PROBLEM/SITUATION: Develop an accurate, cost-effective method of remediating radioactive contamination in the Kerr-McGee residential area Superfund site.
SOLUTION: Combine GPS, GIS and radiation-detection technologies to provide rapid, accurate identification, analysis, mapping and clean up of site.
JURISDICTION: City of West Chicago, Ill., Dupage County, Ill.
VENDORS: CH2M Hill Inc., Trimble, Sun Microsystems, Oracle, ESRI.
CONTACT: Rebecca Frey, Region 5 project manager, U.S. Environmental Protection Agency, 312/886-4760; Tim Runyon, project manager, Illinois Department of Nuclear Safety, 217/786-6365.
In 1930, the Lindsay Light and Chemical Company Plant in West Chicago began milling naturally occurring radioactive thorium and other rare earths for the manufacture of filament coatings, polishing compounds and other products. In 1958, the plant was purchased by American Potash and Chemical, and in 1957, by Kerr-McGee Corp. When it closed in 1973, wastes from the various milling operations covered much of the 43-acre site. Decades of processing, most predating regulatory control of radioactive materials, left a landscape of thorium tailings (residue from the milling process), sediment piles and leach ponds.
Prior to closure -- and before the dangers of thorium tailings were known -- local residents, contractors and the city of West Chicago were allowed to haul away truckloads of the sandy residue to use as fill material in parks, streets, sidewalks, lawns, swimming pools and septic-tank installations. Runoff from heavy rains carried these wastes into sewers that emptied into a creek running through the surrounding residential area. When the creek flooded, waste from the plant site was deposited in people's yards.
To determine the extent of waste dispersal, aerial radiological surveys were conducted by the Nuclear Regulatory Agency in 1977, and again in 1989 by the U.S. Department of Energy and CH2M Hill, an engineering firm under contract to the federal Environmental Protection Agency (EPA) for remediation of Superfund sites. The surveys indicated that the waste had produced radioactive contamination in a 30-square-mile area around the plant site.
SUPERFUND SITE ESTABLISHED
In 1989, the EPA established the Kerr-McGee residential area as a Superfund site. Today it is the largest and most active of four such sites in West Chicago. In 1992, EPA; its prime contractor, CH2M Hill; Illinois Department of Nuclear Safety (IDNS); and Kerr-McGee Corp., began the actual clean up.
Identifying which of the more than 1,200 properties in the area require clean up is the responsibility of the EPA and the prime contractor. EPA Region 5 project director, Rebecca Frey, described this as the "discovery-characterization phase of the project." It includes surveying 1,200 to 1,400 properties, processing the data, and providing EPA with individual property summaries -- including GIS and GPS information -- and the analytical results from soil sampling.
EPA then passes the information to Kerr-McGee, which is under unilateral order to carry out excavation and property restoration. Following excavation, IDNS conducts soil-sample analysis and gamma radiation tests to determine if the property is "clean." If not, IDNS indicates where further excavation is needed. When the results meet EPA clean-up standards, Kerr-McGee is given authority to back-fill and restore the property.
The EPA requires remediation of properties having five picoCuries-per-gram total radium in the soil above the normally occurring background gamma radiation levels. However, naturally occurring background gamma radiation comes from the content of radium and uranium in the soil, and must be determined by lab analysis of random soil samples from the area. A gamma radiation detector will not do the job because the instrument is unable to distinguish between naturally occurring soil radiation and that "broadcast" by the concentration of thorium tailings at the nearby plant site. A conventional approach would be to measure radium levels by manually analyzing soil samples from hundreds of individual properties. "A slow, costly process," said CH2M Hill Quality Assurance Manager John Fleissner. "It produces insufficient data that often results in too much soil being removed or not enough." A different method of measurement had to be developed.
The solution was provided by CH2M Hill Project Director Alta Turner. In the pilot-study phase of the project, Turner developed a calibration that correlated radium concentrations in the soil with gamma radiation measurements. The detector readings could then be used as a "surrogate" measure to determine radium levels.
A software program on a tiny chip, called an EPROM (Erasable Programmable Read-Only Memory) enabled the combined use of technologies to conduct rapid, accurate and cost-effective radiological soil analyses. The chip translates data from a hand-held Ludlum radiation instrument into ASCII format and sends it to a Trimble Pro XL differential GPS receiver. The receiver sends the data and GPS coordinates to a Trimble TDC-1 datalogger, where they are stored as a single file. In post processing, the GPS coordinates are differentially corrected to sub-meter accuracy and loaded into an Oracle or Arc/Info database, along with the corresponding gamma readings and a time stamp.
