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HomeMy WebLinkAboutNC0001422_CSA Appx C - Methodology 2015-07-31_20150805Duke Energy Progress – L.V. Sutton Energy Complex Groundwater Assessment Report Comprehensive Site Assessment Report Appendix C - Methodology 1 of 13 S:\Proj\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Appendices\Sutton CSA - Appendix C - Methodology 2015-07-31.docx The approach to conducting the Comprehensive Site Assessment (CSA) at the L.V. Sutton Energy Complex was described in the Groundwater Assessment Work Plan (Revision 1, December 2014). The objective was to collect and analyze samples of soil, ash, groundwater, surface water, and sediment to more accurately determine the vertical and horizontal concentrations of Constituents of Interest (COIs). A COI is defined as a parameter detected at a concentration greater than NCDENR/DWR Title 15, Subchapter 2L and Interim Maximum Allowable Concentrations (IMAC). This section describes equipment used and methods employed to collect and preserve appropriate samples and obtain representative analytical results. 1. Subsurface Investigation Characterization of subsurface material was conducted by collecting ash, soil, sediment, ash pore water, groundwater, and surface water samples for analysis. Ash, soil, ash pore water, and groundwater samples were obtained through completion of drilled borings and monitoring wells. The following presents the approach for subsurface sample acquisition and analysis. 1.1 Drilling Methods Sonic drilling methods were employed to collect subsurface samples. The advantages provided by this method include less disturbance of the borehole wall and minimized groundwater sample turbidity. Drilling tools (sonic core barrels and casings) were thoroughly decontaminated prior to starting a boring. Daily equipment rinse samples were collected to confirm the effectiveness of decontamination. Drinking water purchased locally was used for drilling fluid. A sample of the “source water” was analyzed for the full set of GAP parameters (Attachment 4). 1.2 Monitoring Well Installation Each monitoring well was constructed by North Carolina-licensed well drillers using sonic drilling techniques and in accordance with 15A NCAC 02C (Well Construction Standards). Drilling equipment was decontaminated prior to use at each location. Monitoring wells were constructed of 2-inch ID, National Sanitation Foundation (NSF) grade polyvinyl chloride (PVC) (ASTM D-1785-12) schedule 40 flush-joint threaded casing and 0.010-inch machine-slotted pre-packed screens. Well construction also included the use of pre-packed screens with additional sand in the annular space, to minimize sample turbidity. Packed well screens for each well were filled with clean, well-rounded, washed high grade No. 1A silica sand. The filter pack was placed approximately two feet above the top of the pre-packed screen and then an approximate two-foot pelletized bentonite seal was placed above the filter pack. The remainder of the Duke Energy Progress – L.V. Sutton Energy Complex Groundwater Assessment Report Comprehensive Site Assessment Report Appendix C - Methodology 2 of 13 S:\Proj\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Appendices\Sutton CSA - Appendix C - Methodology 2015-07-31.docx annular space was filled with a neat cement grout from the top of the upper bentonite seal to near ground surface. ABMW-2D was installed as double-cased well beneath the ash in the FADA. Protective outer casing was installed using sonic drilling equipment with a 10-inch core barrel below the base of the ash in the underlying surficial formation, which was determined based on observation of continuous cores recovered during drilling. A permanent 6- inch diameter schedule 40 PVC protective outer casing was then installed and grouted in place. After the grout had sufficient time to set (approximately 24 hours), drilling was advanced through the outer casing using a smaller diameter drilling core barrel (~5-inch diameter) and through the surficial aquifer to the top of the Pee Dee formation (determined based on observation of continuous cores) at least 10 feet below the depth of the surface casing. The well was then installed in a similar approach as shallow monitoring wells as described above. Monitoring wells were completed with either steel above ground protective casings or flush mounts (SMW-01) with locking caps, locking expansion caps, and well tags. Protective covers were secured and completed in a concrete collar and a minimum two- foot square concrete pad surrounded by bollards. 