ABSTRACT: In this study research methods are assessed to determine the spatial distribution of petroleum hydrocarboncontamination in the coastal aquifers and to develop a groundwater flow and transport model that can be usedto evaluate the level of natural attenuation that has occurred. The stages of this study include: 1) preliminaryassessment and conceptual model including hydrogeologic characteristics of the site, the history of the site, and anypast or current remedial activities, 2) field and laboratory investigations including soil and groundwater samplingtechniques such as soil borings, multi-level monitoring well installation, aquifer tests and water quality sampling.Parameters to be measured, their measurement methods and use of these data should be explained in detail, 3)physical and geochemical characterization of the study area with the results of the field and laboratory investigations,4) development of the groundwater model with selected software, 5) evaluation of monitored natural attenuationaccording to primary and secondary lines of evidence established during the investigation. The primary linesof evidence, which is a stable or shrinking plume rather than an expanding plume, will be the benzene, toluene,ethylbenzene and xylene (BTEX) contour maps prepared as a result of the groundwater sampling. Secondary linesof evidence, which include geochemical data that serve as indicators of naturally occurring biodegradation andestimates of natural attenuation rates, will be based on electron acceptor/reduction product concentrations measuredwithin the BTEX plume. The results of the groundwater modeling are used to help decide whether the monitorednatural attenuation process results in BTEX contaminant levels declining to acceptable levels within a specified time.If projections of contaminated levels indicate that natural attenuation is not enough for remediation, then additionalremedial alternatives can be recommended for further investigation