WORK PLANS - Laserfiche WebLink

Home Browse Search

Soil Assessment Report 324 East 11th Street Tracy, California October 12,2017 To define the lateral and vertical extent of contamination identified in the Phase II Environmental Assessment Report dated July 23,2013, Pangea coordinated additional site assessment in accordance with the Workplan for Additional Assessment and Subslab Gas Sampling(workplan) dated November 22,2013 and approved in a letter from SJCEHD dated February 13, 2014. On July 10, 2014, Pangea coordinated the drilling of four soil borings (B-7S, B-71), B-8 and B-9) onsite and one soil boring (B-10) offsite at Tracy High School (Figure 1). Soil borings B-7S, B-71) and B-8 were advanced near the potential former piping location, while B-9 was installed northwest (downgradient) of former boring B-1, within the planter along E 11th Street. Boring B-10 was installed within the planter on the north side of E. 11th Street, adjacent to the Tracy High School parking lot. The investigation results were reported in Pangea's Additional Site Assessment Report dated October 8,2014. Site Geology & Hydrogeology Soil from site borings consisted primarily of silty clay to a depth of approximately 17 ft bgs, underlain by more permeable sandy clays or clayey sands observed to a depth of approximately 25 ft bgs. Wet soil (possible groundwater) was encountered in the more permeable sandy clay or clayey sand layers at approximately 17 ft bgs. Soil contamination is primarily located between 1 and 10 ft bgs based on field observations and analytical results. SITE ASSESSMENT PROCEDURES To identify the appropriate next steps at the site, Pangea discussed site conditions with the SJCEHD. SJCEHD geologist Nuel Henderson requested additional source area assessment near boring B-1 and the apparent subsurface piping from the former service station operations. Mr. Henderson also requested assessment for a possible second source area on the east side of the building. The additional site assessment work scope to address SJCEHD concerns was described in the Workplan for Additional Assessment and Sensitive Receptor Survey (workplan) dated January 27, 2017, which SJCEHD approved in its February 13,2017 letter. Pre-Drilling Activities A comprehensive site safety plan was prepared to protect site workers and the plan was kept onsite during all field activities. A drilling permit was obtained from the SJCEHD. A copy of the permit is presented in Appendix A. The proposed drilling locations were marked and Underground Service Alert was notified at least 48 hours before the proposed field activities. Drilling Procedures On February 16, 2017, Pangea coordinated the drilling of three soil borings (B-11 through B-13) onsite (Figure 1). To evaluate potential waste oil tank impact,Pangea advanced soil boring B-11 near soil boring B-1, as shown on Figure 1. To evaluate for a potential second source area, Pangea drilled boring B-12 in 2