Monitoring and Evaluation Report for Stormwater Demonstration Project at the Nevada County Rood Center

Prepared for American Rivers

by the South Yuba River Citizens League (SYRCL) and Kyle Leach

December 7th, 2011

Design and Construction by:

2

1

Contents Introduction .................................................................................................................................................. 1

Methods ........................................................................................................................................................ 2

Storm Event Monitoring ........................................................................................................................... 3

First Flush Monitoring ............................................................................................................................... 4

Sediment Load Reduction ............................................................................................................................. 5

Results ........................................................................................................................................................... 6

Stormwater Detention Time ..................................................................................................................... 6

Stormwater Volume Absorbed ................................................................................................................. 6

Estimates of Pollutant Reduction ............................................................................................................. 6

Total Suspended Solids (TSS) ................................................................................................................ 7

Total Dissolved Solids (TDS) .................................................................................................................. 7

Turbidity ................................................................................................................................................ 7

Other Constituents ................................................................................................................................ 8

Simulated Storm Events ................................................................................................................................ 8

Conclusions ................................................................................................................................................... 9

Introduction This report documents the results of field activities conducted during the fall and winter of 2010-2011

for the Installation of Stormwater Management in Yuba Watershed project located at the Nevada

County Administrative Center (Rood Center) in Nevada City, California.

The project involved design and construction of stormwater Best Management Practices (BMP) features

at the Rood Center site during the summer of 2010. The project design team consisted ofIntegrated

Environmental Restoration Services completed the design and construction, with engineering by PR

Design and Engineering. This report evaluates the performance of two features, a raingarden and

bioswale, through the first winter following construction.

The rain garden was installed to the south of the Nevada County Government Center building, in a

landscaped area surrounded by asphalt parking and bounded by curbs (Figure 1). Curb cuts were

created to direct stormwater runoff from parking lot areas into the rain garden. The impervious

catchment area (paved parking lot) of the rain garden is approximately 21,426 square feet (sf) and the

2

surface area of the feature is 11,485 sf. Stormwater flowed through a series of ponds and any overflow

discharged through a storm drain drop inlet (DI) into a culvert, which discharged at the north side of

Highway 49, south of the site. This culvert discharge also includes runoff from other areas of the site as

well as off-site catchment areas to the north and northeast. The culvert empties into Oregon Ravine,

which flows through downtown Nevada City to Deer Creek, a tributary of the Yuba River.

The bioswale was constructed in the west-central portion of the site in an elongated landscaped area

bounded by curbs and surrounded by parking lots. The bio swale is located between the Rood

Government Center building and the Wayne Brown Correctional facility. Curb cuts were created to

direct stormwater runoff from parking lot areas up slope into the bioswale. The impervious catchment

area for the bioswale is approximately 22,500 sf and the bioswale surface area is 3,890 sf. Stormwater

flows through a small DI, into a subsurface infiltration pipe which extends beneath the eastern portion

of the bioswale. When this pipe is filled, stormwater backs up to the DI and then flows to a second DI,

which directs water westward through a pipe which discharges to a small swale and pond in the western

end of the feature. Any bioswale overflow discharges to a DI which directs stormwater into a culvert

that apparently discharges near the southwest corner of the site and flows down a small, unnamed

tributary to Deer Creek.

A second rain garden was installed in a median of the Madelyn Helling Library in the eastern portion of

the site. Because this feature was constructed with cost savings incurred during the construction of the

other two features and was not planned prior to developing a monitoring plan, the Library Rain Garden

received only cursory observations of feature performance.

The purpose of stormwater monitoring for the project was to evaluate, and quantify when feasible, the

benefits of two BMP features. Potential benefits of the features include: 1) reduction in overall runoff

by increased stormwater runoff retention time and infiltration volumes and 2) reduction in the sediment

and pollutant loads in the parking lot runoff.The 2010/2011 rainy season in the Sierra Nevada foothills

region produced greater than average precipitation totals with a relatively wet late fall/early winter, a

dry January and a wet late winter/early spring. The total rainfall recorded on the gauges used for the

project during the project monitoring period of October 1, 2010 through March 31, 2011 was 60.3

inches, 30% above the average rainfall for the period. Approximately 33 storms (75 days with

measurable precipitation) occurred during the monitoring period, 8 of which produced snow or mixed

rain and snow (13 days with measurable snowfall).

