This is the second
Review Report for Bridge Surface Runoff from Carriageway Monitoring prepared by
ENSR Asia (HK) Ltd. (ENSR), the designated Environmental Team (ET), for the operational
phase of the Project “Hong Kong-Shenzhen Western Corridor”. Operation of the
Project commenced on 1 July
2007. This report presents the results and findings of the bridge
runoff monitoring work during the second monitoring period (January to March
2008).
Monitoring of
surface runoff from the carriageway was required to be carried out on 6
occasions in the first three months and another 6 occasions in months 7 to 9
after the operation of the HK-SWC bridge. The monitoring of the first
monitoring period has been postponed due to the time required for obtaining
relevant permits and licences before working on the expressway. The monitoring
events commenced in September 2007.
Breaches of
Reference Criteria and Action Level
There were a total
of 6 monitoring of bridge surface runoff from carriageway carried out in the
reporting period to fulfill the requirement stipulated in the Environmental
Permits (EP-162/2003/B and EP-290/2007) and EM&A Manuals.
Elevated Event Mean Concentration (EMC) of
nitrite and nitrate was recorded on 19 January 2008. No 3 consecutive monitoring results of nitrite
and nitrate exceeded the
reference criteria and hence, no action level exceedance was triggered. The elevated EMC of a parameter in one single
event was considered unlikely due to inadequate road cleaning along HK-SWC.
No action level exceedance
was recorded in the reporting period.
Key
Issues and Findings
Key
issue to be considered during the operation of the HK-SWC includes:
·
Sufficient cleaning of the carriageway to be carried out by vacuum air
sweeper(s) to remove grits and pollutants.
Reporting
Change
Further to the comments provided by EPD, further
revision of the review report is required to elaborate the monitoring results.
The monthly summary of vehicular traffic using
the HK-SWC between July 2007 and August 2008 were available during the report preparation and is included in
Appendix A and information was updated in Section 1. Weather information of
March 2008 is also available and is enclosed in Appendix D.
Background
1.1
ENSR Asia (HK) Ltd.
(ENSR) (hereinafter called the “ET”) was
appointed by Highways Department (hereinafter
called the “Client”) to undertake Environmental Monitoring and Audit for “Hong
Kong-Shenzhen Western Corridor” (hereinafter called the “Project”) during
operational phase. Under the requirements of Section 6.4 of Environmental
Permit EP-162/2003/B, Section 3.2 of the Environmental Permit EP-290/2007 and
relevant sections of the EM&A Manuals, bridge runoff monitoring was
required to be carried out on 6 occasions in the first three months and another 6 occasions in
months 7 to 9 after commencing the operation of the HK-SWC bridge.
1.2
Operation for the Project commenced on 1 July 2007. Commencement of the first
monitoring period for bridge runoff monitoring was postponed to September 2007
due to the time required for obtaining relevant permits and licences before
working on the expressway. This report summarises the results and findings of the bridge
runoff monitoring work during the second monitoring period (January to March
2008).
1.3
Due to safety concern and limitation on working on the
bridge deck of HK-SWC, an alternative method was approved by EPD. Detailed
information is provided in Section 2 of this report.
1.4
Further to the comments provided by EPD on the report,
revision of the review report is required to elaborate the monitoring results.
Environmental Status
1.1
The Hong
Kong – Shenzhen Western Corridor came into operation since 1 July 2007. According to
the statistics of the vehicular traffic using the HK-SWC from the “Transport
Monthly Digest” issued by Transport Department, the average daily vehicles
(two-way) using the HK-SWC increased from 1,292 nos. in July 2007 to 5,407 nos.
in March 2008. The monthly summary of vehicular traffic using the HK-SWC
abstracted from the Transport Department’s “Transport Monthly Digest” is
provided in Appendix A.
1.2
As stipulated in the EPs and
the EM&A Manuals, the HK-SWC bridge deck is required to be cleaned by
vacuum air sweeper(s) twice a week to remove grits and pollutants. The layout
of the Project site is provided in Figure 1.1.
Implementation
Status
1.3
It was required by the EPs and
EM&A Manuals that the carriageway should be cleaned twice a week by vacuum
air sweeper(s) to remove grits and pollutants.
1.4
Since the commencement of
operation of HK-SWC, the cleaning and maintenance work was carried out by the
maintenance contractor.
1.5
During the operation of the
HK-SWC in the reporting period, vacuum air sweeper was used for road cleaning
on the bridge deck and the cleaning events were carried out at least once every
two days along the hard-shoulder and left-lane of both bounds, which was
already higher than the frequency recommended in the EPs and the EM&A
Manuals. Gullies along HK-SWC were cleaned and stagnant water inside the
gullies was removed once every 6 months.
