Date of Award


Degree Type


Degree Name

Master of Science (MS)


Civil and Environmental Engineering

Committee Chair(s)

Michael McFarland


Michael McFarland


David K. Stevens


Gilberto E. Urroz


Phosphorus Site Index (PSI) is a phosphorus transport assessment tool used to estimate the risk of P transport from soils. Various components, such as soil erosion, P fertilizer application rate, plant available P in soil, etc. that have an influence on P transport from a site, are weighted and given ratings, and a combination of these components are expressed as PSI. This study has considered two biosolids land application sites in Utah, which received biosolids amendments over time, to develop a specialized PSI for the state of Utah.

Phosphorus from land application of biosolids has been considered a potential risk to eutrophication. While EPA Part 503 Title 40 Code of Federal Regulation (CFR) regulations mandate certain application practices, a more accurate tool is necessary to estimate P losses from biosolids land application sites.

The PSI for the two biosolids land application sites in Utah was calculated and the validity of their weighting factors and loss ratings were established. Erosion-Productivity Impact Calculator (EPIC) model was used to simulate P transport over these sites to further determine the accuracy of PSI. While application of the P-Index is not currently a regulatory requirement in Utah, increasing public and regulatory concerns have led to development of P-Index charts in various states, which can be used to estimate the potential risk of phosphorus mobility and environmental impact. Based on the validated PSI model, a PSI worksheet was developed in an easy to use form, covering recommended best management practices and methods of preventing P transport from soils, based on ranking of the PSI values.


Publication made available electronically January 13, 2012.