United States Environmental Protection Agency Office of Emergency Management Consequence Management Advisory Team Erlanger, Kentucky 41018 May 2013 Radiological Survey of Coldwater Creek North St. Louis County, Missouri Airborne Spectral Photometric Environmental Collection Technology ------- Coldwater Creek Survey May 2013 Team Members EPA Region 7 Matthew Jefferson, Superfund Remedial Project Manager ASPECT Mark Thomas, PhD - Scientist, Team Lead John Cardarelli II, PhD, CHP, CIH, PE - Health Physicist, Rad Lead Timothy Curry, MS, PE - Finance and Operations Paul Kudarauskas, MLA - Environmental Scientist Kalman Co. Inc., Contract Support: Jeff Stapleton, MS - Principal Engineer Robert Kroutil, PhD - Senior Project Engineer Dave Miller, PE - Integration Engineer Airborne ASPECT Inc., Contract Support: Sam Fritcher, President Beorn Leger, Pilot Ken Whitehead, Pilot Richard Rousseau, System Operator Mike Scarborough, System Operator ii ------- Coldwater Creek Survey May 2013 Table of Contents Executive Summary iv Acronyms and Abbreviations v 1.0 Introduction 1 2.0 Descriptions of the Sites and Survey Areas 2 3.0 Natural Sources of Background Radiation 5 4.0 Survey Equipment and Data Collection Procedures 7 4.1 Radiation Detectors 7 4.2 Flight Parameters 7 5.0 Data Analyses 8 5.1 Radiological 9 6.0 Results 13 6.1 Radiological Results 13 6.2 Electronic Data 16 Appendix I : Uranium Decay Chain 17 Appendix II 18 Discussion about radiological uncertainties associated with airborne systems 18 Background radiation 18 Secular Equilibrium Assumption 18 Atmospheric Temperature and Pressure 19 Soil moisture and Precipitation 19 Topography and vegetation cover 19 Spatial Considerations 19 Comparing ground samples and airborne measurements 20 Geo-Spatial Accuracy 21 References 22 iii ------- Coldwater Creek Survey May 2013 Executive Summary The United States Environmental Protection Agency (EPA), Office of Emergency Management (OEM), Chemical Biological Radiological and Nuclear (CBRN) Consequence Management Advisory Team (CMAT) manages the Airborne Spectral Photometric Environmental Collection Technology (ASPECT) Program. This program provides scientific and technical support nationwide to characterize the environment using airborne technologies for environmental assessments, homeland security events, and emergency responses. In January 2013, the Agency for Toxic Substances and Disease Registry (ATSDR) asked EPA Region 7 if it would be possible to collect additional data along Coldwater Creek due to several health concerns received from the community. ATSDR believed this additional data would assist in addressing those health concerns. EPA Region 7 requested that the ASPECT Program conduct a radiological survey over the Coldwater Creek area in North St. Louis County, Missouri. The survey was conducted on March 8, 2013 between 10:00 a.m. and 12:00 noon. Investigations by the EPA, the United States Department of Energy (DOE) and the United States Army Corps of Engineers (USACE) have attributed potential radiological contamination in Coldwater Creek to runoff or windblown migration of prior storage of uranium-processing residues and wastes from the North County portion of the St Louis Formerly Utilized Sites Remedial Action Program (FUSRAP) sites. The St. Louis FUSRAP Downtown and North County sites were placed on the Superfund National Priorities List (NPL) in 1989. The USACE has removed the North County sources of these wastes, which came from ore-processing activities at the Downtown portion of the St. Louis FUSRAP sites. The purpose of the radiological survey was to identify areas of elevated gamma radiation in the Coldwater Creek areas. The ASPECT results for Coldwater Creek showed surface gamma emissions consistent with background levels throughout the Coldwater Creek survey area. RADIOLOGICAL About 2,200 gamma radiation measurements were collected and none indicated excess uranium or uranium decay products. The ASPECT measures gamma radiation from Bismuth-214 which is the ninth decay product in the Uranium-238 decay chain because Uranium-238 is not a strong gamma emitter. In this survey, Bismuth-214 most likely indicates the presence of Radium-226 (the fifth decay product of Uranium-238) rather than Uranium-238 since the original uranium ore was chemically separated from the rest of its decay products. The separation process invalidates a key assumption in the algorithms used to estimate equivalent uranium concentrations from the gamma radiation data; therefore, throughout this report "equivalent radium" will be reported instead of equivalent uranium. No elevated gamma radiation measurements were detected during the Coldwater Creek Survey. iv ------- Coldwater Creek Survey May 2013 Acronyms and Abbreviations AEC Atomic Energy Commission AGL above ground level ASPECT Airborne Spectral Photometric Environmental Collection Technology ATSDR Agency for Toxic Substances and Disease Registry Bi bismuth CBRN Chemical Biological Radiological Nuclear CERCLA Comprehensive Environmental Response, Compensation, and Liability Act CMAT Consequence Management Advisory Team cps counts per second DOE Department of Energy ENVI Environment for Visualizing Images EPA Environmental Protection Agency 214 eRa Equivalent Radium based on Bi region of interest eTh Equivalent Thorium based on 208T1 region of interest 214 eU Equivalent Uranium based on Bi region of interest FOV Field of view ft feet FUSRAP Formerly Utilized Sites Remedial Action Program GPS Global Positioning System Hz hertz IAEA International Atomic Energy Agency K potassium MeV Mega electron volts NCP National Oil and Hazardous Substances Pollution Contingency Plan Nal(Tl) sodium iodide thallium drifted detector NPL National Priorities List NORM Naturally Occurring Radioactive