Thames Coromandel District Council Moanataiari Subdivision ... Council/Council Projects... · 1 Moanataiari Subdivision, Thames Phase 4 - Assessment of Response Options T&T Ref. 61570.002

REPORT

Report prepared for:

Thames Coromandel District Council

Report prepared by:

Tonkin & Taylor Ltd

Distribution:

Thames Coromandel District Council 3 copies

Tonkin & Taylor Ltd (FILE) 1 copy

November 2012

T&T Ref: 61570.002

Thames Coromandel District Council

Moanataiari Subdivision, Thames

Phase 4 - Assessment of Response

Options

Moanataiari Subdivision, Thames Phase 4 - Assessment of Response Options T&T Ref. 61570.002

Thames Coromandel District Council November 2012

Table of contents

1 Introduction 1

2 Scope of works 2

3 Response objective 3

4 Selection of response options 4

4.1 Ministry of the Environment 4

4.2 Ministry of Health 5

5 Assessment of potential response options 6

5.1 Introduction 6

5.2 Additional information 6

5.3 Response options workshops 7

5.4 Health Precautions (Management controls) 7

5.5 Partial Capping (Containment) 9

5.5.1 Ministry for the Environment advice 9

5.6 Ministry of Health Advice 11

5.6.1 Thin cap 12

5.6.2 Thick cap 13

5.7 Land use controls 14

5.8 Summary of potential response options 15

6 Applicability 19

7 References 20

Appendix A: Figure

Appendix B: Golder HRA Figure 5

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Executive summary

This Assessment of Response Options has been prepared for the Moanataiari Project Governance

Group and Thames-Coromandel District Council (TCDC) to provide an assessment of the response

options resulting from a Human Health Risk Assessment (HRA) prepared by Golder and Associates

(Golder).

Preliminary response options for the subdivision were developed by Tonkin & Taylor in August

2012 and presented to the Moanataiari residents at a series of workshops. The preliminary

response options were then used to inform the HRA undertaken by Golder. T&T were instructed

that the results of the Golder HRA should be the starting point for this Response Options report.

This report details how contaminated land guidance published by the MfE (and to a lesser extent

the Ministry of Health) relates to the response options resulting from the HRA. The relative

advantages and disadvantages of each option are also discussed.

MfE guidance states that no one single remedy represents the optimal selection for all

contaminated sites. The selection of a response option is very site-specific and depends on many

factors. Primarily evaluation should be on the ability of an option to reduce risk, and then on its

cost-effectiveness and the future site utility.

A summary of the response options resulting from the HRA is provided in Table 3 of this report,

along with an evaluation against the key decision-making aspects. With all of the potential

response options, a management plan will be required. The level of controls required to be

included in the management plan will be dependent on the response option(s) selected.

The Golder HRA provides a plan (Figure 5) showing the minimum response options required to

meet the statutory requirements of risk in different areas of the site and this plan has been

enclosed in Appendix B of this report for convenience.

In summary, the HRA has concluded that the following options would provide the minimum

human health protection to meet statutory risk reduction requirements:

• Management controls (Health Precautions): continuation of the existing management

regime, possibly with the provision of raised planter beds (referred to as Gardening

Controls in the Golder HRA) - Minimum requirement for Zone 7.

• Management controls as above, with planters provided for vegetable growing (Health

Precautions and gardening controls) - Minimum requirement for Zones 1, 4 & 8.

• Containment (Partial Capping): constructing a cap over the contamination – Minimum

requirement in Zones 2 & 3.

Land use controls are also an option, involving purchasing properties, demolition and

redevelopment (eg as parkland or commercial properties). Such measures would be in excess of

the minimum requirement for all areas of the subdivision.

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1 Introduction

The Moanataiari Project was commissioned by the Moanataiari Project Governance Group and

Thames-Coromandel District Council (TCDC) to investigate and address potential health risks

within the subdivision as a result of soil contamination. This report relates to Phase 4 of the

project as set out in the project management plan for the Moanataiari Subdivision.

Preliminary response options for the subdivision were developed by Tonkin & Taylor in August

2012 and presented to the Moanataiari residents at a series of workshops. The preliminary

response options were used to inform a Human Health Risk Assessment (HRA) undertaken by

Golder Associates (Golder, Oct 2012). T&T were instructed that the results of the Golder HRA

should be the starting point for this Response Options report.

This report covers all 216 residential properties within the Moanataiari Subdivision as shown in

Figure 1 (Appendix A). Description of the subdivision environs and history has been provided in

previous reports, along with details of the contamination present (See References in Section 7 of

this report).

This report has been produced by Tonkin & Taylor Ltd (T&T) in general accordance with The

Ministry for the Environment’s Contaminated Land Management Guideline No. 1 “Reporting on

Contaminated Sites in New Zealand” and in accordance with our agreement with TCDC dated 21

June 2012.

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2 Scope of works

T&T’s scope of work for this report is as follows:

• Provide an assessment of the advantages and disadvantages of the range of response

options suggested by the Golder HRA.

