| Project Description: |
The County of Ventura (County) Government Center provides 3,200 parking spaces within 39 acres of impervious parking lot surfaces within well-established urbanized area of City of Ventura. The Green Streets urban retrofit project replaced traditional concrete gutters with pervious concrete gutters to capture, treat and infiltrate stormwater and dry weather flows. The innovative pervious gutter design incorporated pervious concrete atop infiltration trenches supplemented with dry wells. The intent was to minimize retrofit area for future maintenance, but at the same time maximize stormwater capture and reduction of stormwater pollution. Approximately 5,000 lineal feet of pervious gutters, 13,000 square feet of pervious concrete strips, and over 500 shallow dry wells were constructed to capture over 60% of runoff in 2014-15 wet season. This unique, low-cost, and low-maintenance retrofit for stormwater treatment has the potential to be replicated regionally and nationally to meet NPDES Municipal Stormwater Permit and Total Maximum Daily Load requirements, as well as provide for groundwater recharge. Project design plans and additional info are available at http://uninc.vcstormwater.org/.
The project was funded primarily by the Proposition 84 Storm Water Grant Program. The required 20% match came from the County’s General Fund. Additional funding was received by the State Used Oil Block Grant Program. The combined construction cost was $1.5 million. |
| Project Justification: |
Previously at the Government Center, stormwater and incidental dry-weather runoff from the parking facilities carried untreated urban pollutants such as: leaked fuel; lubricants; hydraulic fluids; residual fertilizers, bacteria, and others. In today’s environmentally conscious and stormwater permitted age, it is increasingly important and required to slow and retain polluted stormwater on-site to help reduce pollutant loading and hydromodification in downstream water bodies. The recently adopted Los Angeles and Long Beach NPDES Municipal Stormwater Permits for cities and the County include requirements to evaluate stormwater retrofitting opportunities within the urban areas, specifically at the municipal facilities and public properties. In addition, permit required Total Maximum Daily Load regulations to retain and treat stormwater runoff are estimated at very high costs.
Our Green Streets urban retrofit project provides low-cost and low-maintenance alternative to meet stringent Clean Water Act requirements and help our creeks and rivers to stay clean. Replacement of 39 acres of our parking lot area with pervious concrete was estimated at $16,900,000. Instead, project’s goals of reducing discharge volumes, pollutant loads and peak flows were achieved with $1,500,000 plus all parking spaces were retained. In addition, future maintenance requirements for less than 0.5 acre of pervious concrete instead of 39 acres will result in long-term cost savings while providing for stormwater infiltration and groundwater recharge.
Removal of all dry weather flows and infiltration of very significant portions of wet weather flows (over 200,000 gallons per event) from 39 acres of impervious surfaces within well-established urban area are valuable achievements for watershed health. By targeting the first flush, known to have higher concentrations of pollutants, the project effectively maximized pollutant load reduction while minimizing the overall BMP footprint which directly correlates to minimized construction and maintenance costs.
Funded by Proposition 84 Storm Water Grant, the constructed improvements created storage capacity of over 200,000 gallons of stormwater per rain event. Based on monitoring results from the project robust sampling program conducted during 2014-15 wet season, the system exceeded its design goals by capturing over 60% of runoff from 39 acres of impervious parking lot surfaces.
The design and implementation verifies that even with very difficult site constraints (i.e., poor shallow infiltrative soils, poor documentation of existing utility infrastructure, high project visibility, and high vehicle and pedestrian traffic) high-volume, effective stormwater capture and treatment/infiltration systems can be implemented. Additionally, the project construction was completed under difficult circumstances at night and over the weekend to meet the project schedule and under budget. |
| Special Circumstances: |
Construction Flexibility:
The County Government Center has several thousand employees and visitors accessing the site on a daily basis. It contains the Hall of Administration, Hall of Justice, Sheriff’s Office, and Pre-Trial Detention Facility. To minimize inconvenience to the daily operations of facility’s public services construction was completed at night and during weekends. Nighttime construction posed several challenges. Shifting worker and inspector hours from day to night caused additional fatigue, increased probability of injury, hindered quality control, decreased efficiency, and increased costs due items such as keeping batch plants open at night and additional traffic control and work area illumination.
The Government Center is very busy, not only with employee and visitor access but with various special events taking place throughout the year. Events and site uses affecting specific parking lot areas were factored into the work schedule. This included events such as park and ride shuttle services for the 4th of July festivities and the two-week long Ventura County Fair. These types of events became the driving factor in construction scheduling in order to provide those services without any inconvenience to the public due to construction.
