ENVIRONMENTAL FATE AND TRANSPORT OF DEICERS IN SOIL AND THEIR IMPLICATIONS ON BURIED PIPE

Mehdi Honarvar Nazari

doi:10.7273/000007050

Deicers are essential for managing snow and ice on pavements, enhancing road safety and mobility cost-effectively. However, the hidden costs or risks associated with deicer use, particularly their environmental impact, are not well understood. Continuous use of deicers can lead to environmental contamination, affecting soil, water, and the overall ecosystem. Chloride-based deicers (road salts), in particular, are concerning due to their high mobility, water solubility, and non-degradable nature, which allows them to rapidly migrate in the environment and accumulate toxic effects over time. Due to its water solubility and corrosive nature, salt can significantly threaten the service life of infrastructure, particularly underground pipes. A study by the American Water Works Association (AWWA) in 2012 estimated that upgrading aging water distribution systems would cost US water utilities over $1 trillion in the next 25 years. Approximately 54% of this expense would be related to replacing corroded pipes. The fundamental question is how environmental links establish the interdependency between the water network and the road network. To achieve a quantitative understanding of these relationships, this research employed a deterministic model (e.g., Ogata-Banks model) to predict the fate and transport of two commercial deicers and an innovative eco-friendly deicer in roadway soil. Additionally, a stochastic model (e.g., Weibull model) was used to assess the service life of buried pipes under external corrosion, considering variations in soil pore solution composition. Chapter one of this dissertation summarizes relevant data from recent literature and provides a state-of-the-art review of the latest findings regarding the adverse effects of deicers on surface water and groundwater, as well as their toxicological impacts on aquatic species and human health. Additionally, it discusses knowledge gaps and identifies areas where future research is most needed. In chapter two, the performance and impacts of several innovative agro-based deicers, along with a traditional chloride-based deicer (salt brine) and a commercial bio-based deicer (beet juice blend), were evaluated. A statistical design of experiments (central composite design) was employed to develop deicers consisting of cost-competitive chemicals such as agro-based compounds (e.g., Concord grape fiber), glycerin, sodium chloride, sodium metasilicate, and sodium formate. The following experimentally obtained parameters were examined as a function of the formulation design: ice-melting capacity at −3.9°C, splitting strength of Portland cement mortar (PCM) samples after 10 freeze-thaw/deicer cycles, corrosivity of C1010 carbon steel after 24-hour immersion in deicer, and the impact of deicer on asphalt binder. One viable formula, identified as the “best performer,” was tested for pH, chemical oxygen demand (COD), biological oxygen demand (BOD), DSC thermograms, and the friction of asphalt pavement treated by the anti-icing formulation (compared to 23 wt.% NaCl and a sugar beet blend) at −3.9°C after being applied at 30 gallons per lane mile (1 hour after simulated trafficking and plowing). Laboratory data provided insights into the selection and formulation of innovative agro-based snow and ice control chemicals that can significantly reduce the costs of winter maintenance operations. In chapter three, the fate and transport of three types of deicers in long and short soil columns were studied. In this regard, the long soil columns had three effective lengths: 60 cm, 90 cm, and 120 cm. The effective length of the short columns was 20 cm. Three types of deicers were used in this chapter: diluted 30% MgCl2, diluted 23% NaCl, and diluted BP-4. The leachates from these columns were collected and further analyzed. Finally, a deterministic model was applied to fit the results of short soil columns experiments. Chapter four represents the corrosion behavior of ASTM A1008 CS Type B carbon steel (C1008), ASTM A48 class 35 grey cast iron (GCCL35), and ASTM A536 65-45-12 ductile cast iron (Ductile(65-45-12)) in the simulated soil solution in the presence and absence of beetroot juice (briefly beet juice), a bio-derived additive. Two types of deicers including 23% NaCl and 30% MgCl2 at different dilution ratios (1:30 and 1:90) were added to the test media to simulate the practical cases of buried pipes adjacent to roadways. In chapter five, the effects of the simulated soil solution associated with different applied deicers, pipe materials, and various ion concentrations in the simulated soil solution were studied. The Weibull distribution was successfully used to study the service life of three groups of pipes ‒ C1008, DC65-45-12, and GCCL30 ‒ exposed to wet/dry cycles in corrosive media. These media consisted of three groups of simulated leachate from soil columns subjected to diluted 30% MgCl2, diluted 23% NaCl, and diluted BP-4 deicers. Chapter six presents comprehensive conclusions from all the chapters in this dissertation.

ENVIRONMENTAL FATE AND TRANSPORT OF DEICERS IN SOIL AND THEIR IMPLICATIONS ON BURIED PIPE

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