• Produce this assessment report presenting the results of the response options assessment.

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3 Response objective

Concentrations of contaminants in the soils at the Moanataiari Subdivision, principally arsenic and

lead, are above NES soil contaminant standards (SCS) for assessing and managing contaminants in

soil to protect human health. The response objective is to reduce/manage exposure of people

within the subdivision to these contaminants down to acceptable levels and not necessarily to

reduce the levels of these contaminants to below the NES SCS.

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4 Selection of response options

4.1 Ministry of the Environment

Guidelines on the response to contaminated land in New Zealand is provided by the Ministry of

the Environment through a range of technical documents produced in the late 1990s. The health

risk-based soil acceptance criteria contained in these guidelines have been superseded by the soil

contaminant standards under the National Environmental Standard for Assessing and Managing

Contaminants in Soil to Protect Human Health (NES). The NES doesn't currently apply to this site

as it is not applied in retrospect and will only be triggered as and when activities requiring consent

are undertaken. However, these documents still provide valid guidance on the selection of

response options.

No one single remedy represents the optimal selection for all sites (MfE 1997a). The selection of a

remediation or management option is very site-specific and depends on many factors (MfE 2006),

including:

• Type, extent and depth of contamination.

• Location of contamination relative to receptors.

• Area and volume of the contamination relative to the size of the property.

• Proximity to a safe disposal location (including on-site disposal) if excavation and

replacement are being contemplated.

• Availability of clean soil.

• Future use of the site, and

• Financial resources available.

Site management options should be evaluated primarily on their ability to reduce risk, and then on

their cost-effectiveness and the future site utility (MfE 1997a). Ideally, the option that best

reduces the risk, maximises environmental merit and minimises costs would be chosen (MfE 2006).

The risks include those to site users, the general public, and the environment, during and after

implementation of the management strategy. Also important in evaluating site management

options are (MfE 1997a):

• Timing - if a site management option could take a long time to reduce contaminant

concentrations, what are the risks to human health and the environment in the intervening

period?

• Failure - if the contamination is contained [or capped] in situ, what will happen if the

containment system fails?

• Off-site disposal - if the contaminants are to be disposed of off-site what risks are associated

with moving the contaminants?

At each site, the remedial system design must (MfE 2006):

• Evaluate the practicality of using a specific remedial option.

• Attempt to evaluate the cost.

• Assess the problems that may be associated with that option, and

• Assess the timeframe for the treatment.

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4.2 Ministry of Health

Guidelines are provided by the Ministry of Health (MoH) to assist public health units in achieving

tolerable levels of lead in the environment to limit adverse health effects (MoH, 2012). Whilst this

document addresses only lead (mainly from paint), there is relevance to Moanatairi in that the

document discusses responses to lead in soil. The guidelines were first published in 1998 and

were updated in 2012 for the National Environmental Standard for Assessing and Managing

Contaminants in Soil to Protect Human Health.

The MoH lead guidelines emphasise the aim of providing a ‘lead-safe’ environment, which is not

the same as a lead-free environment. The guidelines advocate education of site occupiers that in

most circumstances, abatement cannot be considered as a complete or permanent solution, but

must be complemented by ongoing behavioural adjustments to reduce (remaining) exposure.

[Although] education to change the daily behaviour of children, caregivers, visitors and so on, is

very difficult to sustain long term.

The guidelines include abatement strategies for reducing blood-lead levels, central to which is a

management plan, typically incorporating both behavioural (educational) and environmental

(abatement) strategies, developed in consultation with the family.

The choice of soil abatement strategy will be based on the risk assessment. The key variables are:

• soil lead concentration (and bioavailability).

• location and use pattern.

• condition of existing surface cover (if any).

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5 Assessment of potential response options

5.1 Introduction

The Ministry for the Environment (and to a lesser extent the MoH) provides guidance on a range

of potential response options for contaminated land. These include:

• Land use controls (eg only allowing the land to be used for commercial purposes where

concentrations of contamination in the near-surface soils are too high to enable other land

uses without physical works).

• Management controls (eg the management controls that are currently in force across the

subdivision, controlling consumption of homegrown produce etc). Referred to as Health

Precautions in the Golder HRA.

• Intrinsic remediation (ie allowing contamination to reduce over time).

• Containment (eg capping the contamination with clean materials). Referred to as Partial

Capping in the Golder HRA.

• Remedial treatment systems (ie removing or reducing contamination concentrations), and

• Disposal to landfill.

The HRA has concluded that from the above options, the following are technically feasible for

addressing contamination within the residential properties on the subdivision:

• Management controls (Health Precautions): continuation of the existing management

regime, possibly with the provision of raised planter beds (referred to as Gardening

Controls in the Golder HRA).

• Containment (Partial Capping): constructing a cap over the contamination.

• Land use controls: purchasing properties, demolition and redevelopment (eg as parkland or

commercial properties).

