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HomeMy WebLinkAbout0403_Chambers_Phase5_DesignHydroWorkplan_SWSReview_DIN27399_20170214 ROY COOPER Governor MICHAEL S. REGAN Secretary MICHAEL SCOTT Director February 14, 2017 Mr. Ed Stephens, PG Civil & Environmental Consultants, Inc. 1900 Center Park Drive, Suite A Charlotte, North Carolina 28217 Re: Chambers Development MSWLF – Anson County (Permit 0403) Review of Proposed Phase 5 Design Hydro Work Plan DIN 27399 Dear Ed, We’ve reviewed the revised proposed design hydro work plan for a proposed Phase 5 for the Chambers MSWLF submitted via email on February 8, 2017. The work plan proposes to conduct a boring program in a stepped approach to hydrogeological subsurface data collection. As described, the initial effort will use a limited number of borings (approximately 29, with an additional four deeper borings paired/nested with a shallow boring) across the 83-acre investigation area. CEC Inc. states the initial locations selected to get an understanding of the site’s hydrogeological subsurface conditions are based on field observations of the area of investigation. The stated objective is to optimize the investigation and data collection effort. The Section generally agrees with this staged approach to evaluate the site hydrogeologic conditions. As a staged or stepped approach to the site investigation, CEC will evaluate the data from the initial investigation stage and decide whether additional data collection would be warranted. Depending on what is found, CEC may or may not expand the investigation during the initial site work. Results of the initial boring program will be presented to the Section for review to determine completeness and whether the requirements for Site and Design hydro investigation have been met to adequately define subsurface hydrogeological conditions. If additional hydrogeological design data is required, a follow-up investigative boring effort will be proposed to fill any data gaps. Please note that the Section reserves the right to request additional information (ie, borings etc) upon review of any site or design hydrogeological report(s). Also be cautious about excessive extrapolation of subsurface conditions between widely-spaced data points without good cause. It is ultimately incumbent upon the design engineer and hydrogeologist to adequately Page 2 evaluate the hydro and subsurface conditions for design considerations consistent with rules requirements (including vertical separation to water table and top of rock, foundation standards, effective water quality monitoring system, and others). If you have any further questions, please feel free to contact me at (919) 707-8258 or at perry.sugg@ncdenr.gov. With Best Regards, Perry Sugg, PG Permitting Hydrogeologist Solid Waste Section Cc: Nelson Breeden – Waste Connections Scott Brown PE – CEC, Inc. Nathan Bivins PE – CEC, Inc. Ed Mussler – SWS Permitting Branch Supervisor Donna Wilson – SWS Permitting Engineer -i- Revised Work Plan for Phase 5 Hydrogeologic Investigation February 7, 2017 (Rev. 1) TABLE OF CONTENTS Page 1.0 INTRODUCTION..............................................................................................................1 1.1 Site Description ....................................................................................................... 1 1.2 Physical Setting ....................................................................................................... 2 1.3 Local Geology/Hydrogeology ................................................................................ 4 2.0 PROPOSED WORK PLAN FOR SITE-SPECIFIC HYDROGEOLOGICAL INVESTIGATION .................................................................6 2.1 Reliance On Previous Data ..................................................................................... 6 2.2 Proposed Work Plan for Stepped Investigation Approach ..................................... 6 2.3 Scope Of Work ....................................................................................................... 8 FIGURES Embedded Figure 3-1 – USGS Topographic Map Attached Figure 1 – Proposed Phase 5 Boring Location Map -1- Revised Work Plan for Phase 5 Hydrogeologic Investigation February 7, 2017 (Rev. 1) 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 initial boring program 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. It is proposed herein that the boring program for Phase 5 be conducted in a stepped approach for optimal subsurface data collection to satisfy both the requirements of .1623(a) Site Hydro Report and .1623(b) Design Hydro Report. Results of the initial boring program will be submitted to the Solid Waste Section for review to determine the completeness and suitability of the initially obtained data. Should data gaps exist, a follow-up boring program will be designed and implemented to provide additional hydrogeological design data. -2- Revised Work Plan for Phase 5 Hydrogeologic Investigation February 7, 2017 (Rev. 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. -3- Revised Work Plan for Phase 5 Hydrogeologic Investigation February 7, 2017 (Rev. 1) -4- Revised Work Plan for Phase 5 Hydrogeologic Investigation February 7, 2017 (Rev. 1) 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 -5- Revised Work Plan for Phase 5 Hydrogeologic Investigation February 7, 2017 (Rev. 1) 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. -6- Revised Work Plan for Phase 5 Hydrogeologic Investigation February 7, 2017 (Rev. 1) 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 PROPOSED WORK PLAN FOR STEPPED INVESTIGATION APPROACH 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 5 expansion. The investigation will be performed in general accordance with NC Solid Waste Management Rule -7- Revised Work Plan for Phase 5 Hydrogeologic Investigation February 7, 2017 (Rev. 1) 15A NCAC 13B .1623(a) Site Hydro Report and .1623(b) Design Hydro Report. CEC will implement a Work Plan in a step-wise approach for optimal subsurface data collection to satisfy both the requirements of .1623(a) and .1623(b). Results of the initial boring program outlined below will be submitted to the Solid Waste Section for preliminary review to determine the completeness and suitability of the initially obtained data. Should additional data be required by the Solid Waste Section, a follow-up boring program will be designed and implemented to provide additional hydrogeological design data. 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 initial boring program may provide an adequate design hydrogeologic study for 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). For the initial boring program, CEC proposes that a total of twenty-nine (29) boring sites be completed as temporary piezometers or permanent monitoring wells that will provide a boring density of approximately 1 per 2.86 acres, which may be adequate based on the apparent uniformity of the previously characterized hydrogeologic units. 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 the borings/piezometers/wells proposed for the initial boring program are shown on Figure 1. CEC assumes that the Solid Waste Section will review our proposed initial investigation scope and will authorize the proposed alternate exploration density; while reserving the right to review the completeness and suitability of the initially obtained data and to request additional data should significant data gaps be determined. Should significant data gaps exist, a follow-up boring program will be designed and implemented to provide additional data. -8- Revised Work Plan for Phase 5 Hydrogeologic Investigation February 7, 2017 (Rev. 1) 2.3 SCOPE OF WORK This section outlines the proposed initial boring program to provide 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: • 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. Initial Boring Program - 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. -9- Revised Work Plan for Phase 5 Hydrogeologic Investigation February 7, 2017 (Rev. 1) 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. 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 -10- Revised Work Plan for Phase 5 Hydrogeologic Investigation February 7, 2017 (Rev. 1) 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, 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. -11- Revised Work Plan for Phase 5 Hydrogeologic Investigation February 7, 2017 (Rev. 1) Preliminary Review of the Initial Boring Program Data Results of the initial boring program will be submitted to the Solid Waste Section for review to determine the completeness and suitability of the initially obtained data. Should significant data gaps exist, a follow-up boring program will be designed and implemented to provide additional hydrogeological design data. 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; • 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 -12- Revised Work Plan for Phase 5 Hydrogeologic Investigation February 7, 2017 (Rev. 1) 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. 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. 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 -13- Revised Work Plan for Phase 5 Hydrogeologic Investigation February 7, 2017 (Rev. 1) 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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