SITE INFORMATION AND CORRESPONDENCE

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RUBLE 1 -CHECKLIST OF REQUIRED DATA FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES ,e Site Name and Location: Husky Crane,2373 Mariposa Road, Stockton, San Joaquin County 1. Distance to production wells for municipal, domestic, agriculture, industry Two production wells were recorded at the site. ' and other uses within 2000 feet of the site; One is located 200'SE and the other is 250' south of the site. Available information shows a west/southwesterly groundwater flow direction. 2. Site maps, to scale, of area impacted showing locations of former and existing tank systems, In 1987,one 500-gallon diesel excavation co.Ontours and sample locations, boring and monitoring well elevation contours, and one 1,000-gallon gasoline gradients, and nearby surface waters,buildings, streets, and subsurface utilities; tank were removed without a permit or inspection. A site investigation began when the RP requested closure. 0 3. Figures depicting lithology(cross section), treatment system diagrams; No treatment system was used. F1 4. Stockpiled soil remaining on-site or off-site disposal(quantity),- Excavated soil returned to the tank pit 5. Monitoring wells remaining on-site, fate; No monitoring wells were installed. F_NA_j 6 Tabulated results of all groundwaterele ations and depths to waterW Groundwater elevation is estimated between 70-75'bgs. 7. Tabulated results of all saling and analyses: In 1991, TPHd as high as 2,500 mg/kg and TPHg at 150 were detected in soil y samples from beneath theformer tank. In 1994,six soil borings were❑ advanced Detection limits for confirmation sampling around the site. TPHd as high as 490 mg/kg was detected in one of the boring's. ❑Lead analyses In 1999, TPHd at 1,300 mg/kg and TPHg at 26 mg/kg were detected in soil samples. TPHd at 0.5 mg/kg and low concentrations of BEX were found in groundwater samples. No MWE was detected in samples from the site Y 8. Concentration contours of contaminants found and those remaining in soil f and groundwater, and both on-site and off-site: N❑ Lateral and y❑ Vertical extent of soil contamination [q Lateral Lateral and F1 Vertical extent of groundwater contamination I Y� 9.Zone of influence calculated and assumptions used for subsurface No subsurface remediation system was used at remediation system and the zone of capture attained for the soil and this site. groundwater remediation system; i v❑ 10.Reports/information y❑ Unauthorized Release Form NA MRs(Dates) Welland boring logs EIPAR FRP Other(report name) 0 11.Best Available Technology(BAT) used oran explanation for not using BAT, The diesel and gasoline tanks were removed from the site.--.:x 0 12.Reasons why background was/is unattainable using BAT; r 13.Mass balance calculation of substance treated versus that remaining; !"No mass balance calculations in available data. N❑ 14.Assumptions,parameters, calculations and model used in risk assessments, and fate and transport modeling; _ It YE 15.Rationale why conditions remaining at site will not adversely Low concentrations of diesel and BEX were found in the 1999 Impact water quality, health, or other beneficial uses;and groundwater sample. Due to their chemical properties,these hydrocarbons will degrade over time,but do not pose a significant❑ threat to water quality. 16.WET or TCLP results Y In 1991,lead at 5.0'mg/kg was detected in one soil sample. 1! By: f Comments: TPHd concentrations in the former tank pit were lower in 1999 than in 1991. With the absence of any remediation system, this suggests diesel concentrations are naturally attenuating at the site. In 1999, the highest diesel concentrations were Date: detected in soil at 11 feet bgs;soil was not impacted below 31 feet. TPHd at 500 pg1l,benzene at 1.0 pg/J,ethyl benzene at 1.0 r l Ng/l, and xylene at 2.0 pg11 were found in groundwater samples. Two production well are documented within 200 feet of the site; l U// however,due to the low mobility of of hydrocarbons from the UST release,it is unlikely that these wells will be impacted. Also, {{{ groundwater flow is estimated in a southwesterly direction. MtBE was not detected in any samples from the site. Based on the information provided and the absence of MtBE at the site,staff concurs with San Joaquin County's closure recommendation. ' Ip 1