Landfill History

New Hanover County’s Secure Landfill opened in 1981 as the first lined landfill in the state of North Carolina.  Liners only became federally mandated as of the late 1990’s.  The landfill facility encompasses 689 acres of which approximately 230 are natural wetlands bordering both the Northeast Cape Fear River and Fishing Creek.  The landfill is permitted by the North Carolina Department of Environment and Natural Resources, Division of Solid Waste Management.  Wastes not accepted include liquid waste, yard waste, medical waste, hazardous waste, radioactive waste, tires, oil, batteries, and paint.  Wastes permitted for acceptance include mixed construction debris (shingles, concrete, brick, building supplies, wood waste, etc.), commercial waste, and residential waste (household).  The goal of the New Hanover Landfill is to protect the best interests of the County by offering a cost effective, environmentally sound and sensible municipal solid waste management system to the citizens of New Hanover County.

Cost Effective: reducing expansion costs by extending the life of the facility through waste reduction from waste-to-energy (WASTEC), recycling, construction/demolition waste processing, and integrating new technologies.

Environmentally Sound: utilization of the highest quality liner systems to protect against potential groundwater contamination and landfill gas migration, use of best management practices and cutting edge technologies including constructed wetlands for the treatment of landfill leachate, employment of highly trained and educated employees .
 
Sensible: management and accountability of New Hanover County’s waste without reliance on others for proper handling and disposal, protection from environmental liability.
 
 
  
 How Are Landfills Constructed?
 
Municipal solid waste landfills are designed and constructed to meet specifications to ensure the protection of the environment including our surface waters, groundwater, and air quality.  The two most important aspects of landfill design include liner installation and landfill leachate collection/management.  Landfills are designed into cells.  Cells are individual waste disposal units or mini-landfills that inter-connect by welded liner systems.
 
Liner Installation:   The base of each landfill cell is composed of many layers of liner material. The liners are constructed of high density polyethylene (HDPE) plastic. The first layer is composed of an over-lapping geo-synthetic clay layer (GCL).  The GCL is composed of the equivalent to bentonite clay and offers the last defense against leakage of leachate to the groundwater.  If liquid comes into contact with the GCL it immediately softens and expands to close off any holes, therefore halting any leaks.  The middle layer consists of the primary and secondary liners.  These impermeable HDPE liners are the main defense against leachate leakage.  A geo-textile composite drainage layer separates the primary and secondary liners.  The geo-net allows any leakage from the primary liner to flow by gravity, along the top of the secondary liner, to a sump to be pumped out for treatment.  If a leak is detected between the two liners it can be located and repaired. The final layer is comprised of another geo-textile composite drainage layer.  This layer is located on top of the primary liner system and allows leachate to flow quickly into the leachate collection system and offers protection against objects which could possibly penetrate the liner systems.
 
The HDPE liners are welded together to cover the entire surface area of the landfill.  The liner panels are welded together by a machine “mouse” that forms a double fusion weld.  This type of weld forms an air channel between the weld of two liner panels.  The air channel is then “air tested” and must hold specified air pressures for an extended period of time to ensure that no leakage can occur.  Another weld typically performed during landfill construction is the extrusion weld.  This weld is conducted by heating a string of HDPE to a specified temperature, thereby melting it to form a “bead”.  The bead is then forced against the interface of two sections of liner.  After the HDPE bead has cooled the weld is “vacuum” tested to ensure no leakage can occur.  During construction further quality assurance testing is also conducted.  These tests include sheer, peel, and conformance testing of the liner systems to meet strict specifications.
 
Leachate Management: All precipitation that falls onto an open landfill cell is absorbed into the waste.  As the precipitation leaches through the waste it picks up contaminants such as metals, nitrogen, silt, salts, volatile organic compounds, and other oxygen demanding wastes.  The liquid waste, known as leachate, is collected from the bottom of the lined landfill in the leachate collection system.  The leachate collection system is comprised of a network of inter-connected perforated collection piping that flows by gravity to a sump area.  From the sump, leachate is pumped to a stabilization basin for pretreatment.  After pretreatment, the leachate undergoes further treatment through a conventional wastewater treatment plant or constructed wetland treatment system.  Tertiary treatment through the use of a continuous backwashing sand filter polishes the treated leachate (effluent) exiting the wastewater treatment plant before discharge into the Northeast Cape Fear River.  This discharge is permitted by the North Carolina Department of Environment and Natural Resources, Division of Water Quality.  The permit allows for the discharge of 50,000 gallons/day.  The effluent must meet permit limits for Biochemical Oxygen Demand, ammonia nitrogen, pH, Total Suspended Solids, zinc, phenol, alpha-terpineol, benzoic acid, and p-cresol.
 
