Bioretention cells (e.g. rain gardens) are becoming increasingly popular as a Best Management Practice to lower concentrations of heavy metals in urban run-off. The Culver City Rain Garden (CCRG) was built to decrease heavy metal concentrations in Ballona Creek, Los Angeles, California. While mass loading from influent and outflow stormwater in this garden has been assessed, no research has been done on heavy metal concentrations or partitioning between soil fractions in the CCRG. This study analyzed soil fractions in CCRG soil to determine the amount of heavy metal partitioning and to elucidate mechanisms controlling heavy metal partitioning by soil fraction. A simulated run-off experiments was also conducted on CCRG soil and porewater was extracted to assess redox changes. Heavy metal (As, Cr, Cu, Ni, Pb, and Zn) partitioning in different soil fractions was analyzed using a sequential extraction procedure. This study revealed that the majority of heavy metals (83% +/- 7% of As, 54% +/- 14% of Cr, 82% +/- 6% of Cu, 87% +/- 5% of Ni, 66% +/- 16% of Pb, and 68% +/- 10% of Zn) in CCRG soil are in the reducible fraction (amorphous and mineral oxide associated). This study establishes a baseline for future studies to elucidate geochemical mechanisms involved in heavy metal sequestration in CCRG soil. Additionally, this study found that CCRG soil heavy metal concentrations are mostly below regulatory guidance, though Ni and Zn do exceed screening levels for Invertebrate, Avian, and Mammalian Health.