In June 2019, South Coast AQMD (SCAQMD) reported higher levels of Hexavalent chromium or chromium 6 in an industrial part of West Rancho Dominguez (WRD), an unincorporated community in Los Angeles County (see Figure 1). SCAQMD conducted investigations to identify the source of these emissions and worked with facilities to reduce them.
At the beginning of the SCAQMD investigation, monitors found that levels of chromium 6 in the industrial area of WRD were 50 to 100 times higher than average levels in the Los Angeles Area. However, these levels have decreased substantially since 2019. Ambient chromium 6 levels have continued to show a downward trend during 2020-2021, with occasional elevated levels reported in the industrial area on certain dates due to equipment repairs, loss of power for emission control devices, and other malfunctions. While ambient air Hexavalent chromium levels near residential areas have been consistently lower than those seen near industrial sources, overall average levels remain above the regional range (0.04 to 0.06 ng/m3). Please see Figure 2 below.
AQMD's Hexavalent chromium monitoring efforts led to improvements in emissions controls and a permanent closure of one plating facility unable to achieve sufficient emission controls. These changes resulted in improvement in Hexavalent chromium levels. Since average Hexavalent chromium levels in the residential areas of West Rancho Dominguez have reached levels comparable to other parts of the Los Angeles region, SCAQMD has deemed it appropriate to discontinue their Hexavalent chromium monitoring efforts as of June, 2022. However, quarterly routine inspections of industrial operations will continue in order to keep Hexavalent chromium levels within an acceptable range.
Details about the SCAQMD investigation, including air monitoring data and enforcement actions can be found in West Rancho Dominguez Emissions Investigation page.