1.2.1 Monitoring Well Development Following installation, monitoring wells were developed to remove drill fluids, clay, silt, sand, and other fines which may have been introduced into the formation or sand pack during drilling and well installation, in addition to establishing connectivity of the well with the aquifer. Well development was performed using a portable submersible pump that was repeatedly moved up and down the well screen interval until the water was relatively clear. Some wells were initially developed with a bailer to remove the most turbid water and were later completed by developing with a submersible pump or a peristaltic pump. Development continued by sustained pumping until monitoring parameters (e.g., conductivity, pH, DO, and temperature) were generally stabilized, estimated quantities of drilling fluids, if used, were removed, and turbidity decreased to acceptable levels (approximately 10 NTUs). Wells were developed no sooner than 24 hours after well installation to allow for an adequate grout cure time. Duke Energy Progress – L.V. Sutton Energy Complex Groundwater Assessment Report Comprehensive Site Assessment Report Appendix C - Methodology 3 of 13 S:\Proj\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Appendices\Sutton CSA - Appendix C - Methodology 2015-07-31.docx 1.3 Sample Collection and Analytical Methods Methods used for the collection and preservation of samples for various analyses are described in this section. Samples were collected in accordance with the quality assurance and quality control procedures outlined in the Work Plan. 1.3.1 Soils and Ash Sampling and Analysis 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). Rinse blanks from soil sample collection equipment were collected for each soil boring/well installation location. At times, drilling for one location took more than one day and the rinse blank was collected on the first day. Rinse blanks for soil samples were collected by pouring deionized water through the sonic drill bit or through the hand auger bit. These pieces of equipment are normally the first introduced into the subsurface for a soil boring. Laboratory results for the rinse blanks are provided in Appendix D. Soil and ash samples were collected wearing nitrile gloves and prepared and analyzed using the following methods: Duke Energy Progress – L.V. Sutton Energy Complex Groundwater Assessment Report Comprehensive Site Assessment Report Appendix C - Methodology 4 of 13 S:\Proj\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Appendices\Sutton CSA - Appendix C - Methodology 2015-07-31.docx 1.3.1.1 Metals Soil and ash samples were placed in amber glass bottles and stored on ice for shipment for total metals analysis. Concentrations of metals present in soils and ash were determined using analytical parameters presented on Table 6-2. 1.3.1.2 Organic Constituents Soil and ash samples were placed in amber glass bottles and stored on ice for shipment for total organic carbon (TOC) analysis. TOC content of soils and ash were determined in accordance with EPA Method 9060. 1.3.1.3 Leaching Characteristics Select soil and ash samples were placed in amber glass bottles and stored on ice for shipment forthe mobility of inorganic analytes present using the Synthetic Precipitation Leaching Procedure (SPLP) following U.S. EPA Method 1312. 1.3.1.4 Bulk Chemistry Select soil and ash samples were stored and shipped in sealable plastic bags for bulk chemistry analysis. Identification and relative concentration of bulk chemistry was determined by American Assay Laboratories. Samples were dried at 80 oC overnight and pulverized to - 150 mesh and analyzed as follows: XRF-PP – a known sample amount was combined with binder, ground finer, and pressed into a disk. The disk was then analyzed by X-ray fluorescence (XRF). ICP-D4A – A sample pulp was digested with a combination of HF, HClO4, HCl, and HNO3 for a near-total digestion. The solution was then analyzed by Inductively Coupled Plasma (ICP)-Atomic Emission Spectroscopy (AES) and ICP-Mass Spectroscopy (MS). ICP-NF – A sample pulp was fused with Na2O2 and digested with HCl. The solution was then analyzed by ICP-AES and ICP-MS. Eltra Carbon & Sulfur – A sample pulp was combined with tungsten and iron accelerator and combusted in Eltra furnace for analysis of carbon and sulfur. Duke Energy Progress – L.V. Sutton Energy Complex Groundwater Assessment Report Comprehensive Site Assessment Report Appendix C - Methodology 5 of 13 S:\Proj\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Appendices\Sutton CSA - Appendix C - Methodology 2015-07-31.docx Loss of Ignition (LOI) – A sample pulp was gradually heated in a gravimetric furnace to 1000° C while sample loss was calculated. 