|
I
<br /> I- Work Plan-Soil and Groundwater Remediation
<br /> CSUS Multi-Campus Regional Center,Stockton,CA
<br /> March 3,2003
<br /> Page 3 of 8
<br /> The January 11, 2002 report recommended quarterly groundwater monitoring, additional lateral and
<br /> vertical groundwater characterization, and soil over-excavation. The soil over-excavation was a
<br /> I suggested remedial alternative that was most likely to result in rapid mitigation of site contamination. In
<br /> a letter dated April 26, 2002 to Mr. Bailey of CSUS, Ms. Setliff of the SJCEHD agreed with the
<br /> monitoring and additional groundwater investigation portion of the recommendations, but requested the
<br /> f evaluation of the feasibility of at least two remedial options for the site.
<br /> Condor prepared a Problem Assessment Work Plan (PAWP) for the site dated January 23, 2003, to
<br /> describe additional groundwater investigation at the site. The PAWP was prepared at the request of Mr.
<br /> David Rosso for the Trustees of the California State University in response to a letter dated April 26,
<br /> 2002 from Ms. Setliff of the SJCEHD. The purpose of the work is to further investigate the lateral and
<br /> vertical extent of petroleum hydrocarbon contamination in groundwater at the site through the proposed
<br /> installation of direct push borings to further evaluate the site hydrogeology; collection of discrete interval
<br /> groundwater samples, and installation of at least one shallow monitor well and one deep monitor well to
<br /> verify the results of the direct push sampling over time. As requested by the SJCEHD, the PAWP,also
<br /> included a remedial feasibility evaluation that compares and discusses remedial techniques for site
<br /> remediation. Over-excavation and in-situ groundwater remediation has been selected to minimize total
<br /> remediation time.
<br /> Condor has conducted four quarterly monitoring events at the site (December 2001; June, September, and '
<br /> December, 2002); field activities included measurement of water levels and collection of water samples
<br /> from the three monitor wells, MW-1, MW-2, and MW-3. The quarterly monitoring data indicate that
<br /> groundwater conditions at the site have remained relatively static. Monitor well MW-1 is located up
<br /> gradient of the contaminant plume; and, to date, no petroleum hydrocarbon constituents have been
<br />!,
<br /> LG detected in the groundwater samples collected from MW-1. Toluene and 1,2-dichloroethane (1,2-DCA)
<br /> have consistently been detected in the groundwater samples collected. from monitor well MW-2;
<br /> Benzene, ethylbenzene, total xylenes, total petroleum hydrocarbons quantified as gasoline (TPH-G);and
<br /> 1,2-DCA were also detected in the groundwater samples collected from monitor well MW-2 during the
<br /> December 2002 monitoring event. A slight petroleum odor has consistently been noted in the field
<br /> inspection samples collected from monitor well MW-3. BTEX, TPH-G, methyl tertiary-butyl ether
<br /> (MTBE), and 1,2-DCA have consistently been detected in the groundwater samples collected from
<br /> monitor well MW-3. In addition, tertiary-butanol (TBA) was detected in the groundwater sample
<br /> collected from MW-3 during the December 2001 monitoring event. The groundwater gradient direction
<br /> has fluctuated from slightly north of east to southeast.
<br /> 3.0 SITE GEOLOGY
<br /> Cross sections (Figure 4, Appendix A) through the hydrocarbon impacted soil at the site and are shown
<br /> in Figures 5, 6, and 7, Appendix A. Soils underlying the site consist predominantly of interbedded clays
<br /> and silts with interspersed thin beds of sand. Silty and sandy horizons form discontinuous, undulatory
<br /> interbcds and lenticular features.
<br /> The clay stratum underlying the site varies in composition from dominantly stiff to very stiff, fine-
<br /> gained clay to siltylsandy clay. The silty horizons range in composition from clayey silt to sandy silt; a
<br /> relatively continuous silty horizon with clay interbeds is present immediately below the former
<br /> excavation area (Figures 5, 6, and 7, Appendix A) from approximately 14-32 feet below ground surface
<br /> (bgs). This silty horizon appears to pinch out rapidly to the north, east and south of the former excavation
<br /> Ih
<br /> area. ,��,�4�
<br /> L
<br /> . 4Ps
<br /> �irl� CONDOR
<br />
|