Chapter 6 · Section 6.4 below). Chapter Eleven contains limited design guidance for these secondary practices. 6.3.1 Conventional Practices Conventional or “public-domain” (as

Chapter 6Introduction to Stormwater Treatment Practices

Chapter 6 Introduction to StormwaterTreatment Practices

6.1 Introduction ...................................................................................................6-2

6.2 Primary Stormwater Treatment Practices ..............................................6-2

6.3 Secondary Stormwater Treatment Practices..........................................6-3

6.3.1 Conventional Practices ............................................................6-4

6.3.2 Innovative/Emerging Technologies .........................................6-4

6.4 Stormwater Treatment Train ......................................................................6-8

6.5 Maintenance ...................................................................................................6-8

Volume 1I: Design

2004 Connecticut Stormwater Quality Manual 6-1

2004 Connecticut Stormwater Quality Manual6-2

6.1 Introduction

Stormwater treatment prac-

tices are structural controls

primarily designed to remove

pollutants from stormwater

runoff, but they also can pro-

vide other benefits including

groundwater recharge, peak

runoff attenuation, and stream

channel protection. As

described in Chapter Three of

this Manual, stormwater treat-

ment practices are one

element of a comprehensive

stormwater management

strategy, and should be

selected and designed only

after consideration of effective

site planning/design and

source controls that can

reduce the volume of runoff

and the size and cost of

stormwater treatment.

This chapter introduces stormwater treatment practices that are acceptablefor water quality treatment in Connecticut, either alone or in combinationwith source controls and other treatment practices. The following sectionsdescribe three categories of stormwater treatment practices:

❍ Primary Stormwater Treatment Practices

❍ Secondary Stormwater Treatment Practices

❍ Stormwater Treatment Train

This chapter also provides general information on maintenance considera-tions and performance monitoring for stormwater treatment practices.

6.2 Primary Stormwater Treatment PracticesThe stormwater treatment practices listed in this section, referred to as pri-mary stormwater treatment practices, are capable of providing high levelsof water quality treatment as stand-alone devices. A growing body ofresearch on stormwater treatment practices throughout the United States,as well as field experience in Connecticut and other northeastern states,has demonstrated that these practices are capable of:

❍ Capturing and treating the design water quality volume (WQV) ordesign water quality flow (WQF) (see Chapter Seven)

❍ Removing at least 80 percent of the average annual total suspendedsolids (TSS) load

❍ Removing at least 80 percent of floatable debris, including oil andpetroleum products, for all flow rates up to the design water qualityflow, either alone or in combination with pretreatment

❍ Acceptable performance or operational longevity in the field

(NYDEC, 2001; MDE, 2000). The above performance standards assume thatthese stormwater treatment practices are properly selected, sited, designed,constructed, and maintained in accordance with the guidelines containedin this Manual.

The State of Connecticut has adopted the 80 percent TSS removal goalbased on EPA guidance and its widespread use as a target stormwater qual-ity performance standard. TSS is considered a suitable target pollutantconstituent for a removal standard because of its widespread impact onwater quality and aquatic habitat degradation, because many other pollu-tants including heavy metals, bacteria, and organic chemicals adsorb tosediment particles, and because it has been the most frequently and con-sistently sampled stormwater constituent (MADEP, 1997).

Primary stormwater treatment practices can be grouped into five majorcategories:

Stormwater Ponds: Stormwater ponds maintain either a permanent poolof water or a combination of a permanent pool and extended detention.The permanent pool of water in these systems enhances pollutant removalthrough mechanisms such as sedimentation, biological uptake, microbialbreakdown, gas exchange, volatilization, and decomposition. This categoryof stormwater ponds does not include traditional dry detention ponds ordry flood control basins, which do not provide significant water quality


treatment functions (see the Secondary TreatmentPractices described in this chapter). Treatment prac-tices in this category include:

❍ Wet pond

❍ Micropool extended detention pond

❍ Wet extended detention pond

❍ Multiple pond system

Stormwater Wetlands: Stormwater wetlands are con-structed wetland systems designed to treat pollutedstormwater runoff by several mechanisms, includingsedimentation, adsorption, biological uptake, pho-todegradation, and microbial breakdown. Stormwaterwetlands typically include sediment forebays, shallowand deep pool areas, meandering flow paths, and veg-etative measures to enhance pollutant removal.Stormwater wetlands are engineered specifically forpollutant removal and flood control purposes. Theytypically do not have the full range of ecological func-tions of natural wetlands or wetlands constructed forcompensatory storage or wetland mitigation.Stormwater wetland practices in this category include:

