Grease Trap Requirements

Fats, oil, and grease, or FOG, can clog sewer lines. For this reason, Charleston Water System requires food service establishments that are connected to our sewer system to install and maintain a grease trap in accordance with our specifications.

Our Wastewater Collection Department reviews and approves grease trap plans, inspects traps after installation, and conducts periodic inspections of grease traps. For complete information about our grease trap requirements, including diagrams, forms, etc., please review the Grease Trap and Grease Interceptor Standards.

Overview of Requirements for Food Establishments


  • Complete the Grease Trap/Interceptor Application Form (page 18 of the Grease Trap Standards) and submit it along with plans, specifications, plumbing diagrams, riser diagrams, etc.
  • After receiving an approval letter from CWS, install the grease trap.
  • Contact CWS to schedule an inspection.
  • Keep a Maintenance Log record. Grease traps/interceptors must be thoroughly pumped out and/or cleaned at least four times a year, or at a frequency determined by the CWS Inspector.

Fees


  • Application Fee: $25  
  • Inspection Fee: $50
  • Re-inspection Fee: $50
Application to Install a Grease Interceptor
Grease traps that are found to be unsatisfactory during an inspection will be required to be re-inspected.
Questions? (843) 308-8277 or (843) 308-8299.

FAQs
Q. Our new business location already has a grease trap. Why do we need to submit an application?
Grease traps are available in various sizes – ranging from less than 20-gallons volume to over 2,000-gallons volume. There are also a wide range of grease trap operational mechanisms. The existing installed grease trap must be of a size and type that is acceptable to CWS. A number of factors are considered in determining the minimum size required, and while the trap may have been adequate for the previous business owner – that may not be the case for your new business. There are also some traps discharging to the CWS wastewater collection system that are unknown to us and have never been approved by CWS.

Q. The vendor we are working with has recommended a much smaller trap than CWS is requiring. Why can we not use what is being recommended to us?
CWS uses the sizing methods prescribed in Section V of this Standard, which specifies a minimum required volume (gallons). This method is premised on removal of the Fats, Oils and Grease (FOG) from your discharged kitchen wastewater using passive means only. While this may typically result in a larger required volume than proprietary designs utilizing various mechanical means to promote and assist the gravity separation – CWS considers this to be the most reliable and effective long term method of ensuring proper removal of FOG and ensuring the discharge concentration limit of 100mg/l is not exceeded. Exceedance of this discharge limit may lead to costly enforcement action imposed by CWS to bring the trap back into compliance.

Q. Our licensed Architect/Engineer has sized the grease trap already. Why must we comply with CWS’ sizing which may result in a larger required minimum volume?
The methods and equations for sizing grease trap volume for grease traps discharging to the CWS collection system are prescribed in this Standard. However, the calculated volume is subject to a significant extent to the values entered for some of the variables AND constants used in the equations. The CWS will determine these values based on various factors, that may include - for instance – the location of your business. A business discharging FOG to our system where there is a high density of food serving establishments has potential to cumulatively cause more damage to our system than one where it may be the only discharger within the locale. CWS has the experience and detailed system knowledge to reliably, appropriately and consistently apply the sizing equation variables and constants. CWS will not defer this calculation to third parties that represent individual applicants rather than the collective interests of its customer base as a whole.