Abington Friends School Raingarden Water Quality Summary Prior to Installation through almost 1.5 Years of Operation John Komlos and Andrea Welker Villanova University June 30, 2017 Installation of the Abington Friends School raingarden began in late October 2015 and the system went online on November 24, 2015. This raingarden treats stormwater prior to discharge into Jenkintown Creek. Below is a summary of the water quality data at the Abington Friends site prior to the construction of the SCM (August 2015 to October 2015) as well as the water quality assessment over time that includes before, during and after the SCM was put online. Finally, this report concludes with an overall interpretation of the results to date and how they relate to the performance of the raingarden. 1. Water Quality Assessment Prior to SCM Construction: Water quality data was collected prior to the installation of the raingarden in order to document the downstream water quality characteristics pre-raingarden. Site locations for the pre- raingarden sampling can be found in Figure 1.1. Grab samples were collected between August 2015 and October 2015 and included five baseflow events and three storm events. The grab samples are located at the beginning of the Jenkintown Creek just downstream of the raingarden (AG03; 40.095280 latitude, - 75.118952 longitude), at the wall of the retention basin for the dam (AG04; 40.094263, -75.117721), and near the flow meter under the bridge (AG05; 40.093889, -75.116656). Water quality parameters measured included nitrite, NOx (nitrate and nitrite), total Kjeldahl nitrogen (TKN), phosphate, total phosphorus, chloride, total suspended solids (TSS), total dissolved solids (TDS), pH and conductivity. This data was compared with Tookany/Tacony Watershed data collected from April 2014 to August 2015 downstream of the restoration project and in the vicinity of AG05 (site ID TTF200; Jenkintown Creek: Abington Friends School; 40.0939 latitude and -75.1167 longitude). All TTF200 samples were collected under conditions such that no rain > 0.25” had fallen in the 48 hour prior (and thus are considered baseflow samples).
Transcript
Abington Friends School Raingarden Water Quality Summary Prior to Installation through almost 1.5 Years of Operation
John Komlos and Andrea Welker
Villanova University
June 30, 2017
Installation of the Abington Friends School raingarden began in late October 2015 and the system went online on November 24, 2015. This raingarden treats stormwater prior to discharge into Jenkintown Creek. Below is a summary of the water quality data at the Abington Friends site prior to the construction of the SCM (August 2015 to October 2015) as well as the water quality assessment over time that includes before, during and after the SCM was put online. Finally, this report concludes with an overall interpretation of the results to date and how they relate to the performance of the raingarden.
1. Water Quality Assessment Prior to SCM Construction:
Water quality data was collected prior to the installation of the raingarden in order to document the downstream water quality characteristics pre-raingarden. Site locations for the pre-raingarden sampling can be found in Figure 1.1. Grab samples were collected between August 2015 and October 2015 and included five baseflow events and three storm events. The grab samples are located at the beginning of the Jenkintown Creek just downstream of the raingarden (AG03; 40.095280 latitude, -75.118952 longitude), at the wall of the retention basin for the dam (AG04; 40.094263, -75.117721), and near the flow meter under the bridge (AG05; 40.093889, -75.116656). Water quality parameters measured included nitrite, NOx (nitrate and nitrite), total Kjeldahl nitrogen (TKN), phosphate, total phosphorus, chloride, total suspended solids (TSS), total dissolved solids (TDS), pH and conductivity. This data was compared with Tookany/Tacony Watershed data collected from April 2014 to August 2015 downstream of the restoration project and in the vicinity of AG05 (site ID TTF200; Jenkintown Creek: Abington Friends School; 40.0939 latitude and -75.1167 longitude). All TTF200 samples were collected under conditions such that no rain > 0.25” had fallen in the 48 hour prior (and thus are considered baseflow samples).
