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HomeMy WebLinkAbout0403_Chambers_Phase5_Draft_DesignHydroWorkplanReview_DIN27406_201702011 Sugg, William P From:Sugg, William P Sent:Wednesday, February 01, 2017 9:21 AM To:'Stephens, Ed'; Bivins, Nathan Cc:Wilson, Donna; Mussler, Ed Subject:RE: Phase 5 Expansion Design Hydrogeologic Investigation Work Plan - Anson Waste Management Facility - 165-276 Ed/Nathan, Based on review of the proposed Phase 5 work plan you all submitted and feedback from staff, the Section offers the following: General The proposed Phase 5 area appears to be outside of the previously approved site study/site hydro boundaries for the facility. This may mean treating the Phase 5 as a new facility under 15A NCAC 13B .1603, rather than an expansion of the existing landfill. With that, any hydro study would mean meeting requirements of .1623(a) Site Hydro Report and .1623(b) Design Hydro Report. Regardless that should not be a significant problem based on adjoining landfill information and proposed work plan approach. Proposed Design Hydro Work Plan The primary deviation from .1623(b) in the proposed design hydro work plan is a significant reduction in site borings required in .1623(b)(1), “an average of one boring for each acre of the area of investigation”. The proposed footprint of Phase 5 covers approximately 83 acres. The number of borings proposed is 29, or about one boring for every 3 acres. The Section’s position is that this proposal for reduced boring density as presented would be inadequate for providing the more detailed and localized subsurface and hydrogeological data necessary for the basis of site design and constructability, particularly the vertical separation requirements in .1624(b)(4) and possibly engineering foundation standards. Uncertainty in subsurface prediction for this area can be expected due to the following: •The existing landfill and proposed Phase 5 area lie directly on top of the contact boundary zone between the Triassic basin and Carolina Slate belt. In addition, hi-angle diabase dikes have been identified, and can be expected, in the immediate vicinity as well. The exact boundary between the Triassic and Slate Belt rocks through the site is not known. •Previous excavation of the existing landfill has revealed unexpected subsurface conditions with perched water table due to rock lenses or other conditions, resulting for the need to install unplanned underdrain systems during construction. •Phase 5 area is sited along a narrow extended ridgeline with steeply sloping side slopes down to the adjacent floodplain. As such, top of bedrock surface may vary quite dramatically over a short distance. Conversely, the potentiometric surface could likewise be expected to change somewhat sharply over short distances as well. Investigative borings spaced too widely would lead to excessive extrapolation of actual subsurface conditions. 2 Let us know if you need any further assistance with this. Sincerely, Perry Sugg, PG Permitting Hydrogeologist Division of Waste Management – Solid Waste Section NC Department of Environmental Quality Phone: (919) 707.8258 perry.sugg@ncdenr.gov Physical Address: 217 West Jones St / Raleigh, NC / 27603 Mailing Address: 1646 Mail Service Center / Raleigh, NC / 27699-1646 http://portal.ncdenr.org/web/wm/sw E-mail correspondence to and from this addresss may be subject to the North Carolina Public Records Law and therefore may be disclosed to third parties. -i- Work Plan for Phase 5 Hydrogeologic Investigation January 2017 TABLE OF CONTENTS Page 1.0 INTRODUCTION..............................................................................................................1 1.1 Site Description ....................................................................................................... 1 1.2 Physical Setting ....................................................................................................... 1 1.3 Local Geology/Hydrogeology ................................................................................ 3 2.0 PROPOSED WORK PLAN FOR SITE-SPECIFIC HYDROGEOLOGICAL INVESTIGATION .................................................................5 2.1 Reliance On Previous Data ..................................................................................... 5 2.2 Purpose Of Work Plan ............................................................................................ 5 2.3 Scope Of Work ....................................................................................................... 