A discussion of each of the options considered to be technically feasible or practical is provided in

this section, which is summarised in Table 3 at the end of the section.

The following options were not considered technically feasible:

• Intrinsic remediation: the arsenic, lead and thallium within the soils will not degrade.

• Remedial treatment systems: No practical remedial treatment systems were identified for

the subdivision. Two innovative systems were presented at workshops, in the interests of

completeness (electrokinetic and phytoremediation), however both these would require

trials to assess suitability and at this stage are likely to prove unsuitable in terms of ability

to practically reduce the contamination.

• Disposal to landfill: Removal of all the contaminated soil to landfill is unfeasible as it forms

the entire thickness of the subdivision (ie to remediate a property would require removal of

the whole property down to the original marine sediments).

5.2 Additional information

A schedule of quantities for TCDC to populate with costs for the conceptual response option(s)

was produced as a separate document to allow TCDC to develop conceptual costs for each

response option.

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5.3 Response options workshops

Three two-hour workshops were held to discuss response options with the community. Two

workshops were held on 19th

July 2012 and one on 21st

July 2012. The workshops were facilitated

by Tonkin & Taylor (with members of the Project Team in attendance). A virtual online workshop

was also broadcast by the Project Team and feedback requested.

The purpose of the workshops was to obtain early feedback from the community regarding

appropriate response options (ie feedback was required on which options would have been

appropriate to develop further for use in the health risk assessment and assessments of response

options). In line with the adopted approach of the Project Team, the workshops were undertaken

before a full assessment of response options was completed and before a preferred option(s) was

selected by the Governance Group. In particular, the Human Health Risk assessment work

package had not yet been approved at that stage, the funding arrangement had not yet been

decided. This would have affected the feedback obtained.

Those who provided feedback stated that they wanted to return the subdivision “back to normal”

and make the subdivision a healthy place to live. Preserving the financial equity in the properties

was also a main concern. Generally the feedback on the response options provided was that the

thick capping option would be the preferred solution, with some preferring the thin cap option.

The management option was viewed as being insufficient to address the human health issues.

It was stated at the time that the process whereby these options would be evaluated would

include financial analysis. If an option wasn't practical from a cost perspective it would most likely

not be implemented.

A total of 62 people attended the workshops, some of which were from the same households and

so the number of properties represented could have been of the order of 20% of the whole

subdivision. Based on our experience of consultation processes and the fact that the issues

directly affect all the properties on the subdivision, this is a relatively low attendance. We

understand that TCDC intend consulting on individual response options with individual property

owners prior to finalising a programme of works.

5.4 Health Precautions (Management controls)

Ministry for the Environment guidance states that:

Management controls [Health Precautions] are usually required where contamination is to be left

on site at depth or under structures or paving. Controls are necessary to avoid uncontrolled

excavation in the future which could result in the contamination being exposed. Imposing

management controls acknowledges that the land is not suitable for uncontrolled use (MfE

1997a).

Each of the response options discussed in this section will require a management plan, although

the extent to which the management plan will be applied will vary dependent on the option, or

combination of options, selected.

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Currently, human health risks for the residential properties on the subdivision are addressed

through application of a management plan (Health Precautions), which provides the following

advice1:

• Take care with personal hygiene (ie hand washing after handling soil).

• Make sure children don't eat or play in soil.

• Remove footwear before going indoors to avoid carrying soil dust indoors - particularly for

households with very young children.

• Cover soil (eg grassing, paving, gravel) to reduce dust and direct access by young children.

• Don’t eat home grown vegetables, especially young children, until further quantification of

the contamination is available and the risk can be assessed, unless it is known that the

garden soil is clean fill. If home grown vegetables are chosen to be eaten, then thoroughly

wash produce that may be contaminated with soil, and peel the skin off root vegetables.

If the current Health Precautions were to continue, then all soil disturbing activities would need to

be undertaken in accordance with a management plan, and bare soil would need to be minimised

as much as possible throughout the subdivision. Vegetables would need to be grown in clean

imported soil. A management plan would include procedures for handling contaminated soil to

allow for certain activities, eg excavation for a new building, driveway or swimming pool.

In addition to the above, the management plan would need to clearly define responsibilities, eg:

who is responsible for disposal of soils and provision of clean materials (is a facility provided by

council, or is it the sole responsibility of property owners). Consideration would also need to be

given to an education/awareness programme and also monitoring the implementation of the

management plan to provide confidence that this solution is effective in the long term.

Further details on this solution are as follows:

Human health risk reduction: This solution relies on self-management by the occupiers of the

properties and requires that future owners/occupiers have an awareness of the health issues

associated with the contamination within the soils on their properties.

Cost: Costs for this solution are likely to be significantly lower than other solutions. Rough order

costs have been estimated separately by TCDC.

Future site use: Continuing the current Health Precautions would rely on controls and so would

give the least flexibility to property owners. Future redevelopment of properties would possibly

require replacement of planters.

