UC Merced

Between the 1940s and the 1980s, 1,2,3-trichloropropane (TCP) was widely applied to agricultural soils as an impurity in soil fumigants to eliminate plant parasitic nematodes. TCP is a suspected human carcinogen that has subsequently leached into groundwater, contaminating numerous wells across North America, Europe, and Asia. In this dissertation, I investigated TCP contamination in groundwater through geospatial mapping and treatment analysis. First, I conducted a systematic review of available treatment technologies in peer-reviewed literature. I found that granular activated carbon (GAC), bioremediation, and chemical reduction using Zero Valent Zinc (ZVZ) are the most effective methods for reducing TCP levels in groundwater. However, the practicality of GAC technology is hindered by its low to moderate adsorption capacity which necessitates frequent media replacement. I also found that the global prevalence of TCP contamination in the hydrosphere needs increased monitoring and modeling. To address the dearth of monitoring data, I developed a predictive model for TCP contamination in California’s Central Valley, one of America’s most important agricultural regions. I used three decision tree machine-learning models to predict TCP contamination in groundwater using various explanatory variables. The Random Forest algorithm emerged as the top performer, with precipitation, redox state, and nitrate levels as the most important predictive variables. To estimate the scale of contamination in California, I performed a mass balance model to estimate that between 110,000 to 4.3 million kg of TCP have accumulated in the California subsurface due to historical fumigant applications. Next, I addressed the scarcity of data on point-of-use treatments and alternative carbon feedstocks for TCP removal. I found through lab experiments that pitcher point-of-use filters can reduce TCP levels by up to 99%. Thus, households can use these low-cost filters to reduce the risk of TCP exposure and improve the safety of their water supply. Regarding alternative carbon feedstocks, I performed a batch isotherm analysis of almond biochar. Almond biochar was less efficient compared to coconut shells and coal-based granular activated carbon sorbents. However, considering the lower energy costs of producing almond biochar and its abundance as a local agricultural byproduct, I recommend a Life Cycle Assessment to evaluate its sustainability. Finally, my dissertation concludes with a science policy analysis that recommends a federal maximum contaminant level for TCP for public health. In summary, my investigations yielded valuable results to guide TCP monitoring and treatment efforts and provide practical information and policy guidance to affected communities and decision-makers.