SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

San Joaquin County DIRECTOR ° Environmental Health Department Donna Heran,REHS QASSISTANT DIRECTOR 600 East Main Street U) ` Stockton, California 95202-3029 Laurie Cotulla,REHS PROGRAM COORDINATORS Carl Borgman,RENS N /pop s\ Website: wwW.sjgov.Org/ehd Mike Huggins,REHS, RDI Phone: (209)468-3420 Margaret Lagodo,REHS Fax: (209)464-0138 Robert McClellon,REHS Jeff Carruesco,REHS,RDI STEPHANIE FURGAL Kasey Foley,REHS CHEVRON ENVIRONMENTAL MANAGEMENT COMPANY 'JUL 2 6 2007 6001 BOLLINGER CANYON ROAD ROOM K2240 SAN RAMON CA 94583 RE: Chevron Service Station 9-2033 508 Charter Way Stockton, California San Joaquin County Environmental Health Department (EHD) has reviewed Additional Groundwater Assessment Work Plan dated July 12, 2007, prepared and submitted by ARCADIS U.S., Inc. (ARCADIS BBL) on your behalf for the above-referenced site. The work plan was submitted in response to EHD's letter dated May 10, 2007, directing additional monitoring wells be installed to monitor chemicals of concern (COC) both in the upper groundwater zone at approximately 20 feet below ground surface (bgs) and in the deeper water zone at approximately 50 to 60 feet bgs. In this work plan ARCADIS BBL proposes to install four groundwater monitoring well clusters down gradient of the former underground storage tank (UST) and dispenser/piping system. Each cluster will consist of one shallow well screened at approximately 17 to 27 feet bgs and one deep well screened at approximately 50 to 60 feet bgs. The shallow wells will be installed using eight-inch diameter hollow stem augers; and the deep wells will be double-cased with conductor casing to approximately forty-five feet bgs using 15.5-inch diameter hollow stem augers followed by advancing a borehole through the conductor casing to total depth of approximately 60 feet bgs using eight-inch augers. During monitoring well installation, soil samples from the deep soil borings will be collected continuously for soil characterization from approximately eight feet bgs to total borehole depth and soil samples will be screened for volatile organic compounds using a photo-ionization detector (PID). What is unclear to EHD is whether the shallow zone wells' objective is to target the "low permeability clay/silt/sand deposits" commonly encountered at approximately 20 feet bgs or the sand layer commonly encountered at 30 feet bgs; also, ARCADIS BBL states that "the actual screen and depth interval will be determined based on observations in the field." It is unclear what specific field data will be used and how it will be utilized to achieve the desired investigation objectives when installing these wells. As the depth to water has ranged from approximately 18 to 33 feet bgs, the EHD recommends increasing the screen lengths and total depths of the shallow Wells by five feet if the monitoring objectives will not be compromised; this would extend the shallow wells' utility should the depth to groundwater drop to historical depths.