Environmental Engineering Reference
In-Depth Information
performed on the same area in 2002 examined the impact of this method of sludge
application on soils and ground water and is discussed in Chapter 9.
4.4
Impacts evaluation
This study focused on surface water quality assessment in terms of the impacts from the
farm area, which reflect the combined effect of surface runoff, seepage from the under-
drain system and possible recharge from ground water. The impacts have been discussed
in terms of seasonal variations of water quality at each sampling point, as well as in terms
of spatial variation between the control point and the other points, reflecting the impact of
the farm.
Results of field measurements are presented in Table 8.3. Seasonal variations of
turbidity show increased values during the wet season at all points. The significant spatial
increase from 18 NTU to 33 NTU at SW2 compared to SW1 is an indication of the
washout of suspended colloidal substances from the farm area. Spatial and seasonal
variations of pH were not significant. Results on conductivity do not show a significant
spatial variation due to pasture impact, but seasonal variations show an expected
reduction of values due to the dilution in February.
Results of the rest of the tested parameters are presented on Figures 8.7, 8.8 and 8.9.
Seasonal variations were studied by testing for a statistically significant difference of the
mean values with respect to each one of the studied parameters. The mean values for a
given season were compared with the ones, representing the other seasons at the same
sampling location, e.g. with respect to SW
1
the TP mean values for October were
compared with those for November and for February, and those for November were
Table 8.2. Average annual sludge application rates
to Crowborough Farm.
Cr
+6
TKN
TP
Pb
Zn
Cd
Ni
Sludge & Effluent (mg/kg.d.w)
12899
2133
73
133
20
72
873
Application rate (kg/ha.year)
684
113
4
7
1
4
46
Limit SA (kg/ha.year)
-
-
0.41
2.83
0.13
14*
21
Limit ZW (kg/ha.year)
600
-
4
-
-
Limit USA (kg/ha.year)
-
-
15
140
1.9
150*
1.6
* Total Chromium
Table 8.3. Field measurements results.
October
November
February
SW1
pH
7.8
7.5
7.6
T (ºC)
18
21
21
