Proposal to Use Excavated Soil among Public Fill in Capping Layer

of Contaminated Mud Pits at East Sha Chau (ESC)

 

Method Statement

 

        The methodology of implementing the capping works through using excavated soil among public fill is summarised in paragraphs below:

 

At Public Fill Reception Facilities (e.g. Barging Point)

 

1.          All incoming trucks would be visually inspected by site supervisory staff of the Civil Engineering and Development Department (CEDD) at the reception point of the public fill reception facilities. Visual inspection will be conducted by a staff who is positioned high enough to overlook truckloads. Truckloads with unsuitable materials will not be diverted to ESC. Among the public fill[1], only the excavated soil with size below 200 mm and have no abnormal colour or odour which signifies contamination could be used for forming the inner capping layer at ESC Pit IV.

 

2.          CEDD will conduct spot checks on those truck loads considered to be visually suitable for capping, aided by a grab, to the inner portion for ensuring the homogeneity of the materials. Grab inspection to reveal underlying materials will be conducted 1 day in a week and on about 20% of the truckloads for that day

 

3.          For incoming materials generated from identifiable projects, CEDD will implement a trip-ticket system, involving issue of Delivery Form at sources and receiving of the Form at the public fill reception facilities. CEDD will ensure the Delivery Forms will be vetted on entry of the truck concerned and cross-compared with a list of Acceptable Work Sites (see para. for the list). Truckloads from work sites not on the list will be considered not acceptable for ESC capping. If these materials satisfy the requirements as mentioned in paragraphs 1 and 23, they can be used for capping at ESC Pit IVa, Pit IVb and Pit IVc. The list of Acceptable Work Sites will be updated and provided by CEDD from time to time.

 

4.          For those materials generated from non-identifiable projects, the truck vehicle number, arrival time, type of material and district of the source, will be recorded in a computer database at the public fill reception facilities. If these materials satisfy the requirement as mentioned in paragraphs 1 and 22, they can be used for capping at ESC Pit IVb and Pit IVc only.

 

5.          No materials shall be coming from the “Decommissioning Projects” under the EIAO. A letter or memo would be sent to the concerned project offices and private clients to remind them not to deliver these materials to the public fill reception facilities.

 

6.          CEDD has installed CCTV surveillance system at each of the public fill reception facilities for recording all the image of every incoming truck and the materials contained in its hopper. CCTV cameras are positioned at positions to view and visually record truckloads, truck license plates, unloading from trucks of materials to ESC vessel. CEDD will deploy at all time a staff to supervise the unloading activity at the tipping hall to ensure only those trucks loads defined as suitable material for capping after visual screen would be unloaded into the right barge for transportation to ESC.

 

7.          For the truckloads diverted to ESC, CEDD will ensure records be kept about truck licence plates, time-in to and time-out from facilities and sources of material (for identifiable projects) or district of material generation (for non-identifiable projects).

 

 

Transportation of Suitable Material to ESC

 

8.          Material that passes process in para 1,2, 3 and 6 and confirmed to be from acceptable work sites would be directed by CEDD to be off-loaded from trucks onto the derrick lighter destined to ESC Pit IVa, Pit IVb or Pit IVc. Materials that passes process in para 1,2, 3 and 6 and confirmed to be from non-identifiable source would be directed by CEDD to be off-loaded from trucks onto the derrick lighter destined to ESC at Pit IVb and Pit IVc separately. At present, the Kai Tak Barging Point (KTBP) is receiving public fill only from identifiable sources. The excavated soil received at KTBP, subject to the aforesaid relevant processes, would be disposed of at Pit IVa, Pit IVb and Pit IVc. The other public fill reception facilities are receiving public fill from identifiable and non-identifiable sources, their received excavated soil suitable for capping would, subject to the aforesaid relevant processes, be disposed of at Pit IVb and Pit IVc only. If these public fill reception facility can be provided with two tipping halls for unloading of materials onto barges, suitable material from identifiable sources would be disposed of at Pit IVa and non-identifiable source would be disposed of at Pit IVb and Pit IVc separately.

 

9.          The material considered to be not suitable for capping at ESC would be loaded into another barge or stockpiled on land, for subsequent transportation to Fill Banks.

 

10.      Only derrick lighters equipped with Automatic Self Monitoring System would be used to receive excavated soil from trucks for capping. As the bottom of derrick lighters cannot be opened for dumping, illegal dumping or leakage of materials during the transportation of the material to ESC would unlikely happen. 

 

At ESC

 

11.      All derrick lighters shall report to the management team of ESC contaminated mud pits upon arrival at ESC and conduct works at ESC in accordance with the Site Management Scheme for Capping to ESC Contaminated Mud Disposal Facility.

 

12.      The derrick lighter operator shall follow the instructions of the management team of ESC contaminated mud pits to position their barge at designated area within the pits.

