ARCHIVED REPORTS XR0009669 - Laserfiche WebLink

Home Browse Search

determine the lateral extent of impacted soil. On July 13, 1994, one soil boring was drilled at the site. Boring B-6 was installed approximately 7 feet north of monitoring well MW-I. The boring was advanced to a depth of 45 feet and backfilled the entire depth with Portland cement. Auger returns were placed on plastic sheeting and stored on-site. The boring location is shown on Figure 2. The boring was drilled using a truck-mounted B-53 drill rig. The drill rig and two-man crew ' were supplied by Mitchell Drilling Environmental Corp. of Rancho Cordova, California. During drilling, auger returns were monitored for the presence of organic vapors using a photo-ionization detector (PID: Thermo Environmental 580A, 10.0 eV, calibrated to ' isobutylene). Soil samples were collected ahead of the drill bit using a split-tube sampler loaded with three pre-cleaned 2-inch by 6-inch brass sleeves. The samples were collected at five-foot intervals, using a 140-pound hammer to advance the sampler 18 inches. The ' number of blows required to advance the sampler in 6-inch increments was recorded on the boring logs. To avoid cross-contamination, the sampling equipment was washed in an alconox solution and rinsed twice with water prior to each sampling run. For each sample, both ends of the lead tube were covered with aluminum sheets, capped and sealed with tape. The samples were then stored on-ice and transported under chain-of- custody to Western Environmental Science & Technology (WEST) in Davis, California. I Soil was extruded from the second brass tube and screened for the presence of organic vapors, using a PID, and the readings were recorded on the boring logs. The soil was then described in accordance with the Unified Soil Classification System (see Boring Logs, ' Appendix B). 4.0 FINDINGS 4.1 Groundwater Elevation ' The relative groundwater elevations for the monitoring wells were calculated by subtracting the water depth from the casing elevation (Table 1). Comparison of the February and May 1994 measurements indicate that groundwater depths have risen approximately 1 foot since ' February. This rise in groundwater follows the normal seasonal variation. j 4.2 Groundwater FIow Direction and Gradient ' As in previous quarters, there appears to be a flexure in the groundwater gradient (Figure P 9 � PP 3). However, the flexure was more dramatic during the May 1994 monitoring. South and east of the former UST, groundwater flows to the north. West of the former UST, groundwater flow is to the northeast. The cause of the flexure is uncertain, but may be influenced by local agricultural or domestic well pumping. a��i A.&S�h. w axn 11h ORVi-9V--1.16 i