❍ Shallow wetland

❍ Extended detention wetland

❍ Pond/wetland system

Infiltration Practices: Infiltration practices aredesigned to capture, temporarily store, and infiltratestormwater into porous soils. Pollutant removaloccurs through adsorption of pollutants onto soil par-ticles, and subsequent biological and chemicalconversion in the soil. Infiltration practices aid in recharging groundwater but must be carefullydesigned and maintained to prevent clogging and system failure. Infiltration practices in this categoryinclude:

❍ Infiltration trench

❍ Infiltration basin

Filtering Practices: Filtering practices treat stormwa-ter runoff by capturing, temporarily storing, andfiltering stormwater through sand, soil, organic mate-rial, or other porous media. As the water flowsthrough the filter media, sediment particles andattached pollutants, as well as some soluble pollu-tants, are removed through physical straining and

adsorption. Pretreatment is generally required toremove debris and floatables, and prolong the life ofthe filter. Filtering practices in this category include:

❍ Surface sand filter

❍ Underground sand filter

❍ Perimeter sand filter

❍ Bioretention

Water Quality Swales: Water quality swales reducethe velocity of and temporarily store stormwaterrunoff and promote infiltration. Pollutant removalmechanisms in water quality swales are similar toconstructed wetlands and include sedimentation,adsorption, biological uptake, and microbial break-down. These practices differ from conventional grasschannels and ditches that are primarily designed forconveyance, as they provide higher levels of pollutantremoval. Practices in this category include:

❍ Dry swale

❍ Wet swale

The above practices generally have the highestremoval efficiencies for pollutants such as nutrientsand metals, in addition to TSS. Pollutant removal sum-mary data for stormwater treatment practices areincluded in Chapter Eight.

Other stormwater treatment practices not listedabove, such as the secondary treatment practicesdescribed in the following section, may be classifiedas primary practices at the discretion of the localreview authority and/or DEP. In order to be consid-ered a primary stormwater treatment practice, apractice must demonstrate the ability to treat thedesign water quality volume or an equivalent designwater quality flow, meet the 80 percent TSS and float-ables criteria, and have proven operational longevity.It is conceivable that as treatment systems age, theymay lose their effectiveness and may further be con-sidered a pollutant source. The following sectionsdescribe criteria for acceptance of new technologiesas primary treatment practices.

6.3 Secondary StormwaterTreatment Practices

A number of stormwater treatment practices may notbe suitable as stand-alone treatment because theyeither are not capable of meeting the water qualitytreatment performance criteria described in the previ-ous section or have not yet received the thorough

2004 Connecticut Stormwater Quality Manual6- 4

evaluation needed to demonstrate the capabilities formeeting the performance criteria. These practices,termed secondary stormwater treatment practices,generally fall into either of the following categories:

❍ Conventional Practices

❍ Innovative/Emerging Technologies

Table 6-1 summarizes the rationale for the lim-ited use of these practices for water quality control, aswell as applications suitable for their use, such as pre-treatment or use in a treatment train to achievemultiple stormwater management objectives and tosatisfy the design criteria in Chapter Seven (seeSection 6.4 below). Chapter Eleven contains limiteddesign guidance for these secondary practices.

6.3.1 Conventional PracticesConventional or “public-domain” (as opposed to pro-prietary) secondary treatment practices are practicesthat have traditionally been used to provide somewater quality benefits, but that do not provide thesame level of treatment or broad water quality func-tions as primary stormwater treatment practices.Consequently, their application is limited to use aspretreatment or supplemental treatment practices inconjunction with primary practices (i.e., a treatmenttrain), or to achieve other objectives such as ground-water recharge, channel protection, and peak runoffattenuation. Conventional secondary treatment prac-tices addressed in this Manual include:

❍ Dry Detention Ponds

❍ Underground Detention Facilities

❍ Deep Sump Catch Basins

❍ Conventional Oil/Particle Separators

❍ Dry Wells

❍ Permeable Pavement

❍ Vegetated Filter Strips and Level Spreaders

❍ Grass Drainage Channels

6.3.2 Innovative/Emerging TechnologiesThe other category of secondary treatment practicesaddressed in this Manual includes innovative andemerging technologies, which are typically propri-etary systems. Stormwater treatment practices arecontinually evolving in response to advances in treat-ment technology, availability and affordability of new

technology, and recognition of new treatment needs.These innovative and emerging technologies arethose for which preliminary performance data indi-cate that they may provide a valuable stormwatertreatment function. However, unlike the primarystormwater treatment practices described previouslyin this chapter, these technologies have not been eval-uated in sufficient detail to demonstrate provencapabilities for meeting established performance stan-dards, including pollutant removal and field longevity(see Table 6-1).

