PUBLIC HEALTH ASSESSMENT
PADUCAH GASEOUS DIFFUSION PLANT (U.S. DOE)
PADUCAH, MCCRACKEN COUNTY, KENTUCKY
ATSDR scientists identified completed and potential pathways of human exposure to plants andanimals containing contaminants of concern.
ATSDR scientists estimated human exposure doses using the maximum and average contaminantconcentrations in Tables 18A and 18B and other conservative assumptions. We estimated exposuredoses for a child (1 to 6 years old) who weighs 13 kg and for an adult who weighs 70 kg. Weassumed average food consumption rates for persons from the United States in each biota category(Table 19). For fish consumption, we assumed average intake rates for subsistence fishers and theirchildren and for recreational fishers and their children. We also assumed that 20% of all food in aperson's diet was harvested from a contaminated source. Estimated chemical exposure doses are inTables 20A and 20B for a child and an adult, respectively. The estimated doses (total committeddoses) for radioactive contaminants are in Tables 21A and 21B for children and adults, respectively.
|Age Group||Fish |
|Apples, Grapes |
|Nuts, Legumes |
|Green Vegetables |
|Yellow Vegetables |
(1 to 6 years)
|1 Fish consumption rates are for average subsistence fishers and recreational fishers. Intake rates for all other types of biota are based on average U.S. persons (for game), average U.S. per capita rates (for persimmons), or southern U.S. per capita rates (for apples, nuts, legumes, dark green vegetables, yellow vegetables, and tomatoes).|
|Sources: Fish = Columbia River Inter-Tribal Fish Commission (CRITFC), 1994, and EPA Exposure Factors Handbook (EFH), 1999 . |
Game = U.S. Dairy Association (USDA) Nationwide Consumption Survey, 1987-1988, in EPA, 1995 .
Apples, nuts, legumes, dark green vegetables, yellow vegetables, and tomatoes = EPA, 1995 , reference EPA, 1984d.
Grapes and persimmons = U.S. EPA's Dietary Risk Evaluation System (DRES), in EPA, 1995 .
|Key: g/day = grams per day; g/kg/day = grams of food per kilogram of body weight per day; S = subsistence; R = recreational|
ATSDR scientists then compared the total estimated exposure doses for chemicals to appropriate health guidelines. Tables 20A and 20B illustrate this comparison. (Appendix C of this report describes the health guidelines we used.) Only the PCB exposure doses for specific exposure scenarios exceed the health guideline; they will be discussed further in the public health implications section. For radioactive materials, the estimated annual committed effective doses for this exposure pathway are less than 1 millirem, which would not cause an adverse health effect. Nonetheless, the public health implications section discusses exposure to radioactive contaminants for each exposure pathway; therefore, they are included in Table 22.
