5.8.2.6 The percentage differences in E. coli levels of Option 2 relative to Option 1 are presented in Table 5.15 while Table 5.15b show the differences of Option 2 relative to Baseline scenario. Large differences were observed at the indicator points (NM3, NM5, NM6, DM5, marine park at Sha Chau/Lung Kwu Chau (H1) and Chinese White Dolphin feeding ground in the Urmston Road Channel (G1)) located near the outfall location. In comparison with both baseline and Option 1, the model results indicated that the adoption of disinfection at San Wai STW would significantly reduce the E. coli levels and the water quality impacts in terms of E. coli at Urmston Road would be low. The predictions for the other parameters were consistent with those for Option 1. Thus, similar improvement in water quality as to Option 1 was observed in inner to mid Deep Bay region. The effluent discharge for Option 2 is not likely to cause significant water quality changes in the vicinity of the discharge location. The impacts to the water quality sensitive receivers located further away from the discharge location would become lower and are considered insignificant. In addition, during wet season (within March to October period), no exceedance in WQO was predicted at both gazetted and non-gazetted beaches for Option 2.
Table 5.15 Differences
in E. coli Levels Between Option 1 and
Option 2
|
Indicator
Point |
Percentage
change in E.coli levels |
|
DM1 |
0% |
|
DM2 |
0% |
|
DM3 |
-5% |
|
DM4 |
-33% |
|
DM5 |
-93% |
|
NM1 |
-45% |
|
NM2 |
-26% |
|
NM3 |
-91% |
|
NM5 |
-96% |
|
NM6 |
-94% |
|
NM8 |
-84% |
|
C1 |
-37% |
|
D1 |
-86% |
|
E1 |
-7% |
|
E2 |
-6% |
|
E3 |
-2% |
|
F1 |
0% |
|
F2 |
0% |
|
G1 |
-95% |
|
H1 |
-95% |
|
A1 |
0% |
|
B1 |
-53% |
|
B2 |
-43% |
|
D2 |
-87% |
|
D3 |
0% |
|
D4 |
-90% |
|
L1 |
-2% |
|
J1 |
-1% |
|
E4 |
-7% |
|
E6 |
-10% |
|
E7 |
-12% |
|
E8 |
-6% |
|
E11 |
-3% |
|
E13 |
-25% |
|
F3 |
-92% |
Note:
All the percentages are calculated as (Option 2 – Option 1)/Option 1 x
100%
Values are to the nearest percent
Table
5.15b Differences in Water
Quality Conditions Between Baseline and Option 2
|
Indicator
Point |
DO |
Bottom DO |
TIN |
UIA |
SS |
E.coli |
BOD5 |
|
DM1 |
4% |
4% |
-8% |
-12% |
-5% |
-13% |
-9% |
|
DM2 |
3% |
3% |
-6% |
-10% |
-3% |
-5% |
-6% |
|
DM3 |
2% |
2% |
-4% |
-9% |
-2% |
-6% |
-4% |
|
DM4 |
1% |
1% |
-1% |
-5% |
-1% |
-28% |
-2% |
|
DM5 |
0% |
0% |
0% |
1% |
0% |
-92% |
-2% |
|
NM1 |
0% |
0% |
0% |
0% |
0% |
-40% |
0% |
|
NM2 |
0% |
0% |
0% |
0% |