Monitoring
Requirements
2.1
The monitoring is to determine
the characteristics of bridge runoff in particular the first flush from the
HK-SWC bridge during rain-storm events and to review the frequency of road
cleaning.
2.2
The original method on road surface
runoff monitoring involves installation of equipments onto the bridge deck or
the parapets on both sides of the expressway. After reviewing by relevant
government departments, including the Hong Kong Police Force and Fire Services
Department, the installation of equipment was considered causing disturbance to
other road users including the fire services and police vehicles during
emergency operation and considered relatively unsafe for the ET staff working
on the expressway.
2.3
A procedural guide detailing
the methodology of using a water tanker to simulate an artificial rainfall by
spraying water onto the catchment area of the monitoring gully during bridge
closure at night was prepared. The guide was vetted by the IEC and the Engineer
and was reviewed by EPD.
2.4
The proposed criteria, action level and actions
required are included in Appendix B.
Monitoring Equipment
2.5
A portable automatic sampler of
non-contact type, equipped with a suction pipe, was used for sampling. The pump
flow rate is adjustable. Table 2.1 summarises the equipment used.
Table
2.1 Road Surface Runoff from
Carriageway Monitoring Equipment
|
Equipment
|
Model
|
|
Variable
Speed Sampler (with pump head)
|
Masterflex
Model 7571
|
|
Pump
Head
|
Masterflex
Model 7518
|
Monitoring
Parameters, Frequency and Duration
2.6
Monitoring
should include in total 12 sampling / rainstorm events (12 sets of data) and
cover the dry season period. A total of 6 sets of sampling data should be
collected during the first 3 months after the opening of the HK-SWC bridge. The
other 6 sets of sampling data should be collected in month 7 to month 9 after
opening of the HK-SWC
Bridge. The minimum
interval between two sampling events shall not be less than 4 days.
2.7
The
commencement of the road surface runoff monitoring programme was postponed to
September 2007 due to time required for obtaining consent and relevant permits
and licenses from relevant government departments for working on the bridge
deck. The first monitoring period of road surface runoff from carriageway was
from 27 September 2007 to 10 November 2007, while the second monitoring period
was from 5 January 2008 to 1 March 2008.
2.8
All
samples were cooled to 4°C without being frozen and delivered to a HOKLAS
laboratory within 24 hours for analysis for the following pollutants in highway
runoff:
ŸTotal Suspended Solids
ŸTotal Organic Carbon
ŸChemical Oxygen Demand
ŸNitrite and Nitrate
ŸTotal Kjeldahl Nitrogen
ŸTotal Phosphorus
ŸCopper
ŸLead
ŸZinc
Monitoring
Locations
2.9
In each monitoring
event, water samples were collected from six different road gullies, three on
each side of the carriageways.
2.10
The exact monitoring locations were recorded in terms
of nearby lighting pole / highways chainage. The exact monitoring locations are
shown in Figure 2.1 and are listed in Table 2.2 below.
Table 2.2 Locations of Road
Surface Runoff Monitoring
|
Date
|
Shenzhen bound
|
Hong Kong bound
|
|
5 January 2008
|
Lighting
Pole BD3720
|
Lighting
Pole BD4568
|
|
Lighting
Pole BD3701
|
Lighting
Pole BD3614
|
|
Lighting
Pole BD4626
|
Lighting
Pole BD3652
|
|
12 January 2008
|
Lighting
Pole BD3764
|
Lighting
Pole BD4553
|
|
Lighting
Pole BD3742
(Chainage
3.0N)
|
Lighting
Pole BD3615
(Under
the speed sign)
|
|
Lighting
Pole BD4638
(Under
the speed sign)
|
Lighting
Pole BD3645
(Under
the speed sign)
|
|
19 January 2008
|
Lighting
Pole BD3748
(Under
the speed sign)
|
Lighting
Pole BD4562
|
|
Lighting
Pole BD3713
(Chainage
2.0N)
|
Lighting
Pole BD3610
(Chainage
2.0S)
|
|
Lighting
Pole BD4634
|
Lighting
Pole BD3639
(Chainage
3.0S)
|
|
16
February 2008
|
Lighting
Pole BD3742
|
Lighting
Pole BD4568
|
|
Lighting
Pole BD3721
|
Lighting
Pole BD2650
|
|
Lighting
Pole BD4647
|
Lighting
Pole BD3624
|
|
23
February 2008
|
Lighting
Pole BD3748
|
Lighting
Pole BD4574
|
|
Lighting
Pole BD3728
|
Lighting
Pole BD3610
|
|
Lighting
Pole BD4642
|
Lighting
Pole BD3627
|
|
1
March 2008
|
Lighting
Pole BD3771
(Chainage
4.0N)
|
Lighting
Pole BD4555
|
|
Lighting
Pole BD3731
|
Lighting
Pole BD3615
(Under
the Speed Sign)
|
|
Lighting
Pole BD4640
|
Lighting
Pole BD3654
|
Monitoring
Methodology
2.11
A
water tanker with sprinklers was deployed to spray water on the road surface around
the catchment area of the monitoring gully. It simulated an artificial rain and
provided a washing effect on the road surface under rainstorm event.
