no. 225 to march 12, 2014 executive summary...mar 12, 2014 · ada county highway district • 3775...

___________________________________________________________________________________________________________________ Ada County Highway District • 3775 Adams Street • Garden City, ID • 83714 • PH 208 387-6100 • FX 345-7650 • www.achdidaho.org

John S. Franden, President Mitchell A. Jaurena, Vice President Rebecca W. Arnold, Commissioner

Sara M. Baker, Commissioner Jim D. Hansen, Commissioner

To: Ada County Highway District Commissioners, Director and Deputy Directors From: Darrin Carroll, Design Engineer Date: March 3, 2014 Subject: Ordinance No. 225 – Amendments to Section 8000 – Drainage and Stormwater Management REGULAR AGENDA ‐ March 12, 2014

EXECUTIVE SUMMARY Staff requests formal adoption of amendments to Section 8000 – Drainage and Stormwater Management by Ordinance No. 225. Staff has solicited and obtained input from the various cities, public agencies and stakeholders in Ada County. ACHD has resolved and addressed all of these comments. ACHD Legal has reviewed and approved this policy update. FACTS & FINDINGS 1. The final documents for amendments to Section 8000 “Drainage and Stormwater Management” are

attached. Amendments to Section 8000 are proposed to be adopted by Ordinance No. 225. A pdf version is saved at the following location:

Q:\Engineering\Design\8000‐8200 STORMWATER POLICY UPDATE 2. ACHD Legal has reviewed and approved the proposed 8000 policy update. 3. Policy review history:

a. The draft 8000 policy was sent out for internal and external review December 12, 2012. Every city and stakeholder having interest in ACHD operations was sent a copy of the draft policy with opportunity to comment. Exhibit A is the stakeholder recipient list.

b. A Technical Advisory Committee (TAC) was formed to review and discuss the draft policy updates. Draft documents were sent to the TAC on November 27, 2013. The TAC met on January 22, 2014.

4. On February 19, 2014, staff held a work session with the Commission to discuss the policy amendments

and answer questions. 5. All received comments have been addressed and are attached as Exhibit B.

6. The draft policy amendments integrate with Green Stormwater Infrastructure (GSI) practices and new pond landscaping standards being developed. These items are referenced as external documents currently being developed by the Stormwater Section.

7. The second part of this policy, Section 8200 – ACHD Stormwater Design Tools and Approved BMPs, is scheduled on the regular agenda for adoption on April 16, 2014 by Resolution No. 2035.

FISCAL IMPLICATIONS 8. There will be a cost savings for ACHD and developers in adopting the policy amendments as follows:

a. The amendments propose to reduce the number of sediment tanks used on projects without adversely impacting water quality.

i. The estimated construction cost savings per mile of 5‐lane arterial is approximately $30k. ii. The long term maintenance cost per mile of 5‐lane arterial is estimated to save

approximately $25k. b. The policy amendments no longer require forebays on small ponds, less than 1500 sf (approx.

40’x40’) bottom footprint. i. The estimated land and construction cost savings is approximately $4.5k (2014 valuation)

The cost breakdown for these items is shown in Exhibit C. ALTERNATIVES 1. Approve Ordinance No. 225. 2. Do not approve and remand back to staff for changes. 3. Do nothing. RECOMMENDATION Staff recommends the Board of Commissioners adopt the proposed Ordinance No. 225 attached hereto. Attachments: Proposed Ordinance No. 225 EXHIBIT A – 8000/8200 Stakeholder Review List EXHIBIT B – Review Comment Summary

PROPOSED ORDINANCE NO. 225 FOR SECTION 8000

EXHIBIT A – 8000/8200 STAKEHOLDER REVIEW LIST The parties below received the draft 8000/8200 Stormwater Policy on December 12, 2012. ACHD, INTERNAL Bruce Wong Bruce Mills Steven Price Michael Brokaw Craig Quintana Sabrina Anderson Greg Holverson Dorrell Hansen Brandon Johnson Gary Inselman Christy Little Terry Little Dennis Meredith Tim Nicholson Kaci Bader Jake Spencer Lawrence Korgan Josh Crill Jon Herman Regina Cunningham Jeanne Gage Kristy Heller Dale Kuperus Erica Anderson‐Maguire Kathy Murin‐Waddell Mindy Wallace Jim Pickard Pierson Dewit Justin Bledsoe Kadee Porter Paul Daigle Jim Buffington Timothy Morgan Don Shaw Randy Noble Rich Shaw

OUTSIDE ACHD Tim Burgess – Civil Survey Consultants Matt Hart ‐ Civil Survey Consultants Gordon Law – City Engineer, City of Kuna Justin Walker – City Engineer, City of Star Cathy Ward – City Clerk/Treasurer, City of Star Mollie Mangerich – City of Meridian,

Environmental Division Manager David Miles – City of Meridian, Surface Water

Administrator Kyle Radek – City of Meridian, Assistant City

Engineer Warren Stewart – City of Meridian, Engineering

Manager Steve Siddoway – City of Meridian, Parks &

Recreation Director Bill Vaughan – City of Eagle, Zoning Administrator Rob Bousfield – City of Boise, Assistant City

Engineer Brian Murphy ‐ City of Boise PW Hal Simmons ‐ City of Boise, Planning Director Paul Woods – City of Boise, Environmental

Manager Jim Wyllie – City of Boise, Civil Engineer Joe Canning – Garden City Engineer, B&A

Engineers Colin Schmidt ‐ Garden City, PW Operations

Manager Jenah Thornborrow – Garden City Planning &

Zoning Administrator Mike Williams – City of Eagle, Floodplain and

Current Planning Supervisor Scott Stanfield – Mason & Stanfield, Inc. Gene P. Smith – The Land Group (formerly ENW) Jason Densmer – The Land Group Kathy Stroschein – Engineering Solutions Jay Walker – Brighton Corporation Dave Yorgason – Capital Development David Bailey – Bailey Engineering Ben Thomas – Civil Innovations Jack Harrison ‐ HyQual Nate Runyan – JUB Engineers Doug Camenisch ‐ Parametrix