|Apples||Persimmons||Nuts, Legumes||Yellow or Green Vegetables||Estimated Total Exposure Dose per Chemical||Health Guide-line1||Is Total Exposure Dose > Health Guideline?|
|Fluoride||0.0043||0.0043||0.05 to 0.06||No|
|PCB (Aroclor 1254)||0.00164||0.00164||0.00002||Yes|
|1 For an explanation of health guidelines and exposure calculations, refer to Appendix C.|
|Key: NR = not reported; ND = not detected; PCBs = polychlorinated biphenyls|
|Apples, Grapes||Persimmons||Nuts, Legumes||Yellow Vegetables||Estimated Total Exposure Dose per Chemical||Health Guide-line1||Is Total Exposure Dose > Health Guideline?|
|Fluoride||NR||NR||NR||NR||NR||NR||0.0043||0.05 to 0.06||No|
|PCB (Aroclor 1254)||0.00092||NR||NR||NR||NR||NR||0.00092||0.00002||Yes|
|1 For an explanation of health guidelines and a discussion of the dose calculations, refer to Appendix C.|
|Key: NR = not reported; PCBs = polychlorinated biphenyls|
|Radioactive Contaminant||Fish||Game |
|Apples, Grapes||Other Fruit |
|Nuts, Legumes||Green Vegetables||Yellow Vegetables1||Tomatoes||Total Estimated Committed Effective Dose|
|Technetium 99||0.018 |
|Uranium 234||0.006 |
|Uranium 235||0.002 |
|Uranium 238||0.002 |
|Thorium 230||0.008 |
|Plutonium 239||0.010 |
|Americium 241||0.004 |
|Neptunium 237||0.000 |
|Strontium 90||0.029 |
|Cesium 137||0.000 |
|Estimated annual committed effective dose||0.036 |
Total estimated annual committed effective dose for all above radioactive contaminants in food crops is 0.39 millirems (or 3.9E-03 millisieverts)
|1 "Yellow vegetables," in this table, includes eggplant, mixed vegetables, soybeans, carrots, corn, and squash.|
|Radioactive Contaminant||Fish||Game |
|Apples, Grapes||Other Fruit |
|Nuts, Legumes||Dark Green Vegetables||Yellow Vegetables1||Tomatoes||Total Estimated Committed Effective Dose|
|Technetium 99||0.024 |
|Uranium 234||0.017 |
|Uranium 235||0.004 |
| 0.044 |
|Uranium 238||0.004 |
|Thorium 230||0.027 |
|Plutonium 239||0.015 |
|Americium 241||0.007 |
|Neptunium 237||0.000 |
|Strontium 90||0.035 |
|Cesium 137||0.000 |
|Estimated annual committed effective dose||0.076 |
Total estimated annual committed effective dose for all above radioactive contaminants in food crops is 0.70 millirems (or 7.0E-03 millisieverts)
|1 "Yellow vegetables," in this table, includes eggplant, mixed vegetables, soybeans, carrots, corn, and squash.|
Chemical and radioactive contaminants have been detected in fish samples from Little Bayou andBayou Creeks and from outfalls east of the plant. Most of the biota sampling data reflect current orrecent past conditions.
The estimated total annual committed effective doses for all radioactive contaminants in biota do notexceed 1 millirem. This level would not produce an adverse health effect; however, radioactivematerials from the combined exposure pathways will be discussed in the public health implicationssection.
The estimated total exposure doses for total PCBs and Aroclor 1254 exceed the health guidelines.PCB exposure doses were calculated under two different exposure scenarios (subsistence fishers andrecreational fishers) for adults and children in Bayou Creek, Little Bayou Creek, andOutfall#11/Little Bayou Creek. Outfall #11 had the highest concentrations of PCBs in fish. Thisoutfall has restricted access and is posted with fish consumption advisory signs . It is unlikelythat anyone would regularly fish in Outfall #11 and/or regularly eat fish caught at Outfall #11. Fishcollected from Little Bayou Creek had higher PCB concentrations than fish from Bayou Creek.(Our site visits and observations indicate that people are more likely to fish in Bayou Creek.) Itshould be noted that the Ohio River provides a more extensive fishing area and offers easier access;therefore, fishing in the PGDP area is probably rarer than we estimate it to be. PCB analyses werenot conducted for food crops; however, uptake of PCBs by plants is very low , and fishconsumption would be the main exposure pathway for PCBs. ATSDR's assumptions areconservative and may overestimate exposure doses. Despite uncertainties in estimating humanexposure doses, total PCBs and Aroclor 1254 were selected as contaminants of concern forcurrent biota exposure pathways.
Since the majority of off-site releases occurred in the 1950s and early 1960s, and no sampling dataare available for that time period, ATSDR scientists assumed that higher concentrations of chemicaland radioactive contaminants in biota were possible. Also, outfalls to the creeks would not havebeen posted or restricted as they now are. Having discussed the matter with staff at the KentuckyDepartment for Environmental Protection, however, we believe that very few fish, if any, lived inLittle Bayou Creek during these early years and very few people, if any, chronically fished in theseareas. Since there were better places to fish in close proximity, we believe fishers would not haveroutinely fished in this creek system; however, despite the uncertainties, we selected total PCBsand Aroclor 1254 as contaminants of concern for past biota exposure pathways.
