DEVELOPMENT OF A BIOLOGICAL CRITERION BASED TMDL FOR THE RED RIVER, NEW MEXICO

Under the Clean Water Act, a Total Maximum Daily Load (TMDL) regulation establishes the greatest loading or mass of pollutant(s) that can be introduced into a watercourse or stream reach on a daily basis without resulting in a violation of applicable state water quality standards. The objective of a TMDL is to allocate loads among all of the pollutant sources throughout the watershed or water course segment so that appropriate control measures can be implemented and water quality standards achieved.

The Red River watershed is an important tributary to the Rio Grande in Northern New Mexico, and is fed by melt water from winter snowpacks and summertime convective storms. A combination of natural and anthropogenic processes affect water quality in the Red River watershed. For example, natural adverse effects to aquatic resources appear to be associated with fine sediments and chemicals draining from the hydrothermal scars in the watershed. During significant runoff events, these geological features are eroded so that they release acidic (pH values of 2-3), metal laden water through extensive head cutting and down-gradient gully formation which liberates large masses of sediment. While many of these geologic features are natural in origin, some of the documented effects may have been magnified by anthropogenic activities, including logging, mineral exploration, and roads. Water quality standards for a cold water fishery (CWF) need to be attained in the Red River. The extent and cause of the impairment to the CWF is not fully known, therefore the specific standard that should be applied in the TMDL analysis was investigated. Because most direct water quality standards are currently being met, an indirect loading standard is proposed based on geochemical modeling and biological criteria. This paper reports on the development of the indirect standard.