Date: 12/07/99. FINAL REPORT Micco E Exfiltration Pipe Project Demonstration Project DEP Contract # WM603. Prepared by:

Transcription

1 FINAL REPORT Micco E Exfiltration Pipe Project Demonstration Project DEP Contract # WM603 Prepared by: John C. Royal and Gordon England, P.E. Brevard County Surface Water Improvement Program Building A, Suite Judge Fran Jamieson Way Viera, Florida Phone (321)

2 Page 1 TABLE OF CONTENTS Section Page 2.0 Project Description Site Identification and History 3.0 Sampling Summary 3 Sampling Field Activities 3 Monitoring Site Photographs 4.0 Laboratory Results and Physical Measurements Laboratory QC Summary Conclusions & Recommendations 10 Appendix A Quality Assurance Project Plan 12 Project Drawing

3 Section 2.0 PROJECT DESCRIPTION Section 2.0 Page Site Identification and History Site Name: Micco E Site Address: Main Street, Micco, Brevard County, Florida Site History As part of the Brevard County Surface Water Improvement Program, a Stormwater Master Plan was completed to address water quality and quantity problems throughout the contributing Micco watersheds. The basin study completed in December of 1991 proposed a number of alternative pollution abatement methods for stormwater runoff treatment. Numerous smaller projects have been identified and tailored to existing sub-basins in order to maximize the proposed treatment levels and minimize construction and land acquisition costs. The areas in which the projects were proposed had little or no treatment currently and discharge directly to the Indian River Lagoon system. The total contributing drainage area of the water quality treatment systems is 15.5 acres. Approximately 16,786 cubic feet of storage has been provided in various sizes of exfiltration pipe up to 24 in diameter. This is about 0.39 inches over the watershed. The watershed is dominated by single family residential land use. The receiving waters of the Sebastian River discharge to the South Central Segment of the Indian River Lagoon, an Estuary of National Significance, and classified by DEP as Class II, a shellfish harvesting area. Main Street was an existing paved road with no curbs, gutters or swales. Stormwater ran down the edges of the pavement creating considerable erosion and sediment to be discharged down the boat ramp at the low spot in the road. Due to lack of right-of-way, 1536 linear feet of exfiltration trenches were installed under the existing pavement, with inlets periodically placed along the edge of pavement. Asphalt curbing was constructed to prevent erosion and to funnel water to the inlets. Three sections of the exfiltration system were installed in a flow through, online configuration and one section was in an offline configuration. A representative section of 65 linear feet of 18-inch diameter off-line exfiltration pipe was selected for evaluation with access before and after discharge. A weir prevents discharge at or below design flows, therefore, providing 100% treatment of captured flow. During flow in excess of design, stormwater is discharged at the downstream end of the exfiltration pipe, over a weir to the next section of exfiltration pipe for treatment. Project expenditures were as follows: Activity 319(h) Funds County Funds Design and permitting $29,008 BMP Implementation $176,260 $43,971 Monitoring $ 5,150 Total $176,260 $78,129 Total Project Cost: $254,389

4 Section 3.0 Page 3 Section 3.0 Sampling Summary In establishing the monitoring program for this system, several variables and configuration limitations were considered. A variable groundwater level that was 6 above the invert of the pipe during wet season led to variable percolation and treatment capabilities. As with any type of system relying on retaining the first flush, rainfall events with runoff volumes less than the retention volume would receive 100% pollutant capture and larger storms would receive a gradually decreasing removal efficiency as runoff volumes increased. Therefore, monitoring of mass loadings was attempted. One auto sampler was set up at the upstream inlet of the western pipe stretch. The sample lines were inserted several feet into the pipe, rather than just in the inlet sump. In order to do this, the skimmer was removed from the end of the pipe. Samples were then taken from the runoff standing in the pipe system. Sampling of the standing water within the inlet box was performed on one event January 30, 1997 to evaluate background conditions. There was no inflow during non-storm periods other than groundwater directly into the inlet sump due to a high water table. Additional sampling was conducted during three storm events, to evaluate the treatment provided in a representative section. Flow rate was to be measured at the inflow of the exfiltration pipe section being evaluated. An ISCO 4150 Doppler Velocity Flowmeter and 3700 Autosampler were installed at the upstream inlet prior to the first sample event. An ISCO 3230 bubbler flowmeter was installed at the discharge weir to record when overflow occurred over the weir. Photographs of the sample site are attached. Sample Site West End of Main Street, Micco, Florida *Note Small aluminum box downstream at the outlet weir contains only a flowmeter. Section 3.0 Page 4

5 MONITORING SITE PHOTOGRAPHS Sampler Enclosure. Inlet Skimmer removed to facilitate installation of the flowmeter sensor and suction strainer

6 Section 3.0 Page 5 Installation of strainer and sensor in the inlet pipe. Completed setup. Residual concrete on inlet grate.

