Melbourne Water
Social and Environment Data
2005 / 2006

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Western Treatment Plant inputs and discharges

Raw sewage monitoring

(All data in mg/L unless otherwise indicated)

Parameter (unit) 2004/05 Median 90th Percentile Maximum
Flow (ML/day) 448 499 791
BOD5 400 530 780
Suspended Solids 380 470 850
Ammonia as N 33 37 41
Total Nitrogen 60 68 90
Total Phosphorus 11 13 17
Colour (Pt/Co units) 85 118 120
Anionic Surfactants 4.6 7 10
Silicate 13 14 14
Electrical Conductivity (µS/cm) 1,800 1,900 7,600
TDS 950 1000 1400
Cadmium 0.00065 0.0016 0.0022
Chromium 0.034 0.048 0.12
Copper 0.12 0.14 0.14
Lead 0.009 0.012 0.018
Mercury 0.0002 0.00048 0.0006
Nickel 0.025 0.045 0.082
Zinc 0.17 0.19 0.29
pH (pH units) 7.3 7.6 8.5
Benzene 0.0005 0.0019 0.002
Toluene 0.0025 0.0048 0.008
Total Phenols 0.44 0.66 0.73
Total PAHs 0.0045 0.0089 0.014

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Licence compliance

The following tables show the plant’s compliance performance. Plant wide limits for all discharge parameters in the licence are based on a flow weighted average calculated using the formula:

Weighted average formula

Conditions of the EPA Victoria discharge licence outline the performance limits for effluent discharged to Port Phillip Bay via the four discharge points at the Western Treatment Plant.

The licence states that compliance with all licence parameter limits are to be calculated on a flow-weighted basis.

There is a plant wide limit of 700 million litres a day averaged over the year. The Western Treatment Plant complied with licence waste discharge limits for all parameters.

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Annual and average daily discharges for 2005/06

Outlet Total Flow (ML) Average Daily Flow (ML)
15East 78,736 216
145West 29,648 81
Lake Borrie 13,287 36
Muirtcam Main Drain 1,145 3
Total 122,816 336

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Annual discharge to Port Phillip Bay

The treatment plant’s performance against the EPA licence limits for 2005/06 shown below shows that the Western Treatment Plant complied with the effluent discharge limits for all parameters. The results for 2005/06 are shown below:

(All data in mg/L unless otherwise indicated)

Parameter Median 75th Percentile 90th Percentile Maximum
Limit Result Limit Result Limit Result Limit Result
CBOD5 10 2.6 20 5.8 7.3
Suspended Solids 30 22 60 46 54
Ammonia as N 10 4.5 11 30 14
Total Phosphorus 8.8 15 10 11
Colour (Pt/Co units) 200 47 400 55 61
Anionic Surfactants 0.2 0.8 0.29 1 0.4
Cadmium 0.0011 0.00017 0.00019 0.005 0.00019
Chromium 0.04 0.0061 0.0071 0.1 0.0073
Copper 0.028 0.0087 0.0089 0.1 0.0091
Lead 0.015 0.0034 0.0039 0.06 0.0045
Mercury 0.0004 0.000096 0.00011 0.001 0.00012
Nickel 0.029 0.019 0.02 0.06 0.021
Zinc 0.06 0.025 0.026 0.2 0.03
Benzene 0.005 0.0005 0.0005 0.01 0.0005
Toluene 0.005 0.0005 0.0005 0.01 0.00052
Total Phenols 0.04 0.0081 0.0092 0.08 0.0098
Total PAHs 0.0004 0.000086 0.00009 0.0008 0.000093

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Annual nitrogen load to Port Phillip Bay

The nitrogen output from the Western Treatment Plant was 1,969 tonnes per annum for 2005/06. The annual loads for the last three years are shown in the following table, which demonstrates that Melbourne Water has complied with the maximum target of 3100 tonnes per annum.

Year 2005/06 2004/05 2003/04 3 Year Average EIP Target January 2005
Total N Load (tonnes/annum) 1969 2713 2769 2484 3100
Dioxins and furans

Melbourne Water monitors polychlorinated dibenzo dioxins and furans (PCDD/F), as toxic equivalents of 2,3,7,8 tetrochloro-dibenzo-p-dioxin. Sampling of PCDD/F is carried out at the 15 East Outlet in the month of January, 145 West outlet in April, Lake Borrie outlet in July and Murtcaim Outlet in October each year. The raw sewage is sampled for PCDD/F each time an outlet is sampled (i.e. 4 times a year).

The toxic equivalent (TEQ) is calculated for each sample using the World Health Organisation’s toxic equivalency factors (WHO98-TEQ) method and is represented in the following table.. Results for preceding years are also presented for comparison.

PCDD/F as World Health Organisation Total Toxic Equivalents of 2,3,7,8 TCDD for 2004/05 (All results in picogram/L)
SITE WHO98-TEQ - Excluding LOD Values WHO98-TEQ - Including Half LOD Values
2005/06 2004/05 2003/04 2005/06 2004/05 2003/04
Lake Borrie (July) 1 16 7.1 5.3 16 11
Murtcaim (October) 0.59 0.08 0.64 4.3 2 2.3
15E (January) 0.007 0.13 0.07 2.7 7 1.1
145W (April) 0.38 0.62 7.3 2.4 3.6 9
Raw Sewage (July) 1.4 1.8 1.7 5 3.6 3.2
Raw Sewage (October) 4.2 1.5 3.9 8.6 4.1 6.9
Raw Sewage (January) 2.5 2.4 2.7 6.4 7.3 3.4
Raw Sewage (April) 24 15 10 24 19 13

Whilst the best techniques available in Australia are used for the testing of dioxins and furans, many of the results are less than the level of detection and the detection limits achieved in the analytical procedures vary, even for a single sample site. Hence it is difficult to make any substantive interpretation of trends in the results.

Bacteriological monitoring

Melbourne Water conducts bacteriological monitoring by collecting a sample of seawater in 60 centimetre depth of water off-shore from Beach Road and 160 South Road every seven days and analysed to determine the concentration of E.coli in the sample. These two points are public access points to Port Phillip Bay within the Western Treatment Plant and outside the designated mixing zones for E.coli.

The State Environment Protection Policy (Waters of Victoria) schedule F6 for the Werribee segment requires the 42 day geometric mean E.coli values to be less than 1000 orgs/100ml. Melbourne Water has calculated the 42 day Geometric mean and 42 day 80th percentile for the E.coli at the two sites.

The maximum of E.coli recorded for each site during 2005/06 was 220 orgs/100ml for both the 160 South Rd and Beach Rd points.

E.coli 42 Day Geometric Means and 80th Percentiles (All results orgs/100 ml)
42 Day Period Ends Geometric Mean 80th percentile
160 South Rd Beach Rd 160 South Rd Beach Rd
19/07/2005 4 5 10 34
30/08/2005 1 1 2 0
11/10/2005 2 0 4 0
22/11/2005 15 11 54 42
3/01/2006 3 7 20 10
14/02/2006 9 3 90 6
28/03/2006 2 3 2 12
9/05/2006 3 1 10 2
21/06/2006 3 4 10 10

The above results indicate that the two sites within the Werribee segment achieve the State Environment Protection Policy (Waters of Victoria), Schedule F6, Werribee Segment, bacteriological organisms quality objective of <1000 E.coli organisms / 100ml.

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