6 FIGURES Embedded Figure 3-1 – USGS Topographic Map Attached Figure 1 – Proposed Phase 5 Boring Location Map -1- Work Plan for Phase 5 Hydrogeologic Investigation January 2017 1.0 INTRODUCTION 1.1 SITE DESCRIPTION The Anson Waste Management Facility is situated in the south-central portion of Anson County, North Carolina. The landfill facility is classified as a municipal solid waste (MSW) landfill and operates under Permit Number 0403. Development of the landfill facility is progressing incrementally in five phases with each phase being comprised of smaller cells. The general intent is to construct a phase incrementally within the landfill when needed. Permits to Construct for Phase 1 and Phase 2 expansions were issued by NCDEQ in 2000 and 2008, respectively. The footprint of Phase 1 is approximately 40.38 acres, and Phase 2 consists of 32.78 acres. Both these existing phases are currently operational. A Permit to Construct Application for Phases 3 and 4 was completed by CEC in November 2016, and has been subsequently submitted to the NC Solid Waste Section for review and approval. Phases 3 and 4 will include a total of 60 acres, bringing the total landfill area to 133 acres. The subject proposed Phase 5 expansion area lies adjacent and to the north of Phases 3 and 4. The preliminary proposed Phase 5 expansion footprint contains approximately 83 acres. A site map is attached as Figure 1 that depicts the preliminary Phase 5 boundaries and the approximate locations of soil borings/piezometers proposed for the subject Phase 5 Design Hydrogeologic Investigation. Further, the detection monitoring wells proposed for the Phase 3 & 4 expansions which are located within the subject Phase 5 expansion area are also shown on Figure 1. 1.2 PHYSICAL SETTING The site location is shown on Figure 3-1 below. The facility is located in south-central Anson County between Polkton and Wadesboro along US 74. The site is bounded on the northwest by Brown Creek, on the east by Pinch Gut Creek, and on the south by the CSX railroad. The immediate surrounding area is rural and primarily wooded. There is limited residential development south of the landfill facility. Site topographic features are shown on the USGS Polkton, NC 7.5-Minute Topographic Quadrangle Map that is presented in Figure 3-1 below. -2- Work Plan for Phase 5 Hydrogeologic Investigation January 2017 -3- Work Plan for Phase 5 Hydrogeologic Investigation January 2017 The site consists of a series of rolling hills that reach elevations of ±300 feet above mean sea level and low-lying areas adjacent to Brown and Pinch Gut Creeks at an elevation low of approximately 240 feet above sea level. Generally, surface drainage from the landfill facility is to the northwest toward Brown Creek and northeast toward an unnamed tributary of Pinch Gut Creek. 1.3 LOCAL GEOLOGY/HYDROGEOLOGY The Phase 5 expansion area is predominantly underlain by Carolina Slate Belt lithologies. The Carolina Slate Belt consists mostly of rocks originally deposited on or near the earth’s surface by volcanic eruption and sedimentation (NC Geological Survey 1985). This lithologic belt is so named because low-grade metamorphism has imprinted many of the rocks with a “slaty” cleavage. The belt is intruded by coarse-grained granites in several places; although, intrusive rocks have not been reported locally. The previously identified local rocks include primarily argillites described as light gray to bluish-gray or brown, fine-grained, well-bedded, with pronounced bedding plane cleavage. Other rocks present include mudstones, silty sandstone, and conglomerate. High-angle diabase dikes have been mapped in adjacent landfill areas and may occur in the Phase 5 area. Surficial rocks have differentially weathered to form an upper “saprolite” zone consisting of unconsolidated silts and clays transitioning at depth to partially weathered rock (PWR) that is coarser-grained, often containing boulders, less weathered, and a denser porous residuum. Depths to PWR vary with the occurring rock type’s resistance to chemical weathering and are typically shallower in higher areas and deeper in low areas. Underlying rocks are typically fine-grained and exhibit variable fracture density. Three basic hydrogeologic units have been characterized at the site by others. The uppermost hydrogeologic units are two density-based zones within a typical Piedmont unconfined “water table” aquifer within the saprolite zone, which consists of variably dense silty clayey sand and silt derived from in-situ weathering of the parent rock. A third hydrogeologic unit is underlying fractured bedrock within which groundwater occurs under unconfined to partially confined conditions. The density of bedrock fracturing and fracture apertures tend to decrease with -4- Work Plan for Phase 5 Hydrogeologic Investigation January 2017 increasing depth such that groundwater flow is significantly restricted within a depth of 200 to 300 feet. Groundwater recharge largely occurs