Ripley Refutes Leaky Logic of County’s STEP vs. Gravity Comparison

Dana Ripley, presenting Ripley Pacific’s probing “STEP Collection Rebuttal Report” at the May 28th County Planning Commission meeting, told board members: “We, as a society, should really rethink building gravity sewers anywhere. The problems that we are identifying here in Los Osos are symptomatic of the gravity technology everywhere.”

Dana Ripley, presenting Ripley Pacific’s probing “STEP Collection Rebuttal Report: Regarding the Los Osos Wastewater Collection Project” at the May 28th County Planning Commission meeting, told board members: “We, as a society, should really rethink building gravity sewers anywhere. The problems that we are identifying here in Los Osos are symptomatic of the gravity technology everywhere.”

Ripley, author of the 2006 LOCSD-commissioned “Ripley Plan Update,” and an outside consultant for STEP system builder W. C. Lyles, spoke at the May 28th Planning Commission meeting, where he presented board members with copies of Ripley Pacific’s “STEP Collection Rebuttal Report: Regarding the Los Osos Wastewater Collection Project.” Here is a transcription of his comments before the Planning Commission:

“There was a lot of discussion on April 30 (at the Planning Commission meeting) regarding pipes and pipe seals and how the collection system would go together. I asked for your consideration even though we had a straw vote at the last meeting, and STEP, on a straw vote basis, has been eliminated. I would ask that you not officially exclude the set STEP alternative, particularly in the light of discussions we’ve just heard with respect to sea level elevation relative to pipes.

“(LOWWP Project engineer) Mr. (John) Waddell is correct. There is controversy as to what the sea level rise will be in California. Mr. Waddell said the IPCC (Intergovernmental Panel on Climate Change) estimate was 22 inches. The Pacific Institute just released a report about two months ago that predicts the entire California coast sea level rise at 4 feet in the next century. These elevations are critical.

“What’s most important is the discussion we’re having here is really on an infiltration issue, that is groundwater infiltrating into the collection system. I thought about that, I asked my associates about how best to discuss this sort of issue, and the first response I get (is) from one of my team members, Mike Saunders. I asked Mike, ‘What is the difference in the test procedure between a pressure collection system and a gravity system, understanding that in all systems there are seals?’ The question is, how good a seal? Mr. Saunders has provided us a memo here talking about the test pressure of being about 2 to 4 pounds per square inch for a gravity sewer, as compared to a pressure system, which would be very similar to a potable system of about 150 pounds per square inch, over a 24-hour period.

“With that as a seed, I decided to investigate the relative coefficients that are used for estimating infiltration, and for the STEP system really there is no infiltration. There can be infiltration on the lot, there can be down spouts, roof spouts that enter into the septic tank that can be corrected; but a STEP system is under pressure, therefore if there’s leakage, it’s leakage out of the pipe, not into the pipe. Therefore, STEP system infiltration relative to groundwater is really a non-issue, simply because the interior pipe pressure is greater than any groundwater pressure.

“Our position was that the fine screening report identified an infiltration rate of about 300,000 gallons a day to the Los Osos wastewater collection system, and we think, based on the potable water standards for pressure systems, that the infiltration rate will be about 12,000 gallons per day. That’s just a significant difference…

“The bottom line is, there was an infiltration rate assumed for the gravity sure system of about 500 gallons per day per acre for the collection system as a whole. The infiltration rates are looked at with two parameters generally, one is the gallons per day per acre and one is the gallons per day per inch mile. I compared the coefficients that were used in the fine screening report, being about 500 gallons per day per acre and about 780 gallons per day per inch, and compared those to EPA references … The bottom line is, I believe the 500 gallons per day per acre may be an appropriate value for certain areas of the collection system, but I believe the low-lying areas that are subject to groundwater, that could have tidal influence, sea-level-rise influence and also flooding influence, that my recommendation in this report is that those specific infiltration rates be reevaluated based on certain areas of the collection system. You cannot take it as a blanket…

“We, as a society, should really rethink building gravity sewers anywhere. The problems that we are identifying here in Los Osos are systematic of the gravity technology everywhere.

“My recommendation (to) the Planning Commission: continue what you’re doing. You’ve taken a straw vote, we know where we stand, but my feeling is that at the end of this deliberation, when you’ve taken a look at the ag exchange and you look at the importance of the effluent quality for the agriculture folks and for the urban reuse — sea-level rise is the major issue, in terms of salt water, in terms of salinity of the effluent — once you have all the pieces, then it’s time to evaluate the whole.”

For the full version of Dana Ripley’s “STEP Collection Rebuttal Report,” Click Here.