ARCHIVED REPORTS_XR0012407 - Laserfiche WebLink

Home Browse Search

1 ARCAD 1 S G ERAG HTY&MILLER groundwater is limited to an area south and east of the former underground storage tanks. The extent of hydrocarbons has been delineated to nondetect levels to the northeast (downgradient) in Well MW-7, and to the north (crossgradient) in ' Wells MW-1 and MW-5. TPHg was detected to the southwest (upgradient) in Well MW-8, and to the south(crossgradient)m Well MW-9, at concentrations of 93 and 1 I0 micrograms per liter (ug/L), respectively Benzene was not detected in Wells MW-8 and MW 9 ' In 1996, PEG performed a 6-month, on-site, SVE pilot study. PEG estimated (Remedial Action Performance Summary - October through December ' 1996, letter report, Pacific Environmental Group, February 4, 1997) that approximately 2,745 pounds (450 gallons) of TPH-g and 12 pound (1.6 gallons) of benzene were removed by SVE during the pilot study. ' Soil Conditions ' The site is underlain by primarily fine-grained deposits consisting of interlayered clays and silts to an approximate depth of 50 feet Silts and silty sands occur to a depth of approximately 25 feet Occasional interlayered silty sands(up to 50 feet thick)were found to the total depth explored y Existing hydrocarbon drocarbon concentrations in the soil appear to be limited to the pp area around the former product islands Soils in the vicinity of the northern product ' island at location VW-2, within the depth interval of 20 to 30 feet, were found to have TP 11.9 concentrations ranging from 1,400 to 17,300 mg/Kg with benzene concentrations ranging from 0 27 to 28 mg/Kg Within 15 feet of VW-2, at loca- tions MW-2 and KB-2, soil concentrations decreased to below 28 mg/Kg TPHg and less than 1 mg/Kg benzene between depths of 25 and 30 feet bgs In the area around the southern product island, Boring KB-3 contained 239 mg/Kg TPHg and ' 11.2 mg/Kg benzene Groundwater Conditions ' Groundwater occurs beneath the site within fine-grained deposits Groundwater at the site has been consistently observed to flow northeast,since 1988, ' at an approximate gradient of 0 002 The maximum groundwater fluctuation of 17 5 feet was measured in Well MW-1 between 1988 and 1993. Because of the fluctuations in groundwater, Wells MW-1 and MW-2 were dry between 1990 ' and 1992. Well MW-3 continued to be dry through the first quarter 1993. Separate-phase hydrocarbons have not been observed in site wells Historically, the highest hydrocarbon concentrations have been observed in on-site ' monitoring wells MW-2 and MW-6. PEG previously analyzed five sets of our ret Page ' WM_SAMTA_BARBARASaATA%APRO ASO%UNOCALIC VMIEYWVPS REWACVOMkDOC 4/11