INTRODUCTION 



This report evaluates the biological integrity, support of 

 aquatic life uses, and probable causes of impairment to those 

 uses in the Tongue River of southeastern Montana. The purpose of 

 this report is to provide information that will help the State of 

 Montana determine whether the Tongue River is water-quality 

 limited and in need of TMDLs , and to assess the effects of 

 discharges from coal-bed methane (CBM) test wells upstream. 



The federal Clean Water Act directs states to develop water 

 pollution control plans (Total Maximum Daily Loads or TMDLs) that 

 set limits on pollution loading to water-quality limited waters. 

 Water-quality limited waters are lakes and stream segments that 

 do not meet water-quality standards, that is, that do not fully 

 support their beneficial uses. The Clean Water Act and USEPA 

 regulations require each state to (1) identify waters that are 

 water-C[uality limited, (2) prioritize and target waters for 

 TMDLs, and (3) develop TMDL plans to attain and maintain water- 

 quality standards for all water-quality limited waters. 



This evaluation is also part of a study being conducted by 

 staff of the Montana Department of Environmental Quality (MDEQ) 

 to determine the chemical and biological effects of CBM well 

 discharges to streams in southeastern Montana. The discharged 

 groundwater originates from test wells that are being used to 

 dewater underlying coal beds for the purpose of determining the 

 capacity and economic feasibility of methane gas production. 



Evaluation of use support in this report is based on the 

 species composition and structure of periphyton (phytobenthos, 

 benthic algae) communities at 6 sites that were sampled on August 

 17-18, 2001. The periphyton community is a basic biological 

 component of all aquatic ecosystems. Periphyton accounts for 

 much of the primary production and biological diversity in 



