Understanding Compliance Inspection using the 6Ps Model

Staff from  the City of Los Angeles Sanitation Department’s Bureau of Sanitation’s Industrial Waste Management Division, explain how metal finishers can utilize the 6Ps Model.
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The City of Los Angeles Sanitation Department (LASAN) administers four environmental programs for the city: clean water, watershed protection, solid resources and environmental quality (livability). LASAN’s Industrial Waste Management Division, which administers the city’s Source Control and Pre-Treatment Program, launched a program called LA Industry to demystify regulations and create collaborative business-friendly pathways to help achieve sustainability in the environment and economy. The group notes that the success of its local businesses is crucial to a healthy and vibrant city; and, as such, it is focused on the continued growth, retention and success of businesses in the city. In alignment with LASAN’s effort to explore strategies and opportunities for businesses to strive economically, this article seeks to inform metal finishing facilities in LA about methods for increasing their regulatory compliance rates.

Clean Water Act

The Clean Water Act (CWA) is a legislation entity that aims at eliminating or reducing pollutants that get into the nation’s water bodies as a requirement to achieve high quality, fishable and swimmable waters. The Los Angeles Municipal Code’s (LAMC 64.30) industrial waste control ordinance states, “It is the policy of the City of Los Angeles to ensure that the highest and best use of the Publicly Owned Treatment Works (POTW) is for the collection, treatment and disposal of domestic wastewater”1. This means that POTW sewer systems are designed to collect and treat domestic wastewater only. Hence, any facility generating industrial wastewater needs to obtain an industrial wastewater permit governed by the industrial waste control ordinance and administered under the jurisdiction of the Public Works Board. 

As stated above, because these POTW systems are not designed to treat industrial wastewater containing toxic pollutants, Industrial Users (IUs) are required to employ best management practices that help reduce or eliminate such pollutants. It is important to note that the goal of the CWA is to eliminate, reduce or change pollutants to a lesser contaminating state before they reach U.S. waters. The National Pretreatment Program, published in Title 40 of the Code of Federal Regulations (40 CFR) part 403, provides the regulatory basis that requires IUs to comply with pretreatment standards in order to fulfill CWA goals. These are to:

  1. Prevent interference with POTW operations and sludge disposal.
  2. Eliminate pollutants that may pass through the POTW and eventually end up in U.S. waters.
  3. Improve opportunities to recycle and reclaim municipal and industrial wastewaters and sludges2.

Pretreatment Compliance Inspection (PCI)

Pretreatment Compliance Inspection, also known as an audit, is an oversight mechanism used by regulators to evaluate the compliance of approved pretreatment programs. Below are some things inspectors need to know for pretreatment compliance inspections:

  • Review POTW’s records on monitoring, inspections and enforcement activities of its IUs to increase effectiveness of inspection audits. The pretreatment regulations in 40 CFR 403.8 (f) (1) (v), require the control authority, which refers to the POTW, carrying out all inspections, surveillance and monitoring of IUs within its service area and determines the compliance of its permittees.
  • Inspectors ensure that the POTW implements its Enforcement Response Plan (ERP) and is authorized to issue a Notice of Violation (NOV) if not in compliance.
  • Incorrect application of categorical pretreatment standards would also be noted. For example, an IU performing electroplating operations is subject to categorical effluent guidelines. Failure to identify and, therefore, categorize such will cause the POTW pretreatment program to be noted as deficient3.

Introducing the 6Ps

LASAN’s Industrial Waste Management Division (IWMD) has developed inspection forms to be used during routine inspections. The 6Ps model serves as a navigational tool for IWMD inspectors and stands for Products, Processes, Pollutants, Pretreatment System (PTS), Parameters and Plan of the Shop. An application of this model can be seen when a metal finishing facility engaged in the manufacturing of products, utilizing one or more processes, generates pollutants that will have to be treated in a pretreatment system before it is discharged into a POTW to meet limiting parameters outlined in the control mechanism,otherwise known as an industrial wastewater permit. These Ps are not mutually exclusive, but form a collective of a single unit. If an IU decides to offer another process at the shop, this change may add a new pollutant, which can affect the PTS and other parameters in the permit. Such changes may alter the documented schematic or process flow diagram depicted in Plan of the Shop.

diagram of 6Ps Model System

6Ps Model System



The 6Ps model system allows inspectors and IUs to pay attention to critical aspects of the process. In addition to the 6Ps model representing a management system that is easy to implement due to its practicality, a change in one P implies a response from the other Ps due to their codependence on each other. Neglecting one of the Ps of the 6Ps model may trigger non-compliance issues. This model is not only a SMART (Specific, Measurable, Attainable, Realistic and Timely) tool for inspectors during routine inspections, but can also be useful for IUs to stay in compliance and help them be better prepared for inspections.

