(1) All unmitigated impacts from the consumptive use of water from the reserves and impacts from implementation of ecology approved mitigation plans shall be debited against the maximum depletion amount for each affected subbasin.

(2) The maximum depletion amounts shall not be exceeded.

(3) No new use that would result in impacts to closed surface waters exceeding the maximum depletion amounts during the critical period shall be allowed. If the cumulative impact calculated for a subbasin exceeds the maximum depletion amount, additional mitigation must be achieved before new uses impacting that subbasin can be authorized.

(4) Ecology shall maintain a record of all appropriations that result in deductions against the maximum depletion amounts. Ecology will account for water use from the maximum depletion amounts by debiting the calculated impact to each closed surface water. The impacts to surface water are calculated as a percentage of the consumptive portion of estimated or measured water use. The deductions from the maximum depletion amounts will be determined after consideration of any implemented mitigation.

(a) For parcels served by an individual or community septic system, ten percent of indoor water use is assumed consumptive.

(b) For parcels served by a sanitary sewer system, one hundred percent of indoor water use is assumed consumptive.

(c) Ninety percent of outdoor water use is assumed to be consumptive.

(d) Impacts to the closed surface waters listed in Table III will be calculated using the 2008 Dungeness Groundwater Flow Model (Pacific Groundwater Group, 2009), unless, in the future, ecology determines a better method is available.

(e) The amounts deducted against the maximum depletion amounts may be adjusted periodically by ecology, to reflect actual use based on the best information available.

(5) Maximum depletion amounts are associated with, and not in addition to, the reserve amounts listed in WAC 173-518-070. Table V shows the maximum depletion amounts for each subbasin management unit.