1.3.1.5 Mineralogy Select samples were stored and shipped in sealable plastic bags for mineralogical analysis. Identification and relative concentration of mineral types were determined by X-ray diffraction (XRD). The original sample was dried at 80° C (no pulp) and combined with water and disaggregated in an ultrasonic bath. The sample was then wet sieved at 63 micrometers to separate and quantify the sand fraction. The slurry was centrifuged at a calculated rotation per minute and time to separate the clay particles from the silt. The clay solution was then decanted off. Sand and silt fractions were dried, quantified, and analyzed using XRD as random mounts (XRD is a process by which X-rays are scattered by atoms that comprise the crystal structure of a given mineral, creating a pattern). Clay particles are deposited on slides forming an oriented mount for XRD. After the analysis, the clay particles were placed in an ethylene glycol environment overnight to test for expanding clays. When necessary, the clay particles are then heated to 400° C and re-analyzed for collapsing layers. 1.3.1.6 Development of Kd Terms To determine the sorption capacity of site soils, select samples were collected along proposed flowpath transects. Samples were collected, handled, and preserved in order to eliminate impacts of ambient air on the oxidation-reduction potential (ORP) and hydrous ferrous oxide (HFO) on sampled materials. Samples were collected in plastics bags and sealed with a conventional vacuum sealer. The samples were stored on ice for shipment and kept out of direct sunlight. Samples were prepared and analyzed by the Civil and Environmental Engineering Department of the University of North Carolina at Charlotte (UNCC). Prior to sorption determinations, soil samples were dried at room temperature and periodically mixed throughout the drying process to prevent grain aggregation. Once dry, samples were sieved using a No. Duke Energy Progress – L.V. Sutton Energy Complex Groundwater Assessment Report Comprehensive Site Assessment Report Appendix C - Methodology 6 of 13 S:\Proj\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Appendices\Sutton CSA - Appendix C - Methodology 2015-07-31.docx 10 U.S. standard sieve (10 mm) with 0.0787 inch openings. To quantify soil partition coefficients (Kd), column and batch tests were performed. Effluent samples collected from these tests were analyzed by inductively coupled plasma-mass spectroscopy and ion chromatography. To provide a basis for estimating COI source terms, leaching tests were performed on ash samples. Details of the analytical procedures/methods are briefly discussed below with more detail included in the analytical reports. 1.3.1.6.1 Column Tests Column tests were conducted by compacting soil and ash samples into 8 inch long (20.3 cm) polyethylene tubes (with dimensions 0.675 in. (16 mm) I.D. by 0.75 in. (19 mm) O.D) and plugged with two polypropylene end caps. Using groundwater and ash pore water analytical results from the site, feed solutions amended with all COIs found above the NCAC 15A 02L .0106(g) standards were produced and pumped into the columns. Analyses and equipment used are provided in the table below: Analyte Method Trace metals (Sb, As, B, Cd, Cr, Fe, Mn, Pb, Tl) EPA 200.8 Sulfate EPA 300.0 pH Standard Method 4500 B Conductivity Standard Method 2510 Oxidation-reduction potential (ORP) ASTM method G200-19 1.3.1.6.2 Batch Tests Batch tests were conducted in accordance with U.S. Environmental Protection Agency Technical Resource Document EPA/530/SW-87/006-F. COI-amended feed solution (described above in 1.3.1.6.1) and soil samples were mixed across a range of soil-to-solution ratios, followed by shaking until chemical equilibrium was achieved. Once equilibrium was achieved, Duke Energy Progress – L.V. Sutton Energy Complex Groundwater Assessment Report Comprehensive Site Assessment Report Appendix C - Methodology 7 of 13 S:\Proj\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Appendices\Sutton CSA - Appendix C - Methodology 2015-07-31.docx solutions were drawn and analyzed as described in the above table. 1.3.1.6.3 Hydrous Ferrous Oxides Analysis The method for HFO determination in soil and ash samples was adapted from Chao and Zhou (1983). Following this method, soil samples were extracted using a 0.25M NH2OH·HCl-0.25M HCl combined solution. 