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89 The Effect of Aircraft Loading on Cost of Structures The biggest factor that increases the cost of certain airport drainage infrastructure such as catch basins, drain manholes, and pipes is the design live load, or the load of moving objects such as trucks, buses, and cars. These live loads can differ between highways and airport settings, making it difficult to translate highway costs to the airport setting. For public infrastructure projects such as roads and highways, design depends on total expected live load (American Association of State Highway Transportation Officials, 2011). For example, a typical live load is Highway, Semi-Trailer-20 (HS-20), which represents a typical load imparted by a vehicle, measured in kips or pounds. Airport drainage infrastructure, on the other hand, is typically exposed to high live loads from varying sizes and types of aircraft. Figure E1 shows a schematic of a catch basin design appropri- ate for an airport. Two primary factors affecting aircraft live load are the weight of the aircraft and the number and configuration of landing gear. A typical airline aircraft in service today is a Boeing 737. These aircraft can range in weight from 110,000 pounds to 187,000 pounds, depending on model type, passenger load, and fuel load (FAA, 2014b). A concrete structure manufacturer must upsize many different parts of a drainage structure for airport loading in order to prevent structural failure when an aircraft rolls over the top of it. Typical material cost differences include concrete slab thickness, the number and size of steel A P P E N D I X E Factors Affecting Costs of Stormwater Infrastructure Projects at Airports Cost Difference â Airport Versus Roadway 2015 AIP Project, Burlington, VT Higher design load requirement = greater cost. Roadway drainage with HS-20 loading vs. airport drainage with heavy aircraft loading, Burlington International Airport. Structures within 90 ft. of each other (one near aircraft, one against a security fence). Item Unit Cost 4-ft-diameter manhole (aircraft loading) $8,516.00 4-ft-diameter manhole (HS-20 Loading) $5,625.00 Cost differential $2,891.00 or â¼51% (Burlington International Airport, 2015)
90 BenefitâCost Analyses Guidebook for Airport Stormwater Source: Hoyle, Tanner & Associates, 2016. Figure E1. Schematic of aircraft loading catch basin.
Factors Affecting Costs of Stormwater Infrastructure Projects at Airports 91 reinforcement bars, and the thickness and strength of the structure rim or grate on top. In addi- tion to material cost increases, the design of these structures typically requires more engineering time, material forming and layout time, and quality control time. The Effect of Airport Operational Constraints on Cost of Stormwater Facilities There is also a premium on installation of drainage structures on active airfields because contractors are often subjected to limited and nonstandard work hours. Therefore, the cost of labor in the field is typically much higher due to overtime requirements and the built-in cost of start-and-stop operations on an airfield. Airports are required to maintain safe operations on their airfields; therefore, construction must always be second priority (Figure E2), and the duration of a project is often extended due to the necessary âstart-and-stopâ schedules (FAA, 2011c). When a contractor is required to stop and demobilize from a construction site, it typically cannot easily transport its equipment to another active project site, so there is an inherent cost to the schedule as the equipment lays inactive. This cost is typically anticipated and is built into a contractorâs estimate for doing work. It is intended to assist in the recovery of lost time and rental and maintenance costs for inactive equipment. The Effect of Wage Rates on the Cost of Stormwater Facilities AIP projects are funded with federal government dollars. Therefore, all AIP projects require that contractors adhere to federal labor wage rates. Additionally, most AIP projects are co-funded with state government dollars, and this also requires that contractors adhere to state labor wage rates, which can sometimes exceed federal wage rates (Integrated Acquisition Environment, 2017). Contractors are required to adhere to the higher of the two, and as a result, labor costs are marginally higher than municipal or private construction labor costs. Source: Hoyle, Tanner & Associates, 2016. Figure E2. Airport operations, safety, and security control have an enormous effect on the cost of stormwater projects.
