Subsurface Flow (SSF) Constructed Treatment Wetlands (CTW)
- A passive system operating under gravity flow that treats storm water runoff from a 162 acre watershed
- Approximately 3 feet deep and consists of phragmites sp. Rhizomes growing on a sand and gravel bed. 2,000 rhizomes were planted on 3-foot centers in a 3-inch layer of ¾-inch gravel.
- Can handle a mean flow of 100,000 gpd, and maximum flow of 400,000 gpd
- Constructed over a low elevation 0.6-acre area and has a trapezoidal cross section.
- Hydraulically isolated from surrounding soils by a 30 mil PVC liner
- Perforated inlet and outlet pipes buried in subsurface coarse rock layers that run along opposing inside edges of the SSF CTW. The inlet pipe runs close to the surface and the outlet pipe runs close to the base liner.
- Storm water to be treated enters the SSF CTW through the perforated inlet pipe, flows horizontally through the root zone in the granular media and exits through the perforated outlet pipe.
Naval Facilities Engineering Service Center
Robert L. Knight
Wetland Solutions, Inc.
2809 N.W. 161 Court
Gainesville, Florida 32609
Phone: (386) 462-1003
Nonhalogenated semivolatiles: aircraft deicing fluids - propylene glycol, ethylene glycol and additives
- On average, 10,000 gallons of aircraft deicing fluid used annually at Westover ARB
- 50,000 gallons of aircraft deicing fluid used during period of demonstration (2002 2003)
- Peak influent biochemical oxygen demand (BOD) concentrations ranged from 974 to 15,098 mg/L in 10 deicing events during 2002.
Aircraft deicing operations resulting in contamination of storm water runoff.
Type/Quantity of Media Treated:
- Approximately 12.2 million gallons of storm water was treated between December 2002 and May 2003
Purpose/Significance of Application:
Demonstration of SSF CTW for treatment of aircraft deicing fluids-contaminated storm water runoff at the Westover ARB.
Regulatory Requirements/Cleanup Goals:
Compliance with NPDES permit requirement monthly mean BOD in effluent less than 30 mg/L.
- Results are based on performance between December 2002 and May 2003.
- Average monthly influent BOD ranged from 165 to 2,655 mg/L. Average monthly effluent BOD ranged from 100 to 1,667 mg/L. BOD reduction ranged from 11.2 to 78 percent.
- The NPDES permit requirement for BOD was not met during the demonstration. However, the NPDES permit changed from individual to multi-sector during the project. It was therefore suggested that comparison of demonstration results to individual permit criteria was not valid.
- Other parameters measured were chemical oxygen demand (COD), methyl-1H-benzotriazole (deicing fluid additive), dissolved oxygen (DO), pH, redox, temperature and turbidity. Significant changes in average influent and effluent pH were observed. The average pH of influent and effluent was 7.58 and 9.54 respectively.
- Capital cost for the demonstration totaled $326,000. The cost included design, mobilization, equipment purchase, construction, management, permitting and demobilization.
- Operation and maintenance cost during the demonstration totaled $6,900. The cost included labor, utilities, equipment and equipment maintenance.
- Projected annual cost for operation and maintenance was $2,000. The cost included analytical testing.
Westover ARB, located in Massachusetts, is situated approximately 2 miles east of the Connecticut River, and is traversed and bounded by Cooley and Stony Brooks. The Base performs deicing and anti-icing on its aircrafts and runways during snow storms and freezing rain events. This generates contaminated storm water runoff that can impact adjacent surface waters.
The demonstration of CTW was performed to evaluate it as an alternative for treating runoff from Westover ARB. A passive SSF CTW was constructed over 0.6 acres of land to handle an average flow of 100,000 gpd and a maximum flow of 400,000 gpd. The CTW consisted of phragmites sp. rhizomes grown over a sand and gravel base. Stormwater runoff was delivered to the CTW through a perforated inlet pipe and exited it through a perforated outlet pipe.
The regulatory goal of the demonstration was to comply with the NPDES permit requirement of a monthly mean BOD in effluent of less than 30 mg/L. The CTW treated almost 12.2 million gallons of water during the demonstration. The average monthly influent BOD ranged from 165 to 2,655 mg/L, and the average monthly effluent BOD ranged from 100 to 1,667 mg/L. The regulatory goal was not met. Noncompliance with the goal was attributed to its inapplicability to the multi-sector permit for this site.
The capital cost for the demonstration totaled $326,000, which included design, mobilization, equipment purchase, construction, management, permitting, and demobilization costs. The O&M cost totaled $6,900, which included labor, utilities, equipment and equipment maintenance.