Environmental Engineering Reference
In-Depth Information
60-90
F2
179.40
82
7
18
0.01
51
60-90
F3
198.90
154
7
16
0.01
54
60-90
F4
175.50
102
7
14
0.01
47
180.38
110.00
6.75
16.75
0.01
53.75
60-90
S1
156.00
92
6
12
0.01
66
60-90
S2
140.40
82
6
13
0.01
52
60-90
S3
140.40
122
6
16
0.01
70
60-90
S4
140.40
86
5
13
0.01
66
Average 144.30
95.50
5.75
13.50
0.01
63.50
5 IMPACTS ON GROUNDWATER
5.1 Methodology
The farm did not have suitably located boreholes for monitoring the effect of wastewater
irrigation on groundwater quality. For this reason, well drilling was carried out following
the procedures in Chapman (1998) and Todd (1980). A 50 mm diameter steel hand auger
was used to drill holes to a depth of about 3 m below ground level at five locations within
the study area (Fig. 10.3). About 10 cm of the pipe was left above the ground to prevent
runoff getting into the well. The wells were then capped to avoid direct irrigation water
getting in. Two wells were drilled at a site grown to a sprinkler-irrigated pasture of
Kikuyu and Star grass, one at the upper aquifer gradient part of the block and the other at
the down aquifer gradient part of the block. The same was done on a furrow-irrigated
pasture of the same grass species. Another well was drilled at the control site at the upper
aquifer gradient of the area and taken as the control well. Soil samples collected at 0-30,
30-60 and 60-90 cm during drilling were sent to laboratories for trace metal and nutrient
analysis. The auger holes were fitted with perforated 32 mm diameter polyvinyl chloride
(PVC) pipes. Well logging was done during drilling at each site by 'finger' assessment.
To determine the direction of groundwater flow and variation in the water level over
time, groundwater levels were measured using a steel tape. On average, the groundwater
water table was 1.5 m from the ground surface.
Groundwater samples were collected from monitoring wells using a suction plastic
hand pump (Nalgene pump, Newark Enterprises). The pump has a flexible polythene
extension tube, which was lowered to a depth 2.5 m into the PVC tube. In between
sampling, the suction pump was rigorously cleaned 5 times with distilled water following
the recommendations of Chapman (1998). Monitoring wells were purged for 10 minutes
before sampling. The first 20 ml of the sample were used to rinse the sampling equipment
and the sample bottle following recommendations of Quevauviller (1995).
The effluent and ground water samples were analyzed for Cd, Cu, Zn, and Cr (as total
metals) at the IMR laboratory and for ortho P, nitrate, ammonia, FC, TC and TKN at the
Water Quality Laboratory, Civil Engineering Department, UZ. Ca, Mg, Na and K at the
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