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San Joaquin County <br /> .� Environmental Health Department DIRECTOR <br /> Linda Turkatte, REHS <br /> 1868 East Hazelton Avenue <br /> (1): ` { Stockton, California 95205-6232 PROGRAM Robert McCCOORDINATORS <br /> Oo DINA ORS <br /> .. :. <br /> --: Jeff Carruesco,REHS,RDI <br /> FOR��P Website: www.sjgov.org/ehd Kasey Foley, REHS <br /> 209 468-3420 Adrienne Ellsaesser,REHS <br /> Phone: <br /> ( ) Rodney Estrada, REHS <br /> Fax: (209)464-0138 Willy Ng, REHS <br /> March 15, 2016 <br /> Mr. Thomas Black C 0, ? <br /> v <br /> 12761 Silver Fox Rd <br /> Los Alamitos, CA 90720 <br /> Subject: Tracy Office Plaza <br /> 324 E. Eleventh St <br /> Tracy, CA 95376 <br /> Additional Characterization Directive Letter <br /> Dear Mr. Black, <br /> The San Joaquin County Environmental Health Department (EHD) has received and reviewed <br /> Phase 11 Environmental Site Assessment Report (Phase II), dated 23 July 2013, and Additional <br /> Site Assessment Report (ASAR), dated 08 October 2014, both assessing an unauthorized <br /> release (LIAR) of petroleum hydrocarbon from a former underground storage tank (UST) facility <br /> removed from the site circa 1973. In addition, the EHD reviewed data collected as part of the <br /> investigation of a hydrocarbon release on the Tracy High School (THS) site north of the subject <br /> site at 315 E. Eleventh Street. <br /> The Phase II investigation was conducted in 2013. A geophysical survey of the site had <br /> encountered an anomaly identified as possibly being a 20-foot length of pipe or fuel line in the <br /> subsurface near the suspected former UST locations; the type of anomaly was not noted in the <br /> reports reviewed. Six soil borings were advanced to assess for petroleum hydrocarbons: two in <br /> the vicinity of the suspected product line (B-1 and B-4), two along the west and southwest <br /> portions of the property (B-2 and B-3), and two along the north margin of the property in the <br /> suspected downgradient direction (B-5 and B-6). Soil impacted by petroleum hydrocarbons was <br /> encountered in borings B-1, B-5 and B-6; soil in the latter two borings was minimally impacted, <br /> but total petroleum hydrocarbons quantified as gasoline (TPHg) was detected in the B-1 soil <br /> samples at concentrations as high as 2,400 milligrams per kilogram (mg/kg) and benzene at 2.3 <br /> mg/kg, along with other petroleum hydrocarbons, demonstrating that a UAR had occurred on <br /> the site. Grab groundwater samples from B-1, B-4 and B-6 contained dissolved TPHg and <br /> benzene at concentrations as high as 6,200 micrograms per liter (dig/1) and 750 dig/l, <br /> respectively, among other petroleum hydrocarbons (detectable dissolved benzene was present <br /> only in the B-1 grab groundwater sample). <br /> Additional soil and groundwater samples were collected for laboratory analysis 10 July 2014 <br /> from four onsite soil borings (B-7S, B-7D, B-8 and B-9) and one off-site soil boring (B-10) as <br /> reported in ASAR. The off-site soil boring was placed to refine the offsite delineation of impacted <br /> groundwater characterized by a mix of monitoring well groundwater samples and grab <br />