Appendix 6. Permeable Alley Preliminary Evaluation

Transcription

1 Appendix 6 Permeable Alley Preliminary Evaluation

2 ACHD Alley Retrofit Project Initial Evaluation Site Selection, Design, and Construction (October 2014) The purpose of this document is to characterize the process associated with the selection, design and construction of two alleys that were retrofit with permeable pavers in downtown Boise in Based on this experience and internal conversations, recommendations will be identified that will inform the use of permeable pavers in alleys going forward. Project selection The initial list of potential alleys was developed by City of Boise staff and a representative of the Downtown Business Association. A primary consideration appeared to be the presence of cooking oil containers. The history of spills is down to 1-2 per year, and the list did not include any active 55 gallon barrels, an old style that is more susceptible to random, late-night tipping events. Another consideration identified by the City was that a few buildings have shallow wells rigged with cooling loops for air conditioning. When the injection well fails, the water pours into the alley. The City s list was reviewed and prioritized by ACHD Maintenance staff and a short list was developed by Stormwater staff. Considerations included the presence of roof drains, basements, easements within the alley, roof composition, and the age of building, redevelopment plans, and below grade windows. The following table describes the additional issues that were evaluated for the final locations for which a design was completed. Alley Evaluation/Selection Factors Issue 3 rd -4 th, Main and Idaho 5 th -6 th, Idaho and Bannock 13 th -14 th, Main & Idaho Demolition Yes Yes Gravel surface Parking St. Luke s has offered to Three buildings would lose NA provide for all buildings during construction parking with alley only access Access Reconfigure Wells Fargo Hurless Brothers drive-through and Chandlee Bldg parking lot No. of property Five Six Four owners (# of Easements) Cost Estimate $123,440 $121,902 $117,886 Dirt Tracking Sources Tuller Dental Ochi Gallery Other potential paver 512 Idaho Ochi Gallery opportunities Hepworth building Visibility High pedestrian traffic Drainage Problems Yes Yes Yes CCDC Activity 2014: Streetscape 2015: Streetscape ACHD Projects 2014: signing, striping, lighting, signal mods. 2015:road work and maintenance 2015:road work/maintenance 2015: road work/maintenance; signal modification; signing, striping, lighting 1

3 Design The alleys selected for design are located between 3rd and 4th Street, north of Main; between 13th and 14th Street, north of Main Street; and between 5 th and 6 th, north of Idaho. As part of the site evaluation, a double-ring infiltrometer test was performed in general accordance with ASTM D in test locations between 3 rd and 4 th and 13 th and 14 th Streets. The tests were performed with a head of water between 6 and 9 inches with rates that varied over time from 0.8 inches to 0.4 inches. Repeated attempts were made to perform a double-ring infiltrometer test at location between 5 th and 6th. However, due to rapid infiltration, the test apparatus could not maintain a constant head during testing. As a result, Terracon performed several falling head permeability tests within the double rings at this test location. The falling head test was performed with an initial head of 15 inches, and the test was repeated for a total of four cycles. Contributing areas from roof drains and adjacent parcels were estimated. The pavement sections for this project were designed to recommendations in the Interlocking Concrete Pavement Institution (ICPI) Permeable Interlocking Concrete Pavement Design Manual (Smith, 2006). The base course was designed to store the 80th percentile storm event, a 1-hour event producing 0.34 in/hr with a 60 minute time of concentration. The designed infiltration rate for the system is 0.5 in/hr. The base course section is designed to be 1.5 foot deep. Construction This past summer (2014) two of the alleys were retrofit with pavers; between 3rd and 4th Street, north of Main and between 13th and 14th Street, north of Main Street. This work was preceded by replacement and/or relocation of utility infrastructure during the 3-4 weeks preceding construction. Construction-related issues included the following: Access: In areas where there was space to work adjacent to the construction area, the contractor was able to proceed more quickly. Utilities: The following work was done prior to construction: a gas line was lowered in one alley; the sewer line was replaced in both alleys; Idaho Power infrastructure was relocated in one alley though a portion of this work was related to the remodeling of the adjacent building owned by Idaho Power; and Century Link replaced/relocated lines in one alley. The Century Link infrastructure in the second alley was not modified at the time though work did occur following the rainfall event the weekend of Sept This work required removal of a section of concrete and dismantling of a 60 foot section of pavers and sub-base materials. Construction duration: Alley construction took longer than anticipated due to the utility work that preceded it. As a result, adjacent property owners did not receive accurate information about the duration of the project. Construction impacts: Property owners expressed concern about noise, dust, compaction, vibration, loss of parking and loss of access to delivery areas. Pilot Project Evaluation 2