2.12
At each monitoring location, the
water tanker stopped on the left lane near the monitoring gully and spray water
over the catchment area. The water would wash the whole area and drain into the
monitoring gully. The position of the tanker and spraying angle of the
sprinkler were adjusted to achieve the best washing effect.
2.13
A portable automatic sampler
was used for sampling. The suction tube inlet was placed at the mid level of
the sedimentation pond inside the monitoring gully. The sampling works was
started once bridge runoff discharge was observed from the gully to the
connected down pipe.
2.14
Each water sample collected was
of 1L in volume and 24 individual samples were collected in each monitoring
event. Four composite samples, each of 6L, were prepared from the 24 individual
water samples for laboratory analysis. The first composite sample was a mix of
the first water sample collected from each monitoring gully. Similar
preparation procedure applied to the remaining three composite samples.
2.15
Upon mixing, the composite
samples were filled into suitable containers (preserved / non-preserved) based
on the testing parameters before delivery.
2.16
An additional composite sample
was prepared by mixing the samples taken from the water tanker before and after
the monitoring. This sample was collected to understand the quality of spraying
water and for reference purpose. The concentration of pollutant of the
reference sample was subtracted from the raw monitoring data to derive the
increment, which was then compared against the reference criteria.
2.17
The samples were cooled to 4°C without being frozen. The samples were delivered
to the ALS Techichem (HK) Pty Ltd., a HOKLAS laboratory, within 24
hours for analysis.
QA/QC Procedure and Detection
Limits
2.18
ALS Technichem Pty. Ltd. followed
comprehensive quality assurance and quality control programmes. For QA/QC
procedures, at least one duplicate sample was analysed for every batch of 20
samples as required by HOKLAS. The QA/QC results are summarised in Appendix C.
2.19
The detection limits for the
monitoring parameters are listed in Table 2.3.
Table 2.3 Detection Limit for
Monitoring Parameters
|
Parameter
|
Recommended
Method
|
Detection
Limit (mg/L)
|
|
Total
suspended solids
|
APHA 2540D
|
2
|
|
Total organic
carbon
|
APHA 5310 B
|
1
|
|
Chemical
oxygen demand
|
APHA 5220
C&D
|
2
|
|
Nitrate
|
APHA 4500-NO3-
|
0.01
|
|
Nitrite
|
APHA 4500-NO2-
|
0.01
|
|
Total
Kjeidahl Nitrogen
|
ASTM
D3590-89B
|
0.1
|
|
Total
phosphorus
|
ASTM D515-88B
|
0.1
|
|
Copper
|
APHA 3120B
|
0.001
|
|
Lead
|
APHA 3120B
|
0.01
|
|
Zinc
|
APHA 3120B
|
0.01
|
Results
and Observations
2.20
There
were six monitorings of road surface runoff from carriageway carried out in the
reporting period. All monitorings were carried out under fine weather
condition. Meteorological Data, including daily total rainfall, were obtained from
the Hong Kong Observatory on-site wind station at Lau Fau Shan. All weather
data extracted from Lau Fau Shan weather station for January, February and
March 2008 are annexed in Appendix D.
2.21
The
average flow rate of water spraying by the water tanker was about 4.0 L/s.
Collection of each of the 1L
sample was completed within 2 – 3 minutes.
2.22
In order to
determine the pollutant concentration due to bridge runoff water only, the
concentration of pollutant of the reference sample was subtracted from the raw
monitoring data to derive the increment due only to bridge runoff. The concentration of
pollutant of the reference sample was assigned to be zero when its
concentration is below the detection limit.