OUTSIDE ACHD (Continued) Sarah Cordova – Boise State University Greg Vitley – Idaho Transportation Dept. Scott Rudel – Idaho Transportation Dept. Ryan Armbruster – Drainage Dist #3 Frankie Hickman ‐ BCA David Baker ‐ CH2M Engineering Larry White ‐ Six Mile Engineering Kevin McCarthy –KM Engineering Joe Pachner –KM Engineering Mike Dimmick – Drainage Dist #4 Bryce Farris – Attorney for NMID, SID, DD2, DD4 Matt Munger – Munger Engineering Barry Semple – RiveRidge Engineering Jim Conger – Conger Management Group Jim Coslett – Rock Solid Civil Chad Kinkela ‐ CK Engineering

The parties below received the newest draft 8000/8200 Stormwater Policy on November 27, 2013. ACHD, INTERNAL Bruce Mills Erica Anderson‐Maguire Joan Meitl Dale Kuperus Pierson Dewit Kathy Murin‐Waddell Justin Bledsoe Timothy Morgan Tim Nicholson OUTSIDE ACHD David Bailey Scott Sherrow

EXHIBIT B – REVIEW COMMENT SUMMARY

6. The draft policy amendments integrate with Green Stormwater Infrastructure (GSI) practices and new pond landscaping standards being developed. These items are referenced as external documents currently being developed by the Stormwater Section.

7. The second part of this policy, Section 8200 – ACHD Stormwater Design Tools and Approved BMPs, is scheduled on the regular agenda for adoption on April 16, 2014 by Resolution No. 2035.

FISCAL IMPLICATIONS 8. There will be a cost savings for ACHD and developers in adopting the policy amendments as follows:

a. The amendments propose to reduce the number of sediment tanks used on projects without adversely impacting water quality.

i. The estimated construction cost savings per mile of 5‐lane arterial is approximately $30k. ii. The long term maintenance cost per mile of 5‐lane arterial is estimated to save

approximately $25k. b. The policy amendments no longer require forebays on small ponds, less than 1500 sf (approx.

40’x40’) bottom footprint. i. The estimated land and construction cost savings is approximately $4.5k (2014 valuation)

The cost breakdown for these items is shown in Exhibit C. ALTERNATIVES 1. Approve Ordinance No. 225. 2. Do not approve and remand back to staff for changes. 3. Do nothing. RECOMMENDATION Staff recommends the Board of Commissioners adopt the proposed Ordinance No. 225 attached hereto. Attachments: Proposed Ordinance No. 225 EXHIBIT A – 8000/8200 Stakeholder Review List EXHIBIT B – Review Comment Summary

PROPOSED ORDINANCE NO. 225 FOR SECTION 8000

EXHIBIT A – 8000/8200 STAKEHOLDER REVIEW LIST The parties below received the draft 8000/8200 Stormwater Policy on December 12, 2012. ACHD, INTERNAL Bruce Wong Bruce Mills Steven Price Michael Brokaw Craig Quintana Sabrina Anderson Greg Holverson Dorrell Hansen Brandon Johnson Gary Inselman Christy Little Terry Little Dennis Meredith Tim Nicholson Kaci Bader Jake Spencer Lawrence Korgan Josh Crill Jon Herman Regina Cunningham Jeanne Gage Kristy Heller Dale Kuperus Erica Anderson‐Maguire Kathy Murin‐Waddell Mindy Wallace Jim Pickard Pierson Dewit Justin Bledsoe Kadee Porter Paul Daigle Jim Buffington Timothy Morgan Don Shaw Randy Noble Rich Shaw

OUTSIDE ACHD Tim Burgess – Civil Survey Consultants Matt Hart ‐ Civil Survey Consultants Gordon Law – City Engineer, City of Kuna Justin Walker – City Engineer, City of Star Cathy Ward – City Clerk/Treasurer, City of Star Mollie Mangerich – City of Meridian,

Environmental Division Manager David Miles – City of Meridian, Surface Water

Administrator Kyle Radek – City of Meridian, Assistant City

Engineer Warren Stewart – City of Meridian, Engineering

Manager Steve Siddoway – City of Meridian, Parks &

Recreation Director Bill Vaughan – City of Eagle, Zoning Administrator Rob Bousfield – City of Boise, Assistant City

Engineer Brian Murphy ‐ City of Boise PW Hal Simmons ‐ City of Boise, Planning Director Paul Woods – City of Boise, Environmental

Manager Jim Wyllie – City of Boise, Civil Engineer Joe Canning – Garden City Engineer, B&A

Engineers Colin Schmidt ‐ Garden City, PW Operations

Manager Jenah Thornborrow – Garden City Planning &

Zoning Administrator Mike Williams – City of Eagle, Floodplain and

Current Planning Supervisor Scott Stanfield – Mason & Stanfield, Inc. Gene P. Smith – The Land Group (formerly ENW) Jason Densmer – The Land Group Kathy Stroschein – Engineering Solutions Jay Walker – Brighton Corporation Dave Yorgason – Capital Development David Bailey – Bailey Engineering Ben Thomas – Civil Innovations Jack Harrison ‐ HyQual Nate Runyan – JUB Engineers Doug Camenisch ‐ Parametrix

OUTSIDE ACHD (Continued) Sarah Cordova – Boise State University Greg Vitley – Idaho Transportation Dept. Scott Rudel – Idaho Transportation Dept. Ryan Armbruster – Drainage Dist #3 Frankie Hickman ‐ BCA David Baker ‐ CH2M Engineering Larry White ‐ Six Mile Engineering Kevin McCarthy –KM Engineering Joe Pachner –KM Engineering Mike Dimmick – Drainage Dist #4 Bryce Farris – Attorney for NMID, SID, DD2, DD4 Matt Munger – Munger Engineering Barry Semple – RiveRidge Engineering Jim Conger – Conger Management Group Jim Coslett – Rock Solid Civil Chad Kinkela ‐ CK Engineering

The parties below received the newest draft 8000/8200 Stormwater Policy on November 27, 2013. ACHD, INTERNAL Bruce Mills Erica Anderson‐Maguire Joan Meitl Dale Kuperus Pierson Dewit Kathy Murin‐Waddell Justin Bledsoe Timothy Morgan Tim Nicholson OUTSIDE ACHD David Bailey Scott Sherrow

EXHIBIT B – REVIEW COMMENT SUMMARY

Section 8000 Stormwater Policy Summary of Changes

Section # Title From Comment

General Moved exhibits to a new Appendix instead of intermingling within the text.

