This is the first 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 first monitoring period (September to November 2007).

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.

Nitrate concentration in the reference sample taken from the water tanker was found to be around 1.08 – 1.66 mg/L and was already above the reference criteria of 0.72 mg/L. The water used for surface runoff monitoring was tap water from the Water Supplies Department (WSD). According to the “Drinking Water Quality for the Period April 2006 – March 2007” issued by WSD, the range of nitrate concentration in the water supply is <2.5 to 9.9 mg/L with an average of 3.6 mg/L. The nitrate concentration of this level, i.e. 1.08 – 1.66 mg/L, is still within WSD requirements for potable use.

Elevated nitrate levels were recorded in the 1st and 2nd composite samples on 27 October 2007. The increments of the 1st and 2nd composite samples over the reference sample were 1.74 mg/L and 0.93 mg/L respectively, against the reference criterion of 0.72 mg/L. No action level exceedance was triggered.

No exceedance was recorded in other parameters 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 on the report, further revision of the review report is required to provide justification on the monitoring results.

1. INTRODUCTION

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 first monitoring period (September to November 2007).

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, further revision of the review report is required to provide justification on 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 1,362 nos. in July 2007 to 4,136 nos. in November 2007. 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 EP and the EM&A Manual, 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 EP and EM&A Manual 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 EP and the EM&A Manual. Gullies along HK-SWC were cleaned and stagnant water inside the gullies was removed once every 6 months.

2. bridge runoff monitoring

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. The procedural guide is also provided in Appendix B of this report.

2.4 The proposed criteria, action level and actions required are included in Appendix C.

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 carried out from 27 September 2007 to 10 November 2007, while the second monitoring period commenced in January 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

29 September 2007

Lighting Pole BD3776

Chainage 4.2 N

Lighting Pole BD 4568

Lighting Pole BD3742

Chainage 3.0 N

Lighting Pole BD3610

Chainage 2.0 S

Lighting Pole BD4638

(Under the speed sign)

Lighting Pole BD3644

Chainage 3.2 S

6 October 2007

Lighting Pole BD3779

(Under the speed sign)

Lighting Pole BD4565

Lighting Pole BD3742

Chainage 3.0N

Lighting Pole BD3610

Chainage 2.0S

Lighting Pole BD4643

Lighting Pole BD3655

13 October 2007

Lighting Pole BD3767

Lighting Pole 4555

Lighting Pole BD3742

Chainage 3.0N

Lighting Pole BD3615

(Under the speed sign)

Lighting Pole BD4638

(Under the speed sign)

Lighting Pole BD3640

27 October 2007

Lighting Pole BD3748

(Under the speed sign)

Lighting Pole BD4553

(Under the speed sign)

Lighting Pole BD3720

(Under the instruction sign)

Lighting Pole BD3615

(Under the speed sign)

Lighting Pole BD4642

(Under the instruction sign)

Lighting Pole BD3638

Chainage 3.0S

3 November 2007

Lighting Pole BD3756

Lighting Pole BD4553

(Under the speed sign)

Lighting Pole BD3720

(Under the instruction sign)

Lighting Pole BD3615

(Under the speed sign)

Lighting Pole BD4642

Lighting Pole BD3638

Chainage 3.0S

10 November 2007

Lighting Pole BD3747

Lighting Pole BD4551

Lighting Pole BD3720

(Under the instruction sign)

Lighting Pole BD3618

Lighting Pole BD4636

Lighting Pole BD3644

(Under the speed sign)

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 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 D.

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 September, October and November 2007 are annexed in Appendix E.

2.21 All monitoring results and graphical presentation are provided in Appendix F.

2.22 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.

Total Suspended Solids (TSS)

2.23 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.

2.24 The TSS levels in six monitorings were generally low. The highest concentration of TSS was 20 mg/L and the lowest concentration was below the detection limit (i.e. <2 mg/L).

2.25 There was no TSS exceedance recorded in the first monitoring period.

Nitrate and Nitrite (NO₃^-+NO₂^-)

2.26 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.

2.27 In comparison with the reference criteria, a relatively high nitrite and nitrate concentration was recorded and it was mainly attributable to high nitrate content since the nitrite concentration was generally below 0.01 mg/L in all monitoring results. In fact, nitrate concentration in the reference sample taken from the water tanker was around 1.08 – 1.66 mg/L and was already above the reference criterion of 0.72 mg/L. The water used for surface runoff monitoring was tap water from the Water Supplies Department (WSD). According to the “Drinking Water Quality for the Period April 2006 – March 2007” issued by WSD, the range of nitrate concentration in the water supply is <2.5 to 9.9 mg/L with an average of 3.6 mg/L. Nevertheless, the nitrate concentration of this level, i.e. 1.08 – 1.66 mg/L, is still within WSD requirements for potable use.

