The water treatment facility, the Blacksburg, Christiansburg, VPI Water Authority, located in Montgomery County pulls water from the New River to use as the local drinking water supply. When fresh water comes into the household it has been treated with all kinds of chemicals. The water goes through some chemical treatment to insure safe quality to the local residents. The raw water is treated with chlorine, flocculants and fluoride to make it safe for consumption. Some of the chemicals stay in the water to help disinfect it while others are precipitated out. The particles that are precipitated out, usually sand, silt and coagulant agents, are trapped in sand and anthracite and washed or backwashed into settling ponds. The ponds collect the waste sediments until it is full of solids. The backwashed water is then diverted to another settling pond while the other is cleaned out.
This is one of the two settling ponds. The Water Authority has two settling ponds and a drying pond to allow for the closing one for maintainance. This one is full of sludge and is ready to be drained.
The dike in between two pond are broken to allow the drainage of the water. The accumulation of the sludge become apparent as the water is drained off.
This is a close up of the drainage of the water from the settling pond.
The pond is allowed to dry for two to three weeks before the sludge is removed.
This photo shows remove of the dried sludge. The dump truck containing the dry sludge is brought to Montgomery County Landfill. The 6.70 % solid concentration sludge is used as daily cover for the municipal waste in the landfill. The solids are considered hazardous waste because it has been chemically treated.
This is the final step in sludge removal. This pond is the polishing pond with a 4.70 % solids concentration. It settles out any remaining sludge from the settling pond. In the upper left hand corner of the pond, the top of the water skimmed off. The water flows into a nearby tributary of the Strobble's Creek. This pond accumulates sludge at a lower rate than the settling ponds. It is cleaned out about every three years.
The potential for groundwater contamination could be very high because of the location of the settling and polsihing ponds. There are two settling ponds, one drying pond and one finishing pond. None of these ponds are lined so seepage is inevitable. A natural stream is located just behind the drying pond so water will run towards it. The waste water can run or filter towards the water table.
The main components of the sludge are aluminum, copper, sliver, calcium, magnesium, potassium, and nitrogen. The high aluminum content is due to alum used as a coagulant in flocculation. The sludge has been recommended for land applications on local crops such as fields of corn and winter wheat. No adverse affects have been found. The Department of Environmental Quality (DEQ) have evaluated the treatment process and decided monitoring wells around the settling and finishing ponds were not necessary. If the components of the sludge changes, monitoring wells may be required. The monitoring wells would have to be placed according to the geologic and hydrologic formations in the area. Existing wells and spring may be approved for monitoring use. Otherwise, monitoring wells should be installed to sample to top portion of the groundwater. The sampling of the wells should follow procedure to obtain an uncontaminated sample. For a quality background groundwater data, sampling from the wells should be taken before the facility is operating. In the Water Authorities case, this would not be possible, because the facility is already open. The periodic test to determine if wells are need, could be used as possible background data. The monitoring samples are tested for:
Olver Incorporated tested the polishing pond sludge. Here are those results:
Analysis of Polishing Pond Shallow Sludge |
|||
| Analysis | Result | MDL | |
|---|---|---|---|
| Total Solids | 11.0% | N/A | |
| Ammonia as N | ND | 10 mg/kg | |
| Total Kjeldahl Nitrogen | 4,330 mg/kg dry solids | 50 mg/kg | |
| Nitrate/Nitrite | 18 mg/kg dry solids | 1 mg/kg | |
| Total Phosphorus | 291 mg/kg dry solids | 5 mg/kg | |
| Total Aluminum | 79,400 mg/kg dry solids | 100mg/kg | |
| Total Arsenic | ND | 5 mg/kg | |
| Total Cadmium | 1.0 mg/kg dry solids | 0.5 mg/kg | |
| Total Calcium | 3,490 mg/kg dry solids | 1 mg/kg | |
| Total Chromium | 49 mg/kg dry solids | 1 mg/kg | |
| Total Copper | 164 mg/kg dry solids | 1 mg/kg | |
| Total Lead | 58 mg/kg dry solids | 3 mg/kg | |
| Total Mercury | ND | 0.25 mg/kg | |
| Total Magnesium | 3,430 mg/kg dry solids | 1 mg/kg | |
| Total Nickel | 18 mg/kg dry solids | 4 mg/kg | |
| Total Potassium | 1,250 mg/kg dry solids | 1 mg/kg | |
| Total Sodium | 257 mg/kg dry solids | 1 mg/kg | |
| Total Zinc | 253 mg/kg dry solids | 1 mg/kg |
MDL= Minimum Detection Limit
N/A= Mot Applicable
ND= Not Detectable
*data from Olver Incorporated
Another report from CH2M Hill on the composition of the water treatment plant showed that the results were similar to other water treatment plants also using alum or ferric coagulants. Except for high concentrations of cadmium, lead, and chromium in comparison to the National Sewage Sludge Survey's mean values in which nondetect is set to sample-specific limit of detection. The other exception was the low concentration of total phosphorus (1.4) in comparison with 5,000 readings from water treatment plants sludge for plants using alum or ferric coagulants. The Virginia DEQ monitors sludge ponds for possible contamination of groundwater supplies. They look at all the data in the water treatment plant and require testing on the sludge to determine if monitoring wells are needed. The Water Plant tested the sludge and water in all the ponds to determine if it is hazardous. The data must comply with EPA regulations in order to maintain their operating permit.
Presently, the DEQ still does not require the water authority to install monitoring wells. The results were good enough not to have monitoring wells at this time. Even with the exceptions, the waste is still suitable for land application and for cover in the Montgomery landfill. If the composition of the waste changes, installation of monitoring well might be in the future for the Blacksburg, Christiansburg, VPI Water Authority. However, the Blacksburg, Christiansburg, VPI Water Authority is up for permit renewal and will have to go through the same tests again to prove they are not contaminating the groundwater supply.
Send comments or suggestions to:
Student Authors: Heather Bell, kermithdb@aol.com
and Leigh Ann Daigle
Faculty Advisor: Daniel Gallagher, dang@vt.edu
Copyright © 1998 Daniel Gallagher
Last Modified: June 7, 1998
