The stickiness is due to thecohesive properties of the fines, which is also associated with the plasticity, and therefore claysare called cohesive soils. Gravels, sands and silts are called granular soils.

The grain size distribution of a coarse grained soil is generally determined through sieve analysis,

where the soil sample is passed through a stack of sieves and the percentages passing differentsizes of sieves are noted. The grain size distribution of the fines are determined throughhydrometer analysis, where the fines are mixed with distilled water to make 1000 ml ofsuspension and a hydrometer is used to measure the density of the soil-water suspension atdifferent times. The time-density data, recorded over a few days, is translated into grain size andpercentage finer than that size. Hydrometer analysis is effective for soil fractions down to about0.5 m.

Figure 2.8: Typical particle size distribution of soils.

Figure 2.9: Textural classifications of soils.

Three limits are in general used to characterize the clayey soils:Shrinkage limit, which is the water content at which the soil passes from solid to semisolidstatePlastic limit, which is the water content at which transition from semisolid to plastic statetakes placeLiquid limit, which indicates the water content required in order for the clayey soil to beginexhibiting flow characteristics like liquids


16/72


2.5 Soil testThe BS 5930:1999 (Code of Practice for Site Investigations) summarizes the purposes oflaboratory testing to be to describe and classify the samples, to investigate the fundamentalbehavior of the soils in order to determine the most appropriate method to be used in theanalysis, and to obtain soil parameters relevant to the technical objectives of the investigation.

The laboratory tests for soils commonly carried out include: Moisture content, which read in conjunction with liquid and plastic limits gives an indication of undrained strength; Liquid and plastic limits to classify fine grained soil and the fine fraction of mixed

soils; Particle size distribution to give the relative proportions of gravel, sand, silt and clay; Organic matter which may interfere with the hydration of Portland cement; Mass loss of ignition which measures the organic content in soil, particularly peat; Sulfate content which assesses the aggressiveness of the soil or groundwater to buried

concrete;

pH value which is usually carried out in conjunction with sulfate contents tests; California bearing ration (CBR) used for the design of flexible pavements; Soil strength tests such as Triaxial compression, unconfined compression and vane shear; Soil deformation tests;

Soil permeability tests.


17/72


Lectures 3

3.0 Principal geochemical processes affecting contaminants mobility in the ground and theirimpact on groundwater and surface waters quality

Figure 3.1: Sources of groundwater contamination

3.1 Process of waste mixes with soilContaminant can enter soil through:i. Dissolve in liquid phase in soilii. Absorb inorganic matter in soiliii. From mineral structure residue.

Figure 3.2: Adsorption of contaminant in soil

The ways of in which contaminant sorbed into soil and sediment varies with the nature of thecontaminant and the makeup of the soil and sediment. The composition of soil and sedimentincludes both mineral matter and organic matter as the primary constituents.In the presence of water with many contaminants, water is adsorbed on the surface of mineralmatter, whereas, contaminants are absorbed into the organic matter by a partition process.

Under relatively dry conditions, the soil/sediment mineral matter acts as an adsorbent, where thesorbed organic compounds are held on the surface of the mineral grains. The soil/sediment

organic matter (SOM) acts as an absorbent, or a partition medium, where the sorbed organiccompounds dissolve (partition) into the matrix of the entire SOM. The soil or sediment, then, ischaracterized as a dual-function sorbent, in which the mineral matter sorbs the contaminant byadsorption while the SOM sorbs the contaminant by a partition process.

Consider a natural water system with many organic contaminants present. Adsorption tosoil/sediment mineral matter occurs as a consequence of the competition between all species,including water. In the presence of water, the soil/sediment mineral matter prefers to adsorbwater because of their similar molecular polarities, while the soil organic matter prefers to absorbthe contaminants (organic solutes) in water. This means that the (nonionic) organic


18/72


contaminants are not signicantlyadsorbed to minerals, and that the partition of a contaminantis not affected by water or by other contaminants. So two processes are at work:

i. The organic contaminants are competitively prevented by water from adhering to thesurface of the soil mineral matter, while at the same time,

ii. The organic contaminants are able to partition independently into the SOM. Becauseso many environmental contaminants are transported by ground water and surfacewater, it is important to understand the unique function of the soil organic matter

within these aquatic systems and how the partition processes affect the fate ofcommon environmental contaminants.

3.1.1 Contaminant substance in Soil - Key Properties of Contaminants :

Water SolubilitySolubility is defined as maximum amount of a contaminant that can be dissolved in thewater at a specified temperature. The solubility of a compound tends to be inverselyproportional to the amount of sorption that the contaminant can undergo.

Polarity of the CompoundThe polarity of a compound plays a major role in mobility of the compound. PolarSubstances and, therefore adsorb to soil particles less.

Kow ( Octanol Water Partition Coefficient)Water partition coefficient, is simply a measure of the hydrophobicity (water repulsing) ofan organic compound. The more hydrophobic compound, the less soluble it is, thereforethe more likely it will adsorb to soil particles.

3.1.2 Chemical Fate

Chemical fate is the eventual short-term or long-term disposition of chemicals, usually to anotherchemical or storage. Some examples that fit the concept of short-term and long-term fate aregiven in Table 3.1. If a polychlorinated biphenol (PCB) compound is in groundwater, the mediaare soil and water. The short-term fate will be that the PCB will primarily adsorb to the soil. Thelong-term fate is that the chemical will desorb, when the PCB-laden water has left, andeventually be bioremediated by microbacteria looking for carbon sources. If this PCB is in theatmosphere, it will be adsorbed primarily to aerosols and particles in the short term, whereas its

long-term fate will probably be photocatalyzed degradation.