The following section provides examples ofrecently developed innovative and emerging tech-nologies for stormwater treatment. Chapter Elevenalso provides limited design guidance for these tech-nologies. As secondary treatment practices, innovativeand emerging technologies are suitable for pretreat-ment or for use in a treatment train approach.Emerging technologies generally are also good candi-dates for stormwater retrofits and where land isunavailable for larger systems. Their use as stand-alone treatment devices (i.e., primary treatmentpractices) should be evaluated using consistent andtechnically rigorous protocols. This section describesrecommended criteria for evaluating new or emergingstormwater treatment technologies. New or emergingtechnologies that meet these criteria may be accept-able as primary treatment practices.

Examples of Innovative and EmergingTechnologiesMost innovative or emerging technologies are propri-etary devices developed by various manufacturersand vendors. System designs vary considerably,although most currently available technologies gener-ally can be grouped into one of the followingcategories:

Catch Basin Inserts: As the name implies, catchbasin inserts are placed directly inside of existingcatch basins to remove pollutants from stormwater.Stormwater flows into the catch basin and is treatedas it passes through the structure. The insert consistsof a structure, such as a tray, basket, or bag that typ-ically contains a pollutant removal medium (i.e., filtermedia) and a method for suspending the structure inthe catch basin (Lee, 2001). Although filter media iscommonly used, basket-type inserts constructed ofwire mesh and fabric bag-type inserts are also usedwithout filter media for removing gross particles (i.e.,trash and debris). Although they have the potential toremove total suspended solids, organics, and metals,the removal capabilities depend on the pollutant load-ing characteristics of the stormwater and the choice offilter medium. Because these devices are limited bythe size of the catch basin, there is a relatively shortcontact time between stormwater and the media for

Practice Reasons for Limited Use Suitable Applications

Conventional Practices

Dry Detention Ponds

Catch Basins

Conventional Oil/Particle Separators

Underground DetentionFacilities

Permeable Pavement

Dry Wells

Vegetated Filter Strips

Grass DrainageChannels

Level Spreaders

Catch Basin Inserts

Hydrodynamic Separators

Media Filters

Underground InfiltrationSystems

Alum Injection

Advanced Treatment

❍ Not intended for water quality treatment. Designed toempty out between storms; lack the permanent pool orextended detention required for adequate stormwatertreatment

❍ Settled particulates can be resuspended between storms

❍ Limited pollutant removal❍ No volume control❍ Resuspension of settled particulates

❍ Limited pollutant removal❍ No volume control❍ Resuspension of settled particulates

❍ Not intended for water quality treatment❍ Particulates can be resuspended between storms

❍ Reduced performance in cold climates due to cloggingby road sand and salt

❍ Porous asphalt or concrete recommended for limiteduse in Connecticut

❍ Not intended as stand-alone stormwater runoff qualityor quantity control

❍ Potential for clogging/failure❍ Applicable to small drainage areas❍ Potential groundwater quality impacts

❍ Typically, cannot alone achieve the 80% TSS removal goal



❍ Limited performance data available❍ High maintenance and susceptible to clogging

❍ Limited performance data available❍ Performance varies with flow rate

❍ Limited performance data available

❍ Limited performance data available

❍ Requires ongoing operation and monitoring❍ Limited performance data available❍ Potential for negative impacts to downstream receiving

waters

❍ Requires ongoing operation and monitoring❍ High cost and level of complexity❍ Limited performance data available

❍ Flood control and channel protection

❍ Pretreatment or in combination with other stormwater treatment practices

❍ Stormwater retrofits

❍ Pretreatment or in combination with other stormwater treatment practices

❍ Highly impervious areas with substantial vehicle traffic

❍ Flood control and channel protection❍ Space-limited or ultra-urban sites

❍ Modular concrete paving blocks, modular concrete or plasticlattice, or cast-in-place concrete grids are suitable for use inspillover parking, parking aisles, residential driveways, and roadside rights-of-way

❍ Infiltration of clean rooftop runoff❍ Stormwater retrofits❍ Space-limited ultra-urban❍ Pretreatment or in combination with other stormwater

treatment practices

❍ Pretreatment or in combination with other treatment practices❍ Limited groundwater recharge❍ Outer zone of a stream buffer❍ Residential applications and parking lots

❍ Part of runoff conveyance system to provide pretreatment

❍ Replace curb and gutter drainage❍ Limited groundwater recharge

❍ Pretreatment or in combination with other treatment practices❍ Use with filter strips and at outlets of other treatment practices

to distribute flow❍ Groundwater recharge

❍ Stormwater retrofits, ultra-urban sites❍ Small drainage areas without excessive solids loadings❍ Pretreatment or in combination with other treatment practices