Methods Monitoring activities were performed in general accordance with SYRCL’s March 5, 2010 Monitoring

Plan for Stormwater Demonstration Project at the Nevada County Rood Center and a July 6, 2010 Quality

Assurance Project Plan prepared for the project. Monitoring activities performed during the 2010- 2011

rain season included:

3

Storm event monitoring of seven storms, between October 2010 and March 2011. Storm event

monitoring included: timing of first influent and effluent flows, rainfall volumes, grab samples

and subsequent analysis for selected constituents identified in the first flush sampling.

First flush sampling of influent and effluent (when the feature overtopped) storm water and

analysis for water quality constituents typically identified in stormwater runoff from paved

parking lots.

Two simulated storm events performed to calibrate data from storm event monitoring and

estimate infiltration rates during unsaturated and saturated soil conditions.

Storm Event Monitoring

Seven storm events were selected to provide a representative cross section of storms and soil moisture

conditions present throughout the rainy season. We did not monitor small events that appeared

unlikely to overtop the features. Nor did we monitor snow events or mixed rain/snow events because

snow removal operations made it impossible to estimate inflow volumes.

During the 2010/2011 storm season, the first measurable rainfall and seven subsequent storm events

were monitored on the following dates:

First Flush- October 5, 2010

Storm Event 1- October 23, 2010

Storm Event 2- November 7, 2010

Storm Event 3- December 5, 2010

Storm Event 4- December 17, 2010

Storm Event 5- January 29-30, 2011

Storm Event 6- February 14-15, 2011

Storm Event 7- March 18, 2011

During storm events, measurements included:

1. Time of first influent and time of first effluent;

2. Precipitation amounts recorded at a nearby Weather Underground rainguages

(www.wunderground.com) located at Lake Vera (approximately 2 miles east of the site, with a

similar topographic aspect and elevation). One exception was the use of National Oceanic and

Atmospheric Administration (NOAA) rainfall records for Nevada City for the October 5 first flush

event, since only minimal rain (0.05”) was recorded on the Lake Vera gauge for that day, which

was not consistent with our field observations, which included a relatively short period of hard

rain and heavy runoff which was more consistent with the 0.23” recorded on the NOAA Nevada

City gauge;

3. Influent grab samples collected within the first hour of initial inflow. Effluent grab samples were

collected as soon as possible after first effluent was observed from the features (generally

within two hours of first effluent). Grab samples were obtained using a dedicated scoop dipped

into the center of the flow path. Temperature, pH and conductivity were measured in the field,

then samples were transferred into laboratory-supplied containers and transported to the

4

laboratory. Influent and effluent samples were analyzed at the SYRCL office and/or Cranmer

Analytical Laboratories for turbidity, total suspended solids (TSS), total dissolved solids (TDS).

First Flush samples were analyzed at Cranmer Laboratory for additional analytes as described

below. Bacteria analysis for total coliform and E. coli was performed on samples from Storm

Event 4 since first flush samples were out of hold time for bacteria analysis.

Details of sampling and field testing procedures are included in the monitoring plan

(http://www.americanrivers.org/assets/pdfs/reports-and-publications/monitoring-plan.pdf) and QAPP

(http://www.americanrivers.org/assets/pdfs/reports-and-publications/stormwater-monitoring-qapp.pdf)

prepared for the project.

The volume of stormwater captured by the BMP features before overtopping was calculated for each

stormwater monitoring event using the total rain fall during the time period between first influent and

first effluent multiplied by the design catchment areas for the feature. A runoff coefficient of 0.9 was

used for paved surfaces and a coefficient of 1.0 was used for the BMP feature surface area itself.

