<![CDATA[This study examines how mixing groundwater and palm oil mill effluent affects groundwater quality. Groundwater and palm oil mill effluent samples were mixed in the laboratory with different concentration ratios, namely 0%, 25%, 50%, 75%, and 100%. The mixture was tested using five water quality parameters, namely Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Dissolved Oxygen (DO), power of Hydrogen (pH), and Total Suspended Solid (TSS). The water quality standards for these five parameters refer to Government Regulation Number 22 of 2021. The study results showed that increasing the concentration of palm oil mill effluent in the groundwater mixture caused a decrease in groundwater quality. The COD and BOD values ??in the mix with a concentration of 25% to 100% palm oil mill effluent exceeded the class 4 water quality standards set for plant irrigation, with a maximum COD reaching 1506 mg/L and a maximum BOD of 378 mg/L. The DO parameter decreased with increasing concentration of palm oil mill effluent, indicating a decrease in dissolved oxygen in the water. However, the pH and TSS values ??remained within the standard range, although TSS increased with increasing waste concentration. These results indicate that groundwater pollution by palm oil liquid waste significantly impacts the decline in water quality. Groundwater contaminated with palm oil mill effluent with a concentration of more than 25% is unsuitable for irrigation purposes (class 4) or for other higher water class categories. The percentage changes in BOD, COD, pH, and TSS values ??were positive, while the DO parameter experienced a percentage change with a negative value along with the increasing concentration of palm oil mill effluent.]]>
