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MOUNTAIN HOUSE PROPOSED MACHADO TENTATIVE MAP 4. ENVIRONMENTAL CHECKLIST 4.7 HAzARDs L b) Create a significant hazard to the public or the environment through reasonably foreseeable upset and accident conditions involving the release of hazardous materials into the environment? L The project site was formerly used for a dairy and irrigated pasture land. Pesticides, herbicides,and equipment fuels used in dairy operations have been used and stored on the site since 1950. The SPIIIEIR identified the agricultural chemicals used within the Specific L Plan III area over the years and indicated that most of these chemicals have half-lives less than 14 days after application with the exception of paraquat,which has a half-life of more than 1,000 days (23/4 years)(EDAW, 2005b). In addition,the MEIR identifies r organophosphorus as a possible agricultural chemical with a long decay time, and that application should cease several months to two years prior to construction of houses at Mountain House Community. 6. It is possible that other potentially hazardous materials could be disturbed or handled during construction of the proposed project. In addition, conditions resulting from the historic use of the Machado property, as a dairy and pasture land and the existence of the former Shell oil pipelines, could create a significant hazard to the public or the environment. The Limited Phase R Environmental Site Assessment and Surface and Subsurface Contamination Report for the Machado property found the following hazards: r • Manure and manure-impacted soils that create high nitrate levels in groundwater exist at the site of the former dairy. These soils would have to be removed for proper disposal before the RWQCB would issue a closure permit for the dairy. • Groundwater beneath the dairy is contaminated with high nitrates,total dissolved solids, ` and electrical conductivity levels. Contaminated groundwater could impact groundwater quality down-gradient(i.e., to the northeast) of the Machado property. • Organics and redoxymorphic soils line the sides of dairy ponds and ditches. These ►. organics and soils could create explosive methane gas and cause geotechnical design concerns. The contaminated soils should be removed for proper disposal. 6. • Dead cows may be buried on the dairy site. If so, the carcasses and skeletons should be located and exhumed for proper disposal. • Motor oil in concentrations over 1000 milligrams/liter(mg/1)was found in three surface V, soil samples at the dairy. The contaminated soils should be removed for proper disposal. • Soil contamination from the former Shell oil pipelines that cross the Machado property from northwest to southeast was found at 14 sites along the pipeline alignment, 6. particularly southwest of the dairy settling pond. These soils should be excavated, tested, and disposed of(if necessary) as proposed by Shell Oil Products US and documented in the Remedial Action Plan (SAIC, 2006). ho • There is one well and two septic tanks at the dairy that will have to be properly L • abandoned. The well should be abandoned in conformance with California Department of Health requirements. The septic tanks should be abandoned in conformance with San Joaquin County Environmental Health Department(SJCEHD)requirements. L 4-37 L