With access restrictions to areas near Outfalls #10 and #11 and posting of signs along Little BayouCreek, potential future chronic exposure is not expected. However, other off-site fishing areas, suchBayou Creek and some nearby ponds, are potential sources of fish with chemical and radioactivecontaminants and should continue to be monitored. Until the site remediation is completed, cropsand game may continue to be contaminated at low levels. Therefore, ATSDR scientists identifiedpotential future exposure pathways for biota. If additional biota sampling data become available, these human exposure pathways will be re-evaluated.
|Major Source||Contaminants||Point of Exposure||Route of Exposure||Exposed Population||Period of Time||Maximum Estimated Exposure Doses|
|Plant operations and waste disposal activities that release contaminants to soil, surface water, and air that are transported to creeks and pond near the plant||Total PCBs |
|Fish from Little Bayou Creek||Ingestion||Children and adults who eat 20% of their fish intake from Little Bayou and Bayou creeks||Past, Current, and Potential Future |
Access to Little Bayou creek is partially restricted and fishing advisories are posted
|Total PCBs |
Adults: 0.00215 mg/kg/d
Children: 0.00387 mg/kg/d
|Radioactive contaminants||All biota in Tables 20A and 20B||Ingestion||Children and adults who eat 20% of their intake of fish, game, fruits and vegetables from areas near PGDP||Radioactive Contaminants |
Adults: 0.7 mrem (0.007 mSv)
Children:0.4 mrem (0.004 mSv)
|Key: mg/kg/d = milligrams of contaminant per kilogram of body weight per day; mrem = millirems; mSv = millisieverts|
Uranium hexafluoride (UF6) is a solid stored under vacuum in steel cylinders in outdoor storage yards . Most of the cylinders are 12 feet (about 3 ½ meters) long and 4 feet (about 1 meter) in diameter, with a nominal wall thickness of 5/16 inch (8 millimeters). The largest storage area at PGDP is in the southeast corner of the site. There are about 40,351 cylinders of depleted UF6 stacked two layers high at Paducah; 28,351 of them were generated by DOE and about 12,000 were generated by the U.S. Enrichment Corporation (USEC)(5) [5,103].
Although DOE believes that these cylinders do not present a health concern directly, the storage oflarge quantities of this material in one place has raised concerns among the local community andothers. In 1994 and 1995, the Defense Nuclear Facilities Safety Board visited the gaseous diffusionplants at Paducah, Portsmouth, and Oak Ridge . Their recommendation included a program tobetter maintain the physical condition of the cylinders, to better protect the cylinders from exposureto the elements and from damage during handling, and to study the feasibility of storing the materialin a more suitable chemical form for long-term storage of the depleted uranium. In 1995, DOEsubmitted a plan to implement these recommendations. The plan included repainting cylinders toavoid excessive corrosion, removing cylinders from ground contact, spacing cylinders better tofacilitate improved inspections, and improving handling procedures. DOE also completed a baselineinspection of all cylinders in 1994. Their plan calls for inspecting 25% of the cylinders each yearand inspecting all the older cylinders each year .
Depleted UF6 is a white, crystalline solid when it is stored at temperatures below 134oF (57oC) atatmospheric pressure . If one of the cylinders leaked, the UF6 would react with moisture in theatmosphere to form hydrogen fluoride (HF) gas and uranium reaction products such as solid uranylfluoride. The solid would seal small leaks or cracks, preventing the escape of radioactive andchemical materials from the cylinders. If there were more severe damage to a cylinder, however,these materials might escape into the atmosphere and be a potential source of exposure to nearbyresidents, especially if the incident involved a fire.