Material pCi/g picocuries per gram Ra radium ROD Record of Decision ROI Region-of-Interest Rn radon SLAPS St. Louis Airport Sites Th thorium T1 thallium U uranium |jR/hr microRoentgen per hour USACE United States Army Corps of Engineers ------- Coldwater Creek Survey March 2013 1.0 Introduction The EPA initiated the Airborne Spectral Photometric Environmental Collection Technology (ASPECT) Program shortly after 9/11. Its primary focus was the detection of chemicals using an infrared line scanner coupled with a Fourier transform infrared spectrometer mounted within an Aero Commander 680 twin-engine airplane. In 2008, ASPECT significantly upgraded the radiological detector system to improve its airborne gamma-screening and mapping capabilities. In 2012, a neutron detection system was installed. Currently, ASPECT is the only program in the United States with a 24/7/365 operational platform that conducts remote sensing for hazardous chemicals, gamma/neutron emitters, and aerial imaging. It has deployed to more than 130 incidents involving emergency responses, homeland security events, and environmental characterizations. Up to a four member crew, two pilots and two technicians, operate the airplane. A scientific support staff provides additional assessment and product development commensurate with the site specific needs. In January 2013, EPA Region 7 requested that the ASPECT Program conduct a radiological survey over the Coldwater Creek area located in North St. Louis County, Missouri. The survey was conducted on March 8, 2013. The purpose of the radiological survey was to identify areas of elevated radiation contamination as compared to normal background concentrations.* ASPECT uses multiple algorithms to produce a variety of products for decision makers. One algorithm requires measurements to be collected over an unaffected area to establish a local background. This area was located near Cora Island, northeast of the survey area. These measurements were used to determine the statistical significance for any excess eRa and the results are represented in a product called a "sigma plot." One sigma represents one standard deviation from expected background levels. While subsurface concentrations of gamma-emitting isotopes can be detected by the instrumentation, self- shielding of the ground limits its effective detection to a depth of about 30 centimeters or 12 inches (Bristol, 1983). * A "normal background" area was selected by the ASPECT subject matter experts to be an area northeast of the site where no known contaminants exist. Page 1 of22 ------- Coldwater Creek Survey May 2013 2.0 Description of the Coldwater Creek Survey Area Figure 1: Coldwater Creek area consists of an irregular shape area covering over 5,000 acres (8 square miles). It was separated into three sections designated A, B, and C for convenience. The St. Louis FUSRAP sites are comprised of the "Downtown" site located at the Mallinckrodt Chemical Plant in downtown St. Louis and the "North County" sites located near the Lambert St. Louis International Airport in St. Louis, Missouri. The North County sites consist of three areas previously used for storing radioactive and other wastes from uranium processing operations conducted by the Atomic Energy Commission (AEC) and its successor, DOE. None of the three areas is now owned by the Federal Government. The St. Louis Airport Site (SLAPS) area covers 21.7 acres immediately north of Lambert St. Louis International Airport, approximately 15 miles northwest of downtown St. Louis. It is bounded by a railroad track, Coldwater Creek (Figure 1), and McDonnell Boulevard. Radioactive metal scrap and drums of waste were stored in the SLAPS area in uncovered piles from 1947 to the mid-1960s, when they were transferred 0.5 mile northeast to the Hazelwood Interim Storage Site (HISS) area. Buildings in the airport area were razed, buried, and covered with clean fill after 1967. In 1969, the land was conveyed to the Lambert St. Louis Airport Authority. HISS and the Futura Coatings Co. plant cover 11 acres adjacent to Latty Avenue, Coldwater Creek, and Hanley Avenue. In 1966, Continental Mining and Milling Co. acquired the property and recovered uranium from wastes purchased from AEC's St. Louis operations. In 1967, the company sold the property and by 1973, most processing residues had been removed. LJnder the direction of the Nuclear Regulatory Commission (NRC), the present owner excavated contaminated soil and stored it in two large piles in the eastern portion of the 11 acres. Since the 1970s, Futura Coatings, a manufacturer of plastic coatings, has leased the western portion. Page 2 of21 ------- Coldwater Creek Survey May 2013 Congress transferred responsibility for FUSRAP site characterization and remediation to the USACE in October 1997 as part of the Energy and Water Development Appropriations Act of 1998. USACE is remediating the remaining sites within the framework of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) and the National Oil and Hazardous Substances Pollution Contingency Plan (NCP). While the DOE retains responsibility for FUSRAP, USACE implements the program under a USACE/DOE Memorandum of Understanding. The St. Louis FUSRAP cleanup began as follows: • March 1974 - AEC established FUSRAP • October 4, 1989 - The EPA listed St. Louis FUSRAP Downtown and North County sites on the NPL • June 29, 1990 - DOE and the EPA signed a Federal Facilities Agreement committing DOE to clean up low-level radioactive-contaminated soils at the Downtown and North County sites • August 27, 1998 - St. Louis Corps District issued a Record of Decision (ROD) for the Downtown sites • September 5, 2005 - St. Louis Corps District issued a ROD for the North County sites The remedy for the St. Louis FUSRAP