| Summary: | Samas area which located by the beach is area with high level of groundwater usage,
which the groundwater used for the needs of agriculture, horticulture, and daily necessities. The
purpose of this research is to determine the condition of geology, hydrogeology, and the saltwater
interface area. The research was conducted by collecting data geology and hydrogeology. The
results of geological observations show that the morphology of research area is divided into
Alluvial Plain Unit with lithology in the form of coarse sand and medium sand, Flood Plain Unit
with lithology in the form of fine sand, and the sand dunes unit with lithology in the form of loose
sand. Generally, groundwater flow patterns leading from north to south and southeast to the
beach streams and rivers. Hydraulics gradient research area has an average of 5,036 x 10-3, and
for velocity of groundwater flow on average by 0.047 m/day or 0.059 m/day in the sand dunes Unit
and 0,036 m/day on Coarse-Fine Sand unit. Through slug test method, it can be known that the
score of hydraulic conductivity ranged from 1,324 x 10-4 � 9,708 x 10-5 m/s, which means that
research area is included in the criteria of a good aquifer. Results of laboratory tests produces
groundwater TDS values ranged from 103 mg/l - 557 mg/l, EC values range from 216 μs/cm - 856
μs/cm, CL- values ranged from 11 mg / l - 72.6 mg / l. Based on calculations by using the formula
Ghyben-Herzberg, research area has not experienced saltwater intrusion, but in actual conditions,
the research area has begun to show indications of increased levels of dissolved salts (EC) in
groundwater pumping test indicated from the results of with measurement of dissolved salts (EC).
Given this research is expected that local communities can control usage groundwater, to prevent
further saltwater intrusion.
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