# Engineering Site Visit Report for Denver International Airport Denver, CO

Prepared for:



## U.S. Environmental Protection Agency

Engineering and Analysis Division
Office of Water 1200 Pennsylvania Avenue, NW Washington, D.C. 20460

Prepared by:



### Eastern Research Group, Inc. 14555 Avion Parkway
Suite 200 Chantilly, VA 20151

November 2007

EPA Contract No. 68-CO2-095 Work Assignment 3-151 Engineering Site Visit Report for

Denver International Airport Denver, CO

1.0 P LACE AND D ATE

Denver International Airport

8500 Peña Boulevard Denver, Colorado 80249

November 8, 2005

2.0 A TTENDEES

Denver International Airport Janet Kieler, Senior E ngineer (303) 342-2636 Janell A. Barrilleaux, Environmental Scientist Supervisor (303) 342-2730 Keith Pass, Environmental Scientist II (303) 342-2689 Craig Schillinger, Environmen tal Scientist II (303) 342-2834 Ron Schlotthauer, DIA/Ramp Operations Eric B. Hall, DIA Operations Ron Morin, DIA Maintenance/Engineering

Inland Technologies International Ltd. Jim Collins, Vice President (812) 549-5332 Michael Svedruzic, USA Oper ations Manager (703) 788-6804 Brian Stierman, Denver Site Op erations Manager (303) 342-6811

U.S. Environmental Protection Agency

Brian D = Amico, Environmental Engineer (202) 566-1069

Eastern Research Group, Inc. (technical contractor to U.S. EPA) Mary Willett, ERG Work Assignment Manager (703) 633-1615 Steve Strackbein, ERG Proj ect Scientist (703) 633-1656

3.0 B ACKGROUND AND O BJECTIVES

The U.S. Environmental Protection Agen cy (EPA) and its technical and economic contractor, Eastern Research Group, Inc. (E RG), conducted a site visit at the Denver International Airport (DIA) on November 8, 2005. Th e primary purpose of the site visit was to

increase EPA = s understanding of technical and economic i ssues associated with airport deicing operations. Technical issues are described in this report and include: aircraft, runway, and taxiway deicing/anti-icin g processes; deicing equipment; wast ewater generation; and wastewater collection, handling, recycling, and discharge. A secondary purpose of the meeting was to identify potential sampling points and gather othe r pertinent information should the airport be selected for future sampling. This information is being collected by EPA's Office of Water as part of the Effluent Guidelines project for Ai rport Deicing Operations. Denver International2 Airport was selected for a site visit because it receives a heavy amount of snowfall and operates an on-site recycling system for spen t aircraft deicing fluids (ADF).

4.0 F ACILITY D ESCRIPTION

DIA is operated by the City and County of Denver, Department of Aviation, and is a municipal airport facility serving the Denver, Colorado metropolitan area. The airport opened on February 28, 1995 and includes 4 north-sout h and 2 east-west runways for a total of 6 runways, five of which are 12,000 feet in lengt h and one which is 16,000 feet in length. The airport has 89 gates and associat ed taxiways, aircraft parking ap rons; three airside concourses; and passenger and cargo terminals. DIA is lo cated 23 miles northeast of downtown Denver on a site encompassing 34,000 acres (53 square miles). A map of the airport is presented in Figure 1.

Currently, the airport includes major ai rlines, commuter airlines, multiple cargo carriers, and two fixed-base operators (FBOs). Th e major airlines at the airport include United, Continental, Frontier, AirTran, Alaska, America West, American, ATA, Delta, Northwest, US Airways, Great Lakes, and Jet Blue. Commuter airlines include JetExpress (Horiz on), Midwest Express and United Express. International ca rriers include British Airways, Mexicana and Luftansa. Cargo carriers operating out of the ai rport include FedEx, UPS, DHL and Airborne Express. Aircraft Service International Group (ASI G) and Integrated are the two major FBOs at

DIA. 1

5.0 D EICING O PERATIONS AT D ENVER A IRPORT

A major safety concern for all airports is the clearing of ice and snow build-up on runways, taxiways, roadways, gate areas, and aircraft. Aircraft deicing and anti-icing operations at DIA are performed by the airlines and FB Os. DIA personnel generally perform deicing on runways, taxiways and roadways. The potential deicing/anti-icing season at the airport is October through April.