Because the cylinders are currently being stored outside, the community is concerned about thepossibility of a major accident that would damage the cylinders and result in large-scale release ofUF6, and other reaction products, to the environment. Severe lightning storms, tornadoes,earthquakes, transportation accidents, or plane crashes are examples of major incidents. These arediscussed below.
A search of storm event data from the National Oceanographic and Atmospheric Administration'sNational Climatic Data Center (NCDC) revealed historical information for Ballard and McCrackencounties in Kentucky . Information on tornado activity is available from January 1, 1950,through December 31, 1991, and from January 1, 1995, through December 1998. During these 46years, two tornadoes were recorded in Ballard County, with winds ranging from 40 to 206 miles perhour (64 to 332 kilometers per hour). In McCracken County, seven tornadoes and one funnel cloudwere recorded, with winds from 73 to 157 miles per hour (118 to 253 kilometers per hour). Theseare considered small to mid-size tornadoes. Due to the cylinders' weight (each weighs 10 to 14 tons,or 9 to 12 metric tons), shape, and design, it is improbable that one of these storms would damage ormove the cylinders. Other severe weather conditions causing property damage, injury, or death haveonly been recorded by NCDC from January 1, 1995, through December 31, 1998. During these 4years, Ballard County and McCracken County each had one lightning storm that caused propertydamage. Since lightning is usually attracted to the highest structure in the area--which would not bethe cylinder yards--and it is not common for lightning to cause property damage in this area, it isimprobable that one of these storms would damage the cylinders.
The Paducah area has a high probability for moderate earthquake activity in the near futureaccording to U.S. Geological Survey scientists .
In the winter of 1811/1812, three of the largest earthquakes in North America occurred in the NewMadrid seismic zone, adjacent to western Kentucky. Each of these three earthquakes hadmagnitudes of over 8.0 on the Richter Scale(6) , or moment magnitude1 of 7.1 to 7.5 accordingto recent reports . However, based on recent unpublished data it is now estimated that thelargest earthquake of the series was a moment magnitude of 7.7. On February 7, 1812, the lastearthquake's epicenter was located near New Madrid, Missouri, which is 60 miles (97 kilometers)southwest of the current Paducah Gaseous Diffusion Plant site. Two other earthquakes of similarsize occurred on December 16, 1811 and January 23, 1812, and thousands of aftershocks rocked theregion during that winter . Since then two major earthquakes have occurred . Amagnitude 6.5 earthquake occurred near Marked Tree, Arkansas in 1843, and a magnitude 6.8earthquake occurred near Charleston, Missouri in 1895. Earthquakes of smaller magnitude haveoccurred in the past and continue to occur today. Most are too small to be felt by humans. Thelargest earthquakes in this seismic zone in recent times were a magnitude 5.0 earthquake in 1976and a magnitude 4.8 earthquake on September 26, 1990.
It is not possible to predict the exact date, duration, or magnitude of an earthquake. Frominformation known about the region, scientists can estimate the potential for different magnitudeearthquakes. Scientists at the Center for Earthquake Research and Information estimated thepotential for different magnitude earthquakes to occur in this region by computing sets of probabilities, as shown in the table below .
|Magnitude||Average Repeat Time (in years)||Probability of occurrence in 15 years (%)||Probability of occurrence in 50 years (%)|
|6.3||70 +/- 15||40 - 63||86 - 97|
|7.6||254 +/- 60||5.4 - 8.7||19 - 29|
|8.3||550 +/- 125||0.3 - 1.0||2.7 - 4.0|
The magnitude of the earthquake is a measurement of the total energy released. The energy istransferred by movement in the ground which is modified as it moves through local rock and soil. The ground movement may arrive at the ground surface with lesser or higher violence(intensity of shaking) depending on the frequency of the motions. In the Paducah area, it appearsthat low-frequency motions are amplified by thick soils and virtually unaffected by thin soils.However, high frequency motions are attenuated by thick soils and amplified by thin soils .