There are as many or more examples of short-term and long-term fate as there are chemicalmedia combinations. An important consideration for this topic is whether we are interested inshort-term or long-term fate. This is often a question to be answered by toxicologists. We will, forexample, take the results of their computations and experiments and track the more toxic formsof a spill. Sometimes this involves a short-term fate, and sometimes this involves a long-termfate. The time scale of the calculations is important in determining how we deal with the problemor how we set up our solution.

Table 3.1: Examples of short-terms and long term fates


19/72


3.2 Mass TransportSoil, the fragile and fertile interface between the atmosphere and the subterranean realm, ischaracterized by massive transfers of mass and energy. Energy and mass fluxes through thisporous medium of the soil are not only significant for the healthy functioning of soil as the cleanand productive base for agriculture, but also they are critical for the role that the soil plays inprotecting the environment of both underground and surface reserves of water.

3.2.1 Mass and Transport in soilThe Objectives of mass and transport in soil to determine how contaminant is migrates in the

subsurface relatives to pore water.The transport of dissolved contaminant is via advection. TheImportant factor for advection is the direction of the hydraulic gradient. Hydraul ic gradientcanshow the direction of dissolved contaminant transport. The pore veloci ty(Darcy velocity dividedwith porosity) is an important indicator because when a chemical with the concentration (Co) isintroduced into soil system, the contaminant migrates as a sharps front at a velocity equal to thepore velocity.

In reality, there are other mechanisms augmenting advection. The saturated soi l systempossesses concentration gradients in addition to hydraulic gradient because of the localizedpresence of the dissolve chemical. These concentration gradients exercise kinetics activity andprovide for an additional mechanism transport namely diffusion.

3.2.2. Transport ProcessesA transport process, as used herein, is one that moves chemicals and other properties of thefluid through the environment. Diffusion of chemicals is one transport process, which is alwayspresent. It is a spreading process, which cannot be reversed (without the involvement of anothermedia such as in reverse osmosis). Diffusion is the flux of solute from a zone of higherconcentration to one of lower concentration due to the Brownian motion of ionic and molecularspecies.

Figure 3.1: Illustration of convection and diffusion of a chemical cloud along x-space coordinate (x-axis).

Molecular Diffusion- the molecular scale movementof a chemical within a medium (i.e., soil, air,water) can be conceptualized as a spontaneous mixing process. Loss of spatial unevenness inthe distribution of mass (or concentration), heat, or other attributes of a system is amanifestation of the second law of thermodynamics, i.e., in the absence of an external energysource, entropy of a system increases until equilibrium is reached:

a. In other words, molecules will tend to rearrange themselves so that the system has thelowest energy.

b. Molecules thus move from regions of high chemical potential to regions of low chemicalpotential.


20/72


Figure 3.2: Model for diffusion. At time = 0, a chemical is released into one end of the narrow tube filledwith water. The time = t, the chemical will have moved through the water filled tube. No net movementoccurs when the system has reached equilibrium (entropy is maximized; free energy is minimized.

Convectionor advection is the transport of chemicals from one place to another by fluid flow.The convection and diffusion of a chemical cloud, as represented in Figure 3.1, are the

movements of the cloud and spreading of the cloud over time.

Turbulent diffusion is actually a form of advection, but the turbulent eddies tend to mix fluid witha random characteristic similar to that of the diffusion process, when viewed from enoughdistance. The representation given in Figure 3.1could also be used to represent convection andturbulent diffusion, except that the pace of turbulent diffusion is normally more than one order ofmagnitude greater than diffusion.

Molecular diffusion is important mainly on the microscopic scale; it brings reactants into contactwith each other and causes transport of chemicals across boundaries (e.g., across a cellmembrane; from water onto a particle surface; across the air-water interface). On a macroscopicscale (rivers, lakes, aquifers), molecular diffusion is extremely slow in causing transport. Overlarge distances, transport is caused by the motion of the fluid itself, i.e., advection; only at very

short distances, where viscosity inhibits fluid motion, does transport by molecular diffusionbecome relevant (such areas exist in the pore space of sediments and at the various interfaces)

This higher pace of turbulent diffusion means that diffusion and turbulent diffusion do notnormally need to be considered together, because they can be seen as parallel rate processes,and one has a much different time and distance scale from the other. If two parallel processesoccur simultaneously, and one is much faster than the other, we normally can ignore the secondprocess.

Dispersion is the combination of a nonuniform velocity profile and either diffusion or turbulentdiffusion to spread the chemical longitudinally or laterally. Dispersion is something very differentfrom either diffusion or turbulent diffusion, because the velocity profile must be nonuniform fordispersion to occur. The longitudinal dispersion of a pipe flow is illustrated in Figure 3.3.

Figure 3.3: Illustration of longitudinal dispersion of a tracer plane at t =0 to a dispersed cloud at t =T, C is the cross-section mean concentration.


21/72


The nonuniform velocity profile creates a dispersion that is much greater than would occur withdiffusion alone. The other important difference is that dispersion reflectsthe spreading of a cross-sectional mean concentration, while diffusion represents the spreading of a local concentration. Insome contexts, typically in atmospheric applications, turbulent diffusion is also considered to be aform of dispersion. This is only a semantic difference, and herein we will continue to distinguishbetween turbulent diffusion and the dispersion of a mean concentration.

Interfacial transfer is the transport of a chemical across an interface. The most studied form ofinterfacial transfer is absorption and volatilization, or condensation and evaporation, which is the

transport of a chemical across the airwater interface. Another form of interfacial transfer wouldbe adsorption and desorption, generally from water or air to the surface of a particle of soil,sediment, or dust.

