Stormwater Runoff Water Quality Characteristics From Highways in Lake Tahoe, California

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California State University, Sacramento (CSUS) University of California, Davis (UCD) California Department of Transportation (Caltrans) Stormwater Runoff Water Quality Characteristics From Highways

1 California State University, Sacramento (CSUS) University of California, Davis (UCD) California Department of Transportation (Caltrans) Stormwater Runoff Water Quality Characteristics From Highways in Lake Tahoe, California Presented at: StormCon 2002, San Marco Island, Florida, August 12-15, Author: Louis C. Regenmorter, CDM, Sacramento, CA Masoud Kayhanian, Caltrans/ UCD Environmental Program Kuen Tsay, Caltrans Environmental Program Disclaimer: This work reflects the author s opinions and does not represent official policy or endorsement by the California Department of Transportation, the California State University, or the University of California. Storm Water Program CSUS Office of Water Programs 7801 Folsom Boulevard, Suite 102, Sacramento, CA PP038

2 STORMWATER RUNOFF WATER QUALITY CHARACTERISTICS FROM HIGHWAYS IN LAKE TAHOE, CALIFORNIA Louis C. Regenmorter, CDM, Sacramento, CA Masoud Kayhanian, University of California, Davis, CA Kuen Tsay, California Department of Transportation, Sacramento, CA Introduction The State of California Water Quality Control Board has established water quality limits for all stormwater discharges in the Lake Tahoe Basin, California as the means to protect and restore the water clarity of Lake Tahoe. These limits are published in the Water Control Plan for the Lahontan Region North and South Basins. Surface water runoff, which directly enters Lake Tahoe or a tributary, is required to meet the maximum levels shown in the column entitled Surface Discharges in Table 1. Surface water runoff, which is directed to infiltrate into the soil, is required to meet the maximum levels shown in the column entitled Infiltration Systems. Table 1. Tahoe Basin Stormwater Discharge Limits Tahoe Stormwater Limits Parameter Units Surface Infiltration Discharges Systems Turbidity NTUs Oil & grease mg/l 2 40 Total Nitrogen mg/l Total Phosphorous mg/l Total Iron mg/l The State Water Quality Control Board has established that all stormwater discharges must be in compliance with these discharge limits by the year The application of total maximum daily loads (TMDLs) has been discussed for the Tahoe Basin, but none have been developed or adopted at this time. The California Department of Transportation (here on referred to as the Department) is actively participating in stormwater management with other local agencies in the Basin. The Department has been engaged in a water quality-monitoring program in the Tahoe Basin since the year While the scope of the Department s monitoring program in Tahoe Basin is broad, the focus of this paper is to discuss: (1) The quality of highway runoff from representative roadway conditions (elevations above lake level, geographic distribution within the basin, traffic volume, adjacent land use, and stormwater treatment facilities). (2) The comparison of runoff water quality to stormwater discharge limits established for the Tahoe Basin and the implications of the results as they pertain to stormwater management and treatment options. 1

3 Study Area Description The Lake Tahoe Basin is located along the border of California and Nevada. The Basin encompasses 506 square miles with elevations that range from 6,200 to over 10,000 feet. The Tahoe Basin is comprised of forested lands, meadows, small urban centers, ski resorts, and vacation housing. The Department operates 68 miles of roadways within the basin that range in elevation from 6,250 to over 7,200 feet. The majority of the roadways are two lanes. The Department performs snow management operations along all the roadways during the winter including the application of traction sand and salt. Monitoring Methods A total of six monitoring sites were selected within the Tahoe Basin to represent the range of roadway conditions. The water quality samples are collected at the edge of pavement and represent untreated runoff. At each site, the runoff is provided treatment after being sampled and prior to being discharged to the lake or adjacent land. Samples of runoff are collected, along with continuous flow and precipitation measurements, throughout the year using automated equipment. The equipment includes flow meters with data logger, tipping bucket range gages, and automatic samplers along with housing, power sources, flow control devices, and tubing. Monitoring and sampling has been successfully performed throughout the year, including winter. New maintenance routines have been implemented at the monitoring stations to keep them operational during winter conditions. Details of the monitoring program are presented in a comprehensive Sampling and Analysis Plan (Caltrans 2001). Flow-weighted composite samples are collected of individual runoff events. Runoff is generated during three types of events: summer thunderstorms, fall and spring storms that produce rain or rain mixed with snow, and snowmelt. Individual aliquots are collected over the duration of the runoff event on a flowpaced basis. The aliquots are then combined to form a single composite sample that is sent to the laboratory for analysis. Daily composite samples are collected during multiple day snowmelt events. Grab sampling is performed for oil and grease analysis. The composite water samples are analyzed for a standard suite of 34 parameters that include solids, conventional indicators, nutrients, chloride, and metals. The results are estimates of the event mean concentration (EMC) for a runoff event. The Department requires all monitoring programs apply a standard set of analytical methods, reporting limits, and laboratory quality assurance and quality control procedures. Analytical results are evaluated using standard data checking and validation procedures develop for the Department. All data are flagged based on the data quality objectives established for both the Department and the individual projects. Flow and precipitation data are check with a hydrologic tool to identify sample coverage and accuracy of the measurements. All analytical and time series results are then reported in a standard format that includes information on the monitoring site and the individual runoff events. This information is entered into a database maintained by the Department. 2

