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C20-2023-030 ORDINANCE AMENDMENT REVIEW SHEET Amendment: C20-2023-030 Site Specific SOS amendment Description: Amends Land Development Code (LDC) 25-8 Article 13 Save Our Springs Initiative of the Land Development Code as it relates to impervious cover limits and water quality treatment for proposed development on a 2 lot subdivision at 1905 & 1908 Airole Way. Proposed Language: Consider an ordinance regarding a site-specific amendment to City Code Chapter 25-8, Subchapter A, Article 13 (Save Our Springs Initiative), as minimally required to address development related to the proposed resubdivision and development at 1905 and 1908 Airole Way. This action concerns land located in the Barton Springs Zone. Summary of proposed code amendment The amendment under consideration is related to proposed development and resubdivision of two platted residential lots at 1905 (Lot 19) & 1908 (Lot 18) Airole Way and an unplatted lot (Tract 2) in the Barton Hills neighborhood. The property is located in the Barton Creek Watershed, in the Barton Springs Zone, and within the recharge zone of the Edwards Aquifer, which pursuant to current city code and the Save Our Springs (SOS) ordinance, requires non-degradation water quality treatment for all development and impervious cover limited to 15% Net Site Area (NSA). The proposed development of the site includes the renovation and expansion of an existing historic residence on the combined area of Lot 18 and Tract 2, and construction of a new residence on the currently undeveloped Lot 19. The existing total combined area of the site (Lot 18, Lot 19 and Tract 2) is 0.55 acres (24,023 sqft). The SOS ordinance would limit the total impervious cover for the subdivision to 15% NSA (0.0539 acres or 2348 sqft). The proposed SOS amendment requests an impervious cover limit of 32.9% Gross Site Area (GSA) (0.1818 acre or 7920 sqft). Additionally, single family residential make it difficult to meet SOS non-degredation water quality control requirements so the proposed SOS amendment also includes a request to allow the project to meet water quality treatment requirements by providing rainwater capture of ½” off the roof. Lastly, because LDC 25-8-515 prohibits variances from the SOS Ordinance, a site-specific amendment to the SOS Ordinance approved by a supermajority of the City Council is necessary to allow the proposed resubdivision and associated development of 1905 & 1908 Airole Way. The proposed site-specific SOS amendments are being requested to allow the following improvements: • Renovation and expansion of an existing historic A.D. Stenger home 1 12 C20-2023-030 - Airole Way Site Specific SOS Amendment1 of 9C20-2023-030 • On-site water quality controls where none currently exist using a rainwater harvesting • Landscaping around the home utilizing native plants and trees with enhancement to cistern and infiltration areas. the quality of existing vegetation. Background: On September 14th, 2023, City Council approved Resolution No. 20230914-079 to initiate variances and amendments to the Land Development Code, including site-specific amendments to Chapter 25-8, Subchapter A, Article 13 (Save Our Springs Initiative) as minimally required to address development related to the proposed resubdivision and development at 1905 and 1908 Airole Way. The existing lots at 1905 & 1908 Airole Way were platted before the adoption of the SOS ordinance and are not currently required to comply with its requirements. The proposed resubdivision of 1905 & 1908 Airole would add the unplatted Tract 2 to Lot 18 and adjust the lot line separating Lot 18 & 19, resulting in the vacation of vested rights for both lots. The applicant is proposing a site-specific SOS amendment to allow for the proposed development of the resubdivided lots while providing on site water quality treatment, native plantings, and renovation of a historic home. Staff Recommendation: Staff recommends approval of the proposed amendment and associated variances for the following reasons: • Provide onsite water quality controls that will capture the first ½” of runoff from 4,651 sqft of roof area from both lots combined; designed and maintained per the Environmental Criteria Manual. • Direct site runoff to the flatter portion of the site and away from the steep hillside to reduce erosion and sedimentation of the waterways. • Utilize native plants and trees to reduce water demand and fertilizer usage which will limit runoff and pollution. • Reduce current allowable Impervious Cover by 500 sf. Board and Commission Actions December 6th, 2023, Recommended for approval by Environmental Commission, 6-0-1, Brimer abstaining. December 13th, 2023, Recommended for approval Codes and Ordinances Joint Committee. 