Advantages: Continuing with the current Health Precautions for the subdivision and not

undertaking significant physical works is the least intrusive option to address the potential health

risk (ie no truck movements or disturbance of properties).

Practicality: This solution is practical where contamination levels are commensurate with

acceptable levels of increased risk.

Problems associated with solution: Problems relate to future site use as described above.

Timeframe: The solution is in place now and so is the quickest solution. Provision of planters

(Gardening Controls) likely to be achievable in a matter of months.

1 “Facts Sheet 1: Moanataiari subdivision, Public health advice”, http://www.tcdc.govt.nz/Global/1_Your%20Council/

Council%20Projects/Current%20Projects/Moanataiari%20Project/Facts%20Sheet%20One%20-

%20MoH%20Public%20Health%20advice.pdf

9



Community feedback: Feedback from the community was largely negative. Land owners were

concerned about the potential health effects, particularly on children, effects on property prices

long term, and how to ensure that the management plan is implemented by everyone long term.

5.5 Partial Capping (Containment)

5.5.1 Ministry for the Environment advice

Ministry for the Environment guidance (MfE 1997a, MfE 1997b) on capping contaminated land is

that:

Reduction of the exposure of site users to contaminated soil by the engineered containment of

areas of soil contamination is an acceptable remediation/management strategy in some

circumstances. Containment may involve the use of an impermeable surface cap of bitumen or

concrete paving. A well-defined management plan should accompany such a containment

strategy. Very high levels of contamination may be acceptable with such a containment strategy,

provided the contamination does not produce other off-site impacts eg via groundwater or surface

rainfall run-off.

In addition, mechanisms must be put in place to ensure the long-term integrity of any

management plan and containment works, taking into account property transfer and other

possible scenarios. The implementation of a containment strategy is most practical in the context

of ongoing commercial/industrial use, or possibly high-density residential use.

The protection offered by pavement is, however, highly dependent on the integrity of the

pavement. A relatively new area of paving of high integrity is likely to effectively eliminate

exposure of site personnel to ground contamination except where the pavement is disturbed and

the integrity of the pavement compromised. Where an area of pavement is relatively old and

broken, with say 30 to 50% of the area seriously affected, so that soil can spread from areas of

pavement failure to areas remaining intact, the pavement may provide negligible protection for

site personnel. The integrity of an area of pavement and its likely effectiveness in reducing

exposure must be evaluated on a site-specific basis.

On this basis, the guidance suggests a fivefold protection factor where paving is present, when

compared to sites where paving is absent (ie paving is appropriate where soil contamination

concentrations are less than five times the human health acceptance criteria that would be

applied if the paving were absent). Such a factor was applied to the acceptance criteria and

although those criteria are now superseded by the NES, the concept of a five-fold protection

factor still provides a basis for preliminary assessment of where paving may be appropriate.

The placement of clean fill over the site can also form an effective cap. MfE guidance states that:

The placement of such clean fill provides a barrier to the exposure of site users to soil

contamination, and therefore higher contaminant concentrations may be allowable below such

fill.

Considerations relevant to the appropriate use of such a cleanfill cover are stated in Table 2 along

with the potential relevance to the Moanataiari Subdivision.

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Table 2 – Considerations for the appropriate use of cleanfill as part of a containment

solution

MfE consideration Consideration for Moanataiari

The root zone of most home vegetables and the

depth of digging as part of gardening activities

does not generally extend beyond 0.5 m.

If plants2 and vegetables are to be grown at the site,

0.5m of cleanfill would be required, or raised garden

beds greater than 0.5m thick or with a geofabric base

would be required.

Normal maintenance activities at a residential

site (eg maintenance of underground services)

may bring contaminated soil to the surface and

spread it around.

Maintenance activities would need to be addressed in a

management plan for the site.

A greater depth of cleanfill and use of geofabric would

act to reduce the likely disturbance from maintenance

activities.

Contaminants below a cover layer should not

pose a short-term health risk to people who may

disturb the contamination.

An assessment undertaken on behalf of the

Moanataiari Project in November 2011 (PDP 2011a)

concluded that for arsenic, the principal contaminant

on the subdivision, an acute guideline value for non-

pica children is 65,000mg/kg for potentially lethal

effects, which is well above the maximum value of

4,700 mg/kg detected during the site investigation

works, and 975mg/kg for the onset of observable health

effects, which is above the upper confidence limit

values tabulated in the Golder HRA (Golder, Oct 2012,

Tables 4 and 5). Therefore no acute risk is indicated.

Contaminant concentrations below a cover layer

should not significantly impact on the health of

trees and other plants where the root zone may

extend beyond 0.5 m

No significant die-off of trees or vegetation was noted

during the property inspections and property owner

interviews, which indicates that this is not an issue at

the subdivision.

Ongoing management, and re-establishment of

the cover layer after significant works or

redevelopment, are required.

Ongoing management would be addressed in the

management plan for the site.

