ARCHIVED REPORTS_XR0004898 - Laserfiche WebLink

Home Browse Search

Fuller Mobile Home Park 365 F_ Louise Ave-, Lathrop, California February 23, 1995 Phase H Site Characterization - Continued Page: 6 (Figures 7 & 8) Soil Samples from B-5 & 6 and MW4, 5, 6 & 7 were all ND (Table 1 & Appendix A) The lateral extent of soil contamination has been defined (Figure 9) 5.0 Groundwater Conditions The water table was approximately 12 feet below ground level as the wells were being drilled Subsequent water levels before sampling recorded water levels in the vicinity of 11 feet below ground level (Table 3) The maximum groundwater elevation variation across the site was 0 11 feet The extremely shallow water table and flat gradient is very sensitive to rain and errors in measuring depth to water as small as 0 01 feet After the wells were surveyed (Appendix E), a groundwater gradient ranging between 0 0004 and 0 0011 ft/ft was calculated (Figure 4) The direction is variable across the site It appears to be influenced by the new stormwater retention ponds whose bottom elevations are approximately five feet above the water table I 6.0 Conclusions and Recommendations The soil contamination "plume" has been defined at this site With the exception of an P P isolated interval of gasoline in MW-2, a groundwater contamination plume exists from near 10 feet below ground level in the area of the former underground tanks The lateral extent is not completely defined to the northeast and south, because all monitoring wells showed some traces of contamination The groundwater gradient direction is (at the time of sampling - Jan 22, '95) off-site to the NE and SW With the shallow water table and the exceptionally flat groundwater gradient, contanunants have been moving laterally with the variable gradients caused by pumping of wells, irrigation of nearby fields and precipitation The Dellu sand that covers the area is a very permeable sand that overlies & sandy silt (in some areas) that is in contact with the water table This is evidenced by I contamination over 50 feet up gradient and over 60 feet laterally from the present gradient, and both soil and water samples have higher contamination levels to the west and northwest of the former tank site IIt is the recommendation of WHF that an additional boring be drilled to the north of the former tank site, and access to existing wells and/or well data south of Louise Avenue on ' Libby-Owens property The above represents our best professional opinion as to environmental conditions at this site These opinions were derived using data at hand, and using standards of care common to the environmental consulting community in Northern California Additional work or sampling at this site may generate data that could lead to a change of opinion regarding I