Compilation of the pre-raingarden water quality data prior to the installation of the raingarden can be found in Figure 1.2. Regarding nitrogen, the total nitrogen concentration in water is the addition of NOx (nitrate + nitrite) and TKN (ammonia + organic nitrogen). Results from the data analysis show that nitrite concentrations were well below the NOx (nitrate + nitrite) concentrations (Figure 1.2a and 1.2b), indicating that nitrate comprised the majority of the NOx sample. In addition, comparison of Figures 1.2b and 1.2c shows that nitrate was the dominant form of nitrogen present during baseflow conditions. NOx, chloride, total dissolved solids (TDS) concentrations (as well as conductivity) trended higher during baseflow conditions compared to storm events (Figure 1.2b, 1.2g, 1.2h and 1.2j) while TKN, phosphate and total phosphorus concentrations trended higher during storm events compared to baseflow events (Figure 1.2c, 1.2e and 1.2f). Comparison of total suspended solids (TSS) concentrations between baseflow and storm conditions was inconclusive due to the large variability in the baseflow TSS concentrations (Figure 1.2d). In general, the baseflow concentrations at AG05 collected between August 2015 and October 2015 correlated with the values from the Tookany/Tacony Watershed database collected in the vicinity of AG05.
Figure 1.1. Locations of grab samples collected prior to the installation of the Abington Friend School raingarden. AG03 is a grab sample location just downstream of the raingarden; AG04 is a grab sample location farther downstream located at an existing dam; AG05 is a grab sample location farthest downstream of the raingarden located under an existing bridge.
Figure 1.2. Water quality data collected prior to the installation of the Abington Friends School raingarden. “Below SCM”, “at Dam”, and “at Bridge” refer to sampling locations AG03, AG04 and AG05, respectively, from Figure 1.1. “TTF data” (when available) refers to site ID TTF200 from the Tookany/Tacony Watershed database. There was no TTF data for nitrite, TKN, and TDS. Values show the average (+/- std) and “n” is the number of samples.
2. Water Quality Assessment Before and after SCM Construction:
Construction of the raingarden began in late October 2015 and was put online November 2015. Nitrite, NOX (nitrate+nitrite), Total Kjeldahl Nitrogen (TKN, which is ammonia and organic nitrogen), phosphate, total phosphorus, chloride, total suspended solids (TSS), total dissolved solids (TDS), pH and conductivity were monitored over time during both baseflow and stormflow conditions. Although the site is still actively sampled, water quality results in this report only extend through April 2017.
2.1 Nitrogen
Total nitrogen is the sum of NOx (nitrate + nitrite) and TKN (ammonia + organic nitrogen). NOx concentrations downstream of the raingarden were higher (p-value < 1x10-7) prior to the installation of the raingarden (6.8 ± 1.3 mg/L, n=18) compared to after raingarden installation (4.1 ± 1.4 mg/L, n=27) during baseflow conditions (Figure 2.1a) indicating that the installation of the raingarden had a positive effect on Jenkintown Creek during baseflow conditions with respect to NOx. The same trend was observed during stormflow conditions with NOx concentrations after raingarden installation (2.4 ± 1.3 mg/L, n=28) lower than (p-value <0.05) NOx concentration prior to raingarden installation (3.9 ± 1.4 mg/L, n=15). Prior to the installation of the raingarden, baseflow NOx concentrations were lowest just downstream of the raingarden and NOx concentrations increased with distance downstream of the raingarden (Figure 2.1.1a). During stormflow conditions, the lowest NOx concentrations were generally measured in the raingarden bowl and at the raingarden outlet (0.4 ± 0.6 mg/L, n=14) compared to Jenkintown Creek (2.4 ± 1.3 mg/L, n=28) indicating that the water exiting the raingarden was not the major source of NOx to the stream. The low nitrite concentrations (< 0.3 mg/L) during baseflow and stormflow conditions (Figure 2.1.2) compared to NOx concentrations (Figure 2.1.1) indicate that the majority of the NOx was as nitrate.
The average of all baseflow concentrations indicate that TKN (ammonia + organic nitrogen) concentrations in Jenkintown Creek were higher (p-value < 0.002) during stormflow conditions (1.1 ± 0.97 mg/L, n=28) compared to baseflow conditions (0.14 ± 0.14 mg/L, n=29) (Figure 2.1.3) indicating that stormwater runoff was a significant contributor to the TKN concentrations in the creek. No difference in TKN concentration in the creek before and after raingarden installation was observed to date during either baseflow or stormflow conditions (p-value > 0.1).
Comparison of average NOx and TKN concentrations indicate that the majority of nitrogen in Jenkintown Creek is in the form of nitrate. Regarding nitrogen removal by the raingarden, there were six storm events that had NOx data for both the ponded bowl of the raingarden and the raingarden outlet and none of those six events showed NOx concentrations lower at the outlet than in the ponded region. Therefore, no decrease in NOx concentrations was observed with this limited set of data. There was only three storm events where there was TKN data for both the ponded bowl of the raingarden and the raingarden outlet (which is too small a sample size to make any conclusions).
