Performance of Engineered Barriers: Lessons Learned
Craig H. Benson, PhD, PE, NAE
Wisconsin Distinguished Professor University of Wisconsin‐Madison/CRESP 1415 Engineering Drive Madison, Wisconsin 53706 USA
(608) 262‐7242 [email protected] Barrier Systems for Waste Containment
Cover system Gas collection Groundwater monitoring well
Waste Native soil
GdtGroundwater Leachate Liner system collection system Challenges – Predicting the Future
? rty ee ? Prop
g
nn As‐Built ACAP Exhumations ? Analogs gineeri nn E
1 10 100 1000 Time (years) Conventional Resistive Covers with a Soil Barrier
Compacted Geosynthetic • Performance controlled Clay Clay Liner Cover (()GCL) Cover by saturated hydraulic conductivity of clay barrier, either natural compacted clay or Soil Soil geosynthetic clay liner
Waste • Install barrier to achieve Compacted Clay hydraulic conductivity goal and protect barrier GCL from damage that alters WtWaste hydraulic conductivity.
4 Conventional Resistive Covers with a Composite Barrier
Clay-GM GCL-GM • Performance controlled Composite Composite bttdhdliby saturated hydraulic conductivity of clay barrier and integrity of Soil Soil geomembrane. • Lifespan o f
Compacted Waste geomembrane controls Clay service life of cover.
Geomembrane GCL • Current thinking 500- (GM) Waste 1001500 yr. 5 Alternative Water Balance Covers
Monolithic Capillary Barrier Barrier • Performance controlled bttddby saturated and unsaturated hydraulic properties of cover soils. Fine Fine Textured • Physically and Textured Soil Soil bio log ica lly ac tive systems.
Coarse Soil • Properties affected by environment, Waste Waste “d“pedogenes i”is.” 6 Composite Liner
• Performance controlled by saturated hydraulic conductivity of clay barrier and integrity of geomembrane. • Lifespan of geomembrane controls service life of barrier. • Impact of LLW on GCLs and geomembranes
unknown. 7 1.5 mm LLDPE Textured GbGeomembrane
8 Geosynthetic Clay Liner
9 Focus for Today
• Covers -- hydraulic properties of soil barriers in conventiona l an d wa ter balance covers o Saturated hydraulic conductivity o Unsaturated hydraulic properties
• Liners – hydraulic properties of GCLs & service life of
geomembranes in LLW 10 Clay Barriers in Covers Factors affecting long-term performance include: • Cracks caused by wet-dry cycling • CkCracks cause dbfd by freeze- thaw cycling • Cracks caused by differential settlement • Biota intrusion • Long-term mineralogical change
11 Cracks
12 Field Cover Performance: ACAP Lysimeters
20
Root Interim LLDPE LLDPE Barrier Cover Soil Cutoff Cutoff Cover
Earthen Earthen Berm LLDPE Berm Percolation Geomembrane Existing Slope (>2%) Pipe Geocomposite Drain
13 Aerial view of completed test sections at Kiefer Landfill, Sacramento County, California.
14 Borehole Test – Monticello U Tailings Repository
15 Collecting Block Samples
16 Preparing Blocks for Hydraulic Properties Tests
Block sample Trimming roughly to take ring‐off
Placing the block sample Trimming to the pedestal size Field Site in Albany, GA 4000 250
3500 Precipitation spiration, (mm) nn 3000 Soil Wa Soil Dry Period Soil Water Storage 200 2500 rcolation Evapotra ter Storag ee
2000 ff, and P andff, e r Applied, oo ee 1500 (mm) 150 1000
tive Wat Evapotranspiration rface Run aa
Su 500 Percolation Runoff Cumul 0 100 4/1/00 10/20/00 5/11/01 11/30/01 6/20/02 1/9/03 7/31/03 18 Percolation constituted 8.6% of precipitation before drought, 29.3% afterwards. Field Hydraulic Conductivity Measurements on Clay Barrier - February 2004
Hydraulic Conductivity Test Kf/Ko (cm/s) As-Built 4.0x10-8 1.0 SDRI 2.0x10-4 5000 TSB - 1 5.2x10-5 1300 TSB - 2 3. 2x10-5 800 TSB - 3 3.1x10-3 77,500
19 Rock Armor Covers – Cheney Field Experiments
30 cm RkRiRock Riprap 15 cm Bedding Layer
45 cm Protection Layer
Compacted 45 cm Soil Layer (Rn Barrier)
Tailings ECAP Test Sections at Cheney Collecting Block Samples for Hydrologic Properties Evolution of Frost Protection Layer and Radon Barriers 2007‐13
