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F am <br /> am <br /> MMWFr1ff`e� <br /> From Science to Solutions <br /> HPP-BTR MP#204.4 <br /> Vernalis Pump Station <br /> Reports <br /> DCN:C20-SAI-Vernalis-PS-01-15485 <br /> April 28,2008 <br /> Mr. M. Scott Mansholt <br /> Chevron Environmental Management Company <br /> 6001 Bollinger Canyon Road <br /> P.O. Box 6012 <br /> San Ramon, California 94583-0712 <br /> Subject: First Semi-Annual 2008 Groundwater Monitoring and Sampling Report <br /> Vernalis Pump Station <br /> 35500 Welty Road <br /> Vernalis, California <br /> Dear Mr. Mansholt: <br /> Science Applications International Corporation(SAIC)prepared this report at the request of Chevron <br /> Environmental Management Company(CEMC)to summarize groundwater monitoring and sampling <br /> activities conducted at the Vernalis Pump Station site(the site),Vernalis, California(Figure 1).This report <br /> summarizes the 4th quarter 2007 and the 1St quarter 2008 sampling events. The groundwater monitoring <br /> and sampling program at the site was initiated at the request of the California Regional Water Quality <br /> Control Board—Central Valley Region(RWQCB)to characterize the extent of affected groundwater from <br /> operation of the former Old Valley Pipeline(OVP) system. The RWQCB concurred with SAIC <br /> recommendations to reduce the sampling frequency for on-site wells MW-1 through MW-5 from <br /> quarterly to semi-annually and to monitor off-site wells MW-6 and MW-7 located on the Bogetti property <br /> on a quarterly basis.' The RWQCB requested that the off-site wells be monitored and sampled on a <br /> quarterly basis until the down-gradient extent of petroleum-affected groundwater has been characterized. <br /> The quarterly sampling data for wells MW-6 and MW-7 will be reported on a semi-annual basis. Seven <br /> groundwater monitoring wells are currently utilized to evaluate hydrologic and water-quality conditions at <br /> the site. Site features and the locations of site monitoring wells are shown on Figure 2. <br /> BACKGROUND <br /> SITE DESCRIPTION AND USE <br /> The site is located at 35500 Welty Road,Vernalis, San Joaquin and Stanislaus counties, California <br /> (Figure 1). The former pump station consists of two properties: the Bellini property(formerly known as <br /> the Roberts property) and the Arcos property. The Bellini property is located on the northern part of the <br /> site, and the Arcos property is located on the southern part of the site(Figure 2). The Bellini property is a <br /> triangular-shaped, 5.73-acre vacant lot. The Arcos property is irregularly shaped and is currently used as <br /> a storage facility for equipment and materials. A residence and an office are also located on the Arcos <br /> property. The former pump station site is located in a rural and light-industrial area and is bordered by <br /> Welty Road on the west,Union Pacific Rail Road(UPRR)tracks and Highway 33 on the northwest, light- <br /> industrial facilities on the southeast, and agricultural areas on the south. Currently,Kinder Morgan <br /> 1. RWQCB,2007. Review of Second Quarter 2007 Groundwater Monitoring and Sampling Report—Former Vernalis Pump <br /> Station Property,Vernalis,San Joaquin and Stanislaus Counties. August. <br />