General BCA

Letter saying they were not included in the 2010 review process, SD facilities increased size over 40% per comments from

JUB. Response: see next item

General JUB, ACEC

What necessitated the 2010 policy? What failures were there? Storage facility size increased over 40%. Response: The

40% volume increase is false. Changes were made to simplify and improve consistency of calcs, mostly seepage beds:

deleted 2/3 sidewall method, deleted 1‐ft freeboard, perc during first hour.

8001 Purpose of This Policy ACHD‐DC Deleted redundant text about the purpose of the Policy.

8002

ACHD Stormwater Design

Tools and Approved BMPs ACHD‐DC Deleted redundant text also found in 8003 regarding updates.

8004 Definitions LEI‐SS Add NPDES to list of definitions. DONE

8004.6 HEC‐14, HEC‐22 ACHD‐DC Referenced "current edition."

8004.7

Home Owner’s Association

(HOA) ACHD‐DC Grammar correction.

8004.11 Inlet Protection ACHD‐DC Grammar correction.

" " LEI‐SS Take policy out of definition terms: references to examples. DONE

" " ACEC Add approved equal for inlet protection. Done.

8004.13

Pre & Post‐Development

Discharge LEI‐SS

Add the words "stormwater" and "runoff" around the word "discharge". Take out reference to more stringent if irrigation

dist defines differently. DONE

8004.14

Pretreatment, Pretreatment

Facilities LEI‐SS Take policy out of definition terms: references to examples. DONE

8004.15

Primary Treatment/Storage


8004.16

Primary Treatment/Storage


8004.18 Riprap LEI‐SS Redefine riprap: angular rock, delete concentrated runoff reference. DONE

8004.19 Treatment Train LEI‐SS Take policy out of definition terms: references to examples. DONE

8004.2

Water Quality Capture

Volume (Vwq) LEI‐SS Delete high flows can be bypassed… DONE

8007 Performance Standards LEI‐SS Change "where SW mgt is reqd to under ACHD mgt authority. DONE

8007.1 Standard No 1: Infiltration LEI‐SS Delete reference to filter sand. DONE

8007.2 Standard No 2: Pretreatment LEI‐SS Revise language about high flows being bypassed, not true for roadside swales. DONE

8007.4

Standard Number 4: Water

Quality Management ACHD‐DC Grammar correction. DONE

8008.1

Ditch Abandonment, Ditch

Perpetuation LEI‐SS Revise the term "certify" for Engineer shall certify if a ditch can be abandoned. Clarify easement language. DONE

8009.1 Site Evaluation/Feasibility LEI‐SS Reference to retention ponds and seepage beds as generally being used is not needed. DISAGREE, NO CHANGE

8009.1 Site Evaluation/Feasibility LEI‐SS Remove statement for a rep from Stormwater Sect. to be invovled at concept design. DONE

8009.1 Site Evaluation/Feasibility BE‐MP/DB Add ROW locations pervious/impervious areas as considerations. DONE

8009.2 Infiltration Feasibility ES‐KS

Impractical to get test pits dug within 200' of SD storage facilities at the concept phase. Revised language to change the

200' requirement to "digging multiple test pits or bore holes on the site to establish the initial soil profile, infiltration rate,

water table, and/or depth to bedrock."

8009.2 Infiltration Feasibility LEI‐SS Grammer, bullet 3, say infiltration facilities not permitted first. DONE

8009.3 Groundwater ES‐KS

Impractical to put observation wells at the ultimate infiltration facility location. Revised language to change one well at

each final facility to "multiple observation wells shall be installed on the site to determine the groundwater profile for use

in final design."

8009.3 Groundwater ACHD‐DC Grammar correction.

" " ACHD‐GI Added Boise River influence to groundwater should also be addressed. In response to Marianne Williams Park SD

" " ACHD‐DK No changes. Q: Is 3‐ft separation to GW mandated somewhere or is this our preference? ACHD preference. No change.

" " ACEC

Comment spreadsheet said ACHD requires a min 1.5‐ft separation to groundwater. Make allowance for <3‐ft separation

to groundwater with variance. Response: IDEQ and IDAPA say 1‐ft and 2‐ft min (>2500 GPD) separation, ACHD "is

responsible for protecting the health of its citizens and fulfilling the requirements set forth by state and federal rules and

permits.” ACHD will stay at 3‐ft separation. A variance of the 3‐ft separation may be considered for roadside swales that

take sheet flow off the pavement, but not storm facilities with concentrated pipe flow.

" " BE‐MP/DB

Does not mention impervious barrier. RESPONSE: See first sentence: GW must be separated 3‐ft unless there is an

impervious barrier.

8009.4 Observation Wells ACHD‐DK No changes. Q: Is 3‐ft separation to GW mandated? No, it is an ACHD requirement. No change.

" " ACEC

Is 3‐ft separation to groundwater is not the requirement, suggest changing to "verify the separation requirements are

met…" Response: Facilities require 3‐ft separation.

8009.5

Boise River & Surface Water

Influences ACHD‐DC

Added language to evaluate project sites close to the Boise River or other surface water to consider the influence that

changes in surface water flow rates and depths have on the storm system. For the Boise River, the Engineer shall

demonstrate that the storm system is free draining (no surcharge of pipes) for the various Boise River flow rates up to and

including 7000 cfs.

