1                    Sediment Quality


1.1              Introduction


In accordance with the recommendations of the EIA for the present Project, a monitoring programme examining sediment quality will be instituted to verify the EIA predictions and ensure that there is no build-up in contamination adjacent to the pits.  Sediment chemistry has long been an important component of monitoring programmes at the East of Sha Chau mud disposal complex.  Since 1997 a comprehensive list of Contaminants of Concern (COCs) comprising 8 heavy metals and 1 metalloid, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorine pesticides (eg DDT) and Tributyltin (TBT).  These contaminants (which correspond to the list of COCs in ETWBTCW 34/2002) in sediments should be measured in the present monitoring programme and changes over time and distance should also be examined.


1.2              Objective


The main objective of this task is to determine if there are any changes and/or trends in the concentrations of contaminants in sediments adjacent to the pits caused by disposal activities.  This objective is most appropriately addressed through two separate but intrinsically linked sub-tasks:


·                Near-field monitoring of sediment quality - conducted to examine near field impacts of backfilling operations on the spread of contaminants from the pits and to allow for rapid detection of any adverse environmental impacts and, if necessary, changes to the operations plan.

·                Regional monitoring of sediment quality - conducted to analyse the ambient conditions in the North Lantau region and to investigate whether any impacts to marine sediments are occurring due to the dispersion of contaminants from the active pits. 


1.3              Hypotheses


The impact hypothesis for this task is as follows:

There is no increase in sediment contaminant concentrations over time at individual stations or a trend of increasing concentrations with proximity to the active pit.

As a result of the separation of this programme into two sub-tasks, two sets of null hypotheses should be tested:

Near-field monitoring of sediment quality


H0      There is no increase in sediment contaminant concentration in the area adjacent to the active pits as compared to levels observed in the area under recently conducted, comparable monitoring programmes. 


Regional monitoring of sediment quality


H0      There is no increase in sediment contaminant concentration over time in the area of contaminated mud disposal activity.

H0      There is no increase in sediment contaminant concentration with proximity to the active pits.


1.4              Sampling Design


The designs for assessing the impacts of disposal of contaminated mud in the active pits on the sediment chemistry of remote and adjacent areas take into account the following factors:


·                The null hypotheses being tested;

·                Background levels of contaminants in the region;

·                Predictions taken from the EIA on sediment plume locations;

·                Spatial variability in sediment chemistry;

·                Temporal variability in sediment chemistry; and,

·                Expected statistical treatment of the data.

·                As mentioned in Section 1.7.2 the EM&A Manual is an evolving document that should be updated to maintain its relevance as the Project progresses.  This includes the relocation of monitoring stations to best suit the requirements of the monitoring programme and to take into account other work that is occurring in the direct vicinity of the active facility.


1.4.1        Near-field monitoring of sediment quality


Sediment samples shall be collected on a monthly basis from two sites in the active pit, two sites on the edge of the active pits and two sites in close proximity to the pits (Figures 4.4a and 4.4b).  Twelve replicates of composite samples (ie 5 grab samples obtained using a cluster grab) will be collected from each of the sites.  Replicates have been based on analysis of data conducted as part of the monitoring of CMP IVa (Agreement No. CE 44/97).  Under this EM&A programme, Cumulative Running Mean Tests determined optimum sample size for stabilising mean and standard error values was 12 samples for sediment analysis.  The technique of clustering stations within one site has been proven to be an effective way of testing hypotheses and removing the confounding effects of spatial variation from the interpretation.  The number of stations within a site and the precise locations of the sampling stations should be confirmed in advance of the commencement of disposal activities and agreed with EPD subject to the detailed design of the disposal facility. 


1.4.2        Regional monitoring of sediment quality


Sediment samples should be collected twice during the dry season and twice during the wet season at stations distributed throughout the North Lantau area.  The stations should be located in three discrete areas, with two sites in each area.  The areas should be located at increasing distances from the disposal operations (ie Near Field, Mid Field, Far Field and any additional sensitive receiver sites indicated on Figures 4.4a and 4.4b).  Twelve replicates of composite samples (ie 5 grab samples obtained using a cluster grab) will be collected from each of the sites.  The exact positions of the stations should be determined in advance of the commencement of disposal activities and agreed with EPD.


