Contaminated Land

Question 1

What is a source?

Answer 1

The location or feature from which contamination is, or was, derived. This could be the location of the highest concentration of the contaminant in either the soil or groundwater.

Question 2

What is a pathway?

Answer 2

A route, means or mechanism by which a contaminant comes into contact with or affects a receptor.

Question 3

Name some potential pathways both natural and man made.

Answer 3

• Ingestion, inhalation, direct contact
• consumption of home grown vegetables
• through roots into plants
• vapour and gas migration
• horizontal migration through the ground - preferential pathways
• vertical migration through the ground such as capillary action or gravity
• movement with and through groundwater

Question 4

What is a receptor?

Answer 4

Something that could be adversely affected by a contaminant such as people, living organisms, ecological systems, controlled waters, atmosphere, structures and utilities.

Question 5

Name some potential receptors.

Answer 5

• Temporary site or construction workers
• End users, future residents, home owners, adults and children.
• Neighbours
• Shallow perched groundwater
• Deeper groundwater
• Surface waters
• The ecological system
• Services e.g. water supply pipes, phenols penetrate plastic water pipes
• Property e.g. buildings, land and crops

Question 6

Describe the concept of source-pathway-receptor linkage (pollutant linkage)

Answer 6

This underpins the way in which land affected by contamination is assessed and the associated risks are managed.
On any individual site there may be only a single pollutant linkage or several.
Different pollutant linkages my related i.e. the same contaminant may be linked to two or more distinct types of receptor by different pathways or different contaminants and/or pathways may affect the same receptor.
Not all receptors will be relevant in every context and new pollutant linkages may be created by changes over time.
Each pollutant linkages needs to be separately identified understood and dealt with if appropriate.
For there to be a risk presented to a certain receptor, both a source and a pathway must be present. For a source to present a risk, a pathway and a receptor must be present
Missing link = no risk

Question 7

What are NAPLs?

Answer 7

Non-aqueous phase liquids are organic contaminants that exist as a separate immiscible phase when in contact with water/air. They have different viscosity and density to water.
High viscosity > Lower K > Slower flow
High density > Higher K > Faster flow

Question 8

Relate capillary pressure to infiltration

Answer 8

P(NW) - P(W) = P(C) = 2σ/r
Higher surface tension, σ and/or a smaller radius, r, will lead to higher P(C).
If P(C) = 0 there will be no infiltration
If P(C) > 0 there will be infiltration of the first few pores
If P(C)&raquo_space; 0 there will be infiltration of many pores.
Infiltration will stop when P(NW) = P(W) when there is either not enough NAPL to continue infiltrating or the pore size is too small to allow infiltration.

Question 9

Zone I (simplified relative permeability diagram)

Answer 9

NAPL occurs as a potentially mobile, continuous phase and saturation is high. Water is restricted to small pores. Relative permeability of water is low.

Question 10

Zone II (simplified relative permeability diagram)

Answer 10

Both NAPL and water occur as continuous phases. However, relative permeability of each fluid is greatly reduced by the saturation of the other fluid.

Question 11

Zone III (simplified relative permeability diagram)

Answer 11

NAPL is discontinuous and trapped as residual in isolated pores. Flow is almost exclusively the movement of water, not NAPL.

Question 12

Briefly outline for your client the main stages; from before they buy the site to handover to the end users; that need to be carried out in connection with land affected by contamination in order to develop the site.

Answer 12

• The whole process should be a Step by Step or phased process; with information gained at
  each stage used to determine the most appropriate next step.
• Desk Study and Site Reconnaissance.
• Preliminary Conceptual (site) Model.
• Intrusive ground investigation, in situ and laboratory sampling and testing.
• Factual Report.
• Interpretative Report; identifying amongst other things; “sources” > “pathways” >
  “receptors” – “pollutant linkages.
• Risk Assessment; either qualitative or quantitative; including human health risk
  assessment & controlled waters (groundwater & surface waters) risk assessment.
• A modified Conceptual (site) Model.
• Liaison with the regulators; the Local Authority and the Environment Agency.
• Options Appraisal; looking at the advantages / disadvantages / costs / sustainability etc of
  different remediation options.
• Prepare a Remediation Strategy and Specification.
• Implementation and remediation carry out the remediation on site; modifying the strategy
  depending on the actual findings on site; an ongoing part of the overall process.
• Validation Testing to factually demonstrate that the remediation has been carried out and
  completed in accordance with the specification.

