Improving the EPA Multi-Sector General Permit for Industrial Stormwater Discharges (2019) / Chapter Skim
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3 Stormwater Sampling and Data Collection
3 Stormwater Sampling and Data Collection
Pages 45-66
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From page 45... ...
This is not laboratory analysis, and data management to improve always the case, however, because changing rainfall industrial stormwater management under the MSGP. intensity during a storm can provide energy mid-storm that may scour the drainage areas and produce high CHALLENGES OF QUANTIFYING concentrations after the first flush.
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From page 46... ...
Carefully collected and analyzed EMC = = Td �0 Q dt T Total Pollutant Mass grab samples, as part of benchmark monitoring, have Total Stormwater Volume value in this regard. Sampling the first runoff could add further consiswhere C is the pollutant concentration, Q is the flow tency and comparability to the grab sample data set and rate, t is time, and Td is the storm duration.
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From page 47... ...
The goal, whether in grab or composite sampling, is to find a location where Automated Composite Sampling. The most compre- the flow and solids are well mixed (Fischer et al., 1979; hensive approach for assessing pollutant discharges is Saunders et al., 1983)
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From page 48... ...
Facilities regulated multiple samples may have to be collected at different under the current MSGP that have multiple discharges points spatially in order to generate a clear picture of may collect their stormwater samples at one discharge the pollutant concentrations. point and list it as being representative of all discharge Variation in sample processing and analysis propoints.
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From page 49... ...
ing the 2008 MSGP, EPA discontinued all remaining The current MSGP requirement for grab samples composite sampling and essentially disallowed the use of during the first 30 minutes to capture the first flush is composite sampling in favor of grab sampling to characinconsistent with the methods used to derive bench- terize the high pollutant concentration that would occur mark thresholds. Technology-based MSGP benchmark during a first-flush effect (EPA, 2008b)
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From page 50... ...
monitoring. Technology verification for SCMs used in The number of samples required to be statistically municipal stormwater requires monitoring of a miniconfident that the sample mean is less than a spe- mum of 12 storm events (composite sampling)
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From page 51... ...
sampling for those that qualify for monitoring relief to ensure that appropriate stormwater management Role of Training for Sampling and Laboratory continues throughout the permit term and to provide Personnel additional data to indicate the effectiveness of SCMs. Furthermore, EPA should also analyze COVs for Data and field experience show substantial differs ector- and site-specific industrial stormwater data to ences in the reliability of samples collected by facility evaluate the benefits of additional increases in sampling personnel as compared to trained (watershed agency)
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From page 52... ...
in California that were greater than 40 percent for The industrial stormwater matrix poses particular some stormwater pollutants, the Southern California challenges in analysis because many of the pollutants Stormwater Monitoring Coalition (SMC) developed of concerns (e.g., metals, organics)
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From page 53... ...
is considered here in the broadest sense and includes hardware, software, sensors, sampling techniques and TIERED APPROACH TO MONITORING timing, mobile technologies, and apps. Visual monitoring information could be addressed The current MSGP monitoring approach could be with the future development of mobile apps that may substantially improved to provide more useful informabe useful in identifying stormwater clarity, sheens, or tion on the quality of stormwater discharges and their other visual water quality indicators via still imaging impact on receiving waters while balancing the net or video.
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From page 54... ...
Category 3: Sectors/subsectors for which the Visual, industry-wide (pH, TSS, Similar to current MSGP for sectors Benchmark permitting authority determines, COD) , and sector-specific with benchmark monitoring, Monitoring based on most recent data and benchmark monitoring in addition except chemical monitoring industry literature review, that to routine facility inspections.
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From page 55... ...
Facilities would be allowed to rely on inspections as an alternative to chemical discharge The value of facility inspections to evaluate monitoring if they exhibit a low risk of contributing to site conditions and pollutant discharge potential water quality problems via stormwater discharge. This was recognized early in the implementation of industrial stormwater permitting as an important determination would be facility based rather than sec supplement to chemical monitoring.