1.5              Statistical Treatment of Data


1.5.1        Near-field monitoring of sediment quality


Observed differences in the levels of contaminants should be tested each month using analysis of variance (factors = Area and Site) followed by Student Newman Keuls (SNK) multiple comparison procedures to isolate which treatments differ from others.  Once a time series of data has been gathered, the data should be re-analysed to examine the differences within and between the sites over time.  This should be achieved using an analysis of variance with site, Area and Month as the factors.


For all of the analysis of variance techniques performed during the monitoring programme, initial analyses should be performed to ensure that the data complies with the specific assumptions of analysis of variance.  These assumptions state:


·                the data within and among samples must be independent of each other;

·                the variance within samples must be equal (tested through the use of tests such as Levene's median test); and,

·                the data among the samples must be normally distributed (tested through the use of tests such as the Kolgomorov-Smirnov test). 


Should the data not comply with these assumptions then the appropriate transformation should be applied to the data (eg, arc-sin for percentage data, log (x+1) for abundance data, or rank transformation if necessary).  If, after transformation, the data are still non-compliant then non-parametric equivalents to ANOVA such as Kruskal-Wallis tests should be used. 


1.5.2        Regional monitoring of sediment quality


The design of the regional monitoring programme should allow the use of nested analysis of variance techniques to be employed.  These techniques shall be used to analyse the data at different spatial and temporal scales of replication.  Statistical differences should be tested at the following levels: between sites in each area and between each area at each sampling time.  An advantage of this sampling design is that it removes the possibility of detecting differences simply due to inherent variation over spatial scales in the active area and thus facilitates clearer attribution to disposal operations.  By replicating within each area, ie by sampling two sites in one area, any statistically significant differences detected between areas are more likely to be due to factors other than spatial variation (eg, disposal operations).  This approach is now an internationally recommended technique for use in monitoring programmes ([1]).  Multidimensional scaling ordination techniques shall also be applied to the data. 


1.6              Use of Data


Should significant increases be detected in the level of contaminants in sediment samples, a review of the other monitoring parameters should be undertaken.  This review shall focus on sampling stations in the vicinity of the sediment quality monitoring stations where increases were detected to see if these can be attributed to contaminant migration from the active pits.  Assessment of the statistical significance of the data, confidence in the data and the presence of supporting data from other components of the monitoring programme should be jointly assessed.  If appropriate, changes to the operations plan should be considered.


1.7              Data Collection Parameters


The parameters that should be measured in sediments collected during the two sub-tasks and the rationale for each are given below.  The contaminants listed are the "Contaminants of Concern" for which Lower and Upper Chemical Exceedance Limits (LCEL/UCEL) exist. 


1.7.1        Near-field monitoring of sediment quality


(a)     Total Organic Carbon (TOC) - an indicator of organic load and the impact on bottom layer dissolved oxygen.  TOC is an important factor influencing the chemical partitioning and toxicity of hydrophobic organic compounds such as PAHs, PCBs and pesticides.  High TOC often infers that hydrophobic contaminants are less bioavailable;

(b)     Inorganic Contaminants - metals and metalloids present in the disposed sediments which may be bioaccumulated;

(c)     Polycyclic Aromatic Hydrocarbons (PAH) - a class of organic compounds some of which are persistent and carcinogenic.  These compounds may be bioaccumulated and stored in the fatty body tissues of mammals;

(d)     Total Polychlorinated Biphenyls (PCB) - a class of persistent man-made chemicals which tend to bioaccumulate through the food chain and can cause reproductive failure and cancer;

(e)     Organochlorine Pesticides (DDE & DDT) - contaminants which are persistent, highly lipophilic (can be accumulated and stored in fat), have high bioaccumulation and biomagnification potential, and high toxicity to aquatic organisms; and,

(f)           Tributyltin (TBT) (in sediment and interstitial water) - moderately persistent toxic compound found in marine sediments which may be bioaccumulated and cause growth abnormalities and reproductive failure.


