COMPLIANCE INFO_EW-5 INSTALL PERMIT PACKAGE 2/14/25

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Mr. Brenden Kenny Central Valley Regional Water Quality Control Board February 1, 2023 www.arcadis.com 4/6 Well Development Groundwater monitoring well(s) will be developed no sooner than 48 hours after installation to allow adequate time for the well seals to cure. The well(s) will be developed by airlift, surging, bailing and/or over-pumping to remove sediment introduced during drilling and/or well construction. During well development, the volume of any mud dispersant solutions or fresh water added (if necessary), water removed, and field parameters will be measured, including pH, electrical conductivity, turbidity, oxidatio n- reduction potential, dissolved oxygen, and temperature. Development will continue until the turbidity is reduced to below 5 nephelometric turbidity units and/or when field parameters have stabilized (less than 10% variation in readings). Extraction Well Testing Hydraulic testing, including step and constant rate testing, will be conducted in accordance with the Revised Work Plan Addendum (Arcadis 2022b) after installation of the groundwater extraction wells and piezometers, to assess the extraction well capacity, aquifer response and area of capture in accordance with the methods presented in the Revised Work Plan Addendum. The period of pumping for the constant rate test will be determined based on the hydraulic response of the well during development and step testing but is anticipated to be up to approximately 8 hours for pumping duration, with comparable recharge fluid level recovery monitoring conducted. The results of the hydraulic testing will assist w ith finalizing the design of the interim remedial action. Reporting Following completion of the proposed field activities, Arcadis will evaluate the data and prepare a summary of the results. A report will document the items in the Revised Work Plan Addendum (Arcadis 2022b) and this Second Work Plan Addendum and will include the following: • Background and history. • A scaled site plan illustrating locations of the interim remedial action extraction well and piezometers, and SI soil borings/temporary soil vapor probes and temporary wells (if applicable), and other relevant site features. • Documentation of the remedial extraction well and piezometer installations, and interpretation of hydraulic testing activities. • Documentation of groundwater, soil vapor, and soil sampling. • Results of the laboratory analyses performed on the groundwater, soil vapor, and soil samples collected during the first phase of SI completed in June and July 2022. • Analytical results posted on plan view and on cross -sectional view figures. • Discussion of the potential source(s) and extent(s) of the VOC mass in groundwater and soil vapor beneath the CDCR property.