Green Parking Lot Resource Guide
TABLE OF CONTENTSINTRODUCTION ............................................................................... 1CHAPTER 1: ...
CHAPTER 6: LANDSCAPING                                            AND IRRIGATION .................................... 35Ov...
INTRODUCTIONG                                                   ■	“           reen” parking lot is a term increas­        ...
CHAPTER 1IMPACTS         OF    PARKING LOTSP        arking lots are a ubiquitous feature        high rate and volume, nega...
Water Supply Impacts                             ide (CO), volatile organic compound (VOCs),                              ...
combined with stormwater runoff from the             fauna. The velocity and volume of runoff fromparking lot also affects su...
management of greenspace is essential to            ing walking and bicycling, and encouragesachieving and maintaining sus...
ings due to the hotter air temperatures (a          Distributional Issuescost to the building owner and potentially to    ...
CHAPTER 2“GREEN” PARKING LOT TECHNIQUESI    nnovative approaches to planning and           of transport, through company s...
traffic interaction, thus making for a morepedestrian-accessible area. These practicesaim to improve the character of the de...
PARKING SURFACE MATERIAL                            economical for developers than incurringSELECTION                     ...
CHAPTER 3PLANNING ASPECTSP          arking lot design and parking avail­      quantity of spaces in a parking lot. It is t...
municipalities regulate the minimum number           City of San Francisco, where city plannersof parking spaces, they typ...
setting limits on the total amount of park­        stalls to achieve the greatest car capacity,   ing spaces allowed in a ...
rear of a building, increasing the intercon-      States, and promoting sustainable land use nectedness between pedestrian...
CHAPTER 4STORMWATER MANAGEMENTA          pivotal component of green park­         project alone can be minimal, but multip...
through effective rainfall retention, pollutant     ter runoff, and often are incorporated toremoval, and water infiltration....
(i.e., up to 48 hours). They are effective           and filled with stone to form a subsurface  at treating certain runoff c...
determine those useful for specific site condi­    source of pollutants in parking lot runoff, in­tions. Considerations shou...
EXHIBIT 1: BMP EFFECTIVENESS                                       Typical Pollutant Removal Efficiency (percentage)        ...
high aesthetic value. Developers may also       protect the health of waterbodies, but alsogain from local government ince...
CASE STUDY 1: STORMWATER BEST MANAGEMENT PRACTICES (BMP)BLOEDEL DONOVAN PARK, BELLINGHAM, WASHINGTON54Stormwater runoff in ...
COST AND POLLUTANTS REMOVAL                         in-ground storage and treatment stormwa­EFFECTIVENESS                 ...
CHAPTER 5ALTERNATIVE PARKING SURFACE MATERIALST        he majority of parking lots are made         Permeable pavements pr...
that water does not rise to the pavement          significant downstream benefits.66 Althoughlevel. Stormwater settles in th...
ally infiltrates over time into the subgrade        last 15 to 20 years, a length similar to con­soils. In addition to stor...
ment can be used in soils with low porosity       that if properly installed, success rates for aif a discharge pipe is in...
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
Green Parking Lot Resource Guide
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Green Parking Lot Resource Guide

  1. 1. Green Parking Lot Resource Guide
  2. 2. TABLE OF CONTENTSINTRODUCTION ............................................................................... 1CHAPTER 1: IMPACTS OF PARKING LOTS ........................................... 2Environmental Impacts of Parking Lots .....................................................................................................2 Costs of Parking Lots.......................................................................................................................................5CHAPTER 2: “GREEN” PARKING LOT TECHNIQUES............................. 7Planning Aspects .............................................................................................................................................7On-Site Stormwater Management ..............................................................................................................8Parking Surface Material Selection .............................................................................................................9 Landscaping and Irrigation ...........................................................................................................................9 CHAPTER 3: PLANNING ASPECTS ..................................................... 10Municipal Parking Requirements ............................................................................................................. 10Parking Lot Placement and Aesthetics.................................................................................................... 12Linking Parking to Smart Growth ............................................................................................................. 13CHAPTER 4: STORMWATER MANAGEMENT....................................... 14Green Parking Lot Stormwater Management Techniques ................................................................. 14BMP Pollutant Removal and Effectiveness ............................................................................................. 17BMP Cost Considerations............................................................................................................................ 18 Case Study 1: Stormwater Best Management (BMP) —Bloedel Donovan Park, Bellingham, Washington .................................................................. 20CHAPTER 5: ALTERNATIVE PARKING SURFACE MATERIALS ............... 22Porous Pavement .......................................................................................................................................... 22Alternative Pavers ......................................................................................................................................... 23Design and Installation Considerations .................................................................................................. 24Maintenance of Permeable Pavement .................................................................................................... 25Infiltration & Pollutant Removal Effectiveness of Permeable Pavements ...................................... 27Cost Considerations ..................................................................................................................................... 29 Case Study 2: Parking Surface Alternatives—Heifer International, Little Rock, Arkansas 31 Case Study 3: Parking Surface Alternatives—University of Rhode Island, Kingston, Rhode Island ........................................................................................................................................ 33 Green Parking Lot Resource Guide—February 2008 i
  3. 3. CHAPTER 6: LANDSCAPING AND IRRIGATION .................................... 35Overview of Natural Landscaping and Irrigation ................................................................................. 35 Environmental Benefits of Using Natural Landscaping and Associated Irrigation ...................... 38Cost Effectiveness of Using Natural Landscaping ................................................................................ 40 Case Study 4: Landscaping and Irrigation—Heifer International, Little Rock, Arkansas .. 42CHAPTER 7: REDUCED INFRASTRUCTURE BURDEN ............................. 44Regional Stormwater and Wastewater Impacts.................................................................................... 45Cost Effectiveness ......................................................................................................................................... 45 Case Study 5: Reduced Infrastructure Burden —Green Streets Program, Portland, Oregon ............................................................................... 47KEY RESOURCES .................................................................................... 49United StatesEnvironmental Protection AgencyOffice of Solid Waste and Emergenc Response (5101T)EPA-510-B-08-001February 2008http://epa.gov/oswer/iwg/Recycled/Recyclable—Printed with vegetable oil based inks on 100% postconsumer,process chlorine free recycled paper. Table of Contents ii
  4. 4. INTRODUCTIONG ■ “ reen” parking lot is a term increas­ Chapter 2 provides an overview of the ingly used to describe parking lots benefits of green parking lot development that may incorporate a variety of techniques, briefly describing major plan­environmentally preferable features, includ­ ning, design, and material considerations.ing a minimized footprint and/or impervi­ ■ Chapters 3 through 6 provide detailedous surfaces, stormwater best management information on specific elements of sus­practices (BMPs), and alternative parking tainable parking lot approaches includingsurface materials. To date, however, informa­ planning and design approaches (Chaptertion on green parking lots has been scattered 3), sustainable stormwater managementacross planning, construction, stormwater, techniques (Chapter 4), alternatives toengineering, and landscaping resources. The asphalt parking surfaces (Chapter 5), andgoal of this resource guide is to present the water efficient landscaping and irrigationfundamental planning and design concepts (Chapter 6).of a green parking lot and connect readers toexisting resources on the environmental ben­ ■ Chapter 7 discusses how green parkingefits and cost effectiveness of green parking lots can help municipalities reduce futureapproaches. This document is expected to be stormwater infrastructure and utilityparticularly useful for local government of­ maintenance costs.ficials involved in planning and development Case studies are included throughout theactivities, as well as construction industry guide to provide real world examples ofprofessionals (developers, project managers, green parking lot techniques.facility managers and other decision makers)interested in green parking lot technologies. Key resources consulted in developing this guide are listed in the back of the document.The guide is organized into seven chapters:■ Chapter 1 describes the environmental and cost impacts associated with conven­ tional parking lots. Green Parking Lot Resource Guide—February 2008 1
