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Site-Specific Uncertainty Management and Incremental Sampling in Conjunction with Field-Portable X-ray Fluorescence to Delineate Metal Contamination in Residential Soil at the Jacobs Smelter Site in Stockton, Utah

Triad Elements Used

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Table of Contents

  1. Site Information
  2. Project Information
  3. Triad Approach Information
  4. Supporting Information



The Jacobs Smelter Site is an EPA Region 8 Superfund Site with the State of Utah Department of Environmental Quality (DEQ) as the project lead. Several of the operable units (OUs) include residential subdivisions with properties and lots that were previously assessed and remediated for lead using 5-point composite samples, off-site inductively coupled plasma (ICP) laboratory analysis, and excavation of contaminated soil. At the request of concerned residents, the Utah DEQ remedial project manager returned to the site several years after remediation activities to evaluate limited properties using a field portable x-ray fluorescence (FP-XRF) instrument. Risk-based action levels at the site were previously set at 500 parts per million (ppm) lead in surface soil and 800 ppm at depth. Within minutes of evaluating the first residential lot the project manager measured lead concentrations exceeding 1,000 ppm in surface soil in areas previously assessed and excavated prompting the need for improved characterization to meet adequate clean-up levels.

This profile highlights the application of an ICS design driven by the use of real-time FP-XRF measurements and statistics to determine the appropriate number of increments for DUs in the field. The program utilized in situ and ex situ XRF measurements, vario-plots, real-time custom data evaluation spreadsheets, and EPA?s VSP software, to assess variability and determine the appropriate number of increments for ICS samples in the field. Resulting ICS samples were evaluated using collaborative data sets from FP-XRF and laboratory-grade XRF along with a percentage of samples for off-site laboratory ICP analysis. The high-resolution data resulted in several updates to the conceptual site models (CSM), exposure assumptions, and property use that had not been previously considered.

Systematic planning was performed in September and the field work was performed from October to November 2009.

1. Site Information

Site Name Jacobs Smelter Superfund Site
Location Stockton, UT
Site Type  Metal Ore Mining and Smelting
Site Regulatory ID  EPA ID#: UT0002391472/ Site ID#: 0801674
Project Lead Type  State Lead
Regulatory Lead Program  Superfund Remedial
Triad Project Status Field Program Ongoing
Reuse Objective Identified  Yes
Proposed Reuse:  Residential and Recreational

Background Information About Site 

The area around Stockton, Utah, was heavily mined for silver beginning in the 1860s until near the turn of the century. Smelting and milling operations in the area produced large amounts of ore along with flue dust and smelter slag. Over the next century, most of the physical evidence of Stockton?s mining history disappeared and residential properties were built on land containing heavy metal contaminated soil, mill tailings, and smelter wastes. The Jacobs Smelter Site was added to the Comprehensive Environmental Response, Compensation, and Liability Information System (CERCLIS) in 1995 and to the National Priorities List in 2000. It is now an EPA Region 8 Superfund Site with Utah DEQ as the project lead.

Operable Unit 2 (OU2) of the Superfund Site includes two residential subdivisions (Rawhide Ranchettes and B&B Subdivision) as well as the Waterman Smelter. The subdivisions consist of 2- to 7-acre lots that were assessed and remediated for lead in 1999 using 5-point composite samples, off-site ICP laboratory analysis, and excavation of contaminated soil. Action levels for the properties were set for lead at 500 ppm for surface soils and 800 ppm at depth. The selected remedy involved the excavation and removal of approximately 150,000 tons of lead and arsenic contaminated soil over two years. Six to 18 inches of soil were removed at specific properties and confirmation sampling was conducted at the base of each excavation.

At the request of homeowners, additional characterization of some OU2 properties was performed by Utah DEQ using FP-XRF in September 2008. Sampling identified lead concentrations above clean-up levels, spurring the need for further characterization and remediation actions at the Jacobs Smelter Site. With input from the State of Utah risk assessor and help from the EPA Technology Innovation and Field Services Division (TIFSD), a dynamic work strategy (DWS) utilizing real-time technologies was developed at the site in order to better define and fully characterize residential decision units relative to previously established clean-up goals, and resolve the scope of further remediation needs.

