2011 Grand Prize - Operations Management

Recovery and Treatment of Construction Stormwater Peace River Manasota Regional Water Supply Authority

Location: Desoto County, Florida
Entrant: AECOM
Engineer in Charge: Roberto Gonzalez, P.E.
Media Contact: Roberto Gonzalez, P.E.; 407-843-6552; Robbie.Gonzalez@aecom.com

Construction site stormwater runoff increased turbidity in 0.6 - BG source water reservoir.	Bench-scale jar testing confirms full-scale treatability alum dosage for construction water runoff.	Two plants treating vastly different surface waters at the same time.
Muddy construction water runoff being treated at plant.	Differences between the treated and untreated construction water runoff.	Successful treatment of construction water runoff recovers 1.5 BG.

Entrant Profile

Suffering from a continuing drought in Southwest Florida and facing high construction costs for its reservoir, the PRMRWSA (Authority) and AECOM developed a unique approach that saved an estimated $10 million in construction costs, yielded approximately 1.5 BG of additional water supply during a drought and eliminated the greatest possibility for off-site environmental impacts.

To build the new reservoir, 800 acres of improved pasture, palmetto prairie and shallow herbaceous wetlands would be disturbed. Significant volumes of surface water were expected from stormwater runoff and groundwater seepage collected by an extensive shallow rim ditch system. This water would need to be pumped continuously to keep the reservoir site dry enough to be workable. The large site required continuous dewatering for 16 months with dewatering volumes approaching 10 MGD during July and August 2008. Project team members realized the challenge of managing stormwater runoff from such a large site in a manner to avoid environmental impacts and possible construction halts from excessively wet conditions. However, SW Florida was undergoing an extensive drought that was taxing both surface and groundwater systems alike and every possible water source was being considered. Recovery of this stormwater by treating it in the water plant became the best option. Turbidity in this stormwater runoff often exceeded 2,000 NTU, and when combined with a diesel fuel spill and the scramble to remove dozens of portolets from the site during named hurricanes were some of challenges faced and overcome as a part of this remarkably innovative project.

Project Description

Some Say Stormwater, We Say Source Water

The Peace River Manasota Regional Water Supply Authority (Authority) is a water supplier for a four county region located in Southwest (SW) Florida. The Authority's main operations center is the Peace River Facility (PRF) which treats water withdrawn from the Peace River. Growing needs in the region drove the utility to double the PRF treatment capacity from 24 to 48-MGD and construct a new 6-billion gallon (BG) off-stream reservoir. This $171-million dollar project was the largest of its kind ever built within the 4 county region and made possible with $80-million in grant funding from the Southwest Florida Water Management District and the Florida Legislature with another $9-million in federal grants administered by the USEPA.

The Authority and AECOM developed a unique and innovative approach to manage the construction stormwater runoff. This approach captured stormwater runoff from the reservoir construction site, and diverted this water to the Authority's existing potable water treatment plant. This eliminated the requirement for the reservoir contractor to construct stormwater management facilities. Turbidity in this stormwater runoff often exceeded 2,000 NTU. This combined with a diesel fuel spill left the team in a scramble to remove dozens of portolets from the site during multiple hurricanes.

The project team realized that managing stormwater runoff from such a large site in a manner that would avoid environmental impacts and possible construction halts due to wet conditions would be challenging. However, SW Florida was undergoing an extensive drought that was taxing both surface and groundwater systems alike and every possible water source was being considered.

One of the project's key success factors was that Reservoir No. 1 is a man-made impoundment, not a natural lake and so that diversion of turbid water into this water body would not constitute impact to a natural system. Team members realized that the reservoir construction site had potential to yield about 1- BG per year if that water could be captured and put to beneficial use. At the time, the Authority was using up to 6-BG of raw water per year to meet its customer demands. Total annual rainfall on the 800 acre site was projected to amount to approximately 15% of the Authority's annual raw water needs. Thus, it appeared the construction water run-off could be used in a very practical manner. The most critical piece of the puzzle was projecting construction site water quality characteristics and assessing if the treatment systems in place at the PRF would be suitable without costly or significant retrofitting.

