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C S I R O L A N D a nd WAT E R

Recharge Enhancement Using Single or Dual Well

Systems for Improved Groundwater Management

in the Bandung Basin, Indonesia

By Susanne Fildebrandt, Paul Pavelic and Peter Dillon, CSIRO Land and Water, Adelaide

and

Notoatmodjo Prawoto, University of Padjadjaran, Bandung

CSIRO Land and Water, Adelaide

Technical Report 29/03, May 2003

Report to

Department of Education, Science and Training on a National Priority Reserve Project

Funded by

Department of Education, Employment, Training and Youth Affairs

© 2002 CSIRO To the extent permitted by law, all rights are reserved and no

part of this publication covered by copyright may be reproduced or copied in any

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Water.

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contained in this publication comprises general statements based on scientific

research. The reader is advised and needs to be aware that such information may

be incomplete or unable to be used in any specific situation. No reliance or

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To the extent permitted by law, CSIRO Land and Water (including its employees

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in whole) and any information or material contained in it.

ISSN 1446-6163

Recharge Enhancement Using Single or Dual Well

Systems for Improved Groundwater Management

in the Bandung Basin, Indonesia

By Susanne Fildebrandt, Paul Pavelic and Peter Dillon, CSIRO Land and Water, Adelaide

and

Notoatmodjo Prawoto, University of Padjadjaran, Bandung

CSIRO Land and Water, Adelaide

Technical Report 29/03, May 2003

Report to

Department of Education, Science and Training on a National Priority Reserve Project

Funded by

Department of Education, Employment, Training and Youth Affairs

ACKNOWLEDGMENTS

This work was supported by the Department of Education, Science and Training

on a National Priority Reserve Project and funded by the Department of

Education, Employment, Training and Youth Affairs. The project was administered

by Carolyn Vicary of the Research Grants Section, Flinders University of South

Australia.

Assistance from following people is sincerely appreciated:

Diah Wihardini (University of Adelaide), Prof. N. Prawoto (University of

Padjadjaran) and Dr. Edi Utomo (LIPI).

1

SUMMARY

The City of Bandung in the province of West Java faces a significant number of

groundwater resource problems. In this Joint Australia-Indonesia Project involving

the Padjadjaran University and CSIRO Land and Water, the potential for recharge

enhancement in the most heavily exploited shallow aquifer system of the

Bandung Basin, was investigated.

As the surface water that could be utilised for injection has a high likelihood of

being contaminated by microbial pathogens as well as by other contaminants, any

water injected into the subsurface should meet water quality criteria to ensure

that the recovered water is fit for use and that other groundwater users are

protected. Taking account of natural attenuation of contaminants within the

aquifer makes it possible to set criteria that can be achieved with very simple pre-

treatment or source selection measures.

Conservative simplifying assumptions about solute transport and degradation in

aquifers have been used to determine distances over which 1- and 4- log

pathogen removal would be achieved during aquifer storage and recovery (ASR),

as these are the expected minimum requirements for roof-runoff and surface

water respectively. It was found that the minimum separation distances between

injection and recovery wells would range from 20 to 1000 m, depending on the

specific hydrogelogical conditions. The minimum separation distance needs to

increase where an aquifer has a steep hydraulic gradient, high permeability

(reflected by high well yield), low porosity or is thin. Based on available

information on hydraulic gradients and well yields, the Bandung Basin was

classified into subregions with different recommended minimum separation

distances. These indicate that largest separation distances are needed in the

steeper margins of the basin, and in the flatter centre of the basin acceptable

separation distances may be smaller. Given these distances are larger than the

average size of land holdings, undoubtedly any landholder injecting water of poor

quality could adversely impact other groundwater users. Hence it is

recommended that only clean roof-runoff be used for injection. The techniques

developed and utilised in this study may have widespread application in the

design of ASR systems.

A pilot study on recharge enhancement using infiltration basins is currently being

conducted by the University of Padjadjaran, and a series of recommendations are

provided within for similar studies involving injection wells.

2

TABLE OF CONTENTS

ACKNOWLEDGMENTS 0

SUMMARY 1

1. INTRODUCTION 4

1.1 Background 4

1.2 Objectives 5

2. INVESTIGATION AREA 5

2.1 Geography and climate 5

2.2 Hydrogeology 7

3. ASR 12

3.1 ASRRI

4. ANALYTICAL SOLUTIONS FOR FATE OF INJECTED CONTAMINANTS 14

4.1 Single well systems 15

4.2 Dual well systems 16

4.3 Nomogram for dual well system 18

5. WELLS AT DIFFERENT ORIENTATIONS TO THE REGIONAL GRADIENT 19

5.1 Recovery well upgradient of the injection well 20

5.2 Recovery well positioned at different angles to the injection well 20

6. APPLICATION TO THE BANDUNG BASIN 24

6.1 Hydraulic gradients 24

6.2 Well yields 26

6.3 Separation distances between wells 27

7. CONCLUSIONS 31

8. RECOMMENDATIONS 32

9. REFERENCES 33

3

List of Tables

Table 1: Contaminant hazards.................................................................. 11

Table 2: Terminology used in the analytical solutions .................................. 15

Table 3:Zones defined by overlapping well yields and hydraulic gradients map . 27

Table 4: Recommended seperation distances between injection and recovery

well for 4-log removal for different zones, τ =10 days ...................... 28







List of Figures

Figure 1: Location map of Citarum River Basin and Bandung Basin ................. 6

Figure 2: Geology of the Bandung Basin ....................................................... 7

Figure 3: Sequence of aquifers in the Bandung Basin ..................................... 8

Figure 4: Schematic representation of single and dual well ASR systems ........ 12

Figure 5: Idealised distribution of injected contaminants for single well and dual

well systems.............................................................................. 14

