Interview with Sarah Limb

March 31, 2016

Sarah Limb is a pretreatment inspector and manages the FOG program at the City of Springfield Department of Environmental Services in Missouri.  I recently learned that the jurisdiction had modified its FOG ordinance to disallow concrete interceptors.  I was very intrigued by this development so I reached out to Sarah to ask some questions.  She was eager to share the details and gave me permission to share her comments.

In my first contact with Sarah I asked the following:

I am being told that Springfield has gone back to the 2012 IPC for grease interceptor requirements with some modifications such as no concrete units allowed? I went to the Springfield FOG website but it seems to only provide all of the requirements from 2006. Do you have anything in writing regarding the changes your jurisdiction has adopted?

Sarah replied as follows:

Here is the new adoptive language for our plumbing ordinance:

F. Amend Section 1003, Interceptors and Separators, Subsection 1003.3.4, as follows:

1003.3.4  Hydromechanical grease interceptors and automatic grease removal devices.  Minimum required size of Hydromechanical grease interceptors and automatic grease removal devices shall be sized determined in accordance with ASME A112.14.3 Appendix A, ASME112.14.4, CSA B481.3 or PDI G101.  Use of ASME A112.14.3 Appendix A shall be mandatory.  Drainage period used in calculations to size hydromechanical grease interceptors and automatic grease removal devices shall be no more than 1 minute.  Hydromechanical grease interceptors and automatic grease removal devices shall be designed and tested in accordance with ASME A112.14.3 Appendix A, ASME 112.14.4, CSA B481.1, PDI G101 or PDI G102.  Hydromechanical grease interceptors equipped with manholes for access shall be equipped with a manhole for each chamber in the interceptor.  Concrete grease interceptors will not be allowed.  Hydromechanical grease interceptors and automatic grease removal devices shall be installed in accordance with the manufacturer's instructions.  Where manufacturer's instructions are not provided, hydromechanical grease interceptors and grease removal devices shall be installed in compliance with ASME A112.14.3, ASME112.14.4, CSA B481.3 or PDI G101.  This section shall not apply to gravity grease interceptors.  Gravity grease interceptors shall be subject to the approval of the Authority Having Jurisdiction.

We haven't updated our website quite yet, we just updated the ordinance very recently.  We have been testing the pH of the tank contents as well as the effluent in the sampling manhole and we've found that the pH inside the tanks vary from 3.0 to 5.0, generally 3.0-4.0.  I have dozens of concrete interceptors that currently require immediate replacement.  It's much easier to not allow them anymore.  Plus the new interceptors are engineered so much better now! Let me know if you have any question!

I followed up with Sarah to ask the following questions:

  1. How long have you been with Springfield?

10 years.  I was a restaurant inspector for 7 years and I moved over to Environmental Services 3 years ago to manage the City's FOG program.

  1. "roughly" how many FSEs do you have in your jurisdiction?

We have about 1150 FSEs 

  1. When did you start measuring for pH?  What was the reason for adding this measurement?

We started spot checking for pH about a year ago.  I do not like the 25% rule and I was looking for something more scientifically solid to get these restaurants to clean their interceptors more frequently.  The idea was that the longer the waste sits in the tank the lower the pH.  Out of all the tanks that I sampled every single GGI had pH readings lower than 5.0.  I still have quite a bit more evidence to collect if I want to prove that pH could be used as a means to regulate the FSEs.  However, because we were seeing such low pH readings and so many tank failures, we were able to take these findings to the City's Building Development Services and had the language of the ordinance changed so that we no longer allow concrete GIs. 

  1. What kind of resistance have you received since implementing the "no concrete" requirement?

None from the manufacturers. The designers, architects, and engineers really don't care what type of GRD that they install as long as the City is happy and their client is happy.  The haulers have complained a bit about the new tanks.  Of course, they complained about the old tanks too.  I'm actually a little bit surprised that we haven't heard from some of our local concrete tank manufacturers. 

  1. Beyond deterioration of the tanks, has the jurisdiction formed any opinions regarding the efficiency of GGIs?

I've read quite a few studies that have shown that when GGIs are being well maintained and in peak performance their efficiency is still only around  85%.  The evidence that I've seen in the field would back this up.  I'll also add that there is no standard design which is frustrating.  You never know what you're going to find and good luck trying to find any specifications. 

  1. How long has the new policy been in effect?

Officially since February 2016 but we've [been] asking that new facilities and replacements to not install concrete interceptors for almost a year now.  Back in September 2015 we started denying plans based on interceptor design.  We were able to do this because the ordinance at the time had only one type of concrete interceptor approved and it was the "Public Works Standard" that you saw on our website.  The company that manufactures it is no longer able to provide us any type of certification for the liner so we would not approve them.  

  1. Has the jurisdiction formed any opinions regarding the efficiency of hydromechanical grease interceptors in "real world" installations?  I am referring to the newer high-capacity type HGIs.

We have quite a few Great Basin interceptors being installed all over town.  Many of our facilities have small indoor interceptors and very limited space for larger units.  They can take out an old 40lb interceptor and replace it with a Schier GB product that is roughly the same size but has twice the FOG holding capacity.  We use the Schier grease production calculator to calculate the cleaning frequency for all of the GIs in town no matter the make or model.  If the owners/operators maintain the interceptors at the frequency that we've set then they are incredibly efficient.  What has surprised me about the high capacity HGIs is that they continue to function pretty well even when they are not being maintained at the correct frequency.  We are also seeing quite a few of the larger GB250 interceptors being installed.  These units appear to be very efficient when being maintained at the correct frequency and when they have been installed correctly.  I'm seeing quite a few variations with installations.  Some are in line and some are side by side.  Some have flow splitters upstream and some do not.  These are all factors that will impact the efficiency and we will be keeping an eye on all of these interceptors.  Overall, we like these products.  We have new facility that is installing a Trapzilla that I'm pretty excited about.  It'll be the first one in the city.


1 comment

  • Michael Farrell

    Apr 19, 2016

    I’m assuming the concern with the extended period between evacuations and the lower PH is that it indicates reduced Dissolved Oxygen (as aerobic degradation has occurred) and the likelihood of anaerobic/acidic conditions that will exacerbate corrosion of the network. Do Great Basins come in 500 and 1000 gallon capacity? Or are they replacing external concrete interceptors with internal plastic/fibreglass grease ‘traps’. Wouldn’t the high temperatures associated with surge flows pass the emulsified grease straight into the sewer network?? As an aside what size range do you believe FOG droplets are in influent entering grease interceptors from modern kitchens with modern detergents and commercial dishwashers? 30 – 200 micron in diameter??


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