OVERVIEW OF REGIONAL GEOLOGY AND HYDROGEOLOGY, AND SUBSURFACE INVESTIGATION METHODS:

CONSIDERATIONS FOR MSW LANDFILLS IN TEXAS

Presented by: Terry Virtue and Eric CleggWaste Permits Division

2018 TCEQ Environmental Trade Fair

Photograph from AGS Website (William R. Muehlberger)

AGENDATerry Virtue

1. Geology regions of Texas

a) Gulf Coast

b) Llano Uplift

c) North Central Texas

d) Panhandle

e) West Texas

2. Texas Aquifers

Eric Clegg1. MSW Geology Report

2. Subsurface Investigation

3. Interpretation of Field Data

photo from USGS.

LimestoneLimestone

MJJ

Clay

Gneiss

Sandstone

Granite

Volcanics

Sand

Siltstone

Shale

Sand Schist

GULF COAST

30 TAC 584(b)(4): 1,000 feet protected and 5,000 feet not protected.

Shrink/Swell Clays

330.547: Flooding

Shallow Groundwater

Channel

Sediments

Beach

Barrier IslandBay

photo from texascoastgeology.com

FAULTING AND SUBSIDENCE

Faulting caused by subsidence.

Groundwater withdrawal & recent subsidence.

200 foot buffer & ½ mile rule for active Faults: 30 TAC 330.555

Edwards Aquifer: 30 TAC 330.549 (Chapter 213).

Unstable areas are restricted according to 30 TAC 330.559.

Balcones Fault Zone Hidden Valley Fault scarp

LLANO UPLIFT

photos courtesy of Terry Virtue

Enchanted Rock

Town Mountain Granite

Packsaddle Schist

Lack of natural clays for liner and cover requirements.

Hard rock makes excavation difficult.

NORTH CENTRAL TEXAS

Pennsylvanian (blue), Permian (light blue) and Cretaceous rocks (greens) north of the Llano uplift.

Most landfills in impermeable limestones and shale.

Smithwick Formation

photo from Austin Geological Society website.

PANHANDLE

Caprock canyon photo from Caprock Canyon State Park website. Wink Sinkhole photo from beg.utexas.edu.

WEST TEXAS

Chisos Mountainsphoto from Brian Hunt, AGS

SEISMIC HAZARDS

Area >10% probability of >.10 g in 250 years

Seismic Impact Zones: 30 TAC 330.557

Seismic hazard map from USGS

FENCE DIAGRAMLack of clay for cover

and liner systems.

Deep groundwater beyond 200 feet depth in Quaternary Alluvium.

Landfills located mostly in alluvial deposits.

AQUIFER CONSIDERATIONS

Class I cell rules: 30 TAC 335.584(b)(1)

Taylor Clay

Terrace Deposits

GEOLOGY REQUIREMENTS FOR MSW FACILITIES

Includes: Description of regional geology,

faults and subsidence, and groundwater resources/regional aquifers from research

The results of a subsurface investigation that describes all borings logged using USCS descriptors.

Cross-sections prepared from the logs.

A narrative that describes the licensed professional's interpretations of the subsurface

GEOLOGY REPORT required by: 30 TAC §330.63(e) and §332.47(6)(B).

Photo courtesy of www.tourtexas.com

PRIMARY GEOLOGIC AND HYDROGEOLOGIC QUESTIONS TO BE ADDRESSEDA good permit application needs to:

Clearly define the uppermost aquifer, any underlying connected aquifers, and underlying aquitard (depths and thicknesses) in relation to the proposed landfill

Determine the direction of groundwater flow and any influence from lithology

Propose wells in the right places (Well spacing/ point of compliance (POC) vs. upgradient/background)

Determine if there is an uplift concern or if dewatering is required

THE SUBSURFACE INVESTIGATION STARTS WITH THE BORING PLAN. WHAT DOES A BORING PLAN REQUIRE?

