c. alternatives to dumping at sea
TRANSCRIPT
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C. Alternatives to Dumping at Sea
Attachment C.1(i): Alternative Dredge Material Management
The OSPAR Convention recognises that dredging is essential to maintain navigation in ports and
harbours as well as for the development of port facilities and that much of the material removed
during these necessary activities requires disposal at sea. Within the OSPAR Convention framework
dredged materials have been listed in Article 3.2 of Annex II as being permitted to be dumped at sea.
However the OSPAR Convention requires consideration of beneficial use of dredged materials, over
dumping at sea, where possible. The OSPAR Commission’s Guidelines for the Management of
Dredged Material (2009) states “that where no beneficial or financially viable use for dredged
material is available then disposal of material at sea is acceptable”.
When planning for both maintenance and capital dredging projects over the past decades the Port of
Waterford has assessed numerous potential dredge material management techniques other than
disposal at sea. However, to date all have been rejected due to technical, logistical, environmental and
economic issues (E.I.S. by Malone O'Regan, Attachment C.1(ii)).
However, prior to this license application a review of potential alternatives was undertaken for a
variety of techniques based on the hierarchy for prioritising dredge material management. This
hierarchy has been developed from the Waste Framework Directive (2008/98/EC), from which
Ireland’s Waste Management Acts are derived.
Hierarchy for Prioritising DM Management
Prevention
Re-use
Recycling
Treat to improve DM properties for potential reuse
Dispose DM in the aquatic environment or on land
Desirability
Processing/Recovery
Disposal
Retain the DM within the local
estuarine system
(Sediment Cell Maintenance)
Apply a beneficial use
technique
Avoid
dredging,
minimise
dredge
quantity
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Prevention
Without major capital works to train the flow of the rivers prevention of dredging is unfeasible.
Options to train individual sections of the River Suir to reduce sedimentation and hence dredging
requirement have been investigated substantially but to date no economically viable scheme has been
identified.
Minimising the quantity of dredge material generated should therefore be a priority as prevention is
impractical. However, consideration of the minimisation of dredging volumes is constantly being
undertaken by the Port of Waterford. Dredging is only undertaken when absolutely necessary to allow
trade safely navigate the approach channels and berths.
To minimise the volume of dredging undertaken the Port of Waterford operate a limited access
procedure in their navigation channels. This restricts the size of trade vessels that can reach suitable
berths at times other than high water. Further feasible methods to minimise the volumes dredged have
not been identified.
Beneficial Use
A beneficial use for DM is one that uses the material in a productive manner rather than mere
disposal; this recycling approach is not a new concept. Beneficial uses of DM can be categorised as
follows:
• Engineering uses;
• Environmental enhancement;
• Agricultural and product uses.
A review of the available information pertaining to the above categories was undertaken to determine
what the merits and limitations of each potential scheme was. The results of this review are included
in the following tables.
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Beneficial
Use
Description Advantages (+)/Disadvantages(-)
Land
Improvement
Filling, raising and
protecting a periodically submerged area and/or generally improve the quality of the land (e.g. public parks, replenishing agricultural soil, golf courses, sports fields, etc).
+ Provides a possibly cheaper and more environmentally conscious alternative to
disposal + Facilitates creation of land for port, industrial or agricultural use. + Potential profits to be made are substantial. � Not all DM may facilitate the basic requirements to sustain plant and animal life or
support appreciable loads. � Consolidation and drainage is slow, thus the strength achieved may be low. � May only be suitable for capital dredging projects. If long term development is not
acceptable sporadic maintenance dredging spoil cannot be used.
� Requires extensive impact studies of the local environment and ecology. � Water bed depth must be adequately shallow. � Quality of the foundation material must be adequate for final design use � Potential land ownership issues must be resolved.
Land
Reclamation
Raising a permanently
submerged area to use for a specific motive
Beach Nourishment
Replacement of the required quantities of sand and gravel material lost through the natural erosion
of beaches and shorelines.
+ Provides a naturally occurring aquatic material to replace a shortfall in a similar material.
+ Process could potentially operate in tandem with maintenance DM collection. + Tourism may be dramatically improved upon completion.
+ Value of surrounding land may increase. � DM may be contaminated with material unsuitable for the beach environment � Material must be the same size or larger than insitu material � Material must be the same colour shade as the original material or slightly darker. � Quantity of material must be sufficient for both the visible portion of the beach and
the submerged portion.
Offshore Berms
Creation of submerged berms to moderate the
inshore wave climate, thus, reducing the loss of beach material
+ Using a wide range and collection of material from rock, sand and clay. + May be created by simple discharge of DM from hoppers.
+ Can protect areas of high land value (e.g. beaches) from erosion. � Identification of the most destructive wave direction is crucial � Optimum placement area must be located and be sufficiently shallow � The height of the berm is critical in calculating the reduction in wave force.
Coastal Protection
The use of geotubes to contain DM to aid in coastal erosion defence.
Excavated rock can also be used as cover material.
+ Can prevent flooding and coastal erosion + Use of geotubes retains and isolates contaminants. + Reduces quantity of quarried material required
+ Reduces large scale transport of quarried material � The size and weight of the rock is important in the design of coastal protection
structures. � Hydraulic equipment is required for geotubes.
Landfill Cover
Landfill cover is used daily to minimise odour and rodents. Substantial material is also required for
a permanent cap when areas of the landfill are at capacity.
+ Should be a vast improvement in the aesthetics of the area upon completion of project.
+ The regeneration of plant life will revitalise wildlife. + Possible amenity and recreation areas for locals can be created.
+ Value of surrounding lands increase as well as the developed land itself. � Desalination will be needed to stimulate plant growth � Dewatering will be required in most cases and in all cases where hydraulic dredgers
are used. � Contamination levels must be at a suitable level for the materials intended use. � Growth testing will have to be carried out to ensure that the material can support
growth annually.
Capping Material
Using clean DM as a cover to envelop contaminated DM disposed in open water or as covering in solid waste landfills.
+ Provides an effective method of controlling contaminated DM within the aquatic environment.
+ More economical than treatment of contaminated DM + No additional costs than disposal at sea � Coarse uncontaminated material necessary. � Water depth must be acceptable. � Accurate placement is essential. � Monitoring and maintenance may be required periodically. � Organic content should be low to deter organisms.
� Placement should be carried out during low wave action at a low velocity with the potential use of a diffuser.
Table 2 Engineering Beneficial Uses of Dredge Material
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Beneficial Use Description Advantages (+)/Disadvantages(-)
Upland Creation/Enhancement
Creating or enhancing an upland habitat usually refers to a bird habitat. This area does not have to be in an
elevated area but can be located by the water or even on an artificial island.
+ Almost any material that is clean can be used. + Benefits to environment must be compared with the
losses. + Possible creation of tourist attractions and areas of
conservation under the European habitat and birds directives.
� Transport costs can be excessive especially in rural areas. � Timing of the work may be hindered by migration
patterns of certain species. � Elevation, location and the topography of the area must
be appropriate.
Wetland Creation/Enhancement
DM sediment is used to create/stabilise eroding natural wetland shorelines or nourish subsiding wetlands.
+ Project would improve the overall environmental conditions onsite.
+ Can drastically improve flood defence and erosion issues. + Provides a soft engineering solution which can be a
cheaper and more attractive option than a concrete structure.
� Contamination levels must be extremely low. � Material used must be silty in nature with good organic
content.
� Lengthy planning involved which may disrupt dredging project.
� It is easier to enhance an area of wetland than to create a wetland.
� Large scale EIS must be carried out. � Biological testing, which would include numerous
bioassay’s, would be required.
Sediment Cell Maintenance The 'in estuary' placement of DM during beneficial use schemes, either by trickle charging or direct intertidal placement, ensures that perturbations to an estuary's cell maintenance during essential dredged is
minimised. Also known as sustainable relocation. Applies exclusively to maintenance dredging
+ Is a more environmentally friendly solution than disposal at sea
+ Can prevent erosion on the down-drift side of the port/harbour.
+ No extra equipment is required. + Contamination levels should be low as the material
concerned will be recently deposited sediment. + No requirements on type of material dredged.
+ Can be more economical than disposal at sea � Wave environment must be assessed. � The time in the tidal cycle when the work is done must be
optimised
Table 3 Environmental Enhancement Beneficial Uses of Dredge Material
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Beneficial Use Advantages Disadvantages
Manufactured
Topsoil
+ Beneficial alternative
to dumping at sea.
+ Saves on quarried
material
+ Price dependent on
quality of material but
generation of a profit
is possible.
+ Some products will require no capital
equipment
+ Some products can
lock in contaminants
+ Provides a sustainable
annual beneficial use
programme
+ Regularly reduces
disposal at sea charges
+ Dewatering is essential and a prerequisite.
+ Saline content and levels of pH must be evaluated.
+ Grading of material must be appropriate.
+ Some areas of public use, i.e. parks, or agricultural
use may not be suitable for this material depending
on the pollutants present and overall quality of the
material.
+ Relevant technical standards must be met and
adjustment in chemistry of manufactured goods must be assessed.
+ Optimum mixes must be found and tested.
+ Time frame for the availability of material decisive
in construction projects to avoid costly delays.
+ Considerable equipment required for processing.
+ Transport will have to be done by trucks at delivery
stage.
+ Constant supply of material necessary to make the
project sustainable into the future.
+ Public prejudice against technologies/processes used
to treat and manage sediments.
+ Lack of consist or total absence of applicable state regulations.
+ Intermittent, variable sediment characteristics
associated with typical dredging projects.
+ Required development of market and acceptance of
products produced from dredged sediments.
+ Resistance from labour groups to displacement of
traditional products and associated jobs.
+ Long-term liability and legal responsibilities
associated with produced products.
Fill Material
Landfill Liner
Road Sub-base
Lightweight
Aggregate
Brick Manufacture
Production of
Ceramics
Table 4 Agricultural and Product Beneficial Uses of Dredge Material
In addition to the above general characteristics of each beneficial use methods the specific site
restrictions were identified to fully allow their consideration. For the Port of Waterford these include:
• Specific sediment characteristics;
• Available dredging and transport methodology;
• Locally protected sites;
• Volumes of material;
• Local discharge points (e.g. quays);
• Timing and frequency of operations.
Land Reclamation/Improvement
Land Reclamation is perhaps the best known use of dredge material and involves raising the level of
land which is either just below or adjacent to the water. Land improvement is a variety of this which
raises the level of already established land to prevent against flooding.
The Port of Waterford was granted planning permission for a reclamation project covering
approximately 75 acres of land downstream of the Belview Berths. However, justification could not
be made for the expense of undertaking this reclamation, with no current demand for additional
facilities at the Port. Due to this decision the planning permission has since lapsed.
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Other than the above case there is no justification for reclaiming land in the locality. Furthermore, the
impact of any reclamation is substantial as it will destroy any habitats on the bed or intertidal areas
and the presence of protected European sites will deem any proposed reclamation unfeasible.
Beach Nourishment
Beach nourishment is a technique used internationally to compensate beach material losses by placing
suitable material at optimum positions. While beach nourishment is an option to help manage coastal
erosion it can also prevent localised flooding, lessens the impact of storm damage by dissipating
energy and maintains a wide recreational beach.
Beach nourishment generally require hydraulic dredgers, which the Port of Waterford utilise. The Port
has considered the use of its maintenance dredge material at a variety of local beaches such as
Duncannon, Passage East and Woodstown. However, no notable erosion is present at of these
beaches. There is also no demand to expand these beaches for recreational purposes.
In cases where no erosion is present on a beach when sediment of a similar particle distribution to that
insitu is placed it is likely to be eroded as the equilibrium has been altered. To overcome this coarser
grained material that that insitu is required to be placed. The coarsest material dredged by the port of
Waterford is fine sand and unsuitable for these beaches.
Additionally, even if a demand was created for sediment a detailed study would be required to be
undertaken on both placement method and location to ensure the sediments did not return to the
navigation areas of the estuary.
No other appropriate sites within close proximity to the dredged areas have been identified.
Coastal Protection using Geotubes
Geotubes are large ‘bags’ made from a high tensile strength woven polypropylene geotextile.
Geotubes are designed to receive and retain pumped sediment while allowing the water to escape
through the fine pores of the geotube. As the water drains from the geotubes, the contained volume
decreases, allowing further filling. Initially designed as a dewatering mechanism Geotube have since
evolved and are now used for containment of sediments in marine structures.
An analysis was undertaken on the use of geotubes in a coastal protection study to train the flow of
the river at Cheekpoint and reduce the annual volume of sediment dredged at this location. This
proposal was potentially economically attractive and used material regularly dredging in maintenance
dredging campaigns as the fill material. However, technical issues such as the high flow rate of the
River Suir, the depth of placement (>11m) and the impact an impermeable marine structure had on the
rock armour specification required could not be overcome.
Manufactured Topsoil
A detailed study was recently completed into the potential use of the Port of Waterford’s dredge
material, in conjunction with household organic waste, to produce a manufactured topsoil product.
This would have the benefit of producing a regular destination for a portion of the annual material
produced from dredging.
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The published results of this research are included in Attachment C.1(i). In summary, the results
indicate that, under certain site conditions, the proposed process is a feasible DM management option.
However, it was found that for the Port of Waterford, the proposed alternative dredge material
management technique was not a feasible option for the following reasons:
• Insufficient local demand;
• Unclear legislative standards for waste designation;
• Technical characteristics of available dredging plant;
• Potential increase in CO2 emissions;
• Increase in dredging cycle time and cost.
Aggregate Industry
Dredged aggregates are an attractive alternative to land based sources. When compared with onshore
quarrying activities extraction and emissions costs are less than 50%. Transport costs are less than
15% as a 5000t Trailing Suction Hopper Dredger transports the equivalent of 250 trucks. It has been
estimated that, for example, 1 tonne of onshore material costs the same as the equivalent of 6 tonne
from offshore.
