Aberdeen's conclusion that the SCCC flow will not exacerbate its wastewater systems existing problems largely relies upon the erroneous conclusion that the SCCC detention facility will allow the SCCC to avoid adding wastewater to the Aberdeen system during storm events. The purpose of the detention facility is to provide temporary storage of the SCCC wastewater during a heavy rainfall when the Aberdeen wastewater flow into the treatment plant exceeds the peak plant capacity of 13.0 mgd, as determined by MSA. Preliminary Engineering Report, p. 5-10, 5-12. Footnote 5 This is critical because, as discussed below, the Aberdeen WWTP and system lacks sufficient capacity to handle even its existing waste loads and flows.
In fact, as discussed below, there are bottlenecks that would occur even below 13.0 mgd. For example, KCM's evaluation of the plant's hydraulic capacity found overflow problems could occur in the effluent outfall at a plant flow of only 9.1 mgd. KCM Audit at 7-2. In addition, PS No. 2 could experience bypass when the SCCC flow is added to the system, reducing the pumping capacity of PS No. 2 to below that necessary to reliably pump the sewage from South Aberdeen to the WWTP.
Even assuming for the sake of argument that the detention facility would not need to be utilized until the flow reached 13.0 mgd, the detention facility is still inadequate. According to the MSA determination, in the event of a storm that exceeds a 10-year period, or that causes plant influent to exceed 13 mgd for two days, the SCCC wastewater flow to the force main would have to be continued. Footnote 6 In this event, the additional flow would further exacerbate the numerous existing capacity problems in the WWTP and system, which will be discussed below.
For example, as discussed below, by adding the SCCC flow to the force main below Pump Station No. 2 ("PS No. 2"), the capacity of PS No. 2 will be reduced. As a result, one of the Aberdeen system's most serious problems -- the discharge of raw sewage into the Chehalis River -- will intensify.
The existence of routine storm events lasting longer than two days demonstrates the inadequacy of the detention facility. While Mr. Bledsoe claims in his memo that the possibility of plant flow exceeding 13 mgd for two days is unlikely, the facts speak otherwise. Subsequent to the issuing of the MSA report, Aberdeen bypassed raw sewage to the Chehalis River for a full 48-hours, between December, 1996, and January 1997. A 3-day bypass occurred on December 19 though 21, 1994 with 2-day rainfall of 6.26 inches, which is within the 10-year rainfall recurrent interval determined by MSA. Footnote 7
It is not at all uncommon for flows to the WWTP to exceed 13.0 mgd, which would require use of the detention facility. According to the Aberdeen WWTP records the 1998-99 winter experienced 13 days, not 10 days as Mr. Bledsoe stated in his memo, on which the plant effluent flows exceeded 13.0 mgd. This is confirmed by the most accurate data on flow entering the Aberdeen WWTP, prepared by Aberdeen's consultant Earth Tech, Inc. According to the Earth Tech data, daily influent flows exceeded 13.0 mgd on five occasions just between November 11, 1998, through December 19, 1998. See Table A. Footnote 8
While the detention facility is effective for storm events causing short exceedances of the 13.0 mgd plant capacity, it will be ineffective during longer storm events. For example, in the three days November 24 through 26, 1998, the daily flows were 14.3 mgd, 16.8 mgd, and 15.4 mgd, respectively, all exceeding 13.0 mgd . In such event, the SCCC detention facility would fill up and the SCCC flow would be added to the already overburdened WWTP and collection system. Mr. Bledsoe's assertion that the SCCC facility can be operated to allow the Aberdeen plant to handle the SCCC flow within the peak hydraulic capacity clearly is incorrect.
