SITE INFORMATION AND CORRESPONDENCE_FILE 2

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A ` Jerry Moore L, 5491 F Street, Banta, California Page 2of2 • A single well, located obliquely down-gradient to cross-gradient from the suspected source area will not be adequate to demonstrate dissolved plume stability; and • Asa practice, the EHD does not approve utilizing domestic wells as monitoring wells — real monitoring wells should be placed to detect encroaching plumes that potentially threaten domestic wells so there may be opportunity to take appropriate measures to protect such domestic wells before they are impacted. The proposals in the AEI Letter do not address the fundamental directive of the EHD letter of 11 April 2007 regarding the CPT groundwater analytical data, namely to confirm the presence and identify the chemicals the laboratory reported as TPH-mo, but also reported as not matching the typical pattern of TPH-mo. This is an important step; if the substance detected and reported is determined to not be related to your unauthorized underground storage tank (UST) system releases, this agency will not direct further investigation of it. If the substance is determined to be probably related to your UST system releases, the finding will be the technical justification for additional investigation and characterization of the plume. The AEI Letter also contained a proposal to "revise the installation plans for MW-15 to drill the monitoring well to a depth of 100 feet bsg. Placing MW-15 to a depth of 100 feet bsg will allow..." The EHD is not certain whether this change is merely to advance the boring to 100 feet bsg, then back fill the boring and build the well to the originally proposed 20 feet bsg, or if AEI now proposes to set the bottom of the well screen at 100 feet bsg. A clarifying proposed well construction diagram was not provided. The EHD points out that the original justification for installing MW-15, which was to delineate the shallow dissolved plume toward the northeast, must still be satisfied. The EHD cannot approve this proposal without clarification. Provide the clarification to the EHD by 02 July 2007. Questions or comments may be directed to Nuel Henderson at (209)468-3436. Donna Heran, RENS, Director Environmental Health Department Nuel C. Henderson, Jr., PG Margar Lagorio, RETS Engineering Geologist Program Coordinator Unit IV- Site Mitigation Unit IV—Site Mitigation C: James LL Barton, PG —CVRWQCB Daniel Lafontaine, PE—Chemical Engineer—APEX Envirotech, Inc.