FIELD DOCUMENTS - Laserfiche WebLink

Home Browse Search

Chronology page 2 Unocal #0123, 1034 Central Ave., Tracy. May 1995 Eight exploratory borings drilledlonsite (U-A thru U-H), and three monitoring wells installed ("U-1, U-2, and U-3") by Pacific Environmental Consultants for Unocal under a work plan approved by PHS-EHD. Additionally, more exploratory pits were dug and two USTs were encountered at the northwest boundary of the site, as well as product piping in the area south of U-2. (These USTs were two of the three "First generation USTs' previously described as "abandoned" by Unocal. 11/26/96 Two 550 gallon, riveted steel USTs and approximately 20' of steel piping removed under PHS-EHD permit. Small over-excavation to about 13 feet below ground surface ('bgs) conducted at removal time. High petroleum odors and heavy soil staining on all walls and at bottom. Excavation to west reveals additional anotherl(hidden) UST, the 1,000-gallon "First generation UST" stili under the sidewalk and mostly north under 11th Street. 12/11/96 The 1,000-gallon, last of "First generation UST", grouted in place with structural concrete under PHS-EHD approval. City of Tracy would not allow roadway excavation for UST removal, so UST abandoned in-place. Fourth monitoring well, "U-4" installed in city right of way under permit through this UST area. Soil samples from monitoring well installation indicate TPHg at 2,300 ppm at 8' bgs, with BTEX at <1.2, 8.1, 32, & 26 n at U-4 diminishes to non-detect at 15' respectively. Soil contaminatio and 20' bgs at detection limits of 10 ppm. Groundwater data from U-4 hottest for site with TPHg at 3,600 ppb and BTEX at 61, 6.1, 18, & 19 ppb. TPHd at 500 ppb. Groundwater gradient = NNW @ 0.004'Ift. Depth to groundwater at U-4 on 3-3-97 was 8.82' bgs. 09/28/98 Highest MtBE was detected only in U-1 groundwater at 5.3 ppb. 10/06/98 Onsite monitoring well "U-5" and offsite monitoring well "U-6" installed. U- 6 reports TPHg at 220 ppm in soil at 11' bgs sample depth and TPHg in the groundwater at 968 ppb. No significant soil hits in U-5 and the only groundwater contamination was TPHd in the 60-70 ppb range. Second soil boring with "134" designation installed onsite in SE corner of site at old asphalt patch area (old exterior hydraulic car lift). Only B-4 soil contamination was TPHd at 21,5 ppm at 10' bgs. B-4 groundwater hits of TPHd hit at 115 ppb, DCA at 0'.51 ppb, PCE at 2.97 ppb, and DCE at 1.39 ppb at 25' bgs sample depth. ,I 04/09/99 Groundwater sampling continu'ies and most recent report still supports PHS-EHD conclusion that groundwater plume not defined to NW and W. No recommendations from Unocal included in reports. - I