Phase II MS4 audit process

What permittees can expect during a compliance evaluation of their stormwater program

Unlike other National Pollutant Discharge Elimination System (NPDES) permits, Municipal Separate Storm Sewer System (MS4) permits do not contain specific end-of-pipe discharge effluent limits. Municipal Separate Storm Sewer System permits use programmatic requirements to reduce pollutants discharged to the “maximum extent practicable” (MEP) through the implementation of Best Management Practices (BMPs). Permittees are granted flexibility in selecting the types of BMPs implemented to meet permit requirements.

The Minnesota Pollution Control Agency (MPCA) is mandated by the U.S. Environmental Protection Agency to evaluate permittees for program compliance, the appropriateness of their identified BMPs, and progress towards achieving their identified measurable goals.

Audit types

Because permittee conditions differ greatly and maintain flexibility to select BMPs, it is necessary to use a comprehensive set of questions and answers to determine the level of success that a permittee’s stormwater program has attained in meeting its goals. Audits may consist of questions and answers related to all six minimum control measures (MCMs), or they may focus on any combination of MCMs. Audits may also include a field component. In this case, MPCA staff, along with the appropriate permittee staff, will visit and evaluate private or municipally owned construction sites or stormwater facilities.

Notification process

Once the MPCA selects a permittee for an audit, staff will contact the permittee by phone in order to target an audit date. MPCA staff will email a date verification and a checklist of items that the permittee should gather in preparation for the audit. The checklist contains items that the MPCA staff requests for review prior to the audit. The permittee must submit these items to the MPCA within seven business days. PDF icon Phase II MS4 Audit Checklist. Examples of information that the MPCA may request include:

  • public outreach materials, organizational chart, staff training, and responsibilities
  • ordinances, pond maintenance plans or other agreements, etc.
  • list of three-four active construction sites that may be visited
  • inspection forms and reports, or other database tracking information

Length of audits

The length of the audit will range from half a day to two days depending on the depth of the audit, the preparedness of the permittee, the complexity of the permittee’s stormwater program and whether the audit includes field visits.

What to expect during the audit

The audit will take place in the permittee’s jurisdiction. The permittee’s designated stormwater coordinator will be responsible for getting all necessary participants to attend and selecting the meeting site.

The purpose of the audit is to assess how successfully the permittee’s stormwater program meets the requirements of the MS4 permit and water quality regulations. MPCA staff will evaluate program effectiveness based on three different areas:

  • the permittee’s response to questions
  • whether or not the permittee has met the goals of its Stormwater Pollution Prevention Program (SWPPP)
  • other outcomes that the permittee has achieved

The audit process will allow permittees to describe their unique approach to each program area. The evaluator will ask questions from a standard questionnaire form in order to ensure that all topics are covered consistently and in sufficient depth for each permittee. The interview will be conversational and will allow the permittees ample opportunity to explain their answers and provide background information throughout the interview process.

Review of construction activities

MPCA staff may decide to visit active construction sites, or they may contact other MPCA staff from the Construction Stormwater Program regarding compliance at construction sites within the jurisdiction of the permittee. 

Post audit activities

Immediately after conducting the MS4 audit, MPCA staff will have time scheduled for an exit interview. The exit interview is intended to provide a preliminary assessment of the permittee’s stormwater program, based on responses to questions, permit requirements, and the permittee’s SWPPP. Generally, within two weeks of the audit, the MPCA will provide the permittee with an official audit report. The audit report will summarize all findings, and may include recommended or required actions for the permittee to take if issues were identified, or if the MPCA feels that there are aspects of the permittee’s stormwater program that could be improved.

While the primary function of the audit is to assess and improve MS4 permittee program performance, as with all regulatory programs, there is potential for enforcement actions with penalties for alleged violations. In addition, if deficiencies or violations are identified during the initial audit, a follow-up audit may be necessary. Permit holders will have an opportunity to respond to any concerns noted by MPCA staff.

For more information, call 651-296-6300 or 800-657-3864 and ask for MS4 stormwater permit program staff.