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ATRANS

Analytical Solutions for Three-Dimensional Solute Transport from a Patch Source

Appendix A: Derivations of the solutions

D:\ATRANS\Documentation\ATRANS_Manual_Appendix_A.doc

Table of Contents

__________________________________________________________ Page

1. Governing Equation __________________________________________________ 2

Initial and Boundary Conditions_________________________________________ 2 Inflow Boundary Conditions____________________________________________ 3

2. Green’s Function: Solution for a Point Boundary Condition of Time-Varying Concentration _______________________________________________________ 4

3. Solution for a General Time-varying Patch Boundary Condition ______________ 11

4. Solution for Constant Inflow Concentration_______________________________ 13

5. Solution for an Arbitrary Inflow Concentration Defined as a Set of Steps _______ 15

6. Solution for an Exponentially Decaying Inflow Concentration ________________ 18

7. Solutions for Degenerate Cases ________________________________________ 21

7.1. 2D Solutions ____________________________________________________ 21 7.1.1. 2D Areal Transport _______________________________________________ 21 7.1.2. 2D Cross-sectional Transport _______________________________________ 23

7.2. 1D Transport ____________________________________________________ 38

1. Governing Equation Starting from the statement of mass conservation:

2 2 2x y zc c c c cR q D D D R ct x x y z

θ θ θ θ θ λ∂ ∂ ∂ ∂ ∂= − + + + −

∂ ∂ ∂ ∂ ∂

divide through by θ :

2 2 2x y zc c c c cR v D D D R ct x x y z

λ∂ ∂ ∂ ∂ ∂= − + + + −

∂ ∂ ∂ ∂ ∂

where: qVθ

= = average linear ground-water velocity

Dividing through by R yields:

2 2 2' ' '

2 2 2' x y zc c c c cv D D D ct x x y z

λ∂ ∂ ∂ ∂ ∂= − + + + −

∂ ∂ ∂ ∂ ∂

where: ' vvR

= ; ' xx

= ; ' yy

R= ; ' z

Initial and Boundary Conditions • Initial conditions: ( ), , ,0 0.0c x y z = • Boundary conditions:

i) ( ) ( ) ( ) ( ) ( ) ( )( )

0 0 0 1 20, , ,:

, , , 0

c y z t c t H y y H y y H z z H z zx

c y z t

⎡ = + − − − − −⎡ ⎤ ⎡ ⎤⎣ ⎦ ⎣ ⎦⎢∞ =⎢⎣

ii) ( )( )

, , , 0:

, , , 0

c x z ty

c x z t

−∞ =⎡⎢

∞ =⎢⎣

iii) ( )

, ,0, 0:

, , , 0

c x y tzzc x y B tz

∂⎡ =⎢∂⎢∂⎢ =⎢∂⎣

Interpretation of the inflow boundary conditions The function ( )H α β− is the Heaviside step function, defined as:

( ) 01

H α β− =

α βα β

The function ( )0c t represent an arbitrary time-varying concentration history at the patch on the inflow boundary.

2. Green’s Function: Solution for a Point Boundary Condition of Time-Varying Concentration

The solution for a general time-varying boundary condition is derived using a Green’s function approach. The general solution is expressed as:

( ) ( ) ( )00

, , , , , ,t

c x y z t G x y z t c dτ τ τ= −∫

In the general formula, G represents the Green’s function, which is the solution for a pulse boundary condition.. The boundary condition for the Green’s function solution is: ( ) ( ) ( ) ( )00, , , ' 'c y z t c t y y z zδ δ= − − 1) Applying the Laplace transform w.r.t. time:

( ), , ,0pc c x y z−2 2 20 ' ' '

2 2 2' 0x y zc c c cv D D D cx x y z

λ∂ ∂ ∂ ∂⎡ ⎤ + − − − + =⎢ ⎥⎣ ⎦ ∂ ∂ ∂ ∂

Substituting in the initial conditions:

' ' '2 2 2' 0x y z

c c c cpc v D D D cx x y z

λ∂ ∂ ∂ ∂+ − − − + =

∂ ∂ ∂ ∂

The transformed boundary conditions are:

( ) ( ) ( ) ( )( )( )( )

00, , , ' '

, , , 0

, ,0, 0

, , , 0

c y z p c p y y z z

c y z p

c x z p

c x z pc x y pzc x y B pz

δ δ= − −

−∞ =

∂∂

2) Applying the Fourier exponential transform w.r.t. y:

2 2' 2 '

12 2' 0x y zc c cpc v D D c D cx x z

α λ∂ ∂ ∂+ − + − + =

∂ ∂ ∂

( ) ( ) { } ( )( )

0 10, , , exp ' '

, , , 0

, ,0, 0

, , , 0

c z p c p i y z z

c z pc x pzc x B pz

α α δ

= − −

∂∂

3) Applying the finite Fourier cosine transform w.r.t. z:

( ) ( ) ( )2 2 2

' 2 '12 2' 1 0 0n

x y zc c c c np c v D D c D B c cx x z z B

πα λ≡ ≡

≡ ≡ ≡ ≡⎡ ⎤∂ ∂ ∂ ∂+ − + − − − − + =⎢ ⎥

∂ ∂ ∂ ∂⎢ ⎥⎣ ⎦

Substituting in the boundary conditions:

' ' 2 '12 2' 0x y z

c c np c v D D c D c cx x B

πα λ≡ ≡

≡ ≡ ≡ ≡∂ ∂+ − + + + =

∂ ∂

( ) ( ) { }

0 1'0, , , exp ' cos

, , , 0

n zc n p c p i yB

πα α

⎛ ⎞= − ⎜ ⎟⎝ ⎠

4) The transformed governing equation can be written as:

' 0x x

c v c p cx D x D

≡ ≡≡∂ ∂

− − =∂ ∂

where: 2 2

' 2 '1 2y z

nP p D DBπλ α= + + +

The general solution of the transformed governing equation is:

{ } { }exp expc A r x B r x≡

− += +

where: 2 2

' ' ' ' ''

' ' ' 1 '2 2 2 4x x x x xx

v v P v vr PD D D D DD

± ⎛ ⎞= ± + = ± +⎜ ⎟

⎝ ⎠

The coefficients A and B are evaluated by considering the boundary conditions.

a. x → ∞ : Since the solution is bounded, we must have:

b. 0x = : The general solution reduces to:

{ }expc A r x≡

−= Evaluating the boundary condition:

( ) { }

, , , exp

'exp ' cos

xc x n p A r x

n zc p i yB

≡−

⎛ ⎞= − ⎜ ⎟⎝ ⎠

∴ ( ) { }0 1'exp ' cos n zA c p i y

Bπα ⎛ ⎞= − ⎜ ⎟

⎝ ⎠

Therefore, the transformed solution is:

( ) { }1

0 1 ' ' '

' ' 'exp ' cos exp exp2 4x x x

n z v x v xc c p i y PB D D Dπα

≡⎧ ⎫

⎧ ⎫ ⎛ ⎞⎪ ⎪⎛ ⎞= − − +⎨ ⎬ ⎨ ⎬⎜ ⎟⎜ ⎟⎝ ⎠ ⎩ ⎭ ⎝ ⎠⎪ ⎪⎩ ⎭

5) Applying the inverse Laplace transform:

{ } ( )

11 0' ' '

' ' 'exp ' cos exp exp2 4x x x

n z v x v xi y L c p PB D D Dπα

≡−

⎡ ⎤= ⎢ ⎥⎣ ⎦⎡ ⎤⎧ ⎫

⎧ ⎫ ⎛ ⎞⎪ ⎪⎛ ⎞ ⎢ ⎥= − − +⎨ ⎬ ⎨ ⎬⎜ ⎟⎜ ⎟ ⎢ ⎥⎝ ⎠ ⎩ ⎭ ⎝ ⎠⎪ ⎪⎢ ⎥⎩ ⎭⎣ ⎦

The inverse Laplace transform is evaluated using the convolution theorem:

( ) ( ) ( ) ( )1

L f p g p f g t dτ τ τ− ⎡ ⎤⋅ = −⎣ ⎦ ∫

Letting:

( ) ( ) ( ) ( )

'exp4 x x

f p c p f t c t

v xg p PD D

= → =

⎧ ⎫⎛ ⎞⎪ ⎪= − +⎨ ⎬⎜ ⎟⎝ ⎠⎪ ⎪⎩ ⎭

The second inverse is evaluated using the shift theorem:

( )2 2 2

' 2 ' 11 2 ' '

'exp exp4y z

n v xg t D D t L pB D Dπλ α −

⎡ ⎤⎧ ⎫⎧ ⎫⎡ ⎤⎛ ⎞⎪ ⎪ ⎪ ⎪⎢ ⎥= − + + + −⎨ ⎬ ⎨ ⎬⎢ ⎥⎜ ⎟⎢ ⎥⎝ ⎠⎪ ⎪⎣ ⎦ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎣ ⎦

The inverse Laplace transform is given by Churchill (1972) A.2 #82:

[ ]3 2

exp42 xx

x xL tD tDπ

−− ⎧ ⎫⋅ = −⎨ ⎬

⎩ ⎭

∴ ( )3 2 2 2 2

' 2 '21 2 ' ''

