Modification of GLEAMS for modeling movement of organic contaminants from land-applied biosolids

Municipal biosolids are commonly applied to agricultural lands as fertilizer, but this also poses potential risks to groundwater and surface water quality from constituents that may be mobilized during storm events. In the present study, an existing model, Groundwater Loading Effects of Agricultural Management Systems (GLEAMS), is modified to predict the fate and transport of organic contaminants from land-applied biosolids, primarily via addition of a labile biosolids organic carbon phase distinct from soil organic carbon. While capable of simulating contaminant transport in runoff and via percolation, only the runoff portion of the model was able to be calibrated using existing experimental data, and showed good agreement with field runoff data for acetaminophen, ibuprofen, triclosan, triclocarban, and estrone, but substantially under-predicted concentrations for carbamazepine, androstenedione, and progesterone. The model is applied to various scenarios using varied chemical properties, application date in the arid west, and application method (i.e., surface spreading vs. incorporation). Chemicals with longer half-lives and lower K_OCs exhibited higher losses in runoff than chemicals with shorter half-lives and higher K_OCs. For short half-life chemicals (i.e., ≤100 days), application at the beginning of the dry season resulted in the lowest losses. However, for long half-life chemicals (∼1000 days) with high K_OC (10,000-100,000), application during the rainy season resulted in the lowest losses, because this caused organic carbon to be high during the period of highest runoff. While further work is necessary to calibrate the percolation and subsurface transport portion, the model can help predict environmental risk from land-application of biosolids, highlight gaps in our knowledge about how chemicals are mobilized and transported from biosolids, and help identify management practices that result in minimal impacts to water quality.