5-1, Commissioner Stern against. January 9th, 2024.Considered by Planning Commission Council Action Feburary 1st, 2024: A public hearing will be scheduled. Ordinance Number: TBD City Staff: Leslie Lilly Phone: (512) 535-8914 Email: Leslie.lilly@austintexas.gov 2 12 C20-2023-030 - Airole Way Site Specific SOS Amendment2 of 9Exhibit 1. Existing Conditions for 1905 & 1908 Airole Way, and Tract 2 C20-2023-030 Exhibit 2. Proposed Resubdivision and Development 3 12 C20-2023-030 - Airole Way Site Specific SOS Amendment3 of 95906 Old Fredericksburg Road Suite 300 Austin, Texas 78749 (512) 301-3389 www.tdi-llc.net December 8, 2023 Mr. Eric Erickson Erickson Builders, Inc 2002 Arthur Lane Austin, Texas 78704 RE: Water Quality and Sustainability Memo Resubdivision of Lots 18, 19, A.D. Stenger Add. Austin, TX (TDI# 1148-103.1) Mr. Erickson: The existing 2 lots, 18 and 19 (1908 and 1905 Airole Way), can currently both be developed to 45% impervious cover without any water quality features. In order to avoid demolition of the existing home it is desired to add to the rear of the home on lot 18 onto “tract 2” which is not platted. By city of Austin rules, this requires a re-subdivision, the rules for which treat the land as if it has no current rights and applies all current requirements to all portions of the land. Therefore, adding this tract triggers water quality provisions across all lots as well as limits the allowable impervious cover to 15% of the Net Site Area. Practically this would require water quality pond and would limit the allowable development to less than the area already taken by the single house that exists on the 2 lots. It is proposed that a site-specific amendment be made to the Land Development Code that allows for the development of the 2 lots, while adding in “tract 2”. The proposal is to bring in the additional tract without increasing the current allowable impervious cover and also provide some Water Quality mitigation above that which is currently required on the 2 existing lots. This will provide an increase in environmental protection over building on the 2 existing lots while also allowing the current house to be reused rather than demolished. In order to provide water quality while enabling development that maintains the existing structure, it is proposed to: 1) Direct site runoff to the flatter portion of the site and away from the steep hillside to reduce erosion and sedimentation of waterways 2) Utilize native plants and trees to reduce watering demand and fertilizer usage which will limit runoff and pollution 3) Reduce allowable Impervious Cover from current values by 500 sf. 4) Provide on-site controls capturing roof runoff sized to capture the first half-inch of runoff from portions of new the roof area of lot 18A and 19A. Provide maintenance and inspections of the water quality facilities in accordance with the standards and schedules in the ECM. THINK DESIGN innovate, integrate, implement… 1 of 4 12 C20-2023-030 - Airole Way Site Specific SOS Amendment4 of 95906 Old Fredericksburg Road Suite 300 Austin, Texas 78749 (512) 301-3389 www.tdi-llc.net Impervious Cover The 2 lots (18 and 19) and “tract 2” total 0.5515 acres and the current (pre re-subdivision) allowable impervious cover (IC) is 0.1933 acres. The proposed (post subdivision) IC via amendment is 0.1818 acres, resulting in 500 sf less IC, see Table 1. in Without Re-subdivision Table 1 – Allowable Impervious Cover (IC) Areas acres Lot Gross Area NSA Allowable IC Tract 2 0.1603 Lot 18 0.1943 Lot 19 0.1969 NA 45% GSA 0.0874 0.1153 15% NSA 0.0173 NA 45% GSA 0.0886 IC percentage without Re-Subdivision Lot Allowable IC IC percentage of Amendment By Rule Total 0.5515 Lot 18A Lot 19A Total 0.1556 0.3959 0.5515 0.2684 15% NSA 0.0403 0.0909 15% NSA 0.0136 0.0539 0.1933 35.1% Amendment (Proposed) Lot 18A Lot 19A Total Amend- ment 0.1250 31.57% Amend- ment 0.0568 36.50% 32.96% 0.1818 The existing and proposed IC on lots 18A and 19A (post subdivision) are presented in Table 2. Existing Proposed Lot 18 Tract 2 Lot 19 Lot 18A 1,314 Table 2 – Existing and Proposed IC Areas in sf Lot Existing Roof New Roof Existing Drive 476 New Drive Existing Other 883 New Other Contingency Total Total (acres) 2,673 0.0614 0 0 1,314 3,065 423 340 302 0 5,444 0.1250 Lot 19A Total 1,314 4,651 1,586 423 517 517 340 675 373 0 0 7,920 2,476 0.1818 0.0568 THINK DESIGN innovate, integrate, implement… 2 of 4 12 C20-2023-030 - Airole Way Site Specific SOS Amendment5 of 95906 Old Fredericksburg Road Suite 300 Austin, Texas 78749 (512) 301-3389 www.tdi-llc.net Water Quality The 2 lots (18 and 19) don’t currently (pre re-subdivision) require any Water Quality Controls. The proposed new Water Quality Controls are for lot 18A and would capture the first ½ inch of rainfall runoff from the new roof area on lot 18A. The proposed new Water Quality Controls are for lot 19A and would capture the first ½ inch of rainfall runoff from 90% of the new roof area on lot 19A On lot 18A, In order to capture the first ½ inch of new roof runoff, a cistern of 1,000 gallons will be provided (3,206 sf of new roof x 0.5 inches / 12 in per foot x 7.48052 gallons per cf). It is proposed to hold the runoff for 12 hours and then pumped out over 108 hours for a total of 120 hours after a rain