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Climate Resilience in Stormwater Management

"},"title":"Climate Resilience in Stormwater Management","subHeaderText":"Theresa Hughes, Ph.D., and Madelline Ogborn (KC Harvey Environmental)","pageSections":[{"sectionColor":{"color":["{\"color\":\"#F5F5F5\",\"background\":\"bg-aventia-gray\",\"text\":\"text-aventia-black\",\"button\":\"dark\",\"border\":\"border-aventia-black\"}"]},"backgroundImage":[],"sectionPadding":"p-0","urlId":null,"vizyContent":{"nodes":[{"__typename":"VizyNode_Heading","type":"heading","tagName":null,"html":"

Executive Summary

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Environmental protection and permit compliance are critical issues for industrial site operators. When climatic conditions such as temperature and precipitation patterns change at a site, operators must adapt site practices to maintain compliance. Extreme weather events driven by long-term climate change create major challenges for operators and increase the risk of environmental impacts and permit violations.

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Extreme weather events are not the only source of risk. Climate change on a seasonal timescale presents similar risks. A single unusually dry season can lead to major consequences at a site in terms of revegetation, soil erosion, water supply, and fugitive dust emissions. Drought also increases the risk of wildland fires, which often pose a threat to sites due to their locations. Unusual precipitation patterns and shifts in the snowmelt period can quickly overwhelm existing stormwater diversion and collection systems. Operators may be faced with cyclical problems of extremes, with periods of flooding or below-average cold temperatures, followed by periods of drought or above-average hot temperatures. Incorporating climate resilience strategies into environmental protection measures and permit compliance activities is vital.

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This article describes climate resilience strategies for industrial site operators and focuses specifically on practical approaches for stormwater management.

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The Fundamentals: What is a Stormwater Management System and How is Performance Measured?

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Stormwater is water from rain or snowmelt flowing across land surfaces. If the land surface is saturated or impervious, the stormwater may flow across substantial distances before eventually evaporating or infiltrating. Sediment, chemicals, oil, and other pollutants on the land surface can contaminate stormwater. If uncontrolled, stormwater runoff can transport contaminants to receiving waters and contribute to water quality degradation.

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Stormwater management systems (SMS) are designed for multiple functions. The primary purpose of an SMS on an industrial site is to prevent contamination of stormwater. In addition, SMS control the movement of stormwater across the site to protect infrastructure and roads and limit flooding of operating areas.

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Section 402 of the Clean Water Act (33 U.S.C §§ 1251 et seq.) established the National Pollutant Discharge Elimination System (NPDES) permit program. An NPDES permit is required for stormwater discharges associated with industrial activities, construction activities, and municipal separate storm sewer systems (MS4s). There are two general NPDES permits for stormwater discharges associated with industrial activities and construction activities: the Multi-Sector General Permit (MSGP) and the Construction General Permit (CGP). These general permits apply to areas of the United States where the Environmental Protection Agency (EPA) is the permitting NPDES authority, including four states, most U.S. territories, federally operated facilities in certain states, and other areas. The 46 states that do not use the EPA as the NPDES permitting authority have their own permits, each specific to the state and activities being proposed while complying with NPDES requirements.

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Eleven general categories of industrial activities — including coal and mineral mining, oil and gas exploration and processing, and manufacturing (refer to 40 CFR 122.26(b)(14)(i)-(xi)) — are required to obtain NPDES permit coverage for stormwater discharges if the site either discharges or has the potential to discharge stormwater to a municipal separate storm sewer system or to Waters of the United States (WOTUS).

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MSGP eligibility is limited to discharges from sites in specific “sectors” of industrial activity. These sector descriptions are based on Standard Industrial Classification Codes and Industrial Activity Codes and may be found in Appendix D of the MSGP. The MSGP defines stormwater monitoring and reporting requirements for indicator parameters, benchmark parameters, and parameters with effluent limits for each specific sector covered under the permit. The MSGP also defines requirements for corrective actions when benchmark thresholds or effluent limits are exceeded, operation and maintenance of the SMS, inspections and visual assessments, analytical monitoring of discharges, and the contents of the Stormwater Pollution Prevention Plan (SWPPP) for the site.

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For further information on the 2021 MSGP, including SWPPP requirements, read more here.

