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Adam Wolfe - 3 - 14 October 2021 <br /> Department of Corrections and Rehabilitation <br /> anticipated. If all primary sample devices perform as intended the additional <br /> canister could be used for an additional indoor air sample location if an <br /> appropriate location is identified, or as a duplicate sample. <br /> 2. Section 4.4 indicates that permanent soil gas sampling wells will be installed in <br /> borings advanced to up to 20 feet bgs, with wells set at depths of roughly 5 and <br /> 15 feet below ground surface. However, groundwater levels at the nearest <br /> groundwater monitoring wells, MW-9-BP and MW-8-BP, have varied between <br /> approximately 4.6 and 6.8 feet bgs over the past 5 years and the maximum depth <br /> to water observed across the Site over the past 20 years is approximately 12 feet <br /> bgs. Staff therefore recommends installing the shallower sampling point at a <br /> depth likely to remain above the water table, and no deeper than 5 feet bgs. If <br /> lithologic logging and measured depth to water during drilling activities suggests <br /> a deeper sampling point may be of value, Staff agrees that a deeper sampling <br /> point should also be installed, but based on available water level data priority <br /> should be given to installing the shallow sampling point at an interval where it will <br /> be able to consistently provide quality data. Staff agree that an initial boring to a <br /> maximum depth of 20 feet bgs for lithologic logging is acceptable, but <br /> subsequent borings should target the proposed soil gas well interval(s). <br /> Central Valley Water Board staff concurs with the proposed site investigation work plan <br /> with the notes above. Due to the restrictions on site access, please notify staff as soon <br /> as the field schedule is confirmed so that staff may be present to observe sampling <br /> activities. Please submit the proposed Technical Memorandum providing results of the <br /> investigation to this office no later than 24 December 2021. <br /> If you have questions regarding this letter or would like to discuss the technical aspects <br /> of the Site, please contact me by email at Durin.Linderholm(Dwaterboards.ca.gov, or by <br /> phone at 916-464-4657. <br /> oHw,6je° <br /> Durin Digitally signed by � ` '.0 0 }+® <br /> Durin Linderholm e®, <br /> Linderholm Date: 2021.10.14 <br /> 16:40:33-07'00' 9342 <br /> Durin Linderholm, P.G. <br /> Engineering Geologist <br /> Site Cleanup Unit <br /> �Of <br /> Digitally signed by MAL CAs° O< <br /> Nathan Casebeer Q�?►� a <br /> �I Date: 2021.10.14 <br /> 16:43:15-07'00' 8359 <br /> Nathan Casebeer, P.G. <br /> Senior Engineering Geologist <br /> Chief, Federal and Private Site Cleanup Unit CW <br />