5.1 Runway, Taxiway, Apron, and Ramp Deicing/Anti-Icing

DIA airport personnel are responsible for deicing pavement areas. DIA uses physical removal methods, includi ng plows, blowers, chemical trucks, brooms and sander plows as much as possible to keep the pavement areas clear. DIA = s airfield snow removal fleet includes 97 pieces of equipment, none of which are mu lti-functional. In addition, other storm event equipment includes ambient air temperature sens ors which are mounted on 14 vehicles, vehicle measurement of percent chemical left on th e runway and runway friction, and surface temperature monitors embedded in the runway pavement. When necessary, potassium acetate (Cryotech 36) is applied as a deicer and ther e is also use of runway sand. Annual usage of Cryotech 36 averages 500,000 to 600,000 gallons per year.

1 As of 2006, Integrated no longer operates at DIA, and Pennauille Servisair is a new FBO.3 Figure 1. Map of Denver International Airport4 Contaminated and non-contaminated snow is not segregated. Airport personnel

indicated that the snow at DI A does not usually get contamin ated by ADF. Airport snow is collected at a snow dump area lo cated to the east of Concourse A. Melted snow from this snow dump area drains to feed storage pond 001. In ab ove-average snow conditions an overflow snow dump area to the north of Concourse C is utili zed. Melted snow is not collected from this overflow snow dump area.

Airport personnel use an information sy stem called Weather Support to Deicing Decision Making (WSDDM) to help predict and ma nage storm events at the airport. This product consists of a graphical display that provides real-time A nowcasts @ of snowfall events and

other winter weather conditions. Th is system displays weather information related to aircraft deicing that is easily underst ood by non-meteorologists. The WS DDM system uses real-time radar data, weather reports, and locally deploye d snow gauges and weather stations to provide

users with:

 Real-time snow gauge data updated every minute,

 Real-time radar reflectivity from depict ing current locations of precipitation and snow,

 Meteorological data at the airport and several sites 10-20 km away from the airport updated every minute; and

 30 minute “nowcasts” of radar reflectivity to predict the next 30 minutes of weather, updated every 6 minutes.

5.2 Aircraft Deicing/Anti-Icing

Aircraft deicing at DIA is performed by the airlines, cargo carriers and/or the FBOs. All deicing is done on deicing pads, with th e exception of low level gate deicing (up to 25 undiluted gallons of ADF) to allow for safe plane movement. The passenger aircraft deicing pads are located next to the airport concourses. Pad A is located just west of Concourse A, Pad B is located just west of Concourse B, and Pads C a nd J are located just west of Concourse C. There are six other remote deicing pads, two of whic h are located at the Continental and United hangers, a pad (designated as the EE pad) located just east of the United hangar, a pad in the general aviation area, a pad at the cargo area, and a pad (designated as the D pad) located east of the cargo area. (See Figure 1). Airport personnel indicated that the Cont inental hanger pad and the D pad are not used; in addition, the EE pad gets very little use. The de icing pads located west of the concourses (A, B, C and J) were designe d to discharge ADF-contaminated stormwater to the recycling plant storage system if economical ly viable (i.e. the c oncentration of propylene glycol is greater than one per cent). However, none of the remo te deicing pads are currently feeding stormwater to the recyc ling plant, either because the pa ds are not used or because the pads are infrequently used and the deicing stormw ater is diverted to nearby storage ponds for discharge to the publicly ow ned treatment works (POTW), the Metropolitan Wastewater

Reclamation District.5 All of the airlines and FBOs at DIA mu st use propylene glycol-based Type I or Type IV ADF for aircraft deici ng and anti-icing. Most of the propyl ene glycol (PG) used at the airport is stored in a centralized supply area where Inland Technologies In c. is responsible for distribution. Inland also currently does onsite blen ding of pure PG with additives (purchased as an “add pack”) to make Type I ADF. Type IV ADF is purchased ready to use. This centralized ADF area feeds dispensers located at the A a nd J deicing pads. All car go airlines and United Airlines do not use this centralized system. Th e cargo airlines utilize remote storage tanks for type I and type IV ADF while United Airlines has its own ADF storage/supply/distribution system. For the 2004-05 deicing season, DIA st aff estimated that 867,000 gallons of ADF (concentrated) were used for aircraft deicing/anti-icing.