0% |
-22% |
-1% |
|
NM3 |
0% |
0% |
0% |
1% |
-1% |
-88% |
-2% |
|
NM5 |
0% |
0% |
0% |
1% |
-1% |
-94% |
-3% |
|
NM6 |
0% |
0% |
0% |
1% |
-1% |
-93% |
-2% |
|
NM8 |
0% |
0% |
0% |
0% |
0% |
-80% |
-1% |
|
C1 |
0% |
0% |
0% |
0% |
0% |
-33% |
0% |
|
D1 |
0% |
1% |
0% |
-1% |
-1% |
-83% |
-2% |
|
E1 |
0% |
0% |
0% |
0% |
0% |
-5% |
0% |
|
E2 |
0% |
0% |
0% |
0% |
0% |
-5% |
0% |
|
E3 |
0% |
0% |
0% |
0% |
0% |
-2% |
0% |
|
F1 |
4% |
4% |
-12% |
-18% |
-7% |
-33% |
-17% |
|
F2 |
1% |
1% |
-4% |
-13% |
-2% |
-39% |
-8% |
|
G1 |
0% |
0% |
0% |
1% |
-1% |
-93% |
-3% |
|
H1 |
0% |
0% |
0% |
1% |
-1% |
-94% |
-2% |
|
A1 |
9% |
9% |
-10% |
-11% |
-6% |
-23% |
-11% |
|
B1 |
0% |
0% |
0% |
-1% |
-1% |
-47% |
-2% |
|
B2 |
0% |
0% |
0% |
0% |
-1% |
-38% |
-2% |
|
D2 |
0% |
0% |
0% |
1% |
-1% |
-84% |
-2% |
|
D3 |
0% |
0% |
0% |
0% |
0% |
0% |
0% |
|
D4 |
0% |
0% |
0% |
0% |
-1% |
-87% |
-1% |
|
L1 |
0% |
0% |
0% |
0% |
0% |
-2% |
0% |
|
J1 |
0% |
0% |
0% |
0% |
0% |
-1% |
0% |
|
E4 |
0% |
0% |
0% |
0% |
0% |
-6% |
0% |
|
E6 |
0% |
0% |
0% |
0% |
0% |
-8% |
0% |
|
E7 |
0% |
0% |
0% |
0% |
0% |
-10% |
0% |
|
E8 |
0% |
0% |
0% |
0% |
0% |
-5% |
-1% |
|
E11 |
0% |
0% |
0% |
0% |
0% |
-3% |
0% |
|
E13 |
0% |
0% |
0% |
0% |
0% |
-22% |
-1% |
|
F3 |
0% |
0% |
0% |
1% |
0% |
-90% |
-2% |
Note:
All percentages are calculated as (Annual Option 2 – Annual
Baseline)/(Annual Baseline) x 100%
Values are presented to the nearest percent
5.8.2.7 Comparison of the predicted water quality results between Option 3 and Option 2 shows the difference in BOD5 levels. Figure 5.10 presents the contour plots for BOD5 for Option 3 (middle plot) and Option 2 (upper plot). The absolute difference in the lower plot of Figure 5.10 showed that the increases in BOD5 levels were minimal.
5.8.2.8 Table 5.16 to 5.18 summarise the predicted water quality results for Option 3 for wet season, dry season and annual results while Table 5.19 shows the percentage differences in BOD5 levels for Option 3 relative to Option 2. There were slight increases in BOD5 levels in the receiving water near the discharge location for Option 2 scenario when compared to the Option 3 scenario. The percentage differences recorded at the nearest indicator points DM5, NM3, NM5, Chinese White Dolphin feeding ground in the Urmston Road Channel (G1) and marine park at Sha Chau/Lung Kwu Chau (H1) were 2%, 3%, 1%, 2% and 2% respectively. The relative absolute differences were below 0.01 mg/L and were mainly in the areas near the discharge