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8. STRATEGY AND PROCEDURES FOR A SOIL AND GROUNDWATER INITIAL SITE ASSESSMENT INVESTIGATION FOR PETROLEUM HYDROCARBON CONTAMINATED SOIL AND GROUNDWATER The intent of this work plan is to present the methodologies to be used to assess the horizontal and vertical extent of petroleum hydrocarbon contaminated soil and groundwater from the unauthorized release of product from former UST's and dispensers at the site The basic assumption regarding the petroleum hydrocarbon contamination in soil and groundwater beneath the site is that an ongoing unauthorized release of gasoline fuel was most likely occurring during the life of the service station (1950 to 1984) Groundwater flow direction of the shallow aquifer has typically been to the southwest or south (Figure 5) and information gathered from previous investigations at the site substantiates this Groundwater levels have risen and fallen over time and during high-water level periods the contaminate soil is most likely in direct contact petroleum hydrocarbon saturated soil causing petroleum hydrocarbon concentrations in local groundwater to increase This relationship is depicted on Figure 6 which is a hydrograph of monitoring well PT-MW-1 Figures 7 and 8 depict TPH-g and benzene concentrations in groundwater beneath the site and on adjacent properties that is based on the existing monitoring well sampling results from the 1' quarter of 2003 and previous CPT hydropunch soil boring groundwater grab sample analytical results Based on these maps it is clear that a significant release of petroleum hydrocarbons has occurred from the Parmar Texaco site and that local migrating groundwater has potentially moved it offsite several hundreds of feet The summary strategy to implement the tasks contained in the workplan is to initially define the horizontal extent of petroleum hydrocarbon contamination within the soil and first groundwater bearing zone encountered beneath the site The vertical extent of petroleum hydrocarbon contamination of deeper or"second water zones" will be addressed in a follow-up effort once horizontal extent of shallow contamination is verified We currently estimate that the soil and groundwater petroleum hydrocarbon plume has migrated offsite, mainly in the southwesterly direction However, cross-gradient and upgradient zero lines for petroleum hydrocarbon contamination have not been identified to date by past investigations It is anticipated that the initial effort will be to conduct a Sensitive Receptor Survey of the site and immediate surrounding area The information developed from the sensitive receptor survey and existing data from the Parmar Texaco site and nearby LUST sites will be used to develop a preliminary working model (Site Conceptual Model) that will guide future soil and groundwater exploratory work Prior to conducting any further drilling on site a geophysical investigation will be conducted to confirm where underground facilities • Main\D\EnvuonmentaMarmarTexaco\Workplan\042003 wpd 10