Finally, there is multiphase transport, which is the transport of more than one phase, usuallypartially mixed in some fashion. The settling of particles in water or air, the fall of drops, and therise of bubbles in water are all examples of multiphase transport. Figure 3.4illustrates three flowfields that represent multiphase transport.

Figure 3.4: Illustration ofmultiphase transport.

3.2.3 The Importance of MixingMixing is a rate-related parameter, in that most rates of reaction or transport are dependent onmixing in environmental systems. When mixing is dominant (the slowest process), the first-orderrate equation can be described as

Rate of process Mixing parameter Difference from equilibrium

Thus, we need two items to compute the rate of the process: the equilibrium concentrations forall species involved and the mixing rate parameter. A common example would be dissolvedoxygen concentration in aquatic ecosystems.

3.2.4. Resistance to Transport

An important concept for environmental transport is resistances. The inverse of a rateparameter is a resistance to chemical transport. Or, in equation form:

1Rate parameter Resistance to chemical transport R

Figure 3.5gives an example of the adsorption of a compound to suspended sediment,modeled as two resistances in series. At first, the compound is dissolved in water. Forsuccessful adsorption, the compound must be transported to the sorption sites on the surfaceof the sediment. The inverse of this transport rate can also be considered as a resistance to

transport, R1. Then, the compound, upon reaching the surface of the suspended sediment,must find a sorption site. This second rate parameter is more related to surface chemistry thanto diffusive transport and is considered a second resistance, R2, that acts in series to the firstresistance. The second resistance cannot occur without crossing the first resistance oftransport to the sorption site; so, they must occur in series.


22/72


Figure 3.5: adsorption analogy to resistance series (adsorption of an organic compound to sediment)

Figure 3.6: Transport to sorption site and the resistor analogy.

Figure 3.6illustrates this concept with the transport of a compound from the water body to asorption site on a solid. In the bulk solution, there is diffusion and turbulent diffusion occurringsimultaneously. Transport can occur from either process, so there are two different paths that may

be followed, without the need of the other path. These transport processes are operating inparallel, and the faster transport process will transport most of the compound. When thecompound comes close to the solid, however, the turbulent diffusion dissipates, because eddiesbecome so small that they are dissipated by viscous action of the water. Now, we are back to onetransport path, with the act of sorption and diffusion acting in series. Thus, the slowest transportpath once again becomes the important process.

3.3 Mass Transfer MechanismAs specific chemical element and compound may exist in groundwater in any of the following forms:

a. Free ion surrounded by water moleculesb. Insoluble species. Example Ag2Sc. Metalligand complexes. Example Al(OH)

-2d. Absorbed species

e. Species held on ion exchangef. Species that differ by oxidation state. Example Fe+2

The various chemical existing in one or more of these from, thus its will influence the transportmechanism, so transfers mechanism will be use to these type of chemical. The mass transfer can bedivided into two groups:3.3 Abiotic processrefers to those that are non biological in nature.3.4 Biotic process- involves mass consumption of the chemicals by microorganism.

3.3.1Transport MechanismsAdvection: Dissolved substances carried along with bulk fluid flow.Hydrodynamic Dispersion: Solute spreads out from path expected to be followed by advectionalone.

a) Pore channel velocity: molecules travel at different velocities.


23/72


b) Mixing of pore channels, tortuosity, branching.

c) Difference in pore sizes (different velocities)

d) Variable conductivity in soil layers

e) Molecular Diffusion (Sometimes considered a distinct process)Molecules spread out from areas of high concentration to areas of low concentration(Thermodynamics, Brownian motion)

Longitudinal and Transverse dispersion

Longitudinal dispersion Spreading in the direction of flow

Transverse dispersion Spreading in the direction perpendicular to flow

Generally, longitudinal > transverse


24/72


3.3.2: Abiotic ProcessIt is convenient to treat the mass transfer mechanisms under two groups: (1) abiotic processes; and(2) biotic processes. The abiotic processes refer to those that are nonbiological in nature. The bioticprocesses involve mass consumption of the chemicals by microorganisms, often referred asbiodegradation. The population growth/decline of microorganisms in the presence of variouschemicals is of primary importance in these processes. In reality, both abiotic and biotic processesoccur concurrently. The microorganisms involved in the biotic processes act as catalysts for some ofthe reactions in abiotic processes.

i. Acid Base ReactionThe process acid base reaction is involving the exchange of Hydrogen ion (H +). This activitycan alter the pH of contaminant. Because of the pH exchanges, the chemicals participating inthis reaction may influence transport of contaminant. pH often referred to as a mastervariable in describing water composition, no single factor plays amore universal role indefining the characteristics of an aqueous system than pH. Water undergoes auto ionization,resulting in the production of H+and OH.

Acid-base behavior determines the physicochemical characteristics of many othercompounds. For example, H2S is a relatively volatile, toxic compound. It is a product of someanaerobic biochemical processes, and can yield the sulfide ion (S 2

), which can play an

important role in determining the solubility and mobility of metals. The sedimentation ofinorganic chemicals by the formation of complexes with organic or inorganic compounds andpH-dependent equilibrium reactions are fall into this category. Accumulations of metals inriver and sea sediments can also be included here, since they depend on the chemical andphysical composition of the water.

ii. Hydrolysis of Organic ChemicalMass process transfer is a result of substitution between an organic compound and water. Itcan represent as;

(R-X) +H2O = (R-OH) + X-+ H+

R= the main part of organic molecule X= the attached of Halogen, carbon, phosphorus ornitrogen.