Question 13

Describe the forms that contaminants in soil and groundwater may take.

Answer 13

• Solid, liquid, gas.
• Heavy metals, Phytotoxic metals, Organic chemicals, Inorganic chemicals, Bacterial.
• Mobile (e.g. migrating gas, e.g. leaching into groundwater).
• Immobile, attach to clay particles;
• DNAPLs: Dense non aqueous phase liquids, denser than water, sink; chlorinated solvents,
  TCE, etc
• LNAPLs: Light non aqueous phase liquids, lighter than water, float, etc.

Question 14

Explain the term ‘Pollutant Linkage’ and how such a linkage might impact on the client’s development plans.

Answer 14

There are potentially many “pollutant linkages” on a contaminated site.
If there is NO “pollutant linkage” there is no risk, there no “significant harm” or NO
“significant possibility of such harm” to receptors and therefore no need for any
remediation.
Source: a substance [ or contaminant ] that is in, on or under the land and has the potential to
cause harm [ to people, living organisms, ecological systems ] or to cause pollution of controlled
waters. e.g. contaminants in soil, groundwater and gaseous phase
Source: is the location or feature from which contamination is, or was, derived. NB This could be
the location of the highest concentration of the contaminant in either the soil or groundwater. e.g.
chemical containers, tanks, pipelines, spills, fuels etc
Sources are the actual original source of contamination or areas of land or controlled waters
(groundwater or surface waters) that are contaminated by one or several contaminants.
Pathway: is a route, means or mechanism by which a contaminant comes into contact with, or
otherwise affects, a receptor. e.g. potential pathways, natural and man made, could be:
 ingestion, inhalation, direct contact, dermal contact;
 consumption of home grown vegetables etc.;
 through roots into plants;
 vapour and gas migration;
 migration through the ground, horizontally, preferential pathways;
 migration through the ground, vertically, capillary action, gravity;
 movement with and through groundwater.
Pathways are routes by which the contaminant can migrate or move to a receptor.
Receptor: is something that could be adversely affected by a contaminant, such as; people, living
organisms, ecological systems, controlled waters, atmosphere, structures and utilities. e.g.
potential sensitive receptors could be:
 temporary site or construction workers;
 end users, future residents, home owners; adults & children;
 neighbours;
 shallow perched groundwater;
 deeper groundwater;
 surface waters;
 the ecological system, and finally;
 services, (e.g. water supply pipes, phenols penetrate plastic water pipes)
 property (e.g. buildings, land, crops etc)
Receptors are things that can be “harmed” by the contaminant such as; living organisms, people,
site workers, ecological systems or property, buildings, foundations or underground services.

Question 15

Explain why your client would have to remediate a proposed housing development with detached houses and private gardens to a different standard than a Tesco Supermarket development.

Answer 15

The UK approach adopts the principle of “suitable for use” or “suitable for the proposed end
use” and the principle of “source” > “pathway” > “receptor” – “pollutant linkage applies.
If there is NO pollutant linkage there is on risk and no need to remediate the site.
A typical receptor at a “proposed housing development with detached houses and private gardens”
is young children, in particular the “pica” child which has an eating disorder and can eat
contaminated soil thus causing “harm”. Also householders could grow and eat vegetables etc in
their gardens which could become contaminated and cause “harm”.
A “housing development with detached houses and private gardens” is a more sensitive end use
than a “Tesco Supermarket”.
It is most likely that any “pollutant linkages” that existed at a “Tesco Supermarket” would or could
be broken by for example the car park surfacing, the ground floor slab etc.
However consideration may have to be given to other “pollutant linkages” such as ground gases
such as methane (explosive and an axphixant) or carbon monoxide (an axphisant) of hydrocarbon
fumes etc.
However consideration may also have to be given to other pollution of groundwater, if present.