'exp exp4 42

y zx xx

x n v xg t t D D tB D D tDπλ α

− ⎧ ⎫⎡ ⎤ ⎧ ⎫⎛ ⎞⎪ ⎪= − + + + −⎨ ⎬ ⎨ ⎬⎢ ⎥⎜ ⎟⎝ ⎠⎪ ⎪ ⎩ ⎭⎣ ⎦⎩ ⎭

Substituting into the convolution integral yields:

{ } ( )( )

( ) ( )

1 0' '0

2 2 2 2' 2 '

1 2 ' '

' 'exp ' cos exp2 2

'exp4 4

y zx x

n z v x xc i y c tB D D

n v xD D t dB D D t

πα τ τπ

πλ α τ ττ

−⎧ ⎫⎛ ⎞= − −⎨ ⎬⎜ ⎟⎝ ⎠ ⎩ ⎭

⎧ ⎫⎡ ⎤⎛ ⎞⎪ ⎪⋅ − + + + − −⎨ ⎬⎢ ⎥⎜ ⎟ −⎝ ⎠⎪ ⎪⎣ ⎦⎩ ⎭

6) Applying the inverse Fourier exponential transform:

{ } ( )( )

( ) ( )

1 0''0

2 2 2 2' 2 '

1 2 ' '

' 'cos exp exp '22

'exp4 4

y zx x

x n z v x i y c t tB DD

n v xD D t dB D D t

π α τπ

πλ α τ ττ

−−

⎡ ⎤= ℑ ⎢ ⎥⎣ ⎦⎡⎧ ⎫⎛ ⎞= ℑ − −⎨ ⎬ ⎢⎜ ⎟

⎝ ⎠ ⎩ ⎭ ⎣

⎤⎧ ⎫⎡ ⎤⎛ ⎞⎪ ⎪⋅ − + + + − − ⎥⎨ ⎬⎢ ⎥⎜ ⎟ − ⎥⎝ ⎠⎪ ⎪⎣ ⎦⎩ ⎭ ⎦

Re-arranging the order of operations we can write:

( )( )

( ) ( )

{ } ( ){ }

2 2 2 2'

1 ' 21 1

' 'cos exp22

'exp4 4

exp ' exp

x n z v xc c tB DD

n v xD tB D D t

i y D t d

π τ τπ

πλ ττ

α α τ τ

⎧ ⎫⎛ ⎞= −⎨ ⎬⎜ ⎟⎝ ⎠ ⎩ ⎭

⎧ ⎫⎡ ⎤⎛ ⎞⎪ ⎪⋅ − + + − −⎨ ⎬⎢ ⎥⎜ ⎟ −⎝ ⎠⎪ ⎪⎣ ⎦⎩ ⎭⎡ ⎤⋅ℑ − − −⎣ ⎦

The inverse can be evaluated using the convolution theorem:

( ) ( ) ( ) ( )11 1e f g f g y dα α ξ ξ ξ

∞−

−∞

⎡ ⎤ℑ ⋅ = −⎣ ⎦ ∫

( ) { } ( ) ( )

( ) ( ){ } ( )( ) ( )

1 1 ''

exp ' '

1exp exp42

f i y f y y y

yg D t g yD tD t

α α δ

α α ττπ τ

= − → = −

⎧ ⎫⎪ ⎪= − − → = −⎨ ⎬−− ⎪ ⎪⎩ ⎭

Therefore, the inverse is:

[ ] ( )( )

( )( )

1' exp42

D tD t

ξδ ξ ξ

τπ τ

∞−

−∞

⎧ ⎫−⎪ ⎪ℑ ⋅ = − −⎨ ⎬−− ⎪ ⎪⎩ ⎭∫

Noting the properties of the Dirac δ function, the inverse reduces:

[ ]( )

( )( )

'1 exp42

y yD tD t τπ τ

−⎧ ⎫−⎪ ⎪ℑ ⋅ = −⎨ ⎬−− ⎪ ⎪⎩ ⎭

Finally, substituting into the solution for c yields:

( )( )

( ) ( )( )

0 2'' '0

22 2 2 2'

2 ' ' '

' ' 1cos exp24

''exp4 4 4

zx x y

x n z v xc cB D tD D

y yn v xD t dB D D t D t

π ττπ

πλ τ ττ τ

⎧ ⎫⎛ ⎞= ⎨ ⎬⎜ ⎟⎝ ⎠ −⎩ ⎭

⎧ ⎫⎡ ⎤ −⎛ ⎞⎪ ⎪⋅ − + + − − −⎨ ⎬⎢ ⎥⎜ ⎟ − −⎝ ⎠⎣ ⎦⎪ ⎪⎩ ⎭

7) Applying the inverse Fourier cosine transform:

[ ]( ) ( )

0 2 cos

c n n zc nB B B

= ⎛ ⎞= + ⎜ ⎟⎝ ⎠

∴ ( )( )0 2'' '

' 1exp24

x v xc cD tB D D

ττπ

⎧ ⎫= ⎨ ⎬

−⎩ ⎭∫

( ) ( )( )

( )( )

( ) ( )( )

( )( )

0 2'' '0

' 'exp

' 1exp22

' 'exp

'cos exp cos

v t y yxt dD D t D t

x v x cD tB D D

v t y yxtD D t D t

n z n n zD tB B B

τλ τ τ

ττπ

τλ τ

π π πτ∞

⎧ ⎫− −⎪ ⎪⋅ − − − − −⎨ ⎬− −⎪ ⎪⎩ ⎭⎧ ⎫

+ ⎨ ⎬−⎩ ⎭

⎧ ⎫− −⎪ ⎪⋅ − − − − −⎨ ⎬− −⎪ ⎪⎩ ⎭⎧ ⎫⎛ ⎞ ⎛ ⎞⋅ − −⎨ ⎬⎜ ⎟ ⎜

⎝ ⎠ ⎝ ⎠⎩ ⎭

∑ dτ⎟

The final form of the Green’s function solution is obtained by recognizing that:

( )( )

( )( )( )

' ' ' '

'''exp exp exp2 4 4 4x x x x

x v tv tv x xD D D t D t

τττ τ

⎧ ⎫− −⎧ ⎫−⎧ ⎫ ⎪ ⎪ ⎪ ⎪⋅ − − ≡ −⎨ ⎬ ⎨ ⎬ ⎨ ⎬− −⎪ ⎪⎩ ⎭ ⎩ ⎭ ⎪ ⎪⎩ ⎭

Collecting terms and simplifying:

( )( ) ( )( )

( )( )

0 2 ' '' '0

' '1 exp4 44

'1 2 cos exp cos

x yx y

x v t y yxc c tD t D ttB D D

n z n n zD t dB B B

ττ λ τ

τ ττπ

π π πτ τ∞

⎧ ⎫− − −⎪ ⎪= − − − −⎨ ⎬− −− ⎪ ⎪⎩ ⎭⎡ ⎤⎧ ⎫⎛ ⎞ ⎛ ⎞⋅ + − −⎨ ⎬⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎩ ⎭⎣ ⎦

3. Solution for a General Time-varying Patch Boundary Condition

The patch boundary condition is derived by extending the Green’s function solution from –y0 to y0, and from z1 to z2.

i.e., ( )02

, : ', : ', ' 'yz

c c x y y z z t dy dz−

= ∫ ∫

Substituting in the Green’s function solution and re-arranging yields:

( )( )

( ) ( )( )( )

( )( )

0 2' '0

' 'exp

'1 2 cos exp cos ' '

z yx y

xc ctB D D

x v t y yt

D t D t

n z n n zD t d dy dzB B B

ττπ

τλ τ

π π πτ τ

⎧ ⎫− − −⎪ ⎪⋅ − − − −⎨ ⎬− −⎪ ⎪⎩ ⎭⎡ ⎤⎧ ⎫⎛ ⎞ ⎛ ⎞⋅ + − −⎨ ⎬⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎩ ⎭⎣ ⎦

∫ ∫ ∫

Re-arranging the order of integration:

( )( )

( ) ( )( )( )

( )( ) ( )

0 2 '' '0

2 2 2'

'1 exp44

' 'exp ' 1 2 cos exp cos '4

znyy z

x v txc c tD ttB D D

y y n z n n zdy D t dz dD t B B B

ττ λ τ

ττπ

π π πτ ττ

⎧ ⎫− −⎪ ⎪= ⋅ − − −⎨ ⎬−− ⎪ ⎪⎩ ⎭⎧ ⎫ ⎡ ⎤− ⎧ ⎫⎪ ⎪ ⎛ ⎞ ⎛ ⎞⋅ − + − −⎨ ⎬ ⎨ ⎬⎢ ⎥⎜ ⎟ ⎜ ⎟− ⎝ ⎠ ⎝ ⎠⎩ ⎭⎣ ⎦⎪ ⎪⎩ ⎭

∑∫ ∫

Noting the following integrals:

i) ( )( ) ( ) ( )