Consider the process of metal finishing which changes the surface of metals to enhance the corrosion-resistant properties, decorative appearance, electrical conductivity, or durability of a metal4. Broadly speaking, the entire process comprises surface preparation, the actual finishing and posttreatment. In each step, rinses used may contain pollutants. First, before the actual finishing step, metal parts are immersed into an alkaline or acidic chemical solution for cleaning purposes; this step is called surface preparation. The actual finishing step (electroplating) follows next, which may produce dragout or rinse water that contains the metal(s) used in the plating process solutions. Pollutants found in all rinsing solutions (all finishing steps), may include oils and grease, organics, inorganics, oxides, dirt, cyanide and the metals contained in process tanks . Inspectors and IUs require some training to be able to detect all the visible and invisible pollutants found in waste streams. To remove or to bring the concentration of pollutants to acceptable levels specified in the industrial wastewater permit, a facility first needs to precipitate the metals in solution; this is called metal precipitation, which is usually accomplished upon the addition of caustic soda to the rinses containing metals. The precipitated produced is called metal hydroxide. During promulgation of the metal finishing, effluent limitations EPA-prescribed metal precipitation followed by removal of precipitated metals by clarification and final sludge dewatering for common metals treatment, with pretreatment steps for chromium reduction and cyanide oxidation. This was referred as best practical technology (BPT). According to Dr. Kenneth Kerri, pioneer water educator and founder of the Office Water Programs, adequate pretreatment before discharge to wastewater collection systems is important in preventing toxic, corrosive, flammable and explosive threats from damaging collection system and treatment plants, and posing safety hazards to operators and the general public5.

Evaluation of the pretreatment system is the most important aspect of an inspection. The treatment system can be inspected against established standards for providing adequate treatment. This standard is set in 40 CFR 403.3, which calls for the reduction, elimination or alteration of the nature of pollutants in wastewater prior to discharge6. Consider the reduction of hexavalent chromium to meet effluent control limits. This process is achievable in two steps. Initially, hexavalent chromium (Cr⁺⁶) is reduced to trivalent chromium (Cr⁺ᶾ) and then Cr⁺ᶾ is precipitated out of solution as a metal hydroxide. Hydroxide ions are available by the addition of sodium hydroxide to form a nontoxic precipitate (a solid that comes out of solution, which is visible at bottom of the container)7.

In practice, inspectors and IUs are to track if the reaction of chromium reduction comes to a completion using a pH/ORP meter, sulfuric acid and sodium metabisulfite (SMBS). Sulfuric acid is added to wastewater to ensure its pH is between 2 and 3, and the ORP meter should be set to a reading range of 200-300 mV. SMBS is then added to the acidic wastewater solution to serve as the electron donor for Cr⁺⁶ to Cr⁺ᶾ reduction. In the absence of SMBS, wastewater cannot be treated. The next step in the treatment of wastewater is to raise the pH from 2-3 to 7.5-8 by adding caustic soda that aids in the precipitation of chromium (III) hydroxide. For maximum efficiency, flocculent is added to the solution and allows the precipitate to collect at bottom of tank as sludge8. The final step is pumping the sludge through a filter press to remove water and dry it to specifications of lawful shipment as a hazardous waste. The Plan of the Shop is affected by every change in processes. Should an IU decide to add a new finishing process to the metal part, a new solution tank and associated rinses need to be depicted in the process flow diagram. Existing permits would likely have to be modified to reflect the new limiting parameters.

Miguel Rodas  work for the City of Los Angeles Sanitation Department, in the Bureau of Sanitation’s Industrial Waste Management Division. Visit lacitysan.org.


  1. City of Los Angeles Municipal Code (LAMC) 64.30: A https://www.lacitysan.org/cs/groups/public/documents/document/y250/mda4/~edisp/cnt008646.pdf 
  2. Objectives of General Pretreatment Regulations: 40 CFR 403.2. https://www.law.cornell.edu/cfr/text/40/403.2
  3. Guidance for Conducting a Pretreatment Compliance Inspection, US EPA, and (September 1991): page 2.
  4. US EPA: Metal Finishing Effluent Guidelines https://www.epa.gov/eg/metal-finishing-effluent-guidelines#what-is
  5. Kenneth Kerry, Treatment of Metal Wastestreams (Sacramento,1990):section 5.2
  6. US EPA: Industrial user Inspection and Sampling Manual for POTW https://www.epa.gov/compliance/industrial-user-inspection-and-sampling-manual-publicly-owned-treatment-works
  7. US EPA: Guidance Manual for Electroplating and Metal Finishing Pretreatment Standards https://www.epa.gov/sites/production/files/2015-10/documents/electroplating-and-metal_finishing_pretreatment-guidance_feb-1984.pdf
  8. DTSC: Electroplating Facility Inspection Manual: Emphasis on Cyanide Plating Facilities. (January, 2009) http://www.dtsc.ca.gov/hazardouswaste/upload/Electroplating_Manual2009.pdf