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 3-15
1

Engineering Site Visit Report for 

Denver International Airport 

Denver, CO 

1.0 PLACE AND DATE

Denver International Airport 

8500 Peña Boulevard 

Denver, Colorado 80249 

November 8, 2005 

2.0 ATTENDEES

Denver International Airport

Janet Kieler, Senior Engineer (303) 342-2636 

Janell A. Barrilleaux, Environmental Scientist Supervisor (303) 342-2730 

Keith Pass, Environmental Scientist II (303) 342-2689 

Craig Schillinger, Environmental 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 Operations Manager (703) 788-6804 

Brian Stierman, Denver Site Operations 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 Project Scientist (703) 633-1656 

3.0 BACKGROUND AND OBJECTIVES

 The U.S. Environmental Protection Agency (EPA) and its technical and economic 

contractor, Eastern Research Group, Inc. (ERG), conducted a site visit at the Denver 

International Airport (DIA) on November 8, 2005. The primary purpose of the site visit was to 

increase EPA=s understanding of technical and economic issues associated with airport deicing 

operations. Technical issues are described in this report and include: aircraft, runway, and 

taxiway deicing/anti-icing processes; deicing equipment; wastewater generation; and wastewater 

collection, handling, recycling, and discharge. A secondary purpose of the meeting was to 

identify potential sampling points and gather other 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 Airport Deicing Operations. Denver International 
2

Airport was selected for a site visit because it receives a heavy amount of snowfall and operates 

an on-site recycling system for spent aircraft deicing fluids (ADF). 

4.0 FACILITY DESCRIPTION

 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-south and 2 east-west runways for a total of 6 

runways, five of which are 12,000 feet in length and one which is 16,000 feet in length. The 

airport has 89 gates and associated taxiways, aircraft parking aprons; three airside concourses; 

and passenger and cargo terminals. DIA is located 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 airlines, commuter airlines, multiple cargo 

carriers, and two fixed-base operators (FBOs). The 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 (Horizon), Midwest 

Express and United Express. International carriers include British Airways, Mexicana and 

Luftansa. Cargo carriers operating out of the airport include FedEx, UPS, DHL and Airborne 

Express. Aircraft Service International Group (ASIG) and Integrated are the two major FBOs at 

DIA.1

5.0 DEICING OPERATIONS AT DENVER AIRPORT

 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 FBOs. 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, including 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 multi-functional. In addition, other storm event 

equipment includes ambient air temperature sensors which are mounted on 14 vehicles, vehicle 

measurement of percent chemical left on the 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 there 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 Airport 
4

 Contaminated and non-contaminated snow is not segregated. Airport personnel 

indicated that the snow at DIA does not usually get contaminated by ADF. Airport snow is 

collected at a snow dump area located to the east of Concourse A. Melted snow from this snow 

dump area drains to feed storage pond 001. In above-average snow conditions an overflow snow 

dump area to the north of Concourse C is utilized. Melted snow is not collected from this 

overflow snow dump area. 

 Airport personnel use an information system called Weather Support to Deicing 

Decision Making (WSDDM) to help predict and manage storm events at the airport. This 

product consists of a graphical display that provides real-time Anowcasts@ of snowfall events and 

other winter weather conditions. This system displays weather information related to aircraft 

deicing that is easily understood by non-meteorologists. The WSDDM system uses real-time 

radar data, weather reports, and locally deployed snow gauges and weather stations to provide 

users with: 

 Real-time snow gauge data updated every minute, 

 Real-time radar reflectivity from depicting 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 the 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 and J are located just west of Concourse C. There 

are six other remote deicing pads, two of which 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 Continental hanger pad and 

the D pad are not used; in addition, the EE pad gets very little use. The deicing pads located west 

of the concourses (A, B, C and J) were designed to discharge ADF-contaminated stormwater to 

the recycling plant storage system if economically viable (i.e. the concentration of propylene 

glycol is greater than one percent). However, none of the remote deicing pads are currently 

feeding stormwater to the recycling plant, either because the pads are not used or because the 

pads are infrequently used and the deicing stormwater is diverted to nearby storage ponds for 

discharge to the publicly owned treatment works (POTW), the Metropolitan Wastewater 

