analysing underground contamination

8/3/2019 Analysing Underground Contamination

1/21

P 1

Analyse the risks and suggest

strategy for remediation for any

unacceptable risks if found during

the course of investigation and

analysis.


2/21

P 2

CONTENTS

S.No. Topic Page

No.

1.1 Definition of The Problem 3

1.2. Causal relationship and approach 4

1.3. Contamination Conceptual Model 4

1.4. Qualitative Risk Assessment 6

1.5. Quantitative Risk Assessment 7

1.5.A. Identification Of Fate & Transport Mechanism 7

1.5.B Tier-2 Model 9

1.5.B.1 Selection of Parameters for Model 10

1.6 Comparison With Acceptable Values 12

1.6.B Up Take Rates 13

1.7 Parametric Modeling and Uncertainty 14

1.8 Probalistic Approach in Modeling 161.9 Sensitive Analysis 19

1.10 Recommending Remediation 20List of figures

Fig.1A Flowchart showing the approach to the problem 3-4

Fig.2A O&B worksheet 11

Fig.2B Graph showing C/Co for distance(x) and time(t) 12

Fig.2C O&B Spread sheet showing definition of assumptions and forecast 16

Fig.2D frequency distribution chart showing concentration of dinoseb 18Fig.2E frequency distribution showing 95% probabily of concentraion

above.290

18

Fig.2F sensitivity analysis chart 19

Fig.3A-3E

Assumptions made for different parameters 17

List of tables

Table.1A Conceptual Model 6

Table.1B Risk Assessment with Impact analysis 7

Table.1C Health Based Limits for Dinoseb 13

Table.1D parametric modelling & uncertainty 16

APPENDIX

1. Table of value group 1-8 21

2 Table of values group 9-16 21


3/21

P 3

3 Table showing data/values 211.1 Definition Of The Problem:

An industrial site has been losing chemicals from a tank for several years.

Investigation of the sludge at the bottom of one of the storage tank shows that thecontaminant is DINOSEB, a contact herbicide banned in many countries mainly for

its acute toxicity to humans as it is considered a possible carcinogen and alsosuspected to be an endocrine disrupter.

It is believed that the chemicals have leaked into the soil and has entered the watertable. The geology of this site consists of a shallow gravel aquifer with clay

underneath.It has been suspected that there may be potential risk of contamination of land on site and

ground and surface water more specifically:- Water table observations suggest that the groundwater slopes towards a lake 35

metre away from the site and it passes beneath a primary school. The school takes water from a borehole for drinking washing and cooking, located

13 metre from the source..

Our concern here is to analyze the risks and suggest strategy for remediation for anyunacceptable risks if found during the course of investigation and analysis.

1.2 The causal relationship and our Methodology and approach to the problem is

outlined in following diagram:-

No

Yes

Definition of the Problem

Conceptual model for Source-Pathway-Transportanalysis

Initial Qualitative Risk Assessment- -

Defining an appropriate Fate and Transport Mechanism

TIER-2 Modeling for estimation of contaminant

concentration at identified targets

Validating model against Field observations and public

health standards

Agree

Y


4/21

P 4

No

Yes

No

Yes

Fig.1A- flow chart showing causal relationship1.3 Contamination Conceptual Model:

The report aims at analyzing and identifying the risk / risks posed by leaking of a chemical

known for its toxic nature. As we know by the legal definition of the contamination of landas provided in Section78A(2) Part II A of the Environmental Protection Act 1990,

any land which appears to the Local Authority in whose area it is situated to be in such acondition, by reason of substances in, on or under the land, that-

(a) significant harm is being caused or there is a significant possibility of such harm

being caused; or

(b) pollution of controlled water is being, or is likely to be, caused.

Agree

Sensitivity Analysis using Probabilistic Approach

XX

Comparison with published guidelines

Is the model an

appropriate predictive tool(sufficiently accurate in

meeting objectives)

Time Scaled Remediation Methods for unacceptablerisks

Task Accomplished

Additional

DataRequired

Y


5/21

P 5

What includes controlled waters is clarified in section 78A(9) of the ibid act according towhich in simple term ground water, coastal water and water in surface courses- rivers,

lakes etc. may be considered.Furtherpollution of controlled water is defined as one of the situation where harm is to be

regarded as significant.