The use of a barrier may not be appropriate in a

flood plain zone or other areas subject to

significant erosion

Significant flooding/erosion has not occurred since the

installation of the flood protection measures around

the subdivision however a water permeable barrier may

be appropriate to reduce impacts on flooding.

The existence of contamination below any

barrier should be notified via the LIM system

administrated by the TLAs

TCDC has indicated that all relevant information will be

placed on the LIM system for all affected properties.

On this basis, preliminary assessment using the protection factor of 5 is suggested [by MfE] as

appropriate (consistent with that assigned to paving [discussed above]) to the placement of

500 mm of clean fill or topsoil, provided that an appropriate management plan is in place and the

existence of contamination beneath the barrier is recorded on a LIM [ie the guideline value is

multiplied by a factor of five for this option]. The owner, occupier, and purchaser of the site as

well as the TLA will be made aware of the contamination so that this can be taken into account

during any maintenance or construction activities.

2 Residents can come into contact with contaminated soils during planting activities.

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5.6 Ministry of Health Advice

Ministry of Health advice for addressing lead in soil by capping is that if the ground cover is poor

(ie, there are patches of bare soil exposed) at a particular location, reasons for this should be

determined, because this will influence abatement method selection. Bare soil is commonly

exposed in:

• heavily used play areas

• pathways

• areas shaded by buildings or trees.

In other situations, all that is required [to address lead exposure] is the removal of gross

contamination (visible paint chips) followed by covering the area with 25 mm of turf, 50 mm of

bark chips or similar. Usually, this will involve removal of some surface soil or a partial grass

cover, to prepare the surface for the laying of turf or bark. This may temporarily increase the

amount of bare contaminated soil potentially accessible to a child, or available to contribute by

wind transport or tracking to interior surface dust. Care should be taken to minimise disturbance

to the soil, and to contain, collect and safely dispose of any soil that has to be removed.

A grass cover has been shown to be capable of reducing exposure to soil lead by 80 percent3.

Behavioural adjustments to reduce outdoor play, relocate outdoor play areas, reduce soil

ingestion, and minimise soil transfer and tracking into the house, are necessary complementary

strategies.

More permanent [lead exposure] abatement options should be reserved for situations where a

simple grass or bark cover is unlikely to be sufficient or sustainable.

Paving is the preferred option when contaminated soil is found in high-traffic areas. Contaminated

soil should be disturbed as little as possible in preparing the surface, and precautions must again

be used in managing any soil that must be removed.

While many paving materials are available, a high-quality concrete or asphalt cover is

recommended, with appropriate allowance for thermal expansion and traffic loadings, so that

cracks will not develop over time. Any areas of bare (contaminated) soil remaining at the edges of

the paved surface should receive a grass or similar soft cover.

The guidelines state that soil removal and replacement is the most expensive and also the most

hazardous soil abatement option. It should only be considered when soil contamination is

extensive, behavioural factors are unfavourable (eg, a child with pica), and soft or hard ground

cover is unlikely to be sustainable. In this situation, core samples should be taken from the

affected area in a grid pattern to check that the expected decline in soil lead content with depth

occurs (ie, that sublayers do not have equally or even higher lead content than the surface layer,

as a result of historical events such as previous building or renovation on the site).

The guidelines refer to studies from 1993 and 2003 on the effectiveness of soil removal in

reducing blood-lead levels in children. The guidelines state that based on these studies, for soil

lead levels in the range of 1000 to 3000 mg/kg, soil removal is probably not indicated, and

measures such as improving ground cover and behaviour modification (eg, relocating the principal

play area away from the house) may suffice. At soil lead levels less than 1000 mg/kg bare soil

areas should still be covered (a soft cover such as grass or bark chips is generally adequate), if

indicated by use pattern analysis, as soil lead tracked or blown into the house will be contributing

to dust lead in the home. Care should be taken in applying this advice to Moanataiari as the

3 The Golder HRA will already have taken this reduction into account.

12



studies targeted lead contamination at individual houses and were relatively short-term. The 1993

study concluded that a greater reduction in lead may have been observed if the study had

extended for longer. In addition, the 2003 study concluded that soil abatement was associated

with significant decline in children’s blood lead and indoor environmental levels of lead and

arsenic.

5.6.1 Thin cap

The thin cap solution acts to isolate people from the contaminated soils by forming a surface

barrier on top of the existing soils using:

• Imported topsoil (50mm to 100mm thick) underlain by a geofabric barrier.

• Decking.

• Paving or concrete, or

• A combination of the above.

In addition to the above, bark or river stones over geofabric may be suitable as a thin barrier for

small untrafficked areas or around trees.

At Moanataiari, a combination of these barrier-types is likely to be the most practical, eg

imported topsoil in existing grassed areas, paving in narrow trafficked areas and decking in other

small areas.

It is understood that the Ministry for Health and Waikato District Health Board would not support

any solutions that involved disturbance of soil.


