austin, texas 78704 phone: 512-326-8880 e-mail: lauren ... · austin, texas 78704 phone:...
TRANSCRIPT
1405 Hillmont Street Austin, Texas 78704
Phone: 512-326-8880
e-mail: [email protected]
Glenrose Engineering, Inc. glenrose.com Texas Board of Professional Engineers Number F4092
February 17, 2018 Mr. Chad Gilpin City of Dripping Springs City Engineer PO Box 384 Dripping Springs, Texas 78620 Via email: [email protected] Subject: Civil Site Development Plans for Mark Black Wedding Venue
Dear Mr. Gilpin:
I have reviewed the stormwater management and pollution reduction measures
proposed for the Mark Black Wedding Venue. The proposed measures fail to achieve
City of Dripping Springs standards to protect the high quality and character of its
creeks, streams, springs and environment. The applicant’s failure to demonstrate the
required pollution reduction in stormwater treatment and the failure to provide
required storm runoff retention or detention for erosion control constitute major
shortfalls. They are not addressed by supplemental information that has been
provided to the applicant in response to our previous comments. The proposed
stormwater controls must be re-engineered to meet the City’s standards.
My review does not constitute an endorsement of any assumptions, calculations, or
engineering conclusions in the Civil Engineering Site Plans. There are assumptions,
and calculations which contradict both other information in the submittal and widely
published sources. To the extent that these are either insignificant, or could be easily
addressed, I have not included them in this letter.
Basis for Opinions
My opinion below are based on my review of these documents:
• Preliminary Drainage Study; Mark Black Wedding Venue by Kimley Horn,
November 2017;
Friendship Alliance, Inc. February 17, 2018 Page 2 of 6
Glenrose Engineering, Inc. glenrose.com Texas Board of Professional Engineers Number F4092
• Letter from Andrew Evans, P.E., Kimley-Horn and Associates, Inc. to Chad
Gilpin, P.E., Dripping Springs City Engineer, November 30, 2017;
• Civil Site Development Plans for the Mark Black Wedding Venue sealed by
Andrew S. Evans, P.E., on December 18, 2017;
• Letter from Andrew Evans, P.E., Kimley-Horn and Associates, Inc. to Chad
Gilpin, P.E., Dripping Springs City Engineer, February 12, 2018;
• Sizing Vegetative Filter Strips for S.O.S. Requirements, no date or seal;
• City of Dripping Springs, Texas Code of Ordinances Title II Building and
Development Regulations;1
• City of Dripping Springs Technical Construction Standards and Specifications
(TCSS) Manual; and
• City of Austin Environmental Criteria Manual, Section 1 – Water Quality
Management.
Failure to Comply with Title II Building and Development
Regulations: Missing Information
• §22.05.015(c)(3) requires the applicant to demonstrate 90% removal of the
net increase for the design storm event of total suspended solids, total
phosphorus, and oil and grease. The following required information is missing.
References in parentheses document the location of the requirement.
o Erosion and Sedimentation Control Engineering Report (City of
Dripping Springs TCSS, §7.2.5(f));
o Water Quality Control Engineering Report (City of Dripping Springs
TCSS, §7.2.5(c));
1 http://z2.franklinlegal.net/franklin/Z2Browser2.html?showset=drippingspringsset, accessed on February 15, 2018.
Friendship Alliance, Inc. February 17, 2018 Page 3 of 6
Glenrose Engineering, Inc. glenrose.com Texas Board of Professional Engineers Number F4092
o Water Quality Control Design Report (City of Dripping Springs TCSS,
§7.2.5(i));
o The length, width, and area of each vegetative filter strip (required for
the necessary calculations);
o Information regarding the length of the contributing drainage area to
vegetative filter strips in direction of flow (maximum 150 feet; level
spreader required at greater than 72 feet) (Austin ECM 1.6.7.B.
Vegetative Filter Strips);
o Information regarding the two-year, three-hour hydraulic loading rate
(<0.05 cfs/ft) to each vegetative filter strip (Austin ECM 1.6.7.B.
Vegetative Filter Strips);
o Failure to demonstrated at least 65% infiltration over the length of the
filter strip (Austin ECM 1.6.7.B. Vegetative Filter Strips);
o Failure to provide information regarding filter strip area per
contributing area (Austin ECM 1.6.7.B. Vegetative Filter Strips);
o Baseline pollutant loading calculations;
o Designation of vegetated filter strip easements or conservation lots
(Austin ECM 1.6.7.B. Vegetative Filter Strips);
o An Approved Integrated Pest Management Plan with recorded
restrictive covenant (Austin ECM 1.6.7.B. Vegetative Filter Strips);
o Accurate information regarding soil infiltration rates based on
published data (Austin ECM 1.6.7.B. Vegetative Filter Strips);
o Information regarding soil infiltration based on field sampling (Austin
ECM 1.6.7.B. Vegetative Filter Strips); and
o Calculations demonstrating 90% removal of increased with either total
phosphorus or oil and grease (City of Dripping Springs Code of
Ordinances §22.05.015(c)(3).
• §22.05.019(e) requires site designs to provide for discharge of stormwater
into a waterway, adequate retention and/or detention to limit flows into the
Friendship Alliance, Inc. February 17, 2018 Page 4 of 6
Glenrose Engineering, Inc. glenrose.com Texas Board of Professional Engineers Number F4092
receiving waterway to the level consistent with the flow rate of the two-year,
three-hour rainfall event evenly distributed over a 24-hour period.
Failure to Comply with Title II Building and Development
Regulations: Wrong Information
• Sheet 37/42 Note 3 states the following: “According to TCEQ RG-348, vegetative
filter strips have a TSS removal efficiency of 85%, Bayfilters have a TSS removal
efficiency of 87% and rainwater harvesting has a TSS removal efficiency of
100%.” Firstly, City of Dripping Springs requires calculations based on the City
of Dripping Springs TCSS and the TCSS references the City of Austin
Environmental Criteria Manual as a basis for calculations, not TCEQ RG-348.