  5. 5. CHAPTER 1IMPACTS OF PARKING LOTSP arking lots are a ubiquitous feature high rate and volume, negatively impacting of the American landscape. Perhaps the surrounding ecosystem. Hence, parking because they are so commonplace, lots degrade water quality, strain stormwa­the significant environmental and cost im­ ter management systems, consume largepacts associated with parking lots are often amounts of land and resources, and enableoverlooked. In this chapter, we provide an urban sprawl. Furthermore, materials usedoverview of these impacts. to construct parking lots have a variety of impacts on air, water, and biodiversityENVIRONMENTAL IMPACTS OF throughout their life cycle. Some of the majorPARKING LOTS environmental impacts of traditional parkingThe prevailing low-density American devel­ lots are described below.opment pattern (i.e., urban sprawl) necessi­ Water Quality Impactstates reliance on automobiles, along with theconstruction of parking lots to accommodate, Parking lot runoff is a major contributor toand many times overaccomodate, demand non-point source pollution of our waterways.for parking. As parking lots have become a Conventional parking lots quickly movedominant feature of urban and suburban stormwater into receiving water bodies. Aslandscapes, their environmental impacts it flows across pavement, the water picks uphave also become increasingly apparent. pollutants from the surface. This results in large volumes of polluted runoff enteringMost parking lots are made of pavement—a surface water and groundwater resources,combination of asphalt concrete, the most negatively affecting water quality.widely used paving material in the UnitedStates, and aggregates such as sand, gravel, Contaminants in parking lot runoff canor crushed stone. Pavement is an impervi­ originate from a variety of sources, includ­ous, heat absorbing material that collects ing the paving materials used to build them.stormwater on its surface and does not allow Recently, the U.S. Geological Survey (USGS)it to filter into the soil, inhibiting the natural pinpointed parking lot sealants as a signifi­water cycle. With this in mind, parking lots cant source of non-point source pollution,have traditionally been built with the primary specifically polycyclic aromatic hydrocarbonsgoal of channeling stormwater into receiving (PAHs), a known carcinogen that can be toxicwater bodies as quickly as possible, via means to fish and wildlife.1 Automobiles are also asuch as gutters, drains, and pipes. As a result, major source of pollutants in parking lot run­runoff that is contaminated with many types off, including antifreeze, oil, hydrocarbons,of petroleum residues, fertilizers, pesticides, metals from wearing brake linings, rubberand other pollutants from parking surfaces particles from tires, nitrous oxide from carenters receiving waters at an unnaturally exhausts, and grease. CHAPTER 1—Impacts of Parking Lots 2
  6. 6. Water Supply Impacts ide (CO), volatile organic compound (VOCs), polycyclic aromatic hydrocarbons (PAHs), andConventional parking lots consist of large ar­ carbon dioxide (CO2) during the manufactur­eas of impervious surfaces that do not permit ing process. The activities associated withthe infiltration of water into the soil. Unlike the construction and maintenance of park­natural conditions where rainwater filters ing lots also generate emissions, typically ininto the ground, impervious surfaces halt the form of dust, fumes, and equipment andthis process, inhibiting a watershed’s natural vehicle exhaust. For example, the use of hothydrological cycle and preventing ground­ mix asphalt, a common process where thewater recharge. As a result, water tables are asphalt is heated to extremely high tempera­lowered, reducing streamflow during dry tures prior to application, can cause healthperiods, depleting water supplies, and exac­ problems for workers including headache,erbating the negative impacts of droughts. skin rash, fatigue, throat and eye irritation,Stormwater Management breathing problems, and coughing. DieselImpacts emissions from on-site equipment can also cause similar health effects.2 In addition, theAccording to the USGS, an impervious, typical after effects of parking lot construc­man-made surface will generate two to six tion, such as fewer trees and less vegetationtimes more runoff than a natural surface. In due to clearing, as well as heat island effectaddition to the direct impact of paving, con­ (see below), also lead to higher amounts ofventional parking lots also typically include CO2 in the air.pipes, curbing, gutters, and drains to helpspeed water off of parking surfaces. These Heat Island Effectsystems cause runoff to move even faster Heat island effect (HIE) occurs in urban areasdownstream, increasing the risk of stream where materials that have heat-absorbingflooding. Sewer systems often become over­ properties, such as asphalt, are prevalent.whelmed by the rapid runoff of stormwater, In urban areas, the combined effect of suchcausing them to overflow and, in the case of surfaces can cause a change in the energycombined sewer and stormwater systems, (temperature) balance, leading to hotter airdischarge raw sewage into receiving water­ and surface temperatures. Recent researchways. In addition to the human health risks indicates that urban areas are 2 to 8ºF hotterrelated to combined sewer overflows, these in summer due to this increased absorbeddischarges can cause algal blooms to form, heat.3depleting aquatic oxygen levels and alteringa waterbody’s habitat. Parking lots contribute significantly to HIE. Asphalt, one of the most common pavingAir Emission Impacts materials used in parking lots, is a dark, heatPollutant air emissions occur throughout absorbing material.4 When asphalt cools atthe lifecycle of a parking lot. Asphalt cement night, all the heat it has absorbed duringplants emit particulate matter, nitrogen ox­ the day is released into the air, slowing theides (NOX), sulfur oxides (SOX), carbon monox­ rate of nighttime cooling. This hot surface, Green Parking Lot Resource Guide—February 2008 3
  7. 7. combined with stormwater runoff from the fauna. The velocity and volume of runoff fromparking lot also affects surrounding water- parking lots can damage plant, fish and inver­bodies. When water is forced to flow quickly tebrate habitat. During storm events, runoffoff the lot’s surface, not enough time is al­ can erode stream banks and alter the naturallowed for evaporation to occur, again limiting shape of a waterway. Stream edge habitatnatural cooling of the air. In addition, the land and stream channel protection removedclearing needed to create space for parking during the construction of the parking lotlots diminishes tree cover and other natural increases the potential for erosion. Sedimentsvegetation that can help shade land and entering the waterway as a result of erosionmoderate temperatures. can smother habitat and stress aquatic organ­ isms. The turbidity created from the sedi­The environmental impacts of the HIE are mentation can disrupt an aquatic ecosystemvaried. Hotter temperatures can lead to by diminishing light transmission, reducingmore CO2 emissions due to increased energy plant growth, altering food supplies, interfer­demand to cool neighboring buildings.5 HIE ing with navigation, decreasing spawningcan also increase smog, and subsequently habitat, and reducing shelter.exacerbate pulmonary and cardiovascularhealth problems. During rain events, paved The contaminants in parking lot runoff alsosurfaces can transfer heat to runoff, increas­ pose a risk to wildlife. Toxic substances froming the temperature of receiving waters. This contaminated ground and surface water sup­warmer water can be detrimental to the natu­ plies have the potential to bioaccumulate inral habitats of fish and other aquatic life. the tissue of fish and other organisms in the wildlife food chain. They can also accumulateWaste Impacts in sediments, posing risks to bottom feedingThe traditional production and application organisms and their predators.of asphalt relies heavily on the use of virgin The impact of parking lots on water suppliesstone and aggregate and non-renewable, affects local ecology. Unnaturally low streampetroleum-based materials. Use of fresh flows as a result of decreased infiltrationasphalt in parking lot construction creates a can negatively impact deep water and swiftlost opportunity for reusing waste products, flowing habitats. Impaired water quality, andsuch as recycled asphalt, which would reduce increased volume and velocity of runoff, canthe amount of material sent to landfills lead to habitat loss, stress aquatic species,and increase the amount of virgin materi­ and have an overall negative effect on bio­als conserved. The use of recycled asphalt is logical diversity in abutting areas.common in the construction of roads, buthas yet to become prevalent in parking lot Decrease In Greenspaceconstruction. Greenspace is a finite resource with a wideDisturbance of Habitat and Local range of intrinsic values, including conserva­Ecology tion, recreation, and agricultural purposes, as well as its scenic qualities and contribution toTraditional parking lots can have a host of the overall character of a city or town. Propernegative impacts on adjacent habitat and CHAPTER 1—Impacts of Parking Lots 4