Frost Protection Layer Radon Barrier 10-3 • Hydraulic conductivity of 10-4 frost protection ity (cm/s) vv 10-5 and radon barrier increased, 10-6 lic Conducti lic approx. 10-7 cm/s
-7 -6 10 as-built to 10
ated Hydrau cm/s (()10x) rr 10-8 Satu
-9 • Preliminary, more 10 FP As-Built FP 2013 RB As-Built RB 2013 testing currently being conducted. 23 Cheney Water Balance Data
1400 20 • Episodic Cheney (R) Percolation on, on, 1200 Cumulative percolation
15 indicative of 1000 On-Site R e (mm) apotrasnpirati Precipitation macro-structure in unoff and Pe and unoff vv gg 800 radon barrier and 10 Soil Water Storage 600 frost protection itation andE rcolation (mm Water Stora Water pp layer. 400
and Soil 5 On-Site Evapotranspiration ulative Preci ulative ) • Performance still
mm 200 Surface Runoff Cu excellent, avg. 0 0 10/31/07 11/9/08 11/20/09 11/30/10 12/11/11 12/20/12 12/31/13 percolation = 1.0 and28d 2.8 mm /y
24 Changes in Sat. Hydraulic Conductivity
10-4 (a) 1000:1 100:1 10:1 1:1 If no change, data
) -5 ss 10 would scatter (m/ si 10-6 In-Service around 1:1 line y, K rated
tt Hydraulic Conductivity Data coalesce into 10-7 band with K = 10‐7 vice Satu vice
onductivi s rr
CC ‐5 10-8 ‐ 10 cm/s ? In-Se Albany Monticello independent of
draulic draulic Altamont Omaha yy 10-9 Apple Valley Underwood H Boardman Polson initial Ks Cedar Rapids Sacramento Helena 10-10 10-10 10-9 10-8 10-7 10-6 10-5 10-4 As-Built Saturated Hydraulic Conductivity, K (m/s) sa Effect of Climate
100000 sa KK
/ Alterations in Ks si 10000 often assumed to atio, K be unique to drier RR 1000 climates. ductivity ductivity nn 100 Similar increases in Ks for humid and raulic Co raulic 10 sub‐humid climates.
Sat. Hyd 1 Humid and Sub-Humid Arid and Semi-Arid Climate 26 Caisson Lysimeters – Monticello, UT
1 m Fine Textured Bill Albright Soil
030.3 m Cobble & Soil 0.3 m Sand 0.3 m Clay Radon 27 Eric MacDonald Radon Barrier – Monticello, UT Roots seek out water in wet fine‐ grained soils, e.g., clay radon barriers, even at 1.6‐ 191.9 m depth Unsaturated Hydraulic Properties –Soil Water Characteristic Curve 0.50
In Service Soil becomes less dense (higher porosity 0.40 or saturated water tent nn As-Built contt)tent) and has 0.30 broader distribution
WaterCo of pore sizes. 0.20 Impact on water olumetric
VV storage and 0.10 percolation depends on site specific 0.00 0 1 2 3 4 5 6 conditions. 10 10 10 10 10 10 10 29 Matric Suction (kPa) Geosynthetic Clay Liners
• For low hydraulic Typical Cross-Cross-SectionSection conductivity, Na- bentonite granules must swell to from a gel (paste) .
• Gel must be maintained to retain low hydraulic Upper Granular Lower conductivity (~ 10-9 Geotextile Bentonite Geotextile cm/s) .
• If granules do not swell and form gel, higher hdhydrauli c cond ucti tiitvity (>10-9 cm/s). Hydraulic Conductivity of Exhumed GCLs
10-4
Lower K High er K • Strong relationship with -5 10 water content
(cm/s) 10-6 yy • Transition pp,oint lower, but sufficient water for 10-7 osmotic swell (> 50%) onductivit CC • Rapid and sufficient 10-8 hydration yield low Hydraulic 10-9 hydraulic conductivity
10-10 20 40 60 80 Exhumed Gravimetric Water Content (%) 31 Exhumed Water Content 250 )
%% 200 ontent (
CC 150 Composite GCL GCL-only Water Water
dd 100
Exhume 50
0 A B E-01 E-02 F-03 F-05 S D N O
Site Cover Exhumation at LLW Disposal Site in Southeastern USA
600 mm surface layer
30 cm sand drainage layer 1.5 mm geomembrane GCL 300 mm low hydraulic conductivity soil layer
Foundation layer
33
Hydraulic Conductivity of GCLs
Sample Water Content Hydraulic Conductivity (%) (cm/s) GCL1a 112.2 9.6x10‐10 GCL1c 115.0 8.6 x10‐10 GCL2a 110.4 9.5 x10‐10 GCL2c 119.6 7.0 x10‐10 GCL3a 102.6 8.6 x10‐10 GCL4a 129.4 9.0 x10‐10 GCL4b 151.5 8.6 x10‐10
37 Hydraulic Conductivity of Soil Barrier Gravimetric Hydraulic Sample Sampling Location Condition Water Content Conductivity (()%) (cm/s) Away from BS1 No cracks 15.2 2.2×10‐5 Distortion Away from Contains small BS2 16.0 151.5×10‐5 Distortion cracks Contains large Middle of BS3 crack, GCL ND 8.4×10‐8 Distortion overlay