Safe Management Practices:
The night work took its toll on the workers and inspectors. Decreases in efficiency were noticed during final hours of shifts with workers and inspectors yawning and moving slower than earlier in the shift. The contractor often changed shift durations between 8 and 12 hours depending on the type of work being completed and availability of specialty sub-contractors and materials. To combat this, the County decided to rotate in new inspectors to finish each shift to keep the eyes on the project as fresh as possible. A typical night shift would have the primary inspector work from 6 PM until 4 AM and would be relieved by another inspector to finish out the shift from 4 AM until 6 AM. There were 5 rotating secondary inspectors that helped in this fashion, each rewarded with a couple of overtime hours prior to their normal daily work responsibilities.
To ensure the safety and minimal inconvenience to the public, very specific traffic control measures were required of the contractor. All excavations had to be covered prior to leaving the site each day (Figure 5) to allow pedestrians to cross the work areas, as almost all improvements were directly adjacent to walkways, a minimum 3/4” plywood spanning the width of excavations were installed over trenches. Excavations affecting vehicles were steel plated or excluded from traffic with temporary chain link fencing.
Community Relations:
High visibility of the project area provided excellent opportunity for public outreach and education. The pervious concrete was purposefully colored tan so that it would stand out from typical concrete and asphalt surfaces. To make it more noticeable, 30 “Clean Drain” placards were affixed to the pervious concrete improvement locations. The placards serve as informational items to pedestrian traffic; they include the web address of a project-specific website (http://uninc.vcstormwater.org/) as well as a QR code that can be scanned with a smartphone for additional project information. Two educational kiosks were constructed in heavy pedestrian traffic areas outside the most frequented Government Center buildings, Hall of Administration and Hall of Justice.
Government Center employees were notified by email of upcoming phases of construction, durations, and applicable parking and access restrictions. Additionally, fliers were placed on windshields of vehicles near upcoming phases as a secondary means of notification. Only one area of construction was in close proximity to a residential area, where the work hours were limited from 3 PM to 10 PM to minimize any disturbance.
Mass project public outreach was established through various articles in the Ventura County Star, the Public Works Association’s publication “The Pipeline,” and various other mediums such as Amigos805, PRLog, PressReleasePoint, Pub Memo, Community “Acorn” publications, and the VCReporter. Interviews were completed and broadcasted on the KCLU radio station. Additional information and posts were listed on the Ventura County Public Works Agency’s Facebook page. The County staff organized on-site and professional project presentations and the ribbon cutting ceremony in October 2014. These events drew media personnel, County employees and residents, and local stormwater industry professionals.
The extensive educational outreach implemented as part of this project has made several public impressions and helped others not immersed in the stormwater field understand the need for similar projects. Additionally, his project has provided an innovative design standard for other agencies or designers to build on, or incorporate, within other areas of the State, or Country. The County of San Diego has already began implementing this design within its stormwater CIP projects. Project information and design plans are available at http://uninc.vcstormwater.org/
Project Presentation at Professional Meetings
The project was awarded 2014 project of the year by local chapters of both the American Public Works Association (APWA) and the American Society of Civil Engineers (ASCE). We are awaiting a decision from the California Stormwater Quality Association.
Numerous presentations of the project were given for County employees and general public, Watershed Councils, at two annual CASQA Conferences and local chapter ASCE and APWA meetings. The project engineer has received several inquiries from industry professionals looking to incorporate similar improvements. Also, the County of San Diego has already begun implementation of similar improvements as a result of this project. Project information and design plans are available at http://uninc.vcstormwater.org/. Two educational kiosks and about 40 “Clean Drain” markers with QR codes for the project website have been designed and installed within the project area. The County Government Center has great educational potential with high visibility and daily visitations by employees and visitors.
Effectiveness Monitoring
A robust stormwater monitoring program has been implemented to verify volume infiltrated and pollutant load reduction as a result of this innovative stormwater retrofit. Two automated flow and sampling monitoring stations were installed in 2012 to collect baseline flow and water quality data prior to construction followed by data collection to evaluate the post-construction conditions and to track project treatment efficiency.
Although pervious concrete has been around for a few decades, there is little industry knowledge regarding its performance, strengths, suitability, longevity, and effectiveness. As part of this project the County has implemented a rigorous evaluation program to monitor the long term effectiveness of the pervious concrete and evaluate maintenance needs. This is very important to sustain the volumes of infiltration and reductions of pollutants year after year.