The use of the Port of Waterford maintenance dredge material for aggregates was considered however
a number of current issues were identified:
• Downturn in aggregate demand in recent years;
• Local quarries have adequate capacity for demand;
• Only limited portion of total material dredged potentially feasible;
• Fine nature of sand present with presence of silt and organics;
• Elevated saline and pH levels;
• Mechanical dredging not undertaken by the Port;
• Hydraulic dredgers used cannot be unloaded at quays.
For the above reasons landing dredged sediment ashore at a suitable location is not deemed feasible
until at least the market demand for aggregates has increased locally.
Recycling
Sediment Cell Maintenance
Sediment Cell Maintenance involves the 'in estuary' placement of dredge material, either by trickle
charging or direct intertidal placement, to ensure that perturbations to a location from essential
dredging works is minimised. This is also known as sustainable relocation and applies exclusively to
maintenance dredging as this sediment is inherently mobile within the local environment. Undertaking
plough dredging or water injection dredging is generally termed as sediment cell maintenance as the
material is retained with the local environment. However, for other dredging methods of dredging that
recover the sediment a placement site is required.
The Port of Waterford’s harbour limits are extensive, but in general narrow. The placement of any
dredging is currently an average distance of 21km from all of the dredging locations proposed. This
site was selected to ensure negligible environmental impact and also guarantee that the material does
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not return to the Port immediately as this would negate the entire operation. However, the narrow
characteristics of the estuary indicate that a suitable site is unlikely to be found for sediment cell
Maintenance that guarantees the material does not return to the navigation channels. Due to the
method of dredging selected based on the volumes required to be dredged trickle charge would not be
suitable method of placement, with only direct placement available. Large scale hydrodynamic
modelling of any proposed location would be required. Furthermore, due to the variance in the
characteristics of the material dredged several sites may be required depending on the particle
distribution of the sediment. The impact on fisheries and archaeological sites would also require
substantial investigation.
Due to the unlikelihood of identifying a suitable site(s) and the potential cost of undertaking such a
process, consultation was not undertaken with the various stakeholders within the estuary regarding
sediment cell maintenance.
Processing/Recovery
As outlined in attachment B.1(ii) the sediment dredged annually by the Port of Waterford is clean
uncontaminated material. Therefore, there is no benefit from processing the material, excluding
dewatering and desalination for specific beneficial uses outlined above.
Best Practical Environmental Option
After discussion of the above assessment it is deemed that disposal at sea, at the historic disposal site,
is the most appropriate method for the disposal of material from the Port of Waterford. This is largely
due to the current disposal site providing adequate performance logistically, economically and
environmentally to the satisfaction of all of the stakeholders. Despite the above finding, alternative
options to disposal at sea will continue to be investigated by the Port of Waterford, with the goal of
implementing the best social, economic and environmental dredge material management process
possible.
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Attachment C.1(ii): Relevant Extracts of E.I.S. – Section 3, Malone O'Regan, February
1999
© Anthony D Bates Partnership LLP 26 | P a g e
Attachment C.1(iii): Port of Waterford Manufactured Topsoil Research
Resources, Conservation and Recycling 54 (2010) 1377–1385
Contents lists available at ScienceDirect
Resources, Conservation and Recycling
journa l homepage: www.e lsev ier .com/ locate / resconrec
A technical assessment of topsoil production from dredged material
C. Sheehan a,∗, J. Harringtonb, J.D. Murphy c
a Department of Civil, Structural and Environmental Engineering, Cork Institute of Technology, Rossa Avenue, Bishopstown, Cork, Irelandb School of Building and Civil Engineering, Cork Institute of Technology, Bishopstown, Cork, Irelandc Department of Civil and Environmental Engineering, University College Cork, Cork, Ireland
a r t i c l e i n f o
Article history:
Received 4 November 2009
Received in revised form 24 May 2010
Accepted 24 May 2010
Keywords:
Port of Waterford
Dredge material
Beneficial use
Topsoil
Desalination
Growth trials
a b s t r a c t
This paper presents an investigation into the technical feasibility of producing manufactured topsoil from
dredged material from the Port of Waterford, Ireland. A survey of the local topsoil market was undertaken
yielding information on topsoil cost, volume of material used annually and the concerns of the users
regarding dredged material. The dredged material was analysed for its physical, chemical and nutrient
characteristics. Fourteen different dredge material mixes were developed with two mixes of established
topsoil for testing and growth trials. Dewatering and desalination of the mixes was undertaken with
continuous monitoring. pH adjustment and organic amelioration, from household organic waste, was
analysed. Growth trials were undertaken to compare the growth performance of the dredged material
mixes with the established sources available on the marketplace. The optimal mix identified was a 60%
coarse, 40% fine mix with organic amelioration to 6% and pH adjustment to 6.75. The treatment process
improved both the germination rate and the overall biomass production. The creation of manufactured
topsoil from dredge material was found to be technically viable.
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
The Republic of Ireland is a small island nation situated in
the north west of Europe. Ireland’s maritime transport industry
accounts for over 99% of imports and exports (by volume) and has
grown significantly in recent years in line with Ireland’s economic
performance (Shields et al., 2005). As an island nation Ireland’s
dredging industry is essential to the operation of its Ports and Har
bours with the volumes dredged small by international standards.
Historically, the average annual maintenance dredge requirement
for disposal at sea is approximately 1.2 million wet tonnes for the
Republic of Ireland (OSPAR Commission, 1997–2006). Studies for
Ireland (Harrington et al., 2004; Sheehan et al., 2008) have iden
tified the extremely limited amount of beneficial use of dredge
material (DM) practiced, particularly for the fine grained fraction.
This paper proposes the use of coarse grained and fine grained
DM from the Port of Waterford with local organic household
waste to produce manufactured topsoil. Manufactured Soil (MS)
is described by Lee and Sturgis (1996) as a material that can be
created using DM and recycled organic waste material. MS has the
benefits of finding a long term management solution for DM, as
well as for household waste. The proposal would also reduce the
volume of DM disposal offshore from the Port of Waterford and
may be applicable elsewhere in Ireland or internationally.
∗ Corresponding author. Tel.: +353 21 432 6469; fax: +353 21 434 5244.
Email address: [email protected] (C. Sheehan).
Irish standards for topsoil are set out in the British Standard
3882, 2007 (BS:3882, 2007). The most challenging parameters to
comply with are the organic matter, pH and salinity, as sedi
ment from an estuary generally has low organic content, a high
pH and a high saline content. The proposal includes dewater
ing and desalination monitoring to assess the time required for
the topsoil to have improved handling properties and to reach
the required saline level. Organic testing is undertaken to anal
yse quantities of organic amelioration to improve seasonal growth
and pH testing for pH adjustment to maximise the potential
nutrients available for growth. Several mixes of dredged mate
rial from the Port of Waterford were prepared for growth trials
to give an indication of the optimum mix. The local market for
topsoil and the public’s perception of such a product is also
assessed.
The Port of Waterford is one of the largest commercial ports
in Ireland, is situated 4 miles downstream from Waterford City
in Southeast Ireland (Fig. 1) and handles approximately 2.5 mil
lion tonnes of cargo annually. The Port has the largest annual
maintenance dredge requirement of the Irish Commercial Ports at
approximately 500,000 wet tonnes. The Port is operating under a
5year Dumping at Sea License (2008–2013) with no beneficial use
of DM. The areas within the river/estuary system that are dredged
are illustrated in Fig. 2. The main areas of dredging are around the
main port facilities on the River Suir, at Cheek Point (CP) and further
downstream in the main channel at Passage East (PE). The mate
rial dredged is approximately 46% silt and 54% sand. In general, the
finer material is found at Cheek Point, where the River Suir meets
09213449/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.resconrec.2010.05.012
1378 C. Sheehan et al. / Resources, Conservation and Recycling 54 (2010) 1377–1385
Fig. 1. Location of the Port of Waterford.
Fig. 2. Dredge locations in Waterford Bay.
the River Barrow, with the coarser fraction dredged at the main bar
at Passage East.
2. Topsoil market survey and dredge material properties
2.1. Existing topsoil market
The local topsoil target market was surveyed to establish if a
market for topsoil existed and also to gauge the public’s view of
dredged material as manufactured topsoil. For example, Riddell
et al. (1989) stated that the public perception of a scheme utilis
ing a ‘waste’ material is crucial to its successful implementation.
Hardcopy topsoil survey forms were sent to the target market of
local contractors, landscapers, garden centres and local authorities
in April 2008. Additionally, phone surveys were also conducted. In
total 43 survey forms were sent out to 4 nurseries, 10 landscapers,
28 general contractors and the Local Authority. The overall response
rate for the survey was 28%. The survey included questions on mate
rial quantities used annually, the source of the material, the quality
of the material and canvassed opinion on the use of dredged mate
rial as a topsoil material. The survey form specifically included the
following questions of the stakeholders:
• What quantities of topsoil material are used annually;• What are the current sources of the material;• What is the average cost of the material;• Opinion on the quality of the material used (several options pro
vided);• Rank parameters in order of importance when considering a top
soil product (cost, grading, delivery options, source of material,
organic content);• Would the stakeholder consider using a topsoil material from
recycled material (e.g. dredge material and household organic
waste);• Would the stakeholder expect the material to be cheaper then
other sources of topsoil on the market;• Would the stakeholder expect the quality of this material to be
competitive in comparison to other sources;• Would the stakeholder consider purchasing this recycled mate
rial if it was economically competitive.
The survey forms were manually analysed in a rigorous man
ner. The survey results from purchasers showed that the main
end destination of the topsoil was with local contractors, the
local authorities, landscapers and nurseries as well as a signifi
cant amount consumed annually by the general public. Most of this
material was sourced from local topsoil companies and from local
Table 1
2008 price variations of topsoil.
Source of topsoil No. of facilities Average cost per tonne Range of cost per tonne
Construction sites 4 D 19.66 D 13.64–25
Topsoil wholesalers 12 D 25.26 D 10–56
Garden centres 6 D 166.23 D 166–167
C. Sheehan et al. / Resources, Conservation and Recycling 54 (2010) 1377–1385 1379
Table 2
Summary of physical test results.
Parameter Coarse sample (Passage East) Fine sample (Cheek Point)
BS 5930
grading
Fines 8.8% 85%
Sand 91.2% 15%
Gravel 0% 0%
In situ moisture content 25.9% 55.4%
construction sites where land was stripped of topsoil. In general, the
overall rating of topsoil received was considered good to very good.
Key areas for improvement of the topsoil they received were iden
tified as organic content, moisture content, screening completely
free of weeds and particle size distribution with coarser material
preferred to improve drainage properties of the material. Overall
86% of respondents stated that they would consider using manufac
tured topsoil from dredged material and organic waste. The topsoil
demand in the area based on survey results is estimated at between
25,000 and 50,000 tonnes annually.
A phone survey of 19 local topsoil suppliers regionally was also
completed to establish the current price per tonne of topsoil in
the area. The main survey results from the sellers of the mate
rial were the different ranges in topsoil cost (Table 1) reflecting
the quality of the material which can differ significantly in par
ticle size distribution, organic content and moisture content. For
many of the topsoil wholesalers the market is seasonal as they
do not provide storage for the material, meaning handling of the
material during the wetter months, from October to January, is not
possible.
2.2. Characterisation of dredged material
A review of the Port of Waterford’s technical analysis of its DM
indicated sampling at two locations to provide a mix of fine and
coarse material. Cheek Point (CP) was identified as the best source
of fine grained material while the area of channel dredging by Pas
sage East (PE) was selected for coarse material. The fine/coarse mix
gave a particle size distribution similar to highquality topsoil with
good drainage with a silt and clay fraction allowing adequate water
and nutrient retention.
Samples were taken from both locations and tested physi
cally and chemically. The particle size distribution for Passage East
(Table 2) indicates that the material is a silty loamy soil with low
clay content (0.39%). Cheek Point’s particle size distribution is finer
but would be difficult to handle due to its silty nature and high
in situ moisture content. The clay content is higher at 6.2% and
would provide improved moisture and nutrient retention for any
mix created. Both samples (Table 3) met the Dumping at Sea criteria
(Cronin et al., 2006) indicating no contamination and a potentially
valuable raw material not requiring treatment.
Nutrient testing was undertaken for the DM samples, for com
post from a local composting facility in Waterford, which is the
material identified for the organic amelioration of the manufac
tured topsoil, and a topsoil sample from a local construction site.
Samples were tested for all the topsoil nutrient characteristics
listed in the British Standards for topsoil (potassium, phosphorus,
nitrogen and magnesium) as well as calcium carbonate (Table 4).
Electroconductivity (EC) testing was also undertaken to deter
mine salinity levels present in both samples. Upon sampling, the
fine grained material sampled from Cheek Point had an EC level
of 19.26 mS/cm while the coarser grained material from Passage
East had a level of 15.36 mS/cm, such EC levels would inhibit plant
development and thus desalination is essential.
The results show that, in general, both DM samples had higher
levels of nutrients than the standard construction site topsoil, due
mainly to the higher silt and clay levels in the dredged material pro
viding greater water and nutrient retention. The compost showed
Table 3
Summary of chemical analysis results and comparison to dumping at sea standards.