2' 0 0

'exp '

yyy y y

y y y y y ydy D t erfc erfcD t D t D t

π ττ τ τ−

⎡ ⎤⎧ ⎫ ⎧ ⎫⎧ ⎫− − +⎪ ⎪ ⎪ ⎪ ⎪ ⎪⎢ ⎥− = − −⎨ ⎬ ⎨ ⎬ ⎨ ⎬⎢ ⎥− − −⎪ ⎪ ⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭ ⎩ ⎭⎣ ⎦∫

ii) ( )2

'1 2 cos exp cos 'z

n z n n zD t dzB B Bπ π πτ

⎡ ⎤⎧ ⎫⎛ ⎞ ⎛ ⎞+ − −⎨ ⎬⎢ ⎥⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠⎩ ⎭⎣ ⎦

∑∫

( ) ( )2 2

'2 12 1 2

2 1 sin sin cos exp zn

n z n zB n z nz z D tn B B B B

π π π π τπ

⎧ ⎫⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞= − + − − −⎨ ⎬⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎩ ⎭∑

The final form of the solution becomes:

( )( )

( ) ( )( )( )

( ) ( )

0 3 ''0 2

0 0' '

2 22 1 '2 1

'1 exp44

2 1 'sin sin cos exp

x v txc c tD tD t

y y y yerfc erfcD t D t

z z n z n z n z nD tB n B B B B

ττ λ τ

τπ τ

π π π π τπ =

⎧ ⎫− −⎪ ⎪= ⋅ − − −⎨ ⎬−⎪ ⎪− ⎩ ⎭

⎡ ⎤⎧ ⎫ ⎧ ⎫− +⎪ ⎪ ⎪ ⎪⎢ ⎥⋅ −⎨ ⎬ ⎨ ⎬⎢ ⎥− −⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎣ ⎦

− ⎧ ⎫⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞⋅ + − − −⎨ ⎬⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎩ ⎭

dτ∞⎛ ⎞

⎜ ⎟⎝ ⎠

4. Solution for Constant Inflow Concentration A constant inflow concentration is defined as: ( )0 0c t C=

Substituting for ( )0C t in the general solution yields:

0 3 '' ' '0 2

2 22 1 '2 1

'1 exp44 2 2

2 1 sin sin cos exp

xx y y

x v y y y yxc C erfc erfcDD D D

z z n z n z n z nD dB n B B B B

ξλξ

ξπ ξ ξξ

π π π π ξ ξπ

⎡ ⎤⎧ ⎫ ⎧ ⎫⎧ ⎫− − +⎪ ⎪ ⎪ ⎪ ⎪ ⎪⎢ ⎥= − − −⎨ ⎬ ⎨ ⎬ ⎨ ⎬⎢ ⎥⎪ ⎪ ⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭ ⎩ ⎭⎣ ⎦

⎛ ⎞− ⎧ ⎫⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞⋅ + − −⎜ ⎟⎨ ⎬⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎩ ⎭⎝ ⎠

The integral can be accelerated by scaling to the fourth power.

Defining: 14τ ξ=

→ 4ξ τ= and 34d dξ τ τ= the limits of integration become:

= → =

Therefore, the solution can be rewritten as:

4 0 00 3 ' 4' ' 4 ' 4

2 22 1 ' 42 1

'14 exp44 2 2

2 1 sin sin cos exp

xx y y

x v y y y yxc C erfc erfcDD D D

τλτ

τ τπ τ τ

π π π π τπ

⎡ ⎤⎧ ⎫ ⎧ ⎫ ⎧ ⎫− − +⎪ ⎪ ⎪ ⎪ ⎪ ⎪⎢ ⎥= − − −⎨ ⎬ ⎨ ⎬ ⎨ ⎬⎢ ⎥⎪ ⎪ ⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎩ ⎭ ⎣ ⎦⎛ ⎞− ⎧ ⎫⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞⋅ + − −⎜ ⎟⎨ ⎬⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎩ ⎭⎝ ⎠

∑ τ

5. Solution for an Arbitrary Inflow Concentration Defined as a Set of Steps

Consider a time-varying inflow concentration defined as a set of NP steps:

Denoting ti as the starting time for the ith step, and ∆Ci as the concentration change at the start of the ith step, the inflow concentration history is defined as:

( ) ( )1

o i ii

C t C H t t=

= ∆ −∑

( )H ⋅ is the Heaviside step function:

( ) 01

H t U− =

t Ut U

Substituting for ( )0C t in the solution for an arbitrary inflow concentration history:

( )( )

( ) ( )( )( )

( ) ( )( )

3 ''10 2

2 10 0' '

'1 exp44

2 1 sin sin cos exp

i ii xx

x v txc C H t tD tD t

z zy y y yerfc erfcBD t D t

n z n z n z nDn B B B

ττ λ τ

τπ τ

π π ππ

⎧ ⎫− −⎪ ⎪= ∆ − − − −⎨ ⎬−⎪ ⎪− ⎩ ⎭

⎡ ⎤⎧ ⎫ ⎧ ⎫ −⎛− +⎪ ⎪ ⎪ ⎪⎢ ⎥⋅ −⎨ ⎬ ⎨ ⎬ ⎜⎢ ⎥− − ⎝⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎣ ⎦

⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞+ − −⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦

∑∫

∑ ( )2 2

2 t dBπ τ τ

⎞⎧ ⎫− ⎟⎨ ⎬

⎩ ⎭⎠

Making use of the properties of the Heaviside function and re-arranging:

( )( ) ( )( )

( ) ( )( )

3 ''1 2

2 10 0' '

2 2'2 1

'1 exp44

2 1 sin sin cos exp

ii xtx

x v txc C tD tD t

n z n z n z nDn B B B B

τλ τ

τπ τ

π π π ππ

⎧ ⎫− −⎪ ⎪= ∆ − − −⎨ ⎬−⎪ ⎪− ⎩ ⎭

⎡ ⎤⎧ ⎫ ⎧ ⎫ −⎛− +⎪ ⎪ ⎪ ⎪⎢ ⎥⋅ −⎨ ⎬ ⎨ ⎬ ⎜⎢ ⎥− − ⎝⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎣ ⎦

⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞+ − −⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦

∑ ∫

∑ ( )2 t dτ τ⎞⎧ ⎫

− ⎟⎨ ⎬⎩ ⎭⎠

Make a change of variables:

→→

τ ξτ ξ

= −= −

= −=

Therefore the solution becomes:

3 ''1 0 2

2 10 0' '

2 2'2 1

'1 exp44

2 1 sin sin cos exp

it tNP

x vxc CDD

z zy y y yerfc erfcBD D

ξλξ

ξπ ξ

π π π π ξπ

⎧ ⎫−⎪ ⎪= ∆ − −⎨ ⎬⎪ ⎪⎩ ⎭

⎡ ⎤⎧ ⎫ ⎧ ⎫ −⎛− +⎪ ⎪ ⎪ ⎪⎢ ⎥⋅ −⎨ ⎬ ⎨ ⎬ ⎜⎢ ⎥ ⎝⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎣ ⎦⎞⎧ ⎫⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞+ − −⎨ ⎬⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎩ ⎭⎠

∑ ∫

∑ dξ⎟

Note: If NP=1 and t(1) = 0.0, the solution collapses to the solution for a constant patch concentration, with ( )1

0 1C C C= ∆ = . The integration can be accelerated by scaling the variable of integration to the 4th power:

Let: 14τ ξ=

→ 4ξ τ= ; 34d dξ τ τ= the limits of integration become:

it tξξ

== −

→ = −

and the solution is written as:

( ) ( )

3 ' 4'1 0

2 10 0' 4 ' 4

2 2' 42 1

'14 exp44

2 1 sin sin cos exp

it tNP

x vxc CDD

τλτ

τ τπ

π π π π τπ

⎧ ⎫−⎪ ⎪= ∆ − −⎨ ⎬⎪ ⎪⎩ ⎭

⎡ ⎤⎧ ⎫ ⎧ ⎫ −⎛− +⎪ ⎪ ⎪ ⎪⎢ ⎥⋅ −⎨ ⎬ ⎨ ⎬ ⎜⎢ ⎥ ⎝⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎣ ⎦

⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞+ − −⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦

∑ ∫

∑ dτ⎞⎧ ⎫⎟⎨ ⎬

⎩ ⎭⎠

6. Solution for an Exponentially Decaying Inflow Concentration

An exponentially-decaying concentration is defined as: ( ) { }0 0 expc t c tγ= − , where γ is the “source decay constant” (units of T-1).

