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oF CAL1FO <br /> o <br /> n M <br /> Q <br /> V ' <br /> QUA 1'�� <br /> L <br /> From: Daniel Villanueva<dvillanueva@advgeoenv.com> <br /> Sent: Wednesday, October 17, 2018 3:57 PM <br /> To: Buehler,Alan@Waterboards<Alan.Buehler@Waterboards.ca.gov> <br /> Cc: Robert Marty<rmarty@advgeoenv.com>; Brian W. Millman <bmillman@advgeoenv.com> <br /> Subject: RE: Ralph's Square <br /> Mr. Buehler, <br /> Advanced Geo Environmental Inc. (AGE) has reviewed the Central Valley Regional Water Quality <br /> Control Board (Water Board) letter dated 06 August 2018, for the property located at 2122 South <br /> Airport Way, Stockton, California (herein referred to as site). In the letter, Water Board staff requests <br /> that the responsible party install two (2) groundwater monitoring wells downgradient of monitoring <br /> well MW-5 to further assess historically elevated methyl tertiary butyl ether (MTBE) and recently <br /> elevated tertiary butyl alcohol (TBA) concentrations from an unauthorized release from the former <br /> underground storage tank (UST) system at the site. AGE provides the following responses to items <br /> referenced in the letter: <br /> • A total of seven (7) groundwater monitoring events have been performed at downgradient <br /> shallow (MW-14, MW-16 and MW-17) and intermediate wells (MW-12, MW-13 and MW-15) <br /> since being installed in January 2015. These downgradient groundwater monitoring wells <br /> have been monitored over a period of over 3 years and have been non-detect for <br /> constituents of concern. In the Regional Board letter referenced above, two additional wells, <br /> upgradient to wells MW-12 through MW17 are being requested. Based on drilling <br /> accessibility (residential housing east of the site), and City of Stockton requirements, <br /> potential well locations would need to be proposed in the sidewalk areas west of the <br /> existing shallow and intermediate wells. The potential well locations have been illustrated in <br /> the attached figure. Based on the location, drilling accessibility and City requirements, well <br /> locations would be placed at an estimated distance of 30 and 70 feet from existing wells. <br /> Considering that the potential locations are upgradient of wells that were installed for the <br /> purpose of defining the downgradient extent of the dissolved hydrocarbon plume, it does <br /> not appear necessary or reasonable to install additional groundwater monitoring wells in <br /> these locations. Installation of additional wells is not cost effective, nor would it provide <br /> additional data that is necessary to determine if the site meets the criteria established in the <br /> Low-Threat UST Case Closure Policy (LTCP). <br /> • AGE has conducted an additional review of the site as it relates to the LTCP. Evaluating all <br /> current and historical data, the site meets Scenario 4 of the groundwater specific criteria. <br /> Assuming that the plume has reached the currently installed downgradient wells, the plume <br /> would: 1) remain less than 1,000 feet in length, 2) there is no free product, 3) the nearest <br /> existing water supply well or surface water body is greater than 1,000 feet from the defined <br /> 2 <br />