Figure 6: Theoretical exponential decay curve ............................................. 15

Figure 7: Breakthrough curves illustrating retardation and biodegradation ...... 17

Figure 8: Nomogram for dual well ASR system (recovery well positioned down-

gradient of injection well)............................................................ 18

Figure 9: Nomogram for dual well ASR system (recovery well positioned

upgradient of injection well) ........................................................ 19

Figure 10: Relationship of variables for injection-recovery well pair with areal flow

of 180 degrees .......................................................................... 21


of 0 degrees .............................................................................. 22


of 135 degrees .......................................................................... 23

Figure 13: The proportion of injectant reaching a recovery well positioned at

different angles relative to aerial flow for different values of q/av0 ... 24

Figure 14: Hydraulic gradients of the shallow aquifer of the Bandung Basin ...... 25

Figure 15: Well yields in the Bandung Basin ................................................. 27

Figure 16: Zones with different separation distances between wells ................. 31

4

1. INTRODUCTION

1.1 Background

Indonesia is one of the world’s most densely populated countries. Rapid

population and economic growth in Indonesia has resulted in a number of

environmental problems, with the availability of good quality water supplies

because of the increasing demand of clean and fresh water for daily life activities

being one of the most severe (Suryantoro, 1999).

Issues of water resources management will be increasingly important in the years

ahead, especially on the island of Java, which has 60% of the nations population,

70% of its irrigated agriculture, and 75% of its industry. Issues related to water

quantity include emerging conflicts between competing uses (agriculture, industry

and municipal) of surface water and groundwater in rapidly growing urban areas

(World Bank, 1995). The Bandung Basin in Java is an area with a warm climate,

high rainfall and fertile soils, and is one of the most densely populated regions on

Earth. The high population density creates stress on the environment and on the

water resources in particular (Wagner, 1990). The city of Bandung, which has an

important role in the economic development of the province of West Java, is

facing increasing stress on the quantity and quality of its groundwater resources

due to the rising population, increasing water demand, changes of land usage and

inadequate groundwater management (Soetrisno, 1998ab). According to

Suryantoro (1999), groundwater abstraction in the Bandung Basin increased from

47 Mm3 to 61 Mm3 per year between 1990 and 1994, and groundwater levels are

falling by 2-4 m per year.

In recent years the Indonesian government has become more active in regard to

groundwater protection. Examples include the establishment of wastewater

treatment plants and the development of methods to enhance groundwater

recharge (Bukit, 1995). The possibility of using excess stormwater runoff to

replenish depleting aquifers in the Bandung Basin warrants consideration. As an

initial step to assess water quality issues associated with storing stormwater in

the upper aquifer, a DEETYA supported Joint Australia-Indonesia Project

commenced in 1997 involving the Padjadjaran University and the Centre for

Groundwater Studies via CSIRO Land and Water, Adelaide.

5

1.2 Objectives

The principal aim of the project is to identify the fate of pathogens that may be

introduced into aquifers by recharge of stormwater via wells. This leads to an

evaluation of the minimum spacing of wells in order to achieve specified removal

of pathogens between injection and recovery, which in turn suggests

management strategies such as source water selection.

• This report documents the development of graphical and analytical tools to

predict water quality impacts of different recharge enhancement systems,

and the application of these tools to the Bandung Basin. Clearly these

techniques may be applicable to other water-short areas in Indonesia and

elsewhere.

2. INVESTIGATION AREA

2.1 Geography and climate

Bandung is the capital city of the province of West Java and within its 2,250 km2

area includes several medium sized towns which collectively form greater

Bandung. The total population of greater Bandung was known to be about 3.5

million in 1995, but was expected to exceed 5 million by 2001. Bandung is

surrounded by a number of volcanic mountains in the north and south. The

Citarum River originates in the south and continues to flow northwest through the

Citarum River Basin, and eventually into the Java Sea (Wihardini et al, 1999)

(Figure 1). In the centre of the basin lies the plain measuring 40 km east-west

and 30 km north-south where most of the urban and industrial areas are located.

Settlement occurs mainly along the tributaries of the Citarum River. Agriculture is

the traditional economic basis of greater Bandung, but urban and industrial

development is changing the land usage from open land or rain-fed and irrigated

paddy fields to housing complexes, business districts, and industrial areas

(Soetrisno, 1998a). This change in land use has had a negative impact on the

quantity and quality of groundwater recharge (Soetrisno, 1998b). The major

industrial activities comprise textiles and garments, metal products and

machinery, food and beverages, chemicals, pharmacy, plastics, paper and

printing (Ruds, 1990).

6

Figure 1: Location map of Citarum River Basin and Bandung Basin

7

The climate of Java is tropical and characterised by distinct wet and dry seasons. From

November to May is the wet season whilst the rest of the year is the dry season. The

mean annual precipitation within the basin is strongly dependent upon the altitude, but is

typically between 1900 - 2200 mm/yr in the urbanized areas. In the lower western part of

the basin the mean annual precipitation is about 1500 mm/yr and in the mountainous

areas is about 3500 mm/yr (Soetrisno, 1998b).

2.2 Hydrogeology

Figure 2 shows the surfacial geology of the Bandung Basin.

Figure 1: Geology of the Bandung Basin (after Suhari and Siebenhuner, 1993)

8

The western edge of the Bandung Basin is composed of Tertiary sandstone, claystone and

limestone. The remainder of the Basin is composed of various Quaternary sediments that

are of volcanic origin: andesitic and dacitic lava, breccia, agglomerate, tuff, lahar and

intrusive rocks. At the centre of the basin alluvial and fluvial reworked volcanic sediments

are widespread. In the northern part of the basin an elongated east-west fault of volcanic

origin has developed in the Quaternary sediments, whereas the faults mostly occur in the

Tertiary sediments (Suhari and Siebenhuner, 1993).