location. The differences were almost indistinguishable in the area located further away from the discharge location. The model results supported that upgrading the treatment method from CEPT with disinfection (Option 2) to secondary treatment with disinfection (Option 3) would not have a significant improvement in reducing the BOD5 levels in the nearby water quality sensitive receivers.
Table 5.16 Wet
Season Water Quality Results for Option 3
|
Indicator
Point |
DO (mg/L) |
Bottom DO (mg/L) |
TIN (mg/L) |
UIA (mg/L) |
SS (mg/L) |
E.coli (count/100mL) |
BOD5 (mg/L) |
|
DM1 |
2.3 |
2.2 |
2.16 |
0.125 |
41.1 |
1506 |
5.38 |
|
DM2 |
2.6 |
2.6 |
1.67 |
0.073 |
31.8 |
560 |
2.90 |
|
DM3 |
3.4 |
3.4 |
1.11 |
0.021 |
20.9 |
90 |
1.00 |
|
DM4 |
3.6 |
3.3 |
0.90 |
0.008 |
16.6 |
63 |
0.58 |
|
DM5 |
3.8 |
3.8 |
0.79 |
0.004 |
17.5 |
27 |
0.47 |
|
NM1 |
4.9 |
4.9 |
0.53 |
0.002 |
7.3 |
3 |
0.24 |
|
NM2 |
4.6 |
4.6 |
0.62 |
0.002 |
8.7 |
43 |
0.27 |
|
NM3 |
4.5 |
4.6 |
0.63 |
0.003 |
9.3 |
3 |
0.28 |
|
NM5 |
4.2 |
4.2 |
0.72 |
0.004 |
12.8 |
15 |
0.37 |
|
NM6 |
4.1 |
4.0 |
0.76 |
0.003 |
12.7 |
4 |
0.37 |
|
NM8 |
4.2 |
4.0 |
0.73 |
0.003 |
11.5 |
2 |
0.33 |
|
C1 |
5.0 |
5.0 |
0.52 |
0.002 |
7.1 |
2 |
0.24 |
|
D1 |
3.9 |
3.9 |
0.79 |
0.004 |
15.2 |
47 |
0.45 |
|
E1 |
5.1 |
5.0 |
0.48 |
0.002 |
7.0 |
32 |
0.26 |
|
E2 |
5.0 |
5.0 |
0.50 |
0.002 |
6.8 |
23 |
0.24 |
|
E3 |
5.0 |
4.9 |
0.51 |
0.002 |
6.9 |
92 |
0.24 |
|
F1 |
2.3 |
2.3 |
2.16 |
0.128 |
40.9 |
2708 |
5.28 |
|
F2 |
4.4 |
4.4 |
0.87 |
0.008 |
17.7 |
2824 |
0.69 |
|
G1 |
4.1 |
4.1 |
0.75 |
0.004 |
13.3 |
21 |
0.39 |
|
H1 |
4.0 |
4.0 |
0.75 |
0.003 |
13.2 |
6 |
0.38 |
|
A1 |
0.6 |
0.5 |
3.22 |
0.222 |
60.9 |
2325 |
11.31 |
|
B1 |
4.4 |
4.1 |
0.76 |
0.004 |
12.8 |
25 |
0.38 |
|
B2 |
4.2 |
4.1 |
0.77 |
0.004 |
11.8 |
101 |
0.48 |
|
D2 |
4.4 |
4.4 |
0.67 |
0.003 |
10.6 |
8 |
0.30 |
|
D3 |
5.4 |
4.7 |
0.57 |
0.002 |
9.2 |
147 |
0.54 |
|
D4 |
4.3 |
4.2 |
0.70 |
0.003 |
10.7 |
1 |
0.31 |
|
L1 |
5.0 |
4.6 |
0.60 |
0.002 |
8.6 |
249 |
0.34 |
|
J1 |
5.0 |
4.6 |
0.60 |
0.002 |
8.8 |
196 |
0.43 |
|
E4 |
5.0 |
4.9 |
0.51 |
0.002 |
6.9 |
31 |
0.24 |
|
E6 |
5.0 |
5.0 |
0.50 |
0.002 |
6.8 |
15 |
0.24 |
|
E7 |
5.0 |
5.0 |
0.50 |
0.002 |
7.0 |
20 |
0.24 |
|
E8 |
4.8 |
4.6 |
0.63 |
0.002 |
8.5 |
138 |
0.31 |
|
E11 |
5.0 |
4.7 |
0.62 |
0.002 |
8.3 |
149 |
0.33 |
|
E13 |
4.6 |
4.5 |
0.63 |
0.002 |
8.9 |
71 |
0.30 |
|
F3 |
4.0 |
3.9 |
0.78 |
0.003 |
14.6 |
7 |
0.41 |
Table 5.17 Dry
Season Water Quality Results for Option 3
|
Indicator