Storm Event Raingarden BowlRaingarden OutletJust Downstream of Raingardenat Damat Bridge
Nitr
ate
+ Ni
trite
(mg/
L)
Figure 2.1.1 NOx (nitrate + nitrite) concentrations over time for a) baseflow and b) stormflow conditions. Dashed vertical line data shows the approximate time the raingarden was installed.
Figure 2.1.2 Nitrite concentrations over time for a) baseflow and b) stormflow conditions. Dashed vertical line data shows the approximate time the raingarden was installed.
Figure 2.1.3. TKN (ammonia + organic nitrogen) concentrations over time for a) baseflow and 2) stormflow conditions. Dashed vertical line data shows the approximate time the raingarden was installed.
2.2 Phosphorus
Phosphate concentrations were measured over time (Figure 2.2.1). Results indicate that baseflow phosphate concentrations in Jenkintown Creek before and after raingarden installation (0.023 ± 0.012 mg/L, n=35) were lower (p-value < 0.0002) than during stormflow conditions (0.056 ± 0.048 mg/L, n=23) during this same period (Figure 2.2.1). The average phosphate concentration in the raingarden bowl and at the raingarden outlet (0.33 ± 0.44 mg/L, n=10) was higher (p-value < 0.005) than that of Jenkintown Creek during stormflow conditions after raingarden installation (0.051 ± 0.048 mg/L, n=20).
Total phosphorus concentrations were also measured over time (Figure 2.2.2). Similar to the phosphate results, total phosphorus concentrations in Jenkintown Creek during baseflow conditions before and after the installation of the raingarden (0.039 ± 0.021 mg/L, n=46) were lower than during stormflow conditions (0.15 ± 0.16 mg/L, n=23) during that same time period (Figure 2.2.1). The average total phosphorus concentration in the raingarden bowl and at the raingarden outlet (0.66 ± 0.57 mg/L, n=12) was higher than (p-value < 0.001) that of Jenkintown Creek during stormflow conditions (0.15 ± 0.16 mg/L, n=23). For comparison purposes, the raingarden total phosphorus concentrations are within the range for urban and roadway runoff (0.02 to 9.4 mg=L with a typical value of 0.4 mg=L) reported by Davis et al. (2006) based on references cited therein.
Even though both the phosphate and total phosphorus results indicate that the raingarden is a significant source of phosphorus to Jenkintown creek, all of the total phosphorus concentrations during baseflow conditions are below the U.S. Environmental Protection Agency (USEPA) desired goal of 0.1 mg/L total phosphorus in surface water bodies for the prevention of excessive plant growth (Pardue et al. 2005). However, most of the total phosphorus concentrations measured in the creek during stormflow conditions are greater than the USEPA desired goal limit of 0.1 mg/L. It should be noted that this limit was also exceeded prior to the installation of the raingarden.
Regarding total phosphorus removal by the raingarden, there were six storm events that had total phosphorus data for both the ponded bowl of the raingarden and the raingarden outlet. Of those events, the majority (5 of 6) had lower total phosphorus concentrations leaving the raingarden than found in the bowl, indicating total phosphorus removal by the raingarden. However there were only four storm events where there was phosphate data for both the ponded bowl of the raingarden and the raingarden outlet. Of those four storms, only two had lower phosphate concentrations at the outlet compared to the ponded region. That said, four to six events is a limited dataset and more storms are needed before the performance of the raingarden can be understood with confidence. Also, the baseflow phosphate concentration in the creek after the raingarden was installed (0.019 ± 0.008 mg/L, n=20) was lower (p-value < 0.004) than before the raingarden was installed (0.030 ± 0.014 mg/L, n=15), indicating that the raingarden had a positive effect on Jenkintown Creek. Although the baseflow total phosphorus concentration was also lower after the raingarden was installed (0.037 ± 0.021 mg/L, n=28) compared to before the raingarden was installed (0.044 ± 0.021 mg/L, n=18), this difference was not statistically significant (p-value =0.14).
