ARCHIVED REPORTS_XR0011927 - Laserfiche WebLink

Home Browse Search

e . 1.0 INTRODUCTION r A drilling investigation utilizing hollow-stem auger drilling equipment was conducted during the fourth quarter of 2004 at 3931 Newton Road The purpose of the work was to extend the investigation of the three Riverbank Formation aquifers underlying the site Four borings were drilled, and seven nested monitoring wells were installed in these borings Soil and groundwater Samples were collected from each aquifer to assess the vertical and lateral extent of contamination in this formation Quarterly sampling of the existing monitoring wells was also performed The results are presented in this report The project site is located in an industrial area on the northeast outskirts of Stockton near U S Highway 99 (Figure l) Originally agricultural property, the site was developed as a commercial truck terminal in 1973 A diesel and gasoline fueling facility, consisting of two underground storage tanks (UST's), was formerly present on the south side of the storage yard (Figure 2) This facility was removed in 1989, and evidence of soil contamination was discovered Several thousand cubic yards of contaminated soil were removed from the UST excavation in 1990 and treated using above-ground enhanced bioremediation methods, and several phases of drilling have been completed since then to investigate the extent of groundwater contamination and residual soil contamination Based on the results of those earlier phases of work, the San Joaquin County Environmental Health Department (EHD) concluded that further investigation is required to determine the full extent of contamination In September 2004, EHD approved the work plan to drill and install several new monitoring wells 2.0 PROCEDURES 2 1 DnIling and Soil Sampling Drilling was performed on October 29 and November 1-4 V&W Drilling, Inc mobilized a BK-81 hollow-stem auger drilling ng and advanced four borings into the Riverbank Formation under the supervision of Upgradient Environmental Consultants Boring locations were selected in consultation with Mr Nuel Henderson of EHD and are shown in Figuie 2 Soil samples were collected at 5-foot intervals for lithologic description, and selected samples were preserved in a cooled ice chest for subsequent laboratory analysis Boring logs were prepared and samples were screened for visual o`r olfactory evidence of diesel or gasoline contamination When the borings reached total depth, 2-inch diameter monitoring wells were constructed The boring logs are contained in Appendix A Boring GT-12 was planned for a total depth of approximately 140 feet, but flowing sand was encountered at a depth of 95 feet and drilling became difficult With approval from Mr Henderson, this boring was terminated at 105 feet and a monitoring well was constructed within the 2nd Riverbank aquifer in the depth interval of 85-105 feet Bon ngs GT-13 through GT-15 were also planned to penetrate the base of the 3rd Riverbank aquifer at an approximate depth of 140 feet GT-13 and GT-15 succeeded in reaching the base of this aquifer, but GT-14 did not GT-13 was terminated at a depth of 127 feet and monitoring wells were 2