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850 Milgeo, Manteca <br /> Page 2 <br /> 6. The grab groundwater sample result from P7 was 1,100 micrograms per liter TPH-diesel. <br /> AGE's WP does not include installation of an MW near P7. The EHD recommends that <br /> you relocate the proposed MW9 to the P7 area. <br /> 7. Three off-site borings (B-20, B-21 and B-22)are proposed for grab groundwater <br /> sampling, but a technical justification was not provided for the borings and their locations. <br /> EHD cannot approve the three borings until provided an adequate technical justification. <br /> Since groundwater samples from MW1 have high concentrations of TPH-d and the rose <br /> diagram shows groundwater gradient has at times been to the northwest, EHD <br /> recommends a shallow monitoring well be placed northwest of MW1, possibly between <br /> proposed B-20 and B-21, so that groundwater samples can be collected repeatedly. In <br /> addition there is no monitoring well to the southeast of the former UST area and the rose <br /> diagram shows groundwater gradient has at times been to the southeast, EHD <br /> recommends a shallow monitoring well be placed in the area of proposed B-22, so that <br /> groundwater samples can be collected repeatedly. <br /> 8. One on-site boring (B-23)is proposed within 10 feet of an already completed boring (P- <br /> 10). Soil results that were below detection limits from a sample collected at 30 feet BGS <br /> from P-10 has demonstrated the vertical extent of impacted soil beneath the former UST. <br /> The investigation of the vertical extent of groundwater contamination should be <br /> conducted outside of the former UST location. A completed soil boring (P-1)did not <br /> define the extent of the soil contamination west of the former UST area. EHD <br /> recommends that the proposed soil boring B-23 be located west of P-1 to provide more <br /> useful soil data. <br /> 9. Interim corrective action in the former UST location was discussed at the TanoAarl "0'7 <br /> meeting. The submitted WP does not address this nor does it have any <br /> recommendations to reduce soil and/or groundwater contaminant concentrations. Soil <br /> excavation and groundwater extraction should be considered and addressed, along with <br /> any other potentially applicable remediation methods in a feasibility study. A high priority <br /> for EHD is that you are working towards corrective action to mitigate the near free <br /> product concentrations in groundwater. <br /> Please prepare and submit an addendum to the WP, permit applications, and fees by 6 June <br /> 2007 and have the approved work completed by 1 August 2007. <br /> After completion of the work, a report of findings, a feasibility study and an updated Conceptual <br /> Site Model is to be submitted to EHD by 1 October 2007. <br /> If you have any further questions regarding this matter, contact Harlin Knoll at (209)468-3442. <br /> Donna Heran, REHS, Director <br /> Environmental Health Department <br /> 4LJ'111� 7v4mt)_� _7� 6 <br /> MargaretSHarlin Knoll, Senior REHS Marg <br /> LOP/Site Mitigation Unit IV Program Coordinator Unit IV <br /> Cc: SWRCB-Cleanup Fund <br /> CVRWQCB-James Barton <br /> AGE-Bill Little <br />