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DocuSign Envelope ID: FC9986C3-F179-4A3D-BACO-D8CA9F8B93A7 <br /> Proposal for Additional Remedial Investigation <br /> Hillsborough Dump <br /> ID No. NONCD0000483 <br /> Task Orders 483DP-19 thru 25 <br /> Aim <br /> S&ME Project No.4305-17-061G <br /> S&ME will take photographs of areas or objects that may be disturbed before site services begin. If <br /> needed, photographs of affected areas and objects, restoration efforts, and noteworthy items <br /> encountered during task activities will also be taken. Photographs will be submitted to the Unit to <br /> determine whether photographs will be included in the subsequent report. <br /> Soil samples will be logged and classified to identify soil types according to the Unified Soil Classification <br /> System (USCS). <br /> If needed, soil borings will be closed by filling the bore holes with drill cuttings. If there are voids after <br /> placing cuttings in a boring,the remainder of the bore hole will be filled with bentonite. <br /> GPS coordinates will be collected at all final boring locations. Coordinates will be reported in decimal <br /> degrees to the seventh order using the North American Datum of 1983 (NAD83) and in latitude and <br /> longitude using WGS 84. GPS coordinates will be differentially corrected and provided in an appendix <br /> with brief location descriptions/designations. <br /> One duplicate sample per media will be collected per day of sampling. <br /> Groundwater Monitor Well Installations (9) <br /> Groundwater Protection Rules for Orange County and Proposal Assumptions <br /> Per the Groundwater Protection Rules for Orange County(Rules), monitor wells that penetrate consolidated rock <br /> shall be subject to the Rules and require permits from the Orange County Health Department(OCHD) prior to <br /> construction. Most notably,the OCHD Rules require monitor wells (including temporary wells)that penetrate <br /> consolidated rock to be constructed with 6-inch steel outer casings and grouted. The placement of grout for each <br /> well must be visually inspected during construction in the field by OCHD staff. Likewise, abandonment of each <br /> well also requires inspection by OCHD staff. <br /> Based upon previous groundwater assessment activities at this site, it is anticipated that groundwater will be <br /> encountered within 2 to 20 feet below ground surface(bgs).The depths of the proposed 9 monitor wells are <br /> estimated at 15 to 30 feet bgs. It is not anticipated that consolidated rock will be encountered. However,for <br /> budgeting purposes, bids received from drilling subcontractors include well construction methods for one well in <br /> accordance the Rules and associated costs for using six-inch steel outer casings,allowing time for inspections, etc., <br /> and using air-rotary drilling methods. Monitor well borings that encounter groundwater prior to encountering <br /> consolidated rock will not require air drilling, and will not require 6-inch steel outer casing. <br /> Nine additional permanent groundwater monitor wells(MW-21 through MW-29) are proposed to be installed at <br /> the locations shown on Figure 1. Borings will be advanced to an approximate depth of at least seven feet below <br /> the observed groundwater table(e.g., moist/wet conditions). This will be the termination depth of the borings <br /> and the depth to which the well screens will be installed. Monitor wells that penetrate consolidated rock will be <br /> constructed per the OCHD Rules, referenced above,with two-inch diameter, PVC well screens and casings within <br /> six-inch diameter steel outer casings. Well casings will be installed to approximately three feet above the ground <br /> surface(stick-up). A sand pack will be installed in the boring annulus, around the well screen up to at least one <br /> foot above the well screen. A one-foot thick bentonite seal will be installed above the sand pack. Grout will be <br /> placed in the annular space between the outermost casing and the borehole wall from the land surface to the top <br /> of the bentonite seal. The wells will be developed with a pump or bailer until turbidity measurements are below <br /> 10 NTU or representative of background conditions. GPS coordinates will be collected at each installed monitor <br /> well location. <br /> March 10, 2022 7 <br />