Environmental Stewardship/Watershed Protection Grant
ME# 350-488
Voluntary Minimal Lawn Chemicals Campaign
Sustainable Society Action Project, Inc.
Report on Sampling and Analysis Activities
Nov - Dec 2002
Laura Toran, Temple University
In November, a presentation on this project was given at the Annual American Water
Resources Association Meeting. The talk described the long term monitoring data and
the statistical relationships between NO3 and NH4 concentrations and the potential
variables influencing storm discharge. These variables include: the area drained by the
storm pipe, lot size, season, assumed usage of lawn chemicals, size of the storm, and the
time since the last storm. The rest of this report summarizes these results. More details
will be provided in the final report, but this summary gives an overview.
Approximately 500 samples were analyzed in the course of the project. All of the
analyses were done by undergraduate students in the Department of Geology at Temple
University. Most of the sample collection was done by undergraduates, with the
assistance of faculty. The sample analysis included NO3 and PO4 for all samples, and
NH4 and K for selected samples in 2001 and all samples in 2002. Approximately
quarterly, samples were collected and sent to the Philadelphia Water Dept. for herbicide
analysis.
In the five rounds of samples collected for herbicide analysis, very few were above
detection limits. At each storm pipe, low concentrations were obtained for a few
herbicides, but there were no persistent hits.
The NO3 concentrations were below 6 mg/L, and most sites had less than 3 mg/L. The
peak concentrations were observed in the summer of the first year (2001) and in the
spring of the second year (2002). NH4 concentrations were more variable than NO3,
with the peak concentration was between 4 and 8 mg/L at all but one site. In between the
peaks, the concentrations were lower, nearly zero in many cases. Again, the peak was in
the summer of the first year (2001) and in the spring of the second year (2002). In the
case of NH4, there is a statistically significant difference between 2001 and 2002
concentrations at the one site where they were measured both years.
We hypothesize that lawn chemical usage was curtailed in 2002 because of the drought.
Originally, the sampling program was set up to see if there would be a reduction in
concentrations in the discharge due to the lawn chemical campaign. However, it was
hard to test this concept when the overall concentrations were low, making it difficult to
establish the background. Nonetheless, it is possible that lawn chemical usage fell off
during the drought, and the signal was picked up in the NH4 concentrations.
There was no significant relationship between NO3 concentrations and the size of the
storm or time since last storm. There was a slight increase in NO3 concentration as the
area of capture increased. This could be caused by a larger number of homes increasing
likelihood of contaminated storm runoff. The amount and NO3 concentration of runoff
per home could vary, and the larger area enhances the chances that a high hit occurs.
A comparison of the NH4 and K ratios showed a difference between creek water and
stormwater. The ratio was nearly constant in the Wissahickon Creek, which suggests a
biological source. The ratio varied, creating a scatter plot of NH4 v. K, in the
Wissahickon North stormpipe samples. This variation suggests the source is more
variable, which would be the case for lawn chemicals. Thus, the stormwater bears the
signature of lawn chemical input.
In terms of overall concentration, the storm pipe samples were compared to creek
samples at two sites. On Prophecy Creek, the creek had lower concentrations of NO3
than one storm pipe, and similar concentrations to the other pipe. On the Wissahickon
Creek, the concentrations tended to be higher than the storm pipe, suggesting that other
sources of NO3 discharge to the creek.
In summary, we have shown that lawn chemicals show up in discharge of the storm
pipes, albeit at low concentrations. The concentrations were higher in either the spring or
summer, when usage would increase. We found that NH4 was a useful variable to
monitor, when previously it was thought to be unstable. The variation in concentrations
has been related to possible usage changes, but more study is needed to determine what
the key factors are.