SITE INFORMATION AND CORRESPONDENCE

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Sgnt By�- SASELINE; 510 420 1707; Nov-9-99 18:23; Page 4129 Under current conditions,there are no complete exposure pathways for human receptors. No current exposure pathways were Ilierefore evaluated in the PEA. Under proposed future use of the site a's a water square, potentially complete exposure pathways evaluated included contact with soil, volatilization of contaminants into air (ambient and indoor air), and ingestion and&ermal contact with shallow groundwater underlying the site. Although steal low groundwater is not currently used (or proposed to be used)as a drinking water source,this exposure pathway was added at the request of DTSC. An ecological screening evaluation was also conducted for the site. This PEA concluded that the excess cumulative lifetime cancer risk and hazard from ingestion and dermal contact with soil, ambient air,indoor air, and groundwater ingestion and showering/bathing with shallow groundwater underlying the site,was 3.3 x 10'5 and 0.67,respectively. The cumulative excess lifetime cancer risk exceeded a threshold of 1 x 10"6 (one-in-one million); the presence of contamination at the site may be considered by DTSC to pose a significant threat to human health at the Site if the site were used for future residential development. The pathways that exceeded the I x 10"6 threshold limit included soil and ingestion and dermal contact, and ingestion and bathing/showering with shallow groundwater underlying the site, It is important to note that these calculations were conducted assuming residential use of the site and conservative default assumptions; actual exposures and rislcs/hazards as experienced under the proposed redevelopment $ of the site as a water square would be less than experienced by a theoretical residential site user. It is also important to note that other regulatory agencies consider risk estimates from I x 10'4(one-in- ten thousand) to 1 x l(Y6 as posing a significant threat to public health. The calculated cumulative excess lifctimc cancer risk for the Weber Block property is within this range of risk estimates. Blood lead concentrations were also calculated for adults and children, based on the maximum concentration of lead reported at the site. The calculated blood lead levels were below the DTSC level of concern of 10 µg leadidl blood established for the 99th percentile exposed receptor. Proposed redevelopment of the site would therefore not be expected to contribute to blood lead levels in excess of DTSC levels of concern. The PEA also concluded that there are no potentially significant ecological habitats or species at the site, with the exception of the aquatic habitat and the Center Street Bridge for nesting swallows during the breeding season. The Stockton Channel supports a variety of resident and non-resident game fish species. However, as the Stockton Channel provides limited aquatic habitat for fish species, it is unlikely to support sensitive fish species (]ones & Stokes, 1999). The Stockton Channel is limited in terms of vegetation, tends to.flush slowly, has steep banks, and fine bottom substrates all of which limits habitat for aquatic species. Any construction- or project-related impacts to ecological receptors (i.e., fish and swallows) associawad with the Weber Block redevelopment would be mitigated during construction and operations to reduce these to less-than- significant impacts. Based on the findings of this PEA, the following actions are recommended: r - No additional groundwater or soil investigations are recommended at this time to fill any data k gaps. Several environmental investigations have taken place at the site since the early 1990s. i i ti