Locations and depths of all proposed borings

The required number of borings per the table

All borings be at least 5 feet below the elevation of the deepest excavation (EDE) with a min. number of borings to a depth at least 30 feet below the EDE

Size of Area in Acres Number of Borings Min. No. of Borings 30 Ft below the EDE

5 or less 2‐4 2

5‐10 4‐6 3

10‐20 6‐10 5

20‐50 10‐15 7

50‐100 15‐20 7‐12

100‐150 20‐23 12‐13

150‐200 23‐26 13‐15

200‐250 26‐29 15‐16

250‐300 29‐32 16‐17

300‐350 32‐35 17‐18

350‐400 35‐38 18‐20

400‐450 38‐42 20‐21

450‐500 42‐44 21‐22

500‐550 44‐47 22‐24

550‐600 47‐50 24‐26

More than 600 Determined in consultation with the executive director

Note: Different for Arid Exempt (AE) landfills

EDE

Not the EDE

5’ > EDE

30’ > EDE

5’ > EDE

30’ > EDE

HOW DOES THE REGIONAL GEOLOGY AND AQUIFERS RELATE TO THE SUBSURFACE INVESTIGATION?

Regional geology will indicate most likely drilling method required.

Knowing the depth below grade and the thickness of a Texas Major or Minor Aquifer under your site can tell you whether they are shallow enough to be included in the subsurface investigation.

Edwards Aquifer recharge zone areas are prohibited from Type I landfills

DRILLING METHODS3 COMMON METHODS IN USE FOR ENVIRONMENTAL DRILLING

Hollow-Stem Auger Air/Mud Rotary Geoprobe/Direct Push

Courtesy of Keely and Boateng, 1987 Courtesy of geoprobe.com

METHOD COMPARISONMethod Advantages DisadvantagesHollow-Stem Auger (HSA) • Continuous sample collection

• Borehole walls can’t collapse in soft sediments

• Slow• Seams can get clogged in very

fine sands

Air/Mud Rotary • Can drill into hard bedrock• Provides blow counts to

determine sediment density (n-value)

• Slow• Boreholes can cave in while pipe is

out of the hole (Esp. with air)• Difficult to collect samples in

saturated zones

Geoprobe/Direct Push • Quick• Very mobile• Continuous sample collection• Also provide blow counts• Can use acetate sleeves to seal

& save cores

• Can’t drill through hard sediments/gravels/bedrock

• Typically can only drill to ~50’• Small 2” diameter borehole only

allows for small diameter wells

WHAT DOES THE FIELD GEOLOGIST DOCUMENT IN THE FIELD? They assess the core samples to determine and record

where breaks between different lithologies occur.

Use the Unified Soil Classification System (USCS) to describe the soils at set intervals (every 5’ to 10’) or whenever changes occur and record it on a boring log.

Keep track of:

drilling info (dates, times, location, rig type/model, size of borehole/augers);

depths (to water, bottom of hole, sample intervals, etc.); and

well materials used and depths to each component of wells, if constructed.

USCS CHART

USCS is useful for logging non-bedrock soils, first by overall grain size percentages, then gradation, plasticity, particle shape/roundness, moisture, density, color, etc.

Courtesy of W.F. McCollough

Gradation

Grain size distributionCOARSE-GRAINED DESCRIPTORS

COARSE-GRAINED DESCRIPTORS (CONT.)

Shape/RoundnessDegree of Compaction (using N-Value)

PlasticityDegree of Compaction (using N-Value)

FINE-GRAINED DESCRIPTORS

THEN THE FIELD DATA IS TURNED INTO A BORING LOG

THEN THE LOGS ARE TURNED INTO CROSS-SECTIONS

OTHER USES OF THE DATA…

Structure Contour Maps

Fence Diagrams

3D Computer Models

Courtesy of pubs.usgs.gov

Courtesy of British Geological Survey

World Journal of Environmental Engineering. Vol. 3, No. 3

THANK YOU!

Contact Information

Texas Commission on Environmental QualityP.O. Box 13087, Austin, Texas 78711

MSW Permits SectionTerry Virtue, P.G. Eric Clegg, P.G.

terance.virtue@tceq.texas.gov eric.clegg@tceq.texas.gov

512-239-3142 512-239-1270Photograph from Austin Geological Society website (Brian Hunt)