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The third scenario assesses the Chicago Center 1 for Green Technology, a retrofit of an
2 existing commercial building on a 3.3 acre brownfield site that employs a partial green
3 roof, native plantings, water harvesting in cisterns, permeable pavement and a
4 constructed wetland.
5 Although the actual construction costs for this project were likely higher than what the Green
6 Values™ Calculator estimates (since the project was a first-generation demonstration completed
7 in about 2002), the scenario evaluates costs and performance assuming the same features were
8 constructed at 2009 rates. The modeled results, which the city has monitored as diverting 81
9 percent of annual runoff volume, would reduce life cycle costs by 20 percent and prevent nearly
10 2.5 million gallons of runoff from entering sewers.
11
12 Cost-benefit calculations from the Green Values™ Calculator include preliminary estimates of
13 selected additional benefits that green infrastructure practices have been documented to produce,
14 such as ground water recharge, energy savings, and carbon sequestration.17 Philadelphia
15 evaluated the additional economic and social benefits stemming from a community scale program
16 of green and conventional stormwater practices, designed to deliver similar stormwater
17 performance in several watersheds. The analysis tallied estimated benefits in 11 categories,
18 attributing a greater than $2.7 billion additional benefit to the option utilizing 50% green
19 infrastructure (Table 6).
20
21 Kansas City, Missouri, has also developed a city-scale plan for green infrastructure as part of its
22 combined sewer overflow long-term control plan (Kansas City Water Services Dept. 2008).
23 Evaluating the degree to which planned conventional upgrades could be eliminated with street
24 trees, pervious pavement, green roofs, stormwater planters, and curb extension swales, local
25 authorities identified three sub-watersheds that can achieve equivalent stormwater service using
26 green infrastructure as a portion of the infrastructure investment (Leeds 2008). See Table 7,
27 below.
28
29 Kansas City also recognized that green infrastructure solutions leverage private investment, in the
30 form of anticipated green roofs and permeable pavement on private property, so that ―Public
31 investment can be reduced with significant investment by [the] private sector.‖
32 Kansas City‘s analysis also includes estimates of construction costs for green infrastructure
33 practices. Depending on the type of practice, the cost estimates range from $2.28 to $7.13 per
34 gallon (rain garden or bioretention retrofits) to $10.86 per gallon for curb extension swales, $5.50
35 per gallon for permeable parking lots, $11.24 per gallon for permeable sidewalks, $22.68 per
36 gallon for green roofs. The gallons refer to the design capacity of the practice. (This is in contrast
37 to the volumes, in cubic feet, in Table 4 where the reference is to volume infiltrated over the life
38 of the practice).
17 See http://greenvalues.cnt.org/national/benefits_detail.php for a list of benefits associated with green
infrastructure practices and published references to their quantification.
