Title: Introduction (1 of 2) Text: Background analysis is a necessary component of the site assessment process because both natural and anthropogenic processes may result in elevated concentrations of various chemicals including hazardous substances at a given site. For example, natural processes such as the weathering of naturally occurring metallic mineral deposits can contribute to elevated levels of metals in soil, sediment, or groundwater. An anthropogenic process such as the deposition of lead from internal combustion engine exhaust might also contribute to elevated levels of lead in soil. These background chemicals are derived from sources not related to site-specific Navy activities or operations, and should not be considered Navy releases. Failure to distinguish between Navy releases and background conditions may lead to unnecessary remediation and delay property transfer and re-use.

Title: Introduction (2 of 2) Text: In order to address the issue of potential background chemical contributions at Navy sites, NAVFAC has published a three-volume set of guidance documents to provide instructions for identifying background chemicals in soil, sediment, and groundwater. The objective of this Web tool is to provide an overview of these guidance documents and the methods available for estimating background concentration ranges to distinguish between media that have been impacted by a site-related chemical release and those that have not. The background analysis methods described in this Web tool should be conducted as early in the site investigation process as possible in order to ensure that only media that have been impacted by a chemical release are targeted for cleanup.

Title: Background Conditions Text: Background area or reference area refers to an area where detected chemicals are attributed to natural or anthropogenic (i.e., nonsite-related) sources only. These nonimpacted background or reference areas may be located off site, or within the designated site boundaries.

Title: Background Analysis: Soil Text: This tool presents techniques for evaluating site-specific chemical, geochemical and geological data to distinguish between soils that have been impacted by a site-related release and those that represent background conditions. Natural and anthropogenic background processes may result in elevated concentrations of various chemicals in otherwise nonimpacted soils. Naturally-occurring background chemicals Anthropogenic background chemicals

Title: Naturally-occurring bkg chemicals Text: Ambient concentrations of chemicals present in the environment that have not been influenced by human activity.

Title: Anthropogenic background chemicals Text: The presence of widely distributed chemicals present in the environment due to human activities. Ranging from localized to ubiquitous, the chemicals are attributed to past or present 'legal' applications not related to other point sources or releases.

Title: Background Analysis: Sediment Text: Sediments are defined as materials deposited on the bottom of water bodies, such as lakes, seas, rivers, harbors, storm drains. Chemicals from both natural and anthropogenic sources are often adsorbed to sediment particles and accumulate in the porewater within the sediment. Impacted sediments can be transported to locations far away from their original sources. Contaminated sediments pose a particularly important and complex problem for the Navy. Most Navy facilities are located within marine or estuarine sediment basins and watersheds along the coastline. Because contaminants in the aquatic environment can be transported long distances from many potential sources, it can be particularly difficult to identify contaminant sources, and determine the scope of Navy cleanup responsibility. In response to this challenge, the Chief of Naval Operations (CNO) has issued a specific policy on sediment site investigation and response action. Click here to view policy.

Title: Background Analysis: Groundwater Text: Contaminants associated with Navy and non-Navy releases, as well as naturally-occurring and anthropogenic background chemicals may occur in groundwater. The Navy is not responsible for cleanup of either natural or anthropogenic background chemicals; therefore, at most Navy groundwater investigation sites, background analysis will be necessary to define the nature and extent of site-related groundwater contamination and assess the need for cleanup.

Title: Objectives and Scope Text: The objective of this Web tool is to summarize various methods that can be used to compare chemical concentrations detected in samples collected during the site investigation to corresponding data representing background chemicals. The CNO Policy on the Use of Background Chemicals includes the flowchart shown here, which provides an overview of the role of the background analysis process in the selection of chemicals of potential concern (COPCs) at a given site. This type of background analysis is important because the failure to distinguish between concentrations associated with a site-related chemical release and those from natural or anthropogenic sources may lead to establishing cleanup levels within the background range and therefore resulting in unnecessary and costly remediation.

Title: Navy Background Policy Text: Click here to view the Chief of Naval Operations (CNO) Policy on the Use of Background Chemicals. The policy requires that cleanup efforts at Navy sites should address only those risks associated with chemical concentrations that are elevated as a result of site-related releases. Because the Navy is not responsible for cleanup of either natural or anthropogenic background chemicals, it is therefore necessary at most sites to determine background chemical concentrations. The policy specifically requires the following: Chemicals that may have been released at the site must be clearly identified to ensure that the Navy is focusing on remediating the COPCs associated with the release. Chemicals detected at concentrations below the upper bound of the background range must be excluded from the full baseline risk assessment. All chemicals screened out as a result of background considerations should be documented in the baseline risk assessment. Cleanup levels must not be below the upper bound of the background range.

