SITE INFORMATION AND CORRESPONDENCE_CASE 1

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i TABLE 1 - CHECKLIST OF REQUIRED dTA FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES Site Name and Location: Manteca Unified School'District, 2901 Louise Avenue, Manteca, San Joaquin County 1. Distance to production wells for municipal, domestic, agriculture, Four water supply wells were identified within industry and other uses within 2000 feet of the site; 2.000 feet of the site. The two nearest wells are 150 and 175 feet to the south and upgradient of the site. 2. Site maps, to scale, of area impacted showing locations of former and existing tank systems, One lion diesel UST 0 excavation contours and sample locations, boring and monitoring well elevation contours, was reemovmov ed in March 1997. gradients, and nearby surface waters, buildings, streets, and subsurface utilities; 3. Figures depicting lithology(cross section), treatment system diagrams; Site lithology.consists primarily of silty sand with minor silty clay lenses to 30 feet, the total depth investigated. 4. Stockpiled soil disposed off-site (quantity); The disposition of excavated soli was not presented. The soil was likely returned to the tank pit excavation. 5. Monitoring wells remaining on-site, fate; Three monitoring wells have been installed for this investigation. The wells will be properly destroyed pending site closure. - .7rtie depth to ►iva-ter varr'ed tram 10 t_6 feet,and Q�6. Tabulated results of all groundwater elevations and depths to water,' the groundwater'flow direction is to the northwest FY 1 7. Tabulated results of all sampling and analyses: December 2001 groundwater monitoring results show benzene at ❑Y 0.3 pg/1, toluene at.1.1 pg11, ethyl benzene at 0.4 pg/1, and xylenes at Detection limits for confirmation sampling 3.0 pg/l. TPHd was non-detect at X50 pg/l in all three monitoring wells. N�Lead analyses A groundwater grab collected in 11198 was non-detect for all oxygenates at acceptable detection limits. 8. Concentration contours of contaminants found and those remaining in soil The one on-site soil boring and three and groundwater, both on-site and off-site: monitoring wells define the extent of FiLateral and FIVertical extent of soil contamination contamination. Lateral and F1Vertical extent of groundwater contamination 9. Zone of influence calculated and assumptions used for subsurface Based on the limited extent of soil N remediation system and the zone of capture attained for the soil and contamination, an engineered remediation groundwater remediation system; system was not warranted at this site. 10.Reports 1 information Unauthorized Release Form QMR(12/01) F Boring logs N❑ PAR FRP (Limited Soil and Groundwater Assessment, 1199) 11.Best Available Technology(BAT)used or an explanation for not using BAT; Remove USTs,natural attenuation. Minor soil and groundwater contamination remains on-site at the former diesel 12.Reasons why background wasris �,�, , unattainable usirig'BAT,�` r USTarea:~ r 1 13.Mass balance calculation of substance The consultant estimates that 2.9 pounds(0.4 gallons) of TPHd remain f in treated versus that remaining; shallow soils in the area of the former diesel UST. N❑ 14. Assumptions,parameters, calculations and model used in risk assessments, and fate and transport modeling;and A risk assessment was not required. 15. Rationale why conditions remaining at site will not adversely Soil contamination is limited in extent. Groundwater impact water quality, health, or other beneficial uses. contamination is below water quality objectives, and will continue to degrade. By: Comments: The former UST site is part of the Manteca School District maintenance yard and farm site. One 250-gallon MH diesel UST was removed from the site in March 1997. TPHd was identified in tank pit soil samples, and in one soil boring from 8 to 13 feet. Three monitoring wells were installed on 29 November 2001, and sampled on 17 December 2001. Low Date: levels of BTEX constituents were identified in the three water samples;however TPHd was non-detect. A domestic well and an irrigation well exists at 150 and 175 feet south and upgradient of the former UST area, respectively. The domestic 1212102 well was sampled for TPHd and BTEX on 29 November 2001, and found to be non-detect for all constituents. Based on the low remaining mass in soil, and groundwater contamination below wafer quality objectives, Board staff concur with San Joaquin County's Closure Recommendation.