8009.6 Bedrock ACHD‐DK

No Changes. Q: Is 3‐ft separation to bedrock mandated somewhere or is this our preference? Preference, needed for 3‐ft

filter sand. No change.

8009.7

Design Life, Cost Analysis

(Capital Projects) ACHD‐DK

The required cost analysis for BMP maintenance costs makes consultant projects expensive. Agree. Removed the

requirement.

8010.1.1 IDWR Requirements LEI‐SS

Who is the Engineer to submit IDWR forms, what if they are nto part of construction. CLARIFIED LANGUAGE the "design"

Engineer. DONE



8010.1.2

8010.1.2 Setbacks and

Horizontal Separation

Distances ACHD‐DK No Changes. Q: Is 3‐ft separation to GW mandated...No change.

" " ACHD‐DK Clarify meaning of structures to be homes. Done.

" " ACEC

Does 50‐ft separation from surface waters include all surface waters like irrigation facilities or just perennial waters?

Response: Added "perennial" to surface waters.

" " ACEC

Horizontal separation distances between potable water and infiltration facilities is currently 25‐feet. Revised guidance to

10‐ft. Does ACHD allow 10‐ft? Response: 10‐ft is allowed, changed to 10‐ft.

" " LEI‐SS

Review language, confusing, strike reference to 10‐ft separation from storm mains. DONE Reworded to clarify, deleted 10‐

ft separation to storm main reference.

" " ACEC

25‐ft separation to potable water vs. 10‐ft? Response: Revised language to be 10‐ft separation, 1.5‐ft vertical for

crossings, >1.5‐ft vertical per IDAPA. Added language "A minimum 10‐foot horizontal separation is required between

potable water mains, storm mains and subsurface infiltration facilities... Facilities not meeting the separation requirement

will require mitigation measures to prevent potential hydrocarbons in stormwater from coming into contact with PVC

potable water pipe..."

8010.1.3

Subsurface Infiltration

Facilities ACHD‐DC, LEI‐SS Clarification that seepage beds should be in common lots, second priority is in a planter strip, followed by under sidewalk.

" " ACHD‐DC

Revised language for markers: "Subsurface infiltration facilities without a manhole access at each end longitudinally

require an ACHD Storm Drain Marker, per Detail 1 in the Design Manual."

8010.1.6

Alternative Procedure for

Infiltration Testing LEI‐SS Delete reference to 5‐in casing for flexibility. DONE

8011 Requirements for Ponds ACHD‐DC Move reference to lengthen flow path from all ponds to detention ponds. DONE

8011.1 Pond Slopes (NEW SECTION) ACHD‐DC, BE‐MP/DB Added new section to specify 4:1 side slopes, 3:1 max.

8011.2 Inlet Pipe Flow Protection LEI‐SS

Reconsider riprap instead of flow spreader at pipe outfalls. DONE, Back to Riprap, Flow Spreader doesn't slow the flow,

just spreads it.

8011.3

Forebays & Primary Storage

Basin Bailey‐DB, ACHD‐DC Exception for forebay requirement if pond bottom <1500 sf

8011.3

Forebays & Primary Storage

Basin ACHD‐DC Removed orifice plate as an option, require removable slide on plastic cap.

8011.5 Emergency Spillway Options LEI‐SS

Should encourage emergency spillways, within guidelines of approval from irrigation companies. RESPONSE: messaged

the language to encourage.

8011.6.2 Outlets for Detention Facilities ACHD‐DC Removed orifice plate as an option, require removable slide on plastic cap.

" " ACHD‐DC, LEI‐SS Add language for staged discharge <=predevelopment for 2, 25, and 100‐year design flows. DONE

8011.7

General Landscape Guidelines

for Stormwater Facilities ACHD‐DC

Added spec for fencing on ACHD owned ponds: 22 mil vinyl thickness and 12 gauge thickness for the steel. Specify (4' tall?)

6' height for fence.

" " ACHD‐DC Added language to clarify exposed sand for infiltration facilities, grass allowed for multi‐use upon approval by ACHD.

" " ACHD‐DC

Added "with a top rail" language to the 6‐foot tall black poly coated chain link fence requirement for ACHD ponds. NEED

TO ADD TO STD DWG

8011.9

Landscape Guidelines for

Stormwater Ponds ACHD‐DC

Changed section to apply to ACHD ponds instead of just ponds in Meridian. Reference detail 8. Added HOA ponds to this

standard without a fence.

8012

SW Design Methods &

computations Bailey‐DB

Seepage beds have become excessively large given all the safety factors ACHD has added. Response: seepage bed sizing

has been revised, storm conveyance changed from 100‐yr to 25‐yr.

8012.2 Rational Method ES‐KS, ACHD‐DC,TN,GI,BGM

Objection to using the entire lot area in drainage calcs. Revised language to allow 1/2 of lot. ACHD has not had a problem

with half the lot in the past. We received many comments requesting this change. New language reads: "For subdivisions,

the drainage contribution area shall include the areas that flow to the storm drain including the portions of the lot graded

to the street or one‐half of each lot area, whichever is greater."

8012.2 Rational Method JUB Object to using entire lot area in calcs. See ES‐KS above.

8012.2 Rational Method LEI‐SS Take out reference to triangular hydrograph, doesn't add value. Agree. DONE

8012.2.1 Coefficients of Runoff BC‐RB

Provide C‐Factors that factor in the entire lot, slope of the lot. Clarify differences in home/lot density (Harris Ranch skinny

vs. normal lot). No change ‐‐Weighted averages will adjust for smaller, impervious lots.

" " ACHD‐DC Modified C Factor table align Single Family & Multi Family C Factors.

8012.3.1 Design Storm Runoff Volume JUB

Clarify if WQ volume is in addition or part of the 100‐year design volume. Response: WQ is deducted from the total 100‐

year design volume.

