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When the plant first opened in the mid-1870s, gas manufacturing was accomplished by the coal carbonization process. A detailed discussion of this and other gas manufacturing processes is found in an document prepared by the USEPA (1988). At the time the plant opened under the name Marshalltown Gas Light Company, it occupied only Lot 5 of Barden's subdivision. In 1884, the site consisted of the gas plant building (at the approximate location of the present substation materials building), a coal house, and two gasometers (pressurized gas holders) located north of the plant building. Barbed wire and furniture manufacturing facilities and a stockyard existed to the west of the plant on what is now IES Utilities property. The properties to the east were apparently vacant at this time.
Electric generation began at the site sometime between 1888 and 1892. The electrical plant was built on a portion of the gas plant property and Lots 1, 2 and 3 of Cunningham's Addition. Residential properties and warehouses were present to the east of the gas plant at this time, on what is now the IES property. In 1892, the Marshalltown Gas Company, the Marshalltown Electric Company, and the Marshalltown Street Railway Company consolidated into the Marshalltown Light, Power and Railway Company, bringing the electrical and gas operations under common ownership.
By 1901, the original, smaller gasometer had been removed, and the operation utilized a single 25,000 cubic foot gas holder located west of what is now the regulator building. Between 1901 and 1910, a new 200,000 cubic foot gas holder was built just east of the current regulator building.
The gas manufacturing process was converted from coal carbonization to carbureted water gas sometime between 1910 and 1921, and ownership transferred to the Iowa Railway and Light Corporation. During this period, the original purifier room operations were moved to a separate building (now the IES substation department building) and water gas generators were installed in the place of the old purifiers. In addition, a 12,000-gallon tar well was installed east of the new water gas generator building, and an oil storage tank was installed at the north edge of the property west of the original gas holder to feed the carburetion process.
The original coal gasification facilities were demolished sometime in the 1920s. Also during this period, a new 50,000 cubic foot gas holder was constructed immediately south of the 200,000 cubic foot gas holder, and the original 25,000 cubic foot holder was taken out of service but apparently left in place until the plant was shut down completely in 1950. A second oil tank was also added in the 1920s north of the purifier building.
Although documentation was not available regarding the disposition of tar produced by the gas manufacturing processes, a substantial portion of the tar may have been disposed on site. This is evidenced by, among other things, a 1953 photograph in the McDonald (1986) report showing an excavation immediately east of the present electric substation filled with a substance described as tar. The pit was opened for a construction project, and the tar was pumped from the pit and disposed at an unknown location.
Previous investigations
Documented investigation of the presence of waste product disposal at this site began with a preliminary study by D. B. McDonald Research Associates in 1986. This investigation consisted of gathering regional hydrologic and geologic data and historical information about the operation of the plant, including interviews with former employees.
Later in 1986, a USEPA contractor, Ecology and Environment (E&E), performed a reconnaissance investigation of the site. The E&E investigation included similar historic data and added information regarding fate, transport and exposure routes of the contaminants of interest. A followup site investigation by E&E in 1987 included surface geophysics and some shallow soil, groundwater, surface water and manhole sampling. The geophysics work consisted of ground penetrating radar in areas where subsurface structures were suspected. The soil samples indicated the presence of PAH compounds at levels substantially above background levels.
A report prepared by Tuthill, Inc., in 1988 contained a detailed synopsis of the site history, including the development and ownership changes of the site. Tuthill also prepared a report in 1989 which provided a summation of the information contained in the previous reports discussed above. The 1989 report contained data from a public water quality assurance program which had been initiated locally. Also in 1989, Tuthill prepared a detailed report containing more information about the history of the site.
An underground storage tank (UST) was removed in November 1988 from an area near the west end of the site along the east wall of the former spray pond. Soil and groundwater samples were collected as a part of the UST closure operation. Petroleum hydrocarbons in excess of applicable action levels were detected.
BVWST began a detailed remedial investigation of the site in 1990. The investigation included a comprehensive program of soil and groundwater sampling and hydrogeologic characterization. The investigation also included sampling and characterization of material contained in the void space beneath the floor of the former electric generation building. The results are documented in a report submitted to the IDNR (BVWST 1992).
The Marshalltown FMGP is located south of East Nevada Street between 4th and 6th Avenue in the SE of the NE of Section 35, T.84N., R.18W. The contiguous property presently owned by IES Utilities is also partially located in Section 36. The site contains several buildings from the FMGP and former electric plant and is currently used as the service and materials distribution center for the IES gas and electric operations. It is located adjacent to an active railroad switching yard owned by the Chicago and Northwestern Railroad.
Physiography/Topography
The site is in an old industrial area of Marshalltown. Nearby industries include an inactive foundry, a scrap metal recycling business, and a variety of manufacturers. The site is situated on the edge of the floodplain of a meandering stream (Linn Creek) within a glacial drift terrain. The ground surface is flat to gently sloping, with approximately 10 feet of relief across the site. Linn Creek is a tributary of the Iowa River and flows from west to east approximately 800 feet south of the FMGP site. Its confluence with the Iowa River is located approximately 2.5 miles northeast of the site.