Table B shows an analysis of how the SCCC detention facility would have operated between November 15 and December 16, 1998, based upon MSA's calculations of SCCC flow, storage capacity and pumping capacity, and Aberdeen's actual flows as measured by Earth Tech. The result is devastating. The detention tank would have been full on nine of the 32 days -- almost one third of the time. During each of these days, plant capacity would have been exceeded -- likely causing controlled or uncontrolled bypasses of raw sewage, or at the very least a dangerous surcharging condition. Between November 22 through 27, in particular, the tank would have been full every day. The likely bypass for the 32 days would have been 26.537 million gallons. Of this amount, the SCCC would have contributed over 5 million gallons to the bypass problem.
Table B (Excerpt)
Storage/Bypadd Analysis with SCCC Flow
November 19, 1998 through November 29, 1998
| Date |
Flow Aberdeen + SCCC mgd |
Flow Over 13 mgd |
Volume Stored MG |
Volume Withdrawn MG |
Volume In Tank MG |
Volume Bypassed MG |
Bypass Contrib. by SCCC MG |
| 11/19/98 |
9.76 |
-3.24 |
0 |
0 |
0 |
0 |
0 |
| 11/20/98 |
16.773 |
3.773 |
0.778 |
0 |
0.778 |
2.995 |
0 |
| 11/21/98 |
13.265 |
0.265 |
0.265 |
0 |
1.043 |
0 |
0 |
| 11/22/98 |
13.596 |
0.596 |
0.517 |
0 |
1.56(Full) |
.079 |
.079 |
| 11/23/98 |
13.525 |
0.525 |
0 |
0 |
1.56(Full) |
.525 |
.525 |
| 11/24/98 |
15.052 |
2.052 |
0 |
0 |
1.56(Full) |
2.052 |
.778 |
| 11/25/98 |
17.54 |
4.54 |
0 |
0 |
1.56(Full) |
4.54 |
.778 |
| 11/26/98 |
16.209 |
3.209 |
0 |
0 |
1.56(Full) |
3.209 |
.778 |
| 11/27/98 |
13.608 |
0.608 |
0 |
0 |
1.56(Full) |
.608 |
.608 |
| 11/28/98 |
11.891 |
-1.109 |
- |
1.095 |
0.465 |
0 |
0 |
Earth Tech's I&I Study, Footnote 9 based on an extensive hydrologic analysis, indicates that last winter's precipitation was representative of rainfall that regularly occurs in Aberdeen. Earth Tech I&I Report, at 5-3. In addition, we are at the beginning of a wetter-than average period of a long-term climate cycle, which some atmospheric scientists predict to last as long as 20 to 30 years. Footnote 10 Records from previous years reveal routine large storm events that would have exceeded the capacity of the detention facility, thereby exacerbating problems in the system. For example, between January 1993 and March 1997, six storms would have exceeded the detention facility's capacity, including the storms on January 1993, November 1994, November 1995, February 1996, December 1996, and March 1997. In each of these situations, the SCCC could have contributed to a bypass of raw sewage to surface waters.
During these times that the detention facility becomes full, the SCCC flows are added to the system at the time when the system is already over capacity, as discussed below. The addition of the SCCC flows would then magnify the existing problems with the WWTP and system, including both treatment and hydraulic capacity limitations.
The Consent Decree subsection 6(a) stipulates that the capacity of the Aberdeen WWTP system shall be established by evaluating the performance of the system's components. This mandatory analysis, while absent from Mr. Bledsoe's determination, is presented below.
Aberdeen's consultant, MSA, prepared a Preliminary Engineering Report presenting calculations of the capacities of the system components along the route in which the SCCC wastewater will flow and analyzes the impact of the SCCC flows on the wastewater system. Preliminary Engineering Report, p. 5-11 and 5-12. The analysis focuses on the force main at the Pump Station No. 2, the "H" Street trunk sewer, and the Interceptor "A". The analysis reveals capacity limitations that must be addressed before adding the SCCC flow to Aberdeen's system, as discussed below.
Pump Station No. 2
Addition of SCCC wastewater will decrease the capacity of the Pump Station No. 2 and increase the possibility of bypass problem. PS No. 2 has been the site where the Aberdeen wastewater system frequently bypasses its raw sewage into the Chehalis River, making this one of the most critical places to assure adequate capacity before adding the SCCC flow to the system. Footnote 11 In his capacity determination memo, Mr. Bledsoe fails to evaluate this component of the Aberdeen wastewater system, as required by the Consent Decree.