RODs involves USACE contractors excavating radioactively-contaminated soils from numerous private and municipally owned properties and shipping these soils by rail car to disposal facilities in Idaho or Utah. Soil excavation work is ongoing in several locations in the Downtown and North County properties. USACE excavated 177,000 cubic yards of soil from the Downtown sites and 852,000 cubic yards of soil around the North County sites through September 2012. Investigations by EPA, DOE and USACE have attributed potential radiological contamination in Coldwater Creek to runoff or windblown migration of the prior storage of uranium-processing residues and wastes from the North County portion of the St. Louis FUSRAP sites. USACE has removed the North County sources of these wastes, which came from ore-processing activities at the Downtown portion of the St. Louis FUSRAP sites. The USACE conducts bi-annual sediment and water sampling at six different locations in Coldwater Creek as part of its environmental monitoring program. USACE reviews and evaluates data in its annual environmental monitoring reports. Although USACE has sampled sediment and water along Coldwater Creek since 1998, some data gaps exist. As part of the plan to work from upstream to downstream, the USACE sampled Coldwater Creek from McDonnell Boulevard to Frost Avenue in October and November 2012. The results of the sampling will be summarized in a report expected at the end of 2013. In addition, USACE is developing a sampling plan for the portion of Coldwater Creek from Frost Avenue to St. Denis Bridge. Once the sampling plan has been issued, the USACE will begin sampling this stretch of the creek. The results will determine the density of sampling required throughout the remainder of the creek to the mouth of the Missouri River. The purpose of the final round of sampling will Page 3 of21 ------- Coldwater Creek Survey May 2013 be to confirm the creek meets the North County ROD's cleanup requirements or to identify and quantify any material requiring removal to meet these requirements. Page 4 of 21 ------- Coldwater Creek Survey May 2013 3.0 Natural Sources of Background Radiation Naturally occurring radioactivity originates from cosmic radiation, cosmogenic radioactivity, and primordial radioactive elements that were created at the beginning of the earth about 4.5 billion years ago. Cosmic radiation consists of very high-energy particles from extraterrestrial sources such as the sun (mainly alpha particles and protons) and galactic radiation (mainly electrons and protons) and contributes to the total radiation exposure on earth. The intensity of cosmic radiation increases with altitude, doubling about every 6,000 ft, and with increasing latitude north and south of the equator. The cosmic radiation level at sea level is about 3.2 |iR/h and nearly twice this level in locations such as Denver, CO. (Grasty, et al., 1984). Cosmogenic radioactivity results from cosmic radiation interacting with the earth's upper atmosphere. Since this is an ongoing process, a steady state has been established whereby cosmogenic radionuclides (e.g., 3H and 14C) are decaying at the same rate as they are produced. These sources of radioactivity were not a focus of this survey and were not included in the processing algorithms. Primordial radioactive elements found in significant concentrations in the crustal material of the earth are potassium, uranium and thorium. Potassium is one of the most abundant elements in the Earth's crust (2.4% by mass). One out of every 10,000 potassium atoms is radioactive potassium-40 (40K) with a half-life (the time it takes to decay to one half the original amount) of 1.3 billion years. For every 100 40K atoms that decay, 11 become Argon-40 (40A) and emit a 1.46 MeV gamma-ray. Uranium is ubiquitous in the natural environment and is found in soil at various concentrations with an average of about 1.2 pCi/g. Natural uranium consists of three isotopes with about 99.3% being uranium-238 ( U), about 0.7% being uranium-235 235 234 ( U), and a trace amount being uranium-234 ( U). Thorium-230 and Radium-226, as decay products of Uranium-238 would be expected to have the same activity concentrations as background Uranium-238 except that in some instances, changes in soil chemistry may cause one species to migrate with the groundwater and disrupt the local equilibrium so that the concentrations of Ra-226 and Th-230 may differ slightly from the U-238 concentration. The ninth decay product of Uranium-238 is Bismuth-214 which is used to estimate the uranium present since it is relatively easy to detect. Bismuth-214 has a very short half-life relative to Ra-226, Th-230 or U-238, therefore it can be used to infer the presence of Ra-226, Th-230, and U-238 for airborne applications. When it is used to estimate these isotopes, the precursor designator "e" (which means equivalent) is used to identify that a decay product was used to estimate the Ra-226, Th- 230, or U-238 levels and is reported as eRa, eTh, and eU accordingly. See Appendix 1 for the Uranium decay chain. Thorium-232 is the parent radionuclide of one of the four primordial decay chains. It is about four times more abundant in nature than uranium and also decays through a series of decay products to a stable form of lead. Thorium-232 is not part of the Uranium decay chain. The thorium content of rocks ranges between 0.9 pCi/g and 3.6 pCi/g with an average concentration of about 1.3 pCi/g (Eisenbud, 1987). The ninth decay product, Page 5 of21 ------- Coldwater Creek Survey May 2013 208 thallium-208 ( Tl), is used to estimate the presence of thorium by its 2.61 MeV gamma- ray emission. All these primordial radionuclides are present in varied concentrations in building materials which make-up