  8. 8. management of greenspace is essential to ing walking and bicycling, and encouragesachieving and maintaining sustainable com­ automobile travel, disconnecting communi­munities. Nevertheless, greenspace areas are ties and decreasing the habitability of citiescommonly paved to accommodate demand and towns. The resulting increase in vehiclefor parking. For example, it is estimated that miles traveled and the associated high levels30 to 40 percent of a typical American down­ of mobile source air emissions exacerbatetown is used for parking spaces.6 air quality issues, and contribute to global climate change.Ineffective local government zoning restric­tions also result in the creation of larger areas COSTS OF PARKING LOTSof paved surface than necessary to meet theparking demand. Many municipalities require Beyond their environmental impacts, parkinga minimum number of parking spaces per lots have economic and social costs relateddevelopment project, often forcing devel­ to their construction—costs that are oftenopers to build more spaces than needed much higher than consumers realize. More­to meet actual demand. For instance, com­ over, parking costs are shouldered by manymercial parking lots frequently have 60 to stakeholders, including developers, local70 percent vacancy rates.7 Parking stall sizes governments, parking users, and communityrequired by zoning can also be larger than members. Below we describe the types ofnecessary, eliminating opportunities to alter costs related to parking lot construction, asparking lot configuration designs to achieve well as who pays.higher car capacity and minimize impervious On-site Costssurface area. On-site costs include the construction, opera­Conventional parking lots are often viewed as tion, maintenance, and disposal of materialsunattractive, hostile, and sometimes unsafe needed to develop and maintain parking lots,areas. In contrast, green parking lots with including paving materials and infrastructureurban greenscaping provide aesthetic ben­ such as gutters and curb cuts. In addition,efits, including privacy and noise reduction, on-site costs include the cost of parking lotto landowners and to communities. These landscaping that, depending on the shrubs,benefits are lost when conventional parking trees, and turf chosen, vary in their need forlot construction and paving techniques are mowing, pruning, and irrigation. These costsused. are typically paid by developers, althoughUrban Sprawl local governments sometimes subsidize infrastructure costs. HIE can add to parkingUrban sprawl and prevailing low-density lot user costs, by decreasing an automobile’sdevelopment patterns characterized by free, value by quickening the deterioration of theplentiful parking reinforce dependence on vehicle’s paint, plastics, and tires while onautomobiles for commuting to work, shop­ the lot. HIE can also shorten the life of theping, and social activities. Thus, conven­ pavement, causing it to become brittle andtionally designed parking is an enabler of weak (a cost to parking lot owners); and canurban sprawl. Conventional parking creates increase the energy costs of adjacent build-barriers to alternative transportation, includ­ Green Parking Lot Resource Guide—February 2008 5
  9. 9. ings due to the hotter air temperatures (a Distributional Issuescost to the building owner and potentially to Parking lots provide a value to consumersthird parties). who use them, but result in negative im­Infrastructure Costs pacts for neighbors and other community members who do not use them. CommunityLocal governments bear the brunt of infra­ members would be better served by almoststructure costs related to parking. The high any other land use, particularly in cases ofvolume and velocity of polluted run-off from excessive sizing of paved areas, which canparking lots can stress stormwater man­ reduce adjacent property values.agement systems and hasten the need forrepairs, upgrades, and expansions to handle Community Development Costswater flow and treat runoff. Flooding caused Parking lots and associated sprawl decrease aby runoff can also degrade bridges, roads, community’s habitability, livability, and senseand other parts of a city’s infrastructure. of identity, a cost to all community members.Additionally, groundwater shortages due to Unattractive expanses of pavement placeddisruption of the water cycle can increase in front of buildings create voids and discon­the frequency, and thus cost, of pumping nectedness, discouraging pedestrian-friendlygroundwater. communities and alternative methods ofOpportunity Costs transport. The presence of multiple conven­ tional parking lots can also signal develop­Parking lots consume large areas of open ers that a community accepts urban sprawlspace that could otherwise be used for development. This signal can create a cyclicalalternative, higher value purposes, such as effect on a community’s future developmentparks, wildlife habitat, recreation, agriculture, patterns. Subsequent developments in thesehousing or other businesses. Building park­ areas are far more likely to have a similar pat­ing instead of other types of development tern of urban sprawl, further disconnectingcould reduce the property tax base, a cost the link with any older non-sprawl develop­to local governments and local taxpayers. ment, and eroding or precluding uniqueEnforced minimum parking requirements characteristics that establish a community’sdo not benefit developers either. They limit sense of place.the development potential of land; the moreparking spaces that are required, the less landavailable for more profitable uses. This can becostly because parking is relatively expensiveto construct and yields little return, or noreturn where parking is free. CHAPTER 1—Impacts of Parking Lots 6
  10. 10. CHAPTER 2“GREEN” PARKING LOT TECHNIQUESI nnovative approaches to planning and of transport, through company support or design can greatly mitigate many of the subsidies. Another alternative is for mu­ negative impacts of parking lots, includ­ nicipalities to institute an optional fee thating diminished recharge of groundwater, developers can pay towards an appropriatehigh rates of stormwater runoff, and non- municipal fund, such as a traffic mitigationpoint source pollution, by decreasing imper­ fund, in lieu of meeting minimum parkingvious surface area, protecting water quality, requirements.8reducing stormwater management and Depending on the site, developers may notmaintenance costs, and increasing aesthetic opt for constructing less parking because itvalue. Below, we introduce green parking lot may make a site less marketable. A techniquetechniques, many of which are described in applicable in this case would be to set park­detail in subsequent chapters. ing maximums and/or area wide parkingPLANNING ASPECTS restrictions, which would limit the number of spaces allowed across a larger area, eve­Local planners regularly reinforce car depen­ ning the playing field for the marketability ofdence through zoning bylaws that, although sites in the area.meant to meet a community’s parking needs,can result in an oversupply of parking. As a Beyond reducing the number of parkingresult, cities and towns are increasingly trying spaces required, municipalities and develop­new approaches to parking management ers can also encourage practices that reducethat allow for greater flexibility and adapt­ stall dimensions by creating more compactability by determining parking space num­ car spaces and realistic stall size require­bers on a project-specific basis, rather than ments. Some local zoning laws currentlythrough a one-size-fits-all regulation. require unnecessarily large stall dimensions that are bigger than even the largest SUV.9One such technique is to reduce minimum In many cases smaller, more realistic, stallparking requirements based on project sizes would be sufficient while reducing thelocation or demographics. For example, local amount of disturbed land and imperviousgovernments can encourage projects that are surface associated with a project.located near public transportation to reducethe demand for parking spaces. Adaptations Improving the aesthetic of the parking lot isof this technique include municipalities also a central technique in green parking lots.allowing a reduction in the minimum park­ For instance, placing a parking lot behind aing requirements in return for a developer/ building rather than in front of it creates aemployer agreeing to implement a transpor­ more inviting and pedestrian-friendly envi­tation demand management program to en­ ronment. Reducing the number of curb cutscourage employees to use alternative modes also decreases the frequency of pedestrian/ Green Parking Lot Resource Guide—February 2008 7