6.0 W ASTEWATER G ENERATION , C OLLECTION , AND D ISPOSAL

The Denver airport was designed with a cen tralized deicing system comprised of four deicing pads that are used for passenger aircraft, with a fifth under construction, general aviation and cargo ramps, and a deicing pad (Pad D) which is occasionally used by cargo aircraft. As stated previously, very little deicing is performe d in the general aviation and cargo areas. See Figure 1 for a schematic of the airport, runways, deic ing pads, and storage ponds. All deicing pads are shown in solid green and the storage ponds are shown in green outline. A single deicing pad can accommodate multiple aircraft at once. Each of the passenger aircraft deicing pads (Pads A, B, C, and J) and Pad D feeds hi gh concentration ADF stormw ater (greater than 1 percent glycol) to one of five 420,000 gallon storage tanks located at the glycol recycling plant. All five of the 420,000 gallon storage tanks can feed the recycling plant but, in general, four of the tanks are used for storage and one tank is used to feed mixed/equalized stormwater into the recycle system. When the passenger aircraft deici ng pad stormwater contai ns low concentrations (less than 1 percent) of glycol , it can be redirected to storag e pond 002, where is it discharged to the POTW. Other low concentration streams pum ped to the POTW include runoff from the general aviation deicing pad, co llected in pond 004; runoff from the cargo ramp, collected in pond 005; and runoff from taxiways and runways, which is collected in pond 009.

DIA has six storage ponds that collect st ormwater contaminated with low levels of glycol:

 Pond 001 is located east of the UAL hangar;

 Pond 002 is located north of the c oncourse deicing pads and collects stormwater from the passenger aircraft de icing pads that is too dilute for the recycling plant;

 Pond 003A is located just next to the glycol recycling plant;

 Pond 004 is located in the general avia tion area and collect s runoff from the general aviation deicing pad;

 Pond 005 is located in the cargo area and collects runoff from the cargo ramp;

and6  The WADS pond is new and is located west of the recycling plant.

The total capacity of the six ponds is 61.6 million gallons. Most of the ponds have a two cell configuration, so that only one cell is receiving stormw ater while the other is being mixed, prepared and batch discharged to th e local POTW. The WADS pond has three cells,

where two cells receive and hold stormwater an d the third cell is mixed and provides an equalized flow for metering and discharge to the POTW. Along with the new WADS ponds, DIA has installed new pumps and piping for thei r POTW discharge. This system includes a continuous COD monitor and variable pumps so th at the airport can more closely control the COD load that is discharged. Denver = s current POTW discharge permit requires them to comply with monthly COD discharge load limits. The c ontinuous COD monitor is being pilot-tested, as the POTW has not approved its use. The airport is also required to adjust the COD load up or down over time to minimize shock to the POTW sy stem. Other parameters monitored by DIA for its POTW discharge include pH and lower explosive limit (LEL).

Denver = s individual NPDES stormwater permit is current and expires in July

2006. 2 DIA was in the process of negotiating this permit when EPA last visited the airport in 1998 during the preparation for the Agency’s Pr eliminary Data Summary. In 1996, glycol had been found downstream of the airpor t at significant con centrations (in the ra nge of thousands of mg/l). The permit authority, Colorado Department of Public Health a nd Environment (DPHE), was evaluating whether to require numerical limits for the airport = s direct discharge stormwater permit. In an effort to address this issue, th e airport blocked the creek to which it discharged (Third Creek) in 1998 with a dam and sent the creek = s flow to the POTW for treatment.

The airport ceased this practice after about a year and installed a fugitive collection system which included stormwater collec tion from a larger area of the concourse and parts of the winter departure runways. (See the ou tlined area in the upper left corner of Figure 1.) The fugitive collection system was effective in reducing the amount of AD F that made it to the receiving stream. DIA also contracted with CD M, Inc. for a receiving water study to evaluate the impact of the airport = s direct discharge on dissolved oxyg en and overall water quality in

Third Creek and in a control creek located on the airport = s property. The control creek was not affected by airport or industr ial practices but both the cont rol creek and Third Creek are impacted by agricultural runoff. The results of the receiving wa ter study showed greater water quality impairment at the control creek compared to Third Creek. In addition, the study showed greater water quality impacts from nutrients (whi ch are likely caused by agricultural runoff) than ADF. The study was inconclusive in making a c onnection between ADF discharge and dissolved

oxygen.

