Impairment Verification Monitoring—Volume 1: Physical, and Chemical Components Segment 1427 Onion Creek Prepared for Total Maximum Daily Load Program Texas Commission on Environmental Quality P.O. Box 13087, MC - 150 Austin, Texas 78711-3087 By James S. Bonner, Ph.D., Principal Investigator F.J. Kelly, M. Beaman and R. Wilkinson Conrad Blucher Institute for Surveying and Science Texas A&M University-Corpus Christi 6300 Ocean Drive Corpus Christi, Texas 78412 Under Texas Engineering Experiment Station Project No. 32525-60880 CC Texas Commission on Environmental Quality Contract No.582-4-58897, Amendment 1 Questions concerning this quality assurance project plan should be directed to: Jim Bonner, Ph.D., P.E., Executive Director Conrad Blucher Institute for Surveying and Science Texas A&M University-Corpus Christi 6300 Ocean Drive Corpus Christi, Texas 78412-5503 (361) 825-2646 [email protected] Impairment Verification Monitoring—Volume 1: Physical, and Chemical Components Segment 1427 Onion Creek EXECUTIVE SUMMARY This report describes the water quality data collected on Onion Creek (Segment 1427) during the three-year period from 2002 through 2004. It has been prepared for the Texas Commission on Environmental Quality (TCEQ) by the Conrad Blucher Institute for Surveying and Science (CBI) at Texas A&M University-Corpus Christi under an inter-agency contract between the TCEQ and the Texas Engineering Experiment Station. Onion Creek (Segment 1427) in the Colorado River Basin originates in extreme eastern Blanco County, Texas. It flows 78 miles eastward through Hays County into the Colorado River in eastern Travis County, southeast of Austin. The watershed includes the cities of Dripping Springs, Buda, and extreme southeastern Austin. The stream is fed by natural springs and the watershed represents a significant recharge feature for the Edwards Aquifer. Major land uses in this watershed include agriculture and residential. Onion Creek was included on the 2000 State of Texas Clean Water Act 303(d) list as impaired due to concentrations of dissolved oxygen below criteria associated with a high aquatic life use. Volume 1 presents the water quality data, including TCEQ water quality criteria, for 24-hr dissolved oxygen, pH, water temperature, conductivity, and nutrients. Basic statistics are provided for each water quality constituent by station and sampling type. Volume 2, prepared by project partner Ecological Communications Corporation (ECOMM 2004), describes the biological sampling and analyses conducted by ECOMM. Water quality assessment has evolved since the 1999 305(b) Water Quality Inventory with the introduction of new methodologies. These include the development of hydrologically unique assessment units on Onion Creek, the use of the binomial approach for analysis, and the use of 24-hour dissolved oxygen measurements. Each of the five impairment verification monitoring stations had 14 sampling events. For the 24-hour average values of dissolved oxygen, Assessment Units 1 and 2 had only one exceedance each, and Assessment Units 3 and 4 had two each. However, the mean of the 24-hour average dissolved oxygen values was above 5 mg/L at all stations. For the 24-hour minimum values, Assessment Units 1 and 4 had one exceedance each, and Assessment Units 2 and 3 had none. The mean of the 24-hour minimum dissolved oxygen values was above 3 mg/L at all stations. Routine water samples yielded no significant levels of nutrient impairment in the segment. Routine water samples collected exhibit nutrient levels well below established screening values. Based upon the 24-hour dissolved oxygen data collected for this study, Onion Creek appears to be meeting the high aquatic life use and should be removed from the State’s list of impaired waters. 1 Impairment Verification Monitoring—Volume 1: Physical, and Chemical Components Segment 1427 Onion Creek (BLANK PAGE) 2 Impairment Verification Monitoring—Volume 1: Physical, and Chemical Components Segment 1427 Onion Creek INTRODUCTION Onion Creek (Segment 1427) in the Colorado River basin originates in extreme eastern Blanco County, Texas. It flows 78 miles eastward through Hays County into the Colorado River in eastern Travis County, southeast of Austin (Figure 1). The watershed includes the cities of Dripping Springs, Buda, and extreme southeastern Austin. The stream is fed by natural springs, and the watershed represents a significant recharge feature for the Edwards Aquifer. Based upon data from the early 1990s, major land uses in this watershed include agriculture and residential (Figure 2). More recent land use data provided by the City of Austin indicates that single family residential now represent more than 50% of the total area of the watershed and could now be considered