SITE INFORMATION AND CORRESPONDENCE

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Wendy L. Cohen -2- 15 March 1993 Potential Contamination Migration Pathways 1. The report identified specific data gaps, including lack of information on the disposition of irrigation well 8R2, status and locations of three Port of Stockton pipelines, migration pathways on the SFPP terminal , two underground tanks, and underground piping and delivery systems at Unocal . No work is proposed to fill in these gaps. Furthermore, the report does not describe the significance of the existing information, or how any additional information will change conclusions that can be drawn from the existing information. This task did not identify contaminant sources. 2. The report also provided specific information on the location at each facility of manholes, hydrants, buried pipelines, storage tanks, sumps, utility lines, etc. However, the information was not related to the contamination at each facility or the Port of Stockton fuel terminal as a whole. 3. The oil/water separators at ARCO and ST Services are not shown on any map. Field Screening Investigation 1. Cone penetrometer tests (CPTs) were used to define the stratigraphy and the lateral extent of hydrocarbon contamination, and to optimize monitoring well placement. CPT or some other method is needed to define the lateral extent of contamination in the B-zone and possibly in the C-zone. 2. Well installation included placement of ten shallow wells next to CPTs, six well pairs screened in the shallow and medium depth zones, and one medium depth background well . Additional wells are needed to define the lateral extent in the B-zone and determine if there is contamination in the C-zone. An investigation is needed to determine the base of the B-zone. Site Geology/Hydrogeology 1. The geology section describes four geologic units underneath the site, but does not relate the four units to the presence of contamination. 2. The report states that the degree of lateral and vertical hydraulic connection between water bearing zones has not been defined, but no work is proposed to address the situation. Since contamination has been confirmed in the B-zone, additional work is needed to determine if contamination exists in the C-zone. 3. The report states that the limited migration of petroleum hydrocarbons towards the east-southeast within the A-zone may be the result of the higher permeability sandy units pinching out to the east into the low permeability soils. The results also suggest that since the dissolved contaminants may be hindered laterally, they have no other place to go but downward. Preliminary Ground Water Monitoring Results A preliminary sampling program was implemented to identify the downgradient extent of petroleum hydrocarbons and to optimize the CPT and monitoring well locations.