6.3 Mitigation Measures during Construction Phase.. 6-5

6 LAND CONTAMINATION

6.2 Remedial Action

6.2.1 The estimated quantity, nature and the proposed remediation methods for the contaminated soil at A King Shipyard are shown in Table 6.1 while the estimated contamination extent are shown in Figure 6.1. In summary, the contaminated soil shall be treated by either ‘excavation and landfill disposal’ or ‘ex-situ cement solidification / stabilization (CS/S)’.

Table 6.1 Estimated Quantity of Contaminated Soil

Area ID	Contaminants	Estimated Vertical Contamination Extent (m below ground)	Estimated Horizontal Contamination Extent (m²)	*Estimated Volume of Contaminated Soil ^ (m³)**	Proposed Remediation Method
Area B1	TPH, copper, lead, zinc and barium	0.0-0.8	49	39.2	Excavation & landfill disposal
Area B2	Copper and lead	0.0-0.8	570.5	456.4	CS/S
Area B3	Copper	1.2-2.0	49	39.2	CS/S
Area C1	Lead	2.5-3.5	49	49	CS/S
Area C2	Lead	1.0-2.0	49	49	CS/S
Total Estimated Volume of Contaminated Soil:				632.8
(TPH and Heavy Metals: 39.2m³; Heavy Metals only: 593.6m³)

Notes: * The soil volume may vary subject to the testing of confirmatory samples collected at the defined contaminated zone boundary as well as the site specific conditions (e.g. encountering of boulders).

6.2.2 The following key steps/milestones shall be carried out for the handling/treatment of contaminated soil:

(i) Landfill disposal for TPH contaminated soil

(ii) Excavation and stockpile of heavy metals contaminated soil

(iii) Cement solidification / stabilisation and treatment performance criteria

(iv) Handling of treated soil

(v) Preparation and submission of Remediation Report

Landfill Disposal for TPH contaminated soil

6.2.3 The essential steps for the excavation and landfill disposal are attached in Appendix J.

6.2.4 Excavation of TPH contaminated soil shall be carried out as shown in Figure 6.2 (Area B1). It is anticipated that the excavation works will be of short duration and where practicable, no excavation shall be allowed on rainy days to avoid possible migration of contaminants while working on site and during disposal. Stockpiling is not recommended, as all excavated soil shall be transported to a designated landfill on every working day. A disposal license / permit shall be granted from EPD for the disposal of the contaminated soil to EPD’s designated landfill prior to excavation.

6.2.5 While stockpiling of contamination soil is required, the stockpile shall be fully covered by impermeable sheeting to prevent dust emission and runoff. The assigned area shall have suitable warning posted. Impermeable sheeting shall also be placed at the bottom of the stockpile and leachate collection sump shall be constructed along the perimeter of the stockpile to prevent leachate from contaminating the underlying soil / groundwater. The collected leachate shall be disposed of as chemical waste.

6.2.6 General construction practice shall be exercised to control the spread of dust from the site to the nearby residential areas. Decontamination shall be properly executed to workers and vehicles before leaving the site.

6.2.7 Due care must be exercised during the transportation of the excavated contaminated soil to the landfill for disposal. The soil shall be properly contained and covered to avoid spillage during transportation. Suitable warning signs about the nature of the contaminated soil shall be displayed on both the vehicle and the soil itself.

6.2.8 A closure assessment shall be undertaken after the excavation to confirm the clean-up for the excavation of contaminated areas. The objective is to determine if all organic contaminated soils have been fully removed.

6.2.9 At least one sample from the base of the excavation and four samples evenly distributed along the boundary of the excavation pit shall be collected for laboratory analysis for TPH. The parameters, detection limits and reference methods for the laboratory analysis of soil samples for closure assessment are tabulated in Table 6.2.

Table 6.2 Parameters, Detection Limits, Reference Methods and Assessment Criteria for Confirmatory Test on TPH Contaminated Soil Samples

Item	Parameter	Detection Limit (mg/kg)	Reference Method	Dutch B Criteria (mg/L)
1	TPH	C6-C9: 2 C10-C14: 50 C15-C28: 100 C29-C36: 100	USEPA 8015	1,000

Item

Parameter

Detection Limit (mg/kg)

Reference Method

Dutch B Criteria

(mg/L)

TPH

C6-C9: 2

C10-C14: 50

C15-C28: 100

C29-C36: 100

USEPA 8015

1,000

6.2.10 If the laboratory analysis indicated that there is presence of contamination (ie above relevant Dutch B criteria), the excavation shall be extended further (with 0.5m increment in vertical direction and 1.0m in horizontal direction). Further sampling and confirmation test shall be undertaken. The process of excavation, sampling and confirmation test shall continue until all organic contaminated soils are removed.