We have used source pathway target methodology for risk assessment. Which meansthat if one of the three viz,;

1. source of pollution

2. pathway for the pollutant to move3. and the receptor that is affected by the pollutant

Applying the methodology the risk to the environment can be assessed based on the

nature of the source, presence and ability of pathway to carry the pollutant and thedegree of exposure of the receptor to the pollutant and the sensitivity of the receptor. It

can be assumed safely that if any of the three factors i.e. source-pathway-receptor is

missing there is no risk.

Source:

Primary source here is a tank of chemical Dinoseb which is releasing the chemical intosurface soil. Surface soil and ground water may be called secondary source.

Pathway:

Aerial route is insignificant as the pollutant the groundwater can be identified aspotential pathway as the geology under the surface reveals gravels leading to sand stone

aquifer resting on clay sloping towards the potential receptor a school well and a lake.

Target/Receptors:The main receptor here is water environment as the pollutant is known to have been

entered the water table and there is a bored well down-slope the aquifer 14m fromsource which is used by school children further the aquifer leads to a lake

On the basis of available information the conceptual model is visualized as

follows:-

Potential types and spread of contaminationlikely to be present

Widespread presence of pollutant theDinoseb, in the environment is highly

unlikely as the chemical is not known to

accumulate in environment. However,pollution of groundwater and water bodiesdown slope the source is very likely as we

believe that the pollutant has reached thewater table and the geology favors spread

of the polluted towards the potentialreceptors/targets

Vertical and horizontal stratification ofsoils below the site

Soils below the site consist of shallowgravel aquifer lying on clay

Variation of strata and their permeability Variation of strata is not observed.


6/21

P 6

across the site permeability of strata is likely to be

medium/ high within sand stone aquifer.

Potential migration routes Under lying geology is classified as gravel

aquifer hence a significant migration route.Aerial deposition of the pollutant is not

significant.

Presence of buried features such as servicetrenches, drains, underground schemes,buried storage tanks

No such under ground features as mayinfluence contamination migration wereobserved

Presence of ground water below the site Ground water, not much below the surface,sloping towards a lake has been observed

Use of ground water for drinking or otherpurpose

Ground water is observed to be passingbeneath a school, which takes water from a

bore hole for drinking, washing andcooking purposes

Presence of surface water bodies on or nearthe surface of site

Ground water is sloping towards a lake 35meter from the site which feeds water to

Drinking water supply scheme to a townand further to a river which also supplies

drinking water to another town

Other potential receptors Site workers, future residents and plants

Table 1A-CONCEPTUAL MODEL

1.4 Qualitative Risk Assessment:

As discussed we are basing risk assessment on Source-Pathway-Target model. We

examine whether a target( ground water user for example) will be at risk from acontamination source say release of a pollutant (Dinoseb in our case).so first we

determine if the source i.e. Release of Dinoseb, is present or not then we investigate if apathway is present to link the source to the target ( in our case to a ground water user to

the exposure to Dinoseb hazard)

Target(Receptor) Potential Source-Path waylinkage

Estimateddegree of

risk totarget

Remarks

Site users /future

residents

Inhalation of vapors, odours or

dust

Low Dinoseb occurs in

solid or liquid state,is less volatile and breaks down slow

and is not known toaccumulate in

environment

Ingestion of ,and dermal contact

with contaminated soil

Low There is no

informationavailable of soft

land scaping


7/21

P 7

Indirect ingestion (ingestion of

contaminants in vegetables etc.)