4 Results The runoff quality data are characterized by first calculating the general statistics and distribution. The Department s data analysis tool (DAT) is applied to generate these statistics. This tool provides a standard method for handling datasets that include censored (non detected) data. All the Department data evaluations apply this tool to maximize the comparability among various monitoring program results. Table 2 summarizes the water quality data available from the FY and FY Tahoe Basin highway runoff monitoring programs. The data summary is presented in terms of the units, reporting limits, number of samples, range of values, the mean of all data, the median of all data, and standard deviation. Only data meeting the quality objectives established for the project are used to generate this summary. The data presented in Table 2 indicates the majority of the parameters are found in the runoff samples and at concentrations above the reporting limits. The range of concentrations are highly variable as demonstrated by differences between the minimum and maximum values, differences between the mean and median values, and the high values of the standard deviation compared to the mean values. This finding is not uncommon in stormwater water quality data. However, the seasonal application traction sand and salt on the roadways for snow management has an impact on both the runoff quality and the variability in the quality data. A comparison of the data to the stormwater discharge limits presented in Table 1 indicates the concentrations often exceed the limits. The mean and median values for the five parameters in Table 1 are three to forty times higher than their surface discharge limits. The minimum value is lower than the limits for all parameters indicating one or two samples have concentrations that are below the limits. Both the mean and median values for total phosphorous, oil & grease, and TKN plus nitrate and nitrite (total nitrogen) are below their respective infiltration limits. The mean and median values for turbidity and total iron are still above their respective limits. Discussion The data presented in Table 2 represent untreated runoff from roadways in the Tahoe Basin. Comparison to the established stormwater discharge limits indicates the quality of the untreated runoff often exceeds these limits. The Department is developing a stormwater management program for its facilities in the Tahoe Basin to meet the discharge limits. The runoff generally receives some type of treatment prior to discharging to the lake or adjacent lands. Treatment options currently applied by the Department in the Tahoe Basin include roadside infiltration, infiltration basins, wetlands, sand traps, drain inlets with filters and road sweeping. These treatment facilities and operations do provide treatment. For example this past year influent and effluent monitoring was performed at double barrel sand traps. A schematic of a typical double barrel design is presented in Figure 1 and a photograph of one of the Tahoe Basin monitoring sites in shown Figure 2. Runoff from the highway is directed into the first barrel and after this barrel fills, the water spills over into the second barrel. After this second barrel fills, the runoff is discharged. This system is designed to capture sand and any other heavy debris that will settle out of the runoff. Water samples are collected at the entrance to the first barrel (influent) and downstream of the outlet of the second barrel 3

5 Table 2. Summary of Available Runoff Water Quality Data from FY and FY Parameter Units of Reporting Sample Range Standard Mean Median Measure Limit Number Min Max Deviation Conventionals ph ph units EC umhos/cm Turbidity NTUs Hardness as CaCO3 mg/l TSS mg/l TDS mg/l TOC mg/l DOC mg/l Chloride mg/l Oil & Grease mg/l COD mg/l Color Units Nutrients TKN mg/l NO3 (as N) mg/l NO2 (as N) mg/l NA NA NA NH3 - N mg/l Total Phosphorous mg/l Diss. ortho-phosphate mg/l Total Metels Arsenic ug/l Cadmium ug/l Chromium ug/l Copper ug/l Iron mg/l Lead ug/l Nickel ug/l Zinc ug/l Dissolved Metels Arsenic ug/l Cadmium ug/l NA NA NA Chromium ug/l Copper ug/l Iron mg/l Lead ug/l Nickel ug/l Zinc ug/l Notes: NA - Not Available. Statistics are not calculated for data sets with a low number of detections. The statistics presented above have been evaluated by using an Excel add-on to help statistically analyze data with NDs (U) for all data reported as equal to or less than the reporting limit. 4

6 Figure 1. Schematic of Double Barrel Sand Trap (with influent and effluent monitoring locations identified) Figure 2. Sand Trap Monitoring Station (with view of the double-barrel sediment traps shown in the lower right) 5

