ARCHIVED REPORTS XR0002718 - Laserfiche WebLink

Home Browse Search

i i } , from a depth of 22 feet to a depth of 38 feet and has a length of approximately 20 feet. Assuming a width of approximately 10 feet, the volume of impacted soil on-site is calculated . to be approximately 150 cubic yards. ; Obtaining an average hydrocarbon concentration is more tenuous. However, estimating a , ' weighted average of .200 ppm, the total volume of remaining hydrocarbons on-site is calculated to approximateIy_1l_ gallons. 1' Beneath Harding Way, the volume of impacted soil becomes more speculative. However, estimating the affected area to contain approximately 250 cubic yards of impacted soil and ' with a weighted average concentration of 1,050 ppm, the total volume of remaining hydrocarbons beneath Harding Way is approximately 100 gallons. The volume of hydrocarbons beneath Harding Way is approximately nine times the volume remaining on- site. 4.2 Remediation Alternatives for Hydrocarbon Impacted Soil IImpacted soil was originally excavated to a depth of approximately 22 feet in the former fuel island area; excavation was terminated because of equipment limitations. The remaining ' impacted soil on-site is at depths in excess of 22 feet and located within 10 or 15.feet of-the City of Stockton right-of-way. Based upon the relatively low concentration of hydrocarbons and small volume of remaining soil, further excavation would not result in the removal of a significant volume of hydrocarbons. Furthermore, an excess of "clean" soil (overburden) would have to be removed to excavate the impacted soil. Obviously, excavation would not be cost-effective, and would be logistically difficult. On-site, clayey soil is present between 15 and 45 feet; therefore, all remaining hydrocarbons on-site are in a clayey soil, which is not conducive to in-situ remediation methods. It is very likely that vapor extraction, soil venting or bioremediation would all be ineffective in treatment of the remaining impacted soil on-site, based upon remaining hydrocarbon concentrations (low), hydrocarbon composition (predominantly long-chain hydrocarbons) ' and soil type (clay). In addition, remediation cost versus contaminant removal would be high. ' 4.3 Hydrocarbon Impacted Groundwater The laboratory results of groundwater samples collected in July 1994 confirm that no TPH as gasoline, TPH as diesel or BTE&X are present at the site. However, motor oil was detected in four of the monitoring wells. A review of previous groundwater Iaboratory results do not indicate the presence of motor oil during past sampling events, either targeted specifically by the laboratory or quantified in the TPH as diesel range (see Table 5). The source of the motor oil in the groundwater samples is uncertain. Since petroleum hydrocarbons have been detected only intermittently at the site at very low A.&:<nk..lx 11 y�yyyma,ow sve-cswsa