SUBJECT:
Title
Fawn Lake Estates - Improvement Plan - 001215 - Waiver Request to Improvement Plan in Review
Parcel #: 9027-0000-02 #WaiverPIR-001428-2026
Tillman & Associates Engineering, LLC
LDC 6.13.6.A(3)(c) Stormwater quality criteria
CODE states Dry retention systems that have a depth of six feet or less, measured from top of bank to pond bottom, with side slopes that are no steeper than 4:1 and sodded bottoms;
APPLICANT requests a waiver for 7' pond depths. The proposed ponds are 7' deep with 4:1 sodded side slopes and bottoms. The additional 1' of pond depth is not a significant departure from code criteria, which limits pond depths to 6'. DRA’s 1, 2 and 3 are dry retention ponds with overflow elevations at 5.0 ’depth in DRA’s 1 and 2 and overflow depth of 4.0’ in DRA 3. DRA's 1 & 2 have a total depth of 7.0' and DRA 3 is 6.0' deep. DRA’s 1A, 2A and 3A are wet detention ponds with a total depth of 4.5’ deep from the control elevation to the overflow of the wet detention ponds and a total wet pond depth of 6'. This project is within an open drainage basin, and extra depth was needed for attenuation of the rate of discharge.
LDC 6.13.7(B)(2) Geotechnical criteria
CODE states Number of tests. At least two tests shall be performed within the boundary of each proposed retention/detention area. For each half acre of pond bottom area and for each lineal retention/detention area of 250 feet, an additional test shall be conducted. The County Engineer or his designee, may require additional tests if the initial tests indicate the need for them.
APPLICANT requests to allow only one boring and permeability test per pond area based on the proximity of the DRA’s 5a and 5b to each other and similar results in the permeability of these strata of soil. Both DRA’s are being constructed at grade and will remain in the same strata of soil, and we have applied a safety factor of two to those field measured permeabilities.
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