Infiltration testing was completed immediately after cure to measure its initial infiltration capabilities and every 100 days for the first year after project completion to determine the rate of clogging that occurs during dry weather. Initial results indicated extremely high infiltration rates averaging about 1,300 in/hr through the approximate 21% void ratio of the pervious concrete. After 100 days the infiltration rates decreased about 40% before being restored to about 90% following scheduled maintenance. The maintenance program of the pervious concrete is designed to include monthly street sweeping and semi-annual pressure washing and vacuuming combined with more infiltration testing taking place immediately after to measure the effectiveness of the maintenance. The periodic infiltration testing will be used to adjust maintenance frequency and procedures for the long term operation and maintenance plan.
Accomplishments:
- Construction completed on time with change orders amounting to < 2% of total cost.
- Extremely visible project with thousands of employees and visitors daily, yet only one complaint was received (noise at night).
- Utility locating and markings were responsibility of County as DigAlert cannot mark out utilities on private property. Utility as-builts from 1978 and subsequent improvements were not well documented and legacy knowledge was lost from retired workers. Careful excavation and spotting resulted in minimal utility breaks, which is exceptional since utilities were misrepresented on as-builts and almost all excavation was done at night.
- Pre- and post-construction monitoring has confirmed project goals have been met for infiltration volumes and pollutant load reductions.
Engineering Innovations:
Pre-design in situ soil testing indicated very poor infiltration potential (less than 0.5 in/hr) to a depth of 13 feet bgs due to high clay content. At the 13 foot depth infiltration rates were measured at an average of about 12 in/hr which is well above the acceptable infiltration rates for stormwater retention BMPs. In order to implement the most cost effective infiltration-based BMP, a unique vertical BMP design was developed to combine three separate stormwater BMPs (pervious concrete, infiltration trenches, and dry wells). This innovative design allowed capture of large volumes of water for successful infiltration below the clay to soils that can accept the water.
These unique infiltration-based improvements provide the most cost effective option for retrofitting any developed area including a long term cost savings due to minimizing the footprint at the surface which directly correlates to less maintenance and lower operational costs.
Quality control was an extremely important part of the projects success. Early on it was recognized that wet density testing (ASTM 1688) and infiltration testing (ASTM 1701) of each pervious concrete truck poured was needed. Pervious concrete is a very sensitive material that requires tight controls on water to cement ratios. There is an extremely fine line between “too wet” which results in surface sealing not allowing infiltration, and “too dry” which will crack and ravel.
In an attempt to speed up the pervious concrete placement a conveyor system was utilized. This system allowed for two pervious concrete trucks to pour simultaneously in the same location, essentially cutting the time to pour in half. However, this method was only used for one night of pouring as the batch plant was unable to supply enough trucks, due to state-mandated driver hour restrictions, to keep up. At that point it became too expensive to justify use. If a different pervious concrete project was able to pour during the day and get reliable truck delivery from the batch plant this would be an extremely effective method with large time and cost benefits.
The construction activities sparked a lot of public interest and questions about the project from County employees and facility visitors. The positive comments were more frequent during the recent storm events when stormwater infiltration could be observed. |
| Suggested Award Summary: |
When a rain falls on asphalt parking lots or streets, it runs into storm drain full of pollutants contaminating downstream waterbodies. The Ventura County Public Works retrofitted 39-acre parking lot at the County Government Center located in Ventura, CA to capture, treat, and infiltrate stormwater runoff. By targeting the first flush, determined and documented to be most polluted portion of the runoff, the Ventura County Public Works was able to minimize retrofit area for future maintenance, but at the same time maximize stormwater capture and pollutant reduction. The innovative Green Streets urban retrofit project replaced traditional concrete gutters with pervious concrete gutters incorporating pervious concrete atop infiltration trenches supplemented with dry wells. The dry wells were used to overcome poor infiltration within the tight and compacted top soils. Approximately 5,000 lineal feet of pervious gutters, 13,000 square feet of pervious concrete strips, and over 500 shallow dry wells were constructed to capture over 60% of runoff generated from 39 acres of impervious surface area as measured during 2014-15 wet season. This unique, low-cost, and low-maintenance stormwater treatment system has potential be replicated regionally and nationally to meet Clean Water Act requirements to prevent stormwater pollution and provide for groundwater recharge. Project design plans and additional info are available at http://uninc.vcstormwater.org/. Installed at high visibility area, the system and associated educational signs and placards offer educational outreach about stormwater pollution prevention. The project was funded in parts by the Proposition 84 Storm Water Grant Program. The total construction cost was $1.5 million. |