Parameters Unit Lower guide level Upper guide level Passage East Cheek Point
Arsenic mg/kg 9 70 6.6 1.05a
Cadmium mg/kg 0.7 4.2 0.15 0.16a
Chromium mg/kg 120 370 38 7.4a
Copper mg/kg 40 110 6.8 5.3a
Lead mg/kg 60 218 22 13.2a
Mercury mg/kg 0.2 0.7 0.02 0.11a
Nickel mg/kg 21 60 16 4.5a
Zinc mg/kg 160 410 75 56.7a
Iron mg/kg N/A N/A 16,000 3360a
Manganese mg/kg N/A N/A 480 232a
6TBT and DBT mg/kg 0.1 0.5 0.003 0.012a
6PAH mg/kg 4000 N/A 2314 1766a
PCB (6ICES 7) mg/kg 7 1260 <20 <1a
HCB mg/kg 0.3 1 <0.02 Unknown
pH N/A N/A N/A 7.56 8.21
Salinity mS/cm N/A N/A 15.36 19.26
Organics % N/A N/A 0.53% 2.5%
a Analysis undertaken by the Port of Waterford (2008).
Table 4
Summary of nutrient analyses.
Sample location/type Calcium carbonate (mg/kg) Potassium (mg/l) Phosphorus (mg/l) Nitrogen (mg/kg) Magnesium (mg/kg)
Passage East sediment 934 132.8 11.7 364 3429
Cheek Point sediment 1137 372.1 7.6 1259 5757
Construction topsoil 47.5 6.2 1.8 671 3044
Compost 675 1050.7 309.8 17,751 2093
1380 C. Sheehan et al. / Resources, Conservation and Recycling 54 (2010) 1377–1385
Fig. 3. Dewatering and desalination process.
the highest levels of potassium, phosphorus and nitrogen. How
ever the levels of magnesium (present in seawater) and calcium
carbonate (the main component of marine organism’s shells) were
higher in both DM samples. The finer grained material from Cheek
Point generally had higher nutrient levels than the coarse grained
material from Passage East.
3. Methodology for the beneficial use of dredge material
The initial DM assessment confirmed high water content, high
saline content, an elevated pH level (8.23–8.74), compared to nat
ural soils in Ireland, and low to moderate organic content. These
characteristics will not allow satisfactory growth results and thus
topsoil treatment to meet British Standard 3882:2007 is required.
The overall goal of the treatment and growth trials is to achieve an
optimum mix of dredge samples from the two locations identified.
Several mixes were created with quantities of DM from both
Passage East (PE) and Cheek Point (CP) separated by weight into
several different mix ratios from 80% PE/20% CP through to 20%
PE/80% CP yielding a wide representative range (a total of seven
mixes). Construction topsoil (the most popular source of topsoil
material in the local area) from a local site was also used to monitor
and compare its dewatering and desalination results with those of
the DM mixes.
3.1. Dewatering and desalination
Desalination is essential to the creation of manufactured topsoil
due to the adverse growth reaction of plants to high saline content.
The dewatering and desalination process (Fig. 3) involves expos
ing the different mixes to the climate and monitoring moisture
content and saline levels. This is essential to optimising turnover
of the material and ensuring maximum production rates. Weed
development was also recorded. Once the mixes reached a stable
steady state moisture content and acceptable salinity [electro
conductivity (EC)] they were prepared for growth trials.
The dewatering and desalination process needs to be eco
nomically achieved while also attaining the greatest turnover of
material. Bohemen (2005) describes this process as the ‘ripen
ing’ process where the material experiences a decrease in organic
content due to biological activity, an increase in consistency and
an overall reduction in volume due to the reduction of its water
content. Both the dewatering and desalination processes were
undertaken in an exposed external location and daily rainfall levels
were recorded. These rainfall levels, averaged by month, exceeded
the average monthly rainfall experienced at the proposed produc
tion site in Waterford (Fig. 4) suggesting that irrigation on site, to
boost desalination rates, would be necessary.
The thickness of the mixes was 200 mm reflecting a recommen
dation of a maximum of 0.5 m for dewatering (Riddell et al., 1989)
with greater turnover anticipated for such a thinner mix. The dewa
tering process was undertaken for a 15week period from the 25th
July to the 17th November (see Fig. 5). After sampling the dredge
material was stored before it was mechanically mixed into the
desired mixes. The addition of coarser material to the finer Cheek
Fig. 4. Average monthly rainfall in Waterford region and at the test site (Met Eireann,
2008).
Point material significantly improved its drainage characteristics
during the mechanical mixing as well as producing a homoge
neous material. A significant amount of water was removed from
the mixes upon surface pooling. These mixes were placed in an
exposed area for dewatering. All mixes created reached a stable
moisture content level after 3–4 weeks reducing the moisture con
tent from an average of 32.8% to 18.3%. The variations shown in
Fig. 5 illustrate the effect of precipitation prior to measurement.
The overall objective of the desalination process was to reduce
the electroconductivity (EC) to a target level suitable for plant ger
mination and growth of 2 mS/cm (KotubyAmacher et al., 2000). EC
readings were taken periodically during desalination to determine
the saline content (Fig. 6). The results show that, in general, it takes
2–3 months depending on the mix to reach the target EC level.
The coarser mixes met the target more rapidly. It can be concluded
Fig. 5. Moisture content during the dewatering and desalination process.
C. Sheehan et al. / Resources, Conservation and Recycling 54 (2010) 1377–1385 1381
Fig. 6. Electroconductivity readings during desalination.
from the dewatering and desalination stages that if the material is
placed in a 200 mm layer that the desalination stage is the defining
factor due to the longer time duration requirement. Irrigation was
required to increase the rate of desalination as the rainfall itself was
insufficient over the time period. Irrigation would be needed onsite
to maintain high production levels.
An example of weed development is shown in Fig. 7. It was
noted that the construction topsoil had a substantial amount of
weed growth, moderate weed and fungus growth was found on
the DM during the desalination process.
3.2. Organic amelioration and pH adjustment
The material mixes were split into two portions after dewater
ing and desalination. One portion was treated with chemicals (to
lower pH) and mixed with compost from the local recycling cen
tre (organic amelioration to boost the organic content of the mix).
The other portion was left untreated for comparative analysis. Both
were prepared for growth trials together with the construction site
topsoil. The treatment process is shown in Fig. 8. A sample of high
quality manufactured topsoil (bagged topsoil) was also obtained
and used as a benchmark. Treated mixes are denoted in this paper
with a ‘c’. In total 14 DM mixes, one sample of construction topsoil
and one sample of bagged topsoil were prepared.
The amount of organic amelioration applied is important both
for the economics and to ensure that the applied organic amend
ments do not create excessive nitrate and phosphorus in the soil
(Morris et al., 2008). While it is recognised that dredged material
can support substantial first season growth, subsequent acceptable
seasonal growth results are not sustained (Riddell et al., 1989) mak
ing the organic content present in the soil essential for successful
continued growth. In a study (Ersahin and Brohi, 2006) of 140 sam
ples of topsoil the results showed a minimum % organic content of
1.9%, mean of 3.8% and a maximum value of 5.8%. Wetmore (2008)
recommended that a stable upper limit of 5–7% organic content.
A target of 6% organic content was chosen for this work based on
the above and that the organics could be recovered free of charge
from a local compost recycling facility. Each mix was tested for its
organic content and the amount of compost required was added
to reach the target level of organic content. The amount of organ
ics added ranged from 47.6 kg/tonne to 32.7 kg/tonne depending
on the mix. The pH was also adjusted by this process, particularly
so for the coarser mixes. This is shown in Fig. 9 together with the
target pH level of 6.75 based on Gardiner and Garner’s work (1953).
Aluminium sulphate [Al2(SO4)3] was added to each mix to reach
the target pH and to optimise potential nutrient availability. A test
amount (1 g) of aluminium sulphate was added to a sample of each
mix and the amount of pH adjustment recorded (Fig. 10). From
these results the amount of Al2(SO4)3 needed per mix to reach the
Fig. 7. Weed development in mixes during the desalination process.
Fig. 8. Testing and treatment process postdesalination.
1382 C. Sheehan et al. / Resources, Conservation and Recycling 54 (2010) 1377–1385
Fig. 9. pH levels with/without compost.
target pH level was calculated and added prior to growth trials.
The results show that the finer the mix the greater the amount of
Al2(SO4)3 that is required, which has economic implications. Thus
all the treated mixes, while having different particle size distribu
tions, all had a pH level of 6.75 and an organic content of 6% prior to
the commencement of growth trials. Table 5 shows the amounts of
Al2(SO4)3 required for each of the mixes created to reach the target
levels. On average, the mixes without compost required approxi
mately 27% more Al2(SO4)3.
3.3. Growth trials
The growth trials were conducted indoors over a 6week period
using common grass test species, the most common crop planted in
the Republic of Ireland. A total of 384 seeds were planted in the 16
different mixes 25 mm below the surface. Artificial light was pro
vided as well as water and rotation to ensure equal light coverage to
all mixes. Seed germination data was collected daily to determine
emergence rates and total percentage germination. Growth rates
were also monitored by daily height measurements. Final height
and dry above ground biomass were determined upon harvest.
Observations of plant health were also recorded. Photographs were
Fig. 10. Effect of 1 g of Al2(SO4)3 on pH levels of dredge material mixes.
taken to document visible growth performance and plant health
differences (Fig. 11). Germination occurred over a 3week period.
The individual germination success rates of all the mixes shows
the consistently better germination rates achieved by the treated
mixes, relative to the untreated mixes (Fig. 12). This is further
highlighted in Fig. 13, which shows the germination results of
the sum of the treated and untreated mixes. Overall, the 60/40
treated mix was the best performing of the DM mixes and achieved
better germination results than the construction topsoil (CT), but
slightly less than the bagged topsoil (BT), which achieved an 83.3%
germination rate. The treated mixes averaged 56.9% germination
while the untreated DM mixes achieved an average of 31.5% ger
mination. Overall treated mixes outperformed untreated mixes by
56.4%.
Daily height readings were taken during the growth period. The
sum of the treated and untreated DM mix height growth levels is
shown in Fig. 14. This figure shows that the height development of
the treated mixes is moderately better than the untreated mixes
with the sum of the treated mixes ranging from 22 mm to 73 mm
higher than the untreated mixes in daily monitoring. Fig. 15 high
lights the growth results of the individual mixes upon harvest. The
untreated mixes had on average 4.5% better growth per germina
tion than the treated mixes. However, the results are inconclusive
Table 5
Quantity of Al2(SO4)3 required for different dredge material mixes.
Type of mix 80/20c 80/20 70/30c 70/30 60/40c 60/40 50/50c 50/50 40/60c 40/60 30/70c 30/70 20/80c 20/80
Al2(SO4)3 addition (kg/tonne) 23.97 30.77 28.53 35.00 28.37 39.94 29.84 39.57 35.71 43.92 37.19 45.96 44.75 52.89
Note: Treated dredge material mixes are denoted by a ‘c’.
Fig. 11. Germination and growth during growth trials.
C. Sheehan et al. / Resources, Conservation and Recycling 54 (2010) 1377–1385 1383
Fig. 12. Seed germination rates for different dredge material mixes. Note: Treated
dredge material mixes are denoted by a ‘c’.
Fig. 13. Sum of seed germinations for treated/untreated mixes.
as the treated mixes had greater growth height in three of the seven
mixes. However, when combined with the germination data the
total harvest height (Fig. 16) outlines the contrasting overall growth
results of each individual mix. The treated mixes had, on average,
56% greater total height development results than the untreated
mixes, due mainly to the greater germination rate. From this we
Fig. 14. Sum of grass heights for different dredge mixes.
Fig. 15. Average height per germination upon harvest.
may conclude that plant height development is not significantly
effected by the treatment process postgermination.
Upon harvest the biomass of each mix was established (Fig. 17).
On average the treated mixes achieved 47.5% greater biomass than
the untreated mixes. The biomass created by each mix is directly
affected by the germination rate and the height development. The
mix with the greatest production of biomass was the 60/40c mix,
producing slightly more than the 50/50c mix.
Table 6 ranks the dredge mix performance by germination rate,
average growth height, sum of growth heights and biomass pro
duction. An overall ranking for each mix is also provided, giving
each individual parameter equal weighting. Three of the top four
rankings are for the treated mixes (60/40c, 50/50c, 30/70c) with
construction topsoil ranked third. The highest ranked untreated
mix was fifth (80/20).
4. Discussion
This paper examines topsoil production from dredged material
and assesses the potentially problematic areas of:
• Whether a market demand exists for such a product locally;• The public’s perception of topsoil produced from waste materials;• The comparison of DM properties to existing topsoil market stan
dards;• Sourcing and acquiring sufficient biomass (biological material)
for mixing;
Fig. 16. Sum of total grass height readings upon harvest.
1384 C. Sheehan et al. / Resources, Conservation and Recycling 54 (2010) 1377–1385
Fig. 17. Grams of biomass per mix upon harvest.
• Optimal dewatering and desalination to optimise production
rates;• pH issues effecting growth and potential treatment;• Germination and growth performance of DM compared to market
standards.
The data collected from the topsoil survey determined if there
is a market for such a product. This was essential in identifying
the target market, the level of potential interest and assessing
the general perception of manufactured topsoil. Analysis of the
target market suggests that the public would be open to using
a topsoil product produced from dredged material and house
hold organic waste. No negative views were registered from any
of the survey respondents on DM classification as a waste and
its potential use as topsoil material. However, as the production
rate of dredge material is substantially larger than the market
demand for topsoil the authors believe that other beneficial use
techniques should also be investigated to support the current pro
posal to reduce disposal at sea. Nevertheless, the production of
manufactured topsoil from dredge material provides a sustain
able end use for annual dredgings from the Port of Waterford.
This proposal provides a product based beneficial use from the
annual maintenance dredging; it is an environmentally sustainable
approach allowing implementation of a specific dredge material
management strategy. However, matching the market demand
for topsoil with the dredge material production for a site is a
key aspect in determining the proposal’s feasibility. Other sites
in Ireland and internationally may have the potential to more
closely match the dredge material production rate and the market
demand.