92 BenefitâCost Analyses Guidebook for Airport Stormwater The Effect of the Type of Construction on the Cost of Stormwater Facilities Stormwater project prices are also affected by the type of construction that is required. New construction on unimproved sites will typically be less expensive than rehabilitation projects on existing sites. AIP projects are typically completed in phases and over many years due to fund- ing constraints and airport operations limitations. Each airport project must have an approved construction safety phasing plan, which will outline the various site constraints, how each phase will be prosecuted, and all proposed safety-related initiatives (FAA, 2011c). This piecemeal and phased approach often dictates that stormwater facilities must be replaced in confined spaces, causing contractors to expend more time planning the phasing of projects and often necessitat- ing inefficient and time-consuming heavy equipment operations. Additionally, the connection between new stormwater structures and existing, degraded structures requires additional time and expensive supporting material costs to ensure durable and water-tight connections. Often, these types of connections require temporary stormwater flow bypass operations, which require site dewatering equipment and significant amounts of fuel to run the equipment continuously during construction. Figure E3 shows an aerial photograph of an AIP project with significant upgrades and a stormwater bypass. The Effect of Environmental Compliance on the Cost of Stormwater Facilities Many airport stormwater infrastructure projects connect to or directly affect surrounding wetlands. Depending on the scope of the project, certain environmental study and permitting may be required at the federal, state, and local government level. The required scientific study, data collection, analysis, and permit application steps can require significant time, report writing, government review, permit application administration, public meetings and public outreach, and in many cases, environmental mitigation fees. There are different state and local published stormwater BMPs documents, all created to assist the public in determining appropriate and Source: Hoyle, Tanner & Associates, 2016. Figure E3. Example of a complicated airport AIP project with significant utility upgrades and stormwater bypass and rehabilitation within a confined area.
Factors Affecting Costs of Stormwater Infrastructure Projects at Airports 93 feasible methods to plan for and design stormwater projects. For example, Florida has terrain and an environment that are almost unique, and the state makes guidance available on how to manage stormwater project planning and design (Florida Department of Transportation â Aviation Office, 2013). One of the most common ways to mitigate the environmental impacts of activities such as extending a runway or taxiway within a wetland or rare species area is to recreate and replace these environmental habitats on site. The challenge for AIP-funded projects is that airports are inherently a poor place for some habitats such as wetlands, which can attract wildlife deemed a hazard to flight operations. Stormwater BMPs must be designed to address FAA AC 150/ 5200-33B: Hazardous Wildlife Attractants on or near Airports the (FAA, 2007b; FAA, 2012) to limit wildlife attractants (e.g., open water or vegetation); this is sometimes accomplished by using nets or bird balls on detention basins. For instance, designing a mitigation area consist- ing of a stormwater detention pond or a recreated wetland near an active airport is not feasible since it will likely attract certain avian species and mammals that can be struck by an aircraft, causing a major safety accident. As a result, alternative mitigation solutions typically increase costs either by necessitating more expensive facilities on site or requiring off-site mitigation fees, which are dictated by state and local cost schedules and sometimes amount to over a million dollars. Figure E4 shows an example where the stormwater storage and treatment are constructed underground; the projects meet federal, state, and local requirements but are more expensive than traditional above-ground detention ponds. It should also be noted that AIP projects involve federal funding in addition to any state or local funding. This leaves them subject to significantly more review and permitting requirements than projects without federal funding. In some cases, airports prepare stormwater master plans, which include existing airport con- ditions and how to most effectively implement future water quality and water quantity treat- ment systems. This allows the airport to analyze its entire property and associated watershed system by doing an inventory of existing conditions such as soil type, wetlands areas, ground- water levels, and ground cover. These plans allow a comprehensive look at future development Source: Hoyle, Tanner & Associates, 2016. Figure E4. Construction of a below-ground stormwater storage and treatment facility at BostonâManchester Regional Airport.
94 BenefitâCost Analyses Guidebook for Airport Stormwater and how to appropriately design stormwater systems. Such an approach prevents piecemeal, disconnected stormwater design and treatment. Ormond Beach Municipal Airport and Ocala International Airport have completed storm- water master plans, and each plan results in recommendations for comprehensive storm water treatment systems for all future improvements within the airportsâ capital improvement plans (Hoyle, Tanner & Associates, 2016; GPI Southeast Inc., 2013). The money invested in these efforts is likely offset by the results and recommendations that are offered in the plan. The recommendations for future stormwater treatment allow an airport and potential tenant investors to clearly identify stormwater development costs and thus eliminate the typical uncertainties of how an individual project may be analyzed by state and local regulators. This wholesale approach to airport project development planning is a well-accepted practice by FAA and airport sponsors (Gresham, Smith and Partners, 2011).