City of Dripping Springs City Council
511 Mercer Street
Dripping Springs, Texas 78620
Dear Honorable Mayor Todd Purcell:
The three engineers previously engaged by The Friendship Alliance (FA) for this project have reviewed the Mark Black Wedding Venue (MBWV) design documents submitted with a letter from Kimley-Horn dated February 19, 2018. These documents were produced by the applicant in response to the February 12, 2018 letter from Dripping Springs’s (DS) City Engineer, Mr. Chad Gilpin, which included five “specific items that are being requested by the City to be included in the Site Development Plan Set and/or Engineering Report to address the FA letters”. Four reports from FA engineers were also referenced, which were provided to Kimley-Horn by the City.
The FA engineers (Brian Dudley, P.E., Lauren Ross, PhD, P.E., and Jeff Kessel, P.E.) have determined that the newly produced Kimley-Horn materials are unresponsive to the City Engineer’s letter and the other engineering review reports referenced therein. The deficiencies that remain in the Site Plan are summarized below in the order of the comments contained in the City Engineer’s letter, dated February 19, 2018. Additional details are provided in the attached FA engineers’ reports. The project remains materially out of compliance with the City ordinance provisions listed at the end of this letter.
Items requested by the City are listed below and followed by our summary review comments:
- Final design for Curb Inlet/Bay‐Filter system that you volunteered to add to address a specific FA concern. Basic design was previously shown in supplemental data.
Sheet 41: Curbs adjacent to inlets need to be labeled and the drainage area serving the curb inlets needs to be correctly delineated (including the handicapped parking area downgrade from BF-1 and the roadway containing a ditchline downgrade from BF-2).
In reviewing the Bay Filter performance tables on Sheets 37, 38 and 43 (2 places), the TSS results are different in every one of the tables. Also when compared to the 12/18/2017 Plan set, the same areas, IC and results show up in the various tables. The filter system has not been redesigned even though K-H said that BF-2 would have to be “upsized” with the added curb inlets (2/12/18 letter). Also, nowhere do we find any required stormwater storage calculations that are discussed in the Guidance Manual Appendix that was part of K-H’s resubmittal. Thus, the added curb inlet system has not been engineered as proposed by K-H or as required by the WQP ordinance.
Other deficiencies are listed in both Dr. Ross’ attached letter and her February 17 letter. These have not been addressed by the resubmittal and additional engineering is necessary for compliance with City of DS’s Ordinance.
- Clarification of the pollutant load removal efficiency of the Bay Filter units you are proposing.
The Technical Guidance Manual that was provided details design and calculation methods including pretreatment, bypass, stormwater storage and filtration. The Application does not contain complete calculations and the design features described in this manual. See also comment in No 1 above. Information on the Flexstorm product was included, but it is not apparent how this project may use this product. Dr. Ross’ attached letter further describes limitations of some of the provided resources.
- Oil/Grease and Phosphorus removal back up calculations including VFS areas per BMP sub-basin.
Dr. Ross’ attached letter lists a number of factors that have not been properly considered or designed which result in the project failing to meet the 90% removal of the increase in Total Suspended Solids and Total Phosphorous.
- Existing vs Proposed condition hydrograph(s) to clarify your statement of “no increased flow resulting from proposed conditions”. In addition, provide discussion elaborating on the “improved conditions of site vegetation” after development and resulting curve numbers.
The Engineer’s selected points of analysis (along the downstream creek channel) are too far from the drainage systems that would be most affected by the proposed development. In particular, the drainage channel immediately below the developed Venue A site will be subject to larger volumes of runoff, over longer flow durations as a consequence of the added impervious cover. The City’s water quality code (22.05.019 (e) is written to protect these on-site drainage ways from the erosive effects of the increase flow volumes and velocities. The Engineer’s updated plans do not comply with this code requirement. His original calculation was not done per code at this location or using the proper design storm as outlined in my original review comments (Feb 19), and this comment was not addressed in his recent (Feb 26) response. Applying this WQ code, we estimate a much lower allowable peak flowrate than that implied by K-H estimates near this location, by a factor of 10. In my opinion the natural drainage channel in Drainage Area 2 (PR-2) will be subject to a significantly higher erosion potential under the proposed conditions than under today’s conditions. A drainage analysis is required for this channel using the 2 year, 3 hour storm information and demonstrating a flow rate a prescribed in the ordinance.