The general direction of groundwater flow is from the northern and southern mountain

ranges towards the Citarum River (see Figure 2). The main source of recharge for the

groundwater exploited in the basin is considered to occur in the northern area, based on

an evaluation of natural stable isotope concentrations in the groundwater (Geyh, 1990).

The multi-layer aquifers of the Bandung Basin may be simplified into two hydrogeologic

systems: the shallow aquifers and the deep aquifers (

Figure 2: Sequence of aquifers in the Bandung Basin

The shallow aquifers are principally unconfined or semi-confined and occur within the

upper 40 m. These aquifers are composed of volcanic products, such as basaltic lava,

coarse tuff, volcanic conglomerate and breccia from the young volcanic complexes

bordering this basin (Cikidang Aquifer) (Rosadi et al, 1993) and of lake sediments, which

were deposited while the central part of the basin was inundated (Kosambi Aquifer)

(Soetrisno, 1998a). The shallow aquifers in general have low to moderate hydraulic

conductivities (10-2 to 10-1 m/day)(Sukrisno, 1990) and low (< 2 L/s) or low to moderate

well yields (2-10 L/s) and therefore are not so widely exploited (Suhari and Siebenhuner,

1993).

The deep aquifers are semi-confined to confined and are present at depths of between

40 m and 150 m. The two uppermost deep aquifers are the Cibeurum aquifer and the

underlying Cikapundung aquifer.

Kosambi aquifer

Cibeurum aquifer

Shallow aquifer

Deep aquifers

Cikapundung aquifer

9

The Cibeurum aquifer is the most intensively exploited aquifer in the basin due to its high

well yields (Soetrisno, 1998a). The Cibeurum aquifer, composed of young volcanic

deposits, has a moderate to high transmissivity (between 110 and 880 m2/day) and well

yields (2-10 L/s to >10 L/s) whilst the Cikapundung aquifer, which consists of old volcanic

deposits, has a moderate to low transmissivity (110-150 m2/day) and moderate well yields

(2-10 L/s)(Soetrisno, 1998b).

The shallow aquifers as well as the deep aquifers have experienced piezometric head

declines due to increased abstraction. Soetrisno, (1998b) calculated the total abstraction

to be 70 Mm3 per annum by assuming that 60% of the total population of 3.5 million

(1995) use 90 litres of groundwater per person per day. The abstraction from the shallow

aquifers is used for local domestic supply of groundwater (dug wells or shallow boreholes).

The groundwater level in the centre of the Basin has declined from 1 to 2 m below the

ground surface elevation to about 5 m below the surface. In the elevated areas the

groundwater level has fallen to around 15 m below the surface (Sukrisno, 1990).

Due to excessive abstraction in the deep aquifers by industry, the current piezometric

head of groundwater in the basin has declined markedly. In 1970 there were 96 deep

wells registered, 971 in 1990 and by 1995 it was estimated that there were up to 4700

deep wells (Supriyo et al, 1999). In the early 1900’s the piezometric level was usually

present between 20 and 25 m above surface, while now it lies generally more than 50 m

below the surface. The piezometric head has been declining continuously at a rate of

between 2-4 m/yr, which is altering the groundwater flow system. Vertical downward

leakage now occurs within the Bandung area, as the heads in the deep system are now

generally lower than in the shallow system (Soetrisno, 1998b).

The natural groundwater quality of the Bandung Basin is characterised by low salinity (EC:

<500 µS/cm) on the mountain slopes, with an increase to moderate values (EC: 500-1000

µS/cm) towards the lower parts of the basin. The predominance of HCO3- (45-90 meq%∞),

low content of SO42- (<20 meq%) and high concentrations of Fe (exceeding 1 mg/l) are

typical over most of the basin (Soetrisno, 1998b).

∞ meq%= milliequivalent percentage, which expresses the molar proportion of an anion with respect to total

anions.

10

In 1981 the shallow groundwater system was of a quality suitable for all purposes and no

indications of anthropogenic pollution had been detected (Bender, 1981). In more recent

times the quality of the shallow groundwater has deteriorated measurably. The main

sources for pollution are poor drainage and leakages from the sewerage system in densely

populated areas, improper waste disposal sites and industrial wastewaters (Soetrisno,

1998b) that are released without treatment into streams and channels (Ruds, 1990). Until

1992 there was no sanitation system, and it is still far from complete (Soetrisno, 1998b).

Agricultural activities may also be a source of pollution because of the heavy usage of

fertilizers, insecticides and pesticides.

The major groundwater quality concerns therefore are (Table 1) (Wagner et al, 1991):

• Elevated concentrations of

o total dissolved solids (salinity)

o nitrogen compounds

o boron and phosphate

o trace metals

o organic contaminants (e.g. pesticides, detergents)

• Contamination by bacteria and viruses

• Change in the pH and oxygen content

Areas with industrial and domestic pollution are the city of Bandung, in particular its

industrial suburbs such as Cimahi, Leuwigajah and Dayeuhkolot, as well as medium size

towns with industrial areas, e.g. Majalaya. Heavy contamination from waste disposal sites

occur e.g. in Dago, to the north of Bandung. Agricultural areas with elevated nitrate

concentrations can be found in the Lembang plain and the eastern Bandung plain (Rosadi

et al, 1993). The Citarum River is well known to have been polluted for a long time

principally due to industrial wastes (Soetrisno, 1998b).

Up to now no anthropogenic contamination to the deeper aquifer system has been

recorded. However, because of the potential for downward migration from the upper

system due to stress in the deeper system, this aquifer system is also vulnerable to

pollution (Soetrisno, 1998a).