Contaminant(s) of Concern 

Contaminated Media 

Project Results and Outcomes 

The customized DWS provided updates to the CSMs of the residential areas to address data gaps remaining from the previous 5-point composite sampling strategy. The new data set also resulted in updates to exposure assumptions and allowed the team to consider property uses that had not been previously considered. In addition to investigation of the residential areas, the efficiency of the field investigation allowed for limited delineation in other areas of OU2, historically associated with the Waterman Smelter, that had other current land uses (e.g., recreational).

Compared to traditional 5-point composite sampling, which provided limited data coverage across the previously defined DUs, statistical analysis of data generated in real-time through ICS succeeded in establishing appropriately-scaled DUs (0.25 acres) and statistically derived ICS representative of those DUs. This process saved time and money compared with the traditional 5-point sampling program and fixed-base laboratory analysis.

Based on the refined CSMs, additional soil removal was completed at the Rawhide Ranchettes subdivision in the Fall of 2010. Remedial activities are pending for the B&B subdivision and the Waterman Smelter Area.

2. Project Information

Remedial Phase

Site Investigation (Includes RI/FS or Similar Detailed Investigation Work)

Triad Project Benefits 

The number of increments for each ICS necessary to meet statistical project objectives for all quarter-acre DUs within a residential property was determined empirically using real-time data input into EPA?s VSP software. This process saved the project time and money by deriving statistically based ICS for each property based on observed media specific variability. Use of FP-XRF produced a high-density data set (~2,000 samples), and confidence in these data were assured through real-time evaluations of analytical uncertainty and correlations with off-site laboratory data (as demonstrated sufficiently through the analysis of 5 percent the samples by off-site ICP methods).

3. Triad Approach Information

Systematic Project Planning 

The objective of the project was to use the Triad Approach to re-evaluate soil quality at residences at Jacobs Smelter Site following a request from homeowners to the Utah DEQ. The DWS was created with input from the technical team. Buy-in from the full team, including contractors and EPA Region 8 risk assessment staff, was obtained after initial discussions regarding the proposed "non-conventional" investigation approach and tools, including the use of incremental sampling: vario-plots, real-time statistics, and VSP. Concerns regarding DU size, surficial sampling depth interval of interest, locations of depth samples, and sampling density were noted and incorporated into the DWS. Decision units were reduced to one quarter-acre to reflect risk assessment exposure assumptions. Real time use of FP-XRF, spreadsheets, and VSP was used to derive a statistically confident, high-resolution ICS design for each property. Previous iterations of the CSM were evaluated and updated sampling maps were developed to visualize the XRF sampling strategy and subsequent field sampling results. Historical sampling results were extensively reviewed and found only one instance of a depth sample exceeding the 800 ppm action level for lead where the surface sample from that same DU did not exceed the surficial 500 ppm action level. Using this CSM element, the project team agreed to target a depth sample within each DU at the highest observed FP-XRF surface in situ result. This procedure allowed time and cost savings associated with depth sampling but maintained the risk assessment needs for evaluating exposures for contamination found at depths up to 18 inches while focusing resources on the greatest risk concerns associated with surficial soil.

Project Team Description 

The Jacobs Smelter Site is an EPA Region 8 Superfund Site and the Utah DEQ is the site lead. Site stakeholders also included local area residents in the Rawhide Ranchettes and the B&B subdivisions. Representatives and contractors of EPA Region 8 and Utah DEQ, along with members of the EPA TIFSD, created the technical team that established the DWS for the Site.

Utah DEQ and EPA Region 8 personnel approached TIFSD for assistance because they had recently taken a one day course entitled ?Advanced Design Application and Data Analysis for FP-XRF in Soil Matrices? presented by TIFSD personnel. Based on the concepts presented in this course and newer advances in FP-XRF instrumentation, the project managers requested support from EPA TIFSD to assist with design and implementation of an efficient and effective FP-XRF sampling design to re-evaluate properties associated with Jacobs Smelter.

