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ENVIRONMENTAL HEALTHOE <br /> PARTMENT <br /> °p4U�M SAN JOAQUIN COUNTY <br /> > . .5o <br /> y Donna K. Heran, R.E.H.S. <br /> Director 304 East Weber Avenue,Third FloorUnit Supervisors <br /> Laurie A. Cotulla, R.E.H.S. Carl Borgrnan,R.E.H.S. <br /> Program Manager <br /> Stockton,California 95202-2708 Mike Huggins, R.E.H.S., R.D.I. <br /> Telephone: (209)468-3420 Douglas W. Wilson, R.E.H.S. <br /> Fax: (209) 464-0138 Margaret Lagorio,R.E.H.S. <br /> Jl�n, — Robert Mcciellon, R.E.H.S. <br /> Y74- t� Website:www.sjgov.org/chd/ Jeff Carruesco, R,E.H.S, <br /> e7i a P 4/i 9/04 <br /> F-49- -90 ,APR 0 4 2006 <br /> hal s ej J <br /> 97 348 <br /> RE: H&H Engineering and Construction Facility SITE CODE: 507797 <br /> 212 Industrial Drive RO: 623 <br /> Stockton, California 95206 <br /> San Joaquin County Environmental Health Department (EHD) has reviewed Second Semi- <br /> Annual 2005 Groundwater Monitoring and Sampling Report and Request for Case Closure, <br /> dated September 27, 2005, prepared by Ground Zero Analysis, Inc. (Ground Zero) on your <br /> behalf. In this report Ground Zero presented information requested by EHD by letter dated <br /> June 13, 2005, to assess conditions necessary for site closure. <br /> Based on the information presented in the above-referenced report, EHD cannot support a <br /> recommendation for site closure at this time. The Risk Based Corrective Action (RBCA) Tool <br /> Kit for Chemical Releases Version 1.3a model (developed by Groundwater Services, Inc., <br /> 2000) and general contaminant concentrations levels show that the site is nearly ready for <br /> closure, but EHD is concerned about the overall increasing benzene concentrations found in <br /> monitoring well MW-3 as demonstrated in Appendix C. Rising concentrations may be an <br /> indication of an unstable plume, therefore EHD needs additional data to evaluate the benzene <br /> concentration trend in MW-3. It may be that the concentrations have peaked and may <br /> stabilize or decline. To collect data more quickly, you are directed to sample MW-3 <br /> quarterly, instead of semi-annually, for total petroleum hydrocarbons as gasoline (TPH-g) <br /> and benzene, toluene, ethyl benzene, total xylenes (BTEX). <br /> Continue sampling MW-1 and MW-2 semi-annually. You may remove methyl tertiary-butyl <br /> ether (MTBE), tertiary-butyl alcohol (TBA), 1,2-dibromoethane (EDB), ethyl tertiary-butyl <br /> ether (ETBE), di-isopropyl ether (DIPE), and tertiary-amyl methyl ether (TAME) from the <br /> analytical list of compounds for all monitoring wells at this site since these compounds have <br /> not been detected in any groundwater samples collected during the semi-annual sampling <br /> events in 2005. Continue to report TPH-g, BTEX, and 1,2-DCA during future semi-annual <br /> groundwater monitoring events and continue collecting depth to water measurements in all <br /> wells during each quarterly groundwater monitoring event for the purpose of determining the <br /> groundwater gradient. <br />