Pacific Southwest, Region 9
Serving: Arizona, California, Hawaii, Nevada, Pacific Islands, Tribal Nations
Naturally Occurring Asbestos
El Dorado Hills
Multimedia Exposure Assessment
Preliminary Assessment and Site Inspection Report Interim Final
Definitions
(in order of use on this page)
- HRS
U. S. EPA ’s Hazard Ranking System - NPL
National Priorities List (also called Superfund List) - AHERA
Emergency Response Act - chrysotile
A regulated mineral in the serpentine group of minerals that can crystallize as asbestos.
Chrysotile is also known as serpentine asbestos. - amphibole
One of the two groups of minerals (serpentine and amphibole) that can crystallize as asbestos. The regulated asbestiform minerals of this group are crocidolite, amosite, anthophyllite asbestos, tremolite asbestos, and actinolite asbestos.
6.0 Hazard Ranking System Factors
- 6.1 Sources of Contamination
- 6.2 Groundwater Migration Pathway
- 6.3 Surface Water Migration Pathway
- 6.4 Soil Exposure Pathway
- 6.5 Air Migration Pathway
The Hazard Ranking System (HRS) is the principal mechanism EPA uses to place sites on the National Priorities List (NPL). It is a numerically-based screening system that uses information from initial, limited investigations to assess the relative potential of sites to pose a threat to human health or the environment.
The HRS uses a structured analysis approach to determining site scores. This approach assigns numerical values to factors that relate to risk based on conditions at the site. The factors are grouped into three categories:
- Likelihood that sources of contamination at a site have released or have the potential to release hazardous substances into the environment;
- Characteristics of the waste (e.g., toxicity and waste quantity); and
- People or sensitive environments (targets)affected by the release.
Four pathways can be scored under the HRS:
- Groundwater migration (drinking water);
- Surface water migration (drinking water, human food chain, sensitive environments);
- Soil exposure (resident population, nearby population, sensitive environments); and
- Air migration (population, sensitive environments).
6. 1 Sources of Contamination
6. 1. 1 Areas of Concern
In all the locations that are the subject of the El Dorado Hills Naturally Occurring Asbestos Multimedia Assessment, areas of concern are those areas where the presence of asbestos in exposed and disturbed soil may be causing releases to air. The original expectation at the outset of the project was that asbestos present in soils would be from naturally occurring sources and would pose a potential threat of exposure because of activities that disturbed it from its natural state. Several of the playing fields where START found asbestos during activity-based air sampling (e.g., baseball playing fields at the Community Park) have imported infield mix, however, so the possibility that not all of the asbestos is endemic to El Dorado Hills must be considered.
6. 1. 2 Contaminant Types and Quantities
Types
In samples collected during activity-based air sampling, the laboratory identified chrysotile and amphibole asbestos. The following regulated (indicated with an asterisk) and non-regulated asbestiform minerals were in air samples above the laboratory levels of detection:
- actinolite*
- amosite*
- anthophyllite*
- chrysotile*
- edenite
- ferro-edenite
- richterite (one sample)
- tremolite*
- winchite
Quantities
The New York Creek Nature Trail runs almost 2 miles starting from Harvard Way, traversing through the El Dorado Hills Community Park, and ending near Jackson Elementary School. The three baseball playing fields at the Community Park have “skinned” infields, which means that there is no grass in their infields. There is grass covering the outfield areas, which are also used as soccer playing fields. The baseball bases are set at 60 feet apart. Imported “infield mix,” which is composed of 50% topsoil and 50% crushed lava rock, is present within the infield.
The Dirt Embankment is about 1, 200 feet along the downslope edge. The width of the Dirt Embankment varies, but is estimated from aerial photographs to be about 75 feet wide at its widest point.
The Silva Valley Elementary School baseball playing field has a grass infield. When the field is maintained, the outfield and the area inside the baselines is grass (except for the pitcher ’s mound), and the rest of the infield is exposed dirt (e.g., see Figure 5-4: Silva Valley Elementary School Baseball Playing Field Activity-Based Outdoor Air Sampling Locations–Maintenance Scenario). According to school district personnel, imported “infield mix” would typically be used in the dirt areas of the infield including on the basepaths and pitcher’s mound. The baseball bases are set at 60 feet apart.
6. 2 Groundwater Migration Pathway
In determining a score for the groundwater migration pathway, the HRS evaluates:1) the likelihood that sources at a site actually have released, or potentially could release, hazardous substances to groundwater; 2) the characteristics of the hazardous substances that are available for a release (i.e., toxicity, mobility, and quantity); and 3) the people (targets) who actually have been, or potentially could be, impacted by the release. For the targets component of the evaluation, the HRS focuses on the number of people who regularly obtain their drinking water from wells that are located within 4 miles of the site. The HRS emphasizes drinking water usage over other uses of groundwater (e.g., food crop irrigation and livestock watering), because, as a screening tool, it is designed to give the greatest weight to the most direct and extensively studied exposure routes.
According to the Draft Water Resources Development and Management Plan for El Dorado County, usable groundwater is limited in the western slope of the county. Groundwater quality in this region is said to be satisfactory but marginal. There are some wells, typically in the range of 100 to 200 feet below ground surface, but the amount of water they provide to serve the community’s drinking water needs compared to surface water sources is minimal.
