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Work Plan for Additional Subsurface Assessment,.Former Unocal#0123 October 12,2000 Phase. I report' identified twelve sites' in the vicinity of the subject site that had impacted soil and .groundwater: None of the sites were located,in the immediate'up'gradient direction from the subject site. Two of the sites identified were former service stations that were located across from and d'owngradient of the subject site: a former Shell Oil service station at the northwest corner of 11't' Street and Central Avenue (operating from apXioxiniately.1949 to 1962); and�a former service station (possibly Chevron)at the northeast..corner of.11 and Central Avenue (operating from approximately 1913 to at least, 1962). Because of their closures prior to the mid to late 1960's, neither of the facilities on the north side of 116' 'Street.have had,environmental assessments. Sanborn Maps included in Appendix B from 1945 and 1947 show.the Shell Oil service station located at the northwest corner of I Vh Street and Central Avenue. IA Sanborn map from 1926 shows a building located at that corner identified as having gasoline and oil on-site. .Based'on the configuration of the former Shell Oil station'shown on the 1947 Sanborn map,the inferred former dispenser islands location is just east of boring B-5 installed.by GR on January 12, 20{00;and the boring could potentially be in the area of the former USTs'at that site (Figure 2),although the exact location of the former USTs could.not be determined based on the.information in the Enviros report or the Sanborn naps. PROPOSED SCOPE OF WORK To further evaluate the distribution of petroleum hydrocarbons.in soil and groundwater northwest of the subject site, GR proposes.to install two groundwater monitoring wells. GR's Field Methods and Procedures are included in.Appendix C: To complete this scope of work, GR proposes the following six tasks: Task 1. : Pre-Field Activities GR will.update the site-specific safety plan and obtain the necessary,well installation permit from. -the SJCPHS-EM. -An encroachment permit will.be obtained from the City.'of Tracy. A.copy of. the encroachment permit application package sent to.the City•of Tracy Community Development Department.on October 12, 2000 is included in Appendix D.. Underground Service Alert (LISA) will be notified a minimum of 48 hours prior to drilling. A private utility line. locator will.be contracted to clear all boring locations Task 2.. Weil Installation r GR will instail two groundwater monitoring:wells at the locations shown on Figure 2-on approval from the.City.of Tracy. The wells will be installed by a California licensed well driller. A GR geologist will monitor the drilling activities and prepare a log of each boring. The well borings will be drilled, using 8-inch-diameter hollow-stem augers. The wells will be constructed,of 2-inch- diameter Schedule.40 polyvinyl chloride (PVC) well casing and 0:02-inch machine-slotted well screen. The wells will be installed in 207foot deep borings with screened intervals from.5 to 20 feet below:ground surface(bgs): Proposed well'construc:ion details are presented in Figure 3. Soil samples for description and possible chemical analysis will be obtained from the well borings` at five-foot intervals, as aminimum. Soil samples will be collected with -a split spoon sampler fitted with clean brass sample rings. The.actual number of samples submitted for chemical analysis v 2400073.04 .