  11. 11. traffic interaction, thus making for a morepedestrian-accessible area. These practicesaim to improve the character of the develop­ment while maintaining accessibility to thelot. Additionally, parking lots can be dividedinto two or more parking areas, again project­ing a more visually welcoming appearance. Strategically sloped vegetated strips are a better option than conventional grassy parking islands for collecting and filtering runoff.The impact of locating a parking lot at thefront of a building can be mitigated by by 25-30 percent compared to conventionalproviding ample space between the lot and approaches.10the road, and then creating a buffer with Stormwater BMPs include structural controlslandscaping, fencing, or a wall. Landscaping and bioengineering techniques designed toinside the parking lot is also an important facilitate natural water cycling processes (i.e.technique. Beyond making the parking lot evaporation, transpiration, and groundwatermore visually pleasing, vegetation and land­ recharge) by capturing, filtering, infiltrating,scaping (including trees) around and inside and/or storing stormwater. Componentsthe parking lot reduce HIE and help to absorb of these soil- and plant-based systems canCO2 emissions. Landscaping is discussed carry out one or more of the aforementionedbelow. functions, including some that store water forChapter 3 provides detailed information on various durations (from 24 hours to perma­green parking planning. nent storage). Examples of BMPs include swales, vegetated buffer strips, and bioreten­ON-SITE STORMWATER tion areas.MANAGEMENT Unlike traditional stormwater managementInnovative stormwater management strate­ systems designed only for efficiency in storm-gies are increasingly being incorporated into water removal, which can lead to negativeparking lot design as part of the overarching downstream effects, BMPs represent a shiftconcept of Low Impact Development (LID). towards a sustainable approach to storm-LID stormwater techniques (also known as water management. Thus, in the context ofBest Management Practices, or BMPs) man­ parking lots, BMPs add value by minimizingage stormwater on-site, reducing negative environmental impacts of runoff, and oftenimpacts on receiving waters and municipal lower site development costs while improv­stormwater management systems, and ing aesthetics.decreasing the need for costly infrastruc­ture such as pipes, gutters, and curbs. Done Chapter 4 provides detailed information onon a small-scale, these controls attempt to greener stormwater management and BMPs.mimic the pre-development ecological andhydrological processes of an area and canreduce stormwater and site developmentdesign, construction, and maintenance costs CHAPTER 2—”Green” Parking Lot Techniques 8
  12. 12. PARKING SURFACE MATERIAL economical for developers than incurringSELECTION the rising costs in some states for disposal of construction, demolition, and clearing debrisThe negative impacts associated with large in landfills.impervious surface areas in parking lots canbe reduced through the use of new perme­ Chapter 5 provides detailed information onable materials as substitutes for pavement. greener choices for parking surface materials.A number of paving substitutions have beendeveloped to reduce the range of environ­ LANDSCAPING AND IRRIGATIONmental impacts associated with the use of Green parking lot techniques work to mini­pavement. Types of permeable and semi­ mize the amount of land cleared for construc­permeable alternative pavers include gravel, tion, conserving as much of a site’s naturalcobble, concrete, wood mulch, brick, open vegetation and open space as possible,jointed pavers filled with turf or aggregate, and retaining habit for local wildlife. Whenturf blocks, natural stone, and pervious designing a parking lot area, landscapersconcrete. can use native trees and shrubs rather thanBased on a site’s characteristics (i.e. traffic non-indigenous species, which are more suit­volume, soil type, climate etc.), alternative able to local climates and, therefore, requirepavers may not be an option for the entire less irrigation. The benefits of increasing thesurface of primary parking areas.11 However, amount of greenscape in and around park­in many cases, the aisles and driveways can ing areas include reduction of CO2 in the air;be constructed using conventional pave­ improved stormwater runoff managementment, while alternative pavers can be used in including water storage; increases aquiferparking stalls, crosswalks, and overflow lots. recharge and flood protection; and increasedAlternative pavers slow the flow of runoff, human comfort through mitigation of HIEs.allowing it to filter into the soil, sustaining an Wetlands preservation or creation is particu­area’s natural hydrological cycle, and in some larly beneficial, as they can act as naturalcases, allowing microbes to break down con­ bioretention basins, providing water qualitytaminants before entering the soil layer. improvements, flood protection, and ero­ sion control. Wetlands also provide excellentOpportunities for materials recycling ex­ habitat for local avian and fish species, andist in the management and construction of are invaluable for water storage; one acre ofparking lots. For example, the use of recycled wetlands can store over million gallons ofasphalt in parking lot construction is not only water.12environmentally beneficial, but can makeeconomic sense. Other environmentally pref­ Chapter 6 provides detailed information onerable materials, such as recycled rubberized green parking lot landscaping and irrigation.asphalt, may also be used in parking lot con­struction. Recycling materials can be more Green Parking Lot Resource Guide—February 2008 9
  13. 13. CHAPTER 3PLANNING ASPECTSP arking lot design and parking avail­ quantity of spaces in a parking lot. It is these ability are vital to transportation regulations that manage a community’s park­ management throughout the United ing capacity, and thus a large amount of itsStates. Parking availability may determine a impervious surface area.customer’s willingness to visit a business, and Zoning requirements for developers toit is often a sought after feature in urban resi­ provide off-street parking first began in thedential areas. However, parking lots should 1930s as a solution to an on-street parkingbe designed efficiently so that spaces are shortage. Over the years, off-street parkingused frequently and not left empty a majority requirements expanded in response to theof the time. When developing a parking lot, a population’s dependence on automobiles.number of factors combine to determine the Today, according to the U.S. Department oflot’s size, layout, and design. These decisions, Transportation, 87 percent of trips of lessmade during the planning stages of a devel­ than 50 miles are made by personal motoropment, can transform a parking lot from a vehicles.13 Americans have become accus­sparsely landscaped expanse of impervious tomed to the availability of free parking andpaving to a space that is more aesthetically automobile travel, rather than public transitpleasing, land efficient, and community and or other alternative methods, even for veryenvironmentally friendly. short distance trips. Increased parking avail­Local governments can use better park­ ability encourages more driving, more drivinging planning as a tool to promote infill and requires more parking, and so on.smart growth developments while reducing One of the most important local parkingthe direct environmental impact of park­ ordinances addresses minimum space re­ing. In many cases, revisions to zoning and quirements, or parking ratios. Typically, localother parking ordinances may be needed to governments require developers to constructachieve better parking planning. This chap­ the minimum number of parking spacester provides a summary of parking planning needed to satisfy peak demand. These mini­considerations that have environmental mum parking regulations often result in animplications, including municipal parking oversupply of parking. One study found thatlot regulations, parking lot aesthetics and the average parking supply at worksites is 30design, and the connection between parking percent greater than peak parking demand.14and smart growth. In many instances, minimum parking require­MUNICIPAL PARKING ments are inflexible to adaptation or vari­REQUIREMENTS ances. Also, the methods to determine these minimum parking requirements are oftenIn most urban and suburban areas, a num­ excessive and over-generalized, leading to anber of zoning laws govern the layout and oversupply of parking.15 In addition, although CHAPTER 3—Planning Aspects 10
  14. 14. municipalities regulate the minimum number City of San Francisco, where city plannersof parking spaces, they typically do not put eliminated minimum parking require­a cap on the maximum. Thus, developers ments for development within a half milecan frequently construct even more than the of train stations and one-quarter mile ofrequired minimum, which is often the case major public transit routes.17at large retail developments, leading to a Municipalities can also consider the landfurther surplus in supply. uses in the surrounding area. For instance,In addition to requirements for the number it is possible that existing nearby develop­of spaces in a parking lot, regulations for the ment and parking may already providesize of each space are also common. Some some of the parking necessary to sup­local zoning laws require unnecessarily large port a new development. Mixed usedstall dimensions that are bigger than even developments often have natural parkingthe largest SUV.16 In many cases, smaller flexibility; an office where peak parkingstall sizes would satisfy parking needs while demand occurs during the day can sharereducing impervious surface, and the entire the same parking spaces with restaurants,footprint, of the parking lot. entertainment venues, or residential units that have peak parking demands at nightRe-thinking Municipal Parking and on weekends. Shared parking is alsoRequirements an option for single use developments inThere are a number of planning alternatives mixed-use areas.18to minimum parking requirements that lead­ • Maximum Limits on Parking—Theing local governments throughout the United opposite of parking minimums, parkingStates are implementing to minimize land maximums limit the number of spacesdedicated to parking. These include reducing that a developer can construct, which isminimum parking requirements; assessing often determined by the development’sparking needs on an individual project basis square footage. Portland, Oregon is onerather than using a generic formula; en­ city that has successfully implementedcouraging shared parking; and establishing the use of parking maximums. Benefitsparking maximums, area wide parking caps, of such a policy include open spacein-lieu parking fees, and reduced parking preservation, reduction in imperviousspace dimensions. surface area, traffic congestion reduction,• Reduced minimum parking require­ promotion of alternative transport, and ments—Parking requirements should the development of pedestrian-friendly be determined on a project-by-project urban design. For developers, such limits basis instead of by formula, taking into mean lower parking lot construction consideration how a project’s location can costs.19 Similar policies include setting shape parking needs. This approach may both a parking minimum and maximum, decrease the required parking capac­ or determining a median parking ratio. ity where there is accessibility to public • Area wide parking caps—Municipalities transportation and/or a high level of foot can control the amount of parking by and bike traffic. Such was the case for the Green Parking Lot Resource Guide—February 2008 11