Human health risk reduction: Once installed, this solution would isolate the contaminated soils

from people on the subdivision. However, over time, the capping is likely to deteriorate, which

may allow contaminated soils to migrate to the surface. This is not indicated by the Golder HRA

to be a significant health issue at Moanataiari4.

Cost: Relatively low cost. Some disposal to landfill of surface materials (eg topsoil) likely to be

required. Rough order costs have been estimated separately by TCDC.

Future site use: This solution would address all areas of exposed soil and would allow for

everyday residential activities to be carried out without requiring special precautions. Growing of

plants and vegetables would need to be undertaken in raised gardens with clean imported soil

underlain by a geofabric barrier layer. Any activities which are likely to disturb soil beneath the

barrier layer would need to be done in accordance with a management plan. Future

redevelopment of properties would possibly require replacement of the thin cap.

Advantages: This option would involve minimal excavation of existing soils, and a relatively low

level of disruption to property and residents.

Practicality: The type of cover used could be tailored to individual properties to incorporate the

needs of individual property owners.

Problems associated with solution: See future site use above.

4 As a preliminary screen, MfE guidance indicates that this solution may not be suitable in areas where contamination

concentrations exceed five times the human health guideline values. Only a single result exceeds five times the

Golder HRA criteria.

13



Timeframe: Relatively short timeframe anticipated. Assuming that the critical path installation of

a thin cap would take one week per property (ie excluding finishing works, snagging, etc), it would

take approximately three months to complete the physical works for one third of the subdivision.

Community feedback: people were concerned about drainage, ponding and flooding as a result of

changes in ground levels and increasing impervious coverage. Some people viewed this as a short

term solution only.

5.6.2 Thick cap

The thick cap solution acts to isolate people from the contaminated soils by forming a surface

barrier through either:

• Raising ground levels by say 200mm to 300mm using clean imported soil.

• Excavating 300mm to 600mm and replacing with clean soil.

• Undertaking a combination of excavation and ground raising.

TCDC have stated that they consider solutions involving ground raising to be impractical for

Moanataiari, due to natural servitude stormwater issues and the risk of inducing settlement

within the soft soils beneath the subdivision. Therefore ground raising solutions have not been

considered further in this report.

It is understood that the Ministry for Health and Waikato District Health Board would not support

any solutions that involved disturbance of soil.

The greater the thickness of clean soil, the greater the level of activity that can occur on

properties without the need for specific management actions. Placement of a geofabric barrier

layer beneath the clean soil would also act to prevent contaminated soils migrating to the surface.


Human health risk reduction: Over time, the capping is likely to be disturbed by activities,

although the thicker the cap, the less likely this is to occur, especially with a geofabric layer placed

at the base of the cap. This is not indicated by the Golder HRA to be a significant health issue at

Moanataiari5.

Cost: Relatively high cost, due to the importation of the soil, with the highest cost being for the

excavation solution, which would involve removal of contaminated soils to landfill plus relocation

and temporary housing of displaced residents. A staged approach could be considered, with

works being undertaken in discrete stages over time as funds become available, possibly with the

application of a management plan, or even thin capping, in the interim. Rough order costs have

been estimated separately by TCDC.

Future site use: This solution would address all areas of exposed soil and would allow for

everyday residential activities to be carried out without requiring special precautions. Growing of

plants and vegetables could be undertaken wherever more than 500mm of clean soil is placed, or

a lesser thickness of clean soil (eg 300mm) with an underlying geofabric (otherwise raised garden

beds containing clean imported soil would be required). Any activities which are likely to disturb

soil beneath the barrier layer, or disturb any pre-existing soil at a property will be required to be

undertaken in accordance with a management plan.

5 As a preliminary screen, MfE guidance indicates that this solution may not be suitable in areas where contamination

concentrations exceed five times the human health guideline values. Only a single result exceeds five times the

Golder HRA criteria.

14



Advantages: Less need for future management of activities, especially if a 600mm cap is placed

(few residential activities are likely to disturb soils below 600mm depth).

Practicality: This solution would probably be most practical if it were undertaken over a series of

adjacent properties (ie this solution would be more difficult than the thin cap option to tailor to

individual property owner needs). Although this solution may also be suitable for individual

properties where redevelopment is proposed and it is practical to remove all the above ground

structures;

Problems associated with solution:

• This option would involve a high level of disruption to local residents and the subdivision as

a whole and would interfere with underground services and above ground structures

(residents are very unlikely to be able to live in the properties during physical works). Also

the highest level of community disruption is associated with this solution (eg truck

movements, dust and noise).

• Would not be suitable beneath the drip line of trees that are to be retained (we note that

there are trees in the road reserve that overhang some properties on the subdivision).

Beneath drip lines a thin cap or management plan approach would be required).

• Construction of a thick cap may not be suitable for some areas where access is restricted

(eg in small areas bounded by structures). In these situations a thin cap may be more

practical.

• Occupiers would likely need to vacate the properties during the works.

