Hexavalent Chromium Concentrations In Urban Runoff, Soil Moisture And Groundwater In The Los Angeles Basin

Between 2000 and 2007 a water augmentation study was performed in the Los Angeles Basin to assess the potential impact from recharging groundwater with urban storm water runoff. Six background locations were selected to monitor storm water runoff, vadose zone soil moisture and underlying groundwater quality for a large suite of parameters including total chromium and hexavalent chromium (Cr⁶⁺). The sites selected represented industrial, commercial, residential and recreational land uses. Storm water runoff, soil moisture and groundwater were sampled over a seven year period. While Cr⁶⁺ in stormwater was generally less than 1 µg/L, soil moisture concentrations varied over several orders of magnitude spatially and temporally with concentrations well in excess of the current MCL (10 µg/L). Underlying groundwater showed varying degrees of Cr⁶⁺ impacts from ND to 10’s of µg/L. The potential sources of Cr⁶⁺ and it’s mobility in the vadose zone as well as the potential implications for locating groundwater augmentation facilities is examined.