Excavation and Stockpile of Heavy Metals Contaminated Soil

6.2.11 Excavation shall be carried out as shown in Figures 6.2 (Area B2, B3, C1 and C2). Excavation at Area B2 and B3 shall only be carried out after the confirmation of clean-up at Area B1 for TPH as discussed above.

6.2.12 The contaminated soil shall be excavated and transported to a designated area for treatment. The treatment area would be preferably conducted near the designated area to minimise transportation of contaminated soil. No excavation shall be allowed on rainy days to avoid possible migration of contaminants while working on site and during disposal.

6.2.13 Measures as discussed in Section 6.3 shall also be implemented if applicable.

6.2.14 A closure assessment to confirm the clean-up for the excavation of contaminated areas shall be undertaken. The objective is to determine if all contaminated soil has been removed before filling takes place.

6.2.15 Confirmatory soil sampling shall be collected at the side walls and at the bottom of the excavation pit. It is proposed that one soil sample at the base of the excavation and at least four samples at mid-depth of the excavation pit boundary be collected for laboratory analysis. The soil sampling and testing procedures must be carried out to confirm soil at the final boundary of the excavation pit is ‘clean’ (ie below relevant Dutch B criteria), before the backfilling takes place.

6.2.16 The confirmatory soil samples shall be collected using stainless steel hand tools and contained in appropriate containers as provided by the laboratory. During sampling, the sampling tools shall be decontaminated by thoroughly washing with laboratory-grade detergent and then rinsing by clean water. At each sampling point, sufficient soil sample shall be taken to fill up the container upon sample collection. The collected soil samples shall be analyzed by a HOKLAS accredited laboratory. The parameters, detection limits, reference methods and corresponding Dutch B criteria for the laboratory analysis of soil samples for the closure assessment are tabulated in Table 6.3.

Table 6.3 Parameters, Detection Limits, Reference Methods and Assessment Criteria for Confirmatory Tests on Heavy Metals Contaminated Soil

Item	Parameter	Applicable Contaminated Area	Detection Limit (mg/kg)	Reference Method	Dutch B Criteria (mg/L)
1	Lead (Pb)	B2, C1 & C2	1.0	USEPA 6020	150
2	Copper (Cu)	B2 & B3	1.0	USEPA 6020	100
3	Barium (Ba)	B2	0.5	USEPA 6020	400
4	Zinc (Zn)	B2	20	USEPA 6020	500

6.2.17 If the laboratory analysis indicated that there is presence of contamination (ie above relevant Dutch B criteria), the excavation shall be extended further (with 0.5m increment in vertical direction and 1.0m in horizontal direction). Further sampling and confirmation test shall be undertaken. The process of excavation, sampling and confirmation test shall continue until all contaminated soils are removed.

Cement Solidification/Stabilisation and Treatment Performance Test

6.2.18 Prior to solidification, metal-contaminated soils shall be screened to segregate soil from debris, rock fragments, and other materials and to break soil clumps into sizes to allow effective mixing with solidifying agents.

6.2.19 During the cement SS process, cement, water and other additive(s) (such as fly ash, lime, soluble silicates and clays) are added to the contaminated soils to form soil block. It is important that soil/cement/water is uniformly mixed. The cement solidification / stabilization mixing process can be carried out within a pugmill, lorry mixer or equivalent.

6.2.20 The total volume of the concrete blocks could increase by up to about 10% from the original soil volume. For easy handling, the solidified blocks shall be broken up into a number of smaller blocks after verification procedure. Considerations for cement solidification /stabilisation shall include the followings:

· Soil characteristics (e.g. metal content, physical characteristics);

· Required solidified soil properties (e.g. leachability, permeability, compressive strength);

· Operational and economical factors (e.g. cost of cement and availability & cost of other additives, materials handling, volume and weight increase) and;

· Test methods (e.g. leachability)

6.2.21 The soil mixture in the concrete blocks shall be solidified within about 1 week. Test for leachability shall then be carried out. The sampling frequency for the leachability test shall be 1 TCLP sample per 100 m³ of broken up hardened mixture after cement SS treatment. Each TCLP sample shall be a composite sample collected at 5 locations over the treated pile and roughly the same volume of sample shall be collected at each of the 5 locations so that the composite sample is not biased.

6.2.22 Any hardened samples to be submitted to laboratory for TCLP analysis shall be broken up by the Contractor to small pieces with maximum diameter of 10cm. The sample preparation method of USEPA Method 1311 shall be followed for the TCLP analysis. It is specified in USEPA Method 1311 that the maximum grain size of samples to be analysed is 1cm. As such, the samples shall be further broken up in the laboratory prior to TCLP analysis. TCLP tests shall be conducted in accordance with USEPA Method 1311 and USEPA Method 6020 for metals lead, copper, barium and zinc. The results of the TCLP tests shall comply with the “Universal Treatment Standards” (UTS) before reuse on site. As there are no UTS standards for copper, the acceptance criteria for copper adopted in the Decommissioning of Cheoy Lee Shipyard, which made comparison between Drinking Water Standards for the USEPA and the USEPA Federal Register, was therefore used. The UTS for the concerned heavy metals are listed in Table 6.4 below.