• A management plan would still be required for this option (although to a lesser extent than

other options).

• MoH guidelines on addressing lead contamination in soils suggests that soil removal should

only be considered when soil contamination is extensive, behavioural factors are

unfavourable (eg, a child with pica), and soft or hard ground cover is unlikely to be

sustainable.

• The Ministry for Health and Waikato District Health Board have stated on a number of

occasions that they are concerned with the additional risk to human health associated with

dig and dump type works.

Timeframe: Relatively long timeframe anticipated, this is especially the case if staged funding

requires progressive works. Assuming that the critical path installation of a thick cap would take

three weeks per property (ie excluding finishing works, house cleaning, snagging, etc), it would

take approximately seven months to treat one third of the subdivision.

Community feedback: Feedback from the community for a thick cap option (prior to release of

the HRA and without the benefit of rough order costs) was that this option presented the most

benefit to them in terms of health benefits and property values. There was concern that the use

of a thin cap at some properties and a thick cap at other properties would result in a property

value differential. Some concerns were raised around security of properties when vacant during

physical works and where people would be relocated to. While some commented on the

disruption to the entire subdivision, practical implications of implementing the solution and the

potential change in character of the subdivision most people saw this as a permanent solution

even though it would still require a management plan highlighting restrictions on these

properties.

5.7 Land use controls

The subdivision is currently fully developed with residential housing and so land use controls

would require purchasing of property from owners, demolition and then possibly physical works

15



to address exposure of people (eg so that the properties were appropriate for use as public

allotments or sold on as commercial properties). The type of response could be any of those

listed in the above sections, or a combination thereof (the Golder HRA indicates that no further

response is required for commercial land use).


Human health risk reduction: The risk reduction will be dependent on the actual solution

adopted, however it is anticipated that the land would be operated by TCDC and so there would

be more control over activities which could occur there.

Cost: Likely to be most costly solution due to the need to purchase and demolish the properties in

the first instance. Rough order costs have been estimated separately by TCDC.

Future site use: The properties could be adapted to provide an appropriate use.

Advantages: The land use could be tailored to minimise risk from ground contamination and by

maintaining ownership or physical works could be undertaken (if required) and the properties

sold (eg for commercial use).

Practicality: This solution is most practical for a group of properties in a suitable location for a

land use change. It is not practical for all parts of the subdivision and not for properties where

owners do not wish to sell.

Timeframe: This is likely to be an expensive option and, dependent on the funds available, may

have to be undertaken over a number of years as funds become available, short term response

solutions may be required to address health risks before the land use change can be

implemented.

Community feedback: Community feedback on redevelopment options was mixed. People did

not want to see the whole of Moanataiari redeveloped, however at an individual or group level it

was considered to be viable for some properties due to the perceived health risk at that time.

5.8 Summary of potential response options

A summary of the potential response options is provided in Table 3 along with an evaluation

against the key aspects that have been considered. With all of the potential response options, a

management plan will be required. The level of controls required to be included in the

management plan will be dependent on the response option(s) selected.

The Golder HRA provides a plan (Figure 5) showing the minimum response options required to

meet the statutory requirements of risk in different areas of the site and this plan has been

enclosed in Appendix B for convenience.

16



Table 3 – Summary of potential response options

Response

option

Zones6 Human health risk

reduction

Cost Future site use Timeframe Advantages Disadvantages

Health

Precautions

7 High level of self

management required.

Minimum response

options to meet

statutory requirements

of risk in Zone 7

Lowest High level of control required

into the future.

No implementation time,

already in place.

Low cost

Rapid

implementation

and no disruption.

High level of control

required.

Risk of negative public

reaction (although likely to

be welcomed by some)?

Thus careful explanation of

the HRA results likely to be

required.

Health

Precautions and

Gardening

Controls

(planters for

vegetable

gardens)

1, 4, 7 &

8

High level of self

management required.

Minimum response

options to meet


of risk in Zones 1, 4 & 8

Low High level of control required

into the future.

Likely to be implemented

in a matter of weeks.

Low cost

Rapid

implementation

and little

disruption.

High level of control

required. Planting can only

occur in raised beds and

beds would possibly need

replacing if redevelopment

occurred.

Risk of relatively negative

public reaction (although

likely to be welcomed by

some)? Thus careful

explanation of the HRA

results likely to be required.

6 Zones in which this option would meet statutory risk reduction requirements. Zones are as defined in the Golder HRA figure 5 enclosed in Appendix C

17



Response

option


reduction


Partial Capping -

Thin cap

1,2,3,4,7

& 8

Will effectively contain

contamination but may

be compromised as a

result of degradation

or site activities in

future.

Minimum response

option to meet


of risk in Zones 2 & 3

Relatively

low in

comparison

with the

Thick Cap

option

Raised gardens needed for

vegetable growing. No

precautions required for most

everyday activities but

management plan applies to

all activities which disturb soil

beneath the thin cap.