Flow meters were not used in the project, therefore it was not possible to directly measure stormwater

volumes absorbed by the features. The average volume captured before overtopping was used as an

estimate for the volume infiltrated (evapotranspiration was assumed negligible). The stormwater

captured before overtopping is a reasonable estimate of stormwater absorbed, when infiltration rates

are low, and captured volumes are averaged across storms. Infiltration rates must be low, because an

additional, unquantified, volume of stormwater infiltrates between the time when the feature overtops

and the end of the storm. The April 14th simulated event confirmed low rates of infiltration during the

rainy season. In some cases, when storms followed in close succession, standing water may be left in

the feature, unabsorbed at the beginning of the next storm (e.g., event 7). However, when averaged

across storms, captured volumes can be used to estimate absorbed volumes because the volume of

unabsorbed standing water from one event reduces the volume captured before overtopping during the

next event.

First Flush Monitoring

First flush monitoring was performed during two storm events on October 5, 2010 (influent) and

October 23, 2010 (effluent). The October 5 storm selected for first flush monitoring and from which

influent samples were collected, did not have enough precipitation to overtop either feature. Therefore

first flush effluent samples were collected from the first effluent discharged during the larger second

storm of the season on October 23. The October 23 event was also considered the first storm

monitoring event.

First flush influent and effluent surface water grab samples were analyzed for standard water quality

parameters: Total Suspended Solids (TSS), Total Dissolved Solids (TDS), turbidity, Resource Conservation

and Recovery Act (RCRA) metals (chromium, copper, lead, mercury, nickel, and zinc), nutrients (nitrogen

as nitrate and phosphate as phosphorus) and total iil and grease. Laboratory methodology, reporting

limits and quality assurance procedures are included in the attached laboratory reports.

5

Sediment Load Reduction Sediment load reduction for the two BMP features was calculated based on comparison of influent and

effluent total dissolved solids (TDS) concentrations and total suspended solids (TSS). Turbidity

reductions were similarly calculated.

Highly accurate mass estimates would require multiple influent and effluent samples distributed

through the storm duration and flow-weighted sampling using an autosampler. However, the project

work plan and budget only allowed for analysis of one influent and one effluent grab sample from each

storm event and one set of pollutant water-quality constituent analyses for the first flush event. The

following assumptions were made in calculating sediment load mass reductions:

We did not include the mass of sediment and pollutants removed by each feature, after the

feature overtopped (during the flow-through period), due to lack of data. Vegetated areas (e.g.,

filter strips) have been shown to reduce sediment and pollution concentrations from flow-

through stormwater 1 , thus this assumption tends to underestimate the mass of pollutants

removed.

Concentrations from samples collected within one hour of the start of stormwater flow into the

BMP feature were assumed to represent average concentrations. This assumption may

overestimates average pollutant and sediment concentrations if loads decrease throughout the

storm, as would be the case following a first flush.

The mass of sediment captured by the BMP features was calculated in two parts to estimate 1) mass

reduced during the first flush event and 2) mass reduced during all storms for the remainder of the

monitoring period. First flush mass reductions were estimated based on the assumption that first flush

influent concentrations were representative of all first flush stormwater and the observation that 100%

of the stormwater was absorbed by the BMP feature (no effluent). Sediment mass reductions during

the remainder of the monitoring period were calculated as the difference between the influent and

effluent sample concentrations averaged across all storms in the monitoring period multiplied by the

volume of storm water captured by each feature before overtopping (calculated as the % captured

before overtopping multiplied by the total stormwater volume during the monitoring period).

Experiences with this monitoring project lead also to suggestions for any additional monitoring of this

type. Improved BMP feature aspects such as flumes or weirs installed at feature inflow and outflow

locations would allow flow measurement and improve sample reliability.

Additional sampling during future stormwater monitoring projects would allow better estimates of

sediment and pollutant load mass reductions. Ideally this would include the use of flow weighted

composite samplers. A less costly alternative would be to collect at least two influent and two effluent

samples at different times during each storm event. Flow weighted composite grab sampling would also

improve data quality.

1 “EPA - Stormwater Menu of BMPs.”

