The study was based on environmental assessment of petrochemical wastewater parameters discharged to Eleme River. Three methods: physical, chemical and biological were employed for the assessment on the physiochemical parameters. Laboratory tests were done on the sample using FEPA set standard for industrial effluent water test. The data obtained from the laboratory tests, further assessment was performed to examine the impact of these parameters to the receiving water body with respect to FEPA standard for industrial wastewater discharge to the inland water. The result showed that some parameters; Biochemical Oxygen Demand (BOD), Total Suspended Solids (TSS), pH, Temperature and Total Dissolved Solid (TDS), TSS, pH, Temperature, and TDS of the wastewater exceeded the FEPA standard by 80%, 91%, 76%, 24%, and 71% respectively. The conceptual model used for the existing treatment plant in Eleme Petrochemical is inadequate and needs improvement. The paper presented a new model as a way forward to improve the quality of wastewater generate from Eleme Petrochemical. Therefore, a new treatment plant design calculations was carried out to modify the existing plant for optimum performance. Finally, the information obtained from this study should be useful tools for further assessment of petrochemical wastewater parameters even to other industrial wastewater in nature.