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Er � �-�� 'y, �'.� ��'.rr -;t, G.33,,�,,z:`*SF"',�,.`..". �w ��^' rn-ti"^^'1. �a.�R,._,"�"" ��°i'. A^�..,_�".2�`'c.,,HY`�-�-, �" C`��a:. ,,',,,;C -.ten•` rte. i�- � a �� . Y7�f. `"L.'^� ��&� y `�.-:" �. 7r.,- '.+i+� '� r-r�., ''N"�N�:r�'' �•:4 ��' =::ar'-''� .w�-"' ��,,y�4.ry�-` Ms. Diane Hinson March 6, 1490 Page 3 Cross-sce!ion locations are illustrated in Figure 3,and LL:cross-sections appear as Figures 4 (A-A) and 5 (B-B'). Each monitoring well was consiructcd of 4-inch diameter,schedule 40 PVC material to a depth of 40 feet below grade. The wells were screened from 40 to 20 feet below grade with #20-slot (0.020-inch slot width) screen. Details of monitoring welt construction are contained in Enclosure G The monitoring wells were developed, purged, and sampled in accordance with methods outlined in Enclosure A,Sections 3,4, and S. A ground water sample from each well was submitted for analysis of benzene,toluene,ethylbenzene,and xylenes(BTEX),and total petroleum hydrocarbons as gasoline (TPH(g)) using U.S. Environmental Protection Agency (EPA) and California Department of Health Services (DHS) approved methods. Soil Samnle_Analvtical Results A portion of each soil sample collected from the soil borings was sealed in a plastic bag and brought to ambient air temperature. The headspace of the bag was then screened with a photoionization detector (PID). The highest PID reading for each sample was recorded on the boring logs (Enclosure B). PID measurements were made using an hNu which was calibrated to a benzene standard. Readings provide only a relative measure of organic vapor content. Readings are reported in `hNu units',which are approximately correlative to parts per million(ppm). PID screening results indicate that organic vapors were present above background levels in soil samples collected from borings for monitoring wells MW-2,MW-5,and MW-7 at depths between 10 and 30 feet below grade. The highest PID readings recorded in samples collected from boring MW-2 were M and 50 ppm at 15 and 25 feet below grade, respectively. The PID readings recorded for MW-5 indicated vapor concentrations of 80 ppm at 25 and 30 feet below grade. The highest PID readings for soil samples collected from MW-7 were 680 and 2200 ppm at 20 and 30 feet below grade, respectively. PID screening results are compiled in Table I. TABLE I PID Screening Results Depth Below Grade (feed MW-1 MW-2 MW-3 MW-4 MW-5 MW-6 MW-7 5 0 0 0 0 14 0 10 10 0 3 0 0 20 0 80 15 0 80 8 0 20 0 75 20 0 15 15 0 24 Il 680 25 0 50 19 15 80 0 54 30 0 30 1 5 80 2 2 00 35 0 25 3 10 20 1 30 40 0 23 11 --' 20 ... 25 NOTES: All measurements made on sample:container hendspace usin,a PID(hNu). The hNu was calibrated to a benzene standard to read in parts per million. Readings reflect relative organic .anc.r concentrations. 'Not sampled.