NOTE: There are two websites for this site. This one is for the Time Critical Removal action and the other one is for the Non-Time Critical Removal Action. Much of the information is overlapping as the projects occurred simultaneously for many years.
The following is a breakdown of previous studies that have been completed at the site:
Aboveground Storage Tank Area
In August 1994, Dames and Moore provided oversight for the removal of three aboveground storage tanks located on the southwest portion of the facility. This included removing a 7,000-gallon xylene product tank, a 7,000-gallon xylene-based varnish tank, a 1,000-gallon paint thinner tank, and the excavation and removal of the underground conveyance piping and pump assembly. Sections of the piping associated with the xylene and varnish tanks could not be removed and were left in place and grouted closed.
During the 1994 removal of the aboveground storage tanks and underground conveyance piping, soil impacted by the xylene and/or varnish aboveground storage tank systems was encountered. Emerson excavated portions of the impacted soil and took soil samples of the excavated areas at approximately three feet below ground surface. In addition, the lateral extent of the contamination was investigated by excavating a trench. Soil impacted by Volatile Organic Compound (VOC) was detected at the base along the entire length of the trench. Field screening results indicated that product releases had affected soil quality beneath the secondary containment area and along the underground piping runs. Approximately 150 tons of affected soil was removed. Due to the presence of a stiff chert layer encountered beneath the southwestern portion of the facility, the excavations could only extend approximately three feet below ground surface. A total of 17 soil samples were collected during these removal activities and analyzed for toluene, ethylbenzene, and total xylenes due to the contents of the aboveground storage tanks. The analytical results ranged from non-detect to 2.13 parts per million (ppm) for toluene; non-detect to 309.1 ppm for ethylbenzene; and non-detect to 867.6 ppm for xylenes. These results showed that affected soil extended beyond the limits of both the piping run excavation and the secondary containment area excavation.
Subsurface Investigation
In November 1994, Emerson conducted an additional subsurface soil investigation to delineate the vertical and horizontal impact observed during aboveground storage tank removal. Soil samples were collected from the vadose zone at a depth of five to seven feet below ground surface, which revealed concentrations of total xylenes in each of the nine soil samples collected. The highest concentration of total xylenes (487 ppm) was detected in a sample collected approximately 15 feet south of the former tank locations. Ethylbenzene was detected in seven of the nine soil samples collected. The highest concentration of ethylbenzene was detected in this same sample at a concentration of 154.2 ppm. Toluene was not analyzed during this investigation. The results of this investigation indicated that impacted soil remained to the east, west, and south of the tank containment area. The southern extent could not be determined during the investigation. In addition, the investigation revealed that the shallow groundwater may have been impacted and a groundwater investigation was recommended.
Groundwater Investigation
In January and February 1996, Emerson conducted a groundwater investigation beneath the southwest portion of the facility. The investigation included installing and sampling three groundwater monitoring wells. The groundwater flow direction was determined to be southwest. The groundwater sampling results documented that xylenes and ethylbenzene in all three monitoring wells were at levels above EPA maximum contaminant levels (MCLs) for drinking water. The highest concentration of total xylenes was detected in a sample from MW-3 at 94,941 parts per billion (ppb). The MCL for xylene is 10,000 ppb. The highest concentration of ethylbenzene was also detected in MW-3 at 23,139 ppb. The MCL for ethylbenzene is 700 ppb. MW-3 is located in an area just north of the former xylene and varnish tanks.
Dual-Phase Vapor Extraction System
In July 1996, Emerson installed one dual-purpose groundwater and soil vapor extraction well and a dual vapor extraction (DVE) system to address the groundwater and soil impacted by the xylene and/or varnish aboveground storage tanks. The pilot test of the DVE system began on July 23, 1996, and ran for three weeks. Approximately 200 lbs. of VOCs were recovered during the pilot test. The samples of the wastewater discharged from the extraction system exhibited concentrations of ethylbenzene at 1,800 ppb and 1,700 ppb and of total xylenes at 12,000 and 11,000 ppb. In November 1996, two monitoring wells (MW-1 and MW-2) were converted to extraction wells. A groundwater sample collected from MW-1 exhibited concentrations of ethylbenzene at 11,000 ppb and total xylenes at 52,000 ppb. The water derived from the extraction system was not treated prior to disposal into the city of Ava’s sanitary sewer system for treatment by the city’s treatment plant. Due to operational problems, the DVE system did not run on a consistent basis.