The addition of SCCC wastewater to the force main directly below PS No. 2 will increase the back-pressure in the pumping system and thereby decrease the operating capacity of the pumps in PS No. 2:
The estimated flow from the proposed SCCC sewage pumping station connection into the new force main, just downstream from PS No. 2, is approximately 1,300 gpm. This will reduce the PS No. 2 capacity to approximately 3,800 to 4,000 gpm with one pump running and 5,800 to 6,200 with two pumps running, while simultaneously operating the SCCC station.
October 11, 1996, MSA Memorandum to Aberdeen, p. 2 (emphasis added).
By decreasing the capacity of the PS No. 2 during a severe storm event, the bypass problem will increase. This will occur because 1) the size of the storm event necessary to create a bypass situation would be reduced; and 2) if there was a bypass, the quantity of sewage bypassed would be increased.
The addition of the SCCC flow to the force main will immediately decrease the size of the storm event that will be necessary to force a bypass situation at PS No. 2. This will occur because there are only two pumps at PS No. 2. When a storm event exceeds the capacity of PS No. 2, then one of the two pumps must be diverted to bypassing sewage to the Chehalis River. When the SCCC flows reduce the pumping capacity of PS No. 2, a smaller storm event could cause this event. As discussed, the addition of the SCCC flow will occur when the SCCC detention facility is full, during those same storm events that are overloading the hydraulic and treatment capacity of the WWTP and system.
Since there are two pumps in PS No. 2 and one must remain a standby unit, Footnote 12 PS No. 2 has a pumping capacity of only 3,800 to 4,000 gpm while the SCCC flow is entering the force main. This capacity is significantly less than the required capacity to handle the MSA's estimated current peak flow of 4,900 gpm from South Aberdeen.
"H" Street Trunk Sewer
The "H" Street trunk sewer, which receives wastewater from the PS No. 2 force main and a separate gravity system, also has inadequate capacity to handle the SCCC flows. MSA's analysis has determined that the "H" Street trunk sewer will be surcharged if the wastewater from the SCCC is allowed into it. Preliminary Engineering Report, at p. 5-12. Again, Mr. Bledsoe fails to evaluate this system component in his memo. The following paragraphs describe MSA's findings:
The capacity of the "H" Street Trunk may not be sufficient to accommodate the estimated combined flow rate of 6,270 gpm from the SCCC, the gravity system, and Pump Station No. 2. The total estimated peak flow from Pump Station No.2, the gravity sewer area and the SCCC combined exceeds the flow capacity of the "H" Street trunk,
Preliminary Engineering Report, Page 5-12 (emphasis added). MSA's memorandum to the City, dated October 11, 1996 further states:
If one SCCC pump is operating, the total flow rate will be approximately 110 percent capacity of the "H" Street Trunk, and approximately 1 to 2 feet of surcharging will occur in the trunk manholes."
It should be noted that MSA's calculation of the "H" Street Trunk is based on an optimal capacity of a concrete pipe. The true capacity of the pipe may be significantly less, meaning that the surcharging would worsen. In its comments on the MSA's Preliminary Engineering Report to the City, dated August 27, 1996, the Department of Ecology raises this concern. Footnote 13
Surcharging in the sewage system is a significant performance problem that will worsen with the addition of flows form SCCC. Again, the SCCC flow will be added at a time when the system is already overloaded, and when the risk of controlled or uncontrolled bypasses is at its greatest. As Aberdeen's consultant acknowledged, this surcharging causes sewage backing up into households and through manholes to the point where sewage flows into the streets, resulting in uncontrolled bypasses.
Interceptor "A"
Mr. Bledsoe also fails to analyze the capacity of Interceptor "A", located on State Street, which carries flow from the "H" Street trunk sewer to the WWTP.