Table 6.4 Universal Treatment Standards for Soil Remediation

Parameter	Universal Treatment Standard (mg/L as TCLP)
Barium	21
Copper*	7.8
Lead	0.75
Zinc	4.3

* Adopted acceptance criteria from the remediation of Decommissioning of Cheoy Lee Shipyard.

6.2.23 Any pile of broken up solidified mixture that does not meet the concerned UTS shall be crushed and re-treated by cement solidification. The re-treated pile shall be tested again for TCLP to confirm if it can be reused on site.

6.2.24 The treated material shall be allowed to set to achieve the unconfined compressive strength (UCS) of not less than 1 mPa with reference to the USEPA guidelines (1986) – Handbook for Stabilization / Solidification of Hazardous Wastes, EPA/540/2-96-00. The test procedure of UCS test shall be based on BS 1377.

Handling of Treated Soil

6.2.25 Upon completion of the leachability testing and meeting the UTS and the UCS requirements, the solidified materials shall be reused on site as filling materials. As the maximum grain size of filling material is 250mm (according to the general practice), the solidified soil shall be broken down to below this size before being used as filling materials. Whenever the soil is to be reused as filling materials, the soil shall be put below at least 1m of clean fill layer.

Preparation and Submission of Remediation Report

6.2.26 A Remediation Report shall be prepared and submitted to EPD for record. The Remediation Report shall demonstrate that the clean-up is adequate and all excavated contaminated soil has either undergone the proper soil remediation to meet the relevant standards or disposed properly at designated landfill. All relevant information, including details of closure assessment, sampling results, photographs, certification of independent checker, quantity of treated soil and final backfill site of treated soil shall be included in the report.

6.3 Mitigation Measures during Construction Phase

6.3.1 The Contractor for the excavation works shall take note of the following points for excavation:

· Excavation profiles must be properly designed and executed;

· In case the soil to be excavated is situated beneath the groundwater table, it may be necessary to lower the groundwater table by installing well points or similar means;

· Quantities of soil to be excavated must be estimated;

· It maybe necessary to split quantities of soil according to soil type, degree and nature of contamination.

· Temporary storage of soil at intermediate depot or on-site maybe required. The storage site should include protection facilities for leaching into the ground. eg. Liner maybe required.

· Supply of suitable clean backfill materials is needed after excavation.

· Care must be taken of existing buildings and utilities.

· Precautions must be taken to control of ground settlement

· Speed controls for vehicles should be imposed on dusty site areas.

· Vehicle wheel and body washing facilities at the site’s exit points should be established and used.

6.3.2 The following environmental mitigation measures should be strictly followed during the operation and/or maintenance of the cement solidification and stabilization facilities:

Air Quality Mitigation Measures

· The loading, unloading, handling, transfer or storage of cement should be carried out in an enclosed system.

· The loading, unloading, handling, transfer or storage of other materials which may generate airborne dust emissions such as untreated soil and oversize materials sorted out from the screening plant and stabilized soil stockpiled in the designated handling area, should be carried out in such a manner to prevent or minimise dust emissions. These materials should be adequately wetted prior to and during the loading, unloading and handling operations.

· All practicable measures, including speed controls for vehicles, should be taken to prevent or minimize the dust emission caused by vehicle movement.

· Tarpaulin or low permeable sheet should be put on dusty vehicle loads transported between site locations.

Noise Mitigation Measures

· The mixing facilities should be sited as far as practicable to the nearby noise sensitive receivers.

· Simultaneous operation of mixing facilities and other equipment should be avoided.

· Mixing process and other associated material handling activities should be properly scheduled to minimise potential cumulative noise impact on the nearby noise sensitive receivers.

· Construction Noise Permit should be applied for the operation of powered mechanical equipment during restricted hours (if any).

Water Quality Mitigation Measures

· Stockpile of untreated soil should be covered as far as practicable to prevent the contaminated material from leaching out. The leachate should be discharged following the requirements of WPCO.

Waste Mitigation Measures

· Treated oversize materials will be used as filling material for backfilling within the site. Sorted materials of size smaller than 5 cm will be collected and transferred to the mixing plant for further decontamination treatment.

· Stabilized soils should be broken into suitable size for backfilling or reuse on site.

· A high standard of housekeeping should be maintained within the mixing plant area.

· If necessary, there should be clear and separated areas for stockpiling of untreated and treated materials