1.7.2        Regional monitoring of sediment quality


(a)     Percentage of Silt/Clay (% < 63mm) - organic contaminants and metals bind more readily to finer particles than coarser particles due to their larger surface area and consequent larger number of binding sites;

(b)     Total Organic Carbon (TOC);

(c)     Inorganic Contaminants (1);

(d)     Polycyclic Aromatic Hydrocarbons (PAH) (2);

(e)     Total Polychlorinated Biphenyls (PCB);

(f)     Organochlorine Pesticides (DDE & DDT) (3); and,

(g)          Tributyltin (TBT) (in sediment).


1.8              Sampling Procedure and Equipment


All samples should be collected by an experienced sampling team (with ISO 9002 certification), deployed on a survey boat equipped with fully calibrated sampling equipment and precision navigational instruments.  All vessel positioning should be accomplished with a calibrated Differential Global Positioning System (DGPS), ensuring station location accuracy to < ± 1 m (95% confidence), with sample position automatically logged and mapped by the navigation computer.  Where sample stations are located in close proximity to the pit area, positioning should be further validated by use of an echo sounder to detect whether the vessel is within the boundaries of the pit.


At each sampling station the top 5 cm of seabed sediment should be collected using a 5-component cluster grab sampler which collects surficial sediments with a minimal disruption to the surface layer and is designed to work effectively in soft sediment such as those found in the area.  The cluster grab should be deployed once at each of the stations located within each sampling area (eg Pit, Pit-Edge).  The grabs can customised and a fine mesh lid added, which ensures that the fine fluid sediments on the surface of the seabed are retained in the sample.  Utilisation of this cluster sampler allows a large volume of sediment to be collected in a single deployment.  Other similar samplers (eg Petit-ponar) collect less sediment in each deployment and can have difficulty collecting adequate samples in soft sediments, such as those within the study area, thereby reducing efficiency and increasing collection time.  The five-cluster grab should be collected and combined, and the sample, labelled, double-bagged and stored in an ice chest cooled to a temperature of 4oC with ice packs.  The sediment sampler and all other utensils should be rinsed with seawater after each sample has been collected to avoid cross contamination between samples.  On completion of the survey, all samples should be promptly transported, in chilled containers, to the testing laboratory for analysis.


1.9              Quality Control & Assurance Procedures


A broad range of contaminants should be analysed in sediment samples including metals, metalloids, PAHs, PCBs, pesticides and Tributyltin in both sediment and interstitial water.  The method detection limits should be consistent with previous monitoring programmes at East of Sha Chau.  Other QA/QC procedures to be implemented for marine sediment analyses include:


·                Laboratory blanks - an analyte free matrix to which all reagents shall be added in the same volumes or proportions as used in the standard sample preparation to monitor contamination introduced in the laboratory (organics and inorganics);

·                Batch duplicates - an intralaboratory split sample randomly selected from the sample batch to monitor method precision (intrabatch) in a given sample matrix (inorganics only);

·                Certified Reference Materials - analysis of a material with a known concentration of contamination to determine the accuracy of results in a given matrix (inorganics only);

·                Single Control Samples - a known, interference-free matrix spiked with target analytes used to monitor laboratory preparation techniques (organics only);

·                Duplicate Control Samples - multiple single control samples designed to monitor preparation technique reproducibility (organics). 


1.10          Data Quality Objectives


Data Quality Objectives (DQOs) have been developed to address precision, accuracy and analyte recovery.


1.10.1    Inorganic Analyses


Details of quality control specifications for inorganic testing should be included in the updated EM&A Manual prior to commencement of disposal activities. 