The Infiltration and Inflow Study prepared by Aberdeen's consultant, Earth Tech, Inc., indicates that the measured wastewater flow during the 1998-99 winter exceeded the capacity of Interceptor "A" as determined by the MSA calculations. Footnote 14 This resulted in significant surcharging. Footnote 15 This surcharging likely results in a controlled or uncontrolled bypass, depending upon the actions of the operators.
During significant storm events exceeding the capacity of the SCCC detention facility, the added flow from SCCC will certainly exacerbate the surcharging and bypass problem.
Wastewater Treatment Plant
Mr. Bledsoe based his capacity determination largely upon the conclusions of MSA in the SEIS, which determined that the addition of the SCCC flows would bring the WWTP to only 87 percent of capacity. Footnote 16 However, Mr. Bledsoe's reliance upon MSA in this regard is unwarranted under the Consent Decree because MSA's conclusions are not based upon an evaluation of the performance of the system components. Instead, MSA based its analysis upon the design criteria of the Aberdeen WWTP stipulated in the City's current NPDES permit. Preliminary Engineering Report, p. 5-13, fn. 15
In contrast, Aberdeen's consultant KCM, Inc. has prepared a comprehensive audit of the WWTP that thoroughly analyzes the performance and capacity of system components. City of Aberdeen Comprehensive Sewage Facilities Plan, Treatment Facilities Audit April, 1999 ("KCM Audit"). Using the protocol required by the Consent Decree, KCM concludes that numerous system components of the WWTP lack capacity to handle the SCCC flows. Footnote 17
The KCM Audit's detailed process performance evaluations of the treatment system components reveal insufficient capacity to accept the SCCC wastewater flow. This conclusion is succinctly described by KCM in its executive summary:
A detailed evaluation of each unit process in the wastewater treatment facility was conducted to determine its effectiveness in treating current and future flows. Field-testing was conducted to measure primary and secondary sludge settling rates. Two-dimensional modeling was conducted of secondary sedimentation tanks. Dynamic modeling was completed for the activated sludge process. Two future flow and loading conditions were evaluated:
Startup of the Stafford Creek Correctional Center in 2000
The end of the planning period in 2020
Critical criteria were developed for each unit process. Criteria were based on manufacturer's listed capacity, Ecology standards, or KCM calculations and modeling. It was determined that the following unit processes will have a capacity problem when the SCCC opens in 2000:
- Influent pumping station
- Headwork comminuters
- Dissolved oxygen aeration system
- Secondary sedimentation tanks
- Chlorine contact tanks
Page ES-10 (emphasis added).
The following paragraphs describe KCM's conclusion as to the major deficiencies of the hydraulic and process capacity of the Aberdeen WWTP:
Influent Pumping Station The influent pumping station (PS No. 1), with three active pumps installed, does not have sufficient capacity to handle currently experienced influent sewage flows. KCM Audit, p. 7-11 to 7-13. KCM performed hydraulic analysis of the piping around the influent pumps and determined that the actual capacity with two pumps on was only 9.1 mgd, Footnote 18 and with three pumps only 11.1 mgd, far less than the peak hydraulic capacity of 13.0 mgd. KCM Audit at p. 4-34, Table 4-12. The flow exceeds the capacity to the level of substantially surcharging the influent sewers. KCM notes that surcharging must be avoided to prevent controlled and uncontrolled bypasses. KCM Audit p. 7-12. In addition to KCM's conclusions, it must be noted that the station is currently operating with all three pumps on during high flows, a reliability problem that will be magnified by the addition of SCCC flows, as discussed below.