part our naturally occurring radioactive background (Table 1) (NCRP, 1987). Other radiation sources that contribute to our external radiation include nuclear fallout and man-made radiation such as medical and industrial uses of radiation or radioactive sources. Table 1: Average concentrations of uranium and thorium in some building materials Material Uranium-238 Thorium-232 (pCi/g) (pCi/g) Granite 1.7 0.22 Sandstone 0.2 0.19 Cement 1.2 0.57 Limestone concrete 0.8 0.23 Sandstone concrete 0.3 0.23 Wallboard 0.4 0.32 By-product gypsum 5.0 1.78 Natural gypsum 0.4 0.2 Wood - - Clay brick 3 1.2 Page 6 of 21 ------- Coldwater Creek Survey May 2013 4.0 Survey Equipment and Data Collection Procedures 4.1 Radiation Detectors The radiological detection technology consisted of two RSX-4 Units (Radiation Solutions, Inc.. 386 Watline Avenue, Mississauga, Ontario, Canada) (Figure 2). Each unit was equipped with four 2"x4"xl6" thallium-activated sodium iodide (NaI[Tl]) scintillation crystals. The Radiation Solutions RSX-4 unit was used during this survey for airborne detection and measurement of low-level gamma radiation from both naturally occurring and man-made sources. It can also be used for ground-based measurements. These units use advanced digital signal processing and software techniques to produce spectral data equivalent to laboratory quality. The unit is a fully integrated system that includes an individual high resolution (1,024 channel) advanced digital spectrometer for each detector. A high level of self diagnostics and performance verification routines such as auto gain stabilization are implemented with an automatic error notification capability, assuring that the resulting maps and products are of high quality and accuracy. 4.2 Flight Parameters The ASPECT airplane used the following flight procedures for data collection on March 8,2013: Altitude above ground level (AGL): 500 feet Target Speed: 110 knots (125 mph) Line Spacing: 500 feet Data collection frequency: 1 Hz for radiological survey Figure 2: USX4 unit showing four detector locations. Page 7 of21 ------- Coldwater Creek Survey Figure 3: Flight lines for the radiological survey over the Coldwater Creek site. For environmental radiation surveys using a fixed-wing airplane, flying height above ground level has been more or less standardized at 400 feet (IAEA 1991, 2003) and 5). ASPECT target height for this survey was 500 feet to permit safer flying conditions. Aerial and ground-based surveys collected over phosphate mines in central Florida provided evidence that the increased altitude flight parameters have no significant effect on the airplane sensitivity or resolution for environmental surveys (Cardarelli et al., 2011a, 2011b). 5.0 Data Analyses A unique feature of the ASPECT chemical and radiological technologies includes the ability to process spectral data automatically in the airplane with a full reach back link to the program QA/QC program. While data are generated in the airplane using automated algorithms, a support data package is extracted by the reach back team and independently reviewed for scientific validity and confirmation. The following sections detail the analyses completed for this survey. Page 8 of21 ------- Coldwater Creek Survey May 2013 5.1 Radiological Aerial gamma spectroscopy analyses have several distinctive considerations that must be addressed in order to obtain accurate and meaningful products. Due to the unique interactions of gamma rays with matter, special techniques are used to process the data. For a uranium/radium survey, care must be taken to account for the background levels of uranium/radium. This process was described in Section 3. The ASPECT measures gamma radiation from Bismuth- 214 which is the ninth decay product in the Uranium-238 decay chain because Uranium-238 is not a strong gamma emitter. In this survey, Bismuth-214 most likely indicates the presence of Radium-226 (the fifth decay product of Uranium-238) rather than Uranium-238 since the original uranium ore was chemically separated from the rest of its decay products. The separation process invalidates a key assumption in the algorithms used to estimate equivalent uranium concentrations; therefore, throughout this report "equivalent radium" will be reported instead of equivalent uranium. Several environmental factors, such as moisture, may significantly affect the detector response. Specifically, precipitation disturbs the equilibrium of the uranium decay chain and soil moisture actually shields some of the gamma rays and prevents them from reaching the detectors. There are several similar considerations that are discussed in Appendix II. In the days leading up to the survey, the St. Louis area had received significant snowfall. During the survey, the snowfall had melted, but the ground was likely fairly saturated. This additional moisture in the ground would serve as a partial shield and reduce the intensity of radiation reaching the detectors. A 10 percent increase in soil moisture would decrease the total count rate by about 10 percent. The higher than average energy from Bismuth-214 would be slightly less affected, because soil moisture affects the detection of lower energy gamma rays more than higher energy gamma rays. Radiological spectral data are collected every second along with GPS coordinates and other data reference information. These data are subject to quality checks within the Radiation Solutions internal processing algorithms (e.g. gain stabilization) to ensure a good signal. If any errors are encountered with a specific crystal during the collection process, an error message is generated and I Upload data to ASPECT servers for postprocessing Page 9 of 21 ------- Coldwater Creek Survey May 2013 the data associated with that