 

13.      The excavated soil among public fill shall be placed on the prevailing seabed level by using grab method. Any incidental unsuitable material loaded into the derrick lighter will not be grabbed for deposition into the capping layer. Also, the grab shall be lowered below sea level for releasing the excavated soil evenly layer by layer to prevent concentrated load acting on the underlying layers.

 

14.      To minimize any floating refuse that may arise during the placement of materials, floating refuse boom would be installed for enclosing the disposal spot for each derrick lighter.

 

15.      Refuse collection boat(s) will be provided at ESC for picking up occasional floating refuse arising from the placement of excavated soil among public fill for capping.  In case where the refuse boom and the refuse collection boat(s) could not control the spread of floating refuse (possibly due to severe wave conditions etc), MD’s VTC and EPD would be notified immediately.

 

Site Supervision

 

16.      The whole operation at the public fill reception facilities and at ESC dumping ground would be supervised/monitored by the site staff of CEDD. In fact, a team of site supervisory staff stationed on a floating office is already in place at ESC for monitoring the contaminated mud disposal activities and capping works.

 

17.      An operation guideline for the site supervisory staff to control of the quality of the capping works at different stages is attached in Appendix A.

 

Environmental Monitoring

 

18.      Since the contaminated mud Pit IV was put into operation for receiving contaminated mud in December 1997, a comprehensive EM&A programme which covers the whole area of the pits has been in place. It comprises 5 major components, namely sediment quality monitoring, sediment toxicity, water quality monitoring, benthic infauna sampling and identification, and trawling and tissue analysis of demersal fauna. An independent environmental consultant, under the Consultancy Agreement No. CE 64/99, and a contractor are being employed for implementing the EM&A programme and associated field sampling and testing works. The EM&A programme is overseen by a Working Group comprising representatives from EPD, CEDD and AFCD. Findings from the EM&A have been regularly reported to the ACE.

 

19.      In view of that the capping work will render no environmental change nor cause more adverse environmental effect, it is considered that the present EM&A programme is sufficient for monitoring the environmental impact even when the subject proposed capping work is implemented.

 

20.      As a prudent approach, water quality monitoring including suspended solid, temperature, dissolved oxygen, salinity and turbidity could be stepped up from a monthly basis to weekly basis at the initial four months of the capping work to ascertain any impact. The water quality monitoring will be carried out by the existing independent environmental consultant and the independent field sampling and testing contractor referred in paragraph 17 above.  Details of the monitoring programme is to be worked out by the independent environmental consultant under the Consultancy Agreement No. CE 64/99 and endorsed by EPD (WP).

 

21.      As detailed in Appendix B, If the suspended solid parameter reaches the respective levels of concern level, the Contractor would be instructed by the management team to implement the mitigation/remedial actions accordingly including slowing down the capping or stopping.

 

Statistical Checking of Project Activities

 

22.      For non-identifiable projects, a statistically random sampling exercise will be carried out to verify that the likelihood of excavated soils from unknown origins being contaminated will be acceptably low. The methodology of this sampling exercise will be as follows:

(a)        In accordance with the Building Ordinance, the AP/Engineer of the private projects need to provide submissions to Building Department (BD). If the project is related to soil works, the AP/Engineer should also provide geotechnical submissions to Geotechnical Engineering Office (GEO) of this Department. As the active private projects list maintained by BD will include building & super-structure projects which would seldom produce excavated soil for disposal, the active private projects list from GEO which cover most of the soil related private construction projects in Hong Kong seems to be more appropriate for use in our survey. Based on this active projects list, about 30% or 60 numbers of these projects/contracts, whichever is the less, would be randomly selected to carry out a site survey in order to check whether previous activities taken place at the work sites would have likely caused land contamination. A list of these activities which is provided by EPD would be used as the basis for forming the checklist to assist in the site survey. As the change of the active private projects in the list is not frequent, such statistically random sampling survey would be carried out on a half-yearly basis.

(b)       In view of that some of the small private projects may not be required for submission to BD and thus not included in the GEO’s active projects list, a random selection of some incoming trucks at the facilities to trace the source of the materials and then carry out the site visit as mentioned in sub-paragraph (a) above by our survey team. Such survey would be carried out on two consecutive days on a quarterly basis.

 

23.      For identifiable projects, a desk-top exercise would be carried out, based on the submitted projects/contracts information, to compile a list of projects/contracts which are suitable for providing materials to form the inner capping layer at ESC. In addition, we will randomly select some projects/contracts from the above list to conduct a similar site visit as mentioned in paragraph 21(a) above in order to supplement the accuracy of the compiled list.

 

 

 

 

Fill Management Division

Civil Engineering and Development Department

January 2005

 

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[1] Public fill – The main constituents include soil, broken rock, building debris, concrete etc. which are generated from construction and demolition activities of the construction industry. Public fill shall be uncontaminated materials and free from household refuse, plastic, metal, industrial and chemical waste, animal and vegetable matter.