Low There is no

informationavailable of gardens

and cultivated landnear the site

Students and

staff of school/groundwater/other two

bores A&B

Ingestion and skin contact with

the polluted ground water

Moderate -

high

School is known to

use water fordrinking andwashing from a

bore feeding onground water down

slope the site,which may be

contaminated.although the

chemical is notreadily soluble in

water but is knownto pollute water

Population ofthe town using

water suppliedfrom the lake

Ingestion and contact with waterpossibly polluted

Moderate Possiblecontamination of

lake water throughground water

Population ofthe town using

water suppliedfrom the river

feeding partly on

lake

Ingestion and contact withpossibly contaminated water

Low-moderate

Water may becontaminated but

the concentration islikely to be very

low

Surfacewater/Flora and

fauna of lakeand river

Ingestion and contact withcontaminated water

Moderate Possibility of water pollution. The

chemical is knownto be toxic to

aquatic life

Buildings and

structures

Flow of land fill gas into building Low Possible

contamination ofland on site

Contaminant penetrating throughleaking water supply pipes

Low-Moderate

-

Table 1 B- Table showing comparative risk

In this qualitative risk assessment a low risk implies that the remedial action is unlikelyto be required. So we have identified contamination of bore wells especially water used

by school and lake water as the most important risks which need quantitative riskassessment and further analysis so we proceeded further by discussing Fate and

transport mechanism of the contaminant:-

1.5 Quantitative Risk Assessment:

1.5 A. Identification/definition of Fate & Transport Mechanism:


8/21

P 8

As discussed we are concerned here primarily with the fate and transport mechanism ofthe contaminant Dinoseb in the sub surface soil and the ground water. As in this case

the contaminant being released directly into subsoil by way of leakage from a storagetank, not being applied as herbicide in the fields.

The following three factors determine the fate and transportation of the contaminant:

1.Properties of Contaminant:a. solubility

b. adsorptionc. persistence

2. Properties of Soil

a. texture/permeabilityb. presence of organic matter

c. presence of macropores

3. Site Conditions:

a. Permeability of vadose zoneb. type of aquiferc. depth of ground water

d. climate/ rainfalle. soil temperature

We know that Dinoseb occurs mainly in solid state in nature as orange crystals withsolubility of about .052g/L at 25degree centigrade; tends to form salts which are highly

soluble in water.With Soil sorption coefficient:Koc =124 (measured) ;in a scale of highly mobile-5, the contaminant is classified as mobile.

With vapour pressure of1mm Hg at 151.1o

C. The estimated Henry's Law constant of5.04 x 10

-4atm cu m/mol , and diffusion rate of 6.25e

-006, diffusion in water is

insignificant.With a half life of75 days in soil( estimated to be around 100 in sandy loam vadose

region), the chemical is classified as moderately persistent or slow / readily degradable.We can sum up that Dinoseb is expected to biodegrade in slowly and bind weakly to

soil. Therefore, leaching in soil is possible. So the leaching of the chemical is highlylikely in our case and hence confirms the available information that the chemical has

reached water table .Dinoseb has been detected in groundwater in many countries.However, it may bind more strongly to clay soils, especially at acidic pH. Photolytic

degradation of Dinoseb from soil surface may be important. Volatilization is not

expected to be significant.Bioconcentration is expected to be insignificant. A bioconcentration factor (BCF) of68for dinoseb was estimated from its water solubility (50 mg/L)

Now we look at property of the surface and sub soil we observe that the vadose zone isnot thick followed by shallow gravel aquifer (depth -17-22-21m from the three bores

between the tank and the lake).Site is an industrial site and no vegetation has beenreported so the presence of organic matter in the soil may be assumed to be

insignificant. Hence the sub soil is highly permeable.


9/21

P 9

And then we examine the site conditions and come to know that the water tableobservations around the site suggest that the ground water (shallow gravel aquifer

resting on impervious clay) is sloping towards the bores and the lake.

Hence it is highly likely that the contaminant has leached into the ground water

and has been moving towards the identified targets.

Other factors that influence the contaminant transport that are required for quantitativeassessment and modeling are:

1. Mass of contaminant entering the system/ at source(Co)2. Recharge (dilution and contaminant loading/leaching)

3. Hydrualic conductivity (K)(rate of contaminant transport and arrival time atreceptor, calculated ground water dilution)

4. Hydraulic gradient(i=dh/dx)) (rate and direction of ground water flow, calculatedground

water dilution)1.5B. Tier 2 Model:

So the next step is to assess the concentration of the contaminant at the identified

targets and prepare a suitable model. Our goal is to calculate the concentrationof the contaminant, Dinoseb in the ground water feeding Bore B,which is

being used by school for drinking, cooking and washing purposes.( it is

presumed that bore A and C are for investigative purpose and water from thesebores is not being used for any purpose).with the problem as defined earlier and

the amount of available information/ data Tier- 2 model will be most appropriateapproach the meet the Goal.