Title: Regulations (1 of 2) Text: Numerous federal and state laws, regulations, and guidance are pertinent to background analysis as shown in this flowchart. Federal law requires the Navy to protect human health and the environment and comply with applicable or relevant and appropriate requirements (ARARs) at all Navy chemical release sites. Navy policy and guidance documents summarized in this tool were developed to ensure compliance with laws and regulations that address background analysis and its role in the site assessment and cleanup process. The Navy/Marine Corps Installation Restoration Manual provides an overall synopsis of environmental laws and regulations that define and affect the Navy Installation Program (IR Program). According to this Manual, all actions at IR sites shall comply with the following: Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) Superfund Amendments and Reauthorization Act (SARA) National Oil and Hazardous Substances Pollution Contingency Plan (NCP).

Title: Regulations (2 of 2) Text: Federal laws, including the CERCLA/NCP, require protection of human health and the environment at sites where CERLCA hazardous substances have been released. To comply with the CERCLA/NCP, the Navy must determine whether CERCLA hazardous substances have been released to the environment, assess the nature and extent of contamination, and evaluate associated risks to human health and the environment. To achieve these objectives, background analysis must be included as an integral component in the site assessment and cleanup process. U.S. EPA requirements acknowledge the importance of background analysis. CERCLA (42 USC 9604(a)(3)(A)) recognizes that remediation may be impractical or impossible if naturally occurring background levels are higher than regulatory criteria. Resource Conservation and Recovery Act (RCRA) requirements also recognize the importance of background analysis, giving the U.S. EPA authority to require cleanup of releases that impact environmental media within designated areas. Other U.S. EPA and State requirements are also applicable.

Title: CERCLA Guidance Text: "The President shall not provide for a removal or remedial action under this section in response to a release or threat of a release of a naturally occurring substance in its unaltered form, or altered solely through naturally occurring processes or phenomena, from a location where it is naturally found."

Title: Structure of Guidance Text: Step-by-step instructions for background analysis techniques are presented in the Navy guidance documents and are discussed in the media-specific sections of this Web tool. For many sites and target chemicals, background concentration ranges can be estimated by spatial analysis and probability plotting techniques referred to as Exploratory Data Analysis. If this initial analysis does not produce a technically defensible and reliable estimate of the background concentration range for a particular chemical, appropriate statistical methods for further background analysis need to be identified based on the particular media of interest. Detailed instruction for analysis using the Geochemical Method and the Comparative Method (if relevant to the media) are then presented. Case studies are also presented for soil, sediment, and groundwater to illustrate the application of each method. Click one of the following links to find the preface, table of contents (TOC), or to view the entire guidance document for soil, sediment, or groundwater: Soil Preface (PDF 147k) Soil TOC (PDF 177k) Soil Full (PDF 5,928k) Sediment Preface (PDF 121k) Sediment TOC (PDF 98k) Sediment Full (PDF 5,049k) Groundwater Preface (PDF 131k) Groundwater TOC (PDF 105k) Groundwater Full (PDF 2,955k)

Title: Scientific Basis of Background Analysis Text: Project teams may unnecessarily remediate chemicals and/or areas where no releases have occurred, unless background conditions are accounted for in one of the following two ways: Distinguishing COPCs from Background Chemicals. Determining Background Levels of COPCs. Techniques for statistical analysis of chemical data are fundamental components of the background analysis process. However, statistical analysis alone is not sufficient to fully understand and define the background conditions that exist at a particular site. An understanding of the geological, geochemical, and hydrological processes that control the occurrence and concentrations of naturally occurring chemicals is also essential. Background chemicals that occur at a site, and the fate and transport of COPCs, depend on physical and anthropogenic characteristics of the site and the surrounding area. Site-specific factors, which include site geology, geochemistry, hydrogeology, as well as past and present land uses, must be considered during the background analysis.

Title: Distinguishing COPCs from Background Chemicals Text: In this case, the project team must screen out background chemicals from the list of detected chemicals. Failure to make these distinctions could confound the investigation and remedial decisions. Chemicals detected at concentrations that do not exceed the upper background range should be eliminated from consideration at the appropriate point in the risk assessment process. The remaining chemicals then are carried forward as COPCs for further evaluation during the risk assessment.

Title: Determining Background Levels of COPCs Text: If an individual chemical detected at a site is present due to both site-related and background sources, then the project team will need to quantify the concentration range that represents background conditions. The upper bound of the background concentration range must be identified to: (a) delineate the extent of a site-related chemical release; (b) calculate residual risks caused by a site-related release; and (c) determine the scope of required cleanup, should remediation become necessary.

Title: Geology Text: The distribution of background chemicals at a site depends upon the types of soil and rock that occur at the site; therefore, the physical, geochemical, and biological characteristics of the soil and its parent rock should be evaluated carefully. Vegetation also can affect the distribution of background chemicals in soil. For example, some metals (e.g., silver, arsenic, cadmium, copper, mercury, lead, antimony, and zinc) can be significantly concentrated in surface soils due to uptake by plants and adsorption by organic matter.