crystal are removed from further analyses. Prior to the survey, the RSX-4 units go through a series of internal checks. When powered up, the crystals go through an automated gain stabilization process. The process uses naturally occurring radioelements of potassium, uranium, and thorium to ensure proper spectral data collection. If no problems are detected, a green indicator light notifies the user that all systems are good. A yellow light indicates a gain stabilization issue with a particular crystal. This can be fixed by waiting for another automatic gain stabilization process to occur or the user can disable the particular crystal via the RadAssist Software application. A red light indicates another problem and would delay the survey until it can be resolved. The "background data" in this context includes radiation contributions from radon, cosmic, and airplane sources. These are unwanted contributions to the radiation measurements and must be subtracted from the raw measurements to properly estimate radiation contributions from terrestrial sources only. Ideally, these data are collected over water at the survey altitude but when a large body of water does not exist, research has shown that an acceptable alternative is to collect data 3,000 ft above the ground (AGL) (Bristow, 1983). At this altitude, atmospheric attenuation reduces the terrestrial radiation to a negligible level but is still low enough that cosmic radiation is not significant. A "test line" in this context is flown at survey altitude near the survey area. The line is not expected to contain any known elevated concentrations of naturally occurring radioactive material (NORM) or man-made radionuclides. For this survey, an area near Cora Island, west of the site, was used for this purpose. Hence, this test line serves as the natural background area (after the radon, cosmic, and airplane sources are subtracted) from which the survey data is compared to determine if any statistical anomalies occur within the survey area. The calibration coefficients were determined based on methodology published by the International Atomic Energy Agency (IAEA, 2003). One of the possible software programs available to the ASPECT team for processing radiological data is the Environment for Visualizing Images (ENVI) code. For this survey, ENVI® Version 5.0; ASPECT Version 9.1.1.2, Build 1302282009 (Exelis Visual Information Solutions, Boulder, CO) was used to produce excess eRa sigma point plots 214 showing locations where Bi was out of balance with the surrounding environment. The process is depicted below. Page 10 of 21 ------- Coldwater Creek Survey May 2013 ENVI ASPECT Method I Live time correction I Subtract cosmic and airplane background contribution (3,000 ft AGL) I "Test line" (determines "normal") Height correction (|i=0.0018 m-1) Calculate 214Bi ROI K-value (median) I Subtract radon contribution (test lines) I 214 Determine net count rate for Bi and standard deviation (sigma value; o) I Determine Sigma Values (<-6o, -6 to -4; -4 to -2; -2 to 2; 2 to 4, 4 to 6, >6o) I Create excess eRadium sigma plots The excess eRa sigma plots are used to help determine whether the detected radiation associated with the Bi-214 is consistent with areas known not to contain any elevated radiation signatures, e.g. a background area. Because the uranium/radium concentration will vary slightly from point to point, a statistical analysis is used to help make this determination. The first step of this process is to determine the background variation. This is done by measuring an area that is close to the site but not contaminated by the site or containing any similar contaminants from other sources. All of the site measurements are then compared to this to make sure the variation is within the variation of the background data. Points that are noticeably different from the background points are likely to be of man-made origin. Excess eRa sigma points were determined using an algorithm based on the assumption that natural background radioisotope contributions are stable over large geographical areas. This will result in a spectral shape that remains essentially constant over large count rate variations. ASPECT used the ENVI code analysis wherein a background "test line" is flown with similar characteristics in an area physically close to the survey location but not affected by the contamination. This background is used to compare the readings by statistical methods. For this survey, the area was near Cora Island just northeast of the site. Page 11 of 21 ------- Coldwater Creek Survey May 2013 214 To determine excess radium count rate, the region-of-interest (ROI) around Bi (1659 keV to 1860 keV) is compared to the ROI represented by nearly the entire spectrum, called the Total Count ROI (36 keV to 3,027 keV). The count rate ratio between these windows (e.g., Uranium ROI / Total Count Rate ROI) is relatively constant and is referred to as the "K" value. A K-value was determined from the "test line" data collected before and after each survey. The median K-value (e.g., most common Re- value) was used in the algorithm to determine excess eRa. K-value = Count rate in tarset region-of-interest Count rate in "Total Count" region-of-interest Excess activity can be estimated using the following formula: Excess eRa activity = Measured eRa activity - Estimated eRa activity Where: Measured eRa activity = the measured count rate within the eRa ROI during the survey Estimated eRa activity = K-value * measured count rate in Total Count ROI during the survey The equation for excess activity becomes: EXCESS eRa = Measured eRa ROI - (K * Measured Total Counts ROI) The most likely value of net "excess eRa" should be zero, and since radiological disintegrations are randomly occurring events, the second-by-second "excess eRa" results are statistically distributed about the mean in a normal Gaussian distribution (Figure 5). Page 12 of 21 ------- Coldwater Creek Survey May 2013 Normal Gaussian Linear Distribution /I h- P(x) - 50% (PE) - - 68.27% (ox) - . 