event. The captured runoff will be irrigated into areas that are less than 15% slope and that total 1,500 sf or less, based on the infiltration rate of the soil. On lot 19A, In order to capture the first ½ inch runoff from 90% of new roof, a cistern of 500 gallons will be provided (1,586 sf of new roof x 0.5 inches / 12 in per foot x 7.48052 gallons per cf). It is proposed to hold the runoff for 12 hours and then pumped out over 108 hours for a total of 120 hours after a rain event. The captured runoff will be irrigated into areas that are less than 15% slope and that total 750 sf or less, based on the infiltration rate of the soil. Based on the City of Austin Watershed Protection Departments, “Stormwater Load Analysis Tool (SLAT)” the pollutant load leaving the site is presented in Table 3. The SLAT calculations are attached to this Memo. The proposed pollutant loads are shown to be reduced by 39% to 50% of the maximum loads that could be experienced from the site without a re-subdivision. THINK DESIGN innovate, integrate, implement… 3 of 4 12 C20-2023-030 - Airole Way Site Specific SOS Amendment6 of 95906 Old Fredericksburg Road Suite 300 Austin, Texas 78749 (512) 301-3389 www.tdi-llc.net Table 3 – Pollutant Load (per SLAT 2.1.) Areas acres (A) Existing in (C) Rule By (D) Amendment (Proposed) Reduction 100% -D/B (B) Without Re- subdivision 0 0% 0.1933 35.055% None IC base IC developed WQ controls 0 0% 0.0614 11.126% None COD E. coli Pb TN TP TSS Zn  2.36E+01 4.88E+04 3.45E‐03 9.58E‐01 1.71E‐01 7.16E+01 1.78E‐02  6.93E+01 1.18E+05 1.25E-02 2.32E+00 4.13E-01 1.73E+02 6.18E-02  Sustainability 0 0% 0.0539 9.771% Per ECM 4.90E-01 1.02E+03 5.87E-05 2.40E-02 4.27E-03 1.34E+00 3.15E-04  0 0% 0.1818 32.963% ½” new roof runoff Lot 18A & 90% 19A 3.88E+01 7.24E+04 6.22E‐03 1.51E+00 2.69E‐01 1.03E+02 3.45E‐02  44%  39%  50%  35%  35%  41%  44%  Allowing this project to proceed as proposed will increase sustainability in the following ways: 1) Provide for revitalization of the old home while avoiding the majority of demolition otherwise required by the limited site area, thus reducing waste to landfills Please contact me at with any questions. Sincerely, Jeff Shindler, P.E. Principal THINK DESIGN innovate, integrate, implement… 4 of 4 12 C20-2023-030 - Airole Way Site Specific SOS Amendment7 of 9 ENVIRONMENTAL COMMISSION RECOMMENDATION 20231206-003 Second by: Mariana Krueger Date: December 6, 2023 Subject: Airole Way Site Specific SOS Amendment C20-2023-030 Motion by: Jennifer Bristol WHEREAS, the Environmental Commission recognizes the applicant, in response to Council Resolution 20230914-079, consider a site-specific amendment to City Code Chapter 25-8, Subchapter A, Article 13 (Save Our Springs Initiative), as minimally required to allow for the resubdivision and proposed development of the lots located at 1905 and 1908 Airole Way. WHEREAS, the Environmental Commission recognizes the site is located in the Barton Creek Watershed and the Barton Springs Zone; and WHEREAS, the Environmental Commission recognizes that staff recommend this Site Specific SOS Amendment with conditions, THEREFORE, the Environmental Commission recommends the requested Site Specific SOS Amendment with the following: Staff Conditions 1. Development proposed for 1905 and 1908 Airole Way shall comply with 25-8, Subchapter A, Article 13 (Save Our Springs Initiative) at the time of permit application except as modified below. a. Section A of 25-8-514 (Pollution Prevention Required) shall be modified to allow a maximum impervious cover for the site of 34.7% gross site area. b. Section A of 25-8-514 (Pollution Prevention Required) shall be modified to allow water quality control requirements to be satisfied with on-site controls capturing roof runoff. Water quality controls shall be sized to capture the first half-inch of runoff from 4792 square feet of roof area from both lots combined. The water quality control shall be designed and maintained per the Environmental Criteria Manual to discharge the water quality volume within 120 hours through an irrigation or infiltration system. 2. Additionally, development proposed for 1905 and 1908 Airole Way shall comply with the following requirements: a. Direct site runoff to the flatter portion of the site and away from the steep hillside to reduce erosion and sedimentation of the waterways. b. Utilize native plants and trees to reduce water demand and fertilizer usage which will limit runoff and pollution. c. Reduce current allowable Impervious Cover by 87 square feet. Environmental Commission Conditions 1. Reduce current allowable Impervious Cover by 500 square feet. Vote: 6-0 12 C20-2023-030 - Airole Way Site Specific SOS Amendment8 of 9 For: Perry Bedford, Jennifer Bristol, Mariana Krueger, Haris Qureshi, Melinda Schiera, and David Sullivan Against: None Abstain: Richard Brimer Absent: Hanna Cofer, Peter Einhorn, Colin Nickells, and Kevin Ramberg Attest: Kaela Champlin Environmental Commission Liaison 12 C20-2023-030 - Airole Way Site Specific SOS Amendment9 of 9