Dr. James Beavers from the University of Illinois at Urbana and Deputy Director of the Mid-America Earthquake Center has estimated that the topsoil peak ground acceleration(7) at PGDP during a 2% probability earthquake in 50 years (moment magnitude of 7.75) would be approximately 0.5 g . This would create a relatively high potential for earthquake damage unless the structures were designed and constructed under the strictest construction codes.
Citizens have raised concerns about the consequences of a major earthquake on the stored uraniumcylinders. For the 2% probability earthquake in 50 years, it is likely that the cylinders would movearound and potentially be breached. The consequences could include on-site fatalities from physicalinjuries and from exposure to UF6 and the reaction products and significant off-site injuries fromexposure to UF6 and the reaction products.
Cylinders could be damaged or burn during transportation accidents, or plane crashes. Currently,DOE is not transporting cylinders to or from the PGDP site. Plane crashes are a possibility, since theBarkley Airport is about 3.7 miles (6 kilometers) southeast of the site. A plane crash accompaniedby fire could damage the cylinders. As part of the Programmatic Environmental Impact Statementfor Alternative Strategies for the Long-Term Management and Use of Depleted UraniumHexafluoride , Argonne National Laboratory used a FIREPLUME model to predictconcentrations of materials released from UF6 cylinders under five accident scenarios and twoweather conditions (F and D stability classes). These scenarios include:
- Vehicle-induced fire with the rupture of three full 48G cylinders. (Primarily used for depleted UF6 storage.)
- Vehicle-induced fire with the rupture of three full 48Y cylinders. (Primarily used for transporting natural UF6).
- Small aircraft-induced fire with the rupture of two full 48G cylinders.
- Small aircraft-induced fire with the rupture of two full 48Y cylinders.
- Vehicle-induced fire with the rupture of two heel cylinders.
The model assumed that UF6 contained in cylinders was damaged in the accident, causing therelease of HF gas and uranyl fluoride particulates to the atmosphere. For each scenario, theypredicted concentrations at distances of 30 to 12,068 meters (about 100 feet to 7.5 miles) from theaccident. They determined that the maximally exposed individual was 30 meters downwind of theaccident. At each distance, the estimated dose was directly influenced by the airborne concentrationsand the length of exposure time. The worst-case scenario (number 2) was a vehicle-induced fire withthe rupture of three full 48Y cylinders (assuming F stability). Under this scenario, the maximallyexposed individual would be exposed to 2,700 mg/m3 (or 3,293 ppm) of HF and 180 mg/m3 (or2,250 ppm) of uranyl fluoride .
The estimated HF and uranyl fluoride exposure concentrations for the maximally exposedindividual in accident scenario 2 (described on previous page) are high enough to pose atemporary urgent public health hazard; however, the probability of this type of accidentoccurring is very low. These substances are discussed below since they relate to this accidentscenario. They may also be discussed in the public health implications section of this report.
HF is a colorless gas or liquid with a strong, irritating odor. It can be smelled in the air atconcentrations of 0.5 to 3 ppm. The gas will readily react with water, releasing corrosive and toxicgases. Contact with metal can produce flammable hydrogen gas. Containers of HF can explodewhen heated or contaminated with water .
HF is highly corrosive and produces adverse effects at the point of contact, which is usually therespiratory tract (nose, throat, trachea, bronchi), eyes, and skin. Because HF is absorbed into thebloodstream, it can affect other organs in the body, such as the lungs, liver, kidney, and heart. Short-term exposure to HF in air at concentrations as low as 20 ppm can be tolerated for 1 minute,although concentrations of 120 ppm irritate the nose, throat, eyes, and skin in humans . Vaporscan cause ulcers of the respiratory tract at concentrations of 50 to 250 ppm--this concentration canbe dangerous, even for brief exposures. Inhalation of HF at higher concentrations can cause severethroat irritation, cough, lung injury, and pulmonary edema (swelling) resulting in death. HF readilypenetrates the skin and can cause deep tissue destruction and burns following dermal exposure.Exposure to the eye can result in irritation to severe ocular damage and visual effects.
