Environmental Engineering Reference
In-Depth Information
100
Pre-monsoon
Post-monsoon
90
80
PERMISSIBLE TO
DOUBTFUL
70
EXCELLENT
TO
GOOD
60
DOUBTFUL TO
UNSUITABLE
50
GOOD TO
PERMISSIBLE
40
30
20
10
0
0
500
1000
1500
2000
2500
3000
3500
Electrical Conductance(microhms/cm) at 25 C
Fig. 7 RatingofgroundwatersamplesonthebasisofECand%Na(AfterWilcox 1955 )
post-monsoon seasons. According to the Richards ( 1954 ) classification based on
SAR values, all samples belong to the excellent category in the study area (Table 2 ).
SAR can indicate the degree to which irrigation water tends to enter cation exchange
reactions in soil.
Residualsodiumcarbonate(RSC)iscommonlyusedtoassessthesodiumper-
meabilityhazardbyconsideringthebicarbonate/carbonateandcalcium/magnesium
concentrationinirrigationwater.RSCisimportantbecauseitmainlyconsidersthe
relative concentrations of bicarbonate and carbonate as compared to those of cal-
cium, magnesium and sodium instead of the absolute bicarbonate and carbonate
concentrations.ApositiveRSCindicatesthatsodiumbuildupinthesoilispossible.
TheclassiicationofirrigationwateraccordingtotheRSCvalueindicatesthatwater
withanRSCofabove2.5meq/lisnotsuitableforirrigation,thosewithRSCsof
1.25-2.5meq/lareconsidereddoubtful,andthosewithRSCsbelow1.25meq/lare
good for irrigation (Table 2 ). Based on this classification, 56 % and 44 % samples
are good and doubtful category in pre-monsoon, whereas in post-monsoon 100 %
groundwater samples are of good category.
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