over broad uplands and gentle slopes. Little recharge occurs in areas of steeper topography. Typically, groundwater occurrence is localized within a relatively porous PWR zone, which transitions with depth to bedrock. Groundwater discharge occurs along area streams (i.e., Brown Creek and Pinch Gut Creek), which converge at the northern corner of the site. Based on earlier site hydrogeologic characterization by others, the groundwater flow patterns are not expected to change significantly due to seasonal climatic variation, except that groundwater levels in recharge zones are expected to exhibit normal seasonal fluctuation. -5- Work Plan for Phase 5 Hydrogeologic Investigation January 2017 2.0 PROPOSED WORK PLAN FOR SITE-SPECIFIC HYDROGEOLOGICAL INVESTIGATION 2.1 RELIANCE ON PREVIOUS DATA On behalf of the facility owner, CEC recently submitted a Permit to Construct Application for Phases 3 and 4 to the Solid Waste Section for review and approval. Appendix E includes a Design Hydrogeologic Investigation Report prepared by SCS Engineers, PC dated October 5, 2015 that provides a discussion of hydrogeologic data collected at the site since initial site suitability work was performed by GZA Environmental, Inc. in 1992. A Phase 1 Design Hydrogeologic Report was prepared by TRC Environmental dated December 1998. This document included the Water Quality Monitoring Plan and deep coring data. The earlier site studies focused on diabase dikes and included borings advanced to depths up to 200 feet. The Phase 2 design study was completed by ESP Associates and Davis Garrett & Associates between 2003 and 2007. This investigation included 41 soil borings within which 34 piezometers were constructed, including seven nested pairs. The Phase 2 study included 35 slug tests to determine hydraulic conductivities of the defined hydrogeologic units. SCS Engineers, PC prepared the Design Hydrogeologic Investigation Report included in the recent Permit to Construct Application for Phase 3 and 4. The combined Phase 3 & 4 hydrogeologic study included 34 new borings that were advanced to auger refusal to characterize the top-of- bedrock surface. All but four borings encountered the water table such that 30 piezometers were constructed. Rock was cored at three site locations. Previous available information included rock core data from eight earlier borings. Like the proposed Phase 5 expansion area, Phase 3 & 4 areas are predominantly underlain by Slate Belt argillite. 2.2 PURPOSE OF WORK PLAN CEC will perform a Design Hydrogeologic Investigation for the Anson Waste Management Facility Phase 5 expansion area. The purpose of the study is to characterize hydrogeological units, determine approximate top-of-bedrock and seasonal high groundwater table elevations, and collect representative samples for geotechnical testing to provide landfill design parameters for the Phase -6- Work Plan for Phase 5 Hydrogeologic Investigation January 2017 5 expansion. This investigation will be performed in general accordance with NC Solid Waste Management Rule 15A NCAC 13B .1623 (b) Design Hydrogeologic Report. Prior hydrogeologic investigations have been performed by others in permitting four previous landfill phases that have provided considerable knowledge of local subsurface conditions. CEC assumes that additional borings, wells, and/or piezometers will be necessary within the Phase 5 footprint to supplement and confirm work previously performed by others as well as fill gaps in the project area where data is not available or is limited. The proposed investigation area is approximately 83 acres. It is CEC’s technical opinion that an adequate design hydrogeologic study can be completed on the Phase 5 expansion area with an exploration density less than one test boring per acre as specified by 15A NCAC 13B .1623 (b) (1). A total of twenty-nine (29) boring sites to be completed as temporary piezometers or permanent monitoring wells are proposed for the Phase 5 study area that will provide a boring density of approximately 1 per 2.86 acres, which is adequate based on the apparent uniformity of the previously characterized hydrogeologic units. In addition, four of these boring sites will include a nested deeper boring/piezometer. It is anticipated that eight of these proposed borings can be converted to permanent detection monitoring wells for the Phase 3 & 4 expansion areas. The approximate locations of proposed borings/piezometers/wells are shown on Figure 1. CEC assumes that the Solid Waste Section will review our proposed investigation scope and will authorize the proposed alternate exploration density. 