Using this approach we will use Mthematical model based on the Ogata and Banks

equation to make estimates of the likely range of contaminant at our identified targets.

Goal: Estimation of concentration of Dinoseb at the bore B(11-15M from the source) inorder thereby to assess the level of risk to the identified targets viz. students and staff of

school using water from bore B.

Assumptions:

1. The model is assumed to be at steady-state, where all variables are constant over

time.2. Emissions/leakage from the source of contamination are continuous and result in a

constant contaminant concentration in the soil.3. Contaminat is leaking from the whole surface of the tank in contact with soil

surface

Equation:

C/Co = e((x(1-

)/2(D/v))

0.5 erfc ((x-(v/R) t)/(4(D/R)t)0.5

) Eq. 1.1

Where: =(1+4 R L/v) - Eq.1.2

R = retardation factor

x = distance from source(m)


10/21

P 1 0

v= true velocity of ground water flow(m/day) C/Co = e((x(1-

)/2(D/v))

0.5 erfc ((x-(v/R)

t)/(4(D/R)t)0.5

)

t = time(days)= decay constant

D= dispersion lengthA spread sheet on MS Excel 2007 was prepared using Ogata and banks Eqaution, as model

for calculation/estimation of Concentration.

1.5 B(1) Selection of parameters:Following in put values/parameters were selected:-

Co(concentration of contaminant at source(not in the tank))Co= Rate of Leakage in Kg/Year/Flow Rate in M/year

Rate of leakage=42 kg/year(taking the mean of 16 values)Flow Rate(Q)=Vd *Y *Z ; where Y=Width of the tank i.e. 30m in our case and

Z (mixing Depth )==(0.0112 L2)0.5+ b(1 -exp[(-L*Inf)/(K*dh/dx*b))]; where

L=Source length/length or Dia of tank i.e. 30m (see appendix-3)b=Aquifer thickness i.e. 20m (taking the mean of the three values) (see appendix-3)

Inf=Infiltration rate viz. rainfall-runoff-evaporation= 0.3m/year ( assumed)

dh=.8 (given difference of water level between bore A and bore C)(see appendix-3)

dx=35 (mean value calculated from the group of 16 ) (appendix-3)hence Z=3.29

FLOW RATE =1.143*30*3.29=112.81 M/year

Co =42/112.81=.372 kg/m (see appendix-1&2)

K(Hydrualic conductivity)=50m/day (30 to 70 m/day given mean value taken)(A-3)

Porosity(n)=.23 (given) (see A-3)

D(Dispersion length)D(diffusion coefficient) We can estimate Diffusion/Dispersion combination usingDL = L v + D*

DL= longitudinal dispersion coefficient m2/day. This is what we use asD in the Ogata and Banks

equation, a combination of dispersion & diffusion.

L is called the dynamic dispersivity and is the amount of dispersion caused by water flowingaround the soil particles

Lcan be estimated very approximately 0.1 x flow path length. Lcan also be estimated using fromL= 0.83 (logL)2.414forL


11/21

P 1 1

D=14Rf(Retardation Factor)= 1+density of dry soil/porosity(Kd)

Where Kd = foc Koc=3.1Foc=.5*organic matter in soil =.025(assuming the presence of organic matter to be 5 %)

Koc=124 (calculated value taken from EPA Literature);hence

Rf=23.913 (1+1.7/.23(3.1))

Density=1.7 (from table) (decay constant) can be calculated from the half life & vice versa half life of Dinoseb inground water is estimated to be 100days(decay const=.693/half life ) i.e.