8012.3.1 Design Storm Runoff Volume LEI‐SS Modify language instead of saying spreadsheet is required to say it is the format required. NO CHANGE

8012.3.2

Allowance for Sediment

Storage JUB

Clarify if 15% sediment for ponds applies only to WQ or total volume? Does seepage bed 25% sediment factor apply to

entire volume or just WQ? Is a S/G Trap considered approved pretreatment to reduce the 25%? Response: Clarified

section by removing "unless an approved pretreatment system sized for the VWQ is included." Seepage bed calcs were

revised, see next item.

8012.3.2


Storage ACHD‐DC,TN,GI,BGM

Revised sediment storage requirement for seepage beds and other subsurface facilities. "The entire design storm runoff

volume shall be adjusted for sediment storage as follows:

a. In‐situ infiltration rates <8 in/hr, sediment factor is 15%.

b. In‐situ infiltration rates >=8 in/hr, sediment factor is 0%."

8012.3.2


Storage LEI‐SS Delete reference to sizing seepage beds for the largest storm in a 24‐hour period. DONE

8012.3.4 Time of Concentration Calcs ACHD‐DC Added TR‐55 to list of approved methods.

8012.4 WQ Flow LEI‐SS Strike reference on ips to 100‐year storm. DONE

8012.6 Conveyance ACHD‐DC,TN,GI,BGM, ACEC Revised language to 25‐year primary conveyance from 100‐year.



8012.6.4

Hydraulic Capacity and Pipe

Size ACEC

48‐inch max pipe diameter size may not be adequate for 100‐year conveyance. Response: changed to 25‐year

conveyance.

8012.6.5 Velocities ACHD_DC, ACEC, LEI‐SS

Changed min pipe velocity to 3 fps for self cleaning and max 15 fps. This is average for other agencies. Old standard was 2

fps min and 8 fps max.

8012.6.8 Siphons ACHD‐GI Added language that all conveyance pipes shall be free draining.

" " ACHD‐GI

Siphons cannot be avoided on some capital projects ‐‐ revised language to say "unless a variance is specifically approved in

writing."

8013.3

Stormwater Concept Plans

(Capital Projects) ACHD‐DC

Consider removing requirement for in‐house projects. Agree, internal projects have concept reviews from Stormwater

staff.

8013.4

Stormwater Concept &

Master Plans (Development

Projects) Bailey‐DB

Master SD Plans for development should be followed for subsequent phase reviews. Response: Added language to say

reasonable effort will be made to follow master plans on future phases subject to policy changes.

8013.4 ACHD‐GI Change from coordinate with Stormwater Staff to Development Review Staff. Response: done.

8013.5

Temporary Stormwater

Storage Facities (Development

Projects) ACHD‐TN, LEI‐SS

Move part about temp ponds being outside future R/W to new section. Added max gutter flow length of 100‐ft with no

structures.

" " ACEC

Requirement for stormwater report and basin map will increase project design cost. Response: Noted, but is needed for

all project reviews.

8013.5 .6

Stormwater Preliminary Plan

Submittal ACHD‐DC Clarified that O&M Manuals are required for Development Projects only.

" " ACHD‐DC Added requirement for subbasins to be color and hatched for readability.

" " ACHD‐KB

Added note to provide a typical section for storage facilities, design elevations, note for who prepared the soils report and

source of groundwater data, design infiltration rate.

8013.5 &

8013.15

Operation & Maintenance

(O&M) Manual JUB

Is an O&M manual for light maintenance only? Does ACHD require an O&M for public facilities they maintain? Response:

O&M for light maintenance only, O&M is not required for public facilities ACHD maintains. For 8013.5 added "See Section

8013.15 for details regarding O&M Plans".

8013.9

Maintenance Access and

Easements ACHD‐KB,JG Curb cut for maintenance access, even with rolled curb

8013.10

Post‐Construction

Submissions ES‐KS

11x17 drawings are not scalable if they were originally 24x36. Revised language to delete scalable. We don't need 11x17

plans to be scalable when there are hard dimensions.

8013.10.2 Easements ACHD‐DC, BE‐MP/DB Simplify language to clarify.

8013.16

Operation & Maintenance

(O&M) Manual ACHD‐TN

CC&R's shall include the O&M Manual and shall be recorded. HOA and dues paying organization responsible for light

maintenance.

8015.4 Catch Basins, Frames & Grates ACHD‐JG HILL SLOPE >3%, VANED GRATES, added new language.



8201.2 Modifications and Addenda LEI‐SS

Add timeframe or send notifications when updates will be posted to website. RESPONSE: cannot commit to

having updates on a regular basis, users need to check the website to verify they have the current version. No

change.

8200 details ACHD‐PD Misc. markups on 8200 details

" ACEC Several dimensions missing when compared to prior version.

8200 pond details ACHD‐KB Add the word "light" before maintenance (typ). Clarify staged outlet control structure.

8202.1

Intensity Duration Frequency Curve (IDF

Curve) ACHD‐DC Updated IDF Curve to include SID 30 year storm

8202.2 ACHD Stormwater Design Spreadsheet ACHD‐DC Changed Template to Spreadsheet. Revised language to reference MS Excel spreadsheet.

" " ACHD_DC Clarify references to spreadsheet and worksheet ‐‐ Done, changed to spreadsheet.

" " ES‐KS

Spreadsheet is difficult to use for multiple drainage areas. Added new language: "ACHD may approve an

Engineer’s alternative format to the spreadsheet if the volume and peak flow calculations are summarized for

each storage facility and the calculations meet or exceed the ACHD calculated minimum values. Computer

software printouts that are not summarized by storage facility will not be accepted."

8202.5 8202.5 Inspection Checklists ACHD‐DC Grammar.

8202.6 Appendix E Detail 1 ACHD SD Marker ACHD‐KB Added language to allow alternative markers: brass cap, MH, observation well at end of beds

" " ACEC

Is contact info for excavator's use provided on brass cap or MH? Response: No, marks limits of seepage bed

only.

