Mopac Intersections Project
North of Slaughter Lane to South of La Crosse Avenue
TxDOT -Travis County, TX
• Geologic inspection of karst features encountered during construction by a Professional Geologist (PG)
• Monitoring and directing void excavations
• Void survey and mapping
• Void inspection using down-hole camera in drill shafts
• Karst biological surveys for endangered species habitat by a USFWS Permitted Biologist
• Design and development of highly specialized void mitigation plans
• Report preparation and submittal of void mitigation package to the Texas Commission on Environmental Quality (TCEQ)
• Coordination with TCEQ, Barton Springs Edwards Aquifer District, and the City of Austin as needed
• Storm Water Pollution Plan Inspection (SW3P) monitoring and reporting
The Mopac Intersections Project is located in Austin, Texas and includes major improvements to the Slaughter Lane and La Crosse Avenue intersections. The site lies within the Barton Springs Segment of the Edwards Aquifer Recharge Zone and is known to have high potential for karst development, aquifer recharge, and endangered karst species habitat.
The design of the project included excavation of over 700,000 cubic yards of material to complete two underpasses and over 200 drill shafts for bridges and sound barriers. Through the course of these activities over 80 karst features were encountered on graded surfaces and with drill shafts. A licensed Professional Geologist (PG) and a USFWS Section 10(a)(1)(A) Permitted Biologist with aci environmental provided inspection for each void encountered during construction.
Several of the voids required extensive excavation with heavy machinery to ensure a stable environment for construction of the road way and to address public safety concerns. Given the unique characteristics of each void encountered, aci personnel worked closely with operators to direct safe and carefully executed feature excavation.
After excavations were complete, aci conducted surveys to a high degree of precision and developed cave maps to show the spatial relationship of the voids to the planned improvements. aci worked closely with TxDOT engineers to develop highly specialized and novel solutions for void closure that would best protect water quality and potential endangered species habitat while still addressing structural integrity and public safety.
In addition to work surrounding karst geology and biology, aci managed Storm Water Pollution Plan (SW3P) inspections and reporting for the project site. This included maintaining proper BMPs surrounding each karst feature and regulating any potential discharge to nearby waterways, Slaughter Creek and three associated tributaries. Management of stormwater during construction was critical to the success of the project as water recharge and habitat degradation was of utmost concern.
*aci was nominated for the TxDOT Environmental Achievement Award, based on the environmental excellence displayed through diligent and carefully considered work on this project.