11

Table 1: Contaminant hazards (Wagner et al, 1991)

Increased concentration of: Change in: Main contamination sources

according to present land use TDS

Nitrogen compounds

Boron PhosphateTrace metals

Organic contaminants

pHOxygen content

Contamination by bacteria and viruses

Domestic sewage

♦ ♦ ♦ ◊ ◊ ♦ Domestic and

industrial wastewater Industrial

waste water ♦ ♦ ♦ ♦ ♦ ♦

Perennial paddy

irrigation

◊ ♦ ◊

Seasonal paddy

irrigation

◊ ◊ ◊ Intensive agriculture

Vegetable farming, gardens

◊ ♦ ◊

Solid waste disposal

Leachate ♦ ♦ ♦ ◊ ♦ ♦ ♦ ♦ ♦

♦ Major hazard ◊ Minor hazard

12

3. ASR

The key aim of ASR (aquifer storage and recovery) is to store surplus surface water in

aquifers via injection wells for subsequent recovery for irrigation or drinking water

purposes (Dillon and Pavelic, 1996). The injection and recovery is implemented either by a

single well which is used for recharge and recovery (single well system) or by separate

injection and recovery wells (dual well system) (Figure 4). Figure 4 shows the piezometric

cone of impression during recharge and the cone of depression during recovery.

Figure 3: Schematic representation of single and dual well ASR systems

Single well systems must be operated with intermittent injection and recovery. It is

possible to have concurrent injections and recovery from dual well systems.

The purposes for recharge enhancement are numerous and range from augmenting water

supplies, reducing the native groundwater salinity, precluding seawater intrusion,

mitigating floods and purifying surface waters, through to more novel applications such as

controlling land subsidence and storing and reusing thermal energy.

13

The injected waters can be from different sources, such as rivers and lakes, treated

sewage effluent, groundwater from other aquifers and stormwater runoff. Each ASR site

has particular requirements for the source water quality because subsurface conditions

vary and because the recovered water may be used for different purposes or be required

to meet different regulatory standards. In general, it is advisable to inject waters of high

quality not only to protect the ambient groundwater quality and ensure public health, but

also to prevent clogging of injection wells. Depending on the source water quality and

aquifer characteristics, the injectant might have to be pre-treated. The quality of the

injectant may improve during ASR due to natural attenuation processes, adsorption and

mixing in the aquifer (Pavelic and Dillon, 1997). The changes that take place may include:

• pathogen removal

• removal of synthetic organics such as disinfection byproducts (and their precursors)

• changes in chemical composition; H2S, Fe, Mn, As, Na, Cl, HCO3The change in water

quality during ASR is controlled by a number of physical, chemical and microbiological

factors between the time of injection and the time of recovery. Specific parameters include

the effective porosity, aquifer thickness, flow velocity, hydraulic conductivity

(heterogeneity) and temperature. In the analytical solutions considered next various

simplifying assumptions must be made (Section 4).

The distribution of the injectant for a single well system for a homogeneous and isotropic

aquifer where the regional hydraulic gradient is negligible is circular (radial spreading).

The concentration of biodegradable components in the injectant gradually decreases

towards the margins of the plume where the residence time is longest (Figure 5). If the

biodegradation is regarded in terms of “log-removal” (defined later), this concentration

decline can be divided into zones of differing log-removals. This is an attractive way to

describe attenuation for potential contaminants that may be in the injectant where there

are no existing guidelines (e.g. some trace organics) or where input concentrations are

difficult to define (e.g. viruses). For instance, a 4-log removal is one where there has been

a 99.99 % reduction relative to the initial concentration. The minimum storage time of the

injected water in the aquifer for a single well system should be taken to be from the

cessation of injection to the beginning of recovery if the injectant contains biodegradable

contaminants.

The distribution of the injectant for a dual well system with no regional hydraulic gradient

in a homogenous aquifer is elliptic and the concentration of biodegradable components in

the injectant gradually decreases towards the recovery well (Figure 5). Depending on the

aquifer parameters, specific distances between the two wells may be determined to

achieve a given log removal (as will be shown later).

14

Figure 4: Idealised distribution of injected contaminants for single well (left) and dual

well (right) systems

3.1 ASRRI

ASRRI (Aquifer Storage and Recovery Risk Index) is a computer program recently

developed by CSIRO that calculates the risk of contamination for a range of single and

dual well ASR systems (Miller et al, 2002). The risk indexes calculate whether specific

trace organic or microbial contaminants in the recovered water would reach its target

attenuation ratio (log removal) or its guideline value for a given scenario. The calculations

performed by ASRRI are, as described in this section, simulate the worst-case scenario to

provide a firm basis for the effective management of ASR systems.

4. ANALYTICAL SOLUTIONS FOR FATE OF INJECTED CONTAMINANTS

Analytical solutions are given for the two ASR systems. The single well system is

considered first, then the dual well system where the two wells operate along a

groundwater streamline, with the recovery well situated downgradiant of the injection

well. Next, different orientations between the injection-recovery well pair and the regional

hydraulic gradient are considered. The terminology used in section 4 is shown in Table 2.

