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SHAc)-136 tomyrfifFACHan work MR maDF10 GMEMmn Sharpe we placed on National Priorities List In 19 and entered into m B,m o a four partyFederal Facility Agreement(FEA)in 1989 (United States Department ofthe Army, 1989). As described in the FFA, authority for environmental restoration decislon-making rests with a team of remedial protect managers from the California Environmental Protection Agency, including Department ofToxicSumrtaees Control and CMB, from the U.S. Environmental Protection Agency Region 9, and from Sharpe. Deprom logistics Agency aned Sharpe back to the Autry effective October 1, 2014. The Army is the lead agency responsible for funding and implementing remerfiala ions at Sharpe The FIFA established two operable units (OUs) to fxigm a environmental restoration at Sharpe. OU-1 addresses groundwater in four saturated monitoring zees (designated An A, B, C, and DI contaminated primarily with volatile organic compounds. The final pemmtlbl lnvestpenksn/FeasibAiry Study otDDRW- ecordo)Dec¢don (RODG Opemnts Unitl (OU;ESE, 1993) documents groundwaterextractlon, import and discharge of[re s the selected remedy few contaminated The i ExpMrmdon of SignPmnc DiJfrences to the OU 1 ROD (URS, 2014a) was signed and prmxW by the I regulatory agencies and the Army in September 2014 and added In situ treatment of high levels of subsurface contamination and CUCs. OU-2 addresses soil and soil gas above the water table. The OU-2 ROD (ESE, 996) documents extraction and treatment of volatile organic compound contaminated soil vapor and also documents no further action decision at multiple sites. The FinalAmendmenf to the DO 2 OD (URS 011) modified the my further arrive decision to encore protectiveness by adding UUCs atten sites and biological monitoring attwo sites for the burr owing owl (Athene cunkwlorio),a California species spe cial ecial concern. 1.2.1 Geplogyand Rydmgeology i In the Sharpe area, there is one complex, heterogeneous aqugersystem in whichfour hydrostratigraphic zones have been Identified in the hytlergeologic system between 14 and 270 feet (ff( below ground su dace(fogs).These hydrnnratgmph is zones are considered distinct zones to monitor hydraulk gradients ' ( n. The zones include several saturatetl transmissivelayers (sands) 5 to 12 feet thick In contaminant follow ng depth intervals: ( 0 AZone—watertabletoll0fiventigs ' ( 0 liZone-40tog0teetings i t 20 • Dion 270- 1]0 toet fogs fee fogs n the A groundwater is generally unconfined; , the fine grained dep he low e ta 1 Zone and Upper B Zone (also known as me AID ayurd) loony create confining conditions. Although o there is good continuity of the confining layer across Sharpe, groundwater and dissolved wnmmients can move from the A Zone through the B Zone and into the C Zane because the confining layer in some amas is thinner and contains m ve be ore sand and because there haw strong vertical hydraulic gradients I � caused by pumping of on Report and offaepot water supply wells. The B, C, and D Zones have hydraulic 4 characteristics of leaky confined aquifers. Subsurface soils vary from clayarvl slit to coarse sand. Within each of the zones, deposits containing each of the soil types can be found; however, the deposits vary in thickness vertically and horizontally across Sharpe.Silt and on are the dominant soil types beneath Sharpe,and those deposits are interbelded with sands. The deposit that apparently he the greatest continuity conies of a mix of clay and silt with thin AminFnwranmenzW, Im, 2