McCOOK, Nebraska -- The levels of the other two chemicals, tetrachloroethylene -- PCE -- and chloroform, that were discovered during a December 2010 soil and vapor sampling of the trichloroethylene -- TCE -- contaminated area neighboring the former TRW Facility in McCook, are also too low to cause a health risk for residents in the area. According to Sue Dempsey, Risk Assessor for the Nebraska State Department of Health and Human Services, the vapor emission from a business suit returning from the dry-cleaners would cause higher levels of PCE in your home than those that were found at the site.
She also told the Gazette, Wednesday during a phone interview, that the risk assessment performed by Milco Environmental Services Inc. of McCook on behalf of Northrop Grumman, "was a very conservative risk assessment." Dempsey explained that the risk model that Milco ran for every sampling location assumed a worst-case scenario of the chemical migrating directly above its location and maintaining the level below ground at which it was sampled.
"They did that at every location and assumed it would be a resident living there full time and found nothing risk wise," said Dempsey.
Dempsey was reluctant to answer specific questions that sought to establish a threshold between a safe and harmful level of PCE and chloroform, that could then be compared to the soil sample levels provided in Northrop Grumman's report. She said the models that must be used were very complex and utilized a large number of variables. She did estimate that it would take levels of PCE and chloroform significantly higher than those discovered to warrant any type of investigation into their origination. She added that a typical male has a one in two risk of contracting cancer during his life and a woman one in three. Contracting cancer from exposure to PCE and chloroform at levels similar to those in the vicinity of the TRW facility were right at one in a hundred million.
Northrop Grumman released its December soil sampling report in a March 1 Gazette story, after saying they had previously released the report to the city, the state and a concerned resident of the area. As of March 18 there has still not been a formal statement from any state or other entities, regarding the findings, aside from the informal conversation with Dempsey. This may have contributed to speculation and even confusion, that seems to have mounted about whether the levels of the three chemicals found at the site are safe for neighboring residents.
A representative from the Nebraska Department of Environmental Quality confirmed that no land use restrictions had been placed on the TRW Facility property, even though the December soil sampling report states the site is in excess of the New York State Department of Health maximum level for unrestricted land use. The NYSDOH standards were used during the soil analysis because there are no federal regulations pertaining to levels of the chemicals.
Further investigation by the Gazette into the 5.0 ug/m3 level, that NYSDOH uses, revealed that the level was set to encourage practices that would minimize presence of the chemical and exceeding the level does not necessarily indicate a risk to public health nor does it trigger actions to reduce exposure.
According to information found on their website, it takes long-term exposure to air containing TCE levels generally greater than 40,000 ug/m3 before it is linked to effects on the central nervous system (reduced scores on motor coordination tests, nausea, headaches and dizziness) and irritation to the mucous membrane. Short-term exposure to higher levels, greater than 300,000 ug/m3 can irritate the eyes and respiratory tract, as well as effect the central nervous system. During the December soil analysis the highest level of TCE at the TRW Facility was only 36 ug/m3, which came from a sample 15 feet deep and directly adjacent to the main building.
McCook Utility Director Jesse Dutcher told the Gazette, earlier this week, that he was concerned that the publicized statements from the Northrop Grumman report, specifically regarding chloroform, may have been confusing. He said that the report stated, "Chloroform is typically associated with potable water system leakage of chlorine disinfection byproducts," and according to Dutcher, while the statement is true, chloroform is a byproduct of chlorine and occurs as it reacts with other compounds it comes in contact with. "The chloroform would have not been in the water but formed as the chlorine reacted with the soil. According to the report the highest concentration of the chloroform was located on East 16th Street at a point about halfway between TRW and East C Street," said Dutcher, who further explained that McCook only has one water line in the area where the highest level of chloroform was recorded. "The water line in that area is a service line and it is not leaking and has not leaked in the past. The meter for this particular service line is located at the intersection of East C and 16th street, any leak would have been registered as a high usage on the meter, there were none," said Dutcher.
"Chloroform is not just limited to the water industry, it is a naturally-occurring chemical but most often is man-made and is a member of a group of chemicals called trihalomethanes. It is used to make coolants, as a fumigant for grain, and is a dry cleaning spot remover, along with being in other solvents, dyes and pesticides," said Dutcher.
McCook's water system is tested annually for the trihalomethane group and the city's annual test for chloroform was conducted on July 22, 2010. According to Dutcher the 2010 results for chloroform were 1.06 ug/L, well within the safe level and equal to about .009 of a pound in one million gallons of water.
Northrop Grumman also stated in their report that the original TCE plume at the TRW facility was significantly decreased, since mitigation efforts began in 1993. The company also offered to provide the Gazette with data supporting the decrease of the plume, after having the opportunity to present the information to city staff in a meeting Thursday.