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of the CCR. A copy of these specifications can be found Appendix "C" of this report. The regulation states that all on-site construction within 1,000 feet of the boundary of any disposal areas shall be designed and constructed to prevent gas migration into a building, unless an exemption has been issued. The United States Department of Agriculture - Natural Resources Conservation Service (USDA- NRCS) shows the on-site soils to consist mostly of San Joaquin sandy loam (#237). The Unified Soil Classification System (USCS) identifies the surface soils as a silt and silty clay (ML and CL-ML). According to the USDA Handbook, the surface layer is a brown sandy loam with a claypan of brown clay below this surface soil. Extending from 20 inches to 60 inches is Iight brown hardpan of cemented silts and clays. The main limitations with these soils are the very slow permeability in the substratum. Since the subject property has not been in agricultural production, an evaluation of environmental fate data for agrichemical residues as a nonpoint source of potential contamination was not done. The science of pesticide residues in soil, air, surface water and groundwater is extremely complex and variable. Environmental models that attempt to predict pesticide behavior and transport in the environment are beyond the scope of this investigation. Since the three vacant Parcels are proposed to be developed into single family residences (SFR), pesticides with long half-lives that nay have been applied decades ago to surrounding properties and drifted onto the subject property, primarily DDT, may be of an extremely slight concern. It is a possibility that DDT was applied to surrounding properties in the 1940s, 1950s and possibly 1960s before it was banned in 1972. DDT was used extensively throughout the agricultural fields of the San Joaquin Valley and degradates of DDT are round in virtually all of these soils. Previous Exposure Assessments made on typical San Joaquin Valley soils suggest an extremely low probability of adverse health effects from soil DDT/DDD and DDE concentrations (if the concentrations even exist). It is important to note that the surface soils currently in-place will undergo significant and considerable physical and chemical changes during project development. These alterations include increases in ultraviolet light exposure, moisture content and aeration. It can be reasonably concluded that the DDT, DDE and DDD concentrations will continue to degrade (if they exist) as reported in the published environmental fate data. The environmental fate data for DDT and its degradates DDD and DDE are illustrated below: DDT. Common name: Agritan, Anofex. Azotox, et al. Half-lives in the environment: Air: 17.7 -177 h. Surface water: 73.9 h for a pond 1 in deep. Degradation half-life of about 10 yr - average from loss rates determined in Lake Michigan. Groundwater: 16 d to 31.3 yr. Sediment: 3 to 5 yr Soil: 2-15.6 yrs based on observed rates ol'biodegradation in aerobic soils under field conditions. Avg. half life of-12 yrs in 3 different soils for --50 ppm in soil. Page -4- Chesney Consuftit&