Thus, this process can transform an organic compound (non-biodegradable) to degradable

compound because of the present of hydroxyl. It is known that many pesticides lose theirtoxic properties through hydrolysis in the environment; thus the reactivity of a pesticide inaqueous solutions can be used as an important criterion for its ecotoxicological behavior.

iii. OxidationsThis process is involved exchange of the electrons, similar to exchange of protons. Thetransfer of electrons provides the energy to cell to growth. Oxygen can react with certainorganic compounds, giving a hydroperoxide. Oxidation and reduction refer to the removaland acceptance of electrons, respectively.

Oxidation/reduction potential is by definition the electrical potential (in volts) of theoxidation/reduction reaction occurring between the electron donor and electron acceptor. Inpractice when considering conditions in the environment the term redox potential is

commonly used. Redox potential typically refers to the reduction potential of the dominantelectron acceptor in the environment.

iv. ComplexationComplexation involves reaction between simple cations (usually metallic), and anions calledligands. The ligands might be inorganic, such as Cl -, F-, Br-, SO42-, PO4

3-, and CO3

2-,or

organic, such as amino acid. Complexation reactions may also occur in series, with complexof one reaction participating with ligand in another reaction.


25/72


v. Precipitation and DissolutionThese processes are fundamental in nature and are responsible for the vast amounts ofmass transfer occurring in the subsurface environment. Water is an excellent solvent forseveral chemicals in gas, solid, as well as liquid phases. Dissolution refers to completesolubilizing of a given element in groundwater. This mechanism alone might be responsiblefor bringing contaminants into the pore fluid at the source. These processes remove massfrom pore water into the gaseous phase.

vi. Exsolution and votilization

These processes involve mass transfer between gaseous and either liquid or solid phases.Similar to precipitation, these processes remove mass from the pore water into the gaseousphase. They are controlled by the vapor pressure, which is the pressure of the gas inequilibrium with respect to the liquid or solid at a given temperature. Vapor pressure reflectsthe solubility of a compound in gas and is therefore an indicator of the compounds tendencyto evaporate.

Radioactive DecayRadioactive decay is the process whereby unstable isotopes (atoms of the same elementthat differ in their mass) decay to form new ones. It involves emission of particles from theelements nucleus. The processis termed decay or decay depending on whether theelement loses an particle (helium) or a particle (electron). The decay is an irreversibleprocess, with the parent element continuously decaying over time while the daughter isotopeincreases in quantity. Of importance in geoenvironmental engineering are the radioactivespecies released into groundwater from such activities as mining, milling, and storage ofwastes. The movement of radioactive isotopes such as uranium, plutonium, cesium, andselenium, away from high-level radioactive waste repositories and defense installations, is ofutmost importance.

vii. SorptionTransfer of contaminant from liquid to solid phase. Sorption is dominant process affectingalmost all dissolved species in groundwater. Sorption refers to the exchange of moleculesand ions between the solid phase and the liquid phase. It includes adsorption and desorption.

Typical chemical reactions are: acid-base reactions, solution, volatilization, dissolution andprecipitation, complexation reactions, surface reactions (sorption, adsorption), oxidation-reduction reactions, hydrolysis, and isotopic processes.An example of the complexity of the

chemical processes as they interact with the soil medium is shown in Figure 3.7.

Figure 3.7: Interaction of multiple phases: solid, fluid, and gas.


26/72


3.3.3 NAPL and DNAPLThe principles discussed in the previous section will enable us to formulate conceptually howNAPLs move into the subsurface. Because of some important effects of density of NAPLs(relative to that of water) on the transport phenomena, it is convenient to treat the LNAPLs andDNAPLs separately. Compounds which display extremely low aqueous solubility can exist as aseparate liquid phase in groundwater systems, if present in sufficient quantities.

3.3.3.1 Light Nonaqueous-Phase Liquids (LNAPL)In groundwater systems, these contaminant phases are referred to as nonaqueous phase

liquids (NAPLs) and their behavior will be fundamentally different from that of the bulkaqueous phase. In the case of an NAPL with density less than the surrounding water, thenonaqueous phase is referred to as a light NAPL (LNAPL), and will generally be found at ornear the phreatic surface (see Figure 3.7). Fluctuations in the height of the phreatic surfacewill cause the LNAPL to disperse. LNAPL spills often are attributable to leaking undergroundstorage tanks (LUSTs) used for storage of petroleum hydrocarbons (fuels).

3.3.3.2 Dense Nonaqueous-Phase Liquids (DNAPL)Low-solubility organic compounds with density greater than water can exist as a dense NAPL(DNAPL) phase; their characteristics are fundamentally different from those of LNAPLs.DNAPL compounds, because of their high density, tend to sink in groundwater systems.Often these compounds have lower viscosity than water as a result, they tend to sinkaccording to a pattern known as viscous fingering (see Figure 3.8). As they sink, they leavea trail of residual DNAPL compound among the solids (soilparticles) and liquid (water) intheir wake. A DNAPL phase will continue to sink until it completely disperses among the soiland water phases, or it reaches an impermeable boundary, such as a clay lens or bedrock(see Figure 3.8). As they sink, they leave a trail of residual DNAPL compound among thesolids (soil).DNAPL pools are extremely difficult to locate and are often difficult (orimpossible) to remediate using existing technologies. Furthermore, because DNAPLs areoften comprised of halogenated solvents, microbiological activity is slow to bring aboutchanges in their molecular structure, and the products of microbial degradation involvingthese compounds are sometimes more toxic than their parent compounds. Possibly the mostcommon examples of DNAPL compounds are trichloroethylene (TCE) and perchloroethylene(PCE). As in the case of LNAPLs, the source of DNAPL spills is often leakage or failure ofunderground storage tanks.

