1. Water Balance Alternative Final Covers
May, 2017
Dwight C. Russell, P.E.
Municipal Solid Waste Permits Section
Waste Permits Division

2. Presentation Overview
What is a Water Balance Cover?
Regulatory Context
History of Water Balance Covers in Texas
Four Options in the Guideline

3. Water Balance Cover

4. Water Balance Cover Soil Moisture Storage

5. Advantages of Water Balance Covers
Over much of the state, a WB Cover can be constructed that will minimize percolation at less expense than the prescriptive cover in TCEQ rules
WB Covers provide a better medium for robust plant growth
WB Covers provide a bio-filtering mechanism for landfill gas
WB Covers have increased geotechnical stability

6. Regulatory Framework reducing infiltration.
Per 30 TAC Section (d), an Alternative Final Cover must demonstrate equivalency to the Prescriptive Cover in terms of:
reducing infiltration.
providing equivalent wind and water erosion resistance.
Authorization can be a new permit, permit amendment, or a permit modification.

7. Brief History of WB Cover Guidance
1st Draft Guidance Released April, 2007
Presented at TCEQ Trade Fair - May, 2007
WB Cover Conference in Austin - April, 2010
Two Industry Stakeholder Meetings
2nd Draft Guidance Issued - January, 2011
Final Guidance (RG 494) - January, 2012
Presented at TCEQ Trade Fair - May, 2012
Water Balance Cover Study to 2016
Report Issued - August, 2016
Revised RG 494 Issued - March, 2017

8. TCEQ RG-494

9. RG 494
This guideline is a living, breathing document that is based on currently available information and data. As new information comes forth through research, this document will be revised as appropriate.

10. Options for Requesting Water Balance Alternative Final Covers
Sites with ≤ 25 inches Average Annual Precipitation
Option 1. Statewide Design Table
Option 4. Modeling Using Site-Specific Data
Sites with > 25 inches Average Annual Precipitation
Option 2. Cover Performance Verification
Option 3. Model Calibration

11. Landfill Distribution vs. Rainfall

12. Permitting Option 4 Site Specific Modeling (≤25 Inches Average Annual Precipitation)
Initial
Site specific soil and weather data
Modeling description, input values and results
WB cover design
Cover construction QA/QC
Authorization issued for entire landfill or portion requested

13. Options for Requesting Water Balance Alternative Final Covers
Sites with ≤ 25 inches Average Annual Precipitation
Option 1. Statewide Design Table
Option 4. Modeling Using Site-Specific Data
Sites with > 25 inches Average Annual Precipitation
Modeling
Option 2. Cover Performance Verification Option
Option 3. Model Calibration Option

14. Permitting Option 2 Cover Performance Verification
Initial
Site specific soil and weather data
Modeling description, input values and results
WB cover design
Cover construction QA/QC – Verification Test Area
Authorization issued for entire landfill
Final
Construct Verification Test Area
Monitor Test Area for 3-5 years
Verify effectiveness of cover design
Determine outcome based on percolation results

15. Permitting Option 2 Cover Performance Verification
Measured Percolation
Action
≤8mm/yr
Design Accepted; Construction Authorized
>8mm - ≤ 12mm/yr
Modify Design Based on Model Recalibration; Construction Authorized
> 12mm/yr
Modify Design Based on Model Recalibration; Verify Design

16. Options for Requesting Water Balance Alternative Final Covers
Sites with ≤ 25 inches Average Annual Precipitation
Option 1. Statewide Design Table
Option 4. Modeling using site specific data
Sites with > 25 inches Average Annual Precipitation
Modeling
Option 2. Cover Performance Verification Option
Option 3. Model Calibration Option

17. Permitting Option 4 - Model Calibration
Initial
Site-specific soil and weather data
Modeling description, input values, and results
WB cover design
Calibration Test Plot construction QA/QC
Authorization issued for Calibration Test Plot
Final
Calibrate Model (≤ 4mm/yr) using Calibration Test Plot Data, site-specific soil and weather data
Cover construction QA/QC
Calibrated design approved for entire landfill