  15. 15. setting limits on the total amount of park­ stalls to achieve the greatest car capacity, ing spaces allowed in a certain area. This again reducing the amount of land neces­ strategy is being used in major U.S. cities sary for the lot. including Boston and San Francisco. Such regulations require greater research and PARKING LOT PLACEMENT AND planning efforts by the city or town to AESTHETICS ensure that the parking cap is appropriate Parking lots have been described as “sterile, and reasonable, but if done properly, it unattractive environments that deaden city can be very successful in minimizing the and suburban streets alike, further isolate land area used for parking and encourag­ users and preclude lively pedestrian-friendly ing use of public transportation. This op­ streets.”24 Although all parking lots do not tion is appropriate for areas with adequate match this description, many are eyesores access to public and alternative transpor­ that inhibit the usability and walkability of tation, as well as desirable location that an area. Several techniques can be incorpo­ would outweigh the perceived drawbacks rated into the design and layout of a parking of more limited parking.20 lot to improve aesthetics and help connect• In-Lieu Parking Fees—Towns such as parking lots to community design. This not Berkeley, California, Lake Forest, Illinois only benefits the user, but also the organi­ and Orlando, Florida incorporated systems zation or business adjacent to the lot, as a of in-lieu parking fees. This optional fee more pleasing atmosphere will help draw in is offered to developers by municipalities the public. Plantings around the perimeter, in-lieu of meeting minimum parking re­ especially trees and shrubs, can screen the lot quirements. This fee is typically allocated from passer-bys and break-up the otherwise to an appropriate municipal fund, such as continuous strip of asphalt and cars from a traffic mitigation fund.21 An alternative the street to the parking lot. This can also be under the in-lieu system is that in return achieved through the use of fencing or a wall. for the developer’s fee, the city provides Vegetation can also be used to divide one existing centralized, off-site parking to the large lot into two or more smaller lots, again new development’s tenants and visitors.22 increasing the site’s visual appeal. Equally important, landscaping within the lot pro­• Reduced stall size requirements— vides an environmental benefit by decreasing Adjusting a local government’s stall size dust, wind, noise, glare and air pollution; and requirements may reduce impervious sur­ minimizing heat island effect.25 face coverage as well. Alternatives include creating a certain number of compact The placement of a parking lot is a simple, car spaces and/or limiting stall dimen­ yet fundamental feature that can improve a sions to feasible sizes. For example, in the development’s attractiveness. A majority of town of Needham, Massachusetts, up to parking lots are placed in the front of build­ 50 percent of off-street parking can be ings, between buildings and streets, requiring reduced dimension spaces designed for pedestrians and bicyclists to cross expanses compact cars.23 If possible, developers can of parking in order to enter a building. Alter­ also adapt the layout and angle of parking natively, parking lots could be placed at the CHAPTER 3—Planning Aspects 12
  16. 16. rear of a building, increasing the intercon- States, and promoting sustainable land use nectedness between pedestrians and the patterns. With many cities designed aroundbuilt environment. This simple zoning change use of the automobile, planners are oftenis incredibly effective in shifting the orienta­ presented with the conflicting challenge oftion of a streetscape from cars to pedestrians. promoting smart growth development whileThis also helps give the community a greater supporting the parking needs of a popula­sense of place and interconnectedness. In tion. Green parking planning approachesrecognition of such benefits, the City of Fort support smart growth by creating moreCollins, Colorado requires that no more than sustainable land use patterns and decreasing50 percent of the parking for a retail devel­ the environmental impacts of conventionalopment be located between the principle parking lot development. By promoting andbuilding and the primary abutting street.26 supporting alternative transport and com­Limiting the number of curb cuts also makes muting, local governments may reduce thea parking lot more pedestrian friendly and parking needs.inviting. Furthermore, by minimizing the A concept linked to smart growth is “transit­number of vehicular entries to parking areas, oriented development,” defined as develop­pedestrian mobility is improved, and pedes­ ment placed within close proximity of publictrian/traffic is minimized. transportation, designed to create walkableLINKING PARKING TO communities and alleviate traffic conges­SMART GROWTH tion and environmental impacts caused by urban sprawl. When building parking lots,Smart Growth is a state and local government local governments can encourage or requireplanning movement aimed at improving the developers to incorporate features that helplong-term habitability and sustainability of reduce automobile reliance, such as bicyclecities and towns by minimizing environmen­ racks. Employers can support use of alterna­tal impacts, improving human health, build­ tive transport options by subsidizing the costing a sense of community, creating walkable of public transit, encouraging participationneighborhoods, promoting traditional and in a commuting program, and/or providingalternative transport, and preserving open shower facilities on-site so that staff can bikespace. Most fundamentally, smart growth to work.entails moving away from the urban sprawldevelopment pattern common in the United Green Parking Lot Resource Guide—February 2008 13
  17. 17. CHAPTER 4STORMWATER MANAGEMENTA pivotal component of green park­ project alone can be minimal, but multiplied ing lots is the inclusion of innova­ by the current, and growing, number of tive stormwater management commercial and residential parking lots, thetechniques, often referred to as stormwater combined effect of stormwater runoff has be­“best management practices” (BMPs). BMPs come the leading cause of non-point sourceare practices, techniques, and measures pollution to our waterbodies.29that prevent or reduce water pollution from As discussed in Chapter 2, the environmen­non-point sources (i.e. runoff ) using the most tal effects of increased volume and velocityeffective and practicable means available.27 of stormwater include not only diminishedStormwater management BMPs often include water quality in surrounding waterbodies,engineered, on-site systems that, when but also:coupled with reduction of impervious surfacearea, can help significantly reduce detrimen­ • Degradation of stream channels resultingtal environmental effects and infrastructure erosion and sedimentation;burden from stormwater runoff. • Minimized groundwater recharge, whichIncreased development and conventional can diminish water flow in the dry weath­stormwater systems have significantly er, and lead to poorer water quality duringchanged the characteristics of stormwater low flows;flow from land into receiving waters. Accord­ • Higher water temperatures, whiching to the Natural Resources Defense Council, negatively impact aquatic organisms andthe amount of rain converted to runoff under plants; andnatural conditions is less than ten percent ofthe rainfall volume.28 However as more devel­ • More frequent and severe flooding.30opment occurs, rainwater or snow melt that This chapter provides an overview of greenwould have infiltrated into the soil, evapo­ parking lot stormwater management BMPsrated into the air, or been absorbed by plants, that can help mitigate these impacts, in­instead flows quickly off of the pavement as cluding information on pollutant removalstormwater runoff. Moreover, conventional efficiency and cost considerations.stormwater management exacerbates thisproblem. Conventional parking lot stormwa­ GREEN PARKING LOT STORMWATERter management typically consists of costly MANAGEMENT TECHNIQUESsystems of man-made drains, pipes, gutters,storm ponds, and paved channels that direct Green parking lots offset environmental im­runoff from impervious lots into storm drains pacts of parking by using on-site stormwaterand neighboring waterbodies. The environ­ infrastructure that more closely mimics themental ramifications of one development natural water cycle, and manages stormwater CHAPTER 4—Stormwater Management 14