❍ Pretreatment or in combination with other treatment practices❍ Stormwater retrofits, ultra-urban sites

❍ Pretreatment or in combination with other treatment practices❍ Stormwater retrofits, ultra-urban sites

❍ Groundwater recharge❍ Stormwater retrofits

❍ Stormwater retrofits, ultra-urban sites❍ Pretreatment or in combination with other treatment practices

❍ Only as required, where other primary or secondary practicesare insufficient

Table 6-1 Summary of Secondary Stormwater Treatment Practices


Innovative/Emerging Technologies


pollutant removal and little storage area for thematerial that is removed. Consequently, frequentmaintenance is typically required to avoid clogging ofthe insert and there is the possibility of re-suspensionof filtered pollutants (Washington, 2000).

Hydrodynamic Separators: This group of stormwa-ter treatment technologies is designed to remove largeparticle total suspended solids and large oil droplets.They consist primarily of cylindrical-shaped devicesthat are designed to fit in or adjacent to existingstormwater drainage systems (Washington, 2000). Themost common mechanism used in these devices isvortex-enhanced sedimentation, also called swirl con-centration. In these structures, often called swirlconcentrators, stormwater enters as tangential inletflow into the side of the cylindrical structure. As thestormwater spirals through the chamber, the swirlingmotion causes the sediments to settle by gravity,removing them from the stormwater (EPA, 2002).Some devices also have compartments or chambers totrap oil and other floatables.

Although swirl concentration is the technologyemployed by most hydrodynamic separators, somesystems use circular screening systems or engi-neered cylindrical sedimentation. Circular screenedsystems use a combination of screens, baffles, andinlet and outlet structures to remove debris, largeparticle total suspended solids, and large oildroplets. Structures using engineered cylindricalsedimentation use an arrangement of internal baf-fles and an oil and sediment storage compartment.Other proprietary technologies incorporate an inter-nal high flow bypass with a baffle system in arectangular structure to simulate plug flow opera-tion. When properly engineered and tested, thesesystems can also be an improvement over conven-tional oil/particle separators and offer removalefficiencies similar to swirl chamber technologies.Absorbent materials can also be added to thesestructures to increase removal efficiency of oil andhydrocarbons (Washington, 2000).

Media Filters: In this type of treatment practice,media is placed within filter cartridges that are typi-cally enclosed in concrete vaults. Stormwater ispassed through the media, which traps particulatesand/or soluble pollutants. Various materials can beused as filter media including pleated fabric, activatedcharcoal, perlite, amended sand and perlite mixes,and zeolite. Selection of filter media is a function ofthe pollutants targeted for removal. Pretreatment priorto the filter media is typically necessary for stormwa-ter with high total suspended solids, hydrocarbon,and debris loadings that may cause clogging and pre-mature filter failure (Washington, 2000).

Underground Infiltration Systems: Various typesof underground infiltration structures, such as pre-manufactured pipes, vaults, and modular structures,have been developed as alternatives to infiltrationtrenches and basins for space-limited sites andstormwater retrofit applications. Similar to traditionalinfiltration trenches and basins, these systems aredesigned to capture, temporarily store, and infiltratethe design water quality volume over several days.Performance of underground infiltration structuresvaries by manufacturer and system design. These sys-tems are currently considered secondary treatmentpractices due to limited field performance data,although pollutant removal efficiency is anticipated tobe similar to that of infiltration trenches and basins.

Advanced Treatment: The pollutant removal tech-niques utilized in drinking water treatment processesare potential advanced treatment options forstormwater (Lee, 2001). Alum has been used exten-sively as a coagulant in pond and lake managementapplications. Alum injection has also been used morerecently in stormwater applications for reducing con-centrations of fine sediment and phosphorus instormwater discharges to eutrophic water bodies.Water-soluble anionic polyacrylamide (PAM) has alsobeen used as a coagulant in drinking water treatmentand pond dredging operations to enhance settling ofsolids. PAM has also been land applied as an erosionand sedimentation control measure. Recently, the useof PAM in pre-formed shapes such as logs in ditchesor open swales has been introduced to enhanceremoval of fine sediment in stormwater runoff.However, the practicability of methods such as ionexchange, reverse osmosis, disinfection, and ultrafil-tration is undocumented for stormwater treatment.The success of these methods in drinking water treat-ment suggests that they may have potentialapplications in areas where conventional stormwatertreatment methods are unable to meet stringentstormwater quality standards or established wasteload allocations. However, these technologies arebeyond the scope of this Manual.

