| Summary: | A sub-urban area of northern part of Yogyakarta city is a sub-urban area that
now devolved physically into an urban area. Increasing of human population
causes the area has a complex activity. The complex activity has a potency to
contaminate groundwater resources, especially pollutants that come from
septictank. The purpose of this research is to understand about the zoning of
potential groundwater pollution and to evaluate the suitability of LeGrand
mothod based on analysis of fecal coli in the actual groundwater.
LeGrand method is used in this research. This method considers five factors such
as depth to watertable, watertable gradient, horizontal distance from pollutant
sources, sorption above watertable, and permeability. Characteristics of each
factor will determine the quick or slowness of pollutants to reach watertable. This
method has a GIS-based system with assessment techniques (scoring). In the
measurements of depth to watertable use systematic sampling method while the
pollutant sources and groundwater samples use purposive sampling method.
Quantitative analysis is done to calculate watertable gradient and horizontal
distance from the pollutant sources. Descriptive analysis is done to describe the
characteristics of groundwater. Spatial analysis explains zoning of potential
groundwater pollution and groundwater quality from each zone formed, spatially.
The results show that the potency of groundwater pollution in the research area is
formed three zones according to analysis of LeGrand method, zone II (possibly
contaminated), zone III (maybe contaminated but it is difficult), and zone IV
(difficult area to be polluted). Zone II, III, and zone IV has an area of 76 Ha
(22%), 173 Ha (50%) and 98 Ha (28%), respectively. The suitability level of
LeGrand method of groundwater pollution is 67%. Zone II has fecal coli about 75
MPN/100ml, 39 MPN/100ml, and 46 MPN/100ml. Zone III has fecal coli about 11
MPN/100ml up to 15 MPN/100ml and zone IV has fecal coli about 3 MPN/100ml
up to 7 MPN/100ml.
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