Point |
DO (mg/L) |
Bottom DO (mg/L) |
TIN (mg/L) |
UIA (mg/L) |
SS (mg/L) |
E.coli (count/100mL) |
BOD5 (mg/L) |
|
DM1 |
4.1 |
4.1 |
2.51 |
0.073 |
37.8 |
7629 |
6.82 |
|
DM2 |
4.8 |
4.8 |
1.76 |
0.042 |
27.7 |
3231 |
4.38 |
|
DM3 |
5.6 |
5.5 |
0.97 |
0.015 |
17.1 |
431 |
2.09 |
|
DM4 |
5.9 |
5.7 |
0.65 |
0.007 |
12.2 |
196 |
1.21 |
|
DM5 |
6.1 |
6.0 |
0.47 |
0.004 |
8.9 |
57 |
0.77 |
|
NM1 |
6.4 |
6.4 |
0.20 |
0.002 |
5.0 |
6 |
0.35 |
|
NM2 |
6.3 |
6.3 |
0.24 |
0.002 |
5.6 |
122 |
0.42 |
|
NM3 |
6.3 |
6.2 |
0.27 |
0.003 |
6.0 |
9 |
0.46 |
|
NM5 |
6.2 |
6.1 |
0.38 |
0.004 |
7.6 |
31 |
0.63 |
|
NM6 |
6.2 |
6.2 |
0.38 |
0.003 |
7.9 |
7 |
0.67 |
|
NM8 |
6.4 |
6.4 |
0.33 |
0.003 |
7.7 |
2 |
0.68 |
|
C1 |
6.4 |
6.4 |
0.20 |
0.002 |
4.9 |
6 |
0.34 |
|
D1 |
6.1 |
6.0 |
0.47 |
0.004 |
9.1 |
78 |
0.80 |
|
E1 |
7.4 |
7.3 |
0.14 |
0.002 |
5.0 |
1 |
0.56 |
|
E2 |
6.4 |
6.3 |
0.19 |
0.002 |
4.8 |
49 |
0.32 |
|
E3 |
6.4 |
6.3 |
0.19 |
0.002 |
4.8 |
143 |
0.33 |
|
F1 |
4.6 |
4.6 |
2.35 |
0.063 |
35.1 |
10090 |
6.23 |
|
F2 |
6.2 |
6.2 |
0.89 |
0.012 |
16.6 |
4522 |
2.04 |
|
G1 |
6.1 |
6.1 |
0.40 |
0.004 |
7.9 |
37 |
0.66 |
|
H1 |
6.2 |
6.1 |
0.40 |
0.003 |
8.1 |
12 |
0.68 |
|
A1 |
3.1 |
3.1 |
3.29 |
0.104 |
45.6 |
4461 |
8.56 |
|
B1 |
6.2 |
6.0 |
0.40 |
0.003 |
8.8 |
53 |
0.77 |
|
B2 |
6.2 |
6.1 |
0.40 |
0.004 |
8.2 |
422 |
0.73 |
|
D2 |
6.2 |
6.2 |
0.31 |
0.003 |
6.5 |
31 |
0.52 |
|
D3 |
7.3 |
6.8 |
0.18 |
0.002 |
7.5 |
452 |
0.99 |
|
D4 |
6.3 |
6.3 |
0.32 |
0.003 |
7.0 |
2 |
0.61 |
|
L1 |
6.4 |
6.2 |
0.22 |
0.002 |
6.7 |
170 |
0.58 |
|
J1 |
7.0 |
6.6 |
0.20 |
0.002 |
6.2 |
597 |
0.71 |
|
E4 |
6.4 |
6.3 |
0.19 |
0.002 |
4.8 |
78 |
0.34 |
|
E6 |
6.4 |
6.3 |
0.19 |
0.002 |
4.8 |
29 |
0.32 |
|
E7 |
6.4 |
6.3 |
0.19 |
0.002 |
4.8 |
28 |
0.32 |
|
E8 |
6.5 |
6.4 |
0.22 |
0.002 |
6.0 |
167 |
0.52 |
|
E11 |
6.7 |
6.3 |
0.21 |
0.002 |
7.0 |
166 |
0.70 |
|
E13 |
6.4 |
6.3 |
0.24 |
0.002 |
5.7 |
176 |
0.45 |
|
F3 |
6.2 |
6.1 |
0.43 |
0.004 |
8.5 |
16 |
0.72 |
Table 5.18 Annual
Water Quality Results for Option 3
|
Indicator
Point |
DO (mg/L) |
Bottom DO (mg/L) |
TIN (mg/L) |
UIA (mg/L) |
SS (mg/L) |
E.coli (count/100mL) |
BOD5 (mg/L) |
|
DM1 |
3.2 |
3.2 |
2.33 |
0.0989 |
39.5 |
3390 |
6.10 |
|
DM2 |
3.7 |
3.7 |
1.71 |
0.0570 |
29.7 |
1345 |
3.64 |
|
DM3 |
4.5 |
4.5 |
1.04 |
0.0181 |
19.0 |
197 |
1.54 |
|
DM4 |
4.7 |
4.5 |
0.77 |
0.0072 |
14.4 |
111 |
0.89 |
|
DM5 |
5.0 |
4.9 |
0.63 |
0.0041 |
13.2 |
40 |
0.62 |
|
NM1 |
5.6 |
5.6 |
0.36 |
0.0020 |
6.1 |
4 |
0.30 |
|
NM2 |
5.5 |
5.4 |