Substituting for ( )0c t in the solution for an arbitrary time-varying inflow concentration:

{ }( )

( ) ( )( )( )

( ) ( )( )

0 3 ''0 2

2 10 0' '

2 2'2 1

'1exp exp44

2 1 sin sin cos exp

x v txc c tD tD t

n z n z n z nD tn B B B B

τγτ λ τ

τπ τ

π π π ππ

⎧ ⎫− −⎪ ⎪= − − − −⎨ ⎬−⎪ ⎪− ⎩ ⎭

⎡ ⎤⎧ ⎫ ⎧ ⎫ −⎛− +⎪ ⎪ ⎪ ⎪⎢ ⎥⋅ −⎨ ⎬ ⎨ ⎬ ⎜⎢ ⎥− − ⎝⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎣ ⎦

⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞+ − −⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦

∑ ( ) dτ τ⎞⎧ ⎫

− ⎟⎨ ⎬⎩ ⎭⎠

Collecting terms and re-arranging slightly:

( )( )( ) ( )

( ) ( )( )

0 3 ''0 2

2 10 0' '

2 2'2 1

'1 exp44

2 1 sin sin cos exp

x v txc c tD tD t

n z n z n z nD tn B B B B

τλ τ γτ

τπ τ

π π π π τπ

⎧ ⎫− −⎪ ⎪= − − − −⎨ ⎬−⎪ ⎪− ⎩ ⎭

⎡ ⎤⎧ ⎫ ⎧ ⎫ −⎛− +⎪ ⎪ ⎪ ⎪⎢ ⎥⋅ −⎨ ⎬ ⎨ ⎬ ⎜⎢ ⎥− − ⎝⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎣ ⎦

⎧⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞+ − − −⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦

∑ dτ⎞⎫⎟⎨ ⎬

⎩ ⎭⎠

Rearranging, this can be written as:

{ }( )

( )( )( ) ( )( )

( ) ( )( )

0 3 ''0 2

2 10 0' '

2 2'2 1

'1exp exp44

2 1 sin sin cos exp

x v txc c t tD tD t

τγ γ λ τ

τπ τ

π π π ππ

⎧ ⎫− −⎪ ⎪= − − + − −⎨ ⎬−⎪ ⎪− ⎩ ⎭

⎡ ⎤⎧ ⎫ ⎧ ⎫ −⎛− +⎪ ⎪ ⎪ ⎪⎢ ⎥⋅ −⎨ ⎬ ⎨ ⎬ ⎜⎢ ⎥− − ⎝⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎣ ⎦

⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞+ − −⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦

∑ ( )2 t dτ τ⎞⎧ ⎫

− ⎟⎨ ⎬⎩ ⎭⎠

Make a change of variables:

Define: tξ τ= − ∴ d dτ ξ= −

the limits of integration become:

ξ→ =→ =

and the integral is written as:

{ } ( ) ( )

0 3 ''0 2

2 10 0' '

2 2'2 1

'1exp exp44

2 1 sin sin cos exp

x vxc c tDD

n z n z n z nD dn B B B B

ξγ γ λ ξ

ξπ ξ

π π π π ξπ

⎧ ⎫−⎪ ⎪= − − + −⎨ ⎬⎪ ⎪⎩ ⎭

⎡ ⎤⎧ ⎫ ⎧ ⎫ −⎛− +⎪ ⎪ ⎪ ⎪⎢ ⎥⋅ −⎨ ⎬ ⎨ ⎬ ⎜⎢ ⎥ ⎝⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎣ ⎦⎞⎧ ⎫⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞+ − − ⎟⎨ ⎬⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎩ ⎭⎠

∑ ξ

Note: The integral can be accelerated by scaling the variable of integration to the 4th power.

Letting: 14τ ξ=

→ 4ξ τ= ; 34d dξ τ τ=

the limits of integration become:

= → =

The solution is written as:

{ } ( ) ( )

40 3 ' 4'

2 10 0' 4 ' 4

2 2' 42 1

'1exp 4 exp44

2 1 sin sin cos exp

x vxc c tDD

τγ γ λ τ

τ τπ

π π π π τπ

⎧ ⎫−⎪ ⎪= − − + −⎨ ⎬⎪ ⎪⎩ ⎭

⎡ ⎤⎧ ⎫ ⎧ ⎫ −⎛− +⎪ ⎪ ⎪ ⎪⎢ ⎥⋅ −⎨ ⎬ ⎨ ⎬ ⎜⎢ ⎥ ⎝⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎣ ⎦

⎧⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞+ − −⎨⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦

∑ dτ⎞⎫⎟⎬

⎩ ⎭⎠

Check: The solution for a constant source concentration should be obtained if 0.0γ = . Substituting for 0.0γ = yields:

4 0 00 3 ' 4' ' 4 ' 4

2 22 1 ' 42 1

'14 exp44 2 2

2 1 sin sin cos exp

xx y y

x v y y y yxc c erfc erfcDD D D

τλτ

τ τπ τ τ

π π π π τ τπ

⎡ ⎤⎧ ⎫ ⎧ ⎫ ⎧ ⎫− − +⎪ ⎪ ⎪ ⎪ ⎪ ⎪⎢ ⎥= − + −⎨ ⎬ ⎨ ⎬ ⎨ ⎬⎢ ⎥⎪ ⎪ ⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎩ ⎭ ⎣ ⎦⎞−⎛ ⎧ ⎫⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞+ − − ⎟⎨ ⎬⎜ ⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎩ ⎭⎝ ⎠

as before.

7. Solutions for Degenerate Cases 7.1. 2D Solutions 7.1.1. 2D Areal Transport The solution for 2D areal transport is obtained by specifying that the patch along the inflow boundary extends over the full thickness of the aquifer.

For 1 0z = and 2z B= , the general solution reduces to:

( )( )

( ) ( )( )( )

( ) ( )

0 3 ''0 2

0 0' '

'1 exp44

x v txc c tD tD t

y y y yerfc erfc dD t D t

ττ λ τ

τπ τ

ττ τ

⎧ ⎫− −⎪ ⎪= − − −⎨ ⎬−⎪ ⎪− ⎩ ⎭

⎡ ⎤⎧ ⎫ ⎧ ⎫− +⎪ ⎪ ⎪ ⎪⎢ ⎥−⎨ ⎬ ⎨ ⎬⎢ ⎥− −⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎣ ⎦

a. Solution for a Constant Patch Concentration

( )0 0c t c=

Substituting for ( )0c t in the general solution yields:

( ) ( )( )( )

( ) ( )

0 3 ''0 2

0 0' '

'1 exp44

x v txc c tD tD t

y y y yerfc erfc dD t D t

τλ τ

τπ τ

ττ τ

⎧ ⎫− −⎪ ⎪= − − −⎨ ⎬−⎪ ⎪− ⎩ ⎭

⎡ ⎤⎧ ⎫ ⎧ ⎫− +⎪ ⎪ ⎪ ⎪⎢ ⎥−⎨ ⎬ ⎨ ⎬⎢ ⎥− −⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎣ ⎦

Letting tξ τ= − , the integral is written as:

0 3 '' '0 2

'1 exp44 2

x v y yxc c erfcDD D

y yerfc dD

ξλξ

ξπ ξξ

⎡ ⎧ ⎫⎧ ⎫− −⎪ ⎪ ⎪ ⎪⎢= − −⎨ ⎬ ⎨ ⎬⎢⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎣

⎤⎧ ⎫+⎪ ⎪⎥− ⎨ ⎬⎥⎪ ⎪⎩ ⎭⎦

b. Dicretized Inflow Concentration History

3 ''1 0 2

0 0' '

'1 exp44

it tNP

x vxc CDD

y y y yerfc erfc dD D

ξλξ

ξπ ξ

ξξ ξ

⎧ ⎫−⎪ ⎪= ∆ − −⎨ ⎬⎪ ⎪⎩ ⎭

⎡ ⎤⎧ ⎫ ⎧ ⎫− +⎪ ⎪ ⎪ ⎪⎢ ⎥⋅ −⎨ ⎬ ⎨ ⎬⎢ ⎥⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎣ ⎦

∑ ∫

c. Exponentially-decaying Inflow Concentration

{ } ( ) ( )2

0 3 ''0 2

0 0' '

'1exp exp44

x vxc C tDD

y y y yerfc erfc dD D

ξγ γ λ ξ

ξπ ξ

ξξ ξ

⎧ ⎫−⎪ ⎪= − − + −⎨ ⎬⎪ ⎪⎩ ⎭

⎡ ⎤⎧ ⎫ ⎧ ⎫− +⎪ ⎪ ⎪ ⎪⎢ ⎥⋅ −⎨ ⎬ ⎨ ⎬⎢ ⎥⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎣ ⎦

7.1.2. 2D Cross-sectional Transport The solution for 2D cross-sectional transport is obtained by specifying that patch is very extensive along the transverse horizontal. 0y → ∞ Noting the following limits:

( )( )

−∞ =

the general solution reduces to:

( )( )

( ) ( )( )( )

2 10 3 ''

2 2'2 1

'1 exp42

2 1 sin sin cos exp

x v t z zxc c tD t BD t

n z n z n z nD t dn B B B B

ττ λ τ

τπ τ

π π π π τ τπ

⎧ ⎫− − −⎛⎪ ⎪= − − −⎨ ⎬⎜− ⎝⎪ ⎪− ⎩ ⎭

⎞⎧ ⎫⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞+ − − − ⎟⎨ ⎬⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎩ ⎭⎠

a. Constant Patch Concentration

Substituting for ( )0 0c t c= in the general solution yields:

( )( ) ( )( )

( )( )

2 10 3 ''

2 2'2 1

'1 exp42

2 1 sin sin cos exp

x v t z zxc c tD t BD t

n z n z n z nD t dn B B B B

τλ τ

τπ τ

π π π π τ τπ

⎧ ⎫− − −⎛⎪ ⎪= − − −⎨ ⎬⎜− ⎝⎪ ⎪− ⎩ ⎭

⎞⎧ ⎫⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞+ − − − ⎟⎨ ⎬⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎩ ⎭⎠