Furthermore, TCEQ RG-348 does not list Bayfilters as having a TSS removal
efficiency of 87%. Procedures for determining Bayfilter removal efficiencies
are described in TCEQ RG-348 Addendum Section 3.4.19.
• Based on information regarding the Bayfilters provided in the plans, the
Bayfilters proposed by the applicant would not achieve a removal efficiency of
85%. The estimated removal efficiencies, based on TCEQ RG-348 methods, are
significantly lower than those assumed by the applicant, as I have
demonstrated in the following table.
Pollutant Removal System
TSS Removal Efficiency Assumed
by Applicant
TSS Removal Efficiency based on TCEQ RG-348
Methods2
BF 1 87% 65%
BF 2 87% 68%
BF 3 87% 52%
BF 4 87% 58%
2 Based on the methods outlined in TCEQ RG-348 Addendum Section 3.4.19 and Bayfilter information presented on Sheet 42 of 42.
Friendship Alliance, Inc. February 17, 2018 Page 5 of 6
Glenrose Engineering, Inc. glenrose.com Texas Board of Professional Engineers Number F4092
• The applicant has presented a calculation of total phosphorus and oil and
grease removal based on an analysis that assumes one single vegetative filter
strip to treat the entire site area of 64 acres.3 Based on the proposed plans,
however,4 the drainage areas to the vegetative filters will be significantly less
than 64 acres. The vegetative filter strip pollution load calculations also
assume that the 10 percent impervious cover proposed for the site is
distributed across this larger area. Both assumptions do not apply to the site
and, therefore, the calculated required filter strip area is meaningless. The
sizing methodology is based on LCRA Nonpoint Source Pollution Control
Technical Manual, January 1991, which is not equivalent to the City of Dripping
Springs standards for water quality protection. The document is not signed,
sealed, or dated by a Texas Registered Professional Engineer and is, therefore,
an unacceptable basis for site plan approval.
The applicant proposes numerous vegetative filter strip controls. The
effectiveness of each of these vegetative filter strips depends on its size relative
to the size and imperviousness of the contributing area. The applicant has
failed to provide the necessary information to evaluate effectiveness, which is
required both by the applicable engineering methods and by applicable City of
Dripping Springs standards.
• Sheet 25 of 42: The soil hydrologic group is identified as “C”. Most of the site,
including areas for which vegetative filter strips are proposed is designated as
hydrologic group “D”.5
3 Sizing Vegetative Filter Strips for S.O.S. Requirements, no date or seal.
4 See • Civil Site Development Plans for the Mark Black Wedding Venue sealed by Andrew S. Evans, P.E., on December 18, 2017 5 See attached relevant map and information from the USDA Natural Resources Conservation Service Soil Web Survey.
Friendship Alliance, Inc. February 17, 2018 Page 6 of 6
Glenrose Engineering, Inc. glenrose.com Texas Board of Professional Engineers Number F4092
Please let me know if I can answer any questions.
Sincerely,
Lauren Ross, Ph. D., P. E. President Glenrose Engineering, Inc. Attachments: Sections from City of Dripping Springs TCSS Manual (sections of noncompliance highlighted) Sections from City of Austin Environmental Criteria Manual Sections from TCEQ RG-348 Addendum
Sealed on February 16, 2018
City of Dripping Springs TCSS
1
TABLE OF CONTENTS SECTION 1. STANDARD SPECIFICATIONS AND DETAILS 1
1.1. General 1 1.1.1. Earthwork 1 1.1.2. Subgrade and Base Construction 1 1.1.3. Street Surface Courses 1 1.1.4. Concrete Structures and Miscellaneous Concrete 2 1.1.5. Underground Piped Utilities 2 1.1.6. Environmental Enhancement 3 1.1.7. Incidental Construction 4 1.1.8. Urban Transportation 4 1.1.9. Project Management 5 1.1.10. Electrical 6
1.2. Standards 6
1.3. Exceptions to the Referenced Standards 6
1.4. City of Austin, Texas Standard Specifications 6 1.4.1. Series 200 – “Subgrade and Base Construction” 6 1.4.2. Series 400 – “Concrete Structures and Miscellaneous Concrete 6 1.4.3. Series 500 – “Underground Piped Utilities” 6 1.4.4. Series 600 – “Environmental Enhancement” 7 1.4.5. Series 700 – “Incidental Construction” 8 1.4.6. Series 800 – “Urban Transportation” 8 1.4.7. Series 1800 – “Private Development” 8
1.5. Additions to the Referenced Standards 9 1.5.1. General 9 1.5.2. Indemnification 9
SECTION 2. TRANSPORTATION FACILITIES 10
2.1. General 10 2.2. Definition of Transportation Systems 10 2.3. Exceptions to the Referenced Standards 10
2.3.1. General 10 2.3.2. Hays County Subdivision and Development Regulations 10 2.3.3. Hays County Specifications for Paving and Drainage
Improvements 10 SECTION 3. WATER AND WASTEWATER FACILITIES 11
City of Dripping Springs TCSS
2
3.1. General 11
3.2. Exceptions to the Referenced Standards 11
SECTION 4. DRAINAGE FACILITIES 12
4.1. General 12
4.2. Definition of Drainage Facilities and Systems 12 4.3. Exceptions to the Referenced Standards 12
4.3.1. General 12 4.3.2. City of Austin, Texas Drainage Criteria Manual 12 4.3.3. City of Austin, Texas Standard Specifications 13
SECTION 5. ENVIRONMENT 14 5.1. General 14 5.2. Definition of Environmental Facilities and Systems 14 5.3. Exceptions to the Referenced Standards 14
5.3.1. General 14 5.3.2. City of Austin, Texas Environmental Criteria Manual 14 5.3.3. City of Austin, Texas Standard Specifications 17 5.3.4. Calculation of the Impervious Cover allowance for Isolation of
Roof Runoff and Irrigation 17
SECTION 6. BUILDINGS 20
6.1. General 20
