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Mr.M. Scott Mansholt—CEMC <br /> ' Soil Sampling Work Plan August 1,2006 <br /> Surland Homes Property Page 3 of 8 <br /> ' monitoring for the two on-site groundwater monitoring wells. On May 5,2003 the RWQCB <br /> issued a letter approving the work, and a report detailing the sampling results was submitted in <br /> October 2003. <br /> ' INITIAL RESPONSE TO COMMENTS <br /> t The DTSC letter dated December 19, 2003 contained comments and questions regarding the <br /> HRSE. The comments were divided into two categories: site characterization and HRSE <br /> comments. Preliminary responses have been developed below for certain of the comments. <br /> Presented below is a discussion regarding the site conceptual model(SCM), which as noted in the <br /> DTSC letter, has not previously been developed for the site. Following the SCM discussion are <br /> responses to specific items in the DTSC letter. For reference,the DTSC letter is included as <br /> Attachment A. <br /> SCM <br /> A SCM evaluates sources,transport mechanisms, exposure media,and exposure pathways. <br /> ' Potential source media include surface and subsurface soil, groundwater and surface water. <br /> Transport mechanisms include dust emissions,volatilization,and leaching to groundwater. <br /> Potential exposure media include soil, outdoor and indoor air, groundwater, and surface water. <br /> ' Potential exposure pathways include ingestion of and/or dermal contact with, soil,groundwater, <br /> or surface water,inhalation of volatiles, and consumption of aquatic species from surface water. <br /> The HRSE performed by Geomatrix included inhalation of volatile organic chemicals from soil <br /> ' and groundwater,inhalation of airborne dust from soil, ingestion of soil and groundwater,and <br /> dermal contact with soil and groundwater. <br /> Figure 3 presents a SCM for the site taking into account current site conditions. Ingestion, <br /> ' inhalation of volatiles from, and dermal contact with groundwater have been eliminated as <br /> exposure pathways as the residential development is supplied with water from the City of Tracy <br /> (the City). The City has enacted an ordinance prohibiting installation of private water supply <br /> ' wells;therefore, exposure to groundwater is not a complete exposure pathway. Based on the <br /> absence of surface water in the vicinity of the site,no complete exposure pathways exist for this <br /> exposure medium. As noted in the DTSC letter, site data do not suggest the need to <br /> quantitatively evaluate risk from indoor air exposure,and thus inhalation of outdoor air has also <br /> ' been eliminated. Therefore, ingestion and dermal contact with soil remain as the exposure <br /> pathways, and will be evaluated. <br /> ' As seen on Figure 3, the status of the ecological receptors has not been established. As requested <br /> in the DTSC letter, an ecological risk evaluation will be performed. <br /> The following section contains responses to the DTSC comments (the comments are paraphrased <br /> ' below in italics and are followed by SAIC's response). <br /> RESPONSE TO SITE CHARACTERIZATION COMMENTS <br /> ' 1. Pipelines. Locations and depths ofpipelines, ifpipeline removed, and source of backfill need <br /> to be indicated. <br /> To the extent the information can be collected, this information will be provided in the revised <br /> ' health risk assessment. <br /> Z West Side Irrigation Ditch Feature. A description of this feature, uses, and potential <br /> contamination is requested, as well as when and how potential contamination in this area will be <br /> addressed. <br />