The physical testing concluded that the PE fraction of dredged
material from the Port of Waterford had positive engineering
characteristics including free of contamination (that would have
potential beneficial use if brought ashore) and mixes well with CP
material to improve its drainage characteristics while maintaining
highquality moisture and nutrient retention. Sufficient biomass
material was sourced from a local composting facility recycling
organic household waste. This material is available free of charge
and its use benefits both schemes; providing a continuous end use
of compost from the facility and improving the nutrient character
istics of the manufactured topsoil material.
Dewatering to a stable level for all mixes was established in 3
weeks after storage and mixing was completed. It should be noted
that the construction topsoil carried far less water than the DM
samples throughout the dewatering and desalination process. This
was attributed to the low percentage of silt and clay in the con
struction topsoil. The time needed for the mixes to dewater to an
acceptable level is not seen as crucial as the desalination process
takes significantly longer for a layer depth of 200 mm. Desalina
tion took between 8 and 13 weeks depending on the permeability
properties of the mix. It should also be noted that the ripening pro
cess was undertaken during the summer and autumn months. It
is anticipated that results would be less advantageous over winter
and spring months due to reduced temperatures and greater pre
cipitation. Slightly reduced desalination was noted during times of
less precipitation. Average monthly precipitation for the Waterford
region is less than recorded during the testing and trials and con
sequently irrigation may be required onsite to ensure a suitable
desalination rate.
The pH and organic testing found that for one tonne of the opti
mum mix (60% PE and 40% CP) 47.57 kg of organic material and
37.19 kg of aluminium sulphate is required to boost the organics to
an acceptable level while ensuring that the pH is at such a level that
growth in most of the plants is not impacted. The addition of organ
ics alone reduced the pH level by 0.5–0.75 depending on the mix.
The effect of the aluminium sulphate on the mixes depended on
the differential between the original pH of the sample and the pH
of the chemical itself, with supplementary additions providing less
adjustment. The amount of organic amelioration and pH modifica
tion required was directly affected by the particle size distribution
of each mix with coarser mixes requiring less aluminium sulphate.
The growth trial results determined that treated dredged mate
rial can compete with the market standards of topsoil currently on
the market. Germination rates of the treated dredged material were
Table 6
Ranking of growth trial results.
Mix Germination rate Average growth height Sum of growth heights Biomass production Overall ranking
80/20c 6 14 7 12 10
80/20 4 10 5 5 5
70/30c 8 13 11 10 12
70/30 13 15 14 14 15
60/40c 2 5 1 1 1
60/40 12 6 13 13 13
50/50c 5 2 2 2 2
50/50 15 11 15 15 15
40/60c 10 12 10 7 10
40/60 14 1 12 6 7
30/70c 7 4 4 4 4
30/70 16 3 16 16 14
20/80c 9 8 8 8 7
20/80 11 7 9 11 9
BT 1 16 6 9 6
CT 3 9 3 3 3
Note: The lower the ranking the higher the performance i.e. 1 designates best performance and 15 designates poorest performance. BT denotes bagged topsoil and CT denotes
construction topsoil. The top three mixes for each parameter are highlighted in bold.
C. Sheehan et al. / Resources, Conservation and Recycling 54 (2010) 1377–1385 1385
encouraging, although the untreated dredged material was less
successful due to elevated pH and saline content. Both treated and
untreated mixes, in general, had poorer germination results than
both construction and bagged topsoil (with the exception of the
optimum mix 60/40c mix). It can be concluded that the treatment
of the dredged material increases germination rates (on average
56.4% better than the untreated) while producing more biomass
per height grown. Untreated DM suffers from weakened germina
tion but has comparable height and biomass results as highlighted
by the ranking table presented. However, due to its high pH lev
els the range of species is limited (due to nutrient availability) and
repetitive seasonal growth requires further investigation due to the
low to moderate amount of organic content. It is anticipated that
the treated mixes would perform well seasonally due to its sta
ble organic content. The best performing treated dredged material
mixes (60/40c, 50/50c, 30/70c) had growth levels comparable with
both construction topsoil and bagged topsoil. These results show
that treated dredged material is of a high quality and can be com
petitive when compared to current market standards. Further large
scale, seasonal growth trials are recommended with a larger range
of plant species tested to indicate the potential for DM use in the
agricultural and food industries for grain and energy crops.
5. Conclusions
The results of the topsoil survey show a positive public per
ception of the DM product and that the topsoil demand for the
area is significant. The average price of topsoil was established to
be D25.36 per tonne in the Waterford area with a considerable
number of suppliers available. Construction sites stripped of their
topsoil were found to be the most common source of material to
the market. Local demand and public perception are crucial to the
successful implementation of such a beneficial use scheme. Deter
mining the existing markets characteristics is vital to providing a
product that meets or exceeds the current standard of material
available at a reasonable price.
The DM testing highlighted its topsoil characteristics post
mixing, with good drainage, adequate nutrient and water retention
capabilities and above average nutrient content. pH, salinity and
water content levels were all problematic in the context of topsoil
standards. However, the implementation of the treatment process
provides an adequate topsoil standard. Dewatering and desalina
tion of 200 mm mix layers, with continuous irrigation, significantly
improves the time required for these stages compared to previous
research on layers of greater thickness (Thomas, 1990). A local com
posting source was identified for the required biomass for organic
amelioration. This source of compost is free as it is recycled house
hold waste which enhances the positive environmental aspect of
this proposed scheme.
In all cases, the treated mixes compared favourably with cur
rent market standards for topsoil. The highest ranked treated mixes
had satisfactory germination rates, height and biomass results and
exceeded results for the construction topsoil. The untreated mix
germination rates were significantly affected by their increased
pH levels but had substantial height and biomass production
upon germination. The treatment process implemented signifi
cantly boosted the germination rate of the treated DM mixes, which
directly effects total grass height development and biomass pro
duction.
The ranking table (Table 6) presents a summary of the germi
nation rate, average growth height, total height development and
biomass production data collected from the growth trials. From this
the optimum mix was identified as the treated 60/40 mix with the
highest biomass growth and the most successful germination rate
for the DM mixes. The results from the dewatering and desalination
stage identified that the treated 60/40 mix would require at least
10 weeks to achieve the EC level required, with the finer mixes tak
ing longer. Organic testing showed that 47.58 kg of compost would
be required per tonne to reach the desired organic content level for
the 60/40 mix. 32.49 kg of Al2(SO4)3 per tonne is required for the
selected mixes to modify the pH level of the selected mix to max
imise the nutrients available for plant growth. The top three ranked
DM mixes (60/40c, 50/50c, 30/70c) were all treated to boost both
the organic content and to modify the pH and salinity levels for
optimum growth development, these mixes yielded better perfor
mance than the conventional sources of topsoil, CT and BT. Based
on the research undertaken producing manufactured topsoil using
DM is technically viable and compares well with market standards
after treatment.
Acknowledgements
The authors wish to acknowledge the funding received from the
Irish Environmental Protection Agency under the Science, Tech
nology, Research and Innovation for the Environment (STRIVE)
Programme 2007–2013. We would like to thank Michael Clooney
of the Port of Waterford, Anthony Bates Consultants, Paul Mitchell
of UK Dredging, Jonathan Derham and Kevin Motherway of the
Irish Environmental Protection Agency and Mick Storan of Veolia
Environmental Services for all their help and assistance.
References
Bohemen H. Ecological engineering: bridging between ecology and civil engineering,Rijkswaterstaat, Delft Technical University. Netherlands: Uitgeverij Æneas BV;2005.
British Standard:3882. Specification for topsoil and requirements for use, BritishStandard 3882:2007. London, United Kingdom: British Standards Institute;2007.
British Standard:5930. Code of practice for site investigations, British Standard5930:1999. London, United Kingdom: British Standards Institute; 1999.
Cronin M, McGovern E, McMahon T, Boelens R. Guidelines for the assessment ofdredge material for disposal in Irish waters. Galway, Ireland: Marine Institute;2006.
Ersahin S, Brohi A. Spatial variation of soil water content in topsoil and subsoil of aTypic Ustifluvent. 60250 Tokat, Turkey: Department of Soil Science, AgriculturalFaculty, Gaziosmanpasa University; 2006.
Gardiner HW, Garner HV. The use of lime in British agriculture. Farmer and StockBreeder Publication Ltd; 1953.
Harrington JR, Sutton S, Lewis AW. Dredging and dredge disposal and reuse inIreland—a small island perspective. In: Proceedings of world dredging congressXVII, B45; 2004. p. 1–14.
KotubyAmacher J, Koenig R, Kitchen B. Salinity and plant tolerance. USA: ElectronicPublishing, Utah University; 2000.
Lee CR, Sturgis TC. Manufactured soils: a productive use of dredged material. In:Proceedings US/Japan experts meeting. Vicksburg, MS: US Army EngineersWaterways Experiment Station; 1996.
Met Eireann. Rosslare climatic monthly data. The Irish Meteorological Online Service; December 2008.
Morris TF, Ping J, Durgy R. Soil organic amendments: how much is enough? Department of Plant Science, University of Connecticut; 2008.
OSPAR Commission. Dumping of wastes at sea 1997 to 2006. London, UK: OSPARCommission; 1997–2006.
Port of Waterford. Analysis of samples from Inner Port, Belview, Cheek Pointand Duncannon by Mercury Analytical Ltd. Appendix VI. Lab No. 021236;2008.
Riddell JF, Fleming G, Smith PG. The use of dredged material as a topsoil; 1989. Terraet Aqua, No. 39, p. 11–19.
Sheehan C, Harrington JR, Murphy JP, Riordan JD. An investigation into potentialbeneficial uses of dredge material in Ireland. In: WEDA XXVIII and Texas TAMU39th dredging seminar; 2008.
Shields Y, O’Connor J, O’Leary J. Ireland’s Ocean Economy & Resources. Marine Institute, Marine Foresight Series No. 4; 2005.
Thomas BR. Clyde sediments: physical conditioning in relation to use as a topsoil product for land reclamation. PhD thesis, Department of Civil Engineering,University of Strathclyde; 1990.
Wetmore J. Environmentally friendly lawn care: organic matter, Series 5. NewBrunswick, Canada: Canadian Nursery Landscape Association; 2008.
Resources, Conservation and Recycling 55 (2010) 209–220
Contents lists available at ScienceDirect
Resources, Conservation and Recycling
journa l homepage: www.e lsev ier .com/ locate / resconrec
An environmental and economic assessment of topsoil production from
dredge material
C. Sheehan a,∗, J. Harringtonb, J.D. Murphy c
a Department of Civil, Structural and Environmental Engineering, Cork Institute of Technology, Bishopstown, Cork, Irelandb School of Building and Civil Engineering, Cork Institute of Technology, Bishopstown, Cork, Irelandc Department of Civil and Environmental Engineering, University College Cork, Cork, Ireland
a r t i c l e i n f o
Article history:
Received 5 July 2010
Received in revised form
22 September 2010
Accepted 24 September 2010
Keywords:
Port of Waterford
Dredge material
Beneficial use
Topsoil
Organic waste
a b s t r a c t
This paper investigates the environmental and economic feasibility of producing manufactured topsoil
at the Port of Waterford, Ireland from two waste streams; dredge material and household waste. Four
dredging and dredge material transport scenarios to a topsoil production facility are proposed; a trail
ing suction hopper dredger (TSHD) with pipeline transport, a grab hopper dredger (GHD) with barge
transport, a small purchased port owned dredger (TSHD) with hopper transport and a leased dredger
(GHD) with hopper transport. The stringent legislative framework governing the proposal is outlined. A
detailed environmental and economic analysis is presented for each scenario. The environmental analysis
presents results for CO2 transport emissions and also presents sensitivity analyses for different projects
parameters. The economic analysis presents the annual profits or losses for each scenario for a range of
topsoil production quantities and integrated into the current dredging regime at the Port of Waterford.
Economic sensitivity analyses are presented for different project parameters. This paper recommends,
based on the analysis undertaken, the use of a leased dredger with hopper transport to transport the
dredge material to the topsoil production site as the most feasible option currently available at the Port
of Waterford. The proposal provides an environmentally sustainable end use for dredge material as an
alternative to disposal at sea.
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
1.1. Dredged material management in Ireland
In Ireland the dredging industry is small by international stan
dards but is essential to the continued operation of Irish Ports and
Harbours. Practically all maintenance dredge material (DM) is cur
rently disposed offshore (Sheehan et al., 2009). Environmentally
sustainable DM management plans for Irish ports and harbours
must be developed and must be economically feasible for successful
implementation.
1.2. Proposal
Manufactured soil (MS) is described by Lee and Sturgis (1996)
as a material that can be created using DM and any recycled organic
waste material. Sheehan et al. (2010) presented the technical feasi
bility of producing a manufactured topsoil product from DM (from
the Port of Waterford) and household organic waste. Other signif
∗ Corresponding author. Tel.: +353 21 432 6469; fax: +353 21 434 5244.
Email address: [email protected] (C. Sheehan).
icant research has been undertaken into the feasibility of dredged
material as a topsoil material at StrathCylde University, Glasgow
(Riddell et al., 1989; Thomas and De Silva, 1991) and by the United
States Army Corps of Engineers (USACE, 1999, 2000a,b). In 1988
a full scale soil factory was set up on a former quay on the Clyde
in Glasgow which was capable of producing 2000 tonnes/week of
topsoil, selling at £5.20 per tonne (D18.10/tonne in 2010 prices)
excluding delivery (Burt, 1996) and produced a net revenue to
the producers while reducing disposal at sea costs for the Port
Authority. Depending on the various logistics and technical aspects,
estimates of the cost to produce manufactured soil using dredged
material range from approximately $3.90 to $13.50 per cubic metre
produced (D14.34–49.64/tonne in 2010 prices) with the economic
incentive for the port the potential to receive approximately $0.06
per cubic metre (D0.22/tonne) (Ruff and Lee, 1997). However the
feasibility of this type of beneficial use is very site specific. USACE
(2000b) concluded, after a comprehensive study of a proposal to
manufacture topsoil from New York/New Jersey Harbour mate
rial, that after factoring in the cost of leaching salt and the cost
of treatment it would not be economically feasible to use dredged
material for manufactured topsoil unless the cost of the treatment
procedure could be substantially reduced. These previous research
studies provide quality information for comparisons.
