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. Work Plan Addendum - May 2001 <br /> LANGSTON'S NLA_'12KET <br /> 15615 South 7' Street,Lathrop, California <br /> 1.0. INTRODUCTION ` <br /> At the request of Mr James Langston., Advanced GeoEnvironmental, Inc (AGE) has prepared the <br /> enclosed work plan addendum for the Langston's Market site located at 15615 South 7" Street, <br /> Lathrop, California The location of the site is illustrated on Figure 1 A plan of the site is illustrated <br /> on Figure 2 <br /> This addendum has been prepared as required by the San Joaquin County Public Health Services - <br /> Environmental Health Division(PHS-EHD)by letter dated 08 May 2000 to assess an unauthorized <br /> release of petroleum hydrocarbon compounds from an underground storage tank (UST) formerly <br /> Iocated at the site Additionally, this work plan addendum is prepared in accordance with Central <br /> Valley Regional Water Quality Control Board(CVRWQCB)guidelines for the investigation ofUST <br /> sites <br /> The purpose of this additional site assessment is to complete the assessment of the lateral and <br /> vertical extent of petroleum hydrocarbon impacted soil and groundwater in the northwestern and <br /> . eastern portions of the site This work plan addendum provides a description of the scope of work <br /> and procedures to be used in soil probe borings,soil and groundwater sample collection and analysis, <br /> and soil boring abandonment <br /> 2.0. BACKGROUND <br /> In June 1990, following a helium pressure test, a 4,000 gaIIon gasoline UST failed and <br /> approximately 1,200 gallons of unleaded gasoline were released Between 1990 and 2000, 18 soil <br /> borings and numerous side-wall samples ha-c been ccllCcted and analy zcd, and S aiouitoring w ells <br /> (Including four destroyed original wells) have been installed at the site <br /> In December 2000 AGE installed four additional monitoring wells at the site (MW-5 to MW-S) <br /> Quarterly monitoring events in December 2000 and March 2001 detected high concentrations of <br /> TPH-g as well as MTBE in the ground water samples from MW-5, located in the original tank pit <br /> area <br /> Since AGE began quarterly groundwater monitoring activity at the site in March 1999,groundwater <br /> gradient determinations have indicated a consistently northwest ground-water flow There has been <br /> no monitoring wells northwest of the former UST locations since 1995, and the presence of MTBE <br /> has not been assessed in soil or ground water samples collected and analyzed at the site prior to the <br /> first AGE monitoring event in 1999 <br /> Advanced GeoEnvironmental,Inc <br />