In a series of blog entries on Local Limits, this month’s blog entry focuses on Collection System concerns that must be taken in to account while developing or evaluating local limits.

To meet requirements of 40 CFR 403.5 (b) and to address about the collection systems, including the health and safety of workers at treatment plants, POTWs should address the following collection system concerns:

  1.  Fires and Explosion (40 CFR 403.5(b)(1)): Regulations prohibit the discharge of pollutants creating fire or explosion hazard to the treatment plant which includes waste streams with a closed cup flashpoint of less than 140°F which can be calculated using the test methods specified at 40 CFR 261.21. POTW can either establish a local limit equal to flashpoint provision or develop other protection methods. Flash point provisions are explained in EPA’s Local Limits Development Guidance, Chapter 8.
  2. Corrosion (40 CFR 403.5(b)(2)): Regulations prohibit discharges of pollutants causing corrosive structural damage and discharges with a pH lower than 5.0 unless the treatment is specifically designed to treat such discharges. Other corrosive pollutants can include Sulfide, Sulfate, Chloride, Chlorine, Nitrate, Nitrite, Dissolved Salts, Suspended Solids, Organic Compounds.
  3. Flow Obstructions (40 CFR 403.5(b)(3)): Discharge of solid or viscous pollutants in amounts will obstruct flows to treatment plant primarily polar fats, oil and grease (FOG). It can reduce the capacity of pipes, interferes with treatment plant operations and reduces treatment efficiency. It can be controlled through grease traps, surcharge programs or other pollution prevention measures as necessary.
  4. Temperature (40 CFR 403.5(b)(5)): Regulations prohibit heat discharges that will inhibit biological activity in a POTW and result in interference. Discharges shall not increase the temperature at the headworks above 40° C (140° F) unless approval authority approves alternative temperature limits upon request of the POTW. In addition, temperature is a hazard to workers entering the sewer system and POTWs should require Industrial Users to reduce the temperature of its discharge.
  5. Toxic gases, vapors or fumes (40 CFR 403.5(b)(7)) causes acute worker health and safety problems. Discharge screening levels are developed to identify industrial user discharges that can have potential to generate toxic gases or vapors in the sewer. Detailed calculation process for wastewater screening levels are explained in EPA’s Local Limits Development Guidance, Chapter 8.

In my next blog, I will be talking on Recordkeeping and Reporting Requirements under the Pretreatment Program.

Please contact me if you have any questions.

Shri Vani Sripada is a Project Engineer at Smith Management Group. Shri Vani can be reached at

Source: EPA’s Local Limits Development Guidance, July 2004.