Geophysical Methods for Screening and Investigating Utility Waste Landfill Sites in Karst Terrain

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1 Geophysical Methods for Screening and Investigating Utility Waste Landfill Sites in Karst Terrain Gary Pendergrass, PE, RG, F.NSPE Principal Geological Engineer Kansas City Geotechnical Conference 2017 Overland Park, KS April 20, 2017

2 U.S. Karst Map

3 Primary Focus of UWL Siting in Karst Structural Stability Groundwater Monitoring

$Groundwater flow occurs along fractures (secondary permeability).$

4 Formation of Karst Limestone has no appreciable primary permeability. Groundwater flow occurs along fractures (secondary permeability). Dissolution of limestone is a surface phenomenon.

5 Formation of Karst As dissolution of limestone progresses along vertical fractures, the fractures widen.

6 Formation of Karst Just as differing colors of strata indicate differing depositional environments and differing chemical constituents, certain stratigraphic zones can be preferentially soluble due to differing CaCO 3 content.

$Formation of Karst This roadcut illustrates how preferential groundwater flow along horizontal fractures$

7 Formation of Karst This roadcut illustrates how preferential groundwater flow along horizontal fractures and preferential dissolution of limestone along bedding planes can produce horizontal solution cavities.

$Formation of Karst Dissolution along vertical fractures/joints and dissolution along$

8 Formation of Karst Dissolution along vertical fractures/joints and dissolution along preferential bedding planes produce the vertical and horizontal components of karst systems.

9 Modes of Sinkhole Formation Solutional Sinkholes Collapse Sinkholes

10 Formation of Solutional Sinkholes Solutional sinkholes tend to be relatively stable. Many hold water and are utilized as farm ponds. Easily identified and avoided in landfill siting.

11 Formation of a Collapse Sinkhole

Formation of Collapse Sinkholes Discrete, isolated

12 Formation of Collapse Sinkholes Discrete, isolated features that originate at the soil - solution cavity interface within a joint. Surrounding soil is typically undisturbed and intact. Basically a hole in the soil that propagates toward the surface. Typically triggered by a change in soil moisture content.

13 Stabilization of Collapse Sinkholes Locations susceptible to sinkhole collapse will be identified and stabilized prior to UWL development

14 Stabilization of Collapse Sinkholes

15 Groundwater Monitoring in Karst Limestone has very low primary permeability. Groundwater moves preferentially through joints and fractures.

16 Groundwater Monitoring in Karst A monitoring well sited in massive limestone would likely be a dry hole.

17 Groundwater Monitoring in Karst A monitoring well sited near a joint or fracture trend would more likely capture the groundwater moving through the system.

18 Goals in UWL Siting Identify areas susceptible to collapse sinkhole formation and pre-emptively stabilize There are no perfect sites, but all can be engineered Identify groundwater flow pathways beneath prospective sites and determine if site can be effectively monitored

19 Characteristics of Karst Karst is not swiss cheese. Karst is a very well-organized, logical system which develops and behaves in a very well-organized, logical fashion Karst processes are well understood Karst can be accurately characterized using appropriate investigative techniques.

20 Use of Geophysical Techniques for Karst Investigations Electrical Resistivity Tomography (ERT) ERT measures the electrical resistivity of earth materials ERT also provides an indication of moisture content

21 Use of Geophysical Techniques for Karst Investigations Multi-channel Analysis of Surface Waves (MASW) MASW indicates the nature and strength of earth materials MASW works very well in combination with ERT Top Rock ~52 feet

22 Elements of UWL Preliminary Site Screening and Investigation Review and compilation of existing site data Establishment of a 3D GIS model Site reconnaissance to delineate existing surficial karst features ERT screening survey (traverses on 100-foot centers, 100-foot depth) MASW soundings on 400-foot grid Confirmatory drilling & coring Development of a comprehensive site model Evaluation of prospective UWL sites Selection of a preferred UWL site

23 Site Reconnaissance Entire area of investigation was walked and inspected by GeoEngineers geologists in a systematic fashion. Distinct surficial karst features identified. Features mapped by walking the rims with ipad linked to GPS. Photo log/descriptions keyed to map numbers. Locations to be surveyed by licensed land surveyor. Suspected karst features those which were simple closed depressions (no visible eye) or altered (filled with rock, etc.) are further evaluated by comparison to closest ERT profiles.

24 Site Reconnaissance

25 Preliminary Geophysical Investigation

26 Preliminary Geophysical Investigation

27 Multi-channel Analysis of Surface Waves

28 Multi-channel Analysis of Surface Waves

29 Representative ERT Profile

30 Representative ERT Profile

31 Interpreted Joint Sets Karst Cultural Drainage

32 Schematic Cross-section

33 3D GIS Database/Model

34 3D GIS Database/Model

35 3D GIS Database/Model

36 3D GIS Database/Model

37 Preliminary Site Investigation Conclusions A stable utility waste landfill foundation can be ensured by detailed characterization of the subsurface, identification and proactive mitigation of potentially unstable areas, and appropriate landfill design which provides for stabilization of moisture content, stormwater diversion, and groundwater control A groundwater monitoring system which effectively monitors the uppermost continuous aquifer can be sited and installed on the basis of detailed ERT surveys, focused drilling/coring, and hydrologic testing

38 Elements of a Detailed Geophysical Investigation ERT survey (traverses on 20-foot centers, 160-foot depth) Processing of 3D ERT data MASW soundings on 200-foot grid Confirmatory drilling & coring Development of a comprehensive 3D GIS site model

39 ERT

40 Site Mapping

41 Top of Bedrock Map

42 Site 1 Horizontal Slices

43 3D ERT Model

44 3D ERT Model

45 3D GIS Modeling

46 USEPA Coal Combustion Residuals Rule On April 17, 2015, USEPA finalized the CCR Rule Response to TVA Kingston Plant CCR release in December 2008 The rule established requirements for disposal of CCR in utility waste landfills (UWLs) and surface impoundments.

47 Location Restrictions for Utility Waste Landfills The rule establishes five location restrictions to ensure UWLs are properly sited. Placement above uppermost aquifer (new units) Wetlands (new units) Fault Areas (new units) Seismic Impact Zones (new units) Unstable Areas (new and existing) The rule requires a qualified Professional Engineer (PE) to certify that the technical requirements of the rule are being met. Existing UWLs must be certified with respect to unstable areas by October 17, 2018.

48 U.S. Karst Map

49 Geophysical Investigation GeoEngineers has developed techniques to produce high resolution 3D imagery of UWLs using Electrical Resistivity Tomography (ERT) and Multi-Channel Analysis of Surface Waves (MASW).

50 Geophysical Investigation Marine ERT can be utilized to image beneath landfill ponds and closed surface impoundments

51 What we expect to see Higher resistivity (dryer) materials beneath the liner. Horizontal stratification of materials within the fill material. Karst features (sinkholes) would be represented as vertical anomalies.

52 What we expect to see Differential settlement would be represented by lateral offset in resistivity pattern. Lower resistivity anomalies at landfill toe (drainage anomalies). Lower resistivity linear anomalies representing solution-widened joints or fracture trends

53 UWL 3D ERT Profile

54 UWL Groundwater Monitoring System Proposed monitoring well location

55 Summary Geophysical techniques provide a sound basis, rationale and justification for UWL certification and provide the scientific documentation necessary for public acceptance.

56 Questions? Gary J. Pendergrass, PE, RG, F.NSPE Principal GeoEngineers, Inc S. Delaware Avenue Springfield, MO

CCR Rule Compliance: Innovative Use of Geophysics to Certify Landfill Stability and Site Groundwater Monitoring Wells

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