=.00693

L=3 (between 2.35 & 3.5)Hence we have obtained/selected all the in put values for our model.No value was found to be out side the typical values. Values were fed in to the O&B spread sheet. No in-

consistencies were found and the contaminant concentration at the borehole used by school

was calculated and found to be .671kg/m , as can be seen below in the fig-1A

fig. 2. A (Ogata n bank worksheet)we can see here in the fig 1 A above that the concentration of the contaminant at the

distance of 13 m from source or at the bore B is .357, interestingly the value is same for 1year and 22 years.Although the values/concentration diminishes slightly as the distance

from the source increases but values are well above MCL(.007) even at the distance of15m.(if the distance of bore B is taken to be 15 m)


12/21

P 1 2

Fig.2.B. Graph showing movement of contaminant

1.6.Comparision of results with acceptable standards:

Published and legal standards( source EPA) are tabulated below for reference:-

Health Based Limits for Dinoseb

Standard Description Level

Maximum

ContaminantLimit (MCL)

The enforceable standard which defines the highest level of a

contaminant that is allowed in drinking water. MCLs are setas close to health-based limits (Maximum Contaminant

Level Goals, or MCLGs) as feasible using the best availableanalytical and treatment technologies and taking cost into

consideration. Source: U.S. Environmental ProtectionAgency.

0.007 mg/l

Maximum

ContaminantLimit Goal

(MCLG)

A non-enforceable health goal that is set at a level at which

no known or anticipated adverse effect on the health of persons occurs and which allows an adequate margin of

safety. Source: U.S. Environmental Protection Agency.

0.007 mg/l

Lifetime health- based limit, non-

cancer risk

Concentration of a chemical in drinking water that is notexpected to cause any adverse, noncarcinogenic health

effects for a lifetime of exposure. The Lifetime health-basedlimit (or Health Advisory, HA) is based on exposure for a a

70-kg adult consuming 2 liters of water per day. Source: U.S.

Environmental Protection Agency.

0.007 mg/l


13/21

P 1 3

California Public

Health Goals

Defined by the State of California Office of Environmental

Health Hazard Assessment (OEHHA) as the level ofcontaminant that is allowed in drinking water. For acutely

toxic substances, levels are set at which scientific evidenceindicates that no known or anticipated adverse effects on

health will occur, plus an adequate margin-of safety. PHGs

for carcinogens or other substances which can cause chronicdisease shall be based solely on health effects without regardto cost impacts and shall be set at levels which OEHHA has

determined do not pose any significant risk to health.

0.014 mg/l

Drinking Water

Equivalent Level

A lifetime exposure concentration protective of adverse,noncarcinogenic health effects, that assumes all of the

exposure to a contaminant is from drinking water. Source:U.S. Environmental Protection Agency.

0.035 mg/l

Children's health-

based limit for 1-day exposure

Concentration of a chemical in drinking water that is not

expected to cause any adverse, non carcinogenic healtheffects for up to one day of exposure. The One-Day health-

based limit (or Health Advisory, HA) is typically set to protect a 10-kg child consuming 1 liter of water per day.

Source: U.S. Environmental Protection Agency.

0.3 mg/l

Children's health- based limit for

10-day exposure

Concentration of a chemical in drinking water that is notexpected to cause any adverse, noncarcinogenic effects for

up to ten days of exposure. The Ten-Day health-based limit(or Health Advisory, HA) is typically set to protect a 10-kg

child consuming 1 liter of water per day. Source: U.S.Environmental Protection Agency.

Table; 1C- Health base limits for Dinoseb

0.3 mg/l

Comparing the estimated value of concentration i.e. .671g/l with the above tabulatedacceptable standards we see that the level of concentration of contaminant alarmingly

above the laid down standards.

1.6 B. Uptake rate of targets:As our concern is the school which takes water from borehole B for drinking, cooking and

washing purposes(ingestion, dermal contact and contact with eye.)It is known that there are around 200 children aged 5-10 yrs and 10 staff aged 23-45 yrs.

The school is open 40 weeks per year. Thus if a child is assumed to intake 1 ltr of water /day by way of direct drinking and in food served in school 7 days a week(assuming the

school to be residential school)for 40 weeks in a year average child intake comes to be280*.357=99.96g and if an adult is assumed to consume 2 ltrs of water daily the avg yearly

up take rate can be estimated to be 199.92 g per year respectively.Hence the up take rates are far higher than the acceptable for the targets so the level

of risk is not acceptable.

Interpreting these results within the meaning of Section 78A(2) Part II A of the

Environmental Protection Act 1990,


14/21

P 1 4

any land which appears to the Local Authority in whose area it is situated to be in such acondition, by reason of substances in, on or under the land, that-

(a) significant harm is being caused or there is a significant possibility of such harm

being caused; or

(b) pollution of controlled water is being, or is likely to be, caused.