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CGP eligibility is limited to discharges of stormwater (and certain authorized non-stormwater discharges) from construction sites that disturb one acre or more of land and from smaller sites that are part of a larger, common plan of development. Under the CGP, the only stormwater discharges required to be sampled for water quality are dewatering discharges to sensitive waters, which must be monitored for turbidity. For all other discharges, the CGP defines requirements for erosion and sediment controls, soil stabilization, dewatering, pollution prevention measures, prohibited discharges, and surface outlets, rather than requiring stormwater samples to be analyzed for specific parameters. The CGP also defines requirements for corrective actions when specific conditions exist or turbidity benchmark thresholds are exceeded, operation and routine maintenance of the SMS, inspections, turbidity monitoring reports, and the contents of the site SWPPP.

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The remainder of this article is focused on the MSGP. For further information on the CGP, read more here. For further information on MS4 permitting, read more here.

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Stormwater Control Measures

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The United States Environmental Protection Agency describes a wide range of best management practices related to stormwater pollution prevention, including site planning, stormwater control measures, good housekeeping, and materials management. This section is focused on stormwater control measures in three key categories: erosion control, sediment control, runoff control, and detention.

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Best management practices are often most effective as a system rather than stand-alone measures. Using a combination of erosion controls, sediment controls, and runoff controls as “treatment trains” is typically more resilient to higher flows.

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Erosion control is critical in stormwater management. Minimizing or preventing erosion can substantially decrease the costs, risks, and effort associated with downstream controls and treatment to remove sediment and other pollutants from stormwater.

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Erosion control measures for resilience to high-flow events include:

Compost Blankets
Geotextiles, Matting, and Netting
Land Grading
Mulching
Riprap
Permanent Seeding
Soil Retention
Soil Roughening
Temporary Slope Drains

Sediment control measures for resilience to high-flow events include:

Fiber Rolls
Filter Berms
Sediment Basins and Rock Dams
Sediment Filters and Sediment Chambers
Sediment Traps
Silt Fences
Storm Drain Inlet Protection
Straw or Hay Bales
Vegetated Buffers

Runoff control measures for resilience to high-flow events include:

Check Dams
Grassed Swales and Channels
Infiltration Basins
Infiltration Trenches
Land Grading

Detention measures for resilience to high-flow events include:

Constructed Wetlands
Dry Detention Ponds
Wet Extended Detention Ponds

For information on the applicability, siting and design considerations, costs and limitations for these, and other stormwater control measures, read more here and here.

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For industry-specific guides to best management practices for stormwater, read more here.

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Snow and Ice

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Removal of snow and ice from site roads, parking lots, and operating areas should be considered part of stormwater management due to the associated impacts on stormwater volumes and water quality. Where practicable, snow should be placed in designated storage areas which enable snowmelt to be directed to sediment controls.

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Consider the use of de-icing agents when selecting revegetation plant species for areas near roads and lots. Placement of snow plowed from roads in designated storage areas may result in stormwater with elevated salt content. Use of native salt-tolerant species to revegetate these areas may be warranted.

Keeping the SWPPP Current and Complaint

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A SWPPP must be developed for a site when it initially obtains MSGP coverage. The SWPPP must include:

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Stormwater pollution prevention team
Site description, including site activities and a general location map
Stormwater pollution prevention team
Site description, including site activities and a general location map
Summary of potential pollutant sources
Description of stormwater control measures, including location, type, purpose, and basis for selection
Schedules and procedures, including those for routine facility inspections and quarterly visual assessments, maintenance, spill prevention and response, treatment chemical use, employee training, and good housekeeping
Schedules and procedures for monitoring and reporting, including those for indicator, benchmark, effluent limitations guidelines, state- or tribe-specific, and impaired waters
Documentation to support eligibility pertaining to other federal laws (such as ESA and NHPA)Signature requirements
Detailed site map showing:
- Boundaries of the property and the size of the property in acres
- Location and extent of significant structures and impervious surfaces
- Directions of stormwater flow, including flows with a significant potential to cause soil erosion
- Locations of all stormwater control measures
- Locations of all receiving waters, including wetlands, impaired waterbodies, and Tier 2, Tier 2.5, and Tier 3 waters
- Locations of all stormwater conveyances, including ditches, pipes, and swales
- Locations of potential pollutant sources
- Locations where significant spills or leaks have occurred
- Locations of all stormwater monitoring points
- Locations of stormwater inlets and discharge points and the areas draining to each discharge point
- If applicable, locations of discharges to municipal separate storm sewer systems (MS4s)
- If applicable, areas of Endangered Species Act-designated critical habitat for endangered or threatened species
- Locations of specific activities (relevant to industrial sites) and where such activities are exposed to precipitation at the site
- Locations and sources of run-on from adjacent property that contains significant quantities of pollutant

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Each time an updated MSGP is issued by the permitting authority (typically every 5 years), the SWPPP must be revised to comply with any changes in the permit. For information on the proposed 2026 MSGP, read more here.

