Agenda - 03-17-2009 - 7a - Laserfiche WebLink

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22 transport factors. The transport factors describe the attrition of nutrients as they travel down through a subwatershed. If the local export was reduced by 8%, the delivered Toad would also be reduced by 8°~. The local export and delivered load would not be the same "mass," but they will be the same `percent mass." Can the DWQ provide some Gariflcation? 4. The cost estimates for additional regulatory transactions on the part of [oval governments for new development (pg. 35) and for riparian buffer protection are significantly under- estimated. Cost estimates assume negligible costs for additional regulatory transactions on the part of local governments for new development (pg. 35) and for riparian buffer protection, partly because local governments already have programs that deal with new development stormwater controls and stream buffer protection to some degree. However, the Jordan Rules for new development stormwater treatment and r-iparian buffer protection are sufficienily different in many ways, and much more strict in other ways, to require extra time and effort from local jurisdictions for increased inspection and enforcement costs (in order to ensure compliance, which is the responsibility of local governments), increased plan review costs (experience has shown that more complex engineering calculations require significantly more plan review), and increased public education and outreach. 5. Cost calculations for new developments use a weighted average for the entire Jordan watershed, rather than different calculations for the different subwatersheds (pg. 37). This greatly underestimates costs for those in the Upper New Hope Arm subwatershed and overestimates costs for others. 6. In the section concerning new development, the calculation methodology assumes no regulatory costs to developers in 2009 or 2010 (for some reason they are merged with riparian buffer protection -but not all riparian impacts happen in the course of development) (pg. 49}. However, prudent jurisdictions are likely to attempt to modify their development ordinances to approximate the expected stormwater program rules in order to minimize the amount of retrofitting they have to. do to very new developments. Similarly, it assumes there will be no maintenance costs for BMPs in 2009 and 2010 as well (pg. 46). 7. In the section concerning new development, costs are likely underestimated for Chapel Hill as proportionately more of its development will be moderate-to-higher density residential and mixed development, incurring much greater treatment requirements (average TN load 15.0 Ib/acJyr) than for residential (average TN load 4.04 Ib/ac/yr) (pg. 40}. A likely unintended side effect of the nutrient management strategy encourages. sprawling residential development over compact forms that set aside open space because the nutrient treatment requirement is so much greater for compact development. 8. Cost calculation methods for new development also used an allowable nitrogen value of 3.66 Ib/aclyr, higher than the 2.2 Ib/ac/yr that Upper New Hope Arm (UNHA) developers will be allowed (pg. 40). Using the designated UNHA target, developers will have to treat up to 85°~ of nitrogen coming off their sites. With an average BMP efficiency for nitrogen of 36%, and the problems of using BMPs in series (lower BMPs in series only remove a portion of what is left), developers would have to install a minimum of three BMPs to get down to the 4.0 Ib/ac/yr threshold for buying nitrogen credits and would have to use five BMPs per acre to get below the ultimate 2.2 Iblaclyr goal. Even residential, with 113 acre ,lots, would require two BMPs per acre. Calculations only use a single BMP cost- effe~iveness value, which you can only assume if you use only one BMP. BMPs in series will have progressively poorer cost-effectiveness. Treatment efficiencies for BMPs are Page 7 of 9