HEAVY METAL UPTAKE IN STORMWATER GARDENS (SPOKANE, WA)

Low impact development technology has become a viable resource in combating the increased amount of stormwater runoff in urban settings, and a key physical aspect of this is the bio-infiltration cells, or storm gardens. Stormwater samples were collected from several storm gardens located on a major arterial in Spokane, WA, and from an adjacent city park pond into which the treated stormwater is discharged. Stormwater samples were also collected on a parallel arterial that does not contain storm gardens. Water samples were analyzed for concentrations of heavy metals using an ICP-OES with a particular focus on zinc due to its impacts on the aquatic ecology of the Spokane River. Concentrations of trace metals and common cations showed spatial variation between locations with no observable patterns. For example, zinc concentrations ranged from 0.009 – 0.048 mg/L which are below the stormwater permit benchmark (0.117 mg/L). Magnesium concentrations ranged from 14.4 mg/L – 90.0 mg/L, and calcium concentrations ranged from 5.93 mg/L – 35.3 mg/L with the highest concentration being at the Cannon Hill pond (discharge site). Plant material will be compared between storm garden and non-storm garden flora in order to assess the degree of heavy metal uptake from the vegetation within the garden. Understanding the impacts these storm gardens have on the geochemical makeup of stormwater will play a crucial role in future discussions of stormwater mitigation and the implementation of low impact technology into city or county projects.