6.2. Exceptions to the Referenced Standards 20
SECTION 7. ENGINEERING SUBMITTALS 21
7.1. Licensed Engineer Requirements 21 7.1.1. General 21 7.1.2. “Issued for Review” 21 7.1.3. “Issued for Construction”, “Issued for Permitting”, “Issued for
Platting” 21 7.1.4. Licensed Engineer Sealed Documents 21
7.2. Content of Engineering Submittals 24 7.2.1. Non-Residential Building Plan Requirements 24 7.2.2. Drainage 24 7.2.3. Transportation 28 7.2.4. Utilities 33
City of Dripping Springs TCSS
3
7.2.5. Water Quality Management 40
SECTION 8. SITE PLAN REQUIREMENTS 46
8.1. Cover Sheet 46 8.2. Notes 46
8.3. Approval Blocks 46
8.4. Base Information 46
8.5. Additional Requirements 50
8.5.1. Compatibility Standards 50 8.5.2. Off-Site Parking 50
8.6. Drainage Plan 51 8.7. Construction Details 52
8.8. Environmental Site Plan and Report Submittal Information 53
8.9. Engineer’s Summary Letter 61
SECTION 9. DRAINAGE AND WATER QUALITY CONTROL DESIGN AND CONSTRUCTION ENVIRONMENT COMPATIBILITY REQUIREMENTS 63
9.1. General 63 9.2. Compatibility Design Standards 63
9.2.1. General 63 9.2.2. Drainage Control 63 9.2.3. Water Quality Controls 64
SECTION 10. NON-POINT SOURCE POLLUTION CONTROL MANAGEMENT PERFORMANCE STANDARDS 66
10.1. Removal of Annual Pollutant Load 66 10.1.1. For development not using on-site irrigation with treated
wastewater effluent 66 10.1.2. For development using on-site irrigation with treated wastewater
effluent or with septic system effluent 66 10.1.3. Background and Developed Sites Pollutant Concentrations and
Pollutant Loads 67 10.1.4. Water Quality Volume 67 10.1.5. Impervious Cover 67 10.1.6. Impervious Cover Allowances 68 10.1.7. Critical Water Quality Zones (CWQZ) 69
City of Dripping Springs TCSS
4
10.1.8. Critical Environmental Features (CEF) 69 10.1.9. Overlapping Critical Water Quality Zones 69
10.2. Impervious Cover 70
10.2.1. The following shall be considered as impervious cover 70 10.2.2. The following will not be considered as impervious cover 70 10.2.3. The following shall not be included in the total site area against
which the allowable impervious cover percentage limit is applied 70 10.2.4. Restrictions 71
10.3. Critical Water Quality Zones (CWQZ) 71
10.3.1. All development activities, including temporary construction activities and landscaping activities, shall be restricted from the CWQZ, except the following development activities may be allowed if approved by the City 71
10.3.2. All utilities, other than wastewater shall be located outside the CWQZ except for crossings 71
10.3.3. All water quality control discharges and stormwater discharges onto a CWQZ shall 71
10.4. Overland Flow 72
10.5. Infiltration 72
10.6. Steep Slopes 72
10.7. Vegetation 73
10.8. Water Quality Controls (WQC) 73
10.9. Erosion Control Requirements 75
10.10. Isolation of Roof Runoff and Irrigation 76
10.11. Erosion Hazard Setbacks 77
10.12. Non-Residential and Multi-Family Permanent Construction 77
10.13. Residential Lots with a Building Permit 77
City of Dripping Springs TCSS
22
SECTION 5. ENVIRONMENT
5.1. General
The environmental assessments and the design and construction of environmental facilities and systems within the incorporated limits and the ETJ of the City of Dripping Springs shall comply with the following standards, which are incorporated herein by reference and which are modified herein:
City of Austin, Texas Environmental Criteria Manual, Section 1 "Water Quality Management", latest edition; City of Austin, Texas Standard Specifications, latest edition;
5.2. Definition of Environmental Facilities and Systems
Environmental facilities and systems shall include environmental assessments, water quality controls, temporary erosion and sedimentation controls, permanent erosion and sedimentation controls, and on-site irrigation with wastewater effluent.
5.3. Exceptions to the Referenced Standards
10.3.4. General
(a) The following exceptions shall apply to the referenced standards.
(b) All references to the City of Austin shall be construed to mean
the City of Dripping Springs. (c) All provisions and standards of the City of Dripping Springs
Code of Ordinances shall be applicable and shall govern if there is a conflict with the standards referenced in Section 5.1.
10.3.5. City of Austin, Texas Environmental Criteria Manual, Section
1.
(a) Section 1.2.1 "Fiscal Security". Fiscal security shall be determined by the owner's consulting engineer in accordance with Subsection (c).
(b) Section 1.2.3.1. "Submittal Requirements for Projects in the
Barton Springs Zone". This section does not apply. (c) Subsection A, “Application of SOS Ordinance”. This
Subsection does not apply.
City of Dripping Springs TCSS
23
(d) Section 1.2.3.2. "General Rules" (1) Subsection G. "Operating Permits"
i) Annual operating permits shall be required
for all water quality controls. ii) "Commercial" shall be construed to mean
"non-residential". iii) The City will not operate or maintain water
quality controls.
(e) Section 1.2.3.3. "Site Management". This section does not apply.
(f) Section 1.4.1.1. "City of Austin Erosion and Sediment Control
Policy".
(1) Subsection D. "Ordinance Authority". This section does not apply.
(g) Section 1.4.4 "Vegetative Practice". Vegetative types for
erosion and sedimentation control shall comply with the City of Dripping Springs Code of Ordinances.
(h) Section 1.5.0 "Revegetation Criteria". Revegetation types shall
comply with the City of Dripping Springs Code of Ordinances. (i) Section 1.6.0 "Design Guidelines for Water Quality Controls".
