Labwork and Analysis
Drying and Sieving
Drying and sieving was done in accordance to the USEPA 6200 methodology chosen in the Sampling Analysis Plan (SAP), except for the following deviations. Deviations were discussed and agreed upon by the team and technical advisor.
XRF Analysis
X-ray fluorescence (XRF) Analysis was completed in accordance with the SAP, except for the decided upon deviations. Deviations were discussed and agreed upon by the team and technical advisor. The only deviation from the SAP was that the team only took 5 readings of each sample opposed to the suggested 9 per sample. This was chosen because of the relative homogeneity of the site shown in in-situ XRF results.
ICP-MS Analysis
Because the main contaminant of concern is arsenic and FAAS analysis is for elements in the higher ppm range in soil, SPNG proceeded exclusively with the ICP-MS analysis for subset verification. The ICP-MS analysis was completed in coherence with the Work Plan SAP and according to EPA Method 6020A.
QA/QC
QA/QC procedures were followed throughout the entirety of the labwork and analyses stages.
Contaminants of Concern
Human Health
Determination of human health COCs was completed by comparing the XRF data with the values found in the Arizona Administration Code, Title 18, Chapter 7. This document can be found in the Appendices of the PA/SI found on the Documents page. The only value relavant to this site was Arsenic, which has a non-residential limit of 10 mg/kg.
- Arsenic
Environmental
Ecological contaminants of concern were determined using the published EPA ecological soil screening levels. The ECO-SSL is a set value from a literature review to be used to identify potential COC’s at a site. The existing concentration range of six contaminants were determined from the XRF analysis, and compared to the ECO-SSL’s. The contaminants of concern for the ecological risk assessment were determined to be arsenic, cadmium, copper, lead, manganese, and zinc because they often were higher than the ECO-SSL as seen in the table below. The table below contains all the contaminants of concern determined for the ecological risk assessment due to the concentrations found at the site.
Results Maps
Using the concentrations found during the XRF and ICP-MS analyses, the following site maps were created to show the risk.
Sitewide Maps of Each Ecological COC: Arsenic, Cadmium, Copper, Lead Mangenese, and Zinc
Final DU Maps with Human Health Risk and Arsenic Concentrations
Ecological Health Risk
After determining the ecological COCs, the specific ecological screening levels for each COC were compared to the collected XRF data. These screening levels, which were taken from the EPA ecological risk assessment guidelines, can be seen in the table below.
The table below shows the expected impacts of the ratings given in the table above.
Human Health Risk Analyis
Statistical Analysis
A statistical analysis was conducted, by taking the As data and lognormally distributing it. The 50% and 95% EPCs were found to be 18.95 and 24.87 with the applied correlation, and 23.85 and 31.29 without the applied correlation.
Human Health Risk Calculations
Due to the recreational nature of the site, the only exposure pathways present are oral ingestion of soil and dermal contact with soil. The exposure scenario chosen to represent the maximally exposed individual is a camper staying there for the BLM limit of 14 days per year. There are no residential or worker scenarios at the site. This exposure scenario is also used for the child scenario. The adult and child recreational user exposure scenarios were evaluated at the 50% and 95% exposure point concentrations (EPC) to obtain risk values for an average exposed individual and a maximally exposed individual. Before calculating risk, intake values were determined using the general equation shown below:
The equation above is modified to calculate dermal exposure. This equation is shown below:
Some of the values in the equations above are obscure, so assumptions were made that overestimated the exposure of an individual to provide a conservative value for intake. These values and their justifications are located in the tables below. Table 6-1 shows the assumed values and their justifications from the ingestion intake equation 5-2:
Table 5-5 shows the assumed values and their justifications for the dermal exposure equation:
Equation 5-2 and 5-3 were used to create the intake values shown in Table 5-3 below. All values shown are in mg of soil/kg body weight • day:
The intake values calculated can then be used to determine risk values for carcinogenic and non-carcinogenic (hazard index). Equations 5-4 and 5-5 are used to calculate risk and hazard index, respectively:
Risk and Hazard Index (HI) are both used to describe how dangerous a site is. Typically, a risk value must be below 1 in 1,000,000 or 10-6 to indicate that a site does not pose a carcinogenic risk to people. Hazard values below 1 indicate that a site does not pose a danger to human health (non-carcinogenic). Table 5-4 shows the risk and HI values for each scenario and each EPC for the site:
As can be seen in the table, all of the risk and HI values are below the critical threshold for posing a danger to human health. Because of this, the risk for human health at the Emerald Isle Mine is very low.
Sampling and Analysis Photo Log
Below are a few selected pictures from the team's Photo Log (found in the Documents page).
