Martin Hill TM Void mitigation:

planning and construction

Presented at the BCP Infrastructure

Workshop

October 30, 2014

Sylvia R. Pope, P.G.

City of Austin, WPD, Environmental

Resources Management Division

Karst geohydrology

• Karst definition

– Karst refers to terrain that contains sinkholes, caves, sinking streams, and karren (bedrock sculpted by dissolution). Dissolution of rock, typically limestone or dolomite, forms these features.

• Edwards Group and Georgetown Formation

– Karst terrain that comprises the Recharge Zone of the Edwards Aquifer. Cave passages, fractures, void horizons transmit significant volumes of groundwater. Rapid recharge and travel time through the aquifer.

• Characteristics of formations that have lead to cave and sinkhole development

– Caves typically occur below contact with less soluble strata and along structural trends. Dolomitic strata may contain evaporite layers that are easily dissolved.

Balcones Fault Zone Edwards Aquifer Segments

Why protect voids?

• It’s required by rules and regulations.

• The goal of void mitigation is to preserve the function of the void while protecting and isolating it from infrastructure.

• Mitigating voids helps preserve mesocaverns that may harbor endangered karst invertebrate species.

• Protecting caves and karst features maintains the water quantity and quality recharging the Edwards Aquifer. We are the ultimate consumers of that water.

• Voids convey water to the aquifer or to springs, even if they appear dry when intercepted by trenching.

Infrastructure planning

• Where to look for information?

• When to contact agencies during planning process? – During initial route selection

• Whom to contact for more detailed information? – Austin Water Utility, Wildlands Conservation

Division, BCCP Permit Coordinator, Kimberlee Harvey at 512-972-1686

– Watershed Protection Dept., Environmental Resources Management Division geologists (Sylvia Pope, David Johns, Nico Hauwert, Scott Hiers) at 512-974-2550

What permits are required?

• Are BCCP infrastructure permits are required? – If the project is within Karst Zones 1 or 2 and the City of

Austin/Travis County’s 10(a) permit area; yes.

• What City of Austin permits apply to construction of infrastructure projects? – Either small project, site plan or general permit. Refer to the

Administrative Criteria Manual or contact the Development Assistance Center (DAC)

• Are there additional requirements from other agencies ? – TCEQ may require a Water Pollution Abatement Plan or

Organized Sewage Collection System Plan, if in the TCEQ-defined Recharge Zone

• When to contact the permitting agency? – At the project concept stage

What types of projects require a

BCCP infrastructure permit?

• Wastewater lines and infrastructure

• Water lines and infrastructure

• Power lines and transmission facilities

• Stormwater control structures

• Drilling projects for geological investigations

• Roadways

• Gas or fuel pipelines

• Cable TV and communication infrastructure

• Other infrastructure, not otherwise specified

Geological data – Project Summary

• Geotechnical boreholes per AWU criteria

• Geophysical studies in proximity to BCCP

cave cluster along project alignment

• Karst survey per COA and TCEQ

requirements

• Hydrogeological study of BCCP caves

along project alignment (more from Nico

Hauwert, next presentation)

Project specific void planning

• Borehole void protocol – Triggers, notification and mitigation protocol within

presumed hydrogeologic basin of BCCP caves. AWU Wildlands, BCCP program and WPD

– downhole video logging for biological survey

– Bait and trap for biological survey

– Borehole grouting protocol

• Trenching void protocol – Trench inspection by Texas P.G. – consultant

• Void mitigation protocol – Standard COA and TCEQ void mitigation or

determined by BCCP Infrastructure Coordinator?

– Cave-sized voids require engineering design of a mitigation strategy specific to the void

Borehole

void

Mitigation

may be

required as a

condition of

BCCP

Infrastructure

Permit. This

example is

for an LCRA

power pole

project.

Construction phase: Reporting Voids

• Void and Water Flow Mitigation Rule (LDC 25-8-281

(D), COA ECM 1.12.0 and Item No. 658S of the SSM)

requires that work stop and the void be reported to

the City of Austin

• Report the void to the COA inspector (general permit

or CIP or site/subdivision or environmental) and to

ERM Watershed Protection Dept. hydrogeologists

• TCEQ also has solution feature discovery

notification requirements. ALWAYS report voids to

the TCEQ, even if you have been told that it isn’t

necessary by a TCEQ staff member

Construction phase: Mitigating Voids

• Submit site plan correction to COA Watershed

Protection Dept. (WPD) (LDC 25-8-281 (D)) and

partner departments

• Submit mitigation plan to TCEQ per the solution

feature discovery requirements

• Coordinate void mitigation design with COA WPD

and TCEQ to minimize conflicts (i.e., concrete

specification, encasement material)

• Mitigation measures are installed after approval is

given

Other potential considerations for Void

Mitigation

• USFWS-permitted biologist for evaluating voids intercepted during construction

• Equipment and standby time for biological evaluations

• Licensed geologist (Texas P.G.) for inspecting trenches greater than five (5) feet deep and all other voids intercepted during construction activities

• Equipment and standby time for geological evaluations

• Engineer to prepare and submit void mitigation plans

• Provisions for an engineer to conduct structural analysis and develop a specific void mitigation for a cave-sized void

These expenses may not be incurred if you don’t intercept voids but

budgeting for them decreases delays.

Initial geotechnical

investigation

borehole BH-7 for

a project near the

Martin Hill TM

intercepted a void

within the

presumed

drainage basin of

Fossil Garden

Cave. Specific

protocol for

biological

investigation was

required.

Void 1

Voids 1, 3, 4 – minor features

Void 3

aperture

Void 4

Void 3

interior

Void 2 – safety considerations of

investigation

Void 2 – safety concerns for inspection,

mitigation review ??, TCEQ enforcement

Geophysical survey anomalies

over Void 5

Void 5 photos

Void 5 – Cave size. Structural analysis

required.

Void 5 photos of mitigation

Questions for ERM

geologists?

• Contact Sylvia Pope at: – 512-974-3429

– Email sylvia.pope@austintexas.gov

• Contact Nico Hauwert at: – 512-974-2148

– Email nico.hauwert@austintexas.gov

• Contact David Johns at: – 512-974-2781

– Email david.johns@austintexas.gov

• Contact Scott Hiers at: – 512-974-1916

– Email scott.hiers@austintexas.gov