Laserfiche WebLink
1 <br /> C'1010gia reclattcs lay. Page 6 <br /> Groundwater Monitoring Report <br /> Project No 989 2 <br /> November 18,2004 <br /> ' elevation for MW-1 Chart 2 is a plot of MtBE versus groundwater elevation for MW-6 <br /> Figure 5 is a contour of the MtBE plume and Figure 6 is a contour of the TPH-G plume in <br /> ' groundwater as generated by Surfer® 7 0 software <br /> During purging of the monitoring wells, field measurements of the oxidation-reduction <br /> ' potential (ORP) of the water were taken using an YSI 3560 Flowcell meter During this <br /> groundwater-monitoring event, dissolved oxygen was measured in all the wells using an YSI <br /> dissolved oxygen meter These measurements are summarized in Table 4 of Appendix A and <br /> ' in the field logs of Appendix B <br /> ' 2.4 Groundwater Parameters <br /> • pH measurements recorded in the water table wells range between 7 72 and 8 03 This <br /> range is conducive to aerobic biodegradation activity <br /> Temperature of the groundwater during the October 2004 event ranged between 68 4° and <br /> 72 7° Fahrenheit This range is conducive to aerobic biodegradation activity <br /> ' • Oxidation Reduction Potential (ORP) measurements were negative in all monitoring <br /> wells <br /> • Dissolved oxygen (DO) measurements recorded in the water table wells during the <br /> October 2004 monitoring event are relatively low, ranging from 0 34 to 190 ppm There <br /> is no significant difference between impacted and non-impacted wells <br /> • Electric Conductivity (EC) ranges between 820 and 1546 in the water table wells There <br /> ' is no significant difference between impacted and non-impacted wells <br /> ' 3.0 CONCLUSIONS AND RECOMAMNDATIONS <br /> The following conclusions have been drawn from the data generated from this site <br /> ' investigation work <br /> Conclusions <br /> ' a Concentrations of TPH-G and BTEX have progressively decreased since 1996, <br /> suggesting that the plume is attenuating from natural causes <br /> ' • TPH-G fluctuates with groundwater and has decreased exponentially over time as seen in <br /> Chart 1 MW-1 TPH-G vs Groundwater Elevation <br /> • MTBE plume has moved downgradient from the source, the former UST's <br /> ' • Seven of the site's ten groundwater-monitoring wells show the presence of MtBE <br /> o Three of the impacted wells have concentrations above MCLs <br /> o One of the impacted wells has concentrations below MCLS <br /> o The three remaining impacted wells have concentrations below the taste and odor <br /> threshold <br /> o MTBE concentrations are low and potential risks are negligible <br /> t <br />