STORMWATER DISCHARGE ABOVE THE PERFORMANCE STANDARD – JULY 19, 20 and 21, 2010
USEPA, PADEP, and Throop Borough were kept informed
on stormwater management activities during the period from July 19 to August 2,
2010.
A formal
non-compliance report
covering the period from July 19 to August 2, 2010 was submitted to PADEP on
August 4, 2010.
(Click
here to review the July 19, 2010 Non-Compliance Report.)
July 19, 2010
- On July 19, 2010,
after a heavy storm in the late afternoon (over 1.5 inches of rain was received
on July 19, 2010), there was a stormwater discharge above the performance
standard. The skimmer was in the discharge position in accordance with the
Stormwater Management Design Plan. After the heavy rainfall, AGC took a
turbidity reading at the discharge point and the turbidity meter gave an “Error”
message indicating that the levels were above the range of the instrument.
(Turbidity is a measurement of the cloudiness of the water which is caused by
sediment.) The skimmer was flipped to discontinue flow from the basin and
a
flocculant (Pond-Clear)
was added to the basin to enable the sediments to settle out of the water to the
bottom of the basin. Samples of the discharge were taken for the monthly total
and dissolved lead analysis.
The dissolved lead result was
below the laboratory detection limit of 1.0 ug/L. The NPDES permit standard for
maximum dissolved lead for the Site is 650 ug/L. The total lead result
was 368 ug/L. There is not an NPDES standard for total lead. The very low total and dissolved lead
results provide reassurance that even though the turbidity levels were
above the performance standard, there was NOT a release of lead from the
site that would affect the creek or the river.
July 20, 2010
- On the morning of
July 20, 2010, between 7:13 AM and 7:40 AM, the water in the basin appeared
clear, and several readings were taken on the western side of the basin as
follows:
69.8 NTU, 116 NTU,
92 NTU, 120 NTU, 122 NTU, 83.8 NTU, 99.1 NTU, 92.7 NTU, 117 NTU, and 89.8 NTU
Based on these
readings, the
skimmer
was flipped at 8:28 AM. After water reached the discharge point
at the perimeter fence, two readings were taken at the fenceline at 8:40 AM.
The results were 61.4 NTU and 79.0 NTUs. The 200 NTU standard was checked as
well and read 197 NTU. In early afternoon (2:10 pm), AGC checked the basin again. The
basin and the discharge appeared turbid. A turbidity reading of 2292 NTUs
was obtained at the discharge point. The skimmer was again flipped to stop
flow. Additional Pond Clear was added to the basin to further
expedite
sediments
settling out of the water.
July 21,
2010 - On July 21,
2010, additional turbidity readings were collected in the basin between 3 and 6
inches below the water surface. All readings in the basin were in the 40 NTU
range. Based on these readings, the skimmer was flipped to allow discharge from
the basin. Turbidity readings were once again collected at the discharge point
immediately following discharge from the basin. Visual observations at the
discharge pipe showed clear water consistent with the basin readings. However,
the initial turbidity reading was 290 NTUs. After one minute of flow, the
turbidity reading at the discharge point dropped to 190 NTUs. It is possible
the initial 290 NTU reading at the discharge point was due to sediment within
the discharge channel. A third turbidity reading was collected at the discharge
point 10 minutes later; the reading was 140 NTUs. Approximately a half-hour
later the discharge turbidity reduced to 16 NTUs. Based on these readings,
discharge was allowed to continue with periodic monitoring until approximately
45 minutes later when the turbidity increased to 390 NTUs. The skimmer was then
flipped again to prevent discharge from the basin. Further investigation
revealed that the basin water is clear in the top few inches, but below that the
turbidity is much higher indicating the Pond Clear is working, but that
additional “doses” are needed. Samples for total and dissolved lead were
collected on July 21, 2010. Two sets of samples were collected: one when
turbidity was low and one when turbidity was high. The dissolved lead results
were both below the laboratory detection limit of 1.0 ug/L. The NPDES permit standard for
maximum dissolved lead for the Site is 650 ug/L. The total lead results
were .91 ug/L
and 38.3
ug/L, respectively. There is not an NPDES standard for total lead. The very low total and dissolved lead
results provide reassurance that even though the turbidity levels were
above the performance standard, there was NOT a release of lead from the
site that would affect the creek or the river.
Additional
Pond Clear was added to the basin on July 22, 2010.
Note: Due to
questions on the accuracy of the initial turbidity meter being used, a second
meter was sent to the Site and is now being used.