Figure 3.7: Schematic illustration of the behavior of LNAPL compounds. Under some conditions (a), the mass of an LNAPLspill is insufficient to allow penetration to the capillary fringe. With additional compound introduction (b), LNAPL product willreach the water table and begin to spread, though the compound will not penetrate far beyond the phreatic surface. If thesource of LNAPL is eliminated (c), removal of LNAPL will allow for rebound of the water table


27/72


Figure 3.8:Schematic illustration of the behavior of DNAPL compounds. Under some conditions (A), the mass of a DNAPLspill is insufficient to allow penetration to the intact DNAPL to the capillary fringe; vertical movement of the DNAPL is byviscous fingering. With additional compound introduction (B, C), DNAPL product will reach the water table and continue tomove vertically until it reaches an impermeable boundary.

Figure 3.9: Residual NAPL and DNAPL trapped in pores between soil and sediment Particles.

APL: Aqueous PhaseLiquid (dissolves readily inwater)

NAPL: Non-AqueousPhase Liquid (does notdissolve readily in water)

LNAPL: Light Non-Aqueous Phase Liquid(floater)

DNAPL: Dense Non-aqueous Phase Liquid(sinker)


28/72


3.4 Equation for mass Transport

i. Ficks law of diffusionDiffusion is the flux of solute from a zone of higher concentration to one of lowerconcentration due to the Brownian motion of ionic and molecular species. Under steady-stateconditions the diffusion flux F is described by Ficks law.Solute molecules, dissolved in gasor liquid, move from high to low concentration driving force for movement is difference inconcentration with distance transport is formulated by Ficks law of diffusion. Base on FickFirst Law:

J= -D* C/ x

J= The Mass Flux D = effective effusion C/ x = concentration gradient

Ficks first law provides us with aformal representation of the diffusion process. Analogous toDarcys law, it states that the flux of diffusing chemical,J, (mass of solute per unit area perunit time, M/L2T) is directly proportional to the concentration gradient, where C is the solute

concentration (M/L3), D* is the diffusion coefficient for the soil medium (L2/T), and C/ x isthe concentration gradient, which is negative in the direction of diffusion. Concentrationgradients are applied over a soil sample and the observed chemical flux is used in Ficks firstlaw to determine the diffusion coefficient D*.

It was described that the flux was equal to the negative diffusivity times the change inconcentration divided by the change in distance.For diffusion in water, D ranges from 1 10

9to 2 109m2/s. For diffusion in porous media, Freeze and Cherry (1979) suggest taking an

effective diffusion coefficient D* = D, with ranging from 0.5 to 0.01, to account for thetortuosity of the flow paths.

ii. AdvectionThe advection/dispersion equation is based on the conservation of mass. This equation isapplicable when

The soil is saturated Flow is steady Darcy's Law is applicable

Base on Darcy Law:

Q = -KA dh/dl

where:Q = rate of water flow (volume per time)K = hydraulic conductivityA = column cross sectional area

dh/dl = hydraulic gradient, that is, the change in head over the length of interest.

Select an equation to solve for a different unknown

flow rate seepage velocity Darcy velocity or flux

flow rate seepage velocity Darcy velocity orflux

hydraulicconductivity

Darcy velocity or fluxhydraulicconductivity

hydraulicgradient

flow gross crosssectional area

hydraulic gradient

flow crosssectional area

voids effective crosssectional area


29/72


Kin equation is called the hydraulic conductivityAdvection is the transport of solute by the bulk groundwater flow. The average pore velocity,v, is obtained by dividing the Darcy flux q by the effective porosity ne

V= q/ne

iii. Radioactive Decay and Degradation

It was assumed that the adsorption was fast compared to the advection of the contaminant.If, instead, the reaction is slow compared to the travel time and chemical equilibrium is notattained, then it is necessary to describe the kinetics of the reaction. The simplest model isthe irreversible (i.e., the solute cannot be desorbed) first order model:

C/t = -CRadioactive decay is the process whereby unstable isotopes (atoms of the same elementthat differ in their mass) decay to form new ones. It involves emission of particles from theelements nucleus. The process is termed decay or decay depending on whether theelement loses an particle (helium) or a particle (electron). The decay is an irreversibleprocess, with the parent element continuously decaying over time while the daughter isotopeincreases in quantity. Of importance in geoenvironmental engineering are the radioactivespecies released into groundwater from such activities as mining, milling, and storage of

wastes. The movement of radioactive isotopes such as uranium, plutonium, cesium, andselenium, away from high-level radioactive waste repositories and defense installations, is ofutmost importance.

3.4.1 Calculation principles of flow through porous media by Darcy Law

i. Transport time of groundwater between two wellsAn underground storage tank has been discovered to be leaking diesel fuel into groundwater.A drinking water well is located 200 m from the fuel spill. To ensure the safety of the drinkingwater supply, a monitoring well is drilled halfway between the drinking water well and the fuelspill. The difference in hydraulic head between the drinking water well and the monitoring wellis 40 cm (with the head in the monitoring well higher). If the porosity is 39 percent andhydraulic conductivity is 45 m/day, how long after it reaches the monitoring well would the

contaminated water reach the drinking water well?

Solution: To calculate this period, we need to determine the true velocity of the groundwaterbetween the two wells. The time for travel between the two wells will then be.

The hydraulic gradient is equal to.

The Darcy velocity is given by

The true velocity is equal to this value divided by the porosity

Thus, the period for flow from the monitoring well to the drinking water well is

days.

This result is typical of groundwater flow speeds---groundwater transport is usually very slow.


30/72


ii. Calculation of groundwater velocity: Unfractured clayey aquitard

Average linear groundwater velocity v = KV * h/L* 1/n= 10-8 cm/s * 1/5 * 1/1/3= 2 cm/yearTransit Time (A-B)t = distance/velocity= time to travel= 5 m / 0.02 m/yearacross the aquitard= 250 years

iii. Calculation of groundwater velocity and travel time across an unfractured clayaquitard (5 m thick).