Preliminary results showing evidence of phosphorus removal by the raingarden, even though no evidence of nitrogen removal was observed, is encouraging because phosphorus is typically the limiting nutrient in freshwater lakes and rivers (i.e., phosphorus is the nutrient that needs to be removed to minimize the negative effects of excess nutrients in the water body). A phosphorus-limited water body typically has an N/P ratio greater than 10. The average total nitrogen and average total phosphorus concentrations after the installation of the raingarden were used to confirm that the system is phosphorus limited. An estimated N/P ratio for the creek > 20 (Table 2.2.1) indicates that the creek is in fact phosphorus limited.
Table 2.2.1. Estimation of the N/P ratio in Jenkintown Creek using average N and P data from all three creek sampling location (just downstream of raingarden, at dam, at bridge) after the installation of the raingarden.
Figure 2.2.1. Phosphate concentrations over time for a) baseflow and 2) stormflow conditions. Dashed vertical line data shows the approximate time the raingarden was installed.
Figure 2.2.2. Total phosphorus concentrations over time for a) baseflow and 2) stormflow conditions. Dashed vertical line data shows the approximate time the raingarden was installed.
2.3 Chloride, Total Dissolved Solids (TDS) and Conductivity
Chloride (Figure 2.3.1), TDS (Figure 2.3.2) and conductivity (Figure 2.3.3) were monitored over time during baseflow and stormflow conditions. Conductivity is an indication of the dissolved ions in the water. Therefore, conductivity and TDS values should correlate if the majority of the TDS (i.e. the filtrate that passes through a ~1 µm filter) are ions and not colloidal material. Likewise, if the chloride concentration makes up the majority of the ions in solutions (not uncommon in colder climates during winter months due to salting of paved surfaces), the chloride concentration should correlate with the TDS concentration and the conductivity reading.
Results show that the sampling location at the dam (followed closely by the sampling location at the bridge) has the highest chloride, TDS and conductivity readings during baseflow conditions. The sampling location at the dam is between the raingarden and the bridge. Higher dissolved solids concentrations at the dam indicates that there is a source of dissolved solids downstream of the raingarden. Analysis of stormflow data showed multiple events where conductivity (2/3/2016, 4/12/2016, 4/26/2016, 5/1/2016), TDS (4/12/2016, 4/26/2016, 5/1/2016, 7/25/2016) and chloride (4/12/2016, 8/21/2016) levels in the raingarden bowl and/or at raingarden outlet were higher than in all creek sampling locations. That said, all chloride concentrations in the raingarden and in the creek during both storm and baseflow conditions were below chloride concentration levels that correlate with the EPA freshwater quality criteria for chronic (230 mg/L) and acute (860 mg/L) toxicity (USEPA 1988).
Figure 2.3.1. Chloride concentrations over time for a) baseflow and 2) stormflow conditions. Dashed vertical line data shows the approximate time the raingarden was installed.
Figure 2.3.2. Total Dissolved Solids (TDS) concentrations over time for a) baseflow and 2) stormflow conditions. Dashed vertical line data shows the approximate time the raingarden was installed.
Figure 2.3.3. Total Dissolved Solids (TDS) concentrations over time for a) baseflow and 2) stormflow conditions. Dashed vertical line data shows the approximate time the raingarden was installed.
2.4 Total Suspended Solids (TSS)
The sampling location just downstream of the raingarden also had the highest TSS concentration (compared to at the dam and at the bridge) in six of the seven baseflow events where this sample was collected since the raingarden was put online (Figure 2.4.1a). Likewise, the TSS concentration in the raingarden bowl and raingarden outlet was higher than that measured in the creek for seven of the 11 times the raingarden was sampled during storm events since the raingarden was installed (Figure 2.4.1b). Therefore, TSS concentrations over time during both baseflow and stormflow conditions indicate relatively high TSS concentrations in the raingarden bowl and raingarden outlet compared to the creek. It is important to note that the raingarden was not operating to its potential up through early 2017 due to a lack of ponding in the raingarden bowl caused by water exiting the raingarden too fast. Therefore, it is assumed that the lack of ponding decreased the pollutant removal capacity of the raingarden and sample collection in a shallow raingarden bowl with little to no ponded water could have caused the elevated TSS concentrations. This problem was addressed through the installation of a reducer at the outlet pipe in February 2017 to slow down flow exiting the raingarden. It should be noted that no spikes in TSS concentrations were observed in the raingarden after February 2017 when water was allowed to pond in the raingarden bowl. Also, the high TSS concentrations in the raingarden (when they did occur) did not appear to increase the TSS concentration downstream at the dam and bridge during either baseflow or storm conditions.