8202.6

Appendix E Detail 5 Emergency Spillway

Access ACHD‐DC Deleted detail, not used.

8202.6

Appendix E Detail 5 Access Roads and

Turnarounds ACHD‐DC, KB

Delineator needed? Response: Changed detail number to 5. Modified width to 14‐ft. No delineators are

required.

8202.6

Appendix E Detail 6 & 7 Groundwater

Observation Well Drill ACHD‐DC,DM Created separate well details for drill and one for trench beds. Added locate wire.

" " ACHD‐DC

Make well pipe 4" to 6" for both drill and pit. 2" is preferred for drill as it fits our data loggers, is cheaper and is

industry standard. For pits, 6" is appropriate because it gets backfilled and is subject to damage. Added locate

wire.

" " ACHD‐DC Add 2" PVC with slots per SD‐627. Response: DONE

" " ACEC Gauge of locator wire. Response: Specifiec 18 ga copper with green insulator

8202.6 Appendix E Detail 8 ACHD Ponds ACHD‐DC Deleted references to City of Meridian, standard for all ACHD ponds

" " CSC‐MH

Some pond details show access ramps to the primary and some to the forebay. Should be forebay only?

Response: Correct, forebay only. Moved access ramps to forebay on the pond details.

" " ACHD‐DC Introduce S/G Trap diversion with orifice cap on WQ pipe.

8202.6 Appendix E Detail 9 Borrow Ditch ACHD‐JG New detail

" " ACEC

Specify Pitrun per ISPWC, Slope 3:1 or flatter instead of MAX, Is 3' gravel shoulder in addition to paved

shoulder?. Response: Done

8202.6 Appendix E Detail 10 Shallow inlet ACHD‐DC,DM New detail

" " ACEC

Standardize fonts, Show sections, add dimensions to B‐B, Length of rebar in apron, Reference swale detail, Is

slot CIP, Reinforcing dimensions. Response: Done

8202.6 Appendix E Detail 11 Scupper Inlet ACHD‐DC New detail

" " ACEC

Standardize fonts, Show sections, add dimensions to sections, Reference swale detail, dimensions, Rename to

delete scupper reference. Response: Done

8202.6 Appendix E Detail 12 Drop Inlet Layout ACHD‐DM,JS New detail

" " ACEC Provide not to clarify purpose of detail. Response: Done

8202.6.8 List of Approved Stormwater BMPs ACHD‐DC

Added language to clarify any approved primary treatment BMP can be used for pretreatment but pretreatment

BMPs cannot be used for primary treatment. A Treatment Train consisting of an approved pretreatment and

primary treatment BMP shall be used.

8202.7 List of Approved Stormwater BMPs ES‐KS, LEI‐SS

Table is confusing, not sure what the purpose is. Revised the table to remove the combination Primary

Treatment/Storage part which was confusing. Response: Revised to clarify.

New BMP Horizontal Sand Filter ACHD_DC Added detail for new horizontal sand filter for high GW.

BMP01 Sand/Grease Trap BC‐RB

S/G Traps that discharge to sensitive waterways should have more strict requirements. No changes. Clarified

that S/G Traps are pretreatment only, a pond, seepage bed or other primary BMP is required in a treatment

train.

" " LEI‐SS Do not use S/G Tank as energy dissipater. AGREE, REVISED LANGUAGE to require diversion MHs.

BMP02 Infiltration Basin With Forebay JUB, ACEC

The inlet pipe to a pond is above the 100 year WSE which is not practical. Why is 3‐ft sand required for ponds

when DEQ and ACHD seepage beds require only 1.5‐ft? Response: Agree, the pipe location has been modified

on all pond drawings. The 3‐ft sand requirement for ponds instead of 1.5‐ft is an extra buffer for light

maintenance. The sand must be tilled, raked, and sediment removed which reduces the total thickness so the

extra 1.5‐ft is so the total thickness does not go below 1.5‐ft.

" " CSC‐MH

Decrease sand thickness in primary basin, agree 3‐ft sand in the forebay. Response: Can be no sand ‐‐ clean

pitrun in the primary

BMP03 Detention Pond With Forebay ACHD‐KB

Changed requirement to match Pre Q25, 50, 100 flow rates to "pre‐project flow rates." Provide detail for outlet

structure.

BMP04 Seepage Bed With Optional Chambers JUB

Why 25% sediment requirement if S/G Trap and 30" perf pipe are used for sediment? Response: INTERIM Policy

revised to 0% sed. With 8"/hr perc rate, otherwise 15%

" " ACHD‐JP, DH, GH

Sleeve crossings through seepage beds 10‐ft either side of bed, use C900 or SDR‐35. Response, made new std

drawing, extends 5‐ft



" " ACHD‐DC

Clarify seepage bed sizing is the max volume in 24‐hrs. Added to 8012.3.2. Also added 8012.3.1 to establish

ACHD Stormwater Design Spreadsheet establishes the minimum conveyance and storage sizes.

" " ACHD‐DM

Clarify bed must be clear of the full roadway section, is 24" half perf pipe allowed? Response: Done, yes 24" or

18" is allowed under the road.

" " ACHD‐KB

Provide note for compaction if under the road. Response: Created new detail that includes water compaction

requirement.

" " ACHD‐KB Separate details for 30" isolator and chambers. Response: Shaded linetypes to differentiate.

" "

ACHD‐

DC,BGM,TN,GI Change isolator pipe to 18" standard for all beds.

" "

ACHD‐

DC,TN,DM,KB,TM Specify min 1‐ft Pitrun top of bed to subgrade, if <1‐ft use angular rock, woven fabric at top of bed

" " ACHD‐DC For splitter, allow S/G Trap or hydrodynamic separator

" " ACHD‐JG UPDATE BMP01 DETAIL FOR BOTTOM BAFFLE AT CENTER PERF PIPE ELEV. Done

BMP06 Bio‐filtration swale ACHD‐KB Revise depth from 0.5 inches to 0.5 ft. Response: Done.

