This aerospace client had installed an a “patented media filtration system for enhanced industrial stormwater treatment” on their site about 5 years ago.  However, it never achieved benchmark compliance and was well known for plugging completely up after a couple of rain events.  The filter even overflowed on the first rain event!  With that filter manufacturer’s sole solution being to rebed the filter 2 or 3 times each rain year.

Gullywasher was commissioned to re-engineer and refurbish this system into one of its biofilter process designs.  The cost to perform this biofilter redesign was in line with the cost of just one rebed charge.

Upon inspection of the original system design, we have found the following deficiencies:

(It was if this filter process was designed to fail!)

  • Prior Problem: The piping is of a light commercial Sch 40 PVC.  This type of PVC piping can be used in buried or shady areas; however when exposed to direct sunlight, the Sch 40 PVC material will get embrittled and subject to fracture.  

Gullywasher Solution: Gullywasher solely used Sch 80 PVC for pipe and fittings for better UV protection and longer process life.

  • Prior Problem:  The filter bed inlet design that will not evenly distribute the incoming stormwater across the entire bed.  This will allow for flow channeling and short-circuiting of the filter bed.  

Gullywasher Solution: Gullywasher uses a launder design that ensures even distribution.

  • Prior Problem:  There is a nylon tarp placed on the sand bed to act as a dispersion plate.   This will focus the stormwater to migrate in the center section of the sand bed – causing flow channeling and short-circuiting of the filter bed.  

Gullywasher Solution: Gullywasher uses a launder design that ensures even distribution and ensures proper contact time throughout all of the media.

  • Prior Problem:  The sand media they are using is in the fine grit sizing.  It is much like dust.  This does allow for capture of smaller near-colloidal suspended solids; but is extremely sensitive to any moderate to large loadings of suspended solids.  It will just plug up as its performance history shows due to the sand filter surface loading up immediately.

Gullywasher Solution: Gullywasher uses a larger grade size sand which is washed, rinsed, and suitably sized for depth filtration.

  • Prior Problem:  The sand media does not look like that of stormwater treatment grade.  It is very common to get a sub-standard sand in the market that was repurposed from sand casting operations.  So one does not know whether their sand is adding metals to the stormwater.

Gullywasher Solution: Gullywasher uses a properly graded (certified by AWWA) sand sourced directly from the sand processing sites.

  • Prior Problem:  Their gravel media is of a pea gravel sizing with sharp angles – much like one would see in landscaping supply stores.  This will not allow for an adequate level of suitable void space for the filtered stormwater to collected over the entire area of the filter bed.  As much as half of the filter bed could be static with the rest of the filter bed seeing it filter rate velocities double.  

Plus, there is no understanding on how much metal (iron?) could be in the gravel’s makeup.  No one at the landscape supply store will even understand that question.

Gullywasher Solution:  Gullywasher uses a larger washed/rinsed filter-grade gravel sourced directly from the mine site.

  • Prior Problem:  To compensate for the pea gravel sizing, the system drainage collector is a thin wall corrugated plastic pipe with slits cut into it on all sides.  This will not allow for proper collection of the filtered stormwater and could allow for developing channels within the sand bed. 

Gullywasher Solution: Gullywasher uses a Sch 80 PVC header collector design (known as our Trident collectors) which allow for the water to flow evenly into collection from the entire filter bed. 

Plus it seems that their overall process design enhanced the marginal performance of their stormwater filter – allowing their sales force to ignore the base problem and blindly recommend faster bed changeout cycles.  Ka-Ching!

We proposed the Gullywasher Solution to the site’s environmental engineer who immediately gave us the go ahead to fix the system.  Gullywasher did the work in 3 days.  Now the client has a new filter system that has been working and showing great results in obtaining benchmark compliance!!!

This is what we call Success!

Below is the performance for the system with the Gullywasher Retrofit.  We expect this system will last up to four (4) years before a biochar rebed is necessary.  Not like the 2 to 3 times per year experienced with the previous design and medias. 

Analyte Sample Date Inlet,mg/L1st Stage, mg/L1st stage% removal 2nd Stage mg/L2nd stage % removal overall % removal 
Aluminum 10/14/20219.824.1857.430.46188.9795.31
Copper 10/14/20210.0620.02265.270.00577.5092.19
Iron10/14/202134.37.5278.080.61891.7898.20
Zinc 10/14/20210.8140.30762.290.00797.8299.18

Do Not Hesitate – Call Us!  We can inspect your system and make it better!

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