ARCHIVED REPORTS XR0010164 - Laserfiche WebLink

Home Browse Search

2.0 Introduction This report presents the results of the soil excavation and limited groundwater removal at the site at 595 East 11`h Street in Tracy, California The San Joaquin County Environmental Health Department (SJC EHD) reviewed the corrective action plan and area of proposed excavation in the Wright report and work plan dated October 10, 2003 and in discussions with Wright personnel SJC EHD representatives observed portions of the excavation work, dewatering point placement and all soil and water sampling Two monitoring wells (MW-3 and MW-9) were abandoned under SJC EHD permits during the excavation since the wells were located within that area The purpose of the work was to remove suspected residual soil petroleum contaminants in the vadose zone, capillary fringe and upper aquifer strata in the area of the historic groundwater plume (see Figures 1 and 2). Two large utility lines are present on-site and limited the excavation limit The West Side Irrigation District owns a 48-inch diameter irrigation pipeline that crosses the site The City of Tracy owns a 36-inch main sanitary sewer line that crosses the site dust east of the irrigation line (approx 25 feet apart, see Figure 1) These are large and sensitive pipelines and the respective owners had expressed concern and reluctance regarding previous plans by Wright for excavation in this area Both pipeline owners had representatives present to locate the lines and periodically observe the excavation work and discuss the limit of digging near the edge of the lines with their approval Wright promptly backfilled open excavations to prevent sidewall caving that might have caused problems to the pipelines Some other excavation delays were caused by rainy weather 3.0 Field Methods 3 1 Excavation An "L" shaped area roughly defined by monitoring wells MW-9 and MW-3, and just down gradient of the former underground tank pit The area was excavated to depths of 10 to 11 feet and in some areas a maximum depth of about 16 feet Wright initially located the utilities, removed pavement, and a tree prior to starting the work Excavation continued at intervals from February 21 to April 4, 2004 The work was delayed at times due to weather and the need to perform backfilling around pipelines and to move surface objects to open the area to excavation equipment Some on-site equipment and trailers were relocated or moved so the excavation work could proceed The area of excavation was marked and the pipelines located for the lateral limits of excavation The irrigation pipeline defined the western limit and the City of Tracy sewer line marked the eastern limit Soil was excavated in the area of the capillary fringe and into the aquifer strata to depths of about 16 feet below grade (BG) The soil was removed on the basis of apparent contaminant presence (color staining and vapor). Soil samples were collected for soil off-site disposal and at the limits of excavation (see Figures 1 and 2, Site Photographs and Tables 1 and 2) Page 4 of 13