Northrop Grumman: TCE levels are safe for neighboring residents

McCOOK, Nebraska -- The levels of man-made chemicals in the soil gas, related to the former TRW facility in McCook, do not represent a health hazard to residences located in the vicinity of the facility, a media relations director for Northrop Grumman told the Gazette Monday. The comment came as a recap of a soil sampling analysis the company had completed in December, as part of program enhancements to the groundwater cleanup program they are carrying out with the supervision and approval of the Nebraska Department of Environmental Quality (NDEQ).

TRW Inc. (now Northrop Grumman) manufactured capacitors at its McCook facility from the mid-1960s to 1984 and was located at the intersection of F Street and Airport Road. Trichloroethylene (TCE) was used as a solvent and a carrier for the epoxy coating on the capacitors, prior to TRW ceasing operations in 1984 and closing the facility in 1986.

Soil containing TCE was discovered when the City of McCook was searching for a new source of water, due to nitrate contamination of the existing sources. After extensive investigations, TRW began groundwater remediation activities in 1993 and still operates five active extraction wells and water treatment equipment at the treatment plant located on airport property.

According to the December soil analysis the remediation system has resulted in a significant reduction in the plume size and a decrease in overall TCE concentrations.

"Any levels attributable to the TRW plant which were detected were extremely low," said Margaret Mitchell-Jones, corporate director of media relations for Northrop Grumman.

The analysis, available here, performed in December 2010 by Milco Environmental Services Inc. of McCook, consisted of installing temporary probes and collecting soil gas samples from 10 locations along East 16th Street, seven locations along East C Street, and three locations around the perimeter of the residence at 1507 East C Street. A combined 40 samples were collected and submitted to a laboratory for analysis, taken at approximately five and 15 feet below the surface along with two ambient air samples.

TCE was detected in 10 of the 40 samples, with concentrations highest in soil samples collected adjacent to the former TRW facility, property now owned by the McCook Economic Development Corporation. TCE levels were higher in samples taken at 15 foot depth, compared to the five-foot samples and decreased with distance from the facility.

Although TCE has previously been linked to the TRW Facility, Tetrachloroethylene (PCE) was detected in 22 of the 40 soil gas samples. The highest concentrations were encountered near the intersection of 16th and C Streets. According to the analysis, PCE was not used at the former TRW Facility and is not present in groundwater samples collected around the facility.

Chloroform was also detected in 12 of the 40 soil gas samples. The highest chloroform concentration of 3.3 ug/m3 was detected in a 15 foot sample taken approximately midway between the facility and the intersection of East C and East 16th Streets. The analysis also states that "Chloroform is not considered a site-related constituent and is typically associated with potable water system leakage of chlorine disinfection byproducts."

Citing U.S. Environmental Protection Agency (USEPA) methods, the analysis states the cancer risks and non-cancer hazards estimated are below the regulatory threshold values and no significant cancer or non-cancer hazards are anticipated to occur as a result of residential exposures to estimated concentrations in indoor air. Results of the evaluation also indicate that the levels reportedly detected in soil gas do not represent a significant health threat to residential occupants adjacent to the former TRW Facility. The report states that in all cases, the estimated cancer risks are lower than the maximum acceptable risk level established by the USEPA for residential receptors.

While residents in the area may be safe as the report states, the TCE levels detected at the TRW site show unsafe levels for unrestricted land use. The analysis uses a TCE air guideline of 5.0 ug/m3, which the State of New York considers to pose no significant health risk and therefore would be acceptable for unrestricted land use.

One sample, taken at a five foot depth adjacent to the former TRW facility, was identified at 5.5 ug/m3, exceeding the screening level. Because the closest residence is beyond 450 feet from location, residents were deemed safe.

The 15 foot sample taken at the same location was determined to be at 36 ug/m3, significantly in excess of the safe level. TCE concentrations reduce drastically in samples taken further away from the facility, one taken approximately 100 feet from a residence contained a TCE concentration of 0.69 ug/m3, well under the NYSDOH screening level.

The report further states that, "It should be noted that this risk evaluation was based on site-specific soil gas data as well as conservative (health-protective) assumptions, estimates, models and parameters. Therefore, the results are not absolute estimates of health risks but are health-protective estimates."

The State of Nebraska is reportedly reviewing the report and is anticipated to provide their comment, if any, to the company sometime this spring.