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420 Yosemite,Manteca Rainwater Car Wash, Page 2 The groundwater plume has not been defined horizontally, especially towards the north. The groundwater gradient direction for the First Water Zwr is to the north. It is unknown if this gradient direction is the same at greater depths. Hydraulic conductivity is unknown at this point but is potentially high. Due to the high concentration of contaminants in groundwater and the persistent and soluble nature of MTBE, migration of the plume Will increase the complexity of the investigation and the cost of the clean up. Therefore, interim remediation to control migration of the plume must be implemented as soon as possible. At the meeting,the date April 16,2001 was agreed to as a goal to install and implement an interim pump and treat system in the area of the highest on-site.groundwater contamination to control the plume from moving off-site. In order to expedite the approval process at the ' State Clean Up Fund,the site will be placed on the MTBE Priority List. The pump and mat. system will be based on the results of the ground water extraction test. ' In a letter dated January 2, 2001,PHS/El-1D directed you to submit to PI-1/El-11) a work plan for a ground water extraction test. This work plan has not been received at this office. It was agreed at the meeting that this work plan proposal,which will include a plan for the ' installation of additional observation monitoring wells/piezometers for the ground water extraction test,will be submitted to PHS/EHD no later than March 16, 2001. PI-5/El3D requests that analyses of all groundwater samples collected in future investigation and quarterly sampling events include the complete suite of analytes reportable by EPA Method 82608 including all fuel oxygenates,ethylene dibromide, 1,2- dichicroethane, methanol, ethanol, and solvents such as PCE and TCF. Additional investigation to define the vertical and lateral extent of the contamination is ' required. In a conversation with AGE staff at the site in December 2000, during the CPT work,PHS/EHD concurred with AGE's recommendation to advance continuous core borings to depth below 130 feet bsg to correlate with the data from CPT borings. ' PHS/ElM also concurs with the report's recommendation to install additional shallow and deep-screened ground water monitoring wells to define the vertical and horizontal extent of the contamination. Submit a work plan that will investigate the extent of the contamination ' to PHS/EHD by June 1, 2001. Donna Henan,RENS,Director ' Environmental Health Division /J �4 C, �, �✓✓� may, Ir�- Jeffrey Wong,Sr. RENS Dot Lofstrcm RG LOP/Site Mitigation Unit IV LOP/Site Mitigation Unit IV ' c: RWQCB, Central Valley Region-Marty Hartzell c: Advanced GecEnvironmental, Inc.- Tun Cuellar