Example-2:A confined aquifer has a source of recharge as shown in the figure below. The hydraulicconductivity of the aquifer is 50 m/day and its porosity is 0.2. The piezometric head in two wells1000 m apart is 55 m and 50 m, respectively, from a common datum. The average thickness ofthe aquifer is 20 m and the average width is 5 km. Determine the rate of flow through theaquifer and the time of travel from the head of the aquifer to a point 4 km downstream (assumeno dispersion or diffusion).

Recharge area

Confined-aquifer

++

1000 m


31/72


Solution:

Area of cross section of flow (A ) = 25m 5km = 12.5 104m2

Hydraulic gradient (i) =1000

5055= 5 10-3

Rate of flow, Q = K A i= (50 m/day) (12.5 104m2) (5 10-3)

Q = 31,250m3/day

Darcy velocity (v)=24

3

10151250,31

mdaym

AQ = 0.208 m/day

Seepage velocity (Vv) =2.0

208.0v= 1.042 m/day

Time to travel 4 km downstream:

daym

m

daym

km

/042.1

4000

/042.1

4t = 3,840days or 10.5years

iv. Example of DNAPL movement in a groundwater

Suppose 1 m3

of aquifer is contaminated with 30 L of trichloroethylene (TCE). The aquiferhas porosity of 0.3, groundwater moves through it will an actual speed 0.003 m/day and theTCE has a dissolved concentration equal to 10 percent of its aqueous solubility.(Aqueous solubility for TCE =1100 mg/L, specific gravity TCE= 1.47)

a. Find the mass of dissolved TCE and the mass of undissolved DNAPLb. Estimate the time for TCE to be removed.

Solution:

a. The actual dissolve of TCE 10% from 1100 mg/L= 10/100 X 1100 = 110 mg/LThe porosity is 0.3, so the volume of fluid in 1 m

3of aquifer is 0.3 m

3

The amount of dissolved TCE is:

Dissolved TCE = 30 L X 0.3 m

3

X 10

3

g/kg = 33 000 mg = 33 g

The specific gravity TCE= 1.47 that is 1.47 time the 1 =kg/L density of water. The total massof TCE in the aquifer is therefore:Total TCE = 30 L X 1.47 X 1 kg/L X 103g/kg = 44 100 g

Since 33 g TCE are dissolved in groundwater, the remaining is44 10033 = 44067 g is NAPL mass. That is 44 067/44 100 X 100 = 99.92 %

1 m 33 g/m3

1 m

1 m

DNAPL Dissolved TCEFluid leaving= 1 m

2X 0.03 m/day = 0.03 m3/ dayTaking away an amount of TCE equal toTCE flux through 1 m

2= 1 m

2X 0.03 m/day X 33 g/m

3= 0.99 g/day

0.03 m/day


32/72


So the time needed to remove all 44, 100 of TCE would be

Time to remove TCE = 44 100 g = 122 years0.99 g/day X365 day/yr

3.5 Application of Mass Transport and Transfer

The Groundwater Quality Technical Committee of the Environmental Engineering Division of the

ASCE (American Society of Civil Engineers) launched a group of activities in 1991 in an attemptto summarize the state of the art of contaminated-groundwater modeling practice and to provideguidelines for model users. Use for Modeling such as CFEST, DYNTRACK, MIGRATES, MOC,MT3D, POLLUTE, RANDOMWALK, RESSQ, RITZ, SOLUTE, andSUTRA. In general, thepopular applications are:

estimate contaminant plume migrationDetermine sensitivity of contaminant migration to various Hydrogeological andsource parameters.

The various transport processes simulated by these models are listed in Table 3.2.The modelsessentially solve the advection-dispersion equation in one form or another, using eitheranalytical, semi analytical (potential theory, finite-layer technique), or numerical (finite-difference,finite-element) methods. All of the models are capable of simulating mass transport due to

advection and molecular diffusion, and only RITZ does not simulate transport due tohydrodynamic dispersion. RITZ was a model developed to investigate land treatmentalternatives in the disposal of oil sludges, primarily originating from petroleum refinery wastes,and is the only model that can simulate multiphase flow (the next chapter is devoted to issues ofmultiphase flow). All of the models except RITZ can simulate the effects of radioactive decay,and only CFEST, MOC, and SOLUTE do not simulate the effects of chemical biodegradability.Sorption process is simulated in all the models through a user-defined retardation factor;however, most of the models can also simulate sorption and/or other chemical reactionsindirectly, using parameters such as bulk density, organic carbon content, solubility, sorptionconstant, cation-exchange capacity, reaction rate constants, and partition coefficient.

Table 3.2 Practical Applications of Frequently Used Transport Models

Applications Models

Estimate contaminant plume migration plume migration. All

Determine sensitivity of migration to various parameters. AllAssess leachate collection systems below waste sites. MIGRATE, POLLUTEDesign barriers in a landfill. MIGRATE, POLLUTELocate landfill, hazardous waste, and nuclear waste sites. CFEST, MOC, MT3D,

RNDWALK,

Help calibrate flow model. CFEST, MOC, MT3D,RNDWALK,SUTRA DYNTRACK, RESSQ

Investigate contaminant source distribution and loading history CFEST, MOC, MT3D,RNDWALK,SUTRA DYNTRACK, RESSQ

Investigate remedial action alternatives interceptor drains andwithdrawal/injection wells) for cleanup or containment of

contaminatedwater

(inter- CFEST, MOC, MT3DRNDWALK , DYNTRACK,

RESSQ

Simulate saltwater intrusion. CFEST, SUTRASimulate energy transport CFEST, SUTRALand treatment and cleanup criteria of petroleum refinerywastes.