Transformer Area Soil Excavation
In December 1996, solvent and/or varnish-impacted soil was encountered during construction of a new transformer pad. The source of the impact appeared to be a leak of the xylene and/or varnish product lines from the previously removed aboveground storage tanks. Approximately 57 tons of soil was removed and treated offsite via low temperature thermal desorption. Confirmatory samples indicated that impacted soil remained within the area of excavation. Specifically, the concentration of toluene ranged from non-detect to 38 ppm; ethylbenzene was detected from 0.053 ppm to 61 ppm; and xylenes were detected from 0.33 ppm to 363 ppm. Emerson determined that the DVE extraction system would be expanded to address the remaining impacted soil. In August 1997, two additional extraction wells were installed (MW-5 and MW-6) to address the additional soil impact observed during the transformer pad excavation activities.
MDNR Investigation
In December 2000, the MDNR sampled the wetland area and the associated drainage ditch to the south of the facility as part of the ESI for the Sentinel Wood Treating Site. The results of the department’s sampling indicated that the wetland area and the associated drainage ditch appeared to be a discharge point of VOCs not necessarily associated with the Sentinel Wood Treating Site. High levels of total xylenes (27,600 ppb), ethylbenzene (10,500 ppb), cis-1,2-dichloroethane (146 ppb), toluene (79.3 ppb), 1,1-dichloroethane (51.5 ppb), PCE (2.4 ppb), benzene (2.3 ppb) and other compounds were reported in the surface water sample from the ditch. In April 2001, pursuant to the Sentinel Wood Treating Site ESI, the department collected a groundwater sample from the southern portion of the Sentinel Wood Treating Site from a shallow, bedrock monitoring well. Total xylenes were detected in this sample at 5,770 ppb and ethylbenzene was detected at 2,100 ppb.
EPA Investigation
The EPA conducted a limited Site Screening Assessment on January 18, 2001, at the site to identify specific potential sources of contamination at the facility and other nearby facilities. The EPA identified a seep with a distinct sheen along the north side of 12th Avenue (across the street and up-gradient from the wetland area) in a roadside ditch. The sediment sample collected from this ditch contained very high levels of gasoline range organics (up to 34 ppm) and substantial concentrations of xylenes (up to 0.2 ppm). The ditch drains into the unnamed tributary to Prairie Creek on the north side of 12th Avenue. Both the surface and subsurface drainage associated with the wetland area discharge directly onto residential property located immediately south of the Sentinel property before entering the unnamed tributary to Prairie Creek. The highest concentrations of VOCs identified by the EPA were found in the sample collected from the residential property. Additionally, the EPA’s assessment found that both the surface water and sediment samples collected at the discharge point of the PVC pipe draining the wetland area (SW-01 and SD-01, respectively) contained very high levels of xylene (17,900 ppb and 20 ppm respectively), ethylbenzene (3,660 ppb and 0.37 ppm, respectfully) and other gasoline range organics (64,700 ppb and 31 ppm, respectively). These values are comparable to those identified by the MDNR at approximately the same location during the December 2000 sampling.
Emerson’s Phase I Investigation
In March 2001, Emerson conducted a soil and groundwater investigation (referred to as the Phase I Investigation) along the south and west portions of the facility and along the north portion of the Douglas County Health Department Property to the south of the facility. A total of 29 groundwater samples and 17 soil samples were submitted for analyses of semi-volatile organic compounds (SVOCs), VOCs, and metals. Soil samples collected in a borehole between seven and eight feet below ground surface contained concentrations of ethylbenzene at 140,000 ppm, xylenes at 680,000 ppm, 1,1,1-TCA at 190 ppm, and toluene at 260 ppm. This sample was collected immediately above the water table, and the concentrations are likely representative of residual concentrations from affected source area groundwater in the capillary zone. The soil collected from another borehole (0-0.5 feet below ground surface) was also saturated, and the concentrations of ethylbenzene (550 ppm) and xylenes (2,400 ppm) may also be associated with affected source area groundwater. The SVOCs detected in the soil were bis(2-ethylhexyl)phthalate, 2,4,-dimethylphenol, and di-n-octylphthalate. Arsenic, copper, chromium, and lead were detected in the soil along the western and southern portions of the site. Every soil sample collected had concentrations of arsenic that exceeded the EPA Region IX’s Preliminary Remediation Goals of 2.7 ppm for industrial soil. The highest level of arsenic (60 ppm) was detected between seven and eight feet below ground surface along the Sentinel and Copeland property boundary (possibly indicating a natural source).
