|
Sent By.: BASELINE; 510 420 1707; Nov-9-99 16.30; Page 21129
<br /> fir.✓ Q
<br /> The maximum concentration of MTBE in groundwater at the former ARCO site was 9.9 mg/L in 7
<br /> February 1999;the result from the June 1999 sampling event,was 0.766 nrg/L in this well (SECOR,
<br /> 1999; Langevin, 1999). The maximum concentration of petroleum hydrocarbons, aromatic
<br /> hydrocarbons,chlorinated hydrocarbons,and other compounds at this off-site location are as follows
<br /> (sce also Appendix A): benzene, 0.503 rng/L; toluene, 0.0177 mg/L; ethylbcnzcnc, 0.707 mg/L;
<br /> xylenes, 1.55 mg/L;NTIBE,9.99 mg/L;TPH as gasoline, 15 mg/L;n-butyl benzene, 0.0638 mg/L;
<br /> sec-butyl benzene, 0.0143 mg/L; cis 1,2-DCE, 0-0876 mg/L; trans 1,2-DCE, 0.00262 mg/L;
<br /> chloroform, 0.0213 mg/L; isopropyl benzene, 0.0592 mg/L; naphthalene, 0.372 mg/L; n.
<br /> propylbenzene; 0.216 mg/L; 1,1,2,2 tetrachloroethane, 0.00704 mg/L; tetrachluruethane, 0.0025
<br /> mg/L; 1,1,2 trichloroethane,0.00236 mg/L;TCE, 0.433 mg/1, 1,2,4-trimethylbenzene, 1.21 tng/L4;
<br /> and 1,3,5-trimethylbenzene, 0.0299 mg/L.5
<br /> DISCUSSION OF RESULTS
<br /> ON-SITE
<br /> Phase iI Investigation
<br /> Analytical results for groundwater samples,as identified in Table 2 and Appendix B,were compared
<br /> to primary California and Federal maximum vontaminunt limits (MCLS) established,for each
<br /> compound in the Phase Il investigation report. This is considered a very conservative; assumption
<br /> since the shallow water-bearing zone is not a drinking water source. Analytical results for
<br /> groundwater were not compared to surface water aquatic criteria since groundwater generally flows
<br /> in an easterly direction away from the Channel (Black & Veatch, 1998a). Based on this
<br /> comparison, a groundwater sample collected from one sampling location (WBGW3) exceeded
<br /> screening levels for two metals: aluminum and lead. This result may, however, have been due to
<br /> sediment in the sample, since the grab groundwater samples were not filtered prior to analysis. A
<br /> groundwater sample for the off-site location(WBGW4) also exceeded established screening levels
<br /> for MTBE and benzene,vinyl chloride, 1,1-DCE,and cis 1,2-DCE,which are likely due to 6peration
<br /> of a former ARCO gasoline station at this off-site location. No groundwater samples analyzed for
<br /> SVOCs or pesticides/PCBs were reported above the applicable MCLs (Black & Veatch,1998a).
<br /> Data from soil samples were compared to EPA Rcgion IX Preliminary Remediation Goals(PRGs)
<br /> (Smucker, 1998). PRGs are risk-based tools that are used to establish preliminary screening
<br /> concentrations of chemicals to assess whether remediation and/or further investigation may be
<br /> necessary at a site. Based on this comparison, iron was above residential PRGs almost uniformly
<br /> across the site at all depths. Lead exceeded the PRG in three samples(WBSB 1,WBSBS,WMSB9),
<br /> each collected between 7 and 9 feet bgs. One sample, collected at 13 feet bgs(WBSB2), exceeded
<br /> the PRG for arsenic. Also, one SVOC,benzo(a)pyrenc, was estimated in three samples(WBSB3,
<br /> WBSB9 two collected at 9 feet bgs and one collected at 2 feet bgs) at above the residential FRG.
<br /> These metals in soil were thought to be either naturally occurring or the result of historical site uses
<br /> that are typical of soils along the entire waterfront. The concentration ofbenzo(a)pyrene exceeding
<br /> Another table indicates the rnaximum concentration as 1.55 mg/L,It is unknown which concentration is correct.
<br /> Anothertabte indicates the maximum concentration as 0.348 mg/L.It is unknown which concentration is correct.
<br /> 9736%%1 ,pra.wpd-11/9199 15
<br />
|