DIA personnel indicated that both the a ddition of the fugitive collection system and the results of the receiving water study c onvinced Colorado DPHE to require only best management practices (BMPs) and not numerical limits in the stormwater permit. In addition, the airport has added a low flow diversion to th e receiving stream so that ADF contaminated

flow can be rerouted to one of the PO TW discharge storage ponds if needed.

2 Subsequent to EPA’s site visit, the permit authority has administratively extended the permit.7 The airport has evaluated estimates of its deicing fluid usage compared to the spent fluid collection rate. These estimates show that 68 percent of applied ADF is recovered; this is comprised of 42 percent recycled ADF, and 26 percent sent to the POTW. The fate and transport of the remaining 32 percent is unknown; however, the most likely mechanisms include:

 Wind-borne transport;

 Loss of ADF through pavement joints and underground util ity structures;

 Aircraft drippage and wind shear loss; and

 Tracking of ADF on vehicle wheels to areas outside the collection system.

7.0 R ECYCLING

The on-site glycol recycling plant ow ned by DIA and operated by Inland. Inland has been in charge of the recy cling plant since July 1, 2004. On September 31 of a typical year, the drain valves at deicing pads J, A, B, and C are opened, allowing the runoff from the pads to enter the recycling plant storage tanks. The valv es at the deicing pads can be changed to bypass the storage tanks and go to the storage ponds dur ing rainfall events when no deicing occurs.

Figure 2 presents a schematic of the gl ycol recycling plant. The plant storage tanks feed five mechanical vapor recompre ssion units (MVRs). The MVRs concentrate the storage tank influent, which range s from 1 to 12 percent PG, to a final concentration of 50 to 55 percent. Each MVR has a capacity of 3,250 gallons per day. The effluent from the MVRs goes to a storage tank until 150,000 gallons is stockpiled. The stockpiled effluent is sent to a distillation system, which increases the glycol concentration to 98 to 99 percent PG. The distillation system runs 24 hours a day for a three-week cycle and processes about 225,000 gallons of PG before the system is halted for cleaning and maintenance. The distillate from both the MVRs and the distillation column are discharged to the ai rport’s WADS storage ponds. The distillate is monitored for biological oxygen demand (BOD) prio r to discharging to the storage ponds. The

distillation column bottoms are classified as specialized non-hazardous waste and are sent to a landfill (operated by BFI Waste Systems). The 98 to 99 percent PG from the distillation column is pumped to a polisher where it is concen trated to greater than 99.3 percent PG.

The recycling plant r ecycled 306,000 gallons of PG in the 2004/2005 season, approximately 42 percent of the applied ADF.8 Figure 2. Recycling Plant Flow Diagram for Denver International Airport

8.0 P OTENTIAL S AMPLING L OCATIONS

During the tour of the re cycling plant, Inland personnel indicated that sampling could potentially be done at any st age of the process. Stormwater flow into the six storage tanks occurs through three header lines and each of these lines are fitted with a tap so that the glycol concentration coming into the recycling plant st orage tanks can be asse ssed. The most likely locations for sampling the recycling sy stem influent and effluent include:

1. The 420,000 gallon feed tank into the syst em (this feed will best represent the equalized influent into the system);

2. The waste distillate from the m echanical vapor recompression units (which is pumped to the airport = s POTW storage ponds);

3. The holding tank that feeds the distillation system; and

4. The distillation overheads (which ar e pumped to the airport’s POTW storage ponds). (5)420,000 Gal Recycle Plant Holding Tanks (5) MVR Units (Parallel/Series) 1-12% Holding tanks (3) Distillation

Columns (Series) ~50% ~50%

~ 98% Polisher (Carbon Filter/ Deionization) Final Odor

Filter (Specialized Media) > 12% ADF

Stormwater

+ 99 % <1% Storage ponds Local

POTWDistillate Distillation Overheads

For Sale

via Inland >1%