Title: Geochemistry Text: Geochemical processes transport and redistribute naturally occurring chemicals, particularly metals, in the geologic environment. Geochemical knowledge is the key to understanding the underlying causes of natural concentration anomalies in soil. It is also useful when differentiating between background metals and metals that may be associated with a chemical release. Metals which occur naturally in soils originate in the minerals that form the rocks of the earth's crust. Soil is formed when rocks and their component minerals are broken down by weathering, resulting in a change in the overall chemical composition. The natural geochemical relationships existing in the parent rock are usually reflected in the soil which can be used to evaluate soil background conditions. The electronic structure and chemical properties of the elements can be very useful to predict geochemical relationships for different soil types and to identify relationships that may be useful for background analysis.

Title: Hydrogeology Text: The hydrologic cycle involves the transfer of water to and from the atmosphere, ocean, and land. Water enters the atmosphere by evaporation from the bodies of water and transpiration through plants. These processes are known collectively as evapotranspiration. Water can also be transmitted directly from solid form to gaseous form through sublimation. As water vapor rises in the atmosphere, it cools with increased elevation and is transferred back to liquid form through condensation. After accumulating in clouds, the liquid water falls to the earth as precipitation. Water from precipitation infiltrates the ground surface and collects in surface reservoirs such as lakes and rivers. After percolating down through the unsaturated zone, water collects in the saturated zone below the water table. After entering the saturated zone, groundwater flows in a downslope direction until it is discharged to surface water bodies or at the ground surface.

Title: Past and Present Land Uses Text: Background chemicals include widely distributed constituents present in the environment due to past and present human activities, including those associated with agricultural activities, urban sources, transportation, and legal application of chemical products. These anthropogenic chemicals include vast array of pesticides, such as arsenicals and DDT, as well as chemicals related to urban pollution, such as lead and PAHs from automobiles. The characterization of site background conditions requires a thorough review of past and present land uses at the site. Available sources of information for such review include: (a) USGS quadrangle maps that show regional topography, water bodies, landforms, streets, and general concerning land use; (b) tax maps that show land ownership and key information concerning land use or activities at the site and its surrounding areas; (c) Chronological photogrammetric aerial surveys (i.e., aerial photographs) that show a pattern of historical land use; and (d) Historical/archealogical maps that show areas that have been affected by natural processes or human activities.

Title: Overview of Background Data Evaluation Text: During the data review and assessment phase, the data should be evaluated to identify data gaps, determine the scope of supplementary sampling and analysis (if required), and compare suspected COPC concentrations to risk-based screening criteria. Supplementary sampling and analysis may be necessary to complement the existing dataset and ensure adequate site coverage. After the dataset is complete, representative exposure concentrations are computed and compared to their corresponding risk-based criteria. Chemicals that do not pose unacceptable risks will require no further action. The remaining chemicals should be subjected to exploratory statistical and spatial data analysis to estimate background ranges. If exploratory statistical and spatial data analysis do not yield technically defensible and acceptable background range estimates for all suspected COPC metals, then investigators should select a method (or methods) for further background analysis. This background analysis often involves statistical testing. For more information on the statistics, click here. The proper methods to be used for further background analysis are specific to the media (i.e., soil, sediment, and/or groundwater) being addressed. Soil and sediment guidance documents provide step-by-step instructions for Exploratory Data Analysis and if necessary, for two background analysis methods: the Geochemical Method and the Comparative Method. The groundwater guidance document provides instructions for Exploratory Data Analysis, and if necessary, the Comparative Method. Both the comparative and geochemical methods are used to compare site data with background data, or in other words they are methods that will help determine which chemicals are site-related and which chemicals are non-site related. Please click on the appropriate link for a description of the course of action to be taken for each media type. Soil Analysis Sediment Analysis Groundwater Analysis

Title: Statistics Text: Background analyses often involve comparison of site and reference area (background) datasets. This process is referred to as statistical testing, which determines whether there is a statistically significant difference between the two datasets. For this purpose, the statistical test generates a quantitative measure of difference between the two datasets that is referred to as the test statistic. The difference is considered as statistically significant, if the test statistic exceeds a predefined critical value that usually is obtained from a special table. Statistical testing determines whether the data are convincing beyond a reasonable doubt that a specified null hypothesis (e.g., the site and background datasets are derived from the same statistical population) is false and rejected in favor of a specified alternative hypothesis. A number of statistical techniques and tests require normality of their test variables. These tests are known as parametric. In contrast, the nonparametric tests do not require any distributional assumptions. The appropriate choice of statistical test(s) or method(s) depends on the characteristics of the available data. These characteristics are determined through the review of descriptive statistics of the site and/or background datasets. These descriptive measures, along with graphic tools, are used to develop an understanding of the range, variability, and shape of the underlying distribution of the measurements, as well as the number of non-detects and possible outliers that are present.

Title: H Null - Rollover Text: The dataset is derived from an underlying normal distribution.

Title: H Alternative - Rollover Text: The dataset is not derived from an underlying normal distribution.

Title: Type I Error - Rollover Text: Type I error, or false positive decision error, is the error made by rejecting H null when H null is true.

Title: Type II Error - Rollover Text: Type II error, or false negative decision error, is the error made by not rejecting H null when H null is false.