6

Results Stormwater monitoring data collected during the 2010/2011 rainy season was evaluated to estimate

stormwater detention time, stormwater volumes absorbed, sediment reduction and pollutant load

reduction for the two BMP features at the Rood Center site. Tables 1, 2, and 3 summarize monitoring

and laboratory data from the project. Two unusual storms were included in this analysis. Storm event

7 (on March 18, 2011), occurred during a particularly wet period, after approximately 4 inches of rain

had fallen in the five previous days. Runoff from those storms had not been absorbed and standing

water was present in both BMP features at the start of storm event 7. At the other extreme, storm

event 6 (on February 14, 2011) included an extended period of light rainfall after a prolonged dry period.

This allowed greater than normal infiltration during event

Stormwater Detention Time

The rain garden captured all runoff from the catchment area for a period at the beginning of each storm,

which ranged from one hour, five minutes (1:05) to eleven hours (11:00), with a seven-event average of

4:40 (Table 1). The bioswale captured all runoff from the catchment area for a period ranging from 1:55

to 27:30 with a seven-event average of 8:55.

Stormwater Volume Absorbed

The calculated volume of rainfall absorbed by the rain garden before first effluent for each monitored

storm ranged from 192 cubic feet (cf) to 1,398 cf, with a seven-storm-event average of 850 cf infiltrated

(Table 1a). Total storm runoff from the catchment areas during each of the seven events ranged from

1,371 cf to 14,481 cf (average of 6,655 cf), thus the rain garden absorbed an average of 12.8% of the

total storm runoff from each event. Based on the total precipitation recorded by the rain gauges during

the monitoring period (60.3”), and assuming the above rate of capture, the rain garden absorbed a total

of over 21,148 cf of stormwater runoff during the 2010/2011 project monitoring period. An additional

but unquantified volume of stormwater was also infiltrated by the raingarden between the time effluent

started and influent stopped.

The calculated volume of rainfall absorbed by the bioswale before first effluent ranged from 302 cubic

feet (cf) to 1,971 cf for a seven event average of 1,187 cf (Table 1b). Comparison of this value with the

total storm runoff from each of the seven events which ranged from 1,006 cf to 10,622 cf (average 4,889

cf), indicates the bioswale absorbed an average of at least 24.3% of the total storm runoff from each

event. Based on the same assumptions described for the raingarden, the bioswale absorbed a total of

over 29,449 cf of stormwater runoff during the 2010/2011 project monitoring period.

Estimates of Pollutant Reduction

In order to estimate the mass of solids and pollutants attenuated by the BMP features, we compared

influent and effluent sample concentrations. Solids were analyzed as TSS and TDS. Turbidity was also

measured (Table 2). Chemical pollutant concentrations were measured for the first flush only (Table 3).

Bacteria were analyzed for storm event 4 (Table 4).

Using these assumptions, changes in sediment load were estimated for the following constituents:

7

Total Suspended Solids (TSS)

Based on the rain garden first flush TSS concentration of 263 mg/L and 100% absorption of the first flush

volume of 631 cf, approximately 6.2kilograms (kg) of sediment was removed during the first flush event

(Table 2).

The mean influent TSS concentration at the raingarden was 42mg/L and the mean effluent

concentration was 14 mg/L. This resulted in an effective decreased concentration of 28 mg/L. Assuming

12.8% of the total runoff volume was treated by the rain garden (12.8% of 20,517 cf), TSS contributed to

an estimated decreased mass of 16.3 kilograms (kg) of sediment to the rain garden during the remainder

of the monitoring period. Adding first flush and remaining season results, an estimated 22.4 kg of

suspended sediment (as TSS) was removed by the rain garden during the project monitoring period.

Based on the bioswale first flush TSS concentration of 6,280 mg/L and 100% absorption of the first flush

volume of 463 cf, approximately 82.3 kilograms (kg) of sediment was absorbed during the first flush

event. The mean influent TSS concentration at the bioswale was 79mg/L and the mean effluent

concentration was 21 mg/L. This resulted in an effective decreased concentration of 58 mg/L. Assuming

24.3% of the seasons total runoff volume was treated by the bioswale (24.3% of 28,986 cf), TSS

contributed to an estimated decreased mass of 47.6 kg of sediment to the bioswale during the

remainder of the monitoring period. Adding first flush and remaining season results, an estimated 129.9

kg of suspended sediment (as TSS) was removed by the bioswale during the project monitoring period.