09213449/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.resconrec.2010.09.011
210 C. Sheehan et al. / Resources, Conservation and Recycling 55 (2010) 209–220
Fig. 1. Location of the Port of Waterford.
Manufactured topsoil has the benefits of finding a long term
sustainable management solution for DM, as well as for house
hold waste, while reducing quantities disposed at sea. The process
proposed included mixing DM with organic household waste for
organic amelioration, pH adjustment to improve nutrient avail
ability, and dewatering and desalination. Growth trials were
undertaken to identify the optimum DM mix. Total demand for top
soil in the Waterford region was determined to range from 25,000
to 50,000 tonnes per year (Sheehan et al., 2010).
This paper focuses on the logistical, environmental and eco
nomic aspects of integrating the proposed beneficial use scheme
into the annual Port dredging programme. Different transport sce
narios, based on available equipment, are analysed to assess their
technical and economic feasibility. The technical and legislative
requirements of the production facility site are also investigated,
as well as their environmental impacts. A sensitivity analysis is
undertaken for the economic and environmental aspects of the pro
posal to identify the most critical components of each transport
scenario.
1.3. The Port of Waterford
The Port of Waterford is one of the largest commercial ports in
Ireland situated 4 miles downstream from Waterford City in South
east Ireland (Fig. 1) and handles approximately 2.5 million tonnes
of cargo annually. The port has the largest annual maintenance
dredge requirement of the Irish Commercial Ports at approximately
500,000 wet tonnes. All DM is currently dumped to an offshore
disposal site located approximately 22 km from the dredging site.
The Port currently operates under a 5year Dumping at Sea License
(2008–2013) with no history of beneficial use practiced. A multi
annual dredging contract with UK Dredging will terminate at the
end of 2012.
The areas within the river/estuary system that are dredged are
illustrated in Fig. 2. The primary areas of dredging are around the
main port facilities on the River Suir, at Cheek Point (CP) and fur
ther downstream in the main channel at Passage East (PE). The
material dredged is approximately 46% silt and 54% sand. In gen
eral, the finer material is found at Cheek Point, where the River
Suir meets the River Barrow, with the coarser fraction dredged
at the main bar at Passage East. All samples analysed met the
Dumping at Sea criteria indicating no contamination and a poten
tially valuable raw material not requiring treatment (Sheehan et
al., 2010).
2. Dredge material transport scenarios
Several transport scenarios were developed to assess the recov
ery and transport of the DM to the topsoil production site. The
scenarios developed are based on the equipment currently avail
able to the Port as part of their dredging contract with UK Dredging,
as well as other options open to the port for maintenance dredg
Fig. 2. Overview of areas dredged in Waterford Bay.
C. Sheehan et al. / Resources, Conservation and Recycling 55 (2010) 209–220 211
Scenario A - TSHD Scenario B -GHD Scenarios C & D
Dredge into Hopper Dredge with Grab Dredge into Hopper
Sail to Pipeline & Couple Fill Barge Sail to Docking Position
Pump into Pipeline Barge Sails to Shore Unload to Trucks
Uncouple and Return to Dredging Site
Unload to Truck Transport Transport to Production Site
Fig. 3. Dredge material transport scenarios proposed.
ing. Each scenario involves different transport logistics, technical
constraints and economic issues. The dredgers available are cen
tral to any transport process proposed for a manufactured topsoil
beneficial use scheme for the Port of Waterford. The four scenarios
selected (see Fig. 3) for analysis are:
• Scenario A—trailing suction hopper dredger (TSHD) with pipeline
transport (UK Dolphin).• Scenario B—grab hopper dredger (GHD) with barge transport
(Cherry Sand).• Scenario C—a small purchased port owned dredger (PPOD) TSHD
with hopper transport (Argos).• Scenario D—a leased dredger (LD) with hopper transport (Hebble
Sand).
2.1. Site selection
Site selection is crucial to the feasibility of a manufactured top
soil product and the site should be relatively close to the target
market (Waterford City and surrounds) to maximise sales and min
imise delivery distance. In this case, the site would have to be
located on the west shore of Waterford Bay close to the city of
Waterford. A general location for the site in the vicinity of Dunmore
East approximately 11 km from Waterford City (Fig. 2) was identi
fied with an allowance for transport of the DM of 2 km distance from
the docking/coupling position of the dredger (pipeline or truck).
The Port of Waterford has indicated that a docking location is not
currently available at the Port itself. The site selected for the pro
duction facility will have to meet all the technical requirements
based on a site zoning and designation.
2.2. Scenario A—TSHD
The TSHD used at the Port of Waterford currently disposes
of the DM offshore via bottom opening doors in its hull from
its 2189 m3 hopper. The proposed beneficial use scenario would
require pipeline transport to the onshore production site. Cycle
times for dredging and transport dictate the cost of any dredging
project. A typical dredging cycle consists of loading, steaming and
discharge. The cycle times for the TSHD currently in operation at
the Port of Waterford are shown in Table 1, as well as the antici
pated times for the pipeline transport scenario. The data is based
on sailing times for dredging operations in the Port of Waterford
and consultation with dredging contractors. The pipeline would be
located in waters sufficiently deep for the dredger to manoeuvre
and also close to the Dunmore East production site. The analysis
shows that the pipeline method would lengthen the cycle times
by approximately 31 min, an increase of approximately 12% rela
tive to the current practice of disposal at sea. The pumping time
to empty the dredger’s hoppers after it anchors and couples to a
pipeline accounts for approximately 47% of the total cycle time. For
this scenario the distance between the couple site location and the
production site is crucial, as for larger distances a booster station
would be required, increasing costs further.
Consultation with the Port of Waterford identified potential dif
ficulties with the positioning of the pipeline. At present locating
a pipeline in the vicinity of the shipping lane is not possible due
to the narrowness of the bay and the considerable ship traffic.
Despite these concerns, further analysis is presented to determine
the feasibility of this scenario should these potential difficulties be
overcome. In addition, this recovery and transport scenario, and the
research undertaken, may be applicable to other dredging sites.
2.3. Scenario B—GHD
The GHD available to the Port of Waterford uses a hopper
(785 m3 capacity), the hopper well is fitted with a grid to avoid
debris being deposited at sea, and discharges via hydraulically oper
ated bottom doors. The GHD scenario would have to use barges to
transport the dredged sediment as, due to technical issues onboard
the vessel (the debris grid), its hopper is unable to be unloaded. The
barges would be loaded by the GHD and then sail to the docking
position where they would be unloaded for truck transport. The
GHD with barge transport process is technically viable, however
the transport distance for barge transport to the nearest available
docking position of approximately 11 km is an issue.
2.4. Scenario C—purchased port owned dredger (PPOD)
The feasibility of purchasing a small port owned dredger that
can work continuously around the port was investigated. This
Table 1
Comparison of cycle times using a TSHD.
Average cycle time to
disposal site
Time (min) Average cycle time to
pipeline
Time (min)
Dredging 73 Dredging 73
Sailing to dump site 83 Sail to pipeline 13
Dumping 13 Coupling time 23
Sailing from dump site 76 Pumping time 132
Decoupling time 23
Return to dredging site 13
Total average hopper
cycle time
245 Total average pipeline
cycle time
277
212 C. Sheehan et al. / Resources, Conservation and Recycling 55 (2010) 209–220
method is not intended to replace the annual maintenance dredg
ing contract but to supplement the existing annual dredging by
external contractors. For this scenario a suitable TSHD currently for
sale was sourced from Londonderry Port in Northern Ireland. The
small TSHD has a hopper capacity of 400 m3 and currently dredges
60,000 tonnes annually.
This dredger could recover DM and transport it via its own
hopper to the docking position at Dunmore East where it could
be unloaded for truck transport. The possibility of leasing this
machine to other ports and harbours around Ireland that have
leased dredgers in the past, such as the Port of Cork, Fenit Har
bour, Kilkeel Harbour, the Port of New Ross and Dublin Port, would
significantly reduce its cost to the port but this potential revenue
stream was not included in the analysis presented in this paper.
2.5. Scenario D—leased dredger (LD)
The fourth scenario proposes using a GHD, the Hebble Sand,
owned by Dundalk Harbour which is used in dredging its own har
bour and is leased to other harbours, depending on availability. It
has a 550 m3 hopper capacity and uses its bottom opening doors for
discharge. However, it can be unloaded upon docking by either its
own grab or by port side equipment. The dredger’s transport sce
nario postdredging would be the same as Scenario C, using truck
transport once unloaded at Dunmore East.
3. Legislative framework
The stringent legislative framework governing the manufacture
of a topsoil product from dredged material in the Republic of Ire
land is outlined in Table 2. For analysis in this paper the production
site was assumed to be agriculturally zoned, in reality this would be
considered at the preplanning stage prior to any application to the
Environmental Protection Agency (EPA). If the land required were
designated industrial, the purchase cost of the site would be sig
nificantly higher. The proposed production facility would require
planning permission through Waterford County Council, an envi
ronmental impact statement would need to be produced based on
the size, type and location of the development, as well as the charac
teristics of the surrounding environment. A waste permit or license
would be required depending on the quantity of the material to be
treated.
The waste status of the product posttreatment is unclear. Arti
cle 6 of the Waste EU Directive (2008/98/EC) states that waste shall
cease to be specified as waste when it has undergone a recov
ery operation and complies with specific conditions. Currently, as
there are no specific standards for waste designation in Ireland,
the topsoil produced is certified by an independent soil scientist
(e.g. Teagasc who are the National Agriculture and Food Devel
opment Authority) as a quality riskfree soil material suitable for
use on land, then it would be classed as a product and no further
waste authorisation would be required. The standards required to
be met would be determined when an application is made to the
Environmental Protection Agency who currently assess each waste
license application on a case by case basis. The processing of such a
waste license application can take from 6 to 18 months with each
application requiring extensive testing and evaluation to ensure
the material is risk free.
4. Environmental analysis
4.1. Transport emissions
The proposed scheme involves significant transport of both
dredge and organic material producing carbon dioxide (CO2). The
0
0.5
1
1.5
2
2.5
3
Scenario A -
TSHD
Scenario B -
GHD
Scenario C -
PPOD
Scenario D -
LD
Disposal at
Sea
CO
2 E
mis
sio
ns p
er
ton
ne
of
DM
(kg
/tn
)
Dredging Sailing Truck/Pipeline Transport Organic Material Truck Transport
Fig. 4. CO2 produced for the different DM transport scenarios.
quantities of CO2 in kg generated per tonne of DM and transported
to the production site are shown in Fig. 4 (and subdivided to
highlight individual process contributions). Also shown is an esti
mate of the CO2 produced from the current practice of offshore
disposal. These estimates are based on data for CO2 emissions for
diesel engines (US Environmental Protection Agency, 2005) and the
engine power for each scenario. The CO2 produced from the overall
proposal has several sources including dredging the material and
transport to shore and to the production site. For scenarios that
require docking and truck transport the CO2 produced from truck
ing is a constant 0.241 kg CO2 per tonne of DM transported, based
on a fuel consumption of one litre per 2.124 km of haulage (Murphy
and McCarthy, 2005). CO2 emissions from the production site are
not included.
Disposal at sea, the current DM management option practised,
produces 1.1 kg of CO2 per tonne dredged and transported to the
disposal site. The pipeline transport for Scenario A produces the
least amount of CO2 (0.56 kg/tn) of all the options available due to
minimal hopper transportation. Both the PPOD and the GHD sce
narios have greater CO2 emissions than disposal at sea (1.7 kg/tn
and 1.72 kg/tn respectively) with the LD producing 2.55 kg/tn.
These higher rates are due to both large barge and hopper sailing
distances. The delivery of the organic material for all the proposed
scenarios is a constant of 0.09 kg/tn for a delivery distance of 15 km
from the recycling facility to the proposed production location and
this value is included in the analysis for each scenario. The truck
transport of both the organic and the DM would lead to a sub
stantial increase in traffic of 500 trips per 10,000 tonnes produced
per annum. The impact on CO2 emissions of the proposed topsoil
production beneficial use in comparison to others beneficial uses
developed for dredge material is unable to be undertaken due to a
lack of comparative information.
4.2. Sensitivity analysis on transport emissions
Sensitivity analyses have been undertaken to assess the most
critical components of the proposed scenarios in terms of the
CO2 transport emissions. Highlighting the critical components may
allow management measures to be implemented subsequently.
Sensitivity analyses were undertaken for:
• The capacity of the hopper/barge used for transport;• The distance from the production site to the quay/couple site;• Power consumption during dredging;• Distance from source of organic material.
Each scenario was examined for an annual topsoil production
level of 50,000 tonnes. This quantity was selected for analysis as
it was at the upper end of the demand in the area. The sensitiv
ity analysis is undertaken on the basis that the dredger selection,
C. Sheehan et al. / Resources, Conservation and Recycling 55 (2010) 209–220 213
Table 2
Legislative framework for manufactured topsoil production.
Legislation Responsible agency Comments
Production site legislation
Planning Permission (Planning and
Development Act, 2000)
Waterford County Council Required for a production facility. Public consultation process
required. Typical 3 month permitting timeframe (in parallel with other
required permits).
Environmental Impact Assessment
EC Directive 85/337/EEC
Waterford County Council, Environmental
Protection Agency
Ensures that projects that are likely to have significant impacts on the
environment are assessed.
Waste legislation
Waste Management Act
(1996–2005)—Licenses/Permits
Environmental Protection Agency Applied to any waste material (>100,000 tonnes) segregated, stored or
disposed onshore. License takes an average of 6 months to acquire;
more complex cases can take up to 18 months.