Plan view of distribution of injected contaminant in aquiferfor single and dual well ASR systems for homogeneous system

and with no regional hydraylic gradient

ASR injection and recovery well

Log removal zones

ambientgroundwater

ambientgroundwater

ASR injection well

ASR recovery well





ASR injection and recovery well

Log removal zones

ambientgroundwater

ambientgroundwater

ambientgroundwater

ambientgroundwater

ASR injection well

ASR recovery well

Plan view of distribution of injected contaminant in aquifer

for single and dual well ASR systems for homogenous system

and with no regional hydraulic gradient

15

Table 2: Terminology used in the analytical solutions

System Symbol Interpretations Units

Single/Dual C(t) Concentration of species in groundwater and recovered water at any time

mg/l

Single/Dual C0 Concentration of species in injectant mg/l

Dual L Distance from injection to recovery well m

Dual Q Rate of pumping m3d-1

Single/Dual t Time of residence of water in an aquifer d

Single ts Minimum storage time from end of injection to start of recovery

d

Dual D Aquifer thickness m

Dual νdo Component of Darcian velocity vector in aquifer parallel to the vector in the direction from the injection well to the recovery well

md-1

Dual ne Porosity of aquifer m3m-3

Dual R Retardation factor (due to linear absorption isotherm)

Single/Dual λ Decay rate constant for biodegradation or pathogen inactivation

d-1

Single/Dual τ 1/λ, and is called the one-log10 removal time, that is the time for contaminant concentrations or viable pathogen numbers to fall to 10% of their initial value

d

4.1 Single well systems

Since single well systems use the same well for both injection and recovery the minimum

residence time of the injected water is equivalent to the storage time ts. The

biodegradation of any contaminant that may be present in the injectant during this time is

assumed to follow simple first-order exponential decay (Figure 6). This is given as:

: where t= ts: Eqn. (1)

Biodegradation

t

c

Figure 5: Theoretical exponential decay curve

C(t)=C010-λt

τλ /1010)(

ss tt

oC

tC −− ==

16

No allowance is made for absorption within the aquifer nor for mixing with the ambient

groundwater. Recall that a 1-log removal is the time for removal of 90 % of the

concentration of any contaminant, a 2-log removal 99 %, a 3-log removal 99.9 % and a

4-log removal is 99.99 %.

4.2 Dual well systems

The worst-case scenario considers the water that has travelled to the recovery well along

the shortest flow path when the injection and recovery wells are operating continuously (at

the same rate). This gives the minimum travel time (tmin) over which biodegradation can

occur. The smallest travel time occurs when there is a regional hydraulic gradient in the

aquifer and the recovery well is situated directly downgradiant of the injection well.

Dilution with ambient groundwater is neglected as this effect leads to enhanced

contaminant attenuation. Adsorption is considered to retard the transport of contaminants,

thereby extending the time available for biodegradation to occur.

The analytical solutions that follow allow the calculation of the minimum travel time and

distance between wells for various configurations that are necessary to achieve the desired

level of contaminant attenuation.

Dual well systems operate with distinct injection and recovery wells, which are separated

by the distance L [m]. It is assumed that the flow system is in steady-state and that the

injection and recovery rates, Q are equal and both wells operate continuously. The aquifer

is assumed to be homogeneous, with uniform thickness D [m] and porosity ne. The

Darcian velocity νdo describes the initial uniform flow field in the aquifer before the ASR

system operates, where νdo is defined as positive in the direction from the injection well

towards the recovery well.

In such a two well system, it can be shown that the minimum residence time of water

between injection and recovery is given by equation 3, as derived in Rhebergen and Dillon,

(1999).

do

e

vDLQ

Lnt

+=

π3min Eqn.(3)

If the ambient groundwater velocity is small with respect to the gradients induced by the

injection and recovery wells, then the groundwater velocity can be ignored and the

equation simplifies to:

Q

LDnt e

3

2

min

π= Eqn. (4)

17

As continuous concurrent injection and recovery rarely occur, this equation is likely to

underestimate travel time because when wells are operated intermittently the average

hydraulic effective gradient over the time of travel will be less than the value which has

been assumed in this equation (worst-case scenario).

4.2.1 Adsorption

If adsorption of some contaminant follows a linear isotherm, then it can be shown that the

movement of that contaminant is retarded with respect to the movement of water. That

is, the minimum residence time of species, t min i is given by:

t min i = R tmin Eqn. (5)

where R, the retardation factor, is defined as:

R = 1 + Kd ρ / ne Eqn. (6)

and Kd = foc Koc Eqn. (7)

where Kd is the distribution coefficient for a linear adsorption isotherm [m3/kg]

ρ is the dry bulk density of the porous media [kg m-3]

foc is the weight fraction of organic carbon in the porous media [-]

Koc is the adsorption coefficient related to organic carbon content [m3 /kg OC]

Figure 7 illustrates the effect that retardation has on the travel time and the

biodegradation has on the concentration of the injectant. In this diagram of breakthrough

of contaminants at a recovery well, retardation extends the mean travel time from t1 to t2.

Biodegradation results in concentrations less than in the injectant reaching the recovery

well.

Figure 7: Breakthrough curves illustrating retardation and biodegradation

degradation

Retardation t1/t2

t

C 50%

Cg

Co

t1

t2

18

4.3 Nomogram for dual well system

According to Iyanaga and Kawada, (1980) a nomogram is a graphical plot which can be

used to solve certain types of equations. Figure 8 is the nomogram produced here that

combines equations 1, 3 and 5 for dual well systems. The nomogram is based on three

nondimensional terms, each of which have a practical meaning:

Term 1: The ratio of travel time to one log10 removal time τmint

Term 2: Advective transport expression due to pumping wells τQ

DRLne2

Term 3: Advective transport due to regional hydraulic gradient τdo

e

v

LRn

Term 1 is plotted against term 2 for constant values of term 3 (Figure 8). Because the log-

removal is linearly dependent on the travel time and decay rate λ, it is advantageous to

plot this as a second y-axis.

0

1

2

3

4

5

6

0 25 50

(ne*L2*D*R)/(Q*τ)

log

rem

ova

l

0

2

4

6

8

10

12

14

t min

/ τ

Legend

1

3

5

10

15

20

25

35

50

100

infinity

ne*L*R/vdo*τ

Figure 8: Nomogram for dual well ASR system (recovery well positioned down-gradient of

injection well)

The nomogram provides a useful tool for the planning of a dual well system, since one can

substitute values of separations distance L and flow rate Q, and for given aquifer

characteristics calculate the non-dimensional variables and immediately look up the

minimum travel time and corresponding extent of log-removal for the selected

parameters.

