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R5-2008-0149-049 -2 - 3 April 2014 Former JM Equipment 1245 W. Charter Way, Stockton San Joaquin County PROJECT DESCRIPTION A pilot study using injection of hydrogen peroxide was conducted at the former JM Equipment in 2011 and 2012. Results from the pilot study indicate hexavalent chromium was mobilized during the study but returned to levels below background within one to two calendar quarters, and total petroleum hydrocarbons as gasoline declined from 32,000 micrograms per Liter (ug/L)to 22,000 ug/L. Benzene concentrations also declined from 3,400 ug/L to 1,800 ug/L. GZAI proposes to inject a 7.5% to 12.5% hydrogen peroxide solution into injection wells IW-1 through IWA 1 for full scale remediation. Analytical testing will be performed on five monitoring wells per the attached Monitoring and Reporting Program (MRP), to determine if hydrogen peroxide injection is effective in reducing petroleum hydrocarbons and to monitor for increases in dissolved levels of specified metals, which may be caused by oxidation of naturally occurring metals in local soil. There is no surface water monitoring associated with this project. ADDITIONAL REQUIREMENTS Excerpts from the revised NO] are italicized in the following paragraphs and our comments to the revisions follow. 1. "in order to establish background and contingency plan compliance concentrations for metals, GZAI recommends that additional groundwater samples be collected from the following wells: • Background well MW-7 • Transition wells MW-6 and MW-8 • Compliance wells MW-2 and MW-3 "...GZA recommends that the three (3) additional groundwater monitoring events be performed on the wells listed above in order to determine the groundwater quality prior to establishing the compliance concentrations. Due to the wide fluctuations, GZA recommends that the highest concentration value be accepted as the base concentration for the given well. ...GZA believes that the compliance concentrations for wells MW-6 and MW-8 should reflect not only the background concentrations established for MW-7 but also the concentrations in these wells prior to it being impacted by remedial activities. GZA believes that wells MW-6 and MW-8 are too far down gradient to have experienced chemical alteration from the Phase 1 (pilot study) activities...Upon completion of the three (3) groundwater monitoring events, a short report will be submitted including the analytical results and a discussion regarding the establishment of background and contingency plan compliance concentrations. This report will be completed and submitted prior to the 2"d Quarter 2014 groundwater monitoring event which will be completed in June 2014. This will allow for the June 2014 groundwater monitoring data to be compared to the contingency plan compliance levels and the WQOs...Begin hydrogen peroxide injections 312012014... Background levels must to be established from wells that are not impacted by pollutants, therefore it is not appropriate to use data from wells MW-2, MW-3, MW-6 or MW-8 to establish background metals concentrations. The pilot study background levels and Action Levels will remain in effect until new background levels are established. Action Levels for triggering the implementation of the Contingency Plan are shown in Table 1 below. If background levels already exceed Water Quality Objectives (WQOs), then no increases, may be allowed. In other words, if the average of the three rounds of sampling in compliance wells MW-2