(i)
Section 3 (Potential Contaminated Land
Issues) of Annex 19 “Guidelines for Assessment of
Impact on Sites of Cultural Heritage and Other Impacts” of the Technical Memorandum on Environmental Impact
Assessment Process (EIAO-TM).
(ii)
Guidance
Note for Contaminated Land Assessment and Remediation” (Guidance Note).
Guidance
Note sets out the requirements for proper assessment and management of potentially
contaminated sites such as oil installations (e.g. oil depots, petrol filling
stations), gas works, power plants, shipyards/boatyards, chemical
manufacturing/processing plants, steel mills/metal workshops, car
repairing/dismantling workshops and scrap yards. In addition, this Guidance
Note provides guidelines on how site assessments should be conducted and
analysed and suggests practical remedial measures that can be adopted for the
cleanup of contaminated sites.
(iii)
Practice
Guide for Investigation and Remediation of Contaminated Land (Practice Guide).
Practice
Guide, newly published in August 2011, presents the standard investigation
methods and remediation strategies for the range of potential contaminated
sites and contaminants typically encountered in Hong Kong. It has superseded the
1999 Guidance Notes for Investigation and Remediation of
Contaminated Sites of Petrol Filling Stations, Boatyards and Car Repair
/Dismantling Workshop.
(iv)
Guidance
Manual for Use of Risk-based Remediation Goals for Contaminated Land Management (Guidance Manual).
Guidance Manual
introduces the risk based approach in land contamination assessment and present
instructions for comparison of soil and groundwater data to the Risk-based
Remediation Goals (RBRGs) for 54 chemicals of concern commonly found in Hong
Kong. The RBRGs were derived to suit Hong Kong conditions by following the
international practice of adopting a risk-based methodology for contaminated
land assessment and remediation and were designed to protect the health of
people who could potentially be exposed to land impacted by chemicals under
four broad post restoration land use categories. The RBRGs also serve as the
remediation targets if remediation is necessary.
·
Desktop study to review the current and
historical land uses;
·
Acquisition of information related to
potential land contamination from Environmental Compliance Division of
Environmental Protection Department (EPD), Fire Services Department (FSD) and
Water Supplies Department (WSD); and
·
Site reconnaissance to identify the existing
land uses and potential contamination hotspots.
·
Selected aerial photographs from Lands
Department;
·
Selected geological reports from Civil
Engineering and Development Department;
·
Hong Kong Geological Survey Maps (Series HGM20) – Sheet No. 7 (1:20,000);
·
Information on dangerous goods and spillage
incident from FSD; and
·
Information on chemical wastes, records and
photographs obtained during the Project site visit.
(i)
Energy Dissipating Chamber;
(ii)
Raw Water Inlet Channel, Overflow Channel,
Dividing Chamber and its Extension;
(iii)
Clarifiers No. 1-4 and associated
Distribution Chamber;
(iv)
Filter Beds (South Works) and Filtered
Gallery (South Works);
(v)
Filtered Water Pumping Station (South
Works);
(vi)
Grit Trap and Washwater Recovery Tanks No.
1-3;
(vii)
Chemical House and Lime Chloride Solution
Preparation Tank;
(viii)
Chlorination House (To be maintained under
this Project);
(ix)
Alum Saturator Tanks;
(x)
Covered Storage Area (Workshops);
(xi)
Open Storage Area;
(xii)
Dangerous Goods Store and Chemical Waste
Storage Area;
(xiii)
Generator House;
(xiv)
Transformer House;
(xv)
Administration Building;
(xvi)
Staff Quarters; and
(xvii) Bungalow (NTE1 Region & INSTRUMENT/M (NTE2)).
Table
11.1 Details of Chemical Storage and Usage Areas within the Project
site
Usage/ Stored Location |
Involved Chemicals |
Purpose |
Clarifiers No. 1-4 |
Lubrication oil
and grease |
Maintaining motors |
Filtered Water
Pumping Station (South Works) |
Lubrication oil
and grease |
Maintaining pumps |
Chemical House
& Lime Chloride
Solution Preparation Tank |
1.
Lubrication oil and grease 2.
Sodium hexafluorosilicate, alum,
polyelectrolyte, lime and lime chloride |
1.
Maintaining pumps 2.
Water treatment |
Alum Saturator
Tanks Pump House |
Lubrication oil
and grease |
Maintaining pumps |
Generator Set for Chlorination
House |
Lubrication oil,
grease, fuel and diesel |
Driving and
maintaining backup generator |
Covered Storage
Area (Workshops) |
Lubrication oil
and grease |
Small scale
maintenance |
Open Storage Area |
1.