19

Increasing vdo or τ values reduces the ratio of travel to removal time (Term 1)

biodegradation, which results in a lower log removal. The figure clearly shows that there

are some combinations of characteristics where no realistic system design will produce

adequate log removal for satisfactory performance. In those areas ASR should be

prevented unless the injected water is adequately pre-treated. Conversely, higher ne, L

and R, values increase terms 2 and 3 to give more time available for biodegradation, and

result in a higher log removal. Note that the curve parameter tends towards infinity as vdo

approaches zero.

The nomogram can be used in various ways. For example, if the aim is to achieve a 4-log

removal then the curve parameter (term 3) must be greater than 25 and term 2 (i.e. x-

axis value) needs to exceed 14. To get a higher curve parameter or term 3 one can only

increase L (or Q) as the other parameters are intrinsic characteristics of the aquifer.

5. WELLS AT DIFFERENT ORIENTATIONS TO THE REGIONAL GRADIENT

Section 4 dealt with the worst-case scenario by considering the fastest flow path in a two

well system. An account of wells at different orientations to the regional gradient is given

to show the influence of regional flow on the travel time and also on the quantity of

injectant that can be recovered. Section 5.1 deals with the specific case where the

recovery well is upgradient of the injection well.

Figure 9: Nomogram for dual well ASR system (recovery well positioned upgradient of

injection well)

Dual well

0

1

2

3

4

5

6

0 2 4 6 8 10

(ne*L2*D*R)/(Q*t)

log

rem

ova

l

0

2

4

6

8

10

12

14

t min

/t

infinity

-100

-50

-20

-10

-3

-1

const. ne*L*R/vdo*tDual well

0

1

2

3

4

5

6

0 2 4 6 8 10

(ne*L2*D*R)/(Q*t)

log

rem

ova

l

0

2

4

6

8

10

12

14

t min

/t

infinity

-100

-50

-20

-10

-3

-1

const. ne*L*R/vdo*t

20

5.1 Recovery well upgradient of the injection well

For a horizontal initial hydraulic gradient (i.e. when term 3 is infinity) the line plotted on

Figure 9 corresponds exactly with that on Figure 8. For non-zero gradient the travel times

to an upgradient well (Figure 9) are all longer than this (νdo =0) case. Note that by

definition (Table 2) νdo is negative in this case and when its magnitude exceeds 3Q/πDL

there is a stagnation point between the injection and recovery wells that indicates no

injectant will reach the recovery well.

5.2 Recovery well positioned at different angles to the injection well

For completeness and in the event that this may be of interest, the effect was evaluated of

having well pairs that are not aligned with the direction of groundwater flow, Grove et al,

(1970) using the same assumptions as in this report (steady state flow, infinite confined

gomogeneous isotropic aquifer, uniform regional flow field and fully penetrating wells

operated simultaneously at the same uniform rate of injection and recovery), calculated

the proportion of injectant reaching the recovery well. This accounted for entrainment of

native groundwater, and considered advective flow only without dispersion. Results are

presented in Figures 10 to 13 for the recovery well downstream (∅=180o) (Figure 10)

upstream (∅=0o) (Figure 11) and for an intermediate case (∅=135o) (Figure 12).

The plots present the elapsed time for various percentages of injectant between the

injection and recovery wells. An angle of 0 degrees to the regional flow field is regarded as

upgradient flow from the injection to the recovery well, an angle of 180 degree as

downgradiant flow as described in section 4. The distance between the two wells is L = 2a.

The figures can be used in the following way: by calculating q/av0 one obtains the time

that a certain percentage of injectant will take to travel from the injection well to the

recovery well. Results for regional groundwater flow angles of 0, 135 and 180 degrees are

given. They depict three principal areas of flow: large values of q/av0 where pumping rates

or low regional groundwater velocities dominate, a transition zone or area where the curve

is nonlogarithmic, and low values of q/av0 where the regional groundwater flow component

predominates. For values of q/av0 larger than 104 the figures show that corresponding

values of tv0/aθ for identical percent returns are relatively independent of variations in the

angle and magnitude of areal flow. For very low pumping rates the magnitude and

direction of regional groundwater flow predominates. At areal flow angles of 180 degrees

(Figure ), as q/av0 approaches zero, the value of the tv0/ane approaches 2. This

represents the time for the water to flow 2a at a velocity v0/ne. For any angle other than

180 degrees there is a lower limit of q/av0 for which no flow will return to the well and the

value will increase without limit. This is evident for the flow angle 135 degrees (Figure 12).

21

Figure 12 shows zero return for an angle of 135 degrees and a q/av0 value of

approximately 1.8, which would represent the lower value of q/av0 that could return any

flow from one well to the other.

Figure 13 shows the composite effects of all angles on the proportion of injectant

recovered for different values of q/av0. It is possible to accumulate the proportions of

recovered flow with different residence times in order to deduce log removal but this has

not been done in this report.

Figure 10: Relationship of variables for injection-recovery well pair with areal flow of 180 degrees (from Grove et al, 1970)

22

Figure 11: Relationship of variables for injection-recovery well pair with areal flow of 0 degrees (from Grove et al, 1970)

23

Figure 12: Relationship of variables for injection-recovery well pair with areal flow of 135

degrees (from Grove et al, 1970)

24

Figure 13: The proportion of injectant reaching a recovery well positioned at different angles relative to aerial flow for different values of q/av0 (from Grove et al, 1970)

6. APPLICATION TO THE BANDUNG BASIN

In this section some of the techniques that have been described are applied to the

Bandung Basin. The minimum separation distance between the injection and recovery

wells will be determined for a range of hydrogeologic and operating conditions that are

typical of the shallow aquifers. It was previously shown that the two major parameters

that influence the travel time from the injection to the recovery well are the hydraulic

gradient and the pumping rate, and an evaluation of the existing spatial data for each of

these parameters will be evaluated.

