3                                            Remediation Actions

Following the completion of the land contamination site investigation at the Site, the following remediation programs are proposed.

The scope of work for soil remediation shall include:

3.1                                      Demolition of the No.4 and No. 5 Light Oil Tanks and the Oil Separation Sump, Soil Excavation and Confirmation/Verification Sampling

No. 4 and 5 Light Oil Tanks and the oil separation sump will be demolished and soil materials around and underlying the tank and sump will be excavated during the retrofit programme.

3.1.1                                No. 5 Light Oil Tank

·           For the remediation of light petroleum hydrocarbon contaminated soil around the No.5 Light Oil Tank (TPH detected at BH3 0.8 m bgl above Dutch B level), the following steps are proposed.

·           Cleaning of the tank prior to demolition.  Oily water and sludge collected from the cleaning shall be collected and disposed of as chemical waste at Government chemical waste treatment facility.

·           Only licensed waste contractors shall be used to collect and transport any chemical waste.  The necessary waste disposal permits will be obtained, as required, from the appropriate authorities, in accordance with the Waste Disposal Ordinance (Cap 354C) and Waste Disposal (Chemical Waste) (General) Regulation (Cap 35), as required.

·           Excavation of the No. 5 Light Oil Tank and bund wall foundations (parcel 18x18 m2) and underlying soil strata from 0 to 1.5 m bgl or to the rock head for temporary stockpile.  The proposed initial excavated parcel at the No.5 Light Oil Tank is shown in Figure 3.1a.

·           Stockpile shall be contained (eg soil will be stored on a liner sheet and covered with HDPE sheets).

·           Conduct verification sampling for TPH contamination in soil around the excavated parcel.  The soil samples shall be obtained at the north, west, south and east boundaries of the parcel at 0.5 and 1.5 m bgl; and in the middle of the parcel at the bottom of the excavation.  Soil samples shall be taken using excavator and hand tools.

·           If the analytical results of the verification samples are below the Dutch B levels for TPHs, the removal of the contaminated material shall be considered completed.

·           If the analytical results of the verification samples exceed the Dutch B levels, additional soil shall be excavated either laterally or vertically, depending on the analytical results and the verification sampling and analysis processes repeated until all confirmation samples are below the relevant action levels.  The excavation will be limited to the Site area only.

·           The excavated contaminated soil will be remediated to remove volatile and semi-volatile fractions of TPH and bio-remediate the contaminated soil respectively in accordance with the EPD’s Guidance Notes for Investigation and Remediation of Contaminated Sites of Petrol Filling Stations Boatyards, and Car/Repair/Dismantling Workshops, May 1999.  The treatment will be carried out either at the Site or at the Lamma Power Station Extension area.

·         Remediation of hydrocarbon impacted soils can be conducted through the use of enhanced bioremediation in a ‘biopile’.  The soil treatment is accomplished by stimulating naturally occurring hydrocarbon-degrading bacteria in the soils by providing optimal conditions for the bacteria within the biopile.  The method for construction of a typical biopile treatment cell is presented below and diagrams of a typical biopile cell are presented in Figures 3.1b and c ([1]).  A method statement for the on-site treatment of contaminated soil will be prepared and submitted to EPD prior to the commencement of the treatment work.

·           Periodic sampling and analysis of the soil materials during the treatment shall be carried out to monitor the progress of the treatment.  The number, frequency and testing methods for the treatment monitoring will be specified in detail in the treatment method statement.

·           Where the treated soil showed TPH concentrations below the Dutch B value, the treatment is considered completed and the soil can be used as fill materials on-site, at the Lamma Extension area.

·            Vehicles containing any excavated materials shall be suitably covered to limit potential dust emissions or contaminated wastewater run-off, and truck bodies and tailgates shall be sealed to prevent any discharge during transport or during wet conditions.

·           Records of the quantities of wastes generated and disposed of will be maintained.

·           Excavated area will be backfilled with clean filled materials and the surface reinstated.

·           A decontamination verification report shall be prepared upon completion of the decontamination works.

3.1.2                                No. 4 Light Oil Tank and Oil Separation Sump

Groundwater was found to be contaminated in the groundwater samples collected from the wells in the No. 4 Light Oil Tank and Oil Separation Sump.  These included the groundwater from BH1 with the total TPH at concentration 1,185 µg/L, from BH3 with the total TPH at concentration 1,424 µg/L, BH4 with total TPH at concentration 421 µg/L, BH5 with total TPH at concentration 706 µg/L and BH6 with total TPH at concentration 381 µg/L.  As such, it is proposed to sample and test the soil materials on all bottoms and all sides of the No.4 Light Oil Tank and oil separation sump after demolition and excavation to identify potential TPH contamination.  The following steps are proposed.

·           Cleaning of tanks and sumps prior to demolition.  Oily water and sludge collected from the cleaning shall be treated at the on-site wastewater treatment facility.  Oily water and sludge collected from the cleaning shall be collected and disposed of as chemical waste at Government chemical waste treatment facility.

·           Only licensed waste contractors shall be used to collect and transport any chemical waste.  The necessary waste disposal permits will be obtained, as required, from the appropriate authorities, in accordance with the Waste Disposal Ordinance (Cap 354C) and Waste Disposal (Chemical Waste) (General) Regulation (Cap 35), as required.

