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ANNEX E
EXCAVATION AND LANDFILL DISPOSAL
Excavation
Description
This is an "ex-situ" method whereby the contaminants are removed by excavation of the contaminated soil. General characteristics of this method are:
Advantages
- excavation of contaminated soil is a relatively quick technique
- contamination is removed definitely
Disadvantages
- demolition of buildings may be necessary
- valuable landfill space is consumed
Points to note concerning 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 may be necessary to split quantities of soil according to soil type, degree and nature of contamination
- transport of excavated soil
- temporary storage of soil at intermediate depot or on-site
- supply of suitable clean backfill material
To facilitate excavation work, the following precautions must be taken:
- care must be taken of existing buildings and utilities
- control of ground settlement
- protect the integrity of existing structures
- traffic diversions
- provisions concerning hygienic and safe working conditions
In case it is necessary to lower the groundwater table, attention must be paid to the following points:
- selection of suitable groundwater lowering schemes
- suitable discharge points
- possession of valid Water Pollution Control Ordinance (WPCO) discharge licence from EPD where applicable
Landfill Disposal
Excavated contaminated soil has to meet certain criteria before disposal to landfills is allowed. The criteria are set primarily in terms of Toxicity Characteristic Leaching Procedure (TCLP) limits, as shown in Table E1.
If excavated soil contains other contaminants in addition to the parameters in Table E1, approval for disposal will be assessed on a case by case basis. Apart from the landfills, another possible disposal outlet is the Chemical Waste Treatment Centre (CWTC) if volume of disposal is small and the concentration of contaminants is so high that the soil can be classified as chemical waste.
Table E1 Landfill Disposal Criteria for Contaminated Soil
| Parameter |
TCLP Limit (ppm) |
| Cadmium |
10 |
| Chromium |
50 |
| Copper |
250 |
| Nickel |
250 |
| Lead |
50 |
| Zinc |
250 |
| Mercury |
1 |
| Tin |
250 |
| Silver |
50 |
| Antimony |
150 |
| Arsenic |
50 |
| Beryllium |
10 |
| Thallium |
50 |
| Vanadium |
250 |
| Selenium |
1 |
| Barium |
1000 |
| Note: |
Soil samples should be stored at 0 - 4oC. The allowable storage time for mercury in soil samples is 8 days while the storage time for the rest of the parameters (in Table E1) in soil samples can be up to 6 months. Soil samples, if stored beyond the allowable storage time, are not considered representative of the actual site conditions. (from American Society for Testing and Materials, ASTM-E1391-90) |
TCLP or other relevant tests on soil samples should be included during the early stage of contamination assessment. Table E2 below summarizes the appropriate action at each stage of assessment and remediation.
Table E2 Procedure of Contaminated Soil Disposal
| Stage |
Action |
| Preparation of CAP |
| a. |
If exceedance of the relevant land contamination standards is likely, and excavation and disposal is envisaged to be the only suitable cleanup method during site appraisal, then the investigation plan should include TCLP or other relevant tests on every soil sample that will be analyzed for land contamination standards. Furthermore, TCLP or other relevant screening tests must be done on at least 3 samples from the most contaminated areas. A screening test is one that analyzes for the full suite of parameters in Table E1 irrespective of whether a parameter has been identified as a contaminant of concern during site appraisal. |
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| b. |
If the most suitable cleanup method has not been identified during site appraisal, extra soil samples should be collected and stored for TCLP or other relevant tests in the future (except the parameter of mercury, see note to Table E1), should exceedance of land contamination standards be confirmed and excavation and disposal be selected as the cleanup method. This approach may save the costs of unnecessary TCLP or other relevant tests during the CAP stage, but would require extra time in the project programme if TCLP or other relevant tests become necessary during CAR and RAP preparation. | |
| Preparation of CAR and RAP |
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If any TCLP or other relevant test results exceed the disposal criteria, the "non-complying" part of contaminated soil must first be pretreated or stabilized before disposal. The RAP should propose the most suitable method of pretreatment or stabilization. | |
| After approval of CAR and RAP |
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A copy of the approved CAR and RAP must be submitted together with an application to Waste Facilities Group (WFG) of EPD 3 months before disposal. WFG may limit the daily disposal quantity and require additional testing to confirm that other pollutants of concern are not present. | |
| Implementation of RAP |
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The authorized person or resident engineer on site will be required to certify on an admission ticket that excavation, segregation and delivery of soil for disposal is done according to the approved RAP. For soils requiring pretreatment or stabilization, typically one sample per 400 tonnes of treated or stabilized soil is to be taken and subjected to TCLP or other relevant tests to confirm that the soil can be accepted at landfills according to the criteria in Table E1 or other relevant criteria. Only those parameters with concentrations exceeding the criteria during the initial testing need to be included in the confirmatory test. Every load of contaminated soil to be disposed of at landfills should be accompanied by an admission ticket and if applicable, confirmatory test results. | |
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