General Guidelines for Environmental Monitoring at Solid Waste Landfills
The following information is intended to provide guidance for submitting a new groundwater and methane monitoring plan for a solid waste landfill.
GROUNDWATER MONITORING PLAN
As referenced in the North Carolina Solid Waste Management Rules (15A NCAC 13B, Section .0600), solid waste management facilities are required to provide such groundwater monitoring capability as the Division of Waste Management determines to be necessary to detect the effects of the facility on the groundwater in the area. In order to comply with this requirement all facilities must have an approved groundwater monitoring plan. Our office recommends that all water quality monitoring plans be prepared by an environmental consulting firm under the seal of a board certified licensed/professional geologist that has experience with the design and construction of groundwater monitoring wells and plans. Since groundwater monitoring wells are significantly different in design from drinking water wells, the wells should be installed by a certified well driller with experience in the construction of groundwater monitoring wells. Monitoring plans should include the following information:
1. A site map delineating the entire landfill and adjacent properties. This map should clearly show the permitted location of the landfill with respect to the entire property.
2. A site-specific topographic map of the landfill area itself illustrating the configuration of the landfill pursuant to the permit description. Also indicated should be areas of landfilling activities (if active), and proposed groundwater monitoring well locations.
3. A sampling and analysis plan that describes sample collection and handling. A groundwater monitoring system has at least one upgradient well. The number of downgradient wells is site-specific. Numbers and locations are based on topography, geologic conditions, and hydrogeological features. Most detection monitoring wells are designed to monitor the upper portion of the aquifer and consequently are not deep. The groundwater monitoring wells are constructed of 2 inch PVC pipe and have a screened interval to allow the infiltration of water. They are installed in a borehole with a sand filter pack around the screen and bentonite clay seal over the filter. The remainder of the borehole is grouted to the ground surface and a protective casing is installed over the riser.
METHANE MONITORING PLAN
Organic matter begins to decompose almost immediately after being placed at a disposal site. Typically the decomposition goes through several stages depending on several factors such as pH, temperature, moisture content, and the composition of the organic matter. The final stage results in the production of methane. The rate and time frame varies but methane can continue to be produced for as long as 40 years at a disposal site. Although methane is not toxic, it is explosive at concentrations between 5 and 15 percent when sufficient oxygen is present. It is odorless and slightly lighter than air and moves by diffusion and pressure gradient.
A methane monitoring plan is similar to a groundwater monitoring plan. The disposal site is surrounded by a number of methane monitoring wells that are installed outside the waste boundary to depths equal to the waste or to an impermeable barrier. The number and location of methane monitoring wells is dependent on several factors - landfill design, subsurface soil stratigraphy, proximity of buildings or dwellings (receptors), natural barriers, etc. Typically a methane monitoring well is constructed of 2 inch PVC pipe with a screened interval to allow infiltration of methane. It is placed in a borehole and surrounded by a gravel pack. The borehole is then sealed from the gravel to the ground surface. It is similar, but not identical to a groundwater monitoring well. They are never installed to depths below the water table. The methane monitoring plan should propose the number and locations of methane monitoring wells and describe in detail the construction and specifications.l. The locations may be indicated on the same site map that describes the groundwater monitoring system. All immediate potential receptors also should be shown on the map. A proposed monitoring schedule or frequency is to be included. A contingency plan addressing corrective action should be included in the event that methane is detected at concentrations exceeding regulatory levels (100 % of the lower explosive limit) in any of the methane monitoring probes.
The Solid Waste Section recommends that all consultants contact this office before proposed environmental monitoring plans are designed and submitted. This will hopefully prevent problems