Total Dissolved Solids (TDS)

Based on the Rain Garden first flush TDS concentration of 202 mg/L and 100% absorption of the first

flush volume of 463 cf, approximately 3.6 kilograms (kg) of dissolved solids were absorbed during the

first flush event. Rain Garden TDS event mean influent vs. event mean effluent concentrations

increased from 33.0 milligrams per Liter (mg/L) to 106.3 mg/L for an effective increased concentration

of 73.3 mg/L. Assuming 12.8% of the remaining monitoring period’s total runoff volume is treated by

the rain garden (12.8% of 20,517 cf), an estimated increased mass of 42.6 kilograms (kg) of dissolved

sediment during this period. The combined effects of the first flush and subsequent monitoring periods

resulted in a 39.0 kg increase in TDS in rain garden runoff during the monitoring period.

Based on the bioswale first flush TDS concentration of 438 mg/L and 100% absorption of the first flush

volume of 463 cf, approximately 5.74 kilograms (kg) of dissolved sediment was absorbed during the first

flush event. Bioswale TDS event mean influent vs. event mean effluent concentrations increased from

14.4 mg/L to 26.5 mg/L for an effective increased concentration of 12.1 mg/L. Assuming 24.3% of the

seasons total runoff volume is affected by the bioswale (24.3% of 28,986 cf), TDS contributed to an

estimated increased mass of 10.0 kilograms (kg) from the remaining monitoring periods runoff for a

total increased dissolved sediment load from bioswale runoff of 4.3 kg.

Turbidity

The raingarden first flush turbidity of 93 Nephalometric turbidity units (NTU) was decreased by 100% as

a result of complete absorption of runoff. Rain Garden turbidity event mean influent vs. event mean

effluent concentrations for the remainder of the season decreased from 23.7 NTU to 18.5 NTU a

decrease of 22.0%.

8

The Bioswale first flush turbidity of 6000 NTU was also completely captured. The event mean influent

vs. event mean effluent concentrations for the remainder of the period decreased from 55.4 NTU to

22.7 NTU a decrease of 59.2%.

Turbidity measurements are not mass concentrations, therefore mass reductions cannot be calculated

for turbidity.

Other Constituents

Pollutant load reductions for other constituents calculated for the first flush event only (Table 3).

Percent reduction calculations were based on the difference between first influent (October 5, 2010)

and first effluent (October 23, 2010) sample results. First flush pollutant mass reductions were

estimated based on the observation that first flush influent concentrations were representative of all

first flush stormwater and that 100% of the stormwater was absorbed by the BMP feature (no effluent).

Mercury and Total Oil and Grease were not detected in the first flush influent samples so these were not

measured in the corresponding effluent samples.

Bacteria analytical results for total coliform and E. coli were obtained from from Storm Event 4 only.

Results indicated high concentrations of total coliform in both influent and effluent samples from both

features. Total coliform concentrations in these samples exceeded a most probable number per 100

millileters (MPN per 100mL) 2419.2. E. coli concentrations were reduced from 15.6 to 9.8 MPN per

100mL, a 37% reduction. The bioswale reduced E. coli concentrations from 12.2 to 7.4 MPN per 100mL,

a 39% reduction.

pH was monitored for all influent and effluent samples in the field and at Cranmer Laboratory. pH

results are summarized in Tables 7A and 7B. Rain Garden pH influent ranged from 5.2 to 7.2 with a

mean of 6.6. Bioswale influent pH ranged from 4.8 to 7.4 with an event mean influent pH of 6.3 and

event mean effluent pH of 6.3.

Simulated Storm Events Two simulated storm events were performed on the bioswale. The first event was on October

1, 2010 before the first storm when soil conditions were assumed to be relatively unsaturated.

