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ARCADIS Ms. Amy Terrell January 29, 2014 The 10-year time frame of biweekly LNAPL hand-bailing is a relatively low estimate and will likely take much longer. The 10 years is based on a linear"no loss" assumption. That is, this assumes the LNAPL recovers 100 percent during every event with a constant source. This is an optimistic assumption because every bailing event would reduce the source (minimally); therefore, the source is minimally depleting over time in addition to the NSZD rate which is also reducing the source. An equivalency would be much longer than 10 years due to the diminishing returns. Historical Active Remediation Summary As documented in the Mobility Report, previous active remediation of diesel product proved futile. Diesel product removal attempts (including product skimmers, bailing, bilge bags, and hydrophobic absorbent socks)were conducted from 1989 to November 2007 at 11 wells in the source area. Approximately 650 pounds of product were removed from the subsurface between 1995 and 2006 (Environmental Resources Management[ERM] 2006). A skimmer system was installed and operated but removed only 6.1 gallons of product between August 1992 and May 1996, when it was removed and replaced with two bilge bags (ERM 2006). Passive diesel product recovery using bilge bags and absorbent socks was conducted until August 2007. During that time, only a limited volume of product(approximately 32 gallons) was recovered and passive product recovery was discontinued in August 2007. Based on this information, the skimmer system was not effective for removing LNAPL. A dual-phase extraction system operated from December 2000 to July 2002. It was concluded that the dual-phase extraction system was not effective for remediation of residual VOCs and diesel product remaining in the source area; therefore, the dual- phase extraction system was shut down. The dual-phase extraction system removed approximately 53 gallons (380 pounds) of LNAPL. Conclusions and Recommendations Results from the CO2 traps indicate that LNAPL is being depleted through natural processes as evidenced by the CO2 flux and 14C analysis. NSZD rates were quantified, and the total average LNAPL volumetric loss rate due to NSZD is approximately 1,224 gallons per year within the LNAPL plume footprint. Continued NSZD monitoring is not warranted to demonstrate that LNAPL is being depleted through natural processes. Page: G:\Projeds\UPRR Roseville\RC000709_Tracy Mnt Faci1dy\3 DELIVERABLES\2014.01 NSZD Rpt\Tracy ca-Maint Fadlity_NSZD Rpt(01-29-14).doc 7/9