·           Excavation of the No. 4 Light Oil Tank and bund wall foundations (parcel 18x18 m2) and excavation of oil separation sump structures (parcel 12x9 m2 to the sump depth of about 1.65 m).  The proposed initial excavated parcels at the No.4 Light Oil Tank and oil separation sump are shown in Figure 3.1a.

·           Conduct verification sampling for TPH contamination in soil around the excavated parcels.  The soil samples shall be obtained at the north, west, south and east boundaries of the parcels at 0.5 and 1.5 m bgl for the No. 4 tank; at the north, west, south and east boundaries of the parcels at 0.5 and 1.65 m bgl for the sump; and in the middle of each of the parcels at the bottom of the excavation.  Soil samples shall be taken using excavator and hand tools.

·           Stockpiling, sampling, testing, further excavation and disposal of soil materials shall follow the same procedures as described in the Section 3.1.1.

3.2                                      Groundwater Handling

As groundwater is not used for either domestic or industrial purposes at the Site and in the adjacent areas, remediation of TPH detected in the groundwater of the Site is not considered necessary.  No groundwater pumping is anticipated during the construction of the foundation of the project as the proposed excavation during the demolition and construction are at levels well above the measured groundwater table at the Site.  However, if the groundwater is encountered during the retrofit programme, the groundwater abstracted or collected should be recharged back to the Site. 

3.3                                      Health and Safety Control Measures

The remediation work will involve tank cleaning, oil tank and oil separation demolition, soil excavation, soil stockpiling, and soil sampling.  The tanks will be cleaned by an explosive-proof, manual operated steam or water cleaner then by manual wiping.  In order to minimise the contacts of the workers with the contaminated materials and to ensure safe work environments during the remediation works, the following control measures are proposed.

·           Prior to commence any remediation work, a health and safety risk assessment should be performed for the remediation work to identify potential work related hazards and prepare appropriate control measures.

·           Appropriate personal Protective Equipment (PPE) such as safety hat, chemical protective gloves, masks (for both dust and vapour), eye goggles, protective clothing and protective footwear shall be provided to staff who would be involved in the tank cleaning and contaminated area (BH3) remediation works.  No works should be allowed without the suitable PPE.

·           Workers shall inspect and check their PPE before, during and after use. In cases where any of the PPE is impaired.  The worker shall stop work immediately and inform their supervisor.  The worker shall not be allowed to re-start his work until the impaired PPE is replaced.

·           As the oil tank is defined as a confined space, appropriate control measures and procedures for entering a confined space should be provided and followed when entering the tanks during the remediation.

·           Workers shall always maintain basic hygiene standard (e.g. hand wash before leaving the contaminated work area).  Workers shall also be responsible for cleaning and storing their own PPE in a secure place before leaving the site.

·           Eating, drinking and smoking must be strictly prohibited within the contaminated site area.

·           The designated site management representatives must be informed if any workers feel uncomfortable physically or mentally during the remediation works.  All workers shall leave the work areas and the work shall be temporarily suspended until the reason for the uncomfortable feeling has been identified.

·           The works shall be stopped or discontinued when any typhoon signal number 3; yellow, red or black storm signals are hoisted.  All stockpile materials (if any) shall be covered immediately by tarpaulin or other similar protective and waterproof materials.

·           The use of bulk earth-moving excavator equipment would minimise construction workers' potential contact with contaminated materials.


 



([1])  Note: Typical configurations of biopile treatment method is described in the following.
The base of the treatment cell is constructed by placing a liner (such as tarpaulin) on a flat graded surface.  Bunds such as hay bales or concrete blocks are then placed along the perimeter of the liner to create a containment berm for the treatment cell.  Perforated collection pipes are then installed on top of the base liner to collect excess moisture from the treatment cell (ie, leachate).  The leachate collection pipes are covered with pea gravel (or coarse sand) and a geotextile liner.  Soil requiring treatment is then placed on top of the geotextile liner in lifts of typically 2 to 3 feet.  A nutrient mixture used to increase hydrocarbon-degrading bacteria is sprayed on the impacted soils while they are being placed into the treatment cell.
After each lift of soil is placed in the cell, slotted ventilation pipes and soil vapour monitoring points are installed on top of the lift.  The ventilation pipes are used to supply oxygen to the bacteria in the soil and the vapour monitoring points are used to monitor carbon dioxide in the treatment cell (carbon dioxide is one of the primary by-products of the hydrocarbon biodegradation process).  Alternating additional lifts of soil and piping are then installed to the top of the cell.  Once the cell is complete, it is covered with a liner that is anchored to the ground. 
The ventilation pipes are connected to a blower system to create airflow through the cell.  As necessary, the air discharge from the blower can be connected to a treatment system to reduce emissions to the atmosphere.  Monitoring of the cell is conducted through measurement of carbon dioxide concentrations in vapours within the cell and hydrocarbon concentrations in air extracted from the treatment cell.  As remediation progresses, both carbon dioxide and hydrocarbon concentrations will decrease until successful reduction of the chemical concentrations in the soil has been achieved.  Confirmation samples are then collected from the formerly impacted soils to confirm the remedial goals have been reached.