Surface relief between the uplands and valleys is 50 to 150 feet. Maximum upland elevations range generally from 900 to 1000 feet above sea level (ASL) in the Marshalltown area. The Linn Creek and Iowa River floodplains vary in elevation from 860 to 880 feet ASL in the Marshalltown area.
Geology and hydrogeology
The stratigraphy of the glacial sediments in the Marshalltown area consists of loess over Kansan till. The terminal moraine of the younger Wisconsin glaciation is located approximately 10 miles to the west of Marshalltown. The thickness of glacial deposition varies markedly around the Marshalltown vicinity, from 0 to 150 feet in the upland areas and from 25 to 250 in valleys.
The glacial drift unconformably overlies Mississippian-age limestone and Pennsylvanian shale bedrock. The limestone units encountered immediately below the alluvial sediments at the site are identified in Remedial Investigation Report: Marshalltown, Iowa, Former Manufactured Gas Plant Site (BVWST 1992). as a part of the Mississippian Burlington and Gilmore City Formations and are part of the regional Mississippian aquifer. Outcrops are rare, but several are reported along railroad cuts and stream channels in the Marshalltown area. The former bedrock erosional surface is incised by multiple minor channels tributary to the pre-glaciation channel of the Iowa River, referred to as the Poweshiek Channel. The Poweshiek Channel more or less follows the general trend of the present Iowa River floodplain and varies from one to two miles in width (Hansen, 1985). The City of Marshalltown is situated above a bedrock knob located south of the Poweshiek Channel. The FMGP site itself is situated over the northeast flank of the knob.
The near-surface stratigraphy of the site is reported in Remedial Investigation Report: Marshalltown, Iowa, Former Manufactured Gas Plant Site (BVWST 1992). Limestone bedrock is approximately 50 feet below the surface. According to drilling information reported by BVWST, a steep ridge in the bedrock surface with about 25 feet of relief, trends northwest-southeast across the site. Near surface soils consist of a wide range of fill materials (clay, gravel, sand, cinder, and other debris) of low plasticity and varying in thickness from 0.5 to 14 feet. This is underlain by fine-grained cohesive soils consisting of low plasticity silty clay with interbedded sandy and gravelly clays, ranging in thickness from 6 to 14 feet.
The cohesive silty clay unit grades into alluvial sands and gravels, varying significantly in silt and clay content, except at the farther northeast portion of the remedial investigation area. The thickness of the unit varies from 0 to 26 feet, with the greatest thickness found near the center of the site, possibly indicating the presence of a portion of a former stream channel.
A layer of low plasticity clayey lacustrine sediment and low to high plasticity glacial till separates the alluvial sediments from bedrock in most areas around the site. This unit was logged as absent in one boring near the east edge of the site. The surface of the unit slopes toward the south and generally mimics the bedrock surface.
The water table surface is approximately 18 to 20 feet below grade, correlating to the granular alluvial sediments. Hydraulic conductivity (K) measurements obtained by falling head slug tests indicated K values in the range of 0.0029 to 0.00076 cm/sec for the granular sediments. According to the work done by BVWST (1992), groundwater flow in the alluvial sediments is to the south toward Linn Creek. Bedrock groundwater flow characteristics are not well established and appear to be strongly influenced by the activity of production wells in the area which tap the Mississippian aquifer.
Groundwater and land use
According to McDonald (1986), the City of Marshalltown municipal water supply is derived from multiple wells set in the alluvial aquifer of the Iowa River, the buried channel aquifer of the Poweshiek Channel, and the Mississippian aquifer. The relative location of these wells and the distance from the FMGP site make them unlikely receptors of contaminants from the site.
The Marshalltown FMGP property is surrounded on all sides by properties currently and formerly used for industrial purposes. Some nearby properties are currently commercial. The nearest residential properties are located to the north several hundred feet. Nearby commercial/industrial facilities include a scrap metal recycler to the east, the Chicago and Northwestern (C&NW) railroad yard to the south, a container redemption/recycle center, former freight depot and restaurant to the west, and C&NW offices to the north. Farther from the site exist a former iron foundry and several industrial manufacturing operations.
Facilities which formerly occupied adjacent properties included a brewery, pickle works, furniture manufacturing and warehousing, barbed wire manufacturing, canning plant, lumber works, and farm implement manufacturers.
