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Ms.Amber Ginorio,RWQCB January 30,2023 Addendum to Sampling and Analysis Plan 2478 Wilcox Road,Stockton,California Page 8 retained where changes to sediments occur, or stratigraphic contacts are identified. The ends of the sample will be lined with Teflon sheets, capped, labeled,placed in a re-sealable plastic bag, and stored in an ice-chilled cooler. Strict chain-of-custody procedures will be followed from the time the samples are collected until the time the samples are relinquished to CLS. Stratus will submit one soil sample from approximately one foot below the total depth the air knife advances,as well as select soil samples(e.g. high PID readings and from contacts between fine- and coarse-grained sediments), for laboratory analysis. The exact number of samples submitted for laboratory testing will be determined at the time of the investigation. All sampling equipment will be cleaned in an aqueous non-phosphate solution cleanser, rinsed with tap water, and rinsed a second time with deionized water to prevent cross- contamination between sample intervals. The groundwater monitoring wells will be constructed with 2-inch diameter Schedule 40 PVC blank and 0.020-inch slot screened casing with a screen interval from approximately 55 to 70 feet bgs. It is presumed that first encountered groundwater is at a depth of 60 feet bgs,based on information obtained on Geotracker from wells located in the vicinity of site. The actual screened interval will depend on the depth at which groundwater is first encountered. A filter pack of#3 sand will be placed in the annular space around the well casing from the bottom of the well screen to approximately three feet above the top of the well screen (52 to 70 feet). Approximately two feet of bentonite chips will be placed on top of the filter pack and hydrated with clean water to provide a transition seal for the well. Neat cement will be used to backfill the remaining annular space around the well casing. A watertight locking cap will be placed over the top of the well casing, and a traffic-rated vault box will be installed around the top of the well. The actual well construction may be modified in the field based on conditions encountered at the time of the investigation. A proposed well construction diagram is available in Appendix C. Task 2E: Contingency Monitoring Well Installation(MW-4) In the event that grab groundwater samples cannot be collected from boring SB-6, an additional groundwater monitoring well(MW-4)will be drilled and installed at the location shown on Figure 2. The alternate location is presumed to be downgradient of the septic system based on available groundwater gradient information from nearby sites presented in GeoTracker. The details for well boring advancement and well construction will be the same as described in Task 2D. Soil samples will be collected continuously from the total depth the air knife advances to the total depth of each boring using acrylic tubes. The Stratus geologist will utilize the entire tube for lithologic analysis in accordance with the USCS and will screen the soils in the field for VOCs using a PID. The bottom-most 6-inch-long section of every five feet will be cut off and retained for possible chemical analysis. Additional samples may be T:\Stockton Propeller\Addendum to SAP\SM_Addendum to Sampling and Analysis Plan.docx STRATUS