WORK PLANS - Laserfiche WebLink

Home Browse Search

Remedial Action Plan RE: 425 W. Larch Street, Tracy, CA October 1 , 2008 W&A Project No. FTIM-08-001 Page 5 of 11 bsg . TPHg and related compounds were reported in only two of the boreholes, V-5 and V-6, and in small concentrations (Table 2) 3 .2 .4 Remediation Studies In August of 2005, BEII performed a pump test on the shallow water-bearing zone in the area near the former UST farm. The study pumped on MW-3R and measured draw-down on MWs- 21 , 22, and 23 . MW- 13 was also monitored, but it was a deep well. The pump test showed that the two water-bearing zones were not connected. The pump test results showed that the zone could sustain a pump rate of 2.5 gallons per minute, and that the draw-down, once stabilized in MW-3R was almost 4 feet. The draw-down in MW- 22 was approximately 1 . 15 feet, in MW-23 was 0.69 feet, and in MW-21 was 0. 12 feet. MW-22, MW-23, and MW-21 were 10 . 5 , 21 . 5 , and 56 .3 feet away from well MW-3R respectively. The data showed that the shallow water-bearing zone could support pumping. The report of the pump test is provided in Appendix 3 . 3 .2 . 5 Remedial Effort In August of 2005 , BEH excavated approximately 325 tons of soil from the area of the former UST-farm. BEII excavated a pit approximately 30 feet by 30 feet by 15 feet deep at the comer of the building, where the former UST farm had been (Figure 3). BEII collected soil samples from the side walls of the excavation when the excavating work was finished. Samples were collected fJ) from 4 and 12 feet in depth along the side walls. Generally there were no, or very little, A plT y concentrations of TPHg, BTEX, or MtBE reported in the samples collected from a depth of 4 feet. However, significant concentrations of TPHg and TPHd were reported in the samples collected from the depths of 12 feet (the capillary fringe). Concentrations of BTEX and MtBE were also reported in those samples. 4 CURRENT SITE CONDITION Based on the site history, and current groundwater condition, it appears that there was a release of gasoline from the former UST farm at the northeastern comer of the building. The vadose , e zone is a relatively tight clay, and groundwater is relatively shallow (approximately 12 feet bgs). 1 Cross-section diagrams are provided as the 5a' and 6th Figures, but are labeled as Figures 7 and 8 as they are from a different report. Because the vadose zone in which the tanks were set is relatively tight, there has been very little spread of the gasoline and related products through it. This is evidenced through lack of TPHg, BTEX, or MtBE in almost all of the soil samples collected from the vadose zone (except in, or very near the UST farm location) or in the vapor samples collected from the shallow subsurface (again, with the exception of those collected near the UST farm) . However, because groundwater is so shallow, the bottom of the former USTs farm was below the groundwater level and as such, the leaking product from the UST(s) was able to migrate readily to groundwater and then partition into the dissolved phase. As is also shown through groundwater well construction and soil samples collected in those boreholes, the contaminants are moving westerly with the groundwater and are spreading along the capillary fringe. The plume appears to extend just outside the westerly and easterly boundaries of the site, but is located within the site in the north and south directions. ^—y CI VIINEPIrySLD E PSSOHTFS• rNC. i Nei ELO AMe OCI axs `leis