Droplet impacts on liquid pools are ubiquitous in daily life: thermal sprays, fuel injection, inkjet printing, raindrops on liquid reservoirs, and ocean sprays are all fundamentally droplet impacts. The post-coalescence mixing of impacted droplets with the liquid pool is critical to understanding the heat-mass transfer and chemical reaction rates. Impacts on shallow pools, with depths on the order of the droplet radius, form coherent 3D structures that are greatly affected by the inertial expansion and capillary retraction of the impact cavity. For water-water impacts, inertial and capillary effects dominate the ensuing flow phenomena. Experimental diagnostics include shadowgraphy, particle image velocimetry (PIV), and planar laser-induced fluorescence (LIF). Shadowgraphy captures the evolution of the impact cavity formed. Simultaneous LIF and shadowgraphy are used to contextualize the flow structures and droplet fluid transport with the cavity dynamics. Three impact regimes are identified based on the cavity geometry formed soon after coalescence. Simultaneous PIV and LIF characterize the vorticity fields and scalar mixing processes. From PIV data, vortices are identified, and the circulation and translation after coalescence are quantified. LIF images are used to quantify the radial concentration distribution of the droplet liquid over time. The concentration distribution over time is analyzed and shown to evolve with the cavity and vortex dynamics.