This date was chosen so that wells that were in existence in 1990 would be included, to better match the 1990 census survey. The date the well was drilled was also recorded when available, but it was not used as a criterion. As a result, some wells that were drilled after 1990 could be included. The decision to include these wells was based upon the desire to capture as many domestic

wells as possible that existed from 1990 to present. Estimating the location SD-208 of domestic wells was accomplished by using the information gathered from the plotting, sampling, and coding of digital WCRs collectively called the “well-log survey”. The results from the well-log survey were downscaled from the PLSS township scale to the section scale. The downscaling method assumes that the number of domestic wells in a township is proportional to the number of domestic wells in each section within that township. For any given township, the number of domestic wells identified

by the analysts was divided by the total number of WCRs viewed by the analysts (both accepted and rejected) regardless of well or image type, to create a ratio of domestic wells to WCRs, hereafter called the “township ratio” (TRt):(TRt): equation(1) TRt=DWtWCRtwhere DWtDWt is the number of identified domestic wells within a township and WCRtWCRt is the number of WCRs viewed within a township. For example, if there were 48 WCRs in a township, seven were rejected, and five were accepted RGFP966 chemical structure with three being domestic wells, TRtTRt would equal 0.25 because three of the twelve viewed WCRs were domestic wells. The township all ratio was used to estimate the number of domestic wells per section (DWs)(DWs) by multiplying TRtTRt by the total number of WCRs located in that section (WCRs);(WCRs); equation(2) DWs=TRt×WCRsDWs=TRt×WCRs

For example, if a PLSS section contained 15 wells, and the TRtTRt for the township that the section belonged to was 0.2, then the section would be estimated to contain 3 domestic wells. This process was used to assign each section a number of domestic wells. Finally, the number of domestic wells within a section were divided by the area of the section (the size of each section varied slightly), forming a density (ρWs);(ρWs); equation(3) ρWs=DWsAswhere As = total area of the section. This density calculation was then used to aggregate to other geospatial boundaries, such as Groundwater Units, described is Section 2.3. The well-log data provided by DWR was incomplete in San Luis Obispo (SLO) County. Therefore, an alternative method to estimate the distribution of domestic wells in SLO County was developed.