ARCHIVED REPORTS_XR0011160 - Laserfiche WebLink

Home Browse Search

CAMBR A Table 1 Site Conceptual Model,Shell-branded Service Station,2494 East Fremont Street,Stockton,California 2 5 BTEX Plume Stability and BTEX concentrations are showing a stable or decreasing trend in well S- Concentration Trends i Wells S-2, S-3, and S-4 typically do not contain BTEX and therefore cannot be used for trend analysis Deep wells S-2-82, S-3-84, and 5-4- 83 BTEX concentrations are typically near or below the detection limits Deep well 5-1-85 contains BTEX levels that fluctuate some, but generally show a declining trend 2 6 Groundwater Definition Status MTBE has been detected (by EPA Method 8260) in groundwater sample (oxygenates and lead from wells at this site at concentrations no higher than 8 5 ppb The only scavengers) exception to this is well S-6 which has contained MTBE as high as 100 ppb MTBE is sufficiently defined considering the low detections and the existing well network DIPE has been detected in groundwater samples from the wells at concentrations as high as 18 ppb The existing well network should be sufficient for delineation of DIPS in groundwater Ethanol,TBA, ETBE, and TAME have not been detected in groundwater samples collected from the site wells Methanol has been detected once in two wells at concentrations of 4,300 and 5,600 ppb Subsequent methanol sampling has shown that methanol delineation appears to be complete EDB has been detected only in well S-1 at concentrations as high as 350 ppb Grab groundwater samples collected from borings drilled at the site have not contained EDB, which demonstrates that EDB is not a widespread problem at this site 1,2-DCA has been detected in each site well at concentrations as high as 600 ppb CPT borings SB-20 through SB-25 provide some lateral delineation of 1,2-DCA at various depth intervals (Figure 2 of the main report) In general 1,2-DCA concentrations decline with distance away from the site and also decline with depth 2 7 Oxygenate and Lead MTBE concentrations appear to be stable, which would be expected as Scavenger Plume Stability and MTBE has been removed from the fuel that is sold at the site(since Concentration Trends January2003) DIPS concentrations appear to be stable or decreasing Ethanol,TBA, ETBE, and TAME have not been detected in groundwater samples collected from the site wells Methanol has been detected once in two wells at concentrations of 4,300 and 5,600 ppb EDB detections appear to be declining 1,2-DCA concentrations appear to be relatively stable or showing a declining trend 2 8 Groundwater Flow Direction, Shallow groundwater flow direction varies at the site, but is predominantly Depth Trends and Gradient toward south-southeast The gradient in the shallow zone ranges from Trends 0 0002 to 0 005 Depth to water (in the shallow groundwater zone), has ranged from 46 to 55 feet below grade The groundwater flow direction in the deep zone is typically toward the southeast Depth to water in the deep groundwater zone has ranged from approximately 51 to 55 feet below grade The vertical gradient between the shallow and deep groundwater zones appears to be neutral (i e , groundwater elevation in oil I the shallow zone is generally the same as it is in the deep zone) 0955 Page 2 0£5 Date Modified 12/1612004