Statewide non-point-source pollution assessment methodology

We present a new methodology for performing Virginia's statewide, watershed -level non-point-source pollution assessment. The problems and inconsistenc ies inherent in previous methodologies were addressed and improved upon. Th e revised methodology utilizes geographic information system technology, a database management system, and computer modeling. Statewide land cover, so ils, and topographic digital data were used to develop input parameters for a simple nutrient and sediment loading model, resulting in an assessment b ased on estimated loadings for each of the predefined 493 hydrologic units in the state. The resulting model output includes runoff volume, sediment l oading, and dissolved and sediment-attached nitrogen and phosphorus. The es timated loads were used to rank the hydrologic units for potential non-poin t-source pollution and compared with rankings from a previous assessment. T he revised methodology is based on annual pollutant loadings, and no attemp ts were made to "weight" or subjectively impose importance to sources or co nstituents as with the previous methodology. The new methodology, resulting watershed priorities, and recommendations for further refinement are prese nted in this paper.