Metals in Retention Pond Sediments

coriandercultureMechanics

Feb 22, 2014 (3 years and 8 months ago)

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Sedimentation and
Sediment Quality in SUDS
Ponds

Alan J Jones


Industrial CASE PhD Studentship

Funded by:

Overview

1.
Background Context

2.
Physical sedimentation &
geomorphology in Retention Ponds

3.
Geochemical processes &
contamination in Retention Ponds

4.
Aims & direction of research

Justification


Excessive build
-
up of sediment in Retention Ponds


reduction in flow attenuation capacity


Water residence time reduced


less time for
settling of suspended sediments and contaminants


Need to establish maintenance costs:


Frequency of excavation


Volumes of sediment involved


Quality of excavated sediments


Route of disposal


Permeable substrate


leaching of contaminants
into aquifers


contamination of potable water

Retention Ponds


Flow attenuation of retention ponds is well
-
characterised: lumped modelling (Wallis
et
al.
, In press)


Research into sedimentation:


Field
-
based sampling (numerous studies)


Flume
-
based transportation modelling
(Krishnappan and Marsalek, 2002)


Computational fluid dynamics (CFD) modelling
of storage tanks (Adamsson
et al.,
2003)


But need to understand sedimentological
effects on the long
-
term performance of
ponds

Retention Ponds

Falkirk Stadium Retention Pond (Undeveloped catchment)

Retention Ponds

Lidl Distribution Centre, Livingston
-

Retention Pond (Loading
bay, Carpark runoff)

Physical Sedimentation
Processes

Inflow
Outflow
Precipitation
Evaporation
Advection and Diffusion
Deposition
Morphological
Feedback
Flocculation
Infiltration
Sediment
Accumulation
Sedimentation in Retention
Ponds


Rates in ponds are generally low:





Highly variable spatially and temporally, and
depends upon several factors:


Climate


Land
-
use


Grain size


Basin design


Position in treatment
-
train

Yousef
et al.

(1994)

Striegl (1987)

Marsalek
et al.

(1997)

0.00783 m a
-
1

0.02 m a
-
1

0.02 m a
-
1

Morphological

Development

Morphological
Conditioning?


Research into channel confluences has
shown that form and process cannot be
easily separated (Lane, 1998)





Reflexive and reciprocal nature


positive
feedback


In less dynamic structures, such as
retention ponds, is this concept tenable?

Hypothesis: Flow short
-
circuiting


Flow short circuiting is
demonstrated in the
literature (Marsalek
et
al.
, 1997) and known
to occur in retention
ponds in Scotland
(Stenton Pond,
Glenrothes)



Does this exacerbate morphological conditioning?


Is this based purely on the inlet/outlet configuration
or does pond
-
design (i.e. initial morphological
state) promote or inhibit flow
-
short circuiting?


What structures develop as retention ponds age?


Morphological Evidence

Plunge pool
/ Scour Zone

Bar Deposits

Graded Deposits

(Coarse


Fine)

Morphological Evidence

Fan
Development

Sediment Quality


What are the processes controlling the
depositional fate of contaminants in
ponds?



Need to examine:


Sources


Transportation/conveyance processes


Depositional processes

Land
-
Use & Contamination

Vehicles

Pavement

Surface Debris

Brakes

Tyres

Frame &
Body

Fuels &
Oils

Concrete

Asphalt

De
-
icing
Salts

Litter

Cadmium (Cd)

Chromium (Cr)

Copper (Cu)

Iron (Fe)

Lead (Pb)

Nickel (Ni)

Vanadium (V)

Zinc (Zn)

Chlorides

Organic Solids

Inorganic Solids

PAHs

Phenols

(Beasley and Kneale, 2002)

Heavy Metal
-
Sediment
Dynamics


No obvious signature for heavy metals and
land
-
use


As metals are transported from source to
deposit


variety of processes occur:


Partitioning


Metal Speciation


Adsorption


Complexation


Precipitation


Extraneous influence of local lithology (Vicente
-
Beckett, 1992) and seasonality (Mungur
et al.,

1995)

Metals in Retention Pond
Sediments


Literature review


Pond data


Examined ponds in Sweden, Florida,
Oregon, North Carolina, Ontario,
Dunfermline and Edinburgh.


Aggregate of the data shows:


No association between 6 metals studied


Zinc (Zn) has the largest range of values,
Cadmium (Cd) the smallest.

C
o
n
c
e
n
t
r
a
t
i
o
n

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i
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r
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r
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m
s
/
g
r
a
m
)
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n
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b
C
u
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r
C
d
8
0
7
0
6
0
5
0
4
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0
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0
0
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n
t
e
r
v
a
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l
o
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o
f

C
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,

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r
,

C
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,

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b
,

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,

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n
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a
r
s

a
r
e

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M
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a
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Metals in Retention Pond
Sediments

Metals in Retention Pond
Sediments


Concentrations in Inlet/Outlet deposits
show no consistent relationship


0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Cd
Cr
Cu
Pb
Ni
Zn
Metal
Concentration (micrograms/gram)
Inlet
Inlet
Outlet
0
5
10
15
20
25
Cd
Cr
Cu
Pb
Ni
Zn
Metal
Concentration (micrograms/gram)
Inlet (EF1)
Outlet (EF3)
Echo Farms Pond, Wilmington, North Carolina

(Mallin et al., 2002)


Vallby, Vasteras, Central Sweden

(Färm, 2002)

Increase

in
concentration from Inlet
to Outlet

Decrease

in
concentration from Inlet
to Outlet

Sediment Quality Issues


Need to understand the relationships and
relative importance of metal
-
sediment
interactions:


For source
-
to
-
deposit transportation
and


Depositional fate in retention ponds


Can these processes be modelled for
individual ponds?


Look further at tracing techniques since
fingerprinting techniques (e.g.
137
Cs and
mineral magnetics) have proven ineffective
(Charlesworth
et al.
, 2000)


Research Questions

1.
What processes control the spatial and temporal
distribution of


sediments within retention ponds?


heavy metals within retention ponds?

2.
Which morphological structures develop over time within
retention ponds?

3.
To what extent does morphological feedback control the
hydrodynamics of the retention pond?

4.
Do these morphologies affect the capability of the pond to
attenuate flow and capture sediment?

5.
Does any relationship exist between emergent
morphological structures and the depositional fate of heavy
metals?

6.
How can this information be used to inform remedial
practices such as the dredging of sediments?

7.
What are the cost
-
effective and environmentally friendly
disposal routes for excavated SUDS sediments?

Current Work: Method
Development


Scoping study of Retention Ponds in Scotland:


22 sites visited in the last few weeks


Assess the suitability of GPR for constructing a
high resolution DEM of pond bathymetry:


In conjunction with core samples, reconstruct depositional
history of the basin


Examine tracing techniques:


Provenance of sediment


Influence of land
-
use on pond sediment geochemistry


Review existing modelling capabilities:


Computational modelling/CFD


Simulation of different initial pond designs


Simulate dispersal of heavy metals