(1) Section 1.6.1. "Introduction". "Commercial" shall
be construed to mean "non-residential" (2) Section 1.6.3. "Maintenance and Construction
Responsibilities".
i) Subsection A. "Maintenance Responsibilities". Owner/developer shall maintain all water quality controls.
ii) Subsection B. "Maintenance Design Requirements".
Fencing and barriers shall comply with the City of Dripping Springs Code of Ordinances.
(3) Section 1.6.8 "Rules to Implement On-Site Control of the Two-Year Storm ". All development shall be subject to the two-year storm runoff control requirements of this section.
City of Dripping Springs TCSS
24
(4) Section 1.6.9.2 "Pollution Prevention Measures".
i) Subsection B through Subsection F.
These subsections do not apply. (5) Section 1.6.9.3 "Control Measure Design".
i) Subsection A. "Baseline Pollutant Load
Calculations". Baseline pollutant loads shall be calculated for all areas which are to be developed for the pollutants listed in the City of Dripping Springs Code of Ordinances.
(6) Table 1-9 "Runoff Coefficient Table". The runoff
values for the "NonRecharge Zone Runoff' shall be used.
(7) Table 1-10 "Baseline Pollutant Concentrations and
Unit Area Loads for Undeveloped Sites". Oil and Grease pollutant concentrations shall be added to Table 1-10 and shall be 0 mg/l.
(8) Table 1-11 "Standard Pollutant Concentrations for
Developed Sites".
i) "Commercial" shall be construed to mean `non-residential".
ii) Oil and Grease pollutant concentration shall be added to Table 111 and shall be 5 mg/1 for all conditions. The load calculation for oil and grease under developed conditions shall represent only the paved surfaces of the development and is not required to include rooftops.
(j) Section 1.7.0 "Floodplain Modification Criteria".
(1) Section 1.7.1 "Introduction". These guidelines apply only to development proposed in a floodplain or in a critical water quality zone.
(2) Section 1.7.3 "Application of Guidelines". These
guidelines apply to the development of all floodplains and critical water quality zones located within the jurisdictional boundaries of the City.
City of Dripping Springs TCSS
25
(3) Section 1.7.4 "Appeals". This section does not apply.
(k) Section 1.8.0. "Impervious Cover Calculation Criteria".
(1) Section 1.8.1 "Calculations"
i) Subsection A. Impervious cover calculations shall include all swimming pool surface areas and sidewalks.
ii) Subsection D. Maximum pavement width for imperious cover calculations shall be 30 feet.
iii) Subsection E. Maximum pavement width for impervious cover calculation shall be 30 feet.
(2) Section 1.8.2. "Construction on Slopes"
i) Subsection A. This subsection does not apply. ii) Subsection B.
Building and parking areas may be constructed on slopes in excess of 15 percent, subject to the requirements of Subsection B.2 through B.6.
Subsection B.1. This subsection does not apply.
Subsection B.2. This subsection applies to development on slopes in excess of 15 percent.
Subsection B.3. This subsection applies to development on slopes in excess of 15 percent.
(l) Section 1.9.0 "Need for Water Quality Controls". This section does not apply.
(m) Section 1.10.0 "Point Recharge Identification Criteria". This
section does not apply.
10.3.6. City of Austin, Texas Standard Specifications.
The exceptions of the City of Austin's Standard Specifications with respect to environmental controls are given in Section 1.00 of this TCSS Manual.
10.3.7. Calculation of the Impervious Cover Allowance for Isolation of Roof Runoff and Irrigation
(a) General
City of Dripping Springs TCSS
26
This section provides guidelines and example calculations for determining the impervious cover allowance if roof runoff is isolated, treated as a water quality control, and used for on-site irrigation.
(b) Guidelines and Example Calculations
(1) Example:
i) Non-residential development ii) 3-acres lot (130,680 square feet) iii) Roof area of 40,000 square feet iv) Requesting total impervious cover of 58,000
square feet (44.4% impervious cover) v) Requesting the use of isolation and treatment
and irrigation of roof runoff for the 40,000 \ square feet of roof area.
(2) Calculate the background TSS pollutant load for the
roof area.
i) Roof area = 40,000 ft2 = 0.9183 acres ii) TSS background pollutant load = 55 x 0.049 x
32.5 x 0.2267 x 0.9183 = 18.23 lbs/yr
(3) Calculate the total TSS pollutant load for the roof area. Example:
2. TSS total pollutant load = 110 x 0.248 x 32.5 x
0.2267 x 0.9183 = 184.57 lbs/yr
(4) Calculate the 95% TSS pollutant removal requirement.
i) TSS pollutant caused by development = 184.57
-18.23 = 166.34 ii) 95% removal = 0.95 x 166.34 = 158.03 lbs/yr
(5) Compare the 95% removal requirement against the pollutant removal capacity of the rainwater collection/irrigation system:
i) 1. If the capacity of the proposed system does
not exceed the 95% removal requirement, then zero impervious cover allowance is allowable.
ii) 2. If the capacity of the proposed system exceeds the 95% removal requirement, then
City of Dripping Springs TCSS
27
proceed with the following calculations to determine the allowable allowance.
Example: In this case the capacity of the proposed system is being calculated, which will then be used in selection of the appropriate system that meets the capacity requirement.
(6) Calculate the allowable pollutant removal capacity of the system, which will be the lesser value of the following:
i) 1. Rated pollutant removal capacity of the
proposed system minus the 95% removal requirement; or
ii) 2. Baseline pollutant load plus 5% of the TSS pollutant load caused by development.
Example: The system capacity to be selected must at least be capable of removing the baseline pollutant load plus 5% of the TSS pollutant load caused by development.
Minimum System Capacity = 18.23 + (0.05 x 166.34) = 26.55 lbs/yr
(7) Calculate the developed impervious surface area that would contribute a TSS pollutant load equivalent to the minimum system capacity.