1.3.1.6.4 Ash Leaching Tests Ash leach tests were performed to provide a basis for estimating COI source terms to develop the Kd terms. Ash samples were prepared and analyzed using EPA Method 1313 [2] (Liquid-Solid Partitioning as a Function of Extract pH Using a Parallel Batch Extraction Procedure) and EPA Method and EPA Method 1316 [3] (Liquid-Solid Partitioning as a Function of Liquid-Solid Ratio using a Parallel Batch Extraction Procedure). Method 1313 provides COI concentration as a function of pH (the test was conducted only at natural pH). Method 1316 provides COI concentration as a function of liquid to solid ratio. 1.3.1.7 Index Property Sampling and Analysis Select soil and ash samples were collected for laboratory analysis of physical properties to provide data for use in groundwater modeling. Samples were collected at selected locations for the following analyses using the described methods:  Natural Moisture Content Determination, in accordance with ASTM D-2216  Grain size with hydrometer determination, in accordance with ASTM Standard D-422 In addition, thin-walled undisturbed tubes (“Shelby” tubes) were advanced in ash and soil at select locations. Undisturbed samples were tested for the following: Duke Energy Progress – L.V. Sutton Energy Complex Groundwater Assessment Report Comprehensive Site Assessment Report Appendix C - Methodology 8 of 13 S:\Proj\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Appendices\Sutton CSA - Appendix C - Methodology 2015-07-31.docx  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 Sample porosity was calculated from parameters measured during these tests. 1.3.2 Ash Pore Water and Groundwater Sampling and Analysis New and existing wells were sampled using low-flow sampling techniques in accordance with the USEPA Region 1 Purging and Sampling Procedure for the Collection of Groundwater Samples from Monitoring Wells (revised January 19, 2010), the Groundwater Monitoring Program Sampling, Analysis and Reporting Plan, L.V. Sutton Energy Complex (SynTerra, October 2014), updated by the Low Flow Sampling Plan, Duke Energy Facilities, Ash Basin Groundwater Assessment Program, North Carolina, June 10, 2015. NCDENR conditionally approved the Low Flow Sampling Plan in a June 11, 2015 email with an attachment summarizing their approval conditions. Equipment blanks for groundwater sampling were collected daily. The sample was collected from a laboratory-supplied container of deionized water into laboratory-supplied bottle ware. The equipment consisted of the pump to be used for sample collection that day and tubing was pulled from the supplies planned for the day. Ash pore water and groundwater samples were analyzed in the field and laboratory. The analytical parameters and associated analytical methods are summarized on Table 6-3. Only select samples were analyzed for radionuclides and metals speciation included on Table 6-3. For speciation analysis, select ash pore water or groundwater samples were collected with a peristaltic pump as described above but with acid-washed tubing and following a condensed version of EPA Method 1669. Duke Energy Progress – L.V. Sutton Energy Complex Groundwater Assessment Report Comprehensive Site Assessment Report Appendix C - Methodology 9 of 13 S:\Proj\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Appendices\Sutton CSA - Appendix C - Methodology 2015-07-31.docx 2. Hydrogeologic Evaluation Testing To characterize hydrogeologic conditions, hydrogeologic testing and measurements were performed. Measurements and testing procedures are discussed below. 2.1 Potentiometric Surface Measurements During groundwater sampling activities, water level measurements were recorded at existing site monitoring wells, observation wells, piezometers, and newly installed wells. The data were used to generate potentiometric maps for each separate hydrogeologic zone as well as to determine the degree of residual saturation beneath the ash basin. Water level measurements used for preparation of flow maps were collected during a single 24-hour period and prior to purging for sampling. 