SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

ENVIRONMENTAL HEALTH DEPARTMENT SAN JOAQUIN COUNTY Unit Supervisors R an Donna K.Her ,R.E.H.S. Carl Borgman,R.E.H.S. 304 East Weber Avenue, Third Floor w. � Director Mike Huggins,R.E.H.S.,R.D.I. Al Olsen,R.E.H.S. Stockton, California 95202-2708 Douglas W.Wilson,R.E.H.S. cv• ��P Program Manager Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S. F o R Laurie A.Cotulla,R.E.H.S. Robert McClellon,R.E.H.S. Program Manager Fax: (209) 464-0138 Mark Barcellos,R.E.H.S. MAY 1 3 2002 DONALD F RODGERS JUNIUS MCKELVEY 11190 S UNION ROAD 515 W CHARTER WAY MANTECA CA 95336 STOCKTON CA 95206 RE: The Transmission Shop SITE CODE: 9321 515 W. Charter Way Stockton CA 95206 San Joaquin County Environmental Health Department(SJC/EHD) has reviewed the"Groundwater Monitoring Well Installation Work Plan Addendum No. 1 and Feasibility Study' dated April 12, 2002 that was submitted by IT Corporation (IT) on your behalf and has the following comments. The addendum modifies the March 13, 2002 work plan that was conditionally approved by SJC/EHD. The modification includes the installation of one groundwater monitoring well pair for investigation of the vertical extent of the plume near the source area and for determination of the potential vertical groundwater gradient at the site, and the performance of a step-drawdown groundwater extraction test and an air sparge test. The addendum also proposes to begin pulse operation of the current soil vapor extraction (SVE)system. The boring for the monitoring well pair(MW-4R)will be drilled to approximately 80 feet below surface grade (bsg), or until two consecutive soil samples show absence of petroleum hydrocarbon impact. The boring will be continuously sampled from 40 feet bsg to total depth, and a minimum of three soil samples will be submitted for laboratory analysis of the constituents listed in the work plan addendum. The proposed monitoring well pair will include one shallow well built with 15 feet of screened casing to approximately 30 feet bsg, and one deep well built with 5 feet of screened casing at a depth to be determined pending results of the continuous core boring. In a phone conversation on May 7, 2002 between IT and SJC/EHD, it was agreed that the bottom of the deeper well would be set 5-10 feet below any petroleum hydrocarbon impacted soil. The goal is to find the vertical extent of the contamination, and to set the well below that depth. If the well subsequently is found to be impacted with contaminants, the need for additional vertical assessment will be evaluated. The step-drawdown groundwater extraction test is proposed to be performed on the shallow well of the proposed well pair, MW-4R-S. The test will be conducted at four different discharge rates,for a time interval of ninety minutes at each rate. At selected time intervals during the test, depth to water measurements will be made on the test well and on surrounding wells MW-1 R,VW-2 and VW-3. After the test, evaluation of the data will focus on the relationship between discharge and drawdown. In the May 7, 2002 conversation IT explained that the rebound curve of the step drawdown test would be used to calculate aquifer properties using the Bouwer& Rice or similar method. The work plan proposes to conduct an air sparge test on VW-2 and VW-3 by injecting them with ambient air containing a helium tracer. The injection flow rate and injection pressure will be monitored to develop a flow rate versus pressure relationship. Pressures at observation points will be measured at ten minute intervals throughout the test. Before and after the test, measurements will be made of dissolved oxygen, carbon dioxide, percent lower explosive limit and vapor concentrations of petroleum hydrocarbons at the injection and observations points. The radius of influence for air sparge wells will be estimated by evaluating the changes in pressures, dissolved oxygen, carbon dioxide and petroleum hydrocarbon concentrations, and detection of the helium tracer gas at the monitoring locations. It is proposed that the air sparge test will be performed in conjunction with operation of the SVE system.