90 % _ - 95.45 %(2a) - - 99.7 % (3o) - Standard deviation (g, sigrna) represents the spread of the data about the mean. In this survey, the mean value (net "eRa") was zero. 1 g = 68.27% of the data 2 g = 95.45% of the data 3 g = 99.73% of the data 4 g = 99.99366% of the data 5 o = 99.99994% of the data 6 o = 99.999999% of the data Figure 4: Normal Gaussian Distribution and associated confidence intervals. Every measurement was scored according to its "sigma" value and color coded according to the ranges in Figure 5. The color code and range were arbitrarily selected to limit the risk of false positives to 1 in about 15,800,000 samples (greater than or less than 6 sigma). Sigma Values (Excess Bismuth-214) Less than-6.0 ^^-2.0 to +2.0 Greater than +6.0 ^ -6.0 to-4.0 <^+2.0 to +4.0 ^ -4.0 to-2.0 ((§)) +4.0 to +6.0 Figure 5: Standard Deviation Legend for Excess eRadium 6.0 Results This survey on March 8, 2013 covered over 8 square miles of land and consisted of about 2,200 radiological data points. 6.1 Radiological Results The radiological product consisted of an eRa sigma plot, which represents the number of standard deviations from a normal background. Page 13 of 21 ------- Coldwater Creek Survey May 2013 6.1.1 eRa Sigma Plots Since uranium (and radium) is a naturally occurring radionuclide and is ubiquitous in nature, an analysis was conducted to determine the statistical significance of any deviation from naturally occurring background levels. The analysis is referred to as a sigma plot and is discussed in Section 5. Areas on a sigma plot with values greater than 4 sigma are very likely to contain uranium or its decay products in concentrations greater than background, while values greater than 6 sigma almost certainly indicate above background levels for uranium and its decay products. Of the nearly 2,200 data points collected in this survey, none was within 4 to 6 sigma (standard deviations) from the mean value and none was greater than 6 sigma from the mean. Table 2 summarizes the sigma plot results for excess eRa for the entire survey Coldwater Creek area. Approximately 94 percent of the area surveyed was below the 2 sigma threshold. Less than 6 percent of the surveyed area fell between 2 and 4 sigma, accounting for all of the data taken. No data points indicated variation from background above the 4 sigma level. All areas were consistent with natural background. Table 2: Statistical data of eRa results for each survey area. Fit. Block Area # Data < 2 Sigma > 2 Sigma >4 Sigma >6 Sigma 1 Coldwater Creek A 891 834 57 0 0 2 Coldwater Creek B 462 441 21 0 0 3 Coldwater Creek C 822 777 45 0 0 Totals 2,175 2,052 123 0 0 94.3% 5.7% 0% 0% Page 14 of 21 ------- Coldwater Creek Survey Figure 6: Excess eRadium Sigina Plot Coldwater Creek Survey March 8, 2013 May 2013 ^Florissant '©'Spanish Lak^ © 2013 Google -0 Berkeley '.lit 38 769515 Ion -90'?58646' Sigma Values (Excess Bismuth-214) Less than-6.0 (<§J> -2.0 to +2.0 Greater than+6.0 ^ -6.0to-4.0 (@) +2.0 to +4.0 ^ -4.0 to -2.0 +4.0 to +6.0 Flight Parameters 500 ft altitude 500 ft line spacing 110 knots 1 second acquisition time All areas were consistent with natural background. This image should not be used independently to assess potential health risks. Additional information is necessary to make appropriate health-related decisions. Page 15 of 21 ------- Coldwater Creek Survey May 2013 6.2 Electronic Data Access to the electronic data can be provided by contacting: Matthew Jefferson Superfund Remedial Project Manager for St. Louis FUSRAP/Coldwater Creek EPA Region 7 Jefferson.Matthew@epa. gov Page 16 of 21 ------- Coldwater Creek Survey May 2013 Appendix I : Uranium Decay Chain Page 17 of 21 ------- Coldwater Creek Survey May 2013 Appendix II Discussion about radiological uncertainties associated with airborne systems. Ideally the airborne radiation measurements would be proportional to the average surface concentrations of radioactive materials (mainly NORM). However, there are several factors that can interfere with this relationship causing the results to be over- or under- estimated, as described below. Additionally, two other sections in this Appendix discuss how airborne data should be interpreted and compared to ground-based surface measurements. Background radiation Airborne gamma-spectroscopy systems measure radiation originating from terrestrial, radon, airplane, and cosmic sources. To obtain only the terrestrial contribution, all other sources need to be accounted for (subtracted from the total counts), especially for this survey where small differences are important. Radon gas is mobile and can escape from rocks and soil and accumulate in the lower atmosphere. Radon concentrations vary from day to day, with time of day, with weather conditions (e.g., inversions and stability class), and with altitude. It is the largest contributor among background radiation and its decay 214 product, Bi, is used to estimate radium and uranium concentration in the soil. Radon is normally accounted for in the processing algorithm by flying specific test lines before and after each survey and comparing the results. Cosmic and airplane radiation (e.g., instrument panels and metals containing small amounts of NORM) also provide a small contribution to the total counts. These are accounted for in the processing algorithm by flying a "high-altitude" or "water" test line and subtracting these contributions for the survey data. Secular Equilibrium Assumption Secular equilibrium is assumed in order to estimate