0.43 |
0.0023 |
7.1 |
72 |
0.34 |
|
NM3 |
5.4 |
5.4 |
0.45 |
0.0027 |
7.6 |
6 |
0.37 |
|
NM5 |
5.2 |
5.2 |
0.55 |
0.0036 |
10.2 |
22 |
0.50 |
|
NM6 |
5.1 |
5.1 |
0.57 |
0.0032 |
10.3 |
5 |
0.52 |
|
NM8 |
5.3 |
5.2 |
0.53 |
0.0027 |
9.6 |
2 |
0.51 |
|
C1 |
5.7 |
5.7 |
0.36 |
0.0020 |
6.0 |
4 |
0.29 |
|
D1 |
5.0 |
4.9 |
0.63 |
0.0043 |
12.1 |
60 |
0.62 |
|
E1 |
6.2 |
6.1 |
0.31 |
0.0016 |
6.0 |
6 |
0.41 |
|
E2 |
5.7 |
5.7 |
0.35 |
0.0019 |
5.8 |
33 |
0.28 |
|
E3 |
5.7 |
5.6 |
0.35 |
0.0019 |
5.8 |
115 |
0.29 |
|
F1 |
3.5 |
3.5 |
2.25 |
0.0958 |
38.0 |
5227 |
5.76 |
|
F2 |
5.3 |
5.3 |
0.88 |
0.0101 |
17.2 |
3574 |
1.36 |
|
G1 |
5.1 |
5.1 |
0.57 |
0.0038 |
10.6 |
28 |
0.53 |
|
H1 |
5.1 |
5.0 |
0.58 |
0.0034 |
10.6 |
9 |
0.53 |
|
A1 |
1.9 |
1.8 |
3.25 |
0.1631 |
53.3 |
3221 |
9.94 |
|
B1 |
5.3 |
5.0 |
0.58 |
0.003 |
10.8 |
36 |
0.58 |
|
B2 |
5.2 |
5.1 |
0.59 |
0.004 |
10.0 |
206 |
0.61 |
|
D2 |
5.3 |
5.3 |
0.49 |
0.003 |
8.6 |
16 |
0.41 |
|
D3 |
6.3 |
5.8 |
0.38 |
0.002 |
8.4 |
257 |
0.76 |
|
D4 |
5.3 |
5.3 |
0.51 |
0.003 |
8.9 |
2 |
0.46 |
|
L1 |
5.7 |
5.4 |
0.41 |
0.002 |
7.6 |
205 |
0.46 |
|
J1 |
6.0 |
5.6 |
0.40 |
0.002 |
7.5 |
342 |
0.57 |
|
E4 |
5.7 |
5.6 |
0.35 |
0.002 |
5.9 |
49 |
0.29 |
|
E6 |
5.7 |
5.7 |
0.34 |
0.002 |
5.8 |
21 |
0.28 |
|
E7 |
5.7 |
5.7 |
0.35 |
0.002 |
5.9 |
24 |
0.28 |
|
E8 |
5.7 |
5.5 |
0.42 |
0.002 |
7.3 |
152 |
0.41 |
|
E11 |
5.8 |
5.5 |
0.42 |
0.002 |
7.7 |
157 |
0.52 |
|
E13 |
5.5 |
5.4 |
0.44 |
0.002 |
7.3 |
112 |
0.38 |
|
F3 |
5.1 |
5.0 |
0.60 |
0.003 |
11.5 |
11 |
0.57 |
Note:
Values are calculated as average of wet and dry season results
E.Coli values are calculated as geometric mean
Table 5.19 Differences
in DO and BOD5 Levels Between Option 2 and Option 3
|
Indicator
Point |
DO |
BOD5 |
|
DM1 |
0% |
0% |
|
DM2 |
0% |
0% |
|
DM3 |
0% |
0% |
|
DM4 |
0% |
0% |
|
DM5 |
0% |
-2% |
|
NM1 |
0% |
0% |
|
NM2 |
0% |
-1% |
|
NM3 |
0% |
-2% |
|
NM5 |
0% |
-3% |
|
NM6 |
0% |
-1% |
|
NM8 |
0% |
-1% |
|
C1 |
0% |
0% |
|
D1 |
0% |
-2% |
|
E1 |
0% |
0% |
|
E2 |
0% |
0% |
|
E3 |
0% |
0% |
|
F1 |
0% |
0% |
|
F2 |
0% |
0% |
|
G1 |
0% |
-2% |
|
H1 |
0% |
-2% |
|
A1 |
0% |
0% |
|
B1 |
0% |
-1% |
|
B2 |
0% |
-1% |
|
D2 |
0% |
-2% |
|
D3 |
0% |
0% |
|
D4 |
0% |
-1% |
|
L1 |
0% |
-1% |
|
J1 |
0% |
0% |
|
E4 |
0% |
0% |
|
E6 |
0% |
0% |
|
E7 |
0% |
0% |
|
E8 |
0% |
-1% |
|
E11 |
0% |
0% |
|
E13 |
0% |
-1% |
|
F3 |
0% |
-1% |
Note:
All the percentages are calculated as (Option 3 – Option 2)/Option 2 x
100%
Values are presented to the nearest percent