Tools for cleaning up contaminated sites

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.

• MTCAStat 97: Site Module allows you to calculate whether you’re in compliance with your site’s cleanup levels. It helps answer questions like: "if one sample is above your cleanup level, does it mean your remediation failed?" 
• MTCAStat 97: Background Module: Some of the harmful chemicals you’ll need to clean up can also occur naturally. This tool helps identify the “natural background level” for certain chemicals at your site so we can adjust your cleanup levels.
• 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:

1. Soil using MTCA Methods B or C, and
2. Groundwater using MTCA Method B.

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

• Workbook for calculating cleanup levels for petroleum contaminated sites (MTCATPH 12.0 Excel workbook) allows you to calculate cleanup levels for petroleum mixtures. Workbook Updated Nov. 2023.
• In November 2023, we updated the chemical database for petroleum mixtures in this workbook.  Find CLARC guidance about the update in Toxicity data and physical/chemical properties for petroleum mixtures (Nov. 2023). 
• Workbook for calculating cleanup levels for individual hazardous substances (MTCASGL 12.0 Excel workbook) allows you to calculate cleanup levels for any contaminant. Workbook Updated Nov. 2023.

Additional help for these workbooks

If you're new to the workbooks, check out the user's guide first. It answers questions, shows how to use the workbooks, and helps you understand your results: Workbook tools for calculating soil and groundwater cleanup levels under the Model Toxics Control Act Cleanup Regulation: users guide 12.0 (Nov. 2023).

Troubleshooting Excel compatibility associated with the MTCASGL 12.0 Excel workbook helps address common problems when using different versions of Excel.

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 will answer 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 will answer 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.

Additional 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.