Waterford County Council Applied to any waste material (<100,000 tonnes) segregated, stored or
disposed onshore. The permitting process takes a maximum of 21 days.
Waste Management Collection
Permit Regulations 2008 (S.I. No. 87 of
2008)
Environmental Protection Agency, Waterford
County Council
Regulations apply where a haulier is transporting waste to and from a
site, or transporting waste for disposal or recovery.
Article 6 EU Directive 2008/98/EC on
Waste Management
Environmental Protection Agency Classifies the sediment as no longer a waste material and can be used
as a product, waste regulations then no longer apply.
Adapted from Harrington et al. (2004).
the production site location and other key site parameters can be
changed. Trendlines are fitted to the data points for each sensitiv
ity analysis undertaken with the goodness of fit represented by the
coefficient of determination (R2) value; a value of 1 provides the
perfect fit.
4.2.1. The capacity of the hopper/barge used for transport
A sensitivity analysis on the hopper/barge capacity size was
undertaken to establish the effect on the CO2 emission rates for each
scenario. The transport capacities used for the scenarios developed
vary with Scenario A (TSHD) having a capacity of 2189 m3, Sce
nario B (GHD) with a capacity of 785 m3, Scenario C (PPOD) with a
capacity of 400 m3, Scenario D (LD) with a capacity of 550 m3 and
Disposal at Sea (TSHD) with a capacity of 2189 m3. This analysis
assumes that the capacity of the dredger can vary with no nega
tive economic or environmental impacts. Fig. 5 shows the effect a
change in transport capacity has on CO2 emissions assuming that
the production rate and engine output (kilowatts) for each scenario
remains constant. A change in hopper/barge capacity changes the
transport efficiencies and thus impacts on CO2 emission rate. The
relationships developed are nonlinear with an increase in trans
port capacity reducing the CO2 emissions because of fewer sailing
trips.
4.2.2. The distance from the production site to the quay/couple
site
Fig. 6 shows how a change in the location of the production site
effects the CO2 emissions for each scenario. The production site
0
1
2
3
4
5
6
7
100806040200-20-40-60-80-100
Change in Hopper/Barge Capacity (%)
Scenario A - TSHD Scenario B - GHD Scenario C - PPOD
Scenario D - LD Disposal at Sea
CO
2 E
mis
sio
ns p
er
ton
ne
of
To
pso
il P
rod
uced
(kg
/tn
)
Fig. 5. CO2 Emissions based on a change in hopper/barge capacity.
was specified to be 2 km from the couple site; with DM pumping for
Scenario A and DM trucking for the other scenarios. A change in the
pipeline/truck transport distance impacts on the CO2 emission rates
for this part of the transport chain. For Scenario A (TSHD), which
uses pipeline transport, an increase of 1 km to the DM transport
distance will result in an increase of 0.050 kg/tn in CO2 emissions.
For Scenarios B–D, which use truck transport, an increase of 1 km in
transport distance will increase the CO2 emissions by 0.122 kg/tn.
4.2.3. Power consumption during dredging
The power consumption is a key characteristic in determining
the CO2 transport emissions. The power consumption of a dredger
is linked to the efficiency of the engine. If a reduction in power
consumption can be achieved while maintaining production rates
the efficiency of the engine is increased, reducing emission rates.
Each scenario proposed involves a different recovery process. The
power consumption of the dredgers used for each scenario devel
oped varies with Scenario A (TSHD) having a power output during
dredging of 600 kW, Scenario B (GHD) having a power output of
178 kW, Scenario C (PPOD) having a power output of 281 kW, Sce
nario D (LD) having a power output of 300 kW and Disposal at Sea
(TSHD) having a power output of 600 kW. This analysis assumes
that the dredger selected can change from those identified in Sec
tion 2.0. Fig. 7 shows the change in CO2 emissions based on a change
in power consumption during dredging, while maintaining the pro
duction rate. Due to the different power consumptions for each
transport scenario the impact on the CO2 emissions will differ for
0
0.5
1
1.5
2
2.5
3
3.5
0 2 4 6 8 10 12
Distance to Production Site From Quay/Couple Site (km)
CO
2 E
mis
sio
ns p
er
ton
ne
of
To
pso
il P
rod
uced
(kg
/tn
)
Scenario A - TSHD Scenario B - GHD
Scenario C - PPOD Scenario D - LD
y = 0.1222x + 1.658
y = 0.0534x + 0.6052
R2 = 1
Truck
Transport
Pipeline
Transpor t
Fig. 6. CO2 Emissions based on a change in the distance to the production site from
the quay/couple site.
214 C. Sheehan et al. / Resources, Conservation and Recycling 55 (2010) 209–220
0
0.5
1
1.5
2
2.5
3
-100 -80 -60 -40 -20 0 20 40 60 80 100
Change in Power Consumption during Dredging (%)
CO
2 E
mis
sio
ns
pe
r to
nn
e
of
To
pso
il P
rod
uced
(kg
/tn
)
Scenario A - TSHD Scenario B - GHD Scenario C - PPOD
Scenario D - LD Disposal at Sea
y = 0.0063x + 1.9022 y = 0.0033x + 1.4711
y = 0.0037x + 1.3622
y = 0.001x + 0.71
R2 = 1
Common
dredger
Fig. 7. CO2 emissions based on a change in power consumption during dredging.
each scenario. The dredger used for Scenario A is also the dredger
currently used for disposal at sea by the Port of Waterford and
an increase of 10% in power consumption would increase the CO2
emission rate by 0.010 kg/tn. A 10% increase in power consump
tion for Scenarios B–D would increase the CO2 emission rates by
0.037 kg/tn, 0.033 kg/tn and 0.063 kg/tn respectively. This analysis
highlights the importance of engine efficiency rates to minimise
CO2 emissions.
4.2.4. Distance from source of organic material
Organic material is required to be added to the DM to boost the
overall organic content of the created topsoil product. The quan
tity of organic material required was determined by the original
and target organic content of the mixes. For this analysis the initial
organic content was set at 2% with a target organic content of 6%.
Therefore, for 50,000 tonnes of topsoil to be produced per annum
2000 tonnes of organic material is required annually for addition.
This material is transported from an established local source by
truck. This sensitivity analysis highlights the importance of the
transport distance for the organic material from its source to the
production site and would assist during the planning stages when
identifying potential production sites and determining the over
all feasibility of the proposal. Fig. 8 highlights the effect a change
in distance to the source of the organic material has on the CO2
emissions. An increase of 10 km in delivery distance would increase
the CO2 emission level by 0.051 kg/tn of topsoil produced for each
scenario (the increase in delivery distance is common to each
scenario).
0
0.5
1
1.5
2
2.5
0 10 20 30 40 50 60
Distance to Source of Organic Material (km)
Scenario A - TSHD Scenario B - GHD
Scenario C - PPOD Scenario D - LD
R2 = 1
Truck
Transport
CO
2 E
mis
sio
ns p
er
ton
ne o
f
To
pso
il P
rod
uced
(kg
/tn
)
Fig. 8. CO2 emissions based on a change in the distance to the source of organic
material.
R2 = 0.8756
R2 = 0.8503R
2 = 0.8722
R2 = 0.854
0
10
20
30
40
50
60
250000200000150000100000500000
Topsoil Produced (tn/year)
Co
st
of
To
pso
il P
rod
ucti
on
(€/t
n)
Scenario A - TSHD Scenario B - GHD
Scenario C - PPOD Scenario D - LD
Fig. 9. Cost per tonne of topsoil produced for each DM transport scenario.
5. Economic analysis
5.1. Economic feasibility
An economic analysis has been undertaken on a treatment pro
cess for DM proposed (Sheehan et al., 2010) for each of the transport
scenarios. Land purchase, machinery purchase, land preparation
and the construction of a storage building are required for each
scenario. The value of agricultural land at the identified site loca
tion is approximately D17,000 per hectare (Central Statistics Office,
2005) and this reflects current values, despite fluctuations in the
price of agricultural land in recent years. The area of land required
varies with the amount of topsoil production as the dewater
ing and desalination area, as well as the storage of material,
increases with increased production. The land area required varies
from 1.5 hectares for 10,000 tonnes produced per annum to over
30 hectares for 250,000 tonnes produced per annum. The purchase
of a small port owned dredger is required for Scenario C, increasing
the initial capital costs and annual repayments.
The running costs include DM transport, as well as transport of
the organic material from the local composting facility. The recycled
organic material is currently provided free of charge from a local
recycling facility. Irrigation, mixing and layering are all required
during the desalination stage. Sampling and testing would need
to be undertaken monthly to ensure that all relevant standards
are adhered to. Insurance, labour, cost of capital repayments on
land and machinery and the economic effect of longer cycle times
on the maintenance dredging programme are all included. In the
case of Scenario C (PPOD) the annual labour, fuel and maintenance
charges are included. The costs associated with the pipeline and
barge transport are included where appropriate. Overheads are
assumed to be 10% of the total annual liabilities.
The economic analysis was undertaken for each transport sce
nario for a range of treated DM volumes ranging from 10,000 tonnes
to 250,000 tonnes (also included are 25,000 tonnes, 50,000 tonnes
and 100,000 tonnes); thus the work is applicable to a wide rang
ing topsoil demand. The analysis takes account of a wide range
of inputs from the Port of Waterford, Consulting Engineers and
Dredging Companies, some of which is confidential due to con
tractual obligations. All information gathered has been validated.
Tables 3–6 present detailed costings by dredge volume produced
for each transport scenario.
Figs. 9 and 10 show the overall results of the economic analy
sis with individual data points representing results for a specific
dredge volume. Logarithmic trend lines provide the best fit to the
data points. The cost of producing manufactured topsoil using the
four scenarios outlined is shown in Fig. 9. The overall production
C. Sheehan et al. / Resources, Conservation and Recycling 55 (2010) 209–220 215
Table 3
Capital and annual costs and liabilities for topsoil production using a TSHD (Scenario A).
Cost Volume (tn)
10,000 tonnes 25,000 tonnes 50,000 tonnes 100,000 tonnes 250,000 tonnes
Capital costs D521,121 D577,759 D691,671 D870,807 D1,286,490
Annual liabilities D548,382 D548,382 D1,374,269 D2,370,622 D5,249,939
Annual assets D252,600 D631,500 D1,263,000 D2,526,000 D6,315,000
Annual profit D−479,124 D−236,944 D−111,269 D155,378 D1,065,061
Profit/loss per tn D−47.91 D−9.48 D−2.23 D1.55 D4.26
Table 4
Capital and annual costs and liabilities for topsoil production using a GHD (Scenario B).
Cost Volume
10,000 tonnes 25,000 tonnes 50,000 tonnes 100,000 tonnes 250,000 tonnes
Capital costs D521,121 D577,759 D691,671 D870,807 D1,286,490
Annual liabilities D447,314 D889,971 D1,600,121 D3,005,124 D7,110,391
Annual assets D252,600 D631,500 D1,263,000 D2,526,000 D6,315,000
Annual profit D−258,471 D−258,471 D−337,121 D−479,124 D−795,391
Profit/loss per tn D−25.85 D−10.34 D−6.74 D−4.79 D−3.18
Table 5
Capital and annual costs and liabilities for topsoil production using a PPOD (Scenario C).
Cost Volume
10,000 tonnes 25,000 tonnes 50,000 tonnes 100,000 tonnes 250,000 tonnes
Capital costs D911,121 D967,759 D1,081,671 D1,260,807 D1,676,490
Annual liabilities D457,578 D711,904 D1,108,169 D1,885,403 D4,107,359
Annual assets D282,600 D706,500 D1,413,000 D2,826,000 D7,065,000
Annual profit D−174,978 D−5404 D304,831 D940,597 D2,957,641
Profit/loss per tn D−17.50 D−0.22 D6.10 D9.41 D11.83
Table 6
Capital and annual costs and liabilities for topsoil production using a LD (Scenario D).
Cost Volume
10,000 tonnes 25,000 tonnes 50,000 tonnes 100,000 tonnes 250,000 tonnes
Capital costs D521,121 D577,759 D691,671 D870,807 D1,286,490
Annual liabilities D361,360 D655,286 D1,117,551 D2,026,784 D4,644,741
Annual assets D282,600 D706,500 D1,413,000 D2,826,000 D7,065,000
Annual profit D−78,760 D51,214 D295,449 D799,216 D2,420,259
Profit/loss per tn D−7.88 D2.05 D5.91 D7.99 D9.68
cost ranges from D16/tn to D55/tn depending on the topsoil quantity
produced and the scenario proposed. Fig. 10 presents the profit/loss
per tonne for each transport scenario, with Table 7 presenting the
trend line equations developed (and associated R2 values), where
y represents the profit/loss per tonne per annum and x is the
quantity of topsoil material produced in tonnes per annum. Eco
nomic breakeven points, based on the trend lines generated are
also shown.
The economics for Scenario A, TSHD with pipeline trans
port, show that annual production quantities greater than
101,000 tonnes are required before the scheme can breakeven. The
main costs involved in this scenario are installing, maintaining and
using the pipeline method of transport. The cost of producing top
soil ranged from D21/tn to D55/tn depending on the topsoil quantity
produced. However, the large annual costs involved suggest that
only a relatively small profit can be made from this method even
when large quantities are produced. Due to navigational constraints
at the Port of Waterford a permanent fixed pipeline is not fea
sible. Therefore, as the pipeline must be mobilised and installed
annually during times of dredging, these costs are annual liabilities.
However, when considering other potential sites for manufactured
topsoil savings may be made through the purchase and installation
of a permanent pipeline as a capital expense.
The results from the GHD (Scenario B) using barge transport
show that this method of DM recovery and transport is not econom
ically viable. The main cost involved for this method compared to
the other methods is the transport cost for an 11 km sail distance
to the quay by barge due to the technical issues associated with
Table 7
Economic trendline equations and breakeven points for each DM transport scenario.