Headworks According to KCM, the existing headworks is subject to overflows under existing flow conditions. KCM Audit p. 7-48. Also, the existing comminuters are relatively ineffective in capture of rag material, a situation that will worsen with the addition of SCCC flow. KCM Audit, p. 7-48. KCM determined that the hydraulic capacity of the comminuters are limited to a maximum month flow ("MMF") of 8.21 mgd, KCM Audit, p. 7-13, which is below the plant's MMF design capacity of 8.75 mgd. The plant's current flow is 7.75 (in 1998), whereas the SCCC flow will bring it to 8.49 mgd, above the headworks capacity. KCM Audit, ES - 8, Table ES-2; p. 7-7 to 7-8.
Aeration System KCM's evaluated the process capacity of the existing four aerators in the activated sludge system and concluded that they have insufficient capacity for oxygen demands under conditions of maximum day loading for the SCCC startup loads. KCM Audit at p. 7-48. The aeration safety factor is determined to be only 0.40. Footnote 19 (Design Field Oxygen Transfer/Carbonaceous Oxygen Demand = 5,766 pounds per day/14,584 pounds per day = 0.40) with the SCCC flow, far below the minimum requirement of 1.00. See KCM Audit Appendix D, Treatment Plant Design Data. Without SCCC flow, the safety factor is 0.44 (5,766/13,131) meaning that non-compliance is worsened with the SCCC flow.
Secondary sedimentation Tanks - KCM conducted field testing, steady state modeling, dynamic two-dimensional sedimentation modeling, and coupled process modeling with a one-dimensional sedimentation model for the existing two secondary sedimentation tanks. KCM concluded that the volume of existing sedimentation tanks limit the plant capacity in a maximum month to a MMF of 6.6 mgd. KCM Audit, p. 7-23. Adequate capacity for settling of solids in the activated sludge process (secondary treatment) is paramount for achieving efficient waste treatment. Again, this is well below the plant's current MMF (in year 1998) of 7.75 mgd. KCM Audit, p. 7-7, and the MMF with the SCCC of 8.49 mgd. Thus, the capacity of these tanks is insufficient to handle present flows, and will be even less sufficient with the addition of SCCC flows.
Chlorine Contact Tank KCM determined that the existing chlorine contact tank has inadequate volume to accommodate the SCCC flow. KCM Audit p. 7-48. The plant would be limited to a MMF of 8.3 mgd, barely sufficient for the Aberdeen's existing flow, and insufficient for the SCCC flow. KCM Audit, p. 7-29, 7-30.
Plant Hydraulic Capacity KCM performed hydraulic analyses of various tidal conditions and the existing treatment facility and found significant limitation in the existing plant to accommodate both existing and future hydraulic loads under the conditions of annual extreme high tide. KCM Audit, p. 7-49. The analysis showed the following problems caused by the significant hydraulic limitations in the existing plant, which already exist and need to be resolved in order to accommodate existing and future hydraulic loads.
- Overflow of treated wastewater from the manhole on the outfall pipeline; KCM Audit, p. 7-2.
- Submergence and flooding of the effluent metering structure Id.;
- Overtopping of the headworks at the influent box upstream of the comminuters Id.;
- Inadequate capacity of the influent pump station Id. at 7-3.
- High velocity of raw sewage in the force mains that convey raw sewage from influent pumps to the headworks Id.
These problems are unacceptable and should not exist in a plant. They are detrimental to proper operation and maintenance of the plant during high flow situations.
Reduced Reliability.
Detailed evaluations of various plant components also shows a lack of reliability that will worsen with the addition of the SCCC flow. The WWTP influent pump station (PS No. 1) is an example of a system component that does not meet reliability standards. The KCM Audit determined the firm capacity of PS No. 1 to be 9.1 mgd with the largest pump out of service, far below the 13.0 mgd peak hydraulic capacity of the WWTP. KCM Audit p. 4-34. Thus, in order for PS No. 1 to handle such flow, all pump units are required to be running, without the standby capability required by the reliability standards of the USEPA and State Department of Ecology. See Footnote 12.
