The purpose of this research is to determine the presence of pesticide, chlorpyrifos in Pampanga River basin and to develop or modify existing model to make it useful in predicting concentration levels of micro contaminants along the river channel. Sampling is done within a period of one year to cover the entire dry and wet seasons. Method of analysis include the preparation of samples in accordance with the standard test available using GC-MS. The analyses were conducted at the National Sciences Research Institute- Research Analytical Services Laboratory. The widely acceptable water quality model (WASP8) provided by the USEPA is used with an added feature like Monte Carlo Program is incorporated in this model to predict future concentration results. Risk assessment is also added in the study where target/non target organisms are points of concern.