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Home My WebLink AboutNC0004774_CSA Report Appx D_Soil and Rock Characterization_20150823Sampling Procedures Sampling Overview Characterization of subsurface materials was conducted through the completion of soil borings and borings performed for installation of monitoring wells as described below. Installation details for soil borings and monitoring wells, as well as estimated sample quantities and depths, are described below. For nested monitoring wells, the deep monitoring well boring was utilized for characterization of subsurface materials and collection of samples for laboratory analysis. Shallow, deep, and bedrock monitoring well borings were logged in the field as described below. Ash and Soil Borings Characterization of ash and underlying soil was accomplished through the completion and sampling of borings advanced at ten locations within Cells 1, 2, and 3 and on the Cell 1 and Cell 3 dams (designated as AB-1 through AB-10) and three locations within the Ash Storage Area located immediately east of Cell 1 (designated as AS-1 through AS-3). In addition, 14 soil borings (designated as GWA-1 through GWA-11 and BG-1 through BG-3) were completed outside of ash management areas to provide additional soil quality data. Field data collected during boring advancement was used to evaluate: • the presence or absence of ash • areal extent and depth/thickness of ash • groundwater flow and transport characteristics if groundwater was encountered Borings were advanced using hollow stem auger, roller cone drilling, or sonic drilling techniques to facilitate collection of down -hole data. Standard Penetration Testing (SPT) (ASTM D 1586) and split -spoon sampling were performed at 5-foot increments using an 18-inch split -spoon sampler. Continuous coring was performed from auger refusal into partially weathered/fractured rock at locations where monitoring wells were to be set into the transition zone between saprolite/weathered rock and competent bedrock (designated as D soil boring/monitoring well locations), and coring was performed to a depth of at least 50 feet into competent bedrock for installation of bedrock monitoring wells (designated as BR soil boring/ monitoring wells). Borings were logged and ash/soil samples were photographed, described, and visually classified in the field for origin, consistency/relative density, color, and soil type in accordance with the Unified Soil Classification System (ASTM D2487/D2488). Borings within Ash Basin Waste Boundary In areas where ash was known or suspected to be present (i.e., AB- and AS -borings), solid phase samples were collected for laboratory analysis from the following intervals in each boring: • Shallow Ash — approximately 3 feet to 5 feet bgs • Deeper Ash — approximately 2 feet above the ash/soil interface • Upper Soil — approximately 2 feet below the ash/soil interface • Deeper Soil — approximately 8 feet to 10 feet below the ash/soil interface If ash was observed to be greater than 30 feet thick, a third ash sample was collected from the approximate mid -point depth between the shallow and deeper samples. The ash samples were used to evaluate geochemical variations in ash located in the ash basin and ash storage. The upper and deeper soil samples were used to delineate the vertical extent of potential soil impacts beneath the ash basin and ash storage. Ash and soil samples were analyzed for total inorganic compounds. Select ash samples were analyzed for leachable inorganic compounds using the Synthetic Precipitation Leaching Procedure (SPLP) to evaluate the potential for leaching of constituents from ash into underlying soil. The ash SPLP analytical results were compared to Class GA Standards as found in 15A NCAC 02L .0202 Groundwater Quality Standards, last amended on April 1, 2013 (2L Standards). Ash was located at varying depths beneath the ponded water areas within the active ash basin Due to safety concerns, borings were not completed where ponded water was present within the ash basin. Safety concerns may also prevent access to proposed boring locations on ash areas where saturated ash presents stability issues. Borings Outside Ash Basin Waste Boundary Borings located outside the ash basin waste boundary were designated as GWA and BG borings. The GWA soil samples were used to provide additional characterization of soil conditions outside the ash basin boundary. Solid phase samples were collected for laboratory analysis from the following intervals