" " ACHD‐KB What is plant/soil complex? Response: Included topsoil spec, plants up to designer.

" " LEI‐SS

Add 200‐ft min length per IDEQ. DONE. Consider 2% min slope. RESPONSE: much of the valley is flat plus want

swale flat to infiltrate. NO CHANGE.

BMP07 Rural Swale ACHD‐DM Change sandy topsoil thickness from 12" to 6". Response: Done

" " ACHD‐KB Delete reference to ACHD owned facility since swales are all ACHD owned. Response: Done.

" " ACHD‐KB Clarify language on Note A, the 1' shoulders extend total width to 56'/28' half width

BMP09 Sand Filter Extended Detention Pond ACHD‐KB

Does 6‐inch pipe get cleaned? When is gravel vs sand used for the underdrain? Done, Yes, a 6" pipe could be

cleaned per M&O.

BMP10 Wet Extended Pond ACHD‐KB

Would water in the forebay become stagnant? If aerated, would particles resuspend? Response: Added

comment for aerator, otherwise water gets stagnent. There would be some minor resuspension.

" " ACHD‐KB Move high flow bypass note, makes it look like high flows go to the forebay. Response: DONE

8202.9 Other Resources ACHD‐DC Updated DEQ weblink.

BMPs All ACHD‐DC Made general edits to standard drawings for clarity

BMP01 Sand and Grease Trap ACHD‐TM

Request from M&O to reduce the number of structures to clean as pipes self clean from water velocity.

Reduced S/G Tanks to one 1000 gal tank per 3.33 cfs at downstream prior to seepage bed or pond or

hydrodynamic separator w/bypass. All S/G Traps will divert high flows to a bypass pipe in the inlet chamber.

A removable slide‐on orifice cap at the outlet pipe will meter flow through the baffles. A removable 90°

elbow is proposed on the bypass pipe so floatables are retained in the inlet chamber.

" " ACHD‐DC

Minor language to clarify combo box is only allowed as an alternative where a standard inlet with Sand and

Grease Trap or Water Quality Unit may not be practical due to utility conflicts.

" " ACHD‐JG Show Inv out requirement above bottom of perfs for BMP04.

" " ACHD‐DC, KB

Deleted ADS Water Quality Units, not being used and new high flow bypass pipes won't work out the side of a

round tank.

" " ACHD‐TN Is diversion from MH before S/G Trap? Response: Diversion is proposed at S/G Trap out of the inlet chamber.

" " ACHD‐KB

Include detail for the reducer and invert elevations to 30" pipe. Response: Not applicable, no longer show Snout

Hoods as a standard for seepage beds.

" " ACEC

S/G Traps designed by the precaster via shop drawings after contract award. How will designer know how tank is

configured since design is by the precaster? Response: No change.Plans will need to show invert elevations and

top of box to properly size the orifice.

" " ACEC Add note for Engr. to design orifice opening, Elev conflict on elevation of high flow outlet. Response: Done

BMP02 Infiltration Pond With Forebay ACHD‐DC Clarify pond stores the peak design storm...with no discharge from the site.

" " ACHD‐DC Added New POND NOTES, typical for all ponds.

" " CSC‐MH Show access road going to ramp and structures, 3:1 side slope all sides‐‐Done

" " ACHD‐KB Note D & E should swap. Done.

" " ACHD‐KB Is there a detail for the high flow bypass structure? Response: Added more detail to BMP01 S/G Trap.

" " ACHD‐KB

Why 3:1 slope on 1 side and 4: on other? Can access road go to the ramp and structures? Why does road go all

the way around? Response: Revised access road to only go to structures and included turnarounds.

" " ACHD‐KB Change note to backfill over‐ex with pitrun instead of uncrushed agg. Response: Revised to say Pitrun.

" " ACEC

Is intent of emergency spillway for Q>100 or if pond plugs? Suggest deleting the >. Response: Removed

emergency spillways from pond details and added a note: "Emergency Spillways Encouraged Where Possible."

BMP03 Detention Pond With Forebay ACHD‐KB Added language to reference downstream receiving facilities.

" " ACHD‐KB Show required distance of turnaround from last structure ‐‐ DONE, 50‐ft

" " ACHD‐KB Outlet structure does not match other ponds ‐‐ DONE, clarified with Pond Notes

" " ACHD‐KB

Legend notes 11 & 12 don't match detail, add OW location 15'‐20' from pond, Note 5 says min slope 0.4% but

plan shows 1%, slope 1% and 2% confusing. Response: Deleted concrete valley gutter, specified 1% min



" " ACHD‐KB Specify length of access road before a turnaround is needed. Response: Revised to say 05‐ft on Ponds Note E.

" " ACEC Requirement for liner on low flow channel. Response: Removed low flow channel.

ACHD‐DM, DC

Impervious liner on pond details, change to grass and C/D Soils, liners bad ‐dirt slides, etc. Response: Added

Type D & C Soils, Clay or other to BMP03‐Detention Pond.

8209.9.4

BMP 04 Seepage Bed With Optional

Stormwater Chambers (Pretreatment,

Primary Treatment & Storage) ACHD‐DC

Removed 60" MH with skimmer hood as an alternative. The MH is not as effective for end of line treatment as a

S/G Tank with bypass.

" " ACHD‐DC Revised language to clarify entire 100‐yr storage is for beds & chambers.

" " ACHD‐DM Identify cover requirements under road/sidewalk.‐‐ Done, added note to design by engineer

" ACHD‐DM

Provide separate detail for bed and storage chambers.‐‐Done, increased separation for clarity, made chamber

option light lines.

" " ACHD‐DM Set maximum bed width to 15‐ft‐‐DONE

" " ACHD‐DM

Note 6 & 11 same. Response ‐ Deleted Note 11. Also, increase 1' cover to 1.5' to allow for form placement

without punching fabric with stakes. Response ‐ DONE. Change to 1.5‐ft

" " CSC‐MH, ACEC

Optional MH at the end of seepage beds. Is it needed for maintenance? Response: MH was deleted as M&O

said they do not need it.