The National Institute of Occupational Safety and Health recommends that exposure to HF byworkers not exceed 3 ppm (or 2.5 mg/m3), with a 15-minute ceiling of 6 ppm (or 5 mg/m3). Therecommendations are intended to protect workers from effects on the respiratory tract, eyes, skin,and bones. The recommendations are based on occupational studies of workers and laboratoryanimals. One study of rabbits and guinea pigs exposed to HF, at concentrations of 24 to 8,000 ppmfor 5 to 41 minutes, reported eye and respiratory tract irritation at all exposure concentrations .A significant number of animals died within 5 minutes when they inhaled air containing 1,500mg/m3 of hydrogen fluoride. Weakness and appearance of illness were apparent in all animals atconcentrations above 500 mg/m3 for 15 minutes or longer. Rabbits that survived returned to normalwithin a few weeks, but guinea pigs showed a definite tendency to delayed response and deathbetween the fifth and tenth week following exposure.
Argonne's estimated exposure levels were at least 10 times higher than reported to cause adverseeffects in humans (workers) and animals. Therefore, ATSDR concludes that potential futureexposure to HF, at an estimated exposure level of 3,300 ppm for a hypothetical maximallyexposed individual in accident scenario 2, poses an urgent health hazard.
Uranyl fluoride is water-soluble. Its toxicity is determined primarily by route of exposure; exposureconcentration, duration, and frequency; and particle size. Ingestion generally produces less toxicitythan inhaled uranium, because uranium is poorly absorbed from the gastrointestinal tract followingingestion. Respiratory and kidney toxicity are the targets for inhaled uranium.
ATSDR has developed an intermediate-duration health guideline for exposure to uranyl fluoride inair. The guideline is 0.0004 mg/m3 (or 0.005 ppm) and is based on a study in which dogs wereexposed to uranyl fluoride in air daily for 5 weeks . The lowest dose at which adverse effectson the kidney were observed in these animals was 0.15 mg/m3 (or 2 ppm). ATSDR applied a safetyfactor of 90 to this lowest dose, because humans may be more sensitive than dogs, some humansmay be more sensitive than others, and there was no dose at which no adverse effects were seen.Although Argonne National Laboratory's estimated exposure concentration (180 mg/m3, or 2,250ppm) was several orders of magnitude higher than the health guideline, the health guideline wasbased on an intermediate-duration study in which animals were exposed for 5 weeks. It is likely thatexposure to uranyl fluoride during an accident will occur over a shorter (acute) duration.
A similar study in dogs acutely exposed to uranyl fluoride (one exposure lasting ½ to 1 hour) foundextensive degeneration in kidney tissue following exposure at a concentration of 250 mg/m3 (morethan 3,000 ppm) . ATSDR considered these effects to be too severe to use the study as a basisfor developing a health guideline. If we did derive a "guideline" by applying a similar safety factorof 90 to this concentration, the resulting "guideline" would be about 35 ppm. Argonne's estimatedexposure concentration for uranyl fluoride, for the maximally exposed individual under scenario 2,was considerably higher than this "guideline." Therefore, ATSDR concludes that potential futureexposure to uranyl fluoride, at an estimated exposure level of 180 ppm for a hypotheticalmaximally exposed individual in accident scenario 2, poses a public health hazard.
DOE is evaluating the feasibility of building a facility (or facilities) to convert its UF6 to a morestable form for long-term storage, use, or permanent disposal. DOE prefers to begin converting thedepleted UF6 inventory to uranium oxide or uranium metal, or a combination of both, as soon aspossible, but to allow for use of as much inventory as possible. Conversion to oxide for use or long-term storage would begin as soon as possible, with conversion to metal only if uses for the metal areidentified . DOE is now participating in a conversion pilot project with the private sector .