Other analysis concerns, including additional engineering design needed for the temporary sedimentation ponds, are contained in Jeff Kessel’s attached letter. Dr. Ross’ letter contains information supporting use of more appropriate curve numbers in the drainage analyses.
- Updated roadway typical section with notes and symbology to clarify your stated intent to place topsoil and revegetation up to the edge of pavement.
This is a nonstandard design as 2.5 inches of topsoil over compacted crushed stone is not a sufficient root zone to establish vegetation and create conditions significantly different from impervious cover. With calculations and maintenance provisions it may qualify for partial area credit towards the impervious cover percentage.
Because of limitations, errors, and calculation omissions listed above and in described in reports from our engineers, the design and alleged performance has not been demonstrated and is not verifiable. The Site Plan remains out of compliance with:
- 05.015 Performance Standards
- 90% Removal of 3 Constituents (Section (c)(3)), and
- 05.019 Erosive Flow Control
- Stormwater discharge into a waterway (Section (e)).
Additionally, until BF-2 is engineered to filter water captured by the curb inlets, the design is out of compliance with:
- 05.016 Impervious Cover
- Impervious cover downstream from water quality controls (Section (f)), and
- 05.019 Erosive Flow Control
- Untreated runoff over a CEF (Section (a)).
Finally, the impervious cover calculations require revision using innovative method credits to demonstrate compliance with:
- 05.016 Impervious Cover
- 10% Impervious Cover Limit (Sections (a)-(e)).
In sum, the newly produced materials only serve to confirm that the Applicant’s design fails in numerous material respects to comply with the City’s own ordinances, which the City itself is required by state law to enforce. We remain seriously concerned about these engineering deficiencies and resulting regulatory noncompliance by the proposed Mark Black Wedding Venue. Supporting reports prepared by engineering experts are attached, and objections raised in their previous reports, which were attached to our February 19, 2018 letter, persist as significant problems that have not been addressed at all, much less adequately addressed by the Applicant.
Based on the engineering deficiencies and proposed code/ordinance violations associated with this project, which are again confirmed by the newly produced materials, the Application should be denied, as Kimley-Horn has already been granted more than sufficient time to achieve compliance. If additional revisions are made by Kimley-Horn, we respectfully request that we be given sufficient “quality” time to verify and vet those revisions.
Finally, pursuant to state law and the City’s own procedures, please also accept this letter as a formal request by The Friendship Alliance to submit public comments at the next City Council meeting with respect to the late filed materials produced last Monday at 5 p.m., which were required to have been furnished by the Applicant prior to the last city council meeting. Unfortunately, through no fault of anyone except the Applicant, Kimley-Horn did not timely furnish any of these materials or other data necessary to correct previous deficiencies. However, the omission deprived citizens of the legal right to comment on those materials.
Accordingly, please advise us in writing before 5 p.m. on Wednesday, March 7, 2018, whether the City will allow public comment at the March 13, 2018 City Council meeting regarding the newly furnished materials.
We thank you for your consideration of this letter requesting that the application be denied, or alternatively, that any decision by the City be postponed in order to bring his project into regulatory compliance with the City’s own ordinances and state law.
If you have any questions, please feel free to contact me.
Respectfully,
Carlos Torres-Verdin, Ph.D.
President, The Friendship Alliance, Inc.
Brian Dudley, P.E.
cc:
City of Dripping Springs’ Council Members, Michelle Fischer, Ginger Faught, Chad Gilpin, P.E.