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Tri-Ag Services, Inc. 3 July 11,2017 During the July 10, 2017 phone conversation, Mrs. Martin requested an explanation for the requested sampling of Dichlorodiphenyltrichloroethane (DDT), Dieldrin, and Oryzalin in groundwater. These analytes were detected in soil samples at concentrations exceeding the EPA Region 9 Regional Screening Levels' (RSLs) for impact to groundwater. Central Valley Water Board staff required these constituents be included in the domestic well sampling analysis to determine if these chemicals of concern (COCs) have leached to groundwater and migrated to the domestic well. Further review shows that Dichlorodiphenyldichloroethane (DOD) and Dichlorodiphenyldichloroethylene (DDE) also exceeded the impact to groundwater RSL for Residential Soil to Groundwater and should be added to the sampling analyte list. Central Valley Water Board staff required the domestic well be sampled for DDT, Dieldrin, Oryzalin, nitrates, 1,2,3-TCP, and 1,2-DCP and report the sample results to this office by July 28, 2017. Based on impact to groundwater RSLs, DOD and DDE must be added to the list. In a phone conversation with Mrs. Martin, she stated that this was too short a timeframe for this work and requested an extension. I find this request reasonable and the new due date for submittal of the domestic well sampling results is September 28, 2017. As previously stated, to expedite the process Central Valley Water Board staff are willing to complete the sampling for the property owners if onsite access for this one-tme event is provided While 1,2,3-TCP and 1,2-DCP were not detected in MW-3, they were previously not detected in any monitoring well during Kleinfelder's 2003 sampling event either. This could potentially be due to a preferential migration path or well construction parameters. To determine if there is a potential exposure risk from the domestic well, sampling for the COCs listed in Comment #3 above must be completed. This requirement for a report is made pursuant to Water Code Section 13267, which allows the Regional Water Board to require technical or monitoring program reports from any person who has discharged, discharges, proposes to discharge. or is suspected of discharging waste that could affect water quality. The attachment provides additional information about Section 13267 requirements. Any extension in the above deadline must be confirmed in writing by Central Valley Water Board staff. In addition to a hard copy you are also required to submit all documents in electronic format to the State Water Resources Control Board's GeoTracker database pursuant to the California Code of Regulations (Title 23, Section 3890 et.seq.). Guidance for electronic information submittal is available at: http://www.waterboards.cagov/water_issues/programs/ust/electronic_submittal/. 1 See EPA webpage: https://www.epa.qoviriskiregional-screening-levels-rsis-generic-tables-june-2017