Criteria for Evaluating New PracticesNew and emerging stormwater treatment practicesmay be acceptable as primary treatment practices ifthey demonstrate the ability to achieve treatmentresults consistent with the primary treatment practicesdescribed at the beginning of this chapter, specifically:

❍ Capture and treatment of the design water qual-ity volume (WQV) or design water quality flow(WQF)


❍ Removal of at least 80 percent of the averageannual total suspended solids (TSS) load

❍ Removing at least 80 percent of floatable debris,including oil and petroleum products, for allflow rates up to the design water quality flow(WQF), either alone or in combination with pre-treatment

❍ Acceptable performance or operational longevityin the field

❍ Automatic operation during runoff events (i.e.,no need for manual activation)

These capabilities must be demonstrated throughfield and laboratory testing. Independent validation ofdata that support specific treatment technology per-formance claims is recommended. Field performancedata should come from field studies conducted undera variety of conditions (e.g., flow rates, contaminantloadings, antecedent moisture conditions, rainfall dis-tribution, land use, percent imperviousness,maintenance intervals) (TARP, 2001). Ideally, the fieldstudies should be conducted over a one-year demon-stration period, including cold weather and winterconditions, to capture possible seasonal variations inperformance and performance variations as a functionof rainfall intensity.

Field data is valuable for verifying performanceunder actual field conditions. However, the variabilityof site conditions leads to site-specific performancevalidation that may be difficult to develop into sizingmethodologies. It is recommended that laboratorytesting be conducted to establish performance curvesfor technologies over the full operating range of thesystem. Performance curves based on laboratory datafor various technologies, developed using the sametest criteria, applied to the same rainfall and TSSremoval model, enable direct comparison betweentechnologies. Laboratory testing must be conducted inaccordance with an established protocol for knownparticle sizes in known concentrations. The MaineDepartment of Environmental Protection has estab-lished one such protocol for comparing innovativetechnologies.

Performance claim data sets should be collectedunder a Quality Assurance Project Plan (QAPP) toensure that the data sets meet data quality objectivesand are defensible, and should include flow rates, res-idence times, and rainfall intensity data with which tointerpret these claims. USEPA provides guidance onthe development and minimum requirements for aQAPP. (See USEPA references at the end of this chap-ter.) Standardized test methods and procedures mustbe used in the collection of data. For example, ASTMmethods for flow measurement methods, ASCE

hydraulic flow estimation methods, and EPA testmethods for water quality analysis are typical stan-dardized test methods. (See TARP (2001)) for a listingof standardized methods for flow and water con-stituent analysis).

It is recommended that stormwater quality databe collected in accordance with guidance outlined inthe Technology Acceptance and ReciprocityPartnership (TARP) Stormwater BMP DemonstrationProtocol (2001). The TARP Stormwater BMPDemonstration Protocol has been endorsed by thestates of Massachusetts, New York, New Jersey,Illinois, California, Maryland, Pennsylvania, Texas andVirginia to provide a uniform method for demonstrat-ing stormwater technologies and developing testquality assurance plans for certification or verificationof performance claims. Treatment efficiencies shouldbe calculated using methods outlined in the joint EPAand ASCE technical memorandum DeterminingUrban Stormwater Best Management Practice (BMP)Removal Efficiencies (URS Greiner Woodward Clydeet al., 1999). In addition, to demonstrate that the per-formance claims are reliable, significant, and withinconfidence limits, statistical evaluation of the datamust be performed and made available. Performanceclaims should be given with appropriate confidenceintervals (i.e., removal rate of 85% ± 5% at a 95% con-fidence interval). The EPA Data Quality AssessmentGuidance Manual (EPA, 1998) provides informationon statistical methods for comparison and validationof data sets.

In addition to performance claims and validation,the following specifications for the treatment technol-ogy should be provided:

❍ Description of the underlying scientific andengineering principles

❍ Standard drawings, including a process flowdiagram

❍ Minimum siting and design specifications neces-sary to achieve the stated performance

❍ The full range of operating conditions for thetechnology, including minimum, maximum,and optimal conditions to meet the stated per-formance claims (flow rate, residence time,rainfall intensity, etc.)

❍ Minimum maintenance requirements to sustainthe stated performance

❍ Description of hydraulics and system sizing tomeet the performance claims

❍ Discussion of any pretreatment required to meetthe stated performance claims

2004 Connecticut Stormwater Quality Manual6- 8

❍ Identification of any special licensing or haulingrequirements, safety issues or access require-ments associated with installation and/oroperation and maintenance

❍ Discussion of the generation, handling, removaland disposal of any discharges, emissions, or otherwaste byproducts of the treatment technology

(TARP, 2001). Evaluation protocols and methods sim-ilar to those of the TARP Stormwater BMPDemonstration Protocol have also been developedthrough EPA’s Environmental Technology Verification(ETV) program. With funding from the ETV program,the Civil Engineering Research Foundation estab-lished the Environmental Technology EvaluationCenter (EvTEC), an independent, non-profit verifica-tion center that evaluates environmental technologies.EvTEC is collaborating with the Washington StateDepartment of Transportation to verify performanceof innovative stormwater treatment practices underfield operating conditions. These evaluations areexpected to provide comparable, peer-reviewed per-formance data on these systems (CERF, 2002).

