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GeosyntecO GeosyntecO consultants consultants first encountered during drilling.Two monitoring wells were identified in the two study areas for The vacant suite that has been selected for this pilot study is located in the former source area sampling:MW-007A near the occupied suite(240 Lincoln Center)and PT-11 near the vacant where some of the higher concentrations of VOCs have been observed in first encountered suite(858 West Benjamin Holt Drive). The Supplemental Guidance recommends using soil groundwater and therefore where the VI potential is higher.The vacancy of this suite allows for vapor data collected from a minimum of two depths be used in the initial screening for VI risk full flexibility in the investigation activities and reduces the number of variables that are caused (CalEPA,2020).A permanent,nested soil vapor probe will be installed near each of the two by typical business activities.The suite's location in the former source area presents a worst-case groundwater monitoring wells.Soil samples will be collected continuously during soil vapor scenario for the potential for vapor intrusion.The occupied suite is located in an area where probe installations,logged by a geologist or engineer under direct supervision of a licensed elevated concentrations of VOCs have been observed in first encountered groundwater as well professional,and select soil samples will be submitted to a geotechnical laboratory for and is located outside of the anticipated area of influence of the recent ISCO injections.Residual confirmation of soil classification.The selection process of soil samples for geotechnical VOCs were detected in soil vapor in both of these study areas(Geosyntec,2013). analysis are discussed in Section 4.4.This data will provide accurate,Site-specific physical characteristics of the soil which can be used in the J&E model to assess future VI risk.Paired 4.2 Pre-Field Activities groundwater and soil vapor samples will be collected from the well and the data will be used to Prior to initiating intrusive fieldwork at the Site,pre-field activities will be completed including evaluate the attenuation of VOCs from groundwater to the vadose zone. revising the Site Health and Safety Plan,procuring permits and property access approvals,and The vacant suite(858 West Benjamin Holt Drive)is approximately 300 square feet and currently conducting a utility survey in the area of the proposed injections. These pre-field activities are consists of the main store front in the northern portion of the suite and a breakroom and discussed in this section. bathroom in the southern portion of the suite.There is a single heating,ventilation,and air 4.2.1 Health and Safety Plan Addendum conditioning(HVAC)unit that services the entire suite and is not shared by neighboring suites in the building.The occupied suite(240 Lincoln Center)is approximately 800 square feet and is Current field conditions will be reviewed by staffbefore commencing field activities. The currently occupied by a clothing store.Information regarding the HVAC system operations are assessment will include the following items: currently unknown. . Evaluating health and safety concerns with respect to proposed scope of work; A minimum of three,collocated sub-slab soil vapor and indoor air sample locations are . Evaluating existing and previously existing utilities in relation to the proposed boring recommended for small buildings(less than 1,500 square feet)to evaluate VI.Three sub-slab probes will be installed in of each of the suites to collect sub-slab soil vapor.The sub-slab probes locations; will be used to collect chemical data to assess the concentrations of VOCs beneath the slab of the . Ensuring safe access and movement within the work area; building.The sub-slab probes will also be used to collect differential pressure data prior to, during,and after collection of the sub-slab analytical soil vapor sample.The differential pressure . Determining operational and traffic safety requirements;and data will provide information about the pressure inside the suite compared to the pressure beneath the slab.This data can be used to gain a better understanding of the movement of air • Assessing general health and safety hazards presented in this scope of work. between the sub-slab and indoor air and provide another line of evidence to evaluate the current After a review of the field conditions has been completed,a Site-specific task hazard analysis and future VI risk,in accordance with Step 4 of the Supplemental Guidance. (TINA)will be prepared to supplement the existing Site Health and Safety Plan(HASP). The Indoor air samples will be collected simultaneously with the chemical sub-slab soil vapor THA will ensure safe work practices to prepare for and minimize the possible hazards to human samples.Three indoor air samples will be collected in each of the suites.The concentrations of health and to the environment with regard to the proposed scope of work.Hazards and controls chemicals reported in the indoor air and sub-slab samples can be used to evaluate attenuation of developed in the HASP addendum will be communicated with all field personnel.In addition, vapors across the slab from the subsurface into indoor air. due to the current coronavirus disease(COVID-19)pandemic,a THA focused on health and The variability observed in conventional indoor air sampling is largely caused by fluctuations in safety procedures to follow during the pandemic will be included in the HASP addendum. the differential pressure in buildings.Traditionally,multiple indoor air sample collection events 4.2.2 Permitting and Access are recommended to collect temporal data to understand the variability of indoor air The proposed activities will be completed solely on property owned by Lincoln Properties,Ltd. concentrations with the naturally occurring fluctuations in building differential pressure that (LPL)under the existing access agreement between LPL and the Trust.Geosyntec will notify occur seasonally.Building pressure control(BPC)allows the differential pressure variable to be and gain approval from LPL regarding the proposed scope of work,work hours,and schedule in controlled using a blower fan door or manipulating the building's HVAC system.BPC may be advance of field implementation. implemented at the Site to provide a reasonable worst-case scenario by depressurizing the suite to collect indoor air samples.BPC is recommended in the Supplemental Guidance to provide Boring permits will be obtained from the San Joaquin County Environmental Health Department another line of evidence in evaluating current and future VI risk. (SJCEHD)for each proposed boring prior to the implementation of the Work Plan. 202003 Lincoln Center VI Pilot Study WP.docx 10 April 2020 202003 Lincoln Center VI Pilot Study WP.docx 11 April 2020 a