Example: 26.55 = 110 x 0.248 x 32.5 x 0.2267 x area
area= 0.1321 acres= 5,754 ft2
(8) Calculate the impervious cover allowance, which will be the lesser of: i) The equivalent impervious surface area times
50%; or ii) Site area times 5%.
Example:
Equivalent impervious surface area times 50%
0.50 x 5,754 ft2 = 2,877 ft2
Site area times 5%
0.05 x 130,680 ft2 = 6,534 ft2
City of Dripping Springs TCSS
28
Maximum allowable increase in impervious cover = 2,877 ft2
City of Dripping Springs TCSS
52
(d) Water Quality Phasing Plan (with the Water Quality Engineering Report) - Provide documentation of conformance with the standards for:
(1) Delineation of each phase of water quality control
construction; (2) Water quality engineering information necessary to
construct the proposed development for each phase of development.
(e) NPS Annual Operating Permit Application
(1) Delineation of the number and location and type of each water quality control;
(2) Water quality report; (3) Maintenance plan for all required water quality
controls; (4) Concurrence letter certifying that the engineer has
inspected the control and that it is operating as designed.
(f) Erosion and Sedimentation Control Engineering Report -
Provide documentation of conformance with the standards for:
(1) Drainage control analysis; (2) Sedimentation control and filtration analysis; (3) 2-year frequency flood peak flow and velocity for
temporary control; (4) 25-year and 100-year frequency flood peak flows
and velocities for permanent controls; (5) Identification of drainage patterns and disturbed
areas; (6) Identification of drainage control points; (7) Identification of the function of the controls,
including diversion, flow spreading, detention/filtration, and detention/sedimentation;
(8) Selection of control devices;
City of Dripping Springs TCSS
53
(9) Design computation for flow through barriers;
diversion, interceptor and perimeter dikes; interceptor and perimeter swales; stone outlet structures; rock berms; silt fences; sediment filter dikes; sediment basins; sediment traps; stabilized construction entrances; pipe slope drains;
(10) Design computations for permanent controls
including diversions; grasslined swales; level spreaders; stone riprap; gabions; subsurface drains; land grading; grade stabilization structures, paved chutes, and paved flumes;
(11) Vegetative and re-vegetative practices; (12) Permit requirements.
(g) Building and Site Development Plans and Specifications for the Erosion and Sedimentation Control Plan.
(1) Detailed sequence of development showing phases
of construction and at what time and what specific controls are required during each phase of the development;
(2) Schematic representation of each control measure
for each phase of construction, with adequate specifications and details for the controls;
(3) For detention/filtration control devices, a summary
of calculations for runoff from the 2-year storm, including runoff flow rate and assumed flow capacity for each barrier;
(4) Approved areas for materials and equipment storage
and staging, construction traffic, parking, vehicular maintenance, concrete truck washing, and, if appropriate, vehicle washing;
(5) Temporary spoils storage areas, including size, time
of use, and ultimate re-vegetation schedules; (6) On-site permanent spoils disposal areas, including
size, depth of fill and re-vegetation procedures; (7) Contour maps, showing lightly dashed lines for
existing contours and solid lines for proposed
City of Dripping Springs TCSS
54
contours, with each having a contour interval of two (2) feet;
(8) A map of suitable scale on which are indicated all
contributing drainage subareas both on and off-site; (9) Re-vegetation plans for all disturbed areas including
topsoil requirements; seed, sod, and mulch type and rate of application; watering requirements, application technique; maintenance requirements for each specific area, delineation of temporary and permanent vegetation; clear definition of criteria to be utilized in determining when acceptable re-vegetation has taken place;
(10) Delineation of specific areas where specified
slope stabilization techniques are to be utilized and the extent of stabilization to be achieved; and all detention, sedimentation, or sedimentation/filtration ponds;
(11) The identity, address and phone number of
the owner, the owner's engineer, and the designated representative(s) of the owner who will be responsible for the maintenance of the controls and who can authorize appropriate changes to the control plan, if it is discovered to be inadequate;
(12) Dust control.
(h) Building and Site Development Plans and Specifications for the Re-Vegetation Plan for Erosion and Sedimentation Control
(1) Description of vegetation currently existing within
the limits of the development; (2) Description of vegetative cover to be installed,
including temporary and permanent vegetative covers;
(3) Results of analysis of available soil nutrients (N, P,
K, Zn, Mn, Cu, and S) for materials proposed for use as topsoil and a discussion of nutrient amendments required to support the proposed vegetative cover;
(4) Specifications of re-vegetation, including site
preparation; soil nutrient amendments; seed bed
City of Dripping Springs TCSS
55
preparation; seeding rates and composition; mulching rates and composition;
(5) Specifications of re-vegetation using transplanted
live plant materials, including site preparation; soil nutrient amendments; preparation of substrate; transplanting rates and composition; mulching rates and composition;
(6) Maintenance plan for re-vegetation areas including
irrigation, replanting of bare areas; erosion control, fertilizer application; weed control.
(i) Water Quality Control Design Report (as part of the Water
Quality Engineering Report) - Provide documentation of conformance with the standards for:
(1) Delineation of contributing and non-contributing
areas to the water quality volume; (2) Water quality volume calculations; (3) 25-year and 100-year floods peak flows rates and
routing through water quality ponds; (4) Maintenance design requirements; (5) Selection criteria for type of water quality controls; (6) Design calculations for sizing water quality
controls; (7) Calculation of pollutant removal efficiencies; (8) 2-year flood detention analysis; (9) Calculations of baseline pollutant loads; (10) Calculations of developed condition
pollutant loads; (11) Calculations of requirements for reductions
in pollutant loading; (12) Evaluation of the water quality controls to
meet the required pollutant reduction; (13) Calculation of pollutant removal efficiencies
City of Dripping Springs TCSS
56
(j) Plan for Land Application of Treated Wastewater Effluent -
Provide documentation of conformance with the standards for:
(1) Determination of Depth of Effective Soil;
i) General soil survey, ii) Detailed soil survey.
(2) Calculation of living unit equivalents; (3) Delineation of irrigation areas; (4) Delineation of slopes in excess of 15 percent
gradient; (5) Delineation of critical environmental features and
water quality buffer zones and easements; (6) Delineation of the 100-year floodplain; (7) Irrigation system details.
Austin, TX Environmental Criteria Manual about:blank
1 of 7 2/15/2018, 4:42 PM
Austin, TX Environmental Criteria Manual about:blank
2 of 7 2/15/2018, 4:42 PM
≤
≤
Austin, TX Environmental Criteria Manual about:blank
3 of 7 2/15/2018, 4:42 PM
Austin, TX Environmental Criteria Manual about:blank
4 of 7 2/15/2018, 4:42 PM
Austin, TX Environmental Criteria Manual about:blank
5 of 7 2/15/2018, 4:42 PM
Austin, TX Environmental Criteria Manual about:blank
6 of 7 2/15/2018, 4:42 PM
″
Austin, TX Environmental Criteria Manual about:blank
7 of 7 2/15/2018, 4:42 PM
Addendum Sheet
Complying with the Edwards Aquifer Rules
Technical Guidance on Best Management Practices
RG-348 (Revised July 2005)
January 20, 2017
This addendum sheet lists additional information that is approved for inclusion in “Complying with the Edwards Aquifer Rules Technical Guidance on Best M a n a g e m e n t Practices” (Revised July 2005). The list indicates the location (chapter and section) where this additional information will be placed in a subsequent r e v i s i o n of the manual and provides the specific technical language that has been approved by the TCEQ Edwards Aquifer Protection Program.
RG-348 Location
RG-348 Language Justification
1.4.19 1.4.19 Sediment Control Rolls TCEQ Figure 1-44 Sediment Control Rolls (SCRs) trap detached sediments, reduce slope lengths, and
decrease runoff velocity while allowing runoff to filter through the device. They are reusable, recyclable and constructed of overlapping layers of perforated polymeric sheets
Approval of Innovative Technology
and one or more integrated filter. They are typically hollow tubular or rectangular assemblies that include a location flap and a method to interconnect. This measure has been tested by TxDOT and is approved for use on their projects.
They function similar to silt fences, but because of their lower height are not appropriate for use where overtopping will occur except for extreme events. SCRs reduce runoff water velocity, filter out dislodged soil particles and significantly reduce the effects of slope steepness. SCRs are also used as water flow velocity dissipaters, filtering and trapping sediment. SCRs are designed to be reshaped after being run-over by construction equipment. A picture of a SCR installation is shown in Figure 1-44. This technology may be appealing for use in areas adjacent to foot traffic, since the lack of posts reduces the potential for injury.
Figure 5 Schematic of the BaySeparator System
Selection Criteria
Use only when space constraints make installation of a surface treatment system infeasible
Appropriate for retrofits as well as new development
Achieves greater than 80% TSS removal when properly sized
Can be used as a stand-alone system or in a treatment train configuration Limitations
Requires annual removal of accumulated pollutants
Cost for annual pumping and disposal of accumulated material in the facility is substantial
Manhole cover must be removed to determine whether maintenance is required
Below grade installation may inhibit maintenance access and require special equipment to remove accumulated sediment and other pollutants
Cost Considerations
The cost for a BaySeparator System, based on price/acre and the volume of runoff treated, may be significantly higher than many alternative technologies. Consequently, its primary use will be in space-constrained locations where surface systems such as sand filters may not be feasible.
Section 3.4.19
Design Criteria for BaySeparator System
The BaySeparator is available with several manhole configurations to provide ample options when sizing according to surface area. Table 1 below lists the BaySeparator
units and manhole configurations currently available.
BaySeparator should be located as far upstream in the drainage system as possible. The frequency of the magnitude of a flow rate is dependent on the upstream drainage areas and the level of imperviousness of that drainage area. If the drainage area is too large, the required capture rate may exceed the capacity of a single unit; therefore, the use of multiple units located on lateral storm lines rather than the main trunk line may be more beneficial both physically and economically.
Table 1: BaySeparator Manhole size and surface area (ft2)
Model
Number Surface
Area (ft2) Model
Number Surface Area
(ft2)
1/2K-48” 25.13 5K-72” 56.54
1/2K-60” 39.26 5K-96” 100.53
1K-48” 25.13 10K-120” 157.07
1K-60” 39.26 10K-144” 226.19
3K-60” 39.26
3K-72” 56.54
Design Methodology
As a flow-based BMP, the BaySeparator is designed using the treatment flow rate for the site, as calculated using the Rational Method. The runoff rate from the tributary area is calculated using Equation 3.4:
Q CIA
Where Q = flow rate (cfs)
C = runoff coefficient for the tributary area
I = design rainfall intensity (1.1 in/hr)
A = tributary area (ac).
The runoff coefficient is calculated as the weighted average of the impervious and pervious areas. Runoff coefficient for impervious areas is assumed to be 0.90 and runoff coefficient for pervious areas is assumed to be 0.03.
The overflow rate (hydraulic loading rate) is calculated using Equation 3.5:
VOR Q / A
Where VOR = overflow rate (ft/s)
Q = flow rate calculated using Equation 3.4
A = combined surface area of the primary and storage manholes
The overflow rate can then be used with Table 2 to determine the annual TSS removal for the proposed unit. Select the BaySeparator unit that provides the desired TSS removal.
The BaySeparator unit should be designed to treat the 1.1 in/hr storm, as well as passing the 4 in/hr storm through the unit. In this way, the system will treat virtually all of the annual runoff, and can be assumed to have a value of F = 1 (where F is the fraction of annual runoff treated by the BMP, in Equation 3.9).
For flows in excess of the 4 in/hr storm that may be required to meet local design requirements, the need for external bypass should be evaluated. External bypass needs should be evaluated on a case-by-case basis.
Table 2: BMP Efficiency and Overflow Rate (VOR)
Below is an example sizing using the sizing form required for the BaySeparator. This example shows a BaySeparator being sized for a 0.15 acre site with 0.10 acres of impervious cover.
