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J.M Equipment Company - 2 - 18 May 2017 1245W. Charter Way Stockton, San Joaquin County In the Work Plan Addendum due 21 July 2017, please include a proposal for the installation and sampling of a soil gas well near the northeast corner of the southern "shop" structure, in accordance with Department of Toxic Substances Control (DTSC) guidance. The Work Plan indicates that collected soil samples will be analyzed for 1,2-DCA and ethylene dichloride (EDC). However, these are different names for the same compound. In the Work Plan Addendum due 21 July 2017, please include ethylene dibromide (EDB) in the analytical suite for each soil sample. In the 16 December 2016 letter, Central Valley Water Board staff responded to GZA's Request for Reduction in Monitoring Frequency (Request Letter), dated 8 September 2015, and the 2016 1st Semi-Annual Groundwater Monitoring & Remedial Effectiveness Report (First 2016 Semi-Annual Report), dated 11 August 2016. In these submitted reports, GZA requested a reduction in monitoring frequency from quarterly to semi-annual related to the existing Monitoring and Reporting Program (MRP) in place for hydrogen peroxide injection at the Site. In the December 2016 letter, Central Valley Water Board staff included a draft revised MRP for review and comment by you and GZA staff. However, Central Valley Water Board staff have the following comments on peroxide remediation at the Site: Upon further review, it appears that metals detected during December 2016 exceeded Action Levels established in the 3 April 2014 Notice of Applicability (NOA) for coverage under General Order R5-2008-0149-049. Historical groundwater data indicates that a number of exceedances have occurred since full-scale injection began in 2014. It also appears that the some of the metals detected in compliance zone wells MW-2 and MW-3 exceeded the MW-7 background concentrations during the March 2014 background sampling event. Central Valley Water Board staff would like to discuss appropriate Action Levels prior to issuing a revised MRP for the Site and request that hydrogen peroxide injection cease until further information can be gathered. As noted in the NOA, the Contingency Plan to be implemented in the event of exceedances consists of 6 months of sampling, followed by evaluating the need for high fructose corn syrup (HFCS) injection. Central Valley Water Board staff request that you implement the 6 months of sampling, but postpone HFCS injection until completing the additional sampling. As the NOA does not detail the frequency of the sampling during the 6-month period, and as it has been 5 months since the December 2016 sampling event, please collect two (2) monthly samples from treatment, transition, compliance, and background zone wells during May and June 2017. By 30 July 2017, please submit a Groundwater Monitoring Report with data from the Contingency Plan sampling, as well as the second quarter 2017 sampling event. 4. While GZA has injected over 19,000 gallons of hydrogen peroxide solution at the Site since 2014, petroleum hydrocarbons in MW-9 remain high [13,000 micrograms per