© Anthony D Bates Partnership LLP 17 | P a g e

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

© Anthony D Bates Partnership LLP 18 | P a g e

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.

© Anthony D Bates Partnership LLP 19 | P a g e

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

© Anthony D Bates Partnership LLP 20 | P a g e

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

© Anthony D Bates Partnership LLP 21 | P a g e

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.

© Anthony D Bates Partnership LLP 22 | P a g e

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.

© Anthony D Bates Partnership LLP 23 | P a g e

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

© Anthony D Bates Partnership LLP 24 | P a g e

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.

© Anthony D Bates Partnership LLP 25 | P a g e

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: colm.sheehan@cit.ie (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: colm.sheehan@cit.ie (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.