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The Clean Water Act is the primary water quality legislation in the United States. The Act is designed to uphold the physical, chemical and biological integrity of the nations waters. In Virginia, benthic macroinvertebrates are the primary indicator used to assess biological integrity. When the biota of a given waterbody is deemed impaired, the TMDL process is initiated. The primary stressors on the biota are then determined and the necessary reductions to those stressors are calculated. These stressors can come from either point or non-point source pollution.

In this paper, the reference watershed approach for benthic TMDLs is examined. Since the stressors causing the benthic impairments may not have state-mandated water quality standards, the TMDL goal is sometimes not obvious. A reference watershed that does not have a benthic impairment is chosen for comparison and the TMDL goal in the impaired watershed is the stressor load in the area-adjusted reference watershed. What are differences in stressor load reductions when different reference watersheds or different land use sources are used? These questions will be evaluated for the benthically impaired Stroubles Creek, in Montgomery County, Virginia using four reference watersheds and two land use sources for comparison.