  18. 18. through effective rainfall retention, pollutant ter runoff, and often are incorporated toremoval, and water infiltration. Although still pre-treat and remove sediment beforein the early stages of wide-spread implemen­ water enters infiltration devices such astation, cities and towns are recognizing the bioretention areas.34 Other benefits in­benefits of stormwater BMPs, and many have clude protection of riparian areas, habitatintroduced both voluntary and mandatory creation, and streambank stability.policies for their inclusion in development Vegetated filter strips are frequently usedprojects.31 in combination with riparian buffers, an­Some of the most commonly used structural other common BMP, to increase pollutantBMPs are described below. It also should be removal effectiveness. Riparian buffersnoted that incorporating BMPs is not lim­ are vegetated strips along waterways thatited to new development. As illustrated by trap and filter contaminants, encouragethe case study of building a rain garden at infiltration, and slow stormwater flow.Bloedel Donovan Park in this chapter, exist­ They also help to preserve streambanking parking lots can be retrofitted to include stability.them. • Bioretention Areas (Rain Gardens)• Swales One of the more well-know BMPs, biore­ Swales are open channels or depressions tention treatment areas (a.k.a., rain with dense vegetation used to transport, gardens) consist of a grass buffer strip, decelerate, and treat runoff. In parking shallow ponding area, organic layer, plant­ lots, they are designed to help direct ing soil, and vegetation. These areas are water into bioretention areas. Swales can typically used in parking lot islands. Unlike come in the form of a grassed channel, dry swales, bioretention areas are well-suited swale, or wet swale. They can be used in for parking lots in denser, urban areas most climatic regions of the United States, with less available open space. but may be unsuitable for densely urban • Dry Detention Basins areas as they require a large amount of pervious surface area.32 A dry detention basin is a vegetated basin with controlled outlets, designed to• Vegetated Filter Strips/Riparian detain runoff (lowering flows and reduc­ Buffers ing velocity) for a short amount of time Vegetated filter strips are flat pieces of (e.g. 24 hours or less), partially removing land with low slopes, which are designed pollutants before the water is discharged. to encourage natural sheet flow of storm- This helps limit flooding and other storm- water as opposed to channeled runoff. water impacts, such as stream channel Vegetated filter strips are well suited for erosion and wildlife habitat destruction. low-density development or areas with Dry extended detention basins are better less concentrated amounts of runoff.33 suited for pollutant removal than standard They function by using soil and vegeta­ dry detention basins because they retain tion to remove pollutants from stormwa­ the water for an “extended” period of time Green Parking Lot Resource Guide—February 2008 15
  19. 19. (i.e., up to 48 hours). They are effective and filled with stone to form a subsurface at treating certain runoff contaminants, basin, where water is stored until it infil­ particularly those contained in spring trates into the soil. This system greatly re­ and winter runoff in colder climate areas. duces the volume of runoff, and is particu­ However, because water temperature larly good for groundwater recharge as it increases while in this type of system, dry allows a significant amount of rainwater to detention basins discharge warmer than infiltrate. Both of these BMPs are consid­ natural water into waterbodies, which ered effective for pollutant removal when should be taking into consideration. Both used in conjunction with a pre-treatment dry detention and dry extended detention BMP such as a swale. However, potential basins are normally dry between storm drawbacks include higher failure rates events, thus giving them their name.35 due to improper design and maintenance, limited site applicability, and increased• Wet Retention Basins sediment clogging.38 Wet retention basins are designed to cap­ Porous pavement is another type of infil­ ture, filter, store, and infiltrate storwmater, tration technique used in green parking and have storage capacity adequate for lots; as it is also an asphalt alternative, it flood volumes of water. Because they have is discussed in Chapter 5: Parking Surface the capacity to store a permanent pool of Materials. water, wet basins can be very effective for water control, and can provide the bene­ • Constructed Wetlands fits of aesthetic value and wildlife habitat, Constructed wetlands are designed to both terrestrial and aquatic. Although not capture, filter, and store stormwater simi­ suitable for smaller areas because of their lar to a wet retention basin. However, they size, when applicable, retention basins are also contain a large quantity of wetland a very effective BMP.36 vegetation and have wetland channels.• Infiltration Systems Although they are not built to replicate all of the ecological functions of wetlands, Infiltration systems are designed to constructed wetlands help simulate the capture and retain stormwater runoff, natural water cycle, recharge groundwa­ allowing water to gradually infiltrate into ter, remove pollutants, reduce erosion, the ground over a period of hours or days, and provide wildlife habitat. They are depending on the design.37 Two common considered to be a very effective pollutant infiltration systems used in green parking removal option.39 Constructed wetlands lots are infiltration basins and infiltration have a few limitations; they are not ap­ trenches. An infiltration basin is an open plicable in arid climates and, due to their depression that covers a relatively large large size, they are not suitable for dense area. It is constructed to work in conjunc­ urban areas. tion with filter strips or swales, which help direct runoff from a parking surface into It is not necessary for developers to in­ the basin. Infiltration trenches are shallow corporate all available green stormwater excavated ditches lined with filter strips techniques into a project; rather, they should CHAPTER 4—Stormwater Management 16
  20. 20. determine those useful for specific site condi­ source of pollutants in parking lot runoff, in­tions. Considerations should include all fac­ cluding antifreeze, oil, hydrocarbons, metalstors that affect the amount, speed, and pol­ from wearing break linings, rubber particleslutant loadings of runoff: soil type, the slope from tires, nitrous oxide from car exhausts,and landscape of the site, amount of impervi­ and grease. Other polluting materials includeous surface, local precipitation patterns, and pesticides, fertilizers, litter, pet waste, dirt,rainfall surface retention.40 Carefully choos­ and sand.45ing the appropriate BMP(s) is important to One of the main goals of a green parking lotavoid any secondary environmental impacts is to decrease pollutant levels in stormwatercaused by the use of an inappropriate BMP. runoff as much as possible before it enters aBMPs should address peak discharge, runoff waterbody. Exhibit 1 shows a range of pol­volume, infiltration capacity, base flow levels, lutant removal efficiencies for selected BMPs.ground water recharge, and maintenance of Understanding the effectiveness of each BMPwater quality, so that they are ideally man­ for pollutant removal is a complex undertak­aged in the pre-development stormwater ing because pollutant removal is affected byfiltration conditions of the site.41 a large number of variables. Fundamentally,It should be noted that BMPs are helping to removal effectiveness depends on: 1) BMPmeet the Clean Water Act’s mandate to “re­ type, 2) the quantity of runoff treated, andstore and maintain the chemical, physical and 3) the type of pollutant being removed.46biological integrity of the Nation’s waters”.42 Variation in one of these factors can affectBy 2025 the U.S. population is predicted to a BMP’s efficiency. For example, infiltrationgrow 22 percent, which could mean an ad­ trenches show a high pollutant removal ef­ditional 68 million acres of development, a ficiency for pathogens, but much lower forgood fraction of which will be dedicated to phosphorus. However, these effectivenessparking.43 Thus, BMPs may play a larger role ranges can vary based on the climate, soil,in the future to mitigate non-point water and land type of a particular site. Infiltra­pollution. tion trenches may be less effective in colder climates when surface waters freeze and can­BMP POLLUTANT REMOVAL AND not allow runoff to flow into them, a limita­EFFECTIVENESS tion that can be partially remedied throughStormwater can carry a number of harmful proper design and maintenance, but may stillpollutants, and is the prime contributor to reduce pollutant removal effectiveness.47non-point source pollution. Runoff contami­ As seen in Exhibit 1, not all BMPs have a highnants can originate from a variety of sources, level of pollutant removal effectiveness.including the paving materials used to build Instead, they serve other roles in control­the parking lots. Recently, the USGS pin­ ling the impacts of runoff. This is the case forpointed parking lot sealants as a large source dry detention basins, which serve to reduceof non-point source pollution, specifically peak discharges of stormwater to neighbor­polycyclic aromatic hydrocarbons (PAHs), a ing waterbodies, as well as limit erosion andknown carcinogen that can be toxic to fish downstream flooding.and wildlife.44 Automobiles are also a major Green Parking Lot Resource Guide—February 2008 17