thorium or uranium concentrations 208 214 from one of its decay products, T1 or Bi respectively. Secular equilibrium exists when the activity of a decay product equals that of its parent radionuclide. This can only occur if the half-life of the decay product is much shorter than its parent and the decay product stays with its parent in the environment. In this case, the measurement of 214Bi gamma emission is used to estimate the concentration of its parent radionuclide, uranium, 222 if one assumes all the intermediate radionuclides stay with each other. However, Rn is a noble gas with a half-life of 3.8 days and may de-gas from soils and rocks fissures due to changes in weather conditions. Due to the relatively long half-life (relative to 214Bi) and the combined effect of radon gas mobility and environmental "chemical" migration, it is not certain whether the secular equilibrium assumption is reasonable. In addition, human intervention in this natural chain of events may have caused an increased uncertainty in uranium concentration estimates. This becomes more complex with uranium ore waste materials, where the uranium has been extracted and the resulting waste materials contain mostly uranium decay products, e.g. radium. In this situation, the Page 18 of 21 ------- Coldwater Creek Survey May 2013 eRa concentration would be a better estimate for radium concentration rather than uranium concentrations, as is the case in this survey. Atmospheric Temperature and Pressure The density of air is a function of atmospheric temperature and pressure. Density increases with cooler temperatures and higher pressures, causing a reduction in detection of gamma-rays. This reduction in gamma-ray detection is called attenuation and it is also a function of the gamma-ray energy. Higher energy gamma-rays are more likely to reach 214 the detectors than lower energy gamma-rays. For example, 50% of the Bi 1.76 MeV gamma-rays will reach the detector at an altitude of 300 ft whereas only 44% of the 40K 1.46 MeV gamma-rays will reach the detector. Temperature and pressure changes contribute little to the overall uncertainties associated with airborne detection systems as compared to other factors. Despite the nominal correction, the ASPECT program accounts for temperature and pressure effects. Soil moisture and Precipitation Soil moisture can be a significant source of error in gamma ray surveying. A 10% increase in soil moisture will decrease the total count rate by about the same amount due to absorption of the gamma rays by the water. Snow cover will cause an overall reduction in the total count rate because it also attenuates (shields) the gamma rays from reaching the detector. About 4 inches of fresh snow is equivalent to about 33 feet of air. There was no significant precipitation during this survey; however, the ground was likely saturated from recent snow melt. Topography and vegetation cover Topographic effect can be severe for both airborne and ground surveying. Both airborne and ground-based detection systems are calibrated for an infinite plane source which is referred to as 2% geometry (or flat a surface). If the surface has mesas, cliffs, valleys, and large height fluctuations, then the calibration assumptions are not met and care must be exercised in the interpretation of the data. Vegetation can affect the radiation detected from an airborne platform in two ways: (1) the biomass can absorb and scatter the radiation in the same way as snow leading to a reduced signal, or (2) it can increase the signal if the biomass concentrated radionuclides found in the soil nutrients are present in the leaves or surfaces of the vegetation. Spatial Considerations Ground-based environmental measurements are usually taken 3 ft above the ground with a field of view of about 30 ft2. The ASPECT collected data at about 500 ft above the ground with an effective field of view of about 10 acres. These aerial measurements provide an average surface activity over the effective field of view. If the ground activity varies significantly over the field of view, then the results from ground- and aerial-based systems may not agree. It is not unusual to have differences as much as several orders of magnitude depending on the survey altitude and the size and intensity of the source material. For example, in the figures below, if the "A" circle represents the * Attenuation coefficients of 0.0077m"1 for 1.76 MeV and 0.0064m"1 for 1.46 MeV. Page 19 of 21 ------- Coldwater Creek Survey May 2013 detector field of view and the surrounding area had no significant differences in surface activity, a 500 ft aerial measured could correlate to a ground-based exposure-rate of 3.5 |iR/h, However, if all the activity was contained in a small area such as a single small structure containing uranium waste materials (represented by the blue dot within the field of view of "B"), a 500 ft aerial measurement may still provide the same exposure-rate measurement but the actual ground-based measurements could be as high as 3,150 |iR/h. Detector Field of View Concentration A = Concentration B Aerial measurement is Aerial measurement a good indicator of will not capture average ground differences in smaller activity. areas of intense activity. Illustration of aerial measurement capabilities and interpretation of the results Comparing ground samples and airborne measurements Aerial measurements are correlated to ground concentrations through a set of calibration coefficients. The ASPECT calibration coefficients for exposure-rate, potassium, uranium, and thorium concentrations were derived from a well characterized "calibration" strip of land near Las Vegas, Nevada. In-situ gamma spectroscopy and pressurized ionization chambers measurements were used to characterize the area. One