The effect of surfactant and ionic strength concentration on colloid transport through saturated or partially saturated media has typically been studied using breakthrough curves. In this study, we performed pore-scale observations in a small flow chamber to quantify colloids retained on the grain, air and liquid interfaces using a confocal microscope system and ImageJ image analysis software. Stacks of images were analyzed for colloid retention in tests in which the ionic strength and concentration of surfactant (nonionic Surfynol 485) were varied. Colloid retention primarily occurred at the thin film along the edge of meniscus where the air-water and water-solid (AW, WS) interfaces closely approach each other (also called the air-water meniscus-solid (AWmS) interface). The results show that colloid retention at the AWmS decreased with increasing concentrations of ionic strength. At the same time more colloids were attached to the sand grains, resulting in overall increased colloid retention with increasing ionic strength. We also observed that increasing the surfactant concentration reduced colloid retention at the AWmS interfaces due to decreased contact angle and surface tension. The results are consistent with the theory that capillary forces are mainly responsible for colloid retention at the AWmS interface.