  21. 21. EXHIBIT 1: BMP EFFECTIVENESS Typical Pollutant Removal Efficiency (percentage) BMP Type Suspended Nitrogen Phosphorus Pathogens Metals Solids Dry Detention Basins 30-65 13-45 15-45 <30 15-45 Retention Basins 50-80 30-65 30-65 <30 50-80 Constructed Wetlands 50-80 <30 15-45 <30 50-80 Infiltration Basins 50-80 50-80 50-80 65-100 50-80 Infiltration Trenches/ 50-80 50-80 15-45 65-100 50-80 Dry Wells Grassed Swales 30-65 15-45 15-45 <30 15-45 Vegetated Filter Strips 50-80 50-80 50-80 <30 30-65 Source: U.S. EPA, 1993, Handbook Urban Runoff and Pollution Prevention Planning, EPA-625-R-93-004, taken from Purdue Uni­ versity Engineering Department’s Long-Term Hydrologic Impact Assessment (L-THIA): http://cobweb.ecn.purdue.edu/~sprawl/ LTHIA7/lthia/lthia_index.htm.BMP COST CONSIDERATIONS constructing a BMP considerably because of excavation costs.Innovative structural stormwater BMPs aremore effective than conventional storm- Another significant variable in the compara­water management in removing pollutants tive cost of BMPs is the value of land; in areasand maintaining the environmental quality where real estate prices are high, construct­of a site. However, because some of these ing a BMP may take up too much space to betechniques are relatively new and have not cost effective.49 BMPs operation and mainte­achieved market penetration, it is not clear nance costs can also be significant. The long-their costs compare to conventional storm- term cost to maintain certain, more complex,water management approaches.48 Calculating stormwater BMPs over a 20-25 year periodthe cost-effectiveness of a stormwater BMP can be close to its initial construction cost.50is a very site-specific endeavor, and current However, some BMPs, such as swales andcost information is limited and inconsistent. bioretention areas, are less expensive to buildThe main factors affecting the relative costs than their conventional counterparts of pipeof BMPs include the cost of land, engineering and gutter systems. These BMPs can decreaseand design, permitting, construction, and development costs by reducing or eliminat­operation and maintenance. These costs can ing the high cost of conventional stormwatervary greatly due to individual site characteris­ infrastructure such as piping, gutters, andtics such as climate, topography, government drains, as well as reduced long-term mainte­regulations, soil type, time of year of con­ nance costs for such systems. Furthermore,struction, drainage, accessibility of equip­ some BMPs, such as constructed wetlands,ment, and economics of scale. For instance, may increase the property value by creat­very rocky soils may increase the cost of ing a water feature and vegetation that has CHAPTER 4—Stormwater Management 18
  22. 22. high aesthetic value. Developers may also protect the health of waterbodies, but alsogain from local government incentives that because they can avoid long-term costs.encourage incorporating structural stormwa­ Without stormwater BMPs, many waterbod­ter BMPs. For instance, the City of Portland, ies and water infrastructure may deteriorate.Oregon will give up to a 35 percent discount Taxpayers bear the cost burden to slowoff its stormwater utility fee to properties or repair damage caused by downstreamwith on-site stormwater management.51 In flooding, stream and aquatic habitat dete­addition, some costs are tax deductible, and rioration, and repairs and upgrades to wornoperating costs may be fully deductible as town stormwater infrastructure systems, allexpenses in the year they are incurred.52 of which are very expensive and time-con­ suming.53 Infrastructure costs associated withAlthough the costs of BMPs vary by site and stormwater management and how greentype, they are almost always a good invest­ parking can help mitigate these costs arement from the perspective of local govern­ discussed further in Chapter 7.ments and taxpayers, not only because they Green Parking Lot Resource Guide—February 2008 19
  23. 23. CASE STUDY 1: STORMWATER BEST MANAGEMENT PRACTICES (BMP)BLOEDEL DONOVAN PARK, BELLINGHAM, WASHINGTON54Stormwater runoff in Bellingham, Washing­ton, like much of the U.S., is a foremost waterquality issue. The Washington Department ofEcology estimates that roughly one-third ofthe state water bodies with pollution relatedproblems are impaired because of stormwa­ter runoff impacts. In an effort to protect thereceiving waters of nearby Lake Whitcomfrom such impacts, City of Bellingham of­ficials chose to retrofit stormwater manage­ment at the heavily used Bloedel DonovanPark parking lot. Rather than choosing aconventional technique, they elected to buildan innovative rain garden to manage storm- The raingarden in Bloedel Donovan Park helps protect the water quality in nearby Lake Whatcom, and recharge groundwater supplies.water on-site. of drain rock, and topped with a layer ofDESIGN AND CONSTRUCTION fabric to constrain the sand and restrictDesigned on a 550 square-foot section of the any plants from growing through. Anparking lot near the catch basin, the park’s 18- to 24-inch layer of sand composed ofrain garden supports runoff from 80 parking twenty percent organic materials is thespaces and two parking lanes. To meet water top layer .quality guidelines, the rain garden was also • Landscaping—For landscaping, the citydesigned to treat 91 percent of the runoff chose native plants that could survive thefrom a 50-year storm event. Aspects of its year-round climatic conditions of the site.construction included: This included plants that prefer wet soil,• Site excavation—From site topography but could also tolerate drought. and soils logs, the city determined the maximum allowable depth for water to EXHIBIT 2: CASE STUDY INITIAL pond in the rain garden. Under a 50-year COST COMPARISON storm event, the depth should be no more Conventional stormwater than six-feet. Thus, the site was excavated technique $52,800 three to four feet. (4,400 ft3 wet vault)• Layering of materials—The rain garden Rain Garden $12,820 is composed of three layers of non-woven Cost Savings $39,980 geotextile fabric alternated with six inches CHAPTER 4—Stormwater Management 20
  24. 24. COST AND POLLUTANTS REMOVAL in-ground storage and treatment stormwa­EFFECTIVENESS ter system (see Exhibits 2 and 3). This was achieved through reduced construction andThe benefits from incorporating this rain equipment costs, as well as reduced laborgarden are numerous. It adds aesthetic value costs from the relative ease of installation,to the site, increases wildlife habitat, and is a some of which was accomplished by volun­highly effective BMP for treating stormwater teer landscaping help. These costs savings dorunoff. According to officials at the Belling­ not include future regular maintenance costs.ham Public Works Department’s, monitoringshows that approximately 80 percent of total A more detailed case study of the city ofrunoff is captured by the rain garden, with Bellingham’s rain garden can be foundoverflows running through media filtration on the Puget Sound Action Team’s Weband then another infiltration bed. Further­ site at www.psat.wa.gov/Publications/more, Bellingham saved 70 percent in initial Rain_Garden_book.pdf.costs compared to installing a conventional EXHIBIT 3: COST FOR BLOEDEL DONOVAN PARK RAINGARDEN Labor $3,600 Vehicle use 1,900 Amended soil 1,650 Concrete 1,200 Asphalt 1,200 PVC/grates/catch basins/fabric/other misc. 1,000 Washed rock 805 Excavator rental (1.5 days) 500 Plants 400 Debris Removal 300 WCC crew planting time 265 Total Cost $12,820 Green Parking Lot Resource Guide—February 2008 21
  25. 25. CHAPTER 5ALTERNATIVE PARKING SURFACE MATERIALST he majority of parking lots are made Permeable pavements provide a sustainable of a combination of asphalt concrete, alternative to the conventional asphalt and the most widely used paving material concrete parking materials widely used today.in the United States, and aggregates such as Permeable pavements are a broadly definedsand, gravel, or crushed stone. Conventional group of pervious paving options that allowpavement is an impervious, heat absorb­ natural infiltration rates of stormwater intoing material that collects stormwater on its the soil through certain design techniquessurface, and does not allow it to filter into the and material substitutions.58 For this reason,soil, inhibiting the natural water cycle. As a re­ like many of the techniques mentioned insult, parking lots must be designed to quickly Chapter 4, permeable pavements are consid­remove the water that gathers during storms ered a best management practice (BMP) forby channeling it off the lot via means such stormwater management. However, perme­as gutters, drains, and pipes. The stormwater able pavement should be used in combina­is directed into receiving water bodies at tion with other BMP techniques to magnifyunnaturally high rates, causing a number of benefits and provide back-up systems in caseadverse impacts including increased down­ of BMP failure.59 Two basic types of perme­stream flooding, combined sewer overflow able paving designs exist: 1) porous pave­events, diminished groundwater supplies, ment and 2) alternative pavers. This chapterstreambank erosion, and non-point source describes these permeable pavement alterna­water pollution from runoff contaminated by tives, considering their functionality, infiltra­vehicular residues and other pollutants. tion and pollutant removal effectiveness, and cost implications.To combat several of the negative impactsof conventional parking lot paving, develop­ POROUS PAVEMENTers are increasingly incorporating modestchanges, such as using light colored concrete Porous pavement is a permeable pavementinstead of asphalt to reduce heat-island surface, often built with an underlying stoneeffect, or using recycled rather than virgin reservoir, which temporarily stores storm-asphalt to reduce emissions and natural re­ water before it infiltrates into the underlyingsource consumption. For example, 80 percent soil.60 Porous pavement works by eliminatingof asphalt pavement removed each year the finer aggregates typically used in con­during widening and resurfacing projects is ventional paving, and binding the remain­reused, with contractors typically incorpo­ ing aggregates together with an asphalt orrating up to 20 percent recycled material in Portland cement binder. By eliminating finerconcrete mixes.55, 56 However, these changes aggregates, a less dense material is createddo not address the fundamental problem of that allows stormwater to seep through. Theparking lot impermeability.57 underlying stone bed is designed with an overflow control structure, helping to ensure CHAPTER 5—Alternative Parking Surface Materials 22
