Letter Regarding Cumulative Effect Report for Colorado's Plan for Future Depletions

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wells. In the future SPWRAP plans to work with other augmentation plans /recharge groups upstream of Sterling to the Morgan - Washington County line. All of these plans have been decreed in Colorado Water Court and accounting procedures are reviewed by the Division Engineer's office. Inflows to all recharge areas are recorded with flumes and meters approved by the Water Commissioner and pond evaporation is subtracted per decreed procedures. Net pond evaporation in the winter months is typically around 2;% of inflows. All recharge areas have decreed groundwater flow parameters (i.e., river and boundary distances, harmonic transmissivity, specific yields or SDF values). The decreed AWAS (Alluvial Water Accounting System; I)ttp ids. colostate .edu /index.11tail ? / projects solatt software utilizing Glover methodology developed by the Integrated Decision Support Group -IDS at CSU is used to compute the lagged groundwater return flows /accretions for the net groundwater recharge at the ponds (i.e., net recharge is measured inflows minus net pond evaporation). Table 4 is a summary of the mitigation accounting for the initial reporting period of 2007 and 2008. Block 1 of Table 4 lists on an irrigation year (Nov -Oct) basis the accretions from the CPFD analysis and the depletions in May /June (depletions are those from Figure I and 1B). CPFD accretions are utilized at the Tamarack SWA recharge project (Block 2) with any remaining CPFD accretion (Block 3) utilized prorata in the other recharge projects. Block 4 of Table 4 lists the total net recharge in the other recharge projects while Block 5 lists the amount of the remaining CPFD accretions after Tamarack -SWA diversions that are diverted by the other projects. Block 6 shows that not all diversion by the other projects are counted or "colored" as coming from CPFD accretions. Block 7 computes the quantity of CPFD accretions utilized and shows that most all are diverted. Block 8 is the output from the AWAS groundwater model and lists the lagged groundwater return flows from the recharge of the CPFD accretions with totals for May /June. These lagged return flows from recharging CPFD accretions are from recharge activities starting in 1998 and following these same accounting procedures of "coloring" actual net recharge diversions as CPFD accretion water. For 2007, 2008 the average May /June replacement was 2,502 acre -feet, which on an average annual basis adequately replaces the May /June average CPFD deficit of 1,642 acre -feet listed in Block 1. Replacements are higher in 2007 because it was a wetter May /June and the other augmentation /recharge plans had more excess because their augmentation needs were less. Lagged groundwater return flows from the recharge of CPFD accretion return to the river in all months. As noted in Block 1 and 8 of Table 4, some of these return flows in March 2007 and March 2008 are rediverted by the projects further downstream if they have remaining capacity in an effort to "recycle" more of the CPFD accretion water and have it return in the May /June months for CPFD depletion mitigation. Note that the reason the CPFD has depletive effects in May and June is because the main diversion of native South Platte flows under junior water rights occurs in these two months of snowmelt runoff. The CPFD analysis as described earlier is based on an average 2005 -2009 call scenario for the determination of an average water source percent from new native South Platte flows but it is the wetter years like 2007 where more diversions under a junior water right will occur so having more replacement in 2007 as shown in Table 4 Block 8 is a good mitigation buffer. The CPFD analysis will be updated if a running average on calls indicate a consistently wetter or drier period average than assumed for 2005 -2009. 7