Nov 09, 2021

Multi Sector General Permit: How You Can Prepare

Part 2 of a series on the Multi-Sector General Permit

industrial water
The first step in complying with the Multi-Sector General Permit is sampling storm water runoff.

The recent EPA issuance of the final 2021 Multi-Sector General Permit (MSGP) sounded the alarm for eventual adoption of stricter standards for storm water discharges from industrial facilities. The permit immediately applied to a handful of states and U.S. territories and certain industry properties, but the norm is for other states to adopt EPA regulations.

With potential costly requirements that come with higher compliance tiers, facilities should start to look beyond basic housekeeping and towards eventual benchmark compliance. The most important initial step to be taken should be additional storm runoff sampling to pinpoint high concentration source areas. It is the first step to the winning formula: Prepare, get covered, take action and follow up.

Some facilities have invested a significant amount of time and effort into improving site cleanliness as part of their routine compliance requirements. Unfortunately, housekeeping efforts alone do not guarantee results that meet the new benchmarks consistently. There are many variables that contribute to this problem such as:

  • The nature of the pollutants, and whether they are dissolved nutrients resistant to conventional storm water best management practices;
  • Inaccessibility of source areas, such as accumulations of pollutants inside of drainage structures or on top of buildings; and
  • The number of pollutants that are inherently created or discharged at these sites.

Many facilities will find that they are not currently meeting the proposed MSGP standards. As with any environmental compliance problem, facilities should start off by looking for the low-hanging fruit: solutions that offer the most impact for the least expense. Even if these solutions do not get a facility across the compliance finish line, they may significantly lessen the impact of potential noncompliance, while additional solutions are developed.

Stay Out of the High Tiers, Start with Sampling

The final 2021 Multi-Sector General Permit takes a three-tier approach based on the number of benchmark threshold exceedances over given periods of time. The tiers of violations are outlined in part one of this series in the June issue of iWWD. In general, enforcement increases with the magnitude and frequency of exceedances.

The high and frequent exceedances will result in more severe punishment and operator expense and pain. Operators can take common sense, simple measures to turn a Tier 3 violation into Tier 1 and demonstrate to regulators it is serious about complying. It is impossible to know what the situation is without precise sampling.

Typically, an industry samples for criteria pollutants listed in their EPA National Pollutant Discharge Elimination System (NPDES) permits on a quarterly or annually schedule. The samples are taken from the individual facility outfalls and sampled for their permit specific benchmark parameters.

multi sector general permit
Low cost strategies with high value should be at the top of the priority list for MSGP compliance as they can lessen the influence of potential noncompliance.

The samples give concentrations of benchmark parameters at their outfalls, or the point at which water leaves the facility. The samples are important to acquire as they can show that an industrial site will comply with the three-tier system or show which violation tier they fall into. Samples collected at each outfall location must be documented and shared with the EPA or state specific regulators.

If an industrial facility collects their storm water samples at their outfalls and the benchmark concentrations for constituents that were analyzed fall below the benchmark, then the facility will comply. On the opposite end of this, if the facility sample concentrations are above the benchmarks, then the facility must determine which tier it falls into. After determining the appropriate tier, a facility must determine methods to find where these high concentrations are coming from.


Targeted Sampling to Find Sources of Pollutants

It is not unusual for a facility with high storm water pollutant loads to have the majority of the pollutant coming from a small area of the facility. This can be for a number of reasons such as exposed material stockpiles, construction activities, deteriorated sewer pipes or even a high population of birds or rodents in a portion of the site. A well-planned set of additional samples can give a facility many insights into the source and nature of their storm water pollutant loads.

water sampling
Common causes for permit violations are due to stockpiles, construction or vermin.

Grab vs. Composite Sampling

Under the MSGP, facilities are generally required to collect two types of samples: grabs and composites.

Grab samples are single runoff volumes collected within 30 minutes of the beginning of storm water discharge. Composite samples, on the other hand, are generally collected every 15 minutes during the first three hours of discharge, or the entire discharge if less than three hours. Grab samples represent a snapshot of the initial runoff quality while composite samples are more like a video of the entire event.

Taking both grab and composite samples can give a facility information on how pollutants run off within the first 30 minutes of rainfall and how that compares to the runoff event. Sampling can be done by using manual techniques where one goes out and fills a container in the field, or by using a programmable sampler to pull samples at designated intervals.

Internal sampling, taken from inside a facility, can be very useful to find areas of high concentration of pollutants. Finding sampling points upstream of the designated outfall allows facilities to test for the same benchmark parameters that they sample at the outfalls, or for more specific indicator pollutants unique to the facility’s operations.

Many times, facility operators will have concerns over the collection of additional sample data, and ask, “What if the results are high or I discover a new pollutant? Will I get in trouble with the regulators?”

grab sample

composite sampling
Under MSGP, facilities are generally required to sample with either grab samples or composite samples.

Generally, the answer is No. One of the benefits of sampling at a location other than a defined NPDES outfall is that the results would not be required to be included with routine permit reporting. Here’s how internal and outfall sampling can work together to measure concentrations of suspended solids.

For example, an outfall sample shows total suspended solids have been averaging more than 2,000 mg/L. The internal samples at two locations inside the facility show a higher concentration of solids in one area than the other internal location. Based on these results, a management scheme can be devised to improve results.

More samplers can be used at different internal locations upstream to identify more data points. This gives more information about internal flow structure and different concentrations. Portable flow meters check flow and determine the difference between concentrations and loads in sub-areas. Filtered versus unfiltered samples can tell the difference between sediment-bound and dissolved pollutants.

About the author

Trent Humphrey is environmental engineer-in-training for Stanley Consultants. Humphrey can be reached at [email protected].