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California Regional Water Quality Control Board <br /> Central Valley Region ' s <br /> Robert Schneider, Chair <br /> Linda S.Adams Arnold <br /> Secrataryfor Fresno Branch office Schwarzene <br /> Environmental 1685 E Street, Fresno,California 93706 gger <br /> 559 445-5116 •Fax 559 445-5910 Governor <br /> Protection � ) � ) <br /> htt p:liwww,wate rb o a rds.c a.g ovlce n t ra Iv a I I ey <br /> 20 November 2006 <br /> NOV 2 5 200E <br /> M. Scott Mansholt <br /> Chevron Environmental Management Company cr. <br /> 6001 Bollinger Canyon Road <br /> Rm K2066 <br /> San Ramon, CA 94583-2324 <br /> REVIEW OF THIRD QUARTER 2006 GROUNDWATER MONITORING AND SAMPLING <br /> REPORT— US CAN- WELTY ROAD PROPERTY, VERNALIS, SAN JOAQUIN COUNTY <br /> Regional Water Board staff has reviewed the referenced groundwater sampling report, dated <br /> 25 October 2006 and prepared for Chevron by Science Applications International Corporation <br /> (SAIC). The US Can-Welty Road site and the adjacent Vernalis Pump Station sites — Bellini <br /> and Arcos properties were previously owned and operated by predecessors of Chevron as <br /> part of the historical Old Valley Pipeline (OVP) system. <br /> Six monitoring wells (MWs; two offsite and four onsite) associated with this site have been <br /> monitored irregularly since 1999 and on a quarterly basis since early 2005. The monitoring <br /> and sampling event was completed 16 August 2006. <br /> Two of the onsite wells contain a sheen and are not sampled (petroleum-adsorbing devices <br /> are used in these wells) and the other two onsite wells did not have sufficient water for <br /> sampling. However, the two offsite wells, MW-5 (installed in 2005) and WFSMW-1 contained <br /> sufficient water and were sampled. Groundwater flow is easterly at an approximate gradient of <br /> 0.001 ft/ft. Depth to water is between 32 and 36 feet. <br /> Samples were submitted for analysis of total petroleum hydrocarbons as gasoline (TPHg), <br /> TPH as diesel (TPHd), benzene, toluene, ethylbenzene, and xylenes (BTEX), and polynuclear <br /> aromatic hydrocarbons (PAHs). TPHg and BTEX were ND for both samples and TPHd was <br /> ND in sample MW-5; TPHd at 230 ugll and 120 ugll VVFSMW-1 and the WFSMW-1 duplicate <br /> sample, respectively. PAHs were ND in both samples except for phenanthrene at 0.013 ugll in <br /> WFSMW-1 and WFSMW-1 D. This low concentration is below the Environmental Screening <br /> Level of 4.6 ugll for phenanthrene. <br /> SAIC recommends reducing the monitoring frequency from quarterly to semi-annual. <br /> Additionally, since TPHg and BTEX have not been detected in groundwater for some time, <br /> SAIC also recommended these constituents be eliminated from the analytical suite for future <br /> sampling events. Further, considering that groundwater elevations have slowly declined over <br /> recent years and the onsite monitoring wells do not have adequate water for purging and <br /> sampling, SAIC recommended that MW-3 and MW-4 be destroyed. <br /> California Environmental Protection Agency <br /> Z�Recycled Paper <br />