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From page 56... ...
is accurate and that the SCMs are in place and Industrial stormwater discharges from these mid-sized functioning; and facilities would be expected to produce much lower • Identifying actions that need to be taken to effecpollutant mass loadings compared to smaller facilities tively manage stormwater pollution. with more active operations.
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From page 57... ...
BOX 3-2 California's Industrial Stormwater Practitioner Certification The California Industrial Stormwater General Permit issued in 2014 establishes requirements for industrial storm water permittees to have a Qualified Industrial Stormwater Practitioner evaluate and certify the adequacy of corrective actions at industrial facilities when basic numeric action levels or EPA Sector Specific Benchmarks are exceeded (CA NPDES Permit No. CAS000001; Order No.
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From page 58... ...
However, the committee recommends that all inspections of Category 1 facilities, or recommendafacilities without sector-specific benchmark monitor- tions of the permitting authority for sites that are large ing conduct industry-wide monitoring for pH, TSS, and complex with high pollutant discharge potential and COD, as discussed in Chapter 2, in addition to or where TMDL development and implementation the currently required visual monitoring of stormwater merits additional monitoring. The largest facilities will discharge and routine site inspections by facility staff.
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From page 59... ...
water discharge than by using grab-sample first-flush benchmark monitoring. Full-storm data can provide a No Exposure much more complete picture of the industrial stormwater discharge from a site.
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From page 60... ...
the permitting authority to exclude facilities from By its very nature, industrial stormwater discharges the MSGP and require individual NPDES permits occur during wet weather conditions when the receivwhen special considerations such as a large quan- ing stream is expected to be flowing at some reasonable tity of pollutant discharge, proximity to receiving capacity above base flow, which could provide dilution waters, and the characteristics of pollutants are at of stormwater discharges. NPDES regulations allow for issue (40 CFR § 122.28(b)
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From page 61... ...
the metals measured as dissolved consists of small Calculating a stormwater mixing zone based on particulate or colloidal metals that are able to pass best available science may require the use of data sets through the filter or metals that are complexed with characterizing upstream flow and water quality condi- organic ligands, which may not be biologically availtions and dynamic water quality models to understand able. Dissolved metals require field or laboratory filtrathe impact of stormwater runoff on receiving waters.
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From page 62... ...
total metals benchmarks to analyze receiving waters to When EPA reviewed benchmark monitoring data calculate pollutant toxicity associated with a facility's for development of the 2015 MSGP, only 485 of the stormwater discharge. However, the facility would need 1,200 covered facilities required to perform benchmark to do additional sampling beyond the current MSGP monitoring submitted their results electronically and requirements to acquire the data needed by the BLM.
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From page 63... ...
For example, California Water Boards' data explained by improvements in pollution prevention center contains industrial stormwater effluent water measures that have been implemented in this time quality data and an assessment tool that can be used for period, including the removal of lead from gasoline and FIGURE 3-2 Median lead concentrations at sites in California Water Board, Los Angeles Region, from monitoring from the past 5 years, with results less than (left) and greater than (right)
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From page 64... ...
The current MSGP benchmark monitoring EPA's disallowance of composite sampling and relirequirement focuses on low-cost, coarse indicators ance on grab sampling in the interest of discrete charof site problems, and the usefulness of the data can acterization of the highest pollutant concentration is frequently be hampered by its variability. Stormwater not warranted based on the methods used to derive monitoring data display variability that originates from benchmark thresholds.
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From page 65... ...
Sectors that merit addiEPA should analyze industrial stormwater data and tional pollutant monitoring, based on the most sector-specific coefficients of variation to recommend recent data and industry literature review, would additional increases in sampling frequency, consistent conduct sector-specific benchmark monitoring in with EPA's determination of an acceptable level of error addition to pH, TSS, and COD, which would be for this indicator of SCM performance. Additional collected by all facilities with chemical monitoring.
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From page 66... ...
Electronic reporting has only been ties to analyze trends. EPA should develop national required of permittees since 2016, and the data man- visualization tools that can be used to easily examine agement capabilities are still developing to make the data for patterns, trends, and correlations.
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