The groundwater results from Emerson’s March 2001 investigation documented ethylbenzene, xylenes, toluene, 1,1,1-TCA, 1,1-dichloroethene, TCE, and cis-1,2-DCE were present at levels above the MCLs. Ethylbenzene was detected at levels above the MCL in 18 of the 29 groundwater samples collected. The highest concentration of ethylbenzene (540,000 ppb) was detected in a floating product sample located just south of the former aboveground storage tanks. Approximately 0.25 inch of free product was detected at this location. Total xylenes were detected at levels above the MCL in 15 of the 29 groundwater samples collected. The highest concentration of xylenes (2,400,000 ppb) was also detected in the floating product sample collected. Toluene and TCA were also detected above the MCLs in the floating product sample collected. Toluene was detected at 1,400 ppb and 1,1,1-TCA was detected at 1,700 ppb. The MCL for toluene is 1,000 ppb and 200 ppb for 1,1,1-TCA. In two borings, 1,1-DCE was detected above the MCL at 10 ppb and 94 ppb. The MCL for 1,1-DCE is 7 ppb. TCE was detected above the MCL in two borings at 160 ppb and 110 ppb. The MCL for TCE is 5 ppb. Cis-1,2-DCE was also detected above the MCL in two borings at 110 ppb and 95 ppb. The MCL for cis-1,2-DCE is 70 ppb. One boring contained dissolved concentrations of lead at 32.1 ppb, exceeding the MCL for lead of 15 ppb.
Emerson’s Phase II Investigation
In June and July of 2001, Emerson Electric Company conducted an additional soil and groundwater investigation (referred to as the Phase II Investigation). The purpose of the Phase II Site Investigation was to further define the horizontal and vertical extent of affected groundwater between the facility and a marsh located approximately 2,500 feet southwest of the facility where groundwater discharges to the surface. The investigation was also designed to characterize the potential offsite migration pathways within the upper most water-bearing zones and aid in the design of an interim measure.
Groundwater results indicate that ethylbenzene, xylenes, benzene, TCE , and PCE are present at levels above the MCLs. Also, the results show that the mass of affected groundwater in the northern portion of the site is predominantly flowing through the fractured bedrock (approximately 30 feet total depth), not the shallow overburden material (approximately 15 feet total depth) as originally presumed.
Groundwater samples collected from the wells screened within the upper portion of the fractured bedrock generally contain higher VOC levels than groundwater samples collected from the shallow overburden wells. The preliminary results of groundwater samples collected from the deep well show that affected source area groundwater is restricted to the overburden and the upper fractured bedrock. The samples collected from the deep well did not contain VOC levels above the MCLs.
Emerson Removal Assessment
As required by the AOC, Environmental Strategies Consulting, LLC (ESC) conducted a removal assessment in 2002 at the site that consisted of three main objectives: 1) a site-wide assessment, 2) an evaluation of the Time-Critical Removal Action, and 3) a determination to alter or expand the initial Time-Critical Removal Action.
Results of the site-wide assessment helped to further define the vertical and horizontal extent of the affected source area groundwater plume. The plume is an elongated oval shape with the axis trending to the southwest. The vertical extent of the plume does not appear to have extended below what is considered competent bedrock. Evaluation of the initial Time-Critical Removal Action revealed that after its initiation, the creek down-gradient from the site no longer contained Emerson contaminants of concern above MCLs, thus accomplishing the goal of the action. It was determined to expand the initial Time-Critical Removal Action by adding an extraction well system and treatment unit at the original spill location.
EE/CA
ESC then performed field activities in order to prepare the Engineering Evaluation/Cost Analysis (EE/CA) report. Field activities included the addition of new monitoring wells, sampling of all existing wells, a geophysical study of the source area, and a vapor intrusion study at the former Rawlings facility. EPA has completed review of the EE/CA report and approved it with comment. EPA has also completed reviewing and approving the Non-Time-Critical Removal Action Work Plan and associated Health and Safety Plan and Quality Assurance Project Plan. The Non-Time-Critical Removal Action is scheduled to begin during the first half of September 2009, and will consist of additional extraction wells and treatment of the contaminated ground water source area.