PROJECT: BaySeparator 10K-120” OT Example Watershed: 1 Date: 3/19/09
EAPP BaySeparator EXAMPLE Compensation Worksheet (Rev. 3/19/09): Use additional sheets for additional catchment areas.
Table 1
Use additional sheets for additional BMPs.
AI = Impervious Cover
Ap = Pervious Cover
A = Total Area
P = Avg. Annual Rainfall (33” for example)
ANI = Increase in impervious cover (new IC – existing IC)
TSS = LM = 27.2 x ANI x P
Effective Area (ac) BaySeparator Model
Surface Area (ft2)
EA < 0.03 1/2K/1K-48” 25.13
0.03 < EA < 0.05 1/2K/1K-60” 39.26
0.05 < EA < 0.07 3K/5K-72” 56.54
0.07 < EA < 0.12 5K-96” 100.53
0.12 < EA < 0.19 10K-120” 157.07
0.19 < EA < 0.27 10K-144” 226.19
Eff (%) Overflow (ft/s) Eff (%) Overflow (ft/s) Eff (%) Overflow (ft/s) Eff (%) Overflow (ft/s)
40% 1.74E-02 55% 6.28E-03 70% 2.54E-03 85% 8.38E-04 41% 1.66E-02 56% 6.00E-03 71% 2.42E-03 86% 7.78E-04 42% 1.58E-02 57% 5.72E-03 72% 2.30E-03 87% 7.18E-04 43% 1.51E-02 58% 5.44E-03 73% 2.18E-03 88% 6.58E-04 44% 1.43E-02 59% 5.16E-03 74% 2.06E-03 89% 5.98E-04 45% 1.35E-02 60% 4.87E-03 75% 1.93E-03 90% 5.36E-04 46% 1.27E-02 61% 4.59E-03 76% 1.81E-03 91% 4.95E-04 47% 1.20E-02 62% 4.35E-03 77% 1.69E-03 92% 4.54E-04 48% 1.12E-02 63% 4.11E-03 78% 1.57E-03 93% 4.13E-04 49% 1.04E-02 64% 3.87E-03 79% 1.45E-03 94% 3.72E-04 50% 9.65E-03 65% 3.63E-03 80% 1.33E-03 95% 3.31E-04 51% 8.88E-03 66% 3.39E-03 81% 1.23E-03 96% 2.90E-04 52% 8.11E-03 67% 3.14E-03 82% 1.13E-03 97% 2.49E-04 53% 7.34E-03 68% 2.90E-03 83% 1.04E-03 98% 2.08E-04 54% 6.56E-03 69% 2.66E-03 84% 9.38E-04 99% 1.67E-04
List only the uncaptured area being compensated for in the BMP. TSS compensation for uncaptured areas can be divided up between multiple BMPs.
BMP Catchment Area A Uncaptured/Untreated Areas (for compensation in BMP)
AI1 = 0.10 AI2 = 0.00
AP1= 0.05 AP2= 0.00
A1 = 0.15 A2 = 0.00
ANI1 = 0.10 ANI2= 0.00
LM1= 90 LM2= 0.00
1 BaySeparator Model Sizing based on Individual Catchment Area to the BMP. Use additional sheets as necessary.
Effective Area (EA) = (0.9 x AI) + (0.03 x AP)
EA = (0.9 x 0.10 _) + (0.03 x 0.05 ) = 0.0915 EA
Model (from Table 1to start) _5K-96” ; Surface area (SA) of model (Table 2) 100.53_ Sq. Ft.
Required TSS Removal for Catchment Area
LM1= 27.2 x 0.10 AI x 33_ P” = 90 _#TSS
2 Overflow Rate
(EA) x 1.1 / Unit surface area (SA)
(( 0.0915 ) x 1.1) / 100.53 = 0.001 f/s
3 BMP Efficiency (Table 2) If the overflow rate is between two percent efficiencies, use the smaller percent efficiency (round the overflow rate to the larger overflow value). Enter rounded overflow value:
Vor = .00104 f/s
BMP % = 83 % / 100 = 0.83 BMP Eff
4 Maximum TSS Removal of BMP: LR1
LR1 = (BMP Eff x P) x [(AI1 x 34.6) + (AP1 x 0.54)]
LR1 = (0.83 x _33 ”) x [( 0.10 x 34.6) + ( 0.05 x 0.54)] = 96 #TSS
TSS Load Credit (LC) to be counted towards untreated areas = LR1 – LM1
LC = [( 96 _) – ( 90 )] = _6 #TSS
5 Required TSS Removal for Uncaptured Area LM2 = 27.2 x 0 ac x _33 ” = 0 #TSS
6 Treatment Available?
If TSSC > TSSUC; Model size is adequate.
If TSSC < TSSUC; Model size is inadequate. Choose a larger model size or redefine the catchment areas. Repeat steps 1 - 6.
6 TSSC (<, >, >, pick) 0 TSSUC
Final Model Size: 5K-96”
7 TSS Treatment per BMP
TSSCA (step 1) + TSSC (step 5) = TSS Removal by BMP
90 #TSS + 0_ #TSS = 90_ #TSS
8 Sub-catchment
Area
Model Number
Drainage Area (Acres)
Impervious Cover (Acres)
Target TSS Removal (lb/yr)
BaySeparator Model
TSS Removal Provided (lb/yr)
BMP Catchment 5K-96” 0.15 0.10 90 5K-96” 90
Uncaptured/Untreated 0.00 0.00 0.00 0.00
Total --- 0.15 0.10 90 90
BaySeparator Worksheet 3_9_09
Table 2: BMP Efficiency and Overflow Rate (VOR)
Table 3: BMP Summary Table for the Site
Complete this table to show the types of BMPs and TSS treatment amounts for the site. Provide additional, as needed.
