ARCHIVED REPORTS_2014_8 - Laserfiche WebLink

Home Browse Search

is considered representative of future leachate. In fact, since the standard of practice for load checking and waste stream controls is likely to improve with time and the potential for high concentration leachate will be further reduced, this assumption is considered reasonably conservative. 3.4 Dilution -Attenuation Characteristics of the Proposed Single Composite Liner The leachate fate and transport analyses that were performed for the project indicate that leachate constituents would be significantly reduced during transport through the CCL (Appendix A). This is primarily related to the fact that the volume of liquid in a leachate release would be small relative to the volume of pore water included in the CCL as a part of initial construction operations. In fact, owing to the low permeability properties of the clay liner and the small volumes that would be associated with leachate leakage, leachate transport in the CCL would occur very slowly as unsaturated flow. Ignoring the biodegradation processes that would likely greatly reduce the VOC concentrations in leachate, dispersion of leachate during the first 9 years of unsaturated flow through the CCL is calculated to result in a 99% reduction in concentration. This calculated reduction conservatively assumes that one -foot of leachate head is constantly applied on the clay liner and suggests that actual Forward liner performance will be even better if the calculated maximum leachate head (i.e., 1.6 -inches) is achieved. Given the fact that the typical leachate head condition on the liner would likely be significantly less than 1 -foot, or even 1.6 inches, and recognizing that the anticipated Forward site life is only 18 years, elevated leachate concentrations are not expected to reach the bottom of the liner system. However, since leachate constituent concentrations would incrementally increase at the base of the liner after additional time (assuming that high leachate head levels are maintained), the fate and transport analyses detailed in Appendix A also evaluate leachate fate within the vadose zone. As described in Section 4.2, the results of these analyses indicate that leachate leakage would have an insignificant (essentially undetectable) affect on groundwater quality beneath the site. 3.5 Lysimeter Impact A number of lysimeters underlie the existing lined cells at the Forward Landfill and monitoring of these lysimeters has indicated that no significant liquid phase release has occurred from the facility. This data further substantiates the inference that the single composite liner proposed for the Forward Landfill expansion is effective. 4.0 MITIGATING SITE CHARACTERISTICS Whether or not a leak in the composite liner system could result in actual groundwater pollution depends on several additional factors including: the volume of the leak through the CCL, the chemicals that leak, the concentrations of the leaking chemicals, the IM CA2000-04SWorwnrd Composite Liner V3 .doc109119/02 Geologic Associates