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On October 1, 1998, Region VI U.S. Environmental Protection Agency (EPA) requested the Agency for Toxic Substances and Disease Registry (ATSDR) determine if lead and arsenic contaminated soil pose a health threat to residents living near the Stephenson-Bennett Mine site. Removal and cleanup activities are coming to a close at residential properties; however, contaminated soil had to be left under trailer homes because removal would have compromised the integrity of the structure.

The Stephenson-Bennett Mine is an inactive silver mine located ten miles northeast of Las Cruces, New Mexico [1]. Mining waste have washed down an arroyo (a creek/stream in an arid region) into nearby residential yards. In March - June 1997, the EPA collected surface soil samples (0 to 6 inches) from residential properties and analyzed them for lead, arsenic, cadmium, and zinc. EPA also collected indoor dust samples from the homes where surface soil samples were collected. Elevated levels of lead (32,200 parts-per-million (ppm)) and arsenic (860 ppm) were detected in the soil samples [1]. Elevated levels of lead (7647 ppm) and arsenic (310 ppm) were also detected in the indoor dust samples. The mine tailings are reportedly in the form of lead carbonate, which increases its water solubility and bioavailability [1].

On June 16, 1997, ATSDR evaluated the sampling data and initiated an exposure investigation to determine if exposure to the soil was occurring [1]. The exposure investigation targeted residents of homes where soil lead levels exceeded 400 ppm, and offered blood lead testing for children between the ages of six months and six years. Older children were also eligible to participate, along with women of child-bearing age [1].Blood lead levels were tested in 93 residents (69 children and 24 adults). Blood lead levels were determined to be elevated (10-14 micrograms/deciliter) in eight children. Health follow-up activities were conducted for the eight children with elevated blood lead levels. Health education on ways to reduce exposure to contaminated soil and dust was provided to parents of children with elevated blood lead [1].

In early February 1998, EPA initiated soil cleanup activities at the residential properties impacted by mine run-off waste. Residential soil cleanup levels of 500 ppm and 20 ppm were established for lead and arsenic, respectively. [2]. There are several vacant lots in the same residential area as the trailer homes that did not undergo cleanup of soil contamination because EPA was denied access to the lots by the property owners. The homes where the indoor dust was found to be contaminated with lead and arsenic are scheduled for remediation in November-December 1998 after soil removal activities are completed [2].

On October 13, 1998, during a telephone conversation between ATSDR and EPA, the EPA onsite coordinator stated that the potentially contaminated soil under the homes would not be removed because removal operations would compromise the structural integrity of the homes.

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