the single major land use. The aquatic life use in Onion Creek was identified as impaired in the 2000 Water Quality Inventory (also known as the Clean Water Act Section 305(b) report) (TNRCC 2002a). The assessment found that some dissolved oxygen concentration samples in the lower 10 miles of the stream were lower than the criterion established to assure optimum conditions for aquatic life. During the assessment process for the 2002 Water Quality Inventory, the TCEQ determined that there was an insufficient number of 24-hour dissolved oxygen samples collected since 2000 to allow for a reassessment of standards attainment, and the TCEQ initiated a project to verify the impairment through the collection of additional physical, chemical, and biological data. In 2001, TCEQ contracted the services of the South Texas Environmental Institute at Texas A&M University-Kingsville to lead this effort, together with the Conrad Blucher Institute for Surveying and Science (CBI) at Texas A&M University-Corpus Christi and Ecological Communications Corporations (ECOMM), to design and implement a monitoring plan to verify the impairment and then take the necessary actions to restore uses where necessary. Sampling activities began in August of 2002 to provide the TCEQ with 24-hour dissolved oxygen, physical and chemical analyses, and biological assessments at five stations along this segment. In September of 2003 CBI took over as the contract lead on the project under a contract between the TCEQ and the Texas Engineering Experiment Station (TEES) and continued the data collection on Segment 1427 in collaboration with ECOMM. The information provided in this report is included in two volumes. Volume 1 describes the 2002 through 2004 physical and chemical data and analyses for water quality on Segment 1427. These data are presented in tabular format and are statistically summarized. It includes 24-hr dissolved oxygen (DO) as compared to TCEQ water quality criteria, pH, water temperature, conductivity, and nutrient data. Basic statistics are also provided for each constituent by station and sampling type. Volume 2, prepared by ECOMM (2004), describes the biological sampling, data and analyses conducted by ECOMM for Onion Creek. 3 Impairment Verification Monitoring—Volume 1: Physical, and Chemical Components Segment 1427 Onion Creek Figure 1. Map showing Station Locations and the reach of each Assessment Unit. 4 Impairment Verification Monitoring—Volume 1: Physical, and Chemical Components Segment 1427 Onion Creek Figure 2. Land Use Map for Segment 1427 of the Onion Creek Watershed (USGS, 1992). 5 Impairment Verification Monitoring—Volume 1: Physical, and Chemical Components Segment 1427 Onion Creek HISTORICAL REVIEW Onion Creek was originally included on the 1999 303(d) as partially supporting the aquatic life use due to depressed dissolved oxygen levels in the lower 10 miles of the stream. The contact recreation, public water supply and general uses were fully supported; fish consumption was not assessed due to insufficient data. The results of the assessment of samples for subsequent 2000 and 2002 Water Quality Inventories are given in Table 1 and Table 2, respectively. A plot of all available historical grab samples of dissolved oxygen for the same period as the 2000 303(d) evaluation period (06/01/94 - 05/31/99) is shown in Figure 3. Of the 267 samples, 15 exceed the 5-mg/L criterion indicated by the heavy line. Because an insufficient number of 24-hour dissolved oxygen values were available in 2002 to determine if the criterion was supported, this segment was identified as not meeting the standard for dissolved oxygen until sufficient 24-hour measurements were available to demonstrate support. Table 3 lists all TCEQ Monitoring Stations on this segment, and Figures 4-8 are photographs of the five Monitoring Stations used in the impairment verification monitoring for 2002 through 2004. The Station specific uses and criteria for Onion Creek, as identified in the 2002 Texas Surface Water Quality Standards (TNRCC 2002), are as follows: • Aquatic Life Use • Contact Recreation Use • General Use • Fish Consumption Use • Public Water Supply Use. Table 1. Assessment Samples for Segment 1427 Onion Creek for the 2000 Inventory Segment Uses or Samples Rec Year Method Exceeded Percentage Mean Location ID Criteria Taken HIGH DISSOLVED 10 MILES WEST OF BUDA TO 1 1427 2000 AQUATIC 0 OXYGEN END OF SEGMENT LIFE HIGH COLORADO RIVER TO DISSOLVED 2 1427 2000 AQUATIC 42 8 19 MCKINNEY FALLS STATE OXYGEN LIFE PARK HIGH MCKINNEY FALLS STATE DISSOLVED 3 1427 2000 AQUATIC 19 0 0 PARK TO 10 MILES WEST OF OXYGEN LIFE BUDA 6 Impairment Verification Monitoring—Volume 1: Physical, and Chemical Components Segment 1427 Onion Creek Table 2. Assessment Samples for