2.3 SCOPE OF WORK This section outlines the proposed Scope of Work to provide appropriate geotechnical and hydrogeological evaluations for the Phase 5 Expansion Area. Field Work An area hydrogeological investigation (field study) will be conducted to obtain the geologic/hydrogeologic/geotechnical samples and data needed to evaluate site suitability and for landfill design purposes. In general, CEC activities as part of this task will include: -7- Work Plan for Phase 5 Hydrogeologic Investigation January 2017 • NC-licensed geologist to plan the site boring/monitoring well/piezometer program and data collection approach; • Field geologist to locate, observe, and log all soil borings and rock cores; • Collection and preparation of representative samples for geotechnical laboratory testing; • Gauge and record water levels in piezometers; and • A magnetometer survey to identify the location and orientation of potential diabase dikes in the Phase 5 area, if any. Test Borings With the prior approval of the NCDEQ Solid Waste Section, eight (8) soil test borings advanced in the Phase 5 area will be located at sites previously proposed by others for detection groundwater monitoring wells MW-13 through MW-20 for Phases 3 and 4 as shown on the attached Figure 1. These borings will be subsequently converted to permanent monitoring wells constructed in accordance with 15A NCAC 2C guidelines. Up to twenty-one (21) additional soil test borings (PZ5-1 through PZ5-21) will be advanced at the approximate locations shown on the attached Figure 1. The latter soil borings will be converted to temporary shallow piezometers. Also, four (4) additional piezometers (PZ5-6D, PZ5-7D, PZ5-8D, and PZ5-11D) will be nested with four shallow piezometers (PZ5-6, PZ5-7, PZ5-8, and PZ5-11) to provide head data to evaluate vertical hydraulic gradients. Soil test borings will be advanced by an ATV-mounted drill rig using hollow-stem augers to a depth of auger refusal. Standard penetration tests (SPT) will be performed at a minimum of five- foot intervals in accordance with ASTM D 1586-84 (continuous SPT over the bottom ten feet of each boring) to evaluate relative density and soil strength. Split-spoon samples collected while performing SPT will be visually classified in the field and representative samples will be retained for geotechnical classification via the Unified Soil Classification System (USCS) and other geotechnical testing. Select undisturbed representative samples will be collected for geotechnical testing by advancing up to ten (10) thin-walled Shelby tubes in the bottom ten feet of several borings. -8- Work Plan for Phase 5 Hydrogeologic Investigation January 2017 Rock Cores Rock cores will be obtained at five (5) boring locations by advancing at least NQ-size core barrels for wireline recovery. Preferred rock coring locations are those borings which are targeted for conversion to deep piezometers and/or borings advanced to auger refusal prior to reaching the local water table. Rock cores will be obtained at a minimum from the upper ten (10) feet of bedrock in each test boring. The rock cores will be observed for rock classification and structural features, core recovery values, and Rock Quality Designation (RQD) values. Permanent Monitoring Wells Permanent monitoring wells will be installed in borings MW-13 through MW-20 as shown on Figure 1. Each soil boring will be extended to auger refusal at which depth the bottom of the well screen will be placed. Each well will be constructed of two-inch Schedule 40 PVC riser and 0.010- inch slotted PVC well screen. Each well screen interval will be selected in the field based on existing site conditions. Well installations will be performed under the direction of a qualified geologist. Permanent monitoring wells will be constructed in accordance with 15A NCAC 2C guidelines. Temporary Piezometers The remaining soil test borings to be converted to shallow piezometers will also be advanced to auger refusal. A temporary piezometer will be installed in each boring such that the bottom of the well screen is coincident with the depth of auger refusal. Borings for deeper piezometers will likely be advanced into bedrock. A temporary piezometer will be installed in each boring such that the well screen is screened in the bedrock unit. Each piezometer will be constructed of two- inch Schedule 40 PVC riser and 0.010-inch slotted PVC well screen. Each piezometer screen interval will be selected in the field based on existing site conditions. Piezometer installations will be performed under the direction of a qualified geologist. Monitoring Well/Piezometer Gauging The monitoring wells and piezometers that will be installed in the Phase 5 expansion will be gauged for water levels at the time of boring, 24 hours after installation, and following stabilization of water levels. Stabilized water level elevations will be compared with hydrographs of area