Development of ADOT Application Rate Guidelines for Winter Storm Management of Chemical Additives through an Ambient Monitoring System

The Arizona Department of Transportation (ADOT) is responsible for keeping state and federally owned/operated transportation corridors safe and operational during winter months when snow and ice accumulate on these roads. A common practice is the application of anti‐icing and deicing chemicals, primarily sodium chloride (salt). ADOT’s Winter Storm Management Operations Manual (WSMOM) presents guidelines for the application of anti‐icing and deicing chemical based on specific storm events and roadway conditions. Sodium and chloride can be dispersed to areas adjacent to roadways though melting snow and ice and by vehicle splash and spray. Upon reaching vegetation and soil, these compounds can negatively impact the environment. To evaluate the relationship between salt applications and potential impacts to soil and vegetation, data from winter storm management activities (frequency of application, quantity of salt applied, and adherence to ADOT WSMOM guidelines) were compared to sodium and chloride concentrations in soil and vegetation samples collected at varying distances from the roadway. Data collection and review included 16 sites along State Route 260 and U.S. Routes 180 and 191, all in ADOT’s Globe District. Analyses of soil and vegetation samples show that sodium concentrations are greatest nearest the roadway and decrease with increasing distance from the roadway. There is no evidence that sodium concentrations in the soil exceed levels considered tolerable for vegetation, nor is there a significant seasonal difference between fall readings and spring readings of sodium and chloride concentrations in soil and vegetation. Additionally, sodium concentrations in soil samples did not appear to have a statistically significant impact on the level of sodium in vegetation samples. Therefore, it cannot be concluded that sodium concentrations in soil are directly impacting sodium concentration in vegetation near the roadway. There is no evidence to support that ADOT should deviate from its current chemical application rate guidelines.