|
Soil samples for all
the testing described below were obtained from holes inside each pit and
one hole located in between the pits (null). The soil beneath the
pits is a silty sand (SM) according to the Unified Soil Classification
System. In addition to classifying the soils, the following tests
were performed:
- Bacteria
- Copper
- Total Carbon
- Total Nitrogen
- Cation
Exchange Capacity
- pH
- Infiltration
rate
Only the
results of the bacterial, copper, and infiltration testing are presented
here. Complete results can be found in Matthew Gore's thesis, which will
be posted on the VUSP website soon.
Biological Testing Results
Understanding that a sewer
line had
been connected to the Monastery seepage pit, data needed to be gathered to
determine whether the system would be a safe environment for a study.
The results for the two pits, plus a control site located in between the
two pits, are shown below at a depth of 6 inches. Total coliforms and some e-coli coliforms were found.
Because bacteria were also found in the null site, it can be concluded
that the bacteria occur naturally in the soil and that the site
presented no health and safety problems.
|
Monastery
|
0.1/50 ml
|
1.0/50 ml
|
10/50 ml
|
|
coliforms
|
40
|
150
|
500
|
|
e-coli
coliforms
|
3
|
7
|
30
|
|
total
|
43
|
157
|
530
|
|
Tolentine
|
|
|
|
|
coliforms
|
80
|
212
|
500
|
|
e-coli
coliforms
|
0
|
11
|
65
|
|
total
|
80
|
223
|
565
|
|
Null
|
|
|
|
|
coliforms
|
5
|
147
|
500
|
|
e-coli
coliforms
|
0
|
0
|
6
|
|
total
|
5
|
147
|
506
|
Copper Testing Results
Copper entered the
pits from the copper gutters, downspouts, and sheathing used on the
rooftops. While elevated levels of copper were found in the pits as
compared to the null site, the soil in the pits would still be
considered clean fill by the PADEP.
Infitration Testing Results
The infiltration rate
was determined for both the Tolentine and Monastery pits. The
infiltration rate of the Tolentine pit was excellent; unfortunately,
there are no easily accessible lines to connect to this pit. The
infiltration rate of the Monastery pit was low and we investigated a
plan to restore the infiltration rate using earthquake drains.
 
Top
left - Earthquake Drain Manufactured by Nilex
Top
right - Earthquake Drain Installation
Unfortunately, there
was not much improvement in the infiltration rate after the earthquake
drain installation as can be seen in the figure below which compares the
infiltration rates at a head of 0.76 m.
Although we are
unable to say definitively why there was no improvement in the
infiltration rate, we believe there are two possible explanations.
First, the most logical explanation is that the deeper soil is not any
more permeable than the upper soils. Second, we were only able to
install one out of four drains because of the size of the
entryway into the pit. It is our opinion that more would be required to see
a change in the infiltration rate. We still believe that an earthquake
drain can be effective if the infiltration rate is being compromised by
a low hydraulic conductivity layer at the surface. |
