Environmental Engineering Reference
Fig. 5 Skeletal fluorosis from Ralla Anantapuram village of Anantapur district
Vanaja 2001 ). Crippling skeletal fluorosis can occur when a water supply contains
more than 10 mg/l (WHO 1984 ; Boyle and Chagnon 1995 ). Figure 5 shows the skel-
etal fluorosis from Ralla Anantapuram village of Mudigubba mandal where the fluo-
ride concentration is 4.6 mg/l. Ralla Anantapuram, Mallepalli, Pathabathalapalli,
Dorigallu and Yerravankapalli villages are having fluoride concentration more than
4.0 mg/l limit while samples from five other locations have fluoride less than even
1 mg/l. This low fluoride may be used safely as the fluoride traces are useful for healthy
growth of teeth and bones. A concentration less than 0.8 mg/l results in 'dental caries'.
Other samples have fluoride well within the lower and upper limits recommended and
therefore potable. Due to the higher fluoride level in drinking water several cases of
dental and skeletal fluorosis have appeared at alarming rate in this region.
Spatial Analysis of Groundwater Quality
The GIS based analysis of spatiotemporal behaviour of the groundwater quality in
the study area was done by using the spatial analyst module of Arc GIS 9.3. Powerful
spatial analysis is feasible once the database is established. The interpolation tech-
nique used in the analysis is inverse distance weighted (IDW) method. The IDW is
an algorithm for spatially interpolating or estimating values between measurements.
Each value estimated in an IDW interpolation is a weighted average of the sur-
rounding sample points. The weights are computed by taking inverse of the distance