2.5 pH
pH was measured over time during baseflow and stormflow conditions (Figure 2.5.1). The pH in the creek before the raingarden was installed (6.72 ± 0.27, n=18) was comparable (p-value = 0.12) to the pH after the raingarden was installed (6.83 ± 0.36, n=33) during baseflow conditions. However, the pH in the creek after the raingarden was installed (6.96 ± 0.23, n=33) was greater than (p-value < 0.005) the pH before the raingarden was installed (6.80 ± 0.21, n=18). During baseflow conditions, the increase in pH in the creek after the raingarden was installed correlates with a pH in the raingarden bowl and raingarden outlet (7.43 ± 0.30, n=14) that is higher than the pH in the creek.
Figure 2.4.1. Total Suspended Solids (TSS) concentrations over time for a) baseflow and 2) stormflow conditions. Dashed vertical line data shows the approximate time the raingarden was installed.
Figure 2.5.1. pH over time for a) baseflow and 2) stormflow conditions. Dashed vertical line data shows the approximate time the raingarden was installed.
3 Interpretation of Results with Respect to Raingarden Performance
A raingarden was installed in the Fall 2015 at the headwaters of Jenkintown Creek as a stormwater control measure. Water quality results related to the performance of the raingarden include nutrient data (nitrogen, phosphorus, chloride) prior to raingarden installation up through February 2017 as well as additional water quality parameters (TSS, TDS, conductivity, pH) through April 2017.
Total nitrogen, nitrate and total phosphorus were measured in Jenkintown Creek during baseflow and/or storm conditions to be above the national background stream concentrations of 1.0 mg/L, 0.6 mg/L and 0.1 mg/L, respectively, and thus the water quality of the stream is considered to have been affected by human activities (USGS, 1999). Average concentrations for both nitrogen and phosphorus are above concentrations that have been shown to cause eutrophic conditions. Comparison of average nitrogen and phosphorus concentrations indicate that the creek is phosphorus limited (and thus removal of phosphorus would correlate with an increase in water quality with respect to eutrophication). All chloride concentrations in the creek during both storm and baseflow conditions were below chloride concentration levels that correlate with the EPA freshwater quality criteria for chronic (230 mg/L) and acute (860 mg/L) toxicity (USEPA 1988).
Installation of the raingarden had a positive effect on Jenkintown Creek water quality with respect to nitrate (both baseflow and storm conditions) and phosphate (just baseflow conditions) and had a negative effect with respect to TSS during stormflow conditions. Whether there was a positive or negative effect on the creek as a result of the raingarden installation was inconclusive for the other parameters due to a limited sample size and/or large standard deviation at each sampling location.
It is important to reemphasis that the raingarden was not operating to its potential from when it was put online (November 2015) up through early 2017 due to a lack of ponding in the raingarden bowl caused by water exiting the raingarden too fast. Therefore, it is assumed that the lack of ponding decreased the pollutant removal capacity of the raingarden. This problem was addressed through the installation of a reducer at the outlet pipe in February 2017 to slow down flow exiting the raingarden. The installation of this reducer succeeded in allowing water to pond in the raingarden. Limited water quality data is available to date to assess any performance improvements caused by the ponding. Any changes in raingarden performance caused by the ponding will be quantified once an adequate number of baseflow and stormflow events are sampled and analyzed.
References
Davis, A. P., Shokouhian, M., Sharma, H., and Minami, C. (2006). “Water quality improvement through bioretention media: Nitrogen and phosphorus removal.” Wat. Environ. Res., 78(3), 284-293.
Pardue, J. H., et al. (2005). “Chemical and microbial parameters in New Orleans floodwater following Hurricane Katrina.” Environ. Sci.Technol., 39(22), 8591–8599.
USEPA - U.S. Environmental Protection Agency) (1988) “Ambient Water Quality Criteria for Chloride” USEPA Report EPA 440/5-88-001. Office of Water Regulations and Standards Criteria and Standards Division, Washington, D.C.
USGS - U.S. Geological Survey (1999) “The Quality of our Nations Waters” USGS Circular 1225. (https://pubs.usgs.gov/circ/circ1225/)