DOE stores the majority of its depleted uranium cylinders at PGDP. Many of the storage cylindersare not approved for transportation; therefore, it is logical that the conversion facilities would bebuilt at or near the gaseous diffusion plants. On August 11, 1998, President Clinton signed PublicLaw 105-204 (Section 1. United States Enrichment Corporation) which states:
(a) Plan. -- The Secretary of Energy shall prepare, and the President shall include in thebudget request for fiscal year 2000, a plan and proposed legislation to ensure that allamounts accrued on the books of the United States Enrichment Corporation for thedisposition of depleted uranium hexafluoride will be used to commence construction of, notlater than January 31, 2004, and to operate, an on-site facility at each of the gaseousdiffusion plants at Paducah, Kentucky, and Portsmouth, Ohio, to treat and recycle depleteduranium hexafluoride consistent with the National Environmental Policy Act....(c) Sense ofthe Senate. - It is the sense of the Senate that Congress should authorize appropriationsduring fiscal year 2000 in an amount sufficient to fully fund the plan described in subsection (a).
(We assume that these facilities would also be used to dispose of DOE's depleted UF6.)
The community is concerned about transportation accidents that might occur if cylinders from othersites were brought to PGDP. Since conversion facilities are proposed at two sites, about 4,700cylinders at Oak Ridge, Tennessee, would have to be transported. The material in these old cylinderswill need to be transported in cylinders or overpacks approved for transport by appropriateregulatory authority before the transfer occurs. ATSDR recommends using approved transportcylinders or overpacks to transport any depleted uranium cylinders to or from PGDP.
The community is also concerned about potential environmental contaminants that the new facilitymight produce. The potential environmental contaminants from a conversion plant at a specific siteare hard to predict until the technology is decided upon and the facilities are planned. When plansfor the new facilities are proposed for the two sites, Environmental Impact Statements (EIS) requiredby the National Environmental Policy Act of 1969 will assess the site-specific impact of theproposed facilities on human and natural environments. DOE's final Programmatic EnvironmentalImpact Statement  issued in April 1999 presented alternatives for long-term management of thedepleted UF6 and included a comparison of impacts on human health and the environment for thealternative management strategies; however, it did not include the detailed, site-specific informationthat would be required in an EIS.
Potentially contaminated concrete rubble from PGDP was used at PGDP, the Tennessee Valley Authority Shawnee Steam Plant reservation, the Western Kentucky Wildlife Management Authority (WKWMA), and the Ballard County Wildlife Management Area approximately 11 miles (18 kilometers) west of PGDP, for bank erosion control, dam and structural support, and roadway stabilization [10,11]. Since the concrete was potentially contaminated, DOE and the Commonwealth of Kentucky surveyed the rubble piles and the adjacent soils and sediments. Contaminated soil piles were removed from an area at the WKWMA in July 1996; no further remedial actions are planned. The remaining rubble piles do not pose a public health hazard.
5. In May and June 1998, DOE assumed management responsibility for approximately 11,400 cylinders generated by USEC.
6. The Richter Scale is a logarithmic scale ranging from 1 to 10, for expressing the magnitude or total energy of an earthquake. This scale was invented in 1935, but is rarely used today byscientists. Instead moment magnitude, a scale of numbers developed by Hiroo Kanamori in 1977, isused. For both scales, the stronger the earthquake is the higher the number. They are nearly identicalfor most earthquakes with a magnitude less than 7; however, moment magnitude more accurately describes the strongest earthquakes .
7. Peak ground acceleration is a measurement of the amount of surface ground movementand is defined as the maximum acceleration an object attached to the ground would experience during an earthquake. (The earth's gravity always subjects an object to 1 g; the peak ground acceleration would be the number of additional g's the object would be subject to.)