FIELD DOCUMENTS_FILE 2 - Laserfiche WebLink

Home Browse Search

Closure Report �J p rt Former Mobil Bulk Plant 04-343, Tracy; California Aril 14, 1997 concentrations in soil between 1988 and 1995 indicate degradation of the remaining hydrocarbons beneath the site is taking place • Measurable free product has never been observed in any well at the site. The remaining !, dissolved-phase hydrocarbons have been adequately characterized and are limited in extent. No significant offsite hydrocarbon migration has occurred. The reduction in dissolved-phase petroleum hydrocarbon concentrations can 1 e'attributed to source removal efforts and natural attenuating processes. These natural processes should continue to decrease the hydrocarbon concentrations in groundwater. f. • No public or domestic supply',wells were identified within a half-mile radius of the site. The poor groundwater quality makes the futureinstallation of any shallow supply wells unlikely. q Any future deep supply wells would be constructed to California Well Standards, and therefore any lower aquifers would be protected from ,any residual contamination present in the shallow water bearing zone. For these reasons, no wells, deeper aquifers, or surface bodies are likely to be impacted and no potentially adverse affects to human health or the environment are anticipated. i • In summary, empirical data derived during the course of site assessment, remediation, quarterly groundwater monitoring, and confirmation s61l borings analyses, provide sufficient site specific . data to demonstrate that: most'hydrocarbonconcentrations in soil have been removed through over-excavation, remediation; and natural' processes; hydrocarbon concentrations in j groundwater are at residual! levels leaving natural biodegradation to further decrease concentrations; and remaining residual concentrations of petroleum hydrocarbons in soil do not pose an appreciable threat to human health or the environment. 7.0 RECOMAMNDATION I Based on the factors described above;'formal site closure is requested. Upon receipt of site closure acknowledgement, all existing monitoring wells will be abandoned in accordance with applicable standards and regulations and a well abandonment report will be prepared and submitted to the San Joaquin County Environmental Health Division (SJCEHD) and the Regional Water Quality Control t Board(RWQCB), Central Valley Region. 9 8.0 IXOTrATTONS u The activities in this report have been conducted in accordance with current practice and the standard �. of care exercised by geologists and engineers performing similar tasks in this area. No warranty, expressed or implied, is made regarding the conclusions and recommendations presented in this report. The conclusions and recommendations"are based solely upon an analysis of the observed conditions. If actual conditions differ from those described in this report, our office should be notified. 6