Environmental Engineering Reference
In-Depth Information
TABLE 4.9. Load Allocation for Fecal Coliform
Exceedance
(%)
nonpoint Source Load
(LA) (×10
10
CFU/d)
Exceedance
(%)
nonpoint Source Load
(LA) (×10
10
CFU/d)
Exceedance
(%)
nonpoint Source Load
(LA) (×10
10
CFU/d)
0.0
1360
35.0
45.7
70.0
14.2
2.5
335
37.5
42.2
72.5
13.1
5.0
258
40.0
38.5
75.0
12.1
7.5
205
42.5
34.9
77.5
11.1
10.0
170
45.0
32.2
80.0
9.97
12.5
140
47.5
29.5
82.5
8.82
15.0
119
50.0
27.0
85.0
7.84
17.5
103
52.5
24.7
87.5
6.94
20.0
92.3
55.0
22.6
90.0
6.20
22.5
81.7
57.5
20.8
92.5
5.55
25.0
72.3
60.0
19.1
95.0
4.81
27.5
64.4
62.5
17.8
97.5
3.89
30.0
57.1
65.0
16.5
100
0.00
32.5
50.8
67.5
15.5
-
where
i
is the measurement index. Given multiple sets
of paired measurements (
Q
i
,
c
i
), the analysis procedure
is as follows:
Identification of Contaminant Sources.
When used to
identify likely sources of contamination, multiple syn-
optic measurements of contaminant concentration,
c
i
(ML
−3
), and flow rate,
Q
i
(L
3
T
−1
), are used in the analysis,
Step 1.
For each flow measurement,
Q
i
, determine
the corresponding exceedance percentage,
e
i
, from
the flow duration curve of the stream. The mea-
sured load
Q
i
c
i
therefore corresponds to a flow
condition with an exceedance percentage of
e
i
.
Step 2.
For each set of paired measurements (
Q
i
,
c
i
),
plot the load
Q
i
c
i
versus the corresponding exceed-
ance percentage,
e
i
, on the LDC. An example of
this plot is shown in Figure 4.18.
Step 3.
Any measurement point (
e
i
,
Q
i
c
i
) that plots
above the LDC represents a violation of the water-
quality standard, and conversely any point that
plots below the LDC represents compliance with
the water-quality standard. Since the LDC is seg-
regated by flow condition, the types of flow condi-
tions (e.g., low low) in which the water-quality
violations occur can be identified. If the majority
10
14
10
13
MOS (margin of safety)
10
12
TMDL
LA (nonpoint sources)
10
11
WLA (point sources)
10
10
0
10
20
30
40
50
60
70
80
90 100
exceedance percentage (%)
Figure 4.17.
Fecal coliform TMDL.
10
6
10
5
10
4
high
ows
moist
conditions
10
3
mid-range
ows
dry
conditions
low
ows
10
2
0
10
20
30
40
50
60
70
80
90
100
exceedance percentage (%)
Figure 4.18.
Load measurements plotted on load duration curve.
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