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Treadwel'&Rolk) A LANGAN COMPANY Request for Low-Threat Case Closure 6 June 2013 RWQCB case#391149 and#391162 Page 2 420 and 423 N Madison Street Stockton,California Project:731589001 In June 2003,Advanced GeoEnvironmental, Inc. (AGE) of Stockton, California advanced eight borings(B- 1 through B-8) at the site and collected soil samples at all boring locations and groundwater samples at all locations except boring B-5. Boring B-3, located in the sidewalk east of the USTs contained detectable concentrations of total petroleum hydrocarbons as gasoline and diesel (TPHg, and TPHd) in soil and groundwater. TPH were not detected in soil or groundwater in any of the other borings by AGE (AGE, 2003). In January 2004,T&R advanced six borings(CSB-1 through CSB-6) and collected soil samples from all borings and groundwater samples from borings CSB-1 through CSB-4(Figure 2). The highest concentrations of petroleum hydrocarbons were detected in soil and groundwater samples from boring CSB-2, located approximately 23 feet east of boring B-3 (T&R, 2004c). The three USTs at the Carando site were removed in April 2004 (Figure 2) and the soil around the USTs was excavated to 25 feet bgs in June 2004(T&R, 2005a). During the June 2004 excavation, 1U approximately 425 cubic yards of soil and 20,000 gallons of groundwater were removed. A soil_ a" //Z5 confirmation sample was collected from the excavation bottom and a woundwater sample; C(_ PT-E.C_.W was also collected from the bottom of the excavation.The pump island area was also excavated to an S ��:,�✓ average depth of 10 feet bgs. A confirmationsam. le from near the northwestern corner and deepest / r•ti,( part of the excavation at 19 feet bg CPT-EXC-BT-19 contained TPHg and TPHd at concentrations up to 2,300 milligrams per kilogram (mg/kgl. Therefore,-another excavation was performed in April 2005 by T&R to approximately 25 feet bgs in the area of CPT-EXC-BT-Approximately 150 cubic yards of soil was removed from below 15 feet bgs and approximately 7,500 gallons of groundwater was removed from the excavation. Confirmation samples were collected within the excavation at the bottom and side-walls. Prior to back-filling this excavation, approximately 800 pounds (lbs)of ORCO, oxygen-release compound, 4 was placed at the bottom to accelerate biodegradation of impacted groundwater(T&R, 2005a). Historical soil and groundwater data for Carando are included in Attachment 1. 423 N Madison Street The 423 N Madison Street site (423 Madison) is located approximately 60 feet west of Carando across N Madison Street(Figure 1). 423 Madison was originally developed in the early 1900s, redeveloped in the 1950s for use as an auto repair facility, and redeveloped beginning in 2004 by the City of Stockton as part of the Stockton Arena and Event Center redevelopment project. All structures at the Site were demolished in preparation for remediation and redevelopment activities beginning in 2004. The northeastern portion of the Site is mostly paved and used for parking whereas a portion of the Stockton Arena is located on the southwest portion of the Site. USTs that reportedly stored gasoline or diesel were identified as USTs No. 1 to 6, and 8 (Figure 3), and were previously removed. Soil and groundwater contamination was observed during removal of these USTs. These USTs were associated with the recently closed RWQCB case #390110, which was also known as the former Chase Chevrolet. ��y',`�;p�o�ow The remaining open case at the site isociated with the B-6 UST, discovered during soil excavations in March 2004. The B-6 UST was a 1,50 gallon single-walled, open-top UST located in the north central portion of 423 Madison near boring 15B-6 (Figure 3). The UST was empty when it was discovered, and