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The SWPPP must also be regularly updated to describe the SMS as accurately as possible. Changes in facility conditions, updates to stormwater control measures, corrective actions, and Additional implementation Measures must be documented.

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Adaptive Management — What is it?

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Stormwater management for compliance with the MSGP is an ongoing and iterative process. An adaptive management approach is ideal for stormwater management because the conditions are dynamic and unpredictable. For most industrial sites, the SMS requires modification over time due to changes in site operations, development, and land use, and operators use adaptive management to respond to such changes. Using this same approach, operators can incorporate climate resilience into their SMS. In this context, an adaptive management approach requires a process of identifying problems, locating the failures in the SMS, selecting and implementing appropriate response actions, and monitoring to check if the problems are resolved.

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Adaptive Management of Stormwater for Climate Resilience

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Identify Problems

Was the area prepared to limit stress added to stabilization measures during peak precipitation events?
Was stormwater quality degraded?
Was system capacity exceeded?
Did high channel flows lead to scouring? Did flooding occur on roads or in low-lying areas?
Are revegetated areas stabilized, or is plant growth limited due to weather?

Locate the Failures in the SMS

If stormwater quality was degraded, identify where and why the contamination occurred.
Were problems related to system overloading?
Was retention time in sediment basins too short to achieve required sediment removal?
Did site stabilization measures perform poorly?
Were the existing best management practices ineffective?
Did a localized spill enter the SMS?

Implement Appropriate Response Actions

Improve runoff diversion and collection systems.
Increase maintenance on existing erosion and sediment controls.
Complete proper dirt work preparation for stabilization, including surface roughening perpendicular to slopes and grading and shaping soil stockpiles to limit side slopes and height.
Install additional erosion controls and sediment controls.
Evaluate and adjust the revegetation seed mix for adaptability to weather changes.
Adjust inspection frequencies to reflect precipitation patterns.

Monitor to Check if the Problems Are Resolved and Document All Observations

Conduct frequent system inspection, monitoring, and maintenance.
Photo document issues during peak flow periods to aid in implementing corrective measures when the system is at low flow or dry.
Keep detailed records for SMS performance reviews and MSGP reporting.

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Adaptive Management on Industrial Sites

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Consider two industrial sites with stormwater discharges covered by MSGPs. The weather at both sites is observed to be changing in recent years. The frequency of storm events in the spring and summer has increased. The number of days with above-average temperatures and below-average precipitation in summer has also increased. The changes in weather have impacted the sites in different ways, but the site operators face the same challenge — they must each adapt their SMS to improve performance under new conditions or risk violating their MSGPs and incurring penalties and fines. The following illustrative examples describe the problems caused by changes in weather and the adaptive management actions taken to resolve them.

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Site A

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Background

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Site A is a metal mine in the construction phase. The site is located in a previously undeveloped, remote, high-elevation, forested area. Large areas have been cleared, graded, and excavated to construct buildings, facilities, pipelines, and roads. Timber and shrubs were removed, and the native soil was stockpiled for reclamation and revegetation use.

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Stormwater volumes at this site were typically driven by snowmelt and spring rain events.

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The SMS was comprised of riprap-lined diversion ditches and unlined sediment basins. Stormwater from site roads was collected in the diversion ditches and conveyed via culverts to the sediment basins.

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Snow plowed off the site roads was piled along the roadside. Snow plowed from construction zones and parking areas was placed either in small piles at the edges of the cleared areas or in stormwater diversion ditches. Deicer (magnesium chloride) was used on all site roads.

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Problem

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The planned approach to stabilization of bare ground (erosion control) at this site was primarily through revegetation. However, despite the operator conducting planned revegetation activities, the weather-related challenges limited plant establishment across much of the site. Despite annual reseeding (typically by broadcast seeding), large disturbance areas intended to be revegetated remained unstabilized due to poor plant establishment. The operator observed that erosion had negatively impacted the salvaged soil that was replaced to support revegetation efforts. Sediment loading in the stormwater was substantial.

