ARCHIVED REPORTS XR0006987 - Laserfiche WebLink

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1 ' (iroiurdwatei LIL)-1t1On measurements collected at thy, site on JnnL 21 2000 indicated that the average depth to groundwater sxas ippinximately sig ILLt below the monitor well and water surface measuring points • (imundwatcr Llc\anuli contours for lune, 21 2000 indicate that tI1L groundwater gradient at the site is generally ' consistent with the historical groundwater gradient In a letter dated June. M 2000 Mr RowL (It the. ',an Joaquin County P11S/I'HD directed the submittal of a work ' plan airicndnicnt to modify the sLopc of wnrl. proposed in the ahovc refeienctcl work plan and work plan addendum \LLOrdtng to kir Rowe the woil. plait amendment was to desci ibe vertical character iration of the potential M 1131- plume and bt suhmitted by August 1 2000 ( ondor subsequently prepared the Stutus Report ' antl Ithh,whim if) thi itmk flora dated July- 2000 Mr Rowe, approved the work plan ainLndialent in a taxed MLssage dated Ausust 1 2000 [n a tLILphorsc conversation with Mr Rowe on August 3 2000 ( ondor requLsted that the submittal datL for the report of findings bL eYttnded to OLtober 6 2000 Mr RowL verbally ' concurred with the LXtension and rcqucsted that ( ondor prepare a letter to dOLUITient the, conversation ( ondor fo11UwLd up with a [ettcr dated August 1 2000 ' Me installation and sampling of the, soil borings described by the Work Plan Work Plan Addendum, and Work Plan Annendmcnt were conducted at the site between September I 1 and September 13 2000 The results of the investigation were described in the Soil and Groundwater Investigation and Sensitive Receptoi Suivey Report ' dated OctohU 2, 2000 Direct push ((,eoprohe), hand auger, and hollow-stem auger techniques were used to advance 13 borings at the site (Borings DP-1 through DP-9, SP-1 and HP-1 through HP-3) Soil sampling was conducted with direct push coring or Simulprobe techniques, as necessary Groundwater sampling was conducted with the direct push groundwater sampling tool (hydropunch style) The purpose of the work was to Ifurther investigate the Luent of petroleum hydrocarbon contamination in the east portion of the site and the propLr-ty (agricultuia] flLld) adjacent to the east portion of the site lie I aboratory analyt:cal results indicated that iM I BF was present in the soil Samples collected at approximately 4 feet bgs from DP-4 and at approximately 8 feet bgs from DP-5 at concentrations of 1,600 and 7,100 pg/Kg, respcetively IAMI was also present tri the soil sample collected at approximately 8 feet blas from DP-5 at a ' conLLritration of 180 pg/Kg None of the analytes of interest were detected at or above the laboratory reported detection limas in any of the soil samples collected trom DP-3, DP-6, DP-7, DP-8 Laboiatoty analytical results of the groundwater Samples indicated that an elevated concentration of MTBE (37,000 I1.011) was present in the shallow groundwater at the location of DP-5 Benzene, ethyl benzene, total xylenes I P11-(j and I AM[ wcrc also present at that location at concentrations of 330 fig/I 80 1rg/1, 1 10 pg/L, ' 1 7 ing/L and 130 [L-A i cspectrvely FPI-I-(� was present at a concentration of 0 28 mg/1 in the gi oundwater sample collected at approximately 24 feet bgs fiom HP-1 With the exception of these two groundwater samples, none, of the analytes of interest other than M I BI- were detected in any of the other grow ndwatei samples at or above the. laboratoi v i eported detection I units Ti ace to moderate concentrations of M`i BI-I ranging from 2 2 to 181 pg/L were detected in shallow groundwater samples collected from DP-1 DP-2, DP-3 DP-4 DP-6, DP-8, and DP-9 With the exception of a concentration of 5 4 pg/1 in the groundwater sample collected from ' approximately 31 feet bgs in HP-2, MTBE was not detected at of above the laboratory reported detection limit in any of the groundwater samples collected fiorn the deeper strata in HP-1, HP-2, and HP-3 ' Field observations indicated that the site soil present to the depth investigated generally consists of peat, very fine to fine-anaincd sand elate,, sand silt) sand sift} clay, and sand} clay The stratigraphy beloNN the peat at the site as observed in the three deep coittutuously cored borings (DP-3, DP-7, and DP-8) is tine-grained and complex with a relatively high degree of heterogeneity and anisotropy Sand, silt, and clay content alternate and vary frequently with an increase in depth The stratigraphy indicated in DP-7 correlates well with the . stratigraphy in DP-8 The stratigraphy indicated in DP-3, however, does not correlate as closely with that of DP- ' 7 and DP-8 rhes indicates that the various soil strata at the site are not laterally extensive but instead vary in composition within a relatively short distance The presence of a laterally and vertically extensive clay horizon