What includes controlled waters is clarified in section 78A(9) of the ibid act according towhich in simple term ground water, coastal water and water in surface courses- rivers,

lakes etc. may be considered.Further it has been clarified that pollution of controlledwater is defined as one of the situation where harm is to be regarded as significant.

Here the harm is significant hence it is situation of pollution of controlled waters

1.7Parametric modelling and uncertainty:

As we know uncertainties are attached with the variables we have used as in puts in ourmodel as dislayed in following table:-

There are various parameters involved in the modelling and the influence of these

parameters were seen on the contaminant transport was analysed.

Parameter Influence oncontaminant

Transport

PDF Main uncertainities

Source term y Mass ofcontaminantentering the

system

y Contaminant

concentration inground water

Log triangular

Uniform

Mass and timing ofcontaminant of

release

Source concentration

andgeometry(boreholeinvestigation may not

allow plumegeometry to have been defined such

that maximumconcentration is under

estimated).

Hydraulicconductivity(K)

Weight of contaminanttransport and arrival

time at receptor

Log triangular Contaminanttransport is sensitive

to this parameter.Field measurement

can often vary bymore than order of

magnitude due tonatural heterogeneity

of most aquifers

Hydraulic

gradient(i)

Rate and direction of

ground water flow

Uniform Minimum three

boreholes required,hydraulic gradient


15/21

P 1 5

and direction of flow

can vary with time, itis dependent on K,

steep gradientsunlikely to occur in

zone of high

permeabilityOrganic partitioncoefficient(Koc)

Used in calculation ofretardation and rate of

contaminant migration

Uniform Often based onliterature values

although a range ofdifferent values may

be given in literaturesources.

Fraction of organiccarbon(Foc)

Calculation of partitioncoefficient

uniform For low Focvalues(


16/21

P 1 6

conditions

Determinationof degradation

rates fromfield

observation

usually relianton havingtime series of

monitoringdata covering

a number ofyears.

Table-1D parametric modelling & uncertainty

It looks convenient and effective to change one variable at a time and analyse the result and

to test the model for sensitivity towards the values / parameters (variables/uncertainitieslues).But the method has limited exploration in space.Another plausible

approach is to in put 20 groups of values in the O&B spread sheet to have a look at thevariation in out put vis a vis the input.that too has limited exploration besides being a

cumbersome process.Hence the probalistic approach using computerized simulation wasadopted.Monte Carlo simulation was used in Crystal ball and result were analysed.

Fig.2. C O&B Spread sheet showing definition of assumptions and forecast

1.8USING THE PROBALISTIC APPROACH;It can be can seen here that the assumption cells are highlighted in flourecent green andforecast cell in light blue.


17/21

P 1 7

As we have taken mean value of leakage in kg/year we will put min(28). And max(53)using these values min. Co is put as .248 and max.470-(see appendix-1&2)

Fig.3ASince the value of k is given to fall between 30-70 and is expected to be closer to mean

rather than the extremities a triangular distribution with 30 and 70 as min and max valuesand 50 as mean was selected.(see appendix-1&2)(S(

Fig.3B

Similarly min and max from the vailable range of values was selected in uniform

distribution for dx

Fig.3.C

As discussed in selection of parameters vale of D is slated to fall between 11.65 and 17.3.

Fig.3.DAlso the distance of the bore as provided in 16 groups(A-1&2) rangimg from 11 to 15 was

selected.


18/21

P 1 8

Fig.3.E

Fig2D frequency distribution chart showing concentration of dinoseb

We can see from the frequency distributin chart (using 5000 runs/trials)that highest probability of concentration ranges from .330-.360. Interestingly the concentration

estimated without using the simulation viz..357 falls right within the range

Fig.2E-frequency distribution showing 95% probabily of concentraion above.290


19/21

P 1 9

Now again the simulation was run to see 95% probability and we can see that there is 95%probability of concentration being .290 at the identified target viz. bore B

It is observed that the estimated concentration even if .290 is considered is far above theacceptable limits of .007.especially when the majority of the target group comprises of

children with long term exposure extending many years. The estimated concentration ofcontaminated far exceeds the .3g/l limit for children in case of one day exposure.