2.23
Event
Mean Concentrations (EMCs) was calculated from the monitoring results, i.e.
locally generated EMC values for specific pollutant in the particular site in
concern, Shenzhen Western Corridor, were worked out. The EMCs values of the
monitoring results are then compared with the reference criterion. EMC is commonly used for stormwater runoff
monitoring. EMC has been adopted in studies for evaluation of characteristics
of highway runoff and government reports in different countries such as USA, Toronto, Malaysia and Korea. EMC was also presented in Urban Stormwater
Management Manual for Malaysisa. The
same analytical technique was used by Driscoll and by Barrett in Table EM4.6 of
EM&A Manual.
2.24
The EMC
for a pollutant was derived from the average concentration for each of the
events monitored. Pollutants that were
present in the samples at concentrations at concentrations below the detection
limit were assigned the value of the detection limit when event mean
concentrations (EMC) were calculated.
Therefore, the EMC of a pollutant that is present in amounts below the
detection limit is reported as greater than the actual concentrations in the
sample.
2.25
The
calculation of all monitoring results and graphical presentation are provided
in Appendix E.
Total
Suspended Solids (TSS)
2.26
TSS is
the key element in measuring the road surface runoff monitoring since a high
TSS level does not only imply high concentration of particles, but also cause
high concentration of other pollutants, including heavy metals, nutrients,
which would be adsorbed onto the surface of the particles.
2.27
The TSS
levels in six monitorings were generally low. The highest EMC of TSS was 19
mg/L and the lowest concentration was 5 mg/L.
2.28
There was
no exceedance of EMC of TSS recorded in the second monitoring period.
Nitrate
and Nitrite (NO3-+NO2-)
2.29
Nitrate and
Nitrite are two of the nutrients for aquatic life. Nitrite ion itself is
relatively unstable and is a transition stage ion to nitrate ion, which is a
more stable form. Nitrite, to aquatic life, is more toxic than nitrate.
2.30
It was recorded
that high nitrite and nitrate concentration was found in the reference sample
taken from the water tanker, ranging from 1.32 – 1.80 mg/L, The magnitude is relatively high in
comparison with other parameters.
2.31
Only one
EMC of Nitrite & Nitrate on 19 January 2008 was over the reference
criterion in the second monitoring period.
No 3 consecutive monitoring results of nitrite and nitrate exceeding the
reference criteria. No Action Level was
triggered.
Total
Kjeldahl Nitrogen (TKN)
2.32
The Total
Kjeldahl Nitrogen is the sum of ammonia, ammonium and total organic nitrogen.
Since organic nitrogen, ammonia and ammonium undergo nitrification to form
nitrite or nitrate, the nitrification process would consume oxygen. High
concentration of TKN would cause depletion in oxygen and thus causes impact to
the aquatic system.
2.33
The TKN
concentrations in all the samples were low. The highest EMC of TKN measured was
0.9 mg/L.
2.34
All EMCs
of TKN monitoring results complied with the reference criterion.
Total
Phosphorus (TP)
2.35
Phosphorus
is one of the major nutrients for the aquatic life. Since phosphorus is usually
the limiting nutrients in the aquatic system, excess phosphorus input to the
aquatic environment could lead to eutrophication and trigger algal bloom.
2.36
The total
phosphorus concentration of all monitoring samples were below detection limit
(i.e. <0.1 mg/L). There was no exceedance in total phosphorus recorded in
the second monitoring period.
Total
Organic Carbon (TOC)
2.37
The TOC
concentration measures all the carbon content in organic form. The input of the
organic carbon into the water body may be considered as an addition of
nutrients, since the organic carbon could be decomposed and reused in the
aquatic environment.
2.38
The highest
EMC of TOC calculated was 17 mg/L.
2.39
All EMCs
of TOC monitoring results complied with the reference criterion.
Chemical
Oxygen Demand (COD)
2.40
Chemical
oxygen demand measures the concentration of oxidizable chemicals, usually used as
a measurement of organic compound in water.
2.41
All EMCs
of COD were below the reference criterion. The highest EMC of COD calculated
was 44mg/L.
Copper
(Cu), Lead (Pb) and Zinc (Zn)
2.42
Copper, lead
and zinc are heavy metals, which are the most commonly found pollutants in
highways runoff. These heavy metals are usually combined / associated with
sediment particles and are considered to have a direct impact to aquatic life
at a high concentration.
2.43
Copper
deposited onto the carriageway could be generated from the brake pads / other
metallic parts of the vehicles, while zinc could be deposited from tyres of
vehicles. Lead could come from fuels of trucks and is considered to be one of
the most toxic / acute pollutants in water.
2.44
The
concentrations of copper, lead and zinc were generally low throughout the
reporting period.