"The purpose of measuring radium content in the soil," Turner said, "is to identify hot spots that must be excavated. As technicians walk over the property, the datalogger records a GPS point, a corresponding gamma reading and time stamp every two seconds. Field crews can survey a 10,000-square-foot property in an hour, achieving on the order of 2,000 x-y gamma data points. The incredible density of data provides maps with a very high degree of resolution of the radiological hot spots."
The original basemaps with parcel lines and owner identification were provided by the DuPage County Processing Department. IDNS contractors added planimetric data, including streets, sidewalks, driveways, etc. The maps were converted to North American Datum (NAD) 83 to provide a common coordinate system for GPS points, corresponding gamma readings and spatial attributes in the various data layers.
In Arc/Info, GPS-point coverage and corresponding gamma readings are "layered" over the basemap, or displayed as contours of gamma concentrations. Referring to EPA's requirement for remediation of properties with five picoCuries-per-gram total radium in the soil above the normally occurring background gamma radiation levels, Turner said, "we contour the x-y coordinates and color-code them to indicate three possible conditions: less-than-background plus five; an indiscriminate gray zone; and greater-than-background plus five -- clearly requiring remediation."
BENEFITS OF COMBINED TECHNOLOGIES
"The process is accurate, fast and cost-effective," said Runyon. "During initial testing, I was able to survey a site in 45 minutes using combined GPS and radiological measuring equipment, post-process the data in 15 minutes, and from there produce a contour map in 30 minutes -- one-and-a-half man hours! If you were to do radiological surveys as we originally did them -- laying out the property in a grid, walking behind the survey technician and writing down gamma readings, then producing an AutoCAD, or other computer graphics display of the site -- you would have at least 24 hours tied up."
Runyon concurs that without the capability to rapidly and accurately collect and analyze geographical and radiological data, remediation on such a scale would probably take several years longer and carry an astronomical price tag.
Runyon emphasized that having all parties use the same basemaps, technologies and standards reduces overall cost and makes for efficient coordination and smooth operation. "The technology itself makes the process cost-effective for everybody, particularly in the construction-related phases. We can make a pretty quick decision on turnaround, whether a property should be back-filled or have additional work. When you have a piece of heavy equipment sitting on site, or operators and technicians you are paying, you don't want them standing around waiting for a decision," he said. "Another viewpoint we sometimes forget is the home owner's. The sooner CH2M Hill does their work, Kerr-McGee does their excavation, and we do our verification -- the less impact on the home owner."
Bill McGarigle is a freelance writer specializing in GIS, GPS, and marine-related topics. E-mail: .
Aerial radiological survey -- survey by helicopter equipped with sodium-iodide pods, an instrument that measures pulses created by the interaction of gamma rays with the sodium-iodide medium. Sensitive enough to pick up naturally occurring radiation from granite tombstones in cemeteries.
Curie -- basic unit for measurement of radioactivity, equal to 37 billion disintegrations per second, approximately the decay rate of 1 gram of radium 226.
Gamma radiation -- high-energy, short-wavelength electromagnetic radiation, capable of penetrating 100mm of lead.
Naturally occurring background radiation -- concentrations of radium, thorium and uranium that occur naturally in uncontaminated soil.
Radium -- decay (daughter) product of Thorium 232 (Th-232) and Uranium 238 (U-238), generically referred to as radium. The specific radiums are Ra-228 (or Actinium-228) from Th-232, and Ra-226 from U-238.
Radium level -- concentration of combined Ra-228 plus Ra-226 in the soil, in picoCuries per gram of soil (pCi/g).
Thorium -- Thorium 232, a naturally occurring radioactive ore, processed from monazite sands. The ore is used in the production of gas mantles and various industrial polishing compounds. The comparison between background radiation and contamination levels on and around the Kerr-McGee site can be expressed in either concentrations or gamma exposure rates. For example, in this immediate area, the background concentrations for combined radium (Ra-226 plus Ra-228) is approximately 2.2 pCi/g. The concentration in some of the highly contaminated materials identified in the surrounding residential area is as high as 500-600 pCi/g. The mean background exposure rate as measured with an organic scintillation, micro-Roentgens-per-hour (uR/h) meter is approximately 10 uR/h. Exposure rates as high as 2000 uR/h have been identified.
Trimble XL differential GPS receiver.
4000SSE base station and TDC-1 datalogger.
Ludlum 2221 scaler rate meter with sodium iodide detector.
Sun Microsystems UNIX workstations.
Trimble Pathfinder differential correction.