The fate of pathogens in the groundwater represents the greatest single threat to public

health from recharge enhancement using waters of impaired quality and therefore the

focus of this analysis will be in achieving a minimum degree of microbial attenuation. A 4-

log removal is recommended for surface water that could be injected, whilst for roof-runoff

a 1-log removal would normally be enough as it is inherently of better quality. Rates of

pathogen attenuation are derived from the literature (Toze et al, 2003).

6.1 Hydraulic gradients

The shallow aquifers of the Bandung Basin were classified into regions with different

hydraulic gradients. The classification system used is derived from Scott, (1982) who

partitioned hydraulic gradients into several classes. From the mountain ranges in the north

and south towards the Citarum River valley there is a gradual decline in the hydraulic

gradient (Figure 14). The flatter areas have a hydraulic gradient of <1 %. In areas above

the 670 m contour level the hydraulic gradient may be as high as 17 %.

25

Figure 14: Hydraulic gradients of the shallow aquifer of the Bandung Basin (modified

from Sukrisno and Suyono, 1990)

26

6.2 Well yields

The Bandung Basin was divided into regions with different well yields by Suhari

and Siebenhuner, (1993)(Figure 15). The classification is as follows:

• generally low well yields (< 2 l/s)

• low to moderate well yields (2 – 10 l/s)

• moderate to high well yields (> 10 l/s)

The major part of the shallow aquifers have low well yields. In the centre of the

Bandung Basin and around the townships of Majalaya, Ciwidey, Cicalengka and

Lembang the shallow aquifers have low to moderate well yields. Moderate to high

well yields only occur in isolated patches in the centre of the basin and north and

east of Lembang. In this analysis it is assumed that well yield is a reasonable

approximation of injection and recovery rates.

Figure 15: Well yields in the Bandung Basin (after Suhari and Siebenhuner, 1993)

27

6.3 Separation distances between wells

The well yield and hydraulic gradient maps were reproduced to the same scale

and overlain as best as could be achieved given the accuracy of the maps. The

formation of zones with a specific hydraulic gradient (i) and well (Q) yield allows

the assignment of L, the distance between the injection and recovery well

necessary for a certain log removal, for each region. There were nine possible

combinations (3 hydraulic gradients x 3 well yields). Zone 1 corresponds with the

smallest separation distance and zone 9 the largest. Seven of the nine different

combinations of well yields and hydraulic gradients occur in the basin (Table 3),

although zones 7 and 9 did not occur (Figure 16). Zones 1 and 2 take in most of

the area of the Bandung Basin, whereas the other zones are mostly distributed as

small patches.

Table 3: Zones defined by overlapping well yields and hydraulic gradients map

i Q <2l/s Q = 2-10 l/s Q >10 l/s

<1 % Zone 1: low i, low Q Zone 4: low i, moderate Q Zone 7: low i, high Q

1 to 10 % Zone 2: low to moderate i, low Q Zone 5: low to moderate i, moderate Q Zone 8: low to moderate i, high Q

10 to 17 % Zone 3: moderate i, low Q Zone 6: moderate i, moderate Q Zone 9: moderate i, high Q

To calculate L values for each zone the following assumptions were made:

• Typical aquifer parameters of the Bandung Basin are:

o K= 1m/d upper (worst-case) estimate from Sukrisno and Suyono,

(1990)

o ne= 0.1 to 0.3 (estimated range)

o D= 10 to 40 m (from Soetrisno, 1998b)

• R= 1 (i.e. no retardation)

• Injection and recovery rates (from well yield data):

o <2 l/s is set to 1 l/s

o 2 – 10 l/s is set to 5 l/s

o > 10 l/s is set to 10 l/s

• Hydraulic gradients:

o < 1% is set to 0.01 %

o 1 – 10 % is set to 10 %

o 10 – 17 % is set to 17%

• τ = 10 to 40 days (from Toze et al, 2003 for most pathogens)

• Target removal is either 1- log or 4- log

The calculated separation distances (L) for 4-log removal are: 27 to 365m (for

τ =10 days); and 57 to 947m (for τ =40 days) (Tables 4 & 5).

For the calculations of a 1-log removal the results are: 13 to 159m (for τ = 10

days); and 27 to 365m (for τ = 40 days) (Table 6).

28

High values of L are required for low aquifer thickness, low porosity, high

hydraulic gradient and high flow rate. Conversely, low values of L are required for

high aquifer thickness, high porosity, low hydraulic gradient and low flow rate.

Table 4: Recommended separation distances (m) between injection and recovery wells for different zones for 4- log removal, τ =10 days

τ =10d

D=10m

D=40m

Zone Q [l/s] Vdo [m/d] ne=0.1 ne=0.3 ne=0.1 ne=0.3

1 1 0.01 92 52 48 27

2 0.1 144 68 109 45

3 0.17 195 83 168 62

4 5 0.01 200 114 102 58

5 0.1 246 129 154 74

6 0.17 288 142 203 88

7 10 0.01 280 161 143 81

8 0.1 326 175 191 96

9 0.17 365 187 237 110


τ =40d

D=10m

D=40m


1 1 0.01 193 107 107 57

2 0.1 438 179 388 141

3 0.17 671 249 638 220

4 5 0.01 409 231 214 119

5 0.1 615 295 452 190

6 0.17 813 352 682 258

7 10 0.01 570 325 295 165

8 0.1 765 386 516 232

9 0.17 947 439 730 295

29


τ =10

D=10m

D=40m


1 1 0.01 45 25 23 13

2 0.1 56 29 36 17

3 0.17 67 32 49 21

4 5 0.01 99 57 50 29

5 0.1 110 60 62 32

6 0.17 119 63 72 35

7 10 0.01 139 80 70 40

8 0.1 150 83 81 44

9 0.17 159 86 91 47


τ =40d

D=10m

D=40m


1 1 0.01 92 52 48 27

2 0.1 144 68 109 45

3 0.17 195 83 168 62

4 5 0.01 199 114 102 58

5 0.1 246 129 154 74

6 0.17 288 142 203 88

7 10 0.01 280 161 142 81

8 0.1 325 175 191 96

9 0.17 365 187 237 110

30

Figure

16:

