25C - AGMT - OCWD CENTENNIAL PARK

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Section 5 Similarly, zone SAFE -10/2 increased to .a MaXiMUM Of 10.3 Ug/L, before subsequently declining to 8,9 ug/L. Zone SAR-10/3 has remained non,-detect (ND, less than 1 ug/L) before and after the arrival of GWRS water. Zone SAR- 1014 has displayed the most significant shows a significant increase in vanadium with the arrival of GWRS water increasing, from approximately 3 ug/L to a maximum of 311 ug/L, before subsequently declining to 137 ug/L. For data from monitoring well SAR-1 1, none of the three zones at this well show any discernible change in vanadium concentration with the documented initial arrivals of GWRS water. Vanadium typically displays rerfox behavior similar to chromium, generally portioning strongly onto solids under reducing conditions and more weakly under oxidizing conditions. However, no increases in chromium have been observed at either SAR-10 or SAR-1 1 with the arrival of GWRS water. Field parameter data from monitoring well SAR-1 0 include dissolved oxygen (DO), oxidation-reduction potential (ORP), pH, and temperature. Since the arrival of GWRS water as SAR- 10, zone 2 has shown a steady increase in DO from approximately 3 mg/L to nearly 6 mg/L, while zone I to has decreased from approximately 3 mgJL to <2 mg/L. Zones 3 and 4 have largely remained at their background levels of 0-2 mg/L. ORP levels in all SAR-1 0 zones 1, 2, and 3 haven't changed significantly with the arrival of GWRS water. The SAR-1 0/4 has displayed a shift from a pre-injection negative ORP to generally positive ORP post-GWRS water arrival; this may help explain the observed mobilization of vanadium in this zone. The field-measured pH in all SAR-1 0 zones has increased steadily with the arrival of GWRS water, from a pre-injection level of -7.5 - 8.0 to 8.0 - 8.7. Similarly, the field-measured temperature in all SAR-10 zones has also increased. Iron and imanganese are two naturally-occurring groundwater constituents that are sensitive to redox conditions in the aquifer. Result at SAR-1 0 for iron and manganese do not show any dear trends with the arrival of GWRS water. NDMA concentrations were evaluated at monitoring well SAR-1 0. Prior to the onset of injection at MBI-1, all zones were consistently ND for NDMA. Since the beginning of injection, concentrations across all zones at the well have varied between 2 - 10 ng/L. The DDW NIL for NDMA is 10 ng/L and the RL is 300 ng/L. Appendix F provides a more detailed discussion of the groundwater quality data. The groundwater quality data from monitoring wells SAR-1 0 and SAR-11 1 indicate that though there are some increases in arsenic, vanadium, and NDMA concentrations, these increases are temporal in nature and localized and are not anticipated to negatively impact water quality such that water quality standards would be violated or beneficial uses of the water would be impaired. Therefore, water quality impacts are determined to be less than significant, Mid Basin Centennial Park gj§&r�40Project Final EIR 5-113 �k..o