Subscribe to our

Rocky Soil Conditions

Rock can be one of the most costly and difficult factors in construction. Gravity sewers have wide excavated trenches and go deeper with each foot of length. This means the price per foot is significantly higher than installations in normal soil.

Installation in areas of solid rock can make system costs economically unfeasible. In cases such as these, contractors recommend alternatives such as pressure sewer systems. The fact that this alternative requires dramatically narrower and shallower trenches makes it feasible in places like solid rock where gravity systems are literally impossible.

High Groundwater Levels

Locations with high groundwater, whether seasonal or year round, present other challenges in both construction and operation of gravity sewers.

During construction, the work site must be dewatered by generous use of pumps and well points distributed along the proposed trench route, and powered 24 hours a day. Such dewatered soil can be very unstable and potentially dangerous to work in. Therefore, continuous shoring and bracing are usually required.

Even if these obstacles are overcome by expenditure of much money, care and effort, there remains the necessity to successfully operate the completed gravity sewer for the next 40 or 50 years. Consider that once the dewatering pumps are shut down and the ground water returns, the sewer must operate in what is tantamount to a submerged condition - this without causing infiltration and or inflow, both notorious enemies of overall water quality goals.

Lakeside Or Oceanfront Properties

One of the most desirable properties, sought out by millions of people around the world, is "a place beside the water."  It doesn't really matter whether it's a pond, creek, lake or reservoir, riverfront, an estuary or an ocean.  People desire to live near water.

The topographical features, which create these precious water bodies, are dominated by the fact that the land almost always slopes down toward the shore. With failing septic systems, the untreated wastewater can potentially pollute the body of water.

Since these systems must be down slope from the houses, they cause the disturbance, degradation and sometimes destruction of the most important feature of waterfront properties; namely, the "front yards" facing the shore. In some cases, land is so precious and the demand so great that tiny cabins are crowded against each other and literally pressed down as close as they dare to the water. It is very expensive, environmentally damaging, and seldom entirely satisfactory to put gravity sewers in such waterfront locations.

The pressure sewer has proven to be an environmentally friendly, cost-effective solution in these waterfront applications.  

Lots On The Wrong Side: Sewer Must Go Under A Stream Or Highway

Sometimes, property is developed in a strip along one side of a highway, road or stream. Often there are highly desirable, perhaps isolated, building lots on the "wrong side of the street." Until pressure sewers came along, these choice lots were listed as "unbuildable" and might be ignored for decades with a casual "that's too bad."

 Layout of a typical 230-volt grinder pump control panel circuit.

Pressure sewers bored under the stream or highway using a trenchless technology, or carried overhead on a bridge crossing, make such difficult sites easily accessible to whatever sewers already serve the strip community.

Houses Near But Not Directly Serviceable By An Existing Gravity Sewer

It is always desirable, and sometimes absolutely mandatory, that public sewers be deep enough to serve fixtures at, or just under, the basement floor level.

It often happens that when a gravity sewer is designed to serve a certain area, the basements of houses at the ends of the served streets end up just level with the sewer. If such streets are later extended "further out into the country," the new houses will be too low to have basement sewer connections. Or the distance to the gravity sewer may require a pump system.

The answer is to put grinder pumps in or next to these basements and create a pressure sewer line that can pump into the nearest gravity pipe or pumping station with available capacity for the additional flow.