ARCHIVED REPORTS_XR0012772 - Laserfiche WebLink

Home Browse Search

' Ms Diane Hinson - September 14, 1994 Page 4 ' ARCO No 760 The subsurface materials containing the majority of residual hydrocarbons beneath the ARCO ' Lodi site consist of laterally continuous units of sand/silty sand (fine- to coarse-grained sand)and silt with trace to little clay ranging in tluckness from 6 to 10 feet The silt units contain isolated ' sand and silty sand lenses Soil type of the upper portion of the aquifer (based on current groundwater elevation) has been clarified as fine- to coarse-grained sand Ranges of intrinsic permeabilities for sand and silty sand are approximately 10-3 to 107' cm/s and 10.5 to 10-3 cm/s, respectively (FetterC W Applied Hydrogeology, 1988 and Freeze and Cherry, Groundwater, 1979) Inic perrneabdities for slit range from 10' to 10'3 t nscm/s However, the presence of clay in the silt units will decrease the permeability, ranges of intrinsic permeabilities for clay are ' approximately 10-9 to 10-6 cm/s ARCO No 548 The subsurface materials containing the majority of residual hydrocarbons beneath the ARCO Stockton site consist predorrunantly of silt containing trace to some clay with laterally discontinuous beds and lenses of sandy silt The aquifer material consists primarily of silt with some clay Ranges of intrinsic permeabilitfes for silt and sandy silts are approximately 10-6 to 10' cm/s (Fetter, C W , Applied Hydrogeology, 1988 and Freeze and Cherry, Groundwater, ' 1979) The presence of clay in the soil will decrease the permeability PROXIMITY TO WATER SUPPLY WELLS A well survey is scheduled to be performed for the ARCO Lodi site during the next phase of work which includes further offsite assessment The results of the well survey will be included ' in the Problem Assessment Report (PAR) A well survey was previously conducted for the ARCO Stockton site to identify any municipal or domestic water supply wells within a 1/2 mile radius of the site The results of the survey were presented in the Preliminary Investigation and Evaluation Report, dated July 26, 1992 and also included in the Addendum to the PAR, dated August 16, 1994 Figure 11 presents the ' location of recorded water supply wells The nearest municipal well is approximately 1,000 feet to the south and the nearest domestic well is approximately 1,200 feet to the southeast ' RESULTS The estimated total mass of residual hydrocarbons beneath the ARCO Lodi site is approximately 489 lbs, where as the ARCO Stockton site contains a total mass estimated at approximately 383 lbs The groundwater flow direction does not appear to be consistent at the ARCO Lodi site, based on two quarters of monitoring The groundwater flow direction at the ARCO Stockton site I