WORK PLANS - Laserfiche WebLink

Home Browse Search

The Newark Group, Inc. -4 - 27 February 2013 800 W. Church St., Stockton San Joaquin County 2. The Report text and Table 4 did not provide the rationale how the Report calculated the square footage of the areas used to estimate the residual mass, and two borings with measurable TPH mass (B-22 and B-27) are not located within the plume boundaries in Figure 4. Using Figure 4 to just scale the length and width distances between all of the borings with detected TPHd and TPHg, while not providing an estimated radii of contaminated soil column around those borings, expands the contaminant areas to approximately 6,250 sq' (Area B-7) to 5,525 sq' (Area B-14) and to 3,750 sq' (Area B-15). A staff contaminated soil total area (maximum extent in plan view) estimate of 15,525 sq.' is over an order of magnitude greater than the 1,347.7 sq.' total area used to calculate mass in soil as indicated in the Report Table 4. The soil bulk density used for the Report calculations was converted from the metric 1.3 kilograms per Liter to 81.156 pounds per cubic foot, which is significantly lower (20%) than the accepted average bulk density of 100 to 110 pounds per cubic foot. These factors (total area and soil bulk density) indicate that the Report mass in soil was underestimated. For an example in Area B-7, TPHd concentrations >1 to 2900 mg/kg in one 2' thick layer, the calculation would be 6250 ft2 x 2' x 100 Ib/ft3 x 0.0001450 mg/mg x 2.2 Ib/kg = 797.5 lbs. of residual TPHd in soil, not the Report 234.63 lbs. of TPHd listed in Table 4 for the >40<2900 mg/kg section of Area B-7 covering 506.8 ft2. Please see Comment 4 below. 3. Since the Report states that TPHd and TPHg detected in Area B-14 do not have a connection to a known UST, the Area B-14 release will be referred to the Regional Board Site Cleanup Section for evaluation as a spill case. 4. URS requested consideration for USTs case closure upon my review of the Report in an email dated 30 January 2013. The following items need to be adequately addressed prior to consideration for closure: a. Provide a rationale why the Letter recommended onsite investigation to west and south of boring B-33 is no longer necessary to determine the lateral extent of contamination for Area B-15, or provide a work plan to continue soil and groundwater investigation of Area B-15 by 30 March 2013. See g. and i. below. b. Provide mass estimates in soil and groundwater based on a revised area of extent of contamination at the Site as discussed above, using an average soil bulk density (or provide the geotechnical data to support the lower soil bulk density used in the Report), c. Provide an estimated time for TPHd and TPHg in groundwater to reach WQGs,