" " ACHD‐KB

Clarify note 5 omit 2" drain rock in high groundwater, angular rock not clearly delineated. Response: dimensions

from GW control depth of drain rock, chips revised to show as triangles.

" " ACHD‐DM,JS Split into two drawings: 1‐in common lot, 2‐under road.

" " ACHD‐TN

1‐Are optional 15" and 18" perf pipes being considered? 2‐Show baffle wall to center of 30" pipe, 3‐Verify Note

#5, 4‐Callout OW 5' inside and 20' outside bed, 5‐is MH with Snout still an option? Response: 1‐Yes 18" is now

standard, 2‐done, 3‐DONE, 4‐DONE, 5‐NO

" " ES‐KS

Requirement to assume 0 infiltration and 25% sediment for sizing seems excessive compared to old way

allowing deduction for 1‐hr infiltration and only 15% sediment. Response: Interim policy changed to 0 sed for 8

in/hr. NO CHANGE.

" " ES‐KS

Do not agree with eliminating Snouts & MHs instead of Sand/Grease Trap. Cannot always get 0.35' drop

through S/G Trap, MH and Snout allows 0.1' drop. NO CHANGE. S/G Trap was revised previously to allow 0.20

drop.

" " ACHD‐TM

For seepage beds, show MH at end of perf pipe after S/G Trap to clean back without need to remove orifice

caps. Response: DONE

ACHD‐DC, ES_KS Standardize orifice caps. Response: Done

" " ES‐KS Provide detail for 90⁰ elbow and removable orifice cap, table of orifice size per cfs. Response: Done

" " ACHD‐JP

Sleeve crossings through seepage beds 10‐ft either side of bed, use C900 or SDR‐35. Response: DONE, new

detail #13 created

" " ACHD‐DC

Void Ratio for 3/4" Chips in seepage beds is 0.40, same as 2" round per sources for ADS and Urban Runoff

Quality Management Manual.

" " ACHD‐DC Show seepage beds in profile view.

BMP05 Sand Vault ACHD‐DC Moved description from Design section.

" " ACHD‐KB Move MH to be over sand, print quality hard to read. Response: shifted MHs, fixed lines to improve quality.

BMP06 Bio‐filtration swale ACHD‐KB

Change 12' access road to 14', show flow apron or riprap. Response: Widened access road, showing flow

spreader or approved energy dissipater.

BMP07 Rural Swale ACHD‐KB Clarified 2' penetration to free draining, continuous sand

ACHD‐DM Added new SD to show check dams for swales with slope & swales with curb measure from curb FL.

BMP09

Sand Filter Extended Detention Pond With

Forebay (Pretreatment, Primary Treatment

& Storage) ACHD‐DK No Changes. Do these 6" pipes get cleaned out, can M&O clean that small ‐ Yes they can be cleaned

BMP10

Wet Extended Retention or Detention Pond

With Forebay (Pretreatment, Primary

Treatment & Storage) ACHD

Why is there a requirement for permanent pool areas to be at least 4 feet deep? Delete extra "deep" in 2nd

paragraph ‐‐ Done, Deleted depth

BMP11

Constructed Wetlands Pond With Forebay

(Pretreatment, Primary Treatment &

Storage) ACHD‐DK

No changes. Does the forebay in a wetland basin treat water and store sediment? YES, No Change required

BMP12 Hydrodynamic Separators

No changes. Can these be used any more? YES for pretreatment only, same as a S/G Trap, no change ‐‐Took

out standard drawings, text only

Detail 2 Inlet Protection Apron and Flow Spreader ACHD‐DC Deleted "Child" reference on protection grate.

" " ACHD‐KB Add riprap sizing requirements as alternate to concrete apron. Response: Added 4xDpipe option.

Detail 4 Flow Spreader Detail ES‐KS

Do not understand intent of detail. Modified detail title to add "For Ponds and Swales." Deleted dimensions in

the center that do not apply. Added note "A FLOW SPREADER SHALL BE USED WHEN LONGITUDINAL GRADE

>1% FOR 100‐FEET OR MORE."

" " ACHD‐KB Remove pipe ‐legend note 1. Response: Deleted pipe

Detail 5 Access Road andTurnarounds ACHD‐DM Change Type 2 road with topsoil over base to Grasscrete/pavers

Detail 6 &

7 Observation Well ES‐KS

Why two details, when is each required? How would 3‐ft deep well look? Why 5' bentonite seal? Revised

details, added new notes to explain drill & pit, modified 5' bentonite dimension to 0‐60".

" " ACHD‐KB

Print is poor quality and detail is hard to read, should be 14' wide instead of 12'. Revised width to 14', plotted

darker with clean lines.

" " ACHD‐KB

What are locator wires for? Dimensions confusing 12‐36" sand and perforations. Response: Inspection

requested the locator wire. Added note to clean up depth, see ES‐KS.



Detail 11 Supper Inlet ACHD‐DM Consider 8" pipe or 10" instead of 12". Response: Changed to 8" so it can be lowered and get more cover.

" " ACHD‐TN

1‐Make Section A‐A detail larger, 2‐is pipe above grate as depicted? 3‐Is there enough cover over pipe?

Response: all modifications were made, for #3‐specified 8" C900 and lowered to match top of grate elev.

Detail 12 Drop Inlet Layout ES‐KS New inlet detail for outlet pipe greater than 18"

" " ACHD‐TN

Add note to not allow pipes from the short end of DI. Response: Inspectors determined a short pipe run <=20‐ft

would be allowed max.

" " ACHD‐DM Specify max 12" pipe into the side, max run 20'. Response: Done.

Detail 13 ACHD‐DH New detail to show seepage bed conflict with sewer line: sleeve and split bed options.

Appendix E ACHD‐TN No callout on the Table of Contents. Response: Fixed.

no. 225 to march 12, 2014 executive summary...mar 12, 2014 · ada county highway district • 3775...

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