must exercise caution when using a laboratory to analyze soil samples to verify or validate aerial measurements because differences will occur. In addition to local variations in radionuclide concentrations, which are likely to be the most significant issue, differences may arise due to laboratory processing. Laboratory processing typically includes drying, sieving and milling. These processes remove soil moisture, rocks and vegetation, and will disrupt the equilibrium state of the decay chains due to liberation of the noble gas radon. Thus reliance on 208T1 and 214Bi as indicators of 232Th 238 and U (as is assumed for aerial surveying) is made more complex. In addition, aerial surveys cannot remove the effects of vegetation on gamma flux. Intercomparisons must minimize these differences and recognize the effects of differences that cannot be eliminated. Page 20 of 21 ------- Coldwater Creek Survey May 2013 Geo-Spatial Accuracy All aerial measurements collected by the ASPECT airplane are geo-coded using latitude and longitude. The position of the airplane at any time is established by interpolating between positional data points of a non-differential global positioning system and referencing the relevant position to the time that the measurement was made. Time of observation is derived from the airplane computer network which is synchronized from a master GPS receiver and has a maximum error of one second . Timing events based on the network running the Windows-based operating system and the sensor timing triggers have a time resolution of 50 milliseconds, so the controlling error in timing is the network time. If this maximum timing error is coupled to the typical ground velocity of 55 meter/sec of the airplane, an instantaneous error of 55 meters is possible due to timing. In addition, geo-positional accuracy is dependent on the instantaneous precision of the non-differential GPS system which is typically better than 30 meters for any given observation. This results in an absolute maximum instantaneous error of about 80 meters in the direction of travel. For measurements dependent on airplane attitude (photographs, IR images), three additional errors are relevant and include the error of the inertial navigation unit (INU), the systemic errors associated with sensor to INU mounting, and altitude errors above ground. Angular errors associated with the INU are less than 0.5 degrees of arc. Mounting error is minimized using detailed bore alignment of all sensors on the airplane base plate and is less than 0.5 degrees of arc. If the maximum error is assumed, then an error of 1.0 degree of arc will result. At an altitude of 150 meters (about 500 feet) this error translates to about 10 meters. Altitude above ground is derived from the difference in the height above the geoid (taken from the GPS) from the ground elevation derived from a 30 meter digital elevation model. If an error of the model is assumed to be 10 meters and the GPS shows a typical maximum error of 10 meters, this results in an altitude maximum error of 20 meters in altitude error. If this error is combined with attitude and the instantaneous GPS positional error (assuming no internal receiver compensation due to forward motion), then an error of about 50 meters will result. The maximum forecasted error that should result from the airplane flying straight and level is +/- 130 meters in the direction of travel and +/- 50 meters perpendicular to the direction of travel. Statistical evaluation of collected ASPECT data has shown that typical errors of +/- 22 meters in both the direction of and perpendicular to travel are typical. Maximum errors of +/- 98 meters have been observed during high turbulence conditions. * The ASPECT network is synchronized to the master GPS time at system start-up. If the observed network/GPS time difference exceeds 1 sec, at any time after synchronization, the network clock is reset. Page 21 of 21 ------- Coldwater Creek Survey May 2013 References BRISTOW, Q. (1983). Airborne y-ray spectrometry in Uranium Exploration. Principles and Current Practice. International Journal of Applied Radiation and Isotopes 34(1), 199-229. CARDARELLI, J., THOMAS, M., and CURRY, T. (2011). Environmental Protection Agency airborne detection capabilities. Health Physics Society Midyear Meeting: Radiation Measurements. Charleston, South Carolina, February 8, 2011. (page 27) Abstract available at http://www.hps.org/documents/2011 midyear final program.pdf Accessed on 10 April 2013. CARDARELLI, J., THOMAS, M., CURRY, T., KUDARAUSKAS, P., and KAPPELMAN, D. (2011). Aerial and Ground Radiological Surveys: Phosphate Mines in January 2011. US EPA. Available at http://epa.gov/region4/superfund/images/nplmedia/pdfs/coroiflrt2011.pdf Accessed on 12 March 2013. EISENBUD, M., (1987). Environmental Radioactivity: From Natural Industrial and Military Sources. 3rd Edition. Academic Press, Inc., New York, NY. GRASTY, R.L., CARDSON, J.M. CHARBONNEAU, B.W., HOLMAN, P.B., (1984). Natural Background Radiation in Canada, Geol. Surv. Can. Bull. 360. IAEA (1991). International Atomic Energy Agency. Airborne Gamma Ray Spectrometer Surveying. Technical Report Series No. 323. (International Atomic Energy Agency, Vienna). IAEA (2003). International Atomic Energy Agency. Guidelines for radioelement mapping using gamma ray spectrometry data. Technical Document 1363. IAEA, Vienna. Available at http://www- pub.iaea.org/mtcd/publications/pdf/te 1363 web.pdf. Accessed on 12 March 2013. NCRP (1987). National Council on Radiation Protection and Measurements. Exposure of the Population in the United States and Canada from Natural Background Radiation. NCRP Report 94 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). 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