7 Section 3.0 Page 6 During several storm events, numerous problems were encountered. The flowmeter was programmed to initiate sampling with a two-inch rise in water level in the inlet pipe of the exfiltration pipe and a minimum of.5 inch in rainfall. On one event, it appeared that a good storm event occurred, however, insufficient rain was recorded at the sampler gauge. The rainfall requirement was subsequently lowered to.25 inches. The flowmeter worked perfectly, however, the sampler skipped bottle sets inconsistently about every other storm, yet sampled correctly when tested, or on minor events that did not last long enough to be considered representative or provide adequate sample volume. The sampler was therefore replaced. Due to the limited length of cable for the Doppler flowmeter sensor and the necessity of mounting the sampler enclosure off the roadway, the flowmeter was hung under the inlet box grate. Storm Event 1 The first event sampled (April 16, 1997) was a high volume (1.75 inches) long duration storm which not only overtopped the discharge weir, but filled the inlet box up above the inlet pipe. The flow into the grate was of such intensity that the flowmeter was floating. While the flowmeter is supposed to be waterproof a corroded prong on the cable connection was found to have been broken, therefore, sampling was not initiated. As the storm was continuing, a grab sample was collected by manually initiating the sampler. Oil and grease, and Fecal Coliform samples were collected by manual grab into the original containers. Unfortunately, the volume treated could not be determined due to the broken flowmeter. A bubbler flowmeter (which provides level only) was later installed to replace the damaged Doppler flowmeter. Two additional grab sample events were conducted June 10, 1997 and August 15, 1997 with sample results summarized in Table 1. Storm Event 2 The second event sampled on June 10, 1997 resulted from a.22 inch event. Grab sampling was again required, as the bubbler flowmeter plotter jammed and blew a fuse. Although there is insufficient information to determine flow rate, the weir was not overtopped therefore, 100% treatment was provided. Storm Event 3 On August 15, 1997 sampling was initiated at.85 feet (10.2 inches) 2 inches above background. The maximum level recorded was 1.25 feet (15 inches in the 18 inch pipe) which slowly bled down over a period from 2:18 to 8:00 pm resulting from a.11 inch storm. The outlet weir was not overtopped therefore, 100% treatment was provided It was intended that efforts would continue to obtain Autosampler collected samples. Sample collection was complicated by an extended period of drought conditions during the winter of 1998 followed by wildfires that lasted from March to May. During the wet season, May through November, the groundwater level again remained high, with standing water remaining six inches above the bottom of the inlet pipe for most of the season. This indicated that the soil around this length of the exfiltration pipe was saturated and during this period the exfiltration pipe was not functioning as efficiently as intended. Sand had to be cleaned from the bottom of Section 3.0 Page 7

8 the inlet pipe on several occasions indicating that the downstream weir was at least providing retention of sediments. The exfiltration pipe on higher ground proceeding east up main street appeared to function properly providing more treatment, but because the inlet grates were actually in the roadway it would have been difficult, if not impossible, to sample. On February 16, 1999, equipment blanks were collected from the autosampler. The sampler initiated but the bubbler flowmeter at the inlet blew a fuse and did not record level so the samples were discarded. The sampler was cleaned and another equipment blank was collected on May 3, On or about May 8, 1999 a cement truck working in the area flushed the truck of residual concrete into the inlet sump of the section being evaluated. It was decided that the concrete probably negatively impacted the exfiltration capabilities of the system and no further evaluation was performed. The inlets in this system have been cleaned twice as of December A total of 14,076 lbs. of sediment have been removed.