To perform the first event we simulated the runoff from a 2 year recurrence interval, 6 hour

rain event. The runoff from rainfall rate of 0.35 inches per hour over the paved catchment area

was estimated to be 97 gallons per minute. Nevada County Consolidated Fire Department

provided assistance, running hydrant water through the truck to achieve the requested flow

rate onto pavement above the curb cut and into the bioswale. The feature overtopped after

64 minutes when approximately 830 cubic feet (cf) of stormwater had been collected. This was

compared with the estimated saturated capacity for the bioswale of 736 cf (5,505 gallons) to

estimate an infiltration rate of 94 cubic feet for the first hour

9

We then monitored infiltration by periodic measurements of water levels on a stage plate

installed in the terminal pond of the bioswale, and in two vertical pipes extending to the

horizontal infiltration pipe installed near the base of the eastern portion of the bioswale.

Infiltration rates generally decreased through the measurement period. The water level in the

vertical pipes dropped to the depth of the base of the infiltration pipe in approximately 5:50.

Although it was not possible to estimate the volume of water infiltrated with the available

information, this represents nearly complete drainage of the bioswale.

A second Simulated Event was performed on April 14, 2011, during a period of saturated soil

late in the rainy season. In the second simulated event, both the bioswale and rain garden

were filled to overflow and only infiltration data was collected. The water level in the vertical

pipes in the bioswale dropped to the depth of the base of the infiltration pipe in approximately

10:38, nearly twice as long as the infiltration period observed during the first dry season event.

Stage plate measurements were made in the bioswale during the first and second simulated

events and in the rain garden during the second event only. Water level on the bioswale stage

plate dropped approximately 2.04 “ in 118 minutes during the first event and 1.80” in 700

minutes during the second event. Water levels on the rain garden stage plate dropped very

slowly (less than 1 inch in 10 hours) during the second simulated event. These results do not

represent true infiltration rates, but rather represent localized conditions suggesting the

presence of relatively impermeable soil beneath the pond areas of the raingarden, particularly

during late season saturated conditions.

Conclusions Rain Garden stormwater detention times varied considerably from storm to storm. Several factors likely

contributed to the variability including intensity and duration of precipitation, antecedent soil moisture

conditions, and the amount of residual standing water within the features at the start of the storm

event. On average, the Bioswale detained runoff nearly twice as long (average of 8:55 per storm event)

as the Rain Garden (average of 4:40 per event).

Both the Rain Garden and Bioswale absorbed a significant amount of runoff and reduced storm runoff

volumes into receiving waters. As with stormwater detention times, runoff volume reductions varied

considerably, depending on storm intensity, soil moisture, and the amount of residual water in the

features. The Bioswale reduced stormwater runoff volumes by an average of approximately 1,187 cf per

storm, or 24.3% of total storm runoff, capturing the first 0.59” of rainfall. In comparison, the Rain

Garden reduced stormwater volumes by 850 cf per storm or 12.8% of total storm runoff, capturing the

first 0.31” of rainfall.

Both features reduced suspended sediment loads and the turbidity of receiving waters but increased

TDS impacts during most storms after the first flush. The Bioswale reduced suspended sediment loads

10

by an estimated 129.9 kg and turbidity by 59%. The Rain Garden reduced suspended sediment loads by

an estimated 22.4 kg and turbidity by 22%. Accumulations of sandy sediment near the inflows to the

Bioswale and Rain Garden support these conclusions.

Total Dissolved Solids were reduced in each feature during the first flush by an estimated mass of 3.6 kg

in the Rain Garden and 5.7 kg in the Bioswale. However, these benefits were negated by increased TDS

in subsequent storm event effluent over the remainder of the season. Cumulative TDS increases over

the monitoring period were estimated at 38.98 kg in the Rain Garden and 4.3 kg in the Bioswale. These

increases in TDS may be the result of fine sediment disturbed during recent feature construction

activities or organic soil amendments. If so we would expect TDS increases to lessen or reverse over

time.

Comparison of first flush influent and effluent concentrations indicate reductions by constituent ranging

from 62% to 100% in the Rain Garden and from 76% to 100% in the Bioswale. One highlight was

reduction of total lead influent concentrations from 14 µg/L to below detection limits in Rain Garden

effluent, and from 81 µg/L to 1.1 µg/L in Bioswale effluent, as compared with a regulatory action level of

15 µg/L.