RITZ

Analytical solutions to several practical problems. POLLUTEStimulate multiphase flow. RITZ

Source: American Society of Civil Engineers (1996).


33/72


Lectures 4

4.0 Site InvestigationSite investigation has been defined as investigation of the physical characteristics of the site andincludes documentary studies, site surveys and ground investigation. The last item refers to theactual surface or subsurface investigation, including on site and laboratory tests. In broad sense,site investigation should also include study of the site history and environment, interpretation andanalyses of all available data, and making recommendations on the favorable/unfavorablelocations, economic and safe design, and prediction of potential risks.

4.1 Principle Site InvestigationSite Investigation and Analysis of Soilsprovides guidance on how to gather information andcollect soil samples to provide data that allows an assessment of land where hazardoussubstances are present or suspected. This includes formulating data quality objectives, designingthe sampling strategy to meet the objectives of the investigation, quality assurance for analysis,and data interpretation. A flow chart summarizing the recommended staged approach to siteinvestigation is presented in Figure 4.1.

Set investigation objectives

Review existing datapreliminary site study and inspection

Establish conceptual model and data quality objectives

Determine detailed site investigation sampling design and strategy

Collect soil samples

Analyse soil samples

Interpret data

Revise conceptual model

Report data

Figure 4.1: Recommended approach to site investigation

4.1.1 The data quality objective processData quality objectives (DQOs) are qualitative and quantitative statements that specify thequality of the data required. Together the objectives form a DQO process, which is made up ofseven distinct steps (US EPA, 2000). The DQOs focus on the nature of the problem beingsolved by the investigation. The approach to a site investigation will then be determined by thedata required.

The first step in setting DQOs should therefore be to identify the purpose of the site investigation(state the problem, and identify the decision(s) that need(s) to be made). The most commonpurposes are to:

establish the condition of a site before sale, purchase or redevelopment and determineenvironmental liabilitiesdetermine the environmental or health risks posed by contaminants in the soildetermine if hazardous substances in the soil pose a hazard to an ecosystemassess the applicability of a particular remediation option


34/72


benchmark the contamination status of a site following clean-up

The next step in the DQO process involves defining the study boundaries and the development ofa conceptual site model. At this stage the conceptual site model is based on a review of existinginformation and usually includes an initial working hypothesis covering the potential nature andsources of contaminants, their likely spatial distribution in the soil (and other environmentalmedia), and the potential effects of the contaminants on receptors at or adjacent to the site. Anydata gaps should be identified. On the basis of the conceptual site model, the type and quality ofadditional data needed for the site investigation should be determined. Site-specific DQOs forsubsequent stages of the investigation should then be defined.

4.1.2 Conceptual site modelA conceptual site model is a system diagram identifying contaminant sources, routes ofexposure (pathways), and what receptors are affected by contaminants moving along thosepathways. The conceptual site model, which should be developed before undertaking a detailedsite investigation, identifies the zones of the site with different contamination characteristics (eg,whether contaminants in the soil are likely to be on the surface or at depth, distributed over anentire area or in localized hot spots). Exposure pathways and receptors should be identified forboth current and future uses of the site (where appropriate). The model will be based on areview of all available data gathered during the various investigation phases, and should beused to design the detailed site investigation.

When determining the approach for the investigation, the contaminant distribution must beincluded as part of the soil-sampling strategy, as this will affect the sample locations and thenumber of samples collected. The contaminant distribution at a site can be affected by a numberof factors, including (i) the nature of the contaminant source and contaminant type, (ii) pathwaysfor migration and dispersion, (iii) the type and physical nature of the soils/geology and anyphysical disturbance of the contaminants.

The soil profile within a site where hazardous substances are present or suspected can bevariable; comprising a mix of natural soils (natural ground) and fill materials (made ground).Fill often comprises a complex mix of materials, including plant remains, scrap wood, scrapmetal, soil and ash. Fill materials can have a marked effect on the migration of contaminantsthrough the soil, and can also be a source of contaminants (eg, heavy metals present in ash fill).It is also sometimes difficult in the field to distinguish certain types of fill from the natural soils.

4.2Investigation phasesThe investigation of a site where hazardous substances are present or suspected should beundertaken in phases. The five main investigation phases identified in USEPA and Ministry ofZealand Environment guideline and common alternative terms used to describe each phase arepresented in Table 4.1.

Table 4.1: The five main investigation phases, and common alternative descriptors

Main investigation phases

USEPA and Ministry of ZealandEnvironment guideline

Common alternative descriptor

Preliminary site investigation (study) Preliminary site study, stage 1; Phase 1 desk top study; Phase 1background information study; Phase 1 contaminated site audit;Phase 1 environmental site assessment (ESA)

Preliminary site inspection Site walkover survey; Phase 1 site inspection

Detailed site investigation Stage 2; Phase 2 field investigation; Phase 2 ESA;environmental benchmarking

Supplementary site investigation Additional phase 2 ESA; Phase 3 ESA

Site validation investigation Remediation validation investigation; soil benchmarking


35/72


Table 4.2: Summary of the difference levels of investigations typically undertaken for themanagement of contaminant land

Type of site Investigation Level of Detail

Phase 1 environmental siteassessment (ESA)

A phase 1 ESA is used to gather sufficient information to develop anindependent professional opinion about the environmental condition ofthe property and to indentify actual or potential environmentalcontaminant which may impact the property value or effect claim to aninnocent land owner exemption following acquisition.