7 (effluent). Preliminary results after one season of monitoring indicate treatment is provided as demonstrated by the lower mean values of selected effluent data presented in Table 3. Table 3. Comparison of Stormwater BMP Influent and Effluent Results Parameter Units Influent Effluent EMC Mean EMC Mean Turbidity NTUs Oil & grease mg/l N/A N/A Total Nitrogen mg/l Total Phosphorous mg/l Total Iron mg/l N/A sufficient data not available However, the effluent levels do not meet all the discharge limits presented in Table 1 as occurred with the untreated runoff data presented in Table 2. A detailed comparison of two seasons of untreated runoff data and one season of sand trap effluent data is presented in dot-density graphs shown in Figures 3 and 4. The dot-density graphs compare the distribution of the all data for a given parameter to the discharge limits (horizontal dashed lines). Red dots represent individual effluent data points from the sand traps and blue dots represent individual untreated runoff data points. Dots located above a given dashed line represent data with higher concentrations and dots below a dashed line represent data with lower concentrations. Dots along the same horizontal plane have similar concentrations. All the graphs reveal the majority of the untreated and effluent concentrations are higher than the surface discharge limits (Surface) for all five parameters. Very few individual points fall below the lower dashed-line. A comparison of data to the infiltration discharge limits (Infiltration) indicates the majority of samples have total nitrogen, total phosphorous, and oil & grease concentrations that are lower than the limits. The majority of the samples have total iron and turbidity concentrations that are higher than the limits. Summary The stormwater discharge limits for the Tahoe Basin are relatively stringent and will most likely require all stormwater to undergo treatment to meet these limits. Although current best management practices implemented by the Department do provide treatment, preliminary studies indicate additional treatment may be necessary depending on where the discharge is located in regards to Lake Tahoe. Removing the last portion of the pollutant load can be the most challenging element of the stormwater management process. The Department is currently conducting research studies on improving treatment efficiency through the use of coagulants. The Department has also revised the specification for the traction sand it uses during its snow management operations. The sand now has lower phosphorous content and harder material that can better resist being ground down into finer particles. Studies are being conducted to determine methods to minimize erosion from the cut slopes that are adjacent to many of the roadways. 6

8 3000 Effluent from Sand Traps Untreated Runoff 16 Effluent from Sand TrapsUntreated Runoff Turbidity (NTU) Total Nitrogen (mg/l) Infiltration Li 0 Infiltration Lim Surface Limit 0 Surface Limi 12 Effluent from Sand TrapsUntreated Runoff 170 Effluent from Sand TrapsUntreated Runoff Total Phosphorous (mg/l) 8 4 Total Iron (mg/l) Infiltration Limit Surface Limit 0 Infiltration Limit Surface Limit Figure 3. Comparisons of Monitored Data to Stormwater Discharge Limits 7

9 100 Oil & Grease (mg/l) Infiltration Surface Figure 4. Comparisons of Untreated Runoff Oil & Grease Data to Stormwater Discharge Limits Treatment options are often limited by available land adjacent to the roadways and seasonal conditions. The topography of the Tahoe Basin is mountainous with the roadways often constructed on the side slopes. Very little additional space is available to construct treatment facilities that required large areas such as wetlands and infiltration basins. Development has all ready occurred in those areas where the topography provides enough space to build. The Tahoe Basin experiences temperatures below freezing on a daily basis for much of the winter season. However, snowmelt also occurs on a daily basis, which generates runoff. The freezing temperatures limit the effectiveness of some treatment facilities such as wetlands and filters. The runoff can often pass through untreated. All these limitations must be considered when selecting and designing treatment facilities. The monitoring program being implemented by the Department to characterize the runoff from its roadways in the Lake Tahoe Basin has demonstrated runoff quality often exceeds established discharge limits. The monitoring results have provided the Department with the data to support their stormwater management programs and identify the level of treatment that will be required to meet the limits. The monitoring program in the Tahoe Basin will continue in order to complete the characterization of runoff, determine the treatment effectiveness of current treatment facilities and new treatment technologies, and support any future TMDL program. 8

10 References California Department of Transportation Guidance Manual: Stormwater Monitoring Protocol, Second Edition, revised July California Department of Transportation. Sampling and Analysis Plan Caltrans Tahoe Basin Water Quality Characterization and Sediment Trap Effectiveness Studies (CTSW-RT ). November California Regional Water Quality Control Board Lahontan Region. Water Quality Control Plan for the Lahoton Region, Table Acknowledgements The Department provided funding for this study under contract 43A0036 and Task Orders 2 and 14. The CDM team members who contributed to the success of this study including Stefan Schuster, Tim Boyer, Barb Wells, Charlie O Neill, Miriah Hass, Blake Johnson, John Downs, and Rick Chappell. 9

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