Final Report for the Onion Creek Recharge Project Northern Hays County, Texas August 2011 Cover photo: Onion Creek and Antioch BMP after upgrade showing main vault, 36-inch diameter, 12-ft intake pipe for flow measurements, and 36-inch diameter, 32-ft long intake screen. Photo by Brian B. Hunt. i Prepared by the Barton Springs/Edwards Aquifer Conservation District in Cooperation with the Texas Commission on Environmental Quality and the U.S. Environmental Protection Agency The preparation of this report was financed in part through a grant from the U.S. Environmental Protection Agency through the Texas Commission on Environmental Quality Agreement No. 582-10-90499 Brian A. Smith, Ph.D., P.G., Principal Hydrogeologist, Aquifer Science Team Leader Brian B. Hunt, P.G., Senior Hydrogeologist Joseph Beery, Hydrogeologist Barton Springs/Edwards Aquifer Conservation District 1124 Regal Row Austin, Texas 78748 (512) 282-8441 [email protected] www.bseacd.org August 2011 ii Board of Directors of the Barton Springs/Edwards Aquifer Conservation District Mary Stone, Precinct 1, President Gary Franklin, Precinct 2, Vice President Craig Smith, Precinct 5, Secretary Jack Goodman, Precinct 4 Robert D. Larsen, Precinct 3 General Manager Kirk Holland, P.G. iii Acknowledgments The Barton Springs/Edwards Aquifer Conservation District thanks the U.S. Environmental Protection Agency and the Texas Commission on Environmental Quality for providing funds for a large portion of this project (Agreement No. 582-10-90499). We also express our appreciation to Don Rauschuber who provided engineering expertise for the project and Russell Park for his help with configuring the CWQMN system and other monitoring equipment. Centex Materials and Munoz Construction donated a considerable amount of material and labor for the work at Antioch and Munoz Construction served as the prime contractor for the project. Centex Materials provided access to the Antioch site through their property during installation of the second valve on the BMP. The City of Austin provided access to the CWQMN Low Water Dam site on the Onion Creek Management Unit. C&C Groundwater Services of Boerne, Texas drilled and helped install the multiport monitor well at Antioch. Alex S. Broun, P.G. provided geologic expertise with the subsurface geology of the multiport monitor well. District staff members who worked on the project were: Brian Smith- Project Manager Joe Beery- Field Supervisor Brian Hunt- Quality Assurance Officer Nathanael Banda- Data Manager Dana Wilson- Project Accountant Guy Rials- Field Assistant Julie Jenkins- Cave Specialist Kirk Holland- District General Manager Tammy Raymond- Administrative Assistant Shannon DeLong- Administrative Assistant iv TABLE OF CONTENTS Page Abstract .................................................................................................................................... 1-1 1. Introduction ....................................................................................................................... 1-1 1.1. Background ................................................................................................................. 1-3 1.1.1. Purpose and Scope of Project ......................................................................... 1-3 1.1.2. Previous Work: 1993-1998 Onion Creek Recharge Project .......................... 1-5 1.1.3. Hydrogeologic Setting .................................................................................... 1-7 1.1.3.1. Barton Springs Aquifer ................................................................... 1-8 1.1.3.2. Recharge .......................................................................................... 1-9 1.1.3.3. Groundwater Flow ......................................................................... 1-11 1.1.3.4. Water Levels and Storage .............................................................. 1-11 1.1.3.5. Geology of the Antioch BMP Vicinity .......................................... 1-12 1.1.3.6. Stormwater Contamination in Onion Creek .................................. 1-14 1.2. Education and Outreach ............................................................................................ 1-15 2. Methodology ..................................................................................................................... 2-1 2.1. QAPP ......................................................................................................................... 2-1 2.2. Continuous Water Quality Monitoring Network (WQMN) Sites .............................. 2-1 2.2.1. Antioch CWQMN Site ................................................................................... 2-2 2.2.2. Low Water Dam CWQMN Site ..................................................................... 2-2 2.3. Upgrade of Antioch BMP ........................................................................................... 2-3 2.4. Stormwater Sampling ................................................................................................. 2-4 2.5. Calculation of Contaminant Reduction ...................................................................... 2-4 2.6. Multiport Monitor Well .............................................................................................. 2-5 2.6.1. Installation of Multiport Monitor Well .......................................................... 2-7 2.6.2. Groundwater Sampling and Water-Level Measurements .............................. 2-9 3. Results of Sampling and Data Collection .......................................................................... 3-1 3.1. Sampling of Storm Events .......................................................................................... 3-1 3.1.1. Storm Event 1 ................................................................................................. 3-5 3.1.2. Storm Event 2 ................................................................................................. 3-5 3.1.3. Storm Event 3 ................................................................................................. 3-5 3.1.4. Storm Event 4 ................................................................................................. 3-6 3.1.5. Storm Event 5 ................................................................................................. 3-7 3.1.6. Storm Event 6 ................................................................................................. 3-7 3.2. Comparison of Storm Events ...................................................................................... 3-7 3.3. Contaminant Reduction from Operation of BMP ....................................................... 3-9 3.3.1. BMP Operation During Storm Event 3 .......................................................... 3-12 3.4. Results from Multiport Monitor Well ....................................................................... 3-14 3.4.1. Head Measurements ..................................................................................... 3-14 3.4.2. Multiport Monitor Well Sampling ............................................................... 3-15 3.4.3. Future Sampling and Aquifer Testing .......................................................... 3-15 4. Conclusions ........................................................................................................................ 4-1 5. References .......................................................................................................................... 5-1 v Appendices A. 3-D Model Summary .................................................................................................. A-1 B. Education and Outreach Activities ..............................................................................B-1 C. Quality Assurance Project Plan ...................................................................................C-1 D. As-Built Designs of Antioch Upgrade ........................................................................ D-1 E. Laboratory Analytical Results ..................................................................................... E-1 Figures Figure 1-1. Location map of the study area and a portion of the Edwards Aquifer ......... 1-2 Figure 1-2. Photograph of the entrance to Antioch Cave ................................................. 1-4 Figure 1-3. Photograph of the near-finished BMP at Antioch Cave ................................. 1-5 Figure 1-4. Aerial photographs of the Antioch Cave site ................................................. 1-6 Figure 1-5. Schematic cross section across Onion Creek ................................................. 1-7 Figure 1-6. Cross sections of study area generated by 3-D geologic model ................... 1-10 Figure 1-7. Regional potentiometric map along Onion Creek ........................................ 1-12 Figure 1-8. Surface geologic map and cross section generated by 3D geologic model . 1-13 Figure 1-9. Map of Antioch Cave showing plan and profile views ................................ 1-14 Figure 1-10. Flow in Onion Creek at the USGS Driftwood station ................................. 1-15 Figure 2-1. Installation of 2nd valve on Antioch BMP .................................................... 2-3 Figure 2-2. Schematic diagram of multiport monitor well components ........................... 2-6 Figure 2-3. Photograph of layout of multiport monitor well components ........................ 2-8 Figure 2-4. Multiport monitor well during a sampling event ..........................................