Hence the ground water shall be termed as contaminated within the meaning of Part II Aof the Environmental Protection Act 1990,

Hence the level of risk to the targets is unacceptable. Therefore a strategy to remedy thesituation by way of reduction or removal or both needs to be recommended.

1.9Sensitive Analysis:As discussed the probalistic approach using computerized simulation was adopted.Monte

Carlo simulation was used in Crystal ball and result were analysed. Sensitivity analysis

chart appended below explains the sensitivity of the variables. We can see that variable k,with huge uncertainty range of 40 has about 50 % effect on the result where as dx (28-42)

and distance from source with range of 4 m(11-15) have around 25% sensitivity. It is

interesting to note here that the time (in years) of leakage has virtually no effect on theresult for the distance from the source is only 13m. Also variation in concentration atsource(Co) has little effect on the results.

As our primary concern is assessment of risks to the identified targets and the level of

concentration is far higher even when the min. values of variables are taken. Hence thedata can be considered sufficient to achieve the goal with reasonable accuracy through the

model and no need of further data or refinement of existing data was required toarrive at the result and hence further investigation is not recommended/required;

Athough the information on location of the site would have immensely helped in

understanding the problem better, obtaining relevant data as rainfall, runoff and

evaporation values etc. and also in recommendation of treatment/remediation.

;

Fig. 2 F sensitivity analysis chart


20/21

P 2 0

1.10 Suggesting remediation:

As discussed the level of risk is unacceptable hence the contamination needs remediation

through reduction and removal.As our site meets the most of the requirements for successful implementation of in situ bio

remediation identified by by Suflita (1989) :

(1) A homogeneous and permeable aquifer;(gravel aqufer with .23 porosity)(2) A contaminant originating from a single source; (storage tank)

(3) a lowground-water gradient; (.8/35)(4) no free product;

(5) no soil contamination; and(6) an easily degraded, extracted, or immobilized contaminant.

Especially high value of K(up to 70) andcomparatively less volume with Distance from

source(x)=13, Mixing Depth(Z)=3.9 and width of the source(Y)=30 for treatment in situ

bio remedial method is suggested. In which chemicals to treat the contaminated soil orwater are injected in to the aquifer.

Remediation of dinoseb with Zerovalent iron(Fe0) . In a recent case study It was found

out that zerovalent iron (Fe0) could remediate dinoseb-contaminated soil. This was

accomplished by conducting a series of batch experiments where first Fe0

was used toremove dinoseb in aqueous solutions, then in contaminated soil slurries, and finally, inunsaturated soil microcosms (25 C, g = 0.30 kg H2O kg

1). Results have showed

quantitative dinoseb removal in the presence of Fe0

in all three media (aqueous solutions,

soil slurries, moist soils) and that removal increased by including either ferrous oraluminum sulfate with the iron treatment. Incubating contaminated soils with Fe

0or Fe

0

plus salts (FeSO4 or Al2(SO4)3) resulted in100% removal of dinoseb within 7 d. Liquidchromatography/mass spectrometry (LC/MS) analysis of degradation products have

showed the transformations imposed by the iron treatments were reduction of one or bothnitro groups to aminogroups. These amino degradation products were further transformed

to quinonimine and benzoquinone and did not persist. These results support the use ofzerovalent iron for on-site treatment of dinoseb contaminated soil.

Hence an situ remediation using Zerovalent iron(Fe0) is recommended with a time

frame of one month allowing time for further investigation required and collection of

samples.

Immediate closure of bore B till the no trace of contaminant is observed(detectable

limit is reached) in the sample and immediate removal of the source is recommended.

Enclosed:2. Table of value group 1-8

3. Table of value group 9-164. Table of data/values

References:1.http://www.epa.gov/

2.http://www.opsi.gov.uk/

3.http://www.epa.gov/safewater/pdfs/factsheets/soc/tech/dinoseb.pdf

4.http://en.wikipedia.org/wiki/


21/21

P 2 1

Appendix-1

Appendix-2

Appendix-3

analysing underground contamination

Documents