Transport scenario Trendline equation R2 Economic breakeven point (tn/annum)
Scenario A—TSHD y = 10.113 Ln(x)−116.51 0.8503 101,000
Scenario B—GHD y = 4.895 Ln(x)−61.868 0.8756 Unfeasible
Scenario C—PPOD y = 8.7718 Ln(x)−92.985 0.854 40,000
Scenario D—LD y = 5.2718 Ln(x)−53.489 0.8722 26,000
Notes: x denotes the topsoil quantity produced in tonnes per annum and y denotes the profit/loss per tonne produced per annum.
216 C. Sheehan et al. / Resources, Conservation and Recycling 55 (2010) 209–220
R2 = 0.8756
R2 = 0.8503
R2 = 0.854
R2 = 0.8722
-40
-30
-20
-10
0
10
20
0 50000 100000 150000 200000 250000
Topsoil Produced (tn/year)
Pro
fit/
Lo
ss
pe
r T
on
ne
of
To
pso
il P
rod
uced
(€/t
n)
Scenario A - TSHD Scenario B - GHD
Scenario C - PPOD Scenario D - LD
Breakeven
Point Breakeven
Point
Breakeven
Point
Fig. 10. Profit/loss per tonne treated for each DM transport scenario.
the dredger hopper; this accounts for between 25% and 39% of the
annual liabilities. The cost of producing topsoil using this method
ranged from D28/tn to D45/tn depending on the topsoil quantity
produced. However, this scenario, under the current conditions,
cannot breakeven and thus does not make a profit for any of the
quantities analysed.
The results for the PPOD (Scenario C) are encouraging and eco
nomically viable. Despite this method having larger capital costs
due to the purchase of a dredger it breaks even at approximately
40,000 tonnes produced annually. The dredger also saves the Port
money by reducing the quantity of material dredged by the annual
dredging contract holder and this saving is included in the analysis.
The results for the LD (Scenario D) are similar to the PPOD although
the economic breakeven point is reached at a lower volume of top
soil produced making this the more attractive scenario for smaller
quantities of topsoil production. The annual liabilities are covered
once approximately 26,000 tonnes of topsoil is produced and sold.
For smaller quantities of production the leased dredger is more
attractive than the purchased dredger as it breaks even at a lower
volume, however, as Fig. 10 highlights for greater production rates
purchasing a dredger is more attractive economically.
The economic analyses presented highlight the potential prof
its/losses associated with each of the proposed scenarios. The
analyses show that the LD or the PPOD schemes are the most feasi
ble from an economic point of view depending on the demand for
topsoil in the area. The most suitable for the Port of Waterford at
present, when considering local demand for topsoil, is the leasing
of a dredger (Scenario D) to recover and transport the DM to the
production site. If the topsoil demand increased to approximately
80,000 tonnes per annum then Scenario C (PPOD) would become
the more viable option. This analysis does not take into account the
potential additional revenue that Scenario C (PPOD) may provide
by undertaking external contracting work.
5.2. Sensitivity analysis
Sensitivity analyses have been undertaken to assess the most
critical components of the proposed scenarios on the potential
profit/loss that may be achieved. Identifying and analysing the
critical components may allow management measures to be imple
mented to reduce the most significant cost items. Each scenario
was examined for a production rate of 50,000 tonnes of topsoil pro
duced annually as per the environmental sensitivity analysis. The
components examined are:
• Sale price of topsoil;• The distance from the production site to the quay/couple site;• Cost of organic material;• The effect of the introduction of a disposal at sea waste charge.
-25
-20
-15
-10
-5
0
5
10
15
20
25
€10 €20 €30 €40
Sale Price of Topsoil (€/tn)
Po
ten
tial P
rofi
t/L
os
s (
€/t
n)
Scenario A - TSHD Scenario B - GHD
Scenario C - PPOD Scenario D - LD
Breakeven
Point
Breakeven
Point
Breakeven
Point
R2 = 1
Fig. 11. Potential profit/loss based on a change in topsoil sale price.
5.2.1. Sale price of topsoil
A sensitivity analysis on the sale price of the topsoil was under
taken. A survey undertaken indicated the average price of topsoil
in the Waterford region as D25.26/tn (Sheehan et al., 2010). Fig. 11
shows the potential profit/loss for each scenario as the topsoil price
varies from D10/tn to D40/tn. A change of D1/tn in the sale price will
result in a change of D1/tn in the potential profit as the sale price
of the topsoil is the sole revenue stream. The breakeven point for
each scenario is also shown. For the current site conditions outlined
Scenario A (TSHD) would require a sale price of at least D27.60/tn to
achieve economic feasibility. Scenario B (GDH), which has higher
transport costs, would require D32.12/tn, with Scenario C (PPOD)
and Scenario D (LD) requiring D19.14/tn and D19.33/tn respectively
to cover the annual liabilities.
5.2.2. The distance from the production site to the quay/couple
site
The potential profit/loss with a change in the distance of the
production site to the quay/couple site for each scenario is pre
sented in Fig. 12. This distance (currently 2 km) has a significant
influence on the potential profit due to the extensive transport by
truck or pipeline. Scenario A (TSHD) uses a pipeline to transport the
DM between the couple site and the production site and a change
of 1 km in transport distance will result in a change of D1.82/tn
in the potential profit. Breakeven for Scenario A is for a pipeline
length of 0.578 km, which is not surprising due to the high costs of
mobilising, installing and maintaining a pipeline. Scenarios B–D use
truck transport and a 1 km increase in transport distance reduces
the potential profit by D0.26/tn. Under the current site conditions
Scenarios C and D remain economically feasible if the trucking dis
-100
-80
-60
-40
-20
0
20
0 10 20 30 40 50 60
Distance to Production Site From Quay/Couple Site (km)
Po
ten
tial P
rofi
t/L
oss (
€/t
n)
Scenario A - TSHD Scenario B - GHD
Scenario C - PPOD Scenario D - LD
y = -0.2641x - 6.5871
y = -1.8218x + 1.0531
Breakeven
Point
Breakeven
Point
R2 = 1
Truck
Transport
Pipeline
Transport
Fig. 12. Potential profit/loss based on the location of the production site.
C. Sheehan et al. / Resources, Conservation and Recycling 55 (2010) 209–220 217
-15
-10
-5
0
5
10
0 20 40 60 80 100 120
Cost of Organic Material (€/tn)
Po
ten
tial P
rofi
t/L
oss (
€/t
n)
Scenario A - TSHD Scenario B - GHD
Scenario C - PPOD Scenario D - LD
R2 = 1 Breakeven
Points
Fig. 13. Potential profit/loss based on the cost of organic material.
tance remains below 24.2 km and 23.5 km respectively. Scenario B
does not achieve economic feasibility.
5.2.3. Cost of organic material
The production facility identified for the supply of organic mate
rial currently does not charge for collection. However, this may
change or a different source may be chosen. Fig. 13 shows the effect
of the introduction of a charge for organic material on the potential
profit/loss. A D1/tn change in the price of organic material reduces
the potential profit by D0.06/tn for each scenario. It should be noted
that the initial and target organic content will have an effect on both
the purchase price and the transport of the organic material due to
the change in the quantity required. Scenarios C and D are no longer
profitable at organic material costs of approximately D111/tn and
D108/tn respectively.
5.2.4. The effect of the introduction of a disposal at sea waste
charge
Currently there is no incentive for Irish ports and harbours to
alter their DM management plans with the Disposal at Sea charge
for any DM quantity a paltry D63.49. Should a disposal charge
be introduced that is comparable to other waste materials gate
fees in Ireland (D132 per tonne for landfill in 2008—Forfas, 2009)
or other international fees for disposal at sea, e.g. approximately
D0.09–0.43/tn ($0.10–0.45/yd3) in Washington State (Washington
State, 2010) a significant impact on the economics of each sce
nario could be achieved, as Fig. 14 outlines. The introduction of a
waste charge for Scenarios C and D would only increase the poten
tial profit. However, Scenarios A and B would require a disposal
-10
-5
0
5
10
15
20
€0 €2 €4 €6 €8 €10
Disposal at Sea Charge (€/tn)
Po
ten
tial P
rofi
t/L
oss (
€/t
n)
Scenario A - TSHD Scenario B - GHD
Scenario C - PPOD Scenario D - LD
Breakeven
Point
Breakeven
Point
R2 = 1
Fig. 14. Potential profit/loss based on the introduction of a waste charge on disposal
at sea.
charge of D2.34/tn and D6.86/tn respectively to breakeven. A D1/tn
change in the waste charge results in a D1/tn change in the potential
profit/loss.
6. Discussion
The selection of a location for the production site is crucial
to optimising the economics of the proposed scheme. The local
demand for topsoil is crucial to both the selection of the produc
tion site location and the overall feasibility of the facility. The site
must be located near both the target market and the proposed dock
ing/coupling position. Zoning/legislative issues for the production
site remain unclear but the EPA would present site requirements at
the formal preapplication/Environmental Impact Statement pro
cess stage.
The technical logistics of each proposed scenario highlight
several areas where these different methods may be more eco
nomically feasible under the appropriate site conditions. The TSHD
scenario is not technically feasible at the Port of Waterford at
present due to navigational constraints. However, this method of
recovery and transport is feasible under certain site conditions.
The GHD scenario, while technically feasible, has financial con
straints due to technical issues onboard the vessel. The PPOD and
LD scenarios are both technically feasible but involve large trans
port distances. Technical constraints at the Port of Waterford and
other smaller quays in the area (due to traffic flow and vessel
draft requirements) negatively impact on the financial feasibility
of DM transport to the nearest docking position at Dunmore East.
However, if an alternative unloading site were available then the
transport distance would be shorter and would improve the eco
nomic feasibility of each scenario.
Irish legislation has recently changed to encourage greater con
sideration of long term DM beneficial use. 5Year Dumping at Sea
License applications must now include a detailed investigation of
beneficial use options. The timeframes involved in acquiring the
licenses require long term planning as a prerequisite. In general,
DM being classified as a waste despite its inert chemical character
istics (i.e. uncontaminated material) is also a contentious issue. For
a manufactured topsoil product from DM to be successfully imple
mented the waste licensing issues would have to be resolved with
the EPA. Appropriate quality standards would have to be deter
mined and set for the DM for it to be no longer classed as a waste.
The lack of legislation for waste designation is in general an impor
tant issue for DM management in Ireland. Due to the extensive
planning that a beneficial use of DM, such as the production of man
ufactured topsoil, requires the lack of pertinent national legislation
or guidelines creates uncertainty for the potential successful exe
cution of a beneficial use proposal. This hinders the potential use of
DM as a resource as, without appropriate standards, the material
can only be classified as a waste. Implementation of waste stan
dards would aid in the advanced planning of DM management and
increase the potential consideration of beneficial uses of DM, such
as manufactured topsoil, as proposed in this paper.
The proposed beneficial use for the DM will require an Environ
mental Impact Statement as it is planned for an agriculturally zoned
site. Negative environmental impacts would include truck trans
port of the DM and the organic material, leading to a substantial
increase in traffic volumes in the local area. The EPA has indicated
that site requirements would be specified at the appropriate stage,
including any noise, odour and leachate retention issues.
Transport of the DM and the organic material is an important
part of the overall logistics of the proposal and has environmental
implications. For Scenario A (TSHD) the CO2 transport emissions
account for 33% of the overall emissions primarily from the use
of a pipeline for DM transport (the sail distance is only 4 km). The
218 C. Sheehan et al. / Resources, Conservation and Recycling 55 (2010) 209–220
Table 8
Summary results for the environmental sensitivity analysis.
Scenario Parameter Current status 10% Change Change in emissions
(kg CO2/tn)
Environmentally
ranked significance
Scenario A (TSHD) Capacity of the hopper/barge 2189 m3−219 m3 0.058 1
Distance from the production site to the quay/couple site 2 km 0.2 km 0.01 3
Power consumption during dredging 600 kW 60 kW 0.01 2
Distance from source of organic material 5 km 0.5 km 0.0025 4
Scenario B (GHD) Capacity of the hopper/barge 340 m3−34 m3 0.085 1
Distance from the production site to the quay/couple site 2 km 0.2 km 0.0244 3
Power consumption during dredging 178 kW 18 kW 0.037 2
Distance from source of organic material 5 km 0.5 km 0.0025 4
Scenario C (PPOD) Capacity of the hopper/barge 400 m3−40 m3 0.105 1
Distance from the production site to the quay/couple site 2 km 0.2 km 0.0244 3
Power consumption during dredging 281 kW 28 kW 0.033 2
Distance from source of organic material 5 km 0.5 km 0.0025 4
Scenario D (LD) Capacity of the hopper/barge 550 m3−55 m3 0.124 1
Distance from the production site to the quay/couple site 2 km 0.2 km 0.0244 3
Power consumption during dredging 300 kW 30 kW 0.063 2
Distance from source of organic material 5 km 0.5 km 0.0025 4
other three scenarios that use hopper or barge transport have trans
port emissions accounting for between 58% and 65% of the total
emissions for each scheme. The current practice of disposal at sea
has CO2 transport emission rates which account for approximately
85% of the overall emissions. From the analysis undertaken pipeline
transport is the most environmentally friendly option as shown in
Fig. 4.