Stormwater infiltration data collected during two simulated storm events, one during the dry season

before feature saturation and on during the late rainy season, when soil conditions were relatively

saturated, indicated bioswale infiltration rates were half as fast saturated conditions. Infiltration in the

rain garden appeared to be significantly slower than in the bioswale, likely due to the shallower

construction depth of the rain garden and the presence of relatively impermeable fine grained soil.

The Bioswale was more effective than the Rain Garden, likely due to the greater depth of the feature

and due to variation in the underlying soils; at both locations, soils were composed of more than 20 feet

of compacted fill that is rich in clays and silts. Rain Gardens and Bioswales constructed in locations with

well developed natural soil profiles would likely function at a higher efficiency. It should be expected

that performance of the site BMP features will improve with age as the planted vegetation matures and

soil infiltration properties develop.

11

Raingarden Stormwater Capture

Date Event

Rain Duration

Before Feature

Overtops

Rainfall Captured

Before Overtopping

Storm Total

Total Volume Captured

Before Overtopping(cf)

Total Storm Runoff

(cf)

10/5/2010 First Flush

did not overtop 0.23" 0.23" 631 631

10/23/2010 Storm

Event 1 4:20 0.34" 5.28" 933 14481

11/7/2010 Storm

Event 2 4:00 0.51" 1.80" 1399 4937

12/5/2010 Storm

Event 3 3:00 0.18" 2.05" 494 5622

12/17/2010 Storm

Event 4 4:25 0.22" 4.40" 603 12067

1/29/2011 Storm

Event 5 5:15 0.45" 1.13" 1234 3099

2/14/2011 Storm

Event 6 11:00 0.41" 1.84" 1125 5046

3/18/2011 Storm

Event 7 1:05 0.07" 0.50" 192 1371

Average

(does not include First Flush)

4:40 0.31" 2.43" 850 6665

Table 1a. Stormwater captured before the raingarden overtops.

During an average storm, the raingarden captured the first 0.31 inches

rainfall before overtopping. The raingarden absorbed an average of

850 cubic feet per storm (plus an additional volume that was infiltrated

after overtopping; see text.) The feature captured and absorbed 13% of

the total rainfall during the monitoring period (October 1, 2010 – March

31st, 2011).

12

Bioswale Stormwater Capture

Date Event

Rain Duration before Feature Overtops

Rainfall Captured Before Overtopping

Storm Total

Total Volume Captured Before Overtopping(cf)

Total Storm Runoff (cf)

10/5/2010 First Flush

did not overtop 0.23" 0.23" 463 463

10/23/2010 Storm

Event 1 9:20 0.98" 5.28" 1972 10622

11/7/2010 Storm

Event 2 4:30 0.64" 1.80" 1288 3621

12/5/2010 Storm

Event 3 3:55 0.31" 2.05" 633 4124

12/17/2010 Storm

Event 4 8:45 0.53" 4.40" 1066 8852

1/29/2011 Storm

Event 5 6:45 0.57" 1.13" 1147 2273

2/14 /2011 Storm

Event 6 27:30 0.97" 1.84" 1951 3702

3/18/2011 Storm

Event 7 1:55 0.15" 0.50" 302 1006

Average

(does not include First Flush)

8:55 0.59" 2.43" 1187 4889

Table 1b. Stormwater captured before the bioswale overtops. The bioswale captured the first 0.59 inches rainfall before overtopping. The bioswale absorbed an average 1187 cubic feet per storm (plus an additional volume that was infiltrated after overtopping; see text.) The bioswale captured and absorbed 24% of the total rainfall during the monitoring period (October 1, 2010 – March 31st, 2011). The first storm did not overtop either BMP.

