Improving the EPA Multi-Sector General Permit for Industrial Stormwater Discharges (2019) / Chapter Skim
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4 Consideration of Retention Standards in the Multi-Sector General Permit
4 Consideration of Retention Standards in the Multi-Sector General Permit
Pages 67-80
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From page 67... ...
replace monitoring, but would provide another struc- Infiltration is an attractive management option tural approach to control pollutant discharges. for stored stormwater; it has been used widely and successfully in municipal stormwater applications to STORMWATER RETENTION reduce stormwater impacts on local water bodies and to recharge groundwater.
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From page 68... ...
control, washing, toilet flushing) will be practiced at Stormwater retention systems are typically sized many industrial sites due to the water quality treatment according to the retention standard and site-specific requirements and/or likely small or inconsistent water information such as the drainage area, the runoff coefdemand from these applications (NASEM, 2016)
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From page 69... ...
Some states, such as California would need to infiltrate or be used on site fully within and Oregon, have developed specific requirements 24 hours. Sites with insufficient infiltration rates to for industrial stormwater retention if it is used as meet this requirement can increase the size of their part of stormwater management (OR DEQ, 2017; retention storage (California Water Boards, 2018)
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From page 70... ...
FIGURE 4-2 Cumulative 24-hour rainfall distribution curve (black line) at the Baltimore/Washington International Thurgood M arshall Airport and cumulative percent retention with a given design storm (red line)
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From page 71... ...
This Benefits: section examines the merits and concerns when using retention standards for industrial stormwater. • contaminants are removed through treatment If or infiltration processes, retention reduces con taminant loads to receiving aters.
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From page 72... ...
This stormwater manual prohibits stormwater infiltration issue is discussed in more depth at the end of the at "potential stormwater hotspots" that might have the chapter. potential to produce relatively high levels of pollutants in the case of spills, leaks, or illicit discharges, includ- CONSIDERATIONS FOR RETENTION ing storage areas, efueling areas, vehicle storage, and r AT INDUSTRIAL SITES material transfer areas.1 alifornia allows infiltration of C industrial stormwater in its general permit and includes Successful use of retention/infiltration at an indusstate groundwater protection requirements for on-site trial facility for treatment of industrial stormwater compliance (California Water Boards, 2018)
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From page 73... ...
persist in groundwater for years. For example, simple Therefore, before stormwater retention and infiltration hydrocarbons can readily biodegrade in aerobic enviare considered, expected stormwater pollutants at a site ronments, although maintaining aerobic environments should be carefully assessed.
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From page 74... ...
Many existing industrial sites may infiltrating industrial stormwater to minimize risk to lack the land to site an appropriately sized infiltration groundwater, assuming that specific evaluation of con- basin; some sort of subsurface infiltration gallery with taminant mobility and/or treatment is not provided to underground storage may instead be employed (see remove the pollutants: Figure 4-1b)
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From page 75... ...
Soils with low organic matter In addition to site-level analyses, regional analyses content would not be expected to provide significant of potential effects on stormwater infiltration on existattenuation and removal of organic pollutants. Values ing soil or groundwater contamination may be needed.
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From page 76... ...
If The use of drinking water standards as cleanup goals the stormwater exceeds drinking water limits for total for contaminated groundwater is well established. The dissolved solids, chloride, specific conductance, and/or 2018 amendments to the California equivalent of the sulfate, costly technologies, such as reverse osmosis or MSGP allows infiltration of industrial stormwater if other desalination processes, would be required, likely the water meets drinking water quality standards by making infiltration economically unfeasible.
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From page 77... ...
Given the site-specific lation of infiltration systems. Additionally, a growing nature of the suitability of retention with infiltration at body of practitioners has experience and knowledge industrial sites, numeric retention standards as a TBEL to evaluate where industrial stormwater retention and could not be established in EPA's MSGP or as bestinfiltration retention systems are appropriate.
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From page 78... ...
Chemicals covered by the Safe Drinking and peak flows, assuming infiltration is suitable based Water Act and unregulated chemicals with known on groundwater considerations, it should develop addi- human health risks at concentrations of concern should tional guidance on appropriate design storm standards, be evaluated. Meeting stringent water quality requireperhaps in consideration of regional precipitation pat- ments may make infiltration cost prohibitive at sites terns.
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From page 79... ...
The most significant incentive groundwater. The guidance should include informawould be assurance that installation of infiltration in tion on applied water quality, treatment offered within accordance with EPA guidance for determining the the infiltration zone, monitoring requirements, natural appropriate design storm provides relief from the cor- attenuation of pollutants, groundwater use designarective action process associated with episodic bypass tions, and possible impacts of pollutant dilution or that exceeds benchmark thresholds.
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