Zon

es w

ith d

iffe

rent

separa

tion

dis

tance

s bet

wee

n w

ells

31

Clearly for simplicity, zones with similar minimum separation distances could be

merged. More work is needed to define actual die-off rates of pathogens in these

aquifers and to evaluate water quality impacts of existing trials being undertaken

by the University of Padjadjaran. This would involve drilling observation wells,

recording injection volumes and timing, sampling and analysis of injectant and

groundwater.

7. CONCLUSIONS

Conservative simplifying assumptions about solute transport and degradation in

aquifers have been used to determine distances over which a preconditioned

minimum level of pathogen die-off occurs in aquifers during ASR (this may also

be used as an analogue for biodegradation of synthetic and organic compounds).

Maps of hydraulic gradient and well yield have been used to characterize regions

in the shallow aquifer system of the Bandung Basin for which pathogen die-off are

expected to be consistent. The results obtained indicate that 1-log removal

distances vary from 17m to 365m, for 4-log removals from 27m to 947m. This

suggests that individual domestic scale ASR with water containing pathogens are

quite likely to influence groundwater users at nearby wells. Hence we recommend

that at domestic scale only roof runoff be admitted to injection wells, so that the

level of dependence on the aquifer for water treatment may be reduced unless

surface water is adequately disinfected prior to recharge. If only 1-log removal is

needed because of the improved quality of the injectant, this approximately

halves the distance for removal as compared to 4-logs for the dual well case.

It is possible that by consolidating neighbouring small wells into a water supply

from one single well, that the spacing between wells could increase so that 4-log

removal is achieved before injectant reaches a supply well. Larger scale systems

involving offices and factories may be viable where land parcels are larger and

production wells are already further apart. The contrast in minimum

recommended distances between wells in the different characteristic regions

ranges over a factor of 4. The smallest acceptable separation distances occur in

flat low yielding areas that most commonly occur in the central part of the

Bandung Basin. The more problematic areas, requiring larger separation distances

between wells occur on the margins of the Bandung Basin where the aquifer is

higher yielding and hydraulic gradients are steeper.

The application of either single or dual well ASR systems in the Bandung Basin

would be improved through the collection of further hydrogeological data in

conjunction with the undertaking of pilot recharge enhancement trials. One

promising project is taking place in the area between the cities of Soreang,

Banjaran and the Citarum River, where Dr. Prawoto of the University of

32

Padjadjaran is investigating recharge enhancement to the shallow aquifers using

infiltration basins.

8. RECOMMENDATIONS

It is recommended that before adopting recharge wells as a strategy to mitigate

further declines in groundwater levels, that pilot trials of recharge wells using roof

runoff be undertaken. These trials should include observations of:

• rainfall intensity and magnitude

• volume and rate of runoff harvested and injected

• quality of water injected

• groundwater levels

• groundwater quality

• production rates and volumes from nearby wells

• quality of water from nearby wells

Sites should be chosen to match:

• area of catchment of high quality water to yield of wells

• to avoid areas with shallow or polluted water tables

• where measurements can be easily undertaken and where there is a

demand for groundwater

Better understanding is needed of:

• aquifer hydraulic properties

• pathogen attenuation rates (by research at demonstration sites)

• groundwater quality

The relevant government authorities should consider approaches to regulating

recharge enhancement to:

• encourage good practices

• encourage its practice at locations where it is desirable

• prevent harm to the aquifer and public health

Develop operating principles to:

• isolate water to be injected from potential pollutants – e.g. by cleaning of

gutters and pipes

• managing clogging of wells – e.g. by back flushing, rapid sand filtration

• managing runoff by use of storage tanks to increase the proportion of

rainfall that is recharged and to control local flooding

33

9. REFERENCES

Bender, H. (1981): Training in the Bandung Basin: Contributions to the

hydrogeology of the Bandung Basin; Technical Cooperation

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unpublished.

Bukit, Nana Terangna (1995): Water quality conservation for the Citarum River in

West Java; Wat. Sci. Tech Vol.31, No.9, pp.1-10, IAWQ, Great

Britain.

Dillon, P.J. and Pavelic, P. (1996): Guidelines on the quality of stormwater and

treated wastewater for injection into aquifers for storage and

reuse. Urban Water Research Assoc of Aust., Research Report No

109, July 1996, 48p.

Geyh, M.A. (1990): Isotopic hydrological sounding in the Bandung Basin,

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recharging and discharging well pair in an aquifer having a

uniform regional flow field; Water Resources Research, Vol.6,

No.5, pp.1404-1410.

Iyanaga, S. and Kawada, Y. (1980): Encyclopaedic Dictionary of Mathematics.

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34

Rhebergen, W. and Dillon, P. (1999): Riverbank filtration models for assessing

viability of water quality improvement. Centre for Groundwater Studies Report

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protection in selected parts of the Bandung Basin; Project Report

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Land Use and Research, Commonwealth Scientific and Industrial

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for water conservation in Bandung Basin; 2nd CGS National Short

Course on ASR, Adelaide, 27-29 October 1999.

35

Suryantoro, Ir.S. (1999): Groundwater resources management in Indonesia;

paper presented at the National Seminar on the decentralization

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