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Drilling Work Plan Project No.: 1086 March 16, 2022 dated May 2, 2018, and the Addendum Path to Closure Impediment Discussion & Site Investigation Work Plan dated April 30, 2019 based on requests made by the CVRWQCB in a letter dated June 29, 2018. The work plan addendum was approved by the CVRWQCB in a letter dated June 28, 2019. The site investigation work was conducted during November 2019 and December 2019 and a summary was provided in the Groundwater, Soil & Soil Vapor Investigation Report dated February 3, 2020. Included in the site investigation was the installation and sampling of five (5) soil vapor sampling wells to evaluate the vapor intrusion potential into buildings at the Site. The soil vapor sampling locations address the potential vapor intrusion risk of the existing building, in the vicinity of the groundwater contaminant plume core and along the eastern property boundary. Two soil vapor sampling events were conducted on December 26, 2019 and July 10, 2020. The results were summarized in the Groundwater, Soil & Soil Vapor Investigation Report and the Soil Vapor Sampling Report, respectively. The S WRCB completed a Review Summary Report — Additional Work: Fifth Review — June 2020 stating that the case does not meet all the required criteria of the LTCP. The review does state that the case meets all eight General Criteria and Criteria 3(a) for the direct contact and outdoor air exposure requirements. The S WRCB directed the collection of additional groundwater data and for future soil vapor sampling events to include naphthalene. The July 2020 soil vapor sampling event included naphthalene as a constituent. A CSM was submitted on January 20, 2021 with a recommendation to prepare a Site Closure Evaluation based on the LTCP. The CVRWQCB responded in a letter dated June 17, 2021. According to the letter, the CVRWQCB does not concur with the recommendation for a site closure evaluation and states that the 1,2 -DCA groundwater plume has not been defined laterally or vertically to the north, northwest and northeast of the Site. In response to Ground Zero's Path to Closure Impediment Discussion & Additional Groundwater Investigation Work Plan dated September 15, 2021, CVRRWQCB issued a letter dated November 8, 2021 requesting advancement of five direct -push cone penetration testing borings. To determine the vertical and horizontal extent of the groundwater contamination north and northwest of the Site, we will collect groundwater samples via a CPT drilling rig. Ground Zero will perform the following work. Pre -field Work and Permitting Activities In order to further assess the lateral and vertical extent of the groundwater contaminant plume to the north and northwest of the Site, Ground Zero will install at total of 25 direct - push borings in five locations with five borings at each location as shown on Figure 2. A CPT rig equipped for the collection of discrete groundwater samples will be utilized. The location of the borings is described below: