Calculate Your ICM Rating


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Use this spreadsheet to calculate your ICM Rating: [Excel Spreadsheet]

What is an ICM Rating?

An Impervious Cover Model (ICM) Rating tells you whether your property helps or hurts the Creek. The percentage of impervious surface has a direct affect on the health of the Bay and its tributaries. The ICM Ratings are:

Percentage Impervious CoverICM Rating
0% - 10%Supporting
10% - 25%Impacted
over 25%Non-Supporting

Most urban and suburban houses have ICM Ratings that are either Impacted or Non-Supporting. Here is how a typical house in the Weems Creek Watershed rates:

The good news is, with a few simple changes, you can change your property from a Non-Supporting yard to a Supporting oasis:

Use this spreadsheet to calculate your ICM Rating: [Excel Spreadsheet]

You can mitigate the impervious surface you have with rain barrels, rain gardens, pervious surfaces and more. See our other pages for projects you can take on to change your effective ICM Rating.

For additional information, contact Corinne Reed-Miller.