6. 3 Surface Water Migration Pathway
In determining the score for the surface water pathway, the HRS evaluates:
- the likelihood that sources at a site actually have released, or potentially could release, hazardous substances to surface water (e.g., streams, rivers, lakes, and oceans);
- the characteristics of the hazardous substances that are available for a release (i.e., toxicity, persistence, bioaccumulation potential, and quantity); and
- the people or sensitive environments (targets) who actually have been, or potentially could be, impacted by the release.
For the targets component of the evaluation, the HRS focuses on drinking water intakes, fisheries, and sensitive environments associated with surface water bodies within 15 miles downstream of the site.
The El Dorado Irrigation District is the primary water purveyor in El Dorado Hills. The water supply comes from a variety of sources, essentially all from surface water sources. The largest water supply source for El Dorado Hills Irrigation District is Jenkinson Lake (Sly Park Reservoir and Dam). In addition, Folsom Lake, the South Fork of the American River (at Kyburz), the North Fork of the Cosumnes River, and Clear Creek (Crawford Ditch) provide significant supply to the system. Of these sources, all except Folsom Lake are geographically upslope of the area of concern. The New York Creek, which is an ephemeral stream, flows through the Community Park along the New York Creek Nature Trail, past Jackson Elementary School to Folsom Lake, with the point of entry just over 3 miles from the northern boundary of the Community Park.
Folsom Lake State Recreation Area is an 18,000-acre lake and recreation area offering opportunities for angling, hiking, biking, running, camping, picnicking, horseback riding, water-skiing and boating. The lake has trout, catfish, big and small mouth bass and perch.
6. 4 Soil Migration Pathway
In determining the score for the soil exposure pathway, the HRS evaluates:
- the likelihood that there is surficial contamination associated with the site (e.g., contaminated soil that is not covered by pavement or at least 2 feet of clean soil);
- the characteristics of the hazardous substances in the surficial contamination (i.e., toxicity and quantity); and
- the people or sensitive environments (targets) who actually have been, or potentially could be, exposed to the contamination.
6. 4. 1 Contamination
The contaminant of concern is asbestos. The START collected soil samples from areas of concern within 2 feet of ground surface. The soil samples are still being analyzed by a laboratory, and U. S. EPA is currently evaluating preliminary data. The results are not available for release at the time of this report.
6. 4. 2 Population
According to the State Department of Finance, as of January 2005 there were about 31,000 residents in El Dorado Hills. The population of El Dorado Hills has grown rapidly in the last few decades. The residential area of El Dorado Hills is about 28 square miles.
There are about 800 students and 50 to 55 teachers and staff members at Rolling Hills Middle School. At Silva Valley Elementary School there are about 650 students and 49 teachers and staff members. Jackson Elementary School is reducing its size, and next fall there are expected to be about 470 students and 35 teachers and staff members. According to the California Department of Education, at the nearby Oak Ridge High School, there were reportedly 1,829 students and 87 staff members for the 2003 2004 school year.
There are 26 full-time and about 8 part-time year-round staff members at the CSD offices at the Community Park. There are seasonal changes in part-time staff (e.g., life guards) at the Community Park. About 35 to 40 children attend day camp at the Community Park during the school year, and about 150 attend during the summer. The Community Park and the schools have staff who maintain the play areas and the Dirt Embankment. The CSD is responsible for maintaining the New York Creek Nature Trail as well.
6. 4. 3 Sensitive Environments
Based on review of biological resources maps included in the draft Environmental Impact Report for the El Dorado County General Plan as well as the draft Water Resources Development and Management Plan for El Dorado County, there do not appear to be terrestrial or aquatic sensitive environments or special status species documented within 4 miles of the areas that are the subject of the El Dorado Hills Naturally Occurring Asbestos Multimedia Assessment.
6. 5 Air Migration Pathway
In determining the score for the air migration pathway, the HRS evaluates:
- the likelihood that sources at a site actually have released, or potentially could release, hazardous substances to ambient outdoor air;
- the characteristics of the hazardous substances that are available for a release (i.e., toxicity, mobility, and Asbestos Hazardous quantity); and
- the people or sensitive environments (targets) who actually have been, or potentially could be, impacted by the release.
6. 5. 1 Release of Asbestos to Air
The START collected activity-based air samples containing elevated levels of asbestos (i.e., relative to ambient reference air samples that were collected during the same time periods). Table 6-1 (Summary of Sample Results) shows a comparison of the results from the personal air monitors with results from ambient reference air samples collected simultaneously. The table shows:
- the ratio of the average personal asbestos exposure measurement to the average ambient air asbestos concentration measured simultaneously in the same general area,
- the average personal asbestos exposure concentration as measured by the personal samplers during the simulated activity, and
- the average concentration of asbestos measured in nearby ambient air at the same time the simulated activity was taking place.
6.5.2 Population
See discussion of population for the soil exposure pathway in Section 6.4.2.
6.5.3 Sensitive Environments
See discussion of sensitive environments for the soil exposure pathway in Section 6.4.3.
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