|
cw em`,N�
<br />Nater Boards
<br />Central Valley Regional Water Quality Control Board
<br />6 August 2018
<br />Ralph Lee White Peter Bui & Kimberly Hoang
<br />2201 E. 8"' Street 4004 Maddie Circle
<br />Stockton, CA 95206 Stockton, CA 95209
<br />RALPH'S SQUARE, 2122 S. AIRPORT WAY, STOCKTON, SAN JOAQUIN COUNTY, CASE#
<br />390995
<br />Central Valley Regional Water Quality Control Board (Central Valley Water Board) staff reviewed the
<br />Groundwater Monitoring Report — First Quarter 2018 (Monitoring Report) dated 25 April 2018,
<br />submitted on your behalf by Advanced GeoEnvironmental Inc. (AGE) for the Ralph's Square
<br />unauthorized petroleum release at 2122 S. Airport Way in Stockton (Site). In the Report, AGE presents
<br />March 2018 groundwater monitoring and sampling data, and recommends that the Site be considered
<br />for case closure under the Low Threat Underground Storage Tank Case Closure Policy (LTCP).
<br />Central Valley Water Board staff concurs with AGE's conclusion that the Site meets the LTCP's
<br />Petroleum Vapor Intrusion and Direct Contact and Outdoor Air Exposure media specific closure criteria.
<br />However, Central Valley Water Board staff does not concur with closure at this time and requests that
<br />you conduct additional Site investigation to assess for the presence of petroleum hydrocarbons
<br />downgradient from the Site.
<br />Monitoring data indicate that samples from well MW -2 contained up to 380,000 micrograms per liter
<br />(pg/1) methyl tertiary butyl ether (MTBE) in 2008. Groundwater monitoring was suspended from 2008
<br />through 2014 and after resuming groundwater monitoring in 2014, the detected concentration of MTBE
<br />in groundwater appears to have decreased significantly. However, due to an absence of monitoring
<br />data, the fate of the MTBE remains unclear.
<br />Based on the recent MTBE concentration decreases, it is likely that MTBE has mobilized beyond the
<br />on -Site monitoring wells. In addition, recent groundwater sampling indicates that up to 46,100 pg/I
<br />tertiary butyl alcohol is present in groundwater at the Site (MW -5). However, groundwater samples
<br />collected from downgradient monitoring wells MW -12 through MW -17 have not contained petroleum
<br />hydrocarbons above their respective detection limits since commencing sampling in January 2015
<br />indicating that the mobilized MTBE has not yet reached these wells. As a result, the nature and mobility
<br />of the residual petroleum hydrocarbon plume remains unknown and the residual plume length unknown.
<br />By 12 October 2018, Central Valley Water Board staff requests that you submit a Work Plan for the
<br />installation of two monitoring wells downgradient from monitoring well MW -5 along the western edge of
<br />South Phelps Street to assess for the presence of petroleum hydrocarbons in groundwater. Central
<br />Valley Water Board staff also request that you provide a discussion regarding the fate of the MTBE
<br />historically detected in groundwater at the Site.
<br />KARL E. LONGLEY SCD, P.E., CHAIR j PATRICK PULUPA, E50., EXECUTIVE OFFICER
<br />11020 Sun Cenler Drive 9200, Rancho Cordova, CA 95670 1 www. water hoards. ca.0 ovrcen lralva Hey
<br />L,+ sMYCLEn -OE11
<br />Ea. - G. Einov ; JA
<br />l:��I
<br />LcvErt on
<br />M-nlrEr. Ro.A,ouEz
<br />SC Cnf.fAP• FOe
<br />ENVIAov!IEn lA� PIOii CilOr;
<br />RALPH'S SQUARE, 2122 S. AIRPORT WAY, STOCKTON, SAN JOAQUIN COUNTY, CASE#
<br />390995
<br />Central Valley Regional Water Quality Control Board (Central Valley Water Board) staff reviewed the
<br />Groundwater Monitoring Report — First Quarter 2018 (Monitoring Report) dated 25 April 2018,
<br />submitted on your behalf by Advanced GeoEnvironmental Inc. (AGE) for the Ralph's Square
<br />unauthorized petroleum release at 2122 S. Airport Way in Stockton (Site). In the Report, AGE presents
<br />March 2018 groundwater monitoring and sampling data, and recommends that the Site be considered
<br />for case closure under the Low Threat Underground Storage Tank Case Closure Policy (LTCP).
<br />Central Valley Water Board staff concurs with AGE's conclusion that the Site meets the LTCP's
<br />Petroleum Vapor Intrusion and Direct Contact and Outdoor Air Exposure media specific closure criteria.
<br />However, Central Valley Water Board staff does not concur with closure at this time and requests that
<br />you conduct additional Site investigation to assess for the presence of petroleum hydrocarbons
<br />downgradient from the Site.
<br />Monitoring data indicate that samples from well MW -2 contained up to 380,000 micrograms per liter
<br />(pg/1) methyl tertiary butyl ether (MTBE) in 2008. Groundwater monitoring was suspended from 2008
<br />through 2014 and after resuming groundwater monitoring in 2014, the detected concentration of MTBE
<br />in groundwater appears to have decreased significantly. However, due to an absence of monitoring
<br />data, the fate of the MTBE remains unclear.
<br />Based on the recent MTBE concentration decreases, it is likely that MTBE has mobilized beyond the
<br />on -Site monitoring wells. In addition, recent groundwater sampling indicates that up to 46,100 pg/I
<br />tertiary butyl alcohol is present in groundwater at the Site (MW -5). However, groundwater samples
<br />collected from downgradient monitoring wells MW -12 through MW -17 have not contained petroleum
<br />hydrocarbons above their respective detection limits since commencing sampling in January 2015
<br />indicating that the mobilized MTBE has not yet reached these wells. As a result, the nature and mobility
<br />of the residual petroleum hydrocarbon plume remains unknown and the residual plume length unknown.
<br />By 12 October 2018, Central Valley Water Board staff requests that you submit a Work Plan for the
<br />installation of two monitoring wells downgradient from monitoring well MW -5 along the western edge of
<br />South Phelps Street to assess for the presence of petroleum hydrocarbons in groundwater. Central
<br />Valley Water Board staff also request that you provide a discussion regarding the fate of the MTBE
<br />historically detected in groundwater at the Site.
<br />KARL E. LONGLEY SCD, P.E., CHAIR j PATRICK PULUPA, E50., EXECUTIVE OFFICER
<br />11020 Sun Cenler Drive 9200, Rancho Cordova, CA 95670 1 www. water hoards. ca.0 ovrcen lralva Hey
<br />L,+ sMYCLEn -OE11
<br />
|