Immediately BS4 No cracks 13.2 4.7×10‐5 Below Distortion Away from BS5 No cracks 14.0 1.1×10‐5 Distortion Contains large BS6 Top of Distortion 14.0 3.0×10‐4 crack Notes: ND = not determined. Specimens fragile due to cracks. 38 Composite Liner
• Performance controlled by saturated hydraulic conductivity of clay barrier and integrity of geomembrane. • Lifespan of geomembrane controls service life of barrier. • Impact of LLW on GCLs and geomembranes
unknown. 39 Accelerated Geomembrane Testing
• Immersed at 25, 50, 70, and 90 °C • Synthetic LLW leachate with (RSL) and without
(NRL) radionuclides 40 Leachates
Major Cations/Anions (mM) Trace Metals (mM) Ca 4 As 0.001 Al 0.03 Mg 6 Ba 0.002 Mn 0010.01 Na 7 Cu 0.0002 Ni 0.0003 K 0.7 Fe 0.04 Sr 0.02 Sulfate 7.5 Li 0.02 Zn 0.0005 Cl 8 Chemical Characteristics 5 mg/L Nitrate 1.5 TOC (mg/L) 8 surfactant and Alkalinity 3.5 ORP (mv) 120 3 mg Radionuclides pH 7.2 acetate U‐238 (µg/L) 1500 Ionic Strength (mM) 43.6 H‐3 (pCi/L) 120000 Ratio of monovalent to divalent cations (M1/2) 0.077 Tc‐99 (pCi/L) 800 (l(Kolsta d et al. 2004)
41 Antioxidant Depletion in Geomembranes
250 (a)
200 e (min) mm 150
RSL-25
Induction Ti 100 nn RSL- 50 RSL-70 RSL-90
Oxidatio 50
0 0 2 4 6 8 10121416 Time (()month)
42 Service Life Predictions • Antioxidant 1800 depletion in
1600 DI (Immersion Test) approx. 700 yr, NSL (Immersion Test) 1400 RSL (Immersion Test) first degradation RSL (Composite Liner) phase. e (years) 1200 mm
1000 • Actual lifespan
pletion Ti pletion longer; 800 Representative field temperature 15 °C induction & 600 polymer xidant De xidant oo 400 oxida tion Anti 200 phases, 1000-
0 1500 yr . 10 20 30 40 50 Temperature (°C) GCLs in Synthetic LLW Leachate
10-9 3
ity (m/s) ity (m/s) -10 vv 10 2 Conduciti cc 10-11 • CtilConventional btitbentonite GCLs 1 • Polymer‐modified bentonite GCLs
Hydrauli • Bentonite‐polymer composite GCLs
10-12 0 0 102030405060 Pore Volumes of Flow
44 Impact of Radionuclides
10-9 C1 • Essentially the
/s) C2 mm same hydraulic R1 R2 conductivity with -10 d toRSL ( 10 BPC ee 2x or without radionuclides in
ivity Expos leachate. tt 2x
-11 10 • Major cations ulic Conduc aa control swelling
Hydr and hydraulic 10-12 10-12 10-11 10-10 10-9 conductivity. Hydraulic Conductivity Exposed to NSL (m/s) 45 Impact of LLW Leachate on Hydra u lic Conducti vit y of GCLs
10-9 Open= GCL exposed to RSL Solid = GCL exposed t o NSL Hydraulic Conductivity Relative to DI Water 100 x (m/s) ee 10-10 • CtilConventional 10 x bentonite: ~ 100x 5 x
ity to Leachat to ity 2x2 x vv • Polymer‐modified
-11 10 C1 bentonite: ~ 10x ulic Conducti C2 aa R1 Hydr • Composite: ~ 2x R2 BPC
10-12 10-12 10-11 10-10 10-9 Hydraulic Conductivity to DI Water (m/s) 46 Conclusions: Soil Barriers & GCLs in Covers
•Soil barriers undergo pedogenesis, altering their hydraulic properties. Plan for this in design and account for long‐term properties in PA. •Impact of changes on performance highly site specific, from sublbstantial to insignificant. Avoid generalizations about impact. •Changes occur in all climates (not just arid), and occur at depth. Depth dependence is an issue requiring more study. 47 Conclusions: Soil Barriers & GCLs in Covers
•GCLs can maintain very low hydraulic conductivity in covers even with cation exchange if they are adequately hydrated initially and they are protected from desiccation. •GCLs and other geosynthetics can bdbridge distortion due to differential settlement.
48 Conclusions: Liners •Impact of LLW leachate on geomembranes and GCLs is due to primary cations and metals in solution. Radionuclides not important from perspective of degradation. • Geomembrane service life at least 700 yr, ppyrobably > 1000 yr when all three phases considered. • GCLs are more permeable in LLW leachates than to water and other more common leachates (e.g ., solid waste). Can address with polymer
modified bentonites. Account for in PA. 49