An environmental sensitivity analysis was undertaken for each
scenario to determine the critical parameters. In general, a change
in any of the key parameters outlined (the capacity of the hop
per/barge used for transport, the distance from the production site
to the quay/couple site, power consumption during dredging, or
distance from source of organic material) will have a linearly pro
portionate effect on the overall CO2 emissions with the exception of
a change in hopper/barge capacity. Table 8 presents a summary of
the results of the analysis and also provides a ranking approach for
CO2 emissions for each individual scenario. This table ranks the key
parameters analysed for each scenario to highlight the areas most
appropriate for implementation of potential alternatives or miti
gating measures. The adjustment for each parameter in Table 8 is
10% from its current status. It should be noted that despite the dif
ferences in the scenarios’ individual logistics the ranking system
established for each scenario in Table 8 is the same. The capac
ity of the hopper/barge was found to have the greatest impact
when considering CO2 emission rates. Reducing the hopper/barge
capacity impacts substantially on the efficiency, with more sailing
trips required. A 10% change impacts on each scenario differently
ranging from 0.058 kg CO2/tn (Scenario A) to 0.124 kg CO2/tn (Sce
nario D). The power consumption of the dredger was found to be
the parameter of second highest importance with a 10% change
causing CO2 emissions to change from 0.010 kg CO2/tn (Scenario
A) to 0.063 kg CO2/tn (Scenario D) depending on the power out
put of each individual dredger. This highlights the importance of
optimising the efficiency of the engines to produce the highest pos
sible production rate. The distance from the production site to the
quay couple site was the third most important parameter with a
10% change causing CO2 emissions to change by 0.010 kg CO2/tn
for Scenario A and 0.024 kg CO2/tn for the other scenarios. This is
an important aspect when considering the environmental impact
of a topsoil production facility due to the large volume of mate
rial requiring truck/pipeline transport. It should also be noted that
substantial truck transport will have a negative impact on the local
traffic network. The distance to the source of the organic material is
important depending on the quantity of material required (based
on the initial and target organic content levels) but the sensitiv
ity analysis undertaken showed that a 10% increase increased the
emission rates by 0.0025 kg CO2/tn.
The economics of recovering and treating DM were investigated.
Relationships were developed from the analysis to assess potential
profit/loss for each scenario. However, with the annual demand
in the locality estimated at between 25,000 and 50,000 tonnes,
and some other sources of topsoil already available, the breakeven
point for each of the processes proposed is relatively high for
the anticipated demand. The most feasible scheme (Scenario
D—LD) is economically viable if the annual production is approx
imately 26,000 tonnes (25,700 tonnes of DM with 5% organic
addition).
An economic sensitivity analysis was also undertaken for each
scenario. A change in any of the key parameters outlined (sale price
of topsoil, the distance from the production site to the quay/couple
site, cost of the organic material, or the effect of the introduction
of a disposal at sea waste charge) will have a linearly proportion
ate effect on the overall profit/loss. Table 9 summarises the results
and ranks the parameters examined. The change in each individual
parameter analysed is based on the most appropriate charge for
that particular parameter. The topsoil sale price was established as
the parameter of highest economic importance due to it being the
sole revenue stream. A change of 10% in the sale price of topsoil
affects the potential profit/loss by D2.53/tn. This is the key revenue
stream associated with topsoil production and maximising the level
of income is crucial to economic feasibility. The cost of the organic
material is second most important economically due to the poten
tial change in the price per tonne (D0/tn to a potential D30/tn). If
similar charges were implemented for the organic material sourced
the potential profit would reduce by D1.80/tn. Introducing disposal
at sea charges as practiced elsewhere is the third most important
parameter and its introduction would have a substantial impact on
the potential profit/loss. The elimination of a disposal at sea charge
from a dredging project is a cost saving and therefore treated as
revenue in any proposed alternative scheme. If a charge of D0.43/tn
(the upper cost for disposal in Washington State, US is $0.45/yd3)
was introduced, for example, the potential profit would increase by
D0.43/tn. A 50% change (1 km) in the distance from the production
site to the quay/couple site impacts differently for each scenario. It
is the least important for Scenarios B–D, which use truck transport,
and is ranked fourth in economic importance with an increase of
1 km in trucking distance for these scenarios resulting in a increase
of D0.26/tn in their potential profit. However for Scenario A, which
uses pipeline transport, it is the second most important parameter
due to the high annual costs incurred with an increase of 1 km in
DM pumping distance resulting in an increase of D1.82/tn in the
potential profit. This ranking approach can assist DM management
practice during the planning stages of a project, identifying areas
where cost reduction can be implemented.
C. Sheehan et al. / Resources, Conservation and Recycling 55 (2010) 209–220 219
Table 9
Summary results for the economic sensitivity analysis for costs/revenues common to all scenarios.
Economic parameter Current price/status Change Change in profit/loss Economically ranked significance
Sale price of topsoil D25.26/tn D2.53/tn D2.53/tn 1
Introduction of a disposal at
sea waste charge
D0/tn D0.43/tn D0.43/tn 3
Distance from the production
site to the quay/couple site
2 km 1 km D1.82/tn for Scenario A;
D0.26/tn for Scenarios B–D
4
Cost of organic material D0/tn D30/tn D1.8/tn 2
Both the environmental and the economic sensitivity analy
ses undertaken analysed a range of parameters for the production
of 50,000 tonnes of topsoil annually. This level of production was
selected as it is at the upper end of the local topsoil demand
and as Waterford is a city with a relatively small population
the sensitivity analysis undertaken may be useful for locations
with a larger population base. The selection of a smaller topsoil
quantity would not impact the linear nature of the trend lines pro
duced for the environmental and economic sensitivity analysis.
Total CO2 emissions will decrease for a lower level of produc
tion; CO2 emissions per tonne of DM transported will remain
constant. However, the economic breakeven points will be differ
ent. For example, for an annual production rate of 50,000 tonnes
for Scenario D the economic breakeven point occurs at a top
soil sale price of D19.33/tn. When this scenario is reanalysed for
a production level of 25,000 tonnes per annum the breakeven
point increases to D21.46/tn. This increase is due to the capi
tal costs being spread over a smaller number of units (tonnes
produced) increasing the unit cost of topsoil production. Simi
larly it can be shown that an increase in the annual production
rate above 50,000 tonnes would lower the economic breakeven
point.
Table 10 provides a logistical, environmental and economic
ranking system for each scenario. The logistical and economic
analyses show that the leased dredger (Scenario D) is the most
suitable choice for the site conditions outlined with the lowest
economic breakeven threshold when production remains below
80,000 tonnes per annum. However, when this production rate is
exceeded Scenario C (PPOD) is the most attractive option. Logisti
cal issues are increased through the introduction of fuel, labour and
maintenance but additional revenue may be generated through the
leasing of this dredger to suitable regional ports. The CO2 emissions
of the PPOD are also considerable lower than the LD. Consequently,
the choice between these two scenarios is site specific, depend
ing on topsoil demand, annual dredging rates and the potential
for additional revenue through leasing. The defining condition in
the case of the Port of Waterford is the local demand for topsoil,
designating Scenario D (LD) as the most suitable option. Environ
mentally Scenario A (TSHD) is most suitable because of its low CO2
emission rates due to the use of DM pipeline transport, however,
the economic breakeven point makes the scenario unfeasible. Sce
nario B (GHD) is unfeasible due to onboard logistics preventing
unloading, high annual costs preventing economic breakeven and
unfavourable CO2 emissions. It should be noted that these rank
ings may change for other locations with different site conditions
Table 10
Logistical, environmental and economic ranking of the scenarios proposed.
Scenario Logistical Environmental Economic
Scenario A—TSHD 3 1 3
Scenario B—GHD 4 3 4
Scenario C—PPOD 2 2 2
Scenario D—LD 1 4 1
Notes: The lower the ranking the higher the performance, i.e. 1 designates best
performance, 4 designates poorest performance.
but the overall approach presented here provides an assessment
framework for other potential sites.
This proposal provides a beneficial use for two designated waste
streams, DM and household waste. While it is not practical to use
all of the DM at the Port of Waterford for topsoil manufacture, due
to limited demand in the area, a reduction in the quantity of mate
rial disposed at sea would be achieved. This proposal also provides
a guaranteed end use for a proportion of the compost (organic
material) produced locally thus providing improved stability and
sustainability to the compost market.
7. Conclusions
This paper presents an environmental and economic assessment
of DM transport and production of manufactured topsoil from DM
and recycled household waste to provide an environmentally sus
tainable alternative to disposal at sea. The overall process alters the
material’s status from a waste substance to a valuable product pro
viding environmental sustainability. The site selection is crucial to
determining the potential of and feasibility for implementation of
the proposal. The site should be located close to the dredging site to
minimise DM transport with its associated cost and CO2 emissions
while ensuring that the transport distance to the target market is
not excessive. The four scenarios analysed use different DM recov
ery and transport methods to identify the most appropriate for the
Port of Waterford. The environmental analysis showed Scenario A
(TSHD) to be the lowest CO2 emitter (0.56 kg/tn) due to the use
of a pipeline for DM transport. The other three scenarios analysed
all exceed the CO2 emissions (1.1 kg/tn) for disposal at sea due to
significant hopper and truck transport.
The sensitivity analysis undertaken highlights the potential
variability of the feasibility of this proposal depending on logis
tical parameters such as dredger selection and DM transport
distance. The environmental sensitivity analyses identified the
relative importance of individual aspects of the different DM trans
port processes proposed. By establishing a ranking approach DM
management measures can focus on the most critical issues. The
analyses highlight the importance of the dredger in minimising
CO2 emissions both in the recovery and in the transport phases
of operation by optimising engine efficiency and hopper capacity.
From an economic viewpoint the scenarios involving either
the purchasing or leasing of a dredger (Scenarios C and D) are
most feasible. This is due to the potential profit that can be
realised and the low annual breakeven points (40,000 tonnes and
26,000 tonnes respectively) relative to Scenario A or B. Scenario
A (TSHD) would require a substantial topsoil demand of approxi
mately 101,000 tonnes/year to be economically feasible (this is in
addition to the technical constraints previously identified) while
Scenario B (GHD) is not economically feasible. The most econom
ically feasible option is Scenario D (LD) where the topsoil can
be produced for D22/tn for an annual topsoil production rate of
50,000 tonnes. For this scenario and the site characteristics out
lined for the Port of Waterford at least 26,000 tonnes per annum of
topsoil would be required to sustain the project economically. In
summary, Scenario D is the most suitable DM management option
available.
220 C. Sheehan et al. / Resources, Conservation and Recycling 55 (2010) 209–220
The economic sensitivity analyses identified the key parameters
which need to be prioritised at the project planning stage. The local
sale price of topsoil is most crucial when determining the economic
feasibility at a site. At the Port of Waterford the cost of the organic
material was established to be important. As the organic material
can currently be sourced without charge any cost would have a
significant impact on the potential profit. This is a key issue to be
considered when analysing other potential sites for manufactured
topsoil production from DM. With sufficient long term planning and
communication between all the relevant stakeholders, dredging
projects can be made more environmentally sustainable.
Acknowledgements
The authors wish to acknowledge the funding received from the
Irish Environmental Protection Agency under the Science, Tech
nology, Research and Innovation for the Environment (STRIVE)
Programme 2007–2013. We would like to thank Michael Clooney
of the Port of Waterford, Anthony Bates Consultants, Paul Mitchell
of UK Dredging, Jonathan Derham and Kevin Motherway of the
Irish Environmental Protection Agency and Mick Storan of Veolia
Environmental Services for all their help and assistance.
References
Burt TN. Guidelines for the beneficial use of dredge material. Report SR488 HRWallingford, Oxford, England; 1996.
Central Statistics Office. Agricultural land sales 2005. Dublin, Ireland: Central Statistics Office; 2005.
Directive 2008/98/EC. New Waste Framework Directive—Article 6. European Parliament and Council, Official Journal of the European Union; 2008.
Forfas. Annual Competitiveness Report 2009, Volume Two: Ireland’s Competitiveness Challenge. Dublin: National Competitiveness Council; 2009.
Harrington JR, Sutton S, Lewis AW. Dredging and dredge disposal and reuse inIreland—a small island perspective. In: Proceedings of World Dredging CongressXVII, B45; 2004. p. 1–14.
Lee CR, Sturgis TC. Manufactured soils: a productive use of dredged material. In:Proceedings US/Japan Experts Meeting. Vicksburg, MS: US Army EngineersWaterways Experiment Station; 1996.
Murphy JD, McCarthy K. Ethanol production from energy crops and wastes for useas a transport fuel in Ireland. Applied Energy 2005;82(2):148–66.
Riddell JF, Fleming G, Smith PG. The use of dredged material as a topsoil. Terra etAqua 1989(April (39)):1989.
Ruff JR, Lee CS. Beneficial use of dredged material is “in the bag”, environmental effects of dredging. Vicksburg, USA: Army Engineer Waterways ExperimentStation; February 1997.
Sheehan C, Harrington JR, Murphy JD. Dredging and dredge material beneficial reusein Ireland. Terra et Aqua 2009;115:3–14.
Sheehan C, Harrington JR, Murphy JD. A technical assessment of topsoil production from dredged material. Journal of Resources, Conservation and Recycling2010;54(October (12)):1377–85.
Thomas BR, De Silva MS. Topsoil from dredgings: a solution for land reclamation inthe coastal zone. In: Davies MCR, editor. Land reclamation: an end to dereliction?London, UK: Elsevier; 1991.
USACE. Manufactured soil screening test. United States Army Corps of Engineers,ERDC TNDOERC6; May 1999.
USACE. Equipment and processes for removing debris and trash from dredged material. United States Army Corps of Engineers, ERDC TNDOERC17; August 2000.
USACE. Innovative dredged sediment decontamination and treatment technologies.United States Army Corps of Engineers, ERDC TNDOERT2; December 2000.
US Environmental Protection Agency. Emission Facts: Average Carbon Dioxide Emissions Resulting from Gasoline and Diesel Fuel, EPA420F05001. Washington,DC: United States Environmental Protection Agency; February 2005.
Washington State. Fees for use of aquatic land dredged material disposal sites authorized, Legislation RCW 79.105.520. United States: Washington State; 2010.