2.45
The
concentrations of lead in most of the monitoring samples were below detection
limit (i.e. <0.01 mg/L), while the maximum concentration was 0.02 mg/L. The
low concentration could be due to the restriction of use of leaded petrol /
fuel in vehicles.
2.46
The EMCs
of copper, lead and zinc in all samples were within the reference criteria.
Other
Factors Affecting the Monitoring Results
2.47
The stagnant water inside the gullies that contains certain amount of
pollutants would affect the monitoring results.
The samples were collected from the gullies, therefore, the samples
collected was not only due to surface runoff in Shenzhen Western Corridor, but
also include pollutants that already existed in stagnant water inside gullies .
2.48
Meteorological factors like air quality might be influential to
pollutant concentrations in runoff.
Spraying water from water tanker has the potential to entrain airborne
pollutants, especially nitrogen and phosphorous.
Actions Taken in the Event
of Exceedance
2.49
No action
level exceedance was recorded.
Review of Effectiveness of
Road Cleaning Frequency
2.50
For assessing the effectiveness
of road cleaning frequency, the bridge runoff monitoring data, the cleaning
work carried out by the maintenance Contractor employed by
the Client and site observations were reviewed.
2.51
In the
reporting period, one elevated EMC of nitrite and nitrate was recorded on 19
January 2008. Other than that, no
elevation of other parameters was recorded.
2.52
It was
recommended in the EPs and EM&A manuals, the cleaning frequency shall be twice
a week with any consecutive cleaning events not separated by more than four
days. The cleaning frequency of the carriageway of the Project by the
maintenance Contractor was higher than the minimum cleaning frequency as stated
in the EPs and EM&A Manuals. In the reporting period, the carriageway was
cleaned at least once every two days along the hard-shoulder and left-lane of
both bounds by a suction road sweeper.
2.53
No action
level exceedance was recorded. Thus, the
current road cleaning practices and frequency was considered effective and
sufficient.
Review of Monitoring
Methodology and Reference Criteria
2.54
After
reviewing the monitoring method stated in the EM&A manual, it is not guaranteed
that sufficient rainfall events would happen within the monitoring months and
due to the safety concern on working on the bridge deck, an alternative
methodology, which includes using a water tanker to simulate an artificial
rainfall, for bridge runoff monitoring was adopted.
2.55
Since
the bridge runoff monitoring at HK-SWC was the first bridge runoff monitoring
established in Hong Kong and there was no
background information and data available before the first monitoring period,
no review of the reference criteria was carried out.
2.56
Since
Deep Bay
is an area of ecological importance, particularly to shorebirds, any input of
pollutants to the Deep
Bay water should be
minimized. The most concerned pollutants would be heavy metals. The EMCs of heavy
metals (copper, lead and zinc) were low and were well below the reference
criteria. Impacts from heavy metals in road runoff water are considered small.
Besides heavy metals, input of nutrients, including organic carbon,
nitrogen-containing chemicals and phosphorus-containing chemicals, would be
another concern, since these nutrients can lead to extensive growth of algae in
the Deep Bay. Yet, the concentrations of these
pollutants are low, the impact to the Deep Bay
environment is considered small.
2.57
The
Deep Bay catchment area is about 535km2, which is much larger
as compared to the surface area of the bridge deck. As the concentration of
pollutants are low and the volume of runoff from the bridge deck is small (due
to the relatively small surface area), the impact to water quality and ecology
was considered insignificant.
2.58
It
was recommended that samples should be collected from storm drain inlet of the
gutter, i.e. before runoff entering into gullies, to prevent the monitoring data
affecting by the stagnant water inside the gullies which contain certain amount
of pollutants. Referring to the
methodology in study by Barrett, the runoff samples were collected from a
single storm-drain inlet located along the gutter of a curbed section of the
highway.
2.59
Use
of EMC is a general and appropriate method to evaluate the effects of storm
water runoff on receiving waters.
Obtaining local event mean concentration for the area of concern was
suggested to have accurate estimation, determination of reference criteria and
monitoring programme as well. Whereas
obtaining local event mean concentration is not feasible, applying literature
event mean concentration could be used as a guideline.
3.1
Six bridge surface runoff from carriageway
monitoring events were carried out in January to March 2008. All monitoring
results in the reporting period were checked and reviewed.
3.2
All monitoring results complied
with the reference criteria except one EMC of nitrite and nitrate is over the
reference criterion occurred on 19 January 2008.
3.3
No 3 consecutive monitoring with the same parameter (1 or more than 1
parameter) exceeded the reference criteria. No Action Level was triggered.
3.4
The current
cleaning frequency and method of the bridge deck was considered sufficient and
effective.
