Laserfiche WebLink
California Re anal Water Quality C ltrol Board`r. <br />Central Valley Region <br />Robert Schneider, Chair <br />Alan C. Lloyd, PhD Arnold Schwanenegger <br />Secretary for 11020 Sun Center Drive #200 Rancho Cordova, CA 95670-6114 Governor <br />Environmental (916) 464-3291 • Fax (916) 464-4704 <br />Protection ht_pt ://www.swrcb.ca.gov/rwacb5 <br />TO: Thomas Pinkos <br />Executive Officer <br />Brian Newman A - <br />Supervisory WRCE <br />RS UST Program Manager <br />UST Case File <br />FROM: Jim Barton <br />Engineering eologist <br />DATE: 15 April 2005 <br />SUBJECT: RECOMMENDATION TO ALLOW TEMPORARY CESSATION OF <br />OPERATIONS OF GROUNDWATER PUMP & TREATMENT SYSTEM, <br />CLEANUP AND ABATEMENT ORDER (CAO) NO. 5-00-704, <br />CHEVRON STATION #9-5775,301 WEST KETTLEMAN LANE, LODI, <br />SAN JOAQUIN COUNTY <br />Background: The site is a former Chevron service station. Regional Board CAO No. 5-00-704, <br />issued 20 April 2000, requires groundwater remediation by means of continuous operation of the <br />groundwater pump and treatment (GWP&T) system, with the only exception being normal <br />periodic and scheduled maintenance, unless the Regional Board Executive Officer approves <br />otherwise. GWP&T provides onsite hydraulic control of the groundwater plume. Site <br />characterization for soil and groundwater has adequately defined the vertical and lateral extent of <br />petroleum hydrocarbon contamination. Quarterly monitoring shows a declining concentrations <br />trend of total petroleum hydrocarbons as gasoline and MtBE. Maximum groundwater <br />concentrations of total petroleum hydrocarbons as gasoline (onsite well EX71) have dropped two <br />orders of magnitude since the third quarter of 2004, from 1,400 micrograms per Liter (µg/L) to <br />58 µg/L. MtBE in EX -1 has also shown a similar decline, dropping from 1,500 µg/L to <br />150 µg/L. Because of high suspended solids, EX -1 is not a part of the GWP&T system. All <br />remaining monitoring and extraction wells sampled during November 2004 are at, or just above, <br />detection limits for all analytes. <br />In order to determine if the groundwater plume is stable and concentrations are continuing to <br />decline due to natural attenuation, a rebound test without active GWP&T is necessary. The <br />Groundwater Modeling Report (discussed below) recommends temporarily stopping the <br />California Environmental Protection Agency <br />Ca Recycled Paper <br />