EPA and NSF International, an independent, non-profit testing organization, have developed a testingprotocol under the ETV program to determine the via-bility of runoff treatment technologies and other wetweather flow controls, including urban runoff, com-bined sewer overflows (CSO), and sanitary seweroverflows (SSO). Participants in the study include ven-dors who want to demonstrate the effectiveness oftheir technologies. Results of the pilot will be useful toa variety of stakeholders including municipalities, busi-nesses, vendors, consulting engineers, and regulatoryagencies. Once verification reports have been com-pleted, vendors may use the results in their marketingefforts. Results will be made publicly available throughEPA’s and NSF’s Web sites at http://www.epa.gov/etvand http://www.nsf.org/etv, respectively.

6.4 Stormwater Treatment TrainStormwater treatment practices can be combined inseries to enhance pollutant removal or achieve multi-ple stormwater objectives. The use of a series oftreatment practices, as well as site planning tech-niques and source controls, is referred to as“stormwater treatment trains”. The use of a treatmenttrain approach can:

❍ Increase the level and reliability of pollutantremoval

❍ Accomplish multiple stormwater managementobjectives (pollutant removal, groundwaterrecharge, channel protection, peak runoffattenuation, etc.)

❍ Increase the lifespan of treatment devices bydistributing pollutant removal over multiplepractices or controls

❍ Reduce the potential for resuspension of sedi-ment by reducing flow velocities and increasingflow paths

❍ Allow the use of a wider array of treatmentpractices, including supplemental practices forpretreatment

A treatment train may consist of the followingtypes of practices in series to satisfy the design crite-ria in Chapter Seven:

❍ Multiple primary treatment practices

❍ A combination of primary and secondary treat-ment practices

❍ Multiple secondary treatment practices (at thediscretion of the review authority)

The use of multiple stormwater treatment prac-tices increases the maintenance required topreserve the overall effectiveness of the system. Ingeneral, the least expensive and most easily main-tained components should be placed at the mostupstream point in the treatment train to reduce themaintenance requirements of the downstream com-ponents (Metropolitan Council, 2001). Theindividual treatment practice descriptions inChapter Eleven include guidance on routine andnon-routine maintenance.

6.5 MaintenanceStormwater treatment practices require regularmaintenance to perform successfully. Failure toperform adequate maintenance can lead to reduc-tions in pollutant removal efficiency or actuallyincrease pollutant loadings and aggravate down-stream impacts. Stormwater treatment practicesshould be routinely inspected and maintainedfollowing construction to ensure that the controlsare in proper working condition and operating asdesigned. General maintenance guidelines forstormwater treatment practices are summarizedbelow. Chapter Eleven contains recommendedmaintenance for specific stormwater treatmentpractices. Appendix E contains maintenanceinspection checklists for specific stormwatertreatment practices. Additional information onmaintenance of stormwater treatment practicescan be found in the documents listed at the end ofthis chapter.


General maintenance requirements for stormwa-ter treatment practices include:

Inspections: Inspections should be performed atregular intervals to ensure proper operation ofstormwater treatment practices. Inspections shouldbe conducted at least annually, with additionalinspections following large storms. Inspectionsshould include a comprehensive visual check forevidence of the following (not all items apply toevery treatment practice):

❍ Accumulation of sediment or debris at inlet andoutlet structures

❍ Erosion, settlement, or slope failure

❍ Clogging or buildup of fines on infiltration surfaces

❍ Vegetative stress and appropriate water levels foremergent vegetation

❍ Algae growth, stagnant pools, or noxious odors

❍ Deterioration of pipes or conduits

❍ Seepage at the toe of ponds or wetlands

❍ Deterioration or sedimentation in downstreamchannels and energy dissipators

❍ Evidence of vandalism

❍ Evidence of structural damage by beavers,muskrats, and other wildlife

Routine Maintenance: Routine maintenance shouldbe performed on a regular basis to maintain properoperation and aesthetics. Routine maintenance shouldinclude:

❍ Debris and litter removal

❍ Silt and sediment removal

❍ Terrestrial vegetation maintenance

❍ Aquatic vegetation maintenance

❍ Maintenance of mechanical components (valves,gates, access hatches, locks)