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The operator installed straw bales in several large diversion ditches and at the outlets of all sediment basins in an effort to capture sediment, but the volumes entering the sediment basins during storm events exceeded the design capacities, and hydraulic retention time was too low for effective treatment. The operator also installed fiber rolls on several steep slopes to control sediment, but stormwater frequently undercut or flowed around the fiber rolls, limiting their effectiveness.

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Stormwater sheet flow across large, relatively flat, bare ground construction areas was transporting sediment into recently reseeded perimeter areas, smothering seedlings and limiting plant growth. Revegetated soil stockpile berms near roads had been establishing good plant cover in the first few construction seasons, but the plants showed new signs of stress, with stunted growth and leaf burn.

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Permit

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Visual assessments in the spring and summer identified increased suspended solids and poor clarity in stormwater discharges. By early summer, sediment basins had filled with sediment to more than half their capacity, indicating a substantial increase in sediment loading compared to the initial years of MSGP coverage. Therefore, the MSGP requirement for corrective actions was triggered.

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Root Cause

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The operator of Site A determined that the critical issue was erosion control and proceeded with adapting the SMS.

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Response

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In areas where revegetation was required, the operator reseeded the unstabilized steeper slopes by hydroseeding and covered the hydroseeded slopes with matting. On relatively large flat areas, the operator roughened the soil surface using tracked equipment, hydroseeded, and installed matting.

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In areas where construction was ongoing, the operator installed fiber rolls. Fiber rolls on slopes were placed on the contours of the slopes with the ends curved upslope to prevent stormwater from flowing around the ends. For additional sediment control, the operator installed silt fencing around the perimeters of active construction areas. In areas where rill erosion was widespread, the operator regraded the surfaces. Sediment traps were also constructed at multiple points upgradient of the diversion ditch inlets draining the construction areas to serve as temporary sediment controls.

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Accumulated sediment and straw were removed from the diversion ditches and culverts. Riprap check dams were added to major diversion ditches. Accumulated sediment was removed from the sediment basins and fresh straw bales were installed at the basin outlets.

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The operator considered the roadside vegetation problems and determined that the plants on the revegetated soil stockpile berms were becoming stressed due to salt from road deicing. After coordination with the appropriate permitting authorities, several salt-tolerant species of native grasses and shrubs were selected to be added to the revegetation mix for roadsides. After broadcast seeding the new mix on the berms, the operator covered them with straw mulch. The operator also adjusted the winter road maintenance program by changing the deicer from magnesium chloride to calcium magnesium acetate during warmer periods, increasing the frequency of snow plowing, and designating snow storage areas so plowed snow would not be piled on the roadside berms. Storage areas were also designated for snow plowed from construction zones and parking areas. Downgradient of the snow storage areas, sediment basins were installed, and the new seed mix with salt-tolerant species was broadcast seeded.

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Because of the high hydraulic load and sediment load in the stormwater, the operator considered that revised designs for higher storage capacity in some diversion ditches and sediment basins might be required in the SMS. However, the operator confirmed that the system was designed based on the guidance from the permitting authority and decided to re-evaluate the need for increased capacity after erosion control was improved.

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Site B

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Background

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Site B is an agricultural chemical manufacturing facility. The site was constructed in a highly developed industrial complex. The majority of the ground surface at the site is paved and impervious. Landscaping and vegetated areas are limited to small areas of ornamental plants near building entrances and grass strips at the outer perimeter of the site.

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Stormwater volumes at this site were typically driven by spring and summer rain events.

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The SMS collected stormwater from the main roads, large lots, and roof runoff outside the areas of industrial activity and discharged it directly to storm drains without treatment.

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In areas of industrial activity, stormwater was collected in area drains and conveyed via underground piping to holding ponds for sediment removal. From the ponds, stormwater was either recycled as cooling tower makeup water or discharged to the storm drains.

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Discharges to the storm drains reported to a municipal separate storm sewer system (MS4)

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Problem

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During storm events, the storm drain system capacity was exceeded, leading to flooding of low-lying roads and around buildings. Pumps were used to transfer the water from these locations to the area drains (and ultimately the holding ponds) to keep road and building access open.

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The cooling towers were experiencing more biofouling than normal, and the plant decreased its usage of the pond water, suspecting that the observed changes in pond water quality were the cause. Therefore, the operator discharged more pond water to the MS4 rather than recycling it.

