Appendix
3.2
Soil Mix Specification for
Lok Ma Chau Station Marsh Area
Appendix
3.2
Specification
for wetland soil in Marsh within LMC Fishpond
Ecological
Mitigation Area
The imported topsoil (termed
“Mix Type A”) shall be composed of 50% existing pond bund materail (obtained
from the wetland mitigation area), 35% completely decomposed granite and 15%
clean river sand by volume.
Completely Decomposed Granite
shall be as described in Geoguide 3, Guide to Rock and Soil Descriptions 1988.
River sand shall be clean
natural medium or fine texture ‘sand’ as defined by the HK Government Geoguide
No.3 (1988) and shall be free from salt with rounded, as opposed to angular
particles. All particles must be
between 0.2mm and 0.06mm in diameter. The Contractor shall have a sample of the
sand tested by an approved laboratory to show details of origin, particle size,
salt content, pH, organic content.
The Contractor shall state the origin of the river sand and produce
authenticating documents. Results
shall be to the approval of the Engineer. The Contractor shall note that river
sand must originate from a terrestrial/inland location and that marine sand
shall not be accepted.
The Contractor shall submit
samples of the completely decomposed granite and river sand for approval by the
Engineer.
The Contractor shall prepare
topsoil mix on site. Mixing shall
not take place during periods of heavy rain, nor when the soil is
saturated. Mixing operations shall
cease if the moisture content of the topsoil is too high to achieve thorough
mixing of the conditioner with topsoil.
The topsoil mix shall not
include any pre-planting fertiliser.
The topsoil mix shall contain
stones exceeding 25 mm in diameter.
The proportion of stones, by volume within soil shall not exceed 10%.
Topsoil Mix Type A shall
comply with the following:
·
pH
value : 5.5
‑ 7.5
·
Total
nitrogen : <1,000
mg / kg
·
Available
phosphorus : <6.0
mg / kg
·
Moisture
content :
>10%
After mixing, three random 2
kg samples of the mix shall be taken by the Engineer. These shall then be
tested for pH, total nitrogen content, available phosphorus, organic matter,
organic carbon, proportions of sand, silt and clay particles and moisture
content. Soil testing shall be arranged by the Contractor and the report shall
be submitted to the Engineer for approval.
If the results of the test for
Topsoil Mix A show that the soil mix does not meet the nutrient and pH status
required for the soil mix, then the Contractor shall make good the soil mix by
bringing it to the nutrient and organic status specified through the variation
of the ratio of the three components described above. The Contractor shall
submit his proposed remedial measures to the Engineer for approval before
undertaking any work.
Approval of the mix must be
obtained before bulk delivery commences. The constituent materials of the mix
shall be monitored. Changes to the mix shall be submitted to the Engineer for
approval before use.
The Contractor shall ensure
that soil mix heaps are properly maintained and that soil mix shall be placed
in its final position within 6 months of importation to Site or, for site strip
material, deposition for storage on Site.
Weed control shall be carried out by spraying with approved weed killer.
If the period
between the analysis of the soil mix as above and the commencement of any
deposition of soil mix exceeds 6 months then the Contractor shall carry out a
second analysis of the soil mix.
If this second analysis shows that the soil mix has deteriorated in the
nutritional requirements for soil mix the Contractor shall make good the soil
mix by bringing it to the nutrient and organic status specified.
The Contractor shall give the
Engineer four weeks notice of his intention to commence deposition of soiling
operations in order to allow for the results of the analysis to be available
before commencing soiling.
No change in the source of
topsoil mix shall be allowed without the prior approval of the Engineer based
on such tests and samples as specified herein.
No change in the source of
soil mix shall be allowed without the prior approval of the Engineer based on
such tests and samples as specified herein.
Specification for soil storage
1.
The
stockpiling of soil must be minimised to reduce potential degradation of soil
condition during storage.
2.
The
necessity for the storage of wetland topsoils during the preparation and
construction of the wetland mitigation areas must be agreed in advance with the
Engineer.
3.
Soils
shall be stockpiled in a designated area, to be proposed by the Contractor for
approval without objection by the Engineer.
4.
The
soil shall be stockpiled to a total depth of no more than 1.5m by loose
tipping. Under no circumstances shall the movement of vehicles over the
stockpile be allowed. The stockpile shall be turned completely at least once a
year to maintain aeration in the soil.
5.
An
impermeable bund or barrier shall be constructed around the edge of the
stockpile area to hold rainfall and prevent silt-laden run-off during heavy
rainfall. The bund must also prevent potentially polluted run-off entering the
stockpile area. Drainage of the
bunded stockpile area must be controlled via an adjustable sluice so that water
levels between 0 and 30 cm depth can be held within the stockpile area.
6.
The
soil must be tested for moisture levels at least once per week. Moisture levels
must be kept above field capacity levels by flooding and spray irrigation as appropriate and
according to weather conditions.
7.
A
silt trap must be placed within the stockpile drainage system to prevent silt
accumulation in watercourses.
8.
Weed
growth shall be controlled on the stockpile area through the use of an approved
non-persistent herbicide as agreed with the Engineer.