A typical Phase 2 ESA involves the collection of original sample of soil,groundwater or building materials to analyze for quantitative values ofvarious contaminants. The most frequent substances tested arepetroleum, hydrocarbons, heavy metals, pesticides, solvents, asbestosand mold.


A Phase 3 ESA investigation involves the remediation of a site. Phase3 ESA investigation aims to delineate the physical extent ofcontamination based on recommendations made in Phase 2assessments. These investigations may involve intensive testing,sampling, and monitoring, fate and transport studies and othermodeling and the design of feasibility studies for remediation andremedial plans. Its normally involves assessment of alternatives cleanup methods, costs and logistics. The associated reportage details the

steps taken to perform site clean up and follow-up monitoring forresidual contaminants.

4.2.1 Preliminary site investigation (study)The main objective of the preliminary site investigation (study) is to provide backgroundinformation relevant to the DQOs. For a full site investigation, information on the present andpast uses of the site should be included in order to identify the nature of potential contaminants,their likely location and significance, and potential pathways for migration within the site or off-site. The preliminary site investigation involves gathering and compiling information about thesite to form the initial conceptual site model. It is often combined with a preliminary siteinspection. Information gathered in the preliminary site investigation and preliminary siteinspection should be documented in a preliminary site investigation report, and where possiblesupporting information should be appended to the report. The preliminary site investigationshould identify the sources of contamination, pathways for release and environmental receptors.The scope of the preliminary site investigation should include the following.

4.2.1.1 Site identificationThe site must be identified, including the site name, address, legal description, site boundaries,a map reference and geographic co-ordinates. Information on site identification can beobtained from the site owners/occupiers, maps, rates demands and from current certificates oftitle. The land area where contaminants may be present, or suspected, may not correspondwith legal boundaries, and site identification should establish the boundaries of the study.

4.2.1.2 Site historyA chronological history of the site and previous site uses should be traced from the present dayback to the initial use (if possible). The previous activities and processes on the site, and thechemicals and products used, stored or disposed of at the site, should be identified. Any

previous investigation and remediation work should be reviewed and gaps in the informationrecorded. The sources of information for the site history may include:

interviews with site personnel and neighbours (usually undertaken during thepreliminary site inspection), covering questions relating to site history, any knownincidents, management practices, waste disposal, and any chemical storage areasa review of discharge permits, consents or licences (eg, land-use consents; consentsto discharge to air, water or ground; trade waste consents; and dangerous goods[hazardous substances] licences)


36/72


a review of available environmental reports, environmental incident investigationreports, tank removal records, process descriptions, waste disposal and chemicalinventories, material safety data sheets and newspaper articleslocal authority record reviews, including land information memoranda (LIM) andregional council databasescertificates of titlea review of historical society records, and any relevant literature relating to the sitethe layout of current and historical facilities, and site drainage plansPhotographic records, including aerial photos.

4.2.1.3 Topography and hydrologyThe site hydrology assessment should include information on the nearest surfacewatercourses to the site, the location of surface water drains and stormwater drainagechannels, the direction of surface water flow, and information on surface water discharges andabstractions and flooding (if relevant). Typical information sources include topographical mapsand regional council records, as well as observations made during site inspections.

4.2.1.4 Geology and hydrogeologyThe site geology assessment should include a description of the types of strata and soil typesand information on fill material (if present). Information sources include published geologicalsurvey maps and memoirs, soil classification publications, and information from previousenvironmental or geotechnical investigations.

The site hydrogeology assessment should include information on:the extent and use of groundwater aquifers in the arealocal and regional direction of groundwater flowanticipated depth to groundwaterseasonal or tidal influencesspringslocal groundwater abstraction and uselocal groundwater and/or surface water monitoring informationPreferential pathways to groundwater (soak holes, etc.).

Information sources include regional council records on groundwater, and previous siteinvestigation records.

Figure 4.2: (a) Geology Map (b) Topography Map


37/72


4.2.2 Preliminary site inspectionThe preliminary site inspection is undertaken as part of, or following, the preliminary site study.The objective in this phase is to augment or confirm the findings of the preliminary site study andidentify any information that may assist with the design of the detailed site investigation.Information gathered during a preliminary site inspection typically includes:

general site condition, current use, local topography and surrounding environmental settinglocation and condition of surface watercourses, local surface drainage systems, ponds andsprings, and information on groundwater use, wells and drainsvisible signs of contamination or potential contamination, such as evidence of spills or leaks,

surface staining, chemical storage on unsealed ground, stressed vegetation and odoursVisible signs of areas of fill, stockpiled material, ground disturbance, burnt areas and formerbuilding foundations.location of chemical storage and transfer areas, bunding, waste storage areas, discharges toground and existing tanks, pits, drains, pipelines and sumpsadjacent, surrounding, or up gradient land uses and the potential for contamination fromthese sourcesLocation of former buildings, processes or activities undertaken on the site.

4.2.3 Detailed site investigationSoil samples should be analysed for contaminants identified on the basis of the preliminary sitestudy and/or preliminary site inspection. Samples may initially be analysed for a broad screen ofcontaminants which, based on experience, have typically been found on similar sites. Before

undertaking the physical works of the detailed site investigation, the potential hazards at the siteshould be assessed and appropriate health and safety precautions taken.

4.2.4 Supplementary site investigationsSupplementary site investigations are usually undertaken to provide:

data on areas of concern not investigated during the detailed site investigationa clearer delineation or definition of a particular area or depth of contaminationinformation to address specific technical matters (eg, to confirm the applicability of aparticular remedial option)Certainty regarding environmental liability.

4.2.4 Site validationSite validation is undertaken after completing remediation activities on a site. The objective is

cn 301 lectures notes -1[1](1)

Documents