Question 16

A house builder/developer contacts you, as an experienced professional Geo-Environmental
/ Contaminated Land Consultant, and asks you to submit, to them, the steps and activities
that you recommend should be carried out, to assist them with the purchase,
remediation (if any is required) and re-development of a 20 ha plot of land for residential
end use (private, mainly detached housing with private back gardens).
They are an experienced house builder, but they have only built on greenfield sites before
and are relying on you to advise them on the way forward and what needs to be done to
investigate and eventually develop this challenging site. They provide you with the
following information:
 They have not yet bought the site. But, depending on your advice, they hope to buy the
site and apply for planning permission, for residential / housing end use.
 The western half of the site, 10 ha, is currently a disused tannery, comprising:
o derelict buildings still standing across the south of the site, old cow hides are still
hanging on rafters,
o a tannery waste lagoon across the north of the site, where fat, waste and other
scrapings from the cow hides have been historically dumped and buried;
o an un-bunded oil heating tank on the east side of the derelict buildings;
 The eastern half of the site, 10 ha, is currently agricultural land / farmers fields.
 The entire site overlies alluvial sands and gravels, roughly 10 m thick, overlying coal
measures, with a Principal Aquifer at relatively shallow depth, say 3.5 m below ground
level.
 Immediately to the west of the site, along the western boundary of the former tannery,
there is a stream that was used to power a waterwheel to supply power to the tannery.
The stream is part of a wider Site of Special Scientific Interest (SSSI) to the west of the
site.
 The site slopes gently from east to west, towards the steam.
Make a first draft of your reply and advice to the house builder.
Your “answer” does NOT have to be a formal final letter to the house builder. It should be
in the form of your first draft of the key steps and activities that you recommend should
be carried out to assist them with the purchase, remediation (if any is required) and redevelopment
of the site, i.e. from start to finish. The use of bullet points is encouraged.
In addition, list the key redevelopment challenges and how you propose to investigate and
resolve them further.

Answer 16

Geo-features:
Alluvial sands and gravels – permeable and therefore a means for pollutant transport.
Coal Measures at ~10 m depth. These rocks typically include sequences with sandstone, siltstone, mudstone,
and coal. Sandstone may be highly permeable and therefore a pathway for pollutant transport. With their
proximity to the surface is there a risk of historical mining that might affect the project?
Principal Aquifer at ~ 3.5 m depth : - have high intergranular and/or fracture permeability – meaning they
usually provide a high level of water storage. They may support water supply and/or river base flow on a
strategic scale. Issues : may provide for pathway for spilled pollutants with implications for both domestic
consumption, crops on neighbouring farm land and/or the stream and SSSI.
Stream is part of a wider Site of Special Scientific Interest (SSSI)
Discuss potential pollutants on site:
Potential contaminants, including Chromium, chloride, sulphate, ammonium, phenols, hydrocarbons and land
gases may originate from historic escapes of tannery effluent, historic land filling practices and hydrocarbon
storage on site.
Pesticides/herbicides used on farm land and/or hides?
Remediation options:
Bioremediation of chromium extant in tannery waste involves different strategies that include biosorption,
bioaccumulation,bioreduction, and immobilization of biomaterial(s)
Cover systems – appropriateness questionable given groundwater conditions
Dig and dump – large site, expensive option given hazard level
Chemical immobilisation
Process:
The steps and activities that you recommend should be carried out:
 Consult Environment Agency and local planning authority
 Desk study
 Ground & site investigation
 Protection from potential contamination in demolition phase
 Remediation of existing contamination
Purchase, remediation (if any is required) and re-development:
 Issues for planning permission
 Responsibility for cost of remediation