The addition of the SCCC flow will increase the extent of Aberdeen's non-compliance with this critical reliability requirement. For example, the addition of the SCCC flow will make it increasingly necessary for Aberdeen to operate all three pumps in PS No. 1, in derogation of the reliability standards. In addition, increasing the flows into a system that already lacks required reliability safeguards increases the risk posed to public health and the environment. For example, in the event that lack of required safeguards leads to a discharge, the discharge will be more significant and the impact to human health and/or the environment will be greater.
Reliability non-compliance is also found at the bypass control gate located at the influent box at the head of the plant. EPA's reliability requirements call for screened, gravity overflow required with alarm, annunciation, and measurement of flow discharged, all of which are not provided. See Footnote 12, EPA Design Criteria 211.4. Another reliability non-compliance is found in the solids handling facilities. There is only a single sludge digester provided. It needs to be shut down for maintenance but there is no standby unit. EPA reliability criterion requires that at least two digester tanks be provided. Id. at 222.3.1. Nor is there a temporary sludge holding facility with a sufficient capacity for the digester's emergency use, as required. Id. at 222.1
.
Under the Consent Decree subsection 6(a), Aberdeen must have gone twenty-four months with three or fewer bypass and/or days on which effluent violations occurred before Aberdeen may be allowed hookup of the SCCC sewage flow. Mr. Bledsoe incorrectly states that Aberdeen has achieved this standard.
Effluent Chlorine Residual Non-compliance -- October 2, 1998.
According to Aberdeen's wastewater treatment plant process report, the daily chlorine residual in the effluent was recorded at 1.00 mg/l on October 2, 1998. The allowable maximum chlorine residual is 0.75 under the NPDES permit provision S1. Aberdeen further violated its permit by failing to properly disclose or explain this exceedence as part of its report to the Department of Ecology. This non-compliance was also documented in City's letter to the Department of Ecology dated October 7, 1998. Footnote 20
Reported BOD Non-compliance -- December, 1998.
Aberdeen reported non-compliance with its monthly BOD effluent limitation in December 1998. NPDES Permit Ï S1. The reported BOD removal in that month was reported to be 77%, well below the permitted 85% set forth under the NPDES permit provision S1.
Unreported BOD Non-compliance -- November 1998, January 1999.
While an analysis of the WWTP performance indicates several other BOD effluent violations during the past twenty-four months, these violations were obscured by Aberdeen's non-compliance with monitoring and/or record keeping requirements. Aberdeen's NPDES permit required Aberdeen to conduct daily monitor of BOD removal rates and to report such results. For example, Aberdeen is required to take representative sampling, whereas Aberdeen's missing data days are predominantly on days having extremely high flow.
Review of the plant monthly records during the 1998-99 winter revealed that BOD records were missing for 21 days. Among these days, the plant records shows plant effluent flow in excess of 13 mgd (the Plant's maximum design capacity) on 10 days. No explanation has been provided for why these critical data were missing.
In my peer review Footnote 21 of the KCM Audit, I presented an analysis demonstrating that the lack of required BOD removal data during high flow events has the effect of hiding occurrences of non-compliance. By filling in the missing records with average high flow BOD reduction rates, these violations become evident. KCM concurs:
Mr. Fann discussed what he calls "missing records" and concludes that by estimating data for these days he can calculate BOD removal efficiency rates for the plant that are a few percentage points lower than the rates calculated by the plant staff. We don't feel that it is in doubt that the plant has had difficulty meeting its permit requirements for percentage removal of BOD . This is due to dilution of the influent flow by rainwater.
KCM Response to Fann Peer Review Report (undated, received 8/10/99), at Page 7 (emphasis added).
In order to illustrate the methodology of my analysis, Tables C through F are attached. These tables compile recorded data obtained from the WWTP Process Control Reports for these four month under review. The records include daily plant effluent flows and daily percent BOD removal rates. All reported BOD removal rates (a total of 99 days) are plotted on the attached Figure 1 as a function of the plant effluent flows. A regression line is developed to represent the BOD percentage removal performance. Figure 2 is a graph showing the regression line. The regression results are listed in Table G. This line is used to determine the performance for the days with missing records. The missing records were filled with values taken from the performance line and the results were shown in the attached Tables H through K. The resultant monthly averages are listed in the table below.