18. Options for Requesting Water Balance Alternative Final Covers
Sites with ≤ 25 inches Average Annual Precipitation
Option 1. Statewide Design Table
Option 4. Modeling Using Site Specific Data
Sites with > 25 inches Average Annual Precipitation
Modeling
Option 2. Cover Performance Verification Option
Option 3. Model Calibration Option

19. Permitting Option 1 Statewide Design Table Geoclimatic Design of Water Balance Covers For Municipal Solid Waste Landfills in Texas by Dr. Milind V. Khire, Ph.D., P.E.

20. Delineated Geoclimatic Regions for Texas with Average Year annual Precipitation Contours

21. Figure 1: Peak annual percolation predicted by UNSAT-H vs
Figure 1: Peak annual percolation predicted by UNSAT-H vs. thickness of storage layer for in-service storage layer hydraulic conductivity of 10-6 cm/s (Figure 18 in the Khire report).

22. Figure 2: Peak annual percolation predicted by UNSAT-H vs
Figure 2: Peak annual percolation predicted by UNSAT-H vs. thickness of storage layer for in-service storage layer hydraulic conductivity of 5 × 10-6 cm/s (Figure 19 in the Khire report).

23. Figure 3: Peak annual percolation predicted by UNSAT-H vs
Figure 3: Peak annual percolation predicted by UNSAT-H vs. thickness of storage layer for in-service storage layer hydraulic conductivity of 10-5 cm/s (Figure 20 in the Khire report).

24. Minimum Storage Layer Thickness for Bare Ground (ft)
Permitting Option 1 - Summary of minimum storage-layer thicknesses required to meet TCEQ criterion of 4 mm peak percolation (Table 8 in Khire report).
Geoclimatic Region
KAs-Built (cm/sec)
KIn-Service (cm/sec)
Minimum Storage Layer Thickness for Bare Ground (ft)
1-Childress
1.00E-08
1.00E-06
1 ft 0 in
5.00E-08
5.00E-06
1.00E-07
1.00E-05
4.50E-07
4.50E-05
1 ft 7 in
5.40E-05
2.70E-04
5 ft 8 in
2-Lubbock
10 ft
3-Del Rio
1 ft 3 in
1 ft 10 in
6 ft 2 in
4-Austin
1 ft 8 in
2 ft 7 in
3 ft 11 in
5-San Antonio
1 ft 11 in
2 ft 11 in
5 ft 10 in
6-Corpus Christi
2 ft 6 in
7-Dallas
3 ft 10 in
8 ft
8-Lufkin
3 ft 1 in
6 ft 0 in
9-Houston
10 ft 0 in

25. Minimum Storage Layer Thickness for Bare Ground (ft)
Permitting Option 1 - Summary of minimum storage-layer thicknesses required to meet TCEQ criterion of 4 mm peak percolation (Table 8 in the Khire report).
Geoclimatic Region
KAs-Built (cm/sec)
KIn-Service (cm/sec)
Minimum Storage Layer Thickness for Bare Ground (ft)
4-Austin
1.00E-08
1.00E-06
1 ft 8 in
5.00E-08
5.00E-06
2 ft 7 in
1.00E-07
1.00E-05
3 ft 11 in
5-San Antonio
1 ft 11 in
2 ft 11 in
5 ft 10 in

26. Permitting Option 1 Statewide Design Table
Initial
Borrow source soils are evaluated
Hydraulic conductivity and storage layer thickness is determined
WB cover design
Cover construction QA/QC
Authorization issued for entire landfill or portion requested

27. Links to Publications
Dr. Khire’s Report: txswana.org/images/downloads/Water_Balance/txswana_water_balance_covers_khire_uncc_final_report.pdf
RG-494:

28. Questions?