2.28 Regarding the elevated nitrate levels recorded on 27 October 2007, the increments of the two composite samples over the reference sample ranged from 0.93 – 1.74 mg/L and exceeded the reference criterion of 0.72 mg/L. In general, the measured concentrations of all parameters were similar for all 4 composite samples.

2.29 According to the observations during the monitoring, there was no adverse observation / condition, which would contribute to high level of pollutants, identified on the bridge deck. On the other hand, the accumulated water inside the gully may increase the pollutant levels in the first or even the second sample. Currently, water sample was collected at the mid level of the gully once runoff is observed discharged from the gully to the downpipe. The existing pollutant inside the gully may also be a factor of elevating pollutant level.

2.30 From the results of Deep Bay Water Quality Monitoring by EPD from 2005 – 2006 at stations DM1 to DM5, the range of the nitrate concentration was 0.08 – 2.00 mg/L. The maximum increment of the nitrate concentration in the reporting period was 1.74 mg/L; all monitoring results in the reporting period lied within the normal range of nitrate concentration in the Deep Bay Water. This indicated that under normal rainfall condition, the nitrate input from the bridge runoff water would not have an adverse impact on the environment and ecology in the Deep Bay Water.

2.31 Furthermore, the associated environmental impact was considered minimal due to the relatively small volume of runoff water as compared to the whole Deep Bay area and the low concentration of the pollutants in the runoff water.

2.32 Temperature, humidity, wind direction and background air quality, are also factors that would affect the measured concentration of nitrate and nitrite. Different humidity indicates different amount of water particles / water content in the atmosphere. Air pollutants, including NOx, tend to affiliate with water particles and some would dissolve in water. The concentration of NOx in the Shenzhen Bay area is relatively high and the water content in the air around HK-SWC is considered to be high due to the close proximity to the water body of the bridge. Small amount of pollutants from the air might be contributed to the measured value.

2.33 According to the air quality monitoring data from Environmental Protection Department, the hourly concentration of nitrogen oxides (NOx) between the period 1 August 2006 and 31 July 2007 ranged from 5 mg/m³ to 597 mg/m³ with an average of 106.26 mg/m³ at Yuen Long air quality monitoring station. Hourly concentration of nitrogen oxides (NOx) between the period 1 August 2006 and 31 July 2007 at Tap Mun air quality monitoring stations ranged from 0 mg/m³to 171 mg/m³ with an average of 18.28 mg/m³and at Mong Kok roadside air quality monitoring station ranged from 61 mg/m³ to 1451 mg/m³ with an average of 337.63 mg/m³were also provided for reference.

2.34 Besides the abovementioned exceedances recorded on 27 October 2007, there was no exceedance recorded in nitrate and nitrite concentration in the reporting period.

2.35 There was no action level exceedance triggered in the reporting period since there was no 3 consecutive monitoring in nitrate and nitrite concentration exceeded the reference criteria.

Total Kjeldahl Nitrogen (TKN)

2.36 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.

2.37 The TKN concentrations in all the samples were low. The highest concentration of TKN measured was 1.5 mg/L.

2.38 All TKN monitoring results complied with the reference criteria.

Total Phosphorus (TP)

2.39 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.

2.40 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 first monitoring period.

Total Organic Carbon (TOC)

2.41 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.

2.42 The TOC concentrations in all 6 samples were generally low. There was a slight increase in the TOC concentration on 27 October 2007, which was still below the reference criteria, was considered to be affected by the pollutants accumulated inside the gullies prior to the monitoring event.

2.43 The highest measured TOC concentration was 24 mg/L. There was no exceedance in TOC recorded in the first monitoring period.

Chemical Oxygen Demand (COD)

2.44 Chemical oxygen demand measures the concentration of oxidizable chemicals, usually used as a measurement of organic compound in water.

2.45 The measured COD concentrations in the monitoring samples were generally low. All measured COD concentration were below the reference criteria except for the 1st composite sample taken on 27 October 2007.

2.46 The measured COD concentration in the 1st composite sample taken on 27 October 2007 was over the reference criteria. However, the increment was still within the reference criterion and it was not considered as an exceedance.

2.47 There was no exceedance recorded in the first monitoring period.

Copper (Cu), Lead (Pb) and Zinc (Zn)

2.48 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.

2.49 The concentration of copper and zinc was slightly increased in the samples taken on 27 October 2007. It was considered that the increased amount of copper and zinc was due to the pollutants accumulated inside the gullies prior to the monitoring. 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.

2.50 Lead is considered to be one of the most toxic / acute pollutants in water. The concentrations of lead in all monitoring samples were below detection limit (i.e. <0.01 mg/L). It could be due to the restriction of use of leaded petrol / fuel in vehicles.