 

Pilot Constructed Wetlands Project
 
In 1990 staff began to research the use of constructed wetlands to treat landfill leachate as a viable option versus conventional treatment.  At this time the use of constructed wetlands as treatment systems was relatively new and there were no existing projects that used them to treat landfill leachate specifically.  In 1992 staff chose to pursue wetland treatment options further based on preliminary findings and began moving forward with the design of a pilot system.  The primary purpose of the pilot constructed wetlands project was to determine the feasibility and treatment efficiency achieved by using manmade wetlands to treat landfill leachate.
 
In July 1993, New Hanover County’s Department of Environmental Management was awarded a Coastal Area Management Act (CAMA) grant from the North Carolina Division of Coastal Management.  The grant was awarded to fund the development of an educational program to be used in conjunction with the constructed wetlands pilot project.  The educational program targets junior high school students and teaches them the importance of and the effects of specific pollutants on water quality.  Parameters tested for include ammonia nitrogen, pH, dissolved oxygen, nitrates/nitrites, and total nitrogen. 
 
In October of 1994 a second grant was awarded by the Water Environment Research Foundation to North Carolina State University to conduct research on the project. The North Carolina Sea Grant program was also involved in the construction of the system and research conducted at the site. 
 
The pilot project consists of two surface flow wetland cells and three subsurface flow wetland cells.  In the surface flow cells there is approximately twelve inches of surface water in which leachate is allowed to flow through freely prior to exiting the system.  In the subsurface flow cells leachate is forced to flow through rounded river rock below the surface before exiting the system.  Wetland plants were established in the Spring of 1995 and leachate was gradually introduced beginning in September of the same year.  The wetland system was then monitored over the following four year period.  
 
Species of plants in the pilot system include:
     Softstem bulrush/Scirpus validus
     Pickerel weed/Pontederia cordata
     Arrowhead/Sagittaria latifolia
     Soft rush/Juncus effusus 
     Sweetflag/Acorus calamus
     Arrow arum/Peltandra virginica
     Lizard's tail/Sarurus cernuus 
     Burreed/Sparganium americanum
 
The system proved to be a viable treatment option. Results of the research indicated that the constructed wetlands could be used for either primary or tertiary treatment.  Other benefits from using constructed wetlands versus conventional treatment include providing wildlife habitat, creating an aesthetically pleasing treatment system, create educational opportunities, research opportunities, lower operation and maintenance costs, and lower capital costs.   Students and interns from both the University of North Carolina in Wilmington and North Carolina State University have participated in various stages of the project or have used the wetlands to conduct research for Masters and Ph.D. degree thesis.  The research results obtained led New Hanover County to pursue construction of a full scale system.  In 2002 New Hanover County was awarded grant funding in the amount of $785,000 from the Clean Water Management Trust Fund. This money was used in conjunction with $243,500 of matching funds from New Hanover County to design and construct the system.
 
 
  
Full Scale Constructed Wetlands   
   
The full scale constructed wetland treatment system is capable of treating all the leachate generated at the landfill.  The landfill now operates this 5.66 acre wetlands treatment and irrigation system designed to treat up to 60,000 gallons/day.  The treated leachate from the wetlands is irrigated onto closed landfill space as low grade liquid fertilizer.  Currently the system treats approximately 7,000,000 gallons of leachate each year.  This total represents approximately 40% of our permitted discharge to the Northeast Cape Fear river from the wastewater treatment plant. 
 
As additional landfill space is closed in the future, the irrigation system will be extended in order to irrigate more treated leachate.  Eventually, the use of constructed wetlands and irrigation will allow us to eliminate the wastewater treatment plant and our discharge to the river.  In essence, closing the loop by re-directing and reusing our treated leachate in an effort to protect the water quality of surface waters in southeast North Carolina from pollutants leaving our facility.  This system serves as a model for other industries and municipalities as an alternative to conventional treatment practices.  The wetland treatment system is cost effective, aesthetically pleasing and provides wildlife habitat.  The irrigation of treated leachate also cuts costs by helping to maintain and increase the vegetative cover of our closed landfill space as well as to protect the landfill side slopes from storm water erosion.
 
Both constructed wetland projects have gained international attention.  Representatives from the government of Thailand and India have visited and shown interest in the project as potential low cost alternatives versus conventional treatment as their countries continue to develop.
 
For additional information or to arrange facility tours, presentations, or participate in the Constructed Wetlands project, call 798-4400.