Reclamation District. 
5

 All of the airlines and FBOs at DIA must use propylene glycol-based Type I or 

Type IV ADF for aircraft deicing and anti-icing. Most of the propylene glycol (PG) used at the 

airport is stored in a centralized supply area where Inland Technologies Inc. is responsible for 

distribution. Inland also currently does onsite blending 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 and J deicing pads. All cargo airlines and United 

Airlines do not use this centralized system. The 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 staff estimated that 867,000 gallons of ADF 

(concentrated) were used for aircraft deicing/anti-icing. 

6.0 WASTEWATER GENERATION, COLLECTION, AND DISPOSAL

 The Denver airport was designed with a centralized 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 performed in the general aviation and cargo 

areas. See Figure 1 for a schematic of the airport, runways, deicing 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 high concentration ADF stormwater (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 deicing pad stormwater contains low concentrations 

(less than 1 percent) of glycol, it can be redirected to storage pond 002, where is it discharged to 

the POTW. Other low concentration streams pumped to the POTW include runoff from the 

general aviation deicing pad, collected 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 stormwater contaminated with low levels 

of glycol: 

 Pond 001 is located east of the UAL hangar; 

 Pond 002 is located north of the concourse deicing pads and collects 

stormwater from the passenger aircraft deicing 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 aviation area and collects runoff from the 

general aviation deicing pad; 

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

and 
6

 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 stormwater while the other is being 

mixed, prepared and batch discharged to the local POTW. The WADS pond has three cells, 

where two cells receive and hold stormwater and 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 their POTW discharge. This system includes a 

continuous COD monitor and variable pumps so that 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 continuous 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 system. 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 Preliminary Data Summary. In 1996, glycol had 

been found downstream of the airport at significant concentrations (in the range of thousands of 

mg/l). The permit authority, Colorado Department of Public Health and Environment (DPHE), 

was evaluating whether to require numerical limits for the airport=s direct discharge stormwater 

permit. In an effort to address this issue, the 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 collection from a larger area of the concourse and 

parts of the winter departure runways. (See the outlined area in the upper left corner of Figure 1.) 

The fugitive collection system was effective in reducing the amount of ADF that made it to the 

receiving stream. DIA also contracted with CDM, Inc. for a receiving water study to evaluate 

the impact of the airport=s direct discharge on dissolved oxygen 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 industrial practices but both the control creek and Third Creek are 

impacted by agricultural runoff. The results of the receiving water 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 (which are likely caused by agricultural runoff) than 

ADF. The study was inconclusive in making a connection between ADF discharge and dissolved 

oxygen. 

 DIA personnel indicated that both the addition of the fugitive collection system 

and the results of the receiving water study convinced 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 the receiving stream so that ADF contaminated 

flow can be rerouted to one of the POTW 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 utility structures; 

 Aircraft drippage and wind shear loss; and 

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

7.0 RECYCLING

 The on-site glycol recycling plant owned by DIA and operated by Inland. Inland 

has been in charge of the recycling 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 valves at the deicing pads can be changed to bypass 

the storage tanks and go to the storage ponds during rainfall events when no deicing occurs. 

 Figure 2 presents a schematic of the glycol recycling plant. The plant storage 

tanks feed five mechanical vapor recompression units (MVRs). The MVRs concentrate the 

storage tank influent, which ranges 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 airport’s WADS storage ponds. The distillate is 

monitored for biological oxygen demand (BOD) prior 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 concentrated to greater than 99.3 percent PG. 

 The recycling plant recycled 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 POTENTIAL SAMPLING LOCATIONS

 During the tour of the recycling plant, Inland personnel indicated that sampling 

could potentially be done at any stage 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 storage tanks can be assessed. The most likely 

locations for sampling the recycling system influent and effluent include: 

1. The 420,000 gallon feed tank into the system (this feed will best represent 

the equalized influent into the system); 

2. The waste distillate from the mechanical 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 are 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 

POTW

Distillate

Distillation Overheads

For Sale 

via Inland

>1%