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RECEIVED <br /> ARCADISJAN 312014 ARCADIS U.S.,Inc. <br /> Infrastructure-Srva,or t,v..ircnment Nurkitng, 101 Creekside Ridge Court <br /> ENVIRONMENTAL14EALTH Suite 200 <br /> PERMITISERVICES RosevilleCalifornia 95678 <br /> Tel 916.786.0320 <br /> Ms. Amy Terrell <br /> Private Sites Cleanup Unit Fax 916.786.0366 <br /> Central Valley Regional Water Quality Control Board www.arcadis-us.com <br /> 11020 Sun Center Drive#200 <br /> Rancho Cordova, CA 95670-6114 <br /> ENVIRONMENT <br /> Subject: <br /> Natural Source Zone Depletion Evaluation Summary Report <br /> Union Pacific Railroad Company <br /> Tracy, CA—Maintenance Facility <br /> Date: <br /> January 29, 2014 <br /> Dear Ms. Terrell: Contact: <br /> Scott Hackman <br /> ARCADIS U.S., Inc. (ARCADIS) has prepared this summary report on behalf of the Phone: <br /> Union Pacific Railroad Company (UPRR) regarding the former Tracy Maintenance 916-786-7369 <br /> Facility located at 720 East 6th Street in Tracy, California (the Site; Figures 1 and 2). <br /> Email: <br /> Background scott.hackman@arcadis-us.com <br /> Our ref: <br /> The California Regional Water Quality Control Board (RWQCB) sent a letter to RC000709.0003 <br /> UPRR dated May 18, 2012 (the RWQCB Letter) regarding the Phase 11 Field <br /> Investigation and LNAPL Mobility Evaluation Report, prepared by ARCADIS and <br /> dated November 29, 2010 (LNAPL Mobility Report; ARCADIS 2010). The RWQCB <br /> Letter requested that UPRR provide a proposal and schedule to address free product <br /> removal by August 24, 2012. <br /> In response, the Response to Comments— Phase 11 Field Investigation and LNAPL <br /> Mobility Evaluation Report, prepared by ARCADIS and dated November 14, 2012 <br /> (the Response to Comments; ARCADIS 2012) was submitted to the RWQCB. The <br /> Response to Comments letter proposed conducting a natural source zone depletion <br /> (NSZD) study to evaluate light non-aqueous-phase liquid (LNAPL) degradation by <br /> natural processes. The NSZD study would occur concurrent with physical bailing of <br /> LNAPL from six on-site wells to compare LNAPL depletion rates by natural <br /> processes to the volume of LNAPL recovered physically. The RWQCB conditionally <br /> approved the strategy in their letter to UPRR dated December 21, 2012, provided <br /> UPRR add two additional background carbon dioxide (CO2) sample locations (four <br /> samples total for 2013) outside the LNAPL plume footprint(Station 3 and Station 4). <br /> Imagine the result <br /> g:\projects\uprr_rosevilleVc000709—tracy mnt facility\3—deliverables\2014.01 nszd rptvracy u-maint facility_nud rpt(01-29-14).doc <br />