Laserfiche WebLink
Quarterly Groundwater Monitoring Report - First Quarter 2016 <br /> L&M Operable Unit- West Weber Avenue and North Lincoln Street, Stockton, CA <br /> April 29, 2016 <br /> 4.4 APSV SOIL VAPOR CONCENTRATION TRENDS <br /> TPHg Trends <br /> TPHg concentrations in vapor samples collected from APSV-6, APSV-9, APSV-10, APSV-11, <br /> APSV-15, and APSV-1 5-D decreased from concentrations reported during 4Q15 <br /> There was no change in TPHg concentrations reported for all other APSV wells during 1 Q16. <br /> Benzene Trends <br /> There was no change in benzene concentrations reported for all APSV wells during 1 Q16. <br /> Naphthalene Trends <br /> There was no change in naphthalene concentrations reported for all APSV wells during 1 Q 16. <br /> Methane Trends <br /> Methane concentrations in vapor samples collected from APSV-3, APSV-6, APSV-7, APSV-12, <br /> APSV-15, and APSV-15D decreased from concentrations reported during 4Q15. <br /> Methane concentrations in vapor samples collected from APSV-9 and APSV-10 increased from <br /> concentrations reported during 4Q15. <br /> There was no change in methane concentrations reported for all other APSV wells during 1 Q16. <br /> 4.5 SOIL VAPOR SAMPING CONCLUSIONS <br /> Based on current soil gas investigations and following the recent soil vapor additional assessment <br /> report of findings report, the following conclusions may be inferred: <br /> • Methane concentrations in UPSV wells appear to be relatively stable; while methane in <br /> APSV wells appeared to generally decline from 4Q15 to 1 Q16. <br /> • The presence of elevated methane in some soil vapor samples could be due to the <br /> previous existence of a natural marsh and/or riparian wetland at the property prior to <br /> development. There does however appear to be some correlation between TPH and <br /> methane in several soil vapor wells sampled recently and historically. As a precautionary <br /> measure, Stantec monitored methane in 37 locations throughout the Delta View <br /> Apartment complex in confined spaces where accumulation of methane pockets would <br /> be possible. None of the field measurements detected methane at or above the LEL, <br /> and all reported methane concentrations were below levels of concern (see Stantec's <br /> Soil Vapor Assessment Report dated May 15, 2015). <br /> • In general VOCs have decreased since 2Q15. <br /> 5 Stantec 14 <br />