ARCHIVED REPORTS XR0000890 - Laserfiche WebLink

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On May 2 and 3,2000 the soil borings for both MW#5 and MW#6 were made as described in the Work Plan of 3/17/2000. Monitoring wells were installed in both of these soil bores. The Work Plan of 3/17/2000 also included a soil bore and monitoring well(MW44)to be installed in the sidewalk on the north side of Lafayette Street.This soil bore was not completed as planned.An unknown underground storage tank was encountered in the direct path of the soil bore.As a result of this encounter,the soil bore was abandoned and the local agencies were notified. CPT#3 was installed on June 13,2000 in the Caltrans right of way. This CPT is northeast ofthe site, and the data gathered is in the report issued for that work. All monitoring wells have been sampled quarterly, and a recap of the findings is attached. A Work Plan to expand the horizontal definition ofthe contamination plume was approved in December of 2000.This Work Plan called for the installation of three new CPT's within the Caltrans R/W to the north of the project site.These CPT's were completed on March 8,2001 and soil and water samples were extracted to a depth of 125 feet. Also, included in the Work Plan of December 2000 was the installation and testing offour new monitoring wells,(MW-8S,MW-81),MW-7,MW-9) to be placed on the project site or the adjacent property. These monitoring wells were completed on April 11,2001. Procedure On December 14,200 1,Del Tech Geotechnical Support Services secured water samples from all ofthe monitoring wells on the above stated property.The work was supervised by Foothill Engineering.All monitoring wells were in good condition and samples were taken using the standard recommended procedures.All samples were extracted using the tube with check valve pump system.Purge rates were +/- 1 g.p.m.and the physical properties of the groundwater can be found in the Del-Tech Field Report which is attached and part of this report. The replacement and original monitoring wells were sampled for analysis and the original monitoring wells(MW-1,MW-2,MW-3)were used to establish the groundwater elevation and hydraulic gradient. All samples were transported under chain of custody to Sherwood Labs of Hilmar, California for analysis by EPA method SW8020. All water sample analysis and groundwater elevations are summarized in the attached tabular recap sheet (see attached recap sheets). Copies of the original Laboratory data sheets from this sampling event are also attached and are a part of this report. Findings The groundwater elevation in the wells has lowered+/-0.7 feet for both the shallow and deep wells from the last sampling date of September 19, 2001. MW-1 continues to have the highest concentration of gasoline contamination for TPHg at 196000 ppb.which is lower than 203000 ppb.of the last sampling event. MW-8D has recorded a major change with a drop in TPHg to non-detect (Report limit of 50 ppb),from a high of 289 ppb.for the third quarter groundwater sample from this well(see recap sheet attached). The groundwater hydraulic gradient was calculated at 5=0.003 with the down slope in the east direction.This gradient applies to the shallow well data of MW-1,MW-2,and MW-3 only(see a site map attached). This is a significant change in direction from the third quarter sampling event. Conclusions The hydraulic gradient for this monitoring event has changed back toward the more traditional 2