9 Section 4.0 Page 8 Laboratory Analytical Results Parameter Units Background Storm 1 Storm 2 Storm 3 Date COD mg/l 57 BDL BDL 91 N02+N03 mg/l BDL BDL NH4 mg/l BDL 0.23 O-P mg/l TKN mg/l 1.47 BDL BDL 0.8 O&G mg/l BDL BDL BDL BDL TP mg/l TSS mg/l BDL Aluminum mg/l Arsenic mg/l BDL BDL BDL BDL Barium mg/l BDL BDL BDL Cadmium mg/l BDL BDL BDL BDL Chromium mg/l BDL BDL BDL BDL Copper mg/l BDL BDL BDL Iron mg/l Lead mg/l BDL Mercury mg/l BDL BDL BDL BDL Nickel mg/l BDL BDL BDL BDL Selenium mg/l BDL BDL BDL BDL Silver mg/l BDL BDL BDL BDL Zinc mg/l BDL Turb NTU BOD mg/l BDL BDL BDL 10 FC cfu/100ml PHYSICAL MEASUREMENTS Water Temp degc ph su X DO mg/l X Cond umhos/cm X Sal ppt X Air-Temp degc WinDir Winvol mph Cloud % Rainfall in H2O Vel fps 0 X X X

10 Section 4.0 Page 9 Laboratory QC Summary Background Sample Event All parameters were below detection limit except Ortho Phosphorus at.02 mg/l, and Total Kjeldahl Nitrogen detected at.15 mg/l. First Storm Event The equipment blank for the autosampler was collected February 19, 1997 with all parameters being below detection limit except Ammonia at 0.14mg/L, and Total Phosphorus at 0.04 mg/l. Second Storm Event The autosampler equipment blank was collected April 29, 1997 with all parameters below detection limit except BOD, which was 3.4 mg/l. Third Storm Event Equipment blanks were not collected the third storm event, as samples were collected by grab sample directly into the containers supplied by the laboratory. Hydrolab Calibration for background sampling and storm events one and two were within ± 2% for all physical parameters. The Hydrolab was not operational during the third sample event, therefore physical measurements were not made.

11 Section 5.0 Page CONCLUSIONS/RECOMMENDATIONS The difficulties encountered in measuring flow rate prevented a determination of pollutant loading and removal efficiency. High groundwater levels during the wet season also reduced the percolation rate and efficiency of the first length of exfiltration pipe, which was the section to be evaluated. However, large amounts of sediment were retained in this section and when discharge occurred over the downstream weir the second section of pipe provided further treatment. In order to avoid the equipment problems encountered on this project and assure flow measurement for future projects, six new ISCO 4250 Doppler velocity flowmeters have been purchased and three of the six samplers have been factory repaired. The exfiltration trenches along Main Street have shown to be an effective method of stormwater treatment. The combination of curbing and inlets have eliminated the erosion and sediment problems along the edge of the pavement and prevented direct runoff of polluted water to the Sebastian River. As has been experienced at other monitoring sites, equipment failures and limitations often inhibit the effectiveness of well-intentioned monitoring efforts. Most monitoring equipment has its roots in sanitary sewer applications. Application of this equipment for use in stormwater monitoring for which the equipment was not designed often challenges the user and the equipment. While it is easy to propose to test for certain parameters or removal efficiencies, attaining these results is sometimes beyond the technological limits available today. Compounding this is the diffuse nature of rainfall patterns, extended periods of equipment setup at remote locations without telemetry for notification of events and the large areas of the County assigned to limited number of personnel for monitoring. Exfiltration systems are very effective for the first flush treatment, provided the soil has high percolation and a low groundwater table. The high groundwater elevation at this site limited the effectiveness of the section of exfiltration pipe selected for evaluation. Testing results showed that the pollutant loads in this rural area were very low or often non-detectable. Because of the low readings, pollutant removal effectiveness could not be established, other than to say that 100% pollutant removal was achieved when storms were small enough that there was no outflow from the system. Although the TSS levels were very low, over 14,000 lbs. of sediment were removed from the system. This points to the inability of sampling equipment to measure large sediment particles that roll along the bottom of the pipe. Yet, large volumes of these sediments were removed. In order to extend the life of the exfiltration system, it is important to have some sediment sumps at each inlet and a skimmer over each pipe to keep floating trash, grass, and leaves out of the pipes. If possible, exfiltration systems should not be placed under pavement. Their lifetimes are limited and replacement will be expensive and disruptive. They should also be placed at least 12 above the seasonal high groundwater level. Section 5.0 Page 11

12 Traditional monitoring for concentrations is not applicable for these types of installation. Mass based monitoring should be considered in the development of TMDL s and PLRG s for at least some BMP s. This will be difficult due to technological limitations, but technology will evolve to provide for these needs.