wells, -9- Work Plan for Phase 5 Hydrogeologic Investigation January 2017 meteorological/climatological data, and other available information to estimate a long-tern seasonal high water table. Groundwater flow directions, rates, and gradients will be estimated from existing and newly obtain hydrogeological data. Note: In-situ permeability tests were performed in 24 piezometers during the previous design hydrogeologic investigation for Phases 3 and 4. CEC assumes that the available permeability test data will be representative of similar subsurface materials that will be encountered in the Phase 5 expansion. Existing data will be used to estimate geometric mean permeability for the identified hydrogeologic units. Magnetometer Survey CEC will conduct a proton-procession magnetometer survey of the Phase 5 area for the purpose of mapping potential diabase dikes. Whereas previous mapped dikes in the area of the landfill facility have a roughly north-south orientation, four perpendicular east-west traverses will be performed over the Phase 5 area. Should a magnetic anomaly be detected, additional localized traverses will be performed to determine its extent. Design Hydrogeologic Report CEC will provide a narrative to discuss previous published area geology/hydrogeology, design hydrogeologic investigation methods, data interpretations, and findings to include: • A report on local and regional geologic and hydrogeology based on research of available literature for the area. This report will include a fracture trace analysis and Rose Diagram based on inferred structurally– controlled lineaments identified on an area topographic map; • A report on field observations that includes topographic setting, springs, streams, drainage features, existing or abandoned wells, rock outcrops (including strike and dip), groundwater discharge features, and other pertinent features that may affect site suitability; -10- Work Plan for Phase 5 Hydrogeologic Investigation January 2017 • A groundwater contour map will be generated based on the estimated seasonal high water table that is superimposed on a topographic map and includes the location of borings and rock cores and the water table elevations at each location used to generate the groundwater contours; • A bedrock contour map of the upper surface of the bedrock that is superimposed on a topographic map and includes the location of borings and rock cores and the top-of-rock elevations at each location used to generate the upper surface of bedrock contours; • A 3-D groundwater flow net or several hydrogeologic cross-sections that characterize the vertical groundwater flow regime for this area; • A report on the groundwater flow regime for the area including flow paths for both horizontal and vertical components of groundwater flow, horizontal and vertical hydraulic gradients, flow rates, and recharge and discharge areas; and • A certification by a Licensed Geologist that all borings at the site that have not been converted to permanent monitoring wells will be properly abandoned in accordance with the procedures for permanent well abandonment as delineated in 15A NCAC 02C .0113. Geotechnical Sample Collection and Laboratory Testing The scope of work includes a geotechnical field-testing program and associated slope stability and settlement analysis for the Phase 5 expansion in general accordance with 15A NCAC 13B .1624 Construction Requirements and 15A NCAC 13B .1627 Closure and Post Closure Requirements for MSWLF Facilities. Geotechnical properties of the soils will be estimated by various geotechnical laboratory tests. These tests and their estimated number are listed in the table below. -11- Work Plan for Phase 5 Hydrogeologic Investigation January 2017 Laboratory Test Est. Number of Tests Moisture Content 25(1) Sieve Analysis 25(1) Hydrometer Analysis 25(1) United Soil Classification System 25(1) Atterberg Limits 25(1) Porosity 25(1) Shelby Tubes 10(2) Standard Proctor 5 Permeability (Remolded) 5(3) One-Dimensional Consolidation (Undisturbed) 2 CU Triaxial (Remolded) 2 CU Triaxial (Undisturbed) 2 Notes: 1. Moisture content, sieve analysis, hydrometer analysis, USCS, Atterberg limits, and porosity will be performed at each boring location to demonstrate soil consistency. 2. Only four tests require undisturbed samples, however, additional Shelby tube samples should be collected and archived for possible future testing requirements. 3. Number of proposed tests assumes soil uniformity in Phase 5 area. Design Analysis CEC will perform a slope stability and settlement analysis for the Phase 5 expansion. In addition, CEC will perform an anchor trench design and a geotextile cushion design for the proposed geotextile-clay liner system. 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