2.51 The concentration of copper, lead and zinc in all samples were within the reference criteria.

Other Factors Affecting the Monitoring Results

2.52 The background water quality, i.e. water in the water tanker, would affect the measured concentration of the target pollutants. Therefore, a “blank” composite sample was taken from the tanker before and after the monitoring events and would be used as a reference to compare with the measured value in the other composite samples. Since the water used for the monitoring is from the water supply from the Water Supplies Department, the concentration of pollutants in the water is low. Thus, the influence by the background water quality on the pollution load from bridge runoff water, which ultimately enters the Deep Bay Water, is considered insignificant.

Actions Taken in the Event of Exceedance

2.53 A notification of exceedance was issued for the exceedance in nitrate and nitrite concentration on 27 October 2007 in the reporting period.

2.54 Since exceedance in water quality in the reporting period did not trigger the action level, i.e. no 3 consecutive monitoring with the same parameter exceeded the reference criteria, no further action was recommended.

Review of Effectiveness of Road Cleaning Frequency

2.55 Concerning 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.

2.56 In the reporting period, elevation in nitrate and nitrite concentration was recorded in the monitoring event on 27 October 2007. Other than that, no elevation of other parameters was recorded.

2.57 It was recommended in the EP and EM&A manual, 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 compatible with the cleaning frequency as required by the EP and EM&A Manual. 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.

2.58 From the weekly site audits in the reporting period and the site observation during the monitoring events, no specific adverse condition was observed.

2.59 In view of the current road cleaning practices and frequency, the elevation in nitrite and nitrate concentration recorded on 27 October 2007 was unlikely attributed to inadequate road cleaning. Rather, such elevation was considered in relation to the existing pollutants inside the gully, relatively high NOx content in the ambient air in the region and the application of mean or median value of data obtained from overseas journals in establishing the criteria, which would be further discussed in Sections 2.58 to 2.62. Thus, the current road cleaning practices and frequency was considered effective and sufficient.

Review of Monitoring Methodology and Reference Criteria

2.60 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. The procedural guide for the alternative method was provided in Appendix B.

2.61 The reference criteria set out in the EM&A manual were proposed using the mean or median value of the data from different overseas journals. 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.

2.62 From the results of Deep Bay Water Quality Monitoring by EPD from 2005 – 2006 at stations DM1 to DM5, the range of the nitrate concentration was 0.08 – 2.00 mg/L. The maximum increment of the nitrate concentration in the reporting period was 1.74 mg/L; all monitoring results in the reporting period lied within the normal range of nitrate concentration in the Deep Bay Water. This indicated that under normal rainfall condition, the nitrate input does not have an adverse impact on the environment and ecology in the Deep Bay Water.

2.63 Furthermore, the associated environmental impact was considered minimal due to the relatively small volume of runoff water as compared to the whole Deep Bay area and the low concentration of the pollutants in the runoff water.

2.64 It was considered inappropriate to use the mean / median value of the data as the reference criteria since this would implicate that, under normal circumstances, there would be about 50% of chance that the monitoring results would exceed the reference criteria. It is considered that a more reasonable but relatively higher percentile level on the obtained data would be more appropriate to be used for establishment of the reference criteria / action & limit levels.

2.65 In current monitoring, nitrate, nitrite and total kjeldahl nitrogen concentration were used for determining the nutrient levels, in terms of nitrogen content, in the water. It is recommended that monitoring of these parameters should continue.

2.66 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 measured concentrations 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 environmental is considered small.

2.67 The Deep Bay catchment area is about 535 km², 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.

2.68 However, a comprehensive review of recent studies and literature was recommended and raw data from current monitoring should also be reviewed for determining the new monitoring programme or reference criteria in any future road surface runoff from carriageway monitoring in Hong Kong.

3. CONCLUSIONS

3.1 Bridge surface runoff from carriageway monitoring was carried out in September to November 2007. All monitoring results in the reporting period were checked and reviewed.

3.2 Six road surface runoff monitoring events were carried out in the reporting period. All monitoring results complied with the reference criteria except nitrite and nitrate level on 27 October 2007. The increments of the two samples ranged from 0.93 – 1.74 mg/L against the reference criterion of 0.72mg/L. The impact from the elevated nitrate and nitrite concentration to the environment was considered minimal.

3.3 The measured COD level in the 1st composite sample was over the reference criterion taken on 27 October 2007. However, the increment was still within the reference criterion and it was not considered to be an exceedance.

3.4 No action level exceedance was recorded in the reporting month.

3.5 The current cleaning frequency and method of the bridge deck was considered sufficient and effective.