BMP BMP Type Total Impervious Calculated TSS TSS Treatment by
Eff (%) Overflow (ft/s) Eff (%) Overflow (ft/s) Eff (%) Overflow (ft/s) Eff (%) Overflow (ft/s)
40% 1.74E-02 55% 6.28E-03 70% 2.54E-03 85% 8.38E-04
41% 1.66E-02 56% 6.00E-03 71% 2.42E-03 86% 7.78E-04
42% 1.58E-02 57% 5.72E-03 72% 2.30E-03 87% 7.18E-04
43% 1.51E-02 58% 5.44E-03 73% 2.18E-03 88% 6.58E-04
44% 1.43E-02 59% 5.16E-03 74% 2.06E-03 89% 5.98E-04
45% 1.35E-02 60% 4.87E-03 75% 1.93E-03 90% 5.36E-04
46% 1.27E-02 61% 4.59E-03 76% 1.81E-03 91% 4.95E-04
47% 1.20E-02 62% 4.35E-03 77% 1.69E-03 92% 4.54E-04
48% 1.12E-02 63% 4.11E-03 78% 1.57E-03 93% 4.13E-04
49% 1.04E-02 64% 3.87E-03 79% 1.45E-03 94% 3.72E-04
50% 9.65E-03 65% 3.63E-03 80% 1.33E-03 95% 3.31E-04
51% 8.88E-03 66% 3.39E-03 81% 1.23E-03 96% 2.90E-04
52% 8.11E-03 67% 3.14E-03 82% 1.13E-03 97% 2.49E-04
53% 7.34E-03 68% 2.90E-03 83% 1.04E-03 98% 2.08E-04
54% 6.56E-03 69% 2.66E-03 84% 9.38E-04 99% 1.67E-04
Catchment Area
or Model Drainage Area (ac)
Cover (ac) Removal (lb/yr) (Lm)
BMP (lb/yr)
A 5K-96” 0.15 0.10 90 90
B C D
Uncaptured --- 0.00 0.00 0.00 ---
Total --- 0.15 0.10 90 90
Section 3.5.21
Maintenance Guidelines for BaySeparator™ System The BaySeparator system should be inspected at regular intervals and maintained when necessary to ensure optimum performance. Like any system that collects pollutants, the BaySeparator™ systems must be periodically maintained for continued effectiveness. Maintenance is a simple procedure performed using a vacuum truck. One of the advantages of the BaySeparator™ systems is the ease of maintenance. The systems were designed to minimize the volume of water removed during routine maintenance, reducing disposal costs. Contractors can access the pollutants stored in each manhole through a 30″ manhole cover. This allows them to gain unobstructed access to the full depth of the system. There is no confined space entry necessary for inspection or maintenance. Vacuum hoses can reach the entire sump area of both manholes to remove sediments and trash. The entire maintenance procedure typically takes less than an hour.
Local regulations may apply to the maintenance procedure. Safe and legal disposal of pollutants is the responsibility of the maintenance contractor. Maintenance should be performed only by a qualified contractor. Contact BaySaver Technologies Inc. at 1-800- 229-7283 for a list of approved contractors in your area.
Inspection and Maintenance
Periodic inspection is required to determine the need for and frequency of maintenance. Inspections should be performed initially every six (6) months. Accumulated sediment and other pollutants must be removed at a minimum every 12 months or when 2 feet of sediment (1.5 feet for the 1/2K model) has accumulated in the bottom of either structure or when visual inspection shows a large accumulation of debris or oil, whichever comes first. Oil or gasoline/diesel spills should be cleaned out immediately.
Inspection Instructions
1. For each BaySeparator™ unit, there are 2 manholes to inspect: the Primary Manhole and Storage Manhole.
2. Remove the manhole covers to provide access to the pollutant storage.
3. Use a dipstick tube equipped with a ball valve (typically a Sludge Judge® or Core Pro®). Follow the proper operating instructions associated with the dipstick tube.
4. Measure the sediment depth in each manhole. After recording the sediment levels, let the dipstick tube drain back into the BaySeparator unit to ensure
pollutants do not leave the unit or the site. Conduct maintenance if necessary.
5. Conduct a visual observation of the unit for trash/debris and structural integrity (cracks, slumping pipes, etc.).
6. Replace the two manhole covers.
7. Conduct a visual observation of the discharge point for soil erosion.
Maintenance Instructions
1. For each BaySeparator™ system, there are 2 manholes to clean: the Primary Manhole and Storage Manhole.
2. Remove the manhole covers to provide access to the pollutant storage.
3. Storage Manhole: Use a vacuum truck to remove and collect all water, debris, oils, and sediment.
4. Storage Manhole: Use a high pressure hose to clean the manhole of all the remaining sediment and debris. Then, use the vacuum truck to remove the rinse water.
5. Primary Manhole: Use a submersible pump to pump the bulk of the water from the Primary Manhole into the clean Storage Manhole. Stop pumping when the water surface falls to one foot above the accumulated sediments.
6. Primary Manhole: Use a vacuum truck to remove and collect all remaining water, debris, and sediment.
7. Primary Manhole: Use a high pressure hose to clean the manhole of all the remaining sediment and debris. Then, use the vacuum truck to remove the rinse water.
8. Both Manholes: On sites with a high water table or other conditions which may cause flotation, it is necessary to fill the manholes with clean water after maintenance
9. Replace the two manhole covers.
10. Dispose of the polluted water, oils, sediment, and trash at an approved facility.
Most local regulations prohibit the discharge of solid material into the sanitary system. Check with the local sewer authority for any required permits and/or conditions to discharge the liquid.
Many places require the pollutants removed from BaySeparator™ systems to be treated in a leachate treatment facility. Check with local regulators about disposal requirements.
11. Additional local regulations may apply to the maintenance procedure.
This procedure is intended to remove all the collected pollutants from the system while minimizing the volume of water that must be disposed. Additional local regulations may apply to the maintenance procedure. Safe and legal disposal of pollutants is the responsibility of the maintenance contractor; therefore maintenance should be performed only by a qualified contractor.