Storm Water Sampling and Monitoring

The industrial storm water permit requires all permittees to sample and analyze the storm water discharge from the outfall(s) identified on their Notice of Intent (NOI). An outfall is a location where storm water discharges off the site or to an on site water of the state which includes wetlands. Some examples of outfall locations include, but are not limited to pipes, ditches, swales, and other structures that carry storm water. A grab sample should be collected and analyzed annually from all outfalls that receive storm water discharges from your industrial activity. The results of your storm water sampling will help you assess the effectiveness of your Storm Water Pollution Prevention Plan (SWP3).

Storm water sampling requirements and monitoring schedule

The storm water samples are required to be analyzed for the following constituents: Any potential pollutant associated with the facility, pH (field measurement), oil and grease, carbonaceous biochemical oxygen demand (CBOD), chemical oxygen demand (COD), Total suspended solids (TSS), Total Kjeldahl nitrogen (TKN), Total phosphorous, and nitrate plus nitrite nitrogen.

Note: The pH measurement must be taken at the time the grab sample is collected (i.e., due to holding time exceedances, pH cannot be analyzed by an off-site laboratory), and cannot be estimated using a color comparison (i.e., test strips).

Samples must be taken at a point representative of the discharge but prior to entry into surface waters of the state or a storm sewer conveyance. For discharges that flow through on-site detention basins, samples must be taken at a point representative of the discharge from the basin. Run-off events resulting from snow or ice melt should not be sampled and cannot be used to meet the annual monitoring requirements of Rule 6.

The storm water sample is required to be taken during a rain event greater than one-tenth (.10) of an inch. The sample should be collected within the first thirty minutes of discharge. There should be at least seventy-two (72) hours between the measurable storm event being sampled and the previous measurable storm event.

Samples must be collected at least annually, with the first sample collected prior to implementation of the Storm Water Pollution Prevention Plan. Within the first permit year (365 days from the submittal of the NOI) the permitted facility is required to take and analyze a grab sample of the storm water discharges. During the following permit years (permit year two through five), the permitted facility is required to continue to take and analyze a grab sample of the storm water discharges, and the sampling should be conducted no later than one year from the previous sampling date.

Storm water outfall sample data collected more frequently than annually must be reported to IDEM.

Preparation for conducting the sampling

There are several things a facility must do to prepare to conduct storm water sampling. First, the permitted facility should select a laboratory (lab) to analyze the samples. When selecting a lab you should ask the following questions:

  • What type and size bottles are needed?
  • How do you fill the bottle?
  • How full do you fill the bottles?
  • Are there any labels or additional forms required?
  • Can you walk me through the chain of custody form?
  • Are there any sample preservation requirements and/or holding time restrictions?
  • How to deliver the sample to the lab?
  • Is overnight delivery required?
  • What are the costs?

Once a lab has been selected the facility should prepare to conduct sampling. The facility should have the sampling equipment (sampling bottles from a lab, sampling instruments, and personal safety equipment) ready, as well as the field sheet to document the required information.

The following items should be listed on the field sampling sheet and included in the storm water discharge monitoring report:

  • Person who conducted the sampling
  • Date and time of discharge
  • Length of storm event
  • Time between sampled storm event and previous storm event (at least 72 hrs)
  • Total rainfall during storm event

Reporting requirements

Permitted facilities are required to submit a storm water monitoring report with the required information and the required attachments annually. Sampling data results shall be submitted to IDEM within thirty (30) days after laboratory analyses have been completed. There shall be a minimum of three (3) months between reported sampling events. The analytical techniques and results (laboratory analysis report) of all required analyses and measurements shall be submitted in concurrence with the storm water discharge monitoring report form, and a completed chain of custody form. A chain of custody form ensures there was no tampering of the sample from the time it was collected to the time it was analyzed.

Laboratory Quality Assurance and Quality Control (QA/QC)

Additional data may be requested by IDEM. All records of analyses performed, calibration and maintenance of instrumentation, and information resulting from the monitoring activities required must be retained on site.

Additional storm water sampling guidance [PDF] is available from U.S. EPA (on the IDEM Web site).

The Step-by-Step Process for Compliance with 327 IAC 15-6 page provides specific permit timelines and information regarding compliance with the rule.

Additional Information

For more information regarding the applicability requirements for 327 IAC 15-6, please contact the Storm Water Permit Coordinator.