in each boring: • Approximately 2 feet to 3 feet above the water table • Approximately 2 feet to 3 feet below the water table • Within the saturated upper transition zone material (if not already included in the two sample intervals above) • From a primary, open, stained fracture within fresh bedrock if existent (bedrock core locations only) The boring locations designated as BG borings were used to evaluate site -specific background soil quality. Solid phase samples were collected for laboratory analysis from the following intervals in each boring: • At approximately 10-foot intervals until reaching the water table (i.e., 0 feet to 2 feet, 10 feet to 12 feet, 20 feet to 22 feet, and so forth) • Approximately 2 feet to 3 feet above the water table • Approximately 2 feet to 3 feet below the water table • Within the saturated upper transition zone material (if not already included in the two sample intervals above) • From a primary, open, stained fracture within fresh bedrock if existent (bedrock core locations only) The laboratory analyses performed on the GWA and BG samples depended on the nature and quantity of material collected. One or more of the above listed sampling intervals may be combined if field conditions indicate they were in close proximity to each other (i.e., one sample was obtained that was applicable to more than one interval). Index Property Sampling and Analyses In addition, physical properties of ash and soil were tested in the laboratory to provide data for use in groundwater modeling. Split -spoon samples were collected at selected locations with the number of samples collected from the material types as follows: • Fill - 5 samples • Ash - 5 samples • Alluvium - 5 samples • Soil/Saprolite - 5 samples • Soil/Saprolite - immediately above refusal - 5 samples Select split -spoon samples were tested for: • Natural Moisture Content Determination in accordance with ASTM D-2216 • Grain size with hydrometer determination in accordance with ASTM Standard D-422 Split -spoon samples were collected from the following boring locations: • Fill — AB-9S/D (two samples) and AB10S/D (three samples) • Ash — AB-1 D, AB-3S/D, AS-2D, AB-4S/D, and AB-6D • Alluvium (if present) — AB-4S/D, AB-5S/D, AB-7S/D, AB-9S/D/BR (two samples) • Soil/Saprolite (two locations each as stated above) — BG-1 S/D/BR, BG-2S/D/BR, GWA- 9S/D, AS-1 S/D, and AS-3S/D The depth intervals of the select split -spoon samples were determined in the field by the Lead Geologist/Engineer. In addition to split -spoon sampling, a minimum of five thin -walled undisturbed tubes ("Shelby" Tubes) in fill, ash, and soil/saprolite layers were collected. Sample depths were determined in the field based on conditions encountered during borehole advancement. The Shelby Tubes were transported to a soil testing laboratory and each tube was tested for the following: • Natural Moisture Content Determination in accordance with ASTM D-2216 • Grain size with hydrometer determination in accordance with ASTM Standard D-422 • Hydraulic Conductivity Determination in accordance with ASTM Standard D-5084 • Specific Gravity of Soils in accordance with ASTM Standard D-854 The results of the laboratory soil and ash property determination were used to determine additional soil properties such as porosity, transmissivity, and specific storativity. The results from these tests were used in the groundwater fate and transport modeling. The specific borings where these samples were collected from were determined based on field conditions with consideration given to their location relative to use in the groundwater model. Sampling Variances Variances from Groundwater Assessment Work Plan Soil and Rock Characterization Variance— 1 [AB-4 UD sample 10' below ash/soil None Shelby tube was attempted but could not be taken interface due to refusal 2 AB-8 UD sample 2' above ash/soil interface AB-9BR Packer test AB-10 UD sample in ash Shelby tube was pushed across ash/soil interface None None None None Could not tell where ash/soil interface was when pushing the tube Bedrock was too deep to use standard equipment for packer testing No ash present 3 4 5 GWA-3 UD sample 10' below water table Shelby tube was attempted but could not be taken due to refusal Shelby tube was attempted but could not be taken due to refusal Test was attempted. Pumped 300 gallons of water into the boring at 60 gallons per minute. Water level did not rise, so test was aborted. _ 6 GWA-6 UD sample 10' below water table GWA-6 permeability test 7 None