SITE HISTORY - Laserfiche WebLink

Home Browse Search

The main soil types that exist in this type of deposit are sand,silt,gravel and clay that are irregularly interstratified. The primary mechanism for sedimentation in this area has been fluvial. The subject property is underlain by layers of silt,sandy silt,and silty sand(URS Greiner Woodward Clyde(URSGWC) 1999)• Depth to groundwater in onsite wells was approximately 45 to 50 feet below grade(fbg)during 2001 and 2002. During the excavation activities performed in 2005,groundwater was encountered in the excavation at approximately 75 fbg. Geologic cross sections prepared along a southeast-northwest transect(A-A') and along a northeast-southwest transect(B-B')are shown on Figure 3. Groundwater elevations have been monitored since September 2000.The depth to groundwater, and groundwater elevation data are provided in Table 1. During the most recent groundwater monitoring event(July 28, 2010),the groundwater flow direction was toward the north-northeast at an average hydraulic gradient of o.001 feet per foot. Groundwater elevations and elevation contours are shown in Figure 4. Historically the groundwater flow direction at the Site has been predominantly to the northeast and northwest as summarized in the Rose Diagram provided in Figure 5. 2.3 Summary of Site Investigations and Remedial Actions 2.3.1 Summary of Site Investigations A list of all investigative reports,remedial action reports and monitoring reports are included in Appendix B, and summarized below. January26, lgc)g: One 1,000-gallon diesel and one 6,000-gallon gasoline underground storage tank(UST) were previously maintained onsite for an unknown period of time and were removed from the Site by Thorpe Oil Company in January 1999. One soil sample,collected from the diesel tank excavation at 9 feet below grade(fbg)contained 8,00o milligrams per kilogram (mg/kg) total petroleum hydrocarbons as diesel(TPH-d) (Hydro-Environmental Technologies, Inc. (HETI) 2004). August 2-3, iggg: Five soil borings(B-1 through B-5)were drilled to a maximum depth of 56.5 fbg. TPH-d was detected in 14 of the 28 soil samples collected at depths ranging from 10 to 55.5 fbg. The maximum TPH-d concentration was detected in the sample collected from B-1 at to fbg at a concentration of 22,000 mg/kg. TPH-d was detected at 94,000 micrograms per liter(4g/1) in the grab groundwater sample collected from B-1,which was the only groundwater sample collected during this investigation(URSGWC 1999)• As part of the 1999 investigation, URSGWC completed as survey of all domestic,agricultural, industrial, and municipal wells within a one half mile radius of the Site. A total of five(5)water wells were identified within the search radius. However,only one of the five wells was located in the established path of groundwater flow beneath the Site, approximately 2,200 feet north- northeast of the Site. According to the information provided in the water well report,the public supply well was screened at depths of between Zoo and 56o fbg, much deeper than the shallow Site groundwater currently being monitored. July 12, 2000: HETI drilled six soil borings(B-1 through B-6)to total depths of 50 fbg. Grab groundwater samples were collected each of these borings. Analytical results for all soil and 2 M