Lubrication oil or scraped metals parts from disused mechanics 2.
Lubrication oil and grease |
1.
Temporarily storing the scraped mechanics for further collection and
disposal 2.
Small scale workshop and storage area for sub-contractor |
Dangerous Goods
Store |
Lubrication oil,
grease, fuel, diesel, transformer oil and laboratory used agents |
Storing the
chemicals for daily operation of the treatment works |
Chemical Waste
Storage Area |
Spent lube oil |
Temporarily
storing the spent chemicals and containers for further collection and
disposal |
Transformer |
Transformer oil |
Electrical
insulating and cooling |
Generator House |
Lubrication oil, grease,
fuel and diesel |
Driving and
maintaining backup generator |
Storage Compound
in Staff Quarter |
Bleaching
solution, paint and lubricants |
Storing the
chemicals for daily maintenance |
Bungalow |
Paint and
household cleansing agents |
Storing the
chemicals for daily maintenance |
·
Direct ingestion of contaminated soil through
eating, drinking or smoking onsite; and
·
Dermal contact with contaminated soil.
Table 11.2 Potentially Contaminated
Hotspots Identified
Area ID |
Current Land
Use (Size) |
Reference Figure |
A |
Filtered Water Pumping Station (South Works) (~540 m2) |
|
B |
Chemical House (~2,600 m2) |
|
C |
Pump House of Alum Saturator Tanks (~20m2) |
|
D |
Generator Set for Chlorination House (~30m2) |
|
E |
Covered Storage Area (Maintenance Workshop) (~500 m2) |
|
F |
Open Storage and Contractor Workshop (~1,400 m2) |
|
G |
Dangerous Goods Store and Chemical Waste Storage Area (~100 m2) |
|
H |
Generator House (~18m2) |
|
I |
Transformer (~30m2) |
|
J |
Lawn beside Access
Road to Washwater recovery Tanks (The Scene of Crane Lorry Overturn Incident)
(~25m2) |
|
K |
Staff Quarters
Storage Compound (~240m2) |
|
L |
Disused Diesel
Storage Tank (~4m2) |
·
Nature and level of contamination;
·
Extent of contamination;
·
Site characteristics (such as site
hydrogeology, soil and groundwater chemical characteristics);
·
Site constraints (such as available space,
surrounding areas); and
·
Time available for remediation.
·
Technical and cost effectiveness;
·
Technology development status;
·
Environmental benefits and disbenefits;
·
Commercial availability;
·
Experience; and
·
Expertise requirement.
Table
11.3 Potential Remediation Techniques
Remediation Measures |
Descriptions |
Applicability |
Limitations |
Soil |
|
|
|
Biopile |
Bioremediation
method that bacteria grow in the piled contaminated soil and degrade the
waste into harmless products. |
·
Very effective to petroleum carbon ranges with few successful local
case studies ·
Most cost-effective for large volumes of contaminated soil ·
Can be designed to be a closed system; vapor
emissions can be controlled |
·
Labour-intensive; require considerable maintenance ·
Space required for biopile construction ·
Time-consuming (~1 year required) and not cost-effective for treating
small volume of soil. |
Soil venting |
in situ bioremediation
method that uses indigenous bacteria to degrade contaminants. Activity of the
bacteria is enhanced by inducing air flow (using extraction or injection
wells) and, if necessary, by adding nutrients. |
·
Very effective to petroleum carbon ranges ·
Suitable for remediation in built up areas because wells can be placed
between or below buildings ·
Applicable to large sites with widespread contamination ·
Uses readily available equipment; easy to install ·
Vapour emissions can be controlled but not to the extent of biopiling due to underground soil in situ properties |
·
This method is usually applied for the case with large area of organic
contaminated soil. ·
Effectiveness is limited by underground soil features e.g. soil
moisture content, permeability, etc. ·
May induce possible air emission to the sensitive receivers. ·
Require large space for the system development. |
Soil Washing |
ex situ soil separation
processes mostly based on mineral processing techniques. It is a water-based process for scrubbing
soils ex-situ to remove
contaminants. |
·
Applicable to clean organic and inorganic contaminants from
coarse-grained soils |
·
The effectiveness of the treatment depends on soil particle size. Fine
soil particles (e.g. silt) may require the addition of a polymer to remove
them from the washing fluid. ·
Complex waste mixtures make formulating washing fluid difficult. ·
Require further treatment and disposal for residuals. |
Chemical Methods |
Include chemical
oxidation, dehalogenation, soil flushing, solvent
extraction, etc. Use chemicals to destroy pollutants in soil. |
·
Destroys pollution in situ
without having to dig it up for transport to a treatment system ·
Significant cost savings |
·
Chemicals used are site specific and depend on the contaminants
present. Very specialized contractors required. ·
Requires handling of large quantity of hazardous oxidizing chemicals. ·
