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4L41 -CHECKLIST OF REQUIRED DATA
<br /> FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES
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<br /> Site Name and Location: JH Simpson Company,4025 Coronado Avenue,Stockton,San Joaquin County
<br /> A well survey was not conducted. The County
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<br /> 1. Distance to production wells for municipal, domestic,agriculture,industry indicates that drinking water wells or surface
<br /> and other uses within 2000 feet of the site, waters are not affected by site conditions.
<br /> aIn 1996,one ZOO-gallon
<br /> 2.Site maps, to scale,of area impacted showing locations of former and existing tank systems, gasoline tank was removed
<br /> excavation co.Ontours and sample locations,boring and monitoring well elevation contours, from the site.
<br /> gradients,and nearby surface waters,buildings,streets,and subsurface utilities;
<br /> F .3. Figures depicting lithology(cross section), treatment system diagrams,
<br /> 0 4. Stockpiled soil remaining on-site or off-site disposal(quantity); An unspecified amount of excavated soil was returned to the
<br /> tank excavation.
<br /> 5.Monitoring wells remaining on-site, fate; One monitoring well was Installed. The well will be decommissioned pending site
<br /> closure.
<br /> N 6. Tabulated results of all groundwater elevations'and depths to water, Groundwater elevations varied from 43 to 75 feet bgs,and
<br /> -groundwater flow is northerly.
<br /> 0 7.Tabulated results of all sampling and analyses: In 1936,using.EPA Method 8020,up to 1,000 pgft of UIBE was detected in soil
<br /> from the tank excavation. In 1998,a grab water sample collected during a soil
<br /> Y❑Detection limits for confirmation sampling vapor survey revealed low levels of TPHg and TEX in 1998,soil borings SB-1
<br /> Lead analyses and SB-2(later converted to well MW-1)were drilled 10 to 11'bgs,respectively.
<br /> N❑ No contaminants were detected In soil samples below seven feet During the
<br /> August 1999 sampling event,DIPE at 0.69 p94 was the only constituent
<br /> detected In the water sample. MtBE was not detected using EPA Method 8260.
<br /> 0 y 8.Concentration contours of contaminants found and those remaining in soil
<br /> and groundwater, and both on-site and off-site:
<br /> Lateral ando Vertical extent of soil contamination
<br /> 0 Lateral and Vertical extent of groundwater contamination
<br /> 9.Zone of influence calculated and assumptions used for subsurface The site map shows the limits of the tank
<br /> remediation system and the zone of capture attained for the soil and excavations.
<br /> groundwater remediation system;
<br /> 10.Reports/information Q Unauthorized Release Form rT-j OMRs(Dates)2/93—10/99
<br /> ❑Y Well and boring logs El PAR FRP Other(report name)January 14,2000 Closure Summary
<br /> y� 11.Best Available Technology(BAT)used or an explanation for not using BAT; The tank,dispensers,and piping were removed
<br /> from the site.
<br /> The remahnfng hydroembons require time to
<br /> 12.ftaons why background wae✓is unattainable using BAT;
<br /> 0 13.Mass balance calculation of substance treated versus that remaining;
<br /> 14.Assumptions,parameters,calculations and model used in risk
<br /> assessments,and fate and transport modeling;
<br /> 15.Rationale why conditions remaining at site will not adversely
<br /> impact water quality, health,or other beneficial uses;and
<br /> 16.WET or TCLP results
<br /> B Comments:In 1996,one UST was removed from the site. Using EPA Method 8020,elevated levels of MtBE were detected in soil
<br /> samples following the removal of the tank. However,because Method 8020 was used,the County speculates this initial MtBE
<br /> a e. detection could have been a laise positive" in 1998,soil vapor samples revealed elevated levels of petroleum constituents. A grab
<br /> water sample collected during the vapor survey showed minor concentrations of TPHg and TEX. In 1998,one soil boring(SB-1)
<br /> J was installed in the former tank excavation, whereas another boring(SB-2)was drilled midway between the former tank location and
<br /> Z� L dispensers. No contaminants were detected in samples from SB-1. Soil samples from SB-2 revealed TPHg and TEX but not below
<br /> five feet. In 1998,traces of ethyl benzene and xylenes were detected in groundwater samples,and a trace amount of DIPE was
<br /> detected in 1999. MtBE was not detected after the initial detection. Based on the absences of MtBE in soil and groundwater
<br /> samples and the minor contamination remaining in the subsurface,staff concurs with San Joaquin County closure recommendation.
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