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Brownfields Site Assessment June 2014 South Gifford Road Landfill, Vero Beach, Florida 4.3 Landfill Cover Evaluation Results Typical soil cover required for redevelopment of a landfill, such as Gifford Road Landfill, is two ft; however, alternative cover systems have been approved by FDEP (e.g., a geonet or geotextile overlain by one ft of cover soil). Approximate landfill cover thickness observed in the assessment area is presented on Figure 6. Data collected during the 2008 test pit excavation activities were used to supplement the data collected from TP -101 through TP -110. Two ft of landfill cover was observed at all but three test pit locations (TP -101, TP -102, and TP -103). In addition, less than two ft of landfill cover was observed at soil boring locations between TP -106 and TP -107 and near TP -102. Selected photographs from the cover thickness evaluation fieldwork are included in Appendix E. Improvements to the existing cap can easily be completed during grading operations when construction is underway for site development. The design of the final cover system for the landfill will need to be approved by FDEP prior to construction. 4.4 Soil Gas Results Field screening results from the soil gas probes are presented on Figure 7. The results indicated that methane, which is found in LFG, is present in soil gas in the subsurface within the assessment area. LFG is created when organic materials decompose under anaerobic conditions. LFG is typically composed of methane (50 to 55%), carbon dioxide (45 to 50%), and trace amounts of other gases (e.g., oxygen, nitrogen, and hydrogen sulfide). Field screening results were found to generally be within the typical ranges for landfills, with observed carbon dioxide concentrations being slightly less and methane being slightly higher. In addition to waste decomposition, naturally - occurring organic material in the subsurface and natural attenuation of VOCs present in groundwater at the Site (through ongoing bioremediation activities) may also contribute to methane soil gas concentrations. PID measurements ranged from non -detect in LFG06 to 18.5 parts per million (ppm) in LFG04. Soil gas samples were collected from LFGO1, LFG04, and LFG06 on 11 April 2014. The soil gas results are tabulated in Table 2. Soil gas results were compared to Default Concentrations for LFG Constituents found in Table 2.4-1 of the 1998 USEPA AP 42, Fifth Edition, Compilation of Air Pollutant Emission Factors, Volume 1: Stationary Point and Area Sources. Of the 67 constituents analyzed, 33 were detected in one or more soil gas probes. None were above the USEPA default concentrations, suggesting that the soil gas concentrations measured as part of this effort are indicative of conditions at typical closed/former landfills. There are currently no state regulatory drivers in Florida to evaluate the chemical composition of soil gas; however, any construction projects should consider potential impacts from combustible gas. FR0766H 10 7/8/2014