CORRESPONDENCE_2017 - Laserfiche WebLink

Home Browse Search

Landfill Gas Monitoring Program Based on the available methane gas data collected from the soil-gas probe installed in the former waste handling area for the site, which is discussed in the Summary of SWIS Site Investigation, methane gas is not present at the site at concentrations that should trigger a requirement for ongoing landfill gas monitoring. However off-site deposition of waste on the adjacent property required a landfill gas (methane) monitoring program and two additional landfill gas probes have been required. As soil gas (methane) data from the on-site evaluation is acceptable, a mitigation system was not proposed. Comments: A report of LFG monitoring results (e.g., summary of LFG monitoring conducted and tabulation of analytical data) was not available for review and therefore comments can not be provided. It is recommended that this document be provided, accompanied by laboratory analytical reports. In addition, terminology should indicate if the well is a soil-vapor well, landfill gas probe, or a LFG well. Are additional LFG wells planned as requested by the LEA? Planned Earthwork Activities Project earthwork construction will involve the disturbance, redistribution, and grading of soils across essentially the entire 48-acre parcel, including the landfill area on the northwesterly portion of the site. The project specifications call for the complete excavation of loose soils/fill materials (including remnant buried glass waste) to expose underlying firm, native undisturbed soils. In some areas, the depth of required excavation to remove fills/wastes could be several feet or more. The excavated soils (and mixed-in glass materials) will be moisture conditioned as necessary, and placed and compacted as engineered fill within various project areas (potentially including areas outside of the current landfill footprint). Any deleterious materials encountered other than glass and deemed un-acceptable to the Geotechnjical]cial Engineer(such as piping, rubbish, large metal fragments, etc.) will likely need to be segregated for removal and offsite disposal. Following earthwork construction and site development, the vast majority of the property will be `capped" with a thick section of pavements. Comments: These proposed activities suggest that the removal and reuse of wastes is based on geotechnical requirements for constructing the building and that wastes are planned to be placed back into the ground, including at locations of the proposed building footprint. This type of "remedial action" could be referred to as on site reconsolidation of wastes. If this is what is planned, then the locations where wastes are planned to be removed and where they are planned to be reconsolidated needs to be clearly indicated on an appropriate figure. As previously indicated, based on information provided, it appears that analytical testing was restricted to soils and not wastes; therefore it appears the wastes have not been characterized with respect to their potentially hazardous nature. Additionally, some background documents from the 1980's suggest the wastes may have been hazardous. The PCLUP needs to clearly indicate where wastes are proposed to be excavated and replaced and what type of "cap" will be constructed and locations where wastes are planned to remain. This proposed scope of work is inconsistent with clean closure. It may be that the PCLUP is only referring to the removal of wastes conducted in 2015. If this is the case, based on available information, it does not appear that the waste removal activities were adequately documented and there appears to be an absence of confirmation samples to confirm wastes were adequately removed. Such waste removal activities may constitute a partial clean closure of the WDS, if adequate documentation and information is provided. Because the wastes are reportedly relatively shallow, has a cost analysis been conducted to evaluate offsite disposal of these wastes at locations underlying the building footprint and/or moving the building footprint since wastes reportedly are only present at the northwestern most area? Ninyo&Moore 1 500 E.Louise Avenue,Lathrop,San Joaquin County,California 1 104690095 1 August 11,2017 67