It is so simple for a client to miss this important fact.  The client is so fixed on the pump sizes, the control options, the electrical requirements…  Surely the treatment process equipment manufacturer has the right medias installed into their equipment.  Right?

Not really.  In fact, there are suppliers who do not worry about the quality of their media, since having media that fails sooner means more money to them.

There are a couple of general source parameters that are common with all medias.

Needs to Be Clean: The supplier needs to assure that their medias have been washed and rinsed thoroughly.  Keep in mind that your stormwater process is removing suspended solids.  Does it make sense to have dirt/muck/foulants in the initial media for a process that needs to get down to low part per million levels? 

That is why Gullywasher solely purchases its medias washed & rinsed.

The Source of Its Makeup:  There is a lot of gravel and sand that contains metals.  Afterall, the metals do come from the ground, also.  The foundries use sand to cast their metal parts. When the sand cannot be reused anymore, they will take the used sand, sift it for cleaning out the metal chunks, and bag it for customer sales.

That is why Gullywasher solely purchases its medias from known originating sources.


As mention above, the larger the gravel, the more interstitial void space there is between the gravel rocks.  It is more expensive; but, the gravity filter process dictates the need for maximum permeability while optimizing distribution/collection.

Some supplier uses landscaping pea gravel of which closes down the available pathways for the stormwater to easily flow through.  This will eventually allow for increases in plugging up and bypass channeling.

Gullywasher uses a nickel-sized quartz gravel that is washed and rinsed.  It is shipped directly from the mine site to us. 


There needs to be a careful balance between having the sand grain small enough to capture the solids and having the sand grain large enough to allow for these solids to be removed at different levels in the sand media.  

  • If the sand is too fine, all of the solids will be trapped on the sand bed surface and plug up prematurely.  
  • If the sand is too large, then too much solids will be released by not being trapped with the sand bed.

The balance between these two extremes is what depth filtration is all about.  Allowing for optimal permeability (flow) while trapping the solids at different layers of the sand bed.

Of course, it would be easy and cheaper to supply the finer sand media as our competition does, and state that you need yet another rebed of your filter due to all of the ‘sticky’ solids coming in from your site.  “Ka ching!”

Gullywasher uses a certified filter grade quartz sand that is sized for typical use in swimming pool filters.  The sand is sourced directly from its mining sites.


Biochar does not perform the same way when it is from different plant material.  Trees, such as Douglas firs, have microscopic tubular channels that allow the stormwater to pass through, while dynamically hitting the charged wall surfaces.  The metals in stormwater will solidify themselves to these wall surfaces and thus purify the stormwater stream.

Other biochars from different plant/tree sources will have dramatically different configurations.  As you can see on the picture below, other biochar sources are chunks with surface depressions or an irregular honeycomb with limited channels.  These do not allow for proper transfer dynamics in order to obtain the high efficiencies needed for metals removal.

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Plus, the biochar production accepts the organic material with a lot of dirt/muck/foulants mixed in.  It is extremely necessary to remove these materials by (again) thoroughly washing and rinsing these contaminates out of the biochar.

Finally, we have found out that the larger pellets of biochar granules make the best filtration media, as opposed to the dust, fines, and small particulates.  Therefore, a grading of the biochar is also necessary for obtaining the industrial stormwater benchmark compliance.

Gullywasher solely uses Oregon Douglas Fir as its biochar source.  It is water washed, air washed, and water rinsed again, prior to being graded for proper size. 


Like biochar, there are many types of peat on the market.  The differences lie with how much organic acids and what type they are.  As with the biochar, we have found that the large granules perform better for industrial stormwater treatment. 

One supplier tried to substitute a peat product used as a farm animal food supplement… The results were miserable!

Gullywasher uses organic or vulcanized peat sources that have been lab & field tested for sustainability and effectiveness.


Great for opening up permeability; however, the metals removal will suffer.  So one has to be careful on what the targeted end result will be. 

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