4 This project is designed to address a Stormwater NPDES requirement to evaluate the effectiveness of selected green stormwater infrastructure (GSI) techniques or practices for three selected pilot projects. The alley evaluation will consider design parameters, construction issues, system performance and maintenance requirements. For the Alley Pilot Project, an important area of investigation is the internal design and performance to achieve more accurate sizing for retention of specified volumes at specified storm event-return time design storms. The critical design element to the ultimate volume reduction for any of these facilities is the design storage volume relative to the inflow volumes. Success of GSI implementation will then depend on sizing based on site specific conditions. Studies are also needed to characterize local site environmental conditions that contribute to the technology performance. An overview of environmental conditions that should be considered is provided in the ACHD GSI Guidance Document. More site-specific information will be developed though the site-evaluation process for GSI projects and in evaluation of long-term project performance. For this study, soil conditions affecting exfiltration around permeable pavement as well as seasonal meteorological patters will affect GSI performance. Finally, the long term tracking of maintenance and performance of GSI practices is an important component in the use and success of these systems. The ultimate performance will involve not just the largely passive performance of the technologies themselves, but also the active and integrally important role of construction, operation and maintenance of facilities carried out by ACHD, partners and adjacent property owners. As part of this study, the following management actions will be evaluated: construction installation, stockpiling of excavated soils near permeable pavement surfaces, utility disturbance and reinstatement, tracking, and winter maintenance activities. Whole Life Cost of Stormwater Controls The project evaluation process will also include a cost analysis that includes initial capital costs and the long term operations and maintenance. An investment in roadway infrastructure requires some investment to keep it in usable condition. For roadways, this includes ongoing surface maintenance, periodic restoration and eventual base rehabilitation. In addition, focusing only on capital costs makes it less likely that projects will adopt stormwater controls that may have higher initial costs, but are less expensive to operate and maintain in the long term. There are also non monetary risks and costs associated with stormwater systems that are relevant to decision making. According to the report, Life-Cycle Cost Management of Interlocking Concrete Block Pavements - Methodology Report from ARA/ICPI, a paver system is expected to last 30 or more years before it reaches the trigger pavement condition index where rehabilitation is required. During this time, the following level of maintenance is expected. 3

5 Paver installations have demonstrated life spans that exceed 30 years, as compared to traditional pavement which typically lasts years. At years 8 and 28, it is expected that approximately 2% of the pavers over the entire surface will have become cracked or chipped and will need to be replaced. In years 20 and 35, a more significant maintenance is expected to take place - this includes removal of a larger area of pavers (most likely in the wheelpaths), leveling/replacement of the bedding sand underneath, then reinstatement of a majority of the original pavers. Whole life costing (also known as life cycle cost analysis) is about identifying future costs and referring them back to present-day costs. In the greater sense, the present value also includes the values of benefits that arise from implementation of stormwater controls. When compared to the equivalent life cycle costing of other traditional paving practices, the results for paver systems are often better because of the: 1. Higher performance life of pavers as compared to asphalt. 2. Lower capital cost of pavers compared to cast in place concrete 3. Lower/easier maintenance requirements 4. Reduced vulnerability to utility cuts 4

6 At this time, costs analysis are provided from other projects though comparable analysis will be completed for this project once more is known about maintenance costs. The analysis will focus on actual expenses though non-quantifiable benefits will be listed. Preliminary estimates in NCHRP Report 565 show that the cost of treating stormwater can vary from $0.10 to $3.00 per gallon based on the treatment methodology (Huber et.al, 2006). Case studies of 17 green stormwater infrastructure installations for stormwater flow control and quality management were completed by the Environmental Protection Agency in Results of the study showed that applying GSI techniques usually reduced project costs and had the added benefit of improved environmental performance (for both flow control and quality of discharge). In some cases, GSI was more expensive than conventional best management practices, due in part to contractor unfamiliarity. In most cases, significant capital costs were reduced by avoiding grading, stormwater infrastructure, additional paving and vegetation. Savings ranged from percent with the few exceptions mentioned (EPA, 2007). Issues and Preliminary Recommendations Appropriate locations: Develop and apply project selection criteria so that appropriate locations can be identified for planning purposes. Utilities: Issues include conflicts, compaction of surrounding soils, relocation, and reinstatement following utility maintenance activities. Require utility upgrades prior to alley retrofit or sign release form. Proactive outreach to utility contractors regarding reinstatement. Provide list of ICPI-certified installers. Set standards/requirements (e.g. setback requirements and/or conduits) for utility locations in project areas. Create partnership with utilities for potentially implementing retrofit projects where utility rehabilitation is planned. Design: Develop other designs to allow more flexibility, including designs that are narrower and deeper. Use infiltration rates for design purposes that are realistic based on compaction that will occur following utility work. Parking and Access: Obligation for alternative parking and access during construction. Set more realistic expectations for construction duration. 5

7 Potential for contamination: Avoid the following site: brownfields, presence of restaurants/oil barrels, and adjacent hot spots. Construction access related to width of alleys: Potentially allow contractor to use one lane of adjacent roadway for staging. Sizing of sub-base: Dependent on infiltration rates and treatment objectives. Use in new development versus use as retrofit: Less conflicts in new development but site conditions should be carefully evaluated prior to selection as drainage control Construction: Protection of infiltration surface, adequate cleanup of staging areas following project completion Impacts to system from adjacent properties following construction (e.g.power washing, leaf litter, winter activities): Provide information to property owners and signage for public. Maintenance requirements Outreach: More outreach to public and adjacent property owners. Provide visual representation of work. Provide conservative time estimates for construction. References Applied Research Associates/Interlocking Concrete Paver Institute Life-Cycle Cost Management of Interlocking Concrete Block Pavements - Methodology Report Environmental Protection Agency (2007). Reducing Stormwater Costs through Low Impact Development (LID) Strategies and Practices. [Publication Number EPA 841 F , December 2007 Huber W.C., Strecker, E.W., Heaney, J.P., & Weinstein, N. (2006). Evaluation of Best Management Practices and Low Impact Development for Highway Runoff Control User s Guide for BMP/LID Selection Guidelines Manual. National Cooperative Research Program Smith, D. R. (2006). Permeable Interlocking Concrete Pavers. Interlocking Concrete Pavement Institute. Third Edition 6