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1 <br /> n Mon AsOciates <br /> 1433 North Market Boulevard•Sacramento.California 95834-1943 • (916)928-3300.Fax(916)928-3341 <br /> QJ <br /> OCT 1 u 1994 October 13, 1994 <br /> Project OC42-001.20 <br /> ENVIRONMENTAL HEALTH <br /> PERMIT/SERVICES <br /> Mr. Philip Isorena <br /> Regional Water Quality Control Board <br /> Central Valley Region <br /> 3443 Routier Road, Suite A <br /> Sacramento, California 95827-3098 <br /> Re: Port of Stockton Phase II Assessment, Total Lead Concentrations Detected In <br /> HydroPunch Groundwater Samples <br /> Dear Mr. Isorena: <br /> On behalf of the Stockton Terminals Technical Committee (STTC) EMCON Associates <br /> (EMCON) reexamined the total lead concentrations reported for HydroPunch® groundwater <br /> samples collected during the Port of Stockton phase II site assessment (EMCON Phase II Site <br /> Assessment Report, September, 1994). Total lead concentrations detected in HydroPunch <br /> groundwater samples ranged from 17 to 320 micrograms per liter (µg/L) as shown on Table 1. <br /> EMCON's reexamination of the data is discussed below. <br /> The HydroPunch sample analytical results suggest total lead concentrations locally exceed <br /> 100 µg/L. Several of these sample locations (PS/CPT93-6, PS/CB93-1, and PS/CB93-4) are near <br /> or beyond the downgradient dissolved petroleum hydrocarbon plume in respective water-bearing <br /> zones. This suggested the elevated lead concentrations are unrelated to STTC facility operations. <br /> Further review of the sampling methods indicated that the HydroPunch groundwater samples <br /> submitted for total lead analysis are field filtered with the coarse stainless steel filter of the <br /> HydroPunch. Groundwater monitoring well samples submitted for total lead analysis are typically <br /> field filtered using a 0.45 micron paper filter to remove sediment and reduce sample turbidity. <br /> Sediment and sample turbidity may result in artificially elevated total lead concentrations reported <br /> by the analytical laboratory. <br /> Comparison of phase II HydroPunch and monitoring well groundwater sample analytical results <br /> supports the elevated lead concentrations resulting from the non-filtration of the HydroPunch <br /> samples. Total lead concentrations of B-, C-, and D-zone HydroPunch samples collected at the <br /> ST Services, Time Oil, and Tesoro distribution terminals ranged from 9.3 to 120 µg/L. <br /> Monitoring wells were subsequently installed adjacent to the HydroPunch sample locations and <br /> screened at equivalent stratigraphic intervals. Total lead concentrations detected in field-filtered <br /> groundwater samples collected from the monitoring wells ranged from below the analytical <br /> SAGPJUIX4Z\OC420012.OAM-94/LFC:2 <br />