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Permit

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Routine facility inspections and visual assessments in spring, summer and fall identified oil sheen, poor clarity, and settled solids (primarily grit) in stormwater discharges. Therefore, the MSGP requirement for corrective actions was triggered.

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The four-quarterly annual average discharge water quality in the areas of industrial activity exceeded several benchmark thresholds. Therefore, the MSGP requirement for Additional Implementation Measures was triggered for those benchmark parameters.

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This facility was also subject to effluent limitation guidelines addressing limits on stormwater discharges.

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Annual samples of discharge quality in the areas of industrial activity approached, but did not exceed, these limits.

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Root Cause

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The operator of Site B determined that the critical issue was volume control and proceeded with adapting the SMS.

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Response

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The operator evaluated the areas of non-industrial activity for opportunities to divert stormwater away from the storm drains to prevent flooding. The main employee parking lots and the roads and pavements around the administrative buildings were paved with impervious asphalt and concrete, and the stormwater from these areas was diverted and conveyed by curbs and gutters to the storm drains. The operator constructed infiltration trenches with pea gravel and grass sod around the parking areas and diverted stormwater to the trenches wherever practicable by modifying curbs with cuts, installing culverts, and rerouting small drain pipes. The operator implemented increased maintenance in the areas draining to the trenches to remove litter, grit, and grease, and developed a schedule for trench monitoring and maintenance.

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In the areas of industrial activity, the operator’s primary concern was water quality. A solution was sought to improve the water quality in the stormwater without major equipment or expansion of the existing SMS footprint. In the areas of industrial activity, there was no available area for installing stormwater infiltration basins or trenches. Similarly, the pond capacities could not be increased because there was no available space. The operator identified the area drains where the majority of the stormwater from the areas of industrial activity was collected. At these locations, stormwater inlet controls (catch basins) with sediment pre-filters followed by media filters designed to remove the parameters with effluent limits were installed.

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The operators of Sites A and B followed their MSGP requirements for documentation and follow-up.

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Sites A & B

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Documentation and Follow-up

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The operators for Sites A and B documented the following for the Annual Report:

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Conditions and triggering events requiring corrective actions and Additional Implementation Measures responses (description and date of events documented within 24 hours of discovery)
Description of immediate actions taken to minimize or prevent the discharge of pollutants (description and date of immediate actions documented within 24 hours of discovery)
Descriptions of corrective actions and Additional Implementation Measures responses (documented within 14 days of discovery), including date initiated or expected to initiate and date completed or expected to complete
Updates to site maintenance and good housekeeping practices
Updates to monitoring plans, including new monitoring locations

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The operators updated the SWPPPs to include all changes, included the updates in training materials for future training sessions, and signed and dated new certification statements.

How Can KC Harvey Help You?

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The issues and response actions described in the illustrative examples above are typical of those faced by industrial site operators managing stormwater under an MSGP. These examples also demonstrate the effort required to successfully manage stormwater on industrial sites as weather patterns change in response to climate change. By careful monitoring, problems were identified, and appropriate response actions were taken before permit violations occurred.

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KC Harvey offers field services and consulting services to support all aspects of stormwater management and MSGP compliance on industrial sites. We can assist in developing climate-resilient SMS and support permit compliance in the following ways:

Consulting Services

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Reviewing National Historic Preservation Act and Endangered Species Act requirements to confirm MSGP eligibility
Identifying applicable water quality requirements (including state- and tribe-specific requirements)
Conducting preconstruction site assessments to determine suitable soils and vegetation for post construction stabilization
Recommending optimal erosion control, sediment control, runoff control, and detention measures
Developing the site or larger common plan SWPPP
Developing and submitting the Notice of Intent (NOI) and Notice of Termination (NOT)
Managing monitoring data and preparing and submitting both discharge monitoring reports and annual reports
Troubleshooting SMS performance
Maintaining the SWPPP for permit compliance
Attending and facilitating compliance inspections by permitting authorities

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Field Services

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Providing qualified personnel knowledgeable in principles and practices of industrial stormwater controls
Installing, maintaining, and troubleshooting erosion, runoff, and sediment controls
Monitoring stormwater quality
Construction management prior to interim and final stabilization
Routine inspections
Visual assessments
Implementing all revegetation activities, from site preparation and seed sourcing to monitoring and reporting
Conducting invasive species and noxious weed monitoring and control activities

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