Non-routine Maintenance: Non-routine mainte-nance refers to corrective measures taken to repair orrehabilitate stormwater controls to proper workingcondition. Non-routine maintenance is performed asneeded, typically in response to problems detectedduring routine maintenance and inspections,and can include:

❍ Erosion and structural repair

❍ Sediment removal and disposal

❍ Nuisance control (odors, mosquitoes, weeds,excessive litter)

Stormwater treatment practice operation andmaintenance requirements are an integral part of asite stormwater management plan (see ChapterNine). These requirements should include, at a min-imum, detailed inspection and maintenance tasks,schedules, responsible parties, and financing provi-sions. The owner typically maintains stormwatertreatment practices at commercial, industrial, andrental residential developments. These facilities gen-erally have staff dedicated to maintenance activitiesor contract for such services. Maintenance of non-rental residential installations is typically performedby private landowners or property/homeownersassociations, which in many cases do not have thetechnical expertise, resources, or funds to inspectand maintain their stormwater systems. In somecases, local government may accept responsibilityfor inspecting and maintaining stormwater treatmentpractices. Local governments should require legallybinding maintenance agreements for stormwatertreatment practices to clearly delineate maintenanceresponsibilities. Potential funding mechanismsinclude general tax revenues, stormwater utility fees,inspection or permit fees, and dedicated funds fromland developers. Public education is critical for thesuccess of any stormwater financing program.

Many municipalities consider stormwater treat-ment practices such as ponds, wetlands, and other“wet” treatment systems as regulated wetland areas,and therefore subject to local inland wetlands andwatercourses regulations. Sediment removal andother common maintenance activities may requireapproval from the local Inland Wetlands andWatercourses Commission, which presents a poten-tial regulatory hurdle to consistent maintenance. Tofacilitate this approval process, municipalities couldissue up to a five-year maintenance permit in con-junction with the primary Inland Wetlands andWatercourses permit for the development or rede-velopment project. The permit holder would beresponsible for renewing or requesting reissuance ofthe maintenance permit at five-year intervals.Municipalities should identify all such stormwatermanagement facilities for which they are responsibleand issue a five-year renewable maintenance permit.This type of an approach is analogous to DEP’srenewable five-year maintenance permits issued toDOT and other state-regulated entities for statewidedrainage maintenance activities.


6.6 Performance MonitoringCurrently, there are very limited performance data forstormwater treatment practices in the State ofConnecticut. Performance data from the majority ofprevious monitoring studies conducted throughoutthe United States are limited by differences in design,performance goals, site parameters, storm events,flow and pollutant loadings, seasonal variations, mon-itoring methods, efficiency calculation methods orsimply by the lack of or inadequacy of information.Several major initiatives are underway nationally toprovide a more useful set of data on the effectivenessof individual stormwater treatment practices, and tobetter understand the relationship between treatmentpractice design and performance. These include:

❍ The Center for Watershed Protection’s NationalPollutant Removal Performance Database(Winer, 2000)

❍ The American Society of Civil Engineers (ASCE)National Stormwater Best Management Practices(BMP) Database (Urban Water ResourcesResearch Council of ASCE and Wright WaterEngineers, Inc., 2001)

❍ Water Environment Research Foundation(WERF) Critical Assessment of StormwaterControl (BMP) Selection Issues (WERF, inprogress)

These databases contain the results of perform-ance studies for individual stormwater treatmentpractices throughout the United States. While theyprovide a starting point for pollutant removal esti-mates, the usefulness of the data is still extremelylimited for many of the reasons stated above. Thereliability of the data will continue to increase as theresults from additional studies are added.

Very few performance monitoring studies havebeen performed in Connecticut or elsewhere in NewEngland. Performance monitoring is recommendedfor new and existing stormwater treatment practicesin Connecticut to develop a representative and reli-able performance database that is specific to the Stateof Connecticut. Performance monitoring is designedto provide information on the following issues:

❍ What degree of pollution control does the treat-ment practice provide under typical operatingconditions?

❍ How does efficiency vary from pollutant to pollutant?

❍ How does efficiency vary with various input concentrations?

❍ How does efficiency vary with storm characteris-tics such as rainfall amount, rainfall density,antecedent weather conditions?

❍ How do design variables affect performance?

❍ How does efficiency vary with different opera-tional and/or maintenance approaches?

❍ Does efficiency improve, decay, or remain thestable over time?

❍ How does the system’s efficiency, performance,and effectiveness compare relative to otherstormwater treatment practices?

❍ Does the treatment practice reduce toxicity toacceptable levels?

