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TAS 1 - CHECKLIST OF REQUIRED [ATA
<br /> FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES
<br /> Site Name and Location: Hinamon Trust(Former Chevron#9-6258),2409 Main Street,Stockton, San Joaquin County
<br /> 1. Distance to production wells for municipal, domestic, agriculture, Two private(50'north & 1,050' northwest),one
<br /> industry and other uses within 2000 feet of the site; industrial (2,000" northwest),one unknown (1,800'
<br /> south)and two municipal wells(650'southwest&
<br /> 2,000'southwest)are located within 2,000 feet of site.
<br /> EJ2. Site maps, to scale, of area impacted showing locations of former and existing tank Two 5,000-gallon and one 2,000-
<br /> systems, excavation contours and sample locations, boring and monitoring well elevation gasoline USTs were removed
<br /> contours,gradients, and nearby surface waters, buildings, streets, and subsurface prior to 1976. From 9/96 to 10/96,
<br /> utilities; one 500-gallon waste oil tank and
<br /> piping were removed,and the
<br /> gasoline USTs tank pit was
<br /> overexcavated.
<br /> 3. Figures depicting lithology(cross section), treatment system diagrams; Site lithology consists of sand,silt and clay.
<br /> The total depth investigated was 75 feet.
<br /> 4. Stockpiled soil disposed off-site(quantity)' Approximately 380 cubic yards of contaminated soil was transported to
<br /> Vasco Road Landfill.
<br /> F5. Monitoring wells remaining on-site,-fate; Four monitoring wells(MW-1 to MW-4)were installed for this investigation.
<br /> The 4—wells will be abandoned.
<br /> 0 6. Tabulated results of all groundwater elevations and depths to water, The depth to water varied from 48 to 56 feet.
<br /> Groundwater flow direction varied from southeast
<br /> to southwest.
<br /> Ya 7. Tabulated results of all sampling and In 4/99,maximum confirmation soil results were: TPHg(4,000 mg/kg),
<br /> analyses: toluene(57 mg/kg), ethylbenzene(70 mg/kg),xylenes(430 mg/kg),
<br /> methanol(250 mg/kg),and lead(6.4 mg/kg). Boring soil results in 4/02
<br /> Y Detection limits for confirmation sampling were all ND. Grab groundwater results in 5/97 were: TPHg(32,000 Ng/L),
<br /> Lead analyses benzene(9 pg/L), toluene(990 Ng/L),ethylbenzene(630 Ng/L),and xylenes
<br /> (3,300 Ng/L). In 4/04,groundwater monitoring results were all ND.
<br /> 8. Concentration contours of contaminants found and those remaining in soil
<br /> and groundwater, both on-site and off-site: The extent of contamination is defined by
<br /> Y® Lateral and ®Y Vertical extent of soil contamination soil borings and monitoring wells.
<br /> Lateral and Vertical extent of groundwater contamination
<br /> Q9.Zone of influence calculated and assumptions used for subsurface Based on the limited extent of
<br /> remediation system and the zone of capture attained for the soil and contamination,an engineered remediation
<br /> groundwater remediation system; system was not required at this site.
<br /> 0 10.Reports/information 0 Unauthorized Release Form Y❑ 21 QMRs(4/99 to 4/04)
<br /> El Boring logs N❑ PAR N❑ FRP 0 Other. Site Assessment Reports(1999 and 2003)
<br /> 0 11.Best Available Technology(BAT) used or an explanation for not using BAT,• Remove USTs, overexcavation, and natural
<br /> attenuation.
<br /> 12.Reasons why background was/is Decreasing concentrations have been attained at all monitoring wells. Minor
<br /> unattainable using BAT,, soil contamination remains on-site.
<br /> 0 13.Mass balance calculation of substance The consultant did not estimate remaining soil or groundwater contamination
<br /> treated versus that remaining; left onsite.
<br /> N❑ 14.Assumptions,parameters, calculations and model A risk assessment was not required.
<br /> used in risk assessments, and fate and transport
<br /> modeling;and
<br /> 15. Rationale why conditions remaining at site will not Soil contamination is limited in extent,and based on 21 quarters
<br /> adversely impact water quality, health, or other of groundwater monitoring showing a decreasing trend in
<br /> beneficial uses. concentrations, contamination is not continuing to leach to
<br /> groundwater. .
<br /> By: Comments: Two 5,000-gallon and one 2,000-gasoline USTs were removed prior to 1976. From 9/96 to 10/96, one 500-
<br /> JLB gallon waste oil tank and piping were removed, and the gasoline USTs tank pit was overexcavated at the subject site.
<br /> Contamination was reported in soil and groundwater. In 4/99, maximum confirmation soil results were: TPHg
<br /> Date: (4,000 mg/kg), toluene(57 mg/kg), ethylbenzene(70 mg/kg),xylenes(430 mg/kg), methanol(250 mg/kg),and lead
<br /> (6.4 mg/kg). Boring soil results in 4/02 were WIND. Grab groundwater results in 5/97 were: TPHg(32,000 Ng/L),
<br /> 10/5/04 benzene(9 Ng/L) toluene(990 Ng/L), ethylbenzene(630 Ng/L),and xylenes(3,300 pg/L). In 4/04, groundwater monitoring
<br /> results were all ND. Based on the limited extent of soil contamination and decreasing contaminant concentrations in
<br /> groundwater, Board staff concur with San Joaquin County's Closure Recommendation.
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