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Rainwater Harvesting Legal Framework Page 5 B. Rainwater Harvesting Pilot Project Process Using Regional Factors Project sponsors in areas where Regionally Applicable Factors (Factors) have been adopted by CWCB can follow a process similar to Section A but may opt to rely on the Factors rather than collecting two years of site-specific data for a site-specific estimate of historic natural depletion. The reliance on Factors allows an applicant to operate and beneficially use the historical natural depletion amount without collecting two years of climate and operation data with 100 percent replacement. For a proposal that will rely on the Factors, once step 2 of Section A (Document Plan) is completed, the sponsor may move to step 5 of Section A (Operate with Natural Depletion Credit) (see also flowchart, attached). As described in section 37-60-115(6)(b)(VI), the Factors "specify the amount of precipitation consumed through evapotranspiration of preexisting natural vegetative cover". Existing documentation by Denver Urban Drainage and Flood Control District and others has led to a broad understanding of the relationship between rainfall and runoff from different types of surfaces for rainfall of varying intensity and duration. Precipitation is partitioned between runoff that quickly returns to the stream and infiltration. Infiltrated water will either be trapped in soil moisture storage or deep percolation to become a groundwater return flow. Infiltrated water trapped in soil moisture storage is available for plant ET. In this case, the ET amount, which is the majority of infiltrated water, would be the historical natural depletion. Using the Factors described in the Criteria and Guidelines, a project sponsor would use the template accounting for the surface conditions at their site in order to quantify the historical natural depletion credit that can be beneficially used without replacement after any given storm event within their development area. Section 37-60-115(6)(b)(VI) describes, "If an applicant uses the factors, the state engineer shall give the factors presumptive effect, subject to rebuttal." Within section 37-60-115(6) and the Criteria and Guidelines, the Factors are described only in the context of an SWSP. Therefore, the Factors do not have a presumptive effect with the water court for augmentation plans. In fact, in regards to decreed augmentation plans for rainwater harvesting, section 37-60-115(6)(c)(II)(A) requires that the amount of historical natural depletion be proven "by a preponderance of the evidence ,7. Therefore, a system may operate pursuant to an SWSP using the Factors but would likely need to rely on a site-specific data to operate permanently pursuant to an augmentation plan. C. Unique SWSP Application Requirements for Rainwater Harvesting The existing guidance available for SWSP submittals is generally applicable to rainwater harvesting projects. The following lists additional requirements for rainwater harvesting SWSP applications: 1. Summarize the overall rainwater harvesting and stream replacement operation. The statutes and Criteria and Guidelines only describe the Factors in terms of their use and acceptance in the SWSP / pilot project process but stop short of precluding use of the factors in an augmentation plan.