Abstract

 Section 303(d) of the United States Clean Water Act requires States to identify waters that are not supporting their designated use, and develop total maximum daily loads (TMDLs) for the constituent causing the impairment. Currently, over 20,000 water bodies nationwide have been listed as impaired. The number one cause of impairment on these 303(d) lists is sediment, responsible for over 6000 impairment listings.
The maximum daily load process is designed to define the maximum loading rate that will maintain compliance with water quality standards. Development of TMDLs for sediment impairment is difficult for many reasons. The primary reasons are:

• Many of the impairments caused by excess sediment (e.g. habitat destruction) are not covered by numeric water quality standards. The TMDL is a numeric quantity, and requires that the environmental endpoints be defined numerically. Theredore, sediment TMDL assessment requires specification of a numeric measure that reflects attainment with the designated use.
• Quantitative linkages between sediment loading and resulting environmental quality are poorly understood. As a result, it is difficult to determine the exact loading reductions required to meet desired environmental endpoints.

  Despite the above problems, a legal mandate exists requiring that these TMDLs be developed over a short period of time. This presentation will detail the problems that have been encountered in developing sediment TMDLs, and present the authors' experience in developing TMDLs for a wide range of sites nationwide. The results of recent research designed to address some of the problems discussed above will also be covered. The focus of this talk will be on "clean" sediments (as they are responsible for the great majority of impairments, although contaminated sediment TMDL examples will be included as well.