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u `"1 Mr.Nuel Henderson <br /> Page 4 of 4 <br /> .. bromate level in well MW13B is similar to the level detected during the baseline <br /> sampling event. <br /> • ORP levels initially ranged from -140 millivolts (mV) in well VW2 to 132 mV in MW6. <br /> Negative ORP is associated with the wells most impacted by dissolved hydrocarbons and <br /> is indicative of biodegradation of the hydrocarbons. During the May 17, 2011 sampling <br /> event ORP levels measured wells VWl, VW2, MW2, MW5 and MW13B all increased to <br /> positive values. Measured ORP levels ranged from 10 mV in MW2 to 98 mV in VW2. <br /> • Arsenic was detected in all wells sampled during second quarter sampling events, except <br /> V W 1 on March 28, 2011 were none was detected. Concentrations of arsenic, which <br /> appear to be at naturally occurring levels, in many of the wells exceed the MCL of 10 <br /> parts per billion(ppb). <br /> • Iron concentrations continue to decrease during the subsequent sampling events in <br /> comparison to the baseline sampling event(08/11/10). <br /> SUMMARY AND DISCUSSION <br /> • Groundwater levels rose since previously monitored during the first quarter of 2011. Flow <br /> remains predominantly to the east and northeast. <br /> • H202 injection events were conducted on March 31, 2011, May 4, 2011, June 1, 2011 and <br /> June 27, 2011. <br /> 6. • As expected, a change from reducing to oxidizing conditions along with reduced levels of <br /> hydrocarbon contaminants has been observed in the treatment zone wells, due to regular <br /> H202 injection events. Transition zone wells MW5 and MW13B are now beginning to <br /> show signs of a change from reducing to oxidizing conditions along with reduced levels <br /> of hydrocarbon contaminants. <br /> If you have any questions or comments regarding this report, please contact us at your earliest <br /> convenience. <br /> Respectfully, <br /> Ground <br /> /Zero Analy�Inc. , <br /> ]Z: Joseph L. Vasquez, �� GREGMP <br /> � Staff Geologist ^ * sTara <br /> �/�' ` <br /> d / No.5023 �F <br /> s <br /> 9l a��P <br /> Fp <br /> Gregory P. Stahl, PG 5023 o CALIF <br /> CA Certified Hydrogeologist No. 264 <br /> Attachments <br /> ` cc: Mr. Carl Knowles <br /> Mr. James L.L.Barton, RWQCB Sacramento <br /> Mr. Tasnim Akhtar <br /> Ms. Marla Nahom, Environmental Closures, Inc. <br /> G.\GROUNDZE ROEKTX,PORTS\Peroxide Pilot Tesl\Reports\2QTR2011 Remedial Progress Report doe <br />