Ordinance -- Page 5 of 9 <br />RESPONSE: The standard factor of safety for design infiltration rates is 2, which means that <br />whatever field-tested infiltration rate was determined, that number is divided by two in order to <br />design the infiltration facility. If we are now saying that facilities must be considered infiltration <br />facilities with an infiltration rate of only 0.6 inches per hour, that means that the design infiltration <br />rate will be 0.3 inches per hour, and therefore will mean that the infiltration facility will need to be <br />excessively large in order to mitigate stormwater runoff, proportionately speaking. Infiltration <br />facilities do not have underdrains that allow stormwater runoff to quickly drain into an approved <br />point of discharge, which means that these infiltration facilities that have a lower infiltration rate will <br />likely become overburdened by stormwater runoff. The previous codified infiltration rate of 2 inches <br />per hour was a much more appropriate rate for infiltration facilities. Realistically speaking, many <br />filtration facilities are designed as infiltration facilities, as they do not have a bottom liner. But to not <br />have some sort of underdrain in low infiltrating soil is not a good idea and will likely lead to the <br />failure of many facilities. <br /> <br />2b. Bedrock is less than 5 feet below the ground surface; <br /> <br />3c. Groundwater elevations are less than 6 feet below the ground surface; or, <br /> <br />4d. Ground surface slopes are greater than 10%. <br /> <br />2. If subsection (3)(b)1 exempts infiltration, extended filtration (filtration through <br />natural or engineered media) shall be utilized to treat the water quality design <br />storm runoff from the impervious surface areas. <br /> <br />3. If the development site has insufficient land area to construct an infiltration or <br />extended filtration facility to treat the water quality design storm runoff without <br />reducing the size of the proposed development, and the proposed development is <br />otherwise consistent with all other applicable lot and development standards, the <br />applicant shall demonstrate that there is insufficient land area by submitting a <br />report that includes a site plan of the proposed development and the required <br />sizing of the stormwater quality facility based upon the water quality design storm <br />requirement. <br />RESPONSE: What sort of OBJECTIVE criteria is used to evaluate whether an applicant has <br />demonstrated that there really is an “insufficient land area”? I have worries that this criteria is far <br />too subjective to be enforced with any sort of consistency. How does this language take into <br />account the landscaping standards, which currently does not align very well to allow stormwater <br />facilities count toward minimum landscape areas? What does “insufficient” mean? <br /> <br />(c) An applicant that makes the demonstration required by subsection (3)(b)3 will be <br />subject to the Low Impact Development component of the City’s system development <br />charge improvement fee, including any system development charge credit for an approved <br />on-site mechanical treatment facility. <br /> <br />(b) For land use applications proposing the construction of a public street, stormwater <br />quality facilities to treat the stormwater runoff from the proposed public street shall be <br />selected from the Stormwater Management Manual and shall be based on the following <br />priority order: infiltration, filtration, mechanical treatment. <br /> <br />1. If selecting an infiltration or filtration facility to treat the stormwater runoff from the <br />public street, the facility can be sized to also treat the stormwater runoff from the single-