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

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

Water Balance Cover

Water Balance Cover Soil Moisture Storage

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

Regulatory Framework reducing infiltration. Per 30 TAC Section 330.457(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.

Brief History of WB Cover Guidance 1st Draft Guidance Released April, 2007 Presented at TCEQ Trade Fair - May, 2007 WB Cover Conference in Austin - April, 2010 Two Industry Stakeholder Meetings - 2010 2nd Draft Guidance Issued - January, 2011 Final Guidance (RG 494) - January, 2012 Presented at TCEQ Trade Fair - May, 2012 Water Balance Cover Study - 2013 to 2016 Report Issued - August, 2016 Revised RG 494 Issued - March, 2017

TCEQ RG-494

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.

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

Landfill Distribution vs. Rainfall

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

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

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

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

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

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

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

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.

Delineated Geoclimatic Regions for Texas with Average Year annual Precipitation Contours

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).

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).

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).

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

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

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

Links to Publications Dr. Khire’s Report: txswana.org/images/downloads/Water_Balance/txswana_water_balance_covers_khire_uncc_final_report.pdf RG-494: https://www.tceq.texas.gov/publications/rg/rg-494.html

Questions?