Dynamic Work Strategies 

Real-time data was collected using a FP-XRF to establish the variance and standard deviation (SD) potentially present within each quarter-acre DU of a given residential property. Vario-plots (12? X12? grids) were established at each property to guide the initial sampling pattern and help determine short-scale heterogeneity on the order of 2 to 17 feet. The most conservative real-time statistical results (i.e., the highest standard deviation (SD) for any vario-plot FP-XRF in situ sample pair) were input into EPA?s VSP software to determine the number of increments per each ICS within each DU for a given residential property. The resulting ICS design was customized for each property, yielding quarter-acre DUs with ICS samples. The number of increments comprising each ICS was derived using property- and media-specific vario-plot inputs for the VSP incremental sampling module. Real-time data was then corroborated with laboratory data and a refined CSM was established showing mean lead concentrations for each DU. The resulting CSM can be used to guide future remediation efforts within the residential Ous.

The sampling strategy focused on the upper 2 inches of soil as the layer of greatest concern for residential and recreational exposure. However, depth samples were taken at the highest in situ location within each DU to further assess the vertical extent of contamination (supported by historical data, CSM, and re-confirmed via XRF).

Real-Time Measurement Technologies 

Real-time measurement technologies included the use of a FP-XRF instrument in combination with EPA?s VSP software and field generated statistics. Initially, in situ XRF analyses (?point and shoot? analyses on in-place surficial soil) were performed to assess worst case variance within each DU. Based on initial variance inputs, the number of increment samples was refined through the use of vario-plots and the VSP software. Resulting ICS samples were evaluated using collaborative data sets from FP-XRF and laboratory-grade XRF along with a percentage of samples for off-site laboratory ICP analysis. More than 2,000 XRF samples were collected and 90 of these samples (focusing around the 500 ppm and 800 ppm action levels for lead) were sent for off-site ICP laboratory analysis. The resulting correlation between XRF and ICP is provided here. A demonstration of methods applicability (DMA) was performed early in the program to optimize the use of the FP-XRF.

Technology Category(s) for Sampling and Analysis 

Technology Vendor(s)

Attached Technology Quick Reference Sheet (TQRS) Form 

TQRS not prepared

Data Quality Assessment 

Data Management Approach and Tools 

Real-time data management tools were critical to the success of the investigation and included the following:

4. Supporting Information

Key Triad Project Milestones 

Project timeline as adapted from the Second Five Year Review Report for the Jacobs Smelter Superfund Site (UDEQ 2010):

Source(s) of Information

Electronic Documentation of Supporting/Related Information

Link Five-Year Review Report: Second Five-Year Review Report For Jacobs Smelter Superfund Site, Stockton, Utah

Point(s) of Contact 

Stephen Dyment
U.S. EPA, Office of Superfund Remediation and Technology Innovation Technology Integration and Information Branch
1200 Pennsylvania Ave., NW (5203P)
Telephone icon 703-603-9903
Fax icon 703-603-9135
E-mail icon

Lisa Lloyd
EPA Project Manager
U.S. Environmental Protection Agency, Region 8
1595 Wynkoop Street (8EPR-SR)
Denver, Colorado  80202-1129
Telephone icon 303-312-6537
E-mail icon

Kathy Hernandez
EPA Project Manager
U.S. Environmental Protection Agency Region 8
1595 Wynkoop Street (8EPR-SR)
Denver, Colorado  80202-1129
Telephone icon 303-312-6101
E-mail icon

Tom Daniels
Utah Department of Environmental Quality
195 North 1950 West, Box 144840
Salt Lake City, Utah  84114-4840
Telephone icon 801-536-4090
E-mail icon

Last Update:  12/11/2011

To update this profile, contact Cheryl T. Johnson at or (703) 603-9045.