Tools for cleaning up contaminated sites

Tools just for petroleum contamination

Since about 95 percent of cleanup sites in Washington are contaminated by petroleum, we've assembled tools for cleaning up petroleum contaminated sites in one place. You'll find several of the tools on this page, plus extra guidance for managing the challenges of cleaning up petroleum contamination.

Statistical guidance and tools

These tools help you calculate compliance and background levels. They include tests you must use to show you’re meeting requirements of the state's cleanup law, the Model Toxics Control Act (MTCA). The statistical programs help you calculate upper confidence limits and background values for describing your site. It’s not always obvious what data means just by looking at it, so the statistical guidance can help.

• EIM Data Analysis Tool (EDAT) is an online statistics tool that allows you to use Environmental Information System (EIM) data to calculate whether you’re in compliance with your site’s cleanup levels. It can also be used to calculate natural background concentrations. Compliance statistics can help answer questions like: "if one sample is above your cleanup level, does it mean your remediation failed?" Because some of the harmful chemicals can also occur naturally, some sites may use natural background levels to adjust cleanup levels. Note: This tool replaces the MTCAStat 97 Site and MTCAStat 97 Background Excel-based workbook modules.

• Statistical guidance for Ecology site managers: Information about compliance, background statistics, and toxics cleanup.

Workbooks for calculating cleanup levels

These tools allow you to calculate cleanup levels for two media:

• Soil using MTCA Methods B or C, and

• Groundwater using MTCA Method B.

These cleanup levels protect against harm from direct contact with soil. They also protect against harm from contaminants leaching into groundwater. Please visit our Vapor Intrusion page for information on evaluating the vapor pathway.

For petroleum mixtures

• Workbook for calculating cleanup levels for petroleum contaminated sites (MTCATPH 12.0 Excel workbook)
  • Updated April 2025. Now has more soil leaching model outputs, including density of NAPL, volumetric NAPL content, and NAPL saturation (see section 3.3.4 of User's Guide).
  • See the MTCATPH User's Guide for instructions and help understanding results.

For individual hazardous substances

• Workbook for calculating cleanup levels for individual hazardous substances  (MTCASGL 12.0 Excel workbook) allows you to calculate cleanup levels for any contaminant.
  • See the MTCASGL User's Guide for instructions and help understanding results. This guide was formerly Appendix F in the MTCATPH user's guide, and is now a stand-alone document.
  • See Troubleshooting Excel compatibility for help addressing common problems when using different versions of Excel with the MTCASGL 12.0 Excel workbook.

Natural attenuation of petroleum contaminated groundwater

Natural attenuation means relying on natural processes to decrease (or "attenuate") concentrations of contaminants in soil and groundwater. You can use this tool to predict when natural attenuation will allow groundwater cleanup levels to be met, or to demonstrate that levels have been met. This tool is split into two packages.

Package A answers questions about:

• Plume stability.
• Length of time for groundwater concentrations to reach a target level.
• The site’s ability to break down contamination.
• The possibility that changing groundwater elevation is affecting concentrations.

Package B answers questions about:

• Distance a dissolved plume will extend without intervention.
• Length of time until a target location reaches a cleanup level.
• Percent of mass that can be broken down naturally.
• Amount of source material that must be removed to let natural breakdown reach a target level by a certain date.

Help for the natural attenuation package

User's manual: Natural attenuation analysis tool package for petroleum-contaminated ground water (2005) provides guidance under MTCA on how to evaluate the feasibility and performance of natural attenuation for groundwater contaminated with petroleum hydrocarbons.