10179096_2103 S. GRAND - Plan (2)

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Former Circuit One 2103 S. Grand Avenue, Santa Ana, California Proiect No. 11-0106 The Santa Ana River Basin is comprised of two sub basins, Upper and Lower Santa Ana River Basins. The Site is located in the Lower Santa Ana River Basins. It contains six reservoirs, consisting of the Laguna, Lambert, Peters Canyon, Rattlesnake, Sand Canyon, and Siphon Reservoirs. There are two lakes located in this sub basin, Anaheim Lake and the Irvine Lake (Santiago Reservoir). According to the Water Quality Control Plan, groundwater at the site is of beneficial use. 2.3.4 Hydrogeologic Settings Orange County consists of an alluviated coastal plain occupying the north western part of the county and mountainous area extending to the Pacific Ocean in the south western portion of the county (California Department of Water Resource [CDWR], 1967). The site is located within the Coastal Plains of Orange County Basin (CDWR, updated 2003). The Orange County Groundwater Basin is located adjacent to the Pacific Ocean. It is found within the Lower Santa Ana River shed. Groundwater in this basin typically flows from the Santa Ana Mountains through the Irvine sub basin and out westerly into the Main Basin (DWR, 1967). Locally, the first groundwater is found in a thin groundwater bearing zone starting at about 20 feet below ground surface (bgs). In the shallow groundwater in the vicinity of the study area, the groundwater flow directions are affected by infiltration, pumping groundwater and absence of infiltration by pavements. The shallow groundwater flow in the area is typically to the southwest. 2.4 Previous Investigations and Extent Of Contamination Between December 1988 and August 2012 several investigations and some remedial activities were conducted at the Site and within Industrial Plaza. The investigations included the sampling of seventy soil borings including thirty two by RS, converting six of the soil borings to soil vapor extraction wells that were eventually not used due to tight soil conditions, converting three of the soil borings to dual air sparging wells that were not implemented for remediation purposes, converting fifteen of the soil borings to groundwater monitoring, conducting cone penetration testing (CPT) at eleven locations within Industrial Plaza. A groundwater pump and treat (P&T) system was installed within Industrial Plaza to treat groundwater that was extracted from some of the groundwater wells. The P&T operated from about 1992 to 2012. The P&T system was shut off in May 2012 and its operation was terminated in August 2012. TCE, some breakdown compounds of TCE and copper were found in the soil beneath the Site. The groundwater is impacted by similar VOCs and 1,4-dioxane but copper was not found in the groundwater above its reporting limit. Assessments conducted by RS have delineated the extent of TCE and copper impacted soil at the Site (RS 2012A and RS 2012B). In 2012, vapor intrusion risk evaluation (VIRE) was conducted for Suites 2103 and 2105 S. Grand Avenue (RS 2012C). Based upon the VIRE, it was determined that the estimated cancer risks from the VOCs affected subsurface are below the known cancer risk for the U.S. population and are considered acceptable under California Proposition 65. Similarly, the estimated Hazard Quotient is below the Hazard Index of 1.0, which is considered acceptable to the California Environmental Protection Agency. No significant cancer risks or health hazards were anticipated to occur as a result of worker exposure to chemicals detected in soil vapor under the two suites. In April 1990, nineteen (19) soil borings that ranged from 2 feet to 15 feet bgs were sampled at the Site and at 2105 S. Grand Avenue (GRI 1992). The locations of these borings are shown on Figure 3. Some individual soil samples, composite soil samples and concrete core samples REMEDIATION SCIENCES 3