Defining tξ τ= − , the solution can be written as:

( ) ( )22 1

0 3 ''0 2

2 2'2 1

'1 exp42

2 1 sin sin cos exp

x v z zxc cD BD

ξλξ

ξπ ξ

π π π π ξ ξπ

⎧ ⎫− −⎛⎪ ⎪= − −⎨ ⎬⎜⎝⎪ ⎪⎩ ⎭

⎞⎧ ⎫⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞+ − − ⎟⎨ ⎬⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎩ ⎭⎠

The integral can be evaluated by first splitting it into two parts: 1 2I I I= + where:

( ) ( )

1 3 '0 2

2 3 '10 2

'1 exp4

'2 1 1exp sin sin4

cos exp

z z x vI d

x v n z n zID n B B

n z nD dB B

ξλξ ξ

ξ π πλξπ ξ

π π ξ ξ

⎧ ⎫− −⎪ ⎪= − −⎨ ⎬⎪ ⎪⎩ ⎭

⎧ ⎫− ⎡ ⎤⎪ ⎪ ⎛ ⎞ ⎛ ⎞= − − −⎨ ⎬ ⎜ ⎟ ⎜ ⎟⎢ ⎥⎝ ⎠ ⎝ ⎠⎣ ⎦⎪ ⎪⎩ ⎭

⎧ ⎫⎛ ⎞⋅ −⎨ ⎬⎜ ⎟⎝ ⎠ ⎩ ⎭

∑∫

(i) Evaluating the first integral:

( ) ( )22 1

1 3 '0 2

'1 exp4

z z x vI d

λξ ξξξ

⎧ ⎫− −⎪ ⎪= − −⎨ ⎬⎪ ⎪⎩ ⎭

Expanding and re-arranging the exponential term:

' 'exp exp exp2 4 4x x x

xv v xD D D

λ ξξ

⎧ ⎫⎧ ⎫ ⎛ ⎞⎪ ⎪⋅ = ⋅ − + −⎨ ⎬ ⎨ ⎬⎜ ⎟⎪ ⎪⎩ ⎭ ⎝ ⎠⎩ ⎭

Defining:

The integral becomes:

( ) 22 1 2

1 3'0 2

' 1exp exp2

z z xv bI a dB D

ξ ξξξ

− ⎧ ⎫ ⎧ ⎫= − −⎨ ⎬ ⎨ ⎬

⎩ ⎭⎩ ⎭∫

The integral is given in S.H. Cho’s table of integrals #2.9.5:

{ } { }

exp 2 exp 22

t ba d

b bab erfc a t ab erfc a tb t t

ξ ξξ

⎧ ⎫− −⎨ ⎬

⎩ ⎭

⎛ ⎞⎧ ⎫ ⎧ ⎫= − − + +⎨ ⎬ ⎨ ⎬⎜ ⎟⎩ ⎭ ⎩ ⎭⎝ ⎠

Substituting for a and b, I1 becomes:

' 2 22 1

1 ' ''

1 12 22 2

' '' '

' 'exp exp2 4

' 'exp4 42

x xx x

Dz z xv x vIB D x DD

x v x verfc tD DD t D

x verfc tDD t

⎛ ⎧ ⎫− ⎧ ⎫ ⎛ ⎞⎪ ⎪⎜= − +⎨ ⎬ ⎨ ⎬⎜ ⎟⎜⎩ ⎭ ⎝ ⎠⎪ ⎪⎜ ⎩ ⎭⎝

⎧ ⎫ ⎧ ⎫⎛ ⎞ ⎛ ⎞⎪ ⎪ ⎪ ⎪⋅ − + + +⎨ ⎬ ⎨ ⎬⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭

⎞⎧ ⎫⎛ ⎞⎪ ⎪⎟⋅ + +⎨ ⎬⎜ ⎟ ⎟⎝ ⎠⎪ ⎪⎟⎩ ⎭⎠

(ii) Evaluating the second integral:

2 12 3 '

'2 1 1exp sin sin4

cos exp

x v n z n zID n B B

n z nD dB B

ξ π πλξπ ξ

π π ξ ξ

⎧ ⎫− ⎡ ⎤⎪ ⎪ ⎛ ⎞ ⎛ ⎞= − − −⎨ ⎬ ⎜ ⎟ ⎜ ⎟⎢ ⎥⎝ ⎠ ⎝ ⎠⎣ ⎦⎪ ⎪⎩ ⎭

⎧ ⎫⎛ ⎞⋅ −⎨ ⎬⎜ ⎟⎝ ⎠ ⎩ ⎭

∑∫

Re-arranging the orders of the summation and integration, collecting the exponential terms and expanding, the exponential term becomes:

{}2 2 2 2

'' ' 2 '

' 'exp exp exp2 4 4z

xv v n xDD D B D

πλ ξξ

⎧ ⎫⎧ ⎫ ⎛ ⎞⎪ ⎪⋅ = ⋅ − + + −⎨ ⎬ ⎨ ⎬⎜ ⎟⎪ ⎪⎩ ⎭ ⎝ ⎠⎩ ⎭

Defining:

2 2 22 '

v na DD B

πλ= + +

2 12 '

2 ' 1exp sin sin cos2

n z n zxv n zID n B B B

π π ππ

ξ ξξξ

⎧ ⎫ ⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞= −⎨ ⎬ ⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦⎩ ⎭⎧ ⎫

− −⎨ ⎬⎩ ⎭

Using the integral given in S.H. Cho’s table (#2.9.5) again, and defining:

2 2 2 2'

v nDD B

πµ λ⎡ ⎤

= + +⎢ ⎥⎣ ⎦

and substituting for a and b, I2 becomes:

2 12 '

Dn z n zxv n zID n B B B x

x xerfc tD D t

ππ π ππ

⎧ ⎫ ⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞= −⎨ ⎬ ⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦⎩ ⎭⎛ ⎧ ⎫ ⎧ ⎫⎪ ⎪ ⎪ ⎪⎜⋅ − −⎨ ⎬ ⎨ ⎬⎜ ⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎝

⎞⎧ ⎫ ⎧ ⎫⎪ ⎪ ⎪ ⎪⎟+ +⎨ ⎬ ⎨ ⎬⎟⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎠

Substituting for I1 and I2:

1 12 22 2

' '' '

1 12 22 2

' '' '

'exp22

' 'exp4 42

x xx x

xc I ID

Dz zx xvB D xD

x v x verfc tD DD D t

− ⎧ ⎫= ⎨ ⎬

⎩ ⎭

⎛ ⎧ ⎫ ⎧ ⎫⎛ ⎞ ⎛ ⎞⎪ ⎪ ⎪ ⎪⎜ − + − +⎨ ⎬ ⎨ ⎬⎜ ⎟ ⎜ ⎟⎜ ⎝ ⎠ ⎝ ⎠⎪ ⎪ ⎪ ⎪⎜ ⎩ ⎭ ⎩ ⎭⎝

⎧ ⎫ ⎧⎛ ⎞ ⎛ ⎞⎪ ⎪ ⎪+ + + +⎨ ⎬ ⎨⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠⎪ ⎪⎩ ⎭ ⎩

n z n zxv n zD n B B B

D x xerfc tx D D t

x xerfc tD D t

π π ππ

πµ µ

⎞⎫⎪⎟⎬⎟

⎪ ⎪⎟⎭⎠⎧ ⎫ ⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞+ −⎨ ⎬ ⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦⎩ ⎭⎛ ⎧ ⎫ ⎧ ⎫⎪ ⎪ ⎪ ⎪⎜⋅ − −⎨ ⎬ ⎨ ⎬⎜ ⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎝

⎞⎧ ⎫ ⎧ ⎫⎪ ⎪ ⎪ ⎪⎟+ +⎨ ⎬ ⎨ ⎬⎟⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎠

Simplifying:

( )2 10'

1 12 22 2

' '' '

1 12 22 2

' '' '

'exp2 2

' 'exp4 42

x xx x

z zc xvcD B

−⎧ ⎫= ⎨ ⎬

⎩ ⎭⎛ ⎧ ⎫ ⎧ ⎫

⎛ ⎞ ⎛ ⎞⎪ ⎪ ⎪ ⎪⎜⋅ − + − +⎨ ⎬ ⎨ ⎬⎜ ⎟ ⎜ ⎟⎜ ⎝ ⎠ ⎝ ⎠⎪ ⎪ ⎪ ⎪⎜ ⎩ ⎭ ⎩ ⎭⎝⎞⎧ ⎫ ⎧ ⎫

⎛ ⎞ ⎛ ⎞⎪ ⎪ ⎪ ⎪⎟+ + + +⎨ ⎬ ⎨ ⎬⎜ ⎟ ⎜ ⎟ ⎟⎝ ⎠ ⎝ ⎠⎪ ⎪ ⎪ ⎪⎟⎩ ⎭ ⎩ ⎭⎠

sin sin cos

n z n z n zB B B

x xerfc tD D t

π π π

⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞− ⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦⎛ ⎧ ⎫ ⎧ ⎫⎪ ⎪ ⎪ ⎪⎜⋅ − −⎨ ⎬ ⎨ ⎬⎜ ⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎝

⎞⎧ ⎫ ⎧ ⎫⎪ ⎪ ⎪ ⎪⎟+ +⎨ ⎬ ⎨ ⎬⎟⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎠

b. Discretized Inflow Concentration History

( ) ( )22 1

3 ''1 0 2

2 2'2 1

'1 exp42

2 1 sin sin cos exp

it tNP

x v z zxc CD BD

ξλξ

ξπ ξ

π π π π ξ ξπ

⎧ ⎫− −⎛⎪ ⎪= ∆ − −⎨ ⎬⎜⎝⎪ ⎪⎩ ⎭

⎞⎧ ⎫⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞+ − − ⎟⎨ ⎬⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎩ ⎭⎠

∑ ∫

Defining the integral as:

( ) ( ) ( )2 22 1

3 3' '0 2 2

2 2'2 1

' '1 2 1exp exp4 4

1 sin sin cos exp

z z x v x vI

ξ ξλξ λξ

ξ π ξξ ξ

π π π π ξ ξ

⎡ ⎤ ⎡⎧ ⎫ ⎧ ⎫− − −⎪ ⎪ ⎪ ⎪⎢ ⎥ ⎢= − − + − −⎨ ⎬ ⎨ ⎬⎢ ⎥ ⎢⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎢ ⎥ ⎢⎣ ⎦ ⎣⎤⎧ ⎫⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞⋅ − −⎨ ⎬⎥⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎩ ⎭⎦

The integral can be evaluated by first splitting it into two parts: 1 2I I I= + where:

( ) ( )2

2 11 3 '

'1 exp4

z z x vI d

λξ ξξ

− ⎧ ⎫− −⎪ ⎪= − −⎨ ⎬⎪ ⎪⎩ ⎭

( )22 1

2 3 '10 2

'2 1 1exp sin sin4

cos exp

x v n z n zID n B B

n z nD dB B

ξ π πλξπ ξ

π π ξ ξ

− ∞

⎧ ⎫− ⎡ ⎤⎪ ⎪ ⎛ ⎞ ⎛ ⎞= − − −⎨ ⎬ ⎜ ⎟ ⎜ ⎟⎢ ⎥⎝ ⎠ ⎝ ⎠⎣ ⎦⎪ ⎪⎩ ⎭

⎧ ⎫⎛ ⎞⋅ −⎨ ⎬⎜ ⎟⎝ ⎠ ⎩ ⎭

∑∫

( ) ( )22 1

1 3 '0 2

'1 exp4

z z x vI d

λξ ξξξ

− ⎧ ⎫− −⎪ ⎪= − −⎨ ⎬⎪ ⎪⎩ ⎭

' 'exp exp2 4 4x x x

xv v xexpD D D

λ ξξ

⎧ ⎫⎧ ⎫ ⎛ ⎞⎪ ⎪⋅ = ⋅ − + −⎨ ⎬ ⎨ ⎬⎜ ⎟⎪ ⎪⎩ ⎭ ⎝ ⎠⎩ ⎭

Defining:

( ) 22 1 2

1 3'0 2

' 1exp exp2

z z xv bI a dB D

ξ ξξξ

−− ⎧ ⎫ ⎧ ⎫= − −⎨ ⎬ ⎨ ⎬

⎩ ⎭⎩ ⎭∫

1 exp exp 22

b ba d ab erfc a t tb t t

bab erfc a t tt t

πξ ξξ

− ⎛ ⎧ ⎫⎧ ⎫ ⎪ ⎪⎜− − = − − −⎨ ⎬ ⎨ ⎬⎜ −⎩ ⎭ ⎪ ⎪⎩ ⎭⎝

⎞⎧ ⎫⎪ ⎪⎟+ + −⎨ ⎬⎟−⎪ ⎪⎩ ⎭⎠

1 12 22 2

' '' '

1 12 22 2

' '' '

' 'exp4 42

ix xx x i

Dz z xvIB D x

x v x verfc t tD DD D t t

− ⎧ ⎫= ⎨ ⎬

⎩ ⎭⎛ ⎧ ⎫ ⎧ ⎫

⎛ ⎞ ⎛ ⎞⎪ ⎪ ⎪ ⎪⎜⋅ − + − + −⎨ ⎬ ⎨ ⎬⎜ ⎟ ⎜ ⎟⎜ −⎝ ⎠ ⎝ ⎠⎪ ⎪ ⎪ ⎪⎜ ⎩ ⎭ ⎩ ⎭⎝⎞⎧ ⎫ ⎧ ⎫

⎛ ⎞ ⎛ ⎞⎪ ⎪ ⎪ ⎪⎟+ + + + −⎨ ⎬ ⎨ ⎬⎜ ⎟ ⎜ ⎟ ⎟−⎝ ⎠ ⎝ ⎠⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎠⎟

( )22 1

2 3 '10 2

'2 1 1exp sin sin4

cos exp

x v n z n zID n B B

n z nD dB B

ξ π πλξπ ξ

π π ξ ξ

− ∞

⎧ ⎫− ⎡ ⎤⎪ ⎪ ⎛ ⎞ ⎛ ⎞= − − −⎨ ⎬ ⎜ ⎟ ⎜ ⎟⎢ ⎥⎝ ⎠ ⎝ ⎠⎣ ⎦⎪ ⎪⎩ ⎭

⎧ ⎫⎛ ⎞⋅ −⎨ ⎬⎜ ⎟⎝ ⎠ ⎩ ⎭

∑∫

{}2 2 2 2

'' ' 2 '

' 'exp exp2 4 4z

xv v n xexp DD D B D

πλ ξξ

⎧ ⎫⎧ ⎫ ⎛ ⎞⎪ ⎪⋅ = ⋅ − + + −⎨ ⎬ ⎨ ⎬⎜ ⎟⎪ ⎪⎩ ⎭ ⎝ ⎠⎩ ⎭

Defining:

2 2 22 '

v na DD B

πλ= + +

2 12 '

1 expi

n z n zxv n zID n B B B

π π ππ

ξ ξξ

⎧ ⎫ ⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞= −⎨ ⎬ ⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦⎩ ⎭

⎧ ⎫− −⎨ ⎬

⎩ ⎭

2 2 2 2'

v nDD B

πµ λ⎡ ⎤

= + +⎢ ⎥⎣ ⎦

Dn z n zxv n zID n B B B x

x xerfc t tD D t t

ππ π ππ

⎧ ⎫ ⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞= −⎨ ⎬ ⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦⎩ ⎭⎛ ⎧ ⎫⎧ ⎫⎪ ⎪ ⎪ ⎪⎜⋅ − − −⎨ ⎬ ⎨ ⎬⎜ −⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎝

⎞⎧ ⎫⎧ ⎫⎪ ⎪ ⎪ ⎪⎟+ + −⎨ ⎬ ⎨ ⎬⎟−⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎠

Assembling the final solution and simplifying:

1 12 22 2

' '' '

1 12 22 2

' '' '

1 'exp2 2

' 'exp4 42

ix xx x i

z zxvc CD B

x v x verfc t tD DD D t t

−⎧ ⎫= ∆⎨ ⎬

⎩ ⎭⎛ ⎧ ⎫ ⎧ ⎫

⎛ ⎞ ⎛ ⎞⎪ ⎪ ⎪ ⎪⎜⋅ − + − + −⎨ ⎬ ⎨ ⎬⎜ ⎟ ⎜ ⎟⎜ −⎝ ⎠ ⎝ ⎠⎪ ⎪ ⎪ ⎪⎜ ⎩ ⎭ ⎩ ⎭⎝

⎧ ⎫ ⎧⎛ ⎞ ⎛ ⎞⎪ ⎪ ⎪+ + + + −⎨ ⎬ ⎨⎜ ⎟ ⎜ ⎟

−⎝ ⎠ ⎝ ⎠⎪ ⎪⎩ ⎭ ⎩

2 1 sin sin cos

n z n z n zn B B B

x xerfc t tD D t t

π π ππ

⎞⎫⎪⎟⎬⎟

⎪ ⎪⎟⎭⎠⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞+ − ⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦

⎛ ⎧ ⎫⎧ ⎫⎪ ⎪ ⎪ ⎪⎜⋅ − − −⎨ ⎬ ⎨ ⎬⎜ −⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎝

⎞⎧ ⎫⎧ ⎫⎪ ⎪ ⎪ ⎪⎟+ + −⎨ ⎬ ⎨ ⎬⎟−⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎠

• General solution:

{ } ( ) ( ) ( )22 1

0 3 ''0 2

2 2'2 1

'1exp exp42

2 1 sin sin cos exp

x v z zxc c tD BD

ξγ γ λ ξ

ξπ ξ

π π π π ξ ξπ

⎧ ⎫− −⎛⎪ ⎪= − − + −⎨ ⎬⎜⎝⎪ ⎪⎩ ⎭

⎞⎧ ⎫⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞+ − − ⎟⎨ ⎬⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎩ ⎭⎠

Alternative Solution Valid for ( )2

γ λ> − :

The solution can be re-written in an alternative form by splitting the integral into two parts:

( ) ( ) ( )