Effectiveness less certain when applied to sites with low-permeability
soil or stratified soils |
Solidification/
Stabilization |
ex-situ immobilization technique treats
contaminated soil by mixing soil with binding agents, e.g. cement so that the
contaminants become physically bound within stable mass. |
·
Applicable to clean-up inorganic contaminants such as heavy metals ·
Solidification/stabilization has been used on certain contaminated
sites in Hong Kong and demonstrated as a successful treatment method for
inorganic contaminated soil. |
·
The effectiveness reduces with the presence of organic contaminants. ·
Large boulders may hinder the mixing process. Soil sorting is
necessary before the treatment taken place. |
Landfill Disposal |
ex-situ method whereby contaminants are removed by excavation of the
contaminated soil and direct disposal to landfill |
·
Applicable to all waste or mixture but it should be considered as the
last resort ·
Cost-effective for localized and small quantity of soil contamination ·
Short clean-up time ·
Contamination is removed definitely |
·
Landfill space limited and valuable ·
Indirect costs to the landfill management on monitoring and
maintenance ·
Least desirable management option. ·
All contaminated soil to be disposed in the landfill should meet the
Landfill Disposal Criteria, as stipulated in Table 4.4 of Practice Guide and
obtain EPD’s approval. |
Groundwater |
|
|
|
Air Sparging |
in situ technology in which air is injected into the subsurface saturated zone to remove the contaminants
dissolved in groundwater |
·
The target contaminant groups are VOCs and fuels. ·
Implemented with minimal disturbance to site operations ·
Requires no removal, treatment, storage, or discharge considerations
for groundwater. |
·
Cannot be used if free product exists. ·
Requires detailed pilot testing and monitoring to
ensure vapor control and limit migration. ·
Air injection wells must be designed for site-specific conditions. ·
Stratified soils may cause air sparging to
be ineffective. |
Recovery Wells/
Trenches |
Free product is
recovered from a pit or trench without recovering groundwater |
·
Applicable to settings in which the amount of free product is small
and exists in permeable conduits such as utility bedding or buried underground
open structures ·
Low cost and simple operation and maintenance ·
Ideal for shallow groundwater level and soil excavation works |
·
Recovery rates depend on pit/trench size ·
Frequent media replacement ·
Requires manual adjustment |
Chemical Methods |
Include chemical
oxidation, dehalogenation, soil flushing, solvent
extraction, etc. Use chemicals to destroy pollutants in groundwater. |
·
A wide range of contaminants are treatable. ·
Destroys pollution in situ
without having to pump it out for transport to a treatment system. ·
Relatively low cost |
·
Chemicals used are site specific and depend on the contaminants
present. Very specialized contractors required. ·
Requires handling of large quantity of hazardous oxidizing chemicals. ·
Effectiveness less certain when applied to sites with low-permeability
soil or stratified soils. |
·
Excavation profiles must be properly designed
and executed with attention to the relevant requirements for environment,
health and safety;
·
Excavation should be carried out during the dry
season as far as possible to minimise contaminated runoff from contaminated
soils;
·
Supply of suitable clean backfill material is
needed after excavation;
·
In case chemicals are used in remediation, they
should be stored securely, separately and away from sources of ignition or oxidizable items.
Handling should be undertaken by persons specifically trained and
wearing appropriate PPE.
·
Vehicles containing any excavated materials
should be suitably covered to limit potential dust emissions or contaminated
wastewater run-off, and truck bodies and tailgates should be sealed to prevent
any discharge during transport or during wet conditions;
·
Speed control for the trucks carrying
contaminated materials should be enforced;
·
Vehicle wheel and body washing facilities at the
Project site’s exit points should be established and used; and
·
Pollution control measures for air emissions,
noise emissions, and water discharges should be implemented and complied with
relevant regulations and guidelines.
·
Set up a list of safety measures for site
workers;
·
Provide written information and training on
safety for site workers;
·
Keep a log-book and plan showing the
contaminated zones and clean zones;
·
Maintain a hygienic working environment;
·
Avoid dust generation;
·
Provide face and respiratory protection gear
to site workers if necessary;
·
Provide personal protective clothing (e.g.
chemical resistant jackboot, liquid tight gloves) to site workers if necessary;
and
·
Provide first aid training and materials to
site workers.
~
End of Section 11 ~