SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Pq U I/y ~-' San Joaquin County _VW DIRECTOR Environmental Health Department Donna Heran,REHS 00 East Main Street ASSISTANT DIRECTOR 6 N < Laurie Cotulla,REHS • 3'• Stockton, California 95202-3029 PROGRAM COORDINATORS c •• c Carl Borgman,REHS A�IFOR�` Mike Huggins,REHS,RDI Website: www.sjgov.org/ehd Margaret Lagorio,REHS Phone: (209)468-3420 Robert McClellon, REHS Fax: (209) 464-0138 .teff Carruesco, REHS,RDI Kasey Foley,REHS JERRY MOORE MOORE PETROLEUM MAY 2 3 2007 885 PORTOFINO DR BRENTWOOD CA 94513-6539 RE: Quarterly Monitoring Report Recommendation and the Proposed Cancellation of the MW-15 Installation. 5491 F Street Banta CA 95304 San Joaquin County Environmental Health Department (EHD) has received and reviewed Motor Oil Delineation Letter(the AEI Letter), dated 16 May 2007, prepared by Apex Envirotech, Inc. (AEI) on your behalf. The AEI Letter was prepared in response to directives and comments included in the EHD letter dated 11 April 2007, that directed submittal of a work plan to confirm and identify the dissolved contaminant detected and quantified as total petroleum hydrocarbons as motor oil (TPH-mo) in grab groundwater samples collected between 28 feet and 78 feet below surface grade (bsg) in CPT-2 and at 72 feet bsg in CPT-1. In the AEI Letter, AEI proposes to add TPH-mo and total petroleum hydrocarbons quantified as diesel (TPH-d) and as kerosene (TPH-k) to the analytical suite for the monthly water samples collected from the nearby Rhodes domestic well to confirm the presence of the reported TPH-mo. The EHD approves adding TPH-mo, TPH-d and TPH- k to the analytical regimen for the Rhodes well, but does not concur that this will confirm the presence of the TPH-mo detected at depth in the CPT borings; certainly the absence of TPH-mo in the Rhodes well samples will not demonstrate that the substance does not occur. Also in the AEI Letter, AEI states that if the samples from the Rhodes well do not contain TPH-mo, TPH-d or TPH-k above the analytical method detection limits that AEI will consider the plume to be delineated and stationary. The EHD cannot concur with this interpretation for the following reasons: • The aquifer properties are not well known, nor are the total and instantaneous discharge (amount of water produced) from the domestic well, therefore the capture zone of the well when pumping cannot be modeled and the influence of pumping from the domestic well on the dissolved plume cannot be predicted; 0 A three-dimensional dissolved plume cannot be delineated by only one well that is located obliquely down-gradient to cross-gradient from the suspected source area;