SITE INFORMATION AND CORRESPONDENCE

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sent By;: BASELINE; 510 420 1707; Nov-9-99 16:28; page 181129 U miles per hour (California Department of Water Resources 1998). Wind speeds are gen all y highest during the spring months and lightest in the fall and winter. The San Joaquin Valley Air Basin has surface-based inversions during the morning hours throughout the year. Elevated inversions are much less frequent than surface inversions. In terms of mean mixing depth (the layer of air available for vertical mixing of pollutants), winter has the worst inversion characteristics (California Air Resources Board, 1974 as cited in Paoli and Associates, 1991). In addition, Stockton receives 10 to 15 inches of precipitation annually (Oregon Climate Service, 1995). No human receptors are currently exposed to contaminants in air under current site conditions. Future human receptors frequenting the water square could potentially be exposed to contaminants € in air,if releases from surface soils via wind or volatilization from subsurface soils or groundwater occurred. Under the proposed redevelopment plans, the majority of the site would continue to be capped or covered with imported soil and landscaping materials. However, volatilization and/or wind dispersal of subsurface contaminants could take place on-site in areas not paved.The number of people exposed under the future conditions cannot be estimated.It is expected that exposure to any releases to air would be greatest for on-site occupants, and substantially less for off-site receptors, which are primarily commercial site users. No schools, day care centers, hospitals, nursing homes, retirement communities, coastal or freshwater wetlands, national parks, or other sensitive populations are within the area adjacent to or nearthe project site;these sensitive receptors would therefore not be affected by any on-site releases. (See the Ecological Screening Evaluation, below, for special status ecological species.) SUMMARY OF SAMPLING ACTIVITIES AND RESULTS ON-SITE, { Phase II Investigation Sampling of subsurface soils, groundwater, sediments, and wood pilings was conducted by Black & Veatch and their subconsuitant for the project site, as described in the Phase 11 Environmental 4 Investigation Report, Weber Block(Area 9) (Black&Veatch, 1999a). Sampling activities did not include collection of samples near the former Shell Station/Bridgestone facility;sampling activities at this location are described below.All field sampling activities were conducted in accordance with a Sampling and Analysis Workplan for Weber Block (Black & Veatch, 1998b), and under the P S direction of a Health and Safety Plan(BASELINE, 1998). Both plans were reviewed and approved r by DTSC prior to the sampling. U.S.EPA also reviewed the Sampling and Analysis Workplan. All samples,described below, were collected on 16 and 20 April 1998. j Soil samples from nine soil borings,four grab groundwater samples(including one sample from an off-site,upgradient position near the former ARCO facility),three sediment samples,and four wood piling samples were collected as part of this investigation. Quality assurance/quality control samples were also cu1lected and analyzed as part of this investigation as de.5cnbcd in the Phase 11 investigation. No composite or background samples were collected as part of this investigation. Also, no air or surface water samples were collected. 97369sstk,pon.wpd-1 119/99 12 1