( ) ( )

2 1 3 3'0 02 2

'1 2 1exp4

' 1exp sin sin4

cos exp

x v BI z z dD

x v n z n zD n B B

n z nD dB B

ξγ λ ξ ξ

ξ πξ ξ

ξ π πγ λ ξξ

π π ξ ξ

⎧ ⎫−⎪ ⎪= − − + − +⎨ ⎬⎪ ⎪⎩ ⎭

⎧ ⎫− ⎡ ⎤⎪ ⎪ ⎛ ⎞ ⎛ ⎞⋅ − + − −⎨ ⎬ ⎜ ⎟ ⎜ ⎟⎢ ⎥⎝ ⎠ ⎝ ⎠⎣ ⎦⎪ ⎪⎩ ⎭⎧ ⎫⎛ ⎞⋅ −⎨ ⎬⎜ ⎟

⎝ ⎠ ⎩ ⎭= +

∫ ∫

where: ( ) ( ) ( )2

1 2 1 3 '0 2

'1 exp4

x vI z z d

γ λ ξ ξξξ

⎧ ⎫−⎪ ⎪= − − + −⎨ ⎬⎪ ⎪⎩ ⎭

and: ( ) ( )2

2 3 '0 2

'2 1 exp4

x vBID

ξγ λ ξ

π ξξ

⎧ ⎫−⎪ ⎪= − + −⎨ ⎬⎪ ⎪⎩ ⎭

1 sin sin cos exp zn

π π π π ξ ξ∞

⎧ ⎫⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞⋅ − −⎨ ⎬⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎩ ⎭∑

( ) ( ) ( )2

1 2 1 3 '0 2

'1 exp4

x vI z z d

γ λ ξ ξξξ

⎧ ⎫−⎪ ⎪= − − + −⎨ ⎬⎪ ⎪⎩ ⎭

{} ( )2 2

' 'exp exp exp2 4 4x x x

xv v xD D D

γ λ ξξ

⎧ ⎫⎧ ⎫ ⎛ ⎞⎪ ⎪⋅ = ⋅ − + − −⎨ ⎬ ⎨ ⎬⎜ ⎟⎪ ⎪⎩ ⎭ ⎝ ⎠⎩ ⎭

Defining:

γ λ= − − this is a valid expression if 2 0a >

21 2 1 3'

' 1exp exp2

xv bI z z a dD

ξ ξξξ

⎧ ⎫ ⎧ ⎫= − − −⎨ ⎬ ⎨ ⎬

⎩ ⎭⎩ ⎭∫

1 exp exp 22

t b ba d ab erfc a tb t

bab erfc a tt

πξ ξξξ

⎛⎧ ⎫ ⎧ ⎫− − = − −⎨ ⎬ ⎨ ⎬⎜⎩ ⎭⎩ ⎭ ⎝

⎞⎧ ⎫+ +⎨ ⎬⎟⎩ ⎭⎠

( ) ( )

1 2 1 '

1 12 22 2

' '' '

1 12 22 2

' '' '

' 'exp4 42

x xx x

DxvI z zD x

γ λ γ λ

⎧ ⎫= − ⎨ ⎬

⎩ ⎭⎛ ⎧ ⎫ ⎧ ⎫

⎛ ⎞ ⎛ ⎞⎪ ⎪ ⎪ ⎪⎜⋅ − − − − − −⎨ ⎬ ⎨ ⎬⎜ ⎟ ⎜ ⎟⎜ ⎝ ⎠ ⎝ ⎠⎪ ⎪ ⎪ ⎪⎜ ⎩ ⎭ ⎩ ⎭⎝⎞⎧ ⎫ ⎧ ⎫

⎛ ⎞ ⎛ ⎞⎪ ⎪ ⎪ ⎪⎟+ − − + − −⎨ ⎬ ⎨ ⎬⎜ ⎟ ⎜ ⎟ ⎟⎝ ⎠ ⎝ ⎠⎪ ⎪ ⎪ ⎪⎟⎩ ⎭ ⎩ ⎭⎠

( ) ( )2

2 3 '0 2

2 2'2 1

'2 1 exp4

1 sin sin cos exp

x vBID

ξγ λ ξ

π ξξ

π π π π ξ ξ∞

⎧ ⎫−⎪ ⎪= − + −⎨ ⎬⎪ ⎪⎩ ⎭

⎧ ⎫⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞⋅ − −⎨ ⎬⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎩ ⎭

{} ( )2 2 2 2

'' ' 2 '

' 'exp exp2 4 4z

xv v n xexp DD D B D

πγ λ ξξ

⎧ ⎫⎧ ⎫ ⎛ ⎞⎪ ⎪⋅ = ⋅ − − − + −⎨ ⎬ ⎨ ⎬⎜ ⎟⎪ ⎪⎩ ⎭ ⎝ ⎠⎩ ⎭

Defining:

( )2 2 2

2 '' 2

v na DD B

πγ λ= − − +

2 12 '

n z n zB xv n zID n B B B

π π ππ

ξ ξξξ

⎧ ⎫ ⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞= −⎨ ⎬ ⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦⎩ ⎭⎧ ⎫

− −⎨ ⎬⎩ ⎭

2 2 2 2'

v nDD B

πµ γ λ⎡ ⎤

= + − +⎢ ⎥⎣ ⎦

Dn z n zB xv n zID n B B B x

x xerfc tD D t

ππ π ππ

⎧ ⎫ ⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞= −⎨ ⎬ ⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦⎩ ⎭⎛ ⎧ ⎫ ⎧ ⎫⎪ ⎪ ⎪ ⎪⎜⋅ − −⎨ ⎬ ⎨ ⎬⎜ ⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎝

⎞⎧ ⎫ ⎧ ⎫⎪ ⎪ ⎪ ⎪⎟+ +⎨ ⎬ ⎨ ⎬⎟⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎠

Substituting for I1 and I2:

( ) '2 1

1 12 22 2

' '' '

1 12 22 2

' '' '

'exp22

' 'exp4 42

x xx x

Dz zx xvc cB D xD

− ⎧ ⎫= ∆ ⎨ ⎬

⎩ ⎭

⎛ ⎧ ⎫ ⎧ ⎫⎛ ⎞ ⎛ ⎞⎪ ⎪ ⎪ ⎪⎜⋅ − + − +⎨ ⎬ ⎨ ⎬⎜ ⎟ ⎜ ⎟⎜ ⎝ ⎠ ⎝ ⎠⎪ ⎪ ⎪ ⎪⎜ ⎩ ⎭ ⎩ ⎭⎝

⎧ ⎫ ⎧ ⎫⎛ ⎞ ⎛ ⎞⎪ ⎪ ⎪+ + + +⎨ ⎬ ⎨⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠⎪ ⎪ ⎪⎩ ⎭ ⎩

Dn z n zxv n zD n B B B x

x xerfc tD D t

ππ π ππ

⎞⎪⎟⎬⎟⎪⎟⎭⎠

⎧ ⎫ ⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞+ −⎨ ⎬ ⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦⎩ ⎭⎛ ⎧ ⎫ ⎧ ⎫⎪ ⎪ ⎪ ⎪⎜⋅ − −⎨ ⎬ ⎨ ⎬⎜ ⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎝

⎞⎧ ⎫ ⎧ ⎫⎪ ⎪ ⎪ ⎪⎟+ +⎨ ⎬ ⎨ ⎬⎟⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎠

Simplifying yields the final form of the solution:

( ) ( )

1 12 22 2

' '' '

1 12 22 2

' '' '

'exp2 2

' 'exp4 42

x xx x

z zc xvc tD B

γ λ γ λ

−⎧ ⎫= − +⎨ ⎬

⎩ ⎭⎛ ⎧ ⎫ ⎧ ⎫

⎛ ⎞ ⎛ ⎞⎪ ⎪ ⎪ ⎪⎜⋅ − − − − − −⎨ ⎬ ⎨ ⎬⎜ ⎟ ⎜ ⎟⎜ ⎝ ⎠ ⎝ ⎠⎪ ⎪ ⎪ ⎪⎜ ⎩ ⎭ ⎩ ⎭⎝⎞⎧ ⎫ ⎧ ⎫

⎛ ⎞ ⎛ ⎞⎪ ⎪ ⎪ ⎪+ − − + − −⎨ ⎬ ⎨ ⎬⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎠

2 1 sin sin cos

n z n z n zn B B B

x xerfc tD D t

π π ππ

⎟⎟⎟

⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞+ − ⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎣ ⎦⎛ ⎧ ⎫ ⎧ ⎫⎪ ⎪ ⎪ ⎪⎜⋅ − −⎨ ⎬ ⎨ ⎬⎜ ⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎝

⎞⎧ ⎫ ⎧ ⎫⎪ ⎪ ⎪ ⎪⎟+ +⎨ ⎬ ⎨ ⎬⎟⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎠

7.2. 1D Transport The solution for 1D transport is obtained by specifying that the patch along the inflow boundary both penetrates the aquifer completely, and is laterally extensive: i.e.,

0zz By

==→ ∞

For this case the general solution reduces to:

( )( )

( ) ( )( )( )