❍ Does the treatment practice cause an improvementor protect in downstream biotic communities?

❍ Does the treatment practice have potential down-stream negative impacts?

(URS Greiner Woodward Clyde et al., 1999).Standardized test methods and procedures should beused for stormwater performance monitoring stud-ies. Performance monitoring should be consistentwith the methods and protocols described previ-ously in this chapter for evaluating new stormwatertreatment technologies and the guidance documentsreferenced therein.


Additional Information Sources

Technology Acceptance and Reciprocity Partnership(TARP), Pennsylvania Department of EnvironmentalProtection,URL: http://www.dep.state.pa.us/dep/deputate/pollprev/techservices/tarp/index.htm.

Water Environment Federation (WEF) and AmericanSociety of Civil Engineers (ASCE). 1998. UrbanRunoff Quality Management (WEF Manual ofPractice No. 23 and ASCE Manual and Report onEngineering Practice No. 87).

Watershed Management Institute, Inc. 1997.Operation, Maintenance, and Management ofStormwater Management Systems. In cooperationwith U.S. Environmental Protection Agency, Office ofWater. Washington, D.C.

United States Environmental Protection Agency (EPA).2001. Environmental Technology Verification (ETV)Program. URL: http://www.epa.gov/etv.NSF International. 2001. Verification Program to testEffectiveness of Wet Weather Flow Technologies. URL: http://www.nsf.org/etv.

References

Civil Engineering Research Foundation (CERF). 2002.Stormwater Best Management Practices (BMP)Verification Program. Fact Sheet Updated February2002. Environmental Technology Evaluation Center(EvTEC) website.URL: http://www.cerf.org/evtec/eval/wsdot2.htm.

Maryland Department of the Environment (MDE). 2000.2000 Maryland Stormwater Design Manual, Volumes Iand II. Baltimore, Maryland. Prepared by Center forWatershed Protection, Ellicott City, Maryland.

Massachusetts Department of EnvironmentalProtection (MADEP) and the Massachusetts Office ofCoastal Zone Management. 1997. StormwaterManagement, Volume Two: Stormwater TechnicalHandbook, Boston, Massachusetts.

Metropolitan Council. 2001. Minnesota Urban SmallSites BMP Manual: Stormwater Best ManagementPractices for Cold Climates. Prepared by BarrEngineering Company, St. Paul, Minnesota.

New York State Department of EnvironmentalConservation (NYDEC). 2001. New York StateStormwater Management Design Manual. Prepared byCenter for Watershed Protection. Albany, New York.

Technology Acceptance and Reciprocity Partnership.2001. Stormwater Best Management PracticeDemonstration Tier II Protocol for InterstateReciprocity Endorsed by California, Massachusetts,New Jersey, Pennsylvania, and Virginia.

United States Environmental Protection Agency(EPA). 1992. NPDES Stormwater Sampling GuidanceDocument. EPA/833-B-92-001. Washington, D.C.

United States Environmental Protection Agency(EPA). 1998a. Data Quality Assessment GuidanceManual. (QA/G-9) EPA/600/R-96/084. Washington, D.C.

United States Environmental Protection Agency(EPA). 1998b. Guidance for Quality AssuranceProject Plans. (QA/G-5) EPA/600/R-98/018.Washington, D.C.

United States Environmental Protection Agency(EPA). 2001. EPA Requirements for QualityAssurance Project Plans. (QA/R-5) EPA/240/B-01/003. Washington, D.C.

United States Environmental Protection Agency(EPA). 2002. National Menu of Best ManagementPractices for Stormwater Phase II. URL:http://www.epa.gov/npdes/menuofbmps/menu.htm,Last Modified January 24, 2002.

Urban Water Resources Research Council of theAmerican Society of Civil Engineers (ASCE) andWright Water Engineers, Inc. 2001. NationalStormwater Best Management Practices (BMP)Database.

URS Greiner Woodward Clyde, Urban Waterresources Research Council of the American Societyof Civil Engineers, U.S. Environmental ProtectionAgency. 1999. Development of PerformanceMeasures, Task 3.1 – Technical Memorandum,Determining Urban Stormwater Best ManagementPractice (BMP) Removal Efficiencies.

Washington State Department of Ecology(Washington). 2000. Stormwater ManagementManual for Western Washington, Final Draft,Olympia, Washington.

Winer, R. 2000. National Pollutant RemovalDatabase for Stormwater Treatment Practices, 2ndEdition. Center for Watershed Protection. EllicottCity, Maryland.

Documents

Chapter 6 · Section 6.4 below). Chapter Eleven contains limited design guidance for these secondary practices. 6.3.1 Conventional Practices Conventional or “public-domain” (as