Impairment Verification Monitoring in Eleven Texas Waterbodies: Step 1 for the Development of Successful and Cost Effective TMDLs

Rigorous validation of use impairments on 303(d) listed waterbodies is essential to the development of successful, cost effective TMDLs. Intensive water quality monitoring throughout the entire watershed is necessary to collect more complete data sets to verify the existence and extent of water quality concerns identified on the 303(d) list of impaired waterbodies. Such monitoring will: 1) Ensure that the impairment is not the result of a transient condition and 2) Determine the geographic extent of the impairment. This will allow for the prioritization of water quality concerns in planning TMDL projects.This study represents the first two years of a TMDL program sponsored project to address eleven aquatic life and four recreational use impairments in eleven waterbodies throughout the south central portion of Texas. These waterbodies were identified as impaired on the State's 1999 303(d) list. The objective of the initial phase of this project was to collect additional data to verify identified 303(d) listings and examine the spatial extent of the impairment. Chemical, physical and biological data were collected at thirty-two stations throughout the eleven watersheds over a two year period. Data collection activities in these waterbodies would result in one of four outcomes: 1) Removal from the 303(d) List, 2) An evaluation of applicable water quality standards (aquatic life use impairments only) 3) TMDL or 4) Additional monitoring to better characterize the impairment. Based upon 24-hour dissolved oxygen and biological data, five of the eleven waterbodies originally identified as having aquatic life use impairments were found to be attaining designated aquatic life uses. TMDLs are currently being planned to address aquatic life uses in another four of the waterbodies, and the remaining two waterbodies will need additional data collection. Based on the bacteriological data collected on the four waterbodies designated as impaired for contact recreation, three waterbodies will require a TMDL and additional data collection was necessary for the remaining stream.This intensive monitoring has provided vital information which has allowed the TMDL program to focus on TMDL development for truly impaired waterbodies. This effort has also prevented the expenditure of additional TMDL funds on waterbodies that would be delisted or subject to a water quality standards revision at a future date. Resources can now be effectively allocated to TMDL development for seven use impairments (as opposed to 15 use impairments) with the confidence that the problem will best be addressed through a TMDL.