THE SUITABILITY STUDY OF SURFACE WATER SOURCES FOR DESIGNING SUB-DISTRICT WATER SUPPLY SYSTEMS: A CASE STUDY OF NONG PHO SUB-DISTRICT MUNICIPALITY, KHUAN KHANUN DISTRICT, PHATTHALUNG PROVINCE

Abstract

The objectives of this research were to 1) analyze the suitability of surface water sources regarding quantity, quality, and balance, 2) design guidelines for a surface water supply system to integrate with the existing groundwater system of Nong Pho Subdistrict Municipality, Khuan Khanun District, Phatthalung Province. A mixed-methods approach was employed, involving field surveys, hydrological data collection, and laboratory water quality testing. The results revealed that the case study of the surface water source (excavated pond, Moo 6 Ban Khuan Phli, area 16,000 sq.m., average depth 3-5 m) had sufficient water storage capacity year-round. With total losses from evaporation and seepage accounting for approximately 30%, the source is suitable as a supplementary raw water supply during the dry season. Regarding raw water quality, the overall condition was good, with Dissolved Oxygen (DO) at 9.2 mg/L and Biological Oxygen Demand (BOD) at 0.8 mg/L. However, the average pH was 5.8, with turbidity at 5.2 NTU and Fecal Coliform bacteria contamination at 230 MPN/100 mL. Meanwhile, the existing groundwater system in Moo 3 encountered Total Dissolved Solids (TDS) of 680 mg/L, exceeding the drinking water standard. Consequently, a conventional water treatment system was designed, emphasizing pH adjustment (6.5-7.5), coagulation-flocculation, rapid sand filtration, and effective disinfection maintaining free residual chlorine of at least 0.2 mg/L. The study results demonstrated that integrating treated surface water with existing groundwater could effectively resolve the excessive TDS issue, sustainably enhance community water security, and provide a cost-effective solution.