Duplicates (1 in every 10 samples) should be used to monitoring the precision of the analysis.  Results should be flagged for reference when:


·                For all analytes, except metals, with concentration >4x Method Detection Limit (MDL), the duplicate results have more than a 20% Relative Percentage Deviation (RPD)

·                In water samples, for metals with a concentration >4x MDL, the duplicate results have more than a 15% RPD

·                In sediment and biota samples, for metals with a concentration >4x MDL, the duplicate results have more than a 25% RPD

·                For all analytes with concentration <4x MDL, the duplicate results should be reported as analysed and no bounds should be quoted




Standard and certified reference material (CRM) shall be used to monitor accuracy and precision within and between batches:  Results should be flagged for reference if:


·                The variation of the standard from its true value is more than ± 15% (for mercury: ± 20%).




Post digest spikes should be used to determined the recovery of determinants in complex sample matrices.  Results should be rejected if:


·                Spike recoveries are more than ± 25% from the theoretical recovery for waters, sediment and marine biota.  An exceptional case would be if the sample concentration is greater than four times the spike value, the spike may be disregarded. 

1.10.2    Organic Analyses


Samples should be analysed in lots of less than 20.  In order to measure the laboratory performance within each batch of samples, a single control sample (SCS), a duplicate control sample (DCS) and a method blank (MB) should be processed concurrently with the samples.  A SCS or DCS consists of an interference free control matrix that is spiked with a group of target compounds representative of the method analytes.


Method blanks, also known as reagent, analytical, or preparation blanks, should be analysed to assess the level of contamination that exist in the analytical system and which might lead to the reporting of elevated concentration levels or false positive data.  For organic analyses, the concentration of target analytes in the blank must be below the reporting limit for that analyte in order for the blank to be considered acceptable.


Accuracy is expressed as the average percent recovery of the SCS/DCS pair and precision is expressed as the relative percent difference (RPD).  For control limits that are not established due to insufficient data sets, the QC Acceptance Criteria of US EPA Method 8080 and 8270A should be used as a supplement.  Once enough data are collected, the in-house control limits should then be calculated. 


The accuracy and precision data for SCS and DCS should be evaluated against laboratory established control limits.  QC results falling outside the control limits should be automatically flagged.  The acceptance criterion is that 100 percent of the precision and accuracy values must fall within the control limits.  If this criterion is not met, corrective action must be taken.  This may include repeat sample analysis.


The relative percentage difference of SCS/DCS pair should be compared to the limit set for each compound being monitored (Table 4.1).  In normal instances, an RPD of less than 20% is deemed to be acceptable.


For multianalyte organic tests, if greater than 20% of the accuracy or precision results for the DCS are outside of the control limits, the data are considered suspect and the samples associated with the unacceptable DCS are reprepared and/or reanalysed. 

Table 4.1    Quality Control Acceptance Criteria for Organic Analyses

Target Analytes

Percent Recovery Measured


74 - 126


69 - 125


73 - 119


81 - 129


74 - 131


63 - 116


73 - 134


59 - 129


77 - 136


53 - 130


51 - 103


78 - 126


73 - 121


87 - 120

Total PCBs

79 - 127


80 - 115

D B Detected, result must be greater than zero


([1])     AJ Underwood (1997) Experiments in Ecology: their logical design and interpretation using analysis of variance.

([2])     Cadmium (Cd), Chromium (Cr), Copper (Cu), Lead (Pb), Mercury (Hg), Nickel (Ni), Silver (Ag), Zinc (Zn) and Arsenic (As).

([3])     Acenapthene, Acenaphthylene, Anthracene, Fluorene, Napthalene, Phenanthrene, Low Molecular Weight PAHs, Benzo(a)anthracene, Benzo(a)pyrene, Chrysene, Dibenzo(a,h)anthracene, Fluoranthene, Pyrene, High Molecular Weight PAHs and Total PAHs

([4])     Total Dichlorodiphenyl-trichloroethane (DDT) and Dichlorodiphenylchloroethane (p,p'-DDE).