0 3 ''0 2

'1 exp42

x v txc c t dD tD t

ττ λ τ τ

τπ τ

⎧ ⎫− −⎪ ⎪= − − −⎨ ⎬−⎪ ⎪− ⎩ ⎭∫

a. Constant Inflow Concentration

Substituting ( )0 0c t c= in the general solution yields:

( ) ( )( )( )

0 3 ''0 2

'1 exp42

x v txc c t dD tD t

τλ τ τ

τπ τ

⎧ ⎫− −⎪ ⎪= − − −⎨ ⎬−⎪ ⎪− ⎩ ⎭∫

Defining tξ τ= − , the solution is written as:

0 3 ''0 2

'1 exp42

x vxc c dDD

ξλξ ξ

ξπ ξ

⎧ ⎫−⎪ ⎪= − −⎨ ⎬⎪ ⎪⎩ ⎭

Expanding the exponential term in the integrand:

{} ( )22

2 ' 'exp exp

' 'exp exp4 4 4

x xv vD

xv x vD D D

ξ ξλξ

λ ξξ

⎧ ⎫− +⎪ ⎪⋅ = − −⎨ ⎬⎪ ⎪⎩ ⎭

⎧ ⎫⎧ ⎫ ⎛ ⎞⎪ ⎪= − − − +⎨ ⎬ ⎨ ⎬⎜ ⎟⎪ ⎪⎩ ⎭ ⎝ ⎠⎩ ⎭

Letting: 2

The solution is written as:

20 3''

' 1exp exp42

x xv bc c a dDD

ξ ξξπ ξ

⎧ ⎫ ⎧ ⎫= − − −⎨ ⎬ ⎨ ⎬

⎩ ⎭⎩ ⎭∫

The integral is given by S.H. Cho #2.9.5:

{ } { }exp 2 exp 22

b bI ab erfc a t ab erfc a tb t tπ ⎛ ⎞⎧ ⎫ ⎧ ⎫= − − + +⎨ ⎬ ⎨ ⎬⎜ ⎟

⎩ ⎭ ⎩ ⎭⎝ ⎠

Substituting for a and b:

1 1 12 2 22 2 2

' ' ''

1 12 22 2

' '4 4 42

x x xx

v x x vabD D DD

x vb at tD D

⎛ ⎞ ⎛ ⎞ ⎛ ⎞= + = +⎜ ⎟ ⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠ ⎝ ⎠

⎛ ⎞ ⎛ ⎞− = − +⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠

⎛ ⎞ ⎛ ⎞+ = + +⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠

1 1 1' 2 2 22 2 2

' ' ''

' 1 'exp4 4 4

x x xx

D x v x vI erfc tx D D DtD

πλ λ

⎛ ⎧ ⎫⎧ ⎫ ⎡ ⎤⎛ ⎞ ⎛ ⎞ ⎛ ⎞⎜ ⎪ ⎪ ⎪ ⎪⎢ ⎥= − + − +⎨ ⎬ ⎨ ⎬⎜ ⎟ ⎜ ⎟ ⎜ ⎟⎜ ⎢ ⎥⎝ ⎠ ⎝ ⎠ ⎝ ⎠⎪ ⎪ ⎪ ⎪⎜ ⎢ ⎥⎩ ⎭ ⎣ ⎦⎩ ⎭⎝

1 1 12 2 22 2 2

' ' ''

' 1 'exp4 4 4x x xx

x v x verfc tD D DtD

λ λ⎞⎧ ⎫⎧ ⎫ ⎡ ⎤

⎛ ⎞ ⎛ ⎞ ⎛ ⎞⎪ ⎪ ⎪ ⎪⎟⎢ ⎥+ + + +⎨ ⎬ ⎨ ⎬⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎟⎢ ⎥⎝ ⎠ ⎝ ⎠ ⎝ ⎠⎪ ⎪ ⎪ ⎪⎟⎢ ⎥⎩ ⎭ ⎣ ⎦⎩ ⎭⎠

Defining

µ λ⎛ ⎞

= +⎜ ⎟⎝ ⎠

, the solution becomes:

' ' ' '

'exp42

exp exp2 2

x x x x

Dx xvc cD xD

x x x xerfc t erfc tD D t D D t

µ µµ µ

⎧ ⎫= −⎨ ⎬

⎩ ⎭

⎛ ⎞⎧ ⎫ ⎧ ⎫ ⎧ ⎫ ⎧ ⎫⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪⎜ ⎟⋅ − − + +⎨ ⎬ ⎨ ⎬ ⎨ ⎬ ⎨ ⎬⎜ ⎟⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭ ⎩ ⎭ ⎩ ⎭⎝ ⎠

Simplifying:

' ' ' '

1 'exp2 4

exp exp2 2

x x x x

xvc cD

x x x xerfc t erfc tD D t D D tµ µµ µ

⎧ ⎫= −⎨ ⎬

⎩ ⎭⎛ ⎞⎧ ⎫ ⎧ ⎫ ⎧ ⎫ ⎧ ⎫⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪⎜ ⎟⋅ − − + +⎨ ⎬ ⎨ ⎬ ⎨ ⎬ ⎨ ⎬⎜ ⎟⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭ ⎩ ⎭ ⎩ ⎭⎝ ⎠

b. Discretized Inflow Concentration History

3 ''1 0 2

'1 exp42

it tNP

x vxc c dDD

ξλξ ξ

ξπ ξ

⎧ ⎫−⎪ ⎪= ∆ − −⎨ ⎬⎪ ⎪⎩ ⎭

∑ ∫

Making use of the integral:

{ } { }

exp 2 exp 22

U ba d

b bab erfc a U ab erfc a Ub U U

ξ ξξ

⎧ ⎫− −⎨ ⎬

⎩ ⎭

⎛ ⎞⎧ ⎫ ⎧ ⎫= − − + +⎨ ⎬ ⎨ ⎬⎜ ⎟⎩ ⎭ ⎩ ⎭⎝ ⎠

the solution becomes:

' ' '1

1 'exp exp2 4 2

i iix x x i

xv x xc c erfc t tD D D t t

x xerfc t tD D t t

⎛ ⎧ ⎫⎧ ⎫⎧ ⎫ ⎪ ⎪ ⎪ ⎪⎜= ∆ − − −⎨ ⎬ ⎨ ⎬ ⎨ ⎬⎜ −⎩ ⎭ ⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎝⎞⎧ ⎫⎧ ⎫⎪ ⎪ ⎪ ⎪⎟+ + −⎨ ⎬ ⎨ ⎬⎟−⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎠

where:

µ λ⎛ ⎞

= +⎜ ⎟⎝ ⎠

• General solution:

{ } ( ) ( )2

0 3 ''0 2

'1exp exp42

x vxc c t dDD

ξγ γ λ ξ ξ

ξπ ξ

⎧ ⎫−⎪ ⎪= − − + −⎨ ⎬⎪ ⎪⎩ ⎭

An alternative form of this situation is written by expanding the exponential term in the integrand:

( ) ( )

2 ' 'exp4

' 'exp exp2 4 4

x xv vD

xv x vD D D

ξγ λ ξ

ξ ξ γ λ ξξ

ξ γ λ ξξ

⎧ ⎫−⎪ ⎪− + −⎨ ⎬⎪ ⎪⎩ ⎭

⎧ ⎫+ −= − + −⎨ ⎬

⎩ ⎭⎧ ⎫⎧ ⎫ ⎛ ⎞⎪ ⎪= − − − −⎨ ⎬ ⎨ ⎬⎜ ⎟⎪ ⎪⎩ ⎭ ⎝ ⎠⎩ ⎭

Substituting into the solution yields:

( )2 2

0 3' ' ''0 2

' 1 'exp exp2 4 42

x x xx

x xv x vc c t dD D DD

ξγ γ λ ξ ξξπ ξ

⎧ ⎫⎧ ⎫ ⎛ ⎞⎪ ⎪= − + − − − −⎨ ⎬ ⎨ ⎬⎜ ⎟⎪ ⎪⎩ ⎭ ⎝ ⎠⎩ ⎭

Alternative solution:

For the case of 2

γ λ≥ − , we can make use of the integral:

{ } { }

exp 2 exp 22

U ba d

b bab erfc a U ab erfc a Ub U U

ξ ξξ

⎧ ⎫− −⎨ ⎬

⎩ ⎭

⎛ ⎞⎧ ⎫ ⎧ ⎫= − − + +⎨ ⎬ ⎨ ⎬⎜ ⎟⎩ ⎭ ⎩ ⎭⎝ ⎠

and the alternate solution can be written as:

0' ' '

'exp exp2 2 2

c xv x xc t erfc tD D D t

x xerfc tD D t

µγ µ

⎛ ⎧ ⎫ ⎧ ⎫⎧ ⎫ ⎪ ⎪ ⎪ ⎪⎜= − + − −⎨ ⎬ ⎨ ⎬ ⎨ ⎬⎜⎩ ⎭ ⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎝⎞⎧ ⎫ ⎧ ⎫⎪ ⎪ ⎪ ⎪⎟+ +⎨ ⎬ ⎨ ⎬⎟⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭⎠

where: ( )1

µ γ λ⎛ ⎞

= − −⎜ ⎟⎝ ⎠

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