The analysis reveals that the omission of required data concealed additional BOD violations in November, 1998 and January 1999.
| Month |
BOD Removal Rates With Missing Data Footnote 22 |
BOD Removal Rates With Imputed Data Footnote 23 |
BOD Removal Rate Required |
| November, 1998 |
86% |
84% |
85% |
| December, 1998 |
77% |
75% |
85% |
| January, 1999 |
85% |
81% |
85% |
| February, 1999 |
92% |
87% |
85% |
Raw Sewage Bypasses.
In addition to the four effluent violations discussed above, Aberdeen has experienced numerous uncontrolled bypasses within the past twenty-four months. These bypasses have been obscured by Aberdeen's failure to comply with the reporting requirement under its NPDES permit. NPDES Permit Ï G4, G5.
All recorded sewage bypasses in the Aberdeen wastewater system are controlled bypasses. These bypasses occurred when personnel purposefully opened up the bypass valves, usually with the purpose of reducing surcharging in the collection system and/or reducing over-capacity flow to the WWTP. Aberdeen's records indicate that it bypassed raw sewage to the Chehalis River in 1994, 1995, and then in December 1996 through January and March 1997. Footnote 24 The January, 1997 bypass lasted 48 hours, discharging a total of 6.2 million gallons of raw sewage into the Chehalis River.
Since the Consent Decree was executed, Aberdeen has avoided controlled bypasses even during the most significant rain events. As explained by the City's consultant, Earth Tech, in its Infiltration and Inflow Study, artificially eliminating the controlled bypasses has intensified surcharging in the Aberdeen sewer system. I/I Study, Vol I of III, p. 2-9.
The increased surcharging has been so significant so as to cause the sewage to back up in the manholes to the point where the sewage flows over the ground. Discharge of large quantities of untreated raw sewage inevitably reaches surface waters, creating an uncontrolled bypass. On the ground, or in the surface water, any discharge of untreated raw sewage, however dilute, has a potential impact upon public health as well as water quality. The following paragraphs describe two witnessed incidents of uncontrolled bypasses during the 1998-99 winter.
The I&I Study indicates that during the winter of 1998-99, at least one overflow that was an apparent result of system surcharging was observed during the course of the I&I Study. I/I Study, Vol. I of III, p. 2-9. In Appendix of Volume I of III of the Study, a picture depicts the overflowing raw sewage gushing through a 24-inch manhole to reach a height of 15 inches above the ground. Judging from the height of the sewage flows over the manhole rim, the estimated discharge rate is about 12,000 to 13,000 gallon per minute. It is not known how long the discharge lasted. Assuming a two-hour period, the total volume of such overflow/bypass would be about 1.5 million gallons.
The City's sewer crew documented another uncontrolled bypass. In a memo dated March 30, 1999, the crew describes observation of raw sewage lifting manhole castings off and blowing through manhole covers. Footnote 25 When the pressure in the surcharged sewer is so high to generate such a phenomenon as described, the rate of uncontrolled bypass must be extraordinarily high.
These observances of uncontrolled bypasses are consistent with Earth Tech's findings that the surcharging problem is contributing to uncontrolled bypasses:
During the period of record for the flow-monitoring element of the Study, 15 out of 21 flow monitoring sites surcharged on at least two occasions. Many of the sites surcharged during each of the five significant rain events recorded. During the period November 13 through December 13, 1998, flow meters recorded widespread surcharging throughout most of the system. Recorded surcharge depths indicate the system is surcharged to elevations that can cause side sewer backups, overflows at vented points in the system. "
Page 3-10.
The observed uncontrolled bypasses occurred in spite of the widespread use of bolt-down manhole covers installed throughout the City. Due to the lack of compliance with reporting requirements, it is not known how many more uncontrolled bypass events besides the above described two events occurred in the last winter.
