WORK PLANS - Laserfiche WebLink

Home Browse Search

TECHNICAL APPROACH SUMMARY The objective of these proposed excavation and soil management tasks is to remove the maximum volume of impacted soil and groundwater from the vicinity of the former 4,000-gallon UST, without encroaching on the Caltrans right-of-way. To remove the maximum volume of heavily impacted soil from the vicinity of the former UST without Caltrans encroachment, the proposed excavation will be shored. Approximately 50 feet of shoring will be installed along the property line between the former UST and Caltrans right-of- way. To access the heavily-impacted soil between the former UST and the area of onded Y• P water to the west, approximately 25 feet of additional shoring would be installed along the west side of the proposed excavation. For support of the shoring system, the east side of the excavation may also be shored. Upon regulatory approval of this conceptual shoring and excavation pian, an engineered shoring plan will be designed and certified by a state of California registered civil engineer. The proposed excavation is a rectangular area measuring approximately 50 feet by 25 feet by X18 feet deep. Given that groundwater is present beneath the site at approximately 14 feet bgs, the proposed excavation includes the removal of up to four feet of potentially saturated soil. The .A. pactual depth of the excavation will depend on the amount of groundwater recharge into the X�`1w excavation and the competency of soils beneath the expected groundwater surface. l° e`f\$To maximize the depth of excavation and to remove petroleum hydrocarbons on the groundwater surface, groundwater will be pumped from the excavation.- All of the pumped { groundwater will be contained in a rented water storage tank. Upon completion of the de- watering operation, the contained groundwater will be treated with granular activated carbon, sampled and discharged to the local sewer system. \1 During excavation, soil samples will be collected. At an excavation depth of 10 feet bgs, 12 soil samples will be collected. Soil samples will be collected at each of the four corners of the S' d- i�� excavation, every 15-feet along the excavation side-walls and on 15-foot centers from the floor �� of the excavation. If possible, 12 additional soil samples will be collected from the same locations at 14-feet and 18-feet bgs. Each of the soil samples will be analyzed for TPH-as- diesel, TPH-as-gasoline, BTEX and MTBE by Modified EPA Methods 8015 and 8020. � (-r Once excavation and de-watering operations are complete, the excavation will be bac pkfilled. �d ea# � The backfill material will be placed to achieve a 90 percent compaction rate. Compaction testing will not be conducted. Once the excavation has been backfilled, the shoring will be removed. aG� n The surface will be finished with a thin layer of aggregate base rock. No asphalt or concrete 0- lop rpavement will be applied. Two disposition options are presented. The first option involves off-site disposal and the second option includes beneficial re-use. To beneficially re-use the soil, a re-use plan must be prepared. A project report documenting all of the proposed work activities will be prepared and distributed. This report will also include a detailed documentation of the Geoprobe soil and groundwater- grab sampling and monitoring well sampling activities performed on February 25, 1999.