2.2 Slug Tests After the development and sampling of monitoring wells, hydraulic conductivity tests (rising head slug tests) were conducted on each of the new wells. Slug tests were performed in accordance with ASTM D4044-96 Standard Test Method (Field Procedure) for Instantaneous Change in Head (Slug) Tests for Determining Hydraulic Properties of Aquifers and NCDENR Performance and Analysis of Aquifer Slug Test and Pumping Test Policy, dated May 31, 2007. Prior to the performance of each slug test, static water level was determined and recorded and a Solinst Model 3001® Edge electronic pressure transducer/data logger, or equivalent, was placed in a well at a depth of approximately six-inches above the well bottom. The Levelogger® was connected to a field laptop and programmed with the well identification, approximate elevation of the well, date, and time. Slug tests were conducted by lowering a PVC “slug” into a well casing. The water level within the well was then allowed to equilibrate to a static level. After equilibrium, the slug was rapidly withdrawn from the well, decreasing the water level in the well instantaneously. During well recovery, the water level within a well was measured and recorded electronically using the pressure transducer/data logger. Two separate slug tests were conducted for each well. Slug tests were performed for no less than ten minutes, or until such time as the water level in the well recovered 95 percent of its original pre-test level, whichever occurred first. Slug tests were terminated after two hours even if the 95 percent pre-test level was not achieved. Duke Energy Progress – L.V. Sutton Energy Complex Groundwater Assessment Report Comprehensive Site Assessment Report Appendix C - Methodology 10 of 13 S:\Proj\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Appendices\Sutton CSA - Appendix C - Methodology 2015-07-31.docx Data obtained during the slug tests were reduced an analyzed using AQTESOLVTM for Windows, version 4.5, software to determine the hydraulic conductivity of soils in vicinity of wells. 3. Screening Level Risk Assessments To support the groundwater assessment, potential risks to human health and the environment were assessed in accordance with applicable federal and state guidance. Screening level human health and ecological risk assessments were conducted that included development of conceptual exposure models (CEM) to serve as the foundation for evaluating potential risks to human and ecological receptors. The purpose of the human health and ecological CEMs was to identify potentially complete exposure pathways to environmental media associated with the site and to specify the types of exposure scenarios relevant to include in the risk analysis. Potential exposure pathways were considered complete when all of the following elements applied: 1) a constituent source; 2) mechanisms of constituent release and transport from the source area to an environmental medium; and 3) feasible routes of potential exposure at the point of contact (e.g., ingestion, inhalation, dermal or ambient contact). Maximum constituent concentrations were compared to appropriate risk-based screening values as a preliminary step in evaluating potential for risks to human and ecological receptors. Based on results of the screening level risk assessments, a refinement of COPCs will be conducted and more definitive risk characterization will be performed as part of the corrective action process if needed. 3.1 Human Health Risk Assessment The screening level human health risk assessment process involved comparison of constituent concentrations in various media to the following risk-based screening criteria:  Soil analytical results collected from the 0 to 2 foot depth interval compared to US EPA residential and industrial soil Regional Screening Levels (RSLs) (US EPA, June 2015);  Groundwater results compared to NCDENR Title 15A, Subchapter 2L Standards (NCDENR, 2006);  Surface water analytical results compared to North Carolina surface water standards (Subchapter 2B) and US EPA national recommended water quality criteria (NCDENR, 2007; US EPA, 2006). Duke Energy Progress – L.V. Sutton Energy Complex Groundwater Assessment Report Comprehensive Site Assessment Report Appendix C - Methodology 11 of 13 S:\Proj\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Appendices\Sutton CSA - Appendix C - Methodology 2015-07-31.docx  The surface water classification as it pertains to drinking water supply, aquatic life, high/exceptional quality designations and other requirements for other activities (e.g., landfill permits, NPDES wastewater discharges) were noted;  Sediment results compared to US EPA residential and industrial soil RSLs (US EPA, October 2014 or latest update); and  Sediment, soil and ground water results compared to available local, regional and national background sediment, soil and ground water data, as available.  