Estimated three months

for treatment of one third

of the subdivision

Relatively low cost

Relatively rapid

implementation

and low disruption.

Control of everyday

activities not

required

Can be tailored to

individual

properties.

Degradation of thin cap over

time.

Will take months to

implement.

Future development of

property would possibly

require replacement of cap

Partial Capping -

Thick cap

1,2,3,4,7

& 8

Will effectively contain

contamination and is

less likely to be

compromised by

future site activities.

High (but if

it includes

temporary

relocation of

the house/

structures

then this

becomes the

most

expensive

option.)

No precautions required for

everyday activities but

management plan applies to

all activities which disturb soil

beneath the cap.

Estimated seven months

for treatment of one third

of the subdivision. Could

stage over an extended

period to meet funding

availability.

Low long-term

maintenance

required.

Control of everyday

activities not

required.

Community

feedback from the

workshops was

generally positive

about this solution.

High cost

Will take several months to

implement.

High disruption and truck

movements.

Not suitable beneath tree

drip lines.

Not suitable in restricted

access areas.

Occupiers would likely need

to vacate the property

during works.

Cannot be tailored for

individual properties (would

need several adjacent

properties to adopt this

solution).

Not supported by MoH or

Waikato District Health

18



Response

option


reduction


Board.

Land use controls

(redevelopment)

1,2,3,4,7

& 8

Solution could be

tailored to ensure

management of health

risk.

Highest cost

as this

includes the

purchase of

the

property.

Response action can be

adapted to allow for

maximum usage under

proposed redevelopment

scenario.

Several months, especially

if properties are to be sold

on.

Site use could be

adapted to one

suitable for the

levels of

contamination.

High cost

Will take months to

implement.

Occupiers would need to

permanently vacate the

property would be removed

from the subdivision

housing stock.

Would probably require

several adjacent properties

to adopt this solution.

Community feedback mixed

for this solution.

Shading indicates advantages relative to other options. Light grey shading indicates a big advantage, dark grey shading indicates a disadvantage.

20



7 References

Contaminated Site Investigation, June 2010, Moanataiari Subdivision, Thames, Scoping Report –

Historical Contamination Review, prepared for Environmental Waikato.

Golder Associates, 30 March 2012, Phase 3 – Desktop study and background sampling

methodology for Thames Area, prepared for Thames-Coromandel District Council.

Golder Associates, 29 June 2012, Interim report on bioaccessibility feasibility study, Moanataiari

Subdivision, Thames, prepared for Thames-Coromandel District Council.

Golder Associates, August 2012, Soil guideline value for thallium, Moanataiari Subdivision,

Thames, prepared for Thames-Coromandel District Council.

Golder Associates, October 2012, Health Risk Assessment, Moanataiari Subdivision, Thames,

prepared for Thames-Coromandel District Council.

Ministry for the Environment, 1997a, Guidelines for Assessing and Managing Contaminated

Gasworks Sites in New Zealand.

Ministry for the Environment, 1997b, Health and environmental guidelines for selected timber

treatment chemicals in New Zealand.

Ministry for the Environment, revised 2011a, Contaminated Land Management Guidelines No 1:

Guidelines for Reporting on Contaminated Sites in New Zealand.

Ministry for the Environment, 2011b, Methodology for deriving standards for contaminants in soil

to protect human health.

Ministry for the Environment, revised 2011c, Contaminated Land Management Guidelines (CLMG)

No. 2 – Hierarchy and Application in New Zealand of Environmental Guideline Values.

Ministry for the Environment, revised 2011d, Contaminated Land Management Guidelines (CLMG)

No. 5 – Site Investigation and Analysis of Soils.

Ministry for the Environment, 2006, Identifying, investigating and managing risks associated with

former sheep-dip sites: A guide for local authorities

Ministry for the Environment, April 2012, User’s Guide - National Environmental Standard for

Assessing and Managing Contaminants in Soil to Protect Human Health.

Ministry of Health, February 2012, The Environmental Case Management of Lead-exposed

Persons, Guidelines for Public Health Units.

Pattle Delamore and Partners, 15 November 2011a, Calculation of Acceptable Soil Concentrations

for Acute Exposure to Arsenic in Soil.

Pattle Delamore and Partners, December 2011b, Moanataiari Subdivision Site Investigation

Report, prepared for Waikato Regional Council.

Resource Management (National Environmental Standard for Assessing and Managing

Contaminants in Soil to Protect Human Health) Regulations 2011.

Tonkin & Taylor, June 2012, Moanataiari Subdivision, Thames – Phase 2 Overall Contamination

Assessment Report, prepared for Thames-Coromandel District Council

Appendix A: Figure

• Figure 1 – Site plan

Appendix B: Golder HRA Figure 5

Documents

Thames Coromandel District Council Moanataiari Subdivision ... Council/Council Projects... · 1 Moanataiari Subdivision, Thames Phase 4 - Assessment of Response Options T&T Ref. 61570.002