The target analytes for this project consist of 16 polynuclear aromatic hydrocarbons (PAHs) in soils and groundwater that are of concern to the Iowa Department of Natural Resources (IDNR). These 16 PAHs are defined as the total PAHs (TPAHs), and they are grouped into seven non-carcinogenic PAHs (NCPAHs) and nine carcinogenic PAHs (CPAHs). The seven NCPAHs are: naphthalene, acenaphthylene, acenaphthene, fluorene, anthracene, fluoranthene, and benzo(g,h,i)perylene (BgP). The nine CPAHs are: pyrene, chrysene, phenanthrene, benzo(a)anthracene (BaA), dibenzo(a,h)anthracene (DahA), benzo(b)fluoranthene (BbF), benzo(k)fluoranthene (BkF), benzo(a)pyrene (BaP), and indeno(1,2,3-c d)pyrene (IP).
The concentration and distribution of contaminants at the site, along with a site-specific risk assessment, are necessary inputs for IDNR to determine an action level required for remediation. The Ames Laboratory only intends to provide PAH concentration distribution information as part of this work. Geologic data obtained by the Ames Laboratory ESC project may provide useful information for the risk assessment, although the Ames Laboratory will not make evaluations of exposure risk. Because each instrument to be utilized at Marshalltown will have different response to each PAH, the minimum detectable amount of each PAH must be determined.
The IDNR guidance for any combination of the individual TPAHs in soils is 500 mg/kg. In groundwater the action level is 0.2 ppb, except naphthalene which is set at 20 ppb. For the total CPAHs the guidance level is 100 mg/kg for soils and the action level is 0.2 ppb for groundwater. During the BVWST remedial investigation, all of the CPAHs, except DahA, were detected in soils.
The following table lists the 16 TPAHs, their class as NCPAH or CPAH, the range they were detected in previous soil data, and the number of times found out of a total of 53 soil sampling locations, exclusive of building interiors. The on-site data were taken from the BVWST report.
NAME TYPE
______________________________
Naphthalene NCPAH
Acenaphthylene NCPAH
Acenaphthene NCPAH
Fluorene NCPAH
Anthracene NCPAH
Fluoranthene NCPAH
BgP NCPAH
Pyrene CPAH
Chrysene CPAH
Phenanthrene CPAH
BaA CPAH
DahA CPAH
BbF CPAH
BkF CPAH
BaP CPAH
IP CPAH
______________________________
* Remedial Investigation Report BVWST, 1992.
** EQL = estimated quantitation limit, typically 0.66 mg/kg.
^ Knox, Sabatini, and Canter 1993.
ND = none detected
One of the target compound PAHs at Marshalltown is naphthalene, whose vapor pressure defines the boundary between semivolatile organic compounds (SVOCs) and VOCs. Thus naphthalene is an SVOC with the highest vapor pressure and likely would form the highest volume plume. Naphthalene is also an attractive target compound because it was one of the most common PAHs detected in the previous characterizations and it is one of the three most common compounds that make up coal tar. Typically naphthalene ranges from about 1-10 percent by volume of typical coal tar waste. However, some of the methods, e.g., IMA, may not be very sensitive to naphthalene. The relative sensitivity to various PAHs will be a focus of the technology evaluation of these screening methods.
The LIF capability is likely not to have sufficient data quality to assist in the accurate delineation of the PAH plume near the action levels nor will it be able to distinguish more than a subset of the 16 PAHs of interest. Once detailed topography of the upper surface of the lower confining layer has been revealed, either by the geophysical methods from phase one or the four probe sensor of the CPT itself, then shallow depressions near edges of main body or bodies of the PAH plume(s) can be directly sampled for free phase, saturated soil or less contaminated soil for the existence of isolated PAH plumes.
Finally, an innovative optical technique based on chemiluminescence has been identified. It will be compared to the other screening technologies.
Quantitative phase
In the quantitative phase, the focus will be on GC/MS instruments
using five extraction methods: sonic solvent (SOPT), thermal
desorption (IT), supercritical fluid extraction (IT), microwave
extraction (IT), and microextraction (IT). In addition, the LIF
capability of the CPT system, a qualitative but direct method, will
be used in this phase.
Samples for the GC/MS systems will be collected by a GeoprobeTM truck or, if necessary, by the CPT truck for the deeper samples. Although field duplicates will be taken during the subsurface probing that will address site soil inhomogeneity, it will be important to collect a sufficient quantity of each sample so that, after homogenization, they can be split and analyzed by each of the extraction modules.
It is realized that little new information about the contaminant distribution will be learned from these split samples, but these samples are necessary for the comparative evaluation of the extraction methods. It is also realized that some of the extraction schemes have been used before and may even have EPA approval, but again, the opportunity to evaluate them under identical conditions will benefit their effective adoption by DOE and others. Variations in recovery percentages among the extraction methods that are due to soil type are suspected to be important in the selection of appropriate extraction methods for similar soil types. In order to isolate the extraction percentage from the variance among the GC/MS instruments, spiked aliquots will be injected directly into the column.
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Last Modified: 1 January 2002 by dave eckels
Expedited Site Characterization: etd/technologies/projects/esc/technologies/contaminants.html