  26. 26. that water does not rise to the pavement significant downstream benefits.66 Althoughlevel. Stormwater settles in the empty spaces porous pavement looks very similar to con­of the storage bed, infiltrating over time into ventional pavement, it is a far more sustain­the subgrade soils—a process similar to an able alternative, considered by experts to beinfiltration basin.61 the most effective and affordable technique for addressing stormwater managementThe most common types of porous pavement from development.67are porous asphalt and pervious concrete,which are very similar in their design and Porous pavements typically have a greaterapplicability. spectrum of uses than alternative pavers (discussed below), as porous pavement• Porous Asphalt—Developed by the can be applied to both low vehicular traffic Franklin Institute in the 1970s, porous areas and some medium traffic areas. Porous asphalt consists of an open-grade coarse pavements also have been used in a few high aggregate, bonded together by a typical traffic areas, including some highway applica­ asphalt cement in which fine aggregates tions, because the product can provide better have been reduced or eliminated, allow­ traction than conventional pavement and ing water to move through the small voids reduce hydroplaning.68 Ongoing research is created.62 Porous asphalt can be used in working to improve its highway applicability all climates where conventional asphalt is through the use of additives and binders.69 suitable.63 In addition, porous asphalt may help reduce• Pervious Concrete—Pervious concrete noise levels from tires on pavement. In a was developed by the Florida Concrete study measuring acoustical properties of Association. It typically contains a mixture pavement types, porous asphalt was shown of Portland cement; uniform, open-graded to have lower noise levels than conventional coarse aggregate; and water. There is at hot mix asphalt.70 least 15 percent more void space in pervi­ ous concrete compared to conventional ALTERNATIVE PAVERS pavements.64 Pervious concrete can be Alternative pavers, also known as perme­ more durable than porous asphalt, par­ able pavers or unit pavers, are interlocking ticularly in hot weather. However, the State concrete blocks or synthetic fibrous grids of Pennsylvania’s Department of Environ­ with open areas filled with grass, sand, or mental Protection has noted that in colder gravel. Unlike concrete or asphalt poured-in­ northern and mid-Atlantic climates, porous place paving surfaces, alternative pavers are concrete parking lots should always be separate units laid out on a prepared base.71 designed with a stone subbase for storm- When built with a storage bed infiltration water management, and should not be system, alternative pavers function similarly placed directly onto a soil subbase.65 to porous paving systems. The voids betweenThe manufacturing process for porous pave­ the interlocked pavers allow stormwater fromment has the same environmental and health a parking lot’s surface to collect and thenimpacts as the process for conventional pav­ seep into the storage bed, which is made ofing materials, but porous pavement exhibits sand or crushed stone. The water then gradu- Green Parking Lot Resource Guide—February 2008 23
  27. 27. ally infiltrates over time into the subgrade last 15 to 20 years, a length similar to con­soils. In addition to stormwater management, ventional asphalt concrete pavement, whichthe storage bed also provides added struc­ requires resurfacing after 20 years on aver­tural support to the pavers.72 As with porous age.78 However, a number of factors need topavements, the most beneficial element of be assessed when determining whether a sitealternative pavers is the reduction or elimina­ is suitable for a permeable paving system, in­tion of stormwater impacts.73 cluding: slope, traffic volume, subgrade, land use, soil, infiltration and drainage characteris­A number of alternative paver options are on tics, and groundwater conditions.79the market, including but not limited to: Turf-stone®, UNI Eco-Stone®, Checkerbox®, Grass­ Compared to conventional asphalt surfacepave2®, and Gravelpave2®. Of the alternative installation and design, features such as sub-paver options, grass paving systems are the grade, soil type, and installation requirementsmost permeable. However, they have more are more complicated for permeable pavinglimited applicability because grass cannot systems.80 For example, soil, including itssurvive daily traffic; thus, grass-based systems type, porosity, and stability, is considered oneare typically used for emergency fire lanes or of the most important factors to determinetemporary overflow parking areas.74 Pavers site suitability. According to the New Yorkshould be filled with fine gravel or other per­ State Stormwater Design Manual, developersmeable materials when more frequent park­ must ensure that soils are permeable enoughing is expected.75 It should also be noted that to carry out adequate infiltration by consider­certain types of alternative pavers, including ing the natural qualities of a soil type as wellblock, grid pavers, and gravel, are not always as past land uses, because previous grading,suitable for handicap accessible areas.76 filling, compaction, and other disturbances of the land can alter soil infiltration qualities.DESIGN AND INSTALLATION Underlying soils should have a minimum infil­CONSIDERATIONS tration rate of 0.5 inches per hour to accom­A number of uses for permeable pavement modate stormwater volumes, and knowledgeexist beyond new, whole parking lot con­ of the organic matter content of the soil isstruction projects. One option for high traffic also important in determining its pollutantparking lots is to design a hybrid parking lot removal capabilities.81combining permeable pavement parking Permeable pavement is meant to treat smallspots with more conventional paving in the storm events, which can range from 0.5 to 1.5aisles.77 In addition, permeable pavements inches. A site must be designed with an ad­can be used during parking lot retrofits and equate ratio of infiltration area to imperviousreplacements. area, and the soil should have a permeabilityAccording to the U.S. Department of Trans­ of between 0.5 and 3.0 inches per hour inportation, permeable pavements must be order to adequately handle stormwater.82 Oc­properly sited, designed, and installed in casionally, exceptions can be made to alloworder to function fully over their life span. If for permeable paving when sites do not meetplanned correctly, permeable pavements can certain criteria. For instance, permeable pave- CHAPTER 5—Alternative Parking Surface Materials 24
  28. 28. ment can be used in soils with low porosity that if properly installed, success rates for aif a discharge pipe is installed to run from a permeable paving system, particularly po­storage area to a conventional stormwater rous asphalt, can be much higher than earliersystem. This modified system will still treat installations using these materials.88stormwater from small and medium storms,but also will prevent flooding during large MAINTENANCE OF PERMEABLEstorm events.83 PAVEMENTPorous pavement and alternative pavers In the past, studies indicated that permeablealone are not an appropriate BMP to combat pavement applications had a high failureextreme flooding events in channels and rate, due not only to improper siting, butriverbanks. It is recommended that a BMP de­ also poor maintenance. Failure of a perme­signed specifically to control high waterflows, able paving system means that the surfacesuch as a dry detention pond, should be used becomes impervious and behaves like con­in conjunction with porous pavement. This ventional asphalt, yet typically without theapproach is required by some local govern­ fully developed system of piping and guttersments as part of flood protection design used to manage runoff on conventional park­criteria.84 ing surfaces. However, with correct mainte­ nance, permeable pavement can retain itsPermeable pavement should not be used permeability, and be a successful stormwaterin parking lot areas with high volumes of management option.89sediment-laden runoff, high traffic volume,high dust areas, and/or heavy equipment The level of maintenance necessary totraffic.85 Clogging is the main cause of a maintain permeable pavement lots varies.system malfunction that can result from poor Alternative pavers such as concrete grid pav­siting of the permeable pavement system. ers and plastic modular blocks will requireDuring construction, developers can prepare less maintenance because they do not clogfor possible clogging by installing a perim­ as easily as porous asphalt and permeableeter trench connected to the stone reservoir concrete. Location also impacts the amountto treat overflow should the surface clog.86 of maintenance, as areas receiving moreOther common problems to avoid include: sediment will require more maintenance. For example, a parking lot with higher traffic vol­• Compaction of underlying soil, such as umes will tend to require more maintenance through the use of heavy equipment. because of the resulting increased quantities• Contamination of stone sub-base with of soil and particulates brought onto the lot. sediment. Although the new soil alone will not neces­ sarily clog the pavement’s voids, if ground in• Tracking of sediment onto pavement.87 repeatedly by tires, clogging can occur.90,91Like other best management practices, when Regular maintenance can avoid clogging ofpermeable paving systems fail, it is frequently permeable paving systems. Facilities manag­due to mistakes made during the design and ers are generally advised to high pressureconstruction process. Recent studies note hose and then vacuum porous pavement a Green Parking Lot Resource Guide—February 2008 25

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