5

5.8.2.3 Comparing the baseline case with Option 1 in Table 5.11 and Figure 5.2 to Figure 5.8, improvements in water quality were predicted near inner Deep Bay as a result of diverting a greater portion of pollution loads into Urmston Road Outfall. At Tsim Bei Tsui SSSI (F1) for example, there were an overall reduction of UIA, TIN, E.Coli and BOD5 levels of 18%, 12%, 33% and 17% respectively while DO levels were increased by 4% for depth-averaged and 4% for bottom. The water quality improvements were smaller near mid-outer Deep Bay area. On the other hand, significant increases in E.Coli levels were predicted near Urmston Road Outfall as a result of Option 1. Significant increase in E.Coli levels were predicted at G1 (Chinese White Dolphine Feeding Ground in the Urmston Road Channel), H1 (Marine Park at Sha Chau/Ling Kwu Chau), NM5 and NM6 which are in the vicinity of Urmston Road Outfall. In addition, as shown in the absolute difference of E.Coli levels between Baseline and Option 1 in Figure 5.7, the area influenced by Option 1 scenario is quite significant. Comparing to Table 5.7 and Table 5.10, the E.Coli levels at DM5 had increased from 491 count/100mL to 606 count/100mL which is just below the WQO for Deep Bay WCZ of 610 count/100mL. In addition, there were some increases in E.Coli levels at B1, B2 (non-gazetted beach at Lung Kwu Tan) and E13 (Butterfly Beach). Of these 3 beaches, B2 had exceeded the WQO of 180 count/100mL during wet season (within March - October period) for both baseline and option 1 scenario. (Baseline: 183 count/100mL; Option 1: 202 count/100mL)

5.8.2.4 The predicted wet season, dry season and annual results for Option 2 are summarised in Table 5.12 to Table 5.14 respectively. The increase in E. coli levels in the receiving water were determined by comparing Option 2 (CEPT + disinfection) with Option 1 (CEPT). Figure 5.9 presents graphically the differences in E. coli levels for the two options. As can be seen in the figure, the predicted E. coli levels for Option 2 were lower than Option 1 predictions.

5.8.2.5 The time series plots for E. coli during wet and dry season for Baseline, Option 1 and Option 2 at selected indicator points (NM5, DM5, marine park at Sha Chau/Lung Kwu Chau - H1, Chinese White Dolphin feeding ground in the Urmston Road Channel - G1, and CLP's cooling water intake point - D1) are shown in Figures 5.13a to 5.14b. The predicted E. coli levels for Baseline (black line) were slightly lower than Option 1 (blue line) while the predicted E.Coli levels for Option 2 (red line) as a result of disinfection process were significantly smaller than both baseline and Option 1.

Table 5.12 Wet Season Water Quality Results for Option 2

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	2.3	2.14	0.124	40.9	1497	5.35
DM2	2.6	2.6	1.65	0.071	31.6	558	2.88
DM3	3.4	3.4	1.11	0.021	20.8	89	0.99
DM4	3.6	3.3	0.90	0.007	16.6	63	0.58
DM5	3.8	3.8	0.79	0.004	17.5	29	0.48
NM1	4.9	4.9	0.52	0.002	7.3	3	0.24
NM2	4.6	4.6	0.61	0.002	8.7	43	0.27
NM3	4.5	4.6	0.63	0.003	9.3	3	0.29
NM5	4.1	4.2	0.72	0.004	12.8	16	0.38
NM6	4.0	4.0	0.76	0.003	12.7	4	0.38
NM8	4.2	4.0	0.73	0.003	11.4	2	0.34
C1	5.0	5.0	0.51	0.002	7.1	2	0.24
D1	3.9	3.9	0.79	0.004	15.2	47	0.46
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	0.50	0.002	6.9	92	0.24
F1	2.4	2.3	2.14	0.127	40.7	2696	5.25
F2	4.4	4.4	0.87	0.008	17.7	2823	0.69
G1	4.1	4.1	0.75	0.004	13.3	22	0.41
H1	4.0	4.0	0.75	0.003	13.2	6	0.39
A1	0.6	0.5	3.21	0.221	60.7	2309	11.27
B1	4.4	4.1	0.76	0.004	12.8	25	0.39
B2	4.2	4.1	0.77	0.004	11.8	101	0.49
D2	4.4	4.4	0.66	0.003	10.6	8	0.31
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	0.32
L1	5.0	4.5	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	0.49	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	0.62	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	14.5	7	0.42

Table 5.13 Dry Season Water Quality Results for Option 2

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	7630	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	5.8	5.7	0.65	0.007	12.3	196	1.22
DM5	6.1	6.0	0.47	0.004	9.0	59	0.79
NM1	6.4	6.3	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	0.47
NM5	6.1	6.1	0.38	0.004	7.6	32	0.64
NM6	6.2	6.2	0.38	0.003	7.9	7	0.68
NM8	6.4	6.3	0.34	0.003	7.7	2	0.68
C1	6.4	6.3	0.20	0.002	4.9	6	0.34
D1	6.1	6.0	0.47	0.004	9.1	78	0.81
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	6.3	6.3	0.19	0.002	4.8	143	0.33
F1	4.6	4.6	2.35	0.063	35.2	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	38	0.67
H1	6.1	6.1	0.40	0.004	8.1	12	0.69
A1	3.1	3.1	3.29	0.104	45.7	4462	8.56
B1	6.2	6.0	0.40	0.003	8.8	53	0.78
B2	6.2	6.1	0.40	0.004	8.2	422	0.74
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	0.33
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	177	0.46
F3	6.2	6.1	0.43	0.004	8.5	16	0.73

Table 5.14 Annual Water Quality Results for Option 2

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	0.0983	39.3	3380	6.08
DM2	3.7	3.7	1.71	0.0565	29.6	1343	3.63
DM3	4.5	4.5	1.04	0.0179	18.9	196	1.54
DM4	4.7	4.5	0.77	0.0072	14.4	111	0.90
DM5	5.0	4.9	0.63	0.0041	13.2	41	0.63
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	0.35
NM3	5.4	5.4	0.45	0.0027	7.6	6	0.38
NM5	5.1	5.2	0.55	0.0036	10.2	23	0.51
NM6	5.1	5.1	0.57	0.0032	10.3	5	0.53
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	61	0.63
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	0.0020	5.8	115	0.29
F1	3.5	3.5	2.25	0.0951	37.9	5216	5.74
F2	5.3	5.3	0.88	0.0101	17.1	3573	1.36
G1	5.1	5.1	0.57	0.0038	10.6	29	0.54
H1	5.1	5.0	0.58	0.0035	10.7	9	0.54
A1	1.8	1.8	3.25	0.1626	53.2	3210	9.92
B1	5.3	5.0	0.58	0.003	10.8	36	0.59
B2	5.2	5.1	0.59	0.004	10.0	207	0.62
D2	5.3	5.3	0.49	0.003	8.6	16	0.41
D3	6.3	5.8	0.37	0.002	8.4	258	0.77
D4	5.3	5.2	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	5.6	5.5	0.42	0.002	7.3	152	0.42
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	0.58

Note: Values are calculated as average of wet and dry season results

E.Coli values are calculated as geometric mean