13

Raingarden Sediment

Date Event

TSS Influent (mg/L)

TSS Effluent (mg/L)

TDS Influent (mg/L)

TDS Effluent (mg/L)

Turbidity Influent (NTU)

Turbidity Effluent (NTU)

pH Influent

pH Effluent

10/5/2010 First Flush 263 17 202 13 93 20 7.1 5.7

10/23/2010 Storm Event 1 missing 17 13 13 20 17 5.7 6.0

11/7/2010 Storm Event 2 14 12 13 87 4 12 5.2 5.8

12/5/2010 Storm Event 3 21 21 60 79 28 30 7.1 8.9

12/17/2010 Storm Event 4 27 5 27 217 17 9 7.2 7.5

1/29/2011 Storm Event 5 79 20 25 74 24 19 6.7 7.4

2/14/2011 Storm Event 6 72 9 65 134 53 23 6.6 7.3

3/18/2011 Storm Event 7 39 17 27 141 20 20 7.1 7.6

Average (does not include First Flush) 42 14 33 106 24 19 6.5 7.2

Bioswale Sediment

Date Event

TSS Influent (mg/L)

TSS Effluent (mg/L)

TDS Influent (mg/L)

TDS Effluent (mg/L)

Turbidity Influent (NTU)

Turbidity Effluent (NTU)

pH Influent

pH Effluent

10/5/2010 First Flush 6280 40 438 7 6000 163 5.6 4.8

10/23/2010 Storm Event 1 missing 40 7 11 163 23 4.8 4.9

11/7/2010 Storm Event 2 32 15 7 7 17 13 4.8 missing

12/5/2010 Storm Event 3 53 missing 7 missing 17 missing 7.4 missing

12/17/2010 Storm Event 4 32 4 13 40 22 11 7.0 6.2

1/29/2011 Storm Event 5 241 39 13 27 52 24 7.0 6.7

2/14/2011 Storm Event 6 75 26 40 47 100 38 6.9 6.5

3/18/2011 Storm Event 7 43 19 13 47 17 27 6.8 6.3

Average (does not include First Flush) 79 21 14 30 55 23 6.5 6.1

Percent Reductions

% reduction Raingarden Bioswale

TSS 67% 74%

TDS 222% increase 107% increase

Turbidity 22% 59%

Table 2. Total Suspended Solids (TSS), Total Dissolved Solids (TDS), Turbidity, and pH values for the

Raingarden (top panel) and Bioswale (middle panel). Influent and effluent values are shown for the first

flush and each storm event. The bottom panel shows percent reductions in sediment.

14

First Flush Pollutant Concentrations

Raingarden Bioswale

First Flush Parameters units Influent

Concentration Effluent

Concentration %

Reduction Mass

removed* Influent

Concentration Effluent

Concentration % Reduction Mass

removed

Total Dissolved Soilds (TDS) mg/L 202 20 90% 3.61 kg 438 16.7 96% 5.74 kg

pH pH Units 7.1 6.0 -- -- 5.6 4.9 -- --

Total Suspended Solids (TSS) mg/L 263 17 94% 4.70 kg 6,280 40 99% 82.26 kg

Turbidity at SYRCL NTU 135 17 87% 6,000 23 >99%

Total Recoverable Chromium µg/L 41 ND 100% 0.7 gm 492 ND 100% 6.4 gm

Total Recoverable Copper µg/L 130 42 68% 2.3 gm 422 ND 100% 5.5 gm

Total Recoverable Lead µg/L 14 ND 100% 0.25 gm 81 1.1 99% 1.1 gm

Total Recoverable Mercury µg/L ND -- -- -- 143 ND 100% 1.9 gm

Total Recoverable Nickel µg/L 30 ND 100% 0.5 gm ND n/a -- --

Total Recoverable Zinc µg/L 473 ND 100% 8.4 kg 985 ND 100% 12.9 gm

Nitrate as N mg/L 0.8 ND 100% 14.3 gm 2.2 ND 100% 28.8 gm

Phosphate as P mg/L 0.25 0.095 62% 4.5 gm 0.178 0.042 76% 2.3 gm

Oil and Grease mg/L ND n/a -- -- ND n/a -- --

Table 3. Pollutant concentrations of first flush influent (10/5/2010) and first effluent (10/23/2010). Total mass removed during first flush is

estimated based on first flush influent concentrations and total stormwater volume absorbed (630.8 cf).

15

Figure 1. Rood Center site plan, showing the locations of monitored features.

Bioswale

Raingarden

Second Raingarden (Not Monitored)