BUNKER HILL MINING AND METALLURGICAL
KELLOGG, SHOSHONE COUNTY, IDAHO
The Agency for Toxic Substances and Disease Registry (ATSDR) was requested by the U.S. Environmental Protection Agency (EPA), in conjunction with EPA's 5-year site review process, to evaluate the public health significance of contaminants in surface soil, household dust, and fugitive dust in remediated areas of the Bunker Hill Superfund Site. Specifically, ATSDR was asked to (1) review surface soil and household dust sampling data to determine if contaminants were present at levels of public health concern in site surface soils and household dusts, as an indicator of soil barrier effectiveness, and (2) review sampling data for fugitive dust to determine its public health impact.
The Bunker Hill National Priorities List Site is located in Shoshone County, Idaho, approximately 40 miles east of Coeur d'Alene, Idaho. The site covers approximately 21 square miles around a former mine and smelter and includes the cities of Kellogg, Page, Pinehurst, Smelterville, and Warner. Mining and smelting of various metal ores, including silver, lead, zinc, cadmium, copper, and gold, throughout much of the past 100 years have resulted in high concentrations of metals, including lead, arsenic, and cadmium in sediments, soils, and dusts throughout the site. These activities have also resulted in elevated blood lead levels in area children.
In 1986, cleanup of selected common areas, such as city parks and school playgrounds, was initiated. Since 1989, remediation of residential yards with soil lead concentrations greater than 1000 mg/kg has been conducted each summer. Remediation of residential yards involve the following: (1) removal of contaminated soil to a depth of 6 inches, 1 foot, or 2 feet depending on the lead concentration and intended use; (2) installation of a geotextile material as a visual marker between the remaining contaminated soil and the clean replacement soil if soil lead concentrations exceed 1000 mg/kg at a depth of 12 to 18 inches at least one foot (two feet in garden areas); (3) placement of clean soil in the excavated areas; and (4) revegetation with grass seed or sod. In areas where a more durable barrier is needed, such as gravel driveways, a gravel barrier is used instead of grass. Commercial properties with soil lead levels greater that 1000 mg/kg are also excavated, to a depth of 6 inches or 1 foot, and covered with a barrier of clean sand, gravel, or asphalt/concrete pavement.
As discussed above, remediation of residential and commercial properties at the Bunker Hill site does not provide complete removal of contaminated soil. Instead, remediation efforts focus on creating "barriers" (e.g., clean soil, vegetation (grass), gravel, pavement) between soil contaminants and people. Therefore, maintaining the integrity of these remediation "barriers" is critical to minimizing human exposure to site contaminants. In order to help ensure the long-term stability of the barriers, an Institutional Control Program (ICP) was established.
The ICP is a locally enforced set of regulations designed to ensure the integrity of clean soil and other protective barriers placed over contaminants left in place throughout the site. The ICP regulates construction and use-changes involving excavation, grading, and certain interior renovation on all properties where barriers and caps have been installed. The ICP, which is administered by the Panhandle Health District, also provides services, including education, sampling assistance, clean replacement soil for small residential projects and pickup of contaminated soil, and a permanent disposal site for contaminated soils generated site wide. The long-term success of the Bunker Hill cleanup remedy is dependent upon the effectiveness of the ICP.
Remediation of contaminated soils is currently on going in all site cities except Smelterville and will continue until all residential yards, commercial properties, and city right-of-ways (ROWs) with lead levels greater than (>) 1000 mg/kg have been cleaned up. Smelterville is the only site community in which remediation of contaminated yards, commercial properties, and ROWs has been completed. Remediation activities have also been completed in the portion of Kellogg north of Interstate 90 (I-90). EPA estimates that remedial activities in the remainder of the site will be completed by 2003.
EPA's remediation activities at the Bunker Hill site are designed to achieve the following site-wide Remedial Action Objectives (RAOs), as defined in the 1991 and 1992 site Records of Decision (RODs):
- < 5% of children with blood lead levels > 10 micrograms per deciliter (ug/dL), and
- No children with blood lead levels >15 ug/dL (nominally, less than 1% of the population).
Since the RAOs were established, EPA has clarified that the blood lead goal is no greater than a 5% chance of an individual child > 10 ug/dL.
To achieve these blood lead objectives, the following environmental objectives were established for the site:
- remediation of all residential yards, commercial properties, and ROWs with lead soil concentrations > 1000 mg/kg;
- achieving a geometric mean yard soil lead concentration of < 350 mg/kg for each site community; and
- achieving a geometric mean interior house dust lead level of < 500 mg/kg for each community and no individual house dust level > 1000 mg/kg;