If warranted as part of corrective action decisions, site and media specific risk-based remediation standards can be calculated in accordance with the Eligibility Requirements and Procedures for Risk-Based Remediation of Industrial Sites Pursuant to N.C.G.S. 130A-310.65 to 310.77, North Carolina Department of Environment and Natural Resources, Division of Waste Management, 29 July 2011. 3.2 Ecological Risk Assessment The screening level ecological risk assessment (SLERA) for the site included a description of the ecological setting and development of the ecological CEM specific to the ecological communities and receptors potentially exposed to site-related COPCs. A list of potential ecological receptors (e.g., plants, benthic invertebrates, fish, mammals, birds, etc.) was compiled, as well as identification of sensitive ecological populations and critical habitat based on information from the North Carolina Natural Heritage Program, and U.S. Fish and Wildlife Service. Step 1 of the SLERA consisted of completion of an ecological checklist as required by Guidelines for Performing Screening Level Ecological Risk Assessment within North Carolina (NCDENR, 2003). Step 2 of the SLERA consisted of performing screening level exposure estimates and risk calculations. This involved comparison of maximum detected concentrations or maximum detection limits for non-detected constituents to applicable ecological screening values (ESVs) intended to be protective of ecological receptors. If exposure concentrations exceeded ESVs, potential ecological impacts could not be ruled out. The following ESV sources were used in the SLERA:  US EPA Ecological Soil Screening Levels;  US EPA Region 4 Recommended Ecological Screening Values; and Duke Energy Progress – L.V. Sutton Energy Complex Groundwater Assessment Report Comprehensive Site Assessment Report Appendix C - Methodology 12 of 13 S:\Proj\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Appendices\Sutton CSA - Appendix C - Methodology 2015-07-31.docx  US EPA National Recommended Water Quality Criteria and North Carolina Standards. Constituents were identified as a Step 2 COPCs as follows:  Category 1 – Constituents whose maximum detection exceeded the media-specific ESV;  Category 2 – Constituents that generated a laboratory sample quantitation limit that exceeded the US EPA Region IV media-specific ESV;  Category 3 – Constituents with no US EPA Region IV media-specific ESV but were detected above the laboratory sample quantitation limit;  Category 4 – Constituents that were not detected above the laboratory sample quantitation limit and had no US EPA Region IV media-specific ESV; and  Category 5 – Constituents with a sample quantitation limit or maximum detection that exceeded the North Carolina Surface Water Quality Standards. 3.3 Surface Investigation Samples were collected at the ground or water surface to support the screening level risk assessment. Samples were collected wearing nitrile gloves. 3.3.1 Surface Water Sampling Surface water samples were collected to assess groundwater to surface water pathways and evaluate surface water quality. Sample jars that did not contain a preservative were used to collect the water directly from the source. The water was decanted from the sample jars into the jars that required preservative. Surface water samples were analyzed for parameters listed in Table 6-3, except for radionuclides and metals speciation parameters. Stream flow measurements were recorded at the time of sampling with the exception of measurements within major waterways. 3.3.2 Sediment Sampling Sediment samples were collected from the bed surface and co-located with surface and seep samples to evaluate sediment quality and provide data to be used in the screening level risk assessment. Where possible, samples were collected directly into sample jars. If surface water was too deep to safely collect sediment samples directly, sediment was obtained using a sampling dredge. Sediment samples were analyzed for parameters listed in Table 6-2. Duke Energy Progress – L.V. Sutton Energy Complex Groundwater Assessment Report Comprehensive Site Assessment Report Appendix C - Methodology 13 of 13 S:\Proj\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Appendices\Sutton CSA - Appendix C - Methodology 2015-07-31.docx 3.3.3 Seep Sampling Seep samples were collected wearing nitrile gloves to assess groundwater to surface water pathways at the site and support the human health and ecological risk assessment. Seep samples were analyzed for parameters listed in Table 6-3, except for radionuclides and metals speciation parameters. Seep flow measurements were recorded at the time of sampling.