The plant was put into effect in January 2008 and turbidity levels in Reservoir No. 1 rose and fell in response to the mixture of stormwater diverted from the construction site as compared with raw surface water pumped from the Peace River. This insightful approach eliminated the need for extensive stormwater management facilities at the new reservoir construction site and allowed the contractor to focus on their primary task; building a reservoir instead of being distracted by treating stormwater and dealing with environmental impacts.

Quality Project with Integrated Approach

This approach would have cost an additional $10-million by requiring over 95 acres of construction ponds, multiple conveyance systems, temporary stormwater treatment system and discharge permit to the river. This project reflects a conglomeration of ingenuity, innovative planning and the hard work of many dedicated engineers, regulatory personnel and, most importantly, operations staff who tirelessly overcame many difficulties signified with implementing this project. It would have been far easier to simply pay more and require the reservoir construction contractor to manage the construction water. The project team worked alongside the Authority during their greatest hour of need to get the plant working properly and keep water moving to customers.

Originality/Innovation

AECOM engineers truly thought outside the box by breaking free from a traditional stormwater management plan. The project team redefined their thinking to develop a unique and novel approach by eliminating the requirement for construction stormwater management facilities that saved $10-Million in construction costs; harvested 1.5-billion BG of additional water supply that was used in local communities during a drought; eliminated off-site environmental impacts; and identified conventional rectangular floc/sed basins to be more suitable and reliable for high turbidity construction water.

AECOM engineers evaluated coagulants including alum/polymers and provided vital onsite operational assistance as the plant operations staff assimilated the construction water into the treatment plant. The team utilized jar testing for optimizing chemical dosages, sludge blanket levels monitoring and mixing energy adjustment. AECOM assisted that Authority's plant operators for manual operation of the newly constructed plant and provided 24-hour-a-day support as it treated muddy water for three months until automated controls were operational.

Complexity

To evaluate the feasibility of the concept and ultimately to gain acceptance from the Florida Department of Environmental Protection (FDEP) to process the construction water run-off in a public water supply facility, extensive testing was needed. Project team members collaboratively worked with FDEP staff to develop testing protocol to amass a body of data that would speak to project feasibility.

Social/Economic Advancement

Through the team's innovative concept they successfully protected environmentally sensitive areas; saved the Authority and tax payers an estimated $10-million; prevented construction runoff water discharge to the Peace River and utilized innovative engineering techniques which can be applied to benefit other communities in Florida.

This 800 acre construction site had a series of rim ditches to keep it dry enough for the contractor to work even in the rainy season	Over the 18 month construction project approximately 1.5 Billion Gallons of water were pumped to Reservoir No. 1.	The site was circled with a 4 mile long, 5 foot high containment berm to eliminate any potential for offsite discharges.
In the spring of 2008 pumping rates of 1 - 3 million gallons per day were processed off the site.	July 2008 brought over 20 inches of rain to the site.	In the wet season of 2008, pumping ranged up to 15 million gallons per day.
December 2008 - As the dry season approaches, normal raw water from the Peace River begins to displace the highly turbid water from the construction site.	By June 2009 work had finished inside the footprint and we were preparing to begin filling the new reservoir.	August 2009 - Slowly the dark, highly tannic raw water from the Peace River begins to displace and blend away the effects of the muddy construction water.
November 2009 - no lingering effects of the muddy construction water.	The Authority and AECOM developed a unique and innovative approach by eliminating the requirement for construction of stormwater management facilities, saving $10 Million in construction costs, harvesting 1.5 billion gallons of additional water supply, eliminating off-site environmental impacts and identifying Conventional Rectangular Floc/Sed basins to be more suitable and reliable for high turbidity construction water.